Salt Tectonic Controls On Facies And Sequence Stratigraphy Of The Triassic Chinle Formation, Gypsum Valley Salt Wall, Colorado

This study focuses on mapping the facies geometry and depositional sequences of the Chinle Formation adjacent to the Gypsum Valley Salt Wall (GVSW). Interactions between salt tectonics and fluvial systems can affect sediment distribution. The upper Triassic Chinle Formation was deposited across the western U.S. in an intra-cratonic, fluvial environment. Throughout the Paradox Basin in Utah and Colorado, deformation associated with rising salt anticlines and subsiding minibasins coincided with Chinle deposition. In most areas, only small and isolated remnant Chinle outcrops actually expose the contact between Chinle sediments and the salt diapir. In Gypsum Valley three study areas were mapped and sampled based on proximity to the GV diapir, and a fourth location, 12 km from the diapir was chosen as a standard to compare and contrast with Chinle facies documented proximal to the diapir. Fifteen correlated stratigraphic sections illustrate the stratigraphy and the distribution of the Chinle facies. Near the diapir, conglomeratic facies contain clasts predominately composed of carbonate eroded from the diapir caprock. The carbonate conglomeratic lenses disappear within 0.7 km of the diapir. Individual sandstone channels are 0.5 â?? 1.0 m thick and extend roughly 2.0 m on outcrop. Channels are laterally stacked and, in some units, vertically stacked. Red siltstones, over 16 m thick form overbank deposits, that separate channel complexes. Within the expanse of overbank deposits, paleosols 0.5 meters in thickness consist of blocky clay peds, and in some instances exhibit extensive sand-rich lateral rooted horizons. Along strike channels, overbank deposits and lacustrine deposits are traceable for ~3.5 km. Lacustrine units contain abundant septerian nodules and sandstone concretions. Debris flows are restricted to areas where the Chinle Formation is in contact with the underlying diapir caprock. By contrast, 12 km from the diapir, ~50 meters of coarse to medium grained sandstone predominate, no caprock conglomerates occur, indicating that the material either breaks down before traveling far, or the presence of a depositional barrier to the diapir derived carbonate clast/grain dispersal. Petrographic analysis indicates a complex cement history that changes with proximity to the diapir. A fourth Halokinetic Sequence is reported that records angular unconforities of 3-10 degrees