bluuebunny/crossref_metadata_2025 huggingface dataset:
Sustainable mineral development: possibilities and pitfalls illustrated by the rise and fall of Dutch mineral planning guidance
Authors: van der Meulen Michiel J.
Published: April 2008

The Netherlands has major resources of sand, gravel and clay, exploited mainly for construction works and the building materials industry. As in most Western countries, mineral extraction meets with considerable societal resistance. To this end, Dutch minerals policy aims to prevent extraction by promoting economical use of materials, and the use of alternative (secondary or renewable) materials. Until recently, it also included a system of production planning to sustain supplies of regionally scarce materials. Dutch policy development is reviewed and discussed in terms of pitfalls and possibilities for mineral planning in general. Promoting secondary substitution has been quite successful, and presents an example. In contrast, the production planning system has been controversial from the start and ineffective as a result, mainly because it attempted to solve supply problems without properly addressing the underlying resistance. For this reason the system is in the process of being abandoned.
Quaternary telescopic-like alluvial fans, Andean Ranges, Argentina
Authors: Colombo F.
Published: April 2008

The largest rivers that drain the Argentine Andean Ranges are characterized by incised valleys in high mountains and by a variety of Quaternary terraces. The terraces display a fan geometry with the apex located upstream of a tributary junction. Their convex-up morphology suggests that these terraces are related to a series of alluvial fans developed where the tributaries join the main river. The succession of alluvial aggradation and degradation is controlled by local base-level variation conditioned by temporary lake development in the main river valley. All these factors give rise to the inset segmented (terraced) morphology of the fan surfaces, yielding a telescopic-like relationship. The variation in the morphology and number of terraces suggests that they are not controlled by a general/regional base level. Neither tectonic activity nor significant climatic changes account for the alluvial fans at the confluences of the tributaries and the main river. Significant variations in rainfall or thunderstorms induced by the El Niño Southern Oscillation (ENSO) could explain the genesis of these telescopic-like alluvial fans.
Morphometry and depositional style of Late Pleistocene alluvial fans: Wadi Al-Bih, northern UAE and Oman
Authors: Al-Farraj Asma , Harvey Adrian M.
Published: April 2008

Three types of alluvial-fan settings are recognized in the Wadi Al-Bih area of the Musandam Mountains, northern UAE and Oman; mountain-front fans, tributary-junction fans and steep hillslope debris cones. Three styles of fan geometry, only partly dependent on fan setting, can be recognized: telescopic fans, stacked fans and truncated fans. Each style, together with degree of confinement, reflects the topographic and geological context of the fan and its source area. The mountain-front fans are mostly unconfined fans with telescopic styles. The tributary-junction fans are confined fans, some with stacked or telescopic styles, others that have been truncated by base-level-induced toe trimming. Most of the debris cones are simple hillfoot debris cones. Standard morphometric analyses of fan areas and fan gradients in relation to drainage basin area yield results that compare with other studies, but the relationships differ between the three groups of fans, in part reflecting fan style, especially between mountain-front and tributary-junction fans. The morphometry of the debris cones is only poorly characterized by the morphometric relationships. Cone morphology most strongly reflects source-area lithology. Analysis of the residuals from the regression analyses suggests that the morphometric differences between the three groups reflect fan sedimentary processes, fan setting and fan style, particularly relating to confinement.
Differential effects of base-level, tectonic setting and climatic change on Quaternary alluvial fans in the northern Great Basin, Nevada, USA
Authors: Harvey Adrian M.
Published: April 2008

Mountain-front alluvial fans in the northern Great Basin were affected by interactions between the tectonic setting, late Quaternary climatic changes and climatically induced base-level changes through fluctuations in pluvial lake levels. Four fan groups were studied on the margins of and near pluvial Lake Lahontan with varying geology and tectonic settings. All fans were affected by climatically led variations in sediment supply, but only those on steep mountain fronts adjacent to deep lakes were affected by base-level changes during lake desiccation.

Relationships between fan segments and dated lake shorelines, augmented by soil and desert pavement characteristics, have enabled fan segments older and younger than the lake highstands to be identified. Major periods of fan aggradation occurred prior to the last glacial maximum and during the Holocene, with little or no fan deposition occurring during and after the last glacial maximum, at the time of high lake levels. The interactions between tectonics, climate and base-level change have produced distinctive fan geometric relationships between older and younger fan segments, also expressed in the morphometric properties of the fans. Tectonics primarily influence the fan setting, particularly the accommodation space, and interact with sediment supply rates partly related to source-area geology. The climatic signal is present in all four groups of fans, but is modified locally by a base-level signal only where deep pluvial lakes abutted to relatively high levels on fans on relatively steep mountain fronts.
Reconciling the roles of climate and tectonics in Late Quaternary fan development on the Spartan piedmont, Greece
Authors: Pope Richard J.J. , Wilkinson Keith N.
Published: April 2008

The evolution of five alluvial fan systems is discussed in relation to chronology and possible tectonic and climatic triggering mechanisms. Two types of fan have evolved on the Spartan piedmont, Greece. First relatively large, low-angle fans, comprising four segments (Qf1–Qf4) composed of debris-flow and hyperconcentrated-flow deposits, with fluvial sediments restricted to the upper deposits of the distal segments. Second small, steep telescopically segmented fans, which consist of three segments (Qf1–Qf3), formed predominantly by debris-flow and hyperconcentrated-flow deposits. Morphological analysis of surface soils coupled with mineral magnetic and extractable iron (Fe
d
) analyses of B-horizons suggest that individual segments can be correlated across the piedmont and have equivalent age. Luminescence dating of fine-grained deposits suggests that Qf1 segments formed during marine isotope stage (MIS) 6, Qf2 segments during MIS 5, Qf3 segments during MIS 4–2, and Qf4 segments during MIS 2 and 1. Tectonics has exerted a limited influence on fan systems. Regional uplift provides the gross relief conducive for fan development. The locations of fans were determined by transfer faults of Tertiary age, while Quaternary faulting initiated short phases of fan incision. Climate change as manifested by cycles of aridity and low vegetation cover during stadials, and humidity and deciduous woodland during interglacials and interstadials, played a key role in fan evolution during the later Middle and Upper Pleistocene. Aggradation occurred during stadials, with minor deposition and intermittent erosion during most interstadials, and entrenchment during the interglacials and longer interstadials. Deposition during the Holocene is limited in extent.
Tertiary alluvial fans at the northern margin of the Ebro Basin: a review
Authors: Nichols Gary
Published: April 2008

Tertiary alluvial fan deposits along the margin of the Ebro foreland basin north of Huesca, Spain, are remarkable for the range of sedimentological and tectonic features preserved within them. The fan deposits formed after the southern Pyrenean thrust front (the Guarga Thrust) was established in this area, forming steep topography at the basin margin in the mid-Oligocene. Some shortening continued during deposition of the earliest fans resulting in synsedimentary faults, folds and unconformities. Clast compositions in the fan conglomerate beds record unroofing of the thrust front and also reveal differences in bedrock provenance between adjacent, coeval fan deposits. Bedrock provenance also influenced processes of deposition, with fans built up of detritus derived from areas rich in gypsum and mudrock showing more evidence of debris-flow processes. Deposition by debris flows also dominated the smallest fan body, but the majority of the fans were the products of sedimentation from unconfined or poorly confined traction currents. These resulted in sheets of conglomerate in the more proximal areas. Within individual fan bodies the proportion of sandstone increases over a distance of up to 5 km to where the distal fan facies are seen as thin sandstone and mudstone beds. The fringes of the fan bodies interfinger with lacustrine and fluvial facies, which indicate a temperate-semi-aric palaeoclimate. Vertical aggradation of the fan deposits due to rising base level in the Ebro Basin in the Oligocene and early Miocene was followed by deep incision following a late Miocene base level-fall. This led to the partial erosion of the fan deposits and their spectacular exposure in the modern landscape.
Source area and tectonic control on alluvial-fan development in the Miocene Fohnsdorf intramontane basin, Austria
Authors: Wagreich Michael , Strauss Philipp E.
Published: April 2008

Middle Miocene alluvial fans in the intramontane Fohnsdorf Basin of the Eastern Alps originated along normal faults and linked strike-slip faults in a continental half-graben setting. The fans display considerable facies differences. Debris flows of the Rachau fan are characterized by a sandy matrix and large boulders, whereas debris flows of the Apfelberg fan are characterized by higher silt and clay content and smaller clasts. Key control of debris-flow facies is the lithology contrast in the fan source areas. Sand, pebbles and large outsized boulders originated predominantly from the resistant augengneiss- and amphibolite-dominated hinterland of the Rachau fan, whereas a significant higher proportion of mud and silt and smaller boulders have been derived from the Apfelberg fan catchment, which was dominated by mica schists and marble.
The Neuquén Basin: an overview
Authors: Howell John A. , Schwarz Ernesto , Spalletti Luis A. , Veiga Gonzalo D.
Published: April 2008

