Conjugate Margins

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

Jansa, Luba F.<sup>1

1</sup>Emeritus 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.

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

Kang, Dejiang<sup>1

1</sup>Basin 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.

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.<sup>3

1</sup>Saint 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.

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

Karner, Garry D.<sup>1

1</sup>ExxonMobil URC P.O. Box 2189, Houston, TX, 77251-2189, United States

The discovery of exhumed continental mantle rocks and lack of magmas in ocean continent transitions, the existence of top-basement detachments, and the recognition of an “extension discrepancy” across many passive continental margins, as exhibited by preferential thinning of lower crust and the rapid thinning of continental crust in the absence of obvious faulting, have seriously challenged the accepted paradigms for the formation of passive continental margins and the way in which continental lithosphere is deformed in extension. Recent studies have clearly demonstrated that rifting, that is, the offset across high-angle basin bounding normal faults, is only a minor component in the thinning of continental lithosphere. During extension, early fault controlled subsidence tends to be limited to the proximal regions of passive margins while later brittle deformation dominates the distal regions. Kinematic considerations of passive margin subsidence require preferential bulk thinning of the lower crust and lithospheric mantle relative to the upper crust, an observation supported by seismic refraction results across the West African margin and the Exmouth Plateau, northwest Australia. Age considerations indicate that this depth-dependent extension (DDE) of the lithosphere is the significant process for thinning continental crust from its 30-40 km pre-rift thickness to a thickness of ~10 km, but surprisingly, depositional environments seem to be characterized by shallow water and quiescent conditions, as evidenced by Tithonian carbonates of the Iberian margin now at abyssal depths. Such extension partitioning requires a lateral strain balance, which may take the following form: 1) a counterbalancing of upper crustal extension leading to late-stage brittle deformation in the vicinity of the ocean-continent transition zone (e.g., the low angle detachment systems of the distal Iberian margin), and/or 2) the lateral emplacement and exposure of serpentinized and magmatically modified continental mantle and lower crust out from under the adjacent continental lithosphere.

While isostatic considerations of DDE allow the distribution and amplitude of syn- and post-extension accommodation to be calculated, a geological understanding of the thinning process and the modes of crustal and mantle deformation cannot be addressed. Thus, the fundamental question remains: what mechanism(s) allow the continental lithosphere to be thinned from ~30 km to ~10 km and thence to the point of rupture? Lavier and Manatschal (2006), using field observations from the exposed Tethyan margin in the Swiss Alps and geodynamic modeling, have suggested that the Iberia-Newfoundland system is the result of a complex rifting history that can be described as a sequence of different modes of extension. This sequence initiates with a broadly-distributed brittle deformation (stretching phase) and is followed by strain localization and crustal thinning along upper crustal and mantle ductile shear zones decoupled along a mid-crustal decollement, localized and controlled by a relatively weak middle crustal rheology (thinning phase). If and when coupling of the thinned upper and lower crust occurs (i.e., once the crust has reached a thickness of ~10 km), crustal embrittlement and continued extension leads to the formation of crustal-scale detachments along downward-concave faults that are conducive to mantle exhumation (exhumation phase). While this sequencing is a working hypothesis for how continental lithosphere extends, the view is that the final crustal architecture of at least the Iberia-Newfoundland margin is controlled by the stacking of these different modes of extension. Thus, given the field and drilling observations from the Iberia-Newfoundland and Tethyan margins, the proxy for extensional strain partitioning in the crust is the existence of syn-extensional sags and the exhumation of lower crust and continental mantle. The width of these exhumed zones may be 100’s km wide and contain organized magnetic anomalies. However, these magnetic anomalies are likely a consequence of mantle exhumation and serpentinization rather than mid-ocean ridge basalt production at the spreading center, a review of which was recently published by Sibuet et al., (2007).

Many passive continental margins are characterized by such observations, for example, Galicia Bank and the Iberian margin, the Exmouth, Queensland and Marion Plateaus, the Woodlark basin, the West African margin, and the Norwegian margin. While the geological details and sedimentary facies differ between the various margins, the style of deformation is remarkably similar. It would appear that what was once considered an extreme end-member of passive margin formation (viz., the Iberian-Newfoundland margin) may instead be a template for the development of many hyperextended margins around the world, that is, continental lithosphere that has undergone 100’s of percent of extension to the point of rupture. The modes of extension discussed above have immense implications for the heat flow history, environments of deposition, syn-extensional stratigraphy, and basin architecture of passive margin systems. A goal of this presentation is to show examples of depth-dependent extension and changing modes of crustal deformation. Our future challenge is to understand exactly how to link crustal deformation with lithospheric mantle thinning in a predictive way.

References

Lavier, L., and G. Manatschal, 2006. A mechanism to thin the continental lithosphere at magma-poor margins, Nature, 440, 324-328.

Sibuet, J.C., S. Srivastava, and G. Manatschal, 2007. Exhumed mantle forming transitional crust in the Newfoundland-Iberia rift and associated magnetic anomalies, Journal of Geophysical Research, 112, B06105, doi:10.1029/2005JB003856.

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

Karner, Garry D.<sup>1

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

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

RESERVOIR QUALITY, DIAGENETIC HISTORY AND PROVENANCE OF THE LATE TRIASSIC SANDSTONES OF THE WOLFVILLE FORMATION, BAY OF FUNDY, NOVA SCOTIA, CANADA

Kettanah, Yawooz¹; Kettanah, Muhammad²; Wach, Grant <sup>2

1</sup>Dalhousie University Department of Earth Sciences, Halifax, Nova Scotia, B3H 4J1, Canada; ²Department of Earth Sciences, Halifax, Nova Scotia, B3H 4J1, Canada

The provenance of Triassic Wolfville Formation sandstones at Cambridge Cove, Bay of Fundy were investigated using petrography, heavy minerals, and microprobe analysis of tourmalines and garnets as provenance indicators. The study included grain size analysis, diagenesis, porosity, heavy mineral analysis and possible reservoir characteristics dependent on these properties.

These fluvial sandstones are calcite cement-supported feldspathic litharenites to lithic felsarenites. The sandstones have a recycled orogenic provenance derived from metasedimentary and granitic rocks postdating collision and from the early stages of rifting.

The Meguma, Horton and Windsor Groups, and the South Mountain Batholith, which were and still are, the dominant rock units in the area, are the main provenance of Wolfville Formation sediments. Minor contribution from Appalachian exposures north of the Bay of Fundy in New Brunswick, cannot be excluded. However, the absence of volcanics in the studied sediments minimizes that possibility.

The Wolfville Formation, which is overlain by the Blomidon Formation, has a limited exposure area relative to its wide subsurface extension beneath the Bay of Fundy. In this area, it is underlain by the Horton Bluff Formation in the Minas Basin area, and by the Meguma and/or Avalon Terranes in the southwestern parts of the region.

Wolfville sandstones have porosities ranging from 2.6 to 16.6% (averaging 6%). Consequently, in the subsurface (beneath the Bay of Fundy), the sandstones are potentially moderately good reservoir rocks. Hydrocarbon charge could occur where these sandstones overlie potential source rocks; e.g., the organic-rich shales of Horton Bluff Formation, or where overlain by or laterally equivalent to Mesozoic lacustrine shales.

REVISITING THE EAST GEORGES BANK BASIN, OFFSHORE NOVA SCOTIA - WHAT THE EXPLORATIONISTS SAW TWO DECADES AGO

Koning, Tako<sup>1

1</sup>Advisor, Tullow Oil Angola No 43, Largo Ingombotas, --, Luanda, Angola

The East Georges Bank Basin is located offshore Nova Scotia on the southeastern Canadian continental shelf. The basin covers 10,000 square kilometers (2.5 million acres) and is one of the last undrilled basins in North America.

The geological understanding of this basin is based on 16,000 km of seismic data which was studied and interpreted in the 1980’s by Texaco Canada’s geoscientists. The first public presentation of the interpreted data was at a CSPG-GAC-MAC conference in 1988 in St. John’s, Newfoundland and thereafter the geological and geophysical interpretations were presented at a number of oil industry conferences worldwide (San Diego, Calgary, Lagos, Rio de Janeiro). This presentation is a re-presentation of the 1988 and subsequent papers. In 1988, the government placed an oil activity moratorium on Georges Bank. No activity such as seismic surveying has taken place since that time. Therefore, although this presentation is based on old seismic data, it must be viewed as up-to-date since no new data has been acquired on the bank for well over twenty years.

The overall Georges Bank Basin formed during the Triassic when the landmass of Pangea began separating along rift zones. A prominent Paleozoic basement high, the Yarmouth Arch, separated the East Georges Bank Basin from the West Georges Bank Basin, and had a dominant influence on sedimentation until Middle Jurassic. During the Middle Jurassic, major growth faulting and halokinesis commenced in the basin.

The structural and stratigraphic evolution of the East Georges Bank Basin has resulted in the development of a number of economically attractive seismically-defined prospects. The Geological Survey of Canada (GSC) published in 1983 (Proctor et al) that the average hydrocarbon expectation of the basin was 168 x 10⁶m³ barrels oil (1.0 billion barrels) and 150 x 10⁹m³ natural gas (5.3 TCFG). The GSC’s speculative estimate for the basin was 350 x 10⁶m³ barrels of oil (2.1 billion barrels) and 307 x 10⁹m³ gas (10.8 TCFG).

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.<sup>2

1</sup>University 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, Sophie<sup>1

1</sup>University 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.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

McHone, Gregory<sup>1

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

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

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

McInroy, David Burns¹; Hitchen, Ken<sup>2

1</sup>British Geological Survey Murchison House, West Mains Road, Edinburgh, --, EH9 3LA, United Kingdom; ²Murchison 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.

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

Mizintseva, Svetlana F<sup>1

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

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

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

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

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

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

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

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.<sup>2

1</sup>Global 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.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Okwese, Ann Chioma¹; Pe-Piper, Georgia²; Piper, David J.W<sup>3

1</sup>Saint 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.

RIVER SOURCE AND DISPERSION OF LOWER CRETACEOUS SANDS, SCOTIAN BASIN

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

1</sup>Saint 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.

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, Georgia<sup>2

1</sup>Geological 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.

PETROLEUM SYSTEMS OF THE U.S. CENTRAL ATLANTIC MARGIN

Post, Paul J¹; Sassen, Roger<sup>2

1</sup>MMS 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.