Preliminary site report for the 2005 ICDP-USGS deep corehole in the Chesapeake Bay impact crater

First report for the ICDP-USGS 1.7-km-deep corehole drilled into the central part of the Chesapeake Bay impact crater during 2005

Dynamical Disorder in the Mesophase Ferroelectric HdabcoClO4: A Machine-Learned Force Field Study

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Palaeoenvironment of Eocene prodelta in Spitsbergen recorded by the trace fossil Phycosiphon incertum

Ichnological, sedimentological and geochemical analyses were conducted on the Eocene Frysjaodden Formation in order to interpret palaeoenvironment prodelta sediments in the Central Basin of Spitsbergen. Phycosiphon incertum is the exclusive ichnotaxon showing differences in size, distribution, abundance and density, and relation to laminated/bioturbated intervals. Large P. incertum mainly occur dispersed, isolated and randomly distributed throughout the weakly laminated/non-laminated intervals. Small P. incertum occur occasionally in patches of several burrows within laminated intervals or as densely packed burrows in thin horizons in laminated intervals or constituting fully bioturbated intervals that are several centimetres thick. Ichnological changes are mainly controlled by oxygenation, although the availability of benthic food cannot be discarded. Changes in oxygenation and rate of sedimentation can be correlated with the registered variations in the Bouma sequence of the distal turbiditic beds within prodeltal shelf sediments.Funding for this research was provided by Project CGL2012-33281 (Secretaría de Estado de Investigación, Desarrollo e Innovación, Spain), Project RYC-2009-04316 (Ramón y Cajal Programme) and Projects RNM-3715 and RNM-7408 and Research Group RNM-178 (Junta de Andalucía). The authors benefited from a bilateral agreement between the universities of Granada and Oslo, supported by the University of Granada

Geochemical compositions and depositional conditions of Upper Jurassic and Lower Cretaceous Yorkshire clays, England

AbstractFifty-three samples from the Oxford, Kimmeridge and Speeton Clays of the Yorkshire area have been analysed petrographically and geochemically, by X-ray diffraction, X-ray fluorescence, atomic absorption and combustion (TOC). Major elements and the following trace elements have been determined: Rb, Sr, Ba, Cr, V, Co, Ni, Cu, Zn and Mo. P2O5, Rb, Ba, Cr and V show positive correlation to the clastic fraction (quartz, feldspar and clay minerals). CaO, MnO, and Sr and to a lesser extent Ni, Cu and Zn seem to be positively correlated to calcite, while Fe2O5, MnO, MgO and Co are linked to siderite. Stratigraphical variations of element/element ratios have been used to obtain sedimentological information from the petrographical and geochemical data.The Oxford Clay, with its coarse and immature clays, was deposited in a regressive development. An upwards shallowing with ventilated deposition of more mature and altered clastic material took place throughout the unit. During deposition of the Kimmeridge Clay more reducing conditions existed and finer grained, smectite-rich sediments were formed. The fine grained Speeton Clay was deposited during changing depositional conditions, varying ventilation in a generally regressive development. Several sedimentological breaks characterize the unit.</jats:p

Ejecta formation and crater development of the Mjølnir impact

Crater-ejecta correlation is an important element in the analysis of crater formation and its influence on the geological evolution. In this study, both the ejecta distribution and the internal crater development of the Jurassic/Cretaceous Mjølnir crater (40 km in diameter; located in the Barents Sea) are investigated through numerical simulations. The simulations show a highly asymmetrical ejecta distribution, and underscore the importance of a layer of surface water in ejecta distribution. As expected, the ejecta asymmetry increases as the angle of impact decreases. The simulation also displays an uneven aerial distribution of ejecta. The generation of the central high is a crucial part of crater formation. In this study, peak generation is shown to have a skewed development, from approximately 50-90 sec after impact, when the peak reaches its maximum height of 1-1.5 km. During this stage, the peak crest is moved about 5 km from an uprange to a downrange position, ending with a final central position which has a symmetrical appearance that contrasts with its asymmetrical development.The Meteoritics & Planetary Science archives are made available by the Meteoritical Society and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202

Direct dating of authigenic K-feldspar overgrowths from the Kilombero Rift of Tanzania

K-feldspars form important detrital and authigenic components in sediments but may be difficult to separate by conventional means for isotope analysis, particularly geochronology. UV lasers are being increasing applied to in situ analysis since they are strongly absorbed by clear minerals such as K-feldspar, and can achieve a spatial resolution of better than 20 mum for individual Ar/Ar analyses. Here we demonstrate separation of detrital K-feldspar with a mean age of 423 +/- 14 Ma and authigenic overgrowths with a mean age of 138 +/- 5 Ma in elastic sediments from the Msolwa Group of the Kilombero Rift of Tanzania. The young age obtained for authigenic K-feldspar overgrowth demonstrates that precipitation occurred more than 160 Ma after sedimentation, during the period of deepest burial and synchronous with the initial extensional phases of the intracontinental Anza and Sudan rifts, as well as the initial stages in the break-up and separation of South America and Africa

Early Tertiary bentonites from Svalbard

SummaryPaleontological and petrological studies of clay beds in the Basilika Formation (Tertiary age) are presented. The petrology of the beds indicates that their main constituents were derived from volcanic activity and represent bentonites. Differing composition between beds suggests several spatially separated eruptions. The volcanic source area probably lay towards the N of the present Tertiary outcrops of Svalbard. Two foraminiferal assemblages are found in the bentonites: the lower is dominated by arenaceous forms while the upper consists of calcareous species.</jats:p