Post-glacial climate amelioration recorded in the early Permian Aramac Coal Measures (Galilee Basin, Australia)

The end of the Late Palaeozoic Ice Age (LPIA) was characterized by the development of widespread peat-forming mires across Gondwana concurrently with the evolution of the Glossopteris­-flora. The Aramac Coal Measures in the Galilee Basin of Australia represent some of the early phase of humic peat formation following the deglaciation in an ameliorating climate. This work aims to examine two boreholes using a multidisciplinary approach involving palynology, coal petrology, carbon isotope geochemistry and biomarkers to reconstruct the climate, environment and floras of this post-glacial period.

Palynostratigraphy suggests a late Artinskian to early Kungurian age for the Aramac Coal Measures separated from the overlying JK seams by an unconformity. Small-scale sedimentary dykes and cryostructured palaeosols suggest the peats would have formed under permafrost conditions. Palynological assemblages display a typical mix of early Permian elements and remnants of the Carboniferous floras with striate bisaccate pollen representing glossopterids, monosaccate pollen representing cordaitaleans, and spores representing herbaceous ferns, lycopsids and horsetails. Maceral analysis of the coals show high inertinite values, which, along with pristane/phytane ratios indicate an oxidative environment in which the peats were influenced by fire and/or fungi and bacteria. Stable carbon isotope values are typical for terrestrial environments (-22‰ to -26‰) but show an apparent cyclicity that may be related to climatic fluctuations following the end of the glaciation. This indicates the rise of the Glossopteris-flora was a gradual process which may have been influenced by warm and cool climatic phases well into the Permian.