Regional tectonic features played a significant role during the deposition of the Tuscaloosa Formation. The LaSalle Arch and the Wiggins/Hancock County Arches serve as “tectonic bookends” for the Tuscaloosa Fairway. These large tectonic features exerted control over the orientation and subsequent deposition of the ancestral Mississippi River. A regional 2D seismic grid and well logs indicate that the ancestral Mississippi River was very prominent along this fairway as far back as Upper Jurassic (Cotton Valley) time.
The base of the Tuscaloosa Marine Shale (TMS) structure illustrates the structural nosing caused by these features and exhibits a variance in dip across Louisiana. The large volume of Tuscaloosa sand deposition and subsequent loading resulted in a gently dipping structure within the Tuscaloosa Fairway. Prolific Tuscaloosa sand production (green) occurs along this fairway (blue dashed lines). To the west where Tuscaloosa sand deposition did not occur, much steeper structural dips resulted. The impact of the Sabine Uplift is evidenced by the southwestern trend of the structure contours. The cluster of diapiric salt domes down dip of the Tuscaloosa Fairway indicates massive sedimentary loading and a consistent axis of deposition during later geologic time. The modern day Mississippi River still flows through this fairway today. McMoRan currently explores for the Tuscaloosa sands downdip of this fairway in the Gulf of Mexico.
Repetitive, extensive depositional loading events occurred through time and resulted in basinal subsidence, which ultimately led to a unique burial history along the Tuscaloosa Fairway. Thick accumulations of higher resistivities in the TMS align with the Tuscaloosa Fairway. The Tuscaloosa sands and the TMS appear to be part of the same hydrocarbon system. The hydrocarbon source for the Tuscaloosa sands has been determined to be from a combination of Lower Cretaceous, Tuscaloosa shales, and the TMS. The regional structure might provide some insight into the burial history of the TMS. The higher resistivities along the Tuscaloosa Fairway provide evidence for a substantial “hydrocarbon kitchen.” The Tuscaloosa Fairway being positioned in between two significant tectonic features will have likely experienced a different burial history and subsequent thermal maturity than the regions to the east and west. The region of higher resistivities would provide support for this hypothesis.