GEOLOGIC MAPPING INVESTIGATIONS OF GUSEV CRATER, MARS

The geology of Gusev crater (~160 km diameter; 14.53°S, 175.52°E) has been studied through orbital remote sensing and by the MER Spirit rover. We are producing a new 1:250K-scale geologic map of Gusev crater through analyses of high-resolution imaging and topographic datasets, comparisons to geologically recent Martian volcanic features, and studies of geologic contacts at terrestrial analog sites. Our GIS-based mapping investigation utilizes CTX images (5-6 m/pixel) and DTMs (24 m/pixel) to define and characterize geologic units that form Gusev crater and the surrounding terrain. The map region includes Gusev floor units, Gusev rim materials, and distal deposits of Ma’adim Vallis, as well as impact craters and cratered terrain adjacent to Gusev. The crater interior includes ridged plains and an upper flow unit that form most of the floor, plateau and terrace units along the eastern crater rim, and a mesa unit where Ma’adim Vallis dissects the southern rim. Crater size-frequency distributions for the ridged plains and upper flow unit show similar age estimates of ~3.5-3.6 Ga, indicating significant geologic activity, including volcanism, on Gusev’s floor in the Hesperian Period.

The volcanic ridged plains units exhibit smooth to hummocky surfaces with wrinkle ridges. The upper flow unit has been interpreted differently by various previous researchers, including as both part of Gusev’s volcanic floor and as fluvio-lacustrine sediments in part emplaced as debris flows. CTX images reveal morphologic details that suggest some similarities to recent (~100 My) flood lavas in the Cerberus plains, including narrow ridges and larger ridged zones in complex patterns that define adjacent plate-like smooth areas. Both along the interior crater rim and in many locations within floor materials, lobate margins are evident. These surround local topographic highs, such as the Columbia Hills, and also outline small remnant patches of the pre-existing surface(s) that indicate differential burial and/or erosion. We are examining the morphologic and topographic characteristics at geologic contacts and along kipuka margins within floor materials in order to evaluate different emplacement histories for Gusev floor units and refine our geologic map.