Publication Name: The Canning Basin, W.A.
Authors: A.J.W. Gleadow and I.R. Duddy
Date Published: December 1984
Number of Pages: 22
Reference Type: Book Section
Abstract:
Fission track dating of detrital apatites recovered from sediments in hydrocarbon exploration wells in the northwestern Canning Basin shows two distinct trends in apatite annealing behaviour. One trend is the normalreduction in fission track length and apparent age expected in old detrital apatites from increasing temperatures encountered after burial. The other demonstrates the importance of widespread thermal effects associated with dolerite intrusions of late Permian age. The thermal affects are not confined to the immediate vicinity of the dolerite sheets but have produced temperatures in the oil window over a large area.
In Perindi-1 apatites from a thick dolerite sill intruding the Grant Formation in Perindi-1 give a minimum age of about 255 Myr for the time of emplacement and a maximum is given by the age, ?275 Myr, of the youngest sediments intruded. Temperatures in the vicinity of the dolerite, and up to at least 500 m above it, were sufficient to completely erase all pre-existing fission tracks from detrital apatites in the sediments. Similar patterns of fission track age and length were observed in apatites from other wells, such as Fraser River-1 and Wamac-1, which also have dolerite intersections, probably of similar age.
Samples from the Poole and Grant Formations in Kambara-1, where no dolerite was intersected, also have apatite ages which indicate a thermal event of similar age to the dolerites in Perindi. The apatite age and track length data indicates that temperatures reached in these formations in Kambara-1 were lower than those reached in Perindi but still in excess of 90 to ll0?C for some millions of years. Even weaker track annealing effects
were detected in Grant Formation samples in Curringa-1, to the east of Kambara and Perindi, which are consistent with a mild thermal event of similar age. Deeper samples in this well show a sharp change in apatite age over a narrow range of present temperatures probably caused by the effects of burial prior to erosion
represented by unconformities in the sequence.