Geometry, stratigraphy and evidences for fluid expulsion within Crommelin crater deposits, Arabia Terra, Mars

Fluid expulsion processes are being recognized as a relevant process in the formation of deposits hosted in Arabia Terra impact craters. Objects of this study are the Equatorial Layered Deposits (ELDs) in the Crommelin crater area (equatorial Arabia Terra). Some of the depositional processes invoked to explain their origin include spring deposition and mud volc anism. In this work thickness and geometries of the crater filling sediment packages were calculated. Stratigraphic contacts of the Crommelin area were reported within a detailed geol ogical map. Potentially fluids related morphologies, such as furrows and mound clusters, were described in detail using HiRISE images, MOLA)based DEMs and high resolution HiRISE DEMs. The morphometric and morphological analyses revealed that mounds and other structures occur where the ELDs are thick er and crudely layered. Orthorectfied imagery and high)res olution topography seems to indicate the presence of conica l mounds within the upper portion of ELDs near the craters r ims. Those show apical holes and are linked to elongated struc tures resembling veins and dikes. Inside Crommelin crater, within a flat topography, elongated structures, formerly furrows, and concentric strata pattern, that we refer to as ridge and through, were described. MOLA based DEMs revealed that these morphologies are inconsistent with gravitative processes. Mounds, furrows and related structures could be linked with deep fracture systems generated during the impact that trigger, at some – poorly constrained – point after the impact itself the potential upwelling of groundwater.