This file was created by the TYPO3 extension publications --- Timezone: CEST Creation date: 2026-06-03 Creation time: 09:48:26 --- Number of references 70 article Rull2022 Review 2022 10.1016/j.aca.2021.339003 Analytica Chimica Acta 1209 https://www.scopus.com/inward/record.uri?eid=2-s2.0-85114369523&doi=10.1016%2fj.aca.2021.339003&partnerID=40&md5=f342fbcd4979d422030cdddf63ab6ede Cited by: 16; All Open Access, Hybrid Gold Open Access Fernando Rull Marco Veneranda Jose Antonio Manrique-Martinez Aurelio Sanz-Arranz Jesus Saiz Jesús Medina Andoni Moral Carlos Perez Laura Seoane Emmanuel Lalla Elena Charro Jose Manuel Lopez Luis Miguel Nieto Guillermo Lopez-Reyes article Cavosie2021201 High-pressure minerals provide records of processes not normally preserved in Earth's crust. Reidite, a quenchable polymorph of zircon, forms at pressures >20 GPa during shock compression. However, there is no broad consensus among empirical, experimental, and theoretical studies on the nature of the polymorphic transformation. Here we decipher a multistage history of reidite growth recorded in a zircon grain in distal impact ejecta (offshore northeastern United States) from the ca. 35 Ma Chesapeake Bay impact event which, remarkably, experienced near-complete conversion (89%) to reidite. The grain displays two distinctive reidite habits: (1) intersecting sets of planar lamellae that are dark in cathodoluminescence (CL); and (2) dendritic epitaxial overgrowths on the lamellae that are luminescent in CL. While the former is similar to that described in literature, the latter has not been previously reported. A two-stage growth model is proposed for reidite formation at >40 GPa in Chesapeake Bay impact ejecta: formation of lamellar reidite by shearing during shock compression, followed by dendrite growth, also at high pressure, via recrystallization. The dendritic reidite is interpreted to nucleate on lamellae and replace damaged zircon adjacent to lamellae, which may be amorphous ZrSiO4 or possibly an intermediate phase, all before quenching. These results provide new insights on the microstructural evolution of the high-pressure polymorphic transformation over the microseconds-long interval of reidite stability during meteorite impact. Given the formation conditions, dendritic reidite may be a unique indicator of distal ejecta. © 2020 Geological Society of America. 2021 English 00917613 10.1130/G47860.1 Geology 49 Geological Society of America 201-205 Space Science and Technology Centre, Institute for Geoscience Research, School of Earth and Planetary Science, Curtin University, Perth, Western Australia 6102, Australia; School of Earth and Space Exploration, Arizona State University, Tempe, Arizona 85287, United States; GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, 24148, Germany; U.S. Geological Survey, 926A National Center, Reston, Virginia 20192, United States; Department of Lithospheric Research, University of Vienna, Althanstrasse 14, Vienna, A-1090, Austria 2 Offshore drilling; Offshore oil well production; Semiconductor insulator boundaries; Silicate minerals; Structural geology; Zircon, Epitaxial overgrowth; Formation condition; Intermediate phase; Meteorite impact; Ocean drilling programs; Polymorphic transformation; Shock compressions; Theoretical study, Meteor impacts, ejecta; high pressure; microstructure; mineral resource; Ocean Drilling Program; zircon, Chesapeake Bay; United States, Indicator indicator https://www.scopus.com/inward/record.uri?eid=2-s2.0-85100380573&doi=10.1130%2fG47860.1&partnerID=40&md5=2ca2398ac6b5c496a76392cebc1bf9a0 cited By 4 A.J. Cavosie M.B. Biren K.V. Hodges J.-A. Wartho J.W. Horton Jr. C. Koeberl article AssisFernandes2019289 This study presents 40Ar-39Ar step heating ages of four North American tektites (three bediasites and one georgiaite) and of two groundmass samples extracted at different depths from clast-rich impact melt rocks (CB-W61 and CB-W84) recovered by the USGS-ICDP Eyreville B drill-core about 9 km from the centre of the Chesapeake Bay impact structure. Radiometric age determination on both North American tektites and impact melt rocks from within Chesapeake Bay crater offers the first possibility to confirm the origin of these tektites. For this aim, argon isotopic data from 13 samples/aliquots of tektite rims, cores and bulk, and 4 samples/aliquots from two impact melt rocks were obtained over 15 to 26 step heating extractions. Age spectra of all tektite samples show plateaux comprising 62–98% of the 39Ar release over consecutive intermediate and high temperature heating steps. Few low temperature extractions indicate excess 40Ar. Inverse isochron 40Ar/36Ar intercepts of tektite samples are indistinguishable from air (295.5). However, impact melt rock spectra presented complex Ar-release affecting primarily the low temperature heating-steps. Inverse isochrones indicate excess argon from which the 40Ar/36Ar intercept was used to correct the age calculation. CB-W61 and CB-W61-2 40Ar/36Ar intercepts are 354.5 ± 2.5 and 327.2 ± 6.3, respectively, and those for CB-W84 and CB-W84-2 are 332.0 ± 7.3 and 329.6 ± 5.6, respectively. The inverse isochron weighted mean age (according to currently suggested K-decay constants revisions by Schwarz et al. (2011) and Renne et al. (2011)) for all four tektites is 34.86 ± 0.25 Ma (MSWD = 0.96, P = 0.41; n = 4) and for the two impact melt rocks is 37.16 ± 3.65 Ma (MSWD = 0.83, P = 0.36). The combined tektite and impact melt rocks isochron mean age of 34.86 ± 0.23 (0.32) Ma (MSWD = 0.87, P = 0.43) is slightly – though not significantly – higher than the plateau mean age of 34.55 ± 0.27 (0.36) Ma (MSWD = 0.66, P = 0.62). Placing this age in the Global Stratotype Section and Point (GSSP) marine section exposed at Massignano, Italy, it falls below the Eocene/Oligocene (E/O) boundary overlapping with the 10.28 m Ir-anomaly. These results agree within errors with previously reported ages of 35.20 ± 0.54 Ma, especially those derived from K-Ar and Ar-Ar total fusion analysis. An age of 34.86 ± 0.32 Ma sets the Chesapeake Bay impact event close to the youngest of the three Ir anomalies at ∼35.0 Ma in the case the impactor was Ir-rich (e.g, a chondrite, primitive achondrite, stony-iron or iron meteorite). The concordance with the E/O boundary at ∼33.9 Ma seems only marginally possible, and only if the Ir contribution from the ejecta were, potentially, due either to its small amount becoming diluted in the geologic record or the impactor being Ir poor, e.g., of differentiated achondritic composition. This study also brings to front the need to re-establish the stratigraphic and palaeo-magnetic correlations across the globe for the Ir-anomalies and the magneto-stratigraphy during the mid- to late-Eocene and early-Oligocene, and the need to re-evaluate the markers for the Eocene-Oligocene boundary. © 2019 Elsevier Ltd 2019 English 00167037 10.1016/j.gca.2019.03.004 Geochimica et Cosmochimica Acta 255 Elsevier Ltd 289-308 Museum für Naturkunde, Leibniz-Institute for Evolution and Biodiversity Research, Invalidenstraße 43, Berlin, 10115, Germany; School of Earth and Environmental Sciences, University of Manchester, Oxford Road, Manchester, M13 9PL, United Kingdom; Instituto Dom Luiz, University of Lisbon, Lisbon, 1749-016, Portugal; Klaus-Tschira-Labor für Kosmochemie, Institut für Geowissenschaften, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 234-236, Heidelberg, 69120, Germany; Saalbau Weltraum Projekt, Liebigstrasse 6, Heppenheim, 64646, Germany; Zentrum für Rieskrater und Impaktforschung (ZERIN), Nördlingen, Vordere Gerbergasse 3, Nördlingen, 86720, Germany; Florida Institute of Technology, Melbourne, FL 32901, United States argon-argon dating; Eocene-Oligocene boundary; geochronology; impact structure; magnetostratigraphy; melt; meteorite; paleomagnetism; tektite, Ascoli Piceno; Chesapeake Bay; Italy; Marche; Massignano; United States https://www.scopus.com/inward/record.uri?eid=2-s2.0-85063349910&doi=10.1016%2fj.gca.2019.03.004&partnerID=40&md5=a88b722be178770fe56331e4a1c9004b cited By 9 V. Assis Fernandes J. Hopp W.H. Schwarz J.P. Fritz M. Trieloff H. Povenmire article Schwarz2016307 High resolution 40Ar-39Ar step heating dating of australites and indochinites, representing a large area of the Australasian strewn field, and more recently discovered tektite-like glasses from Central America (Belize) and Western Canada, were carried out. Precise plateau ages were obtained in all cases, yielding indistinguishable ages of 789 ± 9 ka for four australites, 783 ± 5 ka for four indochinites, 783 ± 17 ka for one Western Canadian and 769 ± 16 ka for one Belize impact glass. Concerning major elements and REEs, australites and the Western Canadian impact glass are indistinguishable. If the Western Canadian sample was transported by impact ejection and belongs to the Australasian strewn field, this implies extremely far ballistic transport of 9000 km distance, assuming a source crater in southern Asia. The distinct major element and REE composition of the Belize impact glass suggests formation in another separate impact event. We conclude that the Australasian/Western Canadian impact glasses formed 785 ± 7 ka ago in a single event and Belize impact glass in a separate event 769 ± 16 ka ago. The two impact events forming these two strewn fields occurred remarkably closely related in time, i.e., separated by &lt;30 ka. © 2016 Elsevier Ltd. 2016 English 00167037 10.1016/j.gca.2015.12.037 Geochimica et Cosmochimica Acta 178 Elsevier Ltd 307-319 Institut für Geowissenschaften, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 234-236, Heidelberg, 69120, Germany; Klaus-Tschira-Labor für Kosmochemie, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 234-236, Heidelberg, 69120, Germany; Museum für Naturkunde - Berlin, Leibniz-Institut für Evolutions- und Biodiversitätsforschung, Invalidenstrasse 43, Berlin, D-10115, Germany; 7560 Greenboro Drive, #4, West Melbourne, FL 32904, United States; Institut für Planetologie, Universität Münster, Wilhelm Klemm Straße 10, Münster, 48419, Germany; Department of Lithospheric Research, University of Vienna, Althanstrasse 14, Vienna, 1090, Austria; Natural History Museum, Burgring 7, Vienna, 1010, Austria argon-argon dating; impact structure; Quaternary; rare earth element; tektite, Belize [Central America]; Canada https://www.scopus.com/inward/record.uri?eid=2-s2.0-84958535124&doi=10.1016%2fj.gca.2015.12.037&partnerID=40&md5=d37adcb77e5db6b454f4b506ad783662 cited By 27 W.H. Schwarz M. Trieloff K. Bollinger N. Gantert V.A. Fernandes H.-P. Meyer H. Povenmire E.K. Jessberger M. Guglielmino C. Koeberl article Jackson2016946 The occurrence of coesite in suevites from the Chesapeake Bay impact structure is confirmed within a variety of textural domains in situ by Raman spectroscopy for the first time and in mechanically separated grains by X-ray diffraction. Microtextures of coesite identified in situ investigated under transmitted light and by scanning electron microscope reveal coesite as micrometer-sized grains (1-3 μm) within amorphous silica of impact-melt clasts and as submicrometer-sized grains and polycrystalline aggregates within shocked quartz grains. Coesite-bearing quartz grains are present both idiomorphically with original grain margins intact and as highly strained grains that underwent shock-produced plastic deformation. Coesite commonly occurs in plastically deformed quartz grains within domains that appear brown (toasted) in transmitted light and rarely within quartz of spheroidal texture. The coesite likely developed by a mechanism of solid-state transformation from precursor quartz. Raman spectroscopy also showed a series of unidentified peaks associated with shocked quartz grains that likely represent unidentified silica phases, possibly including a moganite-like phase that has not previously been associated with coesite. © 2016 The Meteoritical Society. 2016 English 10869379 10.1111/maps.12638 Meteoritics and Planetary Science 51 University of Arkansas 946-965 U.S. Geological Survey, Reston, VA 20192, United States; Sanya Institute of Deep-Sea Science and Engineering, Sanya, China 5 https://www.scopus.com/inward/record.uri?eid=2-s2.0-84961825632&doi=10.1111%2fmaps.12638&partnerID=40&md5=78ab203a4ca643a2524806d387bf4d66 cited By 7 J.C. Jackson Jr. Horton I.-M. Chou H.E. Belkin article Sanford2013252 High-salinity groundwater more than 1,000 metres deep in the Atlantic coastal plain of the USA has been documented in several locations, most recently within the 35-million-year-old Chesapeake Bay impact crater. Suggestions for the origin of increased salinity in the crater have included evaporite dissolution, osmosis and evaporation from heating associated with the bolide impact. Here we present chemical, isotopic and physical evidence that together indicate that groundwater in the Chesapeake crater is remnant Early Cretaceous North Atlantic (ECNA) sea water. We find that the sea water is probably 100-145 million years old and that it has an average salinity of about 70 per mil, which is twice that of modern sea water and consistent with the nearly closed ECNA basin. Previous evidence for temperature and salinity levels of ancient oceans have been estimated indirectly from geochemical, isotopic and palaeontological analyses of solid materials in deep sediment cores. In contrast, our study identifies ancient sea water in situ and provides a direct estimate of its age and salinity. Moreover, we suggest that it is likely that remnants of ECNA sea water persist in deep sediments at many locations along the Atlantic margin. © 2013 Macmillan Publishers Limited. All rights reserved. 2013 English 00280836 10.1038/nature12714 Nature 503 252-256 US Geological Survey, Mail Stop 431, Reston, VA 20192, United States; US Geological Survey, Federal Center, Box 25046, Denver, CO 80225, United States; US Geological Survey, McKelvey Building 15, Mail Stop 420, 345 Middlefield Road, Menlo Park, CA 94025, United States 7475 ground water; sea water, bolide; coastal plain; crater; Cretaceous; dissolution; evaporite; groundwater; impact; osmosis; salinity; seawater, article; chemical analysis; coastal plain; dissolution; evaporation; heating; Lower Cretaceous; osmosis; priority journal; salinity; sediment; temperature, Atlantic Ocean; Bays; Geological Phenomena; Groundwater; Salinity; Seawater, Atlantic Coastal Plain; Chesapeake Bay; United States https://www.scopus.com/inward/record.uri?eid=2-s2.0-84887602867&doi=10.1038%2fnature12714&partnerID=40&md5=f94cc2c10395f8dcbe11c07cfab49b8f cited By 14 W.E. Sanford M.W. Doughten T.B. Coplen A.G. Hunt T.D. Bullen article Mang20135195 We observed two different Verwey transition temperatures in fragments of crystalline basement rocks and impact sediments from the Chesapeake Bay impact structure, USA. Our study aims to the question if this feature can be used as shock indicator in impact craters. We distinguished three generations of magnetite. (1) Primary magnetite in crystalline basement rocks has average grain sizes up to several hundreds of micrometers and shows a regular TV at ≈ 121 K. (2) Shocked magnetite occurs in fragments of crystalline basement rocks and also in the suevite and impact breccia. These magnetites show two Verwey transitions - a regular one and a "lowerature transition" (LTV) at around 89 K. LTV is related to a small grain size fraction, whereas a larger grain size fraction (some hundreds of micrometers) causes the regular TV. The small grain size fraction contains a distinctly higher amount of superficially oxidized material due to the high surface/volume ratio, which causes a decrease of the Verwey transition temperature (LTV). (3) A secondary magnetite generation shows also two Verwey transition temperatures, one at 121 K and a LTV range between 91 and 105 K. The LTV in this generation is also linked to thin oxidized surface layers. This study shows that especially the Verwey transition temperature of small magnetite grains reacts very sensitively to surface oxidation and can therefore not be used as a reliable pressure indicator for impact structures on Earth. Key Points Reduction of Verwey transition due to nonstoichiometry Degree of nonstoichiometry triggered by grain size Surface/volume ratio crucial for reduction of Verwey transition ©2013. American Geophysical Union. All Rights Reserved. 2013 English 21699313 10.1002/jgrb.50291 Journal of Geophysical Research: Solid Earth 118 Blackwell Publishing Ltd 5195-5207 Institut für Angewandte Geowissenschaften, Karlsruher Institut für Technologie, Adenauerring 20, Geb. 50.41, Karlsruhe, D-76131, Germany 10 basement rock; breccia; crystalline rock; grain size; hysteresis; impact structure; low temperature; magnetite; oxidation; suevite; temperature gradient, Chesapeake Bay; United States https://www.scopus.com/inward/record.uri?eid=2-s2.0-84889009695&doi=10.1002%2fjgrb.50291&partnerID=40&md5=fb1a878d995dd75640733f1a885e6aaa cited By 9 C. Mang A. Kontny article Mang201364 Shock experiments with pressures ranging from 3 to 30 GPa have been conducted on a mixed assemblage of hexagonal and monoclinic pyrrhotite. All samples were studied with respect to their particular shock-induced microstructures and magnetic properties at high and low temperatures. Up to 8 GPa, microstructures in shocked pyrrhotite are characterized by mechanical deformation producing a damage of the crystal structure. At pressures of 20 GPa and upward, amorphization and mechanical twinning are the dominant structural features induced by shock. Within the lower-pressure range coercivity, saturation isothermal remanent magnetization and coercivity of remanence increase with shock pressures, in agreement with more single-domain (SD)-like behavior. Simultaneously, the λ-peak of hexagonal pyrrhotite decreases and the 34 K transition of monoclinic pyrrhotite broadens and is depressed. Magnetic hardening is triggered by grain-size reduction, but also by the formation of SD within discrete multidomain grains. Planar deformation features subdivide such multidomain grains into lath-shaped domains with average sizes lying in the SD range. The planar deformation features disappear at 20 GPa and irregular, nanometer-sized "amorphous domains" occur instead. Pressure release from 30 GPa finally triggers partial melting of pyrrhotite. The sharp interfaces between molten and crystalline pyrrhotite document a rapid change of thermal conditions. Within molten pyrrhotite, quenched iron crystals occur. The presence of native iron strongly influences the magnetic properties, depending on the particular amount in the studied sample and likely affects the magnetic properties of impact lithologies on Earth and extraterrestrial material. ©2013. American Geophysical Union. All Rights Reserved. 2013 English 15252027 10.1029/2012GC004242 Geochemistry, Geophysics, Geosystems 14 Blackwell Publishing Ltd 64-85 Institut für Angewandte Geowissenschaften, Karlsruher Institut für Technologie, Adenauerring 20, Geb. 50.40, D-76131 Karlsruhe, Germany; Museum für Naturkunde, Leibniz-Institut, Humboldt Universität zu Berlin, Berlin, Germany; Laboratorium für Elektronenmikroskopie, Karlsruher Institut für Technologie, Karlsruhe, Germany 1 Coercive force; Experiments; Magnetic properties; Microstructure, Coercivity of remanence; Extraterrestrial material; Grain-size reduction; Mechanical deformation; Mechanical twinning; pyrrhotite; Saturation isothermal remanent magnetizations; shock, Iron ores, crystal structure; deformation; experimental study; grain size; lithology; magnetic property; microstructure; pyrrhotite; remanent magnetization; temperature effect https://www.scopus.com/inward/record.uri?eid=2-s2.0-84879807327&doi=10.1029%2f2012GC004242&partnerID=40&md5=4ee9274ee3c5d51772d1bf852c98572f cited By 21 C. Mang A. Kontny J. Fritz R. Schneider article Mang2012277 Pyrrhotite from suevite of the 35Ma Chesapeake Bay impact structure (CBIS) shows a shock metamorphism and we report on several mineralogical and magnetic features. Pyrrhotite shows strong brittle deformation with a high density of stacking faults, twinning parallel to the hexagonal (001) planes and average fault distances in the order of 10nm. Although the determination of a superstructure was not possible due to the lattice defects, the reflections of the NiAs subcell, which is typical of all pyrrhotite modifications, were clearly detected. This phase is ferrimagnetic with a Curie temperature (T C) between 350 and 365°C, and suevite with this phase does not show the 34K transition. The most peculiar feature is the low metal/sulfur ratio of 0.81, which indicates a distinctly higher vacancy concentration than for 4C pyrrhotite and a composition close to smythite (Fe 9S 11). This phase carries a stable natural remanent magnetization and is relatively hard magnetic. Steep inclinations of the natural remanent magnetization vector, however, suggest that this phase has been remagnetized by the drilling process. A possible explanation is the magnetic domain size of faultless areas of about 10nm in diameter, which is at the lower limit of the single domain size near the threshold, below which superparamagnetic behavior occurs. The low thermal stability of this phase excludes postshock heating above 300°C for the suevite of the CBIS. Our results imply that the iron-deficient pyrrhotite is produced by shock metamorphism, although an iron loss due to shock has never been reported before for pyrrhotite. © 2012 The Meteoritical Society. 2012 English 10869379 10.1111/j.1945-5100.2012.01329.x Meteoritics and Planetary Science 47 277-295 Institut für Angewandte Geowissenschaften, Karlsruher Institut für Technologie, Adenauerring 20, Geb. 50.40, 76131 Karlsruhe, Germany; Bayerisches Geoinstitut, University of Bayreuth, 95440 Bayreuth, Germany; Museum für Naturkunde, Leibniz-Institut an der Humboldt Universität zu Berlin, Invalidenstraße 43, 10115 Berlin, Germany 2 https://www.scopus.com/inward/record.uri?eid=2-s2.0-84856719076&doi=10.1111%2fj.1945-5100.2012.01329.x&partnerID=40&md5=b15cb147d7127c1f2a4996abcf27d52d cited By 8 C. Mang A. Kontny D. Harries F. Langenhorst L. Hecht article Bartosova2011396 The center of the 35.3Ma Chesapeake Bay impact structure (85km diameter) was drilled during 2005/2006 in an ICDP-USGS drilling project. The Eyreville drill cores include polymict impact breccias and associated rocks (1397-1551m depth). Tens of melt particles from these impactites were studied by optical and electron microscopy, electron microprobe, and microRaman spectroscopy, and classified into six groups: m1-clear or brownish melt, m2-brownish melt altered to phyllosilicates, m3-colorless silica melt, m4-melt with pyroxene and plagioclase crystallites, m5-dark brown melt, and m6-melt with globular texture. These melt types have partly overlapping major element abundances, and large compositional variations due to the presence of schlieren, poorly mixed melt phases, partly digested clasts, and variable crystallization and alteration. The different melt types also vary in their abundance with depth in the drill core. Based on the chemical data, mixing calculations were performed to determine possible precursors of these melt particles. The calculations suggest that most melt types formed mainly from the thick sedimentary section of the target sequence (mainly the Potomac Formation), but an additional crystalline basement (schist/gneiss) precursor is likely for the most abundant melt types m2 and m5. Sedimentary rocks with compositions similar to those of the melt particles are present among the Eyreville core samples. Therefore, sedimentary target rocks were the main precursor of the Eyreville melt particles. However, the composition of the melt particles is not only the result of the precursor composition but also the result of changes during melting and solidification, as well as postimpact alteration, which must also be considered. The variability of the melt particle compositions reflects the variety of target rocks and indicates that there was no uniform melt source. Original heterogeneities, resulting from melting of different target rocks, may be preserved in impactites of some large impact structures that formed in volatile-rich targets, because no large melt body exists, in which homogenization would have taken place. © The Meteoritical Society, 2011. 2011 English 10869379 10.1111/j.1945-5100.2011.01162.x Meteoritics and Planetary Science 46 396-430 Department of Lithospheric Research, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria; Museum für Naturkunde, Leibniz-Institute at Humboldt University Berlin, Invalidenstrasse 43, 10115 Berlin, Germany; Natural History Museum, Burgring 7, A-1010 Vienna, Austria; Institute of Mineralogy and Crystallography, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria 3 https://www.scopus.com/inward/record.uri?eid=2-s2.0-79952727590&doi=10.1111%2fj.1945-5100.2011.01162.x&partnerID=40&md5=ae9a6c7aed42d58457019f9684b35feb cited By 3 K. Bartosova L. Hecht C. Koeberl E. Libowitzky W.U. Reimold article Bartosova2011621 The Chesapeake Bay impact structure, approximately 85km in diameter, has been drilled in 2005-2006 at Eyreville (Virginia, USA), to a total depth of 1766m. In the drill cores, the abundance of shock metamorphosed material is very variable with depth. Shocked mineral and lithic clasts, as well as melt particles, are most abundant in suevitic impact breccia section (1397-1451m depth). Shocked quartz (i.e., quartz grains with planar fractures and/or planar deformation features) and melt particles, although rare, are also dispersed in the Exmore Formation unit (444-867m depth). Other lithologies in the Eyreville drill cores show no clear evidence of shock metamorphism. Here, we report on the investigations of 40 samples from the impact breccia section. A total of more than 27,000 quartz grains were examined in about 200 clasts. The abundance of highly shocked clasts tends to decrease with increasing depth. Crystalline clasts derived from the crystalline basement are commonly only slightly shocked (contain generally <10rel% of shocked quartz grains). The clasts of metamorphosed sediments show a low proportion of shocked quartz grains (mostly <10rel%). Sedimentary clasts show a wide range of proportions of shocked quartz grains, with several of them being highly shocked clasts (most values between 0 and 40rel%). Conglomerates show the highest proportion of shocked quartz grains of all types of clasts (up to 83rel%). Polycrystalline quartz clasts are also commonly highly shocked (contain mostly between 10 and 40rel% of shocked quartz grains). These hard nonporous clasts are possibly more liable to show evidence of shock. The investigations suggest that the intensity of shock metamorphism is the result of several parameters, such as original position in the target (both horizontal and vertical) and the properties of each lithology (e.g., grain size, porosity, and amount of matrix). According to the universal-stage investigations, the dominant orientations of planar deformation features in quartz are {101̄3}, {101̄2}, and also {101̄4}. © The Meteoritical Society, 2011. 2011 English 10869379 10.1111/j.1945-5100.2011.01179.x Meteoritics and Planetary Science 46 621-637 Department of Lithospheric Research, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria; Natural History Museum, Burgring 7, A-1010 Vienna, Austria 5 https://www.scopus.com/inward/record.uri?eid=2-s2.0-79955743565&doi=10.1111%2fj.1945-5100.2011.01179.x&partnerID=40&md5=8adf7e9486fc4e4b179052f931517c54 cited By 1 K. Bartosova C. Koeberl article Breuker2011 For the first time quantitative data on the abundance of Bacteria, Archaea, and Eukarya in deep terrestrial sediments are provided using multiple methods (total cell counting, quantitative real-time PCR, Q-PCR and catalyzed reporter deposition-fluorescence in situ hybridization, CARD-FISH). The oligotrophic (organic carbon content of ̃0.2%) deep terrestrial sediments in the Chesapeake Bay area at Eyreville, Virginia, USA, were drilled and sampled up to a depth of 140 m in 2006. The possibility of contamination during drilling was checked using fluorescent microspheres. Total cell counts decreased from 109 to 106 cells/g dry weight within the uppermost 20 m, and did not further decrease with depth below. Within the top 7 m, a significant proportion of the total cell counts could be detected with CARD-FISH.The CARD-FISH numbers for Bacteria were about an order of magnitude higher than those for Archaea. The dominance of Bacteria over Archaea was confirmed by Q-PCR. The down core quantitative distribution of prokaryotic and eukaryotic small sub- unit ribosomal RNA genes as well as functional genes involved in different biogeochemical processes was revealed by Q-PCR for the uppermost 10 m and for 80-140 m depth. Eukarya and the Fe(III)- and Mn(IV)-reducing bacterial group Geobacteriaceae were almost exclu- sively found in the uppermost meter (arable soil), where reactive iron was detected in higher amounts. The bacterial candidate division JS-1 and the classes Anaerolineae and Caldilineae of the phylum Chloroflexi, highly abundant in marine sediments, were found up to the maximum sampling depth in high copy numbers at this terrestrial site as well. A similar high abundance of the functional gene cbbL encoding for the large subunit of RubisCO suggests that autotrophic microorganisms could be relevant in addition to het- erotrophs. The functional gene aprA of sulfate reducing bacteria was found within distinct layers up to ca. 100 m depth in low copy numbers.The gene mcrA of methanogens was not detectable. Cloning and sequencing data of 16S rRNA genes revealed sequences of typi- cal soil Bacteria. The closest relatives of the archaeal sequences were Archaea recovered from terrestrial and marine environments. Phylogenetic analysis of the Crenarchaeota and Euryarchaeota revealed new members of the uncultured South African Gold Mine Group, Deep Sea Hydrothermal Vent Euryarchaeotal Group 6, and Miscellaneous Crenarcheotic Group clusters. © 2011 Breuker, Köweker, Blazejak and Schippers. 2011 English 1664302X 10.3389/fmicb.2011.00156 Frontiers in Microbiology 2 Frontiers Research Foundation Geomicrobiology, Federal Institute for Geosciences and Natural Resources, Hannover, Germany; Faculty of Natural Sciences, Leibniz Universität Hannover, Hannover, Germany; Max Planck Institute for Marine Microbiology, Bremen, Germany JULY Anaerolineae; Archaea; Bacteria (microorganisms); candidate division JS1; Chloroflexi; Chloroflexi (class); Crenarchaeota; Eukaryota; Euryarchaeota; Prokaryota https://www.scopus.com/inward/record.uri?eid=2-s2.0-84870320616&doi=10.3389%2ffmicb.2011.00156&partnerID=40&md5=5f8e1449e7d2d3db36f5bd20726c33cf cited By 38 A. Breuker G. Köweker A. Blazejak A. Schippers article Goderis2010395 Fifteen impactites from various intervals within the Eyreville cores of the Chesapeake Bay impact structure were sampled to measure siderophile element concentrations. The sampled intervals include basement-derived rocks with veins, polymict impact breccias and associated rocks, and crater-fill sediments. The platinum group element (PGE) concentrations obtained are generally low (e.g., iridium concentrations less than 0.1 ng/g) and are fractionated relative to chondrites. There is no clear distinction in concentration between the different impactite units. So far in the Chesapeake Bay material, only the impact melt rocks from the 823-m-deep Cape Charles test hole, drilled over the central uplift of the structure, have generated a bulk chondritic signature of 0.01-0.1 wt% meteoritic contribution based on a mixing model of 187 Os/ 188 Os isotopic ratios and Os concentrations. However, none of the samples studied shows PGE abundances that enable identification of the type of projectile responsible for the formation of the structure. Hence, it is at present not possible to link the Chesapeake Bay impact to the proposed ordinary chondrite falls by projectiles recorded for other late Eocene craters, namely the 100-km-diameter Popigai impact structure in Siberia and 7.5-km-diameter Wanapitei structure in Canada. The absence of a clear projectile signature hinders further discussions on the existence and the nature of the late Eocene shower event (asteroid versus comet). © 2010 The Geological Society of America. All rights reserved. 2010 English 00721077 10.1130/2010.2465(20) Special Paper of the Geological Society of America 465 Geological Society of America 395-409 Earth System Science, Vrije Universiteit Brussel, Pleinlaan 2, BE-1050 Brussels, Belgium; Department of Analytical Chemistry, Universiteit Gent, Krijgslaan 281-S12, BE-9000 Ghent, Belgium; Department of Geology, Katholieke Universiteit Leuven, Celestijnenlaan 200E, BE-3001 Heverlee, Belgium Infill drilling; Meteor impacts; Meteorites; Projectiles, Chesapeake Bay; Chesapeake bay impact structures; Impact structures; Isotopic ratios; Mixing models; Ordinary chondrites; Platinum group elements; Siderophile elements, Core drilling, chondrite; crater; impact structure; impactite; isotopic ratio; meteorite; platinum group element; siderophile element, Canada; Chesapeake Bay; Ontario [Canada]; United States; Wanapitei Lake https://www.scopus.com/inward/record.uri?eid=2-s2.0-78650937770&doi=10.1130%2f2010.2465%2820%29&partnerID=40&md5=2f27c59a6b7c2e5b1ab814394c3a679c cited By 10 S. Goderis J. Hertogen F. Vanhaecke Ph. Claeys article Edwards2010319 Two cores at the outer margin of the Chesapeake Bay impact structure show significant structural and depositional variations that illuminate its history. Detailed stratigraphy of the Watkins School core reveals that this site is outside the disruption boundary of the crater with respect to its lower part (nonmarine Cretaceous Potomac Formation), but just inside the boundary with respect to its upper part (Exmore Formation and a succession of upper Eocene to Pleistocene postimpact deposits). The site of the U.S. Geological Survey-National Aeronautics and Space Administration Langley core, 6.4 km to the east, lies wholly within the annular trough of the crater. The Potomac Formation in the Watkins School core is not noticeably impact disrupted. The lower part of crater unit A in the Langley core represents stratigraphically lower, but similarly undeformed material. The Exmore Formation is only 7.8 m thick in the Watkins School core, but it is over 200 m thick in the Langley core, where it contains blocks up to 24 m in intersected diameter. The upper part of the Exmore Formation in the two cores is a polymict diamicton with a stratified zone at the top. The postimpact sedimentary units in the two cores have similar late Eocene and late Miocene depositional histories and contrasting Oligocene, early Miocene, and middle Miocene histories. A paleochannel of the James River removed Pliocene deposits at the Watkins School site, to be filled later with thick Pleistocene deposits. At the Langley site, a thick Pliocene and thinner Pleistocene record is preserved. © 2010 The Geological Society of America. All rights reserved. 2010 English 00721077 10.1130/2010.2465(19) Special Paper of the Geological Society of America 465 Geological Society of America 319-393 U.S. Geological Survey, 926A National Center, Reston, VA 20192, United States Deposits; NASA; Stratigraphy, Chesapeake bay impact structures; Early Miocene; Middle Miocene; Pleistocene deposits; Pliocene deposits; Sedimentary units; U.s. geological surveys; Undeformed materials, Meteor impacts, crater; depositional sequence; impact structure; Miocene; paleochannel; Pleistocene; stratigraphy, Chesapeake Bay; United States https://www.scopus.com/inward/record.uri?eid=2-s2.0-78650928489&doi=10.1130%2f2010.2465%2819%29&partnerID=40&md5=a1aa225822fa339bee71ddfccd266633 cited By 7 L.E. Edwards D.S. Powars J.W. Horton Jr. G.S. Gohn J.M. Self-Trail R.J. Litwin article Bartosova20101021 The ICDP-USGS Eyreville drill cores in the Chesapeake Bay impact structure reached a total depth of 1766 m and comprise (from the bottom upwards) basement-derived schists and granites/pegmatites, impact breccias, mostly poorly lithified gravelly sand and crystalline blocks, a granitic slab, sedimentary breccias, and postimpact sediments. The gravelly sand and crystalline block section forms an approximately 26 m thick interval that includes an amphibolite block and boulders of cataclastic gneiss and suevite. Three gravelly sands (basal, middle, and upper) are distinguished within this interval. The gravelly sands are poorly sorted, clast supported, and generally massive, but crude size-sorting and subtle, discontinuous layers occur locally. Quartz and K-feldspar are the main sand-size minerals and smectite and kaolinite are the principal clay minerals. Other mineral grains occur only in accessory amounts and lithic clasts are sparse (only a few vol%). The gravelly sands are silica rich (∼80 wt% SiO2). Trends with depth include a slight decrease in SiO2 and slight increase in Fe2O3. The basal gravelly sand (below the cataclasite boulder) has a lower SiO2 content, less K-feldspar, and more mica than the higher sands, and it contains more lithic clasts and melt particles that are probably reworked from the underlying suevite. The middle gravelly sand (below the amphibolite block) is finer-grained, contains more abundant clay minerals, and displays more variable chemical compositions than upper gravelly sand (above the block). Our mineralogical and geochemical results suggest that the gravelly sands are avalanche deposits derived probably from the nonmarine Potomac Formation in the lower part of the target sediment layer, in contrast to polymict diamictons higher in the core that have been interpreted as ocean-resurge debris flows, which is in agreement with previous interpretations. The mineralogy and geochemistry of the gravelly sands are typical for a passive continental margin source. There is no discernible mixing with marine sediments (no glauconite or Paleogene marine microfossils noted) during the impact remobilization and redeposition. The unshocked amphibolite block and cataclasite boulder might have originated from the outer parts of the transient crater. © 2010 The Meteoritical Society. 2010 English 10869379 10.1111/j.1945-5100.2010.01077.x Meteoritics and Planetary Science 45 1021-1052 Department of Lithospheric Research, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria; Department of Geodynamics and Sedimentology, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria; U.S. Geological Survey, 926A National Center, Reston, VA 20192, United States; Department of Geosciences, University of Oslo, P.O. Box 1047, Blindern, NO-0316 Oslo, Norway; Natural History Museum, Burgring 7, A-1010 Vienna, Austria 6 https://www.scopus.com/inward/record.uri?eid=2-s2.0-77957318316&doi=10.1111%2fj.1945-5100.2010.01077.x&partnerID=40&md5=dea78112779d625894bc2c5dbdee4439 cited By 1 K. Bartosova S. Gier J.W. Horton Jr. C. Koeberl D. Mader H. Dypvik article Ormö20101206 To better understand the impact cratering process and its environmental consequences at the local to global scale, it is important to know when in the geological record of an impact crater the impact-related processes cease. In many instances, this occurs with the end of early crater modification, leaving an obvious sedimentological boundary between impactites and secular sediments. However, in marine-target craters the transition from early crater collapse (i.e., water resurge) to postimpact sedimentation can appear gradual. With the a priori assumption that the reworked target materials of the resurge deposits have a different chemical composition to the secular sediments we use chemostratigraphy (δ13Ccarb, %Corg, major elements) of sediments from the Chesapeake Bay, Lockne, and Tvären craters, to define this boundary. We show that the end of impact-related sedimentation in these cases is fairly rapid, and does not necessarily coincide with a visual boundary (e.g., grain size shift). Therefore, in some cases, the boundary is more precisely determined by chemostratigraphy, especially carbonate carbon isotope variations, rather than by visual inspection. It is also shown how chemostratigraphy can confirm the age of marine-target craters that were previously determined by biostratigraphy; by comparing postimpact carbon isotope trends with established regional trends. © The Meteoritical Society, 2010. 2010 English 10869379 10.1111/j.1945-5100.2010.01084.x Meteoritics and Planetary Science 45 University of Arkansas 1206-1224 Centro de Astrobiología (CSIC-INTA), Instituto Nacional de Técnica Aeroespacial, 28850 Torrejón de Ardoz, Madrid, Spain; U.S. Geological Survey, 926A National Center, Reston, VA 20192, United States 7 https://www.scopus.com/inward/record.uri?eid=2-s2.0-78049441916&doi=10.1111%2fj.1945-5100.2010.01084.x&partnerID=40&md5=4dcfa8a6fdb6a987f134cc480f071733 cited By 12 J. Ormö A.C. Hill J.M. Self-Trail article Kulpecz2009811 The Eyreville and Exmore, Virginia, core holes were drilled in the inner basin and annular trough, respectively, of the Chesapeake Bay impact structure, and they allow us to evaluate sequence deposition in an impact crater. We provide new high-resolution geochronologic (&lt;1 Ma) and sequence-stratigraphic interpretations of the Exmore core, identify 12 definite (and four possible) postimpact depositional sequences, and present comparisons with similar results from Eyreville and other mid- Atlantic core holes. The concurrence of increases in δ 18 O with Chesapeake Bay impact structure sequence boundaries indicates a primary glacioeustatic control on deposition. However, regional comparisons show the differential preservation of sequences across the mid-Atlantic margin. We explain this distribution by the compaction of impactites, regional sediment-supply changes, and the differential movement of basement structures. Upper Eocene strata are thin or missing updip and around the crater, but they thicken into the inner basin (and offshore to the southeast) due to rapid crater infilling and concurrent impactite compaction. Oligocene sequences are generally thin and highly dissected throughout the mid-Atlantic region due to sediment starvation and tectonism, except in southeastern New Jersey. Regional tectonic uplift of the Norfolk Arch coupled with a southward decrease in sediment supply resulted in: (1) largely absent Lower Miocene sections around the Chesapeake Bay impact structure compared to thick sections in New Jersey and Delaware; (2) thick Middle Miocene sequences across the Delmarva Peninsula that thin south of the Chesapeake Bay impact structure; and (3) upper Middle Miocene sections that pinch out just north of the Chesapeake Bay impact structure. Conversely, the Upper Miocene-Pliocene section is thick across Virginia, but it is poorly represented in New Jersey because of regional variations in relative subsidence. © 2009 The Geological Society of America. 2009 English 00721077 10.1130/2009.2458(34) Special Paper of the Geological Society of America 458 Geological Society of America 811-837 Department of Geological Sciences, Rutgers University, Piscataway, NJ 08854, United States; U.S. Geological Survey, 12201 Sunrise Valley Drive, Reston, VA 20192, United States; Delaware Geological Survey, 257 Academy Street, Newark, DE 19716, United States; Chevron Energy Technology Company, 1500 Louisiana St., Houston, TX 77002, United States Compaction; Concurrency control; Infill drilling; Offshore oil well production; Sediments; Stratigraphy, Basement structures; Chesapeake bay impact structures; Depositional sequences; Regional tectonics; Regional variation; Sediment starvation; Sequence boundary; Sequence-stratigraphic interpretation, Deposition, deposition; depositional sequence; Eocene; geochronology; glacioeustacy; impact structure; Miocene; Oligocene; Pliocene; sedimentation rate; sequence boundary; sequence stratigraphy; subsidence, Chesapeake Bay; Delmarva Peninsula; New Jersey; United States; Virginia https://www.scopus.com/inward/record.uri?eid=2-s2.0-74949108348&doi=10.1130%2f2009.2458%2834%29&partnerID=40&md5=7b1fffd4bd77bb74e1bcc61eb1b4f490 cited By 15 A.A. Kulpecz K.G. Miller J.V. Browning L.E. Edwards D.S. Powars P.P. McLaughlin Jr. A.D. Harris M.D. Feigenson article Bartosova2009317 The moat of the 85-km-diameter and 35.3-Ma-old Chesapeake Bay impact structure (USA) was drilled at Eyreville Farm in 2005-2006 as part of an International Continental Scientific Drilling Program (ICDP)-U.S. Geological Survey (USGS) drilling project. The Eyreville drilling penetrated postimpact sediments and impactites, as well as crystalline basement-derived material, to a total depth of 1766 m. We present petrographic observations on 43 samples of suevite, impact melt rock, polymict lithic impact breccia, cataclastic gneiss, and clasts in suevite, from the impact breccia section from 1397 to 1551 m depth in the Eyreville B drill core. Suevite samples have a fine-grained clastic matrix and contain a variety of mineral and rock clasts, including sedimentary, metamorphic, and igneous lithologies. Six subunits (U1-U6, from top to bottom) are distinguished in the impact breccia section based on abundance of different clasts, melt particles, and matrix; the boundaries between the subunits are generally gradational. Sedimentary clasts are dominant in most subunits (especially in U1, but also in U3, U4, and U6). There are two melt-rich subunits (U1 and U3), and there are two melt-poor subunits with predominantly crystalline clasts (U2 and U5). The lower part (subunits U5 and U6), which has large blocks of cataclastic gneiss and rare melt particles, probably represents ground-surge material. Subunit U1 possibly represents fallback material, since it contains shard-like melt particles that were solidified before incorporation into the breccia. The melt-poor, crystalline clast-rich subunit U2 could have been formed by slumping of material, probably from the central uplift or from the margin of the transient crater. Melt particles are most abundant near the top of the impact breccia section (above 1409 m) and around 1450 m, where the suevite grades into impact melt rock. Five different types of melt particles have been recognized: (1) clear colorless to brownish glass; (2) melt altered to fine-grained phyllosilicate minerals; (3) recrystallized silica melt; (4) melt with microlites; and (5) dark-brown melt. Proportions of matrix and melt in the suevite are highly variable (̃2-67 vol% and 1-67 vol%, respectively; the remainder consists of lithic clasts). Quartz grains in suevite commonly show planar fractures (PFs) and/or planar deformation features (PDFs; 1 or 2 sets, rarely more); some PDFs are decorated. On average, ̃16 rel% of quartz grains in suevite samples are shocked (i.e., show PFs and/or PDFs). Sedimentary clasts (e.g., graywacke or sandstone) and polycrystalline quartz clasts have relatively higher proportions of shocked quartz grains, whereas quartz grains in schist and gneiss clasts rarely show shock effects. Rare feldspar grains with PDFs and mica with kink banding were observed. Ballen quartz was noted in melt-rich samples. Evidence of hydrothermal alteration, namely, the presence of smectite and secondary carbonate veins, was found especially in the lower parts of the impact breccia section. © 2009 The Geological Society of America. 2009 English 00721077 10.1130/2009.2458(15) Special Paper of the Geological Society of America 458 Geological Society of America 317-348 Department of Lithospheric Research, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria; Department of Earth Sciences, University of Western Ontario, 1151 Richmond Street, London, ON, N6A 5B7, Canada; Museum für Naturkunde-Leibniz Institute, Humboldt University Berlin, Invalidenstrasse 43, 10115 Berlin, Germany; Department of Geodynamics and Sedimentology, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria Binary alloys; Clay alteration; Crystalline materials; Crystalline rocks; Drills; Feldspar; Igneous rocks; Infill drilling; Metamorphic rocks; Mica; Quartz; Sedimentary rocks; Sedimentology; Silicate minerals; Silicon alloys, Chesapeake bay impact structures; Continental scientific drillings; Crystalline basement; Derived materials; Hydrothermal alterations; Planar deformation; Polycrystalline quartz; U.s. geological surveys, Core drilling, breccia; crater; drilling; hydrothermal alteration; impact structure; impactite; petrography; shock metamorphism; suevite, Chesapeake Bay; United States https://www.scopus.com/inward/record.uri?eid=2-s2.0-74949111899&doi=10.1130%2f2009.2458%2815%29&partnerID=40&md5=f6213b90d8ec6edd96de8e5c99e99753 cited By 14 K. Bartosova L. Ferrière C. Koeberl W.U. Reimold S. Gier article Reimold2009655 The International Continental Scientific Drilling Program (ICDP)-U.S. Geological Survey (USGS) Eyreville A and B drill cores sampled crater fill in the region of the crater moat, ̃9 km to the NE of the center of the Chesapeake Bay impact structure, Virginia, USA. They provide a 953 m section (444-1397 m depth) of sedimentary clast breccia and intercalated sedimentary and crystalline megablocks knownas Exmore beds, deposited on top of the impactite sequence between 1397 and 1551 m depth. We petrographically investigated the sandy-clayey groundmass-dominated breccia, which resembles a diamictite ("Exmore breccia"), and which, in its lower parts, carries sedimentary and crystalline blocks. The entire breccia interval is characterizedby the presence of glauconite and bioclastic carbonate, which distinguishes the Exmore breccia from other sandy facies above and below in the stratigraphy. The sediment-clast breccia exhibits strong heterogeneity from sample to sample with respect to groundmass nature, e.g., clay versus sand content, as well as clast content, in general, and shocked clast content, in particular. There is a consistently signifi cantly larger macroscopic sedimentary to crystalline clast content. On the microscopic scale, the intersample sediment to crystalline clast ratios are quite variable. A very small component of shocked material, in the form of shock-deformed quartz, and to an even lesser degree feldspar, and somewhat more abundant but still relatively scarce shardshaped,altered melt particles, is present throughout the section. However, between ̃458 and 469 m, and between 514 and 527 m depths, the abundance of such melt particlesis notably enhanced. These sections are also chemically distinct and relatively more mafic than the other parts of the Exmore breccia. It appears that from the time of deposition of the 527 m material, calming of the ocean occurred over the crater area as a result of abatement of resurge activity, so that ejecta from the plume abovethe crater could accumulate within the crater area to a larger degree. Deposition ofejecta fallout from the collapsing ejecta plume was terminated by the time of deposition of the 458 m material. This raises questions about the positioning of the exact upper contact of Exmore breccia to post-Exmore sediment (Chickahominy Formation), which is currently placed at 444 m depth and which possibly should be revisedto 458 m depth. Based on a signifi cant record of granite-derived material with shocked minerals, the shocked debris component seems to be largely derived from crystalline target rocks. This provides further evidence that the basement-derived material of the basal section of the Eyreville drill cores, which is essentially unshocked, is likely of an allochthonous nature and that the drilling did not intersect the actual crater floor. 76°W. © 2009 Geological Society of America. 2009 English 00721077 10.1130/2009.2458(29) Special Paper of the Geological Society of America 458 Geological Society of America 655-698 Museum f̈r Naturkunde-Leibniz Institute, Humboldt University Berlin, Invalidenstrasse 43, D-10115 Berlin, Germany; Department of Lithospheric Research, University of Vienna, Althanstrasse 14, A-1090 VA, Austria; Lunar and Planetary Institute, 3600 Bay Area Boulevard, Houston, TX 77058, United States; U.S. Geological Survey, MS 926A, 12201 Sunrise Valley Drive, Reston, VA 20192, United States Crystalline materials; Crystalline rocks; Deposition; Drills; Feldspar; Infill drilling; Mica; Rocks; Sedimentology; Sediments; Stratigraphy, Bioclastic carbonates; Chesapeake bay impact structures; Continental scientific drillings; Crystalline target rocks; Derived materials; Microscopic scale; Strong heterogeneities; U.s. geological surveys, Core drilling, bedform; breccia; clast; crater; deposition; heterogeneity; impactite; particle size; petrography; research program; sedimentary petrology; shock metamorphism, Chesapeake Bay; United States; Virginia https://www.scopus.com/inward/record.uri?eid=2-s2.0-74949125250&doi=10.1130%2f2009.2458%2829%29&partnerID=40&md5=964dbbd7a3d357b21a6f3aecd4a7c5bf cited By 27 W.U. Reimold K. Bartosova R.T. Schmitt B. Hansen C. Crasselt C. Koeberl A. Wittmann D.S. Powars article Wittmann2009377 The Eyreville B drill core in the inner annular moat of the 85-km-diameter Chesapeake Bay impact structure recovered the first coherent impact melt volumes from within the crater as two bodies, 1 and 5.5 m thick. This study focuses on the petrogenesis of these well-preserved rocks. Mixing calculations reveal that the chemical composition of these melts can be modeled as a hybrid of ̃40% sedimentary target and ̃60% crystalline basement component. The melt rocks contain abundant lithic and mineral clasts that display all stages of shock metamorphism. Zircon clasts record the cooling of the melt from temperatures above 1700 °C to below 1200 °C within the first minutes after formation. Glassy melt with a peraluminous, rhyolitic composition that contains ̃5 wt% water is preserved. This melt records a crystallization sequence of aluminum-rich orthopyroxene and hercynitic spinel, followed by plagioclase, titanomagnetite and cordierite, and late sanidine. Spherulitic aluminosilicate-SiO 2 -cordierite aggregates that are comparable to buchites at temperatures below ̃1465 °C complement this assemblage. Lack of hyaloclastic fragmentation suggests dry emplacement conditions. Complete cooling by conductive heat transfer took ̃7 weeks and ̃4 years for the 1-m- and the 5.5-m-thick melt bodies, respectively. Alteration stages below ̃100 °C produced smectite, phillipsite, chalcedony, and a rare zeolite phase that is tentatively identified as terranovaite. © 2009 The Geological Society of America. 2009 English 00721077 10.1130/2009.2458(17) Special Paper of the Geological Society of America 458 Geological Society of America 377-396 Lunar and Planetary Institute, 3600 Bay Area Boulevard, Houston, TX 77058, United States; Museum für Naturkunde-Leibniz Institute, Humboldt University Berlin, Invalidenstrasse 43, 10115 Berlin, Germany; Florida Institute of Technology, Melbourne, FL 32901, United States Feldspar; Heat transfer; Infill drilling; Petrology; Silica; Silicate minerals; Structural geology; Zeolites; Zircon, Chemical compositions; Chesapeake Bay; Chesapeake bay impact structures; Conductive heat transfer; Crystalline basement; Emplacement conditions; Mixing calculations; Titanomagnetites, Core drilling, crater; crystallization; impact structure; marine sediment; petrogenesis; shock metamorphism, Chesapeake Bay; United States https://www.scopus.com/inward/record.uri?eid=2-s2.0-74949125572&doi=10.1130%2f2009.2458%2817%29&partnerID=40&md5=e7616e231af48a47e2a9002b0853c5b7 cited By 40 A. Wittmann R.T. Schmitt L. Hecht D.A. Kring W.U. Reimold H. Povenmire article Pierce2009165 The International Continental Scientific Drilling Program (ICDP) and the U.S. Geological Survey (USGS) drilled three core holes to a composite depth of 1766 m within the moat of the Chesapeake Bay impact structure. Core recovery rates from the drilling were high (̃90%), but problems with core hole collapse limited the geophysical downhole logging to natural-gamma and temperature logs. To supplement the downhole logs, ̃5% of the Chesapeake Bay impact structure cores was processed through the USGS GeoTek multisensor core logger (MSCL) located in Menlo Park, California. The measured physical properties included core thickness (cm), density (g cm -3 ), P-wave velocity (m s -1 ), P-wave amplitude (%), magnetic susceptibility (cgs), and resistivity (ohm-m). Fractional porosity was a secondary calculated property. The MSCL data-sampling interval for all core sections was 1 cm longitudinally. Photos of each MSCL sampled core section were imbedded with the physical property data for direct comparison. These data have been used in seismic, geologic, thermal history, magnetic, and gravity models of the Chesapeake Bay impact structure. Each physical property curve has a unique signature when viewed over the full depth of the Chesapeake Bay impact structure core holes. Variations in the measured properties reflect differences in pre-impact target-rock lithologies and spatial variations in impact-related deformation during late-stage crater collapse and ocean resurge. © 2009 The Geological Society of America. 2009 English 00721077 10.1130/2009.2458(08) Special Paper of the Geological Society of America 458 Geological Society of America 165-179 U.S. Geological Survey, 926A National Center, Reston, VA 20192, United States Boreholes; Infill drilling; Magnetic susceptibility; Seismic waves; Thermal logging; Wave propagation, Chesapeake bay impact structures; Continental scientific drillings; Measured properties; P-wave velocity; Spatial variations; Temperature log; Thermal history; U.s. geological surveys, Structural properties, crater; deformation; drilling; geophysical method; impact structure; magnetic susceptibility; P-wave; physical property, Chesapeake Bay; United States https://www.scopus.com/inward/record.uri?eid=2-s2.0-74949088487&doi=10.1130%2f2009.2458%2808%29&partnerID=40&md5=7eb8a5759465febc0a0ce5f7de8d6914 cited By 7 H.A. Pierce J.B. Murray article Mayr2009137 The physical properties of rocks in drill core from impact structures can be used to distinguish individual nonimpact and impact-generated lithologies, and to investigate the effect of the impact process on the target rocks. Here, we present the results of laboratory measurements of porosity, density, velocity, and thermal properties on the densely sampled cores from the Eyreville borehole in the Chesapeake Bay impact structure, USA. With increasing depth, the lithologies encountered (and porosities) are: postimpact sediments (40%-60%), Exmore breccia and sedimentary blocks (27%-44%), a large megablock of granitoids (<1%), suevite and polymict lithic impact breccia (1%-25%), and schist, granite, and pegmatite of the basementderived section (1%-13%). The low bulk densities and thermal properties of the postimpact sediments show a good correlation with the high porosity values. The physical properties within the Exmore bed sequence overall display relatively small variation but are heterogeneous on the core sample scale. Physical properties along the impact-breccia sequence are highly variable on all scales, and they are interpreted to be controlled by the structural arrangement of particles as well as by the highly variable mineral and clast compositions of the samples. The physical properties of the rocks of the lowermost basement-derived section are also heterogeneous and are interpreted as having been influenced by both lithology and overprinting as a result of the impact process. These results are important for further lithological and petrophysical interpretation and for calibrating future geophysical models of the Chesapeake Bay impact structure. © 2009 The Geological Society of America. 2009 English 00721077 10.1130/2009.2458(07) Special Paper of the Geological Society of America 458 Geological Society of America 137-163 Fachgebiet Angewandte Geophysik, Technische Universität Berlin, Sekr. ACK 2, Ackerstrasse 71-76, D-13355 Berlin, Germany; Russian State Geological Prospecting University, 23 Miklukho-Maklai Street, Moscow, 117997, Russian Federation; Geophysical Institute, Universität Karlsruhe, Hertzstrasse 16, 76187 Karlsruhe, Germany Boreholes; Core drilling; Granite; Infill drilling; Lithology; Porosity; Structural geology; Thermodynamic properties, Chesapeake bay impact structures; Geophysical models; Good correlations; Impact structures; Laboratory measurements; Petrophysical interpretation; Small variations; Structural arrangement, Structural properties, breccia; bulk density; impact structure; physical property; porosity; rock property; sedimentary structure, Chesapeake Bay; United States https://www.scopus.com/inward/record.uri?eid=2-s2.0-74949128569&doi=10.1130%2f2009.2458%2807%29&partnerID=40&md5=be039756fc59ae4363635ea566115c4d cited By 8 S.I. Mayr H. Burkhardt Y. Popov R. Romushkevich D. Miklashevskiy D. Gorobtsov P. Heidinger H. Wilhelm article Rostad2009891 Pore waters from the Chesapeake Bay impact structure cores recovered at Eyreville Farm, Northampton County, Virginia, were analyzed to characterize the dissolved organic carbon. After squeezing or centrifuging, a small volume of pore water, 100 μL, was taken for analysis by electrospray ionization-mass spectrometry. Porewater samples were analyzed directly without filtration or fractionation, in positive and negative mode, for polar organic compounds. Spectra in both modes were dominated by low-molecular-weight ions. Negative mode had clusters of ions differing by -60 daltons, possibly due to increasing concentrations of inorganic salts. The numberaverage molecular weight and weight-average molecular weight values for the pore waters from the Chesapeake Bay impact structure are higher than those reported for other aquatic sources of natural dissolved organic carbon as determined by electrospray ionization-mass spectrometry. In order to address the question of whether drilling mud fluids may have contaminated the pore waters during sample collection, spectra from the pore waters were compared to spectra from drilling mud fluids. Ions indicative of drilling mud fluids were not found in spectra from the pore waters, indicating there was no detectable contamination, and highlighting the usefulness of this analytical technique for detecting potential contamination during sample collection. © 2009 The Geological Society of America. 2009 English 00721077 10.1130/2009.2458(37) Special Paper of the Geological Society of America 458 Geological Society of America 891-903 U.S. Geological Survey, Box 25046, Building 95 MS 408, Denver Federal Center, Denver, CO 80225, United States; U.S. Geological Survey, 12201 Sunrise Valley Drive, MS 431, Reston, VA 20192, United States Boreholes; Dissolution; Electrospray ionization; Infill drilling; Ions; Mass spectrometry; Molecular weight; Mud logging; Organic carbon; Stream flow; Water, Chesapeake bay impact structures; Dissolved organic carbon; Electrospray ionization mass spectrometry; Inorganic salts; Low molecular weight; Polar organic compounds; Sample collection; Weight-average molecular weight, Drilling fluids, analytical method; detection method; dissolved organic carbon; drilling fluid; fractionation; impact structure; ionization; mass spectrometry; organic compound; porewater, Chesapeake Bay; United States; Virginia https://www.scopus.com/inward/record.uri?eid=2-s2.0-84874996887&doi=10.1130%2f2009.2458%2837%29&partnerID=40&md5=ce3250ff23a274a01b7ff7d6e20db4bf cited By 5 C.E. Rostad W.E. Sanford article Sanford2009867 We investigated the groundwater system of the Chesapeake Bay impact structure by analyzing the pore-water chemistry in cores taken from a 1766-m-deep drill hole 10 km north of Cape Charles, Virginia. Pore water was extracted using high-speed centrifuges from over 100 cores sampled from a 1300 m section of the drill hole. The pore-water samples were analyzed for major cations and anions, stable isotopes of water and sulfate, dissolved and total carbon, and bioavailable iron. The results reveal a broad transition between freshwater and saline water from 100 to 500 m depth in the postimpact sediment section, and an underlying synimpact section that is almost entirely filled with brine. The presence of brine in the lowermost postimpact section and the trend in dissolved chloride with depth suggest a transport process dominated by molecular diffusion and slow, compaction-driven, upward flow. Major ion results indicate residual effects of diagenesis from heating, and a pre-impact origin for the brine. High levels of dissolved organic carbon (6-95 mg/L) and the distribution of electron acceptors indicate an environment that may be favorable for microbial activity throughout the drilled section. The concentration and extent of the brine is much greater than had previously been observed, suggesting that its occurrence may be common in the inner crater. However, groundwater-flow conditions in the structure may reduce the saltwater-intrusion hazard associated with the brine. © 2009 The Geological Society of America. 2009 English 00721077 10.1130/2009.2458(36) Special Paper of the Geological Society of America 458 Geological Society of America 867-890 U.S. Geological Survey, Mail Stop 926A, 12201 Sunrise Valley Drive, Reston, VA 20192, United States; Centre for Earth, Planetary, Space and Astronomical Research, Open University, Milton Keynes, MK7 6AA, United Kingdom Chemical analysis; Chlorine compounds; Dissolution; Groundwater; Groundwater flow; Hydrochemistry; Infill drilling; Organic carbon; Rock drills; Salt water intrusion; Sulfur compounds, Chesapeake bay impact structures; Dissolved organic carbon; Electron acceptor; Groundwater system; Microbial activities; Molecular diffusion; Pore-water chemistry; Stable isotopes of water, Saline water, cation; dissolved organic carbon; geological survey; groundwater flow; impact structure; microbial activity; microbial community; paleohydrology; porewater; saline intrusion; sediment core; stable isotope; sulfate; transport process; water chemistry; water resource, Chesapeake Bay; United States; Virginia https://www.scopus.com/inward/record.uri?eid=2-s2.0-74949100401&doi=10.1130%2f2009.2458%2836%29&partnerID=40&md5=4d823a7f8f1d692327d86e93d61e6d8d cited By 22 W.E. Sanford M.A. Voytek D.S. Powars B.F. Jones I.M. Cozzarelli C.S. Cockell R.P. Eganhouse article Larsen2009699 In this study, we extend the knowledge of postimpact alteration processes through an investigation of mineralogy and petrology of 24 samples from the Exmore Formation and sedimentary megablock intervals in the Eyreville borehole within the Chesapeake Bay impact structure and comparisons to similar studies of cored intervals of the Cape Charles borehole. The bulk mineralogical studies reveal quartz, feldspars (microcline and albite), muscovite, smectite-vermiculite clays, and kaolinite with variable quantities of pyrite, zeolites, calcite, and chlorite. X-ray diffraction analysis of the clay (<2 μm) fraction of samples indicates that the clays are dominated by expandable clays with lesser quantities of illite, kaolinite, glauconite, and mixed- layered clays. The expandable clays include smectite, vermiculite, and smectite-vermiculite intergrade varieties; illite interlayering is minimal (generally, <10% illite layers). Thin section and scanning electron microscope petrography in the Exmore breccia show evidence for extensive authigenic expandable clay in the matrix and dispersed pyrite lepispheres and fine calcite rhombs. Grain alteration includes feldspar dissolution and albitization, glauconite recrystallization, and dissolution and expandable-clay replacement of micas. Taken together, the results indicate that low-temperature alteration (maximum temperatures 60-80 °C) is prevalent in the sedimentary clast-rich intervals in the Eyreville cores, and the maximum effects are observed between 600 and 970 m depth. In comparison, the Exmore Formation from the Cape Charles borehole, 8 km to the southwest and overlying the central peak of the inner crater, shows more advanced authigenesis with Fe-rich chlorite, common quartz overgrowths, and mixed-layered illite-smectite clay with as much as 20% interlayered illite. A low-temperature hydrothermal mineral assemblage is documented in suevite and crystalline-clast breccia at depths of 725-820 m in the Cape Charles borehole. The fine-grained clastic target material and contained seawater are argued to have limited initial target melting and initial crater-floor temperatures in the Chesapeake Bay impact structure to an even greater degree than that of other marine craters targeted in consolidated sedimentary substrates. Subsequent hydrothermal circulation was confined to the central uplift and neighboring fractured zones, whereas alteration in the overlying sedimentary breccias involved conductive heat flow, reaction with hypersaline pore fluids, and minor fluid flow into more porous, permeable sedimentary blocks adjacent to the central uplift. © 2009 The Geological Society of America. 2009 English 00721077 10.1130/2009.2458(30) Special Paper of the Geological Society of America 458 Geological Society of America 699-721 Department of Earth Sciences, University of Memphis, Memphis, TN 38152, United States Boreholes; Calcite; Dissolution; Feldspar; Flow of fluids; Kaolinite; Mica; Pyrites; Quartz; Rocks; Scanning electron microscopy; Sedimentology; Silicate minerals; Temperature; X ray powder diffraction; Zeolites, Chesapeake bay impact structures; Feldspar dissolution; Hydrothermal circulation; Hydrothermal mineral assemblages; Low temperature alteration; Low temperatures; Maximum temperature; Sedimentary substrates, Clay alteration, albitization; breccia; dissolution; feldspar; hydrothermal activity; hydrothermal alteration; hydrothermal system; impact structure; kaolinite; mineralogy; muscovite; petrography; quartz; recrystallization; research program; sedimentary petrology; smectite; vermiculite, Chesapeake Bay; United States, Calluna vulgaris; Micas https://www.scopus.com/inward/record.uri?eid=2-s2.0-74949114717&doi=10.1130%2f2009.2458%2830%29&partnerID=40&md5=84830b590c51f1bd871febf0271f576c cited By 7 D. Larsen E.C. Stephens V.B. Zivkovic article Durand2009115 During 2005-2006, the International Continental Scientific Drilling Program and the U.S. Geological Survey drilled three continuous core holes into the Chesapeake Bay impact structure to a total depth of 1766.3 m. A collection of supplemental materials that presents a record of the core recovery and measurement data for the Eyreville cores is available on CD-ROM at the end of this volume and in the GSA Data Repository. The supplemental materials on the CD-ROM include digital photographs of each core box from the three core holes, tables of the three coring-run logs, as recorded on site, and a set of depth-conversion programs. In this chapter, the contents, purposes, and basic applications of the supplemental materials are briefly described. With this information, users can quickly decide if the materials will apply to their specific research needs. © 2009 The Geological Society of America. 2009 English 00721077 10.1130/2009.2458(05) Special Paper of the Geological Society of America 458 Geological Society of America 115-118 U.S. Geological Survey, 926A National Center, 12201 Sunrise Valley Drive, Reston, VA 20192, United States Boreholes; CD-ROM; Infill drilling; Photography, Basic application; Chesapeake bay impact structures; Continental scientific drillings; Conversion programs; Data repositories; Digital photographs; Measurement data; U.s. geological surveys, Electronic document exchange, borehole logging; impact structure; information technology; photograph, Chesapeake Bay; United States https://www.scopus.com/inward/record.uri?eid=2-s2.0-74949124364&doi=10.1130%2f2009.2458%2805%29&partnerID=40&md5=bcce477d7ea7509c9a4a4434260da8f1 cited By 8 C.T. Durand L.E. Edwards M.L. Malinconico D.S. Powars article Malinconico2009905 Vitrinite reflectance data from the International Continental Scientific Drilling Program (ICDP)-U.S. Geological Survey (USGS) Eyreville deep cores in the centralcrater moat of the Chesapeake Bay impact structure and the Cape Charles test holes on the central uplift show patterns of postimpact maximum-temperature distribution that result from a combination of conductive and advective heat flow. Within the crater-fill sediment-clast breccia sequence at Eyreville, an isoreflectance (-0.44% Ro) section (525-1096 m depth) is higher than modeled background coastal-plain maturity and shows a pattern typical of advective fluid flow. Below an intervening granite slab, a short interval of sediment-clast breccia (1371-1397 m) shows a sharp increase in reflectance (0.47%-0.91% Ro) caused by conductive heat from the underlying suevite (1397-1474 m). Refl ectance data in the uppermost suevite range from 1.2% to 2.1% Ro. However, heat conduction alone is not sufficient to affect the temperature of sediments more than 100 m above the suevite. Thermal modeling of the Eyreville suevite as a 390 °C cooling sill-like hot rock layer supplemented by compaction- driven vertical fluid flow (0.046 m/a) of cooling suevitic fluids and deeper basement brines (120 °C) upward through the sediment breccias closely reproduces the measured reflectance data. This scenario would also replace any marine water trapped in the crater fill with more saline brine, similar to that currently in the crater, and it would produce temperatures sufficient to kill microbes in sediment breccias within 450 m above the synimsuevite. A similar downhole maturity pattern is present in the sediment-clast breccia over the central uplift. High-reflectance (5%-9%) black shale and siltstone clasts in the suevite and sediment-clast breccia record a pre-impact (Paleozoic?) metamorphic event. Previously published maturity data in the annular trough indicate no thermal effect there from impact-related processes. © 2009 The Geological Society of America. 2009 English 00721077 10.1130/2009.2458(38) Special Paper of the Geological Society of America 458 Geological Society of America 905-930 U.S. Geological Survey, 926A National Center, Reston, VA 20192, United States; U.S. Geological Survey, 431 National Center, Reston, VA 20192, United States; Department of Geology and Environmental Geosciences, Lafayette College, Easton, PA 18042, United States Boreholes; Compaction; Heat conduction; Infill drilling; Reflection; Rocks; Saline water; Sediments; Software testing, Chesapeake bay impact structures; Conductive heat; Continental scientific drillings; Metamorphic events; Reflectance data; U.s. geological surveys; Vertical fluid flow; Vitrinite reflectance, Flow of fluids, black shale; breccia; crater; fluid flow; geological survey; heat flow; impact structure; Ocean Drilling Program; temperature effect; thermal conductivity; thermal regime; uplift; vitrinite reflectance, Chesapeake Bay; United States, Calluna vulgaris https://www.scopus.com/inward/record.uri?eid=2-s2.0-74949126189&doi=10.1130%2f2009.2458%2838%29&partnerID=40&md5=ed452658d198522b310e1a0774420030 cited By 17 M.L. Malinconico W.E. Sanford W.J.J. Wright Horton Jr. article Gibson2009235 Pre-impact crystalline rocks of the lowermost 215 m of the Eyreville B drill core from the Chesapeake Bay impact structure consist of a sequence of pelitic mica schists with subsidiary metagraywackes or felsic metavolcanic rocks, amphibolite, and calc-silicate rock that is intruded by muscovite (±biotite, garnet) granite and granite pegmatite. The schists are commonly graphitic and pyritic and locally contain plagioclase porphyroblasts, fi brolitic sillimanite, and garnet that indicate middle- to upper-amphibolite-facies peak metamorphic conditions estimated at ̃0.4-0.5 GPa and 600-670 °C. The schists display an intense, shallowly dipping, S1 composite shear foliation with local micrometer- to decimeter-scale recumbent folds and S-C' shear band structures that formed at high temperatures. Zones of chaotically oriented foliation, resembling breccias but showing no signs of retrogression, are developed locally and are interpreted as shear-disrupted fold hinges. Mineral textural relations in the mica schists indicate that the metamorphic peak was attained during D1. Fabric analysis indicates, however, that subhorizontal shear deformation continued during retrograde cooling, forming mylonite zones in which high-temperature shear fabrics (S-C and S-C') are overprinted by progressively lower- temperature fabrics. Cataclasites and carbonate-cemented breccias in more competent lithologies such as the calc-silicate unit and in the felsic gneiss found as boulders in the overlying impactite succession may refl ect a fi nal pulse of low-temperature cataclastic deformation during D1. These breccias and the shear and mylonitic foliations are cut by smaller, steeply inclined anastomosing fractures with chlorite and calcite infill (interpreted as D2). This D2 event was accompanied by extensive chlorite-sericitecalcite ± epidote retrogression and appears to predate the impact event. Granite and granite pegmatite veins display local discordance to the S1 foliation, but elsewhere they are affected by high-temperature mylonitic shear deformation, suggesting a late-D1 intrusive timing close to the metamorphic peak. The D1 event is tentatively interpreted as a thrusting event associated with westward-verging collision between Gondwana and Laurentia before or during the Permian-Carboniferous Alleghanian orogeny. It is unclear whether subsequent brittle deformation, described here as D2, could be part of regional dextral Alleghanian strike-slip faulting or younger Mesozoic normal faulting. © 2009 The Geological Society of America. 2009 English 00721077 10.1130/2009.2458(12) Special Paper of the Geological Society of America 458 Geological Society of America 235-254 Impact Cratering Research Group, School of Geosciences, University of the Witwatersrand, P.O. WITS, Johannesburg 2050, South Africa; U.S. Geological Survey, 926A National Center, Reston, VA 20192, United States; Museum für Naturkunde-eibniz Institute, Humboldt University Berlin, Invalidenstrasse 43, 10115 Berlin, Germany Calcite; Core drilling; Crystalline materials; Fault slips; Feldspar; Garnets; Granite; Infill drilling; Mica; Shear deformation; Silicate minerals; Strike-slip faults; Structural geology; Temperature, Amphibolite facies; Brittle deformation; Cataclastic deformation; Chesapeake bay impact structures; Crystalline basement; Metamorphic conditions; Metavolcanic rocks; Strike slip faulting, Crystalline rocks, amphibolite; brittle deformation; crystalline rock; faulting; impact structure; metagreywacke; metamorphism; metavolcanic rock; schist; tectonic evolution; thermal evolution, Chesapeake Bay; United States https://www.scopus.com/inward/record.uri?eid=2-s2.0-74949139873&doi=10.1130%2f2009.2458%2812%29&partnerID=40&md5=a4b46a449cd73b6b00e9a9f1a32862f9 cited By 14 R.L. Gibson G.N. Townsend J.W. Horton Jr. W.U. Reimold article Gohn2009587 An unusually thick section of sedimentary breccias dominated by target-sediment clasts is a distinctive feature of the late Eocene Chesapeake Bay impact structure. A cored 1766-m-deep section recovered from the central part of this marine-target structure by the International Continental Scientific Drilling Program (ICDP)-U.S. Geological Survey (USGS) drilling project contains 678 m of these breccias and associated sediments and an intervening 275-m-thick granite slab. Two sedimentary breccia units consist almost entirely of Cretaceous nonmarine sediments derived from the lower part of the target sediment layer. These sediments are present as coherent clasts and as autoclastic matrix between the clasts. Primary (Cretaceous) sedimentary structures are well preserved in some clasts, and liquefaction and fluidization structures produced at the site of deposition occur in the clasts and matrix. These sedimentary breccias are interpreted as one or more rock avalanches from the upper part of the transient-cavity wall. The little-deformed, unshocked granite slab probably was transported as part of an extremely large slide or avalanche. Water-saturated Cretaceous quartz sand below the slab was transported into the seafloor crater prior to, or concurrently with, the granite slab. Two sedimentary breccia units consist of polymict diamictons that contain cobbles, boulders, and blocks of Cretaceous nonmarine target sediments and less common shocked-rock and melt ejecta in an unsorted, unstratified, muddy, fossiliferous, glauconitic quartz matrix. Much of the matrix material was derived from Upper Cretaceous and Paleogene marine target sediments. These units are interpreted as the deposits of debris flows initiated by the resurge of ocean water into the seafloor crater. Interlayering of avalanche and debris-flow units indicates a partial temporal overlap of the earlier avalanche and later resurge processes. A thin unit of stratified turbidite deposits and overlying laminated fine-grained deposits at the top of the section represents the transition to normal shelf sedimentation. © 2009 The Geological Society of America. 2009 English 00721077 10.1130/2009.2458(26) Special Paper of the Geological Society of America 458 Geological Society of America 587-615 U.S. Geological Survey, 926A National Center, Reston, VA 20192, United States; University of Oslo, P.O. Box 1047, Blindern, N-0316 Oslo, Norway Debris; Deposits; Fluidization; Granite; Infill drilling; Quartz; Sedimentology; Sediments, Chesapeake bay impact structures; Continental scientific drillings; Fluidization structures; Sedimentary structure; Shelf sedimentation; Transient cavities; Turbidite deposits; U.s. geological surveys, Sedimentary rocks, breccia; clast; debris flow; deposition; diamicton; Eocene; fluidization; impact structure; marine sediment; matrix; research program; rock avalanche; sediment transport; sedimentation; turbidite, Chesapeake Bay; United States; Virginia https://www.scopus.com/inward/record.uri?eid=2-s2.0-74949127901&doi=10.1130%2f2009.2458%2826%29&partnerID=40&md5=159b5d2ebbb334eaf6ce5b973386b9ed cited By 28 G.S. Gohn D.S. Powars H. Dypvik L.E. Edwards article Elbra2009119 Chesapeake is a 35-Ma-old shallow-marine, complex impact structure with a diameter of ̃85 km. The structure is completely buried beneath several hundreds of meters of postimpact sediments. Therefore, subsurface information can be obtained only from geophysical surveys and drill holes. Recently, deep drilling into the inner crater zone, at Eyreville near Cape Charles, was carried out in order to provide constraints on geophysical modeling and cratering processes in a multilayered marine target. We analyzed samples of the Eyreville core including postimpact, impactproduced, and basement-derived units in order to clarify the magneto-mineralogy, to provide physical parameters for better understanding the influence of the impact on the petrophysical and rock-magnetic properties, and to provide rock-magnetic data for magnetic modeling. Results show a complex behavior of physical properties of the lithologies in the Eyreville core due to different lithologies having been affected by shock-induced changes. Our data suggest that pyrrhotite and magnetite carry the magnetic properties in most of the core samples, whereas hematite is present in oxidized clays from the uppermost impact-generated unit (Exmore beds) and related sediment megablocks. The granitic megablock appears to be undeformed based on lack of brittle deformation in magnetite and petrophysically appears as a single block. In contrast, the impactite sequence below the megablock shows brittle deformation and magnetic fabric randomization, and the pyrrhotite in the associated schist fragments is strongly fractured. Thus, the Chesapeake Bay deep core provides an extraordinary opportunity to study the effect of impact on magnetite and pyrrhotite, the two main magnetic minerals creating crustal magnetic anomalies. © 2009 The Geological Society of America. 2009 English 00721077 10.1130/2009.2458(06) Special Paper of the Geological Society of America 458 Geological Society of America 119-135 Laboratory of Solid Earth Geophysics, Department of Physics, 00014 University of Helsinki, P.O. Box 64, Finland; Institute of Applied Geosciences, Karlsruhe University, Hertzstrasse 16, 76187 Karlsruhe, Germany Core samples; Deformation; Geomagnetism; Hematite; Infill drilling; Iron ores; Lithology; Magnetic properties; Magnetite; Petrophysics; Structural geology, Brittle deformation; Chesapeake bay impact structures; Crustal magnetic anomalies; Geophysical modeling; Geophysical surveys; Physical parameters; Rock magnetic properties; Subsurface information, Structural properties, brittle deformation; cratering; geophysical survey; hematite; impact structure; magnetic anomaly; magnetic method; magnetic mineral; magnetic property; magnetite; mineralogy; physical property; pyrrhotite, Chesapeake Bay; United States https://www.scopus.com/inward/record.uri?eid=2-s2.0-74949111562&doi=10.1130%2f2009.2458%2806%29&partnerID=40&md5=99a236211722fc3123ed6f7b9db4dce5 cited By 15 T. Elbra A. Kontny L.J. Pesonen article McDonald2009469 This paper documents an attempt to detect a meteoritic component in both washback (resurge) crater-fill breccia (the so-called Exmore breccia) and in suevites from the Eyreville core hole, which was drilled several kilometers from the center of the 85-km-diameter Chesapeake Bay impact structure, Virginia, USA. Determining the presence of an extraterrestrial component and, in particular, the projectile type for this structure, which is the largest impact structure currently known in the United States, is of importance because it marks one of several large impact events in the late Eocene, during which time the presence of extraterrestrial 3He and multiple impact ejecta layers provide evidence for a comet or asteroid shower. Previous work has indicated an ordinary chondritic projectile for the largest of the late Eocene craters, the Popigai impact structure in Siberia. The exact relation between the Chesapeake Bay impact event and siderophile element anomalies documented in late Eocene ejecta layers from around the world is not clear. The only clear indication for an extraterrestrial component related to this structure has been the discovery of a meteoritic osmium isotopic signature in impact melt rocks recovered from a hydrogeologic test hole located on Cape Charles near the center of the structure, and confirmation of a similar signature in suevitic rocks would have been desirable in order to place constraints on the type of projectile involved in formation of the Chesapeake Bay crater. Unfortunately, the current data show no discernible differences in the contents of the platinum group elements (PGEs) among the suevite, the Exmore breccia, and several crystalline basement rocks, all from the Eyreville core hole. Abundances of PGEs are uniformly low (e.g., <0.1 ppb Ir), and chondrite-normalized abundance patterns are nonchondritic. These data do not allow unambiguous verification of an extraterrestrial signature. Thus, the nature of the Chesapeake Bay projectile remains ambiguous. © 2009 The Geological Society of America. 2009 English 00721077 10.1130/2009.2458(21) Special Paper of the Geological Society of America 458 Geological Society of America 469-479 School of Earth, Ocean and Planetary Sciences, Cardiff University, Park Place, Cardiff CF10 3YE, United Kingdom; Department of Lithospheric Research, University of Vienna, Althanstrasse 14, Vienna, A-1090, Austria Crystalline rocks; Hydrogeology; Infill drilling; Isotopes; Meteorites; Platinum; Projectiles; Rocks, Chesapeake bay impact structures; Crystalline basement; Extraterrestrial components; Impact structures; Isotopic signatures; Platinum group elements; Platinum group elements (PGEs); Siderophile elements, Economic geology, breccia; chondrite; coastal sediment; ejecta; Eocene; impact structure; isotopic composition; meteorite; osmium; platinum group element; research program; sediment chemistry; siderophile element; suevite, Chesapeake Bay; United States https://www.scopus.com/inward/record.uri?eid=2-s2.0-74949113207&doi=10.1130%2f2009.2458%2821%29&partnerID=40&md5=e7dacf6de41d8b08642e5cbda3f4ac73 cited By 10 I. Mcdonald K. Bartosova C. Koeberl article Belkin2009447 Optical and electron-beam petrography of melt-rich suevite and melt-rock clasts from selected samples from the Eyreville B core, Chesapeake Bay impact structure, reveal a variety of silicate glasses and coexisting sulfur-rich melts, now quenched to various sulfi de minerals (±iron). The glasses show a wide variety of textures, fl ow banding, compositions, devitrifi cation, and hydration states. Electron-microprobe analyses yield a compositional range of glasses from high SiO 2 (&gt;90 wt%) through a range of lower SiO 2 (55-75 wt%) with no relationship to depth of sample. Some samples show spherical globules of different composition with sharp menisci, suggesting immiscibility at the time of quenching. Isotropic globules of higher interfacial tension glass (64 wt% SiO 2 ) are in sharp contact with lower-surface-tension, high-silica glass (95 wt% SiO 2 ). Immiscible glass-pair composition relationships show that the immiscibility is not stable and probably represents incomplete mixing. Devitrifi cation varies and some low-silica, high-iron glasses appear to have formed Fe-rich smectite; other glass compositions have formed rapid quench textures of corundum, orthopyroxene, clinopyroxene, magnetite, K-feldspar, plagioclase, chrome-spinel, and hercynite. Hydration (H 2 O by difference) varies from ~10 wt% to essentially anhydrous; high-SiO 2 glasses tend to contain less H2O. Petrographic relationships show decomposition of pyrite and melting of pyrrhotite through the transformation series; pyrite? pyrrhotite? troilite→ iron. Spheres (~1 to ~50 μm) of quenched immiscible sulfi de melt in silicate glass show a range of compositions and include phases such as pentlandite, chalcopyrite, Ni-As, monosulfi de solid solution, troilite, and rare Ni-Fe. Other sulfi de spheres contain small blebs of pure iron and exhibit a continuum with increasing iron content to spheres that consist of pure iron with small, remnant blebs of Fe-sulfi de. The Ni-rich sulfi de phases can be explained by melting and/or concentrating targetderived Ni without requiring an asteroid impactor source component. The presence of locally unaltered glasses in these rocks suggests that in some rock volumes, isolation from postimpact hydrothermal systems was suffi cient for glass preservation. Pressure and temperature indicators suggest that, on a thin-section scale, the suevites record rapid mixing and accumulation of particles that sustained widely different peak temperatures, from clasts that never exceeded 300 ± 50 °C, to the bulk of the glasses where melted sulfi de and unmelted monazite suggest temperatures of 1500 ± 200 °C. The presence of coesite in some glass-bearing samples suggests that pressures exceeded ~3 GPa. © 2009 Geological Society of America. 2009 English 00721077 10.1130/2009.2458(20) Special Paper of the Geological Society of America 458 Geological Society of America 447-468 U.S. Geological Survey, 956 National Center, Reston, VA 20192, United States Copper compounds; Corundum; Electron probe microanalysis; Feldspar; Hydration; Iron; Magnetite; Melting; Mixing; Phosphate minerals; Positive ions; Pyrites; Silica; Silicates; Spheres; Structure (composition); Sulfur compounds; Textures, Chesapeake bay impact structures; Compositional range; Glass compositions; High silica glass; Hydrothermal system; Peak temperatures; Pressure and temperature; Spherical globules, Glass, chemical composition; crater; impact structure; marine sediment; silicate; suevite; sulfide, Chesapeake Bay; United States https://www.scopus.com/inward/record.uri?eid=2-s2.0-74949122430&doi=10.1130%2f2009.2458%2820%29&partnerID=40&md5=5ca1226aa9e9420bee23fda38c5ea263 cited By 14 H.E. Belkin J.W. Horton Jr. article Townsend2009255 The Eyreville B core from the Chesapeake Bay impact structure, Virginia, USA, contains a lower basement-derived section (1551.19 m to 1766.32 m deep) and two megablocks of dominantly (1) amphibolite (1376.38 m to 1389.35 m deep) and (2) granite (1095.74 m to 1371.11 m deep), which are separated by an impactite succession. Metasedimentary rocks (muscovite-quartz-plagioclase-biotite-graphite ± fibrolite ± garnet ± tourmaline ± pyrite ± rutile ± pyrrhotite mica schist, hornblende-plagioclase-epidote-biotite- K-feldspar-quartz-titanite-calcite amphibolite, and vesuvianite-plagioclase- quartz-epidote calc-silicate rock) are dominant in the upper part of the lower basement-derived section, and they are intruded by pegmatitic to coarse-grained granite (K-feldspar-plagioclase-quartz-muscovite ± biotite ± garnet) that increases in volume proportion downward. The granite megablock contains both gneissic and weakly or nonfoliated biotite granite varieties (K-feldspar-quartz-plagioclase-biotite ± muscovite ± pyrite), with small schist xenoliths consisting of biotite-plagioclase-quartz ± epidote ± amphibole. The lower basement-derived section and both megablocks exhibit similar middleto upper-amphibolite-facies metamorphic grades that suggest they might represent parts of a single terrane. However, the mica schists in the lower basement-derived sequence and in the megablock xenoliths show differences in both mineralogy and whole-rock chemistry that suggest a more mafi c source for the xenoliths. Similarly, the mineralogy of the amphibolite in the lower basement-derived section and its association with calc-silicate rock suggest a sedimentary protolith, whereas the bulk-rock and mineral chemistry of the megablock amphibolite indicate an igneous protolith. The lower basement-derived granite also shows bulk chemical and mineralogical differences from the megablock gneissic and biotite granites. © 2009 The Geological Society of America. 2009 English 00721077 10.1130/2009.2458(13) Special Paper of the Geological Society of America 458 Geological Society of America 255-275 Impact Cratering Research Group, School of Geosciences, University of the Witwatersrand, P.O. WITS, Johannesburg 2050, South Africa; U.S. Geological Survey, 926A National Center, Reston, VA 20192, United States; Museum für Naturkunde-Leibniz Institute, Humboldt University Berlin, Invalidenstrasse 43, 10115 Berlin, Germany; Department of Geological Sciences, University of Vienna, Althanstrasse 14, Vienna A-1090, Austria Biotite; Buildings; Calcite; Feldspar; Granite; Quartz; Sedimentary rocks; Silicate minerals, Amphibolite facies; Biotite granite; Chesapeake bay impact structures; Crystalline basement; Metamorphic grade; Metasedimentary rocks; Mineral chemistry; Silicate rocks, Mica, amphibolite; crater; geochemistry; granite; impact structure; impactite; metasedimentary rock; petrography; schist, Chesapeake Bay; United States https://www.scopus.com/inward/record.uri?eid=2-s2.0-74949135099&doi=10.1130%2f2009.2458%2813%29&partnerID=40&md5=1c0a2e477486c4610058a2cc1a6ec85c cited By 18 G.N. Townsend R.L. Gibson J.W. Horton Jr. W.U. Reimold R.T. Schmitt K. Bartosova article FerrellJr.2009723 Core descriptions, thin-section analyses, and X-ray powder diffraction analyses of whole-rock samples and clay-sized fractions were employed to interpret the sedimentology and mineralogy of synimpact Exmore beds and the overlying Chickahominy Formation. This study attempts to explain the origin and postdepositional alteration of materials in the Eyreville core from the central zone of the Chesapeake Bay impact crater. Samples were obtained from eight zones extending from core depths of 435 to 1471 m, with emphasis on the interval from 435 to 455 m, representing the upper Exmore beds and the lower Chickahominy Formation. Qualitative clay mineral determinations were aided by peak decomposition procedures to unravel overlapping diffraction bands, and quantifi cation was accomplished by least squares matching of actual and computed patterns. The major facies in approximate ascending order are suevite breccias, poorly sorted conglomerate and sandstone, and upward-fi ning glauconitic sandstone within the Exmore beds followed by parallel laminated sandy siltstone and claystone in the Chickahominy Formation. They all contain clay minerals (mica, smectites, and some serpentine, kaolinite, and chlorite) plus quartz and feldspar. Heulandite, pyrite, calcite, and disordered silica (partly representing nanofossils and microfossils) are present in the Chickahominy Formation. The boundary beds (upper 7 m) of the Exmore beds have higher clay contents but fewer varieties of expandable clay minerals than in the Chickahominy Formation. The Exmore beds are enriched in reworked glauconite, but there are no indications of heulandite, calcite, disordered silica, or pyrite, except in the very top of the 7-m-thick boundary bed interval. The clay fractions of the Eyreville materials are dominated by different species of expanding clay minerals (smectite, fi ne and coarsely crystalline nontronite, and fi ne and coarsely crystalline smectite-illite mixed-layered clay minerals), but dioctahedral mica and illite are also present. Amorphous material and minor amounts of quartz,chlorite, and mixed-layered smectite (0.95)/iron-rich illite (0.05) are common. The abundance of the clays in most intervals is highly variable due to the chaotic assemblage of sediments and crystalline materials from diverse sources. The boundary beds are dominated by a single smectitic mineral, nontronite, which is assumed to be the principal product of melt glass alteration. Amorphous material (melt glass) and nontronite are calculated to represent 13 vol% and 13-19 vol% of the sediments in this interval, respectively. Grain size, or clast size, has a major infl uence on mineralogical variability, i.e., when grain size (clast size) is large, the mineral content of adjacent samples is highly variable. © 2009 The Geological Society of America. 