FILLING THE PARADOX, THE EVOLUTION OF THE PARADOX BASIN STRATIGRAPHY AS MOTIF FOR ANCESTRAL ROCKY BASINS

The evolution of the Pennsylvanian and Permian Paradox basin strata provide a motif to compare other to Ancestral Rocky Mountain basins. The initial flooding of the southeastern Paradox basin margin was shaped by rapid subsidence coupled with glacioeustatic sea level change.  This resulted in the under-filled carbonate/clastic sequences of the Bashkirian Pinkerton Trail Formation, which oscillated between subtidal spiculitic carbonates and thin, coastal plain coal. As foreland basin subsidence and sedimentation became balanced, the Moscovian carbonates of the Barker Creek sequence of the Hermosa Group ringed the basin margins with phylloid and bryozoan carbonate buildups during transgression and highstand, while evaporates filled the basin center during lowstands. On the faulted eastern margin, fluviodeltaic sediments capped were by highstand carbonates including phylloid algal bioherms. The following Akah sequence backstepped to form a wide, but shallow basin producing the most widespread lowstand evaporites, and  transgressive to highstand microbial and Chaetetes bioherms on the adjacent western shelf. Thick, black mudstone facies of the overlying Desert Creek sequence indicate deepest water conditions on the western shelf and maximum flooding of the basin. Stacked phylloid mounds occurred on the fault blocks of the Aneth platform.  The combination of slowed subsidence and high sediment production decreased the extent of the lowstand evaporite basin. The overlying Lower Ismay sequence prograded basinward with phyloid mounds occurring across much of the western shelf, again reducing the extent of the subsequent lowstand evaporate basin.  From this point forward on the western shelf, bioherm development decreased and carbonates became increasingly dominated by grain-rich lithologies. Subsidence decreased until the immense influx of coarse arkosic sedfiments shed off the rejuvenated Uncompaghre Uplift in the Permian.  Subsidence and salt evacuation increased accommodation space in the foldbelt adjacent to the uplift, but sediment supply overwhelmed most of the basin during the Permian. This pattern of combined subsidence and eustasy forming underfilled basins which grew to balanced and ultimately overfilled basins was repeated across the ARM basins at the close of the Paleozoic.