gin; continue study of the crustal structure, sediments, bathy- 

 metry, and origin of the Ceara rise; delineate the diapir zone 

 on the eastern margins of Brazil; map basement structure and 

 sediment thickness in the Pelotas and Santos basins and inter- 

 basin area; and complete petrologic studies of roclcs dredged 

 from the Sao Paulo Plateau and Rio Grande Rise. 



Marine geological work in the Argentine Basin has fol- 

 lowed two lines of micropaleontologic study: 1 ) analyses of 

 pre-Pleistocene cores from the Falkland Plateau, the conti- 

 nental rise, and the continental slope to determine the evolu- 

 tion of the Argentine Continental Margin; and 2) use of 

 Antarctic-source diatoms as tracers to the flow of Antarctic 

 Bottom Water and as indicators of source of sediments. 



Terrestrial geology studies include detailed work on the 

 Lower Cretaceous ophiolite complex in the southern Andes 

 and its relation to and significance for the southern Andean 

 Cordillera. Collections were made for paleomagnetic work and 

 for geochemical studies to determine the tectonic significance 

 of igneous rocks from the Andean Cordillera and from the 

 Quaternary mafic vents, flows, and intrusions east of the Andes. 



Marine geological and geophysical field work for the study 

 of the Argentine Margin was completed with a coring and 

 dredging program in the submarine canyons along the Argen- 

 tine continental rise and slope. The sediment cores, taken in 

 a number of outcrop areas, are being studied to identify the 

 ages and lithologies of major stratigraphic units observed in 

 the seismic data collected during earlier phases of the study. 



Recent seismic work included: surveys between coring 

 sites to aid geologic correlation of samples; a refraction study 

 of the continental rise using sonobuoys, an ocean-bottom seis- 

 mograph, and two ships for recording; and a retraverse of 

 canyon areas sampled on the previous leg. Continuing research 

 includes studies of the basins and shelf, the ocean-continent 

 transition, and the Falkland Plateau and North Scotia Ridge. 

 Gravity and magnetic anomalies in the Argentine Basin have 

 been compared with similar features off southern Africa. These 

 results are very promising for further study and interpretation 

 of: the direction and relative motion between Africa and South 

 America when rifting was initiated, the precise time of the 

 early opening, and the relationship between the structures on 

 the continental margin and its history of early opening. 



Southwest Atlantic continental margin work accomplished 

 includes three periods of marine field work of about 6 months 

 each (early 1972. 1973, and 1974) and field work in the 

 southern end of the Andean Cordillera and on the island of 

 South Georgia (early 1973 and 1974). This work is reported 

 in: Progress Report: A Geophysical Study of the Continental 

 Margin of Argentina and Brazil, Lamont-Doherty Geological 

 Observatory of Columbia University, undated. Reference Grant 

 GX 34410. Marine geophysical data received in 1973 by 

 NOAA Environmental Data Service's National Geophysical 

 And Solar-Terrestrial Data Center include 30,000 nautical miles 

 of bathymetric, magnetic, seismic-reflection profile, 3.5-kHz 

 echo sounder, and sonobuoy data. 



Tossing overboard a sonobuoy. 

 30 



