Braided River-Like Channelization in Toe-of-Slope Sandstones at Castle Creek, Windermere Supergroup, British Columbia

Paul R. Gammon and R. W. C. Arnott
University of Ottawa, Ottawa, ON

Locally, as at Castle Creek in the Cariboo Mountains of British Columbia, the lower Isaac Formation of the Windermere Supergroup (late Proterozoic) contains a succession of meandering channel complexes that are interpreted to represent toe-of-slope feeder conduits for basin floor turbidite fans. Combined, this locality provides a superb outcrop analogue for deep-water slope channels. The uppermost channel complex is substantially thinner, but otherwise similar to those below, being medium to coarse grained, ~1 m thick beds within 2-4 m thick lateral accretion packages. However, unlike the lower channel complexes, the upper complex is surrounded by 80 m of a fine to coarse-grained sandstone with a net:gross of >0.7, potentially excellent reservoir facies that could be overlooked in exploration plays. At bed-scale, this sandstone facies is an anastomosing array of thin channels that resemble the turbiditic equivalent of a braided river. Each channel was probably <1 m in depth, and generally <200 m in lateral extent. Channel erosion means sandstones, although laterally heterogeneous, probably have good connectivity. The facies architecture consists of a central, coarse-grained zone of ~150 m width by 50 m height that gradually fines both laterally and upwards into muddier, non-reservoir facies. On the largest scale available, different “central zones” laterally interfinger to form a combined >600 X 80 m of reservoir facies. As the uppermost sandstones within the Castle Creek channel belt, this unusual facies may represent vertical aggradation that limited channel incision, with the area subsequently abandoned as a turbidite feeder conduit.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005