why permafrost rocks become unstable a rock ice mechanical model in time and space in this paper we develop a mechanical model that relates the destabilisation of thawing permafrost rock slopes to temperature related effects on both rock and ice mechanics and laboratory testing of key assumptions is performed degrading permafrost is considered to be an important factor for rock slope failures in alpine and arctic environments but the mechanics are poorly understood the destabilisation is commonly attributed to changes in ice mechanical properties while bedrock friction and fracture propagation have not been considered yet however fracture toughness compressive and tensile strength decrease by up to 50 and more when intact water saturated rock thaws based on literature and experiments we develop a modified mohr coulomb failure criterion for ice filled rock fractures thatincorporates fracturing of rock bridges friction of rough fracture surfaces ductile creep of ice and detachment mechanisms along rock ice interfaces novel laboratory setups were developed to assess the temperature dependency of the friction of ice free rock rock interfaces and the shear detachment of rock ice interfaces indegrading permafrost rock mechanical properties may control early stages of destabilisation and become more important for higher normal stress i e higher magnitudes of rock slope failure ice mechanical properties outbalance the importance of rock mechanical components after the deformation accelerates and are more relevant for smaller magnitudes the model explains why all magnitudes of rock slope failures can be prepared and triggered by permafrost degradation and is capable of conditioning long paraglacial response times here we present a synoptic rock and ice mechanical model that explains the mechanical destabilisation processes operating in warming permafrost rocks

spectrum of pore types and networks in mudrocks and a descriptive classification for matrix related mudrock pores matrix related pore networks in mudrocks are composed of nanometer to micrometer size pores in shale gas systems these pores along with natural fractures form the flow path permeability network that allows flow of gas from the mudrock to induced fractures during production a pore classification consisting of three major matrix related pore types is presented that can be used to quantify matrix related pores and relate them to pore networks two pore types are associated with the mineral matrix the third pore type is associated with organic matter om fracture pores are not controlled by individual matrix particles and are not part of this classification pores associated with mineral particles can be subdivided into interparticle interp pores that are found between particles and crystals and intraparticle intrap pores that are located within particles organic matter pores are intrap pores located within om interparticle mineral pores have a higher probability of being part of an effective pore network than intrap mineral pores because they are more likely to be interconnected although they are intrap om pores are also likely to be part of an interconnected network because of the interconnectivity of om particles in unlithifed near surface muds pores consist of interp and intrap pores and as the muds are buried they compact and lithify during the compaction process a large number of interp and intrap pores are destroyed especially in ductile grain rich muds compaction can decrease the pore volume up to 88 by several kilometers of burial at the onset of hydrocarbon thermal maturation om pores are created in kerogen at depth dissolution of chemically unstable particles can create additional moldic intrap pores

origin of bedding parallel fibrous calcite veins in lacustrine black shale a case study from dongying depression bohai bay basin abstract the bedding parallel fibrous calcite veins in black shales are common in sedimentary basins and retain significant information about shale diagenesis and organic matter evolution however the origin of the bedding parallel fibrous calcite veins in black shales is still of great controversy carbonaceous black shales of es4s es3x interval are the main source rock in dongying depression bohai bay basin and fibrous calcite veins parallel to bedding are widely spread in these shales petrographic examination fluid inclusion microthermometry and isotopic analyses were conducted to study the timing diagenetic fluid conditions and formation mechanism of fibrous calcite veins the bedding parallel fibrous calcite veins include beef veins and cone in cone structures the beef veins occur as short lenses and are filled with sub vertical fibrous calcite they contain a median line defined with brown granular calcite scattered host rock fragment and pyrite framboids several adjacent beef veins may combine and grow together as a cone in cone structure and black shale laminas involved in it occur as sinusoidal solid inclusions in slices primary two phase inclusions in fibrous calcite have homogenization temperatures th between 86 4 c and 117 4 c the 13c composition of the micritic calcite in host shale ranges from 3 7 to 6 3 vpdb and that of granular calcite ranges from 0 2 to 1 4 vpdb but the fibrous calcite has a moderate 13c values ranging from 1 8 to 5 0 vpdb the 13c compositions of these calcite suggest an evolving carbon source at different burial stages the fibrous calcite likely precipitated from modified pore water at elevated temperature which is supported by its low 18o values 13 7 to 11 4 vpdb the veins formed over two stage and the fibrous calcite growth was continuous and at least partly driven by the force of crystallization the bicarbonate responsible for the fibrous calcite was derived from a mixed source including inorganic carbon from previous carbonate dissolution and organic carbon from both fermentation and thermal decarboxylation

massive recrystallization of low mg calcite at high temperatures in hydrocarbon source rocks implications for organic acids as factors in diagenesis we document massive recrystallization of low mg calcite lime mudstone source rocks at moderately high temperatures in the smackover formation of mississippi this process was driven by organic acids produced during kerogen maturation and holds the implications for studies of primary migration of hydrocarbons secondary porosity generation in reservoirs and global environmental change this interpretation is based on contrasting the following petrographic and bulk rock geochemical characteristics of organic poor vs organic rich lime mudstones

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

shear behaviour of idealized infilled joints under constant normal stiffness the shear behaviour of soft joints containing infill materials was investigated in the laboratory under constant normal stiffness cns conditions tests were conducted on joints with asperities having inclinations of 9 5 type 1 and 18 5 type ii under a given range of initial normal stresses no 0 30 to 1 10 mpa and at a constant normal stiffness of 8 5 kn mm it was found that the shear strength of joints decreases considerably even with the addition of a thin layer of infill results also show that the effect of asperities on shear strength is significant up to an asperity height to infill thickness t a ratio of 1 4 1 8 whereas the shear behaviour is controlled by the infill alone beyond this critical ratio the shear displacement corresponding to the peak shear stress is considerably reduced once the infill starts to govern the shear behaviour of the joint in this study the drop in peak shear stress under cns conditions has been modelled by a hyperbolic relationship in relation to cle

high resolution hydrothermal structure of hansbreen spitsbergen mapped by ground penetrating radar detailed ground penetrating radar gpr surveys at 50 and 200 mhz on hansbreen a polythermal glacier in southern svalbard are presented and interpreted comparison of the variations in character of the radar reflections with borehole thermometry and water levels in moulins suggests that gpr can be used to study the hydrothermal properties of the glacier the high resolution of the gpr data shows that the hydrothermal structure of the glacier is highly variable both along the centre line and on transverse profiles water contents for many places and depths within the glacier were calculated by estimating radar wave velocities to point reflectors we find typical water contents of 1 2 for the temperate ice but wetter ice associated with surface crevassing and moulins typically 4 water content there is evidence that wet ice sometimes overlays drier ice the hydrothermal structure is thus shown to be very complex temperature gradients in the cold ice indicate freezing rates of temperate ice below cold ice of 0 1 0 5 m a while isolated point reflectors within the cold ice indicate large water filled bodies that are probably related to the regular drainage structure of the glacier

natural hydraulic fractures in the wessex basin sw england widespread distribution composition and history bedding parallel veins of fibrous calcite beef are historical in the wessex basin the veins are common in mesozoic mudstones and shales especially of liassic to mid cretaceous ages cone in cone structures which consist of multiple nested cones are also well developed within the beef to investigate the distribution and the context of formation of beef in the basin we have made several field studies and analysed numerous samples the veins are widespread vertically and horizontally in the sedimentary sequence but they are especially common near or within potential source rocks for petroleum or near major tectonic faults the internal structures of some beef veins have revealed that they formed during late cretaceous to tertiary compressional inversion of the basin the typical composition for beef is of calcite with some pyrite and fragments of shale however inclusions or patches of hydrocarbons liquid or solid occur within calcite crystals or between fibres respectively according to some previous studies as well as ours beef veins of the wessex basin represent natural hydraulic fractures which formed as a result of fluid overpressure this may have resulted in part from chemical compaction of petroleum source rocks during late cretaceous to tertiary times indeed source rocks at outcrop in the wessex basin could be more mature than previously thought and the beef veins may be good markers of maturation

formation of bedding parallel fibrous calcite veins in laminated source rocks of the eocene dongying depression a growth model based on petrographic observations abstract bedding parallel fibrous calcite veins commonly referred to as beefs are widely developed within eocene lacustrine laminated organic rich source rocks in the dongying depression of bohai bay basin east china understanding the formation of this type vein is essential to elucidate the diagenetic evolution and fluid migration in muddy source rocks this study investigates the mechanism s of growth of bedding parallel veins in hydrocarbon source rocks of the es4 upper and the es3 lower units in the dongying depression based on systematic observations of macro and micro scale features both in veins and their wall rocks combined with x ray diffraction and analyses of geochemical indicators the source rocks are heterogeneous in both composition and structure the beefs mainly occur in laminated rocks consisting of organic rich laminae which occur together with horizontally continuous banded lamalginites and rare carbonate rich laminae overall corresponding to high toc low carbonate contents and low maturity average ro 0 57 most beefs are embedded in the neighboring lamalginites of organic rich laminae with low clay mineral contents the beefs are products of diagenesis accompanying burial and both the initial fracture opening and subsequent dilation represent early stages of hydrocarbon generation and expulsion the presence of bedding parallel bituminite veins and the median plane or parting is evidence for horizontally oriented hydrofracturing due to fluid overpressure in turn fluid overpressure reflects the generation and primary migration of hydrocarbon bearing fluids hydrocarbon generation organic matter evolution and clay mineral dehydration illitization of smectite were responsible for the fluid overpressure crystal growth within the beefs was a continuous process with an antitaxial growth direction and there was no growth competition between adjacent fibres these observations indicate that the crystal growth and fracture dilation were synchronous and growth space was limited the force exerted by crystallizing vein fill contributed to the high fluid pressure suggesting that fibrous vein minerals actively promoted further dilation as the veins grew vein dilation accompanied the migration of hydrocarbon bearing fluids evinced by the occurrence of primary hydrocarbon inclusions found in the fibrous calcites therefore the hydrocarbon bearing fluids were present at the time of horizontal fluid flow from the start of fracture opening to the end of the dilation

the milankovitch fingerprint on the distribution and thickness of bedding parallel veins beef in source rocks bed parallel mineralized fractures are common in source rocks and generally consist in mm to cm thick veins developed parallel to bedding known as beef or bedding parallel veins considering they can form a dense network of mechanical discontinuities the prediction of beef distribution is a major issue impacting shale reservoir production beef distribution is predominantly controlled by the lithological characteristics of source rocks and we here decipher the relation between mineralogical and chemical proxies controlled by orbital parameters and distribution of the beef along a late jurassic section of the well known vaca muerta formation source rock in the neuquen basin using multiple proxies collected along the beef rich huncal section we show that milankovitch cycles rule the mineralogical evolution and beef distribution in these organic rich mudrocks cycles inferred from the statistical treatment of sedimentary magnetic susceptibility elemental and mineralogical ratios biogenic total organic carbon and diagenetic beef distribution and thickness signals revealed indeed the influence of an astroclimatic fingerprint in sediments and on processes controlling mineralized fracture generation and distribution the astroclimatic memory recorded in many source rocks worldwide is therefore envisaged as a suitable proxy for the prediction of mineralized fracture distribution

shear rupture under constant normal stiffness boundary conditions abstract a grain based distinct element method and its embedded grain based method are used to simulate the fracturing processes leading to shear rupture zone creation in a calibrated massive non jointed brittle rock specimen deformed in direct shear under constant normal stiffness boundary conditions under these boundary conditions shear rupture zone creation relative to the shear stress versus applied horizontal displacement load displacement curve occurs pre peak before the maximum peak shear strength is reached this is found to be the result of a normal stress feedback process caused by the imposed shear displacement which couples increases in normal stress due to rupture zone dilation with shear stress producing a complex normal shear stress path that reaches and then follows the rock s yield strength envelope while the yield envelope is followed the shear strength increases further and shear stress oscillations repeated stress drops followed by re strengthening periods in the load displacement curves occur due to fracture creation as the rupture zone geometry smoothens once the maximum peak strength is reached after a series of shear stress oscillations the largest stress drops occur as the ultimate or residual shear strength is approached the simulation results provide insight into the fracturing process during rupture zone creation and improve the understanding of the shear stress versus applied horizontal displacement response as well as the stick slip behaviour of shear rupture zones that are being created under constant normal stiffness boundary conditions

long term changes in the acid and salt concentrations of the greenland ice core project ice core from electrical stratigraphy continuous electrical records covering a climatic cycle are presented for the greenland ice core project deep ice core from greenland electrical conductivity measurement ecm measures the acid content of the ice and the dielectric profile dep responds to acid ammonium and chloride all features seen can be explained by chemical changes in the ice and there is no evidence so far for any major change in electrical response with depth or age of the ice both records are dominated by the acidity of the ice which varies strongly from acidic in warm periods to alkaline in cold periods controlled by neutralization by alkaline dust calcareous and other mineral dust when ca is low the acidity mainly nitric acid has a fairly constant background level throughout the cycle with slightly lower values in ice believed to be from the last interglacial ca has to rise only slightly to neutralize the available acidity so that acidity is a highly nonlinear reflection of climate changes if neutralization occurred in the aerosol rather than in the ice then the number of cloud condensation nuclei over parts of the northern hemisphere could have been reduced leading to reduced cloud albedo this nonlinear feedback may have some importance for modeling of climate change when both acid and ammonium levels are low the dep signal can be used to give a rapid indication of chloride trends

shear strength of rock joints influenced by compacted infill abstract discontinuities such as fault planes joints and bedding planes in a rock mass may be filled with different types of fine grained material that are either transported or accumulated as gouge due to weathering or joint shearing previous laboratory studies have mainly examined the role of saturated infill that exhibits the minimum shear strength however in practice the infill materials are often partially saturated generating matric suction within the joint that can contribute to increased shear strength to the authors knowledge this is the first study to examine the influence of compacted unsaturated infill on the joint shear strength a series of laboratory triaxial tests on idealised model joints and imprinted natural joint profiles was carried out with constant water contents of the infill being maintained from the laboratory results it is observed that the peak shear strength of infilled joints increased with the decrease of degree of saturation from 85 to 35 for both idealised joints and replicated natural joints based on the laboratory observations an empirical model for describing the infilled joint shear strength was developed

strength of jointed rock masses jointed rock masses comprise interlocking angular par ticles or blocks of hard brittle material separated by discontinuity surfaces which may or may not be coated with weaker materials the strength of such rock masses depends on the strength of the intact pieces and on their freedom of movement which in turn depends on the number orientation spacing and shear strength of the discontinuities a complete understanding of this problem presents formidable theoretical and experi mental problems and hence simplifying assumptions are required in order to provide a reasonable basis for estimating the strength of jointed rock masses for engineering design purposes this paper summarizes some of the basic information upon which such simplifying assumptions can be made a simple empirical failure criterion is presented and its application in engineering design is illustrated by means of a number of practical examples des masses jointives de rochers comprennent des particules angulaires enchevetrees ou des

high resolution dielectric profiling of ice cores a new method for high resolution 3 mm dielectric profiling of ice cores is described the method measures the capacitance and conductance of the ice at a single frequency chosen to be 50 khz in this case the technique requires only a few minutes per metre of core and no sophisticated data analysis the system is designed to operate on ice cores that have been cut longitudinally providing one flat and one curved surface the 50 khz conductance is dependent on the acid and neutral salt concentrations in the ice the new method was tested successfully on the grip core from summit greenland in 1991 it is useful for detecting seasonal variations in impurities in both acidic holocene ice and in normally alkaline wisconsin ice

comparison between models of rock discontinuity strength and deformation one important component in the design of tunnels in urban areas is a correct assessment of the interaction between the underground excavation with other structures in the vicinity in this sense a correct stress strain response by the model representing the rock mass behavior is essential the shear and normal displacement of rock discontinuities and their shear and normal stiffness control the distribution of stress and displacement within a discontinuous rock mass in conditions where an equivalent continuum based approach is not applicable the joint material model should be able to describe important mechanisms such as asperity sliding and shearing post peak behavior asperity deformation and the effect of soft infilling the distinct element code udec was used to simulate the direct shear tests on a natural joint profile and the prediction of two existing models of discontinuity strength and deformation were then compared with a new soil infilled joint model and with experimental data for clean and soil infilled rock joints a numerical modeling of a cavern excavated in a jointed medium is also presented to illustrate the response of different models the proposed soil infilled joint model described more comprehensively the occurrence of dilation and compression with lateral displacements and also better represented the double peak shearing in relation to the adopted squeezing mechanism that could not be captured by the two existing models

conditions for veining in the barrandian basin lower palaeozoic czech republic evidence from fluid inclusion and apatite fission track analysis abstract the interplay between fracture propagation and fluid composition and circulation has been examined by deciphering vein sequences in silurian and devonian limestones and shales at kosov quarry in the barrandian basin three successive vein generations were recognised that can be attributed to different stages of a basinal cycle almost all generations of fracture cements host abundant liquid hydrocarbon inclusions that indicate repeated episodes of petroleum migration through the strata during burial tectonic compression and uplift the earliest veins that propagated prior to folding were displacive fibrous beef calcite veins occurring parallel to the bedding of some shale beds hydrocarbon inclusions within calcite possess homogenisation temperatures between 58 and 68 c and show that the beef calcites originated in the deeper burial environment during early petroleum migration from overpressured shales e w striking extension veins that postdate beef calcite formed in response to variscan orogenic deformations based on apatite fission track analysis afta data and other geological evidence the veins probably formed 380 315 ma ago roughly coinciding with peak burial heating of the strata folding and the intrusion of variscan synorogenic granites the veins that crosscut diagenetic cements and low amplitude stylolites in host limestones are oriented semi vertically to the bedding plane and are filled with cloudy twinned calcite idiomorphic smoky quartz and residues of hardened bitumen calcite and quartz cements contain abundant blue and blue green fluorescing primary inclusions of liquid hydrocarbons that homogenise between 50 and 110 c geochemical characteristics of the fluids as revealed by gas chromatography mass spectrometry particularly the presence of olefins and parent aromatic hydrocarbons phenonthrene suggest that the oil entrapped in the inclusions experienced intense but geologically fast heating that resulted in thermal pyrolysis of its hydrocarbons this implies that the organic fluids in the fractures may have been partly influenced by heating associated with igneous intrusions that are hidden below the surface subvertical n s striking veins represent the most recent fracturing event s some of these veins are only a few millimeters thick and sparsely mineralised with thin leaf like quartz crystals that contain tiny blue and yellow orange fluorescing hydrocarbon inclusions most of the n s veins however occur as thick calcite veins that generally crystallised at 70 c or less from h2o nacl solutions of variable salinity with admixture of petroleum the origin of these fluids is interpreted in terms of deeply circulating meteoric waters that partially mixed with deep basinal fluids wider structural considerations combined with fission track analysis of adjacent host sediments suggest that n s veins formed during post mesozoic uplift of the area probably in response to major tertiary alpine deformations transmitted far into the bohemian massif

