SHORELINE EVOLUTION IN THE MUSQUODOBOIT BASIN OF CENTRAL NOVA SCOTIA DURING THE FIRST TRANSGRESSION OF THE WINDSOR SEA (LATE MISSISSIPPIAN)

The Musquodoboit Basin is a sub-basin of the composite upper Paleozoic Maritimes Basin, which first formed as a series of north-east trending grabens from pull-apart tectonics in late stages of the Acadian Orogeny. Although mainly continental, the Maritimes Basin accommodated 28 transgression-regression cycles during the Viséan (upper Mississippian). It was during the first of these transgressions that the Gays River Formation was deposited in the Musquodoboit Basin. This formation is a dolomite upper bank deposit that oversteps the Upper Devonian Horton Group and onlaps basement rocks of the Meguma Group. A quarry section in Upper Musquodoboit, Nova Scotia, captures the progression of the shoreline during this first transgression of the Windsor Sea. Patches of coarse conglomerate overlie siliciclastic basement rocks of the Goldenville Formation (Cambrian to Ordovician) and contain clasts of it surrounded by a carbonate matrix. The dolomite bank pinches out from one conglomerate patch to the next on the flank of the basement high that limits the Musquooboit Basin to the southwest. In between the patches of conglomerate, dolomite sharply overlies an irregular basement surface, indicating that the sea transgression was jerky. During times of shoreline stability, wave action formed gravel beaches, with well-rounded clasts of basement rocks. These periods of shoreline stability were not long enough to form well-defined wave-cut platforms and the shoreline remained steeply dipping, leading to the formation of coarser and more angular talus deposits offshore from the gravel beaches. Overall, sedimentology of the basal Gays River indicates that the first Windsor Sea transgression was rather rapid in that area and only caused minor erosion of the competent basement rocks that it onlapped.