Unit Name: Mahto Formation
Unit Type: Lithostratigraphic
Usage: Currently in use
Age Interval: Early Cambrian (542 - 513 ma)
Age Justification: Skeletal fossils are extremely rare, but trace fossils including Skolithos and horizontal, branching burrows are common. A few trilobites belonging to the Bonnia-Olenellus Zone, and small archaeocyathid bioherms near the base of the formation have been documented (Fritz and Mountjoy, 1975).
Province/Territory: Alberta; British Columbia
Originator: Walcott, C.D., 1913.
Mount Mahto, 12 km (7.5 mi) northeast of Mount Robson, British Columbia, (53 deg 12'N, 119 deg 03'W).
The Mahto is distinguishable from the McNaughton Formation by the intervening Mural carbonates, which are first recognizable in the vicinity of Jasper townsite and continue northwestward to Pine Pass, a distance of 400 km (250 mi). The Mahto Formation outcrops only in the central and western ranges of the Rocky Mountains, although it has probably been penetrated in several wells in the eastern ranges and foothills. The Mahto Formation thickens in easterly outcrops from about 150 m (500 ft) in northern Jasper Park to 240 m (800 ft) near Mount Sir Alexander, then becomes thinner farther northwest, to about 120 m (400 ft) near Pine Pass. It also thickens from east to west, so that it is 459 m (1505 ft) thick at its type section just north of Mount Robson, and only slightly thinner to the northwest along the Robson Synclinorium.
Predominantly quartzose sandstone in medium- to thick-beds, with rare dolomite and sandy dolomite locally, and one or more shale members in western outcrops. Two large scale shale-sandstone cycles comprise the Mahto Formation in western ranges of the Rocky Mountains of the McBride area. The sandstone is nearly pure quartz, consisting of rounded grains of quartz sand welded together by quartz overgrowth. Glauconite and weathered feldspar are rare; hematite and dolomite are rare cementing materials. Bioturbation, indistinct lamination, cross-bedding, and abundant vertical burrows (Skolithos) are commonly observed in the sandstone beds.
Gradational contact above the Mural Formation and abrupt or gradational upper contact with the Hota or Snake Indian formations. Probably grades laterally westward into the black shale facies of the Dome Creek Formation. Eastward the Mahto probably onlaps the Precambrian basement complex of the Peace River and west Alberta arches.
Campbell, Mountjoy and Young, 1973; Fritz and Mountjoy, 1975; Slind and Perkins, 1966; Walcott, 1913.
Source: CSPG Lexicon of Canadian Stratigraphy, Volume 4, western Canada, including eastern British Columbia, Alberta, Saskatchewan and southern Manitoba; D.J. Glass (editor)
Contributor: F.G. Young
Entry Reviewed: Yes
Name Set: Lithostratigraphic Lexicon
LastChange: 29 Apr 2003