WRRCTMR No.68 Mineralogy of Sediments in Three Estuaries on Oahu, Hawaii

Abstract

Semiquantitative X-ray diffraction was used to determine the relative abundance of minerals in sediments from three estuaries on Oahu, Hawaii. The watersheds of the three sites represent diverse environments: Kaneohe Bay, a windward northeast facing lagoon-bay complex; Maunalua Bay, a leeward south facing, heavily urbanized area; Pearl Harbor, a blend of urban-agricultural estuarine complex on the leeward central portion of Oahu. Five suites of mineralogic assemblages were found: basaltic, secondary clay, hydrothermal-aeolian, marine carbonate, and authigenic. Carbonates prevailed in the sediments in Kaneohe Bay except near stream mouths. Primary minerals of the basaltic suite dominated the terriginous sediments from the streams, but iron-rich secondary minerals were common and quartz and mica of aeolian origin and some hydrothermal christobalite were present. Secondary clay minerals and hematite were the main constituents of the suspended sediments carried to Maunalua Bay. In Pearl Harbor the basaltic suite was dominant near the stream mouths. Secondary clays and aeolian quartz and illite were found where salinity and currents allowed deposition. Authigenic pyrite was formed where anaerobic conditions developed in organic depositions. Montmorillonitic minerals corresponded to the source soils derived from tuff. Heavy metals in Kaneohe Bay resembled the soil and rock levels, but considerably higher levels were found accumulated in the fine sediments in Pearl Harbor.