Print this pageAbstract: Structure and Evolution of North Choctaw Ridge Field,
Alabama, a SaltRelated Footwall 
Uplift
Along the Peripheral Fault System,
Gulf Coast Basin
QI, J.
The University of Alabama, Tuscaloosa,
AL;
J. C. PASHIN
Geological Survey of Alabama,
Tuscaloosa, AL;
R. H. GROSHONG, Jr.
The
University of Alabama, Tuscaloosa
North Choctaw Ridge (NCR) Field is a structural trap producing
from the Jurassic Smackover Formation which is in the Gilbertown graben
system, at the updip limit of the Louann Salt. The field is in the footwall
uplift below of one of the faults forming the northern boundary of the
graben system. The top seal is anhydrite in the overlying Buckner Formation,
and the boundary fault provides a lateral seal. The 325-acre field has
produced 8.1 million barrels of oil and 4.2 tcf of gas since its discovery
in 1972. The geometry and evolution of the structure has been determined
from a threedimensional interpretation of the graben system and from a
balanced and sequentially restorable cross section derived from it. A graph
of graben area versus depth shows that the cross section is both area and
length balanced with a lower detachment near the base of the Louann Salt.
The graph further indicates that significant structural growth began in
Early Cretaceous time. During Early Cretaceous extension, three major southdipping,
down-to-the-Gulf faults formed, creating an imbricate system of half grabens
(the Melvin fault system) with NCR Field being a salt-cored uplift beneath
the southern fault (Melvin C). Subsidence south of the Melvin fault system
indicates contemporaneous salt deflation, but the area-depth relationship
suggests that the NCR Field was simultaneously uplifted above regional
dip, presumably by inflow of salt
. The north-dipping boundary fault of
the Gilbertown graben system (East Gilbertown fault) developed only after
the Lower Cretaceous. Continuing extension produced a full graben between
the East Gilbertown and Melvin C faults.
AAPG Search and Discovery Article #90932©1998 GCAGS/GCS-SEPM Meeting, Corpus Christi, Texas