hydrocarbon evolution of the over mature sinian dengying reservoir of the neoproterozoic sichuan basin china insights from re os geochronology abstract rhenium osmium re os geochronology is a robust technique for constraining the accurate timing of hydrocarbon evolution but its effectiveness in over mature petroleum systems has not been well constrained here we conduct a case study in the neoproterozoic sichuan basin china i e the sinian dengying sequence 635 542 ma re os isotopic data from this highly mature hydrocarbon reservoir yield a re os isochron ages of 414 44 ma with an initial 187os 188os osi of 1 36 0 19 for bitumen and a 78 37 ma age with an osi of 3 21 0 17 for pyrobitumen coupled with thermal evolution of possible source rocks and fluid inclusion homogenization temperatures the 414 ma age marks the timing of oil generation and the 78 ma age indicates the timing of gas generation associated with the thermal cracking of oil and the formation of pyrobitumen in the reservoir a comparison of the osi of the 414 ma bitumen and that of possible source rocks at the time of bitumen formation reveal that it was primarily sourced from shale of the lower cambrian qiongzhusi formation the results of this study provide new insights to better understand the over mature oil gas system in the sinian sichuan basin and show that dengying formation reservoirs in the depocenter areas of the basin are potentially favorable for oil and gas exploration the results further highlight the utility of the re os geochronometer to constrain the accurate age and source of hydrocarbon evolution

petroleum source rock identification of united kingdom atlantic margin oil fields and the western canadian oil sands using platinum palladium osmium and rhenium implications for global petroleum systems this study demonstrates that petroleum and source rocks are enriched in pt and pd to the ppb level and that the 187os 188os composition coupled with the pt pd value permits the fingerprinting of petroleum to its source oils from the united kingdom atlantic margin sourced from the upper jurassic kimmeridge clay fm as well as source rock samples have been analysed for pt and pd when the pt pd value is compared with 187os 188os calculated at the time of oil generation osg the values from both the known source and the oils are similar demonstrating that they can be used as an oil to source fingerprinting tool this inorganic petroleum fingerprinting tool is particularly important in heavily biodegraded petroleum systems where traditional fingerprinting techniques e g biomarkers are severely hampered e g the world s largest oil sand deposit the west canadian oil sands wcos this has caused the source of the wcos to be hotly debated with no present day consensus between inputs from potential source units e g exshaw and gordondale fms 187os 188os and pt pd fingerprinting of the oil sands shows that the majority of the petroleum have similar 187os 188os and pt pd values supporting the hypothesis of one principal source analysis of the potential source rocks establishes that the principal source of the oil sands to be from the jurassic gordondale fm with a minor exshaw fm input thus the combination of previously pioneered re os petroleum geochronology with 187os 188os and pt pd values of petroleum permits both a temporal and spatial understanding of petroleum systems

apatite fission track and re os geochronology of the xuefeng uplift china temporal implications for dry gas associated hydrocarbon systems hydrocarbon evolution is extremely challenging to determine both temporally and spatially in complex tectonic settings here we investigate the western margin of the xuefeng uplift southern china which records multiple and protracted tectonic and hydrocarbon generation events this timing of initial oil generation is recorded by low maturity bitumen type a which yields an re os bitumen date of ca 430 ma consistent with basin models and a ca 405 ma bitumen rb sr date in contrast apatite fission track aft data yield considerably younger dates that reflect the timing and tectonic evolution of the yanshan orogeny from the northwest ca 150 ma to the southeast ca 70 ma the youngest aft date coincides with the western margin of xuefeng uplift where high maturity bitumen type b occurs that yields a ca 70 ma re os date the re os and aft dates imply that both the last stage of the yanshan orogeny and by inference the cessation of dry gas generation occurred ca 70 ma the re os data of this study imply that the re os chronometer can aid in constraining the timing of oil generation and secondary and or more mature hydrocarbon processes e g thermal cracking and or gas generation in hydrocarbon systems worldwide

pronounced changes in paleo wind direction and dust sources during mis3b recorded in the tacheng loess northwest china abstract central asia loess deposits can yield detailed records of aridification across the asian interior as well as the atmospheric circulation in this study we presented grain size heavy mineral assemblage rock magnetism and anisotropy of magnetic susceptibility of a loess section in the tacheng basin in xinjiang region nw china the results of anisotropy of magnetic susceptibility indicated that a near surface se wind prevailed in the tacheng area since marine isotope stage mis 3 while a near surface sw prevailing wind developed during mis3b we inferred that the change of wind direction was due to glacial advance during mis3b combining the result of anisotropy of magnetic susceptibility with grain size heavy mineral assemblage data and previously published low field mass susceptibility revealed that dust transported by the near surface sw wind had a greater ability to enhance magnetic susceptibility and higher amphibole epidote ratio additionally a strong siberian high during heinrich event h 5 at ca 48 ka blocked the advection of moisture into the region via mid latitude westerlies causing glacial recession and the weakening of the prevailing sw wind our study has implications for identifying changes in paleo wind direction and dust source which can aid understanding of the influence of westerlies and the siberian high on dust accumulation as well as their interactions

a palaeomagnetic and mineral magnetic study of the loess sequence at liujiapo xian china employing an average vertical sampling interval of 20 cm oriented samples were collected from 26 m of the loess section at liujiapo near xian china in order to refine the existing magnetostratigraphic record palaeomagnetic results reveal two short reversed polarity subzones within a profile of predominantly normally magnetised sediments an interpretation that is at variance with previous results from this section and from other studies of chinese loess investigation of sediment mineral magnetic properties indicates a close correspondence between down section variations in intensity of magnetisation susceptibility and saturation isothermal journal of quaternary science remanence sirm and lithology the ratios irm 100mt sirm and sirm susceptibility appear to be particularly sensitive indicators of the degree of soil development and hence of palaeoclimate

re os geochronology and fingerprinting of united kingdom atlantic margin oil temporal implications for regional petroleum systems we demonstrate that the re os system can be used to understand the temporal evolution of a petroleum system as well as aid in the identification of source units traditional geochemical methods high performance liquid chromatography carbon isotope gas chromatography and biomarker analysis indicate that the main source of 18 oils analyzed for re os geochronology from the united kingdom atlantic margin clair schiehallion cuillin and foinaven fields is late jurassic marine shales this is supported by the os isotopic composition 187 os 188 os of the late jurassic source 0 9 2 4 at the timing of oil generation being similar to that of the oil 68 ma 0 92 1 12 indicating that the re os system can potentially be used to fingerprint the source of an oil the re os data for the 18 oils yield an age 68 13 ma that agrees with both the relative basin models and absolute ar ar geochronology timing of oil generation indicating that that re os oil geochronology records oil generation events

eruptive history of a low frequency and low output rate pleistocene volcano ciomadul south harghita mts romania based on a new set of k ar age data and detailed field observations the eruptive history of the youngest volcano in the whole carpathian pannonian region was reconstructed ciomadul volcano is a dacitic dome complex located at the southeastern end of the c limani gurghiu harghita neogene volcanic range in the east carpathians it consists of a central group of extrusive domes the ciomadul mare and haramul mare dome clusters and the koves ponk dome surrounded by a number of isolated peripheral domes some of them strongly eroded balvanyos puturosul and others topographically well preserved haramul mic dealul mare one of the domes dealul cet ii still preserves part of its original breccia envelope a large number of bread crust bombs found mostly along the southern slopes of the volcano suggest that the dome building activity at ciomadul was punctuated by short vulcanian type explosive events two late stage explosive events that ended the volcanic activity of ciomadul left behind two topographically well preserved craters disrupting the central group of domes the larger diameter shallower and older mohos phreatomagmatic crater and the smaller deeper and younger sf ana sub plinian crater phreatomagmatic products of the mohos center including accretionary lapilli bearing base surge deposits and poorly sorted airfall deposits with impact sags are known close to the eastern crater rim a key section studied in detail south of b ile tusnad shows the temporal succession of eruptive episodes related to the sf ana sub plinian event as well as relationships with the older dome building stages the age of this last eruptive event is loosely constrained by radiocarbon dating of charcoal pieces and paleosoil organic matter at ca 27 35 ka the age of the mohos eruption is not constrained but we suggest that it is closely related to the sf ana eruption the whole volcanic history of ciomadul spans over ca 1 myr starting with the building up of peripheral domes and then concentrating in its central part ciomadul appears as a small volume ca 8 74 km3 and very low frequency and low output rate volcano ca 9 km3 myr at the terminus of a gradually diminishing and extinguishing volcanic range a number of geodynamically active features strongly suggest that the magma plumbing system beneath ciomadul is not completely frozen so future activity cannot be ruled out

