intensity of the geomagnetic field in western europe over the past 2000 years new data from ancient french pottery 1 we studied 14 groups of french pottery fragments dated between the 4th and 16th centuries the potsherds were analyzed using the thellier and thellier 1959 method revised by coe 1967 intensity values were corrected for thermoremanent magnetization trm anisotropy and cooling rate dependence of trm acquisition we first analyzed modern ceramics produced following ancient techniques and fired in a wood burning kiln inside of which field intensity was measured the recovered mean intensity is within 3 of the expected value which proves the reliability of our experimental procedure thermal experiments carried out at rapid and slow cooling rates clearly indicate that the cooling rate correction is critical in archeointensity studies our data indicate that large variations in intensity occurred in france over the last 2000 years two relative maxima in intensity are observed one between the 8th and 10th centuries and the second between the 14th and 15th centuries similarities are observed between the archeointensity data from france and ukraine yielding some evidence for eastward drift of geomagnetic sources between western and eastern europe from a d 800 to a d 1700 we also show that the dipole moment evolution proposed by mcelhinny and senanayake 1982 and yang et al 2000 for the last two millennia is likely biased toward higher values mainly because of the absence of correction for the cooling rate dependence of trm acquisition in most published archeointensity studies we finally underline a possible relationship valid at least in western europe between changes in direction and intensity of the geomagnetic field

impact of early dolomitization on multi scale petrophysical heterogeneities and fracture intensity of low porosity platform carbonates albian cenomanian southern apennines italy abstract petrographic petrophysical and fracture analyses were carried out on middle cretaceous platform carbonates of the southern apennines italy that represent an outcrop analogue of the val d agri and tempa rossa reservoirs of the basilicata region the studied outcrops which are made of interlayered limestones and dolomites of inner platform environment were selected to study the impact of dolomitization on reservoir properties and the control of dolomite texture on fracture development two types of dolomites both formed during very early diagenesis were found interlayered at a metre scale with micrite rich limestones mainly mudstones and wackestones dolomite a is fine to medium crystalline and makes non planar mosaics dolomite b is coarse crystalline and makes planar s and planar e mosaics the intercrystalline space of the planar e subtype of dolomite b is either open or filled by un replaced micrite or by late calcite or saddle dolomite cement dolomite a and dolomite b have similar average porosities of 3 7 and 3 1 respectively which are significantly higher than the average porosity of limestones 1 4 their poro perm relationships are similar with the notable exception of planar e type b dolomites which generally display higher permeability values the intensity of top bounded fractures is distinctly lower in coarse crystalline dolomites than in fine crystalline dolomites and limestones both at the macro and the micro scale on the other hand neither lithology i e limestone vs dolomite nor dolomite crystal size control the intensity of perfect bed bounded fractures which is strictly controlled by the fracture layer thickness our results provide information that could be used as guidance for the characterization and modelling of fractured carbonate reservoirs made of interlayered limestones and dolomites

a simplified method to estimate saturated and unsaturated seepage through dikes under steady state conditions the seepage rate through homogeneous or zoned dikes includes saturated and unsaturated flow the latter is often neglected but should be considered to obtain the positions of the water table and the seepage face that may develop either on the downstream slope of a homogeneous dike or within the filter layer behind the core of a zoned dike different dikes with heights of 5 10 20 and 50 m have been analyzed numerically with a two dimensional finite element code the cases investigated include the most frequent types of small dikes designed to retain municipal or industrial wastewater solutions are proposed to solve numerically two difficulties related to the representation of saturated and unsaturated physical flow conditions one difficulty is treating a downstream seepage face the other is treating the passage of water from the core into a draining layer the paper presents simple expressions to predict the total saturated and unsaturated seepage flow rate through a dike and discusses precautions

lithologic controls on morphology of pressure dissolution surfaces stylolites and dissolution seams in paleozoic carbonate rocks from the mideastern united states abstract examination of pressure dissolution surfaces stylolites and dissolution seams in carbonate rocks from the mideastern u s demonstrates that the morphology of these surfaces varies with rock fabric one can quantify the morphology of these pressure dissolution surfaces using four parameters thickness t of the insoluble residue defining the surface amplitude of irregularity i of the surface between vertical offsets amplitude of vertical offsets o of the surface and frequency f of vertical offsets along the surface i and o increase with t reflecting progressive development of stylolites whereas f is proportional to 1 t apparently because the physical strength of a stylolite inhibits the formation of offsets mean values of f o and t are greater in grainstones and packstones than in mudstones and wackestones and the abundance of dissolution seams relative to that of stylolites decreases through the lithologic spectrum from mudstones to grainstones these relationships suggest that development of pressure dissolution surfaces to form large stylolites depends on the heterogeneity of the limestone fabric maximum values of t and o in grainstones correlate with cement abundance t and o are low in grain rich cement poor grainstones even though grains are favored as leading or penetrating elements of stylolite columns dissolution seams surfaces with o and f near zero are found only in rocks containing fine grained dolomite t and i of those seams decrease with increasing dolomite abundance in dolomitic limestones and t and o are lower in dolostones than in limestones taken together these relationships suggest that extreme abundance of pressure resistant components such as carbonate grains and dolomite inhibit development of pressure dissolution surfaces in contrast stylolites are most extensively developed i e i t o and f are greatest in carbonate rocks in which these pressure resistant elements are mixed with less resistant components such as cement and carbonate mud the latter rocks which include packstones well cemented grainstones and slightly dolomitic limestones may undergo preferential removal from the stratigraphic record by pressure dissolution

origin and timing of dauphine twins in quartz cement in fractured sandstones from diagenetic environments insight from fluid inclusions abstract electron backscattered diffraction techniques ebsd show that dauphine twins in quartz are widespread in many tectonometamorphic environments our study documents that under diagenetic temperatures

geomagnetic field for 0 3 ka 2 a new series of time varying global models 1 steadily increasing numbers of archeomagnetic and paleomagnetic data for the holocene have allowed development of temporally continuous global spherical harmonic models of the geomagnetic field extending present and historical global descriptions of magnetic field evolution the current work uses various subsets of improved data compilations details of which are given in a companion paper by donadini et al 2009 and minor modifications of standard modeling strategies using temporally and spatially regularized inversion of the data and cubic spline parameterizations for temporal variations to produce five models with enhanced spatial and temporal resolution for 0 3 ka spurious end effects present in earlier models are eliminated by enforcing large scale agreement with the gufm1 historical model for 1650 1990 a d and by extending the model range to accommodate data older than 3 ka age errors are not considered as a contribution to data uncertainties but are included along with data uncertainties in an investigation of statistical uncertainty estimates for the models using parametric bootstrap resampling techniques we find common features but also significant differences among the various models indicating intrinsic uncertainties in global models based on the currently available holocene data model cals3k 3 based on all available archeomagnetic and sediment data without a priori quality selection currently constitutes the best global representation of the past field the new models have slightly higher dipole moments than our previous models virtual axial dipole moments vadms calculated directly from the data are in good agreement with all corresponding model predictions of vadms these are always higher than the spherical harmonic dipole moment indicating the limitations of using vadms as a measure of geomagnetic dipole moments

practical approaches to identifying sealed and open fractures for one essential ingredient of permeable fracture networks degree of fracture pore space preservation in large fractures i show how the characterization challenge presented by sparse fracture sampling can be overcome by measuring a surrogate the abundance of rock mass cement that precipitated after fractures ceased opening sampling limitations are overcome because the surrogate is readily measured in small rock samples including sidewall cores and cuttings permitting site specific diagnosis of the capacity of fractures to transmit fluid over a wider range of sample depths than conventional methods allow a diverse core database shows that this surrogate correctly predicts where large fractures are sealed information on timing of fracture opening relative to cement sequence can be obtained in two ways first evidence of fracture movement history and cement sequences in sparse large fractures can be extrapolated to areas having only cement data alternately evidence of fracture timing can be acquired from sealed micrometer scale fractures distribution of porosity reducing cement is commonly heterogeneous from bed to bed and location to location in siliciclastic and carbonate rocks however because patterns of sealed or open fractures cannot be delineated using fracture observations alone surrogates have practical value for production fairway mapping and other applications in which identifying open fractures is essential this study highlights the vital interplay among structural and diagenetic processes for fracture porosity preservation or destruction

impact of pore structure and fractal characteristics on the sealing capacity of ordovician carbonate cap rock in the tarim basin china abstract evaluating the heterogeneity and sealing capacity of carbonate cap rocks is of great significance for hydrocarbon production however the main controls on pore size distribution in carbonate cap rocks are not well constrained in this contribution we analyze drill core samples of carbonate cap rocks from the ordovician yingshan formation tarim basin to study their pore properties and investigate the controls of pore throat structure and fractal dimension on the sealing capacity of the cap rock results from petrography and a combination of mercury injection capillary pressure and nitrogen gas adsorption tests reveal that there are four lithological cap rock types with micrite being the most prevalent one followed by calcarenite six types of pore throat structures and fractal dimensions from d1 to d6 are classified based on the pore size distributions including macropore i macropore ii mesopore i mesopore ii transitional pore i and transitional pore ii the fractal dimensions show that there is a decreasing trend from d1 to d6 with decreasing pore size diameter suggesting that the macropore and mesopore types present more complex pore throat structures than the transitional type the total fractal dimension dtotal indicates that the pore throat structures are complex and heterogeneous the sealing heights of the gas column have a positive correlation with cement content in calcarenite and a negative correlation with microfracture density mesopore ii and transitional pore types make a significant contribution to enhancing the breakthrough pressure the fractal variations mainly result from macropores and mesopores while transitional pores and micropores weaken the impact of the whole pore system on the dtotal value the heterogeneity and anisotropy of macropores is the main control on the sealing capacity of the cap rock the increasing of d1 considerably contributes to the pore shape heterogeneity and enhances the capillary resistance force to hydrocarbon migration therefore the fractal dimension is an effective approach for investigating the pore throat structure and sealing capacity of carbonate cap rocks

geomagnetic field intensity how high can it get how fast can it change constraints from iron age copper slag article the intensity of the geomagnetic field varies over different time scales yet constraints on the maximum intensity of the field as well as for its maximum rate of change are inadequate due to poor temporal resolution and large uncertainties in the geomagnetic record the purpose of this study is to place firm limits on these fundamental properties by constructing a high resolution archaeointensity record of the levant from the 11th century to the early 9th century bce a period over which the geomagnetic field reached its maximum intensity in eurasia over the past 50 000 years we investigate a 14 c dated sequence of ten layers of slag material which accumulated within an ancient industrial waste mound of an iron age copper smelting site in southern israel depositional stratigraphy constrains relative ages of samples analyzed for paleointensity and 14 c dates from different horizons of the mound constrain the age of the whole sequence the analysis yielded 35 paleointenisty data points with accuracy better than 94 and precision better than 6 covering a period of less than 350 years most probably 200 years we construct a new high resolution quasi continuous archaeointensity curve of the levant that displays two dramatic spikes in geomagnetic intensity each corresponding to virtual axial dipole moment vadm in excess of 200 zam 2

microfractures in the middle carboniferous carbonate rocks and their control on reservoir quality in the zanaral oilfield abstract fractures are considered an important controlling factor for hydrocarbon accumulation in the pre salt carbonate reservoirs of the zanaral oilfield they are also a precondition for the high and stable production of oil and gas based on core observations and descriptions systematic sampling analysis including rock mineral composition analysis petrographic thin sections stained thin sections porosity and permeability the study about the characteristics and major controlling factors of microfractures and their influence on the reservoir seepage capacity was performed on wells 2399a and 2092 the results suggest that although there are few macrofractures microfractures are common in the study area there are several types of microfractures principally including micro tectonic fractures grain breakage fractures microstylolites and micro corrosion fractures the micro tectonic fractures especially those with relatively large apertures are mostly completely filled with calcite the formation of micro tectonic fractures is related to calcite filled macrofractures but unrelated to bitumen filled fractures the distribution of grain breakage fractures microstylolites and micro corrosion fractures differs substantially among the various wells and layers most of the grain breakage fractures are partially filled with calcite or barren and the major corrosion fractures are partially filled with calcite the non tectonic factors controlling the distribution of microfractures are complicated and variable and include facies and differential diagenesis micro tectonic fractures formation is promoted by the local enrichment of brittle minerals small grain size and strong cementation grain breakage fractures are dominant in pure limestones with coarse grains and abundant intergranular pores microstylolites mainly distribute in tight limestones with more impurities and fine grained micro corrosion fractures are associated to porosity density dolomite and acid insoluble residues contents of the limestones intermediate between those of grain breakage fractures and microstylolites dolomite and acid insoluble residues were probably concentrated by the formation of stylolites by contrast low acid insoluble residue content facilitates the formation of corrosion fractures fractures could significantly enhance the seepage capacity of the reservoirs in the study area the contribution of microfractures to reservoir seepage is given by stylolites tectonic fractures corrosion fractures and grain breakage fractures in this order high degrees of filling of the tectonic fractures greatly affect their seepage capacity

acid sulfate alteration of fluorapatite basaltic glass and olivine by hydrothermal vapors and fluids implications for fumarolic activity and secondary phosphate phases in sulfate rich paso robles soil at gusev crater mars 1 phosphate rich rocks and a nearby phosphate rich soil paso robles were analyzed in gusev crater mars by the mars exploration rover spirit and interpreted to be highly altered possibly by hydrothermal or fumarolic alteration of primary phosphate rich material to test mineral phases resulting from such alteration we performed hydrothermal acid vapor and acid fluid experiments on olivine ol fluorapatite ap and basaltic glass gl as single phases and a mixture of phases minerals formed include ca al fe and mg sulfates with different hydration states anhydrite bassanite gypsum alunogen hexahydrite and pentahydrite phosphate bearing minerals formed included monocalcium phosphate monohydrate mcp acid vapor and acid fluid alteration of fluorapatite only and ferrian giniite acid fluid alteration of the ol gl ap mixture mcp is likely present in paso robles if primary ca phosphate minerals reacted with sulfuric acid with little transport of phosphate under fluid rock ratios allowing transport of phosphate a ferric phosphate phase such as ferrian giniite might form instead mossbauer measurements of ferrian giniite bearing alteration products and synthetic ferrian giniite are consistent with spirit s mossbauer measurements of the ferric bearing phase in paso robes soil but are also consistent with ferric sulfate phases in the low p soil arad samra therefore mossbauer data alone do not constrain the fluid rock ratio however the excess iron hematite in paso robles soil which implies aqueous transport combined with our laboratory experiments suggest acid sulfate alteration in a hydrothermal fumarolic environment at fluid rock ratios sufficient to allow dissolution transport and precipitation of secondary chemical components including a ferric phosphate such as ferrian giniite

on archeomagnetic secular variation curves and archeomagnetic dating abstract secular variation sv of the earth s magnetic field can be used for dating purposes by comparing archeomagnetic directions of unknown ages with a well dated reference curve in this study we propose a dating technique based on the statistics of mcfadden and mcelhinny geophys j int 103 1990 725 for testing the hypothesis that two fisherian distributions of individual directions share a common mean direction the statistics are adapted to test the degree of compatibility between one individual fisherian mean direction and a reference curve constructed using the bivariate extension of the fisher distribution furthermore as the density of the data which define the archeomagnetic reference curve varies in time we suggest that one computes the mean directions with moving windows of varying duration where both the window widths and the time shifts between successive mean directions are fixed when a minimum threshold density of data is reached within each time interval in our paper we apply this new procedure to the french archeomagnetic data set

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

bottom up control of geomagnetic secular variation by the earth s inner core temporal changes in the earth s magnetic field known as geomagnetic secular variation occur most prominently at low latitudes in the atlantic hemisphere that is from 90 degrees east to 90 degrees east whereas in the pacific hemisphere there is comparatively little activity this is a consequence of the geographical localization of intense westward drifting equatorial magnetic flux patches at the core surface despite successes in explaining the morphology of the geomagnetic field numerical models of the geodynamo have so far failed to account systematically for this striking pattern of geomagnetic secular variation here we show that it can be reproduced provided that two mechanisms relying on the inner core are jointly considered first gravitational coupling aligns the inner core with the mantle forcing the flow of liquid metal in the outer core into a giant westward drifting sheet like gyre the resulting shear concentrates azimuthal magnetic flux at low latitudes close to the core mantle boundary where it is expelled by core convection and subsequently transported westward second differential inner core growth fastest below indonesia causes an asymmetric buoyancy release in the outer core which in turn distorts the gyre forcing it to become eccentric in agreement with recent core flow inversions this bottom up heterogeneous driving of core convection dominates top down driving from mantle thermal heterogeneities and localizes magnetic variations in a longitudinal sector centred beneath the atlantic where the eccentric gyre reaches the core surface to match the observed pattern of geomagnetic secular variation the solid material forming the inner core must now be in a state of differential growth rather than one of growth and melting induced by convective translation

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

geomagnetic forecasts driven by thermal wind dynamics in the earth s core there exists a fundamental as well as practical interest in being able to accurately forecast the future evolution of earth s magnetic field at decadal to secular ranges this work enables such forecasts by combining geomagnetic data with an earth like numerical model of a convection driven fluid dynamo the underlying data assimilation framework builds on recent progress in inverse geodynamo modelling a method which estimates an internal dynamic structure for earth s core from a snapshot of the magnetic field and its instantaneous rate of change at the surface and takes advantage of linear relationships and long range correlations between observed and hidden state variables here the method is further evolved into a single epoch ensemble kalman filter in order to initialise at a given epoch an ensemble of states compatible with the observations and representative of the uncertainties in the estimation of hidden quantities the ensemble dynamics obtained by subsequent numerical integration of the prognostic model equations are found to be governed by a thermal wind balance or equilibrium between buoyancy forces the coriolis force and the pressure gradient the resulting core fluid flow pattern is a quasi steady eccentric gyre organised in a column parallel to earth s rotation axis in equilibrium with a longitudinal hemispheric convective density anomaly pattern the flow provides induction for the magnetic field which also undergoes a realistic amount of diffusion predictions of the present magnetic field from data taken within the past century show that the ensemble has an average retaining good consistency with the true geomagnetic evolution and an acceptable spread well representative of prediction errors up to at least a secular range the predictability of the geodynamo thus appears to significantly exceed previous theoretical expectations based on the chaotic divergence of ensemble members the assimilation generally outperforms the linear mathematical extrapolations from a 30 yr prediction range onwards with a 40 per cent improvement in earth surface error at a secular range the geomagnetic axial dipole decay observed over the past two centuries is predicted to continue at a similar pace in the next century with a further loss of 1 1 0 3 t by year 2115 the focal or minimum intensity point of the south atlantic geomagnetic anomaly is predicted to enter the south pacific region in the next century with the anomaly itself further deepening and widening by year 2065 the minimum intensity is predicted to decrease by 1 46 0 4 t at the earth surface and the focal point to move 12 8 1 4 deg westwards with a slight northward component this corresponds to a drift rate of 0 26 deg yr 1 similar to the typical geomagnetic westward drift observed over the past four centuries the same drift rate is also predicted until 2115 with a further but more uncertain intensity decrease

earth s magnetic field is probably not reversing the geomagnetic field has been decaying at a rate of 5 per century from at least 1840 with indirect observations suggesting a decay since 1600 or even earlier this has led to the assertion that the geomagnetic field may be undergoing a reversal or an excursion we have derived a model of the geomagnetic field spanning 30 50 ka constructed to study the behavior of the two most recent excursions the laschamp and mono lake centered at 41 and 34 ka respectively here we show that neither excursion demonstrates field evolution similar to current changes in the geomagnetic field at earlier times centered at 49 and 46 ka the field is comparable to today s field with an intensity structure similar to today s south atlantic anomaly saa however neither of these saa like fields develop into an excursion or reversal this suggests that the current weakened field will also recover without an extreme event such as an excursion or reversal the saa like field structure at 46 ka appears to be coeval with published increases in geomagnetically modulated beryllium and chlorine nuclide production despite the global dipole field not weakening significantly in our model during this time this agreement suggests a greater complexity in the relationship between cosmogenic nuclide production and the geomagnetic field than is commonly assumed

a permeability model for naturally fractured carbonate reservoirs abstract based on a detailed structural study performed on a reservoir surface analogue a fracture permeability model for carbonate reservoirs is proposed this involves four hierarchical systems each one assumed to convey fluids exclusively to that of immediately higher order new basic equations are then provided simulating hydrodynamic reservoir response the large scale first order structures consist of faults to which high permeability structures damage zones are associated at the meter scale stratabound joint systems together with bedding joints bounding the mechanical layers form a connected network transporting fluids to the fault system at a lower scale down to crystal size non stratabound joints constitute a pervasive and capillary fracture network which conveys fluids within the rock mass the non fractured host rock constitutes the lower permeability system at the crystal scale as no published works include an effective integration of detailed structural and numerical models the present study aims at covering a significant gap in the literature also providing appropriate theoretical basis for subsequent studies on fracture network modeling and reservoir simulation besides its application in the field of reservoir development and management the illustrated model may also be useful in environmental studies involving ground fluids such as e g in the field of special toxic nuclear waste management

quantifying uncertainties in multi scale studies of fractured reservoir analogues implemented statistical analysis of scan line data from carbonate rocks in this study we performed a fracture analysis on a cretaceous bedded carbonate succession well exposed in the sorrento peninsula the studied succession includes stratigraphic units that are very similar to the productive units of the buried apulian platform reservoir rocks in southern italy we analyzed eight carbonate beds including both limestones and dolomites the basic technique used in this study consisted of measuring fractures along bedding parallel scan lines for one limestone bed a microscale scan line about 15 cm long was also analyzed using a digital microcamera provided the cumulative distribution of fracture apertures is well described by a power law our analysis shows how the uncertainty in the estimate of fracture aperture cumulative frequencies grows for large aperture values this feature results in a large uncertainty in the estimate of the slope of the least squares line in a bi logarithmic diagram approximating the data distribution which is the exponent of the power law as the latter represents a fundamental parameter characterizing a fracture set and fracture distribution over different scales reducing the uncertainty in the estimate of the slope of the curve represents an important objective of quantitative fracture analysis this is obtained in this study by the application of multi scale analysis and by integrating micro scan line data with classic outcrop based scan line analysis the quantification of uncertainties in the cumulative distribution estimates of fracture apertures is performed by analyzing in detail the spacing distribution and consequently fracture density distribution for each aperture value our results suggests that a meaningful statistical analysis of fracture attributes such as aperture or opening displacement may be effectively carried out by using properly determined confidence intervals and by the integration of outcrop based and micro scan line data sets

subterranean clues to the future of our planetary magnetic shield the geomagnetic field generated in the liquid outer core provides a shield from cosmic radiation that can cause damage to man made satellites electrical power grids and the ozone layer 1 in the absence of this shield the solar wind might gradually erode the atmosphere eventually robbing the planet of its water 2 but the dipole magnetic field has decreased in strength over the last 160 y at an alarming rate 3 motivating continued spirited debate 4 6 over whether we are in the early stages of a geomagnetic pole reversal some even believe we are overdue but 160 y is just a blink of the eye in geological terms the record is too short to have great confidence about what these trends might mean about causal processes and the future in pnas trindade et al 7 provide insightful context for these modern changes in the form of a magnetic record from south america that extends 1 500 y into the past we know much about the recent waning geomagnetic field since the time of gauss in 1840 we have had a rich data source in the form of geomagnetic observatory records in the satellite era we have a deluge of data from magnetometers in orbit from analyses of these data we know that the field intensity decrease is concentrated in an area known as the south atlantic anomaly saa a vast swatch stretching from south africa to chile amazingly when one estimates the field structure beneath this region at the core mantle 1 1email john tarduno at rochester edu 1 xref corresp 1 1

natural hydraulic fracturing of tight gas sandstone reservoirs piceance basin colorado natural fractures form preferred pathways for basinal fluid flow and associated heat and mass transport in gas sandstone reservoirs with low matrix permeability fractures provide flow pathways between organic rich source and reservoir layers during gas charge and between matrix pores hydraulic fractures and the well bore during production while the formation of natural fractures has previously been associated with gas generation and pore fluid pressure increase through a process referred to as natural hydraulic fracturing other driving mechanisms such as stress changes by tectonic or exhumation processes remained viable alternatives to test whether these mechanisms contributed to fracture development we investigated the spatial and temporal distribution of fracture formation and its relationship to gas generation migration and charge in sandstone of the cretaceous mesaverde group across the entire production interval on a basinwide scale using fluid inclusion microthermometry of crack seal fracture cement formed concurrently with fracture opening we observed temperature trends that when compared with temperature evolution models of the formation date fracture formation between 41 and 6 ma in the northern and between 39 and 6 ma in the southern piceance basin the onset of fracture formation 20 30 m y prior to maximum burial eliminates changes in stress state associated with exhumation as a mechanism for triggering the onset of fracture formation instead calculated paleo pore fluid pressures of 40 90 mpa 5800 13 000 psi during fracture opening and the presence of methane rich inclusions in fracture cement suggest that fracture formation was aided by high pore fluid pressures during gas generation in organic rich shales and coals and associated charging of adjacent and interlayered sandstone reservoirs a 10 20 m y age progression in the onset of fracture formation from deeper to shallower horizons of the mesaverde group is consistent with gas generation and onset of fracture formation activated by burial temperature with limited upward migration of gas at this stage of reservoir evolution this age progression with depth is inconsistent with fracture formation triggered by changes in stress conditions associated with tectonic or structural processes expected to affect the entire formation synchronously our observations are thus most consistent with fracture formation by natural hydraulic fracturing in response to gas generation in interbedded source layers and reservoir charge based on widespread observations of fractures with similar structural and diagenetic attributes we consider natural hydraulic fracture formation in response to thermocatalytic gas generation to be a fundamental mode of brittle failure in otherwise structurally quiescent basins

holocene enso related cyclic storms recorded by magnetic minerals in speleothems of central china extreme hydrologic events such as storms and floods have the potential to severely impact modern human society however the frequency of storms and their underlying mechanisms are limited by a paucity of suitable proxies especially in inland areas here we present a record of speleothem magnetic minerals to reconstruct paleoprecipitation including storms in the eastern asian monsoon area over the last 8 6 ky the geophysical parameter irmsoft flux represents the flux of soil derived magnetic minerals preserved in stalagmite hs4 which we correlate with rainfall amount and intensity irmsoft flux exhibits relatively higher values before 6 7 ky and after 3 4 ky and lower values in the intervening period consistent with regional hydrological changes observed in independent records abrupt enhancements in the flux of pedogenic magnetite in the stalagmite agree well with the timing of known regional paleofloods and with equatorial el nino southern oscillation enso patterns documenting the occurrence of enso related storms in the holocene spectral power analyses reveal that the storms occur on a significant 500 y cycle coincident with periodic solar activity and enso variance showing that reinforced subdued storms in central china correspond to reduced increased solar activity and amplified damped enso thus the magnetic minerals in speleothem hs4 preserve a record of the cyclic storms controlled by the coupled atmosphere oceanic circulation driven by solar activity

fluid percolations in a fault zone a study of fluid inclusion planes in the st sylvestre granite northwest massif central france abstract a method for relating fluid flow evolution direction of fluid percolation to the bulk brittle network microfracture system at each state in a sequence of deformational events is presented fluids percolating through cracks are generally trapped as fluid inclusion planes alignment of fluid inclusions the method involves the use of fluid inclusions not only as a tool for the establishment of the physico chemical conditions under which fluids were entrapped but also as a microstructural marker of the geometry of permeability the study shows that through the determination of the paleopressures for each stage of fluid migration the chronology of the cracks and p t conditions prevailing during each crack formation can be established this methodology has focussed on a granitic example from the french massif central but may be applied to other geological environments

cyclic fluid flow through a regionally extensive fracture network within the kodiak accretionary prism two types of periodic textures observed in veins from the kodiak accretionary prism attest to cyclic fluid flow through a regionally extensive fracture network buried at 8 12 km depth 1 crack seal microstructures with bands of mica inclusions and 2 collapse microstructures with jagged bands of residue embedded within euhedral crystals of quartz the difference in texture reflects the closure of cracks crack seal microstructures record the complete chemical sealing of the crack after each fracture event whereas the collapse features record longer fluid filled periods followed by more rapid draining of fractures collapse features consist of pressure solution selvages trapped within veins and in the wall rock adjacent to euhedral growth terminations the high concentrations of immobile elements in these selvages indicate that these fractures closed by collapse and penetration of quartz crystals into wall rock analysis of chemical composition on either side of four large euhedral growth veins and whole rock analysis of slates across the kodiak formation reveal local depletion of silica adjacent to veins but no evidence for long distance silica transport within the system both crack seal and collapse textures are observed in a regionally extensive vein system that displays a regular geometry with thin closely spaced 0 5 3 cm near vertical crack seal veins that connect vertically and laterally with thicker euhedral growth veins arranged in widely spaced 500 mm southeast dipping en echelon sets the mesoscopic distribution and textural variability of the vein network suggests that the development of the vein system involved early nucleation and growth of vertical hydrofractures as the fracture density increased arrays of fractures locally provided zones of weakness and southeast dipping brittle ductile shear zones nucleated these en echelon cracks remained open and provided small reservoirs of fluid textures show that en echelon fractures remain open but periodically grow by upward and downward propagation crack tips are then sealed with locally derived silica and fluid drains back into en echelon fracture arrays this local fluid movement is punctuated by less frequent events where the system links up over a greater distance fractured reservoirs become interconnected and the fluid within reservoirs is drained upward or laterally periodic inflation and deflation of en echelon arrays may reflect periodic slip on crosscutting faults and rupture of the seals that separate reservoirs

continuous geomagnetic field models for the past 7 millennia 2 cals7k 1 we present two continuous global geomagnetic field models for recent millennia cals3k 2 covering the past 3000 years and cals7k 2 covering 7000 years from 5000 bc to 1950 ad the models were determined by regularized least squares inversion of archeomagnetic and paleomagnetic data using spherical harmonics in space and cubic b splines in time they are derived from a greatly increased number of paleomagnetic directional data compared to previous efforts and for the first time a significant amount of archeointensity data is used in this kind of global model allowing the determination of evolution of geomagnetic dipole strength while data accuracy and dating uncertainties remain a limitation reliable low resolution global models can be obtained the results agree well with previous results from virtual axial dipole moment vadm studies from archeomagnetic intensity data apart from a systematic offset in strength a comparison of model predictions with the previous 3000 year model cals3k 1 gives general agreement but also some significant differences particularly for the early epochs the new models suggest that the prominent two northern hemisphere flux lobes are more stationary than cals3k 1 implied extending considerably the time span of stationary flux lobes observed in historical models between 5000 bc and 2000 bc there are time intervals of weak dipole moment where dipole power is exceeded by low degree nondipole power at the core mantle boundary model coefficients and evaluation code can be obtained from the earthref digital archive erda together with animations and snapshots plots for every 100 years at http www earthref org detailed urls for the different material are listed in appendix a

depositional environment diagenetic evolution and their impact on the reservoir quality of the carboniferous kt ii carbonate in the zhanazhol reservoir pre caspian basin kazakhstan abstract the carboniferous kt carbonate unit late serpukhovain to early moscovian of the zhanazhol reservoir in the pre caspian basin is a giant condensate reservoir with great heterogeneity although the depositional characteristics and their impact on reservoir quality have been well documented by previous studies few studies have focused on diagenesis the interplay between depositional environment and their controls on reservoir heterogeneity in this study combining sedimentological petrographic and geochemical analyses we reconstructed the depositional settings and diagenetic history of the kt carbonate and assess their impacts on reservoir quality according to the vertical and lateral distribution of 12 observed microfacies types we proposed a depositional model of a northward deepening ramp consisting of tidal flat inner ramp and middle ramp which has played a critical role in controlling the reservoir quality mainly through grain types and matrix content fusulinidal grainstones packstones have the best reservoir quality because of its porous fusulinidal fragments and low micritic matrix content the major diagenetic events including cementation eight cement types dissolution fabric and non fabric selective dissolution compaction pressure dissolution and microfracturing early and late were grouped into six diagenetic environments marine meteoric shallow burial epigenic karstification intermediate burial and deep burial marine cementation and compaction are the main reason for porosity decreasing in upper inner ramp and middle ramp respectively the minor moldic pores created by fabric selective dissolution during meteoric stage were enlarged by freshwater leaching during epigenic karstification and its associated cementation occluded pores in the underlying bioclastic grainstones packstones late non fabric selective dissolution and cementation likely resulted in local porosity rearrangements without net porosity gain or loss but certainly reduced reservoir heterogeneity the interaction between depositional environment and diagenetic evolution played a vital role in the formation of two types of vertical distribution patterns of porosity types and understanding this interaction and its impacts on reservoir quality within a sequence stratigraphic framework can more reliably predict the distribution of reservoir properties and provides insights for adjacent fields with similar settings

diagenesis and origin of calcite cement in the flemish pass basin sandstone reservoir upper jurassic implications for porosity development abstract the flemish pass basin is a deep water basin located offshore on the continental passive margin of the grand banks eastern newfoundland which is currently a hydrocarbon exploration target the current study investigates the petrographic characteristics and origin of carbonate cements in the ti 3 member a primary clastic reservoir interval of the bodhran formation upper jurassic in the flemish pass basin the ti 3 sandstones with average q 86 0 f 3 1 r 10 9 contain various diagenetic minerals including calcite pyrite quartz overgrowth dolomite and siderite based on the volume of calcite cement the investigated sandstones can be classified into 1 calcite cemented intervals 20 calcite and 2 poorly calcite cemented intervals porous petrographic analysis shows that the dominant cement is intergranular poikilotopic 300 500 m calcite which stared to form extensively at early diagenesis the precipitation of calcite occured after feldspar leaching and was followed by corrosion of quartz grains intergranular calcite cement hosts all liquid inclusions mainly in the crystal core but rare primary two phase liquid and vapor fluid inclusions in the rims with mean homogenization temperature t h of 70 2 4 9 c and salinity estimates of 8 8 1 2 eq wt nacl the mean 18 o and 13 c isotopic compositions of the intergranular calcite are 8 3 1 2 vpdb and 3 0 1 3 vpdb respectively whereas fracture filling calcite has more depleted 18 o but similar 13 c values the shale normalized rare earth element ree sn patterns of calcite are generally parallel and exhibit slightly negative ce anomalies and positive eu anomalies fluid inclusion gas ratios co 2 ch 4 and n 2 ar of calcite cement further confirms that diagenetic fluids originated from modified seawater combined evidence from petrographic microthermometric and geochemical analyses suggest that 1 the intergranular calcite cement precipitated from diagenetic fluids of mixed marine and meteoric riverine waters in suboxic conditions 2 the cement was sourced from the oxidation of organic matters and the dissolution of biogenic marine carbonates within sandstone beds or adjacent silty mudstones and 3 the late phases of the intergranular and fracture filling calcite cements were deposited from hot circulated basinal fluids calcite cementation acts as a main controlling factor on the reservoir quality in the flemish pass reservoir sandstones over 75 of initial porosity was lost due to the early calcite cementation the development of secondary porosity mostly enlarged moldic pores and throats by later calcite dissolution due to maturation of organic matters e g hydrocarbon and coals was the key process in improving the reservoir quality

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

rapid digital quantification of microfracture populations abstract populations of microfractures are a structural fabric in many rocks deformed at upper crustal conditions in some cases these fractures are visible in transmitted light microscopy as fluid inclusion planes or cement filled microfractures but because sem based cathodoluminescence cl reveals more fractures and delineates their shapes sizes and crosscutting relations it is a more effective structural tool yet at magnifications of 150 300 at which many microfractures are visible sem cl detectors image only small sample areas 0 5 0 1 mm 2 relative to fracture population patterns the substantial effort required to image and measure centimeter size areas at high magnification has impeded quantitative study of microfractures we present a method for efficient collection of mosaics of high resolution cl imagery a preparation method that allows samples to be any size while retaining continuous imagery of rock no gaps and software that facilitates fracture mapping and data reduction although the method introduced here was developed for cl imagery it can be used with any other kind of images including mosaics from petrographic microscopes compared with manual measurements the new method increases several fold the number of microfractures imaged without a proportional increase in level of effort increases the accuracy and repeatability of fracture measurements and speeds quantification and display of fracture population attributes we illustrate the method on microfracture arrays in dolostone from ne mexico and sandstone from nw scotland we show that key aspects of microfracture population attributes are only fully manifest at scales larger than a single thin section

fracturing and fluid flow in a sub decollement sandstone or a leak in the basement crack seal texture within fracture cements in the triassic el alamar formation ne mexico shows that the fractures opened during precipitation of quartz cements later overlapping calcite cements further occluded pore space previous workers defined four systematic fracture sets a oldest to d youngest with relative timing constrained by crosscutting relationships quartz fluid inclusion homogenization temperatures are higher within set b 148 20 c than in set c 105 12 c these data and previous burial history modelling are consistent with set c forming during exhumation fluid inclusions in set c quartz have higher salinity than those in set b 22 9 v 14 2 wt nacl equivalent respectively and set c quartz cement is more enriched in 18 o 20 2 v 18 7 vsmow under most assumptions about the true temperature during fracture opening the burial duration the amount of cement precipitated and fluid flow patterns it appears that the fracture fluid became depleted in 18 o and enriched in 13 c this isotopic evolution combined with increasing salinity suggests that throughout fracture opening there was a gravity driven influx of fluid from upsection jurassic evaporites which form a regional decollement fracture opening amid downward fluid motion suggests that fracturing was driven by external stresses such as tectonic stretching or unloading rather than increases in fluid pressure

the 2000 r m hardy lecture full scale hydraulic performance of soilbentonite and compacted clay liners the results of laboratory and in situ permeability tests can be used to predict the total leakage rate of a soil bentonite or clay liner this prediction however ignores the large influence that minor defects may have on the total leakage in quebec hundreds of municipal wastewater ponds have been filled with water to measure their total leakage rate before approval the design criteria and the equations to be used for the full scale performance test are briefly reviewed with their capacities to detect hydraulic deficiencies several case histories are presented to illustrate various problems excessive leakage of a stable soil bentonite mix washing of bentonite in a soil bentonite mix internal erosion of a natural clay liner through an inadequate sand filter and effects of freezing on the total leakage of a clay liner key words liner clay bentonite permeability performance full scale test

detecting the oldest geodynamo and attendant shielding from the solar wind implications for habitability abstract the onset and nature of the earliest geomagnetic field is important for understanding the evolution of the core atmosphere and life on earth a record of the early geodynamo is preserved in ancient silicate crystals containing minute magnetic inclusions these data indicate the presence of a geodynamo during the paleoarchean between 3 4 and 3 45 billion years ago while the magnetic field sheltered earth s atmosphere from erosion at this time standoff of the solar wind was greatly reduced and similar to that during modern extreme solar storms these conditions suggest that intense radiation from the young sun may have modified the atmosphere of the young earth by promoting loss of volatiles including water such effects would have been more pronounced if the field were absent or very weak prior to 3 45 billion years ago as suggested by some models of lower mantle evolution the frontier is thus trying to obtain geomagnetic field records that are 3 45 billion years old as well as constraining solar wind pressure for these times in this review we suggest pathways for constraining these parameters and the attendant history of earth s deep interior hydrosphere and atmosphere in particular we discuss new estimates for solar wind pressure for the first 700 million years of earth history the competing effects of magnetic shielding versus solar ion collection and bounds on the detection level of a geodynamo imposed by the presence of external fields we also discuss the prospects for constraining hadean paleoarchean magnetic field strength using paleointensity analyses of zircons

small scale structure of the geodynamo inferred from oersted and magsat satellite data the geodynamo in the earth s liquid outer core produces a magnetic field that dominates the large and medium length scales of the magnetic field observed at the earth s surface1 2 here we use data from the currently operating danish oersted3 satellite and from the us magsat2 satellite that operated in 1979 80 to identify and interpret variations in the magnetic field over the past 20 years down to length scales previously inaccessible projected down to the surface of the earth s core we found these variations to be small below the pacific ocean and large at polar latitudes and in a region centred below southern africa the flow pattern at the surface of the core that we calculate to account for these changes is characterized by a westward flow concentrated in retrograde polar vortices and an asymmetric ring where prograde vortices are correlated with highs and retrograde vortices with lows in the historical 400 year average magnetic field4 5 this pattern is analogous to those seen in a large class of numerical dynamo simulations6 except for its longitudinal asymmetry if this asymmetric state was reached often in the past it might account for several persistent patterns observed in the palaeomagnetic field7 8 9 10 we postulate that it might also be a state in which the geodynamo operates before reversing

application of copper slag in geomagnetic archaeointensity research 1 paleointensity and archaeointensity studies since the 1950s have produced numerous geomagnetic intensity data for the last seven millennia as a consequence of different experiments and materials there is a complex and internally inconsistent picture of the geomagnetic field behavior in this study we present data using a recently developed experimental design on a heretofore unexploited recording medium copper slag deposits our results based on hundreds of specimens from various archaeometallurgical sites of the southern levant demonstrate the applicability of copper slag material for archaeointensity studies in addition to frequently exhibiting good experimental behavior slag has further advantages such as dense multilayer deposits and in cases embedded charcoals which open the door to data sets with excellent age control and resolution the data presented here augment the high quality database from the middle east and support previously observed periods of rapid change of the intensity of the geomagnetic field

unusual drawdown curves for a pumping test in an unconfined aquifer at lachenaie quebec field data and numerical modeling an unconfined aquifer was instrumented with monitoring wells over a surface area of about 100 m 100 m the aquifer is a sand deposit overlying a thick nonfissured layer of champlain sea clay the paper presents the results of a pumping test at a constant flow rate none of the curves of drawdown versus time presented the s shape of current theories however all drawdowns indicated that the aquifer was homogeneous the values for the specific yield were too low and varied with distance and time instead of being constant the theories for steady and unsteady states provided different values for the saturated hydraulic conductivity to understand the field behavior that differs from theoretical predictions the pumping test conditions were modeled numerically using a finite element method the transmissivity was derived from the dupuit equation and different curves for capillary retention and unsaturated permeability were examined the numerical drawdowns agree with the experimental drawdowns several nu

improving geomagnetic field reconstructions for 0 3 ka global geomagnetic field reconstructions on millennial time scales can be based on comprehensive paleomagnetic data compilations but especially for older data these still suffer from limitations in data quality and age controls as well as poor temporal and spatial coverage here we present updated global models for the time interval 0 3 ka where additions to the data basis mainly impact the south east asian alaskan and siberian regions we summarize recent progress in millennial scale modelling documenting the cumulative results from incremental modifications to the standard algorithms used to produce regularized time varying spherical harmonic models spanning 1000 bc to 1990 ad from 1590 to 1990 ad gauss coefficients from the historical gufm1 model supplement the paleomagnetic information in addition to absolute paleointensities calibrated relative paleointensity data from sediments are now routinely included iterative data rejection and recalibration of relative intensity records from sediments ensure stable results bootstrap experiments to generate uncertainty estimates for the model take account of uncertainties in both age and magnetic elements and additionally assess the impact of sampling in both time and space based on averaged results from bootstrap experiments taking account of data and age uncertainties we distinguish more conservative model estimates cals3k nb representing robust field structure at the core mantle boundary from relatively high resolution models cals3k n for model versions n 3 and 4 we assess the impact of newly available data and modifications to the modelling method by comparing the previous cals3k 3 the new cals3k 4 and the conservative new model cals3k 4b we conclude that with presently available data it is not feasible to produce a model that is equally suitable for relatively high resolution field predictions at earth s surface and robust reconstruction of field evolution avoiding spurious structure at the core mantle boundary cmb we presently consider cals3k 4 the best high resolution model and recommend the more conservative lower resolution version for studies of field evolution at the cmb

quantifying and predicting naturally fractured reservoir behavior with continuous fracture models this article describes the workflow used in continuous fracture modeling cfm and its successful application to several projects our cfm workflow consists of four basic steps 1 interpreting key seismic horizons and generating prestack and poststack seismic attributes 2 using these attributes along with log and core data to build seismically constrained geocellular models of lithology porosity water saturation etc 3 combining the derived geocellular models with prestack and poststack seismic attributes and additional geomechanical models to derive high resolution three dimensional 3 d fracture models and 4 validating the 3 d fracture models in a dynamic reservoir simulator by testing their ability to match well performance our cfm workflow uses a neural network approach to integrate all of the available static and dynamic data this results in a model that is better able to identify fractured areas and quantify their impact on well and reservoir flow behavior this technique has been successfully applied in numerous sandstone and carbonate reservoirs to both understand reservoir behavior and determine where to drill additional wells three field case studies are used to illustrate the capabilities of the cfm approach

on the possible occurrence of archaeomagnetic jerks in the geomagnetic field over the past three millennia abstract archaeomagnetism can provide a high resolution full vector description of the earth s magnetic field for the past several thousand years we analyse the bulk of archaeomagnetic data both direction and intensity obtained recently in western europe and the eastern mediterranean covering the past three millennia we demonstrate a remarkable coincidence between sharp cusps in geomagnetic field direction and intensity maxima two clear ones at ad 200 and 1400 two presently less well constrained at 800 bc and ad 800 these sharp changes may constitute a new feature of geomagnetic secular variation archaeomagnetic jerks with time characteristics intermediate between geomagnetic jerks and magnetic excursions

geomagnetic field intensity during the last 60 000 years based on 10be and 36cl from the summit ice cores and 14c abstract based on 10 be 36 cl and 14 c records we reconstruct past changes in the geomagnetic field intensity under the assumption that radionuclide records are mainly influenced by changes in their production rates subsequent comparison of these records with independent geomagnetic field reconstructions allows us to assess the reliability of our approach and to identify periods where our method or the geomagnetic field reconstructions might be problematic the geomagnetic field derived from the 10 be flux to summit in central greenland agrees well with independent geomagnetic field intensity reconstructions however compared to independent palaeomagnetic data the radionuclide record suggests increased geomagnetic field intensities especially for the period from 20 000 to 30 000 years bp 36 cl from the grip ice core agrees well with the 10 be record for the last ice age and hence also the reconstructed geomagnetic field based on the tree ring radiocarbon record it is possible to reconstruct geomagnetic field intensity changes during the holocene a comparison of radiocarbon based and independent geomagnetic field reconstructions indicates that changes in the carbon cycle significantly influenced the atmospheric radiocarbon concentration before 10 000 years bp

fracture zone scale variation of trace elements and stable isotopes in calcite in a crystalline rock setting abstract with an aim to increase the understanding about the isotopic and chemical heterogeneity of calcites in water conducting fracture zones with different crystalline wall rock compositions at different depths we present trace element chemistry isotopic composition 18o 13c 87sr 86sr and biomarkers of euhedral low temperature fracture coating calcite paleohydrogeological fluctuations and wall rock influence on the hydrochemistry in the deep groundwater are explored samples are from several fracture zone sub fractures at 360 to 740 m retrieved during an extensive core drilling campaign in sweden calcite generally showed fracture zone specific values of 13c 18o and 87sr 86sr which indicates precipitation from relatively homogeneous fluid similar to the modern groundwater at the site at the same event in each fracture zone 18o and 13c in the different fracture zones were consistent with precipitation from waters of different salinity and decreasing organic input with depth respectively the latter is also supported by biomarkers showing clear indications of srb related organic compounds e g iso and anteiso c17 0 branched fatty acids except in the deepest zone in contrast to the isotopes variation in trace elements within the fracture zones was generally up to several orders of magnitude manganese and ree as oppose to the other metals were higher in the shallow fracture zones 112 1130 and 44 97 ppm respectively than in the deeper 28 272 and 5 11 ppm respectively in agreement with the groundwater composition although the rock types varied between and within the different fracture zones this had insignificant influence on the trace element chemistry of the calcites co variation was generally relatively large for many trace elements with isometric logratio correlation generally better than 0 75 which indicates that their variation in the calcites is due to variation of ca in the fracture water but other local factors especially uptake in co precipitating minerals clay minerals barite pyrite and zeolites but also microbial activity and metal speciation may have influenced the metal incorporation into calcite these detailed studies of fracture calcite are of importance for the understanding of variation in fluid chemistry and trace metal uptake in fracture zones adding together with hydrochemical studies detailed information optimal for site characterisation

