formation mechanism of tight coal derived gas reservoirs with medium low abundance in xujiahe formation central sichuan basin china although xujiahe formation source rocks in the central sichuan basin china were determined to have low gas generation intensity several large scale gas fields have been found associated with this formation thus origins and formation mechanisms of natural gas in the xujiahe formation have attracted attentions of many researchers in this study geochemistry techniques were deployed to analyze natural gas and formation water in the xujiahe formation tight gas reservoir central sichuan basin by considering geologic background of the gas reservoir its formation mechanism was investigated research results show that the xujiahe formation reservoir contains an independent petroleum system with its natural gas exclusively originated from coal measure source rocks in the xujiahe formation the formation water was determined to be cacl2 type with high salinity h and o isotope values are largely deviated from those of meteoric water line indicating favorable preservation conditions for the formation water the xujiahe formation is composed of multiple coal measure source rocks and superimposed by tight sandstones the well developed formation water provides favorable conditions for generating water dissolved gas structural movements during the himalayan period induced significant uplifting of the central sichuan basin with overlying formations denudated consequently natural gas dissolved in formation water experienced depressurization and exsolution the released natural gas formed free gas phase in structural highs or provided additional natural gas supplies to existing gas reservoirs

paleo tethyan evolution of tibet as recorded in the east cimmerides and west cathaysides the paleozoic early mesozoic geology of tibet was controlled by the rift drift seafloor spreading and subduction zone tectonics of a paleo tethyan realm which evolved between the west cathaysides wc and the east cimmerides ec different suture zones with ophiolites and ophiolitic melanges high pressure metamorphic belts magmatic arcs and accretionary prism complexes separating different terranes mark multiple subduction accretion systems within this paleo tethyan domain reminiscent of the modern western pacific ocean discrete basins separated by different continental blocks and magmatic arcs constituted a complex paleogeography of paleo tethys and these oceanic strands were closed as a result of subduction with different polarities during the late paleozoic triassic the longmu tso shuanghu changning menglian suture zone ls cms in tibet represents the main tectonic boundary between the wc and ec that developed in the devonian the east kunlun a nyemaqen oceanic slab was subducted northward beneath the east kunlun terrane in northern tibet whereas the sumdo oceanic slab was subducted northward beneath the south qiangtang north lhasa terrane in southern tibet the longmu tso shuanghu changning menglian and jinshajiang ailaoshan song ma ophiolites were developed and emplaced in subduction accretion systems with opposite polarities westward and eastward beneath the north qiangtang qamdo simao indochina terrane in central tibet the jinshajiang ailaoshan song ma oceanic slab was subducted westward beneath the north qiangtang simao indochina terrane along the jinshajiang and ailaoshan song ma trenches in a trench ridge trench triple junction plate configuration the emeishan mantle plume produced a large permian basaltic terrane developed on the western passive margin of the south china block the final closure of the paleo tethyan oceanic branches resulted in continental collisions and development of a vast indosinian orogenic collage in the latest triassic jurassic

sedimentary pyrite formation an update sedimentary pyrite formation during early diagenesis is a major process for controlling the oxygen level of the atmosphere and the sulfate concentration in seawater over geologic time the amount of pyrite that may form in a sediment is limited by the rates of supply of decomposable organic matter dissolved sulfate and reactive detrital iron minerals organic matter appears to be the major control on pyrite formation in normal non euxinic terrigenous marine sediments where dissolved sulfate and iron minerals are abundant by contrast pyrite formation in non marine freshwater sediments is severely limited by low concentrations of sulfate and this characteristic can be used to distinguish ancient organic rich fresh water shales from marine shales under marine euxinic conditions sufficient h2s is produced that the dominant control on pyrite formation is the availability of reactive iron minerals calculations based on a sulfur isotope model indicate that over phanerozoic time the worldwide average organic carbon to pyrite sulfur ratio of sedimentary rocks has varied considerably high cs ratios during permo carboniferous time can be explained by a shift of major organic deposition from the oceans to the land which resulted in the formation of vast coal swamps at that time low cs ratios compared to today during the early paleozoic can be explained in terms of a greater abundance of euxinic basins combined with deposition of a more reactive type of organic matter in the remaining oxygenated portions of the ocean the latter could have been due to lower oceanic oxygen levels and or a lack of transportation of refractory terrestrial organic matter to the marine environment due to the absence of vascular land plants at that time

reflectance of dispersed vitrinite in palaeozoic rocks with and without cleavage implications for burial and thermal history modeling in the devonian of rursee area northern rhenish massif germany abstract vitrinite reflectance is used as coalification parameter in coals and as maturity and palaeotemperature indicator in sedimentary rocks in high grade diagenetic rocks i e rocks at the boundary between diagenesis and metamorphism vitrinites become increasingly anisotropic therefore it has been suggested to study maximum minimum reflectance instead of mean reflectance for rocks which reached this stage in the present study vitrinite reflectance data from a folded sequence of the northern rhenish massif germany are combined with microtectonic study of thin sections in samples in which both bedding and cleavage are present we show that vitrinites in different microtectonic domains cleavage domains and microlithons show significant differences in both maximum vitrinite reflectance and vitrinite reflectance anisotropy this behaviour is due to a strong partitioning of deformation in cleavage domains as compared to microlithons so that vitrinite reflectance is controlled by the thermal and deformation history accordingly estimation of maximum palaeotemperatures during burial should be based on vitrinite reflectance measurements in microlithons unaffected by deformation after maximum burial based on this finding burial and temperature history of the rursee area in the eastern rhenish massif is reconstructed numerical simulations indicate a maximum burial at the siegen ems boundary of about 5000 m and a maximum burial temperature of about 220 c

pore structure gas storage and matrix transport characteristics of lacustrine newark shale abstract shale gas production in the u s fuelled research activities in unconventional reservoir rock characterization most studies focused on organic rich shales of marine origin while disregarding lacustrine sequences in this study thirteen lacustrine shale samples from the newark basin nj usa are comprehensively characterised in terms of pore structure gas storage and matrix transport characteristics these thermally overmature vrr 1 4 2 7 shales have a na rich heterogeneous mineralogy with toc contents of up to 3 6 methane sorption capacity and pore structure parameters as identified with low pressure n2 physisorption microporosity bet surface area are neither interrelated with each other nor with any shale components e g clay content toc in contrast porosity shows a positive correlation with toc content which is also typical for many thermally overmature marine shale sequences correspondingly porosity and toc positively correlate to bedding parallel matrix permeability coefficients between 2 and 80 nd at 40 mpa effective stress in contrast permeability coefficients perpendicular to bedding are two to three orders of magnitude lower compared to previous studies on marine lithotypes newark shales have rather poor gas storage properties with average he porosities of 2 3 and average methane sorption capacities of 0 047 mmol g 1

inter and intra group compositional variations in apollo 15 pyroclastic green glass an electron and ion microprobe study abstract representative samples of the five compositionally distinct groups a e of apollo 15 pyroclastic green glass were systematically analyzed for major and trace element abundances by electron and ion microprobe techniques these primary magma compositions define a high co trend groups a and d and a low co trend groups b and c on sr zr ba and nd versus co variation diagrams group e glasses are significantly enriched in sr relative to the glass groups of the two trends pearce element ratio analyses and sr ca ba ca systematics indicate that olivine orthopyroxene and clinopyroxene controlled green glass compositions simple crystal liquid igneous fractionation processes involving such an assemblage however cannot explain the observed inter and intra group trace element variation trends the magmas represented by the high and low co trends are interpreted to have been erupted from two distinct but compositionally variable source regions a source mixing model involving differentiated cumulate trapped residual liquid and extremely fe rich components can successfully account for the compositional ranges of the two sources required to produce the observed chemical variations upon partial melting group e glasses appear to represent a magma erupted from a source with a more limited chemical variability the apollo 15 green glasses represent multiple eruptive events from three chemically distinct but compositionally variable source regions assuming that this mixing model is correct

assessment of shale oil potential using a new free hydrocarbon index abstract shale oil is currently a highlight and frontier field in petroleum industry however the assessment and quantitative evaluation of oil content in the shale is challenging which is one of the critical issues in understanding the resource potential here we explore a new free hydrocarbon index based on a case study in the currently most successful shale oil play case in china i e the eocene hetaoyuan formation in the biyang depression of the nanxiang basin eastern china this index s 1 represents the difference between hydrocarbon generation quantity and pyrolysis free hydrocarbon value s 1 it is new in that it considers not only the residual oil contents in the rocks like previous parameters but also the hydrocarbon expulsion and migration conditions that have rarely been focused before when s 1 1 is around 0 it is implied that the generated oil nearly has not expulsed and resided in the shale and thus there is also a good shale oil potential in contrast when s 1 0 it is implied that certain amounts of generated oils have migrated to external reservoirs and thus there is a poor shale oil potential this method has potential general implications and the results in the biyang can be used in the practical shale oil exploration

origin of lead from green glass of apollo 15426 a search for primitive lunar lead a major obstacle in lunar u pb chronology is the elusiveness of the primary pb isotopic composition and u pb ratio and therefore the pb evolution for the early history of the moon in an attempt to seek the primitive lunar pb isotopic composition green glass from lunar clod 15426 49 was studied for u th pb systematics because it is extremely mg rich and known to be the most primitive among sampled lunar volcanic rocks green glass and yellow impact glass were handpicked washed with water then washed in an acid mixture 0 3 n hbr 0 2 n hf and the washes and residues were analyzed in contrast to the pb from apollo 17 orange glass pb from the surface of the green glass spherules is totally different from that of the spherule interior but is similar to lunar surface lead data for the interior pb yield a 207pb 206pb age of 3 41 ga because of the low pb concentration and high u pb ratio observed for the interior the initial pb was poorly defined nevertheless the data indicate that lunar pb evolved in an environment with 238u 204pb 19 55 which is considerably lower than those for mare basalts around 300 but higher than values for the earth 6 8

cyclostratigraphy and orbital tuning of the terrestrial upper santonian lower danian in songliao basin northeastern china abstract the songke 1 north sk 1n borehole recovered a continuous 1541 66 m late santonian early danian terrestrial succession in songliao basin sb northeastern china it provides a unique record for improving our understanding of continental paleoclimate and ecological system in cretaceous greenhouse world here we use thorium th logging data as a paleoenvironmental and paleoclimatic proxy to conduct a detailed cyclostratigraphic study on the sk 1n core power spectra evolutionary fast fourier transformation and wavelet analysis all reveal significant decameter to meter scale sedimentary cycles in the nenjiang k 2 n sifangtai k 2 s and mingshui k 2 m formations the ratios of cycle wavelengths in these stratigraphic units are 20 5 2 1 and are interpreted as milankovitch cycles of 405 kyr and 100 kyr eccentricity 38 4 kyr obliquity and 20 kyr precession cycles respectively an astronomical time scale ats is established by tuning filtered 405 kyr eccentricity cycles to a target curve of the astronomical solution la2010d based on the magnetostratigraphic time framework of the sk 1n borehole this ats provides precise numerical ages for stratigraphic boundaries biozones geological and geophysical events and serves as a basis for correlation of strata and events between marine and terrestrial systems the cretaceous paleogene k pg campanian maastrichtian santonian campanian boundaries are estimated at core depths of 318 m 752 8 m and 1751 1 m respectively a 3 8 myr long hiatus between the nenjiang k 2 n and sifangtai k 2 s formations occurs from 76 1 to 79 9 million years ago the ages and durations of magnetochrons c33r to c30n are precisely estimated and provide new constraints on the late cretaceous geomagnetic polarity time scale gpts and south atlantic sea floor spreading rates

geochemical characteristics of natural gases in the upper triassic xujiahe formation in the southern sichuan basin sw china abstract the chemical and stable carbon and hydrogen compositions of gases in the upper triassic xujiahe formation xujiahe fm in the southern sichuan basin were analysed and compared with those of gases of the xujiahe gas pools in other areas of the sichuan basin the geochemical characteristics of the xujiahe fm gases in the southern sichuan basin are summarized as follows a gases are dominated by alkane gases and the majority of the natural gas is wet gas b the methylcyclohexane index i mcc6 and cyclohexane index i ch values of the gases are high indicating that the natural gases originated from humic organic matter c the stable carbon and hydrogen isotopes of methane and its homologues in most of the gases display a normal trend i e 13 c 1 13 c 2 13 c 3 13 c 4 indicating that the gases are primary and have not experienced secondary alteration a partial reversal of the carbon isotope trend of a few samples is explained by the mixing of gases from the same xujiahe fm source rock at different maturity levels d the carbon isotope trends of the c 1 c 4 alkanes are very similar to those of the gases produced in the western and central sichuan basin and the light hydrocarbon composition is similar to that in the central sichuan basin both findings support that the source rocks of the gases in the xujiahe fm in the southern sichuan basin are coal measures as in the western and central sichuan basin e the hydrogen isotope values of the alkane gases are higher than those in the western and central sichuan basin indicating a higher salinity of the depositional environment of the xujiahe fm in the southern sichuan basin f a small part of the natural gas in the xujiahe fm in the southern sichuan basin is oil associated gas which was probably derived from sapropelic source rocks of the lower silurian and the lower permian

