Purcell Supergroup
The Purcell Supergroup is composed primarily of argillites, carbonate rocks, quartzites, and mafic igneous rocks of late Precambrian age. It is present in an area of about 15,000 km2 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. Fossil stromatolites and algal structures are common in some of the Purcell Supergroup rocks, 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.
Spectacular outcrops of Purcell and Belt Supergroup rocks can be seen in Glacier National Park in northwestern Montana and Waterton Lakes National Park in southwestern Alberta.
Stratigraphy and lithology
The Purcell Supergroup consists primarily of argillites, carbonate rocks, and quartzites, and includes localized occurrences of igneous rocks. Sedimentary structures are well preserved in the Purcell rocks despite their great age.In the southern Canadian Rockies, the supergroup is subdivided as follows:
| Geological unit | Lithology | Environment of Deposition | Maximum 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 | ||
| Phillips Formation | red, thin-bedded quartz sandstone; siltstone interbedded with argillite and conglomerate; mudcracks and ripple marks are common. | marginal marine to nonmarine | ||
| 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 | ||
| Sheppard Formation | light grey dolomite and stromatolitic dolosmite; red dolomitic siltstone and sandstone; dolomitic argillite. | shallow marine | ||
| 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 | ||
| Siyeh Formation | argillaceous limestone and dolomite; black and green argillite; dolomitic quartzite; stromatolitic dolomite. | marginal marine | ||
| Appekunny Formation | green and maroon argillite; white, grey, green, and pale red sandstone; quartz-pebble conglomerate. | marginal marine | ||
| Altyn Formation | grey, thin-bedded argillaceous limestone and dolomite; massive sandy dolomite and stromatolitic dolomite; dark grey to black argillite. | shallow marine | ||
| Waterton Formation | grey, green and red argillaceous dolomite; banded and streaked limestone and dolomite; grey and green, thin-bedded argillite. | marine | ||
| Tombstone Mountain Formation | dark grey argillite; dolomitic argillite; argillaceous dolomite and limestone. | marine | ||
| 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 |
In the southern Purcell Mountains, the supergroup is subdivided as follows:
| Geological unit | Lithology | Environment of Deposition | Maximum Thickness | Reference |
| Roosville Formation | dolomitic argillite; siltstone; sandstone; and argillaceous and stromatolitic dolomite. | intertidal | ||
| Phillips Formation | red, thin-bedded quartz sandstone; siltstone interbedded with argillite; ripple marks and mud cracks are abundant locally. | shallow water to subaerial | ||
| 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 | ||
| Sheppard Formation | light grey stromatolitic dolomite, interbedded with dolomitic siltstone and argillite; stromatolite mounds up to thick; mudcracks, ripple marks, and rip-up clasts are locally abundant; casts of salt crystals are rare. | intertidal | ||
| Intrusive rocks | fine- to coarse-grained sills and dikes of gabbro and diorite intrude the Aldridge to Van Creek Formations. | intrusive | ||
| 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 | ||
| Van Creek Formation | green to purple argillite and siltstone; mud cracks, ripple marks, and rip-up clasts are locally abundant. | intertidal | ||
| Kitchner Formation | calcareous and dolomitic siltstone and argillite; silty dolomite and limestone; minor quartzite. | shallow subtidal | ||
| Creston Formation | green, grey, and purple siltstone and argillite; mud cracks, ripple marks, and rip-up clasts are locally abundant. | shallow subtidal | ||
| Aldridge Formation | fine-grained quartzite; argillaceous quartzite; rusty-weathering grey siltstone; dark grey argillite; base of formation not exposed. | marine | > |