50-Million-Year-Long Record of Glacial to Postglacial Marine Environments Preserved in a Carboniferous–Lower Permian Graben, Northern Perth Basin, Western Australia

The Perth Basin is an intracratonic rift in Western Australia and contains a Carboniferous to Cretaceous infill in excess of 12 km thick. Some 2 km of mid-Carboniferous to Lower Permian glacially influenced marine strata spanning the Serpukhovian to Kungurian (about 50 My), form one of the longest late Paleozoic cold-climate successions preserved anywhere in Gondwana and record the transition from full glacial to postglacial conditions at high (70°) paleolatitudes. The great thickness of the succession reflects an abundant supply of glaciclastic sediment from the adjacent ice-covered Yilgarn Craton and continued subsidence along the Darling–Urella fault system. The oldest part of the basin fill comprises a 1.5-km-thick succession of massive and laminated marine mudstones with striated dropstones (Nangetty Formation) deposited in a fiord-like environment from plumes of suspended sediment, dilute turbidity currents, and icebergs. Meltwater inputs are recorded by erosionally based multistory channels filled with coarse-grained gravity-flow facies (Wicherina Member) deposited on a fan delta along the steep, faulted basin margin. The Nangetty Formation passes upward into a regressive succession of postglacial mudstones (Holmwood Shale) with bioclastic calcarenites and marine macrofossils, capped by sandstone and mudstone facies (High Cliff Sandstone) deposited in a storm-influenced inner shelf setting on the outer margins of coalesced fan deltas along the basin margin. The overlying Irwin River Coal Measures contain a flora that indicates colonization of fan deltas and the Yilgarn Craton by ferns and lycopods. An overlying thick transgressive shale with ice-rafted debris (Carynginia Formation) records renewed subsidence but continuing seasonally cool climates where coarse debris was rafted by ice into a marine embayment. The sedimentology of the Perth Basin highlights the key role of glacial meltwaters in transporting coarse- and fine-grained clastic sediment to marine basins rather than direct glacial processes per se. The equivalent terrestrial record of glaciation and climate change across the Yilgarn Craton at this time is very limited.