a newly recognized type of slickenside striation abstract this note summarizes current views on the origin of slickenside striations and points to the existence of a type of striation not readily explained by established genetic ideas such striations have been seen on fault surfaces in naturally deformed shale and in experimentally deformed paraffin wax they are defined by arrays of shallow slip parallel ridges and grooves of millimetric width and below on any given slip surface the ridges are as common as the grooves and display similar dimensions and profile shapes across any pair of slip surfaces in contact at the end of faulting ridges protruding from one surface fit into or nest with grooves on the other surface the origin of these features is not yet understood

origin and significance of clay coated fractures in mudrock fragments of the safod borehole parkfield california 1 the clay mineralogy and texture of rock fragments from the safod borehole at 3067 m and 3436 m measured depth md was investigated by electron microscopy sem tem and x ray diffraction xrd the washed and ultrasonically cleaned samples show slickenfiber striations and thin films of ca k bearing smectite that are formed on polished fault surfaces along freshly opened fractures and within adjacent mineralized veins the cation composition and hydration behavior of these films differ from the na montmorillonite of the fresh bentonite drilling mud although there is more similarity with circulated mud recovered from 3479 m md we propose that these thin film smectite precipitates formed by natural nucleation and crystal growth during fault creep probably associated with the shallow circulation of low temperature aqueous fluids along this shallow portion of the san andreas fault

plate tectonic history basin development and petroleum source rock deposition onshore china abstract china comprises a mosaic of distinct continental fragments separated by fold belts these fold belts are suture zones resulting from the accretion of various fragments formerly separated by intervening areas of oceanic crust the major sedimentary basins onshore china can be classified into four groups those in western china are flexural developing as a result of north south compression in contrast those in the east are extensional and related to development of the pacific oceanic margin in central china basins have a more problematic origin those of north central china ordos sichuan are flexural basins controlled by eastward directed thrusting along their western margin in contrast basins further south chuxiong shiwandashan are predominantly extensional and related to major strike slip movements by synthesizing basin stratigraphies across china in tectonostratigraphic terms and in particular comparing the nature and timing of unconformities it is possible to formulate a coherent model for the palaeoreconstruction of china we identify five major tectonostratigraphic breaks which equate with the collision of the following continental fragments tarim north china carboniferous permian south china block permian triassic qiantang late triassic early jurassic lhasa block late jurassic early cretaceous and india early tertiary prior to permian times the southern margin of eurasia ran approximately along the northern border of modern china the late carboniferous collision of tarim north china with eurasia resulted in the development of a flexural basin junggar and deposition of non marine clastics to the south of the suture shallow marine deposition continued in the late permian early triassic the progressive collision from east to west of the south china block with the north china block resulted in a change to fluvial lacutrine sedimentation across the entire north china tarim block open marine carbonate deposition in the north of the south china block passed southward into a deeper marine clastic sequence deposited in a backarc basin further south a subduction zone existed along the southeastern margin of the south china block in western china northward subduction throughout the triassic resulted in the development of the songban ganzi accretionary prism with retroarc thrusting resulting in flexure and the first development of the tarim basin oblique collision of the qiantang block in the late triassic along the east of the south china block resulted in east west directed thrusting which initiated the suchuan and ordos basins continued strike slip deformation along the south western margin of the south china block resulted in the development of basins with a significant extensional component such as chuxiong the collision of the qiantang block with the southern edge of the tarim basin early jurassic resulted in a renewed clastic influx in both the tarim and junggar basins along the eastern pacific margin a compressional arc and retroarc basin in the south passed northwards into an extensional arc system subduction rollback of the extensional arc initiated rifting in the late jurassic in the eren and songliao basins the late jurassic early cretaceous collision of the lhasa block in the west rejuvenated the thrust systems bordering the western basin and resulted in a renewed clastic influx in the southeast the compressional arc phase culminated in widespread thrusting and folding of early cretaceous age in the northeast extension continued with the progressive migration of the rift system southward with time the arrival of the indian block in the early tertiary rejuvenated the bounding thrust belts of all the western basins in the east the change in convergence of the pacific plate to a more westerly direction is marked by extension and widespread rifting along the entire length of eastern china throughout most of china mesozoic and cenozoic deposition occurred in predominantly non marine environments source rocks in such settings comprise principally mudstones deposited in lakes organic rich mudstones these can accumulate in both deep and shallow lakes in order to accumulate substantial volumes the lake must be significant in space and time in china lacustrine orms occur in both rift and flexural basins lacustrine orms deposited under humid climatic conditions are restricted to the period of maximum tectonic subsidence in the flexural basins of western china source rock deposition follows basin initiation by 20 30 ma in the extensional basins of eastern china source rock deposition takes place 5 15 ma after basin initiation by contrast semi arid and arid climate lacustrine orms whilst being best developed during the period of maximum tectonic subsidence occur at all stages in the basin history

a slice and view fib sem study of clay gouge from the safod creeping section of the san andreas fault at 2 7 km depth abstract the san andreas fault is one of the most studied earthquake generating structures on earth but the reason that some sections are anomalously weak and creep without apparent seismicity remains poorly understood here we present results from nanoscale fib sem 3d microstructural observations of weak friction coefficient of 0 095 safod clay fault gouge containing serpentinite clasts recovered from the active central deforming zone at 2 7 km vertical depth our nanoscale observations confirm that frictional slip and extreme weakness occur via deformation of smectite clay that forms a shear fabric within the fault zone we infer that creep initiates by fracture controlled substrate growth of oriented mg smectite on r p and y shears followed by clay smearing and ductile flow of an evolving and expanding clay matrix at the crystal scale pervasive sliding occurs along hydrated smectite interlayers and surfaces occupied by exchangeable mg and ca ions with slip typically spaced at 3 5 lattice layers apart we conclude that the strength and seismic behaviour of major tectonic faults at shallow crustal levels evolves as clay fabric develops with accumulated fault slip

frictional viscous flow of phyllosilicate bearing fault rock microphysical model and implications for crustal strength profiles it is widely believed that around the brittle ductile transition crustal faults can be significantly weaker than predicted by conventional two mechanism brittle ductile strength envelopes factors contributing to this weakness include the polyphase nature of natural rocks foliation development and the action of fluid assisted processes such as pressure solution recently ring shear experiments using halite kaolinite mixtures as an analogue for phyllosilicaterich rocks for the first time showed frictional viscous behavior i e both normal stress and strain rate sensitive behavior involving the combined effects of pressure solution and phyllosilicates this behavior was accompanied by the development of a mylonitic microstructure a quantitative assessment of the implications of this for the strength of natural faults has hitherto been hampered by the absence of a microphysical model in this paper a microphysical model for shear deformation of foliated phyllosilicate bearing fault rock by pressure solution accommodated sliding along phyllosilicate foliae is developed the model predicts purely frictional behavior at low and high shear strain rates and frictional viscous behavior at intermediate shear strain rates the mechanical data on wet halite kaolinite gouge compare favorably with the model when applied to crustal materials the model predicts major weakening with respect to conventional brittle ductile strength envelopes in particular around the brittle ductile transition the predicted strength profiles suggest that in numerical models of crustal deformation the strength of high strain regions could be approximated by an apparent friction coefficient of 0 25 0 35 down to depths of 15 20 km

syntectonic carbonate veins from the barbados accretionary prism odp leg 110 record of palaeohydrology syntectonic carbonate veins were found along the decollement zone between the atlantic and caribbean plates and in two sites 12 and 17 km landward of the deformation front of the barbados accretionary prism odp leg 110 both calcite and lesser amounts of rhodochrosite mnco3 occur in microcrystalline fibrous and blocky mosaic forms in veins deposited along scaly shear zones descriptions of the occurrences textures mineralogy and stable isotope geochemistry of these veins presented herein help trace the hydrological evolution of the barbados accretionary prism which has seen the impact of more deeply derived fluids on elevated sediment temperatures and altered geochemistry of interstitial fluids at one site for example vein forming fluids have been as much as 10 c warmer and 1 more enriched in 18o than expected carbon isotope ratios of veins indicate a mixture of carbon derived from seawater and from oxidized organic matter during sulphate reduction although dissolution of calcareous skeletons may be an additional component the presence of methane is recorded in one vein sample in the accretionary prism indicating that either the plumbing of the prism has changed with time allowing more fluid to leak into the prism in the past or that materials currently 1 km above the decollement zone were once deformed in the decollement using oxygen isotope analyses of rhodochrosite samples from two sites in conjunction with measurements of fluid temperature and 18o values of interstitial fluids it is proposed that the fractionation of oxygen isotopes between rhodochrosite and water 1000 1n 38 at 25 c 10 greater than the fractionation between calcite and water however it appears that substitution of 10 20 mol ca into rhodochrosite reduces the fractionation factor by 2 9 so impure diagenetic rhodochrosite samples from the deep ocean will rarely be this enriched in 18o

field to nano scale evidence for weakening mechanisms along the fault of the 2016 amatrice and norcia earthquakes italy abstract in august and october 2016 two normal fault earthquakes m w 6 0 and m w 6 5 respectively struck the amatrice norcia area in the central apennines italy the mainshocks nucleated at depths of 7 9 km with the co seismic slip propagating upward along the mt gorzano fault mgf and mt vettore fault system mvfs to recognize possible weakening mechanisms along the carbonate hosted seismogenic faults that generated the amatrice norcia earthquakes the fresh co seismic fault exposure i e nastrino exposed along the mt vettoretto fault was sampled and analyzed this exposed fault belongs to the mvfs and was exhumed from 2 3 km depth over the fresh fault surface phyllosilicates concentrated and localized along mm to m thick layers and truncated clasts and fluid like structures were found at the nano scale instead of their common platy lamellar crystallographic texture the analyzed phyllosilicates consist of welded nm thick nanospherules and nanotubes similar to phyllosilicates deformed in rotary shear apparatus at seismic velocities or altered under high hydrothermal temperatures 250 c moreover the attitude of the mt vettoretto fault and its kinematics inferred from exposed slickenlines are consistent with the co seismic fault and slip vectors obtained from the focal mechanisms computed for the 2016 mainshocks all these pieces of evidence suggest that the mt vettoretto fault slipped seismically during past earthquakes and that co seismic slip was assisted and facilitated at depths of w 6 0 amatrice and m w 6 5 norcia earthquakes the microstructures found along the mt vettoretto fault which is certainly a seismogenic fault provide a realistic synoptic picture of co seismic processes and weakening mechanisms that may occur in carbonate hosted seismogenic faults

