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Fluvial Ribbon Deposits of Channel and Valley Origin and Their Relationship to Petroleum Reservoir Development: Glauconite Member (Lower Cretaceous), Southern Alberta

James M. Wood, John C. Hopkins

Stratigraphic fluvial ribbon deposits within the subsurface Glauconite Member (Mannville Group) have been mapped over a 60 × 30-km area of southern Alberta. These ribbons truncate regional markers and have fills comprised of discontinuous sandstone bodies isolated by shales. Ribbons of two distinct types are recognized.

Type 1 ribbons are up to 2 km wide and 25 m thick and have relatively simple fills with pod-shaped sandstone bodies distributed preferentially along the ribbon margins. These ribbons are interpreted as superimposed paleochannels which incised into preexisting sediments during river or distributary avulsion. Sandstone bodies represent lateral bars deposited within active channels, whereas the intervening shales were deposited during abandonment.

Type 2 ribbons are up to 7 km wide and 40 m thick and have complex fills. Sandstone bodies are pod or ribbon-shaped, occur in lateral or mid-ribbon positions, and locally show vertical or lateral amalgamation. These ribbons are interpreted as paleovalleys excavated in response to base level drop associated with northward regression of the Lower Cretaceous Boreal sea. Valleys were filled with deposits from several distinct, confined, underfit streams resulting in highly complex internal facies relationships.

Paleosols are present within strata laterally adjacent to the top of Type 2 ribbons and formed during subaerial exposure associated with valley excavation. Similar surfaces have not been recognized in association with Type 1 ribbons.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.