bluuebunny/crossref_metadata_2025 huggingface dataset:
PETROLEUM AT THE ROOF OF THE WORLD: The geological evolution of the Tibet (Qinghai‐Xizang) Plateau Part I
Authors: .Taner I. , Meyerhoffr A. A.
Published: December 2007

The Tibet (Qinghai‐Xizang) Plateau is underlain by many thousands of mters of Ordovician (and possibly Cambrian) through Middle Eocene, gently‐dipping, essentially undeformed, stable platform sequences. These are largely qf shallow‐water, marine‐shelf origin in the Ordovician‐Triassic sections, but are of mixed continental and marine facies in the Jurassic through Midle Eocene sections. Two east‐west fault troughs ‐ the Banggong Co ‐ Nu Jianand Indus River ‐Yarlung Zangbo ‐ contain thick sections of Triassic, Jurassic, and/or Cretaceous marine flysch associated with ophiolites. The only severe deformation to affect the plateau was during the Mesozoic, and it was concentrated close to the through‐going east‐west fractures.

Post‐early Eocene beds are entirely continental, and are concentrated nsmall‐to‐large grabens. One of these, the Lunpola Basin, has been moderately explored. Drilling here during the 1970s recovered small amounts of heavy, biodegraded oil of non‐marine origin, from a sectionthat ranges in age from Middle Eocene through Quaternary

Plateau‐wide stratigraphic studies reveal that the Ordovician through Early Carboniferous, and Late Permian through Middle Eocene, sections were deposited on a monolithic stable block. All were deposited in essentially warm tropical seas in close proximity, as demonstrated by the, facies, faunas, and floras. These same studies, plus related tectonic investigations, reveal that the through‐going east‐west fracture zones, popularly interpreted as “sutures,” are not sutures at all. Rather, the facies belts in rocks of all ages studied in detail routinely cross the so‐called “sutures,” commonly at very sharp angles, proving that these east‐west fault zones exerted no control overthe general lithofacies deposition patterns of the Himalaya‐Tibet block. The oniy facies control exerted by the fracture zones was in the small, narrow troughs that developed along them. Thus, the Himalaya‐Tibet block behaved as a single structural unit through time, and was never segmen red in to various microcontinents.

Although some potential for commercial petroleum discoveries exists in the post‐middleEocene grabens. the greatest potential of the Himalaya‐Tibet block is in the Paleozoic‐Mesozoicsection. with its promise of multiple source‐beds. reservoirs, traps, and seals. We predict that, one day, this “roof of the world” will host many petroleum Jields.
A REVIEW OF THE CRETACEOUS FORMATIONS IN THE ARABIAN PENINSULA AND GULF: PART III. UPPER CRETACEOUS (ARUMA GROUP) STRATIGRAPHY AND PALEOGEOGRAPHY
Authors: Alsharhan A.S. , Nairn A.E.M.
Published: December 2007

A historical review of the development of the stratigraphy of Upper Cretaceous rocks in the Arabian Peninsula and Gulf provides a partial explanation for many of the different formational names. A type section is presented for the United Arab Emirates, and lithofacies variations within the region are related to it. In addition to the simple model of migration of predominantly shallow‐water facies belts across a shelf, the Upper Cretaceous also contains deep‐water facies due to the onset of plate‐margin tectonic activity, which resulted in the emplacement of the Hawasina complex and the Semail ophiolites of Oman.

As observed in the earlier mid‐ and Lower Cretaceious rocks, two cycles can be recognized. These are found in the SE part of the region, in contrast with the mid‐Cretaceous, where two cycles are more clearly recognized in the NE area.
SALINE DEPOSITS AND ALKALINE MAGMATISM: A GENETIC MODEL
Authors: Momenzadeh M.
Published: December 2007

The temporal and spatical coincidence of saline deposits with rifting and alkaline magmatism is now widely accepted. The congruency of these three phenomena implies, logically, their trilateral genetic inter‐relationship. Conventional models for the formation of saline deposits, i.e. the “evaporation process”, cannot be properly applied to giant saline deposits, such as those of the Mediterranean and Red Sea basins

The alternative “Volcanogenic Model” proposed here offers a genetic explanation for these problems. This Model is compared with both the conventional evaporation model and the deep‐basin evaporation model of fSchmalz. Well‐known saline‐surface basins (e.g. the Red Sea, East African rift system, Dead Sea, Mediterranean, Circum‐Atlantic, Zechstein, and Asian InfraCambrian — Lower Cambrian), and “Kuroko” and “Black Smoker” depostis, are briefly reviewed. The role of alkaline and calc‐alkaline magmatism in producing saline‐surface deposts and the application of the Volcanogenic Model in each case is discussed, and conclusions concerning the suitability of the new model are drawn.
THE JURASSIC SYSTEM IN NORTHERN EGYPT: I. Regional stratigraphy and implications for hydrocarbon prospectivity
Authors: Keeley M. L. , Dungworth G. , Floyd C. S. , Forbes G. A. , King C. , McGarva R. M. , Shaw D.
Published: December 2007

A systematic lithostratigraphical description is presented of those Jurassic rocks encountered in Egypt north of 29d̀N, at surface and in the subsurface. Based upon the scheme first proposed by Al‐Far (1966), five formations (Masajid, Khatatba, Bir Maghara, Shusha and Rajabiah) are shown to make up a continuous succession from late Pliensbachian probably up to early Tithonian: the Gebel el Maghara Group. The compositions of stratigraphically‐useful and diverse biotas are outlined, and used to erect a chronostratigraphical framework. From this, reliable comparisons are made with the Jurassic sequences of Palestine and Saudi Arabia. Furthermore, this more refined means of correlation enables a fuller understanding of the distribution of potential Jurassic source and reservoir rocks in northern Egypt
POLLEN TRANSLUCENCY AS A THERMAL MATURATION INDICATOR
Authors: Lerche I. , McKenna T. E.
Published: December 2007

Using an inversion technique, we show that pollen translucency with depth can be used as a quantitative tool to estimate the thermal history of sedimentary sequences. The overall trend of translucency is a decrease with increasing depth.

