Understanding Sedimentary Sources and Sinks on Mars from Orbit

Reflectance spectra (~0.3-5 um) and visible imagery of Mars acquired at unprecedented spatial resolutions allow us to detect minerals indicative of aqueous processes and sedimentary environments and place them in their proper stratigraphic context. The presence of clay minerals and variations in stratal geometries and textures of beds, for example, make it possible to define several depositional environments within Holden and Eberswalde Craters. The mineralogy and stratigraphy/morphology of deposits in these craters are consistent with alluvial, fluvial, and lacustrine processes. These craters are themselves part of the larger Uzboi-Ladon-Margaritifer (ULM) system, which spans thousands of kilometers from the southern highlands to the northern lowlands. Large, highly eroded craters within this system act as sedimentary sinks, and combining mineralogy from spectroscopy with morphology shows that in some cases the local sediment source area(s) can be defined.

Clays in the Noachian units in the ULM system consist almost entirely of Fe/Mg smectites, suggesting water-to-rock ratios were too low or aqueous conditions too short lived for significant dissolution and formation of secondary Al-bearing phases (e.g. feldspar to kaolinite). This is in contrast to the regional morphology, which suggests that the ULM system records a long history of deposition, erosion, and aqueous processes. Surrounding crater walls and rims contain clays and exhibit fluvial erosion patterns, suggesting they are local source areas. However, the spectral strength of clay features in potential source regions are commonly weaker than clay signatures in the deposits to which they contribute. This may be caused by a preferential accumulation of fine-grained clay-rich material in rock types associated with certain depositional settings (e.g. mudstones/shales) or by in situ formation of clays in standing bodies of water. Sedimentary deposits such as these, which can potentially be linked to their source region, are excellent targets for future exploration and sample return.