The taxonomy and palaeoecology of lower Carboniferous ostracodes and peracarids (crustacea) from southwestern Newfoundland and central Nova Scotia

Abstract

Middle Carboniferous sediments in the Maritime region of Canada were deposited in fluvial basins that were subjected to transgressive marine episodes often associated with hypersalinity. -- A dominantly shallow marine, paraparchitacean ostracode fauna associated with palaeocopids, bairdiaceans and less common cytheraceans and myodocopids, as well as two peracarid genera has been recovered from sediments in southwestern Newfoundland and northern and central Nova Scotia. The paraparchitaceans are ubiquitous and are even found in sediments containing synsedimentary gypsum. Two of the genera and four species are new. -- Seven assemblages have been recognised based upon diversity, occurrence sedimentary facies and inferred environment. -- In the least restricted carbonate environment, representatives of the following genera occur; Kirkbya, Gortanella, Beyrichiopsis, Bairdiacypris and two species of Bairdia associated with Chamishaella, Monoceratina, Acratia, Acutiangulata and Polycope. In a more restricted carbonate environment, Chamishaella is augmented by Paraparchites, Shemonaella, Shishaella and Shivaella; bairdiaceans are less common and the ornate palaeocopids are absent. An amphissitid, Youngiella, Basslerella and "Neokloedenella" occur with Monoceratina, Acratia, Acutiangulata and Polycope to give the total fauna. In the most restricted carbonate environment only representatives of the genera Chamishaella, Gortanella and Acratia occur. -- Three hypersaline-related environments can be recognised. In the carbonate dominated environment, paraparchitaceans occur together with Amphissites, Youngiella, Acratia, "Neokloedenella" and Acutiagulata as well as the peracarid Tealliocaris. In the classic-dominated hypersaline environment, Chamishella, "Neokloedenella", Acratia and Acutiangulata, together with Geisina and "Copelandella" are the main elements of the fauna. Carbonate bands occurring within an evaporite sequence contain Chamishaella, Paraparchites, Beyrichiopsis, Acratia and Acutiangulata. -- Species of the genera Chamishaella, Acratia, Acutiangulata, Geisina and "Copelandella" occur in a deltaic environment. -- The Maritime Basin was a shallow embayment of the northern Hercynian Ocean, with a similar though not conspecific fauna to that of Western Europe. The lower diversity and high degree of dominance shown by the Maritime Basin faunas may be a function of several factors including the restricted circulation of sea waters, attendant hypersalinity as well as the limited duration and extent of the transgressive phases.