In this study, three wells in southern Louisiana were examined, each having Carya (a pollen genus including present‐day Pecans and Hickories) translucency measurements with depth, and one of the wells containing measurements of vitrinite reflectance with depth. High sedimentation rates (>250 ft/MM yrs of shale) require the use of a fluid flow/compaction burial history program linked with the Carya inversion algorithm. Thermal history is estimated by the interaction of a heat flux taken to be linear in time, and a time‐temperature integral for the inversion of Carya translucency. The former involves β, a linear heat‐flux coefficient to be determined, while the latter involves two previously unknown constants: TC, a critical temperature, below which the translucency is stable (no carbonization), and TD, a scaling constant, roughly analogous to a doubling temperature. TD and Tc are chemical constants, and should be consistent in the three wells, while β should be consistent when determined independently by vitrinite reflectance and Carya translucency inversions. Grid searches for an acceptable solution in TC vs. TD vs. βspace were carried out for each of the three wells to determine the best TD TC and β for each well. A goodness‐of‐fit criterion, contoured in TD vs. TC vs. βspace, defines a volume of solutions within fixed error limits. Estimates of TD= 75 ± 30°K and TC= 290 + 20°K, for the genus Carya, are consistent for all of the wells. Acceptable β ranges, determined by the Carya inversion, overlap for the neighbouring wells. and the ranges are also consistent with β determined by the independent inversion of vitrinite reflectance in one of the wells.

We conclude that Carya translucency can be used as a quantitative thermal indicator. Application of the inverse method to translucency measurements on other palynomorphs having longer. or different, age ranges than the Eocene‐Recent lifetime for Carya is recommended.
GEOLOGIC RATIONALE FOR HYDROCARBON EXPLORATION IN THE CARIBBEAN AND ADJACENT REGIONS
Authors: Pindell J. L.
Published: December 2007

Sedimentary basins in the Caribbean and adjacent areas are assessed in terms of the plate‐tectonic and paleogeographic history of the regions. Primary phases of development were rifting and passive margin development during Jurassic‐Cretaceous drift of North from South America; and the Late Cretaceous to Recent relative eastwards migration of the Caribbean Plate from the eastern Pacific area to its present position between North and South America.

Two primary stratigraphic suites of rock occur in the Caribbean region: (I) autochthonous Jurassic, Cretaceous and Cenozoic passive margin sediments deposited along the rifted margins of North and South American basement: and (2) allochthonous oceanic crustal and magmatic arc rocks and overlying sedimentary units of the migrating Caribbean Plate. The tectonic boundary between these suites coincides roughly with the limit of circum‐Caribbean thrusted metamorphic/mafic rocks above the formerly passive Proto‐Caribbean shelf rocks (episutural foredeep basins), and juxtaposition youngs from west (latest Cretaceous in southern Yucatan) to east (late Neogene in Trinidad). Although Jurassic rift/early drift‐related source rocks occur in some areas. such as in Cuba—Bahamas. the primary source rocks in both suites were deposited well after rifting in the “medial” Cretaceous. Basin development during the Late Cretaceous to Recent tectonic juxtaposition of the two suites (i.e. Caribbean migration) directly controlled both clastic reservoir facies deposition and hydrocarbon maturation in many areas around the Caribbean. Basin development, source and reservoir rock deposition, and maturation of source rocks in all basins in the region can be directly related to plate‐tectonic evolution. A satisfactory understanding of the hydrocarbon potential of the Caribbean/northem South American province therefore requires a full appreciation of the region's plate‐tectonic evolution.
SEDIMENTARY BASINS OF THE NE CARIBBEAN PLATE BOUNDARY ZONE AND THEIR PETROLEUM POTENTIAL
Authors: Larue D. K. , Warner A. J.
Published: December 2007

Sedimentary basins in the NE Caribbean Plate Boundary Zone are associated with the evolution of a Cretaceous to Early Tertiary island arc, and with carbonate banks which formed following cessation of volcanism in the Eocene to Oligocene. Neogene sedimentary basins are typically present where crustal blocks in the plate boundary zone have undergone divergence, with or without rotation. Cretaceous through Oligocene basins may also have formed during divergence between crustal blocks, although this is difficult to prove owing to limited exposure and subsequent tectonic deformation. Other basins are associated with localized overthrusting along the plate boundaries.

Absence of source rocks and complicated and variable geothermal gradients make the area one of high risk for petroleum exploration. However. the paucity of data collected in the region allows for significant future discoveries, and the presence of minor seeps and traces of petroleum from two wells gives some hope. Finally, there is some evidence that seismic reflection amplitude anomalies may be associated with gas occurrences in the NE Caribbean, such that imaging of “bright spots” may prove to be a successful exploration tool.
ORGANIC GEOCHEMISTRY AND PETROLEUM POTENTIAL OF JAMAICA
Authors: Rodrigues K.
Published: December 2007

Eleven wells were drilled in Jamaican territory over a 27–year period commencing in 1955: all were abandoned as dry. This study evaluates the island's petroleum potential in the light of new data on the source‐rock quality of the shales penetrated, and on reservoir properties of sandstones and limestones interbedded with these shales.

