50thKaikoura05 -1- Kaikoura 2005 CHARACTERISATION OF NEW ...
50thKaikoura05 -1- Kaikoura 2005 CHARACTERISATION OF NEW ...
50thKaikoura05 -1- Kaikoura 2005 CHARACTERISATION OF NEW ...
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faunal changes within these cores with local<br />
modern radiolarian distributions in surface<br />
sediments to determine how climatic changes over<br />
the last 500 ka may have affected oceanographic<br />
conditions and sea surface temperatures in this<br />
region. We utilise preliminary sea surface<br />
temperature (SST) determinations using the modern<br />
analogue technique (MAT) and a modern dataset of<br />
31 core-top assemblages.<br />
For the coastal region represented by MD97-2121,<br />
the last deglaciation (15-10 ka BP) was<br />
characterised by progressive warming from 15°C to<br />
17°C and decreasing biosiliceous accumulation.<br />
The interaction of the subtropical East Cape<br />
Current and subantarctic waters jetting northward<br />
through Mernoo Gap may have promoted<br />
biosiliceous productivity in this near-coastal region<br />
in glacial times. There is little evidence from<br />
radiolarians for cooling of surface waters during the<br />
intervals correlated with the Antarctic Cold<br />
Reversal or Younger Dryas. However, a warming<br />
pulse is identified close to the termination of the<br />
Younger Dryas, c. 11.5-10 ka. Peak warmth of<br />
17°C at 9-4.5 ka is associated with the Holocene<br />
Climatic Optimum.<br />
For the oceanic regions represented by ODP 1123<br />
and 1124, MAT estimates are coarse, reflecting a<br />
lack of close analogues to the assemblages at these<br />
sites in the local core-top dataset. Nevertheless,<br />
glacial-interglacial cycles are well-defined with<br />
SSTs falling to 14°C in glacials and rising to 17°C<br />
in interglacials – similar to the modern seasonal<br />
range.<br />
POSTER<br />
THE GREENHOUSE BEHIND THE LAB:<br />
WHAT KAIKOURA’S LIMESTONE TELLS<br />
US ABOUT THE CONSEQUENCES <strong>OF</strong><br />
GLOBAL WARMING<br />
C.J. Hollis 1 ,C.P.Strong 1 ,G.J.Wilson 1 ,<br />
G.R. Dickens 2 &M.Nicolo 2<br />
1 GNS Science, PO Box 30 368, Lower Hutt<br />
2 Dept of Earth Sciences, Rice University, Houston,<br />
TX 77005, USA<br />
(c.hollis*gns.cri.nz)<br />
Muzzle Group strata exposed in a narrow gully<br />
behind the University of Canterbury <strong>Kaikoura</strong> Field<br />
Station record deposition at the southern margin of<br />
the Marlborough sub-basin under a greenhouse<br />
climate between 70 and 50 million years ago.<br />
Upper Cretaceous micritic limestone of the Mead<br />
Hill Formation is unconformably overlain by a 7 m<br />
thick interval of Paleocene-Eocene Teredo<br />
Limestone, consisting of highly bioturbated<br />
glauconitic sandstone. This basal member of the<br />
Amuri Limestone is overlain by >20 m of lower<br />
Eocene Lower Marl, which consists of alternating<br />
beds of marl and micritic limestone.<br />
Correlation with similar successions in middle and<br />
northern Clarence River valley (Hollis et al. <strong>2005</strong>a,<br />
b) indicate that lithofacies changes reflect<br />
climatically induced variation in ocean circulation,<br />
oceanic productivity and terrigenous sediment<br />
supply across a bathyal carbonate ramp. While<br />
Paleocene erosion, glaucony, and condensed<br />
sedimentation occurred in proximal settings<br />
(<strong>Kaikoura</strong>, mid-Clarence valley), a thick succession<br />
of biosiliceous sediment was deposited in distal<br />
settings (northern Clarence valley). This implies<br />
vigorous ocean circulation and enhanced coastal<br />
upwelling during a period of relatively cool<br />
climatic conditions. Early Eocene deposition of<br />
thick marl-rich sedimentary successions throughout<br />
the sub-basin suggests sluggish circulation and<br />
reduced upwelling during a period of warm climatic<br />
conditions. Distinctive marl-dominated intervals<br />
that can be correlated across the sub-basin represent<br />
episodes of extreme warming, notably the Initial<br />
Eocene Thermal Maximum (55 Ma) and the Early<br />
Eocene Climatic Optimum (53-50 Ma). These<br />
intervals are characterised by light carbon isotope<br />
signatures, short-lived occurrences of warm-water<br />
calcareous nannoplankton, planktic foraminifera<br />
and radiolarians, and acmes of some warm-water<br />
taxa. A significant increase in terrigenous flux<br />
suggests that the extreme warmth caused increased<br />
precipitation and weathering in the terrestrial<br />
hinterland.<br />
These results are consistent with general circulation<br />
models for Eocene greenhouse conditions (560 ppm<br />
CO2) that place New Zealand within a transition<br />
zone between a warm, subtropical, oligotrophic<br />
gyre to the north and a cool, eutrophic, cyclonic<br />
gyre to the south. Within this regime, additional<br />
warming is predicted to cause southward expansion<br />
of the subtropical gyre and increase precipitation<br />
over the New Zealand landmass.<br />
Hollis, C.J.; Dickens, G.R.; Field, B.D.; Jones, C.J.;<br />
Strong, C.P. <strong>2005</strong>: The Paleocene-Eocene transition at<br />
Mead Stream, New Zealand: a southern Pacific record<br />
of early Cenozoic global change. Palaeogeography,<br />
Palaeoclimatology, Palaeoecology 215: 313-343.<br />
Hollis, C.J.; Field, B.D.; Jones, C.M.; Strong, C.P.;<br />
Wilson, G.J.; Dickens, G.R. <strong>2005</strong> (in press):<br />
Biostratigraphy and carbon isotope stratigraphy of<br />
uppermost Cretaceous-lower Cenozoic in middle<br />
Clarence valley, New Zealand. Journal of the Royal<br />
Society of New Zealand 35 (3): 39p.<br />
ORAL<br />
50 th <strong>Kaikoura</strong>05 -37- <strong>Kaikoura</strong> <strong>2005</strong>