The Neuquén Basin of Argentina and central Chile contains a near-continuous Late Triassic-Early Cenozoic succession deposited on the eastern side of the evolving Andean mountain chain. It is a polyphase basin characterized by three main stages of evolution: initial rift stage; subduction-related thermal sag; and foreland stage. The fill of the basin records the tectonic evolution of the central Andes with dramatic evidence for base-level changes that occurred both within the basin and along its margins. The record of these changes within the mixed siliclastic-carbonate succession makes the basin an excellent field laboratory for sequence stratigraphy and basin evolution. The 4000 m-thick fill of the basin also contains one of the most complete Jurassic-Early Cretaceous marine fossil records, with spectacular finds of both marine and continental vertebrates. The basin is also the most important hydrocarbon-producing province in southern South America, with 280.4 × 10
6
m
3
of oil produced and an estimated 161.9 × 10
6
m
3
remaining. The principal components of the hydrocarbon system (source and reservoir) crop out at the surface close to the fields. The deposits of the basin also serve as excellent analogues to reservoir intervals worldwide.
Tectonic evolution of the Andes of Neuquén: constraints derived from the magmatic arc and foreland deformation
Authors: Ramos Victor A. , Folguera Andrés
Published: April 2008

The Andes of the Neuquén region (36° − 38°S latitude) of the Central Andes have distinctive characteristics that result from the alternation of periods of generalized extension followed by periods of compression. As a result of these processes the Loncopué trough is a unique long depression at the foothills parallel to the Principal Cordillera that consists of a complex half-graben system produced during Oligocene times and extensionally reactivated in the Pliocene-Pleistocene. Its northern sector represents the present contractional orogenic front.

The nature and volume of arc-related igneous rocks, the location of the volcanic fronts, expansions and retreats of the magmatism, and the associated igneous activity in the foreland, together with the analyses of the superimposed structural styles, permit the constraint of the alternating tectonic regimes. On these bases, different stages from Jurassic to Present are correlated with changes in the geometry of the Benioff zone through time. Periods of subduction-zone steepening are associated with large volumes of poorly evolved magmas and generalized extension, while shallowing of the subduction zone is linked to foreland migration of more evolved magmas associated with contraction and uplift in the Principal Cordillera.

The injection of hot asthenospheric material from the subcontinental mantle into the asthenospheric wedge during steepening of the subduction zone produced melting and poorly evolved magmas in an extensional setting. These periods are linked to oceanic plate reorganizations in the late Oligocene and in the early Pliocene.
Tectonic evolution of the Andean Fold and Thrust Belt of the southern Neuquén Basin, Argentina
Authors: Zapata T. , Folguera A.
Published: April 2008

The Andean Fold and Thrust belt between 36° and 39°S can be divided in two sectors. The Eastern Sector corresponds to the Agrio Fold and Thrust Belt (FTB) characterized by a major exhumation during the Late Cretaceous, and minor deformation during the late Eocene and Late Miocene. The Western Sector corresponds to the main cordillera and is characterized by a complex evolution that involves periods of out-of-sequence thrusting with respect to the previously deformed outer sector, and pulses of relaxation of the compressive structure. Cretaceous uplift constituted an orogenic wedge that extended to the inner sectors of the Agrio FTB. Eocene compression was mainly concentrated within the Western Sector but may have reactivated the pre-existing structures of the Agrio FTB, such as the Cordillera del Viento. Late Miocene minor compressional deformation occurred in the retro-arc area and extended into the foreland area. This deformation event produced the closure of a short-lived intra-arc basin (Cura Mallín Basin, 25-15 Ma) at the innermost sector of the FTB. The Pliocene and Quaternary, between 37°30′ and 39°S, have been periods of relaxation of the inner part of the FTB and fossilization of the Agrio Fold and Thrust Belt.

Localization of episodic late Oligocene-Early Miocene and Pliocene to the present extensional structures in the intra- and inner retro-arc is controlled by pre-existing Jurassic half-grabens related to the formation of the Neuquén Basin. The Jurassic rift seems to be controlled by deep crustal-lithospheric discontinuities derived from a Proterozoic-Palaeozoic history of amalgamation in the area, now deeply buried under multiple episodes of Mesozoic-Tertiary synorogenic and synextensional sedimentation.
Sedimentary evolution and depositional architecture of a lowstand sequence set: the Lower Cretaceous Mulichinco Formation, Neuquén Basin, Argentina
Authors: Schwarz Ernesto , Howell John A.
Published: April 2008

The Valanginian-aged Mulichinco Formation was deposited in the Neuquén Basin (west-central Argentina) during and immediately after a major fall in sea level, partially triggered by a tectonic inversion pulse. The formation represents a lowstand wedge where excellent outcrops, together with refined biostratigraphic coverage, have permitted the detailed examination of contemporaneous non-marine and marine deposits. Fourteen facies associations were identified in the Mulichinco Formation. They represent accumulation in a variety of environments ranging from gravelly fluvial braidplains to outer-shelf marine settings. Distribution of depositional environments, together with the identification of key surfaces and stratal patterns, has resulted in the identification of early and late lowstand, transgressive and highstand systems tracts. Accordingly, the Mulichinco lowstand wedge comprises one third-order sequence that lasted about 2 Ma and represents a lowstand sequence set. The character of shoreline sedimentation was highly variable along strike within the Mulichinco depositional area and alluvial deposits were not developed within incised valleys. Tectonically derived topography, basin physiography and fault-controlled subsidence are interpreted to have been the main controls on the evolution of the Mulichinco lowstand wedge. The results of this study have important implications for understanding both the history of Neuquén Basin and illustrating the previously undocumented architectural complexity that may exist within lowstand wedges.
Anatomy of a mixed marine-non-marine lowstand wedge in a ramp setting. The Record of a Barremian-Aptian complex relative sea-level fall in the central Neuquén Basin, Argentina
Authors: Veiga Gonzalo D. , Howell John A. , Strömbäck Anna
Published: April 2008

