Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p51a1415c&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #P51A-1415
Physics
[5419] Planetary Sciences: Solid Surface Planets / Hydrology And Fluvial Processes, [5420] Planetary Sciences: Solid Surface Planets / Impact Phenomena, Cratering
Scientific paper
This study focuses on highland regions to the west (3.9x106 km centered at 42°S, 30°E) and northeast (2.1x106 km2 centered at 20°S, 85°E) of Hellas to discern spatial patterns of impact craters and their interior deposits in order to evaluate: 1) whether crater interior deposits around Hellas represent contemporaneous deposition from a completely inundated Hellas basin (e.g., Hellas paleolake), and/or 2) if individual craters within the highlands represent isolated sedimentary sinks. Our GIS based analysis includes crater morphology and morphometry, identification of fill materials and estimated fill amounts, and spatial distributions and associations of features within the two study areas with respect to distance from the center of Hellas basin as well as within discrete topographic benches that surround the basin. All craters greater than 15 km in diameter (599 in total) were first assigned to one of three degradation classes (highly degraded, moderately degraded, and pristine) based primarily on visual inspection of the extent and preservation of ejecta deposits. These craters were then mapped in detail by subdividing primary crater features (rims, ejecta, and central peaks) and secondary floor deposits (smooth floor, dune, and alluvial fan morphologies). ArcGIS-calculated crater diameter from best-fit ellipses and MOLA gridded topography provided the means to extract the maximum rim height for each crater; smooth floor deposits were isolated and the median floor elevation was extracted. Using crater diameters and equations from Garvin et al. (2003), original crater depths were estimated. From these data, fill percentages were calculated and a geographic spatial distribution analysis done. Initial findings indicate that a greater number of degraded craters are found closer to the rim of the basin and that they contain, on average, a greater amount of fill. Crater degradation states and fill amounts are more variable farther away from the basin in the highlands. Of note, a narrow band of lesser crater fill was found between the elevations of -1800m and 500m in each region; the -1800m contour was previously put forward as a maximum Hellas paleolake high stand (Crown et al., 2005). Although this analysis does not provide irrefutable evidence that the whole of Hellas once contained a basin-wide lake (liquid or ice-covered), we have found evidence of topographically defined zones around Hellas that show location-specific modification processes as revealed by crater retention, degradation, and fill percentages.
Bleamaster Leslie F.
Condit C. B.
Crown David A.
Mest Scott C.
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