VISÉAN (UPPER MISSISSIPPIAN) SEDIMENTATION AND TECTONICS IN THE RISTIGOUCHE, CENTRAL AND MARYSVILLE BASINS OF NEW BRUNSWICK

The Middle Carboniferous (Viséan) Windsor Group is dominated by fine grained clastic rocks, but is defined by its abundant marine carbonates and evaporites, which differentiate it from the mainly continental nature of other groups in the upper Paleozoic Maritimes Basin. Some areas of the Maritimes Basin never had marine influxes during the Viséan, and some had fewer than others. Because Viséan climate in the Maritimes was hyper-arid, no fossils are preserved within continental clastics that are time-equivalent to the Windsor Group, which are therefore only dated by stratigraphic constraints and only poorly correlated form one area to the next. Recent tectonostratigraphic work in the Chaleur Bay area and New Brunswick suggests that the Viséan was characterized by active tectonics and fault-controlled clastic sedimentation in the northwestern sector of the Maritimes Basin. Evidence suggests that only the first transgressive cycle of the Windsor Sea has reached that sector, followed by regression and widespread groundwater calcretization of areas in northern New Brunswick and eastern Quebec that were then bordering evaporitic basins. Coarse red clastics unconformably overlie these groundwater calcretes and comprise the rest of the Viséan stratigraphy in northern New Brunswick (most of the Carboniferous Central Basin) and eastern Quebec (Ristigouche Basin). In the Marysville Basin, the same red clastic succession conformably overlies Lower Windsor Group limestones, the Middle and Upper Windsor Group limestones of Nova Scotia being absent in that sector. According to provenance, paleocurrents and sedimentary facies studies, a series of major Viséan fault scarps fed coarse alluvial fans and gradually expelled the Windsor Sea from the northwestern sectors of the Maritimes Basin. In response to this, the Windsor Sea migrated towards the southeast, leading to basement onlap of Upper Windsor Group limestones in areas of Nova Scotia that were previously outside the reaches of that sea.