Petrographic methods, X-ray diffraction analysis of clay mineralogy, and grain-size analyses were employed to delineate the vertical variation of the Mannville Group strata in the Cold Lake area, and to interpret the environments of deposition.

The Mannville Group of the Cold Lake area is divided into informal A, B, C and D units in descending order. On the basis of petrography, electric-log correlation and limited palynological data, the A and B units correlate with the Grand Rapids Formation, and the C and D units with the Clearwater and McMurray Formations respectively.

Two valleys on the pre-Cretaceous surface begin around Twp. 57, pass through the Cold Lake area, and join just north of Cold Lake. These valleys are a part of a drainage system of rivers which flowed to the northern sea.

Solution and collapse of Middle Devonian Elk Point salt in the Cold Lake area seems to have been most active after the deposition of the C unit, and may have caused an arm of the sea or a lake to be maintained east of Cold Lake in late Mannville time.

The clay minerals of the shales and clay fractions of the sands are admixtures of kaolinite, montmorillonite and illite, with only traces of chlorite. It is suggested that the proportionally greater amount of kaolinite and lesser amount of montmorillonite in the clay fractions of the sands than in the associated shales is a result of inherent clay-mineral grain-size differences and sorting by the depositing currents.

A warm and humid climate, in which efficient leaching produced kaolinite, is suggested. Montmorillonite could have been produced by ponding and stagnation of water or by alteration of volcanic materials. The illite is thought to be mainly comminuted detrital muscovite or N + 1 cycle material.

The sands are fine- to very fine-grained, very poorly to very well sorted, and have grain-size distributions which are positively skewed and meso- to strongly leptokurtic. Deposition by unidirectional flow is suggested.

Three factor components, obtained by factor analysis, account for 95.11 per cent of the grain-size variation of all samples. The factors seem to be related

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to bed-load deposition, initial gravitational deposition and final gravitational deposition.

The sands were transported into the Cold Lake area by currents which had decreased to the point where they could barely maintain a bed load. There is no evidence of surf action on the grain-size distributions. Most of the Mannville Group sediments of the Cold Lake area were deposited in a low-energy fluvial or deltaic environment. The C unit, which contains glauconite and marine palynomorphs, was probably deposited in a shallow-marine environment which was well protected from storm and wave effects.

Reducing and alkaline conditions, during and following deposition, preserved euhedral apatite grains and plant fragments in the sands, and resulted in the development of chert-siderite nodules in the shales.

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