A 3D GEOLOGIC FRAMEWORK MODEL OF THE NORTHERN GREAT PLAINS, USA: PROGRESS TOWARD A NATIONAL SCALE SUBSURFACE MODEL

Digital, Geographic Information System (GIS)-ready, three-dimensional (3D) subsurface models are becoming a standard practice for geological survey organizations (GSOs) to systematically investigate and document the geology within their jurisdictions. These products are in high demand, as publicly available subsurface data facilitates natural resource assessments, engineering or environmental studies, and informed land management decisions. The USGS National Cooperative Geologic Mapping Program (NCGMP) is addressing this demand by developing 3D geologic framework models of the conterminous United States at the local, national, and continental scale (House Report 116-100).

This presentation discusses the NCGMP’s development of a digital 3D subsurface geologic model spanning the northern Great Plains physiographic province of South Dakota, Wyoming, Montana, and North Dakota, and addresses challenges associated with data compilation, synthesis, and dissemination of these products. Over 3 million data inputs from surficial geologic mapping, well logs, raster datasets, geologic cross sections, seismic data, structure contour and isopach maps, geophysical surveys, and previously published model grids were compiled from state GSOs, industry repositories, and academic partners. These data were synthesized into a cohesive 3D geological model consisting of 42 stratigraphic horizons, 64 fault planes, and multiple intrusive bodies which portray the generalized geology of the northern Great Plains. This study depicts how well-studied basins with high data density (such as the Powder River and Williston Basins) correlate across regions of sparse data availability (such as the Miles City Arch or Hartville Uplift). Outcrop patterns at the model’s surface approximate patterns observed in 1:500,000-scale geologic mapping, however deviations from model input data emphasize the importance of quantitative model validation, rigorous data hygiene, and clear uncertainty communication to potential users. Ultimately, lessons learned from this work will be applied to future NCGMP 3D modeling efforts, and may inform future decisions regarding subsurface data standardization, modeling methodology, and accessibility.