Chronology and stratigraphy of the Wet Cave vertebrate fossil deposit, Naracoorte, and relationship to paleoclimatic conditions of the Last Glacial Cycle in south-eastern Australia

Abstract

The Wet Cave vertebrate fossil deposit of the Naracoorte Caves in south-eastern South Australia contains a rich and diverse assemblage of small mammal fauna known to span the Upper Pleistocene–Holocene. Here, we describe five previously unidentified in situ units (A, B, C, E and F) and one likely reworked unit (D) in the Wet Cave sedimentary profile, which are correlated with paleoclimatic conditions associated with the Last Glacial Cycle. Additional radiocarbon dates presented here provide a finer temporal resolution for the upper sections of the sequence than previously available and reveal rapid deposition of polished quartz sands laminated with brown silts during the last glacial maximum (LGM). Change in sediment type and depositional processes are dated from 16.8 to 16.4 k cal y BP and are associated with the onset of deglaciation. The characteristics of the five in situ depositional units are similar to those identified from the contemporaneous fossil and sedimentary sequence of Blanche Cave 3rd Chamber, located approximately 400 m away, reflecting interactions between paleoclimate, sediment mobility and deposition at this locality. Greater variation is evident between the Wet Cave sedimentary profile and the inner chamber of Robertson Cave, located approximately 6 km away and shows that local processes and cave structure exerted some control on sediment accumulation. Paleoclimatic inferences from the depositional sequence of Wet Cave are broadly consistent with those inferred from regional landforms for south-eastern Australia but provide a local signal more suitable for cross-correlation of the fossil faunas. In particular, the Wet Cave sequence suggests that local conditions were relatively stable in the lead up to the LGM despite fluctuation in both local and regional effective precipitation. Sedimentary units associated with the post-LGM deglaciation are characterised by alternating sand and sandy-silt layers, assumed to reflect the impact of enhanced seasonality and/or climatic fluctuation leading towards the Holocene.