Based on the model that during the rifting stage beginning at ca. 590 Ma, the Ottawa Graben, an Iapetan failed arm, localized a large river that flowed into the nascent Iapetus, a search was made for the related fluvial and deltaic deposits. The search led to the identification of fluvial deposits as predicted by the model. Deltaic deposits were also identified despite complications brought about by deformation, metamorphism, and thrusting, although they probably belong to a late phase of delta buildup in the Early Cambrian. Older deltaic deposits of the river probably lie buried beneath a volcanic shield that built up at the proximal end of the graben ca. 554 Ma. The successful application of the model supports the paradigm of rift-arm – failed-arm rivers and their deltas as proposed by K. Burke and J.F. Dewey nearly two decades ago. Investigations based on this paradigm, in appropriate geological situations, may provide insights into problems related to continental rifting and breakup and provide information for the reconstruction of ancient rift–rift–rift (rrr) triple junctions and plate boundaries.