Abstract

Late Givetian to late Famennian reef complexes are well exposed in rough limestone ranges for about 180 miles along the northern margin of the Canning Basin. They have undergone relatively little tectonic disturbance since deposition.

Reef, back-reef, fore-reef, and inter-reef facies are recognized. The reef and back-reef deposits together make up limestone platforms which stood some tens to hundreds of feet above the surrounding inter-reef basins. They are from a few acres to hundreds of square miles in area, and may be 3,000 feet or more thick.

Most of the reef complexes grew on Precambrian rocks, along the mainland shore of the Kimberley Block, around islands, and on submerged ridges. One reef complex grew on Ordovician dolomite.

Each platform is normally rimmed by a narrow reef, which is commonly 100 to 1,000 feet wide, but is discontinuous in some areas. The reefs were built up by blue-green algae, stromatoporoids, and corals. Dolomitization is common. The back-reef deposits were laid down in very shallow shelf lagoons and consist of well-bedded stromatoporoid, algal, coral, and oolitic limestones.

The fore-reef facies was derived principally as talus from the platforms. Depositional dips are often as high as 30 to 35 degrees. The inter-reef facies is composed mainly of terrigenous sediments.

The reef complexes are overlain conformably by the Fairfield Formation, a late Famennian to Tournaisian sequence of shale, limestone and sandstone.

Masses of terrigenous conglomerate interfinger with the reef complexes in some areas, while in others the Devonian rocks are overlain unconformably by similar conglomerates of probable Permian or Carboniferous age.