pore network characteristics of lacustrine shales in the dongpu depression bohai bay basin china with implications for oil retention abstract pore development and the location of retained hydrocarbons are key topics to understand the shale oil system in an attempt to investigate pore network characteristics and oil retention in lacustrine shales 24 samples from the es3 shales in the dongpu depression bohai bay basin were subjected to mineralogical petrological geochemistry and pore structure investigations using x ray diffraction xrd thin section field emission scanning electronic microscope fe sem n2 adsorption desorption after removing retained oil by solvent extraction 12 selected samples were again analyzed by rock eval pyrolysis and n2 adsorption desorption experiment according to the mineral compositions and petrological characteristics six types of lithofacies are identified in the es3 shales in the dongpu depression laminated calcareous shales lenticular calcareous shales laminated argillaceous shales massive argillaceous shales laminated siliceous shales and massive siliceous shales geochemical characteristics of these shales are quite different as calcareous laminated shales have higher toc contents than massive argillaceous and siliceous shales interparticle pores intraparticle pores organic matter pores and fracture pores are observed in the studied samples while bitumens were found retaining in well connected pore network the n2 adsorption desorption experiments on samples before and after solvent extraction reveal the different pore structure characteristics in six lithofacies and the occurrence of oil in lacustrine shales in general pore volumes within pore diameter range of 1 7 10nm and 10 200nm of samples show increase after solvent extraction indicating that large and small pores in shales both play important roles in oil retention oil retained in shales can be divided as free and heavy fractions as from the pyrolysis results in lacustrine shales larger pores are main storage space for hydrocarbon larger pores in different lithologies have similar capacity for free oil retention while those in calcareous and argillaceous shales are more efficient for heavy oil retention for both free and heavy oil small pores in argillaceous shales are efficient for their storage

the thermal history of the upper palaeozoic rocks of southern portugal abstract vitrinite reflectance vr evidence suggests that palaeozoic rocks in the south portuguese zone of southwest portugal are strongly post mature with mean vr r r of 4 28 results from a thin carboniferous coal are very similar to those from associated mudrocks suggesting that the results from mudrocks in the region are not significantly influenced by the presence of reworked vitrinite particles integration of stratigraphic evidence with vr results from a field oriented carboniferous coal sample indicate that peak temperatures were attained post hercynian deformation within the late carboniferous late triassic interval results from the aureole of a minor mesozoic igneous intrusion suggest that these intrusions did not significantly increase the already high maturation level of the palaeozoic country rocks vr r r values from triassic jurassic and cretaceous sections that unconformably overlie the palaeozoic rocks are much lower 0 87 1 14 than those from the palaeozoic and are fully consistent with recorded stratigraphic thicknesses and burial at geothermal gradients of 20 30 c km 1

initiation of bed forms on a flat sand bed the results of a series of 47 bed development experiments are combined with appropriate experimental results of other authors the generation of initial bed waves termed sand wavelets on a plane sand bed is found to be instigated by the occurrence of a random pileup of sediment this pileup subsequently growing as further sediment is trapped by the pileup when the height of the pileup approaches the bed roughness height further pileups are generated at preferred spacings downstream the wavelength l of the sand wavelets so generated is relatively insensitive to the applied bed shear stress and primarily a function of the size d g of the sediment this wavelength can be described by the empirical formula l dg r c0 2 10 2 5 from a theoretical viewpoint this wavelength is approximately described by a reassessment of the flow system instability analyses of richards both ripples and dunes are found to develop from the sand wavelets

formation of ripples in erodible channels formation of ripples and dunes in erodible channels is analyzed by using the hydrodynamic model developed by kobayashi and madsen this issue applying the continuity equation of sediment the propagation velocity of the wavy bed is expressed in terms of the net fluxes of bed load along the wavy bed and suspended sediment out of the bed load transport layer the spatial variation of the bed load transport rate is derived by analyzing the balance of forces acting on a representative bed load particle on a sloping bed the net flux of the suspended sediment out of the bed load transport layer is obtained by solving the diffusion equation for the suspended sediment near the bed the stability analysis predicts that a perturbation that is either fairly short or long relative to the depth of flow will initially grow depending on whether the flow is hydraulically smooth or fully rough thus the model explains why ripples are not observed in experiments involving fairly coarse sediments since in these cases the flow is rough turbulent

direct numerical simulation of pattern formation in subaqueous sediment we present results of direct numerical simulation of incompressible fluid flow over a thick bed of mobile spherically shaped particles the algorithm is based upon the immersed boundary technique for fluid solid coupling and uses a soft sphere model for the solid solid contact two parameter points in the laminar flow regime are chosen leading to the emergence of sediment patterns classified as small dunes while one case under turbulent flow conditions leads to vortex dunes with significant flow separation on the lee side the wavelength amplitude and propagation speed of the patterns extracted from the spanwise averaged fluid bed interface are found to be consistent with available experimental data the particle transport rates are well represented by available empirical models for flow over a plane sediment bed in both the laminar and the turbulent regimes

revisiting the linear theory of sand dune formation a linear stability theory for dune and antidune formation is presented that implements a rotational two dimensional flow model as in previous linear theories the phase lag between sediment transport and bed elevation remains the main mechanism driving instability however it is shown that this phase lag varies significantly in a neighbourhood of the bed moreover since the layer in which sediments are moving has a finite though small thickness it is assumed that the perturbations of the fluid stress driving bedload transport should be evaluated at the top of the layer itself it is shown that such an apparently minor modification of the classical approach alters remarkably the balance between stabilizing and destabilizing effects that drives the instability process this also allows a clarification of the debated role of bedslope on the formation of dunes and antidunes following the above ideas antidunes are shown to form in the absence of suspended sediment load and without any effect associated with sediment inertia the present analysis ultimately allows a successful unification of the theories of dune and antidune formation

flexural subsidence and basement tectonics of the cretaceous western interior basin united states the flexural subsidence history recorded in cenomanian to early campanian 97 to 80 ma strata in the cretaceous u s western interior basin was studied with two dimensional flexural backstripping techniques results indicate that the flexural subsidence resulting from thrust loading was superimposed on epeirogenic subsidence in the foreland basin the flexural component exhibits significant spatial and temporal variations along both the strike and dip relative to the sevier thrust belt the greatest cumulative subsidence occurred in southwestern wyoming and northern utah concurrent subsidence in northwestern montana and southern utah was insignificant temporal trends in subsidence also show a distinct regional pattern from the cenomanian to late turonian 97 to 90 ma subsidence rates were high in utah and much lower in wyoming and montana in contrast during the coniacian and santonian 90 to 85 ma subsidence accelerated rapidly in wyoming increased slightly in montana and decreased in utah we suggest that these spatially and temporally varying subsidence patterns reflect the interplay of several geodynamic factors including 1 temporal and spatial variation in emplacement of the thrust loads 2 segmentation of the basement into adjacent blocks with different rheological properties 3 reactivation of basement fault trends and 4 regional dynamic topographic effects

bedforms in a turbulent stream formation of ripples by primary linear instability and of dunes by nonlinear pattern coarsening it is widely accepted that both ripples and dunes form in rivers by primary linear instability the wavelength of the former scaling on the grain size and that of the latter being controlled by the water depth we revisit here this problem in a theoretical framework that allows to give a clear picture of the instability in terms of dynamical mechanisms a multi scale description of the problem is proposed in which the details of the different mechanisms controlling sediment transport are encoded into three quantities the saturated flux the saturation length and the threshold shear stress hydrodynamics is linearized with respect to the bedform aspect ratio we show that the phase shift of the basal shear stress with respect to the topography responsible for the formation of bedforms appears in an inner boundary layer where shear stress and pressure gradients balance this phase shift is sensitive to the presence of the free surface and the related effects can be interpreted in terms of standing gravity waves excited by topography the basal shear stress is dominated by this finite depth effect in two ranges of wavelength when the wavelength is large compared to the flow depth so that the inner layer extends throughout the flow and in the resonant conditions when the downstream material velocity balances the upstream wave propagation performing the linear stability analysis of a flat sand bed the relation between the wavelength at which ripples form and the flux saturation length is quantitatively derived it explains the discrepancy between measured initial wavelengths and predictions that do not take this lag between flow velocity and sediment transport into account experimental data are used to determine the saturation length as a function of grain size and shear velocity taking the free surface into account we show that the excitation of standing waves has a stabilizing effect independent of the details of the flow and sediment transport models consequently the shape of the dispersion relation obtained from the linear stability analysis of a flat sand bed is such that dunes cannot result from a primary linear instability we present the results of field experiments performed in the natural sandy leyre river which show the formation of ripples by a linear instability and the formation of dunes by a nonlinear pattern coarsening limited by the free surface finally we show that mega dunes form when the sand bed presents heterogeneities such as a wide distribution of grain sizes

finite amplitude river dunes the linear and weakly nonlinear stability of a uniform flow in an infinitely wide open channel with erodible bottom is studied under suitable conditions the flow is found to be unstable leading to the formation of dunes and antidunes at a linear level the corresponding regions of existence are presented and compared with experimental data a weakly nonlinear analysis is then performed in a neighbourhood of the critical conditions for dune and antidune formation the analysis shows that for values of the ratio of the shear velocity to the depth averaged velocity of practical interest dune bifurcation is supercritical whereas antidune bifurcation is subcritical the latter result suggests a possible interpretation of the plane antidune transition where plane bed and antidune configurations are observed to coexist for the same values of the flow and the sediment parameters the supercritical behaviour of the dune bifurcation allows for the prediction of an equilibrium amplitude that successfully compares with the amplitudes measured in laboratory experiments

thermal and tectonic evolution of the southern alps northern italy rifting coupled organic matter maturity analysis and thermokinematic modeling the southern alps were characterized by strong variations both in space and time of heat flow during mesozoic rifting the regional thermal history was reconstructed using organic matter om maturity data from outcropping sediments one dimensional 1 d thermal modeling performed on selected successions suggests that om maturity was mainly controlled by high geothermal gradients heat flow peaks of 85 to 105 mw m2 in the middle jurassic and differential burial during norian early jurassic extensional phases the results of 1 d modeling show an eastward increase of heat flow peak values these results were compared with those obtained with two dimensional 2 d thermokinematic models the models show a time shift ca 10 ma in the heat flow peak aalenian bajocian for 2 d and bajocian for 1 d modeling however the bajocian age was a priori imposed on 1 d models available geochemical data could be fitted assuming aalenian bajocian peak ages consequently this misfit is not alarming the eastward increase in heat flow peak values is tentatively explained with an eastward increase of radiogenic heat production in the crust instead of with differential stretching the comparison of paleothermal data and numerical modeling was done to gain knowledge on the potentials and limitations of numerical modeling in frontier areas although some differences do exist in the results of geochemical and thermokinematic models we can conclude that if a reasonable knowledge of the thermal parameters of both covers and basement is available thermokinematic modeling can provide useful first order estimates in frontier areas of heat flow and temperature evolution through time

lower limit of hydrocarbon generation in source rocks a case study from the dongpu depression bohai bay basin east china abstract with the increasing demand for hydrocarbons exploration tends to be deeper and unconventional resources however whether there are the lower limits for exploration depth or thermal maturity ro appears to be particularly essential it is of considerable significance to determine the lower limit of hydrocarbon generation llhg since this limit can provide guidelines for hydrocarbon potential estimation according to the mechanisms of hydrocarbon generation and expulsion five methods are combined to determine and verify the llhg whose values can be expressed by llhg ro and llhg h source rock samples from the paleogene shahejie formation es in the dongpu depression were taken as an example to determine the llhg and then controlling factors of the llhg were discussed llhg ro values for es range from 3 23 to 3 97 average 3 71 and llhg h values range from 5244 m to 5525 m average 5433 m regionally llhg values display obvious differences between the northern and southern of depression llhg values in the north are roughly larger than those in the south in the northern depression the llhg ro values are ranging from 3 61 to 3 97 average 3 81 and llhg h values are ranging from 5415 m to 5545 m average 5488 m however in the southern part the llhg ro values range from 3 20 to 3 74 average 3 48 and the llhg h values range from 5265 m to 5375 m average 5278 m the main controlling factors for llhg diversity between the north and the south of depression are organic matter om type and abundance formation temperature and pressure

ripple and dune formation in rivers a linear stability analysis for dune and ripple formation is presented that implements a rotational two dimensional flow model valid in the smooth as well as in the transitional and rough flow regimes sediment is assumed to be transported as bedload disregarding the role of suspension therefore the main mechanism driving instability for both ripples and dunes is the phase lag between bed shear stress and bed elevation ripples are shown to be confined to relatively low values of the shields parameter and of the particle reynolds number for higher values of the shields parameter and of the particle reynolds number and thus of the froude number and of the roughness reynolds number ripples are replaced by dunes the present analysis ultimately allows for a successful unification of the theories of dune and ripple formation and for a clarification of the debated role of ripples on the formation of dunes a good agreement between predicted and observed wavelengths for both ripples and dunes is found

