No abstract available

Restricted on advice from A. Barrett

Restricted on advice from A. Barrett

F54/B1-129 Vertical scale: 1000

85% coverage, north east corner missing D53/B1-142 Vertical scale: 10

A correlation chart for the Triassic System in Australia is presented. The base of the System in Australia is taken as the earliest occurrence of the Lunatisporites pellucidus Assemblage Zone in a section of the Rewan Formation in the Bowen Basin, Queensland, and the base of the Jurassic System as the occurrence of Ceratosporites helidonensis with ClassopoWs and Retitriletes austroclavatitides in the Upper Woogaroo Subgroup in a section near Ipswich in the Moreton Basin. Correlations within Australia are based predominantly on microfioral evidence with supporting evidence from fossil vertebrates and, to a minor degree, on macrofiora. Correlation of Australian units with those in other continents depends on ammonites, bivalves, conodonts, vertebrates, and microfiora in Lower Triassic units; and on vertebrates and microfiora in higher units. A cross-indexed bibliography on the Triassic System in Australia covering 21 years to the end of 1973 is also provided.

40% coverage south west D53/B1-150 Vertical scale: 20

H50/B1-64

The Roper Group (minimum age approximately 1300 x 10^6yr) is a shallow water sequence of sandstone, siltstone, and shale, with minor, sub-economic oolitic ironstone. The depositional environments of the Group as a whole, range from fluvial, through deltaic or estuarine, to marine, and a number of different environments of deposition for the ironstones can be recognised. Shales from the McMinn Formation at the top of the Group have yielded an assemblage of microfossils. The microbiota includes algal cells and filaments, large acritarchs and giant filaments of uncertain affinity. A probable life cycle and an example of endospory may indicate that some of the organisms are eukaryotic. The flora is very advanced for its geological age, but this is probably because most other Precambrian microbiotas come from carbonate, stromatolitic environments, where simpler and more conservative forms would have pre-dominated. The microfossils are in a particularly good state of preservation because of the low degree of thermal metamorphism which the sediments have undergone. Geochemical and petrographic studies of the organic matter indicate that its composition and level of organic maturation are appropriate for the generation of oil. The rank of the organic matter is locally increased by proximity to dolerite sills which intrude the Group as a whole.

A review of the lithology, sedimentary structures and palaeontology, supplemented by original investigations, suggests that the Triassic system in the Canning Basin can be subdivided into four broad environmental episodes. The sequence records a slow transgression culminating in the Smithian, when the riverine plain in the southeastern Fitzroy Graben was drowned. The resulting shallow embayment in the Fitzroy Graben supported a much impoverished marine biota, made up of species tolerant of reduced saline conditions caused by substantial run-off of fresh water from surrounding streams. A regression began in the Spathian and continued throughout the later Triassic, although there were minor transgressions with marine incursions: the environment evolved into a low-relief coastal alluvial plain, with meandering streams and lakes. A general trend to increasing aridity is evident, with an increase red beds, and is correlated with the withdrawal of the Blina Sea. Finally in Ladinian time the region became an area of non-deposition and remained so until the early Jurassic.