Showing papers by "S. W. Squyres published in 2011"

Reconstruction of eolian bed forms and paleocurrents from cross‐bedded strata at Victoria Crater, Meridiani Planum, Mars

Abstract: Outcrop exposures imaged by the Opportunity rover at Victoria Crater, a 750 m diameter crater in Meridiani Planum, are used to delineate sedimentary structures and further develop a dune-interdune depositional model for the region. The stratigraphy at Victoria Crater, observed during Opportunity's partial traverse of its rim, includes the best examples of meter-scale eolian cross bedding observed on Mars to date. The Cape St. Mary promontory, located at the southern end of the rim traverse, is characterized by meter-scale sets of trough cross bedding, suggesting northward migrating sinuous-crested bed forms. Cape St. Vincent, which is located at the opposite end of the traverse, shows tabular-planar stratification indicative of climbing bed forms with meter- to decameter-scale dune heights migrating southward. Promontories located between Cape St. Mary and Cape St. Vincent contain superposed stratigraphic units with northward and southward dipping beds separated by outcrop-scale bounding surfaces. These bounding surfaces are interpreted to be either reactivation and/or superposition surfaces in a complex erg sea. Any depositional model used to explain the bedding must conform to reversing northward and southward paleomigration directions and include multiple scales of bed forms. In addition to stratified outcrop, a bright diagenetic band is observed to overprint bedding and to lie on an equipotential parallel to the preimpact surface. Meter-scale cross bedding at Victoria Crater is similar to terrestrial eolian deposits and is interpreted as a dry dune field, comparable to Jurassic age eolian deposits in the western United States.

Field reconnaissance geologic mapping of the Columbia Hills, Mars, based on Mars Exploration Rover Spirit and MRO HiRISE observations

Abstract: Chemical, mineralogic, and lithologic ground truth was acquired for the first time on Mars in terrain units mapped using orbital Mars Reconnaissance Orbiter's High Resolution Imaging Science Experiment (MRO HiRISE) image data. Examination of several dozen outcrops shows that Mars is geologically complex at meter length scales, the record of its geologic history is well exposed, stratigraphic units may be identified and correlated across significant areas on the ground, and outcrops and geologic relationships between materials may be analyzed with techniques commonly employed in terrestrial field geology. Despite their burial during the course of Martian geologic time by widespread epiclastic materials, mobile fines, and fall deposits, the selective exhumation of deep and well-preserved geologic units has exposed undisturbed outcrops, stratigraphic sections, and structural information much as they are preserved and exposed on Earth. A rich geologic record awaits skilled future field investigators on Mars. The correlation of ground observations and orbital images enables construction of a corresponding geologic reconnaissance map. Most of the outcrops visited are interpreted to be pyroclastic, impactite, and epiclastic deposits overlying an unexposed substrate, probably related to a modified Gusev crater central peak. Fluids have altered chemistry and mineralogy of these protoliths in degrees that vary substantially within the same map unit. Examination of the rocks exposed above and below the major unconformity between the plains lavas and the Columbia Hills directly confirms the general conclusion from remote sensing in previous studies over past years that the early history of Mars was a time of more intense deposition and modification of the surface. Although the availability of fluids and the chemical and mineral activity declined from this early period, significant later volcanism and fluid convection enabled additional, if localized, chemical activity.

Evidence for Regional Deeply Buried Carbonate-Bearing Rocks on Mars

Abstract: Wray, S. L. Murchie, B. L. Ehlmann, R. E. Milliken, K. D. Seelos, E. Z. Noe Dobrea, J. F. Mustard, and S. W. Squyres, Department of Astronomy, Cornell University, Ithaca, NY 14853, USA (jwray@astro.cornell.edu), JHU/Applied Physics Lab, Laurel, MD, USA, IAS/Univ. Paris, Orsay, France, Univ. Notre Dame, Notre Dame, IN, USA, Planetary Science Institute, Tucson, AZ, USA, Brown Univ., Providence, RI, USA.

Orbital evidence for iron or calcium carbonates on Mars

Abstract: Carbonates are key minerals for understanding ancient Martian environments. Previous remote sensing has identified Mg-rich carbonates in Martian dust and in a Late Noachian rock unit bordering the Isidis basin. Here we report evidence for potentially older Feand/or Ca-rich carbonates exposed from the subsurface by impact craters and troughs.

Post-Fall Surface Modification Features of Iron Meteorites Found by the Opportunity Rover and Their Implications for Martian Weathering Processes

Abstract: IRON METEORITES FOUND BY THE OPPORTUNITY ROVER AND THEIR IMPLICATIONS FOR MARTIAN WEATHERING PROCESSES J.W. Ashley, M.P. Golombek, P.R. Christensen, S.W. Squyres, T.J. McCoy, C. Schroder, I. Fleischer, J.R. Johnson, K.E. Herkenhoff, T.J. Parker. Mars Space Flight Facility, Arizona State University. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA. Department of Astronomy, Cornell University, Ithaca, NY, USA. Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, D.C., USA. Center for Applied Geoscience, Eberhard Karls University, Tubingen, Germany. Institut fur Anorganische und Analytische Chemie, Johannes Gutenberg-Universitat, Mainz, Germany. Astrogeology Science Center, U. S. Geological Survey, Flagstaff, AZ, USA. E-mail: james.ashley@ser.asu.edu.