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Preliminary results from U–Th dating of glacial–interglacial deposition cycles in a silica speleothem from Venezuela

Published online by Cambridge University Press:  20 January 2017

J. Lundberg ,
C. Brewer-Carias  and
D.A. McFarlane
J. Lundberg*
Affiliation:
Department of Geography and Environmental Studies, Carleton University, Ottawa, Ontario, Canada, K1S 5B6
C. Brewer-Carias
Affiliation:
Sociedad Venezolana de Ciencias Naturales, Edif Torre America PH-B, Ave. Venezuela, Bello Monte Caracas, Venezuela
D.A. McFarlane
Affiliation:
W.M. Keck Science Center, The Claremont Colleges, Claremont, CA 91711, USA
*
⁎Corresponding author. Fax: +1 613 520 4301. E-mail addresses:joyce_lundberg@carleton.ca (J. Lundberg), charlesbrewercarias@gmail.com (C. Brewer-Carias), dmcfarlane@jsd.claremont.edu (D.A. McFarlane).
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Abstract

Recent explorations in Cueva Charles Brewer, a large cave in a sandstone tepui, SE Venezuela, have revealed silica biospeleothems of unprecedented size and diversity. Study of one — a sub-spherical mass of opaline silica — reveals a complex, laminated internal structure consisting of three narrow dark bands alternating with two wider light bands. Uranium–thorium dating has produced 3 stratigraphically correct dates on the light bands from 298 ± 6 (MIS 9) to 390 ± 33 ka (MIS 11). U concentration is only 30–110 ppb. Initial 234U/238U ratios are high and increase over time from 1.8 to 5.3. Growth rate is very low, the fastest, at 0.37 ± 0.23 mm/ka, in MIS 9. Trace element and heavy metal content of the dark bands is distinctly higher than that of the light bands. It is hypothesized that the dark and light bands correlate with drier/glacial and wetter/interglacial periods, respectively, and that this sample probably began to grow in MIS 13. The cave is in a region that straddles a regionally important ecotone: the speleothem isotopic and trace element variations may preserve a useful paleoclimatic signal. This is the first published suite of U–Th dates from a single silica speleothem and the longest Quaternary record for this region.

Keywords

Opal-ASpeleothemU–Th dateSandstoneCaveVenezuelaTepuiGlacialInterglacial
Type
Research Article
Information
Quaternary Research , Volume 74 , Issue 1 , July 2010 , pp. 113 - 120
Copyright
University of Washington

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