investigation of the catalytic effects of indigenous minerals in the pyrolysis of aleksinac oil shale substrates steranes triterpanes and triaromatic steroids in the pyrolysates abstract evidence for catalytic effects of indigenous minerals in the pyrolysis of aleksinac oil shale kerogen was found by investigating the liquid products obtained in the micro activity test mat pyrolysis of raw shale and its demineralized substrates by comparing the corresponding fragmentograms of a demineralized sample with those of a substrate containing only silicate minerals differences in the side chain isomerisation of the steranes and triterpanes and in the side chain cleavage of the triaromatic steroids were observed these findings corroborated the previous conclusion based on mat parameters and tg weight losses that the catalytic effect of the indigenous mineral components during the pyrolysis of aleksinac oil shale kerogen is very low

historical development of the gravity method in exploration the gravity method was the first geophysical technique to be used in oil and gas exploration despite being eclipsed by seismology it has continued to be an important and sometimes crucial constraint in a number of exploration areas in oil exploration the gravity method is particularly applicable in salt provinces overthrust and foothills belts underexplored basins and targets of interest that underlie high velocity zones the gravity method is used frequently in mining applications to map subsurface geology and to directly calculate ore reserves for some massive sulfide orebodies there is also a modest increase in the use of gravity techniques in specialized investigations for shallow targets gravimeters have undergone continuous improvement during the past 25 years particularly in their ability to function in a dynamic environment this and the advent of

correlative geochemical study of crude oils from southeastern and southern parts of the pannonian basin abstract several crude oils from the southeastern yugoslav part of the pannonian basin are correlated for the first time on the basis of many bulk and specific parameters the investigations involved 15 oils from oil gas fields a and b and oil field c from the banat depression and oil field d from south backa depression and four oils from recently discovered oil shows e the kostolac depression on the basis of structural group analysis and other bulk parameters such as api gravity contents of asphaltenes and sulfur as well as content of n alkanes and pristane to phytane ratio the examined oils are classified into four groups however the distributions and relative abundances of n alkanes isoprenoids c19 c20 steranes tricyclic terpanes and pentacyclic triterpanes obtained by capillary gc and computerized gc ms analysis suggest classification of the examined oils into only two genetic types a d and e1 e4 the oils are of relatively high maturity they are not biodegraded except for both oils from field d and the oil a9

origin of crude oils in the jinhu depression of north jiangsu south yellow sea basin eastern china abstract the chemical compositions of 20 crude oils and the extracts of potential source rocks from the jinhu depression of the north jiangsu south yellow sea basin eastern china were studied in detail by geochemical methods in order to understand their genetic relationship the oil samples were collected from the major producing fields in the western slope ws and the biandong yangjiaba minqiao uplift belt bmy the rock samples studied selected after rock eval pyrolysis screening of a large suite of samples consist of 20 shale samples in the e 2 f 2 member of the paleocene funing formation from the oilfield areas ws and bmy and the sanhe sag all within the jinhu depression geochemical characteristics indicate only one single family of oils a number of biomarker features support deposition of the source rocks for these oils under conditions of enhanced salinity stratified water columns a wide thermal maturity range for the oils as indicated by sterane isomerization ratios was not substantiated by other maturity parameters the genetic relationships between the oils and the e 2 f 2 member of the paleocene funing formation present in the deeper parts of the sanhe and longgang sags were suggested using a wide range of molecular parameters variation in the sterane concentrations in source rocks with different maturity suggests that migrational contamination and or in situ extractions of organic matter from caprocks or intra reservoir shales by mature oils could potentially produce oils with apparent immaturity at the molecular level secondary alteration e g biodegradation of oils in the reservoir could also have a similar effect on the bulk oil compositions although we do not discount the possible presence of minor amounts of immature oils exploration focus in the jinhu depression as well as many other rift basins in eastern china should be on mature oils derived from the deep source kitchens

3d stochastic inversion of gravity data using cokriging and cosimulation a new application has been developed based on geostatistical techniques of cokriging and conditional simulation for the 3d inversion of gravity data including geologic constraints the necessary gravity density and gravity density covariance matrices are estimated using the observed gravity data then the densities are cokriged or simulated using the gravity data as the secondary variable the model allows noise to be included in the observations the method is applied to two synthetic models a short dipping dike and a stochastic distribution of densities then some geologic information is added as constraints to the cokriging system the results show the ability of the method to integrate complex a priori information the survey data of the matagami mining camp are considered as a case study the inversion method based on cokriging is applied to the residual anomaly to map the geology through the estimation of the density distribution in this region the results of the inversion and simulation methods are in good agreement with the surface geology of the survey region

two dimensional magnetotelluric inversion of blocky geoelectrical structures 1 this paper demonstrates that there are alternative approaches to the magnetotelluric mt inverse problem solution based on different types of geoelectrical models the traditional approach uses smooth models to describe the conductivity distribution in underground formations in this paper we present a new approach based on approximating the geology by models with blocky conductivity structures we can select one or another class of inverse models by choosing between different stabilizing functionals in the regularization method the final decision whose approach may be used for the specific mt data set is made on the basis of available geological information this paper describes a new way of stabilizing two dimensional mt inversion using a minimum support functional and shows the improvement that it provides over traditional methods for geoelectrical models with blocky structures the new method is applied to mt data collected for crustal imaging in the carrizo plain in california and to mt data collected for mining exploration by inco exploration

geochemistry of petroleum systems in the niuzhuang south slope of bohai bay basin part 1 source rock characterization detailed mapping of the tertiary strata of the dongying depression bohai bay basin reveals that oil shales and dark mudstones in the es4 and es3 members of the eocene oligocene shahejie formation have excellent potential as petroleum source rocks regional distributions of total organic carbon content kerogen type and thermal maturation indicate that abundant mature source rocks are present in the niuzhuang sag whereas source rocks along the niuzhuang south slope are currently immature or marginally mature for the generation of conventional oils this study examined the molecular characteristics for a number of biomarker compound classes and related these to either source facies change or different burial and thermal maturation an important observation made during this study is the significant variation in the relative distributions and absolute concentrations of a wide range of aliphatic and aromatic hydrocarbon markers in the rock extracts as a function of burial depth this variation may potentially explain the uncertainty associated with the maturity assessment and genetic modeling for so called immature oils that are usually defined on the basis of alkane biomarker isomerization ratios and the presence of biomarkers with biological configurations

influence of bed patchiness slope grain hiding and form drag on gravel mobilization in very steep streams steep streams are a major portion of channel networks and provide a link to transport sediment from hillslopes to lower gradient rivers despite their importance key unknowns remain perhaps foremost of which is evaluating in steep streams empirical laws for fluvial sediment transport developed for low gradient rivers to address this knowledge gap we painted sediment in situ over 3 years to monitor incipient sediment motion and sediment patch development in five small drainage areas of 0 04 2 km 2 and steep slopes of 5 37 tributaries of elder creek california united states we found that channel beds organized into size sorted sediment patches which displayed active fluvial transport of gravel annually consistent year to year patch median grain sizes partial transport of bed material and significantly higher values of critical shields stress for incipient sediment motion compared to that observed for lower gradient rivers the high critical shields stresses up to 0 5 for the median grain size agree within a factor of 3 to theoretical predictions which account for slope dependent hydraulics grain hiding and sediment patches for grains of approximately the same size as the roughness length scale slope dependent hydraulics and bed patchiness are the dominant controls on critical shields stress values while grain hiding is important for grains larger or smaller than the roughness length scale form drag exists in our monitored tributaries but has a smaller influence than the above effects our field observations show fluvial processes contribute to sediment mobilization in steep channels which are often considered to be dominated by debris flows

australia s moho a test of the usefulness of gravity modelling for the determination of moho depth abstract in general seismic methods provide a reliable way to image the crust mantle interface which is marked by a rapid increase in seismic velocity the moho however the coverage provided by seismic networks is necessarily limited due to access difficulties and the cost and labour involved in collecting data gravity data provide an alternative way to model the depth to the moho and provide more consistent and broader coverage we discuss the usefulness of gravity data to model moho depth and the advantages and disadvantages of several gravity modelling methods as an example a model of australia s moho is generated through seismically constrained gravity inversion including an estimate of modelling uncertainty the inversion results demonstrate that gravity inversion is generally useful but that its usefulness is subject to the following limitations 1 gravity inversion cannot spontaneously generate thick high density crust nor thin low density crust and unless constrained will not generate a correct moho where such crust exists 2 major errors in the definition of the a priori density structure in particular features that are fixed during inversion will influence the moho results 3 applying a broad range of inversion parameters is necessary to characterise uncertainty model variability maps for australia show that the average error is less than 5 km there is a general relationship with seismic coverage but the areas of highest uncertainty are not necessarily those with the lowest seismic estimate density comparison with previous seismic and seismic gravity models of australia s moho indicates that low seismic data density limits usefulness due to higher uncertainty in the gravity inversion high seismic data density also limits usefulness because moho depth is largely known and there is little scope for change the usefulness of gravity inversion is maximum under conditions where seismic coverage is moderately dense but estimates are well distributed

stable inversion of gravity anomalies of sedimentary basins with nonsmooth basement reliefs and arbitrary density contrast variations we present a new stable method for interpreting the basement relief of a sedimentary basin which delineates sharp discontinuities in the basement relief and incorporates any law known a priori for the spatial variation of the density contrast the subsurface region containing the basin is discretized into a grid of juxtaposed elementary prisms whose density contrasts are the parameters to be estimated any vertical line must intersect the basement relief only once and the mass deficiency must be concentrated near the earth s surface subject to the observed gravity anomaly being fitted within the experimental errors in addition upper and lower bounds on the density contrast of each prism are introduced a priori one of the bounds being zero and the method assigns to each elementary prism a density contrast which is close to either bound the basement relief is therefore delineated by the contact between the prisms with null and nonnull estimated density contrasts the latter occupying the upper part

organic geochemical and petrographical characteristics of coal bearing oligo miocene sequence in the oltu narman basin erzurum ne turkey abstract in the oltu narman erzurum tertiary basin coals occur in the oligo miocene lacustrine sequence in this study n alkane isoprenoid and saturated aromatic biomarker distributions of coals in the sutkans region are found in association with pyrolysis and petrographic data and detailed organic geochemical characteristics depositional environments and hydrocarbon potential of the coals are propounded huminite is the dominant maceral type in coals 51 84 telohuminite is in lesser abundance detrohuminite especially densinite and gelohuminite gelinite are in higher abundance groundwater influence index gwi and gelification index gi are quite high for the studied coals whilst tissue preservation index tpi and vegetation index vi are found to be extremely low according to the results of pyrolysis coal coaly claystone and clayey coal samples contain type ii kerogen although sutkans coals have high ash content 6 28 44 60 average 27 99 their calorific value is quite high 3947 7583 kcal kg random huminite reflectance values of coals vr are 0 4 048 average 0 44 indicating sub bituminous b rank tmax values of coal coaly claystone and clayey coal samples are between 413 and 437 c 20s 20r 20s sterane 22s 22r 22s homohopane ma i ma i ii ta i ta i ii and c28ta c29ma c28ta steroid mpi mpr and mdr ratios which reflect the maturity of coals are very low mpi 1 is intermediate and moretane hopane ratio is high according to petrographical palynological and geochemical data the coal sequence was formed in an environment changing in character from lacustrine to fluvial and coals were accumulated in a swamp area with high water level high ph and intense microbial activity represented by suboxic anoxic conditions

geophysical inversion using approximate equality constraints current inversion methods estimating a physical property on a grid use two kinds of constraints 1 absolute constraints requiring that the solution vector be close to a prespecified vector as for example proximity to the null vector in the ridge regression and 2 relative constraints requiring that the elements of the solution vector be close to each other as for example smoothness imposed by methods requiring that spatial derivatives of the physical property be continuous using just absolute constraints may produce a biased solution conflicting with some true geological attributes of the source on the other hand using just relative constraints may be insufficient to stabilize the inversion we present a stable inversion method incorporating absolute constraints only at points where the physical property is known as for example outcroppings and boreholes elsewhere relative constraints are introduced according to a linear relationship for the spatial distribution of the physical property the proposed method is analogous to an interpolation method applied to the physical property distribution the interpolating function must satisfy some property like continuity and pass through the data the proposed method is versatile in incorporating not only factual but also indirect information such as continuity symmetry and trends in addition it may be applied both to linear and nonlinear problems the relevant results obtained from applying the method to synthetic potential field data were 1 ability to produce reliable mappings of the basement relief of a sedimentary basin from gravity data and of an areal distribution of magnetization using only smoothness constraints and restricted surface and borehole information 2 operational simplicity because of the solution insensitivity to the damping parameter the method is also applied to the bouguer anomaly over san jacinto graben california producing results consistent with previous interpretations

a demonstration of the importance of bedload transport for fluvial bedrock erosion and knickpoint propagation we provide field evidence for the role of bedload in driving fluvial incision and knickpoint propagation using aerial photographs field surveys and hydrological data we constrain the incision history of a bedrock gorge 1200 m long and up to 20 m deep cut by da an river in western taiwan this reach of the river experienced 10 m of uplift during the 1999 chi chi earthquake for five years following the earthquake bedload was prevented from entering the uplift zone the knickpoint was static and little incision took place bedload transport across the uplift zone resumed in 2004 initiating extremely rapid incision with 620 m of knickpoint propagation and up to 20 m of downcutting by 2008 this change highlights the relative inefficiency of suspended sediment and the dominant role of bedload as a tool for fluvial erosion and knickpoint propagation once bedload tools became available knickpoint propagation was influenced by geological structure lithology and drainage organization in particular a change in dip of the sandstone beds at the site caused a decrease of knickpoint propagation velocity copyright 2012 john wiley sons ltd

geochemistry and possible origin of petroleum in palaeozoic reservoirs from halahatang depression abstract the halahatang depression in the tabei uplift of the tarim basin is an active exploration area because it has substantial reservoir potential and contains or is near to many commercial oil fields geochemical analysis indicates that halahatang oils were derived from marine carbonate source rocks deposited under anoxic reducing conditions the maturities for halahatang oils are corresponding to the peak of the oil window and slightly higher than the neighboring tahe oils the halahatang oils feature low pr ph c 21 c 23 tricyclic terpane and c 28 c 29 sterane ratios high c 29 c 30 hopane and c 35 c 34 hopane ratios a v shape in the distribution of c 27 c 28 c 29 steranes and light carbon isotope ratios similar to the tahe oils and correlate well with the middle upper ordovician source rock however some source related biomarker parameters imply a more reducing source organofacies with more zooplanktonic contribution than that for the tahe oils

maturity assessment of oils from the sakhalin oil fields in russia phenanthrene content as a tool a correlation analysis of maturation parameters was carried out on 14 crude oil samples from nine oil fields on sakhalin island russia the oils were taken from reservoir rocks of miocene age at depths ranging from 73 to 2841 m on the basis of gc analysis of the alkane fraction n alkanes and the isoprenoid alkanes pristane and phytane as well as on the basis of the abundance of demethylated hopanes gc ms analysis m z 177 it is assumed that the oils are either biodegraded or are a mixture of biodegraded and nonbiodegraded oils therefore their maturation is assessed on the basis of the distribution and abundance of tricyclic aromatic hydrocarbons that are more resistant to biodegradation than alkane type biological markers the oils may be classified into three groups on the basis of the well established maturation parameter mpi 3 highly mature group i moderately mature group ii and immature group iii the correlation analysis shows that the percentage of phenanthrene p in the tricyclic aromatic fraction of the oils of the sakhalin oil fields can be used as a maturation parameter the highly mature oils group i were found to have a p value of more than 14 the moderately mature oils group ii have values of 7 14 and the immature oils group iii a value of less than 7 the very good correlation between mpi 3 and p also indicates that parallel to methylphenanthrene isomerization dealkylation also occurs in the reservoir rocks by correlation analysis it is shown that these reactions are to a great extent determined by the depth of the reservoir rocks

a bayesian 3 d linear gravity inversion for complex density distributions application to the puysegur subduction system we have developed a linear 3 d gravity inversion method capable of modelling complex geological regions such as subduction margins our procedure inverts satellite gravity to determine the best fitting differential densities of spatially discretized subsurface prisms in a least squares sense we use a bayesian approach to incorporate both data error and prior constraints based on seismic reflection and refraction data based on these data gaussian priors are applied to the appropriate model parameters as absolute equality constraints to stabilize the inversion and provide relative equality constraints on the parameters we utilize a combination of first and second order tikhonov regularization which enforces smoothness in the horizontal direction between seismically constrained regions while allowing for sharper contacts in the vertical we apply this method to the nascent puysegur trench south of new zealand where oceanic lithosphere of the australian plate has underthrust puysegur ridge and solander basin on the pacific plate since the miocene these models provide insight into the density contrasts moho depth and crustal thickness in the region the final model has a mean standard deviation on the model parameters of about 17 kg m and a mean absolute error on the predicted gravity of about 3 9 mgal demonstrating the success of this method for even complex density distributions like those present at subduction zones the posterior density distribution versus seismic velocity is diagnostic of compositional and structural changes and shows a thin sliver of oceanic crust emplaced between the nascent thrust and the strike slip puysegur fault however the northern end of the puysegur ridge at the snares zone is predominantly buoyant continental crust despite its subsidence with respect to the rest of the ridge these features highlight the mechanical changes unfolding during subduction initiation

transects of the ancient and modern continental margins of eastern canada abstract rocks of the west flank of the northern appalachian orogen miogeocline record the history of the late precambrian early paleozoic passive continental margin of eastern north america the ancient margin was destroyed by ophiolite obduction and arc collision during the ordovician taconic orogeny the present sinuous form of the miogeocline is interpreted to reflect ancient promontories and re entrants of a previous orthogonal margin bounded by rifts and transforms four major terranes are recognized east of the miogeocline in newfoundland and nova scotia from west to east these are the dunnage gander avalon and meguma the dunnage and gander terranes were linked to the miogeocline during the middle ordovician taconian orogeny the avalon terrane arrived later possibly during the mid paleozoic acadian orogeny the meguma terrane of southern nova scotia had docked with the avalon terrane by carboniferous time the dunnage terrane contains arc volcanics which lie above an ophiolitic substrate the gander terrane comprises a thick sequence of clastic sedimentary rocks underlain by basement rocks with continental affinities it has been interpreted as a continental margin perhaps once on the eastern side of the paleozoic iapetus ocean the avalon terrane consists of belts of sedimentary and volcanic rocks which are probably underlain by grenvillian basement its tectonic affinities are unclear the meguma terrane comprises a thick sequence of sediments derived from the south east it is found only in southeastern atlantic canada the boundaries between terranes are compressional in the west and steep transcurrent faults in the east the surface extent of the geological terranes is grossly correlative with deep structural zones although no direct evidence exists for linking the two because most surface structures can be traced geophysically to only a few kilometres depth a striking feature of the deep crustal structure is a lower high velocity crustal layer beneath the dunnage and gander terranes the modern margin of atlantic canada developed by rifting and by transform motion between adjacent continents stretching and thinning of the lithosphere and the consequent production of basaltic magma that in places intrudes or underplates the thinned continental crust are the most likely processes responsible for the evolution of the modern margin these processes predict the observed deep sedimentary basins along the margin the thinning of continental crust and the high seismic velocities found within the ocean continent transition zones rifting adjacent to nova scotia began in late triassic early jurassic time between the present african and north american plates these plate motions are also responsible for the major transform margin south of the grand banks separation between iberia and the eastern grand banks occurred in mid cretaceous time before the late cretaceous opening of the labrador sea while the rifted segments of the margin exhibit deep sedimentary basins and thinned continental crust the grand banks transform segment is characterized by a sharp transition zone and a relatively thin sediment cover numerous volcanic seamounts are built on the ocean crust adjacent to this transform segment mimicry of paleozoic promontories and re entrants by modern rift and transform margin segments the location of mesozoic sedimentary basins on ancestral appalachian structures and the reactivation and propagation of major precambrian and paleozoic structural boundaries during the latest phase of ocean opening attest to ancestral controls of the modern margins the rift phase of both the ancient and modern passive margins is characterized by volcanism mafic dike intrusion and by the development of basins filled with clastic sediments the drift phase of both the ancient margin and the present nova scotia margin is marked by a change in sedimentary environment such that carbonates replaced the rift phase clastic sediments two of the markers used to delineate the ancient ocean continent transition zone carbonate banks and steep gravity anomaly gradients should be used with caution as the modern analogs of these markers may lie 100 km or more of this transition zone furthermore it is naive to view the ancient transition as simple and narrow for the modern margins exhibits complex transition zones between 30 and 300 km wide in general the evolution of the ancient and modern passive margins appear to be remarkably similar predictably closing the present atlantic will mimic the evolution of the appalachian orogen

evaluation of the effects of native minerals on the organic matter of aleksinac oil shale based on the composition of free and bound bitumens abstract in order to evaluate the adsorption and catalytic effects of indigenous carbonates and silicates on the organic matter of aleksinac oil shale the free and the bound bitumens were isolated and analyzed by organic geochemical methods the differences in the gross compositions indicated an adsorption effect of both the carbonates and silicates in the examined oil shale the maturation parameters based on n alkanes and isoprenoid alkanes pristane and phytane indicated that bitumen 3 was of the highest and bitumen 1 of the lowest apparent maturity the silicates were shown to have had a thermocatalytic effect on the organic matter of this sediment clay minerals had a catalytic effect primarily on sterane aromatization rearrangement of steranes into diasteranes and their 20r 20s isomerization all evidence obtained by analysis of steranes and aromatic steroids suggested that the differences in bitumen compositions should be explained by the effect of clay minerals rather than by variations in the origin of the precursor biomass

simultaneous 3d depth to basement and density contrast estimates using gravity data and depth control at few points we have developed a gravity inversion method for simultaneouslyestimatingthe3dbasementreliefofasedimentary basin and the parameters defining a presumed parabolic decay of the density contrast with depth in a sedimentary pack assumingpriorknowledgeaboutthebasementdepthatafew points thesedimentarypackisapproximatedbyagridof3d vertical prisms juxtaposed in both horizontal directions of a right handed coordinate system the prisms thicknesses representthedepthstothebasementandaretheparametersto be estimated from the gravity data to estimate the parameters defining the parabolic decay of the density contrast with depthandtoproducestabledepth to basementestimates we imposed smoothness on the basement depths and proximity between estimated and known depths at boreholes we applied our method to synthetic data from a simulated complex 3d basement relief with two sedimentary sections having distinct parabolic laws describing the density contrast variationwithdepth theresultsprovidegoodestimatesofthetrue parameters of the parabolic law of density contrast decay with depth and of the basement relief inverting the gravity data from the onshore and part of the shallow offshore almadabasinonbrazil snortheasterncoastshowsgoodcorrelationwithknownstructuralfeatures

crustal structure of the ocean continent transition at flemish cap seismic refraction results 1 we conducted a seismic refraction experiment across flemish cap and into the deep basin east of newfoundland canada and developed a velocity model for the crust and mantle from forward and inverse modeling of data from 25 ocean bottom seismometers and dense air gun shots the continental crust at flemish cap is 30 km thick and is divided into three layers with p wave velocities of 6 0 6 7 km s across the southeast flemish cap margin the continental crust thins over a 90 km wide zone to only 1 2 km the ocean continent boundary is near the base of flemish cap and is marked by a fault between thinned continental crust and 3 km thick crust with velocities of 4 7 7 0 km s interpreted as crust from magma starved oceanic accretion this thin crust continues seaward for 55 km and thins locally to 1 5 km below a sediment cover 1 9 3 1 km s oceanic layer 2 4 7 4 9 km s is 1 5 km thick while layer 3 6 9 km s seems to disappear in the thinnest segment of the oceanic crust at the seawardmost end of the line the crust thickens to 6 km mantle with velocities of 7 6 8 0 km s underlies both the thin continental and thin oceanic crust in an 80 km wide zone a gradual downward increase to normal mantle velocities is interpreted to reflect decreasing degree of serpentinization with depth normal mantle velocities of 8 0 km s are observed 6 km below basement there are major differences compared to the conjugate galicia bank margin which has a wide zone of extended continental crust more faulting and prominent detachment faults crust formed by seafloor spreading appears symmetric however with 30 km wide zones of oceanic crust accreted on both margins beginning about 4 5 m y before formation of magnetic anomaly m0 118 ma

constrained inversion of geologic surfaces pushing the boundaries during the past 10 years there has been a shift in modelling for geophysical interpretation away from idealized geometrical bodies floating in air and toward fully three dimensional representations this transition has been driven by a number of factors both technological and conceptual the principal conceptual driver has been the growing recognition of the importance of integrated interpretations interpretation is a shared responsibility of geoscientists the common goal being an earth model consistent with all available information

