Fusulinid occurrence density maps to assess paleogeographic models of the Northwest Shelf of the Delaware Basin region

The Permian Basin region of southeast New Mexico and west Texas has been important source of hydrocarbons for more than 80 years. On the Northwest shelf and northern Delaware basin, sediment is described as being deposited in alternating sequences of siliciclastics, limestones, and evaporites, related to complex interactions between cyclic sea level variations, tectonic activity, subsidence, and climate. The Pedernal uplift is long thought to be the primary source of siliciclastic sediment on the Northwest shelf and northern Delaware basin. However, detailed timing and patterns of siliciclastic delivery on the Northwest shelf is lacking. Fusulinid density maps are produced using the latitudinal and longitudinal locations of fusulinid biostratigraphic reports (N=1,721) depicting the Morrowan through the Leonardian on the Northwest shelf and in northern Delaware basin in southeast New Mexico and west Texas. Fusulinid data used to produce the fusulinid density maps comes from the Permian Basin Archival of Biostratigraphic Zone Tops (PABZT) database. The PABZT database is a collection of digitized fusulinid biostratigraphic reports produced by the Paleontological Laboratory of Midland, Texas from the late 1920s to through the late 1980s for several petroleum companies operating in the Permian Basin region. Two different published paleogeographic models depicting uplifted regions and depositional patterns on the Northwest shelf and northern Delaware basin are compared. Several similarities are present in the paleogeographic models; however, there are significant disagreements in terms of the extent and orientation of uplifted areas, and facies distributions in the project area. Because fusulinids are typical of shallow-carbonate, fusulinid density maps are superimposed on the competing paleogeographic models to establish the position of shallow-water carbonate versus siliciclastic-rich facies in the project area. Refined paleodepositional maps are produced by merging fusulinid density maps and selected paleogeographic maps in the project area. Paleogeographic models likely depict eustatic conditions that differ from those depicted in the fusulinid density maps. These differences in eustatic sea levels may cause significant discrepancies between the distribution of shallow water-carbonate established by the fusulinid density maps, and overall facies distributions established by the paleogeographic models. To resolve these issues, fusulinid density maps are compared to paleogeographic models that are likely undergoing similar eustatic conditions.