During the Cretaceous, western Argentina was occupied by the Neuquén Basin, a back-arc-foreland basin that was open through the proto-Andes to the Pacific Ocean in the west. The Neuquén Basin contains a thick succession of sediments that include the offshore marine deposits of the Agrio Formation. These deposits represent a time when the arc was an island chain and the Neuquén Basin was freely connected to the Pacific. This offshore marine succession is punctuated by two intervals of arid continental deposits that represent major, second-order, relative falls in sea level. In both of these cases there is no evidence of tectonic uplift or angular truncation along a basal bounding unconformity. The upper of the two lowstand wedges is characterized by a complex arragement of shallow-marine and continental deposits. Shallow-marine deposits sharply overlying offshore shales and capped by a master sequence boundary are interpreted as falling-stage deposits recording a complex relative sea-level fall. On top of a regional erosion surface, a drying-upwards succession of fluvial-aeolian deposits is developed, recording a fully non-marine stage in the evolution of the basin. These deposits are overlain by a marginal marine evaporite succession. The absence of a return to fully open-marine conditions is attributed to uplift in the Andes and marks the transition of the Neuquén Basin from a back-arc to a foreland system. This succession has important implications for the basin’s evolution and in the timing of the uplift of the Andes, is a very spectacular example of a lowstand wedge and is also a major hydrocarbon reservoir.
Organic facies variations in the Valanginian-mid-Hauterivian interval of the Agrio Formation (Chos Malal Area, Neuquén, Argentina): local significance and global context
Authors: Tyson Richard V. , Esherwood Philip , Pattison Katherine A.
Published: April 2008

Marine shales and marls of the Valanginian-Hauterivian Agrio Formation have been studied at five localities in order to assess lateral variations over a 100 km S-N, shelf to basin transition. The two main organic-rich intervals at the base of the Pilmatue Member (Valanginian) and the base of Agua de la Mula Member (late early Hauterivian) have been characterized using a combination of bulk organic chemistry and palynofacies. Except for the former at the southern end of the transect, both intervals have mean total organic carbon (TOC) contents of 2–3% and are dominated by marine amorphous organic matter, suggesting a similar dysoxic genetic organic facies. The mean hydrogen indices determined from the slope of S2 v. TOC are 174 in the Pilmatue Member, but 387 in the basal part of the Agua de la Mula Member, a difference that mainly reflects the range in thermal maturity (late v. early oil window, respectively). Significant lateral variation occurs in the Pilmatue Member, with dark organic-rich intervals being rare in the south but dominant at the northern (distal) end of the transect; this trend is matched by a progressive increase in the peak or mean carbonate-free TOC and hydrogen indices, the latter reaching 6% and 297, respectively, near Estancia Pampa Tril. The bulk of the Agua de la Mula Member in the south is developed in organic-poor oxic facies, with a predominance of terrestrial phytoclasts and type IV kerogen, but dysoxic-anoxic conditions apparently predominate in the northern area. Valanginian-Hauterivian black shale facies appear generally rare on a global basis, but their occurrence can be related to the combination of the progressive rise in sea level during the Early Cretaceous and locally more restricted conditions.
Analogue benchmarks of shortening and extension experiments
Authors: Schreurs Guido , Buiter Susanne J. H. , Boutelier David , Corti Giacomo , Costa Elisabetta , Cruden Alexander R. , Daniel Jean-Marc , Hoth Silvan , Koyi Hemin A. , Kukowski Nina , Lohrmann Jo , Ravaglia Antonio , Schlische Roy W. , Withjack Martha Oliver , Yamada Yasuhiro , Cavozzi Cristian , Del Ventisette Chiara , Brady Jennifer A. Elder , Hoffmann-Rothe Arne , Mengus Jean-Marie , Montanari Domenico , Nilforoushan Faramarz
Published: April 2008