Altogether. 270 representative shales and mudstones were sampled from the Cretaceous Windsor, Hanover and Sunderland Formations, and from the Eocene Richmond and Chapelton Formations. and subjected to standard organic‐geochemical analyses. Data on organic matter quantity, type and maturity indicate good potential for oil generation in the Chapelton Formation. The other formations analysed have < 1.0% total organic carbon. comprising woody and coaly kerogens, with no potential for oil generation.

Modal compositions of detrital grains were determined on sandstones sampled for reservoir quality evaluation from four formations. Provenance studies indicate derivation from a magmatic‐arc source, with volcanic lithic fragments and feldspars being the dominant constituents. This unstable mineralogy, combined with rapid sedimentation and location of sedimentary basins close to source areas, implies low porosity and permeability in these sandstones.

Other considerations of trap availability, presence and extent of cap rocks. and the likelihood of any petroleum generated being preserved in view of Jamaica's active tectonic history since the Middle Miocene, suggest that conditions for the generation. accumulation and preservation of commercial deposits of petroleum probably may not have existed here.
HYDROCARBON POTENTIAL OF NORTHERN IRELAND: Part II. Reservoir potential of the Carboniferous
Authors: Parnell J.
Published: December 2007

Carboniferous sandstones occur in several basins in the north of Ireland, deposited predominantly in fluvio‐deltaic environments. The Carboniferous is thickest in the west of the region. Primary compositional variations are evident: in particular. the sandstones are more arkosic in the west. Variations in authigenic mineralogy also occur: sandstones in the west contain greater volumes of ciuthigenic quartz, and exhibit hairy/fibrous illite which is lacking in the east. The distribution of carbonate and sulphate cements is more irregular. and is related to the distribution of marine limestone and evaporite beds. Porosity in the sandstones is secondary after dissolution of carbonate and sulphate cements and. to a lesser degree, dissolution of unstable grains. Porosities are generally low (less than 5%) in the west, but sandstones there may he comparable with those in tight gas reservoirs elsewhere. Sandstones in the east exhibit very high porosities in boreholes. Kaolinite is a late phase occupying pore space in the upper parts of most successions. deposited by downward‐migrating meteoric fluids. possibly during Permian times. Late iron oxides in some sandstones were similarly precipitated during deep weathering below the sub‐Permian unconformity Sandstones exhibit very patchy bitumen residues in the west. demonstrating that oil has migrated through these rocks.
FLUID MIGRATION ALONG GROWTH FAULTS IN COMPACTING SEDIMENTS
Authors: Hooper E. C. D.
Published: December 2007

The movement of fluids up growth faults is proposed to be periodic; when faults are active they can concentrate fluid flow, but when inactive, flow is restricted. Higher flow rates are predicted to be caused by fault‐zone permeabilities and fluid potentials increasing at shear stresses close to the shear strength of the rock. In this way, significant flow is confined to the most active sections of moving faults. Since fault activity is related to sediment accumulation rates, the volume of fluid flowing up faults should be greatest when accumulation rates are high.

Periodic flow explains the evidence which indicates that faults can be both barriers and avenues of fluid migration. Evidence for growth faults being avenues of fluid migration is shown by fault‐zone mineralization. lowered fluid potentials. thermal anomalies, salinity anomalies. and isotope studies. In contrast, fault‐zone porosity studies. measured flow rates, high juxtaposed fluid potential differences, differential subsidence caused by groundwater production, and hydrocarbon accumulations, all suggest that growth fault zones are of low permeability.

The flow of‐oil from large pore spaces into smaller, water‐filled pore spaces requires a large potential gradient. Therefore., faults which cut water‐wet sections with variable vertical permeability are usually poor conduits for oil. In contrast, in hydrocarbon‐saturated homogeneous rocks, such as mature shales. the vertical flow of migrating hydrocarbons may be concentrated by faults. The degree of concentration will depend on the permeability of the fault zone.
THE ORGANIC GEOCHEMISTRY OF HYDROCARBON GASES IN FLUORITES FROM NORTHERN ENGLAND
Authors: Ferguson J.
Published: December 2007

A study of the light hydrocarbon gases which occur in saline, fluid inclusions in fluorite, from the Alston Block area of the Northern Pennine Orefield (NPO). is reported. Reproducibility of the data is demonstrated by comparing the analysis of samples collected on two separate occasions. Although it has not proved possible to use the technique to differtntiate zones in individual crystals. it has been shown that there is a good correlation between the amount of gas and the nature of the mineral. Thus. massive fluorite contains roughly twice the total amount of gas as single crystals. The bolance of saturated to unsaturated gases is shown to be dependent on the temperature of emplacement of the mineral. A comparison of this data with data obtained earlier from minerals, from the Askrigg Block and Derbvshire Dome has confirmed these findings. The relationship between these saline. fluid inelusions. and those filled with oil from Derbyshire and ehewhere. has led to speculation on the nature nnd timing of the fluids responsible for mineralization.
THERMAL MATURITY AND HYDROCARBON GENERATION IN ROCKS FROM THE SEDIMENTARY BASINS OF MADAGASCAR
Authors: Ramanampisoa L. , Radke M.
Published: December 2007

Oil exploration in Madagascar has been concentrated on the Morondava Basin in the SW of the island, which is well‐known for its large deposits of tar sand and heavy oil at Bemolanga and Tsimiroro. Petroleum shows have frequently been encountered in exploration wells, but source‐rock identification has remained inconclusive. Thus, the present study of a wildcat was originally related mostly to geochemical prospect appraisal. Due to the inform oraganic matter type and wide range of thermal evolution stages sampled, the case history has more general implications, however, as regards relationships between thermal maturation and hydrocarbon generation.

