Discussion on A progress review of the Hamersley Basin of Western Australia by A. F. Trendall (Bulletin of the Geological Survey of Finland 307, 1980)

Sir, In his paper »A progress review of the Hamersley Basin of Western Australia», Dr. Trendal l (1980, p. 113) aims to provide readers with the knowledge of »which aspects of earl ier accounts may have been superseded» as well as »provide a brief guide to the existing l i terature, par t icular ly for geologists working on the Baltic Shield who may not have ready access to Austra l ian publications». It is wi th similar directives that I am submit t ing this discussion of his paper . Horwitz & Smith (1978) published results indicating that the Hamersley Group was deposited on a submerged Shelf, not in a basin outlined more or less by the present outcrop. The shelf was formed on t h e underlying. Fortescue Group rocks which do not thicken in the centre of a basin. In part icular , we envisaged tha t the Archaean subs t ra tum was domed and tha t there was no shore-line, for ei ther the Fortescue or Hamersley groups, to the southwest against the area now occupied by the Ashburton (Wyloo) Trough. Contrary to references by Trendal l (op. cit. p. 128), these results are independent of the correlation of the Hamersley Basin units wi th those of the Nabberu Basin. The following evidence is submit ted in support of our proposal that the distr ibution of facies and the thickness pat terns agree wi th our model ra ther than tha t of a simple basin. The concept of a shelf environment could modify views on the genesis of banded-iron formations in the Precambrian.