THE PRECAMBRIAN BASEMENT ROCKS OF KANSAS

Surficial and subsurface geologic mapping is critical to understanding geologic hazards, structural geology, and resource potential (oil, gas, critical minerals, CO2 sequestration). While geologic mapping has historically been a fundamental element of state geological surveys like Kansas, new datasets and tools have created the opportunity to produce high resolution subsurface geologic maps. Many updates to the Kansas basement map were recently made since the previous one was published over 45 years ago. Additional well tops, state-of -the-art mapping software, computing power, and updated lithologic boundaries were integrated into the current map. Here we present an early iteration of an integrated subsurface interpretation for the Precambrian basement in Kansas using combined well top datasets with over 5,000 well tops sourced from the KGS and surrounding geological surveys. The convergent interpolation algorithm was used to generate the surface from the data points.

The Precambrian basement (~1.0 Ga and older), is composed of crystalline rocks that include rhyolite and quartzite but is mostly granitic. The basement rocks lay beneath the Paleozoic and younger sedimentary rocks at depths ranging from 6,000-feet below SL to 1,000 feet above SL. Three major fault systems were modelled: the Nemaha fault zone (NFZ), the Central Kansas Uplift (CKU), and the southern extent of the Mid-Continent Ridge (MCR). The throw along the NFZ varies between 0-2500 feet with fault throw generally increasing northwards. Faults in this version were modelled as vertical due to complex intersecting fault geometries and inversion. The 3D faulted framework model was constructed with SLB Petrel software and the output from Petrel, which is a 3D grid was exported to Esri ArcGIS Pro and converted to a DEM with additional metadata to be published on the National Geologic Map Database (NGMDB) website. This workflow will be applied to USGS Statemap subsurface mapping projects in Kansas including a sub-regional map of the lower Mississippian strata and Cretaceous units associated with the Dakota Aquifer System. These maps will be iteratively updated using additional data e.g., well logs, earthquake hypocenter data, seismic data, new wells/core/cuttings, and gravity data, as they become available and can be fully integrated into the statewide 3D subsurface model.