Other ID: UGEO Leg 5; CORPUS 20
Organization(s): USGS, Woods Hole Coastal and Marine Science Center
Location: Liberian continental margin, Liberia, Africa, North Atlantic;
Principal Investigator(s): John S. Schlee
Data Type(s): Seismics: Air Gun / Water Gun, Seismics: Boomer, Seismics: Bubble Gun, Seismics: Sparker, Seismics: Sub Bottom Profiler, Electro-Magnetic: Magnetics, Electro-Magnetic: Gravity, Seismics: Sonobouy, Sampling: Biology, Sampling: Geology, Location-Elevation: Navigation
Scientific Purpose/Goals: The objectives of the geophysical and geological studies were to investigate the structural-stratigraphic framework of the continental margin adjacent to Liberia; to determine the nature of the transition from the pre-Cambrian shield area on land to the ocean floor; and to determine how deep sea fracture zones of the Atlantic Ocean tie to the continental shelf and to the continental geology of Africa. The cruise was divided into two main parts, geophysical profiling along the Liberian continental margin the first 17 days and dredging plus profiling the remaining 5 days of the cruise.
Start Date: 1971-10-29
Start Port/Location: Monrovia, Liberia
End Date: 1971-11-20
End Port/Location: Monrovia, Liberia
Equipment Used: Single channel hydrophone, Sparker system, 3.5 kHz, Marine magnetometer, Gravity meter (wh), Seismic refraction, Dredge, ITT 4007 satellite navigation, Decca radar system
Information to be Derived: Morphology;
Summary of Activity and Data Gathered: With only shipboard examination of data, our results are preliminary and sketchy. 1. Pronounced magnetic anomalies on inner shelf are probably the seaward continuation of diabase intrusives on land, detected in aeromagnetic survey published by Behrendt and Wotorson. 2. A progradation of the shelf and slope along the central third of the Liberian continental margin. 3. Presence of a submarine canyon oblique to the coast off Cape Palmas. The same area is marked by steepened eroded slope, crumpling and faulting of strata, and marked gravity and magnetic anomalies. 4. A thick section of sedimentary rocks beneath much of the outer continental shelf, capped by gently dipping Pleistocene (?) terrace deposits at the shelf break. Sparker and 3.5 kHz profiles: 5400 km (37 tracklines); Sonobuoy refraction profiles: 5; Dredge stations: 7 (chain broke on last station, sample lost, dredge recovered); Magnetics; Gravity.
Staff: John S. Schlee, James M. Robb, Charles J. O'Hara, Frank W. Jennings
Notes: Original Center People field contained: John Schlee - Ch. Sci.; James Robb - geologist; Charles O'Hara - geologist; Frank Jennings - ET.
Schlee, J.S., 1972, Acoustic reflection profiles, Liberian continental margin, International Decade of Ocean Exploration, Leg 5, 1971 cruise, UNITEDGEO I: USGS-GD-72-006, PB-209-871, 30 p. URL: http://www.ntis.gov/search/product.aspx?ABBR=PB209871.