spatial variations in paleowind direction during the last glacial period in north china reconstructed from variations in the anisotropy of magnetic susceptibility of loess deposits abstract anisotropy of magnetic susceptibility ams of chinese loess is considered to be an effective tool for determining paleowind direction however the relationship between ams and the paleowind direction is still a matter of debate this study reports the results of ams measurements of chinese loess deposited during the last glacial period on slopes of varying slope angles and orientations the sites are located on the chinese loess plateau in west qinling and on the eastern margin of qilian mountain the results show that within the same region magnetic lineations are clustered along similar orientations despite differences in slope exposure and slope angle but that different regions exhibit different directions of magnetic lineation these results suggest that the alignment of the magnetic grains during deposition of the eolian deposits was determined by air circulation rather than by water flow on the surface of the slopes and therefore that the ams of chinese loess can be used to determine paleowind directions in addition our results indicate that the ams of chinese loess is determined mainly by the patterns of regional surface wind flow that occurred during dust accumulation rather than by the uniform pattern of large scale atmospheric circulation in addition since wind direction is influenced significantly by regional topography the ams of chinese loess may have the potential to detect significant changes in past regional topography

characterization of the magnetic fabric of rocks abstract an inextensive system of magnetic susceptibility anisotropy factors is suggested which is sufficient in the majority of practical applications for characterizing the magnetic fabric of rocks the system involves three newly devised factors the corrected anisotropy degree the shape factor and the difference shape factor the first of these characterizes the quantity of anisotropy somewhat better than the commonly used anisotropy degree the shape factor characterizes the quality of anisotropy i e the shape of the susceptibility ellipsoid in a convenient way its definition is based on a certain analogy between the anisotropy ellipsoid and the strain ellipsoid the difference shape factor can replace the shape factor when only the differences between the principal susceptibilities are given while the mean susceptibility is unknown

paleomonsoon route reconstruction along a w e transect in the chinese loess plateau using the anisotropy of magnetic susceptibility summer monsoon model abstract the anisotropy of magnetic susceptibility ams was investigated in three chinese loess plateau sedimentary sections along a w e transect 400 km the loess paleosol sequences in our study represent the most recent 130 kyr interval the measured ams was compared to expected theoretically derived magnetic fabrics occurring in strong and weak current airflow conditions the major and minor ams ellipsoid axis orientations were used to evaluate the paleowind direction along the transect previously published models assumed that cold and dry winter monsoons bringing dust from northwestern desert areas were responsible for the magnetic fabric formation of loess sequences in our new interpretation the stronger summer monsoons from the southeast played the major role in magnetic fabric orientation in the studied west and central parts of the chinese loess plateau although the material was brought to the area by the winter monsoon the ams was generated during the rainy summer monsoon when the sedimentary particles including magnetite were rearranged settled and fixed we reconstruct the summer paleomonsoon routes for the last 130 kyr these winds prevail from se to nw but appear to be affected by regional topographic factors in the western section the corridor between the north and south liupan mountains disturbed the summer monsoon route shifting it from se to see

the matuyama brunhes boundary in loess sections in the south of the east european plain and their correlation on the basis of palaeomagnetic and palaeopedologic data abstract the matuyama brunhes boundary mbb in loess sections of the east european plain one of the greatest areas of global loess distribution is a highly debatable issue the ambiguity of the mbb position here results from the complexity of loess soil magnetization processes and an apparent delay in loess remanence acquisition and from the uncertainties of pedostratigraphic interpretations in the don glaciation area the mbb is unanimously placed below the don moraine although the exact position is still controversial in the sites of the northern azov sea the mbb is however placed in the loess horizon considered to be the equivalent of the don moraine in the north the inconsistency of this interpretation is demonstrated by detailed magnetostratigraphic and pedostratigraphic studies in the western sites of zaporozh e dnieper basin novaya etuliya lower danube basin and roxolany lower dniester basin in all these sites albeit with certain minor discrepancies the mbb is found two or three interglacial palaeosols below the don loess which is overlain by the good stratigraphic marker of the vorona pedocomplex a thick polygenetic red brown palaeosol formed supposedly in a mediterranean climate here the mbb is placed in a quadruple soil unit termed roxolany loess soil suite which consists of four closely spaced strongly calcareous soils occupying an interval between the don loess on top and the earlier well developed bobrov loess with reversed matuyama magnetization the roxolany suite can possibly be correlated with the three palaeosols of the pre don ilyinka unit of the russian unified stratigraphic scheme and thus confirms the interpretation of the mbb in the central areas of the east european plain as to the interval between the ternovka second pre don palaeosol and the troitsk third pre don palaeosol

pedosedimentary division rock magnetism and chronology of the loess palaeosol sequence at roxolany ukraine abstract the loess mantle of the viii dniestre terrace at roxolany in the black sea area of ukraine is subdivided into six units which encompass the following palaeosol taxons pedocomplexes pk with evidence for several soil forming and sedimentary episodes incipient monogenetic palaeosols and horizons of carbonate concretions these cyclical loess palaeosol units provide a depositional record from the end of the matuyama chron through the holocene the detailed pedosedimentary subdivision of loesses at roxolany is generally consistent with magnetic susceptibility depth functions and seems to reflect global climatic variations earlier chronologies guidebook of the international geological congress xxvii session 1984 are re estimated on the basis of a revised position of the matuyama brunhes boundary and by detailed rock magnetic and micromorphological studies the strongly developed chernosem of pk 4 at approximately 22 m depth showing features of rubefication and the highest magnetic susceptibility value is viewed as a good stratigraphic marker of the late cromerian and seems to represent the climatic optimum of the brunhes chron oxygen isotope stage 13 the uppermost pk 2 is represented in the lower part by a chernosem analogous to surface soils of the area and is argued to be no younger than the last interglacial oxygen isotope stage 5e the poor preservation of pk 2 seems to result from processes of soil degradation and deflation at the time of interglacial glacial transition the closely spaced palaeosols between pk 2 and pk 4 seem to relate to three independent interglacials highest resolution of the palaeoclimatic record is found at the final matuyama chron from pk 9 to pk 8 and in incipient soils that contain either humic horizons with enhanced magnetic susceptibility or only horizons of large carbonate concretions

ore deposits of the french massif central insight into the metallogenesis of the variscan collision belt the french massif central fmc represents the whole west european variscan wev belt in terms of both the geodynamic evolution and the metallic content thus a study of the metallogenic evolution of the fmc may elucidate the conditions that allow the mineralisation of a collision belt since recent collision belts e g the himalayas or the alps show that mineralisation does not necessarily result from the collision process the palaeozoic history of the fmc is divided into three geodynamic stages unevenly involved from the metallogenic view point the eo variscan stage cambrian to silurian was not important the meso variscan stage devonian early carboniferous was of limited importance and most of the mineralisations formed during the neo variscan stage late carboniferous early permian in addition some more mineralisation was produced during the mesozoic because of the thermal reactivation linked with the alpine orogenies

magnetic fabric of loess and its significance in pleistocene environment reconstructions abstract a summary of approximately three decades and greater than thirty loess magnetic fabric studies is presented here the revised studies cover various loess regions from the chinese loess plateau across the european loess belt to alaska although there is still an ongoing argument about the feasibility of the magnetic fabric of loess in paleowind reconstructions the determination of prevailing wind direction during various periods of the pleistocene is the main goal of magnetic anisotropy analysis of the revised loess successions the magnetic fabric analysis of loess from chinese loess plateau provided significant information about the characteristics of paleomonsoon in east asia and the results from other loess regions such as alaska the european loess belt and siberia are also promising as it is shown in this review the synthesis of the paleowind direction results from the studied profiles may already provide a significant foundation for future climate models by the reconstruction of key climate centres and main continental level wind tracks besides the reconstruction of prevailing paleowind directions there are numerous loess magnetic fabric studies using magnetic anisotropy parameters in the reconstruction of the characteristics of long term climate trends climate transitions and glacial interglacial cycles there are some lesser known aspects contributing to magnetic fabric of loess such as the influence of various types of magnetic contributors on the overall fabric i e the study of sub fabrics and their role in environment reconstruction besides the identification of aeolian magnetic fabric not so many studies focus on the magnetic anisotropy characteristics of materials possibly developed by water lain sedimentation pedogenesis mass movements and permafrost activity novel results from hungarian loess especially from paks connected to some of the latter topics are also presented such topics includes the analysis of the nanofabric in paleosols developed by pedogenesis the comparison of magnetic fabric formed during high energy transportation by aeolian or aquatic agents and the periodicity analysis of magnetic parameters during the early middle pleistocene new research lines introduced in this review may inspire new researches and provide new perspectives for the next generation of magnetic anisotropy studies of loess successions

