Deltaic Deposits at Aeolis Dorsa: Sedimentary Evidence for a Standing Body of Water on the Northern Plains of Mars

Abstract

A fundamental and long-standing question regarding Mars history is whether the flat and low-lying northern plains ever hosted an ocean. The best opportunity to solve this problem is provided by stratigraphic observations of sedimentary deposits onlapping the crustal dichotomy. In particular, the topographic expression of channelized deposits provides a window into past depositional environments in areas where detailed field observations at the outcrop scale are not possible. Here, we use high-resolution imagery and topography to analyze a branching network of inverted channel and channel lobe deposits in the Aeolis Dorsa region of Mars, just north of the dichotomy boundary. Comparison with terrestrial analogs provides insight to the connection between form and process. At Aeolis Dorsa, Observations of stacked, cross-cutting channel bodies and stratal geometries indicate that these landforms represent exhumed distributary channel deposits. We hypothesize that this distributary system was most likely a delta, rather than an alluvial fan or submarine fan, based on the presence of depositional trunk feeder channel bodies, a lack of evidence for past topographic confinement, channel avulsions at similar elevations, and the presence of a strong break in dip slope between topset and foreset beds. Sediment transport calculations using both measured and derived channel geometries indicate a minimum delta deposition time on the order of 400 years. The location of this delta within a thick and widespread clastic wedge abutting the crustal dichotomy boundary, unconfined by any observable craters, suggests a standing body of water potentially 105 km² in extent or greater and is spatially consistent with hypotheses for a northern ocean. This work highlights the potential for reconstructing paleo-environment from increasingly high-resolution remote sensing data using terrestrial scaling relationships.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015