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Storm Influenced Deltaic Deposits, Jurassic, NW Alberta: Insight into the Palaeogeographic Development of the Western Interior Seaway

Miles, Brett D.1; Hubbard, Stephen M.1
1 Geoscience, University of Calgary, Calgary, AB, Canada.

Deposits of the Jurassic-Cretaceous Nikanassin Formation represent the initial coarse-grained pulse of sedimentation into the Western Interior Seaway in northwest Alberta. The lowermost member of the Nikanassin Formation was deposited by a series of prograding deltaic complexes. Deducing the complex interplay between waves, tides, fluvial input and storms during deposition of the delta from a core and wireline log database provides valuable insight into the palaeogeography during this time period.

Storms had a significant impact on numerous deltaic deposits in the Western Interior Seaway. Recent work in a number of different basins has emphasized the link between marine storms and flooding in the catchment basin. Uplift, generated by a major orogenic phase in the Cordillera, provided a considerable source of detritus during deposition of the Nikanassin Formation. Evidence for storms in deltaic deposits of the Nikanassin Formation is present in both prodelta and delta front facies associations. The prodelta facies association consists of normally graded muddy to sandy hyperpycnal flow deposits interbedded with hummocky cross stratified beds interpreted to represent tempestites. The delta front facies association is characterized by traction structured sandstone attributed to channel mouthbar sedimentation; however, a number of intervals contain massive sandstones with fluid escape structures. Bank collapse in deltaic distributary channels, triggered by storm events is speculated as the origin of these units.

Recognition of storm related facies in the Nikanassin Formation provides insights into the early foreland basin palaeogeography and palaeclimatology. Widespread abundance of these facies associations indicates that storms affected most of the basin at this time and were a key processes in the building of deltas into the newly evolved foreland basin.



AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009