Type Formation Underlies Bickford Formation | Unit of Minnes Group Primary Sandstone | |
Overlies Beattie Peaks Formation Thickness maximum 350 m (1,150 ft) | ||
The Monach Formation is a geologic formation of Early Cretaceous (Valanginian) age in the Western Canada Sedimentary Basin that consists primarily of sandstone. It is present in the northern foothills of the Canadian Rockies and the adjacent plains in northeastern British Columbia.
Contents
Lithology
The Monach Formation consists primarily of clean, white to light grey, well sorted, medium- to coarse-grained quartzose sandstone, and grey to brown, thin bedded to finely laminated argillaceous sandstone, with lesser interbeds of dark grey mudstone, thin coal seams, carbonaceous shale, and rare conglomerate.
Environment of deposition
The Monach Formation was deposited in marine and nonmarine environments within and adjacent to the Western Interior Seaway. Depositional settings ranged from marine to shoreline, deltaic, river channel, floodplain, and swamp environments.
Paleontology and age
The age of the Monach Formation has been determined from its fossil fauna, primarily species of the bivalve Buchia.
Thickness and distribution
The Monach Formation is present in the foothills of the Canadian Rockies and the adjacent plains in northeastern British Columbia. It extends from the Chowade River in the north, to south of the Sukunka River where it grades into the Gorman Creek Formation. It attains a maximum thickness of 350 m (1,150 ft) in the foothills, and thins to zero about 80 km (50 mi) or less beyond the eastern edge of the foothills where it was removed by erosion prior to the deposition of the Cadomin Formation.
Relationship to other units
The Monach Formation is part of the Minnes Group. It was deposited conformably on the Beattie Peaks Formation and is conformably overlain by the Bickford Formation, both of which also belong to the Minnes Group. To the east where it was removed by erosion, the Monach Formation is unconformably overlain by the Cadomin Formation. To the south it grades into the Gorman Creek Formation.