Sedimentary Characteristics of Pleistocene Deposits, Neosho River Valley, Southeastern Kansas

Abstract

Clay mineralogy, sedimentary parameters, and heavy mineral content of Pleistocene alluvial terrace (Illinoisan) and flood-plain (Wisconsinan) deposits of the Neosho River valley in southeastern Kansas were investigated. The clay mineral assemblage of the alluvial deposits consists of montmorillonite, a 14Å mixed-layer mineral, illite, and kaolinite. Montmorillonite is the dominant clay mineral in alluvial terrace deposits; illite and kaolinite are variable in proportion. Flood-plain deposits contain montmorillonite, illite, and kaolinite in decreasing order of relative abundance. The diffraction-intensity ratio, derived from X-ray diffraction intensities of illite and kaolinite, is significantly different for alluvial terrace and flood-plain deposits. Relative abundances of clay minerals in each deposit are evaluated in terms of (1) contribution of the source area, (2) weathering, (3) time, (4) topography, and (5) drainage.

Grain-size analyses of alluvial terrace and flood-plain deposits did not reveal a significant difference in parameters such as phi-median and phi-sorting. Alluvial terrace deposits, however, showed greater variation in sorting than the flood-plain deposits. Variation in sorting is not sufficiently marked to be used as a criterion to differentiate terrace deposits from flood-plain deposits.

The heavy mineral assemblage of terrace and flood-plain deposits consists of zircon, tourmaline, staurolite, garnet, topaz, and magnetite. Flood-plain deposits contain minor amounts of epidote and kyanite, which are rare or absent in terrace deposits.