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

Conical mounds and furrows are widely interpreted as the morphological evidences of fluids expulsion on the martian surface. In the Crommelin crater (equatorial Arabia Terra) furrows and conical mounds are exhumed within light-toned equatorial layered deposits (ELDs). Aim of this paper is to describe these landforms and discuss their potential relations with water upwelling in Crommelin area. A comparative study of some of the morphologies hosted in the Crommelin area deposits have been performed by using multiple datasets (CTX, HRSC, MOLA, HiRISE). Then examples of spring and conical mounds on Earth was examined for comparison with analog structures on Mars. In this work thickness and geometries of the crater filling sediment packages have been calculated. Stratigraphic contacts and relations have been also reported in Crommelin area revised geological map, and mound clusters, potentially fluid-related morphologies, from Crommelin, Firsoff and Southern crater have been detailed. The morphometric and morphological analyses revealed that mounds and other structures occur where the ELDs are thicker and crudely layered. In addition, orthorectified imagery and high-resolution topography indicated the presence of conical mounds within the upper portion of ELDs near the craters rims. Mounds show apical holes and are linked to elongated structures resembling veins and dikes. Elongated structures (furrows) and concentric strata pattern that we refer to as ridge-and-through, were described inside to Crommelin crater. MOLA-based DEMs revealed that these morphologies developed within a flat topography and are inconsistent with gravitative processes. The results suggest that the inferred sediments package was likely part of an extensive zone of groundwater upwelling. This long-wavelength flow controlled water and sediments supply into the study area, probably during a major climate shift. Fluid expulsion processes were recognized as a relevant process in the formation of these morphologies. Mounds, furrows and related structures could be linked with deep fracture systems generated during the impact that trigger the potential upwelling of groundwater, at some point after the impact itself. As a consequence, groundwater upwelling could be expected in other craters on Mars with Crommelin-like topographic and geological setting.