bluuebunny/crossref_metadata_2025_split huggingface dataset:
THE PANGAEAN PARADOX: WHERE IS IT?
Authors: Crawford A. R. 
Published: December 2007

The postulation of a Precambrian (about 1,300 Ma) expansion of the Earth by Embleton et al. (1981) and Schmidt and Embleton (1981) to explain paradoxical results from palaeomagnetism, by creating a Pangaea asymmetrically disposed on the Earth, produces more problems than it solves. It is preferable to infer that the present pattern of continent and ocean, which appears to be normal (and is probably non‐random) derives from a Pangaea which covered the Earth completely or almost completely in the Precambrian and dispersed during the Mesozoic‐Cenozoic at a critical stage of persistent, exponentially‐increasing and perhaps mildly‐pulsatory expansion. In this orderly dispersal, the geometrical relations between the continents were maintained. Data from palaeomagnetism for the period 1,000–200 Ma, although amenable to a consistent orthodox interpretation, may nevertheless be illusory and indicative not of any different continental pattern (in terms of geocentric angles) but of some inner disturbance perhaps related to (or at least concurrent with) large‐scale obliquity changes. An earlier critical stage, represented by the ‘Pan‐African event’ over the period 750‐450 Ma, was the time of the first development of future continental outlines.This exponentially‐increasing expansion permitted retention of continental meridionality from the Precambrian, except for Asia, and preservation in their original orientations of imprints of a global fracture pattern on the continents.Major Mesozoic‐Cenozoic expansion avoids the need for a ‘Tethys Ocean’ (as distinct from an epicontinental Tethys Sea). Precambrian expansion would create such an ocean as an extension of a great and equally artefactual ‘Panthalassa’.
LOWER CRETACEOUS LITHOSTRATIGRAPHY NE OF THE SOLE PIT AREA IN THE UK SOUTHERN NORTH SEA
Authors: Crittenden S. 
Published: December 2007

Seven boreholes from block 49, UK sector have been divided lithostratigraphically to illustrate the degree of comparison between the Dutch and British lithostratigraphical schemes for the Lower Cretaceous of the southern North Sea.The two schemes differ in scope and finesse, with the Dutch scheme offering more subdivisions. Both are applicable to boreholes in the British as well as the Dutch sectors of the southern North Sea. Borehole 49/25‐1 (Shell/Esso) is designated as the reference borehole in the British sector to illustrate the Dutch scheme.The Upper Holland Marl Member is considered to be equivalent to the Red Chalk formation while the Speeton Formation is divided into the equivalent of the Middle Holland Shale Member, Lower Holland Marl Member and the Vlieland Shale Member of the Dutch sector scheme.
RELATIONSHIP BETWEEN AGES OF SHIELDS, DIPS OF ADJACENT SEDIMENTARY BASEMENTS, AND OCCURRENCE OF OIL AND GAS
Authors: Rogers John J. W. 
Published: December 2007

Crystalline shields can become stable at different times. This stability is commonly marked by the end of magmatism and compressive deformation and the beginning of deposition of platformal sedimentary sequences. The margins of the shields are then the basements for undeformed sediments that dip away from the exposed crystalline rocks.Dips of basements on shield margins directly underlying Phanerozoic sediments have been determined in seven areas in which the margin has not been altered by rifting or other tectonic activity. The adjacent shields have stabilization ages ranging from more than 3,000 m.y. to 600 m.y. The basement dips (tilts) increase progressively from about 3 m/km for older shields to 16 m/km adjacent to the youngest shield (the Nubian‐Arabian shield). These tilts can only approximately be recalculated into uplift rates of the shields or subsidence rates of their margins. The dips are, however, consistent with Phanerozoic uplift rates of Archean cratons of less than 5 m/m.y., or comparable subsidence rates of the margins; such low uplift rates could be caused almost wholly by erosion and isostatic adjustment. Younger shields have undergone some other, as yet unidentified, process that causes more rapid uplift.The higher dips of basements around younger shields apparently promote the development of thick sections of mildly‐deformed Phanerozoic sediments. Sequences of this type are commonly favorable for accumulation of commercial concentrations of oil and gas. A correlation has been found between age of shield, basement dip, and hydrocarbon occurrence around the western edge of the Canadian shield and the northern edge of Africa. The data show that oil and gas are more abundant in Phanerozoic sediments adjacent to younger shields, which supports the common observation that the world's largest hydrocarbon accumulation (the Arabian Gulf) is adjacent to the world's youngest shield (the Nubian‐Arabian shield).This criterion for hydrocarbon accumulation may be of some value in exploration of little‐known areas. For example, basements of different ages occur adjacent to the overthrust belt of the northern Rockies, and the generally‐young age of Precambrian basement in the eastern US may indicate considerable thickness of sediment under crystalline thrusts in the Appalachians. Different ages of shields in different parts of China may also have broadly affected sedimentary patterns in that country.
AN APPROACH TO “HALOKINEMATICS” AND INTERPLATE TECTONICS (NORTH‐CENTRAL ALGERIA)
Authors: Assaad Fakhry A. 
Published: December 2007

