¹Samuele Boschi,¹Birger Schmitz,¹Ellinor Martin,¹Fredrik Terfelt
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13539]
¹Astrogeobiology Laboratory, Division of Nuclear Physics, Department of Physics, Lund University, Lund, Sweden
Published by arrangement with John Wiley & Sons

Based on sediment‐dispersed extraterrestrial spinel grains in the Bottaccione limestone section in Italy, we reconstructed the micrometeorite flux to Earth during the early Paleocene. From a total of 843 kg of limestone, 86 extraterrestrial spinel grains (12 grains > 63 μm, and 74 in the 32–63 μm fraction) have been recovered. Our results indicate that the micrometeorite flux was not elevated during the early Paleocene. Ordinary chondrites dominated over achondritic meteorites similar to the recent flux, but H chondrites dominated over L and LL chondrites (69%, 22%, and 9%, respectively). This H‐chondrite dominance is similar to that recorded within an enigmatic ³He anomaly (70, 27, and 3%) in the Turonian, but different from just before this ³He anomaly and in the early Cretaceous, where ratios are similar to the recent flux (~45%, 45%, and 10%). The K‐Ar isotopic ages of recently fallen H chondrites indicate a small impact event on the H‐chondrite parent body ~50 to 100 Ma ago. We tentatively suggest that this event is recorded by the Turonian ³He anomaly, resulting in an H‐chondrite dominance up to the Paleocene. Our sample spanning the 20 cm above the Cretaceous–Paleogene (K–Pg) boundary did not yield any spinel grains related to the K–Pg boundary impactor.

¹Michael W. Broadley,²Peter H. Barry,¹David V. Bekaert,¹David J. Byrne,³Antonio Caracausi,⁴Christopher J. Ballentine,¹Bernard Marty
Proceedings of the National Academy of Sciences of the Unites States of America (in Press) Link to Article [https://doi.org/10.1073/pnas.200390711]
¹Centre de Recherches Pétrographiques et Géochimiques, UMR 7358 CNRS—Université de Lorraine, BP 20, F-54501 Vandoeuvre-lès-Nancy, France;
²Marine Chemistry and Geochemistry Department, Woods Hole Oceanographic Institution, Woods Hole, MA 02543;
³Instituto Nazionale di Geofisica e Vulcanologia, 90146 Palermo, Italy;
⁴Department of Earth Sciences, University of Oxford, OX1 3AN Oxford, United Kingdom

Identifying the origin of noble gases in Earth’s mantle can provide crucial constraints on the source and timing of volatile (C, N, H2O, noble gases, etc.) delivery to Earth. It remains unclear whether the early Earth was able to directly capture and retain volatiles throughout accretion or whether it accreted anhydrously and subsequently acquired volatiles through later additions of chondritic material. Here, we report high-precision noble gas isotopic data from volcanic gases emanating from, in and around, the Yellowstone caldera (Wyoming, United States). We show that the He and Ne isotopic and elemental signatures of the Yellowstone gas requires an input from an undegassed mantle plume. Coupled with the distinct ratio of 129Xe to primordial Xe isotopes in Yellowstone compared with mid-ocean ridge basalt (MORB) samples, this confirms that the deep plume and shallow MORB mantles have remained distinct from one another for the majority of Earth’s history. Krypton and xenon isotopes in the Yellowstone mantle plume are found to be chondritic in origin, similar to the MORB source mantle. This is in contrast with the origin of neon in the mantle, which exhibits an isotopic dichotomy between solar plume and chondritic MORB mantle sources. The co-occurrence of solar and chondritic noble gases in the deep mantle is thought to reflect the heterogeneous nature of Earth’s volatile accretion during the lifetime of the protosolar nebula. It notably implies that the Earth was able to retain its chondritic volatiles since its earliest stages of accretion, and not only through late additions.