bluuebunny/crossref_metadata_2025_split huggingface dataset:
Petroleum systems in the South Atlantic margins
Authors: Schiefelbein C. F. , Zumberge J. E. , Cameron N. R. , Brown S. W. 
Published: April 2008

Abstract
Results obtained from the detailed geochemical analysis of more than 150 crude oils were used to : (1) identify a number of different petroleum systems present in the South Atlantic margins; and (2) establish geochemical criteria useful in distinguishing lacustrine-derived oils from marine-derived oils. The multiplicity and type of effective source rocks were determined by using the geochemical characteristics of the crude oils to establish the number of compositionally distinct oil families, and by inferring palaeoenvironmental conditions of source rock deposition and possible age. Using multivariate statistical techniques and bulk geochemical parameters, isotopic compositions and biomarker distributions, a number of general petroleum systems were identified, differing from each other in terms of source palaeoenvironment and age. The oils are separated into two broad groups: lacustrine and marine. Further detailed examination of each broad group, sometimes using more specific geochemical criteria, typically resulted in the establishment of sub-groups of oils according to specific source environment, such as lacustrine fresh v. saline conditions. Areas where oils of mixed provenance occur are also identified. The geochemical criteria used in discriminating between lacustrine and marine oil types were determined based on geochemical differences that exist between known marine-sourced (mainly post-salt) oils from the Kwanza and Gabon (Port Gentil area) Basins and known lacustrine-sourced (pre-salt) oils from the Congo Basin.
Angola: source rock control for Lower Congo Coastal and Kwanza Basin petroleum systems
Authors: Burwood R. 
Published: April 2008

Abstract

The purpose of this paper is to provide an overview of petroleum occurrence and provenance for the 1000 km West African Atlantic Margin from Cabinda to mid-Angola. Over this margin the Lower Congo Coastal and Kwanza provinces cumulatively account for reserves of
c.
6 gigabarrels oil recoverable (GBOR). These are dominantly reservoired in Pinda carbonate traps of the former basin. However, with production from a range of aggradational wedge, carbonate platform and pre-salt reservoirs, a diversity in oil character presupposes complex hydrocarbon habitats charged by multiple sourcing.

Each of these two major Atlantic margin salt basins constitutes a different, source rock driven, hydrocarbon habitat. As classic passive margin pull-apart basins, Early Cretaceous initiated rift events (Pre-rift, Syn-rift I, II, etc.) evolved into the drift phase opening of the southern Atlantic. A striking feature of this progression was widespread evaporite deposition of the Aptian Loeme salt. This separates two distinct sedimentary and tectonic domains of the Pre- and Post-Salt.
The core Lower Congo Coastal habitat is dominated by the Pre-Salt Bucomazi Formation sourced ‘poly’ petroleum system. These lacustrine, often super-rich, sediments reveal considerable organofacies variations between their basin fill (Syn-rift I) and sheet drape (Syn-rift II) development, accounting for the compositional diversity in their progenic petroleums. Of crucial impact is a cognate diversity in their kerogen kinetic behaviour. This controls the conditions and timing of generation and realization of charge potential.
With the Lower Congo Coastal habitat extending southwards towards the Ambriz Spur, the Bucomazi facies proper appears restricted to the northern and deeper proto-lake trend. Over the more weakly subsident margins such troughs host inferior sheet drape potential. Elsewhere, Upper Cretaceous-Palaeogene marine clastic Iabe Formation sourced petroleum systems are hydrocarbon productive, yielding petroleums of unique, and/or mixed Pre-Salt hybrid, source provenance.
A less attractive Pre-Salt source system is reflected in the Kwanza habitat. Consequential effects of salt movement have proved important for halokinetic induced structuration, Cretaceous block rafting and pseudograben (Tertiary trough) source deposition. Marginal reserves of Infra-Cuvo and Cuvo derived petroleums are known. With limitations in charge potential at this level, the modest Kwanza reserves (0.1 GBOR) have a Post-Salt provenance deriving primarily form the Eocene Margas Negras and subordinate Aptian Middle Binga sourced petroleum systems. Cases of multi-sourced hybrid petroleums abound. In addition to the organic-rich Albian micrites, Upper Cretaceous black shales provide unproven possible offshore potential.
Palaeoenvironmental evolution of the Late Cretaceous sequence in the Tarfaya Basin (southwest of Morocco)
Authors: El Albani A. , Kuhnt W. , Luderer F. , Herbin J. P. , Caron M. 
Published: April 2008