sequence stratigraphy in lacustrine basins a model for part of the green river formation eocene southwest uinta basin utah u s a abstract in the middle green river formation of central nine mile canyon uinta basin utah several lacustrine dominated intervals 10 m thick comprise aggradational carbonate parasequence sets and a progradational clastic parasequence maximum flooding surfaces are best identified within profundal oil shale that caps some of the clastic parasequences these lacustrine transgressive systems tracts therefore exhibit parasequence stacking patterns unlike typical marine sequences two types of sequence boundary are identified type a sequence boundaries display evidence for a basinward shift in facies across a regionally mappable surface that is an angular or rarely parallel unconformity and they typically juxtapose amalgamated braided fluvial channel sandstone late lowstand systems tract onto the profundal oil shale they also bound depositional sequences that show a distinct asymmetry being dominated by transgressive systems tracts 5 80 m thick highstand systems tracts are less than 4 m thick and may be removed completely by erosion on overlying sequence boundaries other surfaces satisfy only some of the standard criteria of sequence boundaries and are termed type b sequence boundaries type a sequence boundaries mark pronounced base level falls following times when the uinta lake had merged with a lake in an adjacent basin to form a much deeper lake such merging permitted the establishment of a new threshold at higher elevation following lake level balancing type b sequence boundaries are interpreted as marking base level falls from a barely merged lake or a lake that had an outflow over a 200 m stratigraphic thickness type a sequence boundaries are more common upsection indicating that with time a pluvial climate became more pronounced or that the adjacent lake was more easily filled type a sequence boundaries also become angular rather than parallel unconformities upsection suggesting increased tilting of the basin margin over time

the jura mountains an active foreland fold and thrust belt abstract recently completed in situ stress measurements using the borehole slotter at 33 new test sites within the swiss and french jura mountains combined with previously published stress data allow a detailed description of the contemporary state of stress in this fold and thrust belt and the adjacent foreland five stress provinces can be recognized with two different general orientations of maximum horizontal stress sh 1 the central and southwest provinces with a nnw sse to nne ssw orientation 2 the east northwest and southeast provinces with an e w to nw se orientation stress magnitudes are in general higher in the southern than in the northern jura mountains characteristic of the northern jura is an e w trending zone of low stress magnitudes which can be traced from the bresse depression south of besancon to the eastern end of the jura northwest of zurich boundaries of stress provinces show poor agreement with boundaries of tectonic units in the jura in addition stress provinces extend beyond the boundaries of the jura mountains into their foreland furthermore palaeo stress orientations show large discrepancies with respect to the contemporary stress orientation these findings are considered to indicate a termination of jura thin skinned foreland tectonics which probably took place some time between 9 and 4 ma according to palaeontological and tectonic evidence it is suggested that a new style of tectonics has commenced in the jura mountains deforming both the basement directly below the jura fold and thrust belt and the cover rocks in a similar mode

inter well scale natural fracture geometry and permeability variations in low deformation carbonate rocks regional natural fracture networks often show variations on a scale below that captured by seismic reflection data this variability is not considered in most reservoir models but likely impacts uncertainties in permeability we quantify this uncertainty using a database of 13 000 fractures in nine outcrops digitised in the carbonate jandaira formation potiguar basin brazil distance between outcrops is on average 11 km with a minimum of 300 m which is comparable to the distance between wells in naturally fractured reservoirs in between outcrops significant variations exist in orientation intensity length and topology using discrete fracture matrix flow models we model the permeability of each deterministic pattern and find that small changes in geometry and topology result in permeability variations that are not captured by connectivity based analyses such as percolation probabilities particularly when the matrix is permeable the permeability variations associated with subseismic scale fracture variability are not captured in conventional stochastic models but can be captured using deterministic outcrop models with flow through discrete fractures the deterministic models provide a permeability range associated with subseismic fracture variability that can be assigned to grid cells of fractured reservoir flow models as an alternative to assuming constant permeability in the absence of subseismic scale deformation

influence of the state of stress on the brittle ductile transition in granitic rock evidence from fault steps in the sierra nevada california left lateral strike slip faults in the lake edison granodiorite central sierra nevada california are composed of en echelon segments relative displacements across the faults apparently are transferred between segments by ductile shearing at right steps and by extensional fracturing at left steps the granodiorite within right steps displays mylonitic foliation and thin sections show textures in quartz associated with dislocation glide recovery processes and dynamic recrystallization whereas textures in feldspar are related to fracturing only centimetres outside the right steps the rock fabric is approximately isotropic and deformation is accommodated by mineralized opening mode fractures the stress field calculated for the right step geometry when a boundary element model is used shows an increase in mean compressive stress of up to 25 mpa within the step relative to that outside this difference in stress apparently produced the contrasting behaviors of the granitic rock experimentally derived power law flow laws do not predict these behaviors

mineralogical characterization of protolith and fault rocks from the safod main hole 1 washed cuttings provide a continuous record of the rocks encountered during drilling of the main hole of the san andreas fault observatory at depth safod both protolith and fault rocks exhibit a wide variety of mineral assemblages that reflect variations in some combination of lithology p t conditions deformation mechanisms and fluid composition and abundance regions of distinct neomineralization bounded by faults may record alteration associated with fluid reservoirs confined by faults in addition both smectites occurring as mixed layer phases and serpentine minerals are found in association with active strands of the san andreas fault that were intersected during drilling although their rheological influence is not yet fully known faults containing these mineralogical phases are prime candidates for continuous coring during phase 3 of safod drilling in the summer of 2007

slickenside kinematic indicators abstract a new classification of slickenside kinematic indicators is presented based on 61 criteria these slickensides have been subdivided into eleven major groups v or crescentic markings steps fractures trains of inclined planar structures trailed material asymmetric elevations deformed elements mineralogical crystallographic orientations asymmetric plan view features asymmetric cavities and asymmetric folds this classification constitutes a useful tool for geologists interested in the determination of the shear sense in fault surfaces bearing slickensides examples of application of this classification to natural fault surfaces at different scales are presented

fault relays bends and branch lines abstract branch lines between normal faults and their sub parallel splays mapped from 3d seismic reflection data show a range of forms from straight lines to closed loops the different geometries are interpreted as representing stages in the failure of relay zones and in the progressive replacement of fault tip lines with fault branch lines the geometries of these normal fault branch lines are similar to those for thrusts previously inferred from limited two dimensional data the orientation of the axis of a relay and its associated bends relative to a fault slip direction is identified as an important control on the structures developed within the relay neutral restraining and releasing bends can each occur on any fault type normal reverse and strike slip but data bias is a major factor in determining which bend geometry is most often observed with each fault type on normal faults the initial relay zone geometry controls the dominant branch line orientation and the same control is likely on branch lines associated with the other modes of faulting a review of the relay geometries and strains occurring with all three modes of faulting highlights the role of the orientation of the mechanical anisotropy of a bedded sequence relative to the orientations of fault surface and slip directions this relative orientation determines how the relay strain is accommodated and hence the degree of hard linkage and development of branch lines

patterns of mineral transformations in clay gouge with examples from low angle normal fault rocks in the western usa abstract neoformed minerals in shallow fault rocks are increasingly recognized as key to the behavior of faults in the elasto frictional regime but neither the conditions nor the processes which wall rock is transformed into clay minerals are well understood yet understanding of these mineral transformations is required to predict the mechanical and seismogenic behavior of faults we therefore present a systematic study of clay gouge mineralogy from 30 outcrops of 17 low angle normal faults lanf s in the american cordillera to demonstrate the range and type of clay transformations in natural fault gouges the sampled faults juxtapose a wide and representative range of wall rock types including sedimentary metamorphic and igneous rocks under shallow crustal conditions clay mineral transformations were observed in all but one of 28 faults one fault contains only mechanically derived clay rich gouge which formed entirely by cataclasis clay mineral transformations observed in gouges show four general patterns 1 growth of authigenic 1m d illite either by transformation of fragmental 2m 1 illite or muscovite or growth after the dissolution of k feldspar illitization of fragmental illite smectite is observed in lanf gouges but is less common than reported from faults with sedimentary wall rocks 2 retrograde diagenesis of an early mechanically derived chlorite rich gouge to authigenic chlorite smectite and saponite mg rich tri octahedral smectite 3 reaction of mechanically derived chlorite rich gouges with mg rich fluids at low temperatures 50 150 c to produce localized lenses of one of two assemblages sepiolite saponite talc lizardite or palygorskite chlorite quartz and 4 growth of authigenic di octahedral smectite from alteration of acidic volcanic wall rocks these transformation groups are consistent with patterns observed in fault rocks elsewhere the main controls for the type of neoformed clay in gouge appear to be wall rock chemistry and fluid chemistry and temperatures in the range of 60 180 c

structure kinematics and composition of fluid controlled brittle faults and veins in lower cretaceous claystones lower saxony basin northern germany constraints from petrographic studies microfabrics stable isotopes and biomarker analyses abstract investigation of fault rocks is crucial for the evaluation of sealing properties of rock formations considered as oil and gas storage or for the disposal of heat generating radioactive waste even in tight rock formations fluid flow may concentrate along brittle faults the present study focuses on the sealing properties of faulted lower cretaceous clay and siltstones encountered in drill cores from the central and eastern lower saxony basin germany our investigations are based on a multidisciplinary approach including microstructural mineralogical geochemical stable isotope and biomarker analyses the new data suggest that preexisting discontinuities and or sedimentary heterogeneities played a significant role for the increase in fluid pressure and formation of mode i veins within low permeability claystones high strain domains of fault cores consist of fine grained fault gouge a scaly fabric of varying deformation intensity is present around larger faults calcite precipitation in faults and complex mineralized veins and the differences in trace element concentrations of various veins reflect several phases of palaeofluid activity calcite precipitation in the fault rocks led to elevated amounts of mn ba and or sr isotope signatures indicate a local carbonate source for the origin of thin calcite coatings of fault planes but a more complex palaeofluid interaction for the larger faults and for complex veins consistent with the microfabrics biomarker signatures reveal the presence of mature hydrocarbons pointing to hydrocarbon migration in sections where steep only weakly mineralized faults occur the new results suggest that faulted claystones represent critical zones with a potentially reduced barrier capability consistent with published data

the evolution of mesoscopic imbricate thrust faults an example from the vermont foreland u s a abstract an outcrop of a thin 30 cm bed of micrite surrounded by thicker sequences of well cleaved calcareous shale in the ordovician flysch of western vermont records a complex history of imbricate faulting and associated folding the calcareous shale has been shortened by pressure solution cross cutting relations among the floor ramp and roof faults indicate that faulting progressed from the hinterland east to the foreland west all the ramp faults developed from arrays of w climbing enechelon extension fractures all other faults were controlled by the weaker bedding planes that surround the micrite and are found at various levels in the shale each fault is marked by layers of highly twinned sparry calcite and black carbonaceous shale selvedge simple shear along the floor thrust has rotated the s1 cleavage toward the foreland and produced along with volume change a pressure solution cleavage in the fault zone all cleavages have progressively developed from the hinterland to the foreland during folding and faulting of the micrite layer parallel shortening measured in both rock types is between 11 and 16

effects of smectite to illite transformation on the frictional strength and sliding stability of intact marine mudstones 1 at subduction zones earthquake nucleation and coseismic slip occur only within a limited depth range known as the seismogenic zone one leading hypothesis for the upper aseismic seismic transition is that transformation of smectite to illite at 100 150 c triggers a change from rate strengthening frictional behavior that allows only stable sliding to rate weakening behavior considered a prerequisite for unstable slip previous studies on powdered gouges have shown that changes in clay mineralogy alone are unlikely to control this transition but associated fabric and cementation developed during diagenesis remain possible candidates we conducted shearing experiments designed specifically to evaluate this hypothesis by using intact wafers of mudstone from ocean drilling program site 1174 offshore sw japan which have undergone progressive smectite transformation in situ we sheared specimens along a sawcut in a triaxial configuration oriented parallel to bedding at normal stresses of 20 150 mpa and a pore pressure of 1 mpa during shearing we conducted velocity stepping tests to measure the friction rate parameter a b friction coefficient ranges from 0 28 0 40 and values of a b are uniformly positive both are independent of clay transformation progress our work represents the most direct and comprehensive test of the clay transformation hypothesis to date and suggests that neither illitization nor accompanying fabric development and cementation trigger a transition to unstable frictional behavior we suggest that strain localization in combination with precipitation of calcite and quartz is a viable alternative that is consistent with both field observations and recent conceptual models of a heterogeneous seismogenic zone

seismic structure of the bohai bay basin northern china implications for basin evolution as part of an extensive seismic research program 33 portable broadband seismic stations were deployed along a line crossing the bohai bay basin northern china three teleseismic events were selected to constrain the seismic structure along a 280 km profile across the western edge of the basin we determined the basin structure that described the observed shear horizontal sh wave field the synthetic sh wave was calculated using a finite difference fd method with its computational domain localized in the basin area and input motions at the base of the model extrapolated from the displacement recorded at a nearby hard rock station synthetic seismographs calculated for the models match the observations well in both waveform and travel time numerical tests indicate that the structural features of the preferred models are well resolved the analysis of relations between structures and stratigraphic units along the cross sections allows multiple deformational events in the basin to be inferred in conjunction with a profile across the southern edge that has been presented previously by zhao et al 14 l zhao t y zheng w w xu modeling the jiyang depression northern china using a wave field extrapolation fd method and waveform inversion bull seismol soc am 94 2004 988 1001 the results reveal basin wide extension with local inversion features in the bohai bay basin d 2005 elsevier b v all rights reserved

fault gouge evolution in highly overconsolidated claystones processes of fault gouge evolution in hard claystones start with cataclasis that produces a soft clay gouge which fills the space between the initial fragments this re seals the initially highly porous and permeable damage zone without diagenetic processes we studied this process in shales and sandstones deformed in normal faults after uplift to shallow crustal depths in the ardennes and eifel detailed mapping shows four different lithotypes from intact shale in the wall rock broken wall rock fragments with various amounts of clay to a fully reworked gouge these lithotypes reflect different evolutionary stages the similar mineralogy of the different lithotypes suggests that the main process involved is mechanical fragmentation with minor contribution by diagenetic changes or weathering accompanied by large changes in microstructure porosity and transport properties while the wall rock has a very low porosity and permeability initial deformation results in a much higher porosity with large pores the reworked clay gouge also has a high porosity but its pore size corresponds to a lower permeability and higher capillary seal capacity in upper crustal fault zones in strong brittle lithologies this early re sealing in sections consisting of claystone will lead to local barriers to along fault fluid flow

grain size stabilisation by dispersed graphite in a high grade quartz mylonite an example from naxos greece high grade quartz mylonites from naxos greece consist of alternating thin layers of pure quartz and quartz layers with 0 3 3 vol finely dispersed graphite particles graphite free layers are coarse grained 100 300 mm show undulose extinction subgrains lobate grain boundaries and have a strongly developed crystallographic preferred orientation in these layers dislocation flow is interpreted to be the dominant deformation mechanism in contrast graphite rich layers are fine grained 30 70 mm have equant quartz grain shapes and have a crystallographic preferred orientation that becomes progressively weaker with decreasing quartz grain size given the high temperature of deformation and the need for a c axis fabric destroying mechanism grain boundary sliding is interpreted to be important in these layers analysis shows an inverse relationship between quartz grain size and the graphite dispersion suggesting stabilization of quartz grain size by graphite particles graphite particles larger than 5 mm are concentrated along quartz boundaries suggesting that stabilisation only operates above a certain critical graphite particle size this study shows that a dispersed second phase such as graphite in a naturally deforming rock can inhibit grain boundary migration stabilise the grain size and enhance grain boundary sliding at the expense of dislocation flow q 2002 elsevier science ltd all rights reserved

syntectonic fluid flow and deformation mechanisms within the frontal thrust of a foreland fold and thrust belt example from the internal jura eastern france abstract structural mapping and microstructural analyses are combined with stable clumped and radiogenic isotopes to unravel deformation mechanisms and syntectonic fluid flow during upward propagation along the frontal thrust fuans thrust of the internal part of the jura fold and thrust belt the fuans thrust cuts through upper jurassic lower cretaceous carbonate deposits branches into two splays and generates a system of fault propagation folds folding was accomodated by layer parallel shortening and layer parallel shear which generated flexural slip along bedding surfaces stylolites and foliated fabric in marly limestone interbeds thrusting was characterized by cycles of mutually overprinting pressure solution and brittle processes such as frictional sliding and fracturing veining this generated foliated tectonites in marls and limestones without significant cataclasis of the host rock pressure solution and micrometer slip along slickenfibers are evidence of aseismic slip in agreement with the ongoing aseismic growth of anticlines in the jura fold and thrust while crackle like vein texture may account for episodic seismic fracturing geochemical data show that fuans thrust acted as a conduit for the downward infiltration of meteoric derived fluids which channeled along foliated tectonites during syntectonic fluid flow calcite mineralizations precipitated at temperatures between 54 c and 10 c showing an increased contribution of organic carbon from soils in colder paleofluids this indicates a progressive opening of the system characterized by a more efficient and extensive meteoric fluids circulation considering the highest recorded temperature of 54 c and assuming the modern geothermal gradient of 30 c km thrusting in the study outcrop initiated at a burial depth of at least 1 4 km

the north china basin an example of a cenozoic rifted intraplate basin the north china basin was a stable continental region that has undergone several distinct phases of rifting and subsidence during the mesozoic and cenozoic eras the last major phase featuring block faulting rapid subsidence and widespread calc alkaline basaltic volcanism began during early tertiary time this intraplate rifting appears to be the result of an approximately 30 extension and thinning of the lithosphere beneath the northeastern china by the late tertiary period active rifting had slowed and postrift thermal subsidence had begun this regional extension and subsidence resulted in the present day north china basin a large saucer shaped oil producing basin with thinner crust and lower upper mantle p and s wave velocities than the surrounding regions during the quaternary period however the subsidence rate increased in the north china basin the frequent occurrence of destructive earthquakes and observations of relatively high heat flow suggest that the quaternary tectonic activity differs from the late tertiary simple thermal subsidence pattern and may indicate a new phase of rifting

shear sense indicators in striped bedding veins striped bedding veins are veins that lie subparallel to bedding and have an internal layering or lineation at a small angle to the veins long axis they form during bedding parallel slip and can be used as shear sense indicators solid inclusion trails produce the visible internal layering or lineation and track the opening direction of the veins elongate quartz crystals however can be oriented at an angle of up to 80 to the opening direction are non tracking and contain almost no information on the shear sense the striped bedding veins can be separated into three types according to the geometry of their internal segmentation veins of type b opened parallel to jogs oriented at a low angle to bedding veins of type j opened parallel to jogs oriented at a high angle to bedding and veins of type o opened orthogonal to bedding and jogs striped bedding veins of types b and j contain crack seal inclusion bands and displacement parallel inclusion trails striped bedding veins of type o feature only crack seal inclusion bands the example of striped bedding veins presented in this paper from the orobic alps of italy belongs to type b the lineation in the veins and the orientation of the inclusion bands and inclusion trails as well as the orientation of steps in the vein wall can be used to determine the sense of shear and the direction and amount of vein opening or bedding parallel slip

