Palaeobiology of the Neoarchean Fortescue Group, Pilbara Craton, Western Australia

摘要

The 2.78 to 2.63 Ga Fortescue Group, Pilbara Craton, Western Australia, has been the focus of studies seeking to gain insights into the nature of Neoarchean ecosystems. However, depositional environments for several palaeobiologically-significant Fortescue Group units remain poorly-constrained. This work describes stromatolitic intervals from new and previously reported localities in the Kylena, Tumbiana, Maddina and Jeerinah formations. Depositional settings are inferred through a comparative study of the sedimentology, mineralogy, palaeontology and stratigraphy. Fortescue Group microbialites are investigated through stable isotope geochemistry and the study of microfabrics and modern analogues. Analytical techniques employed include light microscopy, Raman spectroscopy, scanning electron microscopy, x-ray diffraction, mass spectrometry and laser ablation inductively-coupled plasma mass spectrometry. Principal results include both marine and lacustrine interpretations for carbonate intervals in the Kylena, Tumbiana and Maddina formations and a fluvial interpretation for the siliciclastic Woodiana Member, Jeerinah Formation. Methanotrophs probably contributed large volumes of 13Corg-depleted biomass to shallow-water stromatolites accreted as early as 2.74 Ga and as late as 2.63 Ga. Several lines of evidence, including microbialite microtexture, microbialite morphology and comparatively high 13Corg values suggest filamentous phototrophs were important constituents of some microbialite-constructing communities at this time.