¹Erwin Dehouck,¹Scott M. McLennan,²Pierre-Yves Meslin,³Agnès Cousin
¹Department of Geosciences, State University of New York at Stony Brook, Stony Brook, NY, USA
²Institut de Recherche en Astrophysique et Planétologie, CNRS/Université Paul Sabatier, Toulouse, France
³Los Alamos National Laboratory, Los Alamos, NM, USA

X-ray diffraction patterns of the three samples analyzed by Curiosity’s CheMin instrument during the first year of the Mars Science Laboratory mission – the Rocknest sand; and the John Klein and Cumberland drill fines, both extracted from the Sheepbed mudstone – show evidence for a significant amorphous component of unclear origin. We developed a mass balance calculation program that determines the range of possible chemical compositions of the crystalline and amorphous components of these samples within the uncertainties of mineral abundances derived from CheMin data. In turn, the chemistry constrains the minimum abundance of amorphous component required to have realistic compositions (all oxides ≥0 wt%): 21—22 wt% for Rocknest and 15—20 wt% for Cumberland, in good agreement with estimates derived from the diffraction patterns (~27 and ~31 wt%, respectively). Despite obvious differences between the Rocknest sand and the Sheepbed mudstone, the amorphous components of the two sites are chemically very similar, having comparable concentrations of SiO2, TiO2, Al2O3, Cr2O3, FeOT, CaO, Na2O, K2O and P2O5. MgO tends to be lower in Rocknest, although it may also be comparable between the two samples depending on the exact composition of the smectite in Sheepbed. The only unambiguous difference is the SO3 content, which is always higher in Rocknest. The observed similarity suggests that the two amorphous components share a common origin or formation process. The individual phases possibly present within the amorphous components include: volcanic (or impact) glass, hisingerite (or silica + ferrihydrite), amorphous sulfates (or adsorbed SO42−) and nanophase ferric oxides.

Reference
Dehouck E, McLennan SM, Meslin P-Y, Cousin A (2014) Constraints on abundance, composition and nature of X-ray amorphous components of soils and rocks at Gale crater, Mars. Journal of Geophysical Research Planets (in Press)
Link to Article [DOI: 10.1002/2014JE004716]

Published by arrangement with John Wiley&Sons

¹Svetoslav V. Georgiev, ^1,2Holly J. Stein, ^1,2Judith L. Hannah, ³Charles M. Henderson,
^4,5Thomas J. Algeo
¹AIRIE Program, Colorado State University, Fort Collins, 80523-1482 CO, USA
²CEED (Centre for Earth Evolution and Dynamics), University of Oslo, 0316 Oslo, Norway
³Department of Geoscience, University of Calgary, Calgary, Alberta T2N 1N4, Canada
⁴Department of Geology, University of Cincinnati, Cincinnati, 45221-0013 OH, USA
⁵State Key Laboratories of BGEG and GPMR, China University of Geosciences, Wuhan 430074, China

The geochemical record for the Permian-Triassic boundary in northern latitudes is essential to evaluation of global changes associated with the most profound extinction of life on Earth. We present inorganic and organic geochemical data, and Re-Os isotope systematics in a critical stratigraphic interval of pre- and post-extinction Upper Permian-Lower Triassic sediments from Opal Creek, western Canada (paleolatitude of ∼30°N). We document significant and long-lived changes in Panthalassa seawater chemistry that were initiated during the first of four magmatic or meteoritic inputs to Late Permian seawater, evidenced by notable decreases of Os isotopic ratios upsection.

Geochemical signals indicate establishment of anoxic bottom waters shortly after regional transgression reinitiated sedimentation in the Late Permian. Euxinic signals are most prominent in the Upper Permian sediments with low organic carbon and high sulfur contents, and gradually wane in the Lower Triassic. The observed features may have been generated in a strongly euxinic ocean in which high bacterioplankton productivity sustained prolific microbial sulfate reduction in the sediment and/or water column, providing hydrogen sulfide to form pyrite. This scenario requires nearlycomplete anaerobic decomposition of predominantly labile marine organic matter (OM) without the necessity for a complete collapse of primary marine productivity. Similar geochemical variations could have been achieved by widespread oxidation of methane by sulfate reducers after a methanogenic burst in the Late Permian. Both scenarios could have provided similar kill mechanisms for the latest Permian mass extinction.

