Date of Award
Master of Science
Lindsay J McHenry
John L Isbell, Barry L Cameron
CIA, Mars, Paleolakes, Remote Sensing, Tecopa, VNIR
This study focuses on two stratigraphic sections from the Tecopa paleolake and samples from the modern Tecopa and Amargosa River basins as a terrestrial analogue to Martian paleolakes. Previous work shows that the later stages of Pleistocene Lake Tecopa were highly alkaline and saline due to evaporation, which led to the formation of authigenic lacustrine minerals such as zeolites, clays, and precipitates that are potentially similar to Martian paleolakes. Paleolakes can provide information on past aqueous processes, such as the changes in the hydrologic cycle that a particular area experienced over the lifespan of a lake on Earth or Mars. While morphological evidence for paleolakes on Mars is widespread, direct orbital spectroscopic evidence for lacustrine minerals is sparse. Whether this is due to the lack of such deposits, or to limitations in our ability to detect them, is unclear. This study used the overall grain sizes, mineral assemblages, spectral features, and the major oxides of SiO2, Al2O3, K2O, Fe2O3, CaO, Na2O, MgO, TiO2, P2O5 (weight %) and trace elements Zr, Sr, and Ba (ppm) to determine if the surface crusts that developed on the paleolake deposits can mask the true remote sensing signal of the underlying strata. A total of 48 samples, including pairs of samples (surface and subsurface) from two stratigraphic columns, were collected for laboratory X-Ray Fluorescence (XRF), X-Ray Diffraction (XRD), Visible and Near-Infrared Reflectance (VNIR) spectroscopy, and grain size analysis. Major and trace element concentrations using XRF were used for chemical weathering calculations and examined for geochemical differences between the paired samples. XRD data were used to qualitatively identify differences in mineral assemblages between the surface crust and underlying strata. VNIR spectra of surface samples, together with the XRD data, were used to determine which minerals might be identifiable using VNIR remote sensing. The VNIR spectra for the surface was compared to underlying strata to determine changes in the signal and the possible effect it might have on the interpretation. Section 1, located near Greenwater Valley, has smectite, calcite, analcime, K-feldspar, searlesite, and illite. K-feldspar and analcime typically form under more saline-alkaline conditions, closer to the lake basin. Section 1 is dominated by mudstone, siltstone, and white colored volcanic ash beds. Section 2, located near Tecopa Peak, is dominated by mudstone, siltstone, sandstone, and white to green colored volcanic ash beds. Section 2 has phillipsite and clinoptilolite, which is consistent with intermediate saline-alkaline conditions. Some individual sample pairs had significantly different mineral assemblages and elemental abundances compared to each other, including the presence or absence of carbonate minerals, or differences in Al2O3, TiO2, and Zr concentrations, potentially indicating different source lithologies. Such differences could be attributed to sheet flow. Differences in mineral assemblage between surface and underlying strata can change the VNIR signal, especially if these include typical paleolake minerals such as zeolites, clay minerals, and carbonates. This is especially important when using remote sensing to map geomorphic features and minerals on Mars to better understand its geological and climatic history. Ground truthing orbital data with in-situ rover data is thus critical from current and future missions.
Carman, Jason Benjamin, "Analyzing Weathering Patterns in Modern and Paleolake Deposits of Tecopa, California: Implications for the Detection of Paleolakes on Mars" (2021). Theses and Dissertations. 2986.