elastic wave velocity structure of the crust and upper mantle beneath the north china basin travel time residuals from locally and teleseismically recorded earthquakes are used to determine the three dimensional elastic wave velocity structure beneath the central north china basin and surrounding mountains we calculated p wave and s wave travel time residuals for 200 aftershocks of the 1976 tangshan earthquake and p wave travel time residuals for 194 teleseisms recorded by the beijing network between 1976 and 1983 we performed iterative one and three dimensional block inversions for crust and uppermost mantle structure based solely on the aftershock travel time residuals we also performed iterative three dimensional block inversions for crust and upper mantle structure based solely on the teleseismic travel time residuals and based on the combined aftershock and teleseismic travel time residuals we determined that the average thickness of the crust beneath the north china basin and surrounding mountains is about 35 km beneath the onshore portion of the north china basin however the crust is closer to 32 or 33 km thick the velocity structure of the upper 20 km or so of the crust is well correlated with the surface geology and parallels the short wavelength a few tens of kilometers features of the surface topography rocks with low seismic velocities lie in or beneath the basin rocks with high seismic velocities lie in or beneath the mountains the uppermost mantle and possibly even the lower crust appears to be a zone of transition in velocity structure between that of the upper crust and the mantle the trends of relative highs and lows in the velocity structure of the mantle are nearly opposite that of the crust the mantle material underlying most of the north china basin has higher than average seismic velocities while the material beneath the western mountains has lower than average velocities the velocity structure of the mantle parallels the long wavelength tens to hundreds of kilometers features evident in the gravity and topography of north china the high velocity mantle material presently beneath the basin probably represents mantle processes not directly related to the formation of the north china basin we infer that the transition zone between the short wavelength and long wavelength velocity features represents a zone of decoupling between the lithosphere and asthenosphere specifically the lithosphere beneath the north china block is moving eastward with respect to the asthenosphere

a high resolution paleointensity stack of the past 14 to 68 ka from black sea sediments abstract detailed paleo and mineral magnetic analyses of a sediment composite record from the southeastern black sea yielded a high resolution well dated paleointensity record though hampered by some larger hiatuses in some cores and contaminated by diagenetically formed greigite the paleomagnetic composite record obtained from the preserved primary detrital magnetite phase reflects a highly dynamic geomagnetic field during the last glacial period relative variations of paleointensity inferred from the sediments magnetisations were converted into a record of the virtual axial dipole moment vadm lowest vadm values are linked with the laschamp 0 50 10 22 a m 2 at 41 0 ka the norwegian greenland sea 1 5 10 22 a m 2 at 64 5 ka and the mono lake 3 0 10 22 a m 2 at 34 5 ka geomagnetic excursions the fully reversed field during the laschamp excursion exhibits a vadm of 2 0 10 22 a m 2 which is more than 25 of the present day axial dipole moment 7 628 10 22 a m 2 rates of change calculated from the black sea vadm record also give some information on how to assess the global decay of the present day geomagnetic field which is significantly enhanced in the area of the south atlantic anomaly comparison with provided c 14 and 10 be records confirm partly in the very detail the non linear anti correlation of geomagnetic field intensity and the production of cosmogenic radionuclides in the earth s upper atmosphere however discrepancies in the timing of lows and highs in the compiled records points out that the combination of different data sets from different archives remains a challenge

the thermal history of the bowen basin queensland australia vitrinite reflectance and clay mineralogy of late permian coal measures abstract the thermal history of the bowen basin queensland australia has been investigated using vitrinite reflectance data and clay mineralogy vitrinite reflectance data combined with a study of clay mineral reactions indicates that the maximum temperatures which induced organic maturation of the bowen basin coals and extensive clay mineralisation are not related to deep burial metamorphism during the latest middle triassic earliest late triassic as previously believed the results of the present study indicate that the development of a zone of high heat flow in the latest late triassic had a major control on the thermal history of the bowen basin high palaeogeothermal gradients estimated in the northern bowen basin are interpreted to result from convective heat transfer during a hydrothermal event variable heat distributions due to localised fracture enhanced permeable zones acting as hot reservoirs in the deeper part of the basin may have been responsible for some significant local thermal anomalies in the lower coal measures the estimated palaeogeothermal gradients in the southern bowen basin also indicate high heat flow in the lower sections of the stratigraphy sections in the southern bowen basin however are believed to reflect a rock dominated semi closed system with low water rock ratio where rocks are impervious to circulating fluids and thus heat transfer may have occurred by conduction the correlation between vitrinite reflectance and clay mineralogy shows a delay in illitisation reaction relative to organic maturity for many illite smectite i s mixed layer clays in the northern bowen basin this phenomenon can be explained as a result of insufficient time for the completion of mineral reactions and a variable potassium supply in relatively impermeable rocks the relationship between i s expandability and vitrinite reflectance for the bowen basin data compared to basins with known tectonic regimes suggests a thermal history in a rift setting for the bowen basin the effect of thin igneous intrusions on clay mineral reactions is very limited intensive illitisation due to heating of intrusions can only be observed in narrow zones immediately adjacent to intrusive bodies this further demonstrates that mineral reactions are too slow to record the effect of extremely short heating duration in contrast to organic maturity indicators these differences between mineral and organic parameters aid in the identification of local contact metamorphic effects

thermal and tectonic history of the ordos basin china evidence from apatite fission track analysis vitrinite reflectance and k ar dating apatite fission track analysis vitrinite reflectance data and k ar dating of permian carboniferous and mesozoic core samples have been successfully integrated to reconstruct the thermal and tectonic history of the ordos basin china apatite fission track ages of carboniferous jurassic sedimentary rocks range between 3 and 137 ma and are significantly younger than the stratigraphic ages confined fission track lengths demonstrate exclusively mixed length distribution indicating complex thermal history the data suggest that the samples must have all experienced higher paleotemperatures in the past mean vitrinite reflectance values r0 of the triassic rocks range from 0 61 to 1 06 giving a high coalification gradient of 0 36 km and suggesting a high paleothermal gradient of 57 c km permian carboniferous rocks have ro values on the order of 1 0 3 0 and locally up to 4 0 6 0 some high r0 values coincide with positive gravity and magnetic anomalies k ar dating on permian triassi samples reveals distinct illitization at 170 160 ma during which a thermal event occurred due to subsurface magmatic intrusion related to the early yanshanian movement the petroleum source rocks of the upper triassic experienced peak temperatures ranging from 90 to 160 c corresponding to the oil window and permian carboniferous source rocks were heated to more than 150 c passing through and out of the gas window due to rapid uplift and erosion in response to the rise of the qinghai tibet plateau associated with the asia india collision and the himalayan orogeny cooling has taken place at least since approximately 23 ma the difference in the rate and amount of uplift between the eastern and western parts of the basin resulted in differential uplift and the present day s ructural pattern of the basin

exploration of soils developing on volcanic materials on the island of milos greece abstract the island of milos greece part of the south aegean volcanic arc with a typical mediterranean climate is covered with volcanic deposits of different ages the objective of this study was to investigate the physicochemical and mineralogical properties of the soils developing on these volcanic deposits and their classification samples were taken from seven locations of soil on different parent material and of different ages there were substantial differences in their particle size distribution with sand ranging from 19 to 92 silt from 3 5 to 50 and clay from 5 to 46 organic matter content was low 3 equivalents of 1 4 to 24 6 were found and a calcic horizon identified the cation exchange capacity cec and specific surface area ssa varied between profiles ranging from 3 cmol kg 1 to 47 cmol kg 1 and 30 m 2 g 1 to 380 m 2 g 1 respectively the soils exhibited high base saturation the amounts of al fe and si extracted with ammonium oxalate l o fe o and si o were particularly low d was greater than fe o sharing the dominance of crystalline fe oxides al and si extracted with hot 0 5 m naoh al 2 3naoh and si 2naoh and with iron c 6 h 4 na 2 o 8 s 2 al 2 3 and si 2 si 2naoh and si 2 were particularly high mean values 3 4 and 4 5 respectively showing that amorphous silica was present the clay fraction of the soil was dominated by the presence of 2 1 vermiculite and smectite and 1 1 kaolinite clay silicates al o 1 2fe o was low

absence of a regional surface thermal high in the baikal rift new insights from detailed contouring of heat flow anomalies heat flow in active tectonic zones as the baikal rift is a crucial parameter for evaluating deep anomalous structures and lithosphere evolution based on the interpretation of the existing datasets the baikal rift has been characterized in the past by either high heat flow or moderately elevated heat flow or even lacking a surface heat flow anomaly we made an attempt to better constrain the geothermal picture by a detailed offshore contouring survey of known anomalies and to estimate the importance of observed heat flow anomalies within the regional surface heat output a total of about 200 new and close spaced heat flow measurements were obtained in several selected study areas in the north baikal basin with an outrigged and a violin bow designed thermoprobe of 2 3 m length both the sediment temperature and thermal conductivity were measured the new data show at all investigated sites that the large heat flow highs are limited to local heat flow anomalies the maximum measured heat flow reaches values of 300 35000 mw m2 but the extent of the anomalies is not larger than 2 to 4 km in diameter aside of these local anomalies heat flow variations are restricted to near background values of 50 70 mw m2 except in the uplifted academician zone the extent of the local anomalies excludes a conductive source and therefore heat transport by fluids must be considered in a conceptual model where all bottom floor heat flow anomalies are the result of upflowing fluids along a conduit an extra heat output of 20 mw including advection is estimated for all known anomalies in the north baikal basin relative to a basal heat flow of 55 65 mw m2 these estimations suggest an extra heat output in the northern lake baikal of only 5 corresponding to a regional heat flow increase of 3 mw m2 the source of this heat can be fully attributed to a regional heat redistribution by topographically driven ground water flow thus the surface heat flow is not expected to bear a signal of deeper lithospheric thermal anomalies that can be separated from heat flow typical for orogenically altered crust 40 70 mw m2 the new insights on the geothermal signature in the baikal rift once more show that continental rifting is not by default characterized by high heat flow

thermal effects of zechstein salt and the early to middle jurassic hydrothermal event in the central polish basin deep gas potential in the polish basin may factor significantly in european geopolitics and thermal effects can influence that outcome there and elsewhere deep 3 km 9843 ft well data from the kujawy area of the central polish basin reveal average geothermal gradient 36c km thermal conductivity of mesozoic strata k 2 29 w m k and present day heat flow q 82 4 mw m2 that is 3 less than that obtained using the entire borehole the extrapolated surface temperature 6 2c is in good agreement with temperatures during the weichselian glaciation the thermal conductivity of the upper permian zechstein 4 89 w m k is in good agreement with values from the north sea and northern germany steady state heat flow theory one dimensional 1 d predicts present day temperature 199c at the base of zechstein cap rock at 6 km 19 685 ft depth in kujawy this is reduced just more than 10c by low zechstein thermal gradients 16 8c km because of thermal refraction two dimensional and three dimensional models of zechstein salt pillows can significantly negate this cooling effect however such effects appear absent in the kujawy wells studied a widespread early to middle jurassic 195 175 ma hydrothermal event appears to have reached maximum in the kujawy area a 455c paleotemperature at 7 km 22 966 ft depth carboniferous is predicted by 1 d conductive heat transfer however geologic evidence does not support this result the discrepancy is reconciled by convective heat transfer with upward fluid flow 3 3 10 10 m s 10 8 10 10 ft s resulting in a maximum paleotemperature of 273c at 7 km 22 966 ft depth despite a paleoheat flow of 142 mw m2 the trend of intensity of the hydrothermal event correlates with the present day heat flow trend hydrothermal event sites are subparallel to the major northwest southeast structural and regional heat flow trend whereas other sites as close as 14 km 45 932 ft and without hydrothermal event are not the decay of the hydrothermal event is consistent with localized cylindrical plumes 10 km 32 808 ft radius that cool by conduction results suggest a long term 185 m y structural control on heat flow linear regression to vitrinite paleotemperatures yields a 185 ma jurassic surface temperature of approximately 21 3c that is approximately 13c higher than the present day temperature for warsaw poland the duration of maximum reservoir and source rock paleotemperature 50 m y is contrary to the kinetics of nitrogen and co2 producing wells equilibrium thermodynamics predicts approximately 60 methane for present day kujawy reservoirs with considerable uncertainty that should be removed by anticipated new deep drilling

lithospheric thinning uplift and heat flow preceding rifting abstract conversion of lithosphere into asthenosphere provides an active mechanism of lithospheric thinning and formation of intracontinental rifts the movement of the lithosphere asthenosphere boundary lab considered as a phase change is determined by the solution of a stefan like problem the ascent of the lab and the surface heat flow perturbation are calculated for different boundary conditions at the base of the lithosphere the calculations show that the rate of lithospheric thinning is independent of heat conduction across the lithosphere when the temperature increases at the lab the amplitude of thinning is also independent of the thickness of the lithosphere lithospheric thinning to the base of the crust could thus take place rapidly if a temperature perturbation on the order of 250 k is maintained at the lab the characteristic time depends strongly on the latent heat and on the difference between the geothermal and phase transition temperature gradients it is estimated to range between 1 and 30 m y this mechanism of lithospheric thinning appears to be compatible with petrological and geochronometric data on temporal changes in the depth of origin of magmas from the east african rift

determination of elastic wave velocity and relative hypocenter locations using refracted waves i methodology abstract an arrival time difference method utilizing refracted arrivals from earthquakes in a homogeneous layered earth model has been developed for the simultaneous determination of near source in situ velocity and relative locations of earthquakes the method is particularly applicable when analyzing data from arrays in which most of the recording stations are far i e several focal depths from a group of events this iterative scheme locates earthquakes relative to a master event and performs an inversion for in situ velocity using a generalized inverseleast squares estimation procedure direct arrivals when available may be included to stabilize the inversion and increase the accuracy of the event locations we tested this scheme on artificial data contaminated by random and systematic arrival time errors gaps in azimuthal coverage and inaccuracies in the assumed velocity model as usual depth is the least well resolved hypocenter coordinate but this scheme yielded accurate locations of most events while converging to the correct velocity model

soils and their relationship to aspect and vegetation history in the eastern southern alps canterbury high country south island new zealand abstract this study focuses on soils in a mountainous catchment area located in the eastern part of the southern alps south island new zealand the objective was to check the soils for non or poorly crystalline constituents metal organic complexes short range order minerals and if there is a relationship between pedogenesis and aspect and more recent landscape history the morphology of the soils indicates brown soils dystric cambisols dystrudepts with only few signs of podsolisation in contrast selected chemical properties of the soils reveal very strong weathering and leaching feo fed ratios are high and exceeding 0 6 in almost every soil horizon oxalate extractable aluminium and silicon show prominent peaks in the lower subsoil horizons with 1 76 2 52 alo and up to 0 68 for sio on southern aspects this is considerably higher than the values measured for soils on northern aspects 0 59 to 1 07 alo max 0 26 sio this aspect relationship is also applying to phosphate retention reaching values of more than 90 on southern aspects and not more than 70 for northern aspects additionally significant movement of organic matter in soils on southern aspects is evident by measurements of organic carbon and pyrophosphate extractable al and fe thus soil formation can be regarded as more advanced on southern aspects allophane in association with organic matter can be considered as an important constituent in southern aspect subsoils being responsible for the typical andic properties metal humus complexes and ferrihydrite are of subordinate significance considering the actual soil forming conditions under scrub grassland esp soil acidity it is unlikely that weathering and leaching is still strong enough today to allow significant podsolisation and the formation of short range order minerals under consideration of existing soil data from other studies it is proposed that these components and the podsolisation features are relicts caused by more acidic conditions under former forest cover which supported a stronger weathering and leaching

some comments on two layer extensional models for the evolution of sedimentary basins simple extensional models that involve listric faulting in the brittle upper crust and plastic flow in the lower lithosphere have been shown to account for the subsidence history of various continental sedimentary basins and continental shelves in this paper we present structural evidence that extension in the continental lithosphere during rifting is not uniform we review evidence that the rifting process in major intracratonic rift basins is spasmodic rather than continuous that extension and subsidence within the rift during a tectonic phase is generally accompanied by uplift and erosion of the rift flanks that subcrustal heat input during rifting occurs over an area much broader than the rift proper and that there may be broad regional uplift before and or during rifting to explain the uplift of the flanks during rifting and their postrift subsidence we invoke two mechanisms subcrustal thinning by extension below the flanks and tilted major normal faults in the crust between graben and flanks the uplift and erosion of the flanks due to tilted faults probably do not significantly affect estimates of extension from subsidence analysis but uplift due to both sources can in certain cases be incorrectly attributed to regional uplift or doming we present a simplified analysis of the two layer extensional model for the elementary case in which extension is instantaneous and the crust is thinned by a different amount from the subcrustal lithosphere we provide a simple graphical method of data analysis to obtain the parameters that describe thinning of the crust and lithosphere during extension from the subsidence history application of this method to the central part of the pattani trough in the intracratonic gulf of thailand shows that extension and thinning of the lithosphere of a factor of 2 since late eocene can account for much of the subsidence history and the present day heat flow our analysis suggests that thinning of the crust in this area is 20 greater than thinning of the whole lithosphere assuming that none of the lithosphere is removed from the region of extension during rifting we show by simple geometric examples that a process of nonuniform extension implies that much greater thicknesses of sediment can be deposited in the center of a young basin than in the case of uniform extension of both crust and subcrustal lithosphere such an extensional process produces significant uplift of the flanks of the rift and as a result of erosion of the uplifted areas the effective cross sectional area of the basin can be increased by as much as 10 20 depending on the rate of erosion compared to the area that would have been created by a process of uniform extension finally we show that it may ultimately be possible to compute erosion rates from seismic cross sections of basins

adakitic rocks derived from the partial melting of subducted continental crust evidence from the eocene volcanic rocks in the northern qiangtang block abstract eocene is a critical time for the elevation of tibetan plateau and global climate change and previous studies suggested that the eocene elevation was caused by intra continental subduction of the songpan garze block beneath the qiangtang block this paper reports zircon u pb age and geochemistry of the eocene volcanic rocks from the zuerkenwula mountain area in the northern part of qiangtang block and proposes that both slab break off of the neo tethys oceanic slab along the bangong nujiang suture and intra continental subduction of the songpan garze block beneath the qiangtang block caused the extensive partial melting of lithospheric mantle and subducted songpan garze continental crust which resulted in the significant elevation of the tibetan plateau the volcanic rocks have la icp ms u pb zircon age of 40 25 0 15 ma mswd 2 1 2 which is contemporaneous with the eocene eclogites in the great himalayan and k rich lavas in the southeastern tibet they display some adakitic characteristics with sio 2 57 44 to 68 72 tio 2 0 38 to 0 81 na 2 o 2 89 to 4 35 k 2 o 2 77 to 4 48 al 2 o 3 13 92 to 18 22 a cnk 0 69 to 1 03 mgo 0 27 to 5 86 with mg ranging from 13 2 to 72 0 strongly depleted in heavy rare earth elements hrees yb 0 92 to 1 51 ppm and y 10 1 to 24 1 ppm in combination with their positive sr anomalies high sr y ratios and no significant eu anomalies which suggest a garnet in and plagioclase free source residue these volcanic rocks can be divided into high mg 45 and low mg 87 sr 86 sr 0 707412 0 708284 e nd t 4 0 to 5 7 206 pb 204 pb 18 7499 18 8189 207 pb 204 pb 15 7189 15 7384 208 pb 204 pb 39 166 39 262 the geophysical data and regional geological setting suggest that the low mg adakitic rocks were derived from the decompression melting of a subducted lower continental crust when low mg adakitic melts in the overlying peridotite mantle wedge captured some olivine crystals resulting in their elevated mg and mgo values

hydrothermal petroleum genesis migration and deposition in guaymas basin gulf of california hydrothermal activity and seabed mounds have been explored in guaymas basin by the deep sea drilling project dsdp piston coring dredging and diving with the deep submersible research vessel dsrv alvin sedimentary organic matter derived primarily from immature degraded microbial detritus is easily converted to petroleum under the hydrothermal regime these petroleums are mature and migrate in the fluids and by diffusion to the seabed the fluid migration is aided by near critical aqueous solution and supercritical carbon dioxide and hydrocarbons petroleum compositions vary from condensates to naphthenic to waxy all with significant amounts of asphaltenes and hydrothermal products such as olefins and toxic polynuclear aromatic hydrocarbons pah the heavy ends condense at the seabed depositing mainly as a cement with the sulfides and other minerals and to a lesser extent as entrapped oil and crystalline wax in vugs and conduits of the mounds the pah are high temperature resynthesis aromatiza

analysis of factors affecting heat flow density determination in the liaohe basin north china abstract structural relief of the pre cenozoic basement and groundwater flow have been found to be the two most important factors affecting the heat flow density determinations in the liaohe basin the reason for the significant effect of basement relief upon subsurface temperature and heat flow density patterns is the strong contrast of thermal conductivity between basement rock and the sedimentary cover simplified model computations indicate that the heat flow density in the region of basement uplift is 1 35 times greater than that in the region of depressions field observations indicate that the temperatures at shallow depths less than 1200 m are strongly perturbed by groundwater flow leading to reduced temperatures and geothermal gradients in the neogene formation comparison of observed and calculated gradients reveals that reduced gradients and heat flow density occur in the groundwater recharge area whereas these parameters are enhanced in the discharge area after taking the perturbing factors into account a regional heat flow value of 65 9 mw m 2 is obtained

geochemical behaviour of ni cr cu zn and pb in an andosol cambisol climosequence on basaltic rocks in the french massif central abstract the objective of this study is to identify parameters influencing trace elements te vertical distributions in an andosol andic cambisol climosequence in order to understand processes involved in the current distribution of trace elements from basaltic rocks to associated soils six pedons developed on tertiary massive basaltic formations located at similar position in the hill slopes submitted to the same wet mountainous climate but under various microclimatic conditions altitude and annual rainfall were considered the six studied soils are andic and rich in organo metallic complexes two different and quantitative methods were used to compare the geochemical distributions of major and trace elements both being calculated with ti as invariant element isovolumetric mass balance and enrichment factors anthropogenic pedogenetic microclimatic inherited factors were discriminated anthropogenic influences are pointed out for k in two pedons and for pb in all studied sites distributions of other te are affected by discontinuities between underlying rocks and soil horizons zinc and cu distributions are controlled by organic matter whereas cr and ni distributions are influenced by pedogenetic processes results emphasize the relative trace element immobilization in andic soils under temperate climate

magnetostratigraphy of tertiary sediments from the hoh xil basin implications for the cenozoic tectonic history of the tibetan plateau summary we conducted an integrated palaeomagnetic and stratigraphic study on a 5452 8 m thick sedimentary sequence of the hoh xil basin in northern qinghai tibet plateau to obtain a chronostratigraphic framework for these sediments a total of 966 individual oriented palaeomagnetic samples spaced at stratigraphic intervals were collected from six measured sections in the hoh xil basin magnetic directions in these samples were obtained by progressive thermal mainly and alternating field demagnetization experiments most samples exhibit two components of magnetization the lower unblocking temperature component is an overprint resembling the present day geocentric axial dipole field direction at the sampling locality the most stable characteristic remanence chrm appears to be an early chemical remanent magnetization residing mainly in haematite the positive results of fold and reversal tests indicate that the chrm is a record of the palaeomagnetic field close to the time of formation of these sediments further evidence for the magnetization of these sediments acquired close to their time of deposition is the fact that patterns of magnetic reversals can be matched with the established polarity timescale on the basis of the distinct interval of magnetic reversal zones and biostratigraphic datums 13 magnetozones can be recognized at the hoh xil basin that range from chrons c11 to c23 30 1 51 0 ma the age of the fenghuoshan group is palaeomagnetically dated as 51 31 ma early eocene middle early oligocene and the age of the yaxicuo group is between 31 and 30 ma middle early oligocene late early oligocene the new palaeomagnetic data from the fenghuoshan group suggest that it has undergone no significant rotation since the oligocene in contrast declination data from the yaxicuo group in wudaoliang area imply a vertical axis clockwise rotation 29 1 8 5 since the late oligocene the tertiary palaeomagnetic pole position of the hoh xil basin implies a significant northward convergence of the hoh xil basin 1600 km with respect to eurasia siberia since early eocene late oligocene time our results are consistent with the pattern of disturbingly low palaeolatitudes derived from a large number of high quality palaeomagnetic studies of tertiary rocks from sites that reach all the way from eastern china to kyrgyzstan future work is needed to separate the influences of sedimentary inclination shallowing and tectonic shortening

determination of elastic wave velocity and relative hypocenter locations using refracted waves ii application to the haicheng china aftershock sequence we located the aftershocks of the 4 february 1975 haicheng china aftershock sequence using an arrival time difference atd simultaneous inversion method for determining the near source in situ velocity and the location of the aftershocks with respect to a master event the aftershocks define a diffuse zone 70 km 25 km trending west northwest perpendicular to the major structural trend of the region the main shock and most of the large aftershocks have strike slip fault plane solutions the preferred fault plane strikes west northwest and the inferred sense of motion is left lateral the entire haicheng earthquake sequence appears to have been the response of an intensely faulted range boundary to a primarily east west crustal compression and or north south extension the calculated upper mantle p wave velocity is 7 6 0 09 km sec and the inferred crustal thickness is between 31 and 32 5 km the low upper mantle velocity and thin crust may be indicative of local lithospheric extension

early cenozoic two phase extension and late cenozoic thermal subsidence and inversion of the bohai basin northern china abstract the bohai basin is one of a family of early cenozoic extensional basins that lie along the eastern margin of asia from russia to vietnam initial extension was probably triggered by subduction roll back of the oceanic pacific plate from the asian continent there were two phases in the bohai basin s rift history the earlier paleocene early eocene phase resulted in the deposition of the kongdian formation and the fourth lowest member of the shahejie formation in a series of elongate half grabens these half grabens have master faults with a nne ssw orientation secondary normal faults are typically clockwise oblique to the master faults indicating a component of dextral transtension deposition was focused in the west and south of the present basin these rocks are mainly alluvial fan and fluvial red beds the architecture of the basin underwent an important change at ca 43 45 ma middle eocene beginning with the deposition of the third member of the shahejie formation in part these sediments were deposited in the same half grabens as the kongdian formation but the bozhong depression in the central part of the basin originated at this time and became the major depocentre the bozhong depression superficially resembles a pull apart basin it formed when continued transtension of the earlier tertiary fault systems to the east and west created an extensional overlap between them during this phase the basin as a whole had a geometry with elements typical of both pull apart and transtensional basins regional extension in many east asian basins ended at the end of the oligocene probably because of the onset of transpression within eastern asia caused by the collision of australia with the philippine sea plate dextral transpression caused minor inversion of some of the earlier normal faults in bohai but as a whole the basin began to subside in a post rift phase of thermal subsidence that has lasted until the present day

tertiary crustal shortening and peneplanation in the hoh xil region implications for the tectonic history of the northern tibetan plateau abstract the hoh xil basin is the largest cenozoic sedimentary basin in the hinterland of the tibetan plateau tertiary sedimentary strata 5 8 km thick comprising the fenghuoshan yaxicuo and wudaoliang groups provide compelling evidence concerning the crustal shortening erosion and peneplanation of the northern tibetan plateau the basal fenghuoshan and overlying yaxicuo groups span the eocene early oligocene stratigraphically and have been dated by magnetostratigraphy as 56 30 ma old both groups are composed of terrigenous rocks provenance analysis of sandstones and conglomerates demonstrates that permian and triassic strata in the tanggula orogenic zone in the south were the source for the fenghuoshan group in contrast the carboniferous triassic strata in the tanggula bairizhajia and heishishan gaoshan orogenic zones in the north were the source for the yaxicuo group during the late oligocene northern tibet underwent strong north south crustal shortening 43 and thickening extensive erosion which occurred over the entire plateau surface near the end of the oligocene resulted in development of a peneplain surface the latter is overlain by the early miocene wudaoliang group composed of fresh water limestones these are exposed both on summit surfaces as well as on the valley floors showing that a phase of differential uplift occurred after the deposition of the wudaoliang group this post miocene differential uplift was due to regional extension in a region of overall shortening even though we have not succeeded in obtaining conclusive data about the exact timing of phases of rapid uplift of the tibetan plateau it is most likely that the major phase of uplift occurred during the late oligocene

thermal maturation and hydrocarbon migration within la popa basin northeastern mexico with implications for other salt structures some outcrops adjacent to the 25 km 15 mi long salt weld in the la popa basin northeastern mexico are visibly stained and contain enrichment of organic carbon their presence which is known only along the northwestern part of the weld and along the southwestern side of the weld provides evidence for hydrocarbon migration along the weld this distribution is presumed to be partially controlled by the restricted distribution of the source rock that generated the hydrocarbons within the salt withdrawal basin southwest of the weld but may have been in part controlled by a previously existing salt wall or the weld that formed as a result of salt evacuation acting as a barrier to lateral migration and serving as a vertical conduit for fluid flow upturned halokinetic strata adjacent to the weld provided a conduit for migration along bedding planes although no flowing seeps were seen during this study we documented discoloration and remineralization as well as the presence of waxy appearing soil that smelled like crude oil at some sites near the weld organic geochemical analyses confirm the presence of nonbiodegraded hydrocarbons along the salt sediment interface and within adjacent upturned lithologies up to 5 m 16 ft southwest of the weld the results document for the first time the definitive presence of actively migrating hydrocarbons associated with a subaerial salt weld an oil source rock correlation is inferred with the upper mudstone member of the potrerillos formation based on biomarker data thermal and subsidence modeling of the basin indicate that all of the strata in the basin are mature enough to have generated hydrocarbons the lower part of the stratigraphic section entered the gas generation window and much of the cretaceous section and all of the tertiary entered the oil window prior to uplift of the basin significant unroofing as much as 7 km 4 3 mi of sediment may have been removed occurred sometime after the eocene as suggested by previous studies

