GEOLOGY AND STRATIGRAPHY OF THE MARS EXPLORATION ROVER GUSEV CRATER LANDING SITE

Gusev crater is a proposed landing site for one of the Mars Exploration Rovers (MER). Gusev has been interpreted as the depocenter for the Gusev-Ma’adim Vallis fluvio-lacustrine system. Here we use new remote sensing data from the Thermal Emission Imaging System (THEMIS), supplemented by data from the Thermal Emission Spectrometer (TES), Mars Orbiter Camera (MOC), and Mars Orbiter Laser Altimeter (MOLA) to characterize the geology of Gusev crater. Thermal infrared data from THEMIS and TES were used to map thermophysical units based on relative albedos and thermal inertias. THEMIS and MOC visible images were used to map unit morphologies and to determine crater density ages. MOLA data was used to identify unit contacts and stratigraphic relationships. Various data sets were then combined to construct a new surface unit map and stratigraphic column for Gusev. Eight surface units were identified in Gusev, mostly Hesperian in age, but 2 showing evidence of later modification and re-distribution. Six or more surface units and sub-layering is present within the MER-A landing ellipse, attesting to the geologic diversity of this site. Various surface units show features that could be consistent with fluvio-lacustrine, aeolian, and/or volcanoclastic depositional regimes. Resolution of data does not allow the distinction of textures associated with each of the regimes or the identification of unambiguous evidence for a fluvio-lacustrine depocenter. However, a MER rover landing in Gusev provides the opportunity to analyze multiple units within Gusev, distinguish between rock types, examine stratigraphic relationships, and determine the ancient depositional environment for Gusev crater.