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.
P., BP), based on measurable physical and chemical qualities or historical associations such as coins and written records.
The date on a coin is an absolute date, as are AD 1492 or 501 in which the proportion of carbon isotopes is counted directly (as contrasted with the indirect Geiger counter method) using an accelerator mass spectrometer.
The method drastically reduces the quantity of datable material required.
SYNONYMS OR RELATED TERMS: amino-acid dating; aminostratigraphy; amino-acid racemization, amino acid racemization CATEGORY: technique DEFINITION: A method of absolute (chronometric) dating which is hoped to fill the gap between radiocarbon dates and potassium-argon dates.
It is used for human and animal bone and other organic material.
Specific changes in its amino acid structure (racemization or epimerization) which occur at a slow, relatively uniform rate, are measured after the organism's death.The basis for the technique is the fact that almost all amino acids change from optically active to optically passive compounds (racemize) over a period of time.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.