We report a direct comparison of scaled analogue experiments to test the reproducibility of model results among ten different experimental modelling laboratories. We present results for two experiments: a brittle thrust wedge experiment and a brittleviscous extension experiment. The experimental set-up, the model construction technique, the viscous material and the base and wall properties were prescribed. However, each laboratory used its own frictional analogue material and experimental apparatus. Comparison of results for the shortening experiment highlights large differences in model evolution that may have resulted from (1) differences in boundary conditions (indenter or basal-pull models), (2) differences in model widths, (3) location of observation (for example, sidewall versus centre of model), (4) material properties, (5) base and sidewall frictional properties, and (6) differences in set-up technique of individual experimenters. Six laboratories carried out the shortening experiment with a mobile wall. The overall evolution of their models is broadly similar, with the development of a thrust wedge characterized by forward thrust propagation and by back thrusting. However, significant variations are observed in spacing between thrusts, their dip angles, number of forward thrusts and back thrusts, and surface slopes. The structural evolution of the brittle-viscious extension experiments is similar to a high degree. Faulting initiates in the brittle layers above the viscous layer in close vicinity to the basal velocity discontinuity. Measurements of fault dip angles and fault spacing vary among laboratories. Comparison of experimental results indicates an encouraging overall agreement in model evolution, but also highlights important variations in the geometry and evolution of the resulting structures that may be induced by differences in modelling materials, model dimensions, experimental set-ups and observation location.
The numerical sandbox: comparison of model results for a shortening and an extension experiment
Authors: Buiter Susanne J. H. , Babeyko Andrey Yu. , Ellis Susan , Gerya Taras V. , Kaus Boris J. P. , Kellner Antje , Schreurs Guido , Yamada Yasuhiro
Published: April 2008

We report results of a study comparing numerical models of sandbox-type experiments. Two experimental designs were examined: (1) A brittle shortening experiment in which a thrust wedge is built in material of alternating frictional strength; and (2) an extension experiment in which a weak, basal viscous layer affects normal fault localization and propagation in overlying brittle materials. Eight different numerical codes, both commercial and academic, were tested against each other. Our results show that: (1) The overall evolution of all numerical codes is broadly similar. (2) Shortening is accommodated by in-sequence forward propagation of thrusts. The surface slope of the thrust wedge is within the stable field predicted by critical taper theory. (3) Details of thrust spacing, dip angle and number of thrusts vary between different codes for the shortening experiment. (4) Shear zones initiate at the velocity discontinuity in the extension experiment. The asymmetric evolution of the models is similar for all numerical codes. (5) Resolution affects strain localization and the number of shear zones that develop in strain-softening brittle material. (6) The variability between numerical codes is greater for the shortening than the extension experiment.

Comparison to equivalent analogue experiments shows that the overall dynamic evolution of the numerical and analogue models is similar, in spite of the difficulty of achieving an exact representation of the analogue conditions with a numerical model. We find that the degree of variability between individual numerical results is about the same as between individual analogue models. Differences among and between numerical and analogue results are found in predictions of location, spacing and dip angle of shear zones. Our results show that numerical models using different solution techniques can to first order successfully reproduce structures observed in analogue sandbox experiments. The comparisons serve to highlight robust features in tectonic modelling of thrust wedges and brittle-viscous extension.
Interaction between normal faults and pre-existing thrust systems in analogue models
Authors: Corti Giacomo , Lucia Serena , Bonini Marco , Sani Federico , Mazzarini Francesco
Published: April 2008

The influence of pre-existing thrusts on the development of later normal faults was investigated using scaled laboratory analogue models. Experiments consisted of a phase of shortening followed by extension at variable angles of obliquity (α) to the shortening direction. Results suggest that the angle α has a major influence on the surface fault pattern and on the interaction between shortening-related structures and later extensional structures. Three different modes of interactions were identified depending upon the extension kinematics. (1) For orthogonal extension (α = 0°), shortening-related fold and thrust structures strongly influence the development of normal faults: graben structures nucleate within anticlines and the normal faults reactivate thrusts at depth (
branching at depth mode of interaction
). (2) For highly oblique extension (α ≥ 45°), shortening-related structures exert no influence on normal faults as extension-related steeply-dipping faults (characterized by an oblique component of movement) displace early thrusts (
no interaction mode
). (3) For intermediate obliquity angles (α = 15°, 30°), an
intermediate mode of interaction
characterizes the experiments, where the
no interaction
and
branching at depth
modes coexist in different regions of models. Modelling results can be used to infer regional extension directions as is shown for the Northern Appenines (Italy).
Relative importance of trenchward upper plate motion and friction along the plate interface for the topographic evolution of subduction-related mountain belts
Authors: Hampel Andrea , Pfiffner Adrian
Published: April 2008