Abstract
The Late Cretaceous sedimentary evolution of the Tarfaya Basin is reviewed based on late Albian-Campanian outcrops and two cored exploration wells (S13 and S75) with a stratigraphic range from the early Cenomanian to the late Turonian. Standard sedimentological and micropalaeontological methods were used, together with clay mineralogy and organic geochemistry. Two distinct depositional environments were found. The first is late Albian-early/middle Cenomanian in age and dominated by terrigenous silici- and bioclastic sediments containing primarily terrestrial organic matter with a low organic content. Abundant illite and chlorite, eroded from crystalline rocks outcropping in the Anti-Atlas mountain and Mauritanides is present, as is abundant kaolinite reworked from soils surrounding the Tarfaya Basin. The second environment comprises late Cenomanian-Campanian sediments characterized by pelagic marls and limestones with a high organic content and a abundant pelagic macro- and microfauna. These sediments, which were probably deposited in an upwelling system, are characterized by higher contents of smectite.
The interpretation of passive margin depositional processes using seismic stratigraphy: examples from offshore Namibia
Authors: Bagguley Joanne , Prosser Sarah 
Published: April 2008

Abstract
Seismic stratigraphic analysis of the post-rift megasequence of the Namibian passive continental margin has enabled depositional features to be interpreted in terms of the likely controls on their formation. The scale of the information derived from this manner of depositional system analysis is fundamental in understanding processes of sedimentation on passive margins; processes which may not be so readily apparent at field or well-log scale studies. Inner shelf channel forms are interpreted as incised valleys, created during a fall in relative sea level. The horizontal nature of the seismic facies infilling these valleys suggests that they filled during progressive periods of rising relative sea level, implying late lowstand or transgressive sediments. A series of low mounded features can also be identified on the shelf, which may be interpreted as palaeodune fields, carbonate build-ups or longshore clastic mounds. The outer shelf and upper slope positions reveal interpreted canyon and channel forms. The infill to these features contrasts with that of the incised valleys by having a more draped from (sometimes with a chaotic unit below); a geometry consistent with submarine origins. The submarine canyons may be termed attached or detached depending on whether they can be shown to link back into fluvial systems on the shelf; attached canyons will be more likely to be able to support the development of deepwater, sand-rich submarine fans. In the slope/base of slope area both regionally extensive and more localized mounds can be interpreted as mass transport deposits, the trigger for which may be attributed to a relative sea-level fall (due to their connection to the valley and canyon systems), though a transgressive origin may also be consistent in some cases. The mounds seen in positions deepest in the basin have a markedly different seismic facies to those at the base of slope and a different depositional system may be invoked, perhaps that dominated by distal turbidity currents or waning bottom currents.
Facies architecture of the Etjo Sandstone Formation and its interaction with the Basal Etendeka Flood Basalts of northwest Namibia: implications for offshore prospectivity
Authors: Jerram Dougal A. , Mountney Nigel , Stollhofen Harald 
Published: April 2008

Abstract
The Basal Etendeka Flood Basalt stratigraphy in the Huab Basin of northwest Namibia comprises a series of lava flows interleaved with aeolian sandstone bodies of the Etjo Sandstone Formation. The sandstone units are characterized by three main types: (1) the major erg — a mixed aeolian and fluvial facies up to 150 m thick; (2) minor ergs — aeolian facies which occur directly above the first volcanic units and are up to 60 m thick; (3) isolated bodies — multidune, single dune and lava topography infills. A variety of bypass surfaces identified by sand-filled cracks and sediment-lava breccias occur on lava top surfaces. Preserved ripples and pahoehoe lava imprints indicate that the aeolian sand dunes were actively migrating during basalt emplacement.
Observations recorded in the Basal Etendeka Flood Basalts which may be of relevance to offshore hydrocarbon exploration include: a major-minor erg relationship resulting in large sandbodies up to 60 m thick which occur directly after the first volcanic units; the occurrence of sand-filled fissures up to 36 m in depth which would greatly influence connectivity in an offshore setting; the identification of bypass surfaces as marker horizons which may laterally correlate with isolated sandbodies.
Basin evolution and sedimentary fill in the Palaeozoic sequences of the Falkland Islands
Authors: Meadows Neil S. 
Published: April 2008

Abstract
The sedimentary sequences exposed on the Falkland Islands can be referred to two major episodes of basin evolution. On the basis of fieldwork and recent palynological determinations carried out as part of the study from which this publication is taken, the older of these is largely Middle Devonian in age and comprises a marine transgressive-regressive system culminating in extensive fluvial braidplain deposits which are referred to the Gran Malvinas Group. The younger is largely Permian in age, commences with a range of glacial deposits and includes lacustrine, shallow marine and deeper marine deposits before also culminating in fluvial channel deposits and is referred to the Lafonian Supergroup. The facies identified at outcrop and their relationships are described and presented herein as depositional models for the two major systems, while inferences derived from these models are used both to suggest the structural and tectonic history of the islands, and to erect a revised lithostratigraphy which relates to these episodes of basin evolution. It is recognized that this is an interim measure pending much more intensive work on the geology of the Falkland Islands which is currently taking place.
Fractal analysis and percolation properties of veins
Authors: Roberts S. , Sanderson D. J. , Gumiel P. 
Published: April 2008

Abstract

Systematic sampling of vein systems often reveals a power-law distribution of the number of veins (
N
) to the vein thickness (
t
) of the form
N
=

Ct
-D

. A comparison of vein thickness distributions from different geological settings establishes systematic variations between vein populations, with lower
D
-values characterizing well-connected vein systems. Low
D
-value vein systems are reported from mineral deposits and from veins developed within and around fault zones, often at constant vein frequency. Simple models are described to explain the field observations which suggest that the observed variations in vein thickness distributions are directly related to the connectivity of the sampled vein network.
Geometry and population systematics of a quartz vein set, Holy Island, Anglesey, North Wales
Authors: Stowell Julia F. W. , Watson Adrian P. , Hudson Neil F. C. 
Published: April 2008

Abstract

A steeply dipping set of quartz-chlorite-muscovite-biotite veins was emplaced, at depths of at least 14 km and temperatures >400°C, into Môna Complex metasedimentary rocks of Holy Island, after the D4 event. Vein trends range from northeast-southwest to north-northwest-south-southeast. Vein offshoots, consistently oriented
c.
10–35° anticlockwise relative to the main vein, are common. Quartz fibres within different veins show a range of orientations, from northwest-southeast to east-west, and are interpreted as tracking vein opening directions. Vein and fibre orientations are integrated into a four-stage model for vein emplacement. At each stage, new main veins either open extensionally, with fibres subnormal to their boundaries, or by hybrid extension-shear. Hybrid main veins commonly have extensional offsoots. Extensional main veins are orientated progressively further anticlockwise with time from a dominantly northeast-southwest trend to a dominantly north-south trend, but hybrid main veins have out-of-sequence orientations and probably utilized pre-existing fractures. The dominance of extensional and hybrid extension-shear vein opening indicates that the differential stress was small and pore fluid pressure was high. A study of length-thickness relationships has revealed that this vein set is self-affine with vein widening progressing more quickly than elongation during growth. Linear transect analyses show that the vein spacings have fractal characteristics.
Influence of layering on vein systematics in line samples
Authors: Gillespie P. A. , Johnston J. D. , Loriga M. A. , McCaffrey K. J. W. , Walsh J. J. , Watterson J. 
Published: April 2008

