摘要:

Ordovician successions in the Lachlan Fold Belt of southeastern Australia are dominated by quartz-rich sandstone and mudstone within a monotonous turbidite association. The Hotham Group of the Benambra terrane in eastern Victoria is a typical example. It is 5 km thick and dominated by four facies: amalgamated sandstones, thick-bedded turbidites, thin-bedded turbidites and mudstone, with less abundant chert and black shale. Depositional environments of the Hotham Group and regional relationships indicate that the Ordovician turbidite successions of the Benambra terrane formed in submarine channel-levee complexes developed on a turbidite-covered abyssal plain comparable in size to large modern submarine fans. Amalgamated sandstones and thick-bedded turbidites represent deposition in channels that possess largely unordered, vertical bed-thickness trends, whereas the fine grained facies were probably laid down in levee bank and interchannel environments. Flutes and scours in the channel facies indicate palaeoflow towards the east. This pattern is consistent with the distribution of pelagic facies (i.e. chert and black shale) which are much more common in the northeastern part of the Hotham Group. The southwestern part was therefore more proximal to the ancient continental margin and is characterized by a more differentiated succession with several mudstone horizons. Pelagic sediments are not found associated with any particular facies association as in other ancient successions.

ISSN:0812-0099    

DOI:10.1080/14400958908527947

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Seismic reflection profiles across Mesozoic basins in easternmost Australia show that the Esk Trough, Ipswich Basin and Clarence-Moreton Basin were initiated by transtensional events in the Late Permian or Early Triassic. The initial sediments in the basins are unexposed sequences below the Esk Trough and Ipswich Basin. In the Scythian, strike-slip faulting moved eastwards to the site of the present Ipswich Basin, and the Esk Trough subsided due to thermal relaxation. After oblique extension ceased in the Carnian, thermal relaxation subsidence led to deposition of sediments firstly in the Ipswich Basin and then in the more extensive Clarence-Moreton Basin. The structures and sediments of the extension and thermal relaxation phases show a pronounced asymmetry in cross-section, as expected during pure extension, but no low-angle detachment faults have been detected indicating strike-slip movement on the bounding fault of the Esk Trough (the West Ipswich Fault) during extension. Thus the basins developed during a period of transtension (oblique extension) associated with major strike-slip faults in the Early Mesozoic.

ISSN:0812-0099    

DOI:10.1080/14400958908527948

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The Early Permian Staircase Sandstone Member of the Cattle Creek Formation forms part of the Permo-Triassic basin fill in the Denison Trough (southwest Bowen Basin). The interval is interpreted as the deposits of a wave- and tide-influenced delta because of its interbedded lithological character, alternation of marine and non-marine strata, bipolar palaeocurrent distribution and assemblage of preserved sedimentary structures. The Staircase Sandstone delta prograded eastward into the basin from the northwestern margin, passing distally into progressively more offshore facies.

ISSN:0812-0099    

DOI:10.1080/14400958908527949

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The Ventersdorp Supergroup (∼2.7 Ga) consists of a thick pile of sedimentary and volcanic units which are widely distributed over a large part of the Kaapvaal craton. At the southwestern edge of the craton, in the T'Kuip Hills, a sequence of rocks termed the Sodium Group unconformably overlies foliated biotite granite (∼2.8 Ga), and occupies a half-graben along part of the craton margin. This succession is correlated with the Platberg Group of the Ventersdorp Supergroup. Initially piedmont-type arkosic sediments characterized by granite-boulder conglomerate were deposited as proximal facies. Higher in the sequence the grain size diminished and air-fall tuff became an important constituent mixed with the clastic component. Minor lenses of mafic lava and tuff also appeared in the arkose. Flows of felsic volcanics then followed, probably as high-temperature, volatile-poor ignimbrite. As elsewhere in the Ventersdorp Supergroup, mafic volcanism succeeded the felsic phase. This resulted in a varying unit of tholeiitic basaltic and andesitic-dacitic lavas with highly vesicular flow tops. This volcanism was characterized by repeated periods of quiescence, resulting in the deposition of arkose and also near the top, arkose, tuff, shale and carbonate in ephemeral lake environments. The uppermost part of the sequence is composed of vesicular basaltic lavas with pillow zones. Burial metamorphism caused pervasive alteration of the felsic and mafic volcanics of the Sodium Group, replacing some of the original minerals with a greenschist assemblage and changing the original chemical composition. Continued marginal faulting and uplift took place throughout the formation of the Platberg and Sodium Groups. The tectonic setting, conditions of formation and stratigraphy of the Ventersdorp Supergroup are remarkably similar to those of the Fortescue Group of the Pilbara craton in Western Australia.

