mangrove forest evolution in a sediment rich estuarine system opportunists or agents of geomorphic change the majority of the world s mangrove forests occur on mostly mineral sediments of fluvial origin two perspectives exist on the biogeomorphic development of these forests i e that mangroves are opportunistic with forest development primarily driven by physical processes or alternatively that biophysical feedbacks strongly influence sedimentation and resulting geomorphology on the firth of thames coast new zealand we evaluate these two possible scenarios for sediment accumulation and forest development using high resolution sedimentary records and a detailed chronology of mangrove forest avicennia marina development since the 1950s cores were collected along a shore normal transect of known elevation relative to mean sea level msl activities for lead 210 pb 210 caesium 137 cs 137 and beryllium 7 be 7 and sediment properties were analysed with pb 210 sediment accumulation rates sars compensated for deep subsidence similar to 8 mm yr 1 used as a proxy for elevation gain at least four phases of forest development since the 1950s are recognized an old growth forest developed by the late 1970s with more recent seaward forest expansion thereafter excess 210pb profiles from the old growth forest exhibit relatively low sars near the top 7 12 mm yr 1 and bottom 10 22 mm yr 1 of cores separated by an interval of higher sars 33 100 mm yr 1 a general trend of increasing sar over time characterizes the recent forest biogeomorphic evolution of the system is more complex than simple mudflat accretion progradation and mangrove forest expansion surface elevation gain in the old growth forest displays an asymptotic trajectory with a secondary depocentre developing on the seaward mudflat from the mid 1970s two to ten fold increases in 210pb sars are unambiguously large and occurred years to decades before seedling recruitment demonstrating that mangroves do not measurably enhance sedimentation over annual to decadal timescales this suggests that mangrove forest development is largely dependent on physical processes with forests occupying mudflats once they reach a suitable elevation in the intertidal copyright c 2015 john wiley sons ltd

organic carbon δ13c variations in sedimentary rocks as chemostratigraphic and paleoenvironmental tools abstract carbon isotopic variations in marine carbonate rocks and organic matter can provide important information on stratigraphic correlations and paleoenvironments in particular carbon isotopic variations in marine organic materials may yield information about the concentration of oceanic dissolved co 2 and or the physiology of the microalgal community this paper reviews evidence from laboratory experiments and oceanographic studies aimed at understanding controls on carbon isotopic fractionation by marine phytoplankton we also review factors affecting carbon isotopic compositions of bulk sedimentary organic matter and individual biomarker compounds guidelines for analysis of isotopic compositions of organic materials and interpretations of these results for use as chemostratigraphic and paleoenvironmental tools are presented we recommend caution in interpreting carbon isotopic variations of sedimentary organic matter because no environmental factor explains adequately variations in the carbon isotopic composition of modern phytoplankton studies of ancient materials should include compound specific isotopic analyses of known phytoplankton biomarkers or organism specific isotopic analyses with bulk isotopic results to assess the proportions of allochthonous organic materials the degree of reworking and the extent of thermal degradation to confirm any trends present in values of bulk sedimentary organic matter

carbonate source rock with low total organic carbon content and high maturity as effective source rock in china a review abstract carbonate rocks with high maturity and low total organic carbon content are widely distributed in china whether they can be effective source rocks remains controversial but they have great significance for the evaluation of hydrocarbon generation potential and exploration prospects of carbonate rocks dataset reveals that as the depth or maturity increases total organic carbon toc content atomic h c ratio and hydrocarbon generation potential of carbonate source rocks with low total organic carbon csrltoc all decrease because of hydrocarbon expulsion moreover some pyrolysis experiments also indicate that the csrltoc are able to generate and expel a quantity of hydrocarbons the above studies indicate that csrltoc can be effective source rocks for oil gas pools the unique features of carbonate rocks and csrltoc demonstrate that they are easier to expel hydrocarbons and contribute to oil gas reservoirs than shale and thus the lower limit of toc lltoc of effective carbonate source rocks could be smaller than shale 0 5 the lltocs of effective carbonate source rocks with type i ii1 kerogen mainly sapropelic group at the levels of immaturity and low maturity maturity high maturity and over maturity are toc 0 5 0 5 0 3 0 3 0 2 and 0 2 0 1 respectively if the carbonate source rocks are at the high over mature stage we could take 0 2 as the lltoc the present organic poor source rocks with high maturity are possibly moderate or good source rocks at the low mature level in the geological periods especially carbonate source rocks if type i ii1 kerogen some typical oil and gas fields in china derive partly or mostly from the csrltoc proving that csrltoc could be effective source rock in china

de convoluting crude oil mixtures from palaeozoic reservoirs in the tabei uplift tarim basin china abstract geochemical characteristics of 61 crude oil samples collected from palaeozoic reservoirs in the tarim basin 60 from the tabei uplift and one from the tazhong uplift were analyzed the samples proved to be mixed oils of different maturity from diverse source rocks concentrations of 40 biomarkers and carbon isotopic compositions for the whole oils were analyzed by alternating least squares als regression to de convolute the mixtures three endmember em oils were identified em1 is the minimum contributor to the mixed oils accounting for less than 10 of most oils em1 originated from cambrian lower ordovician source rocks in the early to peak oil window stage and experienced two phases of mixing and biodegradation em2 is the secondary contributor with proportions ranging from 10 to 40 in most oil samples em2 originated from middle upper ordovician source rocks at the early oil generation stage and underwent two phases of mixing and one stage biodegradation in the reservoirs em3 is the major contributor to most samples with proportions ranging from 13 to 95 em3 was generated from middle upper ordovician source rocks at the late oil generation stage and mixed with earlier emplaced mixtures in the reservoirs the final mixtures that were not biodegraded are currently exploited from palaeozoic reservoirs in the tabei uplift biomarkers in the crude oils reveal mixed characteristics including evidence for two phases of oil charge and severe biodegradation

the cenomanian turonian oceanic anoxic event in the south atlantic new insights from a geochemical study of dsdp site 530a abstract one of the key objectives of deep sea drilling project dsdp leg 75 was to shed light on the underlying causes of cretaceous oceanic anoxia in the south atlantic by addressing two major hypotheses productivity productivity driven anoxia vs enhanced ocean stratification leading to preservation of organic matter and black shale deposition here we present a detailed geochemical dataset from sediments deposited during the cenomanian turonian c t transition and the global oceanic anoxic event 2 oae 2 at dsdp site 530a located off shore namibia southeast angola basin north of walvis ridge to characterise the succession of alternating black and green shales at this site and to reconstruct the evolution of their paleoenvironmental setting we have combined data derived from investigations on bulk organic matter biomarkers and the inorganic fraction the location of the c t boundary itself is biostratigraphically not well constrained due to the carbonate poor but organic matter rich facies of these sediments the bulk 13corg record and compound specific 13c data in combination with published as well as new biostratigraphic data enabled us to locate more precisely the c t boundary at dsdp site 530a the compound specific 13c record is the first of this kind reported from c t black shales in the south atlantic it is employed for paleoenvironmental reconstructions and chemostratigraphic correlation to other c t sections in order to discuss the paleoceanographic aspects and implications of the observations at dsdp site 530a in a broader context e g with regard to the potential trigger mechanisms of oae 2 global changes in black shale deposition and climate on a stratigraphic level an approximation and monitoring of the syndepositional degree of oxygen depletion within the sediments bottom waters in comparison to the upper water column is achieved by comparing normalised concentrations of redox sensitive trace elements with the abundance of highly source specific molecular compounds these biomarkers are derived from photoautotrophic and simultaneously anoxygenic green sulphur bacteria chlorobiacea and are interpreted as paleoindicators for events of photic zone euxinia in contrast to a number of other oae 2 sections that are characterised by continuous black shale sequences dsdp site 530a represents a highly dynamic setting where newly deposited black shales were repeatedly exposed to conditions of subtle bottom water re oxidation presumably leading to their progressive alteration into green shales the frequent alternation between both facies and the related anoxic to slight oxygenated conditions can be best explained by variations in vertical extent of an oxygen minimum zone in response to changes in a highly productive western continental margin setting driven by upwelling

petroleum charge history in the lunnan low uplift tarim basin china evidence from oil bearing fluid inclusions abstract the petroleum charge history in the lunnan low uplift tarim basin china was investigated by comparing the geochemical characteristics of fluid inclusion fi oils from ordovician and triassic reservoirs with crude oils from stratigraphically different reservoirs quantitative grain fluorescence qgf and total scanning fluorescence tsf were used to screen the reservoir samples so as to identify suitable samples for molecular composition of inclusion mci analysis all of the samples contain c 30 n propylcholestanes diagnostic of marine source rocks the ordovician hosted fi oils differ from the triassic hosted fi oils having higher relative abundances of c 19 tricyclic terpane c 24 tetracyclic terpane and rearranged hopanes ts and c 29 ts and higher pr ph ratios while the triassic hosted fi oils have lower pr ph ratios and higher relative abundances of c 23 tricyclic terpane arylisoprenoids 25 norhopanes and c 35 homohopane several of the crude oils are similar to the triassic hosted fi oils based on the geochemical characteristics of the fi and crude oils combined with information on the burial history of the area at least two petroleum charge episodes can be distinguished in the lunnan low uplift an early charge represented by the ordovician hosted fi oils was biodegraded as evidenced by the presence of 25 norhopanes in the triassic hosted fi oils and crude oils but not in the ordovician hosted fi oils ordovician hosted fi oils provide the only evidence for oil generated from cambrian lower ordovician source rocks triassic hosted fi oils and crude oils in the ordovician carboniferous and triassic reservoirs are mixtures of biodegraded oil from an early charge episode and more mature oil from later charge

catalytic hydropyrolysis of asphaltenes in marine oil from the tarim basin nw china implications to complicated oil charging histories in an old composite basin abstract oil asphaltenes have been used to characterize the source s and timing of expulsion of early charged oils however the application on asphaltene in a complex petroleum basin have been limited marine oils from the tarim basin nw china were selected to release asphaltene bound molecules by the catalytic hydropyrolysis technique hypy the analyzed samples were 10 heavy oils from two major oil production regions the tabei and tazhong uplifts in the basin the asphaltenes may be mixed products from multiple hydrocarbon charging stages if we consider the main oil filling events and the regional geothermal histories of corresponding reservoirs however the similar molecular and isotopic characteristics of the hydropyrolyzates indicate contributions from one major source rock possibly lower cambrian mudstone during relatively early periods based on the presently known source characteristics the preservation of asphaltenes probably reflects a low reservoir temperature after charging the asphaltenes were derived from marine algae deposited in a strongly reducing environment given the biomarker data e g relatively abundant aryl isoprenoids and low pr ph and carbon isotopic data 35 5 to 34 4 asphaltenes were expelled around the oil generation peak moreover molecular ratios indicative of maturity e g tricyclic terpanes hopanes derived by hypy of asphaltenes suggest that the asphaltenes of the tazhong uplift are generally more mature than those of the tabei uplift moreover this is mainly related to different maturities when the oil was expelled the free hydrocarbons in the tazhong uplift show greater molecular and isotopic variations than those in the tabei uplift this might be attributed to more complex accumulation processes in the former late oils with a range of maturities mixing proportions with early biodegraded oils and degrees of alteration by thermochemical sulfate reduction could all have played a role in generating this variability the results indicate that the hydrocarbons released from oil asphaltenes by hypy can provide insights into multiple charging processes in an old composite petroleum basin

decadal sea level variability in the south pacific in a global eddy resolving ocean model hindcast sea level variability and related oceanic changes in the south pacific from 1970 to 2003 are investigated using a hindcast simulation of an eddy resolving ocean general circulation model ogcm for the earth simulator ofes along with sea level data from tide gauges since 1970 and a satellite altimeter since 1992 the first empirical orthogonal function mode of sea level anomalies slas of ofes exhibits broad positive slas over the central and western south pacific the corresponding principal component indicates roughly stable high low and high slas separated by a rapid sea level fall in the late 1970s and sea level rise in the late 1990s consistent with tide gauge and satellite observations these decadal changes are accompanied by circulation changes of the subtropical gyre at 1000 m depth and changes of upper ocean zonal current and eddy activity around the tasman front in general agreement with previous related studies it is found that sea level variations in the tasman sea can be explained by propagation of long baroclinic rossby waves forced by wind stress curl anomalies if the impact of new zealand is taken into account the corresponding atmospheric variations are associated with decadal variability of el nino southern oscillation enso thus decadal sea level variability in the western and central south pacific in the past three and half decades and decadal enso variability are likely to be connected the sea level rise in the 1990s which attracted much attention in relation to the global warming is likely associated with the decadal cooling in the tropical pacific

origin of the unusually high dibenzothiophene oils in tazhong 4 oilfield of tarim basin and its implication in deep petroleum exploration abstract unusually high dibenzothiophene dbt concentrations are present in the oils from the tazhong 4 oilfield in the tazhong uplift tarim basin positive ion electrospray ionization fourier transform ion cyclotron resonance mass spectrometry ft icr ms was used in combination with conventional geochemical approaches to unravel the enrichment mechanisms significant amounts of s1 species with relatively low dbe values 0 8 i e sulfur ethers mercaptans thiophenes and benzothiophenes were detected in three lower ordovician oils with high thermal maturity which were suggested to be the products of thermochemical sulfate reduction tsr in the reservoir the occurrence of tsr was also supported by the coexistence of thiadiamondoids and abundant h2s in the gases associated with the oils obviously low concentrations of the dbe 9 s1 species mainly equivalent to c0 c35 dbts compared to its homologues were observed for the three oils which were probably altered by tsr indicating that no positive relationship existed between tsr and dbts in this study the sulfur compounds in the tazhong 4 oils are quite similar to those in the majority of lower ordovician oils characterized by high concentrations of dbts and dominant dbe 9 s1 species with only small amounts of sulfur compounds with low thermal stability dbe 0 8 suggesting only a small proportion of sulfur compounds were derived from tsr it is thermal maturity rather than tsr that has caused the unusually high dbt concentrations in most of the lower ordovician oils we suggest that the unusually high dbt oils in the tazhong 4 oilfield are caused by oil mixing from the later charged lower ordovician or perhaps even deeper with high dbt abundances from the earlier less mature oils which was supported by our oil mixing experiments and previous relevant investigations as well as abundant authigenic pyrite of hydrothermal origin we believe that tsr should have occurred in the tazhong uplift based on our ft icr ms results however normal sulfur compounds were detected in most oils and no increase of 13c2h6 13c4h10 was observed for the gas hydrocarbons suggesting only a slight alteration of the oils by tsr currently and or recently we suspect that the abnormal sulfur compounds in the lower ordovician oils might also be a result of deep oil mixing which might imply a deeper petroliferous horizon i e cambrian with a high petroleum potential this study is important to further deep petroleum exploration in the area

biodegradation and possible source of silurian and carboniferous reservoir bitumens from the halahatang sub depression tarim basin nw china abstract five core samples comprising three silurian and two carboniferous bituminous sandstones from the halahatang sub depression tarim basin nw china were studied to determine the nature and extent of microbial alteration and possible source s of the reservoir bitumens a total of twelve ordovician crude oil samples from this sub depression were also examined for comparative purposes co occurrence of a series of 25 norhopanes nhs c 28 c 34 variable amounts of chromatographically unresolved complex mixture ucm and diminished concentrations of n alkanes below ca c 20 in saturated hydrocarbon fractions of the silurian and carboniferous bitumens indicates that they are mixtures of heavily biodegraded oil from a former charge and slightly biodegraded oil from a later charge the presence of c 28 c 34 25 nhs suggests a biodegradation level of at least pm 6 for these bitumen samples nevertheless minor differences in terpane and sterane distributions between the silurian and carboniferous bitumen samples were observed which can be attributed to small variations in biodegradation levels values for the 25 nh ratio peters et al 1996 gammacerane gammacerane c 30 hopane c 28 25 nh c 29 hopane and c 29 25 nh c 30 hopane ratios indicate slightly higher levels of microbial alteration for the silurian bitumens compared to the carboniferous bitumens although caution must be exercised when comparing the biodegradation intensities using molecular parameters the ordovician crude oil samples appear to be more severely biodegraded than the silurian and carboniferous bitumens as evidenced by higher concentrations of tricyclic terpanes relative to hopanes and pregnanes and diasteranes relative to the regular steranes although thermal maturity effects cannot be ruled out geochemical correlation studies were successfully applied based on carbon isotopes and biomarkers including tricyclic terpanes and triaromatic steroids which are highly resistant to severe biodegradation pm 6 bulk isotopic compositions distribution patterns and certain ratios of these biomarkers indicate that the ordovician crude oils and the silurian and carboniferous bitumens originated from a single source they were probably derived from middle upper ordovician source rocks

permian early mesozoic tectonism and continental margin formation in israel and its implications for the history of the eastern mediterranean summary the early mesozoic tectonic reorganization of the tethys region also affected the levant area here two processes were superimposed a the pattern of long wavelength vertical motions of the arabo nubian platform changed in the late permian when israel and nearby areas began to subside b rifting occurred in this subsiding area probably in several phases late anisian and ladinian carnian norian and liassic differential movements reached 2 3 km and magmatism occurred in the liassic and perhaps also in the triassic the tectonism was strongly felt up to 50 km landward of the present coast the crust was thinned and modified under the present continental margin and in the main rifts passive margin conditions were established in late liassic times over the previously faulted area later in the jurassic a carbonate shelf was constructed along this subsiding margin its basinward edge was 1 1 5 km high which shows that the adjacent se mediterranean was already a deep sea hence this basin and its passive margin are considered to have been shaped by the early mesozoic rifting which is recognized in israel the rifting process probably signifies oblique separation of the tauride block from the levant part of gondwana

petroleum source in the tazhong uplift tarim basin new insights from geochemical and fluid inclusion data abstract a total of 108 drill stem test dst crude oil samples and 10 reservoir fluid inclusion samples were investigated geochemically to identify the characteristics and origin of the crude oil in the tazhong uplift tarim basin nw china results show that the majority of oils share typical biomarker characteristics from the middle upper ordovician o2 3 source rock and related crude oil features these features include a distinct v shape in the relative abundance of c27 c28 and c29 regular steranes and low abundances of dinosterane 24 norcholestanes triaromatic dinosteroids and gammacerane only a few oils display typical biomarker features indicating a cambrian lower ordovician o1 genetic affinity such as linear or anti l shape c27 c28 and c29 regular sterane distributions and relatively high concentrations of dinosterane 24 norcholestanes triaromatic dinosteroids and gammacerane it appears that most of the oils studied were derived from the o2 3 intervals as suggested by previous studies however the 13c values of individual n alkanes indicate that most of the crude oils in the tazhong uplift represent a mixture of two end member oils an o1 derived oil such as from well td2 or tz62 s and an o2 3 derived oil such as from well ym2 the data suggest that most of the oils in the uplift have a mixed origin and do not originated from the middle upper ordovician strata alone this conclusion is supported by data on the molecular composition of petroleum inclusions this new oil mixing model is critical for reconstructing the hydrocarbon formation and accumulation history for the region and may have important implications for further petroleum exploration in the tarim basin

molecular correlation of crude oils and oil components from reservoir rocks in the tazhong and tabei uplifts of the tarim basin china molecular data from a large set of source rock crude oil and oil containing reservoir rock samples from the tarim basin demonstrate multiple sources for the marine oils in the studied areas of this basin based on gammacerane c31 hopane and c28 c27 c 28 c 29 sterane ratios three of the fifteen crude oils from the tazhong uplift correlate with cambrian lower ordovician source rocks while the other crude oils from the tazhong uplift and all 39 crude oils from the tahe oilfield in the tabei uplift correlate with middle upper ordovician source rocks these two ratios further demonstrate that most of the free oils and nearly all of the adsorbed and inclusion oils in oil containing reservoir rocks from the tazhong uplift correlate with cambrian lower ordovician source rocks while the free and inclusion oils in oil containing carbonates from the tahe oilfield correlate mainly with middle upper ordovician source rocks this result suggests that crude oils in the tazhong uplift are partly derived from the cambrian lower ordovician source rocks while those in the ordovician carbonate reservoirs of tahe oilfield are overwhelmingly derived from the middle upper ordovician source rocks the scatter of c23 tricyclic terpane c23 tricyclic terpane c30 17a 21b h hopane and c21 c21 rc29 sterane ratios for the free and inclusion oils from oil containing carbonates in the tahe oilfield possibly reflects the subtle organofacies variations in the source rocks implying that the ordovician reservoirs in this oilfield are near the major source kitchen in contrast the close and positive relationship between these two ratios for oil components in the oil containing reservoir rocks from the tazhong uplift implies that they are far from the major source kitchen

origin charging and mixing of crude oils in the tahe oilfield tarim basin china abstract forty eight crude oil samples collected from different reservoirs in the tahe oilfield of the tarim basin were investigated based on geochemical characteristics it is concluded that the oil samples originated from multiple marine source rocks deposited in various sedimentary environments and subsequently altered by different levels of thermal maturation these mixtures were de convoluted to three endmember oils em1 em2 and em3 by alternating least squares regression using 38 concentration parameters em1 is the minimum contributor with an average of 13 while em2 and em3 are the main contributors to the mixtures with averages of 52 and 35 respectively em1 oil originated from cambrian lower ordovician source rocks in the early to peak oil window and subsequently experienced two phases of mixing and biodegradation em2 and em3 oils originated from middle upper ordovician source rocks but em2 was generated at lower thermal maturity than em3 the em2 oil underwent two phases of mixing and one stage biodegradation while the em3 oil mixed with previous existing mixtures in the reservoirs the final mixtures that might be affected by secondary processes such as evaporative fractionation are currently produced from the tahe oilfield the general orientation of oil filling was from south to north and east to west based on variations in the relative contributions of ems and the total concentrations of dibenzothiophenes and dibenzofurans in the oils considering the histories of sedimentary tectonic evolution hydrocarbon generation and expulsion and the de convolution results a model of three stages of oil charge and two phases of mixing and biodegradation was established for the tahe oilfield oils

the enigma of the jonah high in the middle of the levant basin and its significance to the history of rifting abstract recent giant gas discoveries within deeply buried structural highs in the middle of the levant basin have attracted the attention of the industrial and academic communities striving to understand the origin of such structures their relations to the tectonic history of the basin and their evolution through time here we focus on the jonah high which is one of the largest structures in the basin and is particularly enigmatic in its geometry dimensions and location compared to nearby structures it is buried under more than 3 km of late tertiary sediments and is associated with one of the largest magnetic anomalies in the basin though no significant gravity anomaly is observed previous studies raised several possibilities explaining its origin an ancient horst related to the early stage of basin formation late paleozoic or early mesozoic a syrian arc fold late cretaceous to neogene a giant volcanic seamount and an intrusive magmatic body a reconstruction of the evolution of this structure is proposed here based on newly produced pre stack depth migration of five selected seismic reflection lines crossing the jonah high combined with a basin wide interpretation of more than 500 2 d time migrated lines we suggest that the jonah high is a horst bounded by grabens most probably formed during continental breakup related to the neo tethys formation however unlike other extensional structures that were reactivated and inverted during the syrian arc deformation the jonah high was never reactivated rather it formed a prominent seamount that persisted for 120 140 ma until the early miocene when it was finally buried in a wider perspective the jonah horst is similar to the eratosthenes seamount a fragment of continental crust between the levant and herodotus basins

multiple sourced features of marine oils in the tarim basin nw china geochemical evidence from occluded hydrocarbons inside asphaltenes abstract the tarim basin nw china is a large composite basin with multiple sets of petroleum source rocks the basin has undergone numerous episodes of hydrocarbon generation migration and accumulation making it difficult to assess the source rocks and oil source correlation for the widespread marine oils in this area protected by the molecular structure of asphaltenes occluded hydrocarbons can provide information about the early source rocks in this work the occluded hydrocarbons released from the asphaltenes by a mild chemical degradation method were compared with the crude oil maltenes and the adsorbed compounds from asphaltenes analysis of biomarker distribution and the carbon isotope composition of individual n alkanes suggests that the widespread marine oils in the tazhong uplift tabei lunnan uplift and halahatang depression were contributed by cambrian lower ordovician source rocks at an early stage and later mixed with hydrocarbons derived from middle upper ordovician source rocks the marine oils in the tarim basin demonstrate extensive characteristics of having been derived from multiple source rocks

application of the monoterpane ratio mtr to distinguish marine oils from terrigenous oils and infer depositional environment in northern tarim basin china abstract six monoterpenoid hydrocarbons including two acyclic two monocyclic and two aromatic components were identified and quantified in 49 oil and condensate samples using comprehensive two dimensional gas chromatography coupled to time of flight mass spectrometry gc gc tofms among them 2 6 dimethyloctane 2 6 dmo and 2 methyl 3 ethylheptane 2 m 3 eh are the most abundant compounds and geochemically significant used in conjunction with other geochemical parameters such as pristane phytane pr ph and dibenzothiophene phenanthrene dbt p ratios the 2 m 3 eh 2 6 dmo ratio monoterpane ratio mtr provides a useful tool for distinguishing marine oils and condensates from those of terrigenous origin oils and condensates derived from marine source rocks have high mtr 0 4 low pr ph and high dbt p values whereas those generated from terrigenous source rocks have lower mtr

geochemistry and possible origin of petroleum in palaeozoic reservoirs from halahatang depression abstract the halahatang depression in the tabei uplift of the tarim basin is an active exploration area because it has substantial reservoir potential and contains or is near to many commercial oil fields geochemical analysis indicates that halahatang oils were derived from marine carbonate source rocks deposited under anoxic reducing conditions the maturities for halahatang oils are corresponding to the peak of the oil window and slightly higher than the neighboring tahe oils the halahatang oils feature low pr ph c 21 c 23 tricyclic terpane and c 28 c 29 sterane ratios high c 29 c 30 hopane and c 35 c 34 hopane ratios a v shape in the distribution of c 27 c 28 c 29 steranes and light carbon isotope ratios similar to the tahe oils and correlate well with the middle upper ordovician source rock however some source related biomarker parameters imply a more reducing source organofacies with more zooplanktonic contribution than that for the tahe oils

the origin migration and accumulation of the ordovician gas in the tazhong iii region tarim basin nw china abstract the ordovician large scale gas reservoir in the tazhong iii region burial depth 6000 m is a typical deep strata gas reservoir in the tarim basin of nw china the origin migration and accumulation of the ordovician natural gas in the tazhong iii region were investigated by integrating geological geophysical and geochemical parameters the parameters that were successfully analyzed included the gas compositions and carbon isotope ratios production data burial and geothermal histories oil compositions and properties together with the diamantane index the results indicated that the ordovician natural gas in the tazhong iii region originated from cambrian ordovician paleo oil cracking accompanied by a large amount of h2s generated from thermochemical sulfate reduction tsr when the oil cracking gas migrated vertically into the ordovician reservoir through the tazhong i fault and strike slip faults it was preferentially charged in the pinnate fault zones of strike slip faults with high porosity and permeability leading to the enrichment of natural gas and an abnormal distribution of the compositions and properties of hydrocarbon then oil cracking gas intruded into and altered the previous oil reservoir from northeast to southwest through the strike slip faults unconformities and pore fracture reservoir belt leading to the differential accumulation of hydrocarbon in districts of the tazhong iii region the ordovician natural gas migration accumulation model in the tazhong iii region indicates a great exploration potential in the deep or super deep strata of the tarim basin further exploration activities in the ordovician reservoir of the tarim basin should be conducted in the regions where cambrian ordovician source rocks are well developed and the stress fracture zones related deep fault should be emphasized

evaluating deep subsidence in a rapidly accreting mangrove forest using gps monitoring of surface elevation benchmarks and sedimentary records abstract ultimately the fate of mangrove forests depends on substrate elevation gains keeping pace with relative sea level rise rslr some of the world s largest mangrove forests occur on tectonically active margins river deltas and sedimentary basins where sea level trends are largely controlled by vertical land motion i e subsidence so that rslr can be markedly higher than sea level rise induced by climate warming the rod surface elevation table marker horizon rset mh method has been applied globally to evaluate coastal wetland resilience to slr by quantifying net rates of elevation change relative to a benchmark a limitation of the rset method is that the stability of the benchmark i e vertical trend is unknown and rslr in wetlands is typically inferred from regional tide gauge records in the present study we evaluate rslr in a rapidly subsiding avicenna marina mangrove forest with a large terrigenous sediment supply firth of thames new zealand using independent and complimentary methods 1 campaign gps surveys of the stability of three rset benchmarks driven 18 m into unconsolidated sediment a tide gauge some 10 km distant and a reference station located on basement rock 2007 2016 that are tied to a network of satellite based geodetic sites and 2 137cs validated 210pb sediment accumulation rates sar measured in cores as a proxy for rslr the similarity of deep subsidence rates at the rset benchmarks located several hundred metres apart 7 7 0 5 to 9 4 0 5 mm yr 1 provides confidence in these results these subsidence rates are two to five fold higher than recorded at the nearby tide gauge 3 6 0 7 mm yr 1 and reference station 1 6 0 5 mm yr 1 weighted average 210pb sar of 9 9 mm and 9 3 mm yr 1 yield similar estimates of deep subsidence i e 8 4 and 6 9 mm yr 1 slr adjusted for vertical land motion indicating that this geological process is the major driver of the long term sea level trend in the mangrove forest our findings suggest that regional tide gauge records may not provide reliable estimates of rslr for all coastal wetlands due to local subsidence associated with natural processes and human activities subsidence rates and rslr within coastal wetlands can be evaluated using campaign gps surveys of rset benchmarks and independently from longer term sedimentary records finally evaluations of the resilience of coastal wetlands to rising sea levels over the coming decades must be based on measurements of rslr from these systems themselves

on the origin mixing and alteration of crude oils in the tarim basin abstract the origin of oil in the tarim basin northwestern china has been debated for decades here we present new insights into this challenging issue based on data from the bachu maigaiti area combined with a synthesis of data from other oil fields in the basin results of the organic geochemical characterization of 39 oil samples from various fields using gc fid py gc gc ms and gc ms ms revealed that the oils in the tarim basin can be generally classified into three families the oils of the first family whose representatives in our study come from the luntaibei condensate field are terrigenous as indicated by highest pristane phytane 2 8 and methylcyclohexane n heptane 1 8 and lowest dibenzothiophene phenanthrene 28 regular steranes and gammacerane a relatively high abundance of c 31 c 35 homohopanes as well as the presence of 1 2 3 4 tetramethylbenzene and aryl isoprenoids from c 13 to c 22 providing evidence for a contribution from green sulfur bacteria thriving under euxinic conditions the occurrence of these two marine oil families implies hitherto unknown organic facies for the respective source rocks family 2 oils may have been generated from cambrian shales deposited under suboxic conditions while family 3 oils could have been generated from cambrian to ordovician sources deposited in euxinic environments in addition biodegradation and mixing is quite common for the oils from the tarim basin mixing is evident not only by the coexistence of an unresolved complex mixture and c 7 c 36 n alkanes in certain oils but also by seemingly conflicting oil maturity parameters the results presented in this communication confirm the complexity of tarim basin petroleum systems in terms of ages and organofacies of the source rocks mixing of migrating and or accumulating petroleum and concomitant biodegradation

ruthenium ion catalyzed oxidation of asphaltenes of heavy oils in lunnan and tahe oilfields in tarim basin nw china abstract the application of ruthenium ion catalyzed oxidation rico products of asphaltenes of heavy oils in lunnan and tahe oilfields and well td2 in oil oil and oil source correlations was explored the rico products included n alkanoic acids di n alkanoic acids branched alkanoic acids tricyclic terpanoic acids hopanoic acids gammacerane carboxylic acid regular sterane carboxylic acids and 4 methylsterane carboxylic acids the n alkyl chains and biomarkers bonded on the asphaltenes were uneasily to be biodegraded the distribution and absolute concentration of n alkanoic acids in rico products of heavy oils in lunnan and tahe oilfields are different from those of well td2 the biomarkers bonded on the asphaltenes especially steranes have a similar distribution to that of the counterparts in the saturated fraction the sterane carboxylic acids and 4 methylsterane carboxylic acids in the rico products of heavy oils in lunnan and tahe oilfields dominated by c30 sterane and c31 4 methylsterane carboxylic acids respectively are significantly different from those of well td2 whose dominating sterane and 4 methylsterane carboxylic acids are c28 sterane and c29 4 methylsterane acids respectively the rico products of asphaltenes further indicate that the upper ordovician may be the main source rock for the twice charged hydrocarbon of heavy oils in lunnan and tahe oilfields

from greenhouse to icehouse nitrogen biogeochemistry of an epeiric sea in the context of the oxygenation of the late devonian atmosphere ocean system abstract the late devonian emergence of extensive arborescent terrestrial ecosystems produced changes in the earth s atmosphere and climate that resulted in substantial changes to the biogeochemistry of marine ecosystems the biogeochemistry of nitrogen in epeiric seas was particularly susceptible to alteration because of its dependence upon the series of redox mediated reactions that comprise the marine n cycle in order to explore the impact of climate change on n biogeochemistry in a late devonian epeiric sea we sampled a core from the appalachian basin that spans the interval from the greenhouse climate at the base of the famennian period to glacial conditions near its conclusion based upon stable isotope analysis of n c and s as well as elemental analysis of n c p s and fe we contend that two distinct biogeochemical regimes obtained during the contrasting climates the greenhouse regime featured low seawater o2 and ph that served to significantly curtail the oxidation of ammonia i e nitrification resulting in an ammonium dominated water column and low sediment 15n values the greenhouse also featured more extensive recycling of c n and p in contrast the higher seawater o2 and ph of the icehouse regime permitted nitrification in the water column resulting in a nitrate dominated system and higher sediment 15n values we conclude that nitrification was the key component of the n cycle that differentiated the two climate biogeochemical regimes

origins of palaeozoic oils in the tarim basin evidence from sulfur isotopes and biomarkers abstract crude oil h 2 s and pyrite samples from palaeozoic formations in the tarim basin have been analyzed for 34 s values together with oil samples for biomarkers and fluid inclusions for chemical composition to elucidate the origin of sulfur in the oil and to address potential applications in oil source rock correlation the results show that crude oil samples have sulfur contents from 0 02 to 2 47 and 34 s values from 11 9 to 28 2 non degraded oils without associated h 2 s gas have 34 s values from 11 9 to 20 5 and are relatively rich in c 28 20r sterane aryl isoprenoids and or gammacerane the features are well correlated with the cambrian and lower ordovician source rocks with 34 s values from 10 4 to 19 4 non degraded oils with associated h 2 s gas have 34 s values from 15 1 to 19 1 close to the h 2 s from 15 0 to 18 5 suggesting that the h 2 s was incorporated into the oils leading to the generation of 2 thiaadamantanes and likely alkyl thiolanes in the oil with a 34 s value of 18 5 heavily biodegraded oils have the highest sulfur contents and show 34 s values from 20 0 to 28 2 significantly heavier than those of any of the potential source rocks 15 3 to 19 4 thus it is likely that isotopically heavy sulfides have been incorporated into the biodegraded oils resulting in 34 s values of the oils becoming closer to cambrian and ordovician age seawater sulfates the sulfides may have originated from thermochemical sulfate reduction tsr as evidenced by the occurrence of h 2 s rich fluid inclusions and late stage and fracture filling pyrite with 34 s values mainly from 25 to 34 in the palaeozoic reservoirs

depositional environment of the lower silurian akkas hot shales in the western desert of iraq results from an organic geochemical study abstract the lower silurian hot shales in the lower part of akkas formation in akkas field western iraq were studied to determine their depositional environments for this purpose organic and inorganic proxies were used these include total organic carbon content toc sulfur pyrite and carbonate content measurements as well as the saturated and aromatic biomarkers organic carbon content toc pyrite and carbonate contents were high and pristane phytane ratio pr ph was low in these hot shales indicating deposition under anoxic marine conditions the presence of gammacerane suggests water column stratification the presence of aryl isoprenoids originating from aromatic carotenoids of green photosynthetic sulfur bacteria indicates deposition under euxinic conditions extending from the photic zone to the sediment water interface the conditions became more oxygenated upward which led to the deposition of organic poor gray green shales in the upper part of akkas formation with low pyrite and carbonate contents and high pr ph ratios

distinguishing cambrian from upper ordovician source rocks evidence from sulfur isotopes and biomarkers in the tarim basin abstract the reported source rocks for the abundant petroleum in the tarim basin china range from cambrian to lower ordovician and or upper ordovician in age however the difference between the two groups of source rocks is not well characterized in this study pyrite was removed from eleven mature to over mature kerogen samples from source rocks using the method of crcl 2 reduction and grinding the kerogen and coexisting pyrite samples were then analyzed for 34 s values results show that the kerogen samples from the cambrian have 34 s values between 10 4 and 19 4 the values are significantly higher than those from the lower ordovician kerogen 34 s of between 6 7 and 8 7 which in turn are generally higher than from the upper ordovician kerogen samples 34 s of between 15 3 and 6 8 the associated pyrite shows a similar trend but with much lower 34 s values this stratigraphically controlled sulfur isotope variation parallels the evolving contemporary marine sulfate and dated oil 34 s values from other basins suggesting that seawater sulfate and source rock age have an important influence on kerogen and pyrite 34 s values the relatively high 34 s values in the cambrian to lower ordovician source rocks are associated with abundant aryl isoprenoids gammacerane and c 35 homohopanes in the extractable organic matter indicating that these source rocks were deposited in a bottom water euxinic environment with water stratification compared with the upper ordovician the cambrian to lower ordovician source rocks show abundance in c 28 20r sterane c 23 tricyclic terpanes 4 23 24 trimethyl triaromatic dinosteroids and depletion in c 24 tetracyclic terpane c 29 hopane thus 34 s values and biomarkers of source rock organic matter can be used for distinguishing the cambrian and upper ordovician source rocks in the tarim basin

the tectonic regime of the southeastern mediterranean continental margin abstract the continental margin of the southeastern mediterranean off israel and sinai is transected by a series of nw se trending faults evidence of lateral displacements along these faults is presented the faults off israel were found to terminate at the eastern edge of the levant basin whereas the faults of the same series which transect the sinai continental margin were found to extend hundreds of kilometers further northwestwards the levant basin and the adjacent continental margin are both covered by a thick sedimentary sequence but whereas the basin is underlain by an oceanic crust the margin is underlain by a continental crust the effects of these two types of crust on the structure of the continental margin are discussed it is suggested that at least since the late neogene the marine province was under a tectonic regime of regional subsidence the continental province was affected by rifting and faulting and the tectonics of the continental margin reflect the superposition of these two regimes

biomarker evidence for heinrich events the so called heinrich layers found in north atlantic sediments have been attributed to quasi periodic discharges of armadas of icebergs originating from the laurentide ice sheet using the distribution of biomarkers in a sediment core bofs 5k we have attempted to provide more information about their origin and the effect of the heinrich events on oceanic circulation and the climatic system estimates of sea surface temperature changes via u3k7 measurements show that the surface ocean underwent significant cooling during the events probably as a result of incoming iceberg meltwater the low sea temperatures and the rapid variation in the accumulation of chlorophyll derived pigments suggest that the events provoked a major change in oceanographic conditions which may have affected the thermohaline circulation in the atlantic ocean within the most recent layers we have also found vanadyl alkyl porphyrins and aryl isoprenoid hydrocarbons diagenetic products of photosynthetic pig ments chlorophylls and carotenoids respectively these components are not expected to occur in late quaternary sediments so their presence demonstrates a contribution to the layers of ancient organic rich sedimentary material of continental origin the presence of vanadyl porphyrins and absence of their nickel counterparts and the distributional features of the aryl isoprenoids e g presence of the c40 reduced carotenoid isorenieratane of green sulphur bacterial origin indicate the existence of anoxic conditions in the photic zone of a marine water column in the original depositional setting of the contributed ancient sediment these results suggest that it should be possible using a biomarker correla tion approach to determine the source area of the ancient sediment eroded by the icebergs copyright 1997 elsevier science ltd

carbonate rocks and related facies with vestiges of biomarkers clues to redox conditions in the mesoproterozoic ocean abstract the raipur group of the chattisgarh basin preserves two major late mesoproterozoic carbonate platforms the lower platform is about 490 m thick separated from the upper platform 670 m thick by a 500 m thick calcareous shale carbonate strata cover almost 40 of the chattisgarh basin outcrop and represent two major platform types a a non stromatolitic ramp the charmuria sarangarh limestone and b a platform developed chiefly in the intertidal to shallow subtidal environment with prolific growth of stromatolites the chandi saradih limestone the first platform consists primarily of the black timarlaga limestone that is locally replaced by early diagenetic dolomite this carbonate platform experienced strong storm waves and was subsequently drowned by a major transgression during which extensive black limestone marl rhythmite was deposited followed by deposition of the gunderdehi shale the carbonate factory was later re established with development of an extensive stromatolite dominated charmuria sarangarh platform that ranged from restricted embayment to open marine conditions sea level change played a major role in controlling the broad facies pattern and platform evolution the 13 c signatures of the chattisgarh limestones falling within a relatively narrow range 0 to 4 are typical for upper mesoproterozoic carbonate rocks 18 o values however have a greater range 5 7 to 13 3 indicating significant diagenetic alteration of some samples likely dysoxic or anoxic conditions prevailed during deposition of the black timarlaga limestone and well oxygenated conditions during deposition of the gunderdehi shale and saradih chandi stromatolite the lack of 17 21 moretanes and high t max values suggest mature organic matter in the non stromatolitic ramp a paucity of diagnostic eukaryotic steroids indicates that algae were rare in the chattisgarh basin a high content of hopanes supports a generally bacterially dominated proterozoic ocean in which various stromatolites flourished

palaeozoic oil source correlation in the tarim basin nw china a review abstract oil source correlation in the cratonic region of the tarim basin nw china has long been controversial current knowledge of the potential source rock distribution end member selection oil source correlation and impacts of secondary alteration processes have been reviewed two source rock systems from the cambrian lower ordovician o 1 and middle upper ordovician o 2 3 potentially contributed to oil accumulations in the cratonic region geochemical correlations suggest that oils are dominantly derived from the o 2 3 source rocks while geological evidence and sulfur isotopic compositions supports the o 1 source rocks as a main contributor such inconsistency is rooted in the selection of end members and their characterization changes in some biomarker parameters such as sterane distribution gammacerane index and ratio of tricyclic terpanes to pentacyclic terpanes are mainly controlled by thermal maturation and biodegradation rather than source input and depositional environment variation no clear boundary between the two source systems can be established using biomarkers except for a few diagnostic components some o 1 source signatures such as even odd predominance of n alkanes unusual tricyclic terpane distribution unusually enriched 13 c carbon isotopic compositions of oils and kerogens and the occurrence of combustion related polycyclic aromatic hydrocarbons largely result from an abnormal heating influence either from igneous intrusion or hydrothermal fluid activity local thermochemical sulfate reduction can also remove most source related signatures these so called markers in currently selected end members result from extensive secondary alteration processes and do not reflect source input differences while more research is needed for full reconstruction of oil source correlation in the cratonic region of the tarim basin the main source rocks most likely reside in the o 1 succession rather than o 2 3

paleozoic oil source rock correlations in the tarim basin nw china we studied a suite of 40 oils and extracts of purported source rocks from the tarim basin in nw china the main group of oils comes from tazhong and tabei wells which sample the largest known petroleum accumulations in the basin these oils can be statistically correlated with extracts of ordovician rocks based upon high relative concentrations of 24 isopropylcholestanes and low relative concentrations of dinosteranes triaromatic dinosteroids and 24 norcholestanes in contrast extracts from cambrian rocks have low relative concentrations of 24 isopropylcholestanes with high relative concentrations of dinosteranes triaromatic dinosteroids and 24 norcholestanes although some tarim basin cambrian rocks yield high total organic carbon contents we see little evidence in the analyzed oil samples to suggest that they came from cambrian source rocks

correlation of crude oils and oil components from reservoirs and source rocks using carbon isotopic compositions of individual n alkanes in the tazhong and tabei uplift of the tarim basin china abstract carbon isotopic compositions were determined by gc irms for individual n alkanes in crude oils and the free adsorbed and inclusion oils recovered by sequential extraction from reservoir rocks in the tazhong uplift and tahe oilfield in the tabei uplift of tarim basin as well as extracts of the cambrian ordovician source rocks in the basin the variations of the 13 c values of individual n alkanes among the 15 oils from the tazhong uplift and among the 15 oils from the triassic and carboniferous sandstone reservoirs and the 21 oils from the ordovician carbonate reservoirs in the tahe oilfield demonstrate that these marine oils are derived from two end member source rocks the major proportion of these marine oils is derived from the type a source rocks with low 13 c values while a minor proportion is derived from the type b source rocks with high 13 c values type a source rocks are within either the cambrian lower ordovician or the middle upper ordovician strata not drilled so far while type b source rocks are within the cambrian lower ordovician strata as found in boreholes td2 and fang 1 in addition the three oils from the cretaceous sandstone reservoirs in the tahe oilfield with exceptionally high pr ph ratio and 13 c values of individual n alkanes are derived or mainly derived from the triassic jurassic terrigenous source rocks located in quka depression the difference of the 13 c values of individual n alkanes among the free adsorbed and inclusion oils in the reservoir rocks and corresponding crude oils reflects source variation during the reservoir filling process in general the initial oil charge is derived from the type b source rocks with high 13 c values while the later oil charge is derived from the type a source rocks with low 13 c values the 13 c values of individual n alkanes do not simply correlate with the biomarker parameters for the marine oils in the tazhong uplift and tahe oilfield suggesting that molecular parameters alone are not adequate for reliable oil source correlation for high maturity oils with complex mixing

temperature and pressure characteristics of ordovician gas condensate reservoirs in the tazhong area tarim basin northwestern china this paper investigates the temperature and pressure distribution characteristics and their evolution in the upper ordovician strata in the tazhong area tarim basin northwestern china based on hundreds of temperature data from boreholes the present day temperature ranges from 100 c to 130 c increasing from the southeast to the northwest and having a cool belt in the central fault horst pore pressures in the upper ordovician reservoirs range from 35 to 62 mpa 5076 to 8992 psi overpressures developed in the southwestern region and along the eastern segment of the central fault horst to the northern slope the lower ordovician reservoirs in the east reached 140 c during the late ordovician but those in the west heated continuously and reached the maximum temperature 130 c during present day paleopressures reconstructed from fluid inclusion data indicate that overpressures caused by hydrocarbon generation were formed in the areas away from fault belts but were absent in the area around the no 1 fault belt the temperature evolution indicates that the middle lower cambrian source rocks reached gas generation stage vitrinite reflectance ro 2 0 at the end of the ordovician whereas the middle upper ordovician source rocks are still in the high maturity stage ro 1 3 at the present day deep oil and gas migration is driven by overpressure and commercial reservoirs are predominantly distributed in the normally pressured zones along the no 1 fault belt the formation of gas condensate is controlled by specific temperature and pressure characteristics

identification of aryl isoprenoids in source rocks and crude oils biological markers for the green sulphur bacteria abstract a series of c13 to c31 aryl isoprenoids 1 alkyl 2 3 6 trimethylbenzenes have been identified in reef hosted oils and their source rocks from the middle and upper silurian of the michigan basin and middle devonian of the alberta basin canada their structure has been confirmed by unambiguous synthesis of the c14 member of the series their structure and isotopic composition indicate that they are derived from isorenieratene from the chlorobiaceae family of sulphur bacteria these results are consistent with geological and geochemical studies that show that the source rocks were deposited under metahaline to hypersaline sulphate and sulphide rich water columns the distribution of other biomarkers in these oils and source rocks indicates that a diverse biota contributed organic matter to the source environment in conjunction with the aryl isoprenoids they show that there is a remarkable similarity in composition between the two sets of oils and source rocks despite their great temporal and geographic separation this reflects the similarity of their environments and emphasizes the importance of sedimentary facies in controlling the composition of organic matter in source rocks and their derived oils

geochemistry of palaeozoic marine petroleum from the tarim basin nw china part 1 oil family classification abstract a series of palaeozoic marine oils ranging from condensates to very heavy oils from the cratonic region of the tarim basin nw china have been examined to delineate oil families crude oils from the mesozoic foreland kuqa depression were also analyzed for comparison the genetic family was assessed using bulk hydrocarbon isotopic composition alkylation pattern of polycyclic aromatic hydrocarbons pahs and biomarker distributions detailed oil oil correlation suggests two distinct families occur in the cratonic region despite the diversity of the reservoir rocks and some variability in oil physical properties the tabei and tazhong oils are classified in general into a single family with a possible indication for secondary subdivision these oils are characterized by low pristane phytane pr ph ratio high dibenzothiophene phenanthrene dbt p ratio light bulk isotopic composition high degree of pah alkylation high proportion of c23 and c24 tricyclic terpanes and low abundance of c24 tetracyclic terpane and triaromatic dinosteroids this family is inferred to have a middle upper ordovician source rock the tadong family distinctly different from the tabei and tazhong families is characterized by relatively high pr ph ratio low dbt p ratio slightly heavier bulk isotopic compositions and low degree of pah alkylation it also has a unique biomarker signature with a high proportion of triaromatic dinosteroids possibly indicating cambrian lower ordovician source rocks the oils from the kuqa depression are easily distinguished from the other two families due to their terrigenous origin the major characteristics of the kuqa oils are high pr ph ratio very low dbt p ratio heavy bulk isotopic composition low pah alkylation degree high proportion of c20 and c21 tricyclic terpanes and c24 tetracylic terpane and abundance of triaromatic dinosteranes and 4 methyl 24 ethyltriaromatic cholestanes these characteristics are consistent with terrestrial organic source rocks deposited under sub oxic conditions

origin and quantitative source assessment of deep oils in the tazhong uplift tarim basin abstract a large amount of deep oil has been discovered in the tazhong uplift tarim basin whereas the oil source is still controversial an integrated geochemical approach was utilized to unravel the characteristics origin and alteration of the deep oils this study showed that the lower cambrian oil from well zs1c 1x was featured by small or trace amounts of biomarkers unusually high concentration of dibenzothiophenes dbts high 34 s of dbts and high 13 c value of n alkanes these suggest a close genetic relationship with the cambrian source rocks and tsr alteration on the contrary the middle cambrian oils from well zs1 2a were characterized by low 13 c of n alkanes and relatively high 34 s of individual sulfur compounds and a general v shape of steranes indicating a good genetic affinity with the middle upper ordovician source rocks the middle cambrian salt rock separating the oils was suggested to be one of the factors responsible for the differentiation it was suggested that most of the deep oils in the tazhong uplift were mixed source based on biomarkers and carbon isotope which contain tsr altered oil in varied degree the percentage of the oils contributed by the cambrian lower ordovician was in the range of 19 100 average 57 controlled by several geological and geochemical events significant variations in the 34 s values for individual compounds in the oils were observed suggesting a combination of different extent of tsr and thermal maturation alterations the unusually high dbts concentrations in the tazhong 4 oilfield suggested as a result of mixing with the zs1c oil 1x and lower ordovician oils based on 34 s values of dbt this study will enhance our understanding of both deep and shallow oil sources in the tazhong uplift and clarify the formation mechanisms of the unusually high dbts oils in the region

diverse slow slip behavior at the hikurangi subduction margin new zealand 1 the installation of a continuous gps cgps network in new zealand since 2002 has enabled the discovery of 15 slow slip events at the hikurangi subduction margin our analysis and interpretation of the cgps data reveal a marked diversity in characteristics of slow slip events sses in the north island with durations varying from 6 days to 1 5 years equivalent moment release between mw 6 3 7 2 and recurrence intervals of repeating sses on the order of 2 years to more than 5 years the duration and magnitude characteristics of hikurangi sses appear to be related to the depth where they occur the deepest longest duration and largest sses occur at the southern hikurangi margin near the downdip limit of deep down to 40 km depth strong interseismic coupling the shallowest shortest duration smallest and most frequent sses occur at the northern and central hikurangi margin near the downdip limit of unusually shallow 10 15 km depth interseismic coupling the direction of slip on the interface in the hikurangi sses is consistent with slip partitioning at the hikurangi subduction margin we also show that moment accumulation rates on the interface for the time periods between sses are 40 higher than for the period of more than a decade averaging through the sses indicating that sses compose a major portion of the overall moment release budget of the hikurangi subduction interface

magnetic anomalies over the central levant continental margin abstract the magnetic field over the central levant continental margin off northern israel and southern lebanon and the adjacent levant basin has two distinct trends mount carmel and its offshore continuation carmel nose which are the surface expression of a large subbottom structure that extends from the land area across the continental shelf to the continental slope form a dividing zone between the two magnetic trends south of the carmel structure the magnetic field trends east west while north of the carmel structure it trends northeast and north northeast several pronounced magnetic anomalies exist mainly north of the carmel structure the majority of which trend north northeast and northeast parallel and sub parallel to the trend of the magnetic field in this area some also trend northwest perpendicular to the trend of the magnetic field in several cases the magnetic anomalies indicate large lithological elements which continue from land to sea gravity and seismic refraction data show that the two magnetic domains north and south of the carmel structure are associated with areas of different crustal structure south of the carmel structure the continetal oceanic crustal transition zone is located beyond the continental margin at the base of the continental slope while north of the carmel structure it is located under the continental shelf near the shore on land there are also differences in the structure of the crust north and south of the carmel structure the crust being much thinner north of the structure than south of it we suggest that some of the large magnetic anomalies off the central levant were formed during the rifting phase of the eastern mediterranean

regional sea level trends in new zealand 1 in terms of sea level data sets able to be used for long term sea level trend analysis the southern hemisphere is a data sparse region of the world new zealand lies in this region presently having four major port data sets used for such trend analysis this paper describes the process followed to compute new sea level trends at another six ports each with very discontinuous tide gauge records in each case the tide gauge has previously only been used for precisely defining an historical local mean sea level msl datum the process used involved a comparison of the old msl datum with a newly defined datum obtained from sea level data covering the last decade a simple linear trend was fitted between the two data points efforts were then made to assess possible bias in the results due to oceanographic factors such as the el nino southern oscillation enso cycle and the interdecadal pacific oscillation ipo this was done by taking the longer time series from the four major ports and assessing the spatially coherent variability in annual sea level using the dominant principal component from an empirical orthogonal function eof analysis the average relative sea level rise calculated from these six newly derived trends was 1 7 0 1 mm yr 1 a result that is completely consistent with the analysis of the long term gauge records most importantly it offers a relatively simple method of improving our knowledge of relative sea level trends in data sparse regions of the world

overview of the late tertiary recent tectonic and palaeo environmental development of the mediterranean region the late tertiary history of the mediterranean region exemplifies processes of ocean basin closure and continental collision as determined from integrated land and marine evidence during the mesozoic early tertiary tectonic settings were dominated by evolution of neotethys this ocean generally widened eastwards with a number of oceanic strands in the eastern mediterranean area great diversity of tectonic settings and palaeo environments developed during the tertiary closure history of these oceanic basins in the eastern mediterranean region more northerly neotethyan strands were closed by the mid tertiary while oceanic crust remained in the south in the present eastern mediterranean sea area northwards subduction of the remaining southerly neotethyan strand was probably active by the early miocene different areas exhibit different stages of convergence and ocean basin closure in the east the amalgamated eurasian plate had collided with the arabian margin africa by the late miocene while oceanic crust still persisted further west steady state subduction during the late tertiary gave rise to the mediterranean ridge as a substantial mud dominated accretionary wedge in the aegean area sufficient northward subduction took place to activate arc volcanism and pervasive back arc extension short of marginal basin opening in the easternmost mediterranean only limited subduction took place associated with supra subduction zone extension e g in cyprus today steady state subduction continues only locally where vestiges of neotethys remain e g herodotus abyssal plain in the western mediterranean area suturing of the african and eurasian plates initially took place in the betic region early mid tertiary where the neotethys had existed only as a narrow connection with the central north atlantic in the central mediterranean region where the western neotethys was wider northward subduction was active apparently as early as the late cretaceous in a widely accepted interpretation an andean type magmatic arc developed along the southern margin of europe and was then rifted off in the late oligocene early miocene to form the corsica sardinia block opening the north balearic marginal basin in its wake the migrating subduction zone and microcontinent then collided diachronously with north africa related continental units north africa and apulia from late oligocene early miocene giving rise to collisional thrust belts in the northern and southern apennines and along the north african continental margin i e the maghrebian chain to the betic rif area from the early miocene onwards a separate subduction system became active related to removal of neotethyan oceanic crust to the southeast ionian sea fueling suprasubduction zone extension and opening of the tyrrhenian sea orogenic collapse is an alternative mechanism of such extension and is widely believed to have caused divergent thrusting in the betic and rif regions of the westernmost mediterranean at the same time as crustal extension and subsidence of the alboran sea

geochemistry and charge history of oils from the yuqi area of tarim basin nw china abstract the geochemistry origin and charge history of oils from the yuqi area of tarim basin have been investigated through gc gc ms and fluid inclusion microthermometry analysis the yuqi oils accumulated mainly in three intervals 1 in the lower middle ordovician yingshan formation o 1 2 y carbonate reservoirs 2 in the overlying upper triassic halahatang formation t 3 h and 3 in the lower cretaceous yageliemu formation k 1 y sandstones oils from different reservoirs have distinct physical properties varying from extra heavy o 1 2 y heavy t 3 h to light oils t 3 h and k 1 y however their geochemical compositions show a high degree of similarity which indicates that they derive from the same source rock abundant tricyclic terpanes gammacerane dibenzothiophene and c 21 c 22 steranes together with a low level of diasteranes indicate an anoxic marine source rock for oils in the yuqi area oil oil correlation shows that yuqi oils derive from the same source bed as tahe oils the co occurrence of intact n alkanes and 25 norhopanes in all the samples supports the proposition that there is a mixture of an early filled severely biodegraded oil and a late filled fresh oil in this study charge history is examined on the basis of integration of fluid inclusion homogenization temperature data with 1d burial thermal history models two episodes of oil charging are identified in the o 1 2 y reservoir well yqx1 1 at around 436 420 ma middle late silurian and 10 3 ma miocene to pliocene respectively for the samples from the t 3 h and k 1 y intervals only one episode of oil charge is indicated by the homogenization temperatures of coexisting aqueous inclusions with an inferred timing around 10 3 ma the t 3 h heavy oil reservoir is assumed to be a secondary hydrocarbon pool which accumulated by re migration and re distribution of hydrocarbons from o 1 2 y hydrocarbon pools the few early biodegraded oils in the k 1 y light oils were probably picked up along the migration pathway during the late fresh oil charging

some outstanding issues in the geology of lebanon and their importance in the tectonic evolution of the levantine region abstract the concept of pervasive and disruptive late neogene quaternary strike slip tectonics in lebanon has made establishing a satisfactory pre neogene palaeogeographic and palaeotectonic history for the area difficult research has allowed clarification of three fundamental issues that permit the setting of lebanon against its adjacent regions to be more firmly assigned the first issue is the identification of the significance of the 100 km long nne ssw trending monocline of the western lebanon flexure this feature is interpreted as a modified and rejuvenated early mesozoic hinge line that is presumed to be the northern continuation of the carmel sinai hinge line to the south the second issue is the correlation of the mount lebanon bekaa and anti lebanon complex with the adjacent intracontinental palmyride fold belt of syria through recognition in each of common divisions in structural style between a higher northern zone dominated by broadly spaced box folds and a lower southern zone with more numerous closely spaced and more internally complex folds the third issue involves the identification of major two stage late cretaceous to palaeogene syrian arc tectonism within lebanon resolution of these issues suggests a tectonic model for the region whereby the levantine region formed in two main phases the first of these was the multiphase late palaeozoic early mesozoic rifting of the area which imposed a fundamental extensional fabric over much of the region the second tectonic phase was the subsequent inversion of these extensional structures in the two stage syrian arc deformation of senonian and late palaeogene age which gave rise to the main lebanon structures it is this syrian arc tectonism rather than the late cenozoic strike slip that was probably the main structuring agent which affected the lebanon area the transpression from the braided dead sea fault motion although locally complex is an essentially neotectonic overprint on an already existing fabric offset of syrian arc structures in lebanon suggests that the total sinistral motion of the yammouneh fault segment of the dead sea fault is around 47 km

geochemistry of alkylbenzenes in the paleozoic oils from the tarim basin nw china a b s t r a c t monoaromatic hydrocarbons alkylbenzenes in paleozoic oils condensates from the tarim basin were quantitatively analyzed using gas chromatography mass spectrometry their relative abundances and distributions show large variation which are most likely controlled by the temperature and duration of the catagenesis stage of petroleum maturation relatively high abundance of long chain linear substituted alkylbenzenes and alkyltoluenes in the studied samples implies that source rocks of these oils condensates contain high contents of algal material the dominance of dodecylbenzene in these n alkylbenzenes suggests the formation of alkylbenzenes from fatty acids via lactone formation dehydration the 1 2 3 4 tetramethylbenzene temb 1 methyl 3 phytanylbenzene 1 m 3 pyb and aryl isoprenoids are mainly derived from carotenoids produced by chlorobiaceae and their occurrence may indicate a highly reducing depositional environment however the concentration of these compounds diminishes significantly at high maturity with increasing thermal maturity the prominent trend of demethylation of alkylbenzenes is accompanied by shortening of alkyl side chains large variation in the c4 alkylbenzene isomer distribution is also controlled by thermal maturity the 1 2 3 5 temb and 1 2 4 5 temb isomers are more stable than other temb isomers and the overall thermodynamic stability of tembs is lower than that of dimethylethylbenzenes therefore several maturity parameters can be derived based on alkylbenzene stability absolute concentrations of alkylbenzenes generally increase with increasing thermal maturity but concentrations of 1 m 3 pyb and aryl isoprenoids decrease significantly at high maturity maturity parameters obtained from alkylbenzenes are especially useful for highly mature oils and condensates when most biomarkers are depleted caution is advised when interpreting the paleoenvironment and thermal maturity of an oil from the alkylbenzene signatures because they are affected by various other processes such as evaporative fractionation thermal cracking and biodegradation as well

source of 1 2 3 4 tetramethylbenzene in asphaltenes from the tarim basin 1 alkyl 2 3 6 trimethylbenzenes and a high relative amount of 1 2 3 4 tetramethylbenzene ttmb have been previously detected in the marine oils and asphaltenes in the oils from the tarim basin in the present study the stable carbon isotopic compositions of ttmb and n alkanes in the pyrolysates of asphaltenes in the marine oils from the northern tarim basin and silurian tar sands from the tarim basin were determined ttmb has stable carbon isotopic compositions in the range from 23 to 24 and are about 12 more enriched in 13c than concomitant n alkanes 35 to 37 in the pyrolysates the results indicate a contribution from green sulfur bacteria chlorobiaceae to ttmb thus the depositional environments of the source rocks for the marine oils and the bitumen in tar sands from the tarim basin are characterized by periods of euxinic conditions within the photic zone

biomarker geochemistry of crude oils and lower paleozoic source rocks in the tarim basin western china an oil source rock correlation study abstract in order to select biomarker parameters that have potential to quantitatively distinguish between the cambrian lower ordovician and upper ordovician source rocks in the tarim basin with a total organic carbon content 0 5 42 lower paleozoic shale samples were collected from a number of wells and outcrops in the tarim basin northwestern china the biomarkers in the extracts of the source rocks were analyzed by gas chromatography mass spectrometry the results show that c23 and c30 were dominant in the tricyclic terpanes and pentacyclic triterpanes respectively and c27 and c29 were both dominant in c27 29 steranes of the source rock samples the distribution of n alkanes isoprenoids and terpanes indicate that the source rock samples have been slightly to moderately biodegraded and they originated from a reducing depositional environment with considerable marine algal input in comparatively upper ordovician source rock samples presented lower values of c28 c29 regular steranes and higher values of c29 20s 20s 20r and c29 abnormally lower values of c29 20s 20s 20r and c29 were observed in the cambrian lower ordovician strata the set of data in this study show that homohopane index including c31homohopane c30hopane c31 35homohopanes c30hopane and the ratios related to the triaromatic steroids including c26 20s c28 20s tas c27 20r c28 20r c26 20r c27 20s c28 20s and c28 c26 c27 tas could serve as potential biomarker parameters to distinguish between the two groups of source rocks in the tarim basin the values of those parameters in above order in cambrian lower ordovician source rocks were 0 3 0 5 0 85 and 0 8 1 9 1 2 respectively the correlation between the source rock samples and 19 oils obtained from the tadong tabei and tazhong uplifts in the tarim basin show that most of the oils in tabei uplift are probably from upper ordovician source rocks the oils in tadong uplift are more likely from cambrian lower ordovician source rocks and the tazhong uplift is more like a mixed oil region with oils from both of the two groups of source rocks

the geneses of sedimentary organic matter with anomalous 13c enriched isotopic composition in saline and freshwater lakes a case study of lacustrine source rocks from dongpu and qikou sags bohai bay basin eastern china abstract the carbon isotopic composition of sedimentary organic matter 13com is notably important for the genetic identification of source rock and its products the sapropelic organic matter mostly plankton with high hydrogen index is generally depleted in 13c as compared to humic organic matter mainly higher plants with lower hydrogen index however some lacustrine sediments contain sapropelic source rocks with anomalous 13c enriched isotopic ratios especially reported in freshwater lakes the purpose of this study is to discuss the geneses of lacustrine sedimentary organic matter characterized by anomalous 13c enriched ratios in saline and freshwater sediments to this end we integrate the detailed organic geochemical data including rock eval analysis data total organic carbon contents total organic carbon isotopic compositions biomarkers and trace element concentrations of 64 saline lake sediments and 39 freshwater lake sediments obtained from the paleogene shahejie formation of dongpu sag and qikou sag separately in bohai bay basin of eastern china both sags exist samples with high hydrogen index values hi 400 mg g and high total organic carbon contents toc 2 but anomalous 13c enriched isotopic ratios up to 21 1 in qikou sag the 13com values of sapropelic kerogen correlate positively with toc contents the anomalous enrichment of 13c in organic matter is associated with extremely high productivity of algae such as algae bloom in dongpu sag the enrichment of 13c in organic matter is attributed to the significant increase of drought and salinity high salinity and aridity climate may lead to the abundance of c4 plants and chlorobium as well as the enrichment of 13c in plankton

molecular proxies as indicators of freshwater incursion driven salinity stratification salinity related stratification in marine environments is one of the main drivers for the development of persistent anoxia and euxinia it therefore plays a vital role in the sedimentary preservation of organic matter and has also been associated with oceanic anoxic events during several mass extinctions in earth s history here we present a novel molecular proxy using relative abundances of methyltrimethyltridecylchromans mttcs as indicators of riverine freshwater incursions into middle to late devonian paleoreefs exposed to conditions of prevailing anoxia photic zone euxinia and water column stratification this paper aims at re instigating a discussion about the origin of these compounds to potentially broaden their utilization as paleoproxies adding freshwater stratification to the general salinity reconstructions the co variation of mttc abundance profiles and 13c values with other biomarker parameters in the sediments studied here indicate a link of mttcs to terrigenous input pointing towards a previously suggested early diagenetic formation of these compounds from phytol with higher plant derived alkylphenols

isotopic compositions and biomarkers in crude oils from the tarim basin oil maturity and oil mixing abstract hydrogen and carbon isotopic compositions of n alkanes as well as biomarkers in various types of oil from the tarim basin were analyzed data were used to discuss the occurrence and formation of marine oils from this old composite basin of which we have limited understanding first hydrogen and carbon compositions of n alkanes clearly classify the collected oils into two distinct groups supporting the reported oil classifications based on biomarkers group i the majority of oil samples is characterized by relative enrichment in d and n alkane d values vary from 110 to 75 group ii includes two heavy oils and d values of n alkanes range from 145 to 142 second variations in the 13c value of n alkanes 2 3 show good correlations with the maturity indices indicating that kinetic isotopic fractionation is one control on the 13c value of n alkanes in the maturation process d values of n alkanes in most oils are also evidently influenced by the oil maturity finally by combining the isotopic compositions with biomarkers of oils two distinct oil mixing processes were recognized in the oils from the tabei and tazhong uplifts in this old composite basin the former process is the mixing of oils from the same source at different maturity stages while the latter involves the mixing of oils from distinct sources at different maturity stages biodegraded oils may contribute to the total oils but their proportions are minor

comparative studies on compounds occluded inside asphaltenes hierarchically released by increasing amounts of h2o2 ch3cooh being the heaviest fraction of crude oils asphaltenes are liable to aggregate and other molecules in the oils can be steadily adsorbed onto and even occluded inside the macromolecular structures of the asphaltenes these occluded compounds inside the asphaltenes can survive over geological time in oil reservoirs owing to effective protection by the macromolecular structures of the asphaltenes the asphaltenes of a crude oil zg31 from the central tarim basin nw china were hierarchically degraded by increasing the amount of h2o2 ch3cooh to release the occluded compounds besides the common components series of even numbered n alk 1 enes and 3 ethylalkanes were detected among the occluded compounds comparison of the biomarker distributions and the compound specific c isotopic results between the compounds from the maltenes and those from the occluded fraction the zg31 reservoir was suggested to have been charged multiple times with different charges being derived from different strata of source rocks

molecular organic geochemistry of the tarim basin northwest china we conducted organic geochemical analyses on the largest suite of oils and source rock extracts from the tarim basin northwest china currently available statistical cluster analysis of the entire suite of tarim oils distinguishes at least seven genetic groups of oils the largest group of oils was collected from the tazhong and tabei uplifts and originated from marine middle upper ordovician anoxic marls that mark slope facies at the margins of structural uplifts two other genetic groups most likely originated from marine middle upper ordovician source rocks but of distinct facies with one an oxic shale rich source west of the bachu uplift and the other an anoxic shale source at tazhong

ptolemais basin the tectonic origin of a senonian marine basin underneath the southeastern mediterranean sea abstract the large litani anticline that was recently discovered in the se mediterranean basin sheds new light on the regional tectonic history of the levant in the late cretaceous the anticline is buried under 5 km of undeformed sedimentary series its apex was leveled by erosion and its folding can be dated to the early senonian the seismic reflection data suggest that shortly after the structural development of the anticline in a shallow marine environment and under compressional stresses the regional tectonic regime turned extensional and the anticline subsided into the open marine environment of ptolemais basin that subsidence can be dated to the senonian as well it is suggested that the litani anticline is a part of the syrian arc and its deformation and subsequence subsidence reflect the complex tectonic regime of southern anatolia where the continental collision with arabia and the subduction of the neo tethys oceanic crust took place concurrently the litani anticline and the ptolemais basin thus show that contrasting tectonic regimes and their structural derivatives could evolve at a very fast rate

geochemistry and possible origin of crude oils from bashituo oil field tarim basin the entire range of hydrocarbons in bashituo oils from devonian and carboniferous reservoirs were investigated to determine their origin as well as their alteration mixing and maturity using gas chromatography gas chromatography mass spectrometry and stable carbon isotope analysis these geochemical studies indicate that the crude oils in the devonian and carboniferous reservoirs share similar c15 molecular marker compositions of marine organic matter origin whereas their light hydrocarbon compositions show distinct differences the carboniferous reservoired oils are characterized by a relatively greater abundance of cycloalkanes and methylcyclohexane which indicate a terrestrial organic matter om contribution based on biomarker and carbon isotope analysis cambrian ordovician j o marine rocks are assumed to be the main source for both the devonian and carboniferous reservoired oils whereas carboniferous rocks with terrestrial om input also contributed to the carboniferous reservoired oils the coexistence of 25 norhopanes evident humps from unresolved complex mixture and intact n alkanes in devonian reservoired oils indicate a mixture of early charged biodegraded oils with late fresh oils corresponding to at least two oil generation episodes by the j o rocks light hydrocarbon indicators suggest a relatively high maturity beyond peak oil generation for the j o sourced late fresh oil whereas c15 molecular marker parameters indicate a maturity equivalent to early peak oil generation for the j o sourced early charged biodegraded oil the maturity of the carboniferous sourced oil is equivalent to peak oil generation the application of the entire range of hydrocarbons is essential when assessing a mixed or altered oil system because light hydrocarbons and biomarkers may yield different source oil correlations and maturities

an updated analysis of long term sea level change in new zealand 1 the original analysis of long term sea level change in new zealand is updated with a new and extended analysis in this new analysis the original hourly sea level data have been re examined to remove obvious errors that were still present new data covering the period 1989 2000 has been added and the sea level record for wellington extended by the inclusion of recently discovered data covering the years 1891 1893 these new results indicate that relative sea levels in new zealand have been rising at an average rate of 1 6 mm yr over the last 100 years a figure that is not only within the error bounds of the original determination but when corrected for glacial isostatic effects has a high level of coherency with other regional and global sea level rise determinations there continues to be no evidence of any acceleration in relative sea levels over the record period

evaluation method and application of the relative contribution of marine hydrocarbon source rocks in the tarim basin a case study from the tazhong area abstract in total 2 37 million tons of marine crude oil originating from mixed source rocks has been discovered in the tarim basin geological and geochemical analyses have confirmed that these mixed hydrocarbons are mainly from two sets of source rocks including the cambrian lower ordovician and middle upper ordovician hydrocarbon source rocks in this study we determined the set of source rocks primarily responsible for the mixed hydrocarbons and the next location to be explored differences in n alkane carbon isotopes in end member oils from cambrian lower ordovician and middle upper ordovician source rocks were examined a material balance model and simulation methods were used to evaluate the relative amounts contributed by each source the results from known reserves in the tazhong area show that the mixing ratio or contribution is up to 65 from cambrian lower ordovician source rocks and is generally higher than that from middle upper ordovician source rocks the discovery of deep hydrocarbons has caused the total oil contribution from the cambrian lower ordovician to increase the mixing ratio of cambrian lower ordovician oil varies depending on the well formation and block it increases from west to east horizontally and from top to bottom vertically hydrocarbons from cambrian lower ordovician source rocks migrate upward along faults and the mixing ratio decreases as the distance from the oil source fault increases favorable areas for cambrian lower ordovician hydrocarbon exploration are deep layers and areas near the fault zone that are connected to deep layers the material balance model for carbon isotopes and evaluation methods for relative contributions considered differences in relative concentration and carbon isotope structure of n alkanes herein new methods for the identification and evaluation of hydrocarbons in the petroleum system of this superimposed basin are presented

chlorobiaceae in palaeozoic seas revealed by biological markers isotopes and geology biomarker hydrocarbons in oils and sediments have considerable potential for assessing the nature of biological processes in the past but only a few can be uniquely related to particular organisms reef hosted oils in the silurian of the michigan basin canada and the devonian of western canada have high abundances of 1 alkyl 2 3 6 trimethylbenzenes their precise structures suggest that they are diagenetic products of aromatic carotenoids of the green sulphur bacteria individual components are enriched in 13c by 7 8 relative to the saturated hydrocarbons of the same oil an isotopic anomaly of this magnitude and direction correlates with a component of photosynthetic carbon assimilation by the reductive tricarboxylic acid cycle these results together with data on palaeoenvironments provide compelling evidence for the existence in ancient restricted seas of microbial communities containing chlorobiaceae organisms with distinctive biochemistry which leave morphologically identifiable remains

new zealand 20th century sea level rise resolving the vertical land motion using space geodetic and geological data 1 investigations in long term instrumental tidal records reveal that 20th century sea level along the coast of new zealand is rising at 1 46 0 10 mm yr in agreement with the regional rates from southern australia and tasmania we extend the advanced altimeter gauge approach of combining satellite altimetry and tide gauge data with constraint equations from long term adjacent tide gauge records to assess its performance in open seas and to explore the impact of vertical land motion on the observed relative sea level this approach has again proven to be a robust method with an accuracy of 0 4 mm yr while no clear sea level rise pattern can be inferred once the tide gauge apparent sea level trends are corrected for vertical land motions from gps the advanced altimeter gauge and geological vertical rates are completely consistent and reveal three temporal phases of sea level rise marked by an increase from 1 46 0 10 mm yr to 1 72 0 10 mm yr during the period 1900 1936 followed by a decrease to 1 48 0 10 mm yr during the period 1936 1956 and a substantial increase to 2 60 0 10 mm yr during the period 1956 1975 in contrast the 20th century microfossil proxy records of absolute sea level rise display twice the tide gauge sea level rise rate of 3 17 0 30 mm yr and 3 28 0 45 mm yr respectively once salt marsh records are corrected using gps and geological vertical rates differential autocompaction and transfer functions are possible factors which need further investigation

organic geochemistry of the lower toarcian posidonia shale in nw europe abstract a suite of core and outcrop samples of the lower toarcian posidonia shale and time equivalent deposits was collected from multiple locations including southern germany swabian alb and franconian alb northern germany the east coast of great britain the netherlands and luxembourg in order to study major differences and similarities with respect to depositional environment and redox potential based on molecular geochemical data all samples are immature or in the early oil window with the highest thermal maturity occurring in the profile from great britain about 0 7 vitrinite reflectance molecular geochemical maturity parameters were used to quantify maturation in detail during shale deposition in the west cleveland basin great britain h 2 s was immediately consumed in the water column by terrigenous input supplying abundant reactive iron to form pyrite these samples are characterized by low dibenzothiophene phenanthrene ratios 95 of 2 and h 2 s in contrast sulfidic euxinic bottom waters possibly with enhanced salinity and stratified water column prevailed due to a more restricted iron supply in luxembourg northern germany and the franconian alb of southern germany a more oxygenated dysoxic bottom water column associated with anoxic sediments i e anoxic dysoxic boundary close to the sediment water interface prevailed in the swabian alb of southern germany despite observed changes within each vertical profile at each site large scale regional trends in depositional conditions can be clearly identified for the early toarcian

geochemistry of paleozoic marine petroleum from the tarim basin nw china part 5 effect of maturation tsr and mixing on the occurrence and distribution of alkyldibenzothiophenes abstract fifty four oils and 20 gas condensates from the cratonic region of the tarim basin nw china were quantitatively analyzed by gas chromatography mass spectrometry to elucidate the influence of thermal maturation multiple charges and mixing and thermochemical sulfate reduction tsr on the relative distributions of alkyldibenzothiophenes dbts vs alkylphenanthrenes which are widely used to interpret depositional environment and lithology concentrations of dbts relative to dbts in the aromatic hydrocarbon fraction and ratios of dibenzothiophene phenanthrene dbt p exhibit wide variations in the studied samples field observations coupled with a suite of oil sand pyrolysis experimental results suggest that dbts are more easily released from kerogen and or asphaltenes and are more easily destroyed in oil than the alkylphenanthrenes the dbt p ratio initially increases during early maturation and then decreases in the post mature stage concentrations of dbts are low in samples from the cratonic region of the tarim basin most samples have dbt p ratios

