Norman O. Frederiksen¹, David J. McIntyre²

(1) U.S. Geological Survey, Reston, VA
(2) Consultant, Calgary, AB

ABSTRACT: Age Control on Campanian and Maastrichtian Strata Along the Colville River North of Umiat, North Slope, Alaska

This study concerns a sequence about 3800 ft thick consisting of the mainly marine Sentinel Hill Member of the Schrader Bluff Formation intertongued with the mainly nonmarine Kogosukruk Tongue of the Prince Creek Formation. About 30 miles east of the Colville River, in the West Sak Field, correlative rocks contain a multibillion-barrel accumulation of heavy oil. Occurrence data on 103 angiosperm pollen and 20 dinocyst taxa from along the Colville are integrated here with published fossil and radiometric data from the area. Three tongues of the Kogosukruk make up nearly 80 percent of the sequence; therefore, pollen and dinosaur bones, as well as radiometric dates from tuffs, furnish the most useful age constraints in most of the section. However, dinocysts and foraminifers are also important for dating the Campanian-Maastrichtian boundary, which is here placed near the top of the middle tongue of the Sentinel Hill Member, close to where Smiley tentatively placed it in 1969. Based mainly on pollen, benthic foraminifers, and radiometric dates, we place the upper/lower Maastrichtian boundary within the middle tongue of the Kogosukruk, just below the base of the "Ocean Point marine beds," which represent the upper tongue of the Sentinel Hill Member. Campanian dinocysts also occur in strata below the Sentinel Hill Member; therefore, the base of this member is considered to be mid(?)-Campanian in age. The 3800-ft thick section consists of about 1315 ft of upper Maastrichtian, about 1525 ft of lower Maastrichtian, and about 960 ft of "middle" to upper Campanian strata.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado