estimation of the hydrocarbon loss through major tectonic events in the tazhong area tarim basin west china abstract the tazhong area located in the central part of the tarim basin is the major commercial oil and gas province in the tarim basin hydrocarbons have been discovered in the ordovician silurian and carboniferous reservoirs most of the hydrocarbon reservoirs in the tazhong area have experienced post charge and accumulation readjustment or loss associated with multiple post charge tectonic movements the relationship between the destroyed hydrocarbon proportion dhp caused by tectonic events and tectonic movement intensity tmi in 15 well blocks has been established for the entire tazhong area using tmi analysis tmi can be quantitatively characterized by the denudation thickness and effective caprock thickness ratio whereas the dhp can be quantitatively determined by the variations of the palaeo and current oil water contacts there appears to be a good relationship between dhp and tmi with a correlation coefficient of 0 9 most of the original ordovician hydrocarbon accumulations formed in the late ordovician had been lost with an average dhp of up to 70 the tectonic movement is much weaker in the late silurian and late permian period with the dhps for the silurian reservoirs and carboniferous reservoirs in the eastern tazhong area averaging 50 all the dhps show a gradual increase from west to the east figure 17 figure 18 figure 19 the preservation condition of the reservoirs is generally better in west than in the east

a preliminary investigation of the optical properties of asphaltene and their application to source rock evaluation organic petrological methods have been used to investigate optical properties of asphaltenes from source rocks humic coals and crude oils with respect to microscopic structure fluorescence and reflectance asphaltenes form a distinctive group all asphaltenes exhibit brown fluorescence with relative intensity ranging from 0 15 to 0 35 the intensity decreasing gradually with increasing maturity of the source rocks from which the asphaltene is extracted asphaltene reflectance is an important geochemical parameter the reflectance of asphaltenes in air medium ra varies in the range of 4 5 8 0 and is affected mainly by source rock type and maturity in general the richer the hydrogen content of a kerogen the weaker the reflectance of its derived asphaltenes the contribution of source matter type to the variation of asphaltene reflectance can be as much as 0 50 ra in the low maturity range there is a nearly linear relationship between asphaltene reflectance and vitrinite reflectance in oil ro and geochemical maturity indicators such as cpi mpr and mpi asphaltene reflectance is a potentially valuable technique for the maturity determination of source rocks and crude oils

petroleum charge history in the lunnan low uplift tarim basin china evidence from oil bearing fluid inclusions abstract the petroleum charge history in the lunnan low uplift tarim basin china was investigated by comparing the geochemical characteristics of fluid inclusion fi oils from ordovician and triassic reservoirs with crude oils from stratigraphically different reservoirs quantitative grain fluorescence qgf and total scanning fluorescence tsf were used to screen the reservoir samples so as to identify suitable samples for molecular composition of inclusion mci analysis all of the samples contain c 30 n propylcholestanes diagnostic of marine source rocks the ordovician hosted fi oils differ from the triassic hosted fi oils having higher relative abundances of c 19 tricyclic terpane c 24 tetracyclic terpane and rearranged hopanes ts and c 29 ts and higher pr ph ratios while the triassic hosted fi oils have lower pr ph ratios and higher relative abundances of c 23 tricyclic terpane arylisoprenoids 25 norhopanes and c 35 homohopane several of the crude oils are similar to the triassic hosted fi oils based on the geochemical characteristics of the fi and crude oils combined with information on the burial history of the area at least two petroleum charge episodes can be distinguished in the lunnan low uplift an early charge represented by the ordovician hosted fi oils was biodegraded as evidenced by the presence of 25 norhopanes in the triassic hosted fi oils and crude oils but not in the ordovician hosted fi oils ordovician hosted fi oils provide the only evidence for oil generated from cambrian lower ordovician source rocks triassic hosted fi oils and crude oils in the ordovician carboniferous and triassic reservoirs are mixtures of biodegraded oil from an early charge episode and more mature oil from later charge

evolution of synmetamorphic veins and their wallrocks through a western alps transect no evidence for large scale fluid flow stable isotope major and trace element systematics quartz rich synfolial veins and wallrocks from different areas of a western alps cross section are examined in an attempt to constrain the scale and mechanisms of fluid flow through metamorphic terrains different portions of this cross section underwent distinct p t evolutions as reflected by the mineralogy of veins a in the greenschist external dauphinois domain veins are characterized by quartz and calcite together with an aluminosilicate pyrophyllite na k bearing phyllosilicates and a femg bearing silicate chlorite b in narrow domains of the brianconnais and piemontais zones with a non eclogitic hp lt evolution followed by rapid cooling veins are characterized by quartz calcite ca and fe mg bearing silicates lawsonite and fe mg carpholite respectively and c in the major part of the brianconnais andpiemontais zones where low grade blueschistfacies metamorphism is followed by a greenschist facies evolution veins are characterized by the replacement of earlier lawsonite and carpholite by na and k bearing micas in order to constrain the provenance of fluids involved in vein formation we determined stable isotope c 0 h and major and trace element compositions in minerals and whole rocks for a large set of veins and wallrocks these rocks are compared with some non metamorphic shales from the northern paris basin considered as protoliths of the alpine schists stable isotope compositions of calcites are regionally distinct 6r80 28 0 smow in the northern paris basin 26 0 in the brianconnais zone 22 0 in the piemontais zone and 18 0 in the dauphinois zone within each studied region calcite g o values are quite homogeneous regardless of rock type vein or wallrock this feature is explained as an isotopic homogenization with the most abundant lithology in each zone rock buffered system where the overall ratio of calcite of marine origin to detrital silicate minerals determines the final isotopic composition of the whole rock w r after equilibration during alpine metamorphism g o gd values of analysed hydrated minerals and whole rocks si80 15 to t 25 0 and 6d 60 0 smow lie within the field of alpine cover rocks and of fluids in equilibrium with these rocks interaction with an external o or d depleted fluid such as hydrothermal waters meteoric water or basement fluid can be ruled out major and trace element systematics indicate an enrichment in si ca p sr y ta and locally eu in the veins with respect to the wallrock related to massive crystallization of quartz and carbonates together with phosphate and oxide potential fluid sources chemical composition of the fluid phase and the mechanisms of fluid flow during vein formation are discussed fluid flow takes place within tectonic units at both hectometric and decimetric scale fluid may also have migrated along and across the major tectonic contacts but this process is poorly documented

coesite and pure pyrope in high grade blueschists of the western alps a first record and some consequences a pyrope quartzite originally described by vialon 1966 from the dora maira massif was resampled and reinvestigated garnet up to 25 cm in size phengite kyanite talc and rutile are in textural equilibrium in an undeformed matrix of polygonal quartz the garnet is a pyrope almandine solid solution with 90 to 98 mol mg end member it contains inclusions of coesite which has partially inverted to quartz resulting in a typical radial cracking of the host garnet around the inclusions several lines of evidence show that coesite crystallised under nearly static pressure conditions and that the whole matrix has once been coesite

from granulites to eclogites in the sesia zone italian western alps a record of the opening and closure of the piedmont ocean the sesia zone italian western alps offers one of the best preserved examples of pre alpine basement reactivated under eclogite facies conditions during the alpine orogenesis a detailed mineralogical study of eclogitized acid and basic granulites and related amphibolites is presented in these rare weak to undeformed rocks microstructural investigations allow three main metamorphic stages to be distinguished a a medium to low p granulite stage giving rise to the development of orthopyroxene garnet plagioclase brown amphibole ilmenite biotite in basic granulites and garnet k feldspar plagioclase cordierite sillimanite biotite ilmenite in acid granulites b a post granulite re equilibration associated with the development of shear zones producing discrete amphibolitization of the basic granulites and widespread development of biotite sillimanite cordierite spinel in the acid rocks c an eo alpine eclogite stage giving rise to the crystallization of high p and low t assemblages in an effort to quantify this evolution independent well calibrated thermobarometers were applied to basic and acid rocks for the granulite event p t estimates are 7 9 kbar and 700 800 c and for subsequent retrograde evolution p t was 4 5 kbar and 600 c for the eo alpine eclogite metamorphism pressure and temperature conditions were 14 16 kbar and 550 c the inferred p t path is consistent with an uplift of continental crust produced by crustal thinning prior to the subduction of the continental rocks in the light of the available geochronological constraints we propose to relate the pre alpine granulite and post granulite retrograde evolution to the permo jurassic extensional regime the complex granulite eclogite transition is thus regarded as a record of the opening and of the closure of the piedmont ocean

a barotropic inverse tidal model for the arctic ocean 1 we describe high resolution 5 km grid linear dynamics and inverse models of arctic ocean barotropic tides obtained with the osu tidal inversion software otis package the 8 constituent dynamics based model uses the latest ibcao bathymetry and open boundary forcing from the recent tpxo 6 2 global barotropic tidal solution this model performs significantly better than the present benchmark arctic tidal model 14 km grid by z kowalik and a proshutinsky as judged by comparisons with 300 coastal tide gauges the greatest improvements are found in the canadian arctic archipelago nares strait and the baffin bay and labrador sea and can be explained by the higher resolution of the new model in these topographically complex regions the new arctic inverse model assimilates coastal and benthic tide gauges and topex poseidon and ers altimetry for further improvements of the 4 dominant constituents m2 s2 k1 and o1

analysis of secondary migration of hydrocarbons in the ordovician carbonate reservoirs in the tazhong uplift tarim basin china the process and mechanisms of secondary hydrocarbon migration in the tazhong uplift tarim basin were investigated based on the analysis of the regional structure and by integrating geologic hydrodynamic and geochemical parameters parameters successfully analyzed included the fluid potential fluid properties production outputs and diamantane index the results indicated that hydrocarbons migrated into the tazhong uplift from the northern part of the manjiaer depression through a series of injection points ips during four orogenies that is the early caledonian 510 ma the late caledonian 439 ma the late hercynian indosinian 290 ma and the yanshanian himalayan 208 ma a total of six ips were identified at the intersections of the northeast trending faults and the northwest trending flower strike faults the hydrocarbons migrated from the ips into traps along regional trends from northwest to southeast and from northeast to southwest the hydrocarbon migration process and patterns determined the distribution of hydrocarbon properties and production rates in the tazhong uplift with increasing distance from the ips daily hydrocarbon production decreases and the hydrocarbons become progressively heavier and display lower gas oil ratios

light hydrocarbons and diamondoids of light oils in deep reservoirs of shuntuoguole low uplift tarim basin implication for the evaluation on thermal maturity secondary alteration and source characteristics abstract the shuntuoguole low uplift in tarim basin is particular because it provides insights into geochemistry of light oils at ultra deep ordovician oil reservoirs 7200 8200 m the light hydrocarbons and diamondoids of 16 oil samples from shunbei no i fault zone f1 and v fault zone f5 were analyzed to investigate their thermal maturity source characteristics and secondary alteration the oils show high similarity in the characteristics of light hydrocarbons and diamondoids the light hydrocarbons are characterized by high contents of alkanes and low contents of cycloalkanes and aromatics and the diamondoids show a domination of adamantanes and their alkylated isomers compared diamantanes thermal maturity indicators derived from diamondoids and c5 c7 light hydrocarbons indicate that the oils are highly mature and the corresponding equivalent vitrinite reflectance rc determined by light hydrocarbons and methyldiadamantane index are in the ranges of 1 2 1 5 signatures of biodegradation and thermochemical sulfate reduction were not observed in the oils the geochemical information from the light hydrocarbons and distribution patterns of molar concentration of n alkanes indicate that the oils from f1 experienced noticeable evaporative fractionation and the oils from f5 did not this was supposed to be the primarily reason for the physical difference between oils from the both fault zones the parameters derived from the light hydrocarbons and diamondoids indicate the oils are from same source rocks which are associated with marine materials with type ii kerogen such as algae and bacteria and both of cambrian lower ordovician o1 and middle upper ordovician o2 3 source rocks in the deep lower palaeozoic strata contributed to the oils

