Middle and Upper Ordovician graptolites, trilobites, and biostratigraphy of Scania and Jämtland, Sweden

Detta är en avhandling från Department of Geology, Lund University

Sammanfattning: Graptolites and some trilobites from Middle–Upper Ordovician siliciclastic and calcareous rocks in Scania (Skåne), southern Sweden, and Jämtland, central Sweden, are described and discussed. Their stratigraphic distribution is discussed on the basis of new and old collections from outcrops and drill cores. The uppermost Middle–Upper Ordovician of Scania consists predominantly of mudstones and dark graptolitic shales with a few limestone interbeds. The graptolitic successions belong to the Scanian Confacies Belt that occupies much of the present SW margin of Baltoscandia, and is representative of outer shelf or foreland basin deposition. Seven formations are recognized within the Upper Ordovician of Scania. In ascending order these are: the Lower Dicellograptus Shale, the Sularp Formation, the Skagen Formation, the Mossen Formation, the Fjäcka Shale, the Lindegård Mudstone, and the basal Kallholn Formation. The shale successions generally contain taxonomically diverse graptolite faunas that are useful for regional and intercontinental correlations. A detailed graptolite biostratigraphy has been established across the base of the Nemagraptus gracilis Zone in the Fågelsång area, W-central Scania, and for the Dicranograptus clingani Zone at Järrestad, southeast Scania, and the interval spanning the Pleurograptus linearis and Dicellograptus complanatus zones in the Röstånga area, W-central Scania. Trilobites are fairly common in Upper Ordovician mudstone-dominated units in Scania. 19 trilobite taxa, among which 15 are identified to species, have been recorded from Upper Ordovician deposits exposed along the Kyrkbäcken rivulet in the Röstånga area. These trilobites are useful for regional correlations and for a biostratigraphic classification of the Upper Ordovician in the Kyrkbäcken section. The Middle–Upper Ordovician Andersö Shale is a lithologically distinctive, and widely distributed unit, in the Storsjön area of Jämtland, central Sweden. It can be subdivided into three lithologic units, a lower and an upper shale member, which are separated by a distinctive limestone unit, the Ståltorp Limestone Member. The Andersö Shale is of particular interest in that it straddles the Middle–Upper Ordovician boundary. Graptolites from the Lower Shale Member and the Ståltorp Limestone are indicative of the H. teretiusculus Zone. The base of the Nemagraptus gracilis Zone is probably at some level in the lowermost portion of the Upper Shale Member.

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