bluuebunny/crossref_metadata_2025_split huggingface dataset:
Balancing sections through inverted basins
Authors: Coward Mike P. 
Published: April 2008

Abstract
Basin inversion and the reactivation of earlier normal faults is now recognized as being widespread in many mountain belts. By ignoring the effects of basin inversion, serious errors in section construction and structural and tectonic interpretations can be made.
Folds produced during thick-skinned basement-involved faulting are generally very different from those produced during thin-skinned thrust tectonics and hence different models must be used for section construction and restoration. In particular, block rotations are important. Rotation about a horizontal axis may lead to shortening of the graben or half-graben, expulsion of material from out of the graben and/or reactivation of the original normal fault. The resultant hanging wall folds are characterized by long gently dipping backlimbs and short hooked forelimbs. Various models for fold development are derived and compared for different inversion geometries and kinematics. Examples are taken from the North Sea.
Many inverted faults involve components of strike-slip or oblique-slip movement, and hence simple 2D methods of section balancing cannot be applied. Basin inversion may have involved rotation of the fault blocks about vertical axes and/or lateral expulsion of material from the basin. Examples are described from South Wales, Syria and the French Alps. Vertical axis rotation appears a common mechanism for intraplate deformation, where the regional shear couple is applied at an angle to earlier fault blocks or crustal lineaments. The analysis of paleomagnetic data together with kinematic data enable the rotation to be determined and amounts of shortening strain estimated.
A strategy for palinspastic restoration of inverted basins: thermal and structural analyses in SE Australia
Authors: Hill Kevin C. , Cooper Gareth T. 
Published: April 2008

Abstract

Constructing balanced sections across inverted basins is difficult because of the different directions of tectonic transport during extension and compression and the imprecise estimates of the magnitude and timing of inversion events. Sections oriented within 25° of all transport directions can be restored and result in ≤10% error in the amount of extension-compression. Extensional faults are commonly oblique to the transport direction, so the inferred extension direction may be verified by dip analysis of the pre-rift section. Where oblique extensional faults are reactivated during compression, the compressional vector is best determined from the orientation and magnitude of large, curved inversion anticlines. For strongly inverted and eroded anticlines, where
T
max
is not at the present day, palaeotemperature gradients determined regionally from borehole vitrinite reflectance and fission track profiles constrain the amount of denudation allowing reconstruction of the original anticline morphology. The timing of inversion and erosion determined by apatite fission track analysis allow the eroded strata to be replaced on the section and the inversion restored to reveal the amounts of extension and compression and the syn-rift basin morphology, which may constrain hydrocarbon migration paths. For the Otway Ranges in SE Australia 45% Early Cretaceous extension followed by 10% mid-Cretaceous compression are inferred.
Benefits and limitations of section restoration in areas of extensional salt tectonics: an example from offshore Louisiana
Authors: Rowan Mark G. 
Published: April 2008

AbstractA composite, multi-level salt system from offshore Louisiana is used to illustrate some benefits and limitations of cross section restoration. The system has a complex three-dimensional geometry in which both salt and overburden have apparently moved in multiple directions during Miocene-Pleistocene deformation. Sequential restorations are beneficial in that they provide a framework for: (1) analysis of the structural evolution of salt and overburden; (2) determination of rates of various processes; (3) prediction of changes in the sea-floor paleotopography; (4) evaluation of evolving sediment transport and deposition systems; and (5) analysis of the timing and pathways of hydrocarbon migration. The limitations of section restoration include possible inadequacies of restoration algorithms to model correctly actual rock deformation. More importantly, the assumption of plane-strain deformation is shown to be invalid in this example. Local pin lines are used to demonstrate that there is significant out-of-plane movement. Thus, cross-sectional area for both salt and overburden may need to be added or removed from the section during restoration if the goals are to illustrate the geometric evolution. If, on the other hand, the goal of restoration is to validate and, if necessary, modify the interpretation, then 2D restoration is not appropriate in this case. Ultimately, 3D restoration is needed to restore accurately complex structural geometries.
The growth of normal faults by segment linkage
Authors: Cartwright Joseph A. , Mansfield Chris , Trudgill Bruce 
Published: April 2008

Abstract

Fault growth is widely described using a scaling law between maximum displacement (
D
) and length (
L
), of the form
D
=

cL
n

. This expression defines a model of fault growth by radial propagation from a single seed fracture or fault. This paper presents geometrical and kinematic evidence from a set of exceptionally well exposed normal faults in Utah for an alternative model of fault growth. This model is referred to as growth by segment linkage, and involves the propagation and linkage of independent fault segments on ascending length scales. The evidence presented focuses on the geometry and displacement variation in the region of relay structures, and on local scaling relationships between
D
and
L
. The
D - L
data from 97 faults in the study area range over three orders of magnitude, and show a general trend to increasing
D
for increasing
L
. There is a large scatter in the data, similar to that recognized in previous
D - L
compilations. It is argued that the scatter cannot be attributed either to measurement errors or to variation in mechanical properties. Instead, we argue that the model of growth by segment linkage provides a simple explanation of this scatter, and propose that the process of segment linkage may explain scatter in other datasets.
Recent advances in analogue modelling: uses in section interpretation and validation
Authors: McClay K. R. 
Published: April 2008

AbstractScaled analogue modelling is a powerful tool for the understanding of the geometric and kinematic development of extensional, strike-slip and inverted fault systems, as well as for some thrust systems. In this paper the results of 2D and 3D scaled analogue model experiments designed to simulate listric fault systems, rift fault systems, and inverted listric faults are reviewed. Simple 2D rift models are characterized by asymmetric rift graben structures with planar rift border faults and domino-style intra-rift fault systems. 2D listric fault models produce roll-over anticlines with associated crestal collapse grabens whereas the ramp-flat listric fault models produce roll-over anticlines associated with each concave-up segment of the main fault system and also a syncline above the convex-up ramp section of the main detachment. The 2D analogue models are directly comparable to natural examples of extensional fault systems. The results of simple 3D analogue models of an orthogonal and a 60° oblique rift are presented. Orthogonal rift models are characterized by both rift-border and intra-rift faults that are nearly orthogonal to the extension direction. Like-dipping intra-rift faults overlap to form relay ramps that transfer displacement between the faults. In contrast oblique rift models are characterized by en-echelon arrays of segmented extensional faults. Rift border fault systems are parallel to the underlying zone of basement stretching whereas the intra-rift faults are segmented and at a high angle to the extension direction. Oblique accommodation zones formed by interlocking conjugate fault arrays separate individual depocentres within the models. No strike-slip or oblique-slip transfer faults are found in these models. The 3D rift models produce fault patterns that are comparable with natural examples of rift systems. Analogue modelling of inverted listric faults is described and the results compared with natural examples of inverted fault systems. The results of the scaled analogue models described in this paper provide important constraints on section interpretation and restoration in that they permit an understanding of the geometric and kinematic evolution of fault (and fold) structures as well as indicating the sequences of faulting and activity on faults. They provide templates for the interpretation of seismic sections in regions of poor data quality and for projecting surface data into the sub-surface.
Numerical modelling of extension in faulted crust: effects of localized and regional deformation on basin stratigraphy
Authors: Ter Voorde M. , Cloetingh S. 
Published: April 2008

