GULF OF MEXICO 



77 



face would have been raised several fathoms. 

 Therefore, it appears that a profile of equilibrium 

 does xiot exist on the outer part of broad Gulf of 

 Mexico continental shelves. 



Sediments carried to the Gulf of Mexico largely 

 remain in that body of water rather than being 

 carried into the Atlantic. The Gulf of Mexico is 

 of no importance to the deep-water circulation of 

 the Atlantic Ocean (Kuenen 1950, p. 44). The 

 unnamed current that becomes the Florida cur- 

 rent is the major current of the Gulf, and "it is 

 essentially a direct continuation of the current 

 through the Yucatan Channel" (Sverdrup, John- 

 son, and Fleming, 1942, p. 642). The waters of 

 the Gulf mainly form independent eddies and are 

 only to a small extent drawn into the Straits of 

 Florida. These eddies appear to be semiper- 

 manent features with their locations determined 

 by the contours of the coast and the configuration 

 of the bottom (idem., p. 641).' 



EARLY STUDIES OF SUBMARINE DEPOSITS 



The Coast Survey instituted a series of investi- 

 gations on physical problems of the deep sea in 

 1846, with emphasis on the Gulf Stream. In 

 1850, L. Agassiz made an extended biological sur- 

 vey of the Florida reefs, and in 1867, Pourtal6s 

 and Mitchell began a more systematic deep-sea 

 exploration. Dredging between Florida and Cuba 

 in 1868 reached depths of 850 fathoms, and the 

 bottom samples obtained showed a closer relation- 

 ship to the cretaceous fauna rather than to or- 

 ganisms of the adjacent shores. 



Commander Howell, U. S. N., began a system- 

 atic exploration of the Gulf of Mexico in 1872, 

 starting in the shallow waters along the west 

 coast of Florida, and the work was continued by 

 Lieutenant Commander Sigsbee in 1875-78, using 

 the United States Coast Survey steamer Blake. 

 The specimens of bottom deposits were sent to 

 John Murray of the Challenger for examination, 

 and he published the results in 1885 (Murray, pp. 

 51-61). Excerpts from his original description 

 are as follows: 



In all the deeper deposits in the Gulf of Mexico and 

 Strait of Florida, the crystalline mineral particles are very 

 small, rarely exceeding one-tenth of a millimeter in diam- 

 eter. They consist principally of small rounded grains of 

 quartz, with fragments of felspars, mica, hornblende, 



' For a detailed discussion of circulation of water in the Oulf of Mexico 

 see article hy D. F. Leippcr, Physical Oceanography of the Gulf of Mexico, 

 in this book. pp. 119-137. 



augite, magnetite, and rarely tourmaline. In a few places 

 there were fragments of pumice, and glauconitic particles 

 were occasionally noticed. The mineral particles and fine 

 clayey matter appear to be almost wholly derived from 

 North American rivers. 



The carbonate of lime in the deposits of these regions is 

 mostly made up of the shells of pelagic Foraminifera and 

 MoUusks. In depths greater than 2,000 fathoms the 

 Pteropod and Heteropod shells appear to be nearly, if not 

 quite, absent — the carbonate of lime then consisting of 

 the shells of pelagic Foraminifera; in less depths the Ptero- 

 pod and Heteropod shells are present, and in depths vary- 

 ing from 200 to 500 fathoms they make up the bulk of the 

 deposits in many places. In several of the deposits, where 

 the percentage of carbonate of lime is very high, the whole 

 has a very chalk-like appearance; it appears, indeed, as if 

 it were in the process of transformation to true chalk. 



The siliceous organisms consist of Radiolarians and 

 Sponge spicules, with a few Diatoms, but these seldom 

 make up more than three or four percent of the whole 

 deposit. 



A study of the United States Coast and Geo- 

 detic Survey maps of the continental shelf ad- 

 jacent to Louisiana shows many different mate- 

 rials forming the Gulf bottom such as sands, muds, 

 clays, shells, and local reefs. These represent the 

 surface of the Gulf floor, and little is known about 

 the material even immediately below the surface. 

 Some borings have been made in the erection of 

 the platforms required for petroleum exploration, 

 but these platforms are all located approximately 

 within the first 30 miles off shore. The wells 

 drilled from these offshore structures have yielded 

 no known information of the surface formations. 

 Likewise, crews making geophysical surveys in 

 the Gulf are not interested in the surface or near- 

 surface formations (Willey 1948, p. 3). 



Trowbridge (1927, p. 148) stated that the United 

 States Coast and Geodetic Survey obtained 600 

 bottom samples in 1921 and that their map of 

 1926 included the results of this work. 



RECENT STUDIES OF SUBMARINE DEPOSITS 



According to Trask, Phleger, and Stetson 

 (1947, p. 460) sediments in the Gulf of Mexico 

 have changed in relatively recent time. During 

 the 1947 expedition of the Atlantis, more than 600 

 cores were taken along 19 lines perpendicular 

 to the Texas and Louisiana coast, crossing both 

 the continental platform and the continental 

 slope and continuing into the depths of the 

 Gulf. The complete results of this expedition 

 have not been published to date, but some data 

 were discussed by Phleger (1950). It was found 



