Toad Formation, Grayling Formation, and Toad-Grayling Formation are obsolete names for the strata of the

Early Early may refer to: History * The beginning or oldest part of a defined historical period, as opposed to middle or late periods, e.g.: ** Early Christianity ** Early modern Europe Places in the United States * Early, Iowa * Early, Texas * Early ...

to Middle Triassic Doig and Montney Formations. They were applied in the foothills and Rocky Mountains of northeastern British Columbia, on the western edge of the Western Canada Sedimentary Basin. Although the names are considered obsolete, their usage persists. The Toad and Grayling strata have yielded fossils of marine organisms, including

ammonite Ammonoids are a group of extinct marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living coleoids (i.e., octopuses, squid and cuttlefish) ...

s, brachiopods, and

bivalve Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bival ...

Stratigraphic history

The Toad and Grayling Formations were originally described by E.D. Kindle in 1944,Kindle, E.D. 1944. Geological reconnaissance along Fort Nelson, Liard and Beaver rivers, northeastern British Columbia and southeastern Yukon. Geological Survey of Canada, Paper 44-16, 16 p. who named them for the Toad and Grayling Rivers, which are tributaries of the

Liard River The Liard River of the North American boreal forest flows through Yukon, British Columbia and the Northwest Territories, Canada. Rising in the Saint Cyr Range of the Pelly Mountains in southeastern Yukon, it flows southeast through British Co ...

in northeasternmost British Columbia. They were combined as the Toad-Grayling Formation by A.D. Hunt and J.D. Ratcliffe in 1959.Hunt, A.D. and Ratcliffe, J.D. 1959. Triassic stratigraphy, Peace River area. Alberta and British Columbia, Canada. Bulletin of the American Association of Petroleum Geologists, vol. 43, no.3, p. 563-589. The Toad-Grayling was replaced by the Doig and Montney Formations by J.H. Armitage in 1962,Armitage, J.H. 1962. Triassic oil and gas occurrences in northeastern British Columbia. Journal of the Alberta Society of Petroleum Geologists, vol. 10, p. 35-36. and the names are now considered obsolete, although their usage persists.Glass, D.J. (editor) 1997. Lexicon of Canadian Stratigraphy, vol. 4, Western Canada including eastern British Columbia, Alberta, Saskatchewan and southern Manitoba. Canadian Society of Petroleum Geologists, Calgary, 1423 p. on CD-ROM. .

Lithology

The Grayling Formation consists of

dolomitic Dolomite () is an anhydrous carbonate mineral composed of calcium magnesium carbonate, ideally The term is also used for a sedimentary carbonate rock composed mostly of the mineral dolomite. An alternative name sometimes used for the dol ...

siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility.Blatt ''et al.'' 1980, p ...

and silty

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especial ...

, with minor silty limestone, dolomite, and very fine-grained sandstone. It reaches a maximum thickness of about 460 metres (1500 ft). The overlying Toad Formation is more calcareous and less dolomitic than the Grayling. It consists of dark grey calcareous siltstone and silty limestone, with minor amounts of silty dolomite and calcareous sandstone and, in the lower part, minor thin, randomly dispersed lenses and nodules of phosphate. It reaches a maximum thickness of about 825 metres (2700 ft).

Relationship to other units

The Grayling Formation unconformably overlies the Permian Fantasque Formation. It is equivalent to the lower Montney Formation in the subsurface of the Peace River plains and to the Phroso Siltstone Member of the Sulphur Mountain Formation in west-central and southwestern Alberta. Its contact with the overlying Toad Formation is gradational. The Toad Formation is conformably overlain by the Liard Formation. North of the Peace River it is overlain, possibly unconformably, by the Ludington Formation, and in the

area it is unconformably overlain by the

Fort St. John Group The Fort St. John Group is a stratigraphic unit of Lower Cretaceous age in the Western Canada Sedimentary Basin. It takes the name from the city of Fort St. John, British Columbia and was first defined by George Mercer Dawson in 1881. Lithology T ...

. It is laterally equivalent to the Doig Formation and the upper two-thirds of the Montney Formation in the subsurface of the Peace River plains, and to part of the Llama Member of the Sulphur Mountain Formation in west-central and southwestern Alberta.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, 61 p.

References

* {{reflist Western Canadian Sedimentary Basin Geologic formations of British Columbia Triassic British Columbia Siltstone formations Shale formations Limestone formations of Canada Dolomite formations

Stratigraphic history

Lithology

Relationship to other units

See also

References