Type Locality:

Roche Miette, northeast shoulder, 34 km (21 mi) north-northeast of Jasper, Alberta along Highway 16 (53 deg 10'N, 117 deg 55'W). Reference Sections: The Palisade, gully on mountain face near north end; 14.5 km (9 mi) north of Jasper, Alberta (53 deg 00'N, 118 deg 08'W). Lithologic description not published: see McLaren, 1955, fig. 3. Medicine Lake, ridge between Medicine and Beaver lakes; 22.6 km (14 mi) east of Jasper, Alberta. 52 deg 52'N, 117 deg 44' (McLaren, 1955).

Distribution:

The Mount Hawk Formation is a widespread basin filling formation present in the front and main ranges of the Rocky Mountains, occurring between carbonate buildups of the Fairholme Group. The Mount Hawk Formation is recognized over a 650 km (400 mi) belt from the U.S border (Price, 1964b) to at least the Smoky River area of west-central Alberta (McLaren, 1953). It is recognized in wells drilled immediately east of the mountain front and is generally correlative with the Ireton and Nisku formations of the plains subsurface. Westward the formation is absent through erosion in most of the main ranges, but occasionally it is preserved, as at Mount Spring Rice (Mountjoy, 1978). Mount Hawk thicknesses recorded in the literature vary with the definition of the formation. The Mount Hawk Formation is thickest near carbonate buildups due to its increased lime content; it thins into the basin. In the modern sense basin sections range from 65 to 120 m (213 to 394 ft) thick (e.g., Medicine Lake section); adjacent to buildups of the Fairholme Group thicknesses of 120 to 200 m (394 to 656 ft) are more typical (e.g., Roche Miette section).

Locality Data:

Thickness(m): Minimum 65, Maximum 200.

Lithology:

In modern usage the Mount Hawk Formation consists of two informal members: Lower Grey Mudstone and Limestone Member: Thin-bedded, medium grey argillaceous limestone, rhythmically interbedded with thin bands of dark grey calcareous shale. The limestone beds increase in thickness upwards at the expense of the shales and may contain brachiopods towards the top. Petrographically the limestones are micrites or microsparites, with finely disseminated clay and small amounts of organic material. Near carbonate buildups they contain increasing amounts of lime sand. The shale interbeds are composed of aligned and intergrown clay minerals, with subordinate lime mud and small dolomite rhombs. The principal clay mineral is illite, with lesser amounts of chlorite (Hopkins, 1972). Upper Argillaceous Limestone Member: The member consists of medium- to thin-bedded medium grey limestone with thin interbeds of argillaceous limestone towards the bottom. The upper member is distinguished by its increased carbonate content, which is dominantly lime mud in the basin but near buildups may contain appreciable quantities of lime sand peloids. It commonly contains brachiopods, which increase in abundance and occur with corals near carbonate buildups and is petrographically similar to the lower member, with a smaller proportion of clays. The upper member may also contain mud mounds (Winnifred Pass, Mount Mackenzie) and buildup-derived "breccia" beds (Hopkins, 1972 and 1977).

Fossils:

Brachiopods (McLaren, 1955) Devonoproductus ex. gr. walcotti (Fenton & Fenton), Nudirostra albertensis (Warren), Cyrtospirifer cf. whitneyi (Hall), Indospirifer n. sp. cf. I. orestes (Hall & Whitfield), Tenticospirifer cyrtinifornis (Hall & Whitfield), Thomasaria rockymontana (Warren), in addition to the corals Alveolites, Thamnopora, Syringopora, Disphyllum and Macgeea.

Relationship:

The Mount Hawk Formation was originally defined as a basin formation. Unfortunately the type section was chosen at, Roche Miette, which is in a transitional position between carbonates of the Miette buildup, located 15 km (9.3 mi) along strike to the southeast, and argillaceous limestones and shales of the basin. McLaren (1955) recognized this problem and suggested the Palisade and Medicine Lake sections as being more typical, without formally designating them as reference sections. Placement of the upper and lower formational boundaries has varied historically because of this complication. In the basin the Mount Hawk conformably overlies Perdrix Formation shales. Both formations contain interbedded limestone and shale, and the contact is placed where the limestone beds become dominant upward. Because or this convention the Mount Hawk Formation weathers slightly more resistant and is lighter in color than the Perdrix Formation. The transitional contact therefore appears conformable in the field. However, basin sections in southern Jasper Park (e.g., Miette and Queen Elizabeth ranges) exhibit a sharp color change on talus covered ridges at the Mount Hawk-Perdrix formation contact, suggesting a distinct formation break which might be paraconformable. This is supported by data from Hopkins (1972), who attributed part of the lighter weathering color of the Mount Hawk Formation to the presence of chlorite in the Mount Hawk and its absence in the Perdrix Formation. The Mount Hawk Formation in the basin is overlain by the Sassenach Formation. The Sassenach Formation consists of siltstone and silty limestones and marks the influx of quartzose clastics into the basin. The contact is placed at the base of the strongly silty carbonates and not at the lowest silty bed, and appears conformable although it approximates the Famennian-Frasnian boundary. The Mount Hawk is replaced laterally by the Southesk Formation of the carbonate buildups of the Fairholme Group, and in proximity to carbonate buildups the Mount Hawk Formation may be overlain by, and interfinger with tongues of detrital and reefal carbonate. Such is the case at the Roche Miette type section. In the Crowsnest Pass area the Mount Hawk overlies the Borsato Formation. The Mount Hawk is lithostratigraphically equivalent to the subsurface Ireton Formation, but may contain age equivalents of the Nisku Formation away from carbonate buildups.

History:

The formation was named after Hawk Mountain, a prominent peak in the Colin Range 16 km (10 mi) north of Jasper. The original type section of de Wit and McLaren (1950) was revised by McLaren (1955), who lowered the top and base of the type section by 25 m (82 ft) and 47.5 m (156 ft) respectively. The revised type section then included 3 informal members: in ascending order the grey mudstone and limestone member, the argillaceous limestone member and the grey limestone member. The type section was amended further by Mountjoy (1965), who omitted McLaren's grey limestone member from the Mount Hawk Formation and assigned it instead to the Arcs and Grotto members of the Southesk Formation The Roche Miette section of Mountjoy (1965) consists of two members subequal in thickness, an upper, fossiliferous grey limestone member, and a lower, argillaceous limestone and shale member, and a lower, argillaceous limestone and shale member. These units are comparable to the two lower member of McLaren's (1955) Mount Hawk Formation (except possibly with respect to the base of the formation, discussed below).

References:

McLaren, D.J., 1953. Summary of the Devonian stratigraphy of the Alberta Rocky Mountains. Alberta Soc. Petrol. Geol, 3rd Ann. Field Conf. Guidebook, p. 89-104.

McLaren, D.J., 1955. Devonian formations in the Alberta Rocky Mountains between Bow and Athabasca rivers; Geological Survey of Canada, Bulletin 35.

Mountjoy, E.W., 1965. Stratigraphy of the Devonian Miette reef complex and associated strata, eastern Jasper National Park, Alberta; Geological Survey of Canada, Bulletin 110, 132 p.

Mountjoy, E.W., 1978. Upper Devonian reef trends and configuration of the western portion of the Alberta Basin. In: The Fairholme carbonate complex at Hummingbird and Cripple Creek; McIlreath, I.A. and Jackson, P.C. (Eds.). Can. Soc. Petrol. Geol.

Price, R.A., 1964b. The Devonian Fairholme-Sassenach succession and evolution of reef-front geometry in the Flathead-Crowsnest Pass area, Alberta and British Columbia, in, Flathead Valley, Special Guide Book Issue, Fourteenth Annual Field Conference, Goodman, A.J. (Jack) (Ed.); The Alberta Society of Petroleum Geologists, Bulletin of Canadian Petroleum Geology, vol. 12 (August), pp. 427-451.

de Wit, Reinout and McLaren, Digby Johns, 1950. Devonian sections in the Rocky Mountains between Crowsnest Pass and Jasper, Alberta; Geological Survey of Canada, Paper 50-23, 66 p.