bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.
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 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.
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.
FORMATION OF NON‐COMPRESSIONAL SEDIMENTARY BASINS ON CONTINENTAL CRUST: LIMITATIONS ON MODERN MODELS
Authors: Lyatsky H. V. 
Published: December 2007

The evolution of non‐compressional sedimentary basins can be modelled in many ways. A number of existing schemes rely on assuming mathematical relationships between such geodynamical parameters as subsidence and heating of a basin and the amount of presumably causative tectonic extension. The usual objective is to determine precisely the geological history of a sedimentary basin, and to predict the unknown parameters.Models inevitably simplify complex natural systems. Many models of basin formation rely on specific assumptions about the dynamics of the crust (pure‐shear or simple‐shear deformation, the Moho as a passive marker, uniform extension, absence of older weakness zones, certain metamorphic reactions at depth, etc.) and about the structure and geological history of the basin (purely conductive heat transfer, existence of an underlying rift, etc.). Such assumptions cannot always be tested in poorly‐studied regions, and in some cases they contradict the available geological information. For simplification to be valid, the, geological system has to be understood in some detail before model parameters are chosen. Misleading results may be obtained if an inappropriate model is applied, or if its parameters are ill‐constrained.Many different geodynamical processes may contribute to basin evolution. In the North Sea region, for example, both mantle‐plume activity and mobility of lower‐crustal material are proposed to have occurred in Mesozoic and Cenozoic times. The Jurassic plume may have been influenced in part by ancient lithospheric structure.The preferred method in basin analysis is the multidisciplinary approach based on a broad range of data, of which quantitative modelling may or may not be a part. In the integrated basin analysis, geological information is used to constrain the interpretation of gravity, magnetic and seismic data, thus revealing the structure of the basin and helping infer its geological history. Combined with geochemical data, these results are a useful guide for hydrocarbons exploration.