factors controlling the burial of organic carbon in laminated and bioturbated sediments off nw mexico implications for hydrocarbon preservation factors controlling the burial of organic carbon oc in late quaternary sediments on the nw mexican continental margin are assessed using a suite of box and piston cores strategically located on the shelf slope rise with respect to the intense oxygen minimum in this region an oc concentration maximum occurs on the mid slope below the core of an intense water column o2 minimum due to current winnowing on the outer shelf the preferential accumulation of organic matter in fine grained deposits and the offshore decrease in the settling flux of organic detritus the organic matter at all water depths is overwhelmingly marine hydrogen indices hi are higher on the slope 300 mg hc g toc than on the shelf 300 mg hc g toc where current winnowing has promoted organic matter degradation but there is no difference in hi in slope sediments accumulating under well oxygenated and o2 deficient conditions the degree of winnowing appears to be the primary factor affecting the preservational quality of organic matter deposited on this margin rates of accumulation of oc and opal are all higher in the interglacial intervals when compared with the glacial deposits over the last 140 000 yr however matrix corrected hi values in the mid and lower slope cores are invariant and are similar to values in the laminated intervals from the oxygen minimum site thus cyclic changes in organic carbon accumulation on this margin have been controlled by production variations rather than differential preservation hi values in late quaternary sediments from several continental margins including nw mexico and euxinic basins correspond to type ii kerogen irrespective of bottom water o2 concentrations therefore the preservation of oil prone kerogen in productive margin settings does not appear to be restricted to sediments deposited under conditions of low bottom water o2 concentrations as envisioned in models of petroleum source rock deposition

devonian to carboniferous tectonic evolution of the kangguer ocean in the eastern tianshan nw china insights from three episodes of granitoids abstract deciphering the tectonic evolution of the kangguer ocean is critical to understand the architecture of the eastern tianshan nw china previous studies for the kangguer ocean mainly concentrated on final closure during the latest carboniferous to permian three distinct episodes of granitoids have been recognized in the kangguer belt late devonian ca 360 ma normal i type granites early carboniferous ca 348 ma fractionated i type granites and late carboniferous ca 317 302 ma adakitic granites attempting to provide constraints on the sources of these rocks which further unravels the evolution of the kangguer ocean during this period the late devonian granites exhibit calc alkaline characteristics with negligible eu anomalies and low k2o na2o cao ratios akin to i type granites without significant fractional crystallization they display high sio2 70 wt with low mgo

lithological and geochemical constraints on the magma conduit systems of the huangshan ni cu sulfide deposit nw china magmatic ni cu sulfide deposits in northern xinjiang china are associated with small mafic ultramafic complexes with the sulfide ores generally occurring in ultramafic rocks the huangshan deposit up to 65 mt of ore at 0 49 ni and 0 31 cu one of the largest magmatic ni cu deposits in northern xinjiang is composed of a layered sequence of lower websterite lower lherzolite websterite norite gabbro gabbro diorite and gabbronorite with sulfide mineralization mainly found in the lower lherzolite lower websterite and websterite systematic variations of the major oxides and trace elements suggest that the rocks of the huangshan deposit are fractionated from the same parental magma with the sharp contact and discontinuous trends of major oxide contents between different lithologies implying intrusion of four distinct stages of magma from a single deep seated staging chamber the reversals in olivine fo contents and major oxides in the lower lherzolite were the result of inhomogeneity in olivine within the lower chamber the se s ratios 63 1 150 10 6 and the negative correlation between se s and 34s 0 63 2 42 of the sulfide ores suggest that a large contribution of crustal s caused the sulfide segregation the sulfides in the lower lherzolite have lower cu contents 1386 2200 ppm and cu pd ratios 2 31 105 1 36 106 relative to those in the mineralized lower websterite cu 2300 to 18 700 ppm and cu pd 6 65 105 to 2 73 106 a positive correlation between pd ir and ni ir for the vein textured sulfides in the lower websterite likely reflects fractionated sulfides picked up by a new pulse of magma in contrast the restricted range of pd ir ratios indicates that the pge contents of the disseminated sulfides in the lower lherzolite resulted from reaction between the sulfides and new pulses of s undersaturated magma

the geotechnical properties of some till deposits occurring along the coastal areas of eastern england abstract deposits of till are found along the coastal areas of eastern england from northumberland to east anglia the geotechnical properties of tills from three areas namely north norfolk holderness and teesside have been investigated the dominant clay minerals in the fine fraction of the tills are kaolinite and illite as would be expected quartz is the other dominant mineral in the fine fraction of the tills deposits of till occur in the anglian and devensian stages of the quaternary succession in norfolk all these tills are matrix dominated with clay generally forming less than a third of the matrix they are either firm or stiff with low or intermediate plasticity and have relatively low values of shear strength the tills are either inactive or have normal activity and all have low sensitivity their consolidation properties are characteristic of stiff clays the glacial deposits of holderness consist primarily of tills except for the oldest of these tills which is wolstonian the others are of devensian age the fine fraction usually constitutes up to 60 80 of the deposits these clays have a low plasticity the tills of holderness have a low sensitivity and a relatively low unconfined shear strength their values of shear strength are reduced from peak values to residual values primarily by a reduction in the cohesion parameter like the tills from the other two areas the pore water pressures on testing in consolidated undrained conditions rose rapidly to a peak which was followed by a gradual falling off as failure was approached the glacial deposits of the teesside area are of late devensian age these lodgement tills were products of successive ice sheets the tills are thickest in the north and west of the area and are characteristically unsorted and matrix dominated they are of low to intermediate plasticity and vary in consistency from firm to hard generally being stiff to very stiff the results of triaxial tests indicate a reasonably wide range of strength

correlation of reservoired gases using the carbon isotopic compositions of wet gas components the carbon isotopic compositions of the wet gas components particularly propane isobutane and normal butane have been found to be particularly valuable for correlating one reservoired gas with another the usefulness of these components for correlation results from their carbon isotopic compositions reflecting both the nature of their source and their maturity this source control is strongest for gases derived from the more highly structured types of kerogen i e woody coaly type iii although the wet gas components carbon isotopic compositions of most gases are at least partly controlled by their source for levels of maturity below the point at which thermal destruction of the wet components occurs as a result the wet gas components are found to provide more ositive correlations than is methane alone three exploration examples illustrate the use of the carbon isotopic compositions of the wet gas components for correlation the leduc reef trend of alberta canada the sleipner area in the north sea and the lena field offshore louisiana united states the three examples also illustrate the need to integrate geochemical interpretations with regional geology to obtain a good understanding of the hydrocarbon source

source rock maturation characteristics of symmetric and asymmetric grabens inferred from integrated analogue and numerical modeling the southern viking graben north sea abstract we present the results of an integrated analogue and numerical modeling study with a focus on structural stratigraphic and thermal differences between symmetric and asymmetric grabens these models enable fault interpretation and subsidence analyses in studies of active rifting and graben migration we imported the surface topography and crustal thinning factors from the analogue models into tectono stratigraphic forward models which allowed an assessment of the relative importance of sediment stacking in the generation of symmetric and asymmetric grabens effects on source rock maturation zones were calculated through 1d thermal modeling for different graben types combined analogue numerical modeling appears to be a useful method to simulate natural examples as shown in this study of the southern viking graben in the northern north sea this area was formed by early permian late jurassic extension with rifting most intense during the late jurassic the thermal structure of the model constrained by lithospheric and sedimentary parameters for this region compares well with actual source rock maturation data on the southern viking graben

physical characteristics of subglacial tills a regional database of the physical properties of glacial tills has been interrogated to produce characteristic design values and baseline construction values glacioterrestrial glacial till one of the most distributed deposits in the world is typically a heterogeneous mixture of clays silts sands gravels and cobbles which can contain remnants of earlier till including glaciolacustrine and fluvioglacial deposits that have been gravitationally compacted and sheared this results in a complex deposit which is spatially variable both in composition and fabric to the extent that the selection of design profiles is challenging a study of the intrinsic properties of the tills in the north east of england together with a statistical analysis has led to the identification of two distinctly different heavily overconsolidated tills that have profiles of strength water content and density that lead to characteristic values based on the regional database and baseline values based on the local database that

lack of evidence for enhanced preservation of sedimentary organic matter in the oxygen minimum of the gulf of california a test of the hypothesis that hydrogen rich organic matter accumulates preferentially in sediments under oxygen minima has been carried out by examining the composition of laminated and homogeneous diatomaceous sediments of the guaymas basin in the gulf of california the laminated sediments occur where an intense oxygen minimum intersects the slope around the margins of the basin above and below the depth of the oxygen minimum the sediments are homogenized by a burrowing infauna the two sediment types have very similar bulk chemical and mineral compositions and the organic matter is overwhelmingly marine the total organic carbon contents and rock eval parameters hydrogen and oxygen indices of the two sediment types are not significantly different whereas a road organic carbon maximum in the homogeneous sediments is centered at roughly 1200 m depth on the slope of the basin this maximum lies deeper than the core of the oxygen minimum thus both the concentration and the nature of the organic matter in the sediments of this highly productive marginal marine basin are not related to the concentration of dissolved oxygen in the bottom waters

major types characteristics and geodynamic mechanism of upper paleozoic copper deposits in northern xinjiang northwestern china abstract syn and post orogenic cu mineralization in the northern xinjiang paleozoic accretionary and collisional orogenic belt in northwestern china is of great economic interest about 40 cu bearing deposits have been discovered in the area making it one of the most important metallogenic belts in china according to their host rocks these deposits can be classified into four principal types 1 volcanic hosted massive sulfide cu pb zn deposits 2 porphyry cu mo au deposits 3 magmatic cu ni sulfide deposits and 4 cu mo au ag skarn deposits tectonically the development of these upper paleozoic deposits was closely associated with subduction and collision of the ancient asian ocean between the siberian block and the tarim craton an important metallogenic epoch involving formation of cu pb zn polymetallic deposits formed during southwestern rollback and associated slab detachment during devonian time 400 370 ma in southern altay southwestern direct rollback and associated slab detachment occurred during the devonian 400 370 ma in response to later collision at the accreted continetal margin xiao w j windley b f badarch g sun s li j l qin k z wang z h 2004 palaeozoic accretionary and convergent tectonics of the southern altaids implications for the lateral growth of central asia journal of the geological society of london 161 339 342 during which the ashele cu pb zn and keketale pb zn deposits formed subduction led to the accretion of the junggar ocean arc system in the middle devonian in the lower to middle carboniferous north dipping subduction beneath the dananhu arc triggered the emplacement of granitic porphyries in the tousuquan and dananhu island arc belt in the east tianshan leading to the formation of the tuwu and yandong porphyry cu mo au ag deposits in the upper carboniferous to lower permian large mafic ultramafic complexes were emplaced during closure of the ancient tianshan ocean resulting in the formation of several magmatic cu ni sulfide deposits including the kalatongke cu ni deposits in north junggar and cu ni sulfide deposits in the huangshan jing erquan area of east tianshan mountains also associated with this extensional event were emplacement of voluminous anatectic granitoids and eruption of volcanic rocks which led to formation of skarn cu mo suoerkuduk cu mo deposit and cu ag deposits weiquan cu ag deposit the tectonic settings geological features and temporal and spatial distribution of these different types of cu deposits reflect to a great extent the accretionary and collisional tectonics that occurred between the siberian block and tarim block

final amalgamation of the tianshan and junggar orogenic collage in the southwestern central asian orogenic belt constraints on the closure of the paleo asian ocean abstract the tianshan and junggar orogenic collage occupies the southwestern part of the central asian orogenic belt and was assembled by collision accretion of several continental blocks and island arcs during late paleozoic early mesozoic time following the consumption of the junggar and south tianshan oceanic basins in the western segment of the paleo asian ocean considerable and continuing controversy has surrounded when where and how this orogenic collage was eventually amalgamated which plays a crucial role in understanding the formation of the central asian orogenic belt this review synthesizes the most recent data and geologic evidence that place critical constraints on the closure history of the oceanic domains a comprehensive data compilation indicates that the formation of ophiolites along major sutures in the tianshan and junggar region lasted to the early carboniferous for the kalamaili suture zone to the mid carboniferous for the west junggar region and the north tianshan suture zone and to the late carboniferous for the south tianshan suture zone ca 325 310 ma ultra high pressure metamorphism along the western part of the south tianshan suture occurred nearly synchronously with the collision between the tarim craton and the central tianshan yili block the oceanic closure and collision events were sequentially followed by widespread and intensive a type granitic and bimodal magmatism which commenced in the mid carboniferous along the kalamaili belt and in the latest carboniferous to earliest permian in other regions contemporaneously large scale strike slip shearing took place along major faults subparallel to main sutures with a dominant dextral sense and deformation time since the carboniferous permian transition available data and geological evidence support an eastward propagating scissor like closure of the western segment of the paleo asian ocean along the south tianshan and north tianshan suture zones over a period from the mid to end carboniferous with the south tianshan belt representing the final suturing site in the early permian the tarim mantle plume likely merely affected the southwestern part of the assembled tarim and tianshan region as indicated by regional discrepancy in type and geochemistry of early permian a type granitoids the amalgamation of the tianshan and junggar orogenic collage was associated with the tectonic bending of the kazakhstan orocline leaving a piece of trapped oceanic crust in its middle part beneath the present junggar basin

identifying the behavioural characteristics of clay cliffs using intensive monitoring and geotechnical numerical modelling abstract coastal monitoring is routinely undertaken to provide an archival record of cliff line movement that can be used in the development and validation of predictive coast retreat and evolution models however coastal monitoring is often purely quantitative in nature and financial necessity requires deployment over extensive coastal sections as a result for local site conditions in particular only limited geomorphological data are available or included during the development of such predictive models this has resulted in many current models incorporating a simplistic or generalised representation of cliff behaviour an approach that progressively loses local credibility when deployed over extensive heterogeneous coastlines this study addresses this situation at a site of extreme coastline retreat holderness uk through the application of intensive monitoring of six representative cliff sections nested within a general geomorphological appraisal of the wider coastline as a whole the data from these surveys have been used to validate a finite difference based geotechnical modelling assessment of clay cliff stability once validated the geotechnical model was used to simulate a range of scenarios that were sufficient to represent the range of topographic hydrogeological geological and littoral conditions exhibited throughout the region our assessment identified that the cliff retreat occurs through the combined influence of direct marine erosion of the cliff with shallow structurally controlled failures or substantial mass failures critically the predisposition to any one of these failure mechanisms arises principally as a result of initial cliff height the results of the numerical modelling have been combined into an empirical slope model that derives the rate of landslide induced retreat that would arise from mass failures under various future scenarios results of this study can be used in the selection and development of retreat models at coastlines of similar physiographic setting to that found at holderness the results represent a key step in linking material deformation properties to the processes of cliff change and the subsequent range of landforms found on clay cliffs as such the results could also be used more generally to illustrate the likely cliff behaviour of other soft rock coastlines

microbial alteration of subsurface natural gas accumulations bacterial alteration of subsurface reservoired hydrocarbon accumulations extends into the range of the c1 c4 gaseous hydrocarbons preferentially attacking the wet gas components in most instances during the initial stages of bacterial gas alteration propane seems to be selectively attacked resulting in anomalous propane carbon isotopic compositions as well as unusual carbon isotopic distributions among the wet gas components extensive bacterial alteration appears to be capable of removing all but traces of the wet gas components resulting in a dry gas that could be confused with overmature dry gas whose wet components have undergone extensive thermal cracking recognition of microbial alteration in subsurface reservoired hydrocarbon gas accumul tions is important for both correlation purposes and maturity estimates

geothermal history and petroleum generation in the norwegian south viking graben revealed by pseudo 3d basin modelling abstract hydrocarbon exploration in the norwegian south viking graben 57 45 60 15 n began in the late 1960s and has now entered a mature phase a map based pseudo three dimensional 3d basin modelling study is performed in order to unravel regional trends in hydrocarbon generation and expulsion and to evaluate the remaining potential of this mature petroleum province generation and expulsion from all major source rock horizons in the area the draupne heather hugin and sleipner formations is simulated using a pseudo 3d model comprising 36 isochronous geological events the map based pseudo 3d model is built from 1d models combined with subsurface and source rock quality maps hydrocarbon expulsion from the middle and upper jurassic source rocks in the area occurred in two major phases the first phase lasted from palaeocene to middle miocene with peak oil and gas expulsion during the early miocene the second quaternary phase of expulsion which supplied 11 and 13 of all oil and gas respectively is related to increased subsidence rates during this period a total of 74 109 sm3 oil and 8 2 1012 sm3 gas has been expelled in the area the frigg area in the north is with 2 9 1012 sm3 gas expelled the most gas prone area and the greater balder area seems to be the most oil prone area with 17 109 sm3 oil expelled the lower syn rift section of the upper jurassic draupne formation dominated oil expulsion 54 of all expelled oil whilst the heather formation dominated gas expulsion with 37 of all gas expelled model predictions were successfully applied to explain the fill and secondary alteration history of the greater balder area norway the modelling supports the draupne formation origin of the oils in the greater balder area as well as the presence of oils deriving from multiple charge phases found in correlation studies based on the modelled cumulative volumes expelled and estimates for in place volumes in the area generation accumulation efficiencies gaes of 1 01 1 05 for oil and 9 67 12 89 for gas have been estimated for the south viking graben in light of comparisons with other petroleum systems and critical evaluation of the elements of the petroleum systems the estimated gaes should be regarded as encouraging for further exploration of the area

petrogenesis and mineralization potential of a granite porphyry intrusion beneath the baishan mo deposit eastern tianshan nw china abstract the baishan molybdenum deposit is located in the eastern section of the jueluotage tectonic belt eastern tianshan there is a granite porphyry intrusion beneath the baishan mo ore bodies discovered by recent exploration drilling and the cu mo minerals are widely distributed in the porphyry the zircon la icpms u pb age of the granite porphyry intrusion is 228 1 8 0 ma which is in coincidence with the age of mo mineralization 227 7 4 3 ma the granite porphyry intrusion is calc alkaline and peraluminous the magma was derived from a lower crustal source it experienced distinct crystal fraction during its evolution and the magma intruded in a triassic compressional background and was probably influenced by far field effects of the tethys system to the south based on the geological geochemical and geochronological characteristics of the granite porphyry intrusion we propose that there is probably a porphyry cu deposit beneath the baishan high re mo deposit

hydrocarbon filling and leakage history of a deep geopressured sandstone fulmar formation united kingdom north sea diagenetic minerals in a water filled borehole from the jurassic fulmar formation united kingdom central north sea record two phases of hydrocarbon filling and emptying initial oil charge was during the late cretaceous at shallow burial depths of about 1 5 km 0 9 mi as we consider that hydrocarbon has preserved porosity during burial this has implications for the understanding of the porosity evolution of the fulmar formation which in other locations is an important hydrocarbon reservoir the early oil charge as recorded by illite k ar ages progressively filled the structure from 84 to 59 ma and possibly precipitated bitumen because of biodegradation the first oil predated many of the burial diagenetic reactions within the sandstone after leak off at ca 60 ma diagenetic reactions continued in an open geochemical system with possible import of co2 products of these reactions include ankerite and quartz overgrowth cements hydrocarbon staining postdates these phases and provides evidence of a hydrocarbon charge probably gas condensate the second hydrocarbon charge also leaked off and the sandstone is now water bearing previous work on the fulmar formation has incorrectly placed all the diagenetic reactions as predating the first arrival of hydrocarbon the present day pore fluids are high salinity high 18o fluids derived from the underlying permian zechstein evaporates these fluids entered the reservoir during a phase of overpressure release that caused fracturing of the framework quartz grains possibly coincident with the second phase of hydrocarbon leak off at 2 5 ma mark wilkinson studied sandstone hosted calcite concretions for his ph d and has subsequently tried to take a more holistic view of the diagenesis of sedimentary basins his career has been funded by a variety of oil companies although he is currently involved in geological disposal of some of the co2 that he was partly responsible for producing stuart haszeldine is a professor at edinburgh university he received his ph d on clastic and coal sedimentology in 1981 from the university of strathclyde after an attempted reeducation in the oil industry he has collaborated with many companies to research on hydrocarbon reservoir quality radioactive waste disposal and coal resources he currently heads the united kingdom s largest group investigating carbon dioxide sequestration tony fallick was educated at the university of glasgow scotland in physics b sc and chemistry ph d he did research at mcmaster university ontario canada and cambridge england before moving in 1980 to the scottish universities research and reactor center where he is currently the director

a review of the western part of the altaids a key to understanding the architecture of accretionary orogens abstract the altaids is one of the largest accretionary collages in the world and the tectonic styles of the accretionary processes have been interpreted in several ways including as an amalgamation of multiple terranes as a result of oroclinal bending of a long single arc or as a caledonian continental collision based on recent tectonostratigraphic analyses together with paleomagnetic data the tectonic styles of the neoproterozoic to paleozoic accretionary processes of the altaids are discussed the western altaids is the main focus of the study which was mainly composed of several independent linear components such as arcs and microcontinents with proterozoic basement and cover rocks various kinds of arcs existed in the paleo asian ocean including a complicated type of arc alaskan type which is a combination of the japan and mariana type intra oceanic arcs and the cordillera type continental arcs these linear components rotated and collided with each other with multiple subduction polarities which could have been an important result of multiple linear element amalgamation and which has contributed greatly to the architecture of the eurasian continent the basic tectonic styles of the altaids can be summarized as arc arc collision oroclinal bending and large scale rotation and multiple subductions with a complicated archipelago paleogeography these basic features of accretionary orogens in general can be attributed to the amalgamation of complicated multiple linear elements some mesozoic to cenozoic accretionary orogens in the world are also characterized by processes of multiple linear element amalgamation more attention should be paid to the multiple linear element amalgamation of ancient accretionary orogens which will shed light on lateral and vertical continental growth

geothermometry from brine analyses lessons from the gulf coast u s a abstract geothermometers based on mineral water equilibria are of limited use at temperatures characteristic of hydrocarbon production from sedimentary basins metastable detrital phases such as alkali feldspars and plagioclase persist to temperatures characteristic of the deepest wells sasmpled approaching 200 c and equilibria involving stable phases such as albite illite and quartz are not commonly achieved empirical relations such as that between mg and li are more successful in predicting subsurface formation water temperatures than are equilibrium relations involving quartz carbonates or feldspars the concentrations of most components in saline formation waters seem to be governed by kinetic rather than by equilibrium considerations

u pb ages and hf o isotopes of zircons from late paleozoic mafic ultramafic units in the southern central asian orogenic belt tectonic implications and evidence for an early permian mantle plume abstract u pb age and hf o isotope data of zircons from the mafic ultramafic complexes and their related rhyolites and granites in the eastern tianshan and beishan regions were obtained by sims and la icpms the hf o isotopic composition and hf model age of the zircons are closely related to their tectonic setting and formation age the zircons from the mafic ultramafic complexes in the bogeda haerlike and jueluotage belts have higher ehf t 8 17 and lower 18o 4 6 whereas most of the zircons in the gabbros granites and rhyolite from the middle tianshan massif and beishan rift display lower ehf t 0 8 and higher 18o 5 8 the positive ehf t and relatively lower 18o values suggest that these mafic ultramafic complexes were derived from depleted mantle which was subjected to subduction related modification processes the hf isotopic composition of zircons in the granites has revealed that the growth of juvenile crust was also very significant in the southern margin of the central asian orogenic belt during the paleozoic the hf model ages of the analyzed zircons together with the regional geology suggest that the beishan area had a northward subduction possibly from ca 900 ma to ca 400 ma whereas the eastern tianshan had a south directed subduction most likely from ca 600 ma to ca 310 ma additionally zircons with ca 280 ma u pb ages display wider and more scattered ehf t and 18o variations than the relatively older and younger ones which further support the early permian mantle plume model

in situ u pb hf and re os isotopic analyses of the xiangshan ni cu co deposit in eastern tianshan xinjiang central asia orogenic belt constraints on the timing and genesis of the mineralization abstract the timing and genesis of the major ni cu co sulfide deposit in the xiangshan intrusion have been studied based on newly obtained in situ u pb hf and re os isotopic analyses the sims u pb zircon ages of the gabbro hosting the ni cu co sulfide deposit indicate that the xiangshan intrusion was emplaced at 279 6 1 1 ma 95 confidence level mswd 1 30 n 15 on the basis of combined geological and geochronological evidence we suggest that the xiangshan and other adjacent ni cu deposits were formed in the same period sulphides have low common os concentrations and high re os ratios similar to sulphide ores from the duluth sally malay and voisey bay complexes the re os isotopic data from the disseminated and massive ores from the xiangshan intrusion do not form a single isochron as they have different initial os ratios the hf and os isotopic data suggest that the xiangshan intrusion and associated ni cu co mineralization were derived from crustally contaminated mantle melts the geochemical data show a tholeiitic affinity and a strong suprasubduction zone signature with negative nb sr and ti anomalies similar to n morb and e morb we suggest that the mafic ultramafic rocks and associated ni cu mineralization of the eastern tianshan orogen formed in an alaska type subduction zone arc setting some diagnostic features of ridge trench interaction are present in the chinese east tianshan orogen e g granites adakites high mg andesites near trench magmatism alaskan type mafic ultramafic complexes high temperature metamorphic belts that prograde rapidly from low grade belts and orogenic gold deposits the above distinctive rock groups are probably related to the same thermal event ridge subduction as in the cenozoic orogen of alaska we suggest that ridge subduction is the most plausible mechanism to provide the necessary heat ridge subduction provides an important promising model for understanding many aspects of the evolution of the chinese eastern tianshan orogen and by inference throughout much of central asia

a new process response coastal recession model of soft rock cliffs abstract the development of cliff erosion predictive models is limited by the complex interactions between environmental processes and material properties over a range of temporal and spatial scales current models incorporate a stochastic representation of cliff behavior based on assumptions regarding the magnitude and frequency of events in a probabilistic framework the new model presented here has been developed to incorporate the behavioral and mechanical characteristics of coastal cliffs which are dominated geologically by overconsolidated clays tills and an associated protective colluvial wedge this model is capable of providing precise and stable responses to some of the inherent uncertainties in cliff recession processes including those caused by different failure mechanisms e g colluvium generation groundwater and erosive tidal cycles material strength is incorporated using the unconfined compressive strength of the material that composes the cliff unlike previous models a calibration parameter is restricted to account for uncertainties linked to marine processes the mechanisms of cliffline retreat have been identified as slump and topple landslides once cliff material has fallen colluvium formation at the cliff foot is incorporated into the model using three different procedures according to the geomechanical characteristics of the debris the model is validated through profile evolution assessment at various locations of coastline retreat on the holderness coast uk higher groundwater content also produces an increase in the number and size of the slope failures the results represent an important step forward in linking material properties to the processes of cliff recession

perturbation of the carbon cycle at the middle late jurassic transition geological and geochemical evidence a compilation of new and published stratigraphic paleontological and geochemical data is used to detect the reciprocal influences of carbon cycling and global environmental changes in the jurassic a major perturbation of the surface carbon cycling accompanied by pronounced climate and sea level fluctuations waxing and waning of continental ice affected earth history around the middle late jurassic transition mljt we establish the respective timing of changes of carbonate and organic matter sedimentation and global fluctuations of sea surface temperatures paleobiogeography and o isotope paleothermometry and sea level sequence stratigraphy so that causative mechanisms and feedback effects can be considered it is apparent that the global sea level rise and warming initiated in the late bathonian led to a constriction of carbonate platforms to low latitudes and enhanced marine organic deposition sea level and temperature optima were achieved several million years later during the middle callovian a detailed record of sea surface temperatures in the northern hemisphere based on migration of marine fauna and isotopic thermometry indicates that a drastic climatic decline set in during the early late callovian just post dating the increased capture of organic matter by marine sediments this decline in temperature is interpreted in terms of an inverse greenhouse effect triggered by drawdown of co 2 consequent upon excess carbon burial the magnitude of refrigeration and its coincidence in time with an abrupt global scale fall of sea level are both suggestive of continental ice formation at this time carbonate sedimentation was jeopardized at the mljt as a result of both global cooling and presumed p c o 2 lowering and resumed abruptly during the middle oxfordian by spreading again over mid latitude zones salient conclusions are that 1 the pattern of excess carbon burial coincident with elevated temperature but followed by climatic deterioration supports the general hypothesis that a major control on mesozoic climate was the abundance of atmospheric co 2 2 significant masses of continental ice may have formed during this part of the jurassic and correlatively high co 2 levels were certainly not sustained throughout this period 3 the global carbonate sedimentation budget correlated with the surface temperature and sea level but the latitudinal spreading of type tropical carbonates was not simply related to the thermal status of seawaters 4 on a global scale the c o r g and c i n o r g burial rates were coupled apparently through the correlation existing between the co 2 level and surface temperature

controls on the oil and gas potential of humic coals abstract humic coals are highly heterogeneous both with respect to maceral content and chemical composition although the oldest known humic coals albeit gas prone are of devonian age the majority of humic coals capable of generating and expelling non volatile oil are of cretaceous and tertiary age from australia new zealand and southeast asia in contrast the middle jurassic humic coals of the sleipner and hugin formations in the south viking graben of the north sea are primarily gasprone but have the capability to expel aliphatic rich volatile oil these coals have toc contents up to 80 and hydrogen indices hi ranging from 200 to 400 they are vitrinite rich with some containing up to 45 inertinite liptinite concentrations are generally around 10 20 chiefly as spores pollen and abundant resinite the main control on the oil potential of humic coals is the concentration of long chain aliphatic hydrocarbons in the coal matrix although the aliphatics have a high h c ratio the inference on hydrogen content from the rock eval pyrolysis hi value can be misleading for hi values below 500 mg hc g oc there is no relation between hi and the potential of the coals to generate non volatile oil consequently the hi is a poor indicator of the non volatile oil potential of humic coals a more robust indicator is the relative amount of c8 aliphatic groups also the bulk measure of liptinite content may also prove misleading when assessing the oil potential of coals high resinite concentrations can lead to an overprediction of the non volatile oil potential as they contribute significantly to the hi value but will generate primarily volatile aromatic rich oils expulsion from the sleipner and hugin coals appears to have occurred in a gaseous phase with preferential release of short chain alkanes

carbon isotope fractionation during natural gas generation from kerogen abstract in petroleum exploration it is important to be able to determine the origin of any gas which is found this paper describes a new method of estimating the source type and maturity of a gas based on a rayleigh fractionation model kerogen is divided conceptually into a labile dominantly oil generating fraction and a refractory gas prone component 13 c of methane from either kerogen type and ethane propane and butane for gases from labile kerogen can be defined as a function of 13 c of the gas precursor groups in kerogen a kinetic isotope fractionation factor k and the extent of gas generation the isotopic ratio of the methane precursors relative to bulk kerogen determined from laboratory pyrolysis are 17 5 for labile kerogen and 1 4 for refractory kerogen values for ethane propane and butane from labile kerogen based on field correlations are 4 9 2 2 and 1 6 respectively the corresponding fractionation factors are 0 9892 0 9919 0 9947 and 0 9975 for methane ethane propane and butane respectively from labile kerogen and 0 9984 for methane from refractory kerogen using these parameters summary diagrams are constructed which allow differentiation of these sources from each other and from biogenic gases and cracked oil and recognition of gases of mixed origin if an independent estimate of 13 c for the source kerogen is possible then 13 c of the gas components can be used to estimate maturity in terms of the gas generation index the fraction of gas potential which has been realized

modeling cyclic recession of cohesive clay coasts effects of wave erosion and bluff stability abstract a mathematical model combining the effects of wave erosion beach sediment and bluff slope stability has been developed to study the episodic cyclical recession of cohesive clay coasts the model was applied to the southern great lakes in north america which although non tidal experience seasonal fluctuations in lake level of about 0 5 m and long term fluctuations of up to 2 m model runs were designed to explore the interaction between various components of the system including profile shape bluff recession rates lake level variations beach morphodynamics the geomechanical characteristics of the material and the type slump topple and size of the slope failures model runs were made for the equivalent of 100 years quasi equilibrium conditions developed in the runs which had similar erosion rates to the field with parallel slope retreat in the upper portion of the profiles and slope decline in the lower portion temporal variations in the rate of recession of the crest of the bluff closely matched changes in lake level the model confirmed previous work that suggested that rates of bluff recession are strongly controlled by the rate of erosion below the water surface but it also provided support for a more recent proposal that rates of bluff recession also influence rates of erosion in shallow water it was found that positive and negative changes in the size of the beach can either promote or hinder bluff and profile erosion depending on local circumstances the model demonstrated that bluff height debris mobility wave undercutting and groundwater levels are key factors in determining the stability of coastal bluffs the model represents a promising new tool to forecast and thereby mitigate the effects of climate change on marine and lacustrine coasts

correlation of carbon dioxide abundance with temperature in clastic hydrocarbon reservoirs relationship to inorganic chemical equilibrium the mol co2 of gas reservoired in sandstones tends to increase with increasing temperature along both the us gulf coast and the norwegian continental shelf each of these provinces displays identical linear correlations between temperature and the log of the partial pressure of co2 i e pco2 in the reservoir fluid that is the product of the mol co2 the reservoir pressure this correlation is the same both in gulf coast reservoirs younger than 17 ma and in norwegian reservoirs of jurassic to triassic age 144 245 ma indicating that it is not dependent on reaction kinetics norwegian shelf data indicate that the same correlation also applies for gas condensate and oil reservoirs we suggest that the log pco2versus temperature correlation is the result of inorganic chemical equilibria between feldspar clay and carbonate minerals a trend of decreasing ph with increasing temperature is fixed by equilibria between aluminosilicate minerals feldspar kaolinite at lower temperatures followed by various reactions between kaolinite illite chlorite and feldspar as temperatures exceed 110 140 c responding to the ph set by the aluminosilicate system co2 activity in the formation water and thereby co2 partial pressure in any gas phase present is controlled by equilibrium with carbonate minerals this model predicts that co2 released by organic maturation will in general result in precipitation of carbonate minerals below 100 120 c and that there should be widespread carbonate dissolution at higher temperatures

immature oil and condensate modification of hydrocarbon generation model for terrestrial organic matter petroleum has been found in canadian frontier basins in reservoirs which have undergone low levels of thermal alteration vitrinite reflectance 0 6 ro paraffin indices stable carbon and hydrogen isotope contents pristane to nc17 ratios and diterpenoid biologic markers have been used to assess the level of maturity of the hydrocarbons in the reservoir independently of the level of maturity of the reservoir itself and of the surrounding shale units in the tertiary of the beaufort mackenzie basin naphthenic oils and condensates have been generated from terrestrially derived organic matter in source rocks juxtaposed with the reservoir at reflectance levels of 0 4 to 0 6 ro however condensates discovered in reservoirs which are th rmally immature on the labrador shelf have undergone extensive vertical migration and can be classed as conventional mature to overmature condensates hydrocarbons discovered in the lower cretaceous of the beaufort mackenzie basin and also those of the scotian shelf are more or less in place in that they are at a level of thermal alteration about equivalent to that of the reservoirs in which they are trapped the source for the early oils and condensates is considered to be resinite occurring dispersed in coal fragments the proportion of resinite liptinite and vitrinite in the organic matter of terrestrial source rocks strongly controls both the level of thermal alteration necessary for the section to function as an effective source rock and the ultimate product gas oil or condensate which will be generated

genesis of permian granites along the kangguer shear zone jueluotage area northwest china geological and geochemical evidence abstract permian mafic and felsic intrusions occur along the kangguer shear zone ksz in the jueluotage area eastern tianshan northwest china this study focuses on the permian felsic intrusions 288 276 2 ma systematic geological and geochemical investigations show that granite plutons in the western ksz dikan guandao and hongshi have lower al and higher alkali contents than those in the eastern ksz longdong huangshan and baishandong the western granite plutons experienced higher degrees of crystal fractionation than the eastern granite plutons both of the western and eastern permian granite intrusions along ksz were derived from juvenile crust the nd pb isotopic characteristics of which exhibit mixed compositions of dm and emii type mantles both of the western and eastern permian granites along ksz were formed within post collision background the dikan guandao and hongshi plutons in the west ksz sector were formed in an extensional tectonic setting whereas the longdong huangshan and baishandong plutons in the east ksz formed in a compressional tectonic setting

geochemical characterization of natural gas a physical multivariable approach and its applications in maturity and migration estimates gas geochemistry has recently been shown to enhance information regarding the geological history of hydrocarbons in this paper graphical representations of physico chemical processes affecting the chemical and isotopic signatures of natural gases are exemplified these diagrams are based on experimental studies and the use of basic statistics to extract significant and synthetic parameters from the geochemical data from 11 chemical and isotopic ratios a statistical analysis pca yields two very important parameters the first parameter using mainly the c2 fraction of the gas relates to maturity and the second parameter involving the proportions and d13c values of methane indicates mainly segregative migration positive values of the second parameter indicate that gases accumulated far from their source whereas negative values correspond to residual gas pools after leakage of a part of the fluids a tentative reconstruction of the gas history has been performed in two brazilian basins the espirito santo basin and part of the reconcavo basin the espirito santo basin is located on the passive continental margin of the atlantic ocean and the reconcavo basin corresponds to an intracontinental aborted rift in both cases the source rocks are mainly lacustrine with thermal maturities ranging between the oil window and the beginning of the gas window results show that in the reconcavo basin a major fault the mata catu fault acts as a drain for hydrocarbon migration at the basin scale associating a major isotopic fractionation to the gas migration with a clear correlation between isotope fractionation and the distance of migration in the espirito santo basin this segregation appears in the platform sediments to a lesser extent and is absent in the gas pools located in the paleocanyons filled with turbidites this long distance migration in the platform sediments suggests that a hydrocarbon kitchen is located offshore

the petroleum potential of some tertiary lignites from northern greece as determined using pyrolysis and organic petrological techniques abstract oil condensate and gas have recently been discovered in the thermaikos gulf area of northern greece the source of these hydrocarbons is not known although there is a possibility that more mature equivalents of certain tertiary brown coals and lignites may be responsible a contribution from tertiary terrestrial organic matter to the epanomi oil is supported by its biomarker distributions especially the predominance of triterpenoid compounds other than hopanes in the m z 191 mass fragmentogram in this study the hydrocarbon potential of a suite of greek tertiary lignites is first examined using rock eval analysis three samples are then further investigated using organic petrography and gas chromatography gc and gas chromatography mass spectrometry gc ms of the extracted hydrocarbon fractions as well as by hydrous pyrolysis an intermontane lignite 6og 5 contains fluorescing huminite together with resinite on extraction this resinite is found to be of predominantly diterpenoid origin rock eval and hydrous pyrolysis support previous proposals that diterpenoid resinite needs a lower activation energy to generate hydrocarbons than most other types of organic matter a sample of a lignite deposited in a deltaic environment mm 3 contains a more diverse collection of liptinite macerals with resinite again predominating the resinite appears to be mostly of triterpenoid and sesterterpenoid origin the best hydrocarbon potential is shown by a sample deposited in a lagoonal environment kas 3 little discrete resinite is observed in this sample but it does contain abundant fluorescing huminite although it has a low s 1 s 1 s 2 ratio it gives a high yield on solvent extraction during which a significant fraction of the s2 is removed the fluorescence of the huminite after extraction is greatly reduced the hydrocarbons of the extract are believed to be predominantly derived from triterpenoid resinite unlike the pyrolysates of the other two lignites but in common with the epanomi oil the triterpenoids in the kas 3 pyrolysate are dominated by resin derived compounds rather than hopanes this and other similarities between the composition of the pyrolysates of kas 3 and the oil support the possibility that a more mature equivalent of this lignite could be the source of the epanomi oil

classification and thermal history of petroleum based on light hydrocarbons abstract classifications of oils and kerogens are described two indices are employed termed the heptane and isoheptane values based on analyses of gasoline range hydrocarbons the indices assess degree of paraffinicity and allow the definition of four types of oil normal mature supermature and biodegraded the values of these indices measured in sediment extracts are a function of maximum attained temperature and of kerogen type aliphatic and aromatic kerogens are definable only the extracts of sediments bearing aliphatic kerogens having a specific thermal history are identical to the normal oils which form the largest group 41 in the sample set this group was evidently generated at subsurface temperatures of the order of 138 149 c 280 300 f defined under specific conditions of burial history it is suggested that all other petroleums are transformation products of normal oils

magma generation and sulfide saturation of permian mafic ultramafic intrusions from the western part of the northern tianshan in nw china implications for ni cu mineralization compared to permian magmatic ni cu sulfide deposits in the eastern part of the northern tianshan such as huangshan and huangshandong those in the western part e g baixintan and lubei are poorly documented zircon id tims u pb age data 279 7 0 2 ma of lherzolite and la icpms u pb age data 277 8 3 4 ma of a hornblende gabbro suggest the lubei intrusion was emplaced in the early permian the baixintan and lubei mafic ultramafic intrusive rocks are characterized by enrichments of large ion lithophile elements and th and u relative to the high field strength elements as well as depletion of nb and ta relative to mid ocean ridge basalt the 87sr 86sr t 0 70354 0 70713 end t 2 80 to 7 05 and ehf t 2 50 18 4 values for the intrusions indicate that they have assimilated tianshan basement rocks whereas the se s ratios 181 10 6 418 10 6 and 34scdt values 0 13 to 0 90 of the sulfides suggest that crustal sulfur has not been incorporated into the magma the decrease in pd zr with increasing th nb pm indicates that sulfide saturation accompanied crustal contamination the olivine compositions and whole rock chalcophile elements of the baixintan and lubei intrusions imply that the parental magma of the intrusive rocks in the west contains higher chalcophile elements than those in the east which suggests that the mafic ultramafic intrusions in the western part of the northern tianshan should be regarded as favorable ni cu sulfide exploration targets

middle cambrian to permian subduction related accretionary orogenesis of northern xinjiang nw china implications for the tectonic evolution of central asia abstract middle cambrian to permian subduction related records are widely distributed in northern xinjiang which can be grouped into the chinese altay east junggar eastern tien shan west junggar yili and tarim domains by integrating paleogeographic and geological data we suppose that the chinese altay east junggar eastern tien shan domain was more closely located to siberia while the west junggar and yili domains occupied an intermediate position near the kazakhstan block in the early paleozoic paleoasian ocean distribution of andean type magmatic arcs island arcs accretionary wedges ophiolitic slices and or microcontinents shows an archipelago paleogeography forming a huge accretionary active margin sequences the tarim domain was on the opposite side of the early paleozoic paleoasian ocean remaining passive margin these tectonic units drifted northwards and approached the southern active margin of the siberian craton in the late paleozoic leading to termination of the paleoasian ocean and formation of a complicated orogenic collage between siberian craton and the tarim block between the end permian and triassic these multiple accretion processes significantly contributed to the lateral growth of central asia

geochemical characterisation and genetic origin of oils and condensates in the south viking graben norway abstract geochemical analysis of oil and condensate samples from all major fields and discoveries in the norwegian south viking graben as well as source rock extracts of upper and middle jurassic source horizons was carried out to characterise reservoired hydrocarbons and establish genetic relationships the south viking graben is in a mature phase of exploration and this study aims at unravelling regional trends to improve predictions in exploration and will show the significance of the play models in the area seven hydrocarbon families have been identified based on interpretation of molecular and isotopic characteristics and multivariate analysis of biomarker data these families can be linked to three source horizons three families originate from different facies of the draupne formation and are characterised by pr ph ratios below 2 dominance of c 27 regular steranes over the c 29 homologues and carbon isotopic values for saturate and aromatic fraction lighter than 28 and 27 respectively the upper jurassic heather formation and the middle jurassic vestland group each source one group of hydrocarbons typical for heather sourced hydrocarbons are elevated pr ph ratios between 2 35 and 3 08 low ratios of c 27 c 29 regular steranes and average isotopic values of 28 4 13 c sat and 26 8 13 c aro hydrocarbons from a middle jurassic source are characterised by very heavy isotopic composition highest pr ph ratios of the data set and dominance of c 29 regular steranes over the c 27 homologues among other factors the two remaining families represent mixtures from upper and middle jurassic sources and are mainly encountered in the greater sleipner area the available data in this study allowed characterisation of 84 of the recoverable oil resources which proved that the main source rock in the area is the upper jurassic draupne formation the play concept including a draupne source and tertiary reservoir proves to be most prolific with 239 10 6 s m 3 of recoverable oil equalling 88 of the total characterised oil resources oils in these tertiary reservoirs are however likely to be affected by biodegradation based on the available data the zone of biodegradation in the south viking graben appears to be limited to depths above 2140 m and temperatures below 70 c

