P038-01
New HiRISE Observations of Gale Crater Rim Surfaces – Evidence for Glacial Processes

Thursday, 10 December 2020: 07:00
Virtual
Horton E Newsom1, Louis A Scuderi2, Zachary Gallegos3, Megan Hoffman4, Joshua Williams2, Livio L Tornabene5 and Roger C Wiens6, (1)University of New Mexico Main Campus, Albuquerque, NM, United States, (2)University of New Mexico, Albuquerque, NM, United States, (3)University of New Mexico, Institute of Meteoritics, Albuquerque, United States, (4)University of New Mexico Main Campus, Earth and Planetary Sciences, Albuquerque, United States, (5)University of Western Ontario, London, ON, Canada, (6)Space Science and Applications, Los Alamos, NM, United States
Abstract:
New HiRISE images of the Gale crater, especially with stereo coverage allowing quantitative analysis, suggest a long history of multiple geomorphic processes that included an early lacustrine sedimentation event with a recent glacial interval followed by a very late fluvial episode. The crater rim watershed surface standing as much as 1300 m above the crater floor is bounded by ridges next to the large scarp into the crater, and consists of weakly interconnected basins, separated by ramps with multiple parallel channels and/or inverted channel deposits leading to the crater floor in only a few locations. Some linear inverted deposits seen in HiRISE images have glacial esker characteristics, including deposits that cut across topography. Erosion of the watershed surface produced a mottled scoured appearance, except for the plucked downhill surfaces of possible roche moutonnée features. The mottled scoured terrain surprisingly includes the surface of several alluvial fans on the crater rim and nearby uplands. Valleys, sometimes U-shaped, penetrate the rim wall ridge but do not show incised fluvial channels. There are elevated saddles where the valleys cross the ridge crest, often only a few tens of meters above the rim basins. Many of the valleys therefore appear to have no access to any fluvial supply from the main watershed. For example, one of the breaches through the crater rim wall, with no incised fluvial channel, is separated from the main watershed on the rim with a high point on the saddle ~ 20 m above the watershed channel area. There is also a lack of highly integrated fluvial channel systems on the crater rim, especially for channels leading to the Peace Vallis alluvial fan. There is evidence, in some areas, for late incision in the crater rim by V-shaped sapping channels that leave hanging earlier parallel shallow u-shaped channels, suggesting a change in geomorphic process. A late glacial epoch in Gale would have likely post-dated the early fluvial episode that led to lacustrine sedimentation in Gale observed by Curiosity, based on the scoured surfaces of early fan-deltas. The glacial epoch was limited in intensity or duration, as earlier fluvial channels were not completely eroded away in the watershed.
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