removing tidal period variations from time series data using low pass digital filters abstract several low pass digital filters are examined for their ability to remove tidal period variations from a time series of water surface elevation for san francisco bay the most efficient filter is the one which is applied to the fourier coefficients of the transformed data and the filtered data recovered through an inverse transform the ability of the filters to remove the tidal components increased in the following order 1 cosine lanczos filter 2 cosine lanczos squared filter 3 godin filter and 4 a transform fitter the godin fitter is not sufficiently sharp to prevent severe attenuation of 2 3 day variations in surface elevation resulting from weather events

late paleoproterozoic extension and a paleostress field reconstruction of the north china craton abstract mafic dyke swarms and aulacogens are major anorogenic extensional events in the late paleoproterozoic north china craton ncc the n nnw mafic dyke swarms are widespread in the ncc whose ages span between 1 83 and 1 77 ga the similar ages and orientations of 1 8 ga dyke swarms in the ncc demonstrate that the amalgamated ncc experienced widespread extension at this time based on the width statistics of dyke swarms on ten survey lines an average crustal extension ratio of 0 35 was found for the ncc the small magnitude of overall extension suggests that the mafic dyke swarms were emplaced into the elastic fractures and indicates that the ncc had become a brittle plate prior to the emplacement of the mafic dyke swarms precisely dated mafic dyke swarms when used as paleostress indicators can be employed in the paleostress field reconstruction of precambrian cratons two dimensional finite element modeling 2 d fem of the ncc in which the various blocks were assigned densities and elastic constants shows that north south compression favors dyke intrusion along generally n nw lines and that deviations in dyke trends can be explained by the effects of boundary constraints and the physical properties of the crust the best fitting model can be considered a plausible representation of the tectonic force acting on the ncc that produces the intraplate stress field that is most consistent with the observed orientation of dyke swarms the results of modeling of the late paleoproterozoic stress field suggest a common tectonic setting for the emplacement of mafic dyke swarms in the central orogenic zone western and east blocks of the ncc the results also show that the north south tectonic forces play an important role in determining the paleostress field in the ncc the widespread extension of the ncc resulted from the north south tectonic forces which may be related to the break up of the late paleoproterozoic supercontinent the paleostress field modeling provides a possible approach to consider the supercontinent paleostress reconstruction and to reveal the mechanisms of the supercontinent break up

extent of power law scaling for natural fractures in rock new data sets from natural faults and extension fractures exhibit simple power law scaling across 3 4 4 9 orders of magnitude regardless of rock type or movement mode the data show no evidence of natural gaps or scaling changes each data set consists of independent measurements made at different observational scales a power law regression to the subset of smaller fractures in each case provides an extrapolation that accurately predicts associated larger fractures consequently data representing a limited range of fracture sizes may be used to characterize a much broader spectrum of fracture sizes

is enso a cycle or a series of events 1 after early ideas that saw el ninos as isolated events the advent of coupled models brought the conception of enso as a cycle in which each phase led to the next in a self sustained oscillation twenty two years of observations that represent the el nino and la nina peaks east pacific sst and the memory of the system zonal mean warm water volume suggest a distinct break in the cycle in which the coupled system is able to remain in a weak la nina state for up to two years so that memory of previous influences would be lost similarly while the amplitude of anomalies persists from the onset of a warm event through its termination there is no such persistence across the la nina break these observations suggest that el ninos are in fact event like disturbances to a stable basic state requiring an initiating impulse not contained in the dynamics of the cycle itself

quantifying the role of oceanic feedbacks on enso asymmetry the role of oceanic feedbacks in determining the asymmetry of el nino southern oscillation enso magnitude spatial structure and duration is quantified on the basis of a novel temperature variance budget results confirm previous studies that in the eastern pacific el nino warm temperature anomalies are larger in magnitude than la nina cold temperature anomalies mainly due to stronger positive oceanic feedbacks for el nino we find that la nina cold anomalies are typically stronger than el nino warm anomalies in the central pacific with a faster growth rate for cold anomalies due to a stronger positive thermocline feedback and weaker nonlinear damping the thermocline feedback related to recharge oscillator dynamics plays a dominate role and leads to asymmetry in the duration of el nino and la nina events in particular the thermocline feedback becomes significantly negative during the late decaying phase of el nino and speeds up its demise

fluid inclusion evidence of petroleum migration through a buried metamorphic dome in the pannonian basin hungary some of the petroleum currently produced in the pannonian basin in hungary stems from buried metamorphic basement domes that form structural highs between neogene sedimentary sub basins in the bekes sedimentary sub basin the source rocks of the petroleum are known to be of middle to late miocene age whereas at least part of the petroleum in the adjacent szeghalom basement dome appears to be of lower miocene age or even older virtually nothing is known about the compositions distribution sources and migration history of this older petroleum although such variables are crucial to future exploration strategies this study addresses the first two of these gaps in knowledge by providing a basic characterization of the older petroleum trapped as fluid inclusions in fracture hosted quartz crystals within the szeghalom dome szd fluid inclusion samples from 9 wells at depths of 1900 to 2200 m were analysed by visible and cie calibrated uv microscopy microthermometry laser raman and 1 h nmr spectroscopy two major types of early miocene oils were found distributed over 5 distinct temporal generations an earlier immature brown oil succeeded by a light gas condensate the early petroleum was undersaturated with respect to methane gas and it migrated through the fracture network at temperatures between about 160 to 130 c entraining blebs of bitumen and flushed by weakly saline water the later gas condensate migration consisted of a heterogeneous mixture of volatile oil methane rich gas weakly saline water at slightly lower temperatures between 135 and 120 c the temperature evolution was caused by cooling of the metamorphic wall rocks during basement uplift culminating in middle miocene exhumation the various hydrocarbons are unevenly distributed across the szeghalom dome showing that pre middle miocene fluid migration through the fracture network was compartmentalized at the km scale 2007 elsevier b v all rights reserved

subsurface fractures and their relationship to stress history in east texas basin sandstone abstract subsurface fractures were sampled with more than 400 m of core from the lower cretaceous travis peak formation a tabular sandstone and shale unit approximately 600 m thick that was deposited in the gradually subsiding gulf coast basin depth to the top of the formation in east texas now ranges between 1800 and 2900 m fractures in sandstone exhibit features that are due to intermittent fracturing and sealing crack seal which suggest that the fractures are the result of episodes of fluid pressure in excess of hydrostatic correlation of the vein mineral precipitation sequence with the diagenetic history and the results of previous 18 o studies of quartz cement indicates that fractures propagated at depths of between 900 and 1500 m during the migration of quartz precipitating fluids fracture permeability provides a mechanism for the passage of large fluid volumes recorded by the precipitation of extensive quartz cement in the formation fractures stopped propagating before maximum burial depth was achieved during approximately 1500 m of subsequent burial fractures either remained partly open or were sealed by postkinematic ankerite and clay minerals

asymmetry in the duration of el nino and la nina abstract el nino and la nina are not a simple mirror image but exhibit significant differences in their spatial structure and seasonal evolution in particular sea surface temperature sst anomalies over the equatorial pacific cold tongue are larger in magnitude during el nino compared to la nina resulting in positive skewness of interannual sst variations the associated atmospheric deep convection anomalies are displaced eastward during el nino compared to la nina because of the nonlinear atmospheric response to sst in addition to these well known features an analysis of observational data for the past century shows that there is a robust asymmetry in the duration of el nino and la nina most el ninos and la ninas develop in late boreal spring summer when the climatological cold tongue is intensifying and they peak near the end of the calendar year after the mature phase el ninos tend to decay rapidly by next summer but many la ninas persist through the following year and often reintensify in

recharge oscillator mechanisms in two types of enso the el ni oscillation enso tends to behave arguably as two different types or flavors in recent decades one is the canonical cold tongue type enso with major sea surface temperature anomalies ssta positionedoverthe easternpacific theotheris awarm pool typeensowith sstacenteredin the central pacific near the edge of the warm pool in this study the basic features and main feedback processes of these two types of enso are examined it is shown that the interannual variability of upper ocean heat content exhibits recharge discharge processes throughout the life cycles of both the cold tongue ct and warm pool wp enso types through a heat budget analysis with focus on the interannual frequency band the authors further demonstrate that the thermocline feedback plays a dominant role in contributing to the growth and phase transitions of both enso types whereas the zonal advective feedback contributes mainly to their phase transitions the westward shift of the ssta center of the wp enso and the presence of significant surface easterly wind anomalies over the far eastern equatorial pacific during its mature warm phase are the two main factors that lead to a reduced positive feedback for the eastern pacific ssta nevertheless both the wp and ct enso can be understood to a large extent by the recharge oscillator mechanism

