Upper Cretaceous rocks in the Colville River region are divided into three formations, which are, in ascending order, the Ninuluk, the Seabee, and the Schrader Bluff. Inoceramus (Inoceramus) dunveganensis McLearn, of Cenomanian age, is abundant in the Ninuluk formation. Inoceramus (Mytiloides) labiatus (Schlotheim) and I. aff. I. (Inoceramus) cuvierii Sowerby occur in the lower part of the Seabee formation of early Turonian age. Inoceramus. aff. I. (Inoceramus) cuvierii occurs alone in the upper part of the Seabee, which probably is of middle to late Turonian age. There is no evidence that this species extends into the Coniacian in northern Alaska. The Barrow Trail member of the Schrader Bluff formation contains Inoceramus (Sphenoceramus) patootensis de Loriol and I. (S). steenstrupi de Loriol, both of late Santonian to early Campanian age. The precise age of the lower and upper members of the Schrader Bluff formation is not certain.

The Seabee formation, 400-1,800 feet thick, contains two ammonite faunas that are assigned to the Turonian stage of the Upper Cretaceous. These ammonites reveal a mixing of elements from the Atlantic and Pacific faunal realms. The species of Scaphites and Watinoceras are Atlantic types whereas the species of Otoscaphites, Borissiakoceras, and Proplacenticeras seem to have a Pacific source. A connection of the Western Interior Seaway with the Pacific Ocean via the Arctic Ocean along northern Alaska seems likely. New species described are Scaphites subdelicatulus, Otoscaphites seabeensis, Borissiakoceras inconstans, and B. ashurkoffae.