a rhaetian 40 ar 39 ar age for the rochechouart impact structure france and implications for the latest triassic sedimentary record ar 39 ar dating of potassium feldspar primary spherulitic blocky and secondary idiomorphic k feldspar separated from impact metamorphosed gneiss found near videix in the western central part of the rochechouart impact structure nw massif central france yielded a rhaetian combined age of 201 2 ma 2r indistinguishable within uncertainty from the age of the triassic jurassic boundary ballen quartz intergrown with the primary k feldspar indicates post shock temperatures exceeding approximately 1000 c that affected the precursor gneiss geochemically both feldspar types represent essentially pure potassium end members apart from the approximately 15 km diameter impact deposit area the youngest crystallization age known for basement rocks in this part of the massif central is approximately 300 ma no endogenic magmatic thermal events are known to have occurred later in this region the k feldspar recrystallized from local feldspar melts and superimposed post shock hydrothermal crystallization probably within some thousands of years after the impact it is therefore suggested that the 40 ar 39 ar age for the videix gneiss as a potassic impact metasomatite dates the rochechouart impact in consistence with evidence for k metasomatism in the rochechouart impactites the new age value is distinctly younger than the previously obtained karnian norian age for rochechouart and thus contradicts the late triassic multiple impact theory postulated some years ago in agreement with the paleogeographic conditions in the western tethys domain around the triassic jurassic boundary the near coastal to shallow marine rochechouart impact is compatible with the formation of seismites and tsunami deposits in the latest triassic of the british isles and possible related deposits in other parts of europe

the latest explosive eruptions of ciomadul csomad volcano east carpathians a tephrostratigraphic approach for the 51 29 ka bp time interval abstract the most recent mainly explosive eruptions of ciomadul the youngest volcano in the carpatho pannonian region have been constrained by detailed field volcanological studies major element pumice glass geochemistry luminescence and radiocarbon dating and a critical evaluation of available geochronological data these investigations were complemented by the first tephrostratigraphic studies of the lacustrine infill of ciomadul s twin craters st ana and mohos that received tephra deposition during the last eruptions of the volcano our analysis shows that significant explosive activity collectively called eppa early phreatomagmatic and plinian activity started at ciomadul in or around the present day mohos the older crater at 51 ka bp these eruptions resulted in a thick succession of pyroclastic fall deposits found in both proximal and medial distal localities around the volcano characterized by highly silicic rhyolitic glass chemical compositions ca 75 2 79 8 wt sio 2 the eppa stage was terminated by a subplinian plinian eruption at 43 ka bp producing pumiceous pyroclastic fall and flow deposits of similar glass composition probably from a proto st ana vent located at or around the younger crater hosting the present day lake st ana after a quiescent period with a proposed lava dome growth in the st ana crater a new explosive stage began defined as mpa middle plinian activity in particular a significant two phase eruption occurred at 31 5 ka bp producing pyroclastic flows from vulcanian explosions disrupting the preexisting lava dome of sf ana and followed by pumiceous fallout from a plinian eruption column related pyroclastic deposits show a characteristic less evolved rhyolitic glass composition ca 70 2 74 5 wt sio 2 and occur both in proximal and medial distal localities up to 21 km from source the mpa eruptions that may have pre shaped a crater similar to but possibly smaller than the present day st ana crater was followed by a so far unknown but likewise violent last eruptive stage from the same vent creating the final morphology of the crater this stage referred to as lspa latest st ana phreatomagmatic activity produced pyroclastic fall deposits of more evolved rhyolitic glass composition ca 72 8 78 8 wt sio 2 compared to that of the previous mpa stage according to radiocarbon age constraints on bulk sediment charcoal and organic matter from lacustrine sediments recovered from both craters the last of these phreatomagmatic eruptions that draped the landscape toward the east and southeast of the volcano occurred at 29 6 ka bp some 2000 years later than the previously suggested last eruption of ciomadul

paleowind directions from the magnetic fabric of loess profiles in central alaska abstract two parallel profiles of alternating loess and paleosol horizons from the halfway house site west of fairbanks in central alaska were evaluated in terms of their potential for preserving paleowind directions combined the profiles span specmap marine oxygen isotope stages 1 6 approximately the last 150 ka our analytical tools consisted of measuring the sample s anisotropy of magnetic susceptibility and characterizing the magnetic mineralogy by multiple approaches both primary eolian and secondary reworked magnetic fabrics are recognized along certain intervals of both profiles primary eolian fabrics display a horizontal magnetic foliation and a well defined magnetic lineation corresponding to the paleodirection of sediment transport and deposition a systematic change in transport direction is observed where long term prevailing winds appear to shift from a nw se to n s direction during glacial and interglacial periods respectively

influence of paleo trade winds on facies patterns of the cambrian shanganning carbonate platform north china abstract the shanganning carbonate platform scp of the north china craton ncc was located in the trade winds belt during the cambrian which influenced its facies development in recent years numerous drillcores have been recovered from these units but the depositional environments and facies architecture of this large 2 0 105 km2 carbonate platform system have not yet been reported in detail in this study we integrate sedimentological and magnetic fabric data collected from outcrops and drillcores in order to document variation in microfacies and facies associations within the scp to infer paleowind directions and constrain the paleogeographic location of the scp and to evaluate eolian controls on platform development this analysis documented numerous carbonate microfacies belonging to six fabric types mudstone wackestone packstone grainstone framestone and dolostone along with rarer siliciclastic sediments these microfacies belong to facies associations representing tidal flat open platform platform margin slope and deep basinal depositional environments anisotropy of magnetic susceptibility ams measurements yielded mean paleocurrent directions for the early middle and late cambrian of 114 63 and 83 30 from paleo north respectively that were relatively consistent for 12 out of 13 platform margin sites all vectors being corrected for a post cambrian 150 clockwise rotation of the ncc these wind orientations are consistent with the scp shifting from south of the paleo equator in the early cambrian to north of it by the middle cambrian paleo trade winds influenced facies patterns across the platform producing a distinct windward leeward zonation the windward margin is characterized by well sorted oolitic grainstone as well as favositids coral and dasycladacean algal sponge framestone and the leeward margin by poorly sorted oolitic wackestone grainstone and fine bioclastic sediments the present study is innovative in 1 integrating microfacies and ams analyses in order to establish paleowind patterns and influences on an ancient carbonate platform 2 documenting windward leeward variation in quantifiable sediment properties across the scp and 3 constraining the paleo hemispheric location of the ncc during the cambrian

roxolany and novaya etuliya key sections in the western black sea loess area magnetostratigraphy rock magnetism and paleopedology abstract loess paleosol sequences in the western black sea area at roxolany 48 m thick and novaya etuliya 30 m thick were studied using paleo and rock magnetic methods in conjunction with micromorphology and mossbauer investigations although seemingly complete the sites show variability in the type and number of loess paleosol cycles and inconsistency of the matuyama brunhes boundary mbb stratigraphic position at roxolany nine pedocomplexes pk and several incipient paleosols alternating with thick loesses were observed with the mbb being located between pk 6 and pk 7 at novaya etuliya 13 pks occur upon terrace xii with khapry fauna and with the mbb in the upper part of pk 7 and the jaramillo subchron within the lower part of pk 8 the depth functions of rock magnetic properties organic carbon content c org both for bulk samples and for clay extracts along with micromorphology and mossbauer spectra allowed objective identification of individual soils within pks and maximizing the resolution of paleopedological reconstructions of global climatic stages the mossbauer studies demonstrate that paleosols are basically enriched in ferric montmorillonite oxidized magnetite ultrafine iron hydroxides and hematite are intimately associated with clay minerals in contrast fe compounds in loess consist mainly of ferrous silicates these data indicate that the paleosol magnetism is basically of bio chemogenic origin and is related to pedogenic transformation of fe compounds in a changing environment while loess magnetism is primarily detrital pedogenic magnetically soft and partly oxidized magnetite may also originate during or even after burial this ensuing transformation of fe minerals in paleosols seems to be crucial for the understanding of the timing of natural remanent magnetization nrm in subaerial sediments given that paleosols formed on the similar parent material loess their typological variability seems to depend on climate and or chronology hence the different paleosol types from roxolany and novaya etuliya provide key information for intra and inter regional correlation of loess soil sequences and represent valid paleoclimatic proxies

