GSA Annual Meeting in Indianapolis, Indiana, USA - 2018

Paper No. 138-8
Presentation Time: 3:30 PM


HOWARD, Alan D., Department of Environmental Sciences, University of Virginia, PO Box 400123, Charlottesville, VA 22904-4123, PURDY, Sharon Wilson, Center for Earth and Planetary Studies, National Air and Space Museum, Smithsonian Institution, Independence Ave at 6th St, SW, Washington, DC 20560, MORGAN, Alexander M., Center for Earth and Planetary Studies, National Air and Space Museum, Smithsonian Institution, 600 Independence Ave SW, Washington, DC 20560 and MOORE, Jeffrey M., NASA Ames Research Center, Space Science Division, MS-245-3, Moffett Field, CA 95129

Discontinuous exposures of layered strata are abundant on the northern slopes of Hellas Basin. Many of these exposures involve light-toned layering that can reach up to 2 km in aggregate thickness as at Terby crater. The origin of this layering is uncertain; lacustrine, airfall, and deltaic origins have been suggested. Exposures of light-toned deposits often form resistant scarps on crater floors and are locally exposed in eroded convolute patterns on high-relief terrain. Diagnostic exposures of light-toned deposits occur south of Nako crater at 30.7S and 82.9E indicate that deposition occurred as a draping mantle over pre-existing terrain with local relief of at least 800 m. The mantle was deposited on a fluvially-eroded landscape and deposition may have been contemporaneous with fluvial activity. The light-toned deposit was subsequently covered with darker deposits. Subsequent aeolian differential deflation has resulted in intricate exposures of the light-toned deposits. Light-toned deposits are common in the nearby craters Batson, Nako and Majuro and their outcrops over ~4 km of relief suggest a widespread event of airfall deposition in the late Noachian or Hesperian, which might have been sourced from explosive volcanic eruption, a large crater impact, or an epoch of intense dust storms. Such light-toned mantles are important regional stratigraphic markers.