摘要:

Whilst acknowledging the geological evidence for a Silurian age of the Tumblagooda Sandstone of Western Australia, this article draws attention to palaeomagnetic data which suggest a significantly older age. The pole position from the Tumblagooda Sandstone provides a strong constraint on the location of the Australian Palaeozoic apparent polar wander path (APWP), and by inference on that of the Gondwana APWP. Although the use of this pole as a key pole cannot be justified because the age of the Tumblagooda Sandstone is not reliably known, comparison of this pole with a Siluro‐Devonian pole from eastern Australia, and Ordovician to Silurian poles from Africa (in an appropriate pre‐breakup reference frame), suggests an age of Ordovician. Palaeontological evidence from large eurypterid tracks suggests a Silurian to Devonian age. While stratigraphic evidence is meagre, isotopic data have been used to support a post‐Early Silurian age. However the isotopic data are shown to be compatible with a significantly older age.

ISSN:0812-0099    

DOI:10.1080/08120099008727938

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The New England Orogen of coastal central Queensland contains the Wandilla terrane in the west and the Shoalwater terrane in the east and north. Both terranes underwent multiple deformation (D1‐D4) and at least one main episode of prolonged metamorphism. The first deformation (D1) resulted from subduction accretion in a Devonian and Carboniferous forearc. Early subduction complex structures in the Wandilla terrane are dominated by steeply dipping melange with lenticular phacoids of tuff and greywacke in a mudstone matrix; whereas in the Shoalwater terrane strata are mainly coherent and the overall structure is inferred to comprise slices repeated by an imbricate thrust system. The second deformation (D2) is widespread in both terranes and formed a mostly subhorizontal to moderately east‐dipping cleavage and tight to open F2folds. A strong down‐dip stretching lineation was generated in the Wandilla terrane. F2folds and S0‐S2relationships have a consistent geometry indicating an antiform to the east. Rotation of bedding, already steeply dipping due to subduction accretion, resulted in overturned strata that are typical of the Shoalwater terrane. D3and D4developed as a progressive sequence during the same general deformation as D2; this occurred in the Middle to Late Permian although farther west its effects continued into the Triassic.

ISSN:0812-0099    

DOI:10.1080/08120099008727939

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The results from a large scale magnetometer array study in the Canning Basin have revealed the existence of a substantial geomagnetic induction anomaly striking to the southeast from Broome right across the basin. The reversal in the vertical field fluctuation can be followed along the anomaly and indicates that the anomaly is essentially a line current. The anomaly appears to be associated with the Jurgurra and Barbwire Terraces of the Fenton Fault system. It is suggested that the anomaly may be caused by the pervasive halite deposits of the Silurian Carribuddy Formation, assuming that some moisture is available to enhance electrolytic conduction. A preliminary analysis of the effect of the induction anomaly on aeromagnetic survey data, suggests that it may introduce errors of tens of nanoTesla during magnetic quiet days and as large as a hundred nanoTesla during periods of substorm activity.

ISSN:0812-0099    

DOI:10.1080/08120099008727940

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

In the Reynolds Range (central Arunta Block), a series of mid‐Proterozoic, clastic shallow marine metasediments, the Reynolds Range Group, unconformably overlies a sedimentary and granitic basement and is intruded by granites. The group comprises five distinct stratigraphic units: a quartzite, a lower calc‐silicate, a pelite, an upper calc‐silicate and a felsic volcanic unit. The quartzite unit that extends along the northeastern flank of the Reynolds Range, and the lower calc‐silicate unit that occurs to the southwest, represent lateral transitions of a basal unit which was deposited on a metamorphic basement in an epicontinental shallow marine basin. A series of northeast‐directed marine transgressions resulted in a deepening of the marine basin which is reflected in the transition to the pelite unit. The upper calc‐silicate occurs as a lens within the pelite unit and represents carbonate build‐ups that were deposited on a raised platform free from siliciclastic input. During the initial stages of the depositional cycle, a thick rhyolitic unit was deposited in the northwest Reynolds Range. The Reynolds Range Group, which represents division 3 sediments in the Arunta Block, correlates with the 10 000 m thick Hatches Creek Group in the Davenport province. The implication is that the entire Arunta Block might have been covered by a potentially thick sequence of sediments that were comparable with the Reynolds Range Group. Such a thick sequence largely explains the lithostatic pressures that existed during subsequent granulite facies metamorphism in the area.

