New Zealand Journal of Geology and Geophysics abstracts
δD values of hydrated volcanic glass: a potential record of ancient meteoric
water and climate in New Zealand
Phil Shane
Department of Geology
University of Auckland
Private Bag 92019
Auckland, New Zealand
email: pa.shane@auckland.ac.nz
Neil Ingraham
National Science Foundation
Earth Science Division
Arlington, VA 22230, USA
Abstract Tephra beds that are well drained and have been
buried by thin paleosols become hydrated within 2-3000 yr on reaction with meteoric
waters. Hence, the absorbed water within silicic volcanic glass shards provides
a potential record of δD values of ancient meteoric water. Such isotopic
records have previously received little investigation. We demonstrate that 1.5-2
m thick tephra beds in central North Island, New Zealand, display uniform δD
values vertically through their profiles and laterally up to 250 m in outcrop.
Reproducibility is not influenced by grain size or age of the tephra. We obtained
an average δD value of -48 ± 3‰ for water within the 1.8 ka
Taupo Tephra. This is similar to the composition of present-day surface waters.
δD values of -73 ± 2 and -60 ± 2‰ for the 25 ka Kawakawa
and 30 ka Mangaone Tephra beds are significantly lower than present waters,
indicating that they have been hydrated under different surficial conditions.
This is consistent with other proxy paleoclimatic indicators that suggest a
cooler, drier, and windier climate at the time of their eruption. Tephra beds
are a potential source of paleoclimatic data in terrestrial environments that
otherwise may lack proxy records.
Keywords stable isotopes; tephra; volcanic glass;
paleoclimate
G01029 Received 7 September 2001; accepted 28 June 2002 ; published 6
December 2002
New Zealand Journal of Geology & Geophysics, 2002, Vol. 45:
453–459
0028–8306/02/4504–0453 $7.00/0
© The Royal Society of New Zealand 2002
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