Marine transgression above the BU, eventually covered the basin with a narrow, shallow and restricted sea within which thin sequences of carbonate and clastic sediments accumulated. Transgressive shallow water to tidally influenced dolomites and clastics were laid down in localized areas on the seaward portion of the margin under slightly restricted marine conditions (Iroquois Formation). A thick succession of coarser grained clastic sediments and shales from fluvial sources (Mohican Formation) was deposited concurrently on the basin margins. The succession was sourced from adjacent high relief terranes and eventually prograded out over the margin to fill graben lows and bury basement highs by the early Middle Jurassic (MacLean and Wade, 1990). The fine muds from this succession were transported by marine processes into deeper water where they slowly infilled basinal lows and blanketed newly formed oceanic crust.
The combination of sea-floor spreading, basin subsidence and global sea level rise caused the Atlantic Ocean to become broader and deeper (~1000 m) by the Middle Jurassic. A prominent carbonate bank developed in the western part of the basin at this time and persisted until the latest Jurassic-earliest Cretaceous. Growth of the carbonate bank was tempered by Upper Jurassic and Lower Cretaceous deltaic depocentres that locally overwhelmed carbonate sedimentation. The carbonate bank succession can be subdivided into a number of members. A carbonate platform and margin succession was established along the basin hinge zone (Scatarie Member of the Abenaki Formation) and prograded out into deeper waters where marls and clastic muds were deposited. Continuing margin subsidence coupled with global sea level rise resulted in transgression during which time the carbonates and other shelf sediments were blanketed by deeper marine shales (Misaine Member of the Abenaki Formation). From the late-Middle to the end of the Jurassic, carbonate reef, bank and platform environments formed and thrived along the basin hinge line on the La Have Platform (Baccaro Member of the Abenaki Formation) (Figure 6). Further north, a shallow mixed carbonate-clastic ramp succession existed on the Banquereau Platform and in deeper water a thin succession of shales and limestones were deposited (DSDP J1 Reflector).
Figure 6:
