The Upper Permian sedimentary successions of the southern Sydney Basin have been the subject of several stratigraphic, sedimentological, and petrographic studies and more recently several studies dating the sedimentary succession using U-Pb zircon and 40Ar-39Ar geochronology. In this study the Broughton Formation of the Lower Permian, part of the upper Shoalhaven Group succeeding the Talaterang Group and underneath the Illawarra Coal Measures was studied. The Broughton Formation is part of a Permian retroarc depositional basin within the Southern Sydney Basin (SSB) which is unconformable on the Lachlan Fold belt to south and west, and in tectonic contact with the New England Fold Belt to the north and east. The chronology of the Upper Permian of the SSB is well constrained. However, the chronology of the Lower Permian of the SSB, including the Broughton Formation, is less well constrained. Thus, there is debate over the timing and absolute length of several glacial and interglacial cyc
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 orientation, petrography and geochemistry of numerous basaltic dykes between Kiama and Gerroa were investigated in this study. Geochemical analysis shows that the dykes range from sub-alkaline to alkaline in composition. The dykes fit into three distinct geochemical groups, with most being transitional from alkali basalts to foidites, followed by alkali basalts and lastly andesites/basaltic andesites. We suggest that three intrusive episodes occurred based on petrographic analysis and geochemical classification. The dykes contain phenocrysts of olivine, plagioclase and clinopyroxene in a fine-grained groundmass. Multiple microtextures were found, including porphyritic, glomeroporphyritic, amygdaloidal, aphanitic and intergranular. Most dykes strike northwest–southeast, two strike east–west, and four strike northeast–southwest. One dyke to the south of Boat Harbour Reserve contains numerous xenoliths, including gabbroic, granitic and charnockitic types. The gabbroic xenoliths