Kotcho Formation
Encyclopedia
The Kotcho Formation is a stratigraphical
unit of middle Famennian
age
in the Western Canadian Sedimentary Basin
.
It takes the name from Kotcho Lake
, and was first described in the Imperial
Island River No. 1 by H.R. Belyea and D.J. McLaren in 1962.
, locally bituminous, with thin argillaceous limestone
beds or lenses.
area, and thins down southwards, disappearing completely on the northern flank of the Peace River Arch.
and conformably overlays the Tetcho Formation
.
To the east, it grades into the upper Wabamun Group carbonate, and to the south-west into the Palliser Formation
. To the east it is replaced by the Besa River Formation
shale.
Stratigraphy
Stratigraphy, a branch of geology, studies rock layers and layering . It is primarily used in the study of sedimentary and layered volcanic rocks....
unit of middle Famennian
Famennian
The Famennian is one of two faunal stages in the Late Devonian epoch. It lasted from 374.5 ± 2.6 million years ago to 359.2 ± 2.5 million years ago. It was preceded by the Frasnian stage and followed by the Tournaisian stage and is named after Famenne, a natural region in southern Belgium.It was...
age
Geochronology
Geochronology is the science of determining the age of rocks, fossils, and sediments, within a certain degree of uncertainty inherent to the method used. A variety of dating methods are used by geologists to achieve this, and schemes of classification and terminology have been proposed...
in the Western Canadian Sedimentary Basin
Western Canadian Sedimentary Basin
The Western Canadian Sedimentary Basin is a vast sedimentary basin underlying of Western Canada including southwestern Manitoba, southern Saskatchewan, Alberta, northeastern British Columbia and the southwest corner of the Northwest Territories. It consists of a massive wedge of sedimentary rock...
.
It takes the name from Kotcho Lake
Kotcho Lake
Kotcho Lake is a lake in north-eastern British Columbia, Canada.It is located east of Fort Nelson, in the Greater Sierra Oil Filed, at an elevation of .The Kotcho Lake Village Site Provincial Park is located on the southern shore of the lake....
, and was first described in the Imperial
Imperial Oil
Imperial Oil Limited is Canada's largest petroleum company. The company is engaged in the exploration, production and sale of crude oil and natural gas. It is controlled by US based ExxonMobil, which owns 69.6% of its stock...
Island River No. 1 by H.R. Belyea and D.J. McLaren in 1962.
Lithology
The Kotcho Formation is composed of green-grey shaleShale
Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable. Shale is characterized by breaks along thin laminae or parallel layering...
, locally bituminous, with thin argillaceous limestone
Limestone
Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....
beds or lenses.
Distribution
The Kotcho Formation reaches a maximum thickness of 210.9 metres (691.9 ft).It is up to 30 metres (98.4 ft) thick in the Fort NelsonFort Nelson, British Columbia
Fort Nelson is a town of approximately 5000 residents in British Columbia's northeastern corner. It is the administrative centre of the newly formed Northern Rockies Regional Municipality, a first for BC. The majority of Fort Nelson's economic activities have historically been concentrated in the...
area, and thins down southwards, disappearing completely on the northern flank of the Peace River Arch.
Relationship to other units
The Kotcho Formation is overlain by the Exshaw FormationExshaw Formation
The Exshaw Formation is a stratigraphical unit of Mississippian age in the Western Canadian Sedimentary Basin.It takes the name from the hamlet of Exshaw, Alberta, and was first described in outcrops on the banks of Jura Creek, north of Exshaw by P.S. Warren in 1937. The formation is of late...
and conformably overlays the Tetcho Formation
Tetcho Formation
The Tetcho Formation is a stratigraphical unit of Famennian age in the Western Canadian Sedimentary Basin.It takes the name from Tetcho Lake, and was first described in the Imperial Island River No. 1 well The Tetcho Formation is a stratigraphical unit of Famennian age in the Western Canadian...
.
To the east, it grades into the upper Wabamun Group carbonate, and to the south-west into the Palliser Formation
Palliser Formation
The Palliser Formation is a stratigraphical unit of Famennian age in the Western Canadian Sedimentary Basin. found in the ranges of the Canadian Rockies and foothills....
. To the east it is replaced by the Besa River Formation
Besa River Formation
The Besa River Formation is a stratigraphical unit of Devonian age in the Western Canadian Sedimentary Basin.It takes the name from Besa River, a tributary of the Prophet River, and was first described in outcrop near the Muskwa River, in the Muskwa Ranges by F.A. Kidd in 1963.-Lithology:The Besa...
shale.