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Late quaternary marine and freshwater swamp deposits of Northwestern Tasmania

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Van de Geer, G (1981) Late quaternary marine and freshwater swamp deposits of Northwestern Tasmania. PhD thesis, University of Tasmania.

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Abstract

A study of marine and freshwater swamp deposits and
landforms in northwestern Tasmania reveals that profound
palaeoenvironmental changes occurred during the late Quaternary
as a consequence of eustatic sea level changes, tectonic and/or
hydro-isostatic uplift, and palaeoclimatic changes.
Prograded bay sand barriers and lagoonal inlets
constitute the most complex and extensively developed Holocene
landforms and deposits on this coast. The barriers clearly
depict marine transgression, followed by a major phase of
barrier progradation and an episode of blowout and parabolic
dune development. In the lagoonal inlets, the effects of strong
tidal current action, halophytic vegetation, and wave and
wind action have resulted in the development of distinctive
depositional environments and landforms.
Pre-Holocene depositional marine landforms and sand
deposits which locally contain a well-preserved fauna of mollusca
and foraminifera, and fossil shore platforms covered with beach
cobble deposits occur extensively in the area. These deposits
occur from below sea level up to 15 to 20 m. The local and wider
stratigraphic relationships of the marine material in relation
to glacial, freshwater and aeolian deposits, and the 14c dating
of some of these deposits consistently point to a Last Interglacial
age for the fossil marine features.Oxygen isotope and chronostratigraphic studies elsewhere
suggest that the maximum level attained by the sea during the
Last Interglacial transgression was 5 to 10 m above present
sea level. Although there is presently no direct evidence
for or information on tectonic deformation or theoretically
calculated data on hydro-isostatic deformation in northwestern
Tasmania or elsewhere on the island, the higher levels recorded in
this study suggest that such uplift and deformation occurred in the
area during the late Quaternary.
Stratigraphic, sedimentary, palynologic, faunal, and
conventiona l and isotopically enriched 1~C analysis of the swamp
and lacustrine deposits formed under the influence of fluctuating
artesian springs provides evidence from which a general
pal aeoenvironmental and palaeoclimatic record of approximately
100,000 years may be constructed.
During the Holocene Stage (10,000-0 BP) climate was warm
and wet, and woody vegetation was dominant throughout the area.
Locally, sand lunettes developed along lee shores of shallow
lagoons. During the late Last Glacial Stage (25,000-10,000 BP)
the climate became progressively drier and grassy open environments
were more widespread. The driest part of this period occurred
between~ 17,000 and 10,000 BP, when spring activity was
very low and temperatures in western Tasmania were markedly
reduced by highland glaciation. Predominantly wet conditions
resulting from high precipitation and/or low evaporation rates
occurred during the middle Last Glacial Stage (25,000-50,000 BP).
The wettest part of this period occurred after about 35,000 BP
during which the springs were very active, and extensive deposition
of coarse river bed loads and alluvial fan gravels occurred elsewhere in the area. Considerably drier conditions occurred
between approximately 55,000 and 45,000 BP during which woody
vegetation was much more important than herbaceous vegetation
and aquatic vegetation was virtually absent from the swamps.
Prior to-55,000 BP, predominantly wet conditions prevailed
on the swamps. These were periodically interrupted by relatively
brief, drier phases during which woody scrub communities were
somewhat more important and herbaceous and aquatic communities
were less important than during the preceding and succeeding
periods of the early Last Glacial Stage.
The direction of general climatic changes presented
in this dissertation appears to be broadly sympathetic with
climatic changes inferred from other southern Australian localities.

Item Type: Thesis (PhD)
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Date Deposited: 02 Jun 2014 04:16
Last Modified: 11 Mar 2016 05:56
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