FAUNAL TRANSPORT WITHIN EVENT HORIZONS IN THE BRITISH UPPER SILURIAN

Many marine fossil concentrations are considered the result of episodi c sedimentological events, and in particular those due to storms. Most storm or tempestite concentrations are identified as autochthonous or parautochthonous assemblages created by a variety of winnowing proces ses within shallow water environments. In contrast, samples described here from both a 'shelf' and a 'basinal' setting within the Ludlow (Up per Silurian) succession of the Welsh Basin reveal the presence of a b iota transported by tempestite activity into a setting dominated by a more offshore biota. Tempestite horizons from within an 'outer shelf' mud dominated setting include shelly lenses with a transported fauna a bounding in gastropods, tentaculitids and atrypid brachiopods, the bac kground sediment being rich in graptolites, cephalopods and small stro phomenid brachiopods. Within the 'basinal' area, distal tempestites ra nge from minor siltstone layers to thicker bioclastic limestone lenses . The siltstones are largely graptolitic (dominated by Bohemograptus), with some small brachiopods, whilst Saetograptus colonus is the only common graptolite in the limestones, which also contain a fauna of bro ken brachiopods and bryozoa. The transport of assemblages distally int o a variety of settings represents a potential source of error in pala eoecological analysis. Transported assemblages may, however, provide e vidence of the composition of both benthic and pelagic shallower water faunas no longer known in situ.