Indirect climatic control of the clay mineral composition of Quaternary sediments from the Cariaco basin, northern Venezuela (ODP Site 1002)

Variations in the clay mineral composition of mid-late Quaternary sediments recovered from the Cariaco basin are interpreted in terms of changes in pa leoclimate. The results indicate the changing contribution of regional and local sediment sources during interglacial high stands vs, glacial low stan ds. The relative contribution of illite increases during interglacial stage s, and decreases during glacial stages. Illite-smectite shows a much weaker negative relationship to glacial eustacy. The abundances of kaolinite and chlorite show no con elation with paleoclimate. Sediments sourced from rive rs adjacent to the Carinco basin contain low illite and provide a significa nt influx of illite-smectite during low sea level stands, but during interg lacial periods, they are probably deposited on the shallow continental shel f bordering the local coastline. Clays sourced from the Amazon and Orinoco rivers are richer in illite, and their contribution is reduced in times of low sea level stands, as the continental shelf becomes much narrower and se diment is discharged directly onto the continental rise. During the last gl acial period, changes in clay mineral composition were magnified relative t o previous glaciations, possibly due to tectonic evolution of the region. T he sill depth between the Cariaco basin and the open Caribbean Sea was redu ced to a minimum, decreasing further the relative importance of the Amazon/ Orinoco contribution. (C) 1999 Elsevier Science B.V. All rights reserved.