bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Trans Mojave-Sierran shear zone and its role in Early Miocene collapse of southwestern North America
Authors: Dokka Roy K. , Ross Timothy M. , Lu Gang 
Published: April 2008

Abstract

The relative motion between the Pacific and North American plates in early Miocene time was not parallel to the overall NW strike of the transform, but was instead oblique and transtensional. It has recently been proposed that in response to this divergence, the western edge of the North American plate east of the transform gravitationally collapsed and moved 100–150 km to the southwest (S50°–60°W). The region of collapse covered an area of nearly 10
6
km
2
and included what is now southern California, southwestern Arizona, and northwestern Mexico. A major structure facilitating collapse between 21 and 18 Ma was the Trans Mojave-Sierran shear zone (TMSSZ). This east-west shear zone linked the classic detachment fault terranes and metamorphic core complexes of the Mojave desert, southeastern California, southern Arizona, and Sonora, Mexico, to the transtensional plate boundary.

To more fully understand the nature and kinematic significance of the TMSSZ and its role in facilitating early Miocene fragmentation of the North American plate, a palinspastic reconstruction of the Mojave desert was performed to remove the disruptive effects of the TMSSZ and younger tectonic events. Features formed just before movements along the TMSSZ were used as markers to assess the TMSSZ deformation. Our analysis indicates that TMSSZ deformation was distributed across a
c.
90 km wide band; restoration of markers to their original positions implies that >80 km of dextral shear occurred along the TMSSZ. First-order dextral shear deformation within the TMSSZ is expressed internally by clockwise vertical axis rotations of large areas that were facilitated by second-order zones of sinistral shear that separated the blocks. These second-order sinistral zones apparently exploited older transfer zones of the 24-21 Ma Mojave Extensional Belt.
Transtensional deformation in the evolution of the Bohai Basin, northern China
Authors: Allen Mark B. , Macdonald David I. M. , Xun Zhao , Vincent Stephen J. , Brouet-Menzies Christine 
Published: April 2008

Abstract
Extensional basins with an element of strike-slip deformation can form because of a perturbation in a strike-slip fault zone (pull-apart and fault wedge basins), or where extension is oblique to the margins of the deforming zone (transtensional basins). Transtensional basins are characterized by en echelon arrays of normal faults which are individually oblique to the basin margins. The Bohai Basin, northern China, has previously been modelled as either (1) a giant pull-apart between NNE-SSW trending dextral strike-slip faults, or (2) a rift basin caused by WNW-ESE extension, without significant strike-slip deformation. We present a model for the Bohai Basin’s rift history in which the basin formed as a result of dextral transtension. The Bohai Basin is one of a family of early Tertiary extensional basins present within eastern Asia from northeastern Russia to southeast China. The structural grain in this basin was inherited from a phase of late Mesozoic sinistral transpression. Tertiary extension began in the Paleocene. Most half-grabens in the eastern and western regions of the Bohai Basin have master faults with a NE-SW or NNE-SSW orientation. Secondary normal faults strike oblique to the main structures, in en echelon arrays which indicate a component of dextral transtension. The central part of the basin, the Bozhong Depression, became a significant depocentre for the first time in the middle Eocene. It formed when activity on transtensional zones to its east and west created an extensional overlap between them. Thus the basin as a whole resembles a giant pull-apart basin, with the Bozhong Depression as its central depocentre, but dextral transtension rather than simple strike-slip controlled the deformation. The component of dextral deformation in the Bohai Basin is shared by other early Tertiary east Asian extensional basins, and is consistent with the sense of shear implied by the oblique convergence of the Pacific and Asian plates: an east-west convergence vector applied to a NE-SW trending plate boundary. The consistency of this dextral shear along the Asian margin, and the fact that several of these basins pre-date the India-Asia collision, supports an origin by subduction roll-back of the oceanic Pacific plate from Asia. The extrusion model for east Asian basin formation, whereby extension was caused by lateral transport of lithospheric blocks out of India’s northward path following the India-Asia collision, is not applicable to major basins east and northeast of the Red River Fault.
Transpressionally driven rotation in the external orogenic zones of the Western Carpathians and the SW British Variscides
Authors: Gayer Rod , Hathaway Tanya , Nemcok Michal 
Published: April 2008

