bluuebunny/crossref_metadata_2025 huggingface dataset:
The Brent Field, Block 211/29, UK North Sea
Authors: Struijk A. P. , Green R. T.
Published: April 2008

The Brent Field was the first discovery in the northern part of the North Sea, and is one of the largest hydrocarbon accumulations in the United Kingdom licence area. There are two separate major accumulations: one in the Middle Jurassic (Brent Group reservoir) and one in the Lower Jurassic/Triassic (Statfjord Formation reservoir). The field lies entirely within UK licence Block 211/29 at latitude 61°N and longitude 2°E. The water depth is 460 ft. The discovery well was drilled in 1971, and six further exploration and appraisal wells were drilled. Seismic data over the Brent Field has been acquired in three separate vintages. The latest acquisition is a 3-D grid recorded in 1986. Reprocessing of the entire 1986 3-D seismic data set was initiated in 1989.

The original oil/condensate-in-place, estimated on 1/1/89, is 3500 MMBBL, and the estimated original wet gas-in-place is 6700 TCF. Oil production is now in the decline phase. Average production in 1988 was 334,000 BOPD, with gas sales remaining at the plateau rate of 500 MMSCFD.

The field is being developed from four fixed platforms, each providing production, water injection and gas injection facilities for both Brent and Statfjord Formation reservoirs. Gas injection is distributed to achieve an intermediate oil rim development in some reservoir units. The platforms were installed between 1975 and 1978. Production commenced in 1976. The slump faulted crestal areas of both reservoirs have yet to be developed.

These crestal areas contain about 5% of the recoverable reserves. Appraisal drilling was carried out in the crest during 1988 and 1989.

The Brent Field is located approximately 100 miles north-east of the Shetland Islands and 300 miles NNE of Aberdeen (Fig. 1). The discovery well location is at latitude 61°05'53.87" North longitude 1°41'30.H" East. The water depth is 460 ft

The field comprises two distinct reservoirs, the Brent Group and the Statfjord Formation, which are of Middle Jurassic and Lower Jurassic/Triassic age respectively. The reservoirs occur in a westerly dipping tilted fault block in a fault controlled unconformity trap (Fig. 2).

The size of the hydrocarbon bearing area is approximately 10 miles from north to south and 3 miles from east to west (Fig. 3).

The reservoirs are in turn divided into seven separate reservoir units; four cycles in the Brent Group reservoir and three units in the Statfjord Formation reservoir. Laterally two major east-west orientated faults divide the field into three separate production areas. A fourth area is the north-south orientated crestal part of both reservoirs, which is faulted and has a series of down faulted slump blocks overlain by 'Reworked Sediment'. This area still has to be developed.

The Shell/Esso joint venture North Sea oilfields are named after water and waterside birds. The Brent Field is named after the Brent goose.
The Hutton Field, Blocks 211/28, 211/27, UK North Sea
Authors: Haig D. Brian
Published: April 2008

The Hutton oil field is situated in the East Shetlands Basin in the UK North Sea on the western side of the Viking Graben. It straddles UK Blocks 211/27 and 211/28. The field was discovered in July 1973 by the Conoco well 211/28-la and is operated by Conoco (UK) Limited. The structure comprises a series of southwesterly dipping tilted fault blocks. The reservoir sandstones are Middle Jurassic in age and were deposited as a result of deltaic progradation across the Hutton area. The oil bearing Brent Group sandstones vary in thickness from 150 ft to 380 ft with average porosities of 22% and permeabilities of 500-2000 md in the producing zones. Original recoverable reserves have been estimated at 190 MMBBL, of which the field has produced 107 MMBBL to date. The field is developed via a tension-leg platform, the first of its kind in the world.
The Osprey Field, Blocks 211/18a & 211/23a, UK North Sea*
Authors: Erickson John W. , Van Panhuys C. D.
Published: April 2008

The Osprey Oilfield is located 180 km northeast of the Shetland Islands in Blocks 211/23a and 211/18a in the UK sector of the northern North Sea. The discovery well 211/23-3 was drilled in January 1974 in a water depth of 530 ft. The trap is defined at around 8500 ft TVSS by two dip and fault closed structures, the main 'Horst Block' and the satellite 'Western Pool'. The hydrocarbons are contained in reservoir sandstones belonging to the Middle Jurassic Brent Group which was deposited by a wave-dominated delta system in the East Shetlands Basin. The expected
STOIIP
and ultimate recovery are estimated at 158
MMBBL
and 60
MMBBL
of oil respectively, which represents a recovery factor of 38%. The 'Horst Block' contains 85% of the reserves with an
OOWC
about 150 ft shallower than in the 'Western Pool'. Reservoir quality is excellent, with average porosities varying from 23-26% and average permeabilities varying from 35-5300 md. The development plan envisages eleven satellite wells, six producers and five water injectors, closely clustered around two subsea manifolds. First production is expected in late 1990/early 1991. The wet crude oil will be piped to the Dunlin 'A' platform for processing and from there to the Cormorant Alpha platform into the Brent System pipeline for export to the Sullom Voe terminal.
The Claymore Field, Block 14/19, UK North Sea
Authors: Harker S. D. , Green S. C. H. , Romani R. S.
Published: April 2008

The Claymore Field is located in UK North Sea Block 14/19 on the southwest margin of the Witch Ground Graben. The principal structure is a southerly tilted and truncated fault block. The field is divided into three producing areas. Major production is from Upper Jurassic paralic sandstones of the Sgiath Formation and turbidite sandstones of the Claymore Sandstone Member of the Kimmeridge Clay Formation in the downflank Main Area. Minor production is from Permian carbonates of the Halibut Bank Formation and Carboniferous sandstones of the Forth Formation in the crestal Central Area. The Northern Area is a northerly plunging nose, extending graben wards from the Claymore tilt block. Production in the Northern Area is from Lower Cretaceous turbidite sandstones of the Valhall Formation.