from andic non allophanic to non andic allophanic inceptisols on alkaline basalt in mediterranean climate a toposequence study in the marghine district sardinia italy abstract the properties of a non andic allophanic inceptisol pom1 and two andic non allophanic inceptisols flm5 and spm8 representative of a toposequence on basanite rocks of mt st antonio central western sardinia marghine sub region were analyzed to better elucidate factors and processes that lead to a different expression of andic properties and allophane formation in xeric mediterranean environment a series of laboratory techniques including physical chemical micromorphological x ray diffraction xrd scanning electron microscopy sem analyses were used all soils are usually rich in organic carbon dystric at the great group level with saturation base from 72 to 10 and with ph from subalcaline to acidic allophanic inceptisol appears more intensely weathered than non allophanic inceptisols volcanic glass content is in any case negligible pom1 formed on the plateau shows a shallow solum 45 cm with a 2 horizon that meets all the criteria for andic soil properties the amounts acid oxalate extractable al o and si o together with pyrophosphate extractable al p typifies such a pedon as allophanic inceptisol 0 19 p al o 2 the allophanic inceptisol pom1 is located at the plateau of the toposequence where lower surface runoff greater water infiltration rate the absence of significant erosion and colluvial movement may have increased the degree of weathering processes in these conditions the prolonged soil moistness prevents the transformation of short order components on the whole the results emphasize the role of topography and the importance of al fe amorphous compounds in expressing soil andic properties and allophane content versus the volcanic origin of parent material and the insufficiency of volcanic glass the results also suggest that the occurrence of soil with andic properties and significant allophane content in hot and dry environments like the mediterranean climate in sardinia may be more widespread than expected

magnetic and chemical parameters of andic soils and their relation to selected pedogenesis factors in the case of andic soils developed on volcanic rocks permanently humid conditions are essential for andosolisation processes although volcanic rocks are usually rich in highly magnetic iron oxides knowledge about these minerals in andic soils with respect to the soil development is missing the aim of this contribution is to investigate the relationship between magnetic and basic chemical properties of soils developed on volcanic basement and parameters related to the pedogenesis factors the studied sites are located on basaltic lava flows in the eastern part of the french massif central investigated pedons with alu andic sil andic and vitric properties were pedologically described and analysed by a set of magnetic and soil chemical methods magnetic parameters include low field volume specific and mass specific magnetic susceptibility frequency dependent magnetic susceptibility remanent properties including s ratio and coercivities chemical parameters included the phh2o soil organic matter total cation exchange capacity base saturation and content of fe and al extracted in dithionite citrate acid ammonium oxalate and pyrophosphate solutions micro morphology of andosols and parent material was observed by scanning electron microscopy completed with energy dispersive spectrometry the pedogenesis factors are represented by parent rock age annual precipitation and soil thickness our findings suggest that 1 precipitation is the most important pedogenesis factor with a strong relationship to the relative magnetic grain size concentration of ferrimagnetic minerals aluminium dissolved in pyrophosphate and acid ammonium oxalate and content of organic matter 2 parent material age shows a well pronounced relationship with magnetic grain size parameters represented by the frequency dependent susceptibility and ratio of saturation remanent to saturation induced magnetisation mrs ms selective dissolution parameters and phh2o 3 thickness of soil profile shows a link to mrs ms phh2o and content of organic matter

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

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

meso cenozoic lithosphere thinning in the eastern north china craton evidence from thermal history of the bohai bay basin north china abstractthe formation and evolution of a rift basin is the shallow response of deep geodynamic processes the bohai bay basin is at the center of lithosphere destruction and thinning in the eastern north china craton ncc in this article the meso cenozoic thermal lithospheric thickness of the bohai bay basin was calculated by reconstructing the thermal history of the sedimentary basin using apatite fission track and vitrinite reflectance data the meso cenozoic thermal modeling results show that the basin experienced four evolutionary stages with two heat flow peaks in the late early cretaceous and in the middle to late paleogene which had heat flow values of 82 86 and 81 88 mw m2 respectively accordingly the thermal lithospheric thicknesses of the basin calculated from the thermal histories experienced two thinning stages in the cretaceous and the paleogene the lithosphere began with an initial thickness of 150 km in the early mesozoic and was thinned to approximately 51 61 km in the late early

cenozoic extensional tectonics in china abstract this paper gives a brief review of the cenozoic extensional structures of china during the cenozoic eastern china was in a rifted setting where divergent plate motion and extensional structures were dominant subsidence has occurred initially in response to attenuation of the crust and was enhanced later by subsidence due to thermal contraction in western china particularly in the qinghai tibetan plateau where rifting occurs in an orogenic setting in which convergent plate movements are dominant the rifting is associated with continental collision and lateral escape and large intra continental transform boundaries extensional structures in china may be grouped into eleven graben systems in eastern china and four in western china they occur in different styles linear rift valley basin and range structures and pull apart basins associated with strike slip faults the geometric characteristics kinematics of extension and the mechanism of continental extension in china are discussed the cenozoic extrusion structural model proposed by tapponnier et al 1982 elegantly accounts for the gross tectonics and the formation of the graben systems of western china however in considering the overall strain pattern during the extension of the early tertiary basin and range region in eastern china a large scale simple shear kinematic model may be preferable to the pure shear rift model

the north china basin an example of a cenozoic rifted intraplate basin the north china basin was a stable continental region that has undergone several distinct phases of rifting and subsidence during the mesozoic and cenozoic eras the last major phase featuring block faulting rapid subsidence and widespread calc alkaline basaltic volcanism began during early tertiary time this intraplate rifting appears to be the result of an approximately 30 extension and thinning of the lithosphere beneath the northeastern china by the late tertiary period active rifting had slowed and postrift thermal subsidence had begun this regional extension and subsidence resulted in the present day north china basin a large saucer shaped oil producing basin with thinner crust and lower upper mantle p and s wave velocities than the surrounding regions during the quaternary period however the subsidence rate increased in the north china basin the frequent occurrence of destructive earthquakes and observations of relatively high heat flow suggest that the quaternary tectonic activity differs from the late tertiary simple thermal subsidence pattern and may indicate a new phase of rifting

eastern asia and the western pacific timing and spatial distribution of rifting in china abstract a compilation of recognized rifts in china indicates that five distinct episodes of rifting have occurred these episodes occurred at approximately 2 3 ga 1 85 1 7 ga 1 0 0 7 ga 550 190 ma and 175 ma to present the timing and location of rifting has largely been a function of tectonic activity along the margins of the various chinese paleocontinents some of the oldest rocks in china are found in the sino korean and tarim cratons and most of the identified precambrian rifts are found within or on the margins of these cratons these cratons are viewed as the continental nucleus of china and fold belts and microcontinents have been accreted to this nucleus through time much of the locus of rifting has migrated away from this nucleus as has the location of the continental margin especially in the paleozoic beginning in the middle mesozoic rifting commenced along the entire eastern margin of china extension occurred concomitantly with subduction in a backarc setting this is the dominant cenozoic extensional regime in china and is still active today to date few cenozoic rifts have been found in western china where most tectonism is probably a consequence of the collision between india and china but it seems likely that more rifts will be discovered in this area as it becomes better studied

evolution of the pannonian basin system 1 tectonics the carpathian arc formed during cretaceous to miocene time by continental collision between europe and smaller continental fragments following southward and westward subduction of ocean floor during the last stages of thrusting in the outer carpathians a set of discrete basins formed behind the carpathian loop these basins are regions of middle to late miocene extension and are connected to each other and to areas of coeval shortening in the outer carpathian thrust belt by a system of strike slip faults sinistral northeast trending and dextral northwest trending sets of conjugate shears reflect overall east west extension of the intra carpathian region during middle to late miocene time palinspastic reconstruction of the basins indicates about 100 50 km of east west extension across the intra carpathian region during this time we interpret the vienna basin which is superimposed partly on the flysch nappes of the outer west carpathians as the result of thin skinned extensional tectonics above a shallow detachment surface within the crust extension of upper crustal rocks above this detachment was probably accomodated by thrusting of the outermost nappes of the west carpathians over the european platform extension of basins farther inside the carpathian loop probably involved rocks at deeper crustal levels and within the upper mantle the most internally situated basins formed by extensional processes that involved the entire lithosphere thus the depth to which extension occurred seems to be closely related to the proximity of each basin to the active thrust front in the carpathians this can be related to the geometry of the subduction zone extension within the intra carpathian basins began first in the northernmost basins and migrated southward and eastward over a ten million year period palinspastic reconstruction of the basins at three different times during the miocene 17 5 16 5 and 13 0 ma predicts eastward migration of the zone of thrusting and shortening within the carpathian mountains to accomodate the synchronous eastward and southward migration of areas of extension from these reconstructions about 120 60 km of east west shortening is predicted across the outer east carpathians from about 17 5 ma until present both predictions are in good agreement with the timing and magnitude of shortening in the carpathian thrust belt as determined directly from rocks within the belt from this we infer a close relationship for middle to late miocene extension of the intra carpathian region and middle to late miocene crustal shortening within the outer carpathians during middle and late miocene time deformation of the pannonian fragment was dominated by extensional and wrench tectonics except along a narrow zone in the outer carpathian thrust belt middle and late miocene thrusting in the carpathians is interpreted as the result of simple shear caused by relative motion between europe and the overriding pannonian fragment at the subduction boundary rather than of regional compression of lithospheric rocks at depth the initiation of extensional tectonics within the intra carpathian region in middle miocene time can be related to reorganization of major fragment boundaries of the eastern european alpine system

geochemical and palynological investigation of the shengli river marine oil shale china implications for paleoenvironment and paleoclimate abstract the shengli river oil shale located in the north qiangtang depression northern tibet plateau represents a potential large marine oil shale resource in china a geochemical and palynological investigation of the oil shale was performed to reconstruct paleoenvironment and paleoclimate during deposition the total organic carbon toc contents 15 05 20 34 and s 2 values 103 27 129 12 mg hc mg rock of oil shale samples are high and the organic matter consists mainly of type ii kerogen the thermal maturity assessed from pi 0 033 0 036 and t max 433 436 shows an immature to early mature stage of the organic matter analyzed oil shale samples from the shengli river area are characterized by a dominance of low carbon number molecular compositions with high c 21 c 21 2 10 2 83 low pr ph 0 63 0 75 and high concentrations of c 27 sterane and homohopanes c 31 c 35 indicating reducing environments highly saline conditions and a prevalent contribution of algae to organic matter accumulation the analyzed oil shale samples have an uncommonly heavy c isotopic composition ranging in 13 c values of bulk organic matter from 20 79 to 21 78 the enrichment in 13 c is mainly attributed to the high productivity of algae rather than solely the result of hypersalinity composition of palynofloras from oil shale samples suggests that the climate of the qiangtang basin region during the deposition of oil shales was warm and humid or sub humid

implications for organic maturation studies of evidence for a geologically rapid increase and stabilization of vitrinite reflectance at peak temperature cerro prieto geothermal system mexico discussion a short term rapid heating and cooling of the rock in well m 94 below 1300 m was caused by a pulse of hot water passing through the edge of the cerro prieto mexico geothermal system below 1300 m the peak paleotemperatures were about 225 250 degrees c but equilibrium well log temperatures indicate a decrease to 150 210 degrees c at present this hot water pulse sharply increased vitrinite reflectance to levels comparable to those measured in the central part of the system even though studies of apatite fission track annealing indicate that the duration of heating was only 10 0 10 1 yr in m 94 in contrast to 10 3 10 4 yr in the central part of the system these data indicate that sedimentary organic matter chemically reacts quickly to temperature increases of about 125 degrees c above ambient even when the higher temperature existed for only 10 0 10 1 yr the quick change of the vitrinite reflectance geothermometer indicates that thermal maturation reactions can stabilize after a geologically short period of heating to a level consistent with peak temperature under moderate to high temperature diagenesis in open fluid rich geothermal systems cerro prieto is one of the most intensively studied and well known geothermal systems in the world thus data from cerro prieto are a benchmark to compare with the predictions of published thermal maturation models such as those formulated by j karweil n v lopatin and a k burnham and j j sweeney these thermal maturation models inaccurately predict duration of heating at cerro prieto the kinetic equations used in these models explicitly allow thermal maturation to continue indefinitely at peak temperature which does not seem to be the case at cerro prieto

reconstruction of the imf polarity using midlatitude geomagnetic observations in the nineteenth century the interplanetary magnetic field imf by component affects the configuration of field aligned currents fac whose geomagnetic response is observed from high to low latitudes the ground magnetic perturbations induced by facs are opposite on the dawn and dusk sides and depend upon the imf by polarity based on the multilinear regression analysis we show that this effect is presented at the mid latitude observatories niemegk and arti in the x and y components of the geomagnetic field this allows us to infer the imf sector structure from the old geomagnetic records made at ekaterinburg and potsdam since 1850 and 1890 respectively geomagnetic data from various stations provide proxies of the imf polarity which coincide for the most part of the 19th and 20th centuries this supports their reliabilities and makes them suitable for studying the large scale imf sector structure in the past

interplanetary magnetic field during the past 9300 years inferred from cosmogenic radionuclides 1 we have reconstructed the interplanetary magnetic field imf its radial component and the open solar magnetic flux using the solar modulation potential derived from cosmogenic 10be radionuclide data for a period covering the past 9300 years reconstructions using the assumption of both constant and variable solar wind speeds yielded closely similar results during the maunder minimum the strength of the imf was approximately 2 nt compared to a mean value of 6 6 nt for the past 40 years corresponding to an increase of the open solar magnetic flux of about 350 we examine four cycles of the hallstatt periodicity in the imf with a mean period of 2250 years and an amplitude of 0 75 nt grand solar minima have largely occurred in clusters during the hallstatt cycle minima around the years 5300 3400 1100 and 1500 a d the last cluster includes the dalton maunder and sporer minima we predict that the next such cluster will occur in about 1500 years the long term imf has varied between 2 nt and 8 nt and does not confirm a proposed floor lower limit there is a slowly changing long term trend of amplitude 1 5 nt with a minimum around the year 4600 and a maximum around 0 a d that may be of solar origin but which also may be due to unknown long term changes in the atmospheric effects or geomagnetic field intensity

the late triassic rift related volcanic rocks from eastern qiangtang northern tibet china age and tectonic implications abstract the late triassic nadi kangri volcanic rocks with nearly ew trending outcrops within the qiangtang basin northern xizang tibet china are composed mainly of acid tuff dacite rhyolite and minor basic volcanic rocks there exists a significant depositional hiatus between the nadi kangri volcanic rocks and underlying strata therefore the nadi kangri volcanic rocks represent a new evolution history of the mesozoic qiangtang basin the magma emplacement age of the nadi kangri volcanic rocks in the geladaindong area is 220 4 2 3 ma representing the onset of the mesozoic qiangtang basin the nadi kangri basalts have high nb zr 0 049 0 058 ta hf 0 12 0 15 and zr y 4 95 6 01 ratios in the tectonic discrimination diagrams such as zr vs zr y and th hf vs ta hf the nadi kangri basaltic rocks mostly plot in the within plate setting field the geological background and the geochemical characteristics suggest that the nadi kangri volcanic rocks were formed in a continental rift setting

the cenozoic tectonic evolution of the great north china two types of rifting and crustal necking in the great north china and their tectonic implications abstract the great north china underwent widespread continental rifting during cenozoic time that caused extension and necking of the crust in this area and formed four major rift systems in this paper we provide geological and geophysical evidence that rifting and extension in the western part of the great north china differs from that in its eastern part in age and nature the space time relationships show that the origins of the western rift group of the great north china are probably related to the tibet plateau tectonics whereas those of the eastern rift group are related to the subduction events in the western margin of the pacific plate furthermore the quaternary tectonic regime in the eastern part of the great north china differs from the neogene tectonic pattern and shows relations with western rifts we speculate that during the quaternary the processes that caused rifting in the west have spread further east and now affect the eastern part of the great north china

permafrost associated natural gas hydrate occurrences on the alaska north slope abstract in the 1960s russian scientists made what was then a bold assertion that gas hydrates should occur in abundance in nature since this early start the scientific foundation has been built for the realization that gas hydrates are a global phenomenon occurring in permafrost regions of the arctic and in deep water portions of most continental margins worldwide in 1995 the u s geological survey made the first systematic assessment of the in place natural gas hydrate resources of the united states that study suggested that the amount of gas in the gas hydrate accumulations of northern alaska probably exceeds the volume of known conventional gas resources on the north slope researchers have long speculated that gas hydrates could eventually become a producible energy resource yet technical and economic hurdles have historically made gas hydrate development a distant goal this view began to change in recent years with the realization that this unconventional resource could be developed with existing conventional oil and gas production technology one of the most significant developments was the completion of the bpxa doe usgs mount elbert gas hydrate stratigraphic test well on the alaska north slope which along with the mallik project in canada have for the first time allowed the rational assessment of gas hydrate production technology and concepts almost 40 years of gas hydrate research in northern alaska has confirmed the occurrence of at least two large gas hydrate accumulations on the north slope we have also seen in alaska the first ever assessment of how much gas could be technically recovered from gas hydrates however significant technical concerns need to be further resolved in order to assess the ultimate impact of gas hydrate energy resource development in northern alaska

heat flow variations in continental rifts abstract in the terrestrial thermal field continental rifts stand out as rather narrow regional thermal anomalies in which augmented heat flow is unevenly distributed heat flow variations are discussed on the example of the baikal east african cordilleran and rhine lybian rift systems rift related disturbance of the asthenosphere lithosphere system is accompanied by a general increase in the surficial heat flow regional thermal anomalies are mainly caused by conductive heat transfer from the asthenosphere local thermal anomalies are caused by magmatic mass transfer into the crust and by fluid convection along porous fracture systems

the erubaz volcanic soil of hungary mineralogy and classification abstract in this study the erubaz soil a shallow soil influenced by volcanic parent rocks is examined with special emphasis on its clay content and clay mineral composition fifteen profiles at seven study areas and with four different parent material types are analysed bulk soil mineralogical and clay mineralogical properties are examined by x ray diffractometry xrd according to the mineralogical analysis the presence of the unstable mafic silicates indicates that the composition of the parent rock is still well reflected in the examined soil profiles illite is the most common clay mineral followed by kaolinite and smectite kaolinite and illite contain ca 15 20 and 10 interlayered of smectite respectively poor crystallisation and composition of secondary minerals suggest that these soils are in an early stage of their pedogenic evolution but are more developed than the typical andosols presence of opal c and cristobalite in the andesitic samples is characteristic our study revealed that the erubaz soil type is not as homogeneous as it was suggested before according to our analysis mainly on the basis of their mineralogy these soils can be divided into two well defined groups these two groups erubaz soils formed on intermediate acidic and on basic lithology can be regarded as subtypes of the erubaz soil type moreover two varieties black and brown mostly based on colour and som content are distinguished in these varieties the conditions of the decomposition of organic material are very different due to the moisture content temperature and ph conditions of the soil the studied soil profiles were included into the wrb system on the basis of threshold values of their diagnostic horizons the studied profiles did not fulfil the criteria of the andosol group and were inserted into the assemblage of phaeozems

solar activity during the last 1000 yr inferred from radionuclide records identification of the causes of past climate change requires detailed knowledge of one of the most important natural factors solar forcing prior to the period of direct solar observations radionuclide abundances in natural archives provide the best known proxies for changes in solar activity here we present two independent reconstructions of changes in solar activity during the last 1000 yr which are inferred from be 10 and c 14 records we analyse the tree ring c 14 data shcal intca104 from 1000 to 1510 ad and annual data from 1511 to 1950 ad and four be 10 records from greenland ice cores camp century grip milcent and dye3 together with two be 10 records from antarctic ice cores dome concordia and south pole in general the be 10 and c 14 records exhibit good agreement that allows us to obtain reliable estimates of past solar magnetic modulation of the radionuclide production rates differences between be 10 records from antarctica and greenland indicate that climatic changes have influenced the deposition of be 10 during some periods of the last 1000 yr the radionuclide based reconstructions of past changes in solar activity do not always agree with the sunspot record which indicates that the coupling between those proxies is not as close as has been sometimes assumed the tree ring c 14 record and be 10 from antarctica indicate that recent solar activity is high but not exceptional with respect to the last 1000 yr c 2006 elsevier ltd all rights reserved less

