The use of stable carbon isotope trends as a correlation tool: an example from the Surat Basin, Australia
Astrid Hentschel A , Joan S. Esterle A and Sue Golding AThe University of Queensland
The APPEA Journal 56(1) 355-368 https://doi.org/10.1071/AJ15026
Published: 2016
Abstract
The Surat Basin’s Middle Jurassic Walloon Subgroup is a productive coal seam gas source in Queensland, Australia. The Walloon Subgroup can be subdivided into the Upper and Lower Juandah coal measures, the Tangalooma Sandstone, the Taroom Coal Measures, and the Eurombah/Durabilla Formation, from top to bottom.
Correlation across the basin is challenging due to high lateral variability and lack of extensive stratigraphic markers. The Walloon Subgroup is also, in places, incised by the overlying Springbok Sandstone, sometimes interpreted as far down as the Tangalooma Sandstone.
New age dates suggest that the Walloon Coal Measures are Oxfordian in age and mark a period of high rates of Corg production and burial, and an intermittent decrease of atmospheric pCO2. The un- or dis-conformable base of the Springbok Sandstone coincides with a turning point of this supposedly global phenomenon.
This study uses organic stable carbon isotope trends as a correlation tool within the Surat Basin’s Walloon Subgroup and its overlying Springbok Sandstone. Analysis of a stratigraphic suite of coal samples from several wells across the Surat Basin shows a gradual enrichment in 13C up section from the Taroom to the Lower Juandah Coal Measures, with the most positive δ13C values within the Upper Juandah Coal Measures. Thereafter there is a rapid reversal to more negative δ13C values for coal samples of the Springbok Sandstone. The upward enrichment occurs well before the shift in maceral composition to increased inertinite content in the coals, suggesting more global allogenic processes are controlling the carbon isotopic trend. The consistency of these trends lends a more confident correlation for sub-units within the Walloon Subgroup, and assists in determining the level of incision disconformity of the Springbok Sandstone.
Astrid Hentschel received her BSc and MSc degrees in resource management from Aachen University of Technology (Germany). Her BSc thesis focused on the depositional history and petroleum generation potential of Toarcian Posidonia Shale in Luxembourg, which provided a great insight into petrography and geochemistry. Astrid worked on her MSc thesis at UQ, focusing on coal petrography and stable isotope geochemistry of the Surat Basin’s Walloon coals and coal bed methane. Following this, Astrid started her PhD at UQ in 2014, evaluating changes in coal and the interburden character within the Surat Basin’s Walloon Subgroup and its transition into the Eromanga Basin’s Birkhead Formation. a.hentschel@uq.edu.au |
Joan Esterle joined UQ full time in 2010, taking up the chair of the Vale-UQ Coal Geoscience Program. The group has grown, with six senior researchers and some 20 under-and post-graduate students working across a range of projects in 2015. Joan’s main research questions focus on geological controls on the origins and distribution of gas in coal, gas and coal production, overburden geotechnical variability, and coal material properties. These applied research projects are underpinned by a fundamental understanding of peat and coal formation. Her projects are supported through the Australian Coal Association, the Centre for Coal Seam Gas, the Australian Low Emissions Coal fund, the Department of Natural Resources and Mines, and a suite of companies. Further information about Joan’s research is available on <www.uq.edu.au/energy/esterle>. Joan received her PhD from the University of Kentucky. j.esterle@uq.edu.au |
Sue Golding is a Professor in the School of Earth Sciences at UQ, with more than 30 years of experience in the application of geochemistry to the origin of resources in sedimentary basins. An important research focus is in the area of energy and environmental technologies for the coal seam gas and mining industries, which rely on the use of natural isotopic tracers to understand geochemical and hydrochemical processes. Sue is Director of UQ’s Centre for Geoanalytical Mass Spectrometry and Isotope Science (CGMSIS) that comprises the Radiogenic Isotope Facility, the Stable Isotope Geochemistry Laboratory, and the Environmental Geochemistry Laboratory. She has published more than 150 peer-reviewed journal articles and book chapters, and edited a pioneering text on CSG entitled Coalbed Methane: Scientific, Environmental and Economic Evaluation. Sue received her PhD from UQ. s.golding1@uq.edu.au |
