Conodont Biostratigraphy of the upper Devonian reef complexes of the Canning Basin, Western Australia

The northern fall of the Central Range, the largest unexplored area in New Guinea (Fig. 1), separates the swampy Sepik Plain in the north from the high dissected plateau forming the backbone of New Guinea to the south. The whole region is rugged and covered by tropical rain forest; it is almost uninhabited, and as there are few tracks, the long meandering southern tributaries of the Sepik River provide the only practicable access. The South Sepik region occupies a small segment of the fundamental break separating the stable Australian continental block from the oceanic crust to the north. This break, which is marked in the South Sepik region by the Lagaip Fault Zone, has had a profound effect on sedimentation in the region throughout the geological record: shelf-type sediments were laid down on the continental block, while geosynclinal sediments were being deposited to the north. The oldest rocks are Middle and Upper Triassic in age and include a widespread and distinctive volcanic unit called the Kana Volcanics. They are succeeded unconformably by a thick sequence of black pyritic shale (Lagaip Beds), which was laid down south of the Lagaip Fault Zone during the Jurassic and Cretaceous.

The systematic part of this paper is the continuation of my study (bpik, 1958) of the anatomy and concept of the genus Redlichia, presented on the basis of Redlichia forresti from the Negri Group of Western Australia, Redlichia idonea from the Yelvertoft Beds of Queensland, and some other, then unnamed, species. At that time (op. cit., p. 36) the taxonomy of the species was reserved for the future. This paper serves a double purpose-first, in presenting such speciestaxa as can be established from selected and properly preserved material, and second, in establishing a sequence of informal 'biostratigraphic operational units' in advance of a scale of Ordian zones. Such a scale of zones would be premature in view of the difference between the specific composition of Redlichia in Queensland and in the Northern Territory, and because of the incompleteness of data regarding the vertical distribution and specific taxonomy of Redlichia in many sites of the Territory, and the numerous undescribed other fossils of the Ordian of Australia. The fossils are kept in the Museum of the Bureau of Mineral Resources and the specimen numbers (CPC) refer to the Commonwealth Palaeontological (type) Collection.

BULLETIN 116 is a collection of palaeontological papers,1968

Most of the Carboniferous brachiopods (excepting productoids and rhynchonellids) so far collected from the Carnarvon, Canning (Fitzroy), and Bonaparte Gulf Basins of Northwest Australia are described. The faunas of the Bonaparte Gulf Basin are the least well represented. Six Carboniferous brachiopod zonal assemblages are distinguished: two of Tournaisian, one of late Tournaisian. to possibly Visean, two of Visean and one of late Visean to possibly Namurian age. The described faunas include species of Rhipidomella, Leptagonia, Schellwienella, Schuchertella, Rugosochonetes?, Prospira, Unispirifer, Spirifer, Anthracospirifer, Ectochoristites?, Brachythyris, Kitakamithyris, Torynifer?, Syringothyris, Punctospirifer, Cleiothyridina, Composita, and an unnamed new spiriferid genus. At least 23 species are new. Affinities with world-wide Dinantian faunas are suggested for the majority. The brachiopods are distributed through the Moogooree Limestone and Yindagindy Formations of the Carnarvon Basin, the Laurel Formation of the Fitzroy Basin, and the Burt Range Formation, Enga Sandstone, Septimus Limestone, Utting Calcarenite, Burvill Beds and Point Spring Sandstone of the Bonaparte Gulf Basin. Four Permian spiriferacean species are also described from the Carnarvon and Canning Basins. They comprise the Sakmarian Lyons Group species Trigonotreta narsarhensis occidentalis subsp. nov., and Cyrtella nagmargensis australis subsp. nov., and the Artinskian Pseudosyringothyris dickinsi sp. novo from the Callytharra Formation and Pseudosyrinx? sinuosa sp. novo from the Madeline Formation. The species support a correlation of the Lyons Group with the Umaria beds of India, part of the Agglomeratic Slate of Kashmir, and early Permian beds of Arabia. Boreal affinities are suggested for P. dickinsi sp. Novo Generic morphological features are discussed. Points of interest include the composite nature of the dental plates in Schellwienella, the initial dental plates of certain Spiriferidae, the adductor muscle attachment function of the syrinx in Syringothyris and the adductor muscle scars on the delthyrial plate in Pseudosyringothyris. The taxonomy of certain families is discussed, notably the Syringothyridae.

The Sydney Basin extends for 380 km along the east coast of New South Wales south of latitude 32°S, and has an onshore area of about 36 000 km2 . About 4800 m of Permian and Triassic sedimentary rocks are preserved in the basin which lies between the New England and Lachlan Fold Belts. The study of the Sydney Basin by the Sedimentary Basins Study Group of the Petroleum Exploration Branch of the Australian Bureau of Mineral Resources was undertaken in co-operation with the New South Wales Department of Mines, who prepared a 1:500 000 geological map (PI. 1). The study has required constant exchange of ideas and information with petroleum exploration companies and the Department of Mines. In addition to the authors of this Bulletin the following members of the Sedimentary Basins Study Group since late 1966 have contributed to the study: D. J. Forman, M. A. Reynolds, K. G. Smith, R. Bryan, A. R. Jensen, P. J. Alcock, P. J. Hawkins, R. B. P. Pitt, S. Ozimic, J. I. Raine, K. Rixon, and B. G. West.

