HR: 1340h
AN: P23A-1092    [Abstracts]
TI: Evidence of a Paleolake in the central Valles Marineris
AU: * Harrison, K P
EM: harrison@boulder.swri.edu
AF: Southwest Research Institute, 1040 Walnut St, Ste 300, Boulder, CO 80302, United States
AB: The Valles Marineris (VM) canyon system of Mars is closely related to large flooding channels, some of which emerge full born from chaotic terrain in canyon floors. Coprates Chasma, one of the largest VM canyons, is connected at its eastern end to chaotic terrain Capri Chasma. Despite the likely large volumes of groundwater that discharged from Capri Chasma [1], no evidence of related fluvial activity in Coprates Chasma has thus far been reported. We present an analysis of the regional topography which, together with photogeologic interpretation of available imagery, suggests that ponding due to late-stage discharge of water from Capri Chasma chaotic terrain produced a shallow lake spanning parts of Melas, Coprates, Capri and Eos Chasmata (MCCE). Overflow of this lake at its eastern end resulted in delivery of water to downstream chaos regions and outflow channels. Our ponding hypothesis is motivated primarily by the identification of scarp and terrace features which, despite a lateral spread of about 1500 km, have similar elevations. Furthermore, these elevations correspond to the maximum ponding elevation of the region (-3562 m). Mean lake depth is 842 m. Simulated ponding in the MCCE system yields an overflow point at its eastern extremity, in Eos Chasma. The neighborhood of this overflow point contains clear indicators of fluvial erosion in a consistent east-west orientation (Figure 4). Specifically, scour marks suggest an eastward convergence of flow lines. Downstream of the overflow point, the direction set by the scour marks is paved by a smooth deposit leading directly to a scoured channel entering the next major region of chaotic terrain, Aurorae Chaos. The smooth deposit is likely made up of remnants of the interior deposit breached by the MCCE paleolake overflow. The next region of chaotic terrain downstream of Aurorae Chasma is Hydraotes Chaos, which lies in a relatively deep depression and would be the next significant ponding location for flow originating in the MCCE region. Crucially, it is also the only other Chryse Planitia chaos to exhibit terraces, which have been attributed a lacustrine origin by other authors [2]. References: [1] Carr M. H. (1979) JGR, 84, 2995-3007. [2] Ori G. G. and Mosangini C. (1998) JGR, 103, 22713-22724.
DE: 1808 Dams
DE: 1821 Floods
DE: 1830 Groundwater/surface water interaction
DE: 5419 Hydrology and fluvial processes
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting