Concurrent with carbonate deposition, regional uplift to the west resulted in an influx of clastic sediments and the establishment of the mixed energy (current and tidal) Sable Delta complex in the Laurentian Subbasin, and slightly later in the Sable Subbasin. In the southwest, a similar progradation of sediments may have occurred at an embayment in the vicinity of the U.S.-Canada border, known as the Shelburne Delta. These sediments were primarily sourced from the adjacent thick (14+ km) blanket of latest Devonian to Permian sediments centred in the Gulf of St. Lawrence region that covered the entire Atlantic Provinces region and parts of New England (Pe-Piper & Piper, 2004; Pe-Piper & MacKay, 2006). The MicMac Formation records this first phase of delta progradation into these subbasins, represented by distributary channel and delta front fluvial sands cyclically interfingering with prodelta and shelf marine shales of the Verrill Canyon Formation. The ancestral St. Lawrence River was well established by the earliest Cretaceous, delivering increasing supplies of clastic sediments into the Scotian Basin that overwhelmed and buried the carbonate reefs and banks on the La Have Platform and later the Banquereau Platform. A series of thick sand-rich deltaic, strandplain, carbonate shoals and shallow marine shelf successions (Missisauga Formation) dominated sedimentation throughout the Early Cretaceous (Figure 7). The Sable Delta prograded rapidly southwest into the Laurentian and Sable Subbasins and over the Banquereau Platform, while in the Shelburne Subbasin the postulated Shelburne Delta disappeared due to the exhaustion of its river's sediment supply. Along the La Have Platform, small local rivers draining off of the southwest Nova Scotia mainland provided modest amounts of sands and shales to this region and associated deeper water realm.
Middle Jurassic and Cretaceous sediment loading of unstable shelf sediment along and to the south of the basement hinge zone initiated subsidence and development of seaward-dipping growth faults which acted as traps for sand. Sediment loading also mobilized Jurassic-age salts creating a complex slope morphology (e.g. Kidston et al., 2002; Shimeld, 2004) analogous to other basins with mobile salt substrates (e.g. Gulf of Mexico). Continuous sedimentation accentuated salt mobility, and in areas where sedimentation was high, like the Sable and possibly Shelburne deltas, salt moved both vertically and in the seaward direction forming diapirs, pillows, canopies and related features. During periods of low sea level, extant rivers incised exposed outer shelf sediments, with shelf-edge delta complexes probably forming at the edge of the continental shelf (Cummings & Arnott, 2005; 2006). Such deltas supplied turbidity currents and other mass transport deposits to the slope during the Middle Jurassic through Cretaceous, where potential reservoirs were deposited in canyons and intra-slope minibasins.
Deltaic sedimentation ceased along much of the Scotian margin following a late Early Cretaceous major marine transgression when the shelf was blanketed by thick shales of the Naskapi Member of the Logan Canyon Formation. Transgressive shales were periodically interrupted during the influx of coarser clastics in the Aptian-Cenomanian (Cree and Marmora members of the Logan Canyon Formation; Wade and MacLean, 1990). Sand was deposited along a broad costal plain and shallow shelf, but these eventually gave way as deeper marine shales (and some limestones) of the Dawson Canyon Formation were deposited as sediment supply decreased from the lower relief hinterland. The end of the Cretaceous period in the Scotian Basin saw a rise in sea level and basin subsidence and deposition of marine marls and chalky mudstones of the Wyandot Formation. These strata were eventually buried by Tertiary marine shelf mudstones and later shelf sands and conglomerates of the Banquereau Formation (Figure 8). Throughout the Tertiary on the Scotian margin, several major unconformities related to sea level falls occurred. During Paleocene, Oligocene and Miocene times, fluvial and deep-water current processes cut into and eroded these mostly unconsolidated sediments and transported sediments out into the deeper water slope and abyssal plain. During the Quaternary Period of the last 2 million years, several hundred metres of glacial and marine sediments were deposited on the outer shelf and upper slope.
Figure 7:
Figure 8:
