Abstract: A semiquantitative study of the surficial clay mineral distribution from 79 cores in the Recent sediments in the Gulf of Mexico shows a regional pattern which can be related to source and environment. The dominant factor controlling distribution of these surficial sediments appears to be source. Montmorillonite is the most abundant clay mineral, and illite, chlorite, kaolinite and mixed-layer minerals are present in almost every sample.
Alteration of the clay minerals is influenced by (a) change of environment, and (b) length of exposure. Initial ion exchange, which is caused by a tendency to reach equilibrium with a new environment, occurs so rapidly in the clay minerals after they enter the marine environment that rate of sedimentation is a minor factor in comparison to environmental change. Slow alteration and adjustment toward a stable end state are most complete in areas of slow deposition and extended exposure of the clay minerals to the environment.