THE SEDIMENTOLOGY AND GEOMORPHOLOGY OF GARU CRATER: IMPLICATIONS AND CONSTRAINTS ON THE TIMING OF LARGE LATE-STAGE LAKES IN THE GALE CRATER REGION (Invited Presentation)

Paleolake deposits offer a valuable record for constraining ancient Martian environments and climate. Orbital data combined with the Curiosity rover’s in-situ investigation of Gale crater provides extensive evidence for a long and complex history of lake level fall and rise. However, the exact timing, source of water, and climate under which these large lakes persisted are still unclear. Here, we investigated the geomorphology, sedimentology, and mineralogy of Garu crater, a 30 km wide crater ~150 km to the east of Gale crater that impacted at ~3.5 Ga (early to mid-Hesperian). Garu hosts several alluvial fans and deltas, including a large NE-prograding Gilbert-type delta deposit that emanates from an incised bedrock canyon. Based on detailed analysis of this deposit, we infer it records steadily rising water levels over 10⁴ to 10⁵ years. This aggradational stage is followed by a period of rapid desiccation, which is evidenced by a lack of post-depositional incision into the delta. Numerical modeling suggests that the highest mapped lake stand in Garu would have been coeval with one of the largest late-stage lakes in Gale, which also resulted in the deposition of a large delta followed by rapid drying. Based on a coupled surface-groundwater model and paleo-flow analysis, both lake stands would have been supported by groundwater, with some surface runoff, under a semiarid climate. Gale does have evidence for a second period of lakes, but in Garu crater, we find no geomorphic evidence of reactivation after dessication. It is possible that during this second (and last) phase of lakes in Gale, that the low elevation of its floor allowed Gale to tap into a deeper groundwater table than Garu or that Gale received more local surface runoff from snow accumulation around its rim and Mount Sharp. Unlike Gale crater, there is no spectral evidence for salts in Garu, which suggests that lacustrine sedimentation in Garu occurred after the deposition and erosion of the sulfate layers within Gale’s central sedimentary mound. The hydro-geomorphologic record of Garu crater suggests that the climatic conditions that allowed for late Hesperian lakes in Gale crater were not isolated, and other nearby craters and basins may have responded to similar forcings from a regionally integrated hydrologic system.