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The AAPG/Datapages Combined Publications Database

CSPG Special Publications

Abstract


Petroleum Geology of the Cretaceous Mannville Group, Western Canada — Memoir 18, 1997
Pages 30-55

Sequence Stratigraphy and Depositional Facies of an Incised Valley Fill, Lower Cretaceous Bluesky Formation, Aitken Creek Field, British Columbia

Robert H. S. Alway, Thomas F. Moslow

Abstract

The principle reservoir facies of the Aitken Creek Field, northeastern British Columbia, Canada, consists of bimodal and polymodal, well-rounded, highly porous and permeable, clast-supported, chert pebble conglomerates within Lower Cretaceous channels. Reservoir facies observed in core from the Lower Cretaceous Bluesky Formation are interpreted as estuarine valley-fill deposits, in channels incised into delta plain facies during an early Albian relative sea level fall. Depositional successions comprise a diverse assemblage of facies that can be grouped into lowstand and transgressive systems tracts. The lowstand systems tract comprises a discontinuous unit of relatively thin fluvial conglomerate in the thalweg of the incised valley. The transgressive systems tract comprises most of the valley-fill, and consists of facies deposited in associated estuarine channel, estuarine bay, tidal channel, and outer estuarine environments.

Several important sequence stratigraphic surfaces accentuate the incised valley-fill: the sequence boundary (SB), the initial transgressive surface (ITS), the tidal ravinement surface, and the wave ravinement surface. The stratigraphic criteria used to recognise the sequence boundary vary, depending on the position within the incised valley. In the thalweg of the valley, the sequence boundary is defined by lowstand fluvial conglomerates that overlie delta plain facies and onlapping transgressive estuarine facies on the valley walls. The sequence boundary on interfluve areas is enhanced by wave ravinement during transgression. This surface is expressed as a co-planar sequence boundary and wave ravinement surface, and is locally ichnologically demarcated by the Glossifungites ichnofacies. The transgressive surface within the incised valley thalweg separates lowstand fluvial valley-fill facies below from transgressive estuarine point bar facies above. The tidal ravinement surface is overlain by a relatively thick lag deposit and separates tidal inlet and tidal delta shoal facies above from estuarine point bar and abandoned channel facies below. The wave ravinement surface is a product of landward shoreface translation during sea-level rise. Transgressive shoreface facies are overlain by open marine facies of the Buckinghorse Formation, and are attributed to regional transgression of the Moosebar Sea.

This study establishes a sequence stratigraphic framework and depositional origin for hydrocarbon-bearing facies of the Bluesky Formation in the Aitken Creek Field. Further regional exploration success will require an improved understanding of the details of lateral facies changes. Additional depositional models will assist in development and exploration strategies for other Lower Cretaceous incised valley-fills in northeastern British Columbia.


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