bluuebunny/crossref_metadata_2025_split huggingface dataset:
Organic ligand distribution and speciation in sedimentary basin brines, diagenetic fluids and related ore solutions
Authors: Giordano Thomas H. , Kharaka Yousif K. 
Published: April 2008

Abstract

The nature, distribution, and interactions of dissolved organic ligands in the shallower zones of sedimentary basins are highly variable and poorly understood. Better understood is the chemistry of dissolved aqueous carboxylic acid species in the deeper regions of sedimentary basins. In most oil-field brines, acetate is generally the dominant organic ligand and is followed in level of concentration by longer chained aliphatic monocarboxylic acid anions. The total concentration of dicarboxylic acid anions is probably lower than previously reported and likely less than 500 mg l
−1
with succinate and glutarate being the dominant species. The highest concentrations of organic acid anions are present in formation waters at 80–120° C. Based on the available field and laboratory evidence, the concentrations of organic anions are controlled mainly by the rates of their generation from kerogen and their destruction thermally or by bacteria. An extensive compilation of experimentally determined stability constants and other thermodynamic data for a large number of non-humic organic ligands is available for temperatures near 25° C. However, corresponding high-temperature data are available for only a few species of interest; most notably, acetate complexes of some rock- and ore-forming metals and protonated species of several carboxylate ligands. Simulations of speciation in oil-field brines show that significant amounts of Ca, Mg, Fe, and Al can be complexed by carboxylate ligands, in the pH range 4–6, if ligand concentrations are on the order of 10–100 mg l
−1
. Calculated speciation in model ore fluids for Mississippi Valley-type deposits and red-bed related base metal deposits show that optimum conditions for Pb and Zn transport by organic ligand complexation are oxidized ore fluids with total reduced inorganic sulphide concentration less than 10
−9
molal.
Modern and fossil mangroves and mangals: their climatic and biogeographic variability
Authors: Plaziat Jean-Claude 
Published: April 2008

Abstract

The variability of mangrove environments (mangals) has generally been underestimated, as has their distribution from temperate to subequatorial climates and their histories in the Atlantic and Indo-Pacific biogeographic provinces. Subtropical, arid and equatorial mangals require different palaeoecological approaches.
In situ
fossilization is paradoxically very rare, and has often been misinterpreted, but current reworked shells, and human shell gathering (middens) provide valuable records of ancient mangals. The identification of ancient mangroves depends on the preservation of pollen or wood while the upward branching root system of
Avicennia
is another reliable indicator. The associated molluscan fauna may also be diagnostic, particularly if encrusting oysters are preserved with imprints of mangrove roots and bark. Several case studies are briefly reviewed and discussed: Holocene buried mangals of Abu Dhabi, Holocene shell middens of the Middle East, Miocene Japanese and European mangals documented by molluscs and pollen, and the Paleocene-Eocene mangals of western Europe. Problems concerning the evolution of the mangal biota and the differences between their distribution in ancient and modern climates forms the basis for discussion of the palaeogeographic and climatic significance of the palaeomangals reviewed in this paper.
Modelling Late Jurassic Milankovitch climate variations
Authors: Valdes P. J. , Sellwood B. W. , Price G. D. 
Published: April 2008

