LATE ORDOVICIAN TO MIDDLE DEVONIAN TECTONO-SEDIMENTARY HISTORY OF THE GASPÉ BELT IN NORTHERN NEW BRUNSWICK

The Upper Ordovician to Middle Devonian stratigraphy of the Gaspé Belt in the Restigouche-Chaleur area of New Brunswick is divided into three sequences separated by unconformities. The oldest sequence provides a record of the infilling of a Late Ordovician-Early Silurian fore-arc basin, and comprises a thick conformable succession of siliciclastic and calcareous turbidites of the Grog Brook and Matapédia groups, respectively, and conformably overlying, mainly siliciclastic rocks of the Chaleurs Group. Shallow marine to subaerial sedimentary and volcanic rocks of the Pridolian to early Emsian Dalhousie Group disconformably overlie the Chaleurs and Matapédia groups above a Late Silurian hiatus corresponding to the Salinic Orogeny. Following a brief Emsian hiatus, late Emsian to early Eifelian fluvial sands and gravels of the Campbellton Formation were deposited unconformably upon the Dalhousie Group.

The Salinic Orogeny was characterized in northern New Brunswick by widespread uplift and erosion, along with gentle, northwest-trending folds without cleavage, inferred in pre-Silurian rocks from the presence of doubly-plunging macrofolds and fold interference patterns. In most areas, the Late Ordovician-Early Silurian shallowing trend culminated in carbonate platform development in the Chaleurs Group (LaVieille and Limestone Point formations). In the eastern part of the belt, these rocks are overlain by voluminous, subaerial, Wenlockian to early Ludlovian mafic and felsic volcanic rocks that immediately underlie the Salinic hiatus. In the Restigouche Syncline, which is bounded by the McKenzie Gulch and Sellarsville faults, the extent of erosion is manifested in the absence of the Chaleurs Group, thinning of the Matapédia Group, and occurrence of Matapédia erosional clasts in the disconformably overlying Indian Point Formation (Dalhousie Group). A Lochkovian transgressive interval, recorded by deposition of the Indian Point Formation, was followed by Pragian regression, with deposition of shallow water to subaerial volcanic and sedimentary rocks of the Archibald Settlement Formation (Dalhousie Group). Terrestrial conditions also prevailed during deposition of the Campbellton Formation.