Unit Name: Nido Formation
Unit Type: Lithostratigraphic
Rank: Formation
Status: Formal
Usage: Currently in use
Age Interval: Pliocene (5.332 - 1.806 ma)
Age Justification: Geochronology. A single sample from the former Kounugu Formation, which yields a date of 7.8 ± 0.3 Ma, is from the base of a thick basalt section that rests on basement southeast of the Spectrum Range, beyond the southern limit of the Armadillo Formation. If this age is correct, then this basalt may span an interval from Raspberry to post-Armadillo time. The three Nido samples, which yield ages from 5.5 to 4.4 Ma, are all from north of Raspberry Pass, where the Nido flows are underlain by Armadillo comendite. One sample has a large error and may be too old as a consequence of its high atmospheric argon content. The average of the remaining Nido ages, weighted according to analytical precision is 4.4 Ma. If the other sample is included, the average increases only to 4.5 Ma (Souther et al., 1984).
Province/Territory: British Columbia
Originator: Souther et al., 1984.
Distribution:
Mount Edziza and northern plateau; Ice Peak, Armadillo Peak and central plateau; Spectrum Range and plateau south of Raspberry Pass (Souther, 1988). The Tenchen Member embraces all the products of Nido volcanism that were erupted north of the Armadillo Highlands, and the Kounugu Member is restricted to the area south of Armadillo Highlands (Souther, 1992).
Locality Data:
Thickness(m): Maximum 150.
Lithology:
The Nido basalts resemble the Armadillo in morphology and mineralogy. The formation contains as many as 20 flow units and is as much as 150 m thick. Aphyric to slightly feldspar- and pyroxene-phyric alkali olivine basalt predominates low in most sections and gives way upward to feldpar-phyric hawaiites (Souther et al., 1984).
Age Determinations:
Method - K/Ar; Material - Whole Rock; Age - 4.5; Err_Minus - 0.3; Err_Plus - 0.3..
Method - K/Ar; Material - Whole Rock; Age - 4.4; Err_Minus - 0.5; Err_Plus - 0.5..
Method - K/Ar; Material - Whole Rock; Age - 5.5; Err_Minus - 1.6; Err_Plus - 1.6..
Method - K/Ar; Material - Whole Rock; Age - 7.8; Err_Minus - 0.3; Err_Plus - 0.3..
Relationship:
The Nido basalt is a remnant of composite shields that were erupted early in the second magmatic cycle of the Mount Edziza Complex (Souther et al., 1984). The formation includes the Tenchen Member (north of Raspberry Pass) and Kounugu Member (south of Raspberry Pass) (Souther, 1988). North of Armadillo Highlands most of the Tenchen basalt rests on the Armadillo Formation or on fluvial gravel carrying clasts of Armadillo rhyolite and trachyte. However, distal flows on the extreme northern edge of the pile extend beyond the apron of Armadillo colluvium and rest directly on pre-Tertiary basement. The upper contact is defined by the Pyramid rhyolite which overlies the Tenchen basalt along the eastern edge of Mount Edziza. South of Armadillo Highlands only those flows that lie close to the southern edge of the Armadillo Highlands are underlain by fluvial gravels and ash from the Armadillo Formation. Most of them rest directly on pre-Tertiary basement or on gravel and colluvium derived from older rocks. The Nido basalt (Kounugu Member) south of Armadillo Highlands is overlain directly by rhyolite of the Spectrum Formation (Souther, 1992).
Other Citations:
Mihalynuk et al., 1996.
References:
Mihalynuk, M., Bellefontaine, K., Brown, D., Logan, J., Nelson, J., Legun, A. and Diakow, L., 1996. Digital Geology, NW British Columbia (94/E, L, M; 104/F, G, H, I, J, K, L, M, N, O, P; 114/I, O, P); Ministry of Energy, Mines and Petroleum Resources, Open File 1996-11.
Souther, J.G., 1988. Geology, Mount Edziza volcanic complex, British Columbia; Geological Survey of Canada, "A" Series Map no. 1623A, 2 sheets.
Souther, J.G., 1992. The Late Cenozoic Mount Edziza Volcanic Complex, British Columbia; Geological Survey of Canada, Memoir 420, 329 p.
Souther, J.G., Armstrong, R.L., and Harakal, J., 1984. Chronology of the peralkaline, late Cenozoic Mount Edziza Volcanic Complex, northern British Columbia, Canada; Geological Society of America Bulletin, March 1984, Vol. 95, Issue 3, pp. 337-349.
Source: GSC file of geological names; T.E. Bolton and J. Dougherty (compiler)
Contributor: Michael Pashulka
Entry Reviewed: No
Name Set: Lithostratigraphic Lexicon
LastChange: 02 Feb 2011