ABSTRACT

Depositional facies and facies sequences in the Gething and Bluesky alloformations of northwestern Alberta are documented in the region of the Peace River Arch. Facies variation is interpreted in terms of relative regional sea level rise and local tectonic influence due to the reactivation of the Peace River Arch and associated structures.

Gething sediments record the slow relative rise in sea level of the southward transgressing Boreal Sea. They begin with mainly fluvial and delta plain sediments, which become interstratified with brackish, inshore, and marine shoreface units in the upper part of the formation. The main body of the Gething was deposited in a broad, northwest-south-east trending trough; at the eastern edge of this trough, a transgressive estuarine system was developed during deposition of the upper Gething. A regionally extensive transgressive erosion surface forms the bounding discontinuity between the Gething and the overlying Bluesky Formation.

The Bluesky Formation is an allostratigraphic unit that records a period of stillstand. The formation consists mainly of storm-dominated, shallow shelf sandstones, with local shoreface development in the trangression of the Moosebar Sea; the upper surface of the Bluesky is a transgressive erosion surface with an associated marine lag deposit, and is overlain by marine Moosebar/Wilrich Formation shales.

Local subsidence in the area overlying the Peace River Arch appears to have led to anomalous east-west thickening of the Gething Formation. Later subsidence during Bluesky deposition may have caused the localization and preservation of shoreline deposits. The eastern extent of the sub-basin in which the units were deposited is limited by a northwest-southeast trending high, which may be associated with the rejuvenation of an underlying basement structure.

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