Plate tectonics continues to dominate geological thinking; the main object of this paper is to explain salt movements due to halokinesis in terms of plate kinematics. A term “halokinematics” is proposed by the author to define disturbances ofsaltflo w caused by continuous indirect geologic events which might be a consequence of plate kinematics. Salt rocks constitute the caprock ofdetrital Upper Triassic reservoirs in the NCzone of Algeria whereas eruptive rocks, mainly basalts andspilites, constitute the cap‐rock of the lowermost series to the SE. The absence of Cretaceous formations to the SW of the Pre‐Atlas zone may be mainly attributed to the presence of salt domes.The study of paleotectonic events on the Epihercynian and African platforms, the wide distribution of spilites in the lowermost series of Triassic detritals and the discovery of flysch facies in the Tellian Atlas may support the existence of two interplates, the Saharan and Atlassic plates. However, detailed geological and geophysical studies would be necessary to confirm this theory.
PERMIAN AND TRIASSIC GEOLOGICAL HISTORY AND TECTONICS OF THE MIDDLE EAST
Authors: Sharief Farooq A. 
Published: December 2007

The paleogeography postulated from the distribution of Permian and Triassic sedimentary rocks in the Middle East is shown and related to the paleostructure of the region. The Middle East region as defined here includes the Arabian Peninsula, Iran, Iraq, SE Turkey, Syria, Lebanon, Jordan, West Jordan, and the Sinai Peninsula. Within the limits of the area included in this study, a relatively stable pre‐Late Triassic tectonic regime can be recognized and distinguished from a succession of diastrophic events of the Late Triassic epoch, which caused marked changes in the types and distribution of facies.Excluding NE Iran, the Middle East was stable from Late Cambrian to Middle Triassic times, as it formed a part of the Arabian Massif and much of the Middle East Platform, which is a broad shelf bordering the positive Afro‐Arabian Massif to the NE and east. The sediments of this plarform have undergone no strong deformation and have been subjected only to epeirogenic movements which interrupted sedimentation locally or regionally. However, from Upper Permian through Middle Triassic times, the predominant facies on this shelf was carbonates which unconformably overlie the non‐marine or extremely shallow marine elastics of the Lower Permian or older strata in most of the region.Upper Triassic strata in the area are markedly different in facies from older beds because of the movement of blocks in Turkey and northern and eastern Iraq and Iran related to the enlargement and broadening of the Tethys. Asa result, much of northern and eastern Iran were separated from the area to the south and west, which continued to be a shelf flanking the Afro‐Arabian Massif. Consequently, three major structural elements existed in the region: the Arabian Shelf, the Tethyan rift zone and the Paleo‐Tethyan trough.
EARTH OUTGASSING AND CARBONATE FACIES DEVELOPMENT vis‐à‐vis MESOZOIC CARBONATES OF HIMALAYA
Authors: Bhat M. I. 
Published: December 2007

Carbonate deposition through the Earth's history shows two distinct changes in terms of volume and chemistry. Whereas carbonates comprise a very small percentage of the total sedimentary rocks in the Proterozoic, they constitute 20–25% at the present time. From the Archaean to Early Palaeozoic, carbonates are dominantly dolomites, whereas afterwards they are dominantly limestone. 87Sr/86Sr, δ180 and δ13C trends show an increase with decreasing age.All these features of carbonate rocks are explicable as being related to the increased episodic outgassing of CO2 and CH4 from the upper mantle throughout the Earth's history.The Mesozoic carbonates of Himalaya are correlatable with the CO2 outgassing associated with rifting and magmatism during the birth of the Tethys ocean.
PHYSICAL CONSTRAINTS OF FAULTING IN A GOPRESSURED SEDIMENTARY BASIN*
Authors: Magara Kinji 
Published: December 2007

