Type Locality:

The type section for the group and most of its formations is on the southwest limb of the Stew Syncline, and consists of three parts. The first part, for the Hawthorne Creek and Heritage Trail formations, has UTM co-ordinates as follows: base at 449100 E, 7057450 N, top at 449400 E, 7057800 N(2093 m peak on map; NTS 105-O/09), and the secton part, for the Keele Creek Formation, has its base at UTM co-ordinates 450300 E, 7059150 N and its top at 450300 E, 7058600 N, Zone 9 (adopted directly from Section 19b of Gordey and Anderson, 1993). The Fourway Formation is only found in one ridge, on the eastern margins of the study area (northeastern Niddery Lake map area) (ridge around UTM co-ordinates 449900 E and 7059900 N, Zone 9). The type section of the Caribou Pass Formation is a section adopted directly from Gordey and Anderson (1993, their section 18 - "Tsichu limestone"), and is located 60 km southwest of the Stew Syncline section, in the North Macmillan Fold Belt. The base of the section is at UTM co-ordinates 404000 E, 7020000N, and the top at 403500 E, 7018500 N, Zone 9, just outside the study area in southwestern 105-O/07 map area (Cecile, 2000).

Lithology:

Quartzites, interbedded shales and carbonates, and carbonates (Cecile, 2000).

Relationship:

The Tsichu Group, from oldest to youngest, consists of the Hawthorne Creek, Heritage Trail, Keele Creek, Caribou Pass, and Fourway formations. The type Hawthorne Creek Formation rests conformably on the Thor Hills Formation (Earn Group) (Cecile, 2000). The Tsichu Group is overlain sharply and unconformably by siliceous shale and chert of the Mount Christie Formation (Gordey and Anderson, 1993). In places where the Mount Christie Formation has been eroded, the Tsichu Group is overlain by the Jones Lake Formation (Cecile, 2000).

History:

Gordey and Anderson (1993) introduced the term Tsichu formation (informal) for a succession of quartzites, interbedded shales and carbonates, and carbonates. No type section was proposed and the unit was considered informal, pending further study. Gordey and Anderson (ibid., their section 19) measured a section through what they considered to be the Tsichu formation in the southeastern part of the northeastern Niddery Lake map area. Here they assigned the name Tsichu formation to a succession of lower Mississippian quartzite, a succession of lower to upper Mississippian shale and limestone, and to a unit of Pennsylvanian carbonates. An unnamed succession of shale and siltstone with limestone below the quartzite was considered to be Earn Group., Prevost? Formation, but it was included by Cecile (2000) in the new Tischu Group (Hawthorne Creek Formation). The Tsichu Group as defined by Cecile (2000) is mostly equivalent to the upper type Earn Group. In the northeastern Niddery Lake map area, and in the Nahanni area, the Earn Group includes significant amounts of immature clastics, mainly chert clasts, whereas the overlying Tsichu Group does not contain immature clastics and includes quartzite and limestone. Earn Group strata in both the northeastern Niddery Lake map area and the Nahanni map area are mainly Devonian in age and may range into the lower Mississippian. Tsichu Group strata in the northeastern Niddery Lake map area and Nahanni map area are early Mississippian, and range up to early Pennsylvanian in age (Gordey and Anderson, 1993). Thus based on lithology and relative ages it is likely that the type Earn Group, in Glenlyon map area, is equivalent to both the Nahanni map area Earn Group and Tsichu formation (informal) of Gordey and Anderson (1993). This division is continued in Cecile (2000) because of the distinct lithological difference between Earn and Tsichu strata, and the Tsichu is upgraded to group status. Tsichu Group is named after the Tsichu River, which has its headwaters near the type section and runs through the adjacent Sekwi map area (Cecile, 2000).

Remark:

Formations of the Tsichu Group represent a complex paleogeography featuring both shallow-water limestone and clastics and deeper water facies. The Heritage Trail, Fourway and Caribou formations are all interpreted as the products of shallow-water environments because of the dominance of limestone and bioclastic material and/or clean quartzite. The Hawthorne and the Keele Creek formations are interpreted as deeper water deposits that accumulated on the peripheries of shallow-water units (Cecile, 2000).

References:

Cecile, M.P., 2000. Geology of the northeastern Niddery Lake map area, east-central Yukon and adjacent Northwest Territories; Geological Survey of Canada, Bulletin 553, 120 p.

Gordey, S.P. and Anderson, R.G., 1993. Evolution of the northern Cordilleran miogeocline, Nahanni map area (105I), Yukon Territory and District of Mackenzie; Geological Survey of Canada, Memoir 428, 214 p.