Fault growth

We use discrete element modeling to investigate three-dimensional fault geometry and the three-dimensional evolution of a fault network that develops above a 60° dipping planar pre-existing weakness striking 60° relative to the extension direction. The evolution of the fault network comprises three stages: (i) reactivation of preexisting structure and nucleation of new faults (0-10% extension); (ii) radial propagation and interaction between reactivated structure and new faults (15%-20% extension); and (iii) linkage between reactivated structure and adjacent faults (20%-25% extension). During the first stage, the pre-existing structure mostly reactivates, forming a long and under-displaced fault. New faults are mainly extensionperpendicular and dip at 60°. During the second stage, 'saw-tooth' fringes grow upwards from the upper tip of the reactivated structure (which becomes the major fault) and influence the density and orientation of surrounding faults. During the third stage, the reactivated structure links laterally and vertically with adjacent faults, creating non-planar fault geometries. Following linkage, the reactivated structure enhances the displacement of linked faults along branch lines. Our study demonstrates that pre-existing weak faults can be reactivated, propagating upwards in an irregular ('saw-tooth') pattern, and affecting fault density, orientation, dip and displacement, and providing the nucleation site of new faults.

Mass transport by aqueous fluids is a dynamic process in shallow crustal systems, redistributing nutrients as well as contaminants. Rock matrix diffusion into fractures (void space) within crystalline rock has been postulated to play an important role in the transient storage of solutes. The reacted volume of host rock involved, however, will be controlled by fluid-rock reactions. Here we present the results of a study which focusses on defining the length scale over which rock matrix diffusion operates within crystalline rock over timescales that are relevant to safety assessment of radioactive and other long-lived wastes. Through detailed chemical and structural analysis of natural specimens sampled at depth from an active system (Toki Granite, Japan), we show that, contrary to commonly proposed models, the length scale of rock matrix diffusion may be extremely small, on the order of centimetres, even over timescales of millions of years. This implies that in many cases the import...

Chief Dr. Andrés Folguera for his support of this project. Janaki Bakthavachalam and Emilie Wang were our contact at Elsevier and provided quick responses to editorial responsibilities and occasional system troubles. We would especially like to thank the scientists that have contributed papers to this issue of the Journal of South American Earth Sciences. The reviewers generously lent us their time and expertise to improve the overall quality of the manuscripts; their comments and suggestions were greatly appreciated by both authors and guest editors of this volume. We thank,

Mass transport by aqueous fluids is a dynamic process in shallow crustal systems, redistributing nutrients as well as contaminants. Rock matrix diffusion into fractures (void space) within crystalline rock has been postulated to play an important role in the transient storage of solutes. The reacted volume of host rock involved, however, will be controlled by fluid-rock reactions. Here we present the results of a study which focusses on defining the length scale over which rock matrix diffusion operates within crystalline rock over timescales that are relevant to safety assessment of radioactive and other long-lived wastes. Through detailed chemical and structural analysis of natural specimens sampled at depth from an active system (Toki Granite, Japan), we show that, contrary to commonly proposed models, the length scale of rock matrix diffusion may be extremely small, on the order of centimetres, even over timescales of millions of years. This implies that in many cases the import...

Up to 10% of the liquid hydrocarbons of the Golfo San Jorge basin come from the Mina del Carmen Formation (Albian), an ash-dominated fluvial succession preserved in a variably integrated channel network that evolved coeval to an extensional tectonic event, poorly analyzed up to date. Fault orientation, throw distribution and kinematics of fault populations affecting the Mina del Carmen Formation were investigated using a 3D seismic dataset in the Cerro Dragón field (Eastern Sector of the Golfo San Jorge basin). Thickness maps of the seismic sub-units that integrate the Mina del Carmen Formation, named MEC-AeMEC-C in ascending order, and mapping of fluvial channels performed applying geophysical tools of visualization were integrated to the kinematical analysis of 20 main normal faults of the field. The study provides examples of changes in fault throw patterns with time, associated with faults of different orientations. The "main synrift phase" is characterized by NEeSW striking (mean Az ¼ 49), basement-involved normal faults that attains its maximum throw on top of the volcanic basement; this set of faults was active during deposition of the Las Heras Group and Pozo D-129 formation. A "second synrift phase" is recognized by EeW striking normal faults (mean Az ¼ 91) that nucleated and propagated from the Albian Mina del Carmen Formation. Fault activity was localized during deposition of the MEC-A sub-unit, but generalized during deposition of MEC-B sub-unit, producing centripetal and partially isolated depocenters. Upward decreasing in fault activity is inferred by more gradual thickness variation of MEC-C and the overlying Lower Member of Bajo Barreal Formation, evidencing passive infilling of relief associated to fault boundaries, and conformation of wider depocenters with well integrated networks of channels of larger dimensions but random orientation. Lately, the Mina del Carmen Formation was affected by the downward propagation of EeW to ESEeWNW striking normal faults (mean Az ¼ 98) formed during the "third rifting phase", which occurs coeval with the deposition of the Upper Member of the Bajo Barreal Formation. The fault characteristics indicate a counterclockwise rotation of the stress field during the deposition of the Chubut Group of the Golfo San Jorge basin, likely associated to the rotation of Southern South America during the fragmentation of the Gondwana paleocontinent. Understanding the evolution of fault-controlled topography in continental basins allow to infer location and orientation of coeval fluvial systems, providing a more reliable scenario for location of producing oil wells.

Chief Dr. Andrés Folguera for his support of this project. Janaki Bakthavachalam and Emilie Wang were our contact at Elsevier and provided quick responses to editorial responsibilities and occasional system troubles. We would especially like to thank the scientists that have contributed papers to this issue of the Journal of South American Earth Sciences. The reviewers generously lent us their time and expertise to improve the overall quality of the manuscripts; their comments and suggestions were greatly appreciated by both authors and guest editors of this volume. We thank,

Spatial distribution and three-dimensional location of cataclastic rocks within fault zones deeply influence their rheology and permeability properties. Despite their importance in hydrocarbon research and development, location and triggering factors of cataclasite formation are poorly understood.

The highly heterogeneous permeability field of the Earth's brittle crust has long been a challenge to those seeking to extract its fluid resources. We discuss the geologic and geophysical evidence that the ambient seismic method of permeability field imaging (PFI) solves this problem not by modeling, but by directly mapping the permeability field in its quantitative manifestation and temporal evolution. Further, we describe a permeabilityproducing mechanism that operates across the full range of micro-to macroscales. These results are placed in the context of the principles of critical state rock physics as they apply to the PFI method. The PFI signal is due to minute elastic vibrations of these fluid-filled voids activated by the near-continuous movement of episodic stress waves through the brittle crust. Passive seismic observation of both ambient and induced seismic events can be recorded, for example, using standard three-dimensional seismic reflection receiver technology. These signals, whose source is the permeability itself and is processed with PFI methods, can produce a five-dimensional (space, time, energy) permeability field map. Whereas sedimentary basins have a prominent role in our discussion, our current knowledge is that PFI permeability field maps can be made for all lower-temperature (<250 C), brittle rock, nonmetamorphic environments.

The Late Eocene (?)/Oligocene-Recent Nakhon Basin located in the western portion of the Gulf of Thailand has a NW-SE trending half-graben structure controlled by a NE dipping boundary fault on the SW margin of the basin. Six marker horizons were interpreted to determine significant geological events in the basin. Faults are subdivided into two sets based on orientation. The NW-SE, NE dipping boundary fault comprises two segments, Y and X. The two fault segments are inferred to follow NW-SE pre-existing fabrics in the pre-rift section. The N-S trending fault sets are separated into two groups, early syn-rift faults and syn-rift faults. During the syn-rift stage (Oligocene-Middle Miocene), the basin was dominated by N-S early syn-rift faults then segment Y exhibited strong displacement in the Oligocene. The fault grew from several isolated strands, reached a maximum length then towards the end of extension. The western part of the fault remained active while the eastern part was inactive.

Paleocene sedimentary rocks in the Golfo San Jorge Basin include the marine Salamanca Formation and the continental Río Chico Formation. Both units contain soft-sediment deformation features and evidence of contemporary tectonics, which include: 1) sediment-filled fissures, hosted in muddy marine sediments of the Salamanca Formation ("Fragmentosa" Section), where the sandy infill of the fissures took place from above; 2) synsedimentary normal faults in the uppermost levels of the Salamanca Formation, with vertical throws rarely exceeding 1 m; 3) fault-graded beds in the "Banco Negro Inferior" (marine-continental transition), which show a deformed sequence with small-scale normal faults at the bottom and intraformational breccias on top; and 4) liquefaction and/or fluidization pillars, "V" or funnel-shaped, with vertical extension of up to 5 m and preserved into fluvial channels of the Río Chico Formation. Deformed strata are bounded by undisturbed horizons and some of these features can be correlated along 60 km of exposures. The suite of soft-sediment deformation structures is considered a secondary evidence of synsedimentary paleo-earthquakes (seismites) in this portion of the South American passive margin. This work shows new evidence of syndepositional tectonic activity in the lowermost Paleogene of the Golfo San Jorge Basin.

Up to 10% of the liquid hydrocarbons of the Golfo San Jorge basin come from the Mina del Carmen Formation (Albian), an ash-dominated fluvial succession preserved in a variably integrated channel network that evolved coeval to an extensional tectonic event, poorly analyzed up to date. Fault orientation, throw distribution and kinematics of fault populations affecting the Mina del Carmen Formation were investigated using a 3D seismic dataset in the Cerro Dragón field (Eastern Sector of the Golfo San Jorge basin). Thickness maps of the seismic sub-units that integrate the Mina del Carmen Formation, named MEC-AeMEC-C in ascending order, and mapping of fluvial channels performed applying geophysical tools of visualization were integrated to the kinematical analysis of 20 main normal faults of the field. The study provides examples of changes in fault throw patterns with time, associated with faults of different orientations. The "main synrift phase" is characterized by NEeSW striking (mean Az ¼ 49), basement-involved normal faults that attains its maximum throw on top of the volcanic basement; this set of faults was active during deposition of the Las Heras Group and Pozo D-129 formation. A "second synrift phase" is recognized by EeW striking normal faults (mean Az ¼ 91) that nucleated and propagated from the Albian Mina del Carmen Formation. Fault activity was localized during deposition of the MEC-A sub-unit, but generalized during deposition of MEC-B sub-unit, producing centripetal and partially isolated depocenters. Upward decreasing in fault activity is inferred by more gradual thickness variation of MEC-C and the overlying Lower Member of Bajo Barreal Formation, evidencing passive infilling of relief associated to fault boundaries, and conformation of wider depocenters with well integrated networks of channels of larger dimensions but random orientation. Lately, the Mina del Carmen Formation was affected by the downward propagation of EeW to ESEeWNW striking normal faults (mean Az ¼ 98) formed during the "third rifting phase", which occurs coeval with the deposition of the Upper Member of the Bajo Barreal Formation. The fault characteristics indicate a counterclockwise rotation of the stress field during the deposition of the Chubut Group of the Golfo San Jorge basin, likely associated to the rotation of Southern South America during the fragmentation of the Gondwana paleocontinent. Understanding the evolution of fault-controlled topography in continental basins allow to infer location and orientation of coeval fluvial systems, providing a more reliable scenario for location of producing oil wells.

In the past few decades, the petroleum industry has seen great exploration successes in petroliferous sedimentary basins worldwide; however, the net volume of hydrocarbons discovered each year has been declining since the late 1970s, and the number of new field discoveries per year has dropped since the early 1990s. We are finding hydrocarbons in more difficult places and in more subtle traps. Although geophysical and engineering technologies are crucial to much of the exploration success, fundamentally, the success is dependent on innovative play concepts associated with spatial and temporal relationships among deformation, deposition, and hydrocarbon accumulation. Unraveling the dynamic interplay among tectonics, sedimentation, and petroleum systems in the subsurface is a challenge and relies on an integrated approach that combines seismic imaging, well logging, physical and/or computational modeling, as well as outcrop analogs. In recent decades, an increasing coverage of high-qu...

When a mechanically layered section of rock is subject to a horizontal strain, faults often nucleate preferentially in one or more layers before propagating through the rest of the section. The result is a high density of small, low-throw faults within these layers, and a much smaller number of large, through-cutting faults which nevertheless accommodate most of the strain due to their much larger displacement. A dynamic model of fault nucleation and propagation has been created by combining analytical and finite element techniques to calculate the energy balance of these propagating faults. This model shows that: 1) faults may nucleate in either mechanically weak layers, or in stiff layers with a high differential stress; 2) fault propagation may be halted either by strong layers (in which the sliding friction coefficient is high), or by layers which deform by flow and thus have low differential stress. This model can predict quantitatively the horizontal strain required for faults to nucleate, and to propagate across mechanical layer boundaries. The model is able to explain the complex pattern of fault nucleation and propagation observed in a mechanically layered outcrop in Sinai, Egypt.

Changes to physical and mechanical properties of pyroclastic flow deposits occur during welding process, resulting from overburden pressure and temperature. A great deal of research has been carried out to identify which physical parameters can enable quantification of the degree of welding within pyroclastic deposits. Material properties, such as density, porosity, hardness, abrasion, and compressive and flexural strength, are critical in assessing the suitability of natural stone as a building material, but they have not been sufficiently integrated. Therefore, an attempt has been made to develop a welding classification which integrates measurements of material properties with petrographic and textural observations. The proposed classification covers physical, index, and strength parameters for pyroclastic flow deposits. The most important aspect of this investigation has been the quantification of material parameters and definition of a welding classification applicable to a wide range of ignimbrites, from nonwelded to densely welded, that are used as natural building stone. This welding classification is proposed to ensure a consistent approach in characterizing key aspects of welded facies in pyroclastic deposits and in the identification of natural stone reserves.

The influence of tectonics on sedimentation and hydrocarbon accumulation is different among extensional, strike-slip, and contractional structural styles. Addressing the role of different structural styles and syntectonic sedimentation in petroleum systems is essential to assess the hydrocarbon potential of sedimentary basins. This 18-chapter volume is small enough to focus on the interplay among tectonics, sedimentation, and petroleum systems. Yet it is big enough to cover the diversity of structural styles in important petroliferous sedimentary basins around the globe, including those in west Africa, east Africa, east Brazil, east United States of America, Gulf of Mexico, South China Sea, the Russian Arctic, and the Mediterranean Sea.

Fabric and timing relations of mode I microfractures are used to test current hypotheses for the origin of damage along large-displacement faults by the processes of fault growth and wear. Oriented samples 0.075 m to 1 km from the Punchbowl fault surface (i.e. ultracataclasite layer) document an increase in development of preferred orientation and increase in density of microfractures towards the ultracataclasite layer, defining a zone of fault-related microfracture damage about 100 m thick. A distinct microfracture set that is perpendicular to the slip direction of the fault is present throughout the damage zone. This implies that the average orientation of the maximum principal compressive stress within the damage zone was nearly normal to the fault surface. Two additional microfracture sets are present, one oriented at low angles to the fault within meters of the ultracataclasite layer, and another low-angle set that occurs in the outermost damage zone. The preferred orientations and timing relations are most consistent with local damage accumulation from stress cycling associated with slip on a geometrically irregular, relatively weak fault surface. Low-angle microfractures nearest the ultracataclasite layer also may record wear associated with the passage of earthquake ruptures, and those in the outermost damage zone may be consistent with Andersonian fault formation and subsequent fault weakening.

Fabric and timing relations of mode I microfractures are used to test current hypotheses for the origin of damage along large-displacement faults by the processes of fault growth and wear. Oriented samples 0.075 m to 1 km from the Punchbowl fault surface (i.e. ultracataclasite layer) document an increase in development of preferred orientation and increase in density of microfractures towards the ultracataclasite layer, defining a zone of fault-related microfracture damage about 100 m thick. A distinct microfracture set that is perpendicular to the slip direction of the fault is present throughout the damage zone. This implies that the average orientation of the maximum principal compressive stress within the damage zone was nearly normal to the fault surface. Two additional microfracture sets are present, one oriented at low angles to the fault within meters of the ultracataclasite layer, and another low-angle set that occurs in the outermost damage zone. The preferred orientations and timing relations are most consistent with local damage accumulation from stress cycling associated with slip on a geometrically irregular, relatively weak fault surface. Low-angle microfractures nearest the ultracataclasite layer also may record wear associated with the passage of earthquake ruptures, and those in the outermost damage zone may be consistent with Andersonian fault formation and subsequent fault weakening.

Entre 1908 y 1922 Stappenbeck, Schiller, Keidel, Wichmann y Windhausen trabajaron en la zona por cuenta de la Dirección de Minas y Geología. En 1922 se creó Yacimientos Petrolíferos Fiscales, YPF, y se nombró al frente de la División Geología al italiano Guido Bonarelli. En 1925 llegó el italiano Egidio Feruglio a la recién creada Sección Geología de Comodoro Rivadavia. En 1926 se incorporó el ruso Vladimiro Vinda, y en 1927 se creó la Comisión Geológica del Golfo San Jorge, a cargo del italiano Enrico FossaMancini. Se integró con un equipo de geólogos italianos, rusos y argentinos. Feruglio, Piatnitzky, Stessin, Serghiescu, Ramaccioni, Chahnazaroff, Franceschi, Tarragona, Conci, Brandmayr, Wellhoefer, Biondi, Casanova, etc, son algunos de los protagonista entre 1927 y 1930. El primer trabajo encarado por la Comisión fue ajustar la estructura del yacimiento a partir de la nivelación de las capas terciarias y generar un modelo estructural de entrampamiento. Siguiendo los lineamientos...

Characterizing the structure of fault zones is necessary to understand the mechanical, fluid flow and geophysical properties of the lithosphere. This paper provides a detailed characterization of two large-displacement, strike-slip fault zones of the San Andreas system in southern California, the Punchbowl and North Branch San Gabriel faults. The faults cut crystalline and well-lithified sedimentary rocks, and consist of broad zones of fractured and faulted rock (damage zone) containing one, or more, narrow, tabular zones of highly sheared rock (fault core). Subsidiary faults and fractures of the damage zone formed in response to stress cycling associated with slip. The fault core is composed of very fine-grained, altered fault-rocks that reflect high shear strain, extreme comminution, and enhanced fluid-rock reactions. The characteristic and relatively ordered structure of these large-displacement faults is consistent with progressive damage accumulation over the lifetime of the fault. Layers of ultracataclasite containing mesoscopic slip surfaces within fault cores record extreme localization of slip at the macroscopic and mesoscopic scale. Progressive accumulation of ultracataclasite from abrasive wear along a slip surface throughout faulting history can explain the particle size distribution, layered structure, and sharp boundaries of the ultracataclasite layer. The longevity and relative stability of the slip surface is evidenced by the accumulation of progressively younger ultracataclasite towards the slip surface. Although not a common feature, the incorporation of slivers of wall rock into the ultracataclasite layer document occasional branching of the slip surface within fault cores. The damage-zone and fault-core characterization may be used to describe the geophysical, mechanical, and fluid-flow properties of brittle fault zones in crystalline and well-lithified sedimentary rocks of the continental crust.

During fast and slow earthquakes deformation localizes along narrow and quasi-planar fault surfaces. However, processes controlling the localization process develop not only on the fault surface but also in the volume surrounding the fault zone. How these processes transition from a dispersed to more localized distribution of damage remains controversial. Moreover, to what degree the localization process controls the speed of coseismic slip is an open question. We perform a series of 4D X-ray microtomography experiments on crystalline rocks (granite, marble), with and without a pre-existing slip surface, and image the development of damage while each sample is loaded until system-size brittle failure. We image and deform the samples under in situ stress conditions of a few kilometers depth using the Hades deformation apparatus installed on the tomography beamline ID19 at the European Radiation Synchrotron Facility. By imaging all the microfractures that develop in the samples, we ch...

Microfractures appearing in thin section as¯uid inclusion trails in quartz crystals were studied in four core samples of Soultzsous-Foreà ts granite. Their orientations in four series of three mutually perpendicular thin sections were estimated using a previously described apparent dip method and a new method involving measurements of strike and apparent dips. Three samples display three microfracture sets and one sample displays two sets. In all samples, one set is nearly vertical and strikes N±S. In two samples, one and two sets are nearly vertical and strike E±W. In two samples, two sets strike NW±SE: one is vertical, the other dips gently to the NE (or SW). Comparing microfracture and mesofractures sets in the same cores shows that (1) the N±S microfracture set is always dominant at both scales and (2) all other microfracture sets have no mesoscopic counterpart. The N±S microfracture sets could have been created during E±W extension of earliest Cenozoic age (Rhine Graben rifting). Dierences between the two scales are explained by a s 1 /s 2 switching which occurred at the crystal scale and generated mutually perpendicular cracks.

We analyze pervasive and discontinuous deformation associated with small faults in a quartz-syenite body in southern Israel. The analysis includes detailed mapping, measurement of in-situ mechanical rock properties and microstructural study of the faults. The mapped faults have 1-100-m-long horizontal traces, consisting of linked, curved segments; the segmented nature of the faults is also apparent at the 1-10 mm scale. The observed deformation features are breccia, as well as intra-and inter-granular fractures; these features are accompanied by reduction of the Young modulus and uniaxial strength of the host rock. The deformation features are zoned from a central fault-core through a damage-zone to the protolith at distances of 0.05-0.06 the fault length. Shear strains up to 300% were calculated from measured marker lines displacements and distortion in proximity to the faults. We argue here that the fault-related deformation during fault propagation is manifested by highly localized deformation in a process zone having a width of 0.001-0.005 of the fault length (fault-related deformation due to subsequent slip along the existing faults is analyzed in Part II). The observed self-similarity of the discontinuities over five length orders of magnitude and the outstanding lack of tensile microcracks suggest fault initiation and growth as primary shear fractures.

Fault-and fold-related fracturing strongly influences the fluid circulation in the subsurface, thus being extremely important for CO 2 storage exploration, especially in terms of reservoir connectivity and leakage. In this context, discrete regions of concentrated sub-parallel fracturing known as fracture corridors or swarms, are inferred to be preferential conduits for fluid migration. We investigate fracture corridors of the middle-late Jurassic Entrada and Curtis Formations of the northern Paradox Basin (Utah), which are characterized by discoloration (bleaching) due to oxide removal by circulating CO 2-and/or hydrocarbon-charged fluids. The analyzed fracture corridors are located in the footwall of a km-scale, steep normal fault with displacement values on the order of hundreds of meters. These structures trend roughly perpendicular and subordinately parallel to the direction of the main fault, defining a systematic network on the hundreds of meters scale. The fracture corridors pinch-and fringeout laterally and vertically in single, continuous fractures, following the axial zones of open fold systems related to the evolution of the main fault. On the basis of the presented data we hypothesize that fracture corridors developed along the hinge of anticlinal/synclinal folds represent preferred pathways for fluid migration rather than the main faults, connecting localized reservoirs at different structural levels up to the surface.

