Pb-Pb zircon dating of tuff horizons inthe Cyrtograptus Shale (Wenlock, Silurian) of Bornholm

Bulletin of the Geological Society of Denmark

Skovsted, C. B.¹  Peel, J. S.:¹ 

[1] The problematic fossil Mongolitubulus from the Lower Cambrian of Greenland. Bulletin of the Geological Society of Denmark, vol. 48, pp. 135–147, Copenhagen.
Spines referred to the problematic phosphatic Small Shelly Fossil Mongolitubulus Missarzhevsky, 1977 are described from the Lower Cambrian of Greenland. The type species, M. squamifer, is reported from the Henson Gletscher Formation of North Greenland, while M. henrikseni sp. nov. is described from the Bastion Formation of North-East Greenland. Co-occurring small plates with broken spine bases suggest that Mongolitubulus henrikseni may have been a bivalved(?) arthropod with a carapace bearing multiple spines, but it is uncertain if this restoration can be extended to the type species.

关键词: Small Shelly Fossils;    problematica;    Cambrian;    john [dot] peel [at] pal [dot] uu [dot] se ]"'>John S. Peel [ john [dot] peel [at] pal [dot] uu [dot] se ];    Department of Earth Sciences (Historical Geology &;    Palaeontology);    Uppsala University;    Norbyvägen 22;    SE-752 36 Uppsala;    Sweden. 6 April 2001.;   

学科分类：地球科学(综合)

来源: Dansk Geologisk Forening

【 摘 要 】

Waterlain fallout ashes are interbedded in the upper part of the Cyrtograptus Shale of Bornholm, theyoungest preserved member of the Lower Palaeozoic sequence at the southern coast of the island.Graptolite faunas indicate that these tuffaceous sediments belong to the Cyrtograptus lundgreni Zonedeposited during Late Wenlock. A 207Pb/206Pb mean age of 430 ± 1.9 Ma obtained by evaporation of idiomorphic single zircons from the tuff layers supports this observation. Geochemical studies of the pyroclastic rocks point to an explosive, calc-alkaline magmatic arc volcanism which probably occurred along or slightly south of the Tornquist-Teisseyre Lineament, and could have been induced by the collision of Avalonia with the southern margin of Baltica during the Silurian. This assumption is supported by the contemporaneous deposition of bentonites on the Swedish island of Gotland which might represent a distal facies of these fallouts. Further, the subduction-related volcanic activity is interpreted as a fingerprint for closing of the Tornquist Ocean during the Caledonian orogeny.

【 授权许可】

Unknown