RECONSTRUCTING THE SEDIMENTARY DEPOSITS OF ARABIA TERRA, MARS

The MER Opportunity rover at Meridiani Planum revealed evidence of layered sulfate and hematite rich rocks that formed and were altered in the presence of water. Images from HiRISE and other cameras show similar layered deposits throughout Meridiani Planum and Arabia Terra. Many of these deposits have unique morphological characteristics. Intracrater deposits are mounds of layered sediments that sometimes rise higher than the rims of the craters they are contained in, which we interpret as erosional remnants. Layered sediments are also exposed in pedestal craters and crater walls. The raised sediment platforms and crater exposures suggest that the layered deposits used to be more extensive. We used these identifications to build a database of points that represents the erosional remains of sediments related to those in Meridiani. CRISM sulfate detections were also added to the database as mineralogically similar deposits. Finally, unique large-scale morphologies were used to add more data points in areas where no high resolution images were available. The shared characteristics of the Meridiani deposits and the isolated deposits throughout Arabia Terra, along with the erosional morphologies of the deposits, suggest that they are related and are the remnants of a once extensive deposit.

The data points were used to reconstruct interpolated surfaces representing the pre-erosional sediments. The surface fits represent likely configurations of the pre-erosional deposits. A krige and a best-fit plane were considered the most representative, as the deposits were likely formed in relation to the water table (a smoothly varying surface). The modern topography was subtracted from each surface in order to estimate the eroded volume. These calculations represent a minimum erosional volume, as the remaining deposits likely did not escape some erosion themselves. The large volume (~2x10⁶ km³) and area (~4.9x10⁶ km²) of eroded deposits demonstrate that the outcrops observed by Opportunity are part of a once much larger deposit. This suggests that water was stable over a large area for a long period while the rocks were forming, but also that erosion rates were high once this activity had ceased. Both of these conditions have important implications for the climatic and geologic history of Mars.