Depositional system transitions and sequence stratigraphic evolution of the Tuscaloosa Group in the Mississippi Embayment, USA: Accommodation space and sediment supply controls

The Tuscaloosa Group (Grp), the basal unit of Upper Cretaceous strata in the northern Gulf of Mexico (GoM), formed during the late Cenomanian transgression across the southeastern United States. Despite its significance, comprehensive sequence stratigraphic analyses of the Tuscaloosa Grp within the south-central Mississippi Embayment (MSE) are limited. This study integrates core data, wireline logs, and field observations to characterize its depositional evolution and sequence stratigraphic architecture, delineating stratigraphic surfaces, systems tracts, and depositional sequences, and examining controlling factors. Four third-order sequences were identified from four sequence boundaries, two transgressive surfaces, and three maximum flooding surfaces. Sequence 1 (S1) includes a lowstand systems tract (LST), transgressive systems tract (TST), and highstand systems tract (HST); Sequence 2 (S2) has a TST and HST; Sequence 3 (S3) contains a LST, TST, and HST; and Sequence 4 (S4) includes a LST and TST. S1 comprises fluvial and incised valley deposits (LST), transitioned to deltaic TST during rising sea levels, and culminated in barrier island and shelf HST. S2 features distal shelf TST deposits followed by a prograding deltaic HST. S3 records a full cycle: fluvial LST, retrograding deltaic TST, and progradational deltaic HST. S4 is less developed, with fluvial LST and localized retrograding deltaic TST deposits. The Tuscaloosa's evolution was driven by accommodation space changes and sediment supply. Subsidence of the MSE in the Late Cretaceous may have increased accommodation and facilitated TST formation in the Upper Tuscaloosa. The Appalachian Highlands supplied most sediments, with the Ouachita Highlands as a secondary source.