Abstract
A numerical model for localized and regional deformation during crustal extension is presented. In this model, the behaviour of the faulted upper crust is coupled with ductile deformation in the lower crust and upper mantle. The incorporation of finite extension rates makes the model an appropriate tool for analysing the effects of synrift processes on the basin structure and stratigraphy.
Modelling results indicate that the shape of a basin depends not only on the fault geometry and the deformation mechanism, but also on the behaviour of the lower lithosphere. The authors demonstrate that onlap and offlap patterns can be caused by successive activation of a series of faults.
As shown by the modelling, the amount of footwall uplift of the fault blocks is determined by the integrated effects of deep-lithospheric and near-surface processes. Of particular importance are the spacing of the faults, the amount of extension, the depth of necking, the depth of the Moho, and the lithospheric rigidity. The rate of extension turns out to be a very important but undervalued factor for the postrift to synrift sediment thickness ratio. It is shown that this ratio increases with the extension velocity.
The role of pre-existing faults in basin evolution: constraints from 2D finite element and 3D flexure models
Authors: Van Wees J. D. , Cloetingh S. , de Vicente G. 
Published: April 2008

Abstract
The lithospheric driving forces which cause intraplate basin deformation are relatively constant over large areas. Consequently, lateral variations in deformation and stress and strain concentrations seem to be primarily caused by (pre-existing) heterogenities in the rheological signature of the continental lithosphere underlying the sedimentary basins. In this paper, we explore the weak character of upper crustal faults and their control on basin shape for a number of case studies on intraplate Phanerozoic basin settings, using a 2D finite element and a 3D flexure model. Of key importance is the integration of seismic data and field observations with the tectonic modelling, allowing the investigation of deformation processes and their expressions on different scales, operating on different levels of the lithosphere. Finite element models for sub-basin scales, incorporating weak upper crustal faults, predict strong control of these weak zones on local stress distributions and subsequent deformation, in agreement with observed deformation patterns. Slip along upper crustal faults control stress distribution and subsequent faulting in overlying sedimentary rocks. The effect of weak upper crustal fault movements on basin-wide (regional) upper crustal flexure is looked at in two case studies on: (1) extensional tectonics in the Lake Tanganyika Rift Zone (East Africa); and (2) compressional tectonics in the Central System and Tajo Basin (Central Spain). Both settings indicate that basement warpings are controlled by large amounts of slip along so-called weak crustal-scale border faults, which are mostly planar. Adopting border fault displacements in the 3D flexure model, the results indicate low effective elastic thickness (EET) values in a range of 3–7 km for induced basement deflection patterns in accordance with observations. The low EET values most likely reflect a (partly) decoupling of upper crustal and subcrustal deformation, facilitated by the weak lower crust, and in agreement with standard rheological assumptions for Phanerozoic lithosphere. In contrast, the inferred weakness of upper crustal faults relative to surrounding rock is not evident from uniform rheological assumptions. However, observations of reactivations of faults which are not preferably aligned with the stress field, and reactivations of basin deformation on long time-scales are in support of this feature.
The use of satellite imagery in the validation and verification of structural interpretations for hydrocarbon exploration in Pakistan and Yemen
Authors: Insley M. W. , Murphy F. X. , Naylor D. , Critchley M. 
Published: April 2008

Abstract
Landsat TM and stereo-SPOT satellite imagery has an important application in the validation and verification of structural models for on-shore hydrocarbon exploration. The lithological discrimination of Landsat TM can be merged with the higher resolution panchromatic stereo-SPOT imagery to produce detailed geological maps at scales of 1:25 000 and 1:50 000 from which to ‘hang’ structural cross-sections. In addition, the calculation of surface dip data and fault off-sets, as well as the construction of structure contour and topographic maps is now possible using SPOT-derived digital elevation models (DEMs), thus providing the necessary information for the construction of structural cross-sections.
Examples of the use of satellite imagery are presented from the Sulaiman Ranges of Pakistan and southeast Yemen. For the Sulaiman Ranges of Pakistan, satellite imagery has been used to constrain the construction of a balanced deformed and restored cross-section from relatively poor quality seismic data. The satellite imagery provides information on structural style and along-strike structural continuity. The construction of a balanced cross-section is used to highlight the contrast between the position of structural closure at surface and subsurface.
In southeast Yemen, satellite imagery is combined with both field and seismic data to develop a viable structural interpretation. The model is complicated by the superposition of Late Tertiary extensional structures on an earlier Mesozoic rift system. Earlier structural trends have been inferred from the interpretation and analysis of the Late Tertiary fault patterns observed on the Landsat MSS and TM and stereo-SPOT imagery. Stereo-SPOT imagery is used at 1:50 000 scale to map out extensional faults, to examine their displacement gradients and identify potential closures at surface. Quantitative analysis of displacement patterns around faults is possible using structure contour maps derived from stereo-SPOT imagery and DEMs. Satellite imagery also enables the validation of structural continuity between seismic lines.
Gravity-driven nappes and their relation to palaeobathymetry: examples from West Africa and Cardigan Bay, UK
Authors: Turner Jonathan P. 
Published: April 2008

