Tucker, Ryan Thomas (2014) Stratigraphy, sedimentation and age of the upper cretaceous Winton formation, central-western Queensland, Australia: implications for regional palaeogeography, palaeoenvironments and Gondwanan palaeontology. PhD thesis, James Cook University.

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Abstract

The mid-Cretaceous Winton Formation is one of Australia's most important sources of Mesozoic terrestrial fossils. In recent years it has produced some of the continent's most significant body and trace fossil records of mid-Cretaceous dinosaurian and crocodilian assemblages. Additionally, the Winton Formation preserves a diverse assemblage of lungfish and primitive ray-finned fish, aquatic lizards, turtles, numerous invertebrates along with a high diversity of plant macrofossils, including some of the world's earliest flowering plants. The Winton Formation is exposed over large portions of remote central-western Queensland, in addition to northern New South Wales, north-western South Australia and the south-western corner of the Northern Territory. Despite its importance for our understanding of Australian terrestrial environments during the latter part of the Mesozoic, very little in the way of detailed geological work has been carried out on the Winton Formation. As a consequence, palaeoenvironmental and palaeoecological conditions associated with many of Australia's key dinosaur faunas are poorly understood. A greater understanding of the stratigraphy, sedimentology, age, and taphonomy of these sites will provide critical context for evaluating Australia's late-Mesozoic vertebrate taxa to other well-known Gondwanan faunas.

This study utilizes detrital zircon geochronology and Lu-Hf isotope analysis to constrain the depositional age, tectonic setting, basin evolution, and stratigraphic context of the Winton Formation, northeastern Australia. A number of geological studies in the past several decades have focused on U-Pb detrital zircon geochronology for maximum depositional age; however, this approach is still underutilized in palaeontology. Thus, these ten samples, which were composed of ~100 grain detrital zircon samples from different stratigraphic levels and key fossil locations throughout the Winton and underlying units (basin wide) were analyzed. Detrital zircon ages were obtained via U-Pb LA-ICPMS geochronology and the resulting U-Pb grain ages were subjected to various metrics to interpret maximum depositional age and sedimentary provenance. The results of this work considerably improve upon existing palynological age constraints, suggesting that there are two distinctly different aged faunas: one that is likely ~ 100-98 Ma (Isisford Fauna); and one that is no older than earliest Turonian or latest Cenomanian (92-94 Ma), which includes most other Winton vertebrates (Lark/Bladensburg Fauna).

The most abundant detrital zircon age population clusters between 92-115 Ma, suggesting that much of the volcanic-rich sediment that characterizes the Winton Formation was eroded syndepositionally or shortly after emplacement of an active continental volcanic arc system located along the eastern margin of Australia (presumably the Whitsunday Volcanic Province). This volcanic arc activity was not a singular event; rather I have identified near-continuous detrital zircon grain ages between 92-330 Ma, indicating intermittent arc volcanism along that eastern margin due to continuous slab subduction of the Phoenix/Pacific Plate under the eastward migrating Gondwana margin. A particularly interesting result is the identification of Jurassic-age grain populations that represent a period not previously associated with significant arc magmatism in northeastern Queensland. The identification of fairly continuous detrital zircon ages is compared with established terranes including the New England Province via Lu-Hf isotopes and found to be of similar isotopic signatures. By combining U-Pb detrital zircon ages and ƐHf values, I interpret that these sediments were derived from a mixed juvenile magma source associated with a fairly long-lived tectonic system (300-92 Ma) on the east coast of northern Australia.

In addition to this, multiple populations have been identified from other, older easterly sources (330 -900 Ma) including but not limited to the Macrossan, Anakie, Cape River, Greenvale and Georgetown Provinces. Small populations of apparently recycled Proterozoic and Archean grains are also variably present in each of the samples. By coupling the above results with the Kolmogorov-Smirnov Test and paleocurrent data, this study provides compelling evidence for sediment input into the Winton Formation from a long-lived continuous subduction margin along the eastern margin of Australia. Eroded materials from this region were transported via transverse fluvial systems westward into the Eromanga Basin and form the principal provenance source for all Winton sandstones investigated in this study. In addition to understanding provenance patterns and refining the age of the Winton Formation, the other primary objective of this thesis was to place the important Winton flora and fauna into a refined palaeoenvironmental context. In order to achieve this, detailed facies and architectural element analysis of both the Winton and the top of the underling Mackunda Formation was conducted and a basin model was developed. Based on a combination of field and core investigation, 23 distinct lithofacies were identified, and these were used to construct nine distinct facies assemblages. The Winton Formation can be informally separated into an upper and lower unit respective of gross changes in depositional patterns, alluvial architecture, and fauna, and confirmed by distinct maximum depositional age constraining zircon populations and a newly constructed basin model. Environmentally, the lower Winton formation preserves the last vestiges of the shallow marine conditions in the Eromanga Basin, and an up section transition from coastal and tidally influenced deltaic strata to alluvial strata. The upper Winton Formation preserves mature floodplain strata, dominantd by a series of stacked channel sandstones with west- to southwest- oriented paleocurrent indicators.

Item ID:	34439
Item Type:	Thesis (PhD)
Keywords:	Australia; Bladensburg National Park; Eromanga Basin; geochronology; Lark Quarry Conservation Park; Lark Quarry Dinosaur Trackway; QLD; Queensland; sedimentation; stratigraphy; Winton Formation
Related URLs:	http://researchonline.jcu.edu.au/33362/
Additional Information:	Appendix 1 (publication) is not available through this repository. Publications arising from this thesis are available from the Related URLs field. The publications are: Romilio, Anthony, Tucker, Ryan T., and Salisbury, Steven W. (2013) Reevaluation of the Lark Quarry dinosaur tracksite (late Albian–Cenomanian Winton Formation, central-western Queensland, Australia): no longer a stampede? Journal of Vertebrate Paleontology, 33 (1). pp. 102-120.
Date Deposited:	06 Aug 2014 06:19
FoR Codes:	04 EARTH SCIENCES > 0403 Geology > 040311 Stratigraphy (incl Biostratigraphy and Sequence Stratigraphy) @ 100%
SEO Codes:	97 EXPANDING KNOWLEDGE > 970104 Expanding Knowledge in the Earth Sciences @ 100%
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