Kootenay Group

Not to be confused with Kootenai Formation.
Kootenay Group
Stratigraphic range: Late Jurassic to Early Cretaceous
TypeGroup
Sub-unitsElk Formation
Mist Mountain Formation
Morrissey Formation
UnderliesBlairmore Group
OverliesFernie Formation
Thicknessmaximum 1,335 m (4,380 ft)
Lithology
PrimarySandstone, siltstone, mudstone
OtherCoal, conglomerate
Location
RegionCanadian Rockies
Country Canada
Type section
Named byD. W. Gibson, 1979[1][2]

The Kootenay Group, originally called the Kootenay Formation,[1][2] 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.[3] It includes economically important deposits of high-rank bituminous and semi-anthracite coal,[4] as well as plant fossils and dinosaur trackways.[2]

Stratigraphy and lithology

The strata of the Kootenay Group were originally described as the Kootenay Formation.[1][5] D.W. Gibson revised the sequence as the Kootenay Group and defined it as encompassing the stratigraphic interval between the Jurassic Fernie Formation and the Lower Cretaceous Blairmore Group. He subdivided it into three formations as shown below and designated a type section for each of the formations, thus eliminating the need for a type section for the group.[2]

Formation Age Lithology Maximum
Thickness		 Reference
Elk Formation earliest Cretaceous interbedded sandstone, siltstone, mudstone, conglomerate; rare thin coal seams 590 m (1,940 ft) [2]
Mist Mountain Formation latest Jurassic to earliest Cretaceous interbedded sandstone, siltstone, mudstone, shale, and mineable coal seams; rare conglomerate 665 m (2,180 ft) [2]
Morrissey Formation latest Jurassic massive cliff-forming fine- to medium-grained sandstone 80 m (260 ft) [2]

Environment of deposition

The Kootenay Group is an eastward-thinning wedge of sediments derived from the erosion of newly uplifted mountains to the west. The sediments were transported eastward by river systems and deposited in a variety of river channel, floodplain, swamp, coastal plain, deltaic and shoreline environments along the western edge of the Western Interior Seaway.[2]

Paleontology

Fossils are rare in the Morrissey Formation, but the Mist Mountain Formation includes plant fossils and dinosaur trackways, and the Elk Formation includes plant fossils, trace fossils and bivalves.[2]

Thickness and distribution

The Kootenay Group is present in the front ranges and foothills of the Canadian Rockies in southeastern British Columbia and southwestern Alberta. It extends from the Canada–US border to north of the North Saskatchewan River. It has a maximum thickness of about 1,355 metres (4,450 ft), and it thins eastward.[6]

Relationship to other units

The Kootenay Group conformably overlies the marine shales of the Fernie Formation. In most areas it is disconformably overlain by the nonmarine strata of the Blairmore Group, although in some western areas the contact may be conformable.[6][7]

North of the North Saskatchewan River the Kootenay Group grades into the Nikanassin Formation. To the south it may correlate with the upper part of the Morrison Formation in Montana. It was originally mis-correlated with the Kootenai Formation which underlies the Morrison.[6]

See also

References

  • Various Contributors to the Paleobiology Database. "Fossilworks: Gateway to the Paleobiology Database". Retrieved 17 December 2021.
  1. ^ a b c Gibson, D. W. 1979. The Morrissey and Mist Mountain formations – newly described lithostratigraphic units of the Jura-Cretaceous Kootenay Group, Alberta and British Columbia. Bulletin of Canadian Petroleum Geology 27: 183–208.
  2. ^ a b c d e f g h i Gibson, D. W. 1985. Stratigraphy, sedimentology and depositional environments of the coal-bearing Jurassic-Cretaceous Kootenay Group, Alberta and British Columbia. Geological Survey of Canada, Bulletin 357, 108 p.
  3. ^ Mossop, G. D. and Shetsen, I. (compilers), Canadian Society of Petroleum Geologists and Alberta Geological Survey (1994). "The Geological Atlas of the Western Canada Sedimentary Basin, Chapter 18: Jurassic and Lowermost Cretaceous strata of the Western Canada Sedimentary Basin". Retrieved 2016-06-20.{{cite web}}: CS1 maint: multiple names: authors list (link)
  4. ^ Mossop, G. D. and Shetsen, I. (compilers), Canadian Society of Petroleum Geologists (1994). "The Geological Atlas of the Western Canada Sedimentary Basin, Chapter 33: Coal Resources of the Western Canada Sedimentary Basin". Retrieved 2016-06-20.{{cite web}}: CS1 maint: multiple names: authors list (link)
  5. ^ Cairnes, D. D., 1908. Moose Mountain district of southern Alberta. Geological Survey of Canada Publication No. 968.
  6. ^ a b c 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. ISBN 0-920230-23-7.
  7. ^ Alberta Geological Survey, 2013. "Alberta Table of Formations; Alberta Energy Regulator". Retrieved 1 May 2018.{{cite web}}: CS1 maint: numeric names: authors list (link)