摘要:

Zircons from a fine-grained granite dyke, penetrating a supracrustal sequence in the Ellenö area, crystallized about 1558 Ma ago, post-dating the supracrustal deposition and the general gneissification of the underlying granitoids. The Rb-Sr systems of the dykes in the area have been disturbed, probably by metasomatic reactions between dykes and country rocks during later metamorphic event(s). The intrusive character of some other medium-grained small granite stocks relative to the supracrustals of the area is not unambiguous, but Rb-Sr data indicate a probable emplacement about 1400 Ma ago.

ISSN:0016-786X    

DOI:10.1080/11035898009455155

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

ISSN:0016-786X    

DOI:10.1080/11035898009455156

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Vase-shaped microfossils occur abundantly in phosphate nodules from near-shore, marine shales and siltstones of the Late Proterozoic (Late Riphean to Early Vendian) Visingsö Beds in southern Sweden. These fossils are not recovered in acid-resistant residues and are only detectable in thin-section. They are regarded as morphologically comparable to vase-shaped microfossils from Upper Proterozoic rocks of the Chuar Group in Arizona, Eleonore Bay Group in East Greenland, Jacadigo Group of Mato Grosso (Brazil), the Murdama Group of Saudi Arabia, and the Akademikerbreen and Roaldtoppen groups of Ny Friesland and Nordaustlandet (Svalbard). The microfossils are tentatively interpreted as remains of loricate, heterotrophic protists which functioned as predators in the near-shore planktic ecosystem, feeding upon bacteria, algae, and other protists. From available data it is concluded that these microfossils may be biostratigraphically significant as indicators of the uppermost Proterozoic (Upper Riphean and Lower Vendian).

ISSN:0016-786X    

DOI:10.1080/11035898009455157

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

ISSN:0016-786X    

DOI:10.1080/11035898009455159

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

The sedimentology of the upper Ashgillian Dalmanitina Beds in the Billingen-Falbygden area in Västergötland is studied. They exhibit facies of shallow-water type. In contrast, the underlying Ulunda, Jonstorp and Nittsjö formations (‘Tretaspis Shales’) and the overlying Llandoverian Rastrites Shale were formed in notably deeper water. A possible explanation for the short-term shallowing, which was accompanied by the development of bahamitic sediments, such as peloids and ooids, would be that a large mass of water became bound in the ice cap that covered part of Gondwanaland.

ISSN:0016-786X    

DOI:10.1080/11035898009455160

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

ISSN:0016-786X    

DOI:10.1080/11035898009455161

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Orthothecid hyolithsBactrotheca dens(Holm) andB. quadrangidaris(Holm) from the Ordovician of the Baltic province have relatively large, smooth embryonic shells indicating a lecithotrophic type of larval development, probably inside egg capsules. Their embryonic opercula are flat, subcircular in outline. Hatching is marked by the retardation of growth of both operculum and shell, and in the appearance of adult longitudinal sculpture on the shell surface. Juvenile post-embryonic opercula have fully developed structures on their internal side.Bactrothecaprobably led a sub-sessile mode of life on its postlarval stages, similar to the Recent gastropodTurritella. Representatives of other hyolith genera,Circotheca stylus(Holm) andDecoritheca excavata(Holm) from the Baltic Cambrian, bear small initial shells with mucros, suggesting a planktotrophic mode of life for the larvae. Data presented here document a high diversity of larval development within particular groups of hyoliths (Monoplacophora), similar to that of gastropods. Inclusion ofSemielliptotheca, Quadrotheca, Trapezotheca, Panitheca, and possiblyNephrotheca, intoBactrothecaas its subgenera is postulated.

ISSN:0016-786X    

DOI:10.1080/11035898009455162

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

ISSN:0016-786X    

DOI:10.1080/11035898009455163

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Detailed studies in five specially selected areas throughout Fennoscandia have shown that a pronounced ice-marginal bulge of the earth's crust took place in that region between ca. 13 000 and 9500 years B.P. During the deglaciation that followed, uplift was rapid initially, but after ca. 8000 years B.P. slowed down to a much lesser rate. Eustatic surges, identified by clear shorelines, were noted at ca. 9800, 7000 and 5000 years B.P. A similar pattern of crustal recovery occurred in Scotland with a phase of marginal bulging probably commencing ca. 14 000 years B.P. Only in Ireland were the oldest group of glacial shorelines found above present sea-level. Throughout northwest Europe the postglacial eustatic rise in sea-level was found to be oscillatory in character.

ISSN:0016-786X    

DOI:10.1080/11035898009455164

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

ISSN:0016-786X    

DOI:10.1080/11035898009455165

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor