TIMING OF SEA LEVEL CHANGES THAT INITIATED CARBONATE PLATFORM AND RAMP DEPOSITION OF THE MIDDLE-LATE DEVONIAN FLUME AND WATERWAYS FORMATIONS; KAKWA PARK, BRITISH COLUMBIA

The Flume Formation in the Walbridge Mountain area of Kakwa Park in eastern British Columbia has historically been studied as an outcrop analog of latest Givetian-early Frasnian age Swan Hills and Beaverhill Lakes reef platform hydrocarbon reservoirs in the subsurface of Alberta. Recent investigations of the Flume in Kakwa Park indicate that the initial major marine flooding over the Middle Devonian Yahatinda Formation along the southern margin of the Peace River Arch in the Kakwa Park area began as early as the upper part of the Middle varcus and no younger than the hermanni Zone (middle-late Givetian). Maximum flooding of Flume sequence 1 is indicated by brachiopod-bearing calcareous siltstones, with highstand marked by the first appearance of Tecnocyrtina and Desquamatia (D.)). A second flooding initiated Flume Sequence 2, with subtidal platform facies that feature a diverse brachiopod fauna including Desquamatia (D.), Tecnocyrtina missouriensis raaschi, and Hypothyridina cf. H. cameroni, capped by prograding stromatoporoid bank carbonates of the lowest Flume reef. The occurrence of H. cf. H. cameroni indicates an age of the initial HST no older than the hermanni Zone. The overlying Flume reefal, lagoonal and reef flat facies succession (Flume Sequences 3-4?), are drowned by a major flooding event represented by subtidal shelf facies of basal Waterways Formation with the brachiopods Tecnocyrtina billingsi and Schizophoria lata. These indicate a correlation with the T. billingsi Zone (no older than late Givetian norrisi conodont Zone) of the Waterways of northeastern Alberta.

The hermanni Zone flooding event of Flume Sequence 2 coincides with a negative oxygen isotope excursion, documented from both brachiopod calcite and conodont apatite in central North America that implies significant global warming. These initial Givetian flooding events along the Peace River Arch have no reported equivalents in Rocky Mountain exposures to the east. The West Alberta Arch in the western Alberta Rocky Mountains appears to have remained sub-aerially exposed until the Upper disparilis Zone flooding that likely initiated Flume sequence 3-4? in the Kakwa Park area. The varcus?-hermanni zones Flume reef cycles probably formed a fringing reef or atoll-like structure around the Peace River Arch prior to drowning in the very late Givetian.