CONGLOMERATES IN CONTEXT: NEW OBSERVATIONS OF MARTIAN FLUVIAL DEPOSITS IN THE FOOTHILLS OF MOUNT SHARP, GALE CRATER

The sedimentary rocks of Gale crater are rich with signatures of fluvial transport and aqueous deposition. The Mars Science Laboratory (MSL) Curiosity rover has encountered isolated conglomerate outcrops at several locations along its traverse of the plains north of Mount Sharp (Bradbury Rise), and in the foothills of Mount Sharp. Previous investigations into the depositional origins of the Bradbury Rise deposits found moderately rounded, moderately sorted fine sand to pebble-sized grains indicative of fluvial transport episodes of moderate flow.

This study provides a new analysis of coarse sedimentary deposits observed by Curiosity within the foothills of Mount Sharp between Amargosa Valley and Marias Pass (Sols ~740-970). These outcrops have rounded, moderately sorted clasts, with rare occurrences of possibly imbricated pebbles. Using the grain size distribution of clasts in six outcrops between Amargosa Valley and Marias Pass, we calculate the hydraulic parameters of the fluvial system required for transport. Flow depths (0.03-1 m) and velocities (0.2-0.85 m/s) for the required systems at the foothills of Mount Sharp are consistent with those required for sediment transport on Bradbury Rise.

Observations of facies variations in the conglomerates throughout the foothills of Mount Sharp allow us to investigate these deposits in the context of previously constrained fluvial systems in Gale. Detailed orbital mapping of the foothills of Mount Sharp, accompanied by local cross-sections, provides a broader stratigraphic context for coarse-grained deposits in this area and helps to constraint the relative timing of fluvial deposition in Gale crater.