soil compressibility in transient unsaturated seepage analyses most levee underseepage and uplift analyses are based on steady state seepage and can yield conservative results although computations are simpler and steady state seepage parameters are easier to

an analysis of horizontal microcracking during catagenesis example from the catskill delta complex horizontal bitumen filled microcracks are common within clay laminae of the finely laminated organic carbon rich shale in the lower half of the heavily jointed upper devonian dunkirk shale western new york state such cracks are not found higher in the dunkirk shale where moderate bioturbation resulted in a relatively porous and permeable microfabric horizontal microcracks in a hydrocarbon source rock that carries regional vertical joints indicating a horizontal least principal stress owe their presence to material properties of the fractured shale and the magnitude and orientation of the crack driving stress during kerogen maturation three material properties favored the horizontal initiation of microcracks in the dunkirk shale 1 the abundance of flat kerogen grains oriented parallel to layering 2 a marked strength anisotropy in large part caused by the laminated nature of the rock and 3 the tight strongly oriented planar clay grain fabric produced by gravitational compaction of flocculated clay at shallow burial depth the latter was especially important to sustaining elevated pore pressure the crack driving stress which was generated by the conversion of kerogen to bitumen poroelastic deformation of the low permeability laminated shale pressurized by catagenesis perhaps enhanced by compaction disequilibrium prior to kerogen conversion elevated the in situ horizontal stress in excess of the vertical stress which remained constant during pore pressure buildup thereby favoring the propagation of microcracks in the horizontal plane

continuous global geomagnetic field models for the past 3000 years abstract several global geomagnetic field models exist for recent decades but due to limited data availability models for several centuries to millennia are rare we present a continuous spherical harmonic model for almost 3 millennia from 1000 b c to 1800 a d based on a dataset of directional archaeo and paleomagnetic data and axial dipole constraints the model named continuous archaeomagnetic and lake sediment geomagnetic model for the last 3k years cals3k 1 can be used to predict both the field and secular variation comparisons and tests with synthetic data lead to the conclusion that cals3k 1 gives a good general large scale representation of the geomagnetic field but lacks small scale structure due to the limited resolution of the sparse dataset in future applications the model can be used for comparisons with additional new data for that time span for better resolved regions the agreement of data with cals3k 1 will provide an idea about the general compatibility of the data with the field and secular variation in that region of the world for poorly covered regions and time intervals we hope to iteratively improve the model by comparisons with and inclusion of new data animations and additional snapshot plots of model predictions as well as the model coefficients and a fortran code to evaluate them for any time can be accessed under http www mahi ucsd edu cathy holocene holocene html the whole package is also stored in the earthref digital archive at http www earthref org

a method to detect natural fracture strike in sandstones in siliciclastic hydrocarbon reservoir rocks economic gas and oil production may depend on the attributes of natural fractures and with the advent of horizontal drilling fractures are increasingly exploration and development targets yet reliable information on such key fracture attributes as orientation strike is sparse because few fractures intersect vertical well bores this paper describes how fracture strike can be documented on a bed by bed basis even in well bores where few or no visible fractures are directly sampled quartz lined opening mode microfractures lengths of microns to millimeters in quartz cemented sandstones commonly are not visible using standard petrographic methods but systematic mapping of these microfractures is possible using photomultiplier based electron beam induced luminescence scanned cathodoluminescence imaging as shown by observations primarily from three natural gas plays and one oil play in the united states microfracture strike is a good guide to the strike of large fractures macrofractures that formed concurrently because microfractures are widespread and small specimens can be used to get accurate fracture strike data this approach can be applied to samples obtained from wireline conveyed rotary drilled sidewall coring devices as well as to samples from full diameter core

microfracture spacing distributions and the evolution of fracture patterns in sandstones abstract natural fracture patterns in sandstone were sampled using scanning electron microscope based cathodoluminescence sem cl imaging all fractures are opening mode and are fully or partially sealed by quartz cement most sampled fractures are too small to be height restricted by sedimentary layers at very low strains 100 datasets show spacings that are best fit by log normal size distributions compared to exponential power law or normal distributions the clustering of fractures suggests that the locations of natural factures are not determined by a random process to investigate natural fracture localization we reconstructed the opening history of a cluster of fractures within the huizachal group in northeastern mexico using fluid inclusions from synkinematic cements and thermal history constraints the largest fracture which is the only fracture in the cluster visible to the naked eye among 101 present opened relatively late in the sequence this result suggests that the growth of sets of fractures is a self organized process in which small initially isolated fractures grow and progressively interact with preferential growth of a subset of fractures developing at the expense of growth of the rest size dependent sealing of fractures within sets suggests that synkinematic cementation may contribute to fracture clustering

colloquium 2004 hydrogeotechnical properties of hard rock tailings from metal mines and emerging geoenvironmental disposal approaches tailings are ground rock particles from which the valuable minerals or metals have been extracted an historical overview on hard rock mines shows that since the 1930s it has become current practice to pump the tailings into storage areas circumscribed by dykes made of the tailings themselves however numerous physical and chemical stability problems were observed mainly owing to the particular hydrogeotechnical and mineralogical properties of the tailings therefore modifications to the conventional methods were proposed but these were relatively costly not always efficient and sometimes difficult to implement new management methods that improve the physical and or chemical stability have hence been developed to reduce environmental risks associated with tailings storage namely densified tailings environmental desulphurization covers built with tailings and co disposal of tailings and waste rock even if many aspects need to be optimized these approaches can be considered today as interest

origin of stylolites in upper permian zechstein anhydrite gorleben salt dome germany abstract stylolites in evaporites are very uncommon in the gorleben zechstein salt dome stylolite horizons have been found in the so called banderanhydrit z3ha11 at the top of the zechstein hauptanhydrit main anhydrite these pressure solution features seems to be related to the presence of thin magnesite clay interlayers five principal stylolite morphologies can be distinguished in the core sections studied the orientation of the sutured seams is generally bedding parallel with the stylolite axes vertical to the bedding surface this demonstrates that pressure solution features clearly predate the formation of the salt dome and that there is no relation between their formation and halokinesis solution rates of up to about 26 have been calculated by measuring maximum stylolite amplitudes in certain core intervals considering the bedding parallel occurrence of the stylolites and the fact that the stylolite seams are crosscut by anhydrite crystals that we interpret as pseudomorphs after gypsum it must be concluded that the stylolites formed before the dehydration of gypsum to anhydrite was completed the lower parts of the hauptanhydrit were excluded from these processes because they had already been converted to anhydrite by the overburden of overlying zechstein units and by ascending compaction fluids of the underlying zechstein 2 salt we assume that the dehydration of gypsum to anhydrite was completed before the end of zechstein sedimentation and that the formation of stylolites thus must be attributed to the same time interval

strength of the geomagnetic field in the cretaceous normal superchron new data from submarine basaltic glass of the troodos ophiolite 1 we present here new paleointensity data from 39 sampling sites collected from the quenched margins of pillow lavas and dikes exposed within the troodos ophiolite similar to 92 ma formed during the cretaceous normal superchron cns a period of approximately 40 million years when the geomagnetic field reversed extremely infrequently if at all monte carlo simulations suggest that a minimum of 25 estimates are necessary for a reasonably robust estimate for the average field strength our data suggest a dipole strength equivalent to the present field or nearly twice the post cns average the mean and standard deviation of the dipole moment 81 43 zam 2 z 10 21 from the 57 data points compiled here agree remarkably well with those predicted from the long paleointensity record derived from dsdp site 522 the new data set for the cns suggests a picture of a strong and stable field during the period of time when it stopped reversing moreover the similarity of the cns data with the present geomagnetic field suggests that it is presently in a state of unusual polarity stability

