Rhythmic Sedimentation Documented in a Late Cretaceous Core (Abstract)

Abstract

A continuous core taken through the Bridge Creek Limestone and Hartland Shale is the basis for a study of rhythmic sedimentation in late Cenomanian — early Turonian deposits in the Western Interior Basin of North America. The core has been cut in half, polished, and peeled, thus providing a detailed record of the large-scale bioturbation rhythms, small-scale lamination rhythms, current events, and volcanic ash falls that occur in 30 meters of the section. Alternating beds of burrowed micritic limestone and laminated organic-rich marls characteristic of the Bridge Creek Limestone are well-suited to the study of rhytmic stratal events and can be interpreted in terms of changing oceanographic conditions. The broad spectrum of sediment types and sedimentation events documented in the peels indicate that this Cretaceous sea oscillated between brackish and marine states, stratified and well-mixed states, and between anaerobic and aerobic bottom conditions.