Abstract A study of the Viking/Bow Island Formations in south-central Alberta has distinguished two major facies associations. Facies Association One ( i.e. FA1) comprises beds of thoroughly burrowed very fine grained sandstone, siltstone and shale, interbedded with rare one to fifteen centimetre thick rippled very fine grained sandstones. An abundant and diverse trace fossil suite consisting of twenty-one ichnogenera characterises the burrowed portions of FA1. In contrast, the overlying Facies Association Two ( i.e. FA2) comprises rarely to moderately burrowed very fine grained sandstone, siltstone and shale, interbedded with thickly bedded (0.15-4.0m) low angle laminated very fine to fine grained sandstones. FA2 is characterised by an ichnofossil assemblage that is impoverished in both diversity and burrowing intensity as compared to FA1. Micro-faulting, synaeresis cracks, apparently structureless sandstones, and soft sediment deformation features are also locally present in FA2. FA2 is thought to represent the sanding upwards continuation of FA1 within an overall conformable succession. The upwards decrease in burrowing intensity and diversity corresponds to a transition from quiet, open marine upper offshore to distal lower shoreface conditions (FA1) to relatively restricted storm dominated lower shoreface conditions (FA2). The relative dearth of trace fossils and the nature of the sedimentology indicate that oxygenation, salinity and turbidity stresses were significant during the deposition of FA2. It is postulated that these stresses may have arisen as a result of the introduction of freshwater and episodic sediment within a storm dominated delta front to proximal prodelta environment.