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

volcanism and a linear vent oriented NE/SW
through Douglas Basin. The Breccia and the source
vents form two topographically high centres, here
referred to as North and South Peaks. Stepping
normal faults, and clastic “dykes” infilling tensional
cracks from above, indicate significant postdepositional
collapse towards the linear vent.
After volcanism ceased a marine strait or
embayment existed between the North and South
Peaks. In this setting coarse grey sandstones
(Landing Point sandstone member) accumulated
immediately above the Rangiauria Breccia on the
rapidly aggrading outer southern slopes of North
Peak. Subsequently these beds were overlain by
finer yellow-brown siltstones (Black Robin
siltstone member). These beds are highly laminated
and cross-stratified having accumulated in the
ocean at the foot of ridges radiating from North
Peak.
Next, gravitational collapses began from high on
the south flank of North Peak, deforming the
previous beds over which they flowed and
accumulating in the marine strait/embayment.
Subsequently, further gravitational collapses
occured northwards from South Peak, (mapped as
Bag End breccia), carrying up to 6.6 m-sized
megaclasts of Rangiauria Breccia into what by this
time was a marine embayment. This blocked the
northwest entrance of the embayment to the sea,
immediately leading to lacustrine conditions under
which the wood-bearing siltstones of the basal
Mangere Formation began to accumulate.
ORAL
PRELIMINARY EVIDENCE OF DEGLACIAL
OCEAN CHANGE IN NEW ZEALANDS
SUBANTARCTIC
Helen L. Neil 1 & Penelope J. Cooke 2
1 NIWA, Private Bag 14-901, Kilbirnie, Wellington,
New Zealand
2 Department of Earth Sciences, University of
Waikato, Private Bag 3105, Hamilton
(h.neil*niwa.co.nz)
We present preliminary stable isotope records from
the subantarctic region off New Zealand which are
used to demonstrate surface and deep-water
responses to the last deglaciation. Data was
obtained from a kasten core collected by the R. V.
Tangaroa in 1997. Fine sampling of this moderate
sedimentation rate core yields a record of SW
Pacific Ocean conditions over the last glacial cycle,
potentially allowing an evaluation of the timing of
deglacial events relative to those in Antarctica and
the Northern Hemisphere. The 3.5 m-long core, Y8,
extends back to at least Marine Isotope Stage (MIS)
6, and was recovered from 1335 m water depth, off
the northeastern flank of Bounty Plateau. Presently,
the site is south of the Subtropical Front (STF), and
is overlain by cool subantarctic surface water and
southern sourced deep intermediate waters. The
site is in a location likely to be influenced by crossfrontal
exchange of surface waters arising from the
generation of cold and warm core eddies and
subsequent transport north or south respectively.
To examine the ocean's response stable isotopes in
foraminifera were analysed from slices averaging
120-250 yr resolution. Surface (up to 400 m deep)
waters were investigated using two planktic
species. Globigerina bulloides is a surface or nearsurface
dweller, but is also associated with periods
of enhanced nutrient supply. These conditions are
often related to upwelling, which can occur in
different seasons in different regions. Globorotalia
inflata’s depth range extending to 400 m, and are
persistent and numerous in the core. Their oxygen
isotopic compositions generally record
temperatures colder than co-existing G. bulloides.
The tendency is for � 13 CofG. bulloides to increase
under high productivity conditions, while that of
other species, including G. inflata, become more
negative during increased upwelling of subsurface
waters enriched in 12 C. For bottom waters, we
examined Uvigerina peregrina, it records the
isotopic signal of pore waters in the upper layers of
sediment, which, for oxygen, is close to that of
bottom water.
POSTER
RHODOLITH-BEARING LIMESTONES AS
TRANSGRESSIVE MARKER BEDS, SOME
NORTH ISLAND EXAMPLES
C.S. Nelson 1 &R.Nalin 2
1 Dept. of Earth Sciences, University of Waikato,
Private Bag 3105, Hamilton
2 Dipt. di Geologia, Università di Padova, Via
Giotto 1, 35137 Padova, Italy
(c.nelson*waikato.ac.nz)
Rhodoliths are nodular structures mainly composed
of superimposed thalli of red coralline algae. Since
their development is controlled by an array of
ecological parameters, rhodoliths are a valuable
source of paleoenvironmental information.
However, despite their common use in
paleoecological reconstructions, the stratigraphic
significance of rhodolith accumulations has seldom
been addressed in detail.
In a study of mid-Tertiary rhodolith-bearing
deposits from the North Island of New Zealand,
rhodolithic units, usually of limited lateral extent,
are systematically found above major
unconformities at the base of deepening upwards
successions. Two types of transgressive rhodolithbearing
deposits may be distinguished on the basis
of texture and rhodolith internal structure. Type A
50 th Kaikoura05 -57- Kaikoura 2005