Sequence Stratigraphy and Heterogeneity in the Upper Cretaceous Regional Aquifer System, Alabama

David T. King Jr.

The outcropping and shallow-subsurface Upper Cretaceous marine section in the inner Coastal Plain of Alabama consists paralic (barrier-island associated) and coeval shallow-shelfal facies deposited in thirteen depositional sequences over the span 85 to 67 Ma (late Santonian to latest Maastrichtian). The section is a significant regional aquifer system including the Ripley-Providence and Blufftown-Eutaw aquifers.

The main aquifer facies are barrier-island tidal-inlet and shore face having estimated average permeabilities of 115-80 darcys. The main aquiclude facies are back-barrier and shallow-shelfal.

A hierarchical scale of aquifer heterogeneity based on cross-cutting relationships includes laminae (first order), cross-strata, cross-strata sets and burrow perforations, constituent facies, parasequence boundaries, transgressive or regressive surfaces, and sequence boundaries (seventh order).

In order of magnitude, the directional scales of heterogeneity are: intrabarrier-island, interbarrier-island (along depositional strike), and across-barrier-island (along depositional dip). The depositional strike varies according to the interplay of tectonics and sedimentation dictating the paleogeography of each depositional sequence.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995