Conjugate Margins

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BALTIMORE CANYON UNTESTED GAS POTENTIAL

Epstein, Samuel Abraham1; Clark, Donald2

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

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

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

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

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

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

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

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

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





THE UPPER CRETACEOUS SOURCE ROCKS AND PETROLEUM TRANSPORTATION OF THE WEST SLOPE REGION IN THE WESTERN SONGLIAO BASIN, DAQING OILFIELD, NORTHEAST CHINA

Kang, Dejiang1

1Basin and Reservoir Research Center China University of Petroleum , Beijing Changping district, Beijing, 102249, China

The Songliao basin is a typical continental petroliferous basin located in northeast China. Its western sector, the west slope region, is an important hydrocarbon province, where one of the most important oil discoveries in China was made. Although Cretaceous source rocks are understood to be important parts of petroleum systems in the western Songliao basin, the identification of Mesozoic source rocks which the oil and gas belong to in the subsurface is poorly understood. Associated shales of Middle Cretaceous have long been considered to be the primary Mesozoic source rocks for the western Songliao basin without any support from subsurface geochemical and geological data, even without the specific source rock layer. However, new data have been gathered from Cretaceous sediments that were penetrated by the new development wells and testing wells with a maximum depth of 2500m (8,240 ft). The well was drilled on the Taikang uplifted structural, the west overlap belt and Fuyu structural belt in 2002 and documented specific effective source rocks. Geochemical analyses indicate that Qingshankou formation(K1qn), which is the Lower Cretaceous mudstones, is good to excellent source rocks for the commercial oil wells in the west slope region whereas the Nenjiang formation (the upper Cretaceous) (K2n) has little function. This discovery revised the former wrong ideas. Combined with seismic data and the evolution of tectonic movements, it is deemed that the hydrocarbon were transported from Qijia—Gulong depression where is located on its eastern area after be generated. In this course, the faults played the important role in change the transportation direction. The whole petroleum system of west slope region in western Songliao basin, with a geographical extent of 17,000 km2 (6560 mi2) and a cumulative amount of source rocks reach 300 m (980 ft), represents a favorable target for future exploration, that is Nenjiang formation in the study area.





PETROLEUM SYSTEMS OF THE U.S. CENTRAL ATLANTIC MARGIN

Post, Paul J1; Sassen, Roger2

1MMS 1201 Elmwood Park Blvd., New Orleans, LA, 70123, United States; 2Dept. of Geology & Geophysics - Geochemical & Environmental Research Group - Texas A&M University, College Station, TX, 77845, United States

From 1975–1988, a single stage of expensive, disappointing hydrocarbon exploration took place on the U.S. Atlantic margin (USAM). Fifty-one wells (5 COST – 46 industry) were drilled in the Georges Bank basin, Baltimore Canyon Trough (BCT), and Southeast Georgia Embayment: none were drilled in the Carolina Trough.

Tested play types included drape/compaction structures, amplitude anomalies, listric fault traps, a dyke-swarm cored uplift, various carbonate margin plays, and slope-apron siliciclastics. The only positive results in the USAM were the gas encountered and/or tested in the eight wells drilled in the four-block Hudson Canyon (HC) 598 area, a listric fault trap in the BCT.

Analogs previously applied to USAM basins are inappropriate. While the same geologic age, they differ in regional and local setting. Carbonate and clean/mature siliciclastic reservoir analogs in the Gulf of Mexico Mesozoic basins are located on salt rollers, or related to salt-cored or salt-withdrawal structures. Other than in the Carolina Trough, similar structures are not widely recognized in USAM basins. The productive Sable sub-basin siliciclastic depocenter is located basinward from the carbonate margin and reservoirs are often overpressured, preserving porosity and permeability. In USAM basins, siliciclastic depocenters are generally landward from the margin and reservoirs encountered to date are not overpressured.

Throughout the USAM, issues regarding petroleum system elements include: generally degrading siliciclastic reservoir quality with depth, poorly developed carbonate reservoir facies, identification and areal distribution of source rocks, and timing of seal deposition/lithification in carbonate margin tests drilled to date. Petroleum system processes; i.e., timing of hydrocarbon generation–migration–accumulation are also poorly understood and appreciated.

Assessment of these basins using a forensic petroleum system approach may provide guidance for future exploration strategies.





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

Odegard, Mark1; Post, Paul J.2; Dickson, William3

1Grizzly 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.3

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

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

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

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





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

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

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

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

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





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

Coffey, Brian P.1; Read, Fred2

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

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

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

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





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

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

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

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

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





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

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

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

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





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

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

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

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

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





RIVER SOURCE AND DISPERSION OF LOWER CRETACEOUS SANDS, SCOTIAN BASIN

Pe-Piper, Georgia1; Triantafyllidis, Stavros1; Piper, David J.W.2

1Saint Mary's University 933 Robie Street, Halifax, Nova Scotia, B3H 3C3, Canada; 2Geological Survey of Canada Atlantic, Dartmouth, Nova Scotia, B2Y 4A2, Canada

Understanding the source and dispersion of Lower Cretaceous deltaic sandstones is important for predicting (1) the distribution of sandstone; (2) the availability of quartz; and (3) regional variation in diagenesis. Many analytical techniques to identify sediment provenance have been applied to samples from conventional cores from offshore Scotian basin wells and fields ranging from Naskapi N-30 in the west to Dauntless D-45 in the east. The results were compared with similar analyses of onshore Chaswood Formation samples.

Geochronology of detrital monazite shows several modes: ~330 and ~400 Ma at the Naskapi N-30 well; ~400 Ma in wells from the Alma field to the Venture field, with minor ~1.0 and ~1.65 Ga modes; and predominant ~1.0 and ~1.8 Ga modes at the Peskowesk A-99 well, with a minor ~380 Ma mode. Detrital zircons show similar modes. However, the ~1.0 Ga mode predominates from the Alma field to the Venture field, and an additional ~650 Ma mode is present. Morphology and texture show that 45–80% of detrital zircon is of first cycle igneous origin, with the proportion of polycyclic zircon decreasing stratigraphically upward. Sources of monazite and zircon are further constrained by mineral chemistry. Variation in abundance and chemical composition of heavy minerals, notably chromite, tourmaline and garnet, has been determined.

Bulk-rock geochemistry provides information on the total source area, whereas mineralogical studies emphasize source rocks containing heavy minerals. The Ti content of Scotian basin shales is almost double the world average due to detrital ilmenite. Fe is also abundant and Ca very low. Sandstones show geochemical variability within the basin; however, shales are more uniform geographically.

The integration of this data suggests that the Naskapi N-30 well was supplied by a river that also furnished sediment to the Chaswood Formation in central Nova Scotia. The sandstones in the area from the Alma field to the Venture field were sourced from a major river draining Newfoundland. Sandstones on the eastern Scotian Shelf were sourced by one or more separate rivers, also draining Newfoundland.





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

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

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

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





UNUSUAL JURASSIC CONDENSATE OF THE HUDSON CANYON AREA, U.S. ATLANTIC

Sassen, Roger 1; Post, Paul J.2

1Geochemical and Environmental Research Group (GERG) 833 Graham Road, College Station, TX, 77845, United States; 2U.S. Department of the Interior, Minerals Management Service, Office of Resource Evaluation / 1201 Elmwood Park Blvd., New Orleans, LA, 70123, United States

Gas and minor condensate was discovered in Late Jurassic and Early Cretaceous reservoirs in the Hudson Canyon (HC) 598 area of the Baltimore Canyon Trough (BCT).

The oldest sedimentary rocks in the BCT are interpreted to be Triassic syn-rift deposits. Predominantly carbonate Early to Middle Jurassic units overlie the Triassic and underlie the Late Jurassic–Early Cretaceous siliciclastic reservoirs.

Condensates from the Kimmeridgian (HC 598-1) and Albian (HC 642-2) reservoirs originate from the same source rock. While biomarkers are absent or in low relative abundance in the condensate, diamondoids, consisting primarily of adamantane and diamantane, along with their methyl and ethyl derivatives, are relatively abundant. The diamondoids have been concentrated during intense thermal cracking of an original oil. The carbon isotopic properties of the condensate are extremely enriched in 13C (-23.7‰ to -24.6‰ PDB), consistent with a Jurassic marine kerogen source. Triassic source rocks appear unlikely to have sourced these condensates because Triassic-sourced oils in the Newark and Culpepper basins are strongly depleted in 13C. The unusual geochemistry of the condensate is interpreted to be the result of extreme thermal cracking of oil sourced from the underlying Early to Middle Jurassic carbonate-rich source rocks. Diamondoid maturity indices suggest that the maturity of the condensate ranges from ~1.3% to ~1.6% vitrinite reflectance (Ro), significantly higher than the estimated ~0.9% Ro of the deepest Kimmeridgian reservoir. Vertical migration of deeper, more mature hydrocarbons into shallower reservoirs was facilitated by faults connecting the source and the reservoir.

The enrichment of diamondoids and 13C are similar to condensates sourced by the Late Jurassic Smackover Formation of the U.S. Gulf Coast. The role of Jurassic oil-prone source rocks in the Central Atlantic is underappreciated.





