GEOMORPHOLOGY AND RELATIVE AGES OF INVERTED CHANNEL DEPOSITS IN JEZERO CRATER’S WESTERN DELTA

The Mars 2020 Perseverance rover mission seeks to assess Jezero crater for ancient habitability, look for evidence of past signs of life, and collect rock samples for potential return to Earth. Among Jezero crater’s distinguishing features are two fans—one sourced from the western crater rim, one from the north—interpreted to be deltaic in origin. The western delta is composed of a sequence which includes finely layered planar strata, truncated curvilinear strata, and blocky deposits, interpreted as prodelta deposits, laterally accreting point-bars formed in meandering channels, and coarse-grained inverted fluvial channel deposits, respectively [Goudge et al., 2018].

Here we use orbiter images and digital terrain models to map and characterize the inverted channel deposits of the western delta to shed light on the evolution of Jezero’s deltaic system. The channel deposits are characterized by blocks resolvable in 25 cm/pixel HiRISE images and form elongate, positive-relief ridges and mesas. We group the channel deposits into ~9 distinct lobes based on cross-cutting relationships and the identification of nodes from which these deposits emanate. These distinct lobes, which show subtle textural and mineralogical differences, preserve a record of avulsions on the top surface of the delta as well as potential changes in provenance for the channel sediments over time. We use cross-cutting relationships to reconstruct the time-order of lobe deposition within the upper delta, and use measured lobe and channel characteristics to examine the intermittency of deposition within the delta.

We also re-examine the stratigraphic relationship between the inverted channel deposits and the underlying curvilinear and planar layered deposits. Previous studies interpret the inverted channel deposits as a time-transgressive facies that is equivalent in age to prodelta and meandering channel deposits within a corresponding time sequence [Goudge et al., 2018]. However, we observe consistent stratigraphic and topographic evidence suggesting that the inverted channel deposits could be a considerably younger subaerial fluvial sequence deposited unconformably on Jezero’s primary deltaic-lacustrine strata.