Mineralogy of the Valles Marineris: Initial Stratigraphic Results from Comparing Tes Endmember Compositions

Introduction: This study tests the proposition that data from the Mars Global Surveyor Thermal Emission Spectrometer (MGS TES) and Mars Orbiting Laser Altimeter (MOLA) can be used to identify stratigraphic and mineralogic layering in the wall and floor deposits of the Valles Marineris (VM). By using TES data at full resolution to identify unique local compositional signatures, our study complements previous studies that averaged data at a regional scale [1]. The absolute elevation, dip, and stratigraphic relationships of observed layering in wall rock is determined using MOLA data. The observed composition and stratigraphic relationships can then be used to constrain the formation process of the Valles Marineris. Background: TES is currently acquiring thermal infrared (5 – 50 μm) spectra of the Martian surface at spatial resolutions of approximately 3 x 6 km per pixel [2]. Spectral absorptions in Martian mid-IR data are attributable to atmospheric CO2 and dust, water-ice clouds, and surface materials. Smith et al. [3] and Bandfield et al. [5-6] have demonstrated that the spectral signatures of the atmospheric components may be removed via radiative transfer modeling, and to first order, by linear deconvolution. The surface spectrum that remains after atmospheric removal is indicative of several properties of the surface materials including bulk composition, relative abundances of minerals, and particle size. The easiest surface spectra to interpret are those obtained in low-albedo, high thermal inertia regions that are dominated by coarse (10’s – 100’s of μm) sands, regolith, and/or bedrock with little dust. Using visible imaging, the Valles Marineris have been characterized as having significant layered deposits, a wide variety of morphologies, and numerous regions with low albedo surfaces. It is important to note that the slopes of the canyon walls in the VM can be steep (up to 34°) causing TES to observe sloped surfaces. Slopes may become a problem in regions where steeply dipping walls meet near-horizontal surfaces (e.g., at the bottom of a canyon wall), which could create spectral complications due to the complex interaction of the radiated energy from the two surfaces [P. Christensen, personal communication, 2000]. Hence, in addition to constraining the stratigraphy and mineralogy of the VM, the results of this study will contribute to understanding this effect. The MOLA data used for this study were derived from the 128 pixel/degree digital elevation model. TES data points were collocated with MOLA data gridded to TES resolution. Method: First we made compositional maps of the end member deconvolutions of the TES dataset that are performed with each downlink from MGS. These maps were then plotted on images of the topography of the