Abstract
Here we present a chitinozoan biostratigraphical framework for the South Wales upper Katian and Hirnantian (Ashgill) succession. The current study indicates that three of the six Avalonian Ashgill chitinozoan biozones are recognised in the Welsh Basin; the bergstroemi, fossensis and umbilicata biozones. The Baltoscandian and Laurentian Hercochitina gamachiana biozone is suggested by the presence of Belonechitina cf. gamachiana and the Spinachitina taugourdeaui biozone is suggested by Spinachitina cf. taugourdeaui. Intervening between these is a newly erected lower Hirnantian regional biozone, the Belonechitina llangrannogensis n. sp. biozone. The late Katian (Cautleyan–Rawtheyan) Conochitina rugata biozone was not recognised, though the index taxon is recorded. The presence of B. cf. gamachiana below the lithological expression of the Hirnantian glacial maximum and alongside Rawtheyan graptolite and trilobite assemblages shows that the local base of the B. cf. gamachiana biozone lies beneath the Katian–Hirnantian boundary. Although at present in open nomenclature, the finds of B. cf. gamachiana and S. cf. taugourdeaui, from sites where these chitinozoans co-occur with graptolites, are potentially important; the area offers the potential to study how B. cf. gamachiana and S. cf. taugourdeaui are taxonomically and stratigraphically linked to the original index species. A composite Katian–Hirnantian chitinozoan biozonation for the Welsh Basin is presented and three new species are defined: Belonechitina llangrannogensis n. sp., Belonechitina ceregidionensis n. sp. and Spinachitina penbryniensis n. sp.
Highlights
The recent development of an integrated Upper Ordovician chitinozoan biozonation in British Avalonia (Vandenbroucke and Vanmeirhaeghe, 2007; Vandenbroucke, 2008a), based on type areas for the British chronostratigraphical scheme (Fortey et al, 1995, 2000), recognises six chitinozoan biozones with two subzones for the upper Katian (Ashgill) and potentially provides a powerful tool for dating Upper Ordovician successions where graptolite preservation is not favourable
The presence of B. cf. gamachiana below the lithological expression of the Hirnantian glacial maximum and alongside Rawtheyan graptolite and trilobite assemblages shows that the local base of the B. cf. gamachiana biozone lies beneath the Katian–Hirnantian boundary
Vandenbroucke (2008a) did not recognise the Laurentian and Baltoscandian Hercochitina gamachiana biozone in Avalonia, but discoveries made as part of this study suggest it may be represented in the Welsh Basin
Summary
The recent development of an integrated Upper Ordovician chitinozoan biozonation in British Avalonia (Vandenbroucke and Vanmeirhaeghe, 2007; Vandenbroucke, 2008a), based on type areas for the British chronostratigraphical scheme (Fortey et al, 1995, 2000), recognises six chitinozoan biozones with two subzones for the upper Katian (Ashgill) and potentially provides a powerful tool for dating Upper Ordovician successions where graptolite preservation is not favourable. We present a regional biostratigraphical scheme that utilises data on chitinozoan abundance and distribution from the well-constrained upper Katian–Hirnantian Welsh Basin succession (Davies et al, 1997, 2009) and compare it to that proposed by Vandenbroucke (2008a). This has allowed the reproducibility of the new British Avalonia chitinozoan biostratigraphical scheme to be tested and, the influence of sedimentary facies (i.e. basin and shelf) to be assessed. Challands et al / Review of Palaeobotany and Palynology 210 (2014) 1–21 makes the area important as a stepping stone between latitudinally restricted polar and tropical chitinozoan provinces that are difficult to correlate (Delabroye and Vecoli, 2010; Vandenbroucke et al, 2010; Ghienne et al, in press)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