The Australian Calibration Line (ACL) , with a total gravity interval of 3 Gal, was established during 1970 between Laiagam in Papua New Guinea and Hobart in Tasmania. During 1973 the Australian Bureau of Mineral Resources and the USSR Geodesy and Cartography Survey made joint observations along the full length of the ACL. Measurements made with eight Soviet GAG-2 gravity meters established a gravity scale for Australia to an accuracy of 2.5 parts in 105. This scale and a datum of 979 671.86 mGal for Sydney A were adopted for Australia in 1973. The Soviet scale established for the ACL appears to be within 1 part in 104 of both the IGSN71 scale established for the Western Pacific Calibration Line by absolute determinations, pendulum measurements and international gravity meter comparisons, and the scale established for the Soviet Calibration Line by OVM pendulums. The Soviet scale for the ACL defines a milligal which is 1.5 parts in 104 larger than that defined by IGSN71 values for the ACL, and 5 parts in 104 larger than the 1965 Mean Australian Milligal that was used as an Australian milligal standard between 1965 and 1973. Both of these scales are partly based on Cambridge pendulum measurements made in Australia during 1950-51. These measurements are now thought to have been incorrect in scale. LaCoste, Romberg gravity meters have been used during six surveys along the whole or part of the ACL. The LaCoste observations have been reduced using the Soviet ACL scale and the new datum for Sydney A. The most probable values for airport gravity stations, calculated from the LaCoste results, have a precision of better than 0.01 mGal and are consistent to within experimental error with values calculated from the GAG-2 results. LaCoste observations reduced using the Soviet ACL scale give more accurate values for the gravity differences of the main intra-city ties and calibration ranges along the ACL.

Special demagnetising apparatus was constructed to study the stability of several samples of basic igneous rocks from three localities in eastern Australia, particular emphasis being placed on the reliability of the directions of NRM. The direction of primary magnetisation acquired when the rocks first cooled was determined for samples at all three sites. Mesozoic dolerite from Red Hill Dyke in southern Tasmania has little or no secondary magnetisation and the mean direction of NRM is representative of the Jurassic in Tasmania. There is no evidence of systematic error due to stress or shape, and therefore the direction of NRM is a reliable estimate of the direction of the geomagnetic field at the time of intrusion. Devonian Nethercote basalt from southern New South Wales can be divided into two distinct groups, one in which the NRM is completely unaffected in either direction or intensity by demagnetisation in peak alternating fields of up to 1000 oersteds, and the other in which secondary magnetisation completely masks any primary magnetisation that may be present. Tertiary basalts from southern New South Wales show a wide range of stability. The NRM consists of primary TRM and varying proportionate amounts of secondary magnetisation, which is almost certainly viscous and which was probably acquired in the present Earth's field. The stability shown by the three rock types makes it more probable that previous palaeomagnetic results, which span a long period from Devonian to Tertiary, form a reliable record of the geomagnetic field in Australia.The general effects of alternating demagnetising fields are also discussed and a comparison made between the theoretical predictions and the data obtained.

Standard curves for interpretation of the magnetic anomalies due to spheres have been derived. The anomalies in the vertical component, and the horizontal component in the direction of the traverse, are each found to be represented by a single family of curves. The horizontal component is found to be not represented by a single family, and separate curves for each field inclination and traverse azimuth are presented. Curves for the anomaly in the total intensity were not computed.

The Georgina Basin is a large Palaeozoic sedimentary basin extending from northwestern Queensland into the Northern Territory. Field parties from the Bureau of Mineral Resources mapped some of the Queensland part of the basin in the early 1950s, and the remainder in the period 1957-65; officers of the Geological Survey of Queensland participated in most of the Queensland surveys. Since 1957, petroleum exploration companies have made geological, gravity, aeromagnetic, and seismic surveys in selected areas, and the Bureau of Mineral Resources has carried out aeromagnetic and reconnaissance gravity surveys over most of the basin, and seismic surveys in Queensland and in small areas in the Northern Territory. Sixteen petroleum exploration wells have been drilled, but no commercial deposits of oil or gas were found; three deep stratigraphic holes were drilled by the Bureau, which also drilled an aggregate of about 3000 m in shallow scout holes. The Georgina Basin covers an area of about 325,000 sq km and extends in a belt trending northwest from latitude 25°S in northwestern Queensland to about latitude 18°S in the Northern Territory. The basin is about 1000 km long and about 500 km wide. The southwestern, western, northern, and eastern margins are defined by Precambrian outcrops, but the northwestern and southwestern margins are concealed by Mesozoic sediments. The position of the northwestern margin has not been resolved, but the southeastern margin has been defined approximately by gravity, seismic, and aeromagnetic surveys and by limited stratigraphic drilling.