microstructural evolution of an incipient fault zone in opalinus clay insights from an optical and electron microscopic study of ion beam polished samples from the main fault in the mt terri underground research laboratory abstract slickensided shear surfaces are ubiquitous in many fault zones however the internal structure the micromechanics and the evolution of these structures are not fully understood and the contributions of crystal plasticity grain boundary sliding microfracturing solution precipitation and mineral transformation under different conditions are subject of debate we studied well preserved core samples from the main fault an up to 3 m wide zone of approximately 10 m offset in the mont terri underground research laboratory ch a site to evaluate long term safety of radioactive waste disposal the drill core breaks easily along many slickensided shear surfaces indicating reverse slip which form an anastomosing network connected by branch lines broad ion beam polishing and scanning electron microscopy shows that the slickensides are invariably revealed by fracture of the drill core along a few m thick shear zone which acts as a crack guide for fracturing the samples in this zone a complex set of processes is inferred leading to extreme localization of strain development of strong particle preferred orientation the formation of nanoparticles and local precipitation of calcite veins in releasing sections in lenses between shear zones homogeneous gouge is formed with a well developed oblique foliation and removal of calcite grains by pressure solution we infer that with progressive deformation the number and density of slickensided shear surfaces increases generating tectonically derived scaly clay and more homogeneous gouge in all deformed elements of the main fault porosity is much smaller than in the undeformed opalinus clay an interesting observation is the almost complete absence of cataclastic microstructures transmission electron microscopy tem of focused ion beam lamellae of this micron wide shear zone shows a strong preferred orientation of clay minerals including nano sized illite particles in tem the shear zones envelop hard particles and confirm an almost complete loss of porosity compared to the protolith we propose that inter and transgranular microcracking pressure solution clay neoformation crystal plasticity and grain boundary sliding are important micro scale processes during the early stages of faulting in opalinus clay and thus need to be considered in extrapolating laboratory results to long term mechanical behavior

back scattered electron imagery of the tectonic fabrics of some fine grained sediments implications for fabric nomenclature and deformation processes back scattered electron investigations of argille scagliose mudstones from the barbados forearc sampled during ocean drilling program leg 110 and the matrix of the okitsu melange southwest japan indicate a variety of microfabric geometries and deformation mechanisms despite the similarity of their mesoscopic scaly fabrics in the okitsu melange the scaly fabric is the mesoscopic expression of an anastomosing microfabric whereas the detailed geometry of scaly fabrics is unrelated to the microfabric in the argille scagliose and leg 110 mudstones care must be taken in the classification and interpretation of scaly fabrics in light of these data and future studies should focus on microstructural investigations

the utilization of sequence stratigraphy in reservoir geology initial applications of sequence stratigraphy focused on basin analysis and exploration problems as finer scale studies were conducted using well logs and outcrops it has become possible to apply the concepts to improving reservoir performance investigations of the fine scale sequence stratigraphy of carbonates has led to its application to enhance production in the complex paleozoic carbonate reservoirs of the permian and paradox basins studies of coastal plain and shallow marine sediments in the colorado plateau and alberta basin has led to effective utilization in alberta basin reservoirs outcrop of and subsurface investigations of fluvial and deltaic sediments in the north sea has improved performance of jurassic reservoirs in the north sea geophysicists are refining statistical and numerical techniques for defining the seismic facies within reservoirs in indonesia africa and the gulf of mexico several sequence stratigraphic concepts are available for application e g genetic sequences t r sequences forced regressions etc allowing the data to speak for itself rather than slavish adherence to only one theory has greatly improved the utilization of sequence stratigraphy at the reservoir level

experimentally produced slickenside lineations in pyrophyllitic clay abstract during shearing of pyrophyllitic clay fault planes bearing slickenlines were generated on previously initiated c and c planes these slickenlines have excess lengths with respect to the measured slip displacement on the fault plane and are of the ridge in groove type with the hangingwall nesting into the footwall and vice versa these features cannot be explained in terms of either frictional asperity ploughing or dissolution reprecipitation but are produced during the development of a complex ductile shear zone that contains the fault plane this initial shear zone nucleates from localized shear bands that link up to form a throughgoing shear plane the nucleation and propagation of the fault post dates the formation of the shear plane and depends on the development of a zone of highly oriented layer silicates within the pyrophyllitic clay the fault is confined to this zone the lineations observed on the fault surfaces are produced while the material behaves plastically prior to the brittle faulting with increasing shear strain the brittle ductile transition is crossed and sliding continues under brittle conditions along the former shear zone

forced regressions in a sequence stratigraphic framework concepts examples and exploration significance sequence stratigraphic concepts suggest that stratal geometries develop and are largely controlled by changes in relative sea level on the shelf lowstand deposits which form during falls and subsequent stillstands of relative sea level can be recognized by the presence of an unconformity at the base the isolated and basinward position relative to the previous shoreline and the abrupt seaward translation of shallow water and shoreline facies into the basin across an unconformity surface this seaward translation of facies and shoreline regression in response to relative sea level lowering is termed a forced regression a forced regression is independent of variations of sediment flux and is in contrast with normal regressions that occur in response to excess sediment flux relative to space available on the shelf i e accommodation forced regressions commonly are associated with a zone of sedimentary bypass subaerial exposure and possible fluvial erosion between the newly formed and preceding shorelines certain shelf sands previously interpreted as offshore or mid shelf sand bodies thus can be reinterpreted as stranded lowstand shorelines associated with forced regressions this alternative interpretation has economic significance insofar as it suggests different subsurface correlations and reservoir geometries with the potential for development of new play types and enhanced recovery in o der fields examples of forced regression can be observed at a variety of scales and ages several such examples include the modern east coulee fan delta and the lower cretaceous viking formation in alberta canada the quaternary rhone delta and the quaternary hudson valley system

the mesozoic cenozoic east china rift system abstract the mesozoic cenozoic rift system of eastern china extends in a n s direction over a distance of some 4000 km and has a width of 600 1000 km to the east it reaches into the coastal areas of the east and south china sea and extends onto the continental shelf this very large rift system evolved on a heterogenous basement consisting of a number of terranes which were amalgamated during the indosinian orogeny a first rifting phase spanned late jurassic early cretaceous times it was followed by a period of relative tectonic quiescence and thermal relaxation a latest cretaceous phase of compressional tectonics giving rise to partial basin inversion was followed by a renewed rifting cycle spanning eocene early neogene times development of the east china rift system involving vertical as well as lateral crustal movements was probably induced by physico chemical changes within the earth s mantle that can be related to activity along the pacific subduction zones the mesozoic cenozoic east china rifts contain some important hydrocarbon provinces which rely to a large extent on syn rift sediments for source and reservoir rocks

experimental investigation into the microstructural and mechanical evolution of phyllosilicate bearing fault rock under conditions favouring pressure solution abstract mature crustal fault zones are known to be zones of persistent weakness this weakness is believed to result from microstructural modifications during deformation such as grain size reduction and foliation development around the brittle ductile transition phyllosilicates are expected to have a significant effect on fault strength in particular under conditions favouring pressure solution to study such effects we performed rotary shear experiments on brine saturated halite kaolinite mixtures aimed at investigating the relation between microstructural and mechanical evolution in a system where pressure solution and cataclasis dominate the results show significant strain weakening and a transition with progressive strain towards more rate sensitive and less normal stress sensitive behaviour this was accompanied by a microstructural evolution from a purely cataclastic microstructure to a mylonitic microstructure consisting of elongate asymmetric clasts in a fine grained foliated matrix the results demonstrate that strain weakening and the development of a typical mylonitic microstructure can occur as a consequence of grain size reduction by cataclasis and a transition to pressure solution accommodated deformation even in the absence of dislocation creep the data raise questions regarding the reliability of microstructures as rheology indicators as well as on the use of low strain monomineralic flow laws for modelling crustal dynamics

bib sem study of the pore space morphology in early mature posidonia shale from the hils area germany abstract this contribution reports on the study of the pore space morphology in two early mature vr r 0 59 and 0 61 samples of posidonia shale from the hils syncline in germany using broad ion beam bib polishing and high resolution scanning electron microscopy sem this allows imaging pores with resolution down to 10 nm in equivalent diameter d eq and quantitative estimation of porosity using a combination of bse and se detectors and semi automatic segmentation of the gigapixel images the representative elementary area of the samples on the scale of a few mm is inferred to be about 140 140 m 2 pore morphologies and pore sizes are clearly related to the mineral fabric with large differences very large typically several microns pores with internal faceted crystal morphology in recrystallized calcite clasts and smaller pores d eq cf schizosphaerella nanofossils typically 200 nm pores are less common in organic material and in pyrite aggregates pore characteristics are very similar for both samples and porosity resolvable by bib sem is 2 75 and 2 74 pore size distribution can be described by a power law with an exponent about 2 0 and 2 2 respectively for the pore population excluding the fossils pores in the carbonate fossils show dual power law distribution with power law exponents of about 1 and 3 by extrapolating the power law distribution for each sample total porosity is estimated to be 4 8 0 9 1 7 and 6 5 2 7 7 2 respectively this estimate can be compared with 3 4 3 7 and 3 3 3 6 as measured by mercury injection porosimetry we interpret this difference to reflect the unconnected for mercury part of the porosity comparison of imaged pores and mercury injection porosimetry suggest a very high pore body to pore throat ratio this results in a pore model where large pores represented mainly by pores in fossils and calcite grains are connected via a low porous and low permeable clay rich matrix with pore throats below 10 nm in both samples

review of major shale dominated detachment and thrust characteristics in the diagenetic zone part ii rock mechanics and microscopic scale abstract characterising large shale thrust zone behaviour down to the diagenetic metamorphic boundary is both simple and complex the task in critical taper analogue and numerical models has been successfully approximated using simple material parameters yet the weakness of shales thrusts on a case by case basis show great variability in key factors across a wide range of scales understanding of these variables and their relationships to different tectonic settings is patchy due to the different objectives of workers studying the various systems e g seismic hazards hydrocarbon exploration structural geology research and the types of available geological and geophysical data early research recognized that megathrusts feature creeping and locked patches which may be described using the rate and state formalism in addition to temperature differential stress and strain rate key controlling factors on thrust weakness are mineralogy amount of weak phase present structure localization mechanisms grain size and shapes porosity permeability and pore fluid pressure the smectite illite transition has been a focus of seismic hazard research due to its coincidence with the top of the seismogenic zone while there may be a relationship other factors such as pore fluid pressure variations or structure localization are also important the critical taper model is a simple means of determining whether basic rock mechanics data e g frictional strength pore fluid pressure is appropriate for natural wedges for example aseismic basal detachments of gravity driven systems smaller critical taper wedges appear to retain higher pore fluid pressures along the basal detachment than seismogenic basal detachments higher critical taper wedges in many continental and deltaic fold and thrust belts high organic carbon content is a very important factor in shale weakness due to 1 the overall more ductile and well cleaved nature of the shale when organic content is high 2 the presence of high overpressures due to maturation of organic material and 3 metamorphism of carbon to low friction graphite this multifaceted influence of organic carbon content is just one example of the diversity of potential influences on shale thrust zone weakness which enable shales to be weak despite considerable lateral deposition related and vertical burial related changes in composition some key variations between different types of fold and thrust belt gravity driven accretionary prism andean himalayan type lie in systematic variations in clay mineralogy magnitudes and origins of overpressures seismic versus aseismic detachments and different structural localization mechanisms further research is required to explore the viability of such distinctions and their impact on structural styles

anisotropy in shale from mont terri anisotropy of shales is the subject of this report and we use an example of the jurassic opalinus clay from mont terri switzerland that is being investigated in the context of radioactive waste disposal the study is targeted at the geomechanical characterization of shale by laboratory testing the overall aim is to improve the constitutive material laws and their application in numerical models

slip perturbation during fault reactivation by a fluid injection abstract slip orientation inferred from fault striae or focal mechanism datasets is commonly used in stress inversion methods based on the wallace bott hypothesis the hypothesis postulates that slip on a fault plane is collinear with the orientation of the resolved shear stress it is valid for a single planar fault subjected to a homogeneous far field stress however the experimental displacement data from an induced fault reactivation experiment conducted in the mont terri rock laboratory switzerland indicated multiple triggered slip orientations thereby preventing application of the above inversion method we present numerical and analytical results of slip on a reactivated fracture with a non uniform fluid pressure distribution using these models we evaluate the reasons for the inconsistency of our observations and the traditional wallace bott hypothesis and test the physical effects of various parameters on fault slip in the fully coupled hydromechanical numerical model three dimensional distinct element method fluid pressure at a point on the fault surface is increased stepwise assumed planar and singular until shear reactivation of the fault is induced we studied two different models with high and low fault plane stiffness to represent hard and soft rock masses respectively the model shows that high fault stiffness preserves the planarity of the fault plane while low fault stiffness permits dilation and morphological changes of the fracture related to fluid pressure diffusion the highest slip perturbation was observed in the low stiffness model due to the change of the fracture shape controlled by the non uniform pressure distribution the eshelby analytical solution confirmed that the more the fracture is dilated the more the corresponding resolved shear stress is perturbed additionally when compared to dilation and fault aperture the friction angle has the most influence on the angular difference between geomechanical slip vectors and resolved shear stress

stretching and subsidence rifting of conjugate margins in the north atlantic region subsidence on rifted conjugate continental margins around the north atlantic is analyzed to derive the amount and areal distribution of stretching in the crust and in the lower lithosphere during continental rifting study areas are the grand banks and orphan basin regions of the eastern canadian continental margin and the goban spur and galicia bank regions off western europe in all areas maps of synrift and postrift sediment thickness and bathymetry were used to derive maps of post and synrift subsidence a two layer lithospheric stretching model with independent amounts of stretching in the crust and in the lower lithosphere was assumed to be applicable with the rifting history approximated by several instantaneous episodes of extension this model was used to derive estimates of stretching at all points on a 0 05 geographical grid where subsidence values were available within the study regions the models are constrained with seismic measurements of crustal thickness the results imply that pure shear stretching predominates at a lithospheric scale while simple shear is more localized laterally and confined to the crust in places there is significant decoupling between crustal and mantle stretching near the continent ocean boundary final continental breakup may be localized on one side of the rift between conjugate margin pairs rather than symmetrically located total extension of the margins is compatible with that estimated from normal fault geometries and indicates that the continent ocean boundary has been extended up to 350 km seaward of its original position which should be considered in plate kinematic reconstructions

regressive and transgressive cycles in a rift basin depositional model and sedimentary partitioning of the middle jurassic hugin formation southern viking graben north sea abstract the jurassic hugin formation consists of shallow marine sandstones that belong to a significant hydrocarbon reservoir in the sleipner area in the norwegian north sea the formation encompasses coarsening upward units of mouth bar and shoreface facies interpreted to record delta outbuilding during regression and fining upward units with tidal channel dune and tidal flat facies interpreted as part of an estuary environment during transgression the correlations reveal that the studied part of the hugin formation consists of 8 sequences each with a transgressive and a regressive unit representing the transgressive systems tract and the highstand systems tract respectively the sequences are stacked retrogradationally landward as a result of rapid tectonic subsidence and rifting of the viking graben rifting led to the development of an elongate graben where tidal currents were amplified wave action damped and longshore drift as sediments supply reduced or absent lowstand and forced regressive systems tracts are not identified and their absence is interpreted to reflect suppression of relative sea level falls in a rapidly subsiding basin where the basin subsidence rate outpaced any potential fall in eustatic sea level through facies interpretation and sequence stratigraphic correlations between wells these regressive and transgressive units are shown to exhibit characteristic thickness trends in the form of sigmoidal shaped wedges stacked in an offset manner in a landward to basinward orientation these thickness trends illustrate sediment partitioning within the sequences and are explained by the relationship between accommodation versus sediment supply in terms of mass balance during regression the focus of sedimentation was pushed basinward and during transgression it was pushed landward as sediments were trapped there the mapping of these sequence stratigraphic units serves as input to reservoir models and to help increase recovery and identify new exploration targets

frictional properties of low angle normal fault gouges and implications for low angle normal fault slip abstract the mechanics of slip on low angle normal faults lanfs remain an enduring problem in structural geology and fault mechanics in most cases new faults should form rather than having slip occur on lanfs assuming values of fault friction consistent with byerlee s law we present results of laboratory measurements on the frictional properties of natural clay rich gouges from low angle normal faults lanf in the american cordillera from the whipple mts detachment the panamint range front detachment and the waterman hills detachment these clay rich gouges are dominated by neoformed clay minerals and are an integral part of fault zones in many lanfs yet their frictional properties under in situ conditions remain relatively unknown we conducted measurements under saturated and controlled pore pressure conditions at effective normal stresses ranging from 20 to 60 mpa corresponding to depths of 0 9 2 9 km on both powdered and intact wafers of fault rock for the whipple mountains detachment friction coefficient varies depending on clast content with values ranging from 0 40 to 0 58 for clast rich material and 0 29 0 30 for clay rich gouge samples from the panamint range front detachment were clay rich and exhibit friction values of 0 28 to 0 38 significantly lower than reported from previous studies on fault gouges tested under room humidity nominally dry conditions including samples from the same exposure samples from the waterman hills detachment are slightly stronger with ranging from 0 38 to 0 43 the neoformed gouge materials from all three localities exhibits velocity strengthening frictional behavior under almost all of the experimental conditions we explored with values of the friction rate parameter a b ranging from 0 001 to 0 025 clast rich samples exhibited frictional healing strength increases with hold time whereas clay rich samples do not our results indicate that where clay rich neoformed gouges are present along lanfs they provide a mechanically viable explanation for slip on faults with dips p f 3 overpressures and or correcting for 5 of footwall tilting furthermore the low rates of frictional strength recovery and velocity strengthening frictional behavior we observe provide an explanation for the lack of observed seismicity on these structures we suggest that lanfs in the upper crust depth

thickening of fault zones a mechanism of melange formation in accreting sediments sediments accreted at subduction zones undergo stratal disruption and form a type of melange the thickness of the disrupted zones grows with progressive deformation this suggests that initial fault surfaces are abandoned and deformation propagates into adjacent undeformed sediment factors causing the abandonment of fault surfaces during continuing deformation include 1 strengthening owing to porosity loss during consolidation 2 localized drops in fluid pressure on fault surfaces that act as dewaterinig conduits and 3 reorientation of fault surfaces the disruptive processes occurring in accretionary prisms result principally from the deformation of a consolidating sediment mass

fan deltas and braid deltas varieties of coarse grained deltas two types of coarse grained deltas are recognized fan deltas and braid deltas fan deltas are gravel rich deltas formed where an alluvial fan is deposited directly into a standing body of water from an adjacent highland they occupy a space between the highland usually a fault bounded margin and the standing body of water in contrast braid deltas here introduced are gravel rich deltas that form where a braided fluvial system progrades into a standing body of water braid deltas have no necessary relationship with alluvial fans as exemplified by fluvioglacial braid deltas braid deltas have previously been classified as fan deltas even though the geomorphic and sedimentologic settings of the two systems can be vastly different braid deltas are a common present day geomorphic feature and are abundant in the geological record fan deltas and braid deltas can be distinguished in the rock record by distinctive subaerial components of these depositional systems the shoreline and subaqueous components of both are similar fan delta sequences have a subaerial component that is an alluvial fan facies comprising interbedded sheetflood debris flow and braided channel deposits fan deltas produce small a few tens of square kilometres wedge shaped bodies of sediment commonly displaying high variability in paleocurrent patterns and abrupt changes in facies the deposits are generally very coarse grained with large out sized clasts very poorly sorted matrix rich polymictic heterolithic partially cemented by penecontemporaneous carbonate and have low porosity and permeability braid deltas in contrast have a subaerial component consisting entirely of braided river or braidplain facies their deposits display better sorting roundness and clast orientation than do fan delta sediments they lack a muddy matrix they display size grading and bar migration they commonly have a sheet geometry with high lateral continuity tens to hundreds of square kilometres and they exhibit moderate to high porosity and permeability valuable paleogeographic and tectonic information concerning the proximity of highlands and major fault zones may be misinterpreted or lost if these two coarse grained deltaic systems are not differentiated

late quaternary high resolution sequence stratigraphy of an active rift the sperchios basin greece an analogue for subtle stratigraphic plays the sperchios basin is an active asymmetric graben bounded to the south by a major border fault system with major fault segments typically 20 30 km long the basin is dominated by a major axial fluvio deltaic system which enters the partially enclosed maliakos gulf to the east lateral sourced depositional systems within the basin comprise hanging wall and footwall derived alluvial fans and a narrow coastal plain along the footwall scarp bordering the maliakos gulf high resolution seismic data from the maliakos gulf reveals three late quaternary progradational parasequences sourced from axial and lateral depositional systems with a regional late pleistocene transgressive surface dated at circa 10 ka bp within the maliakos gulf differential subsidence of the late pleistocene transgressive surface indicates marked variation in subsidence from 2 4 m ka sup 1 at fault segment centers to 0 8 m ka sup 1 at segment boundaries the geometry and internal variability of each parasequence is controlled by the interplay of the local accommodation development and fluctuations in sediment supply and climatic conditions the sperchios rift provides a modem analogue for subtle stratigraphic plays within ancient extensional basins the study of controls on sediment source and transport patterns within active rifts has refined our appreciation of the controlsmore on potential reservoir distribution and geometries less

shear zones in clay rich fault gouge a laboratory study of fabric development and evolution abstract clay rich fault rocks have long been recognized to host distinctive fabric elements and fault rock fabric is increasingly thought to play a fundamental role in fault mechanical behaviour in the brittle regime although the geometries of fabric elements in fault gouges have been described for almost a century the genesis and evolution of these elements during shear and their links to bulk mechanical properties remain poorly understood we characterize the development and evolution of fabric elements with increasing shear in a variety of clay rich experimental gouges over shear strains of 20 and at normal stresses of 2 150 mpa in the double direct shear configuration in addition to sem observations of experiment products at a variety of shear strains we quantified clay fabric intensity and the degree of grain size reduction using x ray texture goniometry xtg and particle size distribution psd measurements we also measured p and s wave velocities during shear to further probe the evolution of shear fabric and gouge properties we find that clay fabric elements develop in a systematic manner regardless of the gouge material riedel shears in the r1 orientation and boundary parallel shears are the dominant fabric elements riedel shears nucleate at layer margins and propagate into the layer shortly after reaching yield stress clay particles rotate into the p orientation shortly after riedels propagate through the layer the riedel shears are through going but are 10 thinner than similar zones observed in coarser granular materials our results suggest that the weakness of clay rich fault gouge may be less a function of anisotropic crystal structure as has been suggested previously and more a consequence of very thin shear surfaces permitting deformation in clay rich materials with minimal dilation or cataclasis the very thin shear surfaces are a function of the fine grain size of the materials and possibly polymodal psd s

shear zone geometries in experimentally deformed clays the influence of water content strain rate and primary fabric in experimentally deformed clays three parameters which influence the geometry of shear zones are water content strain rate and the orientation of the shear zones with respect to any primary fabric the shear zones are the main microstructures induced in the clays within the experimental conditions triaxial compression at water contents between 20 and 35 w w and strain rates between 10 4 and 10 8 s 1 small changes in water content produce a significant change in the appearance of shear zones structures in wetter sediments are more complex and more numerous than those in drier sediments which tend to produce a small number of discrete planar shear zones strain rate is a far less important influence on shear zone geometry the orientation of the zones with respect to a primary fabric is also significant shear zones which are parallel to the fabric have a simpler geometry than zones which intersect the fabric at a high angle knowledge of these factors may help interpret the conditions within which shear zones formed in naturally deformed soft sediments

a tale of two viscosities abstract we describe a series of 12 large strain two dimensional simple shear numerical experiments on two phase linear and non linear viscous materials the modal percentage of the two phases their relative viscosities and the stress exponent of the dependence of viscosity on stress were systematically varied allowing us to observe the effects of these parameters on the flow behaviour of the system all experiments exhibited localisation but the extent and type of localisation varied considerably and the range of parameters allows both classical sc as well as sc structures to form the inter granular finite strain geometries also varied systematically although there is a tradeoff between non linearity of viscosity and the viscosity contrast that results in similar geometries for quite different mechanical behaviour the finite rotation of the harder phases was similar within any one experiment originally parallel passive marker lines thus remain sub parallel after deformation and rotation which may be mistaken for non rotation the internal deformability and interaction between grains allows meta stable grain elongation orientations to form without any additional consideration of external slip surfaces the slight variability of initial grain geometry and subsequent grain interactions leads to a wide variability in final grain shapes for the same initial viscosities

kinematic indicators on active normal faults in western turkey quaternary normal fault zones in western turkey comprise multiple slip planes and zone parallel layers of fault breccia they also contain several little known kinematic indicators that are probably typical of many formed at shallow levels in extending terrains the recent exhumation by contractors of about 2000 m2 of slip planes in a sse dipping fault zone separating quaternary colluvium from bedrock carbonates at yavansu 7 km se of kusadasi permits an unusually complete inventory of the indicators to be compiled the most spectacular indicators are metre scale 69 w pitching corrugations in slip planes and recemented breccia sheets underlying them corrugations characterized by sinusoidal profiles normal to their long axes and less commonly culminations and depression along their axes possibly developed as a result of upwards propagating slip planes seeking undemanding pathways through heterogeneous fault precursor breccias that formed in advance of tip lines parallel to corrugation long axes are those of gutters flat floored sleep sided channels a few centimetres wide probably related to the abrasion of subslip plane breccia sheets centimetre scale tool tracks scored in the uppermost subslip plane breccia sheet by resistant colluvial clasts are irregular at their proximal ends but distally they swing into alignment with corrugation axes frictional wear striae centimetres long but only a few millimetres wide and pitching 78 w are superimposed on the other slip parallel lineations comb fractures nearly perpendicular to slip planes define an intersection lineation which is normal to corrugation axes fault plane solutions of earthquakes on sse dipping active faults in the west anatolian extensional province indicate that mainly normal combined with minor dextral slip is the dominant mode a conclusion in accord with the sense of slip inferred from the indicators exposed on the yavansu slip planes

high resolution stratigraphy of an underfilled lake basin wilkins peak member eocene green river formation wyoming u s a abstract lakes tend to respond noticeably to minor changes in sediment and water balance driven by climatic tectonic or geomorphic processes this unique behavior of lacustrine basins can provide a high resolution record of geologic processes within the continental setting far from the globally averaged record of marine strata the wilkins peak member of the eocene green river formation in wyoming usa is dominated by aggradation of repetitive sedimentary facies successions recording distinct lacustrine expansions and contractions these lacustrine cycles consist of up to four successive facies associations littoral profundal sublittoral palustrine and salt pan because they comprise disparate facies that may never have been simultaneously deposited in the basin wilkins peak member cycles are non waltherian successions that do not readily equate to any established sequence stratigraphic unit the completeness of the stratigraphic record in the wilkins peak member varies continuously across the basin at least 126 cycles are present in the erda white mountain 1 core near the basin depocenter whereas only about one third as many are recognizable 53 km north nearer to the basin margin cycle boundaries terminate northward by gradual amalgamation into palustrine facies reflecting the interplay between varying lake levels and a south dipping deposition gradient evidence for complete desiccation and hiatuses is commonplace even near the basin center a truly complete record may not be present anywhere based on recent 40ar 39ar geochronology of tuffs the average cycle duration in the white mountain 1 core is approximately 10 000 years however the true average duration is shorter due to the presence of lacunae and the time required for deposition of the thinnest cycles may have been less than 1000 years no external driving mechanism is presently known for eocene cycles of such short duration raising the possibility that they are instead autogenic cycles related to geomorphic instability of the surrounding landscape evaporite deposition corresponded closely in time and space to maximum differential subsidence suggesting that tectonic influences on drainage patterns and basin accommodation exerted a primary control differential accommodation was most pronounced during deposition of the lower wilkins peak member and became progressively less so after that time based on structural and stratigraphic observations a period of increased tectonic uplift commenced concurrent with deposition of the lower wilkins peak member

