摘要:

New information is presented on the stratigraphic and geographic distribution of acritarchs of the Lower Cambrian sequences in areas around the southern margin of the Fennoscandian Shield and the Lublin Slope in the southeastern margin of the East European Platform. In the latter area a distinctive radiation of diagnostic acritarchs has been found which abruptly replaces a morphologically depleted acritarch assemblage of Late Proterozoic type from beds of theSabellidites cambriensisZone. This zone is generally regarded as basalmost Cambrian. We contend that this radiation event of algal plankters is synchronous in the investigated areas and suggest that it might be generally significant for defining the Precambrian-Cambrian boundary. The microfossil succession is set in relation to the evidently reliable trilobite-based zonation of the Lower Cambrian, which adds to their usefulness in regional correlations.

ISSN:0016-786X    

DOI:10.1080/11035898609454685

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

ISSN:0016-786X    

DOI:10.1080/11035898609454686

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Continuous seismic reflection profiling has revealed a 2000 m wide, almost circular depression in the crystalline bedrock of Tvären Bay. The depression extends more than 200 m below the present sea level. Originally, it was probably 250–300 m deep. The physical parameters of the structure, which forms a foreign element in the tectonic regime of the Baltic coastal area, are consistent with those of known impact structures. Inclined sedimentary rocks of an assumed Ordovician age are unevenly distributed within the depression, partially smoothening the topographic relief of the structure. A late Lower or early Middle Ordovician time for the meteorite impact is suggested. Drillings into the ‘wall’ surrounding the impact structure and into the sedimentary bedrock inside the depression are proposed as a further step in this investigation.

ISSN:0016-786X    

DOI:10.1080/11035898609454687

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Investigations in Crete and southern Peloponnese show relatively numerous deposits of eolian character. Two types of possible eolian deposits have been observed; pale yellow, 3–5 m thick deposits in Crete situated up to an altitude of about 600 m above sea level, and brownish red, slightly thinner (about 0.5–4 m) deposits which occur at all altitudes. There are strong indications that African dust in present time is deposited on snow patches. At the end of June 1985 several snow patches, discolored by dust, were still lying in the Cretan mountains. Analysis of grain size parameters shows that many of the sediments are typical loess deposits.

ISSN:0016-786X    

DOI:10.1080/11035898609454688

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

ISSN:0016-786X    

DOI:10.1080/11035898609454689

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Lead isotope analysis of 21 low- to high-temperature minerals from the Långban district points to an exhalative-sedimentary origin in an active continental margin environment. A volcanogenic Pb component slightly enriched in radiogenic Pb, thus causing a lowering of the Pb model age, was continuously mixed with a sedimentary Pb component. For the later stages of mineral formation this addition of Pb caused an increase in μ-values and Pb model ages with time.

ISSN:0016-786X    

DOI:10.1080/11035898609454690

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

ISSN:0016-786X    

DOI:10.1080/11035898609454691

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

ISSN:0016-786X    

DOI:10.1080/11035898609454692

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

ISSN:0016-786X    

DOI:10.1080/11035898609454693

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

ISSN:0016-786X    

DOI:10.1080/11035898609454694

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor