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Accurate Age Control in Clastic Deepwater Depositional Systems From Multidisciplinary Chronostratigraphic Analysis


An accurate chronostratigraphic framework is essential for reliable and consistent stratigraphic interpretation of clastic depositional systems. Multidisciplinary Chronostratigraphic Analysis (MCA) is an interdisciplinary technique that constructs chronostratigraphic frameworks, at multiple scales, wherein data derived independently from the fields of geochronology, biostratigraphy, and petrography are used to establish high-confidence, correlative age boundaries. By combining data from independent, unbiased techniques, the composite age uncertainty of MCA is often less than individual analytical uncertainties associated with each method, which are inherently defined by statistical metrics tied to population and sample quality issues. MCA enhances traditional low-to-medium confidence depositional age determination and stratigraphic correlation techniques, especially in deepwater turbidite systems, where frameworks for sedimentary depositional models too often rely on simple lithostratigraphic methods for connecting data points between widespread well locations in basin-scale depositional systems. Here we present an example from the deepwater Paleogene Wilcox Group within the Gulf of Mexico Basin. The Wilcox Group derived primarily from the Central and North American Cordillera and is divided into four main stratigraphic units of varying compositional, textural, and architectural character (and related reservoir properties) that reflect its long record of Laramide orogenic evolution and continental-scale drainage network reorganization. Boundaries between Wilcox Group units are time correlative and MCA, using tools such as improved nannofossil and palynomorph biostratigraphic zonation, recalibrated key chronostratigraphic events in our regional Paleogene stratigraphic model by documenting characteristic changes within turbidite systems over time. The versatility of MCA was then demonstrated in an appraisal setting by influencing a decision to reframe select, time-correlative sand bodies in a major deepwater asset, prompting a reevaluation of field-scale properties such as permeability and gross rock volume. In addition to improved chronostratigraphy, MCA can also resolve paleoclimatic and sediment provenance issues and corroborate geologic process-based stratigraphic interpretations—within a deepwater Wilcox field, evidence of reworked Cretaceous palynomorphs, an absence of Paleogene aged zircon, and increased relative lithic content within some sand bodies indicated a significant erosive event and substantiated a stratigraphically interpreted mass-transport complex.