The Upper Cretaceous Cardium Formation at Seebe Alberta, Shallow Marine Storm Deposits

Abstract

<p>The Cardium Formation in the study area can be defined by twelve different facies. Ordering of facies forms five coarsening upward cycles. Three different 'cycle types are present. The two thicker ones are characterized by 1) basal Bioturbated Siltstone Facies, grading up into 2) various interbedded siltstones and hummocky cross-stratified (H.C.S.) sandstone facies; followed by 3) more massive Bioturbated Sandstone Facies in one cycle type, and H.C.S. Sandstone Facies in the other. These two cycle types terminate sharply with or without a conglomerate veneer. The third cycle type consists of 1) Less Bioturbated Shale Facies which coarsens upward into 2) Bioturbated Siltstone Facies and the cycle is terminated by 3) Concretionary Conglomerate Facies. H.C.S. is a newly-defined sedimentary structure formed by long period storm waves, and commonly preserved below fairweather wave base. In the Cardium, the abundance of H.C.S. accompanied by small wave ripples, graded bedding, and a deeper water fauna (together with the absence of medium scale cross bedding) suggests deposition below fairweather wave base. Near-shore sediment is entrained by powerful storm-surge bottom currents. Storm waves feeling the bottom imprint H.C.S. on these density current deposits. Fairweather conditions cannot rework the H.C.S. and produce only bioturbated siltstones and shales. The main ichnofauna is a Rhizocorallium-Zoophycos assemblage with abundant Chondrites and some Ophiomorpha. This suggests a depositional environment well off-shore in deeper water, which agrees with the interpretation derived from the H.C.S. The foraminiferal assemblage also suggests an open marine rather than nearshore environment.</p>