MIDDLE & UPPER GIVETIAN (MIDDLE-DEVONIAN) RECORD OF SEA LEVEL AND FAUNAL EVENTS IN EASTERN BRITISH COLUMBIA, WESTERN CANADIAN ROCKY MOUNTAINS

The lower part of the Devonian succession in Kakwa Park area of eastern B.C. provide a record of three (or four) major relative sea level events that record the initial, and progressive onlap of the Peace River and West Alberta arches. Faunal data in the upper Yahatinda and lower Flume Formation suggest the initial marine transgression occurred no earlier than upper Middle varcus Zone, coinciding to the initial eustatic deepening of Devonian Transgressive-Regressive (T-R) Cycle IIa of Johnson and others, and T-R cycle IIa-1 of Day and others. The lowest brachiopod fauna of the lower Flume consists of the oldest element of the Tecnocyrtina brachiopod lineage (T. sp. aff T. missouriensis) in North America. Above this initial assemblage, brachiopod-bearing Flume Sequence 1 highstand deposits yield Desquamatia (Desquamatia) with Athyris and comprise the biotic signature of the initial or first Taghanic bioevent in the region. A second significant marine flooding event established middle shelf conditions with diverse Upper Givetian brachiopod fauna (second Taghanic event) including Desquamatia (D.), D. (Seratrypa), Spinatrypa aff. S. bellula, T. missouriensis raaschi, Cyrtina, Nervostrophia sp., and “Hypothyridina” cf. “H.” cameroni, capped by prograding stromatoporoid reef carbonates. This initial phase of fringing reef development in the Kakwa Park area coincided with Slave Point reef development in along the northern flank of the Peace River Arch in northern Alberta. The brachiopod assemblage indicates an age no older than the hermanni Zone and no younger than the lower part of the disparilis Zone indicating that this second marine flooding event began during than hermanni Zone and represents an intra-T-R cycle IIa-1 event new recognized in North American basins. A third marine flooding event may be represented by minor reef platform backstepping, and resumed Upper Flume fringing reef progradation, associated with the occurrence of conodonts of the Upper Icriodus subterminus Fauna. Platform drowning associated with very late Givetian marine flooding of Devonian T-R cycle IIb-1 (first “Waterways cycle”) terminated Flume reef development and introduced deeper shelf faunas with elements of the Tecnocyrtina billingsi Zone fauna.