3D Architecture of Kodiak Butte as Evidence of Fluvial or Shoal-Water Environments in Jezero Crater, Mars

Abstract

The Mars 2020 mission has explored depositional environments recorded in a fan-shaped deposit on the western side of Jezero crater. Kodiak butte is an isolated outcrop of sedimentary rock ∼1 km south of the western fan scarp and may be an erosional remnant of said fan. Sedimentary strata of Kodiak butte were first interpreted to represent Gilbert delta foresets and a lake depth of at least 10 m. Subsequent closer-range images of the northern face of Kodiak have resolved additional details of stratal geometries, permitting alternative interpretations of depositional environments. Rover visible-wavelength images, a three-dimensional digital outcrop model, and principal component analysis-based plane-fitting allow detailed facies mapping and measurements of stratal geometries in Kodiak. We observed three sets of gravel-bearing, steeply inclined beds ∼3, ∼7, and ∼10 m thick with local accretion directions ranging from ∼NW clockwise to ∼SW (covering ∼230° azimuth). These sets are interpreted as deposits from downstream-migrating bars with lobate geometries, consistent with mid-channel bars in a braided river or mouth bars in a shoal-water delta. The geometry of the inclined beds indicate channelized bankfull flow ∼4.2 m deep under persistent currents flowing south-southeast to south-southwest. The proposed hydrodynamic conditions, potentially continuous with the rest of the western fan succession, are high energy with limited settling of fine-grained sediment from suspension in a quiescent setting, indicating a lower biosignature preservation potential than previously hypothesized.