ABSTRACT

Reinterpretation of published palaeontologic data permits establishment of four, possibly five, assemblage zones for Alberta Lower Mississippian strata. Zonal indices are, in ascending order, (?) Spirifer marionensis, S. missouriensis, S. forbesi, S. rundlensis, S. keokuk. Use of these zones establishes a self-consistent correlation of strata in the Alberta Rocky Mountains and southern Plains. The Banff, Pekisko and Shunda Formations in the Mountains between the Athabasca and Bow Rivers are essentially isochronous. Facies changes occur north of Banff: thus both the Pekisko and the Shunda are absent at Banff; the Shunda of the Jasper, Nordegg and North Saskatchewan River areas is an upper type Banff time-equivalent.

In the Bow Valley region the Pekisko Formation becomes successively younger from the Plains westward as the Banff Formation thickens. West of Exshaw the Pekisko becomes indistinguishable, but is lithologically continuous with lower Livingstone strata. The Pekisko Formation at Moose Mountain is a type upper Banff time-equivalent, and the Shunda a lower type Rundle time-equivalent. Type upper Banff time-equivalents of the southern Plains are the upper Pekisko, Shunda and lower Turner Valley Formations. The type Pekisko (Mount Head area) also is a type upper Banff time-equivalent.

Discussion of biofacies relationships illustrates the necessity of using, at present, zones of broad scope in regional Mississippian rock correlation in Alberta.