Lithostratigraphic revision and redescription of the Brule Formation (White River Group) of northwestern Nebraska

Based on geologic mapping, measured sections, and lithologic correlations, the boundaries of the Brule Formation are revised in the type area in northwestern Nebraska. Marker beds used to subdivide and correlate the Brule Formation are rec-ognized as local features of the type area, and their use as stratigraphic boundaries is abandoned in favor of boundaries corresponding to mapped changes in lithology. Using revised lithostratigraphic boundaries, the Brule Formation and its members are redescribed as a series of lithotopes. The revised upper boundary of the White River Group is the unconformable lithologic contact between massive volcaniclastic silt-stones and sandy siltstones of the Brule Formation and brown and grayish-brown fluvial volcaniclastic sandstones, cross-bedded conglomeratic sandstones, and massive tabular volcaniclastic sandstones of the overlying Arikaree Group. These massive silt-stones and sandy siltstones were correlated to the Gering Formation of the Arikaree Group, but are now recognized as the brown siltstone member of the Brule Forma-tion. They are redescribed as a lithotope consisting of pale brown and brown indis