Mass transport by aqueous fluids is a dynamic process in shallow crustal systems, redistributing nutrients as well as contaminants. Rock matrix diffusion into fractures (void space) within crystalline rock has been postulated to play an important role in the transient storage of solutes. The reacted volume of host rock involved, however, will be controlled by fluid-rock reactions. Here we present the results of a study which focusses on defining the length scale over which rock matrix diffusion operates within crystalline rock over timescales that are relevant to safety assessment of radioactive and other long-lived wastes. Through detailed chemical and structural analysis of natural specimens sampled at depth from an active system (Toki Granite, Japan), we show that, contrary to commonly proposed models, the length scale of rock matrix diffusion may be extremely small, on the order of centimetres, even over timescales of millions of years. This implies that in many cases the import...

The deposition of the Salamanca Formation and Rio Chico Group (Paleocene) in the Golfo San Jorge Basin exceeds the basin boundary of the underlying continental units of the Chubut Group (Cretaceous). These Paleocene units show major north-to-south stratigraphic changes for the north flank of the basin. On one hand, the accumulation of bioclastic deposits in the base of Salamanca Formation (Bustamante Member) only took place in the northern basin boundary, where the marine sedimentation occurred overlying Jurassic volcanic rocks of the Marifil Complex. In southward direction, the initial Paleocene transgression is represented by the epiclastic deposits of the Hansen Member (“Glauconitico”), overlying the Chubut Group (Cretaceous). In this way, the bioclastic deposits of the Bustamante Member are interpreted as an evidence of development of substrate-controlled marine invertebrate colonies, in which the volcanic rocks constituted a more favorable substrate to colonization of encrustin...

Cretaceous connexion between the Golfo San Jorge and Cañadón Asfalto Basin (Patagonia): paleogeography, tectonostratigraphic implications and their potential in the hydrocarbon exploration The Chubut Group (Cretaceous) of the Golfo San Jorge Basin begins with a fluvial-lacustrine depositional system associated with the Matasiete-Pozo D-129 Formations (Barremian?-Aptian). This contribution evaluates the correlation among the Matasiete Formation and its temporaly-equivalent units in the Cañadón Asfalto Basin. The fluvial succession of the Los Adobes Formation was characterized in cañadón Puelman and cerro Punta Toro Hosco, in the northwestern margin of the basin. The fluvial sandbodies have a mean maximum thickness (T) of 7 m, a mean real width/maximum thickness ratio (W/t) of 10 and paleoflow direction toward 168º. The Cerro Fortín Formation was analyzed near cerro Ferrarotti; the fluvial channels have mean values of T: 4,6 m, W/t: 16, and a mean paleoflow direction toward 162º. The Matasiete Formation outcrops downstream of both localities and its fluvial channels show a mean T: 7,3 m, W/t: 14 and a paleotransport direction toward S-SE. A similar lithological appearance, uniform paleoflow directions and comparable geometries of the paleochannels support the physical correlation among the above-mentioned lithostratigraphical units. By using modern analogues, a minimum drainage area of ~160000 km 2 was estimated for the Pozo D-129 Formation, with individual watersheds of ~4000 km 2. The results support a paleogeographic scenario with regional fluvial systems that flow from the north-northwest using tectonically-driven sedimentary corridors. The characterization of a continental depositional system connecting areas of the Cañadón Asfalto and Golfo San Jorge basins defines potential guidelines for prospecting hydrocarbon reservoirs in frontier areas.

RESUMEN La depositación de la Formación Salamanca y del Grupo Río Chico (Paleoceno) en la Cuenca del Golfo San Jorge excedió el ámbito de la cuenca continental del Grupo Chubut (Cretácico). Estas unidades muestran cambios estratigráficos significativos en dirección norte-sur para el flanco norte de la cuenca. Por un lado, la acumulación de depósitos bioclásticos basales en la Formación Salamanca (Miembro Bustamante) sólo tuvo lugar en el borde norte de la cuenca, donde la sedimentación marina ocurrió sobre rocas volcánicas jurásicas del Complejo Marifil. Hacia el sur, la transgresión inicial está representada por los depósitos epiclásticos del Miembro Hansen (&quot; Glauconítico &quot;), apoyados sobre el Grupo Chubut (Cretácico). Así, los depósitos bioclásticos del Miembro Bustamante se interpretan como una evidencia del desarrollo de colonias de invertebrados marinos sustrato-controladas, ya que las rocas volcánicas constituyeron un sustrato más propicio para su colonización por o...

According to numerous studies, there are basic and initial scaling relationship for the geometric and kinematic characteristics of faults. The study area is located in the northern part of the Kerman coal province. The statistical calculations are consisting of:  measure the surface density of faults per unite area and division of the area, determining the direction of the dominant faulting and evaluating the relationship between length-displacement, strike-displacement and strike-length. Based on diagrams, the highest fracture density is related to the middle portion (B zone) of study area because that enclosed between the four main faults and sandstone rock assemblage. The relationship between strike-length parameter is calculated as (y=0.0478x + 11.54), and R-squared rate is (R=0.341), strike-displacement is calculated as (y=2.68x + 147.4) and R-squared rate is (R=0.65) and length-displacement is calculated as (y= 243.58 x0.0336) and R-squared rate is (R=0/022). It was determined...

Research conducted over the last few decades have acknowledged the importance of blast-induced fragment conditioning on the comminution and concentration stages. These studies demonstrate that blast-induced conditioning can be considered as a highly relevant factor in the value chain of the mining industry. Despite the significant benefits awarded to this phenomenon, there are few comprehensive studies about the topic and, in contrast, many questions have been asked regarding the mechanisms of generation and extension.This paper presents a critical review on microfracturing induced by blasting which intends to summarise the current knowledge by presenting the key identified factors related to the phenomenon and discussing its impact on downstream processes.► Summarisation of the current knowledge obtained over the last decades regarding microfracturing by blasting. ► Identification of technical challenges to be addressed in next works. ► Discussion of the implications of fragment co...