Abstract

Although largely circumstantial in character, evidence for orbitally-forced (Milankovitch) climate changes in Jurassic microrhythmic successions, such as those of the Lias and Kimmeridgian, is becoming more persuasive. We present here the results of experiments, using a general circulation model, testing ways in which orbitally-induced variations in solar energy might be translated into a Jurassic climate response. In particular, we address the problem of the 100 ka (eccentricity-forced) cycle. This is generally considered to have only a small direct effect on solar input. It would be expected to have little impact on an ice-free Earth (commonly assumed for the Jurassic). Nonetheless, this weak signal is claimed to have been recognized in many Jurassic successions. Our results simulate, for the Late Jurassic, the possible effects at the ‘minimum’ and ‘maximum’ extremes of seasonal forcing (i.e. comparable with those affecting the Earth at 115 and 9 ka
bp
, respectively). Model predictions are critically evaluated against the geological database. At times of ‘minimum seasonal forcing’ there is a significant expansion in the area of the Northern hemisphere monsoon. In the tropics, changes in precipitation predominate over changes in temperature, whereas at high southern latitudes there are very large seasonal variations in temperature, and heavy winter snows. During these times the model is close to predicting a modest, but significant, Jurassic ice-cap in the Antarctic. Ice build-up is particular larly likely over uplands. Such an ice-cap disappears at times of ‘maximum seasonal forcing’. Waxing and waning of ice may thus provide the elusive mechanism for metre-scale sea-level changes. It is argued that apparently similar microrhythms (e.g. limestone-shale) might be the sedimentary response to different climatic signals in different climate zones, cause and effect being exactly the opposite in some circumstances.
Hydrocarbon habitat and classification of inverted rift basins
Authors: Macgregor Duncan S. 
Published: April 2008

Abstract
This shortened paper presents a brief analysis of the relationship between hydrocarbon distribution and the intensity of inversion in rift basins. For this purpose, three intergradational classes of rift were identified according to the intensity and areal extent of inversion-related uplift. Simple rifts, showing no significant inversion, are characterised by high success rates and dispersed hydrocarbon distributions. Locally inverted rifts, such as those showing restricted areas of uplift along faults, also show a high degree of petroleum retention and success, with the key success factor often being the relationship between timing of trap formation and petroleum charge. Regionally inverted rifts show lower success rates, failures being often attributable to a redistribution of hydrocarbons during inversion, with losses having occurred through biodegradation, surface erosion or seepage on surface penetrating faults. Both types of inverted rift frequently show a concentration of reserves in one large field.
Applications of Thermal History Reconstruction in inverted basins
Authors: Green Paul F. , Duddy Ian R. , Bray Richard J. 
Published: April 2008

Abstract

Studies of inverted basins based solely on the preserved section provide only partial insight into the thermal and tectonic history of basin development. Equally important is that part of the history represented by section removed by erosion during inversion. Thermal History Reconstruction, involving application of Apatite Fission Track Analysis (AFTA™) and Vitrinite Reflectance (VR) to define the timing and magnitude of key erosional and/or thermal episodes, and integration of this information with data from the preserved section, provides a more complete description. Case histories from the UK, New Zealand and Australia are presented to demonstrate this approach. Much of northern and eastern England, the Irish Sea and the Southern North Sea was affected by heating apparently due largely to additional burial, followed by early Tertiary cooling due to regional uplift and erosion, synchronous with recognized basin inversion events. Heating associated with this episode caused generation of hydrocarbons throughout the region. Areas conventionally regarded as not inverted appear to have been subjected to km-scale uplift and erosion, which was not restricted to classic ‘inversion axes’. Failure to allow for these effects can lead to a significant underestimation of regional maturity trends. Thermal History Reconstruction is also essential in areas that have undergone more than one episode of inversion. For example in Inner Moray Firth well 12/16—1 maximum palaeotemperatures in the Carboniferous section were reached prior to Hercynian inversion and the chances of preserving any hydrocarbons generated from Carboniferous or older source rocks appear poor. In southeastern Australia, early Cretaceous rift basins underwent mid-Cretaceous inversion at a time of high palaeogeothermal gradients (
c.
60°C km
−1
), and basement margins were also inverted at that time. Again, early generation implies that the chances of preservation of hydrocarbons are small. By integrating stratigraphic and structural relationships within the preserved section with data on the palaeo-thermal history of a section derived from direct measurements of palaeotemperature profiles, the complete history of hydrocarbon generation may be reconstructed with confidence.
Regional Tertiary Exhumation in and around the United Kingdom
Authors: Hillis Richard R. 
Published: April 2008

