Organic matter from the Chicxulub crater exacerbated the K–Pg impact winter

1Shelby L. Lyons,1Allison T. Karp,1Timothy J. Bralower,2Kliti Grice,
2Bettina Schaefer,3,4,5Sean P. S. Gulick,6Joanna V. Morgan,6Katherine H. Freeman
Proceedings of the National Academy of Sciences of teh United States of America (in Press) Link to Article [https://doi.org/10.1073/pnas.2004596117]
1Department of Geosciences, The Pennsylvania State University, University Park, PA 16802;
2Western Australia Organic and Isotope Geochemistry Centre, School of Earth and Planetary Sciences, The Institute for Geoscience Research, Curtin University, Perth, WA 6102, Australia;
3Institute for Geophysics, University of Texas at Austin, Austin, TX 78758;
4Department of Geological Sciences, University of Texas at Austin, Austin, TX 78712;
5Center for Planetary Systems Habitability, University of Texas at Austin, Austin, TX 78712;
6Department of Earth Science and Engineering, Imperial College London, London SW7 2AZ, United Kingdom

An asteroid impact in the Yucatán Peninsula set off a sequence of events that led to the Cretaceous–Paleogene (K–Pg) mass extinction of 76% species, including the nonavian dinosaurs. The impact hit a carbonate platform and released sulfate aerosols and dust into Earth’s upper atmosphere, which cooled and darkened the planet—a scenario known as an impact winter. Organic burn markers are observed in K–Pg boundary records globally, but their source is debated. If some were derived from sedimentary carbon, and not solely wildfires, it implies soot from the target rock also contributed to the impact winter. Characteristics of polycyclic aromatic hydrocarbons (PAHs) in the Chicxulub crater sediments and at two deep ocean sites indicate a fossil carbon source that experienced rapid heating, consistent with organic matter ejected during the formation of the crater. Furthermore, PAH size distributions proximal and distal to the crater indicate the ejected carbon was dispersed globally by atmospheric processes. Molecular and charcoal evidence indicates wildfires were also present but more delayed and protracted and likely played a less acute role in biotic extinctions than previously suggested. Based on stratigraphy near the crater, between 7.5 × 1014 and 2.5 × 1015 g of black carbon was released from the target and ejected into the atmosphere, where it circulated the globe within a few hours. This carbon, together with sulfate aerosols and dust, initiated an impact winter and global darkening that curtailed photosynthesis and is widely considered to have caused the K–Pg mass extinction.

Mass-independent and mass-dependent Cr isotopic composition of the Rumuruti (R) chondrites: Implication for their origin and their significance for planet formation

1Ke Zhu,1Frédéric Moynier,2Martin Schiller,3ConelM. O’D. Alexander,4Jean-Alix Barrat,5Addi Bischoff,1,2Martin Bizzarro
Geochimica et Cosmochimcia Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2020.10.007]
1Institut de Physique du Globe de Paris, Université de Paris, CNRS UMR 7154, 1 rue Jussieu, Paris F-75005, France
2Centre for Star and Planet Formation, Globe Institute, University of Copenhagen, Øster Voldgade 5–7, Copenhagen DK-1350, Denmark
3Earth and Planetary Laboratory, Carnegie Institution for Science, 5241 Broad Branch Road, Washington, DC 20015, USA4Univ. Brest, CNRS, UMR 6539 (Laboratoire des Sciences de l’Environnement Marin), LIA BeBEST, Institut Universitaire Européen de la Mer (IUEM), Place Nicolas Copernic, 29280 Plouzané, France
5Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Str. 10, D-48149 Münster, Germany
Copyright Elsevier

