The survivability of labile light-mineral grains in fluvial, aeolian and littoral marine environments: the Permian Cutler and Cedar Mesa Formations, Moab, Utah |
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| Authors: | GREG H MACK |
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| Institution: | Department of Geology, Georgia State University, Atlanta, GA 30303 |
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| Abstract: | A greater than 50% decrease in the percentage of labile light minerals occurs between the non-marine Cutler Formation (Permian) and its facies equivalent, the marine Cedar Mesa Sandstone, in the vicinity of Moab, Utah. Both the Cutler and Cedar Mesa Formations were derived from crystalline rocks of the Uncom-pahgre Mountains under semi-arid to arid climatic conditions. Furthermore, diagenesis had little effect on the light-mineral fraction. Therefore, the significant change in mineralogy where the fluvial Cutler beds grade into the littoral marine Cedar Mesa deposits can be directly related to active reworking of detritus in the shallow marine environment. Less coarse perthitic alkali feldspar, twinned plagioclase, undulose mono-crystalline quartz, and polycrystalline quartz in the Cedar Mesa with respect to the Cutler suggest that compositional maturation was produced by breakage of mechanically weaker grains during grain-to-grain collisions. Furthermore, the end products of compositional modification by shallow marine processes may be sufficiently different from those produced by weathering and dilution from sedimentary source rocks to allow evaluation of the relative effects of these processes on the origin of compositionally mature ancient sandstones. |
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