Abstract Seismic refraction measurements indicate that the transition from rifted continental crust to oceanic crust takes place at a water depth of over 3000 m northwest of Cuba between the Florida and Campeche escarpments. Along the eastern flank of the Mississippi Embayment, the transition occurs at about 2500 m deep and on the embayment itself inboard of the coast. Off south Texas the boundary between the rifted continental crust and oceanic crust is near the shelf’s edge, off Mexico the boundary is on the continental slope, and off Campeche Bank the boundary is about 100 km northwest of Campeche Escarpment. In the northern Gulf an oceanic crustal high may lie beneath the upper continental slope. This high served as a foundation for a Mesozoic reef. Maximum sediment accumulation took place along the contact between the rifted continental crust and oceanic crust.

Abstract The presence of a geosyncline along the Gulf Coast of Texas and Louisiana is indicated both by geologic and geophysical data. The formations which are exposed at the surface or in drilling are known in general to dip gulfward. The known stratigraphic thickness of formations plus shrewd extrapolation below reach of the drill indicate that the depth to the basement at Houston is greater than 20,000 feet, at Jennings, Louisiana, greater than 25,000 feet, and south of New Orleans greater than 30,000 feet. Seismic prospecting indicates that the basement certainly is deeper than 15,000 feet and, less definitely, that it is deeper than 20,000 feet. The torsion-balance data indicate that the base of the salt core of the salt domes lies at a depth of 17,000–20,000+ feet in the Houston district. The depth of the Gulf of Mexico in the Sigsbee Deep is 12,500, and throughout most of its area, is less than 10,000 feet, Tne thickness of the post-Lower Cretaceous sediments in the central part of the Gulf of Mexico presumably is not more than a very few thousand feet. The basement of the post-Lower Cretaceous beds in the Gulf Coast must be warped down at least 5,000 feet at Houston and at least 15,000 feet in the area south of New Orleans. A regional trough of gravity minimum lies axially along the Gulf Coast. Calculations suggest that it is best explained by a geosyncline on the basement plus a progressive character of the basement from granitic under the land to basaltic under the Gulf of Mexico. A study of the depression of the basement to compensate sedimentation suggests that the trough line of the geosyncline should lie nearly at the present coast line; and that is approximately the position which the gravitational calculations indicated for the actual position of the trough line. Although isostatically negative, the area has been one of continued subsidence; and the rate of subsidence seems to have kept even pace with the rate of sedimentation.

Abstract Sedimentary rocks in the south Louisiana part of the Gulf Coast geosyncline contain at least 111 trillion cu ft of gas, which is one quarter of the proved ultimate natural gas reserve of the United States. The geosyncline, 750 mi long, began to form in Late Triassic time but did not attain maximum development until Cenozoic time. The stratigraphic section in south Louisiana is between 40,000 and 60,000 ft thick, and has a volume of approximately 400,000 cu mi. The sedimentation rate within the geosyncline has increased steadily from Triassic time to the present. Since the Jurassic, the depositional axis has shifted progressively gulf ward. As a result, the optimum producing trends are in younger sedimentary strata toward the Gulf. Concurrently with gulf ward migration of the geosynclinal axis, the depocenter, since Paleocene time, has migrated from south Texas to southeast Louisiana. The maximum thicknesses of the Cenozoic units, and possibly of some Mesozoic units, are on the downthrown sides of growth faults. Such faults, characteristic of the Gulf Coast geosyncline, permitted great thicknesses of sediments to accumulate in local depocenters. The concurrence of a large provenance area, a great volume of sediment, abundant organic matter, rapid deposition and burial, basinal subsidence, and movements of an underlying salt layer— which produced syndepositional structural traps in the geosyncline—created optimum conditions for the generation and entrapment of huge hydrocarbon reserves in south Louisiana. Statistically, more gas than oil is present below 10,000 ft and/or in association with sediments deposited in relatively deeper water. Gas is more abundant where shale is a major constituent of the producing section. Gas reserves generally are smaller where the sandstone percentage is greater. With increasing age and depth, the atomic hydrogen-carbon ratio of the gas decreases.