Despite the moderate thermal maturity of the section, OM in all studied samples is dominantly terrestrial and/or continentally derived, recycled and refractory ancient OM. We argue that, as such, the quantity of the OM in the section mainly reflects changes in terrestrial vegetation and/or weathering, and not in marine productivity. At Opal Creek, a pyrite layer and <20-cm-thick siltstones that are lean in OM mark dramatic and long-lived inorganic geochemical and stable isotope changes. Initial Os isotope ratios decline markedly toward values of ∼0.35 in the pyrite interval, indicating a mantle-sourced or meteoritic trigger for the intensification and expansion of latest Permian anoxia. Subsequent and stronger magmatic or meteoritic pulses recorded by low initial Os isotopes followed the main extinction.

Reference
Georgiev SV, Holly J. Stein HJ, Judith L. Hannah JL, Charles M. Henderson CM, Thomas J. Algeo TJ (2014)Enhanced recycling of organic matter and Os-isotopic evidence for multiple magmatic or meteoritic inputs to the Late Permian Panthalassic Ocean, Opal Creek, Canada. Geochimica et Cosmochimica (in Press)
Link to Article [doi:10.1016/j.gca.2014.11.019]

Copyright Elsevier

^1,3Eve L. Berger, ²Lindsay P. Keller,¹Dante S. Lauretta
¹Lunar and Planetary Laboratory, The University of Arizona, Tucson, Arizona, USA
²NASA Johnson Space Center, Houston, Texas, USA
³GeoControl Systems, Inc. — Jacobs JETS contract — NASA Johnson Space Center, Houston, Texas, 77058, USA

The low-temperature form of CuFe2S3, cubanite, has been identified in the CI chondrite and NASA Stardust mission collections. The presence of this mineral constrains the maximum temperature to 210 °C since the time of its formation. However, until now, the conditions under which cubanite forms were less well constrained. In order to refine the history of the time-varying, low-temperature fluids which existed on the CI-chondrite parent body and Comet 81P/Wild 2 (Wild 2), we synthesized cubanite. The experimental synthesis of this mineral was achieved, for the first time, under low-temperature aqueous conditions relevant to the CI-chondrite parent body. Using a variant of in situ hydrothermal recrystallization, cubanite formed in aqueous experiments starting with temperatures of 150 and 200 °C, pH approximately 9, and oxygen fugacities corresponding to the iron-magnetite buffer. The composition and structure of the cubanite were determined using electron microprobe and transmission electron microscopy techniques, respectively. The combined compositional, crystallographic, and experimental data allow us to place limits on the conditions under which the formation of cubanite is feasible, which in turn constrains the nature of the fluid phase on the CI-chondrite parent body and Wild 2 when cubanite was forming.

Reference
Berger EL, Keller LP, Lauretta DS (2014) An experimental study of the formation of cubanite (CuFe2S3) in primitive meteorites. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12399]

Published by arrangement with John Wiley&Sons

¹Yangting Lin et al. (>10)*
¹Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China
*Find the extensive, full author and affiliation list on the publishers website

Two petrographic settings of carbonaceous components, mainly filling open fractures and occasionally enclosed in shock-melt veins, were found in the recently fallen Tissint Martian meteorite. The presence in shock-melt veins and the deuterium enrichments (δD up to +1183‰) of these components clearly indicate a pristine Martian origin. The carbonaceous components are kerogen-like, based on micro-Raman spectra and multielemental ratios, and were probably deposited from fluids in shock-induced fractures in the parent rock of Tissint. After precipitation of the organic matter, the rock experienced another severe shock event, producing the melt veins that encapsulated a part of the organic matter. The C isotopic compositions of the organic matter (δ13C = −12.8 to −33.1‰) are significantly lighter than Martian atmospheric CO2 and carbonate, providing a tantalizing hint for a possible biotic process. Alternatively, the organic matter could be derived from carbonaceous chondrites, as insoluble organic matter from the latter has similar chemical and isotopic compositions. The presence of organic-rich fluids that infiltrated rocks near the surface of Mars has significant implications for the study of Martian paleoenvironment and perhaps to search for possible ancient biological activities on Mars.