We present finite-element models that investigate the relative importance of both trenchward motion of the upper plate and interplate coupling for the development of topography at convergent margins. Commonly, the role of a trenchward moving continental plate for the growth of topography is neglected in both modelling and field studies. Instead, forces exerted by the downgoing plate on the continental plate as well as interplate coupling are thought to be responsible for the deformation of the upper plate. Our model set-up includes an oceanic plate, which is in contact with a continental plate along a frictional plate interface and driven by slab pull. Both lithospheres have an elasto-visco-plastic rheology. The models demonstrate that friction along the plate interface can only lead to a high topography if the upper plate is moving toward the trench. Without such a trenchward advance, no high topography is generated, as the upper plate subsides owing to the drag exerted by the subducting plate. Increasing the coefficient of friction only amplifies the drag and increases the amount of subsidence. Our findings imply that trenchward motion of the continental plate plays a key role for the development of mountain belts at convergent margins; subduction of an oceanic plate even with high interplate coupling cannot explain the formation of Andeantype orogens.
Analogue modelling of a reactivated, basement controlled strike-slip zone, Sierra de Albarracín, Spain: application of sandbox modelling to polyphase deformation
Authors: Merten S. , Smit W. G. , Nieuwland D. A. , Rondeel H. E.
Published: April 2008

This paper presents the results of an analogue modelling study on the reactivation of Riedel shears generated by basement-induced sinistral strike-slip faulting. It is based on a natural example in the Sierra de Albarracín, Iberian Range (Spain). The area has a polyphase deformation history, defined by the Variscan and Alpine orogenies. Late Variscan deformation was concentrated in a wide NW-SE shear zone with accompanying kilometre-scale E-W Riedel shears, which divided the Palaeozoic basement into large fault blocks. Alpine reactivation resulted in differential movements on the Riedel shears, as evidenced by a NW-SE chain of Palaeozoic inliers surrounded by a Mesozoic cover that generally shows minor deformations except near the E-W Riedel shears, where strata locally appear in near-vertical to overturned position.

Sandbox analogue modelling was applied to improve insight into the structural history. It focused on the kinematics of spontaneously developed en echelon Riedel shears, reactivated in a rotated stress field. Sand with a controlled added strength was used to form Riedel shears in a first deformation phase to act as weak zones for a second phase.

The modelling showed that in the first deformation phase large pop-up structures developed between the Riedel shears in a basement-induced sinistral strike-slip zone. Later reactivation in the N060°E and N135°E shortening directions was taken up respectively by sinistral-reverse and dextral-reverse shear along the pre-existing Riedel shears, but only if the sand on one side of the fault zone was allowed to move freely along the other. Scissor faulting along the Riedel shears with their complex 3D-geometry increased the height of the up-squeezed blocks. For experiments with fixed boundaries and no oil-water emulsion layer between the base plate and sand pack, thrusting at the backstop occurred rather than reactivation of the Riedel shears. This approach provided robust insights on the 4D development of the Sierra de Albarracín area.
Lithospheric scale gravitational flow: the impact of body forces on orogenic processes from Archaean to Phanerozoic
Authors: Rey Patrice F. , Houseman Gregory
Published: April 2008

In the Archaean, the combination of warmer continental geotherm with a lighter sub-continental lithospheric mantle suggests that gravitational forces played a more significant role in continental lithospheric deformation. To test this hypothesis, we compare the evolution of the deformation and the regional state of stress in ‘Archaean-like’ and ‘Phanerozoic-like’ lithospheres submitted to the same boundary conditions in a triaxial stress-field with imposed convergence in one direction. For plausible physical parameters, thickening of normal to cold Phanerozoic lithospheres produces relatively weak buoyancy forces, either extensional or compressional. In contrast, for Archaean continental lithospheres, or for anomalously warm Phanerozoic lithospheres, lateral gravitationally-driven flow prevents significant thickening. This conclusion is broadly consistent with: (1) the relative homogeneity of the erosional level now exposed at the surface of Archaean cratons, (2) the sub-aerial conditions that prevailed during the emplacement of up to 20 km of greenstone cover, (3) the relatively rare occurrence in the Archaean record of voluminous detrital sediments, (4) the near absence of significant tectonic, metamorphic and magmatic age gradients across Archaean cratons, (5) the relative homogeneity of strain across large areas, and (6) the ubiquitous presence of crustal-scale strike slip faults in many Late Archaean cratons.
Analogue and numerical modelling of accretionary prisms with a décollement in sediments
Authors: Yamada Yasuhiro , Baba Kei , Matsuoka Toshifumi
Published: April 2008

