Mid-Pleistocene cave fills, megafaunal remains and climate change at Naracoorte, South Australia: towards a predictive model using U-Th dating of speleothems

The limestone caves of the Naracoorte region in South Australia contain ext ensive deposits of megafauna-rich sediments and intercalated cave formation (speleothems). High-precision thermal ionisation mass spectrometry (TIMS) U/Th dating of flowstones directly associated with several large deposits r eveals a distinct cyclicity in the timing of sediment and flowstone deposit ional events in the Naracoorte caves. This pattern parallels a cyclical alt ernation of 'Wet Phases', and intervening periods with a water deficit over the last 500 ka (Ayliffe et al., 1998. Geology 26, 147). Dates from flowst one interlayers in the fossil deposits coincide with the massive speleothem growth events which characterise Wet Phases. Hiatuses in flowstone deposit ion correlatable through several cave systems imply that water deficits wer e initiated by regional aridity during full glacial and then extended into the succeeding warmer, wetter interglacials. Clastic deposits in caverns wi th restricted entrance shafts correlate with hiatuses, suggesting many of t hese deposits contain fauna representative of full glacial and interglacial climates. Caverns with small openings have often been sealed from the surf ace and dating has constrained the length of accumulation episodes in sever al fossil deposits, one to less than 20 ka. The hydrological regimes and en vironmental conditions inferred from the timing of speleothem deposition ha ve been used to develop a model for cyclic sediment and bone accumulation i n the caverns at Naracoorte over the last 400 ka. The giant Victoria Fossil Chamber deposit accumulated prior to 200 ka and because its entrance is la rge it may contain faunas representative of all climatic phases. There has been no apparent change in faunal diversity at Naracoorte over at least thr ee glacial-interglacial cycles of the Middle Pleistocene. (C) 2000 Elsevier Science B.V. All rights reserved.