Mathematics – Logic
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufm.p31b0141c&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #P31B-0141
Mathematics
Logic
5499 General Or Miscellaneous, 6225 Mars
Scientific paper
Deuteronilus Mensae, a gradational boundary zone in the northern mid-latitudes of Mars, includes the transition from the rugged cratered highlands and polygonal mesas of Arabia Terra to the northern lowlands of Acidalia Planitia. Within this zone, features diagnostic of Martian 'fretted' terrain are observed, including numerous lobate debris aprons. The concentration of aprons indicate that ground ice was, or still is present, which is of great interest because of their potential association with changes in Martian climate. North of the boundary zone are the northern lowlands, a depositional sink that perhaps was once filled by large standing bodies of water. The lowlands have surface elevations that are several kilometers below the ancient highlands with significantly younger surface ages. To better understand the geologic evolution of the Arabia Terra highlands, we have mapped the geology of a north-south transect across the Martian dichotomy boundary from 32.5 N to 47.5 N and 20-25 E. To the south, the ancient highland plateau has been modified by subsurface volatile activity, causing surface collapse and the formation of numerous elongated closed depressions containing blocks of the pre-existing surface. Parts of the plateau have also been dissected by fluvial channels that may have formed by sapping processes or short- lived precipitation-derived overland flow. In the central portion of the map area, the preserved highlands transition to individual mesas with tops that have a similar morphology to the continuous plateau. Below highland escarpments and mesa walls, lobate debris aprons have surface lineations and deflected margins indicating flow of volatile-rich materials. Fretted valleys appear to originate at the highland margin and develop by backwasting of plateau materials. In this central area, we did not find any distinct geomorphologic features related to coastal processes that would support the hypothesis of an ancient lowland ocean. To the north, within areas of smooth and knobby plains, clusters of small mesas and knobs are surrounded by debris aprons. Mesa tops gradually decrease in elevation towards the north and their surfaces are sometimes covered by mantling deposits. Two mesa-forming units with tops at consistently different surface elevations suggest a regional stratigraphic sequence of less-resistant upper mesa materials overlying more-resistant lower mesa materials. Preliminary crater retention age ranges from Viking data are Early-to-Mid Noachian for plateau materials, Early-to-Mid Noachian for dissected plateau materials, and Late Noachian to Early Hesperian for smooth plains materials.
Chuang Frank C.
Crown David A.
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