Abstract North Louisiana is underlain by approximately 5,000-20,000 ft of latest Triassic-Jurassic to Eocene sedimentary rocks deposited in the northern part of the Gulf Coast geosyncline. Most of this section has commercial accumulations of hydrocarbons. These strata were deposited unconformably on an undetermined thickness of sedimentary rocks, so far nonproductive, which range in age from Paleozoic through Late Triassic. The oldest known beds of the Gulf Coast geosyncline are the redbeds of the Werner Formation and the overlying Louann Salt of latest Triassic-Middle Jurassic age. The salt was deposited in the Interior Salt basin, which is bounded on the west by the Sabine uplift—and thus is not continuous with the East Texas Salt basin—and which joins with the Mississippi Salt basin on the east. On the south, the Interior Salt basin may connect with the Coastal Salt basin of South Louisiana and coastal Texas through LaSalle, Avoyelles, and Rapides Parishes. Thirty-one piercement salt domes are known in North Louisiana, but only one of these is productive. This contrasts sharply with the more than 148 piercement domes of South Louisiana, of which 127 are productive. The Late Jurassic-Eocene section above the Louann Salt contains all the hydrocarbons thus far discovered in this region. In general the section thins northward into southern Arkansas and westward onto the Sabine uplift. It thickens south and east toward the coast and the Mississippi embayment, respectively. Facies changes accompany the thickness changes; these changes are particularly pronounced in the Late Jurassic-Early Cretaceous section which grades successively, from north to south, from littoral and continental facies, to shelf facies, carbonate reef facies, and, ultimately, basinal shale facies. Uplift and erosion affected much of North Louisiana before the Upper Cretaceous (Tuscaloosa) transgression. Positive movements of the Sabine uplift restricted the distribution of the basal Tuscaloosa sandstones. The Upper Cretaceous sea gradually transgressed the whole of North Louisiana. The sea retreated again from parts of Louisiana near the end of Cretaceous time and during Paleocene time. Paleocene-Eocene deposition was extensive, but the reservoirs which developed were deposited mainly in the Wilcox (late Paleocene-early Eocene) part of the sequence in eastern and southeastern North and Central Louisiana. The mobility of the underlying Louann Salt caused the formation of numerous traps during deposition of the Late Jurassic-Eocene geosynclinal sequence. Renewed vertical movements of the Sabine uplift—which was in existence before the deposition of the Louann Salt—and repeated tilting toward the Gulf of Mexico and Mississippi embayment caused the formation of numerous structural and combination stratigraphic-structural traps. Many wholly stratigraphic traps also formed. The deposition of the “Monroe Gas Rock” during Late Cretaceous time led ultimately to the accumulation of one of the largest gas deposits in North America—the Monroe field. Exploration of hydrocarbons in North Louisiana is in an advanced stage of development. To date 17 trillion cu ft of gas has been produced. Of this, Monroe field alone has produced more than 6 trillion cu ft. Estimated future gas reserves of North Louisiana are in the order of 8 trillion cu ft. However, Central Louisiana scarcely has been explored, and potentially a large and important reserve remains to be discovered in that region.

Abstract North Louisiana is underlain by approximately 5,000-20,000 ft of latest Triassic-Jurassic to Eocene sedimentary rocks deposited in the northern part of the Gulf Coast geosyncline. Most of this section has commercial accumulations of hydrocarbons. These strata were deposited unconformably on an undetermined thickness of sedimentary rocks, so far nonproductive, which range in age from Paleozoic through Late Triassic. The oldest known beds of the Gulf Coast geosyncline are the redbeds of the Werner Formation and the overlying Louann Salt of latest Triassic-Middle Jurassic age. The salt was deposited in the Interior Salt basin, which is bounded on the west by the Sabine uplift—and thus is not continuous with the East Texas Salt basin—and which joins with the Mississippi Salt basin on the east. On the south, the Interior Salt basin may connect with the Coastal Salt basin of South Louisiana and coastal Texas through LaSalle, Avoyelles, and Rapides Parishes. Thirty-one piercement salt domes are known in North Louisiana, but only one of these is productive. This contrasts sharply with the more than 148 piercement domes of South Louisiana, of which 127 are productive. The Late Jurassic-Eocene section above the Louann Salt contains all the hydrocarbons thus far discovered in this region. In general the section thins northward into southern Arkansas and westward onto the Sabine uplift. It thickens south and east toward the coast and the Mississippi embayment, respectively. Facies changes accompany the thickness changes; these changes are particularly pronounced in the Late Jurassic-Early Cretaceous section which grades successively, from north to south, from littoral and continental facies, to shelf facies, carbonate reef facies, and, ultimately, basinal shale facies. Uplift and erosion affected much of North Louisiana before the Upper Cretaceous (Tuscaloosa) transgression. Positive movements of the Sabine uplift restricted the distribution of the basal Tuscaloosa sandstones. The Upper Cretaceous sea gradually transgressed the whole of North Louisiana. The sea retreated again from parts of Louisiana near the end of Cretaceous time and during Paleocene time. Paleocene-Eocene deposition was extensive, but the reservoirs which developed were deposited mainly in the Wilcox (late Paleocene-early Eocene) part of the sequence in eastern and southeastern North and Central Louisiana. The mobility of the underlying Louann Salt caused the formation of numerous traps during deposition of the Late Jurassic-Eocene geosynclinal sequence. Renewed vertical movements of the Sabine uplift—which was in existence before the deposition of the Louann Salt—and repeated tilting toward the Gulf of Mexico and Mississippi embayment caused the formation of numerous structural and combination stratigraphic-structural traps. Many wholly stratigraphic traps also formed. The deposition of the “Monroe Gas Rock” during Late Cretaceous time led ultimately to the accumulation of one of the largest gas deposits in North America—the Monroe field. Exploration of hydrocarbons in North Louisiana is in an advanced stage of development. To date 17 trillion cu ft of gas has been produced. Of this, Monroe field alone has produced more than 6 trillion cu ft. Estimated future gas reserves of North Louisiana are in the order of 8 trillion cu ft. However, Central Louisiana scarcely has been explored, and potentially a large and important reserve remains to be discovered in that region.