Geological Mapping in Northern Meridiani Planum: Insights into Flooding in Paleo-Dune Fields

Abstract:

Exposed strata north of Meridiani Planum, where the rover Opportunity explored, exhibit a range of complex morphologies that remain poorly understood. Formerly mapped as the ‘Etched Unit’, this terrain preserves diverse surface features and provides a mechanism for studying ancient depositional processes. Combining this work with the context provided by Opportunity produces insights into the interactions between fluvial and aeolian processes and how these might have evolved over time.

The objective of this work was to deduce the mechanisms behind the complex surface textures and therefore gain an understanding of the surface conditions on early Mars. This was completed by using CTX and HiRISE images to create a > 500,000 km² map of geological units, paleo-dune migration directions and ancient fluvial channels. Our results show that the Etched Unit displays morphological evidence for large-scale paleo-dune fields across the inter-crater plains. Despite this, surface textures on the Etched Unit vary and are interpreted to be a consequence of fluvial input based on observations of valleys, inverted channel deposits, polygonal fracturing, and tonal differences and patterns across the surface. The interpreted flow directions from the channels and the orientation of the exposure of the units suggest that water once flowed from heavily cratered highlands down into a large inter-crater basin, flooding the barchan dune fields. The observed stratigraphy suggests that the lowest three subunits, which compose most of the basin area, record a large-scale, long term drying event, with interdune flooding decreasing over time.