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Northeastern Section - 36th Annual Meeting (March 12-14, 2001)

Paper No. 5
Presentation Time: 1:30 PM-5:00 PM

HOLOCENE GLACIAL ACTIVITY IN THE VENEZUELAN ANDES: PRELIMINARY RESULTS FROM LAGUNA MUCUBAJI


POLISSAR, P. J.1, ABBOTT, M.1, WOLFE, A. P.2, FINNEY, B. P.3, BRADLEY, R. S.1 and BEZADA, M.4, (1)Department of Geosciences, Univ of Massachusetts, Morrill Science Center, 611 North Pleasant Street, Amherst, MA 01003-9297, (2)Institute for Arctic and Alpine Research, Univ of Colorado, Campus Box 450, Boulder, CO 80309, (3)Institute of Marine Science, Univ of Alaska, Fairbanks, AK 99775, (4)Ciencias de La Tierra, Instituto Pedagogico de Caracas, Universidad Pedagogica Experimental Libertador, Avda. Paez El Paraiso, Caracas, Venezuela, polissar@geo.umass.edu

Tropical regions (30°N-30°S) are a substantial component of the climate system. They cover 50% of the globe and are important in the global energy balance and hydrologic cycle. Here we present preliminary results from a project which aims to reconstruct the Holocene climate history of the Venezuelan Andes on century to millennial timescales using multi-proxy analyses of lake sediment cores.

The study site, Laguna Mucubaji, is located at 3500m in the Cordillera de Merida, Venezuela. Glaciers are currently absent from the watershed, but relatively unweathered moraines attest to recent glacial activity. The Mucubaji watershed has maximum elevations around 5000m while the existing glacial limit in the Cordillera is approximately 5200m. This suggests that small fluctuation in moisture and temperature could lead to the establishment of glaciers in the Mucubaji watershed.

A 2.25m sediment core from Laguna Mucubaji, Venezuela appears to contain a record of Holocene glacial activity in the Venezuelan Andes. Sediments alternate between units of high and low organic carbon and biogenic silica. Geochemical indicators of organic matter source (C-13, N-15, C/N ratio) change little across the unit boundaries suggesting no change in organic matter source. Rather, it appears that changes in clastic sediment input are responsible for the sediment variations found in the core. We interpret these changes to reflect the establishment and fluctuations of glacial activity in the watershed. Preliminary AMS C-14 dates of macrofossils indicates the base of the core is approximately 7000 calendars years BP. Relatively large fluctuations in organic carbon occur in the lower half of the core while the upper part of the core is dominated by organic rich sediments suggesting a decrease in glacial activity. A small peak in clastic input near the top of the core suggests recent glacial activity and may correlate with the youngest moraines found in the watershed.

Session No. 31--Booth# 27

T2. Paleolimnological Records of Holocene Climate Change (Posters)
Tuesday, 13 March 2001: 1:30 PM-5:00 PM
Geological Society of America Abstracts with Programs. Vol. 33, No. 1, February 2001
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