Abstract
Sonic velocities in the Upper and Middle Chalk, the Bunter Sandstone and the Bunter Shale were used independently to quantify apparent exhumation (amount of missing section) in the UK Southern North Sea (SNS). Apparent exhumation results derived from these units are statistically similar. The consistency of results from chalks, shales, and sandstones in the UK SNS, and in other areas (Inner Moray Firth and Celtic Sea/South-Western Approaches), suggests that, at a formation and regional scale, burial-depth is the primary control on velocity (and porosity) in these units, and validates the use of lithologies other than shale in maximum burial-depth determination. The consistency of apparent exhumation results from units of Early Triassic to Late Cretaceous age suggests that Tertiary exhumation was of sufficiently great magnitude to mask any earlier Mesozoic periods of exhumation, and that maximum Mesozoic-Cenozoic burial-depth was attained prior to Tertiary exhumation.
The analysis of sonic velocities, apatite fission tracks, vitrinite reflectance, normalized drilling rate and clay mineral diagenesis all suggest that there was a regional component of approximately 1 km of exhumation during Tertiary times, which affected structurally uninverted areas in and around the UK. The widely-recognized inversion-related exhumation is superimposed on regional Tertiary exhumation. Regional Tertiary exhumation need not have been contemporaneous with structural inversion. Further refinement beyond Tertiary age is not possible from the sonic velocity data. Regional exhumation, however, is most likely to be associated with regional Palaeocene or Oligocene/Miocene unconformities.
The evidence for regional exhumation implies that there was a pre-exhumational phase of burial (during which the eroded sedimentary rocks were deposited). Exhumation and prior burial associated with the regional Tertiary event need to be incorporated in aspects of basin analysis such as sediment decompaction and diagenetic and maturation modelling, and can, for example, account for the maturity of the Carboniferous of the onshore East Midlands Shelf, and the Lias exposed on the north coast of Somerset. The regional, Tertiary tectonic uplift associated with exhumation must have had a thick-skinned origin, and, in areas where there is no evidence for significant Tertiary igneous activity, a decoupled, two-layer model of lithospheric compression is invoked to account for the subsidence/uplift patterns of both inverted and uninverted areas.
The application of fission track analysis to the dating of barren sequences: examples from red beds in Scotland and Thailand
Authors: Carter Andrew , Bristow Charles S. , Hurford Anthony J. 
Published: April 2008

Abstract
In continental red-beds facies, which often contain little or no organic material for biostratigraphic dating, fission track (FT) analysis of detrital zircon crystals represents one method by which a maximum stratigraphic age may be determined. In addition, FT analysis of detrital apatite provides a means of palaeotemperature estimation, especially in areas where there is insufficient, or unsuitable, organic matter for vitrinite reflectance. Two examples of the application of FT analysis to the solution of stratigraphic problems in redbed sequences are described. In Scotland, the age of the Tongue Outlier is disputed, previous studies having suggested either a Devonian or Permo-Triassic age. Comparison of FT data from both detrital apatite and zircon indicates a Permo-Triassic age. In Thailand, the 3 km thick continental clastic Khorat Group has a well-defined lithostratigraphy but is poorly constrained biostratigraphically. The lower Nan Phong Formation has a Rhaetic age whilst the Khok Kruat Formation at the top of the group has been assigned an Aptian age. In the absence of any biostratigraphic control, the intermediate Phu Kradung and Phra Wihan Formations have been assumed to be of Middle and Upper Jurassic age. FT data presented here for detrital zircons indicate a Lower Cretaceous age for Phra Wihan Formation of the Khorat Group.
Early Tertiary evolution and sequence stratigraphy of the Faeroe-Shetland Basin: implications for hydrocarbon prospectivity
Authors: Ebdon C. C. , Granger P. J. , Johnson H. D. , Evans A. M. 
Published: April 2008

