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Estuarine tidal channel and nearshore sedimentation of a late Cretaceous epicontinental sea, Drumheller, Alberta, Canada
Rahmani, R.A. (1988). Estuarine tidal channel and nearshore sedimentation of a late Cretaceous epicontinental sea, Drumheller, Alberta, Canada, in: de Boer, P.L. et al. (Ed.) Tide-influenced sedimentary environments and facies. Extended versions of papers presented at the Symposium on Classic Tidal Deposits, held August 1985 in Utrecht, Netherlands. pp. 433-471
In: de Boer, P.L. et al. (Ed.) (1988). Tide-influenced sedimentary environments and facies. Extended versions of papers presented at the Symposium on Classic Tidal Deposits, held August 1985 in Utrecht, Netherlands. D. Reidel Publishing: Dordrecht. ISBN 90-277-2622-1. ix, 530 pp., more

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  • Rahmani, R.A.

Abstract
    The transition between the Bearpaw and Horseshoe Canyon Formations of south-central Alberta is a 45 m thick coarsening upward sequence scoured by a tidally dominated estuarine channel and overlain by tidal flats, marshes and swamps. The coarsening upward sequence (CUS) consists of prodelta mud and silt and rooted delta front sand. The overlying channel, up to 20 m in thickness, has a sandy fill for a distance of at least 15 km upstream from shoreline (lower estuary). Landward of this the channel fill is essentially muddy for a distance of 21 km (middle estuary), then becomes sandy again in the upstream direction (upper estuary). This tripartite style of sand-to-mud-to-sand fill is common to estuaries of modern meso-to-macrotidal embayed shorelines. The sand of the lower estuary was sourced from shoreline and nearshore outcrops and dispersed upstream by tides. The muddy stretch (middle estuary) reflects deposition in the turbidity maximum zone that forms at the landward tip of the salt wedge in estuaries of the above mentioned settings. The upstream sand fill (upper estuary) must be of fluvial origin. The CUS was deposited during a river-dominated delta stage. Subsequent relative drop of sea level exposed the delta front and caused some deepening and seaward extension of the delta distributaries. This was followed by a transgression and formation of tidal estuarine conditions in the delta distributaries. Any preexisting channel fill was reworked by the tides and the result is a channel fill that reflects estuarine processes. Modern estuaries that show very similar vertical and lateral tripartite facies relationships are those of the mesotidal Atlantic coastline of Georgia (USA), the Rhine delta estuaries (Netherlands), and the macrotidal coastline of SW France (e.g. Gironde Estuary). This tripartite estuarine model has significant implications to the paleogeography and hydrocarbon exploration in the Mesozoic of the North American Western Interior. It also explains the origin of deep and wide mud-filled channels so common in this area.

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