LATE PLEISTOCENE TO HOLOCENE CLIMATE RECORD BASED UPON STABLE CARBON ISOTOPES MEASURED IN SOIL ORGANIC MATTER, FIELD AND MICROMORPHOLOGIC FEATURES, AND POLLEN, FROM FLOODPLAIN SOILS AND PALEOSOLS IN THE SOUTHEASTERN U.S

Field, thin section, geochemistry (XRF), pollen and stable carbon isotope studies of soil organic matter (SOM) were used to interpret the latest Pleistocene to Holocene climate record from floodplain-terrace systems in southeastern WV and TN. A late Pleistocene (22,940 +/- 150 C-14 yr BP) silt paleosol with low-chroma colors formed from fluviolacustrine sediment deposited during the last glacial maximum (Wisconsinan), and records a cooler full-glacial paleoclimate at the WV site. Fluvial gravel deposited between the latest Pleistocene and earliest Holocene (prior to 6360 +/- 40 C-14 yr BP) was weathered to form Alfisols in the middle Holocene in a warmer and drier climate, possibly correlated with the Hypsithermal and Altithermal Events of the eastern and southwestern US, respectively. The glacial to interglacial climate shift is recorded by: 1) changes from a poorly drained, fine-textured soil landscape setting, characterized by preservation of high organic C and redoximorphic features related to Fe removal and concentration, to a well-drained, coarse-textured setting without gley and with significant argillic (Bt) horizon development; 2) changes from a high Zr and Ti silt-dominated parent material to locally derived, coarse fluvial gravels lower in Zr and Ti, 3) a shift from dominantly spruce and pine pollen in the paleosol to a modern mixed deciduous forest vegetation assemblage, and 4) a shift in δ¹³C values of SOM from –28.1‰ (full glacial) to –24.l‰ PDB, suggesting an ecosystem shift from cooler, C3-dominated flora to one that was mixed C3 and C4, but still dominantly C3. Holocene floodplain Alfisols (6070-6350 +/- 40 C-14 yr BP) developed at the TN site in fine-textured alluvium deposited on a bedrock surface. The δ¹³C values of SOM range from –25.8 to -21.1 ‰ PDB, and there are 2 distinct positive excursions (-21.1‰, 210 cm depth; -22.3‰, 110 cm) that are correlative between 2 soil profiles separated by 150 m distance; less negative δ¹³C values suggest a 65% C3 soil ecosystem during mid-Holocene drier climate conditions. These results indicate that closely spaced (10 cm) δ¹³C depth profiles for SOM measured in floodplain soils and paleosols in the southeastern U.S. provide climate records that are apparently correlative with previously published higher-resolution lacustrine records, and should be examined more systematically in this region.