291-9 Carbonates in ancient Martian weathering profiles

Session: Mineralogy in the Solar System

Presenting Author:

William Farrand

Authors:

Farrand, William H.¹, Horgan, Briony Heather Noelle², Rice, James W³, Broz, Adrian P⁴, Klidaras, Athanasios⁵, Amador-French, Elena S⁶

(1) Space Science Institute, Boulder, CO, USA, (2) Purdue University, West Lafayette, IN, , (3) School of Earth and Space Sciences, Arizona State University, Tempe, AZ, USA, (4) Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN, USA, (5) Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN, USA, (6) Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA,

Abstract:

Recent studies with orbital and rover-based investigations have detected the presence of carbonate minerals in a variety of locations and geologic settings across the surface of Mars. A set of outcrops of great geologic interest in the Noachian-aged terrains of Mars are the weathering profiles or “clay stratigraphies” where Fe/Mg smectites are overlain by Al phyllosilicate minerals. Until recently, there has been no definitive detection of carbonates in association with these outcrops. The finding of siderite on the slopes of Mt. Sharp in Gale crater by the Curiosity rover, where there has been no evidence of its presence from orbital spectroscopy data suggests that spectral absorptions of carbonates near 2.3 and 2.5 microns could be masked by other phases with stronger absorptions. Bultel et al. (2019) made use of the 3 to 4 micron region in CRISM data to map out the stronger carbonate absorption near 4 microns. Those authors reported on the suspected presence of carbonates in the Mawrth Vallis region and also in the Eridania Basin and in NE Noachis Terra. Without observing additional confirming spectral features, these detections can be viewed as tentative. However, through the use of feature analysis/target transformation (FA/TT) technique, used to good effect with CRISM data by Thomas et al (2017) and Amador et al (2018) subpixel exposures of carbonates can be found with higher confidence. Here we report on the presence of carbonates, nominally siderite, in between the Fe-Mg smectite and upper Al phyllosilicate layers in Mawrth Vallis and other clay stratigraphies where carbonates occur in association with Fe-Mg smectite and Al phyllosilicate minerals. Their presence is strongly indicated by strong FA/TT matches as well as by spectral shape in the 3 to 4 micron region. We are using the presence of carbonates in the middle of these clay stratigraphies to try to distinguish between origin scenarios for the stratigraphies, notably whether they represent ancient paleosol sequences or whether they result from lacustrine deposition or groundwater diagenesis.

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