dimensional threshold for fracture linkage and hooking fracture connectivity in rocks depends on spatial properties of the pattern including length abundance and orientation when fractures form a single strike set they hardly cross cut each other and the connectivity is limited linkage probability increases with increasing fracture abundance and length as small fractures connect to each other to form longer ones a process for parallel fracture linkage is the hooking where two converging fracture tips mutually deviate and then converge to connect due to the interaction of their crack tip stresses quantifying the processes and conditions for fracture linkage in single strike fracture sets is crucial to better predicting fluid flow in naturally fractured reservoirs for 1734 fractures in permian shales of the lodeve basin se france we measured geometrical parameters in 2d characterizing three stages of the hooking process underlapping overlapping and linkage we deciphered the threshold values shape ratios and limiting conditions to switch from one stage to another one the hook set up depends on the spacing s and fracture length lh with the relation s 0 15 lh once the hooking is initiated with the fracture deviation length l l 0 4 lh the fractures reaches the linkage stage only when the spacing is reduced to s 0 02 lh and the convergence c is 0 1 l these conditions apply to multi scale fractures with a shape ratio l s 10 and for fracture curvature of 10 20

a weathering intensity index for the australian continent using airborne gamma ray spectrometry and digital terrain analysis abstract weathering intensity largely controls the degree to which primary minerals are altered to secondary components including clay minerals and oxides as weathering intensity increases there are changes in the hydrological geochemical and geophysical characteristics of the regolith thus once calibrated weathering intensity can be used to predict a range of regolith properties a weathering intensity index wii over the australian continent has been developed at a 100 m resolution using regression models based on airborne gamma ray spectrometry imagery and the shuttle radar topography mission srtm elevation data airborne gamma ray spectrometry measures the concentration of three radioelements potassium k thorium th and uranium u at the earth s surface the total gamma ray flux dose is also calculated based on the weighted additions of the three radioelements regolith accounts for over 85 of the australian land area and has a major influence in determining the composition of surface materials and in controlling hydrological and geomorphological processes the weathering intensity prediction is based on the integration of two regression models the first uses relief over landscapes with low gamma ray emissions and the second incorporates radioelement distributions and relief the application of a stepwise forward multiple regression for the second model generated a weathering intensity index equation of wii 6 751 0 851 k 1 319 relief 2 682 th k 2 590 dose the wii has been developed for erosional landscapes but also has the potential to inform on deposition processes and materials the wii correlates well with site based geochemical indices and existing regolith mapping interpretation of the wii from regional to local scales and its application in providing more reliable and spatially explicit information on regolith properties are described

analogue modeling of overlapping spreading centers insights into their propagation and coalescence abstract the propagation and segmentation of mid ocean ridges is studied using centrifuged analogue models built with non linear materials the deformation of the brittle ductile model is controlled by diapiric uprise of buoyant analogous asthenospheric material induced by a centrifugal body force this linear upwelling laterally stretches the model mantle that in turn induces failure in the upper layer simulating the brittle crust arrays of fractures initiate within zones of high stress concentration above the diapir fractures propagate laterally in a direction perpendicular to the maximum tensile the minimum principal stress secondary tension cracks initiate in the vicinity of parent fracture tips through going fractures that crosscut the model surface develop by short fractures propagating toward each other and coalescing in different types of patterns the overlap overstep and inclination of fractures developed at the initial stage of extension control their subsequent growth and coalescence non overlapping sub parallel fractures propagate along nearly straight paths and coalesce to produce a single planar fracture if overlapping fractures are parallel they propagate towards each other along curved paths that enclose an intervening elliptical core of intact material fracture curvature in this case results from crack crack interaction and is similar to that of overlapping spreading centers oscs observed along mid ocean ridges overlapping non parallel fractures tend to coalesce by one of their tips propagating sub parallel to the spreading direction toward the other fracture such offsets can serve as models for the development of the orthogonal ridge transform fault patterns common along mid ocean ridges

evidence for eutrophication in the northwestern pacific and eastern indian oceans during the miocene to pleistocene based on the nannofossil accumulation rate discoaster abundance and coccolith size distribution of reticulofenestra abstract to reconstruct the cenozoic paleoceanographic evolution in particular temporal changes in nutrient levels we studied calcareous nannofossil assemblages from ocean drilling program holes 1210a located in the northwestern pacific ocean and 762b situated in the eastern indian ocean at each site we focused on the relationships among the nannofossil accumulation rate nar relative abundance of discoaster and coccolith size of the genus reticulofenestra the co occurrence of a low nar high discoaster abundance and presence of large reticulofenestra suggest a deep thermocline and nutricline typical of oligotrophic conditions conversely the co occurrence of a high nar low discoaster abundance and presence of small reticulofenestra indicate a shallow thermocline and nutricline typical of eutrophic conditions the combination of these three parameters suggests that the gradual eutrophication and collapse of sea surface stratification occurred in the northwestern pacific ocean at 7 9 6 4 and 5 0 ma in contrast abrupt eutrophication is indicated at 8 8 ma in the eastern indian ocean although the timing of eutrophication differs between the pacific and indian ocean sites it roughly coincides with tectonic and or climatic events around the two oceans this finding suggests that tectonic and climatic events are capable of causing an increase in the terrestrial input and or coastal upwelling of nutrients that subsequently leads to the eutrophication of sea surface waters

scaling and connectivity of joint systems in sandstones from western norway abstract the scaling properties of a joint system in devonian sandstones in western norway have been investigated using seven maps covering areas from 18 to 720 m across which were generated by mapping in the field and from low level aerial photography taken from different heights each map represent a scale window on the fracture population bounded by resolution at small scales and the sample size at large scales a power law relationship between fracture trace length and critical observation height maximum height at which a trace can be identified is derived and used to create a statistical model for the resolution effects the model indicates that a continuous smooth curve without a straight line segment on a log log cumulative frequency distribution plot does not necessarily rule out a power law as the underlying population distribution together the maps indicate a powerlaw trace length distribution with an exponent of 2 1 this power law may be valid over four or more orders of magnitude with natural lower cut off of around 1 m the exponent is significantly different from 2 0 strictly selfsimilar case and is reflected in a decrease in the abundance of fractures with length comparable to map size as map scale decreases the fracture trace length distribution results in a decrease in apparent connectivity with decreasing scale high resolution large scale maps are well connected while the lowest resolution map smallest scale is unconnected fractures in the smallest scale map are however connected by small fractures below the limit of resolution represented by the largest scale map the variation in apparent connectivity with scale has implications for fluid flow when fractures are open to fluid flow the scaling properties of apparent connectivity imply that beyond a certain scale the size of fracture controlling flow will be scale independent in this fracture system this appears to occur in sample areas of around 300 m across

connectivity permeability and channeling in randomly distributed and kinematically defined discrete fracture network models a major use of dfn models for industrial applications is to evaluate permeability and flow structure in hardrock aquifers from geological observations of fracture networks the relationship between the statistical fracture density distributions and permeability has been extensively studied but there has been little interest in the spatial structure of dfn models which is generally assumed to be spatially random i e poisson in this paper we compare the predictions of poisson dfns to new dfn models where fractures result from a growth process defined by simplified kinematic rules for nucleation growth and fracture arrest davy et al 2010 2013 this so called kinematic fracture model is characterized by a large proportion of t intersections and a smaller number of intersections per fracture several kinematic models were tested and compared with poisson dfn models with the same density length and orientation distributions connectivity permeability and flow distribution were calculated for 3d networks with a self similar power law fracture length distribution for the same statistical properties in orientation and density the permeability is systematically and significantly smaller by a factor of 1 5 to 10 for kinematic than for poisson models in both cases the permeability is well described by a linear relationship with the areal density p32 but the threshold of kinematic models is 50 larger than of poisson models flow channeling is also enhanced in kinematic dfn models this analysis demonstrates the importance of choosing an appropriate dfn organization for predicting flow properties from fracture network parameters

sarmatian biostratigraphy of a marginal sea in northern croatia based on calcareous nannofossils abstract calcareous nannofossils of the serravallian tortonian transition known as the sarmatian in the paratethys were obtained from northern croatia central paratethys the nannofossil biostratigraphy of the studied area included early sarmatian biohorizons the reliability of these and previous biohorizons was tested and the known biostratigraphic and magnetostratigraphic datums of the paratethys were compared with those from the adjacent mediterranean and beyond six out of sixteen bioevents were selected to define five subzones pnn6d pnn8b and crossover for the badenian sarmatian boundary variations in the index fossil datums between the paratethys and tethys provide a broad perspective on local versus regional and global impacts on the nannofloras the paratethys tethys gateways ptgs and their progressive geodynamical closure exerted a fundamental control on the salinity circulation patterns and climate of the area the global regression at the end of the badenian and the tectonic events associated with the badenian sarmatian transition also restricted the ptgs initiating acmes of calcidiscus pataecus and reticulofenestra pseudoumbilicus causing a small early sarmatian extinction event that occurred in coastal environments which are the most affected by short term environmental fluctuations stronger connections through the ptgs during the early mid sarmatian transition induced a transgression that brought deep dwelling discoaster species into the area the final closure of the ptg with the mediterranean which had been placed at the badenian sarmatian boundary actually occurred in the late sarmatian as a result of tectonic movements that caused shallowing and a drastic reduction in nannofossil biodiversity the ptg with the indian ocean existed until the early tortonian which allowed an early but brief occurrence of small warm water ceratoliths

palaeomagnetism magnetic fabrics and the structural style of the hornelen old red sandstone western norway the old red sandstone of the hornelen district western norway forms part of a major fold terrane and the principal magnetization is associated with the late devonian to early carboniferous svalbardian solundian orogeny the present fault margins of the hornelen massif claimed by various authors to represent subordinate devonian splay faults associated with megashearing in the north atlantic or lateral ramps in a regional extensional tectonic setting are shown to be post devonian structures and the present outline of the hornelen massif is a mesozoic jurassic graben

formation and interpretation of dilatant echelon cracks the relative displacements of the walls of many veins joints and dikes demonstrate that these structures are dilatant cracks we infer that dilatant cracks propagate in a principal stress plane normal to the maximum tensile or least compressive stress arrays of echelon crack segments appear to emerge from the peripheries of some dilatant cracks breakdown of a parent crack into an echelon array may be initiated by a spatial or temporal rotation of the remote principal stresses about an axis parallel to the crack propagation direction near the parent crack tip a rotation of the local principal stresses is induced in the same sense but not necessarily through the same angle incipient echelon cracks form at the parent crack tip normal to the local maximum tensile stress further longitudinal growth along surfaces that twist about axes parallel to the propagation direction realigns each echelon crack into a remote principal stress plane the walls of these twisted cracks may be idealized as helicoidal surfaces an array of helicoidal cracks sweeps out less surface area than one parent crack twisting through the same angle thus many echelon cracks grow from a single parent because the work done in creating the array as measured by its surface area decreases as the number of cracks increases in cross sections perpendicular to the propagation direction echelon cracks grow laterally each crack overlapping its neighbors until the mechanical interaction of adjacent cracks limits this growth dilation of each crack pinches the tips of adjacent cracks into an asymmetrical form and introduces local stresses that can cause lateral growth along a curving sigmoidal path sigmoidal echelon cracks may link at tip to plane intersections leaving a step in the through going crack wall the geometry of dilatant echelon cracks may be used to infer spatial or temporal changes in the orientation of principal stresses in the earth

geodynamic evolution of the northern dinarides and the southern part of the pannonian basin abstract most of the recent geodynamic interpretations of the pannonian basin focus on its relation to the formation of the carpathians and the alpine orogeny however also the dinarides were severely affected by neogene tectonics related to the formation of the pannonian basin especially in the northernmost dinarides neogene deformation played a very important role in the evolution of this mountain chain geological records clearly show evidence of two phases of plate convergence along the northern and eastern margins of the present day dinarides at the end of the jurassic the dinaridic parts of the tethys ophiolites were obducted onto the northeastern margins of the apulian microplate the second phase is documented in the central part of the northernmost dinarides it is genetically related to an ancient volcanic arc as indicated by late cretaceous palaeogene trench sediments with blueschist olistolithes which are interlayered by basalt rhyolites pyroclastics medium pressure metamorphosed trench sediments and associated synkinematic granitoids in the northern part of the dinarides subduction processes terminated with the eocene compressional event which caused the uplift of the dinarides numerous intramontane basins with shallow marine fluviatile and lacustrine deposits were generated during the oligocene penecontemporaneous andesites which are found along the drava and sava depressions of the south pannonian neogene basin can be correlated with the easternmost periadriatic tonalites however observations do not indicate strike slip faulting at that time in this area the neogene rift stage initiated the evolution of the pannonian basin it is marked by extruded submarine trachyandesites of karpathian age badenian basalts andesites dacites and rhyolites and pannonian alkali basalts which are interlayered by coeval sedimentary rocks main evidence for the large scale tectonic transport of large dinaridic blocks into the pannonian basin area are the periadriatic sava and zagreb zemplen fault systems and subparallel faults the late sarmatian global sea level drop which coincided with a compressional phase is regionally marked by an unconformity throughout the pannonian basin as reported by horvath horvath f 1995 phases of compression during the evolution of the pannonian basin and its bearing on hydrocarbon exploration mar pet geol 12 8 837 844 due to thermal subsidence during the pliocene more than 2000 m of lacustrine freshwater sediments were deposited in the south pannonian basin the pliocene compression phase can be observed in the transdanubian zone and also south of the mura and drava rivers by south and southwest dipping reverse fault systems

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

improved statistical multi scale analysis of fractured reservoir analogues abstract this paper includes the results of the application of novel methodologies for the statistical analysis of tensile fracture attributes spacing density and aperture the statistical methods have been applied to a fractured lower cretaceous carbonate succession cropping out in the sorrento peninsula naples area italy representing a geological analogue of buried reservoirs of southern apennines major oil fields as fracture networks observable from outcrop to the crystal scale can significantly affect the hydraulic behavior of a fractured reservoir the definition of appropriate models of fracture spacing and aperture probability distribution at various scales represents an important goal of structural analysis in order to achieve such an objective sampling has been carried out at different scales by means of traditional scan lines at outcrop as well as micro scan lines carried out both by a digital micro camera 50 and by the optical microscope 200 fracture spacing and density analysis are mainly aimed at establishing the characteristics of joint spatial distribution over a range of scales aperture analysis is aimed at verifying that the aperture cumulative frequency is described by a power law and in the latter instance to provide an effective method for a more precise determination of the exponent of the power law finally new expressions are provided in closed form in order to calculate the confidence interval of the power law exponent the proposed criteria provide handy and effective methods for a significantly improved statistical analysis of fracture attributes

estimating average fracture spacing in subsurface rock knowledge of the spacing of fractures in reservoir rocks i e the distance between parallel fractures in a subsurface joint set can lead to a better understanding of the production characteristics of a reservoir and serve to quantify the relative degree of deformation in subsurface rocks in this paper i present a new method for estimating the spacing of subsurface fractures this new method is easy to use from the standpoint of both data collection and data analysis the average fracture spacing method can be applied with boreholes of any orientation relative to a fracture set the method is especially powerful when it is used for the relatively common case of a borehole nearly parallel to a fracture set e g vertical borehole intersecting vertical fractures average fracture spacing is estimated from an analytical solution based on observed borehole fracture intersections and observed fracture porosity the only data required are the dimensions of the core or imaged borehole and the total height of all sampled fractures because the likelihood of intersecting fractures increases when a well is deviated perpendicular to the fractures of a set fracture reservoirs commonly are candidates for deviated boreholes an informed decision on borehole deviation requires predicting the fracture intersection frequency as a function of both deviation magnitude and direction a new method based on probabilities of borehole fracture intersections uses spacing and height data from subsurface joint like fractures and the borehole diameter to predict fracture intersection frequencies for all possible well deviations fracture intersection frequency solutions are presented with respect to a conventional geographic reference frame thus simplifying even the most complex three dimentional situations

the evolution of the hornelen basin detachment system western norway implications for the style of late orogenic extension in the southern scandinavian caledonides abstract the geology of the devonian hornelen basin and the surrounding western gneiss region wgr western norway has been examined in detail structural clast provenance and geothermobarometric data have been combined to reconstruct the motion history of part of a major late orogenic extensional shear zone in the southern scandinavian caledonides the nordfjord sogn detachment nsd the nsd in the hornelen basin area is a zone of mylonites 4 6 km thick tectonostratigraphically constrained within the lower and middle allochthons lma and the uppermost part of the wgr it separates eclogite bearing gneisses of the wgr from greenschist and amphibolite facies rocks of the middle and upper allochthons marking a profound metamorphic break and indicating major excision of crustal section kinematic indicators give a consistent top to the west shear sense indicating a reversal of the movement sense of the scandian nappes with the ductile strain being distributed through the entire lma section the wgr was exhumed from depths of up to 100 km in the footwall of the shear zone partly aided by pure shear vertical flattening below the nsd and extension and erosion of the hanging wall the majority of the movements on the nsd in the hornelen basin area occurred under amphibolite facies conditions prior to 410 ma subsequent shear caused limited greenschist retrogression along extensional crenulation cleavages depending on interpretation of mica 40 ar 39 ar ages this lower grade shearing may be due to a continuation of movements or renewal of motion associated with opening of the hornelen basin at about 385 ma the lack of clear evidence of penetrative greenschist facies mylonites in the hornelen area may be due to the faulted omission of tectonites of this grade following scandian a subduction and eclogite facies metamorphism at 425 ma the p t t path of the wgr shows very rapid decompression associated with early slip on the extensional detachment horizons unroofing was initially near isothermal followed by a phase of rapid near isobaric cooling after 410 ma decompression and cooling slowed as slip on the nsd slowed or even ceased by the middle devonian the wgr lay at about 10 15 km depth and the crust had almost returned to isostatic equilibrium at this time a brittle fault splaying from the nsd ramped upwards through the upper allochthon opening a scoop shaped west facing half graben the hornelen basin a further 50 km of heave on the nsd occurred during alluvial infilling of the basin subsequently the basin fill was folded by late devonian n s compression and the basin margins were modified by mesozoic faulting these features are consistent with an orogenic collapse model for southern scandinavia that involves large scale backsliding of the scandinavian caledonides within tectonostratigraphic units by this mechanism the baltic shield could have been efficiently unloaded with tectonic translations producing significant metamorphic breaks within a seemingly preserved tectonostratigraphic sequence the model favours orogenic collapse driven by an external pull rather than internal body forces

a statistical scaling model for fracture network geometry with validation on a multiscale mapping of a joint network hornelen basin norway 1 fracture patterns are characterized by a complex geometry which involves a large length distribution and nonhomogeneous density distributions here we address the issue of the modeling of this complex geometry over scales through a first order model providing the characterization of the number of fractures of a given length and at a given scale we propose that the simplest model is a power law in both space and fracture length with three main parameters the exponent a of a power law length distribution the fractal dimension d which fixes the scale dependence of the number of fractures and the fracture density we verify the applicability of this model on seven fracture patterns mapped from the metric scale up to almost the kilometric scale in the hornelen basin the model efficiently describes fracture network properties at all scales with a single set of parameters for the hornelen fracture networks we found a simple relationship between basic exponents a d 1 implying that the fracture network is self similar through this analysis we present different methodological developments for deriving the basic exponents a and d and for verifying the consistency of the model overall the main methodological development is about the normalization of the measurements made from different scales of observation finally we discuss both the limitations and the uses of such a model for analyzing the hydraulic and mechanical properties of fracture networks

hybrid veins from the southern margin of the bristol channel basin uk sinistral and dextral en echelon hybrid calcite veins are exposed on the southern margin of the bristol channel basin north somerset on a liassic carbonate platform these hybrid veins are transitional between pure extensional mode i and shear fractures mode ii mode iii and experienced both extensional and shear displacements during their formation in the study area they occur in conjugate sets with the conjugate angle ranging between 10 and 50 based on the kinematic analysis of these veins a new model for the opening of the bristol channel is proposed

sarmatian calcareous nannofossil assemblages in the sw paratethyan marginal marine environments implications for palaeoceanography and the palaeoclimate abstract the middle miocene marly sediments in the southwestern paratethys central europe have been studied for calcareous nannofossil assemblages palaeoecological and palaeogeographic parameters based on siliceous microfossils diatom and silicoflagellate are emended into the palaeoecological preferences of coccoliths as are data from their modern analogies giving more precise results this study deals with complex shallow and deep water marine systems and the regional and global events that influenced the changes of the marginal part of study area and its species diversity the link between the middle miocene tectonic events and paratethyan gateways resulted in a changing of environments and marine circulations and their concomitant effects on the paleoclimate these impacts induced the earlier appearance of specific and endemic species calcidiscus pataecus noelaerhabdus bozinovicae isolithus semenenko amaurolithus group and a reduced diversity in the highly fluctuating marine environments for the first time the termination of the earth s most recent major warm episode the mid miocene climate optimum is observed in the early to mid sarmatian transition in the north croatian and vienna basins via observations of the changing of the local climate and circulation upwelling systems based on the palaeoecological data of the r selected strategies that dominate the assemblages it was possible to reconstruct the short term small scale variations of the temperature salinity primary productivity nutrient supply freshwater influx and relative sea level changes in the highly dynamic nearshore setting the similarities and differences between the paratethyan basins together with their palaeoecological interpretations contribute to the broader picture of paratethyan evolution climate change and its connectivity with other marine areas

late miocene to early pliocene sedimentary environments and climatic changes in the alpine carpathian pannonian junction area a case study from the danube basin northern margin slovakia abstract the danube basin situated at the alpine carpathian pannonian junction represents a region of the central paratethys strongly influenced by orogen building processes and climatic changes the geodynamic development mirrors gentle docking of the carpathians into the european platform margin associated with synrift and later postrift subsidence of the back arc area onset of the basin inversion characterized the pliocene evolution the aquatic environments gradually changed from marine brackish to caspibrackish and to freshwater within the lake pannon due to isolation followed by development of ephemeral lakes and alluvial plains the terrestrial record documents the extinction of the middle miocene fauna and the retreat of vegetation with subtropical floral elements at the beginning of the late miocene due to changes in paleogeography and climate between 11 5 and 7 1 ma the immigration of a new hipparion fauna as well as the replacement of swamp vegetation by coniferous forest of the temperate zone can be interpreted as the first appearance of seasonality with lowered humidity at the pannonian pontian boundary the late pontian to early pliocene fauna and flora as well as sedimentary environments support the increase of humidity in warm temperate climate between 7 1 and 5 4 ma

interaction and linkage of extension fractures and normal faults examples from the rift zone of iceland abstract field and photogeological studies were made of 90 zones of interacting fracture segments along the rift zone of iceland each zone consists of a pair of extension fractures or a pair of normal faults with lengths from metres to kilometres these zones evolve from an underlapping stage through an overlapping stage the most common configuration and finally to a linkage stage of all the zones only 7 are underlapping whereas 93 are overlapping with hook shaped fracture pairs the length width ratios of the overlapping zones have a mean value of 3 5 the preferred geometry of the overlapping zones depends upon the initial configuration of the interacting fractures length overstep and the development of the interaction in the overlapping zones most fracture pairs show moderate shear strike slip components related to local variations in the extension opening directions vertical displacements on normal faults decrease as the overstep and length of overlapping zones increase both in turn are proportional to the total lengths of the faults forming the pair the geometrical and kinematic features of overlapping spreading centres at mid ocean ridges show close similarities to those reported here these similarities indicate that the architecture and evolution of overlapping zones are scale independent

fluctuations in the composition of late miocene calcareous nannofossil assemblages as a response to orbital forcing fluctuations in abundance between the two calcareous nannofossil species coccolithus pelagicus and reticulofenestra pseudoumbilica are observed in the upper miocene sediments recovered from deep sea drilling project hole 552a a record of these fluctuations cp rp is established for a time interval of similar to 1 35 m y from 4 9 to 6 25 ma and is shown to yield periodicities which correspond to milankovitch periodicities a change in regime occurred at 5 72 ma as indicated by a shift from a series dominated by the 20 kyr cycle to a series dominated by the 100 kyr cycle the cp rp is compared with the isotopic delta o 18 and delta c 13 records from benthic and planktonic foraminifera it is shown that a good correlation between the cp rp and the isotopic records occurs only at times of major global changes this suggests that the cp rp which reflects water masses movements yields a complex paleoclimatic paleoceanographic message which can help improving our understanding of the late miocene history

scaling of fault displacements from the badajoz cordoba shear zone sw spain faulting occurs over a large range of scale parts of which are sampled by various techniques e g microscopy outcrop measurement mapping seismic reflection and other forms of remote sensing use of a single technique to measure displacement or strain will not sample faults at all scales and hence will give a biased estimate in order to assess this bias a knowledge of the distribution over all scales is needed many samples of fault displacement appear to follow a power law distribution with departures which can be attributed to sampling effects the number of faults with a displacement u is given by n u cu d the power law distribution of displacement is consistent with similar distributions of other fault parameters and earthquake magnitudes when sampling along a line e g a bedding trace on a map or section a self similar fault population would have d 1 whereas self affine geometries yield d 1 displacement and extension are dominated by small faults when d 1 and by large faults when d 1 when sampling over areas or volumes these critical values are 2 and 3 respectively a set of strike slip faults from the badajoz cordoba shear zone spain were sampled at two different scales using 1 50000 maps and outcrop measurements displacement ranges over 6 orders of magnitude these and other fault populations typically have d ranging from 0 6 to 1 5 the power law relationship may be integrated to yield estimates of the displacement or extension for faults which lie beyond the resolution of the sampling system for example a knowledge of d allows the extension measured on a map or seismic section to be corrected for faults whose displacement is below the resolution of the survey based on an overall estimate of d 0 9 for the badajoz cordoba data only some 40 of the extension would be recorded by map scale faults a corrected extension of 41 along the shear zone is estimated which if typical for the entire 300 km zone represents some 87 km of along strike extension thus work suggests that significant displacement occurs on faults which are too small to be interpreted from conventional seismic profiles and geological maps

the geometry of listric growth faults in the devonian basins of sunnfjord w norway thick devonian clastic sequences accumulated in fault bounded basins in w norway at the close of the caledonian orogeny and mark the beginning of a phase of crustal extension traditionally the eastern boundary fault to the devonian basins has been regarded as a thrust but cross sections based on the use of a branch line reveal it to be an extension fault there is clear omission of structural section across the boundary and by matching up metamorphic rocks in the hanging and foot walls of the boundary fault over 40 km of extensional dip slip can be measured at the n end of the fault the boundary fault is a flat lying listric fault with rollover anticlines in the hanging wall the fault also cuts up and down section along strike to form lateral ramps parallel to the movement direction these ramps appear as wrench faults in outcrop the ramp flat geometry of the fault may have been inherited from a precursor caledonian thrust fault which reversed its sense of slip in early middle devonian times to form the basins over 25 km of onlapping sediment accumulated in the largest basin during faulting in 14 ma with an average slip rate on the fault of 3 mm yr 1

paleogeographic evolution of the late miocene lake pannon in central europe abstract the paleogeographic evolution of lake pannon within the pannonian basin is reconstructed with eight maps ranging from the middle miocene to the early pliocene the maps are based on the distribution of selected biozones and specific fossils and on complementary sedimentological and seismic information our reconstruction shows that the history of lake pannon can be divided into three distinct intervals an initial stage with low water level which resulted in isolation from the sea at about 12 ma and might have led to temporary fragmentation of the lake an interval of gradual transgression lasting until ca 9 5 ma and a long late interval of shrinkage and infilling of sediments that persisted into the early pliocene the deep subbasins of the lake formed during the transgressive interval in more basinward locations than the deep basins of the preceding sarmatian age the southern shoreline running parallel with the sava and danube rivers along the northern foot of the dinarides changed very little during the lifetime of the lake while the northern shoreline underwent profound changes

meso to microscale fracture porosity in tight limestones results of an integrated field and laboratory study abstract the complex fluid saturation distribution and influence of microscale and mesoscale fractures on the fluid accumulation and flow properties of carbonates are still interesting challenges for petroleum geologists for this reason in order to know the relative role played by the aforementioned features on the storage and migration properties of tight limestones the present work focuses on a surface analogue cropping out in southern italy by first applying a deterministic discrete fracture network dfn modelling to a 1 m3 geocellular volume an amount of 0 3 of fracture porosity and a fracture connectivity configuration above the percolation threshold are computed in addition to mesoscale fracture porosity in order to gather information on matrix porosity and microscale fractures we investigate the pore type geometry and textural anisotropy of selected rock plugs by mean of integrated petrophysical ultrasonic and optical microscopy analyses experiments results show values of connected porosity ranging between 1 and 6 presence of vugs localized along pre existing structural heterogeneities and the predominance of stiff pores within the carbonate matrix the rare microfractures are mainly oriented orthogonal to bedding the estimated crack density 0 19 shows that the contribution of fracture porosity at microscale 0 078 is very low if compared to that of matrix porosity and also a structural configuration above the percolation the present study therefore documents that the carbonate matrix forms an isotropic medium which profoundly affects the storage capability of the study limestones in fact the amount of storage provided by carbonate matrix and microscale fractures is greater than that due to mesoscale fractures moreover we document that the matrix contribution on porosity is much more significant than the contribution provided by microfractures finally the present work shows the importance of integrating different methodologies on the assessment of fracture porosity at different scales of observation in fact a great benefit for development and production operations can be obtained by performing studies of surface analogs which allow the detailed investigation of rock masses below seismic resolution

the age of the sarmatian pannonian transition in the transylvanian basin central paratethys abstract a marked paleoenvironmental change took place at the beginning of the late miocene in the central paratethys with dominantly marine sarmatian successions grading rapidly into mainly brackish pannonian deposits a long and excellently exposed section comprising the sarmatian pannonian transition has been investigated at oarba de mures in the transylvanian basin romania in this paper we focus on both radiometric and magnetostratigraphic dating to provide a chronology for the sarmatian pannonian transition in transylvania two volcaniclastic layers located approximately 40 m below the sarmatian pannonian transition yield excellent 40ar 39ar ages the weighted mean plateau age for biotite and sanidine separates provided isotopic ages of 11 62 0 12 ma and 11 65 0 13 ma this implies deposition during the magnetic chron c5r 2r which is in agreement with the magnetostratigraphic results of the oarba de mures composite section rock magnetic analyses indicate greigite as the main magnetic carrier with characteristics very similar to the magnetosomal greigite found in the carpathian foredeep the newly obtained chronology at oarba de mures constrains the age of the sarmatian pannonian transition in the transylvanian basin to 11 3 0 1 ma slightly younger than the 11 61 ma postulated in the styrian and vienna basins

evolutionary trends of tropical calcareous nannofossils in the late neogene abstract examination of middle late miocene sediments recovered during odp leg 154 in western equatorial atlantic has led to identification of evolutionary transitions in some groups of late neogene calcareous nannofossils through analyses of high resolution samples 10 cm sample interval equivalent to average interval of 6 kyr we were able to document the origin of the genera catinaster amaurolithus and ceratolithus and the nannofossil species discoaster berggrenii and d quinqueramus the presence of intermediate morphotypes between end members representing distinct species sheds new light on phylogenetic relationships and or confirms relationships suggested in previous studies the mode and timing of the evolutionary transitions described are discussed successive branching from triquetrorhabdulus rugosus is demonstrated for amaurolithus primus amaurolithus amplificus and ceratolithus acutus a new genus is therefore established nicklithus type species nicklithus amplificus n comb a new species is described ceratolithus larrymayeri n sp the genera triquetrorhabdulus amaurolithus nicklithus and ceratolithus all belong to the family ceratolithaceae

can γ radiometrics predict soil textural data and stoniness in different parent materials a comparison of two machine learning methods abstract the use of radiometrics for soil proximal sensing is strongly site specific because of the influence of parent material mineralogy on the rays emitted from the soil the work wants to propose a non linear and multivariate computational approach to predict soil textural data and surficial stoniness based on spectroscopy the spectroscopy survey was performed in heterogeneous soils in terms of parent material pedogenesis morphology coarse material and moisture content the radiometrics survey was performed by the mole sensor the netherlands and ray spectra were analysed by a full spectrum analysis 70 experimental points were described and classified according to parent material and surficial stoniness the 70 experimental sites were also sampled during the ray survey and analysed for soil texture and moisture content an explorative pca in the experimental points based on the ray data and the elevation showed 3 groups of cases relating to the three groups of bedrock i calcareous flysch ii feldspathic sandstone and iii other lithologies namely marly shales marine and fluvio lacustrine deposits two machine learning models were used to predict sand clay and surficial stoniness the models were support vector machines svm and artificial neural networks ann an independent validation set of 20 soil samples was used to check the accuracy of the prediction models both svm and ann showed good prediction accuracy for sand and clay although svm showed the lowest errors both models showed lower accuracy for stoniness prediction mainly due to high prediction errors in several sampling points probably the high errors in stoniness prediction were due the strong heterogeneity of rock types and mineralogy however prediction model of stoniness spatial variability is very important in order to an adequate farming management

sedimentology and stratigraphy of the neogene rift type north croatian basin pannonian basin system croatia a review abstract development of the rift type north croatian basin located in the south western neogene pannonian basin system and belonging to the central paratethys realm was controlled by tectonics climate volcanic activity and eustatic fluctuations the extrabasinal controls produced a succession of depositional environments from terrestrial to marine and back to terrestrial and the deposits form a large scale transgressive regressive cycle basin evolution is subdivided into the syn rift phase which lasted from the early miocene ottnangian until the middle miocene middle badenian and in the post rift phase from the middle miocene late badenian to the quaternary these complex controls on deposition generated the opening and closing of connections to the open sea that occasionally resulted in the formation of unfossiliferous continental deposits or generated the radiation of endemic species such that it has been necessary to use regional neogene stages for stratigraphic analysis of the central paratethys history earlier stratigraphic studies of the north croatian basin that had been primarily based on biostratigraphy and superposition were improved by recent results yielded from radiometric dating and integrated biostratigraphy they have been focused mainly on the early middle miocene and the miocene pliocene boundaries that separate intervals of the specific depositional evolution of the basin most important depositional and palaeogeographic differences concern a relatively long period of development of the early continental phase that lasted from the ottnangian to the early badenian in contrast to parts of the pannonian basin system characterized by marine deposition in the early badenian the ncb was characterized by long lived fresh water lacustrine deposition the fresh water lake slavonia that developed from the middle pliocene to the early pleistocene indicates an independent phase of evolution of the south pannonian basin system so the cernikian regional stage was introduced for the lacustrine succession those stratigraphic and palaeogeographic differences additionally support the complexity of the pannonian basin system within the central paratethys realm supporting heterogeneous depositional development of continental rift type basins

a calibrated mammal scale for the neogene of western europe state of the art abstract a magnetobiostratigraphically calibrated mammal scale for the neogene of western europe is presented in this paper the mammal neogene mn units originally proposed by mein report on activity rcmns working groups 1975 have been re defined here on the basis of first appearances of selected small and large mammal taxa the chronology of the lower boundaries of each unit had been established mostly after the significant magnetobiostratigraphic framework developed in the last decade in a number of spanish basins ebro calatayud daroca valles penedes teruel fortuna cabriel and guadix baza in the case of the early and middle miocene particularly mn 1 mn 2 and mn 3 the authors have also taken into account the magnetobiostratigraphic framework developed in the north alpine foreland basin some alternative correlations of the magnetostratigraphic data from this last basin are proposed in order to achieve a higher degree of consistence with the data from the iberian basins a quite well established magnetostratigraphic calibration of the mn boundaries can be proposed for most of the neogene from middle miocene to late pliocene on the other hand the chronological boundaries of the early miocene mn units are still poorly constrained due to 1 scarcity of well studied continuous thick magnetostratigraphic sections 2 the difficulty in defining the boundaries of the mn zones for this time span due to the relative homogeneity and persistence of the fossil rodent faunas and the absence of significant large mammal dispersal events some of the troubles which arise with the application of the mn units strengthen the need to take into account the palaeobiogeographical meaning of these units and their real suitability to date and correlate through extensive geographic areas

orthogonal cross joints do they imply a regional stress rotation abstract orthogonal cross joints extend across intervals between systematic joints in brittle sedimentary strata and abut the systematic joints at about 90 angles these joints typically form a ladder like pattern if viewed on a bedding surface a common interpretation is that orthogonal cross joints define the orientation of the regional stress field during their formation least compressive stress perpendicular to the joints it follows that they indicate a rotation of regional principal stresses by 90 after the formation of the systematic joints using a three dimensional boundary element code poly3d we considered a simple geologic case of vertical systematic fractures developing in horizontal strata under a triaxial remote load with the maximum principal tensile stress being horizontal and perpendicular to the strike of the fractures the intermediate principal stress being horizontal and parallel to the strike of the fractures and the least principal tensile stress i e maximum compressive stress being vertical the results show that the local maximum principal stress is first perpendicular and then parallel to the strike of the systematic fractures as the ratio of fracture spacing to height changes from greater than to less than a critical value when the horizontal remote principal stress ratio the ratio of the intermediate remote principal stress to the maximum remote principal stress under the sign convention of positive for tensile stresses is greater than a threshold value 0 2 thus the fracturing process changes from infilling of systematic fractures to the formation of orthogonal cross fractures this provides an alternative mechanism for the formation of orthogonal cross joints that does not require a systematic rotation of the regional stress field by 90 the critical spacing to height ratio for the local principal stress switch is independent of the least remote principal stress i e overburden it increases nonlinearly with increasing ratio of the horizontal remote principal stresses and decreases nonlinearly with increasing poisson s ratio of the material

a revised stratigraphic framework for later cenozoic sequences in the northeastern mediterranean region this study describes the lithostratigraphic character of mid cenozoic oligocene pliocene sequences in different parts of the northeastern mediterranean area and offers a detailed stratigraphic correlation for this region the sequences concerned are drawn from the camardi area south central anatolia the adana basin the misis mountains and the kyrenia range northern cyprus and the submerged florence rise west of cyprus the stratigraphic relationships identified here indicate the following a following the middle eocene lutetian regression there was uplift throughout the entire region b episodes of fluvial and lacustrine deposition in intramontane settings ensued in most of this region during the late eocene early miocene interval c following a regionally extensive phase of tectonic compression major marine transgression commenced in the late oligocene in northern cyprus and in the early miocene in adjacent southern turkey with the exception of the ecemi fault zone where continental deposition continued d these oligo miocene transgressive sequences comprise a broadly diachronous complex of both shallow and deeper marine facies including reefal carbonates littoral clastics basinal shales and fan turbidites e deeper marine miocene facies persisted longer in the misis area and in northern cyprus f a regional regression occurred throughout most of the area during the late serravallian to tortonian interval and is marked by the abrupt locally discordant appearance of extensive shallow marine deltaic and fluvial deposits g continued regression in the messinian led to the formation of significant evaporite deposits in the western and southern parts of the region but localized uplift of the misis area is attested by the initial deformation of the neogene rocks there and the absence of messinian sediments from this area h in the pliocene there was extensive emergence of the northern parts of the region interrupted by brief marine incursions the present day drainage pattern was established at this time i marine conditions persisted longer in northern cyprus where emergence occurred only in the latest pliocene

multi scale fracture network analysis from an outcrop analogue a case study from the cambro ordovician clastic succession in petra jordan abstract a regional multi scale fracture network is prominently exposed in the cambro ordovician sedimentary succession in south western jordan this succession consists of marine deposits overlain by heterogeneous deltaic sediments culminating in 500 m of massive to cross bedded fluvial sandstones a data set acquired from high resolution satellite imagery and field measurements enables the quantification of the geometry and spatial characteristics of the fracture network in three dimensions five directional fracture sets are identified from the satellite data with mean strikes of 000 040 065 120 and 145 large fracture zones longer than 600 m composed of tightly spaced joints confined in fracture swarms exhibit a log normal trace length distribution and the fracture swarms are regularly spaced the trace length distribution of intermediate fractures 40 600 m long exhibits power law characteristics and the fractures are clustered reflecting different fracture system styles and stratigraphic controls as a function of scale the small scale fracture network is strongly dependent on the distribution of bedding plane discontinuities throughout different parts of the succession the multi scale fracture network is categorized in a three tier hierarchical fracture model that reflects underlying stratigraphic controls in the study area this type of model can be used to improve the representation of fracture networks in fluid flow simulations of fractured reservoirs with hybrid models that combine elements of discrete fracture networks and continuum models

magnetostratigraphy of the vallesian late miocene in the valles penedes basin northeast spain the magnetostratigraphic analysis of the late miocene continental deposits from the valles penedes basin combined with its well documented fossil mammal record has provided a well resolved chronology for the upper basin infill the study is based on the biostratigraphic and magnetostratigraphic cross correlation of 12 sections throughout the alluvial sequences in the western valles area the biostratigraphic framework consists of 21 mammal localities corresponding to the mammal neogene mn9 and mn10 units the composite magnetic polarity sequence is based on 400 paleomagnetic sites correlation with the geomagnetic polarity time scale gpts has led to an absolute dating of the faunal events and a precise chronostratigraphy of the vallesian mammal stage in its type area the hipparion first appearance datum fad at the mn8mn9 boundary is dated at 11 1 ma in the valles penedes basin this age compared to other radiometrically dated localities in europe north africa and turkey is consistent with an isochronous dispersal of this equid through the mediterranean region a possible isochrony at a larger geographical scale old world mesogea must await more reliable ages of the hipparion fad in asia and africa the cricetulodon fad mn9amn9b boundary is dated to 10 4 ma in chron c5n the progonomys fad mn9mn10 boundary corresponding to the intra vallesian faunal crisis is dated at 9 7 ma c4ar 3r the vallesian spans 2 4 myr from 11 1 ma c5r 1n to 8 7 ma c4an and correlates to the early tortonian

propagation and linkage of oceanic ridge segments we have investigated the propagation of spreading ridges and the development of structures that link ridge segments using an analogy between ridges and cracks in elastic plates the ridge propagation force and a path factor that controls propagation direction were calculated for echelon ridge segments propagating toward each other the ridge propagation force increases as ridge ends approach but then declines sharply as the ends pass so ridge segments may overlap somewhat the sign of the path factor changes as ridge ends approach and pass so the overlapping ridge ends may diverge and then converge following a hook shaped path the magnitudes of shear stresses in the plane of the plate and orientations of maximum shear planes between adjacent ridge segments were calculated to study transform faulting for different loading conditions simulating ridge push plate pull and ridge suction we identify a zone of intense mechanical interaction between adjacent ridge ends in which stresses are concentrated for all conditions the shear stress in the interaction zone increases as ends approach and remains large as the ends overlap thus crust in this zone may fracture and weaken in preparation for the formation of a through going transform fault the calculated shear planes rotate toward an orientation about 90 from the strike of ridges as the ends pass thus favoring the orthogonal arrangement of ridges and transforms the magnitudes of mean stresses in the plane of the plate and orientations of principal stress planes were also calculated the mean stress is tensile in the interaction zone so basins may form there except in the case of ridge push loading the planes across which the maximum tension acts are oblique to ridges thus favoring obliquely oriented normal faults bounding the transform valley

two dimensional simulation of controls of fracture parameters on fracture connectivity two dimensional fracture simulation is conducted to analyze the controls of different fracture parameters variations in fracture orientation density and length on fracture network connectivity three different scenarios which are commonly encountered in natural fracture systems are analyzed 1 a single fracture set 2 two fracture sets with one primary through going set and 3 two fracture sets with approximately equal parameters the modeling reveals that certain parameters are more dominant in controlling the connectivity for each of the settings for a single set of fractures increases in length and dispersion and a decrease in spacing all result in higher fracture parallel connectivity but the decrease in spacing is the most important in increasing fracture normal connectivity especially where the dispersion in fracture strike is very low simulations of two sets of fractures reveal that the density length and angle between the two sets are important factors in producing complete connectivity in cases where one set of fractures is a systematic throughgoing set a critical combination of length of the second set and the angle between the two sets results in complete connectivity where both sets of fractures have varying length and density the influence of increasing density of one set has a great effect on connectivity when the other set is short and a more subtle to insignificant change when the other set is long the network also shows higher connectivity with increasing angles up to 90 between the two sets

digital soil pattern recognition in the lower namoi valley using numerical clustering of gamma ray spectrometry data abstract digital soil mapping involves the use of ancillary data e g proximal and remotely sensed as surrogates for soil information to produce maps of soil type or classes two of the most popularly used sources of ancillary data are the proximally sensing electromagnetic em induction instruments and remotely sensed digital elevation model data dem however these data have limitations at the catchment level and are of limited use on predominantly flat alluvial landscapes respectively another option is the use of remotely sensed gamma ray ray spectrometry data which has successfully been used to map the regolith in this paper the use of ray spectrometry data i e potassium k uranium u thorium th and total count tc coupled with a numerical clustering algorithm i e fuzzy k means fkm algorithm is explored in order to identify geological and geomorphological units at the district and soil mapping units at a broader catchment level we do this by using the euclidean distance and the measures of fuzziness performance index fpi and normalized classification entropy nce to identify k 11 classes and a fuzziness exponent 2 0 for interpretation the k 11 classes produce contiguous classes which are consistent with geological and geomorphological interpretations of an eroded landscape alluvial lands and dust mantled alluvial lands at the district level at the sub catchment level the k 11 classes also match broad soil mapping units and also elucidate subtle differences of the alluvial lands which characterise the agriculturally significant parts of the lower namoi valley fuzzy canonical analysis shows that k and tc contribute most to the discrimination of the classes associated with the trachyte rich parts of the eroded landscape the alluvial lands and most of the dust mantled alluvial lands whilst u and th discriminate the basaltic outliers and other geomorphological units of the eroded lands we conclude that the approach allows soil management and landscape units to be identified with the information used as a first approximation to determine where soil sample locations need to be collected to validate the map units identified in order to better incorporate and characterise subsoil properties the inclusion of em signal data e g em38 or dualem 1 may also be appropriate

coalescence of fractures under shear stresses in experiments a series of uniaxial compression tests were performed on gypsum specimens with preexisting fractures to study the failure mechanism of fractures and rock bridges in fractured rock masses the coalescence mechanism of two parallel and offset fractures was investigated by monitoring the process of fracture initiation and propagation with a video camera the tests showed that two inclined parallel fractures can coalesce by shear failure and or tensile failure under a uniaxial load the coalescence path and mechanism mainly depend on the relative position of the two fractures for instance when the two fractures are coplanar or slightly offset coalescence is generated by shear failure when they are overlapping in the loading direction coalescence is generated by mixed shear and tensile failure two types of preexisting fractures one without initial surface contact and hence frictionless and another with surface contact and friction were used to study the influence of fracture contact conditions on the coalescence path and load it was found that coalescence of fractures with surface contact and friction requires loads as much as 35 higher than that for coalescence of fractures without contact and friction a stress analysis was conducted in this study to explain the different coalescence mechanisms the analytical work indicated that different fracture geometries produce significantly different stress fields in the rock bridge area and hence result in different failure modes

plate tectonic evolution of the southern margin of eurasia in the mesozoic and cenozoic abstract thirteen time interval maps were constructed which depict the triassic to neogene plate tectonic configuration paleogeography and general lithofacies of the southern margin of eurasia the aim of this paper is to provide an outline of the geodynamic evolution and position of the major tectonic elements of the area within a global framework the hercynian orogeny was completed by the collision of gondwana and laurussia whereas the tethys ocean formed the embayment between the eurasian and gondwanian branches of pangea during late triassic early jurassic times several microplates were sutured to the eurasian margin closing the paleotethys ocean a jurassic cretaceous north dipping subduction boundary was developed along this new continental margin south of the pontides transcaucasus and iranian plates the subduction zone trench pulling effect caused rifting creating the back arc basin of the greater caucasus proto south caspian sea which achieved its maximum width during the late cretaceous in the western tethys separation of eurasia from gondwana resulted in the formation of the ligurian penninic pieniny magura ocean alpine tethys as an extension of middle atlantic system and a part of the pangean breakup tectonic system during late jurassic early cretaceous times the outer carpathian rift developed the opening of the western black sea occurred by rifting and drifting of the western central pontides away from the moesian and scythian platforms of eurasia during the early cretaceous cenomanian the latest cretaceous paleogene was the time of the closure of the ligurian pieniny ocean adria alcapa terranes continued their northward movement during eocene early miocene times their oblique collision with the north european plate led to the development of the accretionary wedge of the outer carpathians and its foreland basin the formation of the west carpathian thrusts was completed by the miocene the thrust front was still propagating eastwards in the eastern carpathians during the late cretaceous the lesser caucasus sanandaj sirjan and makran plates were sutured to the iranian afghanistan plates in the caucasus caspian sea area a north dipping subduction zone jumped during paleogene to the scythian turan platform the shatski terrane moved northward closing the greater caucasus basin and opening the eastern black sea the south caspian underwent reorganization during oligocene neogene times the southwestern part of the south caspian basin was reopened while the northwestern part was gradually reduced in size the collision of india and the lut plate with eurasia caused the deformation of central asia and created a system of nw se wrench faults the remnants of jurassic cretaceous back arc systems oceanic and attenuated crust as well as tertiary oceanic and attenuated crust were locked between adjacent continental plates and orogenic systems

calcareous nannofossils in extreme environments the messinian salinity crisis polemi basin cyprus the rapidly changing and extreme environmental conditions of the early messinian salinity crisis are reflected in abrupt variations in nannofossil assemblages within the messinian units kalavasos formation from the polemi basin during the messinian sedimentary and microfossil data indicate that the polemi basin was a semi enclosed shallow water basin subject to repeated influxes of marine and freshwater this is supported by the absence of many open marine nannoplankton e g discoaster and by the presence of neritic littoral and freshwater diatoms whilst calcareous nannoplankton are known to occupy near shore habitats they are rarely preserved in such environments due to terrigenous and clastic influx the shallow and eutrophic environments of the messinian polemi basin therefore provide an unusual opportunity to investigate which extinct nannofossil taxa occupied marginal marine environments nannoplankton diversity 3 to 11 species is low in comparison to the open ocean and the assemblages are extremely uneven with high dominance one of five species reticulofenestra minuta reticulofenestra antarctica helicosphaera carteri umbilicosphaera jafari and sphenolithus abies was observed to dominate in all of the assemblages these were broadly distributed marine species but capable of opportunistic behaviour salinity and nutrient levels are thought to be the primary factors controlling the overall nature of the nannoplankton assemblages using the associated diatom and sedimentological evidence we infer the palaeoecology of key nannofossil taxa and speculate on the palaeoenvironments of the messinian polemi basin r antarctica is thought to have dominated in normal salinity mesotrophic shallow water environments h carteri in shallow brackish eutrophic environments u jafari in hypersaline conditions r minuta in eutrophic conditions with an abnormal salinity from brackish to hypersaline and s abies in mesotrophic deeper and normal salinity environments d 2005 elsevier b v all rights reserved

old world first appearance datum of hipparion horses late miocene large mammal dispersal and global events the magnetobiochronological dating of the late miocene hipparionine horses hipparion in the western mediterranean places its first appearance datum fad in the circum mediterranean region at the chron c5r at a minimum age of 11 1 ma this date challenges some of the widely accepted datings of this bioevent in western eurasia and is relevant to the discussion of the mode and tempo of hipparion dispersal the migration of the hipparion north american ancestor is related to the glacioeustatic sea level lowstand of the supercycle tb3 1 early tortonian and to the concurrent deep sea hiatus nh4 and oceanic 18 o isotopic event mi5 the hipparion dispersal was a conspicuous worldwide on land bioevent that was coeval with major late miocene oceanic and high latitude paleoclimatic global changes

the origin of tensile fracture lineaments abstract fracture controlled lineaments commonly seen where brittle basement is exposed at the earth s surface are generally restricted to a small number of sets with angles of 45 90 between sets the length frequency distribution of lineaments in each set follows a truncated poisson function such lineaments usually show almost no shearing offset suggesting a tensile origin a simple mechanical model of tensile fracturing is used to explain the spacing directions and length of lineaments as well as their depth frequency distribution results suggest that the penetration depth of tensile fractures which produce lineaments at the earth s surface is directly related to their length and that the fracture density is inversely proportional to fracture depth finally the angles between lineament sets may be controlled by the ratio of strength of unfractured rock to that of pre existing fractures which might heal with time the most likely source of tension is tectonic uplift fractures due to typical uplifts of 0 5 1 km over distances of 10 100 km may penetrate as brittle fractures to several kilometres into the crust perhaps to the depth at which seismic activity ceases

punctuated evolution of global climate cooling during the late middle to early late miocene high resolution planktonic foraminiferal and oxygen isotope records from the mediterranean high resolution planktonic foraminiferal and oxygen isotope records are presented from a mediterranean deep marine succession dated astronomically between 12 12 and 9 78 ma planktonic and benthic oxygen isotope records are punctuated by two episodes of 18o increase which have astronomical ages of 11 4 and 10 4 ma and correspond to the mi5 and mi6 events of miller et al 1991a these ice growth events coincide with low amplitude variations in the 1 2 myr obliquity cycle and are accompanied by significant faunal changes in the mediterranean such as the arrival of neogloboquadrinids the increase in abundance of the g apertura g obliquus group and the areal differentiation between n atlantica and n acostaensis short term variations in the planktonic foraminiferal and oxygen isotope records correspond to dominantly precession controlled sedimentary cycles features of the sapropel grey marl layers indicate that the short term astronomically controlled circum mediterranean climate changes remained basically the same over the last 12 myr

microcracks in rocks a review abstract in the past decade the number of studies about microcracks in rocks has rapidly increased this review of recent work concentrates on microcracks in rock as separate entities emphasizing microcrack morphogenesis kinematics dynamics population statistics and observational techniques cracks are produced when the local stress exceeds the local strength the local stress may be augmented by twin lamellae interactions kink bands and deformation lamellae stress concentrations at grain boundary contacts and around intracrystalline cavities local strength may be reduced along cleavage planes along grain boundaries and along any internal surface as a result of corrosion by chemically active fluids dislocations appear not to be a significant factor for crack nucleation below about 500 c in silicates spatial and temporal changes in temperature can also induce microcracking as a result of differential thermal expansion between grains with different thermoelastic moduli and thermal conductivities the amount of quartz in the rock has a significant effect on thermally induced microcracks because of its large and variable thermal expansivity the application of hydrostatic pressure between 100 and 200 mpa effectively closes most cracks but the closure may not be uniform if crack wall asperities exist hydrostatic pressure appears to stabilize cracks and make crack growth more difficult the number and average size of mechanically induced microcracks is greater in rock deformed at higher pressures the application of a deviatoric stress field on the boundaries of a rock mass results on a microscopic scale in a very complex stress system which greatly affects nucleation and propagation paths the relative amount of intragranular and intergranular cracking appears to depend upon mineralogy rock type and stress state the vast majority of stress induced microcracks in rocks appear to be extensional statistically they are predominantly oriented within 30 of the macroscopic maximum stress direction crack densities increase as macroscopic deviatoric stress increases above a threshold level crack size distributions may be either lognormal or exponential fracture in rock under compressive boundary loads is a result of the coalescence of many microcracks not the growth of a single crack some crack configurations are more favorable for coalescence than others as deviatoric stress increases and rock failure is approached the microcrack population changes spatially from random to locally intense zones of cracking away from the fault the crack density dies off rapidly to the background level a few grains away under lesser deviatoric stresses slow subcritical microcrack growth can occur as a result of stress aided corrosion at the crack tip the rate governing mechanism may be either the chemical reaction rate or the rate at which water can get to the crack tip important details still remain to be worked out

inferring paleostresses from natural fracture patterns a new method we introduce a method to infer the remote differential stress magnitude from the curvature of overlapping echelon fracture traces the curving paths of overlapping echelon cracks imply the predominance of local crack induced stresses over remote stresses during propagation nearly straight crack paths imply the controlling influence of a remote compressive crack parallel differential stress this method is used to interpret complex joint patterns mapped in sedimentary rock it is also applied to the problem of fracture pattern generation using computer models

boulder coastal deposits at favignana island rocky coast sicily italy litho structural and hydrodynamic control abstract boulders are frequently dislodged from rock platforms transported and deposited along coastal zones by high magnitude storm waves or tsunamis their size and shape are often controlled by the thickness of bedding planes as well as by high angle to bedding fracture network we investigate these processes along two coastal areas of favignana island by integrating geological data for 81 boulders 49 rupture surfaces called sockets and fracture orientation and spacing with four radiocarbon dates numerical hydrodynamic analysis and hindcast numerical simulation data boulders are scattered along the carbonate platform as isolated blocks or in small groups which form as a whole a discontinuous berm underwater surveys also highlight free boulders with sharp edges and sockets carved out in the rock platform boulders are composed of ruditic to arenitic size clastic carbonates their size ranges from 0 6 to 3 7 m 0 55 to 2 4 m and 0 2 to 1 m on the major a medium b and minor c axes respectively the highest value of mass estimation is 12 5 t almost all of boulders and sockets are characterized by a tabular or bladed shape the comparisons between a the fractures spacing and the length of a and b axes and b the frequency peaks of c axis with the recurrent thickness of beds measured along the coastal zone demonstrate the litho structural control in the size and shape of joint bounded boulders these comparisons together with the similarity between the shapes of the boulders and those of the sockets as well as between the lithology of boulders and the areas surrounding the sockets suggest that blocks originate by detachment from the platform edge thus the most common pre transport setting is the joint bounded scenario hydrodynamic equations estimate that the storm wave heights necessary to initiate the transport of blocks diverge from 2 m to 8 m for joint bounded boulders and from few tens of centimeters up to 11 m for submerged boulders the comparison between the wave heights at the breaking point of the coastal zones with the results of hydrodynamic equations shows that waves approaching the coastline are able to transport all surveyed boulders our data suggest that boulders have been transported by several storm events even in very recent times

astronomically forced teleconnection between paratethyan and mediterranean sediments during the middle and late miocene abstract a high resolution correlation between an orbital tuned middle and early late miocene record of the central paratethys and an astronomically calibrated mediterranean deep marine composite record is proposed the astronomical tuning of the sarmatian and pannonian sedimentary record in the vienna basin confirms that the beginning of the pannonian regional stage lower tortonian dated in this work at 11 42 my is very close to the miller event mi5 it coincides with a period of minimum amplitude in the 1 2 myr obliquity cycle which in the mediterranean marine record corresponds with a drastic change in the planktonic foraminiferal fauna in addition the warmer period between mi5 and mi6 corresponding to a maximum in the long term 2 3 myr eccentricity cycle coincides with a long interval of lignite deposition in the paratethyan realm the sedimentation pattern shown by high frequency cyclicity between lignite and normal sediments reflects a primary influence of 100 kyr eccentricity cycles on the sedimentation system of the central paratethys which corresponds with small and large scale sapropel clusters hierarchical organization in the mediterranean record the badenian sarmatian boundary astronomically dated at 13 32 myr does not coincide with a low amplitude variation in the 1 2 myr obliquity cycle and any mi events this orbital configuration is supported by the paleoclimatic and paleoecologic data of the late badenian and early sarmatian which both represent a warm temperate system with stagnant bottom water conditions finally the transitional phase from a temperate early sarmatian to a warmer late sarmatian associated with predominant carbonate sedimentation coincides with the glacio eustatic isotope event mi4 while the entire late sarmatian spans a complete 1 2 myr obliquity cycle

oligocene miocene basin evolution in se anatolia turkey constraints on the closure of the eastern tethys gateway the oligocene miocene was a time characterized by major climate changes as well as changing plate configurations the middle miocene climate transition 17 to 11 ma may even have been triggered by a plate tectonic event the closure of the eastern tethys gateway the marine connection between the mediterranean and indian ocean to address this idea we focus on the evolution of oligocene and miocene foreland basins in the southernmost part of turkey the most likely candidates to have formed this gateway in addition we take the geodynamic evol ution of the arabian eurasian collision into account the musand elazog u basins located to the north of the bitlis zagros suture zone were most likely connected during the oligocene the deepening of both basins is biostratigraphically dated by us to occur during the rupelian early oligocene deep marine conditions between 350 and 750 m prevailed until the chattian late oligocene when the basins shoaled rapidly to subtidal intertidal environment in tropical to subtropical conditions as indicated by the macro fossil assemblages we conclude that the emergence of this basin during the chattian severely restricted the marine connection between an eastern indian ocean and western mediterranean marine domain if a connection persisted it was likely located south of the bitlis zagros suture zone the kahramanmarasbasin located on the northern arabian promontory south of the bitlis zagros suture zone was a foreland basin during the middle and late miocene possibly linked to the hatay basin to the west and the lice basin to the east our data indicates that this fore land basin experienced shallow marine conditions during the langhian followed by a rapid dee pening during langhian serravallian and prevailing deep marine conditions between 350 and 750 m until the early tortonian we have dated the youngest sediments underneath a subduc tion related thrust at c 11 ma and suggest that this corresponds to the end of underthrusting in the kahramanmarasregion i e the end of subduction of arabia this age coincides in time with the onset of eastern anatolian volcanism uplift of the east anatolian accretionary complex and the onset of the north and east anatolian fault zones accommodating westward escape tec tonics of anatolia after c 11 ma the foreland basin south of the bitlis formed not or no longer a deep marine connection along the northern margin of arabia between the mediterranean sea and the indian ocean we finally conclude that a causal link between gateway closure and global climate change to a cooler mode recorded in the mi3b event d 18 o increase dated at 13 82 ma cannot be supported

understanding airborne radiometric survey signals across part of eastern england a low level airborne radiometric survey provides data on the concentrations of gammaemitting elements including potassium k thorium th and uranium u in the upper half metre of the soil where weathering has not penetrated much beyond this depth as in the young soils that cover much of england and wales the signal is likely to be related to the soil s clay content and its parent material in these situations radiometric survey could be valuable for mapping soil digitally we wished to understand how the radiometric signal relates to parent material and soil geochemistry and to identify the spatial structure if not the sources of any unexplained variation we analysed the joint spatial variation of the airborne gamma signal and high resolution soil geochemical survey data across part of eastern england by modelling their coregionalization we also used reml to assess the joint effects of soil geochemistry and parent material on the radiometric signals of k and th the overall correlations of radiometric estimates with soil survey data for k and th were large as were the structural correlations for components of variation spatially dependent up to 49 and 16 km for k and th respectively this suggests that the radiometric signals for these two elements provide effective estimates of the amounts in the soil and their patterns of distribution although class of parent material accounted for a third of of the variance in the radiometric k signal much of the variation within the classes is explained by geochemistry suggesting that subtler changes can be detected a larger proportion of the th signal was accounted for by parent material this supports our expectation that radiometric signals for k and th provide information on parent material in the young landscapes of england and wales we are therefore confident that airborne radiometric surveys would be useful for making thematic maps of soil particularly the soil s texture and closely related properties across england and wales copyright 2007 natural environment research council published in 2007 by john wiley sons ltd

analysing the proximal gamma radiometry in contrasting mediterranean landscapes towards a regional prediction of clay content abstract the analysis of radiometric data from proximal soil sensing measurements can be used to predict key soil properties for environmental and agricultural issues these predictions require prior calibrations that use a large sampling of field data that could be significantly reduced if regional predictions can be established however such predictions may be challenging for mediterranean regions because of the highly contrasted soils and specific geopedological characteristics sedimentary rocks low weathering etc our study focuses on the regional prediction of a key soil property clay content within highly contrasting geopedological groups gpg from the languedoc region the aims of the research were i to understand the relationship between radiometric data and the clay content within the different complex gpgs and ii to predict the clay content from radiometry with a regional calibration based on the gpg as an auxiliary variable a proximal soil survey using the radiometer called the mole was conducted in 8 areas of the languedoc region the plots were selected over different gpgs that are representative of the soil diversity and materials according to their weathering intensity and igneous components in total 242 sites were sampled based on a random grid cell for soil laboratory measurements the soil texture and stoniness were analysed and the particle size fractions were separated for mineral identification via x ray diffraction the activity of 232th 1 to 71 bq kg and 40k 40 to 771 bq kg exhibits the largest range between the different gpgs which spans the range of values measured in previous european studies the relationship between the clay content and 232th is significant at a regional level r2 0 60 rmse 42 g kg the residuals are significantly distributed according to the different gpgs a new linear model based on the 232th activity and the gpgs improves the prediction of the clay content r2 0 72 rmse 35 g kg our study showed that ground radiometry can be used to predict the clay content within a complex mediterranean sedimentary context the 232th radionuclide is the best predictor the disturbance of the relationship between the 232th and the clay content corresponds to the fine earth mineralogy type and the proportion of igneous pebbles

structural controls of fracture orientations intensity and connectivity teton anticline sawtooth range montana the teton anticline is a multiple hinge anticline containing fractured mississippian devonian carbonates in the frontal part of the sawtooth range in montana the structure serves as a good surface analog for fracture patterns and connectivities within subsurface folded carbonate reservoirs the primary fracture sets are longitudinal and transverse relative to the axis of the fold although two additional oblique sets are also present the length and density of the longitudinal fracture sets are strongly controlled by position relative to multiple hinges the transverse fractures are related to changes in fold plunge and exhibit less variation in fracture density fracture connectivity is dependent on the number of fracture sets their orientations and dispersions and the densities of the fracture sets the connectivity is measured using two parameters the fractional connected area fca which represents the fraction of the total sample area that is connected by fractures and the distribution of clusters of different sizes in any given area because the longitudinal fractures represent the dominant fracture set and also show the most variation with structural position the fracture connectivity as measured by both the fcas and the distribution of cluster sizes is greater in the vicinity of the fold hinges the results and approaches used in the study have some important implications for subsurface folded fractured carbonate reservoirs the analysis of sparsely distributed fracture data from wells must be integrated with an understanding of the controls of the macroscopic structure on fracture parameters to effectively simulate fracture patterns and connectivities around subsurface structures

miocene to pliocene calcareous nannofossil biostratigraphy at odp leg 177 sites 1088 and 1090 the calcareous nannofossil biostratigraphy of odp leg 177 sites 1088 and 1090 subantarctic sector from the atlantic ocean is discussed most nannofossil zonal boundaries of martini 1971 and okada and bukry 1980 were recognized for the studied mid high latitude sediments conventional low latitude marker species such as amaurolithus spp discoaster spp triquetrorhabdulus spp ceratolithus spp were recorded as rare and scattered which impeded the development of a detailed nannofossil biostratigraphic zonation of some miocene and pliocene intervals because of the absence of some primary biostratigraphic marker species additional second order bioevents such as the first occurrence of calcidiscus macintyrei and the last occurrence of coccolithus miopelagicus have been used to approximate the base of zones nn7 and nn8 respectively several disconformities disturbing the pliocene and miocene intervals of site 1090 could be determined based on nannofossil distribution although the occurrence of intervals with dissolved nannofloras and low species diversity prevented a reliable age assignment an acme of small gephyrocapsa was recognized near the lower middle pliocene boundary close to the nn15 nn16 zonal boundary presenting an event for further improvement of the calcareous nannofossil biostratigraphy of this interval time the first occurrence of pseudoemiliania lacunosa 4 m occurs close to this interval representing a fairly reliable event to approximate the base of nn15 zone when other biozonal events are absent a paracme of r pseudoumbilicus 7 m was detected in the lower pliocene nn12 and in the upper miocene nn11 these temporary absences of the species seem to be isochronous between high latitude and low middle latitude areas

coccolithus pelagicus subsp pelagicus versus coccolithus pelagicus subsp braarudii coccolithophore haptophyta a proxy for surface subarctic atlantic waters off iberia during the last 200 kyr abstract a multivariate morphon analysis mma of coccolithus pelagicus s l coccoliths was performed on 178 samples from an oceanic core recovered off the portuguese margin md95 2040 in order to define the morphometric boundaries of its morphotypes and their behaviour during the last two glacial cycles the recurrent occurrence of the smaller morphotype of this taxon c pelagicus subsp pelagicus was recognized for the first time off the portuguese coast three sections around heinrich layers 1 and 6 and termination ii eemian were selected to establish high resolution comparisons between c pelagicus subsp pelagicus and c pelagicus subsp braarudii and two independent proxies for cold water masses the records of the planktonic foraminifera neogloboquadrina pachyderma sinistral and ice rafted detritus ird there is an overall negative correlation between c pelagicus subsp pelagicus and c pelagicus subsp braarudii as expressed by mma factor 1 the scores of which respond similarly to those of two non cocolithophore proxies and consequently is proposed as a calcareous nannoplankton proxy for the influence of subpolar waters in the region detailed analysis however showed occasional decoupling amongst these three proxies which are used to highlight significant changes between the cooling warming sequences of distinct events off iberia

paleodepth distribution of neocene deep sea hiatuses the depth of formation of miocene to middle pliocene deep sea hiatuses nh1 to nh8 has been determined using 152 deep sea drilling project sites in the atlantic pacific and indian oceans megahiatuses representing maxima in deep sea erosion occur at three water depths below 3800 m at intermediate depths between about 2000 and 3000 m and in shallower waters above 1500 m paleodepth both the paleodepths and distribution of these hiatus maxima suggest that flow of antarctic bottom water antarctic intermediate water and north atlantic deep water masses largely caused this erosion correlation of the hiatuses with oxygen isotope carbonate and sea level records indicates that prior to 11 ma brief hiatuses including those resulting from nondeposition in high productivity equatorial regions largely correlate with global cooling episodes high carbonate content and lowstands of sea level during the last 11 m y hiatuses also seem to correlate with cooling episodes but carbonate dissolution is characteristic and sea levels may have been rising or at a lowstand during the nh4 nh7 and nh8 intervals it is possible that a rise in sea level corresponds with polar cooling but there is uncertainty in correlation brief hiatuses during rising sea levels can be explained by basin shelf fractionation of carbonates hiatuses during sea level lowstands and cooling episodes may result from intensified bottom water circulation and increased corrosiveness of bottom water due to higher levels of co2 and increased productivity during increased upwelling supplement appendix 1 is availablewith entire article on microfiche orderfrom american geophysical union 2000florida avenue n w washington dc20009 document p87001 2 50 paymentmust accompany order

spatial distribution scaling and self similar behavior of fracture arrays in the los planes fault baja california sur mexico we present a case of detailed analysis of fracture arrays spanning four orders of magnitude in length all of them measured at a single natural site by acquiring images at progressively larger scales there is a high dispersion of cumulative length exponents box dimensions and fracture densities however the fractal analysis supports the fractal nature of fracture arrays our data indicate the existence of an upper limit for the density parameters as similarly reported by other authors we prove that box dimension is in inverse relation with fracture concentration and in direct relation with fracture density these relations are also observed in our data and additionally there is an upper limit for the box dimensions we interpret the dispersion in our results as more fundamental than methodological problems it represents a truncation in the complete evolution of the fracture systems because in natural cases strain initiates overprinting of previous fracture arrays considering that larger fractures accommodate strain more efficiently than small fractures the generation of small fractures is inhibited in the presence of pre existing larger fractures maximum values of fracture density prevent accommodating an excess of strain in a single or restricted range of scales we claim this condition produces migration of fracturing to larger scales originating fracture scaling

arctic sea ice leads from advanced very high resolution radiometer images a large number of advanced very high resolution radiometer avhrr images from throughout 1989 are analyzed to determine lead characteristics the units of analysis are square 200 km cells and there are 270 such cells in the data set clouds are masked manually leads are determined from images of the potential open water a scaled version of the surface temperature or albedo that weights thin ice by its thermal or brightness impact the lead fraction is determined as the mean the monthly mean lead fraction ranges from 0 02 in winter to 0 06 in summer in the central arctic and is near 0 08 in the winter in the peripheral seas a method of accounting for lead width sampling errors due to the finite sample areas is introduced in the central arctic the observed mean lead width for a threshold of 0 1 ranges from 2 or 3 km near the resolution of the instrument in the winter to 6 km in the summer in the peripheral seas it is about 5 km in the winter width distributions are often more heavily weighted in the tail than exponential distributions and are well approximated by a power law the along track number density power law n aw b has a mean exponent of b 1 60 standard deviation 0 18 and shows some seasonal variability mean floe widths in the central arctic are 40 to 50 km in the winter dropping to about 10 km in the summer for floes the power law has a mean exponent of 0 93 and exhibits a clearer annual cycle lead orientation is determined with a method based on the direction of maximum extent

statistical mechanics and scaling of fault populations with increasing strain in the corinth rift scaling properties of fracture fault systems are studied in order to characterize the mechanical properties of rocks and to provide insight into the mechanisms that govern fault growth a comprehensive image of the fault network in the corinth rift greece obtained through numerous field studies and marine geophysical surveys allows for the first time such a study over the entire area of the rift we compile a detailed fault map of the area and analyze the scaling properties of fault trace lengths by using a statistical mechanics model derived in the framework of generalized statistical mechanics and associated maximum entropy principle by using this framework a range of asymptotic power law to exponential like distributions are derived that can well describe the observed scaling patterns of fault trace lengths in the rift systematic variations and in particular a transition from asymptotic power law to exponential like scaling are observed to be a function of increasing strain in distinct strain regimes in the rift providing quantitative evidence for such crustal processes in a single tectonic setting these results indicate the organization of the fault system as a function of brittle strain in the earth s crust and suggest there are different mechanisms for fault growth in the distinct parts of the rift in addition other factors such as fault interactions and the thickness of the brittle layer affect how the fault system evolves in time the results suggest that regional strain fault interactions and the boundary condition of the brittle layer may control fault growth and the fault network evolution in the corinth rift

fractal characteristics of active normal faults an example of the eastern gulf of corinth greece abstract we present a model proposing the evolution of segmented normal faults in a currently extended area allowing an explanation of strong earthquakes hosted by short faults active normal faults accommodating the current extension in the gulf of corinth result from the linkage of smaller component faults well exposed fault zones in the sofiko range are arranged as pairs of graben bounding faults and thus our structural analysis has implications for the evolution of active normal faults as well as graben evolution a basal strip of fresh bedrock at the base of fault scarps suggests continuous seismic or aseismic creep thus the structural analysis of component faults that show a power law length distribution describes an evolved fault zone of particular interest is that faulting in this region is self similar between limits distribution is characterized by a fractal dimension of d 1 and the limits in our study are between 10 m mapping resolution and double the maximum displacement of each fault zone component segments of any compartmentalized fault show a length to maximum displacement ratio of two basin architecture and structural analysis suggest that the nucleation points of faults are detectable over the entire evolution of the fault zone all analyzed faults evolved by an independent nucleation model morphotectonic and kinematic data as well as fractal dimension of trace length population plots all suggest that fault zones defining north and south dipping conjugates are active at least over the late stages of basin evolution although this study was focused on a relatively small area this pattern of fault growth appears to be applicable to the entire fault population in the gulf of corinth and is thus an important model for normal faults

integrated stratigraphy and astronomical calibration of the serravallian tortonian boundary section at monte gibliscemi sicily italy results are presented of an integrated stratigraphic calcareous plankton biostratigraphy cyclostratigraphy and magnetostratigraphy study of the serravallian tortonian s t boundary section of monte gibliscemi sicily italy astronomical calibration of the sedimentary cycles provides absolute ages for calcareous plankton bio events in the interval between 9 8 and 12 1 ma the first occurrence fo ofneogloboquadrina acostaensis usually taken to delimit the s t boundary is dated astronomically at 11 781 ma pre dating the migratory arrival of the species at low latitudes in the atlantic by almost 2 million years in contrast to delayed low latitude arrival of n acostaensis paragloborotalia mayeri shows a delayed low latitude extinction of slightly more than 0 7 million years with respect to the mediterranean last occurrence lo at 10 49 ma at ceara rise lo at 11 205 ma in the mediterranean the discoaster hamatus fo dated at 10 150 ma is clearly delayed with respect to the open ocean the ages of d kugleri first and last common occurrence fco and lco catinaster coalitus fo coccolithus miopelagicus last regular occurrence l r o and the d hamatus neohamatus cross over however are in good to excellent agreement with astronomically tuned ages for the same events at ceara rise tropical atlantic suggesting that both independently established timescales are consistent with one another the lack of a reliable magnetostratigraphy hampers a direct comparison with the geomagnetic polarity timescale of cande and kent 1995 ck95 but ages of calcareous nannofossil events suggests that ck95 is significantly younger over the studied time interval approximate astronomical ages for the polarity reversals were obtained by exporting astronomical ages of selected nannofossil events from ceara rise and the mediterranean to eastern equatorial pacific odp leg 138 site 845 which has a reliable magnetostratigraphy our data from the rio mazzapiedi castellania section reveal that the base of the tortonian stratotype corresponds almost exactly with the first regular occurrence fro of n acostaensis s s as defined in the present study dated at 10 554 ma an extrapolated age of 11 8 ma calculated for the top of the serravallian stratotype indicates that there is a gap between the top of the serravallian and the base of the tortonian stratotype potentially rendering all bio events in the interval between 11 8 and 10 554 ma suitable for delimiting the s t boundary despite the tectonic deformation and the lack of a magnetostratigraphy gibliscemi remains a candidate to define the s t boundary by means of the tortonian global boundary stratotype section and point gssp 2000 elsevier science b v all rights reserved

scaling relationships of joint and vein arrays from the burren co clare ireland abstract we present a study of the systematics of veins and joints in carboniferous limestones of the burren ireland scaling relationships were established for fracture arrays mapped from low elevation aerial photographs that image fractures on numerous limestone pavements for areas up to ca 1 km2 the veins and joints occur in the same sequence but have contrasting scaling properties the veins strike north south and cut many beds to form vertically persistent non stratabound arrays they are strongly clustered and have scale invariant geometric properties vein geometries suggest they grew sub critically under relatively high differential stresses during north south directed variscan compression the joints form stratabound arrays with regular spacings that scale with bed thickness they show greater strike variation than the veins and have lognormal length distributions the joints formed during uplift under low differential stress conditions the contrasting scaling properties of the joints and veins are attributed to different overburden stresses at the time of formation the veins formed at greater depths than the joints in conditions that favoured fracture propagation across mechanical discontinuities resulting in the development of non stratabound scaling properties

scaling and geometric properties of extensional fracture systems in the proterozoic basement of yemen tectonic interpretation and fluid flow implications abstract multi scale mappings of fracture systems in the crystalline basement of yemen are presented fracture datasets are described through statistical analyses of direction length spacing density and spatial distribution results are combined with field observations and can be directly used to model the geometry of the fracture networks in analog basement rocks from multi kilometric to decametric scales the fractured reservoir analog is defined with a dual porosity model in which tectonic and joint systems correspond to the basement reservoir backbone and matrix respectively these two end members reveal contrasting geometrical reservoir and scaling properties in tectonic systems multi scale geometries are self similar the fracture network shows fractal behavior power law length distribution and clustered spacing and fault zones show hierarchical organization of geometrical parameters such as length thickness and spacing in joint systems the fracture network is scale dependent with exponential length distribution and shows anti clustered spacing however these two end members have both well connected properties with fault zones acting as main drain and joint systems acting as the fluid supply

overlapping spreading centres new accretion geometry on the east pacific rise in a detailed seabeam investigation of the east pacific rise epr from 8 n to 18 n a new kind of volcano tectonic geometry associated with fast spreading centres has been discovered figs 1 2 at several locations along the rise axis the neovolcanic zone is discontinuous and is laterally offset a short distance 1 15 km in contrast to a classic ridge transform ridge plate boundary however the offset ridge terminations overlap each other by a distance approximately equal to or greater than the offset they curve sharply towards each other and often merge into one another along strike separating the overlapping spreading centres oscs is a closed contour depression up to several hundred metres deep which is sub parallel to the trend of the oscs the region between the oscs is a complex zone of both shear and rotational deformation with no obvious transform parallel structures based on wax model studies of spreading centres we suggest here that transform faults fail to develop at fast spreading centres where the lateral offsets are small 15 km because the lithosphere is too thin and weak to maintain a classic rigid plate spreading centre transform fault pattern the osc geometry is unstable and evolves rapidly one of the two oscs prevails while the other is abandoned a significant area of sea floor created at fast spreading rates may bear the imprint of this newly observed process

the impact of in situ stress and outcrop based fracture geometry on hydraulic aperture and upscaled permeability in fractured reservoirs abstract aperture has a controlling impact on porosity and permeability and is a source of uncertainty in modeling of naturally fractured reservoirs this uncertainty results from difficulties in accurately quantifying aperture in the subsurface and from a limited fundamental understanding of the mechanical and diagenetic processes that control aperture in the absence of cement bridges and high pore pressure fractures in the subsurface are generally considered to be closed however experimental work outcrop analyses and subsurface data show that some fractures remain open and that aperture varies even along a single fracture however most fracture flow models consider constant apertures for fractures we create a stress dependent heterogeneous aperture by combining finite element modeling of discrete fracture networks with an empirical aperture model using a modeling approach that considers fractures explicitly we quantify equivalent permeability i e combined matrix and stress dependent fracture flow fracture networks extracted from a large outcropping pavement form the basis of these models the results show that the angle between fracture strike and 1 has a controlling impact on aperture and permeability where hydraulic opening is maximum for an angle of 15 at this angle the fracture experiences a minor amount of shear displacement that allows the fracture to remain open even when fluid pressure is lower than the local normal stress averaging the heterogeneous aperture to scale up permeability probably results in an underestimation of flow indicating the need to incorporate full aperture distributions rather than simplified aperture models in reservoir scale flow models

integrated stratigraphy and astronomical tuning of the serravallian and lower tortonian at monte dei corvi middle upper miocene northern italy an integrated stratigraphy calcareous plankton biostratigraphy magnetostratigraphy and cyclostratigraphy is presented for the serravallian and lower tortonian part middle upper miocene of the monte dei corvi section located in northern italy the detailed biostratigraphic analysis showed that both the discoaster kugleri acme and the first influx of neogloboquadrina acostaensis are recorded at monte dei corvi these events which passed unobserved in previous studies play an important role in delineating the serravallian tortonian boundary thermal and alternating field demagnetization revealed a characteristic low temperature component marked by dual polarities the resultant magnetostratigraphy for the upper part of the section can be unambiguously calibrated to the gpts ranging from c5n 2n up to c4r 2r unfortunately the lower part of the section including the serravallian tortonian boundary interval did not produce a reliable magnetostratigraphy despite the fact that some short reversed intervals and a single normal interval are recorded using sedimentary cycle patterns in combination with the calcareous plankton biostratigraphy the section can be correlated cyclostratigraphically in detail to the partially overlapping and previously tuned section of monte gibliscemi on sicily the monte dei corvi section is dated astronomically by calibrating the basic small scale sedimentary cycles to the precession and 65 n lat summer insolation time series of the la93 solution following an initial tuning of larger scale cycles to eccentricity an almost perfect fit is found between the cycle patterns and intricate details especially precession obliquity interference in the insolation target between 8 5 and 10 ma the tuning to precession remains robust for most intervals back to the base of the section dated at 13 4 ma and shows that the section is continuous apart from a possible short hiatus in the tortonian it provides accurate astronomical ages for all sedimentary cycles calcareous plankton events polarity reversals and ash layers and marks a significant improvement of the recently proposed astronomical calibrations of the monte dei corvi section and of parallel sections in the mediterranean astronomical ages for the ancona and respighi ashbeds are significantly older than previously reported 40 ar 39 ar biotite ages even if the revised older age for the fct san dating standard of 28 02 ma is applied the astronomical dating of the magnetic reversals in the monte dei corvi section results in the completion of the astronomical polarity time scale for the last 13 myr the monte dei corvi section has recently been proposed as the stratotype section for the serravallian tortonian boundary despite the moderate to

mid neogene mediterranean marine continental correlations an alternative interpretation recent revised magnetostratigraphic and astrochronologic calibrations of several calcareous planktonic microfossil datum events in particular coccolithus miopelagicus and neogloboquadrina acostaensis combined with our magnetobiostratigraphic investigation of a 10 m thick section at ecotet near lyon france in which terrestrial micromammals vallesian zone mn9 are intercalated with calcareous nannoplankton and planktonic foraminifera belonging to zones nn6 nn8 and n14 15 m11 and m12 respectively lead us to question the recent recalibration by krijgsman et al 1996 eart planet sci lett 142 367 380 of the aragonian vallesian mn7 8 mn9 boundary with chron c5r 1r v11 1 ma and the lower upper vallesian mn9 10 boundary with chron c4ar 2n v9 6 9 7 ma ecotet with a uniform reverse polarity is shown to be assignable uniquely to chron c5r interregional correlation of ecotet with mediterranean terrestrial stratigraphies indicates that progonomys whose first occurrence fo has been traditionally placed in mediterranean mammal zone mn10 was already present in mediterranean zone mn9 at v11 4 ma and did not experience a 2 million year delay in its putative prochoresis from asia

orthogonal fracture systems at the limits of thrusting an example from southwestern wales abstract a well developed orthogonal vein system is located in the autochthonous foreland just beyond the limits of variscan thrusting in southwestern wales the two vein sets trend 200 and 290 perpendicular and parallel respectively to variscan structures the veins contain stretched quartz fibers indicating horizontal extensions of between 0 3 and 2 5 the 200 set has greater extension with a distinctive morphology including shorter more curvilinear fractures that have components of normal offset vein intersections are simple indicating episodic growth by alternating regional propagation of each set during propagation maximum compression was subvertical and the horizontal principal stresses switched direction with the alternation of set growth the system formed during waning variscan compression when the directions of horizontal principal stresses were still controlled by the tectonic compression the differential stress may have been greater during propagation of the 200 set this example indicates that orthogonal fracture systems in forelands beyond thrusting 1 are initiated by fracturing parallel to tectonic compression 2 form in a few stages that are controlled by changes in regional stress and 3 form during waning tectonic compression that controls fracture orientations

evolution of permeability in sand injectite systems abstract sand injectite complexes comprise kilometer scale clastic intrusion networks that act as effective conduits for the migration accumulation and then recovery of hydrocarbons and other fluids an equivalent continuum model is constructed to represent a sand injectite reservoir coupling stress and fluid flow in fractured rock using the continuum simulator toughreact coupled with flac3d to follow deformation and fluid flow a permeability model which uses staged percolation models is proposed to improve permeability estimation of fracture networks by accommodating four different levels of fracture connectivity this permeability model is confirmed against field and laboratory data corresponding to the different connectivities of fracture networks the new constitutive permeability model is incorporated into the coupled hydro mechanical simulator framework and applied to sand injectites with the analysis of permeability evolution mechanisms and mechanical sensitivity the results indicate that when the magnitudes of principal stresses increase in a constant ratio normal closure is the dominant mechanism in reducing fracture aperture and thereby permeability conversely the evolution of stress difference can accentuate aperture and permeability due to an increase in shear dilation for critically or near critically oriented fractures also the evolution of aperture and related permeability of fractured rock are more sensitive at lower stress states than at higher stress states due to the hyperbolic relationship between normal stress and normal closure of the fractures

fluid velocity fields in 2d heterogeneous porous media empirical measurement and validation of numerical prediction the scale invariance of geological material and the consequent absence of a length scale on which to base the upscaling of measurements made on geological samples represent a serious challenge to the prediction of fluid behaviour in rock at economically interesting scales numerical simulation is an important tool for understanding constraints in this problem and current discrete fluid models in which complex boundary conditions can be represented have the potential for testing many possible upscaling schemes at present however there are no accurate empirical data on the distributions of fluid velocities in complex scale invariant geometries with which to validate such models to address this fluid velocity fields in complex 2d media with fractal heterogeneity were measured digital models of rock geometries were created and translated into physical form using electric discharge machining and stereolithography these physical models were then enclosed between parallel sheets of glass and perspex forming a hele shaw cell which was permeated with water doped with small neutrally buoyant spheres and pumped at accurately steady and reproducible velocities local velocity vectors were estimated by the analysis of sequential images captured using high resolution video precision digital control systems were used to move the cell relative to the camera and repeated measurements allowed the construction of full 2d velocity fields the accuracy of the technique was assessed by comparison between automated and manual measurements confirming the accuracy over approaching three orders of magnitude in velocity the results have been compared to the output of lattice boltzmann lb simulations of flow in identical geometries showing that the correlation between simulated and measured velocity fields is strongly dependent on the viscosity used in the numerical simulation in particular the lb scheme used in these tests is incapable of simulating correct viscosities for complex geometries some important effects are shown to be strongly viscosity dependent and it is concluded that some simulations may be able to predict the behaviour of high viscosity fluids only nonlinear effects between fracture and matrix flow are likely to be more important in these cases