Bathymetry of Early Middle Ordovician [Chazy] ostracodes, Lower Esbataottine Formation, District of Mackenzie

Abstract
Silicified specimens of 26 genera of early Middle Ordovician (Chazyan) ostracodes occur in two sections of the lower Esbataottine Formation in southwestern District of Mackenzie . Many of these ostracode genera are widespread in the upper Tulip Creek - lower Bromide formations of Oklahoma; the upper New Market - Lincolnshire - lower Edinburg formations of Pennsylvania and Virginia; and the Day Point - Crown Point - lower Valcour formations of New York. By means of a bathymetric succession of trilobite biofacies already proposed for plat{ orm carbonate strata of the lower Esbataottine Formation, a shallow-water widespread ostracode assemblage I (=Bathyurus-Isotelus bi of acies) and a deeper water ostracode assemblage II (=Calyptaulax-Ceraurinella - proximal Dimeropyge bi of acies) may be distinguished . These ostracode assemblages occur with some modification elsewhere in North America and may be used for the first time to indicate the relative bathymetry of comparable faunas from widely separated segments of the early Middle Ordovician North American continental platform . Five new genera (Palaeocopida: Eurybolbina, Nahanniopsis, Canadabolbina, Valcouropsis; Podocopida: Bolboscapha) and twelve new species are erected. In addition, taxonomic revisions and observations are presented for some previously incompletely known North American Chazy ostracode species and for those taxa observed during the study that may have affinities with Middle Ordovician ostracode faunas from Europe. At present, faunas from both regions require additional detailed study before intercontinental biogeographic considerations may be attempted

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