Publication Name: The Canning Basin, W.A.
Authors: W.D.M. Hall
Date Published: December 1984
Number of Pages: 20
Reference Type: Book Section
Abstract:
A Givetian-Frasnian reef complex, 750 m thick, up to 3 km wide and at least 9 km long, is exposed in the Limestone Billy Hills at the northwest end of the Pillara Range. Limestone deposition commenced when an undulating granitic basement topography was gradually submerged and thin bedded, cyclic limestone formed inshallow water. South of the Limestone Billy Hills the shallow water limestone is overlain by deeper water calcarenite and calcareous siltstone which intertongue with small, local bank developments. The main reef complex developed to the north as a thick fenestral limestone which blanketed the palaeotopography and formed a shallow water carbonate platform. The fenestral limestone is overlain by a sequence of upward shoaling cycles commencing with black, organic rich shale and terminating with fenestral limestone. Towards
the platform margins these rocks pass into a boundstone dominated by laminar stromatoporoids and then abruptly into deeper water, calcareous siltstone with interbedded bioclastic debris beds. The cyclic sequence
passes gradationally up into a lower stromatoporoid limestone which becomes gradually more restricted in
extent, and is overlain by a thick, lower reef cap limestone consisting of laminar stromatoporoids, brachiopods, crinoids and Renalcis.
Above the lower reef cap the platform limestones are restricted between narrow, massive, near vertical, Renalcis-rich margins, which are flanked by brachiopod-rich limestones with breccia beds and steep depositional dips. A middle stromatoporoid limestone is overlain by an upper fenestral limestone and an upper stromatoporoid limestone which includes local upper reef cap developments.
The reef complex is covered by an irregular sheet of sedimentary breccia and buried beneath Gogo Formation calcareous siltstone and Virgin Hills Formation pelagic limestone, mudstone and turbidites. A 10 em thick nautiloid bed within the Gogo Formation forms an important stratigraphic, structural and probably time marker over much of the area.
The reef complex dips gently northwards and is cut by a series of north to northeast trending normal faults with vertical displacements locally in excess of 100 m. The termination of a number of faults close to the base of the Gogo Formation where it onlaps the reef complex, variations in the displacement of different stratigraphic units along the same fault and a local unconformity near the western margin of the platform provide evidence for faulting during the later stages of deposition of the reef complex.