Stratigraphy of two late paleozoic basins : implication for the timing of final emplacement of the Meguma terrane

Abstract

Paleoraagnetic studies indicate the Meguma terrane's final emplacement occurred between the Mid-Devonian and Early Permian. Lithostratigraphic units near the boundary of the terrane were investigated in order to provide constraints on the timing of this compressional event. North of the Cobequid-Chedabucto Fault (Guysborough Basin), volcanic flows, pyroclastics and related sediments are overlain by gravelly to sandy braided fluvial and lacustrine lithofacies. East-southeast paleocurrents and variable (non- Meguma) clast lithologies are typical of these units. South of the Cobequid-Chedabucto Fault (St. Mary's Basin), coarse cobble - rich to sandy braided fluvial lithofacies are dominant. Paleocurrents indicate flow to the north and clast lithologies are representative of the Meguma terrane. Post Acadian (Late Devonian) basement fragmentation and associated volcanism modified the area north of the Cobequid- Chedabucto Fault. Basement block rotation, east end down, initiated Latest Devonian through Mid-Carboniferous sedimentation in a transtensile tectonic environment. There is no lithostratigraphic evidence to suggest the presence of the Meguma terrane immediately south of the Guysborough Basin during this time interval. However, the Meguma terrane was supplying sediment to the St. Mary's Basin by the Early Carboniferous. Collision and wrench faulting probably initiated formation of this basin in a transtensile tectonic environment. Subsequent dextral displacement along the Cobequid-Chedabucto Fault and transpressive tectonic conditions resulted in the removal of slices of both the St. Mary's and GUysborough Basins as these two distinct assemblages were juxtaposed.