HR: 1340h
AN: PP33A-1004    [Abstracts]
TI: Late Pleistocene/Holocene paleoclimate reconstruction and eruptive history of Central American volcanoes from lake bottom sediments of Lake Nicaragua
AU: * Wulf, S
EM: swulf@ig.utexas.edu
AF: Institute for Geophysics, Jackson School of Geosciences, The University of Texas at Austin, J.J. Pickle Research Campus, Bldg. 196, 10100 Burnet Rd., Austin, TX 78758, United States
AU: Dull, R A
EM: robdull@austin.utexas.edu
AF: Department of Geography and the Environment, The University of Texas at Austin, 1 University Station, GRG 334, Austin, TX 78712, United States
AU: Mann, P
EM: paulm@ig.utexas.edu
AF: Institute for Geophysics, Jackson School of Geosciences, The University of Texas at Austin, J.J. Pickle Research Campus, Bldg. 196, 10100 Burnet Rd., Austin, TX 78758, United States
AU: McIntosh, K D
EM: kirk@ig.utexas.edu
AF: Institute for Geophysics, Jackson School of Geosciences, The University of Texas at Austin, J.J. Pickle Research Campus, Bldg. 196, 10100 Burnet Rd., Austin, TX 78758, United States
AU: Gardner, J E
EM: gardner@mail.utexas.edu
AF: Department of Geological Sciences, Jackson School of Geosciences, The University of Texas at Austin, 1 University Station C1100, Austin, TX 78712, United States
AB: A shallow coring program in Lake Nicaragua was completed in May/June 2006 by the University of Texas (UT Department of Geography and UT Institute for Geophysics). A total of 35 sediment cores with lengths ranging between 12 cm and 100 cm along with five longer cores were extracted from the lake using a gravity corer and a modified manual square rod piston corer, respectively. Analyses of lake sediments have the following objectives: 1) to correlate the geophysical results with the core data to provide a stratigraphic framework for the shallow lake sediments; 2) to constrain past climate variability in this rather poorly investigated area; and 3) to establish a time series of explosive volcanic activity based on the identification and dating of tephra layers in the cores. Initial measurements of magnetic susceptibility, dry density, loss on ignition and XRF scanning indicated a dominance of fine-grained homogeneous diatomaceous sediments cover most of the lake floor. Increasing values in magnetic susceptibility in the upper part of several short cores most likely reflect increased erosion caused by land-use changes during the Spanish colonial period (1522-1822). Results on the two longest cores from the northeastern (355 cm) and southwestern (478 cm) parts of the lake reveal complete Holocene paleoclimate records in both areas that are comparable to other terrestrial and marine records in the Central and South- American tropics (i.e. Cariaco Basin). A lithologic change from homogeneous gyttia (diatomaceous mud) to blue- grayish waxy clay at the bottom of these records marks the Late Pleistocene-Holocene transition as indicated by a radiocarbon dating on plant remains. The latter dense clay forms a distinctive stratigraphic marker in the lake basin. Tephra layers to date were detected in most gravity cores recovered west of Ometepe Island (Volcan Concepcion), and in long records in the northeastern basin (San Antonio Tephra, Masaya volcano, ca. 7,400 interpolated cal yr BP) and nearby the Solentiname Archipelago (unknown eruption, Arenal volcano, Costa Rica; 8,810 +/- 25 cal yr BP). These layers allow independent dating and correlation of sediments.
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting