Conodont biofacies and taphonomy along a carbonate ramp to black shale basin (latest Devonian and earliest Carboniferous), southernmost Canadian Cordillera and adjacent Montana

Uppermost Devonian – lowermost Carboniferous strata in the southernmost Canadian Cordillera and adjacent Montana record the onset and termination of low-oxygen conditions in carbonate-dominated epicontinental and shelf seas. Several distinct conodont biofacies representative of shallow-ramp to deep-basin settings are recognized on the basis of conodont distribution and preservation patterns.During early and middle Famennian time, the region was the site of a westward-deepening carbonate ramp (Palliser Formation) that was bordered to the west by a deep, shale basin (Lussier syncline strata). Palliser carbonates contain low-diversity conodont faunas of indigenous to transported Palmatolepis-, Polygnathus-, and Apatognathus-dominated assemblages. Basinal deposits yield a pelagic palmatolepid biofacies. Middle to late Famennian time was marked by termination of carbonateramp sedimentation and flooding of the margin with oxygen-depleted water. Deposition of organic-rich facies began in the expansa Zone in shelf to basin environments (Exshaw Formation and correlative units). These deposits contain indigenous pelagic Palmatolepis- and (or) Bispathodus-dominated assemblages; reworked or transported fragments are primarily polygnathids and icriodontids.Sedimentation of anaerobic to aerobic, deep-water, lower Banff facies occurred intermittently until middle Tournaisian and, locally, late Tournaisian time prior to westward progradation of younger carbonate deposits. Middle Tournaisian biofacies include transported and indigenous assemblages of siphonodellids (deep–middle ramp). Late Tournaisian biofacies parallel lithofacies changes associated with shallowing of the Banff sequence and are characterized by scaliognathid–doliognathid (basin to deep ramp), polygnathid and polygnathid–bactrognathid (deep to middle ramp), and bactrognathid–hindeodid (middle to shallow ramp) indigenous and displaced biofacies. The spatial relations of these Famennian and Tournaisian biofacies are generally consistent with models developed for correlative strata elsewhere.