BASIN DEVELOPMENT AND INVERSION AT THE APPALACHIAN STRUCTURAL FRONT, PORT-AU-PORT PENINSULA, WESTERN NEWFOUNDLAND APPALACHIANS

In the Humber Zone of the Newfoundland Appalachians, Cambro-Ordovician shelf and foreland basin successions are affected by Middle Ordovicia n (Taconian orogeny) and Devonian (Acadian orogeny) deformation. On Po rt au Port Peninsula the presence of the Late Ordovician to Late Silur ian Long Point - Clam Bank succession allows these episodes to be sepa rated. The Taconian foreland basin stratigraphy on Port au Port Penins ula is highly variable. On the west coast, platform carbonates are ove rlain by megaconglomerates of the Cape Cormorant Formation, which reco rd progressive exposure of 1 km of the platform succession. The conglo merates are restricted to a narrow zone, consistent with derivation fr om a fault scarp originally immediately west of the outcrops (in palin spastic restoration). Farther east, at Victors Brook, the Cape Cormora nt Formation is absent, but the overlying, almost undeformed Goose Tic kle Group contains conglomerate derived both from the upper part of th e platform succession and from the Taconian Humber Arm Allochthon. Sou theast of Victors Brook, the top of the platform is overlain directly by scaly shales and melange of the Humber Arm Allochthon, which includ es deformed equivalents of the foreland basin succession. The distribu tion of conglomeratic units, the presence and configuration of faults, and the preservation of the Goose Tickle Group in the Victors Brook a rea imply that a fault-bounded basin developed in advance of the Humbe r Arm Allochthon during the Taconian orogeny. This basin is interprete d to have resulted from flexural extension of North American lithosphe re. The close spatial coincidence between later Acadian structures and the Taconian basin boundaries implies that the basin-bounding faults were reactivated as thrusts and reverse faults, and that the basin und erwent inversion during Acadian thrusting. The western basin-bounding fault, modified by the development of a ''short cut'' thrust, develope d into the present-day Round Head thrust.