^1,2V. P. Singh,^1,2N. G. Rudraswami,^3,4Nittala V. Chalapathi Rao,⁵Matthew J. Genge,¹M. Pandey,^1,2S. Sreekuttan,³S. Chattopadhaya
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14256]
¹National Institute of Oceanography (Council of Scientific and Industrial Research), Dona Paula, Goa, India
²Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, India
³Department of Geology, Institute of Science, Banaras Hindu University, Varanasi, Uttar Pradesh, India
⁴National Centre for Earth Science Studies, Ministry of Earth Sciences, Thiruvananthapuram, India
⁵Department of Earth Science and Engineering, Imperial College London, London, UK
Published by arrangement with John Wiley & Sons

The Cretaceous–Paleogene (K-Pg) boundary represents the extinction of ~70% of species, a prominent Chicxulub impact event and Deccan volcanism. This work reports the first attempt to extract the micrometeorites (MMs) from the Deccan intertrappean horizons. Eighty-one spherical particles were studied for their morphological, textural, and chemical characteristics. Intact cosmic spherules with ferromagnesian silicates (6) and Fe-Ni oxide (7) compositions correspond to MMs from the deep sea and Antarctica. Silicate and Fe-Ni spherules in this study showcase remarkable preservation, a testament to the highly favorable conditions present. Fe spherules (38) with iron oxide compositions exhibit diagenetic alteration during preservation. Textural analysis of 30 Fe spherules reveals a dendritic, interlocking pattern and slightly elevated Mn content, suggesting these may be fossilized I-type MMs. However, eight Fe spherules with blocky and cubical granular textures resemble oxidized pyrite spherules. Al-Fe-Si spherules (30) possess a significant enrichment of Al and Si within their Fe-oxide-dominated composition. Group-I Al-Fe-Si spherules (15) display zoned Al-Fe-Si oxide composition, dendritic Mg-Cr spinel grains, and aerodynamic features, all indicative of impact spherules. The finding of these impact spherules from sampled Deccan intertrappean layer raises the possibility that these paleosols were deposited during the Chicxulub impact event, the only identified impact event with global distribution during the Deccan volcanism time frame. This unique location provides an opportunity for the simultaneous collection of well-preserved MMs, impact, and volcanic spherules. The exceptional preservation of the studied MMs is likely due to a combination of non-marine environments, atypical climatic conditions, and rapid deposition. This study further investigates the potential role of cosmic dust flux in the K-Pg extinction event. We propose that the enhanced cosmic dust flux, a likely scenario during the K-Pg boundary period, synergistically mixing with impact dust in the upper atmosphere, may have intensified and extended the harsh climatic conditions at the K-Pg boundary. Subsequently, the deposition of this dust, enriched in bioavailable iron, on Earth’s surface might have contributed to the swift recovery of life and environmental conditions.

^1,2Y. Srivastava,¹A. Basu Sarbadhikari,³A. Yamaguchi,⁴A. Takenouchi,⁵J. M. D. Day,⁶T. Ubide
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14257]
¹Physical Research Laboratory, Ahmedabad, India
²Indian Institute of Technology, Gandhinagar, Gujarat, India
³National Institute of Polar Research (NIPR), Tokyo, Japan
⁴The Kyoto University Museum, Kyoto University, Kyoto, Japan
⁵Scripps Institution of Oceanography, University of California San Diego, La Jolla, California, USA
⁶School of the Environment, The University of Queensland, Brisbane, Queensland, Australia
Published by arrangement with John Wiley & Sons

Lunar basaltic meteorite Asuka-881757 (A-881757), a member of the source crater paired YAMM meteorites (Yamato-793169, A-881757, Miller Range 05035 and Meteorite Hills 01210), provides information on potassium-rare earth element-phosphorous (KREEP)-free magmatic sources within the Moon. Asuka-881757 is an unbrecciated and Fe-rich (Mg# 36) gabbro with coarse pyroxene (2–8 mm) and plagioclase (1–3 mm). The coarse pyroxene preserves mm-scale, near-complete hour-glass sector zoning with strong Ca and Fe partitioning, similar to some Fe-rich Apollo basalts. In contrast to the most Mg-rich Apollo basalts, A-881757 contains various types of symplectites (~8 vol%) formed by the breakdown of pyroxferroite due to slow cooling, resembling a few extreme Fe-rich (Mg#
40) Apollo basalts. Petrographic observations and thermodynamic modeling suggest crystallizing in the order: Fe-poor pyroxenes (Mg# 58–55) → co-crystallized plagioclase and Fe-rich pyroxenes (Mg# 49–20) → late-stage assemblage including Fe-augite, Fayalite, and Fe-Ti oxides. Combining phase stability at variable P–T with petrographic observations, the minimum depth of formation of the A-881757 parent magma can be constrained to between 60 and 100 km. KREEP-free basalts (such as A-881757 and the YAMM meteorites) originated from a relatively shallow mantle source and later underwent polybaric crystallization that occurred prior to eruption at the lunar surface. In contrast, the Apollo mare basalts mostly crystallized within lava flows from relatively deeper-seated mantle sources. The crystallization of A-881757 and other YAMM meteorites is unlike most Apollo basalts from the Procellarum KREEP terrane, and likely represent hidden cryptomare basalts close to lunar surface.