Abstract

Analysis of two examples of obliquely convergent external orogenic zones, the western part of the Western Carpathians and the northern Variscan margin in southwest Britain, indicates the operation of two dominant stress rotation mechanisms in the transpressionally deformed thrust wedge: (1) the rotation of an inferred stress field; (2) the rotation of a deforming body within a constant stress field. In the thinnest, external parts of the thrust wedge, σ
1
stress trajectory rotations of up to 90° occur with deformation having a relatively small component of pure shear. Towards the hinterland, σ
1
stress trajectories in thicker parts of the wedge are progressively less rotated but develop a larger component of pure shear. Resultant σ
1
trajectories are curvilinear, lying parallel to the orogenic convergence vector in the hinterland but diverging progressively from this direction towards the foreland, where they lie at high angles to the external margin in frontal parts of the thrust wedge. It is argued that balanced cross-sections should be constructed parallel to the curved trace of the σ
1
stress trajectories.
Development of kinematic partitioning within a pure-shear dominated dextral transpression zone: the southern Ellsworth Mountains, Antarctica
Authors: Curtis M. L. 
Published: April 2008

AbstractThe Heritage Range of the southern Ellsworth Mountains, West Antarctica, is composed of Cambrian to Permian sedimentary and volcanic rocks, which were deformed during the Permo-Triassic Gondwanian orogeny. The structural grain of the Heritage Range exhibits a previously unrecognized 18° swing from 333–153° in the north to 315–135° in the south. A change in structural and kinematic style accompanies this strike-swing, with a structure consistent with near-orthogonal shortening present in the south, and a structural style consistent with dextral transpression within the central and northern Heritage Range. Kinematic partitioning is present within the central Heritage Range, where strikeparallel, contemporaneous domains of dextral and reverse shear have developed simultaneously with the regional cleavage. Comparison of the structure and kinematics within both structural domains suggests that the central and northern Heritage Range experienced pure-shear dominated dextral transpression, with an approximate angle of relative shortening (α) of 65–70°. Results derived by integrating field data into a published kinematic partitioning model suggest relatively efficient kinematic partitioning has occurred. However, such efficient partitioning cannot be explained by strain partitioning models based purely on plate boundary conditions. Therefore, it is proposed that pre-existing weak structures were present within the unexposed basement facilitating the apparent high percentage of kinematic partitioning.
Transpressional tectonics along the Karakoram fault zone, northern Ladakh: constraints on Tibetan extrusion
Authors: Searle M. P. , Weinberg R. F. , Dunlap W. J. 
Published: April 2008

Abstract

The Tibetan plateau north of the Himalaya has approximately double normal crustal thickness (60–75 km) and has been homogeneously shortened since the India-Asia collision at 60–50 Ma ago, yet, with minimal erosion rates, has almost no middle or deep crustal rocks exposed at the surface. In the Karakoram range, west of Tibet, early Tertiary crustal thickening and regional metamorphism resulted in Miocene crustal melting producing the Baltoro monzogranite-leucogranite batholith. Late Tertiary transpression along the western margin of the Tibetan plateau, caused by the continued northward penetration of India into Asia, led to exhumation of migmatites in the Pangong range and Baltoro-type granites along the Karakoram fault. Detailed studies of the Karakoram fault zone in northern Ladakh, India, show that Baltoro-type two-mica ± garnet leucogranites, intruded 21–18.0 Ma ago, have been offset a maximum of 150 km right-laterally. Average slip rates since 18.0 ± 0.6 Ma (2σ) are 8.3 mm/a.
40
Ar/
39
Ar mica cooling ages are 11.3 Ma on both sides of the main (southwestern) strand of the fault, suggesting that most of the exhumation of the Pangong migmatites and leucogranites must have occurred between 18.0 and 11.3 Ma. During this time, at slip rates of 8.3 mm/a the rocks would have moved horizontally right-laterally for
c.
56 km and been exhumed by
c.
20 km vertically during transpression, using the measured 20° plunge of lineations.

The high exhumation rate (3.0 mm/a) and amount of erosion (20 km) inferred between 18.0 and 11.3 Ma may also reflect the partitioning between an early transpressional strain associated with crustal thickening and exhumation of the Pangong deep crustal migmatites and leucogranites, and a later dominantly dextral strike-slip phase of fault motion along the central part of the Karakoram fault from
c.
11 to 0 Ma. This timing may also coincide with the initiation of the N-S aligned normal faults and E-W extension in southern Tibet. We suggest that the relatively minor dextral offset (150 km) and the young age of initiation on this bounding fault do not support the model of large-scale extrusion of Tibetan crust, but they suggest instead that deformation of Tibet was taken up predominantly by crustal thickening.
Spectral gamma ray logs: core to log calibration, facies analysis and correlation problems in the Southern North Sea
Authors: Bristow C. S. , Williamson B. J. 
Published: April 2008

Abstract
The aim of this study is to test the usefulness of spectral gamma ray logs in subsurface correlation, lithofacies description and the interpretation of depositional environments of Namurian and Dinantian sandstones in the southern North Sea. Lithofacies and depositional environments were identified from core descriptions and compared with spectral gamma ray logs from thirteen boreholes. The results show that lithofacies and sedimentary environments can be discriminated within single wells. However, there is too much variation between wells to make an unequivocal assessment of depositional environment on the basis of spectral gamma ray logs alone. Comparison of stratigraphically correlated sandstones shows that variations between wells are often greater than variations between lithofacies. The differences between correlated sandstones using spectral gamma ray logs are largely attributed to changes in the logging environment, mainly mud characteristics, borehole quality and contractor. In addition, the occurrence of negative numbers for uranium and potassium in some wells indicates that the algorithm used to calculate elemental concentrations may be in error. For sandstones with a low total gamma ray response, small errors associated with tool calibration and data processing make a comparatively large difference to results, which has made detailed correlation of sandstones untenable. The most significant problem is the correction factor for potassium in KCl drilling mud.
Quantitative density measurements from X-ray radiometry
Authors: Duncan A. R. , Dean G. , Collie D. A. L. 
Published: April 2008

Abstract
Qualitative linear X-ray scanning has an established role in the non-destructive imaging of both slabbed and whole core and has been routinely used in visual assessment and quality control of material being subjected to other physical measurements. Since core may be observed in real time, whole core can be oriented to maximum dip prior to slabbing, especially useful where core has been resin-stabilized within an outer liner. Linear scanning is also useful in the observation of heterogeneous lithologies; the features observed are distinguished by their penetrabilities to X-rays. As a result, the linear scanner produces an image which reflects the density variation in the section analysed. A joint project carried out by Robertson Research International Limited and Amerada Hess Limited on 108ft of heterogeneous sediments has shown that the digital X-ray penetrability values (‘luminance’) can be extracted in order to produce a surface density variation log. X-ray luminance values show a linear relationship with the downhole Formation Density Log and may, therefore, provide an accurate tool for the correlation of core density with log density.
Interpretation of core and log data—integration or calibration?
Authors: Lovell M. A. , Harvey P. K. , Jackson P. D. , Brewer T. S. , Williamson G. , Williams C. G. 
Published: April 2008