A small amount of oil was recovered on a wireline test in 1972 from Permian carbonates in the crestally located 14/19-1 well, in what is now termed the Central Area. In 1974 the Main Area was discovered by the southerly downdip well 14/19-2, and the Northern Area was discovered by the northerly downdip well 14/19-6A. Initial oil in place was 1452.9 MMBBL with currently estimated ultimate proved recovery of 511.0 MMBBL of oil. A 36-slot steel platform was installed in 1977. Two subsea water-injection templates were added in 1981 and 1985. Cumulative production to 6 July 1988 was 322.9 MMBBL of oil and daily production was 75 000 BOPD of oil from 28 producers, supported by 16 injectors.
The Clyde Field, Block 30/17b, UK North Sea
Authors: Stevens D. A. , Wallis R. J.
Published: April 2008

The Clyde Field, which was discovered in 1978, is located on the SW edge of the North Sea Central Graben. The reservoir is developed with Late Jurassic shallow marine sands of the Fulmar Sand Formation. An estimated 408 MMBBL of oil is present (Annex B), of which 154 MMBBL is considered recoverable.

The structure of the Clyde Field takes the form of a rotated Jurassic fault block, truncated at its crest by a major unconformity. Oil is retained within a combination trap, sourced from Late Jurassic Kimmeridge Clay thermally matured in the highly productive basinal lows, adjacent to the field.

Reservoir sand quality is highly variable, ranging from excellent with permeabilities in excess of Id, to poor with permeabilities of less than 1 md. The principal control on reservoir quality appears to be original depositional texture, although strong diagenetic effects are also present.

Production is from a single, centrally located, platform provided with thirty slots. Aquifer support is insufficient to maintain reservoir pressure at the current plateau production rate of 50 000 BOPD and so a programme of water injection has been implemented.
The Forties Field, Block 21/10, 22/6a, UK North Sea
Authors: Wills J. M.
Published: April 2008

The Forties Field is located 180 km (112 miles) ENE of Aberdeen, predominantly in UK Licence Block 21/10. It was discovered in 1970, when an exploration well encountered hydrocarbons in Palaeocene sandstone within an anticlinal structure. Four appraisal wells confirmed the existence of a major oilfield, with an area of approximately 90 sq km (35 sq miles) at a depth of approximately 2000 m (6500 ft). The reservoir occurs in thick Late Palaeocene sandstones deposited in two major sand-rich submarine fan sequences.

The field has been producing oil since September 1975. Stock Tank Oil Initially in Place (STOIIP) has been calculated as 4343 MMBBL, and original reserves estimated as 2470 MMBBL, representing an overall recovery of 57%. The field came off plateau production of 500 000 BOPD in 1981, and by mid-1989 production had declined to about 250 000 BOPD. After fourteen years production, the field has produced more than 2 billion STB. Remaining reserves are about 500 MMBBL which includes recovery via artificial lift. Field life has been projected to extend beyond the year 2000.

Water injection into the aquifer commenced in 1976, and continues at the present day at an average rate of 390 000 BWPD. There is also a significant contribution to pressure support from the underlying aquifer.

At present there are 103 available wells in the field, 81 producers and 22 injectors.
The Scapa Field, Block 14/19, UK North Sea
Authors: McGann G. J. , Green S. C. H. , Harker S. D. , Romani R. S.
Published: April 2008

The Scapa Field is located in UK North Sea Block 14/19 in the Witch Ground Graben, 112 miles northeast of Aberdeen. The field was discovered in 1975 by the 14/19–9 well which tested 32° API crude from the Scapa Sandstone Member of the Early Cretaceous Valhall Formation. The field is a combination structural/stratigraphic trap situated in a NW–SE trending syncline. Updip limit to the NE is by onlap termination of the reservoir sands onto the Claymore tilt block, and to the southwest by fault closure and/or sand pinch-out into tight conglomerates associated with the Halibut Shelf boundary fault. Two thinly bedded, fine- to medium-grained turbidite sand units, in partial pressure communication, form the oil–bearing zone within the Scapa Sandstone Member.

