Abstract:
The occurrence of past habitable conditions in Gale crater is generally associated with lacustrine and alluvial environments present >3 Ga ago, during the Hesperian Period on Mars. However, later-occurring aqueous activity is consistent with superposition relations between some alluvial deposits and bounding materials on the crater walls, preservation of fine-scale morphology on these alluvial deposits, and their superposing crater densities. The alluvial deposits include some not previously considered, and collectively lend confidence to the interpretation that local aqueous activity persisted in Gale crater into the Amazonian, or <2 Ga ago. Our conclusions are generally in accordance with late aqueous activity inferred from geochronology data (Martin et al., 2017, https://doi.org/10.1002/2017JE005445), in addition to late alluvial activity elsewhere. Interpreted late aqueous activity points to possible habitable settings in Gale later than previously recognized. Plain Language Summary Several fan-shaped deposits on the walls and floor of Gale crater formed via deposition of water transported sediment. Overall, the fan deposits are fairly well preserved, and the number of impact craters on their surfaces indicate they are much younger (similar to 2 billion years old or less) relative to the older, more widespread water-related deposits that formed in the crater over 3 billion years ago. The late episode(s) of water-related activity in Gale crater may be associated with late-occurring chemical precipitation within and (or) cementation of older rocks within the crater and suggests that habitable conditions persisted inside the crater later than previously thought.
