The accumulation of oil and gas underground depends on the availability of
The alternating sands and shales of the Gulf area form ideal source and reservoir beds, respectively; the structures associated with salt intrusion form many traps.
Porous beds domed into anticlines, the porous cap rock, beds truncated against the upthrust salt, and porous beds seald off by faults or uncomformities on the flanks of the domes, may all form reservoirs in the Coastal Plain oil fields.
The largest trap in the Gulf Region, at the East Texas Field, is formed by the truncation of the gently dipping Upper Cretaceous Woodbine Sandstone, and is sealed by the impervious Austin Chalk. Petroleum may also be trapped by facies changes as the Frio or Yegua wedge out or become less porous upward along the dip.
To date no discoveries of petroleum have been made in the Atlantic Coastal plain or continental shelf of the United States. Despite an extensive exploration program, potential production of the Canadian shelf has been found only at the Sable Island Field on the edge of the shelf. Salt-cored structures have not been discovered as yet on the United States Atlantic shelf but geophysical surveys of continental slope off the Carolinas indicate that domal uplifts cored by either plastic shales or salt have pushed through the sedimentary layers. The apparent lack of salt domes on the shelf decreases the probability of the discovery of a major new oil province like the Gulf of Mexico there.