Original oil in place was 206 MMBBL. In 1984, prior to development, a long-term production test was conducted via a deviated well drilled from the Claymore platform. Subsequent wells were thus drilled in a dynamic reservoir-pressure environment. Field development utilizes an integrated production/injection subsea template system tied back to the Claymore platform. Template production commenced in 1986 from currently estimated proved ultimate recoverable reserves of 63 MMBBL and averaged 28 000 BOPD in June 1988 from four production wells supported by four injection wells.
The Leman Field, Blocks 49/26, 49/27, 49/28, 53/1, 53/2, UK North Sea
Authors: Hillier A. P. , Williams B. P. J.
Published: April 2008

Discovered in 1966 and starting production in 1968, Leman was the second gas field to come into production in the UK sector of the North Sea. It is classified as a giant field with an estimated ultimate recovery of 11 500 BCF of gas in the aeolian dune sands of the Rotliegend Group. The field extends over five blocks and is being developed by two groups with Shell and Amoco being the operators. Despite being such an old field development drilling is still ongoing in the field with the less permeable northwest area currently being developed.
Granite magmatism
Authors: Atherton Michael P.
Published: April 2008

Read’s two presidential addresses to the Geological Society (1948, 1949) heralded the end of the coherent rearguard action by the ‘granitizers’ against the ‘magmatists’. They were the distillation of his thoughts on the genesis of granite and culminated in his concept of the ‘Granite Series’. In this, he identified a continuity from metamorphic through migmatitic rocks to granite. Although he was wrong on granitization, the general idea remains intact and granites are produced by high-temperature metamorphism leading to partial melting. However the role of migmatites is still contentious. Not all granites belong to the granite series as he presented it; this particularly applies to Cordilleran (Andean) type granites. The genesis of this type will be discussed in the context of the earlier, classic work of Nockolds (1940) on the Garabal Hill complex where he demonstrated fractional crystallization was a major process in producing the diversity present and was similar to that seen in volcanic rocks, which had clearly been liquids. He also proposed that the source was basaltic with the implication, strongly supported by modern isotopic studies, that granites of this type are essentially mantle derived. Nockolds contribution was a geochemical confirmation of Bowen’s belief in the importance of closed-system fractional crystallization in the differentiation of plutonic rocks. Most authorities today would accept this but would not necessarily follow Bowen in the belief that major granitic batholiths formed by differentiation of basalt or that the system was closed. Recent models of the generation of the two main types of granite are presented, incorporating many of the ideas of Nockolds and Read. The discussion focuses on high-level differentiation, partial melting and intrusion in an extensional regime, high-T/low-P metamorphism associated with the magmatism, and the relation of granite to the plate tectonic setting.
Wave-form sheeted contourite drift on the Barra Fan, NW UK continental margin
Authors: Knutz Paul C. , Jones E John W. , Howe John E. , Van Weering Tjeerd J. C. , Stow Dorrik A. V.
Published: April 2008

The lithology of a 30 m long piston core (MD95-2006) and high-resolution, seismic profiles from the lower Barra Fan, Rockall Trough, reveal a sheeted drift form with internal sediment waves deposited over the last glacial-interglacial cycle. Deposition of these mainly fine-grained deposits was controlled by a combination of downslope and alongslope transport mechanisms that interacted with the positive topography created by debrite lobes on the lower fan. The core penetrates a small field of sediment waves (wavelength approx. 1 km, height 3-6 m), which onlap a debrite lobe dated to the last glacial maximum. The sedimentary sequence shows: (1) silty-muddy contourites deposited during the mid-Devensian (Marine Isotope Stage 3), (2) glacimarine hemipelagites and sandy turbidites deposited between 26 and 18 C14 ka BP, followed by a short phase of erosion and redeposition by bottom currents, and (3) glacimarine hemipelagites and silty-muddy contourites representing the glacial to Holocene transition. On the distal fan edge, a drift sequence with upslope-migrating sediment waves (wavelengths approx. 3 km, height 15-30 m) onlaps the tongue of a previous slide event (pre-Devensian?). These bedforms were probably generated by decelerating, low-density glacigenic turbidity currents, but pirated by contour-following bottom currents on the distal part of the drift.
Eastern New Zealand Drifts, Miocene-Recent
Authors: Carter Lionel , McCave I. Nicholas
Published: April 2008

Sediment from New Zealand passes into the north-flowing SW Pacific deep western boundary current (DWBC) to form widespread drifts. South of 49¼S, where the DWBC is reinforced by the Antarctic Circumpolar Current, drifts are small and, in the case of Campbell 'skin' Drift, reduced to a veneer over oceanic sediments. North of 49¼S deposition prevails with (1) Chatham Terrace Drifts - 350 km long and 320 m thick deposits around eastern Chatham Rise at 3000 m depth, (2) Chatham Deep Drift - 400 m thick, 300 km long ridge around the 4500-5000 m deep rise base, (3) Louisville Moat Drift -400 m of sediment within an isostatic depression along Louisville Seamount Chain and (4) Rekohu Drift - a 250 km long, 480 m thick ridge of Oligocene to Recent sediment. These drifts are sparsely surveyed, but two others have sufficient detail to be case studies. North Chatham Drift plasters northern Chatham Rise at 2000-4500 m depth. Drilling recovered 587 m of nannofossil ooze/chalk with cyclical amounts of terrigenous detritus and reworked subantarctic microfossils. Deposition has been almost continuous since the early Miocene. Hikurangi Fan-drift is a 300 km-long lobe, developed down-current of Hikurangi Channel/Fan through redirection of turbidity current plumes by the DWBC at 4850->5500 m depth. Seismically, the drift core comprises 200-360 m of probable Miocene palaeo-drift formed prior to the Pleistocene inception of Hikurangi Channel when 400 m of fan-drift accumulated.
The Foinaven Field, Blocks 204/19 and 204/24a, UK North Sea
Authors: Carruth A. G.
Published: April 2008

The Foinaven Field was discovered in 1992 and is estimated to hold up to one billion barrels of oil, with the current development expecting to recover 250 million barrels. BP Amoco is the operator of the field, holding a 72% interest with Shell UK as partner. The Foinaven structure is a faulted anticline and the trapping mechanism has elements of stratigraphic pinch-out, fault and dip closure. The field is divided into five fault/stratigraphical segments with varying oil-water and gas-oil contacts. The reservoir is Paleocene in age and comprises channelized, silici-clastic turbidites, with three main oil-containing sandstone intervals. Reservoir rock varies in character from thinly interbedded sandstones to massive channel sandstone. The reservoir is good quality, fine to medium grained, with 20-30% porosity, and permeability of 500-2000 mD. The hydrocarbons are from a mixed source of Middle and Upper Jurassic mudstones. Reservoir oil is sweet with an API gravity of 26 degrees, with some wax content and relatively low viscosity. Field development was sanctioned in October 1994. Development drilling began a month later with the first oil being produced in November 1997 through the Petrojarl Foinaven floating production installation (FPSO), which is leased from and operated by Golar-Nor Offshore. Current daily production averages 80 MBOPD and cumulative oil production to end October 1999 is 50MMBBL.
The East Brae Field, Blocks 16/03a, 16/03b, UK North Sea
Authors: Branter Stephen R. F.
Published: April 2008

The East Brae gas condensate field is the most northern of the four Upper Jurassic fields operated by Marathon Oil UK Limited in the UK North Sea. The field lies at the western margin of the South Viking Graben in UK Blocks 16/03a and 16/03b. The field was discovered in 1980 and commenced production in December 1993 from the East Brae platform. Recoverable reserves are estimated as 242 MMBBL of condensate and 1530 BSCF of sales gas.
The Ivanhoe, Rob Roy and Hamish Fields, Block 15/21, UK North Sea
Authors: Harvey M. A. , Currie S.
Published: April 2008

The Ivanhoe, Rob Roy and Hamish Fields lie in the Moray Firth of the UKCS in Block 15/21 and contain undersaturated oil trapped in the prolific Upper Jurassic Piper reservoir in tilted fault block traps. The fields were brought on stream in 1989 and since then the reservoir model has undergone several revisions with changes to the calculated oil in place volumes. The two main areas of uncertainty in the geological model are the position of the faults and the distribution of permeability. Improvements in the quality of the seismic data and the well ties brought about greater confidence in the seismic pick at top reservoir and the placement of the major bounding faults to the fields. The reservoir is generally sand-prone with a high net to gross ratio, porosity and permeability, which suggest that the reservoir would behave in a fairly homogeneous manner to fluid flow. Detailed reservoir description shows that this is not always the case. Improvements to the geological model permit a better understanding of the connection between the injector and producer wells and the degrees of influence from faults and heterogeneities in the reservoir to the fluid flow. Based on the current model the present recoverable reserves are estimated to be 187 MMBBL.
The Pierce Field, Blocks 23/22a, 23/27, UK North Sea
Authors: Birch Philip , Haynes Jamie
Published: April 2008

The Pierce Field contains oil and gas in Palaeocene Forties Sand and fractured Chalk, draped around the flanks of a pair of Central Graben salt diapirs. Whilst the two diapirs constitute a single field containing over 387 MMSTB AND 125 BCF, it took almost 25 years, and several advances in seismic, drilling and production technology, for the field to be brought into production. Many appraisal wells were drilled on the field. Data from these wells were interpreted to suggest the field was highly segmented both in terms of petroleum distribution and pressure variance. On the basis of this interpretation an economic development required a floating production system with long reach horizontal wells to penetrate the many reservoir segments. The results of development drilling have indicated that few pressure seals exist within the field, with concentric faults being more likely to seal than radial faults. The various reservoir pressures and oil-water contacts have been re-interpreted as a single, highly tilted oil-water contact, facilitated by the location of the field in the low permeability toe of the Forties submarine fan, a major conduit for the transport of basinal fluids away from the deep Central Graben

Palaeocene reservoir depositional patterns closely resemble those predicted by analogue models. The greatest reservoir thickness and net/gross are located in areas of flow velocity reduction (depletive flow), on the 'lee' side of the diapirs, but porosity and permeability are optimized in areas of increased flow velocity (accumulative flow), towards the crests of the diapirs

Strontium residual salt analysis has been used to study the charge history of the field. Interpretation suggests that South Pierce was filled before North Pierce, from a local Upper Jurassic source kitchen. Oil and gas subsequently spilled into North Pierce to form a composite trap with a single, tilted oil-water contact. The South Pierce gas cap has since been breached, and the escape of gas is currently leading to the retreat of the tilted water contact, once again isolating the two diapir structures
Grenvillian and Caledonian tectono-magmatic activity in northeasternmost Svalbard
Authors: Johansson Åke , Larionov Alexander N. , Gee David G. , Ohta Yoshihide , Tebenkov Alexander M. , Sandelin Stefan
Published: April 2008

The Nordaustlandet Terrane of NE Svalbard forms an exposed part of the Barentsia microcontinent. Augen gneisses, migmatites, granites and gabbros dominate the scattered outcrops along the northeastern coast of Nordaustlandet, and on the smaller islands to the north and east, as far as Kvitøya. These outcrops probably represent the deepest exposed crustal levels within the folded Caledonian basement of the Nordaustlandet Terrane. In the present study, a variety of rock types have been analysed by different U-Pb dating techniques (conventional, Pb-evaporation and ion microprobe) on zircon, titanite and monazite The major and trace element compositions and Sm-Nd isotope geochemistry of these rocks have also been investigated.

