Stratigraphic Architecture and Coal Character of Late Permian Fort Cooper Coal Measures, Bowen Basin, Queensland
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Stratigraphic Architecture and Coal Character of Late Permian Fort Cooper Coal Measures, Bowen Basin, Queensland Syeda Areeba Ayaz B.Sc (Hons.) (Geology) – University of Karachi M.Sc. (Geology) – University of Karachi A thesis submitted for the degree of Doctor of Philosophy at The University of Queensland in 2015 School of Earth Sciences Abstract This research investigates the tuffaceous Late Permian Fort Cooper Coal Measures (FCCM) and their equivalents of the Bowen Basin. The interbedded and high ash nature of the coals has reduced their economic attractiveness but during the course of this thesis, exploration drilling for metallurgical coal and coal seam gas escalated, providing an opportunity to revisit the FCCM stratigraphy, sedimentary environments and coal character across the basin. This study establishes a regional stratigraphic architecture across the basin using 500 open file wireline logs and examines the controls on coal seam geometry and the sedimentary palaeoenvironment of coal and clastic strata. Four marker tuff horizons were recognised regionally, including the Yarrabee Tuff that acts as the upper stratigraphic boundary of the FCCM from the Rangal Coal Measures. Regionally, the FCCM passes from north to south into the coal-bearing upper Burngrove and lower Fair Hill formations, separated by the marine-derived Black Alley Shale in the southern Bowen Basin. In this study, a sequence of coals, named the Middle Main Seams was recognised as the northern equivalent of the Black Alley Shale. Internal coal seam architecture follows the morphotectonic zones of the basin where thick, coalesced seams are associated with areas of low accommodation, while seam splitting and thinning are associated with high accommodation. The tuff horizons were dated using the CA-IDTIMS technique (Chemical Abrasion-Isotope Dilution Thermal Ionization Mass Spectrometry) to validate the correlations and calculate sedimentation rates in different parts of the basin. The Yarrabee Tuff dated at a range of 252.69 ± 0.16 Ma - 253.07± 0.22 Ma. Three accessary tuffs within the Burngrove Formation have an upper range of 252.85 ± 0.16 Ma – 253.12 ± 0.12 Ma and a lower range of 253.57± 0.18 Ma – 253.77 ± 0.17 Ma. This places them into the upper Changhsingian Stage. One of the accessary tuff from the Fair Hill Formation has an age of 254.03 ± 0.03 Ma and belongs to the lower Changhsingian Stage. The tuff dates were used to calculate sediment accumulation rates in different parts of the basin, taking into account differential compaction of sediment type. The Burngrove Formation had consistently higher rates of 234.5 - 224.5 m/Ma in the Taroom Trough and lower rates of 112 m/Ma in the Roma Shelf, corroborating the variable accommodation setting across the basin. Stratigraphically, the lower Fair Hill showed much higher decompacted sediment accumulation rates at 902m/Ma than the Burngrove Formation at 234.5 m/Ma, representing an upward decrease in accommodation space. This resulted in the southerly progradation of these and the overlying alluvial Rangal Coal Measures in response to shedding from the rising Hunter- Bowen Orogeny that was active during the evolution of the Bowen Basin. ii The rank of the FCCM coals in the southern part of the basin is found to increase eastwards coincident with increasing depth of burial. Unusually high ranks at present-day shallow depths are interpreted to have resulted from deeper thrust loading during the Triassic closure of the basin, followed by hydrothermal activity and magmatism. Tuff frequency declines but the thickness of successive ash falls increases upwards through the Burngrove Formation. This possibly represents intensified volcanism, else more open mire landscapes that could preserve the volcanic ash. Although the coals appear dull and relatively thinly banded in hand sample, compositionally, they are high vitrinite (80-90% mmf) in the Fair Hill Formation and Middle Main Seams (the landward equivalent of the Black Alley Shale) with increasing inertinite content (30% mmf) in the Burngrove Formation. Although subtle in some wells, this may be interpreted to represent increasing aridity in the atmosphere, else follow increased fluctuation in water table as the coal measures prograde southward. Stable carbon isotope (δ13C) analysis of coal shows an overall 13C-enrichment from the Fair Hill through the Middle Main Seams and lower part of the Burngrove that reverts to negative in the top seams of the Burngrove Formation and overlying Rangal Coal Measures. The 13C-enrichment is not coupled to the increased inertinite and in fact shows an inverse relationship at the end of the coal measures. This supports previous findings that atmospheric δ13C values responded to global climatic changes, specifically due to the release of methane hydrates before the Permo – Triassic boundary events. A small part of the thesis investigates gas content variation in the FCCM. From available data, gas content increases directly with coal rank, up to 40m3/t on a dry ash free basis. Gas isotope analysis shows a thermogenic origin of methane, confirming the coal measure as a self- sourcing reservoir. Thinly banded, vitrinite-rich and gassy seams of the FCCM can be considered as a potential CSG target but the great depths and structurally complex areas may reduce permeability and target areas for successful gas production. 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, 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 research higher degree 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, I 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. iv Publications during candidature Peer-reviewed journal papers: Ayaz, S.A., Esterle, J.S. and Martin, M.A., 2015. Spatial variation in the stratigraphic architecture of Fort Cooper and equivalent coal measures, Bowen Basin, Queensland. Australian Journal of Earth Sciences, 62(5): 547-562. Ayaz, S.A., Rodrigues, S., Golding, S.D. and Esterle, J.S., in press. Composition and palaeoenvironment of the volcanolithic Fort Cooper Coal Measures, Bowen Basin, Australia. International Journal of Coal Geology. doi:10.1016/j.coal.2016.04.007 Conference papers: Ayaz, S.A., Esterle, J.S. and Martin, M.A., 2015. Stratigraphic architecture of the Fort Cooper and Equivalent Coal Measures, Bowen Basin. In: Beeston, J.W. (Editor), Bowen Basin Symposium 2015-Bowen Basin and Beyond. The Geological Society of Australia Inc. Coal Geology Group and Bowen Basin Geologists Group, Brisbane, pp. 165-170. Conference abstracts: Ayaz, S.A., Martin, M.A., Esterle, J.S., Amelin, Y. and Nicoll, R.S., 2014. Age of the Yarrabee Tuff Member and its significance towards regional stratigraphy of the Fort Cooper Coal Measures. Australian Earth Sciences Convention 2014, Newcastle. Ayaz, S.A., Martin, M.A. and Esterle, J.S., 2014. Regional variation in stratigraphic architecture of Fort Cooper and equivalent coal measures, Bowen Basin. Australian Earth Sciences Convention 2014, Newcastle. Ayaz, S.A., Esterle, J.S., Rodrigues, S. and Martin, M.A., 2014. Spatial variation in character and composition of the Fort Cooper Coal Measures in Bowen Basin. 31st Annual meeting of the Technical Society of Organic Petrology 2014, Sydney. Ayaz, S.A., Esterle, J.S. and Golding, S.D., 2015. Response of ancient plants to atmospheric nd CO2 levels and associated climatic changes. 32 Annual meeting of the Technical Society of Organic Petrology 2015, Indonesia. v Publications included in this thesis Ayaz, S.A., Esterle, J.S. and Martin, M.A., 2015. Spatial variation in the stratigraphic architecture of Fort Cooper and equivalent coal measures, Bowen Basin, Queensland. Australian Journal of Earth Sciences, 62(5): 547-562. - Incorporated as Chapter 3 Contributor Statement of contribution Ayaz S.A. (Candidate) Compiled well data (100%). Correlated well data (100%). Interpreted well data (100%). Wrote the paper (100%) Esterle, J.S. Reviewed the paper (50%). Martin, M.A. Reviewed the paper (50%). Ayaz, S.A., Rodrigues, S., Golding, S.D. and Esterle, J.S., in press. Composition and palaeoenvironment of the volcanolithic Fort Cooper Coal Measures, Bowen Basin, Australia. International Journal of Coal Geology. - Incorporated as Chapter 5 Contributor Statement of contribution Ayaz S.A. (Candidate) Compiled the data (100%) Analysed the data (70%). Wrote the paper (100%) Rodrigues, S. Assisted in data analysis (15%). Reviewed the paper (50%) Golding, S.D. Assisted in data analysis (5%). Reviewed the paper (20%) Esterle, J.S. Assisted in data analysis (10%). Reviewed the paper (30%) vi Contributions by others to the thesis Professor Joan Esterle (Principal PhD Advisor) has contributed towards the design of the project, sampling strategy for different experiments, obtained a scholarship from QGC-BG Group for research costs, reviewed, and edited the manuscripts that formed the part of this thesis.