LITHOSPHERIC FLEXURE MAPS FOR THE PARADOX BASIN USING GRAPHIC CORRELATION

The Paradox Basin (PB) was a flexural basin during Late Paleozoic Ancestral Rocky Mountains compressional tectonics. Previous studies resulted in two-dimensional profiles showing the flexural subsidence in front of the rising Uncompahgre Uplift. This study involves data for hundreds of wells bundled into six chronostratigraphic stages resulting in a three-dimensional analysis of the PB. Using graphic correlation where the total thickness was set at 100 percent and each stage is an incremental thickness percent of the total starting at the oldest stage (Atokan), the resulting data for each stage could then be mapped. A “hinge well” was chosen in the vicinity of the backbulge to compare stage percentages with the remaining wells. Maps of these differences appear to be sensitive to the paleotopography of the underlying Mississippian paleostructures and buried tectonic features. The influence of these features decreases with continued deposition and eventually disappear.

Results for the Atokan Lower Hermosa interval were mixed because these strata onlapped and buried the Mississippian topography; better information is through maps of the onlapping Lower Hermosa cycles. Results for the Atokan Alkali Gulch cycles are “hazy” because of widespread deposition of thick halite beds during the early stages of tectonic flexure of the PB and sparsity of data in the Deep Fold and Fault Belt (DFFB) with subsequent massive salt flowage. Results for the Desmoinesian Hatch, Ismay, Desert Creek, Akah and Barker Creek were outstanding and provide considerable detail. The foredeep is most of the already mapped DFFB and has a prominent forebulge that follows the southwestern outline of the DFFB. The backbulge basin is the Blanding Subbasin with a narrow trend that extends and expands toward the northwest. The backbulge is peripheral to the outer limits of PB salt deposition and includes the “hinge” trend. The Blanding Subbasin is partly above a wide paleovalley on the eroded Leadville Fm; its northeast margin follows the edge of the paleovalley. Results for the Missourian, Virgilian, Wolfcampian, and Leonardian intervals were muted because of massive siliciclastic deposition masking underlying features. This study suggests a new method in the analysis of flexural basins.