Clay minerals in sediments from the central part of the Guaymas Basin, Gulf of California, hole 478
Clay minerals of Upper Pleistocene sediments were studied from Hole 478 DSDP (a depth of 464 m), that is located in the central part of the Guaymas Basin, Gulf of California. Composition of clay minerals and their quantitative proportions in natural mixtures were determined by X-ray methods based on the modeling of diffraction patterns. Terrigenous clay minerals are represented mainly by dioctahedral micaceous varieties (mixed-layer disordered illite-smectites, illite) with the chlorite admixture and kaolinite in the sedimentary section with the exception of altered sediments from contact zones with roofs of sills. These sediments include newly formed trioctahedral mixed-layer chlorite-smectite and corrensite-chlorite, as well trioctahedral smectite. Terrigenous dioctahedral illite is preserved in these sediments. Terrigenous illite is missing in the sediments from the lower part of Hole 478, that is located on the roof of the sill complex with a thickness of no less than 125 m.