Abstract The contemporary rifted margin off Nova Scotia was formed over the Meguma and Avalon Appalachian terranes in response to plate motions between Africa and North America (Figs. 1 and 2; Williams and Hatcher, 1983; Haworth, 1981). Rifting began in the Late Triassic and produced rift basins beneath the present continental shelf. Of these basins, the Orpheus sub-basin which lies on the Avalon-Meguma boundary is a prominent example. Regionally the rift basins are not uniformly distributed throughout the Nova Scotian margin and southern Grand Banks region. Most are found in the Avalon terrane, rather than the Meguma terrane. Evidence of Triassic mafic volcanism is exemplified by the North Mountain basalts and the Shelburne dike in Nova Scotia, and most of the known occurrences of volcanic rocks appear to lie well inland of the present ocean-continent transition (Poole, 1970; Papezik and Barr, 1981). Triassic rifting was accompanied by the deposition of non-marine clastics within the rift basins. During the Early Jurassic, thick salt beds developed beneath much of the present shelf and slope (Jansa and Wade, 1975). In Early-Middle Jurassic time a deepening, less restricted marine environment led to the construction of carbonate platforms (Jansa, 1981). It was during this time that sea-floor spreading began east of the rifted North American continent. This rift-drift transition does not appear to be marked by a period of uplift, erosion, or by the development of a clear breakup unconformity After the onset of sea floor spreading, the margin subsided and over 10 km of Jurassic

Abstract The East Scotia Ridge exhibits systematic variations in axial morphology and basalt geochemistry. Central segments have morphology typical of intermediate-rate spreading centres and erupt mainly normal mid-ocean ridge basalt (N-MORB). Segments near the ridge ends exhibit anomalous, inflated, axial morphology and erupt more evolved basalts, influenced by the Bouvet plume in the north. As the end segments lie closer to the volcanic arc, these variations could be caused by coupled flow within the mantle wedge, as inferred from similar studies in the Lau Basin. Three of the four zones of crustal accretion defined from the Lau Basin may be identified in the East Scotia Sea, although there is no counterpart to a zone of diminished magma supply observed at the East Lau Spreading Centre. Superimposed on the pattern of plate-driven flow is a ridge-parallel flow related to inflow of Atlantic mantle into the East Scotia Sea back-arc region at both ends of the South Sandwich slab. The inflow causes enhanced magmatism and propagation of the end segments towards the middle of the back-arc region, and may be related to trench-parallel flow beneath the rapidly retreating slab. Alternatively, it may be driven by buoyancy flux from Atlantic hot spots. There is no evidence that retreat was ever driven by escape flow of Pacific mantle.

Abstract Permo-Triassic rift basins offer important hydrocarbon targets along the Atlantic margins. Their fill is dominated by continental red beds, comprising braided fluvial, alluvial fan, aeolian, floodplain and lacustrine facies. These relatively lightly explored basins span both the Atlantic and Tethyan domains and developed above a complex basement with inherited structural fabrics. Sparse data in offshore regions constrain understanding of depositional geometries and sedimentary architecture, further impeded by their deep burial beneath younger strata, combined with the effects of later deformation during continental breakup. This paper provides results from a multidisciplinary analysis of basins along the Atlantic margin. Regional seismic and well data, combined with geochemical provenance analysis from the European North Atlantic margins, are integrated with detailed outcrop studies in Morocco and Nova Scotia. The research provides new insights into regional basin tectonostratigraphic evolution, sediment fill, and reservoir distribution, architecture and quality at a range of scales. Regional seismic profiles, supported by key well data, indicate the presence of post-orogenic collapse basins, focused narrow rifts and low-magnitude multiple extensional depocentres. Significantly, Permo-Triassic basin geometries are different and more varied than the overlying Jurassic and younger basins. Provenance analysis using Pb isotopic composition of detrital K-feldspar yields new and robust controls on the sediment dispersal patterns of Triassic sandstones in the NE Atlantic margin. The evolving sedimentary architecture is characterized by detailed sedimentological studies of key outcrops of age equivalent Permian–Triassic rifts in Morocco and Nova Scotia. The interplay of tectonics and climate is observed to influence sedimentation, which has significant implications for reservoir distribution in analogue basins. New digital outcrop techniques are providing improved reservoir models, and identification of key marker horizons and sequence boundaries offers a potential subsurface correlation tool. Future work will address source and seal distribution within the potentially petroliferous basins.

Location The upper flow units of the North Mountain Basalt Forma tion extend in continuous exposure for 124 mi (200 km) along the Bay of Fundy. The massive lower unit is exposed at several places along the escarpment face of the North Mountain cuesta, and continuously along Saint Mary's Bay (Fig. 1). The five stops described here center on the remarkable exposures near Scots Bay and along the North Shore of the Minas Basin, where structuraland stratigraphic relations are well displayed. Stops are situatedon the Parrsboro and Wolfville 1:50,000-scale map sheets 21-H8and 2 i-Hi, National Topographic System, available from the Canada Map Office, 615 Booth Street, Ontario K1A 0E9. The Geology Map of The Cobequid Highlands (sheet 2), and the Geological Highway Map of Nova Scotia (Bujak and Donahoe,1980) both available from the Nova Scotia Department of Minesand Energy, Halifax, are useful for locating optional sites. Caution. The tidal range of the Bay of Fundy region attains 50 ft (15 m). Shoreline field studies are severely constrained bythe times of the tides, which vary daily. Consult the publishedcurrent tide tables or daily Halifax newspaper to plan for a dayhaving an early morning high tide. The shore should be vacatedwell before high tide to pass promontories that flood early. North Mountain and Scots Bay Syncline Stop 1 is a road cut and quarry at the base of the ridge,2.5 mi (4 km) north of Sheffield Mills on the road to Glenmont (Fig. 2). Stop 2 is on the intertidal shelf at

Abstract Velocity solutions from 165 airgun-sonobuoy reflection/refraction stations on the continental margin of southernmost South America are presented in 10 seismic structure sections. Also included are an isopach map of Cretaceous and Tertiary sediments (seismic velocities generally less than 4.2 km/sec) in the Magellan, Malvinas, Falkland Plateau, and Falkland Trough basins, and three north-south single-channel seismic reflection traverses of the Falkland Plateau, Falkland Trough, and North Scotia Ridge. The Falkland Trough is a sliver of oceanic crust between the Falkland Plateau and the North Scotia Ridge. The acoustic basement and deep sedimentary layers of the plateau extend beneath the trough and then are subducted beneath the northern flank of the ridge. Movement of the ridge and the plateau toward each other has apparently resulted in the deformation and uplift of the overlying sediments to form the northern flank of the ridge.

Abstract The Nova Scotia and Morocco margins formed within a transition between volcanic margins to the south and non-volcanic margins to the north. We present deep seismic profiles to document the nature of this transition. Profiles on the Nova Scotia margin show two major transitions. The first transition represents a sharp reduction in syn-rift volcanism coincident with major changes in the East Coast Magnetic Anomaly and with the southern limit of the Slope Diapiric Province. The second transition represents a further restriction in syn- and post-rift volcanism leading to exposure of serpentinized mantle or the creation of highly tectonized oceanic crust. This transition is marked by highly extended and faulted continental crustal blocks. Revised plate reconstructions show similar transitions along the Moroccan margin. The southern transition occurs at a major change in the West Africa Coast Magnetic Anomaly and the southern limit of the Morocco Salt Basin. The second transition occurs at a major basement high (Tafelney Plateau), which is considered a high relief accommodation zone and contains highly extended faulted crustal blocks similar to those in a conjugate position off central Nova Scotia. This transition marks a major change in rifting asymmetry and separates the margins into two fundamentally distinct segments.

ABSTRACT The Tompkins Hill Gas Field, located in Humboldt County, California, is the only producing field in the Eel River Basin. The field is an anticlinal flexure on the north limb of the Eel River Syncline in the central onshore portion of the basin. The Tompkins Hill anticline is doubly plunging, open, and trends east-west. Stratigraphic units present in the field include the Yager, Eel River, Rio Dell, and Scotia Bluffs Formations. The Yager occurs below a major unconformity, and forms economic basement. Overlying strata of the Eel River, Rio Dell, and Scotia Bluffs Formations represent a progradational basin-fill sequence including submarine fan, slope, shelf, and littoral deposits. The primary productive interval in the field is within the middle of the Rio Dell, and consists of interbedded fine sandstone and mudrock. Portions of the Eel River and upper Rio Dell Formations are also productive.