Abstract
Gravity-tectonics serves to reduce gravitational potential compared to the undeformed state. Consequently, a common setting of gravity-driven faulting is at actively prograding passive margin basins where abrupt shelf-edge relief promotes potentials sufficiently large to induce and sustain large-scale deformation. In the West African Rio Muni basin, Albian gravity-tectonics predates the Senonian drift unconformity and owes its existence to a significant bathymetric deep that characterized the late syn-rift stage of the basin. Thin-skin nappes, detaching on a syn-rift salt and/or shaly horizon, emplace shallow water shelf carbonates in a deep, basinal setting. Seismic mapping indicates that ‘upslope’ extension occurred contemporaneously with ‘downslope’ contraction and that the nappes behaved as small coulomb wedges. It is suggested that structural restoration of these large-scale nappes, retro-deforming them to their pre-deformational position at the palaeo-shelf edge, yields a minimum estimate of palaeobathymetry. In the Rio Muni basin, variations in the inferred palaeobathymetry accord with intra-basinal differences in Bouguer gravity anomaly, here interpreted as an expression of varying crustal thickness and uplift/subsidence rate. Comparable structures in the Jurassic of the UK Cardigan Bay basin occur at the margin of a basin characterized, similarly, by a major negative Bouguer gravity anomaly and which, from evidence on seismic profiles, clearly experienced deep bathymetry during Jurassic deposition.
The development of the Gorleben salt dome (northwest Germany) based on quantitative analysis of peripheral sinks
Authors: Zirngast Max 
Published: April 2008

Abstract
The structure of the most important stratigraphic horizons in the Gorleben salt dome area, northwest Germany, has been studied using reflection-seismic data and drilling results. Epeirogenic, tectonic and halokinetic movements in the area can be reconstructed on the basis of structure-contour maps, isopach maps, and palaeostructure-contour maps. For this purpose the increase of sediment volume in the rim synclines was calculated in three dimensions and compared with the results of the ‘normal’ subsidence. The additional subsidence in the rim synclines was used for calculation of salt flow by volume. By budgeting the salt movements, the flow rate of salt into the diapir and the salt loss by erosion and leaching were determined. The movement of the salt from the Late Buntsandstein (Röt) until today is depicted in 13 successive stages in three-dimensional diagrams using computer programs.
Salt flow by aggrading and prograding overburdens
Authors: Koyi H. 
Published: April 2008

