mount st helens 1980 and mount pelee 1902 flow or surge the far reaching directed blast of mount st helens and the devastating nuees ardentes of mount pelee produced deposits that in many places consist of three main layers a basal gravelly or sandy layer 1 a massive or bedded ash layer 2 and a capping ash cloud layer 3 these thin and in part landscape mantling deposits are generally ascribed to pyroclastic surges and the dune bedding seen in parts of layer 2 has reinforced this interpretation there are several reasons however for preferring a pyroclastic flow origin 1 much of layer 2 is unequivocal pyroclastic flow 2 the tripartite subdivision and landscape mantling habit is similar to that displayed by ignimbrites of the low aspect ratio type 3 the deflation of a pyroclastic surge and the subsequent deposition of particulate material will tend not to conserve the fine ash and dust that are abundant in valley ponded parts of layer 2 and cannot explain the observed tendency for layer 2 to show stronger fines depletion on ridges than in valley bottoms and 4 the coarseness and the variance of grain size found within dune bedded bed sets in mount st helens layer 2 are like those of very weak pyroclastic surges and the dune bedding most likely resulted from local minor turbulence as could have been caused by surface roughness in a mountainous terrain littered with tree stumps and fallen trees in a thin depositing pyroclastic flow the directed blast and nuees ardentes at mount st helens and mount pelee are interpreted to have been violently emplaced pyroclastic flows producing deposits of low aspect ratio type the characteristics of which stem from an exceptionally high flow velocity

origin of fibrous gypsum in the newark rift basin eastern north america abstract cores from the red beds constituting the upper triassic passaic formation a syn rift sequence in the newark basin display subhorizontal fractures veins filled with satin spar gypsum such veins are apparent in the shallow subsurface 100 300 m below present ground level but are not observed in outcrops or in quarries because of groundwater dissolution these fractures are roughly parallel to the present ground surface in the basin suggesting topographic influence on their formation fractures observed in cores are seen to crosscut stratigraphic boundaries indicating that the veins formed after stratal tilting and faulting and thereby post date the early late jurassic the gypsum crystals making up the vein fill grew perpendicular to the fracture walls suggesting that opening and filling of the fractures was contemporaneous and that the fractures are extensional that gypsum crystallizes from meteoric and connate waters and is derived by dissolution of associated evaporites is reflected in the d 18o 34s and 87sr 86sr isotopic compositions of the sulfate fractures are interpreted to be a result of unloading and exhumation fractures were initiated after major depositional and tectonic events took place and post date the late jurassic satin spar precipitated in those fractures carried in by gypsum saturated brines derived either by dissolution of the near surface sulfate evaporites or rehydration of more deeply buried anhydrite such satin spar veins are not evaporites but are composed of chemically remobilized sulfate

a laboratory simulation of fibrous veins some first observations abstract following work by stephen taber 80 years ago we describe vein like arrays of parallel fibrous crystals that grow evaporatively between pairs of brine soaked porous ceramic substrates crystals of solute grow antitaxially from fixed sites on the substrate forcing older parts of the crystals away from the growth site without benefit of any long range cracking parallel to the substrate the nutrients for growth are fed to the growth site advectively or diffusively through the substrate blocks themselves not along the plane of the vein we call such crystallization taber growth and suggest as taber did that it might be an important mechanism for non evaporative fibrous vein development in nature the taber growth model provides a ready explanation for the ability of fibers to track vein opening directions and tracking is indeed the rule in our samples though exceptions are also seen our results lend support to ideas already in the literature that fibrous veins are not necessarily products of a crack seal process and that fibrous veins are not necessarily syntectonic our observations also raise questions about criteria for recognition of syntaxial fibrous veins and underscore the importance of finding new criteria for recognition of the younging direction along fibers

relative partitioning of acoustic and seismic energy during strombolian eruptions the relative elastic energy partitioning during strombolian eruptions can be estimated from acoustic pressure and seismic velocity records we outline methods for determining acoustic and seismic energies for sensors deployed within several kilometers of erupting vents we use these energies to introduce the concept of the volcano acoustic seismic ratio g or vasr which is the ratio of elastic energy propagated through the atmosphere and into the earth eruption vasr is a physical diagnostic of explosive degassing that is appropriate for comparing eruption mechanisms at individual and between various volcanoes here we assess acoustic and seismic energies and corresponding vasr for discrete strombolian explosive events at karymsky and erebus volcanoes we attribute the relatively high and stable vasr at erebus g 8 standard deviation 41 to repeatable source conditions occurring at the surface of a persistent lava lake with accompanying strong coupling to the atmosphere lower and more variable vasr at karymsky g 0 18 in 1998 to g 1 51 in 1991 with standard deviations of 93 and 313 respectively is attributed to changing conditions within a narrow partially choked conduit variable seismoacoustic energy partitioning for karymsky as manifested by the large vasr standard deviation suggests that conduit conditions affecting vasr which include magma properties conduit obstruction or fragmentation depths can evolve both during the course of an explosion and between successive events d 2005 elsevier b v all rights reserved

pressure solution in sedimentary basins effect of temperature gradient abstract pressure solution is an important process in sedimentary basins and its behaviour depends mainly on the sediment rheology and temperature distribution the compaction relation of pressure solution is typically assumed to be a viscous one and is often written as a relationship between effective stress and strain rate a new derivation of viscous compaction relation is formulated based on more realistic boundary conditions at grain contacts a non linear diffusion problem with a moving boundary is solved numerically and a simple asymptotic solution is given to compare with numerical simulations pressure solution is significantly influenced by the temperature gradient porosity reduction due to pressure solution is enhanced in an environment with a higher thermal gradient while porosity decreases much slowly in the region where the thermal gradient is small pressure solution tends to complete more quickly at shallower depths and earlier time in higher temperature environment than that in a low one these features of pressure solution in porous sediments are analysed using a perturbation method to get a solution for the steady state comparison with real data shows a reasonably very good agreement

the transient atmospheric circulation response to north atlantic sst and sea ice anomalies abstract the objective of this study is to investigate the transient evolution of the wintertime atmospheric circulation response to imposed patterns of sst and sea ice extent anomalies in the north atlantic sector using a large ensemble of experiments with the ncar community climate model version 3 ccm3 the initial adjustment of the atmospheric circulation is characterized by an out of phase relationship between geopotential height anomalies in the lower and upper troposphere localized to the vicinity of the forcing this initial baroclinic response reaches a maximum amplitude in 5 10 days and persists for 2 3 weeks diagnostic results with a linear primitive equation model indicate that this initial response is forced by diabatic heating anomalies in the lower troposphere associated with surface heat flux anomalies generated by the imposed thermal forcing following the initial baroclinic stage of adjustment the response becomes progressively more barotropic and increases in both spatial extent an

hydrodynamic aspects of caldera forming eruptions numerical models comparison of results from a two dimensional numerical eruption simulation kachina to calculations based upon a shock tube analog supports the conclusion that the hydrodynamics during the initial minutes of large caldera forming ash flow eruptions may be dominated by blast wave phenomena field evidence for this phenomenology is pyroclastic surge deposits commonly occurring both directly below caldera related ash flow sheets on top of a preceding plinian fall deposit ground surge and separating individual ash flow units we model the eruption of the tshirege member of the bandelier tuff 1 1 ma b p from the valles caldera new mexico in the model a magma chamber at 100 mpa 1 kbar and 800 c is volatile rich with an average h2o abundance above saturation greater than 8 7 wt increasing to nearly 100 wt near the very top of the chamber using a shock tube analogy decompression of the chamber through a wide open dikelike vent 0 1 km wide and 1 to 5 km long forms a shock wave of 3 mpa 3o atm with a velocity greater than 1 0 km s 1 steady flow of material erupted from the vent begins after 20 to 100 s based upon a 7 km depth from the ground surface to a reflective density boundary in the chamber and a rarefaction wave velocity of 100 to 600 m s 1 the velocity of the ash front behind the shock wave is 300 to 500 m s 1 the shock tube model serves as a basis to evaluate the consistency of the kachina code results which are similar to a one dimensional problem along the symmetry axis the results of the kachina simulation show in some detail the effect of multiple reservoir rarefaction reflections and possibly prandtl meyer expansion in generating compressive wave fronts following the initial shock the rarefaction resonance not only prolongs unsteady flow in the vent but tends to promote surging flow of ash behind the leading shock furthermore these results are consistent with a blast wave characterized as a shock front followed by one or more pulses of entrained ash the blast wave shocks ambient air to higher pressures and temperatures the magnitudes of which depend strongly on the initial chamber overpressure distance and direction from the vent in consideration of volcanic hazards our numerical model shows that a shock wave compressed the atmosphere to pressures of 0 2 to 0 7 mpa 2 7 atm and temperatures of 200 to 300 c for distances to 10 km from the bandelier vent s

magmatic model for the mount st helens blast of may 18 1980 analytical and numerical solutions to the hydrodynamic equations of motion constrained by physical properties of juvenile ejecta in the mount st helens blast deposit were used to investigate magmatic conditions required to produce the initial devastating blast phase of the eruption of may 18 1980 evidence that the blast was magmatic includes equivalence in volume of juvenile blast ejecta to preemption inflation of the cone substantial vesicularity of this ejecta and continued vesiculation of large juvenile clasts after eruption observed or inferred ejecta velocities of 100 to 250 m s are shown to require 0 2 to 0 7 wt water vapor preexisting in magma unloaded by a landslide 200 to 900 m thick these conditions imply total magmatic water contents of 0 7 to 1 7 wt respectively such low required water content suggests that volcanic blasts may be regarded as a normal consequence of magma intrusion into an unstable edifice

on the arrangement of solid inclusions in fibrous veins and the role of the crack seal mechanism the arrangement of solid inclusions in veins was examined in three different rock types and tectonic settings common to all samples is a new type of sinusoidal inclusions associated with inclusion bands oriented parallel to the vein wall and inclusion trails at high angle to the vein wall crosscutting relationships of inclusion bands and the sinusoidal inclusions imply that inclusion bands do not reflect individual crack seal increments in our veins inclusion bands are not a sufficient criterion to infer the crack seal mechanism further evidence for solid inclusions not formed by the classic crack seal mechanism is given by inclusion bands in gypsum crystals grown in soft clay during incorporation solid inclusions can become folded or boudinaged depending on their orientation with respect to the opening direction the complex displacement field within the vein is recorded by curved crystal fibres which track the opening direction based on the arrangement of solid inclusions within the vein we suggest that our veins grew continuously during syntectonic vein formation solid inclusions formed by a fluctuation of adhesion at the vein wall interface rather than by crack sealing and vein growth was at least partly driven by the force of crystallisation q 2005 elsevier ltd all rights reserved

pressure solution and viscous compaction in sedimentary basins mathematical models of compaction in sedimentary basins typically assume a relationship between effective pressure pand porosity which is of a non linear type that is p p d however at depths greater than a kilometer pressure solution becomes important and this relationship approaches a viscous one we derive a mathematical model for viscous compaction in sedimentary basins and show how the model suggests different styles of behavior in the limits of slow nd fst compaction the initial pore pressure will be lithostatic over time the sediments compact and the resultant expulsion of pore water allows the pore pressure to approach a hy drostatic limit and in so doing the porosity is reduced at depths up to about a kilometer this compaction is elastic and due to the rearrangement of sediment particles at greater depths cementation and pressure solution occur and the latter causes further compac tion we call compaction by pressure solution viscous compaction and it forms the subject of the present pa per one of the interesting features of overpressuring is that it typically occurs suddenly at depths in excess of 3000 meters hunt 1990 and is often associated

model of a strong volcanic blast and a method of estimating the mass ejected summary a hydrodynamic model of a strong volcanic blast associated with large calderaforming ash gas flow eruptions is presented we show that the mass erupted from a vent influences considerably the damping of the shock wave if the ejected mass flux is constant the shock amplitude as a function of distance will decrease slower in accordance with the inverse 4 3 power law than that of an atomic explosion the inverse cube power law from the modelling we extract a relation connecting the evective energy of a blast with the mass ejected during the blast phase the mass released during the largest explosion of the 1883 eruption of krakatau and the lateral blast energy at mount st helens on 1980 may 18 are estimated on the basis of the equation obtained

widespread bedding parallel veins of fibrous calcite beef in a mature source rock vaca muerta fm neuquen basin argentina evidence for overpressure and horizontal compression in the neuquen basin of argentina beef bedding parallel veins of fibrous calcite is widespread within late jurassic black mudstones a typical vein consists of two grey inner zones and two white outer zones the inner zones contain inclusions of wall rock and hydrocarbons calcite fibres are perpendicular to the margins in the outer zones the angle between fibre and margin varies from about 45 at the vein tips to 90 in the centre imprints of fossils are offset proving that the fibres have grown antitaxially we infer that the veins opened in two phases during phase 1 the opening was vertical against gravity during phase 2 the veins resisted tectonic shortening so that shear stresses acted at the margins the senses of shear account for the fibre angles at outcrop igneous intrusive rocks have cut and metamorphosed the veins from burial curves maturity calculations growth strata and ages of igneous intrusions we estimate that the inner zones of the beef formed in the oil window during the aptian to albian and that the outer zones formed in the gas window during the cenomanian to campanian we infer that the beef is evidence for fluid overpressure during hydrocarbon generation

development of crystal morphology during unitaxial growth in a progressively widening vein ii numerical simulations of the evolution of antitaxial fibrous veins the development of fibrous morphology and capability of fibres for tracking the opening trajectory were investigated using numerical simulations of a natural antitaxial fibrous vein starting from a non unique best case variation of fracture opening velocity grain size wall roughness growth anisotropy and crystal growth velocity shows that these parameters differ in importance for crystal morphology and tracking capability fibrous veins can be simulated using crack seal opening of the fracture grain boundaries track the opening trajectory if the wall roughness is high opening increments are small and crystals touch the wall before the next crack increment starts

tropospheric rossby wave breaking and the nao nam objective analysis of several hundred thousand anticyclonic and cyclonic breaking rossby waves is performed for the northern hemisphere nh winters of 1958 2006 a winter climatology of both anticyclonic and cyclonic rossby wave breaking rwb frequency and size zonal extent is presented for the 350 k isentropic surface over the nh and the spatial distribution of rwb is shown to agree with theoretical ideas of rwb in shear flow composites of the two types of rwb reveal their characteristic sea level pressure anomalies upper and lower tropospheric velocity fields and forcing of the upper tropospheric zonal flow it is shown how these signatures project onto the centers of action and force the velocity patterns associated with the north atlantic oscillation nao and northern hemisphere annular mode nam previous studies have presented evidence that anticyclonic cyclonic breaking leads to the positive negative polarity of the nao and this relationship is confirmed for rwb over the midlatitudes centered near 50 n however an opposite and statistically significant relationship in which cyclonic rwb forces the positive nao and anticyclonic rwb forces the negative nao is shown over regions 20 to the north and south centered at 70 and 30 n respectively on a winter mean basis the frequency of rwb over objectively defined regions covering 12 of the area of the nh accounts for 95 of the nao index and 92 of the nam index a 6 hourly analysis of all the winters indicates that rwb over the objectively defined regions affects the nao nam without a time lag details of the objective wave breaking analysis method are provided in the appendix

the effects of north atlantic sst and sea ice anomalies on the winter circulation in ccm3 part i main features and storm track characteristics of the response observed multidecadal trends in extratropical atmospheric flow such as the positive trend in the north atlantic oscillation nao index may be attributable to a number of causes this study addresses the question of whether the atmospheric trends may be caused by observed trends in oceanic boundary forcing experiments were carried out using the ncar atmospheric general circulation model with specified sea surface temperature sst and sea ice anomalies confined to the north atlantic sector the spatial pattern of the anomalous forcing was chosen to be realistic in that it corresponds to the recent 40 yr trend in sst and sea ice but the anomaly amplitude was exaggerated in order to make the response statistically more robust the wintertime response to both types of forcing resembles the nao to first order even for an exaggerated amplitude the atmospheric response to the sst anomaly is quite weak compared to the observed positive trend in the nao but has the same sign indicative of a weak positive feedback the anomalies in sea ice extent are more efficient than sst anomalies at exciting an atmospheric response comparable in amplitude to the observed nao trend however this atmospheric response has the opposite sign to the observed trend indicative of a significant negative feedback associated with the sea ice forcing additional experiments using sst anomalies with opposite sign to the observed trend indicate that there are significant nonlinearities associated with the atmospheric response the transient eddy response to the observed sst trend is consistent with the positive nao response with the north atlantic storm track amplifying downstream and developing a more pronounced meridional tilt in contrast the storm track response to the observed sea ice trend corresponds to a weaker southward shifted more zonal storm track which is consistent with the negative nao response

the modeled atmospheric response to midlatitude sst anomalies and its dependence on background circulation states abstract the atmospheric response to a midlatitude sst anomaly in the north pacific and its dependence on background flow are examined in a gcm experiments are conducted using the same warm sst anomalies but two different model states perpetual january and perpetual february the atmospheric responses to the sst anomalies are statistically significant in both january and february but are completely different the anomalous circulation in january is characterized by a trough decaying with height immediately downstream of the sst anomalies in february the anomalous circulation is dominated by a downstream ridge growing with height the patterns of the anomalous heights in the two months are nearly orthogonal vorticity and thermodynamic budgets are diagnosed to illustrate how the anomalous circulations are maintained over the sst anomalies low level convergence and ascent are observed in both months in january the anomalous convergence is balanced by a residual due primarily to the forcing by submont

the decompression of volcanic jets in a crater during explosive volcanic eruptions during explosive volcanic eruptions fragmented silicic magma and volatiles exit the vent with pressures typically in the range 10 100 atm and at the speed of sound of the mixture we show that for magmatic volatile contents no in the range 0 03 no 0 06 this has the approximate value 0 95 0 05 nort 12 where r is the gas constant and t is the eruption temperature this speed is nearly independent of the vent pressure and vent radius by assuming there is negligible mixing with the air we have modelled the decompression of such jets following eruption from the vent for free decompression into the atmosphere the velocity of the decompressed jet has the approximate value 1 85 0 05 nort 12 this is nearly independent of the eruption rate for decompression into a crater the process is more complex at low eruption rates with low vent pressure the material becomes underpressured as it rises in the crater a shock then forms in the crater this recompresses the magma volatile mixture which then issues from the crater as a relatively slow subsonic jet at atmospheric pressure as the eruption rate increases such shocks move towards the top of the crater and ultimately cannot form in the crater instead the material issues from the crater as a high speed supersonic jet the upward thrust provided by the crater walls on this high pressure jet then increases the upward velocity above that of a freely decompressing jet the presence of a crater may therfore cause collapse in relatively small eruptions whereas it may promote formation of buoyant eruption columns at higher eruption rates if a crater grows through erosion during an eruption column collapse will typically ensue even if the mass flux remains steady

the general circulation model response to a north pacific sst anomaly dependence on time scale and pattern polarity abstract a general circulation model was integrated with perpetual january conditions and prescribed sea surface temperature sst anomalies in the north pacific a characteristic pattern with a warm region centered northeast of hawaii and a cold region along the western seaboard of north america was alternately added to and subtracted from the climatological sst field long 1350 day runs as well as short 180 day runs each starting from different initial conditions were performed the results were compared to a control integration with climatological ssts the model s quasi stationary response does not exhibit a simple linear relationship with the polarity of the prescribed sst anomaly in the short runs with a negative sst anomaly over the central ocean a large negative height anomaly with an equivalent barotropic vertical structure occurs over the gulf of alaska for the same sst forcing the long run yields a different response pattern in which an anomalous high prevails over northern canada and

the effects of north atlantic sst and sea ice anomalies on the winter circulation in ccm3 part ii direct and indirect components of the response the wintertime atmospheric circulation responses to observed patterns of north atlantic sea surface temperature and sea ice cover trends in recent decades are studied by means of experiments with an atmospheric general circulation model here the relationship between the forced responses and the dominant pattern of internally generated atmospheric variability is focused on the total response is partioned into a portion that projects onto the leading mode of internal variability the indirect response and a portion that is the residual from that projection the direct response this empirical decomposition yields physically meaningful patterns whose distinctive horizontal and vertical structures imply different governing mechanisms the indirect response which dominates the total geopotential height response is hemispheric in scale with resemblance to the north atlantic oscillation or northern hemisphere annular mode and equivalent barotropic in the vertical from the surface to the tropopause in contrast the direct response is localized to the vicinity of the surface thermal anomaly sst or sea ice and exhibits a baroclinic structure in the vertical with a surface trough and upper level ridge in the case of a positive heating anomaly consistent with theoretical models of the linear baroclinic response to extratropical thermal forcing both components of the response scale linearly with respect to the amplitude of the forcing but nonlinearly with respect to the polarity of the forcing the deeper vertical penetration of anomalous heating compared to cooling is suggested to play a role in the nonlinearity of the response to sst forcing

coupled sea ice ocean state estimation in the labrador sea and baffin bay sea ice variability in the labrador sea is of climatic interest because of its relationship to deep convection mode water formation and the north atlantic atmospheric circulation historically quantifying the relationship between sea ice and ocean variability has been difficultbecause ofin situ observation paucity and technical challenges associated with synthesizing observations with numerical models here the relationship between ice and ocean variability is explored by analyzing new estimates of the ocean ice state in the northwest north atlantic the estimates are syntheses of in situ and satellite hydrographic and ice data with a regional 1 38 coupled ocean sea ice model the synthesis of sea ice data is achieved with an improved adjoint of a thermodynamicicemodel modelanddataaremadeconsistent inaleastsquaressense byiterativelyadjustingcontrol variables including ocean initial and lateral boundary conditions and the atmospheric state to minimize an uncertainty weighted model data misfit cost function the utility of the state estimate is demonstrated in an analysis of energy and buoyancy budgets in the marginal ice zone miz in mid march the system achieves a state of quasi equilibrium during which net ice growth and melt approaches zero newly formed ice diverges from coastal areas and converges via wind and ocean forcing in the miz the convergence of ice mass in the miz is ablated primarily by turbulent ocean ice enthalpy fluxes the primary source of the enthalpy required for sustained miz ice ablation is the sensible heat reservoir of the subtropical origin subsurface waters

crack seal patterns records of uncorrelated stress release variations in crustal rocks statistical properties of crack seal veins are investigated with a view to assessing stress release fluctuations in crustal rocks crack seal patterns correspond to sets of successive parallel fractures that are assumed to have propagated by a subcritical crack mechanism in the presence of a reactive fluid they represent a time sequence record of an aseismic and anelastic process of rock deformation the statistical characteristics of several crack seal patterns containing several hundreds of successive cracks have been studied samples were collected in three different areas gold bearing quartz veins from abitibi in canada serpentine veins from the san andreas system in california and calcite veins from the apennine mountains in italy digitized pictures acquired from thin sections allow accurate measurement of crack seal growth increments all the samples show the same statistical behaviour regardless of their geological origin the crack seal statistical properties are described by an exponential distribution with a characteristic length scale and do not show any spatial correlation they differ from other fracture patterns such as earthquake data which exhibit power law correlations gutenberg richter relationship crack seal series represent a natural fossil record of stress release variations less than 50 bars in the crust that show a characteristic length scale associated with the resistance of rock to effective tension and no correlation in time

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

a role for barotropic eddy mean flow feedbacks in the zonal wind response to sea ice loss and arctic amplification abstractprevious studies have suggested that in the zonal mean the climatological northern hemisphere wintertime eddy driven jet streams will weaken and shift equatorward in response to arctic am

bedding parallel fibrous veins beef and cone in cone worldwide occurrence and possible significance in terms of fluid overpressure hydrocarbon generation and mineralization abstract bedding parallel fibrous veins are common worldwide in sedimentary basins especially within strata of low permeability the term beef refers to bedding parallel veins of fibrous minerals where the fibres are mutually parallel and have formed quasi vertically more complex on a smaller scale are cone in cone structures yet these are also common within bedding parallel veins for both beef and cone in cone we have compiled a worldwide catalogue 157 localities typically the veins consist mainly of white gangue minerals for example calcite gypsum or quartz but may also contain accessory minerals of economic interest for example bitumen sulphides emerald pitchblende or gold fluid inclusions may contain oil or gas calcite beef 110 localities is common in organic rich shale of marine carbonate origin especially of 1 cambrian ordovician 2 devonian carboniferous 3 early jurassic or 4 cretaceous to palaeogene ages gypsum beef 30 localities is common in evaporitic or lacustrine strata of continental origin especially of triassic or neogene ages quartz beef 17 localities is common within meta turbidite sequences especially of ordovician or proterozoic ages because these modal ages seem to reflect climatic controls we infer that the fibre forming mineral species have not travelled far vertically the same conclusion holds for accessory minerals typical temperatures of formation are 1 up to 60 c for gypsum beef 2 70 c to 120 c for calcite beef and 3 200 c to 350 c for quartz beef hydrocarbon bearing calcite beef may be a good indicator of a petroleum system in which oil or gas migrate together with aqueous solutions we argue that beef and cone in cone layers result from tensile fracturing and vertical dilation coeval with fibre growth possible causes are either 1 force of crystallization or 2 seepage forces due to fluid overpressure for layers that form at depths of several km fluid overpressure is the more likely cause

compaction driven evolution of porosity and permeability in natural mudstones an experimental study this paper describes a series of experiments designed to investigate the influence of lithology on the compactional loss of porosity and permeability in mudstones two intact samples of london clay with clay fractions of 40 and 67 were compacted to 33 mpa effective stress clay fraction permeability porosity pore size distribution and specific surface area were measured and their evolution was monitored throughout the compaction process electron microscopy was combined with mercury porosimetry to trace the collapse of the pore structure with increasing effective stress in both cases porosity loss occurred primarily by the collapse of large pores this process is more obvious in the coarser grained sample because throughout the compaction process it has a much broader range of pore radii and a much greater mean pore radius consistent with the pore size distributions the permeability of the coarser sample ranges from 10 10 m s 1 to 10 12 m s 1 while that of the finer grained sample ranges from 4 10 12 m s 1 to 5 10 14 m s 1 during progressive compaction from 2 to 33 mpa the compressibility of the finer grained sample is greater than that of the coarser grained sample 0 15 as opposed to 0 07 however in both cases the compressibility is much lower than that inferred for lithologically similar samples compacted over geological timescales the demonstration that both porosity and lithology clay fraction influence the permeability of mudstones should allow the development of more realistic porosity permeability relationships which take into account lithological variations exhibited by mudstones

force of crystallization during the growth of siliceous concretions the force of crystallization is of renewed interest as a diagenetic replacement mechanism we present a quantitative reaction transport model for mineral replacement driven by the pressure exerted by crystal growth based on continuum equations accounting for conservation of mass and momentum a condition of volume for volume replacement during growth and dissolution is shown to arise naturally from the interaction of mechanical and reactive deformation when applied to the postnucleation growth of quartz in a calcite plus amorphous silica host a centimetre scale concretion like feature is shown from our simulations to arise within roughly 17 ka

is the north atlantic oscillation a breaking wave abstract given the recent observational evidence that the positive negative phase of the north atlantic oscillation nao is the remnant of anticyclonic cyclonic wave breaking this study uses a multilevel primitive equation model to investigate important dynamical attributes of the above wave breaking behavior for this purpose a hierarchy of different basic states two and three dimensional and initial perturbations are used with the three dimensional climatological flow as the basic state it is found that initial perturbations located equatorward poleward and upstream of the climatological atlantic jet lead to wave breaking similar to that of the positive negative nao phase consistently analysis of observational data indeed shows that the pacific storm track is displaced equatorward poleward prior the onset of the positive negative nao phase this result suggests that the latitudinal position of the pacific storm track plays an important role for determining the phase of the nao sen

observed atmospheric response to cold season sea ice variability in the arctic abstractthe relation between weekly arctic sea ice concentrations sics from december to april and sea level pressure slp during 1979 2007 is investigated using maximum covariance analysis mca in the north atlantic sector the interaction between the north atlantic oscillation nao and a sic seesaw between the labrador sea and the greenland barents sea dominates the nao drives the seesaw and in return the seesaw precedes a midwinter spring nao like signal of the opposite polarity but with a strengthened northern lobe thus acting as a negative feedback with maximum squared covariance at a lag of 6 weeks statistical significance decreases when slp is considered in the whole northern hemisphere but it increases when north pacific sic is included in the analysis the maximum squared covariance then occurs after 8 weeks resembling a combination of the nao response to the atlantic sic seesaw and the aleutian icelandic low seesaw like response to in phase sic changes in the bering and okhotsk seas w

the initial giant umbrella cloud of the may 18th 1980 explosive eruption of mount st helens abstract the initial eruption column of may 18th 1980 reached nearly 30 km altitude and released 10 17 joules of thermal energy into the atmosphere in only a few minutes ascent of the cloud resulted in forced intrusion of a giant umbrella shaped cloud between altitudes of 10 and 20 km at radial horizontal velocities initially in excess of 50 m s the mushroom cloud expanded 15 km upwind forming a stagnation point where the radial expansion velocity and wind velocity were equal the cloud was initiated when the pyroclastic blast flow became buoyant the flow reduced its density as it moved away from the volcano by decompression by sedimentation and by mixing with and heating the surrounding air observations indicate that much of the flow covering an area of 600 km 2 became buoyant within 1 5 minutes and abruptly ascended to form the giant cloud calculations are presented for the amount of air that must have been entrained into the flow to make it buoyant assuming an initial temperature of 450 c and a magmatic origin for the explosion these calculations indicate that the flow became buoyant when its temperature was approximately 150 c and the flow consisted of a mixture of 3 25 10 11 kg of pyroclasts and 5 0 10 11 kg of air if sedimentation is considered these figures reduce to 1 1 10 11 kg of pyroclasts and 1 0 10 11 kg of air

phase speed spectra of transient eddy fluxes and critical layer absorption abstract tropospheric zonal mean eddy fluxes of heat and momentum and the divergence of the eliassen palm flux are decomposed into contributions from different zonal phase speeds data analyzed are ecmwf operational global analyses covering 1980 87 eastward moving medium scale waves zonal waves 4 7 dominate the spectra of lower tropospheric heat fluxes in both hemispheres and all seasons upper tropospheric wave flux spectra are similar to the low level spectra in midlatitudes but shift to slower zonal phase speeds as low latitudes are approached the cause of this shift is the selective absorption of faster moving components in midlatitudes as the waves propagate meridionally latitude phase speed distributions of eddy fluxes are constructed and compared to the zonal mean wind structure these results demonstrate that upper tropospheric eddies break and decelerate the zonal mean flow approximately 10 20 in latitude away from their critical line where phase speed equals zonal wind speed compari

tertiary deformation history from seismic section study and fault analysis in a former european tethyan margin the mecsek villany area sw hungary abstract outcrop scale structural data and seismic section interpretation are combined to unveil a very complicated tertiary deformation history of a once tethyan margin the mecsek villany area of hungary this combination of data helped to reconstruct the possible activity of individual fault zones at least four ene wsw striking zones the northern imbricates the south mecsek zone the gorcsony mariakemend ridge and the villany mountains were confirmed as regional long lived transpressive zones with very complicated internal deformation frequently with oppositely dipping thrust faults tertiary structural history began with a roughly n s directed shortening in the south mecsek zone it was followed by a ne sw directed transpression activating practically all important wrench zones together with perpendicular transfer faults basins were created along some of these deformation zones but were also affected by major tilts due to inversion after a relatively quiescent period in the middle miocene the late sarmatian inversion followed shortly after this event was relayed by a ne sw directed extension transtension an important inversion period characterised by nw se compression occurred in late pannonian messinian when all the former wrench zones were reactivated as right lateral shear this event is responsible for the present topography of the region

natural fractures in shale a review and new observations natural fractures have long been suspected as a factor in production from shale reservoirs because gas and oil production commonly exceeds the rates expected from low porosity and low permeability shale host rock many shale outcrops cores and image logs contain fractures or fracture traces and microseismic event patterns associated with hydraulic fracture stimulation have been ascribed to natural fracture reactivation here we review previous work and present new core and outcrop data from 18 shale plays that reveal common types of shale fractures and their mineralization orientation and size patterns a wide range of shales have a common suite of types and configurations of fractures those at high angle to bedding faults bed parallel fractures early compacted fractures and fractures associated with concretions these fractures differ markedly in their prevalence and arrangement within each shale play however constituting different fracture stratigraphies differences that depend on interface and mechanical properties governed by depositional diagenetic and structural setting several mechanisms may act independently or in combination to cause fracture growth including differential compaction local and regional stress changes associated with tectonic events strain accommodation around large structures catagenesis and uplift fracture systems in shales are heterogeneous they can enhance or detract from producibility augment or reduce rock strength and the propensity to interact with hydraulic fracture stimulation burial history and fracture diagenesis influence fracture attributes and may provide more information for fracture prediction than is commonly appreciated the role of microfractures in production from shale is currently poorly understood yet potentially critical we identify a need for further work in this field and on the role of natural fractures generally

antitaxial crack seal vein microstructures and their relationship to displacement paths abstract the microstructures developed in an example of a syntectonic crack seal vein indicate that antitaxial fibres do not necessarily track the incremental opening history during crack seal vein growth this observation serves as a caution against the uncritical use of fibrous microstructures to make inferences about displacement histories during fibre formation it is demonstrated that crack seal processes can lead to the development of both irregular and laminated vein microstructures as well as fibrous microstructures the types of microstructures which develop in crack seal veins and the extent to which they reflect the opening paths of veins depend on a range of factors the most important of these include the nucleation and growth kinetics of phases precipitated from fluids in opening fractures and the location of sites of material accretion during successive crack seal increments

the tropospheric jet response to prescribed zonal forcing in an idealized atmospheric model abstract this paper explores the tropospheric jet shift to a prescribed zonal torque in an idealized dry atmospheric model with high stratospheric resolution the jet moves in opposite directions for torques on the jet s equatorward and poleward flanks in the troposphere this can be explained by considering how the critical latitudes for wave activity absorption change where the eastward propagation speed of eddies equals the background zonal mean zonal wind while the increased zonal winds in the subtropics allow the midlatitude eddies to propagate farther into the tropics and result in the equatorward shift in the critical latitudes the increased winds in the midlatitudes accelerate the eastward eddy phase speeds and lead to the poleward shift in the critical latitudes in contrast the jet moves poleward when a westerly torque is placed in the extratropical stratosphere irrespective of the forcing latitude the downward penetration of zonal winds to the troposphere displays a poleward slope for the

observed feedback between winter sea ice and the north atlantic oscillation abstract feedback between the north atlantic oscillation nao and winter sea ice variability is detected and quantified using approximately 30 years of observations a vector autoregressive model var and testable definitions of granger causality and feedback sea ice variability is quantified based on the leading empirical orthogonal function of sea ice concentration over the north atlantic the greenland sea ice dipole gsd which in its positive polarity has anomalously high sea ice concentrations in the labrador sea region to the southwest of greenland and low sea ice concentrations in the barents sea region to the northeast of greenland in weekly data for december through april the var indicates that nao index n anomalies cause like signed anomalies of the standardized gsd index g and that g anomalies in turn cause oppositely signed anomalies of n this negative feedback process operates explicitly on lags of up to four weeks in the var but can generate more persistent effects because o

potential formation mechanisms of early diagenetic displacive veins in the permian boda claystone formation abstract the boda claystone formation is the most promising host rock for the disposal of high level radioactive waste in hungary the formation has several properties obstructing the migration of radionuclides however structural heterogeneities may nonetheless act as migration pathways therefore understanding the tectonic evolution of the formation is vital previous research has identified four different vein generations in the baf 2 well this study deals with the generation of veins that contain characteristic microstructures such as curved wall rock inclusions in bands trails and cone in cone arrangements based on optical cathodoluminescence and electron microscopy together with x ray fluorescence and raman microspectroscopy these veins appear to have potentially formed during early diagenetic processes vein development was continuous and occurred along horizontal surfaces the abovementioned structural elements were formed by growing crystals however primary crystal morphologies were presumably replaced during diagenetic and hydrothermal processes a theoretical model is described which could be responsible for the horizontal and continuous vein opening and simultaneous crystallisation in sediments with high but easily degraded effective porosity according to this model compaction pressure solution elevated pore fluid pressures seepage forces and the force of crystallisation can all play important roles in the formation of these types of veins

crystallization pressure versus crack seal as the mechanism for banded veins banded fibrous veins are often pointed to as evidence for episodic crack opening driven by oscillations in fluid pressure or bulk strain advances in understanding the geochemistry of precipitation data on veins and experiments suggest that pressure due to growing crystals may be an alternate explanation for many observations on these types of veins we propose that some veins originate at sites of precipitation and then propagate due to the pressure exerted by the crystal growth as materials precipitate the vein walls are pushed apart the resulting veins have shapes typical for mode i cracks except that mechanically crystallization pressure replaces the role of internal fluid pressure in their propagation a nonzero remote differential stress serves to align veins mechanical and geochemical considerations suggest that this process will be most important in fine grained rocks such as greenschist grade pelites where diffusion from sites of dissolution rather than advection is the dominant mass transport process veins may owe their orientation to tectonism but their initiation and growth are due to processes that supersaturate the pore fluid veins formed by this mechanism involve cracking to the extent that precipitation forces an original flaw to extend during precipitation cyclic quartz mica bands may indicate geochemical self organization at the vein wall driven by pressure solution enhanced supersaturation in the pore fluid and nonlinear precipitation kinetics at the vein wall

the transient atmospheric response to midlatitude sst anomalies abstract to study the transient atmospheric response to midlatitude sst anomalies a three layer quasigeostrophic qg model coupled to a slab oceanic mixed layer in the north atlantic is used as diagnosed from a coupled run in perpetual winter conditions the first two modes of sst variability are linked to the model north atlantic oscillation nao and eastern atlantic pattern eap respectively the dominant atmospheric modes in the atlantic sector the two sst anomaly patterns are then prescribed as fixed anomalous boundary conditions for the model atmosphere and its transient responses are established from a large ensemble of simulations in both cases the tendency of the air sea heat fluxes to damp the sst anomalies results in an anomalous diabatic heating of the atmosphere that in turn forces a baroclinic response as predicted by linear theory this initial response rapidly modifies the transient eddy activity and thus the convergence of eddy momentum and heat fluxes the latter transforms t

sensitivity of the latitude of the surface westerlies to surface friction the sensitivity to surface friction of the latitude of the surface westerlies and the associated eddy driven midlatitude jet is studied in an idealized dry gcm the westerlies move poleward as the friction is reduced in strength an increase in the eastward phase speed of midlatitude eddies is implicated as playing a central role in this shift this shift in latitude is mainly determined by changes in the friction on the zonal mean flow rather than the friction on the eddies if the friction on the zonal mean is reduced instantaneously the response reveals two distinctive adjustment time scales in the fast adjustment over the first 10 20 days there is an increase in the barotropic component of zonal winds and a substantial decrease in the eddy kinetic energy the shift in the surface westerlies and jet latitude occurs in a slower adjustment the space time eddy momentum flux spectra suggest that the key to the shift is a poleward movement in the subtropical critical latitude associated with the faster eastward phase speeds in the dominant midlatitude eddies the view is supported by simulating the upper tropospheric dynamics in a stochastically stirred nonlinear shallow water model

the 1883 eruption of krakatau the 1883 eruption of krakatau was a modest ignimbrite forming event the deposits are primarily coarse grained dacitic non welded ignimbrite large explosions produced pyroclastic flows that entered the sea generating destructive tsunami grain size studies of the ignimbrite suggest that these explosions were not driven by magma seawater interaction the total bulk volume of pyroclastic deposits including co ignimbrite ash is estimated to be 18 21 km3

role of pressure solution in the formation of bedding parallel calcite veins in an immature shale cretaceous southern uk bedding parallel fibrous calcite veins in black shales cretaceous southern uk were investigated using a combined field stable isotopic geochemistry petrographic and crystallographic method to examine their formation mechanism calcite veins occur in all shale beds and are most abundant in the bituminous shales of the chief beef beds the calcite fibres in these veins exhibit either an antitaxial fibre growth with curvy stylolites as the median zone or a predominantly syntaxial upwards growth the calcite veins range from 0 49 to 1 78 of 13c values and 6 53 to 0 03 of 18o values which are both similar to those of their host shales our petrographic observations demonstrate that subhorizontal and interconnecting microstylolite networks commonly occur within the calcite veins equant calcite grains in the median zones exhibit indenting truncating and also interpenetrating grain contacts it is interpreted that the fibrous calcite veins were sourced by neomorphic calcite from their host shales with evidence from the 13c signatures pressure solution features stylolites microstylolites and grain contact styles and embedded fossil ghosts within the veins the diagenetic fluids from which calcite was precipitated were a mixing of the original seawaters and 18o depleted meteoric waters development of bedding parallel calcite veins is considered to have been enhanced by pressure solution as a positive feedback mechanism which was facilitated by the overburden pressure as the maximum principal stress calcite fibres with a predominant subvertical c axis orientation exhibit a displacive growth in porous shales and a replacive growth at vein limestone contacts this study highlights the critical role of pressure solution in the formation of bedding parallel calcite veins during burial and diagenesis of immature black shales

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

the origin and evolution of saline formation water lower cretaceous carbonates south central texas u s a abstract land l s and prezbindowski d r 1981 the origin and evolution of saline formation water lower cretaceous carbonates south central texas u s a in w back and r letolle guest editors symposium on geochemistry of groundwater 26th international geological congress j hydrol 54 51ndash 74 systematic chemical variation exists in formation water collected from a dip section through lower cretaceous rocks of south central texas chemical variation can be explained by an interactive water rock diagenetic model the cyclic lower cretaceous shelf carbonates of the edwards group dip into the gulf of mexico coast geosyncline and can be considered to a first approximation as part of a complex aquifer contained by paleozoic basement beneath and by relatively impermeable upper cretaceous clay and chalk above the hydrodynamic character of this carbonate system is strongly controlled by major fault systems major fault systems serve as pathways for vertical movement of basinal brines into the lower cretaceous section formation water movement in this sytem has strong upfault and updip components the parent na ca cl brine originates deep in the gulf of mexico basin at temperatures between 200 and 250 c by the reaction halite detrital plagioclase quartz water albite brine other dissolved components originate by reaction of the fluid with the sedimentary phases k feldspar calcite dolomite anhydrite celestite barite and fluorite significant quantities of pb zn and fe have been mobilized as well as the brine moves updip out of the overpressured deep gulf of mexico basin and encounters limestones of the stuart city reef trend the buried platform margin small amounts of galena precipitate in late fractures continuing to rise upfault and updip the brine becomes progressively diluted on encountering significant quantities of dolomite in the backreef facies the ca rich brine causes dedolomitization although thermochemical consideration suggests that small amounts of several authigenic phases should precipitate most have yet to be found minor amounts of several kinds of calcite spar are present however as the brine evolves by dilution and by cooling no systematic changes in any cation cl ratio occur except for regular updip gain in mg as a result of progressive dedolomitization the formation water highly diluted by meteoric water eventually discharges along faults as hot mineral water

atmospheric influence on arctic marginal ice zone position and width in the atlantic sector february april 1979 2010 arctic marginal ice zone miz widths in the atlantic sector were measured during the months of maximum sea ice extent february april for years 1979 2010 using a novel method based on objective curves through idealized sea ice concentration fields that satisfied laplace s equation over the record the labrador sea miz mizl had an average width of 122 km and narrowed by 28 while moving 254 km poleward the greenland sea miz mizg had an average width of 98 km and narrowed by 43 while moving 158 km west toward the greenland coast and the barents sea miz mizb had an average width of 136 km and moved 259 km east toward the eurasian coast without a trend in width trends in miz position and width were consistent with a warming arctic and decreasing sea ice concentrations over the record beyond the trends nao like atmospheric patterns influenced interannual variability in miz position and width mizl widened and moved southeast under anomalously strong northerly flow conducive to advection of sea ice into the labrador sea mizg widened and moved northeast under anomalously weak northerly flow conducive to diminishing the westward component of sea ice drift and mizb widened and moved poleward at the expense of pack ice under anomalously strong southwesterly flow conducive to enhancing oceanic heat flux into the barents sea in addition meridional flow anomalies associated with the nao per se moved mizb east and west by modulating sea ice concentration over the barents sea

latest cretaceous cone in cone structures and soft sediment deformation basque cantabrian basin north spain a record of deep marine paleoseismicity unusual cone in cone structures are preserved in fibrous celestite veins hosted by carbonatic rocks the veins are early diagenetic features formed near the water sediment interface in a deep marine environment of latest cretaceous early maastrichtian age new field and microscopic evidence on the veins and their host rocks indicates that they predate sediment compaction and were related to synsedimentary soft sediment deformation structures the mechanism of cone in cone formation has been related to fluid pressure drops following sediment overpressurization but instantaneous loading during emplacement of submarine slides or other mechanisms might be viable alternatives we argue that this cone in cone structure is an overprinting feature penetrative conical fractures that resulted from seismic wave propagation through a mechanically anisotropic medium submarine amplification of seismic surface waves rayleigh waves induced shock wave formation in the contacts between veins and the bounding lithified calcarenite and unlithified marl sediment layers fracture front wave propagation normal to the seafloor and the rayleigh source across the veins and along the celestite crystal fibers induced crack nucleation in heterogeneities and penetrative conical fracturation the cone in cone structure might thus be regarded as a new paleoseismological indicator in deep sea sediments