The augen gneisses yield U-Pb ages of
c.
950 Ma, indicating that they are deformed late Grenvillian granites, similar to the Grenville-age granites and augen gneisses of northwestern and central Nordaustlandet. Migmatites, grey granites, aplitic dykes and a syenite (boulder) yield U-Pb ages mainly falling in the 430–450 Ma range, slightly older than the 410–420 Ma late-tectonic Caledonian granites further west. Both the Grenvillian and Caledonian granites are of crustal anatectic origin, and the Caledonian granites and migmatites may have formed largely by remelting of Grenvillian crust. The ages of the mafic rocks are uncertain, but Sm-Nd data indicate a possible emplacement age of
c.
700 Ma for two of the gabbros, suggesting that they may be the result of rift-related magmatism in connection with the opening of the Iapetus Ocean. A few enigmatic inherited zircons of similar late Neoproterozoic age found in younger granites may possibly be related to this event. No evidence for late Neoproterozoic orogenic activity, similar to that in the Timanides of northern Russia, is seen in eastern Svalbard. At this time, eastern Svalbard (Barentsia) was probably part of the Laurentian margin, and probably located far away from northern Baltica.
Correlation of the Hellenide nappes in the south-east Aegean and their tectonic reconstruction
Authors: Bonneau Michel
Published: April 2008

The central Aegean nappe pile can be readily related to that of the mainland Hellenides and has the advantage that the deeper levels are well displayed, particularly in the Cyclades.

The following units can be distinguished, from base to top:

(1)

The para-autochtonous
Ida
or
Talea Ori Sequence
, recognized in Crete, Kassos, Rhodes (Lindos sequence) and Amorgos is, in part, a neritic carbonate platform sequence. It can be correlated with the Ionian-Preapulian autochthon of the mainland and most probably with the Menderes sequence of western Anatolia, there exposed in a tectonic window.

(2)

The major
Tripolitza Nappe
, a carbonate platform sequence, with the
Phyllite Nappe
at its base, is well represented in the outer arc as well as in Astypaleia and Santorini.

(3)

The
Pindos
and
Arvi Nappes
of Crete, Rhodes and Tilos are the remnants of an ocean basin active from Upper Triassic to Late Cretaceous times.

(4)

The Cycladic Blueschist Unit
exposed on Syros, Siphnos, Naxos and other islands, occupies a tectonic position similar to the Pindos Nappe. It is interpreted as the subducted margin of the European plate, while the Pindos Nappe, the abyssal plain of the Apulian plate, was obducted just before continental collision in the Late Eocene-Oligocene.

(5)

The
Asteroussia Nappe
, composed of high-grade metamorphic rocks yielding cooling ages around 75 Ma, is present in Crete and in the Cycladic islands of Syros, Nikouria, Denoussa and Keros. It is interpreted as the remnants of a Pelagonian basement nappe, eroded in Miocene times. In the external or outer belt it has been thrust on to the unmetamorphosed Pindos Nappe but in the Cyclades it rests on the Cycladic Blueschist unit.
The three metamorphic belts of the Hellenides: a review and a kinematic interpretation
Authors: Papanikolaou Dimitrios J.
Published: April 2008

New results obtained in the three metamorphic belts of the Hellenides suggest that each belt has a different structure, geotectonic setting and evolution. The external metamorphic belt of Peloponnesus-Crete has probably resulted from nappe movement in the vicinity of an evolving island arc system. The blueschists occurring within this external belt are allochthonous and have been transported with other nappes over the external carbonate platform of the Pre-Apulian-Plattenkalk-Ionian-Tripolitza-Almyropotamos Units. This implies that there was only one true blueschist domain, initiated in the Cycladic area during ?Early Eocene. The kinematic interpretation is based on the distinction of a- and b-structures and on the nature of the shear zones between the different domains, especially that between the metamorphic Hellenides below and the non-metamorphic Hellenides above. The existence of the probably Lower Palaeozoic meta-sedimentary sequence of Kastoria in the northern Pelagonian zone indicates that the overlying, ophiolite-bearing Almopias unit has been derived from within the Hercynian domain. The Kastoria sedimentary sequence, the ophiolites of Vertiskos and the carbonate platform of Pangeon are considered to be most likely elements of a probable Hercynian orogeny.
Tertiary to Quaternary evolution of volcanism in the Aegean region
Authors: Fytikas M. , Innocenti F. , Manetti P. , Peccerillo A. , Mazzuoli R. , Villari L.
Published: April 2008

Widespread orogenic volcanic activity has continued in the Aegean area from the Oligocene to present. Two main phases of activity are recognized. One developed in the North Aegean area from Oligocene to Middle Miocene times and a second started in the Pliocene, building the active South Aegean volcanic arc. Between these two phases, Upper Miocene to Quaternary volcanism of variable petrogenetic affinity occurred to a limited extent, essentially on the margins of the Aegean microplate.

The products erupted during the Oligo-Miocene phase consist mainly of calc-alkaline and shoshonitic intermediate lavas and pyroclastics with minor acidic and basic rock types. The volcanic activity started in the northernmost part of the North Aegean area with mostly calc-alkaline intermediate and acidic volcanics. The volcanism shifted successively southwards becoming progressively enriched in potassium. This evolution is interpreted as being related to an increase in the dip of the Benioff zone under the Eurasian plate, resulting from a reduction in the plate convergence rate after continental collision.

