Relatively closely spaced trackllnes were run in 1971 in the 

 TAG corridor. When combined with previous results, the 1971 

 data allow a standard sequence of magnetic reversal anomalies to 

 be deduced for the central North Atlantic. This sequence can be 

 traced back 60 million years on either side of the Mid-Atlantic 

 Ridge, showing that rates for corresponding time intervals on op- 

 posite sides of the ridge may vary as much as 0.5 cm. /year. A 

 partial sequence of Cretaceous and a nearly complete "Keathley" 

 sequence of Late Jurassic magnetic anomalies were identified to 

 a distance east of the Mid-Atlantic Ridge, corresponding to an 

 estimated crustal age of 155 million years. 



A systematic survey covering a 34,000-km.- area of the abyssal 

 hills in the eastern central North Atlantic was made with a track- 

 line spacing of 18 km. This investigation revealed two intersecting 

 topographic trends — two fracture zones trending 112° and a ridge- 

 and-trough topography trending 47°. The ridge-and-trough topog- 

 raphy is neither orthogonal to the fracture zones nor parallel with 

 the Mid-Atlantic Ridge axis. An analysis of these patterns may 

 allow the stress field on the abyssal floor to be inferred from the 

 strain pattern. The results Indicate that in addition to sea floor 

 spreading about a midocean ridge, other processes are active in 

 the development of abyssal hills. 



A bottom sampling program was also conducted in 1971 along 

 the eastern extension of the Atlantis Fracture Zone. Measurements 

 include studies of the Interstitial water contents and geochemistry 

 of the sediments and petrologic analyses of hard rocks. Outstand- 

 ing results of the dredging program include the finding of thick 

 manganese encrustations along the entire length of the fracture 

 zone and the dredging of deep-water limestone from the Mid- 

 Atlantic Ridge. 



Caribbean Atlantic Geotraverse (CAG). Most of the trackllnes for 

 this project were oriented east-west between the Lesser Antilles 

 Arc and the Mid-Atlantic Ridge and were spaced about 36 km. 

 apart. Additionally, several north-south lines were run across the 

 entire "Funnel-Smith" opening, and a detailed grid (8-km. track- 

 line spacing) was established at the western extension of the Barra- 

 cuda fault (fig. 34). 



The main project objectives were to define the plate margins 

 through the Identification and correlation of magnetic anomalies, 

 interpretation of gravity and seismic reflection data, and observa- 

 tion of changes of sea floor morphological provinces. 



Preliminary analysis of the data suggests: (1) A north-south dis- 

 continuity at longitude 53 'W. that offsets and separates the north- 

 west-southeast faults of the Mid-Atlantic Ridge province from the 

 mainly east-west faults located directly east of the island arc, (2) 

 a very narrow zone of correlatable magnetic anomalies near the 

 ridge-crest, (3) west-northwest extension of the Barracuda fault, 

 and (4) high utility of the gravity anomalies in detecting fault 

 zones In the area. 



In addition it was found that at I2°30'N., 57°05'W., a fault 

 brings a seismic reflector within 200 m. of the sea floor. This re- 

 flector apparently represents an ancient sea floor, which becomes 

 flat 30 km. south of this location, where It is overlain by the sedi- 

 mentary prism deposited by the Amazon and Orinoco Rivers. 



World's Seabed Manganese Deposits 



On January 20-21, 1972, the Lamont-Doherty Geological Ob- 

 servatory of Columbia University convened a workshop on the 

 world's seabed manganese deposits; topics considered Included their 

 distribution, evaluation, growth, and origin. One hundred-fifty exec- 

 utives and scientists from the academic community. Government, 

 and industry participated In the workshop, which included the 

 presentation of 30 research papers and the establishment of several 

 task teams. Among the workshop participants were also scientists 



and representatives from foreign nations, such as, Canada, France, 

 India, Netherlands, New Zealand. United Kingdom and W. Ger- 

 many. 



