Late Triassic Bivalvia (chiefly Halobiidae and Monotidae) from the Pardonet Formation, Williston Lake area, northeastern British Columbia, Canada

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.

Towards accurate numerical calibration of the Late Triassic: High-precision U-Pb geochronology constraints on the duration of the Rhaetian

“…Significant occurrences are known from North and South America, northern Russia, Japan, Timor, and New Zealand (see Tozer, 1980, for a review) that are all demonstrably late Norian. In North America, it is commonly associated with ammonoids and conodonts and usually does not survive to the very top of the G. cordilleranus zone (e.g., Grant-Mackie and Silberling, 1990;Silberling et al, 1997;McRoberts, 2010McRoberts, , 2011. We thus argue that the extinctions of large monotid bivalves and of most ammonoids are synchronous at sub-zone resolution.…”

Macrofaunal Response to the End-Triassic Mass Extinction in the West-Tethyan Kossen Basin, Austria

“…These genera are therefore not indicative for the postulated cooling episode. On the other hand, Meleagrinella first appears in the Anisian in high paleolatitudes of northeast Russia (Dagys and Kanygin, 1996), but by the Norian and well into the Jurassic this genus had dispersed into mid and even lower paleolatitudes (Damborenea, 2002;McRoberts, 2011). As discussed in McRoberts et al (2007), Agerchlamys is primarily known from the earliest Jurassic (although several poorly documented occurrences may be latest Triassic, see Damborenea, 1993) from low to high paleolatitudes at many localities of the circum-Pacific realm (e.g., New Zealand, Nevada, British Columbia, Siberia).…”

From Fore Reef to Lagoon: Evolution of the Upper Triassic Dachstein Carbonate Platform on the Tennengebirge (Salzburg, Austria)

“…5D). Following Balini et al (2012) and McRoberts (2011) this association can firmly be correlated to the latest Carnian (Tuvalian 3/II) Gonionotites italicus subzone of the Tethyan scale and the coeval Klamathites macrolobatus zone of the North American ammonoid scale. At the eastern margin of the patch reef at site B (N 47u30908,70, E 13u11927,50) a brachiopod(?)…”