This Bulletin covers the offshore region west of Tasmania. The western margin of Tasmania, an area of 100,000 sq km contains a thick cover of Late Mesozoic and Tertiary sediments. Most of this sedimentary wedge lies within the Sorell Basin, an extensional passive margin basin that formed as part of the Southern Rift System in the Late Jurassic-Early Cretaceous. See Section 2 - Regional Geology for discussion of the regional geology and development of the western margin. Section 7 - Environmental Features discusses the marine environment and climatic and tidal effects on the western margin. The Sorell Basin Petroleum Prospectivity Package concentrates mainly on the northern part of the basin containing the King Island and Strahan Sub-basins. It is primarily in these two sub-basins that there is sufficient well and seismic data to assess the prospectivity of the Sorell Basin. See Section 6 - Prospectivity for the discussion of the basin's prospectivity.

In a group of Archaean, layered, mafic-ultramafic intrusions in the west Pilbara Block, Western Australia, the Munni Munni Complex (2925 Ma) contains a substantial resource of PGEs (20-30 Mt @ 2.9 ppm Pt + Pd + Au) and other intrusions contain subeconomic resources of Ni and Cu. Contrasting PGE distribution patterns within the group indicate that the timing and mechanism of S-saturation were critical for the formation of PGE-enriched sulphide units. Generally, overlying mafic units are thicker than the rhythmically layered ultramafic components. Olivine and clinopyroxene were usually the first minerals to crystallise and cumulus orthopyroxene is restricted to the upper parts of the ultramafic zones. Chromium partitioned into early crystallising clinopyroxene, thus downgrading the potential for PGE-chromite associations. The parent magmas were probably siliceous, high-Mg basalts of Aldepleted komatiitic affinity. In this study, the variations of PGEs and incompatible trace elements were documented up the entire stratigraphic successions. In the Munni Munni Complex (the intrusion studied in most detail) the PGEsulphide mineralisation is directly below the ultramafic/gabbroic contact and is thought to have resulted from crystal fractionation and mixing of S-undersaturated and S-saturated magmas; as in the Great Dyke of Zimbabwe, it does not occur at or near the base of clearly defined cyclic units. The other (smaller,mainly sheet-like) intrusions studied typically contain basal segregations of PGE-poor Ni-Cu sulphides; the magmas were generally S-saturated early in their evolution and there was no PGE enrichment at higher levels. In exploration, variations in the ratios of precious metals and the trends of the incompatible lithophile and chalcophile elements should be used in association with field and mineralogical evidence to indicate potential PGE-enrichment processes, such as S-saturation, crustal contamination, crystal fractionation, magma mixing, and/or hydrothermal remobilisation.

Several species of Aconeceratinae occur in the Windalia Radiolarite (Upper Aptian) of the Carnarvon Basin of Western Australia. Two of them belong to the genus Aconeceras Hyatt, the third is made the type species of Eofalciferella nov., which is believed to be the ancestor of Falciferella Casey. Two new species of the latter genus have been discovered in the Upper Albian of northern South Australia. This is the first record of the genus outside England. Since Whitehouse (1926b, 1927, 1928) revised the then known Cretaceous species of Eastern Australia very little has been added to our knowledge about Australian Cretaceous ammonites. Spath (1926, 1940) first recorded the occurrence of Senonian and Maastrichtian ammonoid faunas in Western Australia. The important late Albian and Cenomanian assemblages of Northern Australia (Darwin, Bathurst and Melville Islands) are still only sketchily known (Etheridge fil. 1902, 1904, 1907) and are in need of revision, as has become evident from recent bed-for-bed collecting carried out in this area by Dr. B. Daily, of Adelaide. A monograph on this magnificent assemblage will shortly be published by Dr. C. W. Wright. An Upper Albian ammonoid fauna, collected by Dr. H. Wopfner, A. Hess, D. Scott and the author (all of Geosurveys of Australia Ltd., Adelaide), has recently been dispatched to Or. R. A. Reyment (Stockholm) for description. The Aptian/Albian, Senonian, and early Maastrichtian faunas of Western Australia are being described by the writer and the first two parts (Neoammonoidea Irregularia) will appear under the auspices of the Commonwealth Bureau of Mineral Resources, Canberra.

The Pelean type of volcanic eruption, with its swift and deadly cloud of hot, gas-charged particles, was first brought to the attention of a horrified world in 1902, when 29,000 people perished in a few minutes in the morning of May 8th, at St. Pierre on Martinique in the West Indies, only sixteen hours after an eruption of the same type at La Soufriere on nearby St. Vincent had killed 1,650 of the inhabitants and devastated a large area of that island. These eruptions were described by Lacroix, Hovey, Anderson, Flett, and others, and since then several eminent vulcanologists have studied and reported on this fortunately fairly rare type of volcanic activity and the phenomena associated with it. Notable amongst these later works are Fenner's description of the Valley of Ten Thousand Smokes at Mt. Katmai in Alaska, Perret's masterly analysis of the eruptions of Mont Pelee in 1929-32, and the work Stehn and Neumann van Padang in the East Indies. The Mt. Lamington eruption which is the subject of this bulletin is one of the most outstanding examples of the Pelean type of eruption that has occurred in historic times. It was remarkable both as a: manifestation of volcanic violence and because of the character and calibre of the observations that were subsequently made. The area had no volcanic history; local native folk lore contained no legend of eruption, nor were any surface expressions of volcanic activity known in the area. Mt.Lamington was not merely regarded as extinct-it was not even considered as a volcano at all. The presence of a crater had not been recognized-it had never been examined by a geologist-and, being completely open on the northern side, it appeared only as one of the heads of the stream system of the Ambogo river, which rises in a series of rugged hills. It is doubtful if the violence of the eruption itself has been exceeded in modern times by any observed Pelean-type eruption, although Mount Pelee had a more impressive record of human destruction, owing to the particularly vulnerable position of the town of St. Pierre with respect to the crater. Opportunities for recording the phenomena associated with the Mt. Lamington eruption were exceptional: the main outburst was observed and photographed from a passing aircraft at close (almost too close) quarters. A qualified vulcanologist began recording events on the spot barely 24 hours after the main explosion, and observations were continuous from then onwards. A sensitive seismograph was installed at Sangara plantation, 8t miles from the crater, within eighteen days of the eruption. Skilfully manned aircraft were available for daily inspection, photography and recording of crater phenomena and dome growth. The full co-operation and support of the administrative authorities were accorded throughout the investigation to vulcanologist Taylor and the other scientists associated with him. Several reliable observers living 8 to 10 miles from the crater survived the blast and provided details of the eruption and of pre-eruption events. The author of this Bulletin, who combines a fearless devotion in the field to his fascinating but unruly subject with a considerable talent for narrative writing, has supplemented his detailed observations of the progress of the eruptive series with painstaking analysis of a mass of seismograph and other records. The results presented in this Bulletin constitute an important contribution to the literature of volcanoes and volcanic processes.

The lithostratigraphy and biostratigraphy, and the systematics, of larger foraminiferids at several Late Oligocene to Middle Miocene localities in Australia are described. In particular, sediments of this interval in the North West Cape area of the Carnarvon Basin, Western Australia, have yielded diverse faunas of larger and planktic foraminiferids. Sections studied and sampled elsewhere were Ashmore Reef No. 1 well in the Bonaparte Gulf Basin; Gage Roads No. 2 well in the Perth Basin; the Batesford and Bochara Limestones in Victoria; Wreck Island No. 1 well in Queensland; and the Tutamoe, Puketi, and Waitiiti Formations, the Waikuku Limestone, the Stillwater Mudstone, and the Orakei Greensand Member of the East Coast Bays Formation, all in New Zealand. Forty species and subspecies, representing 25 genera or subgenera of larger foraminiferids, have been recorded. Wherever possible, biometric methods have been used to discriminate between taxa. Such studies suggest that the rates of evolution of some groups of larger foraminiferids in New Zealand were different from those in the Australian region. Among the taxa that are illustrated and described in detail are two subspecies of Lepidocyclina (Nephrolepidina) proposed as new: Lepidocyclina (Nephrolepidina) howchini praehowchini and Lepidocyclina (Nephrolepidina) orakeiensis waikukuensis. Topotypes of L. (N.) orakeiensis hornibrooki and L. (N.) howchini howchini have been discussed and figured.

