All ICDP Publications with Abstracts
From parent-sysfolder "Publications" + 2 folder-levels deep
969.
A tephrostratigraphic record for the last glacial-interglacial cycle from Lake Ohrid, Albania and Macedonia
Journal of Quaternary Science,
25
(3)
320 – 338
2010
ISSN: 10991417DOI:10.1002/jqs.1311
Keywords:▾
Albania; Greece; Lake Ohrid; Macedonia [Greece]; caldera; Campanian; ignimbrite; Last Glacial-Interglacial; magnetic susceptibility; marine isotope stage; potassium; stratigraphy; strontium; tephra; tephrochronology; tuff; volcanic eruption; X-ray fluorescence; zircon
Abstract: ▾ Here we present a tephrostratigraphic record (core Co1202) recovered from the northeastern part of Lake Ohrid (Republics of Macedonia and Albania) reaching back to Marine Isotope Stage (MIS) 6. Overall ten horizons (OT0702-1 to OT0702-10) containing volcanic tephra have been recognised throughout the 14.94m long sediment succession. Four tephra layers were visible at macroscopic inspection (OT0702-4, OT0702-6, OT0702-8 and OT0702-9), while the remaining six are cryptotephras (OT0702-1, OT0702-2, OT0702-3, OT0702-5, OT0702-7 and OT0702-10) identified from peaks in K, Zr and Sr intensities, magnetic susceptibility measurements, and washing and sieving of the sediments. Glass shards of tephra layers and cryptotephras were analysed with respect to their major element composition, and correlated to explosive eruptions of Italian volcanoes. The stratigraphy and the major element composition of tephra layers and cryptotephras allowed the correlation of OT0702-1 to AD 472 or AD 512 eruptions of Somma-Vesuvius, OT0702-2 to the FL eruption of Mount Etna, OT0702-3 to the Mercato from Somma-Vesuvius, OT0702-4 to SMP1-e/Y-3 eruption from the Campi Flegrei caldera, OT0702-5 to the Codola eruption (Somma-Vesuvius or Campi Flegrei), OT0702-6 to the Campanian Ignimbrite/Y-5 from the Campi Flegrei caldera, OT0702-7 to the Green Tuff/Y-6 eruption from Pantelleria Island, OT0702-8 to the X-5 eruption probably originating from the Campi Flegrei caldera, OT0702-9 to the X-6 eruption of generic Campanian origin, and OT0702-10 to the P-11 eruption from Pantelleria Island. The fairly well-known ages of these tephra layers and parent eruptions provide new data on the dispersal and deposition of these tephras and, furthermore, allow the establishment of a chronological framework for core Co1202 for a first interpretation of major sedimentological changes. © 2009 John Wiley & Sons, Ltd.
968.
A paleoclimate record with tephrochronological age control for the last glacial-interglacial cycle from Lake Ohrid, Albania and Macedonia
Journal of Paleolimnology,
44
(1)
295 – 310
2010
ISSN: 09212728Keywords:▾
Albania; Greece; Lake Ohrid; Macedonia [Greece]; accumulation rate; climate variation; geochemical method; Last Glacial-Interglacial; lithology; lithostratigraphy; paleoclimate; paleolimnology; Pliocene; proxy climate record; radiocarbon dating; sedimentology; tephrochronology
Abstract: ▾ Lake Ohrid is probably of Pliocene age, and the oldest extant lake in Europe. In this study climatic and environmental changes during the last glacial-interglacial cycle are reconstructed using lithological, sedimentological, geochemical and physical proxy analysis of a 15-m-long sediment succession from Lake Ohrid. A chronological framework is derived from tephrochronology and radiocarbon dating, which yields a basal age of ca. 136 ka. The succession is not continuous, however, with a hiatus between ca. 97. 6 and 81. 7 ka. Sediment accumulation in course of the last climatic cycle is controlled by the complex interaction of a variety of climate-controlled parameters and their impact on catchment dynamics, limnology, and hydrology of the lake. Warm interglacial and cold glacial climate conditions can be clearly distinguished from organic matter, calcite, clastic detritus and lithostratigraphic data. During interglacial periods, short-term fluctuations are recorded by abrupt variations in organic matter and calcite content, indicating climatically-induced changes in lake productivity and hydrology. During glacial periods, high variability in the contents of coarse silt to fine sand sized clastic matter is probably a function of climatically-induced changes in catchment dynamics and wind activity. In some instances tephra layers provide potential stratigraphic markers for short-lived climate perturbations. Given their widespread distribution in sites across the region, tephra analysis has the potential to provide insight into variation in the impact of climate and environmental change across the Mediterranean. © 2010 Springer Science+Business Media B.V.
967.
A high-performance, safer and semi-automated approach for the δ18O analysis of diatom silica and new methods for removing exchangeable oxygen
Rapid Communications in Mass Spectrometry,
24
(17)
2655-2664
2010
ISSN: 09514198DOI:10.1002/rcm.4689
Keywords:▾
helium; oxygen; silicon dioxide, article; chemistry; desiccation; diatom; instrumentation; ion exchange; isolation and purification; laboratory automation; methodology; paleontology; reproducibility; sensitivity and specificity, Automation, Laboratory; Desiccation; Diatoms; Helium; Ion Exchange; Oxygen Isotopes; Paleontology; Quartz; Reproducibility of Results; Sensitivity and Specificity; Silicon Dioxide
Abstract: ▾ The determination of the oxygen isotope composition of diatom silica in sediment cores is important for paleoclimate reconstruction, especially in non-carbonate sediments, where no other bioindicators such as ostracods and foraminifera are available. Since most currently available analytical techniques are time-consuming and labour-intensive, we have developed a new, safer, faster and semi-automated online approach for measuring oxygen isotopes in biogenic silica. Improvements include software that controls the measurement procedures and a video camera that remotely records the reaction of the samples under BrF5 with a CO2 laser. Maximum safety is guaranteed as the laserfluorination unit is arranged under a fume hood in a separate room from the operator. A new routine has been developed for removing the exchangeable hydrous components within biogenic silica using ramp degassing. The sample plate is heated up to 1100°C and cooled down to 400°C in ~7 h under a flow of He gas (the inert Gas Flow Dehydration method - iGFD) before isotope analysis. Two quartz and two biogenic silica samples (~1.5 mg) of known isotope composition were tested. The isotopic compositions were reproducible within an acceptable error; quartz samples gave a mean standard deviation of <0.15%(1σ) and for biogenic silica <0.25%(1σ) for samples down to ~0.3 mg. The semiautomated fluorination line is the fastest method available at present and enables a throughput of 74 samples/week. © 2010 John Wiley & Sons, Ltd.
966.
A freshwater biodiversity hotspot under pressure - Assessing threats and identifying conservation needs for ancient Lake Ohrid
Biogeosciences,
7
(12)
3999 – 4015
2010
ISSN: 17264189Keywords:▾
Lake Ohrid; anthropogenic effect; biodiversity; buffer zone; coastal zone management; eutrophication; future prospect; habitat conservation; hot spot; lake ecosystem
Abstract: ▾ Immediate conservation measures for world-wide freshwater resources are of eminent importance. This is particularly true for so-called ancient lakes. While these lakes are famous for being evolutionary theatres, often displaying an extraordinarily high degree of biodiversity and endemism, in many cases these biota are also experiencing extreme anthropogenic impact. Lake Ohrid, a major European biodiversity hotspot situated in a trans-frontier setting on the Balkans, is a prime example for a lake with a magnitude of narrow range endemic taxa that are under increasing anthropogenic pressure. Unfortunately, evidence for a "creeping biodiversity crisis" has accumulated over the last decades, and major socio-political changes have gone along with human-mediated environmental changes. Based on field surveys, monitoring data, published records, and expert interviews, we aimed to (1) assess threats to Lake Ohrids' (endemic) biodiversity, (2) summarize existing conservation activities and strategies, and (3) outline future conservation needs for Lake Ohrid. We compiled threats to both specific taxa (and in cases to particular species) as well as to the lake ecosystems itself. Major conservation concerns identified for Lake Ohrid are: (1) watershed impacts, (2) agriculture and forestry, (3) tourism and population growth, (4) non-indigenous species, (5) habitat alteration or loss, (6) unsustainable exploitation of fisheries, and (7) global climate change. Among the major (well-known) threats with high impact are nutrient input (particularly of phosphorus), habitat conversion and silt load. Other threats are potentially of high impact but less well known. Such threats include pollution with hazardous substances (from sources such as mines, former industries, agriculture) or climate change. We review and discuss institutional responsibilities, environmental monitoring and ecosystem management, existing parks and reserves, biodiversity and species measures, international conservation activities, and ongoing research on conservation and raising of public awareness. Following this summary, we evaluate the status quo and future of Lake Ohrid and its biota. A comprehensive conservation strategy should include measures that result in an immediate reduction of nutrient input, particularly with phosphorus, in order to slow down the ongoing eutrophication process. The existing watershed management should become more effective. Implementation and particularly with a view to the enforcement of national laws should be enhanced. Increased research on the lakes' limnology, biodiversity, and conservation management practices are necessary. The latter research should identify conservation priorities. Public awareness should be enhanced. Facing these parallel needs to protect the unique biodiversity of Lake Ohrid, we suggest urging (a) implementation and enforcement of the General Management Plan that would ensure long-term integrated and sustainable use of the lake and its watershed, (b) scientific studies on ecology, biodiversity and effects of human impact, (c) the establishment of Core Conservation areas (CCA), including underwater reserves, and (d) Coastal Zone Management (CZM) areas that would constitute buffer zones for the CCAs around the lake. Given the number of identified threats, it is clear that only concerted international action can stop or at least slow down further degradation of Lake Ohrid and the creeping biodiversity crisis already evident. All conservation activities should, among others, ultimately lead to a trans-boundary major conservation area of the Ohrid-Prespa region that would allow long-term integration of both humans and nature. © Author(s) 2010.
965.
