Sedimentation of the Wapiabi-Belly River Transition (Upper Cretaceous) at Lundbreck Falls, Alberta

Abstract

<p> An outcrop of the transition from the Wapiabi Formation to the Belly River Formation was studied in detail at Lundbreck Falls, Alberta. The observed vertical succession of sediments is as follows: 1) interbedded dark shales and Bouma B, BC and C type turbidites; 2) hummocky cross-stratified sandstones and bioturbated silts; 3) swaley cross-stratified sandstones; 4) parallel laminated sandstones; 5) mudstones interbedded with trough cross-stratified sandstone. The turbidites and hummocky cross-stratified sandstones are storm-generated density current deposits. The swaley cross-stratified sandstones have formed below parallel laminated beach deposits and above storm deposits. The section is capped by fluvial deposits containing evidence of subaerial exposure. </p> <p> Paleoflow directions in the lower portion of the section indicate that the regional paleoslope dipped northward. Density currents may have flowed down a topographically significant north-south trending trough. Net sediment transport in the shallow marine portion of the section was towards the east north-east. </p> <p> Petrographic studies indicate that the sandstones are similar to the "barren" basal Belly River sandstones of the Burmis area, studied by Mellon (1961). </p> <p> Another section consisting of continental elastics of the Blairmore Group was studied at Daisy Creek, Alberta. The lower part of the section contains interbedded grey mudstone and cross-stratified sandstone. These are erosively overlain by a 25 m thick, cross-stratified sandstone which caps the section. The sediments have been interpreted in terms of a meandering fluvial system. </p>