ISSN:0016-786X    

DOI:10.1080/11035898009450886

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Post-depositional quicksand structures are described from the Jotnian sandstone of the Nordingrå region, Västernorrland County, where they are developed as point-up structures and sandstone dikes. Disturbance by an earthquake shock wave, uneven compaction of the material, current turbulence and overloading are possible factors which could form these quicksand structures. Earth movements and overloading are the probable causes for the structures in the Jotnian sandstone. The sandstone is essentially an arkose and subarkose with some siltstone and shale.

ISSN:0016-786X    

DOI:10.1080/11035898009450887

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Plagiogmus from the Kalmarsund area in Sweden is an Early Cambrian trace fossil, not Middle Cambrian as originally dated. It is an endichnial burrow, however showing clear affinity to the surfaces of some laminae within the preserving sandstone beds. The previously described ladder-like structure, giving the false impression of an epichnial trail, is the floor of the burrow. The roof of the burrow is preserved as a smooth, almost flat or slightly concave structure, formed by collapse of the roof during compaction, and giving the false impression of a hypichnial trail cast. The animal moved forward by extension and contraction in a strongly mucus-lined burrow, and the transversal ridges across its floor often indicate the direction of movement. Only traces of a very thin infilling of the burrow have been found, in contrast to the thick, laminated backfill found in specimens from Australia, the other area of known common occurrence. In a number of other respects the present material confirms observations made on the Australian material.

ISSN:0016-786X    

DOI:10.1080/11035898009450888

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

ISSN:0016-786X    

DOI:10.1080/11035898009450889

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

The Precambrian of southern Sweden represents a gradual accretion of the Baltic Shield. The Svecofennian region in the east was stabilized by about 1750 Ma. In the west, an orogenic event between ca. 1600 and 1700 Ma added new continental crust to the shield, possibly also reworking a marginal segment of the Svecofennian. A continuous belt of granites and porphyries marks the boundary of the south-western orogen with the stable Svecofennian region. The subsequent development of southern Sweden was essentially ensialic, periods of granite intrusion and metamorphism interrupting anorogenic developments. In a final culmination of activity around 900–1100 Ma, southern Sweden played the role of a crustal segment marginal to the Grenvillian orogen.

ISSN:0016-786X    

DOI:10.1080/11035898009450890

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

This paper gives a survey of the Proterozoic rocks in central Värmland and neighbouring areas to the north. Special attention is given to the Östmark formation of volcanics and sedimentary rocks including the Hålsjöberg quartzite. The predominant rocks of the region are three generations of tectonized Svecokarelian granitoids called gneiss-granites. These seem to be younger than the sedimentary rocks of the Östmark formation. Still younger rocks in the region are a group of post-Svecokarelian Värmland granitoids, a black diabase known as hyperite, and the Gräsmark Formation of volcanics. All rocks mentioned have been tectonized twice during the final Precambrian orogenesis, viz. the Dalslandian (Sveconorwegian). Moreover, the older gneiss-granites have been tectonized during the Svecokarelian.

ISSN:0016-786X    

DOI:10.1080/11035898009450891

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

A compilation of previous and current work in the Proterozoic of the Göteborg region is given in a sketch map. It is concluded that the area to the west of the Mylonite Zone can be treated as a geological unit with the Stora Le-Marstrand supracrustal formation as the oldest component. It was intruded by tonalitic to granitic magmas 1700–1600 Ma ago. These plutons were folded and migmatized before the next period with plutonic intrusions at about 1400 Ma. Compression from west to east with mylonitization followed by folding and migmatization characterized the next period. This metamorphic event ended with the intrusion of granitic batholiths at about 1220 Ma. A major crustal break-up with general uplift, basic dike swarms, erosion and deposition of the Dal Group to the north occurred before the culmination of the Sveconorwegian regeneration at 1000–1060 Ma.

ISSN:0016-786X    

DOI:10.1080/11035898009450892

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

A tentative model of the evolution of the crust lying between the Lerum-Kedum areas of the Mylonite Zone in the west and the Unden area of the Protogine Zone in the east is discussed. Between these two zones the bedrock consists of Archaean red, alkaline gneiss. which undoubtedly is the oldest bedrock in the entire area. This is the basement to the overlying supracrustal sequences on both sides. The supracrustal rocks were at an early stage intruded by differentiated ultramafic-mafic rocks, which are dominated by primary amphiboles orientated in a haphazard fashion. This was later followed by huge granitoid intrusions. The whole rock sequence was then metamorphosed and deformed, giving rise to foliation in the granitoids and to a second foliation in the supracrustal rocks. The outer parts of the ultramafic-matic rocks were to a certain extent altered into amphibolites. Due to anatexis, parts of the alkaline gneiss and to a lesser extent, parts of the granitoids were melted. The anatexis gave rise to massive granitic intrusions accompanied by pegmatites. The last event within the area discussed is the intrusion of the coarse-grained augen granites, named Småland-Värmland granitoids, which cut all structures and rocks present in the Unden area in the east.

ISSN:0016-786X    

DOI:10.1080/11035898009450893

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

The Kongsberg-Bamble-Østfold segment within the Sveconorwegian province is bounded by the Kristiansand-Bang shear zone and the Dalsland Boundary Thrust. The pre-Sveconorwegian basement rocks in this segment were involved in tectono-metamorphic reworking during the Sveconorwegian orogeny, which produced the main regional structures. These structures and opposite thrusting along the eastern and western margins of the segment suggest a large amount of Sveconorwegian crustal shortening in an E-W direction.

ISSN:0016-786X    

DOI:10.1080/11035898009450894

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Promoted by the existence of economic sulphide deposits, much interest through the years has been focused on the geology of the Skellefte field and consequently several hypotheses on the geological evolution of the area have been proposed. This paper summarizes results gained through the work of the Geological Survey of Sweden in the area during the last decade. The importance of the depositional environment for volcanics and sediments is stressed, the latter having been laid down at or close to the boundary between a continental domain to the north and a marine domain to the south. Certain arguments for a plate tectonic interpretation of the observed conditions are presented.

ISSN:0016-786X    

DOI:10.1080/11035898009450895

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor