Physics
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p44a..06b&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #P44A-06
Physics
5464 Remote Sensing, 5470 Surface Materials And Properties
Scientific paper
Recent work on the origin of martian sulfates and their relationship to phyllosilicate deposits suggest that these deposits formed in different eras of Mars' history, under distinct environmental conditions. In southwestern Meridiani Planum phyllosilicates exist in close proximity to sulfate deposits. One possible explanation for this relationship is that it is an unconformable stratigraphic sequence, representing a significant change in aqueous geochemical conditions over time. Specifically, it may be interpreted to record a change in environment from neutral pH aqueous alteration in the Noachian to an acidic evaporitic system in the late Noachian to the Hesperian. On Earth, two different geochemical systems need not be evoked to explain such chemical variation. Acidic playa lakes in Western Australia have large pH differences separated by only a few tens of meters and demonstrate how highly variable chemistries can coexist over short distances in natural environments. Playa lakes on Earth tend to be dominated by lateral flow of water and salts leading to lateral chemical variation. Heterogeneity of playa mineralogy in Australia is due to the varied source rocks of brines and the mixing of dilute oxidizing brines and freshwater with the saturated evaporitic brines. This is evidenced by the ferricretes in the near-shore environment and more soluble phases in basin interiors. Playa lakes on Mars would be much larger than their terrestrial counterparts, leading to the prevalence of large-scale surface and crustal advection of water and salt rather than short-distance lateral flow, except at lake boundaries. Little or no influx of freshwater would preclude the formation of playa rim (e.g., crater rim) ferricretes and silcretes. Instead, we expect to see mainly vertical facies changes, and any diachronous lateral facies changes are expected to occur on very large spatial scales. Comparison of high spatial resolution, hyperspectral airborne data for Australian playa lakes with the OMEGA and CRISM data for regions on Mars that contain both phyllosilicates and sulfates will aid in determining if these deposits on Mars could be formed in a single depositional system. Western Australian ferricretes are spectrally similar to phyllosilicates. We therefore suggest that these analogs point to a single depositional system for Mars if phyllosilicates represent near-shore facies and sulfates interior lake deposits. The identification of ferricretes on Mars would provide an important paleoenvironmental indicator and might reveal sites of dilute brine influx.
Baldridge Alice M.
Bridges Nathan
Brown Adrian
Crowley J.
de Souza Filho Carlos Roberto
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