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Response of brachiopod communities to environmental change during the Late Ordovician mass extinction interval, Anticosti Island, eastern Canada

2008; Wiley; Linguagem: Inglês

10.18261/9781405186643-2008-05

2637-6032

Jisuo Jin, Paul Copper,

Marine Biology and Ecology Research

Multivariate analyses indicate that the brachiopod fauna of the Late Ordovician (Hirnantian) Ellis Bay Formation of Anticosti Island, eastern Canada, is highly distinct from the pre-Hirnantian epicontinental brachiopod fauna of Laurentia. Among the four types of brachiopod associations of the formation, most are unstable spatially and temporally, but have a rather high α- and ß-diversity for an extinction-interval fauna. The Onniella Association is a relatively stable brachiopod community, with frequent recurrences throughout the Hirnantian carbonate succession. The two dominant genera of the association, Onniella and Hebertella, were holdover cosmopolitan Ordovician taxa tolerant of fluctuations in sea level and temperature. The other three associations have short stratigraphic ranges, indicating sporadic pulses of invasion by opportunistic taxa. The Plaesiomys Association, in the Grindstone Member of the basal Ellis Bay Formation, contains abundant rapidly evolving species of typical late Caradocian to mid-Ashgillian genera such as Barbarorthis and Vellamo. In the overlying Velleda Member, the Parastrophinella Association is characterized by species whose genera either made their first appearance, or first became abundant, in the early Hirnantian (e.g. Mendacella uberis, Parastrophinella reversa, and Hindella umbonata); most of these genera experienced decline during the late Hirnantian and some survived into the Early Silurian. The Orthorhynchyllion and Gnamptorhynchos associations in the siliciclastic-rich facies of the Prinsta Member are dominated by exotic taxa (e.g. Hirnantia), locally associated or interbedded with aulacerid sponge biostromes during the mid- Hirnantian. Relatively high diversity during the early and mid Hirnantian was maintained by frequent invasion of opportunists. Lack of such invasions or a decreased rate of species origination in a stressed environment (e.g. shallow water and abnormal salinity) led to a much reduced diversity in the Lousy Cove and Laframboise members of latest Hirnantian age.