Spatial variation in the stratigraphic architecture of the Fort Cooper and equivalent coal measures, Bowen Basin, Queensland

Abstract

The major stratigraphic units of the Fort Cooper Coal Measures (FCCM) have been reviewed, and an internal coal seam architecture using 500 wireline logs in the Bowen Basin, southeast Queensland has been developed. The subdivisions of the coal measures include the Burngrove Formation, Middle Main Seam and Fair Hill Formation in the northern Bowen Basin. To the south of the basin, the Middle Main Seam is interpreted as the stratigraphic equivalent of Black Alley Shale Formation. The Yarrabee Tuff forms the top boundary of the coal measures and is distributed basin-wide except over the southern Denison and southern Taroom troughs. Accessory tuffs beneath the Yarrabee Tuff aided seam level correlation. The geometries of coal seams have been analysed for each morphotectonic zone of the Bowen Basin using gravity data, which highlight high and low topographic sites. The Collinsville Shelf in northwest of the Bowen Basin comprises thick and merged Burngrove and Fair Hill formation coals that split towards northeast in the Nebo Synclinorium and southeast in Taroom Trough. Coal seams split into daughter seams from north to south and are named as first, second or third order, based on the number of splits that occurred. First- and second-order splitting occurs at the boundary of the Nebo Synclinorium and Collinsville Shelf, at the Narrows of Nebo Synclinorium and Comet Ridge. Further, third- and fourth-order splitting occurs at the boundary of the Comet Ridge and Taroom Trough. Splitting zones found at the junction of morphotectonic zones are related to a change in subsidence. In addition, the association of split seams with coarse grain-dominated interburden reflects increased accommodation in low-lying areas such as the Nebo Synclinorium and the troughs. Thick and coalesced coal seams are associated with shelves and ridges of the basin reflecting low accommodation sites. Hence, the variation in the coal seam architecture of FCCM responds to the subsidence associated with different morphotectonic zones of the basin.

KEY WORDS:

• Bowen Basin
• Fort Cooper Coal Measures
• morphotectonic zone
• subsidence
• splitting
• Burngrove Formation
• Fair Hill Formation
• Yarrabee Tuff

ACKNOWLEDGEMENTS

This study is a major part of the author's PhD thesis on regional stratigraphic variations of FCCM in the Bowen Basin. The author would like to thank QGC-BG Group for supporting the study and providing the confidential and open file dataset for correlations. Also, special thanks to Bruce Anderson from QGC-BG Group, Dr Sandra Rodrigues and Laura Philips from The University of Queensland for their reviews and discussions throughout the study. Thanks also go to Jaime Davidson and Mel Prescott (both QGC-BG Group) for their help with the drafting of some of the figures. The authors are grateful to Dr Christopher Fielding and Dr Adrian Hutton for their productive reviews to improve the manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.