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

hydrocarbon bearing fluid inclusions in calcite filled horizontal fractures from mature posidonia shale hils syncline nw germany abstract hydrocarbon bearing fluid inclusions in calcite filled horizontal fractures from mature posidonia shale 0 88 r o were investigated by microscopic microthermometric and chemical methods the fluid inclusions predominantly contain both a liquid hydrocarbon phase which shows bright uv fluorescence colours yellow brownish light blue and a non fluorescent hydrocarbon gas phase the different uv fluorescence colours probably reflect the different gross chemical compositions of the trapped liquid hydrocarbons the saturated hydrocarbon fraction of the fluid inclusions mostly secondary inclusions predominantly consists of low molecular weight n alkanes c 9 c 12 while c 12 c 22 n alkanes are more abundant in the adjacent rock matrix the molecular composition of the fluid inclusions appears to reflect a mobile hydrocarbon phase which was entrapped within the calcitic fill of the horizontal fractures pressure corrected trapping temperatures were estimated for primary fluid inclusions 123 162 c this temperature range is in agreement with the results from numerical simulation studies which indicate a maximum temperature of 148 c coinciding with the period of fracture formation calcite filling and entrapment of primary fluid inclusions

recognition criteria for distinguishing between hemipelagic and pelagic mudrocks in the characterization of deep water reservoir heterogeneity determination of turbidite event magnitude and frequency remains subjective and difficult to define this is because turbidite sedimentation events commonly include both sand and mud with the mud component commonly excluded from bed thickness studies because of the inability to establish a genetic link to the turbidity current pelagic mudrock is defined as fine grained marine sediment derived primarily from biogenic particles whereas hemipelagic mudrock includes both biogenic and terrigenous particles unfortunately these compositional definitions do not account for differences in depositional process scanning electron microscopy field emission scanning electron microscopy and x ray diffraction analyses of 70 samples from el rosario formation outcrops baja california mexico and core from the woodford shale oklahoma illustrate this distinction furthermore these laboratory measurements are calibrated to 192 outcrop samples to provide a robust method for field identification of clay fabric and mineralogy to define turbidite sedimentation units pelagites show organized layering of clay platelets few flocculates and a lower proportion of high density minerals hemipelagites have disorganized and chaotic clay fabrics characterized by visible flocculates and contain a higher proportion of denser particles there may also be a corresponding change in clay mineralogy for example smectite in pelagites versus kaolinite in hemipelagites these results indicate a settling velocity greater than shear velocity in pelagites whereas hemipelagites record the opposite condition turbidity currents support and suspend denser grains generate disorganized and chaotic clay fabrics and provide more time for flocculation discrimination between pelagites and hemipelagites has important implications in the determination of turbidite event frequency and magnitude which affects vertical connectivity and continuity of sand deposited from multipartite turbidity currents in addition distinction between pelagites and hemipelagites provides a better understanding of mudrock reservoir architecture

development and applications of a synthetic material to simulate soft sedimentary rocks due to the fact that a model material can be made homogeneous the influence of different variables on behavioural mechanisms can be investigated independently consequently large experimental scatter attributed to inherent variables generally unknown of a natural material can be avoided this paper presents the development of an artificial material which can effectively simulate the behaviour of an array of weak sedimentary rocks this synthetic soft rock was constituted with gypsum cement fine sand and water and characterized with homogeneous and isotropic properties with insignificant variability from one batch to another it can be easily manufactured in the laboratory and can be cast either in large or small volumes to occupy any predetermined shape of given physical dimensions an experimental application to study the behaviour of reinforced composites simulated bolted rock is also described in this paper puis qu une matiere modele peut etre rendue homogene il est possible d etudier de fac

oil generation as the dominant overpressure mechanism in the cenozoic dongying depression bohai bay basin china the dongying depression in the bohai bay basin is a young prolific oil producing basin in china the gray to black mudstones calcareous mudstones and oil shales of the eocene shahejie formation es3 and es4 are the major source rocks that are primarily dominated by type i kerogens with a high total organic carbon of up to 18 6 the es3 interval is characterized by a sedimentation rate of up to 500 m m y widespread overpressures are present in the eocene es3 and es4 intervals in the depression with pressure coefficients up to 1 99 from drillstem tests among the sonic resistivity and density logs only the sonic log displays an obvious response to the overpressure from which the top of the overpressure can be clearly identified acoustic traveltime versus effective vertical stress analysis of more than 300 wells in the dongying depression suggests that the acoustic traveltime of the normally pressured and overpressured mudstones is reduced with increasing vertical effective stress pore pressures are accurately predicted in the dongying depression using an eaton 1972 exponent of 2 0 by comparing the predicted pressure coefficients with measured pressure coefficients disequilibrium compaction has been previously proposed as the sole cause of the high magnitude overpressures in the eocene strata of the dongying depression because of rapid deposition of fine grained sediments however our data indicate that the overpressures are caused by oil generation from the source rocks within the es3 and es4 intervals the overpressured sediments display a normal compaction as evidenced from the overpressured mudstones exhibiting no anomalously low density the apparent lack of correlation between mudstone densities and effective vertical stress and the overpressured reservoir sandstones showing no anomalous high matrix porosities or anomalous geothermal gradient the depths to the top of the overpressure intervals range from 2000 to 3000 m 6562 9843 ft following closely source rock depths all the overpressured reservoirs and source rocks have a minimum temperature of approximately 87c and overpressured source rocks generally have vitrinite reflectance ro values of 0 6 or higher overpressures are not found in the strata within which the ro values are less than 0 5 the overpressured reservoirs in the es3 and es4 intervals are predominantly oil saturated or oil bearing organic rich source rocks with overpressures are capable of generating hydrocarbons and thus can maintain an abnormally high pressure the calcite precipitation in the calcareous mudstones may have caused a significant reduction in porosity and permeability to form an effective pressure seal the presence of widespread microfractures in the source rocks may relate to episodic expulsion of hydrocarbons or overpressure dissipation overpressures in the reservoir rocks are generated by the fluid transmission from the overpressured source rocks through active faulting and fracturing

source rocks in mesozoic cenozoic continental rift basins east china a case from dongying depression bohai bay basin abstract lake basin evolution microscopic and organic geochemistry characteristics are investigated for the paleocene hydrocarbon source rocks of dongying depression bohai bay basin the upper e 2 3 s 4 and the lower e 2 3 s 3 are balanced filled lake basin sediments which show strong climate driven rhythmicity source rocks of these two units have relatively high organic matter content and are dominated by type i kerogen sedimentary and geochemical characteristics indicate there exist persistent lake water stratification and bottom anoxicity during the deposition process by contrast the middle e 2 3 s 3 is an over filled lake deposit dominated by uniform mudstones lacking obvious transgressive regressive cycles it indicates that the lake water lacks stratification and the bottom water is ventilated source rocks of this unit have relatively low organic abundance and are dominated by types ii and iii kerogen thermal evolution studies show that the upper e 2 3 s 4 has a relatively early and multi stage of hydrocarbon generation process and can generate immature oils while the lower e 2 3 s 3 and the middle e 2 3 s 3 have a relatively late and simple hydrocarbon generation process and mainly generate mature oils in addition the persistent increase of eom toc and total hydrocarbons toc indicates that the expelled hydrocarbons from the middle e 2 3 s 3 are in relatively small amounts compared with the other two units the middle e 2 3 s 3 acts as regional caprocks instead of significant source rocks as previously thought the viewpoint will be of great significance in future exploration

the impact of organic fluids on the carbon isotopic compositions of carbonate rich reservoirs case study of the lucaogou formation in the jimusaer sag junggar basin nw china abstract the processes involved in the interaction between organic fluids and carbonates and the resulting effect on reservoir quality during the evolution and maturation of organic matter remain unclear despite the fact that these processes influence the carbon and oxygen isotopic compositions of carbonates here we provide new insights into these processes using data obtained from a detailed analysis of a mixed dolomitic clastic and organic rich sedimentary sequence within the middle permian lucaogou formation in the junggar basin of nw china the techniques used during this study include drillcore observations thin section petrography scanning electron microscopy sem and electron probe microanalysis and carbon and oxygen isotope analyses oil grades and total organic carbon toc contents represent the amount of oil charging and the abundance of organic fluids within a reservoir respectively and both negatively correlate with the whole rock 13c and 18o of the carbonates in the study area indicating that organic fluids have affected the reservoir rocks secondary carbonates including sparry calcite and dolomite overgrowths and cements are common within the lucaogou formation well developed sparry calcite is present within dark mudstone whereas the other two forms of secondary carbonates are present within the dolomite rich reservoir rocks in this formation comparing thin section petrology with 13c compositions suggests that the carbon isotopic composition of matrix carbonates varies little over small distances within a given horizon but varies significantly with stratigraphic height as a result of the development of secondary carbonates the net change in whole rock 13c as a result of these secondary carbonates ranges from 1 8 to 4 6 with the secondary carbonates having calculated 13c compositions from 18 6 to 8 5 that are indicative of an organic origin the positive correlation between the concentration of fe within matrix and secondary carbonates within one of the samples suggests that the diagenetic system within the lucaogou formation was relatively closed the correlation between 13c and 18o in carbonates is commonly thought to be strengthened by the influence of meteoric water as well as organic fluids however good initial correlation between 13c and 18o of whole rock carbonates within the lucaogou formation resulted from the evaporitic sedimentary environment was reduced by organic fluids to some extent consequently the 13c 18o covariations within these sediments are not always reliable indicators of diagenetic alteration by organic fluids or meteoric water the characteristics and 13c compositions of the sparry calcite within the formation is indicative of a genetic relationship with organic acids as a result of the addition of organic co2 to the reservoir further analysis suggests that both carbonate and feldspar were dissolved by interaction with organic co2 however dissolved carbonate reprecipitated as secondary carbonates meaning that the interaction between organic fluids and dolomites did not directly improve reservoir quality although this process did enhance the dissolution of feldspar and increase porosity this indicates that the 13c and 18o of secondary carbonates and their influence on whole rock carbonate isotopic values can be used to geochemically identify the effect of organic fluids on closed carbonate rich reservoir systems

