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Abstract

Low grade metamorphic rocks of Late Proterozoic age overlie
metasedimentary rocks which have been metamorphosed to the garnet
zone of the greenschist facies. The boundaries between the two
sequences are faulted. The low grade metamorphic rocks form the
Clytie Cove droup, which Consists of a pile Of remobi1iSed clastic
detritus up . to.2000 m thick.. It Was deposited in a fault-controlled
basin which was deepening as the pile accumulated, resulting in a
thinning- and fining-upwards transgressive sequence.
Individual cycles of deposition were established largely by the
location and movement of main channels which descended from the strand
line, and these are represented by depositional units in which the
thickness of coarse-grained beds reduces upwards in the unit. Sediment
accumulation in regions where these channels shallowed are represented
by units in which the bed thickness increases upwards. Symmetrical bed
thickness variations form in areas of slowly laterally migrating shallow
channels. Conglomerate beds are common in each of these environments
and possess very similar lithological traits. Sequences represented
by thinning, thickening and symmetrical trends can'be distinguished
lithologically only by the relative abundance of lithological types
present in thesequences. Bed thickness periodicity, determined by
power spectral analysis, also differs in the three trends.
As a consequence an analysis of palaeoenvitonment could not be
made by studying lithofacies variations of.the conglomeratic flysch
sequences, alone. The mode of emplacement of conglomerate types also
constrains the environmental model built up from sequence trend
variations. A simple submarine fan model is not adequate to account
for the deposits of the Clytie Cove Group and a model is preferred of
multi-channeled flow into an elongated basin which is proximal to a strandline slope controlled and maintained by faulting, with
deposition by flows caused by a change of slope. The model is
favoured largely because of the lithological constraints on the
submarine fan model.
The sequence has been deformed during at least three
compressional phases, producing an east-west trending fold system
which was over-printed by a fold system trenching north-west. Later
events produced box-folds and crenulation cleavages trending eastwest.
These folding events were preceded by deformation and metamorphism
in the underlying metamorphosed sediments.
In a basin of such antiquity with a record of polyphase
deformation, the analysis of the structural geology of the region
was used to establish the juxtaposition of elements Within the basin
as sedimentary and structural. An understanding of deformation was
required to determine the nature of early, pre-folding changes in the
rocks which yielded valuable information regarding palaeoslope and
basin stability during deposition. The structural geology of the
surrounding, metamorphosed rocks was used to time relationships of
faulting, folding and basin formation in relation to orogenic events
documented in other parts of Tasmania, and hence the likely tectonic
setting of the basin. The structural, elements also determine the
elongation of the basin and hence controlled the palaeogeographic
interpretation.

Item Type:	Thesis - PhD
Authors/Creators:	Williams, Peter Roderick
Keywords:	Geology
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 would be pleased to hear from the copyright owner(s).
Additional Information:	Thesis (Ph.D.)--University of Tasmania, 1980. Bibliography: l. 223-234
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