All ICDP Publications with Abstracts
From parent-sysfolder "Publications" + 2 folder-levels deep
1494.
Ries crater and suevite revisited-Observations and modeling Part I: Observations
Meteoritics and Planetary Science,
48
(4)
515-589
2013
Abstract: ▾ We report results of an interdisciplinary project devoted to the 26 km-diameter Ries crater and to the genesis of suevite. Recent laboratory analyses of "crater suevite" occurring within the central crater basin and of "outer suevite" on top of the continuous ejecta blanket, as well as data accumulated during the past 50 years, are interpreted within the boundary conditions imposed by a comprehensive new effort to model the crater formation and its ejecta deposits by computer code calculations (Artemieva et al. 2013). The properties of suevite are considered on all scales from megascopic to submicroscopic in the context of its geological setting. In a new approach, we reconstruct the minimum/maximum volumes of all allochthonous impact formations (108/116 km3), of suevite (14/22 km3), and the total volume of impact melt (4.9/8.0 km3) produced by the Ries impact event prior to erosion. These volumes are reasonably compatible with corresponding values obtained by numerical modeling. Taking all data on modal composition, texture, chemistry, and shock metamorphism of suevite, and the results of modeling into account, we arrive at a new empirical model implying five main consecutive phases of crater formation and ejecta emplacement. Numerical modeling indicates that only a very small fraction of suevite can be derived from the "primary ejecta plume," which is possibly represented by the fine-grained basal layer of outer suevite. The main mass of suevite was deposited from a "secondary plume" induced by an explosive reaction ("fuel-coolant interaction") of impact melt with water and volatile-rich sedimentary rocks within a clast-laden temporary melt pool. Both melt pool and plume appear to be heterogeneous in space and time. Outer suevite appears to be derived from an early formed, melt-rich and clast-poor plume region rich in strongly shocked components (melt ≫ clasts) and originating from an upper, more marginal zone of the melt pool. Crater suevite is obviously deposited from later formed, clast-rich and melt-poor plumes dominated by unshocked and weakly shocked clasts and derived from a deeper, central zone of the melt pool. Genetically, we distinguish between "primary suevite" which includes dike suevite, the lower sublayer of crater suevite, and possibly a basal layer of outer suevite, and "secondary suevite" represented by the massive upper sublayer of crater suevite and the main mass of outer suevite. © The Meteoritical Society, 2013.
1493.
Ries crater and suevite revisited-Observations and modeling Part II: Modeling
Meteoritics and Planetary Science,
48
(4)
590-627
2013
Abstract: ▾ We present the results of numerical modeling of the formation of the Ries crater utilizing the two hydrocodes SOVA and iSALE. These standard models allow us to reproduce crater shape, size, and morphology, and composition and extension of the continuous ejecta blanket. Some of these results cannot, however, be readily reconciled with observations: the impact plume above the crater consists mainly of molten and vaporized sedimentary rocks, containing very little material in comparison with the ejecta curtain; at the end of the modification stage, the crater floor is covered by a thick layer of impact melt with a total volume of 6-11 km3; the thickness of true fallback material from the plume inside the crater does not exceed a couple of meters; ejecta from all stratigraphic units of the target are transported ballistically; no separation of sedimentary and crystalline rocks-as observed between suevites and Bunte Breccia at Ries-is noted. We also present numerical results quantifying the existing geological hypotheses of Ries ejecta emplacement from an impact plume, by melt flow, or by a pyroclastic density current. The results show that none of these mechanisms is consistent with physical constraints and/or observations. Finally, we suggest a new hypothesis of suevite formation and emplacement by postimpact interaction of hot impact melt with water or volatile-rich sedimentary rocks. © The Meteoritical Society, 2013.
1492.
Rock magnetic properties, magnetic susceptibility, and organic geochemistry comparison in core LZ1029-7 Lake El'gygytgyn, Russia Far East
Climate of the Past,
9
(1)
467-479
2013
1491.
