Sedimentology and Diagenesis of Middle Devonian Platform Margin Carbonates (Keg River to Slave Point Formations): An Outcrop Study in the Front Ranges of Northeast British Columbia (Southern Trutch 94G)

Scott Rose and Hairuo Qing
University of Regina, Regina, SK

The Keg River-Slave Point barrier complex of NEBC is exposed northwest of Fort St. John along a narrow thrust belt within the Front Ranges of the Rocky Mountains. A full succession of Upper Elk Point strata is evident in the vicinity of Mt. Bertha and Redfern Lake areas in southern Trutch 94G which include the Stone (Upper Chinchaga?), Keg River, Slave Point, and Besa River formations. An understanding of Middle Devonian platform margin paleogeography and the characteristics and mechanisms for dolomitizaton has important implications for exploring for potential reservoirs in the subsurface of the WCSB.

The barrier complex within the Mt. Bertha / Redfern Lake area is comprised of Upper Keg River and Slave Point reef buildups (stromatoporoid / coral boundstones and rudstones) and backreef lagoonal deposits (interbedded mudstones and Amphipora floatstones). West of the barrier system there are deeper subtidal mudstones with interbeds of crinoidal/ brachiopod wackestones (typical of the Lower Keg River) and fore-slope deposits of stromatoporoid/coral reefal debris indicating close proximity to the barrier reef complex.

Impressive dolomitization styles are evident at Mt. Bertha within the Keg River and Slave Point including pervasive replacement dolomite, selective matrix dolomitization, hydrothermal dolomitization (zebra fabrics and saddle dolomite cement), hydrothermal collapse brecciation, and late calcite cement. Dolomitization is associated with regional North-South fault systems running parallel to the barrier edge. A later set of cross-cutting faults is associated with minor dolomitization and extensive calcite cementation.

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