the shape propagation and mean flow interaction of large scale weather systems abstract for a zonal average operator the eliassen palm flux provides a diagnostic of both eddy behavior and the feedback of the eddies onto the mean flow this paper addresses the diagnosis problem for other averaging operators and in particular for time averaging which has proved in recent years such a powerful means of viewing the three dimensional tropospheric flow the horizontal velocity correlation tensor gives a measure of the characteristic horizontal eddy shape at a point it also implies the direction of the group velocity relative to the mean flow in cases where such a concept is valid however the major emphasis here is on the mean flow feedback of eddies in this respect the eddy vorticity flux is determined by derivatives of the components of the anisotropic part of the tensor making a reasonable approximation allows the eddy vorticity flux convergence to be written in terms of e v 2 u 2 u v a simple interpretation of the mean flow feedback of eddies is then possible a sligh

opposing effects of reflective and nonreflective planetary wave breaking on the nao planetary wave breaking pwb over the subtropical north atlantic is observed over 45 winters december 1958 arch 2003 using ncep ncar reanalysis data pwb is manifested in the rapid large scale and irreversible overturning of potential vorticity pv contours on isentropic surfaces in the subtropical upper troposphere as breaking occurs over the subtropical north atlantic an upper tropospheric pv tripole anomaly forms with nodes over the subtropical midlatitude and subpolar north atlantic the northern two nodes of this tripole are quite similar to the spatial structure of the north atlantic oscillation nao with positive polarity nonlinear reflection is identified in approximately a quarter of all pwb events following breaking two distinct circulation regimes arise one in response to reflective events and the other in response to nonreflective events for reflective events anomalies over the north atlantic rapidly propagate away from the breaking region along a poleward arching wave train over the eurasian continent the quasi stationary wave activity flux indicates that wave activity is exported out of the atlantic basin at the same time the regional poleward eddy momentum flux goes through a sign reversal as does the polarity of the nao for nonreflective events the dipole anomaly over the north atlantic amplifies diagnostics for nonreflective events suggest that wave activity over the azores gets absorbed allowing continued enhancement of both the regional poleward eddy momentum flux and the positive nao

early overpressuring in organic rich shales during burial evidence from fibrous calcite veins in the lower jurassic shales with beef member in the wessex basin uk field petrographic and geochemical analysis of fibrous calcite veins in the lower jurassic shales with beef member in the wessex basin was conducted to investigate the formation mechanism of the veins bedding parallel fibrous calcite veins including beef veins and tabular cone in cone structures are widespread in the black shales the calcite veins consist of subvertical fibrous crystals and a dark median zone the median zone contains scattered clays pyrite microcrystals skeletal fragments and amorphous organic matter the veins exhibit moderate carbon isotope values ranging from 1 515 to 2 732 the oxygen isotope composition ranges from 8 872 to 4 521 which is possibly too negative to reflect the primary porewater oxygen isotope signatures and indicates a porewater modification it is interpreted that the veins mainly derive carbonates from seawater inorganic carbon and bioclasts the veins formed as closed system hydraulic fractures in overpressured cells during sediment degassing in the methanogenic zone the shale beds with a high total organic carbon content could have generated abundant co 2 which may have resulted in either the cementing of the pores in the matrix or overpressure buildup the skeletal fragments provide a control on the spatial distribution of veins as nuclei for calcite precipitation from supersaturated pore fluids

displacive widening of calcite veins in shale insights into the force of crystallization abstract the geometry microtextures and c axis fabrics of calcite beef veins in the lower jurassic black shales wessex basin uk were characterized to investigate the mechanism responsible for widening following fracture propagation isolated beef veins exhibit planar tapering tips whereas closely spaced veins are characterized by blunt tips vein surfaces are generally smooth and flat however circular ridges appear on vein surfaces that protrude into the host clays where there are solid inclusions below or above the ridges fossils with well preserved morphologies which are separated by subvertical calcite fibers are observed on both the lower and upper surfaces of single veins the shale laminations around beef veins are folded and parallel to vein margins the beef veins commonly contain blocky zones of small equant calcite crystals pyrite and organic matter the fibers exhibit a preferred subvertical c axis orientation whilst crystals in the median zones and blocky zones have random c axis orientations the different crystal sizes morphologies and c axis orientations of the fibers from the blocky crystals suggest that the fibers grew without competition with each other under a nonhydrostatic stress field the displacive widening of calcite beef veins which is evident from vein interactions and deformation of individual fossil skeletons demonstrates that fibers grew incrementally because the crystallization pressure of calcite exceeded the overburden load the force of crystallization is suggested to be responsible for the c axis orientations of calcite fibers whereby crystals with free surfaces normal to c axis orientations grew preferentially the present study suggests that the fibrous widening of calcite veins in shale postdates their initiation and may result from displacive crystallization rather than fluid overpressure

characteristics of the atlantic storm track eddy activity and its relation with the north atlantic oscillation abstract this study focuses on feedbacks of the high frequency eddy activity onto the quasi stationary circulation particularly with regard to the north atlantic oscillation nao the methodology consists of analyzing ncep ncar reanalysis data and sensitivity runs from a high resolution nonhydrostatic regional model consistent with recent studies results show that the jet displacement characteristic of the nao phenomenon depends strongly on the dynamics of the synoptic scale waves and the way they break positive and negative phases of the nao are closely related to anticyclonic and cyclonic wave breaking respectively indeed the high frequency momentum flux whose sign is directly related to the type of wave breaking is correlated with the nao index over the atlantic the peak of the momentum flux signal precedes that of the nao by a few days suggesting that wave breaking is triggering nao events two examples illustrate the significant impact of single storms in particular those occurring in the e

the role of rossby wave breaking in shaping the equilibrium atmospheric circulation response to north atlantic boundary forcing abstract the role of rossby wave breaking rwb is explored in the transient response of an atmospheric general circulation model to boundary forcing by sea ice anomalies related to the north atlantic oscillation nao when the ncar community climate model version 3 was forced by an exaggerated sea ice extent anomaly corresponding to one arising from a positive nao a localized baroclinic response developed and evolved into a larger scale equivalent barotropic pattern resembling the negative polarity of the nao the initial baroclinic response shifted the phase speeds of the dominant eddies away from a critical value equal to the background zonal flow speed resulting in significant changes in the spatial distribution of rwb the forcing of the background zonal flow by the changes in rwb accounts for 88 of the temporal pattern of the response and 80 of the spatial pattern of the zonally averaged response although results here focus on one experiment this rwb critical line mechanism appears to be