Paper No. 40-38
Presentation Time: 9:00 AM-5:30 PM
MICROMORPHOLOGICAL INTERPRETATION OF LATE PLEISTOCENE TO HOLOCENE PALEOENVIRONMENTAL HISTORY OF ANDERSON POND, TENNESSEE, USA
Thin-section (micromorphological) analysis of samples from the upper 1.5 m of a core obtained in 2007 from Anderson Pond, Tennessee reveals a coherent 15,000 yr record of late Pleistocene to Holocene climate change supporting interpretations from previous pollen and charcoal records from the site, paleoclimate records from correlative floodplains, as well as a high-resolution speleothem record from Raccoon Mountain Cave, Tennessee. The Holocene record at Anderson Pond is highly condensed due to low sedimentation rates, episodes of erosion, and soil formation during subaerial exposure of sediments of this sinkhole lake. Legacy sediments recording Euro- and Native American(?) disturbance dominate the upper 60 cm of the core (<900 cal yr BP) and are characterized by mixed, darker-colored and coarser-grained deposits containing reworked soil aggregates and medium- to coarse detrital quartz sand grains, which sharply overlie finer-grained and lighter-colored, heavily rooted Middle and Early Holocene sediments. Middle Holocene sediments (73-89 cm) record extensive warm-dry subaerial soil conditions during the Middle Holocene Thermal Maximum (4200-8200 cal yr BP), manifested by birefringent illuviated clay lining root pores and lining ped faces, with partially dissolved siliceous sponge spicules and diatoms, and also contain the highest charcoal concentrations. Late Pleistocene sediments (100-150 cm) are very dark-colored and very organic-rich in thin-section, recording open-water conditions, and include abundant organic grains (fresh to partially decomposed plant tissues, pollen, spores, seeds) as well as “siliceous aggregate” grains at 121-148 cm (13,950-14,400 cal yr BP). These distinctive grains are medium- to coarse silt-sized and consist of very fine- to fine-silt-sized quartz grains cemented by amorphous silica; they are interpreted as recording fire processes and production of wood ash, and formed when loessal silt was admixed with biogenic silica in the ash. Although not commonly used in late Quaternary lacustrine paleoclimate studies, we advocate a multi-analytical approach involving use of thin sections, in addition to more standard methods which emphasize pollen and charcoal, because of enhanced resolution of depositional and pedogenic processes.