field characterization of elastic properties across a fault zone reactivated by fluid injection we studied the elastic properties of a fault zone intersecting the opalinus clay formation at 300m depth in the mont terri underground research laboratory switzerland four controlled water injection experiments were performed in borehole straddle intervals set at successive locations across the fault zone a three component displacement sensor which allowed capturing the borehole wall movements during injection was used to estimate the elastic properties of representative locations across the fault zone from the host rock to the damage zone to the fault core young s moduli were estimated by both an analytical approach and numerical finite difference modeling results show a decrease in young s modulus from the host rock to the damage zone by a factor of 5 and from the damage zone to the fault core by a factor of 2 in the host rock our results are in reasonable agreement with laboratory data showing a strong elastic anisotropy characterized by the direction of the plane of isotropy parallel to the laminar structure of the shale formation in the fault zone strong rotations of the direction of anisotropy can be observed the plane of isotropy can be oriented either parallel to bedding when few discontinuities are present parallel to the direction of the main fracture family intersecting the zone and possibly oriented parallel or perpendicular to the fractures critically oriented for shear reactivation when repeated past rupture along these plane has created a zone of weakness

microstructure and composition of brittle faults in claystones of the mont terri rock laboratory switzerland new data from petrographic studies geophysical borehole logging and permeability tests abstract claystones are considered as a geological barrier however the properties of claystone may be modified if these are cut by brittle faults and fractures investigations of fault rocks are therefore crucial to evaluate the barrier properties of clay rich formations the present study is dealing with the characterization of naturally and artificially deformed opalinus clay of the mont terri rock laboratory in nw switzerland complete core sections covering the artificially excavation damaged zone edz and several tectonic fault zones have been studied using a multidisciplinary approach consisting of geophysical geotechnical mineralogical geochemical and lithological structural data the fault zones encountered are characterized by a high density of planar discontinuities which often show slickenside striations under the microscope the fault zones turned out to be pervasively deformed resulting in open veins and pore space now filled with calcite and celestine fault zone reactivation led to very fine grained cohesionless fault gouge and fragmentation of the previously formed calcite veins packer tests in boreholes reveal excavation induced enhanced permeabilities up to 3 m borehole depth 1 9 m to gallery floor seismic borehole measurements indicate that seismic attributes which are typical for undisturbed opalinus clay are not reached until 7 5 m borehole depth 4 8 m to gallery floor which is larger than in the usual gallery configuration we interpret the anomalies in geophysical measurements as well as the elevated permeabilities measured in the main fault 3 6 m to 4 2 m to gallery floor to result from an enlarged edz influenced by the presence of the brittle fault structures the up to two orders of magnitude higher permeability compared to the intact claystone most probably results from excavation induced stress and a local reactivation of fault planes the results suggest that the presence of a fault zone can alter the extent of the edz significantly and thereby affect the rock integrity at least in the near field of a repository tunnel

depositional systems and sequence architecture of the oligocene dongying formation liaozhong depression bohai bay basin northeast china the sequence stratigraphic framework and depositional systems of an oligocene lacustrine rift succession in the liaozhong depression of bohai bay basin in northeastern china were investigated using seismic profiles complemented by well logs and cores seven sequences are identified on the basis of unconformities on basin margins and correlative conformities in the basin center depositional systems are associated with systems tracts within sequences lowstand systems tracts are dominated by sublacustrine fans transgressive systems tracts are mainly composed of beach bar deposits and highstand systems tracts are characterized by deep lacustrine fan or braid delta deposits episodic tectonic movement was the principal factor that controlled the development of the sequences lake level changes resulting from climatic oscillations may have controlled the development of these sequences the balance between tectonic subsidence and sediment supply controlled the type of lake basin the bohai bay basin was a balanced fill basin in the early and middle stages of the dongying formation and evolved into an overfilled basin at the end of deposition of the dongying formation this study enhances the understanding of depositional system configuration and systems tracts in a typical rift basin and proposes that the most favorable sandstone reservoirs are developed in sublacustrine fan deposits relative lowstand sublacustrine fan deposits capped by relative highstand prodelta or deep lacustrine mudstones form the highest potential lithostratigraphic traps

natural tracer profiles across argillaceous formations argillaceous formations generally act as aquitards because of their low hydraulic conductivities this property together with the large retention capacity of clays for cationic contaminants has brought argillaceous formations into focus as potential host rocks for the geological disposal of radioactive and other waste in several countries programmes are under way to characterise the detailed transport properties of such formations at depth in this context the interpretation of profiles of natural tracers in pore waters across the formations can give valuable information about the large scale and long term transport behaviour of these formations here tracer profile data obtained by various methods of pore water extraction for nine sites in central europe are compiled data at each site comprise some or all of the conservative tracers anions cl br water isotopes delta 18 o delta 2 h and noble gases mainly he based on a careful evaluation of the palaeo hydrogeological evolution at each site model scenarios are derived for initial and boundary pore water compositions and an attempt is made to numerically reproduce the observed tracer distributions in a consistent way for all tracers and sites using transport parameters derived from laboratory or in situ tests the comprehensive results from this project have been reported in mazurek et al 2009 here the results for three sites are presented in detail but the conclusions are based on model interpretations of the entire data set in essentially all cases the shapes of the profiles can be explained by diffusion acting as the dominant transport process over periods of several thousands to several millions of years and at the length scales of the profiles transport by advection has a negligible influence on the observed profiles at most sites as can be shown by estimating the maximum advection velocities that still give acceptable fits of the model with the data the advantages and disadvantages of different conservative tracers are also assessed the anion cl is well suited as a natural tracer in aquitards because its concentration varies considerably in environmental waters it can easily be measured although the uncertainty regarding the fraction of the pore space that is accessible to anions in clays remains an issue the stable water isotopes are also well suited but they are more difficult to measure and their values generally exhibit a smaller relative range of variation chlorine isotopes delta 37 cl and he are more difficult to interpret because initial and boundary conditions cannot easily be constrained by independent evidence it is also shown that the existence of perturbing events such as the activation of aquifers due to uplift and erosion leading to relatively sharp changes of boundary conditions can be considered as a pre requisite to obtain well interpretable tracer signatures on the other hand gradual changes of boundary conditions are more difficult to parameterise and so may preclude a clear interpretation

do scaly clays control seismicity on faulted shale rocks abstract one of the major challenges regarding the disposal of radioactive waste in geological formations is to ensure isolation of radioactive contamination from the environment and the population shales are suitable candidates as geological barriers however the presence of tectonic faults within clay formations put the long term safety of geological repositories into question in this study we carry out frictional experiments on intact samples of opalinus clay i e the host rock for nuclear waste storage in switzerland we report experimental evidence suggesting that scaly clays form at low normal stress 20 mpa at sub seismic velocities 300 m s and is related to pre existing bedding planes with an ongoing process where frictional sliding is the controlling deformation mechanism we have found that scaly clays show a velocity weakening and strengthening behaviour low frictional strength and poor re strengthening over time conditions required to allow the potential nucleation and propagation of earthquakes within the scaly clays portion of the formation the strong similarities between the microstructures of natural and experimental scaly clays suggest important implications for the slip behaviour of shallow faults in shales if natural and anthropogenic perturbations modify the stress conditions of the fault zone earthquakes might have the potential to nucleate within zones of scaly clays controlling the seismicity of the clay rich tectonic system thus potentially compromising the long term safeness of geological repositories situated in shales

stress and deformation along wavy frictional faults locally inhomogeneous stress states are expected along faults owing to slip on geometrically irregular fault surfaces we use an analytical model of elastic deformation along a wavy frictional fault to evaluate the variation in local stress state as a function of surface roughness elastic modulus slip coefficient of friction and far field stress the total stress state along the fault may be described by the sum of a basic stress component resulting from frictional slip on a planar fault surface and a perturbed stress component resulting from the presence of roughness roughness produces a variation in normal stress across the fault surface and assuming roughness and modulus appropriate to crustal faults the normal stress should be reduced to a near zero magnitude locally such that separation of fault walls is likely the large variation in normal stress along the fault surface resulting from fault roughness may be responsible in part for complexity in moment release during large earthquakes and for lateral variation in seismic coupling along faults the variation in principal stress orientations and magnitudes along a fault increases with a decrease in the coefficient of friction of the fault the location and size of regions with a high likelihood for brittle failure depend on the orientation of the far field principal stress and fault friction the average orientation of the principal stresses in the region of likely failure is not the same as the far field principal stress orientation although inversion of earthquake and fabric data for stress orientation along a fault may be possible the model results suggest that inversion results are insufficient to determine far field stress states and fault friction without additional independent data

timing of fault reactivation in the upper crust of the st lawrence rift system canada by k ar dating of illite rich fault rocks11geotop contribution 2012 0002 formed during late proterozoic early paleozoic the st lawrence rift system of eastern north america hosts an active seismic zone also displaying evidence of subsequent tectonic reactivation in paleozoic and mesozoic times however lack of a detailed reconstruction of the basement geometry and limited geochronological constraints limit our understanding of its structural evolution late silurian early devonian fault reactivation is demonstrated here in typical fault sites of the st lawrence rift system by combining structural observations of basement structures and a mineralogical morphological and k ar isotopic study of clay rich fault material 0 4 m et 1 2 m the k ar data of clay rich size fractions from gouges of varied rock types from saint laurent and montmorency faults define two isochron ages at 436 45 and 406 22 ma that are within analytical uncertainty and give an average at 421 15 ma however these two faulting episodes could also picture a single long lasting phase of for

stratigraphic classification of ancient lakes balancing tectonic and climatic controls lakes and lake deposits present two fundamental paradoxes 1 modern lakes are vastly complicated but the rock records of lakes are relatively simple extensive observations reveal three distinct facies associations of common and widespread occurrence these are referred to here as fluvial lacustrine fluctuating profundal and evaporative facies associations 2 most explanations of modern and ancient lakes attribute their nature to climate but neither modern lake parameters lake size depth and salinity nor the character of ancient lake strata thickness extent lithology correlate with measured or inferred climatic humidity we propose that it is the relative balance of rates of potential accommodation mostly tectonic with sediment water fill mostly a function of climate that controls lake occurrence distribution and character lake basins may be termed overfilled balanced fill or underfilled depending on the balance between these rates we conclude that climate and tectonics exert coequal influence on lake deposits at both mesoscales 1 m to hundreds of meters and macroscales hundreds to thousands of meters

