CONODONT BIOSTRATIGRAPHY OF THE LOWER TRIASSIC MACKENZIE DOLOMITE LENTIL, SULFUR MOUNTAIN FORMATION IN THE CADOMIN AREA, ALBERTA

A Lower Triassic stage boundary (Dienerian-Smithian), defined by conod onts in two adjacent samples, occurs within the Mackenzie Dolomite Len til of the Sulphur Mountain Formation 5 km south of Cadomin, Alberta, A sparse lower Dienerian (upper Induan) conodont fauna including Neogo ndolella carinata and Neospathodus kummeli occurs low in the exposed c arbonate. An abundant, lower Smithian (lower Olenekian) fauna, 2.1 m h igher in the section, consists primarily of Neospathodus pakistanensis and N. waageni. These two species are associated with a major episode of transgression that is recorded worldwide. In North America, both f aunas are best represented in the Lower Triassic depocentre of southea st Idaho in the western United States. The apparent absence of upper D ienerian conodonts suggests the Mackenzie Lentil, a complex of offshor e shell banks, may contain an interval of slow deposition or an episod e of erosion. As a byproduct of this study, a modest revision of strat igraphic nomenclature is proposed. We recommend establishing the lower and upper boundaries of the Mackenzie Dolomite Lentil in its depositi onal area, respectively, as the upper boundary of the Phroso Siltstone Member and the lower boundary of the Vega Siltstone Member, thus esta blishing this carbonate lentil as a member of the Sulphur Mountain For mation.