Rock varnish evidence for a Younger Dryas wet period in the Dead Sea basin
Geophysical Research Letters,
40
(10)
2229-2235
2013
ISSN: 00948276Keywords:▾
Dead sea; Dead sea basins; Mean sea level; North Atlantic; Rock varnishes; Surface layers; wet event; Younger Dryas, Lakes; Manganese; Sea level; Varnish, Climate change, belt; depositional environment; glacial environment; Holocene; meridional circulation; shoreline; surface layer, Dead Sea
Abstract: ▾ Rock varnish from 14.6 to 13.2 ka recessional shorelines of late glacial Lake Lisan and fan delta surfaces between 280 and 365 m bmsl (meters below mean sea level) along the western margins of the Dead Sea contains replicable layering patterns, characterized by a low Mn and Ba orange/yellow surface layer and a high Mn and Ba dark basal layer. The deposition of the dark basal layers immediately after the lake recession represents a wet period coinciding with the Younger Dryas (YD) cooling (12.9-11.6 ka), manifesting the influence of midlatitude westerly winds in the eastern Mediterranean-central Levant (EM-CL). In contrast, varnish from the distal base of fan deltas contains only orange/yellow surface layers, diagnostic of the Holocene relatively dry climate. The absence of the dark basal layers in the varnish further indicates a YD high stand at ∼365 m bmsl and a lake level rise of at least 100 m from its Bølling-Ållerød lowstand. This rise stands in contrast to the abrupt drop of the lake level during the Heinrich (H1) cold event, illustrating the opposite response of the EM-CL climate to changes in the North Atlantic climate. The YD wet event most likely reflects a southward shift of the Atlantic meridional overturning circulation-modulated midlatitude westerly wind belt in the EM-CL region. © 2013 American Geophysical Union. All Rights Reserved.
1490.
SAFOD Brittle Microstructure and Mechanics Knowledge Base (BM2KB)
Computers and Geosciences,
5683-91
2013
ISSN: 00983004Keywords:▾
Apache Tomcat server; High resolution image; Interactive web applications; OWL; RDF; SAFOD core; San Andreas fault; Semantic Web technology, Knowledge based systems; Microstructure; Query languages; Strike-slip faults; Unified Modeling Language, Core samples, brittle deformation; brittle medium; drilling; faulting; knowledge; microstructure; San Andreas Fault
Abstract: ▾ Scientific drilling near Parkfield, California has established the San Andreas Fault Observatory at Depth (SAFOD), which provides the solid earth community with short range geophysical and fault zone material data. The BM2KB ontology was developed in order to formalize the knowledge about brittle microstructures in the fault rocks sampled from the SAFOD cores. A knowledge base, instantiated from this domain ontology, stores and presents the observed microstructural and analytical data with respect to implications for brittle deformation and mechanics of faulting. These data can be searched on the knowledge base's Web interface by selecting a set of terms (classes, properties) from different drop-down lists that are dynamically populated from the ontology. In addition to this general search, a query can also be conducted to view data contributed by a specific investigator. A search by sample is done using the EarthScope SAFOD Core Viewer that allows a user to locate samples on high resolution images of core sections belonging to different runs and holes.The class hierarchy of the BM2KB ontology was initially designed using the Unified Modeling Language (UML), which was used as a visual guide to develop the ontology in OWL applying the Protégé ontology editor. Various Semantic Web technologies such as the RDF, RDFS, and OWL ontology languages, SPARQL query language, and Pellet reasoning engine, were used to develop the ontology. An interactive Web application interface was developed through Jena, a java based framework, with AJAX technology, jsp pages, and java servlets, and deployed via an Apache tomcat server. The interface allows the registered user to submit data related to their research on a sample of the SAFOD core. The submitted data, after initial review by the knowledge base administrator, are added to the extensible knowledge base and become available in subsequent queries to all types of users. The interface facilitates inference capabilities in the ontology, supports SPARQL queries, allows for modifications based on successive discoveries, and provides an accessible knowledge base on the Web. © 2013 Elsevier Ltd.
1489.
Petrology of impactites from El'gygytgyn crater: Breccias in ICDP-drill core 1C, glassy impact melt rocks and spherules
Meteoritics and Planetary Science,
48
(7)
1199-1235
2013
Abstract: ▾ El'gygytgyn is a 18km diameter, 3.6Ma old impact crater in NE Siberia. International Continental Scientific Drilling Program-El'gygytgyn hole 1C was drilled on the frozen crater lake, 2.3km from the crater center to a final depth of 517m below the lake floor. Petrographic and geochemical analyses of 26 drill core samples, three impact melt rocks from the surface, and seven glass spherules from surface deposits outside the crater are used to characterize the impactite inventory at El'gygytgyn. The bottom 98m of hole 1C intersected monomict brecciated, unshocked, rhyolitic ignimbrite with minor intercalations of polymict breccia and mafic inclusions. These lithologies are overlain by 89m of polymict breccia whose components occasionally exhibit scarce, low-degree shock metamorphic features. This unit is succeeded by 10m of suevite that contains about 1 vol% glassy impact melt shards <1cm in size and a low amount of shock metamorphosed lithic clasts. The suevite is capped by a reworked fallout deposit that constitutes a transition over 4m into lacustrine sedimentation. A higher abundance of shock metamorphosed lithic clasts, and glass spherules, some with Ni-rich spinel and admixture of an ultramafic component, characterize this unit. We tentatively interpret this impactite section as allochthonous breccia in the vicinity of El'gygytgyn's central ring uplift. The geochemical compositions of seven glass spherules from terrace deposits 2km outside the crater and eight spherules from the reworked fallout deposit in hole 1C show far greater variability than the composition of impact melt shards and impact melt rocks. Some of these spherules also show strong enrichments in siderophile elements. © The Meteoritical Society, 2013.
1488.
Scientific drilling and related research in the Samail ophiolite, Sultanate of Oman
Scientific Drilling,
1564--71
2013
1487.
Petrology, major and trace element geochemistry, geochronology, and isotopic composition of granitic intrusions from the vicinity of the Bosumtwi impact crater, Ghana
Lithos,
177297 – 313
2013
ISSN: 00244937Keywords:▾
Ghana; geochronology; granite; granitoid; igneous geochemistry; igneous intrusion; impact structure; isotopic composition; magmatism; petrogenesis; petrology; Proterozoic; trace element
Abstract: ▾ The Bosumtwi crater is 10.5. km in diameter, 1.07. Ma old, well preserved impact structure located in Ghana (centered at 06°30'N, 01°25'W). It was excavated in rocks of the Early Proterozoic Birimian Supergroup, part of the West African craton. Here, we present a full and detailed characterization of the three granitoid complexes and one mafic dike in the vicinity of the Bosumtwi crater in terms of petrology, major and trace element geochemistry, geochronology, and isotopic composition. This allows us to characterize magmatic evolution of the West African Craton in this area and better understand the geological framework and target rocks of the impact.This study shows that the similar composition (strongly peraluminous muscovite granites and granodiorites) and age (between 2092. ±. 6. Ma and 2098. ±. 6. Ma) of all granitic intrusions in the proximity of the Bosumtwi crater suggest that they are co-genetic. Granitoids were probably formed as a result of anatexis of TTGs (or rocks derived from them) at relatively low pressure and temperature. We propose that the intrusions from the Bosumtwi area are genetically related to the Banso granite occurring to the east of the crater and can be classified as basin-type, late-stage granitoids. Also a mafic dike located to the NE of the Bosumtwi crater seems to be genetically related to those felsic intrusions. Based on those findings a revised version of the geological map of the Bosumtwi crater area is proposed. © 2013.
1486.
New research results of the ries suevite [Neue forschungsergebnisse am riessuevit]
Zeitschrift der Deutschen Gesellschaft fur Geowissenschaften,
164
(3)
417-432
2013
Abstract: ▾ The processes of formation and transport of particles in suevite during impact crater formation remain poorly understood. This paper gives a summary of the investigations at the 14.6 Ma old, 25 km wide Nördlinger Ries Crater in Southern Germany, performed during the last years. The suevite of the Ries Crater occurs in three different geological settings: (1) crater suevite in the central crater cavity inside the inner ring, (2) outer suevite on top of the continuous ejecta blanket, and (3) dikes in the crater basement and in displaced megablocks. For suevite genesis, the following processes have been discussed to-date in literature: (1) fall-back of material into the crater and its periphery upon collapse of an ejecta plume, and (2) horizontal transport of ejected material, akin to (a) an impact melt flow, (b) a pyroclastic flow, or (c) initiated by phreatomagmatic explosion. On the basis of geophysical investigations, numerical models, 3D shape fabrics, modal composition, stereometric and geochemical characteristics fi ve stages will be distinguished for the formation and deposition of the Ries Suevite: (1) an early ejecta plume, (2) a phreatomagmatic explosion after a hiatus, (3) a basal, non-erosive pyroclastic surge, (4) a pyroclastic flow, (5) a second ejecta plume with accretionary lapilli. © 2013 E. Schweizerbart'sche Verlagsbuchhandlung, Stuttgart, Germany.
1485.
