Abstract

The Lower Cretaceous Ostracode member in the Bellshill Lake area (T39-42, R8-15W4) in east-central Alberta provides an excellent subsurface example of an estuarine valley-fill deposit. The Ostracode valley-fill deposit is contained within a regional ESE-WNW trending paleovalley recognized on the pre-Cretaceous unconformity, which was probably a major NW draining tributary of the Edmonton channel system. The Ostracode valley incises into bay sediments (bay sequence 1) of the Ostracode member and the underlying Ellerslie Member, which is speculated to have been deposited under predominantly estuarine conditions. The infill of the Ostracode valley is thought to have a complex history as evidenced by the distribution of sandy and muddy units within the valley. Fluctuations in sea level may have resulted in the shifting, landward or seaward, of the estuary and its associated tripartite zonation. With the infilling of the estuary a return to bay deposition (bay sequence 2) occurred. Overlying this bay sequence is a coarsening-upward deltaic sequence of the Glauconitic member.