New Zealand Journal of Geology and Geophysics abstracts
Stable isotope values in modern bryozoan carbonate from New
Zealand and implications for paleoenvironmental interpretation
Abigail M. Smith
Department of Marine Science
University of Otago
P.O. Box 56
Dunedin, New Zealand
email: abby.smith@stonebow.otago.ac.nz
Campbell S. Nelson
Department of Earth Sciences
University of Waikato
Private Bag 3105
Hamilton, New Zealand
Marcus M. Key, Jr
Department of Geology
Dickinson College
P.O. Box 1773
Carlisle, PA 17013, USA
William P. Patterson
Department of Geological Sciences
University of Saskatchewan
114 Science Place
Saskatoon, SK S7N 5E2, Canada
Abstract Bryozoan carbonate contains useful
geochemical evidence of temperate shelf paleoenvironments. Stable
isotope values were determined for 103 modern marine bryozoan skeletons
representing 30 species from New Zealand. δ18O values range
from –1.4 to 2.8‰ VPDB, while δ13C range from –4.5 to 2.8‰
VPDB (values uncorrected for mineralogical variation). These values are
distinct from those of both tropical marine skeletons and New Zealand
Tertiary fossils. Most bryozoans secrete carbonate in or near isotopic
equilibrium with sea water, except for Celleporina and Steginoporella.
The complex and variable mineralogies of the bryozoans reported here
make correction for mineralogical effects problematic. Nevertheless,
mainly aragonitic forms display higher isotope values, as anticipated.
Both temperature and salinity constrain δ18O and δ13C
values, and vary with latitude and water depth. Ten samples from a
single branch of Cinctipora elegans from the Otago shelf cover
a narrow range, although the striking difference in carbon isotope
values between the endozone and exozone probably reflects different
mineralisation histories. Our stable isotope results from three
different laboratories on a single population from a single location
are encouragingly consistent. Monomineralic bryozoans, when carefully
chosen to avoid species suspected of vital fractionation, have
considerable potential as geochemical paleoenvironmental indicators,
particularly in temperate marine environments where bryozoans are
dominant sediment producers.
Keywords bryozoans; carbonate; oxygen isotopes;
carbon isotopes; New Zealand shelf
G03060; Received 12 June 2003; accepted 23 February 2004; Online
publication date 1 December 2004
New Zealand Journal of Geology & Geophysics, 2004, Vol. 47:
809–821
0028–8306/04/4704–0809© The Royal Society of New Zealand 2004
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