Shear fracture propagation in rock is accompanied by localized microcracking in a process zone surrounding the fracture tip. We investigated the crack microstructures along experimentally formed shear fractures from four granite samples (uniaxial compression tests). Five transects across a macroscopic fracture were inspected optically in transmitted light. Five hundred thirty-two photomicrographs were taken from seven study areas along each transect. We determined length, width, density, and orientation of open cracks and their assignment to intra-, transgranular, or grainboundary cracks. Crack density decreases with increasing distance to the macroscopic shear fracture and toward the fracture tip. The highest crack densities correlate with the maximum number of acoustic emissions. Most cracks enclose a small angle (0±20) with the macroscopic shear fracture. Intragranular cracks are more abundant than transgranular and grain-boundary cracks. The number of transgranular cracks increases towards the macroscopic shear fracture, but the number of grain-boundary cracks decreases. The decrease in crack density with increasing distance to the fault is accompanied by a change from strongly preferred crack orientation in the fault core to a random crack distribution away from the fault. Fracture process zone widths range from 2.10.8 mm (Ag51r) to 5.61.9 mm (Ag18r). The ratio of process zone width to fault length is approximately 0.04±0.07. This observation agrees with observations from natural fault zones. The fracture surface energy ranges from 0.2 to 1.2 J. This corresponds to <10% of the total strain energy.

The Squaw Peak fault places the Miocene Crowder Formation and pre-Cenozoic basement of the San Bernardino Mountains against the Miocene Cajon (Punchbowl) Formation. The fault consists of two west-northwest-trending low-angle segments which occur at different structural levels separated by a north northeast-trending high-angle segment. Meisling and Weldon (1989) suggested that the low-angle segments are thrust faults and that the high angle segment is a dextral lateral ramp connecting them. Mapping of the north end of the high-angle segment, at the scale of 1:500, revealed east-and west-directed contractional structures and evidence for later dextral slip on the high-angle segment. Contraction occurred in three stages: 1) east-directed folding and reverse faulting; 2) west-directed backthrusting; 3) northeast-directed thrust faulting and refolding of stage 1 folds. The high-angle fault cuts these structures. The curved surface of the main fault plane and numerous smaller fault-bend axes within the fault zone plunge gently southeast, suggesting predominant lateral slip; "drag" of rocks adjacent to the fault plus an obliquely oriented thrust fault and fold pair suggest the slip was right-lateral. Three observations suggest that the contraction and strike-slip were part of the same protracted episode: 1) contractional features are spatially related to the Squaw Peak fault; 2) motion on the Squaw Peak fault occurred between 4.2 to 9.5 Ma, possibly from 4.2 to 6.2 Ma; 3) mobilized gouge fills faults of all stages, suggesting similar conditions during slip. Also, the contractional structures trend obliquely to the Squaw Peak fault and display an apparent clockwise rotation through time, suggestive of Formation over a wrench fault. The structural evolution of this study area supports the thrust and ramp model for the Squaw Peak fault. Thrust motion on the two gently north-dipping segments of the Squaw Peak fault, before they were connected by the high-angle fault, set up a rightlateral shear couple. The resultant contraction in the stepover region, represented by stages 1 through 3, preceded propagation of the high-angle fault between the two thrust faults. Further slip within the stepover region occurred on the high-angle fault, effectively shutting off the earlier contractional structures.

Deformation band faults in nonwelded ignimbrites of the Bandelier Tuff record unsaturated fluid flow and transport. More than two thirds of the faults studied display diagenetic minerals virtually absent from adjacent protolith. Stable isotope analyses indicate that smectite enrichment and calcite cementation result from low-temperature meteoric fluid-fault interaction. Fault zone microstructures, rare earth element signatures, and mineralogy indicate that smectite was introduced to deformation band fault zones by a combination of translocation from the surface and in situ alteration of fault gouge. Rod-shaped calcite microcrystallites and the close association of calcite with plant roots suggest a combination of pedogenic, biologically mediated, and physicochemical precipitation. Enrichment in smectite and calcite modified major oxide and trace element contents of deformation bands with respect to protolith. Collectively, these observations indicate that these faults have served as, and may still be, zones of preferential vadose zone fluid flow and transport. These processes alter fault rock permeability; affect the transport of solutes via processes such as dissolution, precipitation, and adsorption, and they change the mechanical properties of the fault zone. Smectite and calcite enrichment results in localization of deformation, effectively halting the further development of deformation bands. Vadose zone alteration therefore is one way to produce a clay-rich fault core at early stages in a fault's history, resulting in fault zone weakening and localization of slip. Progressive burial of growth faults can subsequently bring fault cores into the seismogenic zone.

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Displacement profiles and maps were used in the subsurface of the Golfo San Jorge basin in the Manantiales Behr region to analyze factors affecting the geometric and kinematic evolution of an extensional system and its relationship with the migration and trapping of hydrocarbons. Two fault types were recognized: faults affecting both the basement and the sedimentary cover, and faults restricted to the sedimentary cover. The vertical growth of the faults within the sedimentary cover was constrained by vertical lithologic variations and by intersection with the free surface. Faults involving the basement are synsedimentary and show Dmax/L relationships and aspect ratios that allow their distinction from the shallower fault planes. The geometric coherence shown in the aggregated displacement profile and map suggests a synchronous kinematic evolution for the faults developed inside the sedimentary cover. Observed fault trace lengths and throw values distributions may indicate that those faults grew by the early linkage of isolated fault segments followed by the progressive building of displacement. Reactivation of pre-existent basement fabric had little influence on faulting across overlying sedimentary cover probably because the fine-grained beds of Pozo D-129 Formation acted as a structural decoupling level. The low degree of connection between the shallow and deep portions of the faults disregards the hypothesis of vertical migration from a local source pod. The mapping of fault segments with higher values of displacement and the recognition of transfer zones may help to locate and delineate footwall hydrocarbon traps. Comparison and integration with other studies show that Cretaceous fault systems in the eastern Golfo San Jorge basin have grown mainly by rapid length establishment and subsequent displacement accumulation. Also, most of the basement-involved structures do not connect significantly with overlying fault arrays.

In this paper, information on fracture characteristics in representatively selected sites in the Togo Structural Units (TSU) and Dahomeyan Formation in southeastern Ghana is presented. The study area is locatedat the south most edge of the Pan-African Dahomeyide belt, characterised by intense fracturing. Linear and circular scanline mappings, structural geological mapping, and laboratory investigations of rock samples collected from Site 1 (within the TSU), and Site 2(within the Dahomeyan Formation) were carried out. A total of 1128 fractures were surveyed along a total length of 238 m of scanline at Site 1, and 629 fractures along a total of 156.0 m at Site 2. Fourteen and thirteen circular scanlines were surveyed at Site 1and Site 2 respectively. Statistical analysis of fracture data from the two study sites, and comparing the mean fracture spacing to International Society for Rock Mechanics (ISRM) indicated a close to moderate fracture spacing for the two sites. However, fracturing is more intense in the TSU than the Dahomeyan formation, probably due to the nature of the major rock types, and difference in thickness of the two stratigraphic units. Micro-structural investigation on rock samples also showed mineral grains in the rocks of the TSU are more deformed compared to those of the Dahomeyan. Implications are that, potential for fluid flow and contaminants resulting from waste disposal could travel faster and for wider distances within Site 1 than in Site 2. Site 2 thus, could be a better choice for waste disposal site selection compared to Site 1due to its lesser fractured nature, and the fact that, the Dahomeyan already has natural groundwater quality problems.

Field observations of the Punchbowl fault zone, an inactive trace of the San Andreas, are integrated with results from experimental deformation of naturally deformed Punchbowl fault rocks for a qualitative description of the mechanical properties of the fault and additional information for conceptual models of crustal faulting. The Punchbowl fault zone consists of a single, continuous gouge layer bounded by zones of extensively damaged host rock. Fault displacements were not only localized to the gouge layer, but also to discrete shear surfaces within the gouge. Deformation in the exposure studied probably occurred at depths of 2 to 4 km and was dominated by cataclastic mechanisms. Textural data also suggest that significant amounts of pore fluids were present during faulting, and that fluid-assisted mechanisms, such as dissolution, diffusion, and precipitation, were operative.

The manifestation of brittle deformation within inactive slumps along the North Menan Butte, a basaltic tuff cone in the Eastern Snake River Plain, is investigated through field and laboratory studies. Microstructural observations indicate that brittle strain is localized along deformation bands, a class of structural discontinuity that is predominant within moderate to high-porosity, clastic sedimentary rocks. Various subtypes of deformation bands are recognized in the study area based on the sense of strain they accommodate. These include dilation bands (no shear displacement), dilational shear bands, compactional shear bands and simple shear bands (no volume change). Measurements of the host rock permeability between the deformation bands indicate that the amount of brittle strain distributed throughout this part of the rock is negligible, and thus deformation bands are the primary means by which brittle strain is manifest within this tuff. Structural discontinuities that are similar in appearance to deformation bands are observed in other basaltic tuffs. Therefore deformation bands may represent a common structural feature of basaltic tuffs that have been widely misclassified as fractures. Slumping and collapse along the flanks of active volcanoes strongly influence their eruptive behavior and structural evolution. Therefore characterizing the process of deformation band and fault growth within basaltic tuff is key to achieving a more complete understanding of the evolution of basaltic volcanoes and their associated hazards.

A.A. BALKEMA/ROTTERDAM/BROOKFIELD 11995 Mechanics of Jointed and Faulted Rock, Rossmanith (ed.) © 1995 Balkema, Rotterdam. ISBN 90 5410541 0 Tertiary paleostress variation in time and space near the eastern margin of the Basin and Range province, Utah ABSTRACT: Healed microfracture orientations in quartz grains from several plutons of various ages in the eastern Basin & Range, Utah provide additional evidence for a changing state of stress between 40 Ma and 15 Ma. Prior to about 25-30 Ma, the maximum horizontal stress direction was SW-NE. After this time the direction of maximum horizontal stress changed to SE-NW and then to N-S. This rotation has been documented by several workers using different paleostress markers. Our microcrack data agrees well with this model. Healed microcracks in the plutons we have studied are better indicators of regional stress patterns than are associated macroscopic joints. Like other stress indicators, there is considerable variation in microcrack orientation locally, but a regional pattern can generally be determined by combining the orientation data from several localities throughout a pluton.

The distribution of deformation bands in damage zones of extensional faults in porous sandstones has been analyzed using 106 outcrop scanlines along which the position and frequency of deformation bands have been recorded. The analysis reveals a non-linear relationship between damage zone width and fault throw, a logarithmic decrease in deformation band frequency away from the fault core, as well as a fractal spatial distribution associated with clustering of the deformation bands. Furthermore, damage zones appear wider in the hanging wall than in the footwall, although the deformation band density is similar on both sides. Statistical trends derived from the database imply that fault growth in porous sandstones can be considered as a scale invariant process. From an initial process zone, the damage zone grows by a constant balance between the development of new deformation bands in the existing damage zone and the creation of new bands outside. Moreover, as the width of the damage zone increases throughout the active lifetime of a fault, the distribution of the deformation bands in the damage zone remains selfsimilar. Hence band distribution and damage zone width for seismically mapped faults can be predicted from the relationships found in this paper.

