New Zealand Journal of Geology and Geophysics abstracts
Depth distribution of Recent deep-sea benthic foraminifera east of
New Zealand, and their potential for improving paleobathymetric
assessments of Neogene microfaunas
BRUCE W. HAYWARD
ROWAN CARTER
HUGH R. GRENFELL
JESSICA J. HAYWARD
Department of Geology
University of Auckland
Private Bag 92 019
Auckland, New Zealand
Abstract Paleobathymetric assessments of fossil foraminiferal
faunas play a significant role in the analysis of the paleogeographic,
sedimentary, and tectonic histories of New Zealand's Neogene marine sedimentary
basins. At depths >100 m, these assessments often have large uncertainties.
This study, aimed at improving the precision of paleodepth assessments,
documents the present-day distribution of deep-sea foraminifera
(>63 μm) in 66 samples of seafloor sediment at 90-4700 m water depth
(outer shelf to mid-abyssal), east of New Zealand. One hundred and thirty-nine
of the 465 recorded species of benthic foraminifera are new records for the New
Zealand region.
Characters of the foraminiferal faunas which appear to provide the most useful
information for estimating paleobathymetry are, in decreasing order of
reliability: relative abundance of common benthic species; benthic species
associations; upper depth limits of key benthic species; and relative abundance
of planktic foraminifera. R-mode cluster analysis on the quantitative
census data of the 58 most abundant species of benthic foraminifera produced
six species associations within three higher level clusters: (1) calcareous
species most abundant at mid-bathyal to outer shelf depths (<1000 m);
(2) calcareous species most abundant at mid-bathyal and greater depths (>600
m); (3) agglutinated species mostly occurring at deep abyssal depths (>3000
m). A detrended correspondence analysis ordination plot exhibits a strong
relationship between these species associations and bathymetry. This is
manifest in the bathymetric ranges of the relative abundance peaks of many of
the common benthic species (e.g., Abditodentrix pseudothalmanni 500-2800
m, Bolivina robusta 200-650 m, Bulimina marginata f. marginata
20-600 m, B. marginata f. aculeata 400-3000 m, Cassidulina
norvangi 1000-4500 m, Epistominella exigua 1000-4700 m, and
Trifarina angulosa 10-650 m), which should prove useful in paleobathymetric
estimates.
The upper depth limits of 28 benthic foraminiferal species (e.g.,
Fursenkoina complanata 200 m, Bulimina truncana 450 m,
Melonis affinis 550 m, Eggerella bradyi 750 m, and Cassidulina
norvangi 1000 m) have potential to improve the precision of
paleobathymetric estimates based initially on the total faunal composition. The
planktic percentage of foraminiferal tests increases from outer shelf to upper
abyssal depths followed by a rapid decline within the foraminiferal lysocline
(below c. 3600 m). A planktic percentage <50% is suggestive of shelf depths,
and >50% is suggestive of bathyal or abyssal depths above the CCD.
In the abyssal zone there is dramatic taphonomic loss of most agglutinated
tests (except some textulariids) at burial depths of 0.1-0.2 m, which negates
the potential usefulness of these taxa in paleobathymetric assessments.
Keywords New Zealand; Chatham Rise; Bounty Trough; Hikurangi
Plateau; deep-sea benthic foraminifera; species associations; bathymetric
distribution; paleobathymetric assessment; modern analogue technique; ODP Leg
181; taphonomic loss; species diversity
New Zealand Journal of Geology & Geophysics, 2001, Vol. 44:
555-587
0024-8306/01/4404-0555 $7.00/0 (c) The Royal Society of New Zealand
2001
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