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An Integrated Stratigraphy of the Cenomanian-Turonian Eagle Ford Formation, Texas, USA – Part 1


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) and deposited near the margin of the Gulf of Mexico Carbonate Shelf also in a retro-arc foreland basin setting behind the Cordilleran orogen. He we provide a robust stratigraphic framework within which to better interpret and predict variability in rock quality and the most productive lithofacies. In the vicinity of the intrashelf Maverick Basin, he Eagle Ford Fm consists of a succession of calcite-rich mudstones (marls and limestones) and over 300 volcanic ash layers (bentonites). Shell has been conducting research on road cuts along US Highway 90, and natural outcrops in the vicinity of Del Rio and Austin, Texas that provide excellent exposures of the Buda, Eagle Ford (locally known as Boquillas Fm) and the Austin Chalk Formations. In addition, Shell has drilled two cores, Shell IONA-1 and Shell INNES-1, behind these outcrops, recovering continuous core the entire stratigraphy of Eagle Ford and part of the encasing formations (Austin Chalk and Buda Limestone). Biostratigraphic data, including foraminifera, nannofossils, palynology, and U/Pb geochronology of extracted zircons from numerous bentonite units provide an integrated high resolution stratigraphic framework. We also extracted grey-scale values from core photographs and conducted time series analyses on this and other proxies to astronomically tune our age model to provide high resolution calibration and calculate organic matter flux rates. This framework has been applied at the basin scale to determine infill history and lateral variability of the most productive facies.