^1,2M. L. Gray,^1,2,3M. K. Weisberg,⁴C. M. O’D. Alexander,⁴J. Wang,⁴D. I. Foustoukos,^1,2,5D. S. Ebel
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.70192]
¹Department of Earth and Environmental Sciences, CUNY Graduate Center, New York, New York, USA
²Department of Earth and Planetary Sciences, American Museum of Natural History, New York, New York, USA
³Department of Physical Sciences, CUNY Kingsborough College, Brooklyn, New York, USA
⁴Earth and Planets Laboratory, Carnegie Institution for Science, Washington, DC, USA
⁵Department of Earth and Environmental Sciences, Columbia University, New York, New York, USA
Published by arrangement with John Wiley & Sons

Measurements of bulk H, N, and C abundances and isotopic compositions were conducted on (metal-free) aliquots of 12 powdered enstatite chondrite (EC) samples, from both EH and EL chemical groups, and four aubrites. The ECs covered a range of petrologic types, including both falls and finds. To understand the internal H distributions, the H concentrations of individual silicate minerals were analyzed in situ by NanoSIMS in polished thick sections of six of the ECs. Using these data, combined with published data on H carriers and their modal abundances in ECs, we estimate here that the major silicate minerals, matrix, and mesostasis in unequilibrated ECs account for less than 20% of the total H budget. For the metamorphosed E4–6 chondrites, which exhibit a recrystallized matrix and mesostasis, over 99% of the bulk H contents remain unexplained. We attribute the discrepancies between our analyzed bulk H elemental compositions and the bulk H values reconstituted from in situ measurements are attributed to terrestrial contamination, as water adheres to grain boundaries, surfaces, and fractures. Water also reacts with reduced phases, regardless of whether the meteorite is a fall or find. Similar H isotopic compositions for falls and heavily weathered finds are consistent with, but do not require, that the majority of EC H is terrestrial. Attempts to remove organic terrestrial contamination by solvent extractions only served to moderately shift the H, N, and C isotopic compositions. The δD, δ15N, and δ13C values of EC powders are lighter than BSE, although δD and δ13C values partially overlap with atmospheric values. Reconstruction of the H budget of an EL-like parent body with an onion-shell structure suggests that such bodies could account for at most a fourth of the bulk silicate Earth’s (BSE’s) water budget.

¹Toni Schulz,¹Sophia Wernitznig,¹Christian Koeberl,²Bérengère Mougel,³Alessandro Montanari,⁴Frédéric Moynier
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70174]
¹Department of Lithospheric Research, University of Vienna, Vienna, Austria
²Instituto de Geociencias, UNAM, Queretaro, Mexico
³Osservatorio Geologico di Coldigioco, Frontale di Apiro, MC, Italy
⁴Universite Paris Cite, Institut de Physique du Globe de Paris, CNRS, 75005, Paris, France
Published by arrangement with John Wiley & Sons

Within the Danian Scaglia Rossa Formation appears a regionally correlatable horizon cutting across multiple sections and outcrops within the Umbria–Marche Basin of NE Italy, where it is intercalated with uniform pelagic carbonate successions. This horizon is called “ALE layer” and has tentatively been interpreted as a fine-grained volcanic ash. A key motivation for this study is the striking agreement between the ages of the ALE bed (65.440 ± 0.005 Ma) and the Boltysh impact event (65.39 ± 0.14/0.16 Ma), raising the possibility that the ALE layer preserves a distal Boltysh ejecta component transported over ~1600 km, while its bulk may reflect a longer duration volcanosedimentary depositional interval. To test this hypothesis, we combine impact-scaling considerations with highly siderophile element (HSE) and Cr-Os isotope data for Boltysh impactites and geochemical and Os isotopic analyses of the ALE horizon. Chromium isotope compositions of the Boltysh impactites (as low as ε54Cr = −0.31) may indicate an extraterrestrial contribution; however, their interpretation remains ambiguous. If interpreted as such, implausibly high IIIAB iron meteoritic admixtures would be required. By contrast, HSE abundances and 187Os/188Os systematics indicate clearly resolvable meteoritic components of up to 1 wt% CI-equivalent, forming coherent crust–chondrite mixing arrays. The ALE bed, though dominated by volcanosedimentary material, consistently shows Os–Ir–Pt–Pd enrichments far above the pelagic background, requiring up to ~0.8 wt% CI meteoritic input if interpreted in terms of an impact event horizon. Unradiogenic 187Os/188Os excursions occur primarily within the ALE layer, but in some cases extend into adjacent pelagic carbonate layers stratigraphically above and below the ALE layer. These unradiogenic 187Os/188Os excursions define chondritic-trending trajectories that mirror those in the Boltysh samples and are interpreted as diffusion-modified expressions of an originally ALE-centered meteoritic Os input. Taken together, the temporal coincidence between the Boltysh impact event and the ALE layer, impact-scaling relationships, and HSE- and Os-isotopic signatures favors the interpretation that the ALE layer preserves a distal equivalent of the Boltysh impact ejecta diluted within a volcanosedimentary depositional system that was subsequently modified by diagenetic processes.