Unit Name: Ludington Formation
Unit Type: Lithostratigraphic
Usage: Currently in use
Age Interval: Carnian (228.7 - 216.5 ma)
Province/Territory: British Columbia
Originator: Gibson, 1971.
Mount Ludington, NTS Map 94B/6E Nabesche River (56° 27.75'N, 123° 14.75'W), northeastern British Columbia.
The unit is present in the extreme western foothills north of Peace River (Gibson, 1971) and recognized as far north as Liard River near the Alaska Highway. Complete and well exposed sections are scarce. At the type locality, the Ludington is 499.9 m (1,640 ft) thick; it thickens in the vicinity of Mount Laurier, where Pelletier (1964) recorded 960.1 m (3,149 ft) of Triassic strata above the Liard Formation.
Medium to pale grey weathering, dolomitic to calcareous siltstone, sandstone and silty to sandy bioclastic limestone. Near Mount Laurier at the headwaters of Cypress Creek the formation is characterized by a thick shell accumulation or "bank" of recrystallized and fragmented pelecypod shells, ranging in thickness from zero to an estimated 45.7 m (150 ft).
The Ludington Formation is abruptly and possibly unconformably underlain in most areas of the extreme western foothills north of Peace River by dark grey weathering siltstone, silty limestone, silty shale and lesser amounts of silty dolostone and calcareous sandstone of the Toad Formation. At Calnan Creek, near the headwaters of Halfway River the base of the Ludington Formation is characterized by a 1.5 m (5 ft) thick unit of siltstone containing subangular to well-rounded pebbles, cobbles and boulders of siltstone up to 0.3 m (1 ft) in diameter. Contact relationships with overlying formations are uncertain. At Mount Laurier the Ludington appears to interfinger with dense, well-indurated, light grey weathering limestone of the Baldonnel Formation. At Mount Ludington it is abruptly overlain by the Pardonet Formation. The Ludington Formation is equivalent to the Liard-Halfway, Charlie Lake and Baldonnel formation of the foothills and subsurface plains, the 'Grey Beds' of the Schooler Creek Formation of McLearn and Kindle (1950), and the Whitehorse and upper Sulphur Mountain formations of the Jasper-Banff region of Alberta.
Gibson (1971, 1975) recognized two new formations, the Ludington and Bocock in the Schooler Creek Group between Pine Pass and Sikanni Chief River.
Gibson, D.W., 1971. Triassic Stratigraphy of the Sikanni Chief River-Pine Pass Region, Rocky Mountain Foothills, northeastern British Columbia; Geological Survey of Canada, Paper, 70-31, 105 p.
Gibson, D.W., 1975. Triassic rocks of the Rocky Mountain Foothills and Front ranges of northeastern British Columbia and west-central Alberta; Geological Survey of Canada, Bulletin 247, 42 p.
McLearn, F.H. and Kindle, E.D., 1950. Geology of northeastern British Columbia; Geological Survey of Canada, Memoir 259, 236 p.
Pelletier, B.R., 1964. Triassic stratigraphy of the Rocky Mountain Foothills between Peace and Muskwa rivers, northeastern British Columbia; Geological Survey of Canada, Paper 63-33.
Source: CSPG Lexicon of Canadian Stratigraphy, Volume 4, western Canada, including eastern British Columbia, Alberta, Saskatchewan and southern Manitoba; D.J. Glass (editor)
Contributor: D.W. Gibson
Entry Reviewed: Yes
Name Set: Lithostratigraphic Lexicon
LastChange: 24 Nov 2009