Wind‐Eroded Crater Floors and Intercrater Plains, Terra Sabaea, Mars

Abstract

AbstractAncient impact craters with wind‐eroded layering on their floors provide a record of resurfacing materials and processes on early Mars. In a 54 km Noachian crater in Terra Sabaea (20.2°S, 42.6°E), eolian deflation of a friable, dark‐toned layer up to tens of meters thick has exposed more resistant, underlying light‐toned material. These layers differ significantly from strata of similar tone described in other regions of Mars. The light‐toned material has no apparent internal stratification, and visible/near‐infrared spectral analysis suggests that it is rich in feldspar. Its origin is ambiguous, as we cannot confidently reject igneous, pyroclastic, or clastic alternatives. The overlying dark‐toned layer is probably a basaltic siltstone or sandstone that was emplaced mostly by wind, although its weak cementation and inverted fluvial paleochannels indicate some modification by water. Negative‐relief channels are not found on the crater floor, and fluvial erosion is otherwise weakly expressed in the study area. Small impacts onto this crater's floor have exposed deeper friable materials that appear to contain goethite. Bedrock outcrops on the crater walls are phyllosilicate bearing. The intercrater plains contain remnants of a post‐Noachian thin, widespread, likely eolian mantle with an indurated surface. Plains near Hellas‐concentric escarpments to the north are more consistent with volcanic resurfacing. A 48 km crater nearby contains similar dark‐over‐light outcrops but no paleochannels. Our findings indicate that dark‐over‐light stratigraphy has diverse origins across Mars and that some dark‐toned plains with mafic mineralogy are not of igneous origin.