Abstract

The Lower Cretaceous (Albian) Viking Formation at Joarcam, Alberta, can be divided into four informal allocyclic members (A to D) separated by regionally extensive flooding or unconformity surfaces.

The basal member (A) comprises a coarsening-upward marine sequence averaging 8 to 9 m in thickness, which was deposited in a shelf environment seaward of a prograding shoreline. Member B is composed of a regionally extensive sequence averaging 10 to 12 m in thickness, which coarsens upward from bioturbated marine mudstones to very coarse grained trough crossbedded and massive sandstones, deposited on the upper shoreface of a prograding shoreline. Member C is a transgressive fining-upward sequence (6-8 m) of marine mudstone and siltstone, interbedded at the base with storm-deposited sandstone eroded from a retreating shoreline. Member D is a package of sand-rich sediment averaging 1 to 2 m in thickness, containing no systematic vertical sequence development or lateral facies continuity, and was most likely deposited as a diffuse sheet in a shelf environment, offshore from a stable shoreline.

The regional extent of the member-bounding unconformities or flooding surfaces suggests probable allocyclic tectonic control of sea-level fluctuations and sequence development.