Abstract

New sequences of supposedly Proterozoic strata are described on Promontory Point, Fremont Island, Antelope Island, Sheeprock Range, and the northern Wasatch Mountains. The Big Cottonwood Canyon sequence of Walcott is emended, and a fragmentary sequence in the west end of the Uintas is given. These and other sections already described are correlated insofar as possible and are related to known Cambrian strata overlying them and to the structural features of the region.

The rocks were deposited in deep troughs in and between the northern Utah highland and the Colorado Plateau highland. Each trough was filled with sediments more than 12,000 feet thick. The beds are about half argillaceous and half arenaceous.

The Fremont Island sequence contains a tillite 700 feet thick, and one 1100 feet thick occurs in the Sheeprock Range. Other tillites in the same and in other sections indicate repeated ice advances. The interbedded tillites and associated laminated argillites lead speculatively to the conclusion that the entire sequence of argillaceous, sandy, and tillitic strata may have been laid down during a glacial epoch.

The age of the strata is either lower Cambrian, Proterozoic, or both. Study to date of the degree of metamorphism of Cambrian and underlying strata leads to no definite conclusion. Some deformation and erosion occurred before sands of Lower (?) Cambrian age were deposited, but in light of the highland and trough theory the angular unconformity around the highland margins may not be of great time significance.

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