Occurrence and Alteration of Clay Minerals in Caribbean Sea: ABSTRACT

Abstract

Both vertical and horizontal trends in clay mineralogy are examined in cores from the southwestern and central Caribbean. X-ray diffraction, differential thermal analysis, infrared spectroscopy, and electron micrography are used to determine the clay mineralogy. Montmorillonite, vermiculite, mica, kaolinite, chlorite, halloysite, allophane, and gibbsite are identified by the above methods. Alteration of clay minerals in the marine environment is examined by noting the trends between cores for various selected ratios. Diagenesis of a clay mineral is defined as the alteration of the mineral in such a way that it loses its identifying characteristics. Gibbsite and allophane probably alter to halloysite in the marine environment. Ratios for vermiculite and mica show a decrease in vermiculite with distance from the river mouth. Ratios for montmorillonite to mica show an increase in montmorillonite with distance from the river mouth. The chlorite to mica ratio also shows a decrease in a seaward direction, probably the result of both the alteration of chlorite and the increase in mica. A slight decrease is seen in the ratios for kaolinite and mica in a seaward direction due to mica forming at a faster rate than kaolinite. The chlorite to kaolinite ratio decreases in a seaward direction due to both the alteration of chlorite and development of kaolinite. The clay mineral ratios for the vertical profiles show an irregular pattern. Changes in source area or climate are stronger factors than marine alteration in determining the vertical trends in surface sediment cores. Differential transport is seen in the montmorillonite and halloysite concentrations. Both minerals increase in a seaward direction. Their small particle size causes them to avoid coacervate formation and flocculation upon initial entrance into the marine environment. End_of_Article - Last_Page 1832------------