SILICICLASTIC SEDIMENTS BENEATH THE CALIFORNIA CURRENT SYSTEM (ODP LEG 167): FROM MINERALOGICAL PROVENANCE ANALYSIS TO GEOCHEMICAL SOURCE AND WEATHERING PARAMETERS

During ODP Leg 167 within the California Current System sediments with variable siliciclastic proportions at thirteen drilling locations have been recovered. By combining results of the north-south transsect along the changing hinterland with known lithology with shelf-deep sea transsects, mineralogy governing parameters mineralogy as provenance, transport processes and weathering could be differentiated. The mineralogical composition of the samples has been determined qualitatively by X-ray diffraction analysis. The main siliciclastic minerals are quartz, four different kinds of feldspars, montmorillonite, illite, chlorite, and kaolinite. Quantification of identified phases has been performed using the Rietveld method. Depending on the lithology and morphology in the hinterland, a strong gradient in the feldspars/quartz ratio occurs from south to north - with the most feldspar-enriched sediments in the vicinity of the Santa Ynez mountains. Within the feldspar assemblage the plagioclase/K-feldspar ratio varies depending mainly on the lithology and morphology/weathering intensity in the hinterland. An additional parameter seems to be selective submarine dissolution, as the albite/plagioclase ratio is distinctly lowered in all deep sea locations - without a concomitant decrease in grain size for all but one location. In contrast to the phases mentioned above governed by the hinterland the clay mineral assemblage depicts the additional effect of marine currents. The chlorite/total clay minerals ratio clearly resembles the transportation of fine grained material from the Eel river basin to more southerly locations with surface currents of the California Current system. The geochemical composition of the sediments was determined by X-ray fluorescence analysis. The results were corrected for biogenic carbonate and opal as well as pore water natrium. In accordance with the mineralogy several trace elements clearly differentiate the hinterland sources of the material. On this background, several geochemical provenance and weathering parameters proposed in the literature have been tested.