Petroleum-industry multichannel marine seismic data in the public domain do not support the traditional interpretation of the Acadian deformation front in the Appalachians of western Newfoundland. They show that the Late Ordovician to latest Silurian Long Point-Clam Bank succession is folded in a northwest-facing monocline, whereas the underlying Cambrian-Ordovician platform succession dips southeast. We interpret the intervening region as a structural "triangle zone" similar to those at the foreland edges of other thrust belts. The contact between the Long Point Group and the underlying Humber Arm allochthon, previously interpreted as unconformable on Port au Port Peninsula, is the southeast-vergent upper detachment surface of the triangle zone. The platform succession on the peninsula is probably within the triangle zone and is therefore allochthonous; at least 30 km of Acadian (Silurian-Devonian) northwest transport is implied. The triangle zone continues to the northeast, offshore the Bay of Islands, suggesting that Grenvillian basement of the Long Range massif is also allochthonous.

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