A mid-Permian (late Kungurian) micro-dolerite dyke/sill complex located at Kinghorn Point intruded into the then unconsolidated upper Wandrawandian Siltstone of the lower Shoalhaven Group, southeastern Sydney Basin. The dark grey siltstone was deposited in the deeper part of a coastal seaway characterised by northward-directed paleocurrents, with a Cruziana ichnofacies, crinoid stem fossils and abundant glendonites indicating a cold climate. Thin periodic storm deposits, or tempestites, of fine-grained sandstone of volcanogenic origin are scattered through the siltstone. These paler sandy beds were probably derived from island volcanoes to the south or southeast, indicating that regional volcanism was pervasive during this glacial episode. Evidence for penecontemporaneous igneous emplacement into mid-Permian wet unconsolidated shallow marine sediments includes: destruction of primary sedimentary structures caused by extensive interaction and intermingling between the sedimentary and ig
The Permian of the southern Sydney Basin (Australia) comprises both marine and non-marine sedimentary sequences with evidence of glacial deposition and syndepositional magmatism represented by tuffs, lava flows and hypabyssal intrusions. This succession has been well-studied in lithostratigraphy and sedimentology, but the Lower-Middle Permian chronostratigraphy remains poorly constrained due to a lack of radiometric isotope ages and strong faunal endemism. In this study, we report the first suite of reconnaissance U–Pb zircon ages from this succession, comprising two Wandrawandian Siltstone (WS) tuffs (Green Point tuff 272.6 ± 6.5 Ma population, Callala Bay tuff ≥290 Ma Permian populations) and magmatic zircon ages from three discrete syndepositional intrusions: the Termeil Complex intruding the Snapper Point Formation dated 278.9 ± 3.7 Ma (95% confidence), the Milton Complex intruding the Snapper Point Formation and likely the WS dated 275.5 ± 4.3 Ma, and a dyke/sill at Kinghor