Cenomanian-Turonian Bioevents-Implications for Sequence Stratigraphic Analysis

Dragana Nebrigic
The University of Texas at Dallas, Richardson, TX

Biostratigraphy is essential for identifying ages of stratigraphic sequences and their correlation. Detailed interpretation of eustatic, tectonic, sedimentological and ecologic-paleobiogeographic changes demands a complex and refined system of high resolution biostratigraphy with world-wide application. In the Gulf of Mexico, there is an acute need for recalibration of Upper Cretaceous time scale, as stratigraphic resolution of most biostratigraphic plots, which are commonly not multitaxial, does not anymore meet needs of industry and academia. It is still common, unfortunately, to employ old biostratigraphic zonations based on broad assemblage zones of early workers, exclusively done on single lineages of ammonite and inoceramid bivalves, as well as on an outdated taxonomy of many important biostratigraphic markers. Bioevents within a foraminiferal community of Eagle Ford time (Cenomanian-Turonian) of the Texas Gulf Coast, integrated with nannofossils and their response to sea level changes have been of primary importance to develop a microfossil-based time scale for this time interval. Eagle Ford strata show considerable lithological variability and cyclicity, deposited during global transgression. Particular attention has been given to the Cenomanian-Turonian boundary events (92.5MYA) and their correlation to the events of a newly established global stratotype section and point of lower Turonian in Pueblo, Colorado. This zonal system may provide key information for the biostratigraphic calibration of the sequence and important information for the recognition of depositional system that has been developed during the time of maximum sea level change.