2009 English 00721077 10.1130/2009.2458(31) Special Paper of the Geological Society of America 458 Geological Society of America 723-746 Department of Geology and Geophysics, Louisiana State University, Baton Rouge, LA 70803, United States; Department of Geosciences, University of Oslo, P.O. Box 1047, Blindern, NO 0316, Oslo, Norway Calcite; Crystalline materials; Diffraction; Feldspar; Glass; Grain size and shape; Kaolinite; Mica; Pyrites; Quartz; Sandstone; Sediments; Serpentine; Silicate minerals; X ray powder diffraction; Zeolites, Chesapeake bay impact structures; Clay-sized fractions; Diffraction bands; Disordered silicas; Glass alteration; Layered clay minerals; Least-squares matching; Quantifi cations, Core samples, clay mineral; depositional sequence; facies; glauconite; grain size; illite; impact structure; least squares method; mineral alteration; mineralogy; qualitative analysis; sedimentology; X-ray diffraction, Chesapeake Bay; United States https://www.scopus.com/inward/record.uri?eid=2-s2.0-74949110811&doi=10.1130%2f2009.2458%2831%29&partnerID=40&md5=1a404644b1c3f1ed071b52e5b35c26b0 cited By 19 R.E. Ferrell Jr. H. Dypvik article Wittmann2009349 The International Continental Scientific Drilling Program (ICDP)-U.S. Geological Survey (USGS) Eyreville boreholes through the annular moat of the Chesapeake Bay crater recovered polymict impact breccias and associated rocks from the depth range of 1397-1551 m. These rocks record cratering processes before burial beneath resurge deposits. Quantitative analyses of clast sizes, matrix contents, and distribution of impact melt reveal a shock metamorphic gradient in these impactites. The reason for the low estimated quantity of impact melt in the crater (̃10 km3) remains elusive. Possible causes may relate to increased excavation efficiency due to a high ratio of water column and sedimentary target to depth of excavation, an oblique impact, or a buried melt sheet at depth. A plausible petrogenetic scenario consists of a lower blockrich section that slumped from an outer region of the transient cavity into the annular moat ̃1.5 min after impact. This blocky debris was mixed with the remains of the excavation fl ow, which contained a pod of melt entrained in ground-surge debris on top. Subsequently, melt-rich suevites were emplaced that record interaction of the expanding ejecta plume with fallback material related to the evolving central uplift. A clast-rich impact melt rock that likely shed off the central uplift covers these suevites. Incipient collapse of the ejecta plume is recorded in the uppermost subunit, but the arrival of resurge fl ow terminated its continuous deposition ̃6-8 min after impact. Limited thermal annealing allowed preservation of glassy melt and high-pressure polymorphs. Mild hydrothermal overprint in the central crater was likely driven by the structural uplift of ̃100 °C warmer basement rocks. © 2009 The Geological Society of America. 2009 English 00721077 10.1130/2009.2458(16) Special Paper of the Geological Society of America 458 Geological Society of America 349-376 Lunar and Planetary Institute, 3600 Bay Area Boulevard, Houston, TX 77058, United States; Museum für Naturkunde-Leibniz Institute, Humboldt University Berlin, Invalidenstrasse 43, 10115 Berlin, Germany Boreholes; Debris; Excavation; Infill drilling; Structural geology, Basement rocks; Continental scientific drillings; Continuous deposition; High-pressure polymorph; Oblique impact; Thermal-annealing; Transient cavities; U.s. geological surveys, Rocks, crater; drilling; impact structure; impactite; marine sediment; petrogenesis; suevite, Chesapeake Bay; United States https://www.scopus.com/inward/record.uri?eid=2-s2.0-74949108058&doi=10.1130%2f2009.2458%2816%29&partnerID=40&md5=0961170ceac9858e8ce5a69c92465198 cited By 28 A. Wittmann W.U. Reimold R.T. Schmitt L. Hecht T. Kenkmann article Schulte2009839 A multidisciplinary investigation of the Eocene-Oligocene transition in the International Continental Scientific Drilling Program (ICDP)-U.S. Geological Survey (USGS) Eyreville core from the Chesapeake Bay impact basin was conducted in order to document environmental changes and sequence stratigraphic setting. Planktonic foraminifera and calcareous nannofossil biostratigraphy indicate that the Eyreville core includes an expanded upper Eocene (Biozones E15 to E16 and NP19/20 to NP21, respectively) and a condensed Oligocene-Miocene (NP24-NN1) sedimentary sequence. The Eocene-Oligocene contact corresponds to a =3-Ma-long hiatus. Eocene- Oligocene sedimentation is dominated by great diversity and varying amounts of detrital and authigenic minerals. Four sedimentary intervals are identified by lithology and mineral content: (1) A 30-m-thick, smectite- and illite-rich interval directly overlies the Exmore Formation, suggesting long-term reworking of impact debris within the Chesapeake Bay impact structure. (2) Subsequently, an increase in kaolinite content suggests erosion from soils developed during late Eocene warm and humid climate in agreement with data derived from other Atlantic sites. However, the kaolinite increase may also be explained by change to a predominant sediment input from outside the Chesapeake Bay impact structure caused by progradation of more proximal facies belts during the highstand systems tract of the late Eocene sequence E10.Spectral analysis based on gamma-ray and magnetic susceptibility logs suggests infl uence of 1.2 Ma low-amplitude oscillation of the obliquity period during the late Eocene. (3) During the latest Eocene (Biozones NP21 and E16), several lithological contacts (clay to clayey silt) occur concomitant with a prominent change in the mineralogical composition with illite as a major component: This lithological change starts close to the Biozone NP19/20-NP21 boundary and may correspond to sequence boundary E10-E11 as observed in other northwest Atlantic margin sections. It could result from a shift to more distal depositional environments and condensed sedimentation during maximum fl ooding, rather than refl ecting a climatic change in the hinterland. The distinct 1% increase of the oxygen isotopes may correspond to the short-term latest Eocene "precursor isotope event." (4) The abrupt increase of sediment grainsize, carbonate content, and abundance of authigenic minerals (glauconite) across the major unconformity that separates Eocene from Oligocene sediments in the Eyreville core refl ects deposition in shallower settings associated with erosion, winnowing, and reworking. Sediments within the central crater were affected by the rapid eustatic sea-level changes associated with the greenhouse-icehouse transition, as well as by an abrupt major uplift event and possibly enhanced current activity on the northwestern Atlantic margin. © 2009 The Geological Society of America. 2009 English 00721077 10.1130/2009.2458(35) Special Paper of the Geological Society of America 458 Geological Society of America 839-865 GeoZentrum Nordbayern, Universität Erlangen, D-91054 Erlangen, Germany; Department of Earth and Planetary Sciences, Rutgers University, Piscataway, NJ 08901, United States; Department of Geology and Geophysics, Texas A and M University, College Station, TX 77843-3115, United States; Geologisches Institut der Universität Karlsruhe, Strukturgeologie und Tektonophysik, D-76187 Karlsruhe, Germany; U.S. Geological Survey, 926A National Center, Reston, VA 20192, United States Deposition; Erosion; Gamma rays; Infill drilling; Isotopes; Kaolinite; Lithology; Magnetic susceptibility; Mica; Sea level; Sedimentology; Stratigraphy, Chesapeake bay impact structures; Continental scientific drillings; Depositional environment; Highstand systems tract; Mineralogical compositions; Planktonic foraminifera; U.s. geological surveys; Warm and humid climates, Sediments, biostratigraphy; depositional environment; Eocene-Oligocene boundary; eustacy; geological survey; impact structure; lithology; paleoclimate; progradation; sea level change; sedimentary sequence; sedimentation; sequence boundary; sequence stratigraphy; systems tract, Atlantic Ocean; Atlantic Ocean (West); Chesapeake Bay; United States, Foraminifera https://www.scopus.com/inward/record.uri?eid=2-s2.0-74949144241&doi=10.1130%2f2009.2458%2835%29&partnerID=40&md5=052db37a4ba252be566f77790bcfb9f1 cited By 9 P. Schulte B.S. Wade A. Kontny J.M. Self-Trail article Poag2009747 The late Eocene Chesapeake Bay bolide impact transformed its offshore target site from an outer neritic, midshelf seafl oor into a bathyal crater basin. To obtain a depositional record from one of the deepest parts of this basin, the U.S. Geological Survey (USGS) and the International Continental Scientifi c Drilling Program (ICDP) drilled a 1.76-km-deep core hole near Eyreville, Virginia. The Eyreville core and eight previously cored boreholes contain a rarely obtainable record of marine deposition and microfossil assemblages that characterize the transition from synimpact to postimpact paleoenvironments inside and near a submarine impact crater. I used depositional style and benthic foraminiferal assemblages to recognize a four-step transitional succession, with emphasis on the Eyreville core. Step 1 is represented by small-scale, silt-rich turbidites, devoid of indigenous microfossils, which lie directly above the crater-fi lling Exmore breccia. Step 2 is represented by very thin, parallel, silt and clay laminae, which accumulated on a relatively tranquil and stagnant seafl oor. This stagnation created a dead zone, which excluded seafl oor biota, and it lasted ~3-5 ka. Step 3 is an interval of marine clay deposition, accompanied by a burst of microfaunal activity, as a species-rich pioneer community of benthic foraminifera repopulated the impact site. The presence of a diagnostic suite of agglutinated foraminifera during step 3 indicates that paleoenvironmental stress related to the impact lasted from ~9 ka to 400 ka at different locations inside the crater. During step 4, the agglutinated assemblage disappeared, and an equilibrium foraminiferal community developed that contained nearly 100% calcareous species. In contrast to intracrater localities, core sites outside and near the crater rim show neither evidence of the agglutinated assemblage, nor other indications of long-term biotic disruption from the bolide impact. © 2009 The Geological Society of America. 2009 English 00721077 10.1130/2009.2458(32) Special Paper of the Geological Society of America 458 Geological Society of America 747-773 U.S. Geological Survey, 384 Woods Hole Road, Woods Hole, MA 02543-1598, United States C (programming language); Deposition; Infill drilling; Offshore oil well production; Silt, Agglutinated foraminifera; Benthic foraminifera; Foraminiferal assemblages; Impact craters; Microfossil assemblages; Offshore targets; Paleoenvironments; U.s. geological surveys, Boreholes, accumulation; benthic foraminifera; bolide; crater; deep drilling; deep-sea sediment; deposition; depositional environment; Eocene; fossil assemblage; geological survey; impact structure; paleoenvironment; turbidite, Chesapeake Bay; United States; Virginia, Foraminifera https://www.scopus.com/inward/record.uri?eid=2-s2.0-74949120031&doi=10.1130%2f2009.2458%2832%29&partnerID=40&md5=0791f092ca8f00cfdb1c1b54ddd82c0e cited By 7 C.W. Poag article Self-Trail2009633 Biostratigraphic analysis of sedimentary breccias and diamictons in the Chesapeake Bay impact structure provides information regarding the timing and processes of late-stage gravitational crater collapse and ocean resurge. Studies of calcareous nannofossil and palynomorph assemblages in the International Continental Scientific Drilling Program (ICDP)-U.S. Geological Survey (USGS) Eyreville A and B cores show the mixed-age, mixed-preservation microfossil assemblages that are typical of deposits from the upper part of the Chesapeake Bay impact structure. Sparse, poorly preserved, possibly thermally altered pollen is present within a gravelly sand interval below the granite slab at 1392 m in Eyreville core B, an interval that is otherwise barren of calcareous nannofossils and dinocysts. Gravitational collapse of watersaturated sediments from the transient crater wall resulted in the deposition of sediment clasts primarily derived from the nonmarine Cretaceous Potomac Formation. Collapse occurred before the arrival of resurge. Low pollen Thermal Alteration Index (TAI) values suggest that these sediments were not thermally altered by contact with the melt sheet. The arrival of resurge sedimentation is identified based on the presence of diamicton zones and stringers rich in glauconite and marine microfossils at 866.7 m. This horizon can be traced across the crater and can be used to identify gravitational collapse versus ocean-resurge sedimentation. Glauconitic quartz sand diamicton dominates the sediments above 618.2 m. Calcareous nannofossil and dinoflagellate data from this interval suggest that the earliest arriving resurge from the west contained little or no Cretaceous marine input, but later resurge pulses mined Cretaceous sediments east of the Watkins core in the annular trough. Additionally, the increased distance traveled by resurge to the central crater in turbulent flow conditions resulted in the disaggregation of Paleogene unconsolidated sediments. As a result, intact Paleogene clasts in Eyreville cores are rare, but clasts of semilithified Potomac Formation silts and clays are common. © 2009 The Geological Society of America. 2009 English 00721077 10.1130/2009.2458(28) Special Paper of the Geological Society of America 458 Geological Society of America 633-654 U.S. Geological Survey, 926A National Center, Reston, VA 20192, United States Gravitational effects; Infill drilling; Mica; Stars, Biostratigraphic analysis; Calcareous nannofossil; Calcareous nannofossils; Chesapeake bay impact structures; Continental scientific drillings; Microfossil assemblages; U.s. geological surveys; Unconsolidated sediment, Sediments, biostratigraphy; breccia; crater; diamicton; dinoflagellate cyst; fossil assemblage; infill; microfossil; micropaleontology; Paleogene; palynomorph; pollen; research program; sedimentation; turbulent flow, Chesapeake Bay; United States, Dinophyceae https://www.scopus.com/inward/record.uri?eid=2-s2.0-74949125569&doi=10.1130%2f2009.2458%2828%29&partnerID=40&md5=580f6f3fa77269508c9ff0896daf5bbf cited By 17 J.M. Self-Trail L.E. Edwards R.J. Litwin article Skála2009435 The International Continental Scientific Drilling Program (ICDP)-U.S. Geological Survey (USGS) Eyreville B core hole, drilled into the 35.5-Ma-old Chesapeake Bay impact crater, Virginia, has recovered postimpact sediments, crater-fill breccias, megablocks of the crystalline basement, and suevites with fresh glass shards. Bulk rock analyses of 2 glass shards, 21 crystalline target rocks, and microchemical analyses of 7 glass shards and 3 bediasites (tektites of the North American strewn field) were performed in order to contribute to the understanding of formation processes and to better constrain the precursor materials of these glasses as well as of the bediasites. Statistical treatment (hierarchical cluster analyses) yielded an assignment of the data for the crystalline basement samples into four groups; two of those (various schists, meta-graywackes, and gneisses) display characteristics similar to the impact glasses in the suevites and the bediasites. However, the suevitic glasses show a broad range in composition at the micrometer scale. These data show the frequent presence of schlieren, and in particular, enhanced TiO2 contents that require admixture of an "amphibolitic component" to the melt. Evidence for such a process is provided by the occurrence of relict, in-part thermally corroded grains of rutile and ilmenite, and by formation of Ti-rich tiny mineral aggregates in the glass. The three studied bediasites show only minor inter- and intrasample heterogeneity, and their chemical composition agrees well with previously published data. The new data for the bediasites are compatible with heating of the "tektite melt" to extreme temperatures, followed by quenching. © 2009 The Geological Society of America. 2009 English 00721077 10.1130/2009.2458(19) Special Paper of the Geological Society of America 458 Geological Society of America 435-445 Institute of Geology, Academy of Sciences of the Czech Republic, Rozvojová 269, CZ-16500 Praha 6, Czech Republic; Institut für Geowissenschaften, Friedrich-Schiller-Universität Jena, Burgweg 11, D-07749 Jena, Germany; Bayerisches Geoinstitut, Universität Bayreuth, D-95440 Bayreuth, Germany; Institut für Planetologie, Westfälische Wilhelms-Universität, Wilhelm-Klemm-Strasse 10, D-48149 Münster, Germany Boreholes; Buildings; Cluster analysis; Crystalline materials; Crystalline rocks; Glass; Hierarchical systems; Infill drilling; Oxide minerals; Titanium dioxide, Chesapeake bay impact structures; Continental scientific drillings; Crystalline target rocks; Display characteristics; Geochemical characteristic; Hierarchical cluster analysis; Microchemical analysis; U.s. geological surveys, Core drilling, breccia; chemical composition; crater; impact structure; marine sediment; sediment chemistry; suevite, Chesapeake Bay; United States https://www.scopus.com/inward/record.uri?eid=2-s2.0-74949093425&doi=10.1130%2f2009.2458%2819%29&partnerID=40&md5=7cac119be381fda26f000684562f09f1 cited By 3 R. Skála F. Langenhorst A. Deutsch article Kenkmann2009571 The combination of petrographic analysis of drill core from the recent International Continental Scientific Drilling Program (ICDP)-U.S Geological Survey (USGS) drilling project and results from numerical simulations provides new constraints for reconstructing the kinematic history and duration of different stages of the Chesapeake Bay impact event. The numerical model, in good qualitative agreement with previous seismic data across the crater, is also roughly consistent with the stratigraphy of the new borehole. From drill core observations and modeling, the following conclusions can be drawn: (1) The lack of a shock metamorphic overprint of cored basement lithologies suggests that the drill core might not have reached the parautochthonous shocked crater floor but merely cored basement blocks that slumped off the rim of the original cavity into the crater during crater modification. (2) The sequence of polymict lithic breccia, suevite, and impact melt rock (1397-1551 m) must have been deposited prior to the arrival of the 950-m-thick resurge and avalanche-delivered beds and blocks within 5-7 min after impact. (3) This short period for transportation and deposition of impactites may suggest that the majority of the impactites of the Eyreville core never left the transient crater and was emplaced by ground surge. This is in accordance with observations of impact breccia fabrics. However, the uppermost part of the suevite section contains a pronounced component of airborne material. (4) Limited amounts of shock-deformed debris and melt fragments also occur throughout the Exmore beds. Shard-enriched intervals in the upper Exmore beds indicate that some material interpreted to be part of the hot ejecta plume was incorporated and dispersed into the upper resurge deposits. This suggests that collapse of the ejecta plume was contemporaneous with the major resurge event(s). Modeling indicates that the resurge flow should have been concluded some 20 min after impact; hence, this also likely marked the end of the major episode of deposition from the ejecta plume. © 2009 The Geological Society of America. 2009 English 00721077 10.1130/2009.2458(25) Special Paper of the Geological Society of America 458 Geological Society of America 571-585 Museum für Naturkunde-Leibniz Institute, Humboldt University Berlin, Invalidenstrasse 43, 10115 Berlin, Germany; Impact and Astromaterials Research Centre, Department of Earth Science and Engineering, Imperial College London, London, SW7 2AZ, United Kingdom; Lunar and Planetary Institute, 3600 Bay Area Boulevard, Houston, TX 77058, United States Boreholes; Buildings; Deposition; Drills; Infill drilling; Numerical models; Rocks; Seismology; Stratigraphy; Structural geology, Chesapeake Bay; Continental scientific drillings; Different stages; Drilling projects; Impact craters; Melt fragments; Petrographic analysis; U.S geological surveys, Core drilling, basement rock; breccia; computer simulation; crater; deposition; ejecta; emplacement; impactite; kinematics; lithology; mantle plume; numerical model; petrography; pyroclastic flow; research program; shock metamorphism, Chesapeake Bay; United States https://www.scopus.com/inward/record.uri?eid=2-s2.0-74949105414&doi=10.1130%2f2009.2458%2825%29&partnerID=40&md5=21bb78a881f3fc2407033566586ddc4d cited By 31 T. Kenkmann G.S. Collins A. Wittmann K. Wünnemann W.U. Reimold H.J. Melosh article Vanko2009543 Core samples from the International Continental Scientific Drilling Program (ICDP)-U.S Geological Survey (USGS) Eyreville B core, located in the central crater of the Chesapeake Bay impact structure, were studied to determine the degree to which postimpact hydrothermal activity is recorded in secondary minerals and fluid inclusions. The Chesapeake Bay impact event occurred ̃35 Ma ago on the siliciclastic continental shelf of eastern North America, in up to several hundred meters of water. The combination of hot materials, such as impact melts and suevite breccias, with overlying crater-fill material and seawater is hypothesized to have led to postimpact hydrothermal circulation. Secondary minerals are distinguished from pre-impact minerals by textural features such as the presence or absence of shock metamorphic effects. Minerals in veins and cavities that are shown to have formed after the impact include secondary calcite, chalcedony, phillipsite, clinoptilolite-heulandite, mordenite, and montmorillonite. Some secondary calcite contains liquid-only fluid inclusions with trapping temperatures constrained to be less than or equal to ̃50 °C. Salinities of the inclusion fluids are mostly around 4.3 ± 1 wt% NaCl equivalent, or ̃43 ± 10 g/L total dissolved solids. This salinity is similar to that of the anomalously saline groundwater that currently exists within the crater-fill material, and that could be relict brine that originated just after the impact. © 2009 The Geological Society of America. 2009 English 00721077 10.1130/2009.2458(23) Special Paper of the Geological Society of America 458 Geological Society of America 543-557 Department of Physics, Astronomy and Geosciences, Towson University, Towson, MD 21252, United States Calcite; Clay alteration; Crystalline rocks; Groundwater; Infill drilling; Mineralogy; Sodium chloride; Zeolites, Chesapeake bay impact structures; Continental scientific drillings; Eastern north america; Hydrothermal activity; Hydrothermal alterations; Hydrothermal circulation; Total dissolved solids; U.S geological surveys, Nitrogen compounds, assessment method; breccia; crystalline rock; fluid inclusion; hydrothermal activity; hydrothermal alteration; hydrothermal circulation; hydrothermal deposit; hydrothermal system; impact structure; impactite; petrography; research program; secondary mineral; shock metamorphism; suevite, Chesapeake Bay; United States https://www.scopus.com/inward/record.uri?eid=2-s2.0-74949126684&doi=10.1130%2f2009.2458%2823%29&partnerID=40&md5=045dc6251fd625bf66017647f824a6ed cited By 4 D.A. Vanko article Ormö2009617 Collapse and inward slumping of unconsolidated sedimentary strata expanded the Chesapeake Bay impact structure far beyond its central basement crater. During crater collapse, sediment-loaded water surged back to fill the crater. Here, we analyze clast frequency and granulometry of these resurge deposits in one core hole from the outermost part of the collapsed zone (i.e., Langley) as well as a core hole from the moat of the basement crater (i.e., Eyreville A). Comparisons of clast provenance and flow dynamics show that at both locations, there is a clear change in clast frequency and size between a lower unit, which we interpret to be dominated by slumped material, and an upper, water-transported unit, i.e., resurge deposit. The contribution of material to the resurge deposit was primarily controlled by stripping and erosion. This includes entrainment of fallback ejecta and sediments eroded from the surrounding seafloor, found to be dominant at Langley, and slumped material that covered the annular trough and basement crater, found to be dominant at Eyreville. Eyreville shows a higher content of crystalline clasts than Langley. There is equivocal evidence for an anti-resurge from a collapsing central water plume or, alternatively, a second resurge pulse, as well as a transition into oscillating resurge. The resurge material shows more of a debris-flow-like transport compared to resurge deposits at some other marine target craters, where the ratio of sediment to water has been relatively low. This result is likely a consequence of the combination of easily disaggregated host sediments and a relatively shallow target water depth. © 2009 The Geological Society of America. 