A combined oxygen and silicon diatom isotope record of Late Quaternary change in Lake El'gygytgyn, North East Siberia
Quaternary Science Reviews,
29
(5-6)
774-786
2010
ISSN: 02773791Keywords:▾
Aleutian low; Arctic Circle; Climatic changes; Cooling trends; Environmental change; Global climate system; Holocenes; Isotope record; Last glacial; Last Glacial Maximum; Late quaternary; North Atlantic; North-East Siberia; Seasonality; Solar insolation; Spatial variability; Teleconnections; Thermal maxima, Amplification; Global warming; Isotopes; Oxygen, Glacial geology, climate variation; Holocene; isotopic analysis; oxygen isotope; perturbation; silicon; spatial variation, Atlantic Ocean; Atlantic Ocean (North); Chukchi; Elgygytgyn Lake; Russian Federation, Bacillariophyta
Abstract: ▾ Determining the response of sites within the Arctic Circle to long-term climatic change remains an essential pre-requisite for assessing the susceptibility of these regions to future global warming and Arctic amplification. To date, existing records from North East Russia have demonstrated significant spatial variability across the region during the late Quaternary. Here we present diatom δ18O and δ30Si data from Lake El'gygytgyn, Russia, and suggest environmental changes that would have impacted across West Beringia from the Last Glacial Maximum to the modern day. In combination with other records, the results raise the potential for climatic teleconnections to exist between the region and sites in the North Atlantic. The presence of a series of 2-3‰ decreases in δ18Odiatom during both the Last Glacial and the Holocene indicates the sensitivity of the region to perturbations in the global climate system. Evidence of an unusually long Holocene thermal maximum from 11.4 ka BP to 7.6 ka BP is followed by a cooling trend through the remainder of the Holocene in response to changes in solar insolation. This is culminated over the last 900 years by a significant decrease in δ18Odiatom of 2.3‰, which may be related to a strengthening and easterly shift of the Aleutian Low in addition to possible changes in precipitation seasonality. © 2009 Elsevier Ltd. All rights reserved.
964.
A chemostratigraphic method to determine the end of impact-related sedimentation at marine-target impact craters (Chesapeake Bay, Lockne, Tvären)
Meteoritics and Planetary Science,
45
(7)
1206-1224
2010
ISSN: 10869379
Publisher: University of Arkansas
Abstract: ▾ 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.
963.
Millennial-scale climate variability during the Last Glacial period in the tropical Andes
Quaternary Science Reviews,
29
(7-8)
1017 – 1024
2010
Keywords:▾
Andes; Lake Titicaca; Climatology; Glacial geology; Salinity measurement; Tropics; Climate variability; Climate variation; Deep drilling; Global scale; Greenland; High resolution; Ice core; Last glacial period; Nearshores; North Atlantic; Relative abundance; River transports; Sediment core; Sedimentary units; South America; Summer monsoon; Tropical Andes; Wet period; climate variation; deep drilling; lacustrine deposit; Last Glacial; paleoclimate; resolution; sedimentation; terrigenous deposit; Sedimentology
Abstract: ▾ Millennial-scale climate variation during the Last Glacial period is evident in many locations worldwide, but it is unclear if such variation occurred in the interior of tropical South America, and, if so, how the low-latitude variation was related to its high-latitude counterpart. A high-resolution record, derived from the deep drilling of sediments on the floor of Lake Titicaca in the southern tropical Andes, is presented that shows clear evidence of millennial-scale climate variation between ∼60 and 20 ka BP. This variation is manifested by alternations of two interbedded sedimentary units. The two units have distinctive sedimentary, geochemical, and paleobiotic properties that are controlled by the relative abundance of terrigenous or nearshore components versus pelagic components. The sediments of more terrigenous or nearshore nature likely were deposited during regionally wetter climates when river transport of water and sediment was higher, whereas the sediments of more pelagic character were deposited during somewhat drier climates regionally. The majority of the wet periods inferred from the Lake Titicaca sediment record are correlated with the cold events in the Greenland ice cores and North Atlantic sediment cores, indicating that increased intensity of the South American summer monsoon was part of near-global scale climate excursions. © 2010 Elsevier Ltd. All rights reserved.
962.
Diversity of laboratory-reared prokaryotes in the bottom sediments of the Akademichesky Ridge, Lake Baikal
Inland Water Biology,
3
(1)
38 – 43
2010
ISSN: 19950837Keywords:▾
Akademichesky Ridge; Lake Baikal; Russian Federation; Prokaryota; deep drilling; lacustrine deposit; microbial community; phylogenetics; physiology; prokaryote; species diversity; vertical distribution
Abstract: ▾ Microbial communities in the bottom sediments of the Akademichesky Ridge, Lake Baikal, were studied. The samples were taken by deep drilling BDP-96 (a 100-m core). Vertical distribution of the prokaryotes with different physiological characteristics was studied for the core. The phylogenetic analysis of the organotrophic laboratory-reared microorganisms revealed the clusterization of Baikal strains and species which have not been identified yet. © Pleiades Publishing, Ltd., 2010.
961.
Advances of international continental scientific drilling program
Acta Geologica Sinica (English Edition),
84
(6)
873-886
2010
ISSN: 10009515Abstract: ▾ It has long been a dream for mankind to enter the deep Earth to sample and investigate the structures and inner geological progresses. Until now, scientific drilling has been the unique method in our understanding of the processes and structures of the Earth. This paper try to give a brief introduction of the history, the development, the mission, the structure and management, the membership, the project development scheme of International Continental Drilling Program (ICDP). Great advances have been brought about in many fields of earth sciences by continental scientific drilling in recent years. Based on the recent publications and website materials of ICDP, this paper summarize the main developments in Climate Dynamics and Global Environments, in the Study of Impact Craters, in the GeoBiospherc, in Active Volcanic Systems, in Active Faults, in Hotspot Volcanoes, in Convergent Plate Boundaries and Collision Zones, and in Natural Resources. Special introduction on the scientific results of ICDP drilling at Mt. Unzen, Japan and the Hawaii Scientific Drilling Project (HSDP) is introduced in this paper. Fascinating discoveries such as the gouge layer of San Andreas Fault and the finding of talc in cuttings of SAFOD project are also introduced in this paper. As one of the three founding members of ICDP, China has also gained a lot of developments in continental scientific drilling; typical examples are the achievements of Chinese Continental Scientific Drilling (CCSD) and the progress of Lake Qinghai Scientific Drilling Project. The preliminary progresses . of the third approved ICDP project of China -the Chinese Cretaceous Continental Scientific Drilling Project and the development of ICDP-China are also summarized in this paper.
