SOURCE CHARACTERISTICS, CHEMICAL WEATHERING, AND LITHIFICATION OF THE STIMSON SANDSTONE AND LESSONS FOR THE MARTIAN SEDIMENTARY RECORD
The source rocks for the Stimson sandstone compositionally approximate average Mars and may be very similar to the sources for the modern Bagnold dunes. Potential mineralogical differences between Stimson and Bagnold sources exist, particularly in different modeled pyroxene assemblages, but the angular resolution of CheMin is not sufficient to definitely establish those differences. The most dramatic differences between the Bagnold sand and the Stimson sandstone are likely related to lithification processes, and include a significant decrease in olivine (~17 wt% to undetectable) and amorphous material, and an ~12 wt% increase in crystalline iron oxides in the Stimson relative to Bagnold, which has been interpreted as evidence for olivine dissolution and iron oxide cementation. More subtle geochemical differences within the Stimson itself reveal a chemical weathering trend, where some Stimson samples show less anorthositic plagioclase, more secondary minerals, and a shift to more Mg-rich amorphous material. The Stimson provides a unique dataset for tracing geochemical contributions from source rocks, weathering processes, and lithification of a sedimentary formation on Mars.