2009 English 00721077 10.1130/2009.2458(27) Special Paper of the Geological Society of America 458 Geological Society of America 617-632 Centro de Astrobiología, Consejo Superior de Investigaciones Cientificas, Instituto Nacional de Tecnica Aeroespacial, Torrejón de Ardoz, Spain; Nordic Volcanological Center, University of Iceland, Reykjavík, Iceland; U.S. Geological Survey, 926A National Center, Reston, VA 20192, United States Buildings; Sediments, Chesapeake bay impact structures; Debris flows; Flow dynamics; Granulometries; Sea floor; Sedimentary strata; Shallow targets; Water depth, Deposits, clast; comparative study; crater; debris flow; entrainment; frequency-magnitude distribution; granulometry; provenance; sediment transport; sedimentary structure; unconsolidated medium, Chesapeake Bay; United States https://www.scopus.com/inward/record.uri?eid=2-s2.0-74949102199&doi=10.1130%2f2009.2458%2827%29&partnerID=40&md5=2e5abce2c350a4c28e8f283c75d0fa7b cited By 25 J. Ormö E. Sturkell J.W. Horton Jr. D.S. Powars L.E. Edwards article Cockell2009941 Asteroid and comet impact events are known to cause profound disruption to surface ecosystems. The aseptic collection of samples throughout a 1.76-km-deep set of cores recovered from the deep subsurface of the Chesapeake Bay impact structure has allowed the study of the subsurface biosphere in a region disrupted by an impactor. Microbiological enumerations suggest the presence of three major microbiological zones. The upper zone (127-867 m) is characterized by a logarithmic decline in microbial abundance from the surface through the postimpact section of Miocene to Upper Eocene marine sediments and across the transition into the upper layers of the impact tsunami resurge sediments and sediment megablocks. In the middle zone (867-1397 m) microbial abundances are below detection. This zone is predominantly quartz sand, primarily composed of boulders and blocks, and it may have been mostly sterilized by the thermal pulse delivered during impact. No samples were collected from the large granite block (1096-1371 m). The lowest zone (below 1397 m) of increasing microbial abundance coincides with a region of heavily impact-fractured, hydraulically conductive suevite and fractured schist. These zones correspond to lithologies infl uenced by impact processes. Our results yield insights into the infl uence of impacts on the deep subsurface biosphere. © 2009 The Geological Society of America. 2009 English 00721077 10.1130/2009.2458(40) Special Paper of the Geological Society of America 458 Geological Society of America 941-950 Centre for Earth, Planetary Science and Astronomical Research, Open University, Milton Keynes, MK7 6AA, United Kingdom; U.S. Geological Survey, MS 430 12201 Sunrise Valley Drive, Reston, VA 20192, United States; Institute of Biological Sciences, Microbiology Section, Aarhus University, 8000 Aarhus C, Denmark; Carnegie Institute of Washington, 1530 P Street NW, Washington, DC 20005, United States Biospherics; Lithology; Submarine geology, Chesapeake Bay; Chesapeake bay impact structures; Impact craters; Impact process; Marine sediments; Microbial abundances; Subsurface biosphere; Surface ecosystems, Sediments, abundance; asteroid; biosphere; comet; crater; Eocene; hydraulic conductivity; impact structure; lithology; marine sediment; microbial activity; microbial community; microbiology; Miocene; schist; suevite, Chesapeake Bay; United States https://www.scopus.com/inward/record.uri?eid=2-s2.0-74949085356&doi=10.1130%2f2009.2458%2840%29&partnerID=40&md5=65803cf538c111668057a9c10f301c39 cited By 12 C.S. Cockell A.L. Gronstal M.A. Voytek J.D. Kirshtein K. Finster W.E. Sanford M. Glamoclija G.S. Gohn D.S. Powars J.W. Horton Jr. article Gohn20091 The late Eocene Chesapeake Bay impact structure lies buried at moderate depths below Chesapeake Bay and surrounding landmasses in southeastern Virginia, USA. Numerous characteristics made this impact structure an inviting target for scientific drilling, including the location of the impact on the Eocene continental shelf, its threelayer target structure, its large size (̃85 km diameter), its status as the source of the North American tektite strewn field, its temporal association with other late Eocene terrestrial impacts, its documented effects on the regional groundwater system, and its previously unstudied effects on the deep microbial biosphere. The Chesapeake Bay Impact Structure Deep Drilling Project was designed to drill a deep, continuously cored test hole into the central part of the structure. A project workshop, funding proposals, and the acceptance of those proposals occurred during 2003-2005. Initial drilling funds were provided by the International Continental Scientific Drilling Program (ICDP) and the U.S. Geological Survey (USGS). Supplementary funds were provided by the National Aeronautics and Space Administration (NASA) Science Mission Directorate, ICDP, and USGS. Field operations were conducted at Eyreville Farm, Northampton County, Virginia, by Drilling, Observation, and Sampling of the Earth's Continental Crust (DOSECC) and the project staff during September-December 2005, resulting in two continuously cored, deep holes. The USGS and Rutgers University cored a shallow hole to 140 m in April-May 2006 to complete the recovered section from land surface to 1766 m depth. The recovered section consists of 1322 m of crater materials and 444 m of overlying postimpact Eocene to Pleistocene sediments. The crater section consists of, from base to top: basement-derived blocks of crystalline rocks (215 m); a section of suevite, impact melt rock, lithic impact breccia, and cataclasites (154 m); a thin interval of quartz sand and lithic blocks (26 m); a granite megablock (275 m); and sediment blocks and boulders, polymict, sediment-clast-dominated sedimentary breccias, and a thin upper section of stratified sediments (652 m). The cored postimpact sediments provide insight into the effects of a large continental-margin impact on subsequent coastal-plain sedimentation. This volume contains the first results of multidisciplinary studies of the Eyreville cores and related topics. The volume is divided into these sections: geologic column; borehole geophysical studies; regional geophysical studies; crystalline rocks, impactites, and impact models; sedimentary breccias; postimpact sediments; hydrologic and geothermal studies; and microbiologic studies. © 2009 The Geological Society of America. 2009 English 00721077 10.1130/2009.2458(01) Special Paper of the Geological Society of America 458 Geological Society of America 1-20 U.S. Geological Survey, 926A National Center, Reston, VA 20192, United States; Department of Lithospheric Research, University of Vienna, A-1090 Vienna, Austria; Department of Earth and Planetary Sciences, Rutgers University, Piscataway, NJ 08854-8066, United States; Museum für Naturkunde-Leibniz Institute, Humboldt University Berlin, Invalidenstrasse 43, 10115, Berlin, Germany Boreholes; Crystalline materials; Crystalline rocks; Geophysics; Groundwater; Infill drilling; NASA; Sedimentary rocks; Sedimentology; Structural geology, Chesapeake bay impact structures; Continental scientific drillings; Continental shelves; Pleistocene sediments; Regional groundwater; Scientific drilling; Temporal association; U.s. geological surveys, Sediments, continental margin; continental shelf; deep drilling; Eocene; impact structure; Pleistocene; sedimentation, Chesapeake Bay; United States; Virginia https://www.scopus.com/inward/record.uri?eid=2-s2.0-74949128570&doi=10.1130%2f2009.2458%2801%29&partnerID=40&md5=b2774daedcac94d70d36dd148646b7a3 cited By 16 G.S. Gohn C. Koeberl K.G. Miller W.U. Reimold article HortonJr.2009277 The 1766-m-deep Eyreville B core from the late Eocene Chesapeake Bay impact structure includes, in ascending order, a lower basement-derived section of schist and pegmatitic granite with impact breccia dikes, polymict impact breccias, and cataclas tic gneiss blocks overlain by suevites and clast-rich impact melt rocks, sand with an amphibolite block and lithic boulders, and a 275-m-thick granite slab overlain by crater-fill sediments and postimpact strata. Graphite-rich cataclasite marks a detachment fault atop the lower basement-derived section. Overlying impactites consist mainly of basement-derived clasts and impact melt particles, and coastalplain sediment clasts are underrepresented. Shocked quartz is common, and coesite and reidite are confirmed by Raman spectra. Silicate glasses have textures indicating immiscible melts at quench, and they are partly altered to smectite. Chrome spinel, baddeleyite, and corundum in silicate glass indicate high-temperature crystallization under silica undersaturation. Clast-rich impact melt rocks contain α- cristobalite and monoclinic tridymite. The impactites record an upward transition from slumped ground surge to melt-rich fallback from the ejecta plume. Basement-derived rocks include amphibolite-facies schists, greenschist(?)-facies quartz-feldspar gneiss blocks and subgreenschist-facies shale and siltstone clasts in polymict impact breccias, the amphibolite block, and the granite slab. The granite slab, underlying sand, and amphibolite block represent rock avalanches from inward collapse of unshocked bedrock around the transient crater rim. Gneissic and massive granites in the slab yield U-Pb sensitive high-resolution ion microprobe (SHRIMP) zircon dates of 615 ± 7 Ma and 254 ± 3 Ma, respectively. Postimpact heating was 7lt;~350 °C in the lower basementderived section based on undisturbed 40 Ar/ 39 Ar plateau ages of muscovite and &lt;~150 &lt;C in sand above the suevite based on 40 Ar/ 39 Ar age spectra of detrital microcline. © 2009 The Geological Society of America. 2009 English 00721077 10.1130/2009.2458(14) Special Paper of the Geological Society of America 458 Geological Society of America 277-316 U.S. Geological Survey, MS 926A, 12201 Sunrise Valley Drive, Reston, VA 20192, United States; U.S. Geological Survey, MS 956, 12201 Sunrise Valley Drive, Reston, VA 20192, United States; U.S. Geological Survey, MS 963, Denver Federal Center, Denver, CO 80225, United States; U.S. Geological Survey, MS 954, 12201 Sunrise Valley Drive, Reston, VA 20192, United States Buildings; Corundum; Feldspar; Glass; Granite; Lead alloys; Mica; Quartz; Silicate minerals; Structural geology; Tectonics; Textures; Zircon, Amphibolite facies; Chesapeake bay impact structures; Crystalline target rocks; Detachment fault; High temperature crystallization; Sensitive high-resolution ion microprobe; Shocked quartz; Undersaturation, Crystalline rocks, breccia; crystalline rock; crystallization; Eocene; granite; impact structure; impactite; marine sediment; SHRIMP dating, Chesapeake Bay; United States https://www.scopus.com/inward/record.uri?eid=2-s2.0-74949124057&doi=10.1130%2f2009.2458%2814%29&partnerID=40&md5=6074c29ddf5110532968a2d9be35b5f9 cited By 24 J.W. Horton Jr. M.J. Kunk H.E. Belkin J.N. Aleinikoff J.C. Jackson I.-M. Chou article Declercq2009559 The alteration or transformation of impact melt rock to clay minerals, particularly smectite, has been recognized in several impact structures (e.g., Ries, Chicxulub, Mjølnir). We studied the experimental alteration of two natural impact melt rocks from suevite clasts that were recovered from drill cores into the Chesapeake Bay impact structure and two synthetic glasses. These experiments were conducted at hydrothermal temperature (265 °C) in order to reproduce conditions found in meltbearing deposits in the first thousand years after deposition. The experimental results were compared to geochemical modeling (PHREEQC) of the same alteration and to original mineral assemblages in the natural melt rock samples. In the alteration experiments, clay minerals formed on the surfaces of the melt particles and as fine-grained suspended material. Authigenic expanding clay minerals (saponite and Ca-smectite) and vermiculite/chlorite (clinochlore) were identified in addition to analcime. Ferripyrophyllite was formed in three of four experiments. Comparable minerals were predicted in the PHREEQC modeling. A comparison between the phases formed in our experiments and those in the cores suggests that the natural alteration occurred under hydrothermal conditions similar to those reproduced in the experiment. © 2009 The Geological Society of America. 2009 English 00721077 10.1130/2009.2458(24) Special Paper of the Geological Society of America 458 Geological Society of America 559-569 Department of Geosciences, University of Oslo, P.O. Box 1047, Oslo, NO 316, Norway; Department of Geology and Geophysics, Louisiana State University, Baton Rouge, LA 70803, United States; U.S. Geological Survey, 926A National Center, Reston, VA 20192, United States Chlorite minerals; Clay alteration; Core drilling; Infill drilling; Rocks; Zeolites, Chesapeake bay impact structures; Geochemical modeling; Hydrothermal conditions; Hydrothermal temperature; Impact structures; Mineral assemblage; Suspended material; Synthetic glass, Clay minerals, authigenic mineral; experimental study; hydrothermal activity; hydrothermal alteration; hydrothermal deposit; hydrothermal system; impact structure; numerical model; smectite; suevite, Chesapeake Bay; United States https://www.scopus.com/inward/record.uri?eid=2-s2.0-74949088037&doi=10.1130%2f2009.2458%2824%29&partnerID=40&md5=ef733bf9762a7e3aad0172fe8b93cf51 cited By 7 J. Declercq H. Dypvik P. Aagaard J. Jahren R.E. Ferrell Jr. J. Wright Horton Jr. article Heidinger2009931 The Chesapeake Bay impact structure is a late Eocene complex crater that was excavated -35 Ma ago in a continental shelf environment at the Atlantic margin, in Virginia. It is the largest impact structure in the United States and the seventh largest on Earth. It has an average diameter of -85 km and is centered near Cape Charles. The scientific well Eyreville B drilled within the framework of the International Continental Scientific Drilling Program (ICDP) penetrated the deep crater moat -9 km from the center of the structure. Core holes drilled in impact structures are especially suited for investigations of the infl uence of lithological heterogeneities on petrophysical properties and the thermal field. In the Eyreville B core hole, two high-resolution temperature-logging campaigns and a petrophysical profile measured on core samples spaced at -10 m intervals were recorded. The temperature values of the first campaign in December 2005 were heavily disturbed by outflow of artesian water and could only be used for an estimation of the depth where the fluid originated. For the second campaign in May 2006, a riser was constructed to enable measurements in standing (equilibrated) fluid of the well without opening the well head. This construction yielded a measurement of the undisturbed temperature profile as well as recognition of thermal relaxation after some outflow of artesian water, which wellheated the surrounding rock. The data allowed determination of (1) the origin of the artesian water, (2) equilibrium temperatures derived from the relaxation process, (3) microclimatic effects at the nearby test well STP2, (4) lateral heterogeneities in the core holes STP2 and Eyreville B, and (5) a profile of vertical heat-flow density in the Eyreville B core. From the calculated vertical component of the thermal gradient and the thermal conductivity measured on core samples, a mean heat-flow density of 65 ± 6 mW/m2 in the 440-1100 m depth interval was determined. These data and results are now available for application in numerical models of the local and regional geologic, hydrologic, and geothermal regimes. © 2009 The Geological Society of America. 2009 English 00721077 10.1130/2009.2458(39) Special Paper of the Geological Society of America 458 Geological Society of America 931-940 Geophysical Institute, University of Karlsruhe, Hertzstrasse 16, 76187 Karlsruhe, Germany; Russian State Geological Prospecting University, Miklukho-Maklai 23, Moscow 117997, Russian Federation; Institute of Geophysics, Bocní II/1401, 14131 Prague 4, Czech Republic; Institute of Applied Geosciences, Technical University of Berlin, Ackerstrasse 71-76, 13355 Berlin, Germany; FR Geophysics, Freie Universität Berlin, Malteserstrasse 74-100, 12249 Berlin, Germany Heat transfer; Infill drilling; Lithology; Petrophysics; Thermal conductivity; Wellheads, Chesapeake bay impact structures; Continental scientific drillings; Continental shelves; Equilibrium temperatures; Lateral heterogeneity; Microclimatic effects; Petrophysical properties; Temperature profiles, Core samples, borehole; continental shelf; crater; Eocene; estimation method; geothermal system; heat flow; impact structure; lithology; numerical model; temperature profile; thermal conductivity; thermal regime, Chesapeake Bay; United States; Virginia, Calluna vulgaris https://www.scopus.com/inward/record.uri?eid=2-s2.0-74949090699&doi=10.1130%2f2009.2458%2839%29&partnerID=40&md5=5f711d43ba2baf2e4bd3d4be0a3fc7ad cited By 8 P. Heidinger H. Wilhelm Y. Popov J. Šafanda H. Burkhardt S. Mayr article Gronstal2009951 Knowledge of the deep subsurface biosphere is limited due to difficulties in recovering materials. Deep drilling projects provide access to the subsurface; however, contamination introduced during drilling poses a major obstacle in obtaining clean samples. To monitor contamination during the 2005 International Continental Scientific Drilling Program (ICDP)-U.S. Geological Survey (USGS) deep drilling of the Chesapeake Bay impact structure, four methods were utilized. Fluorescent microspheres were used to mimic the ability of contaminant cells to enter samples through fractures in the core material during retrieval. Drilling mud was infused with a chemical tracer (Halon 1211) in order to monitor penetration of mud into cores. Pore water from samples was examined using excitation-emission matrix (EEM) fl uorescence spectroscopy to characterize dissolved organic carbon (DOC) present at various depths. DOC signatures at depth were compared to signatures from drilling mud in order to identify potential contamination. Finally, microbial contaminants present in drilling mud were identified through 16S ribosomal deoxyribonucleic acid (rDNA) clone libraries and compared to species cultured from core samples. Together, these methods allowed us to categorize the recovered core samples according to the likelihood of contamination. Twenty-two of the 47 subcores that were retrieved were free of contamination by all the methods used and were subsequently used for microbiological culture and culture-independent analysis. Our approach provides a comprehensive assessment of both particulate and dissolved contaminants that could be applied to any environment with low biomass. © 2009 The Geological Society of America. 2009 English 00721077 10.1130/2009.2458(41) Special Paper of the Geological Society of America 458 Geological Society of America 951-964 Planetary and Space Sciences Research Institute, Open University, Milton Keynes, MK7 6AA, United Kingdom; U.S. Geological Survey, MS 430, 12201 Sunrise Valley Drive, Reston, VA 20192, United States; Biology Department, Old Dominion University, Norfolk, VA 23529, United States Contamination; Coremaking; Infill drilling; Mud logging; Organic carbon, Chesapeake bay impact structures; Comprehensive assessment; Contamination assessment; Continental scientific drillings; Dissolved organic carbon; Excitation emission matrices; Fluorescent micro spheres; Microbiological cultures, Core samples, assessment method; biomass; biosphere; deep drilling; dissolved organic carbon; fluorescence spectroscopy; geological survey; impact structure; microbiology; pollution monitoring; porewater; sediment core; sediment pollution; tracer, Chesapeake Bay; United States https://www.scopus.com/inward/record.uri?eid=2-s2.0-74949114892&doi=10.1130%2f2009.2458%2841%29&partnerID=40&md5=5140861b6067ba3c6eaa986bfc067d5a cited By 15 A.L. Gronstal M.A. Voytek J.D. Kirshtein N.M. Heyde M.D. Lowit C.S. Cockell article Schmitt2009481 We investigated whole-rock chemical compositions of 318 samples of Exmore breccia (diamicton), impactite (suevite, impact melt rock, polymict lithic impact breccia), and crystalline basement-derived rocks from 444 to 1766 m depth in the International Continental Scientific Drilling Program (ICDP)-U.S. Geological Survey (USGS) Eyreville A and B drill cores (Chesapeake Bay impact structure, Virginia, USA). Here, we compare the average chemical compositions for the Exmore breccia (diamicton), the impactites and their subunits, sandstone, granite, granitic gneiss, and amphibolite of the lithic block section (1095.7-1397.2 m depth), cataclastic gneiss of the impact breccia section, and schist and pegmatite/granite of the basal crystalline section (1551.2-1766.3 m depth). The granite of the megablock (1097.7-1371.1 m depth) is of I-type and is seemingly related to a syncollisional setting. The amphibolite (1377.4-1387.5 m depth) of the lithic block section is of igneous origin and has a tholeiitic character. Based on chemical composition, the Exmore breccia (diamicton) can be subdivided into five units (444.9-450.7, 450.7-468, 468-518, 518-528, and 528-̃865 m depth). The units in the depth intervals of 450.7-468 and 518-528 m are enriched in TiO2, MgO, Sc, V, Cr, and Zn contents compared to the other Exmore breccia units. In some samples, especially at ̃451-455 m depth, the Exmore breccia contains significant amounts of P 2 O 5 . The Exmore breccia is recognized as a mixture of all sedimentary and crystalline target components, and, when compared to the impactites, it contains a significant amount of a SiO 2 -rich target component of sedimentary origin. The chemical composition of the impactites overlaps the compositional range for the Exmore breccia. The impactites generally display a negative correlation of SiO 2 and CaO, and a positive correlation of TiO 2 , Al 2 O 3 , Fe 2 O 3 , and MgO with depth. This is the result of an increasing basement schist component, and a decreasing sedimentary and/or granitic component with depth. Suevite units S2 and S3 display distinct enrichment of Na 2 O by a factor of ̃2 compared to all other impactite units, which is interpreted to reflect a higher granitic component in these units. © 2009 The Geological Society of America. 