Mathematics – Logic
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p12a..05n&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #P12A-05
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
A currently outstanding question in martian geology is the mechanism by which large and numerous deposits of sulfate-rich and phyllosilicate-rich sedimentary rocks were generated. Hypotheses proposed to explain the origin of layered, sulfate-rich sediments at Meridiani Planum include: a) alteration by acidic fluids in a shallow and intermittently wet groundwater/playa/sebkha system, b) alteration of volcanic ash-flows by acidic sulfur-rich gases, c) reworking of sulfate-rich material by impact base surge, and d) acidic weathering within massive low-latitude ice deposits. We favor the ice-weathering model because this scenario can best explain the geologic and geochemical observations made from orbit and the surface. In addition, this model is in accord with an emerging picture of Mars in which ice-related processes have driven many aspects of sedimentation through time. The ice weathering model may also be relevant for understanding the origin of phyllosilicate deposits located beneath the sulfate-rich deposits at Meridiani Planum as well as at Mawrth Vallis. The Mawrth Vallis phyllosilicate deposits have several special characteristics: they are laterally extensive - occurring within stratigraphic windows over >~2*106 km2, and the mineralogical stratigraphy is the same everywhere that they are observed (Al-phyllosilicates overlying Fe/Mg-phyllosilicates). These observations can only be explained by a process that operated on a large spatial scale, just as with the sulfate deposits at Meridiani. However, if there were in fact massive ice deposits at low latitudes as called for in the Meridiani ice-weathering model, basal melting of these deposits may have driven a large regional groundwater system. Groundwater derived from extensive basal melting would likely have been alkaline due to increased water-rock interaction and increased dilution of the acid present in the ice deposit. Thus, the mineralogical stratigraphy could be explained by this alkaline groundwater system leaching of rocks in the uppermost part of the stratigraphic section to form Al-rich clay minerals, and alteration of the materials to Fe/Mg-rich clay minerals in the deeper section, where groundwater saturation persisted and/or reducing conditions prevailed. While the ages of the phyllosilicate deposits and sulfate deposits are generally considered to be different, this model suggests that the age of the alteration events that formed the sulfate minerals and the phyllosilicate deposits would be equivalent. It is because of later episodes of physical reworking that the age of the sulfate-rich sedimentary rocks would appear to be younger. Therefore, this model may provide a consistent explanation for the formation of sulfate-rich and phyllosilicate-rich sediments early in Mars’ history.
Michalski Jacek
Niles Paul B.
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