Abstract

In the Foothills and Front Ranges of the Canadian Rocky Mountains almost the entire Jurassic is represented by the Fernie Formation which was deposited in five regressive cycles on the west-sloping shelf of the North American cratoin. Lithostratigraphic subdivision of the Fernie, which has been neither exhaustive nor systematic, remains somewhat unsatisfactory due to a lack of persistent marker beds and frequent subtle facies changes along depositional strike in a sequence dominated by fine-grained clastics. Traditional lithostratigraphic units and several new ones are reviewed. In particular, recent usage of the term “Rock Creek Member” is critically evaluated and its definition, precise age and relationship to surrounding units are clarified.

Although continuing study of Fernie biostratigraphy over the last twenty five years has established the presence of many distinctive ammonite faunas, allowing good local and international correlation, comparison with the ammonite Standard Zones of Europe makes it clear that many “faunal gaps” still exist in the Fernie sequence. Such “gaps” do not necessarily indicate depositional hiatuses or unconformities, as has often been assumed. Indeed, recent studies have revealed the presence of new ammonite faunas in strata representing both the Late Bajocian and Bathonian Stages; both had long been thought absent from the Fernie. It is now realised that a major difficulty hindering recognition of late Middle and Late Jurassic ammonites was their separation during those times into at least three faunal realms, with little overlap. The existence of this biogeographic provincialism requires establishment first of locally applicable ammonite zonal schemes and renders international correlation more difficult. Nevertheless, it is playing a useful role in tectonic studies.