Using soil micromorphology to assess the reliability of radiocarbon and OSL dating of fluvial deposits

Two sediment profiles exposed along the floodplain of the Tennessee River provide an excellent opportunity to compare radiocarbon and optically stimulated luminescence dating of fluvial sediments, and to use soil micromorphology as a tool to assess the reliability of these dating methods. The profiles occur as vertical stacks of floodplain soils, buried soils, and fluvial deposits, with the sediments of both profiles indicating an alluvial origin, but with different degrees of soil development. Micromorphological analysis showed pedogenic clay coatings are common in both profiles. These pedofeatures provide evidence of relative age of the deposits, because layered, well-developed, thick clay coatings generally take thousands of years to form. Radiocarbon results indicate that the profiles span from the late early Holocene to late Holocene. OSL dating indicates that one profile is relatively recent (<600 yrs. B.P.) while the other is of late middle Holocene age (3.2 ka B.P. to 5.3 ka B.P.). Clay coatings support the results from OSL because the relatively recent profile has very thin coatings, in contrast with thick, well-developed clay coatings in the older profile. Some of the radiocarbon ages appear to be too old owing to redeposition, but other dates are consistent with soil development and micromorphology.