Sediments and oceanic structural history of the Gulf of Mexico

Abstract

A new technique for underway marine seismic reflection measurements was used in January 1961 to investigate the sediments in the deep basin of the Gulf of Mexico. Reflecting horizons, mapped to depths about 5 km below the ocean bottom or about 10 km below sea level, confirmed and added detail to the section published in 1960 on the basis of refraction data. The reflecting horizons were identified by comparison with seismic refraction and wide-angle reflection data. Measurements were made, in the area of the Sigsbee knolls, along two complete crossings of the deep basin, and along some shorter lines in mid-basin. It was found that: (1) During the present cycle of sedimentation (which extends back to Jurassic time, at least) a minimum of 5 km of sediment has been deposited in the Sigsbee basin. A gentle northerly dip is present throughout, except in the upper layers near the Sigsbee scarp, where the dip is reversed by thickening of some beds to the north. (2) Several reflectors exist within the sediment. The two principal ones and also the floor of the basin in which the sediments have been deposited are identified by refraction measurements. (3) The Sigsbee knolls, which rise a few hundred meters above the floor of the abyssal plain of the Sigsbee deep, in about 3.7 km of water, are found to be the tops of tall vertical columns, apparently intrusive into the sediment. (4) Four additional knolls and 17 buried structures were discovered. All the structures are tentatively called salt domes. (5) Twenty-one of these domes were found by rough reconnaissance survey in an area 90 km wide by 200 km long, which trends north 60°E, is approximately median to the deep basin of the Gulf, and may extend to include the domes on the Isthmus of Tehuantepec. (6) Refraction profiles in this basin indicate that although the sediment is much thicker than that in a typical ocean basin, the crust beneath it is practically identical with that in the permanent ocean basins. Thus it is highly probable that this basin has never been land or shallow sea. (7) These facts suggest that the Louann salt beds, which supplied the domes in the Texas-Louisiana region, continue across the Sigsbee basin at a depth of about 8 km below sea level, and that they were deposited in water depths up to 5 or 6 km. (8) The region in which great thicknesses of sediments have accumulated, sometimes called the Gulf Coast geosyncline, extends to the Campeche scarp. Isostatic adjustments have caused the faults and flexures along the Texas-Louisiana coast region and warping of the basin floor.