Gulfward-dipping Mesozoic and Cenozoic sediments underlie approximately 145,000 square miles in the Central Gulf Coast between Texas on the west and Georgia on the east. Pre-Cretaceous, Coahuilan, Comanchean, and early Gulfian rocks are predominantly red-bed elastics in the eastern portion of this area; westward and downdip marine facies predominate. Extensive marine deposits comprise the middle and late Gulfian; arenaceous facies predominate in the east; argillaceous and calcareous facies are prevalent westward and downdip. Tertiary deltaic sediments center in Louisiana and Mississippi; eastward and down-dip marine deposits prevail. Fluviatile and deltaic Quaternary deposits occur as a surficial mantle over much of the Central Gulf Coast; offshore these deposits are replaced by marine facies.
Stratigraphic studies indicate that major Jurassic and Lower Cretaceous sedimentary units are typically elongate-lenticular while those of the Upper Cretaceous and Cenozoic are ladle-shaped. During Jurassic and Cretaceous times the major source of sediments was apparently eastern United States. In the Cenozoic, appreciable quantities of material appear to have come from western United States.
Regional isopachous maps illustrate variations in thickness of Mesozoic and Cenozoic Stratigraphic units. In the emerged (onshore) portion of the plain, deep wells prove the presence of at least 265,000 cubic miles of sediments. Interpolations based on regional studies indicate that the total volume of Mesozoic and Cenozoic deposits in this area will exceed 300,000 cubic miles.
The known volumes of sediments that accumulated in the emerged (onshore) portion of the Central Gulf Coast during these times are:
Few data are available on volumes of sediments in the submerged (off-shore) portion of the plain, which has an area of approximately 140,000 square miles. Conservatively, it is estimated that at least 200,000 cubic miles of Mesozoic and Cenozoic deposits is present. On the other hand, some evidence indicates the total may exceed 500,000 cubic miles.