pedogenic slickensides indicators of strain and deformation processes in redbed sequences of the appalachian foreland pedogenic slickensides are convex concave slip surfaces that form during expansion contraction in expansive clay soils such as vertisols in the central appalachians they occur near the tops of fining upward cycles in paleozoic redbeds such as the bloomsburg catskill and mauch chunk formations pedogenic slickensides are found in association with other pedogenic or paleosol features such as clay skinned peds in situ calcareous nodules and root impressions repeated movements along these shear planes during pedogenesis produce strongly aligned clay particles adjacent to pedogenic slickensides as a result they are preserved as discrete fractures throughout diagenesis compaction and superimposed tectonic deformation during whole rock deformation pedogenic slickensides segregate penetratively deformed rocks into independent foliated packets and serve as discontinuities that are followed by later structural features because the original morphology of pedogenic slickensides is known they can be used as crude strain markers

origin and behavior of clay minerals in the bogd fault gouge mongolia we analyzed twelve fault gouge samples from the bogd fault in south western mongolia to understand the origin and behavior of clay minerals the investigation relies on x ray powder diffraction xrd scanning electron microscopy sem transmission electron microscopy tem and high energy synchrotron x ray diffraction methods to investigate microstructure and preferred orientation smectite montmorillonite illite smectite mixed layers illite mica and kaolinite are the major clay components in addition to quartz and feldspars which are present in all samples the observations suggest that the protoliths and the fault rocks were highly altered by fluids the fluid rock interactions allow clay minerals to form as well as alter feldspars to precipitate kaolinite and montmorillonite thus newly formed clay minerals are heterogeneously distributed in the fault zone the decrease of montmorillonite component of some of the highly deformed samples also suggests that dehydration processes during deformation were leading to illite precipitation based on synchrotron x ray diffraction data the degree of preferred orientation of constituent clay minerals is weak with maxima for 001 ranging from 1 3 to 2 6 multiples of a random distribution m r d co existing quartz and feldspars have random orientation distributions microstructure and texture observations of the gouges from the foliated microscopic zone alternating with micrometric isotropic clay rich area also indicate that the bogd fault experienced brittle and ductile deformation episodes the clay minerals may contribute to a slip weakening behavior of the fault

seismic reflection imaging of a major strike slip fault zone in a rift system paleogene structure and evolution of the tan lu fault system liaodong bay bohai offshore china the tan lu fault system in the liaodong bay bohai offshore china affords an exceptional opportunity to document the structural features of a major strike slip fault using two and three dimensional seismic reflection data as well as evolution of a strike slip fault developed coeval with a rift system the fault zone displays a relatively straight throughgoing trace longitudinally bisecting the rift valley it consists of positive and negative flower structures and en echelon folds in the south bay and three parallel flower structure systems northward the middle fault bifurcates northward into two semiparallel vertical fault strands to the north the west strand bends clockwise and merges with the east strand the stepping pattern and orientation of en echelon structures indicate right lateral sense and about n10 35e azimuth of slip the fault apparently accrued about 30 40 km 20 25 mi of post early eocene slip based on the current distribution of deformation zones and depocenters tan lu fault segments with clockwise and counterclockwise orientation relative to the regional slip direction are characterized by divergent and convergent structures i e restraining and releasing bends respectively waning of rifting eliminated the cause of a major restraining bend putting an end to development of associated convergent structures in the south bay area near the central north bay deformation occurred along major normal faults related to the basin rifting although a prominent feature reflecting regional strain partitioning the tan lu fault apparently was not a major factor in the paleogene opening of the liaodong bay basin and the larger north china rift basin

influence of carbonate microfabrics on the failure strength of claystones claystones are currently being investigated as a potential host rock for radioactive waste disposal the relevant parameters are hydraulic conductivity swelling and shrinkage water uptake rheological and mechanical behavior much attention is paid to the opalinus clay opa in switzerland and the callovo oxfordian clay cox in france one of the scientific challenges is to develop numerical models to predict the mechanical behavior of claystones under repository like conditions recent studies have demonstrated the influence of carbonates on selected mechanical parameters e g failure strength in this study we show that opa and cox behave differently with respect to their failure strength the failure strength of opa decreases with increasing carbonate content whereas it increases with increasing carbonate content in case of the cox the different behavior is caused by microstructural variations results of carbonate microfabric investigations verify that opa mainly contains coarse grained shell fragments while cox shows a more homogeneous distribution of fine grained mainly non biogenic carbonates in conclusion not only the carbonate content but in addition their grain size distribution their shape and the spatial distribution control the mechanical behavior of both clays

fabric induced weakness of tectonic faults 1 mature fault zones appear to be weaker than predicted by both theory and experiment one explanation involves the presence of weak minerals such as talc however talc is only a minor constituent of most fault zones and thus the question arises what proportion of a weak mineral is needed to satisfy weak fault models existing studies of fault gouges indicate that 30 of the weak phase is necessary to weaken faults a proportion not supported by observations here we demonstrate that weakening of fault gouges can be accomplished by as little as 4 wt talc provided the talc forms a critically aligned through going layer observations of foliated fault rocks in mature large offset faults suggest they are produced as a consequence of ongoing fault displacement and thus our observations may provide a common explanation for weakness of mature faults

postseismic pressure solution creep evidence and time dependent change from dynamic indenting experiments active faults in the earth s upper crust can slide either steadily by aseismic creep or abruptly causing earthquakes seismic and aseismic processes are closely related earthquakes are often followed by transient afterslip creep postseismic displacement rates progressively decrease with time over a period of years or decades so seismic fracturing activates the creep rate and various healing processes progressively reduce it this article presents pressure solution indenter experiments on halite calcite and plaster that show how fracturing and comminution processes induced by dynamic stress loading applied by dropping steel balls drastically accelerate the displacement rates accommodated by pressure solution creep by decreasing the dissolution contact area and the diffusive mass transfer distance along this contact however as fractures progressively heal and dissolution contacts flatten these effects disappear and the displacement rates slow down the time dependent change in indenter displacement after dynamic stress loading has been measured and is best fitted by power laws with exponents that change with time from 0 3 to 1 when healing is achieved natural postseismic afterslip displacement time relationships have been analyzed and also show a power law change with a power law exponent in the range of 0 25 0 4 it is proposed that the variation in power law exponent with time is related to the change in morphology of the dissolution contact that is fractured or comminuted during the dynamic event and is then progressively healed and smoothed in natural faults monitoring the power law parameters could give access to the characteristic healing time in the fault

fault mirrors in seismically active fault zones a fossil of small earthquakes at shallow depths fault mirrors fms are naturally polished and glossy fault slip surfaces that can record seismic deformation at shallow depths they are important for investigating the processes controlling dynamic fault slip we characterize fms in borehole samples from the hanging wall damage zone of the active hsiaotungshi reverse fault taiwan here we report the first documented occurrence of the combination of silica gel and melt patches coating fms with the silica gel resembling those observed on experimentally formed fms that were cataclastically generated in addition the melt patches which are unambiguous indicators of coseismic slip suggest that the natural fms were produced at seismic rates presumably resulting from flash heating at asperities on the slip surfaces since flash heating is efficient at small slip we propose that these natural fms represent fossils of small earthquakes formed in either coseismic faulting and folding or aftershock deformation in the active taiwan fold and thrust belt

climatically driven sedimentary cycles in the late miocene sediments of the pannonian basin hungary abstract by detailed cycle analysis of marginal mostly delta plain facies successions of pannonian sediments the frequency of water level changes of the late miocene pannonian lake hungary can be identified cycle analysis is presented with the object of defining the orbital record preserved in the strata we use the bed thickness as input data for our cycle analysis statistical analysis revealed a slow upward increase of both the frequency and thickness of sand beds in the boreholes resulting from infilling of the lake by a basinward migration of the marginal facies cycles of different order were detected in the sediments the higher order cycles are very close to or are equivalent with the milankovitch climatic cycles 19 ka caused by precession 50 ka caused by obliquity and 400 ka is the longer period of eccentricity the longer 1 m y cycle is very poorly developed here it is probably the analogue of the 3rd order global climatic cycle cycle analysis suggests that one of the main controlling factors of the water level changes of the pannonian lake was high frequency climatic oscillations the long term climatic changes only had a faint impact on the sediments the record of the 3rd order water level changes is very subtle our results show that the water level changes followed the rhythm of that of the eustatic changes but being asynchronous to them i e at high sea level stage the pannonian lake level was low and vice versa

a microphysical model for strong velocity weakening in phyllosilicate bearing fault gouges 1 previous rotary shear experiments performed on a halite muscovite fault gouge analogue system have shown that the presence of phyllosilicates under conditions favoring the operation of cataclasis and pressure solution in the matrix phase can have major effects on the frictional behavior of gouges while 100 halite and 100 muscovite samples exhibit rate independent frictional brittle behavior the strength of mixtures containing 10 30 muscovite is both normal stress and sliding velocity dependent at high sliding velocities 1 m s 1 such mixtures show unusually marked velocity weakening along with the development of a structureless cataclastic microstructure in the present paper a micromechanical model is developed in an attempt to explain this behavior the model assumes a granular flow process involving competition between intergranular dilatation and compaction by pressure solution the predictions of the model agree favorably with the experimental results extension of the model to quartz mica systems implies that the presence of phyllosilicates plus the operation of pressure solution can strongly promote unstable velocity weakening behavior at rapid slip rates on natural faults under midcrustal conditions static stress drop predictions based on the model agree reasonably well with estimates from seismic observations our results may help explain the discrepancy between laboratory derived rate and state friction parameter values obtained for dry low strain and or single phase rock systems and the values for natural fault rocks inferred from seismological data