Petrology of impactites from El'gygytgyn crater: Breccias in ICDP-drill core 1C, glassy impact melt rocks and spherules
Meteoritics and Planetary Science,
48
(7)
1199-1235
2013
ISSN: 10869379Abstract: ▾ El'gygytgyn is a 18km diameter, 3.6Ma old impact crater in NE Siberia. International Continental Scientific Drilling Program-El'gygytgyn hole 1C was drilled on the frozen crater lake, 2.3km from the crater center to a final depth of 517m below the lake floor. Petrographic and geochemical analyses of 26 drill core samples, three impact melt rocks from the surface, and seven glass spherules from surface deposits outside the crater are used to characterize the impactite inventory at El'gygytgyn. The bottom 98m of hole 1C intersected monomict brecciated, unshocked, rhyolitic ignimbrite with minor intercalations of polymict breccia and mafic inclusions. These lithologies are overlain by 89m of polymict breccia whose components occasionally exhibit scarce, low-degree shock metamorphic features. This unit is succeeded by 10m of suevite that contains about 1 vol% glassy impact melt shards <1cm in size and a low amount of shock metamorphosed lithic clasts. The suevite is capped by a reworked fallout deposit that constitutes a transition over 4m into lacustrine sedimentation. A higher abundance of shock metamorphosed lithic clasts, and glass spherules, some with Ni-rich spinel and admixture of an ultramafic component, characterize this unit. We tentatively interpret this impactite section as allochthonous breccia in the vicinity of El'gygytgyn's central ring uplift. The geochemical compositions of seven glass spherules from terrace deposits 2km outside the crater and eight spherules from the reworked fallout deposit in hole 1C show far greater variability than the composition of impact melt shards and impact melt rocks. Some of these spherules also show strong enrichments in siderophile elements. © The Meteoritical Society, 2013.
1484.
Onset of intense permafrost conditions in Northern Eurasia at ~2.55 Ma seen in a cryogenic weathering record from Lake El'gygytgyn
Climate of the Past Discussions,
96255-6285
2013
1483.
Sedimentary evolution of Lake Van (Eastern Turkey) reconstructed from high-resolution seismic investigations
International Journal of Earth Sciences,
102
(2)
571-585
2013
ISSN: 14373254
Publisher: Springer Verlag
Keywords:▾
erosion; lacustrine deposit; lake level; sedimentary sequence; seismic reflection; tephra, Lake Van; Turkey
Abstract: ▾ This paper presents results of a multi-channel seismic reflection survey at Lake Van and provides constraints on the sedimentary evolution of the lake. The geophysical data of the lake confirm the existence of three physiographic provinces: a shelf, a slope, and a deep, relatively flat basin. The most prominent features identified on the shelf and slope are clinoforms, submerged channels, as well as closely spaced lake floor depressions, reflecting a highly variable lake-level history. The morphological depressions are interpreted as resulting from subaquatic erosion by channelized, sediment-laden currents into horizontally bedded fan sediments. Submerged channels on the eastern shelf are interpreted as meandering-slope channels, probably as a consequence of a lake-level fall that exposed the shelf area. Clinoforms on the Eastern fan may represent relict deltas formed during stationary or slightly rising lake-level intervals. Merging subsurface imaging interpretation with morphological studies of exposed sediments reveals lake-level fluctuations of several hundreds of meters during the past ca. ~550 ka. The lake has three prominent basins (Tatvan, Deveboynu, and the Northern basin) separated by basement ridges (e. g., the Northern ridge). The seismic units in the Tatvan and Northern basins are dominated by alternations of well-stratified and chaotic reflections, while the Deveboynu basin subsurface consists mainly of chaotic units. The chaotic seismic facies are interpreted as mass-flow deposits, probably triggered by earthquakes and/or rapid lake-level fluctuations. The moderate-to-high-amplitude, well-stratified facies seen in the deeper parts of the basins are interpreted as lacustrine deposits intercalated with tephra layers. The occurrence of a clinoform in the deepest part of the lake suggests a major flooding stage of Lake Van more than ~400 ka ago. Seismic profiles from the deepest part of the lake basin show remarkably uniform and continuous stratigraphic units without any major erosional feature following the flooding event, indicating that the lake was never completely dry afterward and therefore significantly older than previously suggested. © 2012 Springer-Verlag.
1482.
Modern sedimentation patterns in Lake El'gygytgyn, NE Russia, derived from surface sediment and inlet streams samples
Climate of the Past,
9
(1)
135-148
2013
1481.
