IN WITH SOME OLD, OUT WITH SOME NEW: AN UPDATE ON THE WHITE RIVER GROUP OF NORTH DAKOTA

The White River Group, of the northern Great Plains, is one of the most well-known geologic units in the United States. The group consists of thick sequences of volcaniclastic, fluvial, eolian, and lacustrine strata. In North Dakota, the lithic units that comprise the White River Group were first examined in 1883 by Edward Cope with some more recent studies completed in the 1990’s. Geographically the group is present, although not in continuous sections, in southwestern North Dakota which constitutes the main field locations for this study. Recent work has brought into question the correlation, designation, and physical description of the lithic units within North Dakota. Ten new lithostratigraphic sections were completed and compared to previous studies. These new lithostratigraphic sections have provided clarification on some of the anomalous features, such as abnormally thick units. Additionally, a previously undescribed, stratigraphically controlled collection of over 1,500 vertebrate fossils (housed at the Pioneer Trails Regional Museum) was utilized to better understand the paleodiversity and mammalian biostratigraphy of the White River Group in North Dakota. These specimens, as well as specimens collected from a new fossil horizon within the Arikaree Formation, have provided more biostratigraphic resolution for the North Dakota units. Presently, analysis of the Pioneer Trails Regional Museum collections has resulted in an alpha diversity increase in regards to marsupials and insectivores from the White River Group of North Dakota. Also, this study has provided justification for the species Ankylodon progressus, which was previously known only from Colorado. The Pioneer Trails Regional Museum specimens, and associated stratigraphy, could indicate a potentially distinct regional transition between the typical White River Fauna of South Dakota and Nebraska and the Cypress Hills Formation of Saskatchewan and Alberta, Canada. Finally, with continued study it appears that some of older hypotheses should not be so readily dismissed, while other more recent interpretations are in need of a reassessment.