GULF OF MEXICO 



71 



and sediments dating back to at least the Permian 

 are found in its niar<;inal areas. Eardley believed 

 that the margins of the Gulf have had a near 

 balance between subsidence and deposition, while 

 subsidence has exceeded deposition in the central 

 Mexican Basin. 



King (1951, p. 175) stated his i)elief that the 

 origin of the Gulf coast geosyncline was uncertain, 

 but he believed "that the geosyncline represents 

 an independent tectonic feature and perhaps a 

 new mobile belt in its early stage of development." 



The theory of Weaver that fault scarps bound 

 the present central great deep of the Gulf received 

 additional support by Jordan (1951, p. 1991) who 

 described the escarpment off the panliandle of 

 Florida. This escarpment occurs in 700 to 900 

 fathoms of water, and the sea floor is offset 6,000 

 feet or more in some places. Comments on Jor- 

 dan's paper by Stetson (1951, p. 1993) confirmed 

 the findings of Jordan and noted that the escarp- 

 ment maintains about the same height and slope 

 southward along the west Florida shelf. Stetson 

 further commented that "from the overall picture 

 of the whole area, one gets the impression that 

 the bottom of the Gulf has foundered and that at 

 least this continental slope is due to a normal 

 fault" (idem.). 



To date little exploration in the Gulf of Mexico 

 has had as its objective the determination of 

 major tectonic features. The cost of marine geo- 

 physical surveying and the drilling of offshore 

 wells are such that the tectonics of the Gulf must 

 be approached indirectly by using soundings and 

 bottom samples together with observations of the 

 shore features. 



GEOMORPHOLOGY OF GULF OF MEXICO 



The topography of the Gulf of Mexico is too 

 scantily mapped to show the degree of develop- 

 ment of the different types of topography so far 

 known there. 



As early as 1878 Agassiz (1878-79, p. 1) noted 

 two of the striking topographic features of the 

 Gulf, the great limestone banks: one west of 

 Florida and the other northward from the penin- 

 sula of Yucatdn. In both cases the 100-fathom 

 line is somewhat parallel to the shore and forms 

 the inner edge of the steep slopes descending to 

 the Mexican Basin, which is another major fea- 

 ture of the Gulf. The varying development of 

 continental shelves and the irregular continental 



slope with its escarpments, basins, knobs, and 

 trougiis are also striking features of the Gulf of 

 Mexico. 



GENERAL CHARACTERISTICS 



The continental shelf forms an almost con- 

 tinuous terrace around the margin of the Gulf of 

 Mexico. The major breaks occur in the Straits 

 of Florida and the Yucatdn Channel which form 

 outlets from the Gulf to the Atlantic Ocean and 

 Caribbean Sea, respectively. 



The shelf is not an expressionless plain lacking 

 in interesting physiographic features as may be 

 suggested by some maps with a contour interval 

 too great to properly present the smaller features. 

 This terrace or shelf has numerous depressions, 

 troughs, ridges, minor knobs, coral heads, escarp- 

 ments, and two known submarine canyons. 



The widest parts of the continental shelf in the 

 Gulf of Mexico lie off Texas and the peninsulas of 

 Yucatan and Florida. The shelf width varies 

 from 8 to 117 miles in the northern Gulf, the 

 maximum width being off western Florida. Other 

 shelf widths include: 40 miles off the southern tip 

 of Florida, 52 miles off the Isles of Dernieres, 

 Louisiana, 110 miles off the Sabine River mouth, 

 40 miles off the Rio Grande outlet, and 135 miles 

 off western and northern Yucatdn. 



The continental slope differs from place to 

 place not only in width and steepness but also in 

 physiographic features associated with it. The 

 continental slope, in general, constitutes one of 

 the great relief features of the earth. The edge 

 of the continental shelf is only very roughly paral- 

 lel to the shore line as is shown by the varying 

 width of the shelf. The continental slope varies 

 greatly in width with a minimum width west of 

 Florida and west and northwest of the Yucatan 

 Peninsula. 



ORIGIN OF MAJOR FEATURES 



The continental shelves of the Gulf of Mexico 

 seem to have a close geologic and physiographic 

 relationship with the adjacent land. Broad 

 shelves lie in front of broad coastal plains, and 

 narrow shelves lie between steep continental 

 slopes and rugged near-shore terrain. 



There is no simple explanation of the origin of 

 the shelves and slopes, or of some of the features 

 of these provinces, that has gained wide accept- 

 ance. 



