diagenese differentielle chez les rongeurs fossiles validite des parametres geochimiques pour les reconstitutions des regimes alimentaires abstract the effects of diagenesis during sedimentation and fossilization on the chemistry of bones and teeth are rarely taken into account in quantitative paleoenvironmental reconstructions we demonstrate here that each present day tissue displays its own chemical composition moreover comparison between major and minor chemical contents between modern and fossil rodent skeletal elements through localized microanalyses further indicates the importance of the diagenetic factors alterations of the contents of chemical elements of fossilized tissues are found in comparison with recent ones and variability occurs from one tissue to the other and for different elements the tissue that is most modified by fossilization is the incisor dentine the most variable element is mg sr varies in bone while ca varies in all the tissues thus the reliability of using sr ca and mg ca ratios in paleodiets is discussed and their limits defined the necessity of localized analyses is here demonstrated as well as the importance of further investigations in diagenetic processes

was the black sea catastrophically flooded in the early holocene abstract a catastrophic flooding of the black sea basin was proposed to have occurred during its reconnection to the ocean in the early holocene possible cultural consequences of the flood include the migration of neolithic farmers from around the black sea towards central europe as well as the creation of flood myths stratigraphic and paleo geomorphologic information from danube delta aided by radiocarbon ages on articulated mollusks constrain the level in the black sea before the marine reconnection to ca 30 m below the present sea level rather than 80 m or lower if the flood occurred at all the sea level increase and the flooded area during the reconnection were significantly smaller than previously proposed

stable carbon isotopes of coal derived gases sourced from the mesozoic coal measures in china coal derived large scale gas fields derived from the mesozoic coal measures in china are mainly distributed in the middle lower jurassic coal measures in the tarim junggar and turpan hami basins in northwest china and the upper triassic xujiahe formation coal measure in sichuan basin central china in 2011 the annual production was 21 6 109 m3 and the proved geological reserves were 2485 109 m3 accounting for 21 and 30 of the total in china respectively based on analyses of gas composition and stable carbon isotopes ratios of 203 samples and stable carbon isotopes of 102 co2 samples the following conclusions were made a based on diagnostic plots using the stable carbon isotopic and molecular composition of gas samples alkane gas from the mesozoic coal measures in china is shown to be coal derived b according to the 13c2 vs c2h6 plot of a great number of oil derived and coal derived gases in china it is concluded that gases with 13c2 28 5 are coal derived and those with 13c2 28 5 are oil derived in most cases c among the natural gases from the mesozoic coal measures in china primary coal derived gases with normal carbon isotopic distribution pattern among the c1 c4 alkanes i e 13c1 13c2 13c3 13c4 are dominant d carbon isotopic pattern reversal mainly results from the mixing of coal derived gases having different maturities but the same source and secondly from microbial oxidation of propane e g mu 3 and mu 4 wells in the gumudi gas field junggar basin e co2 in the coal derived gases from the mesozoic coal measures in china has both biogenic and abiogenic origins the biogenic origin is dominant and the abiogenic co2 is mainly found in the kuqa depression in the tarim basin and western sichuan basin f isotopic differences between heavy hydrocarbon gases and methane become less with increasing maturity

geochemical characteristics genetic types and sources of natural gas in the yingjisu depression tarim basin china abstract the yingjisu depression in the tarim basin produces gas with high wetness nitrogen content and ethane carbon isotope is abnormally depleted the hydrocarbon generation capability of the jurassic coal strata in this area has been controversial anomalies in the geochemical characteristics and the actual geological conditions have resulted in challenges in identifying the source and genetic type of natural gas in the yingjisu depression in the present study the composition and carbon isotope of natural gas are investigated in addition the controversial jurassic coal strata are comprehensively evaluated and the biomarkers are analyzed the actual geological conditions of the yingjisu depression are studied combined with geochemical analysis the components and carbon isotope suggest that the natural gas in the yingjisu depression is oil associated gas generated from marine source rocks in the late mature stage the formation temperature of the natural gas was higher than 185 c which represents secondary cracking oil at high thermal maturity the jurassic coal strata has low tmax lower than 435 c and ro 0 3 0 7 these strata cannot be the source rocks of natural gas in the yingjisu depression with high content of n2 typical of marine sediment however the biomarkers confirmed that the oil and gas in the yingjisu depression were derived from the cambrian ordovician source rocks rather than the jurassic therefore the natural gas in the yingjisu depression is the secondary cracking of oil from the cambrian ordovician paleo reservoir according to the actual geological conditions the cracked gas migrated upward along deep faults to accumulate in the silurian and jurassic reservoirs eventually forming the yingjisu depression gas field

variations of natural gas carbon isotope type curves and their interpretation a case study natural gas is dominated by low molecular weight gaseous hydrocarbons c1 c5 whose genetic and diagenetic information is mainly obtained from stable carbon isotope compositions ordos basin is one of the largest natural gas provinces in china by means of examining the carbon isotope compositions of the ordos basin gases altered patterns of the isotopetype curves due to secondary cracking thermochemical sulphate reduction tsr and mixing of gases generated from different sources are recognized and discussed a typical carbon isotope type curve is nearly linear on the natural gas plot chung h m gormly j r squires r m 1988 origin of gaseous hydrocarbons in subsurface environments theoretical considerations of carbon isotope distribution chemical geology 71 97 103 our results show that the isotope type curve pattern of tsr and gas secondary cracking in coal is convex due to catalysis while the isotope type curve of gas secondary cracking in reservoirs is concave the natural gas of yulin suligemiao and wushenqi gas fields is coal derived gas both coal derived gas and mixed gas from oil and gas prone sources exist in the ordovician reservoirs of the jingbian gas field depending on the borehole locations in the ordovician carbonate reservoirs tsr is recorded but uncommon whereas secondary cracking in reservoirs is often observed 2007 elsevier ltd all rights reserved

the new england batholith of eastern australia evidence of silicic magma mixing from zircon 176hf 177hf ratios abstract zircon hf isotopic data from six granite supersuites recognised in the new england batholith of eastern australia indicate that magma mixing is present in all plutons apart from the s type supersuites inherited zircons are rare to absent suggesting that initial melt temperatures were above zircon saturation for the m i and a type granites in all supersuites the range of zircon hf model ages calculated relative to arc mantle varies greatly with younger model ages somewhat less than the permian and triassic age of crystallisation and older model ages indicating derivation from source rocks that may be as old as neoproterozoic the older model ages are consistent with late precambrian rocks in the lower crust that may be elements of the lachlan fold belt underlying the new england fold belt whole rock 18 o and end values 87 sr 86 sr initial ratios sr i and oxidation state fe 2 o 3 feo are summarised for the five named supersuites and for a previously unnamed group of triassic plutons situated east of the main batholith for which we propose the name carrai supersuite supersuites with higher 18 o higher sr i lower 7 li and lower fe 2 o 3 feo ratios indicate a metasedimentary component input the pattern of zircon hf isotopic variation reflects the other isotopic and geochemical indicators closely the additional value being that it preserves a magmatic crystallisation record of hf isotopic variation that is a measure of magma mixing from magma generation to final crystallisation using the above criteria at least three distinct crustal components are considered necessary to explain the compositional and isotopic diversity within the batholith the crustal components indicated are 1 a metasedimentary component of carboniferous and devonian age for the hillgrove bundarra and uralla supersuites 2 a lower crustal k rich and sr rich i type component for the moonbi carrai and possibly uralla supersuites that could be as old as proterozoic and 3 a lower crustal k poor i type component of uncertain age for the clarence river supersuite in all supersuites there is strong evidence of an m type component based on the presence of zircons with high ehf values

ring complexes in the peninsular ranges batholith mexico and the usa magma plumbing systems in the middle and upper crust subvolcanic ring complexes are unusual in that they preserve a rapidly frozen record of intrusive events this sequential history is generally lost or complicated in plutons owing to mixing and mingling in a dynamic state thus subvolcanic ring complexes are more like erupted rocks in their preservation of instantaneous events but the self contained nature of the complexes allows detailed structural and chemical work to be conducted in environments where the relative timing between individual magmatic events is commonly well preserved we suggest that development of subvolcanic ring complexes in the western peninsular ranges batholith prb involved the following three stage generalized sequence 1 fracturing of the roof above a buoyant or overpressured magma chamber which resulted in moderately inward dipping conical fractures that locally hosted cone sheets 2 subsequent loss of magma from the chamber combined with degassing of the melt which facilitated collapse of the roof along near vertical ring faults that locally hosted ring dikes and 3 resurgence of the chamber and or intrusion of a broadly cogenetic nested pluton which locally destroyed evidence for the earlier history of the system this sequence has been repeated twice in one of the ring complexes that we have identified which resulted in nested intrusive centers calderas subvolcanic ring complexes and plutons may represent progressively deeper sections through linked magma plumbing systems and the systematic occurrences of these features in the western prb are consistent with progressively deeper along strike exposures of the batholith from south to north over a distance greater than 250 km in addition to subvolcanic complexes in the western prb deeper crustal levels exposed in the transition zone between eastern and western parts of the batholith preserve ring complexes emplaced at depths of up to 18 km occurrence of these deeper level complexes suggests either that caldera subsidence can extend to mid crustal levels or that other processes can produce ring complexes d 2002 elsevier science b v all rights reserved

carbon isotope reversal and its relationship with natural gas origins in the jingbian gas field ordos basin china abstract the geochemical characteristics of natural gases from lower paleozoic jingbian gas field are abnormal and the carbon isotope of most natural gases has reversed which led to a dispute over the source of natural gas in the lower paleozoic the upper paleozoic yulin gas field is adjacent to the jingbian gas field but the geochemical characteristics of the yulin gas field did not appear abnormal besides the ethane carbon isotope of upper paleozoic yulin gas field is much higher than that of lower paleozoic jingbian gas field in order to identify the reasons for the carbon isotope reversal of natural gas in lower paleozoic jingbian gas field and its relationship with natural gas source we conducted the components and stable carbon isotopes of natural gas from upper paleozoic yulin gas field and lower paleozoic jingbian gas field on the basis of these experiments we compared the natural gas components and carbon isotope of 100 samples from both upper paleozoic yulin gas field and lower paleozoic jingbian gas field the results indicate that higher maturity will break the conventional rule when maturity reaches a certain threshold 13cethane value will decrease with maturity although 13cmethane value will also increase with maturity the extent will be relatively smaller this leads to unusual 13cmethane 13cethane in the region with higher maturity in the process of downward migration of coal derived gas from carboniferous permian coal measures component fractionation and carbon isotope fractionation might occur resulting the ethane components and carbon isotope value of lower paleozoic less than those of upper paleozoic which will lead to the carbon isotope reversal the mixing of oil derived gas and coal derived gas at different ratios may also lead to the reversal of carbon isotopes the natural gas types of jingbian gas field are mainly coal derived gas generated from carboniferous permian coal measure strata with a small amount of oil derived gas generated from carboniferous permian marine terrigenous limestone

paleokarst reservoirs and gas accumulation in the jingbian field ordos basin abstract the jingbian gas field in central ordos basin with a proven initial in place gas reserve of approximately 11 trillion cubic meters is the largest paleokarst carbonate gas field in china paleokarst in ordovician strata of central ordos most commonly occurs in the paleo weathering surface of the o 1 m 5 member of the majiagou formation the karst intervals are generally proximal to the sub upper paleozoic unconformity however dissolution features in strata well below that exposure surface are possibly related to intra majiagou formation unconformities the quality of gas reservoirs are initially controlled by sedimentary facies with anhydrite bearing dolomite flat facies being the most favorable zones for dissolution and dolomitization to form karst and large small dissolution cavities the gases are generally dry derived dominantly from the overlying carboniferous permian coal measures the gases are accumulated in stratigraphic traps related to karst paleo geomorphology and lithologic traps associated with late diagenetic features of carbonate rocks although the precise timings of the thermal events during the evolution of the ordos basin are still subject to considerable debate there is a general consensus that events occurring during the yenshanian orogeny 150 115 ma were the most important for the paleozoic source rocks it appears that two episodes of hydrocarbon charge have occurred in the ordovician gas reservoirs in the jingbian field

early human evolution in the western palaearctic ecological scenarios abstract this review presents the themes of a special issue dealing with environmental scenarios of human evolution during the early pleistocene 2 6 0 78 ma mis 103 mis 19 and early middle pleistocene 0 78 0 47 ma mis 19 base of mis 12 within the western palaearctic this period is one of dramatic changes in the climates and the distribution of palaearctic biota these changes have played their role in generating adaptive and phyletic patterns within the human ancestry involving several species such as homo habilis homo georgicus homo erectus homo antecessor and homo heidelbergensis in the archaeological record these species include the oldowan mode 1 and acheulian mode 2 lithic technologies taphonomic considerations of palaeoecological research in hominin bearing sites are provided and evaluated syntheses are provided for north africa western asia the mediterranean basin britain and continental europe palaeoenvironmental reconstructions based on multidisciplinary data are given for ain boucherit ain hanech and el kherba in algeria dmanisi in georgia atapuerca cueva negra and the orce basin in spain monte poggiolo and pirro nord in italy pont de lavaud in france and mauer in germany the state of the art with the out of africa 1 dispersal model is reviewed a source sink dynamics model for palaeolithic europe is described to explain the morphological disparity of h heidelbergensis we will sometimes use the informal name heidelbergs and early neanderthals other aspects debated here are the selective value of habitat mosaics including reconstructions based on mammal and avian databases and the role of geological instability combined with topographic complexity this review is completed by addressing the question of whether the appearance of evolutionary trends within hominins is concentrated in regions of highest worldwide biological diversity biodiversity hotspots it is concluded that the keys for the activation of evolutionary change in hominins may have been geological instabilities and a shifting physiographical heterogeneity combined with high biodiversity and ecological interaction

abrupt changes of temperature and water chemistry in the late pleistocene and early holocene black sea new mg ca sr ca and published stable oxygen isotope and 87sr 86sr data obtained on ostracods from gravity cores located on the northwestern black sea slope were used to infer changes in the black sea hydrology and water chemistry for the period between 30 to 8 ka b p calibrated radiocarbon years the period prior to 16 5 ka b p was characterized by stable conditions in all records until a distinct drop in 18o values combined with a sharp increase in 87sr 86sr occurred between 16 5 and 14 8 ka b p this event is attributed to an increased runoff from the northern drainage area of the black sea between heinrich event 1 and the onset of the bolling warm period while the mg ca and sr ca records remained rather unaffected by this inflow they show an abrupt rise with the onset of the bolling allerod warm period this rise was caused by calcite precipitation in the surface water which led to a sudden increase of the sr ca and mg ca ratios of the black sea water the stable oxygen isotopes also start to increase around 15 ka b p although in a more gradual manner due to isotopically enriched meteoric precipitation while sr ca remains constant during the following interval of the younger dryas cold period a decrease in the mg ca ratio implies that the intermediate water masses of the black sea temporarily cooled by 1 2 c during the younger dryas the 87sr 86sr values drop after the cessation of the water inflow at 15 ka b p to a lower level until the younger dryas where they reach values similar to those observed during the last glacial maximum this might point to a potential outflow to the mediterranean sea via the sea of marmara during this period the inflow of mediterranean water started around 9 3 ka b p which is clearly detectable in the abruptly increasing mg ca sr ca and 87sr 86sr values the accompanying increase in the 18o record is less pronounced and would fit to an inflow lasting 100 a

deep lacustrine sandy debrites and turbidites in the lower triassic yanchang formation southeast ordos basin central china facies distribution and reservoir quality abstract the deep lacustrine gravity flow deposits are widely developed in the lower triassic yanchang formation southeast ordos basin central china three lithofacies include massive fine grained sandstone banded sandstone and massive oil shale and mudstone the massive fine grained sandstones have sharp upper contacts mud clasts boxed shaped gamma ray gr log but no grading and bouma sequences in contrast the banded sandstones display different bedding characteristics gradational upper contacts and fine upward the massive fine grained sandstones recognized in this study are sandy debrites deposited by sandy debris flows while the banded sandstones are turbidites deposited by turbidity currents not bottom currents the sediment source for these deep gravity flow sediments is a sand rich delta system prograding at the basin margin fabric of the debrites in the sandy debris fields indicates initial formation from slope failure caused by the tectonic movement as the sandy debris flows became diluted by water and clay they became turbidity currents the deep lacustrine depositional model is different from the traditional marine fan or turbidite fan models there are no channels or wide lobate sand bodies in the lower triassic yanchang formation layers within the sandy debrites have higher porosity 8 14 and permeability 0 1 4 md than the turbidites with lower porosity 3 8 and permeability 0 04 1 md consequently only the sandy debrites constitute potential petroleum reservoir intervals results of this study may serve as a model for hydrocarbon exploration and production for deep lacustrine reservoirs from gravity flow systems in similar lacustrine depositional environments

the origin of natural gas and the hydrocarbon charging history of the yulin gas field in the ordos basin china abstract the genetic type source and charging history of natural gas in the yulin gas field in the ordos basin have been studied by combining the carbon isotopic composition of natural gas and geochemical characteristics of light hydrocarbons with carbon isotope fractionation model results and fluid inclusion analysis the carbon isotopic composition of methane and ethane in the yulin gas field is relatively enriched in 13c with 13c1 values ranging from 35 3 to 29 8 average value 32 4 and 13c2 ranging from 26 3 to 23 5 average value 24 8 the c7 light hydrocarbons are predominated by methylcyclohexane accounting for 65 8 to 80 9 average value 71 6 which is characteristic of coal derived gas furthermore the gas geochemistry indicates that although marine limestone source rocks are present in the region the contribution of oil associated gas from this source to the yulin gas field is quite low based on the empirical relationship between 13c1 and ro of gas source rocks and the kinetic isotope fractionation predictions for gases generated in the yulin gas field the observed 13c of methane is heavier than that of natural gas only originated from in situ coal measures this result shows that gas in the yulin gas field is contributed not only by the natural gas generated from local coal measure source rocks but also from the higher maturity natural gas sourced from the coal measure source rocks to the south or southwest of this gas field fluid inclusion analysis proves that the accumulation of natural gas in the yulin gas field has the characteristics of continuous charge

geophysical and isotopic mapping of preexisting crustal structures that influenced the location and development of the san jacinto fault zone southern california we examine the role of preexisting crustal structure within the peninsular ranges batholith on determining the location of the san jacinto fault zone by analysis of geophysical anomalies and initial strontium ratio data a 1000 km long boundary within the peninsular ranges batholith separating relatively mafic dense and magnetic rocks of the western peninsular ranges batholith from the more felsic less dense and weakly magnetic rocks of the eastern peninsular ranges batholith strikes north northwest toward the san jacinto fault zone modeling of the gravity and magnetic field anomalies caused by this boundary indicates that it extends to depths of at least 20 km the anomalies do not cross the san jacinto fault zone but instead trend northwesterly and coincide with the fault zone a 75 km long gradient in initial strontium ratios sr i in the eastern peninsular ranges batholith coincides with the san jacinto fault zone here rocks east of the fault are characterized by sr i greater than 0 706 indicating a source of largely continental crust sedimentary materials or different lithosphere we argue that the physical property contrast produced by the peninsular ranges batholith boundary provided a mechanically favorable path for the san jacinto fault zone bypassing the san gorgonio structural knot as slip was transferred from the san andreas fault 1 0 1 5 ma two historical m6 7 earthquakes may have nucleated along the peninsular ranges batholith discontinuity in san jacinto valley suggesting that peninsular ranges batholith crustal structure may continue to affect how strain is accommodated along the san jacinto fault zone

geochemistry of the granitic rocks and their minerals from serra da estrela central portugal abstract several types of hercynian peraluminous granitic rocks ranging from biotite muscovite granodiorite to muscovite granite occur in the horst of serra da estrela variation diagrams of most major and trace elements of the rocks and biotites and cr and v of muscovites show fractionation trends however nb li rb k rb li mg variation diagrams of the rocks and muscovites and also of sn cs cs k of the muscovites indicate that the muscovite granite probably originated by another mechanism least squares analysis of major elements and modelling of trace elements indicate that the coarse grained porphyritic biotite muscovite granite granite porphyry and fine to medium grained muscovite biotite granite were derived from the granodiorite magma by fractional crystallization of plagioclase quartz and biotite emplacement of granodiorite magma took place at 3 5 3 kb and 720 c granites and granite porphyry probably originated about 690 c but were completely crystallized about 520 c o2 was about 10 17 for the granodiorite and hcl hf was higher whereas log h2o hcl was lower in the granodiorite than in the other granitic rocks of the fractionated series the coarse grained porphyritic biotite muscovite granite was hydrothermally altered between 400 350 c and 260 230 c at about 1 5 1 kb the hydrothermal fluids were probably mainly meteoric in origin but some fluids released during the late stage of granite solidification might also have been involved

permeability of sub critical carbon dioxide in naturally fractured indian bituminous coal at a range of down hole stress conditions abstract understanding reservoir dynamics from a geotechnical and petrophysical perspective is essential for safe and steady fluid extraction transport or injection in the reservoir the recent approach on storage of anthropogenic greenhouse gases ghg for mitigation of climate change in the deep geologic reservoirs has led to fast paced research on resolving storage related issues a coal seam is one such target reservoir where co 2 may be injected for storage this may be coupled with the enhanced extraction of coalbed methane cbm it is known that the interaction of co 2 with coal induces hydro mechanical changes however detailed investigation is mandatory for site specific operation the lack of such studies on indian coal is the motivation for this research a naturally fractured coal specimen was chosen and the subcritical co 2 flow was maintained by monitoring the injection pressures and ambient temperature the variations in permeability under various scenarios were also investigated the results indicate that initial co 2 injection caused coal matrix swelling which took nearly 5 6 h of flow related sorption for maximum closure of the natural fractures linear variation in flow rate with the pressure gradient across the sample indicated laminar or darcian flow of co 2 through the coal fractures deeper coal seams have high confinements the co 2 permeability results for such in situ conditions indicated an exponential decline in naturally fractured coal due to increasing confining pressures the observed reduction of co 2 permeability with increase in gas inlet pressure is debated and may be attributed fully to matrix swelling or partly to the klinkenberg effect this study is vital for successful ghg sequestration in coal seams and for better understanding of the gas flow behaviour in the seams

geology and geochemistry of the burnthill granite and related w sn mo f mineral deposits central new brunswick several significant w sn mo f bearing hydrothermal mineral deposits occur in the miramichi highlands of central new brunswick these deposits are spatially and temporally related to a group o

origin of natural gas from the ordovician paleo weathering crust and gas filling model in jingbian gas field ordos basin china abstract the ordos basin the second largest natural gas producing basin in china is one of the most tectonically stable sedimentary basins favorable to natural gas generation and preservation the origin and potential source of the jingbian gas field one of the five giant gas fields in the basin containing the ordovician paleo weathering crust as reservoir strata remains unclear the question is whether gas is generated from carboniferous permian coal measures or ordovician carbonates this study provides abundant gas geochemical evidence which clarifies its origin and source among 82 natural gas samples collected from the ordovician paleo weathering crust in the jingbian gas field c1 c4 gaseous hydrocarbons are dominant with low amounts of non hydrocarbons co2 h2s and n2 the content of c1 c4 ranges from 79 26 to 99 93 with a gas dryness c1 c1 4 of 0 981 0 999 suggesting that natural gases are dry and possibly originate from a high to over mature source the carbon isotopic compositions of methane and its homologues in natural gases from the ordovician paleo weathering crust vary widely with 13c1 13c2 and 13c3 values of 38 9 to 29 1 37 5 to 22 2 and 30 0 to 20 9 respectively the 13c2 and 13c3 values in the jingbian gas field are much more negative than those of typical coal type gas in sulige wushenqi yulin daniudi and kela2 gas fields the carbon isotopic signature suggests that the natural gas in the ordovician paleo weathering crust in the jingbian gas field most likely originates from ordovician carbonates containing sapropelic organic matter the measured d values of methane range from 177 to 155 and support our hypothesis of the natural gases originating from marine sapropelic organic matter the thermal maturity of the natural gases in the ordovician paleo weathering crust is at a high to over mature stage suggesting that the gases originated from secondary cracking of oil and gas at high temperature and pressure thermochemical sulfate reduction tsr might partially play a role in the alteration of gas dryness and 13c1 in those areas where gypsum is present as an effective cap rock mixing of high to over mature secondary cracking gas from the ordovician source and coal type gas from carboniferous permian coal in the jingbian gas field is minor

tectonic and stratigraphic controls of hydrocarbon systems in the ordos basin a multicycle cratonic basin in central china the ordos basin is the oldest and still an important hydrocarbon province in central china it is a typical cratonic basin developed on the archean granulites and lower proterozoic greenschists of the north china block the development of the ordos basin during the paleozoic mesozoic can be divided into three evolutionary stages cambrian early ordovician cratonic basin with divergent margins middle ordovician middle triassic cratonic basin with convergent margins and late triassic early cretaceous intraplate remnant cratonic basin two hydrocarbon systems are present in the basin the paleozoic gas and mesozoic oil systems in the paleozoic gas system the lower ordovician marine carbonates and pennsylvanian lower permian coal measures serve as source rocks the lower ordovician karst modified dolomites and pennsylvanian bauxitic mudstones form a significant reservoir seal association and the pennsylvanian lower permian deltaic sandstones and upper permian lacustrine mudstones form another effective reservoir seal association in the mesozoic oil system the upper triassic lacustrine mudstones are mature source rocks the upper triassic deltaic sandstones and overlying shallow lacustrine and swamp mudstones form a reservoir seal association and the lower jurassic fluvial sandstones and overlying shallow lacustrine and swamp mudstones form another reservoir seal association in both hydrocarbon systems the stratigraphic variations provide the principal traps the ordos basin is characterized by a stable tectonic setting that controlled the distribution of depositional systems and the development of erosional surfaces and ultimately governed the distribution of oil and gas fields and trap types

distribution isotopic variation and origin of sulfur in coals in the wuda coalfield inner mongolia china abstract this paper describes coal petrographic characteristics sulfur abundance distribution and isotopic signature in coals in the wuda coalfield inner mongolia northern china petrographic studies suggest that depositional environment influences petrographic composition the no 9 and no 10 coal seams which are thought to have formed on a tidal delta plain have high collodetrinite contents up to 66 1 indicating enhanced gelification and bacteria activity during coal accumulation and also have the highest sulfur content 3 46 and 3 42 both organic and pyritic sulfur isotope values 12 3 to 5 8 and 18 7 to 1 1 respectively are variable and generally tend to be more negative in high sulfur coals than those in low sulfur coals in the wuda coalfield the negative sulfur isotope values indicate that a large portion of sulfur in the high sulfur coals has a bacterial origin sulfur isotopic compositions and variations within the section were used to propose a model to explain the origin of sulfur in these coals the presence of pyritized rod like bacteria cyanophyte s gelatinous sheaths and degraded algae organic matter suggests that bacteria and perhaps algae may play an important role in the formation of these high sulfur coals

stable carbon isotope compositions and source rock geochemistry of the giant gas accumulations in the ordos basin china ordos basin the second largest sedimentary basin in china contains enormous natural gas resources each of the four giant gas fields discovered so far in this basin i e sulige yulin wushenqi and jingbian has over 100 billion cubic meters bcm or 3 53 trillion cubic feet tcf of proven gas reserves this study examines the stable carbon isotope data of 125 gas samples collected from the four giant gas fields in the ordos basin source rocks in the upper paleozoic coal measures are suggested by the generally high 13c values of c1 c4 gaseous hydrocarbons in the gases from the sulige yulin and wushenqi gas fields while the 13cic4 value is higher than that of the 13cnc4 the dominant ranges for the 13c1 13c2 and 13c3 values in these upper paleozoic reservoired gases are 34 to 32 27 to 23 and 25 to 24 respectively the 13c values of methane benzene and toluene in gases from the lower paleozoic reservoirs of the jingbian field indicate a significant contribution from humic source rocks as they are similar to those in the upper paleozoic reservoirs of the sulige yulin and wushenqi gas fields however the wide variation and reversal in the 13c1 13c2 and 13c3 values in the jinbian gases cannot be explained using a single source scenario thus the gases were likely derived dominantly from the carboniferous permian coal measures with some contribution from the carbonates in the lower permian taiyuan formation the gas isotope data and extremely low total organic carbon contents 0 2 toc suggest that the ordovician majiagou formation carbonates are unlikely to be a significant gas source rock thus almost all of the economic gas accumulations in the ordos basin were derived from upper paleozoic source rocks

assemblage data and bone and teeth modifications as an aid to paleoenvironmental interpretations of the open air pleistocene site of tighenif algeria abstract variations in the proportions of the various groups of rodentia collected from eight stratigraphic levels at tighenif had previously been interpreted as representing environmental climatic changes however the processes involved in the formation of assemblages are still not well understood examination of fragmentation crystallinity and chemical composition of fossil bones and teeth compared to recent samples shows that a possible explanation for the variations in frequencies is the differential preservation of skeletal remains thus the evaluation of postmortem effects is essential in determining the accuracy of the fossil record the abundance and composition of remains are governed by the complex interaction of many factors as indicated by actualistic studies direct deductions from fauna lists must be avoided as much as possible

the impact of raw material on acheulian large flake production raw material properties and availability have always been considered as having a definitive impact on the morphology size and production technology of acheulian large cutting tools shape and size of the naturally available raw material blocks have been cited as key factors in determining acheulian biface blank production technology as well as tool morphological variability in other words where large blocks of raw material were available africa large flakes were produced and where only smaller cobbles and nodules were to be found europe they become the primary type of blank used in this paper i explore a large body of data collected from acheulian sites from india to morocco and from south africa to england to test this common premise different raw material exploitation patterns as reflected in the bifacial tools in the various assemblages are described and analyzed the results indicate that in large flake based acheulian assemblages raw material constraints did not significantly affect either the blank production process or large cutting tool shape and size variability the acheulian large cutting toolmakers used the rock types available in the vicinity of their site in a sophisticated reduction sequence aimed to produce large cutting tools that are surprisingly similar regardless of the original shape size and type of raw material from which they were produced

dynamics of the coastal north black sea area in late pleistocene and holocene and early human dispersal abstract based on detailed surveys the reconstructions of coastal and marine environments of the north western black sea shelf were carried out for the time spans of ca 25 18 12 10 7 and 7 4 ka bp during the great part of late pleistocene and early holocene the black sea remained a land locked basin of the caspian type which became colonised by early modern humans starting from ca 40 ka the subsequent evolution of coastal landscapes was generally conditioned by the gradual rise of sea level and increasing temperature and precipitation resulting in the formation of coastal wetland landscapes which became the main source of late palaeolithic and mesolithic subsistence the initial indications of farming activities are coeval with the kalamitian stage being conditioned by the increased temperature and precipitation combined with the formation of fertile soils under altithermal conditions the data fail to indicate a catastrophic breakthrough of mediterranean water that could have had any effect on the subsistence or migrations of early farming communities

coalbed methane accumulation and dissipation patterns a case study of the junggar basin nw china abstract the junggar basin is a potential replacement area of coalbed methane cbm development in china to improve the efficiency of cbm exploration we investigated cbm accumulation and dissipation patterns of coal profiles located in the northwestern southern eastern and central junggar basin based on the following criteria burial depth hydrogeological zone cbm origin cbm phase and cbm migration type we identified four types of cbm accumulation patterns 1 a self sourcing cbm pattern containing adsorbed gas of biogenic origin from shallow depth coal within a weak runoff zone 2 an endogenic migration pattern containing adsorbed gas of thermogenic origin from the medium and deep coals within a stagnant zone 3 an exogenic migration pattern containing adsorbed gas of thermogenic origin from deep coal within a stagnant zone and 4 an exogenic migration pattern containing adsorbed and free gas of thermogenic origin from ultra deep coal within a stagnant zone we also identified two types of cbm dissipation patterns 1 shallow depth coal within a runoff zone with mixed origin cbm and 2 shallow and medium deep coal seams with mixed origin cbm cbm migration in low rank coals was more substantial than that adsorbed in high rank coal cbm in shallow coal could easily escape in the absence of closed structures or hydrogeological seals cbm reservoirs occurred in deep coal where oversaturated gas may accumulate future exploration should focus on gas water sealing structures in shallow coalbeds cbm that occurred in adsorbed and free phases and other unconventional natural gas dominated by free gas in the coal stratum should be co explored and co developed

sulige field in the ordos basin geological setting field discovery and tight gas reservoirs abstract the sulige gas field in central ordos basin is one of the largest gas fields in china with about 860 7 billion cubic meters bcm of proven gas reserve this field covers an area of about 500 km 2 with largely tight clastic reservoirs the upper carboniferous lower permian deltaic sandstones and upper permian lacustrine mudstones deposited in a stable cratonic tectonic setting form an effective petroleum system that is favorable for gas accumulation in large scale stratigraphic lithologic traps based on wire line log response drilling stem test and core data a generalized classification system was developed for the gas reservoirs of the sulige field thus type i and ii rocks are capable of gas production without natural and or artificial fracturing type iii rocks are capable of gas production after artificial fracturing and type iv rocks are too tight to produce at commercial rates even with artificial fracturing the discovery of the sulige field not only adds large gas reserve in the ordos basin but strongly indicates the overlook potential of both tight sandstone reservoir rock and relatively porous and permeable sweet spots in it

sea level change glacial rebound and mantle viscosity fornorthern europe northwestern europe remains a key region for testing models of glacial isostasy because of the good geological record of crustal response to the glacial unloading since the time of the last glacial maximum models for this rebound and associated sea level change require a detailed knowledge of the ice sheet geometry including the ice thickness through time existing ice sheet reconstructions are strongly model dependent and inversions of sea level data for the mantle response may be a function of the model assumptions thus inverse solutions for the sea level data are sought that include both ice and earth model parameters as unknowns sea level data from fennoscandia the north sea the british isles and the atlantic and english channel coasts have been evaluated and incorporated into the solutions the starting ice sheet for fennoscandia is based on a reconstruction of a model by denton hughes 1981 that is characterized by quasi parabolic cross sections and symmetry about the load centre both global northwestern europe as a whole and regional subsets of the data solutions have been made for earth model parameters and ice height scaling parameters the key results are as follows 1 the response of the upper mantle to the changing ice and water loads is spatially relatively homogenous across scandinavia the north sea and the british isles 2 this response can be adequately modelled by an effective elastic lithosphere of thickness 65 85 km and by an effective upper mantle viscosity from the base of the lithosphere to the 670 km depth seismic discontinuity of about 3 4 1020 pa s the effective lower mantle viscosity is at least an order of magnitude greater 3 the ice thickness over scandinavia at the time of maximum glaciation was only about 2000 m much less than the 3400 m assumed in the denton hughes model 4 the ice profiles are asymmetric about the centre of the ice sheet with those over the western part being consistent with quasi parabolic functions whereas the ice heights over the eastern and southern regions increase much more slowly with distance inwards from the ice margin

controls on reservoir heterogeneity of tight sand oil reservoirs in upper triassic yanchang formation in longdong area southwest ordos basin china implications for reservoir quality prediction and oil accumulation abstract compared to conventional reservoirs pore structure and diagenetic alterations of unconventional tight sand oil reservoirs are highly heterogeneous the upper triassic yanchang formation is a major tight oil bearing formation in the ordos basin providing an opportunity to study the factors that control reservoir heterogeneity and the heterogeneity of oil accumulation in tight oil sandstones the chang 8 tight oil sandstone in the study area is comprised of fine to medium grained moderately to well sorted lithic arkose and feldspathic litharenite the reservoir quality is extremely heterogeneous due to large heterogeneities in the depositional facies pore structures and diagenetic alterations small throat size is believed to be responsible for the ultra low permeability in tight oil reservoirs most reservoirs with good reservoir quality larger pore throat size lower pore throat radius ratio and well pore connectivity were deposited in high energy environments such as distributary channels and mouth bars for a given depositional facies reservoir quality varies with the bedding structures massive or parallel bedded sandstones are more favorable for the development of porosity and permeability sweet zones for oil charging and accumulation than cross bedded sandstones authigenic chlorite rim cementation and dissolution of unstable detrital grains are two major diagenetic processes that preserve porosity and permeability sweet zones in oil bearing intervals nevertheless chlorite rims cannot effectively preserve porosity permeability when the chlorite content is greater than a threshold value of 7 and compaction played a minor role in porosity destruction in the situation intensive cementation of pore lining chlorites significantly reduces reservoir permeability by obstructing the pore throats and reducing their connectivity stratigraphically sandstones within 1 m from adjacent sandstone mudstone contacts are usually tightly cemented carbonate cement 10 with low porosity and permeability lower than 10 and 0 1 md respectively the carbonate cement most likely originates from external sources probably derived from the surrounding mudstone most late carbonate cements filled the previously dissolved intra feldspar pores and the residual intergranular pores and finally formed the tight reservoirs the petrophysical properties significantly control the fluid flow capability and the oil charging accumulation capability of the chang 8 tight sandstones oil layers usually have oil saturation greater than 40 a pore throat radius of less than 0 4 m is not effective for producible oil to flow and the cut off of porosity and permeability for the net pay are 7 and 0 1 md respectively

geochemical characteristics of he and co 2 from the ordos cratonic and bohaibay rift basins in china abstract according to the compositional and isotopic analyses of he co 2 and ch 4 of 95 gas samples from the ordos basin and 76 gas samples from the bohaibay basin in china this study carried out a detailed investigation on the geochemical characteristics of helium and co 2 from the cratonic and rift basins especially the cratonic ordos basin and rift bohaibai basin in china compared to the rift bohaibay basin the cratonic ordos basin has lower level of helium and co 2 lower r ra ratio and lower 13 c co2 maximum value when the content of co 2 is 2 associated with the hydrocarbon generation process and inorganic co 2 from the thermal decomposition of carbonates or dissolution of organic acid rift basin can also have co 2 20 and 13 c co2 of 6 2 or 4 9 which is of volcanic magmatic or mantle derived origin while cratonic basin has no such type of co 2 the cratonic basins ordos sichuan have co 2 13 c co2 i e 25 6 0 8 26 4 the rift basins have higher level of co 2 r ra ratios and 13 c co2 values the content of co 2 can reach 100 the r ra ratio can be up to 6 45 and the variation range of 13 c co2 is 34 7 27 bigger variation range of 13 c co2 implies stronger tectonic activities which is not favorable for the gas accumulation while smaller variation range means more stable structure which is favorable for the discovery of large gas fields sample in the cratonic basin in china generally has ch 4 3 he of 10 9 10 12 and r ra 4 3 he of 10 5 10 13 and r ra of 0 1 6 45 it is concluded that methane with ch 4 3 he 10 8 is of inorganic origin and methane with ch 4 3 he 10 11 is of organic origin the regression equation for the ch 4 3 he r ra in the cratonic basin is y 3e 11e 46 28x and it is y 4e 10e 1 791x in the rift basin both ordos and bohaibay basins found gas wells with he 0 05 which has significant commercial values and provides a clue for the exploration of helium rich gas fields traps with r ra 2 is a favorable clue for the discovery of co 2 gas fields seven co 2 gas fields have been found in the bohaibay basin but no systematic development has been carried out and only some liquid co 2 has been injected for tight oil from the huagou co 2 gas field

isotope reversals and universal stages and trends of gas maturation in sealed self contained petroleum systems abstract isotope geochemistry is now a tool for shale gas exploration largely due to the association of isotope reversals with mature highly productive shale gas its utility however depends on an understanding of the isotope systematics for the particular region of interest as well as for shale gas maturation in general this paper reviews and re examines isotope data from four published papers that include shale gas from the barnett and fayetteville shales rodrigez and philp 2010 zumberge et al 2012 and gas from fractured reservoirs in the appalachians burruss and laughrey 2010 and the foothills of the western canada sedimentary basin wcsb tilley et al 2011 new shale and tight sandstone gas data are also presented for the wcsb comparisons of these data show that the progression through three stages of gas maturation pre rollover zone rollover zone and post rollover zone is universal in sealed self contained petroleum systems and that each zone has characteristic isotopic relationships and trends that are seen in all areas examined gases in the pre rollover zone are isotopically normal 13 c methane 13 c ethane 13 c propane unless mixing of gases from different sources has occurred in the rollover zone 13 c ethane and 13 c propane become progressively more negative as 13 c methane becomes less negative and ethane and methane are reversed 13 c ethane 13 c methane only towards the most mature portion of the rollover zone at the beginning of the post rollover zone 13 c ethane 13 c methane but as 13 c ethane and 13 c propane become increasingly less negative at varying rates ethane and propane may or may not be reversed with respect to each other at the highest maturities 2 h methane in gases of the post rollover zone approaches isotopic equilibrium with local formation water generally becoming more negative with increasing maturity correct assignment of maturity stage could be of importance because the rollover zone may represent the peak of high productivity shale gas whereas the post rollover zone may represent a decline in productivity burruss and laughrey 2010

gas isotope reversals in fractured gas reservoirs of the western canadian foothills mature shale gases in disguise isotopically reversed gases 13c methane 13c ethane 13c propane occur in fractured mixed clastic carbonate reservoirs of the permian and the triassic in the foothills at the western edge of the western canada sedimentary basin wcsb the 13c methane values 42 to 24 gas dryness and organic maturity ro 2 2 are indicative of mature gases and gas maturity generally increases with reservoir age and from the southeast to the northwest the 13c ethane values range from 44 to 25 with the less negative values in isotopically normal gases to the northeast of the gas fields we studied to explain the gas isotope reversals observed in the wcsb foothills we adopt the concept of a closed system shale in which simultaneous cooking of kerogen oil and gas yields gas with light 13c ethane and heavy 13c methane this gas was released from shales and trapped in fractured folds of brittle clastic carbonate rocks during deformation and thrust faulting of the laramide orogeny creating some of the most prolific gas pools these gases are actually mature shale gases local high abundances of h2s and co2 are most likely the products of thermochemical sulfate reduction tsr reactions in anhydrite rich interbeds and underbeds that admixed to the released shale gas during the tectonic event no evidence exists that tsr is responsible for the isotope reversals variations in 13c ethane are likely caused by local differences in thermal history the timing of gas release from shale and the timing of the fault and fold development less negative 13c ethane values resulting in isotopically normal gases to the northeast of the fields and in the underlying devonian carbonates likely reflect a more open shale system where the earliest generated gas was lost we suggest that isotopic reversals are restricted to closed system maturation and that their magnitude may be related to the relative volume of gas retained in shales

origins of partially reversed alkane δ13c values for biogenic gases in china with increasing molecular weight 13c values of hydrocarbon gases change in two different manners the normal order would be 13c1 13c2 13c3 13c4 partially reversed order is common in gas samples from sedimentary basins in china which can be attributed to one or several of the following four mixing processes a mixing of biogenic and abiogenic gases b mixing of sapropelic and humic sourced gases c mixing of gases from the same types of source rocks with different maturity and d mixing of gases from the same source rock interval of varying maturity

paleogeographic reconstructions of sea level change and coastline migration on the northwestern black sea shelf over the past 18 kyr abstract the paper discusses the main questions of black sea level change during the late pleistocene to holocene based on high resolution lithological genetic and paleogeolographic analyses of the northwest black sea shelf and prichernomorean limans estuaries based on the study of ancient coastlines wave generated coastal landforms such as beaches with radiocarbon dating a paleogeographic map of the northwest shelf is constructed for the period from 18 to 9 2 kyr bp statistical data processing instrumental observations show a direct and robust relationship between sea level and river discharge at intra annual and multi annual periodicities periodicity of sea level change at different frequencies and lengths is calculated using spectral and wavelet analysis for the periodicity investigations analysis included the composition and salinity of bottom sediments of two cores reconstructed from the dnieper river discharge for the past 4000 years and data from instrumental observations for the period of 1818 2001 the results indicate statistically significant periods of sedimentation rhythms dnieper discharge and sea level change which are defined by their common climatic and astrophysical factors of variability there is a relationship between the generations of coastal landforms of dzharylgach island and the holocene transgressive regressive phases of the black sea the data support an oscillatory model of sea level development for the last 18 kyr five regressions drevnechernomorian tyraian khadzhibeian olbian phanagorean and medieval are identified in the holocene

geochemical characteristics and isotopic reversal of natural gases in eastern kopeh dagh ne iran abstract natural gas samples from two gas fields located in eastern kopeh dagh area were analyzed for molecular and stable isotope compositions the gaseous hydrocarbons in both lower cretaceous clastic reservoir and upper jurassic carbonate reservoir are coal type gases mainly derived from type iii kerogen however enriched d values of methane implies presence of type ii kerogen related material in the source rock in comparison upper jurassic carbonate reservoir gases show higher dryness coefficient resulted through tsr while presence of c 1 c 5 gases in lower cretaceous clastic reservoir exhibit no tsr phenomenon carbon isotopic values indicate gas to gas cracking and tsr occurrence in the upper jurassic carbonate reservoir as the result of elevated temperature experienced prior to the following uplifts in last 33 37 million years the 13 c of carbon dioxide and 34 s of hydrogen sulfide in upper jurassic carbonate reservoir do not primarily reflect tsr as uplift related carbonate rock dissolution by acidic gases and reaction precipitation of light h 2 s have changed these values severely gaseous hydrocarbons in both reservoirs exhibit enrichment in c 2 gas member with the carbonate reservoir having higher values resulted through mixing with highly mature completely reversed shale gases it is likely that the uplifts have lifted off the pressure on shale gases therefore facilitated the migration of the gases into overlying horizons however it appears that the released gases during the first major uplift 33 37 million years ago have migrated to both reservoirs while the second migrated gases have only mixed with upper jurassic carbonate reservoir gases the studied data suggesting that economic accumulations of natural gas shale gases deeper than upper jurassic carbonate reservoir would be unlikely

pleistocene water intrusions from the mediterranean and caspian seas into the black sea the hydrological balance of the black sea is governed by riverine input and by the exchange with the mediterranean sea a speleothem record from a cave in northern turkey that tracks the isotopic signature of black sea surface water suggests an open connection to the mediterranean sea in at least twelve periods in the past 670 000 years

stable and radioactive carbon in forest soils of chhattisgarh central india implications for tropical soil carbon dynamics and stable carbon isotope evolution abstract soils from two sites viz kotumsar and tirathgarh located 5 km apart in a tropical reserve forest 18 52 n 81 56 e in central india have been explored for soil organic carbon soc content its mean residence time mrt and the evolution of stable carbon isotopic composition 13c soc stocks in the upper 30 cm of soil layers are 5 3 kg m2 and 3 0 kg m2 in the upper 110 m are 10 7 kg m2 and 7 8 kg m2 at kotumsar and tirathgarh respectively soc decreases with increasing depth bomb carbon signature is observed in the upper 10 cm organic matters in the top soil layers 0 10 cm have mrts of the order of a century which increases gradually with depths reaching 3500 5000 yrs at 100 cm 13c values of soc increase with depth the carbon isotopic fractionation is obtained to be 1 2 and 3 for soils at kotumsar and tirathgarh respectively confirmed using rayleigh isotopic fractionation model the evolution of 13c in soils was also studied using a modified rayleigh fractionation model incorporating a continuous input into the reservoir the depth profiles of 13c for soc show that the input organic matter from surface into the deeper soil layers is either insignificant or highly labile and decomposes quite fast in the top layers thus making little contribution to the residual biomasses of the deeper layers this is an attempt to understand the distillation processes that take place in soc assess the extent of decomposition by microbes and effect of percolation of fresh organic matter into dipper soil layers which are important for stable isotope based paleoclimate and paleovegetation reconstruction and understanding the dynamics of organic carbon in soils

natural gas genesis and sources in the zizhou gas field ordos basin china abstract the zizhou gas field is a large tight sandstone gas field in the ordos basin china based on the analysis of the geological background gas components light hydrocarbon composition carbon and hydrogen isotope values of alkane gases and the geochemical correlation between gases of the zizhou gas field and analogs from other fields in the basin we conclude that a most natural gases in the zizhou gas field are dry with a small content of wet gas b the gases have similar carbon isotopic and light hydrocarbon compositions to the analogs from other fields as well as much more positive 13c values and high contents of c5 7 i alkanes and methylcyclohexanes indicating typical coal derived gas c carbon isotopic reversal in some gas samples is due to mixing of coal derived gases of different maturities d the gases are sourced from mature to high mature carboniferous permian coal measures and e the gas reservoirs represent continuous accumulations

early cretaceous intra arc ductile strain in triassic jurassic and cretaceous continental margin arc rocks peninsular ranges california the cuyamaca laguna mountain shear zone clmsz lies along the axis of the peninsular ranges batholith separating it into an eastern and western plutonic zones the shear zone involves triassic jurassic and early cretaceous plutonic units which intruded the triassic julian schist and transects the eastern edge of a cryptic lithospheric boundary separating oceanic crust on the west from continental crust on the east the julian schist crops out on either side of the cryptic lithospheric boundary and is interpreted to represent an overlap sequence this structural stratigraphic relationship indicates that the contrasting lithospheric types must have been juxtaposed prior to approximately the triassic time and as a result the clmsz probably developed in an intra arc setting at least two periods of deformation produced the polygenetic clmsz structures that formed during d1 include s1 and l1 in triassic jurassic and early cretaceous orthogneisses s1 a pervasive nw striking and ne dipping mylonitic gneissosity obliterates nearly all traces of an older magmatic fabric l1 plunges steeply to the ne lies within the plane of s1 and is locally a well developed stretching lineation d1 structures can be traced from the 115 ma oriflamme canyon protomylonite into the adjacent julian schist and are represented by a well developed s c mylonitic structures indicative of ne sw contraction d1 structures in the oriflamme canyon protomylonite and in the 118 ma pine valley granodiorite developed while these plutons were incompletely solidified hence d1 probably occurred between 118 and 115 ma and had culminated in the 105 my emplacement of the las bancas tonalite normal convergence 125 to 115 ma between the north american and farallon plates is coincident with d1 and the syntectonic emplacement of the pine valley granodiorite and the oriflamme canyon protomylonite this relationship suggests that the mechanically weak thermally and melt softened cryptic lithospheric interface between oceanic and continental lithosphere may have yielded during the normal convergence event resulting in the concentration of strain into the clmsz during arc magmatism such a conclusion underscores the possibility of using intra arc structures to deduce convergence patterns as elegantly argued in several recent papers a 12 km long normal sense shear zone transects d1 structures and formed during d2 mesoscopic structure associated with the normal sense shear zone includes s2 l2 and c2 d2 structures are the record of ne sw extension between 105 and 94 ma they may be related to the vertical loading of the clmsz by the hanging wall block of the westward verging santa rosa and borrego springs mylonite belts or they may represent an early local response to magmatically and structurally overthickened gravitationally unstable crust in the latter interpretation d2 structures are the harbingers of tertiary aged gravity driven collapse of the sw cordilleran margin

the holocene sea level story since 7500 bp lessons from the eastern mediterranean the black and the azov seas abstract this paper addresses the obvious controversy between the so far published sea level curves of the black sea and the mediterranean it starts with a discussion of the methods of reconstructing sea level curves the evaluation of sea level indicators and the application of the radiocarbon dating method at least since 7500 bp when the black sea and the mediterranean were connected both water bodies must have reacted synchronously on glacio eustatic changes it is documented that none of the mediterranean sea level curves shows the major wiggles postulated for the black sea which are supposed to reflect trans and regression cycles the very shallow bathymetric condition of the azov sea and the northern black sea should have led to considerable and traceable shoreline displacements there is neither archaeological nor historical evidence of mid and late holocene regressions of several meters the tectonic setting of the black and azov seas implicates that the tectonic signal often overrides the eustatic one therefore only local sea level curves can be established in this paper based on vibracores a locally valid sea level curve for the taman peninsula is demonstrated layers of paralic peat were used as sea level indicators and for 14 c dating the shape of this curve follows the one known from the mediterranean this study also revealed that the present peninsula of taman evolved out of a former archipelago

geochemistry and accumulation of carbon dioxide gases in china we propose the following identification indicators for co2 of different origins based on data obtained from analyzing the molecular composition of 1198 gas samples the co2 carbon isotope values of 390 samples and the helium isotope composition of 256 samples collected from wells of 16 oil and gas bearing basins and gas seepages in china and reviewing literature on organic and inorganic co2 throughout the world co2 is of organic origin if co2 content 13cco22 is of inorganic origin if dgr13cco2 8 pmil or co2 60 and co2 is of either organic or inorganic origin or a mixtur of organic and inorganic origins if 10 pmil 13cco213cco2 values of organic co2 mainly range from 10 to 22 pmil in tectonically stable oil and gas bearing basins where deep faults and magmatism are undeveloped organic co2 occurs almost exclusively in tectonically active oil and gas bearing basins where active faults and magmatism are present or in areas of modern volcanic activity the dgr13cco2 values of inorganic co2 range from 2 to 8 pmil and are distributed along faults the inorganic co2 with a dgr13cco2 value of 0 3 pmil is of metamorphic origin and that with dgr13cco2 values of 6 2 pmil is mantle derived and of magmatic origin in china the dgr13cco2 values of inorganic co2 gas pools range from 3 41 to 8 44 pmil and the helium ratio r ra is 1 which indicates that these gases are typically derived from the mantle

holocene forest dynamics in northwestern romnania pollen analyses and ams radiocarbon measurements were carried out on peat deposits from the former crater lake preluca tiganului located in a mid altitude area of the gutaiului mountains nw romania in order to reconstruct the postglacial vegetation history at the lateglacial holocene transition the open vegetation was replaced by forest suggesting a fast response to climatic warming the rapid expansion of pinus betula and later picea may be due to their existence in the area during the lateglacial at approximately 11 250 cal yr bp the dense forest was composed primarily of ulmus and some picea betula and pinus a small population of ulmus might also have survived in the area during the lateglacial at 10750 cal yr bp quercus tilia and fraxinus followed by corylus at c 10200 cal yr bp expanded significantly in the forest the delay of approximately 550 years in their establishment as compared to the expansion of ulmus was probably due to their immigration from more distant localities

s type granitoids and an i s line in the peninsular ranges batholith southern california peraluminous to metaluminous s type granitoids occur in the central and eastern parts of the peninsular ranges batholith southern california as highly deformed plutons and anatectic migmatites within metapelitic prebatholithic wallrocks of upper amphibolite fades the granitoids overlap in age with and have undergone a structural history similar to that of the early cretaceous i type granitoids that occur mainly to the west initial 87 sr 86 sr ratios greater than 0 7079 and 18 o greater than 11 8 indicate a significant metasedimentary component in the source rocks of the s type granitoids an i s line that defines the westernmost extent of these rocks lies close to gravity age isotopic and prebatholithic wallrock contrasts within the batholith and together these features probably mark a fundamental change in the mesozoic crust if the western part of the batholith represents an upper jurassic and lower cretaceous accreted tectonostratigraphic terrane then the zone that contains these features may represent a terrane boundary we propose that the s type granitoids and associated migmatites developed at midcrustal levels as a result of collision and crustal thickening and rose as diapirs some dragging an envelope of migmatite and wallrock with them the zone of intense metamorphism and deformation that now forms the axis of the batholith has been uplifted relative to the western part of the batholith possibly as a consequence of unloading

mud coated intraclasts a criterion for recognizing sandy mass transport deposits deep lacustrine massive sandstone of the upper triassic yanchang formation ordos basin central china abstract numerous examples of sandy mass transport deposits smtds in deep marine and deep lacustrine environments have been documented by researchers worldwide in recent years however it is an enormous challenge that how to distinguish the subaqueous mass transport processes from the depositional records after the rigorous examination of several outcrops in the ordos lacustrine basin in central china we propose that the mud coated intraclasts in the deep water thick massive sandstone of the yanchang formation are a viable criterion to recognize deposition from sandy debris flows in delta front environments these so called mud coated intraclasts are a newly discovered special depositional phenomenon in the massive clean sandstones in china s lacustrine basins a mud coated intraclast generally consists of two components an inner core and a mud coating the inner core is generally composed of muddy blobs or sandy lumps the mud coatings are generally composed of thin shales or mud rich fine grained sediments the inner core which is generally coated by nearly concentric ring shaped mud coatings is embedded in massive deep water sandstones because these features have never been documented in the geological literature the present authors called them mud coated intraclasts in the present study the depositional features suggest that the sediments that contain these mud coated intraclasts were characterized by en masse emplacement i e a bingham plastic behavior and were supported by the strength of the plastic medium at all times i e no flow transformations occurred during their transport and deposition accordingly mud coated intraclasts are one of the most significant criteria that indicate sandy debrites as the origin of the deep water thick massive sandstones in the yanchang formation this diagnostic feature may be useful to identify analogous smtds in other locations