a new paradigm for the predominance of standing central pacific warming after the late 1990s canonical el nino has a warming center in the eastern pacific ep but in recent decades el nino warming center tends to occur more frequently in the central pacific cp the definitions and names of this new type of el nino however have been notoriously diverse which makes it difficult to understand why the warming center shifts here we show that the new type of el nino events is characterized by 1 the maximum warming standing and persisting in the cp and 2 the warming extending to the ep only briefly during its peak phase for this reason we refer to it as standing cp warming cpw global warming has been blamed for the westward shift of maximum warming as well as more frequent occurrence of cpw however we find that since the late 1990s the standing cpw becomes a dominant mode in the pacific meanwhile the epochal mean trade winds have strengthened and the equatorial thermocline slope has increased contrary to the global warming induced weakening trades and flattening thermocline we propose that the recent predominance of standing cpw arises from a dramatic decadal change characterized by a grand la nina like background pattern and strong divergence in the cp atmospheric boundary layer after the late 1990s the anomalous mean cp wind divergence tends to weaken the anomalous convection and shift it westward from the underlying sst warming due to the suppressed low level convergence feedback this leads to a westward shift of anomalous westerly response and thus a zonally in phase sst tendency preventing eastward propagation of the sst anomaly we anticipate more cpw events will occur in the coming decade provided the grand la nina like background state persists

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

observations of warm water volume changes in the equatorial pacific and their relationship to el nino and la nina abstract this paper describes observed changes in surface winds sea surface temperature sst and the volume of water warmer than 20 c wwv in the equatorial pacific ocean for the period 1980 99 the purpose is to test recent hypotheses about the relationship between variations in wwv and the el nino southern oscillation enso cycle the results confirm inferences based on theory models and previous empirical analyses using proxy data namely sea level that enso involves a recharge and discharge of wwv along the equator and that the cyclic nature of enso results from a disequilibrium between zonal winds and zonal mean thermocline depth the authors also find that the magnitude of enso sst anomalies is directly related to the magnitude of zonal mean wwv anomalies furthermore for a given change in equatorial wwv the corresponding warm el nino sst anomalies are larger than the corresponding cold la nina anomalies this asymmetry between the warm and cold phases of the enso cycle implies differences

velocity determination for pore pressure prediction overpressured formations exhibit several of the following properties when compared with a normally pressured section at the same depth dutta 2002 1 higher porosities 2 lower bulk densities 3 lower effective stresses 4 higher temperatures 5 lower interval velocities and 6 higher poisson s ratios

predrill pore pressure prediction using seismic data 1a predrill estimate of pore pressure can be obtained from seismic velocities using a velocity to pore pressure transform but the seismic velocities need to be derived using methods having sufficient resolution for well planning purposes for a deepwater gulf of mexico example significant differences are found between the velocity field obtained using reflection tomography and that obtained using a conventional method based on the dix equation these lead to significant differences in the predicted pore pressure parameters in the velocity to pore pressure transform are estimated using seismic interval velocities and pressure data from nearby calibration wells the uncertainty in the pore pressure prediction is analyzed by examining the spread in the predicted pore pressure obtained using parameter combinations which sample the region of parameter space consistent with the available well data if calibration wells are not available the ideas proposed in this paper can be used with measurements made whi

reequilibration of fluid inclusions in low temperature calcium carbonate cement calcium carbonate cements precipitated in low temperature near surface vadose environments contain fluid inclusions of variable vapor to liquid ratios that yield variable homogenization temperatures cements precipitated in low temperature phreatic environments contain one phase all liquid fluid inclusions neomorphism of unstable calcium carbonate phases may cause reequilibration of fluid inclusions stable calcium carbonate cements of low temperature origin which have been deeply buried contain fluid inclusions of variable homogenization temperature and variable salt composition most inclusion fluids are not representative of the fluids present during cement growth and are more indicative of burial pore fluids therefore low temperature fluid inclusions probably reequilibrate with burial fluids during progressive burial reequilibration is likely caused by high internal pressures in inclusions which result in hydrofracturing the resulting fluid inclusions population could contain a nearly complete record of burial fluids in which a particular rock has been bathed

analysis of the non linearity in the pattern and time evolution of el nino southern oscillation in this study the observed non linearity in the spatial pattern and time evolution of el nino southern oscillation enso events is analyzed it is shown that enso skewness is not only a characteristic of the amplitude of events el ninos being stronger than la ninas but also of the spatial pattern and time evolution it is demonstrated that these non linearities can be related to the non linear response of the zonal winds to sea surface temperature sst anomalies it is shown in observations as well as in coupled model simulations that significant differences in the spatial pattern between positive el nino versus negative la nina and strong versus weak events exist which is mostly describing the difference between central and east pacific events central pacific events tend to be weak el nino or strong la nina events in turn east pacific events tend to be strong el nino or weak la nina events a rotation of the two leading empirical orthogonal function modes illustrates that for both el nino and la nina extreme events are more likely than expected from a normal distribution the bjerknes feedbacks and time evolution of strong enso events in observations as well as in coupled model simulations also show strong asymmetries with strong el ninos being forced more strongly by zonal wind than by thermocline depth anomalies and are followed by la nina events in turn strong la nina events are preceded by el nino events and are more strongly forced by thermocline depth anomalies than by wind anomalies further the zonal wind response to sea surface temperature anomalies during strong el nino events is stronger and shifted to the east relative to strong la nina events supporting the eastward shifted el nino pattern and the asymmetric time evolution based on the simplified hybrid coupled rechoz model of enso it can be shown that the non linear zonal wind response to sst anomalies causes the asymmetric forcings of enso events this also implies that strong el ninos are mostly wind driven and less predictable and strong la ninas are mostly thermocline depth driven and better predictable which is demonstrated by a set of 100 perfect model forecast ensembles

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

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 role of reversed equatorial zonal transport in terminating an enso event abstractthis study shows the sudden basinwide reversal of anomalous equatorial zonal transport above the thermocline at the peaking phase of enso triggers rapid termination of enso events the anomalous equatorial zonal transport is controlled by the concavity of anomalous thermocline meridional structure across the equator during the developing phase of enso opposite zonal transport anomalies form in the western central and central eastern equatorial pacific respectively both are driven by the equatorial thermocline anomalies in response to zonal wind anomalies over the western central equatorial ocean at this stage the anomalous zonal transport in the east enhances enso growth through zonal sst advection in the mature phase of enso off equatorial thermocline depth anomalies become more dominant in the eastern pacific because of the reflection of equatorial signals at the eastern boundary as a result the meridional concavity of the thermocline anomalies is reversed in the east this change reve

changes in tropical pacific thermocline depth and their relationship to enso after 1999 abstractthe characteristics of el nino southern oscillation enso variability have experienced notable changes since the late 1990s including a breakdown of the zonal mean upper ocean heat content as a precursor for enso these changes also initiated a debate on the role of thermocline variations on the development of enso events since the beginning of the twenty first century in this study the connection between thermocline variations and el nino and la nina events is examined separately for the 1980 98 and 1999 2012 periods the analysis highlights the important role of thermocline variations in modulating enso evolutions in both periods it is found that thermocline variation averaged in the central tropical pacific including both equatorial and off equatorial regions is a good precursor for enso evolutions before and after 1999 while the traditional basinwide mean of equatorial thermocline variation is a good precursor only before 1999 the new precursor including both high frequency variabili

meridional movement of wind anomalies during enso events and their role in event termination 1 observational analysis has shown that when el nino southern oscillation enso events typically reach their peak amplitude in boreal winter the associated zonal wind anomalies abruptly shift southward so that the maximum anomalous zonal wind is located around 5 7 s here an analysis utilizing multiple wind products identifies a clear enso phase nonlinearity in the extent of this meridional wind movement and its dynamically linked changes in equatorial heat content it is shown that the meridional wind movement and its discharging effect increase with increasing el nino amplitude while both remain relatively small regardless of la nina amplitude this result implies that asymmetries in the extent of the meridional wind shift may contribute to the observed asymmetry in the duration of el nino and la nina events we also evaluate the result sensitivities to wind product selection and discuss eastern pacific ep and central pacific cp el nino event differences

beef veins and thrust detachments in early cretaceous source rocks foothills of magallanes austral basin southern chile and argentina structural evidence for fluid overpressure during hydrocarbon maturation abstract we describe 1 bedding parallel veins of fibrous calcite beef and 2 thrust detachments which we believe provide good evidence for fluid overpressure in source rocks for petroleum our examples are from the surface or subsurface of the magallanes austral basin which lies at the southern tip of south america there the best source rocks for petroleum are of early cretaceous age in the central parts of the basin these source rocks have become overmature but at the eastern edge onshore and offshore they are today either immature or in the oil window in tierra del fuego the foothills of the andes consist mainly of sedimentary rocks which have undergone thin skinned thrusting in the vicuna area chile early cretaceous source rocks have reached the surface above thrust detachments which are visible on seismic data and well data at the surface we have found calcite beef containing hydrocarbons solid and or fluid in the rio jackson and vicuna formations which have reached the wet gas window in the rio gallegos area argentina the source rocks have not reached the surface but seismic and well data provide good evidence for thin skinned thrusting above flat lying detachments in early cretaceous source rock where it is in the early oil window in contrast there is little or no deformation where the source rock is still immature thus the deformation front coincides with the maturity front next to the central parts of the basin where the source rocks have reached the surface within the andes proper they have undergone low grade metamorphism within these source rocks we have found beef veins but of quartz not calcite to the east within the foreland basin seismic and well data provide evidence for a few compressional structures including thin skinned detachments in the deeply buried source rock finally in the northern part of the basin santa cruz province argentina where it is shallower the source rocks have reached the surface in the foothills above a series of back thrusts at lago san martin the source rocks have reached the oil window and they again contain calcite beef in conclusion where we have examined early cretaceous source rocks at the surface they contain either calcite beef if they have reached the late oil window or wet gas window or quartz beef if they are overmature independent evidence for overpressure in the form of source rock detachments comes from subsurface data especially at the southern end of the basin where the source rocks are not overmature and deformation is relatively intense thus we argue that hydrocarbon generation has led to overpressure as a result of chemical compaction and load transfer or volume changes or both

