bluuebunny/crossref_metadata_2025 huggingface dataset:
GEOCHEMISTRY OF LITHUANIAN OILS AND SOURCE ROCKS: A PRELIMINARY ASSESSMENT
Authors: Zdanaviciute O. , Bojesen‐Koefoed J. A.
Published: December 2007

A series of oils and potential petroleum source‐rock samples has been analysed from exploration wells on‐and offshore Lithuania. Despite the limited amount of data, the results indicate the possible existence of partly‐exhausted source rocks within the Cambrian succession. Furthermore, possible source rocks are present within the Ordovician succession, and excellent source rocks occur within the Silurian in several wells. The source rocks are all present within a few hundred metres of stratigraphic succession, and the thermal maturity roughly follows the actual depth of burial, despite the fact that most of the subsidence and maturation took place in the latest Palaeozoic. The most important reservoir rocks are Middle Cambrian sandstones, but petroleum accumulations also occur in Ordovician limestones and Silurian reefal carbonates. Petroleum accumulations in Lithuania probably result from the pooling of oil derived from several sources, with the Lower Silurian (Llandoverian) shales being the most important single contributor.
BURIAL AND THERMAL HISTORY MODELLING OF THE GAFSA‐METLAOUI INTRACONTINENTAL BASIN (SOUTHERN TUNISIA): IMPLICATIONS FOR PETROLEUM EXPLORATION
Authors: Hlaiem A. , Biju‐Duval B. , Vially R. , Laatar E. , M'Rabet A.
Published: December 2007

This paper is a contribution to the evaluation of the petroleum potential of southern Tunisia. Its purpose is to report on the burial and thermal histories of the Gafsa‐Metlaoui Basin and the surrounding area in the time interval between the Triassic and the Quaternary. We have used a one‐dimensional deterministic model, which enabled us to integrate the burial and thermal influences on potential source rocks with kinetic parameters, in order to define the timing of hydrocarbon generation and expulsion in relation to the main structural episodes in the study area.

The Mesozoic burial history of this basin is characterized by two principal phases of rifting, each of which was followed by a brief episode of thermal (post‐rift) subsidence. The first phase occurred during the Triassic and Jurassic, and was related to the breakup of Gondwana; the second phase occurred during the Cretaceous and Early Tertiary, and was related to the opening of the neo‐Tethyan Mediterranean Sea. Geothermal studies of this basin have allowed us to determine an average surface heat flow of 60 m W/sq. m and an average geothermal gradient of about 25.5d̀C/km. Middle Jurassic source rocks expelled oil from the Cenomanian (about 100 million years ago) to the Quaternary.
RELATIONSHIPS BETWEEN HYDROCARBON GENERATION, COAL TYPE AND RANK FOR MIDDLE EOCENE COALS, BULLER COALFIELD, NEW ZEALAND
Authors: Norgate C. M. , Boreham C. J. , Kamp P. J. J. , Newman J.
Published: December 2007

The Buller Coalfield in the northern portion of the Paparoa Trough (NW South Island, New Zealand) contains a middle Eocene bituminous coal‐bearing succession that exhibits marked variations in both coal rank and type. The across‐basin rank changes result from differential late Palaeogene subsidence of the Paparoa Trough and subsequent inversion. Superimposed upon coalification trends are down‐seam variations in coal type, evidenced by isorank variation in conventional chemical parameters. These type variations are not a consequence of changes in maceral group proportions, which are dominated by vitrinite.

Forty‐eight coal samples from fifteen drillholes through the Brunner Coal Measures have been examined for vitrinite reflectance, proximate analysis, specific energy, and sulphur content. Total Organic Carbon (TOC), Rock‐Eval properties and the bulk composition of the bitumen were also determined.

All the coals analysed lie within the high volatile bituminous B to medium volatile bituminous coalification stages. Variation in analytical properties within this suite, and more specifically within serial samples, provides insights into the nature of the organic matter comprising the coals. While TOC varies systematically with ash content, reflecting proximity of the depositional mires to fluvial systems, values increase with rank (68–86% ash free). The Hydrogen Index (HI) decreases from 334 to 190 mg hydrocarbons/g TOC over a range of 429 to 470 d̀C Tmax, analogous to the volatile matter content and vitrinite reflectance, respectively. The more perhydrous coal samples at a given rank are characterised by depressed Tmax/vitrinite reflectance and elevated Hi/volatile matter contents.

