Abstract Seaward dipping reflector or SDR complexes comprise piles of individual basaltic flows and interbedded sediments that are thought to have formed subaerially at the flanks of tholeiitic shield volcanoes like those in the Afar or at larger magmatic complexes like Iceland. During the rift process, these flows subsequently acquire very steep true dips (up to 25°) almost always in the seaward direction. Past explanations for the acquisition of these dips involve progressive burial, loading and flexure by subsequent flows ( e.g ., Pálmason, 1980 ), or listric, landward-dipping faulting and magmatic dilation ( Geoffroy, 2005 ). These factors no doubt play a role, but we feel that such models fall short of a full explanation by exceeding reasonable amounts of flexure and the amount by which huge blocks of continental crust can rotate by faulting alone. Such models also do not provide an explanation for how the topmost SDR layer subsides rapidly to the depth of normal oceanic crust as the latter begins to form, a problem that has been apparent since Mutter et al . (1982) and Hinz (1981) . Here, we present and discuss some of the main observations visible in long-offset, depth imaged seismic reflection records of SDR complexes at magma rich passive margins and propose a new but simple magmatic evacuation model for their production. Having conducted a global review of seismic data imaging SDR complexes, we present a line from the southern Brazilian margin to serve as a template example that shows most of the important criteria worldwide. After identifying the main observations, we propose a simple model of magmatic evacuation, similar to salt or mud evacuation in sedimentary sequences, to explain the observations. We hope that this simple proposal will spawn new avenues of research to refine and support the general model.

Abstract Deep seismic data that have been shot across the world’s passive margins make us reflect that much of the subsidence that post-dates major rifting and continental separation is not thermal in origin, but structural, associated with the localization of extensional displacement on a major fault or shear zone along the subcontinental Moho. Displacement surfaces of this kind have been called ‘exhumation faults’ ( Manatschal et al ., 2007 ),‘detachment faults’ ( Manatschal and Lavier, 2010 ; Reston and McDermott, 2011 ), and ‘outer marginal detachments’ (Pindell et al ., in prep., and this meeting). On non-volcanic margins they may exhume the Moho at the sea bed; on volcanic margins they may represent magma welds (Pindell, this meeting). We believe that the subsidence is structural collapse of the upper part of the continental crust. On volcanic margins it is probably associated with the pinching out (boudinage) of the Lower Crust so that the Upper crust effectively collapses onto the mantle. On volcanic margins with SDRs, the collapse of both the continental edge and the lava flows (SDRs) that overlie it may be due to accommodation space being created along an evacuating magma weld. We believe that this sort of collapse is rapid, far quicker than thermal subsidence, and attempt to support the idea by examples from the Gulf of Mexico, Brazil, the Alps, and the Red Sea. The recognition of rapid collapse is not new. It is well described in classic stratigraphic literature in the Alps and elsewhere. Here we argue that its occurrence is extremely widespread, but is commonly overlooked.

Abstract A simple geometrical explanation is provided for the distribution of the well-known architectural zonation across fully developed magma-poor margins (e.g. , limited crustal stretching, extreme crustal thinning, exhumed mantle, ultraslow or normal “Penrose” oceanic crust). This zonation is observed along the lengths of many margins on the super-regional scale. Diachronous development of the oceanic crust, younging towards the rift tip, indicates that at the plate tectonic scale break-up occurred on these margins by rift propagation. At the local to regional scale propagation occurs by progressive opening of segments. Because the relative motion of crust adjacent to a rift segment can be described by an Euler pole, the local linear plate separation rate can be interpreted as a function of distance to that pole. In turn, plate separation rates influence the architectural zonation and ultimately the degree of melt generation. Within each rift segment, the rift tip propagates by “unzipping” the hyperextended continental crust. A stepwise migration of Euler poles must occur in order for a large continent to break up, leading in turn to faster linear rates and attendant melt generation/oce-anization at margin segments that have become more distal. Although this conceptual rifting model primarily explains magma-poor rift architecture, it may also apply to magma-rich margins. The latter may form when continents break apart at a high extension rate following rapid propagation (e.g. , a long-distance pole jump). Both rifted margin types can be viewed as end members of the same process, firmly rooted in geometric requirements of plate tectonics.

Abstract There are many publications describing a thermal gravity anomaly associated with young oceanic crust at mid-ocean ridges. This anomaly is due to lateral density changes in the lithosphere resulting from temperature variations within the asthenosphere. The amplitude of this thermal Bouguer gravity anomaly can be as large as-300 milliGals at the location where new oceanic crust is formed and is easily observed in the gravity data. A detailed gravity model extending from the West African Craton across the Mid-Atlantic Ridge clearly shows this thermal gravity anomaly and its lateral extent. The model also clearly shows that there is no evidence of a thermal gravity anomaly at the rifted continental margin of the Kwanza basin, offshore Angola.

Abstract The South Atlantic presalt petroleum system has unique elements which are related to the basin bounding structural fabric, accommodation space and climatic conditions. The development of both high total organic carbon lacustrine source rocks and hypersaline/hyperal-kaline microbial carbonates requires sequestration of these basins from marine conditions. Sequestration is accomplished by an outer-high which was isostatically elevated by magmatic under-plating. This magmatic under-plating is occurs along the margin from the Santos Basin to the Espírito Santo Basin and the conjugate Kwanza Basin. Where the outer high is absent, such as in the Brazilian Pelotas Basin and Namibian basins, the presalt petroleum system fails to develop. In Gabon where under-plating and basin sequestration occurs, a Brazilian style presalt system fails to develop due to high clastic influx. Gabon lacks the microbial hypersaline carbonate reservoir. Similar Brazilian style presalt petroleum systems are likely however, to occur on other passive margins where similar structural styles create a sequestered basin. These basins should occur in regions which are transitional from classic volcanic margins to true nonvolcanic margins. Through better understanding of the Brazilian presalt geodynamic setting we can position ourselves to identify new basins with similar petroleum systems which have created the giant Brazilian presalt discoveries.

Abstract Stratigraphic correlations from wells tied to high resolution seismic data offer specific constraints for interpreting tectonic events. Paleogeographic models based on these interpretations can be used to define the paleobathymetry of a basin at specific points in time and space, providing critical constraints on the rifting and subsidence history that are not available from regional structural interpretations. Based on detailed work undertaken to define the play characteristics of the Campos basin, we propose a new subsidence history for the critical presalt to salt transition time. Mapping of the “synrift” to “sag” transitional stratigraphy indicates a significant erosional unconformity at the base salt level across the outer Campos hinge in the southern Campos basin that results in the removal of the uppermost presalt section and portions of the underlying coquina section. We propose that this erosional unconformity truncates presalt stratigraphy where the basin has undergone short wavelength differential subsidence due to ductile extension within the lower crust. The uppermost presalt interval is therefore a late synrift deposit, as opposed to postrift “sag” infill of accommodation created by thermal relaxation of thinned crust. Well correlation within a sequence stratigraphic framework has identified three regionally correlative flooding surfaces and corresponding sequences within the coquina section that can be mapped with good confidence on 3D PSDM data, and extend across the hinge. These indicate a broad, shallow-water lacustrine depositional environment for the coquina and provide an upper limit on the age of differential subsidence. Halokinetic sequences seen in the postsalt section in the Campos basin imply that the original salt thickness was significantly greater downdip of the hinge, which required that enhanced subsidence occurred no later than the end of salt deposition, providing a lower limit on the age of differential subsidence. Our interpretation of subsidence localized at the Campos hinge by extension expressed within the ductile lower crust of the Campos basin is supported by deep seismic imaging that places the zone of maximum crustal thinning, defined by an abrupt shallowing of the Moho reflection, beneath the hinge zone. The localization of extension and subsidence creates a monocline that is subject to erosion just prior to evaporite deposition in the Campos basin. The differential subsidence across the hinge provides the accommodation for thick evaporites in the outer Campos basin, while the inner Campos basin has only thin evaporite deposits due to the lack of accommodation.

