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Cenozoic palaeoenvironment of the Southern Ocean and East Antarctica : geological and paleontological evidence from the Kerguelen Plateau, Vestfold Hills and Prince Charles Mountains

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Whitehead, Jason (Jason Matthew) (2000) Cenozoic palaeoenvironment of the Southern Ocean and East Antarctica : geological and paleontological evidence from the Kerguelen Plateau, Vestfold Hills and Prince Charles Mountains. PhD thesis, University of Tasmania.

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Abstract

Southern Ocean and Antarctic sediments from the Kerguelen Plateau, Vestfold Hills and
Prince Charles Mountains contain evidence that suggest climatic conditions and ice sheet
volume have fluctuated during the Cenozoic. Geological and palaeontological data show
that at certain intervals the Antarctic climate was significantly warmer, and the East
Antarctic Ice Sheet smaller, than today. Marine fossils are used to date these intervals of
ice sheet reduction and to reconstruct the associated climatic conditions. The findings are
compared with previous geological and ice sheet computer modeling studies, to help
reconstruct Antarctica's climate history and test predictive models for ice sheet response to
future global warming.
Fluctuating climatic conditions were identified in Quaternary and Pliocene marine
sediments from the Southern Kerguelen Plateau. Unconformities formed during intense
glacial intervals, when the velocity of the Antarctic Circumpolar Current increased.
Deposition occurred during warmer climatic intervals. During the late Pliocene, 3.1 -
2.64 Ma and 3.2 - 3.1 Ma, the summer sea-surface temperature (SST) was 4.5 C0
warmer than today at 62° S. This could have occurred only if the Antarctic Polar Front
Zone was either -1200 km further south or the temperature gradient across the associated
fronts became significantly shallower.
Pliocene (4.5 -4.1 Ma) marine sediments of the S0rsdal Formation (Vestfold Hills) were
also deposited when the summer SST was between 1.6° and 3.0 C0 higher than today.
When such temperatures are compared to glacial models, an increase in ice sheet volume
would be expected due to increased snow accumulation versus ablation. Previous work -
suggests that the S0rsdal Formation was deposited when the ice margin was -50 km
further inland. This suggests that a lower temperature than that proposed by earlier glacial
models is required for ice sheet retreat. These findings may support more recent modeling
studies that indicate ice sheet reduction can occur due to minor increases in water
temperature.
The Pagodroma Group, in the northern Prince Charles Mountains, consists largely of
diamict, and to a lesser degree, siltstone and sands deposited in the Lambert Graben
during intervals of glacial retreat. In situ and glacially reworked marine diatoms on the
Amery Oasis and Fisher Massif suggest that marine conditions occurred >250 km inland
from the modem Amery Ice Shelf edge in the Plio-Pleistocene (3.1 - 1 Ma), Pliocene (4.9 - 3.7 Ma) and middle Miocene (12.2 - 11.7 Ma), and >300 km inland in the Miocene
(14.2 - 12.5 Ma and 14.2- 6.2 Ma) and Oligocene (-36.6 - 30.2 Ma). Diatoms also
provide an age control for three formations in the Pagodroma Group. Glacially reworked
diatoms and stratigraphic relationships indicate that the Mt Johnston Formation, on Fisher
Massif was deposited sometime between 36.3 - 12.5 Ma. In situ marine diatoms in
Middle Miocene (14.2 - 12.5 Ma) siltstone from the Fisher Bench Formation, on Fisher
Massif, suggest a summer SST of 3.5° to 5°C. An associated relative mean annual air
temperature rise > 15 C°, during ice shelf absence, caused deglaciation of the Lambert
Graben, and is consistent with the predicted response from glacial models. The Bardin
Bluffs Formation was deposited in the Amery Oasis 3.1 - I Ma. The lithostratigraphy of
the formation indicates that the ice sheet volume varied greatly.
The Cenozoic geology of the central Menzies Range in the Southern Prince Charles
Mountains is described. Glacial landforms and deposits formed more recently than 40 Ma
during two climate phases. The first phase was warmer than today, and wet-based glacial
conditions existed. Associated deposits consist of glacial diamict, lacustrine siltstone and
sand deposited in a terrestrial alpine glacial environment. These deposits may be
contemporaneous with the Pagodroma Group; however, age relationships are yet to be
determined. The second climate phase was cold and similar to today's, and caused
relatively minor glacial erosion and deposition.
Previous researchers have found controversial terrestrial higher plant fossils in the
Transantarctic Mountains, which indicate a warmer Antarctic climate sometime in the late
Neogene. The lack of a similar flora in the Vestfold Hills and Prince Charles Mountains
may reflect earlier denudation of this vegetation during ice sheet development. However,
biogeogeographical barriers may have prevented re-colonisation from the Transantarctic
Mountains to other East Antarctic regions during later episodes of deglaciation in the
Lambert Graben catchment identified in this study.

Item Type: Thesis (PhD)
Keywords: Paleoecology, Paleontology, Geology, Stratigraphic, Paleoecology
Copyright Holders: The Author
Copyright Information:

Copyright the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
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Additional Information:

Thesis (Ph.D.)--University of Tasmania, 2000. Includes bibliographical references

Date Deposited: 04 Feb 2015 23:27
Last Modified: 11 Mar 2016 05:54
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