UPPER CRETACEOUS DEPOSITIONAL SEQUENCES IN THE ALABAMA GULF COASTAL-PLAIN - THEIR CHARACTERISTICS, ORIGIN, AND CONSTITUENT CLASTIC AQUIFERS

In central and eastern Alabama there are 13 Upper Cretaceous (late San tonian to latest Maastrichtian; 85 to 67 Ma) depositional sequences in the outcrop and shallow-subsurface stratigraphic section. Each deposi tional sequence is composed of paralic and shelfal facies associations within their transgressive and highstand systems tracts. Within each depositional sequence the gross depositional-strike mode and specific position of shoreline trend are both directly related, to second- and third-order changes of sea level respectively. Depositional-sequence p aleogeography and the sedimentary facies relations within depositional sequences, and their constituent systems tracts (both transgressive a nd highstand), dictate the distribution of coarse-clastic paralic (aqu ifer) facies that have significant primary permeabilities. The coarse- clastic facies, specifically barrier-island and lower-shoreface facies , are significant local confined clastic aquifers that, taken together , constitute significant regional aquifer systems. All depositional se quences and the facies tracts within them have locally and regionally correlative bounding surfaces of hydrogeologic significance.