bluuebunny/crossref_metadata_2025_split huggingface dataset:
A proposed latest Triassic to earliest Cretaceous microfossil biozonation for the English Channel and its adjacent areas
Authors: Ainsworth Nigel R. , Braham William , Gregory F. John , Johnson Ben , King Christopher 
Published: April 2008

Abstract
Three detailed biostratigraphic zonations, based on ostracods, foraminiferids and dinocysts, are proposed for the latest Triassic through to the earliest Cretaceous of the Portland-Wight Basin and its adjacent areas. A total of 112 zones-zonules (34 ostracod zones/subzones, 25 foraminiferid zones, 53 dinoflagellate zones, subzones and zonules) are recognized. All three zonation schemes are based on samples obtained from both outcrop (the Dorset coast) and boreholes, the latter from ditch cuttings, with some conventional and sidewall core samples, in association with published data, and have where possible been calibrated to the standard ammonite zones recognized throughout northwest Europe.
Multiple heating episodes in the Wessex Basin: implications for geological evolution and hydrocarbon generation
Authors: Bray Richard J. , Duddy Ian R. , Green Paul F. 
Published: April 2008

Abstract
The timing of maturity development and hydrocarbon generation with respect to structuring is a primary factor controlling oil and gas accumulation. Hydrocarbon generation is largely a temperature-dependent process and in order to predict accumulation it is necessary to reconstruct thermal history. In this study of the Wessex Basin and adjacent areas, direct thermal history data are obtained from Apatite Fission Track Analysis (AFTA) on samples from wells, shallow boreholes and outcrops, enabling the key facets of a complex thermal and tectonic history to be reconstructed. Several distinct styles of thermal history are recognized, with clear differences across the region in the time of cooling from maximum palaeotemperatures. Areas of east Devon show evidence of an early thermal episode, sometime after the mid-Triassic and before ∼170 Ma. The cause remains uncertain at present. In the area of the ‘Wytch Farm block’ maximum palaeotemperatures were reached prior to cooling in the early Cretaceous, in the range ∼140–100 Ma, due mainly to uplift and erosion. This area remained relatively high through the rest of its history compared to the areas to the north and south. The Lias (early Jurassic) was not heated sufficiently to cause significant generation and any that occurred effectively ceased in the early Cretaceous. South of the Portland-Isle of Wight faults, maximum palaeotemperatures were reached prior to cooling due to uplift and erosion in the mid- and late Tertiary, at ∼40 Ma and ∼20 Ma, respectively. Tertiary uplift and erosion affected a wide region. Maximum erosion occurred immediately to the south of the Purbeck structure where maturation of Lias source rocks continued through peak oil and into the gas generation phase until terminated by the Tertiary cooling. In most wells, AFTA and vitrinite reflectance data define low or non-linear palaeogeothermal gradients indicative of an element of heating due to fluid movement in addition to heating due to burial, making quantitative estimation of erosion difficult, but any reasonable model requires kilometre-scale uplift and erosion over a wide region. West of Portland in Lyme Bay, a key question is whether maturation history is dominated by early Cretaceous or by mid- to late Tertiary events. At present there are not sufficient data to extrapolate confidently from the area of well control east of Portland. No parts of the basin are currently generating hydrocarbons, implying that surface seepages are from previously reservoired accumulations.
Influence of salt on the structural evolution of the Channel Basin
Authors: Harvey Michael J. , Stewart Simon A. 
Published: April 2008

Abstract
The north margin of the Channel Basin is defined in Dorset and the Isle of Wight by Mesozoic extensional faults which were reversed during Tertiary contraction, causing forced folding of the Albian-Oligocene post-rift cover. The resulting contractional structures (the Purbeck and Isle of Wight Monoclines and the reversed Abbotsbury-Ridgeway Fault) have previously been used as type examples for inversion tectonics. The Jurassic-Cretaceous basin margin crosses the eastern edge of a Triassic salt basin (Dorset Halite, Upper Triassic Mercia Mudstone Group) near Swanage. Detachments in Triassic salt around Weymouth resulted in extension and inversion styles which differ from the better known basement-linked structures to the east. The Abbotsbury-Ridgeway Fault is listric and unlike the Tertiary hangingwall folds to the east the Weymouth Anticline formed as an extensional rollover, only tightened during inversion.
Seismic and well data and structure maps are used to illustrate for the first time the increasing effects of salt on structural style as the salt thickens westwards. The onset of detachment on the basin margin is placed at Ringstead, where a north-stepping shift in the margin at pre-salt level defines a relay zone. Here extension was accommodated on many basement faults and the ratio of basement fault displacement to salt thickness was reduced sufficiently to allow the post-salt section to detach throughout extension (Abbotsbury-Ridgeway Fault). Tight Tertiary compressional folds in this area may result from linkage of the pre- and post-salt sections during inversion, a consequence of salt welds developed during the last stages of extension.
In the western part of the Channel Basin (Lyme Bay) the Triassic salt is sufficiently thick to have detached the pre- and post-salt sections over a wide area. North-south shortening during basin inversion may have been accommodated in the Lyme Bay post-salt section by displacements on conjugate, northwest-southeast- and northeast-southwest-oriented, strike-slip faults such as the Mangerton Fault. The Dorset Halite is a complex sequence of halite and mudstone interbeds, different from the ‘pure’ halites seen in the North Sea Basin, and its influence on structural style differs accordingly. Variation in salt tectonics style between the Weymouth area (salt swells and rollers) and Lyme Bay (salt rollers only) may reflect lateral facies variation and hence rheology in the Dorset Halite Formation.
Transpression and transtension zones
Authors: Dewey J. F. , Holdsworth R. E. , Strachan R. A. 
Published: April 2008

Abstract

Transpression and transtension are strike-slip deformations that deviate from simple shear because of a component of, respectively, shortening or extension orthogonal to the deformation zone. These three-dimensional non-coaxial strains develop principally in response to obliquely convergent or divergent relative motions across plate boundary and other crustal deformation zones at various scales. The basic constant-volume strain model with a vertical stretch can be modified to allow for volume change, lateral stretch, an oblique simple shear component, heterogeneous strain and steady-state transpression and transtension. The more sophisticated triclinic models may be more realistic but their mathematical complexity may limit their general application when interpreting geological examples. Most transpression zones generate flattening (
k
< 1) and transtension zones constrictional (
k
> 1) finite strains, although exceptions can occur in certain situations. Relative plate motion vectors, instantaneous strain (or stress) axes and finite strain axes are all oblique to one another in transpression and transtension zones. Kinematic partitioning of non-coaxial strike-slip and coaxial strains appears to be a characteristic feature of many such zones, especially where the far-field (plate) displacement direction is markedly oblique (<20°) to the plate or deformation zone boundary. Complex foliation, lineation and other structural patterns are also expected in such settings, resulting from switching or progressive rotation of finite strain axes. The variation in style and kinematic linkage of transpressional and transtensional structures at different crustal depths is poorly understood at present but may be of central importance to understanding the relationship between deformation in the lithospheric mantle and crust. Existing analyses of obliquely convergent and divergent zones highlight the importance of kinematic boundary conditions and imply that stress may be of secondary importance in controlling the dynamics of deformation in the crust and lithosphere.
Extended models of transpression and transtension, and application to tectonic settings
Authors: Fossen Haakon , Tikoff Basil 
Published: April 2008

Abstract
We introduce a spectrum of transpressional and transtensional deformations that potentially result from oblique plate interaction. Five separate types of deformation are designated, in which a simple shear deformation is combined with an orthogonal coaxial deformation. The types vary in the amount of extension v. contraction, both parallel to the margin and vertically. The interaction between the angle of convergence, kinematic vorticity, infinitesimal strain axes, finite strain, and rotation of material lines and planes is investigated. Quantification of the finite strain indicates that the orientation, magnitude, and geometry (flattening, constriction, etc.) change continually during steady-state transpression.
These results are then applied to the cases of transpression, particularly resulting from oblique plate convergence of terranes. The obliquity of plate motion and the geometry of the plate margin determine which of the types of transpression or transtension is favoured. A component of margin-parallel stretching also potentially causes terrane motion to locally exceed oblique plate motion, or move opposite to the general direction of movement between the converging plate boundaries. The kinematic models also suggest that the boundaries between converging terranes are likely to exhibit vertical foliation, but either vertical or horizontal lineation. Finally, narrow transpressional zones between colliding blocks may have very high uplift rates, resulting in exhumation of high-grade metamorphic fabrics.
Strike-slip partitioned transpression of the San Andreas fault system: a lithospheric-scale approach
Authors: Teyssier Christian , Tikoff Basil 
Published: April 2008

Abstract
Physical and numerical experiments on transpression indicate that strike-slip partitioning is facilitated by low angle of convergence, such as occurs on the modern San Andreas fault system. Cross-sections across the San Andreas fault overestimate the amount of margin-normal contraction, because they do not include the effect of horizontal stretching caused by the wrench component of deformation. When this correction is made assuming a strike-slip partitioned transpression model, contraction estimated from cross-sections is consistent with both the normal and tangential movements imposed by plate motion: there is no San Andreas discrepancy.
Seismic anisotropy (shear-wave splitting) and teleseismic analyses suggest that the upper mantle in the San Andreas region is thick and largely undeformed to the SW of the San Andreas fault, but thin and intensely sheared in a zone 50–100 km wide beneath the NE region of the San Andreas fault system. Seismic anisotropy is best explained by a transpression zone of vertical foliation (and possibly horizontal lineation) which penetrates the asthenospheric mantle. Using a lithospheric-scale approach, the transfer of the displacement field from the penetratively deformed mantle to the strike-slip partitioned upper crust necessitates zones of accommodation in the mid- to lower crust, corresponding to the flatlying detachments that underlie the San Andreas fault system. The mechanics of the San Andreas fault are best considered in connection with the strength of the various lithospheric layers involved in this system.
Transtension in southeastern Africa associated with Gondwana break-up
Authors: Watkeys M. K. , Sokoutis D. 
Published: April 2008

Abstract
The southeastern margin of Africa is marked by a zone of complex faulting associated with crustal extension related to the Mesozoic break-up of Gondwana. The oldest age of faulting (180–175 Ma) displays differences in style in regions with Archaean as opposed to Proterozoic basement. Faulting in the Archaean region shows extension normal to the proto-plate boundary whereas transtension prevailed in the Proterozoic region. The north-south trending normal faulting in the Archaean craton, which cuts across basement trends, displays an asymmetry indicating simple shear extension of the lithosphere. In contrast, transtension occurred in the region of Proterozoic basement by ENE strike-slip movement of blocks along terrane boundaries. As these blocks moved, normal faults developed behind them as well as within them at high angles to the terrane boundaries, to accommodate extension. Analogue modelling reproduced the observed different fault patterns. It is proposed that sinistral movement along the interconnected Gastre Fault System and Falkland-Agulhas Fracture Zone, together with the presence of a releasing bend, are the reasons for extension in the Lebombo region. This movement may have been caused by plate edge events between the Patagonia block and the proto-Pacific Ocean.
Transpressional tectonics and strain partitioning during oblique collision between three plates in the Precambrian of southeast Brazil
Authors: Ebert Hans Dirk , Hasui Yociteru 
Published: April 2008

Abstract

Two orogenic belts have been recognized in south-east Brazil, which are interpreted to have been formed as a product of diachronous collisions between three continental plates. Wide crustal-scale shear belts have developed both between and inboard of the collided and amalgamated plate borders. These shear belts record frontal, oblique or lateral displacements during oblique plate converence and A-type subduction. The overall structural style of each belt depends on the angle subtended between the plate boundary and the convergence vector. The E-W branch between the São Paulo and Brasília plates, the Campo do Meio strike-slip shear belt, has undergone dominantly sinistral wrench dominated transpression along a set of folds and shear zones dipping southwards. The NE-SW branch between the São Paulo and Vitória plates, the Paraíba do Sul strike-slip shear belt, has undergone a partitioned dextral transpression, whereas the north-south branch between the Brasília and Vitória plates, the Paraíba do Sul strike-slip shear belt, has undergone a partitioned dextral transpression, whereas the north-south branch between the Brasília and Vitória plates is essentially a frontal thrust system with only a weak component of dextral strike-slip. These complex structural patterns, formed at deep to mid-crustal levels, reflect temporal and spatial partitioning at all scales between flattening and non-coaxial deformation, and down-dip and strike-slip shearing, in tangential as well as in transcurrent structural domains. Additionally, this area demonstrates that regional flower structures, lateral extrusion and other secondary deformations across the
yz
sections of transpressional belts are important in accommodating shortening in obliquely convergent orogens.
The main phase of the Hercynian orogeny in the Pyrenees is a dextral transpression
Authors: Gleizes G. , Leblanc D. , Bouchez J. L. 
Published: April 2008

Abstract

Synthesis of several recent structural studies in the Pyrenees points to a syntectonic emplacement of granitic plutons, more or less early during the D2 main phase of the Hercynian orogenesis. A dextral E-W component of simple shear is demonstrated for D2, which was previously considered as a pure N-S compression. This component is recorded in the granites by large shear bands and sigmoidal features, and in the country rocks by asymmetrical strain shadows of foliation trajectories in map view and by systematically dextral sense of shear in
xz
sections. The compressive component of D2, well known in the country rocks where it induced a strong flattening related to ubiquitous upright isoclinal tight folds, was also observed in the granites. There, we documented a reverse movement within magmatic or solid-state shear bands. The addition of all these data constrains a new interpretation for the D2 main Hercynian phase in the whole Pyrenees: this phase was a dextral transpression.
Three-dimensional retro-modelling of transpression on a linked fault system: the Upper Cretaceous deformation on the western border of the Bohemian Massif, Germany
Authors: Tanner David C. , Behrmann Jan H. , Oncken Onno , Weber Klaus 
Published: April 2008

Abstract
The Zone of Erbendorf-Vohenstrauß (ZEV) on the western margin of the Bohemian Massif was deformed by an Upper Cretaceous intra-plate deformation event. Dextral transpression was caused by the reactivation of pre-existing structures. Using the extensive geological database available, we have constructed a three-dimensional virtual model of the ZEV. The model was deformed in reverse, to remove the effects of the Upper Cretaceous event. This involved moving the hanging wall (the ZEV) in a sinistral transtensive sense northwards above a composite active fault surface composed of two steep faults, perpendicular to each other in strike, and a detachment intersecting both faults at 9.5 km depth. Hanging-wall deformation was accommodated by antithetic inclined shear. Seven kilometres heave of the hanging wall fulfilled the geological constraints. Calculated uplifts range from 2 to 6 km. Deformation is mostly only contained within the ZEV. The hanging-wall deformation above a linked fault system was highly complex, causing rollover above one fault and drag-folding above the other. The most important control on the vertical movement and deformation of the hanging wall was a 30° change in the strike of one of the coupled faults.
Transpressional kinematics and magmatic arcs
Authors: Blanquat Michel De Saint , Tikoff Basil , Teyssier Christian , Vigneresse Jean Louis 
Published: April 2008