ISSN:0812-0099    

DOI:10.1080/08120099008727941

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The Balcooma prospect is one of three volcanogenic massive sulphide deposits in the (?)Cambro‐Ordovician Balcooma metamorphic belt in northern Queensland. The Balcooma metamorphic belt is an assemblage of multiply deformed metasedimentary and felsic metavolcanic rocks that has undergone amphibolite grade metamorphism. The deposit occurs in a metapelitic lens within a sequence of metagreywacke containing minor interbedded volcaniclastic rocks.

ISSN:0812-0099    

DOI:10.1080/08120099008727942

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Geologists have generally accepted the intuitively appealing concept that rigid objects, which are larger than matrix grains, rotate relative to geographic co‐ordinates during non‐coaxial ductile deformation. This has been reinforced by experiments in which rigid body rotation occurs in continuous media deformed under bulk simple shear. Widespread acceptance of this concept, and its application to rock deformation, incorrectly implies that it has been thoroughly and successfully tested in real rocks. When data obtained from deformed rocks suggest that relatively large rigid objects do not rotate, they have generally been rationalized as products of coaxial deformation and considered rarities. This degree of rationalization is no longer acceptable in the light of accumulating data, as well as more recent modelling which suggests that non‐rotation of relatively large rigid objects during ductile deformation is the more common situation, and that very special circumstances are required for such objects to rotate. If these objects do not rotate relative to geographic co‐ordinates during non‐coaxial ductile deformation, they provide a unique tool for unravelling the kinematic history of orogenic belts.

ISSN:0812-0099    

DOI:10.1080/08120099008727943

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The Late Proterozoic (Sturtian) glacigenic succession in the vicinity of the Yankaninna Anticline, in the central North Flinders Basin, varies in thickness from 60 to 1500 m. These dramatic thickness changes are attributed in part to a pre‐existing topography, but were probably also controlled by contemporaneous faulting. Despite variations in thickness, a common, probably palaeoclimatically‐controlled, four‐fold stratigraphy is present throughout the region. Palaeocurrents, mainly from ripple cross‐laminations in resedimented rocks, indicate a centrifugal pattern of sediment dispersal around the Yankaninna Anticline. Together with megabreccias containing fragments from the underlying Burra Group, this evidence suggests that the area now occupied by the Yankaninna Anticline may have been a submarine(?) high in the central part of the North Flinders Basin during the Sturtian glaciation. Although two distinct Sturtian glacigenic diamictite‐bearing units are present in the area, no evidence was found for an unconformity between them.

ISSN:0812-0099    

DOI:10.1080/08120099008727944

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Three pyroclastic samples that bracket the coal‐bearing Permian System of the northern Sydney Basin have been dated using the zircon U/Pb and hornblende K/Ar methods. The Matthews Gap Dacitic Tuff Member, situated 170 m below the base of the Permian System, gives a best estimate of 309 ± 3 Ma. Its age correlates well with the Paterson Volcanics which suggests that the immediately overlying clastic sediments are equivalent to the Seaham Formation.

ISSN:0812-0099    

DOI:10.1080/08120099008727945

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

A small Early Cambrian carbonate platform occurs at the southeast margin of the Bunkers Graben near Wilkawillina Gorge in the Flinders Ranges. Platform sediments are represented by the Wilkawillina Limestone, with biohermal, calcarenite, lagoonal and peritidal facies present. Sedimentation on the platform was interrupted by several periods of subaerial exposure. Platform and off‐platform facies interfinger, deep water sediments include the slope carbonates of the Parara Limestone and the Oraparinna Shale. Shallow marine off‐platform facies are represented by the Bunkers Sandstone and Edeowie Limestone Member. The platform evolved from a shoal‐rimmed to a reef‐rimmed bypass margin. The platform sequence provides a useful model to interpret similar Early Cambrian successions elsewhere in the Delamerian fold belt and further afield.

ISSN:0812-0099    

DOI:10.1080/08120099008727946

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

ISSN:0812-0099    

DOI:10.1080/08120099008727947

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor