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Stratigraphy and formation of soils on dolerite and their implication for landscape history in southeastern Tasmania


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Osok, Rafael Marthinus 2004 , 'Stratigraphy and formation of soils on dolerite and their implication for landscape history in southeastern Tasmania', PhD thesis, University of Tasmania.

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This study presents work from Mt Nelson and Tolmans Hill in
southeastern Tasmania. Detailed field observations were combined with particle
size and elemental distributions, mineralogical characteristics and radiocarbon
dating information in order to investigate soil stratigraphy and pedological
relationships of soils developed on Jurassic dolerite, and hence to improve
understanding of soil formation history on dolerite.
Field studies of soil morphology and distribution indicated that the soil
profiles were stratified, and their properties and distribution are closely related to
their position on landscape, site drainage and the depth of dolerite weathering.
This study indicates that local dolerite has been subjected to both deep
weathering and severe erosional periods. Pockets of deeply weathered dolerite
occur adjacent to thin topsoil on bedrock (A/C soils) or hard outcropping rock.
Deeper colluvial soil materials occur on lower slopes. The presence of protruding
dolerite columns now largely buried by transported clayey slope-wash materials ,
indicate partial landscape stripping followed by re-burial. The presence of buried
stone-lines separating the upper profile from the clayey subsoils supports the
idea of a second major erosional-depositional cycle.
A pronounced variation between the A and B horizons particle-size
distribution, mineralogy and elemental distribution supports the conclusion that
the modern soils are composed of several sedimentary layers which cap a
variable thickness of in situ weathered dolerite (termed "mealy material") above
fresh dolerite. Bedrock jointing, veins and rock fabric extend upward from the
bedrock into the mealy material but are truncated abruptly at the contact with the
clayey subsoil. Soil forming processes have operated to modify soil colours and
mottling, soil structure and cation chemistry.
Radiocarbon dating of an A2 horizon, profile TH1 (grey brown podzolic) to
7500 years BP indicates that the aeolian transport process may have continued
to the early Holocene, during which soil disturbance and movement have
occurred. A second radiocarbon date of approximately 5,500 years BP on profile
WW (black vertosol) at 190 - 200cm indicates recent soil creep of colluvial activity
occurred during the mid Holocene. In the same soil, the presence of an aboriginal
artefact at 88cm with an age of 2000 - 5000 years indicates a strong link
between the soil disturbance and aboriginal occupation during mid - late
The findings of this study have improved understanding of the formation
and distribution of dolerite derived soils in lowland SE Tasmania, and suggest
that the previous theory on in situ weathering of soils formed on dolerite could not
be applied to all dolerite-derived soils that cover almost one third of Tasmania.

Item Type: Thesis - PhD
Authors/Creators:Osok, Rafael Marthinus
Keywords: Stratigraphy, soils, formation, dolerite, history, Tasmania
Copyright Holders: The Author
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Copyright 2004 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, 2004. Includes bibliographical references

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