CLUSTER ANALYSIS OF COMMUNITY COMPOSITION OF CAMBRIAN, ORDOVICIAN AND SILURIAN KONSERVAT-LAGERSTÄTTEN

Cambrian Konservat-Lagerstätten yield remarkably similar communities, even on different palaeocontinents. Most Silurian Konservat-Lagerstätten are also alike in terms of community composition, but no similar studies have yet been conducted on exceptionally preserved Ordovician biotas. Data on the taxa present in Cambrian, Ordovician and Silurian Konservat-Lagerstätten have been gathered from the literature and from fieldwork, and cluster analyses conducted to assess similarities.

Analysis of the data from Cambrian, Ordovician and Silurian Konservat-Lagerstätten finds that the Cambrian Lagerstätten form a coherent cluster separate from all the Ordovician and Silurian deposits, with the possible exception of the Afon Gam Biota. Ordovician marginal marine deposits appear to have more in common with similar biotas in the Silurian than with the other Ordovician Lagerstätten. This may partly be an effect of environment and partly of geography, because most of the Ordovician and Silurian marginal marine deposits were situated on Laurentia.

The results of cluster analysis of only the Ordovician Konservat-Lagerstätten indicate that those biotas that occupied restricted marine environments (Airport Cove, William Lake, Soom, Winneshiek) form one cluster, with those from more open marine conditions (Fezouata, Beecher’s Trilobite Bed, Llandegley Rocks, Llanfawr Mudstones, Holothurian Bed, Afon Gam, Tonggao) forming another. As well as palaeoenvironment, there are influences from age and geography: the Early Ordovician biotas (Fezouata, Afon Gam and Tonggao) tend to be associated, as do the Middle/Late Ordovician Welsh sites (Llandegley, Llanfawr and the Holothurian Bed). The Upper Tirourine Formation (Late Ordovician, Morocco) appears to be unique among Ordovician Konservat-Lagerstätten.