HR: 16:45h
AN: P24A-04    [Abstracts]
TI: THEMIS and MOLA Provide 3-D Stratigraphy in the Terra Meridiani Region of Mars
AU: * Phillips, R J
EM: phillips@wustite.wustl.edu
AF: Washington University, Dept. of Earth and Planetary Sciences, CB 1169, St. Louis, MO 63130 United States
AU: Hynek, B M
EM: brian.hynek@lasp.colorado.edu
AF: University of Colorado, Laboratory for Atmospheric and Space Physics, 392 UCB, Boulder, CO 80309 United States
AB: The layered rocks observed in the vicinity of the Mars Exploration Rover (MER) Opportunity landing site are part of a vast stratigraphic complex exposed over ~3×10⁵km², encompassing 20° of longitude [Hynek, 2004, Nature]. We have used elevations derived from geoid- and orbit-corrected individual MOLA laser shots to determine the three-dimensional disposition of individual stratigraphic horizons exposed within the complex and as mapped with 100 m/pix THEMIS thermal inertia images (high inertia areas correspond to ``etched terrain''). The Opportunity landing site is near the NW edge of an elongated NE-trending topographic bench that contains the hematite-rich plains unit and is about 500 km wide. Mappable stratigraphic exposures occur mostly in two groups, one near the base of the upward slope (to the Arabia Highlands) on the SE side of the bench and one near the top of the downward slope (to the Northern Lowlands) on the NW side of the bench. The total thickness of the stratigraphic complex is ~1000 m. We fit least-squares planes to individual horizons and tested for quality of fit. Our main interest is the orientations of the planes, so the probability density function of the tangent of the dip azimuth was used as a discriminator for solution acceptance (dip azimuth error range < 30°). Of the 22 horizons sampled, 14 had acceptable solutions. The 14 individual stratigraphic horizons are spatially extensive, with maximum MOLA sampling separations in a given horizon being as much as 200 km (mean for all horizons is 80 km). This implies that the depositional environment for these units was coherent over a scale of typically 100 km. Of the 14 acceptable horizons, 10 have shallow dip azimuths in the direction N to NW, consistent with the long-wavelength (regional) slope, which itself is the result of the global pole-to-pole slope plus Noachian-aged Tharsis-induced membrane deformation [Phillips et al., 2001, Science]. The stratigraphic complex both overlies and is dissected by late Noachian N-NW trending valley networks, suggesting that deposition and valley emplacement were coeval in the late Noachian. We are exploring how various models proposed to explain the origin of the local stratigraphy at the MER Opportunity site fit within the context of this kilometer-thick, coherent, areally extensive, tilted (generally N-NW), late Noachian stratigraphic complex mapped with THEMIS and MOLA data.
DE: 5419 Hydrology and fluvial processes
DE: 5464 Remote sensing
DE: 5470 Surface materials and properties
DE: 6225 Mars
SC: Planetary Sciences [P]
MN: Fall Meeting 2005