POSSIBLE REASONS FOR LIMITED DETECTIONS OF ZEOLITES IN CLOSED BASIN PALEOLAKES ON MARS: LESSONS LEARNED FROM LAKE TECOPA, CALIFORNIA

Zeolites are among the most common authigenic silicate minerals in sedimentary rocks on Earth and are particularly abundant in deposits of saline, alkaline nonmarine environments. Zeolites have also been detected on the surface of Mars using orbital data, though these detections are not widespread, and most studies conclude that they do not provide evidence for in situ aqueous alteration in open and closed basin paleolakes. One of the reasons for limited detection is the difficulty of confirming zeolite detections due to spectral similarity with polyhydrated sulfate spectra.

Here, we examine other possible reasons that could influence the limited detections of zeolites in paleolake environments using orbital remote sensing data using a “textbook” terrestrial example, Paleolake Tecopa, California. We used spaceborne hyperspectral Hyperion and multispectral ASTER data to identify zeolites after a detailed X-ray Diffraction (XRD) and visible-near infrared and shortwave infrared (VNIR -SWIR) spectral analysis of collected samples containing zeolites and/or other associated minerals. We used four of the most common spectral mapping methods: 1) band ratios, 2) minimum noise fraction (MNF), 3) spectral angle mapper (SAM), and 4) linear spectral unmixing (LSU). We identified zeolite-bearing tuff in an abandoned open mine in the study area using orbital spectral remote sensing methods, however it is difficult to identify zeolites in most of the zeolite-bearing paleolake beds using orbital spectral data alone. Field sampling shows that the zeolite-bearing beds are often buried by other beds, mixed with other materials either at the time of deposition or due to physical weathering, or that the areas of exposed beds are mostly smaller than the ground resolution cell (GRC) of the satellite.

Therefore, here we argue that the paucity of detected zeolites on Mars does not preclude their wider presence, either beneath other materials, surface dust, or mixed with more spectrally dominant phases. We therefore emphasize the importance of integrated mapping approaches (e.g. spatial multicriteria decision analysis) to infer the presence of zeolite minerals using the spatial and stratigraphic patterns of other associated minerals along with the morphological evidence of paleolake environments on Mars using orbital data.