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USGS Coastal and Marine Geology Program

Field Activity Details for field activity 1971-005-FA

Other ID: UGEO Leg 5; CORPUS 20

Status: Completed

Organization(s): USGS, Woods Hole Coastal and Marine Science Center

Funding Program(s):

Principal Investigator(s): John S. Schlee

Affiliate Investigator(s):

Information Specialist(s):

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: Sonobuoy, 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 Port/Location: Monrovia, Liberia

End Port/Location: Monrovia, Liberia

Start Date: 1971-10-29

End Date: 1971-11-20

Equipment Used: 3.5 kHz, Sparker , Seismic refraction, Single channel hydrophone, Gravity meter (wh), Dredge, Decca radar system, ITT 4007 satellite navigation, Marine magnetometer

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

Affiliate Staff:
USGS-Denver: John Behrendt - geophysicist; USGS-Corpus Christi: Ray Martin - geologist; USGS-Menlo Park: James Pearl - Phys. Sci. Tech.
William Todd - Phys. Sci. Tech.
Harry Hill - ET
James Nicholson - ET; Liberian Geological Survey
Monrovia: Jenkins Dunbar - geologist; Spanish Institute of Geology and Mines of Spain
Madrid: Jaime Garcia-Rodriguez - geologist

Notes: Original Center People field contained: John Schlee - Ch. Sci.; James Robb - geologist; Charles O'Hara - geologist; Frank Jennings - ET.
Project = International Decade of Ocean Exploration (IDOE), International Decade of Ocean Exploration (IDOE)


Liberian continental margin, Liberia, Africa, North Atlantic;

North: 7 South: 3 West: -12.5 East: -7


photo of United Geo I
United Geo I


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:


Data Acquired

Survey EquipmentSurvey InfoData Type(s)Data Collected
Single channel hydrophone --- Air Gun / Water Gun
Bubble Gun
Sub Bottom Profiler
1971-005-FA-SE-002 ( microfilm of )
1971-005-FA-SE-001 ( Collection of paper record displays of seismic data( SONO) for lines )
Sparker --- Sparker
3.5 kHz --- Sub Bottom Profiler
NGDC MGD77 data ( )
1971-005-FA-BA-001 ( Bathymetric data in InfoBank)
Marine magnetometer --- Magnetics
1971-005-FA-GP-001 ( Magnetics in InfoBank)
NGDC MGD77 data ( )
Gravity meter (wh) --- Gravity
NGDC MGD77 data ( )
1971-005-FA-GP-002 ( Gravity in InfoBank)
Seismic refraction --- Sonobuoy
Dredge --- Biology
ITT 4007 satellite navigation --- Navigation
1971-005-FA-LN-002 ( Navigation data in InfoBank)
1971-005-FA-LN-001-01 ( Navigation trackline plot for field activity 71005)
Decca radar system --- Navigation

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