SEDIMENT SOURCES FOR THE EBERSWALDE DELTA: STRATIGRAPHY AND MINERALOGY OF THE EBERSWALDE CRATER CATCHMENT

Understanding source-to-sink sedimentary pathways on Mars is key to determining the origin of alteration minerals and ancient environmental conditions. The Eberswalde crater delta, a candidate landing site for the Mars2020 mission, contains Fe-Mg phyllosilicates throughout its stratigraphy, and both detrital and authigenic origins have been suggested [1]. Here we present a geologic and compositional study of the catchment in order to test these two hypotheses and to characterize the source region for the Eberswalde delta. We have used hyperspectral observations from MRO CRISM to map the distribution of phyllosilicates, and DTMs and images from MRO CTX and HiRISE to identify headwater regions, perform a hydrologic analysis, and map the depths and distributions of channels that have delivered sediment into Eberswalde crater. We find that all channels begin on local or regional topographic highs, which is consistent with channels that are sourced from precipitation or snowmelt. Ejecta deposits from the Holden crater impact cover the entire Eberswalde catchment [2], and comparisons of channel depth and estimated ejecta thickness indicate that this ejecta is the primary source for the Eberswalde sediments. Previous studies have identified phyllosilicates within the Holden crater walls and ejecta [1,3]; therefore, it is likely that the ejecta is also the primary source for the clay minerals within the Eberswalde delta. However, channels in the northern catchment sub-region incise more deeply than the estimated Holden ejecta thickness, indicating that they may erode some pre-Holden, Noachian-aged materials as well. A local basin within the western the Eberswalde catchment contains a phyllosilicate-bearing, layered sedimentary deposit [4], which has been eroded by the Eberswalde fluvial system, suggesting that some clay minerals in the Eberswalde delta may have undergone multiple episodes of fluvial transport. If selected as the landing site for Mars2020, the Eberswalde delta could provide the first opportunity on Mars to investigate a clear source-to-sink pathway on Mars.

[1] Milliken & Bish (2010), Philosophical Magazine, doi: 10.1080/14786430903575132; [2] Mangold et al. (2012), Icarus, 220, 530-551; [3] Grant et al. (2008) Geology, 36, 3, 195-198; [4] McKeown et al. (2013), LPSC XLIV, 2302.