Reference
Lin Y et al. (2014) NanoSIMS analysis of organic carbon from the Tissint Martian meteorite: Evidence for the past existence of subsurface organic-bearing fluids on Mars. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12389]

Published by arrangement with John Wiley&Sons

¹Jean-Yves Bonnet et al. (>10)*
¹Univ. Grenoble Alpes, IPAG, F-38000 Grenoble, France, CNRS, IPAG, F-38000 Grenoble, France
*Find the extensive, full author and affiliation list on the publishers website

Nitrogen-rich refractory organics are scarce phases recovered as a fraction of stratospheric IDPs and constitute the bulk of the organic matter of some ultracarbonaceous Antarctic micrometeorites. They are likely formed under very specific conditions within a nitrogen-rich environment and may provide valuable clues on the origin of the population of interplanetary dusts accreted by Earth. In this study, we produced relevant analogs of such refractory organics characterized in three ultracarbonaceous Antarctic micrometeorites, starting from the carbonization of an HCN polymer and a tholin. Indeed, carbonization is a process that can increase the polyaromatic character toward a structure similar to that observed in these cosmomaterials. Both these precursors were degraded in an Ar atmosphere at 300, 500, 700 and 1000°C over ∼1 hour and characterized by elemental analysis, micro-FTIR and Raman micro-spectroscopy (at 244 and 514 nm excitation wavelengths). Our results show that the precursors evolve along distinct chemical and structural pathways during carbonization and that the influence of the precursor structure is still very strong at 1000°C. Interestingly, these different carbonization routes appear in the spectral characteristics of the G and D bands of their Raman spectra. Several of the residues present chemical and structural similarities with three recently studied ultracarbonaceous micrometeorites [Dobrica et al. (2011)Meteoritics Planet. Sci.46, 1363; Dartois et al. (2013)Icarus224, 243] and with N-rich inclusions in stratospheric IDPs. However the residues do not simultaneously account for the carbon structure (Raman) and the chemical composition (IR, N/C ratio). This indicates that the precursors and/or heating conditions in our experiments are not fully relevant. Despite this lack of full relevancy, the formation of a polyaromatic structure fairly similar to that of UCAMMs and IDPs suggests that the origin of N-rich refractory organics lies in a thermal process in the proto-solar disk, however radiolysis cannot be excluded.

Reference
Bonnet J-Y et al. (2014) Formation of analogs of cometary nitrogen-rich refractory organics from thermal degradation of tholin and hcn polymer. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2014.11.006]

Copyright Elsevier

¹Oliver Tschauner, ²Chi Ma, ²John R. Beckett, ³Clemens Prescher, ³Vitali B. Prakapenka, ²George R. Rossman
¹Department of Geoscience and High Pressure Science and Engineering Center, University of Nevada, Las Vegas, NV 89134, USA.
²Division of Geology and Planetary Science, California Institute of Technology, Pasadena, CA 91125, USA.
³Center of Advanced Radiation Sources, University of Chicago, Chicago, IL 60632, USA.

Meteorites exposed to high pressures and temperatures during impact-induced shock often contain minerals whose occurrence and stability normally confine them to the deeper portions of Earth’s mantle. One exception has been MgSiO3 in the perovskite structure, which is the most abundant solid phase in Earth. Here we report the discovery of this important phase as a mineral in the Tenham L6 chondrite and approved by the International Mineralogical Association (specimen IMA 2014-017). MgSiO3-perovskite is now called bridgmanite. The associated phase assemblage constrains peak shock conditions to ~ 24 gigapascals and 2300 kelvin. The discovery concludes a half century of efforts to find, identify, and characterize a natural specimen of this important mineral.

Reference
Tschauner O, Ma C, Beckett JR, Prescher C, Prakapenka VB, Rossman GR (2014) Discovery of bridgmanite, the most abundant mineral in Earth, in a shocked Meteorite. Science 346, 1100-1102
Link to Article [DOI: 10.1126/science.1259369]

Reprinted with permission from AAAS