The Cretaceous succession at Mount Tatlow, British Columbia, is a cornerstone of Cordilleran stratigraphy, preserving a mostly continuous record of upper Lower Cretaceous to lower Upper Cretaceous sedimentary strata. The succession is capped by volcanic strata of the Powell Creek formation. Lithofacies assemblages within the Mount Tatlow succession reflect sedimentation in a deep-water submarine fan system at the base of the section, to overlying submarine-fan and to pro-deltaic deposition, and, finally, to delta-plain sedimentation at the top of the succession. Radiolarian and foraminifer fossils from the lower part of the Mount Tatlow section are the first recovered from the Intermontane basins of British Columbia and indicate a middle Albian to Cenomanian age, most likely Cenomanian. The presence of these fossils indicates that open-marine conditions existed locally in the basin at this time, but the strongly altered and pyritized nature of the fauna suggests that a reducing environment fostered early diagenetic pyritization processes in the subsurface sediments. Detrital zircon populations collected from the succession are in agreement with the paleontological ages.