Deltaic deposits indicative of a paleo-coastline at Aeolis Dorsa, Mars

Abstract Recent work at Aeolis Dorsa, Mars has identified exposure of fluvialsedimentary outcropdeposited early in martian history, likely during the late Hesperianor earlier. Here, we examine a ∼1200 km 2 exposure of sedimentary outcropin southeast Aeolis Dorsa. Total thickness of the stratigraphic sectionexceeds 100 m. We identify eight discrete complexes, each of which is primarily composed of branching channel-filling fluvialdeposits associated with a primary feeder, or trunk, channel deposit. Relative ages for the branching complexes are derived from observed stacking relationships, and there is a pattern of eastward younging. Using digital elevation modelsderived from Context Camera (CTX) stereo pair images, we measure the strikeand dipof stratal surfaces mappedthroughout the study area. There is a trend of increasing dip magnitude from north to south. The branching complexes are interpreted as exhumed remnants of the lobes of an aggrading river deltathat shifted its depo-center from west to east over time. The increasing dip magnitude of stratal surfaces towards the south records topset-foreset transitions, an architectural feature associated with river deltas, and indicates paleo-transport was locally southward. The interpreted deltaic lobes indicate that Aeolis Dorsa was a coastal region not presently bound by a modern crater basin, and the studied outcropis part of a larger set of coastal sedimentary deposits identified in the region.