MAPPING LACUSTRINE, FLUVIAL, AND AEOLIAN DEPOSITS WITHIN CRATERS IN THE AEOLIS DORSA REGION OF MARS

The Medusae Fossae Formation on Mars is located west of Tharsis and east of Gale Crater, along the dichotomy boundary. Extensive partial preservation records numerous depositional environments in this region, due to its complex history of deposition and erosion. The westernmost section of the Medusae Fossae Formation contains the Aeolis Dorsa region.

Geologic mapping is currently underway in the Aeolis Dorsa Region, during which five craters were identified as having interior sedimentary deposits with complex relationships. We have been mapping these deposits in detail using Context Camera (CTX) and High Resolution Imaging Science Experiment (HiRISE) images in ArcGIS. Here we describe a selection of these sedimentary deposits and our preliminary interpretations.

Branching Unit – Unit surfaces smoothly transition to different elevations over large areas. Minimal undulations across the surface occur with an overall branching appearance. Some surfaces erode into cliffs with no evidence of large (>25 cm in HiRISE) erosive blocks. Interpretation: inverted stack of fluvial deposits.

Highstanding Ridged Terrain – Highstanding with approximately uniform elevation with parallel ridges and troughs common. The boundary of this unit forms cliffs in most instances. Although most of this unit is areally extensive, limited areal exposures also occur as sinuous ridges. Interpretation: highly eroded depositional fan of deltaic origin.

Sinuous Mesa Unit – Unit surfaces are irregular, discontinuous and undulating with cuspate cliff-forming edges. Areas near the unit boundary or of more limited areal exposure are relatively smooth with depressions that are oblong and often interconnected. This material is fine-grained (<25 cm) and erodes into blocks in some areas. Interpretation: predominantly fine-grained sediment that was deposited in a (relatively shallow) lake environment with its undulating nature formed due to wave action. Longer troughs and ridges appear similar to iceberg scour marks.

Sinuous Unit – Preserved as sinuous ridges, the unit’s surface may smoothly transition or abruptly jump in elevation. When abrupt, steps in elevation strike perpendicular to the length of the feature. This unit rarely occurs with a branching planview. Some surfaces erode into cliffs. Interpretation: Inverted fluvial deposits.