Fluvial architecture in actively deforming salt basins: Chinle Formation, Paradox Basin, Utah

Abstract

Determining the response of fluvial systems to syn-sedimentary halokinesis is important for reconstructing the palaeogeography of salt basins, determining the history of salt movement and predicting development and architecture of sandstone bodies for subsurface fluid extraction. To assess both the influence of salt movement on fluvial system development and the use of lithostratigraphic correlation schemes in salt basins we have analysed the Triassic Chinle Formation in the Paradox Basin, Utah. Results indicate that sandstone body development proximal to salt bodies should be considered at two scales: intra-(local) and inter-(regional) mini-basin scale. At the intra-mini basin or local scale, conformable packages of up to 12 m deep meandering fluvial channel deposits and associated overbank deposits are developed, which may thin, pinch-out or become truncated towards salt highs. When traced down the axis of a mini-basin, individual stories extend for a few hundred metres, and form part of amalgamated channel-belt packages up to 60 m thick that can be traced for at least 25 km parallel to palaeoflow. Where salt movement outpaces sediment accumulation, progressive low angle unconformities are developed along the flanks of salt highs. Significantly, in mini-basins with high sand supply, sandstone bodies are present across salt highs where they show increased amalgamation, decrease in thickness due to truncation and no change in internal sandstone body character. At inter mini-basin or regional scale, spatial and temporal variations in accommodation space generated by differential salt movement strongly influence facies distributions and facies correlation lengths. Broad lithostratigraphic packages (5-50 m thick) can be correlated within mini-basins, but correlation of these units between adjacent mini-basins is problematic. Knowledge of fluvial system development at a regional scale is critical as, fluvial sediment distribution is focussed by topography generated by growing salt bodies, such that adjacent mini-basins can have significant differences in sandstone body thickness, distribution and lateral extent. The observations from the Chinle Formation indicate that lithostratigraphic-based correlation schemes can only be applied within mini-basins and cannot be used to correlate between adjacent mini-basins or across a salt mini-basin province. The key to predicting sandstone body development is an understanding of the timing of salt movement and reconstructing fluvial drainage system development.

Controls on the structural and stratigraphic evolution of the megaflap-bearing Sinbad Valley salt wall, NE Paradox Basin, SW Colorado

“…The Chinle Formation has significant regional facies variations, with depositional environments including lacustrine, fluvial, and eolian (Baars and Doelling, 1987;Hazel, 1994). Regionally, the Chinle thickens southwestward into the Paradox Basin, but locally thins over the diapirs, with local intraformational angular unconformities adjacent to salt walls (Hazel, 1994;Matthews et al, 2007;McFarland, 2016;Hartley and Evenstar, 2017).…”

“…These are consistent with regional unconformities (Orgill, 1971;Hazel, 1994;Condon, 1997;Rasmussen, 2014) identified in subsurface data throughout the Paradox Basin (e.g., Kluth and DuChene, 2009;Rowan et al, 2016; this study), with the first (mid-Cutler) interpreted to mark the time of salt breakthrough. In contrast, the minor, local intra-Moenkopi and Chinle unconformities are observed only in outcrops adjacent to certain salt walls (Shoemaker and Newman, 1959;Hazel, 1994;Lawton and Buck, 2006;Matthews et al, 2007;Trudgill, 2011;Heness, 2016;Hartley and Evenstar, 2017) and probably represent local halokinetic-sequence unconformities generated during passive diapirism (see Giles and Rowan, 2012).…”

“…1A), excellent outcrop exposures and an abundance of subsurface data have facilitated the reinterpretation of stratal geometries and structures adjacent to the salt walls, sparking renewed interest in understanding the salt tectonic and stratigraphic history of the basin (Lawton and Buck, 2006;Trudgill, 2011;Banham and Mountney, 2013;Venus et al, 2015;Rowan et al, 2016;Hartley and Evenstar, 2017;Escosa et al, 2018). For example, the stratal architecture adjacent to salt walls in the northwestern part of the Paradox Basin, including the Salt Valley, Castle Valley, and Moab Valley salt walls, has revealed patterns of fluvial-alluvial deposition in response to salt movement during the Permian through Triassic (Matthews et al, 2007;Mountney, 2013, 2014;Venus et al, 2015;Hartley and Evenstar, 2017) and the identification of steeply dipping strata adjacent to the salt walls (Trudgill, 2011) that are now interpreted as megaflaps (i.e., Giles and Rowan, 2012). Moreover, new mapping and reinterpretation of stratal geometries along the Gypsum Valley and Castle Valley salt walls has identified a number of newly recognized and reinterpreted halokinetic and near-diapir features, including megaflaps, counterregional faults, salt shoulders, radial faults, secondary welds, and lateral caprock (Fig.…”

Colorado Plateau Coring Project, Phase I (CPCP-I): a continuously cored, globally exportable chronology of Triassic continental environmental change from western North America

“…In both eastward and westward subduction models a southwestern source of silicic volcanic debris is generally identified with the postulated Cordilleran arc or Mogollan Highlands (Howell and Blakey, 2013;Riggs et al, 2013Riggs et al, , 2016Dickinson, 2018). Although the active margin, backarc-retroarc models have basin depocenters and syndepositional deformation localized by proximal active compressive and flexural forces of the approaching arc, or slabrelated dynamic subsidence, there is ample evidence that much local deformation and localized subsidence was controlled by early Mesozoic halokenesis (salt tectonics) (Shoemaker et al, 1958;Hazel, 1994;Matthews et al, 2007;Trudgill, 2011;Banham and Mountney, 2014;Hartley and Evenstar, 2017) that might, in fact, prove more important than either basement-involved tectonics or eustasy in structuring much of the stratigraphy (P. E. ). An additional, generally overlooked consideration is that the southern and eastern edges of the western US Triassic-Jurassic sequences lie against the projection of the Central Atlantic rift system, and changes in the uplift of the northwestern rift shoulders related to extensional pulses are plausible factors in modulating rates of supply of sediments to the deposits of the American Southwest (Huber et al, 2016).…”

Paleontology of the Bears Ears National Monument: history of exploration and designation of the monument

“…In northern BENM and vicinity, the Kane Springs beds are at least partly correlative to the Petrified Forest Member and are the lowest Chinle unit in this area (Blakey andGubitosa, 1983, 1984;Martz et al, 2014Martz et al, , 2017; these strata comprise a complex mix of poorly drained floodplain and meandering stream deposits that sometimes incise as paleovalleys into the underlying Moenkopi Formation (Blakey, 1978;Blakey andGubitosa, 1983, 1984;Martz et al, 2014;Hartley and Evenstar, 2018). The Owl Rock Member overlies these two units throughout BENM, and also comprises well-drained overbank and minor channel deposits (Blakey and Gubitosa, 1983;Dubiel, 1994;Dubiel and Hasiotis, 2011); crayfish burrows extending from channel and levee facies into underlying finer-grained paleosols are common Mitchell, 1989, 1993;Hasiotis, 1995).…”