superimposed ice regime of a high arctic glacier inferred using ground penetrating radar flow modeling and ice cores 1 a 900 mhz ground penetrating radar gpr profile collected along 1 7 km of the centerline of a high arctic glacier in svalbard is interpreted using shallow ice core data and thermomechanical flow modeling four distinct zones are visible in the image and correspond to areas of firn recent and older superimposed ice and ablation zone glacier ice on the ground the areas of firn and superimposed ice are characterized by relatively steeply and gently dipping internal reflecting horizons irh respectively in the radar image the irhs arise from permittivity contrasts due to density variations produced in firn by alternating firn and ice layers and in superimposed ice by varying air bubble content recently formed and older superimposed ice can be distinguished in the gpr image a three dimensional flow model is used to indicate the long term mass balance and flow history responsible for the spatial distribution and orientation of superimposed ice irhs in the radar image results indicate that the irh distribution can only be explained by invoking a down glacier shift in mean 30 year equilibrium line altitude ela by 20 30 m compared with measured mean 30 year ela they also suggest that many of the superimposed irhs are relict features produced 100 years b p when the ela was 100 150 lower than at present this work advocates combined gpr and flow modeling as a unique tool for validating mass balance measurements and or inferring the mass balance dynamic history of a glacier beyond a recent measurement period

hierarchies of overpressure retardation of organic matter maturation case studies from petroleum basins in china the effects of overpressure on different aspects of organic matter maturation have been examined in three basins using multiple parameters overpressure in the yinggehai basin has retarded kerogen maturation hydrocarbon generation and thermal cracking of long chain normal hydrocarbons as well as evolution of isoprenoid hydrocarbons overpressure in the dongpu depression bohai bay basin seems to have retarded the maturation of bulk kerogens reflected by rock eval tmax the thermal cracking of long chain normal hydrocarbons and the evolution of isoprenoid hydrocarbons but seems to have had no detectable effects on vitrinite reflectance overpressure in the qiongdongnan basin has had no detectable retardation effects on all aspects of organic matter maturation the observed phenomena suggest differential retardation of organic matter maturation that is different organic matter maturation reactions and different maturity parameters have been retarded by overpressure to different degrees in the same overpressured system and four hierarchies of overpressure retardation hierarchy i retardation is defined as the state where the overpressure has retarded all aspects of organic matter maturation and is proposed to have been caused by the combination of high formation pressure and excess pressure a high water organic matter ratio and strong retention of reaction products in an early developed strong persistent overpressured system hierarchy ii retardation refers to the case in which all aspects of organic matter maturation except the maturation of hydrogen poor kerogens especially vitrinite have been retarded and seem to have been caused by early developed moderate to strong persistent overpressure hierarchy iii retardation refers to the situation where overpressure has retarded only the thermal cracking of liquid hydrocarbons but has had no detectable effect on the maturation of both hydrogen rich and hydrogen poor kerogens and is proposed to have been caused by moderate to strong persistent overpressures that began to develop around peak oil generation hierarchy iv retardation is defined as the situation where overpressure has had no detectable retardation on all aspects of organic matter maturation and may have been caused by cases wherein the overpressure developed too late the intensity of the overpressure was too low the duration of the overpressure was too short or overpressured fluids had been expelled frequently resulting from both the diversities of organic matter maturation reactions and the complexities of overpressure generation and development the hierarchies of overpressure retardation in different basins may be quite different and it is necessary to use multiple parameters to understand the evolution of the petroleum systems in overpressured basins

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

oil generation induces sparry calcite formation in lacustrine mudrock eocene of east china abstract sparry calcite is common in sedimentary rocks in mudrocks it has been reported to occur as veins in bedding parallel oblique and vertical fractures tectonic forces were traditionally suggested to be responsible for the calcite vein formation some recent studies showed that hydrocarbon generation could be responsible for forming bedding parallel calcite veins of fibrous sparry calcite however the process of sparry calcite formation by hydrocarbon generation is not well understood sparry calcite is common in the eocene mudrocks of the zhanhua and dongying sags of the bohai bay basin and the biyang sag of the nanxiang basin east china in this study the petrology carbon and oxygen isotopes minor geochemistry fluid inclusion and drill stem testing characteristics of sparry calcite and or sparry calcite bearing intervals in mudrocks were investigated oil generation could lead to overpressure inducing accommodation space for the precipitation of sparry calcite while organic acids a by product of oil generation promoted the dissolution of micrite providing an ion source for diagenetic sparry calcite growth structureless mudstone can experience elastic deformation before fracture generation forming equant and dispersed sparry calcite laminated shale on the other hand easily reaches the yield point because of its anisotropic nature an upward seepage force by fluid overpressure can induce bedding parallel fractures resulting in three stages of sparry calcite formation characterized by 1 discrete and equant sparry calcite 2 horizontally intergrown and equant sparry calcite and 3 horizontally intergrown and fibrous sparry calcite thus oil generation can be responsible for sparry calcite formation establishing some new characteristics for this process in mudrocks including 1 sparry calcite could also form during the process of elastic deformation as well as fracturing in mudrock and 2 fibrous sparry calcite began its growth from equant sparry calcite

anatomy of a lacustrine stratigraphic sequence within the fourth member of the eocene shahejie formation along the steep margin of the dongying depression eastern china a comprehensive study on rift stratigraphy requires a solid understanding of sequence architecture along the steep margins of rift basins this study analyzes an eocene lacustrine sequence along the steep margin of the dongying depression in eastern china through integrated core well log and three dimensional seismic analyses the lacustrine sequence is bounded by unconformities and their correlative conformities at the base and top and consists of three systems tracts namely an early expansion systems tract eest late expansion early contraction systems tract leecst and late contraction systems tract lcst which record a lake expansion contraction cycle these systems tracts differ in thickness and development of depositional systems the eest is the thickest and contains well developed marginal and basinal fan systems with an overall retrogradational stacking pattern the well developed fan systems are the most striking features within the sequence the leecst is the most widespread and contains dominantly profundal sublittoral deposits the lcst is the thinnest with poorly developed fan systems and is characterized by significant erosion by fluvial incision the variable thickness and development of depositional systems in the three systems tracts are the responses to the interplay of sediment supply and accommodation space accommodation space establishes the framework for sedimentary infill and sediment supply determines spatial distribution and temporal evolution of depositional systems within each systems tract this study provides a lake expansion contraction scheme to divide a lacustrine stratigraphic sequence into systems tracts and highlights the feasibility of applying this approach in studying sequence stratigraphy along the steep margin of a lacustrine rift basin the results also provide understandings for the development distribution and evolution of depositional systems and their controlling factors along the steep margin of other rift basins in the world

emplacement of bitumen asphaltite veins in the neuquen basin argentina veins of solid bitumen asphaltite have been commercially exploited in the neuquen basin argentina for over 100 yr veins are up to 5 m wide and several kilometers in length over a region of 15 000 km2 these veins were emplaced in fractures both parallel and at high angles to bedding in close proximity to their source rocks in the vaca muerta and agrio formations late jurassic early cretaceous two or more phases of bitumen emplacement can be recognized in several localities structures bearing viscous oil are younger than structures having solid bitumen bitumen emplacement was vigorous and caused brecciation and spalling of the host rocks the bitumen was also viscous and supports rock debris ranging in size from sand grains up to meter scale slabs brecciation bedding parallel injection and wall rock impregnation suggest high fluid pressures during emplacement high fluid pressure may have been engendered by substantial hydrocarbon generation from rich source rocks in a low permeability sequence and probably caused the fractures into which the bitumen migrated the bedding parallel veins facilitated decollement during thrusting that took place during and after bitumen emplacement the timing of emplacement relative to thrusting and oil migration constrains bitumen emplacement to the eocene oligocene

methodological approaches to infer end of winter snow distribution on alpine glaciers snow accumulation is an important component of the mass balance of alpine glaciers to improve our understanding of the processes related to accumulation and their representation in state of the art mass balance models extensive field measurements are required we present measurements of snow accumulation distribution on findelengletscher switzerland for april 2010 using 1 in situ snow probings 2 airborne ground penetrating radar gpr and 3 differencing of two airborne light detection and ranging lidar digital elevation models dems calculating high resolution snow depth from dem differencing requires careful correction for vertical ice flow velocity and densification in the accumulation area all three methods reveal a general increase in snow depth with elevation but also a significant small scale spatial variability lidar differencing and in situ snow probings show good agreement for the mean specific winter balance 0 72 and 0 78 m w e respectively the lidar derived distributed snow depth reveals significant zonal correlations with elevation slope and curvature in a multiple linear regression model unlike lidar differencing gpr derived snow depth is not affected by glacier dynamics or firn compaction but to a smaller degree by snow density and liquid water content it is thus a valuable independent data source for validation the simultaneous availability of the three datasets facilitates the comparison of the methods and contributes to a better understanding of processes that govern winter accumulation distribution on alpine glaciers

contributions to geotechnique 1948 2008 engineering geology rock mechanics and rock engineering throughout its history geotechnique has regularly published papers on the fundamentals of engineering geology the core concepts of rock mechanics and the practice of rock engineering in totality these papers provide a concise history of the development of these areas of geotechnics here a review of many of these papers is presented in terms of the specific themes of engineering geology rock slope instability behaviour of intact rock and discontinuities in rock field measurements in rock mechanics discontinuous rock masses numerical modelling and rock engineering papers covering a wide range of issues within these themes are outlined together with an indication of how they have influenced later developments the review clearly demonstrates how geotechnique has been at the forefront of rock mechanics rock engineering and engineering geology for the whole of its 60 year existence

recent fluctuations in the extent of the firn area of austfonna svalbard inferred from gpr in spring during 2004 07 we conducted ground penetrating radar gpr measurements on the austfonna ice cap svalbard with the original aim of mapping the thickness and distribution of winter snow here we further exploit the information content of the data and derive a multi year sequence of glacier facies distribution that provides valuable spatial information about the total surface mass balance smb of the ice cap beyond the usually evaluated winter balance we find that following an initial decrease in the extent of the firn area 2003 04 the firn line lowered within two subsequent years by 40 100m elevation in the north and west and 150 230 m in the south and east of the ice cap corresponding to a lateral expansion of the firn area along the profiles by up to 7 3 and 13 3 km respectively the growth of the firn area is in line with stake measurements from etonbreen that indicate a trend towards less negative smb over the corresponding period

asiras airborne radar resolves internal annual layers in the dry snow zone of greenland 1 we present data from the european space agency s airborne sar interferometric radar altimeter system asiras flown during the cryovex 2004 field calibration validation campaign and new high resolution depth profiles of snow density measured in the field by neutron scattering we combine these data to calculate the depth of internal reflecting horizons in the asiras data the high resolution density data allow us to identify annual layers in the snow density profile and correlate their peaks with the reflecting horizons we use the thickness of the annual layers combined with the density profile to determine the spatial and temporal pattern of snow accumulation along the radar track for a period of 6 years from 1995 2002 our mean annual accumulation rate is 0 47 0 09 ma 1 water equivalent in agreement with the value determined from a core taken in this location in 1992 similarly our inter annual variability shows the same trends as recent model estimates over the entire ice sheet because asiras was designed to mimic as closely as possible the characteristics of the sar interferometric radar altimeter siral the principal payload of cryosat the detection of internal layering with asiras illuminates the possibility of detecting internal layers with a space borne radar and thus the possible application of this technique to the dry snow zones of antarctica greenland and smaller ice bodies

effect of soil infilled joints on the stability of rock wedges formed in a tunnel roof abstract the use of an equivalent continuum for a rock mass is not always suitable for situations where the failure is structurally controlled by discontinuities as in the case of wedges in the tunnel roof in these instances discontinuum approaches are usually preferred rock joints that are filled with soft infill are likely to be the weakest planes in a rock mass having a dominant influence on its overall shear behaviour in this case the joint material model adopted for the discontinuities should be able to describe important mechanisms such as asperity sliding and shearing post peak behaviour asperity deformation and the effect of the soft infilling the latest version of a soil infilled joint model is discussed here it describes more comprehensively than previous models the occurrence of dilation and compression with lateral displacements and also represents the hardening mechanism related to asperity interference as observed in the laboratory that cannot be readily captured by the existing joint models an analytical approach for the analysis of rock wedges structurally controlled by soil infilled joints and a numerical simulation based on a metro station collapse which occurred in brazil in 2007 are presented

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

oxygen isotope composition of diagenetic calcite in organic rich rocks evidence for 18o depletion in marine anaerobic pore water upper cretaceous organic rich carbonates in israel contain benthonic foraminifera and varying amounts of early diagenetic infilling of sparry calcite the sparry calcite has oxygen isotope values down to 9 5 pdb that are significantly lower than those of the coexisting skeletal calcite averaging 2 pdb low 18o values are very common in carbonates that are associated with organic matter these occurrences are conventionally explained as being due to carbonate formation under conditions of low salinity and or elevated temperature on the basis of petrographic data and local geologic evidence however none of the conventional explanations can be applied in this case we advance an alternative model that relates the light oxygen compositions of the diagenetic calcite to depletion of 18o in pore water of normal salinity the proposed operating mechanism is a direct consequence of organic matter decomposition in the sulfate reducing zone being inherent to reducing marine environments this model can be applied to many organic rich rock associations

regional scale development of opening mode calcite veins due to silica diagenesis the formation and distribution of natural fractures in cretaceous paleogene strata in jordan are strongly tied to diagenetic processes which in turn reflect the lithology of the host material observations collected from subsurface cores show that widespread fracturing began before compaction of the host sediment was complete based on ptygmatic folding of one set of mineral filled fractures veins non folded veins are preferentially developed within heavily cemented layers calcium carbonate is the greatest volumetric component of the host sediment and most fractures are at least partially filled by calcite dolomite and silica bearing fractures are present in dolomitized and silicified host beds respectively horizontal veins are filled by cone in cone calcite or rarely silica or dolomite the stratigraphic arrangement and degree of compaction around ptygmatically folded calcite veins and chert nodules suggest that silica diagenesis was an important driver of early fractures nevertheless those fractures were filled with carbonate cements as they opened based on crack seal texture of the vein fill the volume loss associated with silica diagenesis created fracture porosity which was filled coevally by carbonate cements the distribution of later veins reflects embrittlement of host layers by cementation and is consistent with crustal deformation as the primary fracture driver

dynamic modelling of fault slip with barton s shear strength model abstract barton s shear strength model has been incorporated into the flac3d code as a ubiquitous joint model using the plastic flow rule to analyze the potential effect of fault slip bursts on mine openings comparison of the incorporated model with the classical mohr coulomb model is conducted through a case study of a primary fault that is parallel to a steeply dipping tabular ore deposit which is mined out by the sublevel stoping method based on the results obtained from the numerical analyses seismic source parameters are calculated and compared for each case the results show that faults having rough surfaces tend to cause much larger seismic events than faults with smooth surfaces in addition parametrical study with respect to fault surface roughness shows that seismic moment and radiated energy significantly vary with the fault surface roughness and the seismic moment does not necessarily correlate with the radiated energy peak particle velocity excited by seismic waves arising from the simulated fault slips is also examined it is found out from the results that peak particle velocity is strongly dependent upon the fault surface roughness and has a correlation with the radiated energy but not with seismic moment

primary migration by oil generation microfracturing in low permeability source rocks application to the austin chalk texas fracturing of low permeability source rocks is induced by pore pressure changes caused by the conversion of organic matter to less dense fluids oil and gas these fractures increase the permeability and provide pathways for hydrocarbon migration an equation for the pressure change is derived using four major assumptions 1 the permeability of the source rock is negligibly small 0 01 d 10 20 m2 so that the pore pressure buildup by the conversion is much faster than its dissipation by pore fluid flow 2 the stress state is isotropic so that horizontal and vertical stresses are equal the source rock fails when the pore pressure equals the overburden pressure 3 the properties of the rock organic matter and fluids remain constant during oil generation this assumption is valid when the change in depth i e pressure and temperature is small 4 only two reaction rates are required for the conversions a low temperature reaction rate for the kerogen oil conversion e approx 24 kcal mol a approx 1014 m y and a high temperature reaction rate for oil gas conversion e approx 52 kcal mol a approx 5 5 1026 m y the equations for generation rate and pressure change are applied to the austin source rock by adjusting the several variables to fit geochemical data core saturations and observed levels of oil and gas production this application demonstrates that the equations are easily applied in calculating depths of primary migration for low permeability source rocks

