Late Silurian and Early Devonian biostratigraphy in the Hill End Trough and the Limekilns area,New South Wales

Precordilleran Late Palaeozoic brachiopod genera considered for this palaeobiogeographical analysis belong to four faunal associations: the low diversity Early Carboniferous (Tournaisian) Protocanites scalabrinii-Azurduya chavelensis Zone; the Late Carboniferous (Bashkirian-Moscovian) Levipustula fauna, which appears in sequences associated with glacial intervals; the latest Carboniferous-earliest Permian (Gzhelian-Asselian) Rhipidomella-Micraphelia and Tuberculatella-Aseptella associations, and the Early Permian (mid to late Asselian) Tivertonia jachalensis-Streptorhynchus inaequiornatus Biozone. The brachiopod affinities of the Precordillera are compared with the biogeographical Late Palaeozoic regions previously suggested by other authors using cluster analysis. During the Bashkirian-Moscovian, the Precordilleran faunas show a high affinity with the Austral Realm because of the presence of the Levipustula faunal elements in Eastern Australia. At the same time the affinity with the central and North American Regions is very low. The Early Permian Precordilleran faunas demonstrate highest affinity with the Gondwanan Realm with several genera also linked to the Tethyan and Boreal Realms. After the Late Carboniferous glacial episodes that affected the southwestern Gondwanan margin, the Precordilleran region underwent climatic amelioration. Subsequently, the Early Permian Precordilleran brachiopod assemblages are characterized by typical cool to cold water genera widely developed in the core Gondwanan Realm, with fewer genera (such as Kochiproductus, Rhynchopora and Neochonetes) suggesting a warmer water influence. The Precordilleran faunas demonstrate an increase in brachiopod diversity from the Carboniferous to the Permian, related to water temperature changes and to the palaeogeographical evolution of the southwestern Gondwanan margin and the movement of Gondwana across the South Pole.