Modern sedimentation patterns in Lake El’gygytgyn, NE Russia, derived from surface sediment and inlet streams samples
Climate of the Past,
9
(1)
135-148
2013
ISSN: 18149324
Publisher: Copernicus GmbH
Abstract: ▾ Lake El’gygytgyn/NE Russia holds a continuous 3.58 Ma sediment record, which is regarded as the most long-lasting climate archive of the terrestrial Arctic. Based on multi-proxy geochemical, mineralogical, and granulometric analyses of surface sediment, inlet stream and bedrock samples, supplemented by statistical methods, major processes influencing the modern sedimentation in the lake were investigated. Grain-size parameters and chemical elements linked to the input of feldspars from acidic bedrock indicate a wind-induced two-cell current system as major driver of sediment transport and accumulation processes in Lake El’gygytgyn. The distribution of mafic rock related elements in the sediment on the lake floor can be traced back to the input of weathering products of basaltic rocks in the catchment. Obvious similarities in the spatial variability of manganese and heavy metals indicate sorption or co-precipitation of these elements with Fe and Mn hydroxides and oxides. But the similar distribution of organic matter and clay contents might also point to a fixation to organic components and clay minerals. An enrichment of mercury in the inlet streams might be indicative of neotectonic activity around the lake. The results of this study add to the fundamental knowledge of the modern lake processes of Lake El’gygytgyn and its lake-catchment interactions, and thus, yield crucial insights for the interpretation of paleo-data from this unique archive. © Author(s) 2013.
1480.
Moho depth determination from waveforms of microearthquakes in the West Bohemia/Vogtland swarm area
Journal of Geophysical Research: Solid Earth,
118
(1)
120 – 137
2013
ISSN: 21699313
Publisher: Blackwell Publishing Ltd
Keywords:▾
Bohemia; Bohemian Massif; Czech Republic; Germany; Vogtland; crustal structure; focal mechanism; lower crust; microearthquake; modeling; Moho; P-wave; S-wave; seismicity; velocity structure; waveform analysis
Abstract: ▾ The West Bohemia/Vogtland area is known for its increased geodynamic activity with reoccurrence of intraplate earthquake swarms. Previous geophysical studies, namely active and passive seismic investigations, revealed a high velocity lower crust in this area with increased reflectivity. To refine this result and retrieve a more detailed structure of the deep crust and the Moho discontinuity, we analyzed waveforms of local microearthquakes that occurred in this area during the 2008 swarm. The waveforms of earthquakes were grouped into clusters with similar focal mechanisms, and the clusters were processed separately. We developed a new multiazimuthal approach in data processing to increase resolution of Moho phases in the waveforms. We applied the waveform cross-correlation of the P and S waves, and rotated, aligned, and stacked the seismograms to extract the Moho SmS, PmP, and PmS reflected/converted phases. These phases were inverted for laterally varying Moho depth by ray tracing and a grid search inversion algorithm. The model retrieved was verified using modeling of full waveforms computed by the discrete wave number method. The multiazimuthal approach reveals details in the velocity structure of the crust/mantle transition at each station. Instead of a single interface with a sharp velocity contrast, the inversion indicates a reflective zone at Moho depths with one or two strongly reflective interfaces, which is in agreement with the zone interpreted by previous investigations. The thickness of the zone varies from 2 to 4 km within the depth range of 27-31.5 km and is delimited by reflections from its top and bottom boundaries, sometimes with strong reflectors within the zone. The average Vp/Vs ratio determined from the Moho reflections and conversions is 1.73. Key Points Moho topography from waveforms of local microearthquakes New multi-azimuthal approach to reveal details of the crust/mantle transition Combined data processing, ray tracing, discrete wave-number and grid search ©2012. American Geophysical Union. All Rights Reserved.
1479.
Morphochemistry of patterns produced by mixing of rhyolitic and basaltic melts
Journal of Volcanology and Geothermal Research,
25387-96
2013
ISSN: 03770273Keywords:▾
Basaltic melts; Chaotic dynamics; Empirical relationships; High temperature; Linear relationships; Magma mixing; Mixing system; Mixing time; Morphological complexity; Relative mobility; Rhyolitic; Rhyolitic melts; Temporal variation; Time-series experiments, Chemical elements; Experiments; Fractal dimension; Fractals; Igneous rocks; Morphology; Petrography, Mixing, basalt; concentration (composition); element mobility; experimental study; high temperature; igneous geochemistry; magma chemistry; mixing ratio; morphometry; rhyolite; temporal variation; volcanology
Abstract: ▾ In this work we present the results of time series experiments performed by mixing basaltic and rhyolitic melts at high temperature using a device recently developed to trigger chaotic dynamics in a mixing system. The morphology of mixing patterns is quantified at different times by measuring their fractal dimension and a linear relationship is derived between mixing time and morphological complexity. The complexity of mixing patterns is also compared to the degree of homogenization of chemical elements during mixing and empirical relationships are established between the fractal dimension and the temporal variation of concentration variance of elements.New concepts and tools to study the magma mixing process unfold from the experimental results presented in this work. The first one is that the mixing patterns are fractals and they can be quantified by measuring their fractal dimension. This represents a further step in the quantification of the magma mixing process. The second outcome is that the relationship between the fractal dimension of the mixing patterns and mixing time is linear. This has important volcanological implications as the analyses of the morphology of mixing patterns in volcanic rocks can be complemented by experiments to build a new chronometer to estimate the mixing-to-eruption time. A further result from this work is the relationship between the fractal dimension of mixing patterns and concentration variance of chemical elements. This represents the first morphochemical study in igneous petrology bringing with it the potential to infer the relative mobility of chemical elements during the time progression of mixing by analyzing the morphology of mixing patterns in the rocks. © 2012.