Evaluation of eleven rock samples taken at depths of between 1,100 and 2,500m by Rock‐Eval, solvent extraction and vitrinite reflectance (Rr) methods revealed only poor source rocks for oil with marginal through to post‐mature Type III kerogens (Rr between 0.5% and 1.4%) Discrepancies in yield profiles of total C15+ ‐hydorcarbons peaking at higher Rr in the Morondava and Dauala Basin (Cameroon) wells than in a Deep Basin (West Canada) well are tentatively attributed to their different geothermal histories. However, yield trends of specific saturated and aromatic hydrocarbon families, as determined by capillary gas chromatography, did not testify to the suspected effect of geothermal rate variations on generation curves, which hence remain unproven.

Based on systematic changes with depth in the distribution of methylated di‐ and tri‐aromatics, the interpretration of maturation levels with respect to hydrocarbon generation was refined. When converted to vitrinite reflectance equivlents (Rc), molecular parameters such as the Trimithylnaphthalene Ration (TNR 1) and the Methylphenanthrene Index (MPI I) were able to disclose gradual marurity changes.

In contrast to the large Morondava Basin, the smaller Majunga Basin in NW Madagascare has been the site of little explortion activity until recently. Based on organic‐geochemical analysis of seven rock samples from two exploration wells by the above‐mentioned methods, it was found that good source rocks for oil are absent. Some of the samples may have a considerable gas generation potential, which at best has been partially reasised. Certainly, maturities inadequate for substantial gas generation are indicated by aromatic parameters.
POTENTIAL PETROLEUM SOURCE ROCKS IN TRIASSIC LACUSTRINE‐DELTA SEDIMENTS OF THE GUNNEDAH BASIN, EASTERN AUSTRALIA
Authors: Smyth M. , Jian Feng Xu , Ward C. R.
Published: December 2007

Integration of lithofacies, inferred depositional environments and organic petrology of a lacustrine delta sequence in the Permo‐Triassic Gunnedah Basin of eastern Australia has provided a logical explanation for the patterns of distribution of the dispersed organic matter. The data show that: (i) sedimentary processes, such as size sorting and transportation, control the association of maceral assemblages in the dispersed organic matter with depositional environments; (ii) the extent of oxidation of organic matter increases downstream, from floodplain lake to interdistributary bay, delta front, prodelta and off‐shore lake deposits; (iii) coarse, woody material, mostly oxidised to semifusinite, is concentrated in the deta‐front environment; (iv) leaf material is transported preferentially to the prodelta, via the delta front. On the basis of organic matter type, the prodelta was probably the most favourable environment in this depositional system for the accumulation of oil‐prone source beds.
RESERVOIRS IN FRACTURED BASEMENT ON THE CONTINENTAL SHELF OF SOUTHERN VIETNAM
Authors: Areshev E. G. , Dong Tran Le , San Ngo Thuong , Shnip O. A.
Published: December 2007

A number of oil‐ and gasfields have recently been discovered on the continental shelf of Southern Vietnam, the largest of which is White Tiger. The main pay‐zone in this field is in the basement, which is composed of granites and granodiorites, lithologies which are found in the basement elsewhere on the shelf. The granites have undergone severe alteration as a result of tectonic, hydrothermal and surface weathering processes.

Reservoirs are related to cavernous fracture porosity in deep basement zones, and to “porous cavernous” fracturing at more shallow levels. Total reservoir thickness exceeds 1 km, and the oil‐water contact has not yet been located. Flow‐rates reach 2,000 cu. m/d. Drilling data indicates that the granitoids are overlain by argillaceous‐terrigenous rocks of Oligocene and younger ages which have a thickness of 2.5‐4.4 km (up to 8 km in places, according to seismic data).

Source rocks are mostly early Oligocene argillites, from which oil probably migrated into upthrown basement blocks.
OILFIELD BRINES OF METEORIC AND CONNATE ORIGIN IN THE EASTERN NIGER DELTA
Authors: Amajor L. C. , Gbadebo A. M.
Published: December 2007

A study of oilfield brines in the Afam, Imo River, Bodo‐West and Umuechem oilfields in the Eastern Niger Delta petroleum sub‐province of Nigeria was undertaken in an attempt to determine their genetic affinities.

On the basis of their contents of bicarbonate, chloride and sulphate ions, and total dissolved solids, most of the formation waters from the Imo River oilfield are shown to be meteoric in origin, whereas those from Afam, Bodo‐West and Umuechem are connate waters. The relationship betwen salinity and total dissolved solids can be expressed by a simple linear equation.

Formation‐water resistivity and total dissolved solids from these oilfields are parabolically related. The amount of total dissolved solids is also depth‐controlled, and increases with depth. This relationship is thought to be a function of post‐depositional processes.
PALAEOZOIC TECTONIC HISTORY OF SE TURKEY
Authors: Cater J. M. L. , Tunbridge I. P.
Published: December 2007

A review of published data for the Palaeozoic of SE Turkey, together with facies distribution and palaeo‐fault maps derived from regional field data, are used to interpret the Palaeozoic tectonic history of the region.

Intracratonic rifting events in the Early Cambrian and the Early Ordovician led to syn‐rift deposition within fault‐bounded basins. Marine transgressions across the region in the mid‐Cambrian and mid‐to‐Late Ordovician were probably influenced by regional thermal subsidence after each rifting event, in addition to (glacio‐)eustatic mechanisms. Marine transgressions in the Early Silurian and Early Carboniferous are thought to have been entirely eustatic in origin.