paleoreconstruction by biological markers abstract during diagenesis and conversion of the original lipid fraction of biological systems to petroleum hydrocarbons the following four basic events needed for paleoreconstruction can be monitored by biological markets 1 sourcing 2 maturation 3 migration and 4 biodegradation actual cases of applying biological markers to petroleum exploration problems in different parts of the world are demonstrated cretaceous and phosphoria sourced oils in the wyoming thrust belt can clearly be distinguished from one another by high quality source fingerprinting of biomarker terpanes using gas chromatography mass spectrometry identification of recently discovered biological markers head to head isoprenoids allows subtle source differentiation between oils from sumatra the degree of crude oil maturation in basins from california alaska russia wyoming and louisiana can be assessed by specific novel biomarker ratios 20s 20r sterane epimers field evidence from such interpretation is confirmed by laboratory pyrolysis of the rock an example of immature sumatra rock is given extensive migration is documented by biomarkers in several oils the effect of biodegradation on biomarker steranes and terpanes is exemlified in a california basin all biological marker results are consistent with the geological setting and add a new dimension in assisting the petroleum explorationist toward paleo reconstruction

joint inversion of surface and three component borehole magnetic data the inversion of magnetic data is inherently nonunique with respect to the distance between the source and observation locations this manifests itself as an ambiguity in the source depth when surface data are inverted and as an ambiguity in the distance between the source and boreholes if borehole data are inverted joint inversion of surface and borehole data can help to reduce this nonuniqueness to achieve this we develop an algorithm for inverting data sets that have arbitrary observation locations in boreholes and above the surface the algorithm depends upon weighting functions that counteract the geometric decay of magnetic kernels with distance from the observer we apply these weighting functions to the inversion of three component magnetic data collected in boreholes and then to the joint inversion of surface and borehole data both synthetic and field data sets are used to illustrate the new inversion algorithm when borehole data are inverted directly three component data are far more usefu

crustal structure beneath orphan basin and implications for nonvolcanic continental rifting a wide angle seismic profile was acquired across the northeast newfoundland margin seaward to orphan knoll the profile is complemented by existing multichannel reflection data two online deep wells and other deep seismic reflection and refraction lines modeling of data from 15 ocean bottom seismometers provides the seismic velocity structure for a significant portion of the 400 km wide stretched continental crust on this margin prerift metasedimentary rocks have a topographic relief of up to 5 km with a velocity of 5 2 km s increasing to 5 9 km s unaltered crystalline crust below the metasedimentary section has a velocity range of 6 1 6 5 km s most of the lower crust landward of orphan knoll has a typical continental lower crustal velocity 6 8 7 0 km s and the lower crust shallows significantly beneath orphan knoll our model shows no evidence for the 5 km thick 7 35 km s layer modeled from data of an earlier experiment and interpreted as magmatic underplating but instead indicates that thinned continental crust extends seaward for 360 km without underplating implying nonvolcanic rifting for the ne newfoundland margin we suggest that continental stretching persisted from 180 ma to chron 34n time 101 ma when the final breakup between canada and western europe took place leaving a 400 km wide zone of thinned continental crust underneath the shelf and deep water area of the orphan basin on the landward side of the basin gravity modeling indicates a zone of very thin 6 8 km crust possibly a failed rift center formed as a result of the northward progression of nonvolcanic rifting between canada and europe a possible sub moho reflector suggests generally uniform stretching of the crust and upper mantle and the absence of volcanics and underplating is in contrast to the observations on related rift basins of the grand banks

gravity inversion of 2d basement relief using entropic regularization we have developed a gravity interpretation method for estimating the discontinuous basement relief of a sedimentary basin the density contrast between the basement and the sediments is assumed to be known and it could be either constant or vary monotonically with depth the interpretation model consists of a set of vertical juxtaposed prisms whose thicknesses are the parameters to be estimated we used the entropic regularization that combines the minimization of the first order entropy measure with the maximization of the zeroth order entropy measure of the solution vector we validated the method by applying it to synthetic data produced by a simulated basin bordered by high angle step faults we obtained a good definition of the relief particularly of the discontinuities we also applied the method to a profile across the buyuk menderes valley in west turkey and obtained a solution exhibiting a gravity fault with large slip on the northern border of the valley when applied to the interpretation of a discontinuous basement relief the method has a better performance than the global smoothness method it is comparable to the weighted smoothness method but it does not require the a priori knowledge about the maximum basin depth

bayesian estimation in seismic inversion part i principles1 this paper gives a review of bayesian parameter estimation the bayesian approach is fundamental and applicable to all kinds of inverse problems its basic formulation is probabilistic information from data is combined with a priori information on model parameters the result is called the a posteriori probability density function and it is the solution to the inverse problem in practice an estimate of the parameters is obtained by taking its maximum well known estimation procedures like least squares inversion or l 1 norm inversion result depending on the type of noise and a priori information given due to the a priori information the maximum will be unique and the estimation procedures will be stable except in theory for the most pathological problems which are very unlikely to occur in practice the approach of tarantola and valette can be derived within classical probability theory the bayesian approach allows a full resolution and uncertainty analysis which is discussed in part ii of the paper

a three dimensional gravity inversion applied to sao miguel island azores gravimetric studies are becoming more and more widely acknowledged as a useful tool for studying and modeling the distributions of subsurface masses that are associated with volcanic activity in this paper new gravimetric data for the volcanic island of sao miguel azores were analyzed and interpreted by a stabilized linear inversion methodology an inversion model of higher resolution was calculated for the caldera of furnas which has a larger density of data in order to filter out the noncorrelatable anomalies least squares prediction was used resulting in a correlated gravimetric signal model with an accuracy of the order of 0 9 mgal the gravimetric inversion technique is based on the adjustment of a three dimensional 3 d model of cubes of unknown density that represents the island s subsurface the problem of non uniqueness is solved by minimization with appropriate covariance matrices of the data resulting from the least squares prediction and of the unknowns we also propose a criterion for choosing a balance between the data fit which in this case corresponds to residues with rms of the order of 0 6 mgal and the smoothness of the solution the global model of the island includes a low density zone in a wnw ese direction and a depth of the order of 20 km associated with the terceira rift spreading center the minimums located at a depth of 4 km may be associated with shallow magmatic chambers beneath the main volcanoes of the island the main high density area is related to the nordeste basaltic shield with regard to the caldera furnas in addition to the minimum that can be associated with a magmatic chamber there are other shallow minimums that correspond to eruptive processes

geochemistry of petroleum systems in the niuzhuang south slope of bohai bay basin part 2 evidence for significant contribution of mature source rocks to immature oils in the bamianhe field the chemical compositions of 28 representative crude oils and oil sand samples collected from the bamianhe region of the bohai bay basin eastern china were studied in detail in order to understand their genetic relationships biodegradation ranking and thermal maturity level molecular geochemical parameters indicate the presence of one single oil family in the cenozoic reservoirs a number of biomarker features support deposition of the source rocks for these oils under conditions of enhanced salinity stratified water columns the extremely low maturity levels of these immature oils as indicated by sterane isomerization ratios were not supported by other maturity parameters the genetic relationship between the oils and the es4 and es3 members of the eocene oligocene shahejie formation present in the deeper part of the niuzhuang sag but not those along the niuzhuang south slope was suggested using a wide range of molecular parameters variation in the sterane concentrations observed from potential source rocks with different maturity levels in the study area suggests a high probability of migration contamination of mature oils by immature bitumens along migration pathways or from intra reservoir shales variation in the level of oil biodegradation could also create anomalies in the use of gross oil compositions as an indicator of oil maturity although the recent rapid subsidence of the bohai bay basin and the saline depositional environment of one of the potential source rocks favor oil generation at relatively low maturity levels most of the economic oils discovered in the bamianhe region appear to have derived from conventionally mature source rocks but contain lower maturity fluids admixed with them

field measurements of the energy delivered to the channel bed by moving bed load and links to bedrock erosion 1 impact driven fluvial erosion is directly related to the energy delivered to the channel bed by moving bed load using a novel protocol we have measured this energy in four mountain streams in austria and switzerland similar to bed load transport rates the energy delivered to the bed displays large scatter over several orders of magnitude even for a constant discharge we found that only a small fraction 1 of the total energy available to the stream is delivered to the bed and can be used for erosive work empirical predictive equations can be defined for specific sites but there is large site to site variability prediction of energy delivered to the bed using the saltation abrasion model of bedrock erosion only provides the observed trends when measured bed load transport rates are used as input using an empirical transport law calibrated to the conditions at one of the study streams leads to overprediction of delivered energies by more than 2 orders of magnitude this overprediction decreases with increasing discharge and thus at high discharges better predictive results are obtained we find a correlation between the channels bed slope or characteristic grain sizes of the channel bed and the fraction of energy delivered to the bed of the total energy available to the stream this observation provides a tentative link between fundamental fluvial incision processes to the stream power model family that has widely been used to model fluvial bedrock incision in landscape evolution simulations

gravity inversion of basement relief and estimation of density contrast variation with depth we present a method to estimate the basement relief as well as the density contrast at the surface and the hyperbolic decaying factor of the density contrast with depth assuming that the gravity anomaly and the depth to the basement at a few points are known in both cases the interpretation model is a set of vertical rectangular 2d prisms whose thicknesses are parameters to be estimated and that represent the depth to the interface separating sediments and basement the solutions to both problems are stable because of the incorporation of additional prior information about the smoothness of the estimated relief and the depth to the basement at a few locations presumably provided by boreholes the method was tested with synthetic gravity anomalies produced by simulated sedimentary basins with smooth relief providing not only well resolved estimated relief but also good estimates for the density contrasts at the surface and for the decaying factors of the density contrast with depth the method was ap

global crust mantle density contrast estimated from egm2008 dtm2008 crust2 0 and ice 5g we compute globally the consolidated crust stripped gravity disturbances anomalies these refined gravity field quantities are obtained from the egm2008 gravity data after applying the topographic and crust density contrasts stripping corrections computed using the global topography bathymetry model dtm2006 0 the global continental ice thickness data ice 5g and the global crustal model crust2 0 all crust components density contrasts are defined relative to the reference crustal density of 2 670 kg m3 we demonstrate that the consolidated crust stripped gravity data have the strongest correlation with the crustal thickness therefore they are the most suitable gravity data type for the recovery of the moho density interface by means of the gravimetric modelling or inversion the consolidated crust stripped gravity data and the crust2 0 crust thickness data are used to estimate the global average value of the crust mantle density contrast this is done by minimising the correlation between these refined gravity and crust thickness data by adding the crust mantle density contrast to the original reference crustal density of 2 670 kg m3 the estimated values of 485 kg m3 for the refined gravity disturbances and 481 kg m3 for the refined gravity anomalies very closely agree with the value of the crust mantle density contrast of 480 kg m3 which is adopted in the definition of the preliminary reference earth model prem this agreement is more likely due to the fact that our results of the gravimetric forward modelling are significantly constrained by the crust2 0 model density structure and crust thickness data derived purely based on methods of seismic refraction

moho geometry gravity inversion experiment moggie a refined model of the australian moho and its tectonic and isostatic implications abstract at the continent scale models of moho depth based on seismic estimates alone can be inadequate due to irregular or sparse data gravity based moho modelling provides better coverage however the methods used are typically hampered by an inability to explicitly honour seismic constraints and are also limited by over simplistic model conditions e g laterally homogenous layering i present a new method to generate a continent scale moho model based on the constrained inversion of free air gravity data this method explicitly honours seismic moho estimates and accounts for a laterally heterogeneous crust and mantle resolution and sensitivity testing shows that for wavelengths greater than 200 km crustal density and moho depth are recovered with reasonable accuracy 30 kg m 3 and 3 km respectively moggie uses a six layer model incorporating ocean sedimentary basin upper crust lower oceanic crust eclogitised crust and mantle inversion variables were the density of the crustal layers constrained by a standard density model and the depths to intra crustal boundaries and the moho constrained by 230 seismic depth estimates the results demonstrate that a balanced approach to seismically constrained gravity inversion has the capability to generate detailed and well constrained models of the moho and crustal density at the continent scale for australia this is a clear improvement on the sparse and irregular resolution of the moho provided by seismic estimates of crustal thickness which fail to resolve short wavelength features newly defined tectonic features include extensive magmatic underplates crustal scale shear zones and the boundaries between tectonic blocks isostatic analysis reveals that little of the continent is close to isostatic equilibrium with isostatic disequilibria preserved at multiple scales from hundreds of kilometres to the entire continent these disequilibria are interpreted to indicate long wavelength flexure of highly competent continental lithosphere

calculating bed load transport in steep boulder bed channels 1 steep rough channels occupy a large fraction of the total channel length in mountainous regions most sediment mobilized on hillslopes must pass through these streams before reaching lower gradient channels steep channels have wide grain size distributions that are composed of finer more mobile sediment and large rarely mobile grains the large grains can bear a significant portion of the total shear stress and thereby reduce the stress available to move the finer sediment conventional bed load transport equations often overpredict the sediment flux in steep channels by several orders of magnitude we hypothesize that sediment transport equations overpredict the sediment flux because they do not 1 account for the stress borne by rarely mobile grains 2 differentiate between highly and rarely mobile sediment and 3 account for the limited availability of mobile sediment here we modify a conventional bed load transport equation to include these three effects we use measurements of the flow bed properties and sediment flux in a small steep flume to test this equation we supply gravel at a constant rate through fields of regularly spaced immobile spheres and measure the bed coverage by gravel and sphere protrusion the percent of the sphere that protrudes above the gravel deposit for a given sphere spacing the proportion of the bed covered by gravel increases and the sphere protrusion decreases with greater sediment supply thus bed coverage and immobile grain protrusion may serve as proxies for sediment availability in steep rough streams unlike most transport equations that we tested our modified bed load equation predicts sediment fluxes to within an order of magnitude of the measured values our results demonstrate that accurately predicting bed load transport in steep rough streams may require accounting for the effects of local sediment availability coverage by mobile sediment and drag due to rarely mobile particles

geochemical study on a well in the western canada basin relation of the aromatic distribution pattern to maturity of organic matter abstract thirty one rock samples from a western canada basin well have been analysed for aromatics using glass capillary gas chromatography with simultaneous flame ionization and sulfur selective flame photometric detection a uniform aromatic distribution pattern with a marked predominance of di and tricyclic aromatic hydrocarbons was observed throughout a depth interval of 3000 meters comprising cretaceous and jurassic sediments the very high relative abundance of sulfur aromatics at two narrow intervals in the triassic and mississippian is attributed to a major change in facies gradual changes with increasing depth have been observed for a series of compound ratios which had been calculated from the isomers of methyl and dimethylphenanthrene and their parent compounds these changes reflect the increasing thermal maturation of the sedimentary organic matter a methylphenanthrene index mpi has been introduced which exhibited a very good correlation with vitrinite reflectance data the mpi is the first maturity parameter which is based on a series of aromatic hydrocarbons this hydrocarbon internal maturity parameter permits the recognition and definition of maturity levels in extracts which can be compared to the maturity e g vitrinite reflectance of source rocks

estimation of the kinetics of geochemical reactions with geophysical models of sedimentary basins and applications abstract the configurational isomerisation and aromatisation reactions which affect the steroid and triterpenoid hydrocarbons present in most organic rich sedimentary rocks are good indicators of the thermal histories of these rocks the extents to which these reactions have occurred can be assessed by gas chromatography mass spectrometry analysis of the organic extracts of the sediment samples we have assumed the reactions can be described as first order and used the model of sedimentary basin formation by extension of the lithosphere to provide thermal histories for the integration of the relevant arrhenius and rate equations governing the reaction rates the activation energies and frequency factors of the reactions were derived by comparing the reaction extents predicted by the model with geochemical observations from basins northern north sea and pannonian basin formed by lithospheric extension which have not experienced major uplift these values were then used to test the thermal consequences of the lithospheric stretching model for nova scotian continental shelf to calculate the amount of uplift and erosion experienced by lower jurassic sediments in the paris and lower saxony basins and the geographical variation in heat flow in a sedimentary basin formed by lithospheric flexure in the foreland basin of alberta in all cases the figures so calculated appear geologically reasonable and receive support from other independent techniques for their estimation the calculated activation energies of all reactions and the frequency factor for aromatisation are chemically sensible the relative values of the frequency factors for the isomerisation reactions could be expected the more sterically hindered c 20 site in a sterane has a lower frequency factor than that for isomerisation at the less hindered c 22 site in hopanes however both values are very low 0 006 and 0 016 s 1 respectively for the back reactions and imply an entropy change of 282 and 271 j mol 1 c 1 respectively the transition states are therefore much more ordered than the reactants this could be the case if catalysis was important no significant variation in catalytic activity can yet be demonstrated in the rocks investigated here

secondary alteration of ancient shuntuoguole oil reservoirs tarim basin nw china abstract multiple tectonic movements and charge episodes have occurred in the tazhong uplift of the tarim basin nw china contributing to widespread solid bitumen heavy oil normal oil condensate and gas in the shuntuoguole high especially in the lower silurian kepingtage formation a detailed investigation of cores and fluid inclusions from different intervals i e s1k3 3 s1k3 1 s1k1 has been carried out using petrographic analysis gas chromatograph mass spectrometry and micro fourier transform infrared spectroscopy three hydrocarbon charge events in the kepingtage formation have been recognized associated with the late caledonian late hercynian and himalayan orogenies in the late caledonian oils were charged into the s1k3 3 s1k3 1 and s1k1 intervals but evolved to solid bitumen due to biodegradation and water washing as the silurian strata have experienced both strong uplift and erosion during the early hercynian orogeny and the influence of igneous intrusions during the permian hydrocarbons associated with the caledonian contain no regular steranes diasteranes hopanes or extended tricyclic terpanes due to in reservoir thermal cracking the second charge period occurred in the late hercynian which has experienced severe biodegradation and water washing hydrocarbons of this period are characterized by an obvious chromatographic hump of the unresolved complex mixture ucm coupled with petroleum inclusions that fluoresce light blue and yellow possibly indicating variable maturity whether or not high maturity oil charged during this period into the s1k1 interval has commercial production value needs further investigation the third change occurred during the himalayan orogeny highly mature hydrocarbons were emplaced into the s1k3 3 s1k3 1 and s1k1 intervals with the s1k1 interval as being the most significant biodegradation water washing and igneous intrusion had no impact on hydrocarbons charged during this period resulting in higher potential for economic production

selective sorting and abrasion of river gravel i theory most gravel rivers show a tendency for characteristic grain size to decrease in the downstream direction over scales of tens or hundreds of kilometers it has been surmised that this downstream fining is due to some combination of selective sorting by which finer grains are preferentially transported downstream and abrasion by which individual particles are reduced in size here a framework for the simultaneous treatment of both phenomena is developed the analysis is restricted to bed load transport of gravel only abrasion due to binary collisions between moving bed load and stationary bed particles is considered the formulation includes the possibility of differential basin uplift and subsidence due to tectonism and mixtures of rock types with differing coefficients of abrasion the formulation of selective sorting is based on the concept of hiding as applied to a surface based bed load transport relation abrasion is first treated in terms of a lagrangian formulation for individual grains and t

discharge discharge variability and the bedrock channel profile long term bedrock incision is driven by daily discharge events of variable magnitude and frequency with ineffective events below an incision threshold we explore theoretically how this short term stochastic behavior controls long term steady state incision rates and bedrock channel profiles combining a realistic frequency magnitude distribution of discharge with a deterministic detachment limited incision model in which incision rate is a power function of basal shear stress above a critical shear stress our model predicts a power law relationship between steady state slope and drainage area consistent with observations the exponent of this power law is independent of discharge mean and variability while the amplitude factor which controls mountain belt relief is a power law function of mean runoff with an exponent of 0 5 and a complex function of runoff variability in accordance with evidence that incision occurs between 6 and 20 of time in rapidly incising rivers 1 mm yr our model predicts that channel steepness is virtually insensitive to runoff variability runoff variability can only decrease channel steepness for very slow incision rates and or weak lithologies the relationship between channel steepness and incision rate is always a power law whose exponent depends on the channel cross sectional geometry and runoff variability this contradicts models neglecting discharge stochasticity in which the steepness incision scaling is set by the incision law exponent our results suggest that changes in climate variability cannot explain an increase in bedrock incision rates during the late cenozoic within the context of a detachment limited model

bedload transport measurements at the erlenbach stream with geophones and automated basket samplers in the erlenbach stream a pre alpine steep channel in switzerland sediment transport has been monitored for more than 25 years near the confluence with the main valley river stream flow is monitored and sediment is collected in a retention basin with a capacity of about 2000 m3 the basin is surveyed at regular intervals and after large flood events in addition sediment transport has been continuously monitored with piezoelectric bedload impact and geophone sensors since 1986 in 2008 2009 the measuring system in the erlenbach stream was enhanced by installing an automatic system to obtain bedload samples movable metal baskets are mounted on a rail at the downstream wall of the large check dam above the retention basin and they can be moved automatically into the flow to take bedload transport samples the wire mesh of the baskets has a spacing of 10 mm to sample all sediment particles coarser than this size which is about the limiting grain size detected by the geophones the upgraded measuring system permits to obtain bedload samples over short sampling periods and to measure the grain size distribution of the transported material and its variation over time and with discharge the analysis of calibration relationships for the geophone measuring system confirms findings from very similar measurements which were performed until 1999 with piezoelectric bedload impact sensors there is a linear relationship between impulse counts and bedload mass passing over the sensors findings from flume experiments are used to discuss the most important factors which affect the calibration of the geophone signal the bedload transport rates as measured by the moving baskets are among the highest measured in natural streams with values of the order of several kilograms per meter per second copyright 2012 john wiley sons ltd

crustal structure of the flemish cap continental margin eastern canada an analysis of a seismic refraction profile summary the crustal structure of the ne flemish cap margin was determined along a 460 km long refraction wide angle reflection seismic transect flame line to define the thickness structure and composition of the crust and uppermost mantle along the line a p wave velocity model was developed from forward and inverse modelling of dense airgun shots recorded by 19 ocean bottom seismometers a coincident multichannel seismic profile was used to guide the modelling as reflections could be identified down to moho the model displays a sediment cover of up to 3 6 km thick subdivided into three layers with velocities of 1 8 1 9 km s 1 2 8 3 1 km s 1 and 4 7 4 8 km s 1 for the western part of the flame line over flemish cap the p wave velocity model displays an up to 32 km thick three layer continental crust the continental crust has velocities of 5 8 6 1 km s 1 6 3 6 45 km s 1 and 6 65 6 85 km s 1 and thicknesses of about 5 km 7 km and 20 km in the upper middle and lower layers respectively the thick continental crust thins to a two layer 6 km thick crust upper layer is 5 55 6 0 km s 1 and the layer below is 6 65 6 8 km s 1 over a distance of 45 km s wave velocities are determined in the upper layer of the thick continental crust over flemish cap and the transition zone by assigning poisson s ratios in the p wave velocity model comparison of calculated to observed arrival times gives a poisson s ratio of 0 27 in the upper layer and 0 28 in the layer below which suggests that the composition of the crust is primarily continental in both the thick crust and the thin crust of the transition zone the thin continental crust is stretched over a width of 80 km and is underlain by a layer with velocities of 7 5 7 9 km s 1 we interpret this layer as partially serpentinized mantle which is consistent with observationsfromthenewfoundlandmargintothesouth theserpentinizedmantleterminates 30 km seaward of the thick continental crust at the seaward most end of the thin continental crust a prominent ridge feature is observed the seismic refraction and multichannel seismic data results indicate a mixed character between serpentinized mantle with volcanic extrusions or continental crust the reflection seismic data show a high relief basement from the ridge feature and seaward the flame line crosses magnetic anomaly 34 and extends another 50 km seaward well into oceanic crust the ridge is flanked seaward by a two layer oceanic crust the upper layer layer 2 has velocities of 4 8 5 0 km s 1 for the landward most 35 km of oceanic crust and 4 8 6 2 km s 1 for the seaward 60 km the average thickness of layer 2 is 2 km the lower layer layer 3 has velocities of 6 7 7 2 km s 1 and a thickness of 3 5 km the velocity model is consistent with a sharp onset of seafloor spreading seaward of the ridge feature

thinned and subsided continental crust on the rifted margin of eastern canada crustal structure thermal evolution and subsidence history summary seismic refraction measurements were carried out using ocean bottom seismometers over foundered continental crust in orphan basin and flemish pass on the continental margin north east of newfoundland tau p travel time inversion synthetic seismogram analysis and conventional layered model calculations were applied to the data the results show that these outer regions of the margin are underlain by thinned continental crust with a total depth to the m discontinuity of about 22 km there are two main crustal layers with p velocities of about 6 1 and 7 0 km s 1 which appear to be homogenous and separated by sharp interfaces these are overlain by a layer in which p velocities are about 5 5 km s 1 this is interpreted to be precambrian or palaeozoic basement mesozoic and cenozoic sediments cover the basement rocks and are over 4 km thick the results imply that crustal thinning to about 50 per cent of the original crustal thickness occurred the gravity anomaly data show that the thin crust has a maximum horizontal extent of about 450 km from the ocean continent boundary near orphan knoll landward to the outer continental shelf the subsidence history and thermal evolution of the region was computed assuming that the observed thinning is produced by horizontal extension of the lithosphere it is suggested that extension can only satisfy the observed crustal structure and elevation of the margin during the rift phase if more extension took place in the lower lithosphere than in the upper lithosphere the computed subsidence is compared to the observed subsidence and the total amounts of subsidence are similar however the shape of the observed subsidence curves measured in deep exploratory wells differs significantly from the predicted subsidence assuming cooling began when final continental breakup occurred in the late cretaceous the temperature distribution within the lithosphere due to extension may be related to the flexural rigidity of the plate as a function of both time and position across the margin therefore it is suggested that the response of the lithosphere to sediment loading and the large amplitude of the gravity shelf edge anomalies are directly related to the thermal history of the region

comparison of lithosphere structure across the orphan basin flemish cap and irish atlantic conjugate continental margins from constrained 3d gravity inversions regionally constrained 3d gravity inversion results on the orphan basin flemish cap and the irish atlantic conjugate continental margins are compared to investigate crustal structure early rifting history and geological evolution of this part of the north atlantic the full crustal density anomaly distributions provide some of the first depth images of how rifted structures compare along and across these conjugate margins broad similarities in crustal structure are identified with some noticeable differences linked to rifting and crustal stretching processes extreme crustal thinning stretching factors 3 5 is indicated beneath much of the southern porcupine basin the western half of west orphan basin the eastern half of jeanne d arc basin the southeastern half of east orphan basin and in pockets beneath rockall basin this appears to have resulted in the serpentinization and possible exhumation of mantle lithosphere on the irish atlantic and flemish cap margins but not beneath orphan basin a simple evolution model is proposed for the early stages of rifting between the margins it is suggested that ancient orogenic sutures played an important role in controlling the northward migration of rifting and the rotation and displacement of flemish cap out of orphan basin supplementary material enlarged maps from this paper are available at www geolsoc org uk sup18527

bedload transport measurements with impact plate geophones comparison of sensor calibration in different gravel bed streams indirect bedload transport measurements have been made with the swiss plate geophone system in five gravel bed mountain streams these geophone sensors record the motion of bedload particles transported over a steel plate mounted flush with the channel bed to calibrate the geophone system direct bedload transport measurements were undertaken simultaneously at the erlenbach in switzerland a moving basket sampler was used at the fischbach and ruetz streams in austria a helley smith type bedload sampler provided the calibration measurements a bunte type bedload trap was used at the rofenache stream in austria at the nahal eshtemoa in israel reid type slot bedload samplers were used to characterize the response of the geophone signal to bedload particles impacting on the plate geophone summary values were calculated from the raw signal and stored at one second intervals the number of impulses i e the number of peaks above a pre defined threshold value of the geophone output signal correlated well with field measured gravel transport loads and was found to be a robust parameter the relations of impulses to gravel transport loads were generally near linear but the steepness of the calibration relations differed from site to site by comparing the calibration measurements from the different field sites and utilizing insights gained during preliminary flume experiments it has been possible to identify the main factors that are responsible for site specific differences in the calibration coefficient the analysis of these calibration measurements indicates that the geophone signal also contains some information about the grain size distribution of bedload copyright 2013 john wiley sons ltd

the impact of exceptional events on erosion bedload transport and channel stability in a step pool channel sediment transport in the erlenbach a small stream with step pool morphology in the canton of schwyz switzerland has been monitored for more than 20 years during this time three exceptional events events with high sediment yield and long return times that have a large effect on channel morphology have impacted the stream and partly or completely rearranged the existing step pool morphology in the aftermath of the events sediment transport rates at a given discharge and total sediment yield remained elevated for about a year or longer for the last event dated on the 20 june 2007 observations of boulder mobility and step destruction were used to interpret channel stability boulders with median diameters of up to 135 cm and estimated weights of more than 2 5 tons have moved during the 2007 event using hydraulic observations and shear stress calculations boulders up to 65 cm in diameter were predicted to have been fully mobile in peak conditions even if form resistance and increased critical stresses needed for the initiation of motion in steep streams were taken into account for two of the events estimated peak shear stresses at the bed exceeded 1000 pa calculated both from observations of the flow hydraulics and from boulder mobility this suggests that highly energetic flows occur relatively frequently in small steep streams and that large boulders can be transported by fluvial processes in such streams the observations have potential significance for hazard risk mitigation stream engineering and restoration copyright 2009 john wiley sons ltd

gravity inversion of basement relief using approximate equality constraints on depths we present a gravity interpretation method for estimating the relief of an arbitrary interface separating two homogeneous media the upper medium is discretized into rectangular juxtaposed prisms whose thicknesses represent the depths to the interface and are the parameters to be estimated from the gravity anomaly the density contrast of each prism is assumed to be constant and known to stabilize the inversion we introduce two kinds of constraints on the depths the first one requires proximity between the observed and computed depths at isolated points such as those obtained from boreholes absolute equality constraint the second one requires that groups of depths approximately follow an established linear relationship among the depths relative equality constraint both kinds of constraints are imposed in the least squares sense we illustrate the method performance by applying it to a synthetic anomaly produced by a simulated basement relief consisting of four narrow and adjacent structural lows

when does bedload transport begin in steep boulder bed streams the paper presents the results of field measurements of critical conditions for bedload motion conducted in the rio cordon a steep boulder bed stream in the italian alps under conditions of high reynolds numbers and low relative submergence poorly explored before two methods have been used to determine threshold of motion the displacement of marked clasts and the flow competence approach which uses the largest grain size diameter transported by each flood event the high values of confirm the great relevance of non bedload effective shear stresses in step pool streams given by the additional form drag associated with this morphology relative submergence effects on the dimensionless critical shear stress have been quantified by considering the relative submergence ratio rh d84 and the major effect of relative size on the mobility of each particle in steep widely graded bed mixtures has been evaluated finally the dimensionless critical unit discharge has also been adopted in the regression equations as the critical hydraulic parameter because it may represent an easier parameter to use than the critical shear stress for steep rough mountain rivers copyright 2006 john wiley sons ltd

morphology of the basement and hormuz salt distribution in offshore abu dhabi from constrained 3 d inversion of gravity and magnetic data abstract many seismic surveys and exploration wells have been conducted in offshore abu dhabi united arab emirates however the neoproterozoic basement and the infracambrian hormuz salts were not imaged or penetrated by seismic and well data to delineate the morphology of the basement and distribution of salt bodies we applied a 3 d constrained inversion method to aerogravity and aeromagnetic data covering offshore abu dhabi well and seismic data were used to constrain and validate the inversion results the magnetic inversion model resulted in a robust basement model that varies in depth from 8 to 10 km with two highs at 8 and 8 5 km highlighting possibly magmatic bodies in contrast the gravity inversion model does not delineate very well the basement morphology possibly due to the lower density salt bodies masking the gravity response of the higher density basement by calculating and removing the gravity response of the magnetic basement model from the observed gravity data we recovered the residual gravity response of the hormuz salts the 3 d gravity inversion of the residual shows that the hormuz salts are more wide spread and thicker than previously thought with a depth to top of salt varying from 5 5 to 8 5 km this salt model suggests that the giant oilfields in offshore abu dhabi such as umm shaif nasr abu al bukhoosh zakum sarb and hail occur exactly above crests of salt pillows in addition a series of smaller oilfields are found located at the margin of the northern basement high and three structural lineament trends ne sw nw se and n s were identified from the inverted basement and salt models reactivation of these fault trends and associated diapiric salt uplifts as observed in the seismic sections and curvature map played a major role in shaping the basement morphology and mobilization of the hormuz salts

field instrumentation for high resolution parallel monitoring of bedrock erosion and bedload transport river incision is fundamental in shaping the earth s surface in mountainous regions with steep river beds fluvial bedrock erosion by bedload transport is an important mechanism forming channels however there are only a few complete field datasets that can be used to improve process understanding and evaluate erosion models especially at the process scale to provide a simultaneous dataset of hydraulics bedload transport and bedrock erosion at high temporal and spatial resolution a new measuring device has been installed in the erlenbach a gauged stream in the swiss pre alps in this stream bedload transport rates can be calculated from surveying deposits and from geophone plate sensors and bedload transport samples can be taken directly by an automated moving basket system to measure bedrock erosion rates simultaneously two natural stone slabs were mounted flush with the channel bed in a steel frame hosting various measurement devices force sensors below the slabs record normal stress and shear stress at a point erosion rates on the slab surfaces are continuously measured at sub millimetre precision at three locations on each slab in addition the slab topography is monitored following erosive flood events in this article i the erosion scale device is described ii data resolution and data quality is assessed by means of tests and event data and iii the first transport event is discussed the erosion scales are confirmed to provide data at high spatio temporal resolution for process analysis the preliminary data show evidence for the tools effect in bedrock erosion the bedrock slabs can be exchanged to obtain measurements for catchments with different lithologies for comparison copyright 2014 john wiley sons ltd

organic geochemical study of the w oil gas field in the yugoslav part of the pannonian basin the naphthenic crude oil from the w oil gas field differs from almost all other paraffinic base oils discovered until now in the yugoslav part of the pannonian basin in order to explain this difference some geological and organic geochemical investigations were carried out on the basis of the bulk and biomarker parameters determined in oil samples taken from 13 producing wells located at different parts of the field it is concluded that the crude oil throughout the field has an almost uniform composition however some differences in alkane content due to biodegradation and or water washing were found in the northeast part of the field where a tilted oil water layers shows an active hydrodynamism and where the temperatures are the lowest and pressure gradients the highest the isoprenoids pristane and phytane were detected in trace amounts indicating the most intensive biodegradation in the central part where a hydrocarbon accumulation exists in a miocene reservoir somewhat lower biodegradation was observed the crude oil from this field has probably a mixed terrestrial marine origin and is derived from argillaceous source rocks sedimented in marine delta or brackish lakes specific maturation parameters confirmed that the w crude oil has reached a quite uniform and significant thermal maturation considering maturation parameters such as ratios c30 moretane hopane and c29 20s 20s 20r steranes as well as the presence of oleanane it could be proposed that the w oil originates from a pre tertiary source rock at least an upper cretaceous one unlike most pannonian basin oils which are tertiary in age

an organic geochemical study of cenomanian turonian sediments from the western interior seaway canada abstract bulk geochemical and biomarker data were collected for three cenomanian turonian late cretaceous sections in the western canada sedimentary basin western interior seaway canada rock eval and biomarker analyses indicate an east west thermal maturity trend due to progressive deeper burial associated with the tectonic flexure of the foreland basin the source of extractable organic matter is dominantly marine with a minor terrestrial contribution a pseudohomologous family of 2 2 dimethylalkanes 2 2 dmas in the c 16 c 28 range with an even number of carbon atoms exclusively was tentatively identified from mass spectral data in samples from the pasquia hills region easternmost section the specific origin of 2 2 dimethylalkanes remains unclear the presence of isorenieratene derivatives indicates that the northern part of the western interior seaway experienced photic zone euxinic events throughout the transgressive highstand and regressive phases of the greenhorn cycle the differential occurrence of isorenieratane between the canadian sections and the united states transect at maximum sea level high stand indicates that the water column of the northern part of the wis was less oxygenated whereas the water column in the southern wis was more dynamic and well mixed

effects of source thermal maturity and biodegradation on the distribution and isomerization of homohopanes in petroleum abstract the distributions of c31 c35 17 21 h homohopanes in marine petroleums can be used to describe redox conditions in the source rock depositional environment for example high c35 homohopane indices c35 c31 c35 are typical of petroleums generated from source rocks deposited under anoxic marine conditions where the c35 backbone of the precursor bacteriohopanetetrol is preferentially preserved homohopane distributions have been used to distinguish petroleums from different organic facies of the same source rock homohopane distributions are altered by secondary processes for example the c35 homohopane index decreases with increasing api gravity and thermal maturity of related oils from the monterey formation offshore california similar decreases in the homohopane index are observed for expelled oils from monterey source rock during hydrous pyrolysis biodegradation can result in selective loss of high or low molecular weight homologs apparently depending on the bacterial population in the reservoir bacterial demethylation of homohopanes appears necessary to explain 25 norhopanes in at least one biodegraded oil hydrous pyrolysis studies of the phosphatic and siliceous members in the monterey formation show that identical heating conditions result in different homohopane c 22 epimer ratios furthermore a reversal in the trend of the epimer ratio at high experimental temperatures is observed for the phosphatic but not for the siliceous lithology this could be caused by the combined effects of isomerization and differential thermal destruction of epimers at high temperatures possibly mediated by rock mineralogy

experimental evidence for fluvial bedrock incision by suspended and bedload sediment fluvial bedrock incision sets the pace of landscape evolution and can be dominated by abrasion from impacting particles existing bedrock incision models diverge on the ability of sediment to erode within the suspension regime leading to competing predictions of lowland river erosion rates knickpoint formation and evolution and the transient response of orogens to external forcing we present controlled abrasion mill experiments designed to test fluvial incision models in the bedload and suspension regimes by varying sediment size while holding fixed hydraulics sediment load and substrate strength measurable erosion occurred within the suspension regime and erosion rates agree with a mechanistic incision theory for erosion by mixed suspended and bedload sediment our experimental results indicate that suspension regime erosion can dominate channel incision during large floods and in steep channels with significant implications for the pace of landscape evolution

grain size effects on energy delivery to the streambed and links to bedrock erosion fluvial bedrock erosion rates are thought to be proportional to the energy delivered to the channel bed by impacting bed load particles combining methods for field measurements of impact energy and for automatic sensing of grain size distributions in the instrumented channel of the erlenbach we show that the larger a bed load grain is the more efficient it is in transferring energy to the streambed on average the largest grain size class contributes only 9 to the total bed load mass but is responsible for more than 40 of the energy delivery this effect may help to explain the predominance of extreme floods when large grains are mobile in driving long term erosion while the mechanistic saltation abrasion model accounts for hydraulic forcing of energy delivery the observed grain size effect is not captured we suggest that the discrepancy arises from differing transport modes rolling sliding and saltation not currently captured in modeling

large floods alluvial overprint and bedrock erosion depending on their behaviour during extreme floods streams can be divided into two distinct classes which derive from a simple threshold model of transport dynamics flood cleaning streams erode during high flows and deposit during small and medium flows flood depositing streams deposit during high flows and erode during small and medium flows using published descriptions of the geomorphic effects of large floods rivers with a wide range of drainage areas and other characteristics are classified as either flood cleaning or flood depositing in bedrock channels this behaviour can lead to a feedback effect the overprint effect between sediment transport processes and bedrock erosion which can modulate long term bedrock erosion rates the overprint effect arises when alluvium covers the bedrock and typical alluvial channel forms e g meandering or braiding patterns armour layers or bedforms develop which influence sediment transport rates this effect may accelerate or decelerate sediment export from a reach causing increased or decreased long term bedrock erosion rates the overprint effect is illustrated using field data from the erlenbach switzerland and its implications for channel dynamics and bedrock erosion are discussed copyright 2012 john wiley sons ltd

crustal structure of the newfoundland rifted continental margin from constrained 3 d gravity inversion the rifting history of the atlantic continental margin of newfoundland is very complex and so far has been investigated at the crustal scale primarily with the use of 2 d seismic surveys while informative the results generated from these surveys cannot easily be interpreted in a regional sense due to their sparse sampling of the margin a 3 d gravity inversion of the free air data over the newfoundland margin allows us to generate a 3 d density anomaly model that can be compared with the seismic results and used to gain insight into regions lacking seismic coverage results of the gravity inversion show good correspondence with moho depths from seismic results a shallowing of the moho to 12 km depth is resolved on the shelf at the northern edge of the grand banks in a region poorly sampled by other methods comparisons between sediment thickness and crustal thickness show deviations from local isostatic compensation in locations which correlate with faults and rifting trends such insights must act as constraints for future palaeoreconstructions of north atlantic rifting