Chapter 3 Appalachian Foreland Basin of Canada

Abstract

Abstract The Late Proterozoic breakup of Rodinia led to the formation of Laurentia. The continent had a paleosouthern jagged margin that consisted of recesses and salients; the Canadian segment of that margin belongs to the St. Lawrence Promontory and Quebec Reentrant. The stratigraphic framework and paleogeographic evolution of Cambrian–Ordovician shallow- to deep-marine units deposited during the rift, passive-margin and foreland-basin stages are integrated from western Newfoundland to southern Quebec. Major sea-level lowstands and highstands are correlated, with some time discrepancy starting to occur in earliest Ordovician. The passive-margin evolution was primarily controlled by eustatic sea-level changes; although some ancestral faults were sporadically active in Late Cambrian to Early Ordovician in the Quebec Reentrant. The diachronous westerly directed late Early to Late Ordovician tectonic-controlled extensional collapse of the shallow-marine foreland shelf from the St. Lawrence Promontory to the Quebec Reentrant was followed by the diachronous collision of volcanic arcs along Laurentia (Taconian Orogeny) which climaxed in the Middle-Late Ordovician interval with collision occurring first at the St. Lawrence Promontory. Tectonic quiescence was short-lived along the paleosouthern continental margin of Laurentia as more exotic microcontinents (Ganderia, Avalonia) were closing in. The paleoenvironmental history was significantly affected by these Early Silurian to late Early Devonian tectonic events (Salinic and Acadian orogenies). A Late Ordovician to Early Silurian filling stage was followed by two T-R cycles. The first of these cycles was initiated by a tectonically controlled sea-level rise in latest Early Silurian followed by a eustatic sea-level fall in Late Silurian. The cycle culminated in the Salinic unconformity. The second cycle started with a major tectonic collapse in latest Silurian followed by a slow to ultimately rapid sea-level fall from the Early to early Middle Devonian. The cycle ended with sub-aerial exposure and syn-tectonic sedimentation (Acadian Orogeny).