Watsonella crosbyifrom the lower Cambrian (Terreneuvian, Stage 2) Normanville Group in South Australia

Abstract

AbstractCorrelation of lower Cambrian strata is often confounded by provincialism of key fauna. The widespread occurrence of the micromolluscWatsonella crosbyiGrabau, 1900 is therefore an important biostratigraphic signpost with potential for international correlation of lower Cambrian successions. Previous correlations ofW. crosbyifrom Australia (Normanville Group) suggested an Atdabanian- to Botoman-equivalent age. However, in the upper part of the Mount Terrible Formation, stratigraphic ranges ofW. crosbyiandAldanellasp. cf.golubevioverlap prior to the incoming of vertically burrowed ‘piperock’, which is indicative of an age no earlier than Cambrian Stage 2. The stratigraphic range ofW. crosbyiin the Normanville Group, South Australia correlates with the ranges of the taxon in China, France, Mongolia and Siberia (though not Newfoundland). The new Australian data add further support for considering the first occurrence ofW. crosbyia good potential candidate for defining the base of Cambrian Stage 2. The stratigraphic range ofW. crosbyithrough the lower Cambrian Normanville Group has been determined based on collections from measured sections. Although rare,W. crosbyiis part of an assemblage of micromolluscs includingBemellasp.,Parailsanellasp. cf.murenicaand a sinistral form ofAldanella(A.sp. cf.A. golubevi). Other fauna present includeAustralohalkieriasp.,Eremactis mawsoni, chancelloriids andCupithecasp.