Tectonostratigraphic framework of the Lower Keraudren Formation, Bedout Sub-basin: interplay of tectonics and sedimentary systems

Abstract

Recent drilling activity and new seismic data have contributed to the understanding of the Lower Keraudren Formation in the Bedout Sub-Basin. The Lower Keraudren Formation is a thick (>5 km) succession of strata that was deposited rapidly during the Anisian of the Middle Triassic. Distinctive characteristics related to sediment provenance, sediment supply and accommodation have facilitated subdivision of the Formation into eight informal units: the Milne, Crespin, Baxter, Caley, Hove, Barret, Palma, and Huxley members. Tectonic elements of the East Gondwana Interior Rift and the Bedout High influenced the Sub-basin geometry during deposition of the Lower Keraudren. Extensional tectonics of the East Gondwana Interior Rift generated a series of Palaeozoic tilted fault blocks and grabens, which influenced the stratigraphic architecture, sediment dispersal patterns and distribution of reservoir and source rock facies. The structurally proud Bedout High, a roughly circular (~60 km wide) igneous feature, created a northern boundary to deposition. Seismic stratigraphic interpretation has characterised the interval as a series of north west prograding wedges. Well based data indicates the section is dominated by fluvio-deltaic deposits. Separating the Caley and Hove Members is a significant unconformity that is associated with renewed uplift of the Bedout High and a change in sediment provenance. Chemostratigraphy and petrology indicates the Caley and older strata were derived from a more mature sediment source, whereas the Hove and younger a more immature metamorphic source. Distinct changes in reservoir quality are observed above and below the Caley–Hove unconformity. Below the unconformity, the older, more mature sandstones exhibit superior reservoir quality compared with the younger, more immature sandstones.