A clay mineral study of recent and Pleistocene sediments from the Sigsbee Deep, Gulf of Mexico

Abstract

The less than 2μ fraction of 96 samples from five deep-sea cores from the Sigsbee Deep and Campeche Bank, Gulf of Mexico, were analyzed by X-ray diffraction methods in order to evaluate the mineralogical content and the changes of the relative abundance of montmorillonite, chlorite, illite, and kaolinite through the stratigraphic section and between different topographic occurrences. Two of the cores studied were collected from the tops of knolls which rise about 600 feet above the flat floor of the Sigsbee Deep abyssal plain. These cores penetrated three warm- and two cold-water faunal facies. It was found that the relative abundances of illite and chlorite are greatest in the sediments deposited during the inferred cold-water glacial ages and are least in the sediments deposited during the warm-water interglacial ages. Similarly, kaolinite and montmorillonite are most abundant in the sediments deposited during the warm-water interglacial ages and are least abundant in the sediments deposited during the inferred cold-water glacial ages. This observed distribution of the relative abundance of the various clay minerals is believed to be directly related to changes in the weathering environment of the source area which was supplying sediments to the Sigsbee Deep during the Late Pleistocene. Two of the cores studied were collected from the abyssal plain, and one core was collected from the northwest corner of the Campeche Bank. It was found that the relative abundance of montmorillonite and illite was higer while the relative abundance of kaolinite and chlorite was lower in the dark-gray silts and clays which characterize the abyssal plain sediments, compared to the light-colored, highly-calcareous sediments that occur interbedded with the dark-gray silts and clays. The relative abundance of the clay minerals from the light-colored sediments compared very favorably with those observed in the core from the Campeche Bank. It was concluded that the dark-gray silts and clays were derived primarily from the ancient Mississippi River drainage basin and the light-colored sediment originated from the relatively nearby Campeche Bank area. The observed increase in the relative abundance of kaolinite in the various warm-water faunal facies either above or below inferred cold-water faunal facies strongly suggests that kaolinite does not undergo any structural change after introduction into a marine environment.