Stratigraphic Signatures of Icehouse Climate Regimes: The Permian Record of Eastern Australia

Fielding, Christopher R.¹, Jonathan Allen¹, Michael C. Rygel¹, Lauren P. Birgenheier², Tracy Frank¹ (1) University of Nebraska-Lincoln, Lincoln, NE (2) University of Nebraska - Lincoln, Lincoln, NE

The late Paleozoic Gondwanan Ice Age (LPGIA) is recorded in thick stratigraphic successions in several basins in eastern Australia. Our work shows that the section can be divided into alternating glacial intervals and non-glacial intervals, each 2-8 m.y. in duration. This division is based on the presence of glacially-related facies only in certain discrete intervals, which can be correlated over c. 1500 km north-south. A total of eight glacial intervals is recognized, four in the Late Carboniferous and four in the Permian. In this paper, we describe the stratigraphy of the nearshore marine to coastal plain Permian succession in the context of this framework. Glacial intervals are typically heterolithic, and characterized by well-developed (third order) sequences. Facies dislocations across basal sequence boundaries typically imply rapid, relative base-level lowering of 50-80 m. Such sequences are typically thin (<10 – 20 m), incomplete (in terms of systems tracts), condensed and top-truncated. Within sequences, higher frequency cyclicity can be seen in some cases, suggesting influences from orbital forcing. Non-glacial intervals, by contrast, are more sandstone-rich, and are not as readily divisible into sequences. Facies boundaries indicate more modest shifts in relative base-level, and parasequence stacking patterns are well-developed in some formations. Contrary to expectations, sequences less than 20 m thick within the Permian succession can be correlated over distances of hundreds of km, and between basins of differing tectonic context. This distinctive stratal architecture is attributed to the low-accommodation regime of the LPGIA, repeated fluctuations in eustatic sea-level of <80 m, isostatic effects, and strongly periodic sediment supply.