No description available.

Assemblages of Paleozoic age and less significant Triassic and possibly Cretaceous-Tertiary volcanic rocks constitute the Sierra El Aliso, 186 km east-southeast of Hermosillo, Sonora. The Paleozoic section consists of approximately 2000 m of allochthonous Ordovician to Permian pelagic and hemipelagic deposits that accumulated in continental slope, continental rise and ocean floor (?) environments. The lower Paleozoic is characterized by graptolitic black shale and radiolarian chert, quartzite, argillite and local limestone. The upper Paleozoic is predominantly turbidite carbonates rich in benthonic foraminifera, and conodont faunas, subordinate bedded chert, siltstone, sandstone and chert-clast conglomerate. After Early Permian time, but prior to the deposition of the Late Triassic Barranca Group the Paleozoic section was imbricated along south-southeast vergent thrust faults. The Triassic rocks unconformably overlie the Paleo-zoic strata and all thrust faults. The Triassic and older rocks are overlain by the Cretaceous-Tertiary volcanics.

Aujourd’hui, l’un des principaux défis dans l’industrie pétrolière, et particulièrement dans le domaine de l’exploration, est l’exploitation des nouvelles ressources dans des zones structuralement complexes.Nous savons que la géométrie et le glissement le long des failles actives modifie la distribution locale des contraintes. La connaissance du champ de contrainte perturbé actuel est importante pour l’étude des tremblements de Terre, pour la planification de forages ainsi que pour la prédiction de la fracturation induite par l’hydro-fracturation et la prédiction de la réactivation des fractures. Les contraintes perturbées passées, quant à elles sont responsables du développement des fractures naturelles (préexistantes). La détection et la modélisation de celles-ci sont essentielles tant dans le domaine pétrolier (migration et piégeage des fluides) pour une exploitation efficace et à moindre coût des réserves naturelles.Comprendre et quantifier le développement spatial et temporel de ces contraintes a un impact économique non négligeable. L'analyse des paléo-contraintes a été introduite dans un premier temps par Anderson (1905 & 1942) de manière intuitive, puis dans le milieu du siècle dernier, Wallace (1951) et Bott ( 1959) proposèrent les simples postulats que le champ de contrainte est homogène et que la direction du rejet est parallèle à la traction projetée sur le plan de faille. Beaucoup de méthodes d’inversion de contraintes reposent aujourd’hui sur ce principe.Afin d’étudier la validité de l’hypothèse Wallace et Bott, une comparaison avec les vecteurs de glissement générés à partir de modèles numériques (BEM) est effectuée. En testant l’influence de multiples paramètres (géométrie, contraintes au limites du modèle, friction, coefficient de poisson, demi-espace, pression de fluide dans la faille), il est montré que les failles à géométries complexes soumises à certaines contraintes aux limites peuvent engendrer des vecteurs glissements présentant des écarts important avec les la plus grande contraintes cisaillantes résolue sur le plan de faille. A l’inverse, la présence d’une forte friction de glissement permet, dans certaines conditions, de valider l’hypothèse de Wallace et Bott. On s’attache ensuite à comparer les résultats des inversions de contraintes basées sur l’hypothèse de Wallace et Bott (appelé méthode d’inversion classique de contraintes) avec une méthode géomécanique. Pour cela, une faille à géométrie complexe est utilisée dans une étude de sensibilité (contraintes aux limites, friction, échantillonnage) permettant d’analyser l’incertitude des résultats des deux méthodes d’inversion. Cette analyse est ensuite confrontée à l’étude d’un cas de terrain, montrant les avantages et inconvénients des méthodes d’inversions classiques de contraintes.Un des principaux défis de l’industrie pétrolière est l’exploitation des ressources des zones structuralement complexes telles que les réservoirs naturellement fracturés. Connaitre l’état de contraintes hétérogène passé permet d’optimiser la modélisation de ces fractures naturelles. Etant donné que les glissements sur les failles sont difficiles à observer dans les réservoirs pétroliers, les données de d’orientation de fractures (joints, failles, stylolites) sont naturellement prises en compte lors de l’inversion des contraintes. On montre, en utilisant divers exemples de terrain et d’industrie, que dans de tels cas, l’utilisation d’inversions basée sur la mécanique est beaucoup plus appropriée. Cependant, il est parfois difficile de déterminer le type cinématique de fracture observée le long des puits, et très souvent, les zones étudiées ont subi une tectonique polyphasée. La dernière partie vise donc à résoudre le problème des données de types cinématiques non identifiables (joints, failles, stylolites…) et étend parallèlement l’inversion mécanique des contraintes à la séparation de phases tectoniques. / Today, one of the main challenges in the oil industry, especially during the exploration phase, is the exploitation of new resources in structurally complex areas such as naturally fractured reservoirs, salt diapirs, mountain ranges, and unconventional reservoirs.We know that the geometry and sliding along active faults modifies the local stress distribution. Knowing the present day perturbed stress field is important for the study of earthquakes, for the planning of the borehole drilling and stability as well as for the prediction of fractures induced by hydro-fracturing and reactivation of natural fractures. In the other side, perturbed paleostress are responsible for the development of (pre-existing) natural fractures. The detection and modeling of the latter, are essential both in the oil industry (migration and trapping of fluids) for a cost efficient recovery of natural reserves.Understanding and quantifying the spatial and temporal development of the stress distribution has a significant economic and environmental impact. The analysis of paleo-constraints was intuitively introduced first by Anderson (1905 & 1942), then in the middle of the last century, Wallace (1951) and Bott (1959) proposed the simple hypothesis that (i) The stress field is homogeneous in space and constant in time, and that (ii) the slip direction is parallel to the traction projected on the fault plane which gives the direction of the shear stress. Many stress inversion methods are based on this hypothesis while recent studies raise doubts as to their compatibility with rock mechanics.In order to investigate the validity of the Wallace and Bott hypothesis, a comparison with vectors of slip generated with numerical models (BEM) is performed. By testing the influence of multiple parameters (geometry, boundary conditions, friction, Poisson’s coefficient , half-space, fault fluid pressure), it is shown that the complex geometry faults subject to specific boundary conditions can yield slip vectors with significant discrepancies with the maximum shear stress resolved on the fault plane. Conversely, the presence of a high sliding friction, allows under certain conditions, to validate the hypothesis of Wallace and Bott.We then focus on the task to compare the results of stress inversions based on the assumption of Wallace and Bott (called classical stress inversion methods) to a geomechanical method. For this, a complex fault geometry is used in a sensitivity analysis (boundary conditions, friction, sampling) to evaluate the uncertainty of the results of the two inversion methods. This analysis is then compared to a case study, Chimney Rock (Utah, USA), showing the advantages and disadvantages of the classical stress inversion methods.One of the main challenges of the oil industry is the exploitation of resource in structurally complex oil fields such as naturally fractured reservoirs. Knowing the heterogeneous paleostress allows to optimize the modeling of these natural fractures. Since slip on faults is hardly observed in petroleum reservoirs, fracture orientation data (joints, faults, stylolites) are naturally taken into account during the inversion of stresses. It is shown, using various field and industry examples, that in such cases the use of mechanical stress inversions is much more appropriate.However, it is sometimes difficult to determine the fracture kinematics observed along wellbores, and very often the studied regions underwent multiple tectonic phases. The final section aims to address the problem of data with unknown kinematic (joints, faults, stylolites ...) and expends the mechanical stress inversion to the separation of tectonic phases.