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

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

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

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

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

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





4D RIFT ANALYSIS FOR THE JEANNE D’ARC BASIN

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

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

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





FUTURE PROSPECTS OF OIL AND GAS WITHIN SELECTED TARGET AREAS OF SCOTIAN SHELF AND SLOPE, OFFSHORE NOVA SCOTIA, EASTERN CANADA: EVALUATION BASED ON PETROLEUM SYSTEMS RISK ASSESSMENT

Mukhopadhyay (Muki), Prasanta K.1; Harvey, Paul, J.2

1Global Geoenergy Research Ltd. ,, Halifax, --, B3J 2A1, Canada; 2Nova Scotia Department of Energy, Halifax, NS, B3J 3P7, Canada

Recent deepwater drilling surrounding the Sable Subbasin within the Scotian Slope, Eastern Canada has indicated that the successes/failures in finding economic hydrocarbon discoveries are closely related to complex petroleum systems and mobilization of Jurassic salts compared to deepwater basins of both the Gulf of Mexico and Angola. New comprehensive research combining seismic stratigraphy, heat flow assessment, geochemical fingerprinting, and petroleum system modeling of the Triassic-Tertiary sediments from the Scotian Slope reveals that the formation, timing, and fluidity of several large allochthonous salt canopies (Sable Subbasin) or autochthonous salt diapers (area between Sable and Shelburne Subbasins) are closely connected to source rock anoxicity, bypassing of turbidite sands (in early Tertiary and late and middle Cretaceous), and the survival of hydrocarbons within various play types. Early mobilization of Jurassic salt forming large canopies (especially within the Tertiary sediments of the Sable Slope) possibly originated from enhanced heat flow and three-phase fluid flow in the late Jurassic-early Cretaceous. Our study indicates that the various play types (especially the salt flank and salt top reservoirs) in the late Jurassic and early Cretaceous may possibly be charged with three petroleum system hydrocarbons (gas-condensate, light oil-gas and heavy oil-gas) within the Sable (beyond 2500m water depth) and Shubenacadie-Shelburne Slopes (beyond 1500m). The late Triassic/Early Jurassic lacustrine and Jurassic/Cretaceous Verrill Canyon marine source rocks are the most significant components within various petroleum system hydrocarbons although the timing of hydrocarbon charge could be significantly different in various parts of the Scotian Basin.





MID TO LATE CRETACEOUS STRUCTURAL AND SEDIMENTARY ARCHITECTURE AT THE TERRA NOVA OILFIELD, OFFSHORE NEWFOUNDLAND – IMPLICATIONS FOR TECTONIC HISTORY OF THE NORTH ATLANTIC

Sinclair, Iain1; Withjack, Martha O.2

1Husky Energy Suite 901, Scotia Centre, 235 Water St., St. John's, NL, A1C 1B6, Canada; 2Rutgers University, Geological Sciences, 610 Taylor Road , Piscataway, NJ, 08854-8066, United States

Multiple exploration, delineation, and development wells, in association with a high-quality 3D seismic survey over the Terra Nova oilfield, provide a detailed data set for the analysis of the mid to Late Cretaceous structural and stratigraphic development of the Jeanne d’Arc basin on the Grand Banks of Newfoundland.Closely spaced wells allow for recognition of multiple parasequences of shoreface to shelf silciclastic sediments deposited during falling relative sea level in Hauterivian through Barremian time.The northward translation of the coastline with progressive truncation of the parasequences to the south demonstrates that regional uplift of the southern margin of the Jeanne d’Arc basin occurred during and immediately following deposition of these progradational parasequences.The upper bounding surface, defined by an angular unconformity with widespread evidence of valley incision, is dated as mid-Aptian.Highly variable thicknesses of back-stepping coastal plain, shoreface and marine shelf strata document a long-term increase in relative sea level accompanied by abrupt changes in subsidence rates occurring across W- to NW-striking, syn-depositional normal faults active during the mid-Aptian through Middle or Late Albian. What do these patterns of uplift, subsidence, and faulting reveal about the tectonics of the Jeanne d’Arc basin during the mid-Cretaceous? Specifically, are the W- to NW-striking normal faults related to gravity-driven processes or plate-tectonic processes?Although the basin tilting and the presence of Triassic/Jurassic salt would support gravity-driven processes, erosion in the south and deposition in the north would inhibit the northward flow of salt.Additionally, evidence of synchronous detached shortening is lacking.Basement-involved extension would produce W- to NW-striking subsalt and suprasalt normal faults.These decoupled faults occur exclusively to the east of the border fault of the Jeanne d’Arc basin (i.e., the Murre fault).Thus, the Murre fault would have had both normal and strike-slip components of displacement during the mid-Cretaceous extension.





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

Dickson, William1; Odegard, Mark2; Post, Paul3

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

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




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

Rowan, Mark G.1

1Rowan 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.





EARLY INFILL OF THE TRIASSIC FUNDY BASIN: ARCHITECTURE OF THE WOLFVILLE FORMATION AND FLUVIAL EVOLUTION.

Leleu, Sophie1; Hartley, Adrian J.2; Jolley, David W.2; Williams, Brian P.J.2

1University of Aberdeen Meston Building, Aberdeen, Scotland, AB24 3UE, United Kingdom; 2Meston Building, Aberdeen, Scotland, AB24 3UE, United Kingdom

The Fundy Basin forms one of a series of early Mesozoic rift basins developed along the north-western Atlantic margin. Syn-rift continental sediments were deposited during Late Triassic times within the basin. The sedimentary succession comprises the lower fluvio-aeolian Wolfville Fm, the overlying ephemeral fluvial/playa Blomidon Fm capped by basaltic lava (Olsen et al., 1989; Wade et al., 1996). Three sub-basins are present in the Fundy Basin: the Fundy sub-basin, the Minas sub-basin to the east and the Chignecto sub-basin to the north. The Wolfville Fm displays a complex interplay of coarse and fine-grained fluvial sandstones, aeolian dune deposits and alluvial fan sediments. This study focuses on the Wolfville Fm stratigraphy and correlation within the gravely- and younger sandy-dominated fluvial deposits of the Minas sub-basin. This contribution will present a detailed analysis of the large scale architecture (27 km) of a gravely braided river system deposited within this endorheic basin, and will discuss the major changes in fluvial style within the basin. The palaeogeography of the Wolfville Fm is analyzed by determining the size of the braided river system and by taking an allostratigraphic approach to the recognition and correlation of extensive bounding surfaces. The bounding surfaces and cycles within both coarse and fine-grained fluvial units allow correlation across the basin. Together with a palynological analysis, the stratigraphy of the Wolfville Fm is assessed in the Minas sub-basin. This new scheme of the Wolfville Fm architecture in a better constrained timescale has the potential to help predict sand-fairways and reservoir architecture within similar coarse grained alluvial deposits.





CONTINENTAL RIFT BASIN FILLS: EVOLUTION FROM OPENED TO CLOSED STAGE (WOLFVILLE/ BLOMIDON FM, NOVA SCOTIA).

Leleu, Sophie1

1University of Aberdeen Meston Building, Aberdeen, Scotland, AB24 3UE, United Kingdom

Rift basins in continental settings tend to display a similar sedimentary evolution with an initial stage (1) characterized by alluvial fan deposition around the basin flanks and fluvial sequences in the basin centre and a later stage (2) dominated by lacustrine sedimentation in the basin centre. The syn-rift Late Triassic sedimentary succession of the Minas sub-basin (Bay of Fundy, Nova Scotia) shows this evolution. The sedimentary succession comprises the lower fluvio-aeolian Wolfville Fm (stage 1 deposits) and the overlying ephemeral fluvial/lacustrine/ playa Blomidon Fm (stage 2 deposits). This contribution presents a facies analysis of the transition between the two stages. The Wolfville Fm displays a complex interplay of coarse and fine-grained fluvial sandstones, aeolian dune deposits and alluvial fan sediments. The upper part of the Wolfville Fm (250 m of vertical section) which occurs beneath and is transitional into the lacustrine/ playa deposits of the Blomidon Fm is described here. Cyclicity within the sedimentary succession is illustrated by well organized and repetitive alternations of fluvial/ ephemeral fluvial/ lacustrine and aeolian sediments, which suggests a gradual evolution from stage 1 and stage 2 and a strong climatic influence on depositional architecture.





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

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

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

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. This latter, that therefore, must be considered as part of the rift system which led to the formation of the passive continental margin of Morocco, 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 of Ghorbal et al. (submitted) who, on the basis of low-termochronology, have demonstrated the existence of a Late Triassic to Middle Jurassic stage of subsidence followed by a Late Jurassic to Early Cretaceous exhumation.

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





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

Pena Reis, Rui1; Pimentel, Nuno2; Garcia, Antonio2

1University 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 1st 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, Kenneth2

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

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

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

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

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





SEAFLOOR DIAGENESIS OF THE SCOTIAN BASIN: THE ROLE OF FE, TI AND P

Okwese, Ann Chioma1; Pe-Piper, Georgia2; Piper, David J.W3

1Saint Mary's University 923 Robie Street, Halifax, Nova Scotia, B3H3C3, Canada; 2923 Robie Street, Halifax, Nova Scotia, B3H3C3, Canada; 3Geological Survey of Canada, Dartmouth, Nova Scotia, B2Y4A2, Canada

Diagenesis in Lower Cretaceous sandstones of the Scotian basin is an important reservoir quality. Diagenetic processes include the effects of seafloor redox-controlled changes in pore water and the re-mineralization of organic matter; as well as later cementation and secondary porosity resulting from increases in the temperature and pressure with burial and the flux of formation waters and hydrocarbon expelled from compacting shales. Lower Cretaceous rocks of the Scotian basin are deltaic, with cycles of delta progradation characterized by high sedimentation rates capped by transgressive systems tracts typified by low sedimentation rates.

Transgressive systems tracts (TST) in one well (Peskowesk A-99 with 7 conventional cores) from the Scotian basin were identified in conventional cores with the support of available wireline logs, and core photographs (CNSOPB Geoscience Research Laboratory). The TST sediment facies include bioturbated medium- to coarse-grained sandstones with patchy siderite cementation and some bioclasts, grading upward into bioturbated mudstones. Geochemically, the Lower Cretaceous sedimentary rocks of the Scotian basin are unusual in having high titanium (Ti) and iron (Fe) and very low calcium (Ca). As a result, the early diagenetic system is dominated by Fe minerals and locally by phosphorus (P) minerals. Samples have been collected from conventional cores through representative TSTs and underlying high-sedimentation rate deltaic sandstones in the Peskowesk A-99 well for whole-rock geochemical analysis. The vertical variation in particular Fe, Ti and P can be used to understand the seafloor diagenetic system and its relationship to abrupt changes in sedimentation rates in the TST.





DISTRIBUTION OF DIAGENETIC MINERALS IN LOWER CRETACEOUS SANDSTONES WITHIN A DEPOSITIONAL FACIES AND SEQUENCE STRATIGRAPHIC FRAMEWORK: GLENELG, THEBAUD AND CHEBUCTO FIELDS, OFFSHORE SCOTIAN BASIN

Karim, Atika1; Pe-Piper, Georgia2; Piper, David J.W.3

1Saint Mary's University Departement of Geology, 923 Robie St. , Halifax, Nova Scotia, B3H 3C3, Canada; 2Departement of Geology, 923 Robie St. , Halifax, Nova Scotia, B3H 3C3, Canada; 3Geological Surevy of Canada, Dartmouth, Nova Scotia, B2Y 4A2, Canada

The spatial and temporal distribution of diagenetic cements has been constrained in relationship to lithofacies and sequence stratigraphy of the Lower Cretaceous sandstones from the Glenelg, Chebucto and Thebaud fields in the Sable Subbasin. Coated grains of illite and chlorite occur in transgressive systems tracts (TST) in Glenelg N-49 and Thebaud I-93 and are cemented by Fe-calcite. Early kaolinite occurs as booklets and vermicular stacking textures principally in sandstones immediately beneath the TSTs, particularly in cross-bedded, coarse-grained, channel sandstones. Illite occurs as fibrous crystals, which in the Chebucto K-90 are included by ankerite. Fe-rich chlorite rims, found only in the Thebaud samples, have developed from earlier Fe-rich clay. Early pore-filling chlorite occurs in contact with detrital quartz lacking quartz overgrowths and is commonly associated with illite. Quartz cement, well developed in medium and coarse grained sandstones, postdates kaolinite and predates most other cements. Calcite, Fe-calcite, Mg-calcite, ankerite and siderite are the major cementing minerals in the studied wells. In Glenelg H-59, two siderite cements were defined; the earlier one occurs in TSTs as large, corroded crystals and is low in Mg. The late microcrystalline siderite (< 10 μm) is Mg-rich (~ 9 wt.%). It forms the tiny crystals that fringe detrital grains and fill intercrystalline micropores. Early calcite cement is found principally in bioturbated sandstones and mudstones with bioclasts, typical of the highstand systems tract (HST). In samples from the Glenelg field, perthite is replaced by Fe-calcite. Late framboidal pyrite in carbonate cement indicates burial under both reducing and alkaline conditions. Rare traces of francolite (1 to 6wt.% P2O5) are found in the Glenelg wells associated with illite and calcite cements. This study demonstrates that the distribution of diagenetic minerals and their impact on reservoir-quality evolution can be better elucidated when linked to a sequence stratigraphic framework.





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

McHone, Gregory1

1Stones2Gems 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.





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

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

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

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





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.2; Beunk, Frank F.2; Bertotti, Giovanni2; Andriessen, Paul A.M.2; Strasser-King, Victor E.H.3; Fode, Daniel V.A.3

1VU University Amsterdam De Boelelaan 1085, Amsterdam, Noord Holland, 1081 HV, Netherlands; 2De Boelelaan 1085, Amsterdam, Noord Holland, 1081 HV, Netherlands; 3Fourah 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 characterized by the formation of the Central Atlantic Magmatic Province (CAMP), covering once-contiguous parts of North America, Europe, Africa and South America. The Freetown Layered Igneous Complex (FLIC) emplaced within the heart of CAMP and measuring on surface, 65 x 14 x 7 km, is the largest single layered igneous intrusive yet known on either side of the Central Atlantic. Geophysical investigations indicate that the intrusion extends offshore to a depth of about 20 km. Geologically FLIC is a rhythmically layered elongated ultramafic-mafic lopolith divisible into 4 major zones each comprising repeated sequences of troctolitic, gabbroic and anorthositic rocks. A first series of 40Ar-39Ar analyses of plagioclases, biotites and amphiboles from zones 1 and 2 yields plateau ages ranging from 196.3 ± 3 Ma to 228.6 ± 6 Ma Because 40Ar-39Ar dates of these minerals represent cooling ages, we interpret these dates as representing a minimum intrusion-age of the Complex implying that its true emplacement age might be somewhat older than 230 Ma. Given that most established CAMP ages revolve around 200 Ma or younger, we hypothesize that FLIC represents a hitherto unknown pre-CAMP magmatic event that might have thermally triggered the initial break-up of Pangaea to form the Central Atlantic. This view is consistent with field-observations that the Complex is cross-cut by predominantly coast-parallel mafic dykes we attribute to the CAMP dyke-swarm. To ascertain the hypothesis, we are currently carrying out additional 40Ar-39Ar dating of zones 3 and 4 and the cross-cutting dykes to be followed-up by U-Pb zircon dating to establish, precisely, the true emplacement age of the Complex.





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

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

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

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

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





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

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

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

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

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

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

References

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

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

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

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

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

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





HYPERPYCNAL RIVER FLOODS AND THE DEPOSITION OF LOWER CRETACEOUS SANDS, SCOTIAN BASIN

Piper, David J.W.1; Karim, Atika2; Pratt, Heidi2; Noftall, Ryan 2; Gould, Kathleen2; Foley, James2; Pe-Piper, Georgia2

1Geological Survey of Canada (Atlantic) Bedford Institute of Oceanography, P.O. Box 1006, Dartmouth, NS, B2Y 4A2, Canada; 2Department of Geology, Saint Mary's University, Halifax, NS, B3H 3C3, Canada

The large supply of sand to the Scotian Basin in the latest Jurassic and early Cretaceous, resulting from tectonic reactivation of the Appalachian hinterland, produced coarse-grained braided rivers preserved in the Chaswood Formation. Such rivers have the propensity to discharge hyperpycnally during floods. The importance of such hyperpycnal flows can be evaluated from sedimentological criteria in conventional core. Thick bedded reservoir sandstones from fields such as Thebaud and Venture appear to be inner shelf hyperpycnal deposits (facies 9), forming graded sandstone beds decimeters to metres thick, with Bouma Ta-Tc sequences, abundant phytodetritus, detrital intraclasts of mudstone and siderite, and minor bioturbation at the top of beds. This facies passes stratigraphically upward into tidally influenced river-mouth and river-channel sandstones (facies 4) and downward into thinner graded sandstone beds with interbedded mudstone (facies 0). Highly bioturbated thin bedded sandstones (facies 2) in places show hummocky cross-stratification, concentration of shells at the base of beds, and wave-ripples, suggestive of storm reworking. In the Glenelg field, tidally-influenced hypopyncal silts interbed with hyperpycnal sands and both change character distally. Turbidites in the middle Missisauga Formation at Tantallon show petrography and sedimentary structures that indicate deposition from overbank hyperpycnal flows. Exploration models for the Scotian Basin must take account of this reinterpretation of the major sandstone facies. The presence of widespread hyperpycnal flows means that there may have been major transfer of sand to deep water. The rapid deposition of hyperpycnal flow sands, overlain by slowly sedimenting transgression surfaces, may have strongly influenced the style of early diagenesis and the neoformation of iron-rich clays that transformed on burial to chlorite rims.





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

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

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

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





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

Wu, Yue1; Louden, Keith2; Tari, Gabor3

1Dalhousie 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 ~64oW, 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 ~ 60oW 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.





PALEOCEANOGRAPHIC AND PALEOENVIRONMENTAL IMPLICATIONS FOR HYDROCARBON EXPLORATION OF THE CONTINENTAL SLOPE OFF NOVA SCOTIA

Jansa, Luba F.1

1Emeritus Scientist Geological Survey of Canada-Atlantic, Dartmouth, N.S., B2Y4A2, Canada

The continental slope off Nova Scotia has recently become of interest for oil exploration as a potentially new gas province, under the assumption that past success in exploration on the shelf can be extended onto the continental slope. Is such an assumption supported by the sediment depositional history on the shelf and by the general paleoceanography of the Central Atlantic Ocean during the late Mesozoic?

Of all elements of the Petroleum System, only the source rock and presence of reservoir rocks will be discussed. Source rock occurrences depend on marine organic matter generation and preservation. The former are controlled by the availability of nutrients supplied either by continental runoff (therefore controlled by climate), or as a result of coastal upwelling, surface water mixing, and open ocean divergence. Could such conditions have developed during the Mesozoic on the Scotian Slope? An additional constraint to be considered is ocean bottom water oxygenation, as such conditions changed dramatically during Mesozoic-Cenozoic time in the Central Atlantic. During the Late Jurassic, Late Cretaceous and early Cenozoic, oceanic bottom waters in this region were highly oxygenated, resulting in the destruction of organic matter deposited in ocean bottom sediments. In contrast, the middle Cretaceous was a period of organic matter preservation in deep sea and marginal basin sediments, either due to changes in deep water circulation, climate and/or increases in depositional rates.

Occurrence of reservoir rocks is another important parameter to be considered. The existence of both sandstone and carbonate reservoirs was proven by drilling on the shelf. For continental slope exploration, the petroleum industry applied known models of turbidite fans, apparently without giving sufficient consideration to the sediment supply and sea level changes affecting development of the shelf area during the Cretaceous. This may prove to be the major factor in a lack of commercial hydrocarbon discoveries in exploration wells drilled on the Scotian Slope. Deeper understanding of the geologic evolution of the continental margin and paleoceanographic conditions affecting it, together with a modification of exploration strategy are needed to improve the success of hydrocarbon exploration in the Scotian upper slope domain.





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, Mladen3

1Dalhousie 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 45-55o 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, Gabor3

1Petroleo 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.2

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

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




THE PENICHE BASIN:TECNO-SEDIMENTATION AND EXPLORATORY ASPECTS

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

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

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

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

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

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

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





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

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

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

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





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

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

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

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

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

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





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

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

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

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





A QUANTITATIVE 3D OUTCROP MODEL OF A GRAVEL DOMINATED FLUVIAL SYSTEM (LATE TRIASSIC, MINAS BASIN, NOVA SCOTIA, CANADA)

van Lanen, Xavier1; Hodgetts, David2; Redfern, Jonathan2; Williams, Brian3; Leleu, Sophie3

1PhD student Williamson Bld, Oxford Road, Manchester , Lancashire, M13 9PL, United Kingdom; 2Williamson Bld, Oxford Road, Manchester , Lancashire, M13 9PL, United Kingdom; 3Department of Geology & Petroleum Geology, King's College, Aberdeen, Aberdeenshire, AB24 3UE, United Kingdom

The Wolfville Formation was deposited in a rift basin setting during Anisian to Norian age. It is superbly exposed in both cliff sections and on extensive wave-cut platforms along the Minas Basin shore, Nova Scotia (Canada). This nature of the exposure provides unique three-dimensional sections, offering a valuable insight in the sedimentology and the facies geometries and distribution of a red bed braided fluvial-aeolian facies suite.

The selected study area is located on the southern Minas Basin shore and represents the lower unit of the Wolfville Formation. The area measures 400 m by 350 m and comprises Carnian to Norian age sediments that show a cyclicity of conglomerate / pebbly rich sandstone to a coarse lithic sandstone with sparse pebble sized clasts. The limited amount of preserved finer grained material throughout this gravel dominated system contains the faunal remains and palaeosol horizons. The base is characterised by the discordant contact with the Carboniferous and a thin alluvial breccia unit.

To obtain quantitative outcrop data, both LiDAR and DGPS data were collected and integrated with traditional geological field and laboratory data into a digital outcrop model (DOM). In the DOM the observed geological object are mapped and their geometries and distribution evaluated. The results offer a better understanding of the depositional system, and provide a geological framework for reservoir models. Such information aids improved reservoir characterisation and geostatistical modelling, as well as help explain seismic reflection data and improve flow model simulations for subsurface reservoirs.





CONTROLS ON FACIES DISTRIBUTION AND RESERVOIR DEVELOPMENT OF UPPER TRIASSIC RIFT CONTINENTAL SYSTEMS IN INTERMONTANE RIFT SETTINGS: A COMPARATIVE STUDY OF EXTENSIVE OUTCROPS IN SW MOROCCO

Redfern, Jonathan1; Mader, Nadine2; Fabuel Perez, Ivan3; Hodgetts, David3; El Ouataoui , Abedelmajid4

1University of Manchester Williamson building, Oxford Road, Manchester, Gt Manchester, M139Pl, United Kingdom; 2Hess Ltd, London, Greater London, WC2N 6AG, United Kingdom; 3Williamson building, Oxford Road, Manchester, Gt Manchester, M139Pl, United Kingdom; 4ONHYM, Rabat, xx, 10050, Morocco

Upper Triassic (Carnian) sediments in SW Morocco comprise a continental red bed sequence deposited in discrete rifted basins following the break up of Pangea and opening of the Atlantic. This comparative study examines extensive outcrops of the Oukaimeden Sandstones Formation (F5) in the High Atlas and Unit T6 in the Argana Basin, SW Morocco, deposited within a series of narrow fault bounded intermontane basins. Both contain a variety of braided fluvial, overbank, shallow ephemeral lacustrine, alluvial fan and aeolian facies.

Traditional sedimentological data (sedimentary facies logs, palaeocurrent information, gamma ray logs etc) has been combined with high resolution 3D laser (LIDAR) and Differential Global Positioning System (DGPS) to map these outcrops and provide a detailed dataset.

On a basin scale, the often complex facies distribution evident in the Argana Basin suggests a highly variable fill within these basin types. Correlation of individual facies elements is often difficult and relies on identification of key stratal surfaces. Local tectonics control accommodation and influence facies patterns, such as development of alluvial fans and entry points of major drainage systems. Significant changes in fluvial style, from ephemeral to perennial, are recognized in both basins within this interval, which suggests rejuvenation of the source areas and a potential interplay of climatic and tectonic control. An overall drying upward pattern is observed, with increasing influence of aeolian processes towards the top of both the Oukaimeden sandstone (F5) and T6 of Argana. This supports previous work that has demonstrated a change from humid to increasingly arid conditions during the Upper Triassic, recognized both throughout SW Morocco and in the Fundy Basin, Canada, and highlights the climatic control on the depositional system.

These studied sections offer potential analogues for subsurface Triassic hydrocarbon systems in similar settings, and provide valuable information on the tectonic and climatic control on depositional facies and architecture. Analysis of basin-wide facies variation, provenance and sediment pathways provide regional scale analogue data. More detailed field scale reservoir models have also been developed for the high net:gross intervals in the Oukaimeden sandstone.





MESOZOIC SEAFLOOR SPREADING HISTORY OF THE CENTRAL ATLANTIC OCEAN

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

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

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





PERMO-TRIASSIC BASINS FROM IRELAND TO NORWAY: BASIN ARCHITECTURE AND CONTROLS

Shannon, Patrick M.1; Stolfova, Katerina2

1University College Dublin UCD School of Geological Sciences, University College Dublin, Belfield, Dublin, 4, Ireland; 2UCD School of Geological Sciences, University College Dublin, Belfield, Dublin, 4, Ireland

Permo-Triassic strata are locally preserved in a swath of elongate basins of various shapes and sizes along the European margin of the North Atlantic. The burial of these basins beneath Jurassic, Cretaceous and Cenozoic strata, combined with tectonic effects of later rifting and continental breakup, means that the original extent and the large-scale depositional geometries of these basins are poorly constrained. This study uses seismic data, supplemented by core, wireline and outcrop information, to document the extensive development of proven (but poorly dated), largely non-marine, Permo-Triassic strata along the Irish, UK and Norwegian Atlantic margins. Data are examined from basins of different sizes, thicknesses and structural settings in the European North Atlantic region. A wide range of regional depositional geometries is identified within the Permo-Triassic to lowermost Jurassic succession. In some areas basins show pronounced asymmetry, controlled by long-standing reactivated faults. In other areas subtle broad fault-controlled geometries with switching fault polarities are documented. In yet other areas the Permo-Triassic to Lower Jurassic succession is characterized by simple uniform thicknesses across large regions. The basin architecture is controlled by a complex interplay of crustal thickness and thermal structure, inherited Variscan, Caledonian and older basement fabrics, inherited palaeotopography and the spatial and temporal rift history.





MIDDLE CENOZOIC DEPOSITIONAL PROCESSES ALONG THE WESTERN SCOTIAN MARGIN

Campbell, Calvin1; Mosher, David2; Wach, Grant3

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

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

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

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





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

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

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

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





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

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

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

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

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

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





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

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

1Department of Earth Sciences, Dalhousie University, Halifax, Nova Scotia, B3H 4J1, Canada; 2Geological Survey of Canada - Atlantic, Natural Resources Canada, P.O. Box 1006, Dartmouth, Nova Scotia, B2Y 4A2, Canada; 3S