Mud flows in southwestern Utopia Planitia, Mars

Landforms with characteristic flow-like morphology are distributed across the southwestern portion of Utopia Planitia, Mars. Although some of the features have previously been interpreted as mud flows associated with a former presence of partly frozen muddy ocean based on their morphologies and similarities with terrestrial analogues (Ivanov et al., 2014, Icarus 228; Ivanov et al., 2015, Icarus 248), such interpretations remain ambiguous. This is because a) the evidence supporting the presence of such an ocean has been disputed by many, b) models of evolution of Utopia Planitia do not sufficiently explain the emplacement mechanisms of the flow-like landforms, and c) no in-situ measurements are available to confirm their sedimentary origin. Here we present results of a mapping exercise that focused on a field of flow-related landforms spread across a ∼ 500 × 1300 km large area centered around Adamas Labyrinthus in the attempt to provide additional insight about their formation mechanism. We mapped the distribution of 312 edifices and classified them based on their areal extent, shape, and morphological properties. We assert that these features can be grouped into four classes with distinct shapes and sizes. Their shapes are consistent with the ascent and the subsequent movement of liquid over the Martian surface. We interpret an evolutionary sequence among the classes as the differences in their morphologies can be explained by different effusion rates of the source material and the duration of the discharge at the time of their emplacement. As the result of our analysis and considering previous studies focusing on the area of our interest, we propose that all the >300 studied features were formed by subsurface sediment mobilization and that the material likely originated from the same subsurface source area. Consequently, we argue for the presence of a large body of mud within this region in the past. Finally, we note that there are several previously unconsidered sequences of events which could have resulted in such sedimentary-volcanic activity within Adamas Labyrinthus