On the basis of the triaxial stress concept, the tectonic stress required for faulting and sliding in a sedimentary basin can be estimated. The horizontal tectonicstress necessary for thrust faulting, for example, increases with depth from the surface to about 9,000 ft (2.7 km), and decreases below 9,000 ft (2.7 km), primarily because of a changing Poisson's ratio. Changing the vertical effective stress caused by generation of abnormal fluid pressure would also change the tectonic stress requirements for faulting.The internal friction of sedimentary rocks in the subsurface must be exceeded by the tectonic stress applied to the basin for faulting or sliding to take place. Estimates of the internal friction suggest that there is a high probability of faulting at depth if there are thick undercompacted and geopressured sections. Diapirs may also occur in such a physical environment. If the sedimentary rocks are normally compacted and the fluid pressure is hydrostatic from the surface to depth, on the other hand, the rocks are generally too rigid to cause any significant sliding. There would be very little chance of faulting and diapirism in such a case.The concepts developed in this paper may have a practical application in the under‐standing of the physical conditions and constraints of faulting and diapirism in a relatively‐young sedimentary basin with significant geopressuring at depth.
INTERIOR CAVITIES AND EXTERIOR SURFACE TEXTURE OF DETRITAL QUARTZ OF SOME EGYPTIAN CLASTIC SEDIMENTS
Authors: Kholief M. Mahmoud 
Published: December 2007

Cavities of freshly fractured surface and the exterior surface texture of detrital quartz grains were examined and photographed with the help of the scanning‐electron microscope at different magnifications. Three formations of Egyptian clastic sediments are used for this purpose namely: (a) Carboniferous sandstone of west‐central Sinai, (b) the so‐called Nubian sandstone of Early Cretaceous(?) age from southern Egypt, and (c) Oligocene sand accumulations from the vicinity of Cairo.It is concluded from the present study that in most cases the intracrystalline cavities have an average diameter of less than 10 microns. Different shapes can be acquired by these cavities‐ranging between irregular and negative crystal forms. The distribution of ca vities seems to be mainly along the fractures and the planes of growth but random distribution is sometimes observed.Examination of the surface features also shows that the depositional environment for Sinai and Aswan sandstones is aeolian with more effective diagenetic alteration in the first type of deposit. In the case of Cairo sandstone, the surface impressions of the quartz confirm the alluvial environment of deposition.
RESERVOIR GEOLOGY AND ITS ROLE IN THE DEVELOPMENT OF THE L‐III RESERVOUR, BOMBAY HIGH FIELD, INDIA†
Authors: Bhandari L. L. , Jain S. K. 
Published: December 2007

A brief account of the geology of the Bombay High oilfield on the Western Shelf of India is presented. The L‐III reservoir, its development and exploration utilising a 3‐D, 3‐phase black oil mathematical model is discussed in detail.The Bombay High, a giant offshore located 160km WNW from Bombay city on the Western continental shelf of India, was discovered in 1974. It was put in production in two tears and production has been raised gradually to 240,000 b/d. There commercially exploitable hydrocarbon‐bearing zones–L‐II(limestone), S‐I (sand) and L‐III (limestone) of Miocene age have been identified. At present, the emphasis is on xploration of the L‐III reservoir which contains over 80% of the total reserves of the field. It is composed mainly of wackestone, mudstone and monor packstone. Cyclic sedimentation is identified. Each cycle is represented by four facies: in ascending order they are–lagoonal, algal mound, foraminiferal mound and coastal marsh. The porosity is mainly intergranular, intragranular, moldic, vuggy and microfissures. The solution cavities interconnected by micro‐fissures provide excellent permeability.It is a saturated reservoir with a large gas cap and extensive aquifer, which has left a narrow strip for locating production wells to give water‐or gas‐free oil production. For optimum location of production wells, a 3‐D, 3‐phase black‐oil mathematical and radial coning model was adopted. This assumes intervening shales to be non‐barrier between sub‐layers, and intervening shales within the resrvoir to be partly in communication, giving due consideration to spatial variaton in porosity and thickness of layers. This has paid dividends and reservoir performance is in conformity with prediction.
CARBONIFEROUS OIL AND GAS PRODUCTION IN THE EASTERN HEMISPHERE ‐ 1
Authors: Meyerhoff A. A. 
Published: December 2007

Almost all production from Carboniferous formations in the Eastern Hemisphere comes from the Soviet Union, with less importantproduction from the United Kingdom, the Southern North Sea basin, the N W German basin (from the northern Netherlands to Poland), Algeria, Ghana, the Gulf of Suez, China and Australia. However, Carboniferous coals extending from the eastern part of Great Britain to Poland were the source of the hugegas reserves that are found in Permian and Triassic reservoirs in the Southern North Sea‐N W German basin complex. Production of oil during 1978 was approximately 2,680,000 b/dt and of gas, about 20.8 Bcfldf. The USSR share was about 2.6 MM brl and 5.2 Bcf per day. Carboniferous production, which peaked in 1975, has since declined steadily.Most of the USSR's Carboniferous production is from marine carbonates andfrom marine to deltaic sandstones in the Volga‐ Urals, Timan‐Pechora and Dnepr‐Donets basins. The latter basin is mainly gas productive. Smaller amounts of hydrocarbons arepresent in marine beds of the North Caspian (Pricaspian) basin of the European USSR and in similar strata of the Chu‐Sarysu basin of Kazakhstan. Some small, but significant, discoveries have been made in carbonates of the southern part of the West Siberian basin. Although the deep Khuff gas of the Middle East is probably mainly of Permian origin, some Late Carboniferous source materials could have generated part of the gas, inasmuch as the base of the Khuff is probably Late Carboniferous.Hydrocarbons in terrigenous Carboniferous rocks in Egypt are believed to have originated in non‐Carboniferous beds; the petroleum in the Carboniferous sandstone reservoirs of Ghana, China and Australia is generally indigenous, and is non‐marine to deltaic. Oil and gas in the Carboniferous strata of Algeria are in marine and deltaic beds and are partly indigenous. The huge Carboniferous gas reserves in Permian, Triassic and, to a lesser extent, Carboniferous reservoirs of the Southern North Sea‐NW German basin are of non‐marine origin. The source materials were the Upper Carboniferous coals of the same area.The volume of produced Carboniferous oil is about 23 B brl, 21 B brl of it from the Volga‐Urals basin alone. About 63 Tcf of gas has been produced, 51 Tcf from the Southern North Sea‐NW German basin. This volume of gas includes Carboniferous gases in Permian and Triassic reservoirs. Proved and probable reserves of Carboniferous oil are about 13 to 14 B brland 85 Tcf, of which more than 50 Tcf remains in the Netherlands “giant Groningen Barents Sea extensions of the Timan‐Pechora basins, and ‐just possibly ‐ in several Chinese basins. The Arabian Gulf(Persian Gulf) also has a very largegas potential, but thegas, mainly in the Khuff, is of unknown origin and may wellnot be Carboniferous. (The Chu‐Sarysu basin, USSR, could also be important.)
SEQUENTIAL DEVELOPMENT OF HANIFA FORMATION (UPPER JURASSIC) PALEOCNVIRONMENTS AND PALEOGEOGRAPHY, CENTRAL SAUDI ARABIA
Authors: Moshrif Mohamed A. 
Published: December 2007

The Hanifa Carbonate lithofacies (Upper Jurassic) started to develop during Early Kimmeridgian time, when an extensive area in central Arabia was covered by relatively deep marine waters. These rock units were formed along a shoreline, resulting in sucessive lagoonal and tidal‐flat belts, the deposition of pelleted and laminated calcilutites and gypsum, and a restricted fauna. The open shelf lay east of the lagoon zone, accounting for the development of oolites, coral reef and calcarenites, and a diversified fauna on the deeper shelf.At its maximum extent, the “Hanifa Sea” reached west nearly as far as the city of Riyadh in central Saudia Arabia, and extended NE and east, covering Kuwait, Iraq, Oman and Iran. South of Riyadh, the Hanifa lithofacies may be traced towards the SE over the Rub‐al‐Khali area, and SW over Yemen and the Aden Protectorates. North and NW of Riyadh, these same Upper Jurassic shallow‐marine rock units developed over Jordan, Syria, Lebanon, Palestine and northern Sinai, and most probably extended over northern Africa.Although the sediments forming the lower part of the Hanifa suggest that during Early Kimmeridgian tima a transgressive phase began, and most likely continued during part of the Middle Kimmeridgian, a regressive stage ensued towards the end of th Kimmeridgian, when the upper part of the Hanifa was deposited.
SOME CONSEQUENCES OF FAULTING IN THE PRESENCE OF A SALT ROCK INTERVAL
Authors: Jenyon Malcolm K. 
Published: December 2007

