Pueblo, Colorado, USA, candidate Global Boundary Stratotype Section and Point for the base of the Turonian Stage of the Cretaceous, and for the base of the Middle Turonian Substage, with a revision of the Inoceramidae (Bivalvia)

Abstract

An updated account of the candidate Global Boundary Stratotype Section and Point for the base of the Turonian Stage and the base of the Middle Turonian Substage in the Bridge Creek Member of the Greenhorn Limestone exposed in the Rock Creek Anticline west of Pueblo, Colorado is provided. Key ammonite distributions are revised and marker species illustrated. A taxonomic revision of the uppermost Cenomanian to lower Middle Turonian bivalve family Inoceramidae provides, for the first time, an adequately documented detailed zonation for the interval in the form of five successive partial range zones based on species of the genus Mytiloides. These are successive zones of M. hattini ELDER (uppermost Cenomanian), M. puebloensis n.sp., M. kossmati (HEINZ), M. mytiloides (MANTELL) (all Lower Turonian) and M. subhercynicus (SEITZ) (lower Middle Turonian). The base of the Turonian, defined by the first appearance of the ammonite Watinoceras devonense WRIGHT & KENNEDY at the base of bed 86 of the Bridge Creek Member corresponds to the first occurrence of Mytiloides puebloensis, and the base of the puebloensis Zone. The base of the Middle Turonian, defined by the first occurrence of the ammonite Collignoniceras woollgari (MANTELL) in bed 120 of the Bridge Creek Member is just below the first occurrence of M. subhercynicus in bed 121, and the base of the subhercynicus Zone.