Characteristics of soils along the Elk River, southcentral Tennessee : implications for soil and landscape genesis, and archaeology

Alluvial valleys are of special interest to both pedologists and archaeologists as they present a number of problems and opportunities. Complex fluvial landforms are often difficult to interpret, while river terraces allow the study of soil development with time. Landscape reconstructions can be an integral part of archaeological site interpretation as a byproduct of pedological studies, in which the fluvial history and the age and genesis of soils and landforms are examined. Two terrace sequences were identified along the Elk River, south central Tennessee, with four and two terraces, respectively. Profiles in representative areas of the terraces were described and sampled. Laboratory analyses of soils included particle size analysis, determination of bulk density, pH, and organic carbon. Elemental analysis was performed using a dilute (0.77 M) hydrochloric-nitric acid solution. Iron oxides were extracted using acid oxalate and dithionite-citrate-bicarbonate. Clay mineralogy was determined for a limited number of samples and a scanning electron microscope was used to examine quartz sand grains. Alluvial soils were characterized by discontinuities on the lower terraces and progressive development of morphological properties such as color, texture, and structure moving away from the river. Soil pH and organic carbon tended to decrease with depth and age. Extractable Ba and Mn generally had high surface values that decreased with depth and were also good indicators of buried surface horizons. Other elements fluctuated irregularly in response to imperfect drainage. The landscape was formed as the Elk River adjusted to changes in climate. Morphological properties were the most reliable characteristics in establishing dates for terraces. Particle size analysis also showed time dependent trends with sand contents decreasing and clay contents increasing with age. Upper terraces along the Elk River were at least Pleistocene in age and predated the arrival of humans in North America, restricting archaeological materials to the surface. Lower terraces, formed during the Holocene, were available for human occupation and could contain artifacts deposited and subsequently buried in the soil solum.