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A Sequence Stratigraphic Framework for the Wilcox Group, Gulf of Mexico

Abstract

The Early Eocene to mid-Paleocene clastic succession of the Wilcox Group in the deep water Gulf of Mexico contains billions of barrels of untapped oil reserves that provide great exploration opportunities despite the comparatively poor reservoir qualities reported from many of the discoveries made to date. The future exploitation of these reserves will be dependent on oil price, advances in drilling technologies and achieving better geological understanding to help mitigate exploration risks. Underpinning any improvement in predictive modelling of reservoir presence and quality is the establishment of a refined stratigraphic framework and improved understanding of sediment provenance. This paper presents a detailed sequence stratigraphic framework for the Wilcox Group, established after the biostratigraphic analysis of 30+ shelfal well sections from across the Gulf Coast, from the Mexican border of South Texas to Alabama, and from 50+ wells across a broad transect of the deep water GoM. Innovative correlations using a novel, high-resolution palynology biozonation between onshore Gulf Coast well sections and well penetrations in the deep water GoM provide evidence of at least two major unconformities linked to sustained periods of significantly lower relative sea-level. These breaks in deposition led to the historical establishment of the Upper, Middle and Lower Wilcox lithostratigraphic units across the Gulf Coast. Until now linking these units to the deep water stratigraphy, such as the existing Wilcox 1 to 4 scheme of Zarra 2007, has proven problematic. A higher-resolution biozonation based on palynology rather than the historical model based on dissolution prone calcareous micro- and nannofossils provides new insights in to how the onshore and deep water Wilcox correlate. The analysis of regional variations in pollen & spore assemblages across the Gulf Coast also contributes to the determination of sediment provenance.