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

Recent work at Aeolis Dorsa, Mars has identified exposure of fluvial sedimentary outcrop deposited early in martian history, likely during the late Hesperian or earlier. Here, we examine a ∼1200 km² exposure of sedimentary outcrop in southeast Aeolis Dorsa. Total thickness of the stratigraphic section exceeds 100 m. We identify eight discrete complexes, each of which is primarily composed of branching channel-filling fluvial deposits 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 models derived from Context Camera (CTX) stereo pair images, we measure the strike and dip of stratal surfaces mapped throughout 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 delta that 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 outcrop is part of a larger set of coastal sedimentary deposits identified in the region.