Origin of Clay-Size Quartz Particles in Suspended Load of Mississippi River

P. Leschak, R. E. Ferrell, Jr.

A detailed examination of clay-size quartz particles using scanning electron microscopy reveals that these grains contain a variety of provenance-indicative grain morphologies and surface texture features. For this study, quartz grains (2-4 microns) from Mississippi River suspended sediment samples were collected from several locations and size-fractionated for analysis.

The grains typically displayed subequant and rounded shapes completely covered by a variety of chemically produced surface texture features. Chemical precipitation textures dominate the grains and occur as a series of overlapping, amorphous silica sheets and caps over the entire grain surface. Dissolution textures are found as minor, small etch pits and rounded grain protuberances which are sometimes superimposed upon the earlier silica precipitation features. There is a conspicuous absence of flat, plate-like grains or mechanical breakage features similar to those observed in glacial sediments. This assemblage of features reflects intense chemical modification during residence in organic-rich, pedologic-weathering environments. Furthermore, it appears that subaqueous transport proces es have not significantly modified the "inherited" shape and surface texture features of these particles.

Clay-size quartz particles are not produced simply by attrition from larger particles. Morphological comparison with grains from other environments reflects a much more complex history related to both chemical and mechanical processes in the source, as well as in the transport environment. Thus, detailed studies of these small detrital particles may greatly enhance our understanding of the origin of sedimentary deposits.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.