Rangal Supermodel 2015

Abstract

More than 6,000 boreholes were compiled to develop a consistent regional scale stratigraphic framework for the Permian Rangal, Baralaba and Bandana coal measures (CMs) within the Bowen Basin. Coal beds and tuff horizons were used as stratigraphic markers, supported by chemostratigraphy and age dating. Results corroborate the general subdivisions of these different coal measures relative to basin location, but increase resolution on migrating depocentres in response to foreland loading and subsidence on coal thickness and splitting patterns. In the north, the Rangal CMs comprise two main seams, correlated as Leichhardt and Vermont. The Yarrabee Tuff is consistently present and splits the Vermont seam. The main Leichhardt seam exhibits relatively simple offset stacking relationships with the underlying Vermont and overlying Phillips seams. In the southwest, the Bandana CMs comprise two to three significant seams—the Aries-Castor, Pollux (Leichhardt equivalent) and Orion—along with the Pisces containing the Yarrabee Tuff. Seams exhibit complex Z splitting and vertical interburden stacking. Locally super-thick seams (crabs) form from convergence of thinner split seams in areas of relative stability over basement highs. In the Taroom Trough, the Baralaba CMs show the greatest response to loading, as seams thin and split along the eastern margin. The variability in the splitting patterns, coupled with the coal measures total thickness, corroborate the extension of the final basin depocentre northward, which was not preserved.

Environmental change in the late Permian of Queensland, NE Australia: The warmup to the end-Permian Extinction

“…The Bandanna Formation records basin-wide establishment of coastal alluvial plain conditions (Fielding et al, 1993;Sliwa et al, 2017;Fig. 14), with a transgressive interval in the middle of the formation that suggests the axial depocenter of the Taroom Trough became an elongate, estuarine gulf opening to the south for a time (Fielding, 2015).…”

“…The Peawaddy Formation was the subject of a thesis by Belcher (1990), and its equivalents in the northern Bowen Basin were documented by Falkner and Fielding (1993), , Esterle and Sliwa (2002), and Ayaz et al (2015Ayaz et al ( , 2016. The sedimentology of the Black Alley Shale remains largely undescribed, whereas that of the uppermost Lopingian, coal-bearing Bandanna Formation/Rangal Coal Measures has been described by numerous researchers (Beeston and Draper, 1991;Fielding et al, 1993;Stuart et al, 2014;Fielding, 2015;Sliwa et al, 2017).…”

“…4) is used as a standard reference section herein, because it provides continuous, high quality data coverage from the lower Peawaddy Formation to the top of the Permian succession and because several high-precision CA-ID-TIMS ages from tuffs were acquired from this core (Metcalfe et al, 2015). Fielding et al (1997aFielding et al ( , 2019a and Sliwa et al (2017). D. = Dienerian, G. = Griesbachian, Ind.…”

“…7,8,12D). Above this, a distinct, fissile mudrock unit ("Marker Mudstone"; Sliwa et al, 2017;Wheeler et al, 2020) is preserved at many localities and is overlain by interbedded mudrocks with subordinate sandstones that preserve few if any faunal trace fossils, and progressively change in colour upward from drab grey to green, brown, and ultimately red hues. Most older stratigraphic schemes place the end of the Permian succession at the top of the Bandanna Formation at its contact with the overlying Rewan Group.…”

“…Palaeogeographic maps to show interpreted depositional environments across the Bowen Basin during the accumulation times of the 1, Peawaddy Formation (C); 2, Black Alley Shale (D); and 3, Bandanna Formation (E). From Sliwa et al (2017), modified after Fielding et al (2000).…”