960.
EarthScope - The latest advances of the united state's deep exploration program
Acta Geologica Sinica (English Edition),
84
(6)
909-926
2010
ISSN: 10009515Abstract: ▾ The implementation of EarthScope, the deep exploration program in North American continent has become the focus of attention in the field of Earth Sciences. This paper gives a brief description of the background, scientific problems to be solved, observational approaches adopted,some research progresses of the EarthScope program in the fields such as seismic tomographic imaging, earth stress change, continental structure, topographic survey and so on.
959.
Inside the crater, outside the crater: Stratigraphic details of the margin of the Chesapeake Bay impact structure, Virginia, USA
Special Paper of the Geological Society of America,
465319-393
2010
ISSN: 00721077
Publisher: Geological Society of America
Keywords:▾
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
Abstract: ▾ 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.
958.
Migration-based location of seismicity recorded with an array installed in the main hole of the San Andreas Fault Observatory at Depth (SAFOD)
Geophysical Journal International,
182
(1)
477-492
2010
ISSN: 0956540XKeywords:▾
back propagation; body wave; borehole; San Andreas Fault; seismic migration; seismic reflection; seismicity; seismotectonics; spatial analysis; time series analysis; wave propagation
Abstract: ▾ We present the principles of a recently developed event location procedure and its application to seismicity recorded in the main borehole of the San Andreas Fault Observatory at Depth (SAFOD). The basic idea of the location approach is the backpropagation of the recorded wavefield along rays using a Gaussian-beam-type weighting factor. In the case of a sufficient number of receivers, the intersection of these rays results in a distinct maximum at the corresponding hypocentre location. We have applied this technique to data recorded with an 80-level three-component (3C) receiver array in the SAFOD main hole and we have located a number of events in the vicinity of the fault system. A modification of the location algorithm also allowed the precise location of one of the so-called target events, which are the subject of recent drilling activities as well as ongoing research at SAFOD. We summarize the principles of the location method and the performed processing steps, provide estimates of the uncertainties for the target event location and test the robustness of the location using six different 3-D velocity models. Furthermore, we discuss the event locations in comparison with borehole logging data and coincident seismic reflection images and we also show identified events with highly correlated waveforms. © 2010 The Authors Journal compilation © 2010 RAS.
957.
Environmental change within the Balkan region during the past ca. 50 ka recorded in the sediments from lakes Prespa and Ohrid
Biogeosciences,
7
(10)
3187 – 3198
2010
ISSN: 17264189Keywords:▾
Balkan; Lake Mikri Prespa; Lake Ohrid; Turkmenistan; carbonate; core analysis; environmental change; glacial deposit; Heinrich event; Holocene; karst hydrology; lacustrine deposit; organic matter; paleoenvironment; paleolimnology; Pleistocene; radiocarbon dating; sedimentation rate; tephra; trophic status
Abstract: ▾ Lakes Prespa and Ohrid, in the Balkan region, are considered to be amongst the oldest lakes in Europe. Both lakes are hydraulically connected via karst aquifers. From Lake Ohrid, several sediment cores up to 15 m long have been studied over the last few years. Here, we document the first long sediment record from nearby Lake Prespa to clarify the influence of Lake Prespa on Lake Ohrid and the environmental history of the region. Radiocarbon dating and dated tephra layers provide robust age control and indicate that the 10.5 m long sediment record from Lake Prespa reaches back to 48 ka. Glacial sedimentation is characterized by low organic matter content and absence of carbonates in the sediments, which indicate oligotrophic conditions in both lakes. Holocene sedimentation is characterized by particularly high carbonate content in Lake Ohrid and by particularly high organic matter content in Lake Prespa, which indicates a shift towards more mesotrophic conditions in the latter. Long-term environmental change and short-term events, such as related to the Heinrich events during the Pleistocene or the 8.2 ka cooling event during the Holocene, are well recorded in both lakes, but are only evident in certain proxies. The comparison of the sediment cores from both lakes indicates that environmental change affects particularly the trophic state of Lake Prespa due to its lower volume and water depth. © Author(s) 2010.
956.
Melt-bearing impactites (suevite and impact melt rock) within the Gardnos structure, Norway
Meteoritics and Planetary Science,
45
(5)
798-827
2010
Abstract: ▾ Melt-bearing impactites dominated by suevite, and with a minor content of clast-rich impact melt rock, are found within the central part of the Gardnos structure. They are preserved as the eroded remnants in the relatively small complex impact structure with a present diameter of 5 km. These rocks have been mapped in the field and in the Branden drill core, and described according to mineralogy/petrology, including matrix, litho clast, and melt content, as well as geochemistry. Based on our extensive field mapping, a simple 3-D model of the original crater was constructed to estimate tentative volumes for the melt-bearing impactites. The variations in lithic and melt fragment content and chemistry of suevite matrix can mostly be explained by incorporation of mafic rocks into a dominant mixture of granitic, gneissic, and quartzitic target rocks, reflecting mixing of material from different parts of the crater. Melt fragments within suevite occur with a variety of shapes and textures, probably related to different original target rock composition, to the various temperatures the individual fragments were subjected to during the impact event and deposition processes. This study discusses the impact-related deposits based on a sedimentological approach. Their overall composition and structures indicate dominating gravity flow processes in the final transportation and deposition of the suevite. © 2010 The Meteoritical Society.