Bitumen and sulphur contents are not the primary control onperhydrous characteristics. The bitumen content crudely corresponds to the S1 peak plus the initial portion of the S2 peak liberated under low temperatures during Rock‐Eval pyrolysis; however, the bulk of the generative potential is associated with the residual kerogen fraction. Suggate (S) Rank and maximum palaeotemperature appear to be the best indicators of coal rank.

A period of significant hydrocarbon generation and release begins at Tmax∼440d̀C for the Buller coals. The main oil “window” is defined by the interval 440–455d̀C Tmax or 0.8–1.1% vitrinite reflectance (Romax), and by correlation to maximum palaeo‐temperatures, 125–155d̀C. This is further substantiated by mass balance considerations, which indicate that hydrocarbon generation (Petroleum Generation Index (PG1) > 0.1) was occurring in the coals at a maturity level of O. 7–0.9 % Romax (Tmax 440–444 d̀C) with an increase in PGI between ∼0.9 and 1.1% Romax (∼Tmax 445–455 d̀C). Between PGI 0.1 and 0.4, the expulsion efficiency rapidly increased, presumably due to generation and expulsion of the bulk of the oil.
RIPHEAN HYDROCARBON RESERVOIRS OF THE YURUBCHEN‐TOKHOM ZONE, LENA‐TUNGUSKA PROVINCE, NE RUSSIA
Authors: Kuznetsov V. G.
Published: December 2007

The Siberian Craton covers an area of about 4.5 million sq. km in northern Russia, of which up to 3.5 million sq. km may be prospective for hydrocarbons. The craton was consolidated in the Early Proterozoic, and above the basement granitoids and gneisses is a variable thickness of sedimentary strata ranging in age from Riphean (Middle‐Late Proterozoic) to Quaternary.

Reservoir rocks are known to occur in the interval between the Middle Riphean and the Upper Cretaceous; those of Riphean age have produced oil commercially since 1973. Geochemical data indicate that the oil within the Riphean reservoir rocks was generated by source rocks of Riphean age. Riphean reservoir rocks include both carbonates and siliciclastics, but commercial volumes of hydrocarbons have only been discovered within the carbonates.

Three petroleum‐bearing “provinces” or megabasins are located on the Siberian Craton: Lena‐Tunguska, Lena‐Vilyuyand Yenisey‐Anabar. The Yurubchen‐Tokhom Zone in Lena‐Tunguska Province is potentially the most important oil‐producing area in the craton, and comprises a number of distinct fields. Reservoir rocks here consist principally of thick Riphean dolomites. Both the development of reservoir characteristics within these dolomites and the formation of stratigraphic traps are related to an episode of emergence and karstification at the end of the Riphean.
THE LOWER CRETACEOUS PETROLEUM SYSTEM IN NE CHINA
Authors: Lirong Dou
Published: December 2007

NE China is situated on the pre‐Mesozoic folded belt between the Siberian and Sino‐Korean Cratons. Beginning in the Late Jurassic, the oceanic Izanagi Plate was subducted NW wards beneath the Eurasian Plate, resulting in a change in the structural setting from north‐south compression to NW‐SE extension leading to intracontinental rifting. The Early Cretaceous marked a peak in the development of syn‐rift lacustrine basins, and there are about 200 rift depressions in the study area. Left‐lateral strike‐slip activity on the NE‐SW oriented Tan‐Lu Fault, and a change in the rate and direction of subduction of the Izanagi Plate, ended the syn‐rift stage. Thick, post‐rift lacustrine sequences only developed in the Songliao Basin, and today form source and reservoir rocks at the “giant” Daqing oilfield.

Gas‐source rock correlations in the Lower Cretaceous strata of the Songliao Basin, and oil‐source rock correlations in the Erlian and other basins have indicated that all the hydrocarbons were generated in, and have migrated from, Lower Cretaceous source rocks. The Lower Cretaceous syn‐rift sequence has been proved to be a known petroleum system. Twenty‐two oil‐ and gasfields have been found in six basins. Each rift depression constitutes an independent petroleum system, and plays can be divided into four types (boundary fault; deep‐sag; central flexural; and flexural margin), of which the central flexural play is the most prospective. It is anticipated that these small rift basins will become targets for future exploration.
REFLECTANCE RETARDATION (SUPPRESSION) AND SOURCE ROCK PROPERTIES RELATED TO HYDROGEN‐ENRICHED VITRINITE IN MIDDLE JURASSIC COALS, DANISH NORTH SEA
Authors: Petersen H. I. , Rosenberg P.
Published: December 2007

