RESPONSE OF BRACHIOPOD COMMUNITIES TO RAPID GLOBAL CLIMATE CHANGE DURING THE ORDOVICIAN MASS EXTINCTION, ANTICOSTI ISLAND, QUÉBEC

Global climate change can have varied effects on ecosystems, causing community restructuring, faunal turnover, or extinctions. The two pulses of the Ordovician mass extinction coincided with the rapid glaciation and deglaciation of Gondwana. Anticosti Island, Québec, provides an exceptional record of a shallow-marine, shelly fauna during this interval. Brachiopod communities from the Late Ordovician (Vauréal and Ellis Bay Formations) and Early Silurian (Becscie Formation) were sampled from limestone slabs in Paul Copper's collection at the Geological Survey of Canada (Ottawa, Ontario). The collection includes detailed stratigraphic information, allowing for extensive sampling throughout the study interval. Samples were only collected from surfaces that did not show evidence of taphonomic overprinting; taxa were identified to the species level.

Ordinations are a powerful tool in community analysis; different factors (i.e., higher taxonomy or environmental conditions) can be mapped onto the ordination to aid in explaining the observed variation. Both communities and taxa are explored in ordination space: 1) through the entire interval, 2) before the first extinction pulse, 3) between the two pulses, and 4) after the second pulse. When the entire interval is examined, the communities are arranged relative to stratigraphic position, and taxa are generally ordered by higher taxonomy. Within each shorter interval, variation between communities is related to both lithology (Dunham carbonate classification) and stratigraphic position. Taxa are again ordered by high taxonomy, but the relation between clusters of higher taxa is different within each shorter interval. This suggests that there was restructuring of communities during the extinction and associated climate change. Other factors related to the variation between communities include relative water depth, carbon and oxygen isotopic values, taxon size, and presence of other non-brachiopod taxa in the communities. This analysis clarifies the changes in brachiopod communities through the Ordovician mass extinction and potentially offers insight to the responses of other communities during past and present global climate change.