Investigating the stratigraphy and palaeoenvironments for a suite of newly discovered mid-Cretaceous vertebrate fossil-localities in the Winton Formation, Queensland, Australia

The Winton Formation of central Queensland is recognized as a quintessential source of mid-Cretaceous terrestrial faunas and floras in Australia. However, sedimentological investigations linking fossil assemblages and palaeoenvironments across this unit remain limited. The intent of this study was to interpret depositional environments and improve stratigraphic correlations between multiple fossil localities within the preserved Winton Formation in the Eromanga Basin, including Isisford, Lark Quarry, and Bladensburg National Park. Twenty-three facies and six repeated facies associations were documented, indicating a mosaic of marginal marine to inland alluvial depositional environments. These developed synchronously with the final regression of the Eromanga Seaway from central Australia during the late Albian-early Turonian. Investigations of regional- and local-scale structural features and outcrop, core and well analysis were combined with detrital zircon provenance signatures to help correlate stratigraphy and vertebrate faunas across the basin. Significant palaeoenvironmental differences exist between the lower and upper portions of the preserved Winton Formation, warranting informal subdivisions; a lower tidally influenced fluvial-deltaic member and an upper inland alluvial member. This work further demonstrates that the Isisford fauna is part of the lower member of the preserved Winton Formation; whereas, fossil localities around Winton, including Lark Quarry and Bladensburg National Park, are part of the upper member of the Winton Formation. These results permit a more meaningful framework for both regional and global comparisons of the Winton flora and fauna.