three dimensional modeling study of the low permeability petroleum system of the bakken formation the bakken formation of the williston basin is a prime example of an unconventionally produced petroleum system with a low permeability reservoir that requires application of advanced technologies for commercial production a three dimensional model of the williston basin was constructed to integrate and assess the parameters that influence the generation and migration of hydrocarbons in the bakken formation this study tests the applicability of available basin and petroleum system modeling technology on an unusually low permeability petroleum system the model is based on nine surfaces constructed from log tops of thousands of wells in the study area and additional depth and isopach maps of the bakken formation members these were integrated with the established basin evolution in line with published research temperature and thermal maturity were calibrated during model construction from well temperature and geochemistry data the resulting heat flow map supports the existence of a heat flow anomaly along longitude 103w discussed controversially in the literature furthermore the results indicate that the invasion percolation migration approach best describes the distribution of petroleum accumulation and the saturated areas in the bakken members the volume of generated hydrocarbons was calculated and the extent of the highly saturated accumulation beyond the area of the high mature source was mapped furthermore it was demonstrated that petroleum accumulations beyond the high saturation zones have to be related to stratigraphic pinch outs lateral variability in permeability of the bakken members or smaller structural influences that were lost because of the resolution applied in the model

complete archive of late turonian to early campanian sedimentary deposition in newly drilled cores from the tarfaya basin sw morocco an expanded succession of organic rich marlstones and limestones deposited in the tarfaya basin provides an outstanding opportunity to closely retrace climate evolution and sea level changes during the cretaceous greenhouse period we present high resolution x ray fluorescence xrf scanning and bulk carbon and oxygen isotope records from two newly drilled sediment cores in the tarfaya atlantic coastal basin which recovered a continuous upper turonian to campanian succession of 290 m thickness the xrf core scanning records reveal three long term oscillations in the abundance of terrigenous elements increase of al ti k si and fe normalized against ca which correspond to progressive transgressive phases followed by rapid regressions during the coniacian and early santonian sea level highstands during this interval corresponding to the coniacian santonian oceanic anoxic event 3 oae 3 are characterized by overall oxygen depleted to anoxic conditions at the seafloor indicated by the high organic carbon content the presence of laminations and low log mn s high log v ca and high log br ca the upper santonian interval marks the transition from anoxic to oxic bottom water conditions prevalent through the early campanian the composite bulk carbonate 13 c curve exhibits strong similarities to the global stacked 13 c reference curve characterized by negative excursions in the early coniacian navigation and east cliff events and late santonian bracketed by the haven brow and buckle events and by positive excursions in the latest turonian hitchwood event middle coniacian wight fall event and at the santonian campanian boundary during the early campanian enhanced accumulation of fine grained carbonate and clay rich hemipelagic sediments increasing bulk carbonate 18 o and low log br ca and log v ca values indicate climate cooling associated with a substantial improvement in bottom water ventilation two long term 13 c cycles of 2 m y duration probably related to variations in earth s orbital eccentricity are associated with the long term cooling trend initiating the campanian maastrichtian climate transition toward a cool greenhouse state

gas genetic type and origin of hydrogen sulfide in the zhongba gas field of the western sichuan basin china abstract natural gases and associated condensate oils from the zhongba gas field in the western sichuan basin china were investigated for gas genetic types and origin of h 2 s by integrating gaseous and light hydrocarbon geochemistry formation water compositions s isotopes 34 s and geological data there are two types of natural gas accumulations in the studied area gases from the third member of the middle triassic leikoupo formation t 2 l 3 are reservoired in a marine carbonate sequence and are characterized by high gas dryness high h 2 s and co 2 contents slightly heavy c isotopic values of ch 4 and widely variable c isotopic values of wet gases they are highly mature thermogenic gases mainly derived from the permian type ii kerogens mixed with a small proportion of the triassic coal type gases gases from the second member of the upper triassic xujiahe formation t 3 x 2 are reservoired in continental sandstones and characterized by low gas dryness free of h 2 s slightly light c isotopic values of ch 4 and heavy and less variable c isotopic values of wet gases they are coal type gases derived from coal in the triassic xujiahe formation the h 2 s from the leikoupo formation is most likely formed by thermochemical so 4 reduction tsr even though other possibilities cannot be fully ruled out the proposed tsr origin of h 2 s is supported by geochemical compositions and geological interpretations the reservoir in the leikoupo formation is dolomite dominated carbonate that contains gypsum and anhydrite petroleum compounds dissolved in water react with aqueous so 4 species which are derived from the dissolution of anhydrite burial history analysis reveals that from the temperature at which tsr occurred it was in the late jurassic to early cretaceous and tsr ceased due to uplift and cooling thereafter tsr alteration is incomplete and mainly occurs in wet gas components as indicated by near constant ch 4 13 c values wide range variations of ethane propane and butane 13 c values and moderately high gas dryness the 34 s values in so 4 elemental s and h 2 s fall within the fractionation scope of tsr derived h 2 s high organo s compound concentrations together with the occurrence of 2 thiaadamantanes in the t 2 l reservoir provide supplementary evidence for tsr related alteration

stratigraphic and sedimentological constraints on the age and tectonic evolution of the neotethyan ophiolites along the yarlung tsangpo suture zone tibet

numerical simulation of the thermal maturation oil generation and migration in the songliao basin northeastern china abstract the discovery of the giant daqing oil field in the songliao basin led to the realisation of the significant petroleum potential of non marine basins in order to reconstruct the basin evolution and oil formation an integrated organic geochemical basin modelling study along a regional transect across the songliao basin was conducted it provided a regional heat flow evolution model and revealed post orogenic or late syn orogenic maturation in the central depression and pre orogenic maturation in the southeast uplift zone kinetic parameters of petroleum generation for the lacustrine source formations are the basis for the simulation of oil generation and migration in the songliao basin using the principle activation energy peaking at 54 kcal mol and a pre exponential factor of about 4 2 1027 ma 1 the simulation obtained a relatively good match with the measured transformation ratios the qingshankou formation in the west and east central depressions constituted the major source in the basin major oil generation migration and accumulation occurred during the early tertiary in the west central depression the generated oils migrated upwards into the yaojia formation followed by the updip migration into the daqing anticline and towards the local structural high along the west slope in contrast the oil migration in the east central depression was dominated by the downward movement from the lower member of the qingshankou formation followed by the updip migration towards the caoyang anticline the simulated oil accumulations are in good agreement with discovered oil fields implying a potential application of the model for prediction and evaluation of new exploration targets in the basin

shale oil potential and thermal maturity of the lower toarcian posidonia shale in nw europe a suite of drilling cores and outcrop samples of the lower toarcian posidonia shale ps were collected from multiple locations including the swabian alb and franconian alb of southwest germany runswick bay of uk and loon op zand well loz 1 of the west netherlands basin in order to assess the thermal maturity and quantify the petroleum generation potential of the rocks elemental analysis rock eval pyrolysis organic petrographic investigations and molecular hydrocarbon analyses were performed available literature data of the posidonia shale from luxembourg and northwest germany were used for comparison in the discussion the lower toarcian shale is more carbonate rich about 30 on average in sw germany nw germany and luxembourg and is instead more silicate rich in uk and nl with carbonate contents of about 15 on average this coincides with the relative distances of the depositional settings to the clastic source areas on the continents during the early jurassic however hi values are similar approx 500 700 mg hc g toc on average at all sampling localities exhibiting typical type ii kerogen with excellent hydrocarbon generation potential differences in relative abundance of terrigenous organic matter input are deduced from molecular indicators rock eval data and organic petrography the highest abundance of terrigenous organic matter is evident for runswick bay uk samples from outcrops of the lower toarcian shale from runswick bay uk have reached the early stage of the oil window with quite uniform t max values 425 438 c avg 433 c and a narrow range of pi production index values 0 10 0 19 substantiated by mature fluorescing characteristics of telalginite and lamalginite and vitrinite reflectance values of 0 6 0 7 wider ranges of t max values 421 443 c avg 427 c vitrinite reflectance 0 4 0 8 and production indices 0 06 0 29 suggest more variable thermal maturation ranging from immature to almost peak oil generation at the loz 1 well nl although only some intervals indicate advanced thermal maturity there in contrast the lower toarcian marlstones from the swabian and franconian alb of sw germany are clearly immature similar to the samples from luxembourg in nw germany the posidonia shale covers a wide spectrum of maturity ranging from immature to overmature source potential index spi indicates the highest value in the loz 1 nl followed by wickensen nw germany and esch sur alzette lu mainly due to differences in thickness of the studied sections the lowest value was observed in sw germany the lower toarcian jet rock in runswick bay uk is assumed to have a high shale oil potential because of its advanced thermal maturity although its spi is not high due to the limited thickness of the section studied the ps in sw germany has low shale oil potential due to low thermal maturity and limited thickness 2015 elsevier b v

guidelines for assessing the petroleum potential of coaly source rocks using rock eval pyrolysis abstract coaly source rocks are sufficiently different from marine and lacustrine source rocks in their organic matter characteristics to warrant separate guidelines for their assessment using rock eval pyrolysis the rank threshold for oil generation is indicated by the increase in bi s1 toc at rank sr 9 10 tmax 420 430 c ro 0 55 0 6 and the threshold for oil expulsion is indicated by the peak in qi s1 s2 toc at rank sr 11 12 5 tmax 430 440 c ro 0 65 0 85 the pronounced rank related increase in hi s2 toc prior to oil expulsion renders the use of immature samples inappropriate for source rock characterisation a more realistic indication of the petroleum generative potential and oil expulsion efficiency of coaly source rocks can be gained from samples near the onset of expulsion alternatively effective hi values i e his near the onset of expulsion can be estimated by translating the measured his of immature samples along the maturation pathway defined by the new zealand or other defined coal band coaly source rocks comprise a continuum of coaly lithologies including coals shaly coals and coaly mudstones determination of the total genetic potential of coaly source rock sequences is best made using lithology based samples near the onset of expulsion

organic facies of the asbian early carboniferous queensferry beds lower oil shale group south queensferry scotland and a brief comparison with other carboniferous north atlantic oil shale deposits abstract the 71 m foreshore exposure of the queensferry beds at south queensferry is currently the best accessible section of the oil shale group of the midland valley of scotland a combination of bulk organic geochemistry and kerogen microscopy palynofacies organic petrology is used to define four organic facies and one variant organic facies 1 occurs in silty mudstones has a mean toc of only 2 and type iii iv gas prone or inert kerogen hi 800 variant 3a is additionally characterised by an abundance of small 4 m spherical cells of possible cyanobacterial origin occurring in one sample adjacent to a stromatolitic limestone organic facies 2 is transitional between 1 and 3 organic facies 4 has atypically low c s ratios and corresponds to the pumpherston marine band these organic facies can also be distinguished using biomarker parameters pr ph oep c25 c15 predominant carbon number etc the hi is very strongly correlated with the relative fluorescence of the organic matter and strongly correlated with the aom phytoclast ratio and the botryococcus and total alginite contents it is inversely correlated with the diameter of black equant phytoclasts the organic rich shales thus correspond to distal lower energy anoxic conditions during periods of meromixis high preservation low dilution similar carboniferous lacustrine source rocks occur in eastern canada and east greenland all are characterised by large lateral extents 500 2 000 km2 a geographic and temporal association with strong syndepositional subsidence generally low botryococcus contents and a dominance of amorphous type ii kerogen

the character and origin of lacustrine source rocks in the lower cretaceous synrift section congo basin west africa lower cretaceous synrift lacustrine shales from the congo basin west africa have been analyzed with sedimentological and geochemical techniques to characterize source rock quality and identify triggers for deposition of intervals richest in organic carbon the sequence includes a lower active rift section deposited during active faulting and subsidence overlain by an upper late rift section deposited during reduced faulting and subsidence total organic carbon toc averages 2 3 wt throughout the active rift siliciclastic shale section 6 in marls in the lower part of the late rift section and 1 2 in deltaic shales in the upper part of the late rift section organic matter consists of mixed types i and iii kerogen in the active rift shales pure type i kerogen in the late rift marls and a type i and iii mixture in the late rift deltaic shales redox proxies indicate that the deep lake was relatively reducing throughout deposition of the active rift and lower late rift sections therefore enhanced anoxia did not trigger deposition of the richest source rocks decreased sedimentation rates in the late rift do not account for the full increase in toc nor the shift on organic matter type the richest source rocks are associated with high rates of organic productivity and chemical sedimentation indicating that flux of dissolved components to the rift lake including nutrients for algae growth was critical we propose that reduced topography associated with the late rift was necessary for efficient cycling of plant derived carbon into soil carbonate and ultimately the rift lake and for enhancing chemical weathering and nutrient flux

numerical modelling of burial and temperature history as an approach for an alternative interpretation of the bramsche anomaly lower saxony basin the lower saxony basin germany is one of the several sedimentary basins within the central european basin system in its southwestern part anomalously high maturity of organic matter has been observed to reach 4 5 vrr in upper jurassic and lower cretaceous sedimentary rocks in an area which coincides with a magnetic and a positive gravimetric anomaly this anomaly was often interpreted as the consequence of a deep seated igneous intrusion the so called bramsche massif however results obtained from calibrated numerical modelling are not in accordance with this scenario instead a burial by approximately 4 km of now eroded cretaceous rocks was revealed to be the probable cause for the anomaly data and modelling results from six boreholes and two pseudo wells support this view

lunar volcanic glasses and their constraints on mare petrogenesis abstract volcanic glasses from the apollo 11 14 15 and 16 landing sites have been analyzed for major elements and ni by electron microprobe the 19 varieties of volcanic glass define two distinct chemical arrays that provide new insights into a the petrogenesis of mare basalts and b the structure of the deep lunar interior a simple model is proposed whereby mare basaltic liquids may have been derived from two isolated cumulate systems occurring at depths of 300 km and 400 km each system was itself composed of two lithologic components low ti vs high ti that underwent hybridization assimilation or mixing to generate the large compositional range of magmas observed within each array while the distribution of the two components within each system was locally heterogeneous data indicate that the components themselves were chemically uniform on at least a regional scale the surface correlated volatiles associated with the lunar volcanic glasses seem to have come from some other reservoir within the moon the simplicity of the chemical relationships observed among the lunar volcanic glasses allow specific predictions to be made we believe that they should readily reveal any strengths or weaknesses of this new model

geochemical characterisation of early cretaceous lacustrine sediments of bima formation yola sub basin northern benue trough ne nigeria organic matter input preservation paleoenvironment and palaeoclimatic conditions the bima formation is the oldest lithogenetic unit occupying the base of the cretaceous successions in the yola sub basin of the northern benue trough it is differentiated into lower b1 middle b2 and upper b3 bima members integrated organic and inorganic geochemical studies were applied on the lacustrine sediments of the bima formation with the aim of reconstructing the palaeodepositional environment and organic matter input in response to climate and tectonism the analysed sediments were deposited in a freshwater lacustrine environment with a low salinity stratified water column and suboxic to relatively anoxic conditions as indicated by the bulk geochemical parameters the biomarkers provide evidence for a contribution of aquatic algae and microorganisms with a significant amount of terrigenous organic matter input the preservation of the organic matter is possibly attributed to the stratified water column with low salinity and suboxic to relatively anoxic conditions based on the geochemistry of major and trace elements the sediments were deposited during semi arid climatic conditions within passive continental margin setting this agrees with the tectonic events in the west and central african rift system wcars during the early cretaceous period

palaeoenvironmental conditions during deposition of the upper cretaceous oil shale sequences in the songliao basin ne china implications from geochemical analysis abstract excellent hydrocarbon source rocks oil shales containing type i organic matter om were deposited in the continental songliao rift basin during the late cretaceous a major contribution of aquatic organisms dinoflagellates green algae botryococcus and minor input from macrophytes and land plants to om accumulation is indicated by n alkane distribution steroid composition and 13 c values of individual biomarkers microbial communities included heterotrophic bacteria cyanobacteria and chemoautotrophic bacteria as well as purple and green sulfur bacteria the presence of methanotrophic bacteria is indicated by 13 c depleted methyl hopane the sediments were deposited in a eutrophic alkaline palaeolake highly reducing saline bottom water conditions and a stratified water column existed during om accumulation of the qingshankou formation and member 1 of the nenjiang formation this is indicated by low pristane phytane gammacerane index and mttc ratios and the presence of carotane and aryl isoprenoids however an abrupt change in environmental conditions during deposition of member 2 of the nenjiang formation is indicated by significant changes in salinity and redox sensitive biomarker ratios a freshwater environment and suboxic conditions in the deep water prevailed during this period higher input of terrigenous om occurred during deposition of the upper nenjiang formation good oil to source rock correlation was obtained using biomarker fingerprints of oil stained sandstone from the quantou formation and oil shales from the qingshankou formation based on the extent of isomerisation of c 31 hopanes the oil was most probably derived from oil shales of the qingshankou formation in deeper parts of the basin

the isotopic record of lunar volcanism abstract the timing and extent of lunar volcanism was determined primarily by the internal thermal evolution of the moon a late heavy bombardment produced most of the observable lunar basins easily recognized stratigraphic markers and also may have influenced lunar volcanism most of the nearside basins seem to have been produced 3 8 4 0 ga ago during a period often referred to as the lunar cataclysm the pre cataclysm period was characterized by formation of the lunar crust plutonic rocks within the crust and pre mare volcanism isotopic analysis of breccia clasts pre dating the cataclysm has yielded an outline of this period the isotopic record of post cataclysm mare volcanism is clear but incomplete because samples from the youngest mare areas are lacking specifically the isotopic data show that some lunar anorthosites formed 4 45 ga ago consistent with early formation of an anorthositic lunar crust some mg suite norites troctolites and dunites also formed approximately contemporaneously with the oldest anorthosites but others are up to 200 300 ma younger more evolved rocks granites and quartz monzodiorites also formed between 4 4 and 4 0 ga ago the earliest known pre mare volcanism at 4 25 ga ago included aluminous mare like basalts and an olivine gabbronorite similar to apollo 12 basalts kreep basalt volcanism began at least 4 1 ga ago approximately contemporaneously with that of the ancient mare like basalts and continued during the cataclysm recorded instances of high ti mare basalt volcanism began during or immediately after the cataclysm low ti mare basalt volcanism is the most recent for which samples are available the isotopic data record an early primary lunar differentiation during which mare basalt sources formed probably by crystallization of cumulus minerals from a lunar magma ocean the isotopic record of post cataclysm basalts indicates a heterogeneous lunar mantle and can be explained by partial melting of cumulate sources but more complex petrogenesis also has been suggested more complex petrogenetic processes including assimilation and assimilation fractional crystallization afc seem to be required for pre mare volcanics the isotopic data contain a hint that petrogenesis of the oldest pre mare volcanics may be linked to formation of the so called procellarum basin possibly the oldest and largest lunar basin such a basin would provide a geologic context for the pre mare volcanics and its formation may have been a defining moment in lunar history

mesozoic sedimentary evolution of the northwest sichuan basin implication for continued clockwise rotation of the south china block we present new sedimentary data integrated into a regional mesozoic stratigraphic framework to provide a detailed picture of spatio temporal variations in deposition and depocenter migration of the northwest sichuan basin the mesozoic sedimentary evolution is utilized to interpret basin subsidence history and to unravel coeval basin margin tectonics the northwest sichuan basin together with the songpan ganzi terrane behaved as a passive margin south of the qinling paleo tethys from late paleozoic to early middle triassic times and then evolved into a peripheral foreland basin in response to collision of the north and south china blocks since the late middle triassic coeval with strong north south contraction of the songpan ganzi terrane in the late triassic sinistral transpressional deformation of the longmen shan belt led to flexural subsidence of the adjacent western sichuan basin renewed basin margin fold thrust activity triggered recurrence of flexural subsidence of the northwest sichuan basin since the middle jurassic with the depocenter eventually shifting to the northwestern corner of the basin in the early cretaceous sedimentary evolution of the northwest sichuan basin and the basin margin deformation imply that the south china block had been rotating clockwise relative to the north china block throughout the mesozoic with an interim period of early jurassic tectonic quiescence a model is advanced that invokes clockwise rotation of the south china block as a driver for tectonic evolution of both the basin and adjoining structural belts and provides an explanation for several salient features that are otherwise puzzling

the depths of the mare basalt source region chemical data for the parental magmas of the nine known vlt array i pyroclastic glasses show statistically significant trends due to olivine fo83 control during their formation by partial melting the compositional scatter is largely due to compositional variations in the source regions on the 1 level this compositional scatter is small when one considers that the scale of the source region is up to 1000 km but is sufficient to make positive identification of the residual phase s in the source regions difficult nevertheless when the effects of the scatter are properly modeled it is relatively clear that olivine is the residual phase in the source region hence these data and additional constraints indicate that the source regions are at shallow depths in the moon

a biomarker study of depositional paleoenvironments and source inputs for the massive formation of upper cretaceous lacustrine source rocks in the songliao basin china abstract the abundance and composition of total organic carbon aliphatic and aromatic hydrocarbons including biomarkers and the 13c composition of total organic matter and individual compounds in core samples of the nenjiang formation from the sk 1 borehole of the songliao basin provide information on the paleoenvironmental conditions of lacustrine sediments formed during the upper cretaceous the distribution of n alkanes and their 13c composition and 4 methylsteranes and dinosteranes in the first member of the nenjiang formation k2n1 indicate that the organic matter largely originated from algal organisms and is dominated by types i and ii kerogen the occurrence of gammacerane aryl isoprenoids isorenieratane and low pristane phytane and diasterane sterane ratios further suggest a salinity stratified water column associated with anoxic bottom waters as well as possible photic zone oxygen depletion conditions during major source rock deposition of the k2n1 the organic geochemical data also indicate significantly different depositional environments for the second member of the nenjiang formation k2n2 sediments which are interpreted to have been deposited under a uniform salinity non stratified oxic water column consequently although the organic matter in the k2n2 sediments was largely derived from algal and bacterial sources the kerogen types are dominantly iib and iii due to the oxidative degradation of organic matter combined with a gradual increase in land plant input furthermore the occurrence and shift of two saw toothed distribution patterns of the 13c composition of c29 to c33 n alkanes with w and m patterns being isotopically heavy odd and even numbered alkanes respectively is suggestive of organic input shift or an unknown mechanism of carbon uptake or isotopic fractionation in particular the heavy even carbon numbered high molecular weight n alkanes is rare and needs further investigation

the ferroan anorthositic suite the extent of primordial lunar melting and the bulk composition of the moon the geochemical bimodality among compositionally pristine lunar rocks is strong evidence that a major component of the moon s crust is fundamentally unrelated to the plagioclase flotation crust that accumulated over the primordial magma ocean the ferroan anorthositic suite fas has all the characteristics expected for a series of magma ocean plagioclase flotation cumulates but we estimate based on mass balance for al2o3 that 30 wt of the crust and 20 wt of the crust s total al2o3 or roughly 15 of the bulk moon al2o3 content assumed to be 3 4 wt was emplaced by postmagma ocean mg suite serial magmatism remelting of plagioclase bearing magma ocean cumulates cannot plausibly account for the late emplacement of al2o3 because the only plagioclase rich cumulates produced by a deep ultramafic magma ocean would have mg ratios too low to engender the mg suite conceivably remelting of garnet rich magma ocean cumulates supplied the late al2o3 but only if the bulk moon al2o3 content is substantially higher than generally assumed high pressures in the magma ocean acted to enhance the py pyroxene pyroxene olivine ratio of the mo cumulates and the al2o3 content of whatever pyroxene formed remelting of pyroxene rich mo cumulates could conceivably have supplied the late mg suite al2o3 to the crust the source region would have to encompass roughly 40 wt of the mantle another possible source for late al2o3 addition is a large portion of the deepest mantle that avoided more than a slight degree of partial melting and thus remained al rich during formation of the magma ocean the source region would have to encompass 20 30 wt of the mantle ascent of diapiric masses from the lowermost mantle would likely coincide with trigger or be triggered by a large scale overturn of the gravitationally unstable mo cumulate pile with concomitant pressure release melting in which case the mg suite parental melts would be derived from a mix of deepest mo cumulates and the even deeper primitive mantle the popular giant impact hypothesis of lunar origin implies an extremely hot beginning for the moon suggesting that the deep interior was either molten or depleted in al2o3 by differentiation in hot protomoons as it formed origin of 30 wt of the moon s crust by postmagma ocean serial magmatism is more consistent with coaccretion models that form the moon without a giant hot impact in any scenario with a large fraction of the crust originating by partial remelting of deep magma ocean cumulates mass balance for al2o3 implies that the bulk moon normative py ratio must be greater than roughly 0 5 i e significantly higher than generally estimated in this respect the moon appears more compositionally similar to chondritic silicates than to the earth s upper mantle

oil and gas play maps in exploration and assessment geologic note play summary maps show the superimposed boundaries of favorable areas for all key geologic controls of oil and gas occurrence source migration reservoir trap timing seal preservation and recovery for a genetic group of prospects or fields these maps are invaluable for high grading the best areas thereby reducing exploration risks and for quantitatively estimating hydrocarbon volume and success factors in both prospect and play assessment play summary maps are based on standard exploration map suites but demand a systematic integration of all the essential geologic controls none of which can safely be ignored

microfacies and multi isotope records of anisian sequences from the upper yangtze block possible responses to tectonics and climate driven relative sea level change the middle triassic epoch is the key to understanding the environment changes after the permian triassic mass extinction the anisian badong formation is a carbonate and siliciclastic succession deposited on the yangtze platform upper yangtze block in this paper we use facies analysis combined with sequence stratigraphy of the badong formation in the nashuixi section yangtze block to discuss the anisian relative sea level changes microfacies analyses were used to define ten microfacies in four depositional facies zones tidal flat restricted platform restricted to open platform and open platform indicating an epeiric platform depositional environment the lowstand transgressive and highstand systems tracts and two sequences were identified sequence stratigraphy interpretations indicate that relative sea level at nashuixi experienced two rises in the middle anisian which is correlated with those in the yangtze block confirming that sea level changes during the anisian were of eustatic origin however a distinct regression at nashuixi occurred in the late bithynian to iiiyrian while the global sea level rose which is likely to be caused by interference from regional tectonics during iiiyrian the carbon and oxygen isotopic shifts in the nashuixi section exhibit two negative values stage in the time near end of aegean and early pelsonian which is well correlated with the global typical sections indicating two middle anisian warming events our study indicated that the relative sea level at nashuixi was controlled by global sea level change and regional tectonics indosinian orogeny and the c and o isotopes records respond to global climate change

geochemical characterization of source rocks and crude oils in the upper cretaceous qingshankou formation changling sag southern songliao basin abstract the upper cretaceous qingshankou formation is one of the main exploration target in the changling sag southern songliao basin however the origin of source rock deposition and crude oils remains undiscovered a comprehensive geochemical study including rock eval pyrolysis gas chromatography mass spectrometry and carbon isotope analysis on fifteen crude oils and twenty two source rock samples from the qingshankou formation were performed in order to provide new insights into source organic matter depositional environment and correlation between crude oils and source rocks bulk geochemical analysis on source rock samples indicates that the lower member of the qingshankou formation has more hydrocarbon generating potential than the middle member these two potential source rock members were interpreted to be deposited in slightly different environments and have different sources of organic matter determined by biomarker assemblages the lower member is organically rich average toc 1 27 wt oil prone mature and deposited under anoxic conditions with more contribution from sapropelic organic matter the middle member is organically poor average toc 0 78 wt gas prone less mature and deposited under less anoxic conditions with more terrigenous organic matter input biomarker fingerprints and carbon isotope compositions suggest that all the crude oils were genetically related and could be classified into one oil family which has significant contribution from the lower member source rocks and minor contribution from the middle member source rocks

