DRIESE, Steven G.1, HORN, Sally P.2, BALLARD, Joanne

DRIESE, Steven G.1, HORN, Sally P.2, BALLARD, Joanne

DRIESE, Steven G.1, HORN, Sally P.2, BALLARD, Joanne P.2, LI, Zheng-Hua3 and BOEHM, Mathew S.2, (1) Terrestrial Paleoclimatology Research , Dept. of Geology, Baylor Univ., One Bear Place
#97354, Waco, TX 76798-7354, (2) Dept. of Geography, Univ. of Tenn., Knoxville, TN 37996-0925, (3) Earth & Environ. Sci. Div., Los Alamos Nat. Lab., P.O. Box 1663, MS J535, Los Alamos, NM 87545
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 this sinkhole lake. Legacy
sediments recording Euro- and Native American(?) disturbance dominate the upper 60 cm of
the core (<1682 cal yr BP) and are characterized by mixed, darker-colored and coarsergrained deposits containing high charcoal, 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 (6037-8361 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 high charcoal concentrations. Late Pleistocene sediments (100-150 cm) are very darkcolored and very organic-rich 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 (13,951-14,358 cal yr BP). These distinctive siliceous aggregate grains are medium- to coarse silt-sized and consist of very fine- to finesilt-sized quartz grains that are cemented by amorphous silica; they are interpreted as recording fire processes and production of wood ash, and formed when loessal silt and biogenic silica were admixed with the ash within the lacustrine basin. Although not commonly used in late Quaternary lacustrine paleoclimate studies, we advocate a multianalytical 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. 1. Background: 1976 AD -10 + 100 yr BP 2. Study Area: Anderson Pond Sinkhole Lake 4.2 Legacy sediments: Late Holocene, 0-60 cm (-57 to1682 cal yr BP) = Anthropogenic (European and Native American influences) 1.0 mm 1.0 mm Medium- to coarsemonocrystalline quartz sand grains (PPL) = UT-K date = WY date 100 m 1.0 mm 200 m Reworked soil aggregate grains (pedoliths) (PPL) 100 m 100 m 100 m Freshwater diatoms and sponge spicules (PPL) 59-63 cm depth 4.3 Paleosol, subaerial exposure and soil development: 73-89 cm (6050-8361 cal yr BP) = Middle Holocene Thermal Maximum 3. Methods: thin-section micromorphology of new Anderson Pond core collected in 2007 by Jackson and co-workers (Liu et al., 2013) using PPL, XPL and UVf. 2.0 mm 200 m 200 m 200 m 200 m 2.0 mm Root traces and bioturbation (PPL) Macro- and microcharcoal grains (PPL) 200 m Illuviated clay lining root pore (PPL) 200 m 76-82 cm depth 88-94 cm depth Illuviated clay lining root pore (XPL) 4.4 Siliceous aggregate grains 121-148 cm (13,950-14,400 cal yr BP) = period of extensive fires generating wood ash + loessal silt 100 m 100 m 50 m Can micromorphology enhance paleoenvironmental interpretations? 48-52 cm depth Partially decayed plant tissues, spores and algal remains (UVf) 4.1 Whole Thin-section Microscopy: Original AP-76 Anderson Pond core described and 14C-dated by H. Delcourt (1979) 5. Summary with age-depth model (PPL) 50 m (XPL) 121125 cm depth 133137 cm depth 6. Conclusions: 1)Micromorphology is an under-utilized, but very useful, method for independently assessing paleoenvironmental records of Quaternary lakes, supporting charcoal and pollen studies. 2)Legacy sediments (Late Holocene), buried soil (Middle Holocene), and siliceous aggregate grains (Late Pleistocene) observed in thin sections record specific climate and geomorphic conditions at Anderson Pond, Tennessee. 7. Acknowledgments: The authors wish to thank Steve Jackson (U. WY) for allowing use of Anderson Pond core 2007 for this study. The authors gratefully acknowledge support of NSF EAR-0823131 awarded to SGD and EAR-0822824 awarded to SPH and Z-HL for research on Late Pleistocene-Holocene paleoclimate reconstructions in the southern Appalachian region. 50 m (PPL) 138-141 cm depth 50 m (XPL) Laboratory experiments by Ballard (2015) demonstrate environmental conditions for formation of siliceous aggregates (Ballard et al., manuscript in preparation). Ballard, J.P., 2015. Evidence of Late Quaternary fires from charcoal and siliceous aggregates in lake sediments in the eastern U.S.A. Ph.D. Thesis, University of Tennessee, Knoxville. Ballard, J.P., Horn, S.P., Li, Z.-H., in review. A 23,000-year microscopic charcoal record from Anderson Pond, Tennessee. Submitted to Palynology. Delcourt, H.R., 1978. Late Quaternary vegetation history of the Eastern Highland Rim and adjacent Cumberland Plateau of Tennessee, Ph.D. Thesis, University of Minnesota, Minneapolis. Delcourt, H.R., 1979. Late Quaternary vegetation history of the eastern Highland Rim and adjacent Cumberland Plateau of Tennessee. Ecological Monographs 49, 255-280. Driese, S.G., Li, Z.-H., McKay, L.D., 2008. Evidence for multiple, episodic, mid-Holocene Hypsithermal recorded in two soil profiles along an alluvial floodplain catena, southeastern Tennessee, USA. Quaternary Research 69, 276-291. Liu, Y., Andersen, J.J., Williams, J.W., Jackson, S.T., 2013. Vegetation history in central Kentucky and Tennessee (USA) during the last glacial and deglacial periods. Quaternary Research 79, 189-198. Reimer, P.J., et al., 2013. INTCAL13 and MARINE13 Radiocarbon age calibration curves 050,000 years cal BP. Radiocarbon 55(4), 18691887. Reimer, P.J., Brown, T.A., Reimer, R.W., 2004. Discussion: reporting and calibration of post-bomb 14C data. Radiocarbon 46 (3), 12991304. Stuiver, M., Reimer, P.J., 1993. Extended 14C database and revised CALIB radiocarbon calibration program. Radiocarbon 35 (1), 215230.

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