These documents have been scanned by the GA Library. Please refer to the document for contents.

These documents have been scanned by the GA Library. Please refer to the document for contents.

These documents have been scanned by the GA Library. Please refer to the document for contents.

These documents have been scanned by the GA Library. Please refer to the document for contents.

These documents have been scanned by the GA Library. Please refer to the document for contents.

22-3/J54-8/7-1/2 Vertical scale: 600

22-3/I55-4/7-1/2 Vertical scale: 300

The Cobar Basin in western New South Wales formed by sinistral transtension in the latest Silurian to late Early Devonian and evolved through a syn-rift phase of brittle upper crustal faulting and subsidence followed by a post-rift sag phase of passive subsidence which can also be recognised in other Early Devonian stratotectonic elements in western New South Wales. Basin evolution was controlled by regional faults splaying off the Gilmore Suture and the Kiewa Fault. The Cobar Basin was largely inverted - 400 Ma ago with reversal of movement (dextral transpression) on synsedimentary north-northwest-trending strike-slip/oblique-slip faults and on west-northwest-trending dip-slip faults. These faults controlled the partitioning of deformation in surface rocks into a high-strain Zone I developed above a half positive flower structure in the eastern part of the basin, and a lower strain Zone 2 developed above a flat detachment in the central part of the basin. Shortcut faults developed during inversion are the most likely structural targets for sulphide and gold accumulation which is structurally controlled and syntectonic metahydrothermal in origin. Some of these faults have experienced strike-slip faulting as well as contractional movement.

Examination of new Late Cambrian samples from the upper part of the Chatsworth Limestone and lower part of the Ninmaroo Formation from Black Mountain, Georgina Basin, western Queensland (representing the pre-Payntonian, Payntonian and Datsonian Stages) has delineated five conodont assemblages in an interval that had previously not been subdivided using conodonts. Examination of the conodont fauna unambiguously confirms that the entire Payntonian Stage is of Cambrian age, as earlier indicated by the trilobite fauna, and provides three conodont assemblages that may subsequently form the basis for a conodont zonation. The Datsonian Stage, defined by the FAD of the Cordylodus proavus conodont assemblage and previously considered to equate with the Early Tremadoc (= Early Ordovician) of Europe, is now considered to represent the terminal Cambrian stage in northern Australia. The base of the Ordovician, equated with the base of Tremadoc correlatives, lies close to the Datsonian/Warendian boundary on the Black Mountain section. Two new conodont genera, Eodentatus and Hispidodontus, are established, along with four new species, E. bicuspatus, H. resimus, H. appressus and H. discretus. All are found in the Payntonian Stage in the upper part of the Chatsworth Limestone or the lower part of the Ninmaroo Formation.

The Permian Yessabah Limestone, a thick crinoidal limestone unit, appears abruptly in the stratigraphic succession over a large area of the Hastings Block in northeastern New South Wales, disconformably overlying clastic rocks with sharply contrasting facies associations. The formation is part of a thick depositional sequence that began with a major sea-level fall at the end of the Carboniferous. The sea-level fall produced a major basinward shift in facies causing rejuvenation of streams and the deposition of braided-stream gravels in the onshore areas while a mass-movement association, the Parrabel Beds, was deposited offshore in the deep basin (the lowstand systems tract). The Yessabah Limestone was deposited as part of the transgressive systems tract in a shallow-marine high-energy environment as sea level again began to rise. The highstand systems tract then prograded over the Yessabah Limestone in the form of a distal turbidite association , the Warbro Formation and associated units, as sea level reached its maximum. The growth of both crinoids and bryozoa was prolific; their two distinctive faunal assemblages alternately dominated the sea floor, producing thick units of well-washed crinoid-rich limestone followed by a bryozoan-rich unit. As sea level rose, conditions became unsuitable for carbonate deposition and the area was again invaded by clastic sediments, forming a distal turbidite association that prograded across the limestones as part of the highstand systems tract.