Establishing a chronology for the last 1000 years of laminated sediment accumulation at Lake Barrine,a tropical upland maar lake,northeastern Australia

Abstract

Radiocarbon dates from the uppermost 115 cm of laminated mud beneath the centre of a small crater lake are affected by the residence-time in the marginal shallows of the organic detritus which, after transport to deep water, forms alternate layers in the sediment column. The delay is estimated from radiocarbon ages of source materials, trapped seston and the upper levels of the sediment column based on the ‘post-bomb’ atmospheric radiocarbon flux. The ‘contaminating’ component does not reside uniquely in any specific fraction of a mud sample, defined by alkali solubility and particle size, but is generally associated with the detrital layers. The lead-210 method, together with proxy indications from charcoal, exotic Solanum pollen and meteorological correlations, effectively replace radiocarbon for the dating of the sediment column from ad 1987 back to 1965. Beyond that, the selection of the youngest radiocarbon age from those in each of eight depth intervals leads to an acceptable estimate of accumulation rate to ad 1060.