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

indication of the style or extent of Antarctic
glaciation. Therefore further drilling was planned
both through DSDP in other parts of the Antarctic
margin (Antarctic Peninsula and Prydz Bay) and
through the use of a land-based drilling system
from the fast ice of McMurdo Sound, where NZ-led
efforts had identified a sedimentary basin suitable
for drilling close to the edge of the Transantarctic
Mountains (and the East Antarctic ice sheet).
This drilling (www.geo.vuw.ac.nz/croberts ), along
with recent high-resolution deep-sea isotope
records, has now led to the following history.
Around 34 Ma an ice sheet reaches the coast on
both sides of Antarctica. Subsequent ice sheets
advanced and retreated on Milankovitch
frequencies, causing variations in eustatic sea level
of the order of 50 m through Oligocene and early
Miocene times. Low beech forest persisted around
the coast throughout this period.
• Around 14 Ma the ice sheet developed a
•
persistent core with margins close to its present
limits and largely frozen to its bed. During the
warm Pliocene coastal Antarctica was warmer
by several degrees, but there is no firm evidence
that the East Antarctic ice sheet collapsed.
From 2.5 Ma to the present the Antarctic ice
sheet has responded to sea level variations
induced by Northern Hemisphere ice sheets, but
only on a scale of ~15 m of sea level equivalent.
• Future drilling by the ANDRILL consortium
will investigate Quaternary behaviour of the
Ross Ice Shelf, and Antarctic climate during the
middle Miocene transition, in the McMurdo
area (http://andrill.org/ ).
ORAL
THE CAPE ROBERTS PROJECT:
TECTONIC AND CLIMATIC HISTORY OF
THE VICTORIA LAND COAST,
ANTARCTICA OVER THE LAST 34 MA.
P. J. Barrett 1 & Cape Roberts Science Team 2
1 Antarctic Research Centre, Victoria University of
Wellington, P.O. Box 600, Wellington.
2 55 scientists from Italy, United States, New
Zealand, Germany Australia, United Kingdom and
The Netherlands)
(peter.barrett*vuw.ac.nz)
From 1997 to 1999 the Cape Roberts Project
(http/www.geo.vuw.ac.nz/croberts) drilled 3 holes
off the Victoria Land coast at 77.0ºS and 163.7ºE.
The project was a cooperative venture between
scientists, administrators and Antarctic support
personnel from 7 countries. The aim was to
investigate the early history of the East Antarctic
ice sheet and the West Antarctic Rift System, using
a 55 tonne drilling system set up 13 to 16 km
offshore on fast sea ice. Water depths ranged from
153 m to 295 m and core recovery for the 1680 m
drilled was 95%. The cores are a high quality
nearshore marine sedimentary record for the period
from 17 to 34 Ma ago and are well-dated from
volcanic ash, biostratigraphy, Sr isotopes and
magnetostratigraphy.
Key findings are:
i. Provenance studies indicate the Transantarctic
Mountains had achieved most of their present
height by 34 Ma. Apatite fission track studies
show Cenozoic denudation began at ~55 Ma, but
CRP core studies show that most of the 1500 m
of subsidence on the western margin of the
Victoria Land Basin took place from 34 to 29
Ma, slowing down to almost none by 17 Ma, and
none since that time (Wilson et al., Geology,
submitted). This changes the established view of
the West Antarctic Rift System.
ii. The stratigraphy is largely cyclic repetitions of
shallow glacimarine facies, with well-dated
cycles of glacial advance and retreat around 24
Ma showing that the Antarctic ice sheet
iii.
responded to orbital forcing at that time, much as
the Northern Hemisphere ice sheets have done in
the Quaternary (Naish et al., Nature, 2001).
Pollen records show the cooling of the Victoria
Land coast from a temperate climate (>34 Ma) to
a cool temperate climate (34 to ~17 Ma)
(Prebble et al, Palaeogeography,
Palaeoclimatology, Palaeoecology, in press).
This record shows no hint of the late Oligocene
warming inferred from deep-sea isotopes by
Zachos et al (Science, 2001). An alternative
explanation for the apparent warming has now
been provided by Pekar et al (Palaeogeography,
Palaeoclimatology, Palaeoecology, in press).
iv. Rapid sedimentation and multiple dating
v.
techniques on CRP core have provided a new
potential calibration point for the Oligocene-
Miocene boundary at 23.7 Ma (Wilson et al.,
Geology, 2002).
A 2-m-thick shell bed within 43 m of Quaternary
strata in CRP-1, and dated at 1.1 Ma, records a
“super-interglacial” period (MIS 31) when the
Antarctic coast was ice-free and significantly
warmer than today (Scherer et al., Nature, in
review).
Detailed results from individual drill holes can be
found in 10 issues of the journal Terra Antartica
between 1998 and 2001.
POSTER
50 th Kaikoura05 -6- Kaikoura 2005