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

Abstract

Variations in the clay mineral composition of mid-late Quaternary sediments recovered from the Cariaco basin are interpreted in terms of changes in paleoclimate. The results indicate the changing contribution of regional and local sediment sources during interglacial high stands vs. glacial low stands. The relative contribution of illite increases during interglacial stages, and decreases during glacial stages. Illite–smectite shows a much weaker negative relationship to glacial eustacy. The abundances of kaolinite and chlorite show no correlation with paleoclimate. Sediments sourced from rivers adjacent to the Cariaco basin contain low illite and provide a significant influx of illite–smectite during low sea level stands, but during interglacial periods, they are probably deposited on the shallow continental shelf 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 sediment is discharged directly onto the continental rise. During the last glacial period, changes in clay mineral composition were magnified relative to previous glaciations, possibly due to tectonic evolution of the region. The sill depth between the Cariaco basin and the open Caribbean Sea was reduced to a minimum, decreasing further the relative importance of the Amazon/Orinoco contribution.