7000 years of vegetation history and land use changes in the morvan mountains france a regional synthesis this paper aims to reconstruct the vegetation history of a middle mountain the morvan burgundy france since the neolithic i e 7000 years the results of palynological and non pollen palynomorphs npps analysis performed on 10 peat cores document the main phases of human agro pastoral practices and natural resources management which drove the formation of the cultural landscape of the morvan massif over time to document the history of human activities at a regional scale particular attention was given to the determination the characterization and the graphical depiction of phrases of human impact both the quantification of the impact of human pressure and the chronological uncertainty of the different phases identified by pollen and npp analysis were taken into account this study reveals a clear human presence during periods that were formerly poorly documented such as the onset of the neolithic period the bronze age the early iron age and the early middle ages it also sheds new light over periods for which there is better archaeological and historical knowledge such as the widespread occupation of the massif in the late iron age the cultivation of chestnut from the 11th to the 16th century and the impact of modern firewood exploitation on the forest

evolution of the xialiao basin the xialiao depression is one of several small depressions that comprise the north china basin formed during the cenozoic era the xialiao depression is a wedge shaped rift basin with a central horst situated between two grabens the basin is approximately 65 km wide and the grabens reach maximum depths of 6 7 km we present a quantitative analysis of the evolution of the xialiao depression hereafter the xialiao basin within the framework of simple models of crustal extension we find that both uniform and modified two layer extension modelling techniques provide reasonable regional estimates of the rate of extension and subsidence of the basin however estimations of heat flow and subsidence based on the parameters calculated using either modelling technique are not consistent with either the present basin configuration of a central horst flanked by two grabens or the high heat flow in the xialiao basin combining the results of our attempts to model the extension of the basin with results from both body and surface wave studies of the crust and upper mantle beneath northeast china we infer that the xialiao basin has been extended at least 30 of its initial width

tectonic features of oil and gas basins in eastern part of china during the mesozoic cenozoic eastern china underwent two stages of structural development sedimentary basins in eastern china have certain characteristics basement faults are well developed in these basins there was rapid sedimentation during the mesozoic cenozoic the basins are located on either side of the songliao depression the amount of subsidence in these basins is limited with a maximum depth of sedimentation of 4 000 to 6 000 m 13 000 to 20 000 ft during the mesozoic the most intense tectonic movements occurred in the songliao basin where there was much faulting accompanied by volcanic activity the bohai bay basin was the center of major tertiary tectonic activity there are more than 50 major basement faults in this basin basin formation was controlled primarily by movement of the pacific plate and related volcanic activity these basins are epicontinental basins along the margin of continental crust hydrocarbons were generated during the time of basin formation and much of the oil and gas discovered has been in rocks where it was generated or where migration was over short distances

mineralogical and magnetic characterisation of iron titanium oxides in soils developed on two various basaltic rocks under temperate climate abstract the objective of this study was to characterize alteration processes of iron titanium oxides in andic soils developed on basaltic rocks under temperate climate among the magnetic minerals titanomagnetites are the most abundant and represent the major spinel in basalts in order to understand processes involved in the alteration of iron titanium oxides from basaltic rocks associated to soils two pedons developed on tertiary massive basaltic formations submitted to temperate climate were considered the magnetic minerals have been characterized by studying rock and soil magnetic parameters i e magnetic susceptibility and curie temperature chemical composition was investigated by optical and electron microscopy empa sem eds and by micro proton induced x ray emission pixe because mineralogy of the parent rocks controls those of the soils we have first studied the rocks the thermomagnetic curves obtained on the two studied rocks show that initial titanomagnetite is preserved in one sample mc rock while the other pc rock contains near pure magnetite possibly issued from exsolution process microscopic observations confirm the exsolution lamellae on titanomagnetites and show a cr content gradient in chromian spinel partially enclosed in olivine these observations suggest a deuteric alteration the two profiles exhibit increasing curie temperature between the rocks and soil horizons indicating a transformation of magnetic minerals results emphasize the maghemitization of iron titanium oxides in andic soils in a temperate climate

burial metamorphism thermal maturation in cretaceous sediments of the southern benue trough and anambra basin nigeria organic matter reflectance illite crystallinity and fluid inclusion techniques have been used to evaluate burial metamorphic conditions for the lithostratigraphic successions that accumulated during the cretaceous in the southern benue trough and anambra basin of southern nigeria these successions were invaded by intrusives volcanic rocks and vein type lead zinc minerals especially in the albian cenomanian section of the abakaliki anticline the sequence includes lower maastrichtian subbituminous coals in the anambra basin in exposed cretaceous deposits on a northwest southeast section from enugu to abakaliki mean random vitrinite reflectance rom in oil ranges from 0 55 to 0 67 in the lower maastrichtian coals and shales approximately 0 91 in the coniacian shales 0 97 in the turonian shales and up to 4 31 in the albian shales a corresponding increase in the illite content of the illite smectite mixed layer clay fractions is reflected in the low values of illite crystallinity indices coupled with a decrease from 32 to 0 in the percentage of smectite from the northwest southeast maastrichtian albian section fluid inclusion pressure corrected temperatures from vein quartz in the albian shales range from 170 to 250 c the results of this work show that thermal maturation in the cretaceous successions increases from the post santonian campanian maastrichtian anambra basin into the older benue trough where strong diagenetic to anchimetamorphic i e very low grade metamorphism conditions were reached the data suggest that these sediments at the present outcrop levels originally were buried at higher maturity levels maximum erosion appears to have taken place on the axis of the abakaliki anticline the presence of bitumen in fractures and pores of the exposed maastrichtian units in the anambra basin suggests that the matured sediments generated some unknown quantity of petroleum this finding coupled with reported gas finds and some oil in previous exploration wells of the anambra basin enhances the possibilities of cretaceous targets in the downdip regions

on the correlation between heat flow and crustal thickness abstract in this study the results of a search for correlation between terrestrial heat flow and the thickness of the earth s crust are presented the correlation is sought for separately in different categories of the tectonic formations considered these categories are defined by the thickness of the consolidated crust and also the degree of correspondence between the variations of the positions of the upper and lower boundaries of the consolidated crust along particular tectonic units the calculations show a definite correlation to exist between heat flow and moho depths in every category considered this correlation is positive for tectonic formations with thick crust and negative for those with normal and thinned crust it is found that the thinning of the crust with increasing heat flow results in one and the same correlational relationship for three different particular categories of platform structures which however have quite different thermal regimes this particular correlation appears to be stronger than any of the other correlational relationships obtained in this work a physical interpretation of this close correlation will be given in a subsequent paper

the tangshan earthquake sequence and its implications for the evolution of the north china basin the 1976 tangshan earthquake sequence that occurred on the northern margin of the north china sedimentary basin is one of the strongest and most destructive intracontinental earthquake sequences ever recorded by worldwide long period seismograph networks we have studied the source process of the six largest events of this earthquake sequence by formally inverting long period p and sh wave seismograms from the world wide standardized seismographic network our analysis shows that the main shock was caused by motion on at least three fault segments each with a different orientation the initial and dominant faulting occurred on two segments of a north northeast trending right lateral strike slip fault system the last stage of faulting had a significant component of thrusting and occurred on an east northeast trending subsidiary fault at the southern end of the main fault the largest aftershock occurred at the northeastern end of the main fault and had a nearly pure normal faulting mechanism with east west striking nodal planes this event occurred in a pull apart region where the north northeast trending main strike slip fault system steps to the right this region subsided by more than 1 m during the earthquake sequence to the north of this step the main fault is delineated by numerous aftershocks whose mechanisms are by and large consistent with right lateral slip on this segment the large event in 1945 m 6 3 probably occurred on this part of the fault a region of substantial subsidence up to 1 5 m associated with the earthquake sequence was also observed in the south where the main fault system takes another step to the right two of the large aftershocks occurred nearby and had strike slip mechanisms the overall faulting process of the tangshan sequence is well characterized by right lateral slip on a set of right stepping faults the mechanisms and the points of nucleation of the strongest shocks and the extent of the ruptures appear to be closely tied to preexisting fault geometries a compilation of the mechanisms of large earthquake sequences in the north china basin strongly suggests that the present deformation of the entire basin is dominated by motions on right lateral strike slip systems trending north northeast the basin seems to have formed and evolved as a large transtensional structure at an en echelon step of a large scale strike slip system the deformation within the basin is both strike slip and extensional and appears to occur on smaller scales in an approximately selfsimilar fashion as evidenced by the deformation during the tangshan sequence this interpretation provides an explanation for the variable rate of subsidence in both space and time and the scatter in measured heat flow values as well as the overall shape of the north china basin it also provides an explanation for occasional thrust faulting earthquakes that occur apparently as a result of geometrical complexities of the strike slip faults transpression these observations are otherwise difficult to fit into a simple model of regional crustal extension and thermal subsidence

thermal maturity of a fold thrust belt based on vitrinite reflectance analysis in the western foothills complex western taiwan abstract burial depth cumulative displacement and peak temperature of frictional heat of a fault system are estimated by thermal analysis in the fold thrust belt of the western foothills complex western taiwan based on the vitrinite reflectance technique the regional thermal structure across the complex reveals that the rocks were exposed to maximum temperatures ranging from 100 c to 180 c which corresponds to a burial depth of 3 7 6 7 km a large thermal difference of 90 c were observed at the shuilikeng fault which make the eastern boundary of the fold thrust belt where it is in contact with metamorphic rock of hsuehshan range the large thermal difference corresponds to cumulative displacements on the shuilikeng fault estimated to be in the range of 5 2 6 9 km however thermal differences in across the shuangtung and chelungpu faults cannot be determined apparently due to small vertical offsets the large displacement observed across the shuilikeng fault is absent at the other faults which are interpreted to be younger faults within the piggyback thrust system localized high temperatures adjacent to fault zones were observed in core samples penetrating the chelungpu fault three major fracture zones were observed at core lengths of 225 m 330 m and 405 m and the two lower zones which comprise dark gray narrow shear zones a value of vitrinite reflectance of 1 8 higher than the background value of 0 8 is limited at a narrow shear zone of 1 cm thickness at the fracture zone at 330 m the estimated peak temperature in the range of 550 680 c in the shear zone is far higher than the background temperature of 130 c and it is interpreted as due to frictional heating during seismic faulting

a comparative study between present and palaeo heat flow in the qiangtang basin northern tibet china the qiangtang basin is a significant prospective area for hydrocarbon and gas hydrate resources in the tibetan plateau china however relatively little work has been performed to characterise heat flow in this basin which has restricted petroleum and gas hydrate exploration in this study we compare present and palaeo heat flow in the qiangtang basin to provide information on geothermal regime hydrocarbon generation and permafrost that is necessary for further petroleum and gas hydrate exploration we base our study on temperature data from a thermometer well thermal conductivity tests vitrinite reflectance data homogenisation temperature data from fluid inclusions stratigraphic information and a time independent modelling approach our results indicate that in the central qiangtang basin the present thermal gradient is approximately 15 5 c km and heat flow is approximately 46 69 mw m 2 heat flow in the qiangtang basin is not relatively stable since the early jurassic as previous research has suggested and it is generally decreasing with time additionally there is a clear difference between the hottest thermal regime of the southern and northern qiangtang depressions during cretaceous to pleistocene time in the southern qiangtang depression the palaeogeothermal gradient is approximately 32 0 c km and palaeo heat flow is approximately 70 mw m 2 however in