Abstract
Eight seismically resolvable packages have been identified in the Early Tertiary succession of the Faeroe-Shetland Basin. These packages are calibrated with the microfaunal and microfloral biostratigraphy, thus allowing correlation between wells and comparison with other basins. Mapping of the facies distribution within each package has allowed a detailed understanding of the evolution of the southwestern part of the basin, including the Quad 204 acreage. The development of the area can be related to the plate tectonic evolution of the North Atlantic and has highlighted implications for hydrocarbon exploration. In the earliest part of the Palaeocene (Sequences T10–T32) the position of the shelf/slope break was controlled by the underlying end Cretaceous fault induced topography. The depositional character of the submarine fans which accumulated in the basin is aggradational, collecting in basin floor deeps and progressively onlapping basin floor highs. Reservoir quality is initially controlled by depositional facies but is, essentially, excellent. Basinal muds, particularly regionally extensive maximum flooding surfaces, are believed to provide effective seals. Sequences T36–T40 are progradational in character, the position of the shelf/slope break advancing significantly beyond the positions of underlying Cretaceous fault scarps. This change in depositional character is related to thermal doming and rifting in the North Atlantic. The results of this uplift in the Faeroe-Shetland Basin also instigated a change in sediment provenance, volcanism and the deposition of extensive base-of-slope fan systems. Reservoir effectiveness remains excellent in these fan systems and potential seals are provided by downlapping, progradational shelf/slope systems. Sequences T45 and T50 represent flooding of the Palaeocene shelf systems as the thermal dome collapsed and rifting progressed. The overall control on Early Tertiary reservoir effectiveness in the Faeroe-Shetland Basin is depth of burial. In this part of the basin the Early Tertiary reservoir sands are generally buried at depths less than 2.5 km below sea-bed and reservoir quality remains excellent (porosity > 25% and permeability > 100 Md). The challenge to the oil industry is to understand the charge of this attractive hydrocarbon play.
The formation of passive margins: constraints from the crustal structure and segmentation of the deep Galicia margin, Spain
Authors: Boillot G. , Beslier M. O. , Krawczyk C. M. , Rappin D. , Reston T. J. 
Published: April 2008

Abstract
The crustal structure of the Mesozoic deep Galicia margin and adjacent ocean-continent boundary (OCB) was investigated by seismic reflection (including pre-stack depth migration and attenuation of seismic waves with time). The seismic data were calibrated using numerous geological samples recovered by drilling and/or by diving with submersible.

The N-S trending margin and OCB are divided in two distinct segments by NE-SW synrift transverse faults locally reactivated and inverted by Cenozoic tectonics. The transverse faulting and OCB segmentation result from crustal stretching probably in a NE-SW direction during the rifting stage of the margin in early Cretaceous times. The Cenozoic tectonics are related to Iberia-Eurasia convergence in Palaeogene times (Pyrenean event). In both segments of the deep margin, the seismic crust is made of four horizontal layers: (1) two sedimentary layers corresponding to post- and syn-rift sequences, where velocity ranges from 1.9 to 3.5 km s
−1
, and where the
Q
factor is low, the two sedimentary layers being separated by a strong reflector marking the break-up unconformity; (2) a faulted layer, where velocity ranges from 4.0 to 5.2 km s
−1
, and where the
Q
factor is high. This layer corresponds to the margin tilted blocks, where continental basement and lithified pre-rift sediments were sampled; (3) the lower seismic crust, where the velocity (7 km s
−1
and more) and the
Q
factor are the highest. This layer, probably made of partly serpentinized peridotite, is roofed by a strong S-S’ seismic reflector, and resting on a scattering, poorly reflective Moho.

A composite model, based both on analogue modelling of lithosphere stretching and on available structural data, accounts for the present structure of the margin and OCB. Stretching and thinning of the lithosphere are accommodated by boudinage of the brittle levels (upper crust and uppermost mantle) and by simple shear in the ductile levels (lower crust and upper lithospheric mantle). Two main conjugate shear zones may account for the observations and seismic data: one (SZ1), located in the lower ductile continental crust, is synthetic to the tilting sense of the margin crustal blocks; another (SZ2), located in the ductile mantle, accounts for the deformation of mantle terranes and their final unroofing and exposure at the continental rift axis (now the OCB). The S-S′ reflector is interpreted as the seismic signature of the tectonic contact between crustal terranes and mantle rocks partly transformed into serpentinite by syn-rift hydrothermal activity. It is probably related to both shear zones SZ1 and SZ2. The seismic Moho is lower within the lithosphere, at the fresh-serpentinized peridotite boundary.
Permo-Triassic sedimentary and volcanic rocks in basins to the north and west of Scotland
Authors: Hitchen K. , Stoker M. S. , Evans D. , Beddoe-Stephens B. 
Published: April 2008

