A New Reference Section for Palynostratigraphic Zonation of Paleocene Rocks in the Rocky Mountain Region

摘要

A biostratigraphic (palynostratigraphic) zonation of Paleocene rocks was established in the northeastern Wind River Basin near Waltman, Natrona County, Wyoming, in 1978 and subsequently applied extensively by various workers throughout the Rocky Mountain region. Because the original study on which the zonation was based was proprietary, precise details about the locations of the two reference sections and the samples on which the zonation was based were not published and are no longer retrievable. Therefore, it is useful (although not required) to designate formally a new reference section for the Paleocene biozones. Accordingly, exposures of Paleocene and associated strata -within and west of the Castle Gardens Petroglyph Site in Fremont County, Wyoming, in the east-central part of the Wind River Basin, were selected for this purpose. At this location, composite stratigraphic sections encompassing 740 m of strata were measured, described, and sampled. Productive samples yielded characteristic Maastrichtian palynomorphs from the lower part of the sampled interval and diagnostic species of the six palynological biozones zones widely known as PI (lower Paleocene) through P6 (upper Paleocene), through an interval of about 580 m. The Paleocene biozones are present in the same consistent stratigraphic order in the Castle Gardens area as obseived in the 1978 study and subsequent studies throughout the Rocky Mountain region. In accordance with the North American Stratigraphic Code, the historical background is presented; intent to establish the Castle Gardens reference section is declared; the categoiy, rank, and formal names of Liiostratigraphic units within it are specified; and the features of the biozonation are described, including biozone boundaries, ages, and regional relations. Occurrences of biostratigraphically significant palynological species within each biozone in the reference section are tabulated, and presence of these and other species in correlative biozones are discussed. The new reference section in the Castle Gardens area replaces the original reference sections near Waltman and provides a better-documented foundation for Paleocene palynostratigraphy in the Rocky Mountain region.