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Sedimentology and Ichnology of the Bluesky Formation in Northeastern British Columbia
The Bluesky Formation of Lower Cretaceous age consists of sandstones, mudstones and conglomerates, which were deposited as marginally marine nearshore and fully marine offshore sediments following a transgression of the Moosebar Sea. The nearshore setting is represented by relatively thick prodelta/delta front sediments and the offshore by discrete sandstone bar buildups and thin interbar muds. Prodelta and delta front deposits, in the Foothills, consist of coarsening-upward sequences of crossbedded sandstones and burrowed mudstones deposited by fair - and storm-weather processes. The delta front deposits are capped by those of the coal-bearing Chamberlain Formation delta proper. In the Peace River Plains, offshore bar deposits, which are the prolific gas and oil producers, are composed of glauconitic, bioturbated and crossbedded sandstones, and attain thicknesses greater than 30 m. The shallow central bar deposits are typified by high-energy conditions and are dominated by physical sedimentary structures. The deeper, lower-energy, bar margin environment displays increasing biogenic influence and finer grain size.
Bluesky Formation sediments contain five distinct ichnofossil suites which are characteristic of the Skolithos, Cruziana, Glossifungites and brackish water ichnofacies classifications. Infaunal suspension-feeding organisms commonly dominate the higher-energy setting, whereas epifaunal deposit-feeding organisms are most common in the low-energy setting. An impoverished suite of trace fossils indicates brackish water conditions in a delta front setting.
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