Active accretionary prisms at subduction margins generally include a horizontal detachment, décollement, within the sedimentary pile. The décollement, and its extension to undeformed regions (i.e., proto-décollement), corresponds to a layer of high fluid pressure. The deformation of the prisms, including such an anomalous layer, can be modelled and examined using analogue experiments and numerical simulations. Both these methods approximate the material under deformation as an assembly of particles (grains). The décollement layer is found to be best modelled by intercalating a layer with smaller internal frictional coefficient than the surrounding materials corresponding to the sediments. Our analogue experiments with dry sand and microglass beads reproduce structural geometry similar to that of interpreted seismic profiles at the toe of the prisms. Thrust faults originate from the horizontal beads layer and propagate upward with a constant angle of about 30°. Each of the fault bends produces a series of minor back thrusts. A particle image velocimetry (PIV) analysis revealed that the fault activity is characterized by intermittent reactivation and segmentation. The numerical simulations based on the distinct element method (DEM) were performed with similar kinematic settings and material properties as the analogue experiments. The numerical simulation results not only reproduce similar geometries as in the analogue experiments, but also show that the particle assembly experiences temporal variations in the deformation velocity and stress field as deformation propagates. This might be related to stick-slip motion of the frictional fault surfaces, which is a common feature of faulting during accretionary processes at subduction margins.
Integrated four-dimensional modelling of sedimentary basin architecture and hydrocarbon migration
Authors: Clarke S. M. , Burley S. D. , Williams G. D. , Richards A. J. , Meredith D. J. , Egan S. S.
Published: April 2008

Structural geometries, faults and their movement histories, together with the petrophysical properties of flow units, are some of the major controls on hydrocarbon migration pathways within sedimentary basins. Currently, structural restoration, fault-seal analysis and hydrocarbon migration are treated as separate approaches to investigating basin geohistory and petroleum systems. Each of these separate modelling approaches in their own fields is advanced and sophisticated but they are not compatible with each other. Lack of integration produces incorrect palaeogeometries in basin models and inaccurate migration pathways.

A combined structural restoration and fault-seal analysis technique, integrated with fast hydrocarbon migration pathway modelling code based on invasion percolation (IP) methods, is described. These modelling methods are used to develop a 4D basin modelling workflow in which evolving basin geohistories and geometries form an integral part of the analysis of hydrocarbon migration and trapping. By combining structural restoration and 3D fault-seal analysis it is possible to investigate the evolution of structurally complex traps through time. Integration of these techniques with a numerically fast migration pathway modelling technique allows hydrocarbon migration pathways and accumulations to be modelled through the evolution of the basin with time. Additionally, the effects of uncertainties in structural geometry, fault seal or any of the model input parameters can be explored using a risk-driven approach to modelling.

These methods are demonstrated using synthetic, computer generated, 3D models and a well-constrained model of the Moab Fault, Utah, USA. Comparison of modelled structural geometries, fault-seal properties and predicted trapped hydrocarbons with outcrop data is used to validate the integrated modelling approach. The validated techniques are then applied to a seismically derived, 3D model from the southern North Sea, UK, to demonstrate how an integrated, risk-driven approach to modelling allows the effects of uncertainties in the distribution of hydrocarbon accumulations to be investigated.
3D modelling of rifting through a pre-existing stack of nappes in the Gulf of Corinth (Greece): a mixed analogue/numerical approach
Authors: Le Pourhiet L. , Mattioni L. , Moretti I.
Published: April 2008

The Gulf of Corinth is a young (1 Ma) active rift currently extending N00, which displays significant contrasts in structural style along strike. A possible explanation for these variations is the presence of the Phyllades nappe in the basement of the western part of the Gulf. Previous 2D thermo-mechanical models have shown that a strong strength contrast between this metamorphic unit and the rest of the basement can explain the kinematics and the spacing of the faults in the western part. The rift, however, displays a wide variety of 3D features (e.g., en echelon faulting, N30 transverse normal faults) that cannot be taken into account using 2D modelling. To obtain 3D insights into the role of an inherited dipping weakness zone, analogue (sand and PDMS) experiments based on the results of the 2D numerical thermo-mechanical model have been performed. The analogue models show that a 30° discrepancy between the dipping direction of the weak nappe and the direction of extension leads to the formation of en echelon and N30 striking normal faults as observed in the Gulf of Corinth. However, fault spacing and graben width completely misfit both the data and the results of the thermo-mechanical models on which the analogue experiments were based. In order to understand those differences, numerical mechanical benchmarks of the analogue experiments have been run to test different factors (3D lateral displacements, values of the elastic parameters and bottom boundary conditions) that could have affected the dynamics of the analogue model. This approach highlights, for our case study, that the misfits are mostly related to the lack of isostatic compensation at the base of the analogue experiments.
Lower crustal rheological expression in inverted basins
Authors: Sandiford Mike , Hansen David L. , McLaren Sandra N.
Published: April 2008

