Greta Coal Measures in the Muswellbrook Anticline area, New South Wales

Abstract

The Greta Coal Measures are the lower of two main coal‐bearing intervals in the Permian northern Sydney Basin. High quality outcrop and continuous core data are available from the Muswellbrook Anticline area in the Hunter Valley, enabling a sequence‐stratigraphic interpretation of the Greta Coal Measures to be presented for the first time. Age and core relationships indicate an unconformity at the base and the top of the Greta Coal Measures. A correlation between dated tuffs in the upper Greta Coal Measures in the Muswellbrook area and the Maitland Group in the Cessnock area establishes a clear diachronous upper boundary for the Greta Coal Measures resulting from a northwest‐ward marine transgression. The Greta Coal Measures are interpreted to occupy a single sequence in which the lower fluvial and lacustrine Skeletar Formation makes up a transgressive systems tract, the Ayrdale Sandstone Member is an estuarine unit around the maximum flooding surface, and the upper fluvial to deltaic Rowan Formation occupies a highstand systems tract. The overlying Jasdec Park Sandstone Member of the Maitland Group infills incised valleys above a sequence boundary and then occurs as a transgressive shoreline system before passing into the glacial marine Branxton Formation. The Greta Coal Measures represent high accommodation where subsidence and sediment supply were approximately balanced over more than 100 m of accumulation, and the development of 14 recognisable coal seams occurred in a single sequence.