Abstract
Most continental magmatic arcs occur in obliquely convergent settings and display strike-slip movement within, or adjacent to, the magmatic arc, and contractional structures in the forearc and backarc regions. Thus, three-dimensional transpressional kinematics typifies many arc settings, both modern and ancient. Intrusions cause magma-facilitated strike-slip partitioning, even in cases where the relative angle of plate convergence is almost normal to the plate boundary. Transpressional systems are preferentially intruded by magmas because of the steep pressure gradients in vertical strike-slip shear zones and their ability to force magma upward. Both buoyancy and transpressional dynamics cause a component of magma overpressuring, which in turn expels granitic magma upward following the vertical pressure gradient. The tectonic and magmatic processes are linked in a positive feedback loop which facilitates the upward movement of magma.
We propose a lithospheric-scale, three-dimensional model of transpressional arc settings. Strike-slip motion is partitioned into the magmatic arc settings because of the linear and margin-parallel trend of the vertical, lithospheric-scale weakness caused by ascending magma. The parallelism of contraction structures in the forearc and backarc regions is caused by mechanical coupling through the lower crust and upper lithospheric mantle. The displacement field of the basal layer of the arc system provides the boundary condition for the upper-crustal, strike-slip partitioned deformation.
A review of up-scaling and cross-scaling issues in core and log data interpretation and prediction
Authors: Corbett P. W. M. , Jensen J. L. , Sorbie K. S. 
Published: April 2008

Abstract

In a heterogeneous geological formation, each rock petrophysical property (e.g., permeability, porosity, and electrical conductivity) reflects the heterogeneity and varies in a manner related to the underlying changes in fabric (grainsize, mineralogy, lamination, wettability, etc.). However, measurements, both laboratory and downhole, are made at certain volume scales dictated by the size of the core plug used or the wireline log resolution. The comparison of core and log data needs to account for both the
scale
and
physics
of the particular measurements and how these relate to the underlying scale of the geological heterogeneity of the formation.

In this review, these two fundamental issues are addressed as follows:

(a)

measurement scale and how it relates to the ‘true’ or ‘required’ petrophysical properties of the formation is defined as ‘
up-scaling
’;

(b)

measurement physics and how we relate the physics of one measurement (e.g. permeability) to that of another (e.g. density, electrical, or acoustic properties) is termed ‘
cross-scaling
’.

We illustrate how these two issues arise in the comparison and prediction of permeability using several published studies. We also outline an approach to petrophysical measurement reconciliation termed ‘genetic petrophysics’. This combines all three elements—measurement scale, measurement physics, and geology—to provide an integrated and robust model. We illustrate this approach for permeability to provide fit-for-purpose models of anisotropy in the near-well region of a reservoir.
Forward modelling of the physical properties of oceanic sediments: constraints from core and logs, with palaeoclimatic implications
Authors: Lauer-Leredde C. , Pezard P. A. , Touron F. , Dekeyser I. 
Published: April 2008

Abstract

A new methodological approach based on the analysis of core data, logs and high-resolution electrical images of borehole surfaces (FMS) is developed in order to improve the study of oceanic sediments from physical properties. This approach is tested on data obtained in the context of the Ocean Drilling Program (Japan Sea, Leg 128, Hole 798B). The downhole measurements and FMS images exhibit a cyclic pattern reflecting variations in oceanic surface productivity combined with continental aeolian supply due to palaeoclimatic changes. On the basis of m-scale physical measurements, cm-scale FMS images and measurements on core, the objective is to deconvolve the variations in sedimentary supply of oceanic and continental components through time and to compute the intrinsic formation factor versus depth. The latter topic is approached in two ways: first by conventional log analysis, then with a new iterative forward modelling method. In the second case, the low frequency electrical resistivity log (SFL) is modelled using a numerical modelling code (Resmod2D
©
) in order to obtain an accurate formation electrical resistivity model (Rt), where individual beds are derived from FMS images. An analytical routine is also used to model the natural gamma-ray measurement (CGR). While the conventional log analysis allows deconvolution of the sedimentary supplies, the forward modelling leads to a greater resolution and accuracy in more precise sediment characterization, such as that obtained from the derivation of the formation factor.