THE REGIONAL CHARACTER OF THE LOWER TUSCALOOSA SANDSTONE DEPOSITIONAL SYSTEMS (LATE CRETACEOUS): INFLUENCES ON RESERVOIRS FROM SOURCE TO SINK

The lower Tuscaloosa Sandstone is a major hydrocarbon bearing fluvial/deltaic clastic unit that; in the central and eastern Gulf Coast region is increasingly looked to as an onshore target to sequester carbon. In addition, several wells have penetrated the Tuscaloosa equivalent units ~500 km south of the Louisiana coast in the ultra-deep water regions of the Gulf of Mexico. The deposits penetrated in the Tiber well prove the existence of a major deepwater depositional bypass system during late Tuscaloosa time.

The growing importance of pre-Neogene Gulf of Mexico exploration plays suggests a need to revisit the influences on the Tuscaloosa’s sequence framework, controls on its fairways, accommodation sinks, and the nature of a source-to-sink system that spanned well over 500 km basinward. In addition, many questions exist regarding the origin of porosity-preserving chlorite in the formation and glauconite distribution. A database of 668 well log suites, 13 core, and regional seismic data were utilized, to examine the lower Tuscaloosa across a study area of 45,000 km2 in Louisiana, Mississippi and Alabama. Correlation panels and isopach maps show that the units increase in thickness to the south and west and show a decrease in sand percent. The Tuscaloosa was deposited as a series of six regressive-transgressive parasequences with sediment being shed from drainages in southern Arkansas (chlorite-rich) and the northern and southern Appalachia highlands (meta-sedimentary rock fragment rich). Major structures of the Cretaceous appear to have had an affect on lower Tuscaloosa depositional patterns. The Wiggins Arch dammed fluvial deposits to the north of it, as well as possibly influencing the development of two thicks trending north-northwestward and north-northeastward. This talk will discuss regional sedimentary and petrographic trends in the Tuscaloosa, as well as the nature of the deepwater Tuscaloosa facies in the ultra-deep regions of the Gulf of Mexico which reveal volumetrically large, sandy gravity flows whose permeability is occluded by post-depositional calcite growth.