Margin Evolution & Development

NEW PROFILE MODELS OVER THE U.S. EAST COAST CONTINENTAL MARGIN

Odegard, Mark¹; Post, Paul J.²; Dickson, William<sup>3

1</sup>Grizzly Geosciences, Inc. 14019 SW Freeway, Suite 301-735, Sugar Land, TX, 77478, United States; ²U.S. Department of the Interior,, 1201 Elmwood Park Blvd.,, LA, 70123, United States; ³Dickson International Geosciences (DIGs), 10260 Westheimer Rd, Suite 320, Houston, TX, 77042-3160, United States

Profile-based models are excellent for incorporating multiple data sets to illustrate basin architecture. New models across the U.S. East Coast Continental Margin incorporate reprocessed seismic lines, depth-stretched with projected well data, stacking functions and published refraction velocities. Four dip profiles (ranging from 220-480 km each) were tied to a composite (~2,300 km) strike profile; then extended landward and seaward to model long-wavelength crustal variations (from unthinned continental to fully oceanic regimes) defined by our latest gravity and magnetic data. The seismic interpretation constrains shallower horizons while deep crustal structure derives largely from potential field and published refraction data. Intermediate levels, especially acoustic basement, are revealed as other layers are defined. Models frequently constrain the nature and volume of intrusive bodies such as the lamprophyre dike swarm cored Great Stone Dome (Schlee Dome), and allochthonous salt diapirs, as targeted here. The feature extents were then interpreted areally, away from seismic coverage, based on gravity and magnetic imagery.

Comparing our profiles with published interpreted and modeled seismic lines; i.e., DNAG volumes, the authors note significant differences. Previously interpreted “salt structures” in the Georges Bank Basin (GBB) do not exist. Salt structures in the Baltimore Canyon Trough (BCT) appear limited to a small, seismically defined diapir and the salt penetrated in the Hudson Canyon 676-1 well on the flank of Schlee Dome. We validated salt structures in the Carolina Trough (CT), although the CT appears to be more complex and separate from the Blake Plateau Basin and BCT. Sediment thickness maxima in the GBB were confirmed on one model and matched to gravity data that improves the definition of previously indicated sub-basins with some exploration potential. Ongoing work is extending the interpretation of the models across the entire margin and will no doubt reveal further interpretation changes.

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

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

1</sup>Dickson 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.

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

Beglinger, Suzanne¹; Doust, Harry²; Cloetingh, Prof. dr. Sierd<sup>1

1</sup>VU 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.

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, Jan<sup>1

1</sup>VU 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.

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

Gouiza, Mohammed¹; Bertotti, Giovanni²; Hafid, Mohamed³; Ghorbal, Badr<sup>2

1</sup>VU 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.

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, Grant<sup>3

1</sup>Dalhousie 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.

4D RIFT ANALYSIS FOR THE JEANNE D’ARC BASIN

Baur, Friedemann¹; Jaur, Chris²; Littke, Ralf³; Wielens, Hans<sup>2

1</sup>RWTH 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.

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

Dickson, William¹; Odegard, Mark²; Post, Paul<sup>3

1</sup>DIGs (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.

SLOPES, BASIN FLOORS, DIAPIRS, AND CANOPIES: REGIONAL-SCALE SALT-SEDIMENT INTERACTION IN THE NORTHERN GULF OF MEXICO AND THE SCOTIAN OFFSHORE

Rowan, Mark G.<sup>1

1</sup>Rowan Consulting, Inc. 850 8th St., Boulder, CO, 80302, United States

Salt diapirs and allochthonous canopies are well known from the northern Gulf of Mexico and the Nova Scotian offshore. Canopies can be divided into two end-member styles: salt-stock canopies, in which the canopy is linked to the autochthonous salt layer by vertical feeder diapirs and intervening minibasins are characterized by turtle structures; and salt-tongue systems, where the canopies are connected to the deep layer by counterregional welds that have basinward-dipping expulsion-rollover structures in their hanging walls.

The fundamental difference between the two styles is the degree of asymmetry. In salt-stock canopies, diapirs grow vertically and spread radially before amalgamating, and sub-canopy withdrawal geometries tend to be symmetrical. In salt-tongue canopies, diapirs grow up and basinward and extrude basinward, and the withdrawal basins are correspondingly asymmetric. Because both diapirs and allochthonous bodies grow passively at the sea floor, the simplest explanation for the difference is the slope of the sea floor. If it is horizontal, there will be no preferred direction of growth and extrusion, resulting in vertical diapirs and salt-stock canopies. If the sea floor slopes, diapirs will lean basinward and extrude salt tongues basinward. Thus, the structural style is largely determined by the evolving bathymetric profile of the passive margin, which in turn is controlled by the history of sediment progradation.

In the northern Gulf of Mexico, a regional boundary between more proximal salt-tongue canopies and more distal salt-stock canopies roughly parallels the margin and probably represents a long-lived base of slope initially established during Paleogene Wilcox deposition. In the Scotian deepwater, a similar boundary is oriented highly oblique to the margin, with vertical diapirs to the southwest (Shelburne Subbasin) and salt-tongue canopies to the northeast (Sable Subbasin). The structural boundary is located along the southwestern edge of the Upper Jurassic to Lower Cretaceous Mic Mac and Missisauga progradational system, and thus represents a lateral boundary to a broad slope to the northeast, with a basin floor along strike to the southwest. One of the key applications of this model is that it can be used to estimate the paleo-toe of slope and thus regional turbidite facies distribution, with channelized slope facies dominant in areas of salt-tongue canopies and ponded basinal facies more likely in areas with vertical diapirs and salt-stock canopies.

THE LUSITANIAN BASIN (PORTUGAL) –STRATIGRAPHIC AND GEODYNAMIC CORRELATION WITH OTHER PORTUGUESE AND MOROCCAN BASINS

Pena Reis, Rui¹; Pimentel, Nuno²; Garcia, Antonio<sup>2

1</sup>University of Coimbra University of Coimbra, Largo Marquês de Pombal, Coimbra, Coimbra, 3000-272 Coimbra, Portugal; ²University of Coimbra, Largo Marquês de Pombal, Coimbra, Coimbra, 3000-272 Coimbra, Portugal

The Lusitanian Basin is located on the western Atlantic side of Iberia, corresponding to a passive margin of the North-Atlantic Cretaceous opening, conjugate with basins of the eastern North America. However, its late Triasic - early Cretaceous evolution indicates relationship with the Central Atlantic and the Alpine Tethys. This fact can be better understood by looking at other nearby basins, such as the Algarve basin (200 km S), and the Moroccan basins of the Atlas (700 km SE) and Essaouira basin (800 km S). The Lusitanian Basin presents a 1st late Triassic intra-continental rifting, with siliciclastics, evaporites and carbonates. The 2nd rifting starts in the Oxfordian, marked by a regional unconformity and thick marine and continental siliciclastics. The opening of the North-Atlantic, with a 3-stepped diachronous (Berriasian-Aptian) break-up unconformity, is marked by prograding fluvial and coastal mixed deposits. The same broad evolution may be identified at the Algarve basin, with small differences: Sinemurian volcanics, an Aalenian gap and depositional hiatuses coeval with three Cretaceous Atlantic break-up steps, migrating north. The complex Atlas basins are closely related to the Tethys evolution, with important subsidence during the 1^st rifting phase: Triassic red-beds and Liassic carbonates give place to deltaic and continental red-beds (or even depositional gaps) with a generalized upper Jurassic unconformity. Opening to the Tethys marine influences and carbonates became definitive since the Cenomanian. The Essaouira basin, closely related with the Central Atlantic opening, presents a more complete stratigraphic record, with abundant Sinemurian volcanics (CAMP) and post-break-up Jurassic marine and Cretaceous continental deposits. As in the Lusitanian basin, the subsidence is mainly upper Jurassic, but without an unconformity. A comparative approach to these basins supports strong geodynamic correlations, related with the opening of the Central and North Atlantic, as well as the spreading of the Alpine Tethys and detachment of the Iberian plate.

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

McInroy, David¹; Hitchen, Kenneth<sup>2

1</sup>British 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.

REGIONAL SIGNIFICANCE OF CAMP SILLS IN EARLY MESOZOIC BASINS OF EASTERN NORTH AMERICA

McHone, Gregory<sup>1

1</sup>Stones2Gems 9 Dexters Lane, Grand Manan, NB, E5G3A6, Canada

Although regional heat flow was probably elevated, the major thermal effect of the circa-201 Ma Central Atlantic Magmatic Province (CAMP) on Early Mesozoic sedimentary basins was from concordant to partly discordant sheet intrusions, or sills. At least 3,900 km³ of dolerite sills exist within and near the base of Triassic sections of basins in the eastern USA. Diagenetic features due to massive intrusive sheets up to 645 m thick include the growth of cementing minerals such as hematite, quartz, albite, illite, and chlorite produced by hydrothermal groundwater circulation, and temperatures in much of the Triassic sections may have abruptly exceeded 220°C. Concurrent with lithification of formerly weakly consolidated arkose would be a reduction in permeability. Because Triassic strata became more brittle, later generations of CAMP dikes within basins rose directly to the surface to feed lava flows, but not sills. Basin sills thus record the region's initial magma type, which is orthopyroxene-bearing quartz tholeiite in the northeastern USA, and olivine tholeiite in the southeast. Overlying Jurassic strata were not changed by CAMP magmatism. Basins that include no large dikes (such as the Fundy Basin of Atlantic Canada) also have no sills, and so their Triassic sections were likewise unaffected. Diagenesis of non-sill basin strata was through burial, and lithification was thus more gradational with depth and time. Geophysical mapping of large dike systems along the Central Atlantic margins might indicate the presence of sills in subsurface basins, with related effects on their diagenetic histories.

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

Bird, Tim John ¹; Johnstone, David²; Martin, Mark<sup>3

1</sup>PGS 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.

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.<sup>2

1</sup>Rutgers 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.

SYSTEMATIC VARIATIONS IN BASEMENT MORPHOLOGY AND RIFTING GEOMETRY ALONG THE NOVA SCOTIA AND MOROCCO CONJUGATE MARGINS

Wu, Yue¹; Louden, Keith²; Tari, Gabor<sup>3

1</sup>Dalhousie University Department of Earth Sciences, Halifax, Nova Scotia, B3H 4J1, Canada; ²Dalhousie University Department of Oceanography, Halifax, Nova Scotia, B3H 4J1, Canada; ³OMV Exploration and Production, Gerasdorfer Strasse 151, Vienna, 1210, Austria

The Nova Scotia and Morocco margins formed within a complex transition region between volcanic-style margins to the south and non-volcanic margins to the north. We present new results including recent deep seismic profiles that help document the nature of this transition. Seismic profiles along and across the Nova Scotia margin show two abrupt transitions from south to north. The first transition represents a sharp reduction in syn-rift volcanism at ~64^oW, coincident with major changes in the East Coast Magnetic Anomaly (ECMA) and with the southern limit of the Slope Diapiric Province. The second transition at ~ 60^oW represents a further restriction in syn- and post-rift volcanism that leads to exposure of serpentinized mantle basement or creation of highly tectonized ultra-slow spreading oceanic crust. This transition is represented by a major change in basement morphology marked by an oblique zone of highly extended and faulted continental crustal blocks. It is also coincident with a transition in salt deformation from autochthonous diapiric structures to allochthonous canopies.

Revised plate reconstructions of maximum and minimum closure (i.e. before rifting and at final separation), constrained by a set of combined seismic profiles, show similar transitions along the Moroccan margin. The southern transition occurs at a major change in the West Africa Coast Magnetic Anomaly (WACMA) and the southern limit of the Morocco Salt Basin. Thus the two margins are basically non-volcanic except at their southern extremes. The second transition occurs at a major oblique basement structural high (Tafelney Plateau), which has been considered as a high relief accommodation zone (HRAZ), and contains highly extended faulted crustal blocks similar to those in conjugate position off central Nova Scotia. This transition marks a major change in rifting asymmetry and separates the margins into two fundamentally distinct segments.

SEISMIC STRATIGRAPHY, SALT STRUCTURES AND THERMAL AND PETROLEUM SYSTEMS MODELS ACROSS THE CENTRAL NOVA SCOTIA SLOPE BASIN

Louden, Keith¹; Mukhopadhyay, P.K.²; Wu, Yue³; Negulic, Eric³; Nedimovic, Mladen<sup>3

1</sup>Dalhousie University Department of Oceanography, Halifax, Nova Scotia, B3H 4J1, Canada; ²Global Geoenergy Research Ltd., Halifax, Nova Scotia, B3J 2A1, Canada; ³Dalhousie University Department of Earth Sciences, Halifax, Nova Scotia, B3H 4J1, Canada

Two regional deep seismic profiles, GXT NovaSpan 1400 and Lithoprobe 88-1A, are used to better characterize the sediment, salt and basement structures across the Central Nova Scotian Slope Province. Imaging of deeper structures is especially improved, using either pre-stack depth migration with the long offset streamer (NovaSpan 1400) or a combination of pre-stack time migration and wide-angle velocity models (Lithoprobe 88-1A). Seaward of the salt, basement morphology and crustal velocities suggest that highly-stretched and rotated continental crustal blocks extend further into the ultra-deep basin. Beneath the salt, basement is also well-defined except locally beneath major salt diapirs.

Petroleum systems models are derived along the two profiles for various potential source rocks and reservoirs. Along both profiles, salt flank and salt crest Late Jurassic and Early Cretaceous reservoirs form the primary exploration targets. However, significant differences also exist for the two profiles, primarily associated with variations in salt structures. Along NovaSpan 1400, Jurassic Verrill Canyon is the main source rock for both Jurassic and Cretaceous reservoirs. For the Early Cretaceous reservoir, hydrocarbons may contain a major volume of liquids (>75%) with an API of 45-55^o and only mild overpressures. Along Lithoprobe 88-1A, Early Jurassic lacustrine and Late Jurassic salt-associated marine reservoirs are potential exploration targets, although these would lie within an over-pressured, dry-to-wet gas regime. Mass balance calculations for both seismic lines indicate that more preserved hydrocarbons are expected within the various reservoirs on NovaSpan 1400.

Model calculations of present day sea-floor heat flow predict a gradual landward reduction from 55 mW/m² in the ultra deep-water basin to 45 mW/m² on the upper slope. Large variations, however, are caused by high conductivity within the salt diapirs, yielding values as high as 85 mW/m². In July 2008, we plan to take detailed measurements along both profiles in order to verify these predictions.

SEDIMENTARY BASINS IN THE CENTRAL AND SOUTH ATLANTIC CONJUGATE MARGINS: DEEP STRUCTURES AND SALT TECTONICS

Mohriak, Webster Ueipass¹; Brown, David E²; Tari, Gabor<sup>3

1</sup>Petroleo Brasileiro S.A. Avda. Chile, 65 - s. 1302, Rio de Janeiro, Rio de Janeiro, 20035-900, Brazil; ²Canada-Nova Scotia Offshore Petroleum Board, Halifax, Nova Scotia, B3J 3K9, Canada; ³AllyGabor Geoscience, Bellaire, Texas, 77401, United States

The tectonic evolution of Central and South Atlantic conjugate margins has recently been constrained by the integration of geological and geophysical data, including deep seismic reflection profiles extending from the coastline towards the oceanic crust. The syn-rift and halokinetic structures imaged in these profiles have fundamental impact on the petroleum exploration of deep water regions, allowing the identification of sedimentary depocenters with pre-salt and post-salt source rocks. Well and seismic data from conjugate basins along the Canadian (Nova Scotian) and Northwest African (Moroccan) margins indicate an initial phase of subsidence (Triassic rifting) followed by deposition of Late Triassic evaporites, which were coeval with a major magmatic event that is registered in the conjugate margins. Igneous intrusions within evaporite layers have also been recently recognized as part of the CAMP magmatism in the intracratonic Paleozoic basins in northern Brazil, with important effects on the petroleum systems.

The South Atlantic rifting in the Early Cretaceous formed conjugate basins along the Eastern Brazilian and West African margins. The new vintage of regional deep seismic profiles indicate that several segments of the incipient margin are characterized by the presence of seaward-dipping reflectors in the transition from continental to oceanic crust, which appear to be coeval with salt deposition. The pre-salt sedimentary package is characterized by a belt of proximal syn-rift tilted blocks which are overlain by an extremely thick sag basin in more distal areas. Several boreholes have drilled though the salt layer and resulted in important hydrocarbon discoveries in the South Atlantic. We discuss the analogies between structures imaged in the Central (Canada-Morocco) and South Atlantic (Eastern Brazil – West Africa), particularly in the ultradeep water regions that are exploratory frontiers for petroleum exploration.

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.<sup>2

1</sup>VU 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.

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 Cruz<sup>2

1</sup>PETROBRAS- 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.

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, Grant<sup>6

1</sup>Geological 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.

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.<sup>3

1</sup>Bird 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.

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, Djordje<sup>2

1</sup>Dalhousie 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.

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

Blissett, Donovan John¹; Butler, Karl¹; Keighley, Dave<sup>1

1</sup>University 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.

DEPTH-DEPENDENT EXTENSION AND MANTLE EXHUMATION: AN EXTREME PASSIVE MARGIN END-MEMBER OR A NEW PARADIGM?

Karner, Garry D.<sup>1

1</sup>ExxonMobil Upstream Research Company P.O. Box 2189, Houston, Texas, 77251-2189, United States

The discovery of exhumed continental mantle rocks and lack of magmas in ocean continent transitions, the existence of top-basement detachments, and the recognition of an “extension discrepancy” across many passive continental margins, as exhibited by preferential thinning of lower crust and the rapid thinning of continental crust in the absence of obvious faulting, have seriously challenged the accepted paradigms for the formation of passive continental margins and the way in which continental lithosphere is deformed in extension. Recent studies have clearly demonstrated that rifting, that is, the offset across high-angle basin bounding normal faults, is only a minor component in the thinning of continental lithosphere. During extension, early fault controlled subsidence tends to be limited to the proximal regions of passive margins while later brittle deformation dominates the distal regions. Kinematic considerations of passive margin subsidence require preferential bulk thinning of the lower crust and lithospheric mantle relative to the upper crust, an observation supported by seismic refraction results across the West African margin and the Exmouth Plateau, northwest Australia. Age considerations indicate that this depth-dependent extension (DDE) of the lithosphere is the significant process for thinning continental crust from its 30-40 km pre-rift thickness to a thickness of ~10 km, but surprisingly, depositional environments seem to be characterized by shallow water and quiescent conditions, as evidenced by Tithonian carbonates of the Iberian margin now at abyssal depths. Such extension partitioning requires a lateral strain balance, which may take the following form: 1) a counterbalancing of upper crustal extension leading to late-stage brittle deformation in the vicinity of the ocean-continent transition zone (e.g., the low angle detachment systems of the distal Iberian margin), and/or 2) the lateral emplacement and exposure of serpentinized and magmatically modified continental mantle and lower crust out from under the adjacent continental lithosphere. While isostatic considerations of DDE allow the distribution and amplitude of syn- and post-extension accommodation to be calculated, a geological understanding of the thinning process and the modes of crustal and mantle deformation cannot be addressed. Thus, the fundamental question remains: what mechanism(s) allow the continental lithosphere to be thinned from ~30 km to ~10 km and thence to the point of rupture? It has been suggested, using field observations from the exposed Tethyan margin in the Swiss Alps and geodynamic modeling, that the Iberia-Newfoundland system is the result of a complex rifting history that can be described as a sequence of different modes of extension. This sequence initiates with a broadly-distributed brittle deformation (stretching phase) and is followed by strain localization and crustal thinning along upper crustal and mantle ductile shear zones decoupled along a mid-crustal décollement, localized and controlled by a relatively weak middle crustal rheology (thinning phase). If and when coupling of the thinned upper and lower crust occurs (i.e., once the crust has reached a thickness of ~10 km), crustal embrittlement and continued extension leads to the formation of crustal-scale detachments along downward-concave faults that are conducive to mantle exhumation (exhumation phase). While this sequencing is a working hypothesis for how continental lithosphere extends, the view is that the final crustal architecture of at least the Iberia-Newfoundland margin is controlled by the stacking of these different modes of extension. Thus, given the field and drilling observations from the Iberia-Newfoundland and Tethyan margins, the proxy for extensional strain partitioning in the crust is the existence of syn-extensional sags and the exhumation of lower crust and continental mantle. The width of these exhumed zones may be 100’s km wide and contain organized magnetic anomalies. However, these magnetic anomalies are likely a consequence of mantle exhumation and serpentinization rather than mid-ocean ridge basalt production at the spreading center. Many passive continental margins are characterized by such observations, for example, Galicia Bank and the Iberian margin, the Exmouth, Queensland and Marion Plateaus, the Woodlark basin, the West African margin, and the Norwegian margin. While the geological details and sedimentary facies differ between the various margins, the style of deformation is remarkably similar. It would appear that what was once considered an extreme end-member of passive margin formation (viz., the Iberian-Newfoundland margin) may instead be a template for the development of many hyperextended margins around the world, that is, continental lithosphere that has undergone 100’s of percent of extension to the point of rupture. The modes of extension discussed above have immense implications for the heat flow history, environments of deposition, syn-extensional stratigraphy, and basin architecture of passive margin systems. A goal of this presentation is to show examples of depth-dependent extension and changing modes of crustal deformation. Our future challenge is to understand exactly how to link crustal deformation with lithospheric mantle thinning in a predictive way.

CONTINENTAL BREAK-UP MECHANISM; LESSONS FROM SLOW-, INTERMEDIATE- AND FAST-EXTENSION SETTINGS

Nemcok, Michal¹; Stuart, Charles¹; Rosendahl, Bruce ¹; Welker, Chelsea¹; Sheya, Cameron¹; Smith, Stan¹; Sinha, Sudipta²; Choudhuri, Mainak²; Yalamanchili, Rao³; Allen, Richardson¹; Reeves, Colin⁴; Sharma, Suraj²; Srivastava, Deepak⁵; Venkatraman, Sujata⁶; Sinha, Neeraj<sup>2

1</sup>University of Utah 423 Wakara Way, Suite 300, Salt Lake City, UT, 84108, United States; ²Reliance Industries Ltd., Petroleum Business (E&P), Reliance Corporate Park, Block 5, A Wing, Mumbay, India, 400701, India; ³Fugro Robertson Inc., 6100 Hillcroft, 5th floor, P.O. Box 740010, Houston, Texas, 77274, United States; ⁴Earthworks bv, Achterom 41a, Delft, Netherlands, 2611 PL, Netherlands; ⁵Department of Earth Science at IIT Roorkee, Roorkee, Uttarakhand, 247 667, India; ⁶ION Geophysical 2105 CityWest Boulevard, Suite 900, Houston, Texas, 77042-3847, United States

Sea-floor spreading mechanisms vary among slow, intermediate and fast-spreading systems. Do continental break-up mechanisms vary for slow-, intermediate- and fast-extension systems?

Because the slow-extension break-up mechanism is established by studies of conjugate Iberia and Newfoundland margins of the Central Atlantic and European and Adria margins of the Liguria-Piemonte Ocean, this study focuses on intermediate and fast rates, which are known from Gabon-Cameroon and East India, respectively. The study draws from synthetic interpretation of ultra-deep reflection seismic, well, gravity, magnetic and outcrop-derived paleostress data.

The interpretation indicates that continental break-up is done by a single continental mantle unroofing mechanism in all systems, just progressively more masked by magmatism at faster-extension systems. Breaking-up of the intermediately fast Gabon system is characterized by upper continental crust partially decoupled from the continental mantle, while the fast E India system underwent decoupling and its lower crust underwent up-bulging in zones in immediate footwalls of main normal faults. Regardless of the extension rate, the upper crustal break-up is controlled by pre-existing anisotropies, which form a system of constraining “rails” for extending continental crust and which influence the local stress regime. Such local stress regime regains the regional character once the function of constraining rails vanishes during the unroofing of the upper continental mantle. Different regions reach different amounts of upper crustal stretching prior to break-up initiation. The break-up location is then controlled by the upper crustal energy balance principle of “wound linkage”, trying to use the minimum physical work for linking major upper crustal “wounds” and developing the upper crustal break-up.

THE NOVASPAN PROJECT: DEEP IMAGING OF AN ENIGMATIC CONTINENTAL MARGIN

Dinkelman, Menno G.¹; Shimeld, John W.<sup>2

1</sup>ION 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.

4D PHYSICAL MODELLING OF SALT TECTONICS IN SABLE SUB-BASIN, SCOTIAN MARGIN

MacDonald, Cody¹; Campbell, Clarke²; Cribb, Jonathan²; Adam, Juergen³; Nedimovic, Mladen²; Louden, Keith ⁴; Kreszek, Csaba<sup>5

1</sup>Dalhousie University Department of Earth Sciences, Dalhousie University, Halifax, Nova Scotia, B3H4J1, Canada; ²Department of Earth Sciences, Dalhousie University, Halifax, Nova Scotia, B3H4J1, Canada; ³Department of Earth Sciences, Royal Holloway University of London, Egham, Surrey, TW20 0EX, United Kingdom; ⁴Department of Oceanography, Dalhousie University, Halifax, Nova Scotia, B3H4J1, Canada; ⁵Chevron Norge AS, Karenslyst Alle 2, P.O. Box 97, Skoyen, Oslo, 0212, Norway

Salt tectonic structures of the interconnected Sable, Abenaki, and Laurentian sub-basins at the north-central Scotian margin indicate variable rift-basin geometries and tectono-sedimentary environments with high rates of sedimentation and progradation during the Jurassic and Early Cretaceous. The understanding of the deepwater tectono-stratigraphic framework in this area depends on our ability to accurately interpret the variable depositional systems and corresponding salt tectonic structures in these sub-basins. This study integrates seismic interpretation with analogue experiments to gain insight into the mechanics of thin-skinned deformation and halokinetic sequence stratigraphy in the Sable sub-basin. The experimental setup including salt basin morphology, sedimentation patterns and rates, and initial salt thickness is determined using the GXT NovaSpan survey and other public domain seismic reflection and well data. The initial salt basin morphology is modeled as two rift half grabens. Variable original salt thickness combined with high, shelf-oblique, sediment input in landward salt-withdrawal basins during the Middle Jurassic to Early Cretaceous has caused major salt inflation in the mid to distal salt basin. This inflated salt complex had a positive, pronounced, and irregular topography which resulted in localized depocenters throughout the Early to Late Cretaceous. These localized depocenters of the deepwater slope and basin have led to the development of a confined mini-basin bounded by a salt wall or diapir and an extensive allochthonous salt tongue. A compressional phase is seen during the Late Cretaceous in features such as thrusted packages of rafted sediments over a salt pillow and squeezed diapirs. The next phase of the study will focus on the 3D depositional patterns of the entire north-central Scotian margin to analyze the linked structural evolution of the Laurentian, Abenaki, and Sable sub-basins. Improved understanding of the structurally dynamic depositional system of the Scotian Basin will support future exploration activities in the slope and deepwater basin.

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, Csaba<sup>4

1</sup>Dalhousie 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.

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

Bottomley, Steven¹; Jeans, Pete<sup>2

1</sup>Premier 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.

SEQUENCE STRATIGRAPHIC ANALYSIS OF ATLANTIC MARGIN ON NEW JERSEY COASTAL PLAIN: IMPLICATIONS TO GLOBAL SEA-LEVEL STUDIES

Mizintseva, Svetlana F<sup>1

1</sup>Rutgers University 610 Taylor rd, Piscataway, NJ, 08816, United States

Our studies on New Jersey Coastal Plain indicate existence of the Santonian-early Campanian (Merchantville Formation) unconformity-bounded sequences that originated from sea-level changes. The ages of the Merchantville sequence boundaries are similar to those of Russian platform and northwestern Europe, implicating a global cause of their origin. The ages of the Santonian-early Campanian sequences boundaries appear to match the ages of deep-sea benthic foraminiferal δ¹⁸Ο increases from ODP 511 site (Franklin plateau), implying that the Santonian-Campanian δ¹⁸Ο signature was, at least in part, due to development of ice sheets. Miller et al. (2003) explained the presence of ice sheets in the greenhouse world of the Late Cretaceous by proposing that the ice sheets were restricted to Antarctica and paced by Milankovitch forcing. Modeling of Milankovitch forces suggests that about 1/3 of the δ¹⁸Ο increase is attributed to ice and the 2/3 to deep-water cooling. The eustatic falls calculated from Milankovitch orbital solutions are similar to those obtained from the New Jersey margin backstripping analysis. The match of calculated results with our experimental sea-level estimates suggests that the Merchantville sequences on the New Jersey Coastal Plain are connected to the upper Santonian-lower Campanian global climatic variations and provides evidence for existence of small, ephemeral size ice sheets in Antarctica in the greenhouse world.

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, Djordje<sup>1

1</sup>Salt 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.

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

Hogg, John R.¹; Enachescu, Michael E.<sup>1

1</sup>MGM 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 believe that the Industry will resume exploration in the Flemish Pass, Carson and Saglek basins of Newfoundland, the Scotian Slope Basin and Jurassic Carbonate Trend and in 2012, if the George’s Bank moratorium is lifted, we will see exploration in the Georges Bank Basin adjacent to the US border.

Canada’s Atlantic Margin remains an underexplored geological province with high risk and high reward situated in the proximity of world’s largest oil and gas market, in a harsh environment that has been conquered in both the Jeanne d’Arc and Scotian basins by on the shelf technologies.

CONTINENTAL BREAK-UP MECHANISM; LESSONS FROM SLOW-, INTERMEDIATE- AND FAST-EXTENSION SETTINGS

Nemčok, M.¹; Stuart, C.²; Rosendahl, B. R.²; Welker, C.²; Smith, S.²; Sheya, C.²; Sinha, S. T.³; Choudhuri, M.³; Yalamanchili, S. V. ⁴; Allen, R.²; Reeves, C.⁵; Sharma, S.²; Srivastava, D.²; Venkatraman, S.⁶; Sinha, N.<sup>2

1</sup>Energy and Geoscience Institute at University of Utah 423 Wakara Way, Suite 300, Salt Lake City, UT, 84108, United States; ²423 Wakara Way, Suite 300, Salt Lake City, UT, 84108, United States; ³Reliance Industries Ltd., Petroleum Business (E&P), Reliance Corporate Park, Block 5, A Wing , Navi , Mumbai, 400701, India; ⁴Fugro Robertson Inc., 6100 Hillcroft, 5th floor, P.O. Box 740010, Houston, TX , 77274, United States; ⁵Earthworks bv , Achterom 41a, 2611 PL, Delft, Netherlands; ⁶ION Geophysical 2105 CityWest Boulevard, Suite 900, , Houston, TX , 77042-3847, United States

Sea-floor spreading mechanisms vary among slow, intermediate and fast-spreading systems. Do continental break-up mechanisms vary for slow-, intermediate- and fast-extension systems?

Because the slow-extension break-up mechanism is established by studies of conjugate Iberia and Newfoundland margins of the Central Atlantic and European and Adria margins of the Liguria-Piemonte Ocean, this study focuses on intermediate and fast rates, which are known from Gabon-Cameroon and East India, respectively. The study draws from synthetic interpretation of ultra-deep reflection seismic, well, gravity, magnetic and outcrop-derived paleostress data.

The interpretation indicates that continental break-up is done by a single continental mantle unroofing mechanism in all systems, just progressively more masked by magmatism at faster-extension systems. Breaking-up of the intermediately fast Gabon system is characterized by upper continental crust partially decoupled from the continental mantle, while the fast E India system underwent decoupling and its lower crust underwent up-bulging in zones in immediate footwalls of main normal faults. Regardless of the extension rate, the upper crustal break-up is controlled by pre-existing anisotropies, which form a system of constraining “rails” for extending continental crust and which influence the local stress regime. Such local stress regime regains the regional character once the function of constraining rails vanishes during the unroofing of the upper continental mantle. Different regions reach different amounts of upper crustal stretching prior to break-up initiation. The break-up location is then controlled by the upper crustal energy balance principle of “wound linkage”, trying to use the minimum physical work for linking major upper crustal “wounds” and developing the upper crustal break-up.

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 <sup>6

1</sup>Memorial 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, Jeremy<sup>1

1</sup>Memorial 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.

LITHOSPHERIC DENSITY VARIATIONS AND MOHO STRUCTURE OF THE IRISH RIFTED CONTINENTAL MARGIN FROM CONSTRAINED 3-D GRAVITY INVERSION

Welford, J. Kim¹; Hall, Jeremy²; O’Reilly, Brian<sup>3

1</sup>Memorial University of Newfoundland 300 Prince Philip Drive, St. John’s, NL, A1B 3X5, Canada; ²300 Prince Philip Drive, St. John’s, NL, A1B 3X5, Canada; ³Dublin Institute for Advanced Studies, 5 Merrion Square, Dublin, 2, Ireland

The structurally complex Irish margin was separated from its conjugate pair, the northern Flemish Cap/Orphan Basin region, during Late Cretaceous rifting of the North Atlantic. While crustal-scale 2-D seismic surveys have been collected across many parts of the margin, the results generated from these surveys cannot easily be interpreted in a regional sense due to their sparse sampling. We have undertaken a 3-D gravity inversion of the free air data over the Irish margin in order to generate a 3-D density anomaly model that can be compared with the seismic results and used to gain insight into regions lacking seismic coverage. We use the GRAV3D inversion algorithm and constrain our inverted model with bathymetric and sediment thickness information. We are able to closely reproduce the observed gravity anomalies over the margin and use the resultant density anomaly model to interpret the regional Moho structure by identifying a density isosurface appropriate for the crust-mantle transition. Our interpreted Moho shows good correspondence with Moho depths from seismic results while providing a more detailed Moho depth map over the region. This map allows the lateral extent of crustal thinning beneath the Rockall Trough, the Porcupine Seabight Basin and south of Goban Spur to be investigated. We present regional cross-sections through the 3-D model to highlight lateral variations in Moho structure and lithospheric densities. We also compare sediment and crustal thickness across the margin to show deviations from local isostatic compensation. These deviations correlate with faults and rifting trends along the boundaries of most of the main structural features. Ultimately, the insights provided by our results must act as constraints for future paleoreconstructions of North Atlantic rifting.

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. Kim<sup>2

1</sup>Geological 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.

THERMAL EFFECTS OF SALT ON THE PETROLEUM SYSTEM: EVIDENCE FROM FISSION TRACK THERMOCHRONOLOGY, FLUID INCLUSIONS AND BASIN MODELLING

Zentilli, M.¹; Wielens, H. ²; Grist, A. M. ³; Kettanah, Y. ⁴; Negulic, E. ⁴; Brown, E. <sup>5

1</sup>Department of Earth Sciences Dalhousie University, Halifax, Nova Scotia, B3H 4J1, Canada; ²Geological Survey of Canada – Atlantic, NRCAN, Dartmouth, Nova Scotia, B2Y 4A2, Canada; ³Department of Earth Sciences, University of Queensland, Brisbane, Queensland , 4072, Australia; ⁴Dalhousie University, Halifax, Nova Scotia, B3H 4J1, Canada; ⁵Dept. of Geology, St. Mary's University, Halifax, Nova Scotia, B3H 3C3, Canada

The thermal conductivity of salt is up to four times greater than other sedimentary rocks, thus salt diapirs focus geothermal heat resulting in a high-temperature anomaly in overlying basinal sediments. Depending on the shape of the salt body and its depth, the heat flow over the salt can be 2 to 3 times greater than away from the salt, with consequent drastic effects on diagenesis and hydrocarbon maturation; i.e., over mature above, and under mature below salt. In addition to heat conduction, advection of warm fluids (brines, oil and gas) produces highly localized heat anomalies on top of diapirs, as previously proposed by others for offshore Atlantic Canada.

In the Maritimes basin, Early Carboniferous salt of the Windsor Group has risen to the surface locally from a depth of ca. 8 km. Apatite fission track data indicate that the basin was inverted and rocks now at surface cooled below ca. 100^oC during the Triassic-Jurassic Atlantic margin breakup, whereas apatite within siltstone in the salt diapir yields apparent Cretaceous ages; the temperature-sensitive fission-track lengths having been significantly shortened (equivalent to what happens >3 km depth in a well). Time-temperature modelling of the data requires re-burial of the salt structure post-Early Cretaceous, and heating the diapir to higher temperatures than the regional background, confirming the focused thermal effects of the diapir. We have demonstrated similar thermal effects from evaporite diapirs in the Sverdrup Basin in the Canadian Arctic.

We have studied fluid inclusions in autochthonous and allochthonous salt in Atlantic Canada. Supposedly impermeable salt contains a variety of generations of fluid inclusions, some with brines, some with oil and gas. It is evident that salt has been permeable to various fluids. Entrapment temperatures of the fluids vary from 25^oC to more than 100^oC. For autochthonous Jurassic salt this implies a sub-salt source rock or an algal source within the salt.

Modelling of Scotian Basin wells; e.g., Wyandot, using Petromod^® shows that the presence of salt in the stratigraphic column results in drastic changes in the thermal evolution of the petroleum system.

THERMOCHRONOLOGY EVIDENCE FOR MESOZOIC AND CENOZOIC INVERSIONS OF THE CONTINENTAL MARGIN OF NOVA SCOTIA, CANADA

Zentilli, M.¹; Grist, A. M.²; Ryan, R.³; Ravenhurst, C. E.¹; Li, G.<sup>1

1</sup>Department of Earth Sciences Dalhousie University, Halifax, Nova Scotia, B3H 4J1, Canada; ²Department of Earth Sciences, University of Queensland, Brisbane, Queensland, 4072, Australia; ³Nova Scotia Department of Natural Resources, PO Box 698, Halifax, Nova Scotia, B3J 2T9, Canada

Considerable erosion followed the folding, metamorphism and grainotoid intrusion (ca. 380 Ma) of the Devonian Acadian Orogeny. By the Early Carboniferous (ca. 350 Ma) coarse clastics - followed by extensive marine carbonates and evaporites - were deposited non-conformably on exhumed granitoids and metamorphic rocks. The Carboniferous-to-Permian Maritimes Basin developed, accumulating clastic sediments in excess of 12 km in its depocentre further north. Maximum burial of the basin was attained in the Late Carboniferous (ca. 300 Ma), and the youngest sediments preserved in this basin are Lower Permian in age. Apatite fission track thermochronology studies have shown that basin inversion led to erosion of ca. 5 km of strata in the Late Triassic, coinciding with the Atlantic break-up unconformity, and preceding extensive but short-lived basaltic magmatism (ca. 200 Ma). The traditional view of gradual exhumation and peneplanation of the Nova Scotia margin since the Triassic-Jurassic is untenable. During the Aptian-Albian, continental sediments were deposited throughout Atlantic Canada over a weathered surface that included karst and has wide expression along the margin. The exhumation of the land went hand in hand with deposition in the adjacent Scotian Basin, part of the present Atlantic passive margin, an active depositional basin from the Late Triassic-Early Jurassic to the present. In such a passive margin it was expected that rocks deep in offshore wells would be at their maximum temperature today. However, our apatite fission track thermochronology data indicates that rocks in offshore wells were once tens of degrees hotter (e.g. within the oil window) than at present, and that substantial post-Paleocene cooling has occurred. Although higher paleo-mean annual surface temperatures in the Late Cretaceous may account for some of the thermal anomaly detected, the most probable cause for this cooling is inversion of the margin and erosion of ca. 1 km of post-Albian cover from onland and offshore, probably in the Eocene - Oligocene. This Tertiary inversion may have important implications for hydrocarbon maturation, the distribution of deep-water sand bodies, overpressures, and post-Paleocene canyons and unconformities.

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

Beglinger, Suzanne Elisabeth¹; Doust, Harry¹; Cloetingh, Sierd<sup>1

1</sup>VU University, Amsterdam De Boelelaan 1085, Amsterdam, --, 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.

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, Christopher<sup>1

1</sup>Dalhousie 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.

LOWER TERTIARY MASS TRANSPORT SYSTEMS EXHIBITED IN UPPER CRETACEOUS WYANDOT CHALK

Smith, Brenton<sup>1

1</sup>CNSOPB 1791 Barrington St, Halifax, NS, B3J3K9, Canada

The Upper Cretaceous Wyandot formation is a thick, continuous package of limestones, marls and chalks representing deposition on a stable, shallow, open-marine continental shelf.

Extremely detailed mapping of this surface is made possible by the strong seismic signature at the top of the Wyandot limestone. Interpretation of 16 3-D surveys covering 12,000 km² has described a complicated surface with varying degrees of erosion and has detailed several erosional features. The mapping results are displayed as a 3-D surface from which the following can be observed.

• A polygonal pattern covering much of the original chalk surface, possibly caused by brittle deformation of the Wyandot, has widths of up to 150 m.
• Early tertiary deltas prograding onto the Wyandot surface formed a series of troughs and ridges along the toe of these deltas. Most of these patterns were eroded by subsequent mass transport systems.
• Slope failure of the prograding Paleocene and Eocene deltas resulted in erosion of the upper Wyandot formation. A failure plane in the upper Wyandot detached creating a clearly defined head scarp of ~80m in height. This scarp is over 100 km in length. A 5 km wide mass transport corridor leading out to the shelf break is also clearly imaged.
• Large slide blocks over 1 km long within the mass transport systems can be observed. Numerous failure events have overprinted, resulting in a complicated pattern of mass transport systems and varying degrees of Wyandot erosion.

These observations indicate that large quantities of transported Wyandot chalkswere redeposited out to at least the upper slope. These chalks would be mixed with Tertiary delta sediments. Redeposited chalks are a major reservoir in the North Sea. Demonstrating that tertiary deltas transported sediments to the slope provides additional evidence that similarly situated, early and middle Cretaceous deltas may have also transported sediments to the slope.