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ABSTRACT: Preliminary Results of KORDI-USGS Cooperative Cruise for Ferromanganese Crusts in the Western Marshall Islands

Jung-Keuk Kang, James R. Hein, Byong-Kwon Park, Suk-Hoon Yoon

In September 1989, the Korea Ocean Research and Development Institute and the U.S. Geological Survey successfully completed a cooperative cruise in the western EEZ of the Marshall Islands, one of the areas considered to have the greatest potential for ferromanganese crust resources. Twenty-seven dredge hauls sampled crusts on the slopes and summits of 9 volcanic edifices. In addition, 18 CTD-oxygen profiles, 2 bottom camera surveys, and 2000 km of seismic surveys with single-channel airgun and 3.5 kHz high-resolution seismic profilers were completed.

Substrate rocks are predominantly sedimentary breccias with lesser amounts of basalt, limestone, and phosphorite. Sedimentary breccia typically consists of angular to subangular basaltic rock fragments embedded in a matrix of calcareous mud or phosphatized mud. About 90% of recovered rocks are encrusted by ferromanganese oxides. The thickness of the crusts varies from a patina (<1 mm) to 150 mm, and thick crusts averaging over 40 mm were collected in 8 dredge hauls from 6 seamounts. Ferromanganese crust surfaces are predominantly botryoidal with granular oxides common in recessed parts of the crusts. Thick crusts commonly exhibit several (up to 7) layers of various types, such as dense and massive, crudely laminated, and porous. Strong bottom current activity is indicated by fluted and polished botryoidal surfaces on the crusts, as well as by well-developed ripple marks in the foraminiferal sand, which were observed on bottom photographs.

AAPG Search and Discovery Article #90097©1990 Fifth Circum-Pacific Energy and Mineral Resources Conference, Honolulu, Hawaii, July 29-August 3, 1990