post variscan cooling history of the central western sudetes ne bohemian massif poland constrained by apatite fission track and zircon u th he thermochronology abstract apatite fission track aft and zircon u th he zhe dating techniques were combined to reveal post orogenic history of the rudawy janowickie mts in the west sudetes bohemian massif permian to jurassic zhe ages of 271 2 24 8 171 3 11 5 ma obtained for crystalline basement rocks indicate post orogenic cooling and progressive unroofing of the ne bohemian massif on the other hand cretaceous zhe ages of 130 5 8 8 99 7 6 7 ma prove that the rudawy janowickie mts region remained under 190 c during the mid cretaceous suggesting a deep burial zhe ages from the cretaceous sediments located to the east of the rudawy janowickie mts range between 298 8 16 8 and 181 8 11 9 ma documenting that the burial did not exceed 6 km in the axial part of the intra sudetic through aft ages range from 105 9 6 1 to 51 1 4 3 ma the eocene aft ages revealed by the granite basement and the cretaceous aft age revealed by the metamorphic cover suggest the existence of at least two different thermo tectonic blocks experiencing different post variscan cooling and exhumation aft results strongly support 3 3 3 5 km exhumation for the rudawy janowickie mts since the cenomanian which in combination with zhe results clearly contradicts some of the previously proposed evolutionary scenarios for the sudetes

transition from ripples to dunes the bed forms generated by the flow of water over alluvial beds are predominantly treated in terms of stability concepts these generally postulate a constant wavelength and describe the variation of amplitude yet the wavelength is one of the most variable parameters of these features the features are also described as ripples dunes and antidunes but there is no explanation on how ripples transform into dunes on the basis of available data this paper offers a description of the generation of ripples and their transformation into dunes

palaeogeothermal response and record of late mesozoic lithospheric thinning in the eastern north china craton the palaeotemperature recorded by vitrinite reflectance ro in the pre cenozoic uplifted stratigraphic strata and in palaeozoic mesozoic remnant basins outside the cenozoic depocentres has not been overprinted by later thermal events in the eastern north china craton ncc based on downhole ro data from the palaeozoic and the mesozoic subsections we reconstruct the temperature gradients when the subsections reached their maximum palaeotem peratures in the middle triassic and the cretaceous and calculate the corresponding heat flow his tories since the early mesozoic the temperature gradient and heat flow were much higher in the cretaceous 35 43 8 ck m 21 and 73 83 mw m 22 respectively than in the middle triassic and at the present the high palaeo heatflow during the late mesozoicimplies that the thickness of the thermal lithosphere at that time was c 65 km about half the thickness of c 135 km estimated for the early mesozoic the change from a stable thermal regime to an active thermal regime took place during the late jurassic early cretaceous c 110 ma this tectonothermal event was accompanied by extensive surface erosion and is also evidenced in the areas adjacent to the ncc such as the south yellow sea and east china sea basins our study provides not only geothermal evidence for the late mesozoic lithospheric thinning but also additional constraints on the thinning mechanism which is currently being debated

present temperature field and cenozoic thermal history in the dongpu depression bohai bay basin north china abstract the dongpu depression is located in the southern bohai bay basin north china and it has abundant oil and gas reserves there has been no systematic documentation of this depression s temperature field and thermal history in this article the present geothermal gradient and heat flow were calculated for 68 wells on the basis of 892 formation testing data from 523 wells moreover the cenozoic thermal history was reconstructed using 466 vitrinite reflectance data from 105 wells the results show that the dongpu depression is characterized by a medium temperature field between stable and active tectonic areas with an average geothermal gradient of 34 8 c km and an average heat flow of 66 8 mw m2 the temperature field in the dongpu depression is significantly controlled by the changyuan huanghe and lanliao basement faults and thin lithosphere thickness the geothermal gradient twice experienced high peaks one peak was during the shahejie 3 formation depositional period ranging from 45 c km to 48 c km and the second peak was in the middle and late of the dongying formation depositional period ranging from 39 c km to 40 c km revealing that the dongpu depression experienced two strong tectonic rifts during the geothermal gradient high peak periods the geothermal gradient began to decrease from the neogene and the geothermal gradient is 31 34 c km at the present day in addition these results reveal that source rock thermal evolution is controlled by the paleo temperature field of the dongying formation depositional period in the dongpu depression this study may provide a geothermal basis for deep oil and gas resource evaluation in the dongpu depression

thermal history and tectonic subsidence of the bohai basin northern china a cenozoic rifted and local pull apart basin the bohai basin is a part of the larger bohai bay basin a cenozoic rifted intraplate basin heat flow measurements show that the bohai basin is characterized by present day heat flow varying between 53 and 74 mw m 2 with a mean of 63 mw m 2 however thermal history analyses derived from vitrinite reflectance vr and apatite fission track aft data indicate that tertiary cooling took place following a period of much higher paleo heat flow 70 90 mw m 2 prior to 25 million years to the present furthermore tectonic subsidence analysis reveals that the bohai basin experienced episodic sub rifting processes from the eocene to the end of the oligocene the post rift thermal subsidence was superimposed by intensified subsidence from the late miocene 12 million years in the bozhong depression and from the early quaternary 2 4 million years in the east liao bay indicating a rejuvenation of sedimentation related likely to transpressional structures developed locally on strike slip faults the present results indicate that there is good agreement between the reconstructed thermal history and the timing of the tectonic subsidence stages within the bohai basin the bohai basin is an early cenozoic rifted and local pull apart sub basin of the larger bohai bay basin 2001 elsevier science b v all rights reserved

geothermal regime and source rock thermal evolution in the chagan sag inner mongolia northern china abstract the chagan sag has the greatest oil and gas exploration potential among other sags in the yingen ejinaqi basin inner mongolia the average geothermal gradient in the chagan sag is 33 6 c km whereas the heat flow ranges from 65 9 mw m 2 to approximately 85 5 mw m 2 with an average value of 74 5 mw m 2 thermal history reveals that the chagan sag experienced the following 4 stages of thermal evolutions 1 a rapidly increasing geothermal gradient stage from the early cretaceous bayingebi formation depositional period to the early cretaceous suhongtu formation depositional period 2 a geothermal gradient peak stage during the early cretaceous yingen formation depositional period 3 a high geothermal gradient continuation stage during the late cretaceous wulansuhai formation depositional period and 4 a thermal subsidence stage during the cenozoic tectonic subsidence analysis reveals that the area experienced an initial synrift subsidence during the early cretaceous followed by a subsequent long term thermal subsidence since late cretaceous 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 source rock maturation the maturation histories of the 3 sets of source rocks in the sag were modeled on the basis of the present geothermal field thermal history and tectonic subsidence history the results reveal that the hydrocarbon generation of the chagan sag was controlled by the early cretaceous geothermal fields and the source rock maturity reached the maximum at the end of the yingen formation depositional period moreover the maturation evolution degree shows a difference for the 3 sets of source rocks the source rocks of the bayingebi 1 and 2 formations reached the middle mature and dry gas stage in contrast the source rocks of the suhongtu 1 formation only reached the early mature and middle mature stage this work may provide new insights for the understanding of the oil and gas exploration potential of the chagan sag

new evidence on the neogene uplift of south tianshan constraints from the u th he and aft ages of borehole samples of the tarim basin and implications for hydrocarbon generation we identified a neogene rapid uplift denudation event of the south tianshan based on apatite u th he and apatite fission track aft ages in tertiary rocks of the tarim basin using borehole samples the u th he thermochronology can be used to reveal the tectono thermal events with lower temperature than that of aft thermochronology and has not been used previously to study the uplift of the tianshan mountain using these data we show the relationship between the uplift of the south tianshan and the subsidence deposition of the northern tarim basin during the neogene the apatite helium ages reveal the migration of uplift erosion and deposition in the northern tarim basin a rapid uplift of the south tianshan during the miocene and a corresponding rapid subsidence in the northern tarim basin occurred however in the pliocene the kuqa depression and south tianshan uplifted and eroded at the same time and in turn provided the detrital source rocks for the northern uplift of the tarim basin in contrast to earlier studies we arrive at the conclusion that the south tianshan experienced rapid uplift in the miocene based on u th he data of apatite obtained from borehole samples collected in the tarim basin itself and not from the bordering mountain chain combined apatite u th he and fission track thermochronometry enables reconstruction of thermal histories of sedimentary rocks between 40 and 120 c and this has implications for the generation of liquid hydrocarbon in the 65 120 c range in the basin thermal and burial histories of typical samples were also modelled to show the rapid uplift in our study our works not only provide a new evidence for the south tianshan uplift but also indicate that there is a coupling between uplift and subsidence in the south tianshan and adjacent northern part of the tarim basin which controlled hydrocarbon accumulation in the kuqa depression and northern uplift of the tarim basin

cyclic steps review and aggradation based classification abstract cyclic steps are a type of upper flow regime bedform consisting of trains of upstream and upslope migrating bed undulations the overriding flow is characterised by a series of hydraulic jumps occurring in the troughs of the undulations cyclic steps form in open channel flows such as rivers and comprise a common bedform in subaqueous density flows in oceans lakes and reservoirs cyclic steps are associated with alternating froude subcritical and froude supercritical flow on respectively the stoss side and lee side of individual bedforms the transition between these flow states is embodied by the hydraulic jump in the trough of the bedform leading to the permanent or quasi permanent morphology of cyclic steps over the past decade numerous studies affirmed the dominant role of cyclic steps in generating bed undulations in modern and ancient glacial outwash fluvial delta and turbidite environments as reviewed here cyclic steps were previously discriminated as net depositional climbing transportational and net erosional falling in different parts of sedimentary systems the following cyclic step descriptors with distinct depositional signatures are proposed fully depositional partially depositional transportational partially erosional and fully erosional partially depositional cyclic steps are most common they are associated with backset bedded sets high aggradation rate and nested scours filled with massive to backset bedded deposits low aggradation rate the new classification can be used as a predictive tool in the reconstruction of modern and ancient sedimentary successions using repeat bathymetry seismic reflection or outcrop data it is applied in three turbidite case studies classical deep sea system small scale delta slope and line sourced carbonate slope

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

thermal evolution and maturation of lower paleozoic source rocks in the tarim basin northwest china the tarim basin is one of the richest basins in oil and gas resources in china the cambrian and middle upper ordovician strata are the most important source rocks previous early paleozoic thermal histories have led to varied hypotheses on the evolution of the lower paleozoic source rocks causing a significant impact on petroleum exploration in the basin a new paleozoic thermal history of the tarim basin was reconstructed in this article using the integrated thermal indicators of apatite and zircon uranium thorium helium ages apatite fission tracks and equivalent vitrinite reflectance data the modeled results indicate that different parts of the basin experienced widely differing early paleozoic thermal gradient evolution the eastern and central regions of the basin experienced a decreasing thermal gradient evolution from 37 to 39c km during the cambrian and ordovician to 35 to 36c km in the silurian whereas the northwestern region of the basin had an increasing early paleozoic thermal gradient evolution from 28 to 32c km in the cambrian to 30 to 34c km in the ordovician and silurian the lower cambrian thermal gradient resulted from the higher thermal conductivity of the 800 to 1000 m 2625 to 3280 ft thickness of gypsum and salt in the cambrian strata the basin experienced an intracratonic phase during the late paleozoic and a foreland basin phase during the mesozoic and cenozoic with the thermal gradient decreasing to the present day value of 20 to 25c km the sensitivity of thermal modeling by the best fit method is less than 5 in our study and the differences of the early paleozoic thermal gradient evolution in different regions of the basin may result in differential maturation of lower paleozoic source rocks the maturity histories of the source rocks modeled based on the new thermal histories indicate that the lower paleozoic source rocks in most areas of the basin matured rapidly and reached the late mature to dry gas stage during the paleozoic but experienced slower maturation during the mesozoic and cenozoic these new data on the paleozoic thermal history and lower paleozoic source rock maturity histories of the tarim basin provide new insights to guide oil and gas exploration of the basin

geothermal evidence of meso cenozoic lithosphere thinning in the jiyang sub basin bohai bay basin eastern north china craton abstract the bohai bay basin is at the center of lithosphere destruction and thinning in the eastern north china craton ncc in this paper the thermal lithospheric thicknesses of the meso cenozoic jiyang sub basin in the bohai bay basin were calculated by reconstructing the thermal history of the sedimentary basin using apatite fission track and vitrinite reflectance data the results show that the jiyang sub basin experienced two heat flow peaks in the late early cretaceous and in the middle to late paleogene with heat flow values of 84 88 mw m 2 and 85 88 mw m 2 respectively the thermal lithosphere thicknesses of the jiyang sub basin calculated from the modeled thermal histories experienced two thinning stages in the cretaceous and in the paleogene the lithosphere began with an initial thickness of 150 km in the early mesozoic and reached a thinning peak of 51 km in the late early cretaceous the thickness then increased to approximately 80 km at the end of the cretaceous a second thinning peak occurred in the middle and late paleogene with a thickness of only 48 km which corresponds to a rift phase in the bohai bay basin the lithosphere thickened thereafter and is 78 km at present the north china craton now has a thin lithosphere our research provides new geothermal evidence for the lithospheric thinning of the ncc