pyrite morphology in the first member of the late cretaceous qingshankou formation songliao basin northeast china abstract the study of sedimentary pyrite morphological characteristics provides useful information on depositional environments and early diagenic processes and can be used as an indicator of redox conditions in ancient lake bottom waters the results of this study in the songliao basin in northeastern china show that euhedral crystals and framboids are the dominant pyrite forms in the mudstones of the first member of the qingshankou formation k2qn1 the framboidal size distribution indicates that during the deposition of k2qn1 redox conditions in the bottom water fluctuated from oxic dysoxic to euxinic anoxic to oxic dysoxic the presence of euxinic anoxic bottom water suggests that an anoxic event developed in the songliao ancient lake and continued for 196 ka the development of an anoxic bottom environment was the most important factor in hydrocarbon source rock formation in the songliao basin

hydrocarbon migration and accumulation in the upper cretaceous qingshankou formation changling sag southern songliao basin insights from integrated analyses of fluid inclusion oil source correlation and basin modelling abstract the upper cretaceous qingshankou formation acts as both the source and reservoir sequence in the changling sag situated in the southern end of the songliao basin northeast china an integrated approach involving determination of hydrocarbon charging history oil source correlation and hydrocarbon generation dynamic modeling was used to investigate hydrocarbon migration processes and further predict the favorable targets of hydrocarbon accumulations in the qingshankou formation the hydrocarbon generation and charge history was investigated using fluid inclusion analysis in combination with stratigraphic burial and thermal modeling the source rocks began to generate hydrocarbons at around 82 ma and the hydrocarbon charge event occurred from approximately 78 ma to the end of cretaceous 65 5 ma when a large tectonic uplift took place correlation of stable carbon isotopes of oils and extracts of source rocks indicates that oil was generated mainly from the first member of qingshankou formation k 2 qn1 suggesting that hydrocarbon may have migrated vertically three dimensional 3d petroleum system modeling was used to evaluate the processes of secondary hydrocarbon migration in the qingshankou formation since the latest cretaceous during the late cretaceous hydrocarbon mainly originated from the qianan depression migrated laterally to adjacent structural highs subsequent tectonic inversion defined as the late yanshan orogeny significantly changed hydrocarbon migration patterns probably causing redistribution of primary hydrocarbon reservoirs in the tertiary the heidimiao depression was buried much deeper than the qianan depression and became the main source kitchen hydrocarbon migration was primarily controlled by fluid potential and generally migrated from relatively high potential areas to low potential areas structural highs and lithologic transitions are potential traps for current oil and gas exploration finally several preferred hydrocarbon accumulation sites have been identified by this work like western slope southern uplift and eastern slope helping reduce the risk on targeting hydrocarbon potential reservoirs in changling sag

lithofacies and sequence stratigraphy of the barnett shale in east central fort worth basin texas ten barnett shale lithofacies have been recognized in a 223 ft 68 m long core from johnson county texas eight of these lithofacies match those previously identified in the main producing area of the newark east barnett shale field in the northern part of the fort worth basin but two new lithofacies have been identified in this core resedimented spiculitic mudstone lithofacies and lag deposits both of which are indicative of a relatively higher energy environment and downslope resedimentation of shallower water deposits the recognition of cyclical stacking patterns of the lithofacies condensed sections css and transgressive surfaces of erosion were the keys to establishing the sequence stratigraphic framework in these fine grained rocks which consists of seven stratigraphic intervals in the lower barnett shale and nine stratigraphic intervals in the upper barnett shale spectral gamma ray uranium and thorium logs aided in this objective and are recommended for future sequence stratigraphic studies of these and other shales the sequence stratigraphic framework reveals that the lower barnett shale in this area was deposited mainly in a low energy relatively deep water environment somewhat far from a terrigenous source area which probably lies to the northwest by contrast the upper barnett shale was deposited in an oxygenated shallower water environment which had a source area from the west and southwest sides of the basin the higher frequency of sea level fluctuation during development of the upper barnett shale most probably indicates periodic tectonic activity perhaps associated with a structural high that was susceptible to sea level fluctuations alternatively it could have resulted from the onset of glaciations in gondwanaland during this time this higher frequency may indicate that the upper barnett is chesterian in age because cyclicity was higher than during the osagean and meramecian stages if so there may be more high frequency cycles than recognized in this core siliceous sponge spicules are more common in this core than in more northerly cores so more brittle facies might prevail in the southern part of the fort worth basin high gamma ray log responses which are caused by a high total organic carbon and or in situ phosphate minerals are commonly found in css and can be used for regional correlations however high gamma ray phosphatic deposits that have been resedimented to downslope positions by sediment gravity flows are an exception to the previous statement correlation of the barnett stratigraphic intervals now provides a north to southeast stratigraphic framework along the fort worth basin relative hydrocarbon potential rhp is an organic geochemical parameter applied to this core and found to provide an indicator of marine transgressions and regressions we recommend continued testing and use of the rhp parameter for high frequency sequence stratigraphic analysis of unconventional gas shales

organic matter maturation under the influence of a deep intrusive heat source a natural experiment for quantitation of hydrocarbon generation and expulsion from a petroleum source rock toarcian shale northern germany four shallow boreholes were drilled in the hils syncline northern germany in order to determine quantitatively the amount of hydrocarbons generated and expelled during maturation of a typical kerogen type ii bearing source rock the holes penetrated the carbonceous lias shales posidonia shale lower toarcian and part of the adjacent dogger and lias mudstones the maturity of the organic matter in the cores recovered ranges from immature 0 48 r0 to overmature 1 45 r0 due to location of the hils syncline in the vicinity of the vlotho massif which is deep seated intrusive body facies variations of the lias within the short geographical distances in the study area are negligible organic matter mass balance calculations were based on detailed organic geochemical analyses of residual material in the lias shales kerogen bitumen etc and on the evidence of a uniform initial composition of these sediments in the study area dead carbon determinations supported this latter criterion but were not used as a parameter in the calculations about 50 of the initial kerogen was transformed into oil gas and inorganic compounds during the vitrinite reflectance increase from 0 48 to 0 88 ro and only marginally more during the maturity increase from 0 88 to 1 45 ro only a small portion of the generated material remained in the source rock even at a relatively early stage of generation 0 68 ro expulsion efficiency of oil plus gas reached a value of 86 at the end of the main generation stage 0 88 ro

geochronology and petrogenesis of apollo 14 very high potassium mare basalts rb sr k ar and sm nd isotopic studies were undertaken for two apollo 14 very high potassium vhk mare basaltic clasts from breccias 14305 and 14168 the samples are distinctly more radiogenic than other lunar mare basalts rb sr data for the whole rock and mineral separates determine internal isochrons corresponding to essentially identical ages of 3 83 0 08 b y and 3 82 0 12 b y for samples 14305 and 14168 respectively for 87rb 0 0139 b y 1 their corresponding initial 87sr 86sr ratios are indistinguishable and are 0 6995 0 0005 and 0 6997 0 0004 respectively the 39ar 40ar age spectra for the two samples are very similar and give identical plateau ages of 3 85 0 02 b y for 14305 and 3 85 0 05 b y for 14168 the identical rb sr and k ar isotopic results for the two rocks indicate that they could be derived from the same flow the sm nd isotopic data of whole rock and mineral separates for the two vhk basalts define an internal isochron age of 3 94 0 16 b y for 147sm 0 00654 b y 1 and an initial 143nd 144nd of 0 50673 21 the averaged model age relative to the chondritic initial 143nd 144nd of 0 505893 for the basalts is 4 56 0 04 b y the concordance of rb sr k ar and sm nd ages strongly suggests that vhk basalts crystallized from a melt 3 85 b y ago the rb sr and sm nd isotopic data indicate that vhk basalts show very large rb sr fractionation but no significant sm nd fractionation at the time of crystallization the source material for these basalts had a rb sr ratio similar to those of apollo 14 high a1 mare basalts and a nearly chondritic sm nd ratio extreme enrichments of rb sr and k la during the formation of vhk basalts can be adequately explained by an assimilation model that involves basalt granite interaction k rb rich components of granitic wall rocks in highland crust were selectively introduced into ascending hot high a1 mare basaltic magma upon contact a similar crustal assimilation process has been frequently observed in terrestrial mantle derived magma that ascended through the continental crust

apollo 15 yellow brown volcanic glass chemistry and petrogenetic relations to green volcanic glass and olivine normative mare basalts abstract apollo 15 yellow brown glass is one of twenty five high mg primary magmas emplaced on the lunar surface in pyroclastic eruptions forty spherules of this glass were individually analyzed by electron microprobe and inaa for major and trace elements e g sc v cr co la ce nd sm eu ho tm yb lu hf ta and u the abundances demonstrate that this primary magma was produced by partial melting of differentiated cumulates in the lunar mantle models are developed to explain the possible source regions of several apollo 15 and apollo 12 low ti mare magmas as being products of hybridization involving three ancient differentiated components of a primordial lunar magma ocean a early olivine orthopyroxene cumulates b late stage clinopyroxene pigeonite ilmenite plagioclase cumulates and c late stage inter cumulus liquid isotopic constraints on sm nd fractionation and least squares tests of potential mixing models require models of apollo 15 yellow brown glass and apollo 12 and 15 olivine mare basalts involving low f 3 cumulate remelting of sources in which olivine and orthopyroxene are residual phases models of the apollo 15 green glass composition indicate higher 4 7 degrees of melting but with only a slight preference for orthopyroxene rich relative to orthopyroxene free sources the modeled dependence on residual orthopyroxene in mare source regions places source depths at 400 km or greater in order to maintain olivine and orthopyroxene on the liquidus hybridization at such depths would likely result from convective overturn of the primordial magma ocean and suggests that separate fractionating masses were positioned at various depths our models for developing hybridized source regions of primary low ti mare magmas do not require selective contamination of primary liquids the preferred model for apollo 15 yellow brown glass is presented as the commingling of 95 early cumulate olivine orthopyroxene 1 9 clinopyroxene 0 27 pigeonite 1 7 plagioclase 0 02 ilmenite and 0 56 trapped liquid respective proportions for the apollo 15 olivine mare basalt source model are 98 5 0 37 0 0 79 0 16 and 0 13 and the proportions used for the preferred apollo 12 olivine mare basalt model are 97 6 0 73 0 24 0 77 0 42 and 0 21 our preferred model for the green glass source composition f 0 07 requires the commingling of 97 4 early olivine orthopyroxene 0 18 clinopyroxene 1 32 pigeonite 0 85 plagioclase and 0 28 trapped liquid

genetic classification of petroleum systems our genetic classification of petroleum systems is founded on a simple working nomenclature that consists of combining qualifiers from each of the following three categories 1 charge factor supercharged normally charged or undercharged 2 migration drainage style vertically drained or laterally drained and 3 entrapment style high impedance or low impedance the charge factor is estimated on the basis of the richness and volumetrics of mature source rocks the source potential index spi which combines source rock richness and thickness into a single parameter is a convenient shortcut for comparing the petroleum potential of diverse source rocks containing dissimilar kerogen types and for rapidly estimating regional charging capacity in extensively explored basins a positive correlation exists between the magnitude of spi and basin wide petroleum reserves the migration drainage style is determined from the structural and stratigraphic framework of a basin vertical migration drainage which occurs mainly through faults and fracture systems breaching a seal is characteristic of petroleum systems contained within rift basins deltaic sequences salt dome provinces wrench basins and fold and thrust belts in contrast lateral migration drainage is dominant wherever stratigraphically continuous seal reservoir doublets extend over a very large area in a tectonically stable province e g commonly foreland or intracratonic platform basins recognition of the dominant migration style helps to predict the location of zones of petroleum occurrence in relation to the hydrocarbon kitchens the entrapment style which is also dependent on the structural framework and the presence and effectiveness of seals describes the degree of resistance i e impedance working against dispersion of the petroleum charge application of these working concepts should help to significantly reduce geologic risk particularly in new ventures type exploration

comparative study of stable carbon and hydrogen isotopes of alkane gases sourced from the longtan and xujiahe coal bearing measures in the sichuan basin china abstract two sets of coal bearing measures the upper triassic xujiahe formation t 3 x and the upper permian longtan formation p 2 l have been extensively developed in the sichuan basin sw china and some large gas fields related to these coal bearing measures have been discovered the stable carbon and hydrogen isotopic composition of alkane gases sourced from the two sets of coal bearing measures t 3 x and p 2 l gases have been investigated in this study the main controls on the gas composition and isotopic abundances of gases in the sichuan basin have been identified and distinguished on the basis of their molecular and isotopic composition the carbon and hydrogen isotopic compositions of methane 13 c c1 42 5 to 26 8 d c1 173 to 107 vary widely and show a positive correlation with the thermal maturity of the source rocks the 13 c c2 value of the t 3 x and p 2 l gases in the sichuan basin ranged from 28 2 to 21 3 and showed less variations with increasing maturity from r o values of 1 2 to 2 8 however these 13 c c2 values differ greatly from that of oil associated gas in the sichuan basin thus we provide further evidence that the value of 13 c c2 is a useful parameter to distinguish coal derived and oil associated gases the hydrocarbon gases in the xujiahe and jurassic reservoirs in contrast showed little isotopic difference indicating that secondary migration has little influence on their carbon and hydrogen isotope compositions in addition the 13 c values of p 2 l co 2 2 6 to 3 3 may reflect an origin from dissolution of the carbonates in the reservoir by acidic fluids containing h 2 s

