50thKaikoura05 -1- Kaikoura 2005 CHARACTERISATION OF NEW ...

Ma to 1.9 Ma that encompasses Coromandel
Peninsula, the Kaimai ranges, Great Barrier Island,
and the offshore islands east of the peninsula
(except Mayor Island).
Volcanic rocks in the CVZ range from basalts,
basaltic andesites, andesites, dacites, to rhyolites.
Volcanic activity was initiated about 18 Ma along
the western Coromandel Peninsula and Great
Barrier Island, and involved basaltic-andesite,
andesite, and dacite cone volcanism which built up
a large portion of the peninsula. This phase of
activity lasted until about 12 Ma, when eruptions
shifted eastwards and changed to more silicic
caldera-forming volcanism that continued until 1.9
Ma as arc volcanism moved from the CVZ to the
active Taupo Volcanic Zone (TVZ).
Geochemical analyses of a representative suite of
rocks from the CVZ by XRF (at the University of
Waikato) and ICP-MS (at the University of Texas
as Dallas) show that there is a continuous spectrum
of compositions in CVZ. They have similar major
and trace element compositions to TVZ, apart from
the high-K rhyolites (up to 5.5 wt % K2O) which
are common as sanidine-bearing rhyolites in the
CVZ, but rare in the TVZ. REE patterns in CVZ
andesites and rhyolites have moderate slopes (LaN/
YbN average 4 to 8) and moderate Eu anomalies
(Eu/Eu* average 0.6 to 0.95). The general
geochemical similarities between CVZ and TVZ
suggest that they had similar petrogeneses, with the
difference that there is a greater proportion of mafic
magma in CVZ.
ORAL
FACTORS INFLUENCING THE
DISTRIBUTION OF SUBANTARCTIC DEEP-
SEA BENTHIC FORAMINIFERA, SOUTH-
EAST OF NEW ZEALAND
Ashwaq T. Sabaa 1 , Bruce W. Hayward 1 ,
Hugh R. Grenfell 1 ,HelenL.Neil 2
1 Geomarine Research, 49 Swainston Rd, St Johns,
Auckland
2 National Institute of Water and Atmosphere,
P.O. Box 14 901, Kilbirnie, Wellington
(a.sabaa*geomarine.org.nz)
In this study we investigate the combination of
environmental factors that influence the distribution
patterns of benthic foraminiferal tests (>0.63 µm) in
a topographically varied region crossed by both the
Subtropical and Subantarctic Fronts, south-east of
New Zealand. Seafloor sample sites extend from
outer shelf (50 m) to abyssal (5000 m) depths, are
bathed by five different water masses, and receive
phytodetritus from Subtropical, Subantarctic and
Circumpolar surface water masses.
Eight mappable benthic foraminiferal associations
are recognised by Q-mode cluster analysis of the
census data (>63 �m, 214 species, 68 samples).
Canonical correspondence analysis and a
correlation coefficient matrix were used to relate
the faunal data to a set of environmental proxies.
These show that factors related to water depth
(especially decreasing food supply with increasing
depth) are the most significant in determining the
overall foraminiferal distribution. Other
contributing factors include surface water
productivity and its seasonality, bottom water
ventilation, energetic state of the benthic boundary
layer and resulting substrate texture, and bottom
water carbonate corrosiveness.
Three shallow-water associations (50-700 m),
dominated by Cassidulina carinata, Trifarina
angulosa, Globocassidulina canalisuturata,
Gavelinopsis praegeri, andBolivina robusta, occur
in coarse substrates on the continental shelf and on
the crests and upper slopes of four seamounts under
well-oxygenated, high energy regimes, and high
food input. Three mid-bathyal to upper abyssal
associations (500-3300 m), dominated by
Alabaminella weddellensis, C. carinata, and
Epistominella exigua, occur in biopelagic sandy
mud, beneath a region of strongly seasonal food
supply, with composition influenced by total food
flux, ventilation (Oxygen Minimum Zone), and
bottom current strength. An unusual lower bathyal
association (1200-2100 m), dominated by T.
angulosa and Ehrenbergina glabra, occurs in a belt
of coarser sandy substrates that runs along the crest
of the submarine plateaux slopes beneath the
strongly flowing Subantarctic Front. A deep abyssal
association (3500-5000 m), dominated by
Epistominella umbonifera and Globocassidulina
subglobosa, occurs on the abyssal plain beneath
oligotrophic Circumpolar Water south-east of the
Subantarctic Front, and is strongly influenced by
cold, carbonate-corrosive, lower Circum-polar
Deep Water.
ORAL
PROVENANCE OF DEVONIAN BEACON
SUPERGROUP SEDIMENTS IN SOUTHERN
VICTORIA LAND, ANTARCTICA
Jeni Savage, Margaret Bradshaw & Kari Bassett
Dept. of Geological Sciences, University of
Canterbury, Priv. Bag 4800, Christchurch.
(margaret.bradshaw*canterbury.ac.nz)
Conglomerate beds in the basal part of the
Devonian Taylor Group (Beacon Supergroup) in
southern Victoria Land provide valuable evidence
of provenance and palaeoenvironment. The
conglomerates occur within the Sperm Bluff
Formation, a unit that overlies an unconformity
50 th Kaikoura05 -76- Kaikoura 2005