Abstract
Red-bed sequences of known or inferred Permian and Triassic age are preserved in numerous offshore basins to the north and west of Scotland. These developed following the Late Carboniferous Variscan Orogeny, as compressive uplift was superseded by a tensional stress regime causing the fragmentation of the Variscan foldbelt and its northern foreland. Basin formation persisted through the Permian and Triassic periods, and the sediment infills reflect syn- and post-depositional fault activity. Syndepositional basins take the form of deep, fault-bounded half-grabens whose development was controlled by the extensional reactivation of earlier (Precambrian/Caledonian) thrusts and transfer faults. These basins accumulated wedge-shaped packages of sediment dipping into major basin-bounding faults. In contrast, post-depositional basins are characterized by a parallel-bedded infill which appears to reflect local preservation as a result of later faulting. These basins may be Late or post-Triassic in age. The Permo-Triassic rocks were deposited during a period of major regression, with fluviatile, lacustrine and aeolian environments predominating. Principal lithologies include sandstones, that are partly conglomeratic, intercalated with mudstones and claystones. The localized development of carbonates and evaporites indicates some marine influence. Palaeontological data are commonly sparse throughout the succession and generally cannot readily differentiate the two systems. There is limited evidence for both Early Permian and Late Triassic volcanism. The Early Permian volcanism was ‘within-plate’ and ‘continental’ in character, and was probably related to the first phase of post-Variscan continental disintegration. The Late Triassic volcanism indicates a subsequent episode of synrift igneous activity west of Britain and Ireland.
A gravity map of Ireland and surrounding waters
Authors: Readman P. W. , O’Reilly B. M. , Edwards J. W. F. , Sankey M. J. 
Published: April 2008

Abstract
A Bouguer gravity map of Ireland and the surrounding shallow seas has been produced in the form of a vertically illuminated shaded relief image. This method of presentation accentuates subtle trends in the gravity field which reflect complex density variations present in the crust beneath Ireland. These can be correlated with well known geological features in the onshore region, such as Caledonian granites and major faults. The large normal fault systems which bound offshore Mesozoic basins are clearly indicated by strong gravity lineaments with a similar underlying Caledonian trend. In many cases these can be traced onshore to known Caledonian faults. Transverse Caledonian and Variscan tectonic trends are also highlighted by the method.
Tertiary uplift and inversion history in the North Celtic Sea Basin and its influence on source rock maturity
Authors: Murdoch L. M. , Musgrove F. W. , Perry J. S. 
Published: April 2008

Abstract
Tertiary uplift and basin inversion have been widely recognized in the area of the North Celtic Sea Basin offshore Ireland, but the magnitude and timing of the various events have not been well documented. An understanding of these events is important because recent basin history generally has a major influence on hydrocarbon source rock maturity levels. A multi-disciplinary approach was used to investigate the timing and nature of uplift in the North Celtic Sea Basin, involving seismic data interpretation, well log correlation, vitrinite reflectance measurement, apatite fission track analysis and a Cretaceous Chalk Group isopach and velocity study.
Both regional uplift and compressive inversion can be interpreted to have occurred, based on missing geological section, compressive reactivation of earlier normal faults and basin-centred uplift. Two Tertiary erosion events are recognized: a regional uplift in the Palaeocene, and compressive inversion characterized by basin doming and fault reversal, probably associated with an Oligo-Miocene phase of the Alpine Orogeny. Separating these was a period of basinal deposition in the Eocene to Oligocene. A map of the magnitude of erosion generated as a result of the two events shows that the amount of uplift is quite variable. In the northeast part of the basin, where the later event was most severe, uplift was as much as 1100 m. Reconstruction of the basin geometry before inversion, together with thermal modelling at selected well locations, suggests that Upper Jurassic source rocks reached maturity for oil generation only in the central portion of the basin, whereas Lower Jurassic source rocks entered the gas window in much of the basin prior to Tertiary uplift.