New Zealand Journal of Geology and Geophysics abstracts

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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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