A new appraisal of depositional cyclicity in the Neoarchean-Paleoproterozoic Dales Gorge Member (Brockman Iron Formation, Hamersley Basin, Australia)

The Dales Gorge Member (DGM) of the Brockman Iron Formation (Hamersley Basin, Western Australia) is a classic banded iron formation (BIF) that was deposited during the Archean-Proterozoic transition just prior to the Great Oxidation Event. The goal of this study is to apply modem cyclostratigraphic principles to investigate the possible origins of the characteristic stratigraphic banding in this BIF, which indicates the influence of quasi-regular cyclic processes in the deposition of iron-rich and chert-rich lithologies. A grayscale scan series of the DGM 'type section' 47A* drillcore photographs from three cores drilled in the Wittenoon Gorge vicinity is examined using well established methods of time series analysis. Complex banding patterns suggest that Milankovitch forcing may have taken place with orbital-rotational parameters that were significantly modified from the present-day due to continuous planetary tidal dissipation over the past 2.5 billion years. The banding patterns change systematically and dramatically within the member in response to slowly varying environmental conditions, which are interpreted to be related to low-frequency sea level changes and/or tectonic evolution of the Hamersley Basin.