Nearsurface Geology of the Gulf of Mexico Continental Slope

ABSTARCT The continental slope of the Gulf of Mexico covers an area of more than 500,000 sq km. Consisting of smooth and gently sloping surfaces, prominent escarpments, knolls, intraslope basins, and submarine canyons and channels, it is an area of extremely diverse topographic and sedimentologic conditions. The slope extends from the shelf break, roughly at the 200-m isobath, to the upper limit of the continental rise at a depth of 2,800 m. The most complex province in the basin, and the one of most interest to the petroleum industry, is the Louisiana- Texas slope, which occupies 120,000 sq km and in which bottom slopes range from less than 1 degree to greater than 20 degrees around knolls and basins. In the past few years, numerous high-resolution seismic surveys, foundation borings, and drop cores have been acquired on the continental slope. They form the basis the interpretation of the nearsurface geologic framework. INTRODUCTION The complex Gulf of Mexico Basin was characterized during the Tertiary by an extremely large introduction of clastic sediment, mobilization of large salt masses, and formation of highly active penecontemporaneous or growth faulting. Mesozoic and Cenozoic sediments are estimated to attain a total thickness in excess of 15,000 m, the maximum zone of thickness trending east-west near the present day coastal plain of Louisiana and west Texas. Rapid subsidence associated with sediment loading has been responsible for such thick localized sedimentary accumulations. The Gulf Basin has been dominated, from the beginning of the Tertiary to present times, by the sediment yield of the Mississippi River (Martin and Bouma, 1978 Bouma et al., 1978). The submerge part of the Gulf Basin can be divided into several major regions or provinces the northeastern and eastern Gulf (Florida, Alabama, and Mississippi), the central Gulf (offshore Louisiana and Texas), the western Gulf (offshore west Texas and Mexico), and the Golfo and Banco de Campeche, along the southern rim of the Gulf (Figure 1). The Sigsbee Escarpment is the most prominent feature at the base of the slope, This escarpment is nearly continuous along the entire base of the slope from the western Gulf to De Soto Canyon. The scarp is the expression of the lobate frontal edge of the northern Gulf diapiric province and is underlain throughout its length by a complex system of salt ridges, overthrust tongues, and steepsided massifs (Humphries, 1978 Martin 1978, 1984). The continuity of the escarpment is broken locally by diapiric outliers and large, pronounced reentrant of several large interlobal canyons such as the Alaminos and Keathley. The nearsurface geology and topography of the slope is a function of the interplay between episodes of rapid shelf edge and slope progradation and contemporaneous modification of the depositional sequence by diapirism and mass-movement processes during late Wisconsin glaciation and lowered sea level.