GSA Annual Meeting in Denver, Colorado, USA - 2016

Paper No. 20-10
Presentation Time: 10:45 AM


HEYDARI, Ezat1, STACK, Kathryn M.2, CALEF, Fred3, LEWIS, Kevin4, PARKER, Timothy2, ROWLAND, Scott K.5, FAIREN, Alberto G.6 and HALLET, Bernard7, (1)Department of Physics, Atmospheric Sciences, and Geoscience, Jackson State University, P.O. Box 17660, 1400 Lynch Street, Jackson, MS 39217, (2)Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, (3)Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, (4)Department of Earth and Planetary Sciences, The Johns Hopkins University, Baltimore, MD 21210, (5)Department of Geology & Geophysics, University of Hawai‘i at Mānoa, Honolulu, HI 96822, (6)Department of Astronomy, Cornell University, Ithaca, NY 14853, (7)Earth and Space Sciences and Quaternary Research Center, University of Washington, Seattle, WA 98195,

The Curiosity Rover has encountered two lacustrine rock units at Gale crater, Mars. The Striated formation (~1000 m thick) occurs in the central part of the Rover's traverse. It transitions into the Murray formation (~300 m thick) near the margin of Mt. Sharp. Both rock units were deposited during Early Mars, about 4.2 to 3.6 billion years ago.

The Striated formation strikes N65ºE with a depositional dip of 10 - 20ºSE. It is composed of rhythmic layers, each 1 - 4 m thick. Layers fine upward with thick-bedded to massive conglomerate at the base that grades upward to laminated, fine grained sandstone at the top. The formation shows slump folds, soft sediment deformation, and cross-bedding.

The Murray formation is a sandy mudstone with lenses of cross-bedded sandstones. It is horizontally layered and contains abundant irregularly-shaped nodules that are rich in calcium and magnesium sulfate. It is monotonously laminated but laminae are not continuous and show truncation and scoured surfaces. Mud cracks, ripple marks, rip-up clasts, and other waves or current induced features are absent in the mudstones of the Murray formation.

The observed sedimentological characteristics indicate that the Striated and the Murray formations represent a subaqueous fan in a large lake, estimated to be 1 - 3 km deep. Fining-upward layers of the Striated formation are coarse-grained turbidites deposited on the proximal part of the fan by sediments delivered by floods through the northern rim of the crater. The Murray formation formed on the distal part of the fan and extended into the center of the lake in waters so deep that bottom sediments were unaffected by wave actions, lake-level fluctuations, and storm activities. Discontinuous laminations suggest that laminations formed by traction sedimentation associated with waving turbidity flows.

The rhythmic nature of layering indicates a regulated flow of flood waters into the lake, possibly controlled by changes in climate. The most likely forcing mechanism was variations in obliquity. Floods occurred during hothouse periods when the Martian climate was warmer than Present. The lake became saline at least to gypsum saturation during subsequent cold and/or dry climate of icehouse intervals and precipitated sulfate-rich nodules in the Murray formation.