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.

Micropaleontological study of the sedimentary record from the Montagnais impact structure, located on the shelf off Nova Scotia, has shown that the impact had neither regional nor global effects on biological diversity. This result provides new evidence for the lower threshold of extinctions due to the impacts, indicating that impacting bolides must be larger than 3 km in diameter to cause extinctions. We use this evidence to construct simplified curves to test relations between mass extinctions, bolide diameter, and impact periodicity. These data point to reoccurrence of mass extinctions of amplitude comparable to the Cretaceous/Paleogene event an average of once in every 100 to 500 m.y., whereas the probability of extinction of life on Earth triggered by an impact of a bolide larger than 60 km in diameter has an average frequency of once in 1 b.y. Data presented in this chapter do not support a direct parallel between the 26-m.y. extinction periodicity and the impact cratering record in Earth.

Abstract Jurassic paleoceanographic conditions in the Atlantic Ocean can be reconstructed from information derived from the preserved sediments and the biogeography of the fossil fauna, from reconstructed basin paleogeographies (shape, size, depth, and positions of landmasses and seaways), and from indications of paleotopography, paleobathymetry, and paleoclimate. An extensive literature exists about Mesozoic sediments and biota of the Teth- yan realm from Europe and parts of northwestern Africa. Such data, supplemented by my own field studies in central and southern Europe and Morocco, and by studies of oil exploratory wells on the eastern North American margin, were major sources of the Jurassic lithofacies data summarized in Plate 9. Additional data comes from Continental Offshore Stratigraphie Test (COST) wells drilled on the eastern North Atlantic U.S. shelf and summarized in U.S. Geological Survey reports. However, the most important information is derived from the Deep Sea Drilling Project (DSDP), which drilled numerous deep holes in the deep North Atlantic basin and its continental margins. Greater insight into the early evolution of the North Atlantic basin was provided particularly by DSDP Leg 79, which drilled four holes on the deep-water Moroccan continental margin, at water depths of 3151 to 3992 m (Sites 554 to 547, Hinz and others, 1984; Plates 2, 9). These holes provide the only information about the Lower Jurassic in the central North Atlantic basin, and are used extensively in this chapter on the assumption that basin development was similar on both sides of the Atlantic. This assumption is supported

Abstract We here consider the petroleum resources only of the off shelf portion of the western North Atlantic Ocean. Very little information is available for this region; off the eastern United States, only four petroleum exploration holes have been drilled in one restricted area seaward of the shelf, off the Baltimore Canyon trough. However, by interpreting seismic reflection profiles and Stratigraphie data from the Deep Sea Drilling Project (DSDP) and other wells on the adjacent slope and shelf, we can evaluate the geologic conditions that existed during development of the basin and that might lead to petroleum accumulations. The wellknown factors that lead to oil and gas accumulations are availability of source beds, adequate maturation, and the presence of reservoir beds and seals configured to create a trap. The western boundary of the area considered in this paper, the present sloperise break, is one that has developed from the interplay of sedimentation and erosion at the continental margin; these processes are affected by variations in margin subsidence, sedi-ment input, oceanic circulation, sea level, and other factors. Thus the sloperise break has migrated over time and is locally underlain by slope and shelf deposits, as well as deepbasin facies. These changes in depositional environments may well have caused juxtaposition of source and reservoir beds with effective seals. Several papers have been written on the hydrocarbon pros-pects of the (Jansa and MacQueen, 1978; Roberts and Caston, 1975; Dow, 1979; Hedberg, 1976; Mclver, 1975; Schott and others, 1975;