A modern assessment of Ordovician chitinozoans from the Shelve and Caradoc areas, Shropshire, and their significance for correlation

Abstract

-New chitinozoan data are presented from the classical section along the Onny River in the type Caradoc area, and from the deeper-water sections in the Shelve area, including the former British candidate GSSP for the base of the Upper Ordovician Series. The rich and well-preserved chitinozoan fauna of the Onny River has been a standard for 40 years, but new data revise some of the identifications. The assemblages are now attributed to biozones that are more readily applicable for international correlation. The main part of the section can be interpreted as belonging to the originally Baltoscandian Spinachitina cervicornis Biozone, although this is uncertain in the lower part. Within this biozone, the Fungochitina actonica Subzone has been defined. The Onny Formation at the top of the section is equated with the Acanthochitina latebrosa-Ancyrochitina onniensis Biozone; contrary to earlier reports, Acanthochitina barbata is absent. The Lower Wood Brook and Spy Wood Brook section from the Shelve Inlier yielded a great number of moderately to well-preserved chitinozoans, but a low-diversity assemblage. Their ranges have been neatly positioned against the well-known graptolite stratigraphy in the area. A local Eisenackitina rhenana Biozone? has been recognized, allowing us to suggest some international correlations.

Integrated Upper Ordovician graptolite–chitinozoan biostratigraphy of the Cardigan and Whitland areas, southwest Wales

“…In (Vandenbroucke et al 2008), although there it was recognized by its index species, while D. juglandiformis has not been observed.…”

An Upper Ordovician chitinozoan biozonation in British Avalonia (England and Wales)

“…The area's shelly faunas (brachiopods and trilobites) have been used to subdivide the classic Caradoc Series (see overview in Rushton et al . 2000; Vandenbroucke et al . in press a; and references therein).…”

“…For a complete overview of the fauna, we refer to Bettley et al . (2001), Vandenbroucke et al . (in press a) and references therein.…”

“…For instance, the tie between chitinozoan distribution and the British chronostratigraphy has only recently been investigated in more detail (Vandenbroucke et al . 2005, in press a, in press b). Moreover, and in contrast with other palaeocontinents such as Laurentia, Baltica and North Gondwana, a formal Ordovician chitinozoan biozonation for Avalonia has not previously been developed.…”

“…Recent years have witnessed an effort to develop and extend an Upper Ordovician chitinozoan biozonation to the Anglo‐Welsh region, using chitinozoan data from the historical‐type sections for the Caradoc and Ashgill series (Vandenbroucke et al . 2005, in press a) as well as data from additional key sections with good graptolite and/or conodont control (Van Nieuwenhove et al . 2006; Vandenbroucke et al .…”