摘要:

Magnetotelluric data from the central Eromanga Basin indicate that one‐dimensional resistivity models are appropriate for the region. The uppermost Jurassic‐Cretaceous Eromanga Basin sequence contains flowing aquifers and has an average section resistivity in the range 1 to 7 ohm m with a mean of 4 ohm m. This overlies the older sedimentary sequences of the Cooper (Permo‐Triassic) and Adavale (Devonian) Basins with resistivities in the range 10 to 400 ohm m, which present good resistivity contrasts for determining sub‐surface morphology at the base of the Eromanga sequence. The depth extent of the older sequences is not well resolved because of the overlying highly conductive layers, but it appears to be greater than that determined from seismic reflection data in the Coonavalla Syncline and Warrabin Trough.

ISSN:0016-7614    

DOI:10.1080/00167618308729232

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Microscopic features of Cretaceous oil shales at Julia Creek in northwestern Queensland indicate that the rocks are analogous to the white chalks that characterise much of the Upper Cretaceous sequences elsewhere in the world. Julia Creek oil shales differ, however, in that they formed under anoxic conditions, in which the organic matter and the inorganic secretions (coccoliths) of the plankton have been preserved. No external source of material is required to explain the origin of these rocks; they can be derived almost entirely from the sea biomass.

ISSN:0016-7614    

DOI:10.1080/00167618308729233

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Archaean gold deposits of Australia are most abundant in 2.8 ± 0.1 Ga granitoid‐greenstone terrains, where they form both vein‐type and disseminated occurrences. Two‐thirds of total gold production has come from metamorphic (early, peak or late) vein deposits within host rocks of metabasaltic composition and of greenschist to lower amphibolite facies grade.

ISSN:0016-7614    

DOI:10.1080/00167618308729234

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

The Jemba Rhyolite, of Upper Silurian age, outcrops south of Walwa in the Upper Murray Valley, and is temporally and spatially associated with leucogranitoids of similar chemistry and with an extensive dyke swarm. The dyke swarm is litho‐logically bimodal, rhyolite and basalt being the dominant lithologies. The basalts are transitional alkalic in chemistry.

ISSN:0016-7614    

DOI:10.1080/00167618308729235

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Refraction data taken from ocean bottom seismograph recordings in the western Arafura Sea indicate a continental‐type structure for the region. This structure is characterised by a thin column (2 km) of sediments, with velocities ranging from about to 2 to 4 km s‐1, overlying an essentially two layer crust. The compressional wave velocities in the upper and lower crust are 5.97 and 6.52 km s‐1, respectively, with the boundary between the layers at a depth of 11 km. Very weak mantle‐refracted arrivals with a velocity of about 8.0 km s‐1were recorded. Large‐amplitude, later arrivals, beginning at distances near 100 and 150 km, have been interpreted to be part of the retrograde branches from the 8.0 and 7.33 km s‐1layers, respectively. Model studies indicate that a small positive velocity gradient is required between 17 and 30 km, and that the Moho is at a depth of 34 km. A third set of large amplitude, later arrivals starting at a distance near 250 km has been interpreted as most probably multiple refraction‐reflection arrivals from the 5.97 and 6.52 km s‐1layers. Correlation of this structure with the stratigraphic logs from exploratory oil wells in the Arafura Sea using layer velocities indicates that rocks younger than Jurassic appear to thin towards the east.

ISSN:0016-7614    

DOI:10.1080/00167618308729236

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Various authors have recently postulated a thick cover (up to 2 km) over the presently exposed rocks of the Sydney Basin. This paper examines the evidence for such a cover, the various ways in which it might have been emplaced and removed without trace, and the time and space constraints that must be considered. The evidence for a thick cover is poor. Maximum cover was considerably less than 1 km, and heat flow and near‐surface diagenetic processes can account for the variations in coal reflectance and the character of the Hawkesbury Sandstone, both of which are used as evidence of thick cover by some writers.

ISSN:0016-7614    

DOI:10.1080/00167618308729237

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Many Broken Hill (New South Wales) specimens labelled ‘zinco‐calcite’ in museum and private collections are snow‐white, globular forms with a sparkling appearance, on a coronadite or limonite matrix. X‐ray diffraction and microprobe analyses show the globules have a core of nearly pure calcite, overlain by colourless, drusy zincian dolomite with up to 4 mol % ZnCO3and up to 7 mol % excess CaCO3. Although Zn is abundant in the Broken Hill orebody, it apparently entered carbonate, mainly as smithsonite, only during formation of the oxidised zone.

ISSN:0016-7614    

DOI:10.1080/00167618308729238

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

230Th/234U dates on Tasmanian speleothems enable preliminary estimates to be made of ages and rates of evolution of Tasmanian karst caves. Occurrence of speleothem deposition has varied markedly in time, the highest abundance being associated with marine isotope stages 1 and 5. Rates of growth of from 21 to 79 mm/ka have been determined for four equilibrium diameter stalagmites, some of which are known or expected to provide suitable material for isotopic analysis.

ISSN:0016-7614    

DOI:10.1080/00167618308729239

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

The Ediacara fossil assemblage occurs widely in the Flinders Ranges, South Australia, in a single, readily mappable stratigraphic interval—the Ediacara Member of the Rawnsley Quartzite, which is part of the Pound Subgroup of the Wilpena Group. The Member occurs low in the Rawnsley Quartzite and consists of siltstones, medium‐ to thick‐bedded sandstones, and heterolithic units of intercalated siltstone and sandstone. Features such as rhythmical bedding and flaser bedding, interference and flat‐topped ripples, winnowed coarse sand residues, abundant clay galls, and rare desiccation cracks suggest that the heterolithic siltstone/sandstone units represent intertidal deposits. The rich body‐fossil assemblage occurs chiefly in these deposits of probable intertidal origin, and for the most part appears to represent organisms stranded by the tide away from their normal habitat. Associated bioturbation structures include horizontal, penetrative (post‐depositional) burrows, but vertical dwelling burrows have not been found; the Pound Subgroup evidently pre‐dates their widespread appearance.

ISSN:0016-7614    

DOI:10.1080/00167618308729240

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Re‐examination of the Silurian to Early Devonian lithofacies, biofacies and sediment movement patterns for the Melbourne Trough suggests a palaeogeography orientated N‐S. The Melbourne Trough became progressively shallower from the late Wenlock to the early Ludlow, culminating in fringing of the trough margins by limestone and/or shallow water elastics in the Pragian. The central portion of the Trough in the Yea‐Eildon area continued to receive sediments into a deep water environment throughout the preserved depositional history of the trough, until the final depositional phase of the non‐marine red bed facies of the Middle Devonian.

ISSN:0016-7614    

DOI:10.1080/00167618308729241

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor