Paleoecology of Llandovery conodonts, Anticosti Island, Québec

Anticosti Island, Québec, has perhaps the most fossiliferous and complete Llandovery (Early Silurian) sequence in the world. The undeformed limestones are well exposed and yield extremely well preserved conodonts whose taxonomy and biostratigraphy has been studied in detail. In addition to documenting the general temporal and spatial distribution of Llandovery conodonts, a set of 107 conodont samples was taken from four cliff sections in the lower and upper Becscie, lower Gun River, and upper Jupiter formations. These samples were used to examine the relationship of conodont elements and communities with microfacies, and explore their change through time. Over 9300 conodonts elements were identified and subjected to cluster analysis. The sections comprise mainly the background sedimentation of lime mudstones, deposited in 30–100 m of water on a gentle ramp. These mudstones are variably affected by interbeds or channel fill deposits interpreted as tempestites. A pattern of evolving conodont communities is documented for the lime mudstone facies through time. Different communities are found in the tempestite deposits that do not suggest a reworking of the mudstones, but rather the importation of deeper offshore faunas during periods of storm surge onto the ramp. The tempestites contain the highest species diversity and show no evidence of reduced diversity through post-mortem selective sorting by the storms.