{{short description|Mesoproterozoic geological supergroup on the Canadian Shield }} {{Infobox Rockunit | name = Purcell Supergroup | image = | caption = | type = Geological supergroup | age = {{Long fossil range|1500|1200|Mesoproterozoic}} | period = Precambrian | prilithology = Argillite, dolomite, quartzite | otherlithology = Limestone, igneous rocks | namedfor = Purcell Mountains | namedby = R.A. Daly, 1912.<ref name=Daly>Daly, R.A. 1912. Geology of the North American Cordillera at the Forty-ninth parallel. Geological Survey of Canada, Memoir 38, p. 119-136.</ref> | region = {{flag|Alberta}}<br>{{flag|British Columbia}} | country = {{flag|Canada}} | coordinates = | unitof = | subunits = Many | underlies = Windermere Supergroup | overlies = Canadian Shield | thickness = more than {{convert|10,000|m|ft|abbr=on}}<ref name=Glass>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}}.</ref> | extent = | area = {{convert|15,000|km2|sqmi|abbr=on}} | map = }} The '''Purcell Supergroup''' is composed primarily of argillites, carbonate rocks, quartzites, and mafic igneous rocks of late Precambrian (Mesoproterozoic) age. It is present in an area of about {{convert|15,000|km2|sqmi|abbr=on}} in southwestern Alberta and southeastern British Columbia, Canada, and it extends into the northwestern United States where it is called the Belt Supergroup. It was named for the Purcell Mountains of British Columbia by R.A. Daly in 1912.<ref name="Daly" /> Fossil stromatolites and algal structures are common in some of the Purcell Supergroup rocks,<ref name="O'Connor">O'Connor, M.P. 1972. Classification and environmental interpretation of the cryptalgal organosedimentary "Molar-Tooth" structure from the Late Precambrian Belt-Purcell Supergroup. Journal of Geology, vol. 80, no. 5, p. 592-610.</ref><ref name=McMechan>McMechan, M.E. 1981. The Middle Proterozoic Purcell Supergroup in the southwestern Rocky and southeastern Purcell Mountains, British Columbia, and the initiation of the Cordilleran Miogeocline, southern Canada and adjacent United States. Bulletin of Canadian Petroleum Geology, vol. 29, no. 4, p. 583-621.</ref> and the Sullivan ore body at Kimberley, British Columbia, a world-class deposit of lead, zinc, and silver, lies within the Alderidge Formation in the lower part of the Purcell.<ref name="Lydon">{{cite web|last1=Lydon|first1=John W.|title=Geology and metallogeny of the Belt-Purcell Basin. In: Goodfellow, W.D. (ed.), Mineral deposits of Canada: a synthesis of major deposit types, district metallogeny, the evolution of geological provinces, and exploration methods. Geological Association of Canada, Mineral Deposits Division, Special Publication no. 5, p. 581-607.|url=https://www.researchgate.net/publication/228345065|access-date=29 April 2018}}</ref>
Spectacular outcrops of Purcell and Belt Supergroup rocks can be seen in Glacier National Park in northwestern Montana<ref name=Alt>Alt, D.D. and Hyndman, D.W. 1986. Roadside geology of Montana. Mountain Press Publishing Co., Missoula, Montana, 427 p. {{ISBN|0-87842-202-1}},</ref> and Waterton Lakes National Park in southwestern Alberta.<ref name=Gordy>Gordy, P.L., Frey, F.R. and Norris, D.K. 1977. Geological guide for the CSPG 1977 Waterton-Glacier Park Field Conference. Canadian Society of Petroleum Geologists, Calgary, Alberta, 93 p.</ref>
==Stratigraphy and lithology== The Purcell Supergroup consists primarily of argillites, carbonate rocks (limestone and dolomite), and quartzites, and includes localized occurrences of igneous rocks (mafic lava flows, tuffs, pillow basalts, and gabbroic and dioritic sills and dykes). Sedimentary structures are well preserved in the Purcell rocks despite their great age.<ref name=Glass />
In the southern Canadian Rockies (Waterton Park area), the supergroup is subdivided as follows:
{|class="wikitable" |- ! Geological unit !! Lithology !! Environment of Deposition !! Maximum<br>Thickness !! Reference |- | Roosville Formation || green and grey argillite; dolomitic argillite, siltstone and sandstone; argillaceous and stromatolitic dolomite; mudcracks and ripple marks are common. || shallow marine (peritidal) || {{convert|1300|m|ft|-1|abbr=on}} |<ref name=Glass /><ref name=Map600>{{Cite web|url=http://ags.aer.ca/data-maps-models/maps.htm|title=Bedrock Geology of Alberta (Legend). Alberta Geological Survey, Map 600|author=Prior, G. J., Hathaway, B., Glombick, P.M., Pana, D.I., Banks, C.J., Hay, D.C., Schneider, C.L., Grobe, M., Elgr, R., and Weiss, J.A.|year=2013|access-date=2016-06-20|archive-url=https://web.archive.org/web/20160626164710/http://ags.aer.ca/data-maps-models/maps.htm|archive-date=2016-06-26|url-status=dead}}</ref><ref name="TOF">{{cite web|last1=Alberta Geological Survey, 2013|title=Alberta Table of Formations; Alberta Energy Regulator|url=http://ags.aer.ca/table-of-formation|access-date=1 May 2018|archive-url=https://web.archive.org/web/20180501224811/http://ags.aer.ca/table-of-formation|archive-date=1 May 2018|url-status=dead}}</ref> |- | Phillips Formation || red, thin-bedded quartz sandstone; siltstone interbedded with argillite and conglomerate; mudcracks and ripple marks are common. || marginal marine to nonmarine || {{convert|200|m|ft|-1|abbr=on}}||<ref name=Glass /><ref name=Map600 /><ref name="TOF" /> |- | Gateway Formation || red siltstone and argillite; green argillite; dolomitic argillite; dolomitic sandstone; dolomite; and sandy dolomite; casts of salt crystals, mudcracks, ripple marks, and rip-up clasts are locally abundant. || marginal marine || {{convert|1350|m|ft|-1|abbr=on}} |<ref name=Glass /><ref name=Map600 /><ref name="TOF" /> |- | Sheppard Formation || light grey dolomite and stromatolitic dolomite; red dolomitic siltstone and sandstone; dolomitic argillite. || shallow marine || {{convert|275|m|ft|-1|abbr=on}} |<ref name=Glass /><ref name=Map600 /><ref name="TOF" /> |- | Purcell Lava || dark green and reddish green to purple chloritized mafic lava flows, pillow basalts, gabbroic sills and dikes; amygdules of quartz, chlorite, and calcite are common. || shallow marine || {{convert|150|m|ft|-1|abbr=on}}|| <ref name=Glass /><ref name=Map600 /><ref name="TOF" /> |- | Siyeh Formation|| argillaceous limestone and dolomite; black and green argillite; dolomitic quartzite; stromatolitic dolomite. || marginal marine || {{convert|790|m|ft|-1|abbr=on}} || <ref name=Glass /><ref name=Map600 /><ref name="TOF" /> |- | Appekunny Formation || green and maroon argillite; white, grey, green, and pale red sandstone; quartz-pebble conglomerate. || marginal marine || {{convert|1000|m|ft|-1|abbr=on}} || <ref name=Glass /><ref name=Map600 /><ref name="TOF" /> |- | Altyn Formation || grey, thin-bedded argillaceous limestone and dolomite; massive sandy dolomite and stromatolitic dolomite; dark grey to black argillite. || shallow marine || {{convert|300|m|ft|-1|abbr=on}} || <ref name=Glass /><ref name=Map600 /><ref name="TOF" /> |- | Waterton Formation || grey, green and red argillaceous dolomite; banded and streaked limestone and dolomite; grey and green, thin-bedded argillite. || marine || {{convert|250|m|ft|-1|abbr=on}} || <ref name=Glass /><ref name=Map600 /><ref name="TOF" /> |- | Tombstone Mountain Formation || dark grey argillite; dolomitic argillite; argillaceous dolomite and limestone. || marine || {{convert|175|m|ft|-1|abbr=on}} || <ref name=Glass /><ref name=Map600 /><ref name="TOF" /> |- | Haig Brook Formation || light colored, cliff-forming sequence of dolomite; banded and streaked limestone and dolomite; minor argillite; base of formation is not exposed. || marine || {{convert|145|m|ft|-1|abbr=on}} || <ref name=Glass /><ref name=Map600 /><ref name="TOF" /> |}
In the southern Purcell Mountains (Cranbrook area), the supergroup is subdivided as follows:
{|class="wikitable" |- ! Geological unit !! Lithology !! Environment of Deposition !! Maximum<br>Thickness !! Reference |- | Roosville Formation || green and grey argillite; dolomite|dolomitic argillite; siltstone; sandstone; and argillaceous and stromatolitic dolomite. || intertidal || {{convert|300|m|ft|-1|abbr=on}} |<ref name=McMechan /> |- | Phillips Formation || red, thin-bedded quartz sandstone; siltstone interbedded with argillite; ripple marks and mud cracks are abundant locally. || shallow water to subaerial || {{convert|150|m|ft|-1|abbr=on}}||<ref name=McMechan /> |- | Gateway Formation || grey-green, red, and purple siltstone; dolomitic siltstone; minor interbeds of argillite; casts of salt crystals, mudcracks, ripple marks, and rip-up clasts are locally abundant. || lagoonal || {{convert|1350|m|ft|-1|abbr=on}} |<ref name=McMechan /> |- | Sheppard Formation || light grey stromatolitic dolomite, interbedded with dolomitic siltstone and argillite; stromatolite mounds up to {{convert|10|m|ft|-1|abbr=on}} thick; mudcracks, ripple marks, and rip-up clasts are locally abundant; casts of salt crystals are rare. || intertidal || {{convert|125|m|ft|-1|abbr=on}} |<ref name=McMechan /> |- | Intrusive rocks || fine- to coarse-grained sills and dikes of gabbro and diorite intrude the Aldridge to Van Creek Formations. || intrusive || || <ref name=McMechan /> |- | Nichol Creek Formation|| green and purple argillite and siltstone; green volcanic sandstone and tuff interlayered with green or maroon, chloritized and sericitized basaltic to andesitic lavas, some with amygdules of quartz and chlorite. || subaerial || {{convert|750|m|ft|-1|abbr=on}} || <ref name=McMechan /> |- | Van Creek Formation || green to purple argillite and siltstone; mud cracks, ripple marks, and rip-up clasts are locally abundant. || intertidal || {{convert|420|m|ft|-1|abbr=on}} || <ref name=McMechan /> |- | Kitchner Formation || calcareous and dolomitic siltstone and argillite; silty dolomite and limestone; minor quartzite. || shallow subtidal<br>(intertidal at base) || {{convert|1900|m|ft|-1|abbr=on}} || <ref name=McMechan /> |- | Creston Formation || green, grey, and purple siltstone and argillite; mud cracks, ripple marks, and rip-up clasts are locally abundant. || shallow subtidal<br>(intertidal at top) || {{convert|2350|m|ft|-1|abbr=on}} ||<ref name=McMechan /> |- | Aldridge Formation || fine-grained quartzite; argillaceous quartzite; rusty-weathering grey siltstone; dark grey argillite; base of formation not exposed. || marine (subtidal at top) || >{{convert|4200|m|ft|-1|abbr=on}} ||<ref name=McMechan /> |}
