Mathematics – Logic
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmep53f..06b&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #EP53F-06
Mathematics
Logic
[5415] Planetary Sciences: Solid Surface Planets / Erosion And Weathering, [5416] Planetary Sciences: Solid Surface Planets / Glaciation, [5419] Planetary Sciences: Solid Surface Planets / Hydrology And Fluvial Processes, [6225] Planetary Sciences: Solar System Objects / Mars
Scientific paper
An exhumed landscape evidences both the original geologic processes that formed it and the subsequent processes that first buried and then exhumed it. Often additional geologic events in between or subsequent to these processes may also be recorded. An exhumed landscape visible within the Aeolis/Zephyria Plana (AZP) region of Mars shows an extensive history of a variety of geologic processes (Burr et al., 2009). The AZP displays a dense population of sinuous ridges (SRs) predominantly within the erodible western Medusae Fossae Formation (MFF), which is dated as late Hesperian to early Amazonian. Roughly 150 individual SRs are found within an area of ~200,000 km2 at elevations ranging from approximately -800 m to -2800 m (mostly at elevations lower that -2000 m). The largest percentage of the SRs is located within the lower member of the MFF, some of which have associated fan/delta features. A few percent of the SRs are located in Noachian terrain as previously mapped, although on-going mapping may revise this assessment. These SRs span a range of individual and network morphologies. Individually, these SRs have been grouped into 5 morphologic classes. Thin, Flat, and Multilevel (e.g., Fig. 1) interpreted respectively, as) inverted paleochannels, inverted paleo-floodplains, and inverted paleochannels superposed on inverted paleo-floodplains. A fourth morphology, termed Rounded, is tentatively interpreted as glaciofluvial (i.e., esker), and a smaller scale fifth morphology remains enigmatic. The three inverted fluvial morphologies are inferred to have formed from cementation due to water flow occurring preferentially through the more porous fluvial sediments, and subsequent erosion by aeolian abrasion of the surrounding MFF material. Paleodischarge estimates were derived from terrestrial empirical equations using SR width and wavelength measurements and scaled for Martian gravity. Including error, average daily paleodischarge estimates range up to 244 m3 s-1 with an average value of is 59 m3 s-1, and dominant flood paleodischarge estimates range up to 1467 m3 s-1 with an average value of 431 m3 s-1. The extensive vertical range of these fluvial SRs, the highly sinuous nature of most examples, and their occasional cross-layering indicate a long-lasting history of fluvial channel formation, cementation, burial, and exhumation. Channel formation is hypothesized to have resulted from orographic precipitation, which implies a wetter climate at this equatorial location at sometime(s) during the late Hesperian or early Amazonian periods. Cementation by aqueous geochemical cements could have overlapped in time with fluvial runoff or developed under subsequent more arid conditions. The possible glaciofluvial SR(s), which might be one or multiple SRs, imply a process and/or climate that produced low elevation equatorial glaciers. Although many aspects of both the absolute and the relative timing of these events are still unclear, work to date on the AZP reveals an exhumed landscape with a complex sequence of climate-driven events, and provides Hesperian-Amazonian data about fluvial flow at the equator of Mars.
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