THE CLAY MINERALOGY OF THE BOTTOM DEPOSITS OF THE WEST MISSISSIPPI DELTA AREA. Technical Report No. 1

A study was made of 36 samples of surface sediment from the shallow water marine environment to the west of the Mississippi Delta. The clay fraction was examined using x-ray diffraction, differential thermal analysis, determinations of cation-exchange capacity, and electron microscopy. Clay mineral distribution was determined for the surface sediments in the area, and with depth in three cores. Montmorillonite makes up approximately 50% of the clay fraction of the sediments, with nearly 25% each of kaolinite and illite, and a small amount of halloysite. A little quartz was present in the fine fraction of all samples studied. Percentages of the clay minerals were estimated from x- ray-diffraction peak intensities, and from cation-exchange capacity data. Particular attempts to discover chloritc in the sediments were unsuccessful. Controlled heating of samples showed little evidence for a 14 A chlorite, even of low thermal stability. No evidence for clay mineral diagenesis with depth was found in the cores studied. No change in either clay mineral type or degree of crystallization could be discovered to a depth of 334 cm. Attempts to assess the damage caused by chemical methods of removing organic matter and calcium carbonate indicated that such mild and carefully controlled methodsmore » do little if any damage to the clay minerals present. No detectable difference was found in the less than 2 micron and less than 4 micron fraction of the sediments. The clay mineral distribution in the Mississippi Delta area is determined primarily by the types of clay minerals present in the soils of the Mississippi River drainage basin, and secondarily, by the rapid but minor diagene sis occurring immediately upon contact of these minerals with the saline water of the Gulf of Mexico. (auth)« less