The extent of racemization of amino acids in Holocene and Pleistocene marine molluscs in southern South Australia: Preliminary data on a time-framework for calcrete formation
Titel:
The extent of racemization of amino acids in Holocene and Pleistocene marine molluscs in southern South Australia: Preliminary data on a time-framework for calcrete formation
Auteur:
Kimber, R. W. L. Milnes, A. R.
Verschenen in:
Australian journal of earth sciences
Paginering:
Jaargang 31 (1984) nr. 3 pagina's 279-286
Jaar:
1984-09
Inhoud:
A preliminary evaluation of the extent of racemization of a range of amino acids contained in molluscs from fossiliferous marine sediments associated with calcretes has been made for the ultimate purpose of establishing a chronology of calcrete formation in southern Australia. Amino acids detected in molluscs from Holocene and Late Pleistocene marine sediments intersected in trenches cut into alluvial terraces in the valley of the Hindmarsh River at Victor Harbor exhibit distinct d/l ratio differences, as expected from the geological and palaeontological assessment. In addition, the rates of racemization, which are known to vary from amino acid to amino acid, appear to have followed the general order described in the literature. Based on comparitive d/l ratio data for radiocarbon-dated molluscs from a stranded Holocene marine deposit exposed in an excavation 8 km ESE of Robe, an age of approximately 4000 years bp is estimated for the Holocene marine incursion into the Hindmarsh River Valley. The incursion deposited sediments equated palaeontologically with the St Kilda Formation which post-dates the major development of calcretes in South Australia. At this stage we have insufficient amino acid racemization data to speculate on the absolute age of the Late Pleistocene marine incursion into the valley and resulting sediments equated with the Glanville Formation, which commonly in southern Australia exhibits an indurated carbonate crust or is interbedded with calcretes. Further work on the extent of amino acid racemization in molluscs from the Glanville Formation, and from the Early Pleistocene marine deposits (Point Ellen Formation and Burnham Limestone) which predate major calcrete formation in southern South Australia, is in progress.
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