ABSTRACT

In central and eastern Alabama, thirteen Upper Cretaceous (late Santonian to latest Maastrichtian; 85 to 67 Ma) depositional sequences are recognized in the outcropping marine section. Analysis of depositional-sequence paleogeography and the facies relations within depositional sequences (both highstand systems tracts and transgressive systems tracts) permits successful prediction of intrasequence primary permeability, i.e., confined clastic-aquifer distribution. The inferred paleogeographic changes in both gross depositional-strike mode and specific latitudinal position of shoreline trend are directly related, respectively, to second- and third-order changes of sea level. The third-order sea-level changes are eustatic in origin with minor exceptions. Owing to relative tectonic stability of the Gulf passive margin over the Late Cretaceous, eustacy has played a major role in depositional sequence development and thereby promoted a consistent and relatively predictable pattern in the paleogeographic distribution of the constituent confined clastic aquifers.