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Sedimentology and geochemistry of modern temperate bryozoan carbonates around Tasmania, Australia

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Amini, ZZ (2002) Sedimentology and geochemistry of modern temperate bryozoan carbonates around Tasmania, Australia. PhD thesis, University of Tasmania.

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Abstract

This thesis describes various aspects of the modern temperate, shallow
(<200m) shelf sediments around Tasmania (latitudes -38°-44° S, longitudes -144°-
149° E), Australia, and is structured into three different sections: eastern and western
Tasmania, and Bass Strait. These are ideal open shelf environments for carbonate
sedimentation due to availability of nutrients, presence of different water masses,
limited terrigenous input and low variation in seawater temperature and salinity. These
conditions maintain sufficient saturation of CaCO3 and thus preserve extensive
temperate carbonates around Tasmania. In this study, sedimentological and
geochemical properties are combined with present oceanographic features to obtain a
better understanding of the origin, variation and distribution of sediments off
Tasmania. In addition to bulk sediments, specimens of different bryozoan
morphotypes have been selected to evaluate their reliability in recording ambient
environmental conditions, mineralogy and geochemical characteristics.
Cool temperate carbonates dominate over siliciclastics on the continental shelf
around Tasmania. The dominant grain size in all sample studied is very coarse to
medium sand, followed by fine sand, gravel fractions and minor fines (muds) and thus
sediments are moderately to well sorted. The major biota in bulk sediments off eastern
and western Tasmania are bryozoans, followed by foraminifera and molluscs, and the
remaining fauna such as echinoderms, worm tubes, sponge spicules and crustaceans
occurs in small amounts. The term bryoforamol assemblage is applied to this
carbonate skeletal association. However, in Bass Strait, the dominant fauna consists of
bryozoans, followed by molluscs, minor content of foraminifera, and thus the term
bryomol assemblage is used. Skeletal fragments, siliciclastic grains and debris occur in
significant quantities in all sample studied. Pellets and intraclasts comprise minor
components. Biota varies with different size fractions. Bryozoans and molluscs occur
mainly in gravel; mixtures of bryozoan, foraminifera and molluscs in the sand
fraction; and mainly bryozoan and foraminifera in the fine sand fraction. Fines consist
of debris and minor amounts of sponge spicules. Variation in grain size, and biotic and
abiotic constituents in different size fractions is attributed to different factors such as
growth size and susceptibility to breakage of the organisms, depth, latitude and water
energy.
Bryozoans are the major components in bulk sediments and in all different
size fractions as a result of low productivity of the other organisms, normal salinity,
presence of nutrient-rich upwelling sub-Antarctic water, minor amounts of fines (mud)
and availability of hard to particulate substrates. Bryozoan contents increase with
increasing water depth, bivalves are dominant in shallow-depths, foraminifera in middepth
and gastropods are mostly located around 130 m. Some biotic and abiotic grains
are bored and encrusted suggesting slow rates of sedimentation.

Item Type: Thesis (PhD)
Keywords: Bryozoa, Marine sediments, Carbonates
Copyright Holders: The Author
Copyright Information:

Copyright 2002 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
would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (Ph.D.)--University of Tasmania, 2002. Includes bibliographical references

Date Deposited: 25 Nov 2014 00:51
Last Modified: 23 Aug 2017 06:00
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