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Berengere Mougel Frederic Moynier Christian Koeberl Daniel Wielandt Martin Bizzarro 《Meteoritics & planetary science》2019,54(10):2592-2599
The existence of mass‐independent chromium isotope variability of nucleosynthetic origin in meteorites and their components provides a means to investigate potential genetic relationship between meteorites and planetary bodies. Moreover, chromium abundances are depleted in most surficial terrestrial rocks relative to chondrites such that Cr isotopes are a powerful tool to detect the contribution of various types of extra‐terrestrial material in terrestrial impactites. This approach can thus be used to constrain the nature of the bolide resulting in breccia and melt rocks in terrestrial impact structures. Here, we report the Cr isotope composition of impact rocks from the ~0.57 Ma Lonar crater (India), which is the best‐preserved impact structure excavated in basaltic target rocks. Results confirm the presence of a chondritic component in several bulk rock samples of up to 3%. The impactor that created the Lonar crater had a composition that was most likely similar to that of carbonaceous chondrites, possibly a CM‐type chondrite. 相似文献
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The study area, “La Grande Vasière” (LGV), stretches out on the French Atlantic continental shelf (at ca. 100 m water depth), along 250 km from the Glénan Islands at the north to the southwest of Rochebonne at the south. Box-cores were sampled in this mid-shelf area during four cruises in June 1995, and in April, June and September 2002. They were investigated using sedimentological approaches (X-radiographs and grain-size analyses) and radionuclide studies (210Pb geochronology and excess 234Th). The main results are: (1) the surficial sediments are generally organized into a decimetre-scale fining up sequence which can be the result of extreme storms; (2) an upper mixing layer of 7–20 cm reflects an important biological benthic activity and/or the impact of fishing (i.e. trawlers); (3) a thin (i.e. a few mm) surficial mud-rich layer is the result of the present-day sedimentation; (4) an apparent annual sedimentation rate of 1–3 mm is recorded in several loci of the study area. Some seasonal variations appear, corresponding to the deposition of fine material from April to September, and to the reworking and the re-suspension during the winter. This fine material is the result of the decantation of estuarine plumes, mainly the Loire and the Vilaine rivers, over the study area. LGV lies (1) under the influence of a winter-to-spring thermo-haline wedge that acts as a filter for the transfer of fine river-borne material to the slope and the open sea, and (2) below water depths where the mean swell action permits sedimentation, mainly in summer. 相似文献
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Michael F. Sterzik Gregor E. Morfill Berengere Dubrulle 《Astrophysics and Space Science》1995,224(1-2):567-568
We apply our analytic model for the dust diffusivity to calculate the vertical structure of the dust sub-disk in a turbulent protoplanetary nebula. We present a numerical solution of a vertical dust settling equationand a coagulation equation for dust grains covering four orders of magnitude in time and grain size. 相似文献
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Gwénaëlle Chaillou Pierre Anschutz Carole Dubrulle Pascal Lecroart 《Aquatic Geochemistry》2007,13(2):157-172
Biogeochemical processes induced by the deposition of gravity layer in marine sediment were studied in a 295-day experiment.
Combining voltammetric microelectrode measurements and conventional analytical techniques, the concentrations of C, O2, N-species, Mn and Fe have been determined in porewaters and sediments of experimental units. Dynamics of the major diagenetic
species following the sudden sediment deposition of few cm-thick layer was explained by alternative diagenetic pathways whose
relative importance in marine sediments is still a matter of debate. Time-series results indicated that the diffusion of O2 from overlying waters to sediments was efficient after the deposition event: anoxic conditions prevailed during the sedimentation.
After a few days, a permanent oxic horizon was formed in the top few millimetres. At the same time, the oxidation of Mn2+ and then Fe2+, which diffused from anoxic sediments, contributed to the surficial enrichment of fresh Mn(III/IV)- and Fe(III)-oxides. Vertical
diffusive fluxes and mass balance calculations indicated that a steady-state model described the dynamic of Mn despite the
transitory nature of the system. This model was not adequate to describe Fe dynamics because of the multiple sources and phases
of Fe2+. No significant transfer of Mn and Fe was observed between the underlying sediment and the new deposit: Mn- and Fe-oxides
buried at the original interface acted as an oxidative barrier to reduced species that diffused from below. Nitrification
processes led to the formation of a NO3−/NO2− rich horizon at the new oxic horizon. Over the experiment period, NO3− concentrations were also measured in the anoxic sediment suggesting anaerobic nitrate production. 相似文献
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