Tindir Group

Unit symbol: CPxt
Age range Cambrian? and Proterozoic (1600 to 509 Ma)
Lithology: Sedimentary
Group name: Tindir Group
The Tindir Group is commonly divided into upper and lower parts (see Young, 1982; MacDonald and others, 2010). The lower Tindir Group is as much as 2 km thick and divided into several informal units. As the base of the lowest unit is nowhere exposed, true thickness is unknown. The lower shale unit is gray to black mudstone overlain by light-gray quartzite that contains discontinuous stromatolite bioherms. The lower shale is unconformably overlain by a lower dolostone unit (Van Kooten and others, 1996), which is less than 350 m thick and is dominated by branching to massive domal stromatolites. An upper shale unit consists of less than 500 m of fissile black shale with interbedded quartzite and carbonate beds. The uppermost unit of the lower Tindir Group, an upper dolostone, consists of yellow-weathering dolostone that has intraclast breccia, black chert nodules, shale interbeds, and molar tooth structures (Young, 1982). All units in the lower Tindir Group are intruded by north-northwest-trending mafic dikes. Young (1982) separated the upper Tindir Group into five informal units. Unit 1 is “as much as 200 m of green and gray, commonly amygdaloidal pillow basalts and locally cupriferous tuffs and volcanic breccias” (Young, 1982) and minor tuff, shale, sandstone, and conglomerate. Young (1982) described unit 2 as purple mudstone and minor gray and green mudstone and siltstone, as well as thin beds (less than 50 cm) of purple diamictite and graded purple and gray sandstone in a generally coarsening-upward sequence that varies from less than 200 m to more than 700 m thick. Iron formation is locally present near the top of unit 2; elsewhere unit is capped by an orange-weathering diamictite that has a dolomite-rich matrix. Unit 3 of Young (1982) “is composed mainly of crudely stratified purple and red diamictite with much thinner interbeds of purple mudstone and red and orange beds and lenses of chert,” which MacDonald and others (2010) divided into two parts: a lower planar-laminated siltstone and sandstone more 100 m thick that contains minor dolomite marl, and an upper massive diamictite that has clasts as large as boulders. Young’s (1982) unit 4, as thick as 600 m, is highly lithologically variable, generally it consists primarily (about 70 percent of unit) of gray and green shale, which is interbedded with turbiditic dolomitic sandstone, siltstone, and incidental amounts of gray diamictite and volcanic breccia. Locally, a fine-grained buff to gray, locally cherty dolostone constitutes the bulk of unit 4. Young’s (1982) unit 5, the uppermost unit of the upper Tindir Group, is also highly lithologically laterally variable and is primarily described as gray wavy-bedded limestone and calcareous siltstone that has channels filled with granule to pebble conglomerate of largely limestone clasts. Structures indicating deposition by turbidites are common. Elsewhere, parts of the unit stratigraphically above the conglomeratic layers suggest deposition in a shallow-marine, tidally influenced(?) environment (Young, 1982). Locally, the unit is composed largely of dark-gray to black carbonaceous shale that contains minor quartz sandstone and slumped dolostone beds. In contrast to the lower Tindir Group, none of the upper Tindir Group exposures above unit 1 contain mafic intrusions (MacDonald and others, 2010). Age control is limited and open to interpretation. Allison (1981) thought the microfossils she examined from the upper Tindir Group to be of Cambrian age; Young (1982) seems to imply that a hiatus in deposition is likely present between the upper Tindir Group and overlying well dated late Early Cambrian units, making the Tindir Group entirely Proterozoic. Kaufman and others (1992), on the basis of geochemical evidence, interpreted the microbiota of the upper Tindir Group to be of late Riphean age (780 to 620 Ma, middle Neoproterozoic) and therefore also suggested that the Tindir Group is entirely of Proterozoic age. MacDonald and Cohen (2011) suggested abandoning the Tindir nomenclature and placing parts of the lower Tindir Group into the Pinguicula and Fifteen Mile groups, which form the Mackenzie Mountains Supergroup of Turner (2011), putting the uppermost part of the lower Tindir Group and lowermost unit of the upper Tindir Group into the Coates Lake Group of Eisbacher (1981) and placing the remaining parts of the upper Tindir Group into the Windermere Supergroup of Ross (1991). [For a proposal regarding the Canadian stratigraphic nomenclature relative to these units, see MacDonald and others (2011)]

Source map information

Source map Van Kooten, G.K., Watts, A.B., Coogan, James, Mount, V.S., Swenson, R.F., Daggett, P.H., Clough, J.G., Roberts, C.T., and Bergman, S.C., 1996, Geologic investigations of the Kandik area, Alaska, and adjacent Yukon Territory, Canada: Alaska Division of Geological and Geophysical Surveys Report of Investigations 96-6a, 3 sheets, scale 1:125,000.
Symbol pCtds
Unit name Dolomite and shale, Upper Tindir Group
Description Dolomite and shale - Cream-colored, thinly laminated dolomite forms conspicuous yellow-weathering hills. Includes yellow-weathering, thinly bedded gray, cherty mudstone near Mt. Slipper.
Lithology Sedimentary

Correlated geologic units

Label Ztds
Description Upper Tindir Group, dolomitic sandstone and shales, Late Proterozoic
Geologic age Neoproterozoic
Geologic setting Sedimentary, undivided
Lithology Form Importance
Sandstone-mudstone < Mixed-clastic < Clastic < Sedimentary Calcareous Indeterminate, major