The structure, sedimentology, sequence stratigraphy and tectonics of the northern Drummond and Galilee Basins, Central Queensland, Australia

The Late Devonian-Early Carboniferous Drummond Basin and overlying Late Carboniferous-Middle Triassic Galilee Basin are extensive intracratonic basins with predominantly fluvial sediment infill. They are inferred to have developed on Proterozoic and Early Palaeozoic basement similar to the adjacent Charters Towers Province and Anakie Inlier. Depositional and structural architecture of the basins have been investigated through a combination of seismic, geophysical well log and gravity data sets with lithologic information obtain from well cores, surface mapping and sedimentary petrography. Comprehensive interpretation of 750 km of seismic traverse resulted in the recognition of eleven seismic facies, several of which have distinctive internal signatures, separated by reflection boundaries that can be traced basin wide. Lithologic and geophysical logs from sixteen wells and boreholes can be matched to seismic stratigraphic units and allow the basinal infill to be described in terms of the lithostratigraphic frameworks already established in the literature. The construction of structure contours for unit boundary surfaces has identified extensional structures associated with rift phases of basinal development and the pattern of thrust and thrust fold features associated with basin inversion. Eleven new structural features that have continuity through the Drummond and Galilee Basins have been defined and other features noted in the literature have been reinterpreted based on evidence from seismic profiles. The construction of isopachs for each unit has allowed tracking of basinal infill thickness trends through time. Analysis of geophysical and lithologic logs from petroleum wells and boreholes, augmented by sections documented from surface exposure has resulted in the recognition of some 16 discrete sequences, each based on a repeating pattern of three types of non-marine systems tract that mainly reflect basinal tectonics but also the influence of climate and eustatic sea level change. Both basins share a common style of sequence development that is not reflected in the current literature. Provenance interpretation based on petrographic data from 121 thin sections representative of most of the Drummond Basin and all of the Galilee Basin suggests that the majority of basin infill was derived from a recycled cratonic source, such as the Thomson Fold Bel to the west, and less material derived from an eastern volcanic arc than previously thought. However SHRIMP-derived U-Pb age data for zircon populations from two samples broadly representative of quartz arenites prominent in the basinal successions conflict with this view. Such data for a sample from the Mount Hall Formation of the Drummond Basin indicates that its source was largely from Early to Mid Palaeozoic igneous terranes like those represented in the Charters Towers Province to the north and inferred for the Thomson Fold Belt to the west. Zircon ages of a sample of Warang Sandstone of the Galilee Basin indicates a Late Palaeozoic igneous source, with derivation largely from an eastern magmatic arc. The Drummond Basin commenced as a back-arc extensional basin, progressed through a thermal sag phase and ceased development during mild compression associated with a far-field expression of the Kanimblan Orogeny. Structural patterns show initial rift architecture, with compartments separated by newly defined transfer fault zones. Extensional faults between the transfer structures extend further through the basinal succession than previously thought. This basin developed a broad sag phase but the final stages show a foreland influence induced by Kanimblan thrust loading on its eastern margin. Basinal structure has been strongly modified by inversion in the Middle Triassic associated with the Hunter-Bowen Orogeny. The Galilee Basin commenced as a foreland basin expressing continuity with the late-stage development of the underlying Drummond Basin from which its division is arbitrary and based on historical misconceptions of Kanimblan tectonism. Thermal subsidence related to the rift phase of the Drummond Basin continued as an influence in addition to foreland subsidence. Tectonic quiescence marks a mid-stage of basinal development reflected in a regionally developed paraconformity and deposition of a basinwide coal measure sequence related to eustatic sea level rise over a stable substrate. The upper part of Galilee Basin infill reflects a foreland phase of development and records two episodes of thrust loading on the eastern margin associated with the Hunter-Bowen Orogeny. Ongoing crustal contraction during the Hunter-Bowen Orogeny resulted in inversion of the Drummond and Galilee Basins with the development of large-scale thrust dislocations and associated fault bend anticlinal structures. The Middle Triassic Clematis Group is the youngest unit that shows folding due to inversion. Much of the western parts of both basins remain relatively undisturbed apart from gentle regional pre-Middle Jurassic tilting that marked the final phase of Hunter-Bowen tectonism