geochemistry of the sinian cambrian gas system in the sichuan basin china abstract based on the outcrops core samples drilling cuttings seismic and geochemical data natural gases of the sinian cambrian gas system were derived from four sets of over mature high quality source rocks the cambrian qiongzhusi source rock is sapropelic with toc of 1 94 ro eq of 1 83 3 90 and a thickness of 140 m on average the sinian 620 541 ma doushantuo source rock is sapropelic with toc of 1 69 ro eq of 2 08 3 83 and a thickness of 11 m on average the 3rd member of the dengying fm is also sapropelic with toc of 1 43 ro eq of 3 16 3 21 and a thickness of 13 m on average the 2nd and 4th members of the dengying fm are dominated by algal dolomite with toc of exhibiting 0 39 ro eq of 1 97 3 46 and a thickness of 246 m on average most of the 13c2 values are lower than 28 and gas dryness is 99 indicating that the natural gas is oil derived with high maturity the high contents of isoparaffins and cycloparaffin suggest that natural gas in the sinian cambrian reservoir was originated from secondary oil cracking the cambrian longwangmiao gas was mainly derived from the cambrian qiongzhusi source rock and the gas within the sinian dengying formation mainly originated from the three sinian source rock layers the area with gas generation intensity superimposed the four sets of source rocks exceeding 6 109 m3 km2 covered 80 of the sichuan basin the proved reserves exceed 1 0 1012 m3 in the sinian cambrian gas system and the accumulated gas resource in the sinian cambrian gas system might exceed 5 1012 m3

petroleum generation timing and source in the northern longmen shan thrust belt southwest china implications for multiple oil generation episodes and sources the temporal evolution of hydrocarbons 500 million bbl and its relationship to the orogenic events of the longmen shan thrust belt have been extensively debated the hydrocarbons occur as solid bitumen as dykes and or coatings within along faults fractures and as present day oil seeps here utilizing organic geochemistry we demonstrate that all of the bitumen exhibit similar organo geochemical characteristics and were sourced from the upper neoproterozoic lower cambrian doushantuo and qiongzhusi formations in contrast the organic geochemistry of the present day oil seeps are distinct from that of the bitumen and suggest that the source is the permian dalong formation bitumen re os data indicate that the upper neoproterozoic lower cambrian doushantuo and qiongzhusi formations underwent two temporally distinct oil generation events initial oil generation occurred during the late cambrian early ordovician prior to the caledonian orogeny and secondly during the jurassic 165 ma coinciding with the indosinian yanshan orogenies in contrast the re os data of the present day oil seeps are too similar to yield a meaningful age although the source is considered to have undergone hydrocarbon maturation between the triassic and jurassic the temporal hydrocarbon evolution in the longmen shan thrust belt also provides an understanding of the hydrocarbon evolution and future exploration of the adjacent petroliferous sichuan basin

pb ages of detrital zircons in relation to geodynamic evolution paleozoic of the northern gemericum western carpathians slovakia abstract new u pb sensitive high resolution ion microprobe shrimp detrital zircon ages from early paleozoic to permian siliciclastic metasediments are used to constrain provenance and paleogeographic affinity of the northern gemericum unit ngu in the western carpathians central europe the samples span the time period from 480 ma to 260 ma and permit the recognition of provenance changes that reflect the realm s geodynamic evolution the detrital zircon age spectrum of one early paleozoic sample resembles the neoproterozoic and archean ages of the cadomian belt 550 650 ma and the west african craton provenances 1 8 2 7 ga the origin of the early paleozoic ngu rakovec basin is inferred to be the rifting as followed by back arc spreading which occurred at the cambrian ordovician boundary ca 480 ma as continental pieces started to split off from the gondwanan margin the deformation and closure of the early paleozoic basin is coincident with the 355 ma peak of the post tournaisian detrital zircon age assemblage the detrital zircon age spectra of two post mississippian and two post artinskian samples indicate high exhumation and erosion rates in the variscan collision belt pennsylvanian permian sedimentary troughs formed between 318 and 275 ma record contemporaneous unroofing of the variscan collision belt and magmatic activity during post orogenic transtensional tectonics zircon age spectra reflect these three paleozoic 480 419 ma 340 380 ma 320 275 ma tectono thermal events and permit the recognition of provenances both of which supporting the interpreted changes in geotectonic regime from ordovician rifting to variscan compression and the subsequent extension the zircon age data constrain the provenance linkage of the low grade ngu basement to the cadomian fragments within the west european variscides

the regional and temporal significance of primary aeolian magnetic fabrics preserved in alaskan loess abstract the anisotropy of magnetic susceptibility ams data presented herein underscore the resolving power magnetic anisotropy has in non lithified poorly consolidated sediments we turn our attention to primary aeolian sedimentary magnetic fabrics preserved along two coeval loess profiles in central alaska at the halfway house hh3 and gold hill steps ghs2 sites we first demonstrate that published preliminary results along hh1 and hh2 are reproducible moreover the new sample suite the first ever at ghs collected at a higher temporal resolution and statistical confidence permits a better evaluation of the significance of the inferred paleowind directions and their temporal variability the data demonstrate that the resolvability of the magnetic lineation is independent of both the eccentricity of the ams ellipsoid and the strength of the magnetic foliation furthermore the orientations and temporal variability of the most significant magnetic lineations are not artifacts of the data filtering process developed to isolate them we conclude that the temporal variations of inferred paleowind directions along hh3 track paleoclimatic glacial interglacial cycles as well as provide additional constraints to the geochronology of the loess deposit along ghs2 the limited coeval primary magnetic fabrics suggest an influence from a local microclimate not present at the hh site complicating the interpretation of small scale variability in paleowind directions however the overall average paleowind directions are similar to those inferred along hh3 confirming a regional spatial consistency of past surface air circulation

discovery of oil bitumen co existing with solid bitumen in the lower cambrian longwangmiao giant gas reservoir sichuan basin southwestern china implications for hydrocarbon accumulation process abstract natural gas in the recently discovered lower cambrian longwangmiao giant gas reservoir of the sichuan basin in southwestern china has been considered to be from oil cracking and sourced from the underlying lower cambrian qiongzhusi shales similar to the underlying neoproterozoic dengying giant gas reservoir however geological considerations and differences in geochemistry between the longwangmiao and dengying gases bitumens imply different scenarios organic petrology geochemistry and trace element analyses of widely occurring bitumen were conducted to evaluate this hypothesis results show the coexistence of solid bitumen and oil bitumen in this reservoir for the first time which implies a new hydrocarbon accumulation process and associated exploration strategies the two types of bitumen were termed type a solid bitumen and type b oil bitumen which were sourced from the lower cambrian qiongzhusi formation shale and the lower silurian longmaxi shale respectively the type a solid bitumen shows little fluorescence and its color under plane polarized light is almost black this indicates that the type a solid bitumen is likely of high maturity it typically occurs in dissolution pores and accounts for approximately 90 of all bitumen in the reservoir in contrast the type b oil bitumen is brown black in color under plane polarized light and yellow green under fluorescence light indicating that it is mature it occurs in the residual spaces of the solid bitumen and represents approximately 10 of the total bitumen content this suggests that type a bitumen charged the reservoir earlier than did the type b bitumen during the indosinian epoch of the triassic oil generated from the mature qiongzhusi formation migrated into the longwangmiao and dengying reservoirs following this the dengying reservoir reached the temperature threshold for oil cracking since the late cretaceous and it is suggested that oil could have started to crack to gas which is the critical moment for the gas formation however the longwangmiao oils had not been cracked at this stage because the reservoir temperature had not reached the threshold later during the himalayan epoch the gas in the dengying reservoir as well as some kerogen cracking gas from the qiongzhusi shales migrated into the longwangmiao reservoir along faults gas gravity drainage and phase separation took place in the longwangmiao reservoir forming the type a solid bitumen and giant gas accumulation later oil generated from the longmaxi shales migrated into the longwangmiao reservoir forming the type b oil bitumen the case here is an example of a multi stage oil and gas accumulation future exploration targets should include middle upper cambrian reservoir rocks

major elements trace hydrocarbon sources in over mature petroleum systems insights from the sinian sichuan basin china abstract identifying hydrocarbon sources in over mature petroleum systems is important and challenging here we present a pilot study using inorganic geochemistry to trace hydrocarbon sources in the giant natural gas accumulations within the sinian neoproterozoic dengying formation in the sichuan basin sw china we investigated the major elements ti al fe mn mg ca na k and p as tracers of hydrocarbon sources for the first time our results show that the over mature solid bitumen in the reservoirs contains parts per million amounts of major elements in addition to carbon i e organic matter na and k in the bitumen occur mainly in the v ni porphyrin form al fe and mn are present in the fe porphyrin form the behavior of p is relatively complex and it may reside mainly in a non porphyrin organic form the other elements ti mg and ca may be present as emulsified invisible nano minerals the mn fe ratio and ternary 10mn fe p diagram can be used for hydrocarbon source rock correlations based on the proxies it is suggested that the lower cambrian qiongzhusi formation was the main source of hydrocarbons in the dengying formation our data suggest that inorganic geochemistry is an effective method for the study of over mature hydrocarbons and complements traditional organic geochemical approaches

revisiting the chronostratigraphy of late pleistocene loess paleosol sequences in southwestern ukraine osl dating of kurortne section abstract due to the general lack of other high resolution paleoclimate records loess paleosol sequences are crucial archives for disentangling past climate variability in southeastern europe here we present results of a multi proxy sedimentological and geochemical investigation of kurortne loess paleosol section from southwestern ukraine coupled with detailed optically stimulated luminescence osl dating osl investigations were carried out on quartz grains of different grain sizes 4 11 m 63 90 m and 90 125 m using the single aliquot regenerative sar protocol the osl dating results are in line with previous findings on dating loess paleosol sequences along the black sea shore in romania as well as worldwide i ages obtained on different grain sizes are in agreement for equivalent doses of less than 200 gy whereas for higher equivalent doses 4 11 m ages underestimate the coarser fraction ages and ii an inverse correlation between dated grain size fractions and saturation characteristics is reported our combined dating and sedimentological approach would confirm that the investigated uppermost 4 5 m at kurortne cover the last glacial cycle adding important data in better constraining local and regional chronostratigraphic correlations the application of the sar protocol on 63 90 m quartz grains on samples collected from the lower part of s1 soil the kaydaky unit and from the kaydaky pryluky units boundary produced ages of 123 10 ka and 85 6 ka respectively as the temporal range covered by these units in the ukrainian quaternary stratigraphic framework is still debatable our results confirm the broad correlation of the kaydaky pryluky paleosol units at kurortne with the last interglacial i e mis 5 dating the uday and bug loess units produced ages corresponding to mis 4 and mis 2 respectively whereas the sample collected from the vytachiv unit provided an age of 37 7 2 4 ka assigning this paleosol to mis 3 on the basis of trends in the magnetic enhancement the onset of pedogenetic processes likely commenced already around 20 ka but the formation of the topmost s0 soil has begun after 13 8 1 0 ka

direct radiometric dating of hydrocarbon deposits using rhenium osmium isotopes rhenium osmium re os data from migrated hydrocarbons establish the timing of petroleum emplacement for the giant oil sand deposits of alberta canada at 112 5 3 million years ago this date does not support models that invoke oil generation and migration for these deposits in the late cretaceous most re os data from a variety of deposits within the giant hydrocarbon system show similar characteristics supporting the notion of a single source for these hydrocarbons the re os data disqualify cretaceous rocks as the primary hydrocarbon source but suggest an origin from older source rocks this approach should be applicable to dating oil deposits worldwide

evaluation of bitumen as a 187re 187os geochronometer for hydrocarbon maturation and migration a test case from the polaris mvt deposit canada abstract re os analyses of bitumen from the polaris mississippi valley type zn pb deposit demonstrate the potential utility of the re os system for establishing the absolute timing of hydrocarbon migration and generation the polaris deposit is hosted by carbonate rocks of the upper ordovician thumb mountain formation and sulphide mineralization during late devonian time is constrained by a rb sr sphalerite date of 366 15 ma and a paleomagnetic date bitumen occurs in open space fillings and coatings and is interpreted to have formed during the main and late stages of sulphide mineralization samples of bitumen were taken from a variety of locations from the main deposit at polaris re and os contents are 3 78 ppb and 55 1155 ppt respectively the 187re 188os ratios are very high ranging from 300 to 1800 and the os isotopic composition is moderately to highly radiogenic with 187os 188os ratios ranging from 3 3 to 13 7 calculated 187os 188os ratios at 366 ma are variable but an obvious grouping is defined by 11 of 16 analyses on a re os isochron diagram and these data yield a re os date of 374 9 ma mswd 12 model 3 in agreement with rb sr sphalerite and paleomagnetic dates for mineralization at polaris the combined dates suggest that the migration of fluids responsible for both pb zn mineralization and bitumen formation at polaris was broadly contemporaneous and was coeval with the late devonian ellesmerian orogeny though considerable further research is required to understand the re os isotopic systematics of migrated hydrocarbon systems bitumen re os geochronology may provide the possibility of establishing a more comprehensive understanding of mvt deposits sedimentary basin and petroleum systems

high precision 40ar 39ar age of the gas emplacement into the songliao basin the problem of determining an exact isotopic age of hydrocarbon emplacement is complex because minerals suitable for dating with common isotopic methods are often lacking in the sedimentary domain however the igneous quartz from the cretaceous volcanic rocks that host the gas reservoir in the songliao basin northeastern china contains abundant secondary fluid inclusions with high concentrations of k and high partial pressures of methane trapped during gas emplacement quartz with abundant k rich fluid inclusions provides an excellent closed system well suited for 40 ar 39 ar dating three igneous quartz samples were measured by stepwise crushing to release the inclusion based argon gas all three samples yielded well defined isochrons with ages in close agreement precisely constraining the gas emplacement at 42 4 0 5 ma 2 below the daqing oil field in the songliao basin extending possible gas reservoirs from the upper cretaceous to the middle eocene

shock behavior of zircon phase transition to scheelite structure and decomposition abstract both single crystal and powdered specimens of zircon zrsio4 were shocked to peak pressures between 30 and 94 gpa using the gun method and specimens recovered were studied by means of x ray diffraction analysis transmission electron microscopy and infrared spectroscopy transformation to the scheelite structure started above 30 gpa and was completed above 53 gpa in the case of single crystal specimens tetragonal unit cell parameters of the scheelite type zrsio4 at room condition are measured to bea 4 7341 1 a c 10 51 1 a c a 2 219 2 andv 235 5 2 a3 which is smaller than that of the zircon type by 9 9 the recovered scheelite type zrsio4 reverts to the zircon type after rapid heating to 1200 c at room pressure this transformation from the zircon type to the scheelite type is unique in that it is fast displacive like but does not reverse tetragonal zro2 was detected as decomposition product in the single crystal specimen shocked to 94 gpa and further confirmed in a powdered specimen shocked to 53 gpa where enhancement of temperature is expected because of high porosity decomposition behavior of zircon observed in natural shock events is discussed on the basis of present experimental results

subaerial and subaqueous deposition of loess experimental assessment of detrital remanent magnetization in chinese loess abstract loess and intercalated paleosols on the chinese loess plateau clp are the most extensive and continuous terrestrial archive of geomagnetic and paleoclimate variations covering the last 2 6 ma a first order time frame has been established for these sequences using paleomagnetic polarity boundaries major inconsistencies between the positioning of the matuyama brunhes polarity boundary in chinese loess paleosol sequences and marine records previously accounted for by assuming magnetization lock in depths in loess of up to 2 3 m have recently been resolved using a paleoclimatic indicator insensitive to pedogenesis that does require any major post depositional acquisition of a remanent magnetization this resolved controversy accentuates the lack of an adequate understanding of how chinese loess acquires and retains a stable remanent magnetization we report on laboratory re deposition experiments with subaerial and subaqueous simulations of natural loess to elucidate factors controlling the acquisition of magnetization in loess our work complements and extends recently published results from comparable laboratory experiments by zhao and roberts 2010 our major finding is that a stable magnetization is acquired and retained after initial wetting of dry deposited loess with no significant time lag in general accord with recent findings

middle upper pleistocene bio climatic and magnetic records of the northern black sea coastal area loess palaeosol sequences are widespread in the northern black sea coastal area unlike the quasi continuous loess palaeosol series in central asia and the loess plateau of china the incomplete geological record of loess palaeosol successions in europe provokes different stratigraphical interpretations for different sections despite a long history of investigation many uncertainties still remain in the geochronology of the regional stratigraphy in this study some of the most representative loess palaeosol sections of moldova the dniester republic southern ukraine and southern russia were examined a multidisciplinary approach was used to establish stratigraphical markers seven palaeosols pedocomplexes are distinguished within the brunhes chron in the loess palaeosol sequence in the studied area the position of the matuyama brunhes m b reversal is drawn at the base of the kolkotova palaeosol complex in the khadzimus section the jaramillo subchron was revealed at the base of the loess formation this magnetostratigraphic framework is confirmed by biostratigraphical data small mammals are valuable serving as very important evidence for long distance correlation paleopedological data combined with magnetic susceptibility profiles provide additional stratigraphic control for a loess palaeosol correlation the results allow us to conclude that the main paleoenvironmental changes occurred ca 1 ma ago when lagoon and alluvial sedimentation was replaced by increasing loess accumulaton during some intervals erosion or variation in the loess sedimentation rate at different sites are responsible for the variability of the loess palaeosol alternation the correlation of the loess palaeosol succession in the brunhes chron with marine oxygen isotope stages suggests that the beginning of the loess palaeosol formation of the middle pleistocene was forced by more pronounced long paleoclimatic cycles than are noticed prior to the m b reversal

