¹Martin R. Lee,¹Jasper Glazer
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70089]
¹School of Geographical and Earth Sciences, University of Glasgow, Glasgow, UK
Published by arrangement with John Wiley & Sons

Alteration of historic CI1 meteorite falls during their curation demonstrates the susceptibility of smectite-rich carbonaceous chondrites to terrestrial exposure. The discovery of Oued Chebeika 002 in Morocco in June 2024 presents a unique opportunity to document the earliest stages of weathering of a CI1 find. We studied 10–30 mg fragments that had been recovered by September 2024. Grains of quartz and feldspar were implanted into the fragments by wind action whilst on the desert floor. Gypsum is the main product of terrestrial weathering. It encrusts their outer surfaces, in one case covering 5.3% of a fragment, and has filled voids within both fractures and phyllosilicate clasts. Other products of terrestrial weathering are Ca-carbonate grains that have grown within a sand-filled fracture, and rock inhabiting fungi colonizing the surface of a fragment. Chemical weathering was facilitated by water that had been adsorbed by smectite from the humid desert air, and crystallization of gypsum was driven by evaporation from the surfaces of those fragments that were exposed to direct sunlight. The gypsum and Ca-carbonate grew over a period of 3 or 4 months, approximately between June and September 2024, whereas the time scale of fungal colonization can only be constrained to a year or less. The rapid interaction of Oued Chebeika 002 with the Earth’s atmosphere, lithosphere, and biosphere underscores the importance of prompt recovery and careful curation of CI1 and other smectite-rich meteorites.

¹S.James et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.70081]
¹Department of Geology, University of Kerala, Thiruvananthapuram, India
²Department of Earth and Planetary Science, University of Tokyo, Tokyo, Japan
Published by arrangement with John Wiley & Sons

At ~66 Ma, the Cretaceous–Paleogene Boundary (KPB) sections at Anjar and Um Sohryngkew (India) were 14,333 and 16,549 km, respectively, from Chicxulub, making them the farthest distal KPBs. The spatial and temporal proximity of the sites to Deccan volcanism makes them important locations to better understand the impact-volcanism debate. This study integrates petrological, mineralogical, and geochemical techniques to distinguish signatures of the instantaneous Chicxulub impact from those of the prolonged Deccan volcanism (lasting ~10 my). The sites contained two ejecta components: a potential spherule (Um Sohryngkew) and Ir-anomalies. The poorly preserved spherule (~240 μm diameter) exhibited mineral dendrites. At Anjar, two Ir-anomalies are noted: 8.50 ppb (SGA-2; ~3.19 m below Flow IV) and 1.16 ppb (SGA-12). Four Ir-anomalies are noted at Um Sohryngkew: 1.36 ppb (SMU-19; 28.44 m from the oldest layer), 3.17 (SMU-14), 7.00 (SMU-7), and 1.19 ppb (SMU-6). Multiple Ir-anomalies, elevated background-Ir, and glass shards at both sites highlight a greater influence of Deccan volcanism than previously recognized. Deccan magma-based Ir-enrichment is unlikely as such values were not reported in Deccan basalts, but higher Ir-concentrations in sedimentary layers point to indirect contributions from Deccan outgassing. Thus, the findings of the study underscore the complex interplay of Deccan volcanism and Chicxulub impact across the Indian Subcontinent.