Sediment Distribution in the Hawaiian Archipelago l POW-FOONG FAN2 and Ross R. GRUNWALD3 ABSTRACT: Four sediment types were differentiated in 125 samples of marine sediments taken from the sea floor around the Hawaiian Islands. These were: shallow-water carbonates and detritus around the islands, calcareous oozes on bathymetric highs distant from shore, brown clay on the Hawaiian Arch, and siliceous ooze in the Hawaiian Deep and west of the island of Hawaii. A MAP OF SEDIMENT TYPES around the Ha- waiian Islands was prepared from a synthesis of data compiled from recent studies of 111 grav- ity cores and 14 grab samples from the Ha- waiian Archipelago (Fig. 1). Of the 111 samples, 21 were collected by the Scripps In- stitution of Oceanography, and the rest were collected by the Hawaii Institute of Geophys- ics. Due to uneven distribution of the sampling locations, some of the boundaries of the differ- ent sediments shown in Figure 2 are not well defined. However, the general pattern of sedi- ment types portrayed is believed to be essentially correct. Marine sediments in the Hawaiian Archipelago can be classified into the following types: (1) shallow-water carbonates and detritus; (2) cal- careous ooze; (3) brown clay; and (4) siliceous ooze. The shallow-water carbonates, similar to those found in beach sands, comprise foraminif- era, molluscs, red algae, echinoids, coral, and Halimeda. The detritus is composed of olivine, pyroxene, plagioclase, magnetite, ilmenite, gibb- site, palagonite, kaolinite, halloysite, montmoril- lonite, and illite. Allophane and other amor- phous materials were . also found. X-ray diffraction results of the detrital muds, grain diameters « 64p,) show they are character- ized by the kaolinite-montmorillonite-plagio- 1 Hawaii Institute of Geophysics contribution no. 410. This research was supported in part by Office of Naval Research contract Nonr-3748(05). Manu- script received December 28, 1970. 2 University of Hawaii, Hawaii Institute of Geo- physics, Honolulu, Hawaii 96822. 3 South Dakota School of Mines and Technology, Department of Geology and Geological Engineering, Rapid City, South Dakota 57701. clase-magnetite assemblages. The detrital muds are concentrated around the Hawaiian Islands, becoming increasingly intermixed with brown clay farther from shore. However, they remain an important constituent of the sediment as far north of Oahu as the crest of the Hawaiian Arch. Authigenic chlorite derived from gibbsite is reported near the mouth of Waimea River in Waimea Bay off the coast of Kauai (Swindale and Fan, 1967). The clastic sediments being shed from the Hawaiian Islands into the surrounding oceanic depths are primarily detrital muds, but some are silty calcareous sands. Graded beds of silty calcareous sands have occasionally been found in cores from the Hawaiian Trench. It seems logical to ascribe the graded cal- careous sand layers found in the sediments of the Hawaiian Deep to transport and deposition from shallower water by turbidity currents. The detrital muds rarely show graded bedding and are probably carried in suspension by bottom currents into abyssal depths. No comprehensive study of bottom currents has been conducted around the Hawaiian Islands, but J. N. Car- ruthers (Belshe, 1965) measured some bottom currents west of Kauai at depths from 800 to 2,200 meters. These currents were tidal and variable in direction, and velocities sometimes reached magnitudes of one-fourth knot. K. Wyrtki (personal communication) measured similar bottom currents north of the Hawaiian Arch. The brown clay of the Hawaiian Arch is dark yellowish-brown in color, has a median diameter of 2 microns, and consists of less than 1 percent sand. Mineralogically, the sediment is composed of illite, quartz, and chlorite; and lesser amounts of kaolinite, montmorillonite, 484