AN EXCEPTIONALLY PRESERVED BIOTA FROM UPPER SILURIAN SUBMARINE CHANNEL DEPOSITS, WELSH BORDERLAND, UK

An exceptionally preserved biota of Upper Silurian (Ludlow Series) age is found in submarine channel fill deposits around Leintwardine in the central Welsh Borderland. The deposits are of importance as they represent a rare example of exceptional preservation in organisms of Silurian age; they also provide a unique palaeoenvironmental setting.

The channel biota comprises a range of Upper Silurian marine animals; approximately 50 species of invertebrates have been recorded. Along with typical Silurian forms such as brachiopods, graptolites and trilobites, there are also more unusual taxa such as abundant and diverse echinoderms (ophiuroid and asteroid sea stars, echinoids, crinoids and ophiocistioids) eurypterid and xiphosurid chelicerates, phyllocarids and worms. The asterozoans contribute one of the most interesting and diverse groups of the fauna. The ophiuroids (8 species) are by far the most abundant of the echinoderms; the asteroids (4 species) are rare in comparison. The degree of disarticulation varies throughout the invertebrate fauna; the echinoderms are mostly complete, whilst the majority of the arthropod material consists of disarticulated components. Asterozoan specimens are almost always preserved intact, revealing the finest morphological detail. Almost all of the fossils are preserved as 'hard-parts', although occasional soft-body preservation is encountered in the form of possible gut trace preservation in a palaeoscolecid 'worm'. The unusual channel fauna generally occurs in concentrated horizons through the channel fill; much of the remainder of the fill is relatively barren. The starfish fauna appears to occur exclusively within these horizons, although some of the other unusual fauna such as eurypterids and phyllocarids also occurs at other levels. Rare disarticulated components of heterostracan fish are also found.