The volcanic products of the active south Aegean arc are mainly andesites with minor basalts and rhyolites which display the chemical character typical of calc-alkaline series erupted on thin continental margins. The South Aegean arc is believed to be the surface expression of active subduction of the African plate.

Scattered Upper Miocene to Quaternary activity is interpreted as occurring in zones of tensional strain along the borders of the Aegean microplate.
Graben formation and associated seismicity in the Gulf of Korinth (Central Greece)
Authors: Myrianthis M. L.
Published: April 2008

Extensional stresses in the central Aegean region reflect isostatic subsidence and uplift of brittle crustal blocks in response to crustal thinning. Block re-arrangements along active normal faults are probably the general cause for the generation of earthquakes. Reflection seismic data for the Gulf of Korinth graben is given here. It is concluded that the main factor controlling earthquakes is continuing uplift of the Peloponnesos block relative to the Gulf of Korinth graben.
The Western Arabia rift system
Authors: Quennell A. M.
Published: April 2008

The origin of the Dead Sea rift has generally been linked with that of the Red Sea, the widening of the latter involving left-lateral strike-slip on the rift. Its extension through the Lebanese fold belt has been denied by some because of the absence of linear and displacement continuity. Others, however, have been unable to see any other choice in spite of these difficulties, but a satisfying structural model has not yet been offered. The present author claims that the rift system is a transform plate boundary between the Arabian plate and the Sinai-Levant plate, but without uniformity along its length.

It is here suggested that during the Lower Miocene the Arabian planation surface, which before the opening of the Red Sea was the probable extension of the African mid-Tertiary surface, was ruptured by the first phase of movement on the west Arabian transform fault system, which probably reflected a geosuture zone in the continental plate and was originally a simple arc. The Arabian plate moved northward with the opening of the Red Sea and the closing of the Bitlis ocean, leaving behind the Sinai-Levantine part of the African Plate. Oblique compression on the northern Syria unstable platform across the East Anatolian transform fault caused dextral distortion on the Lebanon-Palmyra zone to create mountain ranges of two styles and a translation in the alignment of the rift segment. This inhibited further uniform strike-slip movement on the rift and displacement on the Yammouné fault was subsequently predominantly vertical. The movements on the rifts to the south and the north thus became independent. There was Arabian plate lithosphere consumption north-east of the Houlé depression to accommodate the second phase of rift movement. On the basis of this explanation, the vexed question of transmission of left lateral strike-slip across the Lebanon segment does not arise.
Clastic diagenesis
Authors: Burley S. D. , Kantorowicz J. D. , Waugh B.
Published: April 2008

Diagenesis is the sum of those processes by which originally sedimentary clastic assemblages attempt to reach equilibrium with their environments. The subject has rapidly evolved, over the last 20 years, after several decades of routine petrographical analysis, to become a discipline of sophisticated analytical geochemistry. This progression may be traced through the evolution of depositional facies models, the growth of theoretical geochemistry, and the development and application of quantitative analytical techniques. Consequently, the study of diagenesis today involves the integration of data gathered from a range of interrelated disciplines.

The publication in recent years of such integrated studies, particularly from the Texas Gulf Coast of the U.S.A., has led to a number of wide ranging models being established. These models allow an interpretation of the sequence of authigenic minerals in terms of their relationship to the depositional environment or surface chemistry (eogenesis), burial or subsurface conditions (mesogenesis) and weathering or reexposure to surface conditions (telogenesis).

More specifically, once the pre-depositional controls on diagenesis have been established, it is possible to relate the inferred eogenetic mineral assemblages to exact geochemical sedimentary environments. Sedimentary mineral assemblages chemically are characterized by relative instability and so tend to interact with interstitial pore waters. Thus, in non-marine environments, mineral authigenesis may reflect arid-oxidizing, or wet-reducing pore-water conditions, and in the marine environment, either oxidizing or reducing pore waters.

During mesogenesis different processes become important. Elevated temperatures add energy to the reacting system, lowering reaction barriers and increasing reaction rates. Furthermore, widespread pore fluid migration at depth, transporting large quantities of solute, is likely to impart major, regional diagenetic changes to sediments. That there is a remarkable degree of consistency in deep burial settings suggests that depth-related processes conform to a predictable pattern.

Additional geochemical instability is introduced into the diagenetic system during uplift and exposure to the telogenetic realm. Minerals formed during burial, at elevated temperatures and pressures, and from concentrated formation waters, may become unstable in oxidizing, meteoric waters.

Diagenetic research requires the complete dissection of sedimentary rocks and, subsequently, the quantitative chemical and mineralogical analysis of their individual components. Such an approach to diagenetic studies, when related to an assessment of their paragenesis, may eventually lead to a predictive, integrated model for the evolution of sedimentary clastic rocks.
Role of clastic sedimentology in the exploration and production of oil and gas in the North Sea
Authors: Johnson H. D. , Stewart D. J.
Published: April 2008

The nature and quality of clastic reservoir rocks is the result of a complex interplay of tectonic setting, provenance, depositional environment and diagenesis. In particular, it is now well established that the reconstruction of depositional environments in clastic successions provides the optimum framework for describing and predicting reservoir development and reservoir quality distribution on both regional (exploration) and field (production) scales.