1478.
Multivariate statistic and time series analyses of grain-size data in quaternary sediments of Lake El'gygytgyn, NE Russia
Climate of the Past,
9
(6)
2459-2470
2013
ISSN: 18149324Keywords:▾
breccia; eccentricity; grain size; lacustrine deposit; meteorite; multivariate analysis; obliquity; principal component analysis; Quaternary; research program; sediment property; teleconnection; time series analysis, Chukchi; Elgygytgyn Lake; Russian Federation
Abstract: ▾ Lake El'gygytgyn, located in the Far East Russian Arctic, was formed by a meteorite impact about 3.58 Ma ago. In 2009, the International Continental Scientific Drilling Program (ICDP) at Lake El'gygytgyn obtained a continuous sediment sequence of the lacustrine deposits and the upper part of the impact breccia. Here, we present grain-size data of the past 2.6 Ma. General downcore grain-size variations yield coarser sediments during warm periods and finer ones during cold periods. According to principal component analysis (PCA), the climate-dependent variations in grain-size distributions mainly occur in the coarse silt and very fine silt fraction. During interglacial periods, accumulation of coarser material in the lake center is caused by redistribution of clastic material by a wind-induced current pattern during the ice-free period. Sediment supply to the lake is triggered by the thickness of the active layer in the catchment and the availability of water as a transport medium. During glacial periods, sedimentation at Lake El'gygytgyn is hampered by the occurrence of a perennial ice cover, with sedimentation being restricted to seasonal moats and vertical conduits through the ice. Thus, the summer temperature predominantly triggers transport of coarse material into the lake center. Time series analysis that was carried out to gain insight into the frequency of the grain-size data showed variations predominately on 98.5, 40.6, and 22.9 kyr oscillations, which correspond to Milankovitch's eccentricity, obliquity and precession bands. Variations in the relative power of these three oscillation bands during the Quaternary suggest that sedimentation processes at Lake El'gygytgyn are dominated by environmental variations caused by global glacial-interglacial variations (eccentricity, obliquity), and local insolation forcing and/or latitudinal teleconnections (precession), respectively. ©Author(s) 2013.
1477.
Noise measurements at seismic array in the drilling site of Bagnolifutura, Campi Flegrei
Quaderni di Geofisica,
1
2013
ISSN: 15902595Abstract: ▾ In 2012 two seismic surveys were carried out in the area of Bagnolifutura (Campi Flegrei, Naples), with the aim of characterizing the properties of the seismic noise during the drilling activity performed in the framework of the Campi Flegrei Deep Drilling Project (CFDDP; https://sites.google.com/site/ cfddpproject/). During the first survey, which was conducted from 2 to 4 April, before the drilling, seven broadband threecomponent seismometers were installed in two different array configurations. The second survey started on November 26, in concomitance with the drilling operations and fluid injection, and ended on December 5, four days after the end of the drilling, when the maximum depth of 502 m was reached. During this period seven broadband and one short-period three-component sensors were installed. A preliminary spectral analysis was performed on samples of seismic noise; moreover the root mean square of the amplitude of the signals and the polarization parameters were calculated. The preliminary results show similar spectral and polarization features for the data of the two surveys, whereas the amplitude of the seismic noise collected during the second survey is greatly influenced by the bad meteorological conditions. As future development experimental site transfer functions from Nakamura's technique and surface wave dispersion from array techniques will be calculated to obtain the shallow crustal structure. The results corresponding to the different phases of the drilling activity will be compared, with the aim of establishing if significant variations of the medium properties have occurred during the experiment. Moreover the recorded signals will be deeply investigated in order to detect the eventual occurrence of microseismicity induced by fluid injection and to define its features. © 2013 INGV Istituto Nazionale di Geofisica e Vulcanologia.
1476.
