Chronology and organic chemistry of the Black Creek Swamp Megafauna site (Late Pleistocene), Kangaroo Island, Australia

摘要

The timing of the extinction of the Australian Megafauna and whether it was simultaneous and widespread has been a much researched topic in Quaternary geoscience. The Black Creek Swamp Megafauna site on Kangaroo Island was thought to be a refugium for Megafauna; however, recent and multidiscipline age determinations have established that the fossils are considerably older than the well-quoted extinction age of 45 kyr. Further radiocarbon age determinations, delta 13C isotope analysis and 13C-NMR spectroscopy of the fossil containing organic matter demonstrates that it is highly soluble and accumulated as recently as 31-18 cal. kyr BP. These radiocarbon ages are much younger than the 100-50 kyr age bracket ascertained for the fossil material itself, implying separate episodes of death, deposition and burial. The soluble nature of the organic matter and increasing radiocarbon ages with depth suggests lateral accumulation, probably transported by subsurface waters from elevated areas proximal to the low-lying swamp. Such depositional conditions and 14C age range implies that the site may have experienced an unusually wet Last Glacial Maximum, due maybe to its proximity to the continental shelf and thus to maritime conditions. C3 vegetation dominates the Black Creek Swamp and its organic matter (delta 13C; -30 parts per thousand and -23 parts per thousand); however, variations in delta 13C may indicate climatic shifts. 13C-enrichment and an abundance of salt-tolerant gastropods within the site's final phase of sediment accumulation (< 6 cal. kyr BP) suggest that conditions during this most recent period were not as wet as those of the Last Glacial Maximum.