Part II: Conodont faunas

Abstract

Conodonts from Middle Devonian rocks on the south side of Great Slave Lake range in age from late Eifelian to late Givetian, and are generally well preserved, with Colour Alteration Indices (CAI) of 1 to 1.5. Twenty- three species (including three species with their seven morphotypes) and seven subspecies were recovered. The six formations studied (in ascending order), and their zonal assignments, are as follows: the Chinchaga Formation (probable australis to kockelianus zones); the Keg River Formation (kockelianus to ensensis zones); the Bituminous limestone and Fine-grained dolostone members of the Pine Point Formation (probably the upper (Givetian) part of the ensensis Zone to upper part of the Middle varcus Subzone, and the Buffalo River Member (upper part of the Middle to possibly Upper varcus subzones); the Windy Point Member of the Sulphur Point Formation (possibly Upper varcus Subzone to hermanni Zone); the Watt Mountain Formation (probable Lower subterminus Fauna); and the Slave Point Formation (Upper subterminus Fauna). Samples from the Slave Point Formation were barren in the study area, consequently conodonts from that unit in northeastern Alberta are discussed. Correspondence of these zones with the stratigraphic ranges of megafossils, especially brachiopods, are made in the accompanying paper by A.W. Norris. Middle Devonian strata on the south side of Great Slave Lake can be closely correlated with successions in the Powell Creek area, northern Mackenzie Shelf and Peel Shelf, Mackenzie Mountains, District of Mackenzie, and in southeastern Elk Point Basin (Saskatchewan sub-Basin) in southern and central Manitoba. Equivalent strata in the Powell Creek area are, in ascending order, the Hume, Hare Indian, Ramparts, and the lowest part of the Allochthonous Beds (=Allochthonous foreslope limestone facies of the Ramparts reef complex; Muir et al., 1984). In southern and central Manitoba, they are the Ashern, Elm Point, Winnipegosis, and Dawson Bay formations, and the Point Wilkins Member of the Souris River Formation. The transgressive-regressive (T-R) cycles (Johnson et al., 1985) of the Great Slave Lake area can be most closely matched with those of Manitoba, a not unexpected result since Middle Devonian strata of both areas were deposited in inner shelf environments of an interconnected, intracratonic sea. The Powell Creek area, on the other hand, during the deposition of the upper part of its succession, was the site of deeper water, middle shelf environments. Deposits of the T-R cycle le (start within the kockelianus Zone) are represented by the Keg River and Elm Point formations. The start of Cycle If (within the ensensis Zone) is at the bases of the Pine Point and Hare Indian formations, and in the upper part of the Winnipegosis Formation. The start of Taghanic Onlap (start upper part of Middle varcus Subzone; Cycle IIa of Johnson et al., 1985; IIa-1 of Day et al., 1994, in press) is at the bases of the Buffalo River Member of the Pine Point Formation and of the B Member of the Dawson Bay Formation. The start of Cycle IIa-2 (start Upper subterminus Fauna) is at the bases of the Slave Point Formation, and the Argillaceous limestone beds of the Point Wilkins Member, Souris River Formation; in the Powell Creek area, it marked the beginning of the deposition of the Allochthonous Beds. A more detailed discussion on the T-R cycles, and their close correlations of the south side of Great Slave Lake, southern and central Manitoba, and eastern Iowa, is presented by Day et al. (1994, in press). A new morphotype of Polygnathus linguiformis Hinde, similar to that previously described as morphotype "delta" by Ziegler and Klapper (1976), is described herein and referred to as morphotype "predelta".