GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 295-6
Presentation Time: 2:50 PM


FOX, Valerie1, BENNETT, Kristen2, STACK, Kathryn M.3, DEHOUCK, E.4, THOMPSON, Lucy M.5, RAMPE, Elizabeth B.6, HARDGROVE, Craig J.7, FEDO, Christopher M.8, EHLMANN, Bethany L.9, GROTZINGER, John P.10, GUPTA, Sanjeev11, ARVIDSON, Raymond12 and CZARNECKI, Sean M.7, (1)Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, (2)USGS Astrogeology Center, Flagstaff, AZ 86001, (3)Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, (4)LGL-TPE, Université de Lyon, Lyon, France, (5)University of New Brunswick, Fredericton, NB E3B 5A3, Canada, (6)NASA Johnson Space Center, 2101 NASA Pkwy, Houston, TX 77058, (7)School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287, (8)Department of Earth & Planetary Sciences, University of Tennessee, 1621 Cumberland Avenue, 602 Strong Hall, Knoxville, TN 37996-1526, (9)Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, (10)Geological and Planetary Sciences, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125, (11)Earth Science and Engineering, Imperial College London, South Kensington Campus, London, SW7 2AZ, United Kingdom, (12)Earth and Planetary Sciences, Washington University IN St. Louis, 1 Brookings Drive, St. Louis, MO 63130

The Curiosity rover science team has been exploring the Glen Torridon region on Mt Sharp, where CRISM detected Fe-Al smectites, since Jan. 2019. This area is just south of the hematite-bearing Vera Rubin ridge (VRR) and is overlain by thick sulfate-bearing strata. Observations thus far show the surface is covered with locally sourced cobbles, with only sparse exposures of intact bedrock. Where this bedrock outcrops, we have observed finely laminated mudstones, which may exhibit alternating resistant and recessive intervals, and trough cross-stratified very fine sandstones. Facies observed in the Glen Torridon region are consistent with facies observed previously in the Murray formation lacustrine sediments and no obvious unconformable relationships were observed within the sequence between VRR and Glen Torridon, suggesting that rocks located at equivalent elevations on VRR and within Glen Torridon are also stratigraphically equivalent. Erosionally-resistant knobs of cross-laminated sandstone overlie, or are interbedded with, the laminated mudstone facies, and cap some of the characteristic linear ridges that occur throughout the region.

MSL data of elemental abundances indicate Glen Torridon targets are compositionally in family with other Murray formation members. Samples generally fall into two compositional groups, perhaps reflecting different diagentic paths or source materials: the loose clasts have relatively elevated K values, and intact bedrock blocks have relatively higher Mg values, although some laminations have intermediate compositions. All targets have CIA values suggestive of open system weathering of the protolith. Results from the DAN instrument show increased hydrogen signals associated with regolith surfaces compared to intact bedrock.

Initial mineralogical results indicate that drill targets, located within one of the CRISM smectite “hotspots” close the Vera Rubin Ridge are the most clay-mineral rich samples to date (~30% phyllosilicate), although nearly every other sample obtained by Curiosity (n= 17) has contained clay mineralogy, many exceeding 10-15%. In situ exploration shows that in addition to mineral abundance, erosional properties of clay-bearing bedrock contributes to explaining the spatial patterns observed in the orbital smectite signals in Gale Crater.