Chromium (Cr) isotopes play an important role in cosmochemistry and planetary science, because they are powerful tools for dating (53Mn-53Cr short-lived chronometry), tracing (54Cr nucleosynthetic anomalies) the origins of the materials, and studying the processes involved in volatile element fractionation and planetary differentiation (Cr stable isotopic fractionation). The foundation for using Cr isotopes is to precisely know the compositions of the various chondritic reservoirs. However, the Cr isotope composition of Rumuruti (R) chondrites remains unknown. Here, we report high-precision mass-independent (average 2SE uncertainty of ∼0.02 and ∼0.06 for ε53Cr and ε54Cr, respectively; ε indicates 10,000 deviation) and mass-dependent (uncertainty of average 0.03 ‰ for δ53Cr; δ indicates 1,000 deviation) Cr isotope data for 12 bulk R chondrites of petrologic types 3-6 (included R chondrite breccias), and one R chondrite-like clast (MS-CH) in the Almahata Sitta polymict ureilite. All the R chondrites show homogeneous bulk ε54Cr values, -0.06 ± 0.08 (2SD), similar only to those of the Earth-Moon system and enstatite chondrites. These first ε54Cr data for R chondrites provide significant addition to the ε54Cr-Δ17O diagram, and position them as a potential endmember for planetary precursors. The R chondrites possess a higher 55Mn/52Cr of 0.68 ± 0.04 and higher ε53Cr values 0.23 ± 0.05 (2SD) relative to most of other chondrite groups. This likely results from the lower (e.g. than ordinary and enstatite chondrites) chondrule abundance in R chondrites. The stable Cr isotope composition of R chondrites is homogeneous with a δ53Cr = -0.12 ± 0.03 ‰ (2SD). Combined with previous data of other groups of chondrites, we show that the stable Cr isotopic composition of all the chondrites is homogeneous with δ53Cr of -0.12 ± 0.04 ‰ (2SD, N = 40) and is independent of the petrologic type and redox conditions. The lack of mass-dependent fractionation between all groups of chondrites suggests that the average chondrite δ53Cr value is also representative for the initial composition all differentiated planets in the Solar System. Finally, the MS-CH clast in Almahata Sitta has a Cr isotopic composition (ε53Cr = 0.18 ± 0.04, ε54Cr = -0.16 ± 0.07, and δ53Cr = -0.11 ± 0.05 ‰) that is consistent (within error) with it being an R chondrite-like clast.

Mineralogical and oxygen isotopic study of a new ultrarefractory inclusion in the Northwest Africa 3118 CV3 chondrite

1Yong Xiong,1,2Ai‐Cheng Zhang,3Noriyuki Kawasaki,4Chi Ma,5Naoya Sakamoto,1Jia‐Ni Chen,6Li‐Xin Gu,3,5Hisayoshi Yurimoto
Meteortics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13575]
1State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing, 210023 China
2CAS Center for Excellence in Comparative Planetology, Hefei, China
3Department of Natural History Sciences, Hokkaido University, Sapporo, 060‐0810 Japan
4Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, 91125 USA
5Isotope Imaging Laboratory, Creative Research Institution Sousei, Hokkaido University, Sapporo, 001‐0021 Japan
6Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029 China
Published by Arrangement with John Wiley & Sons

Calcium‐aluminum‐rich inclusions (CAIs) are the first solid materials formed in the solar nebula. Among them, ultrarefractory inclusions are very rare. In this study, we report on the mineralogical features and oxygen isotopic compositions of minerals in a new ultrarefractory inclusion CAI 007 from the CV3 chondrite Northwest Africa (NWA) 3118. The CAI 007 inclusion is porous and has a layered (core–mantle–rim) texture. The core is dominant in area and mainly consists of Y‐rich perovskite and Zr‐rich davisite, with minor refractory metal nuggets, Zr,Sc‐rich oxide minerals (calzirtite and tazheranite), and Fe‐rich spinel. The calzirtite and tazheranite are closely intergrown, probably derived from a precursor phase due to thermal metamorphism on the parent body. The refractory metal nuggets either exhibit thin exsolution lamellae of Fe,Ni‐dominant alloy in Os,Ir‐dominant alloy or are composed of Os,Ir,Ru,Fe‐alloy and Fe,Ni,Ir‐alloy with troilite, scheelite, gypsum, and molybdenite. The later four phases are apparently secondary minerals. The Zr,Sc,Y‐rich core is surrounded by a discontinuous layer of closely intergrown hibonite and spinel. The CAIs are rimmed by Fe‐rich spinel and Al‐rich diopside. Perovskite has high concentrations of the most refractory rare earth elements (REEs) but is relatively depleted in the moderately refractory and volatile REEs, consistent with the ultrarefractory REE pattern. Based on this unusual Zr,Sc,Y‐rich mineral assemblage, the layered distribution in CAI 007, and the REE concentrations in perovskite, we suggest that CAI 007 is an ultrarefractory inclusion of condensation origin. In CAI 007, hibonite, spinel, and probably Al‐rich diopside are 16O‐rich (Δ17O ~–22‰) whereas perovskite and davisite are 16O‐poor (Δ17O ~–3‰). Such oxygen isotope heterogeneity suggests that the UR inclusion formed in the various degrees of 16O‐rich nebular setting or was originally 16O‐rich and then experienced oxygen isotope exchange with 16O‐poor fluid on the CV3 chondrite parent body.

