Late Mesozoic and Cenozoic deposystem evolution in the eastern Gulf of Mexico: implications for hydrocarbon migration

Fillon, R. H., Earth Studies Associates, New Orleans, LA

Abstract

A preliminary analysis of Mesozoic and Cenozoic deposystems in the eastern Gulf of Mexico using published regional stratigraphic and depth to basement studies, reveals striking elements of deposystem history and petroleum system architecture. Integration of thirteen regional studies into a single chronostratigraphic framework provides a basis for defining eight Mesozoic and eight Cenozoic second-order depositional sequences spanning the interval 165 Ma to the present.

Interval accumulation rate mapping reveals that major deposystems shifted in response to the changing tectonic setting of the Gulf basin. The Cotton Valley, Selma, and Pliocene-Pleistocene sequences reflect changes in deposystem architecture corresponding to evolution from hot, thermally dynamic crust of the youthful Gulf basin to cool, thermally stable modern crust where gravity tectonics dominate. The differential compaction caused by shifting depocenters throughout this interval establishes a system of changing pressure gradients that influence lateral migration pathways of both salt and hydrocarbons. Changing accumulation rates and related pressure changes also directly affect hydrocarbon maturation and generation by modifying the temperature and pressure history of buried source rocks.

The mapped data predict that hydrocarbon migration paths locally converge within the sale 181 area, principally because long-term sediment accumulation in the area has been relatively low. While hydrocarbon risk is diminished, low accumulation rates for most sequences suggest that reservoir risk is higher than average. The search for productive reservoir in the sale area should therefore focus on specific parts of the section that exhibit higher accumulation rates than the regional average, the late Albian-early Cenomanian (Paluxy sequence) and the middle Miocene (upper Miocene sequence).