Poorly‐constrained, Late Palaeozoic facies variations across the region can be related to uplift during the Caledonian and Hercynian orogenic episodes. Widespread tilting and erosion before the Cretaceous, which has removed much of the Late Palaeozoic record from this region, resulted from uplift at the edges of a major rift system which was initiated during the Triassic‐to‐Jurassic opening of the Southern Neotethys.
ORGANIC GEOCHEMISTRY AND HYDROCARBON POTENTIAL OF NEOGENE SEDIMENTARY ROCKS IN HUNGARY
Authors: Hetenyi M.
Published: December 2007

Neogene sedimentany, strata in Hungary contain important mineral resourcs: pelitic rocks, deposited during the last major deltaic depositional cycle in the Pannonian Basin. are considered to be the principal sources of petroleum.

The organic‐geochemical investigations presented in this paper show that these Neogene sediments not onlv constitute a good gas‐prone source. but are also a fair oil‐prone source. About 75% of disseminated rganic matter in these deltaic sediments was found to be gas‐prone kerogen (Type III), and more than 13% of the examined samples were oil‐prone, containing Type II kerogen. More than 10% of the sedinirnts contained mixtures of II and III kerogens.

At the end of the Neogene highly oil‐prone, organic‐rich sediments (alginites) were deposited in small volcanic tuff rings which, formed during the, final episode of basaltic volcanism (3–5 ± 0.9 million yrs ago) in the Pannonian Basin. This depositional environment, together with the richness of the biological precursor materical, and the good preservation of algae, resulted in the formation of Types I and II kerogens. which have an excellent liquid hydrocarbon potential.

The qunlity and quantity of organic matter deposited in the two main stages of the deltaic system are different. Thus, sediments deposited during the deep‐water stage were, found to be fair oil source rocks. As a consequence of the frequent lignite horizons. which illustrate the increasing importance of terrestrial conditions, the shallow‐water sequences constitute a gas‐prone source rock. with a high organic carbon content.
LOWER CRETACEOUS PALYNOLOGY AND SANDSTONE DISTRIBUTION IN THE SCAPA FIELD, U.K. NORTH SEA
Authors: Riley L. A. , Harker S. D. , Green S. C. H.
Published: December 2007

Three discrete turbidite sandstone bodies form the Scapa Sandstone Member reservoir units within the limestone, marl and conglomerate sequence of the Early Cretaceous Valhall Formation in the Scapa field (UK North Sea Block 14/19). Eighteen palynological zones have been established for the Valhall Formation, designated as VA in the early Aptian through VR in the latest Ryazanian. Scapa reservoir sandstones are restricted to the late Hauterivian VF to early Valanginian VQ zones. Black, anoxic mudstones of the Fischschiefer Member form a widespread intra‐ early Aptian correlation marker at the base of zone VA in the upper Valhall Formation.

The zonal scheme is based principally on dinocyst distribution, relative abundance and palynomorph associations. Additional micropalaeontological evidence from the top of the Valhall Formation to the top of the Scapa Sandstone Member (zones VA through VF) provides furthrr refinement.

Vertical and lateral variations in the age and abundance of reworked palynomorphs reflect a multisource origin for the Scapa Sandstone Member and deposition via several individually distinct, but coalescing, fan systems. An understanding of sandstone distribution within the Valhall Formation has been determined by the integration of the palynological zonation with wireline log correlation. lithofacies studies and reservoir pressure data.
GEOCHEMICAL PROSPECTING FOR OIL‐AND GASFIELDS IN THE NE USSR (CIS)†
Authors: Glotov V. E.
Published: December 2007

The NE USSR is an area of great interest for oil and gas exploration. Geochemical prospecting methods are particularly useful in areas of permafrost, and the efficiency of these methods has been established by tests in the Anadyr and Khatyrka Basins.

This paper presents data on the spatial and temporal changes in the content of methane and its gaseous homologues in seasonally‐thawed soil layers, near‐surface air and lichens. Annual freezing and thawing of the near‐surface layers has been shown to result in various geochemical processes which were previously unknown. When near‐surface layers are frozen in Winter, gases migrating upwards from the Earth's interior accumulate within them. During warmer weather in Spring, the accumulated gases diffuse into the atmosphere, and the hydrocarbons content of the near‐surface air is then tens or hundreds of times higher than at the end of Summer.

Evidence has been obtained of regular alterations in methane contents. The intensity of solar radiation has been proved to influence the diurnal methane content of the atmosphere. Lichens are accepted to be accurate indices of hydrocarbon pollution at the Earth's surface.

The distribution of hydrocarbon‐oxidising bacteria in tundra is described, and methods of geochemical prospecting are evaluated.
COMMENTS ON “GRAVITY OVERTURNS, EXTENSION, AND BASEMENT FAULT ACTIVATION”
Authors: Hospers J.
Published: December 2007

Koyi (1991) has described physical modelling experiments on the initiation of salt diapirism. He also compares his results with the results of an investigation of salt tectonics in the northern part of the Norwegian‐Danish Basin by Hospers et al. (1988).

