HR: 13:55h
AN: P23B-02    [Abstracts]
TI: The First Plains Geologic Transect on Mars: Spirit Rover Traverse of the Plains in Gusev Crater
AU: * Crumpler, L S
EM: lcrumpler@nmmnh.state.nm.us
AF: New Mexico Museum of Natural History and Science, 1801 Mountain Road, NW, Albuquerque, NM 87104 United States
AB: The location and near-field geologic setting of Spirit were mapped on regional image and remote sensing data during the approximately 2.3 km traverse from the landing site within the Gusev Crater floor plains to the Columbia Hills. Differences in surficial geology together with boundaries between geologic units identified from ground observation were recorded and mapped along a 40 m-wide corridor along the traverse. The observations yield the first systematic geologic transect of a plains surface and multiple impact crater ejecta sheets on another planet. Several concepts were examined or tested: (1) the regional morphologic variability of an Hesperian plains surface, (2) the distribution of small craters on the plains, (3) the relative degree of chemical weathering and importance of impact gardening in modifying basaltic plains, (4) surface characteristics in regions of differing themophysical properties, (5) the systematic structure of crater ejecta, and (6) the ability to locate and identify contacts defined from orbital and remote sensing data during surface traverse. The resulting geologic transect map also provides a base for the systematic measurements made by Athena science instruments. Geologic contacts crossed included ejecta blanket boundaries, crater rims, a two-fold geologic and topographic division of inner and outer ejecta, and the regional contact between the lava plains and the Columbia Hills. A comparison of contacts in geologic maps prepared from orbital data sets prior to the traverse and contacts observed at the surface along the transect confirm that surface traverses on Mars can identify the contact relations defined from orbital image data. Maps prepared from surface traverse and remote sensing differ mainly in the precision of location of boundaries, such as the outer edge of ejecta sheets, and distribution of surficial materials. Apparent vesicularity (ratio of summed vesicle volume from area over rock unit volume) of rocks in the plains lava surface decreased with increasing host rock size and angularity. It is interpreted that this population of vesicular clasts is a result of (1) impact gardening of an upper vesicular zone, and (2) that the vesicular zone is thin compared with that predicted for lava flows on Earth. If supported by additional on-going analysis, the presence of a thin upper vesicular zone in the Gusev plains lavas could be indirect evidence for atmospheric pressure close to current values at the time of Gusev plains basalt emplacement during the Hesperian.
DE: 8450 Planetary volcanism (5480)
DE: 5415 Erosion and weathering
DE: 5420 Impact phenomena (includes cratering)
DE: 5480 Volcanism (8450)
DE: 6225 Mars
SC: Planetary Sciences [P]
MN: 2004 AGU Fall Meeting