This review, in the context of the 21st anniversary of the British Sedimentological Research Group (BSRG), expands the above-mentioned theme in relation to the development of depositional models of each of the major oil- and/or gas-bearing clastic reservoirs in the U.K. sector of the North Sea, which has been the subject of a surge in geological interest following the first gas discoveries approximately 21 years ago.

Each major reservoir interval is used to illustrate specific themes, with emphasis placed on how the application of depositional models has contributed to a better understanding of the exploration for, and the production from, the following reservoirs: (i) Permian aeolian and fluvial sands (Rotliegendes Sandstones, southern North Sea), (ii) Jurassic fluvial, deltaic and marginal marine sands (Lower Jurassic Statfjord Formation and Middle Jurassic Brent Group, northern North Sea), (iii) Jurassic shallow marine and deeper marine (mass flow) sands and conglomerates (Upper Jurassic Fulmar/Piper-type sands and Brae/Magnus-type deposits; central and northern North Sea), and (iv) Tertiary deep marine, turbidite fan deposits (Palaeocene and Eocene sands, central and northern North Sea).
Metamorphism and magmatism during the Himalayan collision
Authors: Le Fort Patrick
Published: April 2008

Collision of India and Eurasia occurred sometime during the Eocene following the Tethyan oceanic subduction. Post-collision metamorphic and magmatic events in Tibet and in the Himalaya are reviewed. Metamorphism is limited to the Himalaya where at least four zones may be recognized which from S to N are, (i) high-pressure metamorphism produced before, but emplaced, during obduction, (ii) a belt of low-grade metamorphism produced during the first nappe emplacement, (iii) the pre-granitic Barrovian metamorphism of the High Himalaya, and (iv) the inverted metamorphism induced during shearing along the Main Central Thrust. Magmatism in the Himalayan domain resulted in two parallel belts of granitoids that were generated in the same way but differ in their mode of emplacement. In Tibet, magmatism spread over most of the domain following collision and magma is probably present now at shallow depths. The relationship between crustal thickening, uplift and magma generation is not clear. The difference in metamorphic and magmatic characteristics in the two domains may help to trace palaeocollision zones.
Collision tectonics in the Western Alps
Authors: Ricou L. E. , Siddans A. W. B.
Published: April 2008

This paper gives a brief review of some different models that have been proposed to account for the tectonic development of the Western Alps, emphasizing the field evidence which indicates the major role played by strike-slip tectonics. Sketch maps of the tectonic evolution since Cretaceous times are presented which interpret the Alps as a strike-slip collision belt followed by ‘hypercollision’ on the western edge of the northward-moving Adriatic Promontary. There was early local collision along N-S strike-slip faults, while intervening E-W trending basins remained open. General collision is considered to have been completed by Eocene times when the pre-existing basins disappeared and the previously stretched lithosphere was restored to normal thickness. The following hypercollision first continued along the same N-S strike-slip displacements, with thickening of the lithosphere and migration of flysch basins. Later Oligocene hypercollision evolved into mainly westward displacement, limited by E-W strike-slip zones, dextral in the N and sinistral in the S. Strike-slip collision and hypercollision are considered as sufficient to explain the particuliarities of the tectonic development of the Western Alps, with associated metamorphisms and basinal evolution, since 80 Ma.
The Distribution of Porosity in Zechstein Carbonates
Authors: Clark D. N.
Published: April 2008

Zechstein carbonates form important gas reservoirs in Germany and the Netherlands and in at least one commercial field in the U.K. southern North Sea but elsewhere they are largely unexploited. The carbonates occur in four separate units and all are known to contain potential reservoir rocks. Distribution of porosity is controlled either by a combination of depositional facies and diagenesis or by the occurrence of collapse breccias. Intragranular porosity resulting from early leaching predominates in shallow-marine grainstones and intercrystalline porosity caused by late leaching occurs in deepermarine carbonate mudstones. Using a knowledge of facies distribution, it is possible to predict where these potential reservoirs might occur and as facies distribution can be related to the overall thickness of each carbonate unit, it is also possible to make tentative predictions of porosity distribution from isopach maps. Collapse breccias, however, are not related to any particular facies and potential reservoirs resulting from this process are most likely to be found around structural highs that became exposed at various times since, the Zechstein.
Metamorphism and crustal rheology—implications for the structural development of the continental crust during prograde metamorphism
Authors: Weber K.
Published: April 2008

Based on its metamorphic development it can be argued that the orogenic continental crust during prograde metamorphism consists of three layers of contrasting bulk rheology: a lower layer of granulite-facies rocks able to carry relatively high flow stresses; a middle layer of migmatites and amphibolite-facies rocks of very low mechanical strength and an upper layer of low-grade and very low-grade metamorphic rocks, the so-called ‘brittle’ crust in the geophysical sense with higher yield strength possibly increasing upward. There are presumably main décollement horizons between the lithospheric mantle and lower crust, in the roof of a granulite-facies lower crust and along the boundary between the middle and upper crust, giving rise to large-scale displacements and the formation of nappe structures of different metamorphic rocks. Granulite-facies rocks of the lower crust will tend to form large-scale folds which pierce the overlying crust during increasing amplification. Further crustal shortening may produce granulite-facies nappes from strongly amplified large-scale fold structures leading to inverse metamorphism which is generally accompanied by granulite-facies nappe complexes.
The South India-Sri Lanka high-grade terrain as a possible deep-crust section
Authors: Newton R. C. , Hansen E.C.
Published: April 2008

Precambrian granulite-facies terrains are regarded as possible models for the deep crust. In the South India-Sri Lanka late Archaean-early Proterozoic terrain, there is a regional gradation from greenschist and amphibolite facies south through an orthopyroxene isograd to the Granulite Massifs of S. India and of Sri Lanka. The metamorphic gradation is unusually complete and continuous and may represent a partial Archaean crustal profile. Large areas of low-grade grey gneiss may have been formed after charnockite in a retrogression event or may have somehow escaped late Archaean granulite facies metamorphism.

