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Report on the asbestos deposit near Bindi Bindi following a visit to the deposit in September, 1943.

Explanatory notes to the Bauhinia Downs 1:250,000 Sheet area.

Lower Cretaceous strata of the Roper River and the Urapunga 1:250,000 Sheets were examined during the 1960 and 1961 field seasons. Field observations on lithology and palaeogeography were summarised in previous Records (Skwarko,1961a,b), and these, together with the identification of the fossils collected and their dating has provided material for this Record. Fossils were collected at only three localities on the Roper River 1:250,000 Sheet area, the greater portion of which is at present covered by the sea, and it has been found convenient to discuss these two sheets under a common title.

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The Polda Basin is an elongate easterly trending trough underlying the continental shelf in water depths of 50-200 m on the eastern side of the Great Australian Bight. It encompasses an area of about I0 000 km2, and contains a Proterozoic-Jurassic sedimentary fill. Although it was originally an intracratonic feature, it shows evidence of several phases of tectonism, of which the most recent culminated in the separation of Australia and Antarctica in the mid-Cretaceous. Seismic interpretation indicates that the trough contains three main depocentres. The eastern Polda Basin lies almost entirely onshore, and contains 1500-2000m of Proterozoic-Jurassic sedimentary rocks. The central Polda Basin and underlying Itiledoo Basin contain a maximum of 5000m of Proterozoic-Jurassic Gontinental sedimentary rocks, including massive halite. They are bounded to the south by a set of normal faults, and to the north by a complex faulted monocline. The western Polda Basin is apparently bounded, north and south, by relatively simple sets of east-northeasterly trending normal faults, and is interpreted to contain a mainly Mesozoic sedimentary fill. The central depocentre, in particular, has been affected by northwesterly oriented wrenching. Overall, the hydrocarbon potential of the Polda Basin is rated as low. None of the three offshore wells drilled encountered significant hydrocarbons; even so, the western depocentre is as yet untested. Potential reservoirs appear to be present, and a number of potential trapping mechanisms can be identified. Such potential traps include halite-induced anticlines, Proterozoic fault-blocks, clastic aprons adjacent to boundary faults, and unconformity traps below the Permo-Carboniferous section. Unfortunately, the existence of suitable source and seal sequences is doubtful, and the basin appears to be too immature for significant hydrocarbons to have been generated. The western Polda Basin is considered to be the most prospective, as inferred by exploration drilling elsewhere in the Great Australian Bight, which shows that Mesozoic sedimentary rocks have some hydrocarbon potential.

The Canning Basin, which covers some 450,000 km2, is the largest sedimentary basin in Western Australia. The earliest Palaeozoic rocks are widespread marine Ordovician limestone, shale and sandstone up to 3260 m thick which unconformably overlie Precambrian metamorphic and sedimentary rocks. Overlying the Ordovician are Devonian rocks, consisting of evaporites and redbeds (probably Early and Middle Devonian) confined to the centre of the basin, and extensive Late Devonian reef carbonates on the northerly and, perhaps, the southerly margin, together with associated shale and sandstone in the centre of the basin. The Devonian sediments are overlain by Carboniferous, Permian, M e s o z o i c and Cainozoic sediments. During the Late Devonian and Carboniferous, sedimentation was virtually confined to the northern half of the Basin: on the Lennard Shelf, in the Fitzroy Trough, and on the Jurgurra Terrace (Fig. 2). The trough contains up to 6000 m of Carboniferous rocks. The Upper Devonian Lower Carboniferous platform sediments consist of alternating beds of limestone, shale, sandstone, and marl. Generally, they postdate the Devonian reef-complex (Playford & Lowry, 1966) and are poorly exposed; consequently they have received less geological attention than the well-exposed reef carbonates. Previous work has resulted in differing interpretations of the formal stratigraphy; including different nomenclatures for the same rock bodies. The presence of an unconformity has also been questioned. During May - August 1972 a joint Bureau of Mineral Resources (BMR) Western Australian Geological Survey (WAGS) Field Party carried out detailed fieldwork in the vicinity of Fitzroy Crossing, Western Australia. Comprehensive collections of petrographic, palaeontological, and geochemical samples were made from the Upper Devonian and Lower Carboniferous to increase the understanding of the sequence. The area of outcrop is situated on the northern margin of the Canning Basin in the Kimberley Division of Western Australia (Fig. 1). Detailed fieldwork was concentrated in three areas; a narrow belt (up to 10 km wide) extending along the southwest face of the Napier and Oscar Ranges from Station Creek in the northwest to Fitzroy Crossing in the southeast, a distance of about 160 km; the Horseshoe and Burramundi Ranges, 65 km east of Fitzroy Crossing; and the Red Bluffs area, 135 km southeast of Fitzroy. METHODS OF STUDY: The outcrop areas were mapped on air photographs at a scale of 1:80,000. Comprehensive sections were measured and samples for petrological, palaeontological, and geochemical studies were collected at intervals of 1.5 m, or more, depending on outcrop. Thirty sections were measured, from which some 500 samples were collected. Detailed reports have been published or are in press dealing with the distinction of limestone's in the sequence (Radke, 1976), the conodonts (Nicoll & Druce, in prep.), and geochemistry (Druce & Radke, 1977). In addition to surface sampling, three holes were drilled to provide information on the sequence between the oldest known Carboniferous rocks and the subsurface equivalents.

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