palaeowind directions and sources of detrital material archived in the roxolany loess section southern ukraine abstract measurements of the anisotropy of whole rock magnetic susceptibility ams and u pb ages of detrital zircons have been combined to define the palaeowind directions and sources of wind blown dust in the loess palaeosol key section at roxolany southern ukraine zircon dating has also been used to determine the age and provenance of the interbedded roxolany tephra the distribution of ams axes in the loess indicates that the prevailing wind during its accumulation blew from the north west the same as the mean present day summer wind direction measured in the nerby city of odessa the u pb isotopic ages of the detrital zircons mostly range between 0 25 and 2 ga with clusters at 0 28 0 32 0 45 0 58 1 0 and 1 5 ga single neoarchean grains ca 2 7 ga were also found these ages indicate that material from carpathian and podolian sources formed the roxolany loess this material initially was transported by the dniester river then was wind blown form the dniester liman and the lower dniester valley located nw of roxolany most of the pyroclastic zircons from the roxolany tephra gave ages of 470 840 ka with a peak between 500 and 750 ka this age range is consistent with their being derived from the ciomadul volcano in romania

the roxolany tephra ukraine new evidence for an origin from ciomadul volcano east carpathians we present major element glass data and correlations for the roxolany tephra a so far geochemically unconstrained volcanic ash layer previously described in last glacial marine isotope stage 2 loess deposits of the roxolany loess palaeosol complex in south west ukraine this exceptionally well preserved 2 3 cm thick tephra layer is characterized by a rhyolitic glass composition that is comparable to that of proximal tephra units from ciomadul volcano in the east carpathians central romania the chemistry particularly matches that of the final latest st ana phreatomagmatic activity pyroclastic fall unit of st ana crater that is radiocarbon dated in the proximal mohos coring site moh 2 to 29 6 0 62 cal ka bp the age of the tephra correlative agrees with the newest radiocarbon and infrared optically stimulated luminescence age constraints from overlying palaeosols and tephra embedding loess of the roxolany sequence respectively which place the tephra between ca 33 and 24 cal ka bp and thus confirm the long debated chronostratigraphy of this important environmental archive the occurrence of a distal ciomadul tephra ca 350 km east of its source indicates great potential for further tephra and cryptotephra findings from this volcanic complex in the south eastern mediterranean and black sea region

pb pb dating of hydrocarbon migration into a bitumen bearing ore deposit north wales previous attempts at u pb dating of uraniferous bitumens have had limited significance because of radioelement migration pb pb dating which can be undertaken regardless of recent lead migration has been successfully applied to uraniferous solidified bitumen from the ty gwyn copper deposit north wales analyses of five bitumen samples with variable mixtures of radiogenic and common lead yield a sup 207 pb sup 206 pb age of 248 plus minus 21 ma early triassic this age is interpreted as the date of hydrocarbon migration into the deposit and is reasonably consistent with the timing of hydrocarbon generation calculated from the regional burial history the pb pb dating method could be applied to date uraniferous bitumens representing hydrocarbon migration in diverse geologic environments

dating of multistage fluid flow in sandstones through ultraviolet laser argon argon dating of potassium feldspar cements containing fluid inclusions we determined temperature composition time data for paleofluids in a sedimentary basin including data for an evolving episode of fluid flow recorded in distinct phases of cement the fluid evolved from mixed aqueous oil 83 million years ago to purely aqueous by 76 million years ago thus dating the time of oil charge in this reservoir

re os dating of maltenes and asphaltenes within single samples of crude oil abstract re os geochronology of oil may constrain the timing of oil formation and improve oil source and oil oil correlations typically asphaltene asph the heaviest and most re os rich oil fraction from multiple oils within an oil field or a larger petroleum system are analyzed to obtain sufficient spread in re os isotopic ratios a mathematical necessity for precise re os isochrons here we offer a new approach for re os geochronology of oil based on isotopic analyses of different fractions within a single sample of crude oil we studied three oils from the gela oil field southern sicily italy recovered from triassic jurassic stratigraphic intervals streppenosa noto and sciacca formations within the gela 1 well asph insoluble in n alkane and maltene malt soluble in n alkane fractions of oil were separated using n pentane n hexane n heptane and n decane solvents the asph contents of the sciacca and noto oils 26 33 wt are notably higher compared to the streppenosa oil 7 12 wt asph we present an optimized re os procedure with sample digestion in a high pressure asher followed by isotopic measurements using negative thermal ionization mass spectrometry very high metal contents of gela oils allowed acquisition of precise re os data systematic variations between the type of solvent used for asph precipitation and the asph content of the oil also known from the literature and the re os contents of the asph and malt fractions first observed in this study provide important practical applications for re os analyses of oil most re and os 96 98 in the noto oil are hosted in the asph fraction in contrast a significant portion of re and os 33 34 is stored in the malt fraction of the lighter but heavily biodegraded streppenosa oil collectively our new data on alkane distribution hopane and sterane biomarkers major and trace element contents and re os concentrations and isotopic ratios of the oils and their fractions support the presence of two oil families streppenosa oil a heavily biodegraded oil generated at an early stage of thermal maturation from a shaly source rock is clearly distinct from the noto and sciacca oils both generated at peak maturation from a carbonate source rock with no subsequent biodegradation two re os ages were obtained crude oil and asph from noto and sciacca oil yield a model 1 isochron age of 27 5 4 6 ma with an initial 187 os 188 os of 3 89 0 43 mswd 1 6 n 19 we interpret this oligocene age as the time of initial oil generation that was probably related to the onset of regional collisional tectonics in southern sicily asph and crude oil from the streppenosa oil yield scattered data perhaps related to effects of biodegradation streppenosa malt yield a model 1 age of 200 0 5 2 ma and initial 187 os 188 os of 1 39 0 11 mswd 0 52 n 4 this age and initial os isotopic composition are consistent with rapid oil generation shortly after late triassic source rock formation perhaps driven by magmatic related heating here we document a potentially powerful geochronological tool that can be applied to single samples of crude oil within each oil the 187 os 188 os and most of the 187 re 188 os ratios in the malt fractions are lower than in the corresponding asph fractions crude oils being physical mixtures of asph and malt have intermediate re os isotopic ratios hence the needed spread in data points for a re os isochron is obtained by analyzing components of a single crude oil this approach eliminates pitfalls in interpretation of re os data from multiple oils with possibly different generation migration or reservoir modification history

evaluation of the rhenium osmium geochronometer in the phosphoria petroleum system bighorn basin of wyoming and montana usa rhenium osmium re os geochronometry is applied to crude oils derived from the permian phosphoria formation of the bighorn basin in wyoming and montana to determine whether the radiogenic age reflects the timing of petroleum generation timing of migration age of the source rock or the timing of thermochemical sulfate reduction tsr the oils selected for this study are interpreted to be derived from the meade peak phosphatic shale and retort phosphatic shale members of the phosphoria formation based on oil oil and oil source rock correlations utilizing bulk properties elemental composition 13c and 34s values and biomarker distributions the 34s values of the oils range from 6 2 to 5 7 with oils heavier than 2 interpreted to be indicative of tsr the re and os isotope data of the phosphoria oils plot in two general trends 1 the main trend n 15 oils yielding a triassic age 239 43 ma with an initial 187os 188os value of 0 85 0 42 and a mean square weighted deviation mswd of 1596 and 2 the torchlight trend n 4 oils yielding a miocene age 9 24 0 39 ma with an initial 187os 188os value of 1 88 0 01 and a mswd of 0 05 the scatter high mswd in the main trend regression is due in part to tsr in reservoirs along the eastern margin of the basin excluding oils that have experienced tsr the regression is significantly improved yielding an age of 211 21 ma with a mswd of 148 this revised age is consistent with some studies that have proposed late triassic as the beginning of phosphoria oil generation and migration and does not seem to reflect the source rock age permian or the timing of re migration late cretaceous to eocene associated with the laramide orogeny the low precision of the revised regression 21 ma is not unexpected for this oil family given the long duration of generation from a large geographic area of mature phosphoria source rock and the possible range in the initial 187os 188os values of the meade peak and retort source units effects of re migration may have contributed to the scatter but thermal cracking and biodegradation likely have had minimal or no effect on the main trend regression the four phosphoria sourced oils from torchlight and lamb fields yield a precise miocene age re os isochron that may reflect the end of tsr in the reservoir due to cooling below a threshold temperature in the last 10 m y from uplift and erosion of overlying rocks the mechanism for the formation of a re os isotopic relationship in a family of crude oils may involve multiple steps in the petroleum generation process bitumen generation from the source rock kerogen may provide a reset of the isotopic chronometer and incremental expulsion of oil over the duration of the oil window may provide some of the variation seen in 187re 188os values from an oil family

spatial u pb age distribution in shock recrystallized zircon a case study from the rochechouart impact structure france abstract age determination of impact structures via the zircon u pb system remains challenging and often ambiguous due to highly variable effects of shock metamorphism on u pb geochronology it is therefore crucial to link the observed zircon microtextures including their temperature and pressure conditions associated with their formation directly to the u pb ages preserved here we analyzed three recrystallized zircon grains and one plastically deformed zircon crystal from the medium sized rochechouart impact structure in the northwestern massif central of france for the rochechouart impact structure the impact age 206 92 0 32 ma 40ar 39ar as well as the tectono themal history is well established making this study site ideal to test concepts about u pb systematics in shocked zircon and to differentiate between shock driven age resetting and pre impact crystallization and metamorphic overprinting zircon microstructures were studied using scanning electron imaging cathodoluminescence imaging and electron backscatter diffraction ebsd mapping further we conducted u pb laser ablation inductively coupled plasma mass spectrometry la icp ms depth profiling analysis allowing us to interpret the resultant age data in discrete steps with increasing ablation time depth the u pb depth profiling data demonstrate that plastically strained grains are incompletely reset and preserve rim and interior age domains reflecting typical pre impact pre variscan and variscan regional tectonic ages our results also reveal that the granular crystals encountered contain microstructural evidence for former reidite in granular neoblastic frign zircon reflecting both high pressure 30 gpa and high temperature 1200 c conditions this signifies that frign zircon is now known from an additional medium sized impact structure further supporting the hypothesis that this impact induced microstructure is commonly preserved in addition frign zircon has a high potential to preserve completely impact reset crystal domains 204 to 207 ma that can be identified by our combined analytical approach of u pb depth profiling and ebsd mapping and thus are suitable for determining reliable impact ages

fault charged mantle fluid contamination of united kingdom north sea oils insights from re os isotopes 187 os 188 os as expected from a kimmer idge clay formation source however oils from the viking graben with which the brent fi eld is associated and main east shetland basin display unradiogenic 187 os 188 os in this study we seek to demonstrate that these anomalous results are due to interaction with a mantle like fl uid that propagated through the main fault zone of the viking graben and east shetland basin this study enhances our understanding of the re os oil systematics and supports cur rent ideas regarding fault architecture crustal thinning and associated fl uid fl ow and interac tion in the north sea oil system abstract united kingdom north sea oils sourced from the kimmeridge clay formation contain unradiogenic 0 17 to 0 48 and radiogenic 1 04 to 3 34 187 os 188 os values the unra diogenic 187 os 188 os values are spatially associated with the main basin bounding faults of the viking graben and east shetland basin in contrast the radiogenic 187 os 188 os values are associated with north sea basins located farther away from the basin boundary faults we suggest that crustal thinning and strain localization within the viking graben and east shetland basin are suffi cient to have allowed basin bounding faults to propagate to suffi cient depth to act as conduits for mantle derived fl uids to interact with oil this hypothesis is sup ported by previous geochemical data for north sea oil fi elds furthermore we demonstrate the use of os isotopes as an important tracker of crustal scale fl uid dynamics and petroleum migration pathways in extensional basins

tectonic and paleogeographic controls on development of the early middle ordovician shanganning carbonate platform ordos basin north china lower middle ordovician platform carbonates are important oil and gas reservoir rocks in the ordos basin of the north china craton ncc in recent years numerous cores have been recovered from these units but the depositional environments and facies architecture of this large carbonate platform system have not yet been reported in detail this study integrates sedimentological and magnetic fabric data collected from outcrops and cores to document variation in microfacies and facies associations within the shanganning carbonate platform scp infer paleowind directions and the paleogeographic location of the scp and evaluate tectonic and paleogeographic controls on platform development this analysis documented 25 microfacies belonging to 7 microfacies fabric and sediment types carbonate mudstone wackestone packstone grainstone evaporite bindstone framestone siliciclastics and dolostone microfacies can be grouped into facies associations that represent tidal flat open platform restricted platform evaporite platform platform margin slope and deep basinal depositional environments these environments are mainly distributed zonally around the l shaped qingyang paleo uplift on the western and southern margins of the scp anisotropy of magnetic susceptibility measurements at five platform margin locales yielded paleocurrent directions of all approximately 318 348 51 81 42 72 80 110 and 54 84 from paleo north after correction for a 120 150 clockwise rotation of the ncc since the ordovician the depositional architecture of the scp depended on a combination of tectonic and paleogeographic wind influences local tectonic movements controlled the spatial distribution of facies associations around the qingyang paleo uplift which was characterized by open restricted and evaporite platform facies in the platform interior and mainly slope and basinal facies on the outer platform margin to the west and south of the qingyang paleo uplift vertical tectonic movements resulted in cyclic submergence and emergence of the platform over its approximately 20 m y long formation history paleo trade winds influenced aspects of facies zonation across the platform including growth of metazoan reefs on the windward platform margin and formation of oolitic grainstone and microbial reefs on the leeward platform margin the facies model for the scp developed in this study should provide a useful reference framework for future carbonate oil and gas exploration in lower middle ordovician units of the ordos basin furthermore this study makes innovative use of magnetic anisotropy data in combination with standard petrographic core and field data to discern facies patterns and controls on a paleo carbonate platform which is an integrated methodology that may serve as a model for future studies of other carbonate platforms

paleoenvironmental significance of the magnetic fabrics in chinese loess paleosols since the last interglacial 130 ka abstract we compare new anisotropy of magnetic susceptibility ams data with previously determined paleoclimatically sensitive parameters for a loess profile at lingtai central loess plateau china to unravel factors that control loess ams magnetic lineations are clustered along ne sw and nw se orientations during cold and warm periods respectively which probably corresponded to paleowind directions of both winter and summer monsoons anomalously steep magnetic foliations coincidentally occur at the paleoclimatic stage boundaries indicating sediment disturbance lineation strength appears to be sensitive to millennial scale rapid paleoclimatic fluctuations generally the winter monsoon produces a lower degree of lineation than the summer monsoon furthermore by studying lineation subsets for the cold and warm periods we find that the cold interval lineation strengths co vary with grain size over the last 70 ka during the last interglacial about 74 128 ka the lineation and declination of the susceptibility maximum dec k max are sensitive to rapid fluctuations in winter and summer monsoons long term trends of magnetic foliation and anisotropy degree replicate grain size variations with superimposed short term peaks related to post depositional compaction as suggested by density the ams shape parameter t indicates oblate fabrics these new findings will not only improve our understandings of loess ams but also expand the possibilities of paleoclimatic studies in the chinese loess

evaluating re os systematics in organic rich sedimentary rocks in response to petroleum generation using hydrous pyrolysis experiments abstract successful application of the 187re 187os geochronometer has enabled the determination of accurate and precise depositional ages for organic rich sedimentary rocks ors as well as establishing timing constraints of petroleum generation however we do not fully understand the systematics and transfer behaviour of re and os between ors and petroleum products e g bitumen and oil to more fully understand the behaviour of re os systematics in both source rocks and petroleum products we apply hydrous pyrolysis to two immature hydrocarbon source rocks the permian phosphoria formation toc 17 4 type ii s kerogen and the jurassic staffin formation toc 2 5 type iii kerogen the laboratory based hydrous pyrolysis experiments were carried out for 72 h at 250 300 325 and 350 c these experiments provided us with whole rock extracted rock and bitumen and in some cases expelled oil and asphaltene for evaluation of re os isotopic and elemental abundance the data from these experiments demonstrate that the majority 95 of re and os are housed within extracted rock and that thermal maturation does not result in significant transfer of re or os from the extracted rock into organic phases based on existing thermodynamic data our findings suggest that organic chelating sites have a greater affinity for the quadravalent states of re and os than sulphides across the temperature range of the hydrous pyrolysis experiments both whole rock and extracted rock 187re 188os ratios show small variations 3 3 and 4 7 for staffin respectively and 6 3 and 4 9 for phosphoria respectively similarly the 187os 188os ratios show only minor variations for the staffin and phosphoria whole rock and extracted rock samples 0 6 and 1 4 and 1 3 and 2 2 these isotopic data strongly suggest that crude oil generation through hydrous pyrolysis experiments does not disturb the re os systematics in ors as supported by various studies on natural systems the elemental abundance data reveal limited transfer of re and os into the bitumen from a type iii kerogen in comparison to type ii s kerogen 0 02 vs 3 7 suggesting that these metals are very tightly bound in type iii kerogen structure the 187os 188os data from the pyrolysis generated phosphoria bitumens display minor variation 4 across the experimental temperatures with values similar to that of the source rock this indicates that the isotopic composition of the bitumen reflects the isotopic composition of the source rock at the time of petroleum generation these data further support the premise that the os isotopic composition of oils and bitumens can be used to fingerprint petroleum deposits to specific source rocks oil generated through the hydrous pyrolysis experiments does not contain appreciable quantities of re or os 120 and 3 ppt respectively in contrast to natural oils 2 50 ppb and 34 288 ppt for re and os respectively which may suggest that kinetic parameters are fundamental to the transfer of re and os from source rocks to oils from this we hypothesise that at the temperatures employed in hydrous pyrolysis re and os are assimilated into the extracted rock as a result of cross linking reactions

