Unit Name: Sassenach Formation
Unit Type: Lithostratigraphic
Usage: Currently in use
Age Interval: Famennian (374.5 - 359.2 ma)
Age Justification: The Sassenach Formation is popularly considered to be Famennian in age with the Famennian-Frasnian boundary occurring at the base of the formation. The Sassenach, however is poorly fossiliferous, particularly in its lower part, and most Famennian fossil collections are from some distance above the base of the formation. For example, at the type section the basal 10 m (33 ft) of the Sassenach Formation are undated (Mountjoy and Mackenzie, 1973). Placement of the Famennian- Frasnian boundary at the base of the Sassenach Formation is convenient and probably correct in eastern outcrop areas. Coppold (1976), how ever suggested on lithostratigraphic grounds that the Sassenach and its thick western Sections may be partly Frasnian (Southesk and Mount Hawk equivalent) in age. This suggestion remains unproven.
Originator: McLaren and Mountjoy, 1962
Ridge southeast of Thornton Creek, 4 km (2.5 mi) southeast of Mount Haultain in northeastern Jasper National Park, Alberta. Located 34 km (21 mi) north of Jasper townsite. (53 deg 10'N, 118 deg 14'W).
The Sassenach Formation is recognized in the Rocky Mountains from northern Jasper National Park to the North Saskatchewan River. Price (1964b) also tentatively identified the Sassenach Formation in the Crowsnest Pass area. The formation thickens to the west and northwest. A basin filling unit it is only fully developed away from carbonate buildup margins of the Fairholme Group (i.e., where it overlies Mount Hawk) . Typical basin thicknesses are: southwestern Ancient Wall 224 m (800 ft); southeastern Ancient Wall type section 183 m (601 ft), Morro Peak 189 m (620 ft); Rocky Forks 128 m (420 ft) and Cardinal Mountain 62 m (203 ft).
At the type section consists of two informal members: a lower silty mudstone and an upper sandy member. The lower member is composed of dark grey to greenish grey mudstones containing quartz silt and variable amounts of limestone and dolomite. There is an upward increase in carbonate, with development of silty and argillaceous limestones towards the top of the member. The upper member is composed of strongly silty limestones and calcareous sandstones. Detailed examination of Upper Devonian basin sections between the Snake Indian and Brazeau rivers (Coppold, 1976 and unpub.) shows the Sassenach Formation to be strongly silty at the top and base, with a thick silk carbonate in the middle. Within these units the Sassenach Formation is composed of interbedded and interlaminated rocks which are divisible into two gross lithologies based on the presence or absence of a strong silty component. The lithologies are always laminated and frequently are cross-laminated. Interbedding relationships may be planar, undulose or nodular. Close to carbonate buildups of the Fairholme Group the basal part of the formation may contain fossils or calcarenite eroded from the buildups. Penecontemporaneous slump structures are common in the lower part of the Sassenach Formation.
The Sassenach Formation is a basin filling formation between the Fairholme Group and the Palliser Formation in the Jasper region. The basal contact in the thicker basin sections (i.e., overlying Mount Hawk Formation) appears conformable or paraconformable. Where it onlaps the Fairholme Group carbonate buildups (i.e., overlying Southesk Formation) the relationship is unconformable. The upper contact with the Palliser Formation is conformable and often gradational over a few metres. The Sassenach Formation is laterally equivalent to the upper member of the Alexo Formation type section at North Saskatchewan River Gap. However, the exact relationship of the Sassenach-Alexo interval south of the North Saskatchewan River has not been resolved. Correlation with the Crowsnest Pass area also remains tentative (Price, 1964). The Sassenach Formation is homotaxial to the Calmar and Graminia formations of the central Alberta subsurface and the Crowfoot Formation of southeastern Alberta.
McLaren and Mountjoy (1962) erected the Sassenach Formation to include all beds between the top of the Fairholme Group and the base of the Palliser Formation in the Jasper area. The formation was named after Mount Sassenach, near its type section. The Sassenach Formation replaced the informal upper member in the type Alexo Formation at North Saskatchewan River Gap. In basin sections far from Fairholme carbonate buildups the Sassenach Formation corresponds closely to previous usage of the entire Alexo Formation interval (e.g., McLaren, 1955).
Coppold, M.P., 1976. Buildup to basin transition at the Ancient Wall Complex (Upper Devonian), Alberta; in, Bulletin of Canadian Petroleum Geology, June 1976, Vol. 24, Issue 2, pp. 154-192.
Mackenzie, W.S. and Mountjoy, E.W., 1973. Stratigraphy of the southern part of the Devonian ancient wall carbonate complex, Jasper National Park, Alberta; Geological Survey of Canada, Paper 72-20, 121 p.
McLaren, D.J. and Mountjoy, E.W., 1962. Alexo equivalents in the Jasper region, Alberta (Report, 4 figures, appendix); Geological Survey of Canada, Paper 62-23, 36 p.
McLaren, D.J., 1955. Devonian formations in the Alberta Rocky Mountains between Bow and Athabasca rivers; Geological Survey of Canada, Bulletin 35.
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.
Source: CSPG Lexicon of Canadian Stratigraphy, Volume 4, western Canada, including eastern British Columbia, Alberta, Saskatchewan and southern Manitoba; D.J. Glass (editor)
Contributor: E.W. Mountjoy; M.P Coppold
Entry Reviewed: Yes
Name Set: Lithostratigraphic Lexicon
LastChange: 14 Mar 2014