Analysis of a population of dilational faults within a densely welded ignimbrite layer reveals fault zone geometries that vary greatly within a single fault and between faults, but does not correlate with displacement. Within an individual fault the thickness of the fault core can differ by up to an order of magnitude along dip. Similarly, joint density adjacent to faults varies along fault dip but does not increase with displacement. A correlation does exist however, between joint density and the degree of ignimbrite welding, which can vary vertically within an ignimbrite layer. Previous work has shown that welding increases ignimbrite strength: non-welded ignimbrites form deformation bands and densely welded ignimbrites form discrete fractures. We observe zones of densely welded ignimbrite with high joint density, while less-welded zones have lower joint density. In turn, high joint densities correlate with narrow fault cores and low joint densities with wide fault cores. We propose a joint based model for dilational fault initiation and growth. Faults initiate on precursory joints and grow by entraining joint bound slabs, hence the correlation between high and low joint density (thin and thick slabs) and narrow and wide fault cores respectively. Ultimately joint density and consequently fault zone architecture are controlled by subtle variations in mechanical strength within the ignimbrite layer.

This paper examines evidence of coupled diagenetic and mechanical processes within growing fractures in sandstones: crack-seal texture and associated, concurrently produced fracture porosity. Crack-seal textures in narrow mineral bridges associated with fracture porosity are common in regional fractures formed at moderate to great depth (.1000-, 6000 m) in quartz-cemented sandstones that otherwise lack significant structure. Use of SEM-based cathodoluminescence systems and superposition of images collected using color filters accurately delineate crack-seal increments in fracture-bridging quartz cement. Bridges and crack-seal texture mark competition between cement precipitation and opening rates during opening-mode fracture growth. These structures document episodic fracture growth that can include tens to hundreds of widening increments in fractures having apertures of a few tens of microns to several millimeters or more. These structures are not the product of unique circumstances in burial history and fluid flow but, rather, reflect the confluence of rock-dominated geochemistry that is widespread in time and space and fracturing caused by a spectrum of loading conditions. q

Closely spaced, sub-parallel fracture networks contained within localized tabular zones (i.e. fracture 47 corridors) may compromise top seal integrity and form pathways for vertical fluid flow between 48 reservoirs at different stratigraphic levels. This geometry is exemplified by fracture corridors found 49 in outcrops of the Jurassic Entrada Formation in Utah (USA). These fracture corridors exhibit 50 discolored (bleached) zones, interpreted as evidence of ancient fracture-enhanced circulation of 51 reducing fluids within an exhumed siliciclastic reservoir-cap rock succession. Extensive structural 52 and stratigraphic mapping and logging provided fracture data for analysis with respect to their 53 occurrence and relationships to larger faults and folds. Three types of fracture corridors, 54 representing end-members of a continuum of possibly interrelated structures were identified: 1) 55 fault damage zone (including segment relays); 2) fault-tip process zone; and 3) fold-related crestal-56 zone fracture corridors. The three types exhibit intrinsic orientations and patterns, which in sum 57 define a local-to regional network of inferred vertical and lateral, high-permeability conduits. The 58 results from our analysis may provide improved basis for the evaluation of trap integrity and flow 59 paths across the reservoir-cap rock interface, applicable to both CO 2 storage operations and the 60 hydrocarbon industry.

The Bolivian Sub-Andean Zone (SAZ) corresponds to a Neogene thrust system that affects an about 10-km thick Palaeozoic
to Neogene siliciclastic succession. The analysis of macro and microstructures and cement distribution in thrust fault zones shows
that they are sealed by quartz at depths >
3 km, due to local silica transfer by pressure-solution/precipitation activated at
temperatures >70–90
C. At shallower depths, faults have remained open and could be preferential drains for lateral flow of
carbonate-bearing fluids, as shown by the occurrence of carbonate cements in fractures and their host-sandstone. Due to
decreasing burial, resulting from foothill erosion during fault activity, critically buried fault segments can be affected by nonquartz-
sealed structures that post-date initial quartz-sealed structures. The integration of textural, fluid inclusion and isotopic data
shows that carbonates precipitated at shallow depth ( < 3 km), low temperature ( < 80
C) and relatively late during the thrusting
history. Isotopic data also show that precipitation occurred from the mixing of gravity-driven meteoric water with deeper
formation water bearing carbonate carbon derived from the maturation of hydrocarbon source rocks (Silurian and Devonian
shales). The combined microstructural and isotopic analyses indicate that: (i) fluid flow in fault zones often occurred with
successive pulses derived from different or evolving sources and probably related to episodic fault activity, and (ii) at a largescale, the faults have a low transverse permeability and they separate thrust sheets with different fluid histories

Shear fracture propagation in rock is accompanied by localized microcracking in a process zone surrounding the fracture tip. We investigated the crack microstructures along experimentally formed shear fractures from four granite samples (uniaxial compression tests). Five transects across a macroscopic fracture were inspected optically in transmitted light. Five hundred thirty-two photomicrographs were taken from seven study areas along each transect. We determined length, width, density, and orientation of open cracks and their assignment to intra-, transgranular, or grain-boundary cracks. Crack density decreases with increasing distance to the macroscopic shear fracture and toward the fracture tip. The highest crack densities correlate with the maximum number of acoustic emissions. Most cracks enclose a small angle (0–20°) with the macroscopic shear fracture. Intragranular cracks are more abundant than transgranular and grain-boundary cracks. The number of transgranular cracks increases towards the macroscopic shear fracture, but the number of grain-boundary cracks decreases. The decrease in crack density with increasing distance to the fault is accompanied by a change from strongly preferred crack orientation in the fault core to a random crack distribution away from the fault. Fracture process zone widths range from 2.1±0.8 mm (Ag51r) to 5.6±1.9 mm (Ag18r). The ratio of process zone width to fault length is approximately 0.04–0.07. This observation agrees with observations from natural fault zones. The fracture surface energy ranges from 0.2 to 1.2 J. This corresponds to