955.
Melt particle characteristics of the within-and out-of-crater suevites from the Bosumtwi impact structure, Ghana: Implications for crater formation
Special Paper of the Geological Society of America,
465411 – 442
2010
ISSN: 00721077
Publisher: Geological Society of America
Keywords:▾
Ashanti; Ghana; Lake Bosumtwi; Feldspar; Glass; Quartz; Rocks; Silicate minerals; Continental scientific drillings; Crater formation; Impact structures; Lateral movement; Mechanisms of formation; Particle characteristics; Planar deformation; Shocked quartz; crater; geochemistry; impact structure; petrography; suevite; Meteor impacts
Abstract: ▾ A petrographic and geochemical comparison of suevites from the LB-07A and LB-08A cores recovered during 2004 by the International Continental Scientific Drilling Program with suevites from outside of the crater rim of the Bosumtwi impact structure indicates contrasting mechanisms of formation for these respective impact breccias. The within-crater suevites form only a small part of the lithic impact breccia-dominated impactite crater fill, in contrast to the impactites from outside of the crater, which consist solely of suevite. The clasts of suevites from within the crater display relatively low levels of shock (for most material <45 GPa). The numbers of shocked quartz grains, as well as fragments of diaplectic glass of quartz and feldspar in suevites decrease with depth through the LB-07A core (maximum three sets of planar deformation features [PDFs]). In contrast, the out-of-crater suevites sampled north and south of the crater contain up to four PDF sets in quartz clasts, ballen cristobalite, and higher proportions of diaplectic glass than the within-crater suevites. In addition, the suevites from outside of the crater contain significantly more melt particles (18-37 vol%) than the within-crater suevites (<5 vol%). Melt fragment sizes in suevites from outside the crater are much larger than those from suevites within the crater (maximum 40 cm versus 1 cm). The currently known distribution of impactites outside of the crater would be consistent with a low-angle impact from the east. We propose that the within-crater suevites and polymict lithic breccias were emplaced either via slumping off the crater walls or lateral movement of some melted and much displaced target rock within the crater. Limited admixture of fallback material from the ejecta plume is evident in the uppermost impactite deposit encountered in core LB-05B. In contrast, the out-of-crater suevites formed by fallout from a laterally differentiated ejecta plume, which resulted in different clast populations to the north and south of the crater. © 2010 The Geological Society of America. All rights reserved.
954.
Melt particle characteristics of the within-and out-of-crater suevites from the Bosumtwi impact structure, Ghana: Implications for crater formation
Special Paper of the Geological Society of America,
465411-442
2010
Abstract: ▾ A petrographic and geochemical comparison of suevites from the LB-07A and LB-08A cores recovered during 2004 by the International Continental Scientific Drilling Program with suevites from outside of the crater rim of the Bosumtwi impact structure indicates contrasting mechanisms of formation for these respective impact breccias. The within-crater suevites form only a small part of the lithic impact breccia-dominated impactite crater fill, in contrast to the impactites from outside of the crater, which consist solely of suevite. The clasts of suevites from within the crater display relatively low levels of shock (for most material <45 GPa). The numbers of shocked quartz grains, as well as fragments of diaplectic glass of quartz and feldspar in suevites decrease with depth through the LB-07A core (maximum three sets of planar deformation features [PDFs]). In contrast, the out-of-crater suevites sampled north and south of the crater contain up to four PDF sets in quartz clasts, ballen cristobalite, and higher proportions of diaplectic glass than the within-crater suevites. In addition, the suevites from outside of the crater contain significantly more melt particles (18-37 vol%) than the within-crater suevites (<5 vol%). Melt fragment sizes in suevites from outside the crater are much larger than those from suevites within the crater (maximum 40 cm versus 1 cm). The currently known distribution of impactites outside of the crater would be consistent with a low-angle impact from the east. We propose that the within-crater suevites and polymict lithic breccias were emplaced either via slumping off the crater walls or lateral movement of some melted and much displaced target rock within the crater. Limited admixture of fallback material from the ejecta plume is evident in the uppermost impactite deposit encountered in core LB-05B. In contrast, the out-of-crater suevites formed by fallout from a laterally differentiated ejecta plume, which resulted in different clast populations to the north and south of the crater. © 2010 The Geological Society of America. All rights reserved.
953.
Major ion chemistry of waters in Lake Qinghai catchments, NE Qinghai-Tibet plateau, China
Quaternary International,
212
(1)
35 – 43
2010
ISSN: 10406182Keywords:▾
China; Qinghai; Qinghai Lake; Qinghai-Xizang Plateau; catchment; chemical composition; crystallization; evaporation; groundwater; lake water; rainwater; river water; water chemistry
Abstract: ▾ Major ion concentrations were measured in lake water, river water, ground water, and rainfall water around the Lake Qinghai catchment. The dissolution of carbonate particles in dust has a strong impact on the chemical composition of rainfall as inferred from the Gibbs model and the ternary plots of the major ions. The chemical composition of the ground water can be divided into two groups, one influenced by river water and the other dominated by deeper aquifers. The chemical composition of lake water can be mainly ascribed to evaporation and crystallization. Total dissolved solid (TDS) of river waters during the wet periods is higher than during the dry periods. Calcium and bicarbonate are the dominant cations and anions of the river waters, and they have higher fractions during the wet periods than during the dry periods. Comparisons between (Mg2+ + Ca2+)/TZ+, (Mg2+ + Ca2+)/(Na+ + K+), HCO3-/Na+, and Cl-/Na+ suggest that the chemical composition of the river waters is mainly controlled by carbonate weathering and that the carbonate weathering is much stronger during the wet periods than during the dry periods. Seasonal melting may be one of the important factors that influence the seasonal variations of water chemistry of the rivers. © 2008 Elsevier Ltd and INQUA.