Although lithospheric modelling has provided extraordinary insights into the processes that shape the continental crust, considerable uncertainty surrounds the basic rheology that governs behaviour at geological timescales. In part, this is because it has proved difficult to identify the geological observations that might discriminate, or unify, models of lithospheric rheology. In particular, the relative strength of lower crust and upper mantle remains a contentious aspect of continental lithospheric rheology. We show that various models for lower crustal rheology may produce distinct patterns of inversion in extensional sedimentary basins, consistent with some of the observed natural variability of inversion styles. Inversion of basin interiors, as is common in European Mesozoic basins, is favoured by a lithospheric rheology more sensitive to lateral thermal structure than to changes in the depth of the Moho, consistent with there being little strength contrast between the lower crust and upper mantle in these settings. In contrast, inversion of basin margins, particularly involving basinward verging structures, is consistent with a rheological sensitivity to the depth of Moho as would apply for a lower crust much weaker than the upper mantle. We use an example from central Australia to demonstrate this latter response, together with thermochronologic data that suggests that a relatively weak lower crust in this setting may reflect abnormally high geothermal gradients.
Using an elastic dislocation model to investigate static Coulomb stress change scenarios for earthquake ruptures in the eastern Marmara Sea region, Turkey
Authors: Muller Jordan R. , Aydin Atilla , Wright Tim J.
Published: April 2008

Using an elastic dislocation model, we incorporate a historical earthquake catalog, mapped Marmara Sea fault traces, and fault slip distributions for the 1999 Izmit earthquake inferred from InSAR and GPS data to determine various stress change scenarios crucial for evaluating future earthquake potential in the eastern Marmara Sea. We have tested six plausible past rupture configurations arising from the uncertainty in the location of the western termination of 1999 Izmit earthquake rupture and the location of the 1963 Yalova earthquake rupture. Coulomb stresses calculated are increased on the Princes’ Islands, Çinarcik, and Armutlu fault segments in each case. In four of the six plausible configurations of previous ruptures, the Çinarcik fault receives the greatest average stress change. In one other configuration, the average stress increase on the Princes’ Islands fault is greatest. In another, the stress changes on the Çinarcik and Princes’ Islands faults are comparable. Moreover, we show that rupture initiating on either the Princes’ Islands or Armutlu faults would be favoured to propagate onto the Central Marmara, or Imrali fault, respectively, based on the favourable geometries of the respective fault intersections. Rupture initiating on the Çinarcik fault, however would be limited to a much shorter length based on its mapped western termination. Therefore, while the earthquake-induced stress changes may, in most cases, be greatest on the Çinarcik fault, an earthquake initiating on this fault segment may produce a shorter cumulative rupture compared to rupture initiated on the two other major eastern Marmara Sea fault segments. These results are encouraging for the use of geomechanical modelling tools in addressing uncertainties inherent in most geological and geophysical data applied to earthquake-related problems.
Oil reservoirs in foreland basins charged by thrustbelt source rocks: insights from numerical stress modelling and geometric balancing in the West Carpathians
Authors: Nemčok Michal , Henk Andreas
Published: April 2008

The West Carpathian thrustbelt advanced northeastwards over the European Platform. Its thrust sheets comprise sediments of the Early Cretaceous rifts that evolved on a passive margin of the European Platform, the Late Cretaceous-Paleocene basins formed by rift inversion, and the Eocene-Oligocene flexural basin. Geochemical analyses established a clear link between pooled oils in the foreland and the Oligocene Menilite Formation inside the thrustbelt. In order to understand the driving forces for this oil migration scenario, finite-element models of fault-propagation and fold-bend folds are used to study the mean stress distribution in the thrust sheets and the foreland. Mean stress has a profound control on the pore fluid pressure through the relationship affected by sediment porosity, and sediment skeleton and fluid compressibilities. Modelling results suggest that only fault-propagation folds are capable of generating foreland-directed mean stress gradients as they are characterized by a large foreland area of decreased mean stress, by coupled increased/decreased mean stress areas on advancing/receding sides of the ramp tip, and an overall mean stress decrease inside the thrust sheet in the direction towards the foreland. This interpretation is in accordance with the dominant fold-and-thrust style in the Western Carpathians inferred from balanced cross-section restoration. It shows that frontal fault-propagation folding was active during the late Oligocene-Early Miocene, providing an effective tectonic driving force for hydrocarbon migration from source rocks inside the thrustbelt towards reservoirs in the foreland.
Relation between effective friction and fault slip rate across the Northern San Andreas fault system
Authors: Provost Ann-Sophie , Chéry Jean
Published: April 2008

The San Andreas Fault system is a complex tectonic ensemble that accommodates most of the relative plate motion between the Pacific and the North American plates. The structure and rheological properties of the faults vary along the plate boundary and lead to the distribution of deformation that we observe today. In order to learn more about the mechanical behaviour of such a fault system, a model of the northern California fault system is built, constrained by heat flow data, GPS and palaeoseismological measurements of slip rates (on the San Andreas, the Maacama and Bartlett Springfaults), and stress orientations. Our basic assumption is that the upper crust has a high frictional strength and that major faults represent weak zones with a lower effective friction. Several combinations of effective fault frictions on the three major faults of the system in the model are tested. We find that slight variations of the effective friction angle on one of the three active strands lead to an important redistribution of slip rates through the system. If present in nature, this fault behaviour could explain why fault slip rates vary in time, as suggested by slip rate variations over geological scales in intracontinental fault systems.