POORLY KNOWN 

 MODERATELY KNOWN 

 BEST KNOWN 



Figure 17. — Conrin«ntal margins of the world. 



(fig. 17). Studies include both the stable continental margins 

 of the South Atlantic and the active margins of Peru-Chile 

 and Southeast Asia. Margins that have undergone long-con- 

 tinued subsidence and sedimentation are potential sites of major 

 oil fields. Subduction zones, which border active margins, are 

 enriched in heavy metals and also are potential sites for hydro- 

 carbon accumulation. Two major studies of the continental 

 margins along the South Atlantic are now under way — one off 

 West Africa extends from South Africa to Portugal, and 

 another along the east coast of South America extends from 

 Argentina to Brazil. 



African Atlantic Margin 



The African studies were initiated in January 1972 when 

 scientists from the Woods Hole Oceanographic Institution 

 began a systematic study extending from Port Elizabeth, South 

 Africa, to the Congo River. Although survey tracks concen- 

 trated on the continental margin, a few tracks were extended 

 out to the Mid-Atlantic Ridge. A total of 50,000 km of seismic 

 reflection, gravity, and magnetic data were recorded. Precision 

 bathymetric data were also obtained, and seismic refraction 

 data, using sonobuoys, were routinely recorded. Location of 

 lines at sea was controlled by satellite navigation. In 1973 the 

 second and final cruise extended the study from the Congo 

 River to Lisbon (fig. 18). 



Preliminary findings from the 1972 work indicated two 

 potential sources of oil accumulation, one in a thick sedimen- 

 tary section off the delta of the Orange River in southwest 

 Africa, and another in a large diapiric salt basin off Angola. 

 The areal extent and thickness of both deposits were outlined 

 using geophysical methods, and their internal structure has 



been analyzed using seismic reflection and refraction data. 

 K. O. Emery, the Principal Investigator from Woods Hole, 

 concluded that: "Within the delta are probably numerous 

 stratigraphic traps capable of retaining oil and gas if they are 

 present and within the diapir field are many structural traps 

 caused by the upward movement of the salt. The landward 

 side of both features underlies the outer continental shelf or 

 the upper continental slope, but the major parts lie much 

 deeper. Nearly all of both features lie within 200 nautical 

 miles ... of the adjacent coasts. While depths of more than 

 about 100 m are too great for present economic exploitation 

 of oil and gas, they may justify testing by the drill within a 

 decade. Successful exploitation of the deepwater features can 

 greatly modify the economy of the adjacent countries and 

 broaden the petroleum supply for the rest of the world." 



On one or more of the various legs, twenty-one scientists, 

 technicians, and students from Argentina, Brazil, the Republic 

 of the Congo, the United Kingdom, France, Portugal, the Re- 

 public of South Africa, and Spain participated. Preparatory 

 to the cruise about 150 African and other interested scientists 

 received a bathymetric atlas and preliminary reports on geo- 

 magnetics, gravity, and sediments. The profiles and charts of 

 geophysical data from the 1972 cruise were printed and dis- 

 tributed in January 1973. 



Work accomplished during the past year is described by 

 Elazer Uchupi and K. O. Emery in "Seismic Reflection, 

 Magnetic, and Gravity Profiles of the Eastern Atlantic Con- 

 tinental Margin And Adjacent Deep-sea Floor. II. Congo 

 Canyon (Republic of Zaire) to Lisbon (Portugal)," Woods 

 Hole Oceanogr. Inst. Tech. Rep., Ref. No. WHOI-74-19, 

 April 1974. Marine geophysical data received last year by 



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