Chitinozoans from key sections in the Upper Ordovician Series: new GSSP’s and classical British sections
Thijs Vandenbroucke1, Richard A. Fortey2, Derek J. Siveter3 and R. Barrie Rickards4
1 Research Unit Palaeontology, Ghent University, Krijgslaan 281 / S 8, 9000 Ghent, Belgium. E–mail: email@example.com
2 The Natural History Museum, Cromwell Road, London SW7 5BD, United Kingdom.
3 The University Museum of Natural History, Parks Road, Oxford OX1 3PW, United Kingdom.
4 Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, United Kingdom.
Key words: Chitinozoans. Stratotypes. British sections. Upper Ordovician. United Kingdom.
The rich and rather diverse chitinozoan assemblages from the Fågelsång section, southern Sweden, the new GSSP for the base of the Upper Ordovician Series have already been studied in detail (Vandenbroucke, submitted). They contain characteristic species allowing the subdivision of the section in three biozones and provide an additional tool for the base of the Upper Ordovician in its type section. In this study, these assemblages will be compared with the equally rich but less diverse assemblages from the Lower Wood Brook Section, Shelve Inlier, UK, the other former candidate for this GSSP, near the Caradoc type area (Bettley et al., 2002). Chitinozoan results from more than 70 samples collected from the upper Onnian to the lower Silurian strata of the Westerdale, Taythes and Murthwaite Inliers within the type area of the Ashgill in the Cautley District, Northern England, will also be presented. Interestingly, the stratigraphy in the area is being revised, as Rickards (2002) has recently shown that the Rawtheyan Stage of the type Ashgill Series, belongs to the linearis graptolite Biozone, implying that the base of the Ashgill, in terms of graptolites, begins at least two graptolite zones earlier than previously believed. Test samples taken from the graptolite slabs have already yielded diverse assemblages of moderately well preserved chitinozoans, including index species such as Lagenochitina baltica and Conochitina rugata. The results from the Ashgill type area will be compared to chitinozoan assemblages from the new GSSP candidates for the international base of Stage 6.
Bettley, R.M., Fortey, R.A. and Siveter, D.J. 2001. High resolution correlation of Anglo–Welsh Middle to Upper Ordovician sequences and its relevance to international chronostratigraphy. Journal of the Geological Society, London, 158: 937–952.
Rickards, R. B. 2002. The graptolitic age of the type Ashgill Series (Ordovician) Cumbria. Proceedings of the Yorkshire Geological Society, 54: 1–16.
Vandenbroucke, T. (submitted). Chitinozoan biostratigraphy of the Upper Ordovician Fågelsång section, Scania, southern Sweden. Review of Palaeobotany and Palynology.
Received: February 15, 2003
Accepted: June 15, 2003