HR: 1340h
AN: H33C-1395    [Abstracts]
TI: Identification of a Martian Sedimentary Platform in Margaritifer Sinus, Meridiani Terra, and Arabia
AU: * Howard, A D
EM: ah6p@virginia.edu
AF: University of Virginia, Dept. Environmental Sciences P.O. Box 400123, Charlottesville, VA 22904-4123 United States
AU: Moore, J M
EM: jeff.moore@nasa.gov
AF: NASA Ames Research Center, MS 245-3, Moffett Field, CA 94035 United States
AU: Irwin, R P
EM: irwinr@nasm.si.edu
AF: CEPS, National Air and Space Museum, Smithsonian Institution, Washington, D.C 20013 United States
AU: Craddock, R A
EM: craddockb@si.edu
AF: CEPS, National Air and Space Museum, Smithsonian Institution, Washington, D.C 20013 United States
AB: A fluvial wedge (the Meridiani Bench (MB)) is postulated to have been deposited at elevations of -1200 to -1700 m. in the Margaritifer-Meridiani-Arabia region during the late Noachian/Early Hesperian. The Meridiani Planum layered deposits, including the hematite-rich lacustrine sediments were deposited near the close of deposition on part of this bench. The cratered terrain in Arabia Terra below about -1800 m may have been occupied by an ice-covered ocean during this period. Previously the low relief of the MB was interpreted to have resulted from intensive fluvial erosion rather than as resulting from fluvial mantling. Evidence for the present interpretation includes: 1) A hypsometric transect across this region shows a prominent peak at the elevation of the hypothesized MB; 2) A sequence of paleochannels of Loire Valles indicate initial flow at the level of the MB surface followed by progressive incision and stream captures; 3) With the exception of a few unusual valleys lacking tributary development, the cratered terrain below -1800m lacks the valley networks that are common above this level; 4) Quantification of the topography and crater frequency/degradation of the MB, the superjacent cratered highlands, and the subjacent cratered lowlands reveals that the three regions have statistically distinct morphometric signatures and cratering statistics; 5) A 600 km valley on the cratered lowlands below the MB lacks tributaries and has a profile that climbs over three broad ridges up to 300m high. We interpret this channel to have formed by sub-ice flow, possibly from the site of an impact into the ice. Mawrth Valles and an unnamed shallow outflow channel near 37N and 10E may also have originated by sub-ice flow. In summary, we suggest that a fluvial depositional bench (MB) was deposited during the late Noachian. The bench was subsequently fluvially incised, but this was followed by local deposition of the layered deposits of Meridiani Planum, including the hematite-rich lacustrine sediments at the Opportunity MER rover site. The lateral confinement for deposition of the fluvial bench and the later Meridiani layered deposits may have been an ice-covered lake/ocean (or possibly a piedmont glacial complex) occupying the low-lying cratered terrain of Arabia Terra.
DE: 0776 Glaciology (1621, 1827, 1863)
DE: 1625 Geomorphology and weathering (0790, 1824, 1825, 1826, 1886)
DE: 1827 Glaciology (0736, 0776, 1863)
DE: 5415 Erosion and weathering
DE: 5419 Hydrology and fluvial processes
SC: Hydrology [H]
MN: Fall Meeting 2005