The Cadomin Formation is a
stratigraphic
Stratigraphy is a branch of geology concerned with the study of rock layers (strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks.
Stratigraphy has three related subfields: lithostra ...
unit of
Early Cretaceous (
Barremian
The Barremian is an age in the geologic timescale (or a chronostratigraphic stage) between 129.4 ± 1.5 Ma (million years ago) and 121.4 ± 1.0 Ma). It is a subdivision of the Early Cretaceous Epoch (or Lower Cretaceous Series). It is precede ...
to
Aptian) age in the western part of the
Western Canada Sedimentary Basin.
It is extends from southeastern
British Columbia
British Columbia (commonly abbreviated as BC) is the westernmost province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include rocky coastlines, sandy beaches, ...
through western
Alberta
Alberta ( ) is one of the thirteen provinces and territories of Canada. It is part of Western Canada and is one of the three prairie provinces. Alberta is bordered by British Columbia to the west, Saskatchewan to the east, the Northwest Ter ...
to northeastern British Columbia, and it contains significant
reservoirs
A reservoir (; from French ''réservoir'' ) is an enlarged lake behind a dam. Such a dam may be either artificial, built to store fresh water or it may be a natural formation.
Reservoirs can be created in a number of ways, including control ...
of
natural gas
Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbo ...
in some areas. It was named after the mining town of
Cadomin, which is an
acronym
An acronym is a word or name formed from the initial components of a longer name or phrase. Acronyms are usually formed from the initial letters of words, as in ''NATO'' (''North Atlantic Treaty Organization''), but sometimes use syllables, as ...
of "Canadian Dominion Mining".
Stratigraphy
The Cadomin
Formation
Formation may refer to:
Linguistics
* Back-formation, the process of creating a new lexeme by removing or affixes
* Word formation, the creation of a new word by adding affixes
Mathematics and science
* Cave formation or speleothem, a secondar ...
is of
Early Cretaceous (
Barremian
The Barremian is an age in the geologic timescale (or a chronostratigraphic stage) between 129.4 ± 1.5 Ma (million years ago) and 121.4 ± 1.0 Ma). It is a subdivision of the Early Cretaceous Epoch (or Lower Cretaceous Series). It is precede ...
to
Aptian)
age. It is the basal unit of the
Bullhead Group
Bullhead Group is a stratigraphic unit of Lower Cretaceous age in the Western Canada Sedimentary Basin of northeastern British Columbia and western Alberta. It was first defined by F.H. McLearn in 1918 as the Bullhead Mountain Formation, but later ...
in northeastern
British Columbia
British Columbia (commonly abbreviated as BC) is the westernmost province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include rocky coastlines, sandy beaches, ...
and of the
Blairmore Group in Alberta.
The formation is a distinctive
marker horizon
Marker horizons (also referred to as chronohorizons, key beds or marker beds) are stratigraphic units of the same age and of such distinctive composition and appearance, that, despite their presence in separate geographic locations, there is no do ...
, and it was sometimes called the "coal conglomerate" because it was useful as a reference point for locating the coal seams of the underlying
Mist Mountain Formation and the overlying
Gething Formation.
[McLean, J.R. 1977. The Cadomin Formation: Stratigraphy, sedimentology, and tectonic implications. Bulletin of Canadian Petroleum Geology 25: 792-827.] It is not fossiliferous.
Lithology
The formation consists primarily of
conglomerate, although at some localities there are minor interbeds of coarse-grained
sandstone
Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks.
Most sandstone is composed of quartz or feldspar (both silicates ...
,
shale, and
coal
Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen.
Coal is formed when ...
. The conglomerate is typically massive and consists of well-rounded pebbles,
cobbles and
boulders of white, grey and green
chert
Chert () is a hard, fine-grained sedimentary rock composed of microcrystalline or cryptocrystalline quartz, the mineral form of silicon dioxide (SiO2). Chert is characteristically of biological origin, but may also occur inorganically as a ...
, and white and grey
quartzite
Quartzite is a hard, non- foliated metamorphic rock which was originally pure quartz sandstone.Essentials of Geology, 3rd Edition, Stephen Marshak, p 182 Sandstone is converted into quartzite through heating and pressure usually related to tec ...
, in a matrix of quartzose sand. In some areas there are also minor pebbles, cobbles and boulders of
limestone
Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...
,
dolomite Dolomite may refer to:
*Dolomite (mineral), a carbonate mineral
*Dolomite (rock), also known as dolostone, a sedimentary carbonate rock
*Dolomite, Alabama, United States, an unincorporated community
*Dolomite, California, United States, an unincor ...
, black
argillite
:''"Argillite" may also refer to Argillite, Kentucky.''
Argillite () is a fine-grained sedimentary rock composed predominantly of indurated clay particles. Argillaceous rocks are basically lithified muds and oozes. They contain variable amounts ...
and, rarely, greenish
volcanics
Volcanic rock (often shortened to volcanics in scientific contexts) is a rock formed from lava erupted from a volcano. In other words, it differs from other igneous rock by being of volcanic origin. Like all rock types, the concept of volcanic ...
. The conglomerate and sandstone beds are cemented with
silica
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is ...
, making them very hard and resistant to erosion, so they tend to form prominent
outcrop
An outcrop or rocky outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth.
