AN EARLY CAMBRIAN DELTAIC - FLUVIAL MODEL FOR AN IAPETAN RIFT-ARM DRAINAGE SYSTEM, SOUTHEASTERN QUEBEC

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 relate d fluvial and deltaic deposits. The search led to the identification o f fluvial deposits as predicted by the model. Deltaic deposits were al so identified despite complications brought about by deformation, meta morphism, and thrusting, although they probably lie belong to a late p hase 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 applicat ion of the model supports the paradigm of rift-arm-failed-arm rivers a nd their deltas as proposed by K. Burke and J.F. Dewey nearly two deca des ago. Investigations based on this paradigm, in appropriate geologi cal situations, may provide insights into problems related to continen tal rifting and breakup and provide information for the reconstruction of ancient rift-rift-rift (rrr) triple junctions and plate boundaries .