Abstract
The thickness and spacing systematics of 30 line samples of vein arrays at ten localities have been analysed. The analytical methods were tested on four synthetic data sets. The synthetic and natural data sets were each analysed with respect to: cumulative thickness v. distance; thickness population; spacing population; the coefficient of variation of spacing, which measures clustering; the mass function, which measures the scaling of strain heterogeneity.
A fundamental distinction is apparent between stratabound arrays, vein arrays in layered rocks where the veins are confined to individual mechanical units, and non-stratabound arrays which occur in rock volumes lacking persistent crack-stopping discontinuities. The stratabound arrays show regular spacing controlled by layer thickness and non-power-law thickness distributions. The non-stratabound arrays are clustered and have power-law thickness distributions resulting from the lack of a controlling length scale. Exponents of the thickness distributions have a modal value of 0.8 and do not vary significantly with lithology. Ore mineralization is favoured in non-stratabound arrays as they are more likely than stratabound arrays to form large clusters connected to a remote fluid source.
Critical stress localization of flow associated with deformation of well-fractured rock masses, with implications for mineral deposits
Authors: Sanderson David J. , Zhang Xing 
Published: April 2008

Abstract

Fluid flow and deformation of fractured rock masses is investigated using numerical models based on distinct element methods (UDEC) which couple mechanical and hydraulic behaviour. A series of numerical experiments is presented in which diffuse flow through fracture networks changes to highly localized flow at a critical stress state. Slip on parts of the fracture network causes the opening up of some fractures, often at fracture intersections. Thus, a change in the stress state results in a sudden localization of deformation and fluid flow. A series of plots of hydraulic conductivity v. differential stress are presented for some natural fracture networks to demonstrate the influence of fracture network geometry and
in situ
stress on the critical phase boundary between diffuse and localized flow.

The onset of localized deformation and fluid flow is a critical point phenomenon, resulting in fractal properties. Fractal and multifractal techniques are used to characterize heterogeneity of the flow in order to generalize the results of the modelling of discrete systems to a continuum-based description of the flow. The significance of the models and their implications for crustal behaviour are discussed in relation to hydrothermal mineralization and natural vein systems.
Alpine plate kinematics in the western Mediterranean: a westward-directed subduction regime followed by slab roll-back and slab detachment
Authors: Zeck H. P. 
Published: April 2008

Abstract
Integration of a wide range of multidisciplinary data, including seismic tomography features, regional tectonic transport directions and ages of subduction/collision, lithospheric extension and slab detachment, suggests a new model for the development of the Alpine belt in the western Mediterranean. The model implies that the backbone of the Alpine Orogeny was formed by a composite SW-NE-striking subduction system, active until some time before 22 Ma. The system which consumed Mesozoic Tethyan lithosphere was dipping westward under the leading edge of Iberia which was drifting eastward with respect to North America under the influence of the opening of the North Atlantic. Allowing for a series of late-stage extensional regimes, with local formation of Neogene oceanic lithosphere, in the Valencia Gulf, Provençal-Algerian basin and southern Tyrrhenian basin, and inherent slab roll-back, the original collision belt may be reconstructed comprising all present Alpine metamorphic core complexes in the western Mediterranean: Betic-Rif, Kabylies and the Sicily-Apennines(-Corsica) belt. It follows that in the western Mediterranean the northward drift of Africa against Iberia/Europe, although influential, e.g., in creating the E-W grain of the Betic Cordilleras, has not been the controlling factor. In contrast, in the eastern Mediterranean the influence of N-S convergence has been much more pronounced due to the hinged sinistral movement of the African plate. A major part of the Europe-Africa N-S convergence was accommodated in a coherent N-dipping subduction zone running from North Africa through Sicily-Calabria to Crete, becoming increasingly significant to the east.
The petroleum systems of the Southeast Basin and Gulf of Lion (France)
Authors: Mascle Alain , Vially Roland 
Published: April 2008

Abstract
The Southeast Basin is the thickest onshore French sedimentary basin where up to 10 km of Mesozoic-Cenozoic sediments can locally be found. This basin is surrounded to the east and to the south by two segments of the Alpine Thrust Belt, the Western Alps and the Pyrenees-Provence respectively, and to the west by recently uplifted elements of the Palaeozoic Basement (Massif Central). The development of the basin was related to several stages of subsidence between late Carboniferous and late Cretaceous times. Partial tectonic inversion took place during two Alpine compressive events in early Tertiary and late Tertiary times. They were separated by an intervening stretching event of Oligocene age which further south led to the opening of the western Mediterranean oceanic basin in Burdigalian times and, as a result, to the formation of the Gulf of Lion passive continental margin. In Neogene times the Palaeozoic basement of the Massif Central was uplifted to approximately 2000 m as the result of an ascending athenospheric plume.
A large oil seep near the city of Gabian has been exploited since the beginning of the seventeenth century. Most of the exploration undertaken from 1945 (onshore) and 1965 (offshore) to the present time has, however, been disappointing as no significant oil or gas accumulations have been discovered, despite drilling of about 150 wells. A recent re-assessment of the potential remaining prospectivity of the Southeast Basin and Gulf of Lion basin has been undertaken by IFP. This study has benefited from scientific researches developed within the Integrated Basin Studies programme. This paper focuses on the source rocks and the petroleum system aspects. The review of all potential source rocks indicates that, from a qualitative and quantitative point of view, the best source rocks are located within three specific stratigraphic intervals (Stephanian-Autunian, late Lias and late Eocene-Oligocene). This analytical work allowed the reconstruction of the history of the different petroleum systems from the Jurassic to the present day. Because of the severe tectonic disturbances that these areas have experienced in Tertiary times, we can conclude that the best potential for economical discoveries are within the Gulf of Lion and some sub-basins of the Southeast Basin where subsidence has been active in Neogene times, or, in other words, where the processes of hydrocarbon generation, expulsion and migration can still be active today.
Lithospheric structure of the Pannonian basin derived from seismic, gravity and geothermal data
Authors: Tari Gábor , Dövényi Péter , Dunkl István , Horváth Frank , Lenkey László , Stefanescu Mihai , Szafián Péter , Tóth Tamás 
Published: April 2008

Abstract
The structure of the Pannonian basin is the result of distinct modes of Mid-Late Miocene extension exerting a profound effect on the lithospheric configuration, which continues even today. As the first manifestation of extensional collapse, large magnitude, metamorphic core complex style extension took place at the beginning of the Mid-Miocene in certain parts of the basin. Extrapolation of the present-day high heat flow in the basin, corrected for the blanketing effect of the basin fill, indicates a hot and thin lithosphere at the onset of extension. This initial condition, combined with the relatively thick crust inherited from earlier Alpine compressional episodes, appears to be responsible for the core complex type extension at the beginning of the syn-rift period. This type of extension is well documented in the northwestern Pannonian basin. Newly obtained deep reflection seismic and fission-track data integrated with well data from the southeastern part of the basin suggests that it developed in a similar fashion.
Shortly after the initial period, the style of syn-rift extension changed to a wide-rift style, covering an area of much larger geographic extent. The associated normal faults revealed by industry reflection seismic data tend to dominate within the upper crust, obscuring pre-existing structures. However, several deep seismic profiles, constrained by gravity and geothermal modeling, image the entire lithosphere beneath the basin. It is the Mid-Miocene synrift extension which is still reflected in the structure of the Pannonian lithosphere, on the scale of the whole basin system.

The gradually diminishing extension during the Late Miocene/Pliocene could not advance to the localization of extension into narrow rift zones in the Pannonian region, except some deep subbasins such as the Makó/Békés and Danube basins. These basins are underlain coincidently by anomalously thin crust (22–25 km) and lithosphere (45–60 km). Significant departures (up to 130 mW m
−2
) from the average present-day surface heat flow (
c.
90 mW m
−2
) and intensive Pliocene alkaline magmatism are also regarded as evidence for the initiation of two newly defined narrow rift zones (Tisza and Duna) in the Pannonian basin system. However, both of these narrow rifts failed since the final docking of the Eastern Carpathians onto the European foreland excluded any further extension of the back-arc region.