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

causes of the el nino and la nina amplitude asymmetry in the equatorial eastern pacific abstract the amplitude asymmetry between el nino and la nina is investigated by diagnosing the mixed layer heat budget during the enso developing phase by using the three ocean assimilation products simple ocean data assimilation soda 2 0 2 soda 1 4 2 and the global ocean data assimilation system godas it is found that the nonlinear zonal and meridional ocean temperature advections are essential to cause the asymmetry in the far eastern pacific whereas the vertical nonlinear advection has the opposite effect the zonal current anomaly is dominated by the geostrophic current in association with the thermocline depth variation the meridional current anomaly is primarily attributed to the ekman current driven by wind stress forcing the resulting induced anomalous horizontal currents lead to warm nonlinear advection during both el nino and la nina episodes and thus strengthen weaken the el nino la nina amplitude the convergence divergence of the anomalous geostrophic mixed layer currents dur

the petroleum generation potential and effective oil window of humic coals related to coal composition and age abstract a worldwide data set of more than 500 humic coals from the major coal forming geological periods has been used to analyse the evolution in the remaining hydrogen index hi and total quality index qi generation potentials with increasing thermal maturity and the effective oil window oil expulsion window all samples describe hi and qi bands that are broad at low maturities and that gradually narrow with increasing maturity the oil generation potential is completely exhausted at a vitrinite reflectance of 2 0 2 2 ro or tmax of 500 510 c the initial large variation in the generation potential is related to the original depositional conditions particularly the degree of marine influence and the formation of hydrogen enriched vitrinite as suggested by increased sulphur and hydrogen contents during initial thermal maturation the hi increases to a maximum value himax similarly qi increases to a maximum value qimax this increase in hi and qi is related to the formation of an additional generation potential in the coal structure the decline in qi with further maturation is indicating onset of initial oil expulsion which precedes efficient expulsion liquid petroleum generation from humic coals is thus a complex three phase process i onset of petroleum generation ii petroleum build up in the coal and iii initial oil expulsion followed by efficient oil expulsion corresponding to the effective oil window efficient oil expulsion is indicated by a decline in the bitumen index bi when plotted against vitrinite reflectance or tmax this means that in humic coals the vitrinite reflectance or tmax values at which onset of petroleum generation occurs cannot be used to establish the start of the effective oil window the start of the effective oil window occurs within the vitrinite reflectance range 0 85 1 05 ro or tmax range 440 455 c and the oil window extends to 1 5 2 0 ro or 470 510 c for general use an effective oil window is proposed to occur from 0 85 to 1 7 ro or from 440 to 490 c specific ranges for himax and the effective oil window can be defined for cenozoic jurassic permian and carboniferous coals cenozoic coals reach the highest himax values 220 370 mg hc g toc and for the most oil prone cenozoic coals the effective oil window may possibly range from 0 65 to 2 0 ro or 430 to 510 c in contrast the most oil prone jurassic permian and carboniferous coals reach the expulsion threshold at a vitrinite reflectance of 0 85 0 9 ro or tmax of 440 445 c

two types of el nino events cold tongue el nino and warm pool el nino abstract in this study two types of el nino events are classified based on spatial patterns of the sea surface temperature sst anomaly one is the cold tongue ct el nino which can be regarded as the conventional el nino and the other the warm pool wp el nino the ct el nino is characterized by relatively large sst anomalies in the nino 3 region 5 s 5 n 150 90 w while the wp el nino is associated with sst anomalies mostly confined to the nino 4 region 5 s 5 n 160 e 150 w in addition spatial patterns of many atmospheric and oceanic variables are also distinctively different for the two types of el nino events furthermore the difference in the transition mechanism between the two types of el nino is clearly identified that is the discharge process of the equatorial heat content associated with the wp el nino is not efficient owing to the spatial structure of sst anomaly as a result it cannot trigger a cold event it is also demonstrated that zonal advective feedback i e zonal adve

