SHRIMP zircon age control of Gondwanan sequences in Late Carboniferous and Early Permian Australia

Abstract

Australia during the Late Carboniferous formed part of the Gondwana supercontinent and was close to the South Pole. Resulting continental glacigene deposits and cold water marine sequences in the Southern New England Orogen cannot be correlated biostratigraphically with Late Carboniferous successions in the northern hemisphere because they contain a low diversity biota endemic to Gondwana. Magnetostratigraphic correlation via the Permian-Carboniferous reversed magnetic superchron is presently uncertain. Sensitive high-resolution ion microprobe (SHRIMP) zircon dating of volcanics horizons in the sedimentary sequence of the Southern New England Orogen is now establishing relationships between the Gondwanan faunas and warm-climate European equivalents. In Continental sediments, correlation of the major Gondwanan glaciation of Late Carboniferous Australia is revised from Stephanian to early Namurian-Westphalian in age, a timing that matches that of the Hoyada Verde glaciation in Argentina. A major hiatus of > 15 Ma between Carboniferous rocks of the Southern New England Orogen and Permian rocks of the Sydney Basin of eastern Australia probably reflects the first deformational movements within the accretionary prism of the orogen. Nothorhacopteris, traditionally a Late Carboniferous indicator in Australia, now ranges from late Viséan to Westphalian, and an 'enriched' assemblage, previously correlated with the top of the Nothorhacopteris flora, is confined to the late Viséan to early Namurian. Palynofloras assigned to the Spelaeotriletes ybertii/Diatomozonotriletes birkheadensis Zones (Namurian-early Westphalian), are now confined to the Namurian, and a mid to late Westphalian age is indicated for a more diverse palynoflora identified as uppermost D. birkheadensis Zone (? = Asperispora reticulatispinosus Zone). In the cold climate marine sequence, the Levipustula levis brachiopod Zone appears to be confined to the early Namurian, and so partly corresponds in age to the continental glaciation. Show more