==Environment of deposition== The Purcell Supergroup was probably deposited in subsiding deltaic to marine environments along the margin of the North American craton,<ref name="Mossop06">{{cite web|last1=Hein, F.J. and McMechan, M.E. 1994|title=Atlas of the Western Canada Sedimentary Basin (Mossop, G.D. and Shetsen, I., compilers), Chapter 6: Proterozoic and Lower Cambrian strata of the Western Canada Sedimentary Basin|url=http://ags.aer.ca/publications/chapter-6-proterozoic-and-lower-cambrian-strata|access-date=11 April 2018}}</ref> possibly in an intracratonic basin where North America and another landmass were joined in a supercontinent called Columbia/Nuna.<ref name=Schieber2>Schieber, J., 1989. The origin of the Neihart Quartzite, a basal deposit of the mid-Proterozoic Belt Supergroup, Montana, USA. Geological Magazine, v. 126, p. 271-281.</ref> Deposition occurred during the Mesoproterozoic era, much of it probably between about 1470 and 1400 Ma (million years) ago.<ref name=Evans>Evans, K.V., Aleinikoff, J.N., Obradovich, J.D. and Fanning, C.M. 2000. SHRIMP U-Pb geochronology of volcanic rocks, Belt Supergroup, western Montana: evidence for rapid deposition of sedimentary strata. Canadian Journal of Earth Sciences, v. 37, p.1287-1300.</ref><ref>{{cite journal | last1 = Halpin| first1 = Jacqueline A.| last2 = Jensen| first2 = Torsten| last3 = McGoldrick| first3 = Peter| last4 = Meffre| first4 = Sebastien| last5 = Berry| first5 = Ron F.| last6 = Everard| first6 = John L.| last7 = Calver| first7 = Clive R.| last8 = Thompson| first8 = Jay| last9 = Goemann| first9 = Karsten| last10 = Whittaker| first10 = Joanne M.| year = 2014 | title = Authigenic monazite and detrital zircon dating from the Proterozoic Rocky Cape Group, Tasmania: Links to the Belt-Purcell Supergroup, North America | journal = Precambrian Research | volume = 250 | pages = 50–67 | doi = 10.1016/j.precamres.2014.05.025 | bibcode = 2014PreR..250...50H}}</ref>
==Distribution and thickness== In Canada, the Purcell Supergroup is present in an area of about {{convert|15,000|km2|sqmi|abbr=on}} that reaches from the southern Purcell Mountains in southeastern British Columbia to the southern Canadian Rockies in the southwestern Alberta.<ref name=Glass /> It extends southward into the United States (western Montana, northern Idaho, northwestern Washington, and western Wyoming) where it is called the Belt Supergroup.<ref name=ISU>{{cite web|last1=Lori Tapanila and Paul Link|title=Mesoproterozoic Belt Supergroup|url=http://geology.isu.edu/Digital_Geology_Idaho/Module2/mod2.htm|website=Digital Geology of Idaho|publisher=Idaho State University, Department of Geosciences|access-date=16 September 2016}}</ref> It reaches a maximum thickness of more than {{convert|10,000|m|ft|abbr=off}} in the Purcell Mountains.<ref name=Glass />
==Relationship to other units== The Purcell Supergroup is equivalent to the Belt Supergroup of the northwestern United States. The base of the Purcell is not exposed in Canada, but it is inferred to rest unconformably on the Canadian Shield. The Purcell is unconformably overlain by the Neoproterozoic Windermere Supergroup in most areas, or by younger Cambrian or Devonian formations where the Windermere is absent.<ref name=Glass />
==Economic resources== The now-closed Sullivan Mine at Kimberley, British Columbia, worked a world-class sedimentary exhalative (SedEx) deposit that is hosted in the lower part of the Purcell Supergroup. During the life of the mine, the Sullivan ore body is reported to have yielded 8,412,077 tons of lead, 7,944,446 tons of zinc, and 9,264 tons of silver, as well as significant quantities of tin and other metals.<ref name="Lydon"/>
==References== {{reflist}}
Category:Western Canadian Sedimentary Basin Category:Stratigraphy of Alberta Category:Stratigraphy of British Columbia Category:Geologic supergroups of Canada