--> Sedimentologic Characteristics of Some U.S. Gulf Coastal Plain Aquifers, a Facies-Analysis Approach, by D. T. King, Jr.; #90986 (1994).

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Abstract: Sedimentologic Characteristics of Some U.S. Gulf Coastal Plain Aquifers, a Facies-Analysis Approach

David T. King, Jr.

Three main sedimentologic parameters permit forecasting of geologic conditions related to facies stratigraphy in both the subsurface and surface-recharge reaches of inner Gulf coastal plain aquifers. These aquifers are typically coarse-grained sedimentary facies which possess parameters that are predictable as to (1) specific constituent facies geometries owing to depositional strike and specific environment of deposition, (2) permeability characteristics arising from grain-size distribution and bulk mineralogy, and (3) lateral and vertical sedimentary facies relations resulting from their position within a stratigraphic sequence. For example, in the Mississippi, Alabama, and Georgia area, wherein formations dip south-southwest at 7.5 m/km, the Upper Cretaceous section includes 50 m o fluvial and other terrestrial facies (Tuscaloosa aquifer) directly overlying the regional crystalline basement, which is in turn directly and disconformably overlain by 450 m of marine paralic and shelfal facies, including both the Santonian Eutaw and Maastrichtian

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 (Cenomanian-Maastrichtian). The most porous and permeable facies are quartz-rich barrier-island deposits (shoreface and tidal-inlet; permeability near 200 darcys). Secondary quartz-rich aquifers (possessing variable permeability, averaging 10 darcys) include clayey-quartzose barrier-associated deposits (e.g., lower shoreface, tidal delta, and lagoonal and shelfal tempestite deposits). Aquiclude and aquitard facies are typically clay-rich back-barrier facies (e.g., lagoon or marsh) and marly inner- and middle-shelf facies (permeabilities less than 2 dar ys). Depositional strike of aquifers in the study area varies between east-west and northwest; depositional dip of linear channel geometries varies from south to southwest. Specific geometries of quartz-rich aquifers in this region include (1) strike-oriented linear and curvilinear bodies (barrier island), (2) sheet-like forms (tempestite units and lower shoreface), and (3) dip-oriented, linear channel shapes (incised valley fills, fluvial channels, and low-slope shelfal debris flows).

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994