Date of Graduation
Subsurface study of Permian evaporites and related strata in the Denver basin reveals that the present distribution of salt has been influenced by a number of depositional and post-depositional controls. Correlations across the basin have identified 13 stratigraphic intervals that, in places, are salt-bearing. Upper Wolfcampian and lower Leonardian salts accumulated in paleolows (Alliance and Sterling evaporite basins and the "Garden County low") which were bounded by low-relief positive features associated with the Transcontinental arch, the Ancestral Chadron arch, and the Ancestral Las Animas arch. Sand (Lyons-Cedar Hills Sandstone) accumulated in eolian and shallow-water environments along paleohighs coeval with deposition of red silts and mud (Salt Plain Formation) and precipitation of halite (salts 9 and 10) in evaporite basins. Paleotectonic elements apparently had little influence on the distribution of younger (upper Leonardian and Guadalupian) salts. Salt has been locally removed by dissolution at various times. Pre-Late Jurassic truncation partially removed Leonardian strata and completely removed Guadalupian and Triassic strata in the eastern part of the basin. Eastern limits of Guadalupian and upper Leonardian salts parallel pre-Jurassic subcrop belts, reflecting the stepwise removal of salt by pre-Late Jurassic erosion or near-surface dissolution. Jurassic and Early Cretaceous removal of upper Leonardian and Guadalupian salt may be related to compaction-driven (centrifugal) groundwater flow from the Lyons Sandstone. Post-Cretaceous (Laramide) dissolution, which locally removed salts and influenced Cretaceous-level structure, is probably related to the introduction of groundwater by gravity-driven (centripetal) flow along a regional Lyons-salt facies change. Timing of salt removal has influenced the distribution and trapping mechanism of oil and gas fields on the eastern flank of the basin. In the western part of the D-J fairway, dissolution (and resultant collapse) pre-dated deposition of D and J Sandstone reservoirs. Here, reservoir-level structure is relatively simple and stratigraphic traps predominate. In the eastern part of the D-J fairway and in the D Sandstone and Niobrara Chalk gas areas, where dissolution post-dated deposition of Cretaceous reservoirs, structure is more complex and structural or structural-stratigraphic traps predominate. Discovery of oil in the subsalt Paleozoic section in 1980 sparked an exploration effort in the northern Denver basin that has greatly increased the amount of subsurface control with which to examine the stratigraphy of Permian salt-bearing units. A subsurface nomenclature is proposed for the salt-bearing interval in the Denver basin subsurface which uses Mid-Continent terminology for the Leonardian and Rocky Mountain terminology for the Guadalupian.
Oldham, David Wayne, "Influence of Permian salt dissolution on Cretaceous oil and gas entrapment, Denver basin." (1997). Graduate Theses, Dissertations, and Problem Reports. 9535.