Stop 17 HAZ Geotour 2020

Location ID: Stop17_Haz_GeoTour2020

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The rock exposed in the stripped area beside the road and in adjacent road cuts is predominantly a volcanic breccia or agglomerate with subrounded to flattened medium grey quartz-feldspar phyric dacite clasts. The matrix of the breccia is light grey feldspar phyric dacite. Further up the road these rocks are seen to be interbedded with red to maroon weathering air fall tuff. The felsic pyroclastic rocks are interpreted to be ash flows that were deposited during a period of localized explosive volcanism late in the depositional history of the Telkwa Formation. The felsic pyroclastic succession, which underlies the summit and east slope of Hudson Bay mountain, is several hundred metres thick and dips moderately to the east. Locally this unit is referred to as the Ski Hill rhyolite because of excellent exposures in the vicinity of the ski hill. Zircons extracted from a sample collected at the top of the ski hill gave a 194.8±0.6 U-Pb isotopic age (R. Kirkham, pers. comm. 1997; dating by Jim Mortenson; unpublished). Similar rocks are found in the Telkwa Range to the south and in the Howson Range to the southwest, where they conformably overlie a thick succession of amygdaloidal basalt flows of Sinemurian age. Felsic pyroclastic rocks also occur sporadically at this stratigraphic position in the Babine Range on the east side of the Bulkley valley but are absent further east in the Babine Lake area. In the Telkwa Range the felsic pyroclastic member of the Telkwa Formation is overlain by early Pliensbachian marine sediments of the Nilkitkwa Formation but on Hudson Bay Mountain it is unconformably overlain by mid-Cretaceous sedimentary rocks of the Skeena Group. On the west side of Hudson Bay mountain the Telkwa Formation is thrust westward over an overturned syncline cored by Middle Jurassic marine sediments of the Smithers and Ashman Formations. The Skeena Group sediments are also involved in this deformation suggesting thrusting is mid-Cretaceous or younger.


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Location Data

Longitude: -127.2411
Latitude: 54.76