952.
Low energy deposition in the Chicxulub crater during the impact to post-impact transition
Earth and Planetary Science Letters,
295
(1-2)
170-176
2010
Abstract: ▾ The crater fill units that were deposited during the terminal stages of the formation of the shallow marine Chicxulub crater in northern Yucatan were interpreted by some authors as products of a catastrophic resurge of water. This interpretation contrasts markedly with the dominant sand grain size <300μm and the abundant small-scale current cross bedding structures indicative of low energy deposition. To solve this discrepancy we applied first principles of physical sedimentology in an analysis of grain size and sedimentary structures to determine current velocities and minimum water depths required to generate the observed sedimentary bedforms. We combine this approach with numerical modeling of crater formation in order to explore the dimensions of the ejecta ring wall being formed by a Chicxulub impactor in water depths of 1000m. We find that the ejecta wall reaches heights in the order of 1200m above sea floor and 200m above sea level. It thus prevented the resurge of water into the crater cavity and consequently also the subsequent formation of a collapse wave. The ring wall significantly retarded the refilling of the crater cavity with seawater, and refilling took place by permeation through and localized erosion of the ring wall. This resulted in low-energy currents with velocities between 1.5 and 0.18ms-1 slowly reentering the crater and depositing the cm-scale, low energy laminated and crossbedded sandy terminal impact deposits. © 2010 Elsevier B.V.
951.
Lipid biomarkers in Holocene and glacial sediments from ancient Lake Ohrid (Macedonia, Albania)
Biogeosciences,
7
(11)
3473 – 3489
2010
ISSN: 17264189Keywords:▾
Lake Ohrid; Animalia; Capra hircus; Ciliophora; Ovis aries; Photobacteria; Suidae; anoxic conditions; aquatic environment; bacterium; biodegradation; biomarker; climate change; glacial deposit; Holocene; hydrology; lacustrine deposit; lipid; organic acid; organic matter; paleoenvironment; primary production; river discharge; soil erosion; soil organic matter; terrestrial environment; vegetation cover
Abstract: ▾ Organic matter preserved in Lake Ohrid sediments originates from aquatic and terrestrial sources. Its variable composition reflects climate-controlled changes in the lake basin's hydrology and related organic matter export, i.e. changes in primary productivity, terrestrial plant matter input and soil erosion. Here, we present first results from lipid biomarker investigations of Lake Ohrid sediments from two near-shore settings: site Lz1120 near the southern shore, with low-lying lands nearby and probably influenced by river discharge, and site Co1202 which is close to the steep eastern slopes. Variable proportions of terrestrial n-alkanoic acids and n-alkanols as well as compositional changes of ‰-hydroxy acids document differences in soil organic matter supply between the sites and during different climate stages (glacial, Holocene, 8.2 ka cooling event). Changes in the vegetation cover are suggested by changes in the dominant chain length of terrestrial n-alkanols. Effective microbial degradation of labile organic matter and in situ contribution of organic matter derived from the microbes themselves are both evident in the sediments. We found evidence for anoxic conditions within the photic zone by detecting epicholestanol and tetrahymanol from sulphur-oxidising phototrophic bacteria and bacterivorous ciliates and for the influence of a settled human community from the occurrence of coprostanol, a biomarker for human and animal faeces (pigs, sheep, goats), in an early Holocene sample. This study illustrates the potential of lipid biomarkers for future environmental reconstructions using one of Europe's oldest continental climate archives, Lake Ohrid. © Author(s) 2010.
950.
