*WINNER* Rocking and Rolling Downhill: Boulder Distribution Patterns on a Martian Terraced Fan, Xanthe Terra

Abstract

Terraced fans are a relatively rare subset of fan-shaped features on Mars that display radial, stepped topography and concave-up profiles. This study focuses on the Camichel Crater fan located in the Xanthe Terra region. Features common on terraced fans are boulders, large rocky detrital fragments visible in high-resolution images. Hypotheses for boulder origins include: (1) impact processes; (2) erosion of steep slopes; (3) preferential removal of finer-grained material through erosion; (4) transport via laminar debris flows; and/or (5) transport via turbulent flood events. The purpose of this project is to conduct high-resolution geologic mapping and test competing hypotheses by analyzing boulder distributions on the fan surface. High Resolution Imaging Science Experiment (HiRISE) images were used to evaluate small-scale features on the fan surface. HiRISE images have a resolution of 0.3 to 0.6 m/pixel; thus, boulders with a diameter of > 0.8 m were mapped in ArcGIS Pro at a scale of 1:3,400. Geologic mapping to identify depositional units was conducted at a scale of 1:4,000. Results show boulders can be linked to erosional and depositional processes. Boulders mapped on the Camichel Crater fan are primarily associated with steep topographic scarps adjacent to feeder channel walls or terrace edges, likely a result of over-steepening and erosion. In distal fan units, however, high boulder distributions in the light-toned unit suggest flow competence and boulder transport during deposition. Future work will compare patterns to boulder distribution patterns in terrestrial fan settings such as alluvial fans and Gilbert-type deltas.