John W. Antoine

Continental Margins of the Gulf of Mexico

The Gulf of Mexico is a small ocean basin whose continental margins are structurally complex and in some cases rather unique. The origin of the Gulf Basin and the subsequent construction of the continental margins are somewhat in contention. The prominent theories contain one of four basic ideas that the Gulf represents: (1) a foundered and oceanized continental mass; (2) a downwarp related to a thermally controlled phase change in the crust and mantle; (3) a gigantic tensioned rift formed in relation to Mesozoic opening of the Atlantic Ocean; and (4) a Paleozoic or older ocean basin.

Metamorphic rocks from northwestern Caribbean sea

During 1971, several dredge hauls were collected in the area between the Yucatan Peninsula-British Honduras, on the south and west, and Cuba on the northeast. One of the dredge hauls recovered metasediments which petrographically are very similar to the Early-Middle Jurassic San Cayetano Group of Pinar del Rio Province, westernmost Cuba. Interpretation of K-Ar dates of these rocks suggests that they are approximately 65 million years old. Therefore, the latest thermal event to affect them occurred during the “Laramide” orogeny. The presence of these rocks southwest of Cuba, close to the Yucatan Peninsula and British Honduras, indicates that the Greater Antilles orthogeosyncline extends to the Central America mainland.

Magnetic Anomalies in Straits of Florida

Seismic-reflection and magnetic profiles across three topographic highs in the western end of the Straits of Florida and southeastern Gulf of Mexico reveal the presence of diapiric structures which have magnetic anomalies greater than 100 ^ggr. These deep-water knolls may be related to the volcanic-anomaly belt of the Florida platform, the ultramafic rock outcrops of northwestern Cuba, or Cretaceous andesitic intrusive rocks of Yucatan and Florida.

Geophysical Studies of Northern Florida Platform, Gulf of Mexico: ABSTRACT

The western edge of the North Florida platform has been delineated in some detail by seismic-reflection investigations. The platform boundary is not apparent from topographic surveys because of the thick sediment cover. The platform edge appears to coincide with the trend of a probable offshore extension of the Lower Cretaceous (Washita-Fredericksburg) reef trend. The presence of a more recent reef, normal to the lower Cretaceous reef, is indicated from interpretation of additional reflection records. This feature trends almost east-west and crosses the buried edge of the North Florida platform. It can be traced for approximately 30 mi and can be aligned with an old buried shoreline on the east. The top of the Upper Cretaceous has been traced over most of the continental slope south of the Florida Panhandle by seismic-reflection profiling. Studies on the outer slope indicate that this horizon rises near the center of the platform, along long. 86°30^prime, to less than 5,000 ft below sea level. On the west, near the edge of the platform at long. 87°30^prime, the top of the Upper Cretaceous is at 7,000 ft whereas on the east where the Florida escarpment intersects 85°30^prime long., the indicated depth is more than 5,700 ft below sea level. The reflection surveys show that erosion has played a very important role in the formation of the western part of the platform. It is evident that erosional processes have been active at least since the Late Cretaceous. This can be interpreted to indicate that the circulation in the Gulf of Mexico, and the loop current in particular, has been essentially the same during the entire Cenozoic Era. End_of_Article - Last_Page 2031------------

Role of Salt Tectonics in Structural History of Western Gulf of Mexico: ABSTRACT

The discovery through the JOIDES drilling program that the Sigsbee Knolls and domes represent intrusive salt bodies has made it necessary to review many old concepts concerning the structural evolution of the Gulf of Mexico. The debate concerning the physiography of the Gulf during the time of salt deposition is now more heated than ever. It has been suggested that, during this time, the Gulf was an ocean basin, a shallow sea, a landmass, or an ocean that had risen to shallow depths above a rising convection cell. Any one of these hypotheses must be able to explain the presence of salt, at least under part of the central basin, if it is to be considered seriously. The possibility that thick salt beds can be deposited at oceanic depths has been questioned. Although at firs thought this may discount a hypothesis that places the Gulf basin at great depth during Triassic-Jurassic time, the structure of the bordering continental slopes of the western Gulf suggests an alternate hypothesis: the Gulf is an oceanic basin along the western margins of which great amounts of salt accumulated. This salt migrated toward the basin. The distribution of salt diapirs throughout the area of subsurface salt is controlled mainly by sediment thickness and the distribution of massive carbonate sequences. The change from simple ridge structure to diapir swarms, south to north along the eastern coast of Mexico, indicates the influence of the sedimentary cover. The abrupt termination of the diapirs on the southeast in the Bay of Campeche and the position of the Sigsbee Knolls and domes indicate the important (negative?) role played by the carbonate platforms in the distribution of salt diapirs. End_of_Article - Last_Page 206------------

Geophysical Studies of South Florida Continental Margin and Western Straits of Florida: ABSTRACT

Seismic-reflection profiles off the western coast of Florida south of 27° N lat. have been recorded during two cruises of Texas A&M Universitys R/V Alaminos in May 1967 and June 1968. They show that the anticlinal ridge present near the top of the West Florida escarpment, which has been proposed to be an extension of the Washita-Fredericksburg reef trend, may possibly be traced southward to the latitude of the Florida Keys. Several crossings have been made of a large knoll in the western end of the Straits of Florida. Preliminary analysis of the real-time records, without benefit of playback, indicates the presence of a terrace at a water depth of 840 fm, and the possibility that an anticlinal feature, remarkably similar to that seen on the Florida escarpment toward the north, is present. Reexamination of earlier data from the Campeche Bank and comparison with those presented here reveal several similarities and provide evidence that the Campeche Bank and the Florida escarpment once might have been connected. However, the presence of deep-water Lower Cretaceous in northern Pinar del Rio Province, western Cuba, may indicate that no connection ever existed. If the two escarpments ever were connected, it is not known whether grabenlike faulting, erosion, or both caused the separation of these two features. More information is being sought in geomagnetic and sedimentological studies now in progress. End_of_Article - Last_Page 1830------------