"Over 40,000 atoms counted this year."
COSMOGENIC CHLORINE-36 EXPOSURE AGES FOR TWO BASALT FLOWS IN THE
NEWER VOLCANICS PROVINCE, WESTERN VICTORIA
J. Stone, J.A. Peterson, L.K. Fifield and R.G. Cresswell
Proceedings of the Royal Society of Victoria 109, 121-131. (1998)
An exposure dating method based on the accumulation of cosmic-ray-produced
Cl-36 has been applied to samples from the Newer Volcanics Province of
western Victoria. Cosmogenic Cl-36 concentrations indicate exposure ages
of approximately 32 kyr BP for the Harman Valley basalt flow from Mt Napier
and 59 kyr BP for the basanite ring barrier at Mt Porndon. The results
extend the chronology of volcanism at these sites back in time beyond minimum
age limits so far obtained from C-14 dating of overlying peat deposits.
The older ages imply slower rates of soil development on basalt and for
re-establishment of drainage systems disrupted by eruptions, and suggest
that both processes may also have been influenced by colder and more arid
Late Pleistocene climatic conditions. Exposure dating complements dating
methods based on soil maturity and C-14 and may be applied to good effect
on other young volcanic rocks in eastern Australia. In particular, there
is scope for dating material either too old to be dated with C-14 or lacking
associated carbonaceous material, yet too young to be dated with the K-40/Ar-40
or Ar-40/Ar-39 methods.