isotopic analysis of basaltic fragments from lunar breccia 14321 chronology and petrogenesis of pre imbrium mare volcanism fragments of aluminous mare basalts high potassium hk aluminous mare basalts and very high potassium vhk mare basalts from apollo 14 breccias have been studied extensively rb sr isochron ages of aluminous mare basalts reported herein range from 3 96 to 4 24 and possibly up to 4 33 ga 87rb 0 0139 ga 1 they include and extend the range for the oldest mare basalts reported clasts of aluminous basalts from breccia 14321 though similar to each other in petrography mineralogy and major element composition have widely differing trace element abundances and are separable into chemical subgroups dickinsonet al 1985 shervaiset al 1985a rb sr and sm nd isotopic analysis of the grouped rocks of dicktnsonet al 1985 grouped rocks hereinafter and hk and vhk basalts shihet al 1986a b 1987 indicates that they differ with respect to time of crystallization t vs initial isotopic composition i parameters t i plots in a systematic way data for this set of rocks suggests radiogenic growth of 87sr86sr in the basalt source region corresponding to 87rb86sr 0 06 similar to the whole moon value earlier proposed nyquistet al 1977 tridymite ferrobasalt and olivine basalt from 14321 display parent daughter evolution distinct from the grouped rocks of dickinsonet al 1985 and the hk and vhk rocks and do not appear to be isotopically related to these rocks assimilation of kreep dickinsonet al 1985 does not appear to be a reasonable mechanism for forming the grouped basalts but assimilation of urkreep residuals binder 1985 or a granitic component shihet al 1986a b 1987 by more primitive magma are alternative possibilities for explaining their trace elemental and isotopic characteristics nd values for the three whole rocks that were analyzed are near 0 the value for an undifferentiated moon these rocks may be linked to the mg suite of highland rocks

the mare basalt magma source region and mare basalt magma genesis given the available data we find that the wide range of mare basaltic material characteristics can be explained by a model in which 1 the mare basalt magma source region lies between the crustmantle boundary and a maximum depth of 200 km and consists of a relatively uniform peridotite containing 73 80 olivine 11 14 pyroxene 4 8 plagioclase 0 2 9 ilmenite and 1 1 5 chromite 2 the source region consists of two or more density graded rhythmic bands whose compositions grade from that of the very low tio2 magma source regions 0 2 ilmenite to that of the very high tio2 magma source regions 9 ilmenite these density graded bands are proposed to have formed as co crystallizing olivine pyroxene plagioclase ilmenite and chromite settled out of a convecting magma which was also parental to the crust in which these crystals were suspended since the settling rates of the different minerals were governed by stoke s law the heavier minerals settled out more rapidly and therefore earlier than the lighter minerals thus the crystal assemblages deposited nearest the descending side of each convection cell were enriched in heavy ilmenite and chromite with respect to lighter olivine and pyroxene and very much lighter plagioclase the reverse being the case for those units deposited near the ascending sides of the convection cells simultaneously with this density controlled settling of the crystals the heating of the magma at the bottom of the convection cells resulted in the partial remelting of significant amounts of suspended but settling plagioclase ilmenite and pyroxene this partial remelting process was also partially responsible for the decrease in the ilmenite content from 9 to 0 2 between the very high tio2 and the very low tio2 source regions and caused the plagioclases and pyroxenes in the former source regions to be more sodic and clinopyroxene richer respectively than in the latter 3 during the mare basalt epoch radiogenic induced remelting of various parts of the density graded bands led to the formation of the initial mare basalt magmas the viscosity of melting systems which decreases rapidly at about 30 5 partial melting appears to have limited the degree of partial melting of the source region to about 30 2 4 these 30 partial melts rose to the crust mantle boundary where they pooled in magma storage chambers the magmas remained in these chambers for different lengths of time cooled to different degrees and lost 0 to 30 olivine or 30 olivine plus 0 to 20 pyroxene by fractional crystallization those magmas which remained in the chambers for very short times and lost no or essentially no olivine before eruption were the parental magmas of the pyroclastic glass units those magmas which lost increasing amounts of olivine pyroxene were the parental magmas of the apollo 12 and 15 magmas the apollo 11 and 17 magmas and the luna 16 and 24 magmas respectively this fractional crystallization phase in the genesis of the magmas explains both the pattern of the mare basalt magmas in the pseudo quaternary phase diagrams and the decrease in the siderophile contents of the magmas as a function of their degree of fractionation 5 the magma storage chambers being located at the crust mantle boundary were located in the zone where urkreep formed during the initial differentiation of the moon due to the low melting point of kreep compared with the initially high temperatures of the magmas residuals of the urkreep layer were assimilated by the cooling magmas since the urkreep materials underwent varying degrees of fractional melting early in lunar history these urkreep residuals had varying degrees of light ree depletion thus the assimilation of up to a few percent of these residuals caused the magmas to have differing eu and light ree depletion patterns as well as a wide range in their ree abundances 6 the fractional crystallization and urkreep residual assimilation phase of mare basalt magma genesis ended with the eruption of the magmas onto the lunar surface

regional stratigraphy elemental chemostratigraphy and organic richness of the niobrara member of the mancos shale piceance basin colorado the elemental chemostratigraphy of the upper cretaceous niobrara member of the mancos shale shows that six chemostratigraphic zones can be identified in the piceance basin colorado based on geochemical data chemostratigraphic correlations of nine wells spaced 20 mi 32 km apart closely match lithostratigraphic correlations made using gamma ray and deep resistivity wireline logs lithologic interpretations made from wireline logs indicate that the niobrara member and equivalent strata consist primarily of interbedded calcareous shale and shaley limestone facies that increase in thickness to the northwest in the basin the geochemical data suggest that during deposition of the niobrara member anoxia and calcium enrichment increased to the east of the basin whereas terrestrial input and clay enrichment increased to the northwest element crossplots suggest that a large part of the silicon is detrital and that the niobrara member becomes an increasingly more clastic than carbonate system to the west and northwest the log r derived total organic carbon toc calculated using a sonic resistivity overlay analysis technique shows that the niobrara member comprises organic rich and organic poor deposits average toc values range between 1 wt in organic poor deposits and 2 37 wt in organic rich deposits with higher toc values recorded in the southern and eastern parts of the basin relative rock brittleness estimates from element and toc data show the stratigraphic variability of alternating ductile toc rich ca and si al poor and brittle toc poor ca and si al rich intervals for the niobrara member

source rock heterogeneity of the upper jurassic draupne formation north viking graben and its relevance to petroleum generation studies abstract the upper jurassic draupne formation in the north viking graben north sea has been studied to identify lateral and vertical variations in source rock characteristics and their effect on the timing of petroleum generation fourteen source rock samples from the western flank of the graben and five from the eastern flank were analysed using rock eval analysis microscopy open system pyrolysis gas chromatography and kinetic experiments two major organic facies with different petroleum generation characteristics were identified a stratigraphically higher thermally less stable facies corresponding to a type ii kerogen with hi hydrogen index values of 350 mg hc g toc and a stratigraphically lower more stable type ii iii facies with hi values

major element analysis of cyclic black shales paleoceanographic implications for the early cretaceous deep western tethys lower cretaceous sediments are frequently characterized by a well expressed cyclicity while the processes influencing environments above the carbonate compensation depth ccd are reasonably well understood almost nothing is known about the deep ocean cretaceous sub ccd sediments from the tethys and atlantic oceans typically show rhythmic black green shale successions to gain insight into the nature of these black green shale cycles we performed detailed geochemical analyses x ray fluorescence rock eval and reactive iron analysis on a 3 m long section of latest aptian age the major element distribution of the analyzed shale sequence indicates a periodic change from a high productivity and well oxygenated green shale mode to a low productivity oxygen deficient black shale mode it is proposed here that the preservation of organic matter was dependent on the strength of salinity driven deepwater generation furthermore the data show that the corg content covaries with changes in the detrital composition therefore we hypothesize that tethyan deepwater circulation was sensitive to changes in the monsoonal system time series analysis suggests that these changes are periodic in nature although we are currently unable to prove that the dominant periodicity is related to the precession component of the milankovitch frequencies

depositional environment thermal maturity and shale oil potential of the cretaceous qingshankou formation in the eastern changling sag songliao basin china an integrated organic and inorganic geochemistry approach abstract the changling sag in the petroliferous songliao basin has produced large amounts of conventional petroleum but studies on unconventional resources are rare a suite of core samples from the cy 1 well drilled in the eastern changling sag was analysed employing a series of micropetrographic geochemical and pyrolysis techniques to reveal the shale oil potential of the lower k2qn1 and middle k2qn2 qingshankou formation in this area for the first time from the lower k2qn1 upwards the sampled section the ratio of k al delineates an increasing palaeo temperature trend but still within a warm climate based on element ratios al2o3 toc and tio2 toc the highest terrestrial matter and nutrient supply on average occurred in the lower k2qn1 triggering bioproductivity toc ts and fe mn show that bottom water anoxia prevailed in the upper k2qn1 and lower k2qn2 providing excellent conditions for organic matter om preservation as compared to the lower k2qn1 high maturity of the studied layers is implied by e g vitrinite reflectance vrr of 1 03 1 09 tmax values over 445 c and molecular organic geochemical indices which correlate very well with vrr kinetic data on petroleum generation from open system pyrolysis were implemented in a numerical 1d basin and petroleum system model the k2qn1 has generated and expelled large amounts of petroleum 78 and 36 transformation of kerogen to petroleum based on kinetics of the low mature qingshankou shale om consisted originally of type i ii kerogen but has lost more than half of its original hydrocarbon generation potential upon maturation oil saturation index osi and s1 suggest that the studied layers show fair shale oil potential but are regarded as good conventional petroleum source rocks a newly proposed shale oil potential index sopi takes also thickness into account application to the qingshankou formation implies that the lower k2qn2 holds the highest shale oil potential

bolsovian pennsylvanian tropical peat depositional environments the example of the ruhr basin germany abstract a set of 11 bolsovian coal seams from the german ruhr coal basin were analyzed in profiles for their organic geochemical and petrographic composition aiming at the reconstruction of depositional environments mainly in terms of water supply and redox conditions for this purpose established maceral indices and a i ratio were employed the seams show the same basic depositional pathways of terrestrialisation and paludification as reported for duckmantian coal seams from the same basin the presence of coals formed as ombrotrophic peat indicates that climate was still wet enough for the formation of domed bogs until the upper bolsovian although the typical densosporite facies does not occur within the uppermost third of the analyzed succession very high ts values for seam parsifal ii indicate the influence of marine waters at the peat stage a marine ingression event was not reported before for this stratigraphical level within the ruhr basin data also reveal some variability in vitrinite reflectance 0 65 0 74 within a given coal seam which cannot be due to thermal maturation for seams with decreased vrr values a correlation with high liptinite contents was found rock eval hi values do not show any strong variation with depths in the recorded maturity interval tmax values vary between 418 c and 444 c showing dependence on both thermal maturity and liptinite content decreasing contents of inertinite macerals throughout the pennsylvanian in the ruhr basin suggest climatic changes during that time span

kinetic simulation of hydrocarbon generation from lacustrine type i kerogen from the songliao basin model comparison and geological application abstract eight lacustrine type i kerogen samples from the songliao basin were pyrolyzed using the rock eval equipment and parallel first order reaction models including the model with a single frequency factor and a discrete distribution of activation energies sff model and the model with multiple frequency factors and a discrete distribution of activation energies mff model were adopted to analyze kinetic characteristics of hydrocarbon generation of the type i kerogen samples the results show that the mff and sff models can satisfactory simulate hydrocarbon generation under laboratory conditions and the type i kerogen shows relatively concentrated activation energy distributions activation energies of mff model range from 190 kj mol to 250 kj mol activation energies of sff model range from 220 kj mol to 240 kj mol which indicates a homogeneous chemical bond structure of the type i kerogen the hydrocarbon generated curves from type i kerogen were calculated by using the two models with a linear heating rate 3 3 k ma it indicates that the hydrocarbon generation potentials reaction fractions are underestimated by using the sff model during the kerogen thermal degradation for the components with chemical bond of lower and higher activation energies while this problem can be avoided by using the mff model the calculated temperatures for 50 transformation ratio tr of all samples differ by as much as 20 c for the sff model the hydrocarbon generation curve obtained by using the weighted averaged kinetic parameters and the sff model almost includes every curve calculated by using its own kinetic parameters while the curve obtained by using the weighted averaged kinetic parameters and the mff model cannot include every curve for all samples it lies at the position of the averaged curve of all samples the application of the mff model in songliao basin shows that if tr 10 is taken as the onset of hydrocarbon generation the threshold depth of hydrocarbon generation is about 1700 m which is consistent with other geochemical parameters such as s 1 toc s 1 s 1 s 2 and hc toc

application of organic petrography in north american shale petroleum systems a review abstract organic petrography via incident light microscopy has broad application to shale petroleum systems including delineation of thermal maturity windows and determination of organo facies incident light microscopy allows practitioners the ability to identify various types of organic components and demonstrates that solid bitumen is the dominant organic matter occurring in shale plays of peak oil and gas window thermal maturity whereas oil prone type i ii kerogens have converted to hydrocarbons and are not present high magnification sem observation of an interconnected organic porosity occurring in the solid bitumen of thermally mature shale reservoirs has enabled major advances in our understanding of hydrocarbon migration and storage in shale but suffers from inability to confirm the type of organic matter present herein we review organic petrography applications in the north american shale plays through discussion of incident light photographic examples in the first part of the manuscript we provide basic practical information on the measurement of organic reflectance and outline fluorescence microscopy and other petrographic approaches to the determination of thermal maturity in the second half of the paper we discuss applications of organic petrography and sem in all of the major shale petroleum systems in north america including tight oil plays such as the bakken eagle ford and niobrara and shale gas and condensate plays including the barnett duvernay haynesville bossier marcellus utica and woodford among others our review suggests systematic research employing correlative high resolution imaging techniques and in situ geochemical probing is needed to better document hydrocarbon storage migration and wettability properties of solid bitumen at the pressure and temperature conditions of shale reservoirs

the origin type and preservation of organic matter of the barremian aptian organic rich shales in the muglad basin southern sudan and their relation to paleoenvironmental and paleoclimate conditions barremianeaptian organic rich shales from abu gabra formation in the muglad basin were analysed using geochemical and petrographic analyses these analyses were used to define the origin type of organic matters and the influencing factors of diagenesis including organic matter input and preservation and their relation to paleoenvironmental and paleoclimate conditions the bulk geochemical characteristics indicated that the organic rich shales were deposited in a lacustrine environment with seawater influence under suboxic conditions their pyrolysis hydrogen index hi data provide evidence for a major contribution by type i ii kerogen with hi values of 400 mg hc g toc and a minor type ii iii contribution with hi values 400 mg hc g toc this is confirmed by kerogen microscopy whereby the kerogen is characterized by large amounts of structured algae botryococcus and structureless amorphous with a minor terrigenous organic matter input an enhanced biological productivity within the photic zone of the water columns is also detected the increased biological productivity in the organicrich shales may be related to enhanced semi arid humid to humid warm climate conditions therefore a high bio productivity in combination with good organic matter preservation favoured by enhanced algae

tectonics of the qinling central china tectonostratigraphy geochronology and deformation history abstract the qinling orogen preserves a record of late mid proterozoic to cenozoic tectonism in central china high pressure metamorphism and ophiolite emplacement songshugou ophiolite assembled the yangtze craton including the lower qinling unit into rodinia during the 1 0 ga grenvillian orogeny the lower qinling unit then rifted from the yangtze craton at 0 7 ga subsequent intra oceanic arc formation at 470 490 ma was followed by accretion of the lower qinling unit first to the intra oceanic arc and then to the sino korea craton subduction then imprinted a 400 ma andean type magmatic arc onto all units north of the northern liuling unit oblique subduction created silurian devonian wnw trending sinistral transpressive wrench zones e g lo nan shang dan and late permian early triassic subduction reactivated them in dextral transpression lo nan shang xiang shang dan and subducted the northern edge of the yangtze craton exhumation of the cratonal edge formed the wudang metamorphic core complex during dominantly pure shear crustal extension at 230 235 ma post collisional south directed shortening continued through the early jurassic cretaceous reactivation of the qinling orogen started with nw se sinistral transtension coeval with large scale early cretaceous crustal extension and sinistral transtension in the northern dabie shan it presumably resulted from the combined effects of the siberia mongolia sino korean and lhasa west burma qiangtang indochina collisions and pacific subduction regional dextral wrenching was active within a ne sw extensional regime between 60 and 100 ma an early cretaceous andean type continental magmatic arc with widespread early cretaceous magmatism and back arc extension was overprinted by shortening related to the collision of yangtze indochina block with the west philippines block strike slip and normal faults associated with eocene half graben basins record paleogene nne ssw contraction and wnw ese extension the neogene is characterized by normal faults and nne trending sub horizontal extension pleistocene quaternary nw se extension and ne sw contraction comprises sinistral strike slip faults and is part of the nw se extension imposed across eastern asia by the india asia collision

marine transgressional events in the gigantic freshwater lake songliao paleontological and geochemical evidence abstract the fossil remains of euryhaline organisms in the mesozoic cenozoic non marine sedimentary records of eastern china may have resulted from either marine transgressions or inland hypersaline lacustrine environments paleontological and organic geochemical results of this study have provided new evidence for marine transgressional events in the gigantic freshwater lake songliao during the late cretaceous

post rift geodynamics of the songliao basin ne china origin and significance of t11 coniacian unconformity abstract the t11 unconformity lies between the qingshankou and yaojia formations in the post rifting sequence of the cretaceous songliao basin ne china it is intimately associated with petroleum reservoirs and considered to be a disconformity forming in the tectonic quiet stage we present the interpretations from new seismic surveys and cored sections of the cretaceous continental scientific drilling borehole ccsd sk 1 in order to resolve the nature and origin of t11 unconformity the t11 is often a low angle unconformity with underlying qingshankou formation having been deformed and eroded prior to deposition of the yaojia formation in the post rift evolution of the basin it marks an abrupt change from a deep lake to shallow lake or subaerial environment documented by reddening of the lacustrine mudstone extinction of the ostracod assemblages and a great increase of coarse detrital inputs the sharp change of depositional environment the truncation of gentle folds and the cluster of volcanic and paleoearthquake activities all happened simultaneously immediately before the development of t11 unconformity indicating a significant regional compressional uplift event in the basin the timing of the t11 unconformity formation is within the interval 88 86 2 ma correlations with coeval unconformities in other cretaceous sedimentary basins in eastern asia indicate that this compressional uplift coincided with an episode of global plate reorganization between the eurasian and paleo pacific plates that culminated at 88 87 ma during this short interval the northeast asian margin in eastern china south korea japan and russian far east experienced widespread violent volcanic and granite emplacement activity triggered by compression resulting from rapid and orthogonal slab subduction the post rift basin tectonic inversion occurred during t11 coniacian time thereafter the basin again evolved in an extension regime two subsidence phases in post rift history took place as the direct consequence of coniacian compression peak which defined the distribution of oil sources and reservoirs

lacustrine depositional environments in the green river formation uinta basin expression in outcrop and wireline logs lacustrine basins are key oil productive areas of the world because fewer lacustrine exist than marine basins lacustrine systems are relatively less well studied this paper investigates fluvial lacustrine depositional environments and their representation in wireline logs in the lower part of the green river formation uinta basin utah the five principal depositional environments of the lower green river formation are 1 deep lacustrine 2 shallow lacustrine 3 lacustrine delta 4 coastal plain and 5 alluvial plain deep lake environments are characterized by laminated oil shales and fine grained carbonates these facies exhibit anomalously high neutron porosity and low bulk density relative to other settings shallow lake environments are dominated by weakly laminated to massive gray mudstones and limestones with occasional thin high bulk density sandstones lacustrine deltas both sand prone and mud prone grade from shallow lake muds to ripple laminated to cross bedded sandstones the upward decrease in clay can be seen in the gamma ray neutron porosity and bulk density profiles of deltaic intervals coastal plain mudstones have a greenish hue and frequently contain organic matter channels in coastal plain settings are typically thin isolated and heterolithic alluvial plain channels tend to be sandier thicker and less isolated than coastal plain channels alluvial mudstones are reddish with abundant pedogenic features the vertical association of depositional environments in the lower green river indicates both high amplitude and high frequency lake level fluctuations however the macro scale trend shows a rapid deepening of the lake lower in the section followed by a gradual filling of the accommodation and a gradual flooding near the top of the studied interval the lower green river depositional environments form key petroleum system components oil shales in the deep lacustrine settings are the major source rock and coastal plain muds are a potential minor source regional seals are formed by deposits of tight lacustrine shale and carbonate deposited in both marginal and deep lacustrine settings delta coastal plain and alluvial plain sands form the principal reservoirs some deep lacustrine mudstones and carbonates are also potential unconventional reservoirs correlation of outcrop observations from well log expressions allows depositional environments to be interpreted in the uinta basin and other lacustrine basins

petroleum generation kinetics single versus multiple heating ramp open system pyrolysis some recent publications promote one run open system pyrolysis experiments using a single heating rate ramp and fixed frequency factor to determine the petroleum generation kinetics of source rock samples because compared to multiple ramp experiments the method is faster less expensive and presumably yields similar results some one ramp pyrolysis experiments yield kinetic results similar to those from multiple ramp experiments however our data for 52 worldwide source rocks containing types i ii iis ii iii and iii kerogen illustrate that one ramp kinetics introduce the potential for significant error that can be avoided by using high quality kinetic measurements and multiple ramp experiments in which the frequency factor is optimized by the kinetic software rather than fixed at some universal value the data show that kinetic modeling based on a discrete activation energy distribution and three different pyrolysis temperature ramps closely approximates that determined from additional runs provided the three ramps span an appropriate range of heating rates for some source rocks containing well preserved kerogen and having narrow activation energy distributions both single and multiple ramp discrete models are insufficient and nucleation growth models are necessary instrument design thermocouple size or orientation and sample weight likely influence the acceptable upper limit of pyrolysis heating rate caution is needed for ramps of 30 50 c min which can cause temperature errors due to impaired heat transfer between the oven sample and thermocouple compound volatility may inhibit pyrolyzate yield at the lowest heating rates depending on the effectiveness of the gas sweep we recommend at least three pyrolysis ramps that span at least a 20 fold variation of comparatively lower rates such as 1 5 and 25 c min the product of heating rate and sample size should not exceed 100 mg c min our results do not address the more fundamental questions of whether kinetic models based on multiple ramp open system pyrolysis are mechanistically appropriate for use in basin simulators or whether petroleum migration through the kerogen network rather than cracking of organic matter represents the rate limiting step in expulsion

high resolution stratigraphy and facies architecture of the upper cretaceous cenomanian turonian eagle ford group central texas rock based studies of the eagle ford group of central texas demonstrate that mudrock deposition is more complicated than previously supposed x ray diffraction x ray fluorescence total organic carbon toc and log data collected from eight cores and two outcrops demonstrate that bottom current reworking and planktonic productivity are primary depositional controls acting independently from eustatic forcing central texas eagle ford facies include 1 massive argillaceous mudrock 2 massive foraminiferal calcareous mudrock 3 laminated calcareous foraminiferal lime mudstone 4 laminated foraminiferal wackestone 5 cross laminated foraminiferal packstone grainstone 6 massive bentonitic claystone and 7 nodular foraminiferal packstone grainstone high degrees of lateral facies variability characterized by pinching and swelling of units lateral facies changes truncations and locally restricted units are observed even at small lateral scales 50 ft 15 m at 10 mi 16 km and greater lateral spacings core and geochemical data significantly underestimate intraformational facies variability approximately 73 of units can be successfully correlated across a distance of 500 ft 152 m 35 are traceable across 1 mi 1 6 km and only 16 of beds are correlative across 10 mi 16 km geochemical proxies enrichment in molybdenum and other trace elements indicate that maximum anoxia occurred within the bouldin member despite being composed of the most calcareous and high energy facies comparison of total gamma ray gr logs to computed gr logs is requisite because gr alone may provide misleading determination of facies toc content depositional environment and sequence stratigraphic implications

two stage models for lunar and terrestrial anorthosites petrogenesis without a magma ocean two stage diapiric models for lunar ferroan anorthosites and terrestrial massif anorthosites are examined the lunar model is developed to explain early lunar differentiation in the absence of a magma ocean if correct the terrestrial model serves as an analog for the development of lunar anorthositic diapirs there is field and textural evidence of transport of mostly crystalline anorthositic material within the terrestrial complexes this evidence combined with the absence of anorthositic lavas and phase equilibrium constraints inhibiting the production of hyperaluminous magmas is consistent with the detachment of plagioclase rich crystalline mushes from large uppermost mantle plutons and multiple diapiric intrusion of these mushes into the upper sialic crust with attendant anatexis rudimentary dynamical calculations suggest that a simple single layer source for the diapirs is improbable either there were several parental magma chambers or there was a single large chamber that was repeatedly replenished the lunar model is a development of wetherill s 1975 suggestion that following accretion the outer portion of the moon consisted of a stack of overlapping layered intrusions and that reheating of these intrusions mobilized their anorthositic layers which intruded upwards to produce the anorthositic lunar crust dynamical calculations show that gravitational instabilities in anorthositic layers 1 km thick could develop into diapirs on a reasonable time scale 50 100 m y only if the outer portion of the moon was partially remelted we suggest that partial melting of the interior due to the decay of long lived radionuclides with the subsequent onset of global convection heated the stack of intrusions from below thus causing melting and allowing the anorthositic diapirs to grow and ascend fairly rapidly as the convecting zone thickened a mass expulsion of anorthositic material out of the lunar interior may have occurred

experimental study of fluid transport processes in the matrix system of the european organic rich shales ii posidonia shale lower toarcian northern germany abstract a laboratory study has been conducted to investigate the transport of gases he ar ch 4 and water in the matrix of lower toarcian posidonia shale samples from three shallow boreholes in northern germany the maturity of the organic matter of the shale samples ranged between 0 53 and 1 45 vitrinite reflectance vr r the measurements were performed at effective stresses ranging between 6 and 37 mpa and a temperature of 45 c the effects of different controlling factors including permeating fluid maturity anisotropy moisture content and effective stress on the fluid conductivity were analyzed and discussed permeability coefficients measured perpendicular and parallel to bedding 3 10 22 to 9 7 10 17 m 2 were within the range previously reported for other shales and mudstones they exhibited a strong dependence on permeating fluid maturity anisotropy moisture content and effective stress the permeability coefficients measured with helium as permeate were consistently higher up to two times than those measured with argon and methane permeability coefficients measured with water were up to three orders of magnitude lower than klinkenberg corrected gas permeability coefficients measured with helium and methane under similar experimental conditions among the samples studied the lowest porosity and permeability coefficients were measured on samples of intermediate thermal maturity 0 88 vr r oil window permeability coefficients he ch 4 measured parallel to bedding were up to more than one order of magnitude higher than those measured perpendicular to bedding permeability coefficients measured with he and ch 4 on a dry sample were up to two times higher than those measured on a sample with the as received moisture content all samples showed a nonlinear reduction in permeability parallel to bedding with increasing effective stress 6 37 mpa the permeability anisotropy and stress dependence of permeability were controlled by the mineralogy

syn and post depositional sand bodies in lignite the role of coal analysis in their recognition a study from the frimmersdorf seam garzweiler open cast mine western germany abstract the lower rhine basin is a cenozoic age rift basin at the nw end of the european cenozoic rift basin in middle miocene times fluctuating sea levels in the north sea and the repeated spreading of paralic mires resulted in the deposition of marine sand units frimmersdorf and neurath sands alternating with thick lignite beds morken frimmersdorf and garzweiler seams within the frimmersdorf seam the presence of sand bodies has been interpreted both in terms of syn depositional emplacement in an estuarine setting as well as post depositional sand injection and soft sediment deformation partly linked to tectonic activity within the lower rhine basin while understanding of the causal mechanisms has improved early recognition of sand concentrations in future mine area remains difficult therefore organic petrological and inorganic geochemical analyses of sand and lignite samples were carried out in order to assess their efficacy as proxies for such studies the results reflect the complexity of the depositional environment which was influenced by both fresh and marine waters ash yields of the lignite samples are variable and sulphur contents as well as ca mg ratios depend on the distance from the overlying marine neurath sand humic substance values of the lignites are dependent on the sampling position within the seam and may be related to sand body deposition moderate contents of gelified macerals and the small size of huminite particles reflect the depositional environment during peat formation but are not influenced by sand body deposition not even when in close proximity to the sands while the geochemical and petrological methods provide much information on the depositional environment of the miocene age lower rhine basin and also on marine versus freshwater deposition of the sands they do not facilitate the differentiation of syn and post depositional sand emplacement in the frimmersdorf seam

stable carbon isotopes of alkane gases from the xujiahe coal measures and implication for gas source correlation in the sichuan basin sw china abstract the upper triassic xujiahe formation in the sichuan basin sw china consists of a series of coal measures the first third and fifth members of this formation are dominated by gas prone dark mudstones and coals the mudstones contain type ii and iii kerogens with average organic carbon contents around 1 96 these source rocks are mature in the central sichuan and highly mature in the western sichuan basin characterized by gas generation with subordinate amounts of light oil or condensate oils the source rocks are intercalated with the sandstone dominated second fourth and sixth members of the xujiahe formation thus leading to three separate self contained petroleum systems in the region the proven gas reserves in the xujiahe formation are only less than that of the triassic feixianguan formation and the xujiahe formation has the second largest gas field guang an gas field in the basin gases derived from the xujiahe formation coals generally show a normal stable carbon isotopic trend for c1 c4 n alkanes with the highest 13c2 values among the nine gas pay zones in the basin 20 7 to 28 3 and 13c1 values as low as 43 0 in the central sichuan gas accumulations with an oil leg have also been found in the eastern and southern sichuan where the thickness of the xujiahe formation is significantly reduced gases in these accumulations tend to show low 13c2 values 30 0 to 36 3 characteristic of oil prone source rocks

organic geochemistry and petrology of posidonia shale lower toarcian western europe the evolution from immature oil prone to overmature dry gas producing kerogen abstract kerogen concentrates as well as whole rock samples of the lower jurassic posidonia shale representing a complete maturity series from immature to highly overmature were analyzed using organic petrography palynology bulk geochemical analysis ft ir and curie point pyrolysis gc ms cp py gc ms in order to investigate changes in kerogen composition with increasing maturation vitrinite reflectance vrr ranges from 0 5 to 3 hi values reflect the maturity trend very well with little scatter in contrast tmax oi and pi values show more scatter and greater differences between kerogen concentrates and whole rock samples ft ir spectra show a decrease in functional group bands with increasing maturation which has been quantified cp py gc ms analyses indicate an increase in hydrocarbons especially for short and medium length n alkanes with a strong predominance of short length alkanes at highest maturities about 3 vrr this effect however depends also on the applied pyrolysis temperature where higher temperatures 920 c as compared to 650 c favor generation of short length n alkanes especially for samples at high levels of maturation ratios of aromatic over aliphatic hydrocarbons or alkenes over alkanes show a non steady evolution depending also on the applied pyrolysis temperatures indicating that higher pyrolysis temperatures are needed for pyrolytic alkene formation with a maximum alkene formation for samples within early overmature maturities 1 4 vrr aromaticity first decreases but increases at high levels of maturation finally weathering of the highly overmature sample 3 vrr resulted in strong oxidation of organic matter with impact on rock eval ftir and curie point pyrolysis data

organic matter composition and distribution through the aptian albian lacustrine sequences of the araripe basin northeastern brazil abstract the main characteristics and distribution of organic matter have been studied through several aptian albian lacustrine units rio da batateira crato and ipubi formations araripe basin ne brazil six main facies have been distinguished on the basis of their lithological sedimentological characteristics and the type and amount of organic matter 1 marginal lacustrine deltaic massive to coarsely laminated mudstones and sandstones found as lenticular sheet and channel infills 2 oxic marginal lacustrine massive to poorly laminated mudstones 3 oxic suboxic inner lacustrine mudstones and laminated bioclastic mudstones 4 anoxic inner lacustrine dark mudstones 5 anoxic inner lacustrine dark clay carbonate rhythmites and 6 anoxic inner lacustrine finely laminated dark micritic limestones these facies make up decimeter to several meter thick parasequences which stack up in several tens of meters thick successions water level changes and variations of the detritic sediment contribution in the basin controlled the evolution of the depositional system palynomorph associations showed that the lacustrine system evolved in an arid semiarid tropical area where the most characteristic flora consisted of conifers gnetales bennettitales and early angiosperms in facies 1 to 3 organic matter was scarce poorly preserved and mainly derived from higher land plants facies 4 is characterised by containing abundant algal bacterial derived well preserved organic matter facies 5 and 6 contained mainly branchlets and pollen debris blown by the wind or fed by lacustrine underflows the pattern of organic matter accumulation and preservation corresponds well with cyclical palaeoenvironmental changes from anoxic to oxic bottom conditions and from a fresh to saline upper water layer which affected the shallow lacustrine system the deposition of thin organic matter rich mudstones facies 4 probably occurred during higher water levels which resulted in relatively low salinity waters and low detrital contribution to the inner lacustrine zones less significant organic matter accumulation is recorded in the clay carbonate rhythmites and in the limestones facies 5 and 6 due to scarce autochthonous aquatic organic matter deposition and pervasive intense bacterial degradation caused by persistent meromictic conditions large differences in the degree and path of evolution of the humic material derived from higher land plants have been detected depending on the depositional conditions the humic material in the oxic facies underwent humification and gelification and had the highest huminite reflectances whereas it showed suppressed reflectance values in the oil shales facies 4 and in the carbonate dominated facies in the latter extensive bacterial reworking of humic material is also observed these differences are considered significant and applicable to other case studies in terms of evaluating the maturity of organic matter in ancient lacustrine systems

interpreting rock eval pyrolysis data using graphs of pyrolizable hydrocarbons vs total organic carbon kerogen the major organic component of sedimentary rocks is commonly analyzed by rock eval pyrolysis plotting the data on a graph of s 2 vs total organic carbon toc and determining the regression equation is the best method for determining the true average hydrogen index and measuring the adsorption of hydrocarbon by the rock matrix such a plot also indicates the type of kerogen present and avoids the problem of increasing hydrogen index with total organic carbon content with the s 2 vs toc diagram the organic component of different suites of samples may be compared and their petroleum generation potentials established as an example the diagrams are used to evaluate the sedimentary environments and petroleum potential of the paleogene evaporitic sediments of the mulhouse basin alsace france

late cretaceous stratigraphy songliao basin ne china sk1 cores abstract the songliao basin is the largest cretaceous oil and gas producing lacustrine basin in china with its greatest aerial extent in the middle cretaceous a coring program sk1 has to date yielded 2485 89 m of continuous core 96 46 recovery and provides significant material for cretaceous research the sequence of the core consists mainly of lacustrine sandstone dark grey mudstone shale and oil shale the upper cretaceous stratigraphic section has been subdivided into the quantou qingshankou yaojia nenjiang sifangtai and mingshui formations in ascending order late cretaceous microfossils are diverse and abundant a detailed biostratigraphic study has subdivided the sequence into high precision biozones 21 ostracode assemblages 10 phytoplankton assemblages 7 palynological zones and 4 charophyta assemblages respectively in addition marine foraminifera were first discovered from the basin three 206pb 238u ages and one 40ar 39ar age were analysed ten local magnetozones have been recognised in the sk1 north and two magnetozones have been indicated in the sk1 south based on biostratigraphy high resolution magnetostratigraphy and sims u pb zircon analyses the sk1 stratigraphy is correlated with upper cretaceous stages in the international geologic time scale the upper part of the quantou formation is the lower turonian the qingshankou formation is the upper turonian lower coniacian the yaojia formation is from the upper coniacian to middle santonian the nenjiang formation is the upper santonian to middle campanian the sifangtai formation is limited to the upper campanian and the mingshui formation is the uppermost campanian to maastrichtian it is likely that the upper part of the mingshui formation belongs to the paleocene and the k pg boundary is within the member 2 of the mingshui formation around the depth of 328 m by new micropalaeontologic and magnetostratigraphic data

tracing bottom water oxygenation with sedimentary mn fe ratios in lake zurich switzerland abstract redox dynamics of manganese mn were studied in the sediment of lake zurich using precise sediment core age models monthly long term oxygen o 2 monitoring data of the water column 1936 2010 and high resolution xrf core scanning the age models were based on bi annual lamination and calcite precipitation cycles if present mn exhibits distinct maxima which coincide with the annual maximum deep water o 2 concentrations in spring according to the monitoring data in contrast the iron fe signal is mainly the result of calcite dilution as indicated by a strong negative correlation between fe and calcium ca xrf data the mn fe ratio in the core from the maximum lake depth zh10 15 137 m revealed a moderate correlation with o 2 measurements in the lake bottom water confirming the successful application of the mn fe ratio to semi quantitatively reconstruct bottom water oxygenation in the lake mostly low ratios were observed between 1895 and the mid 1960s as a result of eutrophication however geochemical focusing and sedimentological factors can reduce the applicability of the mn fe ratio in reconstructing o 2 concentrations in the bottom water of lakes

lithofacies and reservoir characteristics of the lower cretaceous continental shahezi shale in the changling fault depression of songliao basin ne china abstract the increasing enthusiasm for continental shale gas exploration in china has made the shahezi shale in the changling fault depression an important research target due to its impressive demonstrated gas capacity in this work geochemical and petrologic analyses field emission scanning electron microscopy fe sem observation low pressure adsorption isotherms and mercury intrusion porosimetry mip were conducted on 19 core samples to comprehensively analyze the reservoir characteristics of different lithofacies the results show that the shahezi shale has the characteristics of low content of organic matter om high ro high content of clay minerals and small fractions of calcite the kerogen is type iii dominated by vitrinite and inertinite clay minerals are dominated by the mixed illite smectite followed by illite and a small amount of chlorite the shahezi shale develops three kind of stratification structures according to the thickness of laminae laminated structures bedded structures and massive structures on the basis of toc mineral composition and petrologic texture eight types of lithofacies were recognized the organic pores show strong heterogeneity and are poorly developed while clay related pores are ubiquitous the shahezi shale has a high pore volume pv 0 005 0 031 ml g averaging 0 0173 ml g and specific surface area ssa 2 57 27 48 m2 g averaging 16 61 m2 g indicating an excellent storage capacity low pressure co2 and n2 isotherms and mip were utilized to construct the whole range pore size distribution psd based on the whole range psds mesopores were observed to contribute most to the pv followed by macropores micropores and mesopores account for more than 99 of ssa the reservoir capacity of different lithofacies is following the order in terms of pv and ssa from high to low organic medium massive mixed shale ommms organic medium massive argillaceous shale ommas organic rich laminated argillaceous shale orlas organic medium laminated argillaceous shale omlas organic rich bedded mixed shale orbms organic rich bedded siliceous shale orbss organic medium bedded argillaceous shale ombas organic poor shale ops the main controlling factors of pore structure for the shahezi shale are clay minerals rather than om which is similar to the continental chang 7th shale but contrary to the longmaxi shale however the shahezi shale is mainly of low toc and strong heterogeneity pores development result from om macerals while the chang 7th shale is mainly of low maturity ro play an important role in promoting pore development only high content of calcite can greatly improve the pore space due to its solubility this work contributes to the theory of continental shales and how to identify continental high quality shale reservoirs

stable carbon and hydrogen isotopes of natural gases sourced from the xujiahe formation in the sichuan basin china abstract the compound specific hydrogen and carbon stable isotope ratios of alkanes in natural gases from the xujiahe and jurassic formations in the western sichuan basin were investigated to distinguish between coal derived and oil associated gases all gases were determined to be coal derived and sourced from the xujiahe formation thermal maturities of the source rocks are expected to vary from 0 8 1 8 vitrinite reflectance ro according to the empirical relationship between the measured 13cch4 values and ro which is within the scope of the maturities of source rocks 0 7 2 1 in particular c1 3 alkanes of primary coal derived gases which have not undergone any secondary alteration become more enriched in deuterium with increasing molecular mass and the dch4 values increase with increasing thermal maturity of source rocks in the sichuan basin d values of coal derived gases sourced from terrigenous source rocks of the xujiahe formation are more negative than those of oil associated gases sourced from marine organic matter of the sinian permian and triassic formations

