bluuebunny/crossref_metadata_2025 huggingface dataset:
Timing and magnitude of depth-dependent lithosphere stretching on the southern Lofoten and northern Vøring continental margins offshore mid-Norway: implications for subsidence and hydrocarbon maturation at volcanic rifted margins
Authors: KUSZNIR N. J. , HUNSDALE R. , ROBERTS A. M. ,   iSIMM Team
Published: April 2010

Subsidence analysis on the southern Lofoten and northern Vøring segments of the Norwegian rifted margin shows depth-dependent stretching of continental margin lithosphere in which lithosphere stretching and thinning at continental break-up at ~ 54 Ma greatly exceeds that of the upper crust within 100 km landward of the COB. For the southern Lofoten margin lithosphere β stretching factors approaching infinity are required at 54 Ma west of the Utrøst Ridge to restore the top Basalt (inner lava flow) reflectors and top Tare formation (54 Ma) to presumed sub-aerial depositional environments, while for the northern Vøring margin lithosphere β values of 2.5 are required. In contrast, upper crustal extension by faulting shows little stretching with β < 1.1 at break-up or immediately preceding break-up in the Paleocene and Late Cretaceous. The presence of lithosphere depth-dependent stretching and the absence of significant Paleocene and Late Cretaceous upper crustal extension imply that depth-dependent stretching of the southern Lofoten and northern Vøring margins occurred during sea-floor spreading initiation rather than during pre-break-up intra-continental rifting. Depth-dependent stretching, where upper-crustal extension is significantly smaller than whole-crustal or whole-lithosphere extension within 75–150 km of the COB, has been observed worldwide for both volcanic and non-volcanic rifted continental margins. Temperature and hydrocarbon maturation modelling show that the inclusion of depth-dependent stretching has an important effect on temperature and hydrocarbon maturation evolution in depth and time. Failure to include the large β factors for the lower crust and lithospheric mantle (below the less stretched upper crust) leads to a serious under-prediction of temperature and hydrocarbon maturation. While the effect of emplacing thick sill intrusions or magmatic underplating at continental break-up has an important effect on predicted temperature and %VR, their effects can be small in comparison with that of depth-dependent stretching.
Late Mesozoic–Cenozoic structural and stratigraphic correlations between the conjugate mid-Norway and NE Greenland continental margins
Authors: TSIKALAS F. , FALEIDE J. I. , ELDHOLM O. , WILSON J.
Published: April 2010

Late Mesozoic–Cenozoic tectonostratigraphic correlations between the conjugate mid-Norway and NE Greenland continental margins are provided, based on the recently refined structural and stratigraphic framework off mid-Norway, new early opening plate reconstructions of Eurasia versus Greenland between the Jan Mayen and Senja fracture zones, and a sparse regional grid of seismic reflection profiles off NE Greenland. The Norwegian margin exhibits a distinct along-strike margin segmentation governed by across-margin transfer systems. In particular, the Bivrost Fracture Zone and its landward transfer zone prolongation are well-defined features. Corresponding features are here interpreted on the conjugate NE Greenland margin. Together, these conjugate transfer/fracture zones represent a first-order, across-margin tectonomagmatic boundary of prolonged structural inheritance. Regional transects across both margins reveal important vertical and lateral variations in crustal configuration and composition resulting from a complex history of rifting prior to and during the last rift episode in Late Cretaceous–Early Tertiary time, leading to break-up and volcanic passive margin formation. Although the composite Late Jurassic–earliest Cretaceous rifting was the dominant tectonic episode, one also observes structural and stratigraphic relations that indicate an Aptian–?Albian rift phase, probably co-eval with similar events elsewhere on the NE Atlantic margins. Late Cretaceous rifting, with onset in middle Campanian time, was characterized by low-angle detachment faulting, culminating in regional uplift, intrusive igneous activity and subsequent erosion towards the end of the Paleocene. Thick seaward-dipping reflector sequences indicate massive eruptions of lavas during break-up at the Paleocene–Eocene transition. The post-break-up passive margin development was characterized by the transport and deposition of large amounts of sediment in response to margin subsidence and continental uplift, particularly during two distinct phases of outbuilding in Oligocene?/Miocene and Plio-Pleistocene times. Of special interest are a number of mid-Cenozoic intra-basin inversion features recognized both off Norway and off Greenland, revealing a regional compressive regime.
Crustal structure of the Vøring Margin, NE Atlantic: a review of geological implications based on recent OBS data
Authors: MJELDE R. , RAUM T. , BREIVIK A. , SHIMAMURA H. , MURAI Y. , TAKANAMI T. , FALEIDE J. I.
Published: April 2010

Modelling of extensive seismic datasets recorded on Ocean Bottom Seismographs (OBS) on the outer Vøring Margin, NE Atlantic, has provided significant new insights into deeper sedimentary structures, distribution of sill-intrusions in the sedimentary section, top of the crystalline crust, the lower crust and Moho. Primarily based on the modelling of S-waves, it is concluded that the high-velocity lower crust most likely consists of a mixture of plume-related Late Cretaceous/Early Tertiary mafic intrusions mixed with older continental blocks. Northeastwards in the Vøring Basin, the landward limit of the lower crustal high-velocity layer steps gradually seawards, closely related to five crustal scale lineaments. Evidence for an interplay between active and passive rifting components is found on regional and local scales on the margin. The active component is evident through the decrease in magmatism with increased distance from the Iceland plume, and the passive component is illustrated by the fact that all resolved crustal lineaments to a certain degree acted as barriers to magma emplacement. A lithospheric delamination model is invoked to explain the observed variations in crustal velocities and thickness. The location of six Tertiary domal structures in the Vøring Basin is between, or in the vicinity of, pre-breakup high-velocity structures, which may act as rigid blocks during compression. It is proposed that the existence and trend of these high-velocity structures, subject to mild NW–SE compression, is the most important factor controlling the formation, spatial distribution and trend of the domes. Structures in the high-velocity lower crust may be the single most important element in controlling the formation of the domes; all modelled highs in the lower crustal Early Tertiary intrusive layer seem to be related to the formation of domes.
Cretaceous to Palaeogene 3D palaeobathymetry and sedimentation in the Vøring Basin, Norwegian Sea
Authors: KJENNERUD T. , VERGARA L.
Published: April 2010

A new approach to constrain the Cretaceous and early Palaeogene depositional systems in the Vøring Basin has been achieved by combining 3D palaeobathymetry reconstructed from seismic sequence geometries, indicators of zero or shallow water depth, compaction and isostasy. The restorations were calibrated to known exposed intrabasinal highs. The Vøring Basin started out as a segmented and locally deep syn-rift basin during the Late Ryazanian. Water depths in the range 1000–2000m have been restored in the deeper areas. In Late Cenomanian broader deep-water areas formed in the eastern part of the basin. The broadening of the basin was accompanied by shallower water depths during the Coniacian. A switch in basin configuration was fully established during the Early Campanian. The previously deep areas in the Rås and Træna basins became very shallow and the Vigrid and Någrind synclines started to subside, as a response to the reactivation of the Fles Fault Complex. The shallowing trend continued during Late Cretaceous time until regional uplift of the basin floor, and total emergence of the intrabasinal highs known as Gjallar Ridge, Vema Dome, Nyk High and Utgard High occurred around Maastrichtian–Paleocene time. This was followed bydeepening in the Early Paleocene expressed in the depocentres, where the Vigrid and Rås basins now attained water depths of 300–400 m. Further increased subsidence occurred during the Late Paleocene, resulting inwater depths up to 1000min the eastern Vøring Basin.
Basement reactivation and inversion mechanisms in the Timor and Norwegian seas
Authors: KEEP M. , HARROWFIELD M.
Published: April 2010

The North East Atlantic Margin and Australian North West Shelf share similar tectonic evolutions. Both are passive margins of similar age and size, both experienced significant periods of reactivation, inversion and volcanism, and both host significant oil and gas resources. The main differences between these two margins lie in their modern tectonic settings and hydrocarbon resources. The North West Shelf occurs at a present-day collisional plate boundary, the dynamics of which strongly control the location of oil and gas reserves, whereas the North East Atlantic has not yet entered a collisional phase. The North West Shelf tends to be gas prone, in contrast to its European counterpart. Recent mapping of Neogene to Recent modification across the North West Shelf highlights the influence of inherited basement architecture, long-wavelength strain partitioning and continuous flexural deformation. Similarities in the structural evolution of these two margins, especially in terms of the role of the basement structure, episodic modification, the location and extent of Cenozoic inversions and the role of inversion in controlling hydrocarbon distribution, illustrate the importance of these issues in passive margin development. Lessons learned from the Australian example include that structural inheritance has an overwhelming control on later reactivation, and that even small amounts of shortening strain (1–2%) can lead to significant modifications of structural traps and petroleum habitats.
Structure of the Faroe Bank Channel Basin, offshore Faroe Islands
Authors: KESER NEISH J. , ZISKA H.
Published: April 2010

The Faroe Bank Channel Basin, which lies on the North Atlantic Margin southwest of the Faroe Islands, is a large, Mesozoic depocentre covering in excess of 10 000 km
2
. It has undergone little exploration to date and its structural complexity is reflected by the presence of two prominent structural trends: the SW–NE (Caledonian) trend which controls the main Faroe Bank Channel Basin and Faroe Bank Channel Knoll structure and a younger N–S trend which elongates the basin to form the North Faroe Bank Channel Basin area, containing the prominent Regin Smidur volcanic centre. As there is no well control in this frontier basin and seismic data quality precludes conventional interpretation, seismic data in combination with potential field data were analysed in order to determine the structural framework of the area and the geophysical characteristics of the geological units present. Within the basin centre, a thick post-basalt sedimentary section is present. The Paleocene flow basalt sucession is underlain by units of interpreted sedimentary origin which could be considered to be prospective for hydrocarbon exploration. The basin is floored by a block-faulted basement; successive reactivation of basement fault trends by younger tectonic episodes is further demonstrated by the mapping of transtensional features within the basin. Basin structure has been influenced strongly by Paleocene volcanism and subsidence. However, the internal structure of the Faroe Bank Channel Basin has remained relatively unaffected by the younger, Eocene–Miocene compressional events evident on its surrounding margins. Although the Faroe Bank Channel Basin area has yet to be made available for commercial licensing, it is considered to be an interesting area for the future as risk is reduced by exploration not only within the basin but in the adjacent areas to the southeast and in other areas of a similar nature.
Geological development of the Northeast Greenland Shelf
Authors: HAMANN N. E. , WHITTAKER R. C. , STEMMERIK L.
Published: April 2010

Seismic data from the East Greenland shelf show that the northern part of the shelf, north of 75°N, can be subdivided into five, roughly northeast-trending, major tectonic elements. From west to east they are: the Koldewey Platform, the Danmarkshavn Basin, the Danmarkshavn Ridge, the Thetis Basin and the Marginal High. A sixth tectonic element, the Shannon High, has been defined in the southern part of this area. The offshore areas between 72°30′N and 75°N are dominated by Tertiary plateau basalts, which obscure the acoustic signals from the deeper sedimentary succession. Seismic data from the area north of 75°N indicate the presence of a fairly complete succession of ? Devonian to Neogene age, exceeding the recorded interval (8 sec TWT – 13 km) in thickness in the deeper parts of the Danmarkshavn Basin. The succession has been subdivided into 15 seismic mega-sequences. In absence of well control, they have been dated by comparison to the onshore successions of East Greenland and eastern North Greenland, and the offshore successions in the southern Barents Sea and on the mid-Norwegian shelf. The Upper Palaeozoic succession is broadly similar to that of the southern Barents Sea, i.e. marine-dominated, with thick Upper Carboniferous–Lower Permian halite deposits in the northern Danmarkshavn Basin. The Mesozoic succession seems to show greater similarities to the onshore basins of East Greenland: rifting started during the mid-Jurassic and peaked near the Jurassic–Cretaceous boundary. The post-volcanic succession reflects deposition on a passive margin subjected to temporary uplift during the early Miocene and the latest Miocene to earliest Pliocene.
At the edge of a new ocean: post-volcanic evolution of the Palaeogene Kap Dalton Group, East Greenland
Authors: LARSEN M. , HEILMANN-CLAUSEN C. , PIASECKI S. , STEMMERIK L.
Published: April 2010

Following the extensive flood basalt volcanism that accompanied the onset of seafloor spreading and arrival of the proto-Icelandic hotspot in the North Atlantic region, marine sedimentation resumed during the early Middle Eocene. In East Greenland, post-basaltic sediments exposed at Kap Dalton and Savoia Halvø represent the scattered remains of a much more widespread, fluvial to shallow-marine succession. Deposition in the late Paleocene–Eocene was governed by a complex interplay between loading, thermal contraction of the oceanic crust, passage of the hotspot and eustatic sea-level changes. At Kap Dalton extrusion of Early Eocene, Chron C21r flood basalts was followed by subaerial erosion, creating an irregular relief dissected by fluvial channels. The area was transgressed during the early Middle Eocene and, during the Middle Eocene, a muddy, poorly oxygenated shelf was formed. The presence of clean quartz sandstones within the early post-basaltic succession indicates that areas with little or no basaltic cover became periodically exhumed. The depositional events documented in the Kap Dalton succession strengthen the possibility of Middle Eocene non-volcanic reservoir units being present in the offshore areas, lending support to the Eocene play in the northern North Atlantic region.
Controls on the structure and evolution of the NE Atlantic margin revealed by regional potential field imaging and 3D modelling
Authors: KIMBELL G. S. , RITCHIE J. D. , JOHNSON H. , GATLIFF R. W.
Published: April 2010

A regional three-dimensional model has been constructed for the lithospheric structure of the NE Atlantic margin. Starting from the known bathymetry and an initial sediment thickness estimate and making allowance for thermal effects, the geometry of the crystalline crust was predicted using isostatic and flexural principles. Optimization methods were then used to modify the base sediment and Moho interfaces to improve the fit between observed and calculated gravity anomalies. The method provides new insights into basin morphology and into variations in the thickness of both crystalline continental crust and igneous oceanic crust. When combined with imaging of the gravity and magnetic fields, the model highlights the importance of broadly NW-trending lineaments on the development of post-Caledonian basin architecture. In some cases these lineaments are interpreted as pre-Caledonian structures that were reactivated as transfer zones during phases of Mesozoic extension. Some of the lineaments appear to have influenced the early evolution of the oceanic crust by providing the precursors to transform offsets and possibly also by affecting the pattern of asthenospheric flow. The crustal thickening of the Faroe–Iceland Ridge is clearly imaged and its geometry is interpreted to reflect temporal variations in the enhanced oceanic crustal production rate responsible for this feature, including a Late Eocene minimum which can be correlated with plate reorganization in the north Atlantic region. There is some evidence of Cenozoic deformation linked to transpressive reactivation of the lineaments. However, a deflection in the axis of the North Hatton Anticline across the NW-trending Anton Dohrn lineament is more likely to have been inherited from an offset in an underlying, reactivated basement structure than to have resulted from strike-slip movements at the time of folding.
Structure of the Hatton Basin and adjacent continental margin
Authors: SMITH L. K. , WHITE R. S. , KUSZNIR N. J. ,   iSIMM Team
Published: April 2010

In the summer of 2002, new data were acquired along wide-angle and normal-incidence profiles extending from the Hatton Basin, across the adjacent Hatton Bank volcanic continental margin and into the Iceland Basin. Eighty-nine four-component ocean-bottom seismometers (OBS) were deployed along a transect running across the continental margin and along two strike lines located above the region of thickest extrusive and intrusive igneous rock on Hatton Bank and over 44 Ma oceanic crust near the end of the main dip profile. The seismic profiling was optimized for large offset OBS arrivals with a low-frequency airgun source centred at 10 Hz. Wide-angle seismic energy penetrated the extruded basalt, the underlying crust and well into the upper mantle. Initial modelling results from Hatton Basin show a ∼4 km thick sedimentary sequence and provide a new sub-sediment crustal thickness estimate of ∼15 km. This crustal thickness suggests a stretching factor of two relative to the continental crust under Rockall Bank. These new results have been integrated with an established model for the region to demonstrate the variations of crustal structure across the margin. Future processing and modelling of the extensive dataset collected in the 2002 survey will allow refinement of the crustal structure model across the stretched continental crust beneath Hatton Basin and the adjacent continental margin. In particular it will place better constraints on the intrusive and extrusive igneous components produced during continental break-up in the Palaeogene.
Volcanogenic impact on phytogeography and sediment dispersal patterns in the NE Atlantic
Authors: JOLLEY D. W. , MORTON A. , PRINCE I.
Published: April 2010

The Paleocene sedimentary sequences of the Faroe–Shetland Basin, northeast Atlantic, contain abundant palynomorphs (algae, pollen and spores). While one component of the palynoflora, the dinoflagellate cysts, has been used as the basis for biostratigraphical subdivisions of the succession, the terriginous palynoflora is the more abundant. This terriginous component was derived from two primary sources. The first, and most common source has an angiosperm palynoflora dominated by hickory types (
Momipites
species), which occur in association with plane-types (various
Tricolpites
species) and
Ginkgo
. This palynoflora occurs commonly inmost Faroe–Shetland Basin wells throughout the early and mid-Paleocene succession. A second flora, which is restricted to early and mid Paleocene successions in the west of the basin, has an angiosperm component dominated by
Cupuliferoipollenites
and
Cupuliferoidaepollenites
species (broadly, ash and chestnut types). This Greenland Flora is confined to four main stratigraphical pulses in the early and mid-Paleocene, occurring more commonly in proximity to major transfer zones, and west of the Corona Ridge. This distribution pattern provides evidence of argillaceous sediment transportation from the west into the Faroe–Shetland Basin via major transfer zones. Comparison to palaeoclimatic interpretations dispute a relationship between climate change and westerly sediment input into the Faroe–Shetland Basin. Instead, a comparison is invited between pulses of igneous activity in the North Atlantic Igneous Province and sediment transfer from the uplifted eastern zone of the proto-North Atlantic rift.
Paleocene exploration in the Faroe–Shetland Channel: disappointments and discoveries
Authors: SMALLWOOD J. R. , KIRK W. J.
Published: April 2010

While the early drilling in the UK West of Shetlands area was concentrated on structural highs, the 1992 discovery of oil in the deep-water Paleocene sands of the Foinaven Field re-invigorated exploration interest in hydrocarbon traps with a stratigraphic element and encouraged a high level of participation in the UK 16th Licensing Round (1995) west of Britain. Many of the main exploration targets in these rounds were mapped as sand pinchouts onto either the basin margin or onto intra-basinal structural highs, for example, updip to the southeast of the 1989 well, 205/9-1. Few of the initial wells drilled to test this type of pinchout play were commercially successful but, as part of the exploration effort, a large area of the basin was blanketed with 3D seismic data on which more subtle features could be recognized. Seismic anomalies similar to those of the successful discoveries were sought on the new 3D data, as this type of play relied heavily on seismic attributes to help define risks and reserve size. The Foinaven and Schiehallion fields have a suite of attractive seismic characteristics and exploration effort was driven by the search for similar seismic anomaly features throughout the Atlantic Margin. As wells were drilled on 16th Round acreage, some of the targeted seismic reflection anomalies, originally seen as direct hydrocarbon indicators, turned out to have different causes. Representative examples are shown from the central part of Quadrant 205 in which tuning, seismic artefacts, porosity effects and unexpected igneous lithologies contributed to the drilling of unsuccessful exploration wells. The variation with depth of rock physics trends in the area are shown, the characteristics of some direct hydrocarbon seismic indicators are modelled and comments are made on the sensitivity of the modelled seismic response to shear velocity estimation.

The former ‘White Zone’ or undesignated area, the previously unlicensed acreage between the UK and Faroe Islands, was opened through the Faroes 1st and the UK 19th Licensing Rounds in 2000 and 2001. By 2003 the first 8 of 15 commitment exploration wells were drilled in these licenses. Together with an assessment of the seismic anomalies and the risks of stratigraphical traps in the area, analysis of the petroleum system led to the siting of the 6004/16-1z well on the structural high of a Cenozoic inversion anticline. The resulting ‘Marjun’ discovery, the first in the Faroes, consisted of a gross 170 m hydrocarbon column in the T10 Early Paleocene interval, thus opening a new fairway in the area. The challenge has evolved in the last five years from finding an effective reservoir in the basinal areas to the search for a robust trap with an intact sealing lithology.
The structural framework of the Irish Atlantic Margin
Authors: NAYLOR D. , SHANNON P. M.
Published: April 2010

Analysis of the results of regional mapping, integrated with new regional subcrop maps, has yielded significant regional concepts regarding the development of the frontier sedimentary basins west of Ireland. Five provinces of basement and Devono-Carboniferous rocks are mapped across the region. The nature of the basement successions, together with their inherent lineaments and structural fabrics, exerted a major influence on the location and structural segmentation of the basins and in acting as a conduit for Early Cretaceous and Early Cenozoic igneous activity. The major structures in the Porcupine region were N–S throughout its Late Palaeozoic to Cenozoic history, while those in the Slyne, Erris, Rockall and probably Hatton basins were predominantly NNE–SSW to NE–SW. The main structural controls in the Goban region were orientated ENE–WSW and NNW–SSE. The Porcupine Basin is shown to have a more pronounced N–S orientation than has hitherto been proposed. In particular, the basement core of the Porcupine High is shown to extend southwards to the Goban province, thereby isolating the basin for most of its history from the Atlantic region to the west. Separate Permo-Triassic to Jurassic basins occur on the flanks of the main, younger Rockall Basin and their location and orientation were influenced by NE–SW to ENE–WSW structural fabrics. Permo-Triassic sedimentation took place in a series of rift basins in the Porcupine, Rockall, Slyne–Erris and Goban regions. Jurassic rifting was widespread in most of the basins, commencing in Middle Jurassic time in the Slyne Basin but later (Late Jurassic) in the Porcupine and Rockall basins. Early Cretaceous sedimentation was more pronounced in the Porcupine and Rockall basins and shows less control by deep-seated structures. Late Jurassic to Early Cretaceous basin margin uplift on the flanks of the Rockall Basin in particular, is likely to explain the thin to absent nature of such strata in some of the adjacent smaller basins.
The crustal structure and regional development of the Irish Atlantic margin region
Authors: MOREWOOD N. C. , MACKENZIE G. D. , SHANNON P. M. , O’REILLY B. M. , READMAN P. W. , MAKRIS J.
Published: April 2010

During the past decade, a suite of wide-angle seismic reflection/refraction profiles has been shot in the Porcupine, Rockall and Hatton basins, as well as across the Hatton continental margin. Integration of the wide-angle seismic data with normal-incidence reflection profiles and with gravity and magnetic data reveals a clear picture of the regional crustal and upper mantle structure, and of the large-scale sedimentary geometry of the Late Palaeozoic–Cenozoic basins in the area. The region contains a set of large sedimentary basins resting upon variably thinned continental crust. The crust beneath the basin-bounding structural highs is typically around 25km thick, with the crust beneath the basins being as thin as 6km. The Porcupine Basin contains up to 10 km of sediments. Up to 7km of sedimentary strata are indicated in the Rockall Basin, with 4km of sediment in the Hatton Basin. Several seismically distinct layers, with P-wave velocities of 1.8–5.3 kms
−1
, were identified above the basement in the sedimentary basins. A significant variability in thickness of the sedimentary layers is seen on the wide-angle data. These reflect the presence of a number of older Mesozoic rift sedimentary basins. The wide-angle data reveal marked topographic irregularity at the base of the sedimentary succession in the Rockall Basin, interpreted as the result of extensive multi-phase Mesozoic rifting. The Moho beneath the Rockall Basin shows a clear asymmetry, with a steeper gradient along the eastern margin of the basin. The continent–ocean boundary west of the Hatton High has a significant underplated and volcanic component, while that at the southern margin of the Rockall Basin shows evidence of a greater transpressive component. The nature of the lower crust appears to exert a controlling influence on the location of crustal separation. In areas where thinning is accommodated by upper and middle crustal attenuation, the strength of the upper crust (and underlying brittle mantle) has served to preserve the integrity of the continental crust and inhibit seafloor spreading. However, where the lower crust is thinned significantly, as beneath the Hatton continental margin, crustal separation has taken place even though the upper and middle crust remains relatively thick.
The deep structure of the Porcupine Basin, offshore Ireland, from gravity and magnetic studies
Authors: READMAN P. W. , O’REILLY B. M. , SHANNON P. M. , NAYLOR D.
Published: April 2010

Marine gravity and magnetic surveys around Ireland, together with satellite gravity data from the deeper ocean, are used to investigate the large-scale crustal structure of the Porcupine Basin, offshore west of Ireland. The structure of the syn-rift to post-rift sedimentary successions, derived from vertical incidence seismic reflection data, is used to isolate the gravity and magnetic responses of the crust and mantle. The crustal structure derived from wide-angle seismic data in the region is used to control the interpretation and modelling. The results of gravity modelling in the southern part of the Porcupine Basin suggest a crustal thickening in the centre of the basin. Comparison with the Rockall Basin, where axial crustal thickening is seismically defined, suggests a similar pattern of crustal extension. The amount of extension is less across the narrower northern sector of the Porcupine Basin, where a north–south-trending axial gravity high is present resulting from anomalous density variations in the lower crust/upper mantle. A new model for the large-scale structural development of the Porcupine Basin is presented that explains the along-axis variations in crustal structure in terms of changes in the kinematics of crustal extension across NW–SE transfer zones. This model involves tectonic unroofing of the mantle lithosphere and serpentinization of the exhumed mantle peridotites.
Neogene evolution of the Atlantic continental margin of NW Europe (Lofoten Islands to SW Ireland): anything but passive
Authors: STOKER M. S. , PRAEG D. , SHANNON P. M. , HJELSTUEN B. O. , LABERG J. S. , NIELSEN T. , VAN WEERING T. C. E. , SEJRUP H. P. , EVANS D.
Published: April 2010

A regional stratigraphic framework for the Neogene succession along and across the NW European margin is presented, based on a regional seismic and sample database. The stratigraphy provides constraints on the timing and nature of the mid- to late Cenozoic differential tectonic movements that have drivenmajor changes in sediment supply, oceanographic circulation and climate (culminating in continental glaciation). The overall context for Neogene deposition on the margin was established in the mid-Cenozoic, when rapid, km-scale differential subsidence (sagging) created the present-day deep-water basins. The Neogene is subdivided into lower (Miocene–lower Pliocene) and upper (lower Pliocene–Holocene) intervals. The
lower Neogene
contains evidence of early to mid-Miocene compressive tectonism, including inversion anticlines and multiple unconformities that record uplift and erosion of basin margins, as well as changes in deep-water currents. These movements culminated in a major expansion of contourite drifts in the mid-Miocene, argued to reflect enhanced deep-water exchange across the Wyville-Thomson Ridge Complex, via the Faroe Conduit. The distribution and amplitude of the intra-Miocene movements are consistent with deformation and basin margin flexure in response to enhanced intra-plate compressive stresses during a local plate reorganization (transfer of the Jan Mayen Ridge from Greenland to Europe). The
upper Neogene
records a seaward tilting (<1°) of the margin from the early Pliocene, in which km-scale uplift and erosion was accompanied by increased offshore subsidence, resulting in a major seaward progradation of the shelf–slope wedge as well as deep-marine erosion during a reorganization of bottom current patterns. The large amplitude of tilting cannot be accounted for by intra-plate stress variations, but is consistent with a dynamic topographic response to upper mantle convection, in particular edge-driven flow beneath the continental margin. Sedimentary and oceanographic changes resulting from dynamic topographic responses to the evolution of upper mantle convective flow during ocean widening may be characteristic of the development of ‘passive’ continental margins.
Cretaceous and Palaeogene turbidite systems in the North Sea and Norwegian Sea Basins: source, staging area and basin physiography controls on reservoir development
Authors: MARTINSEN O. J. , LIEN T. , JACKSON C.
Published: April 2010

The Cretaceous and Palaeogene succession in the North Sea and Norwegian Sea basins show widely variable deep-water sedimentary systems in terms of processes, facies, geometries, scale and distribution. The primary controls on the large-scale variability are considered to be source area size, basin and basin margin physiography and bathymetry, tectonic history and resulting morphology of drainage and delivery systems of sediments to deep-water areas, and the rate of sediment delivery. The North Sea and Norwegian Sea basins were comparable during the earliest Cretaceous, but thereafter developed in widely different ways as a response to proximity to oncoming North Atlantic seafloor spreading.

In the North Sea Basin, the Cretaceous and Palaeogene turbidite systems were controlled by an inherited structural template from Late Jurassic rifting, and by source area size. Poorly developed or small drainage systems on the Norwegian margin and the broad Horda Platform gave little sand supply from the east to the Viking Graben area. Sand-rich systems were sourced from a relatively large hinterland and shallow marine staging area on the East Shetland Platform. North of the Horda Platform, sand supply was abundant in very discrete periods, particularly in the Early Eocene.

In the Norwegian Sea basins, the Late Jurassic structural template controlled Early Cretaceous deep-water sedimentary systems in a manner similar to the North Sea Basin. Generally small and poorly developed drainage systems caused development of mud-rich systems. In contrast, in the Late Cretaceous, onset of precursor tectonic activity to sea-floor spreading led to increased sand supply from the west into the Vøring Basin. A relatively narrow palaeoshelf and a large source area contributed to forming sand-rich systems. Smaller turbidite systems developed along the Norwegian margin, which were sourced from the east from smaller drainage areas, and partially across broad shelves, such as the Trøndelag Platform. Both in the Cretaceous and Palaeogene, the sandiest systems are found only to the south and the north of the inherited structural features.
Paleocene deep-marine sandstone plays in the Siri Canyon, offshore Denmark–southern Norway
Authors: HAMBERG L. , DAM G. , WILHELMSON C. , OTTESEN T. G.
Published: April 2010

The Paleocene Siri Canyon extends for more than 120 km from the Stavanger Platform to the Tail End Graben along the Danish–Norwegian North Sea boundary. Initial formation of the canyon system took place in the Early Paleocene (Danian) and was related to major, submarine sliding in the uppermost chalk section caused by uplift of the Scandinavian hinterlands. The trend of the canyon partly follows salt structures along the southern edge of the Norwegian–Danish Basin (part of the Northern Zechstein Basin). The canyon fill consists of deep-marine, highly glauconitic sandstones interbedded with hemipelagic and turbidite marls and mudstones. As for many Paleocene deep-marine sandstones in the North Sea, the sandstones of the Siri Canyon are massive and blocky. Frequent occurrence of injected sandstone sills/dykes, injection breccias, as well as erosion and associated rip-down clasts along the upper boundaries of
in situ
sandstones, indicate thorough, post-depositional modification. Fluidization is, thus, likely to be the main reason for the general scarcity of primary sedimentary structures and massive appearance of the sandstones. All sandstones are basically free of detrital clays and most likely formed from non-cohesive, concentrated density flows probably developed as turbidity currents. The sand flows were confined by the canyon and the depositional pattern indicates a complex interaction of turbidity currents, salt-induced seafloor topography and differential compaction. Release of sandy flows was probably caused by seismic shocks resulting in a collapse of unstable shelf sands concentrated on the Stavanger Platform. Transport distances of the sands were up to 120 km and thereby contrast with many Paleocene submarine sandstones in the North Sea. The deep-marine play in the Siri Canyon relies on long distance migration of hydrocarbons, up to 75 km from mature Jurassic source rocks in the Central Graben. This was facilitated by the elongate and confined geometry of the sandstones forming a well-connected system for updip migration.
Understanding petroleum systems: an overview
Authors: FRIES G. , NADEAU P. H. , SCOTCHMAN I. C.
Published: April 2010

Recent developments in petroleum geochemistry and basin modelling have advanced the petroleum system concept linking reservoired hydrocarbons to their source rocks. However, this link is often very complex involving the use of multi-dimensional basinal models to simulate maturation, hydrocarbon generation and fluid flow. New developments and concepts are discussed in this introductory chapter and succeeding section, with their application to both NW European petroleum provinces and frontier exploration areas of the world.
Petroleum system analysis: impact of shale diagenesis on reservoir fluid pressure, hydrocarbon migration, and biodegradation risks
Authors: NADEAU P. H. , BJØRKUM P. A. , WALDERHAUG O.
Published: April 2010

Geological models for the effects of clay diagenesis on shale/mudstone properties are under evaluation for their use in predicting the distribution of hydrocarbon occurrences, and risk of biodegradation. Traditional clay petrology studies show that the onset of reactions, often described as smectite to illite diagenesis, begins at 60° to 80°C in sedimentary sequences. Petrophysical models based on the precipitation of diagenetic clay within shale pore systems indicate rapid and severe permeability reduction at the onset of this reaction. Evaluation of global petroleum systems in a variety of basin settings, including the North Sea and the Gulf of Mexico, indicate an exponential increase in probability of formation fluid overpressure and hydrocarbon occurrences at and above these temperatures, along with concurrent reduction in the risk of biodegradation of reservoired petroleum. The mechanism by which these risks are controlled in both cases can be related to clay diagenetic induced permeability reduction, which when combined with diagenetic porosity reduction models and geological factors restricting lateral drainage, increases the probability of vertical hydrocarbon migration via hydrofracturing of low-permeability shale units to create new petroleum systems/plays. The industry fails to appreciate the exponential increase in exploration risks as a function of reservoir temperature and often drills beyond the optimal entrapment zone of 60° to 120°C, with corresponding reductions in efficiency. Hydrocarbons which migrate to shallower depths and lower temperatures show an increased risk of biodegradation. The proposed migration mechanism is consistent with the distribution of global conventional oil resources at the basin scale. Geologically, however, spill-fill/lateral migration, mainly in foreland basin settings, has resulted in extensive heavy oil/tar sands deposits, which eluded entrapment at optimal conditions for recovery.
Dynamic fault seal analysis and flow pathway modelling in three-dimensional basin models
Authors: CLARKE S. M. , BURLEY S. D. , WILLIAMS G. D.
Published: April 2010

Faults are important elements of petroleum systems that influence the migration and trapping of hydrocarbons in sedimentary basins. When faults undergo displacement, their fluid transmissibility properties change as a result of juxtaposing lithologies across the fault, by smearing semi-permeable or impermeable argillaceous rocks within fault zones and by pumping or valving aqueous fluids. We describe here a 4D hydrocarbon migration model that incorporates juxtaposition and argillaceous smear processes.

The technique uses the geometries of strata that are cut by faults and their physical properties to construct 3D models in which the evolution of cross-fault relationships can be calculated and the development of fault-zone argillaceous smear predicted. Hydrocarbon migration pathways through faulted structures are then investigated with a 4D migration model based on invasion percolation (IP) techniques.

The controls on hydrocarbon migration have been investigated for fieldwork-derived models of rock volumes from the Moab Fault, Utah, USA to test the modelling techniques against reality. As a result predominantly of argillaceous smear, hydrocarbons are shown to accumulate in the hanging wall of parts of the modelled section of the Moab Fault, but leak across juxtaposed sandstones elsewhere on the fault to produce footwall accumulations.

The techniques are then applied to a seismically derived model of the Artemis Field, UK Southern North Sea, to demonstrate how hydrocarbon charging history and pathways are influenced by fault geometries. Multiple model realizations enable the risk associated with charging of individual fault compartments to be assessed.
Plumbing the depths of the Central Graben: towards an integrated pressure, fluid and charge model for the Central North Sea HPHT play
Authors: WINEFIELD P. , GILHAM R. , ELSINGER R.
Published: April 2010

The integration of detailed seismic mapping, overpressure studies, basin modelling and new drilling has provided new insights into the ‘plumbing’ system of the deep, High-temperature, high-pressure (HPHT) play in the Central Graben. Although overpressure distribution in the pre-Cretaceous section is broadly related to depth, large-scale compartmentalization of the main Jurassic/Triassic reservoirs has resulted in the generation of a number of distinct pressure cells. These pressure cells are bounded by major structural faults (e.g. Forties/Montrose High) or by ‘interpod’ settings where the Jurassic/Triassic reservoir sequence thins over salt ridges. Evidence is presented that shows overpressure is a key control on hydrocarbon retention in this area, with several structures known to have blown top seals or to be leaky (i.e. underfilled) at present. The commercial Shearwater structure is shown to be an example of the latter, having evidence for a palaeo-oil column before the seal presumably breached and the trap recharged with a later gas-condensate fill. The length of hydrocarbon column in the structure at present day is controlled by the aquifer pressure and, in turn, by the shallowest point in the Shearwater pressure cell. The overpressure and trap filling history has had important implications for hydrocarbon migration, retention and the resultant composition of hydrocarbon accumulations in this part of the HPHT area. A conceptual model is presented here.
The history of hydrocarbon filling of Danish chalk fields
Authors: VEJBÆK O. V. , FRYKMAN P. , BECH N. , NIELSEN C. M.
Published: April 2010

It is well established that dynamic conditions expressed as tilted fluid contacts characterize most hydrocarbon accumulations in North Sea Chalk reservoirs. Chalk is a low-permeability, high-porosity rock and properties grade smoothly from reservoir over baffle to seal. The natural dynamic conditions prevail because pressure dissipation takes place through the rockmatrix, as fracture-supported flow often is minimal. The dynamic conditions are imposed by processes occurring on a geological time-scale and result mainly in lateral pressure differences in the water zone and even in lateral pressure differences in the oil zone. Re-equilibration of fluid contacts also occurs on a geological time-scale. These processes are of paramount importance for trap definition and impose severe restrictions on migration distances.

Reservoir simulation techniques are applied, in combination with back-stripping, to the simulation of geological time-scale secondary migration and trapping. Flow simulation of the filling dynamics of a chalk reservoir shows a complex filling geometry due to the high capillary entry pressures in the low-permeability chalks. Such internal barriers will re-direct hydrocarbons and residual oil can be left on the migration route. The process of hydrocarbon charging is slow and equilibration of hydrocarbons with respect to pressure gradients, therefore, also occurs very slowly. The Kraka Field and the Dan and Halfdan fields are subjected to studies of primary oil charging and re-migration in this paper and the dynamic oil on Dan Field west flank is successfully mimicked. Results show that a time span in the order of 2 Ma is required for the hydrocarbons to reach the summit in an approximately equilibrium state from a flanking position. However, even dynamic equilibrium may not be fully obtained due to re-perturbation by tectonic movements and changing water zone pressure gradients. Results show that saturation profiles in drilled wells may appear in drainage equilibrium while under partial re-imbibition, which impairs saturation modelling.