Multichannel Seismic Reflection Investigation of the Western Gulf of Mexico

Abstract

ABSTRACT A reconnaissance multichannel seismic survey has been completed in the central Gulf of Mexico. Track lines run from the Sigsbee Scarp on the north to the Campeche Bank on the south and west to include the Mexican Ridge province. Seismic lines tie to the JOIDES drill sites in the Gulf. Seismic sections show that sedimentary sequences found in the drill holes of the central Gulf can be traced laterally throughout much of the abyssal Gulf. A Jurassic salt layer is overlain by a fairly transparent layer thought to be Early Cretaceous pelagic sediments. This transparent layer is in turn overlain by a sequence of strong reflectors thought to be Early to Middle Tertiary turbidites and Pleistocene turbidites with an intervening layer of pelagics. The salt massifs of the Sigsbee Scarp and the Sigsbee Knolls are clearly visible on the sections. The Mexican Ridges do not seem to be underlain by these massifs, and we therefore favor the idea that these ridges formed by gravitational sliding on a decollement. INTRODUCTION The geology of the Gulf of Mexico and adjacent coastal areas has been investigated perhaps more intensively than any other region of comparable size in the world. The petroleum industry, government agencies, and academic institutions have studied the geology of this region for many years. In spite of these investigations, much remains unknown. This is particularly true of the regions outside areas where petroleum exploration is or has been active. The distribution of evaporites in deeper water has been roughly outlined by recent marine" surveys, due mainly to the tendency of evaporites, chiefly salt, to form piercement structures which sometimes rise to within a few hundred feet of the sea floor. The deeper structureof the evaporites lies beneath the bottoms of the holes drilled by the GLOMAR CHALLENGER as part of" the Deep Sea Drilling Project and beneath maximum depth of penetration of single channel analog seismic reflection equipment carried by university research vessels. Seismic refraction profiles have identified subseafloor layers which have velocities similar to velocities of salt. Unfortunately, other rockforming materials have velocities in the same range. Hence, interpretation of the layers as salt remains uncertain. Plate tectonics is perhaps the most exciting new concept in the history of earth science. This concept has contributed immensely to our understanding of the origin of deep ocean basins, island arcs and other features. In the Gulf of Mexico, however, plate tectonic theory has been unable to provide a clear understanding of the genesis of the sea floor. The crust in this area appears oceanic, but the age of the crust is unknown and the origin of many structural elements is enigmatic. Global reconstruction of the positions of the continents prior to the opening of the Atlantic are unsatisfactory in the vicinity of the Gulf of Mexico. Southern Mexico and Central America overlap northwestern South America while the northern Gulf remains unclosed. Clearly, much remains to be learned regarding the role of tectonic forces which formed the Gulf of Mexico.