Observations of the genus Diploneis from Lake Ohrid, Macedonia
Diatom Research,
28
(3)
237 – 262
2013
ISSN: 21598347Keywords:▾
Lake Ohrid; biodiversity; diatom; endemic species; endemism; fossil record; new species; sediment core; taxonomy
Abstract: ▾ Lake Ohrid is an important biodiversity hotspot, including diatom diversity and endemism. Numerous, putatively endemic diatom species have been described from the lake, alongside reports of relict taxa otherwise known only as fossils from European Neogene deposits. Diploneis Ehrenberg ex Cleve is considered to be one of the species-rich genera in Lake Ohrid. This study presents a detailed account of Diploneis in Lake Ohrid, providing additional information on some of the infrequently recorded taxa. In addition, sediment core samples from Lake Ohrid were used to provide an historical account of some of the more abundant taxa and to determine the morphological similarity between fossil (core samples) and extant populations. To this end, detailed light and scanning electron microscope observations were carried out to ascertain the identity and describe the morphological variation of Diploneis taxa. As a result, 15 Diploneis taxa from Lake Ohrid are reported with four potentially endemic species described as new: D. parabudayana, D. rotunda, D. pulchra and D. vetusa. Among the remaining taxa, two endemic species (D. heisingeriae Jurilj and D. tavcharii Jurilj) previously described from Lake Ohrid were observed, along with nine widespread species commonly reported throughout Europe and elsewhere. © 2013 The International Society for Diatom Research.
1475.
Observations on Hippodonta (Bacillariophyceae) in selected ancient lakes
Phytotaxa,
90
(1)
1 – 53
2013
ISSN: 11793163Abstract: ▾ This study provides an evaluation of the diversity and distribution of taxa belonging to the genus Hippodonta (Bacillariophyceae) in selected ancient lakes from different geographical regions of the world. The lakes considered are: Lakes Ohrid, Prespa and Dojran from Macedonia, Lake Tanganyika, Tanzania, Lake Turkana, Kenya and Lake Baikal, Russia. In total, there are 34 Hippodonta taxa. Of these, 21 are described as new, 20 species and one variety. The primary morphological features of each taxon are provided and formal descriptions are given for all new taxa. The distinctive characters distinguishing similar taxa are noted. The genus is most diverse in Lake Baikal with 13 taxa, of which four are described as new species (Hippodonta acuta, H. certa, H. communis and H. pulchra). Lake Tanganyika has six taxa, all of which are described as new (H. angustata, H. avittatiformis, H. cocquytiae, H. conspicua, H. crassa and H. radiata). Lake Turkana has only one taxon, also described as new (H. minuta). In the Macedonian old tectonic lakes, seven taxa were found in Lake Ohrid, with five described as new (H. abunda, H. humboldtiana, H. latelanceolata, H. naviculiformis and H. subrostrata), five taxa were found in Lake Prespa, all of which are described as new (H. affinis, H. costulatiformis var. densistriata, H. exigua, H. media and H. rostratoides), and three known taxa were found in Lake Dojran. © 2013 Magnolia Press.
1474.
Oral histories in meteoritics and planetary science-XXIII: Dieter Stöffler
Meteoritics and Planetary Science,
48
(9)
1733-1751
2013
Abstract: ▾ In this interview, Dieter Stöffler (Fig. 1) describes how his interest in meteorites and impact craters dates from his Ph.D. studies at the University of Tübingen when it was learned that the Ries crater was formed by impact. A paper by Dieter's advisor, Wolf von Engelhardt, also triggered an interest in meteorites. After graduation, Dieter helped to establish a laboratory for high pressure mineralogy and he examined rocks from the Ries crater, which led to the concept of progressive shock metamorphism. The group also worked on newly returned Apollo samples and guided astronauts over the crater. A year at the NASA Ames Research Center taught Dieter about experimental impact research with a light-gas gun. After a few more years at Tübingen, Dieter obtained a professorship at the University of Münster where he created the Institute of Planetology, got involved in planning space missions including comet sample return, and continued high pressure mineralogy in collaboration with colleagues in Freiburg. Through several decades of research, Dieter and colleagues have documented the effects of shock on all the major rock-forming minerals and devised widely accepted schemes for the classification of shocked rocks. After the unification of Germany, Dieter became Director of the Natural History Museum in Berlin, during which he made much progress rebuilding the laboratories and the collections. Dieter also helped to create a museum and research center in the Ries crater. He received the Barringer Award of the Meteoritical Society in 1994 and several prestigious awards in Germany. © 2013 The Meteoritical Society.
1473.