Late Quaternary palaeoenvironmental reconstruction from Lakes Ohrid and Prespa (Macedonia/Albania border) using stable isotopes
Biogeosciences,
7
(10)
3109 – 3122
2010
ISSN: 17264189Keywords:▾
Lake Mikri Prespa; Lake Ohrid; aridification; calcite; catchment; core analysis; geological record; Holocene; human activity; humidity; Mediterranean environment; paleoclimate; paleoenvironment; reconstruction; sediment core; stable isotope; total organic carbon; water level
Abstract: ▾ Here we present stable isotope data from three sediment records from lakes that lie along the Macedonian-Albanian border (Lake Prespa: 1 core, and Lake Ohrid: 2 cores). The records only overlap for the last 40 kyr, although the longest record contains the MIS 5/6 transition (Lake Ohrid). The sedimentary characteristics of both lakes differ significantly between the glacial and interglacial phases. At the end of MIS 6 Lake Ohrid's water level was low (high δ18Ocalcite) and, although productivity was increasing (high calcite content), the carbon supply was mainly from inorganic catchment rock sources (high δ13Ccarb). During the last interglacial, calcite and TOC production and preservation increased, progressively lower δ18Ocalcite suggest increase in humidity and lake levels until around 115 ka. During ca. 80 ka to 11 ka the lake records suggest cold conditions as indicated by negligible calcite precipitation and low organic matter content. In Lake Ohrid, δ13Corg are complacent; in contrast, Lake Prespa shows consistently higher δ13Corg suggesting a low oxidation of 13C-depleted organic matter in agreement with a general deterioration of climate conditions during the glacial. From 15 ka to the onset of the Holocene, calcite and TOC begin to increase, suggesting lake levels were probably low (high δ18Ocalcite). In the Holocene (11 ka to present) enhanced productivity is manifested by high calcite and organic matter content. All three cores show an early Holocene characterised by low δ18Ocalcite, apart from the very early Holocene phase in Prespa where the lowest δ18Ocalcite occurs at ca. 7.5 ka, suggesting a phase of higher lake level only in (the more sensitive) Lake Prespa. From 6 ka, δ18Ocalcite suggest progressive aridification, in agreement with many other records in the Mediterranean, although the uppermost sediments in one core records low δ18Ocalcite which we interpret as a result of human activity. Overall, the isotope data present here confirm that these two big lakes have captured the large scale, low frequency palaeoclimate variation that is seen in Mediterranean lakes, although in detail there is much palaeoclimate information that could be gained, especially small scale, high frequency differences between this region and the Mediterranean. © 2010 Author(s).
949.
Late Quaternary palaeoenvironment of northern Guatemala: Evidence from deep drill cores and seismic stratigraphy of Lake Petén Itzá
Sedimentology,
57
(5)
1220 – 1245
2010
ISSN: 13653091Keywords:▾
Guatemala [Central America]; Lake Peten Itza; Peten; Gastropoda; Anoxic sediments; Carbonation; Climatology; Core drilling; Deepwater drilling; Drills; Gypsum; Lakes; Lithology; Offshore oil wells; Sedimentology; Seismic waves; Seismology; Guatemala; Lake level changes; Lake sediments; Palaeoclimatology; Seismic stratigraphy; climate conditions; deep drilling; deposition; environmental change; Heinrich event; lacustrine deposit; lake level; lithostratigraphy; paleoclimate; paleoenvironment; Quaternary; sediment core; sedimentation; seismic reflection; seismic stratigraphy; Stratigraphy
Abstract: ▾ Long sediment cores were collected in spring 2006 from Lake Petén Itzá, northern Guatemala, in water depths ranging from 30 to 150 m, as part of an International Continental Scientific Drilling Program project. The sediment records from deep water consist mainly of alternating clay, gypsum and carbonate units and, in at least two drill sites, extend back >200 kyr. Most of the lithostratigraphic units are traceable throughout the basin along seismic reflections that serve as seismic stratigraphic boundaries and suggest that the lithostratigraphy can be used to infer regional palaeoenvironmental changes. A revised seismic stratigraphy was established on the basis of integrated lithological and seismic reflection data from the basin. From ca 200 to ca 85 ka, sediments are dominated by carbonate-clay silt, often interbedded with sandy turbidites, indicating a sediment regime dominated by detrital sedimentation in a relatively humid climate. At ca 85 ka, an exposure horizon consisting of gravels, coarse sand and terrestrial gastropods marks a lake lowstand or partial basin desiccation, indicating dry climate conditions. From ca 85 to ca 48 ka, transgressive carbonate-clay sediments, overlain by deep-water clays, suggest a lake level rise and subsequent stabilization at high stage. From ca 48 ka to present, the lithology is characterized by alternating clay and gypsum units. Gypsum deposition correlates with Heinrich Events (i.e. dry climate), whereas clay units coincide with more humid interstadials. © 2010 The Authors. Journal compilation © 2010 International Association of Sedimentologists.
948.
Laboratory-based maximum slip rates in earthquake rupture zones and radiated energy
Bulletin of the Seismological Society of America,
100
(6)
3250-3260
2010
ISSN: 00371106Keywords:▾
California; Crustal earthquakes; Deep gold mines; Earthquake fault; Earthquake rupture; Ground-motion; Maximum slip; Pilot holes; Radiated energies; Repeating earthquake; Rupture process; Rupture zone; San Andreas Fault; Seismic moment; Slip rates; Space and time; Stick-slip friction; Stress parameter, Earthquakes; Experiments; Friction; Gold mines; Gravitational effects; Laboratories; Slip forming; Tectonics, Yield stress, earthquake magnitude; earthquake rupture; fault zone; ground motion; seismic moment; slip rate
Abstract: ▾ Laboratory stick-slip friction experiments indicate that peak slip rates increase with the stresses loading the fault to cause rupture. If this applies also to earthquake fault zones, then the analysis of rupture processes is simplified inasmuch as the slip rates depend only on the local yield stress and are independent of factors specific to a particular event, including the distribution of slip in space and time. We test this hypothesis by first using it to develop an expression for radiated energy that depends primarily on the seismic moment and the maximum slip rate. From laboratory results, the maximum slip rate for any crustal earthquake, as well as various stress parameters including the yield stress, can be determined based on its seismic moment and the maximum slip within its rupture zone. After finding that our new equation for radiated energy works well for laboratory stick-slip friction experiments, we used it to estimate radiated energies for five earthquakes with magnitudes near 2 that were induced in a deep gold mine, an M 2.1 repeating earthquake near the San Andreas Fault Observatory at Depth (SAFOD) site and seven major earthquakes in California and found good agreement with energies estimated independently from spectra of local and regional ground-motion data. Estimates of yield stress for the earthquakes in our study range from 12 MPa to 122 MPa with a median of 64 MPa. The lowest value was estimated for the 2004 M 6 Parkfield, California, earthquake whereas the nearby M 2.1 repeating earthquake, as recorded in the SAFOD pilot hole, showed a more typical yield stress of 64 MPa.