experimental transport of si al and mg in hydrothermal solutions an application to vein mineralization during high pressure low temperature metamorphism in the french alps a study of hydrothermal vein mineralization in meta argillites subjected to high pressure low temperature metamorphism reveals that ferromagnesian e g chlorite and pure aluminosilicate e g pyrophyllite mineralization can be correlated with regimes of increasing and decreasing temperature respectively an experimental study of the transport of silica aluminum and magnesium in hydrothermal solutions has been undertaken to simulate variations in the physical conditions during metamorphism and the accompanying mass transport in a closed system thermodynamic and kinetic analysis of the experimental results indicates that local equilibrium among aqueous and mineral phases controls the distribution and composition of hydrothermal vein mineralization and that vein mineralogy can be used to infer the sense of variation of pressure and temperature during metamorphism

the silurian play in the tazhong uplift tarim basin northwestern china abstract silurian sandstone reservoirs in the tazhong uplift in the tarim basin northwestern china are rich in bitumen and movable oil analysis of the biological markers indicates that the bitumen and movable oil came from two source rocks in the cambrian and middle upper ordovician system both of which are belong to marine facies the silurian system experienced three stages of oil filling namely late caledonian period 400 ma late hercynian period 240 ma and yanshan himalayan 40 ma period most of the oil emplaced in the late caledonian was subsequently oxidized to bitumen the movable oil found at the present time was mainly generated from the middle upper ordovician source rocks with only a minor contribution from the cambrian source rocks generating in the two later periods bitumen and heavy crude were largely trapped below a red mudstone unit while movable oil was concentrated below an underlying gray mudstone unit the middle sub section of bitumen sandstone section lateral migration into the silurian reservoirs took place from northwest to southeast in each stage and was controlled by an inherited palaeohigh while individual relatively limited in extent the tidal flat sandstones of the main reservoir have stacking patterns that generate extensive sand sheets faulting can both enhance connectivity and create traps

internal wave variability in the beaufort sea during the winter of 1993 1994 1 acoustic doppler current profiler observations were obtained at the sea ice mechanics initiative ice camp as it drifted through the beaufort sea over the winter of 1993 1994 in this paper the variability of the internal wave field is examined initially december 1993 january 1994 the camp drifted westward through the central canada basin 75 n 139 153 w numerous anticyclonic baroclinic eddies were encountered internal wave energy levels averaged 1 25 of the garrett munk gm standard shear variance averaged 1 17 gm during february march 1994 the camp drifted meridionally along 156 w near the northwind ridge reversing direction several times large baroclinic vortices were not detected internal wave energy levels were significantly greater during this period peaking at 1 6 gm shear variance peaked at 1 3 gm the waves were predominantly near inertial resulting from three distinct surface generation events downward vertical energy fluxes ranged from typical values of 0 02 mw m2 to a peak value of 0 15 mw m2 two thirds of the downward flux was associated with waves of vertical scale greater than 55 m the remainder with smaller scale waves upward energy fluxes ranged from 0 02 mw m2 typical to 0 10 mw m2 peak supported almost entirely by the larger scale waves high ice water relative velocities atmospheric storms accompanied by ice deformation appear to be necessary but not sufficient to assure a downward propagating wave generation event the highly variable mesoscale has a significant effect on the near inertial wave field propagation the data suggest that the vertical propagation of near inertial waves is strongly affected by the depth variation of the vertical component of mesoscale vorticity the large beaufort sea vortices appear to have a dual effect on the wave field enhanced vertical propagation speed and decreased energy density is found in the negative vorticity cores propagation into the positive vorticity regions surrounding the cores is inhibited the increase in wave energy experienced as the ice camp left the central beaufort sea is jointly associated with the passage of storms and the absence of large baroclinic vortices over the northwind ridge

internal waves in the arctic ocean comparison with lower latitude observations abstract a thermistor chain was moored below the pack ice from 50 150 m in the arctic ocean for five days in 1981 oscillations in temperature are attributed to the vertical dispalcement of internal waves the spectral shape of isotherm dispalcement is consistent with the garrett munk model and other internal wave observations but the spectral level is significantly lower other observations from the arctic ocean also exhibit lower internal wave energy when compared with historical data from lower latitudes the lower energy may be related to the unique generation and dissipation mechanisms present in the ice covered arctic ocean significant peaks in vertical coherence occur at 0 81 and 2 6 cph the peak at 2 6 cph coincides approximately with the high frequency spectral cutoff near the local buoyancy frequency this feature has been observed in many other internal wave experiments the coherent oscillations at 0 81 cph exhibit a node in vertical dispalcement at 75 100 m this is consistent with either

contrasted metamorphic evolutions in thrusted cover units of the brianconnais zone french alps a model for the conservation of hp lt metamorphic mineral assemblages the evolution of organic matter silicate and fluid phases in cover units of the three structural zones of the vanoise area allows one to distinguish differentp t cooling paths these paths depend on whether the cover has been transported western and northern vanoise or not southern vanoise all units first underwent a common high pressure low temperature hp lt metamorphic stage 300 c 6 kbar of blueschist type fe mg carpholite chloritoid facies the cover units transported on the extermal colder zone coal measure series metamorphosed in albite chlorite facies preserved their hp mineralogy fe mg carpholite lawsonite and organic matter content oils wet gases and kerogen while the unit which remained in contact with its more thermally conductive basement polymetamorphic now shows extensive greenschist facies overprinting breakdown of fe mg carpholite and lawsonite appearance of chlorite pyrophyllite chloritoid and clinozoisite absence of oils and wet gases these two tectonic evolutions might serve as a more general model for the preservation of hp lt mineral assemblages

deformation and motion in the western alpine arc we attempt to reconstruct the kinematics deformation and motion of the western alpine arc between the mercantour and aar massifs first we compile a map showing principal extension x direction within three major structural units in the external zone x directions are broadly radial to the alpine arc in the internal zone they are uniform or smoothly varying in some domains whereas in the intermediate zone they often show much scatter next we use geochronological data and p t conditions estimated from metamorphic mineral reactions to time the deformation on each of a series of interval maps we show x directions for strain accumulated during a chosen time interval we argue that these incremental x directions are approximately equivalent to segments of particle paths showing displacements relative to stable europe for 120 100 ma the displacement direction was about n150 and coeval with eclogite facies metamorphism it is interpreted as a direction of overthrusting by the african plate around 40 ma the displacement in the south part of the arc became westerly finally between 25 and 15 ma displacement directions were generally radial to the arc

structural and petrological analyses of the frido unit southern italy new insights into the early tectonic evolution of the southern apennines calabrian arc system abstract this study provides new data on the deformation and metamorphic evolution of the jurassic to upper oligocene frido unit an ocean continent transition oct unit belonging to the ligurian accretionary complex lac by means of the integration of structural analysis petrological investigations and a revision of the stratigraphical setting the frido unit representing the main metamorphic component of the lower middle miocene lac in southern italy is characterized by a multistage tectonic evolution including i two progressive deformation phases involving the development under relatively high pressure metamorphic conditions of an early cleavage associated with isoclinal folds within the framework of a dominant se ward tectonic transport ii a third deformation stage involving the growth of lower pressure na amphibole along extensional shear surfaces therefore probably marking the onset of tectonic exhumation and iii two very low temperature deformation phases characterized by the development of kink folds and associated thrusts probably related to the late tectonic emplacement of the accretionary wedge onto the outer sectors of the apennine domain with a prevailing tectonic transport first toward the ne and then toward the nw in order to clarify the metamorphic evolution of the frido unit petrologic analyses were focused on its metasedimentary pelitic succession here mineral parageneses including carpholite well documented for the first time in this study and potassic white mica yielded peak pressure of 1 2 1 4 gpa and temperature around 350 c thus indicating a high pressure very low temperature metamorphism and a p t t path characterized by a rapid exhumation without any greenschist facies overprint in comparison with similar units cropping out in northern calabria tuscany and corsica the frido unit experienced one of the coldest burial exhumation histories

late paleozoic depositional history of the tarim basin northwest china an integration of biostratigraphic and lithostratigraphic constraints this study provides the first detailed lithostratigraphic and biostratigraphic constraints for improving stratigraphic resolution for hydrocarbon prospecting and exploration in the tarim basin a total of 49 stratigraphic units 38 formations and 11 members ranging in age from the latest devonian to permian are reviewed or redefined in terms of nomenclatures lithology age constraints and lateral distributions based on the detailed field works or newly published data of these the piqiang formation new formation is proposed to include the reefal carbonates of asselian sakmarian age from the northern tarim the subsurface upper paleozoic stratigraphic framework of the desert areas of the basin is also established for the first time the high resolution basinwide stratigraphic correlations reveal that the sedimentation of the basin in the late paleozoic was extremely uneven of these the famennian to changhsingian successions are completely recorded in the southwestern margin areas of the basin here five eustatic sedimentary cycles are well recognizable suggesting the sedimentation was more eustatically controlled and little affected by local tectonism the late paleozoic successions of both kalpin and taklimakan regions are commonly interrupted by major hiatuses at various horizons suggesting that the sedimentation was apparently modified by local tectonism of these the northward movement of the tarim block and its subsequent collision with the yili microcontinent part of the kazakhstan plate may be principally accountable for the discrepancy in the sedimentation of the various regions in the basin in the late paleozoic

on the significance of aragonite occurrences in the western alps aragonite occurrences from two areas of the western alps are described it is shown that aragonite has been formed under blueschist metamorphic conditions in the western vanoise while it has been precipitated under sub surface conditions in the queyras region an uplift p t path of the aragonite bearing rocks of the western vanoise is constructed using two independent methods 1 temperature estimates using the sr content of aragonite in the successive veins and 2 the kinetics of the aragonitecalcite solid state transition the uplift p t path has an unusual shape with an important temperature decrease 100 to 150 c for a pressure decrease of 0 2 gpa following blueschists metamorphism p 0 7 gpa t 300 c thermal models show that this unusual p t path of the western vanoise can be explained if one maintains a low temperature between 125 and 175 c at the base of the tectonic unit containing the aragonite bearing rocks during part of its burial history followed by the whole of its exhumation a tectonic scenario is proposed to account for the observed and modelled p t path

metamorphic petrology of a high pressure low temperature subduction complex in west central baja california mexico the western baja terrane wbt of west central baja california is an uplifted subduction complex that is divided into smaller subterranes on the basis of bounding faults and petrological differences each subterrane contains coherent early jurassic to early cretaceous sedimentary and mafic volcanic rocks not melange that have been metamorphosed under blueschist facies conditions key phases in metabasites and metaturbidites include jadeitic to acmitic clinopyroxene sodic amphibole lawsonite aragonite chlorite titanite and white mica pressure indicators include the jadeite content of clinopyroxene and the presence of aragonite temperature indicators include the presence of lawsonite the absence of greenschist facies minerals and results from vitrinite reflectance studies conditions at the peak of metamorphism were 8 kbar 225 325 c for subterrane 1 7 8 kbar 170 220 c for subterrane 2 and 5 6 kbar 175 200 c for subterrane 3 these correspond to cold geothermal gradients 6 9 km vein assemblages that include aegerine jadeite and aegerine albite aragonite lawsonite and sodic amphibole indicate uplift during continued cold conditions probably during steady state subduction

time and temperature in petroleum formation application of lopatin s method to petroleum exploration n v lopatin in the soviet union has developed a method for taking both time and temperature into account as factors in thermal maturation of kerogen lopatin s time temperature index of maturity tti values correlate with the thermal regimes corresponding to generation and preservation of hydrocarbons because such information is potentially of great interest for oil exploration a calibration and evaluation have been made of lopatin s method within the limitations of the data presently available the following statements can be made 1 the rate of the chemical reactions involved in thermal maturation of organic material appears to double with every 10 c 18 f rise in temperature 2 threshold values of lopatin s time temperature index of maturity tti are 15 onset of oil generation 75 peak oil generation 160 end oil generation 500 40 oil preservation deadline 1 000 50 oil preservation deadline 1 500 wet gas preservation deadline 65 000 dry gas preservation deadline 3 tti values calculated from lopatin reconstructions consistently agree with other maturation parameters commonly used by petroleum geochemists potential applications of lopatin s method for oil exploration include timing of oil generation calculation of volume of hydrocarbons generated within a basin and determination of economic deadlines

multiple phases of hydrocarbon generation and migration in the tazhong petroleum system of the tarim basin people s republic of china abstract organic petrology organic geochemical analysis and fluid inclusion methods were employed to investigate a series of core samples from the tazhong uplift bitumens and organic inclusions were found to occur widely in paleozoic rocks especially carbonates and both can be subdivided into three groups the reflectance ranges of the three bitumen groups are 1 30 1 60 i 0 50 0 80 ii and 0 15 0 40 iii respectively and the corresponding organic inclusion groups are dark yellow fluorescence organic inclusions with a homogenization temperature of 200 240 c blue green fluorescence organic inclusions with a temperature of 160 200 c and the strong yellow fluorescent organic inclusions with a temperature of 80 130 c the wide occurrence of the three group bitumens and organic inclusions in the tazhong uplift reveals that there were three periods of large scale oil migration and accumulation in this area the analysis of hydrocarbon generating history based on paleotemperature and burial history of source rocks shows that they underwent three oil generating peaks in early ordovician triassic and cenozoic respectively which led to three phases of hydrocarbon generation and migration it is believed that the tazhong uplift is an old uplift rich in oil and gas and has been fed with oil and gas from nearby source areas during a long geological history and also that it has great hydrocarbon potential

near inertial internal waves and sea ice in the beaufort sea the evolution of the near inertial internal wavefield from ice free summertime conditions to ice covered wintertime conditions is examined using data from a yearlong deployment of six moorings on the beaufort continental slope from august 2008 to august 2009 when ice is absent from july to october energy is efficiently transferred from the atmosphere to the ocean generating near inertial internal waves when ice is present from november to june storms also cause near inertial oscillations in the ice and mixed layer but kinetic energy is weaker and oscillations are quickly damped damping is dependent on ice pack strength and morphology decay scales are longer in early winter november january when the new ice pack is weaker and more mobile decreasing in late winter february june when the ice pack is stronger and more rigid efficiency is also reduced as comparisons of atmospheric energy available for internal wave generation to mixed layer kinetic energies indicate that a smaller percentage of atmospheric energy is transferred to nearinertial motions when ice concentrations are 90 however large kinetic energies and shears are observed during an event on 16 december and spectral energy is elevated above garrett munk levels coinciding with the largest energy flux predicted during the deployment a significant amount of near inertial energy is episodically transferred to the internal wave band from the atmosphere even when the ocean is ice covered however damping by ice and less efficient energy transfer still leads to low arctic internal wave energy in the near inertial band increased kinetic energy below 300m when ice is forming suggests some events may generate internal waves that radiate into the arctic ocean interior

distinguishing cambrian from upper ordovician source rocks evidence from sulfur isotopes and biomarkers in the tarim basin abstract the reported source rocks for the abundant petroleum in the tarim basin china range from cambrian to lower ordovician and or upper ordovician in age however the difference between the two groups of source rocks is not well characterized in this study pyrite was removed from eleven mature to over mature kerogen samples from source rocks using the method of crcl 2 reduction and grinding the kerogen and coexisting pyrite samples were then analyzed for 34 s values results show that the kerogen samples from the cambrian have 34 s values between 10 4 and 19 4 the values are significantly higher than those from the lower ordovician kerogen 34 s of between 6 7 and 8 7 which in turn are generally higher than from the upper ordovician kerogen samples 34 s of between 15 3 and 6 8 the associated pyrite shows a similar trend but with much lower 34 s values this stratigraphically controlled sulfur isotope variation parallels the evolving contemporary marine sulfate and dated oil 34 s values from other basins suggesting that seawater sulfate and source rock age have an important influence on kerogen and pyrite 34 s values the relatively high 34 s values in the cambrian to lower ordovician source rocks are associated with abundant aryl isoprenoids gammacerane and c 35 homohopanes in the extractable organic matter indicating that these source rocks were deposited in a bottom water euxinic environment with water stratification compared with the upper ordovician the cambrian to lower ordovician source rocks show abundance in c 28 20r sterane c 23 tricyclic terpanes 4 23 24 trimethyl triaromatic dinosteroids and depletion in c 24 tetracyclic terpane c 29 hopane thus 34 s values and biomarkers of source rock organic matter can be used for distinguishing the cambrian and upper ordovician source rocks in the tarim basin

thermochemical sulphate reduction in cambro ordovician carbonates in central tarim h2s and co2 are found in elevated concentrations in palaeozoic reservoirs in the tarim basin in china we have carried out analyses on gas petroleum mineral cement and bulk rock compositions and isotope ratios together with petrography and fluid inclusion to assess the origin of the h2s a deep crustal e g volcanic origin of the h2s and co2 is unlikely since the inert gases n2 and he have isotope ratios totally uncharacteristic of this source organic sources are also unlikely since the source rock has low a sulphur content and the sulphur isotope ratio of the petroleum correlates positively with the sulphur content the opposite of what would be anticipated from petroleum derived h2s bacterial sulphate reduction is unlikely because temperatures are too high for bacteria to have survived thermochemical sulphate reduction of petroleum fluids by anhydrite in lower ordovician and cambrian carbonate reservoirs is the most likely source of both the h2s and the co2 causing isotopically characteristic pyrite co2 gas and calcite cement h2s and possibly co2 migrated into silurian sandstone reservoirs by cross formational flow the h2s with the same sulphur isotope ratio as ordovician anhydrite was partially lost from the fluid phase by extensive growth of late diagenetic pyrite similarly the co2 was partially lost from the fluid phase by precipitation of late diagenetic calcite the h2s that resulted from tsr underwent reaction with the remaining petroleum resulting in locally elevated organic sulphur concentrations in the petroleum and the progressive adoption of the ordovician anhydrite sulphur isotope ratio

opposite vergence of nappes and crustal extension in the french italian western alps in the internal pennine zone of the french italian western alps dora maira monviso rocciavre massifs and queyras region the structural trends define an apparent dome geometry that is truncated to the east by the po basin this geometry is classically interpreted as a backthrusting system the kinematic history of the area has been investigated using structural metamorphic and geochronologic data on the basis of which two main deformation episodes have been distinguished that occurred under differing metamorphic conditions 1 the first deformation occurred under greenschist facies metamorphism it caused a regional scale foliation and an ew trending lineation that lie parallel to ductile deformation zones and thrust contacts sense of shear indicators associated with the lineation indicate contradictory top to the east and top to the west senses of shear from these it is deduced that coeval east and west vergent thrust faulting accommodated major displacements between nappes phengite ar ar data yield late eocene early oligocene ages for the greenschist facies metamorphism 2 the second deformation caused the widespread development of high angle shear bands and normal faults on opposite sides of the dora maira massif resulting in the apparent dome geometry of the massif a steep 50 80 network of west dipping normal faults is particularly well developed on the west side of the dora maira massif differences of 2 3 kbar and 100 150 c between juxtaposed monviso rocciavre and queyras nappes implies 8 km of vertical displacement along the monviso upper tectonic contact these normal faults formed in a more brittle regime only a post early oligocene age can be estimated from microstructural studies for these final movements these deformations postdate hp lt metamorphism and resulted in the juxtaposition of nappes of distinctly different origin age grade and p t t history a kinematic model is presented in which opposite vergence of nappes followed by large scale crustal extension occurred in response to uplift during the convergence between the european and south alpine plates this model may account for rapid uplift rapid unroofing and cooling of high pressure low temperature rocks thereby explaining the absence of amphibolite facies metamorphism overprint in this part of the alps that may have led to the preservation of coesite bearing rocks in the southern part of the dora maira massif

experimental study on the pressure dependence of vitrinite maturation we conducted the first systematic experiments over a pressure range of 0 5 to 20 0 kbar at temperatures of 200 to 350 c and run durations of 2 4 and 7 days to investigate the influence of pressure on vitrinite reflectance the data indicate that applied pressure lowers vitrinite reflectance the suppression appears to be stronger under wet than under dry conditions in addition high pressure favors liptinite preservation at temperatures 300 c whereas at the same temperature range yet at low pressure liptinite is decomposed our data fit an empirical rate equation which expresses rr as a function of pressure temperature and time the derived equation satisfactorily describes our experiments and enables extrapolations to geological timescales values of rr calculated for a pressure of 0 5 kbar are remarkably consistant with previous numerical pressure independent models a literature review shows that previous experimental data and field observations are inconsistent regarding the effect of pressure on vitrinite maturation this and some previous studies suggest that vitrinite maturation is suppressed by increased pressure whereas other workers regarded pressure as having little influence on the rate of coalification we suggest that original virinite composition experimental design and natural environment tectonic regime play important roles regarding the effects of pressure on vitrinite maturation interpretation of geothermal histories of sedimentary rocks based on vitrinite reflectance data must therefore include evaluation of the pressure otherwise vitrinite reflectance data from high pressure terranes should be interpreted with caution if used as a quantitative paleogeothermometer

heat focussing granite genesis and inverted metamorphic gradients in continental collision zones abstract the thermal conductivity of sedimentary rocks is usually much lower than that of crystalline rocks gneisses and granites continental collision zones are characterized by large scale thrusts which superpose crystalline basement and sedimentary layers this leads to heat refraction effects of significant magnitude sedimentary layers act as a barrier to the transport of heat we show that the peculiar geometry of a gently sloping sedimentary layer thrust into more conductive rocks is very efficient in diverting the vertical flux of heat temperatures can vary by more than 50 along the horizontal and reach a marked maximum at the top of crystalline layers these results are in general agreement with the main features of orogenic belts as exemplified by the himalayas they explain why the young leucogranites of the main central thrust mct are confined to a narrow belt at the top of the basement slab they also account for the inverted metamorphic gradient observed there in a crustal accretionary wedge folding and thrusting modify the structure of the upper crust by thickening the sedimentary cover and by introducing sedimentary rocks at depth this leads to high temperatures at shallow depths in specific places les zones de collision continentale se caracterisent par de grands chevauchementsafaible pendage qui empilent les unes sur les autres des couches de socle cristallin et des couches sedimentaires cette structure particuliere engendre d importants effets de refraction thermique en effet leur conductibilitethermiqueetant normalement bien plus faible que celle des roches cristallines les formations sedimentaires font office de barrieres pour le transfert thermique le flux de chaleur se trouve fortement devie dans un plan horizontal la temperature peut varier de plus de 50 les maximaetant situesal interface superieur des dalles cristallines en ces endroits precis les isothermes profonds remontent tres significativement ces resultats rendent bien compte de plusieurs faits essentiels observes dans l himalaya zoneographie inverse du metamorphisme localisation des leucogranites le long d une bandeetroite situee au sommet de la dalle du tibet

