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

faunal changes within these cores with local
modern radiolarian distributions in surface
sediments to determine how climatic changes over
the last 500 ka may have affected oceanographic
conditions and sea surface temperatures in this
region. We utilise preliminary sea surface
temperature (SST) determinations using the modern
analogue technique (MAT) and a modern dataset of
31 core-top assemblages.
For the coastal region represented by MD97-2121,
the last deglaciation (15-10 ka BP) was
characterised by progressive warming from 15°C to
17°C and decreasing biosiliceous accumulation.
The interaction of the subtropical East Cape
Current and subantarctic waters jetting northward
through Mernoo Gap may have promoted
biosiliceous productivity in this near-coastal region
in glacial times. There is little evidence from
radiolarians for cooling of surface waters during the
intervals correlated with the Antarctic Cold
Reversal or Younger Dryas. However, a warming
pulse is identified close to the termination of the
Younger Dryas, c. 11.5-10 ka. Peak warmth of
17°C at 9-4.5 ka is associated with the Holocene
Climatic Optimum.
For the oceanic regions represented by ODP 1123
and 1124, MAT estimates are coarse, reflecting a
lack of close analogues to the assemblages at these
sites in the local core-top dataset. Nevertheless,
glacial-interglacial cycles are well-defined with
SSTs falling to 14°C in glacials and rising to 17°C
in interglacials – similar to the modern seasonal
range.
POSTER
THE GREENHOUSE BEHIND THE LAB:
WHAT KAIKOURA’S LIMESTONE TELLS
US ABOUT THE CONSEQUENCES OF
GLOBAL WARMING
C.J. Hollis 1 ,C.P.Strong 1 ,G.J.Wilson 1 ,
G.R. Dickens 2 &M.Nicolo 2
1 GNS Science, PO Box 30 368, Lower Hutt
2 Dept of Earth Sciences, Rice University, Houston,
TX 77005, USA
(c.hollis*gns.cri.nz)
Muzzle Group strata exposed in a narrow gully
behind the University of Canterbury Kaikoura Field
Station record deposition at the southern margin of
the Marlborough sub-basin under a greenhouse
climate between 70 and 50 million years ago.
Upper Cretaceous micritic limestone of the Mead
Hill Formation is unconformably overlain by a 7 m
thick interval of Paleocene-Eocene Teredo
Limestone, consisting of highly bioturbated
glauconitic sandstone. This basal member of the
Amuri Limestone is overlain by >20 m of lower
Eocene Lower Marl, which consists of alternating
beds of marl and micritic limestone.
Correlation with similar successions in middle and
northern Clarence River valley (Hollis et al. 2005a,
b) indicate that lithofacies changes reflect
climatically induced variation in ocean circulation,
oceanic productivity and terrigenous sediment
supply across a bathyal carbonate ramp. While
Paleocene erosion, glaucony, and condensed
sedimentation occurred in proximal settings
(Kaikoura, mid-Clarence valley), a thick succession
of biosiliceous sediment was deposited in distal
settings (northern Clarence valley). This implies
vigorous ocean circulation and enhanced coastal
upwelling during a period of relatively cool
climatic conditions. Early Eocene deposition of
thick marl-rich sedimentary successions throughout
the sub-basin suggests sluggish circulation and
reduced upwelling during a period of warm climatic
conditions. Distinctive marl-dominated intervals
that can be correlated across the sub-basin represent
episodes of extreme warming, notably the Initial
Eocene Thermal Maximum (55 Ma) and the Early
Eocene Climatic Optimum (53-50 Ma). These
intervals are characterised by light carbon isotope
signatures, short-lived occurrences of warm-water
calcareous nannoplankton, planktic foraminifera
and radiolarians, and acmes of some warm-water
taxa. A significant increase in terrigenous flux
suggests that the extreme warmth caused increased
precipitation and weathering in the terrestrial
hinterland.
These results are consistent with general circulation
models for Eocene greenhouse conditions (560 ppm
CO2) that place New Zealand within a transition
zone between a warm, subtropical, oligotrophic
gyre to the north and a cool, eutrophic, cyclonic
gyre to the south. Within this regime, additional
warming is predicted to cause southward expansion
of the subtropical gyre and increase precipitation
over the New Zealand landmass.
Hollis, C.J.; Dickens, G.R.; Field, B.D.; Jones, C.J.;
Strong, C.P. 2005: The Paleocene-Eocene transition at
Mead Stream, New Zealand: a southern Pacific record
of early Cenozoic global change. Palaeogeography,
Palaeoclimatology, Palaeoecology 215: 313-343.
Hollis, C.J.; Field, B.D.; Jones, C.M.; Strong, C.P.;
Wilson, G.J.; Dickens, G.R. 2005 (in press):
Biostratigraphy and carbon isotope stratigraphy of
uppermost Cretaceous-lower Cenozoic in middle
Clarence valley, New Zealand. Journal of the Royal
Society of New Zealand 35 (3): 39p.
ORAL
50 th Kaikoura05 -37- Kaikoura 2005