ABSTRACT

A continuous and relatively well-exposed section of about 14,000 ft (4,300 m) extends from the Lower Cretaceous strata of the Middle and West Domes through Upper Cretaceous rocks on the south flank of the Shawmut Anticline and on through the Paleocene strata of the north rim of the Crazy Mountains Basin. The following road log encompasses portions of our present study area in the Lower Cretaceous of Middle Dome and the uppermost Cretaceous and Paleocene of the northeastern portion of the Crazy Mountains Basin. One of the primary goals of our mammalian and molluscan research is to provide a biostratigraphic reference section for significant portions of the Paleocene in the northern Great Plains. To accomplish this objective, large sample sizes were obtained from a number of stratigraphically documented localities spanning the Bear, Lebo, and Melville Formations. Through the joint collecting efforts of the authors' field crews from 1985 through 1991, the number of molluscan localities increased from 90 (collected from 1890 to 1984) to 374. Of these, the vast majority lie within strata of the upper Lebo and lower Melville Formations, which span the transition from the middle Paleocene (Torrejonian Land-Mammal Age) to the late Paleocene (Tiffanian Land-Mammal Age). In addition, 83 Paleocene mammalian localities are now known from the basin, including significant quarries in the early (Simpson Quarry), middle (Azzara, Hartman, Gidley, and Silberling Quarries), and early late (Bingo, Glennie, Douglass, and Scarritt Quarries) Paleocene.