摘要:

This study is essentially devoted to the area covered by the Landsat scene 1330–09521 (province of Värmland, parts of the provinces of Dalarna and Västmanland, Sweden). The south-western margin of the Baltic Shield is traversed by a large number of lineaments. The lineament density is approximately twice the density in the neighbouring part of the Svecokarelian principal unit. The angular distribution in the south-western principal unit is more pronouncedly clustered into the range N15W-N30W than in the Svecokarelian unit. The distribution is not unimodal in any of the units. Where checked in the field, the linear structures often constitute localized zones frequently connected with breaks between lithologies. Normally rock structures such as schistosities, fold axes, etc. do not show up. The lineaments are probably due to tectonic movements, which have influenced the bedrock during a large part of its history. Lineaments are observed to cut through the youngest sediment, and to offset the Mylonite Zone, but they also control the intrusion pattern of earlier plutonics.

ISSN:0016-786X    

DOI:10.1080/11035898009448584

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

The Slite Siltstone, the uppermost unit in the Wenlockian Slite Beds of Gotland, Sweden, is fairly unfossiliferous as a whole, but the silty beds are intercalated with a few calcareous beds which contain a diverse and abundant fauna. The brachiopodsStrophochonetes cingulatus and Plagiorhyncha cordataare the characteristic fossils of the siltstone. The preferred orientation of high-spired gastropods (Holopellasp.) and orthoconic nautiloids, recorded at two localities, was probably caused by sediment-sliding. DisarticulatedCypricardiniaspecimens occur in convex-up position and thus indicate a turbulent environment. An assemblage ofStrophochonetes cingulatushas been found in life position, which shows that a rapid burial and a less turbulent environment are probable. The oriented fossils and the faunal composition show that the siltstone was deposited in a shallow marine environment, below the normal wave-base in the central area. In the north-cast and south-west of the siltstone extension, a shallower water depth seems probable. Large-scale transport of sediment was frequent. The presence of‘Atrypa’ dormitzerifrom the locality Svarvare 1 suggests a relation with assemblages from Scania and Bohemia. The siltstone fauna does not correlate with any depth-related assemblage from Wales or the Welsh borderland.

ISSN:0016-786X    

DOI:10.1080/11035898009448585

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

ISSN:0016-786X    

DOI:10.1080/11035898009448586

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

The bryozoan fauna from the Dalmanitina Beds at Kinnekulle in Västergötland, comprising thirteen species, is similar to that from Borenshult in Östergötland, but differs from known contemporary faunas from Dalarna, Öjle Myr (Gotland) and Porkuni (Estonia). The Kinnekulle fauna is dominated byClathropora bifurcata(Brood),Nematopora sublineataMännil andEridotrypella crassan.sp.; the latter is described, together withPhylloporina kinnekullensisn.sp.

ISSN:0016-786X    

DOI:10.1080/11035898009448587

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

ISSN:0016-786X    

DOI:10.1080/11035898009448588

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Pumpellyite-bearing mineral assemblages, formed during one or more episodes of non-deformational regional metamorphism, have been found in post-Svecokarelian rocks of central Sweden. Two different sub-greenschist facies have been established: the prehnite-pumpellyite and the pumpellyite-actinolite facies, in Jotnian and sub-Jotnian rocks respectively. It is here suggested that the common overprinting of post-deformational ‘retrograde’ minerals on amphibolite facies assemblages in Svecokarelian rocks of central Sweden could, at least in part, be attributed to the metamorphic episode(s) mentioned above. Furthermore, ‘deuteric’ minerals in granitoids of the same area could have the same origin.

ISSN:0016-786X    

DOI:10.1080/11035898009448589

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

The rock suite from which the 1450±53 Ma Rb-Sr whole rock isochron age (λ= 1.39×10-11a-1) for the ‘Varberg charnockite’ was derived by Welin & Gorbatschev (1978:Geologiska Föreningens i Stockholm Förhandlingar 100, 225–227) includes examples of both metamorphic and intrusive charnockite. Both types, however, were formed in the same petrogenetic period in the geological history of the region when the cover and basement sequences were both affected by a cycle of igneous activity during which three distinct pulses of mantle-derived gabbroic magma were intruded, accumulations of melt derived from deeper crustal levels were emplaced as differentiated charnockitic adamellite-rapakivi granite complexes, and thermal metamorphism of the metamorphic basement rocks produced localised developments of depleted granulites and charnockites in situ. Tectonism ultimately replaced this period of magmatic activity and the products of the earlier stages were deformed and metamorphosed to a varying extent depending on their location in the cover-basement sequences. The isochron rocks are all from within the basement segment which was that least affected in the late orogenic stage and may, as Welin & Gorbatschev suggested, give the intrusion age. The anorogenic igneous activity is closely similar in style, component composition and age to that of the late Proterozoic of North America and may be its eastern extension to the Baltic Shield.

ISSN:0016-786X    

DOI:10.1080/11035898009448590

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

The Precambrian evolution of south-western Sweden is reviewed concisely to provide a background for the dating of the Varberg charnockite. It is shown that the alleged Gothian and western Pregothian regions pass continuously into each other. In the west, the oldest dated rocks have ages around 1700 Ma. An older (Svecokarelian?) basement may be present in the eastern parts of the region. Basic magmatism, metamorphism and the relationship between orogenic and anorogenic events are discussed.

ISSN:0016-786X    

DOI:10.1080/11035898009448591

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Across Värmland County there stretches in N-S direction a broad belt of black diabases known as hyperites. To the east it borders on a diffuse tectonic zone separating the gneiss complex of southwestern Sweden from the Svecokarelian orogenic belt. To the west, the diabases are partly involved in a late, middle Proterozoic thrust zone, the Mylonite Zone. The hyperite diabases appear as variably boudinated sills and dikes which generally follow the northwest strike of the older gneissic rocks. A pegmatoid variety from the interior of a large dike was collected for radiometric dating. Separated zircons plot on a regression line with an upper intercept with the Concordia at 1550 Ma, which is interpreted to correspond to the crystallization of the hyperite diabase. The lower intercept is at 880 Ma, which coincides with a Rb-Sr total rock-mineral isochron age of 975 Ma within the limits of error. It is concluded that a metamorphic event at 900–1000 Ma has caused Sr isotopic homogenization within the analyzed sample and radiogenic lead loss from the zircons.

ISSN:0016-786X    

DOI:10.1080/11035898009448592

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Stenotheca cornuWiman, 1903, from the Lower Cambrian of the South Bothnian area (southernmost Gulf of Bothnia), is redescribed and referred to the genusLapworthellaCobbold, 1921. It is a small, cornute, phosphatic fossil with pronounced growth ridges crested with denticles, about 10–20 per mm. It differs from the SiberianL. dentataMissarzhevskij, 1969, in having less densely spaced denticles. The specimens described asL. dentatafrom theStrenuellaLimestone at Comley, England, should be referred toL. cornu.

ISSN:0016-786X    

DOI:10.1080/11035898009448593

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor