Regional Stratigraphy and Petroleum Potential of Gulf Coast Lower Cretaceous: ABSTRACT

Abstract

Lower Cretaceous sediments were deposited throughout the Gulf Coast during the Neocomian, Aptian, Albian, and early Cenomanian Epochs. Basal sandstones extend across the entire region, onlapping Upper Jurassic terrigenous strata. Following the initial stage of detrital rock deposition, a shallow epicontinental sea covered the western coastal plain and regions on the south and west. In this area, and also in the seaward parts of the eastern coastal plain, shallow-shelf carbonates were deposited contemporaneously with subsidence. In East Texas and adjacent areas, periods of peneplanation of the bordering land and deposition of carbonates alternated with regressive periods when the hinterland was uplifted and deposition of the land-derived material exceeded subsidence. The s uthern Appalachians rose at irregular rates throughout Early Cretaceous time, and furnished sediments (sand and clay) to the Mississippi embayment and the eastern Gulf Coast. Lower Cretaceous rocks are the most widespread and have the greatest volume of any major Gulf Coast stratigraphic division. They are believed to underlie an area of about 340,000 sq mi and have a volume of more than 200,000 cu mi. The area presently productive of oil and gas, extending from Mexico to southwestern Alabama, has an area of 83,000 sq mi, and a volume of 60,000 cu mi. In this proved belt, 1½ billion bbl of oil and 10½ Tcf of gas have been produced from Lower Cretaceous sandstone and carbonate rock. Landward from the productive belt in Texas and Arkansas is a narrow belt that is considered to be nonprospective. This belt widens eastward across central Mississippi, southern Alabama, Georgia, and northern Florida, where continental redbeds with thicknesses to 4,00 ft are present. A prospective belt and a speculative belt are gulfward from the proved area. Depositional conditions of the extensive and thick Lower Cretaceous sediments were favorable for the development and preservation of vast amounts of hydrocarbon source materials and for the formation of many reservoir rocks and stratigraphic-structural traps. An environmental analysis of each stratigraphic unit indicates a very large petroleum potential for this group of rocks. Many hydrocarbon accumulations will be found in the prospective belt, on land as well as under the continental shelf of Mississippi, Alabama, and Florida. The undiscovered accumulations are in deltaic sandstone, carbonate reefs, and shell mounds. In the speculative belt of coastal and offshore Louisiana and Texas, the objectives are limestone reefs which developed on the landward side of positive blocks. Many n w fields will be found in the productive belt, and there will be lateral and deeper extensions of producing fields. End_of_Article - Last_Page 1790------------