AbstractThe mechanisms responsible for segmentation of salt sheets and their emplacement into higher stratigraphic levels are not separable and act simultaneously. Three sets of centrifuge models with strongly planar anisotropic (anisotropy, δ, the ratio between the effective viscosities in pure and simple shear, ranging between 4.8 and 16.4) microlaminate overburdens are used to study the effect of aggradation and progradation on segmentation and emplacement of allochthonous salt sheets.In the first set of models, a tabular buoyant source layer was overlain by tabular anisotropic overburden simulating aggradation. During centrifuging, the underlying ductile source layer was segmented into individual wall-like diapirs by the subsiding blocks formed due to extension and faulting of the overburden. The extensional zone in these models started at the spreading edge (free face) of the model and migrated backwards.In the second set of models, a tabular buoyant source layer was overlain successively by wedges of anisotropic overburdens simulating progradation. During centrifuging, the buoyant layer was displaced from the back of the model, where loading was higher, towards the free face in the front of the model, where overburden units were thinner. Overburden units extended at the back and the middle of the model while contractional structures dominated at the front, where asymmetric diapirs formed overhangs that spread ‘basinward’ to form ‘salt’ sheets.In the third set of models, a wedge-shaped buoyant source layer was overlain successively by wedges of anisotropic overburden simulating progradation. The overburden wedge created a lateral pressure gradient ranging from 144 Pa at the back of the model to 80 Pa at the front when deformed in the centrifuge. In these models, as in the second set of models, the underlying buoyant mass was displaced ‘basinward’ by the subsiding thicker overburden units at the back of the model. Contractional structures dominated the deformation at the leading edge of the wedge.Comparison of model results suggests that progradation (as in the second and third sets of models) loads underlying ‘salt’ differentially, displaces it downdip and segments it. As it segments at the back, the ‘salt’ flows laterally to areas of lower loading by intruding through the thinner overburden units and forming secondary ‘salt’ sheets at the front. On the other hand, aggradation of uniform overburden segments a buoyant sheet into two-dimensional salt walls or stocks, as in the first set of models.
Numerical modelling of stratal architectures resulting from differential loading of a mobile substrate
Authors: Cohen Harvey A. , Hardy Stuart 
Published: April 2008

AbstractA numerical model is presented in which a viscous layer flows in response to differential loading by deltaic sedimentation. No density effects are cconsidered; the mobile layer and overlying sediments deform solely in response to differential thicknesses of sedimentary overburden. Modelling results include the following key features: (1) sedimentary depocentres are asymmetric and spoon-shaped, with flat-lying shelf strata grading laterally into foreset slope strata at a prograding shelf-slope break; (2) the locus of deformation is controlled by the position of the shelf-slope break; and (3) a displaced bulge of mobile substrate migrates seaward faster than the shelf-slope break progrades. Using viscosities characterisitic of natural salt (η = 1016to 1019Pa s), the sensitivity of the model to several parameters is examined. Increasing the mobile layer thickness increases the rate of substrate withdrawal in a manner similar to decreasing its viscosity. A shorter sediment transport distance results in steeper depositional slopes and faster substrate withdrawal. Comparison with a Miocene example from offshore Texas demonstrates that structures qualitatively attributed to differential loading can be successfully modelled using reasonable values for sediment supply, relative sea-level rise, and substrate thickness.
Temperature dependence of thermal anomalies near evolving salt structures: importance for reducing exploration risk
Authors: Petersen K. , Lerche I. 
Published: April 2008

Abstract
The temperature distribution through time in the subsurface influences hydrocarbon generation. It is therefore of interest to model the spatial variation of temperature through time and the causes of the variation.
The thermal conductivity of salt is a factor of two to three times higher than that of typical sediments. Salt structures often display large vertical relief and so provide low thermal resistance paths for heat conduction to the surface, with focusing through salt at the expense of surrounding sediments. The focused heat re-enters the sediments near the salt structure apex so that local sediments are warmer than remote sediments at equal depth. Sediments close to salt base, and in secondary rim synclines, are cooler than remote sediments at equal depth. Around salt sheets, supra-salt (sub-salt) sediments are warmer (cooler) than remote sediments at equal depth.
Decreasing salt thermal conductivities with increasing temperature are shown to influence thermal anomaly patterns around salt bodies, while temperature anomalies around a laterally moving salt sheet are calculated to exemplify the relative effects of salt shape, depth of burial and heat flow. The spatial temperature history is vital for modelling timing and location of earlier onset of oil generation and maturation above salt structures, and of delay in conversion of trapped oil to gas in deeper sediments compared to the regional regime. The importance of modelling the thermal history in order to reduce exploration risk near salt structures is emphasized.