Type Locality:

Type well B.A. Pyrcz No. 1, in 12-25-50-26W4M, in central Alberta, between 1,544 and 1,624 m (5,065 and 5,327 ft) partially cored. This "on-reef'' section includes only the upper Ireton, and a more representative "off-reef" section is present in Imperial Labyrinth Lake 15-14-48-23W4M, between 1,558 and 1,684 m (5,110 and 5,525 ft), continuously cored.

Distribution:

Present throughout most of central Alberta, the Ireton ranges in thickness from less than 3 m (10 ft) "on-reef" to 250 m (820 ft) in basinal areas. The upper Ireton averages 15 to 20 m (49 to 66 ft), the middle Ireton 120 m (394 ft), and the lower Ireton 30 m (98 ft). In the East Shale Basin the unit averages 150 m (492 ft), thickening westwards as the underlying Duvernay thins. In the West Shale Basin it thickens to over 250 m (820 ft). On the southern Alberta Woodbend shelf it is present as a thin development which may extend into Saskatchewan. To the northeast it is truncated in the subsurface by the pre-Cretaceous unconformity.

Lithology:

Divided into three informal divisions on the basis of lithology. The upper Ireton consists of interbedded, fossiliferous, calcareous grey-green shales and argillaceous limestones. Fossil material is generally present in thin coquinas, and rare silt horizons may exhibit small scale cross-bedding. A number of discontinuity surfaces are present within the sequence, evidence of early lithification. This unit is extensively dolomitized and in places includes a 20 m (66 ft) thick dolomitic carbonate unit referred to as the Camrose Member. The middle Ireton is composed of slightly calcareous, fissile, grey-green shale, with occasional thin (25 cm, 10 in) beds of calcirudite which contain abundant skeletal material and lithoclasts. The lower Ireton is made up of massive, dense, nodular and banded limestones with minor calcareous shale partings, interbedded with grey-green, calcareous, fissile shale. Broadly sigmoidal log marker surfaces present within the sequence reflect preserved depositional topography and cross the lithologic divisions outlined above. These three lithologic divisions represent deposition in platform, slope and basinal settings respectively.

Relationship:

Conformably overlies the Duvernay Formation, the contact often being facies controlled, with Duvernay sediments being the deep water equivalent of slope and platform deposits of the Ireton. This thick shale development represents regressive infilling of basinal areas between Leduc carbonate buildups that proceeded from southeast to northwest. It is conformably overlain in the East Shale Basin by platform carbonates of the Nisku Formation, and Nisku or Winterburn shale equivalents in the West Shale Basin. Further northwards Ireton shales thin into lower portions of the lithologically similar Fort Simpson Shales.

History:

Named after the railway siding of Ireton at the south end of the Leduc-Woodbend field. Originally proposed as a member of the then Woodbend Formation. Elevation of this formation to group status, proposed by Andrichuk and Wonfor (1954, p. 2505), resulted in the Ireton attaining formational status.

Other Citations:

Andrichuk and Wonfor, 1954; Belyea, 1964; Geological Staff, Imperial Oil Ltd., 1950; McCrossan, 1961; Newland, 1954; Oliver and Cowper, 1963; Stoakes, 1979.