Koyi's comments on this investigation are not altogether favourable. Below, I intend to show that Koyi's criticisms are not valid, as they stem from a combination of: (1) built‐in features present in his models which limit their applicability; and (2) an incomplete understanding of the structural setting in which salt diapirism was initiated in the northern part of the Norwegian‐Danish Basin.
THE TEACHING OF PETROLEUM GEOLOGY IN KUWAIT
Authors: Al‐Rifaiy Ibrahim
Published: December 2007

SINCE its establishment in 1966, the Department of Geology in Kuwait University has played a major role in providing the oil industry in Kuwait with qualified geologists. The Department offers a B. Sc (Hons.) Geology course of four year's duration, which currently attracts about 160 students. The geological content of the course increases year‐by‐year. The first two years provide a general geological background, while the last two include more advanced courses. A wide range of subjects is available, including micropaleontology, stratigraphy, structural geology, geophysics, geochemistry, sedimentology, petroleum geology, igneous and metamorphic studies, and the regional geology of the Arabian Peninsula. Optional courses include plate‐tectonics, physical geology, environmental geology, marine geology, and engineering geology.
THE RED SEA—GULF OF ADEN: HYDROCARBON EVALUATION OF MULTINATIONAL SEDIMENTARY BASINS:The methodology of regional cooperation
Authors: O'Connor T.E.
Published: December 2007

Successful hydrocarbon exploration in frontier basins of the developing world is mutually beneficial to the oil industry, and for the economic development of the country concerned. Exploration has proved to be difficult when the basin is overlain by two or more countries. A market survey of the petroleum industry indicated that, to be successful, promotional efforts should include the entire frontier basin rather than one part of it. The Red Sea/Gulf of Aden Basin was chosen by the World Bank as a prototype of regional basin promotion for reasons both of geology and economic development.

Following detailed discussions with the seven governments involved, and the industry likely to be interested, a detailed work plan was produced. Funding came from several donor agencies. Specialized analytical investigations were undertaken with respect to source‐rock geochemistry, palaeontology, sedimentology and heat‐flow studies.

Pivotal to implementation was the provision of data from the governments. The presence of the World Bank as an intermediary between governments and industry provided the required clarity and transparency for the process, free of normal confidentiality issues. The participating governments have expressed a strong desire to preserve the results through the conversion of the project work‐station in Cairo into a regional research centre.
PULL‐APART EVOLUTION OF THE RED SEA
Authors: Makris J. , Henke C. H.
Published: December 2007

The Authors have deduced from seismic, gravity and other geophysical data that strike‐slip processes mainly controlled the early break‐up stages of the Arabian Plate from Africa, initiating the Red Sea Rift. Sea‐floor spreading is only 5 million yrs old, and is still limited in the central and parts of the southern Red Sea. The area was a zone of structural weakness as early as 600 million yrs ago, and was reactivated in the late Oligocene with intense magmatic activity and the development of a continental rift.

Wrench‐faulting shaped most of its western flank as a sharp plate boundary, while the eastern flank is floored by stretched continental crust due to uplifting and shifting of Arabia from Africa. Wrench‐faulting was controlled by pre‐existing fault systems, such as the Najd Shear System, the Central African Fault Zone, or the Onib‐Hamisana and Baraka sutures. As a consequence, both wrench‐faulted transtensional and transpressional areas developed. Transtensional basins are evident offshore Egypt, the Sudan and the Gulf of Aqaba; while the island of Zabargad is a remnant transpressional area.

With Arabia as the “mobile” plate and Africa relatively “stable”, the eastern Red Sea flank was formed through stretching, thinning and diffuse extension, and is floored by attenuated continental crust, thus producing the asymmetry observed in seismic sections between the eastern and western flanks of the Red Sea Rift. The Dead Sea strike‐slip fault only experienced intense deformation during the last 14 million yrs. Plate motion was oblique to the initial orientation of the basin, and could no longer be accommodated by the opening of the Gulf of Suez; the en échelon distribution of gravity and magnetic anomalies as well as the high heat‐flow fields recorded in the northern Red Sea are Gulf of Aqaba oriented due to this process. Similarly, the thinned continental crust between Yemen and Ethiopia is affected by shear‐faults that displace the volcanic centres to the east.

The bathymetry reflects the tectonic processes described above, and the mineralisation in the metalliferous “deeps” is tied either to Recent sea‐floor spreading centres or to the en‐échelon distributed fractures along the Red Sea flanks. Sedimentary basins, aligned along the stretched continental, flanks of the Red Sea, are important for oil and gas exploration.
THE DNIEPER‐DONETS PALEORIFT, UKRAINE: DEEP STRUCTURES AND HYDROCARBON ACCUMULATIONS
Authors: Chekunov A. V. , Kaluzhnaya L. T. , Ryabchun L. I.
Published: December 2007

Numerous deep seismic and borehole studies have been made in the Dnieper‐Donets Paleorift (Ukraine), and, when combined with studies of oil‐ and gasfield distribution, indicate that there exists an interesting relationship between deep lithospheric structure and evolution, and the hydrocarbon potential of the Paleorift.

It has been found that hydrocarbon accumulations tend to be associated with slopes in the Moho discontinuity, where most faults are located, and also where the basement and the lower layers of sedimentary cover have been fragmented by faults. These areas are the most promising for exploration.

