Multiple Episodes of Fluvial Activity in the Gale Crater Region, Mars.

Abstract:

The geomorphic record provides compelling evidence for an early Mars that was warm and wet enough, at least periodically, to sustain liquid water on its surface. For example, a number of fluvially deposited fans have been identified in the region around Gale crater. Several previous studies have interpreted these as deltas that formed either in a northern lowlands ocean or in paleolakes along the martian dichotomy. We build on this previous work by examining the relationship between these fans and their upland source valleys. Immediately upslope from the fans are deeply incised, low ordered canyons (Type 1s) similar to the alcoves associated with Hesperian-aged terraced fans. Further upstream are branched, highly ordered, quasi-dendritic valleys (Type 2s) typical of Late Noachian valley networks. We utilize high resolution digital terrain models derived from CTX images to compare fan volume with the eroded volume of the upslope valleys. Preliminary results indicate a possible correlation between fan volumes and the Type 1 valley eroded volumes . Crater count statistics indicate a much later formation date for the fans and Type 1 valleys than the Type 2 valleys. We interpret the two valley types as forming at different times in martian geologic history, with only the later stage episode (Type 1 valleys) resulting in formation of the observed fans. This may indicate a change from subaqueous to subaerial deposition or may be evidence of a shift in erosional process on early Mars from dominantly chemical (resulting in abundant fines that did not accumulate in fan deposits) to frost shattering (resulting in gravels that built the fans).