KING, DAVID T., JR., Auburn University, Auburn, AL
ABSTRACT: Sedimentary Facies Analysis and the Characteristics of Some Gulf Coastal Plain Aquifers
Gulf coastal plain aquifers are coarse-grained sedimentary facies that typically possess predictable (1) facies geometries owing to depositional strike and specific depositional environment, (2) permeability characteristics owing to grain-size distribution and bulk mineralogy, and (3) lateral and vertical sedimentary facies relations owing to their position within a stratigraphic sequence. These three parameters permit forecasting of geologic conditions related to facies stratigraphy in both the recharge and subcrop reaches of the aquifers. For example, in the inner part of the northeastern Gulf coastal plain (Mississippi, Alabama, and Georgia), where formations dip south-southwest at 7.5 m/km, the Upper Cretaceous section includes 50 m of fluvial and other terrestrial facies (Tuscalo sa aquifer) overlying crystalline basement and overlain by 450 m of marine (paralic and shelfal) facies (including both the Eutaw and Ripley Providence aquifers). Throughout this Upper Cretaceous section, both geometry and depositional strike of terrestrial and marine facies closely track the global pattern of eustatic change over the temporal span between 95 and 65 Ma. The most porous and permeable facies are quartzose barrier-island deposits (shoreface and tidal-inlet, with permeability near 200 d). Secondary quartzose aquifers (possessing variable permeability, usually below 10 d) include clayey quartzose-barrier-associated deposits (e.g., lower shoreface, tidal delta, and lagoonal and shelfal tempestite deposits). Aquiclude and aquitard facies include clayey backbarrier facies (e.g., lagoon or marsh) and marly inner and middle shelf facies. Specific geometries of quartzose aquifers include (1) strike-oriented linear and curvilinear (barrier-island), (2) sheetlike (tempestite and lower shoreface), and (3) dip-oriented, linear channels (incised valley fills, fluvial channels, and low-slope shelfal debris flows). Depositional strike of aquifers in the study area ranges from east-west to northwest; depositional dip of linear channel geometries ranges from south to southwest.
AAPG Search and Discovery Article #90989©1993 GCAGS and Gulf Coast SEPM 43rd Annual Meeting, Shreveport, Louisiana, October 20-22, 1993.