Abstract
Core-log interpretation requires the reconciliation of datasets from different measurements. Measurement process, resolution, scale and quality must be appreciated for each dataset. Calibration of measurements involves the use of standards to enable quantitative comparisons locally or globally; this may involve inter-dataset comparison and the process of equalization with the modification of one dataset in preference for another. Calibration should not be confused with integration which aims to maximize the information in an optimal manner and may require the selective choice of data. The clear recognition of the aims of the study at the earliest opportunity enables the best choice of strategy from measurement acquisition through to integration. The final interpretation should realize the original aims but must be compatible with all observations.
Methods for simulating natural gamma ray and density wireline logs from measurements on outcrop exposures and samples: examples from the Upper Jurassic, England
Authors: Ahmadi Z. M. , Coe A. L. 
Published: April 2008

Abstract

Methods for simulating natural gamma ray and density wireline logs from measurements on outcrop exposures and rock samples have been implemented. The signals have comparable amplitudes and resolution to wireline log signals, although the absolute values do not match precisely. The field gamma ray logs were measured on the outcrops at intervals of 30–45 cm using hand-held gamma ray spectrometers. The field density logs were produced by measuring the volume and grain density of selected rock samples, followed by interpolation and filtering of the data. Both techniques are illustrated for the Upper Jurassic of the Wessex Basin, Southern England, with field data from the exposures on the Dorset coast and wireline log data from 11 boreholes between 0.5 km and 170 km away. The Upper Jurassic comprises a range of rock types, giving a wide range of values on which to test the techniques: wireline gamma ray and density values of these strata cover the ranges 15–140 API and 1.8–2.9 g cm
−3
, respectively. Thus these techniques should be widely applicable for the purpose of correlating outcrops with borehole data.
Lithological classification within ODP holes using neural networks trained from integrated core-log data
Authors: Wadge G. , Benaouda D. , Ferrier G. , Whitmarsh R. B. , Rothwell R. G. , Macleod C. 
Published: April 2008

Abstract
Neural networks offer an attractive way of using downhole logging data to infer the lithologies of those sections of ODP holes from which there is no core recovery. This is best done within a computer program that enables the user to explore the dimensionality of the log data, design the structure for the neural network appropriate to the particular problem and select and prepare the log- and core-derived data for training, testing and using the neural network as a lithological classifier. Data quality control and the ability to modify lithological classification schemes to particular circumstances are particularly important. We illustrate these issues with reference to a 250 m section of ODP Hole 792E drilled through a sequence of island arc turbidites of early Oligocene age. Applying a threshold of > 90% recovery per 9.7 m core section, we have available about 50% of the cored interval that is sufficiently well depth-matched for use as training data for the neural network classifier. The most useful logs available are from resistivity, natural gamma, sonic and geochemistry tools, a total of 15. In general, the more logs available to the neural network the better its performance, but the optimum number of nodes on a single ‘hidden’ layer in the network has to be determined by experimentation. A classification scheme, with 3 classes (claystone, sandstone and conglomerate) derived from shipboard observation of core, gives a success rate of about 76% when tested with independent data. This improves to about 90% when the conglomerate class is split into two, based on the relative abundance of claystone versus volcanic clasts.
Core-derived acoustic, porosity & permeability correlations for computation pseudo-logs
Authors: Bastos A. C. , Dillon L. D. , Vasquez G. F. , Soares J. A. 
Published: April 2008

Abstract

In order to improve hydrocarbon production, it is often necessary to obtain more accurate rock, fluid and petrophysical information. For example, to obtain a reservoir porosity map using seismic data as reference, it is necessary to generate reliable correlations between seismic attributes and petrophysical properties like porosity and permeability. Again, to optimize drilling and/or hydraulic fracturing programs, it is also necessary to estimate better formation static mechanical behaviour from geophysical data. The main goal of this work is to establish for an offshore Brazilian field, relationships between compressional and shear wave velocities and petrophysical properties such as porosity and permeability. The large number of limestone samples (120) gave us a precise empirical relationship between
V
s and
V
p for limestone. In order to obtain a calibration reference, we also made, with the same samples, simultaneous measurements of dynamic and static elastic constants. Using all these laboratory relationships, it was possible to generate unmeasured pseudo-logs of
in situ
parameters, which include: shear wave velocity, static and dynamic elastic constants and permeability. The good experimental relationships obtained between
k
-φ and
V
p-φ in this work together with available logs give us an additional method to estimate permeability which is impossible to obtain from
in situ
measurements.
Dolomite cement distribution in a sandstone from core and wireline data: the Triassic fluvial Chaunoy Formation, Paris Basin
Authors: Worden R. H. 
Published: April 2008