Movement (and diapirism) in salt rock is frequently associated with faulting. In some cases, as in the Southern North Sea Zechstein, the association is clearly demonstrable. In other cases, more subtle effects occur. There is a variety of phenomena which may be observed under different geological circumstances in the salt‐fault association, and this paper discusses some of the more frequently‐encountered of these, offering some rather speculative suggestions as to the mechanisms which may be involved.Comment is also made upon apparent inconsistencies existing in currently‐held views on deformation in salt rock, and on the initiatory causes of diapirism.The ideas expressed and the geological interpretations made, are based on the study of current seismic data which has, where possible, been related to released well information.
MORPHOSTRUCTURAL ANALYSIS AS AN AID TO HYDROCARBON EXPLORATION IN THE AMAZONAS BASIN, BRAZIL
Authors: de Miranda F. P. , Hora M. P. P. da Boa 
Published: December 2007

A significant contribution to regional studies in the Amazonas Basin has been provided by the morphostructural analysis of MSS‐LANDSAT and SLAR imagery. The interpretation of remote sensing data led to the detection of many morphostructural anomalies in the Upper Amazonas Basin. A comparison between these anomalies and the available geological and geophysical data permitted the definition of two distinct morphostructural domains in this region. The first comprises a set of E‐W anomalies, located in a thinner sedimentary cover portion of the Upper Amazonas Basin. This feature was tentatively attributed to a prominent basement hinge line. The second morphostructural domain embraces anomalies situated where the sedimentary pile exceeds 1,600 m. In this domain, many anomalies seem to be related to ENE‐striking reverse faults. These morphostructural anomalies are arranged along ENE and E‐W aeromagnetic trends forming morphostructural trends.Analysis of MSS‐LANDSA T and SLAR imagery near the boundary between the Middle and Lower Amazonas basins indicates that several morphostructural anomalies are aligned in well‐defined directions, also suggesting the presence of morphostructural trends. These trends, often striking ENE, lie among zones with sharp magnetic gradients interpreted as expressions of basement compositional boundaries. Such morphostructural trends are also found near positive small‐wavelength magnetic anomalies, interpreted as possible grabentype structures.
THE EXPULSION CRITERION IN THE EVALUATION OF THE PETROLEUM SOURCE BEDS OF THE TERTIARY NIGER DELTA
Authors: Ejedawe J. E. 
Published: December 2007

Semilog plots of hydrocarbon ratios with depth for four wells in the offshore Niger Delta show that hydrocarbon expulsion has occurred at an interval shallower than the geochemically‐acceptedtop of the oil‐generative window (OGW), This shallow expulsion zone, which spans the maturation range 0.3‐0.6% RO, is related to the transformation of resinite‐ and sporiniterich organic matter to hydrocarbons. The deeper generation/expulsion zone (conventional OGW) has not released its generated hydrocarbons, presumably because of overpressure development.The critical hydrocarbon saturation at the onset of migration is 10–22 mg per gm organic carbon. Within the expulsion zone, expulsion efficiency varies considerably (10–81%; average 50%), and expulsion ceases when the hydrocarbon saturation falls 10–60% below the critical saturation level.The relative contribution of the paralic Agbada and marine, pro‐delta Akata source shales to the reservoired hydrocarbons in various areas of the delta depends on the present depth position of top supernormal pressure (Hsnp), relative to the top of the Akata Formation (Hak), and the top of the OGW (Hogw). Since the top of OGW must be above the top of the overpressure (Hogw < Hsnp) for effective hydrocarbon expulsion, three basic models are recognised in the Niger Delta:—(a) Hak Hsnp > Hogw: developed in the younger offshore and central onshore areas, with the Agbada constituting the major source rock;(b) Hogw < Hak < Hsnp: developed in the northern frame of the central Niger Delta, with both the Akata and Agbada contributing to the reservoired hydrocarbons; and(c) Hak Hogw < Hsnp; developed in the older northern fringe of the delta, with the Akata constituting the majar source rock.