GEOCHEMICAL CHARACTERISTICS OF DEEP-SEA SEDIMENTS (131O10'W-133O50'W, 9O50'-10O30'N FROM THE NORTHEAST EQUATORIAL PACIFIC AND ITS PALEOCEANOGRAPHIC IMPLICATIONS

Core sediments collected from the Clarion-Clipperton Fracture Zone in the NE equatorial Pacific were analyzed for chemical and mineralogical compositions to investigate the environmental and oceanographic variations along the lengths of cores. The sediments were divided into three lithologic units from top to bottom by its color; brown layer (Unit I), pale brown layer (Unit II), and black brown layer (Unit III). 10Be geochronology indicated the depositional age of Quaternary for Units I and II and of Pliocene for Unit III with a short hiatus between them. Interelemental correlation analyses identified three major groups of elements that showed moderate-to-strong correlations: 1) Al, Ti, K, and Fe, 2) Ca, P, REEs, Cu, and Zn, and 3) Mn, Ni, and Co. Each group reflects terrestrial, biogenic, and hydrogenous Mn-oxide components of sediments, respectively. Unit III shows high smectite, likely formed by dispense of siliceous biogenic components, but low quartz and illite contents compared to the upper two units. This mineralogical variation is accompanied by enriched biogenic components such as P, Cu, and REEs. These indicate the reduced supply of terrestrial material and/or increased productivity of surface water at the time of Unit III deposition, which is attributed to Pliocene warming. However, Unit III contains unidentified 8 angstrom mineral, likely amphibole, that are absent in Units I and II, suggestive of the possibility of different sources during Pliocene. Units I and II show similar elemental and mineral compositions, which indicates stable paleoenvironmental and paleooceanographic conditions through the Quaternary. Increased contribution of terrestrial components, indicated by increased amount of illite and quartz in Units I and II, is consistent with paleoclimatic change from Pliocene warming to a global cooling during Quarternary.