UNTANGLING THE PRE-, SYN-, AND POST-RIFT DEVELOPMENT OF THE SCOTIAN MARGIN: NEW RESULTS AND ENDURING QUESTIONS

With >290 000 km² of sparse to dense digital reflection seismic coverage in offshore areas extending from Georges Bank to the Burin Platform, including 23 500 km² of 3D seismic, >156 000 line km of 2D seismic, and ~180 exploration wells, Nova Scotia’s continental shelf and slope is truly data-rich. Over the past eight years these data-sets have been used to refine the distribution of key geological elements within and above crystalline basement, providing insight into the structural and stratigraphic development of the Scotian margin before, during and after rifting. For example, correlation of a Moho reflection across the western margin, as well as a complex array of mid-crustal shear zones and major border faults that sole out along them, coupled with improved mapping of the top of basement, helps constrain crustal thickness and provides information about how the crust beneath the shelf and slope accommodated extension. Layered stratigraphic successions above crystalline basement record potential Late Paleozoic outliers composed of pre-rift strata overlain by synrift strata that record a complex but poorly-constrained multi-phase extensional history. Development of rift-related paleotopography appears equally complex and includes periods of basin inversion. Widespread salt deposition took place during the mid to late synrift, and the distribution of basement highs and lows, along with the correlation of salt feeders allows us to place a more accurate perimeter around the primary salt basin. Postrift mobilization of this salt in turn has played an important role in the younger structural and stratigraphic development of the margin. In the west, most of the expelled salt still lies immediately above the primary salt basin; in the east, expelled salt largely escaped the primary salt basin and now lies in younger strata above oceanic or transitional crust. Despite excellent data coverage there are still many lingering questions that remain unanswered. How does the structure and stratigraphy of rift basins vary as we step across the margin hinge zone? Are we properly distinguishing prerift from synrift stratigraphic successions? Could some inversion structures really record prerift shortening? Why does part of the primary salt basin underlie what is now the shelf, while other parts underlie the present-day slope?