Red beds and evaporates were the dominant deposits during the late pre-rift phase, whereas typical clastic progradational sequences with periods of carbonate deposition dominated the drift phase (Figure 4). These are described in more detail below.
Rifting began in the Middle Triassic Period, about 225 million years ago (Mya). At that time, the Nova Scotia region occupied a near equatorial position, situated adjacent to Morocco, with most of its older Paleozoic rocks having direct Moroccan affinities (Schenk et al., 1980). A series of narrow, interconnected rift basins were created during the rift phase and were filled with fluvial and lacustrine red bed sediments as well as volcanic rocks (Fundy-type sequences). By the latest Triassic-earliest Jurassic, tectonic motion had moved the North American and African plates slowly northward, with the Nova Scotia-Moroccan region in an arid sub-equatorial climate zone (ca. 10-20°N paleo-latitude). Renewed Late Triassic rifting of continental crust further to the north and east in the Grand Banks / Iberia region breached topographic barriers and permitted the first incursions of marine waters from the eastern Tethys paleo-ocean to flood into these interconnected syn-rift basins (Figure 5). Restricted, shallow marine conditions were established with some mixed clastic and minor carbonate sedimentation (Eurydice Formation). Due to the hot and dry climate, the shallow seas were repeatedly evaporated, resulting in the precipitation of extensive salt and minor anhydrite deposits that were as much as two kilometers thick in the central parts of the rift system (Argo Formation).
An earliest Jurassic phase of siliciclastic deposition is observed in the west-central part of the Scotian Basin that may exist elsewhere along the margin and the Moroccan conjugate. This eastward-directed pulse of redbed sediments (Heracles unit) conformably overlies and deforms (through loading) Argo Formation evaporites in the Mohican Graben. The west-dipping listric faults inboard of the margin hinge-line on the Mohican and Naskapi grabens are interpreted as the antithetic response to extension in the Fundy Basin during the Late Triassic (Wade et al., 1996). These grabens acted as loci for clastic deposition for newly established fluvial drainage systems, with the source of the sediments from the current mainland region of Nova Scotia. While not yet encountered in wells or observed elsewhere along the margin, the age of this succession can be reasonably inferred as early Hettangian to perhaps mid- to late Sinemurian since it conformably overlies the Argo Formation and is later truncated by the younger Break-up Unconformity as described below.
Renewed tectonism in the central rift basin during the Early Jurassic (mid-Sinemurian) is recorded by the complex faulting and erosion of Late Triassic and Early Jurassic sediments and older rocks. This phase of the rifting process resulted in the formation of a Break-Up Unconformity (BU), which coincided with the final separation of the North America and Africa continents, the creation of true oceanic crust through volcanism, and opening of the proto-Atlantic Ocean. As a result of the BU, the heavily faulted, complex terrane of grabens and basement highs along the Scotian margin underwent a significant degree on peneplanation.
Figure 4:
Figure 5:
