the relationship of sea surface temperature to thermocline depth at annual and interannual time scales in the tropical atlantic ocean expendable bathythermograph data derived from sequal focal and toga sponsored volunteer observing ship programs in the tropical atlantic ocean are used to study the relationship between the sea surface temperature sst and the underlying thermocline time series up to 8 years long allow investigation of both the annual and interannual variability between 2n and 2s along selected shipping lanes for the annual harmonic a warm sst is correlated with a shallow thermocline everywhere except in the eastern equatorial region near the intertropical convergence zone itcz the 180 phase shift in the annual harmonic of both the sst and the thermocline depth occurs at slightly different latitudes over most of the tropical atlantic the annual cycle of sst is linked to the phase of the net surface heat flux and only in the eastern equatorial and coastal upwelling regions does heat flux across the thermocline become a significant factor for the annual cycle of the sst canonical correlation analysis of the interannual variability reveal two distinct modes with structures similar to the annual cycle the first in which a warm sst is correlated with a shallow thermocline is a dipole with centers of maximum amplitude off the equator at approximately 8s at 12n and a node at the itcz the second mode for which a warm sst is correlated with a deep thermocline peaks at the equator the predominance of the first mode suggests that for most of the tropical atlantic ocean the dynamical state beneath the surface mixed layer has only a limited influence on sst fluctuations

monitoring soil water and displacement conditions leading to landslide occurrence in partially saturated clays abstract shallow landslides frequently occur during transient rainfall infiltration and under partially saturated conditions however a detailed analysis of what triggers them particularly in clayey soils is often hindered by the lack of field measurements it is uncommon in fact to capture their occurrence in an instrumented natural slope this paper presents results from an integrated field experiment monitoring the soil water and displacement conditions that lead to the occurrence of a shallow landslide in partially saturated clays the integration of a variety of experimental techniques allowed for the examination of interplay between soil hydrological and mechanical properties this research also evaluates a slope stability model based on the suction stress concept since the model was applied after the occurrence of the landslide the results are interpreted as a hind casting technique for model evaluation nevertheless the detailed field measurements acquired during the monitoring activity and the occurrence of a landslide during the experiment provided significant information on model parameters and data interpretation the station provides remote satellite monitoring of data on weather variables soil water content and soil suction a time domain reflectometry cable was installed vertically to detect potential soil failure the experimental area had a high probability of landslide occurrence indeed slope failure occurred during the observation period showing the effectiveness of the station in detecting the occurrence time and depth of landslides the landslide was triggered in consequence of changes in suction stress the failure plane occurred at a depth of 1 4 m corresponding to the interface between a superficial layer of higher permeability of 1 to 1 45 m thickness slipping over a compacted substrate having lower permeability the analysis allowed for testing of the validity of the model and the description of the triggering mechanisms of the observed shallow landslide in unsaturated conditions indicating that oscillations in soil matric suction were the dominant variables determining soil failure

investigation of landslide failure mechanisms adjacent to lignite mining operations in north bohemia czech republic through a limit equilibrium finite element modelling approach abstract understanding the impact of data uncertainty is a fundamental part of ensuring safe design of manmade excavations although good levels of knowledge are achievable from field investigations and experience a natural geological environment is subject to intrinsic variability that may compromise the correct prediction of the system response to the perturbations caused by mining with direct consequences for the stability and safety of the operations different types of geoscientific evidence including geological geomorphic geotechnical geomatics and geophysical data have been used to develop and perform two dimensional limit equilibrium and finite element method stability analyses of a lignite open pit mine in north bohemia czech republic affected by recent landslides a deterministic probabilistic approach was adopted to investigate the effect of uncertainty of the input parameters on model response the key factors affecting the system response were identified by specific limit equilibrium sensitivity analyses and studied in further detail by finite element probabilistic analyses and the results were compared the work highlights that complementary use of both approaches can be recommended for routine checks of model response and interpretation of the associated results such an approach allows a reduction of system uncertainty and provides an improved understanding of the landslides under study importantly two separate failure mechanisms have been identified from the analyses performed and verified through comparisons with inclinometer data and field observations the results confirm that the water table level and material input parameters have the greatest influence on the stability of the slope

intraplate stresses and dynamical aspects of rifted basins abstract intraplate stresses play a important role during the syn and post rift evolution of sedimentary basins deviations from long term thermal patterns of post rift subsidence as well as the development of unconformities within rifted basins reflect to a large extent the temporal fluctuations of the regional stress fields in the lithosphere it appears that incorporation of intraplate stresses in dynamical models for basin development together with a quantification of the role of petrological changes in the crust lithosphere system can explain some of the observed shortcomings of thermal models of post rift basin subsidence late neogene accelerations in tectonic subsidence in the deeper parts of rifted basins in the northern atlantic and mediterranean regions could reflect a change in the level of intraplate stress over large areas of the globe non thermal contributions to the subsidence record affect estimates of crustal extension and consequently influence the depth at which hydrocarbon source rocks enter the maturity window stress induced changes in basement topography have also important consequences for the budget of fluid flow in the deeper parts of the sediment fill of the rifted basins as well as on the dynamics of diapirism

coupled isotopic evidence for elevated pco2 and nitrogen limitation across the santonian campanian transition abstract the santonian campanian s c transition notably coincides with the termination of the cretaceous normal superchron a positive carbon isotope anomaly and the enhanced preservation of organic matter associated with an oceanic anoxic event at ca 84 ma the driving factors for the oaes should include global warming widely believed to be from volcanic sources the delivery of nutrients to surface oceans from the continents anoxic sediments and atmosphere and variations in the configuration of ocean basins to further investigate this phenomenon and evaluate whether there was a teleconnection between the marine and continental realm we have studied a lacustrine succession in northeastern china the songliao basin which is 3 the size of lake superior that preserves two thick horizons of oil shales and a positive carbon isotope anomaly recorded in ostracode carbonate near the s c boundary this freshwater basin is one of the many that formed as a consequence of mesozoic extensional tectonics in eastern asia the stratigraphic trends illustrate broad excursions in the isotopic compositions of carbonate total organic carbon including black carbon and total nitrogen the carbon isotope data suggest that maximal fractionation etoc at the s c boundary is caused by enhanced burial of organic carbon and inputs from anoxygenic photoautotrophs and chemoautotrophs or from the buildup of co2 in a lake environment on the other hand the nitrogen isotope data suggest that the lake became limited in nitrogen immediately before the deposition of the younger oil shale resulting in the addition of new nitrogen to the system likely as the result of diazotrophy or ammonium assimilation to some extent all of the features we described from the songliao basin have been recognized in jurassic and cretaceous oaes insofar as climatically sensitive lakes are typically supersaturated with co2 relative to the atmosphere we speculate that nutrient driven primary productivity in massive lake systems may have released enough greenhouse gas co2 ch4 and n2o into the atmosphere and therefore played a role in enhancing global temperatures and driving widespread anoxia in the mesozoic oceans

plastic and viscous shear displacements of a deep and very slow landslide in stiff clay formation deep and superficial displacements have been measured since 2005 in a slow active landslide that has occurred in a stiff clay formation of the italian southern apennines recently new inclinometer casings have been installed to achieve further information on the displacement field in this paper standard inclinometer profiles and fixed in place probe data are analysed over time new data confirm previous hypotheses on geometry and kinematics and add more information on the viscous component of displacements the mechanism of movement in most of the track essentially corresponds to sliding localized on a shear surface consistently with stress and strength distribution however locally internal viscous deformations also occur especially in the weathered and softened zones of the landslide and contribute to the soil discharge continuity viscous displacements can be interpreted by a simplified rheological model based on the bingham equation the residual shear strength has been considered as the creep threshold value and the dynamic viscosity has been considered dependent on the stress level on the basis of long term direct shear tests under controlled shear stresses which were carried out in laboratory

the palliser rockslide canadian rocky mountains characterization and modeling of a stepped failure surface abstract this paper presents the results of an investigation of the prehistoric palliser rockslide rocky mountains canada conventional aerial photograph interpretation and field mapping are complemented by terrestrial digital photogrammetry these techniques allow quantification of the rockslide debris volume and reconstruction of the pre slide topography it has been estimated that the volume of rock involved in the most recent large rockslide is 8 mm 3 terrestrial digital photogrammetry is used in the characterization of the failure surface morphology which is subdivided into four types of step path geometry comprising both pre existing discontinuities and intact rock fractures incorporation of these data into various rock slope stability numerical modeling methods highlights a complex failure mechanism which includes sliding along a large scale curved failure surface intact rock bridge fracturing and lateral confinement a preliminary quantification of the contribution of intact rock bridges to the shear strength of the failure surface is presented in terms of the apparent cohesion apparent tensile strength and cumulative length of the intact rock segments

swelling and softening behaviour of la biche shale free swell semiconfined swell and one dimensional oedometer swell tests were performed on la biche shale specimens in solutions of different salinities the swelling behaviour of la biche shale w

the role of thermal conductivity measurements in modelling thermal histories in sedimentary basins thermal conductivity is an important parameter in thermal maturity modelling yet is often poorly constrained here we examine the consequences for thermal history models of incorporating imprecise and inaccurate thermal conductivity data we adopt a formal inversion scheme to determine the heat flow history of inigok 1 colville basin alaska using an extensive suite of vitrinite reflectance measurements as calibration data the initial model incorporates lithology dependent matrix thermal conductivity values based on published data subsequently we reran the inversion 100 times using different matrix thermal conductivities generated by monte carlo sampling of normal distributions specified for each lithology the mean of each distribution was set to the initial model value and standard deviation was set at 20 of the mean the results show that the relative variation in palaeotemperatures associated with the inversion generated thermal histories is considerably less than that used to generate the thermal conductivity samples this is because the heat flow history compensates for the variations in thermal conductivity to satisfy the constraints afforded by downhole temperature measurements and downhole thermal indicator data these results show that thermal histories modelled with the inversion scheme are robust to imprecise and inaccurate thermal conductivity data however if a meaningful estimate of the actual heat flow is required then accurate thermal conductivity data are necessary

confidence limits on kinetic models of primary cracking and implications for the modelling of hydrocarbon generation abstract kinetic models of primary cracking for use in hydrocarbon modelling are obtained through empirical calibration against laboratory measurements this paper utilizes least squares variance analysis to evaluate the uncertainty in the calibrated kinetic parameters and discusses some consequences for the prediction of hydrocarbon generation it is substantiated that the sensitivity of the average kinetic parameters e a and log e a to micropyrolysis errors can be parameterized by errors in pyrolysis tmax the absolute and relative errors in tmax are modelled by normal gaussian random variables and the variance analysis yields the joint normal probability density distribution of variability in e a and log e a it is found that tmax errors reduce the ability to resolve independently the values of e a and log e a the estimation errors are highly positively correlated and repeated measurements on identical kerogens will produce values of e a and log e a which tend to fall close to and along the line log e a e a irt p constant where tp is an average pyrolysis temperature this correlation is consistent with observations and hence it is suggested that it is mainly an artifact which originates in the experimental errors of laboratory pyrolysis when values of e a and log e a are confined to the region of the confidence ellipsoid the pyrolysis data are satisfied within their error bounds however the variability in predictions of hydrocarbon generation may be large depending on the particular geological temperature history the uncertainties in the depth to the oil window may be several hundreds of metres and the timing of peak hydrocarbon generation rate may vary considerably the inclusion of basin geochemical data in the calibration drastically reduces the ambiguity in e a and log e a and emphasizes the need to validate the laboratory calibrated kinetic models against basin observations

why were sea surface temperatures so different in the eastern equatorial atlantic in june 2005 and 2006 abstract a comparison of june 2005 and june 2006 sea surface temperatures in the eastern equatorial atlantic exhibits large variability in the properties of the equatorial cold tongue with far colder temperatures in 2005 than in 2006 this difference is found to result mainly from a time shift in the development of the cold tongue between the two years easterlies were observed to be stronger in the western tropical atlantic in april may 2005 than in april may 2006 and these winds favorably preconditioned oceanic subsurface conditions in the eastern atlantic however it is also shown that a stronger than usual intraseasonal intensification of the southeastern trades was responsible for the rapid and early intense cooling of the sea surface temperatures in mid may 2005 over a broad region extending from 20 w to the african coast and from 6 s to the equator this particular event underscores the ability of local intraseasonal wind stress variability in the gulf of guinea to initiate the cold tongue seaso

dynamics of the equatorial atlantic from altimetry the first 700 days of topex poseidon altimetric data of the equatorial atlantic are selectively investigated to yield a basin wide description of the zonal pressure gradient along the equator and the meridional gradient across the north equatorial countercurrent necc in the first analysis the gravest empirical orthogonal function mode is found to be zonally constant in midbasin and a quasi stationary linear relationship between the basin wide averaged zonal wind stress and the zonal pressure gradient is demonstrated correlation coefficient of 0 70 with a zero lag in the second analysis the zonal variation of the depth of the necc trough across the basin is described and it and its annual cycle are reproduced with a reduced gravity model calculation correlation coefficient of 0 75 a secondary result of both analyses is an estimate of the adjustment to the working model of the local geoid gradients needed to bring the mean altimetric signal into agreement with the dynamic models and modeled wind field

high resolution geochemical analysis of organic matter accumulation in the qingshankou formation upper cretaceous songliao basin ne china abstract in the well known continental songliao basin the oil shale successions of the cretaceous qingshankou formation are excellent source rocks for oil the oil shale layers with high toc total organic carbon contents developed at the bottom of the formation they are divided into the lower oil shale toc up to 18 3 and the upper oil shale layer toc up to 14 4 the oil shale layers and accompanying mudstones are investigated by high resolution analyses of drill cores by pyrolysis organic petrology organic and inorganic geochemistry the results demonstrate the predominance of type i kerogen derived from algal microbial mats i e lamalginite however increased proportions of plant derived organic matter are indicated by rock eval parameters and the presence of vitrinite in the upper oil shale as evidenced from lower concentrations of hopanes higher sinking rates of organic matter om are suggested to have been responsible for a lower extent of microbial degradation during accumulation of the lower oil shale unit the environmental conditions are characterized by anoxic saline bottom water overlain by an extended zone of freshwater favorable for om production and preservation under these preconditions oil shale thickness and quality are governed by primary productivity related to accommodation space and nutrient supply redox conditions within the water column are the key factor controlling organic matter preservation

seasonal propagation of sea level along the equator in the atlantic in the equatorial atlantic the sea surface height ssh anomaly field is dominated by an annual signal propagating eastward this signal has been previously interpreted in terms of propagating waves in this article it is argued that this propagating signal is not a free equatorial kelvin wave because the phase velocity observed is too small compared to first second or third baroclinic mode kelvin waves and is not the result of an equatorial forced wave because the zonal wind stress does not show a similar propagation rather it is suggested that the eastward propagation in ssh is due to the sum of two independent modes of variability one mainly driven by the wind stress curl off the equator and the other driven by the zonal wind stress along the equator these two modes are uncorrelated in time and space and therefore can be conveniently separated by an empirical orthogonal function analysis of the equatorial atlantic sea surface height the first mode explains 74 of the variance is one signed in longitude and is interpreted as the variability of the warm water volume above the thermocline the second mode explains 24 of the variance consists of an east west tilt along the equator and is driven by variations of the zonal equatorial wind stress

response of the equatorial atlantic ocean to the 1983 1984 wind from the programme francais ocean et climat dans l atlantique equatorial cruise data set variations of the zonal pressure gradient zpg and the equatorial undercurrent euc are described in the equatorial atlantic ocean between 34 30 w and 6 30 e as observed during eight pairs of programme francais ocean et climate dans l atlantique equatorial cruises between october 1982 and august 1984 in 1982 and 1983 the annual cycle of weak trades early in the year followed by comparatively strong and sustained trades were relatively normal in the boreal winter of 1984 the extent of the collapse of the trade winds was exceptional and consequences were observed in the upper layers of the ocean along the equator the 20 c isotherm depth representative of the thermocline depth was unusually deep along the equator in the gulf of guinea a near zero value of the zpg was observed from the greenwich meridian westward an eastward surface current separated from the euc by a layer of reduced velocity was observed over much the same fetch west of 10 w the maximum velocity of the euc showed very little seasonal variation usually between 70 and 80 cm s 1 except in the boreal fall of 1983 when it exceeded 100 cm s 1 during this period in both 1983 and 1984 the euc transport at 23 w reached 25 106 m3 s 1 or twice its annual average which derived not only from the increase in speed but also for a deepening of the current to below 100 m it was also the season when the zpg was strongest and has a similar amplitude at both the surface and 50 dbar relative to 500 dbar the seasonal variations of the euc in the gulf of guinea were even more pronounced during the boreal summer and fall the current weakened while the local zpg reversed direction compared to the west the stronger penetration of the euc into the gulf occurred in the alternate seasons when there was no local reversal in the eastward acting zpg force the large changes in the oceanic and atmospheric circulation during the 1983 1984 period are hypothesized to be related to the suppression of the coastal period are hypothesized to be related to the suppression of the coastal benguela upwelling along the namibia coast this atlantic equivalent to el nino occurred 1 year after the exceptionally strong event in the pacific

oceanic conditions in the tropical atlantic during 1983 and 1984 during 1983 and 1984 oceanographers from france and the usa conducted an extensive field programme in the tropical atlantic ocean the principal goal was to document the annual cycle but unexpectedly a difference was observed between the two years we describe here the observed variations in the thermal field and in the zonal currents along several meridians in early 1984 the upper ocean especially on the eastern side of the ocean basin was substantially warmer than during the corresponding period a year earlier most of this change in the heat content was the result of a deeper thermocline during this time an unusual eastward surface current appeared to the south of the equator undoubtedly contributing to large zonal heat fluxes the decrease in the surface winds1 between 1983 and 1984 is presumably responsible for these changes inspection of the few available long records reveals that in the atlantic warm events such as that of 1984 are rare and that the previous event with comparable amplitude occurred in 1963

sulfur isotope constraints on marine transgression in the lacustrine upper cretaceous songliao basin northeastern china abstract organic rich cretaceous source rocks of the petroliferous songliao basin in northeast china are considered to be lacustrine in origin but paleontological and organic geochemical evidence suggest episodic marine incursions as a test of this hypothesis we applied time series measurements of elemental and isotopic abundances on core and cutting samples to evaluate fluctuations in the sulfur and carbon cycles across the santonian campanian transition preserved in the upper yaojia and lower nenjiang formations the data reveal a spike in pyrite sulfur abundance and a marked negative excursion in 34s at the base of the nenjiang formation when the basin expanded to its maximal extent the elemental and isotopic data suggest that flooding was associated with rapid marine transgression that enhanced sulfate concentrations which promoted microbial sulfate reduction in anoxic bottom waters that were episodically euxinic subsequent restriction of the basin and a decline in marine influence is supported by progressive upsection 34s enrichment up to 30 in nenjiang member i which are interpreted to reflect the distillation of sulfate through enhanced pyrite burial followed by a gradual return to lacustrine conditions that prevailed in overlying strata

the extent and significance of bioturbation on 137cs distributions in upland soils abstract differences between measured 137cs activity depth profiles and idealised undisturbed profiles generated from an exponential model suggest that faunal turbation has redistributed 137cs in mineral and organic upland soils in southern scotland bioturbation is also demonstrated by the vertical displacement of other inputs to the soils of known age non native tree pollen and spheroidal carbonaceous particles scps the causes and mechanisms of bioturbation were further investigated by soil micromorphology well drained mineral soils with active populations of earthworms are the most bioturbated showing near complete homogenisation to depths of about 20 cm enchytraeids also seem to remobilise 137cs by the digestion of organic matter and may be the main cause of 137cs redistribution in organic rich upland soils relative rates of mixing are evaluated by comparing 137cs depth profiles

interpreting rock eval pyrolysis data using graphs of pyrolizable hydrocarbons vs total organic carbon kerogen the major organic component of sedimentary rocks is commonly analyzed by rock eval pyrolysis plotting the data on a graph of s 2 vs total organic carbon toc and determining the regression equation is the best method for determining the true average hydrogen index and measuring the adsorption of hydrocarbon by the rock matrix such a plot also indicates the type of kerogen present and avoids the problem of increasing hydrogen index with total organic carbon content with the s 2 vs toc diagram the organic component of different suites of samples may be compared and their petroleum generation potentials established as an example the diagrams are used to evaluate the sedimentary environments and petroleum potential of the paleogene evaporitic sediments of the mulhouse basin alsace france

an investigation into the development of toppling at the edge of fractured rock plateaux using a numerical modelling approach abstract the mechanisms controlling the onset of minor slope instability at the edges of rocky plateaux exhibiting lateral spreading phenomena are yet to be fully understood hypotheses have recently been introduced to explain the influence of groundwater within these plateaux on geomorphological processes leading to slope instability we present a back analysis of a recent landslide which occurred on 27th february 2014 in the town of san leo italy the role of the softening of basal clay shales and erosion due to seepage is investigated using finite element geomechanical models both processes were observed in the field and are related to groundwater discharging along the contact between the rocky slab and the clay rich substratum fracture propagation paths involving pre existing discontinuities and intact rock bridges failure were simulated using a simplified discrete fracture network dfn model coupled with a voronoi polygonal mesh approach model results allow the failure to be classified as a secondary toppling phenomenon moreover a critical amount of undermining was indicated by the models agreeing with field observations made prior to the failure based on the modelling results an interpretation of the overall mechanism inducing failures at the edges of fractured rock slabs is given in particular the inter relationships between groundwater flow and geomorphic processes acting within the rock masses are presented

basin evolution and oil shale deposition during upper cretaceous in the songliao basin ne china implications from sequence stratigraphy and geochemistry abstract the controlling factors of oil shale formation within the upper cretaceous qingshankou and nenjiang formations of the songliao basin are investigated by petrological and geochemical methods sediment deposition was balanced by basin subsidence resulting in the accumulation of cretaceous strata of high thickness global sea level fluctuations have been related to periods of oil shale deposition within the basin the results indicate a comparable depositional environment during oil shale formation within the two upper cretaceous strata with respect to palaeotectonic and palaeoclimate but differences in the accommodation space during accumulation of the two formations the larger accommodation space during deposition of the nenjiang formation resulted in the higher thickness and wider distribution of the oil shale members total thickness 11 2 32 m distribution area 4 48 103 km2 within the basin as compared to the oil shale of the qingshankou formation total thickness 2 19 3 m distribution area 1 3 103 km2 further differences exist with regard to the palaeoenvironment of oil shale formation and primary productivity deposition of the qingshankou formation 1st member and nenjiang formation 1st member took place within a saline brackish lake under anoxic conditions in the bottom water preservation of organic matter is suggested to have been less favorable during deposition of the nenjiang formation 2nd member higher primary productivity is believed to be the responsible factor for the accumulation of organic rich sediments in the qingshankou formation 1st member the interplay of these two factors i e preservation productivity leads to the formation of oil shale in the qingshankou formation average toc 8 32 tocmax 13 52 average oil yield 5 57 with better hydrocarbon source rock potential and slightly higher oil yield during pyrolysis as in the nenjiang formation average toc 7 76 tocmax 9 7 average oil yield 5 54 primary productivity is suggested as the main controlling factor on differences in oil shale quality and source rock potential between the two formations whereas the variations in quality within each formation mainly depend on the preservation of organic matter the high thickness wide spatial distribution and excellent hydrocarbon potential of the upper cretaceous oil shales in the songliao basin are suggested to have been the result of large accommodation space stable palaeoenvironmental conditions and high primary productivity

effect of air drying duration on the engineering properties of four clay bearing rocks in texas abstract the engineering properties of clay bearing rocks may degrade upon exposure to the air the engineer needs to know quantitatively the effect of the exposure duration on the rock s strength and deformability this paper quantifies the effect of air drying duration on the engineering properties of four clay bearing rocks in central texas usa known as del rio clay eagle ford shale taylor marl and navarro shale their shear strength decreases upon exposure to the air when the liquid limit is greater than 56 and the cation exchange capacity is greater than 29 meq 100 g taylor marl and navarro shale otherwise it is not affected by exposure to the air del rio clay eagle ford shale after 48 h of air drying the elastic modulus was approximately 35 10 15 and 25 of the maximum value for del rio clay eagle ford shale taylor marl and navarro shale respectively most of the reduction took place within the first 4 h of drying expressions are given for the strength and the young s modulus as a function of air drying duration in the jar slake tests degradation occurred only when the material was first air dried and the degradation extent increased with increasing drying duration degradation in the jar slake test may not necessarily imply shear strength loss when the material is gradually rewetted the slake durability index cannot be used to distinguish which material loses strength and does not correlate with loss of stiffness upon exposure to the air

numerical models for planning landslide risk mitigation strategies in iconic but unstable landscapes the case of cinque torri dolomites italy abstract this study deals with the numerical modelling of large deep seated instability processes affecting the cinque torri group dolomites italy which is a unesco world heritage site the aim is to evaluate the role of intrinsic causal factors and to assess the failure mechanism proposed in previous investigations the geological model is based on topographic geological and geomechanical surveys complemented with mineralogical physical and geotechnical lab analyses for parameters determination the numerical simulations have been carried out using a distinct element method code on conceptual and site specific slope models a series of parametric analyses have been performed to characterize the role of the different predisposing factors potentially related with the ongoing rock spreading i load of the rocky pinnacles ii lithology stratigraphy and attitude of the geological units iii discontinuity sets in the rock mass iv degradation of the mechanical properties the results of this study suggest that the shear zone initiation is controlled by stress concentration due to the loading of the dolomitic pinnacles whereas its shape appears to be structurally controlled by the dip slope attitude of bedding in clay rich mudstones the interpretation of the modelling results has provided a better understanding of the ongoing deformation process which can help in targeting effective and low impact landslide risk mitigation strategies in this iconic landscape

an analytical solution for analysis of toppling slumping failure in rock slopes abstract when a slope consists of a horizontal weak rock or soil overlaid by some vertical strong slender rock columns the slope is prone to a secondary toppling failure which is known as toppling slumping failure in the slope rock columns impose pressure on the lower continuous weak rock or soil mass which leads to a differential settlement at the base of each rock column or a circular shear failure in the continuous mass if the differential settlements reach a special threshold rock column overturn and toppling slumping will happen however the circular shear failure of the soil or weak rock mass which is a well recognized failure mechanism will occur when shear stress in the slope exceeds its shear strength in this paper an attempt has been made to better understanding of the toppling slumping failure mechanism through developing an analytical solution for this purpose first an airy stress function is acquired for the lower continuous soil mass and its stress distribution and displacement are accordingly determined analytically due to the overlaid rock columns loads then differential settlements at the base of all rock columns and shear stresses in the soil or weak rock mass are computed and compared with the toppling and shear failure criteria to assess slope failure finally several design charts are developed that determine the stability of a slope against toppling slumping failure mechanism based on geometric characteristics of the slope and shear strength of its constituent material also a mathematica package code was developed to evaluate the stress distribution within the slope and the safety factor the results show that the vertical stress distribution plays a significant role in the settlement of the rock columns results also manifested that at a certain distance from the slope crest the set of rock columns will act like a single column on a half plane the shear or toppling failure of the slope not only depends on the material s strength but also on the geometry and the normalized column distance

time dependent modelling of a mountain front retreat due to a fold to fault controlled lateral spreading abstract the eastern betic cordillera spain exemplifies at the sierra de aitana an impressive case of lateral spreading which involves a mountain anticline ridge dislodged by a post orogenic extensional tectonic the deep trenches testify the ongoing gravitational slope deformation featured by a rock mass lateral spreading the sierra de aitana anticline ridge was dislodged along a normal fault zone which generated a scarp with a kilometric lateral continuity the lateral spreading originated because eocene limestone overlays eocene marls inducing a continuous evolution over time due to visco plastic deformations and isolating huge prismatic blocks to quantify the creep driven stress strain effects at sierra de aitana ridge the mechanical and rheological parameter values of the involved rocks were quantified through field and laboratory tests which allowed to constrain an engineering geological model based on equivalent continuum approach a stress strain numerical modelling aimed at back analysing the sequential morpho structural evolution of the sierra de aitana anticline ridge was performed by reproducing the retreat of the ridge front and the time succession of faults re activations a time dependent solution was approached by assuming a time dependent creep configuration of the modelling and a parametric solution adopted to calibrate rock mass rheology also taking into account tectonic displacement due to the aitana normal fault system by simulating these element as interface in the discretized domain influence of pre existing joint sets by assuming a main anisotropy in the elasto plastic failure solution admissible variations of the regional stress field related to compressive and extensional phases and a generalised visco plastic behaviour representing the ductile marls the numerical modelling outputs that the lateral spreading mainly evolved as a creep driven process while stress release induced by tectonic activity is not sufficient to justify the observed landforms the obtained results highlight a not negligible role of inherited structural elements for regulating the time evolution of the ongoing gravitational process at the sierra the aitana anticline

ocean climate of the south east atlantic observed from satellite data and wind models the near coastal south east atlantic ocean off africa is a unique and highly dynamic environment comprising the cool benguela current warm angola current and warm agulhas current strong coastal upwelling and the congo river strongly influence primary production much of the present knowledge of the south east atlantic has been derived from ship borne measurements and in situ sensors which cannot generally provide extensive spatial and temporal coverage similarly previous satellite studies of the region have often focused on small spatial areas and limited time periods this paper provides an improved understanding of seasonal and interannual variability in ocean dynamics along the south east atlantic coast of africa using time series of satellite and model derived data products eighteen years of satellite sea surface temperature data are complimented by 7 years of sea level data three years of chlorophyll a data illustrate the seasonal biological response but the time series is not of sufficient length for investigating interannual variability in chlorophyll biomass modelled wind fields are used to describe atmospheric forcing of the surface ocean this is the first synoptic scale description of the south east atlantic from a suite of large spatial coverage long time series products previous studies of seasonal and interannual variability in the region are reviewed and used to interpret key oceanographic features and processes identified in the satellite data key findings of this study are 1 descriptions of seasonal and interannual variability from these data show climate forcing of the south east atlantic coast of africa from both the northern and southern boundaries bimodal seasonal signals of equatorial origin propagate poleward along the angolan coast while the trade winds and events in the agulhas region dominate the agulhas bank and southern benguela the northern benguela is a mixed regime under the influence of forcing from both directions 2 the benguela nino years of 1984 and 1995 are clearly observed in sea surface temperature and sea level anomalies and correspond to anomalously weak southerly winds at the equator these conditions were also observed in 1999 suggesting this too may have been a benguela nino year 3 consideration of putative nino type events in the equatorial atlantic from this and other studies suggests that the frequency of these events is much higher than previously estimated and may be similar to the frequency of el nino southern oscillation enso events in the pacific ocean furthermore years of anomalously strong southerly winds at the equator occur during pacific enso years c 2003 elsevier ltd all rights reserved

upper equatorial atlantic variability during 2002 and 2005 associated with equatorial kelvin waves on the basis of moored 35 degrees w 0 degrees and 23 degrees w 0 degrees and satellite observations we contrast the upper equatorial atlantic variability during 2002 with those during 2005 inspection of the interannual boreal summer cold tongue variability revealed a warm cold event in 2002 2005 with relaxed intensified winds in the west and the equatorial undercurrent euc embedded in a shallower deeper thermocline at 23 degrees w during both years 2002 and 2005 equatorial kelvin waves are present in moored observations as 20 degrees c isotherm depth anomalies and dynamic height anomalies basin wide sea surface height anomalies are used to derive an equatorial kelvin wave mode the time evolution of this mode represents the basis for a regression analysis to investigate related oceanic variability compared to the exceptionally strong wave activity in 2002 equatorial kelvin waves were generally weaker during 2005 the main effect of equatorial kelvin waves on zonal velocity anomalies at 23 degrees w 0 degrees is evident well below the euc core their direct influence on cold tongue sea surface temperature is small but they are found to affect the equatorial thermocline slope prior to the cold tongue onset in 2002 2005 the presence of equatorial kelvin waves is associated with a flattened steeper thermocline slope that is crucial for the shallowing deepening of the euc core at 23 degrees w and that might precondition the development of the warm cold event

late cretaceous climate changes recorded in eastern asian lacustrine deposits and north american epieric sea strata abstract cretaceous climate data of the long lived cretaceous songliao basin sb in eastern asia is correlated and compared with the western interior seaway wis on the northern american plate in order to understand better the dynamics of the earth s past greenhouse climates nearly continuous late cretaceous terrestrial deposition in the songliao basin is represented by two cores totaling 2431 m in length the turonian maastrichtian age of the section is based on integrated stratigraphy and is comparable in age with upper cretaceous strata in the wis being consistent with global trends the dynamic late cretaceous climates of both the sb and wis gradually cooled from the warmest albian cenomanian time to the end of the maastrichtian with several intervening warm periods as did the global climate however regional differences existed the songliao basin climate was humid to semi humid warm temperate subtropical and the western interior seaway was in the humid warm temperate zone and experienced only moderate climatic changes the shifts of oxygen isotope data in the songliao basin were frequent and abrupt whereas wis records more gradual change affected mainly by fresh water runoff mixing with southern tethyan and northern arctic waters sedimentary cycles of eccentricity obliquity and precession bands are recorded in both the sb and wis basins the sedimentary cycles in the wis and sb are interpreted to be related to variations of the wet dry runoff cycles which indicate that orbital forcing played an important role in global climate change in late cretaceous the most favorable condition for organic carbon burial in both the sb and wis basin was bottom water anoxia regardless of the cause of the anoxia but the organic carbon burial rate was usually much higher in the songliao lake than in the wi epeiric sea suggesting that giant lakes may serve as important sinks of atmospheric co 2 in both basins organic rich deposits formed during a rise in water level and incursion of saline waters the integration of paleoclimate data from cretaceous marine deposits and terrestrial sedimentary record will promote our understanding of the cretaceous greenhouse climate change and may provide insights for a future greenhouse world

a mesozoic time scale we present an integrated geomagnetic polarity and stratigraphic time scale for the triassic jurassic and cretaceous periods of the mesozoic era with age estimates and uncertainty limits for stage boundaries the time scale uses a suite of 324 radiomenc dates including high resolution 40 ar 39 ar age estimates this framework involves the observed ties between 1 radiometric dates biozones and stage boundaries and 2 between biozones and magnetic reversals on the seafloor and in sediments interpolation techniques include maximum likelihood estimation smoothing cubic spline fitting and magnetochronology

escarpment retreat in sedimentary tablelands and cuesta landscapes landforms mechanisms and patterns abstract although the general concept that escarpments in layered rocks retreat through time was offered more than 150 years ago recognizing the exact mechanisms patterns and rates of retreat remains a challenge in this paper we provide the state of the art of the theme of escarpment retreat reviewing both the classic contributions often forgotten but important case studies and the latest research in separate parts of the paper we discuss 1 terminology applied to the geomorphology of escarpments 2 the main assumptions and pathways of long term evolution of escarpments including conceptual models presented so far 3 processes involved in cliff retreat mainly weathering mass movements and erosion 4 the role of spring erosion and fluvial processes leading to fluvial dissection and development of canyons present in many tablelands 5 the possible role of climate change in escarpment evolution 6 rates of escarpment retreat in conclusions we summarize the major advances in our understanding of escarpment evolution of the last two three decades such as the recognition of the key role of emerging groundwater in non uniform escarpment retreat of an important role of silica dissolution and underground removal of dissolved solids increasing appreciation of rock properties in governing the patterns of escarpment retreat the proposal that cliffs do not necessarily retreat via catastrophic rock slope failures but may disintegrate in situ and the first attempts to date escarpment retreat using cosmogenic isotopes finally the remaining gaps and possible research priorities for the future are identified

daqing oil field people s republic of china a giant field with oil of nonmarine origin the daqing oil field in northeastern china presents an example of the geologic and geochemical conditions necessary for the formation of a giant field in a basin containing only continental nonmarine sediments the geochemical characteristics of the stages of generation expulsion migration and accumulation of oil and gas and their relations to trap development are especially pertinent the model presented shows close coordination of five bodies source bed carrier bed reservoir trap and cap rock and simultaneous evolution through five stages to form the giant oil field in a large eutrophic lake basin

the evolution of the north german basin and the metamorphism of the lower crust in an integrated analysis metamorphic processes in the accreted crust potential field anomalies temperature field and subsidence history are summarized into a model for the development of the north german basin the model integrates observed phenomena such as the high nitrogen content in natural gases in permian sandstone reservoirs and the structure of the crust with model calculations rock density increase subsequent volume reduction and loss of volatiles during metamorphism lead to a depression at the surface of the earth the load of the sediments which will be deposited in the depression enhances the subsidence and the ongoing metamorphism the model provides an alternative to the application of existing tectonic stretching models for the explanation of the subsidence of sedimentary basins

depositional environment thermal maturity and shale oil potential of the cretaceous qingshankou formation in the eastern changling sag songliao basin china an integrated organic and inorganic geochemistry approach abstract the changling sag in the petroliferous songliao basin has produced large amounts of conventional petroleum but studies on unconventional resources are rare a suite of core samples from the cy 1 well drilled in the eastern changling sag was analysed employing a series of micropetrographic geochemical and pyrolysis techniques to reveal the shale oil potential of the lower k2qn1 and middle k2qn2 qingshankou formation in this area for the first time from the lower k2qn1 upwards the sampled section the ratio of k al delineates an increasing palaeo temperature trend but still within a warm climate based on element ratios al2o3 toc and tio2 toc the highest terrestrial matter and nutrient supply on average occurred in the lower k2qn1 triggering bioproductivity toc ts and fe mn show that bottom water anoxia prevailed in the upper k2qn1 and lower k2qn2 providing excellent conditions for organic matter om preservation as compared to the lower k2qn1 high maturity of the studied layers is implied by e g vitrinite reflectance vrr of 1 03 1 09 tmax values over 445 c and molecular organic geochemical indices which correlate very well with vrr kinetic data on petroleum generation from open system pyrolysis were implemented in a numerical 1d basin and petroleum system model the k2qn1 has generated and expelled large amounts of petroleum 78 and 36 transformation of kerogen to petroleum based on kinetics of the low mature qingshankou shale om consisted originally of type i ii kerogen but has lost more than half of its original hydrocarbon generation potential upon maturation oil saturation index osi and s1 suggest that the studied layers show fair shale oil potential but are regarded as good conventional petroleum source rocks a newly proposed shale oil potential index sopi takes also thickness into account application to the qingshankou formation implies that the lower k2qn2 holds the highest shale oil potential

determination of gross kinetic parameters for petroleum formation from jurassic source rocks of different maturity levels by means of laboratory experiments abstract solvent extracted core samples of lower toarcian carbonate rich shales posidonia shale lias of the hils syncline area lower saxony basin northern germany covering a wide maturity range vitrinite reflectance rr 0 48 0 88 and 1 45 and a kimmeridge mudstone rr 0 45 are pyrolyzed at three different heating rates 0 1 0 7 and 5 0 k min by application of non isothermal first order reaction kinetics to the resulting hydrocarbon evolution curves activation energy distributions between 46 and 70 kcal mol and pre exponential arrhenius factors are obtained by an iteration method hypothetical hydrocarbon generation curves are calculated for the lias assuming three geological heating rates 0 5 5 and 50 k 106a peak hydrocarbon generation temperatures range from 135 to 165 c

geodynamic scenario and structural styles of mesozoic and cenozoic basins in china the continental lithosphere of china is situated at the junction of the marginal pacific and tethys himalayan tectonic domains the most manifest tectonic movements responsible for the deformation of the continental lithosphere of china are taphrogenic collisional and shearing these movements played an important role in the mesozoic and cenozoic tectonic evolution of china and formed various types of mesozoic and cenozoic basins in china the marginal pacific crust in eastern china was attenuated by rifting and developed north northeast trending mesozoic and cenozoic basins e g the songliao bohai bay and jianghan basins rifting mainly followed preexisting lineaments or shear zones in the basement then basin range graben horst structures and large fault bounded basins developed extensional structural styles have prevailed in mesozoic and cenozoic basins in eastern china with listric faults and tilted blocks in the basement and detached faults growth faults and rollover anticlines or drape folds in the cover rocks these structures are favorable for hydrocarbon accumulation thus the famous daqing and zhongyuan oil fields formed in songliao basin and bohai bay basin respectively in western china the continental crust thickened by collision and formed a series of mesozoic and cenozoic intermontane and foreland basins such as the junggar dzungaria tarim and qaidam basins contraction structural styles are predominant in mesozoic and cenozoic basins in western china with shortened fault blocks and ramps in basement and thrust faults and folds in the cover rocks the kelamayi and laojunmiao oil fields formed in these compressional basins in addition many great wrench faults played an important role in the evolution of china such as the tan lu fault in eastern china and the altunshan and talaso fergana faults in western china many mesozoic and cenozoic basins of china were characterized by transtension and transpression the mesozoic and cenozoic basins of china have undergone numerous tectonic events the extensional structures have been changed into contractional structures or conversely thus tectonic inversion occurred in successive events and different structural styles may be found in different tectonic levels of these basins these superposed deformations and structures have complicated petroleum exploration but they also enlarge prospective exploration targets and potential hydrocarbon reserves in china

further studies on the response of the equatorial thermocline in the atlantic ocean to the seasonally varying trade winds upper ocean temperature data obtained during the seasonal response of the equatorial atlantic experiment and the francais ocean et climat dans l atlantique equatorial program are used to describe the variations of the thermocline observed along the equator from february 1983 to september 1984 in response to rapid seasonal changes in zonal wind stress the thermocline underwent sequences of upwelling followed by downwelling or conversely depending upon whether the winds were intensifying or relaxing these sequences increased systematically in magnitude and duration to the east both the sequential behavior and its zonal inhomogeneity represent departures from the slowly varying and in phase climatological description of the annual thermocline response an analytical reduced gravity equatorial long wave model forced by zonal wind stress distributions representative of the variations observed along the equator was employed to reconcile the differences between the 1983 1984 synoptic measurements and the climatologically averaged description qualitative agreements between the model results and the data were found for many salient features of the annual cycle including the zonal pressure gradient calculated by finite difference the features in the model arise as interference patterns between directly forced and reflected kelvin and long rossby waves that are generated with each change in the wind stress the manner in which the wind stress changes from year to year is therefore crucial to the equatorial ocean s response

characterization of bi planar and ploughing failure mechanisms in footwall slopes using numerical modelling abstract footwall slopes refer to unbenched rock slopes in which the slope face is parallel to a set of persistent discontinuities e g bedding planes foliation faults these are commonly encountered in weak thinly bedded orthogonally jointed sedimentary rock sequences common failure mechanisms include bi planar failures where shallow dipping crosscutting structures daylight near the slope toe enabling sliding to occur along steep dipping bedding planes in the absence of crosscutting structures failure occurs through deformation and rock mass yielding involving the formation of inter block shear and toe breakout surfaces because of the complexity of the toe breakout mechanism evaluation methods are not well understood an improved understanding of the failure mechanism the role of adverse discontinuities and characterization of the discontinuity intact rock and rock mass strength properties are key for a successful footwall stability analysis this paper investigates the development of the inter block shear and toe breakout surfaces with three approaches i continuum based frictional plasticity theory ii discontinuum based distinct element modelling with voronoi tessellation using the commercial software udec and iii hybrid continuum discontinuum finite discrete element brittle fracture modelling using the commercial software elfen numerical simulations using elfen and udec demonstrated a good agreement with frictional plasticity theory ploughing failure of footwall slopes is also evaluated specifically the influence of cross cutting discontinuity dip angle relative to the slope face the effects of different geometrical parameters e g slope angle and depth height ratio on bi planar and ploughing failure are assessed using a sensitivity analysis approach a damage intensity parameter is introduced and used to quantify damage in the numerical simulations using elfen

marine incursion events in the late cretaceous songliao basin constraints from sulfur geochemistry records abstract songliao basin in ne china developed the most productive oilfield in the world sourced from terrestrial rocks the main source rock of the basin includes member 1 of the qingshankou k2qn1 and members 1 and 2 of the nenjiang formation k2nj1 2 however the exact reasons for the formation of the source rock especially the k2qn1 are still controversial former paleontological and organic geochemical research suggested that organic matter was deposited during marine incursion events of k2qn1 but further geochemical evidence is needed this paper explores the distinct sulfate levels that distinguish marine from fresh waters of the songliao paleo lake we undertook a systematic investigation the sulfur geochemistry of the sediments from top of member 4 of the quantou formation k1q4 to top of member 1 of the qingshankou k2qn1 the ratio of organic carbon to the pyrite sulfur toc pys proved the previously suggested saline conditions during the deposition of k2qn1 and the pyrite sulfur isotope indicated that marine incursion may not only have occurred for k2qn1 but also for top of k1q4 the exact time for the beginning of marine incursion is to be determined the marine incursion within k2qn1 is not strong and partially controlled by the fluctuation of paleo lake level the present study will be helpful for understanding the contribution of marine incursion events to the burial of organic carbon in the songliao paleo lake although further studies are still needed

assessments on the stability of natural slopes prone to toe erosion and man made historical semi underground openings carved in soft tuffs at zelve open air museum cappadocia turkey abstract the zelve open air museum consisting of three valleys is one of the oldest historical semi underground settlements in the cappadocia region of turkey which was designated as a world heritage site in 1985 by unesco particularly in the first valley there are a lot of underground openings of different sizes carved in a soft tuff next to the valley cliffs used for cliff settlement in the past and several antique churches with some geo engineering problems in addition steep natural slopes in this valley are prone to toe erosion resulting in stability problems in this study it is aimed to investigate engineering characteristics of the surrounding tuff and factors affecting them and to assess the effect of rate of toe erosion on the stability of steep valley slopes and structural stability of some selected typical underground openings with large spans subjected to spalling for these purposes some observational experimental and numerical modelling studies were conducted experimental results indicate that strength and deformability properties of the weak tuff surrounding the openings drastically reduce when it becomes wet or saturated this situation suggests that possibility of occurrence of failures is expected to be higher in rainy seasons due to increase in water content of the tuff experimental results also suggest that spalling commonly observed in the valley is related with freezing thawing and wetting drying cycles in nature and that the process of freezing and thawing accelerates further the degradation of the rock the long term measurements at selected locations suggest that erosion in the tuff is important which increases particularly in winter and spring seasons and results in the loss of support accelerating the occurrence of further slope failures the 2 d numerical solutions indicate that no significant change in shear and tensile stresses in steep valley slopes prone to toe erosion would be expected after 100 years however the solutions obtained from the 500 and 1000 year scenarios suggest that failure zones due to the tensile stresses would develop in the form of slabs with thicknesses of 50 60 cm and 90 100 cm respectively which would break off from the slope and fall down the results from 3 d numerical solutions indicate that failure yield zone resulting from tensile stresses around the semi underground openings will develop parallel to the sidewalls these results confirm the observed spalling of the tuff in the form of slabs parallel to the walls of the openings

the art of maturity modeling part 2 alternative models and sensitivity analysis the sensitivity of exploration decisions to variations in several input parameters for maturity modeling was examined for the miti rumoi well hokkaido japan decisions were almost completely insensitive to uncertainties about formation age and erosional removal across some unconformities but were more sensitive to changes in removal during unconformities which occurred near maximum paleotemperatures exploration decisions were not very sensitive to the choice of a particular kinetic model for hydrocarbon generation uncertainties in kerogen type and the kinetics of different kerogen types are more serious than differences among the various kinetic models results of modeling using the tti method were unsatisfactory thermal history and timing and amount of hydrocarbon generation estimated or calculated using the tti method were greatly different from those obtained using a purely kinetic model we strongly recommend use of the kinetic r o method instead of the tti method if we had lacked measured r o data subsurface temperature data or both our confidence in the modeling results would have been sharply reduced conceptual models for predicting heat flow and thermal conductivity are simply too weak at present to allow us to carry out highly meaningful modeling unless our input is constrained by measured data maturity modeling therefore requires the use of more not fewer measured temperature and maturity data the use of sensitivity analysis in maturity modeling is very important for understanding the geologic system for knowing what level of confidence to place on the results and for determining what new types of data would be most necessary to improve our confidence sensitivity analysis can be carried out easily using a rapid interactive maturity modeling program

factors affecting the durability of selected weak and clay bearing rocks from turkey with particular emphasis on the influence of the number of drying and wetting cycles weathering can induce a rapid change of rock material from initial rock like properties to soil like properties the resistance of a rock to short term weathering is described through a durability parameter called the slake durability index as durability is an important engineering parameter particularly for weak and clay bearing rocks it was assessed by a number of tests the main purpose of this study is to assess the influence of the number of drying and wetting cycles and controls of mineralogical composition and strength on durability for this purpose 141 samples of different types of weak and clay bearing rocks were selected from different parts of turkey and relationships between the above mentioned rock characteristics were statistically investigated the samples were subjected to multiple cycle slake durability testing x ray diffraction xrd analysis and uniaxial compression testing in addition to assess the influence of mineralogical composition on durability the mineral contents of the original material and the material passing from the drum of the slake durability apparatus after each cycle were also determined by xrd the results indicate that the type and amount of clay minerals are the main factors influencing the variations of the slake durability index in all samples the durability of the clay bearing rocks studied correlates best with the amount of expandable clay minerals a strong relationship between the uniaxial compressive strength and the fourth cycle slake durability index is found only for the marls among the rock types studied assessment of gradation results of the spoil pile materials consisting of clay bearing rocks also reveals that the increase in percentage of fines in old piles is indicative of material degradation as is evident by multiple cycle slaking it is emphasized that two cycle conventional slake durability testing did not appear to offer an acceptable indication of the durability of weak and clay bearing rocks when compared with multiple cyclic wetting and drying comments on the performance of the test are made that aim to make the testing process and interpretation of the results more reliable

chemical mineralogical and textural properties of the kope formation mudstones how they affect its durability abstract the kope formation is a rock unit that extends over southwest ohio and adjacent areas of kentucky and indiana usa it is characterized by meter scale cycles of mudstones and limestones where thick mudstone is sandwiched between thin limestone layers kope formation mudstones are less durable than the mudstones in the area they cause abundant slope failures in areas of their outcrops this study evaluates chemical mineralogical and textural properties of kope mudstones to determine why it is less durable the two cycle slake durability index id 2 was measured on thirty mudstones belonging to three consecutive cycles of the kope formation chemical composition and mineralogy of kope mudstones do not show significant relationship with the id 2 instead a relationship to fabric was found kope mudstones with two main fabric types were observed in the field laminated mudstones and non laminated mudstones detailed micro fabric analysis on kope mudstones was done using the scanning electron microscope laminated mudstones with turbostratic fabric showed higher id 2 and lower moisture content than the non laminated mudstones with matrix fabric the difference in the id 2 of laminated mudstones and non laminated mudstones is statistically significant both mudstone types exist in many cycles of the kope formation thus core samples should be selected from both types for preliminary tests in geotechnical practice to obtain more accurate estimations of the geotechnical properties of the kope mudstones the results and data interpretations of this study can be correlated with the mudstones and shale in different areas of the world specifically a great attention should be paid to the macro and micro textural properties of any rock type regardless of their classification

seasonal response of the sea surface to the wind in the equatorial atlantic from february 1983 through september 1984 18 inverted echo sounder deployments yielded time series from 10 locations as part of the seasonal response of the equatorial atlantic sequal program using historical and in situ data the sounders travel time data are interpreted as dynamic height 0 relative to 500 dbar and then related to representations of the synoptic wind field the seasonal variations of the zonal pressure gradient along the equator and the height of the dynamic ridge along 3 n relative to the equator and 9 n are described the pressure gradient between 10 w and 34 w has a minimum each april and a maximum each july its value ranges between 1 4 not significantly different from zero and 8 3 10 5 dyn g 1 during the observational period the zonal pressure gradient is correlated with zonal wind stress from an in situ wind sensor at midfetch and a 10 day lag time is indicated the north equatorial countercurrent trough attains a maximum in the late boreal summer and fall and a minimum in the spring it ranges from 39 to 8 dyn cm deep at 38 5 w and from 18 to 1 dyn cm at 28 w a two layer model calculation using monthly mean winds derived by servain et al 1986 for the appropriate time period generally reproduces the observed seasonal variation along the two meridians and the large zonal variation between them tracking the individual terms month by month illustrates the rate of the sverdrup adjustment to the local wind stress with surface elevation rising as fast as 10 cm per month

a new evaluation of palaeo heat flows and eroded thicknesses for the carboniferous ruhr basin western germany palaeo heat flows and thicknesses of eroded carboniferous overburden in the coal bearing ruhr basin western germany were estimated using one dimensional basin modelling techniques thermal and burial histories for 11 localities were calibrated by comparing measured and calculated vitrinite reflectance data based on the assumption of pre tectonic maturation in contrast to former studies the kinetic easy r0 approach applied for the calculation of vitrinite reflectance lopatin s tti algorithm was used in addition for one well in order to demonstrate the impact of the selection of the algorithm for vitrinite reflectance calculation on the simulation results simulated palaeo heat flows for the time of maximum burial most probably in the stephanian range from 64 to 83 mw m2 and decrease towards the south these heat flows are lower than values computed during earlier studies but are still relatively high in comparison to recent foreland basins the regional distribution of palaeo heat flows indicates that the crust beneath the ruhr basin was relatively thin and thickened towards the south at the end of the carboniferous after the stephanian 2200 3500 m of carboniferous overburden were eroded an observed southward increase in eroded thicknesses is caused by an uplift of the area studied which decreased towards the north at the end of the variscan folding large thicknesses of deposited and later eroded carboniferous sediments have to be postulated to explain the maturity data even along the present southern margin of the ruhr basin this indicates that the late carboniferous sediments originally extended far to the south geological arguments suggest that the deposition of carboniferous sediments in the entire ruhr basin continued until the stephanian

hydrocarbon sources and charge history in the southern slope region kuqa foreland basin northwestern china abstract numerous oil and condensate gas reservoirs have recently been discovered in the southern slope region of the kuqa foreland basin in the northern tarim basin northwestern china however their hydrocarbon sources and charge history are still unclear in this study oil source correlation was firstly used to ascertain the sources of oils in different tectonic belts the hydrocarbon charge history was then investigated using an integrated fluid inclusion analysis and basin modelling approach on the basis of a variety of oil source correlation geochemical parameters two distinct oil groups were delineated in this region group i including oils in the yaha and yingmai 7 tectonic belts while group ii comprising oils from the yangtake hongqi and yudong 2 tectonic belts and the ym 21 well oil source correlations show that group i oil is sourced from the upper triassic huangshanjie formation t 3 h while group ii oil is mainly sourced from the lower part of the middle jurassic qiakemake formation j 2 q both source rocks are located in the middle and northern parts of the kuqa foreland basin basin modelling shows that the t 3 h source rock began to generate early mature to mature oil at 34 ma and continued until around 3 ma the j 2 q source rock began to generate early mature to mature oil between after 34 ma and continued to 12 ma mainly in the central part of the j 2 q source rock oil migration modelling indicates that the t 3 h sourced oils did not accumulate in the southern slope region until 12 5 ma whereas the j 2 q sourced oils began to charge into the southern slope region around 5 3 ma coupled with fluid inclusion analysis the modelling shows that oils originated from the t 3 h source rock began to charge into the yaha tectonic belt as early as 6 ma and subsequently to the yingmai 7 tectonic belt which received its initial charge around 4 8 ma oils sourced from the lower j 2 q source rock began to charge into the yangtake tectonic belt around 4 ma and then into the yudong 2 tectonic belt around 3 7 ma oils first charged into the hongqi and ym 21 areas after 4 ma oils from the t 3 h and the lower j 2 q source rocks continued to charge into the southern slope region until 3 ma

annual change of sea surface slope along the equator of the atlantic ocean in 1983 and 1984 for two years beginning in october 1982 oceanographic observations were made in the equatorial atlantic to investigate the relationship between sea level wind stress sea surface slope zonal pressure gradient thermocline depth and equatorial currents here we describe the sea surface slope derived from three complementary methods hydrographic stations pressure gauges and inverted echo sounders the latter two have the advantage of yielding continuous time series but depend on the hydrographic stations for an absolute reference together the three provide a detailed description of the temporal variation of the sea surface slope which is then compared to a wind stress time series the dominant signal in both sea slope and wind stress is the annual cycle although amplitude and phase vary interannually the annual increase in sea surface slope along the equator in the western and central basins lags the onset of the south east trade wind during the boreal winter of 1983 84 a strong rise in sea level occurred against the african coast accompanied by a levelling of the sea surface to the west at the same time an almost complete relaxation of eastward wind stress on the equator was observed near the centre of the basin

the behaviour of clay shales in water a set of clay shales associated with coal measure strata has been examined to determine the mechanisms that lead to slaking on immersion in water the two main mechanisms for the slaking of small unconfined samples are a compression of entrapped air and b osmotic swelling of expansive clay minerals if the dominant exchangeable cation is sodium in the absence of osmotic swelling pore air compression can induce slaking in clay shales of bulk densities less than 2 27 mg m3 osmotic swelling of clay shales occurs in samples with bulk densities less than about 2 45 mg m3 but slaking by this mechanism occurs only for samples with densities less than 2 34 mg m3 dispersion of clay from clay shales develops only after slaking commences and the extent of dispersion depends on the nature of the interparticle bonds key words clay shales clays coal measure rocks slaking dispersion porosity density

structural constraints on deep seated slope deformation kinematics abstract a significant sackung type deep seated slope gravitational deformation dsgsd was recognised for the first time by the authors in the middle part of valfurva east of bormio rhaetian alps italy the reconstruction of its kinematics age and state of activity is presented through a detailed description of its morphological geomechanical and structural features an integrated multi disciplinary approach was performed to achieve a clear comprehension of the phenomenon field surveys and aero photo interpretation were carried out in order to clarify the structural geological and geomorphological setting in which the dsgsd developed a kinematic conceptual model of the slope deformation was developed through the analysis of morpho structures of their significance and relationships with lithological markers and quaternary deposits after a geomechanical characterisation of the rock mass involved in the slope deformation numerical modelling was performed to verify the hypotheses made on kinematics and driving factors of the phenomenon the sackung affects pre permian metapelites metabasites and marbles belonging to the upper austroalpine basement of the campo nappe as well as late pleistocene and holocene glacial and rock glacier deposits the deformation started after the late wurmian age 15 000 11 000 years b p and continued until few centuries ago not excluding a present day low rate activity deformation consists in a large oblique sagging along a deep confined sliding surface associated with gravitational reactivation of pre existing late alpine and recent tectonic brittle structures leading to the formation of n s and wnw ese trending gravitational morpho structures the evolution of the wnw ese trending system resulting in asymmetric trenches led to progressive failure of the lower part of the slope during the last 10 000 years as testified by large paleo landslide accumulations and it is still in progress numerical modelling indicates post glacial unloading as the main triggering factor of the slope deformation the importance of this deep seated slope deformation is enhanced by the occurrence of the 30 mm 3 active ruinon landslide in the lower part of the slope such landslide is subjected to rapid evolution and threatens the valley floor establishing an important risk factor connected to human lives and socio economic activities

formation and evolution of nonmarine petroleum in songliao basin china in large lake basins source rocks containing sapropelic kerogen have a high transformation ratio and a high potential for petroleum and they offer the material basis for the formation of a large nonmarine oil field on the basis of geologic and geochemical data and the results of thermal simulation of kerogen it is confirmed that the maturation sequence of kerogen is type i type ii and type iii

residual strength of kaolin and bentonite the influence of their constituent pore fluid the residual strength of clays is affected by their mineral composition and by the nature of their constituent pore fluid in principle both factors may influence either strength parameters or stresses but it is not yet completely clear how this influence works previous publications have elucidated some aspects of clay residual strength behaviour this paper investigates further the roles of minerals and pore fluid composition on the residual strength of clayey soils it describes and analyses tests on kaolin bentonite and their mixtures exposed to distilled water and sodium choride solutions with given concentrations the results show that the shear strength of kaolin is not affected by the solutions used whereas the residual strength of bentonite varies greatly because of the inward salt diffusion towards the clay further for the clay mixtures with any of the pore fluids considered the weaker component has the greater influence on the behaviour of the mixture la resistance residuelle des argile

heat flow variations in continental rifts abstract in the terrestrial thermal field continental rifts stand out as rather narrow regional thermal anomalies in which augmented heat flow is unevenly distributed heat flow variations are discussed on the example of the baikal east african cordilleran and rhine lybian rift systems rift related disturbance of the asthenosphere lithosphere system is accompanied by a general increase in the surficial heat flow regional thermal anomalies are mainly caused by conductive heat transfer from the asthenosphere local thermal anomalies are caused by magmatic mass transfer into the crust and by fluid convection along porous fracture systems

geochemistry of natural gases in deep strata of the songliao basin ne china chemical composition and stable carbon isotopic studies were undertaken for 27 gas samples from deep strata of the xujiaweizi depression in the songliao basin to investigate their origin gas molecular and carbon isotopic compositions show great variety methane is the main component for all studied samples and its content ranges from 57 4 to 98 2 with an average of 90 1 gas wetness ranges from 0 8 to 16 7 with an average of 2 7 the main non hydrocarbon gases are carbon dioxide and nitrogen with an average of 4 0 and 3 2 respectively carbon isotope data suggest that these deep strata gases are mainly coal type gases mixed with minor amounts of associated oil type gases coal type gases are characterized by heavier carbon isotopic values and drier chemical compositions these gases were generated from the lower cretaceous shahezi formation coals interbedded shales with type iii kerogen during the postmature stage of hydrocarbon generation oil type gases are characterized by lighter carbon isotope and higher wetness which were generated from the lower cretaceous shales with type ii kerogen in the shallow strata during the early mature stage of hydrocarbon generation mixing of two different gases causes unusual carbon isotopic distribution patterns with lighter isotopic values in higher numbered carbons in most gases the discovery of coal type gases in the songliao basin provides new prospects for the exploration in this region

on the accuracy of modelling hydrocarbon generation and migration the egersund basin oil find norway abstract quantitative estimates of kerogen transformation and hydrocarbon charge to the structure of block 9 2 norwegian north sea were obtained by integrated basin modelling a probability distribution was assigned to each input parameter and the sensitivity to these parameters was investigated by subsequently varying each parameter within the assigned ranges the inaccuracy in the modelling results were mainly due to imprecise knowledge of hydrocarbon generation kinetics depth conversion and present day virgin rock temperature kerogen transformation modelling and source rock richness thickness areal extent volumetric charge calculations monte carlo latin hypercube sampling based on the probability distribution of each parameter was performed giving a 40 probability for a dry structure a mean value of 10 7 106sm3 recoverable oil and a considerable high side potential 4 probability for more than 50 106sm3

trade wind fetch related variations in equatorial undercurrent depth speed and transport a dynamical model is developed to examine the dependence of equatorial undercurrent depth speed and volume transport on trade wind fetch the model ocean is linear continuously stratified vertically diffusive and formulated on the equatorial beta plane analytical solutions are derived in closed form for realistic choices of model parameters results indicate that the undercurrent would be significantly shallower and weaker in the atlantic than in the pacific because of the shorter atlantic trade wind fetch

infinite slope stability under steady unsaturated seepage conditions 1 we present a generalized framework for the stability of infinite slopes under steady unsaturated seepage conditions the analytical framework allows the water table to be located at any depth below the ground surface and variation of soil suction and moisture content above the water table under steady infiltration conditions the framework also explicitly considers the effect of weathering and porosity increase near the ground surface on changes in the friction angle of the soil the factor of safety is conceptualized as a function of the depth within the vadose zone and can be reduced to the classical analytical solution for subaerial infinite slopes in the saturated zone slope stability analyses with hypothetical sandy and silty soils are conducted to illustrate the effectiveness of the framework these analyses indicate that for hillslopes of both sandy and silty soils failure can occur above the water table under steady infiltration conditions which is consistent with some field observations that cannot be predicted by the classical infinite slope theory a case study of shallow slope failures of sandy colluvium on steep coastal hillslopes near seattle washington is presented to examine the predictive utility of the proposed framework

formation of the steer s head geometry of sedimentary basins by differential stretching of the crust and mantle if the lithospheric mantle is stretched over a wider region than the crust postrift stratigraphic onlap will occur at basin margins giving rise to a steer s head geometry space problems are avoided by making the total amount of extension in the lithospheric mantle equal to that in the crust the predicted pattern of onlap agrees well with that observed if the lithospheric mantle is stretched over a fractionally wider region than is the crust thus extensive stratigraphic onlap can be produced easily without recourse to sea level rise or flexural rigidity

shale microfacies eagle ford group cenomanian turonian north central texas outcrops and subsurface equivalents abstract the eagle ford group is a mixed siliciclastic carbonate unit that records a late cretaceous cenomanian to turonian transgression a major condensed interval cycle 2 5 of the uza 2 supercycle occurs within the eagle ford shale eagle ford strata are overlain disconformably by the austin chalk the austin eagle ford contact represents the turonian coniacian boundary 89 ma the cenomanian turonian 92 ma boundary occurs within the eagle ford group regionally eagle ford strata consist of two major depositional units a lower transgressive unit dominated by dark well laminated shales exhibiting only minor evidence of bioturbation and an upper regressive unit consisting of thinly interstratified high frequency cycles shales limestones and carbonaceous quartzose siltstones petrographic characterization of shales from eagle ford outcrops near austin waco and dallas texas and subsurface equivalents in a core getty 1 j t wilson from lasalle county texas reveals six microfacies 1 pyritic shales 2 phosphatic shales 3 bentonitic shales 4 fossiliferous shales 5 silty quartzose shales and 6 bituminous claystone and shales transgressive eagle ford shales consist mainly of microfacies 1 4 and 6 the eagle ford condensed interval consists of microfacies 1 2 and 3 and highstand eagle ford shales are comprised of microfacies 4 and 5 eagle ford microfacies exhibit distinctive sedimentological aspects and have source rock characteristics that vary systematically within a sequence stratigraphic framework transgressive eagle ford shales occurring below the condensed interval have optimum oil prone source potential whereas overlying regressive shales are gas prone transgressive and condensed eagle ford strata represent poorly oxygenated low energy below storm wave base marine paleoenvironments of deposition in contrast overlying regressive eagle ford lithofacies accumulated in higher energy above storm wave base well oxygenated shallow marine paleoenvironments

heat flow and thermal maturity modelling in the northern carnarvon basin north west shelf australia abstract the northern carnarvon basin is located at the southern end of the north west shelf of australia it was developed by rifting during the jurassic earliest cretaceous heat flow and thermal maturity in seven wells from three sub basins rankin platform and exmouth plateau of the northern carnarvon basin were modelled using basinmod 1d program multiple thermal maturity parameters were used to constrain the influence of anomalously low vitrinite reflectance those t max data with reliable quality can be applied to correlate with vitrinite reflectance establish thermal maturity and calibrate the modelled results the modelled results indicated that the measured maturity data in some wells were consistent with the rift heat flow model jarvis mckenzie associated with the jurassic rift and the earliest cretaceous seafloor spreading events the maximum values of heat flow were in the range from 67 mw m 2 jurabi 1 to 105 mw m 2 bowers 1 in the exmouth and barrow sub basins on the exmouth plateau the maximum values of heat flow were modelled to be 72 mw m 2 in the jupiter 1 well and 78 mw m 2 in the investigator 1 well these maximum values were modelled to occur during syn rift phase which were 29 88 and 33 37 greater than their current heat flow values in the sub basins and on the exmouth plateau respectively this study suggests that maturity indicators are less diagnostic of rifting thermal histories if the maximum thermal effect is associated with cretaceous and cainozoic burial in this basin

development of a new durability index for compacted shale abstract many highway embankments in the east central united states and around the world have been constructed using compacted shale when weathered shale tends to degrade into a fine grained mass of soil with high compressibility and low shear strength unfortunately there are no reliable methods to predict the long term behavior of compacted shale subjected to deterioration resulting from the weathering process this study presents the results of analyses for index and geotechnical laboratory tests on both weathered and unweathered shale samples durability tests on unweathered samples and compaction and triaxial shear tests on compacted weathered shale samples the result of this effort is the development of a new durability index that better characterizes the durability behavior of shales than the standard slake durability index this new index is simple to perform and is well correlated with index and geotechnical properties of unweathered and weathered shale a secondary result of this study is the development of a simple and reliable means to evaluate the shear strength of compacted shale behavior and swelling of core samples as a function of durability

lacustrine chalky carbonates origin physical properties and diagenesis palaeogene of the madrid basin spain the palaeogene lacustrine chalky carbonates of the madrid basin are a peculiar type of very soft and friable carbonate facies with high porosity despite being covered by more than 800 m of sediment similar physical properties to those described in marine chalk reservoirs emphasize the interest in analysing and characterizing these carbonate facies within a lacustrine depositional system lithologically they are calcitic and or dolomitic poorly cemented carbonate muds with no significant amounts of skeletal debris clay minerals such as illite smectite and palygorskite are present between the carbonate crystals palygorskite is the most common covering the carbonate crystals and forming sheets between them these lacustrine chalky carbonates were formed in the basinal areas of the lake as the result of inorganic carbonate precipitation and or detrital sedimentation related to episodic reactivation of the adjacent fan systems their petrological geochemical and physical properties indicate that few textural and compositional modifications occurred during diagenesis their main physical properties are a very low dry bulk and grain density 1 6 2 2 and 2 62 g cm3 respectively and medium to high porosity 10 40 due to micropores 2 am 30 the convergence of lacustrine sedimentation dynamics rapid sedimentation the original mineralogy of these calcareous lacustrine muds relatively stable low magnesian calcite and dolomite the early formation of the palygorskite cement of these muds and the retention of mg enriched fluids in the pore system were decisive in the partial inhibition of calcite cementation compaction and recrystallization the chalky carbonates are also intercalated between impermeable littoral carbonate facies that impeded fluid flow through their pore systems

back analysis of the joss bay chalk cliff failure using numerical modelling use of numerical modelling for back analysis of slope failure can provide a valuable insight into the underlying failure mechanisms and improve our understanding of factors controlling instability and geomorphology of slopes this paper provides a brief overview of the range of methods that are available for slope instability analyses and their respective benefits using the back analysis of the joss bay chalk cliff failure as a case example a variety of analytical and numerical approaches are used to back analyse the failure to assess the potential impact of both the rock mass strength and discontinuity controlled behaviour on the potential failure mechanism limit equilibrium analysis approaches are used to assess the sensitivity of the simulated model to variation in input parameters numerical simulation constrained by the limit equilibrium models is then used to evaluate the progressive nature of failure mechanism and directly simulate the trigger mechanism importantly the modelling demonstrates that shear strain initiates at the base of the cliff and subsequently extends upwards resulting in tensile failure in the upper part of the slope the case example demonstrates the capability of numerical models to simulate the progressive nature of slope failure and their ability to evaluate the detrimental effects of a wave cut notch at the base of a cliff

petroleum generation and accumulation in the golfo san jorge basin argentina a basin modeling study abstract the golfo san jorge basin located in patagonia is very important for the oil and gas production of argentina in spite of the long history of exploration and production few geochemical studies were performed until now for this study a set of possible source rocks was analyzed by organic geochemical and petrographical methods the samples of the pozo d 129 fm range from mature to overmature and contain from less than 0 5 to 2 45 toc there is some evidence indicating an algal origin of the more hydrogen rich kerogen present in part of the basin almost all the samples of pozo anticlinal aguada bandera and pozo cerro guadal fm are overmature toc values range from less than 0 5 to 2 5 the maturation of source rocks and generation expulsion and migration of hydrocarbons was evaluated by means of 1d and 2d basin models the 1d models constructed for the western part of the basin and 2d models applied for the eastern part both indicate maximum burial in miocene times the thickness of the tertiary at times of maximum burial ranged from 1000 to 1500 m and the generally small tertiary thickness now present in the fold belt region is assumed to be the result of erosion the main tectonic inversion took place in the late neogene the models strongly suggest that a magmatic event between 20 and 30 ma combined with the maximum burial at miocene times produced a very important pulse in hydrocarbon generation within the major part of the basin dated intrusive and extrusive magmatic rocks extended all over the basin account for this period of elevated heat flow migration pathways are extensively discussed for the 2d model probably major faults acted as important conduits for petroleum

numerical simulation of the thermal maturation oil generation and migration in the songliao basin northeastern china abstract the discovery of the giant daqing oil field in the songliao basin led to the realisation of the significant petroleum potential of non marine basins in order to reconstruct the basin evolution and oil formation an integrated organic geochemical basin modelling study along a regional transect across the songliao basin was conducted it provided a regional heat flow evolution model and revealed post orogenic or late syn orogenic maturation in the central depression and pre orogenic maturation in the southeast uplift zone kinetic parameters of petroleum generation for the lacustrine source formations are the basis for the simulation of oil generation and migration in the songliao basin using the principle activation energy peaking at 54 kcal mol and a pre exponential factor of about 4 2 1027 ma 1 the simulation obtained a relatively good match with the measured transformation ratios the qingshankou formation in the west and east central depressions constituted the major source in the basin major oil generation migration and accumulation occurred during the early tertiary in the west central depression the generated oils migrated upwards into the yaojia formation followed by the updip migration into the daqing anticline and towards the local structural high along the west slope in contrast the oil migration in the east central depression was dominated by the downward movement from the lower member of the qingshankou formation followed by the updip migration towards the caoyang anticline the simulated oil accumulations are in good agreement with discovered oil fields implying a potential application of the model for prediction and evaluation of new exploration targets in the basin

identification of indigenous vitrinites for improved thermal maturity evaluation abstract the four methods that we use to improve the analysis of vitrinite reflectance of well cuttings samples are discussed the criteria for properly identifying the indigenous vitrinites a five fold classification of dispersed vitrinites in sediments first cycle second cycle low gray high gray and gray vitrinites a recording of the reflectance value vitrinite type data for each vitrinite particle analyzed a computer assisted microscope system that generates reflectance histograms of the identified vitrinite type data for easy interpretation using this approach we have minimized inaccuracies caused by the presence of mud additives cavings reworked vitrinites and solid bitumen

some consequences of compressional tectonics for extensional models of basin subsidence changes in intraplate stress levels have important consequences for the stratigraphy of rifted basins and provide a tectonic explanation for the generation of sequence boundaries late stage compressional phases during the post rift evolution of basins produce unconformities with offlap phases that increase in magnitude with the age of the rifted basin late stage compression has not only a strong bearing on the generation of unconformities but also induces significant downbending of the centre of a basin ignorance of the vertical motions of the lithosphere induced by late stage compression during post rift evolution can therefore give rise to substantial errors in the estimates of crustal extension derived from analysis of basement subsidence using stretching models consequently late stage compression can be of great significance in estimates of depth and timing of the hydrocarbon window inferred from extensional models of basin subsidence quantification of the subsidence induced by post rift compression has important implications for integrated models of basin subsidence and hydrocarbon generation

lithofacies and depositional setting of a highly prospective lacustrine shale oil succession from the upper cretaceous qingshankou formation in the gulong sag northern songliao basin northeast china the lacustrine shale of the upper cretaceous qingshankou formation is the principal prospective unconventional target lithology acting as source reservoir and seal lithofacies and associated storage capacity are two significant factors in shale oil prospectivity this paper describes an investigation of the lower qingshankou formation lacustrine shale based on detailed description and analysis of cores shale lithofacies characteristics depositional setting and stacking patterns seven lithofacies are recognized based on organic matter content sedimentary structure and mineralogy all exhibiting rapid vertical and lateral changes controlled by the depositional setting and basin evolution an overall trend from shallow water to deep water depositional environments is interpreted from the characteristics of the infilling sequences characterized by increasing total organic carbon toc and total clay content and decreasing layer thickness i e from bedded to laminated then to massive sedimentary structures periods of deposition during shallowing cycles show a reverse trend in the sedimentary characteristics described above the sedimentary rocks in the studied interval show three complete short term cycles each one containing progressive and regressive system tracts massive siliceous mudstones with both high and moderate toc are considered to have the best hydrocarbon generation potential laminated siliceous mudstones bedded siltstones and calcareous mudstones with moderate and low toc could have the same high hydrocarbon saturations as the high toc massive siliceous mudstones but these lithologies contain more brittle minerals than the massive mudstones several siltstone samples show low or zero saturation of in situ hydrocarbons this is considered to be related to a combination of fair to poor hydrocarbon generation potential and extremely low permeability limiting migration moderate toc laminated siliceous mudstones were also observed to have connective pore fracture networks it can be demonstrated that successive thick sequences of moderate toc laminated siliceous mudstones showing high volumes of hydrocarbon in situ a high mineral brittleness index and good permeability combine to form shale oil exploration sweet spots

cretaceous paleogeography and paleoclimate and the setting of ski borehole sites in songliao basin northeast china article i nfo as a paradigm of greenhouse climate in earth s history the cretaceous provides significant rock records of global climate changes under conditions of greenhouse climate the songliao basin among the longest dura tion 85 90 m y of continental sedimentary basins provides an excellent opportunity to recover a nearly complete cretaceous terrestrial sedimentary record extensive lake deposits ten kilometers deep and cover ing an area of 260 000 km 2 of the songliao basin provide unique detailed records that can be tied to the glob al stratigraphic time scale thereby improving our understanding of the continental paleoclimate and ecological system the two coreholes at skis and skin sites were drilled into this basin and completed with a total length of 2485 89 m of recovered core that spanned the complete middle to upper cretaceous strata in the basin the unique geological setting of long term continuous subsidence within the largest cretaceous landmass in the world makes the cretaceous songliao basin of northeastern china an ideal place to study cretaceous climate change on the continent this paper reviews the literature on the paleogeography and paleoclimate of the northern east asia and the songliao basin during the cretaceous based on the climatolog ically sensitive deposits oxygen isotope studies and paleontology the climate during the cretaceous in the songliao basin was temperate and humid with relatively abundant rainfall during the period significant changes four cooling three warming and three semiarid events are generally consistent with the oxygen isotope data from east asia and the four cooling events in berriasian valanginian aptian albian early santonian and campanian maastrichtian may be related to potential glaciations in cretaceous

late cretaceous cenozoic thermochronology in the southern songliao basin ne china new insights from apatite and zircon fission track analysis abstract the late cretaceous cenozoic thermochronology in the southern songliao basin was determined using apatite and zircon fission track analysis data it is crucial to deciphering the evolution of the songliao basin and changes in the movement direction of the pacific plate we present eight new apatite and eight corresponding zircon fission track data from borehole samples across the baixingtu uplift the apatite fission track aft thermochronological modeling reveals that the basin underwent two distinct compression and extension related uplift stages of rapid cooling during the late cretaceous cenozoic stage i during the late cretaceous early paleogene 70 52 ma stage ii in the late paleogene early neogene 38 10 ma the aft data vary from 76 0 5 0 to 25 3 1 9 ma and the zircon binomial peak fitting ages ranged from 79 to 61 ma all younger than the stratigraphic ages 92 88 ma of their host rocks one sample had similar fission track ages apatite 76 0 5 0 ma and zircon 79 0 3 0 ma within reasonable error representing a magmatic event the data were divided into four groups i 79 76 ma magmatic cooling event ii 69 61 ma uplift of the whole region and exhumation and erosion iii 37 34 ma and iv 25 ma various uplift events related to tectonic inversion causing partial uplift exhumation and erosion in the basin this created favorable conditions for formation and storage of mineral resources especially sandstone uranium ore deposits our results combined with previous research suggest that the variation in uplift and exhumation began in the basin s se part and propagated to the nw 5 8 ma later the tectonic inversion in the southern songliao basin at least began 37 34 ma this corresponds with the time of the paleo pacific plate shifting to nww motion and the india asia collision these regional scale uplift exhumation and inversion events were probably responses to the subduction and turning of the paleo pacific plate from the southeast and the collision of the indian subcontinent from the southwest it is important to study the tectonic inversion in the whole east of china since the late cretaceous and the change of the direction of the pacific plate movement

extrapolation of the kinetics of oil and gas formation from laboratory experiments to sedimentary basins it is generally accepted that the formation of oil and gas from sedimentary organic matter or kerogen is adequately described by kinetic models based on first order kinetics with rate constants obeying an arrhenius equation these models which are extensively used in oil exploration to assess the petroleum potential of sedimentary basins are based on geological observations1 2 3 4 5 6 but are formally quite similar to models designed to simulate oil shale pyrolysis7 8 9 or coal processing10 11 12 the idea of blending these two approaches is not new see for example ref 2 but until now the most sophisticated attempts reproduced only the gross features of kerogen cracking on a geological timescale5 or were uncontrolled by geochemical measurements13 14 here we show that the kinetic parameters determined from the laboratory pyrolysis of an immature kerogen sample apply to the conditions of sedimentary basins altough the time and temperature scale are completely different

porosity permeability and textural heterogeneity of reservoir sandstones from the lower cretaceous putaohua member of yaojia formation weixing oilfield songliao basin northeast china abstract with the granulometric analyses mineral composition x ray diffraction xrd analyses porosity and permeability measurements scanning electron microscopy sem observations and mercury porosimetry measurements of the reservoir sandstones from four wells in the weixing oilfield songliao basin ne china the porosity permeability and pore structural heterogeneity features of the putaohua member sandstone of the lower cretaceous yaojia formation have been investigated in this paper the sandstones are mostly characterized by a similar deposition in continental detrital environments with quartz and feldspar taking the majority 97 and argillaceous minerals illite kaolinite and chlorite the minority 3 however their granule size sorting index porosity and permeability vary significantly in contrast to the generality that high porosity permeability often corresponds to large grain sizes and sorting indexes the porosity and permeability here show no good correlations to the grain size and sorting index suggesting the presence of a remarkable textural heterogeneity in terms of sequential change in permeability along the well depth cyclic sedimentation modes have been identified in some sub layers despite the porosity data showing little response to those scenarios this may be ascribed to the sandstone s peculiar intergranular pore structures in which the cementation occurred in pore lining and filling manners to different extents depending on their depositional environments the distributary channel facies tends to have lowest detrital clay content and rather open packed texture in pore lining cementation manner whereas sand sheet facies has pore filling manner the hg porosimetry analytical data are in fairly good agreement with the heterogeneous pore structures observed by sem large sized pores and channels connecting them though only accounting for a low percentage of the total porosity are believed to contribute mostly to the effective permeability in the sandstone reservoir such textural heterogeneities should be closely associated with the dynamic changing sedimentary facies of sandstones in the continental environment

vertical structure of the seasonal cycle in the central equatorial atlantic ocean xbt sections from 1980 to 1988 abstract a set of temperature profiles from expendable bathythermographs collected from 1980 to april 1988 along two ship routes transecting the equatorial atlantic from 11 n to 11 s is analyzed to inter the vertical structure of the annual variability of the temperature and the currents in the upper ocean during the average seasonal cycle the vertical isotherm displacements occur earlier below 300 meters than near the surface at most locations within 4 degrees of the equator at the equator the amplitude of the displacements does not decrease with depth in the upper 500 meters this still holds down to 700 meters but there are less data at these depths the lead of the deeper isotherm displacements with respect to those in the upper thermocline implies that there is a contribution to the pressure forces from these layers that is not in phase with the contribution of the upper thermocline this also suggests that the energy source of the seasonal variability is close to the surface dynamic height and

on the baroclinic response of the zonal pressure gradient in the equatorial atlantic ocean temperature time series obtained from surface moorings deployed along the equator in the atlantic ocean during the seasonal response of the equatorial atlantic experiment and the programme francais ocean et climat dans l atlantique equatorial were used to investigate the baroclinic response of the zonal pressure gradient due to the sloping isopycnals the zonal pressure gradient evolved as a complicated function of time depth and zonal position the most rapid and spatially inhomogeneous variations corresponded to periods of rapidly changing easterly wind stress following these periods the baroclinic response due to the sloping isopycnals was observed to overshoot its intended equilibrium before relaxing to it in so doing it tended to buffer pressure gradient variations at the depth of the equatorial undercurrent euc over much of the year the isopycnal slopes opposed the surface slope after the winds relaxed in winter however the isopycnal slopes reversed and acted in concert with the surface slope thereby enhancing the pressure gradient at the depth of the euc relative to that at the surface this reversal might be important in maintaining the euc during times of weak easterly wind stress the vertical structure of the zonal pressure gradient varied with the depth of the thermocline when the winds were weak and the thermocline was shallow the baroclinic response of the zonal pressure gradient due to the sloping isopycnals was primarily effected in the upper 50 m after the winds intensified and the thermocline deepened the baroclinic response extended down to at least 150 m

equatorial atlantic ocean temperature and current variations during 1983 and 1984 the equatorial regions of the earth s oceans are climatically sensitive ones because of the zonal sea surface temperature contrasts observed there1 equatorial sea surface temperature normally varies on an annual cycle with the prevailing trade winds but deviations from this cycle may have significant global implications as occurred for example during the 1982 83 pacific ocean el nino southern oscillation event2 understanding the annual and interannual variability of the tropical oceans has therefore been the goal of several measurement programmes in the atlantic ocean the seasonal response of the equatorial atlantic sequal experiment and the programme francais ocean et climat dans l atlantique equatorial focal have provided a basin wide and synoptic data set over two annual cycles we present here results from surface moored current meters which were one of several fixed and shipborne measurement systems employed by sequal and focal we will describe the evolution of the upper ocean thermal and zonal velocity component variations in relation to forcing by the trade winds show differences observed along the equator at 28 w and 4 w and compare the oceans responses at these locations during 1983 and 1984 the synoptic data realizations of these years differed from climatology and these differences are related to the rapidly varying nature and intensity of the wind stress in a given year changes in wind stress from year to year result in interannual variability as a modulated annual cycle and 1984 a year of weak winds relative to 1983 offers a case in point the zonal sea surface temperature gradient vanished along the equator in 1984 during the season when it normally would have been a maximum

post rift geodynamics of the songliao basin ne china origin and significance of t11 coniacian unconformity abstract the t11 unconformity lies between the qingshankou and yaojia formations in the post rifting sequence of the cretaceous songliao basin ne china it is intimately associated with petroleum reservoirs and considered to be a disconformity forming in the tectonic quiet stage we present the interpretations from new seismic surveys and cored sections of the cretaceous continental scientific drilling borehole ccsd sk 1 in order to resolve the nature and origin of t11 unconformity the t11 is often a low angle unconformity with underlying qingshankou formation having been deformed and eroded prior to deposition of the yaojia formation in the post rift evolution of the basin it marks an abrupt change from a deep lake to shallow lake or subaerial environment documented by reddening of the lacustrine mudstone extinction of the ostracod assemblages and a great increase of coarse detrital inputs the sharp change of depositional environment the truncation of gentle folds and the cluster of volcanic and paleoearthquake activities all happened simultaneously immediately before the development of t11 unconformity indicating a significant regional compressional uplift event in the basin the timing of the t11 unconformity formation is within the interval 88 86 2 ma correlations with coeval unconformities in other cretaceous sedimentary basins in eastern asia indicate that this compressional uplift coincided with an episode of global plate reorganization between the eurasian and paleo pacific plates that culminated at 88 87 ma during this short interval the northeast asian margin in eastern china south korea japan and russian far east experienced widespread violent volcanic and granite emplacement activity triggered by compression resulting from rapid and orthogonal slab subduction the post rift basin tectonic inversion occurred during t11 coniacian time thereafter the basin again evolved in an extension regime two subsidence phases in post rift history took place as the direct consequence of coniacian compression peak which defined the distribution of oil sources and reservoirs

numerical simulation of hydrodynamics and bank erosion in a river bend we present an integrated analysis of bank erosion in a high curvature bend of the gravel bed cecina river central italy our analysis combines a model of fluvial bank erosion with groundwater flow and bank stability analyses to account for the influence of hydraulic erosion on mass failure processes the key novel aspect being that the fluvial erosion model is parameterized using outputs from detailed hydrodynamic simulations the results identify two mechanisms that explain how most bank retreat usually occurs after rather than during flood peaks first in the high curvature bend investigated here the maximum flow velocity core migrates away from the outer bank as flow discharge increases reducing sidewall boundary shear stress and fluvial erosion at peak flow stages second bank failure episodes are triggered by combinations of pore water and hydrostatic confining pressures induced in the period between the drawdown and rising phases of multipeaked flow events

the art of maturity modeling part 1 finding a satisfactory geologic model an example of one dimensional maturity modeling of the miti rumoi well a stratigraphic test drilled in a frontier area of japan is worked out in detail to illustrate how maturity modeling should be carried out prior to and during modeling an effort was made to integrate all available geological geochemical and geophysical concepts and data to create a single geologic model called here the good model that was as plausible and internally consistent as possible where data sets were internally inconsistent or in conflict with other data decisions had to be made about data reliability some vitrinite reflectance data subsurface temperatures and thermal conductivity measurements were rejected for a variety of reasons the justifications for these decisions which influenced the results of the modeling are discussed in detail using the good model we evaluated the timing and amount of oil and gas generation from coals in the haboro formation the only proposed source rocks in northwest hokkaido japan generation has occurred continually since the middle miocene but the fractional conversion of kerogen to hydrocarbons to date has been small as a result the total volume of hydrocarbons available for expulsion and migration from the haboro source rock probably is small unless very large volumes of coal are present the good model does not represent a unique solution however it thus should be regarded as one of a number of viable models rather than as the only correct one alternative models are considered in a companion paper the modeling process itself by which and during which we learn much about the geologic system is at least as important as the final numerical answer highly interactive modeling programs greatly aid in proper modeling

geochemical characterization of secondary microbial gas occurrence in the songliao basin ne china abstract a suite of natural gases from the northern songliao basin in ne china were characterized for their molecular and carbon isotopic composition gases from shallow reservoirs display clear geochemical evidence of alteration by biodegradation with very high dryness c1 c2 100 high c2 c3 and i c4 n c4 ratios high nitrogen content and variable carbon dioxide content isotopic values show wide range variations 13 c ch 4 from 79 5 to 45 0 13 c c 2 h 6 from 53 7 to 32 2 13 c c 3 h 8 from 36 5 to 20 1 13 c n c 4 h 10 from 32 7 to 24 5 and 13 c co 2 from 21 6 to 10 5 a variety of genetic types can be recognized on the basis of chemical and isotopic composition together with their geological occurrence secondary microbial gas generation was masked by primary microbial gas and the mixing of newly generated methane with thermogenic methane already in place in the reservoir can cause very complicated isotopic signatures system openness also was considered for shallow biodegraded gas accumulations gases from the daqing anticline are relatively wet with 13c enriched methane and 13c depleted co2 representing typically thermogenic origin gases within the longhupao da an terrace have variable dryness 13c enriched methane and variable 13c of co2 suggesting dominant thermogenic origin and minor secondary microbial methane augment the puqian ao nan uplift contains relatively dry gas with 13c depleted methane and 13c enriched co2 typical for secondary microbial gas with a minor part of thermogenic methane gas accumulations in the western slope are very dry with low carbon dioxide concentrations some gases contain 13c depleted methane ethane and propane indicating low maturity primary microbial origin recognition of varying genetic gas types in the songliao basin helps explain the observed dominance of gas in the shallow reservoir and could serve as an analogue for other similar shallow gas systems

unusual conditions in the tropical atlantic ocean in 1984 au cours de la 1ere moitie de 1984 les conditions oceaniques et atmospheriques dans l atlantique tropical ont ete a bien des egards similaires a celles dans le pacifique au cours de l el nino l ocean superieur a ete inhabituellement chaud dans sa partie orientale les pluies ont ete abondantes sur des regions normalement arides au sud de l equateur et l upwelling cotier a ete contrarie dans une region sud ouest africain ou il constitue un phenomene saisonnier le changement de tsm sst qui apparait lorsque d inhabituels courants portant a l est au sud de l equateur transportent de l eau chaude de surface vers l afrique contribue au changement des conditions atmospheriques ces dernieres en retour contribuent au changement de la circulation oceanique et de la tsm