These facts could imply an abiogenic, mantle origin for oil and gas. Alternatively, the hot mantle ascending beneath the Dnieper‐Donets Paleorift may have created thermodynamic or fluid‐flow conditions within the sedimentary cover which were favourable for the transformation of biogenic material into oil and gas. In this case, mantle fluid‐flow along faults assisted the migration of hydrocarbons and its accumulation in traps.
DEPOSITIONAL HISTORY OF THE E2.0 RESERVOIR IN THE KOLO CREEK FIELD, NIGER DELTA
Authors: Oboh F. E.
Published: December 2007

The paleoenvironments of the middle Miocene E2.0 Reservoir in the Kolo Creek field have been reconstructed in cores of Wells 27 and 29 from investigations of sedimentological and microfossil data. The sediments were examined for lithological features, trace fossils, mineralogical composition, diagenetic imprints, palynodéhris, palynomorphs and foraminifera, and these results were integrated with geophysical log data. Seven deltaic sub‐environments of deposition have been recognized: the distributary channel‐fill, lagoon/tidal flat, coastal barrier and delta fringe sub‐environments were common to both cores, while the prodelta was present in the core of Well 27, and lagoonal and flood‐tidal deltas occurred in Well 29. The sequence‐stratigraphic concept has been applied to these sub‐environments, and using the information from Wells 27 and 29, well‐to‐well log correlation across the entire field allowed a reconstruction of the depositional history of the reservoir. The reservoir was deposited as one or two progradational parasequences during a high‐frequency highstand systems tract. There was more open vegetation and extensive development of lagoons/tidal flats in the western part of the field, but the overall depositional trend is similar to that of the present‐day Niger Delta.
MINERALOGICAL STUDIES ON SUBSURFACE JURASSIC AND LOWER CRETACEOUS SANDSTONES FROM THE WESTERN DESERT, EGYPT
Authors: Barakat M. A. K. , Hamed H. A. , Kholief M. M.
Published: December 2007

This paper describes the use of heavy minerals and the characteristics of quartz grains in the study of three exploratory wells (149 core samples) in the northern Western Desert, Egypt.

The studied sandstones are characterized by a predominance of tourmaline, zircon, rutile, anatase. epidote, garnet, monazite. staurolite and chlorite, in decreasing order of abundance. In general, there is no distinctive heavy‐mineral variation between Jurassic and Lower Cretaceous sands.

Examination of the frequency distribution of the different types of inclusions in the quartz revealed that abundant rutile needles reflect a metamorphic terrane and a plutonic environment. Abundant tourmaline, microlites and devitrified magmatic relicts reflect acidic intrusive/extrusive parent rocks. The abundance of rutile with apatite and zircon is interpreted as being derived from host quartz of various parent rocks. The alteration in some inclusions (segmented rutile needles, spotted apatite and dark zircon) suggests possible dynamic disturbance of the area, resulting in the introduction of inclusions and devitrified and/or altered primary solid inclusions.

It is concluded that the Jurassic and Lower Cretaceous sandstones studied were formed in areas characterized by an arid climate. These conditions led to the decomposition of both unstable and metastable heavy minerals.
PETROLEUM POTENTIAL OF CRETACEOUS SHALES IN THE UPPER BENUE TROUGH, NIGERIA
Authors: Idowu J. O. , Ekweozor C. M.
Published: December 2007

A geochemical study of the argillaceous sequences of Turonian—early Santonian age penetrated by ten shallow boreholes in the Upper Benue Trough was carried out.

The average total organic carbon contents of the sampled sections of the Bima, Yolde, Pindiga, Sukuliye and Jessu Formations were 0.30, 1.40, 0.85, 0.60, and 0.54%, respectively. Apart from the Bima Formation, all exceed the minimum value (0.5% TOC) normally required for a petroleum source rock. In spite of the moderate TOC, however, the content of soluble organic matter (SOM) and saturated hydrocarbons (SHC) was generally low.

In terms of organic‐matter type, a predominantly marine fades with some terrigenous input is inferred for the Sukuliye and Pindiga Formations. This indicates that open‐marine conditions might not have been established during the Turonian marine transgression, which deposited these units.

Within the updip sector of the basin, the organic matter is thermally immature. The most promising zones seem to be located south of the study area, where source rocks that have attained optimum levels of maturity for hydrocarbons occur.
THE EFFECT OF BASEMENT FAULTING ON DIAPIRISM
Authors: Koyi H. , Jenyon M. K. , Petersen K.
Published: December 2007

Experimental and natural examples illustrate the influence of sub‐salt horizon basement faults on diapirism. In a series of experimental models, viscous diapirs were observed to form above or close to basement faults. In all the models, basement faults initiated a half‐graben, where thicker overburden units enhanced differential loading on an underlying buoyant layer. The buoyant material flowed updip to the low‐pressure zones in the uplifted block, and updip along the tilted upper boundary of the hanging‐wall. Basement faulting extended the overburden, and provided the space through which the buoyant layer could rise. Subsidence and faulting of overburden layers allowed diapirism along the faulted zones. In all cases, the deformation in the overburden was accommodated within a wider zone of faulting than the discrete basement fault which initiated the deformation. Differential compaction enhances differential loading and accumulation of thicker overburden on the downthrown sides of basement faults.

Seismic profiles from the Danish Basin, Dutch Central Graben, Gulf of Mexico and North Sea show that diapirs are spatially associated with basement faults. However, model results show that diapirs triggered by basement faults are not necessarily located directly above the faults.

