Geomorphic and Stratigraphic Analysis of Layered Deposits in Terby

Introduction: Recently released, high-resolution images from the Mars Orbiter Camera (MOC) and the Thermal Emission Imaging System (THEMIS) reveal a myriad of intriguing landforms banked along the northern edge of Terby Crater located on the northern rim of Hellas (~28°S, 287°W). Landforms within this crater include north-trending troughs and ridges, a remarkable 2.5 km–thick sequence of exposed layers, mantled ramps that extend across and between layered sequences, fan-like structures, sinuous channels, collapse pits, a massive landslide and viscous flow features. The suite of diverse landforms in Terby and its immediate surroundings attest to a diversity of rock types and geologic processes, making this locality ideal for studying landform-climate relationships on Mars. In order to decipher the complicated geologic history of Terby Crater and the nature of the layered deposits, a generalized geomorphic map was created and the slope of the layered deposits was examined. Data Analysis: A preliminary geographic map was generated using all currently released wide-and narrow-angle (NA) MOC images and THEMIS visible and infrared images. These data were obtained, processed and co-registered with Viking Orbiter 2.1 MDIM images and topographic information from the Mars Orbiter Laser Altimeter (MOLA) to generate rectified image mosaics of Terby Crater. Arc GIS (Geographic Information Systems) was used to delineate different geomorphic units within Terby. In order to determine whether the layered deposits are level or sloping, marker beds were traced on MOC NA images that were co-registered with MOLA data (Figure 2). Using Surfer® software, the elevation along points of the marker beds were determined from raw MOLA track data. Using the elevation associated with each latitude/longitude pair, the slope of the layer was determined by fitting a trend surface (polynomial regression) in Surfer. Geomorphic Map of Terby Crater: The deposits in Terby are mapped as late Noachian-aged etched material consisting of fine-grained and friable material that is indicative of dust, loess or tephra that may include interstitial ice [1]. The major geomorphic units in Terby Crater and its immediate surroundings include flat mesa tops, layered deposits, an undifferenti-ated rough unit, crater floor deposits, a moat deposit, mantled terrain, viscous flow features and fan deposits (Figure 1).