Type Locality:

Vicinity of Cache Creek and at Marble Canyon west of Cache Creek near the town of Ashcroft in south-central British Columbia.

Distribution:

Extends from the southern Yukon into British Columbia (Atlin area) and is exposed discontinuously south for over 1,500 km to south of Ashcroft. Similar rocks are exposed to the southwest in the San Juan Islands and northern Cascade Mountain foothills of Washington State (Trafton Sequence), in east-central Oregon, Klamath Mountains and western part of the Sierra Nevada foothills of California. Northward, similar rocks occur near Anchorage, Alaska and on Kodiak Island. The sequences to the north and south of British Columbia do not contain the thick, massive limestones but contain numerous small limestone bodies with the distinctive Tethyan fusuline faunas. These areas may be mélanges derived from former Cache Creek-like outcrops. J.E. Armstrong suggested a thickness of 6,100 m (20,000 ft) or more in the Fort St. John area. The Cache Creek Group is thick but difficult to measure because of deformation and the lenticular nature of many of the subunits.

Lithology:

Divided by Selwyn (1872) into a Lower Cache Creek Group consisting of "massively bedded limestones, thinly bedded shales, volcanic rocks, schists and minor serpentines and soapstones" and an Upper Cache Creek Group of "mainly limestones with minor shales and other rock types". Dawson (1896): Top, massive limestones (Marble Canyon Limestone) with minor intercalations of volcanic rocks, argillites and cherty quartzites. Middle, volcanic materials and limestones, with some argillites, cherty quartzites. Bottom, cherty quartzites, argillites, volcanic materials and serpentine with some limestone. Armstrong, (1949): Characterized by foraminiferal limestones and ribbon cherts. Monger (1975): Abundant thin-bedded, interlayered chert and pelite (ribbon chert), massive, lensoidal carbonate bodies that in places are of considerable extent and thickness, altered basic volcanic rocks with relatively little accompanying pyroclastic material and associated alpine type ultramific rocks. Danner (unpublished): At type locality, the group is characterized by an upper, thick, fusuline-bearing limestone with minor interbedded radiolarian cherts and submarine volcanic flows underlain by a sequence of radiolarian cherts, pillow lavas, volcanic breccias and fine- to coarse-grained clastic sediments. Small bodies of limestone occur throughout. The lower part of the section is cut by serpentines and is in part sheared and broken, strongly resembling a mélange. The limestone is remarkably pure, except where locally dolomitized, and contains minor amounts of secondary chert nodules. North of the Marble Range in the type region, the thick, massive limestone extends down the section to at least an age of Middle Pennsylvanian.

Relationship:

The base is not exposed. The sequence appears to be fault bounded both to the east and to the west. Triassic rocks are often in fault contact. May be overlain by Triassic rocks but only Jurassic sediments are so far definitely identified as overlying it unconformably. At the type area, oldest fossils are early Permian. Northward, it extends down into the Mississippian and possibly the Devonian. To the south, in the San Juan Islands of Washington State. Devonian limestones occur in rocks underlying typical Cache Creek limestones of Permian and Pennsylvanian age. Many rock sequences mapped as the Cache Creek Group in central British Columbia to the east and west of the "typical lithology", are now recognized as belonging to different plate tectonic areas and while correlatable as to age with the Cache Creek Group, they are not correlatable in stratigraphy and paleontology: Sicker Group, Chilliwack Group, Harper Ranch Group, etc. The Taku Group (Yukon) of the older literature has been included within the Cache Creek Group (Monger, 1975).

Remark:

*Same as Cache Creek Complex

Other Citations:

Danner, 1977.

References:

Armstrong, J.E., 1949. Fort St. James map-area, Cassiar and Coast Districts, British Columbia; Geological Survey of Canada, Memoir 252, 210 p. + "A" Series Map 907A, Fort St. James, British Columbia, Scale: 1:380 160 or 1 Inch to 6 Miles (in pocket).

Danner, W.R., 1977. Paleozoic rocks of northwest Washington and adjacent parts of British Columbia, pp. 481-502: in Stewart, J.H., Stevens, C.H. and Fritsche, A.E. (eds.), Paleozoic Paleogeography of the western United States, Pacific Coast Paleogeograph Symposium 1, Pacific Section Society of Economic Paleontologists and Mineralogists, 502 p.

Dawson, G.M., 1896. Report on the area of the Kamloops Map-sheet, British Columbia: Geological Survey of Canada Annual Report 1894, vol. 7, Part B (new series), pp. 3-427.

Monger, J.W.H., 1975. Upper Paleozoic rocks of the Atlin Terrane, northwestern British Columbia and south-central Yukon; Geological Survey of Canada, Paper 74-47, 63 p.

Selwyn, A.R.C., 1872. Journal and report of preliminary explorations in British Columbia; Geological Survey of Canada, Report of Progress 1871-72, pp. 16-72.