Spatiotemporal Variation in the Permian-Triassic Pre- and Post- Extinction Palynology of the Bowen and Galilee Basins (Australia)
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Spatiotemporal variation in the Permian-Triassic pre- and post- extinction palynology of the Bowen and Galilee basins (Australia) Alexander Thomas Wheeler BSc. (Hons.) (Geology) – Rhodes University MSc. (Geology) – University of Pretoria https://orcid.org/0000-0003-1677-6789 A thesis submitted for the degree of Doctor of Philosophy at The University of Queensland in 2020 School of Earth and Environmental Sciences Abstract Palynology has been used as an important tool for exploration and correlation in the late Permian coal measures of the Galilee and Bowen basins. It has seen less application in studying the floras of these basins and the significant effect of the end-Permian extinction (EPE) on the environment and vegetational ecology. The main objective of this thesis is to understand how depositional environment controlled the distribution and variation in floral assemblages in the late Permian, during the EPE and in the earliest Triassic using palynology as a proxy for vegetation. A marker mudstone was previously examined in the Bowen Basin and is thought to represent a P-T Boundary marker horizon. This thesis also examined a potential correlative of this marker mudstone in the Galilee Basin and assesses its temporal relationship to the EPE and its significance for the interpretation of the end-Permian palaeoenvironment. A secondary objective of this work was to test the efficacy of an acid-free palynological processing technique against the conventional processing that employs strong acids (HCl and HF). This technique was previously only used on Cenozoic-aged material and this represents the first application of it on Palaeozoic-aged samples. Samples were sent for conventional processing to a commercial palynological laboratory and splits of the same samples were processed using the acid- free technique at The University of Queensland. Results show large differences in the palynofacies assemblages between the samples, however both processing techniques yielded relatively comparable and well preserved palynomorph assemblages. The acid-free processing appears to yield lower concentrations of palynomorphs relative to organic debris, but also preserves a higher abundance and more diverse assemblage of algae in these samples. To examine floral variation in the late Permian, samples were selected from five localities representing a shift from a proximal, terrestrial environment to a distal, marginal-marine and shallow- marine environment. Palynological samples were collected from the last Permian marine incursion at the base of the Black Alley Shale up to the top of the Bandanna Formation, which is thought to represent the Permian-Triassic Boundary. Palynological assemblages were assigned putative botanical affinities and examined relative to the lithostratigraphy of each section in order to understand temporal and spatial variance in floras at each locality. Fern spores are dominant in lower delta plain settings along with accessory horsetails and lycophyte spores, suggesting that these pteridophytes formed the pioneer flora on prograding delta lobes, and also made up the understory vegetation in a paludal/lacustrine setting. Glossopteris pollen becomes more dominant on the upper I delta plain and alluvial plain, and also makes up a significant part of paludal palynofloras, suggesting that Glossopteris had a relatively broad environmental tolerance. The distribution of other gymnosperm pollen associated with conifers, cordaitaleans, cycads and potentially peltaspems suggest that woodlands developed on better drained soils on the alluvial and coastal plains, but conifers and cordaitaleans also occur as minor components of forest swamp floras. Dulhuntyispora parvithola, previously identified as an important index taxon for late Permian Australia, appears to be more prevalent in coastal regions, which might limit its utility in more proximal parts of the Bowen and Galilee basins. To examine the marker mudstone in the Galilee Basin, samples were taken from below, within and above this 1 m thick carbonaceous shale at the interface of the Bandanna and Rewan formations for palynological processing and stable carbon isotope geochemistry. Palynofacies results show a distinct shift from the base to the top of the marker mudstone. A well-preserved translucent-phytoclast- dominated assemblage shifts to a near-barren opaque-phytoclast-dominated assemblage, indicating a potential increase in terrestrial input from the hinterland due to higher erosion rates, widespread wildfires or redox changes within the water column. Acanthomorph acritarchs and fungal spores were observed within and above the carbonaceous mudstone. Palynostratigraphy places this marker mudstone in the APP5 (Late Permian) zone with the transition to the APP6 zone occurring several centimetres above the marker mudstone. In the Bowen Basin, the marker mudstone was previously placed in the APP6 zone which suggests that the carbonaceous mudstone in the Galilee Basin is either not a direct correlative or that this unit is time-transgressive across the eastern Australian basins. To examine the variation in the earliest Triassic floras, samples were collected from four localities around the Bowen Basin. Samples taken from the Rewan Group generally yielded low abundances or poorly preserved palynological assemblages and many samples were barren. However, yields were good enough in a sufficient number of samples to show that the shift from the APP5 zone to the APP6 and potentially APT1 zones occurs synchronously above the uppermost Permian coal seam and represents the transition from the Glossopteris-flora to a post-extinction flora. The post-extinction vegetation appears to be made up of peltasperm and conifer-dominated woodlands which sit on the more well-drained, sandier soils of the Rewan Group and a fern-dominated lowland which dominates the margins of water bodies created by base-level rise. Variable algal and acritarch assemblages as well as pyrite pockmarked palynomorphs suggest that these water bodies featured fluctuating salinity, localised anoxia and algal blooms caused by increased nutrient input due to high erosion rates causing increased deposition of organic detritus from the hinterland. Increased levels of UV-B radiation are also inferred due to the presence of mutated pollen grains and unseparated spore tetrads. II The findings of this work indicate that the diverse and widespread Glossopteris-flora was quickly and near-synchronously devastated during the EPE. The new flora consisted of hardy survivors and colonisers previously limited to extrabasinal areas. If the marker mudstone in the Galilee Basin is a facies correlative of the uppermost Permian coal seam, it would suggest that environmental perturbation may have already begun to occur immediately preceding the main extinction event. However, more detailed correlations based on densely spaced palynological sample sets from the uppermost Permian coal seams across the basins would be required to fully examine this. III Declaration by author This thesis is composed of my original work, and contains no material previously published or written by another person except where due reference has been made in the text. I have clearly stated the contribution by others to jointly-authored works that I have included in my thesis. I have clearly stated the contribution of others to my thesis as a whole, including statistical assistance, survey design, data analysis, significant technical procedures, professional editorial advice, financial support and any other original research work used or reported in my thesis. The content of my thesis is the result of work I have carried out since the commencement of my higher degree by research candidature and does not include a substantial part of work that has been submitted to qualify for the award of any other degree or diploma in any university or other tertiary institution. I have clearly stated which parts of my thesis, if any, have been submitted to qualify for another award. I acknowledge that an electronic copy of my thesis must be lodged with the University Library and, subject to the policy and procedures of The University of Queensland, the thesis be made available for research and study in accordance with the Copyright Act 1968 unless a period of embargo has been approved by the Dean of the Graduate School. I acknowledge that copyright of all material contained in my thesis resides with the copyright holder(s) of that material. Where appropriate I have obtained copyright permission from the copyright holder to reproduce material in this thesis and have sought permission from co-authors for any jointly authored works included in the thesis. IV Publications included in this thesis The following publication has been incorporated as Chapter 5: Wheeler, A., Van de Wetering, N., Esterle, J. S. & Götz, A. E. (2020). Palaeoenvironmental changes recorded in the palynology and palynofacies of a Late Permian marker mudstone (Galilee Basin, Australia). Palaeoworld, 29(2), 439-452. DOI: 10.1016/j.palwor.2018.10.005. Contributor Statement of contribution % Project conception and design 60 . Alexander Wheeler Core logging and sample collection 100 (Candidate) Analysis of palynological samples 100 Preparation of Figures 100 Writing of Manuscript 90 Nikola Van de Wetering Stable carbon isotope analysis 100 Writing of Manuscript 10 Reviewed and edited the manuscript 20 Joan Esterle (Principal Supervisor) Project conception and design 40 Reviewed and edited the manuscript 50 Annette