Stratigraphy of Lower and Middle Devonian carbonate rocks of northeastern British Columbia

Devonian carbonate rocks of northeastern British Columbia overlie the “sub-Devonian unconformity” and pass upward to shale of the Besa River Formation. Lowermost of these carbonate rocks is the thick Muncho-McConnell Formation shallow marine carbonate rocks. In the northern part of the study area the Wokkpash Formation, a dolomitic, quartz arenite sandstone displaying soft-sediment deformation, separates the Muncho-McConnell from the overlying Stone Formation, but in the south the Wokkpash is absent. The thick, uniformly grey and bluish-grey dolomite units of the Stone Formation display fenestral fabric, mud-chip breccias, and finely laminated beds. The gas-bearing Dunedin, Keg River, and Slave Point formations, overlying the Stone Formation in outcrop, are dominantly micritic to fine-grained fossiliferous marine limestone. Transitions from off-reef to reefal in these strata are accompanied by an increase in fossil abundance and size, and increased dolomitization. Several different breccia types are found within the Dunedin and Stone formations associated with dolomitization. 1 Contribution to the Central Forelands NATMAP Project 1 Resume : Dans le nord-est de la Colombie-Britannique, des roches carbonatees devoniennes recouvrent la «discordance subdevonienne» et passent vers le haut au shale de la Formation de Besa River. Les roches carbonatees epaisses de mer peu profonde de la Formation de Muncho-McConnel constituent l’unite inferieure. Dans la partie nord de la region a l’etude, la Formation de Wokkpash, quartzarenite dolomitique presentant une deformation caracteristique des sediments tendres, separe les roches de la Formation de Muncho-McConnel de la formation sus-jacente de Stone; au sud, la Formation de Wokkpash est absente. Les epaisses dolomies uniformement grises et bleu-gris de la Formation de Stone presentent une structure vacuolaire, des breches avec fragments de boue et des lits en fines lamines. Les formations gazeiferes de Dunedin, de Keg River et de Slave Point, qui recouvrent en affleurements la Formation de Stone, se composent principalement de calcaires marins fossiliferes micritiques ou a grain tres fin. Les transitions de milieux non recifal a recifal dans ces strates s’accompagnent d’un accroissement de l’abondance et de la taille des fossiles et d’une dolomitisation accrue. Des breches de plusieurs types differents associees a la dolomitisation sont presentes a l’interieur des formations de Dunedin et de Stone.