sedimentary control on the formation of a multi superimposed gas system in the development of key layers in the sequence framework abstract based on core observations well logs and test results of siderite bearing mudstone from the benxi formation to the member 2 of the shanxi formations in the linxing block northeastern ordos basin a logging identification model for siderite bearing mudstone key layer was established the porosity characteristics and sealing property were quantitatively evaluated by logging data sedimentary control on the formation of multi superimposed gas bearing system in the development of key layers in the sequence framework was also discussed the results showed that the siderite bearing mudstone has obvious logging response characteristics e g high photoelectric absorption cross section index pe high density den high amplitude natural gamma ray gr low acoustic ac low resistivity m2rx and low neutron porosity cncf the quantitatively evaluated results of the porosity characteristics and sealing property for the key layer showed that the key layer has the characteristics of low porosity with an average of 1 20 percent low permeability with an average of 2 29 10 8 m 2 and high breakthrough pressure with an average of 12 32 mpa in the study area this layer acts as an impermeable gas barrier in a multi superimposed gas system the results also indicated that the material composition of the multi superimposed gas bearing system can be established by the sequence stratigraphic framework the sedimentary evolution results in a cyclic rhythm of material composition vertically the spatial distribution of the corresponding transgressive event layer near the maximum flooding surface mfs in the sequence framework restricts the spatial distribution of the key layer with high breakthrough pressure and low porosity which constitutes the gas bearing system boundary the siderite bearing mudstone formed near the mfs in the second order sequence and constitutes a stable comparison of the first order gas bearing system boundary which has a wide range of regional distribution and stable thickness the siderite bearing mudstone formed near the mfs in the third order sequence is often incompletely preserved due to the late underwater diversion channel erosion and cutting this layer forms the coal bearing reservoirs which we termed as a second order gas bearing system in adjacent third order sequences to form a uniform gas bearing system

structure emplacement and lateral expansion of the san jose tonalite pluton peninsular ranges batholith baja california mexico abstract the 108 km2 san jose pluton forms part of the jurassic to cretaceous peninsular ranges batholith of northern baja california mexico the pluton was formed by three nested southward migrating intrusive pulses and the internal contacts between them indicate juxtaposition while the adjoining pulses were magmas shrimp u pb zircon data indicate that the entire pluton was emplaced in less than 4 4 m y ages of the individual pulses cannot be separated at the 95 confidence interval owing primarily to low uranium content of zircon detailed structural data and geologic mapping are consistent with a component of asymmetrical lateral expansion at the site of emplacement the direction of maximum lateral expansion may have been controlled by thermal compositional and resulting rheological gradients in the surrounding wall rocks a carapace of predominantly solid state deformation marks the northern two thirds of the pluton and the early stages of this fabric may have formed in the presence of a small amount of melt lack of evidence for syn to post emplacement regional ductile deformation around the pluton suggests that this carapace was deformed during the lateral expansion of the pluton

mineralogy and geochemistry of the no 6 coal pennsylvanian in the junger coalfield ordos basin china abstract this paper discusses the mineralogy and geochemistry of the no 6 coal pennsylvanian in the junger coalfield ordos basin china the results show that the vitrinite reflectance 0 58 is lowest and the proportions of inertinite and liptinite 37 4 and 7 1 respectively in the no 6 coal of the junger coalfield are highest among all of the late paleozoic coals in the ordos basin the no 6 coal may be divided vertically into four sections based on their mineral compositions and elemental concentrations a high boehmite content mean 6 1 was identified in the no 6 coal the minerals associated with the boehmite in the coal include goyazite rutile zircon and pb bearing minerals galena clausthalite and selenio galena the boehmite is derived from weathered and oxidized bauxite in the weathered crust of the underlying benxi formation pennsylvanian a high pb bearing mineral content of samples zg6 2 and zg6 3 is likely of hydrothermal origin the no 6 coal is enriched in ga 44 8 g g se 8 2 g g sr 423 g g zr 234 g g rees 193 3 g g hg 0 35 g g pb 35 7 g g and th 17 8 g g gallium and th in the no 6 coal mainly occur in boehmite and the pb bearing selenide and sulfide minerals contribute not only to se and pb contents in the coal but also probably to hg content a high zr content is attributed to the presence of zircon and sr is related to goyazite the rees in the coal are supplied from the sediment source region and the rees leached from the adjacent partings by groundwater

the pleistocene hominid site of ternifine algeria new results on the environment age and human industries a new multidisciplinary research program started in 1981 provided new data on the stratigraphy fauna and human industries as well as the first results on paleomagnetism and sedimentology for the ternifine site in algeria which yielded the earliest hominid remains known in north africa the fossils were deposited in a swamp or lake surrounded by a very open dry environment the lake was fed by artesian springs that raised the underlying miocene sands although nothing suggests a camp or butchery site we discovered the first undisputable bone artifact in this site the earliest known in this part of africa according to paleontological data 700 000 yr b p is a likely age for the ternifine deposits which is consistent with the paleomagnetic results

early holocene marine flooding of the black sea abstract echo sounding data recorded in the black sea in 1969 imaged a chain of hills 5 to 150 m high at a depth of 2000 2200 m that resemble hills on the lower continental rise like those hills the features in the western black sea may have been created by bottom currents the easterly flowing currents inferred to have formed the hills may be related to a catastrophic flood of the black sea from the sea of marmara 7150 yr ago

age and origin of post collision baltoro granites south karakoram north pakistan insights from in situ u pb hf and oxygen isotopic record of zircons abstract origin of post collision plutonism is critical to understand the tectonothermal evolution of the over thickened continental crust in collision zones this has proven difficult to reconcile with the conventional whole rock geochemical and field based studies alone we report in situ study of zircon u pb hf and o isotopes from five samples of the baltoro plutonic unit bpu in south karakoram the plutonic unit is the western part of the southern asian margin of the india asia convergent zone baltoro granites and a biotite rich enclave yielded similar and overlapping u pb ages ranging from 26 to 15 ma hafnium isotopic composition ehf 0 is very heterogeneous ranging from 17 1 to 4 4 while the oxygen isotopic composition of the granites is homogeneous with mean 18 o ranging from 7 2 to 9 4 based on u pb geochronology and hf o isotopic composition the involvement of two main sources is suggested 1 cretaceous calc alkaline karakoram crust and 2 karakoram gneisses moreover possible involvement of metasomatized asian lithospheric mantle is supported by elevated oxygen composition of granites and identical hf composition of biotite rich enclave to the mantle derived baltoro lamprophyre however direct contribution from juvenile pristine mantle is unlikely as no juvenile mantle type hf and oxygen values were obtained this also precludes the involvement of southward juvenile arc related component of kohistan ladakh batholith our new u pb and hf data are comparable to the mesozoic karakoram batholith miocene two mica leucogranites in the pangong range and magmatism from the lhasa terrane in south tibet suggesting a genetic link between the karakoram and the rocks to the east this magmatic event is best explained by lower crust partial melting promoted by both thermal equilibration following crustal thickening and heat advection by ultrapotassic magmas associated with the breakoff of the indian continental margin

natural gas resources of the sedimentary basins in china abstract since 1980s oil and gas resource assessment in china has gone through five development stages resource assessment in different stages differs in data input methodology and key parameters resulting in significantly different conclusions on the oil and gas resource potential in china the latest round oil and gas assessment in china was completed in 2005 with the following characteristics 1 petroleum system analyses in superimposed sedimentary basins were conducted 2 several methodologies were simultaneously used including mass balance geological analogy and statistical approach 3 contrasting criteria areas were used to optimize the assessment parameters and 4 not only resource in place but also recoverable resource were estimated for the assessment result the assessment on 129 onshore and offshore basins indicates that the total aggregated mean conventional gas resource in china is 43 9 trillion cubic meters tcm or 1549 trillion cubic feet tcf including 26 9 8 1 and 8 8 tcm in onshore nearshore and southern south china sea basins respectively the total recoverable conventional gas resource is around 27 5 tcm or 970 tcf including 16 8 5 3 and 5 4 tcm in onshore nearshore and far offshore basins respectively most of these resources are distributed in six areas including the onshore tarim ordos sichuan qidam and songliao basins and the offshore areas in the east china sea and south china sea

a jurassic garnet bearing granitic pluton from ne china showing tetrad ree patterns abstract ne china is characterized by the massive distribution of phanerozoic granitoids most of them are of i and a type granites whereas s type granites are rarely documented the present work deals with the dongqing pluton a small granitic body emplaced in the southern zhangguangcai range the pluton comprises a two mica garnet granite and a garnet bearing muscovite granite the latter occurs as veins in the former the pluton shows a gradational contact with the surrounding host granites rb sr and sm nd isotope analyses on whole rocks and minerals reveal that the two types of granites were emplaced synchronously at about 160 ma the pluton was emplaced coeval with the surrounding i type granitic pluton and had a rapid cooling history it is characterized by an initial sr isotopic ratio of 0 706 slightly negative end t values 0 5 to 1 9 and young depleted mantle model ages 970 1090 ma this suggests that the parent magma originated from partial melting of relatively juvenile crust which is largely compatible with the general scenario for much of the phanerozoic granitoids emplaced in the central asian orogenic belt geochemically the granites of the dongqing pluton are peraluminous with a shand index molar ratio a cnk of 1 0 1 1 for the two mica granites and 1 2 1 3 for the garnet bearing granites all the garnet bearing granites and some of the two mica granites show tetrad ree patterns tetrad group whereas most two mica granites show normal granitic ree patterns normal group the normal group granites exhibit depletion in nb ta p and ti in spidergrams and generally weak positive eu anomalies in ree patterns by contrast the tetrad group granites manifest depletion in ba nb ta sr p and ti and significant negative eu anomalies the trace element data constrain the parental magmas to having undergone extensive magmatic differentiation during their late stage magmatic evolution intense interaction of residual melts with aqueous hydrothermal fluids resulted in the non charac charge and radius controlled trace element behavior and the tetrad effect in ree distribution patterns this in turn leads to the invalidation of the commonly used tectonic discrimination criteria derived from trace element abundances of normal granites in view of this and previous studies we conclude that there were probably no s type granites produced in ne china during the phanerozoic consequently weathered sedimentary material did not play an important role in the genesis of the strongly peraluminous granites in the zhangguangcai range

organic matter provenance and depositional environment of marine to continental mudstones and coals in eastern ordos basin china evidence from molecular geochemistry and petrology abstract cyclothems composed of interbedded mudstone coal and sandstone layers make up the taiyuan and shanxi formations in the late carboniferous to early permian in north china under a marine to continental depositional environment the cyclothems act as important fossil energy hosts such as coalbeds hydrocarbon source rocks and unconventional natural gas reservoirs organic geochemistry and petrology of mudstones and coals in the taiyuan and shanxi formations in the eastern ordos basin were studied to reveal the organic matter sources and paleoenvironments total organic carbon toc contents vary from 1 1 wt mudstone to 72 6 wt coal the samples are mainly within the oil window with the tmax values ranging from 433 to 469 c organic petrology and source biomarkers indicate that the mudstones were sourced from a mixed organic matter input and terrigenous organic matter predominates over aquatic organic matter the coals are mostly sourced by terrigenous organic matter inputs high concentrations of hopanes argue for a strong bacterial input some m z 217 mass chromatograms have peaks at the hopanes retention times as a result of high hopane to sterane ratios these hopane derived peaks do not interfere the identification of the steranes because the hopanes and the steranes have different retention times maturity dependent biomarkers demonstrate that the samples have been thermally mature which agree with the tmax values anomalously low c29 20s 20s 20r and c29 sterane ratios are present in all the samples and are interpreted as due to the terrigenous organic matter input or the coal related depositional environment in addition biomarkers and iron sulfide morphology indicate that the organic matter of the mudstones deposited in a proximal setting with shallow brackish fresh water bodies with consideration of preservation of organic matter the redox conditions are dysoxic redox oscillations resulted in the records of oxic conditions in some samples finally the coals and the mudstones mainly generate gas and have poor oil generative potential

