ABSTRACT

Two tectonic episodes are associated with the Peace River Arch during deposition of the Mississippian Banff and Rundle groups. Each of these episodes gave rise to local basin developments, collectively known as the Peace River Embayment, which were subsequently infilled by shallowing-upward carbonate sequences.

The first Mississippian basin developed between the lower and early middle Tournaisian and was infilled by the Lower to mid-Banff units. The basin had an east-west axis and opened toward the west. Lower Banff carbonates and fine grained terrigenous clastics formed a series of south-westerly prograding clinoforms produced by the lateral migration of upper, middle, and lower slope deposits. These carbonate units encircled the embayment and passed into basinal shales toward the centre. The Middle Banff consists of shallow carbonate platform deposits, and the Upper Banff of supratidal carbonates and siliciclastics. These units prograde over the Lower Banff deposits with little evidence of local basinal influence.

The second episode of basin formation occurred during a time of regional subsidence and transgression in the late middle Tournaisian that marks the base of the Rundle Group in this area. The resulting basin was more local in its development than the Banff embayment. It was semi-enclosed and had an east-west axis of development that approximated the axis of the Banff embayment. Pekisko platform carbonates encircled the basin while deeper water carbonates, shales and siliciclastics locally infilled it. The Pekisko Formation is overlain by the regressive shallow water and supratidal carbonates, anhydrites and siliciclastics of the Shunda and Debolt formations.

The depositional and structural axes of these basins were developed to the north of the axis of the Devonian Peace River Arch. The Devonian axis remained stable during Banff and Rundle Group times, and basin subsidence was centred on the Peace River Arch northern boundary fault. This fault marks the northern margin of the Peace River Arch throughout the Devonian.

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