Palaeopressures indicate an increase from 5 kbar to more than 7 kbar in the Transition Zone, though various fault-bounded blocks in the high-grade massif area show different pressure ranges, indicative of different amounts of uplift. The highest pressures of above 9 kbar are for Rb- and U-depleted intermediate charnockites. Undepleted acid charnockites show pressures of 6.5–7.5 kbar, and supracrustal sequences show still lower pressures. The supracrustal-rich Central Highlands of Sri Lanka show pressures of 6 to 7.5 kbar, and most or all rocks are undepleted in Rb. Associated temperatures of all the Massif rocks are in the range 700°–800°C.

This grossly-stratified Archaean crustal section is only the upper half of a thickened crust: there is no indication of what lies below the deepest exposed section, and no compelling reason that depleted intermediate charnockite continues down to the Mohorovicic Discontinuity. Another possibility is deep thrust-bounded repetitions of the section which is exposed at the surface.
Early rift sedimentation in the Turkana basin, northern Kenya
Authors: Williamson P. G. , Savage R. J. G.
Published: April 2008

The ‘Turkana Grit’ deposits of northern Kenya are a thick sequence of immature arkosic sediments of pre-Plio-Pleistocene age. Originally described by Murray-Hughes in the 1930s, these sediments have been variously considered as of either Mesozoic or Miocene age by subsequent authors. These extremely immature, tectonically controlled sediments clearly reflect intense local deformation; their age is of considerable interest, as they clearly signal the onset of significant tectonic activity in the central sector of the East African rift. A regional survey of the Turkana Grits as currently known, coupled with recently available information from the hitherto unmapped Kajong area in the SE Turkana basin, clearly indicates that these sediments represent two distinct episodes of local tectonism and deposition. On the basis of available radiometric and biostratigraphic evidence, the earlier of these episodes appears to be of Cenomanian-basal Palaeocene age, while the later episode dates from the mid-Miocene. These observations suggest that significant tectonic activity in East Africa commenced in the late Mesozoic rather than—as generally assumed—in the mid-Cenozoic. The earliest (late Mesozoic) episode of clastic deposition in the Kajong area was initially controlled by a set of major E-W trending transform faults; these deposits are primarily preserved in associated fault-wedge basins. The documentation of a major transform element in the Kajong area has important implications for the early development of the African Rift as a whole. We suggest here the possibility that the enigmatic distribution of the late Mesozoic rift sediments—which are restricted to the southern sector of the Western Rift and the northern sector of the Eastern Rift—reflects the fact that the original late Mesozoic rift consisted of a single graben. The southern and northern portions of this graben have been subsequently displaced by a major E-W trending dextral transform system, extending some 500 km from the SE Turkana basin to the present northern termination of the Western Rift on the Uganda-Sudan border.
Mesozoic marine organic-rich shales
Authors: Hallam A.
Published: April 2008

A survey of Mesozoic organic-rich shales in space and time indicates that they are widely distributed through much of the era but are concentrated especially at two levels: Upper Jurassic (Kimmeridgian-Volgian/Tithonian) and Middle Cretaceous (Aptian-Turonian). Stable carbon isotope studies prove to be a particularly useful tool in both palaeoenvironmental and diagenetic analysis. Anoxic events in the ocean may be characterized by high concentrations of δ
13
carbonate carbon. The carbon isotope values obtained may, however, reflect diagenesis in the sulphate reduction zone rather than conditions in the original sea water. Calcite concretions formed at successive stages in diagenesis may record a change from strongly negative to strongly positive values of δ
13
C, indicating a switch from the sulphate-reduction to the fermentation zone.

Analysis of benthic palaeoecology leads to a classification of marine mudrocks into barren laminite, shelly laminite, shelly shale and shelly mudstone, of which the last lacks any significant quantity of kerogen. By analogy with Recent sediments an attempt is made at a tentative estimate of the oxygen content at the sediment/water interface during the original deposition. Environments of deposition are considered in general terms and the respective merits of several facies models for the Mesozoic deposits are briefly discussed.
A review of petroleum source rocks in parts of the Middle East
Authors: Stoneley R.
Published: April 2008

The oils in the Mesozoic and Tertiary reservoirs of the region surrounding the inner Persian/Arabian Gulf were derived from Jurassic and Cretaceous argillaceous and carbonate source rocks, which accumulated at various times in more or less restricted intrashelf basins and depressions, and were preserved under anoxic conditions. Maturation, migration and accumulation took place from the late Cretaceous onwards, at different times in different parts of the region; however, Upper Cretaceous and Tertiary sediments are, for the most part, still immature. This sourcing history is one of a number of favourable circumstances contributing to the richness of the region.