Stratigraphy and sedimentology of the Burdekin Delta, Queensland and comparisons with Permian coastal facies in the Denison Trough, SW Bowen Basin, Australia

Trueman, Jonathon David. (2003). Stratigraphy and sedimentology of the Burdekin Delta, Queensland and comparisons with Permian coastal facies in the Denison Trough, SW Bowen Basin, Australia PhD Thesis, School of Physical Sciences, The University of Queensland.

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Author Trueman, Jonathon David.
Thesis Title Stratigraphy and sedimentology of the Burdekin Delta, Queensland and comparisons with Permian coastal facies in the Denison Trough, SW Bowen Basin, Australia
School, Centre or Institute School of Physical Sciences
Institution The University of Queensland
Publication date 2003
Thesis type PhD Thesis
Supervisor Dr Christopher Fielding
A/Prof. Rod Holcombe
Total pages 256
Collection year 2003
Language eng
Subjects L
260104 Sedimentology
780104 Earth sciences
Formatted abstract

This thesis aims to investigate the stratigraphy and sedimentology of mixed-influenced deltaic systems. The sedimentary processes and sediment body architecture of coastal facies in the modern Burdekin Delta in north Queensland are examined, and compared to a poorly-exposed, analogous system, the early Late Permian Freitag Formation in the Denison Trough, central Queensland.

The Burdekin Delta, previously classified as a wave- and tide-influenced delta has been studied in detail and re-interpreted as a flood-dominated, wave- and tide-modified delta. A model is proposed for the formation of flood-dominated mouth bars in response to the delivery of large volumes of sediment to the delta front following floods of the Burdekin River. Friction-dominated middle-ground mouth bars form in shallow water, initially by aggradation during the waxing and peak stages of floods, until a dynamic equilibrium is reached between discharge velocity, water depth and sediment accumulation. As accommodation space decreases, progradation of the mouth bar occurs throughout the waning stages of the flow and, due to the progressive delivery of finer-grained sediments, results in the formation of an overall uniform or slightly fining-upwards vertical grain-size trend.

The action of tides results in the modification of newly emergent mouth bar surfaces, which become colonised by mangroves and form vegetated intertidal flats. With continued accumulation of fine-grained sediments and elevation, intertidal flats pass transitionally into supratidal flats and ultimately into grass plains. Tidal flats comprise > 50% of the total surface area of the lower delta plain although they constitute a volumetrically minor amount of the preserved sediments.

Rapid progradation of the foreshore following the delivery of large volumes of sediments during floods results in the formation of beach ridges. Ridge elevation is determined by a combination of the height of the mean spring high tide and the height of the waves during the period following the flood; ridge spacing is determined by the volume of sediments delivered, and consequently amount of progradation of the foreshore during the flood.

Northwards longshore drift along the eastern Burdekin Delta results in the formation of barrier spits. The formation of spits sequesters sediments moving northwards along the coast, which as a result, becomes sediment starved. When the base of the spit is breached, the body of the spit moves northwards along the coast and eventually merges into it, resulting in significant local regression. Approximately one third of the annual average sediment supplied to the delta front by floods migrates northwards along the coast and experiences a minor but distinct decrease in mean grain-size and increase in sorting with distance from the source.

The subsurface of the lower Burdekin Delta plain is composed predominantly of laterally-amalgamated mouth bar deposits. The majority of the Holocene lower delta plain has formed since 7500 yr BP in response to nodal avulsion of the Burdekin River. Progradation of delta lobes occurs during minor periods of sea level stillstand. A previously unrecognised delta lobe, here named the Jerona delta lobe has been documented and formed during a minor sea-level stillstand c. 7500-6800 yr BP.

The early Late Permian Freitag Formation comprises a thin (up to 166 m) sequence of broadly coastal deposits but is poorly-exposed. A wireline log facies scheme has been developed for the unit, based on the examination of core, outcrop and fully-cored stratigraphic boreholes and the correlation between core based facies and wireline log character. This electrofacies scheme has been used to interpret an extensive wireline log database in terms of facies architecture and genetic stratigraphy. Six depositional sequences have been identified, which are interpreted to have formed during stillstands or minor sea-level falls (4th order cyclicity) within an overall transgression. The Freitag Formation has been subdivided into a lower unit, comprising predominantly marine embayment, shoreface and shoreline facies and an upper unit comprising predominantly channel/ mouth bar and this shoreface facies. The Freitag Formation is the product of a fluvially-dominated and wave-modified deltaic system.

The Holocene Burdekin Delta is broadly equivalent to a single sequence in the Freitag Formation. Examination of widespread laterally-amalgamated mouth bar and channel deposits in the Burdekin Delta has facilitated the recognition and understanding of similar intervals in the Freitag Formation. The study of the modern Burdekin Delta has significantly aided the interpretation and understanding of the analogous, broadly equivalent but poorly-exposed Freitag Formation.

Keyword Geology -- Queensland -- Burdekin River region
Sediments (Geology -- Queensland -- Burdekin River

Document type: Thesis
Collection: UQ Theses (RHD) - UQ staff and students only
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Created: Fri, 24 Aug 2007, 18:14:32 EST