Geochemistry of the Namurian Lismore Formation, northern mainland Nova Scotia: sedimentation and tectonic activity along the southern flank of the Maritimes Basin

Geochemical and isotopic data from the clastic rocks of the Namurian Lismor e Formation in mainland Nova Scotia identify key episodes of tectonic activ ity during the development of the Maritimes Basin in Atlantic Canada. The L ismore Formation forms part of the Mabou Group and is an upward-coarsening 2500 m thick fluvial sequence deposited in the Merigomish sub-basin along t he southern flank of the Maritimes Basin. Based on stratigraphic evidence, the Lismore Formation can be divided into upper and lower members which ref lect variations in depositional environment and paleoclimate. The geochemic al and isotopic data may also be subdivided into two groupings that primari ly reflect varying contributions from accessory phases, clay minerals, or r ock fragments. This subdivision occurs 115 m above the base of the upper me mber. The data from the lower grouping (group A) show an important contribu tion from underlying Silurian rocks, with a relatively minor contribution f rom Late Devonian granitoid rocks from the adjacent Cobequid Highlands and possibly metasedimentary rocks from the Meguma Terrane to the south. The da ta from the upper grouping (group B) reveal a more important contribution f rom the Cobequid Highlands granitoid rocks. This variation in geochemistry is thought to constrain the age of renewed motion and uplift along the faul ts along the southern flank of the Maritimes Basin and, more generally, sug gests that geochemical and isotopic data of continental clastic rocks may h elp constrain the age of tectonic events that influence deposition of basin -fill rocks.