To characterize and quantify the siliciclastic sediment fraction and its change through late Quaternary times, sediments of Ocean Drilling Program Site 893 were analyzed for their clay and bulk mineralogical composition using X-ray diffraction (XRD) techniques. Throughout the entire sediment sequence, smectite (40%–68%) and illite (25%–44%) are the dominant clay minerals, whereas kaolinite (5%–10%) and chlorite (3%–9%) are only of secondary importance. Quartz contents vary between 12%–25%; quartz fluxes range from 10 to 40 g/cm–2k.y.–1. The Santa Clara River appears to be a major sediment source over the past 160,000 years. During glacial intervals of lowered sea level, a direct sediment transport from the shelf/slope probably became more important. The sandy material is characterized by very high quartz content (55%) and significantly higher k-feldspar/plagioclase ratios. Based on the still-limited data base, short-term fluctuations in clay-mineral composition and quartz content occur, suggesting climate-triggered changes in the terrigenous sediment supply. (Eolian) quartz flux was significantly increased during glacial stages 2, 5d, and near the stage 5/6 boundary. Future high-resolution studies on clay and bulk mineralogy are necessary to prove these preliminary interpretations.
Date of initial receipt: 12 July 1994
Date of acceptance: 19 January 1995
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