Article: Benthic palaeocommunities represented in the Ffairfach Group and coeval Ordovician successions of Wales

The study provides detailed quantitative analyses of faunal assemblages from various Upper Llanvirn shelly facies occurring with the Lower Ordovician successions of mid-Wales. In particular fifteen assemblages occur in about 90 m of varied sediments and bedded pyroclastics constituting the Ffairfach Group stratotype. The assemblages congregate into eleven distinct associations two of which recur five times. The lithological successions and taphonomic structure of the entombed assemblages indicate predominantly shallow-water, shoreface deposits dominated by benthos. The exoskeletal remains underwent only limited postmortem disturbance and mixing and are assumed to represent a series of extinct palaeocommunities. The extent to which these palaeocommunities intergraded, or were entirely separate from one another, may be inferred from the taxonomic and quantitative structures of the associations. A basic distinction can be drawn between very restricted opportunistic palaeocommunities, such as those dominated by Tissintia and Hesperorthis, and diverse recurrent ones dominated by Horderleyella, Dalmanella and Sowerbyella. In each of the last three palaeocommunities it has been possible to infer the main changes which led to the climax in its maturation. The palaeocommunities can be identified in successions elsewhere in Wales and in Shropshire.