ISSN:0812-0099    

DOI:10.1080/14400958908527950

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The Gordon Limestone is characterized by low Mn, moderate Na and high Sr concentrations, similar to those in modern tropical aragonitic carbonates. Mn reflects predominantly original aragonite mineralogy, oxidizing peritidal conditions and the influence of meteoric water. Sr and Na concentrations generally decrease with increasing Mn. Na concentrations are similar in limestones and dolomitic limestones because of the lack of appreciable freshwater influence during dolomitization. Sr concentrations decrease with increasing Mg concentrations, indicating dolomitization in predominantly marine waters. Similar amounts of Mn in both limestones and dolomitic limestones indicate prevalence of oxidizing conditions during their formation.

ISSN:0812-0099    

DOI:10.1080/14400958908527951

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Quaternary calcrete deposits in palaeodrainage basins of the arid zone of Western and central Australia have developed near the surface within a remarkably short span of time. Silicification of the calcrete, involving the filling of voids and replacement of calcite by opaline and quartzose silica, has taken place in both the vadose and phreatic hydrological zones as a late diagenetic event. Diagenetic changes in the textures of silicified calcrete commonly correspond with silica-phase transformation and reflect replacement of carbonate through dissolution and reprecipitation. Silicified calcrete horizons in ancient terrestrial (lacustrine and groundwater) carbonate deposits may be related to the migration history of the silica in palaeohydrological systems. The presence of silica as thin grain coatings, veins and pore and cavity linings is a manifestation of the intricate balance between the solution of host calcrete and precipitation of silica under prevailing arid/semi-arid hydrological conditions. Such cogenesis, although spatially highly variable, has an important bearing on preservation and redistribution of economic mineral ores, and on the occurrence of fresh groundwater aquifers in the internal drainage basins of Australia.

ISSN:0812-0099    

DOI:10.1080/14400958908527952

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

An integrated description is given of some recently developed statistical methods for analysis of one or more samples of measurements of palaeocurrent data, including testing of isotropy, estimating mean or median directions together with assessments of the reliability of the estimates, comparing and combining information from two or more samples of data, and treating data measured as axes or undirected lines, rather than as vectors. Each method described is illustrated on a data set.

ISSN:0812-0099    

DOI:10.1080/14400958908527953

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The Werner deconvolution technique for automatic analysis of magnetic data is a powerful tool for the interpretation of magnetic profiles. In particular, the technique is a valuable aid to the interpretation of deep crustal structures beneath the continental margin which frequently lie below the penetration of all but the most high-powered seismic reflection tools. Inverse modelling of selected simple geological structures (buried scarp, graben, half-graben) confirms that the interface model is valuable in delineating the tops of magnetic bodies, while the thin sheet model gives an indication of the depth extent of the bodies. In the case of horizontal sheets in contact (simulating oceanic spreading anomalies), the thin sheet model delineates the boundary, while the interface model gives estimates which are too shallow.

ISSN:0812-0099    

DOI:10.1080/14400958908527954

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

A 300 km-long linear aeromagnetic anomaly associated with the Karari Fault Zone defines a subvertical, Early Proterozoic, intracratonic shear zone within the Gawler Craton. The shear zone contains various mylonites and separates quartz + sapphirine-bearing granulites to the northwest from upper amphibolite facies gneisses to the southeast. The aeromagnetic anomaly is produced by magnetite-rich metasediments (iron formation), semi-pelitic gneisses and thin pegmaties which have become interlayered on all scales during deformation. All have undergone intense non-coaxial strain with development of both Type I and Type II S-C proto- to ultra-mylonite fabrics. Kinematic indicators, including asymmetrical megacryst tails, elongation lineations, vergence relationships of S-C foliations, and mica ‘fish’ indicate downthrow of the northwestern block with a sinistral strike-slip component. The shear zone represents a major zone of crustal weakness which has remained intermittently active until the Tertiary. Earlier, perhaps Archaean, upthrusting of the northwestern block is suggested.

ISSN:0812-0099    

DOI:10.1080/14400958908527955

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

ISSN:0812-0099    

DOI:10.1080/14400958908527956

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor