New Zealand Journal of Geology and Geophysics abstracts
A tentative New Zealand chemostratigraphy for the Jurassic-Cretaceous
based on terrestrial plant biomarkers
Steve Killops
Richard Cook
Ian Raine
Institute of Geological & Nuclear Sciences
P.O. Box 30 368
Lower Hutt, New Zealand
Rod Weston
Tony Woolhouse
Industrial Research Ltd
P.O. Box 31 310
Lower Hutt, New Zealand
Abstract The previously erected chemostratigraphy
for Late Cretaceous-Eocene coaly sediments in Taranaki Basin, New Zealand,
has been extended to the Jurassic, primarily using samples from the South
Island. Biomarker analysis by selected ion GC-MS indicates that the abundance
of angiosperm-derived triterpanes and gymnosperm-derived diterpanes are lower
relative to hopanes in samples from the mid-Cretaceous Trichotomosulcites
subgranulatus Assemblage (miospore superzone TS) than younger coaly sediments,
and exhibit a significant degree of variation in diterpane distributions
and ratios of angiosperm to gymnosperm biomarkers. The two samples from the
mid-Cretaceous Lycopodiacidites bullerensis-3 Zone (LB3) have similarly
relatively low amounts of woody plant derived terpanes, but almost identical
diterpane distributions. Jurassic coals show the expected absence of biomarker
contribution from angiosperms. They exhibit the simplest diterpane distributions,
dominated by isopimaroids, and suggest a fairly uniform woody gymnosperm
community. The characteristic Jurassic biomarker zone is designated CD*,
after the Australian Callialasporites dampieri Superzone that spans
the mainly mid-Jurassic interval sampled. The angiosperm-gymnosperm index
is not readily extended to include samples older than the Late Cretaceous
(Phyllocladidites mawsonii Assemblage, PM), because of the variable
and sometimes high values exhibited by samples from the TS and LB3 miospore
zones. However, various parameters can be derived from the distributions
of woody-plant terpanes that, when used in combination, permit reasonable
discrimination of the CD*, LB3, and TS Zones from each other and three younger
groups of zones-PM2, PM3-MH1, and MH2-NM. The chemostratigraphy can be applied
to correlating terrestrial oils with their sources, with four main groupings
of floral zones being recognised in New Zealand-LB3+TS, PM2, PM3+MH1, and
MH2+MH3+NM. The previously tentative identification of 18-norisopimarane
is revised.
Keywords angiosperms; coal; diterpanes; floral assemblages;
gymnosperms; miospore zones; 18-norisopimarane; oil; triterpanes
G02009 Received 7 February 2002; accepted 11 November 2002; published
21 March 2003
New Zealand Journal of Geology & Geophysics, 2003, Vol. 46: 63-77
0028-8306/03/4601-0063 $7.00/0 © The Royal Society of New Zealand
2003
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