Abstract

The distribution of mineral cements in oil fields is critical to the spatial variation of porosity and permeability. The distribution of dolomite cement within fluvial Triassic Chaunoy sandstones in the Paris Basin was studied using core description, petrography, core analysis (porosity and permeability), wireline data interpreted to give mineralogy, porosity and permeability data and geochemical data. Petrographic analysis revealed that dolomite and quartz cements are the main diagenetic minerals. Using sonic transit time, density and neutron porosity log, the overall proportions of quartz, dolomite and shale as well as porosity for each depth interval could be resolved. Petrographic and core analysis data showed that permeability could be calculated from wireline-derived porosity and mineralogy data. There is excellent correlation between core analysis porosity and permeability and their wireline-derived equivalents. There is also excellent correlation between wireline-derived mineralogy data and quantitative petrographic mineralogy data. The wireline-derived mineralogy data show that dolomite is preferentially concentrated at the tops of most sand bodies. Porosity and permeability are consequently lowest at the tops of individual sand bodies due to the localized dolomite cement. There are a number of potential causes for this distribution pattern although geochemical and petrographic data showed that a combination of early pedogenetic dolomite cementation and later recrystallization, possibly due to an influx of organically-derived CO
2
, are most likely.
The integration of electrical image logs with core data for improved sedimentological interpretation
Authors: Goodall T. M. , Møller N. K. , Rønningsland T. M. 
Published: April 2008

Abstract
Electrical borehole images allow the direct integration of sub-surface well-log data with core data on a detailed visual level. For sedimentary interpretation, electrical borehole images are primarily used to obtain bedding orientations and to confirm core-derived sedimentology.
The aims of this paper are two-fold: firstly, to discuss how the sedimentological information provided by electrical borehole image logs is integrated with that obtained from other wireline logs and from cores; and secondly, to show that despite the need to integrate these data electrical borehole images can provide the geologist with unique sedimentological information which can not be obtained from either the cores or the other wireline logs. In a case study from the Oseberg Syd oil and gas field, a Fullbore Formation MicroImager (FMI Mark of Schlumberger) log through a complex interval of shallow marine sediments has been investigated. The interpretation of the FMI log led to the acquisition of very detailed orientation data related to the attitudes of sedimentary bedding surfaces. When these data were integrated with the sedimentary facies, identified from core description, they proved fundamental for understanding the activity of different shallow marine palaeocurrents during sediment deposition.
How to characterize fractures in reservoirs using borehole and core images: case studies
Authors: Haller D. , Porturas F. 
Published: April 2008

Abstract

Microconductivity array and acoustic imaging of the borehole wall provide valuable multidatasets which are used to characterize the geological strata and especially the reservoirs in exploration activities and during development of producing zones. This paper presents a tutorial of the main applications and a methodology to follow when performing fracture interpretation. Borehole image interpretation should not be a routine work referring to ‘a cook book’. It must rely on our geological and structural knowledge and experience, on basic notions about tool principles and image processing, and on geometrical calibrations to cores. Vatious examples will be given, showing:

(a)
natural fractures; how to distinguish them from drilling-induced fractures;

(b)
typical drilling-induced fractures and borehole breakouts; how to identify them;

(c)
a tricky case where cemented fractures might be confused with open ones.

The match between interpretation of borehole images and production data appears now to be the most efficient way to manage fractures in reservoirs.