50thKaikoura05 -1- Kaikoura 2005 CHARACTERISATION OF NEW ...
50thKaikoura05 -1- Kaikoura 2005 CHARACTERISATION OF NEW ...
50thKaikoura05 -1- Kaikoura 2005 CHARACTERISATION OF NEW ...
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
indication of the style or extent of Antarctic<br />
glaciation. Therefore further drilling was planned<br />
both through DSDP in other parts of the Antarctic<br />
margin (Antarctic Peninsula and Prydz Bay) and<br />
through the use of a land-based drilling system<br />
from the fast ice of McMurdo Sound, where NZ-led<br />
efforts had identified a sedimentary basin suitable<br />
for drilling close to the edge of the Transantarctic<br />
Mountains (and the East Antarctic ice sheet).<br />
This drilling (www.geo.vuw.ac.nz/croberts ), along<br />
with recent high-resolution deep-sea isotope<br />
records, has now led to the following history.<br />
Around 34 Ma an ice sheet reaches the coast on<br />
both sides of Antarctica. Subsequent ice sheets<br />
advanced and retreated on Milankovitch<br />
frequencies, causing variations in eustatic sea level<br />
of the order of 50 m through Oligocene and early<br />
Miocene times. Low beech forest persisted around<br />
the coast throughout this period.<br />
• Around 14 Ma the ice sheet developed a<br />
•<br />
persistent core with margins close to its present<br />
limits and largely frozen to its bed. During the<br />
warm Pliocene coastal Antarctica was warmer<br />
by several degrees, but there is no firm evidence<br />
that the East Antarctic ice sheet collapsed.<br />
From 2.5 Ma to the present the Antarctic ice<br />
sheet has responded to sea level variations<br />
induced by Northern Hemisphere ice sheets, but<br />
only on a scale of ~15 m of sea level equivalent.<br />
• Future drilling by the ANDRILL consortium<br />
will investigate Quaternary behaviour of the<br />
Ross Ice Shelf, and Antarctic climate during the<br />
middle Miocene transition, in the McMurdo<br />
area (http://andrill.org/ ).<br />
ORAL<br />
THE CAPE ROBERTS PROJECT:<br />
TECTONIC AND CLIMATIC HISTORY <strong>OF</strong><br />
THE VICTORIA LAND COAST,<br />
ANTARCTICA OVER THE LAST 34 MA.<br />
P. J. Barrett 1 & Cape Roberts Science Team 2<br />
1 Antarctic Research Centre, Victoria University of<br />
Wellington, P.O. Box 600, Wellington.<br />
2 55 scientists from Italy, United States, New<br />
Zealand, Germany Australia, United Kingdom and<br />
The Netherlands)<br />
(peter.barrett*vuw.ac.nz)<br />
From 1997 to 1999 the Cape Roberts Project<br />
(http/www.geo.vuw.ac.nz/croberts) drilled 3 holes<br />
off the Victoria Land coast at 77.0ºS and 163.7ºE.<br />
The project was a cooperative venture between<br />
scientists, administrators and Antarctic support<br />
personnel from 7 countries. The aim was to<br />
investigate the early history of the East Antarctic<br />
ice sheet and the West Antarctic Rift System, using<br />
a 55 tonne drilling system set up 13 to 16 km<br />
offshore on fast sea ice. Water depths ranged from<br />
153 m to 295 m and core recovery for the 1680 m<br />
drilled was 95%. The cores are a high quality<br />
nearshore marine sedimentary record for the period<br />
from 17 to 34 Ma ago and are well-dated from<br />
volcanic ash, biostratigraphy, Sr isotopes and<br />
magnetostratigraphy.<br />
Key findings are:<br />
i. Provenance studies indicate the Transantarctic<br />
Mountains had achieved most of their present<br />
height by 34 Ma. Apatite fission track studies<br />
show Cenozoic denudation began at ~55 Ma, but<br />
CRP core studies show that most of the 1500 m<br />
of subsidence on the western margin of the<br />
Victoria Land Basin took place from 34 to 29<br />
Ma, slowing down to almost none by 17 Ma, and<br />
none since that time (Wilson et al., Geology,<br />
submitted). This changes the established view of<br />
the West Antarctic Rift System.<br />
ii. The stratigraphy is largely cyclic repetitions of<br />
shallow glacimarine facies, with well-dated<br />
cycles of glacial advance and retreat around 24<br />
Ma showing that the Antarctic ice sheet<br />
iii.<br />
responded to orbital forcing at that time, much as<br />
the Northern Hemisphere ice sheets have done in<br />
the Quaternary (Naish et al., Nature, 2001).<br />
Pollen records show the cooling of the Victoria<br />
Land coast from a temperate climate (>34 Ma) to<br />
a cool temperate climate (34 to ~17 Ma)<br />
(Prebble et al, Palaeogeography,<br />
Palaeoclimatology, Palaeoecology, in press).<br />
This record shows no hint of the late Oligocene<br />
warming inferred from deep-sea isotopes by<br />
Zachos et al (Science, 2001). An alternative<br />
explanation for the apparent warming has now<br />
been provided by Pekar et al (Palaeogeography,<br />
Palaeoclimatology, Palaeoecology, in press).<br />
iv. Rapid sedimentation and multiple dating<br />
v.<br />
techniques on CRP core have provided a new<br />
potential calibration point for the Oligocene-<br />
Miocene boundary at 23.7 Ma (Wilson et al.,<br />
Geology, 2002).<br />
A 2-m-thick shell bed within 43 m of Quaternary<br />
strata in CRP-1, and dated at 1.1 Ma, records a<br />
“super-interglacial” period (MIS 31) when the<br />
Antarctic coast was ice-free and significantly<br />
warmer than today (Scherer et al., Nature, in<br />
review).<br />
Detailed results from individual drill holes can be<br />
found in 10 issues of the journal Terra Antartica<br />
between 1998 and 2001.<br />
POSTER<br />
50 th <strong>Kaikoura</strong>05 -6- <strong>Kaikoura</strong> <strong>2005</strong>