variation of pore fabric across a fold thrust structure variations of pore orientation pore shape porosity and hydraulic permeability within a siltstone unit of a fold thrust structure are determined using magnatic pore fabric analysis mercury injection porosimetry and scanning electron microscopy sem while samples in the foreland show evidence for the preservation of depositional pore geometry the progressively deformed thrust sheet reveals increasingly oblate pore fabric anisotropy with microcrack planes oriented normal to the tectonic transport direction porosity pore throat sizes and permeability show corresponding spatial variations across the structure independent of the deformation state within the thrust sheet pore and magnetic grain fabric correlate closely in orientation

magnetic susceptibility anisotropy of rocks saturated with ferrofluid a new method to study pore fabric abstract the shape effect of ferrofluid filled cavities on the anisotropy of magnetic susceptibility ams is examined for different geometries principal directions of magnetic susceptibility correspond to principal axes of the shape of the cavity elongation directions and axial ratios are reflected in the ams response which for simple geometries is explained by the anisotropy of the demagnetizing factor the experiments can be carried further for the analysis of pore structure in natural rock samples techniques developed for the injection of fractionated ferrofluid into a porous sandstone successfully lead to a homogeneous saturation of the sample the method potentially provides a new means to determine three dimensional pore fabric anisotropy and to relate it to the anisotropy of various petrophysical parameters

magnetic susceptibility of the rock matrix related to magnetic fabric studies non ferromagnetic minerals constitute what is called the rock matrix whose susceptibility k1 is directly accessible using only high magnetic fields measurements on minerals and a wide range of rock types show that k1 is mainly due to paramagnetism and hardly exceeds 10 3 si with an anisotropy degree p less than 1 35 different methods to estimate the role of the matrix component in low field susceptibility k and its anisotropy include petrological and chemical analysis evolution of p vs k low temperature studies and comparison of k with remanent magnetizations

kaolinitic meniscus bridges as an indicator of early diagenesis in nubian sandstones sinai egypt discussion j marcelo ketzer l fernando de ros and norberto daniuniversidade federal do rio grande do sul instituto de geocie ncias avenue bento gonc alves 9500 91501 970 porto alegre brazil e mail jm ketzer com br lfderos inf ufrgs br norberto dani ufrgs br keywords clay in ltration diagenesis kaolinite microtexture sandstone introductionthe recently published paper by du bernard c moraes de ros 1990 weibel 1998 salem et al 2000 fig 1a this is becausemechanical in ltration is most effective andextensive in semi arid climatic conditions kess ler 1978 walker et al 1978 moraes de ros 1990 under which smectitic clays are the mostcommon weathering products conversely kaoli nite is characteristically formed in humidclimatic conditions under which in ltration isuncommon or volumetrically insigni cant ketzer et al 2003a despite nding the occurrence described by dubernard carrio schaffhauser 2003 interesting we identi ed problems in their methodology anddiscussion the present discussion aims to com ment on these points and to suggest an alter native interpretation of the origin timing andeffects on compaction and reservoir quality of thedescribed clays in the nubian sandstones origin of kaolinitedu bernard carrio schaffhauser 2003 de scribed two types of kaolinite occurrence in thenubian sandstones i nely crystalline 1 5lm and ii coarsely crystalline aggregates 50lm the nely crystalline kaolinite consists of brown under uncrossed polarizers colour pore llingaggregates with meniscus shape a close inspec tion of the backscattered bse scanning elec tronic microscope sem images provided by dubernard and carrio schaffhauser their g 5cand d suggests that the meniscus aggregates arecomposed of several kaolinite booklets g 1b this morphology is typical of diagenetic authi genic kaolinite such evidence indicates an au thigenic origin for the nely crystalline kaolinite as opposed to the in ltrated origin proposed bydu bernard and carrio schaffhauser hence thiskaolinite most probably resulted from the in situreplacement of mechanically in ltrated possiblysmectitic clay minerals owing to active circula tion of meteoric water through the sandstones the origin of the uids responsible for thekaolinitization of the precursor in ltrated claysshould be constrained by o and h isotopicanalyses of the kaolinite morad et al 2003 the preservation of the meniscus morphology ofthe in ltrated clay aggregates after kaolinitizationresulted from the inheritance of the texture of theprecursor clay mineral by the kaolinite it is nosurprise that such preservation occurs as pseudo morphic replacement is rather common amongclay minerals e g in the chloritization or illiti zation of kaolinite morad et al 1998 de ros 1998 the variable in places random orientationof some kaolinite booklets is typical of authigenicaggregates and thus has no direct relationshipwith differences in water volume within themeniscus as suggested by du bernard andcarrio schaffhauser p 1227 additionally therelevance of the theoretical discussion on theaspects of the menisci geometry pp 1225 1227 to the interpretations of the authors is not clear x ray diffraction analysis from the 2 lmfraction revealed that kaolinite is the single claymineral present in the samples as shown in theprovided x ray diffractogram their g 4 thissedimentology 2005 52 213 217

geometry of the pamir hindu kush intermediate depth earthquake zone from local seismic data 1 we present new seismicity images based on a two year seismic deployment in the pamir and sw tien shan a total of 9532 earthquakes were detected located and rigorously assessed in a multistage automatic procedure utilizing state of the art picking algorithms waveform cross correlation and multi event relocation the obtained catalog provides new information on crustal seismicity and reveals the geometry and internal structure of the pamir hindu kush intermediate depth seismic zone with improved detail and resolution the relocated seismicity clearly defines at least two distinct planes one beneath the pamir and the other beneath the hindu kush separated by a gap across which strike and dip directions change abruptly the pamir seismic zone forms a thin approximately 10 km width curviplanar arc that strikes east west and dips south at its eastern end and then progressively turns by 90 to reach a north south strike and a due eastward dip at its southwestern termination pamir deep seismicity outlines several streaks at depths between 70 and 240 km with the deepest events occurring at its southwestern end intermediate depth earthquakes are clearly separated from shallow crustal seismicity which is confined to the uppermost 20 25 km the hindu kush seismic zone extends from 40 to 250 km depth and generally strikes east west yet bends northeast toward the pamir at its eastern end it may be divided vertically into upper and lower parts separated by a gap at approximately 150 km depth in the upper part events form a plane that is 15 25 km thick in cross section and dips sub vertically north to northwest seismic activity is more virile in the lower part where several distinct clusters form a complex pattern of sub parallel planes the observed geometry could be reconciled either with a model of two sided subduction of eurasian and previously underthrusted indian continental lithosphere or by a purely eurasian origin of both pamir and hindu kush seismic zones which necessitates a contortion and oversteepening of the latter

mantle dynamics in the mediterranean the mediterranean offers a unique opportunity to study the driving forces of tectonic deformation within a complex mobile belt lithospheric dynamics are affected by slab rollback and collision of two large slowly moving plates forcing fragments of continental and oceanic lithosphere to interact this paper reviews the rich and growing set of constraints from geological reconstructions geodetic data and crustal and upper mantle heterogeneity imaged by structural seismology we proceed to discuss a conceptual and quantitative framework for the causes of surface deformation exploring existing and newly developed tectonic and numerical geodynamic models we illustrate the role of mantle convection on surface geology a coherent picture emerges which can be outlined by two almost symmetric upper mantle convection cells the downwellings are found in the center of the mediterranean and are associated with the descent of the tyrrhenian and the hellenic slabs during plate convergence these slabs migrated backward with respect to the eurasian upper plate inducing a return flow of the asthenosphere from the backarc regions towards the subduction zones this flow can be found at large distance from the subduction zones and is at present expressed in two upwellings beneath anatolia and eastern iberia this convection system provides an explanation for the general pattern of seismic anisotropy in the mediterranean first order anatolia and adria microplate kinematics and may contribute to the high elevation of scarcely deformed areas such as anatolia and eastern iberia more generally the mediterranean is an illustration of how upper mantle small scale convection leads to intraplate deformation and complex plate boundary reconfiguration at the westernmost terminus of the tethyan collision

characterization of the magnetic fabric of rocks abstract an inextensive system of magnetic susceptibility anisotropy factors is suggested which is sufficient in the majority of practical applications for characterizing the magnetic fabric of rocks the system involves three newly devised factors the corrected anisotropy degree the shape factor and the difference shape factor the first of these characterizes the quantity of anisotropy somewhat better than the commonly used anisotropy degree the shape factor characterizes the quality of anisotropy i e the shape of the susceptibility ellipsoid in a convenient way its definition is based on a certain analogy between the anisotropy ellipsoid and the strain ellipsoid the difference shape factor can replace the shape factor when only the differences between the principal susceptibilities are given while the mean susceptibility is unknown

step drawdown test as a tool for the assessment of the nubia sandstone aquifer in east el oweinat area egypt the cretaceous nubia sandstone aquifer is the main aquifer in east el oweinat area along the egyptian sudanese borders and in ne africa east el oweinat project has been recently considered one of the main agricultural projects in the southwest of the egyptian western desert so the hydrogeological assessment for the nubia aquifer in east el oweinat area has been done through studying and characterising the hydraulic parameters and step drawdown test the well and aquifer losses coefficients c and b respectively the specific capacity and the well efficiency as well as the aquifer and aquitard thickness have been estimated and traced through a total of 46 wells that have been distributed through the study area in two sectors southern and northern for the purpose of further exploration the effective porosity hydraulic conductivity k and transmissivity t have been estimated for the wells in the northern sector in addition an aquifer assessment quality index has been introduced to assess and to rank the studied aquifer therefore it is concluded that the hydraulic and the step draw down parameters as well as the aquifer and aquitard thicknesses are prospective for further exploration to the north and the east of the northern sector in the study area the well efficiency is mostly affected by the studied parameters particularly the well loss coefficient the hydraulic parameters and the well design as well gis approach and arcgis software have been applied to delineate the spatial distribution of the well performance characteristics in order to compare between the studied groundwater wells and to integrate the different acquired data a set of isocontour maps have been introduced to match the lateral variation of the studied parameters and the aquifer potential to refer to the best direction for further underground water exploration

petrophysical and magnetic pore network anisotropy of some cretaceous sandstone from tushka basin egypt summary pore magnetic fabric is a well established technique for the determination of pore elongation and preferred directions for migration of the interstitial fluids this study further exemplify this technique on a set of the nubia sandstones through a comparison with the pore anisotropy obtained from measuring permeability in three orthogonal directions in a gaz permeameter the nubia sandstones are represented in tushka area south egypt by quartz arenite of large porosity 29 40 per cent which was measured on thin sections parallel and perpendicular to the bedding plane and petrophysically by helium pycnometry and ferrofluid injection at 1 bar pressure petrographically there is a detectable difference between the porosity values in the bedding plane and in the perpendicular direction indicating inhomogeneity in the pore space network distribution the petrophysical studies indicate large porosity and permeability values with some differences between the helium and ferrofluid porosity due to presence of micro pore spaces not accessible for the ferrofluid molecules having relatively high diameters and injected at low pressure an overall agreement is observed between the permeability anisotropy and the magnetic grain and pore fabrics magnetic anisotropy measured before and after ferrofluid injection the three fabrics are mainly dominated by a bedding parallel foliation in a few cases maximum permeability appears to be perpendicular to bedding within the bedding plane maximum pore elongation direction from ferrofluid injection is nnw for adindan and kesieba formations and nw for abu simbil formation the maximum pore elongation direction for abu ballas samples showed a direction fluctuating around the e w direction the main fault trends in tushka area the pore fabric of abu ballas formation seems therefore to be structurally controlled while it would be originated from palaeocurrent directions in the other formations

reservoir assessment and quality discrimination of kareem formation using integrated petrophysical data southern gulf of suez egypt abstract the middle miocene kareem formation represents one of the most important reservoirs in the gulf of suez egypt six boreholes locating throughout different structural trends in the southern province of the gulf of suez egypt were selected to study the reservoir properties of the kareem formation the study depends on integrated data of well logs and routine core analysis as well as seismic data the present study is an integrated study aims to study and discriminate the reservoir quality of the kareem sequence using various statistical techniques testerman statistical approach and stratigraphic modified lorenz sml plot were used in reservoir zonation principal component analysis pca and cluster analysis were used to identify the electrofacies distribution within the studied formation the well log data enabled characterizing the reservoir sequence into 6 electrofacies the available core analyses data and core description for the kareem formation 850 feet cored interval in morgan oil field enabled more accurate discrimination for the reservoir sequence into 13 hydraulic flow units 7 of them are potential flow units the studied sequence is differentiated into five lithologic petrophysical facies siltstone dolomitic siltstone dolomitic sandstone sandstone and friable sandstone the sandstone and friable sandstone facies are the best petrophysical facies the dolomite content is the main key factor for reducing the reservoir quality of the studied kareem sequence from the core data a total net pay thickness of 180 feet mostly composed of sandstone with some siltstone intercalations was assigned of fair quality he 14 7 kh 89 1 md so 28 8 reservoir quality index rqi 0 60 m flow zone indicator fzi 3 81 m reservoir potential index rpi 2 with few streaks of good to very good potential however the siltstone samples have less petrophysical potential than the sandstones

towards a mechanical model for the formation of the pannonian basin abstract new maps showing crustal and lithospheric thickness variations in the pannonian basin and the surrounding east alpine carpathian and dinaric mountains have been prepared on the basis of recent seismic seismologic and electromagnetic data a map presenting miocene faults of regional significance has been also constructed for the same region by using a wealth of recently available national and or more local studies it is suggested that observed crustal and lithospheric structural contrasts have been controlled primarily by neogene kinematic history of the region kinematic history is characterized by the following main patterns 1 1 indentation by adria and large scale backthrusting in the southern alps 2 2 eastward escape and extension of the eastern alps 3 3 extensional collapse in the pannonian basin area 4 4 formation of broad wrench fault systems along strike in the dinarides and southern carpathians and the western carpathians with dextral and sinistral shear respectively 5 5 compression and accretion of the external thrust and fold belt in the eastern carpathians these kinematic patterns are thought to be interrelated and all are manifestations of the late stage evolution of an overthickened orogenic wedge in order to arrive at a better understanding of the mechanism of extension which formed the pannonian basin deep crustal seismic profiles hydrocarbon exploration reflection lines and borehole data have been analyzed in the little hungarian plain this plain represents the transition zone between the alps and the pannonian lowlands and the results are illustrated by eight interpreted cross sections one result of regional importance is the clear recognition that the transdanubian central range at the southeastern flank of the little hungarian plain is composed of alpine pre senonian thrust sheets this finding marks the end of a century of debate the allochthony of the substrata of the pannonian basin can be now considered proven another result of more general interest is that these cross sections document the mode of lithospheric extension preexisting compressional detachment planes reactivate as low angle normal faults and lead to tectonic unroofing of deeply buried metamorphic terranes characterized by ductile flow along subhorizontal lineation

thrusting of the hindu kush over the southeastern tadjik basin afghanistan evidence from two large earthquakes we infer from the mechanisms and depths of two large earthquakes that the hindu kush is actively thrusting northwest over the tadjik basin and that the basin is closing rather than being displaced to the west teleseismic body waves were used to determine focal mechanisms and depths for the two largest shallow earthquakes on the southern edge of the basin the two earthquakes on june 24 1972 mb 6 0 and december 16 1982 mb 6 2 have seismic moments of 2 1018 n m and 6 1018 n m respectively focal mechanisms of both events indicate almost pure thrust faulting with nodal planes striking northeast southwest the inferred fault planes dip southeast at 20 for the first event and 50 for the second the p axes for both events are oblique to the direction of relative motion between india and asia suggesting that the pamir is overthrusting the basin to the west depths for both earthquakes are between 20 and 25 km and place them well below the tadjik basin sediments the depths and steep fault planes suggest that these earthquakes represent a downdip extension within the basement of shallow folding and thrusting seen in the sediments northwest of the events thus convergence in afghanistan between india and eurasia is taken up along southeast dipping thrust faults north of the hindu kush as well as by northward subduction under the southern part of the range

afghanistan structure greater india concept and eastern tethys evolution abstract the large and complex area between central asia and the arabia india block includes from north to south the tien shan and hindu kush kun lun hercynian belts the turkman farah rud and tanghla shan neokimmerian belt the zagros makran baluch himalayan alpine belt and relics of corresponding oceanic spaces the angarian or gondwanian affinities of the different blocks separated by these successive peri indian belts are discussed an interpretation is proposed for the paleogeographic and structural evolution of this area from early paleozoic to present this interpretation is based on geologic and paleomagnetic data and on global tectonic considerations the hindu kush kun lun pre hercynian ocean probably separated laurasia from gondwanaland it was an early paleozoic tethys tethys 1 the tien shan ocean may have been a marginal basin for the hindu kush kun lun ocean the turkman farah rud tanghla shan pre neokimmerian ocean resulted from the break up of the gondwanaland margin its opening seems to have been related to the pre hercynian ocean closure resulting in the formation of a new tethys tethys 2 its subsequent closure may also have been related to the opening of the zagros baluch indus tsang po pre alpine ocean tethys 3 according to this interpretation eurasia appears to have increased from early paleozoic to cenozoic by successive accretion of cratonic blocks which came from the south through the tethys this evolution can be compared to the similar mediterranean evolution this interpretation is in agreement with the greater india concept however the northern border of greater india differs according to the stage of the gondwanaland evolution which is considered actually greatest india extended north to the caledonian belt and consequently has recorded the whole history of the eastern tethys

modeling the evolution of continental subduction processes in the pamir hindu kush region several geological and geophysical studies suggest the presence of two converging subduction zones in the western syntaxis of the india eurasia collision zone with steep northward subduction of indian lithosphere beneath the hindu kush and southward subduction of asian lithosphere under the pamir we investigate the geometry and the timing of these subduction processes seismic tomography images are used to constrain the geometry of the two slabs under the pamir and the hindu kush by measuring the tomographically inferred length of the indian slab under the hindu kush region and by comparison with paleomagnetic reconstructions we estimate that the process of indian slab break off most likely occurred at the early stage of the collision at ca 44 48 ma we infer that after slab break off western india continued its northward motion until its northern boundary reached the present hindu kush region where it began to subduct we estimate an age for the initiation of subduction in this region of about 8 ma we apply 2d thermo kinematic and rheological numerical modeling to compute the temperature distribution and brittle field along two vertical sections across the hindu kush and pamir regions for the hindu kush we introduce parameters reproducing fast and near vertical subduction whereas in the pamir region we use the results from published studies to reproduce slower subduction modeling results indicate that faster subduction under the hindu kush results in a deeper brittle region which is consistent with observed deeper seismicity than in the pamir region

hercynian and eocimmerian events in afghanistan and adjoining regions abstract the area centered around afghanistan is a collage of continental blocks derived from gondwanaland this collage comprises among others 1 1 a hercynian orogenic belt widely represented in afghanistan and also by some sparse outcrops in the northern iran it is a subduction type orogen constructed at the margin between the paleotethys and the turan turkestan tarim block 2 2 a northern eocimmerian orogenic belt widely represented in afghanistan and the north of iran it is a collision type orogen constructed in the same place as the hercynian orogenic belt and resulted from the closure of the paleotethys and the collision of the central iran and central afghanistan blocks with the turan turkestan tarim block 3 3 a southern eocimmerian orogenic belt of which outcrops are now confined to southern iran but which may project beneath the neogene and quaternary formations of southern afghanistan it is a subduction type orogen constructed at the margin between the neotethys and the central iran central afghanistan block which itself was at that time subjected to regional extension this belt is now incorporated in the alpine himalayan orogen the geology of these belts suggests that the opening of the neotethys became effective only from the permian or triassic and was in a red sea type phase during the upper devonian its initial rifting possibly occurred during the lower paleozoic much like the paleotethys in which initial rifting also occurred in lower paleozoic time and whose opening became effective from the ordovician thus each of the oceanic realms in this region appears to have possibly resulted from the same extension of gondwanaland during the lower paleozoic after which they followed more or less different paths of evolution moreover the proposed geodynamic interpretation implies that during the permian and triassic there was in this region a certain coexistence of the vanishing paleotethys with the relatively young neotethys which was beginning to subduct

kaolinitic meniscus bridges as an indicator of early diagenesis in nubian sandstones sinai egypt abstract characteristic meniscus geometries formed by kaolinitic in ltration areobserved in nubian sandstones collected on the western coast of the sinaipeninsula egypt based on petrographic and scanning electron microscope sem observations the kaolinite forming the menisci consists of mixed sizediscrete platelets that gather into the corners around the framework grain to grain contacts speci cally the internal fabric of menisci indicates a generalorganizing trend from 1 the centre where the platelets coat the frameworkgrains 2 to the peripheral zone where they are oriented tangentially to grainsurfaces 3 to the pore linings with curvatures that are consistent withtheoretical considerations of air water interfaces this typical arrangementsuggests a detrital origin of kaolinite platelets by mechanical in ltration intosediments lying above the tablewater in vadose conditions this type of claycementation occurring during early diagenesis can prevent delay deep burialdiagenetic processes and therefore preserve excellent reservoir properties keywords clay minerals kaolinite nubian sandstone sandstone diagenesis introductionearly diagenesis of sediment can occur shortlyafter deposition depending on depositional envi ronment the early lithi cation i e the rstdeveloped bonding agent occurs as carbonateprecipitation or particle in ltration that linksframework grains by forming meniscus bridges such grain to grain bridges grow preferentially inthe corners of pore space close to grain contacts dunham 1971 speci cally by developing inconformity to the water air interface the menis cus as a result of differential capillarity pres sures these cements or in ltrating material areassumed to be related to vadose environments dunham 1971 the meniscus geometry forming pore roundinghabit has been described frequently in modernsedimentary environments where carbonate pre cipitation produces beachrocks from carbonatesands meyers 1987 hillga rtner et al 2001 these types of precipitated meniscus cementsconsist mainly of crypto to microcrystallinecalcite or aragonite that display laments whichgenerally grow perpendicular to grain rim miller 1988 rao et al 1994 hillga rtner et al 2001 incontrast precipitated menisci of goethitic ferru ginous material have been reported for a lateriticpro le in basalt horva th et al 1999 several studies have also dealt with the men iscus shape displayed by mechanically in ltratedclay particles in clastic sediments walker 1976 kessler 1978 meyers 1987 matlack et al 1989 moraes de ros 1990 owing to the micro metre scale size of particles the detrital clays aretransported along connected pores by uidscirculating between skeleton grains walker 1976 during a drying period the detrital claysgather where the capillarity pressure preserves uids therefore the accumulated clays exhibitgrain coatings and meniscus shaped bridgeslinking neighbouring grains thus the meniscuscements typically indicate vadose conditionswhere pore spaces are not permanently saturated i e water table level uctuates walker 1976 matlack et al 1989 moraes de ros 1990 sedimentology 2003 50 1221 1229

a note on the depth recurrence and strain release of large vrancea earthquakes the large 1940 vrancea event with body wave magnitude mb 7 3 was investigated in terms of the depth of rupture initiation and extent it was found that the rupture started at 150 km depth and propagated downwards the ruptured zones of the 1977 1986 and 1990 vrancea events were estimated from the distribution of aftershocks located with the joint hypocentre determination method their depth ranges are 90 110 km 130 150 km and 70 90 km respectively because the body wave magnitudes mb were saturated for the last three events and the surface wave magnitudes ms were underestimated not being corrected for depth we chose the moment magnitudes to quantify the four events 7 7 1940 7 4 1977 7 1 1986 and 6 9 1990 respectively the depth interval 110 130 km is found to be unbroken since at least 1838 or 1802 and therefore is expected to accommodate the next large moment release mw 7 0 to 7 4 the strain in the vertical and in the se nw directions is about 0 0003 giving a moderate strain rate of about 10 13 s 1 a correlation between the depth interval of the large events and the year of occurrence in a century is suggested offering a physical basis to the observed quasi cyclicity

correlation between rock fabrics and physical properties of carbonate reservoir rocks three carbonate core samples from an oil and gas reservoir of the nw german basin were chosen to study the correlation between rock fabrics and physical properties of reservoir rocks detailed fabric analyses and texture investigations were carried out as well as laboratory measurements of different physical properties e g density porosity permeability electrical conductivity seismic compressional and shear wave velocities although the three core samples come from a similar depositional facies they show great differences in the occurrence and three dimensional distribution of the rock fabric elements these heterogeneities are the result of various diagenetic and tectonic processes for the correlation between the rock fabrics and the physical properties four main rock fabric types have to be considered a major constituents e g fossils ooides peloides and crystals b pore space with different pore types c fractures and d stylolites the results of the correlation clearly show that the values and anisotropies of the petrophysical properties are fairly related to the observed fabric elements with their different arrangements spatial distributions and preferred orientations these results also provide a fundamental understanding of the petrophysical responses such as seismics to the different geological features e g fractures and their dynamic changes with pressure which can be converted to different depths the knowledge gained from such correlations may lead to an improved interpretation of geophysical data for hydrocarbon exploration and production and therefore to an advanced reservoir characterization

quantitative reconstruction of orogenic convergence in the northeast carpathians abstract the ne outer carpathians form a fold and thrust belt of large displacement this mainly consists of deformed cretaceous tertiary deep water clastics and can be divided into an imbricate stack of four major supracrustal nappes the magura dukla silesian and skole nappes an extensive reflection seismic surface geological and drillhole database is used to constrain the deformed geometry of the two uppermost and southernmost allochthonous units the magura and dukla nappes a retro deformable cross section shows that the cretaceous tertiary sediment piles are detached along a single large decollement at about 5 7 km depth the rear and frontal parts of the magura nappe show steep imbricate fan geometries while the central part has a duplex structure with long thrust horses to the ne the dukla nappe is a stack of imbricate slices and is separated from the subjacent silesian nappe by a large thrust flat reverse modelling of deformation reveals that the magura nappe was horizontally shortened by at least 80 km and the dukla nappe by about 20 km in the ne sw direction together with previously published estimates of shortening in the silesian and skole nappes the total orogenic contraction in the ne outer carpathians is at least 260 km shortening was accumulated between the middle oligocene and the middle miocene almost all of the shortening can be balanced against contemporaneous back arc extension and eastward extrusion of rock masses from the eastern alps

magnetic pore fabric analysis a rapid method for estimating permeability anisotropy summary the average orientation and fabric anisotropy of interconnected pore spaces in sandstones is derived from magnetic pore fabric analysis a new technique which measures the anisotropy of magnetic susceptibility ams of samples impregnated with a magnetic suspension in magnetic pore fabric analysis the permeable part of the porous network consisting of pore bodies connected by pore throats is rendered magnetically susceptible ams directly yields the average elongation direction of pore bodies and offers a simple way to investigate the effect of pore shape anisotropy on petrophysical parameters such as hydraulic and electrical conductivity ams derived pore fabric of sandstones of moderate diagenetic state is compared to permeability anisotropy measured directly on the same specimens for any one sample the orientation of the two tensors and their representation ellipsoids correlate closely the preferred orientation of interconnected pores facilitates fluid flow parallel to the direction of pore elongation and causes the observed anisotropy of permeability axial ratios of the two anisotropy ellipsoids correlate less closely but show a trend of proportionality compared to the time consuming measurement of directional permeabilities magnetic pore fabric analysis may therefore provide a rapid way to estimate the orientation and to a lesser extent the degree of permeability anisotropy in porous sandstones the analysis of six specimens extracted from a large homogeneous block sample proves the accuracy and reliability of the method in five fluvial sandstone samples maximum permeability and pore elongation are roughly parallel to the palaeocurrent direction therefore magnetic pore fabric analysis can also be used to study the relationship between permeability pore fabric and sedimentary structures

geological setting of the lower pleistocene fossil deposits of chilhac haute loire france the chilhac deposits ch2 and ch3 have long been known to contain exceptionally well preserved late pliocene now lower pleistocene fossils as well as alleged pebble culture artifacts found in ch3 attesting to the presence of hominins the geological complexity of the deposits in the small valley previously prevented ascertaining their stratigraphic position recent farm extension upstream the deposits provided a continuous profile and revealed previously unknown geological structures additional trenches dug at the margins of the chilhac deposits confirm the superposition of a lava flow ca 1 8 ma on the ch2 sediments after a major phase of erosion and allowed correlation of these deposits with those of ch3 another lava flow topographically inverted provides an upper limit of 2 5 ma for the age of the deposits these new observations also reveal that the valley underwent several cycles of erosion the structural complexity of the ch3 deposits suggests a landslide event affecting surface deposits volcanic tuffs and the upper part of ch2 sediments this landslide probably occurred shortly after the deposition of the ch2 sediments and the volcanic eruption these observations are compatible with the age of 2 2 ma inferred from the ch2 and ch3 fauna mnq17 biozone

comparison between permeability anisotropy and elasticity anisotropy of reservoir rocks we developed new experimental and theoretical tools for the measurement and the characterization of arbitrary elasticity tensors and permeability tensors in rocks they include an experimental technique for the 3 d visualization of hydraulic invasion fronts in rock samples by monitoring the injection of salt solutions by x ray tomography and a technique for inverting the complete set of the six coefficients of the permeability tensor from invasion front images in addition a technique for measuring the complete set of the 21 elastic coefficients a technique allowing the identification and the orientation in the 3 d space of the symmetry elements planes axes and a technique for approximating the considered elastic tensor by a tensor of simpler symmetry with the quantification of the error induced by such an approximation have been developed we apply these tools to various types of reservoir rocks and observed quite contrasted behaviors in some rocks the elastic anisotropy and the hydraulic anisotr

