Oxic facies and the Late Devonian mass extinction, Canning Basin, Australia

The close association of anoxic or dysoxic sedimentary rocks and the major Late Devonian (Frasnian-Famennian) mass extinction has focused considerable attention on anoxia as the major cause or as a major factor in a multicausal scenario. The record of the Late Devonian biotic crisis in the well-known reef complexes of northwestern Australia (Canning Basin), in contrast to many localities elsewhere, does not display sedimentological evidence of anoxia through the Frasnian-Famennian boundary interval. Analysis of continuous drill core through this interval has yielded three positive delta (super 13) C isotopic excursions, only one of which coincides with total organic carbon (TOC) maxima in our data. Multi-element geochemical proxies suggest that TOC maxima preceding positive shifts in delta (super 13) C most likely resulted from higher productivity caused by nutrient influx from continental weathering, given the close association between TOC maxima and regional relative sea-level falls. Our interpretation supports the view that anoxia was not a fundamental driver of mass extinction and stresses the importance of integrated data sets and understanding regional controls on environmental changes and/or stresses.