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Abstract

Physiographic and stratigraphic associations of relatively coarse-grained (mainly sand) deposits, in the Edmonton and Okanagan Valley areas, Canada, illustrate deposition in glaciolacustrine deltas. Sedimentary successions are described in terms of seven facies states: gravel, cross-bedded sand, flat-bedded sand, crosslaminated sand, alternating beds, parallel-lamination, and diamicton. Proportional thickness, preferred vertical position, and transition probabilities together with grain-size and paleocurrent analysis form the basis of detailed analysis of the deltaic successions. A simple succession is recognized in which flat-bedded sands dominate the lower part and cross-stratified sands dominate the upper part. In these successions, paleocurrent directions are consistent, and there is a significant fining-upward trend. The flat-bedded sands are interpreted as multi-storied lateral-accretion deposits of distributary channels. The cross-laminated sands are interpreted as distributary-mouth bar deposits. The succession of stratification and grain-size illustrates deposition in increasingly distal positions during ice-marginal recession. A second type of succession shows complex, broad cyclicity. Rhythmic beds, with a lower member of cross-laminated or alternating beds and an upper member of parallel-laminated beds, form a thick interval between flat-bedded distributary-channel deposits. The rhythmic beds are interpreted as levee and interdiatributary-bay sediments that were deposited under seasonally fluctuating discharge. The complexity of these successions results from a combination of channel shifting and from increasingly distal position during ice retreat. In the Okanagan section, a deep sedimentation basin and coarse deposits resulted in development of a prograding Gilbert-type delta with steep foresets.

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