measurement of historical cliff top changes and estimation of future trends using gis data between bridlington and hornsea holderness coast uk abstract a key requirement for effective coastal zone management is good knowledge of historical rates of change and the ability to predict future shoreline evolution especially for rapidly eroding areas historical shoreline recession analysis was used for the prediction of future cliff shoreline positions along a section of 9 km between bridlington and hornsea on the northern area of the holderness coast uk the analysis was based on historical maps and aerial photographs dating from 1852 to 2011 using the digital shoreline analysis system dsas 4 3 extension of esri s arcinfo 10 the prediction of future shorelines was performed for the next 40 years using a variety of techniques ranging from extrapolation from historical data geometric approaches like the historical trend analysis to a process response numerical model that incorporates physically based equations and geotechnical stability analysis with climate change and sea level rise implying that historical rates of change may not be a reliable guide for the future enhanced visualization of the evolving coastline has the potential to improve awareness of these changing conditions following the ipcc 2013 report two sea level rise rates 2 mm yr and 6 mm yr have been used to estimate future shoreline conditions this study illustrated that good predictive models once their limitations are estimated or at least defined are available for use by managers planners engineers scientists and the public to make better decisions regarding coastal management development and erosion control strategies

geochemical effects of primary migration of petroleum in kimmeridge source rocks from brae field area north sea i gross composition of c15 soluble organic matter and molecular composition of c15 saturated hydrocarbons in mature oil prone source rocks of the upper jurassic kimmeridge clay in the brae field area north sea the yield and the gross composition of solvent extractabte pctroleum likc compounds as well as the molecular proportions of c15 saturated hydrocarbons are primarily controlled by the effects of hydrocarbon expulsion during primary migration within sample series extending from shale centres towards adjacent reservoir sandstones regular and pronounced yield decreases have been documented as well as marked compositional changes for c15 soluble organic matter and its compound class fractions saturated hydrocarbons aromatic hydrocarbons nso compounds and for normal and isoprenoid alkanes relative migration losses indicating relative expulsion efficiencies were determined for the c15 alkanes throughout the outer five meters of thick shales relative expulsion efficiencies increase regularly and drastically for all compounds considered e g exceeding 90 for the c15 n alkanes in the outermost shale samples samples from thin 5 50 cm shale layers interbedded between reservoir sandstones reveal similarly high expulsion efficiencies for n alkanes the degree of depletion remains uniform throughout the molecular range c15 to c30i e no compositional fractionation occurred during primary migration which is interpreted to reflect expulsion of oil as a single phase fluid a simple conceptual model is proposed to explain the mechanisms and relationships of generation and expulsion processes in time and space a geochemically relevant conclusion is that the c15 soluble organic matter recovered by solvent extraction of mature source rocks represents only a portion of the total non volatile petroleum like material originally generated

petroleum source rock assessment in non marine sequences pyrolysis and petrographic analysis of australian coals and carbonaceous shales a series of australian coals and terrestrial sediments ranging in age from permian through tertiary have been analyzed to assess their petroleum source character and the suitability of various techniques for assessment of source rock potential in non marine sequences the procedures used include organic petrography rock eval pyrolysis elemental analysis and quantitative pyrolysis gas chromatography the latter procedure was used to assess the potential yield of paraffins which is critical to the assessment of most non marine source rocks principal components analysis was used to assist in the analysis of the data although the petroleum potential of the samples follows the broad trends in petrographic composition established for australian coals i e relative proportions of vitrinite inertinite and liptinite there is much variation which cannot be explained petrographically at the maceral group level further pyrolytic hydrocarbon yield is not related to overall elemental composition below an atomic h c ratio of 1 0 the yield of phenols in flash pyrolysis is related to depositional setting as well as degree of maturation the yield and carbon number distribution of normal hydrocarbons in flash pyrolysis varied widely depending on the age nature and amount of liptinite macerals particularly in samples with hydrogen indices below 300 liptinite poor 10 samples may yield significant amounts of hydrocarbons but typically they have a low wax content sporinite rich and liptodetrinite rich samples give lower yields of normal hydrocarbons these are predominantly of lower molecular weight suberinite and to a lesser extent cutinite are associated with high yields of waxy normal hydrocarbons but some samples with high yields did not contain large amounts of these maceral the correlation of tmax to vitrinite reflectance varies with petrographic composition the results have implications for the way source rock analyses are conducted and interpreted in non marine sequences

mixed oils derived from multiple source rocks in the cainan oilfield junggar basin northwest china part ii artificial mixing experiments on typical crude oils and quantitative oil source correlation abstract there are five groups of crude oils in the east junggar basin four of which are derived from single sources viz permian triassic jurassic and carboniferous the crude oils in the cainan field are of a special type in that they have little correlation with any of the four known source rocks in the basin based on their distribution in the reservoir formations and their carbon isotopic and biomarker compositions it is concluded that these crude oils are mixtures of hydrocarbons from permian triassic and jurassic source rocks a mixing calculation using whole oil stable carbon isotope ratios of typical end member crude oils suggests that the contribution of jurassic source rocks to the cainan crude oils averages 50 65 a second calculation based on absolute concentrations of biomarkers indicates that the jurassic contribution averages 62 while those of the triassic and permian source rocks average 15 and 23 respectively artificial laboratory mixing of three typical permian triassic and jurassic oils indicates that the average contribution of the jurassic source rocks is 65 whereas those of the triassic and permian rocks are around 15 and 20 respectively in summary using whole oil stable carbon isotope ratios and biomarker parameters it can be concluded that the jurassic source makes a contribution of 55 70 while the triassic and permian sources each contribute 10 30 therefore the crude oils in the cainan oilfield are mainly derived from jurassic source rocks in the fukang sag

source rock heterogeneity of the upper jurassic draupne formation north viking graben and its relevance to petroleum generation studies abstract the upper jurassic draupne formation in the north viking graben north sea has been studied to identify lateral and vertical variations in source rock characteristics and their effect on the timing of petroleum generation fourteen source rock samples from the western flank of the graben and five from the eastern flank were analysed using rock eval analysis microscopy open system pyrolysis gas chromatography and kinetic experiments two major organic facies with different petroleum generation characteristics were identified a stratigraphically higher thermally less stable facies corresponding to a type ii kerogen with hi hydrogen index values of 350 mg hc g toc and a stratigraphically lower more stable type ii iii facies with hi values

the effect of interbedding on shale reservoir properties north sea oil is overwhelmingly generated in shales of the upper jurassic basal cretaceous kimmeridge clay formation once generated the oil is expelled and ultimately migrates to accumulate in sandstone or carbonate reservoirs the source rock shales however still contain the portion of the oil that was not expelled as a consequence such shales and juxtaposed non source lithofacies can form the targets for the exploration of unconventional oil in this paper we examine part of the kimmeridge clay formation as a hybrid shale resource system within which hot shale and organic lean sandstone and siltstone intervals are intimately interbedded this hybrid system can contain a greater volume of oil because of the increased storage capacity due to larger matrix porosities of the sand silt interbeds together with a lower adsorptive affinity in the interbedded sandstone the relationship between the estimated volume percentages of sand and mudstone and free oil determined from rock eval s1 yields is used to place limits on the drainage of oil from source mudstone to reservoir sand at the decimeter scale these data are used to determine oil saturations in interbedded sand mudstone sequences at peak oil maturity higher values of free hydrocarbon as evidenced by the s1 value in mudstone suggest that more oil is being retained in the mudstone while higher s1 values in the interbedded sands suggest the oil is being drained to saturate the larger pore spaces high silica content in the interbeds confirms the brittleness in this mudstone sandstone lithofacies an important factor to be considered for fracture stimulation to successfully work in a hybrid system the key points of this hybrid unconventional system are the thickness storage capacity and the possibility to capture a portion of the expelled as well as retained oil

geochemical compositional gradients in a mixed oil reservoir indicative of ongoing biodegradation abstract this study reports the results of organic geochemical characterisation of oil extracts from cores through an oil reservoir column within the grane field north sea the results show small gradients in composition attributed to ongoing biodegradation occurring at the oil water contact biodegradation is affecting the labile constituents that have been replenished by recent charging of this mixed oil and there is no apparent ongoing biodegradation effect upon the resistant compounds associated with earlier oil charge the use of principal component analysis has allowed compositional changes due to evaporation during storage to be distinguished from the effects of biodegradation and has highlighted the c19 n alkanes hopanes steranes ratio as a biodegradation sensitive parameter that shows a gradient in composition through the oil column the concentration of the c19 n alkanes though the oil column confirms that the n alkanes are depleted towards the oil water contact this approach has shown that biodegradation related trends indicative of ongoing biodegradation can be identified in reservoirs that contain multiple altered oil charges even when affected by subsequent compositional changes during sample storage

source rocks of the german central graben abstract jurassic to lower cretaceous formations are the most important source rocks for hydrocarbons in the southern central graben area within the dutch central graben the lower jurassic posidonia shale formation is the most prolific source for hydrocarbons while the upper jurassic to lowermost cretaceous bo member of the farsund formation plays this role in the danish central graben oil and gas discoveries in the norwegian dutch and danish part of the central graben proved a prolific petroleum system despite limited success of hydrocarbon exploration in the german part of the central graben various indications suggest migration of gas out of active thermogenic source rocks that are closely related to potential shallow gas accumulations these indications include the restricted location of the bright spots above the jurassic graben system the occurrence of gas chimneys underneath these accumulations and geochemical data from offshore the netherlands which support contribution of thermogenic gas the purpose of this study is to assess the potential for generating thermogenic hydrocarbons from upper triassic to lower cretaceous formations for this reason prominent source rocks of the southern north sea i e the posidonia shale formation and the upper jurassic to lower cretaceous hot shales namely clay deep member offshore the netherlands and bo member offshore denmark were mapped in detail these and other potential formations from the late triassic to the early cretaceous are integrated into an existing petroleum system model of the northern german north sea which was modified for the new requirements the results showed that the main source rocks of the southern central graben the posidonia shale formation and the upper jurassic lower cretaceous hot shales are insignificant as sources for commercial hydrocarbon accumulations within the german central graben area that is either due to marginal occurrence or to low maturity however lower to upper jurassic formations such as marine claystones of the aalburg formation and the lower parts of the kimmeridge clay formation as well as coaly intervals of the central graben subgroup are likely to have generated and still generate hydrocarbons

geological and geotechnical characterisation for offshore wind turbine foundations a case study of the sheringham shoal wind farm abstract this paper characterises the soil conditions at the sheringham shoal wind farm in the north sea in the context of designing foundations for offshore wind turbines the purpose is to provide a realistic reference case study for research and practice in the emerging field of offshore wind energy the soil data was obtained between 2005 and 2008 in an investigation program involving field measurements and laboratory experiments the characterisation focuses on soil properties which are relevant for evaluating the performance of foundations for offshore wind turbines the soil profile at the sheringham shoal site consists of four main units two clay strata interbedded with a sand layer and underlain by a chalk bed the heavily overconsolidated state of the clays and the densely compacted state of the sand dictate the behaviour of these soils the chalk bed is characterised by varying degrees of weathering leading to significant variation in properties ranging from those typical for stiff soil to soft rock these four main units though differ considerably in soil composition share several common characteristics including high shear strength and high stiffness but their shear stiffnesses reduce significantly both at high mobilised static shear strength and at medium to high mobilised strength under cyclic loading the soil stiffness is an important input parameter for the design of offshore wind turbine foundations and hence the degradation of stiffness is an important issue at this wind farm a number of soil properties at the site show considerable variability which requires a specific foundation design tailored for each location in order to be both safe and cost effective

paleozoic multiple accretionary and collisional tectonics of the chinese tianshan orogenic collage abstract subduction related accretion in the junggar balkash and south tianshan oceans paleo asian ocean mainly in the paleozoic gave rise to the present 2400 km long tianshan orogenic collage that extends from the aral sea eastwards through uzbekistan tajikistan kyrgyzstan to xinjiang in china this paper provides an up to date along strike synthesis of this orogenic collage and a new tectonic model to explain its accretionary evolution the northern part of the orogenic collage developed by consumption of the junggar balkash ocean together with paleozoic island arcs northern ili issyk kul and chatkal located in the west which may have amalgamated into a composite arc in the paleozoic in the west and by addition of another two roughly parallel arcs dananhu and central tianshan in the east the western composite arc and the eastern dananhu and central tianshan arcs formed a late paleozoic archipelago with multiple subduction zones the southern part of the orogenic collage developed by the consumption of the south tianshan ocean which gave rise to a continuous accretionary complex kokshaal kumishi which separated the central tianshan in the east and other paleozoic arcs in the west from cratons tarim and karakum to the south cross border correlations of this accretionary complex indicate a general southward and oceanward accretion by northward subduction in the early paleozoic to permian as recorded by successive southward juxtaposition of ophiolites slices of ophiolitic melanges cherts island arcs olistostromes blueschists and turbidites which are mainly paleozoic in age with the youngest main phase being late carboniferous permian the initial docking of the southerly tarim and karakum cratons to this complicated late paleozoic archipelago and accretionary complexes occurred in the late carboniferous early permian in the eastern part of the tianshan and in the late permian in the western part which might have terminated collisional deformation on this suture zone the final stages of closure of the junggar balkash ocean resembled the small ocean basin scenario of the mediterranean sea in the cenozoic in summary the history of the altaids is characterized by complicated multiple accretionary and collisional tectonics

geology and ore genesis of the late paleozoic heijianshan fe oxide cu au deposit in the eastern tianshan nw china abstract the heijianshan fe cu au deposit located in the aqishan yamansu belt of the eastern tianshan nw china is hosted in the mafic intermediate volcanic and mafic felsic volcaniclastic rocks of the upper carboniferous matoutan formation based on the pervasive alteration mineral assemblages and crosscutting relationships of veins six magmatic hydrothermal stages have been established including epidote alteration stage i magnetite mineralization stage ii pyrite alteration stage iii cu au mineralization stage iv late veins stage v and supergene alteration stage vi the stage i epidote calcite tourmaline sericite alteration assemblage indicates a pre mineralization ca mg alteration event stage ii fe and stage iv cu au mineralization stages at heijianshan can be clearly distinguished from alteration mineral assemblages and nature and sources of ore forming fluids homogenization temperatures of primary fluid inclusions in quartz and calcite from stage i 189 370 c ii 301 536 c iii 119 262 c and v 46 198 c suggest that fluid incursion and mixing probably occurred during stage i to ii and stage v respectively the stage ii magmatic hydrothermal derived fe mineralization fluids were characterized by high temperature 300 c medium high salinity 21 2 56 0 wt nacl equiv and being na ca mg fe dominated these fluids were overprinted by the external low temperature in situ sulfur isotopes also indicate that the sulfur sources vary in different stages viz stage ii magmatic hydrothermal iii basinal brine related and iv magmatic hydrothermal stage ii disseminated pyrite has 34 s fluid values of 1 7 4 3 comparable with sulfur from magmatic reservoirs 34 s fluid values 24 3 29 3 of stage iii type a pyrite coexists with hematite probably indicate external basinal brine involvement consistent with the analytical results of fluid inclusions with the basinal brines further interacting with volcanic volcaniclastic rocks of the carboniferous matoutan formation stage iii type b pyrite chalcopyrite pyrrhotite assemblage with low 34 s fluid values of 4 6 10 0 may have formed at low f o 2 and temperature 119 262 c the continuous basinal brine volcanic volcaniclastic rock interactions during the basin inversion 325 300 ma may have leached sulfur and copper from the rocks yielding magmatic like 34 s fluid values 1 5 4 1 such fluids may have altered pyrite and precipitated chalcopyrite with minor au in stage iv eventually the stage v low temperature 160 c and low salinity meteoric water may have percolated into the ore forming fluid system and formed late hydrothermal veins the similar alteration and mineralization paragenetic sequences ore forming fluid sources and evolution and tectonic settings of the heijianshan deposit to the mesozoic central andean iocg deposits indicate that the former is probably the first identified paleozoic iocg like deposit in the central asian orogenic belt

reevaluating the source and accumulation of tight oil in the middle permian lucaogou formation of the junggar basin china abstract the middle permian lucaogou formation in the jimusar sag junggar basin nw china is a world class example of tight oil accumulations in lacustrine sedimentary sequences previous studies have indicated that the main oil accumulation mechanism in this system is near source accumulation within upper and lower sweet spots i e reservoirs here we reveal the complexity of oil source and accumulation in this tight oil system is greater than previously thought a set of mudstones are developed between the upper and lower sweet spots of the lucaogou formation and are thus termed the middle section mudstones they have previously been little studied as few intervened reservoir rocks are developed within the sequences here we report their oil generation and contribution for the first time the mudstones are 97 182 m thick and have total organic carbon contents of 0 67 12 31 wt the kerogen is mainly type ii with small amounts of types i and iii and is in the mature stage these data suggest that the middle section mudstones have good hydrocarbon generation potential oil source correlations reveal a complex history of tight oil migration and accumulation the oils generated in the upper part of the middle section mudstones migrated northward to the basin margins and southeastward to the basin center in contrast oil generated in the lower part of the middle section mudstones migrated westward to the west central and central regions the oil migration resulted in complex tight oil accumulation which reflects the reservoir heterogeneity our data suggest that such reservoir heterogeneity appears to be typical of tight oil accumulations in continental lacustrine basins in the study area future evaluation exploration and exploitation of tight oil should also focus on the middle section mudstones and associated sweet spots in addition to the commonly acknowledged upper and lower sweet spots

kerogen asphaltene sulfur relationships in sulfur rich monterey oils abstract monterey oils in the santa maria basin onshore and offshore are generally low maturity oils because of low thermal exposure relatively shallow burial for short times they are generated as heavy high sulfur oils because of the composition of the unusual type ii source kerogens which are exceptionally rich in organic sulfur 8 14 these high sulfur kerogens which we designate type ii s appear to generate oil at significantly lower thermal exposures than ordinary type ii kerogens with less than 6 s in contrast to common type ii kerogens which generate oil largely by cleavage at oxygen bridge groups and carbon carbon bonds eliminating co2 h2o and hydrocarbon fragments type ii s kerogens have an additional complement of weak bonds associated with bound sulfur the preferential cleavage at weak sulfur linkages tends to produce larger fragments leading to high initial amounts of asphaltenes resins and sulfur rich aromatics together with smaller amounts of saturated hydrocarbons elemental analyses of monterey kerogens and asphaltenes clearly support the concept that the asphaltenes are essentially fragments of kerogen cleaved sufficiently to be soluble or peptized in this heavy oil system solubilization of asphaltenes is attributed to their interactions with the abundant resins and aromatics this sysstem is sufficiently stable under source and reservoir conditions to allow expulsion and migration for reasonable distance without significant fractionation or changes in gross properties initial asphaltenes have essentially the same atomic h c ratios as the source kerogen but have significantlyy lower o c ratios and slightly lower s c ratios the n c ratios are nearly the same for kerogens and their derived asphaltenes with increasing maturity the h c ratios in asphaltenes decrease much like maturation changes in kerogen the s c ratio also decreases significantly however the o c ratios initially low in asphaltenes and n c ratios increase slightly due to material balance caused by other losses these element composition and atomic ratio relationships allow some important inferences concerning source kerogen composition from analysis of asphaltenes alone this can be useful when potential source rock samples are not available for analysis and or when a choice between alternate source rock possibilities must be made

geochemistry and petrogenesis of 270 ma ni cu pge sulfide bearing mafic intrusions in the huangshan district eastern xinjiang northwest china implications for the tectonic evolution of the central asian orogenic belt abstract the central asian orogenic belt caob is composed of remnants of microcontinents island arcs and ophiolites the presence of voluminous phanerozoic a type granites suggest that continental growth occurred through addition of juvenile crust and the presence of mafic ultramafic intrusions provides direct evidence for a mantle contribution the origin of the mafic ultramafic intrusions in the huangshan area eastern xinjiang has been debated because of the lack of precise age data or trace element and isotopic analyses we have studied the geology petrology geochemistry and geochronology of two of the intrusions the huangshanxi and huangshandong intrusions both are typical layered mafic ultramafic intrusions composed of diorite troctolite norite gabbronorite gabbro wehrlite websterite and lherzolite with systematic geochemical variations that are consistent with the following crystallization sequence ol chr ol pyx chr cpx pl and hbl bt igneous zircons separated from a diorite in the huangshanxi intrusion yield a 269 2 ma shrimp u pb age the rocks are enriched in rb ba u k sr relative to th and lree depleted in nb ta relative to th and exhibit positive end values 6 7 to 9 3 ni cu pge sulfide mineralization occurs in the lower parts of the intrusions primarily strata bound within wehrlite or lherzolite and locally stratiform along the margins of the intrusions the parental magmas appear to have been derived from a mantle source that was previously contaminated by subduction of oceanic crust and to have been variably contaminated by upper continental crustal components the intrusions appear to have formed by plume related activity within a continental setting likely related to post orogenic extension following carboniferous amalgamation of arc related terranes in the caob this plume activity was most likely also responsible for providing heat sources to generate large amounts of a type granites across the caob

petrogenesis of the baishan granite stock eastern tianshan nw china geodynamic setting and implications for potential mineralization abstract located in a region rich in cu ni and mo mineralization the baishan granitic stock is barren for reasons that remain enigmatic whole rock elemental and sr nd isotope analysis major element analysis of a number of minerals and zircon trace element u pb and hf isotope analysis were undertaken in order to reveal the petrogenesis of the granites all granites show typical i type characteristics including metaluminous to slightly peraluminous calc alkaline signatures with a strong depletion of nb ta ti and p enrichment of light rare earth elements and large ion lithophile elements e g cs rb th u k in addition a strong depletion in ti and p highly fractionated light rare earth element patterns and less fractionated heavy rare earth element patterns and negative correlations between sio2 and tio2 al2o3 mgo feot p2o5 zr and hf suggest significant fractional crystallization of amphibole apatite zircon and ti bearing minerals whole rock sr nd and zircon hf isotopic compositions show wide variations with 87sr 86sr i values of 0 70358 to 0 70505 end t of 3 8 to 7 2 and ehf t of 2 4 to 12 2 indicating derivation from partial melting of juvenile lower crust with obvious addition of ancient crust zircon u pb ages indicate a formation age of 292 ma significantly older than the ore forming granite porphyry and slightly older than the regional mafic ultramafic a type and diabase magmatism of eastern tianshan the granite stocks were likely derived during heating of ascending asthenospheric mantle above a mantle plume in the early permian mineral chemistry saturation thermometry mineral species and whole rock fe2o3 feo ratios indicate a crystallization temperature of 980 to 665 c pressure of 1 6 kbar and oxygen fugacity of nno for the granite stock comparing the geochemistry magma source and crystallization environment for the early permian barren granite and late triassic ore related granite porphyry the low ratios of sr y and low la yb n and reduced oxidation state nno in the granitic stock are signatures of infertility for the early permian granite this study implies high mo mineralization potential for granitic rocks with high sr y la yb n and highly oxidized conditions

correlation of natural gas by use of carbon isotopic distribution between hydrocarbon components the natural distribution of carbon isotopes between hydrocarbon gas components is used for 1 determining a gas s maturity 2 correlating a reservoired gas to its source 3 correlating one reservoired gas with another and 4 recognizing gas mixtures calculated separations of carbon isotopes between the normal alkane components of a natural gas have been related to source rock maturity by use of a single continuous diagram independent of source type actual data from a wide variety of geologic settings and geologic ages confirm this relationship and demonstrate its applicability to the source rock levels of organic metamorphism ranging from 8 to 13 covering the entire range of oil and wet gas generation at greater maturities the wet gas components are found to undergo thermal degradation losing their usefulness for correlation three examples showing indigenous gas west texas non indigenous gas gippsland basin australia and gas mixtures from multiple sources southeastern alberta illustrate exploration applications

a practical model for organic richness from porosity and resistivity logs a practical method the delta log r technique for identifying and calculating total organic carbon in organic rich rocks has been developed using well logs the method employs the overlaying of a properly scaled porosity log generally the sonic transit time curve on a resistivity curve preferably from a deep reading tool in water saturated organic lean rocks the two curves parallel each other and can be overlain since both curves respond to variations in formation porosity however in either hydrocarbon reservoir rocks or organic rich non reservoir rocks a separation between the curves occurs using the gamma ray curve reservoir intervals can be identified and eliminated from the analysis the separation in organic rich intervals results from two effects the orosity curve responds to the presence of low density low velocity kerogen and the resistivity curve responds to the formation fluid in an immature organic rich rock where no hydrocarbons have been generated the observed curve separation is due solely to the porosity curve response in mature source rocks in addition to the porosity curve response the resistivity increases because of the presence of generated hydrocarbons the magnitude of the curve separation in non reservoirs is calibrated to total organic carbon and maturity and allows for depth profiling of organic richness in the absence of sample data this method allows organic richness to be accurately assessed in a wide variety of lithologies and maturities using common well logs

sequential vertical gas charge into multilayered sequences controlled by central conduits four sets of stacked amplitude anomalies are described from a three dimensional seismic survey acquired in block a of the dutch north sea the amplitude anomalies aas have a subcircular planform and within each set they are stacked vertically they have a high degree of spatial overlap in the vertical succession these sets of aas are interpreted as vertical anomaly clusters vacs composed of five to seven major aas each seismic interpretation of the vacs and quantitative analysis of the reservoir intervals reveal that the vacs are gas bearing silt rich reservoirs hosted in the upper section of the upper north sea group a mixed clastic succession of pliocene to pleistocene age novel analysis based on the geometry of the individual anomalies reveals that these are likely to be the result of a gas migration process characterized by sequential upward gas charge into reservoir units and that the flow across the seals separating these reservoirs is controlled by central regions of focused fluid flow these regions function as seal bypass systems and are most likely formed by hydraulic fracturing

geochemistry of the kalatongke ni cu pge sulfide deposit nw china implications for the formation of magmatic sulfide mineralization in a postcollisional environment the kalatongke also spelt as karatungk ni cu platinum group element pge sulfide deposit containing 33 mt sulfide ore with a grade of 0 8 wt ni and 1 3 wt cu is located in the eastern junggar terrane northern xinjiang nw china the largest sulfide ore body which occupies more than 50 vol of the intrusion y1 is dominantly comprised of disseminated sulfide with a massive sulfide inner zone economic disseminated sulfides also occur at the base of the intrusions y2 and y3 the main host rock types are norite in the lower part and diorite in the upper part of each intrusion enrichment in large ion lithophile elements and depletion in heavy rare earth elements relative to mid ocean ridge basalt indicate that the mafic intrusions were produced from magmas derived from a metasomatized garnet lherzolite mantle the average grades of the disseminated ores are 0 6 wt ni and 1 1 wt cu whereas those of the massive ores are 2 wt ni and 8 wt cu the pge contents of the disseminated ores 14 69 ppb pt and 78 162 ppb pd are lower than those of the massive ores 120 505 ppb pt and 30 827 ppb pd however on the basis of 100 sulfide pge contents of the massive sulfides are lower than those of the disseminated sulfides very high cu pd ratios 4 5 104 indicate that the kalatongke sulfides segregated from pge depleted magma produced by prior sulfide saturation and separation a negative correlation between the cu pd ratio and the pd content in 100 sulfide indicates that the pge content of the sulfide is controlled by both the pge concentrations in the parental silicate magma and the ratio of the amount of silicate to sulfide magma the negative correlations between ir and pd indicate that the massive sulfides experienced fractionation

geothermal regime and hydrocarbon kitchen evolution of the offshore bohai bay basin north china the offshore bohai bay basin located in the central bohai bay basin north china one of the most petroliferous basins in china in this article based on formation testing temperature drill stem tests and bottom hole temperature data 80 thermal gradient values at the depth interval of 0 to approximately 3000 m 9843 ft in the offshore bohai bay basin were obtained the basinwide average thermal gradient is 31 8 4 6c km based on the above thermal gradient data and the corresponding average weighted thermal conductivity data 80 measured terrestrial heat flow values were obtained these values range from 33 5 to 84 0 mw m2 with an average value of 60 8 8 7 mw m2 the heat flow and thermal gradient distribution in this region generally show higher values in the uplifts and lower ones in the sags a thermal history derived from vitrinite reflectance and apatite fission track data indicates that paleogene cooling occurred after a period of much higher paleogeothermal gradient 3854c km tectonic subsidence analysis reveals that the area experienced initial synrift subsidence during the paleogene followed by subsequent thermal subsidence since the neogene thermal and tectonic subsidence histories of this area are of great significance to petroleum exploration and hydrocarbon resource assessment because they bear directly on issues of petroleum source rock maturation the maturation and hydrocarbon expulsion histories of the paleogene shahejie 3 formation e2s3 which is the most important source rock in the offshore bohai bay basin are modeled results show that the shahejie 3 formation is in a high mature stage at the present day and the bozhong and qikou sags are the most important kitchens the huanghekou sag became the third most important hydrocarbon kitchen in the early neogene based on this hydrocarbon kitchen evolution oil and gas mainly accumulated after 12 ma the evolution of kitchen areas may provide new insights for the understanding of the oil and gas exploration potential of the offshore bohai bay basin

hydrocarbon system analysis in a rift basin with mixed marine and nonmarine source rocks the south viking graben north sea the south viking graben of the north sea is a prolific oil and gas province that has recoverable reserves of approximately 176 x 109 sm3 standard cubic meters 6 2 tcf gas 58 x 106 t 412 million boe natural gas liquids and 12 5 x 106 sm3 78 million bbl of black oil contained in the main fields sleipner vest sleipner ost and volve these fields are located primarily within block 15 9 in the norwegian sector and extend into neighboring blocks 15 6 and 16 7 the principal source of black nonvolatile oil is the late jurassic draupne formation which has a predominance of marine algal organic matter the lower section of the draupne formation together with the heather formation are organically leaner and contain a mixture of marine algal and terrigenous organic matter resulting in a potential to generate both oil and gas the middle jurassic hugin and sleipner formations contain humic coals and coaly shales with potential to generate gas and some light liquids these coals contain on average 80 90 vitrinitic woody material with occasional enrichment of resinite high resinite concentrations can lead to an overprediction of oil potential as they contribute significantly to the hydrogen index hi but generate primarily low molecular weight aromatic compounds all source rock facies types have reached maturities sufficient to generate oil and gas basin modeling suggests that onset of oil and gas generation started during the latest cretaceous early paleocene these source rocks have continued to yield oil and gas to the present day in many parts of the catchment area for the sleipner fields detailed geochemical analyses identified five main oil and condensate families family a comprises condensates and oil located in the northernmost part of sleipner vest and dagny generated from a marine clastic source with a predominance of type ii algal organic matter family b is condensates in the middle to southern part of sleipner vest generated from a source or a contribution from several source facies with mixed terrigenous higher plant organic matter and marine algal material family c consists of condensates reservoired in the jurassic of sleipner ost except well 15 9 a15 generated from a mixed algal terrigenous source but with a higher contribution of hydrocarbons from a marine algal source as compared with the sleipner vest family b family d comprises condensates in the jurassic triassic of loke and gungne in well 15 9 a15 from the crest of the sleipner ost structure as well as condensates within the paleocene sands of sleipner ost these condensates have a mixed terrigenous higher plant and marine algal signature and are derived from pre upper draupne formation sources family e is the black oil present in the jurassic volve field derived from a marine calcareous shale with type ii to ii s organic matter the source rock for this oil is unique in the greater sleipner area and is likely located in the isolated subgraben between the northern parts of sleipner vest and sleipner ost the hydrocarbon gases are broadly similar and are interpreted to have been generated from coals and coaly shales of the sleipner and hugin formations as well as those parts of the pre upper draupne section that have a predominance of terrigenous higher plant organic matter

15 9 gamma gas field offshore norway new trap type for north sea basin with regional structural implications the 15 9 gamma gas field lies in the central north sea midway between norway and the united kingdom the field was discovered in 1981 and by mid 1982 3 additional confirmation wells had been completed the reservoir is provided by a complex of paleocene submarine fan sandstones the sandstones decrease in thickness across the field from 150 m 492 ft in the northwest to less than 50 m 164 ft in the southeast the sandstones pinch out entirely a few kilometers beyond the field the volume of gas in place is on the order of 65 109 m3 2 3 tcf the trap in the paleocene sandstones is interpreted as being formed by a mid tertiary compressive phase which reactivated preexisting basement faults detailed structural analysis suggests that wnw e e trending faults have suffered repeated strike slip offset associated with jurassic transtension and mid cretaceous and middle tertiary transpression the writers suggest that the wnw ese trending basement faults represent a northwestward continuation of the tornquist line a fundamental fracture zone bounding the east european scandinavian platform which had previously been considered as terminating at the line of the oslo graben about 250 km 155 mi to the southeast

genetic characterization of natural gases natural gases can be characterized genetically using four properties c2 concentration carbon and hydrogen isotope variations in methane and carbon isotope variation in ethane three diagrams for genetic characterization of gases have been designed in which the carbon isotopic composition of methane is correlated with the other parameters in these diagrams compositional fields have been defined for primary gases biogenic thermogenic associated and thermogenic nonassociated and for gases which result from mixing of these gases these fields are strictly empirical and comprise compositional variations found in about 500 natural gases the isotopic and compositional variations in natural gases can be described in terms of 1 processes during formation of the gases such as bacterial fermentation or maturation of organic matter and 2 processes during secondary migration mixing of primary gases is an important and common process migration of gases predominantly affects the c2 concentration whereas the isotopic properties of gaseous hydrocarbons primarily remain unchanged allowing an assessment of the origin of migrated gases and properties of their source rocks the formation of gas from humic organic matter and coals is not yet clear from published data the diagrams use data from various basins and areas interstitial gases from the gulf of california are entirely of bacterial origin traces of thermogenic gases are formed only in the vicinity of dolerite sills gases in the south german molasse basin and in the vienna basin are of bacterial mixed and thermogenic origins data from the north italian po basin provide examples for genetic characterization of migrated gases

a new approach to bridge the effect of organofacies variations on kinetic modelling and geological extrapolations abstract reliable prediction of petroleum formation is impeded by significant variations in organofacies that result from varying conditions during source rock deposition basin simulation programs can model lateral variations but are limited in their ability to account for vertical variations due to the impact on computation time and lack of representative kinetic parameters here we present a model that merges the petroleum formation characteristics of different organofacies vertically distributed in a heterogeneous source rock prior to kinetic modelling this approach allows the evaluation of one single overall kinetic model that accounts for the different petroleum generation characteristics of a variety of organofacies preserved in a source rock and balance the different petroleum formation processes according to their importance within the different organofacies bulk petroleum generation kinetics were determined on eleven draupne formation samples taken from a well in the tampen spur area using programmed temperature open system pyrolysis at 0 1 0 7 and 5 0 k min the samples covered the entire draupne formation from its bottom to its top in the studied well individual measurements taken at the same heating rate were summed to one pyrolysis yield curve and normalized to the average rock eval s2 value the three summed curves were then used as input to determine a kinetic model that is representative of the draupne formation in this well enhanced kinetic modelling was applied in order to account for the expected variations of frequency factors after geological extrapolation the resulting kinetic model represents the petroleum generation characteristics of the entire draupne formation in the study area accounting for the variability in source potential across organofacies

late paleozoic post collisional magmatism in the eastern tianshan belt northwest china new insights from geochemistry geochronology and petrology of bimodal volcanic rocks abstract the late carboniferous to permian marks an important phase of terrane amalgamation through accretion collision in the central asian orogenic belt caob the tianshan belt forms part of this sequence where the post collisional event generated an e w trending bimodal volcanic zone that extends for ca 500 km from the southern bogda mt to the easternmost tianshan belt here we report the petrology geochemistry and geochronology of the bimodal volcanic rocks to characterize the post collisional tectonic evolution in late paleozoic the major element chemistry of the basalt and rhyolite samples indicates a bimodal high k calc alkaline affinity the basalts are characterized by high abundance in tio2 th u and pb and depletion in nb ta and p together with slight enrichment in lree contents and low hfse lree ratios the rhyolites show a close affinity to aluminous a type granites with enrichment in k na zr ce y and depletion in p nb ta and ti they also exhibit fractionated ree patterns with prominent negative eu anomalies the petrographic and geochemical data suggest that this bimodal rock series was generated in a post collisional setting the mafic rocks are likely derived from a metasomatized lithospheric mantle assimilation of different crustal components played a minor role in the genesis of these basaltic rocks the la icp ms analysis on zircons from four rhyolites and two basalts yielded similar ages ranging from 295 8 2 8 to 293 3 1 7 ma suggesting an early permian event zircons from the basalts show a wide ehf t range from 0 49 to 13 whereas those from the rhyolites show two groups of ehf t values from 5 to 3 and from 6 to 12 suggesting a mixing of crust mantle material the magmatic zircons from the bimodal volcanic rocks yielded two peaks of tdm2 between 600 820 ma and 1160 1360 ma probably representing two significant episodes of continental crust growth the bimodal volcanic rocks are correlated with the early stage of post collision our results suggest that vertical crustal growth through mantle derived magmas in post collisional setting also played a major role in the construction of the caob

noble gases solubility models of hydrocarbon charge mechanism in the sleipner vest gas field abstract noble gases are chemically inert and variably soluble in crustal fluids they are primarily introduced into hydrocarbon reservoirs through exchange with formation waters and can be used to assess migration pathways and mechanisms as well as reservoir storage conditions of particular interest is the role groundwater plays in hydrocarbon transport which is reflected in hydrocarbon water volume ratios here we present compositional stable isotope and noble gas isotope and abundance data from the sleipner vest field in the norwegian north sea sleipner vest gases are generated from primary cracking of kerogen and the thermal cracking of oil gas was emplaced into the sleipner vest from the south and subsequently migrated to the east filling and spilling into the sleipner ost fields gases principally consist of hydrocarbons 83 93 co2 5 4 15 3 and n2 0 6 0 9 as well as trace concentrations of noble gases helium isotopes 3he 4he are predominantly radiogenic and range from 0 065 to 0 116 ra reported relative to air ra 1 4 10 6 clarke et al 1976 sano et al 1988 showing predominantly 98 crustal contributions consistent with ne 20ne 22ne from 9 70 to 9 91 21ne 22ne from 0 0290 to 0 0344 and ar isotopes 40ar 36ar from 315 to 489 air derived noble gas isotopes 20ne 36ar 84kr 132xe are introduced into the hydrocarbon system by direct exchange with air saturated water asw the distribution of air derived noble gas species are controlled by phase partitioning processes in that they preferentially partition into the gas i e methane phase due to their low solubilities in fluids therefore the extent of exchange between hydrocarbon phases and formation waters that have previously equilibrated with the atmosphere can be determined by investigating air derived noble gas species we utilize both elemental ratios to address process i e open vs closed system and concentrations to quantify the extent of hydrocarbon water exchange i e volumetric gas water ratios these data are discussed within the framework of several conceptual models i total gas stripping model which assumes all noble gases have been stripped from the water phase thus defining the minimum volume of water to have interacted with the hydrocarbon phase ii equilibrium model which assumes equilibration between groundwater and hydrocarbon phase at reservoir p t and salinity and iii open and closed system gas stripping models using concentrations and elemental ratios by applying these models to ne ar data from sleipner we estimate volumetric gas water ratios v g v w between 0 02 and 0 07 which are lower than standard geologic gas water estimates of 0 24 estimated by combining gas in place estimates with groundwater porosity estimates sleipner vest data can be best approximated by an open system model which predicts more than an order of magnitude more groundwater interaction during migration than geologic estimates indicating a dynamic aquifer system and or a hydrous migration pathway in an open system the extent of gas loss can be estimated to be between 8 and 10 reservoir volumes which have passed through the system and been lost i e filled and spilled

geochronology and geochemistry of early permian mafic ultramafic complexes in the beishan area xinjiang nw china implications for late paleozoic tectonic evolution of the southern altaids abstract the hongshishan and pobei mafic ultramafic complexes outcrop in the beishan area in the southernmost altaids they consist of olivine gabbros dunites and pyroxenites zircons from olivine gabbros from the hongshishan complex yield a u pb age for emplacement of 281 8 2 6 ma the olivine gabbros have low sio 2 47 08 48 66 tio 2 0 14 0 29 mno 0 07 0 09 and k 2 o 0 06 0 09 but high mg values 81 t fe 2 o 3 4 93 6 29 the hongshishan and pobei mafic ultramafic complexes are characterized by negative anomalies in high field strength elements zr hf nb ta which we interpret as arc related signatures they also have spikes in large ion lithophile fluid mobile elements ba u pb sr and high mobile immobile element ratios i e primitive mantle normalized sr nd ba la 1 which are attributed to an aqueous fluid component in the source zircon hf isotopes indicate that the source magma was derived either from a depleted mantle with some crustal contamination or from an enriched mantle these data are interpreted to indicate that the hongshishan and pobei mafic ultramafic complexes were emplaced in the early permian subduction related environment which suggests that the paleo asian ocean in the southernmost part of altaids did not close until after early permian

volcanic hosted rare metals deposit at brockman western australia rare metals mineralization at brockman western australia is the product of early pyroclastic eruption of trachytic magma enriched in volatiles and incompatible elements such as zr hf nb ta be y and ree and ga the mineralization is fine grained 20 m and is the result of alteration and re mobilization of comparatively simple magmatic precursor minerals such as columbite and zircon by f rich deuteric solutions that were retained in an ash flow tuff the niobium tuff following eruption chondrite normalized ree distributions show strong enrichment in hree gel zircon is the principal residence of the hree disseminated bastnaesite parisite and synchisite carries the lree and bertrandite in late stage calcite veins is the host for be ga occurs in k mica in the groundmass trachytic flows overlying the niobium tuff contain many of the same ore minerals but in trace amounts

palaeozoic arc magmatism in the central asian orogenic belt of kazakhstan shrimp zircon ages and whole rock nd isotopic systematics abstract early palaeozoic tonalite to granodiorite intrusions in northern kazakhstan are associated with lode gold mineralization and have shrimp zircon ages of 457 3 6 6 ma aksu 452 9 5 6 ma and 447 4 5 4 ma both zholymbet the stepnyak intrusion contains large xenoliths with an age of 480 6 5 0 ma one early palaeozoic zircon from a porphyritic diorite at stepnyak has a core with a near concordant 207pb 206pb age of 3888 1 5 ma whereas other xenocrystic grains are between 983 and 2698 ma old the early archaean age is probably inherited from unexposed basement of the kokchetav massif and represents the oldest crustal material so far known from the asian continent it appears that the aksu zholimbet and stepnyak granitoids were emplaced in the late ordovician in an andean or japan type continental arc environment on the margin of the kokchetav massif late palaeozoic granitoids in central kazakhstan have devonian zircon ages of 407 1 3 9 381 1 3 1 and 369 2 4 9 ma whereas the youngest sample from the topar massif has a late carboniferous emplacement age of 314 1 5 1 ma initial end values range from 5 to 1 corresponding to nd model ages of 1 1 0 6 ga the isotopic data are similar to those of other phanerozoic granitoids of the central asian orogenic belt and corroborate melting of predominantly juvenile crustal protoliths our data also confirm that devonian and carboniferous arc magmatism in central kazakhstan assimilated older and already accreted island arc systems yet is derived from primitive sources probably in a subduction setting the range of end values with corresponding nd mean crustal residence ages in the range of 0 6 1 1 ga for most samples indicates variable recycling of late proterozoic largely juvenile continental crust in the formation of the palaeozoic magmatic arcs of central kazakhstan the orogenic evolution terminated with permian anorogenic rift related alkaline granite magmatism end 2 to 8 which reflects melting of juvenile mantle derived lower crust

magnetite geochemistry of the heijianshan fe cu au deposit in eastern tianshan metallogenic implications for submarine volcanic hosted fe cu deposits in nw china abstract the heijianshan fe cu au deposit is located in the aqishan yamansu belt in eastern tianshan nw china as a typical fe cu deposit in the region heijianshan is hosted in the upper carboniferous matoutan formation submarine volcanic volcaniclastic rocks alteration styles mineral assemblages and vein crosscutting relationships divide the hydrothermal alteration and mineralization processes into seven stages namely the chromite stage i epidote stage ii magnetite stage iii pyrite stage iv cu au stage v late veins stage vi and supergene stage vii alteration mineralization stages magnetite mineralization comprises the hematite stage iii a and main magnetite stage iii b mineralization sub stages the heijianshan magnetite ores consist of massive with mushketovite mom or sulfides mos disseminated do and magnetite clasts with chromite mwc or without chromite mnc ores magnetite in massive and disseminated ores is featured by 1 depletion in zr nb and ta 2 low ti f o 2 increased which may represent the major controls on the formation of the various magnetite ore types compositions of the ore fluids and host rocks formation of coexisting minerals and other physicochemical parameters such as t and f o 2 may have variably influenced the magnetite geochemistry in the different heijianshan ore types with fluid compositions probably playing the most important role discrimination diagrams for instance cr vs co ni cr vs ti v vs cr and ni vs cr may be useful for magnetite mineralization type differentiation in other submarine volcanic hosted fe fe cu deposits in the aqishan yamansu belt geochemical discrimination diagrams alteration and mineralization paragenesis indicate that the heijianshan fe cu au deposit is best classified as an iocg like deposit which offers a new insight for classifying and characterizing ore genetic types for similar fe and fe cu deposits in eastern tianshan

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