Recent benthic foraminifera from offshore Taranaki, New Zealand Journal Paper
- Author
- Hayward, B.W.; Grenfell, H.R.; Sabaa, A.; Hayward, J.J.
- Year
- 2003
- Journal / Source
- New Zealand Journal of Geology and Geophysics
- Volume
- 46
- Number
- 4
- Pages
- 489-518
- Summary
- 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 marginata s.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‐Abditodentrixpseudothalmanni (>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.