As relações entre tectônica e sedimentação são fatores primordiais na compreensão geológica de sucessões sedimentares. Por sua vez, o estudo de depósitos fluviais pré-silurianos representa um desafio a esta área do conhecimento em consequência da ausência de interação entre rios e plantas terrestres que ocorre nos depósitos fluviais recentes. A Bacia do Camaquã (Ediacarano a Eocambriano) apresenta extensas exposições que possibilitam neste presente trabalho a discussão da sedimentação sob o ponto de vista de um modelo tectônico definido. Através da análise de fácies sedimentares e arquitetura deposicional, a caracterização da unidade estratigráfica basal do Grupo Guaritas (Eocambriano), a Formação Guarda Velha, um espesso pacote sedimentar de depósitos fluviais, levou à reconstituição das características do ambiente de sedimentação, considerando-se a influência da tectônica sin-deposicional e de fatores climáticos. É interpretado um estilo fluvial entrelaçado com grande variação de vazão, alta taxa de aporte sedimentar e grandes dimensões. Diversas estruturas de deformação sinsedimentares de reologia dúctil originadas por sismos são investigadas como indicadores da atividade tectônica sin-sedimentar e correlacionadas às informações de fácies sedimentares e elementos arquiteturais para caracterização do ambiente deposicional, revelando uma bacia com intensa atividade sísmica penecontemporânea. A caracterização dessas estruturas leva ao questionamento sobre o caráter efêmero do sistema fluvial proposto em trabalhos anteriores para a Formação Guarda Velha. Um importante evento reconhecido através da análise de estruturas rúpteis e responsável pela discordância angular entre os Grupos Santa Bárbara e Guaritas, é caracterizado por falhas transcorrentes e oblíquas geradas por compressão NE-SW. As evidências da intensa atividade sísmica sin-deposicional são correlacionadas ao evento regional distensivo com 3 NW-SE e posterior à compressão NE-SW, atribuído ao evento de subisidência responsável pela deposição do Grupo Guaritas. A Bacia do Camaquã apresentou também intensa atividade tectônica após a deposição do Supergrupo Camaquã, notadamente com eventos transcorrentes deformacionais, distintos dos eventos distensionais formadores da bacia. Notadamente foi reconhecido um evento de deformação transcorrente principal na região com direção principal de esforços WNW, estruturas de direção E-W com cinemática destral e estruturas de direção NNE apresentando cinemática sinistral. Este evento foi seguido então por uma distensão NW, que por sua vez precedeu um evento compressivo com direção principal de esforços NNE a N-S, responsável por estruturas com cinemática contrária à do evento transcorrente principal. Finalmente, foi reconhecido um evento de deformação com falhas predominantemente normais geradas por distensão NE, interpretado como de idade cretácea. Desta forma, as evidências coletadas no presente estudo da Formação Guarda Velha revelam intensa atividade sísmica sin-deposicional relacionada ao evento regional distensivo com 3 NW-SE e concomitante a deposição em planícies aluviais com predomínio de carga de fundo e grande variação de vazão, durante a subsidência inicial do rift continental eocambriano do Rio Grande do Sul. / The relationship between tectonics and sedimentation plays a primordial role in the understanding of sedimentary successions. On the other hand, the study of pre-Silurian fluvial deposits represents a challenge due to the lack of interaction between land plants and river systems which characterizes post-Silurian environments. The Camaquã Basin (Ediacaran to Eocambrian) presents extensive exposures allowing investigations of sedimentary environments under a well defined tectonic model. Through the analysis of sedimentary facies and depositional architecture, the geological characterization of the basal stratigraphic unit of the Guaritas Group (Eocambrian), the Guarda Velha Formation, a thick sedimentary strata composed of fluvial deposits, provided the recognition of the sedimentation environment, considering the influence of sin-depositional tectonics and climatic factors. A braided fluvial style with great discharge variation, high sedimentary load and large dimensions was identified. Many seismically triggered ductile sin-sedimentary deformation structures found in the area bring information about the tectonic activity during sedimentation and were correlated using sedimentary facies and architectural elements analysis in order to describe the depositional environment, revealing a basin system dominated by an intense contemporaneous seismic activity. The characterization of these structures lead to a questioning about the until now accepted model of ephemerous channels for this fluvial system. An important event recognized by means of brittle structures analysis was identified as the origin of the angular unconformity between the Santa Bárbara Group and the Guaritas Group which is characterized by strike-slip and oblique faults generated by a NE-SW compression. The intense sin-depositional seismic activity evidences are correlated to an extensional event with 3 direction NW-SE, which post-dates the compression and was responsible for the subsidence of the Guaritas Group. The Camaquã Basin also records an intense tectonic activity that occurred after the deposition of the Camaquã Supergroup, markedly deformational strike-slip events. The most important event recognized on the studied region had a mean WNW stress direction, with E-W structures showing right-slip kinematics and NNE structures presenting left-slip kinematics. Following this event a NW extension followed by a NNE to N-S compression were recognized, the late showing structures with reverse kinematics to the mean strike-slip event. At last, a NE extension event originated normal faults dated of Cretaceous age. Conclusively, the Guarda Velha Formation here collected data reveals an intense seismic activity related to an extension event showing 3 NW-SE concomitantly to a bed load-dominated aluvial plain deposition and great discharge variability, during the initial subsidence of the Guaritas rift (Eocambrian) in southern Brazil.

Abstract not available

&Ccedil / i&ccedil / ekdagi basin developed on the Central Anatolian Crystalline Complex (CACC) is a foreland basin developed as the southern integral part of the &Ccedil / ankiri Basin during the Late Paleocene to middle Oligocene. The basin has two compartments separated by the &Ccedil / i&ccedil / ekdagi High comprises two sedimentary cycles. The oldest cycle comprises Barakli, Koca&ccedil / ay and Bogazk&ouml / y formationsa and is exposed both in the northern and the southern sectors. They were deposited in marine conditions. The second cycle comprises incik and G&uuml / vendik formations and was deposited in continental settings. The first cycle comprises uniformly south-directed paleocurrent directions in both the northern and southern sectors whereas the second cycle deposits are represented by south-directed directions in the southern sector, and bimodal directions in the northern sector. In addition, the second cycle formations contain progressive unconformities and coarsening upwards sequences indicative of thrusting. Internal structures of the units and paleostress data indicate that the basin experienced over-all compression and local extension due to flexural bending. This gave way to inversion of some of the normal faults and uplift of the &Ccedil / i&ccedil / ekdagi High during the deposition of second cycle in the Late Eocene to middle Oligocene time which subsequently resulted in compartmentalization of the basin.

Spatial ability and the skill to visualize objects is necessary for earth scientist, especially structural geologist. For this reason, undergraduate students within earth science needs to learn this skills, and how is the best way to teach this skills. To implement 3D thinking in undergraduate teaching, three strategies are presented. The first one is to separate and combine objects, which includes to see geological differences and categorize them. Secondly, visualize objects, both many and single ones and see which ones who are connected. Third and lastly is still and moving objects which involves geological processes. It is important to give students time to develop their spatial abilities and help them during the learning process. Another aspect to this is the path of information within the human brain when visualizing an object. The result shows that the process starts with the human eye which perceive the object and its attributes, then the geniculate nucleus sorts the information and directs it toward the visual primary cortex located in the occipital lobe. The primary visual cortex then send the information though the ventral- and dorsal steam which produces a visualization. Aspects which can affect the spatial ability may be earlier experiences, age and the way each person perceive the object. These factors effects how hard humans think the process of visualization is. The questionnaire showed that 3D models help students to visualize and should be used more in undergraduate teaching. / Förmågan att visualisera objekt och förstå dem är nödvändig för en geovetare, speciellt inom strukturgeologi. Därför är det viktigt att studenter på kandidatprogram i geovetenskap får tillfälle att lära sig den förmågan. För att implementera 3D-tänkande i undervisningen har tre strategier tagits fram. Den första är att separera och kombinera objekt, vilket inkluderar att se geologiska skillnader och kategorisera dem. Den andra är att visualisera ett eller flera objekt och se vilka som är kopplade till varandra. Den tredje är att se objekt som är i stilla eller i rörelse, vilket involverar geologiska processer. Det är viktigt att ge studenterna tid för att utveckla sin spatiala förmåga och att hjälpa dem under utvecklingen. Arbetet syftar också till att ta reda på hur visuell information bearbetas av den mänskliga hjärnan. Först bearbetas informationen av ögat, sen till geniculate nucleus som sorterar informationen och skickar den till det primära visuella cortex som ligger i occipital-loben. Därefter processas informationen av ventrala och dorsala stammen och det är här som en visualisering produceras. Faktorer så som ålder, tidigare erfarenheter och hur ögat uppfattar objekten påverkar hur visualiseringen blir och hur svårt individen uppfattar processen. Enkätundersökningen visade på att 3D-modeller hjälper studenter att visualisera och borde användas mer i undervisning på kandidatnivå.