Abstract The continental margin south of the Grand Banks (Fig. 1) is of transform origin and formed by shearing between the African and North American plates. It traces the northern limit of these plate motions. Its age is Early-Middle Jurassic in the northwest where it joins the rifted Nova Scotian margin and Early-Middle Cretaceous at its southeastern terminus. The northwestern segment of this margin (see geological map and Fig. 1) is similar to the adjacent rifted margin off Nova Scotia. The salt diapirs which form the Sedimentary Ridge Province continue northward from that rifted margin, and are present in the northwestern part of the transform margin. A thick sequence of Mesozoic-Cenozoic sediments are present in the South Whale Sub-basin, where stratigraphy and depositional environment is similar to that of the sediments on the Nova Scotia rifted margin. Thus, the junction between the Nova Scotian rifted margin and this transform margin is complex and diffuse. It is only southeast of the South Whale Sub-basin that the geologic style of margin typifies transform tectonics, and the transect crosses the margin in this region. Continental basement beneath the southern Grand Banks comprises rocks of the Meguma and Avalon terranes of the Appalachian Orogen (Hatcher and Williams, 1983). The detailed geology of these terranes is obscured by the overlying Mesozoic-Cenozoic sedimentary cover. Thus the Avalon zone is simply depicted as continental crust on this transect. The boundary between the Avalon and Meguma terranes is defined by the Collector Anomaly (Haworth, 1981), a positive gravity

Abstract Over the past decade, discoveries of super-giant, multibillion barrel presalt oil fields in Brazil’s offshore basins and related discoveries in its African conjugates highlighted the great importance of synrift/prebreakup fluvial-lacustrine successions to the success and efficiency of their petroleum systems. Improvements in seismic acquisition and processing technologies were keys in imaging the architecture of the underlying rift basins, and interpreting the basin fill and internal depositional facies later confirmed by drilling. Middle Triassic to Early Jurassic synrift basins are exposed onshore eastern North America and extend into adjacent offshore areas, including equivalent basins in Northwest Africa. Organic-rich lacustrine successions occur in a number of the U.S. basins and although no commercial discoveries have been made, hydrocarbon shows in outcrops and wells confirm that a working petroleum system exists in virtually every basin. The basin-fill model for these extensional basins’ sedimentary successions defines four tectonostratigraphic (TS) units. In the Fundy-Chignecto rift basin complex, TS I is an unconformity-bounded, early synrift fluvial-eolian sequence of Late Permian age. TS II is a dominantly fluvial (with some lacustrine) sequence believed representative of an underfilled, hydrologically open basin (subsidence < sedimentation). This is followed by either a closed basin or one in hydrological equilibrium (subsidence ≥ sedimentation) dominated by lacustrine (TS III), and later playa/lacustrine (and basal CAMP volcanics) successions (TS IV). The climate sensitive lacustrine facies—especially in TS III—are exquisite recorders of paleoclimate, and with paleomagnetic data refine the determination of the basins’ age and paleolatitudinal positions. Seismic profiles in the Fundy-Chignecto (Canada) and Newark (USA) basin reveal high-amplitude, laterally continuous reflections adjacent to the respective border faults. In the Newark basin, these are calibrated against academic and industry wells revealing a correlation with large scale climatic cycles and lacustrine facies in TS III. In both basins, similar reflections are observed in the undrilled distal portion of TS II fluvial successions and are interpreted as indicating similar lacustrine successions. This architecture departs from the original TS II model (subsidence < sedimentation) by inferring high levels of tectonically driven extension resulting in the basins being closed from their inception (subsidence ≥ sedimentation) thus facilitating lake formation. During TS II deposition (approximately Late Anisian to Early Carnian), paleomagnetic data positions these basins within the north equatorial humid belt. This is a favorable setting for the evolution of lakes; i.e. , elevated precipitation coupled with tectonic extension, and most importantly, under conditions for organic matter creation and preservation. If correct, this interpretation would have a significant impact on the potential for hydrocarbons sourced from Late Triassic lacustrine successions in presalt synrift basins offshore Nova Scotia and Morocco. Importantly, a potential new oil-rich resource play may exist beneath the shallow waters of Chignecto Bay. In the deep water portion of the offshore Scotian basin, presalt synrift basins having similar lacustrine source rock potential may also exist.