2009 English 00721077 10.1130/2009.2458(22) Special Paper of the Geological Society of America 458 Geological Society of America 481-541 Museum für Naturkunde-Leibniz Institute, Humboldt University Berlin, Invalidenstrasse 43, 10115 Berlin, Germany; Department of Lithospheric Research, Center for Earth Sciences, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria; Impact Cratering Research Group, School of Geosciences, University of the Witwatersrand, Private Bag 3, PO Wits, Johannesburg, 2050, South Africa; Lunar and Planetary Institute, 3600 Bay Area Boulevard, Houston, TX 77058, United States Alumina; Aluminum oxide; Buildings; Crystalline materials; Crystalline rocks; Drills; Granite; Hematite; Infill drilling; Magnesia; Sedimentology; Silica; Sodium compounds; Structure (composition); Titanium dioxide, Chemical compositions; Chesapeake bay impact structures; Continental scientific drillings; Crystalline basement; Crystalline targets; Negative correlation; Positive correlations; U.s. geological surveys, Core drilling, amphibolite; basement rock; breccia; chemical composition; coastal sediment; crystalline rock; enrichment; gneiss; I-type rock; impact structure; impactite; lithology; research program; sandstone; schist; sediment chemistry, Chesapeake Bay; United States; Virginia https://www.scopus.com/inward/record.uri?eid=2-s2.0-74949119586&doi=10.1130%2f2009.2458%2822%29&partnerID=40&md5=4d98fae5966f516484085e0f3568d599 cited By 18 R.T. Schmitt K. Bartosova W.U. Reimold D. Mader A. Wittmann C. Koeberl R.L. Gibson article Bartosova2009397 The Chesapeake Bay impact structure, which is 85 km in diameter and 35.5 Ma old, was drilled and cored in a joint International Continental Scientific Drilling Program (ICDP) and U.S. Geological Survey (USGS) drilling project at Eyreville Farm, Virginia, U.S.A. In the Eyreville drill core, 154 m of impact breccia were recovered from the depth interval 1397-1551 m. Major- and trace-element concentrations were determined in 75 polymict impactite samples, 10 samples of cataclastic gneiss blocks, and 24 clasts from impactites. The chemical composition of the polymict impactites does not vary much in the upper part of the section (above ̃1450 m), whereas in the lower part, larger differences occur. Polymict impactites show a decrease of SiO 2 content, and slight increases of TiO 2 , Al 2 O 3 , and Fe 2 O 3 abundances, with depth. This is in agreement with an increase of the schist/gneiss component with depth. Concentrations of siderophile elements (Co, Ni) are lower in the polymict impactites than in the basement-derived schists and do not indicate the presence of an extraterrestrial component. The fi ve petrographically determined types of melt particles, i.e., clear glass, altered melt, recrystallized silica melt, melt with microlites, and dark-brown melt, have distinct chemical compositions. Mixing calculations of the proportions of rocks involved in the formation of various polymict impactites and melt particles were carried out using the Harmonic least-squares MiXing (HMX) calculation program. The calculations suggest that the metamorphic basement rocks (i.e., gneiss and schist) constitute the main component of the polymict impactites, together with significant sedimentary and possible minor pegmatite/granite and amphibolite components. The sedimentary component is derived mostly from a sediment characterized by a composition similar to that of the Cretaceous Potomac Formation. Compositions of the melt particles were modeled as mixtures of target rocks or major rock-forming minerals. However, the results of the mixing calculations for the melt particles are not satisfactory, and the composition of the particles could have been modified by hydrothermal alteration. Carbon isotope ratios were determined for 18 samples. The results imply a hydrothermal origin for the carbonate veins from the basement-derived core section; carbon-rich sedimentary clasts from the Exmore breccia and suevite have a δ 13 C range typical for organic matter in sediments. © 2009 The Geological Society of America. 2009 English 00721077 10.1130/2009.2458(18) Special Paper of the Geological Society of America 458 Geological Society of America 397-433 Department of Lithospheric Research, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria; Museum für Naturkunde-Leibniz Institute, Humboldt University Berlin, Invalidenstrasse 43, 10115 Berlin, Germany; Department of Earth Science, University of Western Ontario, 1151 Richmond Street, London, ON N6A 5B7, Canada; Natural History Museum, Burgring 7, A-1010 Vienna, Austria Alumina; Aluminum oxide; Buildings; Carbon; Clay alteration; Drills; Hematite; Infill drilling; Metamorphic rocks; Mixer circuits; Mixing; Sedimentary rocks; Sedimentology; Silica; Structure (composition); Titanium dioxide; Trace elements, Chesapeake bay impact structures; Continental scientific drillings; Extraterrestrial components; Hydrothermal alterations; Major and trace elements; Metamorphic basements; Rock-forming minerals; U.s. geological surveys, Core drilling, breccia; chemical composition; drilling; geochemistry; impact structure; impactite; marine sediment; trace element, Chesapeake Bay; United States https://www.scopus.com/inward/record.uri?eid=2-s2.0-74949095526&doi=10.1130%2f2009.2458%2818%29&partnerID=40&md5=a301fa5740f3c47995c05de4253e7778 cited By 13 K. Bartosova D. Mader R.T. Schmitt L. Ferrière C. Koeberl W.U. Reimold F. Brandstätter article Edwards200951 The Eyreville A and B cores, recovered from the "moat" of the Chesapeake Bay impact structure, provide a thick section of sediment-clast breccias and minor stratified sediments from 1095.74 to 443.90 m. This paper discusses the components of these breccias, presents a geologic column and descriptive lithologic framework for them, and formalizes the Exmore Formation. From 1095.74 to ̃867 m, the cores consist of nonmarine sediment boulders and sand (rare blocks up to 15.3 m intersected diameter). A sharp contact in both cores at ̃867 m marks the lowest clayey, silty, glauconitic quartz sand that constitutes the base of the Exmore Formation and its lower diamicton member. Here, material derived from the upper sediment target layers, as well as some impact ejecta, occurs. The block-dominated member of the Exmore Formation, from ̃855-618.23 m, consists of nonmarine sediment blocks and boulders (up to 45.5 m) that are juxtaposed complexly. Blocks of oxidized clay are an important component. Above 618.23 m, which is the base of the informal upper diamicton member of the Exmore Formation, the glauconitic matrix is a consistent component in diamicton layers between nonmarine sediment clasts that decrease in size upward in the section. Crystalline-rock clasts are not randomly distributed but rather form local concentrations. The upper part of the Exmore Formation consists of crudely fining-upward sandy packages capped by laminated silt and clay. The overlap interval of Eyreville A and B (940-̃760 m) allows recognition of local similarities and differences in the breccias. © 2009 The Geological Society of America. 2009 English 00721077 10.1130/2009.2458(03) Special Paper of the Geological Society of America 458 Geological Society of America 51-89 U.S. Geological Survey, 926A National Center, Reston, VA 20192, United States; University of Oslo, P.O. Box 1047, Blindern, N-0316 Oslo, Norway Crystalline rocks; Rocks, Chesapeake bay impact structures; Impact ejecta; Local similarity; Quartz sand; Randomly distributed, Sediments, breccia; diamicton; ejecta; impact structure; lithology; marine sediment, Chesapeake Bay; United States https://www.scopus.com/inward/record.uri?eid=2-s2.0-74949119592&doi=10.1130%2f2009.2458%2803%29&partnerID=40&md5=79bd3ed2abeca9c38e56153d8c7aa825 cited By 38 L.E. Edwards D.S. Powars G.S. Gohn H. Dypvik article Edwards200991 A 443.9-m-thick, virtually undisturbed section of postimpact deposits in the Chesapeake Bay impact structure was recovered in the Eyreville A and C cores, Northampton County, Virginia, within the "moat" of the structure's central crater. Recovered sediments are mainly fine-grained marine siliciclastics, with the exception of Pleistocene sand, clay, and gravel. The lowest postimpact unit is the upper Eocene Chickahominy Formation (443.9-350.1 m). At 93.8 m, this is the maximum thickness yet recovered for deposits that represent the return to "normal marine" sedimentation. The Drummonds Corner beds (informal) and the Old Church Formation are thin Oligocene units present between 350.1 and 344.7 m. Above the Oligocene, there is a more typical Virginia coastal plain succession. The Calvert Formation (344.7-225.4 m) includes a thin lower Miocene part overlain by a much thicker middle Miocene part. From 225.4 to 206.0 m, sediments of the middle Miocene Choptank Formation, rarely reported in the Virginia coastal plain, are present. The thick upper Miocene St. Marys and Eastover Formations (206.0-57.8 m) appear to represent a more complete succession than in the type localities. Correlation with the nearby Kiptopeke core indicates that two Pliocene units are present: Yorktown (57.8-32.2 m) and Chowan River Formations (32.2-18.3 m). Sediments at the top of the section represent an upper Pleistocene channel-fill and are assigned to the Butlers Bluff and Occohannock Members of the Nassawadox Formation (18.3-0.6 m). © 2009 The Geological Society of America. 2009 English 00721077 10.1130/2009.2458(04) Special Paper of the Geological Society of America 458 Geological Society of America 91-114 U.S. Geological Survey, 926A National Center, Reston, VA 20192, United States; Department of Earth and Planetary Sciences, Rutgers University, Piscataway, NJ 08854, United States; Delaware Geological Survey, University of Delaware, DGS Building, 257 Academy Street, Newark, DE 19716, United States; Chevron Energy Technology Company, 1500 Louisiana St., Houston, TX 77002, United States; Laboratory of Solid Earth Geophysics, Department of Physics, University of Helsinki, P.O. Box 64, Helsinki, 00014, Finland Deposits; Recovery, Channel fills; Chesapeake bay impact structures; Coastal plain; Lower Miocene; Maximum thickness; Middle Miocene; Pleistocene sands; Siliciclastics, Sediments, crater; Eocene; fine grained sediment; impact structure; Oligocene; Pleistocene; sedimentation, Chesapeake Bay; United States https://www.scopus.com/inward/record.uri?eid=2-s2.0-74949094807&doi=10.1130%2f2009.2458%2804%29&partnerID=40&md5=4bba52c903cbc7aaf1af7c59f1cf17be cited By 28 L.E. Edwards D.S. Powars J.V. Browning P.P. McLaughlin Jr. K.G. Miller J.M. Self-Trail A.A. Kulpecz T. Elbra article WrightHortonJr.200921 The International Continental Scientific Drilling Program (ICDP)-U.S. Geological Survey (USGS) Eyreville drill cores from the Chesapeake Bay impact structure provide one of the most complete geologic sections ever obtained from an impact structure. This paper presents a series of geologic columns and descriptive lithologic information for the lower impactite and crystalline-rock sections in the cores. The lowermost cored section (1766-1551 m depth) is a complex assemblage of mica schists that commonly contain graphite and fibrolitic sillimanite, intrusive granite pegmatites that grade into coarse granite, and local zones of mylonitic deformation. This basement-derived section is variably overprinted by brittle cataclastic fabrics and locally cut by dikes of polymict impact breccia, including several suevite dikes. An overlying succession of suevites and lithic impact breccias (1551-1397 m) includes a lower section dominated by polymict lithic impact breccia with blocks (up to 17 m) and boulders of cataclastic gneiss and an upper section (above 1474 m) of suevites and clast-rich impact melt rocks. The uppermost suevite is overlain by 26 m (1397-1371 m) of gravelly quartz sand that contains an amphibolite block and boulders of cataclasite and suevite. Above the sand, a 275-m-thick allochthonous granite slab (1371-1096 m) includes gneissic biotite granite, fine- and medium-to-coarse-grained biotite granites, and red altered granite near the base. The granite slab is overlain by more gravelly sand, and both are attributed to debris-avalanche and/or rockslide deposition that slightly preceded or accompanied seawater-resurge into the collapsing transient crater. © 2009 The Geological Society of America. 2009 English 00721077 10.1130/2009.2458(02) Special Paper of the Geological Society of America 458 Geological Society of America 21-49 U.S. Geological Survey, 12201 Sunrise Valley Drive, Reston, VA 20192, United States; Impact Cratering Research Group, School of Geosciences, University of the Witwatersrand, P.O. Wits, Johannesburg 2050, South Africa; Museum für Naturkunde-Leibniz Institute, Humboldt University Berlin, Invalidenstrasse 43, 10115 Berlin, Germany; Lunar and Planetary Institute, 3600 Bay Area Boulevard, Houston, TX 77058-1113, United States Biotite; Crystalline materials; Crystalline rocks; Granite; Infill drilling; Levees; Mica; Silicate minerals, Biotite granite; Chesapeake bay impact structures; Coarse-grained; Continental scientific drillings; Debris avalanches; Impact structures; Mylonitic deformation; U.s. geological surveys, Core drilling, crater; crystalline rock; deformation; impact structure; impactite; lithology; pegmatite, Chesapeake Bay; United States https://www.scopus.com/inward/record.uri?eid=2-s2.0-74949138582&doi=10.1130%2f2009.2458%2802%29&partnerID=40&md5=27102863d25ef1c8ea299619c263b6e4 cited By 40 J. Wright Horton Jr. R.L. Gibson W.U. Reimold A. Wittmann G.S. Gohn L.E. Edwards article Plescia2009181 The Chesapeake Bay impact structure is a complex impact crater, ̃85 km in diameter, buried beneath postimpact sediments. Its main structural elements include a central uplift of crystalline bedrock, a surrounding inner crater filled with impact debris, and an annular faulted margin composed of block-faulted sediments. The gravity anomaly is consistent with that of a complex impact consisting of a central positive anomaly over the central uplift and an annular negative anomaly over the inner crater. An anomaly is not recognized as being associated with the faulted margin or the outer edge of the structure. Densities from the Eyreville drill core and modeling indicate a density contrast of ̃0.3-0.6 g cm -3 between crystalline basement and the material that fills the inner crater (e.g., Exmore breccia and suevite). This density contrast is somewhat higher than for other impact structures, but it is a function of the manner in which the crater fill was deposited (as a marine resurge deposit). Modeling of the gravity data is consistent with a depth to basement of ̃1600 m at the site of Eyreville drill hole and 800 m at the central uplift. Both depths are greater than the depth at which crystalline rocks were encountered in the cores, suggesting that the cored material is highly fractured para-allochthonous rock. © 2009 The Geological Society of America. 2009 English 00721077 10.1130/2009.2458(09) Special Paper of the Geological Society of America 458 Geological Society of America 181-193 Applied Physics Laboratory, Johns Hopkins University, Laurel, MD 20723-6099, United States; U.S. Geological Survey, Eastern Mineral Resource Team, Reston, VA 20192, United States; U.S. Geological Survey, Crustal Imaging and Characterization Team, Federal Center, Box 25046, Denver, CO 80225-0046, United States Buildings; Core drilling; Crystalline materials; Drills; Infill drilling, Allochthonous rocks; Chesapeake bay impact structures; Crystalline basement; Crystalline bedrocks; Depth to basements; Gravity anomalies; Impact structures; Structural elements, Crystalline rocks, basement rock; bedrock; crater; crystalline rock; gravity anomaly; impact structure; uplift, Chesapeake Bay; United States https://www.scopus.com/inward/record.uri?eid=2-s2.0-74949097381&doi=10.1130%2f2009.2458%2809%29&partnerID=40&md5=5b5a4709185a3e3e44c33ab91bf24ab2 cited By 6 J.B. Plescia D.L. Daniels A.K. Shah article Powars2009209 The U.S. Geological Survey (USGS) acquired two 1.4-km-long, high-resolution (̃5 m vertical resolution) seismic-reflection lines in 2006 that cross near the International Continental Scientifi c Drilling Program (ICDP)-USGS Eyreville deep drilling site located above the late Eocene Chesapeake Bay impact structure in Virginia, USA. Five-meter spacing of seismic sources and geophones produced high-resolution images of the subsurface adjacent to the 1766-m-depth Eyreville core holes. Analysis of these lines, in the context of the core hole stratigraphy, shows that moderateamplitude, discontinuous, dipping reflections below ̃527 m correlate with a variety of Chesapeake Bay impact structure sediment and rock breccias recovered in the cores. High-amplitude, continuous, subhorizontal reflections above ̃527 m depth correlate with the uppermost part of the Chesapeake Bay impact structure crater-fi ll sediments and postimpact Eocene to Pleistocene sediments. Refl ections with ̃20-30 m of relief in the uppermost part of the crater-fi ll and lowermost part of the postimpact section suggest differential compaction of the crater-fi ll materials during early postimpact time. The top of the crater-fi ll section also shows ̃20 m of relief that appears to represent an original synimpact surface. Truncation surfaces, locally dipping reflections, and depth variations in reflection amplitudes generally correlate with the lithostratigraphic and sequence-stratigraphic units and contacts in the core. Seismic images show apparent postimpact paleochannels that include the fi rst possible Miocene paleochannels in the Mid-Atlantic Coastal Plain. Broad downwarping in the postimpact section unrelated to structures in the crater fi ll indicates postimpact sediment compaction. © 2009 The Geological Society of America. 2009 English 00721077 10.1130/2009.2458(11) Special Paper of the Geological Society of America 458 Geological Society of America 209-233 U.S. Geological Survey, 926A National Center, Reston, VA 20192, United States; U.S. Geological Survey, 345 Middlefi eld Road, MS 977, Menlo Park, CA 94025, United States C (programming language); Compaction; Infill drilling; Seismic waves; Seismology; Stratigraphy, Chesapeake bay impact structures; Differential compaction; High resolution image; High resolution seismic; Pleistocene sediments; Reflection amplitude; Seismic reflections; U.s. geological surveys, Sediments, deep drilling; impact structure; lithostratigraphy; seismic reflection; seismic tomography; sequence stratigraphy, Chesapeake Bay; United States https://www.scopus.com/inward/record.uri?eid=2-s2.0-74949087401&doi=10.1130%2f2009.2458%2811%29&partnerID=40&md5=742a863c80343f4958cab9323b62fef9 cited By 18 D.S. Powars R.D. Catchings M.R. Goldman G.S. Gohn J.W. Horton Jr. L.E. Edwards M.J. Rymer G. Gandhok article Browning2009775 The Eyreville core holes provide the first continuously cored record of postimpact sequences from within the deepest part of the central Chesapeake Bay impact crater. We analyzed the upper Eocene to Pliocene postimpact sediments from the Eyreville A and C core holes for lithology (semiquantitative measurements of grain size and composition), sequence stratigraphy, and chronostratigraphy. Age is based primarily on Sr isotope stratigraphy supplemented by biostratigraphy (dinocysts, nannofossils, and planktonic foraminifers); age resolution is approximately ±0.5 Ma for early Miocene sequences and approximately ±1.0 Ma for younger and older sequences. Eocene-lower Miocene sequences are subtle, upper middle to lower upper Miocene sequences are more clearly distinguished, and upper Miocene- Pliocene sequences display a distinct facies pattern within sequences. We recognize two upper Eocene, two Oligocene, nine Miocene, three Pliocene, and one Pleistocene sequence and correlate them with those in New Jersey and Delaware. The upper Eocene through Pleistocene strata at Eyreville record changes from: (1) rapidly deposited, extremely fi ne-grained Eocene strata that probably represent two sequences deposited in a deep (>200 m) basin; to (2) highly dissected Oligocene (two very thin sequences) to lower Miocene (three thin sequences) with a long hiatus; to (3) a thick, rapidly deposited (43-73 m/Ma), very fi ne-grained, biosiliceous middle Miocene (16.5-14 Ma) section divided into three sequences (V5-V3) deposited in middle neritic paleoenvironments; to (4) a 4.5-Ma-long hiatus (12.8-8.3 Ma); to (5) sandy, shelly upper Miocene to Pliocene strata (8.3-2.0 Ma) divided into six sequences deposited in shelf and shoreface environments; and, last, to (6) a sandy middle Pleistocene paralic sequence (~400 ka). The Eyreville cores thus record the fi lling of a deep impact-generated basin where the timing of sequence boundaries is heavily infl uenced by eustasy. © 2009 The Geological Society of America. 2009 English 00721077 10.1130/2009.2458(33) Special Paper of the Geological Society of America 458 Geological Society of America 775-810 Department of Earth and Planetary Sciences, Rutgers University, Piscataway, NJ 08854, United States; Delaware Geological Survey, University of Delaware, DGS Building, 257 Academy Street, Newark, DE 19716, United States; U.S. Geological Survey, 926A National Center, Reston, VA 20192, United States; Department of Geology and Geophysics, Texas A and M University, College Station, TX 77843, United States Lithology, Chesapeake bay impact structures; Chronostratigraphy; Measurements of; Middle Pleistocene; Paleoenvironments; Pleistocene strata; Sequence boundary; Sequence stratigraphy, Stratigraphy, biostratigraphy; chronostratigraphy; deposition; Eocene; impact structure; lithology; Miocene; paleoenvironment; Pleistocene; Pliocene; sequence boundary; sequence stratigraphy; strontium isotope, Chesapeake Bay; Delaware; New Jersey; United States, Foraminifera https://www.scopus.com/inward/record.uri?eid=2-s2.0-74949114383&doi=10.1130%2f2009.2458%2833%29&partnerID=40&md5=1481ae772c6cd983df02981e4c329037 cited By 27 J.V. Browning K.G. Miller P.P. McLaughlin Jr. L.E. Edwards A.A. Kulpecz D.S. Powars B.S. Wade M.D. Feigenson J.D. Wright article Shah2009195 We use magnetic susceptibility and remanent magnetization measurements of the Eyreville and Cape Charles cores in combination with new and previously collected magnetic field data in order to constrain structural features within the inner basin of the Chesapeake Bay impact structure. The Eyreville core shows the first evidence of several-hundred-meter-thick basement-derived megablocks that have been transported possibly kilometers from their pre-impact location. The magnetic anomaly map of the structure exhibits numerous short-wavelength (<2 km) variations that indicate the presence of magnetic sources within the crater fill. With core magnetic properties and seismic reflection and refraction results as constraints, forward models of the magnetic field show that these sources may represent basementderived megablocks that are a few hundred meters thick or melt bodies that are a few dozen meters thick. Larger-scale magnetic field properties suggest that these bodies overlie deeper, pre-impact basement contacts between materials with different magnetic properties such as gneiss and schist or gneiss and granite. The distribution of the short-wavelength magnetic anomalies in combination with observations of small-scale (1-2 mGal) gravity field variations suggest that basement-derived megablocks are preferentially distributed on the eastern side of the inner crater, not far from the Eyreville core, at depths of around 1-2 km. A scenario where additional basement-derived blocks between 2 and 3 km depth are distributed throughout the inner basin-and are composed of more magnetic materials, such as granite and schist, toward the east over a large-scale magnetic anomaly high and less magnetic materials, such as gneiss, toward the west where the magnetic anomaly is lower-provides a good model fi t to the observed magnetic anomalies in a manner that is consistent with both gravity and seismic-refraction data. © 2009 The Geological Society of America. 2009 English 00721077 10.1130/2009.2458(10) Special Paper of the Geological Society of America 458 Geological Society of America 195-208 U.S. Geological Survey, Denver Federal Center, MS 964, Bldg. 20, Denver, CO 80225, United States; U.S. Geological Survey, National Center, MS 954, 12201 Sunrise Valley Drive, Reston, VA 20192, United States; Institut für Angewandte Geowissenschaften, Universität Karlsruhe-Karlsruhe, Hertzstraße 16, Gebäude 6.36, 76187 Karlsruhe, Germany; Naval Research Laboratory, Marine Physics Branch Code 7421, 4555 Overlook Avenue SW, Washington, DC 20375, United States Buildings; Electromagnetic field effects; Granite; Magnetic materials; Magnetic susceptibility; Magnetization; Refraction; Seismology, Chesapeake bay impact structures; Magnetic anomalies; Magnetic field data; Remanent magnetization; Seismic reflections; Seismic refraction data; Short wavelengths; Structural feature, Structural properties, crater; gravity anomaly; magnetic anomaly; magnetic field; magnetic property; magnetic susceptibility; remanent magnetization; seismic reflection; seismic refraction, Chesapeake Bay; United States https://www.scopus.com/inward/record.uri?eid=2-s2.0-74949087715&doi=10.1130%2f2009.2458%2810%29&partnerID=40&md5=7a28d2346f7869dfc6776ec9c89ca872 cited By 12 A.K. Shah D.L. Daniels A. Kontny J. Brozena article Gohn20081740 Samples from a 1.76-kilometer-deep corehole drilled near the center of the late Eocene Chesapeake Bay impact structure (Virginia, USA) reveal its geologic, hydrologic, and biologic history. We conducted stratigraphic and petrologic analyses of the cores to elucidate the timing and results of impact-melt creation and distribution, transient-cavity collapse, and ocean-water resurge. Comparison of post-impact sedimentary sequences inside and outside the structure indicates that compaction of the crater fill influenced long-term sedimentation patterns in the mid-Atlantic region. Salty connate water of the target remains in the crater fill today, where it poses a potential threat to the regional groundwater resource. Observed depth variations in microbial abundance indicate a complex history of impact-related thermal sterilization and habitat modification, and subsequent post-impact repopulation. 