anomalous sea floor backscatter patterns in methane venting areas dnepr paleo delta nw black sea the relation between acoustic sea floor backscatter and seep distribution is examined by integrating multibeam backscatter data and seep locations detected by single beam echosounder this study is further supported by side scan sonar recordings high resolution 5 khz seismic data pore water analysis grain size analysis and visual sea floor observations the datasets were acquired during the 2003 and 2004 expeditions of the ec funded crimea project in the dnepr paleo delta area northwestern black sea more than 600 active methane seeps were hydroacoustically detected within a small 3 96 km by 3 72 km area on the continental shelf of the dnepr paleo delta in water depths ranging from 72 m to 156 m multibeam and side scan sonar recordings show backscatter patterns that are clearly associated with seepage or with a present dune area seeps generally occur within medium to high backscatter areas which often coincide with pockmarks high resolution seismic data reveals the presence of an undulating gas front i e the top of the free gas in the subsurface which domes up towards and intersects the sea floor at locations where gas seeps and medium to high backscatter values are detected pore water analysis of 4 multi cores taken at different backscatter intensity sites shows a clear correlation between backscatter intensity and dissolved methane fluxes all analyzed chemical species indicate increasing anaerobic oxidation of methane aom from medium to high backscatter locations this is confirmed by visual sea floor observations showing bacterial mats and authigenic carbonates formed by aom grain size analysis of the 4 multi cores only reveals negligible variations between the different backscatter sites integration of all datasets leads to the conclusion that the observed backscatter patterns are the result of ongoing methane seepage and the precipitation of methane derived authigenic carbonates mdacs caused by aom the carbonate formation also appears to lead to a gradual self sealing of the seeps by cementing fluid pathways horizons followed by a relocation of the bubble releasing locations

high resolution surveys along the hot spot affected galapagos spreading center 1 distribution of hydrothermal activity the spatial density of hydrothermal activity along most mid ocean ridges is a robust linear function of spreading rate or magmatic budget but extreme crustal properties may alter this relationship in 2005 2006 we tested the effect of thickened crust on hydrothermal activity using high resolution mapping of plumes overlying the hot spot affected galapagos spreading center from 95 to 89 42 w 560 km of ridge crest plume mapping discovered only two active high temperature vent fields subsequently confirmed by camera tows though strong plume evidence indicated minor venting from at least six other locations total plume incidence ph the fraction of ridge crest overlain by significant plumes was 0 11 0 014 about half that expected for a non hot spot mid ocean ridge with a similar magmatic budget plume distributions on the galapagos spreading center were uncorrelated with abrupt variations in the depth of the along axis melt lens so these variations are apparently not controlled by hydrothermal cooling differences we also found no statistical difference for a significance level of 0 05 in plume incidence between where the seismically imaged melt lens is shallow 2 0 56 km ph 0 108 0 045 and where it is deep 3 4 0 7 km ph 0 121 0 015 the galapagos spreading center thus joins mid ocean ridges near the iceland reykjanes ridge st paul amsterdam south east indian ridge and ascension mid atlantic ridge hot spots as locations of anomalously scarce high temperature venting this scarcity implies that convective cooling along hot spot affected ridge sections occurs primarily by undetected diffuse flow or is permanently or episodically reduced compared to normal mid ocean ridges

radiocarbon evidence for the timing and rate of island development beach rock formation and phosphatization at lady elliot island queensland australia abstract lady elliot island great barrier reef is a coral cay constructed from near concentric shingle ridges composed of coral tridacna shells and bioclastic sand bound by guano derived phosphatic cement radiocarbon dating of individual tridacna samples is used to investigate the evolution of the island and place constraints on the variations in storminess of the last 3200 years a shallow platform reef existed at lady elliot since at least 6500 yrs b p shortly before 3200 yrs b p island growth by shingle progradation commenced and proceeded to the present at a rather uniform lateral rate 60 m ka 1 to leeward and 90 m ka 1 windward phosphatization may have occurred continuously or episodically at any time throughout the last 3200 years the youngest cemented ridge top is less than 770 years whereas at the base of uncemented ridges phosphatization is a modern 1950 a d process similarly low level beach rock has continued to form within the last 25 years a significant period of instability occurred less than 500 years ago during which marine erosion truncated the southwestern extremity of lady elliot island formed an eastern spit and stranded high level beach rock however the radiocarbon ages of tridacna samples from shingle ridges from lady elliot and curacoa islands are uniformly distributed kolmogorov smirnov test throughout the last 4000 years we interpret this to indicate no significant variation in ridge forming processes or fluctuation in average storminess during this interval

diversity and paleoecology of greek late miocene mammalian faunas abstract the late miocene of macedonia has yielded several rich faunal assemblages ranging from late vallesian to late turolian they may be compared to the classical localities of pikermi samos and maragheh taxonomic comparisons based upon updated faunal lists allowed us to compute faunal similarity indices which were submitted to principal component and cluster analysis on the graphs ravin de la pluie is always remote from the other macedonian fossil mammal localities it can only be explained by its vallesian age the other macedonian sites cluster next demonstrating some provinciality of this area during the turolian comparisons of the frequencies of the various taxonomic groups support the installation of a more forested environment in the latest faunal set dytiko the indices of diversity and the rank abundance curves seem also to reflect a change of the ecological conditions during the turolian the fauna of ravin de la pluie and of the vathylakkos prochoma ravin des zouaves group is marked by the predominance of 1 or 2 species while the species frequency of the dytiko set is more balanced suggesting warmer climate and less contrasted climatic conditions another way of evaluating the ecological significance of the fossil assemblages is the analysis of the distribution of the body weight of each category of mammals in each fauna when possible we used the cenogram method or a multivariate analysis of the number of species in each weight class excluding small mammals which are very rare in macedonia we have analysed in this way 25 fossil and 23 recent localities we show that although all the fossil localities are separated from the recent ones it is possible to deduce an open environment in ravin de la pluie and a more forested one in dytiko

stable isotope geochemistry of coal bed and shale gas and related production waters a review coal bed and shale gas can be of thermogenic microbial or of mixed origin with the distinction made primarily on the basis of the molecular and stable isotope compositions of the gases and production waters methane ethane carbon dioxide and nitrogen are the main constituents of coal bed and shale gases with a general lack of c2 hydrocarbon species in gases produced from shallow levels and more mature coals and shales evidence for the presence of microbial gas include 13c ch4 values less than 50 covariation of the isotope compositions of gases and production water carbon and hydrogen isotope fractionations consistent with microbial processes and positive 13c values of dissolved inorganic carbon in production waters the co2 reduction pathway is distinguished from acetate methyl type fermentation by somewhat lower 13c ch4 and higher d ch4 but can also have overlapping values depending on the openness of the microbial system and the extent of substrate depletion crossplots of 13c ch4 versus 13c co2 and d ch4 versus 13c h2o may provide a better indication of the origin of the gases and the dominant metabolic pathway than the absolute carbon and hydrogen isotope compositions of methane in the majority of cases microbial coal bed and shale gases have carbon and hydrogen isotope fractionations close to those expected for co2 reduction primary thermogenic gases have 13c ch4 values greater than 50 and 13c values that systematically increase from c1 to c4 and define a relatively straight line when plotted against reciprocal carbon number although coals and disseminated organic matter in shales represent a continuum as hydrocarbon source rocks current data suggest a divergence between these two rock types at the high maturity end in deep basin shale gas reversals or rollovers in molecular and isotopic compositions are increasingly reported in what is effectively a closed shale system as opposed to the relative openness in coal measure environments detailed geochemical studies of coal bed and shale gas and related production waters are essential to determine not only gas origins but also the dominant methanogenic pathway in the case of microbial gases

geochemical characteristics of tight gas and gas source correlation in the daniudi gas field the ordos basin china abstract the molecular composition stable carbon and hydrogen isotopes and light hydrocarbons of the upper paleozoic tight gas in the daniudi gas field in the ordos basin were investigated to study the geochemical characteristics tight gas in the daniudi gas field displays a dryness coefficient c1 c1 5 of 0 845 0 977 with generally positive carbon and hydrogen isotopic series and the c7 and c5 7 light hydrocarbons of tight gas are dominated by methylcyclohexane and iso alkanes respectively the identification of gas origin and gas source correlation indicate that tight gas is coal type gas and the gases reservoired in the lower permian shanxi fm p1s and lower shihezi fm p1x had a good affinity and were derived from the p1s coal measure source rocks whereas the gas reservoired in the upper carboniferous taiyuan fm c3t was derived from the c3t coal measure source rocks the molecular and methane carbon isotopic fractionations of natural gas support that the p1x gas was derived from the p1s source rocks the differences of geochemical characteristics of the c3t gas from different areas in the field suggest the effect of maturity difference of the source rocks rather than the diffusive migration and the large scale lateral migration of the c3t gas seems unlikely comparative study indicates that the differences of the geochemical characteristics of the p1s gases from the yulin and daniudi gas fields originated likely from the maturity difference of the in situ source rocks rather than the effect of large scale lateral migration of the p1s gases

joint development and tectonic stress field evolution in the southeastern mesozoic ordos basin west part of north china abstract major joint sets trending e w j1 ene wsw j2 ne sw j3 n s j4 nnw sse j5 nne ssw j6 nw se j7 and wnw ese j8 respectively are recognized in mesozoic strata within the southeast of ordos basin among them the j1 j2 and j3 joint sets are systematic joints while the other five joint sets j4 j5 j6 j7 j8 are nonsystematic joints there are three groups of orthogonal joint systems i e j1 and j4 sets j2 and j5 sets and j6 and j8 sets and two groups of conjugate shear fractures ene wsw and nne ssw ene wsw and ese wnw in the study area joint spacing analysis indicates that 1 layer thickness has an effect on the joint spacing but the correlation of joint spacing and layer thickness is low 2 joint density of systematic joints is greater than nonsystematic joints and the joint density of a thin layer is also greater than that of a thick layer and 3 the joints of mesozoic strata in the basin are the result of tectonic events affected by multiple stress fields all these joints in the mesozoic strata are formed in the two main tectonic events since late mesozoic times one is the westward subduction of the pacific plate beneath the eurasia plate which formed the approximately e w trending compressive stress field in the china continent the trends of the j1 joint set e w and the bisector of conjugate shear fractures composed of ene wsw and ese wnw fractures are all parallel to the trend of maximum compressive stress e w the other stress field is related to the collision of the indian and eurasian plates which formed the ne sw trending compressive stress field in the china continent the trends of the j3 joint set and bisector of conjugate shear fractures composed of ene wsw and nne ssw fractures are all parallel to the trend of maximum compressive stress ne sw finally we conclude that the j1 and j4 sets are formed in the e w trending compressive stress field and the j2 j3 j5 j6 j7 and j8 sets are formed in the ne sw trending stress field

isotopic reversals with respect to maturity trends due to mixing of primary and secondary products in source rocks abstract carbon isotopic composition 13 c reversals with respect to maturity trends have been reported for ethane and propane in barnett shale gas in the fort worth basin u s a this trend also exists in some conventional gas reservoirs such as in the ordos basin china and appalachian basin u s a fractionation during mass transport is unlikely to be a significant mechanism because its effect is minor under geological conditions it would have caused more obvious reversal for methane than for ethane and propane and mass transport can not account for the occurrence of the trend both inside and outside source rocks this paper demonstrates that the reversal may result from mixing of indigenous primary gas generated directly from kerogen and secondary gas generated from oil and condensate within source rocks and presents deconvolution results using end members derived from a kinetic isotope fractionation model the results including the wetness and mixing ratio of primary and secondary gases are consistent with geological conditions condensates may be the major precursor of the secondary gas in shale when the reversal occurs a complete trend of 13 c variations in methane and ethane with maturity is proposed that is based on the indigenous mixing mechanism

corrigendum to a holocene dinocyst record of a two step transformation of the neoeuxinian brackish water lake into the black sea quaternary international 197 2009 72 86

prompt transgression and gradual salinisation of the black sea during the early holocene constrained by amino acid racemization and radiocarbon dating abstract the restricted environment of the black sea is particularly sensitive to climatic and oceanographic fluctuations owing to its connection with the mediterranean sea via the narrow bosphorus strait the exact mechanism and timing of the most recent connection between these water bodies is controversial with debate on the post glacial history of the black sea being dependent on radiocarbon dating for numerical ages here we present new 23 accelerator mass spectrometer ams radiocarbon ages on peat and bivalve molluscs supported by the first amino acid racemization aar dating of bivalve molluscs n 66 in the black sea these data indicate infilling of the black sea during the early holocene from an initial depth 107 m below sea level and 72 m below that of the bosphorus sill these data combined with a review of previous radiocarbon ages has enabled a unique perspective on the post glacial black sea a sea level curve based on conventional and ams radiocarbon ages on peat and ams based ages on dreissena sp shells indicate the water level in the earlier lake phase continued until the early holocene to be lower than the bosphorus sill after the younger dryas ended however the absence of ams dated mollusc ages from the shelves of this basin older than the younger dryas is suggestive of sub aerial exposure of the shelves and comparatively lower water levels when the younger dryas began thus post glacial outflow from the black sea occurred through a lowered or open bosphorus seaway basin wide radiocarbon ages on peat indicate a prompt increase in water level from that of the pre existing and unconnected palaeo lake during the earliest holocene 9600 9200 cal a bp mass colonisation of the black sea by mediterranean taxa did not occur until salinity had risen sufficiently a process which took 1000 a or more from the initial transgressive event this gradual change in salinity contrasts with the prompt transgression which would have taken 400 a to occur

o sr isotopic variations in miocene granitoids from the aegean evidence for an origin by combined assimilation and fractional crystallization sr o and d h isotopic compositions have been analyzed in miocene metaluminous to slightly peraluminous i type granitoids of the central aegean individual plutonic complexes display significant variations in their 18o and initial87sr 86sr compositions d and 18o compositions of minerals and whole rocks are mostly in the magmatic range some samples from naxos and mykonos delos show low d and 18o values characteristic of meteoric water hydrothermal interaction but as a whole the changes in 18o and sr isotopic compositions as a result of hydrothermal alteration were slight even in instances where marked alteration is petrographically observable consequently the bulk rock variations of 18o from 8 1 to 12 0 and of87sr 86sr from 0 70438 to 0 71450 may be regarded as primary and indicative of the conditions of their evolution heterogeneous isotopic compositions observed in the individual plutons of serifos ikaria samos and kos may be caused by the multiple intrusion of chemically and isotopically distinct magma pulses with high viscosities and relatively rapid consolidation in most cases preventing complete homogenization the granitoids of serifos ikaria and kos display weak correlations between the initial87sr 86sr and 18o and 1 sr the granitoid province shows a positive correlation between87sr 86sr and 18o and a non linear relationship between87sr 86sr and 1 sr whereby 1 sr increases more rapidly than the isotopic ratio as the degree of fractionation of the rocks increases it is argued that assimilation of older continental material by mantle derived arc magmas with combined fractionation afc is the most plausible model to explain the chemical and isotopic characteristics of the granitoids and the geological situation in which rock types trend from granodiorites in the south west near the inferred oligocene miocene suture to granites in the center and monzonites in the north east of the province

do norwegian deep water coral reefs rely on seeping fluids hundreds of large coral reefs up to 45 m high exist a on the continental shelf and b on morainic threshold ridges in fjords of northern mid and southwest norway they occur in water depths between 400 and 40 m and contain a large variety of megafauna the most common frame building coral is lophelia pertusa l the oldest reef found to date is 8600 calendar years old determined by radiocarbon dating of buried lophelia skeleton even though many of these reefs have been known to science for over 200 years there is as yet no viable and unifying hypothesis to explain their existence in deep cool waters other than perhaps the hydraulic theory presented by the author in 1990 it states that primary producers mainly bacteria are locally formed and concentrated at reef locations due to seepage of light hydrocarbons mainly methane on the continental shelf and nutrient rich groundwater in the fjords the hydraulic theory is supported by the following topographic reflection seismic and geochemical indicators for the continental shelf reefs a seaward dipping sedimentary permeable strata enhanced acoustic seismic reflectors adjacent pockmark craters locally elevated light hydrocarbon sediment content locally elevated seawater methane content for the fjord reefs b threshold morainic substratum rather than adjacent hardrock substratum sub surface dipping sedimentary layers h2s smell of near surface sediment samples these indicators or reef associated observations have been documented by german british and norwegian researchers over the last 10 15 years however all the listed indicators do not necessarily occur at each of the respective shelf and fjord reef locations simultaneously

geology and paleomagnetism of el potrero pluton baja california understanding criteria for timing of deformation and evidence of pluton tilt during batholith growth the 102 ma el potrero pluton in the western foothills of sierra san pedro martir in north central baja california was emplaced during a long period of contractional deformation bracketed between 132 and 85 ma that affected this segment of the peninsular ranges batholith the pluton records regional and emplacement related deformation manifested by 1 a solid state fabric developed on its eastern contact which is produced by eastward lateral pluton expansion 2 cleavage triple point zones in the host rock nw and se of the pluton 3 subhorizontal ductile shear zones indicative of top to the east transport 4 magmatic and tectonic foliations parallel to regional structural trends and regional shear zones 5 variable axial ratios of microgranitoid enclaves close to pluton wall rock contacts 6 evidence of brittle emplacement mechanisms in the western border of the pluton which contrast with features indicating mainly ductile mechanisms toward the east and 7 markedly discordant paleomagnetic directions that suggest emplacement in an active tectonic setting the overall mean for 9 accepted paleomagnetic sites is dec 34 6 i 25 7 k 88 3 95 5 5 and is deviated 35 with respect to the reference cratonic direction this magnetization is interpreted to indicate a combination of tilt due to initial drag during vertical diapiric ascent or westward lateral oblique expansion of the adjacent san pedro martir pluton and later rotation 15 by rosarito fault activity in the southwest this rotation may have occurred as eastward contraction acted to fill the space emptied by the ascending san pedro martir pluton the rosarito fault may have tilted several plutons in the area sierra san pedro martir el potrero san jose and encinosa magnetic susceptibility fabrics for 13 sites reflect mostly emplacement related stress and regional stress paleomagnetic data and structural observations lead us to interpret the el potrero pluton as a syntectonic pluton emplaced within a regional shear zone delimited by the main martir thrust and the younger rosarito fault

genesis of tight sand gas in the ordos basin china abstract based on molecular and stable carbon isotope composition of a large collection of gas samples and integrated with the geological context this article discusses the genesis and migrational characteristics of natural gases from the giant tight sand gas fields of the upper paleozoic strata ordos basin upob our results show that the upob gas is mostly derived from coaly source rocks with a minor contribution of oil associated gas probably from the interbedded carbonate source rocks gas isotope data suggest that the yulin zizhou gas field was likely formed from a single gas charge with no significant alteration whereas the sulige field contains a mixture of gases from successive charges with multiple maturity levels the geographical variation in the observed gas composition is attributed primarily to the effect of source rock maturity with no explicit geochemical fractionation caused by long distance lateral migration

sequence stratigraphy and coal accumulation of lower cretaceous coal bearing series in erlian basin northeastern china the detailed depositional systems and basin evolution of lower cretaceous coal bearing strata in the erlian basin of northeastern china were analyzed based on extensive borehole and outcrop data a total of 7 facies associations are interpreted and consist of 14 distinct lithofacies with lithologies including conglomerates sandstones siltstones mudstones shales and coals five third order sequences were recognized and their internal lowstand transgressive and highstand systems tracts were defined based on six key sequence stratigraphic boundaries these boundaries were represented by regional unconformities basal erosional surfaces of incised valley fills interfluvial paleosols and abrupt depositional facies reversal surfaces sequences i v correspond to the rift initiation stage the early rift climax stage the late rift climax stage the immediate postrift stage and the late postrift stage of the basin respectively the preferred sites for coal accumulation were braided fluvial delta plain meandering fluvial delta plain and littoral shallow lake environments the major coal seams formed during the early and late transgressive systems tract of sequences iii iv and v which were well developed in the eastern northeastern and northeastern parts of the erlian basin respectively three coal depositional models were summarized in the sequence stratigraphic framework including types 1 2 and 3 corresponding to the newark type newark richmond type and richmond type respectively these coal depositional models were closely related to the basin evolution these results could provide preferred depositional environments and favorable areas of coal and coalbed methane cbm for the exploration and development of coal and cbm in the erlian basin with the jiergalangtu huolinhe baiyinhua and a nan sags recommended as the key sags

the dynamic history of 220 million years of subduction below mexico a correlation between slab geometry and overriding plate deformation based on geology paleomagnetism and seismic tomography global tectonic reconstructions of pre cenozoic plate motions rely primarily on paleomagnetic and geological data from the continents and uncertainties increase significantly with deepening geological time in attempting to improve such deep time plate kinematic reconstructions restoring lost oceanic plates through the use of geological and seismic tomographical evidence for past subduction is key the north american cordillera holds a record of subduction of oceanic plates that composed the northeastern panthalassa ocean the large oceanic realm surrounding pangea in mesozoic times here we present new paleomagnetic data from subduction related rock assemblages of the vizcaino peninsula of baja california mexico which yield a paleolatitudinal plate motion history equal to that of the north american continent since late triassic time this indicates that the basement rocks of the vizcaino peninsula formed in the forearc of the north american plate adjacent to long lived eastward dipping subduction at the southern part of the western north american continental margin tomographic images confirm long lived uninterrupted eastward subduction we correlate episodes of overriding plate shortening and extension to flat and steep segments of the imaged slab by integrating paleomagnetic geological and tomographic evidence we provide a first order model that reconciles absolute north american plate motion and the deformation history of mexico since late triassic time with modern slab structure

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

isotopic reversal rollover in shale gases produced from the mississippian barnett and fayetteville formations abstract ethane propane and carbon dioxide show reversed carbon isotopic maturity trends in natural gas produced from the barnett and fayetteville shales at thermal maturities greater than 1 5 vre at this high level of thermal maturity the iso butane to n butane ratio also reverses suggesting wet gas cracking has occurred generating more gas molecules in the same volume resulting in overpressure and increased stabilized production rates in the barnett hydrothermal fluids from the nearby ouachita thrust front apparently enhanced the maturity of the fayetteville and barnett shales water hydrocarbon reactions at these high maturities may account for the isotopic reversals