petrography fluid inclusion isotope and trace element constraints on the origin of quartz cementation and feldspar dissolution and the associated fluid evolution in arkosic sandstones feldspar dissolution quartz cementation and clay cementation are significant diagenetic processes in deep water fan feldspar rich sandstones in the shengtuo area dongying sag east china the timing and origin of these water rock interactions as well as the paleofluids in which relevant chemical reactions occurred were deduced using data from microscopy fluid inclusion microthermometry oxygen isotope microanalysis and trace element microanalysis three distinct separate episodes of quartz overgrowths referred to as q1 q2 and q3 were distinguished by cathodoluminescence microscopy the q1 quartz identified in all porous sandstones from 2500 to 3600 m 8200 to 11 800 ft was formed at approximately 100 c 115 c 212 f 239 f before oil filled the reservoirs the q2 quartz was mainly precipitated at 115 c 130 c 239 f 275 f accompanying or slightly postdating the main phase of oil filling and was identified in samples from 2800 to 3600 m 9200 to 11 800 ft the q3 quartz was only identified in sandstones buried deeper than 3500 m 11 400 ft and was likely precipitated in the quaternary when temperature exceeded 130 c 135 c 266 f 275 f secondary ion mass spectrometry oxygen isotope microanalyses yielded 18ovsmow vienna standard mean ocean water values ranging from 21 42 to 24 35 for q1 quartz from 22 03 to 24 99 for q2 quartz and from 21 72 to 22 91 for q3 quartz a mass balance calculation and quantitative petrography data of the amount of leached feldspars and associated secondary minerals suggest that the internal feldspar dissolution is likely the primary source for the authigenic clays and quartz cements in these sandstones positive 18o water values 0 5 to 4 5 vsmow of quartz forming waters indicate that quartz cementation and feldspar dissolution occurred in a geochemical system with a limited volume of diagenetically modified connate water the variations of 18o cements and trace element compositions from q1 quartz to q2 quartz in individual overgrowth suggest that hydrocarbon filling changed the chemistry of the pore fluid significantly further 18o water values of the pore water increased by approximately 2 vsmow after oil filling meteoric freshwater did not contribute to quartz cementation and simultaneous feldspar dissolution the detected co2 and hydrocarbons in fluid inclusions in the quartz cements the existence of co2 in hydrocarbon rich natural gas and the pyrobitumen in the feldspar hosted pores suggest that acids derived from organic matter kerogen in source rocks and hydrocarbons in reservoirs probably have promoted the extensive subsurface leaching reactions of feldspars in these sandstones the ongoing development of q2 and q3 quartz suggests that quartz precipitation did not cease after oil filling further diagenetic reactions likely have proceeded from water rock interactions to hydrocarbon water rock interactions

imaging of firn isochrones across an antarctic ice rise and implications for patterns of snow accumulation rate it has been an underlying assumption in many studies that near surface layers imaged by ground penetrating radar gpr can be interpreted as depositional markers or isochrones it has been shown that gpr layers can be approximately reproduced from the measured electrical properties of ice but these material layers are generally narrower and more closely spaced than can be resolved by typical gpr systems operating in the range 50 400 mhz thus gpr layers should be interpreted as interference patterns produced from closely spaced and potentially discontinuous material layers and should not be assumed to be interpretable as precise markers of isochrones we present 100 mhz gpr data from lyddan ice rise antarctica in which near surface 50 m deep layers are clearly imaged the growth of the undulations in these layers with depth is approximately linear implying that rather than resulting from a pattern of vertical strain rate they do correspond to some pattern of snowfall variation furthermore comparison of the gpr layers with snow stake measurements suggests that around 80 of the rms variability in mean annual accumulation is present in the gpr layers the observations suggest that at least in this case the gpr layers do approximate isochrones and that patterns of snow accumulation over lyddan ice rise are dominated by extremely persistent spatial variations with only a small residual spatial variability if this condition is shown to be widely applicable it may reduce the period required for measurements of surface elevation change to be taken as significant indications of mass imbalance

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

inorganic calcite morphology roles of fluid chemistry and fluid flow abstract evaluation of calcite crystal habits and fabric and their relation to precipitating fluids in spelean environments indicates that habit variations are controlled primarily by degree of supersaturation at less than 6 times supersaturation crystal habits are limited to those with shallow to steep rhombohedral forms i e 1011 4041 with increasing supersaturation scalenohedrons extremely steep rhombohedrons pinacoids and hexagonal prisms are developed slight elongation due to differences in crystal dimensions of these forms may arise i e scalenohedrons versus shallow rhombohedrons at extreme supersaturation 12 times curvature of crystal faces or curved surfaces appear the development of fibrous versus equant fabrics is the result of changes or modification of reactant supply rates and the number of crystallites nuclei present under rapid flow conditions growth rates are accelerated and greater numbers of nuclei are present thus compromise boundaries parallel to c axis and perpendicular to flow and substrate are rapidly attained in the absence of flow fewer crystallites are present and larger well developed crystals or branching forms dictated by saturation conditions arise in the absence of flow at low supersaturation elongate composite crystals and hence fibrous fabrics may result from migration of the fluid crystal interface as a result of changing or oscillating water levels a flow control mechanism can be applied to numerous geological conditions in which transitions from fibrous to equant crystal morphologies are observed

fractures in mudrocks advances in constraining timing and understanding mechanisms abstract recent advances in fracture timing techniques have led to new insights about sequences and mechanisms of fracture formation in mudrocks methods to constrain fracture timing in mudrocks include i field evidence including crosscutting relationships and evidence of compaction ii petrographic evidence including signs of soft sediment deformation and diagnostic mineral assemblages or textures iii stable isotopic evidence iv thermometric dating using burial history modelling and v radiometric age dating in this contribution we briefly review each method with salient examples from the literature many documented examples of mudrock hosted fractures formed during early burial a non intuitive finding that demands a re assessment of our assumptions about what types of materials can develop opening mode fractures in general the style and distribution of fractures varies dramatically based on fracture timing highlighting the importance of constraining timing for predicting fracture patterns and interpreting their mechanisms including the role of fluid flow

unusual calcite stromatolites and pisoids from a landfill leachate collection system low magnesium calcite stromatolites and pisoids were found to have precipitated within the leachate collection system piping of a palm beach county florida landfill the stromatolites and pisoids formed in an aphotic and anoxic environment that was at times greatly supersaturated with calcite the stromatolites are composed of branching cylindrical bundles of concentrically laminated radial fibrous crystals the pisoids consist of concentric layers of radial fibrous and microcrystalline calcite bacteria likely sulfate reducing appear to have acted as catalysts for calcite crystal nucleation and thus the formation of the stromatolites and pisoids the leachate system stromatolites provide a recent example of stromatolites that formed largely by cement precipitation by acting as catalysts for calcite nucleation bacteria may cause more rapid cementation than would have occurred under purely abiotic conditions rapid calcite precipitation catalyzed by bacteria has interfered with the operation of the palm beach county landfill leachate collection by obstructing pipes and may be an unrecognized problem at other landfill sites

shear strength model for overconsolidated clay infilled idealised rock joints saturated infilled joints can contribute to the instability of rock masses during undrained shearing this paper reports an experimental investigation into the effect of the overconsolidation of infilled rough joints on undrained shear behaviour a revised model is presented for predicting the shear strength of rough infilled joints on the basis of experimental tests carried out on idealised sawtoothed joints with natural silty clay as the infill material tests were conducted under consolidated undrained conditions in a high pressure triaxial apparatus on joints having a dip angle of 60 pore pressure development in the infill materials was monitored the results show that the effect of asperities on shear strength is significant up to a critical asperity height to infill thickness ratio t a whereas the shear behaviour is controlled by the infill alone beyond this critical value the proposed model for predicting the shear strength of rough infilled joints describes how the ocr influences the shear strength pore water pressure development and critical t a ratio

physical modelling of chemical compaction overpressure development hydraulic fracturing and thrust detachments in organic rich source rock abstract geological evidence for overpressure is common worldwide especially in petroleum rich sedimentary basins as a result of an increasing emphasis on unconventional resources new data are becoming available for source rocks abnormally high values of pore fluid pressure are especially common within mature source rock probably as a result of chemical compaction and increases in volume during hydrocarbon generation to investigate processes of chemical compaction overpressure development and hydraulic fracturing we have developed new techniques of physical modelling in a closed system during the early stages of our work we built and deformed models in a small rectangular box 40 40 10 cm which rested on an electric flatbed heater but more recently in order to accommodate large amounts of horizontal shortening we used a wider box 77 75 10 cm models consisted of horizontal layers of two materials 1 a mixture of equal initial volumes of silica powder and beeswax micro spheres representing source rock and 2 pure silica powder representing overburden by submerging these materials in water we avoided the high surface tensions which otherwise develop within pores containing both air and liquids also we were able to measure pore fluid pressure in a model well during heating the basal temperature of the model surpassed the melting point of beeswax 62 c reaching a maximum of 90 c to investigate tectonic contexts of compression or extension we used a piston to apply horizontal displacements in experiments where the piston was static rapid melting led to vertical compaction of the source layer under the weight of overburden and to high fluid overpressure lithostatic or greater cross sections of the models after cooling revealed that molten wax had migrated through pore space and into open hydraulic fractures sills most of these sills were horizontal and their roofs bulged upwards as far as the free surface presumably in response to internal overpressure and loss of strength of the mixture we also found that sills were less numerous towards the sides of the box presumably as a result of boundary effects in other experiments in which the piston moved inward causing compression of the model sills also formed however these were thicker than in static models and some of them were subject to folding or faulting for experiments in which we imposed some horizontal shortening before the wax had started to melt fore thrusts and back thrusts developed across all of the layers near the piston producing a high angle prism in contrast as soon as the wax melted overpressure developed within the source layer and a basal detachment appeared beneath it as a result thin skinned thrusts propagated further into the model producing a low angle prism in some experiments bodies of wax formed imbricate zones within the source layer thus in these experiments it was the transformation from solid wax to liquid wax which led to chemical compaction overpressure development and hydraulic fracturing all within a closed system according to the measurements of overpressure load transfer was the main mechanism but volume changes also contributed producing supra lithostatic overpressure and therefore tensile failure of the mixture

the origins of carbonate minerals of a source controlled lacustrine carbonate succession in the shulu sag bohai bay basin implications for porosity development and paleoenvironment abstract lacustrine carbonates are widely distributed in the third member of the eocene shahejie formation es3l of the shulu sag and other rift basins in the bohai bay basin which can act as reservoirs for hydrocarbon and provide insights into paleoenvironment however the origins of lacustrine carbonate deposition and their implications for porosity development and paleoenvironment are not well understood based on micropetrological characteristics x ray diffraction xrd stable carbon and oxygen isotope analyses and organic geochemistry data four types of calcite calcite debris calcareous biological detritus micrite in fine grained marlstone fibrous sparry calcite and two types of dolomite dolomite debris rhombic euhedral dolomite with distinctly different characteristics and origins are identified the 13c and 18o values of calcite and dolomite debris are consistent with that of the cambrian ordovician carbonate rock in the provenance area suggesting that the carbonate debris was sourced from the surrounding cambrian ordovician carbonate bedrock microcrystalline calcites are commonly developed in organic rich marlstones with a large number of algae the 13c values of the microcrystalline calcites are higher than that of carbonate debris and the positive excursion of the 13c value is along with the increase of toc content these indicate that origin of the microcrystalline calcite was authigenic calcite and was formed by biochemical process bedding parallel fibrous sparry calcite occurs in intervals with high toc contents and within the thermally mature zone of hydrocarbon generation indicating that oil generation should be responsible for the sparry calcite formation rhombic euhedral dolomite commonly occurs as isolated micro crystals with euhedral to subhedral rhombs shape micro sized spherule like dolomite in the early stage of crystal growth were also present rhombic euhedral dolomite are commonly associated with organic matter and developed in organic matter rich intervals with plenty of fossilized bacterial filaments and framboidal pyrite these suggest that rhombic euhedral dolomite were probably microbially mediated dolomite mineral components can affect reservoirs quality the porosities of samples show a positive correlation with dolomite content and the porosities of fibrous sparry calcite bearing intervals are higher than non parry calcite bearing intervals the increase in authigenic microcrystalline calcite content reflects a rise in lake level and an increase in water depth and primitive productivity

use of a rotary shear box for testing the shear strength of rock joints this note describes a rotary shear machine similar to those designed by bishop green garga andersen brown 1971 and bromhead 1979 but suitable for testing rock surfaces especially the shear strength of rock surfaces separated by an infilling of weaker material the machine was constructed in 1986 and has recently been used to complete a series of trial tests on clean flat rock surfaces and similar surfaces separated by clean rock gouge it was specifically designed to accurately measure shear parameters up to peak failure and to follow these parameters beyond failure to their residual or basic angle of friction this permits an accurate study of the mechanisms governing shear resistance in rock joints which are subjeced to large displacements

insights from electron backscatter diffraction into the origin of fibrous calcite veins in organic rich shale from lower es3 to upper es4 jiyang depression china abstract the origin of fibrous calcite veins developed in organic rich shales has attracted great attentions however the growth direction formation temperature and stress state are still controversial the calcite veins in organic rich shale from lower es3 to upper es4 in the jiyang depression has been analyzed with electron backscatter diffraction technology ebsd which can characterize the microstructures and orientation of mineral crystals in situ on the basis of core observation and microscopic identification of petrological characteristics the longitudinal and horizontal profiles of calcite veins were measured by ebsd crystallographic information on calcite veins obtained by pattern quality mapping phase diagrams grain distribution maps euler graphs grain misorientations and pole figures clarifies the origins of these veins the results show that calcite crystals in calcite veins belong to the sharp rhombohedral space lattice structure of the trigonal system calcite crystals have a preferred orientation on the longitudinal profile while there is no obvious preferred orientation on the horizontal profile on the longitudinal profile of calcite veins the misorientation of calcite crystals is the cause of the interference colour and extinction difference of calcite crystals under orthogonal light the crystal interference and extinction characteristics on both sides of middle line in calcite veins are different indicating that the growth direction of calcite veins is syntaxial a shallow burial environment is suggested for calcite veins initial forming by the evidence that crystal morphology of calcite in calcite veins is most in the shape of sharp rhombohedron and some of which have hexagonal prism shape the average orientation difference of calcite veins on longitudinal and horizontal profiles indicates that the average orientation of calcite grains is inhomogeneous the stress concentration of small grains is higher than that of large grains and cracks are developed in the interior or on the border of calcite grains on the longitudinal profile which indicates that calcite veins are formed in the stress environment of three directional extrusion circumstances

spatial variability at shallow snow layer depths in central dronning maud land east antarctica spatial variability at swallow snow layer depths in central dronning maud land east antarctic

effect of shale diagenesis on pores and storage capacity in the paleogene shahejie formation dongying depression bohai bay basin east china abstract compared to other marine shale gas reservoirs in south china the shale that developed in faulted basins in east china possesses peculiar characteristics regarding the mineral types and their evolution the diagenesis of inorganic minerals generation of hydrocarbons and evolution of organic matter control the final features and quality of these shale reservoirs therefore we must analyze this diagenesis based on the essential characteristics of the representative reservoir and discuss the influence of the diagenesis evolution stage on the shale reservoir this topic is also of practical value for contemporary shale oil exploration and development in this paper we observe diagenesis study its essential characteristics such as the structure of the reservoir and pores determine the key factors that control the reservoir s storage capacity and analyze the role of diagenesis organic and inorganic in the evolution of pores and the reservoir s storage capacity the mineral types are diverse and the content of calcite and other carbonate minerals is generally very high organic matter is abundant thermal evolution is low and the hydrocarbon generation capacity is strong because of their high variability some pores are hard to differentiate from microfractures dissolved pores which are generated by intercrystalline pores and the dissolution of calcite dolomite and other carbonate mineral grains are the major component of a macroporous matrix the large proportion of hydrocarbons that are generated by solid organic matter leads to the accumulation of pressure the shale generates a high number of microfractures which form a reservoir space network system that increases the porosity of the reservoir dolomite has a unique supporting role for the matrix pores leading to the development of a matrix pore seam system the reservoir s mineral composition pore diameter porosity and organic matter content determine the reservoir properties and oil saturation organic rich laminated shale has the best physical properties dominated by macro pores and easily connected and merged pore seams the massive shale has the poorest reservoir property the development and evolution of pores are mainly controlled by the transformation of clay minerals the content of carbonate minerals the sedimentary structure and the intensity of diagenesis dissolution depends on the intensity of hydrocarbon generation the expulsion of acid by organic matter the state of the carbonate minerals and organic matter and the smooth depression of the fluid environment organic diagenesis is closely related to the diagenesis and evolution of inorganic matter and is typically reflected in the recrystallization of calcite abundance of organic matter and hydrocarbon generation by organic matter a local alkaline diagenetic fluid environment and reduction in the degree of hydrocarbon generation transform incremental porosity to pore reduction favorable lithofacies and advantageous layer sections should be selected by considering the stage of diagenesis evolution

thresholds of petroleum content and pore diameter for petroleum mobility in shale petroleum mobility in shale is closely correlated with the attributes of shale petroleum and pores however the relationship between these attributes is poorly understood to characterize petroleum mobility in self sourcing reservoirs a suite of mature eocene shales was selected and subjected to organic solvent extraction and both the raw and solvent treated samples were analyzed using pyrolysis nitrogen adsorption and x ray diffraction the results show that the pore surface area and pore volume of these shales are mainly controlled by their clay and quartz content rather than their organic matter om content and are limited by the presence of carbonates correlations of soluble om with pore surface area and volume after solvent extraction indicate that petroleum mobility of studied shales is initiated when the petroleum content reaches 0 70 wt of the rock and the pore diameter is over 12 1 nm these thresholds are established in the studied area and should be similar for the self sourcing reservoirs from similar sedimentary environments this work proposes a method to reveal the thresholds of petroleum content and pore diameter for petroleum mobility in self sourcing reservoirs which is useful in the assessment of petroleum producibility and is of significance for unconventional petroleum exploration and exploitation

a simple shear strength model for interlayer shear weakness zone interlayer shear weakness zone iswz is a widespread zonal weak geotechnical system with variable thickness in rock masses representing a potential threat to the overall stability of structure constructed on or within the rock mass due to their relatively poor mechanical properties its shear behaviour depends on both the interlayer soil and the interlayer soil host rock interface soil rock interface in this study a dynamic approach is adopted by treating iswz as an unfilled joint rock rock interface that is increasingly filled with interlayer soil of variable thickness based on the available experimental data a simple shear strength model is developed capable of describing both the shear behaviours of interlayer soil and soil rock interface because the geometric factors i e the thickness of interlayer soil and the morphology of interface and the mechanical conditions i e normal stress uniaxial compressive strength of rock and shear strength of interlayer soil are all taken into account the combining mechanical effect of interlayer soil and soil rock interface on the iswz is totally included in the model this is partly confirmed by the good agreement between the model prediction and the experimental results from laboratory and field tests

