heat flow study of the emeishan large igneous province region implications for the geodynamics of the emeishan mantle plume abstract the emeishan large igneous province elip is widely considered to be a consequence of a mantle plume the supporting evidence includes rapid emplacement voluminous flood basalt eruptions and high mantle potential temperature estimates several studies have suggested that there was surface uplift prior to the eruption of the emeishan flood basalts additionally the plume s lateral extent is hard to constrain and has been variously estimated to be 800 1400 km in diameter in this study we analyzed present day heat flow data and reconstructed the permian paleo heat flow using vitrinite reflectance and zircon u th he thermochronology data in the elip region and discussed implications for the geodynamics of the emeishan mantle plume the present day heat flow is higher in the inner and intermediate zones than in the outer zone with a decrease of average heat flow from 76 mw m2 to 51 mw m2 thermal history modeling results show that an abnormal high paleo heat flow of 90 110 mw m2 was caused by the emeishan mantle plume activity based on the present day heat flow data we can calculate that there is lithospheric thinning in the central elip region which may be due to the destruction of the lithosphere by mantle plume upwelling and magmatic underplating the permian paleo heat flow anomaly implies that there was a temperature anomaly in the mantle the ascending high temperature mantle plume and the thinned lithosphere may have induced the large scale uplift in the elip region according to the range of the surface heat flow anomaly it can be estimated that the diameter of the flattened head of the emeishan mantle plume could have reached 1600 1800 km our research provides new insights into the geodynamics of the emeishan mantle plume through study of heat flow

postglacial paleoecological history of a cedar swamp manitoulin island ontario canada abstract a cedar swamp on manitoulin island ontario canada was chosen for a paleoecological study of pollen macrofossils and cladocera a new elevation of 316 7 m a s l is given for the position of main lake algonquin on northeastern manitoulin island based on a wave cut feature 4 7 m above the swamp immediately adjacent to the site deposits inferred to predate 10 500 yr b p are dominated by picea artemisia cyperaceae and other herbs likely derived from spruce parkland climate on the small proto manitoulin island group was cool and possibly dry the cladoceran assemblage includes alona lapidicola acroperus harpae and chydorus brevilabris which resembles the modern fauna of wave swept rocky shores of georgian bay this suggests that the site was an embayment of main lake algonquin local lake waters were cold and shallow pinus banksiana resinosa populus cupressineae artemisia pteridium and other herbs dominate pollen assemblages from 10 500 to 10 000 yr b p an open pine dominated woodland prevailed under a warming and dry climate and marked progression towards the holocene climatic optimum on manitoulin island glacial lake algonquin levels fell and the embayment was transformed into a small alkaline lake potamogeton filiformis hippuris vugaris and scirpus plants provided habitat for a diverse littoral and planktonic cladoceran fauna which included chydorus brevilabris c cf gibbus and bosmina longirostris waters in the swamp basin were rich in nutrients warm and possibly transparent from 10 000 to 8000 years b p picea returned as the dominant pollen type and was slightly more abundant than pinus banksiana resinosa toward the end of this period abies larix and betula increased in frequency picea forest with p banksiana resinova grew on shallow well drained soils climate became more continental winters more severe and summers drier and hotter as the moderating effects of the great lakes ceased during the lake stanley lake hough stage at the site a shallow pond with abundant submersed and emergent aquatic plants and a diverse littoral cladoceran community existed at 8000 yr b p pinus strobus replaced picea and pinus banksiana resinosa shortly after tsuga canadensis and larix become important this conifer dominated pollen assemblage persists to the present and reflects modern forests the presence of nyssa pollen and decodon verticillatus seeds contemporaneous with their range extensions elsewhere in the great lakes region implies that the hypsithermal maximum occurred about 6000 yr b p on manitoulin island when climate remained warmer than present but became humid after about 8000 yr b p by 5000 yr b p conditions became cooler prairie and cordilleran floristic elements in the modern manitoulin flora are probably remnants predating 10 000 yr b p the southern floristic element may represent late hypsithermal relicts fluctuating water levels and influence of mineral rich groundwater probably were key factors controlling hydroseral succession in cedar swamps on manitoulin island

chemical models of vitrinite reflectance evolution a global kinetic model of vitrinite reflectance evolution is developed to illustrate a new approach to vitrinite reflectance modelling the method utilizes quantitative pyrolysisgas chromatographic data from isolated vitrinite kerogens to derive the concentrations of structurally specific moieties alkylphenol precursors in vitrinite kerogens as a function of rank this data set is used to calibrate a gaussian distributed activation energy model for phenol precursor loss from vitrinites using published burial histories phenol yield is then correlated with vitrinite reflectance the predictive vitrinite reflectance model based on this phenol system is tested against a well from the us gulf coast area the results being compared with a lopatin model of the same well this type of vitrinite reflectance model is numerically compatible with current generation kinetic models of hydrocarbon production from source rock kerogens and has a better heating rate independence than lopatin s method

burial of organic carbon and pyrite sulfur in sediments over phanerozoic time a new theory in present day marine sediments almost all of which are deposited in normal oxygenated seawater rates of burial of organic carbon c and pyrite sulfur s correlate positively and bear a constant ratio to one another c s 3 on a weight basis by contrast calculations based on the isotopic model of garrels and lerman 1981 indicate that at various times during the phanerozoic the worldwide burial ratio must have been considerably different than the present day value this ratio change is caused by the requirement that increases in the worldwide mass of organic carbon must be accompanied by equivalent decreases in the mass of sedimentary pyrite sulfur in order to maintain a roughly constant level of o2 in the atmosphere such apparently contradictory behavior can be explained if the locus of major organic carbon burial has shifted over time from normal marine environments as at present to non marine freshwater or to euxinic environments in the geologic past a shift to predominantly freshwater burial can help explain predicted high c s ratios in permo carboniferous sediments and a shift to euxinic environments can help explain predicted low c s ratios during the early paleozoic it is demonstrated that the three environments today exhibit distinguishably different average c s ratios

a reconstruction of moorhead and emerson phase environments along the eastern margin of glacial lake agassiz rainy river basin northwestern ontario mapping of quaternary geology in the rainy river lowland northwestern ontario resulted in discovery of several fossil bearing localities organic remains are associated with both the moorhead and

calculation of vitrinite reflectance from thermal histories a comparison of some methods vitrinite reflectance values ro calculated from commonly used methods are compared with respect to time invariant temperatures and constant heating rates two monofunctional methods one involving a time temperature index to vitrinite reflectance correlation tti ro and the other involving a log ro to depth correlation yield vitrinite reflectance values that are similar to those calculated by recently published arrhenius based methods such as easy ro the approximate agreement between these methods supports the perception that the easy ro algorithm is the most accurate method for the prediction of vitrinite reflectances throughout the range of organic maturity normally encountered however calibration of the e methods against vitrinite reflectance data from two basin sequences with well documented geologic histories indicates that although the easy ro method has wide applicability it slightly overestimates vitrinite reflectances in strata of low to medium maturity up to a ro value of 0 9 the two monofunctional methods may be more accurate for prediction of vitrinite reflectances in similar sequences of low maturity an older but previously widely accepted tti ro correlation consistently overestimates vitrinite reflectances with respect to other methods underestimation of paleogeothermal gradients in the original calibration of time temperature history to vitrinite reflectance may have introduced a systematic bias to the tti ro correlation used in this method also incorporation of tai thermal alteration index data and its conversion to ro equivalent values may have introduced inaccuracies

hydrocarbon expulsion model and its application to niigata area japan a one dimensional process response type model has been set up to simulate geologic processes of compaction heat transfer source rock maturation and hydrocarbon generation and expulsion during a basin s development the model can be used to calculate the quantity of oil and or gas expelled from a source rock under certain conditions although the model simplifies chemical and physical conditions within sedimentary rocks it may be used as a first approximation in geologic reconstructions of sedimentary basins when applied to the niigata area japan the model predicted the most significant parameters associated with hydrocarbon expulsion including the rate of burial and the quantity of hydrocarbons generated the model also revealed that the time of hydrocarbon expulsion varied from place to place even within the small northern niigata basin major petroleum fields formed when expulsion favorable timing coincided with the development of structure thus a realistic estimate of the timing of expulsion is a key to hydrocarbon exploration

geopressure evolution hydrocarbon generation and migration in the beaufort mackenzie basin canada results from two dimensional quantitative modelling abstract three cross sections of onshore and offshore areas of the beaufort mackenzie basin were used to simulate geopressure evolution hydrocarbon generation and migration processes of the tertiary section using a two dimensional model two analytical approaches were used 1 adjusting geological geophysical and geochemical parameters to obtain the best fit between the model results and regional geological data in a one dimensional manner and 2 reconstructing the basin evolutionary history in a two dimensional manner the model results indicate that the present day distributions of geopressure and maturity levels at different locations have been modified by late miocene uplift and erosion followed by rapid deposition of the late miocene pleistocene lperk sediments although the occurrence of oil and gas has no obvious relationship to geopressure at the present day the evolution of geopressure in strata older than the mackenzie sequence plays an important part in the maturation of tertiary source rocks geopressure in these older formations caused an increase in thermal gradient and porosity in the deep formations the analysis indicates that the timing of hydrocarbon generation and the evolution of geopressure are critical factors in the development of horizontal migration reindeer reservoirs versus vertical migration kugmallit reservoirs

brightness of pollen as an indicator of thermal alteration by means of a computer driven image processor statistical thermal alteration index sttai abstract the brightness or gray level of pollen of pinus podocarpus abies picea and tsuga from the neogene sediments in northern japan was measured using a transmitted light microscope with a computer driven digital image processor the mean value of the modes for the complete array of the indigenous pollen in a rock sample was called here the statistical thermal alteration index sttai in the present investigation an inverse relationship between sttai and vitrinite reflectance r o in sediments was found the application of sttai to samples from three boreholes indicated a decreasing trend with depth by using this trend threshold values of intense oil generation can be evaluated 145 110 therefore sttai can be a useful parameter for determining organic maturation and for identifying the threshold zone of intense oil generation

basin modeling of tadla basin morocco for hydrocarbon potential the tadla basin morocco is the easternmost major structural subdivision of the meseta south of the central massif after the basin remained relatively stable through the paleozoic movements during the variscan orogeny divided the basin into two subbasins a western subbasin where compressional forces formed large anticlines and an eastern subbasin where intense folding and faulting are associated with uplift and erosion the sedimentary basin fill includes numerous organic shales which provide the source beds also deposited were numerous shallow water to continental clastics and to a lesser extent carbonates providing several possible reservoir rocks for hydrocarbons the results from computer modeling show that the chief formations of hydrocarbon generation are carboniferous and silurian most of these formations may have generated hydrocarbons before variscan movements which probably destroyed preexisting oil and gas traps the only source rocks in the generation stage from mesozoic to the present are the upper visean shales the western part of the tadla basin was the most favorable area for the generation and maturation of hydrocarbons of the upper visean shales

burial and exhumation history controls on shale compaction and thermal maturity along the norwegian north sea basin margin areas abstract the north sea area has been subjected to significant erosion and subsequent deposition of sediments in the basin margin and deeper basin areas respectively during the late neogene a large amount of cretaceous early quaternary sediments have been removed below the angular unconformity along the west and southwest coast of norway and deposited in the huge north sea fan at the mouth of the norwegian channel at the same time a considerable thickness of early quaternary paleocene sediments was also eroded towards the east in the central north sea and subsequently deposited in the deeper basin areas to the west this study seeks to estimate exhumation from compaction and thermal maturity based techniques by using sonic velocities of shales carbonates and vitrinite reflectance data in a large number of boreholes in the central eastern and northern north sea the results indicate no or minor exhumation in the central graben and flanking high areas whereas more than 1 km sediments are eroded in the basin margin areas towards the norwegian coast more than 500 m sediments are eroded in the egersund basin and stord basin areas a similarity of exhumation estimates from the early cretaceous early miocene shales and late cretaceous early paleocene carbonates indicates maximum burial sometime after the early miocene in most of the central and northern north sea areas however the maximum burial throughout the north sea basin may be diachronous seismostratigraphic analysis indicates maximum burial sometime during the oligocene in the sorgenfrei tornquist zone area in the eastern north sea maximum burial in the norwegian danish basin varies from miocene pliocene in eastern parts to early pleistocene in western parts whereas sediments are currently at their maximum burial in the central graben and southern viking graben areas restoration of surface elevations to their original position before the onset of erosion indicated large subaerially exposed areas in the norwegian danish basin and along the southwest coast of norway this is also supported by predominantly coastal and or deltaic environments in the norwegian danish basin area during the late neogene these subaerially exposed areas may be linked to the regional tilting and erosion of the basin margin areas to the east and progressive basinward migration of deposition centres to the west since the oligocene the exhumation had significant effects on the petroleum system in the basin margin areas by cooling down the source rock however the deeper burial of sediments may also have changed the rheological properties of sediments from more ductile to brittle due to compaction and diagenetic processes which makes them more failure prone during exhumation leading to hydrocarbon leakage or seal failure in case of co2 injection

the georges bank basin a quantitative basin analysis study using a one dimensional 1d fluid flow compaction model applied to wells of the georges bank basin east coast usa has enabled a simulation to be made of the history of the sedimentation basement subsidence tectonic activity geoheat flux evolution maturation of organic matter hydrocarbon generation and migration tendency based on the analysis of the basement tectonic activity the basin s development is related to the formation and the evolution of the east edge of the north american plate through the simulation of geoheat flux variation maturation of organic material and hydrocarbon generation at different positions in the basin at different time periods are analysed additionally from the modelling of excess fluid pressure porosity and permeability variations in the strata the potential hydrocarbon migration tendency and stratigraphic traps in the basin are discussed

origin and accumulation mechanisms of petroleum in the carboniferous volcanic rocks of the kebai fault zone western junggar basin china abstract the kebai fault zone of the west junggar basin in northwestern china is a unique region to gain insights on the formation of large scale petroleum reservoirs in volcanic rocks of the western central asian orogenic belt carboniferous volcanic rocks are widespread in the kebai fault zone and consist of basalt basaltic andesite andesite tuff volcanic breccia sandy conglomerate and metamorphic rocks the volcanic oil reservoirs are characterized by multiple sources and multi stage charge and filling history characteristic of a complex petroleum system geochemical analysis of the reservoir oil hydrocarbon inclusions and source rocks associated with these volcanic rocks was conducted to better constrain the oil source the petroleum filling history and the dominant mechanisms controlling the petroleum accumulation reservoir oil geochemistry indicates that the oil contained in the carboniferous volcanic rocks of the kebai fault zone is a mixture the oil is primarily derived from the source rock of the permian fengcheng formation p 1 f and secondarily from the permian lower wuerhe formation p 2 w compared with the p 2 w source rock p 1 f exhibits lower values of c 19 tt c 23 tt c 19 20 tt tt ts ts tm and 20r sterane c 27 c 28 ratios but higher values of tt c 23 c 21 hhi gammacerane c 30 hopane hopane 20s c 34 c 33 c 29 and c 29 20s 20s 20r ratios three major stages of oil charge occurred in the carboniferous in the middle triassic late triassic to early jurassic and in the middle jurassic to late jurassic periods respectively most of the oil charged during the first stage was lost while moderately and highly mature oils were generated and accumulated during the second and third stages oil migration and accumulation in the large scale stratigraphic reservoir was primarily controlled by the top carboniferous unconformity with better porosity and high oil enrichment developed near the unconformity secondary dissolution pores and fractures are the two major reservoir storage space types in the reservoirs structural highs and reservoirs near the unconformity are two favorable oil accumulation places the recognition of the large scale carboniferous volcanic reservoirs in the kebai fault zone and understanding of the associated petroleum accumulation mechanisms provide new insights for exploring various types of volcanic reservoir plays in old volcanic provinces and will undoubtedly encourage future oil and gas exploration of deeper strata in the region and basins elsewhere with similar settings

an upper limit to palaeo heat flow theory and examples from the danish central graben abstract the surface heat flow yields a condensed expression of the subsurface thermal regime while the present heat flow can be measured as the product of thermal conductivity and temperature gradient resolution of the past surface heat flow variations calls for indirect methods such as the modelling of vitrinite reflectance and other organic maturity indicators which represent integrals of the past temperature history this paper argues that regarding the reflectance of vitrinite which is the most common maturity indicator the feature of the past thermal regime which can survive the effects of measuring and modelling uncertainties is the maximum temperature present or past how the maximum temperature was obtained is only rarely resolved given maximum temperature burial history thermal conductivity structure and surface temperature history the one dimensional steady state heat equation yields an approximate upper limit to the surface heat flow artificial examples show that the past heat flow may be similar to the maximum heat flow constraint when the past was significantly warmer than the present however this requires a delicate balancing of burial history and heat flow history to occur the thermal relaxation rate of the hot past must compensate for heating due to burial generally the past heat flow may be well below the maximum constraint examples from the central graben show that vitrinite reflectance samples of upper jurassic age constrain the maximum palaeo heat flow back to 150 ma this is due to the very rapid and significant sedimentation of upper jurassic sediments resulting in immediate deep burial of vitrinite the data of the present study are consistent with a early cretaceous heat flow elevated by about 20 30 above the present and with a heat flow throughout the cenzoic only marginally higher than the present however the data are also fully consistent with a time independent background heat flow history this illustrates the limits of resolution in palaeo thermal reconstruction based on vitrinite reflectance and temperature data the problem is one of finding the space of admissible solutions rather than one of finding a single solution

basin analysis and hydrocarbon generation of the south mozambique graben using extensional models of heat flow abstract the northern south mozambique graben was assessed for hydrocarbon potential by reconstructing its structural burial and thermal histories using a seismic line and an array of basin modelling techniques the structural and depositional history was determined by simultaneously palinspastically restoring and backstripping a depth converted cross section the thermal history was predicted from extensional models which relate palaeoheat flow to basement subsidence maturation potential cross sections were derived by applying a generation model to each of the pseudo wells assuming each layer to be a potential source rock considering the range of uncertainty when using these models this analysis suggested that regardless of the extension model type used and within the maximum and minimum limits of the palaeoheat flow the eastern side of the northern south mozambique graben is more hydrocarbon prone than the west in addition the timing of hydrocarbon generation regardless of the palaeoheat flow possibilities modelled is favourably after source and seal rock deposition and after the development of trapping structures it is apparent from this study that a stratigraphic well with down hole thermal indicator measurements and bottom hole temperature information would greatly enhance the understanding of the hydrocarbon potential of this basin

determination of paleoheat flux from vitrinite reflectance data a method is presented for determining paleoheat flux from the reflectance of vitrinite collected from wells the maturation of vitrinite is modeled using a time temperature integral that assumes pseudo first order kinetics in testing the numerical algorithm it was necessary to introduce a critical temperature of 295 k below which vitrinite does not mature this result is consistent with the latest findings of independent researchers the degree of consistency obtained from a number of wells is not perfect much of the inconsistency can be attributed to large uncertainties in the vitrinite reflectance readings to test the method heat flow history was determined for the north sea basin and the national petroleum reserve of alaska quantitative results were obtained detailing the increase and or decrease of heat flux with time and were consistent with the qualitative behavior inferred for paleoheat flow from current geologic models

thermal history modeling of the georges bank u s a thermal inversion of transmittance color index tci and vitrinite reflectance vr data abstract using a one dimensional basin analysis model for the cost g 2 well in the georges bank area offshore east coast u s a thermal inversion of measured vitrinite reflectance vr data and of the transmittance color index tci converted to an equivalent vr value yielded essentially identical paleoheat flux variations with time the paleoheat flux showed two peaks at 175 ma bp and at 125 75 ma bp the earlier event corresponds to continental breakup and the beginning of the rift phase the latter event corresponds to continued drifting of the continents and formation of new oceanic basement beside answering some important tectonic questions the observations corroborated the theoretical and empirical connections between tci and vr found for the g 2 well and for other wells in different geological settings this fact together with the fact that tci measurements on physically amorphous organic material can be made on rocks devoid of vitrinite or spores and pollen carbonates pre late silurian rocks and siliceous black shales should promote the utility of tci as an effective geothermal history indicator

hydrological and sedimentary controls leading to arsenic contamination of groundwater in the hanoi area vietnam the impact of iron arsenic ratios peat river bank deposits and excessive groundwater abstraction groundwater contamination by arsenic in vietnam poses a serious health threat to millions of people in the larger hanoi area elevated arsenic levels are present in both the holocene and pleistocene aquifers family based tubewells predominantly tap the holocene aquifer while the hanoi water works extract more than 600 000 m3 day of groundwater from the pleistocene aquifer detailed groundwater and sediment investigations were conducted at three locations exhibiting distinct geochemical conditions i e i high levels of dissolved arsenic av 121 g l at the river bank ii low levels of dissolved arsenic av 21 g l at the river bank and iii medium levels of dissolved arsenic 60 g l in an area of buried peat and excessive groundwater abstraction seasonal fluctuations in water chemistry were studied over a time span of 14 months sediment bound arsenic 1 3 22 g g is in a natural range arsenic correlates with iron r2 0 8 with variation related to grain size sediment leaching experiments showed that arsenic can readily be mobilized at each of the three locations low levels of arsenic in groundwater 10 g l generally exhibit manganese reducing conditions whereas elevated levels are caused by reductive dissolution under iron and sulphate reducing conditions average arsenic concentrations in groundwater are twofold higher at the river bank than in the peat area the lower levels of arsenic contamination in the peat area are likely controlled by the high abundance of iron present in both the aqueous and sediment phases with median molar fe as ratios of 350 in water and 8700 in the sediments of the peat area reduced iron possibly forms new mineral phases that resorb or sequester previously released arsenic to the sediment despite similar redox conditions resorption is much less significant at the river bank fe as aq 68 fe as s 4700 and hence arsenic concentrations in groundwater reach considerably higher levels drawdown of holocene water to the pleistocene aquifer in the peat area caused by the pumping for the hanoi water works clearly promotes reducing conditions in pleistocene groundwater this demonstrates that excessive abstraction of water from deep wells i e wells tapping water below the arsenic burdened depth can cause a downward shift of iron reducing conditions and concurrently mobilize arsenic along the way vertical migration of reduced groundwater may also impact aquifers under natural hydrological conditions seepage of doc enriched groundwater derived from degradation of organic matter in the clayey sediments at the river bank was observed to enhance and maintain iron reducing conditions in the aquifer where organic matter is scarce once the aquifer becomes reduced arsenic is released from the aquifer solid hosts but additionally derives from the arsenic enriched groundwater seeping from the clay into the aquifer this behaviour is an important mechanism for arsenic contamination in aquifers that might not necessarily contain enough organic matter in their sediments to induce reducing conditions independently

present day heat flow thermal history and tectonic subsidence of the east china sea basin the east china sea basin is located in the convergence area between the eurasian plate the pacific plate and the philippine sea plate and consists of two depressions the taibei depression in the west and the xihu depression in the east heat flow measurements show that the east china sea basin is characterized by present day heat flow around 70 6 mw m 2 varying between 55 and 88 mw m 2 no significant difference in heat flow is observed between the xihu and the taibei depressions thermal history reconstruction using vitrinite reflectance suggests that the thermal history was however different in the taibei and the xihu depressions paleo heat flow values when the pretertiary formations experienced their maximum temperature at the end of the paleocene reached a mean of 82 mw m 2 in the taibei depression much higher than the present day value the lower tertiary sediments in the xihu depression experienced maximum temperatures at the end of oligocene 35 4 23 3 ma and reached a mean paleo heat flow value of 83 mw m 2 tectonic subsidence analysis shows that the timing of the major rifting episode was different across the east china sea basin the rifting occurred from the late cretaceous w65 ma to the early eocene w55 ma in the taibei depression followed by thermal subsidence from the late eocene to the end of miocene 23 3 5 2 ma in contrast in the xihu depression the initial subsidence lasted until the early miocene and thermal subsidence to the end of miocene from pliocene to the present an accelerated subsidence took place all along the west pacific margin of asia significant thicknesses of strata were removed from the unconformities in the basin the mean amount of erosion was 1147 m from the paleocene and 1208 m above the oligocene in the taibei depression and 1409 m from the oligocene in the xihu depression q 2004 elsevier ltd all rights reserved

evaluation of the shale gas potential of the lower silurian longmaxi formation in northwest hunan province china abstract commercial gas production has been achieved in china s marine shale of the silurian longmaxi formation in the eastern sichuan area and experience for developing shale gas in complex structural areas has been gathered a set of longmaxi formation shales deposited in the northwestern hunan area has close relationship with the eastern sichuan longmaxi shale on both depositional environment and tectonic evolution therefore it is important to undertake an integrated evaluation of the longmaxi formation shale in the northwestern hunan area this work combined field investigations and the laboratory measurements using outcrop samples to study the petrology geochemistry reservoir and adsorption characteristics of the longmaxi shale in the northwestern hunan area the geological settings and reservoir properties were compared with those of the eastern sichuan longmaxi shale using publically available data the results show that the hydrocarbon generation ability organic matter maturity sealing capacity and reservoir stimulation effectiveness of the longmaxi formation shale in the northwestern hunan area are comparable to those in the eastern sichuan area the longmaxi shale in the northwestern hunan area therefore shows early signs of development potential and the drilling of exploration wells is thus warranted to further evaluate its gas content and other in situ reservoir properties for possible shale gas development in the near future

organic molecular evidence in the late neoproterozoic tillites for a palaeo oceanic environment during the snowball earth era in the yangtze region southern china abstract the upper neoproterozoic nantuo and jiangkou formations in southern china have commonly been identified as the deposits of glaciations dating back to 600 ma and 720 ma belonging to the marinoan and sturtian ice ages respectively or the so called snowball earth events in the present study 44 typical upper neoproterozoic to lower cambrian sedimentary rock samples including 16 diamictites have been collected from 12 stratigraphic sections in hubei hunan shanxi chongqing guizhou and yunnan provinces in the yangtze region southern china and analyzed by routine organic geochemical techniques except for the diamictites and cap carbonates most of these rocks have middle to high toc values of up to 0 16 6 50 in the cambrian and 0 12 9 37 in the upper neoproterozoic rock samples by contrast the diamictites and cap carbonates have a toc range only from 0 01 to 0 13 1 2 orders of magnitude lower than those in most of the non glacial sedimentary rocks indicating very limited organic productivity in the palaeo oceanic environment during the snowball earth era phytane and pristane which are derivatives of chlorophyll a and various steranes which are biomarkers of eukaryotes were detected in all the rock samples there is a tendency for positive correlation between toc and the concentrations of phytane and or pristane therefore it implies that photosynthetic autotrophs should have been the primary organisms contributing to the sedimentary organic matter in the yangtze palaeo ocean moreover the concentrations of phytane plus pristane range from 0 024 ng g to 0 446 ng g in most non glacial sedimentary rocks and from 0 005 ng g to 0 076 ng g in diamictites the unusually low concentrations of phytane and pristane reveal a very weak photosynthetic process a restricted euphotic zone and quite limited sunlight within the palaeo oceanic water column even though the productivity of photosynthetic organisms was very low it can still be inferred that photosynthetic process never ceased in the late neoproterozoic palaeo oceanic environment this evidence suggests that the palaeo ocean in the yangtze region during the snowball earth was either covered by a thin sea ice sheet or was covered by a thicker sea ice sheet that included polynyas or areas of open water both these possibilities would have allowed the survival of photosynthetic eukaroytes and other organisms

dynamic hydrocarbon predictions for the northern part of the danish central graben an integrated basin analysis assessment abstract geohistory thermal history source capacity and oil generation have been examined in the north west part of the danish central graben using a one dimensional fluid flow compaction model the burial history suggests that this part of the danish central trough developed through three stages of subsidence a late jurassic differential stage a late cretaceous early tertiary uniform stage and a late miocene quaternary uniform stage pseudo wells drilled on seismic sections in areas without well data are used to improve the spacial distribution of wells the palaeotemperature and palaeoheat flow have been modelled by inversion of vitrinite reflectance data the inversion was carried out on wells with available vitrinite reflectance data and was based on known bottom hole temperature some temperature measurements with depth and the surface temperature the thermal history assessed by inversion of vitrinite reflectance data gives a consistently cooler past the available data s resolution of the thermal history is discussed the modelled maturation history of the upper jurassic shale in terms of vitrinite reflectance suggests that the shale reached maturity some 5 50 ma ago a geochemical study of the upper jurassic shales shows that these shales contain a mixture of type ii and type iii kerogens and have good to excellent source capacity modelling of the hydrocarbon generation data indicates that the peak generation took place some time between 10 ma bp and the present day possible migration paths are determined from modelled excess fluid pressure and four areas of possible accumulation of hydrocarbons are indicated the hydrocarbon potential of the areas are evaluated and an area along the eastern boundary fault between the tail end graben and the ringkobing fyn high is suggested as a new target area for further exploration

thermal history of sedimentary basins maturation indices and kinetics of oil and gas generation temperature is the most sensitive parameter in hydrocarbon generation thus reconstruction of temperature history is essential when evaluating petroleum prospects no measurable parameter can be directly converted to paleotemperature maturation indices such as vitrinite reflectance tmax from rock eval pyrolysis spore coloration thermal alteration index tai or concentration of biological markers offer an indirect approach all these indices are a function of the thermal history through rather complex kinetics frequently influenced by the type of organic matter their significance and validity are reviewed besides the problems of identification e g vitrinite and interlaboratory calibration it is important to simultaneously interpret kerogen type and maturation and to avoid difficult conversions from one index to another geodynamic models where structural and thermal histories are connected are another approach to temper ture reconstruction which could be calibrated against the present distribution of temperature and the present value of maturation indices kinetics of kerogen decomposition controls the amount and composition of hydrocarbons generated an empirical time temperature index tti originally introduced by lopatin does not allow such a quantitative evaluation due to several limitations no provision for different types of kerogen and different rates of reactions poor calibration on vitrinite reflectance it is of limited interest unless one has no access to a desk top computer kinetic models based on a specific calibration made on actual source rock samples can simulate the evolution of all types of organic matter and can provide a quantitative evaluation of oil and gas generated examples from the jurassic source rocks of the paris basin monterey formation of california green river shales of utah paleozoic source eds of the algerian sahara and miocene rocks of the mahakam delta indonesia illustrate various aspects of the discussion geological geochemical models are the most efficient way to integrate geological seismic and geochemical data and they should greatly help to reduce the risk in exploration

dynamic interpretation of organic matter maturation and evolution of oil generative window two phases are recognized in the maturation of organic matter and evolution of the oil generative window ogw a a basinal subsidence phase during which potential source rocks undergo burial through a static initial ogw and maturation is due essentially to increasing temperature with depth and b a postsubsidence phase during which the ogw moves vertically upward through the static sedimentary fill and maturation is due to time effects only the final shallow position of ogw can be defined by geochemical indices of maturity the hydrocarbon generation sequence progresses from bottom to top beginning with the lighter hydrocarbons or even thermogenic gas at the initial ogw at depth followed by progressively heavier hydrocarbons as the ogw moves vertically upward this dynamic model of hydrocarbon generation permits modeling of past positions of ogw relative to basin evolution through interpretation of oil genesis nomographs it also provides genetic explanation for the increase in api gravity with depth areal variation of maturation facies variation in temperature at present tops of ogw with age of source rocks and gas oil volume ratios of sedimentary basins

arsenic enrichment in groundwater of the alluvial aquifers in bangladesh an overview arsenic in the groundwater of bangladesh is a serious natural calamity and a public health hazard most groundwater from the shallow alluvial aquifers 150 m particularly in the holocene plai

a review of the source behaviour and distribution of arsenic in natural waters the range of as concentrations found in natural waters is large ranging from less than 0 5 g l 1 to more than 5000 g l 1 typical concentrations in freshwater are less than 10 g l 1 and frequently less than 1 g l 1 rarely much higher concentrations are found particularly in groundwater in such areas more than 10 of wells may be affected defined as those exceeding 50 g l 1 and in the worst cases this figure may exceed 90 well known high as groundwater areas have been found in argentina chile mexico china and hungary and more recently in west bengal india bangladesh and vietnam the scale of the problem in terms of population exposed to high as concentrations is greatest in the bengal basin with more than 40 million people drinking water containing excessive as these large scale natural as groundwater problem areas tend to be found in two types of environment firstly inland or closed basins in arid or semi arid areas and secondly strongly reducing aquifers often derived from alluvium both environments tend to contain geologically young sediments and to be in flat low lying areas where groundwater flow is sluggish historically these are poorly flushed aquifers and any as released from the sediments following burial has been able to accumulate in the groundwater arsenic rich groundwaters are also found in geothermal areas and on a more localised scale in areas of mining activity and where oxidation of sulphide minerals has occurred the as content of the aquifer materials in major problem aquifers does not appear to be exceptionally high being normally in the range 1 20 mg kg 1 there appear to be two distinct triggers that can lead to the release of as on a large scale the first is the development of high ph 8 5 conditions in semi arid or arid environments usually as a result of the combined effects of mineral weathering and high evaporation rates this ph change leads either to the desorption of adsorbed as especially as v species and a range of other anion forming elements v b f mo se and u from mineral oxides especially fe oxides or it prevents them from being adsorbed the second trigger is the development of strongly reducing conditions at near neutral ph values leading to the desorption of as from mineral oxides and to the reductive dissolution of fe and mn oxides also leading to as release iron ii and as iii are relatively abundant in these groundwaters and so4 concentrations are small typically 1 mg l 1 or less large concentrations of phosphate bicarbonate silicate and possibly organic matter can enhance the desorption of as because of competition for adsorption sites a characteristic feature of high groundwater as areas is the large degree of spatial variability in as concentrations in the groundwaters this means that it may be difficult or impossible to predict reliably the likely concentration of as in a particular well from the results of neighbouring wells and means that there is little alternative but to analyse each well arsenic affected aquifers are restricted to certain environments and appear to be the exception rather than the rule in most aquifers the majority of wells are likely to be unaffected even when for example they contain high concentrations of dissolved fe

relationships between thermal maturity indices calculated using arrhenius equation and lopatin method implications for petroleum exploration thermal maturity can be calculated with time temperature indices tti based on the arrhenius equation using kinetics applicable to a range of types ii and iii kerogens these ttis are compared with tti calculations based on the lopatin method and are related theoretically and empirically via vitrinite reflectance to the petroleum generation window the ttis for both methods are expressed mathematically as integrals of temperature combined with variable linear heating rates for selected temperature intervals heating rates control the thermal maturation trends of buried sediments relative to arrhenius ttis lopatin ttis tend to underestimate thermal maturity at high heating rates and overestimate it as low heating rates complex burial histories applicable to a range of tectonic environments illustrate the different exploration decisions that might be made on the basis of independent results of these two thermal maturation models

thermal subsidence and generation of hydrocarbons in michigan basin temperature histories for selected stratigraphic horizons in the michigan basin are computed from three dimensional continually filled subsidence models mechanical evolution of the michigan basin is modeled as flexure of the lithosphere caused by thermal contraction results are compatible with the subsidence record of the sediments and free air gravity anomalies paleotemperature is determined from excess temperature due to the thermal anomaly plus burial temperature predicted from subsidence curves for an equilibrium temperature gradient of 22 c km 1 2 f 100 ft surface temperature of 20 c 68 f and an equilibrium surface heat flow of 1 1 hfu excess temperature paleotemperature and surface heat flow do not exceed 15 c 27 f 110 76 c 230 f and 2 5 hfu respectively these estimates are consistent with upper limits set by paleomagnetic studies the low value for excess temperature is caused by concentration of the thermal anomaly below 15 km 9 mi in agreement with gravity results the great depth of the thermal anomaly can explain the lack of evidence for an initial heating event prior to subsidence once the thermal history of the sediments is specified the oil potential of the basin can be determined from laboratory derived kinetic equations for degradation of kerogen to petroleum for the michigan basin predicted temperature conditions are sufficient for source rock 25 conversion of type i and type ii kerogen only in ordovician and older rocks in the southern peninsula of michigan by this model petroleum found in rocks younger than ordovician would have had to migrate upward from the older rocks geochemical studies of dundee devonian and trenton ordovician crude oils in michigan are compatible with this interpretation niagaran silurian crude oils appear to come from a different source than the dundee and trenton oils if their source is silurian rocks on the flanks of the basin either the scheme used to calculate maturity is not applicable to these oils or the temperature of the source rocks was significantly higher in the past than today more likely the model underestimates the depth of burial of silurian source rocks near the center of the basin especially in local regions of downfaulting

hydrogeochemistry of arsenic and other inorganic constituents in groundwaters from la pampa argentina groundwaters from quaternary loess aquifers in northern la pampa province of central argentina have significant quality problems due to high concentrations of potentially harmful elements such as as f no3 n b mo se and u and high salinity the extent of the problems is not well defined but is believed to cover large parts of the argentine chaco pampean plain over an area of perhaps 106 km2 groundwaters from la pampa have a very large range of chemical compositions and spatial variability is considerable over distances of a few km dissolved as spans over 4 orders of magnitude 4 5300 g l 1 and concentrations of f have a range of 0 03 29 mg l 1 b of 0 5 14 mg l l v of 0 02 5 4 mg l 1 no3 n of 0 2 140 mg l 1 mo of 2 7 990 g l 1 and u of 6 2 250 g l 1 of the groundwaters investigated 95 exceed 10 g as l 1 the who guideline value and 73 exceed 50 g as l 1 the argentine national standard in addition 83 exceed the who guideline value for f 1 5 mg l 1 99 for b 0 5 mg l 1 47 for no3 n 11 3 mg l 1 39 for mo 70 g l 1 32 for se 10 g l 1 and 100 for u 2 g l 1 total dissolved solids range between 730 and 11400 mg l 1 the high values resulting mainly from evaporation under ambient semi arid climatic conditions the groundwaters are universally oxidising with high dissolved o2 concentrations groundwater phs are neutral to alkaline 7 0 8 7 arsenic is present in solution predominantly as as v groundwater as correlates positively with ph alkalinity hco3 f and v weaker correlations are also observed with b mo u and be desorption of these elements from metal oxides especially fe and mn oxides under the high ph conditions is considered an important control on their mobilisation mutual competition between these elements for sorption sites on oxide minerals may also have enhanced their mobility weathering of primary silicate minerals and accessory minerals such as apatite in the loess and incorporated volcanic ash may also have contributed a proportion of the dissolved as and other trace elements concentrations of as and other anions and oxyanions appear to be particularly high in groundwaters close to low lying depressions which act as localised groundwater discharge zones concentrations up to 7500 g l 1 were found in saturated zone porewaters extracted from a cored borehole adjacent to one such depression concentrations are also relatively high where groundwater is abstracted from close to the water table presumably because this zone is a location of more active weathering reactions the development of groundwaters with high ph and alkalinity results from silicate and carbonate reactions facilitated by the arid climatic conditions these factors together with the young age of the loess sediments and slow groundwater flow have enabled the accumulation of the high concentrations of as and other elements in solution without significant opportunity for flushing of the aquifer to enable their removal

peat formation concentrates arsenic within sediment deposits of the mekong delta abstract mekong river delta sediment bears arsenic that has been released to groundwater under anaerobic conditions over the past several thousand years the oxidation state speciation and distribution of arsenic and the associated iron bearing phases are crucial determinants of as reactivity in sediments peat from buried mangrove swamps in particular may be an important host source or sink of arsenic in the mekong delta the total concentration speciation and reactivity of arsenic and iron were examined in sediments in a mekong delta wetland by x ray fluorescence spectrometry xrf x ray absorption spectroscopy xas and selective chemical extractions total solid phase arsenic concentrations in a peat layer at a depth of 6 m below ground increased 10 fold relative to the overlying sediment extended x ray absorption fine structure exafs spectroscopy revealed that arsenic in the peat was predominantly in the form of arsenian pyrite arsenic speciation in the peat was examined further at the micron scale using xrf and x ray absorption near edge structure xanes spectroscopy coupled with principal component analysis the multiple energy xrf mapping and xanes routine was repeated for both iron and sulfur phase analyses our xrf xanes analyses confirm arsenic association with pyrite a less reactive host phase than iron hydr oxides under anaerobic conditions the arsenian pyrite likely formed upon deposition formation of the peat in a past estuarine environment 5 5 ka bp a process that is not expected under current geochemical conditions presently arsenian pyrite is neither a detectable source nor a sink for aqueous arsenic in our sediment profile and under present geochemical conditions represents a stable host of as under the reducing aquifer conditions of the mekong delta furthermore organic carbon within the peat is unable to fuel fe iii reduction as noted by the persistence of goethite which can be reduced microbially with the addition of glucose

an end member sensitivity analysis of vitrinite reflectance distributions for the cost g 2 well in the georges bank basin abstract vitrinite reflectance vr is one of the most popular thermal indicators in basin analysis studies with the mean values of the vr distribution data usually used for determining the thermal history of sediments abnormally high mean values and thus abnormally high vr derived paleoheat flux may be recorded when recycled or highly oxidized vitrinite macerals are mixed in situ with virgin vitrinite in this study end member sensitivity analysis methods are applied to vr distribution data measured in the cost g 2 well in georges bank basin u s a to investigate the mixing properties of the vr data the modified vr data obtained through a filtering procedure are then used to generate a modified thermal history a 1 d fluid flow compaction model is employed for the basin s burial and thermal history inversion relative to the thermal history derived from the mean vr distribution data the modified thermal history results in a lower paleoheat flux and paleotemperature and is consistent with other geological evidence and with the thermal history obtained from other thermal indicators such as transmittance color index and temperature alteration index

basin analysis predictions of known hydrocarbon occurrences the north sea viking graben as a test case abstract basin analysis can assimilate structural burial and thermal histories to predict hydrocarbon prone zones in speculative areas the validity of the modelling approach was field tested in the north sea viking graben an area for which good data are available a recent birps deep seismic reflection profile across tectonic strike of the graben was interpreted and depth converted with good well control the burial and structural histories were determined by backstripping the chronostratigraphic layers using a one dimensional fluid flow compaction model on pseudo wells after removal of each sequence the section was manually reconstructed the thermal history was examined using thermal indicator tomography extensional models and calculations of depth to detachment lack of resolution required that three different paleo heat flow trends be tested to encompass the range in variability a gradual warming trend a constant heat flow through time and a low heat flow until the cretaceous tertiary boundary where a heat pulse occurred basement subsidence extension depth to detachment calculations and thermal indicator inversions all suggest that the uk side of the graben has developed differently to the norwegian section the generation modelling predicts the position of the oil window in the cross section the areas where this window enveloped the draupne formation kimmeridge clay source rock broadly correlate with the positions of the gullfaks statfjord and thistle oilfields of the uk sector however in the norwegian sector the draupne formation was generally overmature except in the area around the troll oilfield predicted middle to late cretaceous generation in the rift axis may have caused updip oil migration towards the horda platform the correct prediction of oil prone zones validates the use of quantitative basin analysis as a tool for evaluating frontier areas where data are limited

optical properties of organic matter in relation to thermal gradients and structural deformation the general response of macerals to the coalification process the effectiveness of organic geochemical and petrological parameters as estimators of coalification and the applicability of different microscopical parameters in the assessment of rank are reviewed the central role of vitrinite reflectance as the most widely used estimator of coalification from brown coals to the low grade metamorphic zone is established on the basis of its relatively uniform variation with rank specificity ease and rapidity of measurement and cheapness factors influencing the optical properties ofvitrinites are considered temperature has the dominant influence in modifying optical properties with rank but time static pressure and stress can all have significant influences upon the course of optical properties depending upon particular geological conditions static pressure has a retarding effect on the coalification process but it is also responsible for creating increasing anisotropy within the condensing aromatic structures as rank rises hydrostatic pressures and pore pressures can contribute to the overpressuring of sediments thus affecting their thermal conductivities and consequently the rate of coalification stress is responsible for the development of biaxicity in the reflectance indicatrix fast and high levels of heating from igneous bodies cause textural effects on vitrinites as a result of carbonization that are quite different from those of coalification recognizing these different influences upon the optical properties of vitrinites examples are given of the use and application of vitrinite reflectance in the preparation of rank maps in the burial histories of basins in the timing of coalification in relation to orogenesis and igneous activity and in the zones of anchimetamorphism and low grade metamorphism consideration is also given to the problem of provincialism in correlations between chemical and physical parameters and to the future development of optical studies in organic petrology and their relation to organic geochemical investigations

natural organic matter in sedimentary basins and its relation to arsenic in anoxic ground water the example of west bengal and its worldwide implications in order to investigate the mechanism of as release to anoxic ground water in alluvial aquifers the authors sampled ground waters from 3 piezometer nests 79 shallow 80 m wells in an area 750 m by 450 m just north of barasat near kolkata calcutta in southern west bengal high concentrations of as 200 1180 mug l 1 are accompanied by high concentrations of fe 3 13 7 mgl 1 and po4 1 6 5 mg l 1 ground water that is rich in mn 1 5 3 mg l 1 contains 50 mug l 1 of as the composition of shallow ground water varies at the 100 m scale laterally and the metre scale vertically with vertical gradients in as concentration reaching 200 mug l 1 m 1 the as is supplied by reductive dissolution of feooh and release of the sorbed as to solution the process is driven by natural organic matter in peaty strata both within the aquifer sands and in the overlying confining unit in well waters thermotolerant coliforms a proxy for faecal contamination are not present in high numbers 10 cfu 100 ml in 85 of wells showing that faecally derived organic matter does not enter the aquifer does not drive reduction of feooh and so does not release as to ground water arsenic concentrations are high much greater than50 mug l 1 where reduction of feooh is complete and its entire load of sorbed as is released to solution at which point the aquifer sediments become grey in colour as feooh vanishes where reduction is incomplete the sediments are brown in colour and resorption of as to residual feooh keeps as concentrations below 10 mug l 1 in the presence of dissolved fe sorbed as released by reduction of mn oxides does not increase as in ground water because the as resorbs to feooh high concentrations of as are common in alluvial aquifers of the bengal basin arise because himalayan erosion supplies immature sediments with low surface loadings of feooh on mineral grains to a depositional environment that is rich in organic mater so that complete reduction of feooh is common c 2004 published by elsevier ltd

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

mapped plant macrofossil and pollen records of late quaternary vegetation change in eastern north america abstract macrofossil presence absence maps and isopoll maps in 3000 year intervals show how ranges and abundance maxima for 12 eastern north american tree and shrub taxa picea p glauca p mariana larix laricina abies balsamea tsuga canadensis pinus strobus p resinosa p banksiana betula papyrifera b alleghaniensis b series humiles have changed from the last glacial maximum to the present the macrofossil maps corroborate patterns shown by the isopoll maps and provide spatial detail and taxonomic resolution the macrofossils confirm the inference from pollen data that unglaciated southeastern north america was cooler during the last glacial maximum 18 and 15 ka than simulated by the cohmap experiments with the ncar ccm0 general circulation model the geographic distribution of macrofossil occurrences during the late glacial 12 and 9 ka indicate that migration lag of boreal species did not occur at regional to subcontinental scales and that pollen assemblages lacking modern analogs resulted from climate gradients lacking modern analogs early holocene 9 and 6 ka macrofossil maps show rapid northward expansion of tree species ranges into deglaciated regions the data also show modest contractions of northern range limits of temperate species and expansions of southern range limits of boreal species in response to cooling trends during the late holocene 3 and 0 ka comparison of modern macrofossil maps of nine of these taxa with corresponding range maps confirm that the macrofossils record the geographic ranges accurately comparison of the modern macrofossil maps with maps of tree growing stock volume shows that for some taxa abies tsuga macrofossil occurrences were most frequent in regions of maximum tree abundance comparison of modern isopoll maps with the modern range and growing stock volume maps indicate that in contrast to the macrofossil data the pollen data provide poorer resolution of range limits for most taxa but better indications of abundance maxima and minima within the ranges

thermal regime and petroleum systems in junggar basin northwest china abstract the conversion of organic matter into oil and gas depends upon temperature and time and the study of thermal maturation of oil source rocks in a petroleum system is of importance for formation of a petroleum system based on the temperature data from 196 wells and thermal conductivity measurements of 90 core samples altogether 35 heat flow data are obtained in the junggar basin the results show that the junggar basin is a relatively cold basin at present with a mean temperature gradient and heat flow of 21 c km and 42 mw m 2 respectively thermal history reconstructed from vitrinite reflectance data indicates that the paleozoic formations experienced their maximum paleotemperature during the permian and triassic at higher paleoheat flow of about 85 mw m 2 and that the basin then cooled down to the present low heat flow the high paleoheat flow can be attributed to the carboniferous to permian rifting the thermal evolution has a quite important effect on the formation and evolution of the petroleum systems in the junggar basin i e the permian and the jurassic systems the jurassic petroleum system is quite limited in space for the cooled thermal regime during the meso cenozoic and the source rocks of the middle lower jurassic entered the oil window only along the north tianshan foreland region where the jurassic is buried to the depth of 5 7 km at present in contrast the middle lower permian source rocks have experienced oil and gas generation in late permian to triassic and the permian petroleum system was formed prior to the triassic when the upper paleozoic formations reached their maximum paleotemperature due to higher paleoheat flow

the effect of igneous intrusive bodies on sedimentary thermal maturity abstract the high temperatures of igneous intrusives cause localized thermal maturity of sediments far in excess of the regional variation previous studies have shown that igneous bodies cool in less than about a million years for all but the most exceptional geological conditions two case studies are provided which show how the increase in thermal maturity around an igneous body can be used to assess the temperature of the intrusive at emplacement and also the time of intrusion corollorative implications for localized hydrocarbons generation migration and accumulation are also discussed briefly

kerogen conversion and thermal maturity modelling of petroleum generation integrated analysis applying relevant kerogen kinetics abstract kerogen transformation to petroleum and thermal maturity modelling calibrated to vitrinite reflectance utilizing arrhenius equation reaction kinetics are important oil and gas exploration tools for conventional and non conventional resources the range and correlation between activation energies e and frequency factors a on a geological scale is presented to support the theory and application of the time temperature index tti arr method of thermal maturity proposed in 1988 with a single set of e a values e 218 kj mol 52 1 kcal mol a 5 45e 26 my the tti arr method provides a highly sensitive and transparent thermal maturity index it is well correlated with vitrinite reflectance and produces comparable results with models applying theoretically tenuous distributions of e with single a values the sensitively scaled tti arr methodology has the added benefit of providing detailed insight to petroleum generation via the calculation of related transformation factors tf for oil and gas by applying a range of e a values referencing the tti arr thermal maturity scale as a benchmark this study provides analysis of detailed modelling of the transformation process with representative and realistic kinetics for kerogens and mixtures of kerogens for a wide range of heating rates at geological and laboratory scales the results reveal that novel metrics such as maximum transformation gradient and temperature at which it occurs average transformation gradient between 10 and 90 conversion and temperature spread from 10 to 90 conversion can discriminate between the transformation processes of kerogens and mixtures of kerogens at geological and laboratory scales these metrics offer the potential to more precisely define sweet spots of petroleum generation in organic rich shales they also have potential at the laboratory scale to assist in the extraction of kinetic information from existing and future pyrolysis test furthermore the analysis suggests that mixtures of kerogens can in most cases be more effectively identified and characterized and their petroleum transformation modelled with just two or three e a sets as kinetic inputs this approach is preferred to the common practice of using a complex distributions of multiple e values linked with a single a value unrelated to the geological scale e a trend established for kerogens

the transmittance color index of amorphous organic matter a thermal maturity indicator for petroleum source rocks abstract since the mid 1980s texaco has used the transmittance color index tci of amorphous kerogen as an indicator of kerogen thermal maturation the technique simply involves the direct measurement of a white light spectrum as it is transmitted through a particle of amorphous organic matter aom in brief tci values are obtained by the analysis of white light originating from a 100 w 6 v tungsten lamp attached to a photometric microscope the assignment of particular tci values is based on the increasing curvature of spectra with increasing maturity tci curves shift from an average wavelength around 580 nm for samples of immature amorphous kerogen i e material with a mean random vitrinite reflectance of about 0 20 to about 660 nm for samples containing very dark brown to some black particulate material i e kerogen with a mean random vitrinite reflectance of about 2 15 the range of tci values covers all zones of petroleum generation and preservation in our opinion tci can provide as accurate a basis for maturation interpretations as is available from vitrinite reflectance or from the mean random reflectance of some zooclasts such as graptolites and chitinozoans or the widely used visual estimate the thermal alteration index tai or the similarly determined conodont color index cai tci is probably most useful however in those situations where the rocks to be examined have not yet reached the semianthricite coalification stage 2 0 vitrinite reflectance

arsenic associations in sediments from shallow aquifers of northwestern hetao basin inner mongolia understanding the mechanism of arsenic mobilization from sediments to groundwater is important for water quality management in areas of endemic arsenic poisoning such as the hetao basin in inner mongolia northern china aquifer geochemistry was characterized at three field sites sh hf tys in hangjinhouqi county of northwestern hetao basin the results of bulk geochemistry analysis of sediment samples indicated that total as concentrations have a range of 6 8 58 5 mg kg with a median of 14 4 mg kg the highest as concentrations were found at 15 25 m depth in the meanwhile the range of as concentration in the sediments from background borehole is 3 21 8 mg kg with a median value of 9 mg kg the as sediments concentrations with depth from the sh borehole were correlated with the contents of fe sb b v total c and total s generally the abundance of elements varied with grain size with higher concentrations in finer fractions of the sediments distinct lithology profile and different geochemical characteristics of aquifer sediments indicate the sediments are associated with different sources and diverse sedimentary environments up to one third of arsenic in the sediments could be extracted by ammonium oxalate suggesting that fe oxyhydroxides may be the major sink of as in the aquifer sequential extraction results indicate that arsenic occurs as strongly adsorbed on and or co precipitated with amorphous fe oxyhydroxides in sediments accounting for 35 and 20 respectively of the total contents of arsenic the release of as into groundwater may occur by desorption from the mineral surface driven by reductive dissolution of the fe oxide minerals furthermore small proportions of as associated with iron sulfides occur in the reductive sediments

transmittance color index tci of amorphous organic matter new thermal maturity indicator for hydrocarbon source rocks correlation with mean vitrinite reflectance and thermal alteration index tai abstract a new thermal maturity indicator the transmittance color index tci is introduced here the tci eliminates most limitations of these techniques and is measured on particulate amorphous material the most abundant type of organic matter in hydrocarbon source rocks of all geologic ages tci is obtained from rapid spectral screening of transmittance spectra in tungsten light and is based on the increased curving of these spectra with progressive thermal maturity tci shifts from 570 nm for immature material at an anti r sub 0 of about 0 20 to about 680 nm anti r sub 0 2 5 for almost black kerogen thus tci covers all zones of thermal maturity for the same samples an excellent linear correlation exists between tci and vitrinite reflectance anti r sub 0 and the tai thus tci measurements can be converted into equivalent reflectance values r sub e and plotted with actually measured vitrinite reflectance data in depth vs maturity diagrams examples are given of wells where tci analysis provides more accurate maturity profiles than conventional techniques do these include cases where vitrinite is scarce where formations are older than upper silurian in faulted areas where anti r sub 0 data are conflicting or when the maturity is locally increased asmore a result of the occurrence of anhydrites although tci needs further testing this new technique will probably improve organic petrology less

the influence of salt domes on paleotemperature distributions a characteristic of salt domes is that an enhanced heat flux is associated with them due to the contrast in thermal conductivity between rock salt and typical sedimentary formations we present a simple analytical model of heat flow in the vicinity of an isolated salt dome with numerical evaluations for some sample cases in addition to an enhanced surface heat flow these models show that on the upper flanks of a salt dome a temperature higher than the regional trend is predicted thus enhancing hydrocarbon maturation at these depths on the lower flanks a temperature lower than the regional trend is predicted thus inhibiting overmaturation the magnitude of this temperature anomaly depends upon the position of the measurement point both vertical and radial relative to the salt dome roughly speaking it is confined to within one salt dome radius of the salt sediment interface the magnitude of the anomaly can be quite large for typical salt domes these basic ideas are corroborated by observing downhole measurements from a salt dome in the gulf of mexico the good agreement allows us to bracket the height of that particular dome at between 9 000 and 15 000 m and also permits us to determine that the total sediment thickness overlying the basal salt is between 13 200 and 19 200 m at the location of the salt dome these results indicate that the presence of a salt dome can have a significant impact on the subsurface temperature distribution and hence on the thermochemical maturation of any source rocks or hydrocarbon accumulations in close proximity to the salt dome in addition to providing trapping structures a salt dome also provides an enhanced environment for hydrocarbon maturation on its upper flanks and for inhibiting overmaturation on its lower flanks such effects should be included when evaluating the hydrocarbon potential of a salt dome province

geology basin analysis and hydrocarbon potential of mozambique and the mozambique channel abstract the phanerozoic structural and stratigraphic history of mozambique can be separated into a karoo and a post karoo phase outcrops of karoo rocks limited to the zambezi valley and small outliers in the mozambique belt to the north show an eastward facies change marked by an increased argillaceous content and the appearance of carbonates the wide coastal plain and immediate offshore of southern mozambique is marked by extensional horsts and grabens with a mesozoic fill covered by cenozoic sediments little is known of lower stratigraphic horizons in this coastal province there is a facies transition from continental clastics in the northwest and west to more lacustrine and marine deposits to the southeast and east upwards the succession passes into the cenozoic without a noticeable break in the offshore in the north seismic lines help define two basins the zambezi delta basin and the mozambique channel basin separated by the beira high in the south several offshore grabens have been defined one of which the south mozambique graben has been examined here by an integrated basin analysis technique the technique which uses available depositional structural and thermal data provides information on maturation and the timing of hydrocarbon maturation the analysis showed variation in the extension rate with time and two phases of rifting the greatest rate of extension accumulation and subsidence between 96 and 76 ma depends upon interpretational assumptions during this time interval fault blocks were systematically tilted domino fashion this event broadly coincides with the rifting between madagascar and antarctica a period of plate reorganization the earlier rifting phase was probably related to the strike slip separation of madagascar from africa modelling heat flow suggests that the later event is the more important from the maturation hydrocarbon standpoint the offshore and potentially the deeper onshore post karoo basins have traps reservoirs and seals with the presumed source rock within lower cretaceous or jurassic strata there is at the present time no means to evaluate the potential of the karoo rocks

the use of free radicals of organic matter to determine paleogeothermal gradient abstract free radicals in 60 kerogen samples from 5 wells in the qiongdongnan tarim and liaohe basins in china were analyzed by electron spin resonance esr for use in geothermometry based on esr data for 44 kerogen samples from the tertiary qiongdongnan basin a regression curve was shown to fit free radical densities n g with burial depth of samples for use in geothermal gradient estimation using this curve the highest geothermal gradients experienced by carboniferous permian strata well tmc1 in the tarim basin and oligocene eocene strata well lr16 in the liaohe basin were estimated concurrently five samples from liaohe basin were examined by apatite fission track analysis to assess the reliability of the esr kerogen method for geothermal gradient determination results of esr analyses match those of vitrinite reflectance and apatite fission track analysis indicating that maximum geothermal gradients obtained from the esr curve are reliable this paper presents a useful esr kerogen method for estimating paleogeothermal gradients which is especially useful where vitrinite and apatite are not present

the permian hybrid petroleum system in the northwest margin of the junggar basin northwest china in this paper we define the concept of a hybrid petroleum system for the permian petroleum system in the northwest margin of the junggar basin by documenting the complexity in its formation and evolution it is termed hybrid because there are three source rock sequences seven reservoir caprock combinations and three petroleum events and multiple source rocks source the same reservoir and the same source rocks also feed multiple reservoirs the mahu sag centre is the petroleum source area with three sets of source rocks dark shale of the lower permian jiamuhe formation black shale of the lower permian fengcheng formation and black shale of the middle permian lower wuerhe formation the reservoir rocks include volcanic and clastic rocks of upper carboniferous to lower cretaceous age mainly characterized by alluvial conglomerate and sandstone there are three sets of ultimate caprocks among which the mudstone of the upper triassic baijiantan formation is the most important due to its wide distribution throughout almost the whole northwest margin and greatest thickness up to 300 m whereas the lower jurassic and lower cretaceous mudstone acts as an effective seal oil and gas were generated mainly during the middle late permian late triassic and middle jurassic early cretaceous the reconstruction of the oil filling history shows that the three source rocks charged reservoirs mainly in three geologic intervals with common mixing of oils from different sources and or with different maturities these three hydrocarbon charges coincide with the three main stages of petroleum generation related to the hercynian indosinian and yanshannian orogenies during these three petroleum events oil and gas migrated along the migration framework controlled by faults unconformities and good permeability reservoir rocks the faults are mainly well developed and episodically active thrust faults and secondary faults as a result the permian petroleum system in the northwest margin of the junggar basin is hybrid

plant and insect fossils from nipissing sediments along the goulais river southeastern lake superior fossiliferous sediments have long been known to occur along the banks of the goulais river radiocarbon dating has established their time of deposition as late in the nipissing transgression sedimentary environments and fluvial conditions in the ancestral river channel shaped fossil assemblages pollen reflects regional upland forests of pinus and picea with other trees and shrubs such as quercus fraxinus acer ulmus and alnus forested peatlands fens and emergent and submerged aquatic communities were common in lowland valleys and along the floodplain of the river these reconstructions are supported by aquatic insect fossils and hygrophilous taxa such as micropeplus sculptus and elaphrus olivaceus and also are confirmed by plant macrofossils such as myrica gale triadenum virginicum dulichium arundinaceum typha brasenia schreberi potamogeton spirillus and possibly zizania palustris there is no evidence for regional climatic change during this portion of holocene time

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

factors affecting arsenic content of unconsolidated sediments and its mobilization in the ishikari plain hokkaido japan arsenic as contamination of groundwater is often caused by as leaching from geological formations this study focused on factors affecting as content in unconsolidated sediments by using three sediment cores in the ishikari plain hokkaido japan the geochemical properties of the sediments were characterized by the chemical and mineral compositions as well as leaching experiments and sequential extractions of as the results showed that higher as content of 4 9 mg kg was observed in peat layers with organic matter content 10 wt and that higher as contents deeper than 8 m below the surface were also observed the deeper sediments were likely to be formed in brackish water conditions due to lower weight ratios of organic carbon content to sulfur content c s 10 the results of the leaching experiments showed that as was mobilized at slightly alkaline region these indicate that the distribution of as depended on the organic content in the sediments and sedimentation condition and that the mobility of as in the sediment was affected by ph

mobility of arsenic in west bengal aquifers conducting low and high groundwater arsenic part ii comparative geochemical profile and leaching study aquifer sediments from areas of low and high as groundwater were characterized mineralogically and geochemically at a field site in the nadia district of west bengal india leaching experiments and selective extraction of the sediments were also carried out to understand the release mechanism of as in the sub surface the correlation between measured elements major minor and trace from low and high as groundwater areas are only significant for as fe and mn the borehole lithology and percentage of silt and clay fraction demonstrates the dominance of finer sediments in the high as aquifer multivariate analysis of the geochemical parameters showed the presence of four different mineral phases heavy mineral fraction phyllosilicates biotite fe oxyhydroxides carbonates and sulphides in the sediments selective extraction of sediment reveals that amorphous fe oxyhydroxide acts as a potential sink for as in the sub surface the result is consistent with microbially mediated redox reactions which are controlled in part by the presence of natural organic matter within the aquifer sediments the occurrences of as bearing redox traps primarily formed of fe and mn oxides hydroxides are also important factors that control the release of as into groundwater at the study site

thermal and maturation history of jurassic source rocks in the kuqa foreland depression of tarim basin nw china abstract kuqa foreland depression of the tarim basin is one of the largest gas production provinces in china thermal history reconstruction using vitrinite reflectance data indicates that the palaeo heat flow in kuqa depression was relatively high 50 55 mw m 2 during the mesozoic but gradually decreased during the cenozoic to reach the present value of 40 50 mw m 2 the cooling of the kuqa depression is probably attributed to the crust thickening and the rapid sedimentary rate the jurassic source rocks entered conventional oil window at 100 ma and began to generate gas at approximately 75 ma in the kelasu area thermal maturation of the jurassic source rocks accelerated significantly since 23 3 ma especially in the recent 5 2 ma in this foreland depression source rock maturation which is likely controlled mainly by burial history also influenced by the presence of fault thrusting and salt bearing formations