Sedimentology of the Wapiabi-Belly River Transition and the Belly River Formation (Upper Cretaceous) near Ghost Dam, Alberta

Abstract

<p> The Wapiabi-Belly River transition and the Belly River Formation was studied in detail in seven sections in the Ghost Dam spillway, near Ghost Dam,Alberta. Units in the lowest portion of the outcrop (Wapiabi) are characterized by sandy mudstones, often coarsening upwards. The mudstones are overlain by storm generated, hummocky cross-stratified sandstones and beach deposits. The vertical sequence represents a shallowing trend. </p> <p> Above the beach deposits lie sandstone and interbedded mudstone-sandstone units (Belly River) deposited in a meandering river environment. Sandstones thicker than approximately two metres were deposited as point bars, show sedimentary structures representative of channels and often pinch out, or laterally interfinger with mudstone. Interbedded mudstone-sandstone units were formed during flood stances. These overbank deposits are classified as either proximal or distal components of the meandering river system. </p> <p> Several marine trace fossils, (Macaronichnus segregatis, Skolithos, Planolites, Chondrites, Teichichnus, and Ophiomorpha nodasa), found in the Belly River rocks suggest a minor marine influence on the river system. </p> <p> The river system is inferred to have been moderately to highly sinuous and comparable in discharge to the Humber and Credit Rivers (Ontario). </p> <p> Petrographic studies show that point bar sandstones are often characterized by fining upward trends and an upward increase in the proportion of carbonate cement. </p> <p> Distal overbank deposits are normally overlain by proximal overbank deposits which inturn are overlain by either point bars or distal overbank deposits. Point bar deposits may be overlain by either proximal or distal overbank. </p>