subsurface fracture analysis and determination of in situ stress direction using fmi logs an example from the santonian carbonates ilam formation in the abadan plain iran abstract the relationship between the present day stress field and natural fractures can have significant implications for subsurface fluid flow in particular fractures that are aligned in orientations favourable for reactivation by either shear or tensile failure in the in situ stress field often exhibit higher hydraulic conductivities the ilam formation of southwestern iran is an important hydrocarbon reservoir containing numerous natural fractures however little is known about the state of stress in this region or any of iran s petroleum provinces we conducted analysis of the present day maximum horizontal stress orientation and the density orientation and hydraulic conductivity of natural fractures in the ilam carbonates using high resolution formation micro imager resistivity logs in two wells a total of 51 breakouts with an overall length of 215 m were observed in the two wells indicating a maximum horizontal stress orientation of 68 n 7 6 in well a and 58 n 6 3 in well b furthermore the wellbore derived stress orientations determined herein are consistent with those inferred from nearby earthquake focal mechanism solutions indicating that stresses in the sedimentary cover are linked to the resistance forces generated by arabia eurasia collision furthermore the correlation between stress orientations estimated from earthquake focal mechanism solutions and breakouts indicates that focal mechanism solution data which is often considered to be unreliable for stress field analysis near transform margins may provide reliable information on the stress orientation near continental collision zones the image log data also reveals three sets of open and presumably hydraulically conductive fractures with strikes of i 160 170 n ii 110 140 n and iii 070 080 n fracture set iii is consistent with being formed and open in the present day stress field however fracture sets i and ii strike at a high angle to the present day maximum horizontal stress and are interpreted herein to be the result of either pre or syn folding related forces the observation that different sets of open fractures in the field can be either sensitive or insensitive to the present day stress is critical for improving hydrocarbon recovery

palaeoseismic events recorded in archaean gold quartz vein networks val d or abitibi quebec canada archaean gold quartz vein deposits are commonly hosted in high angle reverse shear zones and are interpreted to have formed in a regime of horizontal compression and high fluid pressure environment this paper presents the results of a combined structural and fluid inclusion study on three gold quartz vein deposits of the val d or area abitibi quebec consisting of subhorizontal extensional veins and e w steeply dipping shear veins crack seal structures tourmaline fibres stretched quartz crystals and open space filling textures indicate that the subhorizontal veins formed by hydraulic fracturing under supralithostatic fluid pressure co2 rich and h2o nacl fluid inclusions interpreted as two coexisting immiscible fluids occur typically in microcracks of different orientations interpreted to have formed in the 1 2 plane horizontal co2 rich fluid inclusion planes are contemporaneous with the opening of these veins 3 vertical vertical h2o nacl fluid inclusion planes as well as some microstructures such as deformed minerals indicate that the same extensional veins have experienced episodic vertical shortening 3 horizontal alternating with the opening events deformation and slip opening also occurred in shear veins in which preferred orientation of fluid inclusion planes is not clear except that the h2o nacl fluid inclusion planes tend to be oriented at high angles to the slip direction the successive opening and collapse events in subhorizontal extensional veins are correlated with deformation and slip opening events in shear veins respectively and are attributed to cyclic fluid pressure fluctuations in the system they are thus consistent with the fault valve model sudden drop in fluid pressure from supralithostatic to lower values induces fluid unmixing and occurs immediately post failure following seismic rupturing along the shear zone sealing of the shear veins allows the fluid pressure to build up again and the subhorizontal extensional veins to form the intermittent change in orientation of 3 in horizontal extensional veins is ascribed to a total shear stress release along the neighbouring shear veins after rupture the complex internal structures of the gold quartz veins provide an excellent record of archaean seismic activity along high angle reverse faults

natural fractures in carbonate rich tight oil reservoirs from the permian lucaogou formation southern junggar basin nw china insights from fluid inclusion microthermometry and isotopic geochemistry abstract natural fractures within tight reservoirs form preferred pathways for hydrocarbon charge and provide space for hydrocarbon preservation however the mechanism that controls the formation of natural fractures in tight reservoirs remains controversial this study investigates natural fractures within carbonate rich tight oil reservoirs from the permian lucaogou formation in the jimsar sag southern junggar basin drill core and image log observations show that fractures in the lucaogou formation can be categorized into two types bedding parallel fractures and inclined fractures the carbon and oxygen isotopic compositions of calcite cements in the bedding parallel fractures range from 0 6 to 6 0 13cpdb and from 15 5 to 8 9 18opdb respectively which are similar to those of the organic rich host rock this suggests that the bedding parallel fractures likely formed in a closed fluid system fluid inclusion analyses of the aqueous inclusions in calcite cements from the bedding parallel fractures record homogenization temperatures of 91 5 c 130 4 c indicating that they formed at the cretaceous to cenozoic during when the lucaogou formation reached peak oil generation stage therefore the bedding parallel fractures were most likely generated by hydrocarbon generation overpressure the presence of hydrocarbon inclusions in bedding parallel fracture cements supports natural fracturing by high pore fluid pressure the 13cpdb and 18opdb of calcite cements within the inclined fractures vary from 3 6 to 9 6 and from 11 0 to 2 9 respectively which are close to those of the carbonate rich parent rock this also supports a closed fluid system scenario the relatively lower fluid inclusion trapping temperatures 70 5 c 109 7 c suggest that they were likely generated by decrease of confining stress during uplift processes therefore both an increase in pore fluid pressure and a decrease in confining stress contribute to the formation of natural fractures in the lucaogou formation tight oil reservoirs

migration of atmospheric convection coupled with ocean currents pushes el nino to extremes the warm phase of el nino southern oscillation can grow much stronger than the cold phase but the associated dynamics are not well understood here we show that the anomalous zonal advection of warm water is the major process that pushes el nino to extremes and that this anomalous advection results from the coupling of oceanic currents with eastward migration of the atmospheric convection a greater zonal advection is associated with a greater extent of the eastward migration by contrast there is a limited extent for westward migration during la nina climate models that successfully simulate the amplitude asymmetry display a systematic linkage of a greater longitudinal movement of the convection center with a stronger zonal advection and greater el nino amplitude in a warming world the longitudinal migration of convection response increases as does the role of zonal advection increasing the frequency of future extremes of el nino

regional fractures i a mechanism for the formation of regional fractures at depth in flat lying reservoirs 1 regional fractures may form slowly at depth in extension and parallel to regional horizontal tectonic compression such fracture sets can be common in reservoirs despite the absence of flexure of the strata and are commonly important contributors to reservoir permeability such fractures make good targets for deviated wells high formation pore pressure is crucial to creating low effective confining stresses and brittle rock properties in the reservoirs conditions conducive to fracturing despite deep burial but pore pressure does not exceed the least principal stress and does not cause tensile fracturing the mechanism of natural hydraulic fracturing is incompatible with the characteristics of most regional fracture sets rather many regional fractures form duri g far field compression initiate at locally induced tensile stresses caused by flaws in the rock and propagate in the plane of the maximum and intermediate compressive stresses the differential stress required for initiation and propagation of regional fractures is well below that necessary for shear failure in the presence of high pore pressure fractures can be held open at depth by a tectonic basinwide dilatancy of the strata and the open void space commonly becomes mineralized

el nino la nina and the nonlinearity of their teleconnections the paradigm of an atmospheric system varying linearly with respect to extreme phases of the el nino southern oscillation is questioned it is argued that the global response to tropical pacific sea surface temperature forcing will be inherently nonlinear a physical basis for this intrinsic nonlinearity is the thermodynamic control on deep convection climate statistics for warm and cold events of the tropical pacific are analyzed separately for the northern winter periods during 1950 96 composite analysis of 500 mb heights reveal planetary scale teleconnection patterns as noted in earlier studies a new result is the evidence for an appreciable 358 longitude phase shift between the warm and cold event circulation composites and the two wave trains appear to have different tropical origins a large nonlinear component in north american surface climate anomalies is also found which is consistent with such a phase shift in teleconnections in the tropics rainfall anomalies also show evidence of nonlinear behavior the maximum rain anomalies along the equator are located east of the date line during warm events but west of the date line during cold events the interpretation of this behavior is complicated however by the fact that composite warm event sst anomalies are not the exact inverse of their cold event counterparts idealized atmospheric general circulation model agcm experiments are performed in order to test the question of whether the observed nonlinearity is an intrinsic property of the atmospheric system the model is forced with a composite sst anomaly that undergoes a realistic seasonally varying enso life cycle as described by e rasmusson and t carpenter both positive and negative phases of the sst anomaly are used and a 40 member ensemble of warm and cold event model simulations is conducted a nonlinear climate response in the agcm is found that closely resembles the observed composites including a shift in the equatorial positions of the maxmium rain responses and a phase shift of teleconnection patterns in the upper troposphere barotropic model experiments indicate that the inherent nonlinearity in the tropical rain response may itself be responsible for the phase shift in the extratropical teleconnection patterns

variability of the meridional overturning in the north atlantic from the 50 year gecco state estimation abstract the german partner of the consortium for estimating the circulation and climate of the ocean gecco provided a dynamically consistent estimate of the time varying ocean circulation over the 50 yr period 1952 2001 the gecco synthesis combines most of the data available during the entire estimation period with the ecco massachusetts institute of technology mit ocean circulation model using its adjoint this gecco estimate is analyzed here for the period 1962 2001 with respect to decadal and longer term changes of the meridional overturning circulation moc of the north atlantic a special focus is on the maximum moc values at 25 n over this period the dynamically self consistent synthesis stays within the error bars of h l bryden et al but reveals a general increase of the moc strength the variability on decadal and longer time scales is decomposed into contributions from different processes changes in the model s moc strength are strongly influenced by the southward communication of d

