Relative Dating Techniques to Distinguish Late Pleistocene-Holocene Continental Sediments

Radiometric dating, particularly with 14C, provides ages for those Late Pleistocene and Holocene sediments that contain datable materials. Standard stratigraphic and morphostratigraphic techniques of superposition, geomorphic position, partial overlap, and offlap provide relative chronology in many situations. The use of multiple relative dating (RD) techniques, developed for the study of glacial deposits, makes use of these techniques where possible, but depends heavily on the additional comparison of the results of surface processes that act continuously and more or less uniformly after accumulation is complete. For sediments at the surface that have not been buried, the most important of these processes are weathering and morphological alteration. Soil profile development is progressive; careful field description plus laboratory analysis provide data to distinguish soils of differing maturity, hence, of different ages. Clasts at the surface and within the soil profile weather continuously, and quantification of the degree of their decay permits recognition of age differences. In mountains adjacent to deserts, a veneer of loess accumulates slowly, and is thicker on older alpine deposits. Quantification of gully development provides still another morphometric approach to dating young sediments. These RD methods have been effective in distinguishing relative ages of continental sediments from 102 to 107 yr. old in the western U.S.A. mountains and in the Central Andes