Structural History and Oil Potential of Offshore Area from Cape Hatteras to Bahamas: ABSTRACT

Abstract

The present Atlantic Coastal Plain and continental shelf were parts of the crystalline Appalachians in late Paleozoic time when North America was joined to the African continent, according to current interpretation of plate tectonics. In Early Triassic time this province was uplifted by subcrustal intrusion of hot mantle material which caused a series of rift valleys to develop with trends roughly parallel with the present continental rise. This was the site of a major rift system and the convection cell which later formed the Mid-Atlantic Ridge. This rift system connected the Mediterranean Sea with the newly opened Gulf of Mexico; these were areas of extensive evaporite deposition in Late Triassic and Early Jurassic times. Normal sea water entering during Smackover (Late Jurassic) deposition permitted the growth of great carbonate banks and reefs from the Cape Hatteras area southward to the Bahamas. Active separation of Africa and North America also moved the upwelling lavas of the Mid-Atlantic Ridge away from the coastlines. Cooling of the hot mantle material under the continental margin caused downward flexing of the crust toward the ocean to form a new miogeosyncline. There the deposition of sediments probably kept pace with the crustal downwarp. The subject area is between the Bahama carbonate platform and a mainly siliciclastic depositional province indicated north of Cape Hatteras. The strata are presumed to be transitional in environment of deposition. The shallow-water carbonates are likely to include many rocks with excellent reservoir properties. Source beds for petroleum, as well as shales and fine-grained carbonates and possibly evaporites, which could serve as cap rocks, should be abundant. Although compressive folding seems to be absent as a mechanism for structural growth, block faulting in the basement will serve the same purpose. High basement blocks are favorable sites for bank and reef development and commonly produce structural uplift by renewed movement. Conditions expected here present a challenge for imaginative thinking by geologists. The many similarities to such areas of prolific oil production as the Tampico-Tuxpan embayment and the Jurassic producing province in Saudi Arabia give cause for an optimistic view that giant oil accumulations may be present. Water depths over the Blake Plateau present another type of challenge to operators. The mechanical difficulties should not be insurmountable if industry has sufficient economic incentives to justify the effort. The reasonable expectation of finding oil in sufficiently large accumulations is the most basin of such incentives.