surface layer temperature balance in the equatorial pacific during the 1997 98 el nino and 1998 99 la nina abstract the surface layer temperature balance in the equatorial pacific has been examined for the period of 1996 99 by using data obtained from tropical atmosphere ocean buoy array at four locations along the equator namely 165 e 170 w 140 w and 110 w time rate change of sst horizontal temperature advection and heat fluxes at the sea surface are estimated directly from the data vertical fluxes of heat out of the base of the mixed layer related to changes in vertical mixing and upwelling are calculated as a residual results indicate that all terms in the temperature balance contributed to sst variations during different stages of the 1997 98 el nino and the 1998 99 la nina zonal advection was particularly important during the onset of the el nino in the central pacific the inferred vertical heat flux out of the base of the mixed layer was important most of the time and was especially pronounced in the eastern pacific during the termination phase of the el nino meridional advection due to e

changing fluid conditions during folding an example from the central appalachians abstract fluids inclusion microthermometry and stable isotope analyses of vein minerals in the central appalachian patterson creek anticline record dynamic changes in fluid temperature pressure and chemistry during folding these changes resulted from variations in fracture connectivity and fluid communication between stratigraphically restricted fluid reservoirs minerals in early formed bed parallel and ene nnw striking cross fold veins show that prior to folding fluids in silurian through lower upper devonian rocks were well stratified based temperature salinity and isotopic composition stable isotopes data indicates that the fluid systems were essentially closed with no communication between layers as folding commenced early minerals in ne nw striking veins in the siluro devonian carbonate rocks record 2 km of burial by syn tectonic sedimentation with corresponding increases in fluid temperature and pore fluid pressure an additional 2 km of burial along with the influx of low salinity methane saturated brines into the middle and upper devonian clastic rock sequence is recorded by later quartz in the ne nw striking veins at some point during folding stable isotope data indicate that fluid communication increased along fracture and faults between major stratigraphic fluids reservoirs the culmination of this process was the breaching of the stratigraphic seal at the base of the devonian shales allowing fluid infiltration from the devonian shale sequence into the upper portion of the helderberg group this resulted in the local precipitation of quartz and possibly the enhancement of solution structures

el nino events and their relation to the southern oscillation 1925 1986 relationships among sea surface temperatures ssts at the coast of peru and offshore river discharge in northern peru and sea level pressure at darwin australia during the period 1925 1986 are investigated using time series plots frequency distributions and a simple statistical analysis it is shown that ssts undergo a larger seasonal cycle offshore than at the coast exhibit more interannual variability during the warm than the cool season are positively skewed during much of the year and exhibit greatest month to month persistence during the cool season many but not all episodes of above normal coastal ssts are accompanied by enhanced river discharge in northern peru comparison of the darwin pressure and coastal sst records during the past 60 years shows that el nino events episodes of above normal ssts along the coast of peru have occurred both in advance of and subsequent to major negative swings of the southern oscillation and associated climatic changes in the central equatorial pacific in addition el nino events and negative swings of the southern oscillation have occurred separately hence el nino and the southern oscillation are more loosely coupled than other studies would imply

asymmetric evolution of el nino and la nina the recharge discharge processes and role of the off equatorial sea surface height anomaly observed oceanic and atmospheric anomalies in the tropical pacific are analyzed to understand the symmetric and asymmetric characteristics between el nino and la nina evolutions it is noted that the evolutions are largely symmetric for el nino and la nina prior to and in their mature phase but become asymmetric afterwards it is further demonstrated that this asymmetry is due to the fact that on average the discharge process associated with el nino is stronger than the recharge counterpart associated with la nina the symmetric and asymmetric evolution for different phases of el nino southern oscillation enso is consistent with the associated recharge and discharge processes that are linked with the evolution of anomalous ocean surface current and gradient of sea surface height anomalies sshas it is suggested that the evolution of the meridional gradient of sshas in the central and eastern equatorial pacific is different between el nino and la nina years due to relatively different rates of the ssha changes on and off the equator during the decay of a warm event the equatorial ssha quickly switches from positive to negative meanwhile the off equator areas are occupied by positive sshas such changes on the equator and in the off equatorial regions make the concavity of the meridional ssha favorable for growth and persistence of westward surface zonal current anomaly in the equatorial pacific then for the enso phase transition during the decay of a cold event the slow decrease of the negative ssha on the equator combined with the disappearance of the negative ssha in the off equatorial regions makes the meridional concavity reverse easily and is unfavorable for the steady growth of the eastward surface zonal current anomaly and for the phase transition thus the asymmetric evolution of enso is associated with both the atmosphere and ocean anomalies on the equator and off the equator