A clay mineral investigation of six cores from the Gulf of Mexico

Samples were studied from each color change along six gravity cores from nearshore to deep-sea areas in the Gulf of Mexico. Sieve and pipette analyses, fractionation of the clay-size fraction into a 2-0.2u and <0.2u fraction using a supercentrifuge, X-ray diffraction, differential thermal analysis, thermogravimetric analysis, infrared, and cation exchange capacity were the analytical methods used. Fractionation of clay-size material expedites clay mineral identification and semi-quantitative estimates of abundance. A five gram, clay-size sample passed five times through a supercentrifuge should have the <0.2u fraction removed when the outlined sample preparation method is employed. Duplicate fractionations usually agree within three percent and fractionation efficiency is unaffected by the mineral suite. The clay minerals and semi-quantitative estimates of their abundance suggest that the sum of source conditions has remained constant since and during Pleistocene time. Montmorillonite and kaolinite are not more abundant in warm water sediments and illite and chlorite are not more abundant in cold water sediments from the Gulf of Mexico. Sand-size material is usually a small weight percent of a sample. Silt and clay-size materials are approximately equal except for the cores farthest from the Mississippi delta where clay-size material dominates. In the clay-size fraction, montmorillonite is generally more abundant that illite, while kaolinite is <20 percent and chlorite is <7 percent. Quartz is