aftsolve a program for multi kinetic modeling of apatite fission track data aftsolve is a computer program for deriving thermal history information from apatite fission track data it implements a new fission track annealing model that takes into account the known kinetic variability among different apatite species to fully utilize this model a fission track worker must obtain data that can be used to infer the kinetic characteristics of each apatite grain from which a measurement was taken such data can consist of etch figure lengths or chemical composition the benefit of this overall approach is that it allows useful information to be derived from previously unusable analyses extends the practical range of geological temperatures constrained by fission track analyses and increases overall confidence in model predictions aftsolve also incorporates the effects of fission track orientation relative to the apatite crystallographic c axis variation in initial track length and the biasing effect of 2 5 2 cf irradiation for enhancing confined horizontal track length detection aftsolve is written for windows operating systems and has a graphical interface that allows interactive input of thermal histories and real time generation of estimates for fission track length distributions and ages for up to six simultaneously modeled kinetic populations it also includes procedures for estimating the range of time temperature histories that are statistically consistent with a data set and constraints entered by the user

andean tectonics as a cause for changing drainage patterns in miocene northern south america newdatafromneogenestratainnorthernsouthamericasuggestthatmiocenetectonisminthenortheasternandeswasresponsible for the genesis of the amazon river and changes in the drainage patterns of other major rivers such as the magdalena and the orinoco here we present a new model for the paleogeographic evolution of northern south america during the miocene in the early miocene a large part of the drainage of northwest amazonia was directed northward along the paleo orinoco river system to a deltainlakemaracaibo upliftoftheeasterncordillerainthelate middle miocene caused thefirst development of the amazon river however no connection with the atlantic was established and the amazon fed the paleo orinoco river system which drained toward the caribbean substantial andean uplift in the late miocene resultedinmajorchangesinpaleogeography theorinocochangedits course the amazon established a connection to the atlantic causing the drowning of carbonate platforms and the amazon caribbeanconnectionwasclosed thusthedrainageandpaleogeography ofnorthernsouthamericainthemiocenewerestronglycontrolled by tectonic movements in the northeastern andes

a comparison of burial maturity and temperature histories of selected wells from sedimentary basins in the netherlands sedimentary basins in the netherlands contain significant amounts of hydrocarbon resources which developed in response to temperature and pressure history during mesozoic and cenozoic times quantification and modelling of burial maturity and temperature histories are the major goals of this study allowing for a better understanding of the general geological evolution of the different basins as well as petroleum generation all major basins in the netherlands encountered at least one time of inversion and therefore moderate to high amounts of erosion in order to determine the amount of inversion the basins have experienced a 1d study was performed on 20 wells within three basins west netherlands central netherlands and lower saxony basins new vitrinite reflectance values were obtained and existing data re evaluated to gain a good data base the burial histories of six wells two for each studied basin are presented here to demonstrate the differences in basin evolution that led to their present shape and petroleum potential the permo triassic subsidence phase can be recognized in all three basins but with varying intensity in the jurassic the basins experienced different relative movements that culminated in the cretaceous when the influence of the inversion caused erosion of up to 2 500 m most wells show deepest burial at present day whereas the timing of maximum temperature differs significantly springer verlag 2007

thermal modelling of the melut basin sudan and south sudan implications for hydrocarbon generation and migration abstract the thermal history of the melut rift basin was studied in a number of wells and along a northeast southwest cross sectionacross the basin using 1 d and 2 d basin models modelling was conducted using petromod software to test subsidence thermal history and their implications for hydrocarbon generation migration and accumulations geotherms were found ranging between 24 and 44 c km and average 32 c km and present day heat flow was found to vary between 53 and 65 averaging 59 mw m 2 a geologicaly realistic paleoheat flow model with higher heat flow peaks of 75 70 and 65 mw m 2 during the first second and third rifting phases respectively calibrated against vitrinite reflectance data was employed the model was found sensitive to cenozoic erosions and a 600 m of exhumation did support the vitrinite data in providing a reasonable fit in most locations using the easy ro vitrinite kinetic model for maturity the average present day oil window was found between 1565 and 4050 m in the wells studied and between 1705 and 4200 m along the cross section using type ii kerogen for the aptian albian source rocks the hydrocarbon generation and expulsion were modelled and revealed that the generation started as early as 95 ma in some areas but significant generation rates were during the second rifting phase and expulsion started at around 85 ma calculations of the probable expelled amounts of hydrocarbon from the northern sub basin are high and up to 2 2 10 11 bbls of oil and 2 3 10 14 ft 3 of gas migration of oils from cretaceous source rocks kitchen to the cenozoic traps was probably through faults porous carrier beds and breaching of traps cap rocks the filling of these traps might be periodic during the rifting episodes and hydrocarbons remigrated from deeper traps to shallow ones it is possible that thinner and siltier cap rocks along the hydrocarbon migration path may have allowed gas to scape but holded the oil back it is most probable that part of the hydrocarbons might have been generated from shallower source rocks areas and a 2 d hybrid darcy flow path model have demonstrated this and predicted a number of accumulations which are similar to the known large discoveries such as palogue fal and adar yale oil fields

geodynamic mechanism and classification of basins in the earth system abstract the sedimentary basin is a basic geological unit in the earth system its formation and evolution are controlled mainly by plate tectonics and geodynamics which have produced a variety of basin types the development and evolution of various basins depend not only on the tectonic effect of lithospheric plate but also on sublithospheric and earth surface actions basin classification schemes based on the theories of platform geosyncline or plate tectonics could neither include all basin types nor reflect the complex processes of basin formation and evolution from the viewpoint of earth system we proposed a new basin classification scheme based on geodynamic mechanism that is lithospheric plate sublithospheric and earth surface actions in our geodynamic classification we employed a series of geodynamic settings of basin formation and evolution including the lithospheric plate sublithospheric and earth surface environments the dynamic regimes of basin formation and evolution such as tectonic setting extension compression and shearing the thermal processes and gravity effects the various natures of basin basement and crustal types continental oceanic or transitional crust and the history of basin sedimentary filling and tectonic paleogeography successively as the controlling factors for basin classification this new geodynamic classification scheme highlights both the role of the lithosphere and the effects of the sublithospheric and the earth surface actions on controlling the basin formation and evolution the basic dynamic types of basin classification include the prototype basin forming under a single tectonic thermal or gravity regime and the superimposed basin as well as residual basin forming under multistage thermal and or tectonic regimes thus this classification scheme could provide an evolving understanding of lithosphere crust mantle interaction and geodynamic processes as well as of hydrocarbon accumulation and metallogenic mechanisms in sedimentary basins and would help in the synthetic exploration of various resources

thermal history and source rock characterization of a paleozoic section in the awbari trough murzuq basin sw libya abstract in some areas of the murzuq basin sw libya the lower silurian member comprises highly radioactive shales hot shale which are regarded as the most significant factor controlling petroleum generation in the basin in this context it was the goal of our project to study the distribution and maturity of the hot shale in the framework of basin evolution organic geochemical organic petrological and basin modelling methods were used to obtain a more thorough understanding four wells from the northern and central part of the awbari trough have been selected for this study the hot shale contains mainly type ii kerogen with high toc values ranging from 3 to 23 which is considered as an indication for excellent source rock potential a good petroleum potential is further supported by hydrogen indices varying between 220 and 380 mg hc g toc numerical 1d basin modelling was performed for four wells in order to assess the thermal maturity of the tanezzuft hot shale and its evolution through time mean random equivalent vitrinite reflectance results using vitrinite like particles for lower silurian hot shale pyrolysis t max values and fluorescence colours indicate that the hot shale is immature to early mature in the southern part and clearly more mature in the northern part of the basin other potential source rocks from silurian tanezzuft middle upper devonian awaynat wanin and lower carboniferous marar formations were analysed thermal history modelling indicates that the present day geothermal gradients and heat flows vary at different locations but that paleotemperature evolution is mostly related to deepest burial peak temperatures were reached either in the late carboniferous before hercynian uplift occurred or in the jurassic cretaceous the latter scenario being more probable because much oil has been preserved

tectonic inheritance crustal architecture and contrasting structural styles in the venezuela andes surface and subsurface data image contrasting structural styles for the two flanks of the venezuela andes in the north a flexural basin developed in neogene times between the andes and the lake maracaibo north verging thrusts are mainly detached in the pre cretaceous substratum and form a deeply buried antiformal stack secondary decollement levels occur both in the upper cretaceous and tertiary strata accounting for the passive roof thrust of a conventional frontal triangle zone in the south the barinas basin hardly compares with a flexural basin it is largely dominated by both north and south verging basement involving structures paleogene normal faults are locally inverted and caribbean nappes are frequently reactivated or refolded by younger oblique neogene andean structures seismic profiles in this area also attest to the strong neogene structural inversion of upper jurassic lower cretaceous grabens hercynian or more likely early paleozoic structures account for local preexisting crustal heterogeneities reactivated during both the tethyan rifting and the andean deformations two trans andean regional profiles have been balanced and constrained by an inversion of the gravimetric data they imply a progressive deepening of the northern moho and a south dipping subduction of the infracontinental lithospheric mantle of the maracaibo block the shortening for both sections averages 60 km palinspastic restorations assume a relative cylindricity for the deep crustal architecture of the andes and minimize the possible effects of a progressive right lateral escape of the maracaibo block with respect to stable south america along the bocono fault strain partitioning during neogene oblique convergence induced surficial thrust fronts parallel to the plate boundary strike slip motion in the allochthon along the bocono fault and an asymmetric subduction wedging at depth

geological history and petroleum system of the mittelplate oil field northern germany the geological history of germany s largest and most productive petroleum accumulation the mittelplate oil field in schleswig holstein northern germany is reconstructed by simulating the structural and thermal evolution along a 2d cross section the mittelplate field is located at the western flank of the busum salt dome at the transition from the schleswig holstein mainland to the german north sea sector organic geochemical data confirm the lower jurassic posidonia shale to be the predominant oil source rock in the schleswig holstein area the studied section is characterized by salt walls and salt domes built up by permian evaporites reconstruction of the structural and thermal evolution of the mittelplate field by means of basin modelling reveals the dominating influence of salt dynamics on the entire petroleum system the development of secondary rim synclines during salt rise provided accommodation space for the deposition of the posidonia shale as well as the deltaic middle jurassic reservoir sandstones the rise of the nearby oldenswort salt wall controlled the timing of maturation and petroleum generation during cenozoic times hydrocarbon migration from the posidonia shale into the reservoirs occurred up dip from the deeper subsiding rim syncline into the structural trap with the middle jurassic reservoir sandstones pinching out at the flank of the busum salt dome along the modelled 2d section the field s recent temperature field and its complex reservoir architecture are reconstructed

mesozoic basin development and tectonic evolution of the dabieshan orogenic belt central china 1 the dabieshan orogenic belt is a zone of long lived shortening with late stage extension that formed during mesozoic time in central china regional basin analysis coupled with structural cross sections provides a means of reconstructing the paleogeography of the region from triassic continental collision through early tertiary extension the overall distribution of different basin types in the orogenic belt indicates that there was a prolonged period of shortening throughout the mesozoic that became less intense over time meanwhile extension became more common from jurassic into tertiary time either compression or extension was isochronous but limited to different geographic regions and or crustal levels or alternated repeatedly orogen wide through time nonetheless the orogen underwent gradual transition from overall shortening and crustal thickening to dominantly extension and rift basin formation although these events overlapped in time from the jurassic through early cretaceous penecontemporaneous compression and extension across the orogen may reflect long term 100 m y shortening and crustal thickening leading to gravitational spreading of the resultant thick crustal welt we suspect that this prolonged history of shortening across two nearby 100 km apart suture zones played some role in the exhumation of ultrahigh pressure rocks from beneath the dabieshan

