Conjugate Margins

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BASIN-SCALE SALT TECTONIC PROCESSES AND SEDIMENT PROGRADATION IN THE SLOPE AND DEEPWATER BASIN OF THE NORTH-CENTRAL SCOTIAN MARGIN

Adam, Jürgen ¹; Kreszek, Csaba ¹; MacDonald, Cody ¹; Campbell, Clarke¹; Cribb, Jonathan¹; Nedimovic, Mladen ¹; Louden, Keith ²; Grujic, Djordje¹

¹Salt Dynamics Group Department of Earth Sciences, Dalhousie University, Halifax, Nova Scotia, B3J 3J5 , Canada; ²Department of Oceanography, Dalhousie University, Halifax, Nova Scotia, B3J 3J5, Canada

The complex salt deformation styles characterizing the diverse Scotian Basin salt provinces are the result of complex basement topography in the narrow linked rift basins, variable salt thickness, and high clastic sediment input during the Jurassic and Cretaceous. Salt tectonics concepts developed in salt basins around the Atlantic margins cannot be adapted reliably to the Scotian margin. Consequently, the next generation of basin models must investigate the role of the unique basin characteristics including palaeogeography, sediment supply, and rift basin geometry.

Basin-scale seismic sections of the GXT NovaSpan data allow structural modelling and provide the parameter for scaled physical experiments of regional transects of the Laurentian, Abenaki, and Sable subbasins extending from the shelf to the deepwater basin. The Salt Dynamics Group utilizes physical experiments to analyze salt tectonic processes and their interaction with depositional systems. 4D strain data and experiment sections enable mechanical modelling of salt tectonic processes from early post-rift salt mobilization to late post-rift allochthonous salt complexes. Salt tectonic concepts derived from our experiments relate characteristic salt structures to the palaeo-depositional environment and kinematic stages of the basin evolution.

Our study demonstrates that the Scotian salt provinces differ strongly from the salt basins of the Gulf of Mexico and the younger South Atlantic salt basins. Low mechanical coupling of the sediment overburden due to thick original salt in narrow linked rift basins has favored rapid down-building and sediment aggradation rather than progradation in the early post-rift stage. Salt mobilization and basinward salt inflation started in the Laurentian Basin and propagated in southward direction along the margin due to shelf-parallel sediment transport sourced by the Laurentian Fan from the NE. This depositional pattern has led to diachronous salt extrusion shown by southward younging of allochthonous salt complexes in the North-Central Scotian Basin.

40AR-39AR STUDY OF THE FREETOWN LAYERED IGNEOUS COMPLEX (FLIC), FREETOWN, SIERRA LEONE, WEST AFRICA: IMPLICATIONS FOR THE INITIAL BREAK-UP OF PANGAEA TO FORM THE CENTRAL ATLANTIC OCEAN

Barrie, Ibrahim Jorgor¹; Wijbrans, Jan R.¹; Beunk, Frank F.¹; Bertotti, Giovanni¹; Andriessen, Paul A.M.¹; Strasser-King, Victor E.H.²; Fode, Daniel V.A.²

¹VU University Amsterdam and Fourah Bay College, University of Sierra Leone De Boelelaan 1085, Amsterdam, --, 1081 HV, Netherlands; ²Fourah Bay College, University of Sierra Leone, Freetown, Western Area, Private Mailbag, Sierra Leone

The break-up of Pangaea to form the Central Atlantic and its passive margins began in the Early Jurassic. Geo-tectonically, the break-up was notably characterised by the formation of the Central Atlantic Magmatic Province (CAMP), covering once-contiguous parts of North America, Europe, Africa and South America. The Freetown Layered Igneous Complex (FLIC) emplaced within the heart of CAMP and measuring on surface, 65 x 14 x 7 km, is the largest single layered igneous intrusive yet known on either side of the Central Atlantic. Geophysical investigations indicate that the intrusion extends offshore to a depth of about 20 km. Geologically FLIC is a rhythmically layered elongated ultramafic-mafic lopolith divisible into 4 major zones each comprising repeated sequences of troctolitic, gabbroic and anorthositic rocks. A first series of ⁴⁰Ar-³⁹Ar analyses of plagioclases, biotites and amphiboles from zones 1 and 2 yields plateau ages ranging from 196.3 ± 3 Ma to 228.6 ± 6 Ma. Because ⁴⁰Ar-³⁹Ar dates of these minerals represent cooling ages, we interpret these dates as representing a minimum intrusion-age of the Complex implying that its true emplacement age might be somewhat older than 230 Ma. Given that most established CAMP ages revolve around 200 Ma or younger, we hypothesise that FLIC represents a hitherto unknown pre-CAMP magmatic event that might have thermally triggered the initial break-up of Pangaea to form the Central Atlantic. This view is consistent with field-observations that the Complex is cross-cut by predominantly coast-parallel mafic dykes we attribute to the CAMP dyke-swarm.To ascertain the hypothesis, we are currently carrying out additional ⁴⁰Ar-³⁹Ar dating of zones 3 and 4 and the cross-cutting dykes to be followed-up by U-Pb zircon dating to establish, precisely, the true emplacement age of the Complex. References: Barrie, I.J., P.A.M. Andriessen, F.F. Beunk, J.R. Wijbrans, V.E.H. Strasser-King, D.V.A.Fode, 2006, Tectonothermal Evolution of the Sierra Leone Passive Continental Margin, West Africa: Constraints from Thermochronology. Geochemica et Cosmochemica Acta 70 (18): A36- A36 Suppl. S Aug-Sep 2006. Marzoli, A., P.R. Renne, E.M. Piccirillo, M. Ernesto, G. Bellieni, A De Min,1999, Extensive 200-Million-Year-Old Continental Flood Basalts of the Central Atlantic Magmatic Province. Science284: 616-618. McHone, J.G., 2000, Non-plume magmatism and rifting during the opening of the central Atlantic Ocean. Tectonophysics, 316: 287-296. Wells, M.K., 1962, Structure and Petrology of the Freetown Layered Basic Complex of Sierra Leone. Overseas Geol. Mineral. Res. Bull. Suppl., 4, 115 pp.

The break-up of Pangaea to form the Central Atlantic and its passive margins began in the Early Jurassic. Geo-tectonically, the break-up was notably characterized by the formation of the Central Atlantic Magmatic Province (CAMP), covering once-contiguous parts of North America, Europe, Africa and South America. The Freetown Layered Igneous Complex (FLIC) emplaced within the heart of CAMP and measuring on surface, 65 x 14 x 7 km, is the largest single layered igneous intrusive yet known on either side of the Central Atlantic. Geophysical investigations indicate that the intrusion extends offshore to a depth of about 20 km. Geologically FLIC is a rhythmically layered elongated ultramafic-mafic lopolith divisible into 4 major zones each comprising repeated sequences of troctolitic, gabbroic and anorthositic rocks. A first series of ⁴⁰Ar-³⁹Ar analyses of plagioclases, biotites and amphiboles from zones 1 and 2 yields plateau ages ranging from 196.3 ± 3 Ma to 228.6 ± 6 Ma Because ⁴⁰Ar-³⁹Ar dates of these minerals represent cooling ages, we interpret these dates as representing a minimum intrusion-age of the Complex implying that its true emplacement age might be somewhat older than 230 Ma. Given that most established CAMP ages revolve around 200 Ma or younger, we hypothesize that FLIC represents a hitherto unknown pre-CAMP magmatic event that might have thermally triggered the initial break-up of Pangaea to form the Central Atlantic. This view is consistent with field-observations that the Complex is cross-cut by predominantly coast-parallel mafic dykes we attribute to the CAMP dyke-swarm. To ascertain the hypothesis, we are currently carrying out additional ⁴⁰Ar-³⁹Ar dating of zones 3 and 4 and the cross-cutting dykes to be followed-up by U-Pb zircon dating to establish, precisely, the true emplacement age of the Complex.

THE INS AND OUTS OF BUTTRESS FOLDS: EXAMPLES FROM THE INVERTED FUNDY RIFT BASIN, NOVA SCOTIA AND NEW BRUNSWICK, CANADA

Baum, Mark S.¹; Withjack, Martha Oliver²; Schlische, Roy W.²

¹Rutgers University 610 Taylor Road , Piscataway, NJ, 08854, United States; ²610 Taylor Road, Piscataway, NJ, 08854, United States

Buttress folds form in the hanging walls of non-planar normal faults during basin inversion. Slip occurs more easily along the lower, more gently dipping fault segments, whereas the upper, more steeply dipping fault segments act as buttresses, inhibiting slip and causing the hanging-wall strata to shorten and fold. We have determined the geometry of buttress folds using seismic (both offshore and onshore), field, aeromagnetic and DEM data from the inverted Fundy rift basin, Nova Scotia and New Brunswick, Canada. The buttress folds exhibit a variety of geometries. Generally, the hinges of buttress folds parallel the strikes of the adjacent extensional faults. The tightest folds occur adjacent to the most steeply dipping upper fault segments, whereas broader folds occur adjacent to more gently dipping upper fault segments. Away from the steeply dipping upper fault segments, other folds occur as trains of hanging-wall synclines and anticlines, indicating that a detachment level exists at or above the lower, gently dipping fault segments. Other potential detachment levels include evaporite units in the hanging wall. Therefore, many of the buttress folds in the Fundy basin are a combination of buttress and detachment (buckle) folds. Based on kinematically compatible slip vectors on differently oriented segments of the border-fault systems and results of experimental models of oblique inversion, the regional shortening direction during inversion of the Fundy basin was NE-SW. This inversion-related deformation is, at least partially, partitioned into pure-shear and simple-shear components. The fault-parallel buttress/detachment folds accommodate the pure-shear component, whereas left-lateral strike-slip or gently raking oblique-slip faults accommodate the simple-shear component. Thus, the buttress/detachment folds in the Fundy basin do not necessarily indicate the regional shortening direction. Instead, their trends reflect the variable local shortening direction associated with the pure-shear component of the deformation.

4D RIFT ANALYSIS FOR THE JEANNE D’ARC BASIN

Baur, Friedemann¹; Jaur, Chris²; Littke, Ralf³; Wielens, Hans²

¹RWTH Aachen University Institute of Geology and Geochemistry of Petroleum and Coal (LEK), Lochnerstr. 4-20, Haus B, --, 52056, Germany; ²GSC, PO Box 1006, Dartmouth , Nova Scotia, B2Y 4A2, Canada; ³Institute of Geology and Geochemistry of Petroleum and Coal (LEK), Lochnerstr. 4-20, Haus B, Aachen, 52056, Germany

The study provides for the first time a full 4D (space and time) analysis of heat flow-, subsidence-, maturation- and compaction history for the Jeanne d’ Arc basin, located offshore Newfoundland. The Jeanne d’Arc basin is a typical failed rift basin, whose development and burial history is based on crustal thinning processes Therefore, the basin is an ideal place to quantify and verify rift-related processes such as heat flow history depending on the magnitude of the stretching of the crust and other factors. The study compares the results of simulated geological and geophysical processes and their mutual effects for variations of the McKenzie approach, mostly related to the stretching behavior of the upper mantle. These assumptions have been applied to a 4D numerical basin model extending from the Port au Port area in the south to the Adolphus area in the north in the Jeanne d’Arc basin. The model was simulated with a software package PetroMod^®_, developed by Integrated Exploration Systems. Additionally, a special workaround has been applied to simulate not only single rift events but also multiple-sequence rift events. The simulation technique uses an inverse approach with respect to the traditional McKenzie approach and is called advanced McKenzie approach. Based on the known burial history, the tectonic subsidence is calculated by back-stripping and decompaction. In a second step, the stretching factors can be determined by adjusting them to fit the tectonic subsidence. Lastly, the heat flow history can be calculated based on the calculated stretching factors. The 4D regional Jeanne d’Arc basin model uses the results of over 45 individual 1D models (well locations) and calibration data from 61 wells. Thus, the study of the Jeanne d’Arc basin quantifies the impacts of diverse rift- and heat flow scenarios on the basin based on a non-steady-state finite-element simulation.

BASIN, PETROLEUM SYSTEM AND PLAY ANALYSIS IN THE WEST AFRICAN ATLANTIC BASINS

Beglinger, Suzanne¹; Doust, Harry²; Cloetingh, Prof. dr. Sierd¹

¹VU University, Amsterdam De Boelelaan 1085, Amsterdam, Zuid-Holland, 1081 HV, Netherlands; ²De Boelelaan 1085, Amsterdam, Zuid-Holland, 1081 HV, Netherlands

We report on a study of the relationship between tectono-stratigraphic basin evolution and petroleum system development in West African marginal basins between Angola and Cameroon. For this analysis, a novel framework model has been created. The basins have evolved since the Early Cretaceous from a lacustrine synrift, through a transitional hypersaline stage into a postrift, characterized initially by a shallow marine carbonate, secondly by a deep marine and finally a deltaic depositional environment. This history reflects intra-cratonic rifting followed by the creation of the South Atlantic passive margin: all basins considered have experienced a similar tectonic and sedimentary basin evolution. The petroleum systems identified in these basins can be related to common source facies and may be grouped into families or Petroleum System Types (PSTs). Two proven regionally extensive PSTs and two probably local PSTs have been identified. The regionally extensive PSTs are the Lacustrine Synrift PST and the Marine Postrift PST. The probably local PSTs are the Restricted Marine Hypersaline Transitional PST and the Deltaic/Deep Marine Postrift PST. Families of petroleum accumulations (or plays) that characterize these petroleum systems, and which are defined by their reservoir lithofacies and trap type, are also similar in each of these basins.

This group of similar basins therefore demonstrates the close link between tectonic- and sedimentary basin evolution on the one hand, and petroleum system and play development on the other. We call such a group of basins a basin family; one which can be used for analogue purposes in basin studies.

BASIN, PETROLEUM SYSTEM AND PLAY ANALYSIS IN THE WEST AFRICAN ATLANTIC BASINS

Beglinger, Suzanne Elisabeth¹; Doust, Harry¹; Cloetingh, Sierd¹

¹VU University, Amsterdam De Boelelaan 1085, Amsterdam, --, 1081 HV, Netherlands

THE POST-RIFT EVOLUTION OF THE ATLANTIC MARGIN OF NW AFRICA: A NOT-SO-QUIET PERIOD OF EXHUMATION AND EROSION

Bertotti, Giovanni¹; Andriessen, Paul¹; Barrie, Ibrahim¹; Beunk, Frank¹; Ghorbal, Badr¹; Wijbrans, Jan¹

¹VU University - Amsterdam De Boelelaan 1085, Amsterdan, Netherlands, 1081HV, Netherlands

The post-rift stage of passive continental margins is generally characterized by gentle subsidence decreasing through time. Until now, this is also thought for the Atlantic margin of NW Africa and, in particular, the Moroccan and Sierra Leone transects. In the last years, however, absolute ages obtained with a variety of thermochronometers ranging from ⁴⁰Ar/³⁹Ar to Apatite Fission Tracks and (U-Th)/He on apatites have documented fully unexpected vertical movements, incompatible with the simple scheme hitherto accepted. In Morocco, samples from areas considered as stable, such as the Meseta and the Anti Atlas have provided evidence for a stage of Early to Middle Jurassic subsidence followed by exhumation bringing sampled rocks at the Earth’s surface before the late Cretaceous. At this time, relief developed during the exhumation must have been eroded away as shown by the flat and fairly regular basis of the Upper Cretaceous shallow water sediments. In Sierra Leone, the Freetown Layered Igneous Complex was emplaced at depths of at least a few kilometers at 210-190Ma and was then exhumed in a poorly constrained time span possibly in the Late Jurassic. The emerging picture is one where a very large segment of the rifted continental margin elongated parallel to the margin and located several tens of km E of the continent-ocean transition was exhumed during the post-rift evolution. Km-scale exhumation provoked major erosion and production of terrigenous sediments most of which were brought offshore forming the peculiar coarse-grained terrigenous intercalations in the otherwise monotonous succession encountered in the deep offshore.

MESOZOIC SEAFLOOR SPREADING HISTORY OF THE CENTRAL ATLANTIC OCEAN

Bird, Dale E.¹; Hall, Stuart A.²; Burke, Kevin²; Casey, John F.²; Sawyer, Dale S.³

¹Bird Geophysical 16903 Clan Macintosh, Houston, TX, 77084, United States; ²University of Houston, Houston, TX, 77204-5503, United States; ³Rice University, Houston, Texas, 77251-1892, United States

The history of Mesozoic seafloor spreading in the Central Atlantic Ocean includes asymmetric spreading, between Chrons M25 and M0 (154 Ma to 120.6 Ma), and two ridge jumps at about 170 Ma and 160 Ma. We identify and map twenty-two Mesozoic Chrons, including several in the Jurassic Magnetic Quiet Zone (JQMZ), between the Atlantis and Fifteen Twenty fracture zones on the North American Plate, and between the Atlantis and Kane fracture zones on the African Plate. Chron M40 (167.5 Ma) is mapped about 65 km outboard of the conjugate Blake Spur and S1 magnetic anomalies, over the respective North American and African flanks of the ocean basin. Inboard of these prominent anomalies, the conjugate East Coast and S3 magnetic anomalies, are respectively located about 180 km and 30 km inboard of the BSMA-S1 pair. Therefore the ridge jump to the east between BSMA and ECMA anomalies at about 170 Ma theorized earlier is supported by this study. The Width of the African JMQZ is about 70 km greater (22%) than the North American JMQZ. A second ridge jump is suggested by additional, correlatable anomalies over the African flank. Modeling results indicate that this jump occurred between 164 Ma and 159 Ma (Chrons M38 and M32). The ridge jumps can be related to plate interactions as North America separated from Gondwana. It has not escaped our attention that these ridge jumps, especially the latter, could correspond with the opening of the Gulf of Mexico.

PREDICTIVE TRENDS IN SALT MORPHOLOGY DERIVED FROM SYSTEMATIC ASSESSMENT OF MERGED 3D SEISMIC COVERAGE OVER ENTIRE BASINS

Bird, Tim John ¹; Johnstone, David²; Martin, Mark³

¹PGS Reservoir 17 Marlow Road , Maidenhead, Berkshire, SL6 7AA, United Kingdom; ²17 Marlow Road , Maidenhead, Berkshire, SL6 7AA, United Kingdom; ³PGS Exploration, Walton-on-Thames, Surrey, KT12 1RS, United Kingdom

3D seismic data is acknowledged to have significantly increased both drilling success rate and our understanding of the subsurface geology within localised areas of a basin by revealing detailed 3D relationships between structural geometries and stratigraphy which could not be discerned from a grid of 2D cross-sections. In recent years, the computational power and expertise have developed to merge discrete interlacing and overlapping 3D surveys into a single ‘MegaSurvey’ of normalized, contiguous 3D seismic data covering entire basin systems. No such projects yet exist in the Central Atlantic Margin Province. However, we have examined such ‘MegaSurveys’ over basins on both margins of the South Atlantic and from the North Sea with particular reference to the geometries of salt structures developed and their influence over sag-phase sediment deposition. By systematically measuring the spatial distribution and dimensions of all the halokinetic features within the entirety of each basin, we are able to identify general patterns in, for example, wavelength and amplitude, and the ranges and statistical distribution of these parameters. The trends in these attributes appear to be consistent and independent of the tectono-stratigraphic history of the various salt basins, as a result of which each basin exhibits differences in the age and thickness of the salt, along with variations in the age and character of the overlying sediments. The spatial distribution and aspect ratio of salt walls and diapirs are therefore interpreted to result from the inherent physical properties of the salt itself.

The importance of salt movement for hydrocarbon trap formation and as a control on reservoir distribution is well documented, yet drilling results frequently indicate that the dimensions; i.e., the thickness, height and lateral extent of the salt, is often over- or under-estimated. These parameters from several independent and widely distributed basins, give a valuable calibration for examining salt features in other basins.

VARIATION IN PORE CONNECTIVITY WITHIN ABENAKI FORMATION CARBONATE LITHOFACIES, OFFSHORE NOVA SCOTIA

Blissett, Donovan John¹; Butler, Karl¹; Keighley, Dave¹

¹University of New Brunswick 2 Bailey Drive, Fredericton, NB, E3B5A3, Canada

Three-dimensional MicroCT imaging, together with reflected, transmitted and epifluorescence microscopy of samples from the Abenaki Formation (Jurassic), Scotian Shelf, offshore Nova Scotia, have been used to identify different carbonate phases and assess their roles in affecting pore distribution, geometry and connectivity for different carbonate lithofacies.

Twenty-two core chips from six wells, namely Panuke H-08 (depths 3446-3449 m), Demascota G-32 (depths 3424-4049 m), Acadia K-62 (depths 2822-3397 m), Margaree F-70 (depths 3441-3465 m), Albatross B-13 (depth 2511.5) and Panuke IA/1 (depth 4030.5), were examined. These wells with the exception of K-62 and B-13 (situated in the Acadian segment) are located within the Deep Panuke field (Panuke segment). Sampled textures include: biosparite-biopelmictrite with irregular-shaped vugs and micro fractures; sparse to packed biomicrite and biopelmicrite with microstylolites; drusy dolostone-bioclastic dolostone, drusy dolostone with zoned dolomite crystals, calcitic dolomite, sparry calcite; and fractured oolitic grainstone. The samples are assigned to various lithofacies namely skeletal-rich forereef rubble, proximal forereef slope, oolitic grainstone shoals/intershoals and oncolitic backreef.

Our analyses show that calcification and dolomitization processes contribute to the development of pore spaces in various ways, notably whether or not they are fabric selective, the degree of connectivity and the variations between their preservation and or destruction of their original fabrics. These observations support previous work undertaken using enhanced light petrography, fracture and geochemical analyses which showed that porosity of the Abenaki reservoir is mainly controlled by burial dolomitization and dissolution and that fractures are important components of the permeability network for this reservoir.

VARIATION IN CRUSTAL EXTENSION AND ITS IMPLICATION FOR HYDROCARBON HABITAT IN THE DAKAR – RUFISQUE AREA, OFFSHORE SENEGAL

Bottomley, Steven¹; Jeans, Pete²

¹Premier Oil PLC 23 Lower Belgrave Street, London, SW1W, 0NR , United Kingdom; ²PJ Exploration Ltd, 3, The Paddocks, Whiteshoots Hill, Bourton on the Water, Gloucs., GL54 2LS, United Kingdom

This poster postulates that the variation in post-rift hydrocarbon habitat in the Dakar – Rufisque area of offshore Senegal is primarily controlled by the variation in syn-rift crustal extension between different sectors of the continental margin.

It is postulated that, during rifting of the Atlantic in the Triassic – Lower Jurassic, the sector of the Senegal margin between the Rufisque and Cayar Fracture Zones (the “Dakar Compartment”) suffered a higher degree of crustal extension than the sectors to the north and south. As a result, when post-rift sediments loaded the more highly extended crust in Albian – Upper Cretaceous times, the Dakar Compartment subsided more rapidly and accumulated a greater thickness of sediment. The Dakar Compartment was also intruded by basic igneous rocks that are locally exposed onshore.

In Santonian times, North-South directed compression caused major uplift of the rigid, less extended Rufisque High to the south of the Rufisque transform. The Rufisque High subsided little during Senonian – Palaeogene times, in contrast to the Dakar Compartment, to the north.

In the Oligo–Miocene, the Dakar-Cayar-Rufisque area suffered a regional hypabyssal – volcanic igneous event, with far more pronounced intrusion into the shallow section in the Dakar-Cayar area (thinner crust / leaky transforms) than over the Rufisque High. This resulted in a thermally driven inversion of the pre-existing Late Cretaceous and Paleogene basins, which has resulted in the present topographic expression of the Dakar Penisular.

Several basin-scale observations are postulated to be directly related to the compartmentalisation of the margin and the more highly extended crust in the Dakar Compartment:-

Post-rift passive continental margin depositional systems and facies reflect the additional accommodation space. This is most spectacularly demonstrated by the lateral offset, across the Rufisque Lineament, of the Late Jurassic-Early Cretaceous carbonate bank sequence, coeval to that of the Scotian Shelf
Upper Cretaceous source rock bearing sequences are thicker within the Dakar Compartment as a result of the greater accommodation space created over the thinned crust at the time of deposition .
Outboard of the carbonate margin, source rocks are thermally over-mature (within the gas generation window) due to their greater depth of burial and higher heat flow over the extended crust. The same source rocks in the compartments north and south of the Dakar compartment are thinner and geochemical modeling suggests they are marginally mature. The impact of this on hydrocarbon distribution within the study area will be discussed.
The present Dakar Peninsula is a topographic expression of an east-west, thermally driven, Neogene inversion of the Dakar Compartment. The inversion is clearly expressed on offshore seismic data and is accomplished through the contrast in rigidity between the thinned crust under the Dakar Compartment and the adjacent more rigid (thicker) crustal compartments.
The Cayar Dome, an igneous edifice of presumed Tertiary age, is located on the northern accommodation zone of the Dakar Compartment, illustrating its importance as a crustal scale detachment.
Neogene inversion of the Dakar Compartment may have resulted in avulsion of drainage of the Senegal River Basin from the Dakar area southward to its present position, and rejuvenation of the Banjul River.

Syn-rift compartmentalisation of the shelf to deep water sectors of the Senegal margin is postulated to have a profound effect on the petroleum geology, by influencing;

reservoir fairways and facies distribution within the post-rift section
destruction (or preservation) of effective reservoirs (primarily by differential burial and igneous intrusion)
Thickness of source rocks (variation in accommodation space)
Heat flow, and hence, maturity of source sequences

Recognition of these factors can enable the prediction of optimal areas for hydrocarbon exploration through an integrated model of source rock distribution, timing of maturation, expulsion pathways and accumulation in favourable reservoir facies, and improve the prediction of hydrocarbon phase.

OLIGOCENE CANYON AND FAN DEVELOPMENT: THE RESPECTIVE ROLES OF SEA LEVEL AND SEDIMENT DELIVERY IN EVOLUTION OF THE EASTERN SCOTIAN MARGIN

Brake, Virginia¹; Mosher, David ²; Wach, Grant³

¹Dalhousie University Dalhousie University, Room 3006, Life Sciences Centre, Halifax, Nova Scotia, B3H 4J1, Canada; ²Geological Survey of Canada- Atlantic, Dartmouth, Nova Scotia, B2Y 4A2, Canada; ³Dalhousie University, Room 3006, Life Sciences Centre, Halifax, Nova Scotia, B3H 4J1, Canada

The Cenozoic sedimentary section of the eastern Scotian margin is characterized as a progradational sequence incised by canyons, valleys and gullies. These features provide conduits for offshelf sediment transport, slope by-pass and deposition on the continental rise and abyssal plain during periods of low relative sea level. The Stonehouse 3D seismic volume, spanning outer shelf and upper slope terrain of a portion of the modern eastern Scotian Slope, provides an opportunity to study the detailed Cenozoic stratigraphy and modern and buried seafloor morphologies in this critical shelf to slope transition zone. Sequence stratigraphic concepts were applied to the Neogene section of this depth-migrated 3D data set to map the distribution of seismic facies and their bounding unconformities. Several widespread unconformity surfaces were identified and compared to the present-day seafloor. Canyon incision appears to be episodic throughout the Cenozoic section. As with the modern seafloor, ancient canyon systems are fundamental to slope sedimentary processes and sediment delivery mechanisms. Canyon formation requires significant removal of slope material to the deep ocean floor, following which these canyons act as sediment pathways. A particularly widespread Oligocene (?) erosive surface has a complex morphology that is potentially analogous to the modern Sable Gully canyon system that “drains” much of the central and eastern Scotian Shelf through a system of feeder channels and valleys. The implications of repeated canyon formation on the Scotian Slope imply that the residence period of sediments on the slope is geologically short and that preservation potential is confined to periods of canyon fill or local reductions in gradient. Canyon formation on the slope presumably requires significant sea level lowering, so repeated canyon formation raises the question of eustatic versus tectonic controls on sedimentary processes. Given the extent of the Oligocene (?) erosional unconformity, it is suggested that eustatic change alone cannot explain this consequence, thus tectonic inversion on this passive margin may have contributed to sea level lowering.

MIDDLE CENOZOIC DEPOSITIONAL PROCESSES ALONG THE WESTERN SCOTIAN MARGIN

Campbell, Calvin¹; Mosher, David²; Wach, Grant³

¹Dalhousie University Department of Earth Sciences, Dalhousie University, Halifax, Nova Scotia, B3H 4J1, Canada; ²Geological Survey of Canada Atlantic, Dartmouth, Nova Scotia, B2Y 4A2, Canada; ³Department of Earth Sciences, Dalhousie University, Halifax, Nova Scotia, B3H 4J1, Canada

Extensive 2D and 3D seismic exploration data on the deep water margin off Nova Scotia reveals prospective hydrocarbon bearing structures, yet seven recent exploration wells met with only moderate success. The difficulties encountered in finding quality reservoirs reveal that geologic models successfully applied in other parts of the world need to be refined for the Scotian margin. It is the purpose of this study to develop an understanding of margin-scale geologic process relevant to the middle Cenozoic section of the Scotian margin in order to develop appropriate exploration models.

Published studies of the Oligocene to Pliocene geological history of the outer Scotian margin show that canyon incision on the slope and local depositional lobe progradation dominates sedimentation during periods of relative sealevel lowstands. During this same period, development of Antarctic glaciation and opening of Arctic Ocean circulation established North Atlantic oceanic currents that influenced sedimentation on the lower slope and rise. There is also evidence for occasional tectonic activity, presumably due to changes in intracrustal stress, salt migration, and movement along ancient faults. Throughout the Cenozoic, large scale sediment mass-wasting events wield considerable influence over the evolution of depositional systems along parts of the margin.

Preliminary analysis of 2D and 3D seismic reflection data from the western Scotian margin reveals evidence of widespread erosion and associated depositional elements which, through correlation with biostratigraphic data at the Shubenacadie H-100 and Shelburne G-29 wells, are of Oligocene to Miocene age. Here, the geological history of the outer margin records a complex interplay of down-slope and along-slope processes. The relationship of these various processes; sea level change, canyon cutting, contour current intensification, tectonics, sediment slope by-pass and sediment instability, for example, is unknown at this time but is critical, both for understanding the geology of the Scotian margin and how continental margins evolve in general.

TECTONO-STRATIGRAPHIC EVOLUTION OF SALT STRUCTURES AND DEPO-CENTER MIGRATION IN THE ABENAKI SUB-BASIN AND ITS DEEPWATER EXTENSION, OFFSHORE NOVA SCOTIA

Campbell, Clarke Tyler¹; MacDonald, Cody¹; Cribb, Jonathan ¹; Adam, Juergen²; Nedimovic, Mladen¹; Louden, Keith³; Krezsek, Csaba⁴

¹Dalhousie University Department of Earth Sciences, Dalhousie University, Halifax, Nova Scotia, B3H 4J7, Canada; ²Department of Geology, Royal Holloway University of London, Egham, Surrey, TW20 0EX, United Kingdom; ³Department of Oceanography, Dalhousie University, Halifax, Nova Scotia, B3H 4J7, Canada; ⁴Chevron Norge AS, Karenslyst Alle 2, P.O Box 97, Oslo, Skoyen, 0212, Norway

Despite extensive exploration activity on the Scotian Margin, the latest round of drilling has yielded disappointing results. An in-depth analysis of the interplay between salt tectonic processes and sediment input is required to better understand the regional tectono-stratigraphic framework of the Scotian Basin and its individual sub-basins. We are using scaled analogue experiments to simulate coupled salt tectonic processes and depo-center migration in the Abenaki sub-basin and its deepwater extension. Experiments simulate the salt tectonics history from the early post-rift stage to the allochthonous salt nappe formation on the modern margin. The experiments are constrained by sedimentation patterns and rates, original salt basin thickness, and basement morphology deduced from the GXT Novaspan survey and public-domain 2D seismic reflection data.

Seismic interpretation results of the Abenaki sub-basin show a complex salt basement morphology, which includes a mid-basin high implying variable salt thickness in the early post-rift salt basin. Experiment results suggest that the complex basement morphology and variable salt thickness had a strong effect on the initial salt mobilization and early post-rift depo-centers, and that it controlled the pattern of sediment transport from the Jurassic to the Cretaceous. During the Cretaceous, seaward salt extrusion in the deepwater slope of the Abenaki sub-basin created an allochthonous salt nappe system with new mini-basins developing on this secondary source level. Mechanically constrained salt tectonic concepts and seismic interpretation templates deduced from the experiments will aid further seismic interpretation of the Abenaki sub-basin. These concepts will also give insight into how basement morphology influenced salt structure development, and how sedimentation rates and patterns affect depositional styles. This integrated approach will contribute to our understanding on the evolution of the Abenaki sub-basin and how its evolution relates to the timing of adjacent sub-basins on the Scotian Margin.

PETROLEUM SYSTEMS DEVELOPED ALONG THE NW AFRICA OFFSHORE MARGIN: CHALLENGES FACING EXPLORATION & PRODUCTION COMPANIES

Chaney, Alistair John¹

¹Tullow Oil 3rd Floor, Building 11, Chiswick Park, 566 Chiswick High Rd,, London, NA, W4 5YS, United Kingdom

The offshore NW African Atlantic margin extends from northern Morocco to the Guinea Fracture Zone in the south and comprises up to 6km of Mesozoic and Cenozoic silicilastics and carbonates overlying Triassic salt.

The primary source rocks are Albian, Cenomanian and Turonian mudrocks, with lesser contributions from Palaeocene intervals that are thought to have reached marginal maturity in some areas, and restricted Liassic shelfal carbonates. Deep water gravity deposits provide the main reservoirs and include confined canyon systems and unconfined turbidite lobes. Less well explored plays include carbonate reefs and deltaic topsets further up-dip. The most prominent trapping mechanism along the length of the NW African margin is related to halokinesis. Allochthonous salt diapirs and canopies (largely absent from offshore Western Sahara, Senegal, Gambia and Guinea Bissau) have generated proven and unproven traps including sub-salt, salt stock, and supra salt closures. Other trapping mechanisms include tilted fault blocks (some are counter regional faults), stratigraphic pinchout (Banda gas discovery), extensional roll-over folds, and toe trust compressional folding.

The under explored nature of the NW African Atlantic margin provides E&P companies with numerous challenges. The lack of detailed well control makes prediction of sandstone problematic, particularly as many of the canyons appear to be by-pass systems. Where geobodies have been mapped, lack of seismic imaging makes it difficult to differentiate with confidence between prospective sheet turbidite sandstones and reservoir-poor debrites, particularly in the deeper Cretaceous section. Other pitfalls have recently come to light after drilling. These include reef-like morphologies along the carbonate platform break of slope that are possibly contourites of siliceous ooze, and bright seismic amplitude anomalies that are not hydrocarbon filled sands, but low velocity shales.

These challenges are generally prospect specific, but there are further difficulties which relate to the cost of exploration in immature basins. Increasing water depth places restrictions on rig availability, and requires increasingly larger prospects to be considered commercially viable. As the restrictions imposed by the water depth drive companies to explore deeper in the basin it becomes more likely that prospects will be overpressured as they are in other deep passive margins (e.g. Nigeria, Borneo). This will only increase well costs, placing greater pressures on commerciality.

LITHOLOGY-BASED, HIGH-RESOLUTION SEQUENCE STRATIGRAPHIC FRAMEWORK OF LOWER CRETACEOUS, MIXED CARBONATE-SILICICLASTIC SEDIMENTS, ATLANTIC COASTAL PLAIN, EASTERN UNITED STATES

Sunde, Richard A. ¹; Coffey, Brian P. ²

¹Earth Sciences, Simon Fraser University, 8888 University Drive, Burnaby, BC, V5A 1s6, Canada; ²University of North Carolina / N.C. Geological Survey 205 Perry Creek Drive, Chapel Hill, NC, 27514, United States

A lithology-based sequence stratigraphic framework for the Lower Cretaceous mixed carbonate-siliciclastic sediments of the subsurface Albemarle Basin of eastern North Carolina was developed using thin sectioned well cuttings, wireline logs, and 2D seismic. Thin sections were analyzed to characterise lithology, fossil components, depositional facies, and diagenetic events, because the study interval is confined to the deep subsurface in a basin lacking core control. Integration of lithologic data with 2D seismic data and biostratigraphic control allowed regional correlation of major transgressive-regressive events between wells, resulting in the generation of a sequence stratigraphic framework for the onshore basin. Dominant lithofacies include: (shallow to deep): sandstone, skeletal sandstone, variably sandy mollusk packstone/grainstone, siltstone to shale, skeletal wackestone, variably sandy (quartz and glaucony) lime mudstone, and marl.

Comparison of observed facies with cores and wireline logs from the Baltimore Canyon and Southeast Georgia Embayment confirms that many updip sequences consist of upward-shoaling siliciclastic shoreface successions, with basal open shelf mollusk-rich carbonates often marking transgressive events. Basin-scale depositional trends indicate greater accumulation of the carbonate facies in the southern portion of the basin, with increased fine siliciclastic material to the north. This trend may reflect a major siliciclastic point-source in the vicinity of the ancestral Chesapeake region. The depositional and diagenetic models generated provide insight into the facies and reservoir properties in coeval offshore units comprising frontier exploration targets along the Western Atlantic margin of the U.S. and Canada.

COMPARING CONTROLS ON DEPOSITION OF MESOZOIC AND CENOZOIC MIXED CARBONATE-SILICICLASTIC SYSTEMS FROM THE CENTRAL ATLANTIC MARGIN, NORTH CAROLINA, USA

Coffey, Brian P.¹; Read, Fred²

¹University of North Carolina/ N.C. Geological Survey 205 Perry Creek Drive, Chapel Hill, NC, 27514, United States; ²Virginia Tech Geosciences, 4044 Derring Hall, Blacksburg, VA, 24061-0420, United States

Regional lithology-based sequence stratigraphic frameworks constructed across the subsurface of the Albemarle basin of eastern North Carolina (USA) from Jurassic, Cretaceous, and Paleogene time intervals reveal striking similarities within each of these passive margin shelf successions. Studied units were deposited over a broad temporal range at very different paleolatitudinal positions and global climatic regimes.

Previous interpretation of the Paleogene depositional facies successions concluded that deposition was heavily influenced by paleolatitudinal position (subtropical to warm-temperate), oceanographic controls (boundary currents and nutrients), and with the major global transition from greenhouse to icehouse conditions. However, examination of more deeply buried Lower Cretaceous mixed carbonate-siliciclastic strata from the same basin reveals carbonate lithofacies that resemble late Paleogene updip shelf facies and stacking patterns consisting of admixed quartz sands/silts and mollusk-foraminifera dominated skeletal carbonate sands. Deep shelf marls also are comparable. Preliminary analyses suggest that facies similarities also exist into the underlying Upper Jurassic interval.

These observations suggest that while eustasy and climate strongly influence thickness and stacking patterns, the paleogeographic position of the shelf as a promontory exposed to open ocean wave energy and currents plays a major role in facies development through time. This region of the Atlantic margin was subjected to repeated pulses of ocean-derived elevated nutrient levels, similar to the modern palimpsest Carolina shelf. These observations further suggest that boundary currents (cool, proto-Labrador and warm, ancestral Gulf Stream) may have existed and mixed in this study area during Mesozoic times, albeit with lower intensities than observed in late Paleogene-Neogene icehouse conditions.

INTEGRATED RESERVOIR CHARACTERISATION, DEEP PANUKE GAS POOL, OFFSHORE NOVA SCOTIA

Corbett, Norman¹; Uswak, Gordon ²; Skrypnek, Terrance (Terry)²

¹EnCana Corporation EnCana on 9th 150 -9th Avenue PO Box 2850, Calgary, Alberta, T2P 2S5, Canada; ²EnCana on 9th 150 -9th Avenue PO Box 2850, Calgary, Alberta, T2P 2S5, Canada

The Deep Panuke gas pool is the first, significant carbonate reservoir gas discovery on the Scotian Shelf. Development of the pool is currently proceeding. The Jurassic Abenaki Formation-hosted (Eliuk, 1978), lean, slightly-sour gas accumulation was delineated in two rounds of drilling involving seven wells resulting in five successes (Weissenberger, 2006). Well test rates exceed 50 million cubic feet per day per well.

Diagenesis controls secondary porosity development in the Deep Panuke fractured dolostone and associated leached vuggy limestone reservoir (Wierzbicki et al, 2006). Three litho-types were defined in the reservoir characterisation process: non-reservoir unleached limestone, porous vuggy limestone and dolostone. Petrophysical analysis of the wells defines relationships between lithology, porosity, Sw and fracturing for each litho-type. In particular, it has been important to recognize the presence of a bimodal porosity distribution in the High Permeability Reef Front (HPRF) region of the pool which contains 80% of the gas resource. The bimodality is a consequence of the presence of both dolostone and unleached limestone litho-types. Similar reservoir characteristics have been documented at Simonette, Alberta (Duggan, 2004). Neural Net methods were used to integrate the petrophysical results with 3D seismic-derived rock properties, resulting in bimodal low/mid/high case porosity predictions for the HPRF. This multi litho-type approach and aquifer modeling has led to significant improvements in the integrated reservoir characterisation, well test matches and in the static and dynamic reservoir simulation models.

The approved development plan (EnCana, 2006; CNSOPB, 2007) involves subsea tie-back of wells to a new jack-up production field centre and new export pipeline to shore.

References

CNSOPB, 2007, Deep Panuke Offshore Gas Development, Canada-Nova Scotia Benefits Plan Decision Report and Development Plan Decision Report, Canada-Nova Scotia Offshore Petroleum Board (CNSOPB) 108 p., available online at www.cnsopb.ca

Duggan, J.P., 2004, Burial Dolomites at Swan Hills Simonette Reef, West Central Alberta Basin, Can.Soc.Petrol.Geol. 2004 Dolomite Conference, 29 p.

Eliuk, L.S., 1978, The Abenaki Formation, Nova Scotia Shelf, Canada – A Depositional and Diagenetic Model for a Mesozoic Carbonate Platform, Bull. Can. Petrol. Geol., V. 26, No. 4, p. 424-514.

EnCana, 2006, Deep Panuke Development Plan, available online at www.deeppanukereview.ca/publicrecord/index.html

Weissenberger, J.A.W., R.A. Wierzbicki and N. J. Harland, 2006, Carbonate sequence stratigraphy and petroleum geology of the Jurassic deep Panuke field, offshore Nova Scotia, Canada, in P. M Harris and L. J. Weber, eds., Giant hydrocarbon reservoirs of the world: From rocks to reservoir characterization and modeling: A.A.P.G. Memoir 88/SEPM Special Publication, p.395-431.

Wierzbicki, R., J.J. Dravis, I. Al-Aasm, and N. Harland, 2006, Burial dolomitization and dissolution of Upper Jurassic Abenaki platform carbonates, Deep Panuke reservoir, Nova Scotia, Canada: AAPG Bulletin, V.90, No. 11, p. 1843-1861.

ANALOGUE MODELLING OF SALT TECTONIC PROCESSES AND DEPOCENTER MIGRATION ON THE SHELF AND DEEPWATER SLOPE, WESTERN LAURENTIAN SUB-BASIN

Cribb, Jonathan¹; Campbell, Clarke²; MacDonald, Cody ²; Adam, Juergen ³; Nedimovic, Mladen²; Louden, Keith²; Krezek, Csaba⁴; Grujic, Djordje²

¹Dalhousie University Life Sciences Centre, Halifax, NS, B3H 4J1, Canada; ²Life Sciences Centre, Halifax, NS, B3H 4J1, Canada; ³Department of Geology, Royal Holloway University of London, Egham, Surrey, TW20 OEX, United Kingdom; ⁴Chevron Norge AS, Karenslyst Alle 2, Oslo, Skoyen, PO Box 97, Norway

The Scotian Basin is situated on the Atlantic continental margin offshore Nova Scotia and is composed of a series of interconnected Mesozoic-Cenozoic sub-basins resulting from the rifting of North America from Africa. Thick deposits of late syn-rift Argo Salt coupled with complex basement morphologies and varied sedimentation patterns along the margin have resulted in a complex and laterally variable basin evolution. Unsatisfactory results from the recent round of hydrocarbon exploration in the deepwater slope demonstrate that a better understanding is required about the link between early post-rift salt mobilization and late post-rift formation of canopies and allochthonous salt nappes, and their relation to depocenter migration. We are using scaled analogue experiments comprised of sand and silicone putty to gain such an understanding by simulating basin evolution and salt tectonic processes constrained by seismic data. First-order model parameters of the western Laurentian sub-basin analogue experiment including sedimentation rates and patterns, basement morphologies, and initial salt thickness were constrained by GXT NovaSpan and public-domain seismic data. Experiment results confirmed appropriate timing and speculation of the evolution of this region with diverse structural processes including; (1) numerous passive downbuilding events throughout basin evolution, (2) extension focused in the Cretaceous forming a ramp flat geometry, and (3) minimal contraction in the upper Cretaceous. The next phase of this project includes modeling the interaction of sediment progradation and salt tectonics between the inter-connected Laurentian, Abenaki and Sable sub-basins. This experiment will evaluate the role of margin parallel sediment transport from the northeast via the Laurentian Channel during the early post rift stage of basin evolution and salt tectonics in the NE Scotian Margin. Insight from both models, when compared to regional seismic data, will contribute to our understanding of the structural evolution of the western Laurentian Sub-basin and determine the influence of margin parallel sedimentation.

THE MOHICAN CHANNEL GAS HYDRATE ZONE, SCOTIAN SLOPE: GEOPHYSICAL STRUCTURE

Cullen, Janette¹; Mosher, David C²; Schlesinger, Angela³; Haacke, Ross⁴; Louden, Keith⁵

¹Department of Earth Sciences, Dalhousie University, Halifax, Nova Scotia, B3H 4J1, Canada; ²Geological Survey of Canada - Atlantic, Natural Resources Canada, P.O. Box 1006, Dartmouth, Nova Scotia, B2Y 4A2, Canada; ³School of Earth and Ocean Sciences, University of Victoria, P.O. Box 3055, Victoria, BC, V8W 3P6, Canada; ⁴Geological Survey of Canada, Natural Resources Canada, P.O. BOX 6000, Sidney, BC, V8L 4B2, Canada; ⁵Department of Oceanography, Dalhousie University, Halifax, Nova Scotia, B3H 4J1, Canada

The Cenozoic section of the Scotian margin largely consists of turbidity current, mass transport and glacial sediments, with related canyon and valley formation. A significant portion of the continental slope of this margin falls within the methane gas hydrate stability zone (GHSZ), yet a prominent bottom simulating reflector (BSR) was identified at only one location. 3D seismic reflection, ocean bottom seismometer (OBS) and long offset (9 km) pre-stack 2D multichannel seismic data were used to study the velocity structure, geophysical characteristics and volume of this Mohican Channel gas hydrate zone. The Mohican Channel area shows a double BSR 0.35 to 0.45 s below the seafloor within channel levee deposits in water depths of 1,200 to 1,500 m. Primary and secondary BSRs are ~280 km² and 50 km² in area. A system of polygonal faults extends from an apparent gas-charged zone at ~1.2 s subbottom (Miocene-Eocene Unconformity) to ~0.3 s subbottom. Some faults form vertical chimneys and appear as conduits for gas leakage into the GHSZ. Some chimneys reach the seafloor producing positive-relief gas-charged mounds. A total of 39 OBSs were deployed along 3 profiles; one strike line and 2 dip lines. A few of the P and S-wave velocity profiles derived from these data over the BSR show anomalies consistent with the presence of hydrate and free gas, but others are ambiguous. Dissimilarities within the low velocity zone (LVZ) and amplitude variations suggest hydrate is laterally inhomogeneous. Shear-wave anisotropy appears related to changes in density of polygonal faults. As in any petroleum system, source, pathway, reservoir and trapping mechanisms are necessary for hydrate occurrence. Rare appearance of BSRs on the Scotian margin with low gas and hydrate concentrations imply that gas hydrates are in far less abundance than theoretical calculations suggest.

SECOND-ORDER SEQUENCES AND THEIR APPLICATION FOR EXPLORATION IN THE DEEP-WATER SCOTIAN SLOPE

Davies, Andrew¹; Etienne, James L²; Mike, Simmons D²; Davies, Roger B²; Sharland, Peter R²; Sutcliffe, Owen E²

¹Neftex Petroleum Consultancy Ltd 115BD Milton Park, Abingdon, --, OX14 4SA, United Kingdom; ²115BD Milton Park, Abingdon, --, OX14 4SA, United Kingdom

Large-scale changes in lithofacies and stratigraphic architecture resulting from relative sea-level changes have been a prime research focus for the past few decades. Within industry, prediction of hydrocarbon play elements using sequence stratigraphic techniques is well-established. In 2001 we demonstrated the veracity of a sequence stratigraphic model for the Arabian Plate identifying 63 major Maximum Flooding Surfaces (MFS) and Sequence Boundaries (SB). Ongoing work, incorporating nearly all of Earths sedimentary basins, now demonstrates the occurrence of 118 biostratigraphically constrained sequences that are global and observed independent of tectonics or sediment supply. The rapidity and magnitude of sea-level changes inferred from our model implicate eustatic forcing. In Eastern Canada, recent exploration has shifted focus towards the deepwater of the Scotian Slope driven by successes in other circum-Atlantic deepwater basins. Despite a proven petroleum system, the slope remains underexplored. Sandy lowstand fans comprise the principal reservoir targets, but are risky, borne out by few commercial successes. Biostratigraphically constrained sections from the Scotian Shelf provide a framework within which sequence stratigraphy can be applied. The recognition of large hiatus relating to second-order SB’s allows prediction of viable lowstand reservoirs down systems-tract. For example, the absence of Early Paleocene in many shelf wells, relates to an important late Maastrichtian SB during which significant down-slope transport of sediment is predicted. Major transgressions are often associated with development of organic-rich facies. Such is the case for Naskapi Member source rocks which relate to a second-order intra-Aptian MFS. Here, major second-order sea-level fluctuations are identified which are postulated to have exerted an important control on reservoir and source rock development on the Scotian Slope.

GEOLOGY AND HYDROCARBON POTENTIAL OF THE NW AFRICAN ATLANTIC MARGIN

Davison, Ian ¹

¹Earthmoves Ltd. Chartley, 38-42 Upper Park Road, Camberley, Surrey, Gu15 2EF, United Kingdom

The NW African Atlantic Rift System began to open in Carnian times (ca. 235 Ma) and produced a series of half graben with red-bed clastic fill in Morocco. Near the end of rifting, a 1-2 km thick salt was deposited, and is interpreted to be the same age as the CAMP volcanic rocks (200±1 Ma). Farther south, the deep Triassic rifts have not been drilled, but they could contain good oil prone source rocks similar to the southern USA basins. New evidence is presented that salt is present along the Cap Boujdour area of Aaiun Basin 450 km farther to the south of present mapped salt limit. The salt on the North American margin may also extend farther south, linking the South Georges Basin with the Baltimore Canyon Stone Dome occurrence. The northern limit of the Moroccan salt basin is currently mapped to terminate at the overthrust southern edge of the Rif Thrust Belt, but the salt must continue northward below the Rif. A sub-thrust play exists in Northern Morocco, which has never been tested due to the lack of good imaging below the thrust belt. The Cenomanian-Turonian source rock may be mature in this area, due to the tectonic loading in the Oligo-Miocene. The overlying Jurassic sequence is mainly a carbonate slope facies, but occasionally a rimmed platform edge developed (Senegal, Gambia and Mauritania). The carbonate play has still to be fully tested, because the wells drilled on the USA margin appear to miss the rimmed carbonate edge, and very few wells have drilled the carbonates in NW Africa. The carbonate platform eventually became drowned in the Early Cretaceous, when clastic deltas were deposited. The increased clastic sediment input may be due to the internal rifting and flank uplift occurring throughout North Africa. Cretaceous -Cenozoic clastic sediments constitute the main deepwater target reservoirs. Recent wells in Morocco appear to have failed due to lack of reservoir.

GEOTECTONIC SCENARIOS FOR THE EVOLUTION OF THE SOUTH ATLANTIC BRAZILIAN MARGIN: LEFT-LATERAL LOWER CRETACEOUS OBLIQUE RIFTING FOLLOWED BY UPPER CRETACEOUS TO PRESENT ONGOING COMPRESSION

De Lima, Claudio Coelho¹; Lopes, Marcos Fetter²; Gontijo, Rogerio²; Pessoa Neto, Otaviano Da Cruz²

¹PETROBRAS- SA Ilha do Fundão Q7, Cidade Universitária, Rio de Janeiro, RJ, 21941-915, Brazil; ²PETROBRAS - SA, Rio de Janeiro, RJ, 20031-912, Brazil

We propose that the evolution of South Atlantic Brazilian margin was performed in two successive geotectonic scenarios. The first one was dominated by left-lateral Lower Cretaceous oblique rifting that culminated with South Atlantic seafloor spreading. This scenario produced right stepped NNE-SSW-trending blocks where kitchens are found.

The second scenario has been produced as the South America (SA) plate have been moving westwards with respect to the Africa plate. While moving, this plate is frontally or obliquely “colliding” against other plates (Nazca, Caribbean, Scotia) that are moving eastwards. This geotectonic scenario that began to be delineated in the Upper Cretaceous, was definitely established during the Tertiary and is prevailing in the Present. This scenario is analogous to a huge traffic accident that started in Mid-Upper Cretaceous and is still going on. As a result, the bulk of SA plate has been in horizontal compression since the Upper Cretaceous up until the Present. In such a mechanical environment, we infer that the intraplate deformation across the SA plate will be concentrated along its favorably oriented mechanical discontinuities. On the basis of this rational, the post-rifting evolution of the Brazilian Margin Basins and their petroleum systems should be influenced by compressional/strike-slip reactivation of rift-related and basement structures, modulated by salt tectonics. Results of analyses and modeling of a comprehensive geological and geophysical data set have supported this inference.

Given that intrinsically similar geotectonic scenarios (i.e. rifting followed by sea floor spreading; frontal or oblique “collision”) should be operating across the Central Atlantic conjugate margins as well, we speculate that using such a frame could help understanding the evolution of their petroleum systems eventually.

A REGIONAL TRANSECT ACROSS THE SOUTH NEWFOUNDLAND BASIN, A NONVOLCANIC MARGIN

Deemer, Sharon ¹; Hall, Jeremy¹; Solvason, Krista²; Lau, Helen³; Louden, Keith⁴; Srivastava, Shiri ⁵; Sibuet, Jean-Claude ⁶

¹Memorial University of Newfoundland Dept. of Earth Sciences, St. John’s , NL, A1B 3X5, Canada; ²Nexen, Inc., 801-7th Avenue S.W. , Calgary, AB, T2P 3P7, Canada; ³Cambridge University, Bullard Laboratories, Madingley Road, Cambridge, CB3 0EZ,, United Kingdom; ⁴Department of Oceanography, Dalhousie University, Halifax, NS, B3H 4J1, Canada; ⁵Geological Survey of Canada, Bedford Institute of Oceanography, P.O. Box 1006, Dartmouth, NS, B2Y 4A2, Canada; ⁶Ifremer Centre de Brest, Département des Géosciences Marines, B.P. 70, 29280 Plouzané, France

New seismic reflection data from the Grand Banks of Newfoundland and the Newfoundland Basin add to the knowledge of composition, structure and history of this nonvolcanic margin. Two parallel profiles over the shelf platform image deep crustal fabric representing Precambrian or possibly Appalachian deformation as well as Mesozoic extension. Progressively more intense extension of continental crust is imaged oceanward below the continental slope without the highly reflective detachments frequently seen on profiles off Galicia. A landward-dipping event ‘L’ is imaged sporadically and appears to be analogous to a similar event on the approximately conjugate Iberian IAM9 profile. The transition zone is probably unroofed serpentinized mantle as interpreted off the Iberian margin although there appears to be a difference in the character of ridge development and reflectivity. The distinctive ‘U’ reflection in the Newfoundland Basin is highly regular and continuous except where interrupted by basement highs. ‘U’ is also seen to have a major impact on the ability to image underlying basement. A full transect from completely unextended continental crust to oceanic crust has provided two estimates of extension and the pre-rifting location of the present continental edge; 85 km based on faulting and 120 km based on crustal thickness.

MAPPING POST RIFT SILLS ALONG THE NEWFOUNDLAND PASSIVE MARGIN

Deemer, Sharon ¹; Hurich, Charles¹; Hall, Jeremy¹

¹Memorial University of Newfoundland Dept. of Earth Sciences, St. John’s , NL, A1B 3X5, Canada

A high amplitude reflector package at the base of the sedimentary sequence in the Newfoundland Basin sampled during ODP Leg 210 results from thin diabase sills. Chemical analyses and dating suggest that the sills were emplaced in two separate postrift thermal events, probably related to hot spot activity. Seismic data tied to the borehole reveal that the sills are widespread and continuous over hundreds of square kilometers. Spectral decomposition is used here on high quality seismic profiles (migrated near trace gathers) in order to map the peak energy frequency variation of the U reflections throughout the basin which is then related to thickness of sills. The analysis is complicated due to limited signal bandwidth and the complexity of the sill geometries but trends are apparent throughout the basin. The lowest frequencies (thickest sills) are associated with the central basin, particularly towards the south. Higher frequencies (thinner sill) are associated with the upper sill in the north but the upper sill in the south central basin is low frequency. Based on sill thickness variations, the source of magma is proposed to be in the south central basin close to the present day Newfoundland Seamounts.

VARIATIONS IN CRUSTAL THICKNESS AND EXTENSIONAL STYLE ALONG THE SCOTIAN MARGIN, ATLANTIC CANADA: CONSTRAINTS FROM SEISMIC DATA AND 3D GRAVITY INVERSION

Dehler, Sonya A.¹; Welford, J. Kim²

¹Geological Survey of Canada Natural Resources Canada, Dartmouth, NS, B2Y4A2, Canada; ²Memorial University of Newfoundland, Dept. of Earth Sciences, St. John’s, NL, A1B 3X5, Canada

The opening of the North Atlantic Ocean produced a wide range of rifted margin geometries, with broad differences in subsidence patterns, crustal extension, and volcanism. The continental margin off Nova Scotia is interpreted as the transition from a volcanic style margin in the southwest, along the US Atlantic margin, to a non-volcanic margin that extends to the east and north as far as Labrador. Other characteristics, such as the depth and width of the overlying sedimentary basin, also vary dramatically along the length of the margin. Seismic data have helped to establish the present day geometry of the thinned continental crust along several cross-sections. Gravity data, which cover the entire margin and adjacent continental and oceanic regions, provide a means of extending these interpretations across the region. We examine regional crustal thickness and its links to variations in extensional style along the margin through a 3D inversion of gravity data, with constraints from previous and new seismic interpretations. The resulting pattern of crustal thickness highlights trends that may provide insight into the extensional processes associated with rifting of this margin.

U.S. EAST COAST: CONTINENTAL MARGIN EVALUATION WITH NEW TOOLS, DATA AND TECHNIQUES

Dickson, William ¹; Odegard, Mark²; Post, Paul J.³

¹Dickson International Geosciences (DIGs) 10260 Westheimer Rd, Suite 320, Houston, TX , 77042-3160, United States; ²Grizzly Geosciences, Inc. 14019 SW Freeway, Suite 301-735, Sugar Land, TX, 77478, United States; ³U.S. Department of the Interior, Minerals Management Service, Office of Resource Evaluation, 1201 Elmwood Park Blvd. , New Orleans, LA, 70123, United States

Exploration discussions of the Central Atlantic margins typically omit the U.S. East Coast Continental Margin (ECUS) which has been dormant, without drilling since 1984, despite on-going E&P activities to the north (offshore Nova Scotia), south (offshore northern Cuba), and on the conjugate African margin (Morocco to Mauritania). Shell has documented its exploration success with new ideas and new technology. After a more than twenty year hiatus, we too have new data, technology and ideas along the ECUS, suggesting that timing is favourable for a thorough review.

Our data compilation began with advanced coverages of public domain bathymetry, gravity and magnetic data, all re-levelled, cross-correlated and merged. Our Central Atlantic data set includes five million-odd line-kms each of gravity and magnetic profiles plus a half-million data points. Each data set was carefully merged to regional backgrounds derived from multiple satellites. Stunning imagery of bathymetry, gravity, magnetic and auxiliary data were generated from the final 4 km (super-regional) and 1 km (basin-level) grids. Including multiple data attributes that are somewhat area-dependent, we generated about 40 images, each with specific and general interpretation value.

Evolution of passive margins and adjacent oceanic crust has been studied extensively since the mid-1980's, with continued academic work along the ECUS. The Minerals Management Service is conducting a re-analysis of pre-1985 drilling and seismic data augmenting the older ECUS literature. We make initial comparisons between published interpretations and our new imagery, presenting adjustments, revisions, extrapolations and some speculation. While the dominant structural features are largely unchanged, they are better delineated. This includes evidence of more subtle correlations with published depictions of play-defining features such as areas of salt tectonics and carbonate bank edges. The interaction of these features with plate tectonic elements is also better defined. Each of these observations is illustrated with specific imagery on which feature changes and extensions are highlighted.

US EAST COAST: CONTINENTAL MARGIN EVALUATION WITH NEW TOOLS, DATA AND TECHNIQUES

Dickson, William¹; Odegard, Mark²; Post, Paul³

¹DIGs (Dickson International Geosciences) 615 Ramblewood Rd, Houston, TX, 77079-6904, United States; ²Grizzly Geosciences, Inc. 14019 SW Freeway, Suite 301-735, Sugar Land, TX, 77478, United States; ³U.S. Department of the Interior, Minerals Management Service, Office of Resource Evaluation, New Orleans, LA, 70123, United States

Exploration focii of the Central Atlantic margins omit the US East Coast Continental Margin (ECUS) which has been dormant, without drilling since 1984, despite on-going E&P activities to the north (offshore Nova Scotia), south (offshore northern Cuba), and on the conjugate African margin (Morocco to Mauritania). Shell has documented its exploration success with new ideas and new technology. After a more than twenty year hiatus, we too have new data, technology and ideas along the ECUS, suggesting that timing is favourable for a thorough review. Our data compilation began with advanced coverages of public domain bathymetry, gravity and magnetic data, all re-levelled, cross-correlated and merged. Our Central Atlantic data set includes five million-odd line-km each of gravity and magnetic profiles plus a half-million data points. Each data set was carefully merged to regional backgrounds derived from multiple satellites. Stunning imagery of bathymetry, gravity, magnetic and auxiliary data were generated from the final 4 km (super-regional) and 1 km (basin-level) grids. Including multiple data attributes that are somewhat area-dependent, we typically generated about 40 images, each with specific and general interpretation value. Evolution of passive margins and adjacent oceanic crust has been studied extensively since the mid-1980's, with continued academic work along the ECUS. The Minerals Management Service is conducting a re-analysis of pre-1985 drilling and seismic data augmenting the older ECUS literature. We make initial comparisons between published interpretations and our new imagery, presenting adjustments, revisions, extrapolations and some speculation. While the dominant structural features are largely unchanged, they are better delineated. This includes evidence of more subtle correlations with published depictions of play-defining features such as areas of salt tectonics, carbonate bank edges. The interaction of these features with plate tectonic elements is also better defined. Each of these observations is illustrated with specific imagery on which feature changes and extensions are highlighted.

THE NOVASPAN PROJECT: DEEP IMAGING OF AN ENIGMATIC CONTINENTAL MARGIN

Dinkelman, Menno G.¹; Shimeld, John W.²

¹ION Geophysical 2105 CityWest Boulevard, Suite 900, Houston, Texas, 77042-3847, United States; ²Geological Survey of Canada (Atlantic), P.O. Box 1006, Dartmouth, Nova Scotia, B2Y4A2, Canada

The 2003 NovaSPAN data set comprises over 3400 km of 2-D regional reconnaissance seismic data designed to image down to the base of the crust using large guns (>4200 in³) with a 9 km long cable and 18-second record lengths. The data has undergone Prestack Time Migration (PSTM) as well as Prestack Depth Migration (PSDM - to 40 km). The primary objective of the NovaSPAN survey was to deliver critical insight into the geologic evolution and basin architecture of the Scotian Margin, and the resultant temporal and spatial history of regional petroleum systems. The NovaSPAN survey provides a useful regional structural and stratigraphic framework. An initial fast-track seismic stratigraphic interpretation, largely on the PSTM data, has yielded the following preliminary results: § The discovery of rotated crustal blocks in front of the margin provide evidence of significant changes across this zone along the margin, suggestive of transtension along a transform fault zone. If true, there may be important relationships within a zone of comparatively high basement underlying the slope to shifts of major basin elements such as the basement hinge zone and the position of allochthonous salt basins. § The geometry and nature of syn-rift basins along portions of the LaHave Platform may prove important for understanding how the rifting occurred, while the presence of salt within some of the basins might affect evaluation of overlying prospects in the Abenaki carbonate bank. § The long transects across the upper rise and lower slope allow for detailed subdivision of the seismic stratigraphy which in turn aids correlation of units through areas of complex deformation. § A remarkably high rate of sedimentation during the Late Jurassic is manifested by an extensive synkinematic wedge occurring above a salt detachment system in the eastern part of the survey area toward the Laurentian Channel. The implication of this feature is that the southern limit of allochthonous salt deposition lies roughly 100 km further north than previous workers have assumed.

More recent work underscores the enigmatic nature of the deeply buried basement structure and crustal nature. The GXT SPAN™ surveys provide sufficient aperture and illumination, when combined with the right imaging tools, to reveal how complex basin structuring is controlled by Tertiary, Mesozoic and older deformational events and early basin tectonics. We suggest that these data sets, in conjunction with other detailed “prospect-level” surveys, will aid industry in the definition of petroleum systems and new plays, especially at great depth and in deeper off the shelf waters and can considerably reduce basin exploration risk. The NovaSPAN data set is now at the core of a regional re-interpretation effort of the Scotian Margin by the Nova Scotia Department of Energy in conjunction with the GSC and the Departments of Geology of Dalhousie and St Mary’s universities to build a new tectono-stratigraphic framework and a post-mortem of recent deep water drilling failures.

ABENAKI CARBONATE MARGIN FACIES ASSOCIATIONS: POSTER 2 - SLOPE-FOREREEF SETTINGS AND SPECTRUM OF MICROBIAL MUD/REEF MOUNDS

Eliuk, Leslie¹

¹Dalhousie University Eath Sciences & GeoTours Consulting Box 852 (91 Creighton St), Lunenburg, --, B0J 2C0, Canada

With the exception of M-79 in Deep Panuke and Cohasset D-42 that is a bit back of the margin flexure, all thick shelf margin wells (Marquis L-35 & L-35A, Cohasset L-97, Dominion J-14, Musquodoboit E-23, Demascota G-32, Acadia K-62, Albatross B-13) have a significant portion of their lower and middle sections (lower Baccaro Member or EnCana’s Sequences 2 and 3) in a microbial-hard peloid-carbonate mudstone lithofacies rich in calcite cements. These lithofacies are interpreted as distal carbonate slope with microbial mud/reef mounds. This is strongly supported by core (G-32, K-62, sidewall cores in B-13 and core at the base of the Baltimore Canyon Trough ‘Civet’ OCS-0337 well) which show isopachous submarine cements, marine geopetals, microbial thrombolitic-stromatolitic and even stromatactis textures. The amount and variety of associated biota, degree and openness of submarine cavity systems and presence of debris flows varies, possibly systematically with distance from the Sable Island delta. Color changes show this with B-13 most distal and white and red. In contrast, two wells with core (Penobscot L-30, West Venture C-62) in the Sable Island paleodelta with prograding ramp geometries have microbial mud mound facies that are considerably darker and less biotically varied compared to those of cores in wells to their southwest. Queensland M-88 is the only well drilled completely on the Abenaki carbonate slope to test possible bypass sandstone reservoirs immediately basinward of the Deep Panuke field. Cuttings, strongly supported by drilled sidewall cores, indicate a distal slope setting with abundant microbial mud/reef mound facies. An exception is thin sponge or stromatoporoid-rich limestone beds that define the sequence boundaries with overlying often-black shales. Proximal slope or forereef facies are fairly common in most margin wells especially in Deep Panuke. There, these generally sandier carbonates are often ‘leached’ limestones or dolomites forming much ofthe porous reservoir. Even in core distinguishing forereef from reef flat sands can be a difficultinterpretive problem. However in the Margaree F-70 core, the inclined dips and interbedding of thin in situ relatively low-energy hence deeper-water microbial-sponge-microsolenid coral reeflets support a proximal forereef interpretation for the dolomites and graded echinodermal grainstone interbeds.

CARBONATE AND SILICICLASTIC SEQUENCE STRATIGRAPHY- EXAMPLES FROM THE LATE JURASSIC ABENAKI LIMESTONE AND WEST VENTURE DELTAIC BEDS, OFFSHORE NOVA SCOTIA, CANADA

Eliuk, Leslie¹; Wach, Grant²

¹Dalhousie University Earth Sciences Box 852 (Creighton St), Lunenburg , Nova Scotia, B0J 2C0, Canada; ²Earth Sciences Dept. Dalhousie University, Halifax , Nova Scotia, B3H 4H6, Canada

Relative to their occurrence in thick siliciclastic sections, thin carbonates show utility as sensitive indicators of the surrounding sand and shale sedimentation. When composed of in situ framebuilders (microbial and skeletal) as demonstrated by inter-growth position, bioerosion, associated submarine cements and marine geopetals, the carbonates are particularly helpful for environmental inferences. Within the Sable Island paleodelta, cores in Penobscot L-30 and South Venture C-62 show both dark colors and limited biotic diversity with microbial textures. The C-62 cores are particularly interesting because they provide an independent check on the shelf-margin delta model and sequence stratigraphic scenario previously presented by others for the Venture gas field. In less than 7 meters, facies and fauna in limestone change upward from a biotically depauperate marl to a microbial mud mound, which is succeeded by an argillaceous sponge-microsolenid coral reef mound with some stromatoporoids and possible red algae. The sequence is interpreted to reflect a forced regression and falling sea level. This closely supports the published deltaic sequence stratigraphy as long as it is appreciated that the "condensed limestone facies" is actually a distal composite, recording changes in sea level, nutrient supply, and ultimately sediment type that replaces the carbonate as the delta progrades. The maximum flooding surface (MFS) occurs during the microbial mound stage, below an abrupt lithologic change across a pyritized hardground which is overlain by laminated black shale. This placement of the MFS reflects problematic differences in sequence stratigraphic concepts of carbonates versus siliciclastics. Relative to understanding the Abenaki platform, the C-62 core provides insights into relationships seen only in cuttings and sidewall cores in Queensland M-88 which drilled the slope and basin facies immediately in front of the Deep Panuke (Abenaki reservoir) gas field. M-88 and C-62 may be potential links for correlating and dating the massive (Abenaki) carbonates and the deltaic siliciclastics.

ABENAKI CARBONATE MARGIN FACIES ASSOCIATIONS: POSTER 5 - SPONGE REEFS AND ARGILLACEOUS SPONGE-RICH CARBONATES RELATED TO DELTAS: THE JURASSIC-CRETACEOUS BALTIMORE CANYON-NOVA SCOTIA ABENAKI EXAMPLES COMPARED TO THE MODERN FRASER PRODELTA EXAMPLE.

Eliuk, Leslie¹

¹Dalhousie University Earth Sciences & GeoTours Consulting Box 852 (91 Creighton St), Lunenburg, Nova Scotia, B0J 2C0, Canada

Of the three Jurassic reef-reef mound end-members (see poster 3), the siliceous sponge reef mounds occur uniquely at the top of the Abenaki and at the top of equivalent carbonates in the Baltimore Canyon Trough (BCT). Then shales overlie both. A major oceanographic or relative sea-level carbonate drowning event or series of events affecting both areas seemed like an obvious explanation. However a limestone core just below the Venture Field shelf margin delta, diachronous age dating of sponge-rich beds and their limited distribution on the Nova Scotia shelf (NSS), and the discovery of siliceous sponge reefs adjacent to prodeltaic shales of the Fraser River delta, British Columbia (Conway, Barrie and Krautter 2004), may give an alternative explanation with a modern analogue. Seismic and Ringer’s Valanginian model ( in Eliuk and Prather 2005, repeated at this conference) in BCT show that after and perhaps even contemporaneously with the shelf margin pinnacle reefs, sponge mounds formed in nearby deeper water (several 100 feet or ~50-100m) below the pinnacle reef and in front of small deltas prograding over drowned inner platform carbonate. In the NSS, argillaceous sponge-rich beds at the top of the Abenaki are younger in wells further southwest of the large Sable Island delta. Even further away from the delta on the Western Shelf the Abenaki (Roseway unit) carbonates no longer have a sponge facies but continue in typical shallow platform facies and are younger yet. In the bottom of West Venture C-62 the older thin Late Jurassic #9 Limestone has a few metre thick sponge-stromatoporoid-microbial reef mound capping a pure microbialite reef mound of similar thinness. Laminated black prodeltaic shales at the base of a 50 m thick shelf margin deltaic sequence (Cummings and Arnott 2005) abruptly overlie the limestone. This is like a miniature version of the Abenaki carbonate platform terminations to the southwest and ignoring subsidence indicates an initial water depth around 50m. The change from microbialite up tosponge reef with possible red algae in a total of less than 5m indicates a relative sea-level fall and supports an interpreted forced regression. Like the modern Fraser delta sponge reefs, these more calcareous Jurassic sponge reefs were in deep quiet nutrient-rich waters but not yet engulfed and buried by clay sediment of an encroaching delta. Such a setting was environmentally untenable for shallow-water carbonate sedimentation that had therefore already "drowned".

REGIONAL SETTING OF THE LATE JURASSIC DEEP PANUKE FIELD, OFFSHORE NOVA SCOTIA, CANADA – CUTTINGS-BASED SEQUENCE STRATIGRAPHY AND DEPOSITIONAL FACIES ASSOCIATIONS ABENAKI FORMATION CARBONATE MARGIN.

Eliuk, Leslie¹

¹Dalhousie University and GeoTours Consulting Inc Box 852 (91 Creighton St.), Lunenburg , Nova Scotia, B0J 2C0, Canada

Deep Panuke, discovered in 1998, is the only carbonate gas field in the eastern North America continental shelf. Several recently published studies (Weissenberger et al., 2006; Wierzbicki et al., 2005, 2006; EnCana 2006) give details on the hydrothermally-dolomitized reef margin gas field itself. Expanding on those studies using mainly cuttings and core data, Panuke is placed in a larger context between the northeast contemporaneous major Sable Island paleodelta prograding ramp shelf and the southwest thicker cleaner carbonate platform. Wells can be grouped based on geometry and position relative to the shelf margin as follows: prograding ramp margin (only a few of the numerous wells in the Sable Island paleodelta are included), margin slope, margin with full shoaling sequence, margin with paleohighs and encased pinnacles (typical of Deep Panuke area), margin inboard flexure with shoals, interior platform oolitic shoals, interior platform shaly lagoon and ‘moat’ and near-shore ridge/siliciclastic-rich. The large-scale (second order?) vertical full-shoaling stratigraphic sequence is seen in nearly all margin wells. It comprises a basal transgressive oolite usually, then forereef with microbial mud mounds, then shallow coral-coralline sponge reefs, then oolites and two types of capping beds – either oolites (with or without sandstone interbeds) or lithistid sponge-rich beds. Only Deep Panuke does not show this pattern. Laterally there is a curious pattern to the argillaceous sponge-rich cap beds in being flanked by wells with oolite caps both nearer the delta and southwestward of the Panuke area wells. There is also a regional trend in the color from darker to lighter (and finally even red in the slope beds) away from the Sable Island paleodelta. These facies trends relative to the Sable Island delta and the associated early, deep prodeltaic burial are key factors that contributed to Deep Panuke’s reservoir, trap, seal and charge properties.

ABENAKI CARBONATE MARGIN FACIES ASSOCIATIONS: POSTER 4 - SHELF EDGE OOLITIC SHOALS OF THE INNER MARGIN AND ONCOLITE, BYPASS SAND, UNCONFORMITY THOUGHTS

Eliuk, Leslie¹

¹Dalhousie University Earth Sciences & GeoTours Consulting Box 852 (Creighton St), Lunenburg , Nova Scotia, B0J 2C0, Canada

Worldwide, Jurassic carbonates are also noted for oolites. The Abenaki too has oolite nearly everywhere and in many cases it allows cyclic and sequence subdivision to be made. But rarely are these grainy rocks an important contributor to reservoir porosity at least in the deeply buried Panuke trend, in the carbonate ramp shelf associated with the Sable Island paleodelta, in the basal transgressive beds of the platform, or in the very oolitic Scatarie Member at the base of the Abenaki Formation. Seismically at the inboard margin flexure and sedimentologically, oolites occur in the shallowest carbonate settings and should be subject to effective winnowing and subaerial exposure. Both should create porosity but likely Late Jurassic calcitic seas may have made for less soluble ooids. And most oolites are completely occluded by burial cement except on the Western Shelf where they occur less deeply buried beneath the present-day deep-water slope. At Deep Panuke the oolitic grainstones are impermeable enough to form part of the seal for stratigraphic trapping as opposed to their usual role as platform reservoir rock . A very thick oncolitic facies was defined using core in Acadia K-62 where the common presence of ooids, megalodont clams and coral fragments with the large oncoids suggested a reef flat interpretation. Since the oncolite facies is not obvious in other wells, speculatively it may reflect a more local or special event - possibly nutrient enrichment corresponding to the influx of deltaic clays and siliceous sponge reefing closer to the Sable Island delta. Another facies definitely related to siliciclastic influx is thin bypass sands. These are widespread at particular levels and have been interpreted to represent unconformity related low-stand periods with sand influx. As well the sand may overlie unconformities when reworked during the next transgression. In bracketing the inferred unconformities they represent maximum regression surfaces. Thus they are a key to establishing a sequence stratigraphic framework on the platform whether that is based on transgression-regression or more elaborately on relative sea-level stands of transgressive, high, forced regression and low.

ABENAKI CARBONATE MARGIN FACIES ASSOCIATIONS: POSTER 3 - VARIETIES OF REEFS AND REEF MOUNDS OF THE OUTER MARGIN

Eliuk, Leslie¹

¹Dalhousie University Earth Sciences & GeoTours Consulting Box 852 (Creighton St), Lunenburg, Nova Scotia, B0J 2C0, Canada

Worldwide, the Late Jurassic is noted for great quantities of varied reefs and of hydrocarbons in carbonates. Surprisingly, with just a handful of exceptions, it is not the Jurassic reefs that contain the hydrocarbons but rather platform interior carbonates in structural traps. Deep Panuke is one of those exceptions. The gas is in the reef complex and the trap is partially stratigraphic with even the structural component mainly due to reefal growth. And in the Abenaki margin, all three Jurassic reef-reef mound end-members (Leinfelder’s, 1994) are present: coral reefs, siliceous sponge and microbial (mud) reef mounds. These end-members have intermediate transitional forms but only the shallow-water coral-coralline sponge (stromatoporoids and chaetetids) reef complexes are significant reservoirs. Microbial mud/reef mounds (see poster 2) are well-cemented limestones and occur in slope facies below the reservoir levels. (As a caution against generalizations, some Jurassic Gulf of Mexico microbialite reefs occur in restricted shallow settings and are hydrocarbon reservoirs.) Siliceous (lithistid) sponge reefs (see poster 5) generally occur above the porosity-reservoir levels and actually contribute to the trap seal by their argillaceous content. These three reef type end-members can be distinguished even in cuttings. But only in core can one appreciate and possibly subdivide the shallow-water reef complex into reef flat, core (typically rubbly from bioerosion then storm and wave action) and proximal forereef (cores in Cohasset L-97, Margaree F-70, Panuke H-08, Demascota G-32, Acadia K-62). And in most cases the common presence of carbonate mud in the matrix, crinoidal debris and encrusting microbialites indicate that, unlike many modern Acropora-dominated reefs, these Late Jurassic hexacoral-rich reefs probably grew in slightly deeper margin water not at the crest. Probably particularly true when large phaceloid corals are seen still standing (L-97 core and on FMI in Panuke M-79). Seismic and dip-meter data clearly show that the reef-prone outer margin slope, between the updip oolitic inner flexure and the distally steepened downdip flexure, has considerable local topography. Some forereef beds on local pinnacle-like buildups even dip landward (F-70, MarCoh D-41). Usually that topography is encased by carbonates but Dominion J-14 shows that rarely shale can be trapped between individual buildups. In Baltimore Canyon Trough, the southward extension of the Jurassic gigaplatform, margin pinnacle reefs keep growing as the shelf interior is drowned and buried in shale.

ABENAKI CARBONATE MARGIN FACIES ASSOCIATIONS: POSTER 1 - UPDATED DEPOSITIONAL FACIES TEMPLATE AND VERTICAL-LATERAL MARGIN VARIATIONS AS PIE DIAGRAM SECTIONS-MAPS

Eliuk , Leslie¹

¹Dalhousie University Earth Sciences & GeoTours Consulting Box 852 (91 Creighton St), Lunenburg, Nova Scotia, B0J 2C0, Canada

Although artificially static, a carbonate facies template and schematic carbonate facies model are useful for high-lighting the general relationship of facies in a dip transect of a carbonate platform from shore to basin. The biological-sedimentological criteria in cuttings and core for facies association identification are thus tabulated. However contemporaneous local variability such as channels versus reef buildups versus skeletal shoals at the margin are more difficult to show sometimes even on 3D models. And in some cases facies many not be contemporaneous locally such as argillaceous sponge reef beds versus clear-water deeper coral or microbialite reefs or mounds. While perhaps in the same depositional depth and relative position, they occur widely separated in space and/or time but are shown on a single facies template or model for practical presentation and simplification. Modified from Wilson (1975) template by Eliuk (1978), Eliuk and Levesque (1988) then Wierzbicki, Harland and Eliuk (2002), the Abenaki facies associations are as follows: 1) Open marine shale – bathyal/deep, 2) open marine shale – neritic/shallow, 3A) foreslope channel, 3B) proximal foreslope (forereef), 3C) distal foreslope including microbial mounds (see 5C), 4A) ‘deep’ siliceous sponge reef mound & intermound, 4B) ‘shallow’ siliceous/lithistid sponge mound, 4C) ‘shallow’ lithistid-stromatoporoid/coral sponge reef, 5A) skeletal rich, 5B) shallow coralgal reef (coral-coralline sponge), 5C) pelleted ‘mud’ (see 3C), 5D) oolitic, 5E) oncolitic, 5F) thin bypass sandstones, 6) ‘moat’ open inner shelf (deep lagoon), 7) mixed carbonate-siliciclastic platform interior (nearshore ridge), 8) coastal deltaic-interdeltaic-restricted lagoon (loferite)-continental (coals). As discussed in the accompanying talk, geometry and position relative to the shelf margin (see seismic in Kidston et al. 2005) is another way of subdividing the well ‘magnafacies’ especially when they have a particular vertical depofacies pattern. Yet another method of viewing relative changes is showing percentage lithofacies-essential biotic-sedimentological components on pie diagrams placed vertically on sections or areally on maps by stratigraphic sequences.

BALTIMORE CANYON UNTESTED GAS POTENTIAL

Epstein, Samuel Abraham¹; Clark, Donald²

¹Certified Petroleum Geologist 3701 173 Beach 134 th Street, Belle Harbor, New York, 11694, United States; ²Northeastern Science Foundation, Staten Island, New York, 10304, United States

Emerging markets (China, India, etc.) demand-pull for energy resources have altered the historical petroleum pricing cycle to the upside. As a result, frontier areas may require a reinvestigation using new technology or scientific knowledge. A prime example of this may be in the Baltimore Canyon Trough, offshore eastern United States.

Exploration in the Baltimore Canyon (32 wells) targeted Upper Jurassic and younger clastics and carbonates in structural traps. Five wells encountered hydrocarbons with cumulative flow rates testing 90 mm cfg/d (Ball, 1982). Apparent discontinuity in reservoir extent resulted in project abandonment.

Thus far, organic high mature source rocks have not been identified (Prather, 1991). An organic reinterpretation by (Sassen and Post 2007) of gas condensate from the Hudson Canyon suggests a deeper Lower Jurassic source, analogous to that of the U.S. Gulf Coast’s Smackover Formation, Late Jurassic in age. Even in the Smackover, a highly productive hydrocarbon reservoir, the identified source rock contained only a select few areas of organic rich source rocks (Sassen and Moore, 1998). Reprocessed seismic data (AVO Analysis) indicates reflectors typical of widespread salt layers deposited during the Early Jurassic (60 m thick and 25 km wide) (McKinney, et al, 2004) suggesting arid and restricted depositional climatic conditions in the Early Jurassic. Sea level rise during the Early Jurassic, suggested by Vail, could have set the stage for anoxic conditions and rich organic limestone sources similar to that found in the U.S. Gulf coast, dependent upon the degree of restrictions of the Proto Atlantic. Lacustrine syn-rift source rocks are found inter- fingering with the major evaporitic sequences (salt) in Gabon, West Africa.

Reservoirs should be in carbonates and shelf clastics as in the modeled Early Jurassic. (Lawerence et. al.1990) Analogous Smackover carbonates are extremely productive at depth (6100 meters). Early rift zone carbonates currently experience excellent reservoir characteristics (Epstein and Friedman 1983).

Impermeable evaporates and shales, between the Lower and Upper Jurassic, may provide excellent seals explaining the lack of significant migrated hydrocarbons in porous (30%) rocks of the Upper Jurassic and Cretaceous. Emplacement of igneous rocks from the Middle Jurassic to Cretaceous may have breached the trapped hydrocarbon. Lopatin calculations from a syn-rift section to the south (Bahamas) considered a cold basin (low geothermal gradient) match the core samples from the Baltimore canyon (Ro=.7 at 4250 meters) (Epstein and Brink, 1983). The igneous movements may have burnt out the older potential source rocks or the hydrocarbons diffused out.

A Baltimore Canyon Isopach map of the Triassic-Jurassic suggests that a significant area of Lower Jurassic age rocks is buried to depths of mature hydrocarbon generation (gas) (Schlee, 1980). The United States Geological Survey estimated a total of 500 million bbl of oil and 20 tcf of gas. (D. Dinofi, 1991).

Current depositional analogs are found along the East African Red Sea-Dead Sea-Sea of Galilee rift zone where carbonates, evaporates, and clastics are accumulating penecontemporaneously (Epstein and Friedman, 1981, 1982). In the Dead Sea, 5 km of subsidence has occurred since the Pliocene, reflected in the stratigraphic subsurface, exceeding that of the early Jurassic Baltimore Canyon deep trough.

Prospective areas should focus on deeper sections of Lower and Middle Jurassic nearer to the Baltimore canyon Jurassic depo-center at much greater depths than previously drilled and away from igneous emplacements.

THE LAST 100 MILLION YEARS ON THE SCOTIAN MARGIN, OFFSHORE EASTERN CANADA: AN EVENT STRATIGRAPHIC SCHEME EMPHASIZING BIOSTRATIGRAPHY

Fensome, Rob¹; Gard, Gunilla²; MacRae, Andrew ³; Williams, Graham⁴; Thomas, Frank ⁴; Fiorini, Flavia⁵; Wach, Grant⁶

¹Geological Survey of Canada (Atlantic) P.O. Box 1006, 1 Challenger Drive, Dartmouth, Nova Scotia, B2Y 4A2, Canada; ²5915 Mesa Brook Lane, Houston, Texas, 77041, United States; ³Saint Mary's University, Halifax, Nova Scotia, B3H 3C3, Canada; ⁴P.O. Box 1006, 1 Challenger Drive, Dartmouth, Nova Scotia, B2Y 4A2, Canada; ⁵Smithsonian Tropical Research Institute, Ancon, None, None, Panama; ⁶Dalhousie University, Halifax, Nova Scotia, B3H 3J5, Canada

In the 1970s and 1980s, the principle biostratigraphic groups used for dating the Late Cretaceous-Cenozoic interval were foraminifera, nannofossils and dinoflagellate cysts (dinocysts), although in recent years the last-named group has been the most intensively used. No concerted efforts were made in the early days to marry results from the different microfossil groups, and this was sometimes reflected in diverse age schemes for individual exploration wells. The present study is based mainly on studies of material from seven exploration wells, selected to provise a composite section; the wells are Demascota G-32, Hesper I-52, Onondaga E-84, Sauk A-57, Shelburne G-29. Shubenacadie H-100 and Wenonah J-75, of which Shelburne and Shubenacadieare on the slope and the others are on the shelf. The Late Cretaceous-Cenozoic interval from each of these wells was analyzed for dinocysts and pollen and spores and, in some of the wells, for calcareous nannofossils and planktic and benthic foraminifera. The integration of data from different sub-disciplines, especially the calibration of dinocyst events with nannofossil events and thus indirectly with the largely deep-sea-based magnetostratigraphic timescale, has made possible for the first time a detailed sequence of biostratigraphic events.

THE PENICHE BASIN:TECNO-SEDIMENTATION AND EXPLORATORY ASPECTS

França, Almério Barros¹; Gontijo, Rogério Cardoso¹; Bueno, Gilmar Vital¹

¹Petrobras Avenida Chile, 65 sala 1401, Rio de Janeiro, RJ, 20031-912, Brazil

Petrobras in partnership with Galp and Partex, has acquired a total of 12.000 Km² in the Peniche Basin, offshore Portugal – a counterpart of some Northeast North American basins. The main subject of the present work is to show some geological aspects of the Peniche Basin, based mostly on seismic data and a few wells drilled nearby. There is no well drilled in the whole concession area.

The Jurassic Peniche Basin is bounded by SW-NE lineaments, subdividing the basin into horst and grabens and, by NW-SE lineaments, most likely transfer faults. From the end of the Jurassic onward, compressional stress seems to have predominated, reactivating old lineaments, creating thrusting faults and a series of flower structures. Normal faulting associated with sediment growth due to salt movement (middle to late Jurassic) are also a common feature in seismic lines. Uplifting in the shallow portion of the Peniche Basin brought about slumping and rotation of huge blocks in deep water realm.

Three major unconformities are easily mapped in seismic, corroborated by well data: 1) base of lower Cretaceous; 2) pre upper Jurassic sequence (strongly erosive), and 3) Cretaceous-Tertiary boundary. The erosive phases associated with all the above unconformities have great potential of sediment transport deep into the basin suggesting the possibility of sandstones reservoirs, either channelized or unconfined lobes. Channelized, coarse grained Cretaceous sandstones are well exposed along the coast in Santa Cruz, Portugal. The wells drilled shallow in the basin have shown porosity ranging from 15% to 30% (Cretaceous) and 15% in deeper sandstones (Jurassic).

Carbonates are another possibility as reservoir rocks with porosity ranging from 15% to 20%. Bioconstruction, probably rudist reefs such as the ones exposed in several onshore locations and along the coast, such as Praia do Guincho, near Estoril.

The potential source rocks (Pliensbachian and Kimmeridgian), present in outcrops and wells in the Lusitanian Basin, have been traced to deep horizons in the Peniche Basin, where the sedimentary section is thicker, suggesting greater potential than the shallow areas.

CONTINENTAL SLOPE SEDIMENTATION MODELS: LAURENTIAN CHANNEL AND HALIBUT CHANNEL REGIONS, EASTERN CANADA

Giles, Michael ¹; Mosher, David²; Piper, David²; Nedimovic, Mladen³; Wach, Grant³

¹Dalhousie University 3006 Department of Earth Sciences, Dalhousie University, Halifax, NS, B3H 4J1, Canada; ²Geological Survey of Canada (Atlantic), BIO, Dartmouth, Nova Scotia, B2Y 4A2, Canada; ³3006 Department of Earth Sciences, Dalhousie University, Halifax, NS, B3H 4J1, Canada

Recently acquired seafloor multibeam, and 2D and 3D seismic reflection data of the St. Pierre and Halibut Slope regions provide evidence for successive mass failures at a variety of scales. The occurrence of stacked and regionally extensive mass failures suggests that this is a fundamental process for slope sedimentation in this area; the most recent mass-transport event was in 1929. There are a variety of factors that explain the significance of mass failures in this area: 1) Drainage of the Great Lakes, which are the largest inland bodies of water in North America, cause the St. Lawrence River and Laurentian Channel to act as major fluvial and sediment transport conduits for most of eastern North America. It was also a major ice-outlet corridor during numerous Quaternary glaciations. As a result, sedimentation rates at the mouth of Laurentian Channel and on Laurentian Fan have been periodically high, leading to potential generation of high pore pressures and a thick column of underconsolidated sediment. 2) Sediment sampling in the region has shown the presence of intra-formational methane gas within the shallow portion of the sediment column. Generation of gas within sediment reduces its strength properties. 3) Gas hydrates, which may be indicated by bottom-simulating reflectors, are interpreted to occur in the region. Their dissociation may provide another potential source for shallow gas. 4) Recognition of buried sedimentary bedforms suggests sandy intervals underlying St. Pierre and Halibut Slope areas. Listric faults extending from surface escarpments into this interval suggests that possible detachment surfaces, perhaps in response to generation of overpressures occur within them. 5) The area overlies the Cobequid-Chedabucto fault, a paleo-transform margin, which appears to have a higher level of seismicity than most of the Canadian east coast margin. Ground accelerations due to earthquakes plays a critical role in initiating sediment failure, as in the 1929 Grand Banks submarine landslide during a M7.2 earthquake. Mass transport processes are clearly a significant mechanism of sediment delivery in the shelf to slope setting of the greater Laurentian Channel region. These processes are dependent upon a variety of pre-conditioning factors, both lithologic and structural, yet likely initiated by seismicity. The ubiquitous nature of such processes in the Quaternary section is a critical component to understanding reservoir potential of underlying rocks that reside in the same geologic setting.

SEQUENCE STRATIGRAPHIC EVOLUTION OF THE DEMERARA RISE, SURINAME, SOUTH AMERICA- TRANSITION FROM A RIFTED TO PASSIVE MARGIN; POSSIBLE ANALOGUE TO THE SCOTIAN SLOPE

Goss, Shawn ¹; Mosher, David²; Wach, Grant³

¹Dalhousie University Dept. of Earth Sciences, Room 3006, Life Sciences Centre , Halifax, Nova Scotia, B3H 4J1, Canada; ²Geological Survey of Canada (Atlantic) 1Challenger Dr. P.O. Box 1006, Dartmouth, Nova Scotia, B2Y 4A2, Canada; ³Dept. of Earth Sciences, Room 3006, Life Sciences Centre , Halifax, Nova Scotia, B3H 4J1, Canada

The Demerara Rise is a deep water extension of the continental margin north of Suriname and French Guyana; conjugate to the Guinea Plateau of West Africa. Late-stage Atlantic rifting began in the Mid to Late Cretaceous, resulting in opening of the Atlantic gateway between the North and South Atlantic Oceans. The margin is highly prospective in light of hydrocarbon exploration and production successes to the south, off Brazil. Regional 2D seismic data and a few offshore wells set the stage for the latest phase of exploration activity. RepsolYPF acquired a 3D volume on the inboard margin of the Demerara Rise in 2006, bridging the shelf to slope transition region. These data allow for detailed investigation of the Cenozoic stratigraphy on this portion of the Suriname margin in order to understand shelf to slope linked deposition systems of a relatively recently rifted margin. The Suriname margin, representing the last vestige of the proto-Atlantic, is a possible modern analog to the Jurassic Scotian margin. Understanding forcing functions, sedimentary pathways and depositional patterns are expected to provide insights into exploration models for passive clastic margins.

Exploration seismic data off Suriname show a passive rifted margin reflecting sedimentary sequences of subsidence infill and overall progradation. Early post-rifting, the region was anoxic, resulting in a thick (~90 m) interval of Cretaceous organic black shales outboard of the rise; excellent hydrocarbon source rock. Several significant regional unconformities indicate episodes of extensive erosion, such as during the Mid-Miocene and Oligocene. Offshore, the Cenozoic section is thin, but inboard in the position of the 3D seismic volume, the section is expanded and remarkably complete with classic shelf-to-slope progradational bedding structures. Tracing the shelf-to-slope hinge line, it is apparent that progradation slowed during the Paleogene relative to earlier. In the Neogene, a regional Pliocene unconformity marks the return to rapid progradation that continued into the Quaternary. Interpretation of seismic facies indicates turbidites and mass-failure deposits dominate the sedimentary section on the upper slope.

A number of features were identified from the shallow, near surface section that represent potential geohazards or constraints to offshore hydrocarbon development. Faulting is perhaps the most prevalent. Extensive faults with seafloor offsets, in some cases paralleling the shelf edge, are readily apparent. These faults may be involved in seafloor instability, providing a mechanism for shelf to slope sediment transport and deposition.

QUANTITATIVE KINEMAIC AND THERMOMECHANICAL ANALYSIS OF THE EVOLUTION OF THE MORCCAN RIFTED CONTINENTAL MARGIN

Gouiza, Mohammed¹; Bertotti, Giovanni²; Hafid, Mohamed³; Ghorbal, Badr²

¹VU University Amsterdam De Boelelaan 1085, Amsterdam, Holland, 1081HV, Netherlands; ²De Boelelaan 1085, Amsterdam, Holland, 1081HV, Netherlands; ³Université Ibn Tofail, Kenitra, Kenitra, 14000, Morocco

The Atlantic passive margin of Morocco developed during Mesozoic times in association with the opening of the Central Atlantic. Extension caused the development of extensional basins along the future continental margin and, further to the E, the Atlas rift system. Therefore, the must be considered as part of the rift system, which led to the formation of the passive continental margin of Morocco. It was inverted in Alpine times to form the present-day High and Middle Atlas Mountains. To provide a first quantitative analysis of the evolution of the rifted margin, we have constructed a crustal section from the Anti-Atlas (the plate interior) to the Atlantic Ocean crossing the Atlas system, the Meseta and the Atlantic continental margin in the Doukkala Basin segment. We applied numerical models to test quantitative relations between amounts and distribution of extension and isostasy-related vertical movements. A region of particular interest is the Moroccan Meseta, which is generally considered as a stable region separating the subsiding Atlas and Atlantic margin system. This picture is incompatible with the recent findings, which, on the basis of low-thermochronology, have demonstrated the existence of a Late Triassic to Middle Jurassic stage of subsidence followed by a Late Jurassic to Early Cretaceous exhumation.

We use the results of the quantitative analysis presented above to address the importance and regional tectonics of these syn-rift and post rift vertical movements.

QUANTITATIVE KINEMAIC AND THERMOMECHANICAL ANALYSIS OF THE EVOLUTION OF THE MORCCAN RIFTED CONTINENTAL MARGIN

Gouiza, Mohammed¹; Bertotti, Giovanni¹; Hafid, Mohamed²; Ghorbal, Badr¹

¹VU University Amsterdam Johan Jongkindstraat 244 , Amsterdam, Noord Holland, 1062DK, Netherlands; ²University Ibn Tofail of Kenitra, Kenitra, Gharb-Chrarda-Béni Hssen, 14000, Morocco

To provide a first quantitative analysis of the evolution of the rifted margin, we have constructed a crustal section from the Anti-Atlas (the plate interior) to the Atlantic Ocean crossing the Atlas system, the Meseta and the Atlantic continental margin in the Doukkala Basin segment. We applied numerical models to test quantitative relations between amounts and distribution of extension and isostasy-related vertical movements.

A region of particular interest is the Moroccan Meseta which is generally considered as a stable region separating the subsiding Atlas and Atlantic margin system. This picture is incompatible with the recent findings of Ghorbal et al. (submitted) who, on the basis of low-termochronology, have demonstrated the existence of a Late Triassic to Middle Jurassic stage of subsidence followed by a Late Jurassic to Early Cretaceous exhumation.

We use the results of the quantitative analysis presented above to address the importance and regional tectonics of these syn-rift and post rift vertical movements.

THE EVOLUTION OF THE PERDIDO FOLD BELT IN THE CONTEXT OF SALT TECTONICS OF THE NORTHWESTERN MARGIN OF THE GULF OF MEXICO – INSIGHTS FROM NUMERICAL MODELING

Gradmann, Sofie¹; Beaumont, Christopher¹

¹Dalhousie University 1355 Oxford Street, Halifax, NS, B3H4J1, Canada

The Perdido Fold Belt (PFB) is a prominent salt-cored deep-water structure in the northwestern Gulf of Mexico. In the last decade it has become a major target for exploration. It is characterized by a 4.5 km thick pre-kinematic, folded section, symmetric kink folds, a short duration of folding and associated lack of significant syn-kinematic sedimentation, and a seaward tilt of the fold envelope. The fold belt is located above the pinch-out of the autochthonous salt adjacent to and below the extensive Sigsbee Salt Canopy. This study investigates the previously unresolved temporal and spatial relationship of the folding across the area, the tilting of the fold belt, and the formation of the Sigsbee Canopy.

We use 2D finite-element models in which frictional-plastic sediments overlie a viscous salt layer. The models comprise a passive margin sedimentary sequence from shelf to deep water to account for the dynamical interaction of gravity spreading caused by shelf progradation. Model experiments include sediment compaction, flexural isostasy, and loading by the overlying water column. Parametric calculations include the effects of pore fluid pressures in the frictional-plastic sediments.

Analytical calculations of the stability of a salt-bearing margin reveal that a 4.5 km thick fold belt can have formed by gravity spreading across the passive margin alone. No crustal tectonics was necessarily involved and only moderately high pore-fluid pressures ratios of approx. 0.8 were required.

The model fold belt shows good correlation with the kink-type folds, geometry and dimensions of the PFB. Timing and extent of the folding of the model fold belt are controlled by system parameters such as overburden strength, margin width, salt thickness and salt viscosity. Variability in the latter two can generate two endmember types of fold belts: the fold belt either evolves above the distal section of the salt with folding occurring synchronously or it initiates at the toe of the slope from where it progressively propagates seaward. Although previous studies proposed that an evolving canopy buffered earlier compression and allowed the distal sediments to be deposited undisturbed, the numerical models suggest that the configuration of the system limited early compression to the toe-of-slope region. This deformation then led to localization of diapirs and canopies, which evolved mostly coevally with the fold belt.

GEOLOGICAL EVOLUTION AND HYDROCARBON POTENTIAL OF THE HATTON BASIN (UK SECTOR), NE ATLANTIC OCEAN

McInroy, David¹; Hitchen, Kenneth²

¹British Geological Survey Murchison House, West Mains Road, Edinburgh, --, EH9 3LA, United Kingdom; ²British Geological Survey Murchison House, West Mains Road, Edinburgh, --, EH9 3LA, United Kingdom

The deep-water Hatton Basin (flanked by the Hatton and Rockall Highs) is located 600km west of Scotland (NE Atlantic Ocean) on the western margin of the Eurasian continental plate. Prior to Atlantic opening, the area was adjacent to SE Greenland. The basin straddles the UK/Irish median line. Water depths increase southwards from 1000m to over 1300m.

The basin has never been licensed for hydrocarbon exploration and is currently the subject of ownership negotiations related to the UN Convention on Law of the Sea. Consequently it is under-explored. The deepest borehole penetration is by DSDP borehole 116 which terminated at 854m below sea bed in the Upper Eocene.

The Pre-Cambrian metamorphic basement only crops out on Rockall Bank where high-grade gneiss and granulite have been sampled and dated at c. 1900 to 1700 Ma. This is a different terrane from that which underlies most of Scotland. Palaeozoic rocks have not been proved in the area but may provide some of the pre-rift basin infill. The Hatton Basin probably opened during the Cretaceous. Recent (2007) seismic data suggest the presence of tilted fault blocks on the basin margins. Mid Cretaceous (Albian) sandstones and mudstones have been proved at shallow depth on the Hatton High. The area was affected by massive Late Paleocene to earliest Eocene volcanism which emplaced several large central igneous complexes and caused widespread lavas which degrade the seismic data from the deeper geology. Atlantic rifting commenced west of the Hatton High at about 56 Ma. During the Cenozoic the Hatton Basin was affected by differential subsidence and several unconformity-forming compressional events.

Numerous potential hydrocarbon trap styles have been identified including syn-rift tilted fault blocks, folds, truncations, prograding fans, pinch-outs, scarp fans and traps related to sill intrusions. Reservoir intervals are likely to be present in the Cretaceous, Paleocene and Eocene. The overlying Oligocene to Recent sediments are mudstones and oozes and may provide a seal. The main risks for an accumulation are the presence of a source rock and the shallow occurrence of some of the potential traps.

THE MESOZOIC ATLANTIC CANADA OFFSHORE MARGIN: HISTORY OF EXPLORATION, PRODUCTION AND FUTURE EXPLORATION POTENTIAL

Hogg, John R.¹; Enachescu, Michael E.¹

¹MGM Energy Corp 4100, 350 7th Ave SW, Calgary , Alberta , T2P 3N9, Canada

The Mesozoic Basins of the western Atlantic Margin are a result of intermittent rifting and separation of North America from Africa and Europe during the Late Triassic to Early Cretaceous. The extensional tectonics produced elongated, up to 20km deep, basins and subbasins, containing both synrift and syndrift sedimentary sequences that contain excellent reservoir and source rocks. Numerous structural, stratigraphic and combination traps were formed during the synrift and postrift stages.

Exploration in Atlantic Canada began in the late 1960’s with sporadic successes and considerable exploration failures which have caused several boom and bust cycles. The late 1970’s through to the mid-1980’s was a time of significant discoveries in 1) Newfoundland’s Jeanne d’Arc Basin with giant oilfields Hibernia, Terra Nova, Hebron and White Rose and 2) in the Sable Subbasin, offshore Nova Scotia with gas discoveries at Venture, Thebaud and North Triumph fields. As is typical in most basins, the largest fields were found quite early in the exploration cycle hosted in structural features, easily mapped with seismic data. The following exploration cycle, post 1988, was slowed by a combination of low resources prices and size potential of prospects seen on 2D seismic near the discovered fields.

By the late 1990’s, a new round of exploration began in both Newfoundland and Nova Scotia that was focused on unexplored deepwater basins, the Flemish Pass and Orphan Basins off Newfoundland and the Scotian Slope basin. More than 256,105 km of new 2D seismic and 53,318 km km² of 3D seismic surveys combined to give a much better understanding of the basins and detail structure and stratigraphy control. In the deepwater Nova Scotia one discovery was made at Annapolis, with the subsequent delineation well proving unsuccessful. More, recently, the first deep water, deep penetration well in the Orphan Basin was also an economic failure.

Future exploration in the Canadian East Coast Basins will focus around producing fields in Jeanne d’Arc Basin and new field wildcat work in the East Orphan, Laurentian and Hopedale basins, off Newfoundland and Labrador, while Nova Scotia offshore will witness a return to shelf exploration to support the pipelines. In the long-range we