MICROMORPHOLOGY OF CLAY BANDS (LAMELLAE) THROUGH TIME

Clay bands are common in sandy surface and buried soils, but little is known about their genesis through time. These features are characterized by slight increases in clay and iron and may be the only part of the soil preserved when buried. Although bands enriched in clay do not always form pedogenically, thin section data can determine if argillans are pedogenic or not. However, standard thin section descriptions do not capture the variability seen in bands from late Quaternary eolian sands on the High Plains of Texas and New Mexico. For example, these bands are sandy with irregular pores, have a bridge to coat-and-bridge structure, and the argillans are commonly microlaminated, especially when bridging grains and filling pore bottoms. In order to semi-quantify clay band development through time an index was used based on percent grains with argillans, argillan thickness, and the distribution of argillans. Clay bands with more time to form exhibit somewhat higher values in percent grain coats. Younger clay bands are thinner and have fewer microlaminations. The greatest variation in the micromorphology of argillan development can be seen in the distribution characteristics of clay bands. Younger bands exhibit argillans mostly filling grain irregularities and some grain caps. The argillans are much more complex in older soils, which exhibit argillans filling grain irregularities, grain caps, pore-bottom infillings, and bridges between grains.