Basement faults extend the cover sequences. If detached from the cover by a ductile layer, thick‐skinned extension is accompanied by thin‐skinned extension and decoupling of the cover. The influence of basement faults on diapirs depends on: the thickness and effective viscosity of the ductile layer (e.g. rock salt); the thickness ratio between the buoyant layer and the overburden; the mechanical properties of the brittle cover in the case of clastic sediments; the rate of sedimentation; the displacement rate throw and the dip of the basement faults.
GEOLOGY AND HYDROCARBON POTENTIAL OF THE NEUQUEN BASIN
Authors: Hogg S. L.
Published: December 2007

The Neuquén Basin in western Argentina offers a variety of attractive hydrocarbon plays in both the Jurassic and Cretaceous sequences. Exploration to date has proved hydrocarbon reserves of 800 million cu.m oil‐equivalent 60% of which are gas. These reserves have been found mainly in relatively small structures along the stable platform area, where good reservoir‐quality sandstones and carbonates are present. In the western thrust‐belt, large structures remain untested; however, reservoir quality in this area is a problem. The exploration dilemma is therefore. whether to search for “elephants”, with a high risk of finding adequate reservoirs, or be satisfied with the less risky but smaller rewards associated with foreland traps.
BASIN EVOLUTION AND PROSPECTIVITY OF THE ARGENTINE CONTINENTAL MARGIN
Authors: Keeley M. L. , Light M. P. R.
Published: December 2007

Nine Mesozoic‐Tertiary basins of different orientations lie along the Argentine continental margin, over a distance exceeding 2,000 km: these are the Salado, Colorado, Valdes, Rawson, San Jorge offshore, North Malvinas (San Julian), West Malvinas and Magallanes (Austral) Basins on the Continental Shelf, together with the Continental Slope. These basins formed following the latest Jurassic — Early Cretaceous extension that accompanied the onset of South Atlantic rifting. Strain was modified by earlier basement fabrics, with consequent transtension. The Cape Fold Belt (Permo‐Triassic) provided a NW‐SE grain to pre‐Mesozoic cover off NE Argentina. In the central‐southern sector, several phases of oblique NEwards Pacific subduction and terrane accretion during the Permo‐Triassic formed back‐arc basins and volcanic belts, producing a more variable fabric orientated close to NNW‐SSE. Atlantic basin fill, of Lower Cretaceous‐Tertiary clastics, was deposited as a result of rift‐shoulder erosion and Atlantic flooding, following eastward tilting. Basin fill thickness is typically 2–4 km, but locally exceeds 6km. The hydrocarbon potential of these basins hinges as much upon the preservation of source rocks within the pre‐rift succession as it does on that of those within the base‐rift succession, and subsequent Atlantic anoxic events.
THE TECTONO‐STRATIGRAPHIC DEVELOPMENT OF PATAGONIA, AND ITS RELEVANCE TO HYDROCARBON EXPLORATION
Authors: Light M.P.R. , Keeley M.L. , Maslanyj M.R , Urien C. M.
Published: December 2007

The history of terrane accretion along the Pacific margin, that formed the Palaeozoic basement to Patagonia, is discussed. This pre‐existing NW‐trending basement fabric was periodically reactivated by shear stress, resulting from near‐continuous oblique Pacific subduction processes, producing pull‐apart and extensional grabens. During the Permo‐Triassic, an asymmetric passive rift developed east of an eastwardly‐dipping simple shear, following the axis of the proto‐South Atlantic, and was invaded by a shallow sea. The Falkland (Malvinas) Microplate is shown to have docked with Patagonia in the Early/Mid Jurassic. Clockwise symmetrical rotation and crustal deformation of the Falklands (Malvinas) and other microplates between east‐west trending, dextral strike‐slip faults controlled the development of the southern transverse Atlantic margin basins. Early restricted deposition in these basins (Early Jurassic‐Neocomian) led to the deposition of proved continental source‐reservoir associations. Rifting and transverse dextral strike‐slip shearing propagated northwards, up the axis of the Atlantic. As terrane collision progressed, the rift zone widened SWwards to the Pacific and NEwards to the Colorado Basin. Atlantic sea‐floor spreading in the Neocomian, and subsequent thermal sag of the Atlantic margin, is shown to have culminated in a major transgression in the Maastrichtian, which formed a regional seal for hydrocarbons.
FAULT‐CONTROLLED HYDROCARBON DISTRIBUTION IN THE JUNGGAR BASIN, NW CHINA
Authors: Yugui Yian
Published: December 2007

The Junggar Basin is an important oil‐ and gas‐bearing basin, with thick source rocks, of Carboniferous. Permian. Triassic and Jurassic ages. Hydrocarbon accumulations are controlled by major faults which trend NNW. NW and NE; NE‐striking reverse faults constitute the Kelemay thrust‐zone in the NW basin margin; those trending NW are of lesser importance; and those trending NNW on the southern basin margin control the formation of en echelon anticlines (Kuang, 1989), which are important sites of hydrocarbon accumulations.
KARSTIC RESERVOIRS OF THE MID‐CRETACEOUS MARDIN GROUP, SE TURKEY: Tectonic and Eustatic Controls on their Genesis, Distribution and Preservation
Authors: Cater J.M.L. , Gillcrist J.R.
Published: December 2007

The mid‐Cretaceous Mardin Group is the main producing reservoir interval in the oilfields of SE Turkey. During the mid‐Cretaceous, deposition of lime mudstones and bioclastic limestones took place on a carbonate platform. Repeated tectonic uplift occurred locally throughout this time, during the early stages of the closure of the southern Neotethys. The interplay of eustatic transgressions and regressions with local tectonic uplift controlled deposition and diagenesis, the latter including major secondary porosity development during dolomitization and karstification. Minor shortening and uplift in the Late Cretaceous and Palaeogene created structural traps and may also have enhanced fracture porosity. Major thin‐skinned thrust tectonics breached many reservoirs in the late Miocene. Surface anticlines which formed during the Miocene have attracted most of the exploration drilling to date, but may be the sites of the most intense breaching of the reservoirs. The distribution of the best potential reservoirs is not necessarily linked to the positions of Miocene anticlines.