review of diagenetic facies in tight sandstones diagenesis diagenetic minerals and prediction via well logs abstract the tight sandstones are characterized by low porosity low permeability complex pore structure and strong heterogeneity due to the extensive diagenetic modifications they experienced understanding of the impact of diagenetic alterations on reservoir quality is crucial to the hydrocarbon exploration and production in tight sandstones diagenetic facies which is the comprehensive description of the diagenesis and diagenetic minerals determines the formation and distribution of sweet spot by correlating the diagenetic facies to well log responses the subsurface distribution of porosity and permeability can be predicted however the prediction of diagenetic facies and reservoir quality via well logs in tight sandstones remains a challenging task this paper critically reviews the impact of diagenesis and diagenetic minerals on reservoir quality in tight sandstones and establishes a model for prediction of diagenetic facies via well logs as assessed from peer reviewed papers in the literature as well as from the authors personal experiences this review begins with reviewing the impacts of compaction cementation dissolution and various types of diagenetic minerals on reservoir quality evolution the definition and classification schemes of diagenetic facies are then discussed and the reservoir quality as well as diagenetic evolution sequence of various diagenetic facies is summarized the same diagenetic facies commonly display similar compositional and textural attributes matrix and cement as well as porosity systems the well log responses gr ac den cnl and rt of various diagenetic facies are summarized by the calibration of log values with cores and related thin sections by translating the diagenetic facies to conventional well logs a predictable model which can be used for subsurface reservoir quality prediction is established then the theory of ecs logs is reviewed and the application of ecs logs in diagenetic facies evaluation is discussed at last the quantitative characterization for various type and degree of diagenesis is reviewed and the subsurface diagenetic facies is predicted by quantitative calculation of the compactional porosity loss cementational porosity loss and dissolution porosity content via well logs correlating the diagenetic facies to well logs provides a powerful tool to predict the distribution of high quality reservoirs in tight sandstones this review will provide insights into the reservoir quality evaluation and sweet spot prediction via well logs in tight sandstones

pore throat characterization in highly porous and permeable sandstones several methods have been developed to characterize the pore spaces in sandstone reservoirs using data on the pore throat size distribution obtained from mercury injection tests the winland equation the threshold pressure the displacement pressure and pittman s equation are mostly used for this purpose to delineate the stratigraphic traps and seals this study examines the reliability of these methods applied to the highly permeable nubia sandstones in their type section in southern egypt these sandstones are composed mainly of siliceous sandstones and constitute the main paleozoic cretaceous aquifers and reservoirs in egypt routine core analysis and mercury injection tests were conducted to delineate the pore network characteristics for these rocks the relationships between helium porosity and the uncorrected air permeability from the routine core analysis and the various parameters derived from mercury injection capillary pressure curves were established using multiple regressions this study indicates the high reliability of the displacement pressure at 10 mercury saturation and also reveals the apex of pittman s hyperbole at 45 mercury saturation as a complexity apex at which the pore network becomes highly chaotic despite the great benefits of such types of measurements they are not commonly used because of their high cost this study introduces a series of empirical equations for constructing a partial pore aperture size distribution curve from routine core analysis for the highly permeable rocks

gps velocity field for the tien shan and surrounding regions 1 measurements at 400 campaign style gps points and another 14 continuously recording stations in central asia define variations in their velocities both along and across the kyrgyz and neighboring parts of tien shan they show that at the longitude of kyrgyzstan the tarim basin converges with eurasia at 20 2 mm yr nearly two thirds of the total convergence rate between india and eurasia at this longitude this high rate suggests that the tien shan has grown into a major mountain range only late in the evolution of the india eurasia collision most of the convergence between tarim and eurasia within the upper crust of the tien shan presumably occurs by slip on faults on the edges of and within the belt but 1 3 mm yr of convergence is absorbed farther north at the dzungarian alatau and at a lower rate with the kazakh platform to the west the tarim basin is thrust beneath the tien shan at 4 7 mm yr with respect to eurasia the ferghana valley rotates counterclockwise at 0 7 myr 1 about an axis at the southwest end of the valley thus gps data place a bound of 4 mm yr on the rate of crustal shortening across the chatkal and neighboring ranges on the northwest margin of the ferghana valley and they limit the present day slip rate on the right lateral talas ferghana fault to less than 2 mm yr gps measurements corroborate geologic evidence indicating that the northern margin of the pamir overthrusts the alay valley and require a rate of at least 10 and possibly 15 mm yr

relating pore fabric geometry to acoustic and permeability anisotropy in crab orchard sandstone a laboratory study using magnetic ferrofluid pore fabric anisotropy is a common feature of many sedimentary rocks in this paper we report results from a comparative study on the anisotropy of a porous sandstone crab orchard using anisotropy of magnetic susceptibility ams acoustic wave velocity and fluid permeability techniques initially we characterise the anisotropic pore fabric geometry by impregnating the sandstone with magnetic ferro fluid and measuring its ams the results are used to guide subsequent measurements of the anisotropy of acoustic wave velocity and fluid permeability these three independent measures of anisotropy are then directly compared results show strong positive correlation between the principal directions given from the ams velocity anisotropy and permeability anisotropy permeability parallel to the macroscopic crossbedding observed in the sandstone is 240 higher than that normal to it p and s wave velocity anisotropy and ams show mean values of 19 1 4 8 and 3 8 respectively reflecting the disparate physical properties measured

reservoir quality in the jurassic sandstone reservoirs located in the central graben north sea abstract this study investigates the diagenesis and reservoir quality of upper jurassic sandstones of ula formation from the central graben petrophysical and petrographical studies have been done on cored interval from well 2 1 6 of ula field precipitation of quartz cement is the main porosity destroying process in deeply buried quartz rich sandstone reservoirs of the north sea quartz cement precipitates in the form of syntaxial overgrowth over detrital grain of quartz grain coatings like micro quartz and illite are the main reasons for preservation of porosity in sandstones as they cover the grain and inhibit the quartz overgrowth petrographical data in this study clearly indicates that grain coatings are present in the studied samples micro quartz grain coating is the most common grain coat in the upper jurassic sandstones of ula which is generated from the transformation of siliceous sponge spicules known as rhaxella perforata clay grain coats like illite and chlorite are also present relation between intergranular volume igv versus matrix and quartz cementation versus porosity have also been studied igv is strongly affected by mechanical compaction grain size grain shape quartz and carbonate cements sandstones with high amount of matrix and fine grains have high igv as compared to coarse grains because coarse grains are compacted more when they are subjected to mechanical compaction grain shape also has a pronounced effect on porosity angular grains tend to lose porosity easier as they are subjected to stress

