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Geochemical variation in the Stimson formation of Gale crater: Provenance, mineral sorting, and a comparison with modern Martian dunes

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posted on 12.05.2020, 13:36 by CC Bedford, SP Schwenzer, JC Bridges, S Banham, RC Wiens, O Gasnault, EB Rampe, J Frydenvang, PJ Gasda

The Mars Science Laboratory Curiosity rover has encountered both ancient lithified and modern active aeolian dune deposits within Gale crater, providing an opportunity to study how aeolian processes have changed during Gale crater's geological history. This study uses data from the Chemistry and Camera (ChemCam) and Chemistry and Mineralogy (CheMin) instrument suites onboard Curiosity to; (1) constrain the diagenetic processes that lithified and altered the ancient aeolian Stimson formation, (2) investigate whether the geochemical signature in the Stimson formation is consistent with the aeolian mafic-felsic mineral sorting trend identified in the modern Bagnold dune fields in Gale crater, and (3) discuss the provenance of the Stimson sediments, comparing it to those identified in the modern dune and ancient river and lake deposits also analyzed along Curiosity's traverse.

The ancient Stimson dune deposits that stratigraphically overlie the Gale fluvio-lacustrine units were analyzed in two locations; the Emerson and the Naukluft plateaus. ChemCam data show that the Stimson formation has subtle variations in MgO, Al2O3, Na2O, and K2O between the two localities. An agglomerative cluster analysis of the constrained Stimson dataset reveals five clusters, four of which relate to different proportions of mafic and felsic minerals analyzed by ChemCam. In general, the cluster analysis shows that the Emerson plateau has a greater proportion of mafic minerals and fewer coarse, felsic grains relative to the Naukluft plateau. This variation in mafic and felsic minerals between localities suggests a southwest to northeast net sediment transport direction due to aeolian mineral sorting dynamics preferentially transporting mafic minerals that are easier to saltate than the elongate, often coarser, felsic minerals. This derived transport direction for the Stimson formation supports that determined by sedimentological evidence and is opposite to that previously determined for the active Bagnold dunes inferring a change in the wind regime with time. An opposite sediment transport direction between the ancient and modern dunes in Gale crater further supports geochemical and mineralogical evidence that suggests different basaltic source regions. Compositionally, the bulk Stimson formation is most similar to the subalkaline basalt source region that is inferred to be the dominant sediment source of the fluvio-lacustrine Bradbury group. This is likely the result of the Stimson formation and basaltic Bradbury group sediments sharing a similar local basaltic source region such as the rim and walls of Gale crater.

Funding

CCB was supported through the STFC Open 2015 DTP doctoral training grant (ST/N50421X/1) to the Open University and now acknowledges support from the LPI. LPI Contribution No. 2244. LPI is operated by USRA under a cooperative agreement with the Science Mission Directorate of the National Aeronautics and Space Administration (NASA). JCB and SPS were supported through a UKSA grant (ST/P002110/1). JF acknowledges the support from the Carlsberg Foundation. The MSL engineering, ChemCam, CheMin and science teams are gratefully acknowledged for the acquisition of the data used in this paper. Support for this work in the US is provided by the NASA Mars Exploration Program and in France by CNES.

History

Citation

Icarus Volume 341, 1 May 2020, 113622

Version

VoR (Version of Record)

Published in

Icarus

Volume

341

Pagination

113622 - 113622

Publisher

Elsevier BV

issn

0019-1035

Acceptance date

15/01/2020

Copyright date

2020

Available date

04/01/2020

Publisher version

https://www.sciencedirect.com/science/article/pii/S0019103519307535

Language

en

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