Features
Outcrops do not cover the majority of the Earth's land surface because in most places the bedrock or superficia ...
s.
[Stott, D.F. 1965. Lower Cretaceous Bullhead and Fort St John Groups, between Smoky and Peace Rivers, Rocky Mountain foothills, Alberta and British Columbia. Geological Survey of Canada, Bulletin 152, 279 p. .]
Environment of deposition
Deposition of the Cadomin Formation marked the renewal of subsidence and sedimentation following a long period of uplift, exposure and erosion of older strata.
The Cadomin sediments were derived from sources in the mountains to the west, and were deposited across the
pediment
Pediments are gables, usually of a triangular shape.
Pediments are placed above the horizontal structure of the lintel, or entablature, if supported by columns. Pediments can contain an overdoor and are usually topped by hood moulds.
A pedim ...
surface by systems of
alluvial fan
An alluvial fan is an accumulation of sediments that fans outwards from a concentrated source of sediments, such as a narrow canyon emerging from an escarpment. They are characteristic of mountainous terrain in arid to semiarid climates, but a ...
s and
braided streams. It is postulated that the streams flowed generally northeastward, turning northwestward at the Fox Creek Escarpment.
Paleontology
The Cadomin Formation preserves the oldest dinosaur skeletal fossils from Alberta (and anywhere west of Nova Scotia, in Canada). The fossil material is attributable to a polacanthid ankylosaur, and comes from the basal unit of the Cadomin formation known as the Pocaterra Creek member. Unattributed turtle material was also reported from the formation, and the same locality as the dinosaur material.
[Nagesan, R.S., Campbell, J.A., Pardo, J.D., Lennie, K.I., Vavrek, M.J., & Anderson, J.S. (2019). An Early Cretaceous (Berriasian) fossil-bearing locality from the Rocky Mountains of Alberta, yielding the oldest dinosaur skeletal remains from western Canada. Canadian Journal of Earth Sciences. ust-in Article, December 19th 2019 10.1139/cjes-2019-0166]
Distribution
Outcrop
An outcrop or rocky outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth.
Features
Outcrops do not cover the majority of the Earth's land surface because in most places the bedrock or superficia ...
s near
Cadomin, Alberta are the
type locality. The formation is exposed at the surface in the foothills of the
Canadian Rockies, extending from the
Canada–US border in southeastern British Columbia and southwestern Alberta and to the
Peace River
The Peace River (french: links=no, rivière de la Paix) is a river in Canada that originates in the Rocky Mountains of northern British Columbia and flows to the northeast through northern Alberta. The Peace River joins the Athabasca River in th ...
region in northeastern British Columbia, a distance of more than . It is also recognizable in the subsurface east of the foothills. It ranges in thickness from to more than and is generally thicker and more coarse grained in the west.
[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. .]
Relationship to other units
The Cadomin Formation overlies a major regional
unconformity
An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval ...
caused by pre-Cadomin erosion, although little or no evidence of the angular nature of that unconformity is apparent at most outcrops.
It rests unconformably on the
Fernie Formation, the
Nikanassin Formation, the
Minnes Group or the
Kootenay Group
The Kootenay Group, originally called the Kootenay Formation, is a geologic unit of latest Jurassic to earliest Cretaceous age in the Western Canada Sedimentary Basin that is present in the southern and central Canadian Rockies and foothills. ...
, depending on the location and the extent of the erosion. It is conformably overlain by the
Gladstone Formation in Alberta and
Gething Formation in northeastern British Columbia, and it is equivalent to the base of the
Mannville Group
The Mannville Group is a stratigraphical unit of Cretaceous age in the Western Canadian Sedimentary Basin.
It takes the name from the town of Mannville, Alberta, and was first described in the ''Northwest Mannville 1'' well by A.W. Nauss in 194 ...
.
Hydrocarbon production
Natural gas
Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbo ...
is produced from the Cadomin Formation in the Deep Basin area of western Alberta in the
Hinton-
Grande Cache
Grande Cache is a hamlet in west-central Alberta, Canada within and administered by the Municipal District of Greenview No. 16. It is located on Highway 40 approximately northwest of Hinton and west of Edmonton. Grande Cache overlooks the Smo ...
-
Grande Prairie
Grande Prairie is a city in northwest Alberta, Canada within the southern portion of an area known as Peace River Country. It is located at the intersection of Highway 43 (part of the CANAMEX Corridor) and Highway 40 (the Bighorn Highway), a ...
area, and in the Cutbank area in northeastern British Columbia.
[Varley, C.J. 1984. The Cadomin Formation: A model for the Deep Basin type gas trapping mechanism. In: Stott, D.F. and Glass, D.J. (editors), Mesozoic of Middle North America; Canadian Society of Petroleum Geologists, Memoir 9, p. 471-484.]
Gallery
File:Elbow Falls.JPG, Elbow Falls flows over a Cadomin Formation outcrop.
File:Cadomin_Formation.jpg, Cadomin Formation outcrops along the Centennial Ridge Trail, Mount Allan, Alberta.
References
{{Western Canadian Sedimentary Basin, Canadian Rockies=yes, Northwest_Plains=yes
Geologic formations of Canada
Stratigraphy of Alberta
Cretaceous Alberta
Barremian Stage
Aptian Stage