active faulting and tectonics of burma and surrounding regions this study of the active tectonics of burma and surrounding regions is based mostly on an interpretation of landsat imagery and on fault plane solutions for shallow and intermediate earthquakes fold axes in the indoburman ranges and an east dipping inclined zone of intermediate depth earthquakes suggest that a slab of oceanic lithosphere was recently subducted to the east under the indoburman ranges fault plane solutions of shallow earthquakes however do not show underthrusting at the present time instead p axes are oriented roughly north south parallel not perpendicular to the fold axes in the ranges p axes for fault plane solutions of intermediate shocks also trend north south parallel to the strike of the subducted slab and may indicate that the hanging slab is being dragged north by india through the surrounding asthenosphere the sagaing fault probably accommodates most of the right lateral slip of india past indochina but india s northward movement also causes internal deformation within burma thailand and yunnan differences between the tectonic fabric seen on the landsat images and the tectonic regime compatible with the fault plane solutions throughout the region imply major changes in the directions of relative motion in the orientations of strain and in the style of deformation in the late cenozoic presumably these changes reflect the transition from subduction to collision and strike slip motion as india penetrated into eurasia past burma large parts of burma and thailand may have rotated several tens of degrees clockwise in this process

magnetic pore fabric analysis verification through image autocorrelation the pore fabric of sandstones is studied by impregnating porous samples with a magnetic suspension ferrofluid and subsequently measuring their anisotropy of magnetic susceptibility ams similar to the use of natural ams for estimation of grain fabric we determine average orientation and shape anisotropy of pore bodies in three dimensions this new approach overcomes restrictions of previous methods of pore structure characterization the interpretation of ams in terms of pore fabric anisotropy is tested by comparison with pore shape observed in thin section an image analytical technique is used to derive statistically the elongation direction of digitized pore cross sections by computing the two dimensional autocorrelation function we obtain section ellipses reflecting average pore shape and orientation combination of ellipses of three mutually perpendicular images leads to fabric ellipsoids comparable to ams comparison of the two anisotropies shows a close correspondence between the principal axis directions of ams and fabric ellipsoids owing to the bedded nature of the samples the ellipsoids are of oblate shape with minimum axes perpendicular to bedding however even small anisotropies within the bedding plane can be detected successfully axial ratios of ams and fabric ellipsoids correlate closely if rock sample ams is corrected for pore directional scattering the method represents a powerful tool to analyze pore fabric of sedimentary rocks and to study its effects on petrophysical properties

electric pore fabric of the nubia sandstones in south egypt characterization and modelling summary this study testifies the reliability of the electric pore fabric technique applied on the nubia sandstones in south egypt through a comparison with pre assigned magnetic pore fabric and permeabilityalreadymeasuredforthreeperpendiculardirectionsintheserocks discrepancies between the different techniques were attributed to the fact that the magnetic pore fabric technique has the ability to detect and define accurately the pore volume distribution in 3 d whereas the electric pore fabric technique has the ability to detect the shortest paths for the electric current fluid flow although the magnetic pore fabric is a bulk property the permeability measurements and the electric pore fabric are quantifying transport properties both the magnetic and electric pore fabrics refer mostly to slightly and moderately anisotropic fabrics the integration between both techniques revealed two main directions for fluid migration swinging to the n s and the e w directions one difficulty of the electric pore fabric technique is due to the surface conductivity effects either from the presence of some clay minerals or cracks therefore interpreting the obtained electric pore fabric must be carried out in care for the cracked and clayey rocks the surface conductivity effect could be accounted for by using the true formation factor for calculating the electric pore fabric parameters the electric pore fabric technique can be compared to the 3 d permeability measurements which show very similar directions

seismic imaging of subducting continental lower crust beneath the pamir abstract exhumation of ultra high pressure metamorphic rocks testifies that the continental crust can subduct to significant depth into the mantle despite its buoyancy however direct observation of ongoing subduction of continental crust is rare the pamir is regarded as a possible place of active continental subduction because of the intermediate depth seismicity crustal xenoliths and estimates of crustal shortening versus convergence rates here we present for the first time receiver function images from a passive source seismic array traversing the tien shan and the pamir plateau showing southward subduction of eurasian continental crust in the eastern pamir we observe a southerly dipping 10 15 km thick low velocity zone lvz that extends from 50 km depth near the base of the crust to more than 150 km depth with a dip angle increasing to subvertical while the upper and mid crustal material seems to be shortened and incorporated into the pamir the lower eurasian crust detaches and subducts in its deeper part 80 km the lvz envelopes the intermediate depth earthquakes our observations imply that the complete arcuate intermediate depth seismic zone beneath the pamir traces a slab of subducting eurasian continental lower crust