The trilobite faunas described in this Bulletin are exclusively from the Chatsworth Limestone sensu stricto, as it occurs in the immediate neighbourhood of Chatsworth Homestead, 80 km south-southeast of Duchess, in western Queensland (Fig. 1). The outcrops straddle the Duchess and Boulia 1:250000 Sheet areas, and form the central portion of the Burke River Structural Belt (Shergold, 1975, pp. 4-7; in Shergold, Druce et al., 1976, pp. 4-5). "Although trilobites have been described (Opik, 1963, 1967) from the underlying Pomegranate Limestone, at Pomegranate Creek, 19 km north of 'Chatsworth', no material from the Chatsworth Limestone s.s. has been illustrated previously. Those trilobites presently described are from collections made during initial field mapping of the Boulia Sheet area in 1957-60 (Casey, 1968; Casey et al., 1960), and the Duchess area in 1958 (Carter & Opik, 1963; 6pik, 1963). Frome-Broken Hill Pty Ltd collected two samples from the basal Chatsworth Limestone near 'Chatsworth' in 1958 (Taylor, 1959). Subsequently, collections were assembled by the BMR Northwest Queensland Phosphate Group in 1967 (de Keyser et al., in de Keyser, 1968), by the author in 1969, and by B.M. Radke during the course of 1:100 000 scale mapping. by the BMR Georgina Basin Project in 1974-75. Material is also currently. Available from two BMR stratigraphic boreholes, Boulia No. 6 and Duchess No. 13 (Fig. 2 and Appendix 3), drilled for the Georgina Basin Project in 1974. All material described in this Bulletin is deposited in the Commonwealth Palaeontological Collection (prefix CPC), housed in the Bureau of Mineral Resources, Canberra, Australia. Acknowledgements The author acknowledges the time consuming aid given by H.M. Doyle (BMR) in the preparation of the photographs used herein. B.M. Radke (BMR) is thanked for permitting the reproduction of the Lily Creek section which he measured, and J.M. Kennard (BMR) for making available details of cores logged, and for providing petrographic descriptions of the rocks noted in Appendices 1 and 3. I appreciate the constructive criticism provided by Drs R.A. Henderson, James Cook University of North Queensland, and J.B. Jago, South Australian Institute of Technology, on an earlier draft of this Bulletin. The drawings were prepared by R. Fabbo and G. Clarke of BMR's Cartographic Section.

