New Zealand Journal of Geology and Geophysics abstracts
Recent benthic foraminifera from offshore Taranaki, New Zealand
Bruce W. Hayward
Hugh R. Grenfell
Ashwag Sabaa
Jessica J. Hayward
Geomarine Research
49 Swainston Rd
St Johns, Auckland, New Zealand
email: b.hayward@geomarine.org.nz
Abstract Paleobathymetric estimates based on fossil foraminiferal
faunas play an important role in understanding the paleogeographic, structural,
and burial history of New Zealand’s most important hydrocarbon-bearing
sedimentary
basin—the Taranaki Basin. Bathyal and abyssal estimates have large
ranges of uncertainty, which might be improved using knowledge of the depth
distribution patterns of Recent benthic foraminifera in the same region.
Four benthic foraminiferal groups (and 9–10 associations) are recognised
and mapped in the offshore Taranaki region (0–2150 m depth, eastern Tasman
Sea), based on two separate cluster analyses of census data (231 species,
39 samples) on faunas with tests >63 and >150 µm. The same
depth pattern can be identified using 63 or 150 µm faunas, although
there are major differences in the dominant taxa. Canonical correspondence
analysis and correlation coefficients suggest that the distribution patterns
are strongly depth related: (1) inner shelf (0–50 m) associations (both
shell-size
fractions) are dominated by Rosalina irregularis and Zeaflorilus
parri; (2) outer shelf–uppermost bathyal (50–550 m) associations
are dominated
by Bulimina marginatas.s. and Discorbinella bertheloti (both
sizes) plus Cassidulina carinata (>63 µm) or Cibicides
dispars (>150 µm); (3) middle–lower bathyal (500–1500
m)
associations are dominated by C. carinata-Alabaminella weddellensis-Abditodentrix
pseudothalmanni(>63 µm) and Uvigerina peregrina-Bulimina
marginata f. aculeata(>150 µm); and (4) lower bathyal to
upper abyssal (1400–2150 m) associations are dominated by B. marginata f. aculeata and Globocassidulina subglobosa (both) plus A.
weddellensis (>63 µm) or U. peregrina-Oridorsalis
umbonatus (>150 µm). Comparison of the >63 µm
Taranaki (west coast) faunal data with a similar dataset from east of New
Zealand shows significant differences in composition, relative abundance
levels, and depth ranges of common species, which appear to be a result of
differences in primary productivity, translated into organic carbon flux
(food). Since organic carbon flux reaching the seafloor decreases progressively
with increasing water depth, we infer that this is the major factor producing
the strong depth-related distributional pattern of deep-sea benthic foraminiferal
faunas observed around New Zealand. Thus, highly accurate estimates of paleobathymetry
are unlikely using benthic foraminifera, unless organic carbon flux has remained
unchanged. Notwithstanding the differences between the west and east coasts,
there are sufficient similarities and trends that are bathymetrically consistent
to be useful in improving paleobathymetric estimates. These include, in decreasing
order of reliability: upper depth limits of key benthic species; recognition
of benthic foraminiferal associations; and relative abundance of planktic
foraminifera. Species diversity measures show no useful pattern with depth.
Keywords New Zealand; offshore Taranaki; New Caledonia
Basin; deep-sea benthic foraminifera; species associations; paleobathymetric
assessment; species diversity; upper water depth limits; primary productivity;
carbon flux
G02054; Received 11 October 2002; accepted 4 August 2003; online publication
date 13 November 2003
New Zealand Journal of Geology & Geophysics, 2003, Vol. 46: 479-488
0028-8306/03/4604-0479 $7.00/0 © The Royal Society of New Zealand
2003
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