Arc-continent collisions are believed to be an important mechanism for the growth of continents. Taiwan is one of the modern day examples of this process, and as such, it is an ideal natural laboratories to investigate the uncertain behavior of continental crust during collision. The obliquity of collision between the northern South China Sea (SCS) rifted margin and Luzon arc in the Manila trench subduction zone allows for glimpses into different temporal stages of collision at different spatial locations, from the mature mountain-belt in central-northern Taiwan to the 'pre-collision' rifted margin and subduction zone south of Taiwan. Recently acquired seismic reflection and wide-angle seismic refraction data document the crustal-scale structure of the mountain belt through these different stages. These data reveal a wide rifted margin near Taiwan with half-graben rift basins along the continental shelf and a broad distal margin consisting of highly-extended continental crust modified by post-rift magmatism. Magmatic features in the distal margin include sills in the post-rift sediments, intruded crust, and a high-velocity lower crustal layer that likely represents mafic magmatism. Post-rift magmatism may have been induced by thermal erosion of lithospheric mantle following breakup and the onset of seafloor spreading. Geophysical profiles across the early-stage collision offshore southern Taiwan show evidence the thin crust of the distal margin is subducting at the Manila trench and structurally underplating the growing orogenic wedge ahead of the encroaching continental shelf. Subduction of the distal margin may induce a pre-collision flexural response along the continental shelf as suggested by a recently active major rift fault and a geodynamic model of collision. The weak rift faults may be inverted during the subsequent collision with the continental shelf. These findings support a multi-phase collision model where the early growth of the mountain belt is driven in part by underplating of the accretionary prism by crustal blocks from the distal margin. The wedge is subsequently uplift and deformed during a collision with the continental shelf that involves both thin-skinned and thick-skinned structural styles. This model highlights the importance of rifting styles on mountain-building. / text

The Monashee Complex is a structural culmination which exposes rocks from the lowest stratigraphic levels of the Canadian Cordillera. The Monashee Complex is subdivided into two lesser structural culminations; the Frenchman Cap and Thor–Odin culminations. The lithostratigraphic succession of the Thor–Odin Culmination is completely transposed by penetrative isoclinal folds with amplitudes from microscopic (<1 mm) to regional (10’s km). Lower structural levels are occupied by Proterozoic gneisses and migmatites of the Monashee basement assemblage. These are infolded with overlying metasedimentary rocks of the Monashee cover assemblage, which are Proterozoic to possibly Paleozoic in age. The basement and cover assemblages were subsequently intruded by Eocene granitic pegmatite, aplite and lamprophyre dykes. Regional metamorphism of the basement and cover assemblages reached upper amphibolite to lower granulite facies. The northeastern portion of the Thor–Odin Culmination of the Monashee Complex contains a suite of structures and fabrics, which are classified into four sets, based on their interpreted kinematic significance. These are: 1) transposition related structures (DT); 2) open, upright folds (DO); 3) exhumation related structures (DE); and 4) brittle faults (DB). Each successive set of structures exerted a control on the geometry of the next set. The large-scale geometry of the culmination is an interference structure between DT folds, a DE arch and high-strain zones, and a DB brittle horst. Early, DT fold style varies from intrafolial isoclinal “mature” style folds to upright or inclined asymmetric “immature” folds. This continuum of fold styles, along with evidence of anticlockwise rotation (looking down a vertical axis toward the shear plane) of fold axes and lineations is interpreted as being a result of penetrative triclinic non-coaxial flow. DO upright, symmetrical folds overprint early structures and fabrics, but are only preserved at low structural levels in the culmination where the DE coaxial stretching overprint is weak. DE normal shear bands