DPS 2001 meeting, November 2001
Session 48. Mars Surface
Oral, Chairs: N. Barlow, J. Bell III, Friday, November 30, 2001, 4:30-6:40pm, Regency E

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[48.08] Geomorphic Analysis of the Isidis Region: Implications for Noachian Processes and Environments

J.M. Moore (NASA Ames), A.D. Howard (UVa), P.M. Schenk (LPI)

The southern rim of the Isidis Basin has been strongly modified by erosional processes, including weathering, mass wasting, fluvial incision, and transport and deposition of sediment. Most of this erosion occurred during the Noachian, but a late stage of fluvial incision probably extended into the Hesperian. We conclude that snowmelt runoff rather than groundwater sapping best explain discharge for even late stage dissection. Convexity of the lower portions of valley systems draining northward into the Isidis Basin, and the relative lack of fluvial dissection at low elevations of the Isidis inner rim, are most consistent with early deep oceans in the northern lowlands. The step-like profiles of these valleys also suggests fluvial grading to a series of ocean levels ranging from 2500m to possibly as high as +200m elevation. By this, admittedly controversial, interpretation Mars had a very large initial water inventory with deep oceans in the northern lowlands. If so, water levels dropped in a punctuated manner throughout the Noachian and into the Hesperian. To account for the extensive fluvial degradation of the surrounding uplands, the climate would have had to be warm enough to promote an active hydrological cycle including evaporation from the oceans, precipitation and runoff. If the deep Noachian ocean hypothesis is incorrect, then some process, or suite of processes, modified the Isidis region mimicking the presence of a deep ocean along its northern periphery.


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