摘要:

Two greenstone formations in the Jofjället area, central Swedish Caledonides, have been analysed for major and trace elements in order to establish their petrology and tectonic environment of origin. The formations — the Ruffe Greenstone and the Brackfjället Greenstone — are situated in the uppermost part of the Seve-Köli Nappe Complex. The enrichment in volatiles, depletion in SiO2, redistribution of CaO and alkali contents are certainly caused by post-eruptive alteration processes. The Ruffe Greenstone is a tholeiite of a transition type between ocean-floor and within-plate basalt, while the Brackfjället Greenstone is an alkaline basalt showing a clear within-plate basalt affinity. The basalts are possibly formed during the later stages of rifting and ocean basin opening in a near-continental environment. The basalts can probably be correlated with the Støren greenstone in Norway.

ISSN:0016-786X    

DOI:10.1080/11035898209453720

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Syenitic differentiates from the Fongen-Hyllingen intrusion, which grade downwards into layered gabbroic rocks, give a Rb-Sr whole-rock isochron age of 405 ± 9 Ma and an initial87Sr/86Sr ratio of 0.7047 ± 0.0002. The age is interpreted as dating the time of magmatic crystallisation of these final differentiates. Emplacement at 500–600 MPa, followed by amphibolite facies metamorphism, occurred during the Middle-Upper Silurian (Scandinavian) orogenic event and supports a date of around 400 Ma for the Silurian-Devonian boundary.

ISSN:0016-786X    

DOI:10.1080/11035898209453721

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

As a continuation of earlier work on the Holocene history of the pine forests of northern Fennoscandia, new finds of subfossil pine (Pinus silvestris) are reported from sites in Enontekiö, northwestern Finnish Lapland, and at one location in the Lyngenfjorden area in North Norway. Two pollen diagrams from lake sediments are also presented, one from near Kilpisjärvi in Finland, the other from close to Skibotn in Norway. The megafossil, pollen, and radiocarbon data provide a more or less consistent picture of the history of the pine forests of northern Fennoscandia. Pine spread to the Kilpisjärvi and Lyngen area around 7500–7000 B.P., and the pine forests were at their maximum there from about 7000 to 4000 B.P. Their subsequent gradual decline meant a retreat of the pine limit by some 70 km or so. Discussions are provided on climatic variations in the area, and on possible further research into these and other palaeo-ecological changes.

ISSN:0016-786X    

DOI:10.1080/11035898209453722

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

ISSN:0016-786X    

DOI:10.1080/11035898209453723

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Based on diatom analysis, pollen analysis and radiocarbon dating, a shore-level displacement curve has been constructed for Nord-Jæren, south-west Norway. The upper marine limit on Nord-Jæren, 25–26 m above sea level, must be older than 13 100 ± 190 years B.P. A regression throughout Bølling and Older Dryas times reached down to 11–14 m a.s.l. in Allerød time before a short-lived transgression to approximately 21 m a.s.l. occurred in the transition between Allerød and Younger Dryas. The curve then falls quickly through Younger Dryas.

ISSN:0016-786X    

DOI:10.1080/11035898209453724

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The ‘När block’ (approximately 1 × 1 m) from the Silurian (Ludlovian) Eke Beds of Gotland, Sweden, displays a crinoid thanatotope of 260 specimens belonging to four species,Haereticotaxocrinus aspern. gen., n. sp.,Desmidocrinus pentadactylusAngelin,Carpocrinus petilusn. sp., andC. angelinin. sp. They occur in marked preferred orientation at the upper surface of a lens consisting ofCoenitesfragments and bioclastic debris, and were buried in situ by a sudden influx of the same type of sediment. The fossilizable community comprized crinoids only: those other organisms occurring in the rock, including the ubiquitousCoenites, were washed in with the sediment burying the crinoids and were no part of the community itself. Crinoid stem lengths indicate a multi-level community pattern, withHaereticotaxocrinusforming the upper crinoid level. TheCarpocrinusandHaereticotaxocrinuspopulations include juvenile specimens, whileDesmidocrinuscomprises adults only.

ISSN:0016-786X    

DOI:10.1080/11035898209453725

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The ambulacral pattern of the Caryocystitida differs from that of all other primitive echinoderms. Phylogenetically the number of ambulacra increased from two to three and finally to four. In the Blastozoa three primary ambulacral patterns are recognised: a pentaradiate, a triradiate and a biserial. The pentaradiate pattern is present in several classes, the triradiate is restricted to the Hemicosmitida and the bilateral pattern is confined to the Caryocystitida. There appears to be considerable differences between the three superfamilies of the class Rhombifera. These differences in primary patterns may have important taxonomic significance.

ISSN:0016-786X    

DOI:10.1080/11035898209453726

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Caryocystiteshas five peri-oral plates, as in other members of the superfamily, and a primitive stem with five pentameres. Evolutionary trends include addition of ambulacra, greater regularity in plate distribution and increasing complexity in the development of respiratory pores. InCaryocystites thorslundin.sp. young specimens have only four primary circlets of thecal plates; the peri-oral, peri-gonal, periproctal and basal. Thecal enlargement was accomplished by accretional growth of primary plates and the addition of new thecal plates intercalated between the original four plate circlets.Caryocystitesevolved in the early Middle Ordoviciap and became extinct at the end of the Ordovician. The morphology and evolutionary trends are similar to those of the other caryocystitids. Seven species from Sweden are described morphologically and taxonomically, including three new ones (C. valdari, C. rugosus, C. thorslundi).

ISSN:0016-786X    

DOI:10.1080/11035898209453727

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Red, microcline rich granites occur in the Åmål and western Pregothian tectonic mega-units in south-western Sweden. The Sandsjön granite is the northernmost known occurrence of these rocks in the ‘Western Pregothian’ of Sweden. The Rb-Sr whole-rock dating of the Sandsjön granite fails to give any conclusive age, hypothetically due to either a metamorphic disturbance or to an inhomogeneous distribution of the initial87Sr/86Sr ratio. The zircon age is 1210+16−14Ma (1σ) and is interpreted to correspond to the crystallization of the Sandsjön granite. The emplacement of this granite is thus contemporaneous with previously dated similar granites in the Åmål and ‘Western Pregothian’ mega-units.

ISSN:0016-786X    

DOI:10.1080/11035898209453728

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

ISSN:0016-786X    

DOI:10.1080/11035898209453729

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor