bluuebunny/crossref_metadata_2025 huggingface dataset:
The Columbia River Basalt Group—From the gorge to the sea
Authors: Wells Ray E. , Niem Alan R. , Evarts Russell C. , Hagstrum Jonathan T.
Published: April 2010

Miocene flood basalts of the Columbia River Basalt Group inundated eastern Washington, Oregon, and adjacent Idaho between 17 and 6 Ma. Some of the more voluminous flows followed the ancestral Columbia River across the Cascade arc, Puget-Willamette trough, and the Coast Range to the Pacific Ocean. We have used field mapping, chemistry, and paleomagnetic directions to trace individual flows and flow packages from the Columbia River Gorge westward into the Astoria Basin, where they form pillow palagonite complexes and mega-invasive bodies into older marine sedimentary rocks. Flows of the Grande Ronde, Wanapum, and Saddle Mountains Basalts all made it to the ocean; at least 33 flows are recognized in the western Columbia River Gorge, 50 in the Willamette Valley, 16 in the lower Columbia River Valley, and at least 12 on the Oregon side of the Astoria Basin. In the Astoria Basin, the basalt flows loaded and invaded the wet marine sediments, producing peperite breccias, soft sediment deformation, and complex invasive relations. Mega-invasive sills up to 500 m thick were emplaced into strata as old as Eocene, and invasive dikes up to 90 m thick can be traced continuously for 25 km near the basin margin. Mega-pillow complexes up to a kilometer thick are interpreted as the remains of lava deltas that prograded onto the shelf and a filled submarine canyon southeast of Astoria, possibly providing the hydraulic head for injection of invasive sills and dikes at depth.
DEPENDENCE OF CLUSTERING ON GALAXY LUMINOSITY
Authors: DENG XIN-FA , HE JI-ZHOU , SONG JUN , QIAN XIAO-XIA , WU PING
Published: April 2010

From the flux-limited main galaxy sample of SDSS DR6, we construct three volume-limited samples with different luminosities, and compare clustering properties of three samples. We find that the luminosity dependence of clustering properties does not exhibit a single trend, which is different between the sample fainter than the characteristic luminosity M* of the Schechter luminosity function and those brighter than M*. In the galaxy samples brighter than M*, the brighter galaxies have a more concentrated and less filamentary distribution as compared to the fainter ones. But when performing comparative studies of the luminosity dependence of clustering properties between the sample fainter than M* and ones brighter than M*, an opposite trend is found.
DARK ENERGY MODELS WITH VARIABLE EQUATION OF STATE PARAMETER
Authors: MUKHOPADHYAY UTPAL , RAY SAIBAL , RAHAMAN FAROOK
Published: April 2010

Two phenomenological variable Λ models, viz.Λ ~ (ȧ/a)2 and Λ ~ ρ, have been studied under the assumption that the equation of state parameter ω is a function of time. The selected Λ models are found to be equivalent both in four and five dimensions. The possibility of signature flip of the deceleration parameter is also shown.
CONSTRAINTS ON THE DARK ENERGY EQUATION OF STATE IN PRESENCE OF A VARYING FINE STRUCTURE CONSTANT
Authors: MENEGONI E. , PANDOLFI S. , GALLI S. , LATTANZI M. , MELCHIORRI A.
Published: April 2010

We discuss the cosmological constraints on the dark energy equation of state in the presence of primordial variations in the fine structure constant. We find that the constraints from CMB data alone on w and the Hubble constant are much weaker when variations in the fine structure constant are permitted. Vice versa, constraints on the fine structure constant are relaxed by more than 50% when dark energy models different from a cosmological constant are considered.
CHARGED BLACK HOLES IN VAIDYA BACKGROUNDS: HAWKING'S RADIATION
Authors: IBOHAL NG , KAPIL L.
Published: April 2010

In this paper we propose a class of embedded solutions of Einstein's field equations describing nonrotating Reissner–Nordstrom–Vaidya and rotating Kerr–Newman–Vaidya black holes. The Reissner–Nordstrom–Vaidya is obtained by embedding Reissner–Nordstrom solution into the nonrotating Vaidya. Similarly, we also find the Kerr–Newman–Vaidya black hole, when Kerr–Newman embeds into the rotating Vaidya solution. The Reissner–Nordstrom–Vaidya solution is type D whereas the Kerr–Newman–Vaidya metric is algebraically special of type II by the Petrov classification of space–time. These embedded solutions can be expressed in the Kerr–Schild ansatze on different backgrounds. The energy–momentum tensors for both nonrotating as well as rotating embedded solutions satisfy the energy conservation equations which show that they are solutions of Einstein's field equations. The surface gravity, area, temperature and entropy are also presented for each embedded black hole. It is observed that the area of the embedded black holes is greater than the sum of the areas of the individual ones. By considering the charge to be a function of radial coordinates it is shown that there is a change in the masses of the variably charged black holes. If such radiation continues, the mass of the black hole will evaporate completely thereby forming "instantaneous" charged black holes and creating embedded negative mass naked singularities describing the possible the life of radiation embedded black holes during their continuous radiation processes.
Acquisition and processing techniques to improve the seismic resolution of Tertiary targets
Authors: CROOK H. , PALMER J. E. , PAINTER D. J. , UDEN R. C.
Published: April 2010

The early phases of acquisition and processing in the North Sea produced relatively low resolution seismic sections aimed at penetration to the Jurassic reservoirs and less attention was paid to resolution of potential reservoirs in the shallow Tertiary sections. As the resolution of seismic sections improved due to new acquisition equipment and techniques and particularly due to advances in processing technology, some interesting shallow structures became just visible on seismic sections. More effort has been put into clarifying these elusive structures for the interpreter to delineate more confidently. Analysis techniques are available which can, under favourable conditions, indicate the presence of fluids from seismic data preferably calibrated by well information.
Paleocene reservoirs of the Everest trend
Authors: O’CONNOR S. J. , WALKER D.
Published: April 2010

The Everest trend of stratigraphically-trapped Paleocene gas accumulations was first recognized by the Amoco Group in the late 1970s and tested by the 22/10a-2 well in 1981. The well discovered gas–condensate pay in submarine fan sandstones of the Maureen and Andrew formations of the Montrose Group. These sandstones are absent in the 22/10-1 well, some 8 km to the east, where the entire Paleocene section above the Ekofisk Formation consists of shales of the Rogaland Group. A large stratigraphic trap was mapped, relying on up-dip shale-out to the east, and dip drape over a structural nose in the underlying Jaeren High basement block. No sandstones were found in the age-equivalent section of the Forties Formation in the 22/10a-2 well and so a further, down-dip, stratigraphic accumulation was predicted and subsequently successfully tested by the 22/10a-4 well in 1984. These discoveries are now named the Everest Complex. Simultaneously, the play concept was proven to the north by the Sleipner Øst discovery in 1981, where shale-out of the sandstone occurs over the Ling High. A third, similar, accumulation between these two fields was discovered in 1982 by Well 22/5b-2, which forms part of the Fleming accumulation. Reservoirs, which consist of poor to moderately sorted quartz-rich arenites, exhibit a wide variety of sedimentary facies produced by turbiditic and gravity flow processes. The distribution and form of the sandbodies is controlled by a combination of underlying palaeotopography, regional tectonism and global eustatic events. Correlation of reservoir units is accomplished by integration of wireline logs, detailed biostratigraphy and seismic facies analysis The commercial importance of the trend is reflected in the reserves proven to date, which are in excess of 4 trillion cubic feet (TCF) of wet gas.
Complex deformation and fluidization structures in Aptian sediment gravity flow deposits of the Outer Moray Firth
Authors: DOWNIE R. A. , STEDMAN C. I.
Published: April 2010

Sandstone units enclosed within hemipelagic marine mudstones of the Aptian–Albian Sola Formation of the Outer Moray Firth (principally Blocks 15/28 eastward to 16/28) are informally referred to as the ‘Bosun Sandstone’. These fine- to medium-grained, variably argillaceous sandstones are characterized by irregular and discontinuous argillaceous laminae, dewatering pipes, clastic intrusion phenomena, slump structures and soft-sediment shears. In the context of the enveloping deepwater marine mudstones, a sediment gravity flow origin for the sandstones is suggested. The abundance of detrital mud and virtual absence of ‘primary’ tractional structures indicate that the majority of flows were never fully turbulent, with minimal segregation of fines: that is, they were muddy debris flows or liquefied flows. Polyphase sediment deformation is recognized throughout the 500+ ft thick ‘Bosun Sandstone’, indicating that slope conditions were unstable and a gradient was maintained throughout the development of the ‘normal’ slope apron type system.

The recognition that the ‘Bosun Sandstone’ was deposited largely as liquefied flows on a gravitationally unstable prograding slope has implications for hydrocarbon prospectivity. Slumping and slope failures are likely to have occurred at a wide variety of scales and hence the internal sandbody geometry is likely to be highly complex. The presence of detrital mud in most sandstones has promoted diagenetic degradation of reservoir quality.
Potential reservoir and source rocks in relation to Upper Triassic to Middle Jurassic sequence stratigraphy, Atlantic margin basins of the British Isles
Authors: MORTON N.
Published: April 2010

Atlantic margin basins from the Celtic Sea to the Hebrides and North Minch, west of the British Isles, and in the Northern North Sea, have the same major genetic sequences (
sensu
Morton 1989
) in the Upper Triassic to Middle Jurassic. The basins were tectonically related, and six major sequences can be recognized throughout. The tectono-stratigraphic evolution of the basins was through two episodes of extension comprising: syn-rift phases (1) Late Triassic to Early Sinemurian and (4) Latest Toarcian to Late Bajocian; thermal and loading sag phases (2) Mid Sinemurian to earliest Toarcian and (5) Late Bajocian to Late Bathonian (except North Sea ?); and stabilization phases (3) Toarcian and (6) Late Bathonian and Callovian.

Potential and proven reservoirs (sandstones) occur in the syn-rift sequences (e.g. Statfjord, Bearreraig, Brent) and in the upper parts of sag sequences (e.g. Cook, Scalpa, Elgol, Valtos). Several organic-rich shales (potential source rocks) occur: in the basal parts of sag sequences (e.g. Heather, Cullaidh, Pabba); in stabilization sequences after eustatic sea-level rises (e.g. Drake, Portree); and locally at the base of syn-rift sequences (e.g. Dun Caan).
Biostratigraphic calibration of genetic stratigraphic sequences in the Jurassic–lowermost Cretaceous (Hettangian to Ryazanian) of the North Sea and adjacent areas
Authors: PARTINGTON M. A. , COPESTAKE P. , MITCHENER B. C. , UNDERHILL J. R.
Published: April 2010

Thirty-three regionally correlatable marine condensed sections containing maximum flooding surfaces have been recognized in the area allowing the North Sea Jurassic succession to be subdivided into 32 genetic stratigraphic sequences (
sensu
Galloway). Each event is biostratigraphically calibrated using microfossils (dinoflagellate cysts, radiolaria, ostracoda and foraminifera). The new scheme provides the basis for a basin-wide stratigraphic framework for the Jurassic of the North Sea basin.
The genetic sequence stratigraphy of the Hettangian to Oxfordian succession, Inner Moray Firth
Authors: STEPHEN K. J. , UNDERHILL J. R. , PARTINGTON M. A. , HEDLEY R. J.
Published: April 2010

Application of sequence stratigraphic principles to the Hettangian–Oxfordian succession of the Inner Moray Firth basin has led to a new understanding of its sedimentary fill history at a greater resolution than has been previously possible. This interval was deposited in a variety of shallow marine to terrestrial environments, punctuated by a number of regionally correlatable transgressive events, during a phase of gentle thermal subsidence, prior to the renewal of major extensional rifting in Kimmeridgian times.

Recognition of a significant regional stratigraphic break, the ‘Mid-Cimmerian Event’, allows this succession to be divided into two component depositional packages (Jla: Hettangian–Toarcian; J1b: Bathonian–Late Oxfordian). Identification of seven maximum flooding surfaces permits further subdivision into eight genetic stratigraphic sequences and enables the construction of a new basin-wide stratigraphic template. Erection of such a framework has important implications for our understanding of the basin’s sedimentary and tectonic evolution, and thus enables the Inner Moray Firth to be placed within its regional North Sea setting.

Construction of palaeogeographic maps for a number of J1b genetic stratigraphic sequences allows accurate facies and, hence, reservoir prediction. Furthermore, stratigraphic data give important insights into the nature of the ‘Mid-Cimmerian Event’. The observed progressive increase in amount of truncation below this unconformity, together with the successive migration in the locus of sedimentary onlap above this unconformity, maximizes the stratigraphic separation towards the east. Similar temporal stratigraphic relations elsewhere in the North Sea suggest that this unconformity is related to the initiation and early subsidence of a regional ‘dome’ prior to its more significant collapse between Kimmeridgian and Early Cretaceous times.
Jurassic volcanic centres in the Central North Sea
Authors: SMITH K. , RITCHIE J. D.
Published: April 2010

Well data and seismic reflection profiles have been used to pinpoint three Jurassic volcanic centres in the Central North Sea: the Fisher Bank and Glenn centres are closely juxtaposed and form part of the Forties volcanic province, and the Puffin centre occurs separately on the northern flanks of the Mid North Sea High. A fourth centre, Ivanhoe, has been tentatively located in the Outer Moray Firth. The thickness, distribution, age and stratigraphic relationships of the associated volcanic rocks are described with the aid of maps and seismic sections. In a speculative regional synthesis, it is suggested that various intra-Jurassic unconformities can be related to the growth and development of the volcanic centres. The onset of volcanism at the Fisher Bank centre may have occurred during the late Early Jurassic; the Puffin centre was active during the Mid-Jurassic, and the Glenn centre may be predominantly Callovian in age. As a result, the relationship between the volcanic rocks and the fluvio-deltaic sediments of the Pentland Formation varies across the area. The occurrence of widespread volcanic-related uplift favours models involving a thermal perturbation in the mantle, rather than a period of lithospheric stretching, to account for Jurassic volcanism in the Central North Sea.
Heavy mineral stratigraphy in the UK Trias: Western Approaches, onshore England and the Central North Sea
Authors: JEANS C. V. , REED S. J. B. , XING M.
Published: April 2010

Population studies on the detrital heavy minerals (64–250 μm, specific gravity >2.92) of the Trias in the North Sea Basin demonstrate that there are well-defined regional and stratigraphical variations which are of use in correlation and palaeogeographic reconstruction. Two provinces are recognized: a region comprising the Southern North Sea, onshore England and the English Channel; and a Central North Sea Area.

The heavy mineral assemblages of the Triassic sandstones of the Southern North Sea, onshore England and the English Channel are dominated by tourmaline. Wide-ranging correlation between the Southern North Sea and the English Channel has been achieved by using an horizon at which the heavy mineral assemblage is particularly rich in tourmaline. More detailed and local correlation is possible onshore, where rapid changes in the abundance of garnet, zircon, sphene and staurolite indicate the presence of local sources supplying sand detritus to the Trias.

The Triassic sands of the Central North Sea are characterized by heavy mineral assemblages dominated by zircon, garnet or apatite. The zircon-rich assemblage is associated with the Smith Bank Formation and is interpreted as having been derived from the reworking of the Permian Sandstones to the west. The apatite-rich assemblage is linked to the Skagerrak and Marnock formations and was probably derived from an eastern Scandinavian source. The garnet-rich assemblage is of more limited extent and is restricted to sediments of Early Triassic age: its origin could have been the metamorphic terrain exposed in the region of the Halibut Horst.

Preliminary studies on the chemistry of apatite (%F), tourmaline (%TiO
2
) and garnet (%CaO) grains from selected samples suggest that there is useful variation for the purposes of regional stratigraphy.
Structural development and hydrocarbon occurrence of the Carboniferous in the UK Southern North Sea Basin
Authors: HOLLYWOOD J. M. , WHORLOW C. V.
Published: April 2010

Recent Carboniferous gas discoveries in the UK Southern North Sea display a pronounced structural alignment. Previous efforts to decipher Carboniferous structural development have been hampered by limited well control and poor quality seismic data.

The recent increase in exploration activity in the southern area of Quadrant 44 has facilitated a detailed analysis of the Carboniferous. Interpretation of spectral gamma ray logs and biostratigraphic data from more than 40 deep wells have permitted re-correlation of the Carboniferous section. These new well correlations and VSP data from key wells make it possible to relate seismic reflection character to stratigraphy for several Carboniferous units. More than 2000 km of seismic data were interpreted throughout the southern part of Quadrant 44 to map the distribution of these Carboniferous seismic packages below the angular Base Permian Unconformity.

This interpretation project has resulted in a new understanding of Carboniferous structural development and its relationship to hydrocarbon occurrence. East–west-trending hangingwall roll-overs, formed during Carboniferous crustal extension, were subsequently transected by northwest-trending regional anticlines, generated during the Variscan orogeny. Hydrocarbons have been discovered in both the regional anticlines and localized roll-over structures.
Pseudo-reefs beneath Zechstein salt on the northern flank of the Mid North Sea High
Authors: TAYLOR J. C. M.
Published: April 2010

Seismic sections in North Sea Blocks 28/25, 28/30, 29/21, 29/26 and 29/27 on the northern flank of the Mid North Sea High show many mound-like features in an interval just above the base of the Zechstein. The top of the interval showing these anomalies is defined by a strong, widely traceable seismic reflection beneath thick salt. The mounds have a relief of up to 120 ms TWT and are up to 4 km across. Superficially, they have the appearance of build-ups in the carbonates of Z1 or Z2, possibly reefs. However, examination of all the anomalies reveals features which are not easily explicable by the reef hypothesis. In a few, for instance, the reflector defining their top is broken and one side is markedly displaced vertically from the other. Virtually all are situated below former pillows or diapirs in the overlying salt, and many are associated with faults that cut the Rotliegend. These facts, together with the low position of a unit interpreted as the basinal Plattendolomit in all nearby wells, suggest that the mounds might consist of swells in otherwise thin Z2 evaporites, sandwiched between basinal (i.e. condensed) representatives of the Z3 Plattendolomit, and the carbonates and anhydrites of the first two cycles. The abandoned Amerada Hess Well 29/27-1, drilled on one such mound, supports this explanation. The heart of the mound, which has no hydrocarbon potential, contains the low density magnesium chloride mineral tachyhydrite (rare in marine evaporites) rather than porous carbonates. This result downgrades similar anomalies as drilling objectives. The evaporite swellings appear to have formed in response to whatever factor initiated movement in the overlying salt; an association with basement faults is possible. Known igneous activity nearby may have been a factor, either in mobilizing the evaporites or stimulating their diagenesis. The absence in this area of thick Z2 halite such as is usual in the Southern Salt Basin is characteristic of much of the Northern Salt Basin; it appears to be a depositional feature related to regional differences in subsidence, possibly linked to an early phase of rifting in the Central Graben. The place of the Z2 halite, as the chief active component forming salt structures, is taken north of the Mid North Sea High by thick Z3 salts.
The tectono-stratigraphy of the Solan Basin, west of Shetland
Authors: BOOTH J. , SWIECICKI T. , WILCOCKSON P.
Published: April 2010

The Solan Basin lies in a part of the West Shetland continental margin that has had a complex tectonic history, dominated by extension but punctuated by several episodes of inversion, transpression and extensive erosion. The oldest sedimentary sequence, identified on seismic but not yet penetrated by drilling, may comprise Devono–Carboniferous clastics. In the Permo-Triassic a large system of half-grabens was filled with a thick succession of coarse, continental clastics. These appear to have entered the basin system in two discrete pulses and it is speculated that a third pulse, representing a transition to marginal and fully marine environments, occurred in the Early Jurassic. The area was effectively peneplaned in the late Middle to early Late Jurassic, with the removal of up to 1.5 km of section. Overlying this unconformity is a thin sequence of marginal marine sandstones and organic-rich marine shales, deposited in the latest Jurassic to earliest Cretaceous. Although parts of the region received a major influx of sand derived from the West Shetland Platform in the Early Cretaceous, the equivalent strata throughout most of the Solan Basin are a thin succession of pelagic shales and carbonates. In the early Turonian the basin was inverted. During the Late Cretaceous, extension, related to rifting along the line of the Faeroe–Shetland Trough, resulted in the development of large normal fault systems, providing the space in which a thick sequence of deep marine shales was deposited. In the earliest Paleocene, transpressional reactivation of some faults produced intense, but localized, inversion structures. Generally, however, sedimentation continued uninterrupted through the Paleocene, with the accumulation of deep marine sandstones in the east of the basin. The culmination of Thulean volcanism in the earliest Eocene was marked by the deposition of tuffaceous mudstones, which are overlain by thin coal-bearing, paralic to continental sediments. Regional thermal subsidence began in the early Eocene and continued into the Oligocene with the deposition of a thick sequence of marine clastics. In the Miocene, erosion removed up to 1.2 km of sediment from parts of the Rona Ridge and produced a basin-wide unconformity. This is overlain by Pliocene to Recent glacio-marine sands and gravels.
Structuring and transfer zones in the Faeroe Basin in a regional tectonic context
Authors: RUMPH B. , REAVES C. M. , ORANGE V. G. , ROBINSON D. L.
Published: April 2010

An integrated structural interpretation of the Faeroe Basin within the regional tectonic setting of the North Atlantic margin was derived from gravity, magnetic and regional seismic data. The tectonic framework of the basin was established during the Caledonian orogeny while its subsequent structural evolution was linked to the development of the Greenland–Scotland Ridge and the Iceland hot-spot. Some major transfer zones had previously been identified in the Faeroe Basin area. The gravity and magnetic data defined a series of transfer zones oriented NW–SE across the basin which were also identified on seismic data. These transfer zones have had major influences on the Mesozoic sedimentation patterns, and define basin segments which most likely had different sedimentary and structural histories, thus introducing a diversity of hydrocarbon plays into the Faeroe Basin.
Paleogene sequence stratigraphic framework of the Faeroe Basin
Authors: MITCHELL S. M. , BEAMISH G. W. J. , WOOD M. V. , MALACEK S. J. , ARMENTROUT J. A. , DAMUTH J. E. , OLSON H. C.
Published: April 2010

During Paleogene times up to 15 000 ft (4570 m) of clastic sediment was deposited in the Faeroe Basin, north of the Shetland Islands. A sequence stratigraphic study has shown that the Paleogene deposition in the Faeroe Basin was cyclic with prominent basinward and landward shifts in sedimentation. The correlation of major unconformity surfaces allowed the section to be subdivided into genetically related packages.

The sequence stratigraphic study utilized approximately 5000 km of seismic data with a line density of approximately 10 × 20 km. Available well control was integrated into the study by means of synthetic seismograms. Limited palaeontological control utilizing largely dinocysts and radiolaria allowed the identification of 11 Paleocene/Eocene bioevents.

The section was subdivided into nine Paleocene and six Eocene sequences, each separated by Type 1 unconformities. Four of the Paleocene and one of the Eocene packages had evidence of multiple Type 1 unconformities and these are described as sequence sets.

Sequence development has been related to the tectonic subsidence history of the basin. Early in Paleocene times, rapid subsidence resulted in the deposition of thick sequences with distinct shelf, slope and basinal systems. Nine sequences were deposited with a combined maximum thickness of 12000 ft (3660 m). The following period, late Paleocene to early Eocene, was marked by slower subsidence; thin sequences and ramp systems with seven sequences were deposited with a maximum thickness of 2400 ft (730 m). More rapid subsidence during the late Eocene resulted in five sequences with distinct shelf, slope and basinal systems with a thickness of up to 3500 ft (1070 m). The periods of slower subsidence in the Faeroe Basin may have occurred in response to active rifting in other adjacent basins along the Atlantic margin. The distinct basinal systems which developed during times of more rapid subsidence were more likely to develop sand-prone basin floor deposits.
Seismic structure of the Hatton–Rockall area: an integrated seismic/modelling study from composite datasets
Authors: KESER NEISH J.
Published: April 2010

During 1987–9 the United Kingdom Department of Energy recorded coincident seismic reflection, sonobuoy wide-angle reflection and refraction, and expanding spread refraction data across the Hatton–Rockall Plateau, lying within the continental margin to the west of Scotland. Some 780 km of deep multichannel seismic reflection data were used to define and control the structural model. The presence of Tertiary basalts throughout the area gives rise to severe attenuation of incident energy and substantial velocity inhomogeneities. Information from 53 sonobuoys and 5 reversed expanding spread profiles recorded along the lines allow independent determination of velocity structure. An integrated model is constructed layer by layer from the surface down to Moho. Using information gained from these integrated datasets, the velocity-depth structure of the area can be determined across the entire margin and imaging at depth beneath the basalts substantially improved. Deep, upper mantle reflections are clearly seen beneath Rockall Bank. Evidence of probable Tertiary inversion is seen in Hatton Basin. The main structure of Hatton Bank is fault controlled, and both highly tilted fault blocks and oceanward-dipping reflector sequences are observed. The presence of a two-layer continental crust is revealed, thinned within Rockall Trough and deepening to the east beneath the Hebridean Platform and the west below Hatton–Rockall Plateau.
The structural evolution of the Snorre Field and surrounding areas
Authors: DAHL N. , SOLLI T.
Published: April 2010

The Snorre Field is located on the Tampen Spur, Northern Viking Graben between 61°N and 62°N. Main structural elements are large, westerly tilted fault blocks. The Snorre Structure, one of the largest fault blocks in the East Shetland Basin, extends across Block 34/7 into Block 34/4. The Snorre Fault Block includes the Snorre Field, Tordis Field and the Vigdis Field oil discoveries. Major oil discoveries have so far been made in the Brent Group, the Statfjord Formation and the Lunde Formation. Discoveries have also been made in the Upper Jurassic and Paleocene. Upper Jurassic stratigraphic traps are the main target for further exploration in the area.

The westerly rotated fault blocks on the Tampen Spur are delineated by NNE–SSW- to NE–SW-trending faults. From west to east, these are the Murchison Fault, the Outer Snorre Fault, the Southern Snorre Fault and the Inner Snorre Fault. Other faults recognized are the E–W- and SE–NW-striking cross-faults dividing the elongated fault blocks into minor compartments. The N–S-striking faults are common in the Snorre area. The number of these faults decreases towards the north.

The Snorre Escarpment is the surface expression of the major Inner Snorre Fault representing the eastern border fault of the Snorre Fault Block.

Two major rifting episodes are recognized in the area. In the thermal subsidence phase following the late Permian to early Triassic rifting, large amounts of sediments of the Teist-, Lomvi-, Lunde-, Statfjord Formation, Dunlin- and Lower Brent Group were accumulated. A second major rifting episode resulted in intense fault activity from the early Bathonian to the late Kimmeridgian. Two major pulses of increased tectonic activity are recognized in the second rift episode. In the north, in the Zeta area, there is indication of late Jurassic lateral movements. Late Jurassic faulting, block rotation and footwall uplift, combined with Jurassic to Cretaceous subsidence, make the Snorre Fault Block of the Tampen Spur a very pronounced structural high in the area.
Submarine gas seepage in the North Sea and adjacent areas
Authors: HOVLAND M.
Published: April 2010

The occurrence of sub-seafloor gas accumulations and the seepage of gas through the seafloor are of interest not only to hydrocarbon prospectors, but also to marine construction engineers and to marine biologists. While direct seep observations (visual and acoustic) are rare, the observations of seep indicators, such as gas-charged sediments, pockmarks, carbonate-cemented sediments, clay diapirs, and dense benthic communities are relatively common.

In the North Sea there are several published direct seep observations and numerous observations of seep indicators. In addition, there are new features which have recently been observed in sandwave fields in the Southern North Sea. These are abnormally high-amplitude (‘freak’) sandwaves.

In the Skagerrak there are gas-charged sediments, pockmarks, and suspected sub-surface clay diapirs. In the Kattegat there are numerous gas seeps, gas-charged sediments, pockmarks and extensive areas of carbonate-cemented sediments. In the southeastern portion of the Baltic Sea there are gas-charged sediments and pockmarks. Along the Swedish coast (off Stockholm) small pockmarks, gas-charged sediments and anomalous concentrations of algal mats have been studied.

On the shelf off Mid-Norway there are gas-charged sediments, small areas with pockmarks, suspected clay diapirs, and occurrences of cold-water coral reefs thought to be related to seepage.

Biological, geological and geochemical research is currently being undertaken by British, Norwegian, Danish, German, Swedish and Russian scientists in some of the regions mentioned here. The objective of this research is mainly to determine the origin, fate and relevance of both seeping gas and the gas contained in sediments.
The link between petroleum emplacement and sandstone cementation
Authors: GLUYAS J. G. , ROBINSON A. G. , EMERY D. , GRANT S. M. , OXTOBY N. H.
Published: April 2010

When a reservoir fills with petroleum, the process commonly takes about 10 Ma. Cementation of a sandstone reservoir can occur in a similarly short time. There is much direct evidence that these two processes can occur at about the same time. In petroleum-bearing sandstone reservoirs it is common to find inclusions of petroleum trapped in diagenetic minerals. The effect on reservoir porosity and permeability caused by the interaction of these two processes is dramatic. Fields with a relatively early petroleum charge, earlier that is than cementation, can be saved from the ravages of reservoir quality destruction. Fields in which the two processes were acting at the same time commonly display porosity-depth gradients which are twice the regional average. If cementation beats petroleum in this ‘race for space’ there may be no field to produce, as the petroleum may not be recoverable from the low quality reservoir.

We believe that the processes of petroleum generation/migration and cementation may share a common cause. Both processes are commonly associated with major changes within a basin: rapid burial/heating of the sediment pile and/or major faulting which changes the basin ‘plumbing’.
Beryl Field: geological evolution and reservoir behaviour
Authors: ROBERTSON G.
Published: April 2010

The Mobil-operated Beryl Field is located in UK Block 9/13. Hydrocarbons are present in Triassic and Jurassic sandstone reservoirs, within a large fault-bounded structural trap. Interaction of sub-perpendicular fault trends determined the geological evolution of this structure and controlled the distribution of the sandstone reservoirs.

Hydrocarbon generation and subsequent migration commenced in Paleocene time. Entrapment of these hydrocarbons was influenced by pre-existing geological complexity and reservoir continuity. The distribution of different oil-types and multiple fluid contacts is defined by both structural and stratigraphic compartmentalization. Pre-production, the field reached a state of dynamic equilibrium between influx and leakage of hydrocarbons.

Production of oil commenced in 1976. Gas injection and water injection were initiated to arrest pressure decline. Pressure distribution and fluid movement throughout the field’s productive life are strongly influenced by geological controls. Understanding these geological controls has resulted in more effective reservoir management and optimization of the hydrocarbon resource.
4D evolution of segmented strike-slip fault systems: applications to NW Europe
Authors: DOOLEY T. , McCLAY K. , BONORA M.
Published: April 2010

Scaled, physical sandbox modelling has been used to simulate the progressive deformation of segmented strike-slip fault systems at both releasing (pull-apart basins) and restraining oversteps (‘pop-up’ structures) developed in a weak sedimentary cover above rigid basement. Pull-apart basin evolution is characterized by the initial development of a spindle graben bounded by oblique-extensional faults that cross the ‘basement’ overstep, and subsequent lengthening of the basin as displacement on the master faults increases. The pull-apart basins are bounded by terraced oblique slip extensional sidewall fault systems that link the laterally offset principal displacement zones (PDZ). The sidewall faults show changes in kinematics from dominantly dip-slip extension in their central sections to oblique slip and strike-slip at either end where they merge with the PDZ. The pull-apart basin models are flat-bottomed in the centre of the basin and become asymmetric at either end where the sidewall fault systems join the PDZ. Cross-basin fault systems, which are characteristic of all models, cut the floor of the pull-apart basins and link the offset PDZs. Deformation above restraining offsets is characterized by the formation of rhombic to lozenge-shaped uplifts or ‘pop-ups’ – structures bounded by oblique-slip reverse faults that fan outwards from the PDZ. With increased displacement on the master faults the rhombic-uplifts grow in amplitude. The upper surfaces of the ‘pop-up’ structures are dissected by both synthetic and antithetic strike- and oblique-slip faults. Distinctive asymmetric positive flower structures characterize the lateral margins of the ‘pop-up’ structures.

The analogue models are compared with natural examples of strike-slip pull-apart and ‘pop-up’ fault systems from NW Europe. The models show many strong similarities in structural geometry and stratal architectures with many natural examples, although it must be emphasized that similarities between structures of purely extensional origin (multiphase) and those associated with inversion do exist. Therefore, these analogue models of complex strike-slip structures may provide useful templates for seismic interpretation in petroleum basins provided there is a demonstrable link between strike-slip motion on basement structures and deformation in the cover.
Evidence for pre-Cretaceous rifting in the Rockall Trough: an analysis using quantitative 2D structural/stratigraphic modelling
Authors: NADIN P. A. , HOUCHEN M. A. , KUSZNIR N. J.
Published: April 2010

Quantitative 2D structural and stratigraphic modelling has been used to examine the crustal evolution of the Rockall Trough. The main phase of rifting and subsidence of the basin took place during the Cretaceous to Tertiary. The stratigraphy of the deeper parts of the Rockall Trough has not yet been tested and remains unproven. Two-dimensional forward syn-rift and post-rift modelling of crustal structure and basin geometry has been used to indicate whether a pre-Cretaceous rift system exists within the Rockall Trough. Basin modelling has been carried out on regional crustal profiles across the Rockall Trough derived from seismic reflection, refraction and gravity data. Observed present-day depths to top basement and Moho may be modelled for a range of
β
-stretching factors dependent upon the initial assumptions of Moho depth and bathymetry. Curves, summarizing model solutions, for
β
-factor versus both initial bathymetry and Moho depth, have been produced. Solutions for Cretaceous
β
-factors <3.0 require substantially thinned crust and water depths, prior to Cretaceous rifting, indicative of a preexisting rift basin.
The Hibernia Oilfield – effects of episodic tectonism on structural character and reservoir compartmentalization
Authors: SINCLAIR I. K. , EVANS J. E. , ALBRECHTSONS E. A. , SYDORA L. J.
Published: April 2010

The giant Hibernia Oilfield in the Jeanne d’Arc Basin, the first hydrocarbon development on the Grand Banks of Newfoundland, began production from an ice-resistant, concrete gravity base platform in November 1997. An estimated 615 × 10
6
BBL recoverable oil reserves are trapped in a highly faulted and south-plunging anticline.

The tectonic stresses experienced on the western North Atlantic margin have largely controlled the density and size distribution of faults which limit and partition the Hibernia structure. More than 30 fault blocks have been identified at one major oil and gas reservoir alone, the fluvial–deltaic Hibernia Formation. Interpretations of relationships between the times of tectonism and changing stress directions with fault ages, orientations, and styles are based on comparison of a 1991 vintage 3D seismic survey along with data from one discovery, nine delineation and two development wells. There appear to have been three main episodes of extension that affected the oilfield.

The first extensional episode spanned the Late Triassic into the Early Jurassic. Adjacent to the Hibernia Oilfield, initial rifting resulted in growth of NE-trending, en echelon faults that were subsequently amalgamated into the major basin-bounding Murre Fault. Deposition of the Hibernia Formation sandstones occurred during the second tectonic episode that spanned Late Jurassic into Early Cretaceous time. Faults of this vintage in the Hibernia Oilfield are normal and mostly formed synthetic to the re-activated Murre Fault in response to E–W oriented extension. The most marked fault growth occurred during the third tectonic episode. This late Early Cretaceous rift episode was co-eval with deposition of another major oil reservoir (the marginal to shallow marine ‘Avalon’ formation) which is targeted for development. Numerous normal faults formed orthogonal to the basin margin, thereby transecting and rotating the Hibernia structure. Fault development during the latest rift episode also responded to basin margin effects as a result of reactivation of the Murre Fault as a zone of oblique-slip. For example, the character of the large Rankin and Nautilus faults changes from relatively planar to distinctly listric moving from east to west. Additionally, sinistral deflections in the trace of the Murre Fault corresponding to linkages of the en echelon offsets formed during the first rift episode are interpreted to have controlled the location of the largest northeast dipping faults formed during the third rift episode.

The largest faults formed during the third rift episode clearly compartmentalize the Hibernia reservoir while the sealing capacity of faults formed during deposition of the Hibernia sandstones remains unquantified.
Early Tertiary magmatism in the offshore NW UK margin and surrounds
Authors: RITCHIE J. D. , GATLIFF R. W. , RICHARDS P. C.
Published: April 2010

The Iceland Plume, activated perhaps as early as Late Cretaceous time and extending through the Tertiary, was responsible for the generation of large volumes of igneous rocks, covering an area of roughly 2000 km in diameter, encompassing Greenland. the Vøring Basin, the Faeroes, the Faeroe–Shetland Basin, the Rockall Trough and NW Scotland. Within this large area, magmatism is mainly manifested as lava fields, sediment–sill complexes, and central or strato/shield type volcano complexes.

Towards the continental margin of NW Europe, extrusive rocks occur m two distinct geographical areas. SW of the Munkagrunnur Ridge of the Faeroe Platform, lavas are mainly extruded radially from strato/shield volcano complexes. To the NE, in contrast, seismic evidence suggests that the tipper part of the Faeroe Plateau Lava Group extrusive originate from the same source that formed the Seaward Dipping Reflector Sequences NW of the Faeroes. Towards the SE of the Faeroes, the distribution of the Faeroe Plateau Lava Group (Upper. Middle and Lower Series) lavas is controlled by pre-existing structure and sea-level fluctuations, Seismic and well evidence confirms that, generally, the Upper Series extends furthest into the Faeroe–Shetland Basin while basaltic progradational units form the SE limit of the Lower Series. Similar structures of possibly the same age have been identified within the NE Rockall Trough.

There appear to have been two major phases or pulses of Early Tertiary magmatism within the North Atlantic Igneous Province; an initial outburst at around 62 Ma and a later phase at around 55 Ma.
Anisotropy and amplitude versus offset: a case history from the West of Shetlands
Authors: MARGESSON R. W. , SONDERGELD C. H.
Published: April 2010

An amplitude versus offset (AVO) case study is presented from the West of Shetlands, UKCS in which pre-drill AVO signatures over a prospect were interpreted to be expressions of hydrocarbons but upon study of the data provided by the well were interpreted as a manifestation of anisotropy. The core from the well proved to be crucial in understanding the non-hydrocarbon AVO signature.

The well encountered good quality, high porosity, water wet sand and an underlying tuff sequence. Neither the dipole sonic log nor the check-shot survey revealed any anomalous elastic properties, nor did they detect the presence of anisotropy. Conventional, isotropic modelling using the measured log properties could not match the observed AVO response. Only comparison of the dipole sonic log and the check-shots with the core measurements gave evidence for the presence of substantial elastic anisotropy. Incorporation of anisotropy inferred from core and log measurements in the shales and tuffs gave a reasonable match to the observed AVO. The inferred anisotropies are substantial, averaging 15% for both the compressional and shear velocities and increasing over some depth intervals to 25%. A subsequent walkaway vertical seismic profile (VSP), acquired for the specific purpose of calibrating the AVO response, shows a marked AVO effect at the base of the target sandstone and tuffs, consistent with the surface seismic data. It is clear from this case study and other work that simple transverse anisotropy, for example, produced by the natural layering in shales, can cause first order effects on the AVO response.
The Paleocene deepwater sandstone play West of Shetland
Authors: LAMERS E. , CARMICHAEL S. M. M.
Published: April 2010

Following the discovery of oil in Paleocene sandstones in the Foinaven and Schiehallion fields in 1992 and 1993, exploration in the Faeroe–Shetland Basin has been very active. Most of the basin has been covered with 3D seismic surveys and numerous wells have been drilled for the Paleocene deep water play. However, success in terms of commercial discoveries has been limited. Detailed analysis suggests that the Foinaven/Schiehallion geological setting is unique in terms of hydrocarbon charge history, reservoir quality and trapping style. Oil charge is attributed to the presence of a Mesozoic high (Westray Ridge), which both focused charge and retained oil prior to remigration into Paleocene traps. The T35–T36 sequence which includes the Andrew Tuff appears to provide an effective top seal across the basin and all significant discoveries have been made in the T31–T35 fairway directly underlying it. Although reservoir sandstones similar to those found in the Foinaven and Schiehallion area have been encountered across the entire Faeroe–Shetland Basin, their relatively shallow burial depth and their position at the base of slope at Foinaven and Schiehallion appears to be unique in the basin. Several gas discoveries have been made in the Flett Sub-basin, located to the northeast of the Foinaven/Schiehallion area. The Flett Sub-basin has all the ingredients of a successful Paleocene hydrocarbon play, such as pervasive charge, an effective regional top seal, and stacks of Lower Paleocene deep-water sandstones and shales. However, trap definition is difficult: most remaining structures rely on a stratigraphic trapping component. The definition of top reservoir sand on seismic data is not straightforward, as seismic imaging techniques, including direct hydrocarbon indicator (DHI) analysis, are often ambiguous. T31–T35 sandstones in the deep Flett Sub-basin tend to be tight, although a considerable number have been found to have good reservoir properties. Prediction of areas where reservoir quality is preserved will be a main challenge for continuing exploration in the deep part of the Faeroe–Shetland Basin, including the undesignated area adjacent to Quadrant 204.