2008 English 00368075 10.1126/science.1158708 Science 320 1740-1745 U.S. Geological Survey, Reston, VA 20192, United States; Department of Lithospheric Research, Center for Earth Sciences, University of Vienna, Althanstrasse 14, Vienna A-1090, Austria; Department of Geological Sciences, Rutgers University, 610 Taylor Road, Piscataway, NJ 08854, United States; Museum of Natural History (Mineralogy), Humboldt-University Berlin, Invalidenstrasse 43, Berlin 10115, Germany; Centre for Earth, Planetary, Space, and Astronomical Research, Open University, Milton Keynes MK7 6AA, United Kingdom 5884 sea water, abundance; deep drilling; Eocene; groundwater resource; impact structure; petrology; sedimentary sequence; sedimentation; stratigraphy, article; asthenospheric upwelling; biosphere; controlled study; Cretaceous; drill; hydrology; instrument sterilization; microbial growth; nonhuman; petrology; priority journal; sedimentation; stratigraphy; terrestrial surface waters, Bacteria; Ecosystem; Geologic Sediments; Heat; Salinity; Seawater; Time; Virginia, Chesapeake Bay; North America; United States; Virginia https://www.scopus.com/inward/record.uri?eid=2-s2.0-46449110214&doi=10.1126%2fscience.1158708&partnerID=40&md5=cb49fd084b10d1cb6073d9c85b47ff28 cited By 92 G.S. Gohn C. Koeberl K.G. Miller W.U. Reimold J.V. Browning C.S. Cockell J.W. Horton Jr. T. Kenkmann A.A. Kulpecz D.S. Powars W.E. Sanford M.A. Voytek article Hayden2008327 The Chesapeake Bay impact structure is a ca. 35.4 Ma crater located on the eastern seaboard of North America. Deposition returned to normal shortly after impact, resulting in a unique record of both impact-related and subsequent passive margin sedimentation. We use backstripping to show that the impact strongly affected sedimentation for 7 m.y. through impact-derived crustal-scale tectonics, dominated by the effects of sediment compaction and the introduction and subsequent removal of a negative thermal anomaly instead of the expected positive thermal anomaly. After this, the area was dominated by passive margin thermal subsidence overprinted by periods of regional-scale vertical tectonic events, on the order of tens of meters. Loading due to prograding sediment bodies may have generated these events. © 2008 The Geological Society of America. 2008 English 00917613 10.1130/G24408A.1 Geology 36 327-330 Department of Geosciences, Western Michigan University, 1187 Rood Hall, 1903 W. Michigan Avenue, Kalamazoo, MI 49008, United States; United States Geological Survey, National Center, Reston, VA 20192, United States; Department of Geosciences, Rutgers The State University of New Jersey, Piscataway, NJ 08854, United States 4 Backstripping; Eocene; Impact processes; Passive margin, Sedimentology; Structural geology; Subsidence, Tectonics, deposition; Eocene; impact structure; passive margin; sedimentation; tectonic setting; temperature anomaly, Chesapeake Bay; North America; United States https://www.scopus.com/inward/record.uri?eid=2-s2.0-44449173977&doi=10.1130%2fG24408A.1&partnerID=40&md5=5f41e07e0c250ce5131c8a0d047afbd5 cited By 19 T. Hayden M. Kominz D.S. Powars L.E. Edwards K.G. Miller J.V. Browning A.A. Kulpecz book Koeberl200795 Currently about 170 impact craters are known on Earth; about one third of those structures are not exposed on the surface and can only be studied by geophysics or drilling. The impact origin of geological structures can only be confirmed by petrographic and geochemical studies; thus, it is of crucial importance to obtain samples of subsurface structures. In addition, structures that have surface exposures commonly require drilling and drill cores to obtain information of the subsurface structure, to provide ground-truth for geophysical studies, and to obtain samples of rock types not exposed at the surface. For many years, drilling of impact craters was rarely done in dedicated projects, mainly due to the high cost involved. Structures were most often drilled for reasons unrelated to their impact origin. In the former Soviet Union a number of impact structures were drilled for scientific reasons, but in most of these cases the curation and proper care of the cores was not guaranteed. More recently the International Continental Scientific Drilling Program (ICDP) has supported projects to study impact craters. The first ICDPsupported study of an impact structure was the drilling into the 200-kmdiameter, K-T boundary age, subsurface Chicxulub impact crater, Mexico, which occurred between December 2001 and February 2002. The core retrieved from the borehole Yaxcopoil-1, 60 km SSW from the center of the structure, reached a depth of 1511 m and intersected 100 m of impact melt breccia and suevite, which has been studied by an international team. From June to October 2004, the 10.5 km Bosumtwi crater, Ghana, was drilled within the framework of an ICDP project, to obtain a complete 1 million year paleoenvironmental record in an area for which only limited data exist, and to study the subsurface structure and crater fill of one of the best preserved large, young impact structures. From September to December 2005, the main part of another ICDP-funded drilling project was conducted, at the 85-km-diameter Chesapeake Bay impact structure, eastern USA, which involved drilling to a depth of 1.8 km. In 2008, it is likely that the El'ygytgyn structure (Arctic Russia) will be drilled as well. So far only few craters have been drilled - not enough to gain a broad understanding of impact crater formation processes and consequences. In this chapter we summarize the current status of scientific drilling at impact craters, and provide some guidance and suggestions about future drilling projects that are relevant for impact research. Points we cover include: what is the importance of studying impact craters and processes, why is it important to drill impact craters or impact crater lakes, which important questions can be answered by drilling, which craters would be good targets and why; is there anything about the impact process, or of impact relevance, that can be learned by drilling outside any craters; what goals should be set for the future; how important is collaboration between different scientific fields? In the following report, we first briefly discuss the importance of impact cratering, then summarize experience from past drilling projects (ICDP and others), and finally we try to look into the future of scientific drilling of impact structures. © 2007 Springer-Verlag Berlin Heidelberg. 2007 English 9783540687771 10.1007/978-3-540-68778-8_3 Continental Scientific Drilling: A Decade of Progress, and Challenges for the Future Springer Berlin Heidelberg 95-161 Department of Geological Sciences, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria; Department of Physics, University of Toronto, 60 St. George Street, Toronto, ON M5S 1A7, Canada https://www.scopus.com/inward/record.uri?eid=2-s2.0-62849087451&doi=10.1007%2f978-3-540-68778-8_3&partnerID=40&md5=9355d072f6daf494807ad2d6383dc4f9 cited By 11 C. Koeberl B. Milkereit article Gohn200634 2006 English 18168957 10.2204/iodp.sd.3.07.2006 Scientific Drilling 1 34-37 Geological Survey, 926A National Center, Reston, VA, United States; University of Vienna, Vienna, Austria; Rutgers University, Piscataway, NJ, United States; University of the Witwatersrand, Johannesburg, South Africa; Humboldt University, Berlin, Germany 3 https://www.scopus.com/inward/record.uri?eid=2-s2.0-72649104663&doi=10.2204%2fiodp.sd.3.07.2006&partnerID=40&md5=719f0382bcac1fc833556c453b933246 cited By 13 G.S. Gohn C. Koeberl K.G. Miller W.U. Reimold O. Abramov W. Aleman Gonzalez N. Bach A. Blazejak J. Browning T. Bruce C. Budet L. Bybell E. Cobbs Jr. E. Cobbs III C. Cockell B. Corland C. Durand H. Dypvik J. Eckberg L. Edwards S. Eichenauer T. Elbra A. Elmore J. Glidewell G. Gohn A. Gronstal A. Harris P. Heidinger S.-C. Hester W. Horton K. Jones A. Julson D. King J. Kirshtein T. Kohout T. Kraemer D. Kring A. Kulpecz M. Kunk D. Larson U. Limpitlaw M. Lowit N. McKeown P. McLaughlin K. Miller S. Mizintseva R. Morin J. Morrow J. Murray J. Ormö R. Ortiz Martinez L. Petruny H. Pierce J. Plescia D. Powars A. Pusz D.B. Queen D.G. Queen U. Reimold W. Sanford E. Seefelt J. Self-Trail D. Vanko M. Voytek B. Wade J. Wade D. Webster B. Zinn V. Zivkovic article Gohn2006349 2006 English 00963941 10.1029/2006EO350001 Eos 87 American Geophysical Union 349-355 USGS, Reston, VA, United States; Department of Geological Sciences, University of Vienna, Vienna, Austria; Department of Geological Sciences, Rutgers University, Piscataway, NJ, United States; Museum of Natural History, Humboldt University, Berlin, Germany; Planetary and Space Sciences Research Institute, Open University, Milton Keynes, United Kingdom 35 buried structure; drilling; impact structure; impactite; meteorite, Chesapeake Bay; North America; United States https://www.scopus.com/inward/record.uri?eid=2-s2.0-34247367329&doi=10.1029%2f2006EO350001&partnerID=40&md5=4d398176ab1a88706cb011ed5a8afb23 cited By 51 G.S. Gohn C. Koeberl K.G. Miller W.U. Reimold C.S. Cockell J.W. Horton Jr. W.E. Sanford M.A. Voytek article Deutsch2006689 The Chesapeake Bay impact structure, which is about 35 Ma old, has previously been proposed as the possible source crater of the North American tektites (NAT). Here we report major and trace element data as well as the first Sr-Nd isotope data for drill core and outcrop samples of target lithologies, crater fill breccias, and post-impact sediments of the Chesapeake Bay impact structure. The unconsolidated sediments, Cretaceous to middle Eocene in age, have εSrt=35.7Ma of +54 to +272, and εNdt=35.7Ma ranging from -6.5 to - 10.8; one sample from the granitic basement with a TNdCHUR model age of 1.36 Ga yielded an εSrt=35.7Ma of + 188 and an εNdt=35.7Ma of -5.7. The Exmore breccia (crater fill) can be explained as a mix of the measured target sediments and the granite, plus an as-yet undetermined component. The post-impact sediments of the Chickahominy formation have slightly higher TNdCHUR model ages of about 1.55 Ga, indicating a contribution of some older materials. Newly analyzed bediasites have the following isotope parameters: +104 to +119 (εSrt=35.7Ma), -5.7 (εNdt=35.7Ma), 0.47 Ga (TSsUR), and 1.15 Ga (TNdCHUR), which is in excellent agreement with previously published data for samples of the NAT strewn field. Target rocks with highly radiogenic Sr isotopic comparison, as required for explaining to isotopic characteristic of Deep Sea Drilling Project (DSDP) site 612 tektites, were not among the analyzed sample suite, Based on the new isotope data, we exclude any relation between the NA tektites and the Popigai impact crater, athough they have identical ages within 2σ errors. The Chesapeake Bay structure, however, is now clearly constrained as the source crater for the North American tektites, although the present data set obviously does not include all target lithologies that have contributed to the composition of the tektites. © The Meteoritical Society, 2006. 2006 English 10869379 10.1111/j.1945-5100.2006.tb00985.x Meteoritics and Planetary Science 41 University of Arkansas 689-703 Institut für Planetologie (IfP), Westfälische Wilhelms-Universität Münster (WWU), Wilhelm-Klemm-Str. 10, D-48149 Münster, Germany; Zentrallabor für Geochronologie (ZLG), WWU, Corrensstr. 24, D-48149 Münster, Germany; Department of Geological Sciences, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria 5 crater; Deep Sea Drilling Project; impact structure; isotopic composition; neodymium; strontium; tektite https://www.scopus.com/inward/record.uri?eid=2-s2.0-33744489305&doi=10.1111%2fj.1945-5100.2006.tb00985.x&partnerID=40&md5=09869c079c1b8c29978950a8421aa6d7 cited By 44 A. Deutsch C. Koeberl article Sanford2005185 Groundwater more saline than seawater has been discovered in the tsunami breccia of the Chesapeake Bay impact Crater. One hypothesis for the origin of this brine is that it may be a liquid residual following steam separation in a hydrothermal system that evolved following the impact. Initial scoping calculations have demonstrated that it is feasible such a residual brine could have remained in the crater for the 35 million years since impact. Numerical simulations have been conducted using the code HYDROTHERM to test whether or not conditions were suitable in the millennia following the impact for the development of a steam phase in the hydrothermal system. Hydraulic and thermal parameters were estimated for the bedrock underlying the crater and the tsunami breccia that fills the crater. Simulations at three different breccia permeabilities suggest that the type of hydrothermal system that might have developed would have been very sensitive to the permeability. A relatively low breccia permeability (1 × 10-16 m2) results in a system partitioned into a shallow water phase and a deeper superheated steam phase. A moderate breccia permeability (1 × 10-15 m2 ) results in a system with regionally extensive multiphase conditions. A relatively high breccia permeability (1 × 10-14 m2 ) results in a system dominated by warm-water convection cells. The permeability of the crater breccia could have had any of these values at given depths and times during the hydrothermal system evolution as the sediments compacted. The simulations were not able to take into account transient permeability conditions, or equations of state that account for the salt content of seawater. Results suggest, however, that it is likely that steam conditions existed at some time in the system following impact, providing additional evidence that is consistent with a hydrothermal origin for the crater brine. © Blackwell Publishing Ltd. 2005 English 14688115 10.1111/j.1468-8123.2005.00110.x Geofluids 5 185-201 U.S. Geological Survey, 12201 Sunrise Valley Dr., Reston, VA 20192, United States 3 bolide; hydrothermal circulation; impact structure, Chesapeake Bay; North America; United States; Western Hemisphere; World https://www.scopus.com/inward/record.uri?eid=2-s2.0-22744445158&doi=10.1111%2fj.1468-8123.2005.00110.x&partnerID=40&md5=6dd99367743a9414b4e712f7c96dc329 cited By 31 W.E. Sanford article Poag2005117 This study reexamines seven reprocessed (increased vertical exaggeration) seismic reflection profiles that cross the eastern rim of the Chesapeake Bay impact crater. The eastern rim is expressed as an arcuate ridge that borders the crater in a fashion typical of the "raised" rim documented in many well preserved complex impact craters. The inner boundary of the eastern rim (rim wall) is formed by a series of raterfacing, steep scarps, 15-60 m high. In combination, these rim-wall scarps represent the footwalls of a system of crater-encircling normal faults, which are downthrown toward the crater. Outboard of the rim wall are several additional normal-fault blocks, whose bounding faults trend approximately parallel to the rim wall. The tops of the outboard fault blocks form two distinct, parallel, flat or gently sloping, terraces. The innermost terrace (Terrace 1) can be identified on each profile, but Terrace 2 is only sporadically present. The terraced fault blocks are composed mainly of nonmarine, poorly to moderately consolidated, siliciclastic sediments, belonging to the Lower Cretaceous Potomac Formation. Though the ridge-forming geometry of the eastern rim gives the appearance of a raised compressional feature, no compelling evidence of compressive forces is evident in the profiles studied. The structural mode, instead, is that of extension, with the clear dominance of normal faulting as the extensional mechanism. © 2005 Geological Society of America. 2005 English 00721077 10.1130/0-8137-2384-1.117 Special Paper of the Geological Society of America 384 Geological Society of America 117-130 U.S. Geological Survey, 384 Woods Hole Road, Woods Hole, MA 02543-1598, United States Meteor impacts; Morphology; Stratigraphy; Structure (composition), Chesapeake Bay; Compressive forces; Impact craters; Lower Cretaceous; Normal faulting; Seismic reflection profiles; Siliciclastic sediments; Structural modes, Fault slips, crater; Cretaceous; dominance; faulting; morphology; seismic reflection; stratigraphy; terrace, Chesapeake Bay; United States https://www.scopus.com/inward/record.uri?eid=2-s2.0-73949150401&doi=10.1130%2f0-8137-2384-1.117&partnerID=40&md5=16c16e40d40a07acb7893db2f8163536 cited By 8 C.W. Poag article Shah2005417 We present high-resolution gravity and magnetic field survey results over the 85-km-diameter Chesapeake Bay impact structure. Whereas a continuous melt sheet is anticipated at a crater this size, shallow-source magnetic field anomalies of ∼100 nT instead suggest that impact melt pooled in kilometer-scaled pockets surrounding the base of a central peak. A central anomaly of ∼300 nT may represent additional melt or rock that underwent shock-induced remagnetization. Models predict that the total volume of the melt ranges from ∼0.4 to 10 km3, a quantity that is several orders of magnitude smaller than expected for an impact structure this size. However, this volume is within predictions given a transient crater of diameter of 20-40 km for a target covered with water and sedimentary deposits such that melt fragments were widely dispersed at the time of impact. Gravity data delineate a gently sloping inner basin and a central peak via a contrast between crystalline and sedimentary rock. Both features are ovoid, oriented parallel to larger preimpact basement structures. Conceptual models suggest how lateral differences in rock strength due to these preimpact structures helped to shape the crater's morphology during transient-crater modification. © 2005 Geological Society of America. 2005 English 00917613 10.1130/G21213.1 Geology 33 417-420 Naval Research Laboratory, Washington, DC 20375, United States; U.S. Geological Survey, Reston, VA 20192, United States; Applied Physics Lab., Johns Hopkins University, Laurel, MD 20723, United States 5 Chesapeake bay impact structures; Craters; Melt fragments; Remagnetization, Gravitation; Magnetic fields; Magnetization; Melting; Morphology; Rocks, Tectonics, gravity survey; impact structure; magnetic survey; remagnetization; shock metamorphism, Chesapeake Bay; North America; United States; Western Hemisphere; World https://www.scopus.com/inward/record.uri?eid=2-s2.0-18944362488&doi=10.1130%2fG21213.1&partnerID=40&md5=6298ac1ae137e0211bc65f8aa65a53fd cited By 27 A.K. Shah J. Brozena P. Vogt D. Daniels J. Plescia article HortonJr.2005147 Four new coreholes in the western annular trough of the buried, late Eocene Chesapeake Bay impact structure provide samples of shocked minerals, cataclastic rocks, possible impact melt, mixed sediments, and damaged microfossils. Parautochthonous Cretaceous sediments show an upward increase in collapse, sand fluidization, and mixed sediment injections. These impact-modifi ed sediments are scoured and covered by the upper Eocene Exmore beds, which consist of highly mixed Cretaceous to Eocene sediment clasts and minor crystalline-rock clasts in a muddy quartz-glauconite sand matrix. The Exmore beds are interpreted as seawater-resurge debris flows. Shocked quartz is found as sparse grains and in rock fragments at all four sites in the Exmore, where these fallback remnants are mixed into the resurge deposit. Crystalline-rock clasts that exhibit shocked quartz or cataclastic fabrics include felsites, granitoids, and other plutonic rocks. Felsite from a monomict cataclasite boulder has a sensitive high-resolution ion microprobe U-Pb zircon age of 613 ± 4 Ma. Leucogranite from a polymict cataclasite boulder has a similar Neoproterozoic age based on muscovite 40 Ar/ 39 Ar data. Potassium-feldspar 40 Ar/ 39 Ar ages from this leucogranite show cooling through closure (∼150 °C) at ca. 261 Ma without discernible impact heating. Spherulitic felsite is under investigation as a possible impact melt. Types of crystalline clasts, and exotic sediment clasts and grains, in the Exmore vary according to location, which suggests different provenances across the structure. Fractured calcareous nannofossils and fused, bubbled, and curled dinofl agellate cysts coexist with shocked quartz in the Exmore, and this damage may record conditions of heat, pressure, and abrasion due to impact in a shallow-marine environment. © 2005 Geological Society of America. 2005 English 00721077 10.1130/0-8137-2384-1.147 Special Paper of the Geological Society of America 384 Geological Society of America 147-170 U.S. Geological Survey, MS 926A, 12201 Sunrise Valley Drive, Reston, VA 20192, United States; U.S. Geological Survey, MS 963, Denver Federal Center, Denver, CO 80225, United States; Department of Geology, College of William and Mary, 3012 East Whittaker Close, Williamsburg, VA 23285, United States Argon; Binary alloys; Crystalline materials; Crystalline rocks; Debris; Feldspar; Fluidization; Geochronology; Lead alloys; Mica; Quartz; Rocks; Sediments; Silicate minerals; Structural geology; Zircon, Cataclastic; Chesapeake; Crater; Dinofl agellate; Ejecta; Impact; Nannofossil; Resurge; Shock; SHRIMP, Meteor impacts, abrasion; cataclasite; Cretaceous; ejecta; Eocene; fluidization; impact structure; ion microprobe; leucogranite; melt; muscovite; quartz; research; sand; zircon, Chesapeake Bay; United States https://www.scopus.com/inward/record.uri?eid=2-s2.0-73949090062&doi=10.1130%2f0-8137-2384-1.147&partnerID=40&md5=2f04f8852b2373bea591d26d0e62fe07 cited By 38 J.W. Horton Jr. J.N. Aleinikoff M.J. Kunk G.S. Gohn L.E. Edwards J.M. Self-Trail D.S. Powars G.A. Izett article Poag200422 In July 1983, the shipboard scientists of Deep Sea Drilling Project Leg 95 found an unexpected bonus in a core taken 150 kilometers east of Atlantic City, N.J. At Site 612, the scientists recovered a 10-centimeter-thick layer of late Eocene debris ejected from an impact about 36 million years ago. Microfossils and argon isotope ratios from the same layer reveal that the ejecta were part of a broad North American impact debris field, previously known primarily from the Gulf of Mexico and Caribbean Sea. Since that serendipitous beginning, years of seismic reflection profiling, gravity measurements and core drilling have confirmed the source of that strewn field - the Chesapeake Bay impact crater, the largest structure of its kind in the United States, and the sixth-largest impact crater on Earth. 2004 English 00168556 Geotimes 49 22-25 U.S. Geological Survey, Woods Hole, MA, United States 1 crater; ejecta; Eocene; impact structure; sediment core, Chesapeake Bay; North America; United States https://www.scopus.com/inward/record.uri?eid=2-s2.0-1642278797&partnerID=40&md5=08d22c04a2309e14dac09471ec786a42 cited By 1 C.W. Poag article Sanford2004 2004 English 00963941 10.1029/2004EO390001 Eos 85 American Geophysical Union 369+377 Self-Trail, USGS., Reston, VA, United States; USGS., Lakewood, CO, United States 39 https://www.scopus.com/inward/record.uri?eid=2-s2.0-33646456831&doi=10.1029%2f2004EO390001&partnerID=40&md5=5f5a91690e137aac3373df5bb4806c14 cited By 23 W.E. Sanford G.S. Gohn D.S. Powars J.W. Horton Jr. L.E. Edwards M. Jean R.H. Morin report 2004 10.3133/ofr20041016 2004-1016 http://pubs.er.usgs.gov/publication/ofr20041016 Lucy E. Edwards W.J.J. Wright Horton Jr. Gregory S. Gohn