WESTERN LAURUSSIAN RECORD OF REGIONAL AND GLOBAL MIDDLE-LATE DEVONIAN SEA LEVEL CHANGES AND BIOEVENTS: ALBERTA ROCKY MOUNTAINS

Sea level events that initiated deposition of seven of nine late Givetian-early Famennian 3rd order depositional sequences in western Alberta coincide with Devonian Transgressive-Regressive (T-R) cycles IIa-2 to IIe. Eight of these form the main sequence stratigraphic architectural units of the isolated Miette and Ancient Wall platforms. The initial Givetian transgression of the West Alberta Arch is recorded by the Thornton Creek Member (sequence 1:T-R cycle IIa-2) of the Flume Formation (Fm.) at Ancient Wall. A second sea level rise (T-R Cycle IIb-1) at the base of the norrisi Zone (Z.) resulted in carbonate ramp deposition of sequence 2, represented by the Flume Fm. Evidence of exposure of part of the Flume ramp is observed at the top of the Utopia Member, followed by a deepening recorded by the remainder of the upper Flume (Sequence 3:T-R cycle IIb-2?). The Flume ramp was drowned by a significant early Frasnian deepening (within Montagne Noir (M.N.) Z. 4) that marked the initiation of a prograding rimmed platform recorded by the Maligne-Lower Cairn fms. (sequence 4-upper subdivision of T-R cycle IIb=IIb-3?). The profound middle Frasnian deepening event at the base of M.N. Z. 5/punctata Zone resulted in deposition of the lower Perdrix-Upper Cairn fms. (sequence 5) coincident with the initial flooding of T-R cycle IIc. Another middle Frasnian intra-IIc deepening event initiated deposition of the Middle Perdrix Fm.-Peechee Member of the Southesk Fm. (Sequence 6) during the interval of M.N. zones 7?-10. Major deepening at or near the base of M.N. Z. 11 initiated T-R cycle IId (IId-1) deposition as recorded by the Upper Perdrix/Mount Hawk Fms./ Arcs-lower Simla members of the Southesk Fm. (sequence 7). Most of the typical late Frasnian Mount Hawk brachiopod fauna became extinct just prior to or during the major deepening coinciding with the Lower Kellwasser event in the very late Frasnian. At Ancient Wall the Upper Simla Mb./upper Mount Hawk Fm. (sequence 8) was deposited during the interval of M.N. Z. 13 (T-R cycle IId-2). Extinction of latest Frasnian shelly faunas occurs very high in M.N. Zone 13 indicated by a crisis fauna in the uppermost Simla. The overlying early Famennian Sassenach Fm. (sequence 9) records the initial post-extinction flooding of T-R cycle IIe yielding survivor and post-extinction recovery shelly faunas.