* Astronomy

Title: Mud volcanoes in the geologic record of Mars: The case of Firsoff crater
Authors: M. Pondrelli, A.P. Rossi, G.G. Ori, S. van Gasselt, D. Praeg, S. Ceramicola

We report the detection of mound-like landforms interpreted as mud volcanoes within Firsoff crater, in the Arabia Terra region of Mars. The mounds stratigraphically overlie layered deposits within the crater, which consist of high albedo well-bedded deposits disrupted in meter-sized polygons. Hundreds of mounds are observed on the crater floor, as isolated or composite subcircular cones 100500 m in diameter and tens of meters high. More than one third of the mounds (35%) have subcircular depressions 539 m in diameter at their apices that we interpret as vents. The mounds consist of meter-sized boulders of high albedo, embedded in an apparently finer-grained unit; we interpret these deposits as mud volcanic breccia, containing boulders of reworked light-toned layered deposits carried upward from deeper portions of the succession. The mounds are mainly located near the rim-bordering faults and in places aligned with fractures, suggesting subsurface pathways for fluid migration. The mounds are interpreted as fossil mud volcanoes, recording the upward migration of overpressured fluids through the crater infill from deeper crustal sources, localized by impact-related faults.

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