Abstract

The Upper Triassic of the Williston Lake area of northeastern British Columbia is represented by a nearly continuous series of fossil-rich sediments that were deposited in the Western Canadian Sedimentary Basin in an offshore mid-paleolatitude setting on the western margin of cratonic Pangea. The fossils in this report come primarily from the upper Carnian–upper Norian Pardonet Formation, which has been the subject of numerous paleontologic studies on ammonoids and conodonts, yet has received little attention with regard to its bivalve fauna. Fossil bivalves belonging to the thin-shelled bivalve genera Halobia, Eomonotis, and Monotis dominate the benthic macrofauna and occur within unique shell accumulations that are interpreted to represent oxygen-controlled monospecific paleocommumities that have undergone little post-mortem transportation. Systematic analyses of more than 1,000 individual bivalve specimens resulted in the identification of 25 species-rank taxa, a majority of which belong to the pterioid genus Halobia and the pectinoid genera Eomonotis and Monotis. Of these, four new species are recognized, including 1) upper Carnian Halobia tozeri n. sp. characterized by a unique triangular outline; 2) lowermost Norian Halobia selwyni n. sp. closely related to H. beyrichi and first appearing with H. austriaca which is proposed as a potential datum for the Carnian–Norian boundary; 3) Norian Meleagrinella mclearni n. sp., a new name for previously identified species; and 4) upper Norian Otaparia norica n. sp. which has a delicate thin shell, unique outline, and fine ornament. A revised and refined biochronology of Upper Triassic Bivalvia (chiefly Halobiidae and Monotidae) integrated with conodont and ammonoid zones and standard Triassic stages is presented for the Upper Triassic of the Williston Lake area and permits enhanced correlation to coeval faunas elsewhere in the North American Cordillera, and to the Boreal, Panthalassan and Tethyan faunal realms.

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