Middle Jurassic high volatile bituminous A coals from the Danish North Sea may yield vitrinite reflectance values retarded by 0.10–0.14 %Rr The coals are low in liptinite content, and the reflectance retardation is related to the vitrinite composition. Vitrain (assumed to be pure vitrinite) was hand‐picked from eight samples and characterised by means of element analysis, Fourier Transform infrared spectroscopy and Rock‐Eval pyrolysis. In contrast to the vitrinite from samples yielding “true” reflectance values, the vitrinite from three of the samples yielding retarded reflectances is perhydrous in nature (5.57–5.79 wt‐% (d.a.f.) H) and has H/C atomic ratios of 0.80–0.83. Vitrinite from another reflectance‐retarded sample is enriched in sulphur. The hydrogen enrichment is inherited from oxygen‐deficient, waterlogged and marine‐influenced conditions in the precursor mires. FTIR spectra demonstrate that the perhydrous vitrinites have a lower aromaticity as measured by aromatic hydrogen vibrations in the region 900–700 cm‐1 compared to the “normal” vitrinites. This suggests a reduced maturation rate of the hydrogen‐enriched vitrinite. S1(Vitr), S2(vitr) and HIvitr values from the vitrinite concentrates indicate that the vitrinite is a significant contributor to the overall generative potential; this is particularly the case for the perhydrous vitrinite. Activation energies for the vitrinites are centred at 260 and 268 kJ/mole. It is not possible to detect a measurable difference in Ea between the perhydrous and “normal” vitrinites. This may suggest more‐or‐less similar generation characteristics, or it may indicate that Rock‐Eval kinetics do not replicate Nature in this regard.
THE MFAMOSING LIMESTONE IN SE NIGERIA: OUTCROP‐SUBSURFACE CORRELATION AND RESERVOIR DEVELOPMENT
Authors: Reijers T. J. A.
Published: December 2007

Key sequence‐stratigraphic markers define intervals recognised in outcrops and wells in the Aptian‐Albian Mfamosing Limestone Formation in SE Nigeria. These markers aid in outcrop‐to‐subsurface correlation. The influx of siliciclastics and sea‐level fluctuations controlled carbonate production. Peritidal, lagoonal and reefal carbonates rim the igneous Oban Massif and reflect an initial relative sea‐level highstand. Subsequent sea‐level fall was accompanied by the progradation of carbonates away from the exposed, siliciclastic‐shedding hinterland, and maximal carbonate production took place during a sea‐level lowstand, when an open‐marine carbonate shelf and a mixed carbonate‐siliciclastic shoal co‐existed side by side. In the Ituk area, wave action abraded the sea floor which was occasionally exposed, and hardgrounds and leached horizons were formed. Bed‐ andmatrix‐selective dorag dolomitisation improved the reservoir potential of the carbonates in certain intervals.
TECTONICS AND SEDIMENTATION WITHIN A MESSINIAN FOREDEEP IN THE CENTRAL APENNINES, ITALY
Authors: Bigi S. , Calamita F. , Cello G. , Centamore E. , Deiana G. , Paltrinieri W. , Pierantoni P. P. , Ridolfi M.
Published: December 2007

The Marche‐Abruzzi thrust system is part of the Central Apennine fold‐and‐thrust belt of mainland Italy. Our study area covers the SE portion of the Umbria‐Marche‐Abruzzi region and the northern part of the Gran Sasso Mountains. A thick pile of turbidites is exposed in this area; they were deposited within a Messinian foredeep in front of the evolving fold‐and‐thrust belt. We have used regional structural interpretations together with unpublished well‐log and seismic data to construct a cross‐section across the external portion of the thrust system.

Our work suggests that: (i) deformation of the sediments in the Messinian foredeep began shortly after their deposition, and continued until the late Pliocene; (ii) the restored (pre‐deformation) width of the basin was approximately twice that of the present‐day basin, and the depocentre migrated eastwards at a rate of about 4 cm/yr; (iii) the geometry and physiography of the Messinian foredeep were controlled by a number of longitudinal and transverse structural features which may be related to foreland ramp activity or to differential flexuring of the Apulian lithosphere, respectively.
THE DIVERSITY OF LATE NEOGENE SEDIMENTARY BASINS GENERATED BY WRENCH FAULTING IN THE EASTERN BETIC CORDILLERA, SE SPAIN
Authors: Montenat C. , D'Estevou Ph. Ott
Published: December 2007

In this paper, we review the types of sedimentary basins which are generated by wrench faulting with particular reference to the Late Neogene Eastern Betic Shear Zone, a well‐documented segment of the Trans‐Alboran Shear Zone. The general characteristics of this wrench “corridor” are described, including the role of inherited structures. The diversity of basin types is emphasised, as is the coexistence of basins which developed under compressional or extensional regimes.

