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This study concerns a sequence about 3800 ft thick consisting of the mainly marine Sentinel Hill Member of the Schrader Bluff Formation and the mainly nonmarine Kogosukruk Tongue of the Prince Creek Formation, which intertongue with each other in the Colville River area and form the mid(?)-Campanian to upper Maastrichtian part of the Colville Group. The pollen biostratigraphy and chronostratigraphy presented here are based on the observed distribution of 103 angiosperm pollen taxa in 148 samples arranged to form 21 sample groups. Dinoflagellate cyst (dinocyst) chronostratigraphy is based on distributions of 20 species in 10 samples from the lower and middle parts of the Sentinel Hill Member and on dinocyst species found in 12 samples from strata below the Sentinel Hill. Because of the large number of pollen range tops and range bases, a reasonably fine-scaled biostratigraphic subdivision of the entire sequence is now possible, as demonstrated by a detailed pollen correlation of the lower part of the Kogosukruk Tongue between two stratigraphic sections, the outcropping section and the Sentinel Hill core test 1 section, about 8.0-12.5 mi apart. Chronostratigraphy is based here on pollen and dinocyst data integrated with published information from a large variety of other fossil types and from radiometric data. It is concluded that (1) the CampanianMaastrichtian boundary is near the top of the middle part of the Sentinel Hill Member, slightly below the level where Smiley (1969) placed this boundary, and (2) the (informal) substage boundary between the lower and upper Maastrichtian is near the top of the middle part of the Kogosukruk Tongue, not far below the "Ocean Point marine beds," which represent the upper part of the Sentinel Hill Member. Thus, the "Ocean Point marine beds" are early late Maastrichtian in age. Dinocysts from below the Sentinel Hill Member demonstrate that the base of this member is mid(?)-Campanian in age. Given the chronostratigraphic conclusions, the 3800-ft thick section studied here consists of about 1315 ft of upper Maastrichtian strata, about 1525 ft of lower Maastrichtian strata, and about 960 ft of "middle" to upper Campanian strata.

Palynomorph biostratigraphy of mid(?)-Campanian to upper Maastrichtian strata along the Colville River, North Slope of Alaska