Early Results of Large-Scale Geologic Mapping in East Candor Chasma

Abstract:

The structural evolution of east Candor Chasma and the depositional history of the sedimentary deposits within it are investigated through a new campaign of large-scale geologic and structural mapping using topography derived from High Resolution Imaging Science Experiment (HiRISE) stereo pairs. The overall objectives of this initiative are to understand the relative timing of chasma formation and sedimentation, to investigate the depositional settings of these sediments, and to characterize the styles of syn- and post-depositional deformation. Mapping is done at spatial resolutions that are at least an order of magnitude finer than has been achieved by previous studies in this part of Valles Marineris. Mapping focuses on the north and the southeast slopes of Nia Mensa and on the south slope of Juventae Mensa. Work on the north Nia Mensa map is underway this year and is the focus of this presentation.

The north Nia Mensa map encompasses the contact between the massive sedimentary rocks that comprise most of Nia Mensa and the stratified sedimentary and mass-wasting deposits exposed between Nia Mensa and the north wall of east Candor Chasma. The area also contains a stratified fan-like deposit that appears to be sourced from, and post-date the sediments that constitute, Nia Mensa. This area is mapped using a DEM comprising data from two adjacent HiRISE stereo pairs and orthorectified HiRISE and Context camera images. Work is focused on measuring the orientations of bedding, fractures and unconformities using the Layer Tools plug-in for ArcGIS and the HiRISE-derived topography. Measurements of bedding orientation reveal that the strata within the fan-like deposit dip outward at < ~10°, away from its morphologic apex. Thus the structure of this feature is consistent with a fan deposit. Work is ongoing to further test this interpretation as a fan deposit and to assess possible depositional settings for this feature and associated sediments.