ABSTRACT

The Dunvegan Formation represents a sandy clastic wedge deposited from northwest to southeast in the actively subsiding west Alberta Foreland Basin during the waning stages of the Columbian Orogeny (mid-Cenomanian). The Dunvegan is subdivided into seven allomembers, A through G, each separated by regionally widespread transgressive surfaces. Each allomember represents a progradational event and contains several offlapping shingled units.

The facies relationships and sand body geometry of individual shingles within the southeastern portion of the Dunvegan indicate that they represent various types of shallow marine depositional systems. These range

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from highly river-dominated deltas in the lower allomembers (G, F, and E) to storm- and wave-dominated prograding deltas, barriers, and transgressive sheet sands in the upper allomembers (D, C, B, and A). The northwestern (landward) portion of the Dunvegan is characterized by up to 300m of thick, nonmarine facies, which grade into coarse alluvial fans in outcrops to the far north.

Progradation of the Dunvegan clastic wedge was probably related to erosion of newly uplifted portions of the western Cordillera and may also have been influenced by a global drop in sea level during the mid-Cenomanian. The seven transgressions that punctuate progradation of the allomembers were probably related to episodic thrusting events, which induced times of more rapid subsidence. Autocyclic processes (river avulsion and delta switching) may control the position of channels and deltas in the individual shingled units within allomembers.

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