¹J.A. Berger et al. (>10)
Journal of Geophysical Research (Planets)(in Press) Link to Article [https://doi.org/10.1029/2025JE009350]
¹Amentum at NASA Johnson Space Center, Houston, TX, USA
Published by arrangement with John Wiley & Sons

A major mission goal for the Mars Science Laboratory’s rover, Curiosity, is to investigate the transition from clay-bearing to hydrated-Mg-sulfate-bearing sedimentary strata hypothesized to record a transition from a wet to a dry paleoclimate. Alpha Particle X-ray Spectrometer (APXS) results from this region, named the Clay-Sulfate Transition (CST), indicate an overall ∼5% increase in Ca-sulfate, but Mg-sulfate enrichment is limited to diagenetic nodules. Sulfates in the CST change sharply at the contact with the overlying Mg-sulfate unit, which has ∼5% Ca-sulfate and ∼10% Mg-sulfate in the bedrock matrix. Despite this change in sulfate assemblage, and the transition from fluvial-lacustrine to drier aeolian sedimentary deposits, the bulk chemical composition of the aeolian sandstone (sulfate-free basis) effectively has the same altered basalt chemical fingerprint as the underlying fluvial-lacustrine mudstone. That is, the composition of rocks that record the transition from a wet to a dry paleoclimate is isochemical. It is remarkable that the aeolian sandstone has the same altered bulk chemical characteristics as the fluvial-lacustrine mudstone, notwithstanding very different inferred geochemical regimes. We propose a simplified model wherein older basaltic sediment was aqueously altered in a fluvial-lacustrine regime and reworked, likely during cycles of alteration, salt formation, and reworking. This process led to an averaging of the bulk chemical composition of the Mt. Sharp group sediment, resulting in the isochemical characteristics of the paleoenvironment change.

^1,2Mu-Han Yang, ¹Qian W.L. Zhang, ³Richard W. Carlson, ^1,2Bi-Wen Wang, ¹Dongjian Ouyang^1,2Qiu-Li Li
Icarus (in Press) Open Access Link to Article [https://doi.org/10.1016/j.icarus.2025.116889]
¹State Key Laboratory of Lithospheric and Environmental Coevolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
²College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
³Earth and Planets Laboratory, Carnegie Institution for Science, Washington, DC, USA
Copyright Elsevier

The Moon’s formation time is a key factor for understanding the early evolution of the Earth-Moon system. The lunar magma ocean (LMO) model explains how cumulate mafic materials crystallizing from the LMO form the source of mare basalts (SMB). The SMB with an equilibrated SmNd system is considered to share an identical initial Pb isotope signature (Pb_SMB). Because Pb is volatile while U is refractory, Pb_SMB can provide constraints for the timing of volatile depletion, most likely dating the time of Moon formation by a giant impact. The Pb_SMB is a link between the initial Pb composition of lunar mare basalts and the Moon’s early evolution via a two-stage Pb evolution model that provides a simplified but informative framework. Using four mare basalts with well-constrained ages and initial Pb isotopic compositions, we estimate the Moon’s formation time at  Ma and the SMB formation time at  Ma, which we regard as the preferred solution within the statistical framework of the model. Our modelling strategy also facilitates the dating of mare basalt fragments lacking Zr-bearing minerals using the initial Pb isotopic compositions constrained by U-poor minerals.