Abstract
AbstractDescriptions of exposed salt structures help improve the ability to interpret the geometry and evolution of similar structures imaged in seismic reflection data from salt‐bearing sedimentary basins. This study uses detailed geologic mapping combined with well and seismic data from the southeastern end of the Gypsum Valley diapir (Paradox Basin, Colorado), to investigate the three‐dimensional geometry of the terminations of both the salt wall and its associated megaflap. The salt wall trends NW‐SE and is characterized by highly asymmetric stratal architecture on its northeastern and southwestern flanks, with thicker, deeper, gently dipping strata in the depositionally proximal (NE) minibasin and thinned older strata rotated to near‐vertical in a megaflap on the distal (SW) side. The megaflap terminates to the SE through a decrease in maximum dip and ultimately truncation by a pair of radial faults bounding a down‐dropped block with lower dips. East of these faults, the salt wall termination is a moderately plunging nose of salt overlain by gently southeast‐dipping strata, separated from the down‐dropped NE minibasin by a counterregional fault. From this analysis, and by comparison with analogue structures located elsewhere in the Paradox Basin and in the northern Gulf of Mexico, we propose a series of simple end‐member models in which salt walls and megaflaps may terminate abruptly or gradually. We suggest that controlling factors in determining these geometries include the original thickness and spatial distribution of the deep salt, the presence of nearby diapirs (which determines the fetch area for salt flow into the diapir), spatial patterns of depositional loading, and variations in the nature and location of salt breakout through the roof of the initial salt structure.
Highlights
Steep‐sided salt diapirs can have variable map‐view shapes
We suggest that factors controlling the nature and geometry of these lateral terminations include the type and location of bounding structures, the salt budget for flow into the diapir, the spatial patterns of depositional loading, and variations in the style and location of salt breakout through the roof of the initial salt structure
These are conceptual models of end‐member geometries; most real examples combine elements of these the Paradox Basin and the northern Gulf of Mexico, we have demonstrated or suggested the following: 1. The southeastern end of the Gypsum Valley salt wall is asymmetric, with thicker, deeper, gently dipping strata in the proximal NE minibasin and thinned, rotated older strata forming a megaflap on the distal strata form basinward (SW) side
Summary
Steep‐sided salt diapirs can have variable map‐view shapes. Salt walls may form in a variety of tectonic settings. Salt walls may form by differential loading in the absence of extension or contraction (e.g. Paradox Basin, Trudgill, 2011; La Popa Basin, Rowan, Lawton, Giles, & Ratliff, 2003; Nordkapp Basin, Rowan & Lindsø, 2017), when progradational loading causes inflation above or immediately updip of the pre‐existing presalt faults (Ge, Jackson, & Vendeville, 1997). Regardless of the triggering mechanism, they grow as passive diapirs once the salt has pierced its initial roof
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