Cardium Formation at Seebe, Alberta--Storm-Transported Sandstones and Conglomerates: ABSTRACT

Abstract

End_Page 644------------------------------The Upper Cretaceous (Turonian) Cardium Formation is one of the most productive oil-bearing formations in Alberta. As a result of detailed mapping of two outcrops near Seebe, Alberta, we have defined five coarsening-upward sequences within this formation. The sequences begin with bioturbated mudstones and coarsen into sandstones, commonly with conglomeratic veneers on top. In sequence 2, a 20-cm thick conglomerate has been molded into symmetrical gravel waves. The sandstones are dominated by hummocky cross-stratification, occurring in the upper parts of sequences 1, 2, 3, and 5. The implication is that these sequences terminate in water deeper than fair-weather wave base (10 to 15 m). The trace-fossil assemblage, dominated by abundant Zoophycos and long horizontal Rhizocorallium, suggests similar depths. Foraminifera recovered from sequences 3 and 4 comprise a highly diverse assemblage of agglutinated species, also supporting deposition below fair-weather wave base. In view of the physical and biologic evidence for deposition in a few tens of meters of water, and the total absence of medium-scale cross-bedding, we suggest that the entire Cardium Formation at Seebe was deposited below fair-weather wave base. The sandstones were emplaced by storm-generated density currents, the same storm both generating the flow and imprinting hummocky cross-stratification on the deposit. Finally, we suggest that the conglomerates were also moved rapidly seaward by density currents, there being no evidence for the traditional beach or transgressive lag interpretation of these rocks. End_of_Article - Last_Page 645------------