Soft-Bottom Paleocommunity Dynamics in the Cenomanian - Turonian Boundary Extinction Interval of the Western Interior, United States

Abstract

Extensive species-level, marine biotic turnover is recorded across the Cenomanian-Turonian (C-T) Stage boundary in the western interior of the United States (Fig. 1) and intercontinentally (e.g., Wright and Kennedy, 1981; Elder, 1987; Jarvis et al., 1988). Widespread intensification and expansion of the oxygen minimum zone have been widely proposed as a causal mechanism for the organic-rich deposits and biotic extinctions found in strata of this age (e.g., Schlanger et al., 1987; Jarvis et al., 1988). Accompanying these extinctions were large-scale reorganizations of community compositions and trophic structures. In the western interior, repeated community replacement was associated with widespread cyclic sedimentation, and long-term community turnover was related to extended periods of dysaerobia and possibly low salinity conditions. Community compositions and distributions were therefore largely controlled by physical rather than biological factors. This paper will document how these oceanographic and sedimentologic factors affected community patterns across the C-T boundary.