Petrography, geochemistry, and Hf-Nd isotope evolution of drill core samples and target rocks from the El'gygytgyn impact crater, NE Chukotka, Arctic Russia
Meteoritics and Planetary Science,
48
(7)
1160-1198
2013
ISSN: 10869379Abstract: ▾ El'gygytgyn in northeast Chukotka (Russia) is a 3.6 Ma, 18-km-diameter impact structure. The impact crater was recently drilled in the framework of a project sponsored by the International Continental Scientific Drilling Program (ICDP). Target rocks at the El'gygytgyn area are dominated by the felsic members of the Late Cretaceous Okhotsk-Chukotka Volcanic Belt (OCVB). Such a target lithology is unique among terrestrial impact craters, thereby providing the opportunity to study shock metamorphism in siliceous volcanic rocks. Here, we present a petrographic, geochemical, and isotopic study of the section of the drill core underneath the lacustrine sediments, extending from ∼316 m to 517 m below the lake bottom (blb). The drill core stratigraphy includes ∼80 m of suevite and a cross section through a volcanic suite, which consists of (1) a middle section (∼390-423 mblb) with dominant felsic tuffs and a few mafic members, and (2) a welded rhyolitic-dacitic ignimbrite (∼423-517 mblb). The melt fragments embedded in the suevite are interpreted as being impact-related by comparison with impact glasses from the crater and in opposition to the target rock, which does not include similar melts. A suevitic dyke crosscuts the lower section of the core at the depth 471.40 mblb. Evidence for shock metamorphism is concentrated in the upper 10 m of the drill core and almost limited to the suevitic breccia. The geochemical and isotope (Nd and Hf) composition of samples from the target and the drill core reveals relationships to the "Berlozhya magmatic assemblage" (BMA) arguing for similar source magmas. The primitive upper mantle (PUM)-normalized trace element plot of rocks investigated here confirms a subduction-related signature, as previously proposed for rocks from both OCVB and BMA. © The Meteoritical Society, 2013.
1472.
Origin and significance of diagenetic concretions in sediments of Laguna Potrok Aike, southern Argentina
Journal of Paleolimnology,
50
(3)
275 – 291
2013
Keywords:▾
Argentina; Laguna Potrok Aike; Santa Cruz [Argentina]; diagenesis; environmental conditions; late glacial; maar; metabolism; methane; microbial activity; paleoproductivity; paleosalinity; phosphorus; porewater; pyrite; scanning electron microscopy; sorption; vivianite; water column
Abstract: ▾ Authigenic minerals can form in the water column and sediments of lakes, either abiotically or mediated by biological activity. Such minerals have been used as paleosalinity and paleoproductivity indicators and reflect trophic state and early diagenetic conditions. They are also considered potential indicators of past and perhaps ongoing microbial activity within sediments. Authigenic concretions, including vivianite, were described in late glacial sediments of Laguna Potrok Aike, a maar lake in southernmost Argentina. Occurrence of iron phosphate implies specific phosphorus sorption behavior and a reducing environment, with methane present. Because organic matter content in these sediments was generally low during glacial times, there must have been alternative sources of phosphorus and biogenic methane. Identifying these sources can help define past trophic state of the lake and diagenetic processes in the sediments. We used scanning electron microscopy, phosphorus speciation in bulk sediment, pore water analyses, in situ ATP measurements, microbial cell counts, and measurements of methane content and its carbon isotope composition (δ13CCH4) to identify components of and processes in the sediment. The multiple approaches indicated that volcanic materials in the catchment are important suppliers of iron, sulfur and phosphorus. These elements influence primary productivity and play a role in microbial metabolism during early diagenesis. Authigenic processes led to the formation of pyrite framboids and revealed sulfate reduction. Anaerobic oxidation of methane and shifts in pore water ion concentration indicated microbial influence with depth. This study documents the presence of active microbes within the sediments and their relationship to changing environmental conditions. It also illustrates the substantial role played by microbes in the formation of Laguna Potrok Aike concretions. Thus, authigenic minerals can be used as biosignatures in these late Pleistocene maar sediments. © 2013 Springer Science+Business Media Dordrecht.
1471.
Origin of two Verwey transitions in different generations of magnetite from the Chesapeake Bay impact structure, USA
Journal of Geophysical Research: Solid Earth,
118
(10)
5195-5207
2013
ISSN: 21699313
Publisher: Blackwell Publishing Ltd
Keywords:▾
basement rock; breccia; crystalline rock; grain size; hysteresis; impact structure; low temperature; magnetite; oxidation; suevite; temperature gradient, Chesapeake Bay; United States
Abstract: ▾ 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.
1470.
Origin of two Verwey transitions in different generations of magnetite from the Chesapeake Bay impact structure, USA
Journal of Geophysical Research: Solid Earth,
118
(10)
5195-5207
2013
Abstract: ▾ 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.