FACIES ANALYSIS, GAMMA RAY LOGGING, AND SEQUENCE STRATIGRAPHY OF THE LIMBUNYA GROUP, BIRRINDUDU BASIN, NORTHERN TERRITORY, AUSTRALIA

The greater McArthur Basin preserves relatively pristine Paleo- to Mesoproterozoic sedimentary successions. This extensive intracratonic basin-system comprises a series of broadly correlative basins located in the Northern Territory, Australia, comprising the McArthur, Birrindudu, South Nicholson, and the Fitzmaurice basins. The eastern portion of these basins have attracted attention from an economic perspective due to world-class Zn-Pb deposits and petroleum plays. However, relatively little is known about the architecture and geodynamic evolution of the western portion of the basin-system, the Birrindudu Basin. Although the Birrindudu and the McArthur basins are geographically separated by hundreds of kilometers, they have been tentatively correlated based mainly on general lithological similarities, supported by limited geochronology. The ca. 1.64 Ga Fraynes Formation (Limbunya Group) is coeval with the Barney Creek Formation (McArthur Group), which hosts significant Zn-Pb deposits. Thus, establishing detailed correlation between these two units may inform mineral exploration, while also shedding light on the tectono-stratigraphic evolution of the greater McArthur basin-system. The Limbunya Group consists of 1300m of cyclic mixed siliciclastic and carbonate strata. We examined two drill cores covering 700m of stratigraphy of the Limbunya Group, comprising mainly mixed dolostone, siltstone and mudstone with subordinate sandstone and intraclast carbonate and breccia. Based on decimetre-scale description, we defined four main facies associations: continental to supratidal, shallow subtidal to intertidal, subtidal to lagoonal, and deep subtidal. This facies analysis, together with gamma-ray measurements, allowed us to define second and third-order transgressive-regressive sequences, providing a basis for sequence stratigraphic correlation between the Birrindudu and McArthur basins. These correlations will be tested and refined through application of high precision U-Pb zircon dating and carbon isotope chemostratigraphy.