The contributions of uranium/thorium and marine palynology to the dating of the Lake Wangoom pollen record, western plains of Victoria, Australia

Abstract

Abstract An extended pollen record from Lake Wangoom provides clear evidence for two climatic cycles incorporating three major effective precipitation peaks. The existing radiocarbon dates and age estimates derived from uranium/thorium dating and correlation with the pollen sequence from an isotopically-dated marine record presented here provide conflicting chronologies for these cycles. The radiocarbon dates indicate the youngest and middle precipitation peaks correspond, respectively, to the Holocene and the last major interstadial (oxygen isotope stage 3). By extrapolation, the oldest peak correlates most closely with substage 5c. Uranium/thorium disequilibrium dates suggest both the middle and oldest precipitation peaks occur within the isotope stage 5 complex, the middle phase corresponding with an interstadial and the oldest with the height of the Last Interglacial. The most reliable chronology, at least for the later cycle, is considered to be provided by comparison with the pollen record from a marine core with an oxygen isotope sequence from offshore Victoria. This record indicates that the last time precipitation levels attained those of the Holocene was during the Last Interglacial period and suggests that the Wangoom record extends back to the penultimate interglacial of isotope stage 7.