Tertiary and Cretaceous sand aquifers of the Southeastern United States
Coastal Plain comprise a major multlstate aquifer system informally defined as
the Southeastern Coastal Plain aquifer system, which is being studied as part of the U.S. Geological Survey's Regional Aquifer System Analysis (RASA) program. The major objectives of each RASA study are to identify, delineate, and map the distribution of permeable clastlc rock, to examine the pattern of ground-water flow within the regional aquifers, and to develop digital computer simulations to understand the flow system. The Coastal Plain aquifers in Alabama are being studied as a part of this system.
This report describes the stratlgraphlc framework of the Cretaceous,
Tertiary, and Quaternary Systems in Alabama to aid in delineating aquifers and
confining units within the thick sequence of sediments that comprises the
Southeastern Coastal Plain aquifer system in the State. Stratigraphlc units of
Cretaceous and Tertiary age that make up most of the aquifer system in the
Coastal Plain of Alabama consist of clastlc deposits of Early Cretaceous age;
the Coker and Gordo Formations of the Tuscaloosa Group, Eutaw Formation, and
Selma Group of Late Cretaceous age; and the Midway, Wilcox, and Clalborne Groups of Tertiary age. However, stratigraphlc units of late Eocene to Holocene age partially overlie and are hydraulically connected to clastic deposits in
southern Alabama. These upper carbonate and clastlc stratlgraphic units also
are part of the adjoining Florldan and Gulf Coastal Lowlands aquifer systems.
The Coastal Plain aquifer system is underlain by pre-Cretaceous rocks consisting of low-permeabillty sedimentary rocks of Paleozolc, Triassic, and Jurassic age, and a complex of metamorphic and igneous rocks of Precambrian and Paleozolc age similar to those found near the surface in the Piedmont physiographic province.
Twelve hydrogeologlc units in the Alabama Coastal Plain are defined--slx
aquifers and six confining units. Aquifers of the Coastal Plain aquifer system
are composed of fine to coarse sand, gravel, and limestone; confining beds are
composed of clay, shale, chalk, marl, and metamorphic and igneous rocks.
Additional Publication Details
USGS Numbered Series
Stratigraphic and hydrogeologic framework of the Alabama Coastal Plain