tectono thermal evolution of cambrian ordovician source rocks and implications for hydrocarbon generation in the eastern tarim basin nw china abstract the tectono thermal evolution is an important control on petroliferous basin development however this evolution is difficult to reconstruct in sedimentary basins subjected to multiple tectono thermal events the tarim basin is the largest petroliferous basin in northwestern china and hosts a complex oil gas system comprising several sets of source reservoir and cap rocks that have experienced multiple tectonic thermal and sedimentary events large oil and gas reserves have been discovered in the central and northern tarim basin during the last 30 years but none in the eastern part of the basin this is generally attributed to the high thermal maturity reached by source rocks during the late ordovician and subsequent hydrocarbon loss therefore reconstructing the cambrian ordovician tectono thermal evolution is critical in facilitating successful oil and gas exploration in this region we compiled equivalent vitrinite reflectance data n 178 of source rocks from seven wells in the tarim basin which for cambrian ordovician source rocks are 1 3 beyond the hydrocarbon generation threshold and in the main gas and dry gas generation stages the cambrian ordovician source rocks experienced rapid burial and heating during the caledonian period entered the hydrocarbon generation stage during the middle late ordovician and reached peak hydrocarbon generation at the end caledonian period they might have experienced secondary hydrocarbon generation after the jurassic homogenization temperatures of fluid inclusions n 616 from wells gc4 lx1 md1 and yd2 as well as the modeled thermal evolution reveal a main hydrocarbon generation event during the caledonian period and a secondary event in the yanshanian and himalayan period in other wells lx1 md1 and yd2 hercynian and indosinian uplift and exhumation in the eastern tarim basin controlled the main structures and faulting created favorable conditions for secondary hydrocarbon generation and migration at this time since the yanshanian and himalayan the tarim basin has experienced further sedimentation and heating and the tectono thermal evolution might have been related to the formation of the tibetan plateau in summary our reconstruction of the tectono thermal evolution of cambrian ordovician strata and the hydrocarbon generation history of the tarim basin suggests that the eastern tarim basin may also have hydrocarbon generation potential and can guide future oil and gas exploration

diamondoid hydrocarbon ratios novel maturity indices for highly mature crude oils abstract diamondoid hydrocarbons have been identified in oil and source rock samples from the tarim yinggehai qiongdongnan and other chinese basins two diamondoid hydrocarbon ratios have been used as novel high maturity indices to evaluate the maturation and evolution of crude oils and condensates in these chinese basins the two ratios 1 ma 1 ma 2 ma mai methyl adamantane index and 4 md 1 md 3 md 4 md mdi methyl diamantane index were found to increase with increasing vitrinite reflectance the initial values for the ratios are ca 50 and 30 respectively diamondoid hydrocarbons are products of rearrangement of polycyclic hydrocarbons and their ratios are found to be affected by organic input to a minor extent based on this study crude oils from the tarim basin are generally believed to be very mature ro 1 1 the cambrian ordovician source beds are the major source rocks of crude oils and natural gases in this basin condensates from the tarim yinggehai and qiongdongnan basins have higher maturities equivalent to ro values of 1 6 2 0 gases and condensates from the yinggehai and qiongdongnan basins are generated mainly from tertiary source rocks below 4000 5000 m

thickening history of the western alps a model of evolution for the western segment of the alpine chain is presented available data concerning the structural metamorphic and geochronological evolution in the majorunits involved in the thickening processes are takeninto account io constrain the model the successive stages of the collisional history are correlated with the evolution of thermal structure the african paleomargin was deformed at the onset of collision just after the abduction of the oceanic crust after these initial stages progressive stacking affected more and more external domains of the european plate lastly the deformation of the entire pile is linked io the thermal reequilibration of the considered thickened crust the alpine chain is a good example of a collision zone where the interaction of thermal and mechanical effects can be treated quantitatively

revisiting internal waves and mixing in the arctic ocean 1 to determine whether deep background mixing has increased with the diminishment of the arctic sea ice we compare recent internal wave energy and mixing observations with historical measurements since 2007 the north pole environmental observatory has launched expendable current probes xcps as a part of annual airborne hydrographic surveys in the central arctic ocean mixing in the upper 500 m is estimated from xcp shear variance and conductivity temperature depth ctd derived brunt vaisala frequency internal wave energy levels vary by an order of magnitude between surveys although all surveys are less energetic and show more vertical modes than typical midlatitude garrett munk gm model spectra survey averaged mixing estimates also vary by an order of magnitude among recent surveys comparisons between modern and historical data reanalyzed in identical fashion reveal no trend evident over the 30 year period in spite of drastic diminution of the sea ice turbulent heat fluxes are consistent with recent double diffusive estimates both mixing and internal wave energy in the beaufort sea are lower when compared to both the central and eastern arctic ocean and expanding the analysis to mooring data from the beaufort sea reveals little change in that area compared to historical results from arctic internal wave experiment we hypothesize that internal wave energy remains lowest in the beaufort sea in spite of dramatic declines in sea ice there because increased stratification amplifies the negative effect of boundary layer dissipation on internal wave energy

k ar age determinations on phengites from the internal part of the sesia zone western alps italy k ar age determinations have been carried out on various well defined phengite populations from a small area of the internal part of the sesia zone lower aosta valley there the rocks have suffered high pressure metamorphism attributed to early alpine subduction in the stability field of jadeite quartz p 15 1 kbar at t 550 50 c coarse grained phengites from well preserved high pressure parageneses and phengites re crystallized early during decompression at still elevated temperatures in the stability field of albite yield identical ages close to 80 ma in the most external sample high pressure phengites yield 72 ma the ages around 80 ma are interpeted as essentially undisturbed cooling ages they are not notably influenced by paragenesis chemical composition polymorphism grain size deformation and recrystallization at higher temperatures this part of the sesia zone has cooled down about 80 ma ago to below the blocking temperature for the k ar system of white mica some of the samples show pronounced retrogression of the high pressure assemblages especially formation of albite and fine grained phengite at the expense of jadeite and are affected by intense late deformation at temperatures of about 300 to 350 c estimated from the small grain size of dynamically recrystallized quartz the ages obtained from extremely kinked or sheared coarse high pressure phengites scatter considerably being partly higher partly lower than 80 ma the fine grained phengite fractions from these samples yield lowered ages down to 70 ma these values are interpreted as mixed ages resulting from variable mixtures of fragmented high pressure phengites and new phengite replacing jadeite the k ar data suggest that the new phengites have crystallized between 60 and 70 ma b p all phengites formed at low temperatures at the expense of jadeite reveal high si contents these range up to 6 9 for the coarser grained earlier generations and up to 6 7 for the very fine grained last generation relatively high pressures are required to stabilize phengites so high in si this implies that cooling had not been achieved by uplift and erosion obviously the thermal structure of the crust was still strongly perturbed by continuing subduction and thrusting during the late cretaceous

metamorphic veining and mass transfer in a chemically closed system a case study in alpine metabauxites western vanoise in western vanoise french alps karstic pockets of triassic to jurassic metabauxites embedded in carbonate rocks and containing several generations of metamorphic veins were studied during blueschist facies metamorphism a cumulative amount of 13 vol of water is inferred to have been produced locally by successive dehydration reactions and part of this fluid remained in the bauxitic lenses during most of the metamorphic cycle field and geochemical evidence show that these rocks have been isolated from large scale fluid flow closed system behaviour it is proposed that the internally derived fluid has promoted the opening of fluid filled open spaces as attested by the euhedral habits of vein minerals and served as medium for mass transfer from rock to vein indeed the vein infill is obviously the result of chemical interactions at the millimetre to centimetre scale between the rock minerals and the locally produced aqueous fluid two vein types can be distinguished based on mineralogical and textural features i some veins are filled with newly formed products of either prograde chloritoid or retrograde chlorite metamorphic reactions in this case fluid filled open spaces seem to offer energetically favourable nucleation growth sites ii the second vein type is infilled with cookeite or pyrophyllite that were present in the host rock prior to the vein formation in this closed chemical system the components for the vein infill minerals have been transferred from rock to vein through the fluid in a dissolution transport precipitation process possibly stress assisted these different vein generations all contain al rich mineral infills suggesting that al was a mobile element cm scale during metamorphism in these hp rocks fluid flow may have been restricted and if so mass transfer occurred by diffusion in an almost stagnant fluid metamorphic veins can be seen as witnesses of fluid and mass redistribution that partly accommodate the rock deformation lateral segregation

miocene detachment in crete and exhumation p t t paths of high pressure metamorphic rocks a major problem posed by the geology of crete is the horizontal contact of an upper unit without miocene metamorphism onto a metamorphosed lower one with early miocene high pressure low temperature hp lt parageneses this very sharp contact is roughly parallel to the major oligo miocene thrust planes which were reactivated as a large scale detachment which allowed exhumation of high pressure units we describe the extensional deformation and the metamorphic evolution of the lower plate most first order deformation features relate to the retrogression from high pressure to low pressure conditions a n s pervasive stretching is observed everywhere often associated with a top to the north sense of shear the extreme variation of thickness of the phyllite quartzite nappe upper part of the lower plate is probably the result of large scale boudinage similar to the one seen in large outcrops the most important observation is the systematic occurrence of fresh carpholite immediately below the base of the tripolitza nappe except in northwestern crete where a late extensional shear zone is present deeper in the nappe pile carpholite is systematically retrograded this observation reveals a drastically different pt history for the upper part of the phyllite quartzite nappe it also suggests that the late extensional shear zone found along the northern side of crete cuts inside the metamorphic structure and brings the nonmetamorphosed tripolitza nappe directly in contact with the deeper parts of the phyllite quartzite nappe pt t paths suggest a fast temperature decrease in the top of the phyllite quartzite during retrogression and hence during the top to the north shear the deeper part of the phyllite quartzite nappe shows a low temperature regime throughout but its pt path includes an isothermal decompression in the first stage we produce a tentative map of domains having experienced similar pt trajectories during decompression the overall cool regime is related to the continuous underthrusting of cola continental units during exhumation isothermal decompression observed in the core of the phyllite quartzite nappe implies fast exhumation during extension and the faster cooling of the upper part is related to a continuous displacement toward the north of a cooler unit during exhumation single grain 39ar 40ar ages obtained on phengites 15 25 ma in various structural sites are in good agreement with these conclusions and with the geological context suggesting that underthrusting of cold units at the front the accretionnary complex occurred contemporaneously with unroofing below a north dipping detachment near the top of the wedge the age of this detachment is bracketed between the end of the high pressure event 20 ma and the deposition of the breccia early to middle miocene in the neogene basins

geochemistry of palaeozoic marine petroleum from the tarim basin nw china part 1 oil family classification abstract a series of palaeozoic marine oils ranging from condensates to very heavy oils from the cratonic region of the tarim basin nw china have been examined to delineate oil families crude oils from the mesozoic foreland kuqa depression were also analyzed for comparison the genetic family was assessed using bulk hydrocarbon isotopic composition alkylation pattern of polycyclic aromatic hydrocarbons pahs and biomarker distributions detailed oil oil correlation suggests two distinct families occur in the cratonic region despite the diversity of the reservoir rocks and some variability in oil physical properties the tabei and tazhong oils are classified in general into a single family with a possible indication for secondary subdivision these oils are characterized by low pristane phytane pr ph ratio high dibenzothiophene phenanthrene dbt p ratio light bulk isotopic composition high degree of pah alkylation high proportion of c23 and c24 tricyclic terpanes and low abundance of c24 tetracyclic terpane and triaromatic dinosteroids this family is inferred to have a middle upper ordovician source rock the tadong family distinctly different from the tabei and tazhong families is characterized by relatively high pr ph ratio low dbt p ratio slightly heavier bulk isotopic compositions and low degree of pah alkylation it also has a unique biomarker signature with a high proportion of triaromatic dinosteroids possibly indicating cambrian lower ordovician source rocks the oils from the kuqa depression are easily distinguished from the other two families due to their terrigenous origin the major characteristics of the kuqa oils are high pr ph ratio very low dbt p ratio heavy bulk isotopic composition low pah alkylation degree high proportion of c20 and c21 tricyclic terpanes and c24 tetracylic terpane and abundance of triaromatic dinosteranes and 4 methyl 24 ethyltriaromatic cholestanes these characteristics are consistent with terrestrial organic source rocks deposited under sub oxic conditions

geochemistry of palaeozoic marine petroleum from the tarim basin nw china part 2 maturity assessment abstract the thermal maturity of forty three crude oil samples collected from the cratonic portion of the tarim basin nw china has been assessed using a variety of parameters while compound ratios of diamondoids alkylated naphthalenes methyl phenanthrenes and methyl dibenzothiophenes showed consistent trends with increasing maturity a large discrepancy was observed for the maturity levels of the oils determined from these parameters equivalent vitrinite reflectance values calculated from methylphenanthrene index 1 mpi1 methyldibenzothiophene ratio mdr and methyldiamontane index mdi were in the range of 0 66 0 97 1 11 1 64 and 0 89 1 74 ro respectively while we caution that some of the discrepancy may be related to calibration problems the difference observed from different compound classes could be real reflecting the multiple charge to petroleum accumulations as the diamondoid hydrocarbons were possibly generated at later maturation stages than most aromatic hydrocarbons as diamondoids with methyl substitution on the bridgehead positions are more stable than those with substitution on other positions several compound ratios based on ethyl admantanes dimethyl admantanes trimethyl admantanes and dimethyl diamantanes also correlated with the established maturity indicators such as mdr and mdi while condensates with high maturity levels represent the late charge hydrocarbons some of them with relatively low maturity levels may be affected by evaporative fractionation processes the normal gravity oils cover a wide maturity range consistent with multiple charges and in reservoir mixing while the waxy oils with high apparent maturity levels may be the products of wax precipitation due to a later gas injection into an oil column heavy oils with low apparent maturity levels could be the residue of oil that has lost its light end

alpine high p low t metamorphism of the afyon zone and implications for the metamorphic evolution of western anatolia turkey abstract carpholite chloritoid pyrophyllite association occurs widely in the triassic metaclastic rocks of the afyon zone in west central turkey fe mg carpholite is associated with rare aragonite pseudomorphs and glaucophane in marbles and metabasites respectively the afyon zone consists stratigraphically of a pan african basement and an overlying mesozoic cover sequence the pan african basement which shows barrovian type amphibolite facies metamorphism comprises garnet mica schists intruded by sodic amphibole bearing metagabbros and leucocratic metagranites it is unconformably overlain by a continuous metasedimentary sequence extending from triassic to early palaeocene this cover sequence begins with metaconglomerates which pass upwards into phyllites fe mg carpholite occurs within this metaclastic sequence as rosette like crystals in metapelites and fibres in quartz segregations the metaclastic rocks are succeeded by metamorphosed platform carbonates grading into latest mesozoic metamorphosed pelagic limestones which in turn progress up to a late mesozoic early tertiary olistostrome this sequence is tectonically overlain by the blueschists of the tavsanli zone fe mg carpholite bearing assemblages imply temperatures of about 350 c and minimum pressures of 6 9 kbar corresponding to burial depths of about 30 km for the mesozoic passive continental margin sediments and the underlying pan african supracrustal metasediments and metaintrusives the metamorphic rocks of the afyon zone are unconformably overlain by upper palaeocene lower eocene sedimentary rocks indicating a paleocene age for the regional hp lt metamorphism this implies continuous younging of hp lt metamorphism in the anatolides related to northward subduction of the anatolide tauride platform beneath the sakarya zone from north to south this involved the tavsanli zone campanian 80 5 ma the afyon zone palaeocene the menderes massif middle eocene and the lycian nappes late cretaceous eocene all of which were probably derived from the frontal part of the anatolide tauride platform

salt structures and hydrocarbon accumulations in the tarim basin northwest china the tarim basin is one of the most important hydrocabon bearing evaporite basins in china four salt bearing sequences the middle and lower cambrian the mississippian the paleogene and the neogene have various thickness and areal distribution they are important detachment layers and intensely affect the structural deformation in the basin the kuqa depression is a subordinate structural unit with abundant salt structures in the tarim basin salt overthrusts salt pillows salt anticlines salt diapirs and salt withdrawal basins are predominant in the depression contraction that resulted from orogeny played a key function on the formation of salt structures growth strata reveal that intense salt structural deformation in the kuqa depression occurred during the himalayan movement from oligocene to holocene with early structural deformation in the north and late deformation in the south growth sequences also record at least two phases of salt tectonism in the yingmaili tahe and tazhong areas low amplitude salt pillows are the most common salt structures and these structures are commonly accompanied by thrust faults the faulting and uplifting of basement blocks controlled the location of salt structures the differences in the geometries of salt structures in different regions show that the thickness of the salt sequences has an important influence on the development of salt cored detachment folds and related thrust faults in the tarim basin salt sequences and salt structures in the tarim basin are closely linked to hydrocarbon accumulations oil and gas fields have been discovered in the subsalt intrasalt and suprasalt strata salt deformation has created numerous potential traps and salt sequences have provided a good seal for the preservation of hydrocarbon accumulations large and small scale faults related with salt structures have also given favorable migration pathways for oil and gas when interpreting seismic profiles special attention needs to be paid to the clastic and carbonate interbeds within the salt sequences because they may lead to incorrect structural interpretation in the tarim basin the subsalt anticlinal traps are good targets for hydrocarbon exploration

tectonic implications of lawsonite formation in the sesia zone western alps lawsonite of early alpine age formed in different tectonic sub units of the sesia zone western italian alps in the southern part of the eclogitic micaschists subunit em lawsonite grew with quartz jadeite during the early alpine retrograde path which just post dates the eclogite thermal peak the early retrograde path of the southern em occurred at decreasing temperature and at p t conditions comparable to those of the metamorphic peak in some blueschist facies thrust sheets which separate the em from the southern alps such a post eclogitic cooling path may have been induced by conductive cooling linked to migration of the underthrust surfaces and to stacking with colder nappes like the other sesia subunits or the piemonte metaophiolites stacking and thermal interaction between the different units probably occurred at depth during the early stages of exhumation which followed subduction underthrusting of early mid cretaceous age during the paleogene continental collision between the european and african plates determined further underthrusts of more westerly units these units underwent a high pressure very low temperature recrystallization meso alpine event characterized by the growth of lawsonite at the peak metamorphic conditions consequently propagation of the underthrust surfaces may represent an effective mechanism to prevent the rise of the isotherms and to favor post peak cooling paths in some units of the western alps this effect is more obvious in the structurally upper units which were first brought to deep crustal levels in the early alpine imbricated subduction zone

geochemistry and charge history of oils from the yuqi area of tarim basin nw china abstract the geochemistry origin and charge history of oils from the yuqi area of tarim basin have been investigated through gc gc ms and fluid inclusion microthermometry analysis the yuqi oils accumulated mainly in three intervals 1 in the lower middle ordovician yingshan formation o 1 2 y carbonate reservoirs 2 in the overlying upper triassic halahatang formation t 3 h and 3 in the lower cretaceous yageliemu formation k 1 y sandstones oils from different reservoirs have distinct physical properties varying from extra heavy o 1 2 y heavy t 3 h to light oils t 3 h and k 1 y however their geochemical compositions show a high degree of similarity which indicates that they derive from the same source rock abundant tricyclic terpanes gammacerane dibenzothiophene and c 21 c 22 steranes together with a low level of diasteranes indicate an anoxic marine source rock for oils in the yuqi area oil oil correlation shows that yuqi oils derive from the same source bed as tahe oils the co occurrence of intact n alkanes and 25 norhopanes in all the samples supports the proposition that there is a mixture of an early filled severely biodegraded oil and a late filled fresh oil in this study charge history is examined on the basis of integration of fluid inclusion homogenization temperature data with 1d burial thermal history models two episodes of oil charging are identified in the o 1 2 y reservoir well yqx1 1 at around 436 420 ma middle late silurian and 10 3 ma miocene to pliocene respectively for the samples from the t 3 h and k 1 y intervals only one episode of oil charge is indicated by the homogenization temperatures of coexisting aqueous inclusions with an inferred timing around 10 3 ma the t 3 h heavy oil reservoir is assumed to be a secondary hydrocarbon pool which accumulated by re migration and re distribution of hydrocarbons from o 1 2 y hydrocarbon pools the few early biodegraded oils in the k 1 y light oils were probably picked up along the migration pathway during the late fresh oil charging

geochemistry of alkylbenzenes in the paleozoic oils from the tarim basin nw china a b s t r a c t monoaromatic hydrocarbons alkylbenzenes in paleozoic oils condensates from the tarim basin were quantitatively analyzed using gas chromatography mass spectrometry their relative abundances and distributions show large variation which are most likely controlled by the temperature and duration of the catagenesis stage of petroleum maturation relatively high abundance of long chain linear substituted alkylbenzenes and alkyltoluenes in the studied samples implies that source rocks of these oils condensates contain high contents of algal material the dominance of dodecylbenzene in these n alkylbenzenes suggests the formation of alkylbenzenes from fatty acids via lactone formation dehydration the 1 2 3 4 tetramethylbenzene temb 1 methyl 3 phytanylbenzene 1 m 3 pyb and aryl isoprenoids are mainly derived from carotenoids produced by chlorobiaceae and their occurrence may indicate a highly reducing depositional environment however the concentration of these compounds diminishes significantly at high maturity with increasing thermal maturity the prominent trend of demethylation of alkylbenzenes is accompanied by shortening of alkyl side chains large variation in the c4 alkylbenzene isomer distribution is also controlled by thermal maturity the 1 2 3 5 temb and 1 2 4 5 temb isomers are more stable than other temb isomers and the overall thermodynamic stability of tembs is lower than that of dimethylethylbenzenes therefore several maturity parameters can be derived based on alkylbenzene stability absolute concentrations of alkylbenzenes generally increase with increasing thermal maturity but concentrations of 1 m 3 pyb and aryl isoprenoids decrease significantly at high maturity maturity parameters obtained from alkylbenzenes are especially useful for highly mature oils and condensates when most biomarkers are depleted caution is advised when interpreting the paleoenvironment and thermal maturity of an oil from the alkylbenzene signatures because they are affected by various other processes such as evaporative fractionation thermal cracking and biodegradation as well

formation mechanism of deep cambrian dolomite reservoirs in the tarim basin northwestern china abstract well ts1 which is located in the north uplift of the tarim basin northwestern china has a total depth of 8408 m and is the deepest petroleum well in the world the well penetrates a high quality upper cambrian dolomite reservoir from 6884 m to 8408 m the porosity of this dolomite increases with increasing depth reaching 9 1 at a depth of 8407 56 m a large number of dissolution pores are present in the core retrieved from well ts1 some of the pores are partially filled with coarse dolomite crystals which display saddle shapes and undulose extinction the pore filling dolomites have high concentrations of fe and mn averaging 3158 1 and 172 5 ppm respectively the concentration of ba is up to 4000 3 ppm the oxygen isotope composition of the pore filling dolomites is relatively light and the 18 o values range from 10 9 to 5 1 the 87 sr 86 sr values are relatively high ranging from 0 709361 to 0 709975 the mineralogical and geochemical features demonstrate that the pore filling dolomites were precipitated from hydrothermal fluids that significantly altered the deep cambrian dolomite reservoirs during upward migration along faults and fractures in the permian according to petrologic geochemical and seismic features the dolomite reservoirs were first dissolved by meteoric water during or shortly after deposition and were then significantly altered by hydrothermal fluids during burial a porosity variation model was proposed for the deep dolomite reservoirs that were influenced by hydrothermal fluids the model of increasing porosity with increasing depth in well ts1 indicates that there may be high quality dolomite reservoirs in the deep strata of basins where hydrothermal fluids are active the small amount of liquid hydrocarbon obtained from cores at a depth of more than 8400 m demonstrates that the deep dolomite reservoir is still suitable for hydrocarbon accumulation due to an unusually low geothermal gradient of approximately 20 c km the deep strata in basins with similar geological parameters may therefore be potential exploration targets elsewhere in the world

statistical evaluation and calibration of model predictions of the oil and gas field distributions in superimposed basins a case study of the cambrian longwangmiao formation in the sichuan basin china abstract superimposed basins are commonly characterized by a complex distribution of oil and gas accumulations because they have generally experienced multistage hydrocarbon accumulation and tectonic movement it is challenging to predict favorable exploration zones in these basins the exploration of the deep strata of the sichuan basin i e a typical superimposed basin west china has been unsatisfactory for petroleum prospectors therefore we chose the cambrian longwangmiao formation in the sichuan basin as an example to demonstrate the method i e combination of petroleum system elements to quantitatively predict the petroleum favorable exploration zones based on the detailed analysis of the hydrocarbon accumulation process the source rock s migration m reservoir depositional facies d and regional cap rock c are the most important elements controlling the formation and distribution of oil and gas accumulations in the studied basin by studying the functional relationships among these four elements and the distribution of the petroleum accumulations we determined the accumulation probability related to each element and quantitatively predicted the probability of a favorable hydrocarbon accumulation zone we built a quantitative model of the reservoir preservation probability based on the statistical relationship between the intensity of the tectonic movement and subsequent destruction of existing oil and gas accumulations favorable exploration zones can be determined by overlaying favorable accumulation zones with disturbances associated with the tectonic evolution the results suggest that the most favorable exploration zones of the longwangmiao formation in the sichuan basin are distributed in the regions west of weiyuan and east of gaoshiti moxi pengxi yilong and dazhou kaijiang the production data for existing fields in the sichuan basin show that 87 of the successful wells are in the predicted favorable exploration zones and that the success rate with respect to the prediction of failure wells is 67 this approach highlights the most prospective exploration areas in superimposed basins which in general is challenging and complex for traditional basin modeling tools

garnet chloritoid equilibria in eclogitic pelitic rocks from the sesia zone western alps their bearing on phase relations in high pressure metapelites abstract a detailed study of garnet chloritoid micaschists fom the sesia zone western alps is used to constrain phase relations in high pressure hp metapelitic rocks in addition to quartz phengite paragonite and rutile the micaschists display two distinct parageneses namely garnet chloritoid chlorite and garnet chloritoid kyanite talc has never been observed garnet and chloritoid are more magnesian when chlorite is present instead of kyanite the distinction of the two equilibria results from different bulk rock chemistries not from p t conditions or redox state estimated p t conditions for the eclogitic metamorphism are 550 600 c 15 18 kbar the presence of primary chlorite in association with garnet and chloritoid leads us to construct two possible afm topologies for the sesia metapelites the paper describes a kfmash multisystem for hp pelitic rocks which extends the grid of harte hudson 1979 towards higher pressures and adds the phase talc observed parageneses in hp metapelites are consistent with predicted phase relations critical associations are gt ctd chl and gt ctd ky at relatively low temperatures and gl chl ky and gt tc ky at relatively high temperatures

biomarker geochemistry of crude oils and lower paleozoic source rocks in the tarim basin western china an oil source rock correlation study abstract in order to select biomarker parameters that have potential to quantitatively distinguish between the cambrian lower ordovician and upper ordovician source rocks in the tarim basin with a total organic carbon content 0 5 42 lower paleozoic shale samples were collected from a number of wells and outcrops in the tarim basin northwestern china the biomarkers in the extracts of the source rocks were analyzed by gas chromatography mass spectrometry the results show that c23 and c30 were dominant in the tricyclic terpanes and pentacyclic triterpanes respectively and c27 and c29 were both dominant in c27 29 steranes of the source rock samples the distribution of n alkanes isoprenoids and terpanes indicate that the source rock samples have been slightly to moderately biodegraded and they originated from a reducing depositional environment with considerable marine algal input in comparatively upper ordovician source rock samples presented lower values of c28 c29 regular steranes and higher values of c29 20s 20s 20r and c29 abnormally lower values of c29 20s 20s 20r and c29 were observed in the cambrian lower ordovician strata the set of data in this study show that homohopane index including c31homohopane c30hopane c31 35homohopanes c30hopane and the ratios related to the triaromatic steroids including c26 20s c28 20s tas c27 20r c28 20r c26 20r c27 20s c28 20s and c28 c26 c27 tas could serve as potential biomarker parameters to distinguish between the two groups of source rocks in the tarim basin the values of those parameters in above order in cambrian lower ordovician source rocks were 0 3 0 5 0 85 and 0 8 1 9 1 2 respectively the correlation between the source rock samples and 19 oils obtained from the tadong tabei and tazhong uplifts in the tarim basin show that most of the oils in tabei uplift are probably from upper ordovician source rocks the oils in tadong uplift are more likely from cambrian lower ordovician source rocks and the tazhong uplift is more like a mixed oil region with oils from both of the two groups of source rocks

counterclockwise rotation of the western alps since the oligocene new insights from paleomagnetic data 1 a paleomagnetic study of penninic units in the southern part of the alpine arc has been carried out more than 200 samples 23 sites were collected in brianconnais ammonitico rosso limestones of the high ubaye valley and the ligurian alps a characteristic component of magnetization of reverse polarity was isolated on most of the sites this component does not pass the fold test and is interpreted as a tertiary overprint related to alpine metamorphism mean directions in geographic coordinates are d 121 i 52 95 11 and d 72 i 48 95 15 for the ubaye and the liguria localities respectively indicating large counterclockwise rotations about vertical axis of 68 and 117 relative to stable europe these rotations in agreement with a previous study conducted in the briancon area together with other paleomagnetic data from the western alps show that the internal alps suffered a large but nonhomogeneous counterclockwise rotation since the oligocene the rotations are in agreement with the combination of earlier separately proposed processes the rotation of the adriatic plate accounts for about 25 of rotation remaining rotation and southward gradient would be related to left lateral shear accommodating the displacement between adria and europe at the southern border of the western alps furthermore the southward extrusion of the western alps south of the simplon fault zone may account for up to 10 of rotation rotations appear therefore as a major process accommodating deformation in the western alps since the oligocene

the stacking of thrust slices in collision zones and its thermal consequences the thermal consequences of stacking up thrust slices in collision zones are investigated using simple one dimensional thermal models the metamorphic evolution geotherms and p t time paths of a given tectonic unit belonging to a crustal stacking wedge made of more than two units is governed by three effects cooling and pressure decrease associated with erosion cooling by the lowest units screen effect heating by the upper units cover effect it is shown that the efficiency of these effects are dependent on the tectonic evolution of the collision zone the metamorphic evolutions are very sensitive to the following tectonic parameters the number of thrusted units involved in thickening the time delay between each thrust and finally the mode of stacking of the different units over and understacking it appears that for a given depth of burial the temperature increase during uplift is less important in a crust thickened by three or four units than in the case of two units the screen effect during understacking is more efficient for a short time delay 10 ma between each thrust overstacking leads to higher temperatures before uplift when compared to understacking it is also shown that the thermal perturbation induced in an intermediate unit of the pile is more efficiently recorded when its thickness is rather small 10 km it is shown that for an erosion controlled uplift the shape of the p t t path depends on the position of the rocks within a given unit and on the unit position within the pile finally the general metamorphic evolutions during crustal thickening hp lt metamorphism and subsequent overprint are discussed in terms of the previously mentioned parameters in the case of the western alps it appears that the more or less efficient greenschist overprint of the units involved in thickening can be explained by different time intervals between the thrust events

coesite in subducted continental crust p t history deduced from an elastic model abstract coesite has been found in a metasedimentary rock in a continental unit of the western alps dora maira massif the rock preserves the high pressure low temperature assemblage of nearly pure pyrope talc phengite kyanite in a quartz matrix coesite exclusively occurs as inclusions in pyrope and is partly inverted to quartz textural observations and mechanical considerations suggest that the rock crystallised in the coesite stability field a simple elastic model for a coesite inclusion in pyrope explains why coesite has been exclusively preserved in the inclusions and not in the matrix combined with petrological data the model constrains the crystallisation conditions of the pyrope coesite rock p 28kbar 650 this finding has an important bearing on the significance of p t conditions estimated from minerals occurring as inclusions and on the actual behaviour of continental crust in collision zones

3d seismic interpretation of subsurface eruptive centers in a permian large igneous province tazhong uplift central tarim basin nw china a 1445 km2 high resolution 3d seismic reflection dataset is used to analyze the permian large igneous province in the subsurface of the tazhong area in the central tarim basin in northwestern china constrained by the synthetic seismograms of four wells the top and base of the igneous rocks were identified in the seismic data seven large volcanic craters each 10 km2 in area have been discovered via the application of coherency and amplitude attributes the thickness and volume of the igneous rocks were obtained by time depth transformation in the study area all of the igneous rocks with thicknesses from 120 to 1133 m were formed by eruptions in the early permian these events produced huge erupted volumes 178 km3 and multiple closely spaced volcanic edifices 13 km these features suggest that the study area may be the part of the eruptive center of the permian igneous rocks in the tarim basin

very low grade metamorphic evolution of pelitic rocks under high pressure low temperature conditions nw new caledonia sw pacific the p t gradient in a late eocene low t high p metamorphic belt in northern new caledonia increases from sw to ne metapelites in the pumpellyite prehnite and blueschist zones contain lawsonite mg carpholite fe stilpnomelane and fe glaucophane thermodynamic calculations indicate a progression of metamorphic conditions from less than 0 3gpa and 250 c in a kaolinitebearing rock in the sw up to 1 5gpa and 410 c in a lawsonite glaucophane bearing sample in the ne of the diahot terrane through a multi method investigation of phyllosilicates organic matter and fluid inclusions we demonstrate that the evolution of organic matter and illite crystallinity depends strongly on the evolution of the p t path with time in addition we show that the illite muscovite b cell dimension provides a robust estimate of maximum pressure reached in low temperature domains with polyphase metamorphic histories despite subsequent hightemperature low pressure events fluid inclusion study reveals an isothermal decompression in the diahot terrane

metamorphism of metasediments at the scale of an orogen a key to the tertiary geodynamic evolution of the alps major discoveries in metamorphic petrology as well as other geological disciplines have been made in the alps the regional distribution of late cretaceous tertiary metamorphic conditions documented in post hercynian metasediments across the entire alpine belt from corsica tuscany in the west to vienna in the east is presented in this paper in view of the uneven distribution of information we concentrate on type and grade of metamorphism and we elected to distinguish between metamorphic paths where either pressure and temperature peaked simultaneously or where the maximum temperature was reached at lower pressures after a significant temperature increase on the decompression path the results show which types of process caused the main metamorphic imprint a subduction process in the western alps a collision process in the central alps and complex metamorphic structures in the eastern alps owing to a complex geodynamic and metamorphic history involving the succession of the two types of process the western alps clearly show a relatively simple picture with an internal high pressure dominated part thrust over an external greenschist to low grade domain although both metamorphic domains are structurally very complex such a metamorphic pattern is generally produced by subduction followed by exhumation along a cool decompression path in contrast the central alps document conditions typical of subduction and partial accretion followed by an intensely evolved collision process often resulting in a heating event during the decompression path of the early subducted units subduction related relics and collisional decompressional heating phenomena in different tectonic edifices charac terize the tertiary evolution of the eastern alps the tuscan and corsica terrains show two differ ent kinds of evolution with corsica resembling the western alps whereas the metamorphic history in the tuscan domain is complex owing to the late evolution of the apennines this study confirms that careful analysis of the metamorphic evolution of metasediments at the scale of an entire orogen may change the geodynamic interpretation of mountain belts

a case of obduction related high pressure low temperature metamorphism in upper crustal nappes arabian continental margin oman p t paths and kinematic interpretation in the southeastern oman mountains the saih hatat tectonic window reveals arabian continental material beneath the oceanic sensu lato nappes i e the hawasina sedimentary units and the huge sumail ophiolite the northeastern internal half of the window suffered an intense deformation associated with a high pressure low temperature hp lt metamorphism approximately dated at 80 75 ma according to the available stratigraphie data after the deformation due to the absence of collision the obduction inherited structural and metamorphic pattern was virtually unmodified a metamorphic map is established based on mineral assemblages in metapelites and metabasites low grade assemblages occur in the highest units muscat nappes quryat unit characteristic minerals are femg carpholite lawsonite associated with kaolinite or pyrophyllite and locally sudoite in the metapelites while lawsonite and blue amphiboles are found in the metabasites high grade rocks outcrop in the deepest and easternmost units as sifah antiform and are typified by an epidote glaucophane bearing eclogite assemblage intermediate units hulw show assemblages of intermediate grade chloritoid schists and glaucophane bearing metabasites higher grade assemblages such as talc chloritoid were not found inverted gradients are observed locally in the muscat nappes pyrophyllitebearing units above kaolinite quartz bearing units and these are ascribed to late metamorphic thrust displacements which are demonstrated by microstructures a complex p t evolution is fairly well documented by the mineral assemblages prograde evolution in the subophiolitic continental rocks began with a rather hot gradient of about 30 35 c km with chloritoid growth in the higher units thereafter pressure increased with the temperature remaining constant or even decreasing chloritoid replaced by kaolinite oxides and carpholite growth in synkinematic conditions the peak p t conditions are close to 8 kbar 270 c for the muscat nappes and 11 kbar 400 c for the as sifah unit the corresponding surface related gradient is low 10 15 c km during the retrograde evolution pressure and temperature generally decreased concomitantly but in some of the upper units temperature remained constant or increased slightly for some time at which point sudoite growth from carpholite took place the metamorphic pattern and mineral evolution are interpreted in the framework of the late cretaceous obduction the already cold oceanic lithosphere was thrust upon a relatively hot thinned passive margin with coeval basaltic volcanism pressure progressively increased in the passive margin due to the wedge shape of the advancing ophiolite the maximum thickness of which was about 25 km in the as sifah area in this area the overburden was also attributable to the accumulation of continental material up to 5 km thick by means of a complex set of synmetamorphic often conjugated folds and thrusts the basal peridotites of the obducted slab were probably not hotter than 300 c during its thrusting upon the continental margin the temperature of the tectonic pile below the ophiolite remained low because it was thrust above more external and still colder continental areas late thrusting in the same southerly direction controlled the retrograde evolution together with erosional and gravity driven tectonic unloading

laser induced fluorescence microscopy application to possible high rank and carbonate source rocks abstract it is difficult to obtain useful fluorescence information from coals and source rocks of high maturity by means of conventional fluorescence microscopy due to the low fluorescence intensity of the macerals a laser induced fluorescence microscopy lifm designed by the authors was applied to target the problem an investigation was made by means of this technique on a suite of coals having a range of mean random vitrinite reflectance vro 0 3 2 5 and some high maturity source rocks of early palaeozoic age the results show that lifm greatly improves several functions of conventional fluorescent microscopy lifm is very sensitive to organic matter in sediments and for the suite of chinese coals and possible source rocks investigated considerably extends the maturity range over which visible fluorescence can be observed the range is extended from about 1 40 to 2 0 vro for vitrinite of normal composition from 1 30 to about 1 50 vro for alginite and other liptinites and from about 2 5 to 3 2 vro for organic inclusions and asphalt absorbed minerals with lifm it was found that the organic matter in some early palaeozoic carbonates and argillaceous limestones is distributed very unevenly in these rocks which are believed to have been significant source rocks some microregions are very rich in organic matter or contain a large number of organic inclusions although the total organic carbon toc of the whole rock is low a microchannel network for petroleum expulsion and migration comprised of grain boundaries bedding planes and suture textures containing hydrocarbons was revealed in carbonate strata lifm of organic matter in rocks should extend the application of organic petrology in petroleum exploration

uplift and exhumation of high pressure metamorphic terrains the example of the cycladic blueschist belt aegean sea the cycladic blueschists emerged from a depth of more than 50 km during the tertiary these rocks are now covered only by a thin fraction of the synmetamorphic overburden upper plate remnants of the upper plate include low p crystalline rocks and sediments which have been juxtaposed onto the lower plate blueschists in several stages since the early miocene the low angle contacts operated as normal faults which removed the overburden from above the cycladic blueschists detailed investigations on tinos island indicate that the fractured blocks of the upper plate lying above a low angle normal fault did not rotate this shows that the faults initiated as rather gently dipping fractures similar structures were also reported from other blueschist terrains kinematic analysis of such flat lying faults implies that the synmetamorphic overburden should be mostly located several hundred kilometers away from the present exposure of the blueschists considering that the cycladic blueschist belt exposes successively shallower units in the west and that rocks of the upper plate have an anatolian nature we suggest that these blueschists were dragged from beneath turkey we recognize that the blueschist unit has undergone further thrusting in the final stage of the exhumation as have its counterparts elsewhere in the hellenides the emergence of the blueschists in the tertiary was concomitant with continental collision and thrusting in the hellenides the operation of low angle normal faults with large extensional displacements occurred within this context of collision tectonics this extension occurred parallel to the strike of the convergent orogen

influences of the ocean surface mixed layer and thermohaline stratification on arctic sea ice in the central canada basin 1 variations in the arctic central canada basin mixed layer properties are documented based on a subset of nearly 6500 temperature and salinity profiles acquired by ice tethered profilers during the period summer 2004 to summer 2009 and analyzed in conjunction with sea ice observations from ice mass balance buoys and atmosphere ocean heat flux estimates the july august mean mixed layer depth based on the ice tethered profiler data averaged 16 m an overestimate due to the ice tethered profiler sampling characteristics and present analysis procedures while the average winter mixed layer depth was only 24 m with individual observations rarely exceeding 40 m guidance interpreting the observations is provided by a 1 d ocean mixed layer model the analysis focuses attention on the very strong density stratification at the base of the mixed layer in the canada basin that greatly impedes surface layer deepening and thus limits the flux of deep ocean heat to the surface that could influence sea ice growth decay the observations additionally suggest that efficient lateral mixed layer restratification processes are active in the arctic also impeding mixed layer deepening

depositional facies diagenesis and their impact on the reservoir quality of silurian sandstones from tazhong area in central tarim basin western china abstract the silurian sandstones of the tazhong area are an important oil exploration target in the tarim basin western china this study deals with the lower silurian of the kalpingtag formation which was deposited in a braided delta system four major depositional microfacies are identified consisting of distributary channel interdistributary bay front bar and sand sheet in spite of their large lateral extent exploration of these sandstones is complicated by variation of sediment facies and intense diagenesis which strongly affected reservoir quality depositional environment exerted an essential control on the reservoir quality higher energy well sorted and relatively coarser grained sandstones have better quality than low energy fine grained clay rich sandstones diagenesis was mainly composed of mechanical and chemical compaction and cementation by quartz overgrowths carbonates and various clay minerals mechanical compaction was a significant porosity reducing agent in the silurian sandstones the presence of carbonate cement exerts a dominant influence on porosity and permeability in tazhong area other cements are less important but quartz cement is significant the third significant element is clay minerals the porosity reduction by compaction and cementation and the relative timing of them indicates that compaction was much more important than cementation in reducing porosity

geochemistry of paleozoic marine petroleum from the tarim basin nw china part 5 effect of maturation tsr and mixing on the occurrence and distribution of alkyldibenzothiophenes abstract fifty four oils and 20 gas condensates from the cratonic region of the tarim basin nw china were quantitatively analyzed by gas chromatography mass spectrometry to elucidate the influence of thermal maturation multiple charges and mixing and thermochemical sulfate reduction tsr on the relative distributions of alkyldibenzothiophenes dbts vs alkylphenanthrenes which are widely used to interpret depositional environment and lithology concentrations of dbts relative to dbts in the aromatic hydrocarbon fraction and ratios of dibenzothiophene phenanthrene dbt p exhibit wide variations in the studied samples field observations coupled with a suite of oil sand pyrolysis experimental results suggest that dbts are more easily released from kerogen and or asphaltenes and are more easily destroyed in oil than the alkylphenanthrenes the dbt p ratio initially increases during early maturation and then decreases in the post mature stage concentrations of dbts are low in samples from the cratonic region of the tarim basin most samples have dbt p ratios

phengite compositions and post nappe high pressure metamorphism in the pennine zone of the french alps abstract a systematic study of relict highly substituted phengite micas si 3 6 3 7 formed in the less deformed and less recrystallized rocks of the internal zone of the french alps shows that silica content isograds for phengites cut across major thrust boundaries this indicates that a high pressure metamorphism was post nappe in the orogenic sequence little substituted secondary phengites and those found in highly recrystallized rocks reflect metamorphic conditions which occurred during the later mountain building phases of the orogeny variations of mica phengite content within mineral facies zones indicate rather important differences in pressure along the pennine zone in going from low to high temperature mineral facies

kinematic thermal and petrological model of the central alps lepontine metamorphism in the upper crust and eclogitisation of the lower crust abstract seismic and seismological studies as well as gravimetric models indicate that a slab of european lithospheric mantle and lower crust is currently underthrust below the apulian crust we assume a simple kinematic model in which the lower and upper subducted european crusts are decoupled along a decollement the lower crust goes into subduction without deformation the upper crust deforms by pure shear with a horizontal compressional axis the total erosional flux is adjusted to balance upper crust input so that the belt keeps the same geometry different distributions of erosion being used the computed temperature field is steady state if the kinematic model applies during a minimum time of 40 myr for a convergence rate of 8 mm yr equilibrium mineral assemblages and densities are determined from the computed p t conditions for a granodioritic chemical composition of the upper crust and an andesitic composition of the lower crust assuming local isostasy the density model fits the average topographic profile across the central alps the p t t paths obtained for the part of the upper crust initially at depths 10 to 16 km are compatible with the medium pressure oligocene metamorphism in the lepontine dome the peak calculated temperature for the deepest non subducted crustal rocks is 600 c for a pressure of 0 8 gpa near the lower limit of high pressure amphibolites we thus propose that the lepontine metamorphism corresponds to the steady state thermal regime however either faster erosion rates in the internal part of the belt or tectonic denudation are required for exhumation of the deeper portion of the belt the computed temperature field implies eclogitisation of the lower crust at a depth of 55 to 60 km we conclude that the moho limiting the deepest part of the root may correspond to the eclogitisation phase change lower crust eclogites have a density comparable to or higher than that of the mantle depending on their chemical composition 3 37 for andesitic eclogites 3 56 for gabbroic eclogites thus andesitic eclogites may stay in gravitational equilibrium in the mantle below the root whereas gabbroic eclogites are gravitationally unstable and should sink

exhumation of deep crustal metamorphic rocks and crustal extension in arc and back arc regions we adress the problem of exhumation of metamorphic rocks in arc and back arc positions based on observations of the aegean and tyrrhenian back arc regions in both regions back arc extension has been active for 25 ma at least while convergence and crustal thickening was going on at the thrust front compressional structures are reworked in the back arc domain as extensional flat lying detachments which allow unroofing of the metamorphic pile metamorphic rocks suffer first a dynamic burial during nappe stacking and then fast exhumation when they reach the extensional region we describe a continuous process of burial and exhumation that is contemporaneous with the migration of the thrust front toward external zones the front of extension follows behind at approximately one hundred kilometers at the convergence front continuous subduction of a cold oceanic slab or continuous accretion of continental units keeps a cool p t gradient and hp lt metamorphic rocks are formed at depth the overall cool environment leads to a deep brittle ductile transition and thus to a resistant crust which can sustain its large thickness while the thrust front propagates forward parts of the accretionary wedge which were formed earlier enter the back arc domain which can be already under extension and which is warmer because of a greater distance to the cold slab and the presence of the volcanic arc the brittle ductile transition rises in the thick crust which then becomes unstable and subsequently collapses the exhumation history of metamorphic rocks below detachments is two fold 1 a constantely thickening crust is unroofed by flat lying detachments which rework early thrusts this first period is characterized by a good preservation of hp lt parageneses 2 the second period is when rocks are in the zone of crustal scale extension of the back arc region deep crustal metamorphics are exhumed below flat lying detachements which affect the whole crust

the application of diamondoid indices in the tarim oils this study presents new data for the identification of the source and assessment of the thermal maturity of oils based on the diamondoid indices of oils from the tazhong and luntai uplifts in the tarim basin in northwest china the oil samples were divided into three groups according to biomarker characteristics and the abundance and distribution of diamondoids group i oils are located along the tazhong no 1 fault zone which contained abundant diamondoids and are of high thermal maturity suggesting they are late charged hydrocarbons that were derived from a middle upper ordovician source group ii oils are mainly located in blocks close to the tazhong no 1 fault zone and are dominated by early formed hydrocarbons from cambrian lower ordovician source rocks group iii lacustrine oils comprise relatively low concentrations of diamondoids compared with group i and group ii oils group iii oils were sourced from jurassic or possibly triassic units and are hosted by the low relief yingmaili section of the luntai uplift the thermal maturity of the oils in each group was evaluated using diamondoid parameters a few group i oils exhibit intense thermal cracking to estimate the extent of oil cracking using the concentrations of diamondoids in oils this study proposes a practical approach that facilitates the determination of baseline 4 and 3 methyldiamantane concentrations application of this method indicates that the tarim basin marine oils contain a baseline concentration of approximately 69 ppm

subducted and obducted ophiolites of the central alps paleotectonic implications deduced by their distribution and metamorphic overprint abstract the scenario of the closure of the tethyan realm in the central alps as reconstructed from the distribution and intensity of high pressure overprint can be interpreted as follows in the western part of the alps consecutive subduction and collision occurred in two well separated oceanic domains first in the piemontais domain zermatt saas zone and then in the valais domain versoyen further to the east where the two oceanic domains had merged ino a single ocean closure of the piemontais ocean led to obduction of oceanic crust onto the northern continental margin the ophiolites so produced were later involved in a greenschist facies stage which is related to the second collision and definitive closure of the alpine realm the change in tectono metamorphic evolution is spatially related to the eastern extremity of the brianconnais rise

first paleomagnetic data from the sedimentary cover of the french penninic alps evidence for tertiary counterclockwise rotations in the western alps abstract we present a paleomagnetic study performed in the brianconnais sedimentary cover of the western alpine arc france sampling was focused on upper jurassic rocks of the brianconnais cover in the briancon guillestre area more than 100 samples from 11 sites were collected essentially from ammonitico rosso limestones and sedimentary dykes of the upper jurassic thermal and alternating field demagnetizations revealed three components of magnetization carried dominantly by magnetite 1 a low temperature component with present day magnetic field direction of viscous origin 2 a well defined reverse polarity component with a maximum unblocking temperature of 440 c a component and 3 a weak high temperature component b component that experienced a viscous overprint during heating and was difficult to isolate the a component exhibits a negative fold test and shows a better clustering when corrected for tilting associated with late alpine extension this component is interpreted as a secondary remagnetization acquired during the cooling path related to late eocene early oligocene metamorphism the mean a component direction corrected for late alpine extensional tilting is d 142 i 57 k 44 95 8 this direction significantly differs by 47 13 from the expected direction for eurasia we interpret this difference to be related to a post eocene counterclockwise rotation about a vertical axis of the penninic zone relative to stable europe

molecular correlation of free oil adsorbed oil and inclusion oil of reservoir rocks in the tazhong uplift of the tarim basin china the free adsorbed and inclusion oils were recovered by sequential extraction from eleven oil and tar containing reservoir rocks in the tazhong uplift of tarim basin the results of gas chromatography gc and gc mass spectrometry analyses of these oil components and seven crude oils collected from this region reveal multiple oil charges derived from different source rocks for these oil reservoirs the initially charged oils show strong predominance of even over odd n alkanes in the range n c12 to n c20 and have ordinary maturities while the later charged oils do not exhibit any predominance of n alkanes and have high maturities the adsorbed and inclusion oils of the reservoir rocks generally have high relative concentrations of gammacerane and c28 steranes similar to the cambrian lower ordovician source rocks in contrast the free oils of these reservoir rocks generally have low relative concentrations of gammacerane and c28 steranes similar to the middle upper ordovician source rocks there are two interpretations of this result 1 the initially charged oils are derived from the cambrian lower ordovician source rocks while the later charged oils are derived from the middle upper ordovician source rocks and 2 both the initially and later charged oils are mainly derived from the cambrian lower ordovician source rocks but the later charged oils are contaminated by the oil components from the silurian tar sandstones and the middle upper ordovician source rocks

tracing of deeply buried source rock a case study of the wc9 2 petroleum pool in the pearl river mouth basin south china sea abstract the identification of a deeply buried petroleum source rock owing to the difficulty in sample collection has become a difficult task for establishing its relationship with discovered petroleum pools and evaluating its exploration potential in a petroleum bearing basin this paper proposes an approach to trace a deeply buried source rock the essential points include determination of the petroleum charging time of a reservoir reconstruction of the petroleum generation history of its possible source rocks establishment of the spatial connection between the source rocks and the reservoir over its geological history identification of its effective source rock and the petroleum system from source to trap and evaluation of petroleum potential from the deeply buried source rock a case study of the w9 2 petroleum pool in the wenchang a sag of the pearl river mouth basin south china sea was conducted using this approach the w9 2 reservoir produces condensate oil and gas sourced from deeply buried source rocks the reservoir consists of a few sets of sandstone in the zhuhai formation and the possible source rocks include an early oligocene enping formation mudstone and a late eocene wenchang formation mudstone with a current burial depth from 5000 to 9000 m the fluid inclusion data from the reservoir rock indicate the oil and the gas charged the reservoir about 18 3 5 ma and after 4 5 ma respectively the kinetic modeling results show that the main stages of oil generation of the wenchang mudstone and the enping mudstone occurred during 28 20 ma and 20 12 ma respectively and that the 13 c 1 value of the gas generated from the enping mudstone has a better match with that of the reservoir gas than the gas from the wenchang mudstone results from a 2d basin modeling further indicate that the petroleum from the enping mudstone migrated upward along the well developed syn sedimentary faults in the central area of the sag into the reservoir but that the petroleum from the wenchang mudstone migrated laterally first toward the marginal faults of the sag and then migrated upward along the faults into shallow strata the present results suggest that the trap structure in the central area of the sag is a favorable place for the accumulation of the enping mudstone derived petroleum and that the wenchang mudstone derived petroleum would have a contribution to the structures along the deep faults as well as in the uplifted area around the sag

genetic origins of marine gases in the tazhong area of the tarim basin nw china implications from the pyrolysis of marine kerogens and crude oil abstract although abundant natural gases have been discovered in carboniferous and ordovician reservoirs in the tazhong area central tarim basin their genetic origins is still an open question because of significant variations in chemical and carbon isotopic compositions in the present study three samples representing the possible gas sources were pyrolyzed using sealed gold tubes to investigate their gas potentials and chemical and carbon isotopic signatures the samples were a crude oil a low maturity kerogen and a high maturity kerogen the results show that the chemical and isotopic compositions of gaseous pyrolysates from the three samples are quite different generally the gases from oil cracking are compositionally wetter and isotopically lighter than those from kerogen cracking at similar thermal levels the large quantities of methane experimentally observed in oil cracking gases are mainly associated with the re cracking of wet gases at very high maturity levels methane in gases derived from kerogen especially high maturity kerogen in contrary is mainly generated by the demethylation reaction the diagrams of 13c1 vs 13c2 13c3 and c2 c3 vs 13c2 13c3 along with natural gas plots have proven to be a very effective tool in the genetic interpretation of natural gases from kerogen and oil cracking in the tarim basin their combined application shows that two types of gas source can be identified in the tazhong area the first type is oil cracking gas mainly discovered in carboniferous reservoirs of the central fault horst area but also partly in ordovician reservoirs such as in the wells tz45 tz44b and tz 16 the other is kerogen cracking gas occurring largely in ordovician reservoirs especially in the north slope area the two types of gases however are mixed in many reservoirs as their generation is overlapped in time and or space this mixing process is especially obvious for methane

the tazhong hybrid petroleum system tarim basin china abstract the tazhong petroleum system is geographically located in the central tarim basin including the tazhong uplift the north slope and the southern area of the manjiaer depression the total thickness of early palaeozoic to cenozoic sediments reaches 6500 9500 m the manjiaer depression and the north slope are the two major petroleum source areas with three sets of source rocks cambrian black shales and ordovician dark carbonates of the manjiaer depression and ordovician argillaceous limestones of the north slope there are three sets of reservoir cap rock combinations in this petroleum system the main periods for oil generation from these source rocks occurred during the middle silurian to early devonian late carboniferous to early triassic and tertiary there were three corresponding phases of petroleum migration well developed thrust faults and unconformity surfaces in this area provided the main pathways for petroleum migration as some of the faults cut through all the lower palaeozoic strata the oil in any given reservoir rock may be actually a mixture of oils from different sources complicating the origin and properties of the hydrocarbons in the reservoir and forming a hybrid petroleum system the formation of a typical oil and gas pool in this petroleum system may be attributed to one or all of three petroleum events which were closely associated with the regional tectonics the first event occurred in the early palaeozoic tectonic cycle and the generated oil accumulated in lower silurian sandstone the second event occurred in the late palaeozoic tectonic cycle and formed light oil pools mainly in lower silurian and ordovician reservoirs the third event took place during the cenozoic tectonic cycle and formed normal crude oils the oil and gas generated from different sources in different phases may co exist with one another in a reservoir rock however the commercial oil and gas pools are related to the cenozoic and late palaeozoic events