middle and late pleistocene loess of the western ciscaucasia stratigraphy lithology and composition due to the high preservation of the loess series and the availability of coastal outcrop sections loess cover of western ciscaucasia has ample opportunities for spatial paleogeographical reconstructions for the middle and late pleistocene currently the level of knowledge on the structure and composition of the loess paleosol sequences of western ciscaucasia remains unequal the azov coast is studied in more detail in comparison with the inner part of the region the structure and composition of the loess paleosol sequences of different parts of western ciscaucasia the sea of azov coast and western macroslope of the stavropol upland for the middle and late pleistocene are compared comparison of the loess paleosol sequences key sections are based on investigations of litho and pedostratigraphy magnetic susceptibility grain size elemental and mineral composition and luminescence dating recent results of luminescence dating allowed correcting the structure of the mezin pedocomplex s1 it was found out that this pedocomplex includes three phases of soil formation s1ss1 s1ss2 s1ss3 which approximately correspond to the warm stages of marine isotope stage 5 mis 5 5a 5c 5e in all sections a clear trend towards an increase in the accumulation rates over the last three climatic macrocycles is observed the last interglacial glacial macrocycle miss 2 5 is characterized by the most significant increase in average accumulation rates which were 1 8 times higher compared to miss 6 7 and 2 3 times higher than during the miss 8 9 a likely reason for the regional increase in the average dust accumulation rate was the directional increase in climate aridity the patterns of the spatial distribution of the loess thickness and material composition indicate that the main source of aeolian dust is situated in the east we suppose that the main sources of dust are sand masses of the alluvial plains of lover volga terek kuma and kura rivers in the caspian lowland the lower don sandy province is reconstructed to be a secondary source dust is blown from the sandy terraces of the don and in the past from the don deltas during the period when the sea of azov dried up

rhenium osmium geochronology and oil source correlation of the duvernay petroleum system western canada sedimentary basin implications for the application of the rhenium osmium geochronometer to petroleum systems the re os geochronometer has been applied to many petroleum systems worldwide however it is debated if the re os systematics in petroleum actually record the timing of oil generation here we investigate the re os isotope systematics of the duvernay petroleum system in the western canada sedimentary basin which has been shown to be a relatively simple petroleum system that is associated with oil generated during the late cretaceous early eocene laramide orogeny from a single source the organic geochemistry of the duvernay oils pristane phytane ratios of 1 5 smooth homohopane profile c29 c27 c28 regular sterane distribution and predominance of diasteranes over regular steranes strongly suggests the oil source to be that of type i ii marine organic matter of the upper devonian duvernay formation the asphaltene fraction re os isotope data of the duvernay oil yield an age of 66 31 ma which is in excellent agreement with the timing of the main stage hydrocarbon generation of the duvernay formation based on basin models further the similarity between the 187os 188os compositions of the duvernay formation source rock 0 46 1 48 and the oil 0 55 1 06 at the time of oil generation supports the hypothesis that the 187os 188os composition of an oil is inherited from the source unit at the time of oil generation and therefore shows no or limited influence from interaction with basin fluids this study supports that the re os isotope systematics of an oil can yield the timing of oil generation and be used to trace its source

abrupt last glacial dust fall over southeast england associated with dynamics of the british irish ice sheet loess deposits in southern britain contain a record of dust climate and landscape dynamics over the last glacial yet their age and accumulation rate remain poorly known furthermore the environm

re os geochronology and os isotope fingerprinting of petroleum sourced from a type i lacustrine kerogen insights from the natural green river petroleum system in the uinta basin and hydrous pyrolysis experiments abstract rhenium osmium re os geochronology of marine petroleum systems has allowed the determination of the depositional age of source rocks as well as the timing of petroleum generation in addition os isotopes have been applied as a fingerprinting tool to correlate oil to its source unit to date only classic marine petroleum systems have been studied here we present re os geochronology and os isotope fingerprinting of different petroleum phases oils tar sands and gilsonite derived from the lacustrine green river petroleum system in the uinta basin usa in addition we use an experimental approach hydrous pyrolysis experiments to compare to the re os data of naturally generated petroleum in order to further understand the mechanisms of re and os transfer to petroleum the re os geochronology of petroleum from the lacustrine green river petroleum system 19 14 ma all petroleum phases broadly agrees with previous petroleum generation basin models 25 ma suggesting that re os geochronology of variable petroleum phases derived from lacustrine type i kerogen has similar systematics to type ii kerogen e g selby and creaser 2005a selby and creaser 2005b finlay et al 2010 however the large uncertainties over 100 in some cases produced for the petroleum re os geochronology are a result of multiple generation events occurring through a 3000 m thick source unit that creates a mixture of initial os isotope compositions in the produced petroleum phases the 187os 188os values for the petroleum and source rocks at the time of oil generation vary from 1 4 to 1 9 with the mode at 1 6 oil to source correlation using os isotopes is consistent with previous correlation studies in the green river petroleum system and illustrates the potential utility of os isotopes to characterize the spatial variations within a petroleum system hydrous pyrolysis experiments on the green river formation source rocks show that re and os transfer are mimicking the natural system this transfer from source to bitumen to oil does not affect source rock re os systematics or os isotopic compositions this confirms that os isotope compositions are transferred intact from source to petroleum during petroleum generation and can be used as a powerful correlation tool these experiments further confirm that re os systematics in source rocks are not adversely affected by petroleum maturation overall this study illustrates that the re os petroleum geochronometer and os isotope fingerprinting tools can be used on a wide range of petroleum types sourced from variable kerogen types

hydrocarbon generation capability of sinian lower cambrian shale mudstone and carbonate rocks in the sichuan basin southwestern china implications for contributions to the giant sinian dengying natural gas accumulation the giant natural gas accumulation recently discovered within the neoproterozoic dengying formation in the sichuan basin of southwestern china represents a new and important supplement to the ancient neoproterozoic cambrian petroleum systems worldwide however the source of this gas is controversial because there are five possibilities based on geology from bottom to top including the lower sinian doushantuo mudstone the upper sinian dengying algal dolomite the mudstone of the third member of the dengying formation the lower cambrian maidiping argillaceous dolomite and the lower cambrian qiongzhusi shale to improve the understanding of this issue 33 samples from the five possible source rock units in the study area were investigated for their character and maturity via petrology total organic carbon toc pyrobitumen reflectance kerogen carbon isotope and biomarker analyses based on the results we address their hydrocarbon generation capabilities and contributions to the giant gas accumulation results show that present day toc values of the samples range from 0 03 to 2 36 and vary both regionally and stratigraphically with the qiongzhusi shales in the central basin and the weiyuan ziyang area ranking the highest in contrast the organic matter source and maturity within these rocks are relatively homogenous with slight variation throughout the study area the organic matter is predominantly derived from algae and bacteria with different compositions deposited in marine reducing environments the rocks range in thermal maturity from postmature to overmature these results imply that the generation capability of source rock had been high in the past and the gas in the study area is most likely originated from oil cracking and the late generation directly from the kerogen of source rocks with the qiongzhusi shales being the dominant source rock thus the hydrocarbon migration pattern in the study area is a lateral migration from deep seated and younger cambrian source rocks in sags to shallow seated and older sinian dolomite reservoirs in uplifts the migration process occurred in the oil phase with the oil being later cracked the differences in natural gas geochemistry may be controlled by complex factors e g thermal maturity the migration accumulation process and differing contributions from source rocks besides the dominant qiongzhusi regionally the central basin and the weiyuan ziyang area have had high hydrocarbon generation capability and thus should be considered as favorable targets for natural gas exploration in the future this study of china provides an additional example of neoproterozoic cambrian petroleum systems worldwide and thus can help to synthesize the systematics of such systems and understand the sedimentary transition across the precambrian cambrian boundary