SEDGEFORD FORMATION, A NEW MIDDLE DEVONIAN CRATONIC SEQUENCE FROM CENTRAL QUEENSLAND AND ITS REGIONAL SIGNIFICANCE

A newly discovered Middle Devonian sequence uplifted and exposed along a major thrust fault truncating the western limb of the Mt Beaufort A nticline of the Drummond Basin, Alpha district, central Queensland is described and named the Sedgeford Formation. Two informal members with in the formation consist of a lower unit dominated by non-marine sands tone which is conformably succeeded by an upper unit of richly fossili ferous marine sandstone with limestone interbeds. Conodonts and marine invertebrates indicate that the marine member is of Eifelian (Middle Devonian) age. A locally developed paludal facies within the lower mem ber contains a diverse fish assemblage. The exposed sequence exceeds 1 km in thickness and is unconformably overlain by Upper Carboniferous Joe Joe Formation to the west. To the east it abuts the Bottle Tree Fa ult but boulder-size metamorphic clasts from the Devonian succession s uggest that a metamorphic basement lies beneath, and relatively close to, the lowest preserved horizons. The Sedgeford Formation was deposit ed synchronously with part of the succession of the Adavale Basin loca ted to the southwest and indicates that Devonian basinal development w as more widespread in central Queensland than previously recognized. T he widespread remnant successions of Emsian and Eifelian age developed in cratonic settings in central Queensland represent back-are basinal developments which were contemporary with active margin stratotectoni c assemblages of the northern New England Orogen developed to the east .