Crinoid columnal associations and sequence stratigraphy architecture: the Le Faou Formation

Crinoid columnals are major macrobenthic components of the Lower Devonian faunas of the Massif armoricain particularly in the Seillou section. Three crinoid columnal associations have been delineated based on R and Q-mode cluster analysis. Distribution of these associations is correlated to the sequence stratigraphic architecture, showing the close relationships between crinoid columnal association dynamics and relative sea-level variations. Comparing the distribution of benthic associations, we note a lesser diversity in crinoid columnal associations than in brachiopod ones. Crinoids (high-level suspension feeders) seem to occupy broader specialised niches than brachiopods (reclining and low-level suspension feeders) and are characterised by a different ecological space utilisation.