and boudins overprint all earlier structures. A complex high-strain zone, the Thor–Odin High-Strain Zone, outcrops at high structural levels and along the margins of the culmination. The Thor–Odin High- Strain Zone developed as a result of material moving away from the crest of the culmination, outwards toward the flanks. Eocene brittle faults (DB) and fractures within the Thor–Odin Culmination of the Monashee Complex are divisible into three distinct sets. Initial 340–010º trending strikeslip faults (Set 1) were locally overprinted and reactivated by normal faults with a 325– 020º trend (Set 2). A third set of 255–275º trending fractures (Set 3) are interpreted as conjugates to Set 1, reactivated as transfer faults to the Set 2 normal faults. Large regional faults weather recessively forming topographic lineaments that transect the Monashee Complex. The Victor Creek Fault defines one such lineament. Detailed mapping within the northern Thor–Odin Culmination, reveals piercement points (fold hinges) on the east side of the fault, which are not readily matched on the west side. The minimum displacement required on the Victor Creek Fault to down-drop the fold hinge below the level of exposure on the west side is 1370 m, assuming normal down-to-the west displacement. However, the geometry of the fault is consistent with a Set 1 dextral strike-slip fault. Matching the piercement points in the study area with possible equivalents to the north indicates 55–60 kms of dextral strike-slip displacement. The Monashee Reflection (MR) is a major crustal-scale, cross-cutting reflection appearing on two mutually perpendicular Lithoprobe seismic profiles in the southern Omineca Belt of the Canadian Cordillera. It has previously been interpreted as the downplunge extension of an arched regional ductile thrust fault, the Monashee Décollement, and is described as separating the Monashee Complex from the overlying Selkirk Allochthon. Recent mapping demonstrates that this boundary is not a discrete ductile thrust, but rather transposed and gradational. Overprinting the transition zone is a complex, outward-dipping, normal, structure; the Thor−Odin High-Strain Zone. Three alternative 3-D geometric models have been developed for the MR in order to project the reflection to the surface. The favoured model correlates the surface trace of the Thor−Odin High-Strain Zone with MR. Normal shear sense kinematics are interpreted for the MR based on: 1) the overall geometry and asymptotic relationship between the MR and reflections in the hanging wall and footwall; 2) offset of metamorphic and geochronological gradients, consistent with an extensional zone, rather than with thrust fault interpretation and 3) the cross-cutting nature of the MR is consistent with normal structures throughout the region.

Large-scale accretionary and collisional crustal orogenic architecture is studied combining structural geology, lithostratigraphy, geochronology and magmatic petrology with gravity, magnetic and seismic data. This multidisciplinary approach allows characterizing the structure and composition of the orogenic crust in two accretionary-collisional systems. The Central Asian Orogenic Belt (CAOB) constituting one third of the Asia continent and the Bohemian Massif are two Palaeozoic orogens formed by accretion followed by collision. It is proposed that the CAOB formed by successive Paleozoic accretion of oceanic and continental fragments followed by a late Palaeozoic to early Mesozoic N-S convergence of North Chinese and Siberian Cratons. The comparison between the potential fields and the geological data reveals an incorrect compartmentalization into different lithostratigraphic terranes. In contrast to geology the geophysical approach allows the analysis of the crustal structures on a complete thickness of crustal column. This thesis presents a compilation of geological data combined with unique gravity and magnetic results which are integrated into a preliminary model for the architecture of the continental crust. Conversely, an important collection of complementary data is available for the Bohemian Massif, allow more precise 3D geophysical forward modeling. In this area, geophysical data reveal the occurrence of an allochtonous lower crustal layer with a felsic composition. This indicates that the Variscan orogenic crust actually resulted from the accretion of contrasted crustal fragments.