Stromatolites

Stromatolites are key fossils for understanding the evolution of life, since the forms of life that produced most of our more familiar fossils did not evolve until the Cambrian period about 543 million years ago. Stromatolites are the most common fossil in rocks older than about 543 million years, which cover nearly two thirds of Western Australia and contain many of the State's important mineral deposits. In the last two decades, the Geological Survey of Western Australia (GSWA) has developed a scheme for correlating Precambrian rocks using fossil stromatolites, and Western Australia is now a world leader in using stromatolite biostratigraphy on rocks that are otherwise difficult to date.

Stromatolites are known from many areas of Western Australia. They have been recorded from more than 71 of the 163 1:250 000 geological map sheets that cover onshore Western Australia (nearly 44% of the state) (GSWA Catalogue of Maps and Publications), and no other group of fossils has such a widespread distribution throughout the State. In some cases, stromatolite-bearing rocks act as host rocks for mineralisation, and the organisms that form stromatolites are one of the sources of petroleum. Stromatolites are therefore important because they are useful for correlation purposes, for interpreting the nature of the environments in which they formed, for understanding the origin and evolution of life on Earth, and because of their potential role in mineralisation and petroleum formation.

Some of the best examples of living stromatolites are found in Western Australia. The areas in which they grow act as living laboratories where the nature of stromatolitic structures, the environments in which they form, and the processes that form them, can be studied. The results are then applied in interpretations of the palaeoenvironment in the geological record. The extensive development of living stromatolites at Hamelin Pool, Shark Bay, is world renowned, and Western Australia has several other examples of living and recent stromatolites, such as those at Lakes Clifton, Preston, Walyungup, and Richmond, at Pink Lake near Esperance, and in lakes on Rottnest Island.

Western Australia also has the oldest known examples of stromatolites (3.45 billion years old), occurring as fossils in the Pilbara region between Marble Bar and Port Hedland. In addition, Western Australia has one of the most continuous and best-studied records of fossil stromatolites, representing most periods of geological time. The great majority of Western Australian stromatolites are found in Proterozoic rocks (rocks between 2.5 billion and 543 million years old). A great variety of fossil forms have been recorded from the Pilbara, Ashburton, Gascoyne and Kimberley regions, and in the Gibson, Little Sandy and Great Sandy Deserts. Current GSWA projects involving the use of stromatolites include a study of the petroleum potential of the Officer Basin, stratigraphic and palaeoenvironmental interpretations of several groups of rocks in the Pilbara region, and correlations of rock successions in the Kimberley area and the Bangemall, Earaheedy and Yerrida Basins.