Aspartic acid racemisation dating of mid-Holocene to recent estuarine sedimentation in New South Wales, Australia: a pilot study
The degree of aspartic acid racemisation measured in radiocarbon-dated specimens of fossil estuarine molluscs, collected from Lake Illawarra, a Holocene barrier estuary in New South Wales, Australia, is evaluated in the context of results of laboratory-induced racemisation established in heating (simulated ageing) experiments. The general kinetic trend of aspartic acid racemisation in both heating experiments and fossil molluscs Anadara trapezia and Notospisula trigonella conforms to a model of apparent parabolic kinetics. Using the apparent parabolic kinetic model, numeric ages based on the degree of aspartic acid racemisation in the fossil molluscs have been calculated. An aminostratigraphy of the Lake Illawarra Holocene basin fill has been established based on the extent of aspartic acid racemisation measured in 29 specimens of fossil molluscs. Aspartic acid d/l ratios in A. trapezia and N. trigonella range from 0.079F0.005 to 0.436F0.004, representing an age range from b50 to ca. 5750 years. The aspartic acid chronology has been used to quantify rates of sedimentation within Lake Illawarra over the course of the Holocene and since European settlement. The data indicate that, for much of Lake Illawarra, the rate of sedimentation during Holocene time was b1 mm/ year. Following European settlement within the surrounding drainage basin, rates of sedimentation increased significantly to 2.6-7 mm/year.