AGE OF THE BEAR RIVER FORMATION, WYOMING

The age of the Bear River formation is maintained to be Cenomanian. This age assignment is supported by the fossil content of the formation: (1) species of Pyrgulifera, a characteristic genus of the Bear River, have been recorded abundantly in different parts of Europe, and their known range is Upper Cretaceous (Cenomanian to Danian); (2) species of Pyrgulifera and at least 10 congeneric and closely similar species of the Bear River formation were found in the Gardonian formation in southern France, and the Gardonian is considered a standard representative of Upper Cenomanian; (3) the Pyrgulifera-bearing beds exposed elsewhere in Europe, which are considered to be younger than the Cenomanian, did not yield species closely similar and congeneric with those of the Bear River formation, despite their apparently similar habitat conditions; and (4) species of Pyrgulifera in North America have been found in the beds stratigraphically above the Bear River, but not below it.