摘要:

Radiometric ages of some late Precambrian rocks in south-western Sweden show that the evolution of the Sveconorwegian geochronological province in this area, after the deposition of the Dal Group between 1100 and 1050 Ma (million years) ago, continued for at least about 250 Ma. The Bohus granite intruded in a late-tectonic phase, giving a Rb-Sr isochron age of 910 ± 35 Ma (λ87Rb = 1.39 × 10−11α−1) with an initial strontium-isotope ratio of 0.711. The K–Ar model ages determined on micas separated from the Bohus granite, lie in the range of 861 to 680 Ma. A Rb-Sr isochron age of 1050 ± 40 Ma with an intercept of 0.704 has been obtained for the slate of the Dal Group. The significance of this age is discussed. The K–Ar model ages, determined on whole rocks and minerals from slates and spilites of this sequence, range from 1000 to 715 Ma. The pre-Sveconorwegian granites in the Ljungbergen area yield a Rb-Sr isochron age of 1400 ± 80 Ma with an intercept of 0.704, which probably reflects the age of intrusion. Further evidence of igneous activity during this time is manifested by a Rb-Sr isochron age of 1405 ± 40 Ma, intercepting at 0.708, for granites intersecting the Ellenö supracrustals. A Rb-Sr diagram plotting of granites, formerly reported to be intrusive, in the Härserud area shows a discordant pattern, indicating that metasomatic changes in the rock system seem to have occurred. Isotope analyses and field observations do not favour the theory of an intrusionin situbut an overthrust of the old basement upon the Dal Group.

ISSN:0016-786X    

DOI:10.1080/11035897609454335

出版商:Taylor & Francis Group    

年代:1976

数据来源: Taylor

摘要:

A list of 25 localities with silicified fossils is given. Silicification was selective. At most of the localities, only the bryozoans and brachiopods are affected. Their skeletons originally consisted of low-magnesium calcite. Silicified gastropods (original shells mainly aragonite) and crinoids (original skeletons probably high-magnesium calcite) occur only at three localities. Seven other taxa are also represented. The origin of the silica was tephra, as is indicated by the close connection between the bentonites and the levels with siHcified fossils. The source area for the tephra was probably south of Gotland.

ISSN:0016-786X    

DOI:10.1080/11035897609454336

出版商:Taylor & Francis Group    

年代:1976

数据来源: Taylor

摘要:

A fault with an extension of about 150 km in northern Sweden is preliminarily described. Its relation to late-glacial phenomena shows that movement occurred in late-glacial time in connection with deglaciation of the area. This is the first definite record of Holocene faulting in Sweden.

ISSN:0016-786X    

DOI:10.1080/11035897609454337

出版商:Taylor & Francis Group    

年代:1976

数据来源: Taylor

摘要:

In Karelia, sulphuric pyrite deposits are associated with sedimentary volcanogenous formations of the Early Proterozoic era (2500 ± 100 m.y.). Two formations can be isolated, viz. basalt—andesite—dacite—liparite, with the differentiated succession mentioned, and a non-differentiated basalt formation (spilite—diabase). Two main stages have been isolated in the ore origin: (1) a volcanogenous sedimentary stage (a deposit of pyrite-ore beds), and (2) metamorphogenous stage (recrystallization of pyrite ores and their metamorphic regeneration with the formation of pyrrhotite mineralization). The isotopic age of the pyrite ores, obtained by the isochronic lead method, is 2350 ±100 m.y. and that of the pyrrhotite ores 1875 ± 200 m.y.

ISSN:0016-786X    

DOI:10.1080/11035897609454338

出版商:Taylor & Francis Group    

年代:1976

数据来源: Taylor

摘要:

Three transport directions have been recorded in the Wenlockian Slite Siltstone on the island of Gotland in Sweden — one from the north-west, another from the north, and a third from the north-east. Silicification and dolomitization have also been observed.

ISSN:0016-786X    

DOI:10.1080/11035897609454339

出版商:Taylor & Francis Group    

年代:1976

数据来源: Taylor

摘要:

The present paper constitutes a further report on our work on methodological and palaeoclimatological questions concerning tree rings. Ring indices are related to a meteorological index defined by us, and the correlation coefficient is computed. A rain index is also defined and compared with the differences in standardized values for trees that have grown in contact with water and in dry places. For western Sweden, the yearly precipitation seems to be sufficient for the general growth of the trees. Among our results, we would also mention that spruce and aspen show quite similar yearly growths. Finally, some hints are given on the theory underlying the construction of mean curves for ring-width diagrams.

ISSN:0016-786X    

DOI:10.1080/11035897609454340

出版商:Taylor & Francis Group    

年代:1976

数据来源: Taylor

摘要:

The performance of geochemical prospecting is related to some of its basic principles. Some areas that at present require development are identified. A distinction is made between prospecting techniques and geochemical work aimed at solving the problems of ore genesis and petrology.

ISSN:0016-786X    

DOI:10.1080/11035897609454341

出版商:Taylor & Francis Group    

年代:1976

数据来源: Taylor

摘要:

In connection with the laying of foundations for a storage basin for industrial water and unit I at the Forsmark nuclear-power station, experiments were made on the compression rate of material from sediment-filled joints. The experiments indicated that the material had been exposed to a pre-consolidation load of a magnitude that could not have existed in Holocene time. This fact supports the theory that sedimentation took place in a Pre-Holocene age.

ISSN:0016-786X    

DOI:10.1080/11035897609454342

出版商:Taylor & Francis Group    

年代:1976

数据来源: Taylor

摘要:

The best reference level for use in the construction of a graph of sea-level movements in Europe during the last 15,000 years may be Normaal Amsterdam Peil (NAP) or it may be the centre of gravity of the Earth. Altitudes of dated samples of former coastal deposits now located on land or at sea must be converted to heights relative to the chosen reference level. A decision must be reached concerning what is representative of the present mean surface level of European waters. The assessment of former mean surface levels of the North Sea and the Irish Sea areas must be based almost entirely on the assessment of former mean surface levels in water bodies bordering these seas rather than on data from the sea areas themselves.

ISSN:0016-786X    

DOI:10.1080/11035897609454343

出版商:Taylor & Francis Group    

年代:1976

数据来源: Taylor

摘要:

Mörner (1975aandb) has attempted to extend the Fjärås line (the Gothenburg end moraine) from the west coast of Sweden to the Bredåkra delta in Blekinge, south-eastern Sweden. He has revised the present author's account of the genesis of the Bredåkra delta (Ringberg 1971) and tried to establish a correlation on palaeomagnetic grounds between the Fjärås stadial (dated at 12,350–12.400 B.P., Mörner 19756) and the Bredåkra delta. In this note, the author shows that this revision is based on unreliable calculations and that Mörner's palaeomagnetic work is not dated in a reliable way. The conclusion is that Mörner has not succeeded in his efforts to extend the Fjärås line to the Bredåkra delta and that the relation between the genesis of the delta and the deglaciation of the west coast of Sweden is still unclear.

ISSN:0016-786X    

DOI:10.1080/11035897609454344

出版商:Taylor & Francis Group    

年代:1976

数据来源: Taylor