Mathematics – Logic
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p21c..04g&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #P21C-04
Mathematics
Logic
[4271] Oceanography: General / Physical And Chemical Properties Of Seawater, [5410] Planetary Sciences: Solid Surface Planets / Composition, [6225] Planetary Sciences: Solar System Objects / Mars
Scientific paper
We have mapped layered deposits in Iani Chaos, part of the Margaritifer - Ares Valles outflow system in the southern hemisphere of Mars. These deposits have high thermal inertia relative to their surroundings and they often appear bright in visible images. Context Camera (CTX) and High Resolution Imaging Science Experiment (HiRise) data show the deposits to typically have a fractured and polygonal texture at the 1 - 10 m scale and preserve few craters. The deposits are commonly layered at the several meter scale and may form cliffs that are actively eroding into blocks and rockfalls. Three primary deposits of these materials are present in Iani covering a total area of ~6000 km2 (approximately the size of Great Salt Lake). The deposits lie in topographic lows within Iani and form mounds of material 100s of meters high (range ~ 0 - 1 km). Bright, layered deposits are recognized within the mounds that comprise the chaos terrain itself. The layered deposits within the mounds are conformable to exposed layered deposits suggesting that the deposits are exposed by differential weathering (likely along fractures) between the chaos mounds. In central Iani, a second generation of layered deposits embay the eroded mounds of the chaos formation. Analysis of Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) data for this site positively identifies gypsum (CaSO4●H2O) in the post-chaos layered deposits. Sulfates also comprise the chaos terrain itself. The spectra of these sulfates are consistent with kieserite (MgSO4●H2O) in a mixture containing additional minerals. The stratigraphy at Iani requires at least two episodes of sulfate formation, separated by an uncomformity. We propose the following geologic sequence for Iani Chaos: 1) Formation of Mg (and possibly other sulfates and evaporite minerals) by evaporation of water. 3) Emplacement of non-evaporite materials in the region. 4) Formation of chaos terrain, presumably due to subsurface failure. 5) Erosion of chaotic mounds. 6) Formation of gypsum deposits due to the influx and evaporation of additional water. 7) Burial. 8) Exhumation and active erosion of layered deposits. This history requires two major episodes of recharge separated by an uncomformity, consistent with previous geophysical and geomorphic constraints. The meter-scale layering is likely due to fluctuations in water depth on a shorter time scale. The positive identification of gypsum at Iani makes it rare among layered deposits of the Valles Marineris system in which Mg, Fe-rich and other polyhydrated sulfates are documented (gypsum has been previously identified in Iani Chaos and subsequently challenged in the literature; each of these analyses utilized OMEGA data, which is at a coarser spatial resolution than CRISM). The presence of gypsum in Iani may reflect more Ca-rich source waters due to differences in source rocks and/or weathering intensity or duration. Alternatively, potential gypsum deposits associated with other sulfates may be rendered undetectable by CRISM and OMEGA due to their conversion to anhydrite which occurs at ~130°C. The presence of both Mg and Ca sulfates within Iani may be a consequence of different source waters through time or due to different exposures of predicted evaporative sequences by erosion.
Gilmore Martha S.
Greenwood James Paul
No associations
LandOfFree
Gypsum and Associated Sulfates in Iani Chaos, Mars does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Gypsum and Associated Sulfates in Iani Chaos, Mars, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Gypsum and Associated Sulfates in Iani Chaos, Mars will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1768925