airborne radar stratigraphy and electrical structure of temperate firn bagley ice field alaska u s a helicopter borne 135 mhz short pulse radar profiles of the bagley ice field southern alaska u s a have been analyzed to determine the nature of radio wave propagation through crevassed stratified wet and draining firn diffractions characterize the firn horizons along the trunk and reflections characterize those of overlying snow fields dynamic stacking was used to form and determine firn depths and unstacked diffraction analysis to determine firn layer properties refractive indices range from 4 1 to 4 5 for the near surface from 1 7 to 2 1 at about 13 17 m depth along the main trunk and to 2 6 to 58 m depth within a snowfield average trunk values correspond with volumetric water contents of about 0 09 which agree with values measured for other glaciers the analysis of the airborne recorded diffractions is confirmed by deriving the approximate refractive index of water from a supraglacial lake bottom diffraction the lack of snowfield diffractions suggests that crevassing and not firn structure caused the trunk diffractions the reasonable values of the indices imply that the diffractions originated from single points or edges orthogonal to the profile transect and they predict low interlayer transmission losses the snowfield penetration suggests that several hundred meters might be penetrated in uncrevassed accumulation zones with improved system design

laboratory testing and parameters controlling the shear strength of filled rock joints the shear strength of iofilled rock joints has been studied for a long time but a complete understanding of the mechanisms and of the parameters controlling the process has never been reached this paper reviews test results in the literature and compares them with results obtained by the authors the main parameters controlling the shear strength of infilled joints are discussed and a framework for understanding the failure mechanisms involved in the shearing of such discontinuities is given la resistance au cisaillement des joints rocheux remplis a ete etudiee depuis tres longtemps mais le mecanisme et les parametres controlant le processus n ont jamais ete totalement compris cet article passe en revue les resultats des essais publies et les compare avec les resultats obtenus par les auteurs les parametres principaux controlant la resistance au cisaillement des joints remplis sont discutes et un cadre pour comprendre les mecanismes de rupture associes au cisaillement de telles discontinuites est donne

integrated study of the judy field block 30 7a an overpressured central north sea oil gas field the triassic reservoirs of the judy field an overpressured petroleum accumulation in the central north sea have been studied to determine their pressure and petroleum filling history the magnitude of overpressure in the pre cretaceous aquifer is similar across the field at about 24 mpa 3500 psi but with some higher pressure laterally in areas closest to the major depocentres pressure modelling shows that the magnitude of the overpressure can be attributed almost entirely to disequilibrium compaction and largely due to late rapid tertiary burial although modelling does require nanodarcy i e shale like permeability in the cretaceous chalk section the contributions from other mechanisms which may be relevant in this setting i e gas generation and lateral transfer appear to be small the existence of both aqueous and petroleum phases in secondary fluid inclusions in microfractures in quartz and feldspar grains allows estimation of palaeopressure the data show fracture healing from 115 to 136 c during a time when reservoir palaeopressures were above hydrostatic reconstruction of the temperature history of the reservoir places the timing of the fluid inclusion formation during fracture healing at between 3 and 1 my ago coincident with a period of rapid burial the palaeopressure estimation using fluid inclusions validates the pressure modelling studies which are derived independently from commercial basin modelling software the fluid inclusions also revealed a low gor oil over the whole field prior to late stage flooding by gas leading to the variable low to high gor fluids plus gas condensates within the field today

a shear strength model for idealised infilled joints under constant normal stiffness infill materials found in natural rock joints may cause a reduction in joint shear strength influencing rock mass stability this paper reports a study aimed at developing a semi empirical methodology for predicting the shear strength of infilled joints taking into account joint surface characteristics and the properties of the joint and infill materials a new model for predicting the shear strength of infilled joints is presented on the basis of a series of tests carried out on two types of model joint surface having asperity angles of 9 5 and 18 5 with graphite and bentonite used as infill materials all tests were carried out in a large scale shear apparatus under constant normal stiffness cns conditions the results indicate that at low infill thickness to asperity height ratio t a the combined effect of the basic friction angle b and the joint asperity angle i is pronounced but it diminishes with increasing t a ratio so that the shear strength converges towards that of the infill al

climate driven paleolimnological change controls lacustrine mudstone depositional process and organic matter accumulation constraints from lithofacies and geochemical studies in the zhanhua depression eastern china abstract the influence of paleoclimate on the depositional process of lacustrine mudstone and organic matter accumulation is important to both paleoclimate reconstruction and hydrocarbon exploration here we study the lower third member es3l of the eocene shahejie formation in the zhanhua depression bohai bay basin eastern china in order to understand how paleoclimate influenced depositional processes and organic matter accumulation of lacustrine organic rich mudstone by combining detailed core descriptions and microscopic observations and high resolution mineralogical and geochemical analyses we identified two major lithofacies including massive calcareous mudstone and laminated calcareous mudstone from the luo 69 drilling core the sedimentologic observations and changes of geochemical proxies including detritus index ln al2o3 na2o b ga and v v ni suggest that the massive calcareous mudstone was deposited in a small shallow salt lake that was dysoxic anoxic and the paleoclimate in the lake catchment was cool and arid and the laminated calcareous mudstone was deposited in a large and deep stratified lake which has anoxic highly saline bottom and oxic less saline surface water and the lake catchment was more humid and warm the dominant lithofacies changed from laminated calcareous mudstone to massive calcareous mudstone in the studied core suggesting that the lake became shallower and smaller when the paleoclimate became cooler and drier through time such a climate trend may be a response to global cooling during the middle eocene the average total organic content toc in both lacustrine highstand and lowstand are comparable even though the lake water chemistry and amount of terrigenous input are different we infer that the accumulation of organic matter within the lacustrine highstand was controlled by the combination of primary productivity carbonate production and preservation in anoxic bottom water while accumulation within lacustrine lowstand was only controlled by primary productivity

techniques for measuring high resolution firn density profiles case study from kongsvegen svalbard on an 11 m firn ice core from kongsvegen svalbard we have used dielectric profiling dep to measure electrical properties and digital photography to measure a core optical stratigraphy cos profile we also used a neutron scattering probe np to measure a density profile in the borehole from which the core was extracted the np and dep derived density profiles were similar showing large scale 30 cm variation in the gravimetric densities of each core section fine scale features 10 cm are well characterized by the cos record and are seen at a slightly lower resolution in both the dep and np records which show increasing smoothing a combination of the density accuracy of np and the spatial resolution of cos provides a useful method of evaluating the shallow density profile of a glacier improving paleoclimate interpretation mass balance measurement and interpretation of radar returns

combined use of confocal laser scanning microscopyand pvt simulation for estimating the composition andphysical properties of petroleum in fluid inclusions we present a method to determine the composition and pvt properties of petroleum inindividual petroleum fluid inclusions confocal laser scanning microscopy is used to generatethree dimensional images of single petroleum inclusions because liquid petroleum fluorescesunder the laser the images readily distinguish the liquid and vapour within the inclusion and canbe used to determine the inclusions volumetric liquid vapour ratio using pvt modellingsoftware the liquid vapour ratio is used along with the homogenisation temperature to determinethe bulk composition phase envelope isochore and a range of physical properties of the includedpetroleum this is done using an iterative series of pvt calculations which match twoparameters 1 the molar volume of the petroleum at room and homogenisation temperatures 2 the liquid vapour ratio of the inclusion at room temperature key uncertainties in the methodare explored including the accuracy with which the liquid vapour ratio can be determined thecomposition of the titrant gas used in the iterative procedure and the composition of thepetroleum chosen to model the physical properties of the included petroleum data from coevalinclusions suggest that the saturation pressure gas oil ratio viscosity molar volume densityand surface tension of included petroleum are determined with a precision of a few percent confirmation of the accuracy of the method awaits tests using inclusions grown in the laboratoryunder carefully controlled pvtx conditions however it is likely that the physical properties ofincluded petroleums are more accurately modelled by fluids which are genetically related tothem if proven to be accurate the method will provide a routine method for determiningpalaeopressure in petroleum systems finally we present data from a central north sea examplewhich are geologically realistic and which for the first time record the evolution of fluid pressureand petroleum composition in a petroleum reservoir

strong spatial variability of snow accumulation observed with helicopter borne gpr on two adjacent alpine glaciers the spatial distribution of snow accumulation plays an essential role for the mass balancedistribution on alpine glaciers traditional point measurements snow pits and probes are labour intensive and interpolation in between the points causes uncertainties airborne radar measurements have already been used for snow mapping innon glacierized terrain but not on alpine glaciers to enhance our understanding ofthe spatial distribution of accumulation and pin down reasons for observed variations we have conducted high resolution helicopter borne radar measurements on the temperatedglacier findel and neighbouring adler glacier in southwestern switzerland the radar sensor was mounted underneath a helicopter and operated at a centre frequencyof 500 mhz with a bandwidth of 400 mhz the results were validated withextensive ground based profiling of the snow cover the radar data allows a clearrecognition of the snow cover 6 of the total profile length of 10 km did not allowinterpretation due to missing or disturbed layering and agreed well with the groundbased measurements r2 0 85 reduced accumulation has been observed in allcrevassed zones statistical analysis of the correlation between observed accumulationand terrain characteristics have been performed in a gis environment revealing differingaccumulation patterns on the lower part of findel glacier accumulation showsa clear altitudinal trend while the upper part is dominated by strongly varying snowdepth without an altitudinal trend the accumulation characteristic on adler glacieris similar to the upper part of findel glacier but despite of their close vicinity accumulationis reduced by 40 compared to the same elevation on findel glacier thisstudy reveals a large potential of helicopter borne snow profiling for measurements ofaccumulation distribution on alpine glaciers