Pull‐apart basins do not appear to be the most widespread type of basin in the Eastern Betic Shear Zone. Rather, compressional “groove‐shaped synclines” which run parallel to master strike‐slip faults (regardless of their orientation or direction of movement) are more typical structures. They are characterised by intense synsedimentary deformation and reworking of sediments, depositional processes being dominated by gravity flows. The basins are relatively short‐lived and generally undergo structural inversion. Sedimentary basins also form in extensional areas, most significantly in the triangular zones which occupy the extensional quadrant of a pseudo‐ conjugate strike‐slip fault system.

In the Eastern Betics, it appears that compressional basins are more efficient than extensional basins in terms of their subsidence and sedimentation rates, the thickness of the clastic fill, and the intensity of synsedimentary deformation. Compressional basins may therefore be the more favourable with respect to potential hydrocarbon accumulations.
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.
PETROLEUM GEOLOGY AND FUTURE HYDROCARBON POTENTIAL OF THE IRISH SEA
Authors: Quirk D. G. , Roy S. , Knott I. , Redfern J. , Hill L.
Published: December 2007

The East Irish Sea Basin is hydrocarbon prolific with ten gasfields, two oilfields and another eight gas or oil discoveries. Production is from a widespread Triassic fluvioaeolian reservoir (the Ormskirk Sandstone) which is sealed by salt‐prone mudstones. Three episodes of hydrocarbon generation occurred from a rich, Namurian‐age source rock during deep burial in the Late Carboniferous‐Early Permian, in the Early Jurassic and in the Late Cretaceous. All of the discoveries are in structural traps which are controlled to some degree by N‐S trending normal faults probably active in the Late Jurassic. Consequently, the third (Cretaceous) phase of hydrocarbon generation is the most important. Another phase of uplift and erosion occurred in the Early Tertiary leading to the almost complete removal of Cretaceous and Jurassic strata. This event led to significant primary and tertiary migration as a result of overpressuring in the source rock and gas expansion within the reservoir. Although similar good quality Triassic reservoir occurs in other basins in the Irish Sea, rift‐related uplift and erosion in the Middle Permian caused the widespread removal of potential Carboniferous source rocks in these areas, severely limiting the chance of hydrocarbon charge.
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.
CHARACTERISATION OF ORGANIC MATTER FORMED IN HYPERSALINE CARBONATE/EVAPORITE ENVIRONMENTS: HYDROCARBON POTENTIAL AND BIOMARKERS OBTAINED THROUGH ARTIFICIAL MATURATION STUDIES
Authors: Schreiber B. C. , Philp R. P. , Benali S. , Helman M. L. , de la Peña J. A. , Marfil R. , Landais P. , Cohen A. D. , Kendall C.G.St.C.
Published: December 2007

Sediments deposited under hypersaline conditions, particularly those laid down in the transition zone between marine carbonates and evaporites, are increasingly recognised as a potential source for oil. Recent environments that lie in waters with elevated salinities are sites of very high biological productivity that can be used as models for evaporite‐related sedimentation in the geological record. Of particular importance is the range of elevated salinities well above the range for normal marine biota, in which organic‐rich cyanobacterial carbonates form and accumulate in large quantities. Such organic matter collected from a number of modern evaporative settings has been examined in terms of oil potential and for biomarkers characteristic of hypersaline environments. The regions studied include marine‐fed salinas (Santa Pola, Spain); marine‐fed sabkhas (Abu Dhabi, UAE); and continental ponds and lakes (La Mancha region, Spain). High values of H/C ratio and HI demonstrate the oil source potential of this organic matter. The hydrocarbons generated during artificial maturation of these immature sediments resemble those naturally occurring in ancient petroleum‐generating evaporitic systems. Variations in the total
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.
NEURAL NETWORK PREDICTION OF PERMEABILITY IN THE EL GARIA FORMATION, ASHTART OILFIELD, OFFSHORE TUNISIA
Authors: Ligtenberg J.H. , Wansink A.G.
Published: December 2007

The Lower Eocene El Garia Formation forms the reservoir rock at the Ashtart oilfield, offshore Tunisia. It comprises a thick package of mainly nummulitic packstones and grainstones with variable reservoir quality. Although porosity is moderate to high, permeability is often poor to fair with some high permeability streaks.

The aim of this study was to establish relationships between log‐derived data and core data, and to apply these relationships in a predictive sense to uncored intervals. An initial objective was to predict from measured logs and core data the limestone depositional texture (as indicated by the Dunham classification), as well as porosity and permeability. A total of nine wells with complete logging suites, multiple cored intervals with core plug measurements together with detailed core interpretations were available.

We used a fully‐connected Multi‐Layer‐Perceptron network (a type of neural network) to establish possible non‐linear relationships. Detailed analyses revealed that no relationship exists between log response and limestone texture (Dunham class). The initial idea to predict Dunham class, and subsequently to use the classification results to predict permeability, could not therefore be pursued. However, further analyses revealed that it was feasible to predict permeability without using the depositional fabric, but using a combination of wireline logs and measured core porosity. Careful preparation of the training set for the neural network proved to be very important. Early experiments showed that low to fair permeability (1–35 mD) could be predicted with confidence, but that the network failed to predict the high permeability streaks. “Balancing ” the data set solved this problem. Balancing is a technique in which the training set is increased by adding more examples to the under‐sampled part of the data space. Examples are created by random selection from the training set and white noise is added. After balancing, the neural network's performance improved significantly. Testing the neural network on two wells indicated that this method is capable of predicting the entire range of permeability with confidence.
CHANGES DURING LACTATION IN THE COMPOSITION OF THE MILK OF THE BLACK RHINOCEROS Diceros bicornis*
Authors: Gregory Margaret E. , Rowland S. J. , Thompson S. k. , Kon Vanda M.
Published: December 2007

1. Samples of milk were obtained from a lactating rhinoceros five hours, 12 hours, 28 hours, 52 hours, two weeks and four weeks after the birth of the calf. Subsequently, samples were collected at monthly intervals until the calf was removed after sixteen months.

2. The total solids, fat, protein and lactose contents of the samples were determined. The fat content of the milk was low (0.45 per cent) throughout lactation. That of lactose was lower in colostrum (4.38 per cent) than in mature mdk (6.1 to 6.9 per cent), and that of the protein decreased from 6.4 per cent in colostrum to between 1 and 1.65 per cent in the milk.

3. Variations in the contents of acid, calcium, pantothenate, riboflavin, thiamine, Vitamin b6, Vitamin b12 and biotin in the milk were measured. Those of biotin, Vitamin b12 and pantothenate showed marked fluctations from month to month. That of riboflavin remained low in the milk, having been high in colostrum. The Vitamin b6 and thiamine contents both decreased during the first few months of lactation and then increased gradually.
NEW MONKEY HOUSE AT FRANKFURT ZOO
Authors: Scherpner Christoph
Published: December 2007

The Frankfurt Zoo Monkey House incorporates certain new technical features. Where cages are fronted with glass, reflections have been avoided by angling the glass sharply towards the public. As the result, it has been possible to have glass windows in the wall opposite and thus achieve a good growth of plants in the indoor public area and prevent the house from having a gloomy atmosphere. For reasons of animal psychology, short screening walls have been built into the cages: these split up the space visually for the monkeys but at the same time permit the visitor to see all the animals. Inferior animals in a group can withdraw to a peaceful corner. Great stress has been laid on equipping the inside cages to prevent parasites. Tiled walls, stainless steel climbing poles and plastic floor covering have been used. Another advance is the use of plastic material for the animals' door flaps: the plastic cannot injure the animals and they enable them to have a free choice, even in cold winter weather, between the inside and outside cage. Information is given to the public by means of a globe showing the threatened animal species of the world and by two display boards. Threatened species are also helped by a fountain, from which, each year, a considerable sum of money is collected for conservation purposes.
The Volcano rabbit: in the wild and at Jersey Zoo
Authors: DURRELL GERALD , MALLINSON JEREMY
Published: December 2007

The Volcano rabbit: in the wild and at Jersey Zoo
Preferred environmental temperatures of some captive mammals
Authors: DAGG ANNE INNIS
Published: December 2007

Preferred environmental temperatures of some captive mammals
Observations on Central American river turtles (Dermatemys mawi) at Fort Worth Zoo
Authors: CAMPBELL JONATHAN
Published: December 2007

The task of caring for the Central American river turtle Dermatemys mawi may prove more arduous a task than for other turtles. I observed that they are incompatible with members of their own species, but they can be successfully introduced with other aquatic reptile species. A water temperature of 28 to 30° (82 to 86°F) seems to satisfy their thermal requirements. In the wild, the turtle's diet apparently consists chiefly of aquatic plants. In captivity, however, a substitute diet of vegetables supplemented with fish has proved satisfactory. In selecting exhibits, the soft nature of their shells should be taken into consideration.