Stromatolite Construction, Biofacies and Biomarkers in the Lower Cambrian Hawker Group, Arrowie Basin, South Australia

Abstract

Stromatolites are laminated microbial deposits, normally composed of accretionary layers of cyanobacteria and other (often anoxic) bacteria which form on the sediment-water interface. Stromatolites represent one of the earliest records of life on Earth, dating back at least 3.7 billion years. Stromatolites became extremely diverse and very abundant throughout the Archean era 4-2.5 billion years ago, eventually causing increasing levels of atmospheric oxygen on Earth, as part of the Great Oxidation Event. The emergence and radiation of bilaterian animals and the development of new and more complex food webs during the early Cambrian coincided with a sharp decline in the abundance of stromatolites, yet they continued to exist in a range of Cambrian carbonate environments. The appearance, environment, and possibly the biogeochemistry, of Cambrian stromatolites appears to have been altered after the evolutionary development of epifaunal grazing bilaterians. Stromatolites were sampled from a wide spectrum of carbonate facies in the lower Cambrian Hawker Group in the Flinders Ranges, South Australia. The appearance, construction, distribution, and biogeochemistry of stromatolites from different depositional environments, including phosphatic hardgrounds, intertidal shoals and shelf/ramp settings is being described as part of an investigation into their morphological variation and ecological association, aiding the clarification of specific stromatolitic biofacies, and taxonomic associations. There has been little previous research on the morphology, architecture, growth, and biogeochemistry of Cambrian stromatolites in the Arrowie Basin. This study is designed to provide novel data about stromatolite evolution and ecology during a period dominated by the radiation of complex animals.