DEVELOPMENT OF A NOVEL LUNAR HIGHLAND SOIL SIMULANT (LSS-ISAC-1) AND ITS GEOTECHNICAL PROPERTIES FOR CHANDRAYAAN MISSIONS

1Indaram Venugopal,2Thannasi Prabu,3Kasinathan Muthukkumaran,4Mylswamy Annadurai
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2020.105116]
1C&MG LEOS, U R Rao Satellite Centre, Indian Space Research Organization, Bengaluru, 560 017, Karnataka, India
2Dept. of Civil Engineering, National Institute of Technology, Tiruchirappalli, 620015, Tamilnadu, India
3Dept. of Civil Engineering, National Institute of Technology, Tiruchirappalli, 620015, Tamilnadu, India
4U R Rao Satellite Centre, Indian Space Research Organization, Bengaluru, 560 017, Karnataka, India

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Ag isotopic and chalcophile element evolution of the terrestrial and martian mantles during accretion: New constraints from Bi and Ag metal-silicate partitioning

1K.Righter,21M.Schönbächler,3K.Pando,4R.RowlandII,5M.Righter,5T.Lapene
Earth and Planetary Science Letters 552, 116590 Link to Article [https://doi.org/10.1016/j.epsl.2020.116590]
1NASA-JSC, 2101 NASA Parkway, Houston, TX 77058, United States of America
2ETH Zürich, Inst. Isotope Geology and Mineral Resources, 8092 Zürich, Switzerland
3Jacobs JETS, NASA JSC, Houston, TX 77058, United States of America
4Los Alamos National Laboratory, Mail Stop P952, Los Alamos, NM 87545, United States of America
5Dept. of Earth and Atmospheric Sciences, University of Houston, Houston, TX 77204, United States of America
Copyright Elsevier

The Earth’s timing of accretion and acquisition of moderately volatile compounds is uncertain. Hafnium-W and Mn-Cr isotopic data can bracket the timing of early planetary differentiation and core formation. The Ag-Pd system has also been utilized but its application has been limited by a lack of high pressure and temperature metal-silicate partitioning for Pd and Ag. Because Ag (and Bi) are volatile chalcophile siderophile elements, understanding their early distribution can constrain the origin of volatile elements in differentiated bodies and planets. Unfortunately, neither Ag or Bi have been studied across the wide range of pressure and temperature conditions that are relevant to accretion and core-mantle differentiation. Here, new high-pressure and temperature multi-anvil metal-silicate equilibrium experiments for Bi and Ag have been carried out at conditions relevant to planetary accretion and metal silicate differentiation that allow a more refined and complete understanding of element partitioning during core formation. The new metal-silicate partitioning data are combined with previously reported data, and utilized to predict the distributions of Bi, Pd, and Ag at conditions of accretion relevant for Earth and Mars. Application of the new partitioning results to Earth shows that D(Bi) and D(Ag) (D = metal/silicate concentration ratio) are lowered due to the effect of pressure and Si alloyed in the metallic liquid, resulting in higher predicted mantle Bi and Ag abundances than in the bulk silicate Earth (BSE), as well as high and variable Pd/Ag. The unradiogenic Ag isotopic composition of the BSE could have been generated by early accretion of volatile-poor (high Pd/Ag) pre-cursors, followed by later accretion of volatile–rich (low Pd/Ag) material, in agreement with earlier studies of Pd-Ag and Mn-Cr (Schönbächler et al., 2010). However, these main accretion phases would have to be followed by segregation of a sulfide liquid (at least 1.5% of magma ocean) at high pressures (>30 GPa), to explain the primitive upper mantle (PUM) Bi, Pd, and Ag, as well as Au, Pt, Cu and Ni concentrations as proposed previously. If the early accreted bulk Earth was volatile depleted with high Pd/Ag ratios, portions of the mantle may contain ancient domains that developed positive 107Ag isotopic anomalies (as also argued by noble gases, Nd, W, and Os isotopes). In comparison, Bi, Pd, and Ag concentrations in the martian mantle could have been set by simple metal-silicate equilibrium. Mars accreted and differentiated relatively rapidly, while also developing a deep magma ocean with a high Pd/Ag ratio that could have evolved positive 107Ag anomalies, in contrast to Earth. Measurements on shergottites may reveal these predicted Ag isotopic anomalies.

Kaitianite, Ti3+2Ti4+O5, a new titanium oxide mineral from Allende

1Chi Ma,1John R. Beckett
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13576]
1Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, 91125 USA
Published by arrangement with John Wiley & Sons

Kaitianite, Ti3+2Ti4+O5, is a new titanium oxide mineral discovered in the Allende CV3 carbonaceous chondrite. The type grain coexists with tistarite (Ti2O3) and rutile. Corundum, xifengite, mullite, osbornite, and a new Ti,Al,Zr‐oxide mineral are also present, although not in contact. The chemical composition of type kaitianite is (wt%) Ti2O3 56.55, TiO2 39.29, Al2O3 1.18, MgO 1.39, FeO 0.59, V2O3 0.08 (sum 99.07), yielding an empirical formula of (Ti3+1.75Al0.05Ti4+0.10Mg0.08Fe0.02)(Ti4+1.00)O5, with Ti3+ and Ti4+ partitioned, assuming a stoichiometry of three cations and five oxygen anions pfu. The end‐member formula is Ti3+2Ti4+O5. Kaitianite is the natural form of γ‐Ti3O5 with space group C2/c and cell parameters a = 10.115 Å, b = 5.074 Å, c = 7.182 Å, β = 112º, V = 341.77 Å3, and Z = 4. Both the type kaitianite and associated rutile likely formed as oxidation products of tistarite at temperatures below 1200 K, but this oxidation event could have been in a very reducing environment, even more reducing than a gas of solar composition. Based on experimental data on the solubility of Ti3+ in equilibrium with corundum from the literature, the absence of tistarite in or on Ti3+‐rich corundum (0.27–1.45 mol% Ti2O3) suggests that these grains formed at higher temperatures than the kaitianite (>1579–1696 K, depending on the Ti concentration). The absence of rutile or kaitianite in or on corundum suggests that any exposure to the oxidizing environment producing kaitianite in tistarite was too short to cause the precipitation of Ti‐oxides in or on associated corundum.

Microbial community distribution in variously altered basalts: insights into astrobiology sample site selection

1Brady AL,1,5Gibbons E,2,3Sehlke A,4Renner CJ,4Kobs Nawotniak SE,2Lim DSS,1Slater GF
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2020.105107]
1School of Geography and Earth Sciences, McMaster University, Hamilton, Ontario, Canada L8S 4K1
2NASA Ames Research Center, Moffett Field, California, USA
3Bay Area Environmental Research Institute (BAERI), Moffett Field, California, USA
4Department of Geosciences, Idaho State University, Pocatello, Idaho, USA
5Present address: Department of Earth and Planetary Sciences, McGill University, Montreal, Quebec, Canada

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The fate of sulfur and chalcophile elements during crystallization of the lunar magma ocean

1,2E. S. Steenstra,2J. Berndt,2S. Klemme,3J. F. Snape,1E. S. Bullock,3W. van Westrenen
Journal of Geophysical Research (Planets) (in Press) Link to Article [https://doi.org/10.1029/2019JE006328]
1The Earth and Planets Laboratory, Carnegie Institution of Science, Washington D.C., U.S.A
2Institute of Mineralogy, University of Münster, Germany
3Faculty of Science, Vrije Universiteit Amsterdam, The Netherlands
Published by arrangement with John Wiley & Sons

To assess the viability of sulfide liquid saturation during crystallization of the lunar magma ocean (LMO), we present a new dataset describing both the S concentration at sulfide liquid saturation (SCSS) and sulfide liquid‐silicate melt partition coefficients of many trace elements for various differentiated lunar magmas at lunar‐relevant conditions. Using these parameterizations, we model the SCSS and the distribution of the most chalcophile elements with progressive LMO crystallization in the absence and presence of sulfide liquids. Modeling results for different modes of LMO crystallization show that for proposed lunar mantle S abundances FeS sulfide liquid saturation is expected to occur between 96 and 98 % of LMO crystallization. This is decreased to >91 % for Fe‐S liquids with 30% Ni or Cu. Saturation of S‐poor sulfide liquids can occur at >75% of LMO crystallization. The timing of sulfide liquid saturation depends most strongly on the assumed S content of the lunar mantle following formation of the lunar core and on the sulfide liquid composition. Modeled abundances of chalcophile elements indicate that sulfide‐liquid saturation during late‐stage LMO crystallization would yield much lower abundances of Ni and Cu than observed in KREEP basalts and estimated for the urKREEP reservoir, as well as lower Ni/Co than observed in the latter. Sulfide liquids therefore did not affect moderately siderophile and chalcophile element fractionation within the LMO, supporting the hypothesis that the non‐volatile, siderophile element abundances of the lunar mantle reflect a phase of core formation and/or the addition of a meteoritic late veneer.

Correlated isotopic and chemical evidence for condensation origins of olivine in comet 81P/Wild 2 and in AOAs from CV and CO chondrites

1KoheiFukuda,2Donald E.Brownlee,2David J.Joswiak,3Travis J.Tenner,4Makoto Kimura,1Noriko T.Kita
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2020.09.036]
1WiscSIMS, Department of Geoscience, University of Wisconsin-Madison, Madison, WI 53706, USA
2Department of Astronomy, University of Washington, Seattle, WA 98195, USA
3Chemistry Division, Nuclear and Radiochemistry, Los Alamos National Laboratory, MSJ514, Los Alamos, NM 87545, USA
4National Institute of Polar Research, Tokyo 190-8518, Japan
Copyright Elsevier
Magnesium stable isotope ratios and minor element abundances of five olivine particles from comet 81P/Wild 2 were examined by secondary ion mass spectrometry (SIMS). Wild 2 olivine particles exhibit only small variations in δ25MgDSM-3 values from –1.0 +0.4/–0.5 ‰ to 0.6 +0.5/–0.6 ‰ (2σ). This variation can be simply explained by mass-dependent fractionation from Mg isotopic compositions of the Earth and bulk meteorites, suggesting that Wild 2 olivine particles formed in the chondritic reservoir with respect to Mg isotope compositions. We also determined minor element abundances, and O and Mg isotope ratios of olivine grains in amoeboid olivine aggregates (AOAs) from Kaba (CV3.1) and DOM 08006 (CO3.01) carbonaceous chondrites. Our new SIMS minor element data reveal uniform, low FeO contents of ∼0.05 wt% among AOA olivines from DOM 08006, suggesting that AOAs formed at more reducing environments in the solar nebula than previously thought. Furthermore, the SIMS-derived FeO contents of the AOA olivines are consistently lower than those obtained by electron microprobe analyses (∼1 wt% FeO), indicating possible fluorescence from surrounding matrix materials and/or Fe,Ni-metals in AOAs during electron microprobe analyses. For Mg isotopes, AOA olivines show more negative mass-dependent fractionation (–3.8 ± 0.5‰ ≤ δ25MgDSM-3 ≤ –0.2 ± 0.3‰; 2σ) relative to Wild 2 olivines. Further, these Mg isotope variations are correlated with their host AOA textures. Large negative Mg isotope fractionations in olivine are often observed in pore-rich AOAs, while those in compact AOAs tend to have near-chondritic Mg isotopic compositions. These observations indicate that pore-rich AOAs preserved their gas-solid condensation histories, while compact AOAs experienced thermal processing in the solar nebula after their condensation and aggregation. Importantly, one 16O-rich Wild 2 LIME olivine particle (T77/F50) shows negative Mg isotope fractionation (δ25MgDSM-3 = –0.8 ± 0.4‰, δ26MgDSM-3 = –1.4 ± 0.9‰; 2σ) relative to bulk chondrites. Minor element abundances of T77/F50 are in excellent agreement with those of olivines from pore-rich AOAs in DOM 08006. The observed similarity in O and Mg isotopes, and minor element abundances suggest that T77/F50 formed in an environment similar to AOAs, probably near the proto-Sun, and then was transported to the Kuiper belt, where comet 81P/Wild 2 likely accreted.

Surface weathering on Venus: Constraints from kinetic, spectroscopic, and geochemical data

1,2M. Darby Dyar,3Jörn Helbert,4Reid F.Cooper,1Elizabeth C.Sklute,3Alessandro Maturilli,3Nils T.Mueller,3David Kappel,5Suzanne E.Smrekar
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.114139]
1Planetary Science Institute, 1700 East Fort Lowell, Suite 106, Tucson, AZ 85719, USA
2Department of Astronomy, Mount Holyoke College, 50 College St., South Hadley, MA 01075, USA
3German Aerospace Center (DLR) Institute for Planetary Research, Rutherfordstr 2, Berlin 12489, Germany
4Department of Earth, Environmental, and Planetary Sciences, Brown University, Providence, RI, 02912, USA
5Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
Copyright Elsevier

On Venus, understanding of surface-atmosphere interactions resulting from chemical weathering is both critically important for constraining atmospheric chemistry and relative ages of surface features and multifaceted, requiring integration of diverse perspectives and disciplines of study. This paper evaluates the issue of surface alteration on Venus using multiple lines of evidence. Surface chemistry from Venera and Vega landers is inconsistent with significant breakdown from atmospheric interactions, with <2.0 wt% S or less observed. Consideration of kinetics and breakdown of basalt under Venus conditions indicates diffusion of Ca > Fe > Mg toward the oxidizing Venus atmosphere, favoring creation of anhydrite and carbonate-rich surfaces on basalts with minor addition of hematite. When related to Venus-analog experiments, the kinetic calculations suggest a maximum coating of ~30 μm over 500,000 years. These changes would result in an overall volume increase in the outermost surface materials, which in turn decreases surface rock FeO contents. Those variations can be detected from orbit because emissivity is correlated with total FeO, and the predicted magnitudes are consistent with Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) observations. Models of anhydrite and hematite coatings on basalt mixtures suggest that changes in emissivity (ε) spectra due to chemical weathering can result in ca. <0.08 shifts in total emissivity. Such gradations are small compared to the first-order effect of bulk composition on emissivity, which can cause up to ~0.80 emissivity shifts. For all these reasons, there is at present no evidence to suggest that emissivity spectra should show impenetrable coatings of either hematite (ε = 0.8) or anhydrite (ε = 0.1) are present on Venus. Orbital measurements of surface emissivity on a global scale could therefore produce not only a map of rock type and surface composition based on transition metal contents (largely FeO) (Helbert et al., 2020) but also provide local scale assessments of fresh vs. mature lava flows on the surface.