USING GIS TO MAP, INTERPOLATE, AND VISUALIZE THE TERRESTRIAL CRETACEOUS/PALEOGENE EXTINCTION EVENT IN THE WILLISTON BASIN’S CEDAR CREEK ANTICLINE

Much of the current debate over the Cretaceous/Paleogene (K/Pg) mass extinction event revolves around the mechanism and tempo of the extinction of terrestrial vertebrates: gradual versus catastrophic. Hundreds of known fossil localities, otherwise floating data points, need to be time-correlated and tied to a biostratigraphic range for each taxa in order to rigorously assess the tempo of the K/Pg extinction. Pinpointing the precise location of the K/Pg boundary is also critical for establishing a baseline from which each fossil locality can be correlated. Here we model the K/Pg boundary across a ~475 square mile study area along the Cedar Creek anticline in southwestern North Dakota and southeastern Montana. The formation contact between the Cretaceous Hell Creek Formation and Paleocene Fort Union Formation in the badlands of the Cedar Creek anticline closely approximates the K/Pg boundary and was mapped using a differential GPS in 500 locations across the study area. The elevations for these points were used as the input for creating the K/Pg surface in ESRI ArcMap 10.4 GIS program with the Geostatistical Analyst extension. The resulting surface connects the many points into a continuous plane that intersects the badlands topography at the K/Pg boundary. Fossil localities above this plane are in the Paleocene, while fossil localities below the plane are in the Cretaceous, making the plane an effective tool for tying species in biostratigraphically using elevation. Empirical Bayesian Kriging (EBK) and Local Polynomial Interpolation (LPI) were used to create iterations for both localized and entire study area planes to create the most statistically sound model given the non-uniform outcrop of the contact due to the structural geology and erosional surface of the badlands. As a field check on the models, the actual distance above or below the formation contact was measured by hand for 91 fossil localities using stratigraphic sections or an eye level and Jacob’s staff and compared to the model’s prediction. The EBK method performed the best with 63% of the localities predicted within two meters and 85% predicted within four meters of the field measurements. The final K/Pg EBK plane was then brought into ESRI ArcScene 10.4 to create a 3D animation across the study area to visually communicate the concept and utility of the model.