bluuebunny/crossref_metadata_2025_split huggingface dataset:
THE ORIGIN AND DEVELOPMENT OF NEOGENE BASINS IN THE SE BETIC CORDILLERA (SE SPAIN): A CASE STUDY OF THE TABERNAS‐SORBAS AND HUERCAL OVERA BASINS
Authors: Poisson A. M. , Morel J. L. , Andrieux J. , Coulon M. , Wernli R. , Guernet C. 
Published: December 2007

Neogene— Quaternary sedimentary basins in SE Spain contain a record of the geodynamic evolution of the Internal Zone of the Betic Cordillera. The basement of the Internal Zone is composed of Palaeozoic and Mesozoic metasediments which have undergone variable degrees of metamorphism. The External Zones consist of largely unmetamorphosed sedimentary rocks which were deposited on the SE margin of the Iberian Plate during the Mesozoic and Early Cenozoic. Westward tectonic emplacement of these terranes onto the Iberian Plate took place between the end of the Palaeogene and the middle Miocene. In this paper, we investigate the late Miocene (Tortonian‐Messinian) stratigraphy of two basins in the Internal Zone — the Tabernas‐Sorbas and Huercal Overa Basins. We also consider some recently‐acquired structural data.The Tabernas‐Sorbas and Huercal Overa Basins are east‐west trending depressions bounded to north and south by sierras in which basement rocks are exposed. The basins contain very similar sedimentary successions in which planktonic foraminifera have been preserved. However, the faunal composition is very variable, and the observed sporadic and abrupt changes in foraminiferal populations imply palaeo‐ecologic and palaeo‐oceanographic instabilities which may be associated with local tectonism. Stratigraphic markers were affected by these changes, making precise dating difficult near the Tortonian‐Messinian boundary.Our data indicate that Messinian rocks are more widely distributed than has hitherto been suspected. A Messinian age for the prominent coral limestones in the Tabernas‐Sorbas Basin has long been accepted; similar coral limestones in the Huercal Overa Basin have previously been dated as Tortonian. However, our data show that these carbonates are of Messinian age in both basins.The origin and development of the Tabernas‐Sorbas and Huercal Overa Basins have previously been interpreted in a number of ways. Many (but not all) models favour strike‐slip movement on NE‐SW or east‐west trending basin‐bounding faults. The formation and deformation of the basins occurred during the Tortonian and Messinian, at the same time as the uplift of the sierras. The sierras are here interpreted to represent structural culminations above westward‐verging, deep‐seated thrust faults, and the basins to be lateral folds (or lateral ramps, i.e. oriented parallel to the thrust transport direction). The east‐west trending strike‐slip faults at the margin of the Sorbas‐ Tabernas Basin may be compatible with such a model.Major NE‐SW trending, left‐lateral wrench faults have been described in this area. These faults cut through late Miocene and Pliocene deposits, and are still active at the present day. Although these faults were initiated during the late Miocene, they do not appear to have influenced the development of the Tabernas‐Sorbas and Huercal Overa Basins during the early Tortonian.
TECTONICS AND SEDIMENTATION IN THE TAZA‐GUERCIF BASIN, NORTHERN MOROCCO: IMPLICATIONS FOR THE NEOGENE EVOLUTION OF THE RIF‐MIDDLE ATLAS OROGENIC SYSTEM
Authors: Bernini M. , Boccaletti M. , Gelati R. , Moratti G. , Papani G. , Mokhtari J. El 
Published: December 2007

The Neogene‐Quaternary Taza‐Guercif Basin, northern Morocco, is one of a number of remnants of the basinal “South Rifean Corridor” which connected the Atlantic Ocean to the Mediterranean Sea during the Miocene. The basin has a hybrid structure because its development was influenced both by the Rif orogenic belt to the north and NW and the Middle Atlas Shear Zone to the SW.Stratigraphic and structural studies have been carried out in the basin. The recognition of major unconformities, the distribution in time and space of sedimentary facies, and the areal distribution of deformation structures at various scales have been integrated to reconstruct the tectono‐sedimentary evolution of the basin beginning in the the Tortonian (late Miocene). This evolution is related to outward migration of the Rif deformation front and to tectonic activity in the Middle Atlas Shear Zone. This study highlights the role played by the Middle Atlas Shear Zone as a first‐order element in the evolution of the Rif belt and of the Moroccan Meseta in relation to the African Plate.
A NEW PERSPECTIVE ON THE ZONATION AND CORRELATION OF BARREN STRATA: AN INTEGRATED HEAVY MINERAL AND PALAEOMAGNETIC STUDY OF THE SHERWOOD SANDSTONE GROUP, EAST IRISH SEA BASIN AND SURROUNDING AREAS
Authors: Mange M. , Turner P. , Ince D. , Pugh J. , Wright D. 
Published: December 2007

The integration of data from high‐resolution heavy mineral and palaeomagnetic analyses of samples from nine East Irish Sea wells, and from onshore sections at St Bees Head and the North Cheshire Basin, has generated a temporally‐constrained heavy mineral stratigraphy and regional correlation within the Triassic Sherwood Sandstone Group. These results have shown that the combined application of these two techniques offers an effective tool for extending the zonation and correlation of barren strata into uncored wells. The lateral persistence of the heavy mineral zones, and the significant differences in the distributions of the heavy mineral varieties between individual zones, may reflect tectonic events and, to a lesser extent, climatic variations.Palaeomagnetic results indicate that the original magnetisation of the analysed samples was acquired as a detrital remanent magnetisation and that the characteristic remanent magnetisation in the red beds was acquired during and shortly after deposition. Magnetopolarities have been interpolated using the available data from which a composite reference section has been constructed.All well sequences exhibit a regionally persistent three‐fold zonation (Zones A, B and C, locally with subzones), defined by systematic changes in characteristic heavy mineral suites. Using a common sample set, the independently erected heavy mineral stratigraphy was tied to specific magnetostratigraphic Chrons. Heavy mineral Zone A coincides with a period of dominantly normal polarity, fixed by a 244 Ma Chron of Middle Scythian age. A change in polarity from normal to reversed at > 243 Ma coincides with the boundary of Zones A/B. Zone B is Middle to Upper Scythian and shows a dominantly reversed polarity. A well‐defined Chron of 242.7 Ma has been detected close to the boundary of Zones B/C. Zone C is Anisian in age and is characterised by a dominantly normal polarity.
PALYNOLOGICAL AND GEOCHEMICAL ANALYSIS OF CARBONIFEROUS BOREHOLE AND OUTCROP SAMPLES FROM THE ISLE OF MAN
Authors: Racey A. , Goodall J. G. S. , Quirk D. G. 
Published: December 2007

Palynological and geochemical analyses were performed on Namurian (mid‐Carboniferous) samples from the Ballavaarkish and Shellag Point boreholes from the north of the Isle of Man, and on Dinantian/Namurian outcrop samples from Black Marble Quarry in the south of the island.The boreholes yielded a rich and diverse (over 60 species) Namurian B‐C (Kinderscoutian‐Yeadonian) palynomorph assemblage equivalent to the KV/FR Zones of Clayton et al. (1977). Reworked Brigantian‐Namurian A palynomorphs of the NC/TK Zones were recorded in the Shellag Point borehole. Offshore seismic data indicates a period of major fault activity in the early Namurian which may support this concept of early Namurian reworking. Amorphous organic matter indicating anoxic/dysoxic depositional conditions together with prasinophyte algae and goniatites suggesting a marine environment were recorded in the Shellag Point borehole.Vitrinite reflectance and spore colouration measurements coupled with Tmax data from Rock‐Eval pyrolysis indicate that the Namurian shales from the Shellag Point borehole are currently in the oil window. Rock‐Eval data and kerogen analyses indicate that these shales represent moderate to good gas‐prone source rocks which have yet to attain full maturity. The Namurian samples from Ballavaarkish are mainly in the oil window or late mature zone and have poor gas potential. Extract chromatography indicates a relatively mature product and the possible onset of hydrocarbon biodegradation, particularly in the Ballavaarkish borehole samples.Outcrop samples from near the top of the succession at Black Marble Quarry underwent thermal alteration as a result of dyke intrusion and subsequent volcanism. Although previously believed to be Brigantian (end‐Dinantian) in age based on goniatites, corals and conodonts, the samples have produced a sparse palynological assemblage indicating an apparent age no older than Namurian. The samples are late‐ to post‐mature in terms of hydrocarbon generation and have no remaining source potential.The results indicate that where Namurian sediments are preserved beneath the base‐Permian unconformity, for example in the Solway Basin, hydrocarbons are likely to have been generated.
THE VENEZUELAN HYDROCARBON HABITAT, PART 1: TECTONICS, STRUCTURE, PALAEOGEOGRAPHY AND SOURCE ROCKS
Authors: James K. H. 
Published: December 2007

Venezuela forms part of an important hydrocarbon province, defined by the presence of prolific Cretaceous source rocks, which extends across northern South America. By early 1997, the country had produced 53 billion barrels of oil. Reserves are estimated to total 73 billion barrels of oil and 146 TCF of gas with 250 billion barrels recoverable in the Heavy Oil Belt. Most reserves are located within the intermontane Maracaibo and foreland Barinas‐Apure and Eastern Venezuela Basinx They correspond to more than 1.5 trillion BOE originally in place.The province's hydrocarbon history began with a broad passive margin over which the sea transgressed throughout much of the Cretaceous. Limestones and shales followed basal sands and included rich source rocks. Convergence between the distal part of the area and the Caribbean Plate created an active margin that migrated southwards, so that flysch and wildflysch followed the transgressive facies. The process culminated in Lute Cretaceous to Middle Eocene orogeny with the emplacement of southward‐vergent nappes and the development of northward‐deepening foredeeps. Flysch and wildflysch formed in the north while important deltaic—paralic reservoir sands accumulated in the south. Major phases of hydrocarbon generation from Jurassic‐Cretaceous source rocks occurred across the entire margin of northern South America during the orogeny. They are recorded by Jurassic ‐ Middle Cretaceous graphitic marbles, schists and quartzites (metamorphosed, organic limestones and shales and oil‐bearing sandstones) in the Coastal and Northern Ranges of Venezuela and Trinidad. They probably charged giant fault and stratigraphic traps analogous to today's Oficina‐Temblador and Heavy Oil Belt accumulations.From Late Eocene to Recent times, transpressive interaction between northern South America and neighbouring parts of the Caribbean and the Pacific inverted Mesozoic extensional systems below the remaining passive margin. The area became subdivided into a series of intermontane, foreland and pull‐apart basins bounded by transpressional uplifts, the latter sufering considerable shortening and strike‐slip displacement. Sedimentation progressed from deep marine to deltaic and molassic facies, providing reservoir sands and local source rocks.Inverted faults and foreland flexuring and interplay between structuration and sedimentation produced abundant structural and stratigraphic traps. Hydrocarbons from earlier accumulations suffered further maturation in place, remigrated to younger traps or escaped to the surface. Further hydrocarbon generation, involving Upper Cretaceous source rocks, occurred in local foredeep kitchens. Minor contributions also came from Tertiary source rocks.
BURIAL AND MATURATION HISTORY OF THE HEGLIG FIELD AREA, MUGLAD BASIN, SUDAN
Authors: Mohamed A. Y. , Iliffe J. E. , Ashcroft W. A. , Whiteman A. J. 
Published: December 2007

The NW‐SE trending Muglad Basin (SW Sudan) is one of a number of Mesozoic basins which together make up the Central African Rift System. Three phases of rifting occurred during the Cretaceous and Tertiary, resulting in the deposition of at least 13 km of sediments in this basin. Commercial hydrocarbons are sourced from the Barremian‐Neocomian Sharaf Formation and the Aptian‐Albian Abu Gabra Formation.The Heglig field is located on a NW‐SE oriented structural high in the SE of the Muglad Basin, and is the second‐largest commercial oil discovery in Sudan. The high is characterised by the presence of rotated fault blocks, and is surrounded by sub‐basinal structural lows. We modelled the geohistories of three wells on different fault blocks in the Heglig field (Heglig‐2, Barki‐1 and Kanga‐1) and one well in the Kaikang Trough (May25–1). The models were calibrated to measured porosity‐depth data, temperature and vitrinite reflectance measurements. Predicted present‐day heat flow over this part of the Muglad Basin is about 55 mW/m2. However, a constant heat‐flow model with this value did not result in a good fit between calculated vitrinite Ro and measured Ro at the wells studied. Therefore a variable heat‐flow model was used; heat flow peaks of 75, 70 and 70 mW/m2 were modelled, these maxima corresponding to the three synrift phases. This model resulted in a better fit between calculated and measured Ro.The source rock section in the Sharaf and Abu Gabra Formations was modelled for hydrocarbon generation in the four wells. Model results indicate that the present‐day oil generation window in the Hegligfield area lies at depths of between 2 and 4 km, and that oil and gas generation from the basal unit of the Abu Gabra Formation occurred between about 90 and 55 Ma and from the Sharaf Formation between 120 and 50 Ma. The results suggest that the oils discovered in the Heglig area have been generated from a deep, mature as‐yet unpenetrated source‐rock section, and/or from source rocks in nearby sub‐ basinal areas.
THE PETROLEUM GEOLOGY OF THE EARLY EOCENE EL GARIA FORMATION, HASDRUBAL FIELD, OFFSHORE TUNISIA
Authors: Racey A. , Bailey H. W. , Beckett D. , Gallagher L. T. , Hampton M. J. , McQuilken J. 
Published: December 2007

The Hasdrubal field (offshore Tunisia) comprises an Early Eocene shallow‐marine nummulitic limestone reservoir (the El Garia Formation) sourced by deep‐marine mudstones and limestones of the generally age‐equivalent Bou Dabbous Formation. The field is located on a NNW‐SSE trending horst between a series of en‐echelon normal to oblique faults, and is dip‐closed except to the north where a stratigraphic pinch‐out into the Bou Dabbous Formation is inferred. Middle Eocene shales and dense limestones of the Cherahil Formation form the main seal.The El Garia Formation reservoirs significant volumes of hydrocarbons in Tunisia and Libya. A detailed micropalaeontological and nannofossil study has been undertaken of the El Garia Formation and the immediately over‐ and underlying formations which together form the Metlaoui Group, using subsurface data from the Hasdrubal field. This has permitted a detailed chronostratigraphic and sequence stratigraphic framework to be developed, including the recognition of three flooding events, which can partly be calibrated with second‐order sequences, thus permitting the correlation of discrete reservoir units across the field. A further six microfaunal events are recognized between the Chouabine Formation and the “Compact Micrite Member” within the Metlaoui Group.Previous depositional models for the El Garia Formation are discussed and a new model is proposed. The model partly explains why a number of wells drilled along the El Garia nummulite “bank” trend have failed to encounter the nummulite reservoir fades, and why, even where this fades was encountered, the limestones were frequently tight and/or contained limited hydrocarbons. It is also suggested that proximity to source is a critical factor, with the development of dissolution porosity by acidic pore waters migrating in advance of hydrocarbons. This is critical for enhancing reservoir quality and thus promoting the capacity to reservoir hydrocarbons, as indicated by the location of existing discoveries.
CONSTRAINTS ON DIAGENESIS AND RESERVOIR QUALITY IN THE FRACTURED HASDRUBAL FIELD, OFFSHORE TUNISIA
Authors: Macaulay C. I. , Beckett D. , Braithwaite K. , Bliefnick D. , Philps B. 
Published: December 2007

The hydrocarbon reservoir of the Hasdrubal field (offshore Tunisia) lies within the Eocene El Garia Formation. This formation was deposited on a shallow north‐ to NE‐facing ramp in the Early Eocene and is composed of a belt of nummulitic wackestones‐grainstones. The nummulitic fades occupies a range of depositional environments from outer to mid ramp. In addition to Hasdrubal, several other producing oil‐ and gasfields have been discovered in the variably dolomitised El Garia Formation offshore Tunisia.Cores from three Hasdrubal wells were examined. Reservoir quality shows a limited relationship to primary depositional fabric and has been influenced significantly by compaction and later diagenesis. The highest permeabilities are typically developed within a dolomitised zone which occurs near the middle of the reservoir interval across the entire field, and which may follow a primary wackestone lithofabric (typically 20–30% bulk volume dolomite, with porosities of 15–22% and permeabilities of l‐30mD). Fractures, particularly in zones surrounding faults, have resulted in enhanced permeabilities.Combined results of isotope (δ18 O ‐5.0 to ‐7.3%oPDB) and fluid inclusion (Th 80–90d̀C) analyses of dolomites from this dolomitised zone indicate that matrix dolomites are burial diagenesis cements. Dolomitisation of the reservoir was a “closed system ” event and was not the result of major fluid flow or mixing. Magnesium ions for dolomitisation were derived from the transformation of high‐Mg to low‐Mg calcite in nummulite tests within the reservoir fades.Our analyses indicate that calcite cements were precipitated at temperatures of up to almost 150d̀C in primary and secondary pores and in variably‐sealed fractures Fracture lining and filling cements show a range of δ18 O values, which suggests that the fractures acted as fluid conduits over a range of temperatures during burial diagenesis Fracture densities measured in core increase rapidly close to seismically‐resolvable faults in the reservoir facies Fracturing probably resulted in the leakage of hydrocarbons through the Compact Micrite Member seal which overlies the accumulation, as well as facilitating the ingress of hot fluids from stratigraphically deeper levels in the basin
A REVIEW OF EOCENE NUMMULITE ACCUMULATIONS: STRUCTURE, FORMATION AND RESERVOIR POTENTIAL
Authors: Racey A. 
Published: December 2007

