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

Abstract

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 δ13C isotopic excursions, only one of which coincides with total organic carbon (TOC) maxima in our data. Multielement geochemical proxies suggest that TOC maxima preceding positive shifts in δ13C 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.