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Sedimentology and Stratigraphy of the Late Neoproterozoic Bonney Sandstone

Oyinloye Koyejo, 2014

Masters of Science (Petroleum Geoscience)

Australian School of Petroleum

The University of Adelaide

Abstract

This study represents the first good detailed sedimentological and sequence
stratigraphic analysis of the Bonney Sandstone exposed at the Arkaroola Syncline in
the Northern part of Flinders Ranges, South Australia. The Bonney Sandstone is
located between two prominent Late Neoproteozoic Formations, the underlying
Wonoka Formation and overlying Rawnsley Quartzite. These rocks have become
significant in recent years due to their importance in hydrocarbon exploration in salt
withdrawal basins. However there are few published studies on the Bonney
Sandstone.

Ten lithofacies were identified which formed the five facies associations.
These facies associations include Offshore deposits (FA 5), Offshore transition
deposits (FA 4), Shoreface/Foreshore deposits (FA 3), Mixed Wave-Tidal delta
deposits (FA 2) and Channel Deposits (FA 1). These facies association represent
three major depositional environments, shallow marine, mixed wave-tidal delta and
fluvial deposit.

Sequence stratigraphically, there are shows two significate intervals.The
lower transgressive interval which is made up of siltstone deposits with interbedded
massive sandstones. Low stand system tract deposit which marked the boundary
between the Wonoka Formation and the Bonney Sandstone. The middle to upper
section essentially represents a highstand system tract with normal regression. The
normal regressive interval was characterised by prograding delta and aggrading
channel sandstone deposit. Cyclicity pattern within the Bonney Sandstone are made
up of third and fourth order cycles.

Eastern paleocurrent directions suggest palaeo flow towards the Arkaroola
Syncline. Petrographic interpretation shows basement source rocks with deposition
in a low topographic area with little or no exposure of sediments. Adverse effects of
prevailing climatic conditions significantly affected sediment deposition as observed
within the grain size, mineralogical composition and reservoir potential of the Bonney
Sandstone. Reservoir quality of the Bonney Sandstone is essentially low due very
poor porosity and permeability.

Australian School of Petroleum
THE UNIVERSITY OF ADELAIDE

SA 5005 AUSTRALIA

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