Asking the pikas politely…
Abstract Stratigraphic studies south of Silverton, Colorado, suggest that the boundary between the Pennsylvanian Paradox basin and the Uncompahgre upland was a complex of east-west faults superimposed on a contemporaneous set of northwest-southeast normal faults. Pennsylvanian sediments that crop out in the San Juan Mountains were deposited while the east-west faults were active. Fault movement affected the thickness and facies distribution of these sediments in that (1) the amount of Leadville-Ouray carbonate that was removed by Late Mississippian or Early Pennsylvanian erosion is spatially variable, and the variability is related to faults; (2) the discontinuous distribution of the marine Upper Molas Member and of Pinkerton Trail Limestone is interpreted to be a product of fault movements; and (3) the facies distributions of Early Desmoinesian detrital and carbonate rocks in the Honaker Trail Formation suggest deposition while faults were active. Pennsylvanian fault movement produced a structural platform south of Silverton that appears to be similar to the Sneffels horst at Ouray, 30 km to the north. These structural elements formed a series of east-west-trending horsts and grabens along the southeastern margin of the Paradox basin during Desmoinesian time. Clastic and carbonate sedimentation in the area is cyclic. The cycles were produced by shifting centers of detrital sedimentation superimposed upon sedimentation patterns caused by eustatic sea-level changes. The depositional environments recognized in the area include distributary channels with their associated distributary-front and overbank detrital environments, and very shallow water, open-marine carbonate environments.
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