MULTI-PROXY CORRELATION OF THE EAGLE FORD SHALE IN WEST TEXAS TO THE BRIDGE CREEK LIMESTONE (CENOMANIAN-TURONAIN GSSP) IN CENTRAL COLORADO

The Cenomanian-Turonian boundary (93.5 Ma) represents a unique interval across the globe. Elevated tectonic activity resulted in the highest sea levels of the Mesozoic, creating large epicontinental seas, while a greenhouse climate and global oceanic anoxia accelerated burial of organic matter, which is preserved in marine rocks as a positive excursion of carbon isotopes, termed Oceanic Anoxic Event 2 (OAE2). The Bridge Creek Limestone at the Cenomanian-Turonian Global boundary Stratotype Section and Point (GSSP) in Rock Canyon (RC) near Pueblo, Colorado contains the global hallmarks of OAE2, with regional signals from the Western Interior Seaway superimposed. Rock Canyon has become a key location for comparison of sections of the same age across the globe and throughout the western interior of North America. Here we present correlations between the Bridge Creek Limestone at RC and the Eagle Ford Shale at Lozier Canyon (LC), Terrell County, Texas, using multiple bio- chemo- and lithostratigraphic techniques. The Eagle Ford at LC is separated from the full marine environment of the Gulf of Mexico by the Devil’s Basin uplift to the east. At LC, we find the same sequence of planktic foraminiferal datums as described at Rock Canyon, notably the last occurrences (LOs) of the genus Rotalipora and Globigerinelloides bentonensis. We also find the same calcareous nannofossil datums from the Bridge Creek, notably the LOs of Helenea chiastiai and Corrollithian kennedyi and the subsequent first occurrences (FOs) of Eprolithus eptapetalus and Quadrum gartneri. Geochemical signals are also nearly identical between the two sites. The carbon isotope curve from the Eagle Ford and the positions of biotic datums along it almost exactly mirror the A-B-C structure of OAE2 isotope excursion at RC. Total Organic Carbon (TOC) also parallels the structure of the TOC curve at RC, with the highest TOC values occurring below the global anoxic event. Despite the similarities between the LC and RC localities, the near absence of benthic forams in the basal part of OAE2 at LC suggests that this TX locality was situated within a silled sub-basin or at a shallower paleo-water depth within the oxygen minimum zone compared with deeper water sites at Big Bend TX to the west and RC to the north where a well-developed “benthic zone” has been observed.