persistent high paleosecular variation activity in southern hemisphere for at least 10 000 years abstract direct observations of the geomagnetic field show that secular variation is strong in the atlantic hemisphere and comparatively reduced in the pacific region the dipole has been decaying since at least 1840 ad driven by growth and migration of reverse flux patches in the southern hemisphere we investigate whether anything like this modern pattern of geomagnetic secular variation persists and can be detected in global paleomagnetic field models synthesis of results from two new time varying spherical harmonic models shows that geographically distinct geomagnetic secular variation extends to at least 10 000 bp the models use the same database but differ in methodology leading to some regional differences in results consistent large scale surface features include strong average fields in the northern hemisphere and weaker fields with greater overall variability in the south longitudinal structure is present with weaker average fields in the western pacific than in the east and prominent negative inclination anomalies extending beneath indonesia across africa and to brazil but weaker anomalies in the central pacific marginally positive inclination anomalies occur west of the americas paleosecular variation activity peaks at high southern latitudes and there is a pattern of reduced activity at equatorial and mid latitudes beneath the pacific although the dipole has exhibited both growth and decay over the interval 0 10 000 bp our results show that geomagnetic paleosecular variation is preferentially focused in similar geographic regions to secular variation seen in the modern field

mechanical and fracture stratigraphy using examples from core studies this article shows that separate identification of mechanical stratigraphy and fracture stratigraphy leads to a clearer understanding of fracture patterns and more accurate prediction of fracture attributes away from the wellbore mechanical stratigraphy subdivides stratified rock into discrete mechanical units defined by properties such as tensile strength elastic stiffness brittleness and fracture mechanics properties fracture stratigraphy subdivides rock into fracture units according to extent intensity or some other observed fracture attribute mechanical stratigraphy is the by product of depositional composition and structure and chemical and mechanical changes superimposed on rock composition texture and interfaces after deposition fracture stratigraphy reflects a specific loading history and mechanical stratigraphy during failure because mechanical property changes reflect diagenesis and fractures evolve with loading history mechanical stratigraphy and fracture stratigraphy need not coincide in subsurface studies current mechanical stratigraphy is generally measurable but because of inherent limitations of sampling fracture stratigraphy is commonly incompletely known to accurately predict fractures in diagenetically and structurally complex settings we need to use evidence of loading and mechanical property history as well as current mechanical states

rapidly changing flows in the earth s core variations in the earth s magnetic field over a span of a few months can be resolved despite the potential filtering effects of the electrically conducting mantle and are indicative of rapid flow in the earth s outer core

speleothem record of geomagnetic south atlantic anomaly recurrence the diminishing strength of the earth s magnetic dipole over recent millennia is accompanied by the increasing prominence of the geomagnetic south atlantic anomaly saa which spreads over the south atlantic ocean and south america the longevity of this feature at millennial timescales is elusive because of the scarcity of continuous geomagnetic data for the region here we report a unique geomagnetic record for the last 1500 y that combines the data of two well dated stalagmites from pau d alho cave located close to the present day minimum of the anomaly in central south america magnetic directions and relative paleointensity data for both stalagmites are generally consistent and agree with historical data from the last 500 y before 1500 ce the data adhere to the geomagnetic model arch3k 1 which is derived solely from archeomagnetic data our observations indicate rapid directional variations 0 1 y from approximately 860 to 960 ce and approximately 1450 to 1750 ce a similar pattern of rapid directional variation observed from south africa precedes the south american record by 224 50 y these results confirm that fast geomagnetic field variations linked to the saa are a recurrent feature in the region we develop synthetic models of reversed magnetic flux patches at the core mantle boundary and calculate their expression at the earth s surface the models that qualitatively resemble the observational data involve westward and southward migration of midlatitude patches combined with their expansion and intensification

palaeomagnetic evidence for the persistence or recurrence of geomagnetic main field anomalies in the south atlantic we present a dataset of a full vector palaeomagnetic study of late pleistocene lavas from the island tristan da cunha in the south atlantic ocean the current day geomagnetic field intensity in this region is approximately 25 mu t compared to an expected value of similar to 43 mu t this phenomenon is known as the south atlantic geomagnetic anomaly saa geomagnetic field models extending back to the last 10 ka find no evidence for this being a persistent feature of the geomagnetic field albeit all models are constructed from data which is particularly sparse in the southern hemisphere new ar 40 ar 39 incremental heating dating indicates the studied lavas from tristan da cunha extruded between 90 and 46 ka palaeointensity estimations of eight lava flows made using the thellier method yield an average palaeointensity of 18 6 mu t and virtual axial dipole moment vadm of 3 1 1 2 x 10 22 am 2 the lava flows demonstrate four time intervals comparable to the present day saa where the average vadm of the tristan da cunha lavas is weaker than the global vadm average this suggests a persistent or recurring low intensity anomaly to the main geomagnetic field similar to the saa existed in the south atlantic between 46 and 90 ka c 2016 elsevier b v all rights reserved

ultrasonic and x ray computed tomography characterization of progressive fracture damage in low porous carbonate rocks abstract this paper studies the fracturing process in low porous rocks during uniaxial compressive tests considering the original defects and the new mechanical cracks in the material for this purpose five different kinds of rocks have been chosen with carbonate mineralogy and low porosity lower than 2 the characterization of the fracture damage is carried out using three different techniques ultrasounds mercury porosimetry and x ray computed tomography the proposed methodology allows quantifying the evolution of the porous system as well as studying the location of new cracks in the rock samples intercrystalline porosity the smallest pores with pore radius

interpreting fracture development from diagenetic mineralogy and thermoelastic contraction modeling four sets of thin section scale mode i open mode cemented microfractures are present in sandstone from the eocene misoa formation maracaibo basin venezuela the first set of microfractures is intragranular f1 formed early during compaction and are filled with quartz cement precipitated at temperatures equal to or higher than 100 8c the second set of microfractures f2 is cemented by bituminite pyrite formed at temperatures between 60 and 100 8c and are associated with kerogen maturation and hydrocarbon migration from underlying overpressured source rocks the third set of microfractures f3 is fully cemented by either quartz cement or calcite cement the former has fluid inclusion homogenization temperatures between 149 and 175 8c these temperatures are mostly higher than maximum burial temperatures 160 8c suggesting that upward flow caused by a pressure gradient transported silica vertically which crystallized into the fractures upward decompression may have also caused a pco2 drop which at constant temperature allowed simultaneous carbonate precipitation into the third microfracture set the fourth set of thin section scale microfractures f4 is open or partially cemented by siderite hematite and other iron oxides the presence of hematite and iron oxides in microfractures is evidence for oxidizing conditions that may be associated with the uplift of the misoa formation in order to time and place constraints on the depth of formation of the fourth set of microfractures we have coupled published quartz cementation kinetic algorithms with uniaxial strain equations and determined if in fact they could be associated with the uplift of the formation our results suggest that thermoelastic contraction caused by the formation s uplift erosion and consequent cooling is a feasible mechanism for the origin of the last fracture set hence we infer that meteoric water invasion into the fractures at the end of the uplift cause the precipitation of oxides and the transformation of siderite to hematite d 2005 elsevier b v all rights reserved

fall in earth s magnetic field is erratic earth s magnetic field has decayed by about 5 per century since measurements began in 1840 directional measurements predate those of intensity by more than 250 years and we combined the global model of directions with paleomagnetic intensity measurements to estimate the fall in strength for this earlier period 1590 to 1840 a d we found that magnetic field strength was nearly constant throughout this time in contrast to the later period extrapolating to the core surface showed that the fall in strength originated in patches of reverse magnetic flux in the southern hemisphere these patches were detectable by directional data alone the pre 1840 model showed little or no evidence of them supporting the conclusion of a steady dipole up to 1840

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