947.
Introduction: Impact cratering and planetary studies - A fifty-year perspective
Special Paper of the Geological Society of America,
465vii-xii
2010
ISSN: 00721077Keywords:▾
cratering; impact structure; literature review; planetary evolution
946.
Integrating borehole-breakout dimensions, strength criteria, and leak-off test results, to constrain the state of stress across the Chelungpu Fault, Taiwan
Tectonophysics,
482
(1-4)
65-72
2010
ISSN: 00401951Keywords:▾
Borehole wall; ChiChi earthquake; Density log; Estimated state; Horizontal stress; Insitu stress; Leak-off tests; Limit equilibrium; Principal stress; Shut-in pressure; Slip zones; State of stress; Strength criteria; Thrust faulting; True triaxial strength; True triaxial strength criteria; Vertical stress, Asphalt pavements; Blowouts; Electromagnetic logging; Fracture; Instruments; Maximum likelihood estimation; Radioactivity logging; Stress measurement, Boreholes, borehole breakout; fault zone; in situ stress; integrated approach; pressure effect; stress analysis; strike-slip fault; thrust fault; triaxial test; well logging, Chelungpu Fault Zone; Taiwan
Abstract: ▾ The paper describes the computation of the maximum horizontal stress (σH) magnitude in the vicinity of the Chelungpu Fault, Taiwan, host of the slip zone during the Chi-Chi earthquake (Mw 7.6; 1999). The scientific hole B intercepts the Chelungpu Fault at 1136 m. At the depths of logged breakouts (940-1310 m), the vertical stress (σv) as estimated from density logs increases linearly with depth from 22 to 31 MPa. A series of leak-off tests yielded two reliable shut-in pressures, 23.7 MPa at 1085 m and 29.8 MPa at 1279 m, which are lower than the estimated σv, albeit by only 2.1 and 0.6 MPa, respectively. In our analysis the shut-in pressures were considered to represent estimates of the least horizontal principal stresses (σh) at the respective depths, and consequently the test-induced fractures were assumed to have been vertical. Principal stress directions had been previously determined by others (105°-155° for the maximum horizontal stress, σH, except in the immediate vicinity of the Chelungpu Fault). The contribution of this paper is the estimation of the σH magnitude by considering that the state of stress at the points of intersection between breakout and borehole wall is in a state of limit equilibrium with the true triaxial strength criterion. The resulting σH in the range of logged breakouts increases with depth from 55 MPa at 940 m to 59 MPa at 1310 m. Thus, the estimated state of stress prevailing across the Chelungpu Fault is compatible with strike-slip, but marginally also with thrust faulting. However, the likelihood that the shut-in pressures actually represent σv magnitudes, and that the leak-off test-induced fractures were sub-horizontal, cannot be ignored. In that case the state of stress would clearly favor thrust faulting. © 2009 Elsevier B.V. All rights reserved.
945.
Localized rotation of principal stress around faults and fractures determined from borehole breakouts in hole B of the Taiwan Chelungpu-fault Drilling Project (TCDP)
Tectonophysics,
482
(1-4)
82-91
2010
ISSN: 00401951Keywords:▾
Borehole wall; Downholes; Drilling projects; Drilling-induced tensile fractures; Electrical images; Fracture stress; Geological structures; Horizontal stress; Mesoscale; Principal stress; Stress distribution; Stress fluctuations; Stress orientations; Stress perturbations; Stress state; Stress-induced, Drilling; Fracture; Photography; Rotation; Stress concentration, Boreholes, borehole breakout; core analysis; drilling; electrical method; fault; fracture; image analysis; spatial variation; stress analysis; stress field; tensile stress, Chelungpu Fault Zone; Taiwan
Abstract: ▾ To reveal details of stress perturbations associated with faults and fractures, we investigated the faults and large fractures accompanied by stress-induced borehole breakouts or drilling-induced tensile fractures in hole B of the Taiwan Chelungpu-fault Drilling Project (TCDP). Then, we determined the relationship between the faults and fractures and stress orientation changes. We identified faults and fractures from electrical images of the borehole wall obtained by downhole logging but also from photographs and descriptions of retrieved core samples, and measured the variations in the principal horizontal stress orientation ascertained from borehole breakouts observed on the electrical images in the vicinity of the faults and fractures. Identification of geological structures (faults, fractures, and lithologic boundaries) by electrical images only is difficult and may sometimes yield incorrect results. In a novel approach, therefore, we used both the electrical images and core photographs to identify geological structures. We found four patterns of stress orientation change, or no change, in the vicinity of faults and fractures in TCDP hole B: (i) abrupt (discontinuous) rotation in the vicinity of faults or fractures; (ii) gradual rotation; (iii) suppression of breakouts at faults, fractures, or lithologic boundaries; and (iv) no change in the stress orientation. We recognized stress fluctuations, that is, heterogeneous mesoscale (≥ 10 cm) stress distributions with respect to both stress orientation and magnitude. In addition, we found that stress state changes occurred frequently in the vicinity of faults, fractures, and lithologic boundaries. © 2009 Elsevier B.V. All rights reserved.