TECTONOSTRATIGRAPHIC EVOLUTION OF THE MIDDLE PALEOZOIC GASPÉ BELT IN NORTHERN NEW BRUNSWICK

Tectonostratigraphic evolution of the Middle Paleozoic Gaspé Belt in northern New Brunswick

R.A. Wilson and J. I. Carroll New Brunswick Geological Surveys Branch PO Box 50, Bathurst, New Brunswick, CANADA E2A 3Z1

The Gaspé Belt is a Middle Paleozoic successor basin that developed on Dunnage Zone basement, and merges with the Central Maine Slate Belt to the southwest. The oldest rocks occur in the central part of the Belt, and comprise Ashgillian to Llandoverian turbidites of the Grog Brook and Matapédia groups. West of the central anticlinorium, the Matapédia Group is conformably overlain by Wenlockian to Ludlovian rocks of the Perham Group, which is juxtaposed against the Pridolian to Emsian Fortin Group along the Restigouche Fault. Farther west, the Sainte Florence Fault marks the tectonic contact between the Fortin Group and Emsian rocks of the Gaspé Sandstone Group. On the east side of the Gaspé Belt, the Silurian-Devonian succession is interrupted by two unconformities. Llandoverian to Wenlockian rocks of the lower Chaleurs Group conformably overlie the Matapédia Group, but an unconformable contact with overlying Pridolian to early Emsian rocks marks the Salinic Orogeny. Post-Salinic strata form a transgressive-regressive sequence comprising sedimentary rocks of the upper Chaleurs Group and volcanic rocks of the Dalhousie Group. A middle Emsian unconformity separates the Dalhousie Group from overlying alluvial-lacustrine rocks of the late Emsian Campbellton Formation.

Two deformations are recognized in the study area. In the central anticlinorium, early, northwest-trending folds are overprinted by northeast-trending Acadian folds with penetrative axial planar cleavage; Acadian folding was followed by reverse and dextral strike-slip faulting. Early folds are associated with the Salinic Orogeny, which is also manifested in uplift and erosion of Early Silurian strata. It is proposed that complex patterns of Siluro-Devonian erosion and deposition may be related to vertical displacements during Salinic block faulting. Between the Sellarsville and McKenzie Gulch faults, poor cleavage development and coincident low thermal maturation levels imply shallow burial depths. Devonian, Silurian, and some Upper Ordovician rocks in this area fall within the oil and gas condensate windows.