Abstract It is widely known that, in order to model tectonic processes accurately, 3D approaches are required. However, due to the greater numerical challenges and much enhanced costs, most commercially available software packages only offer two-dimensional or “pseudo three-dimensional” (2.5-D) applications to simplify the underlying mathematics. In the 2.5-D approach, the third dimension is generally created by a mere orthogonal projection of a single section in two directions at a certain distance from its original position. Yet, despite creating a 3D space, lateral variations in the subsurface are ignored and the resulting model often remains an oversimplification that often does not represent natural observations. A particular problem is given in sedimentary basins containing salt. The fluidlike behavior of salt over geological times requires true 3D models to allow for in- and out-of section salt flow and to preserve both the salt mass and its volume. None of this can be achieved in 2D or 2.5-D, respectively. Evaluation of evolutionary models derived from 2D restoration must therefore consider the associated geometric simplifications.

Abstract Oceanic core complexes are generally recognized at ultraslow, slow, and intermediate rate spreading centers at mid-ocean ridges and back arc basins by their domal morphology and/or corrugated surfaces. Oceanic core complexes may comprise more than 50-60% or more of some spreading centers. Although oceanic core complexes are less accessible for direct observations of detachment faults when compared to continental core complexes, there are several advantages for understanding the origin and evolution of core complexes. They represent new mafic oceanic crust and mantle lithospheric components that result from upwelling asthenosphere, they have no complicating preexisting structural history, the detachment faults and domal structures of the core complex are subject to little erosion and masking by sedimentary deposition post formation (which could obscure the structure of the basement detachment surface), and they can be placed in the context of the ridge morphology and depth, basement surface samples collected, and magma supply associated with the particular spreading center. An attempt is made to bridge the gap between continental core complexes and oceanic core complexes in a way that may have significance in our understanding of ocean-continent transitions that may contain mixtures of oceanic crustal, serpentinized mantle, and continental basement types. These basement types could commonly be obscured by thick sedimentary prisms and acoustic and density uncertainties. Considered are: the range of expression of spreading center core complexes, variations in the nature and composition of footwalls and hanging walls associated with core complexes, the extent of rotation of oceanic detachment faults documented, the role of magmatism in core complex development, fluid rock interaction during development, the role of serpentinization in obscuring the definition of mafic oceanic crust and MOHO, the extent of strain localization, variation in the scale of spreading-center-parallel lateral extent of core complexes, the lateral and slip-parallel extent of mantle exhumation on various detachment faults, lateral variation of slip along single detachments, variations in slip amounts among oceanic detachments worldwide, the obscuring effects of rafted or rider blocks in delineating the full extent of detachments, the mechanisms of initiation and termination of core complexes, and the correlations of core complex development with ridge depth and overall magma supply. Finally, modeling results based on mantle composition and magma supply controls on core complex development are assessed.

Abstract Definition of the opening histories of most of the world’s oceans continues to improve. Some improvements concern the drift (sea-floor spreading) history and stem from better resolution of oceanic fracture zones and magnetic anomalies, whereas other improvements concern the rift history and implications for initial conjugate continental reconstructions as provided by new or improved seismic data collected at continental margins. This work addresses two issues. First, it identifies several aspects of Atlantic opening history that affect the early opening kinematic framework between North and South America, showing that (1) the Yucatan Block must have rotated during the Jurassic evolution of the Gulf of Mexico, and (2) that the older elements of the Caribbean plate must be of Pacific origin. Second, it highlights the predictions made for slab subduction beneath northern South America as a result of Atlantic plate kinematic history and the Pacific origin model for Caribbean evolution. It is seen that there is good correlation between these predictions based on plate kinematics and the observed existence of subducted slabs beneath northern South America via passive seismology and mantle tomography.

Abstract We discuss results from a large-scale investigation of the southeastern Caribbean (CAR) plate boundary conducted in Venezuela and the Leeward Antilles by Venezuelan and U.S. scientists. The project, known as BOLIVAR in the U.S. and GEODINOS in Venezuela, included offshore reflection, onshore-offshore wide-angle reflection/refraction profiling, teleseismic body and surface wave tomography, structural geology, and geochemistry. The various types of seismic imaging of the crust and upper mantle in northern South America provide a number of important constraints on the evolution of the Caribbean-South American plate boundary, and identify substantial modifications to crust and upper mantle structure of coastal South America resulting from plate boundary tectonics. As the Atlantic subducts, the southern end of the descending slab applies a load to the adjacent South American lithosphere, depressing the South American lithosphere and providing space for the leading edge of the Caribbean to overthrust northern South America. This has a number of consequences that extend from the surface to the base of the lithosphere: (1) As suggested by others, the descending Atlantic tears from the SA continental margin, producing an isolated nest of intermediate depth earthquakes. This lithospheric tear is associated with, but offset from the eastern end of the South American-Caribbean strike-slip fault boundary. (2) Lithospheric flexure at the South American coast creates space to accommodate overthrusting of South American passive margin deposits and Caribbean island arc and prism terranes, aiding in development of the coastal mountain belts and exhuming HP-LT rocks. (3) Flexure and overthrusting deepens the South American Moho to ~50 km in northeastern Venezuela, and over thrust terranes occupy the upper 25-50% of this thickness. (4) The depressed South American Moho is substantially offset (~15-20 km deeper) from that of the adjacent Antilles arc terranes. (5) Lastly, the subducting Atlantic plate viscously removes the base of the South American passive margin continental lithospheric mantle at least 100 kilometers south of the plate boundary and destabilizes the continental lithosphere farther inland, triggering convective instabilities in the lithosphere south of the plate boundary. Once subduction has migrated eastward from a given point along the margin, the load caused initially by Atlantic subduction is removed, allowing the crust to rebound, shallowing the South American Moho, reducing the Moho offset between coastal South America and the offshore terranes, and enhancing erosion of accreted terranes. We observe that the continental lithosphere west of the subduction zone is thinner than expected between the Guayana shield and the plate boundary. We hypothesize that the subducting Atlantic has viscously removed the mantle lithosphere beneath the South American continental margin and destabilized the lithosphere farther inland, everywhere west of the current subduction zone. Although modulated by the paleogeography of South America and preexisting lithospheric structures on both the South America and Caribbean plates, this simple time transgressive model of subduction, lithospheric loading, flexure, and viscous removal of mantle lithosphere can account for much of the lithospheric structure of northern South America as far west as the Boconó Fault. Development of the Boconó and Santa Marta-Bucaramanga faults has added an additional layer of tectonic complexity in western Venezuela in the past ~10-20 m.y. that overprints, but does not completely destroy, the effects of the migrating Atlantic subduction zone.

Abstract The Cretaceous passive margin deposits of Colombia form part of northern South America’s most prolific hydrocarbon system, which highlights their source rocks as high-potential, self-sourced to hybrid Unconventional resource plays. This succession is characterized by thick and laterally extensive Type II(S)/III shales and carbonates of the Lower Cretaceous Basal Carbonates ( sensu lato ) and Upper Cretaceous Villeta/Gachetá/La Luna/Navay formations, the latter group being broadly coeval with the Eagle Ford Formation of North America. Unlike the Eagle Ford, however, the Colombian basins’ world-class source rocks experienced a subsequent complex tectono-stratigraphic evolution, which can either complete and enhance exploration and commercial viability or detract from it. Basement-involved shortening in Colombia’s supra-subduction zone setting provided the regional framework for these basins to form and has a first-order control on key petroleum system elements and ultimately the location and size of unconventional sweet spots on the play scale. While many of Colombian onshore basins have been Conventionally explored and produced for nearly a century, the understanding of their source rock systems and how they will perform as unconventional plays, is still emerging. In this setting, three key regional evaluation methods that can help to predict resource play behavior are: Unraveling younger structural activity and its superposition on Cretaceous paleogeography using palinspastic plate reconstructions to constrain original gross depositional environment and identify source rock accumulations of the highest quality and net thickness; Understanding the areal and temporal interplay between source rock maturation and deformation or uplift; and Examination of stress regime evolution, natural fracture networks, and the present-day stress field in order to properly plan and execute drilling and hydraulic fracturing. In conjunction with these geologic factors, which ultimately impact static properties of the unconventional reservoir, source rock maturity and correlative fluid properties exert an additional control on dynamic reservoir performance and in combination dictate well estimated ultimate recovery (EUR) volumes. Although many of the Colombian basins contain correlative Cretaceous source rock packages, they are unique in terms of their depositional environments, structural history, and degree of thermal maturation. The Cretaceous of Colombia’s various present day basins are situated in different original parts of the broad, northwest South American passive margin, at varying water depth, nutrient supply, and seafloor morphology, and the Tertiary orogenic history has caused different degrees and timing of sedimentary burial and overthrusting of those sections. Regional palinspastic reconstructions illustrate paleogeography at the time of deposition and help to constrain localities of concentrated, high-TOC facies, as shown by an example of Colombia during the Early Turonian (Fig. 1) . A transgressive surface marks the transition from Late Cenomanian to Early Turonian, and depositional systems step landward leading to the Cretaceous maximum flooding surface (MFS). Figure 1. Palinspastically restored paleogeographic map of the Colombian basins at ~92 ma, Early Turonian ( Kennan and Pindell, 2009 ; Pindell and Kennan, 2009 ; Tectonic Analysis, Ltd., 2009 ). The Early Turonian is a regional condensed section through all the marine sections of Colombia and western Venezuela, characterized in some areas, notably the Upper Magdalena Valley, by a phosphatic deposit about 10 cm thick. This horizon contains phosphate pebbles up to 3 cm diameter and shows various trace and major element abundance peaks. The time interval over which this phosphatic lag was deposited is presently impossible to evaluate. The Early Turonian condensed section is also expressed as a couple of concretion intervals associated with abundant and diverse fauna, which appear seismically as a pair of high-amplitude reflections within the Cretaceous, and which can be used to locate the underlying Cenomanian lowstand deposits. In the Putumayo basin, this transgression may be represented by Upper Villeta facies that are more argillaceous (deeper water) than the underlying Lower Villeta. Alternatively, the Upper Villeta may record the arrival and eastward migration of a peripheral bulge ahead of converging allochthonous terranes or local enhanced uplift and subsidence events associated with plume-related mafic intrusions. The Early Turonian in many places ( e.g ., the Villa de Leiva and Cocuy regions) comprises deeper water facies above shallow-water sandstones or limestones of the Caliza Mermetti. Formation boundaries have been introduced in the literature where this change is obvious. However, although the Caliza Mermetti is regionally extensive, it is laterally discontinuous, and in some regions Early Turonian and Cenomanian shales merge and just one stratigraphic name and age is assigned to both. This has produced nomenclatural correlation problems and misjudgments in sedimentation rates, which in turn have lead to incorrect propositions of large thickness changes in the Upper Cretaceous (growth structures) and unnecessary calls for tectonism at this time ( e.g ., Sarmiento et al ., 2006; Vásquez and Altenberger, 2005 ). The Early Turonian facies are very similar to Late Albian facies, and can easily be confused in the field. Paired with paleogeographic maps of the same interval, stratigraphic cross sections can highlight the diachronous nature of the Cretaceous deposits (Fig. 2) , which are controlled by the regional tectonic configuration. Stratigraphic cross sections do not show the areal and regional distribution of facies but rather a temporal framework for deposition. The section begins with basement and initial rift sediments that then get transgressed by the Cretaceous systems. The base of the section shows the Caqueza Group and equivalent units containing abundant turbidites (basin floor fans, channel-levee systems, and classical turbidites). This unit is prograded across by a shallow-water sandstone, the Caqueza sand, and then transgressed by a regionally extensive surface, the base of the Villeta Group in the Eastern Cordillera. Figure 2. West to East sequence stratigraphy slug diagram of Jurassic-Cretaceous Formations of the Middle Magdalena Valley, Eastern Cordillera, and Llanos Basins (from Villamil and Pindell, 1998 ). The Hauterivian-Barremian boundary at the base of the Villeta cannot be traced to the Upper Magdalena Valley but can be recognized in the Villa de Leiva region as the base of the Paja Formation. The Late Barremian contains abundant calcareous concretions rich in ammonite assemblages and represents a relatively condensed interval. The Aptian stage includes turbidites of the Socotá Formation in the central portions of the Eastern Cordillera and shallow-water facies to the east, near the Llanos. The Albian is represented by the Hilo Formation and its coeval Une Formation to the east. The Middle Albian is a major condensed section that can be recognized regionally in Colombia. The Cenomanian stage is a general regression and a sequence boundary during the Late Cenomanian. Facies of this age are called Une in the eastern portions of the Eastern Cordillera and they are unnamed in the central and western parts. Above the Late Cenomanian lowstand, there is a transgressive surface followed by deposition of the La Frontera Formation condensed section (see Villamil and Arango, 1994). The early Turonian MFS (see also Fig. 1 ) is represented in the Llanos by relatively shallow-water facies rather than distal offshore shales, hemipelagic limestones, and calcareous concretions. This unit is called Chipaque and by many other names in different regions of Colombia. This Cretaceous MFS is prograded over by Cretaceous depositional systems (low-order highstand systems tracts). The first units to prograde over it are some unnamed shales of the Villeta (La Frontera and others), then siliceous shales at the top of the Villeta that are correlative to the Olini, Conejo and other units, and finally by the shallow-marine sandstones of the Guadalupe and coastal plain deposits of the Guaduas Formation. Plate interaction and tectonic history from Upper Cretaceous to Present day exerted the primary control on source rock maturity through combinations of regional burial, exhumation, and structural activity (Fig. 3) . Contemporary foredeep maturation developed farther from the original thrust fronts, as a function of burial and outward propagation of younger thrust faults. In the Lower Magdalena Valley, the San Jorge and Platorifts were deep enough to host maturation within them, but the Plato was uplifted in the Pliocene and maturation was arrested. Figure 3. Map of Present-day maturation and migration ( Kennan and Pindell, 2009 ; Pindell and Kennan, 2009 ; Tectonic Analysis, Ltd., 2009 ). Cauca Valley sedimentation is now sufficiently thick to have resulted in at least local maturation of Cretaceous and early Tertiary source rocks, if they are present. The Sinú Belt has been thickened via ongoing sediment accretion to the point of driving maturation within it. Although some are by now passed their prime in terms of maturation potential, the greatest number of areas within Colombia presently have active, ongoing maturation. Turonian source-rocks are under mature in the Upper Magdalena Valley, while they are mature in the Eastern Cordillera. The reason for this difference may be the thicker initial overburden of the Eastern Cordillera compared to that of the Upper Magdalena Valley. Detailed 3D basin modeling on the Middle Magdalena Valley ( Figs. 4 a, b) suggests that present day burial depth is a proxy for maturity, but it is the regional-scale tilting and differential uplift and erosion of the basin between the Central and Eastern Cordillera, as well as smaller-scale structural activity, that ultimately dictate source rock maturity through time. Figure 4A, B. Oblique view of 3D basin modeling results for the (A) La Luna Formation and (B) Tablazo Formation in the greater Middle Magdalena Valley. Colors show predicted presentday maturity, and contours are derived from regional depth structure maps.

Abstract Recent discoveries in Cretaceous presalt basins of the South Atlantic have brought industry’s attention to a new deep-water play on the conjugate margins of South America and Africa. Some of the key factors impacting exploration success in rifted basins are: basement composition, compartmentalization, and subsidence history. Definition of the continent-ocean boundary and configuration of the passive margin are generally inferred from the extent of identified oceanic magnetic anomalies, paleo plate reconstructions, and presence of evaporites. In the absence of magnetic lineations on oceanic crust during the “Cretaceous quiet period,” the margin configuration at the onset of oceanic spreading in the Atlantic is open for debate. The Equatorial Atlantic Transform Margin was dominated by shear deformation due to adjustment in relative plate motions during separation of North American and African plates to the north and South American and African plates to the south. Rifting along the passive margins adjusted to variations in spreading rate, mantle thermal structure, and rift geometry. To reveal the original basin shape, filtered Bougüer gravity and seismic reflection data were used and aided by modeling of South Atlantic opening. This approach provided boundary conditions for original basin shape and limits of extended continental crustal.

Abstract The West Africa Equatorial Margin has recently become a focus area for petroleum exploration, because of recent material success in the deep-water Cretaceous clastic play. The discovery of the Jubilee Field in 2007 has been the catalyst for more intense exploration scrutiny, and the Tano basin has yielded a number of new discoveries. The Tano basin, located on the equatorial margin off the south coast of Ghana, is a prolific petroleum province defined by the Romanche fracture zone to the southeast and the St. Paul fracture zone to the northwest. The break up on this portion of the south Atlantic, of which the Tano basin is a part, initiated during the Aptian. A series of rift basins developed, eventually connecting to the evolving South Atlantic Ocean. Each of the rift segments has a unique structural and depositional history characterized by the interaction of pull apart and lateral shear motions of rift and transform boundaries, respectively. Asymmetrical rifting dictates alternating narrow and wide margins and, as a consequence, has an enormous influence on the petroleum potential of the basins being created. Deposition of turbidites began during the early drift phase (Cenomanian-Turonian) and continues to this day. Early Cretaceous source rock deposition was strongly influenced by synrift tectonic activity while the postrift marine source rocks were primarily controlled by global oceanic anoxic events. The environments of deposition for these source rocks are evident in the molecular composition of discovered hydrocarbon fluids in the Tano basin and are testimony to the complexity and differentiation between each different basin along the margin. The quality of discovered fluids is further controlled by maturation, migration, and reservoir transformation.

Abstract As Offshore Nigeria enters a third decade of deep-water exploration, unsuccessful wells in the structures of the deep-water Outer Fold and Thrust Belt have spurred a reevaluation of plays in the regional basin. Key lines from a newly-acquired seismic data set having 10 km long-offset, deep-tow acquisition parameters, and modern PSDM processing are examined here and show significant improvements in deep imaging. The interpretation of these lines advances the understanding the Paleogene Akata Shale and structural styles of mobile shale features and focuses new attention towards exploration leads of older sediments in intermediate water depths of the Inner Fold and Thrust Belt. The data show a clearer imaging of crustal structure, and the interpretation of the Tertiary supports the view of the offshore Nigeria as a linked extension to a contraction system driven primarily by gravity spreading. The Inner Fold and Thrust Belt of deep to intermediate water depths has been difficult to image in past data sets showing only thick sections of seismically opaque facies commonly interpreted as shale ‘diapirs’ and only thin sediments. Deep tow data here reveals several deep areas of stacked thrust sheets, within the Paleogene strata, as well as associated floor and roof detachments interpreted throughout the delta. The formation of these ‘duplexes’ uplifted existing Neogene thrusted sediments and folded these sediments often to very shallow depths where they are eroded near the present-day water bottom. Improved resolution of the lower Miocene and Oligocene sediments shows a robust deposition of these sequences that are involved in the inner belt structuring. The Inner Fold and Thrust Belt shows features that form a variety of hidden, deeper reservoir targets, structures of different timings, and areas where the deeper imbricates of the Akata could provide thickened source rock intervals.

Abstract Coastal exposures of Mesozoic sediments in the Wessex basin and Channel subbasin (southern UK), and the Lusitanian basin (Portugal) provide keys to the petroleum systems being exploited for oil and gas offshore Atlantic Canada. These coastal areas have striking similarities to the Canadian offshore region and provide insight to controls and characteristics of the reservoirs. Outcrops demonstrate a range of depositional environments from terrigenous and non-marine, shallow siliciclastic and carbonate sediments, through to deep marine sediments, and clarify key stratigraphic surfaces representing conformable and non-conformable surfaces. Validation of these analog sections and surfaces can help predict downdip, updip, and lateral potential of the petroleum systems, especially source rock and reservoir.

Abstract A synthesis of the knowledge about the Lusitanian Basin is presented here, focusing on its stratigraphic record, sedimentary infill, evolution, and petroleum systems. Petroleum system elements are characterized, including Palaeozoic and Mesozoic source rocks, siliciclastic and carbonate reservoirs, and Mesozoic and Tertiary seals and traps. Related processes, such as organic matter maturation and hydrocarbons migration are also discussed. The characteristics of these elements and processes are analysed and implications for deep offshore exploration are discussed.