modelling of the thermal history of the carboniferous lorraine coal basin consequences for coal bed methane this paper proposes a new scenario for the thermal history of the carboniferous lorraine coal basin following the tectonic model developed by averbuch et al 2012 and establishes some consequences for the coal bed methane cbm exploitation organic matter maturation data vitrinite reflectance determined on eleven boreholes in the eastern lorraine have been used to characterize the lorraine coal basin evolution paleozoic and mesozoic overburials have been calculated using a thermal modelling software petromod results show that 1 paleozoic erosion may be estimated at a maximum of 1200 m which represents a low amplitude event 2 a little erosion occurred between upper paleozoic and lower mesozoic paleotemperature offset is about 20 c and vr data range from 0 7 westphalian d to 0 5 lower triassic 3 cretaceous cover overburial reaches a maximum of 300 m and decreases eastwards and 4 the variation of heat flows is in agreement with the compressive and extensive phases of paleozoic and the extensive phase of mesozoic consequences on the petroleum system are the following organic matter is immature in the jurassic and triassic sedimentary rocks mature oil window in the permian stephanian and westphalian c d highly mature gas window in westphalian a b c and overmature in namurian westphalian a the high methane adsorption capacity of coal and the presence of natural fractures inside coal seams demonstrated by coal tomography allow a high cbm potential in this basin the lorraine coal basin is therefore a target for coal gas

unconventional shale gas systems the mississippian barnett shale of north central texas as one model for thermogenic shale gas assessment shale gas resource plays can be distinguished by gas type and system characteristics the newark east gas field located in the fort worth basin texas is defined by thermogenic gas production from low porosity and low permeability barnett shale the barnett shale gas system a self contained source reservoir system has generated large amounts of gas in the key productive areas because of various characteristics and processes including 1 excellent original organic richness and generation potential 2 primary and secondary cracking of kerogen and retained oil respectively 3 retention of oil for cracking to gas by adsorption 4 porosity resulting from organic matter decomposition and 5 brittle mineralogical composition the calculated total gas in place gip based on estimated ultimate recovery that is based on production profiles and operator estimates is about 204 bcf section 5 78 10 9 m 3 1 73 10 4 m 3 we estimate that the barnett shale has a total generation potential of about 609 bbl of oil equivalent ac ft or the equivalent of 3657 mcf ac ft 84 0 m 3 m 3 assuming a thickness of 350 ft 107 m and only sufficient hydrogen for partial cracking of retained oil to gas a total generation potential of 820 bcf section is estimated of this potential approximately 60 was expelled and the balance was retained for secondary cracking of oil to gas if sufficient thermal maturity was reached gas storage capacity of the barnett shale at typical reservoir pressure volume and temperature conditions and 6 porosity shows a maximum storage capacity of 540 mcf ac ft or 159 scf ton

sedimentological evidence for early uplift oligocene of the venezuelan andes the ongoing andean orogeny is generally believed to have started in miocene time however sedimentological studies of a cenozoic clastic section in the northwestern foothills of the venezuelan andes rio chama yield two lines of evidence that uplift was already underway in the oligocene 1 thick oligocene shales leon formation 300m are dark gray and bioturbated pyrite is absent and the fauna is restricted to benthonic forms r pittelli suggesting deposition in a brackish lake rather than the sea the shales occur throughout the plains northwest of the andes such a large long lived lake implies isolation form the sea suggesting that the andes were already high in the oligocene forming a topographically confined basin similar to the modern lake maracaibo like modern lake maracaibo there was a tenuous connection with the sea allowing marine incursions whenever eustatic sea level was high enough as shown by horizons with marine fossils at other localities 2 the overlying oligocene miocene succession which caps the rio chama section caracol member chama formation basal betijoque formation includes fluvial channel sands with pebbles which can be matched to cretaceous cherts of the adjacent andes ftanita de tachira the first pebbles appear in the caracol member oligocene theymore are thus regarded as the initial andean molasse deposits and their deposition has continued to the present day less

burial and thermal evolution of coal bearing strata and its mechanisms in the southern north china basin since the late paleozoic abstract during the interaction between the south china plate and the north china plate the southern north china basin sncb underwent a strong tectonic thermal evolution in the early mesozoic recently burial history reconstruction and thermal maturity simulation of coal bearing strata from the late carboniferous to the present were carried out in the sncb rock eval pyrolysis 12 samples vitrinite reflectance 60 samples apatite fission track aft analysis 17 samples and petromod 1d were performed on wells located in the sncb geothermal gradients were found to range between 30 3 and 36 4 c km averaging 31 0 c km and present heat flow was found to vary between 51 and 58 averaging 55 mw m2 the paleo heat flow model with higher heat flow peaks of 86 mw m2 during the first rifting phase resulted in the best fit between the calculated and the observed vitrinite reflectance and bottom hole temperatures in the modeling using this model of thermal maturity history combined with aft analysis we analyze the main hydrocarbon generation stages and discuss the coupling relationship of thermal maturity history with tectonic evolution the results indicate that tectonic activities restrict the thermal maturity evolution of source rocks to a large extent by controlling the geotemperature the thermal history demonstrates that two phases of heating 315 163 ma 83 38 ma depositing happened to the source rocks separated by two cooling 163 83 ma 38 23 ma uplifting events the maturity history indicates that the process of hydrocarbon generation can be divided into three stages in the sncb 315 163 ma thermal genesis gas generation stage 163 83 ma gas reservoir destruction stage 83 0 ma secondary biogas generation stage hydrocarbon generation started as early as 198 ma with a peak at 162 ma and expulsion started at around 195 ma the taiyuan and shanxi formations source rocks reached a high maturity 1 0

cretaceous cenozoic history of the southern tan lu fault zone apatite fission track and structural constraints from the dabie shan eastern china apatite fission track aft and structural data outline the late cretaceouscenozoic history of the southern tan lu fault zone tlfz one of asia s major faults the triassic jurassic dabie orogen earth s largest track of ultrahigh pressure rock exposure and its foreland the yangtze foreland fold thrust belt the fission track analyses utilized the independent z and n methods for age determination which yielded within error identical ages ages from triassic jurassic syn orogenic foreland sediments are younger than their depositional age and thus were reset a group of ages records rapid cooling following shallow emplacement of granitoids of the widespread latest jurassicearly cretaceous yanshanian magmatism most ages are 90 to 55 ma and document cooling following reheating at 110 90 ma the time when the basement units of the dabie shan were last at 200 jc this cooling coincides with rifting marked by the late cretaceouseocene red bed deposition in eastern china during this period the dabie basements units exhumed in the footwall of the tan lu fault with the qianshan basin in the hanging wall the associated stress field is transtensional nw trending principal extension direction the youngest fission track ages and temperature time path modeling point to enhanced cooling in the footwall of the tan lu and associated faults at 45f10 ma the related stress field is transtensional with the principal extension direction changing trend from nw to w it may be the far field expression of the india asia collision superposed on the back arc extension setting in eastern china a regional unconformity at f25 ma marks an upper bound for the inversion of the late cretaceouseocene rift structures during the neogene further subsidence in the eastern china basins was accommodated by sub horizontal ne sw extension and followed by the presently active nw se extension the tan lu fault along the eastern edge of the dabie shan had normal

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

organic geochemistry of the woodford shale southeastern oklahoma how variable can shales be woodford shale samples obtained from a cored outcrop in southeastern oklahoma were geochemically analyzed to determine vertical variations of organic facies thermal maturity and an evaluation of their depositional environments total organic carbon values ranged from 5 01 to 14 81 indicating a good source rock potential in this area the woodford shale is marginally mature as indicated by vitrinite reflectance values rock eval data revealed that the samples are dominated by type ii kerogen biomarker ratios based on pristane phytane steranes and hopanes show a mix of marine and terrigenous organic matter high salinity conditions and water density stratification also prevailed during deposition of this formation as indicated by the presence of gammacerane the woodford shale was subdivided into lower middle and upper members based on the integration of geochemical and geologic data moreover the presence and extent of photic zone anoxia pza were determined by the presence of aryl isoprenoids the lower and upper woodford shale members were deposited under dysoxic to suboxic conditions and episodic periods of pza the middle member was deposited under anoxic conditions and persistent pza in addition aryl isoprenoids helped infer the position of the chemocline during deposition of the different members the relative hydrocarbon potential parameter was used in determining transgressive and regressive cycles within the woodford shale this study undoubtedly demonstrates the significant lithologic and chemical variability that occurs within shales the application of this workflow to regional studies can have a direct influence on exploration and production activities in shale gas systems

paleoproterozoic ultrahigh temperature granulites in the north china craton implications for tectonic models on extreme crustal metamorphism abstract ultrahigh temperature uht metamorphic rocks associated with the khondalite belt within the inner mongolia suture zone imsz provide robust evidence for extreme thermal metamorphism in the north china craton ncc the imsz marks the collisional suture between the yinshan block to the north and the ordos block to the south as the ncc was incorporated within the columbia supercontinent amalgam during paleoproterozoic here we present a synthesis of the salient features of the uht rocks from the ncc including petrologic indicators fluid characteristics and monazite and zircon chronometry on the extreme crustal metamorphism the granulites carry diagnostic uht mineral assemblages including sapphirine quartz low zn fe3 spinel quartz high alumina orthopyroxene sillimanite quartz and high temperature mesoperthite the stability fields of the typical mineral assemblages conventional geothermobarometry and phase equilibria modeling using pseudosections as reported in a number of recent studies converge to indicate that these uht rocks experienced metamorphic temperatures up to or in excess of 1000 c at ca 10 kbar followed by an isobaric cooling segment the rocks were exhumed along a near isothermal decompression path microstructures mineral reactions and phase equilibria modeling suggest an anti clockwise p t path similar to those displayed by metamorphic orogens developed in subduction collision settings the dominant category of fossil fluids preserved within the major uht minerals is co2 consistent with the stability of the broadly anhydrous mineral assemblage in these rocks both chemical and radiogenic isotopic ages from monazite and zircon chronometry suggest the timing of the uht event as around 1 92 ga the paleoproterozoic high grade metamorphism younging from 1 95 ga in the western domain to 1 92 ga in the eastern domain of the khondalite belt might suggest a scissor like closure of oblique collision between the yinshan and the ordos blocks the salient features of the uht metamorphism in the ncc include 1 extreme metamorphic temperatures at moderate pressures 2 dominantly anhydrous nature of the mineral assemblages typically the stability of orthopyroxene 3 common presence of co2 rich fluid inclusions as the trace of the ambient fluid 4 regional extent of the uht granulites and 5 the association of the uht orogen with an accretionary belt in a continental collisional suture we evaluate the diverse models on the generation of uht orogens including their formation in thickened and inverted back arcs orogen self heating through heat producing elements heat and co2 input by plume impingement below a carbonated tectosphere and asthenospheric upwelling through ridge subduction and slab window process or during post collisional slab break off the ultra hot and dry uht rocks in the ncc provide one of the well preserved examples from the paleoproterozoic globe for investigating extreme metamorphism and related tectonic processes within the plate tectonic paradigm

geological process of late paleozoic shale gas generation in the eastern ordos basin china revelations from geochemistry and basin modeling abstract during the meso cenozoic the eastern ordos basin eob underwent a complex tectonothermal process influenced by the destruction of north china craton significantly affecting the thermal maturation of the late paleozoic source rocks tectonothermal modeling and maturation of coal bearing shales were performed in the eob to reveal the geological process of shale gas generation organic geochemical data for shales show that toc values vary from 0 96 wt to 21 36 wt and ro values range from 1 56 to 2 47 as well as that organic matter mainly consists of type iii kerogen indicating excellent potential and sufficient maturity for gas generation thermal modeling suggests that heat flow in the eob significantly increased as a result of intense magmatic activities during the yanshanian orogeny with peak values of 108 and 128 mw m2 in the northern and southern regions respectively consequently great variations in maturation history are seen in different regions of the eob with the taiyuan and shanxi shales reaching the wet gas and dry gas stages respectively in the northern region and all shales reaching the dry gas stage in the southern region hydrocarbons were generated at 237 ma and peaked around 162 ma whereas hydrocarbon expulsion began at 230 ma and peaked at 131 ma rapid subsidence in the triassic brought the shales to the oil generation window and early cretaceous magmatic activities led to rapid maturation of shales again reaching the gas generation stage accordingly extremely high levels of thermal maturity are well documented in hydrocarbons alkane composition and stable carbon isotope ratio gas geochemical data 13c1 vs c1 c2 3 13c1 vs c2 imply that that hydrocarbons are from highly mature thermogenic gas generated mainly from humus and this offers great support for thermal maturation modeling regionally coal bearing shales have been steadily uplifted and eroded since the late cretaceous causing partial destruction of gas reservoirs the tectonothermal evolution and hydrocarbon generation of eob were controlled primarily by magmatic thermal effects resulting from the westward subduction of the pacific plate

raman spectroscopy and structural heterogeneity of carbonaceous material in proterozoic organic walled microfossils in the north china craton abstract raman spectroscopy is a minimally intrusive and minimally destructive technique that has played an important role in analyzing precambrian carbonaceous microfossils and microstructures previous studies have shown that heterogeneities in structural order of carbonaceous material cm as revealed by raman spectroscopy can be preserved in proterozoic silicified cyanobacterial fossils however such heterogeneities have not been documented in proterozoic eukaryotic microfossils preserved as carbonaceous compressions in this study we used raman spectroscopy to investigate the structural characteristics of organic walled microfossils including eukaryotes preserved as carbonaceous compressions from the late paleoproterozoic ruyang group and the early neoproterozoic tonian liulaobei formation in the north china craton raman geothermometers indicate that cm experienced low grade metamorphism with apparent peak metamorphic temperatures of 200 c for both the ruyang and liulaobei microfossils heterogeneities in structural characteristics of cm in eukaryotic microfossils were found among different subcellular structures of shuiyousphaeridium macroreticulatum and among different taxa from the same stratigraphic horizon we suggest that these heterogeneities can be attributed to differences in precursor organic compounds thus the importance of organic precursors should be considered in cm raman geothermometry studies especially in environments where heating events occurred quickly the raman data presented here are also consistent with hypotheses that the ruyang microfossils dictyosphaera delicata and s macroreticulatum are biologically conspecific taxa with their vesicle walls having similar cm raman features and that the liulaobei microfossils leiosphaeridia jacutica and l tenuissima are distinct taxa despite their similarities in morphologies other than vesicle wall thickness although more data are needed to verify the consistency of interspecies intraspecies and intraspecimen variability this study indicates that raman spectroscopy may have the potential to provide an independent test of early eukaryote taxonomy which has been traditionally based only on morphological features and to reveal heterogeneities of cm of early eukaryotic organisms