Abstract

Ammonite species of the genera Prionocyclus, Subprionocyclus, and Collignoniceras described here from the Cardium Formation, in combination with scaphitid ammonoids and inoceramid bivalves, allow recognition of all biozones for the Turonian Stage (Upper Cretaceous) established farther south in the United States Western Interior Basin. Although many of the species used in this zonation were endemic to the Western Interior seaway, more cosmopolitan forms at some levels do allow correlation with western European sequences. The presence of Prionocyclus germari Reuss is firmly established in the lower parts of the Leyland Member, confirming the position of the Turonian–Coniacian boundary and earlier proposed constraints on the duration of the Cardinal–Leyland hiatus.

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