In paleoequatorial parts of Europe and North America, late Paleozoic cyclic successions are widely inferred to reflect glacio-eustasy. However, many of these successions accumulated in basins in the Pangean collisional zone, where variations in tectonics and sediment supply could also have generated cyclic successions. Cyclic successions are ubiquitous in the Maritimes Basin of Atlantic Canada but are especially prominent in the Visean and Bolsovian to Cantabrian, when subsidence rates on coastal plains were low and probably steady during periods of thermal subsidence. During relatively humid climatic conditions in the Bolsovian to Cantabrian, fluvial systems generated clastic cyclic successions with deep valleys and mature interfluve paleosols, providing strong evidence for alternate rise and fall of sea level—a characteristic glacio-eustatic feature. Under arid conditions in the Visean, with few rivers, carbonate-evaporite rhythms formed with little evidence for incision. Comparisons with near- and far-field records for Gondwanan glacial activity suggest that these two periods correspond to sea-level changes on the order of a few tens of meters, probably due to melting and accumulation of small ice caps rather than continent-wide ice sheets. Cyclic successions that formed in basins undergoing steady thermal subsidence may provide the most reliable evidence for glacio-eustasy in the paleoequatorial realm.

In eastern Canada, two periods of magmatism were associated with early Mesozoic continental rifting. Triassic dikes in southwest Nova Scotia and the Northumberland Strait F-25 well geochemically resemble alkaline dikes of the coastal New England (CNE) igneous province. Widespread Hettangian tholeiitic magmatism of the eastern North America (ENA) province is represented in eastern Canada by extensive multiple basalt flows around the Bay of Fundy and on the Scotian Shelf and Grand Banks and by several dikes hundreds of kilometers long. The total volume of observed Mesozoic magmatic products on the eastern Canadian margin is small. They were probably emplaced over relatively short time intervals, indicating the importance of tectonic pathways in permitting rise of magma to the surface. Samples from the CNE province and the Glooscap well on the west Scotian Shelf have more highly radiogenic Pb isotope compositions. Samples from southwestern Nova Scotia are enriched in LILE, and have higher Hf/Lu and lower Y/Nb compared with samples from Newfoundland and northern New Brunswick. Such geochemical trends are interpreted to result from the Permian-Triassic hotspot responsible for resetting of K-Ar dates and plutonic activity in New England. The progression from alkalic to tholeiitic magmatism through time is related to this plume. Other early Mesozoic basaltic rocks in eastern Canada have isotopic composition (low ɛ Nd and high 207 Pb/ 204 Pb) and trace element features (such as high La/Ta and low Ti/V) that reflect incorporation of crustal-type material in subcontinental mantle, perhaps by previous subduction. Geochemical comparison with Carboniferous tholeiites suggests that the early Mesozoic tholeiites have not been generally contaminated by continental crust, except for some local fluid phase interaction. The magmas resulted from adiabatic decompression of asthenosphere as a result of continental extension and subsequent plagioclase and pyroxene fractionation in mid-crustal reservoirs. Three major tectonic and igneous phases are distinguished: (1) Anisian to early Hettangian rifting, accompanied by minor alkalic dikes (CNE province), when basins formed by extension and were filled by thick terrigenous clastics and evaporites; (2) a postrifting phase (late Hettangian to Bajocian), separated by a postrift unconformity from underlying strata. This Hettangian unconformity is not a breakup unconformity. ENA magmatic activity (tholeiitic plateau basalts and linear composite dikes, up to 400 km landward of the hinge line) was localized along major deeply penetrating faults. The change in tectonic regime resulted in accelerated lithospheric attenuation accompanied by uplift landward of the hinge zone and an increase in subsidence seaward. (3) The final separation of continental crust and onset of oceanic rifting took place in the Bajocian and was accompanied by only limited igneous activity near the ocean-continent boundary.