The Bunger Hills area, which forms part of the East Antarctic Shield, consists predominantly of granulite facies orthogneiss (pyroxene-quartz-feldspar gneiss), with subordinate maficgranulite and garnet, sillimanite, and cordierite-bearing paragneiss. The igneous precursors of granodioritic orthogneiss crystallised about 1500 - 1700 Ma ago, whereas late Archaean (2640 Ma) tonalitic orthogneiss occurs in the Obruchev Hills, in the southwest of the area. Metamorphism reached a peak of about 750 - 800 ° C and 5 - 6 kb (Mj) 1190±15 Ma ago (U-Pb zircon age) and was accompanied by the first of three ductile deformation events (Dj). Voluminous, mainly mantle-derived plutonic rocks were emplaced between 1170 (during D 3 ) and 1150 Ma. They range in composition from gabbro, through quartz gabbro, quartz monzogabbro, and quartz monzodiorite, to granite. Abundant dolerite dykes, of at least four chemically distinct groups, were intruded at about 1140 Ma. Their intrusion was associated with the formation of shear zones, indicating at least limited uplift; all subsequent deformation was of brittle-ductile or brittle type. Alkaline mafic dykes were emplaced 500 Ma ago. Marked geochronological similarities with the Albany Mobile Belt of Western Australia suggest that high-grade metamorphism in both areas was the result of continental collision between the Archaean Yilgarn Craton of Australia and the East Antarctic Shield. However, Gondwana reconstructions and the composition of the plutonic rocks suggest that the Bunger Hills metamorphics may have formed in an Andean-type continental arc, with the actual collision zone having been to the east of the present Bunger Hills. Exposures west of the Denman Glacier are also mainly granulite-facies gneiss, intruded by a variety of mafic to felsic plutonic rocks. They differ from the Bunger Hills in being partly derived from Archaean protoliths (- 3000 Ma), in lacking isotopic evidence for a Mesoproterozoic high-grade event, and in not being intruded by dolerite dyke swarms. They also show evidence of much more extensive 500 - 600 M a (Pan-African) metamorphism and plutonism (syenite to granite), and in this regard they are comparable with the Leeuwin Block metamorphics of southwestern Australia, although these were derived from significantly younger protoliths (T^D model ages: 1100 - 1500 Ma). If this early Palaeozoic activity was also a consequence of continental collision, it would explain the markedly different geological history of the terranes on either side of the Denman Glacier and could account for the final uplift of the Bunger Hills. However, the compressional tectonic regime implicit in the collision hypothesis was followed by an extensional regime, which, in southwestern Australia, eventually resulted in the formation of the Perth Basin rift zone. This structure is aligned with the Denman Glacier trough on our preferred Gondwana reconstruction, suggesting that it may have extended well to the south before the breakup of Gondwana.

The acquisition of wire-line logs from selected waterbores in the Great Artesian Basin, Australia, the digitising of the logs, the log data, the data on the waterbores logged and the database containing these data are described in this report. The use of the wire-line logs is discussed within the context of an overview of the geology and hydrogeology of the Great Artesian Basin. The geophysical logs allow the definition of geological ie. lithostratigraphic units and hydrogeological units ie. aquifers and confining beds, and their characteristics, and provide an accurate and reliable data set.

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.

The geophysical surveys described in this report were performed during 1935-1937 by the Aerial, Geological and Geophysical Survey of Northern Australia, but the results were not fully published at that time. As mining development has shown that the Tennant Creek Field, originally considered as a goldfield only, now has possibilities as a base metal field, it was considered desirable that the leading features of the surveys and the results thereof be presented in a unified report. The report is confined mainly to geophysical aspects and refers only to the detection of magnetic bodies. Three types of anomaly were observed, and are classified as minor, major and regional. The minor anomalies appear to be of little significance, and the surveyed areas were not large enough to completely delineate the regional anomalies, which are almost certainly associated with the regional geology. The major-type anomalies are well suited to interpretation by theoretical methods. A method of interpretation based on polarization by induction has been applied to these anomalies, and testing performed to date indicates that this method shows the position of the body causing an anomaly with sufficient -accuracy for the siting of an exploratory drill hole. In general, a reasonable estimate can be made also of the extent in depth of the body. More complete evaluation of the magnetic results would 'be assisted by accurate delineation and interpretation of the regional anomalies. An airborne magnetometer survey, with this object in view, has recently been completed by the Bureau and should give valuable information on the structure and limits of the field. Illustrations are presented showing contour maps of most of the major anomalies, and, for the most important areas, observed magnetic profiles are shown alongside profiles based on theoretically determined dimensions of the bodies causing the anomalies. Four appendices give details of the mathematics involved in the method of interpretation which has been adopted.