CONSTRUCTION OF A SOIL CHRONOSEQUENCE IN HOLOCENE SOIL PROFILES USING QUANTIFICATION OF CLAY COATINGS WITH DIGITAL IMAGE PROCESSING

Clay cutans were identified in thin sections from two soil and sediment profiles that are exposed along the floodplain of the Tennessee River and are of different ages. The soil and sediment profiles present as vertical stackings of interbedded sediments and buried soils, with the buried soils recording times of no deposition, and were dated using a combination of optically stimulated luminescence (OSL) and AMS radiocarbon dating. Soil micromorphology shows that the amount of pedogenic clay, and thickness and degree of development of the clay coatings, vary depending on the age of the deposits. Older paleosols and sediments have abundant, thick, and well-developed clay coatings. In contrast, younger paleosols and sediments present less abundant, thin, and moderately- to well-developed clay coatings. The difference in pedogenic clay content between the two profiles and the ages obtained from OSL and ¹⁴C radiocarbon provide an excellent opportunity to construct a model for illuvial clay accumulation and build a time-transgressive soil chronosequence for Holocene soils and sediments. The high heterogeneity observed in the thin sections offers an opportunity to test the use of digital image processing to quantify pedogenic clay accumulation. High-resolution photographs of the entire thin sections were processed with ImageJ software and then compared with micromorphological observations. Results showed a difference in clay accumulation from about 1.0 cm² of pedogenic clays accumulated in clay coatings for the younger deposits (300 yrs. B.P.) to 5 cm² of pedogenic clays accumulated in clay coatings in the older deposits (>7.5 yrs. B.P.). This study demonstrates the potential of using digital image processing of high-resolution photographs together with soil micromorphological observations to analyze heterogeneous thin sections. Results confirm the expected relationship between age of deposits and illuvial clay accumulation as a soil property, despite all deposits being of Holocene age, and contribute to building the chronosequence at our site.