Sedimentology, conodont biostratigraphy, and palaeogeography of a mid-Devonian carbonate/siliciclastic platform margin, Broken River region, north-eastern Australia

Contrasting views on the stratigraphy and sedimentology of some Early to Middle Devonian (late Emsian to mid-Givetian) lithostratigraphic units of the Broken River Group of northeast Queensland are probed by the re-mapping of a pivotal area, sedimentological studies, and consideration of conodont data. Limestone-charged debris flows, limestone olistoliths (rarely up to 100s of metres) and allodapic limestones form part of an extensive submarine fan complex, with some of the debris flows extending > 10 km from the platform margin into the Burges Submarine Valley. In some areas, autochthonous sequences of the Lomandra and Dosey Limestones are separated by a wedge of elastic sediments - a submarine channel facies (eff) connected with the Storm Hill Sandstone, extending into and terminating among the allochthonous sediments of the Burges Submarine Valley. The primarily conglomeratic extension of the Storm Hill Sandstone (serotinus/precostatus to australis zones) was deposited as submarine channel fill, transported downslope by both onshore and offshore processes aided by progradation of elastic sediments during an interval of low sea level, mainly within the costatus Zone. A useful Burges Formation may be excised from the "undifferentiated Broken River sediments" if a clear distinction is drawn between this submarine channel facies with polymictic conglomerate and associated sandstones (Burges Formation) and the basinal facies largely free of debris flows. Conodonts from a broad spectrum of limestone lithologies, from spot sa mples, and from 10 stratigraphic sections provide data on source rocks as well as ages (or approximate ages) of deposition of debris flows, turbidites, allochthonous/slide blocks (olistoliths), and autochthonous limestones.