SHARAD detection of sedimentary infilling within an unnamed crater near Mangala Fossa region, Mars

We present the first Shallow Radar (SHARAD) based observations of subsurface reflections within an unnamed crater centered at 21.0 degrees S, 150.6 degrees W. It is situated south of the Mangala Fossa and Mangala Valles, a major fluvial outflow channel system. We informally name the crater Mangala crater for this paper. In contrast with adjacent Tharsis lava flow, our analysis of radar propagation in the Mangala crater reveals a low loss tangent (0.008-0.009) and lower dielectric subsurface material (average 5.6) for a subsurface unit that is similar to 40 m thick. These values are unexpected in this region. Lava flows dominate the surface and surrounding region, and SHARAD investigations of lava flows in the Tharsis region have detected higher values, creating a discrepancy that we discuss. Based on observed stratigraphy, and subsurface geophysical properties, we propose that the crater infilling is composed of moderate density sedimentary material buried by a layer of lava in the eastern portion of Mangala crater but left exposed in the west. Our measurements are also supported by previously done geologic mapping. We identify two subsurface reflections that provide details to determine one of the layers is sediment rather than lava. Detection of multiple reflections also indicates that infilling occurred in at least four successive events. These results are significant because it adds more context to this highly studied region and provides compelling evidence that water moved large volumes of sediment into this basin.