TRANSGRESSIVE-REGRESSIVE CYCLES IN UPPER CRETACEOUS STRATA, NORTHEASTERN GULF OF MEXICO

Transgressive-regressive (T-R) cycles are recognized in Upper Cretaceous strata of the northeastern Gulf of Mexico. These cycles include the T-R 5 (late middle Cenomanian to late Turonian), T-R 6 (middle Coniacian to middle Campanian), T-R 7 (middle to late Campanian) and T-R 8 (early to early late Maastrichtian) cycles. Recognition of the cycles is based on stratal geometries, facies stacking patterns and large-scale shifts in facies belts. The cycles are controlled by the change in shelfal accommodation space resulting from base-level changes (eustatic and tectonic and loading subsidence effects) and sediment supply and accumulation.

The T-R cycles are composed of a transgressive aggrading and backstepping phase or upward deepening interval and a regressive infilling phase or upward shallowing section, which are separated by a surface of maximum transgression. The aggrading phase, which overlies a subaerial unconformity, marks the change from base-level fall and erosion to base-level rise and sediment accumulation. This phase signals the initiation of creation of shelfal accommodation. The top of the aggrading interval is defined by a ravinement surface or transgressive surface, which is overlain by the backstepping section. The transgressive events of the backstepping interval are widespread and provide regional correlation datums. The progradational events associated with the infilling section represent major influxes of siliciclastic sediments and result in a loss of shelfal accommodation space. The top of the progradational interval is marked by a surface of maximum regression. These Upper Cretaceous T-R cycles are correlated in the northern Gulf of Mexico and have potential for global correlation.