At the workshop. Lamont-Doherty scientists presented new world 

 maps showing the distribution of known deposits of manganese 

 nodules. The maps were prepared from information held in the 

 Lamont-Doherty data bank and gathered from other sources, such 

 as RV Chullenger and Albatross. Florida State University, NOAA, 

 and the Scripps Institution of Oceanography. TTie data were ob- 

 tained from bottom photographs, and from core, dredge, and grab 

 samples. The maps of manganese distribution were prepared so 

 that they may be used as overlays on maps showing the distribu- 

 tion of other properties, such as bottom current velocity, bottom 

 topography, heat flow, occurrence of nepheloid layer, sedimenta- 

 tion rate, and other seabed properties. 



SEABED ASSESSMENT BIBLIOGRAPHY 



TTils bibliography lists some of the post- 1970 reports and abstract 

 prepared with IDOE funds. Several can be obtained from the Na- 

 tional Technical Information Service (NTIS), Sills Building, Spring- 

 field, Va. 22151. 



Behrendt, J.C., J.S. Schlee, and J.M. Robb. Magnetic Anomalies 

 on the Continental Margin Off Liberia Observed on USGS-IDOE 

 Cruise Leg 5, EOS, Transactions American Geophysical Union, 

 Vol. 53, No. 4, p. 408, April 1972. 



Chiburls, E.F., J.J. Dowling, P. Dehllnger, and M.J. Yellin, Pacific 

 SEAMAP 1961-70 Data for Areas 16530-10 and 17530-10, 

 Longitude I65°W to 180°, Latitude 30°N to 36'N, Bathymetry, 

 Magnetics, and Gravity, NOAA Technical Report NOS 49, 158 

 p., July 1972. 



Chiburls, E.F., J.J. Dowling, P. Dehllnger, and M.J. Yellin, Pacific 

 SEAMAP 1961-70 Data for Areas 16524-10 and 17524-10, 

 Longitude 165''W to 180°, Latitude 24°N to 30°N, Bathymetry, 

 Magnetics, and Gravity, NOAA Technical Report NOS 50, 251 

 p., July 1972. 



Chiburls, E.F., J.J. Dowling, P. Dehllnger, and M.J. Yellin, Pacific 

 SEAMAP 1961-70 Data for Areas 15636-12, 15642-12, 16836- 

 12, 16842-12, Longitude 156'W to 180°, Latitude 36°N to 

 48°N, Bathymetry, Magnetics, and Gravity, NOAA Technical 

 Report NOS 51. 509 p., July 1972. 



Dehllnger, P., E.F. Chiburls, and J.J. Dowling. Pacific SEAMAP 

 1961-70 Data Evaluation Summary, NOAA Technical Report 

 NOS 52, 10 p., July 1972. 



Dowling, J. J., E.F. Chiburls, P. Dehllnger, and M.J. Yellin. Pacific 

 SEAMAP 1961-70 Data for Area 15524-10, Longitude 155°W 

 to 165°W, Latitude 24°N to 30°N, Bathymetry. Magnetics, and 

 Gravity, NOAA Technical Report NOS 45, 283 p., January 



1972. 



Dowling, J. J., E.F. Chiburls, P. Dehllnger, and M.J. Yellin. Pacific 

 SEAMAP 1961-70 Data for Area 15530-10, Longitude 155°W 

 to 165°W, Latitude 30°N to 36°N, Bathymetry, Magnetics, and 

 Gravity, NOAA Technical Report NOS 46, 253 p., January 

 1972. 



Dowling, J.J., E.F. Chiburis, P. Dehllnger, and M.J. Yellin. Pacific 

 SEAMAP 1961-70 Data for Area 15248-14, Longitude 152°W 

 to 166°W, Latitude 48°N to 54°N, Bathymetry, Magnetics, and 

 Gravity, NOAA Technical Report NOS 47, 283 p., April 1972. 



Dowling, J.J., E.F. Chiburls. P. Dehllnger, and M.J. Yellin. Pacific 

 SEAMAP 1961-70 Data for Area 16648-14, Longitude 166°W 

 to 180°, Latitude 48°N to 54°N, Bathymetry, Magnetics, and 

 Gravity, NOAA Technical Report NOS 48, 209 p., April 1972. 



22 