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

the field of crustal velocity in asia calculated from quaternary rates of slip on faults rates of quaternary faulting when treated as measures of strain rates within regions several times larger than the depths of brittle faulting yield a velocity field for asia that matches the average relative velocity between the indian and eurasian plates over the past 2 myr nuvel 1a and the velocity of shanghai with respect to eurasia measured with very long baseline interferometry vlbi by using rates of slip on discrete surfaces faults to define average strain rates we explicitly assume that the large scale deformation can be treated as that of a continuum depending on the jcales over which strain rates are averaged 87 to 93 per cent of the assumed strain ites are fit within assigned 1 sigma uncertainties and 97 to 99 per cent are fit within 2 sigma the internal consistency of these data and the agreement with independent rates nuvel 1a and vlbi test the validity of treating large scale deformation of continents as that of a continuum in the calculated velocity field a large fraction 85 per cent of india s convergence with eurasia is absorbed by crustal or lithospheric thickening among consistently misfit assumed strain rates are those dominated by high rates of strike slip faulting strain associated with 20 30 mm a 1 of slip on the altyn tagh karakax and karakorum faults is inconsistent with the distributions of strain in surrounding regions we conclude that these rates all of which are based on correlations of ages of offset landforms with changes in global climate and not on radiometric dating have been systematically overestimated lateral transport out of india s northward path is relatively minor south china is calculated to move east southeast at less than 10 mm a 1

volcanic soils of france abstract in france andic soils mainly occur in the massif central andic and other volcanic soils 5000 km 2 and on the vosges and the morvan hercynian massifs in the massif central silandosols on recent pyroclastics are distinguished from aluandosols on older mio pliocene lavas after a brief introduction to the parent materials soil characterisation survey genesis properties and land use are reviewed in two periods from 1960 to 1979 and from 1980 to 2000 soil distribution is related schematically to topo climatic sequences comparing recent pyroclastics to older volcanic lavas an udic or perudic soil moisture regime is the primary factor in andosol genesis in france silandosols occur only on recent pyroclastics and aluandosols on old lavas after reworking by glacial erosion from a mantle of loose and pre weathered materials the anthropic impacts include accelerated erosion and changes in carbon content

the weathering of basalt and relative mobilities of the major elements at belbex france abstract a basalt and its weathered profile have been analysed for major elements graphical examination shows al fe and ti to have been essentially immobile determining mobility sequences for this deposit is complicated by the long pedogenetic history of the area three different sequences are presented two for different stages of weathering integrated over time and one that reflects the weathering regime of the present day

transformations geochimiques au cours de l alteration meteorique d une basanite pliocene du massif central francais abstract the geochemical changes during surface weathering of a pliocene basanite have been studied in a flow near nebouzat puy de dome 25 km southwest of clermont ferrand a humid temperate area this flow has been exposed since its effusion its weathering results only from cumulated effects of different plio quaternary climatic phases excluding deuteric or pedogenetic evolution processes the mineralogical composition of the fresh rock is labradorite 38 4 titanaugite 21 6 olivine weathered 9 5 titanomagnetite 11 1 glass 12 1 apatite 1 8 and h2o h2o 5 9 weathering of the minerals leads to various products that are concentrated inside the original minerals in isolated concretions or as fillings in intra or extra mineral fissures the change observed for three minerals and for glass were as follows olivine transition smectites montmorillonitic minerals fe ca mg and mn carbonates augites transition smectites and beidellitic minerals labradorite slightly weathered original minerals only glass transition smectites iron oxides and hydroxides the concretions within the rock consist of smectites and carbonates whereas the fissures are filled with smectites that include nontronite and beidellite the variety of secondary minerals on a micrometric scale is an illustration of the fundamental importance of microsite in spite of the pliocene age of the basanite and of the duration of its superficial evolution no 1 1 minerals and no fersiallitization were observed the latter process which leads to development of red soils characterized by a high content of free iron and a large elimination of ca mg k and na has strongly marked the miocene basalts of the massif central thus plio quaternary weathering expresses paleo climatic conditions different from those of the upper miocene in the same area

thermal structure of the crust and upper mantle of the liaohe rift basin north china abstract on the basis of given crustal models and analysis of radiogenic heat mantle heat flow and crustal temperature were calculated for the liaohe rift basin in north china results indicate that the liaohe basin is characterized by a relatively high mantle heat flow 41 mw m 2 but low crustal heat flow 24 mw m 2 both caused by upwelling of the asthenosphere and crustal thinning during rift development in the early tertiary in the studied region this type of thermal structure of the crust and upper mantle seems to be inherent in the region between tectonically active and stable areas and has been considered to be the product of the history of geological evolution of the basin since the mesozoic era a conceptual model of the thermal structure of the crust and upper mantle of the liaohe rift basin has been suggested in this paper

shear wave splitting and mantle flow associated with the deflected pacific slab beneath northeast asia 1 a total of 361 sks and five local s wave splitting measurements obtained at global and regional seismic network stations in ne china and mongolia are used to infer the characteristics of mantle fabrics beneath northeast asia fast polarization directions at most of the stations in the western part of the study area are found to be consistent with the strike of local geological features the dominant fast directions at the eastern part beneath which seismic tomography and receiver function studies revealed a deflected slab in the mantle transition zone mtz are about 100 from north which are almost exactly the same as the motion direction of the eurasian plate relative to the pacific plate and are independent of the direction of local geological features the splitting times at those stations are about 1 s which correspond to a layer of about 150 km thickness with a 3 anisotropy the shear wave splitting observations complemented by the well established observation that most of the eastern part of the study area is underlain by a lithosphere thinned by delamination in the paleozoic era can be best explained by the preferred alignment of metastable olivine associated with the subduction of the deflected pacific slab in the mtz or by back arc asthenospheric flow in the mantle wedge above the slab

heliospheric magnetic field 1835 2009 1 we use recently acquired geomagnetic archival data to extend our long term reconstruction of the heliospheric magnetic field hmf strength the 1835 2009 hmf series is based on an updated and substantiated interdiurnal variability idv series from 1872 onwards and on bartels extension by proxy of his u series from 1835 to 1871 the new idv series termed idv09 has excellent agreement r2 0 98 rms 0 3 nt with the earlier idv05 series and also with the negative component of love s extended to 1905 dst series r2 0 91 of greatest importance to the community in an area of research that has been contentious comparison of the extended hmf series with other recent reconstructions of solar wind b for the last 100 years yields a strong consensus between series based on geomagnetic data differences exist from 1900 1910 but they are far smaller than the previous disagreement for this key interval of low solar wind b values which closely resembles current solar activity equally encouraging a discrepancy with an hmf reconstruction based on 10be data for the first half of the 20th century has largely been removed by a revised 10be based reconstruction published after we submitted this paper although a remaining discrepancy for the years 1885 1905 will need to be resolved

thermal modeling of continental subduction and exhumation constrained by heat flow and seismicity in taiwan abstract the thermal evolution of crustal exhumation subsequent to the subduction of the continental margin is modeled through numerical solutions to the two dimensional heat conduction equation the boundary conditions used in the modeling are basically constrained by available geophysical and geological observations in the taiwan area temperature distributions are calculated at one million year intervals over a 5 ma duration although this study presents a tentative estimation based on some reasonable assumptions the preliminary results not only explain the sharp change in seismicity within the crust but also agree with the general heat flow pattern on the surface of taiwan more specifically both the high heat flow and the aseismic belt beneath the eastern central range which are probably attributed to higher temperatures within the crust are modeled by crustal exhumation after the subduction of the continental margin however the occurrence of deeper earthquakes east of the central range is a result of the lower thermal gradient which is due to the subduction of the cold continental crust into the uppermost mantle in summary preliminary thermal modeling supports the possibility of a tectonic model of active continental subduction and crustal exhumation for the taiwan orogen

evolution of the pannonian basin system 2 subsidence and thermal history analysis of sedimentation and thermal data indicates that for most parts of the pannonian basin observed heat flow thermal gradients rates of thermal subsidence and vitrinite reflectance are about twice those predicted by assuming a uniform extension model for basin formation in late miocene time a modified extension model whereby large amounts of heat are added to the uppermost mantle during extension roughly equivalent to replacing the entire sub crustal lithosphere by asthenosphere produced results in good agreement with observation and could also account for periods of uplift observed during extension crustal extension beneath most parts of the basin is estimated to have been about 80 to 170 1 8 to 2 7 although in the deepest parts of the basin deeper than 4 km crustal extension could have been much greater analysis of extension within the danube and zala basins indicates that the late miocene extension in these basins involved the entire lithosphere but subsidence and heat flow data are not well enough constrained to determine if extra heating is required during extension on the basis of tectonic and structural data the vienna basin has been interpreted as the result of thin skinned extensional tectonics above a shallow detachment surface within the upper crust royden et al this issue analysis of thermal and subsidence data from the northern vienna basin suggests that little or no heating occurred during basin extension these data are consistent with a thin skinned extensional origin for the vienna basin and are in better agreement with this interpretation than with the assumption of a uniformly extended lithosphere beneath the basin this study emphasizes the need for good thermal subsidence and structural data in making reconstructions of extensional and thermal histories of sedimentary basins when such data are available it is found that a simple uniform extension model does not explain very well the evolution of some sedimentary basins such as the vienna and pannonian basins in the first instance the basin is thought to be the result of upper crustal extension only due to its special tectonic setting in the second instance the extra heating during extension is due to some unknown processes in the lower lithosphere that may be a general feature of lithospheric extension thus lithospheric extension and associated heating may be distributed in a variety of ways not all extensional sedimentary basins form in the same way application of a uniform subsidence model to basins for which good thermal subsidence and structural data are not available or not properly analysed can lead to reconstructions of thermal histories in error by a factor of 2 or more

numerical simulation of petroleum generation and migration in the qingshui sag western depression of the liaohe basin northeast china a two dimensional basin modeling study was employed to analyze the petroleum generation and migration history of the qingshui sag in the western depression of the liaohe basin northeast china the eocene oligocene es4 and es3 members of the shahejie formation es are the most important source rocks responsible for the major hydrocarbon accumulations two sandstone beds of fan delta origin the dujiatai djt and the xinglongtai xlt are the primary reservoir rocks in the study area the model indicates that two migration systems can be differentiated they are separated by the thick shale beds of the middle es3 and es1 which acted as important regional seals for the lower and the upper systems respectively the djt bed is the most important pathway for migrating hydrocarbons in the lower system whereas the xlt bed is a significant factor in the upper system calibration of the model with thermal maturity data indicates that the geological evolution is consistent with typical heat flow values for rift basins in the range between 85 and 48 mw m2 all source units reached maturity during the major burial phase which extended from the oligocene to the eocene simulation results further indicate that after a cooling period renewed heating occurred and additional hydrocarbons were generated during the last 5 m y particularly in the southern part of the basin sensitivity tests indicated that the faults particularly the two main faults served as important conduits for petroleum throughout most of the geological history the main phase of migration occurred between the eocene and oligocene and was responsible for major accumulations in the west slope the central anticline and the central rise additional migration between 5 ma and the present is significant in the southwestern area and may have brought about petroleum accumulation in the central depression and central rise

characterization of the sedimentary thermal regime along the corsair growth fault zone texas continental shelf using corrected bottomhole temperatures temperatures of deep 3 km 1 8 mi sediments along the corsair growth fault zone in the texas continental shelf are elevated relative to those off the fault zone this observation is based on a compilation of nearly 400 bottomhole temperatures bhts obtained from about 230 wells widely distributed across the continental shelf the bhts have been individually corrected for the thermal disturbance associated with drill fluid circulation the isotherm of 140 c 284 f derived from the corrected bhts shows more or less continuous peaks along the fault zone thermal gradients in the depth range of 3 to 5 km 1 8 to 3 1 mi shows higher values along the fault zone than off the fault zone these trends are similar to the previous observations made along the wilcox growth fault zone in the texas coastal plain previous studies suggest that the faults of the wilcox system serve as the conduits for hot fluids expelled from deep overpressured sediments a similar mechanism may explain the elevated temperatures along the corsair fault zone

nature of a regional dogleg pattern in maturity profiles from thrace basin northwestern turkey a newly discovered unconformity or a thermal anomaly vitrinite reflectance ro profiles of the thrace basin are characterized by a regional dogleg pattern corresponding to the depths of ceylan and hamitabat formations we investigated the nature of this dogleg pattern using a one dimensional thermal maturity model by simulating three possible geological scenarios 1 two possible newly discovered unconformities one between the hamitabat and soucak or hamitabat and ceylan formations and the other within the hamitabat formation 2 an abnormal paleoheat flow regime paleothermal kick that developed in the oligocene and extended until the end of the early miocene and 3 a sharp thermal conductivity contrast in the stratigraphic column caused by thermally low conductive deposits of the ceylan formation which act as a regional thermal blanket the sensitivity of each suggested scenario within the model and their effect on the observed dogleg pattern have been examined a comparison of the measured and calculated modeled ro profiles from the proposed scenarios shows that the dogleg pattern can be best explained by a combination of the second paleoheat flow and third scenarios thermal conductivity instead of the unconformity scenario however the discovery of these two newly defined discordance surfaces with the help of well and seismic data requires a significant modification to the chronostratigraphy of the thrace basin the hamitabat karaaa ftepe and gaziky formations and the lower sections of the kean formation are suggested to be time correlative counterparts in a newly constructed chronostratigraphy thus the hamitabat formation can be evaluated as a part of the early middle eocene sequence similar to the gaziky formation in this article we suggest that the hamitabat formation be classified as a group instead of a formation

the cenozoic evolution of the north china basin the cenozoic evolution of the north china basin consists of early tertiary rifting and differential subsidence late tertiary regional subsidence and quaternary rifting and differential subsidence present cenozoic sediment fill shows that tertiary subsidence was greatest where the present thickness of pre cenozoic crust is least in contrast quaternary subsidence has been greatest where the present thickness of pre cenozoic crust is greatest the present crustal structure geologic history and cenozoic sediment fill of the basin suggest a nearly constant crustal thickness of 40 km at the onset of rifting middle eocene if the present thickness of pre cenozoic crust is due solely to crustal thinning from early tertiary mechanical extension then the central north china basin has been extended at least 30 of its initial width this is greater than estimates of total mesozoic plus cenozoic extension derived from basement faulting 20 at the present time any possible discrepancies cannot be resolved due to uncertainties in the data tertiary subsidence of the basin derived from backs tripping the present sedimentary sequence is not satisfactorily explained by either a simple uniform or two layer extensional model no single extension parameter uniform or pair of extension parameters two layer can account for the variable sediment thicknesses or the alternating horst and graben configuration of the basin we can however use the parameters derived from simple one or two layer extensional modeling to infer lower bounds for both the average regional extension of the bohai and the local extension of the depressions within the basin for example we find that the neogene subsidence of a major part of the basin the central bozhong depression has been nearly as rapid as that of young oceanic crust furthermore the present heat flow in this area is consistent with that for oceanic crust of 16 24 million years of age post rift time this indicates that the subsidence may be due to decay of a lithospheric thermal anomaly that is nearly as large as that in young oceanic crust this is difficult to understand with a simple extensional framework because reported estimates of early tertiary extension from basement faulting are only 10 30 possible sources of this excess heat are mesozoic tectonics effects of plate subduction at the pacific margin or energy input from regional tectonics during the early tertiary our conclusions cast doubt upon the adequacy of simple extensional models to explain the cenozoic evolution of the north china basin however these conclusions can only be tentative due to inadequacies in the basic data set

magnetic and geochemical characterization of andosols developed on basalts in the massif central france identification of andosols is primarily based upon the content of their colloidal constituents clay and metal humus complexes and on the determining of andic properties this needs time and cost consuming geochemical analyses our primary aim of this study is to describe the magnetic and geochemical properties of soils rich in iron oxides derived from strongly magnetic volcanic basement in this case andosols secondary aim is to explore links between magnetic and chemical parameters of andic soils with respect to genesis factors parent material age precipitation and thickness of the soil profile six pedons of andic properties developed on basaltic lavas were analyzed down to parent rock by a set of magnetic and geochemical methods magnetic data of soil and rock samples reflect the type concentration and particle size distribution of ferrimagnetic minerals geochemical data include soil reaction ph in h2o cation exchange capacity organic carbon and different forms of extractable iron and aluminum content our results suggest the following 1 magnetic measurements of low field mass specific magnetic susceptibility can be a reliable indicator for estimating andic properties and in combination with thermomagnetic curves may be suitable for discriminating between alu andic and sil andic subtypes 2 in the studied andosols strong relationships were found between a magnetic grain size parameters precipitation and exchangeable bases b concentration of ferrimagnetic particles and degree of crystallization of free iron and c parameters reflecting changes in magneto mineralogy and soil genesis parent material age soil depth

mineral and geochemical characterization of a leptic aluandic soil and a thapto aluandic ferralsol developed on trachytes in mount bambouto cameroon volcanic line abstract mineral and geochemical investigations were carried out on soil samples and fresh rock trachytes from two selected soil profiles tm profile on leptic aluandic soils and tl profile on thapto aluandic ferralsols from mount bambouto to better understand geochemical processes and mineral paragenesis involved in the development of soils in this environment in tm profile the hydrated halloysites and goethite occur in the weathered saprolite boulders of bc horizon while dehydrated halloysite gibbsite and goethite dominate the soils matrices of bc and a horizons in tl profile the dehydrated halloysites and goethite are the most abundant secondary minerals in the weathered saprolites of c and bc horizons while gibbsite hematite and kaolinite occur in the soil matrices of bc b and a horizons the highest gibbsite content is in the platy nodules of b horizon in both soil profiles organo metal complexes most likely of al and fe are present in the surface a horizon geochemically between the fresh rock and the weathered saprolites in both soils sio2 k2o cao na2o and mgo contents decrease strongly while fe2o3 and al2o3 tend to accumulate the molar ratio of sio2 al2o3 ki and the sum of ca mg k and na ions trb also decreases abruptly between fresh rocks and the weathered saprolites but increases significantly at the soil surface the tm profile shows intense al enrichment whereas the tl profile highlights enrichment in both al and fe as the weathering progresses upwards both soil profiles are enriched in ni cu ba and co and depleted in u th ta hf y sr pb zr and zn relative to fresh rock they also show a relatively low fractionation of the rare earth elements ree la nd sm eu tb yb and lu except for ce which tends to be enriched in soils compared to ci chondrite all these results give evidence of intense hydrolysis at soil deep in mount bambouto resulting in the formation of halloysite which progressively transforms into gibbsite and or dehydrated halloysite at the soil surface the prominent pedogenetic process refers to andosolization with formation of organo metal complexes in tl profile the presence of kaolinite in soil matrices bc and b horizons is consistent with ferralitization at soil deep in conclusion soil forming processes in mount bambouto are strongly influenced by local climate i in the upper mountain 2000 m the fresh misty and humid climate favors andosolization whereas ii in the middle lands 1700 2000 m with a relatively dry climate both andosolization at the soil surface and ferralitization at soil deep act together