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| Toolebuc Formation | |
|---|---|
| Name | Toolebuc Formation |
| Period | Early Cretaceous |
| Age | Albian |
| Type | Geological formation |
| Unitof | Eromanga Basin |
| Thickness | variable |
| Location | Western Queensland, Australia |
| Namedfor | Toolebuc |
Toolebuc Formation The Toolebuc Formation is an Early Cretaceous sedimentary unit exposed in western Queensland, Australia, notable for its phosphatic limestones, abundant vertebrate fossils, and economic phosphorite deposits. It forms part of the wider Eromanga Basin succession and has been the focus of paleontological, stratigraphic, and resource investigations by institutions and researchers across Australia and internationally. The formation provides key data for correlations with other Cretaceous units and for understanding mid-Cretaceous paleoecosystems, marine transgressions, and phosphate accumulation.
The Toolebuc Formation sits stratigraphically within the Eromanga Basin succession and overlies older units such as the Wallumbilla Formation while being overlain by the Allaru Formation and coeval with parts of the Winton Formation in regional schemes. Regional mapping by the Geological Survey of Queensland and studies from the University of Queensland and the University of New South Wales have refined its boundaries, thickness variations, and local fault-controlled exposures. Correlation efforts link the unit to contemporary deposits interpreted across the Great Artesian Basin margins and to equivalent Albian strata studied by teams at the Australian Museum, the Queensland Museum, and international collaborators at institutions such as the Natural History Museum, London.
Lithologically, the unit is characterized by phosphatic wackestones and packstones, carbonate-rich mudstones, and interbedded siltstones with notable nodular phosphorite and calcareous concretions documented during petrographic and geochemical analyses at the CSIRO and university laboratories. Sedimentological studies conducted by researchers associated with the Australian Geological Survey Organisation describe rhythmic lamination, bioturbation horizons, and condensed intervals interpreted as evidence for episodic upwelling and sediment-starvation events, with detrital input linked to hinterland sources mapped by the Bureau of Meteorology catchment analyses.
The formation is celebrated for a diverse vertebrate assemblage including marine reptiles, fishes, and avian and non-avian dinosaurs recovered by teams from the Queensland Museum and the Australian Age of Dinosaurs Museum. Fossils reported include odontocete-grade ichthyofauna, teleosts, and elasmobranch remains curated alongside preparation work at the Western Australian Museum. Marine reptiles such as plesiosaurs and ichthyosaurs have been documented in field campaigns involving researchers from the University of New England and the Museum Victoria, while fragmentary pterosaur and dinosaur material has been subject to study by paleontologists affiliated with the Royal Society and the Society of Vertebrate Paleontology. Microvertebrate and invertebrate assemblages, including ostracods and foraminifera, have been described in micropaleontological surveys published through collaborations with the Paleontological Association.
Biostratigraphic and radiometric constraints place the unit in the Albian stage of the Early Cretaceous, allowing correlations with Albian sequences in the Gabon Basin, the Western Interior Seaway equivalents studied by researchers at the Smithsonian Institution, and coeval phosphatic horizons reported in the Chatham Islands region. Palynological data generated by teams at the Australian National University and stable isotope work from laboratories at the University of Adelaide support basin-wide transgressive-regressive cycles that align the formation with global Albian events recognized in stratigraphic charts maintained by the International Commission on Stratigraphy.
Sedimentological, paleontological, and geochemical evidence indicates deposition on a shallow, epicontinental, open-shelf setting influenced by episodic upwelling and enhanced biological productivity, as interpreted in joint studies with experts from the International Association of Sedimentologists and the Australian Marine Science Association. Phosphate concentration, laminated carbonates, and preservational modes point to oxygen-poor bottom waters and periodic condensed intervals comparable to depositional models applied to the Phosphate Platform facies described in North African and South American basins by researchers at the University of Paris and the University of São Paulo.
The phosphatic lenses and nodules within the unit have been targeted for phosphate extraction and fertiliser production by companies reviewed by the Queensland Department of Natural Resources. Economic assessments by consultants associated with the Australian Bureau of Agricultural and Resource Economics have evaluated resource potential, while sample characterisation for beneficiation and environmental impact assessments has involved laboratories at the Commonwealth Scientific and Industrial Research Organisation (CSIRO). Secondary uses include engineering-grade limestone for construction and aggregate evaluated in regional infrastructure studies by the Queensland Department of Transport and Main Roads.
Earliest reconnaissance of the unit occurred during exploration campaigns by colonial-era surveyors and geologists linked to the Queensland Department of Mines and field parties from the Royal Geographical Society. Systematic description and the formal name arose from mid-20th-century stratigraphic work by regional geologists collaborating with the Bureau of Mineral Resources and subsequent taxonomic and palaeontological contributions by curators at the Queensland Museum and academics from the University of Queensland, with continuous refinement through publications in journals associated with the Geological Society of Australia and international paleontological societies.