Eocene nummulite accumulations, also referred to as nummullte “banks”, form Important hydrocarbon reservoirs in Tunisia and Libya and may constitute exploration targets in other parts of North Africa, the Mediterranean and the Middle East. Porosities commonly average 10–20% and permeabilities 10–50md. Foraminifera of the genus Nummulites may comprise up to 98% of the bioclasts in these carbonate reservoirs, although only one or two species may be present. The absence of associated fauna is generally taken to indicate an oligotrophic depositional environment.In this paper, the palaeoecology of the genus Nummulites is discussed together with depositional models for two nummulitic carbonate reservoirs — the Middle Eocene Seeb Limestone of Oman and the Early Eocene El Garia/Jdeir Formation of Tunisia and Libya. The El Garia and Seeb Limestone Formations were deposited in ramp settings, and comprise a series of amalgamated sheets or low‐relief banks. In the Hasdrubal field offshore Tunisia, where the El Garia Formation constitutes the reservoir rock, most of the nummulites have been redeposited from shallow into deeper waters whilst in the Bourri field (offshore Libya) they occur as an in situ “bank”.Nummulite accumulations often show evidence that both physical reworking (scouring, winnowing and imbrication) and biological processes (reproduction strategies and bioturbation) have influenced their formation. A general model is outlined for discriminating between physically and ecologically produced biofabrics, and the implications for reservoir quality are discussed.
THE EVOLUTION OF A MODEL TRAP IN THE CENTRAL APENNINES, ITALY: FRACTURE PATTERNS, FAULT REACTIVATION AND DEVELOPMENT OF CATACLASTIC ROCKS IN CARBONATES AT THE NARNI ANTICLINE
Authors: Storti F. , Salvini F. 
Published: December 2007

Recent hydrocarbon discoveries in the Southern Apennines of Italy have focussed attention on the importance of studying fracturing and cataclasis in carbonate rocks because of their fundamental impact on reservoir permeability and connectivity. The Narni Anticline in the central Apennines consists of a stack of easterly‐verging carbonate thrust sheets compartmentalized by extensional and strike‐slip fault zones. The structure provides afield analogue for studying the evolution of superimposed fold‐ and fault‐related fractures in carbonate reservoir rocks.The fracture pattern at the Narni Anticline developed as a result of three mechanisms: (a) layer‐parallel shortening predating folding and faulting; (b) thrust‐related folding and further thrust breakthrough; and (c) extensional and strike‐slip faulting. Along‐strike (longitudinal) fractures developed during progressive rollover fault‐propagation folding, and their intensity depends on the precise structural position within the fold: fracture intensity is high in the forelimb and low in the crest. The 3‐D architecture of the mechanical anisotropy associated with thrusting, folding, and related fracturing constrained the location and geometry of subsequent extensional and strike‐slip faulting. The superimposition in damage zones of a fault‐related cleavage on the pre‐existing fracture pattern, which is associated with layer‐parallel shortening and thrust‐related folding, resulted in rock fragmentation and comminution, and the development of cataclastic bands.The evolution of fracturing in the Narni Anticline, its role in constraining thrust breakthrough trajectories and the location of extensional and strike‐slip faults, and the final development of low‐permeability cataclastic bands, will be relevant to studies of known oilfields in the Southern Apennines, as well as for future exploration.
A PRELIMINARY EVALUATION OF JURASSIC SOURCE ROCK POTENTIAL IN KUWAIT
Authors: Abdullah F. H. A. 
Published: December 2007

Jurassic sedimentary rocks in Kuwait are generally assigned to the Marrat, Dhruma, Sargelu and Najmah Formations (mainly limestones and calcareous shales) and the overlying Hith and Gotnia Formations which are composed of anhydrites and evaporites. This paper reports the results of organic‐geochemical analyses of Jurassic carbonate and shale samples recovered from ten wells in Kuwait. Analytical techniques included TOC analysis, elemental analyses of kerogen, density separation and petrographic analyses. The thermal history of Kuwait was modelled and calibrated with maturity indicators from the studied wells.The analytical results point to the presence of marine kerogen between Types II and III. Generally, the formations show amorphous rich sapropelic organic matter with high H/C ratios and low densities. Biodegradation of some samples resulted in elevated O/C ratios. The results of maturity studies indicate that most of the Jurassic Succession is mature, maturity differences being due to depth variations. Oil generation began in Late Cretaceous to Eocene time when structural traps had already been formed. Jurassic source rocks may therefore have supplied reservoir units in Kuwait. In particular, the Najmah Formation includes well‐preserved amorphous marine algal type organic matter. The high TOC values and thermal maturity of this formation make it one of the most important potential sources of oil in Kuwait.