spatial variation in sediment fluxes redox conditions and productivity in the permian triassic panthalassic ocean abstract two permian triassic boundary sections in central japan provide a rare window into environmental conditions within the panthalassic ocean which encompassed more than half the earth s surface at 252 ma integration of petrographic geochemical and time series data provides new insights regarding the fluxes of major and trace components to the sediment as well as environmental conditions in both the deep and intermediate water masses at each study site the ubara section was located in a high productivity peri equatorial location whereas the gujo hachiman section was located in a moderate productivity location at some distance from the paleoequator an upward transition from gray organic poor cherts to black siliceous mudstones at both sites occurred in conjunction with increased primary productivity intensified euxinia within the oxygen minimum zone omz and decimation of the radiolarian zooplankton community euxinia in the omz of the equatorial panthalassic ocean developed episodically for a 200 250 kyr interval during the late permian followed by an abrupt intensification and lateral expansion of the omz around the permian triassic boundary throughout the study interval bottom waters at both sites remained mostly suboxic a finding that counters hypotheses of development of a superanoxic permo triassic deep ocean as a consequence of stagnation of oceanic overturning circulation

new directions in an established gas play promising dolomite reservoirs in the middle triassic leikoupo formation of the sichuan basin china the discovery of carbonate gas fields in the middle triassic leikoupo formation of the sichuan basin has a complex history in recent years a series of structural fields have been discovered in the western sichuan basin their discovery confirms the immense exploration potential of the leikoupo formation in this study we analyze the characteristics of leikoupo formation exploration plays using exploration wells and test data aiming to provide a reference for further discoveries the leikoupo formation represents the uppermost unit in the sichuan marine carbonate platform succession during its deposition the whole basin was characterized by a restricted and evaporitic platform two classes of reservoirs developed one is pore fracture reservoirs in marginal platform and intraplatform shoals and another is fracture vug reservoirs in the karstic weathering crust of the formation capping unconformity three hydrocarbon accumulation models were established for the leikoupo formation based on the spatial and temporal relationship among the source reservoir and cap rocks two types of exploration plays are present in the leikoupo formation that is shoal including intraplatform shoal and marginal platform shoal dolomite plays and karstic dolomite weathering crust plays including intraplatform shoal karst and marginal platform shoal karst the western sichuan depression in the karstic slope belt presents immense exploration potential because of a proximal hydrocarbon supply charging via an extensive fracture network shoals and karstic reservoir a good seal rock of terrestrial mudstone and potential composite hydrocarbon accumulations in stratigraphic traps making it a promising area for future exploration

the petrogenesis of impact basin melt rocks in lunar meteorite shisr 161 this study explores the petrogenesis of shisr 161 an immature lunar regolith breccia meteorite with low abundances of incompatible elements a feldspathic affinity and a significant magnesian component our approach was to identify all clasts 0 5 mm in size in a thin section characterize their mineral and melt components and reconstruct their bulk major and minor element compositions trace element concentrations in representative clasts of different textural and compositional types indicate that the clast inventory of shisr 161 is dominated by impact melts that include slowly cooled cumulate melt rocks with mafic magnesian mineral assemblages minor exotic components are incompatible element rich melt spherules and glass fragments and a gas associated spheroidal precipitate our hypothesis for the petrologic setting of shisr 161 is that the crystallized melt clasts originate from the upper 1 km of the melt sheet of a 300 to 500 km diameter lunar impact basin in the moon s feldspathic highlands this hypothesis is based on size requirements for cumulate impact melts and the incorporation of magnesian components that we interpret to be mantle derived the glassy melts likely formed during the excavation of the melt sheet assemblage by an impact that produced a 15 km diameter crater the assembly of shisr 161 occurred in a proximal ejecta deposit of this excavation event a later impact into this ejecta deposit then launched shisr 161 from the moon our geochemical modeling of remote sensing data combined with the petrographic and chemical characterization of shisr 161 reveals a preferred provenance on the moon s surface that is close to pre nectarian riemann fabry basin

a glass spherule of questionable impact origin from the apollo 15 landing site unique target mare basalt a 6 mm diameter dark spherule 15434 28 from the regolith on the apennine front at the apollo 15 landing site has a homogeneous glass interior with a 200 m thick rind of devitrified or crystallized melt the rind contains abundant small fragments of apollo 15 olivine normative mare basalt and rare volcanic apollo 15 green glass the glass interior of the spherule has the chemical composition including a high feo content and high cao al2o3 of a mare basalt whereas the major element and sc ni and co abundances are similar to those of low ti mare basalts the incompatible elements and sr abundances are similar to those of high ti mare basalts the relative abundance patterns of the incompatible trace elements are distinct from any other lunar mare basalts or kreep among these distinctions are a much steeper slope of the heavy rare earth elements the 15434 28 glass has abundances of the volatile element zn consistent with both impact glasses and crystalline mare basalts but much lower than in glasses of mare volcanic origin the glass contains siderophile elements such as ir in abundances only slightly higher than accepted lunar indigenous levels and some such as au are just below such upper limits the age of the glass determined by the 40ar 39ar laser incremental heating technique is 1647 11 ma 2 it is expressed as an age spectrum of seventeen steps over 96 of the 39ar released unusual for an impact glass trapped argon is negligible the undamaged nature of the sphere demonstrates that it must have spent most of its life buried in regolith 38ar cosmic ray exposure data suggest that it was buried at less than 2m but more than a few centimeters if a single depth is appropriate that the spherule solidified to a glass is surprising for such a mare composition cooling at about 50 c s 1 is required to avoid crystallization and barely attainable in such a large spherule the low volatile abundances slightly high siderophile abundances and the young age are perhaps all most consistent with an impact origin but nonetheless not absolutely definitive the 15434 28 glass is distinct from the common yellow impact glasses at the apollo 15 landing site in particular in its lower abundances of incompatible elements and much younger age if we accept an impact origin then the trace element relative abundances preclude both typical kreep and the common apollo 15 yellow impact glass from contributing more than a few percent of the incompatible elements to potential mixtures the melted part of any target must have consisted almost entirely of a variety or varieties of mare basalt or glass distinct from any known mare basalts or glasses including apollo 15 yellow volcanic glass or mixtures of them however the rind inclusions similar to materials of local origin do suggest a source near the apollo 15 landing site an impact melt cannot have dissolved much if any of such inclusions a lack of regolith materials in the rind and in the melt component suggest an immature source terrain thus even for an impact origin there is the possibility though not requirement that the volcanic target is younger than most mare plains the crater hadley c 25 km away is a potential source if the 15434 28 glass is instead directly of volcanic origin it represents an extremely young mare magma of a type previously undiscovered on the moon

mare basalt genesis modeling trace elements and isotopic ratios a model of the mare basalt source region and mare basalt genesis has been developed in which the primary magmas were produced by the partial melting 30 2 of shallow 200 km deep olivine dominated 73 to 80 olivine source regions they then assimilated small amounts of urkreep residuals as they cooled and underwent varying degrees of olivine pyroxene fractionation in shallow magma chambers binder 1982 this model was based on the mineralogical major oxide ni co ba and ree data on the basaltic units and a set of distribution equations developed to calculate the trace element evolution in the moon as it crystallized in the crust and mare basalt source region as they simultaneously formed and in urkreep as it formed and evolved this model has now been extended by 1 including the data for k rb and sr as well as the isotopic data for the rb sr and sm nd systems in the modeling 2 considering the effects of melt trapped during the formation of the source regions and 3 by the development of an additional distribution equation that allows the evolution of the trace elements to be calculated in the proposed sequence where crystals are both partially remelting in and being deposited from a convecting magma system the results of this study show that the proposed model does accurately account for the compatible siderophile trace element ni and co incompatible trace element k rb sr ba and the ree and isotopic rb sr and sm nd systems characteristics of the mare basalts and the pyroclastic glass units

geochemistry and time series analyses of orbitally forced upper cretaceous marl limestone rhythmites lehrte west syncline northern germany a cyclic marl limestone succession of middle late campanian age has been investigated with respect to a milankovitch controlled origin of geochemical data in general the major element geochemistry of the marl limestone rhythmites can be explained by a simple two component mixing model with the end members calcium carbonate and average shale like material carbonate content varies from 55 to 90 non carbonate components are clay minerals illite smectite and biogenic silica from sponge spicules as well as authigenically formed zeolites strontian heulandite and quartz the redox potential suggests oxidizing conditions throughout the section trace element and stable isotopic data as well as sem investigations show that the carbonate mud is mostly composed of low magnesium calcitic tests of planktic coccolithophorids and calcareous dinoflagellate cysts calcispheres diagenetic overprint results in a decrease of 2 18 o and an increase in mn of up to 250 ppm however the sediment seems to preserve most of its high sr content compared to the primary low magnesium calcite of co occurring belemnite rostra the periodicity of geochemical cycles is dominated by 413 ka and weak signals between 51 and 22 5 ka attributable to orbital forcing accumulation rates within these cycles vary between 40 and 50 m ma the resulting cyclic sedimentary sequence is the product of a changes in primary production of low magnesium calcitic biogenic material in surface waters within the long eccentricity and the precession demonstrated by the caco 3 content and the mg al mn al and sr al ratios and b fluctuations in climate and continental weathering which changed the quality of supplied clay minerals the illite smectite ratio demonstrated by the k al ratio high carbonate productivity correlates with smectite favouring weathering semi arid conditions conspicuously dry and moist seasonal changes in warmer climates ti as the proxy indicator for the detrital terrigenous influx as well as rb si zr and na shows only low frequency signals indicating nearly constant rates of supply throughout the more or less pure pelagic carbonate deposition of the long lasting third order middle upper campanian sedimentary cycle

source rock potential and depositional environment of upper cretaceous sedimentary rocks abu gharadig basin western desert egypt an integrated palynological organic and inorganic geochemical study abstract the abu gharadig basin in the northern part of the western desert egypt is among the most important petroleum provinces in egypt here cenomanian to santonian rocks of bahariya formation and abu roash a g members from the gpt 3 well were investigated for their depositional environment kerogen quality petroleum generation potential and thermal maturity by geochemical petrological and palynological methods the sediments of the bahariya and abu roash formations excluding the abu roash f member represent variable shallow marine environments with poor preservation of marine organic matter whereas there is an excellent preservation in the abu roash f member the basal part of this member is characterized by anoxic carbonate rich depositional conditions high toc values up to 7 high hi up to 700 mghc gtoc and liptinite dominated organic matter depletion of iron leads to sulfur incorporation into organic matter which is reflected in high thiophene benzene ratios above sediments are enriched in terrestrial elements fe ti as well as k and mn this pattern and the occurrence of the fresh brackish water algae botryococcus suggests a regression phase during deposition the upper part of the abu roash f member is again characterized by fully marine suboxic conditions and a lower thiophene benzene ratio the source rock section demonstrates lower thermal maturity compared to the above and below sections based on all microscopic pyrolysis and biomarker data this indicates thermal maturity retardation suppression most likely due to a different organic facies and early diagenetic transformation of kerogen as indicated by the geochemical and palynological data the source rock heterogeneity indicates a relatively shallow marine environment where the changes in bottom water conditions are very sensitive to sea level fluctuations residual oil characterization reveals two reservoir compartments which are in the abu roash d and c members the abu roash f source rocks are compared with time equivalent sediments in the tarfaya basin in morocco which represent more distal settings the more proximal group a is characterized by s fe ratios between 0 57 and 0 67 indicating suboxic conditions it has toc and hi values not exceeding 4 and 600 mghc gtoc respectively at variable caco3 contents the more distal tarfaya sediments group b have higher toc and hi as well as high organic sulfur contents group a is higher in terrigenous element concentrations the tmax of immature source rocks ranges from 410 to 415 c in organic sulfur rich samples and from 420 to 430 c in organic sulfur poor samples revealing an important impact of organic facies on maturity parameters furthermore there is an inverse relationship between s fe and al2o3 toc which might become an important tool in paleoenvironmental reconstructions as well as petroleum source rock studies

constraints of molecular and stable isotopic compositions on the origin of natural gas from middle triassic reservoirs in the chuanxi large gas field sichuan basin sw china abstract the middle triassic leikoupo formation in the sichuan basin is a gypsum bearing stratum the chuanxi cx large gas field has been recently discovered in middle triassic reservoirs with a controversial gas source the gas geochemistry is analyzed in this study to investigate the gas origin and source the h2s bearing dry gas in the cx gas field has an h2s content ranging from 1 07 to 4 09 with a gas souring index gsi of 0 0120 0 0438 the 13c1 13c2 and 2hch4 values range from 31 8 to 30 4 from 32 9 to 29 6 and from 153 to 136 respectively genetic identification based on the geochemical characteristics suggests that the gas is an oil type and derives from the secondary cracking of oil according to the gsi and alkane carbon isotopes the gas experienced weak tsr alteration without ethane potential high quality source rocks include the upper permian mudstones and marlstones as well as the lower cambrian mudstones with a total organic carbon content generally higher than 2 0 a comparison of the carbon isotopic compositions between ethane in the gas and kerogen and the hydrogen isotopic compositions of methane implies that natural gas has an affinity with the upper permian rather than the lower cambrian source rocks the extremely low development of solid bitumen in the reservoirs suggests the inexistence of large scale paleo oil pools in the leikoupo formation the middle triassic natural gas in the cx gas field originates from the upper permian longtan formation where the gas pools are dominated by direct filling of secondary cracking gas