Devonian Algal Stromatolites from Canning Basin, Western Australia: ABSTRACT

Abstract

Algal stromatolites are present in the reef, backreef, and forereef facies of Devonian reef complexes in the Canning basin of Western Australia. The most varied of these forms are in the forereef facies, where they grew on slopes as steep as 55° and in places that were at least 45 m below sea level. These occurrences negate the common belief that algal stromatolites are diagnostic of intertidal and near-intertidal environments. Sediment-binding stromatolitic algae played an important role in maintaining the steep upper parts of the forereef slopes. Forms represented in the forereef facies are described as columnar, longitudinal, undulatory, contorted-bulbous, mound-shaped, planar, reticulate, and nodular stromatolites. Nonskeletal algae are believed to have been dominant in forming these stromatolites, but recognizable skeletal species (especially of the genera Sphaerocodium, Girvanella, Frutexites, and Pleurocapsites) also are present, and bacteria may have contributed to certain forms. Holdfasts of crinoids and corals are encrusted on some stromatolites, and other conspicuous elements of the associated open-marine fauna include ammonoids, nautiloids, and conodonts. Stromatolites in the reef and backreef facies are generally irregular columnar types, commonly showing birdseye textures. Oncolites are also common in parts of the backreef facies. The reef and backreef stromatolites are believed to be analogous to modern intertidal and near-intertidal forms. End_of_Article - Last_Page 645------------