Whitesail Lake Map-Area

This extension of the Takla group to include Middle and Upper Jurassic strata caused some confusion with the Hazelton group, which is itself com- posed largely of Jurassic rocks. It might be noted here that fossils collected from the Middle Jurassic, Hazelton group rocks of the Whitesail Lake area, were similar to those collected by Lord from the Middle Jurassic strata of the McConnell Creek area.

The discovery by Tipper (1955) in Nechako River map-area of an erosional break between the Lower and Middle Jurassic beds provides a definite marker as a basis of separation between the Takla and Hazelton groups. In Nechako River area the base of the Middle Jurassic beds is a medium to coarse conglomerate, commonly containing numerous chert pebbles. Tipper believed this to be a shoreline deposit with the landmass to the east. He was able to follow this zone of coarse clastics down the length of Nechako River map-area, along its western border. It outcrops only in the northeast corner of Whitesail Lake map-area, where it swings westward from its northerly trend in Nechako River area. Tipper considered this erosional break to be the logical horizon for the division between the Takla and Hazelton groups, at least in the Nechako River area, and this line of demarcation applies equally well to Whitesail Lake area. Therefore, in Whitesail Lake area, the boundary between the two groups is placed at the close of the Lower Jurassic, and the Takla group will be restricted to Upper Triassic and Lower Jurassic strata.

Distribution

Outcrops in Whitesail Lake map-area that have been correlated with the Takla group occur only along the eastern boundary of the map-area, and are westward extensions of much larger areas of similar rock occurring in Nechako map-area. In Whitesail Lake map-area rocks of this group form a prominent hill in the northeast corner, about 7 miles north of Ootsa Lake, which is used by the British Columbia Forest Service as a lookout station, known as Verdun. There an upfaulted block brings these older rocks to the surface over an area of about 6 square miles adjacent to the eastern boundary of the map-area.

Farther south, near the east end of Eutsuk Lake and the west end of Tetachuck Lake, a series of massive green andesites with some minor lime- stone, tuff and breccia is present, which has been included with the Takla group. These rocks occur both north and south of the lakes and underlie an area of about 100 square miles.

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