摘要:

The 2,400‐metre thick Hamersley Group is characterised by its 900 m of banded iron formation, and is the middle of three constituent groups of the Mt Bruce Supergroup, which forms the contents of the 2,300–1,800 m.y. old Hamersley Basin. The Hamersley Basin initially covered about 150,000 km2of northwestern Australia, and in its present widespread outcrop, the Mt Bruce Supergroup is mostly little disturbed or metamorphosed. Within one iron formation unit 142 m thick, the Dales Gorge Member of the Brockman Iron Formation, within the Hamersley Group, there are three scales of stratification, termed macrobanding, mesobanding (the normal ‘banding’ of banded iron formation) and microbanding. Microbands are thin (0.2–2.0 mm) regular laminae, alternately rich and poor in iron, within chert mesobands. Microbands, mesobands and macrobands may all be correlated over the whole of the present outcrop. Microbands are believed to result from annual seasonal control of the primary precipitation in the basin, while alternations between microbanded chert mesobands and the adjacent non‐microbanded chert‐matrix are thought to reflect a 25‐year environment cyclicity. There is also a higher‐order cyclicity. The microbands are chemical evaporitic varves. There are many published accounts of modern non‐glacial varves of a similar order of thickness whose identity as varves is established by direct evidence. Many of these are couplets of laminae, one half being largely organogenic, and similarly structured couplets have been widely accepted as varves in descriptions of Phanerozoic rocks. Evaporitic laminae have also been so accepted, although there are no exact modern analogues. Microbands are closely similar to these in geometry, and all varves are characteristically regular.

ISSN:0016-7614    

DOI:10.1080/00167617208728798

出版商:Taylor & Francis Group    

年代:1972

数据来源: Taylor

摘要:

The distribution, mode of occurrence and population densities of extensive colonies of worms, and the morphology of their thick‐walled tubes are described. Interaction between two species occurring in certain strata enables the feeding habits of the tube‐builders to be reconstructed, and they are thus identified as terebellid worms. The worms when alive were less than 5 mm in diameter and had tentacles 27 mm long. Their environmental situation was near the southern edge of an extensive area of marine deposition covering much of the Sydney Basin. The depth was below wave base. The worm populations were buried alive during deposition of sheets of sediment, probably resulting from intermittent sudden flooding events in coastal rivers.

ISSN:0016-7614    

DOI:10.1080/00167617208728799

出版商:Taylor & Francis Group    

年代:1972

数据来源: Taylor

摘要:

U‐Pb and Th‐Pb studies of rocks from an extensive Palaeozoic volcano‐plutonic province in northeast Queensland support conclusions derived from a previous Rb‐Sr study. The data oppose an earlier hypothesis, that two widespread and fundamentally different magma types are present. Interpretation of the lead data, however, must be treated with some caution since uranium movement apparently begins at a very early stage of weathering; X‐ray fluorescence data are displayed in a manner which suggests a simple rejection criterion.

ISSN:0016-7614    

DOI:10.1080/00167617208728800

出版商:Taylor & Francis Group    

年代:1972

数据来源: Taylor

摘要:

Recognition of time as an important soil‐forming factor suggests the importance of soil stratigraphy in studies of soil genesis and history of landscape development. Some of the principles of recognizing and ranking soil‐stratigraphic units are considered especially in the context of Butler's (1959) K cycle theory.

ISSN:0016-7614    

DOI:10.1080/00167617208728801

出版商:Taylor & Francis Group    

年代:1972

数据来源: Taylor

摘要:

In the past the Mount Dromedary igneous complex has been regarded as a differentiated laccolith, with the more felsic banatite at the summit of the mountain, monzonite on the lower slopes and pyroxenite at sea‐level.

ISSN:0016-7614    

DOI:10.1080/00167617208728802

出版商:Taylor & Francis Group    

年代:1972

数据来源: Taylor

摘要:

There appears to be little correlation of earthquake epicentres with known surface geological features in South Australia. Seismic wave travel‐time residuals are used to derive corrections for the velocity and depth parameters for the simple uniform crustal model which approximates to that in South Australia. Local studies of Moho depth in the seismic zone and analysis of travel‐time station corrections from both local earthquake and teleseismic data suggest that lateral and vertical variations in the South Australian crust are small. Data presented in this paper appear to be consistent with a plate tectonic model derived from focal mechanism studies (Stewart & Mount, 1972) for the active South Australian seismic zones.

ISSN:0016-7614    

DOI:10.1080/00167617208728803

出版商:Taylor & Francis Group    

年代:1972

数据来源: Taylor

摘要:

Within the Pilbara Block of Western Australia, a complex of migmatite, gneissic and foliated granite near Marble Bar is intruded by a stock of younger massive granite (the Moolyella Granite) with which swarms of tin‐bearing pegmatites are associated. The age of the older granite has been determined by the Rb‐Sr method as 3,125 ± 366 m.y., and that of the Moolyella Granite as 2,670 ± 95 m.y. Initial Sr87/Sr86ratios suggest that the older granite is close to primary crustal material, but that the Moolyella Granite consists of reworked material. It probably formed by partial remelting of the older granite.

ISSN:0016-7614    

DOI:10.1080/00167617208728804

出版商:Taylor & Francis Group    

年代:1972

数据来源: Taylor

摘要:

The interpretation of Canberra's landforms as unexhumed survivals from Bowning faulting and mid‐Devonian vulcanicity is opposed. Some major faults are truncated whereas sharp scarps coincide with others. In the nearby Taemas area, the Canberra‐Yass Plains cut across Tabberabberan folds. Summit surface remnants surviving high in the A.C.T. Ranges and discordant river gorges are incompatible with extreme age of the relief. River nick‐points and steps between surfaces are some related and some unrelated to faults, with like import. Stripping of the Murrumbidgee Batholith, also of Bowning age, would have caused substantial filling of the Canberra Rift; during subsequent removal, erosion would not have entirely respected Silurian rocks similar in resistance to Devonian fill. Permian rocks to the east must in part derive from erosion of the Canberra area. Local rates of denudation of 5 cm/1000 y. are hard to reconcile with survival of high steep relief from the mid‐Devonian.

ISSN:0016-7614    

DOI:10.1080/00167617208728805

出版商:Taylor & Francis Group    

年代:1972

数据来源: Taylor

摘要:

In the Mt Lyell area limestone conformably underlying unmineralized Mt Read Volcanics and unconformably overlying mineralized Mt Read Volcanics contains fossils of late Middle Cambrian or early Upper Cambrian age. This suggests an upper limit of late Middle Cambrian or early Upper Cambrian for the mineralization in the Mt Lyell area. The view of Geeet al.(1970) that the Mt Read Volcanics and the fossiliferous Cambrian sequences of western Tasmania are at least partly contemporaneous is confirmed.

ISSN:0016-7614    

DOI:10.1080/00167617208728806

出版商:Taylor & Francis Group    

年代:1972

数据来源: Taylor

摘要:

Dykes and plugs of micaceous kimberlite are found within an area centred 25 kilometres east‐southeast of the town of Terowie in South Australia.

ISSN:0016-7614    

DOI:10.1080/00167617208728807

出版商:Taylor & Francis Group    

年代:1972

数据来源: Taylor