Petrologic and stable isotopic study of the Walloon Coal Measures, Surat Basin, Queensland: peat accumulation under changing climate and base level

Stable carbon isotopes of coal show a distinct positive shift in the Lower Juandah Coal Measures that sets in well before the increased inertinite content in the Upper Juandah Coal Measures. The enrichment in 13C could be linked to a change in climate during the high stand depositional cycle, marking the onset of late stage falling, where base level begins to drop, later creating exposures and water stress. A shift to a less humid climate in the Upper Juandah Coal Measures could have favoured the conditions for desiccation, mouldering and bush fires, which is reflected in the coal's maceral composition. The Surat Basin δ13C isotope trend follows the global trend found in marine carbonate samples from the same age interval that corroborates increasing enrichment towards the top of the coal measures (approximately middle Oxfordian), followed by a shift to more negative compositions, which corresponds to the onset of the Springbok Sandstone deposition on an unconformable surface.