An Integrated Stratigraphy of the Cenomanian-Turonian Eagle Ford Shale, Texas, USA

Eldrett, James S.; Bergman, Steven; Minisini, Daniel; Macaulay, Calum

The Eagle Ford Fm is a prolific source rock and active shale gas and liquid rich unconventional play encompassing the Cenomanian-Turonian oceanic anoxic event 2 (OAE-2). He we provide a robust stratigraphic framework within which to better predict variability in rock qualities and the most productive domains. The Eagle Ford Fm consists of a succession of calcite-rich mudstones (marls and limestones) and over 300 volcanic bentonite layers. Shell has been conducting research on road cuts along US Highway 90, and natural outcrops in the vicinity of Del Rio, Texas that provide excellent exposures of the Buda, Eagle Ford Fm (locally known as Boquillas Fm) and the Austin Chalk. In addition, Shell has drilled two cores, Shell IONA-1 and Shell INNES-1, behind these outcrops, recovering almost 1,000ft of continuous core from the Austin Chalk through the Eagle Ford and Buda Fms. Rock and core material has been processed and analysed for biostratigraphic analyses, including foraminifera, nannofossils, palynology, while numerous bentonite layers have been dated using U/Pb of zircons providing an integrated stratigraphic framework. This framework can be directly applied to the subsurface to determine lateral variability of facies, and also to the Global Stratotype Section and Point (GSSP) at Pueblo, Colorado. Moreover, the refined bio-events and regionally extensive bentonite layers can provide independent verification of the GSSP astronomical tuned age model for the Cenomanian-Turonian Boundary (Meyers et al. 2012). The recovered bio-facies assemblages also provide excellent insight into depositional environment of the Eagle Ford Fm, enabling reconstruction of water column stratification, organic matter influx and preservation.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013