aromatic hydrocarbon composition of the permian kupferschiefer in the lower rhine basin nw germany the aromatic hydrocarbon composition of 25 samples of permian kupferschiefer from the lower rhine basin of nw germany has been investigated using gc gc ms and direct probe ms analysis two narrow sampled profiles were investigated with respect to compositional changes during kupferschiefer sedimentation and samples from 13 different wells covering a depth range from 350 to 1000 m were included in order to study temperature sensitive variations in the kupferschiefer trimethyl substituted aryl isoprenoids in the range from c11 to c21 occur these compounds presumably are degradation products of isorenieratane which is also present in the extracts within the profile the amount of a preferentially occuring c29 chroman increases from the bottom to the top of the kupferscheifer by a factor of about 2 5 the chroman distribution observed in the kupferschiefer points towards euhaline to mesohaline seawater during sedimentation moreover in the investigated profiles a terrestrial source input mainly in the bottom most part of the shale is reflected by the occurrence of a monoaromatic c24 chrysene derivative presumably derived from ring a degradation of pentacyclic triterpenes

the application of diamondoid indices in the tarim oils this study presents new data for the identification of the source and assessment of the thermal maturity of oils based on the diamondoid indices of oils from the tazhong and luntai uplifts in the tarim basin in northwest china the oil samples were divided into three groups according to biomarker characteristics and the abundance and distribution of diamondoids group i oils are located along the tazhong no 1 fault zone which contained abundant diamondoids and are of high thermal maturity suggesting they are late charged hydrocarbons that were derived from a middle upper ordovician source group ii oils are mainly located in blocks close to the tazhong no 1 fault zone and are dominated by early formed hydrocarbons from cambrian lower ordovician source rocks group iii lacustrine oils comprise relatively low concentrations of diamondoids compared with group i and group ii oils group iii oils were sourced from jurassic or possibly triassic units and are hosted by the low relief yingmaili section of the luntai uplift the thermal maturity of the oils in each group was evaluated using diamondoid parameters a few group i oils exhibit intense thermal cracking to estimate the extent of oil cracking using the concentrations of diamondoids in oils this study proposes a practical approach that facilitates the determination of baseline 4 and 3 methyldiamantane concentrations application of this method indicates that the tarim basin marine oils contain a baseline concentration of approximately 69 ppm

euxinia linked to the cambrian drumian carbon isotope excursion dice in australia geochemical and chemostratigraphic evidence abstract the cambrian drumian carbon isotope excursion dice event is a negative carbon isotope 13 c excursion it is associated with the first appearance datum fad of the agnostoid arthropod ptychagnostus atavus whose first appearance in the global boundary stratotype section and point gssp defines the base of the cambrian series 3 drumian stage although this isotopic event has been clearly identified in the great basin usa it has not been consistently reported in other areas of the world here we report a study integrating isotopic and geochemical data from middle cambrian series 3 sections from the northeastern georgina basin australia to investigate the occurrence of the dice event in australia and the paleoenvironmental conditions associated with this event the similarity between the isotopic excursions observed in the georgina basin 2 to 3 2 13 c excursion and that observed in the great basin 2 to 3 6 13 c excursion highlighted the presence of the dice in australia and emphasized the potential use of this event for refining global isotopic correlations the multi proxy correlation used in this study also showed a pulse of euxinia in association with the dice suggesting strongly euxinic conditions near the base of the drumian stage

graben hydrocarbon occurrences and structural style major hydrocarbon occurrences types of traps and structural styles have been synthesized from the sirte basin the suez and viking grabens and from other normal faulted regions hydrocarbons occur in a stacked succession of one or more basins pregraben graben fill and interior sag preservation of pregraben accumulations depends on late initiation of crustal arching and limitation of uplift to the graben shoulders furthermore a stable pregraben tectonic environment is required to ensure internal continuity of subsequent fault block closures hydrocarbon traps in the pregraben and graben fill sediments are primarily dependent on the multidirectional orientation of normal faults tilting of fault blocks and in many cases flexing or erosion parallel with block edges the fault pattern is dominated by longitudinal faults subparallel with the graben axis and secondarily by oblique faults the direction and degree of block rotation are influenced by fault profile planar or listric degree of extension fault pattern doglegs junctions terminations downwarping of the subsequent sag basin and isostatic adjustments between large blocks fold closures result from the upward termination of faults into forced folds which may be accentuated by drag during renewed faulting passive drape and differential compaction extend he folds to shallower depths because they form along block edges the flexures have trends that mimic the multidirectional fault patterns truncation traps are usually developed from the erosional retreat of fault scarps and they can also mimic the fault patterns where the sedimentary succession is complete an interior sag basin is superimposed across the graben its lower part is structured mostly by drape and differential compaction across the underlying graben fault blocks and fault block topography the upper part is usually an unsegmented syncline and hydrocarbon traps at this level include depositional buildups reefs turbidite mounds and salt diapirs or other structures caused by superimposed deformation unrelated to graben tectonics

water column structure during deposition of middle devonian lower mississippian black and green gray shales of the illinois and michigan basins a biomarker approach abstract the extractable organic matter of organic rich black shales and associated organic poor bioturbated green gray shales of the illinois and michigan basins of north america is analyzed to constrain the water column structure during their deposition all black shale samples contain derivatives of the biomarker isorenieratene a diaromatic carotenoid pigment produced exclusively by the brown strain of the green sulfur bacteria chlorobiaceae chlorobiaceae are phototrophic organisms requiring euxinic anoxic and sulfidic conditions to survive and the presence of isorenieratene derivatives indicates that the middle devonian early mississippian epeiric seas of north america experienced bottom water euxinic conditions during black shale deposition analysis of green gray shales also reveals the presence of isorenieratene derivatives and in some cases isorenieratane the highly bioturbated fabric of these sediments indicates the presence of oxygen in bottom waters during their deposition thus we suggest that short term shoaling of the oxycline across the basin slope may have occurred during their deposition though they were deposited predominantly under an oxygenated water column i e above the chemocline most green gray shales contain three pseudohomologous series of branched alkanes with quaternary substituted carbon atoms baqcs which are absent in black shale samples recent studies suggest that baqcs are produced by benthic chemoautotrophs dwelling at the redox boundary separating anoxic sediments from moderately oxygenated waters comparison of the biomarker content i e regular isoprenoid baqcs between black and green gray shales indicates different sources of organic matter and suggests that phytoplanktonic productivity in the upper water column was enhanced during black shale deposition the results of this study indicate that the alternation of green gray and black shales in these basins results from the vertical fluctuations of the chemocline these fluctuations seem to be driven by changes in phytoplanktonic productivity our data when associated to previous studies of other black shales from canada and europe confirm that photic zone euxinia was a widespread feature of low latitude epeiric seas during the middle devonian lower mississippian

evidence for photic zone euxinia in the early albian santana formation araripe basin ne brazil organic matter from two black shale units in the santana formation araripe basin ne brazil has been studied to investigate the palaeoenvironmental conditions prevailing during formation of this famous fossil lagerstatte optical and organic geochemical analyses indicate a predominantly autochthonous source with very limited terrestrial input molecular fossils of green sulphur bacteria show that the water column was stratified with euxinic conditions reaching up into the photic zone thus mass mortality events of fish may be explained by intrusion of sulphide containing waters the low quantity of material derived from land plants in this interior marine setting is interpreted to reflect a consequence of enhanced marine productivity resulting in dilution of the continental signal different depositional scenarios are proposed to explain our findings including 1 coastal erosion and nutrient leaching during a transgressive event 2 intrusion of euxinic waters during an early albian oae or 3 an estuarine circulation pattern associated with thermohaline stratification

aryl isoprenoids and diaromatic carotenoids in paleozoic source rocks and oils from the western canada and williston basins abstract aryl isoprenoids in the range c13 c31 have been identified in source rock bitumens and oils from several paleozoic age petroleum systems in the western canada and williston basins the principal compounds possess the 2 alkyl 1 3 4 trimethyl substitution pattern characteristic of diaromatic carotenoids found in the chlorobiaceae family of photosynthetic sulfur bacteria two c40 perhydrodiaromatic carotenoids which are structurally related to the presumed precursors of the aryl isoprenoids have also been identified in oils and source rock bitumens of the duvernay late devonian petroleum system pyrolysis gas chromatograms of kerogens isolated from several paleozoic source rocks show an unusual abundance of 1 2 3 4 tetramethylbenzene it is proposed that this compound arises from cleavage of diaromatic carotenoid moieties which have been incorporated into the kerogen structure with increasing maturation concentrations of the aryl isoprenoids in duvernay source rock bitumens increase to a point whereas the c40 perhydrodiaromatic carotenoids decrease steadily previous studies have suggested that aryl isoprenoids may be indicators of enhanced salinity environments this is not supported by the present work which shows high concentrations in source rocks associated with presumed normal marine salinities there is however a general association with intervals of condensed clastic or mixed clastic carbonate sedimentation within carbonate depositional systems from the association found and from parallels to modern habitats of photosynthetic bacteria it can be inferred that these biomarkers indicate prolific bacterial growth in a stratified water column at and below the oxic anoxic boundary layer in sub tropical to tropical marine environments

internal configuration of the levantine basin from seismic reflection data eastern mediterranean abstract in the easternmost mediterranean the levantine basin is filled by up to 10 km of mesozoic to recent sediments next to the alpine deformation front of the cyprean arc near the junction between africa and arabia away from the deformation front the basin has undergone little deformation for the past 100 ma as evidenced by deep seismic reflection profiles mostly subhorizontal reflections image the undisturbed sedimentation above a possibly paleozoic basement two marked reflections are identified within the sedimentary fill m and k they correspond to unconformities near the deformation front and their laterally equivalent concordant surfaces basinward in the deepest part of the basin there are more than 4 km of tertiary to recent sediments within which the m reflection is well defined above the 1 5 km thick messinian evaporites and beneath the 500 m thick plio quaternary sedimentary sequence pre tertiary sediments reach up to 6 km thick beneath the k reflection and above the top basement reflection they are little deformed and possibly correspond to late jurassic cretaceous age the limit with the cyprean arc deformation front is a sharp tectonic boundary south of the hecateaus rise where the whole sedimentary fill terminates against a subvertical fault zone that can be followed down to more than 14 km depth to the east this limit changes into a 30 km wide zone of strike slip deformation that includes flower structures progressively buried basinward by tertiary to recent syntectonic sediments possibly since paleocene times the basin corresponds to the almost undisturbed part of a larger basin whose northern side has been incorporated within the alpine deformation of the cyprean arc and limited to the east by the dead sea transform system

source facies of the paleozoic petroleum systems in the tabei uplift tarim basin nw china implications from aryl isoprenoids in crude oils abstract aryl isoprenoids have been detected for the first time in crude oils from paleozoic petroleum systems in the tabei uplift tarim basin northwestern china the principal compounds possess the 1 alkyl 2 3 6 trimethyl substitution pattern characteristic of diaromatic carotenoids found in the chlorobiaceae family of photosynthetic sulfur bacteria with a predominance of c13 c23 homologues in these samples flash pyrolysates of the asphaltene fractions isolated from crude oils show an unusual abundance of 1 2 3 4 tetramethylbenzene an indicator for a significant contribution of diaromatic carotenoids to the source kerogen of these oils the wide distribution of these compounds in crude oils reveals that penetration of the photic zone by sulfidic waters during deposition enabled prolific growth of photosynthetic green sulphur bacteria chlorobiaceae this suggests that the source rocks for the paleozoic petroleum systems in the tabei uplift were likely deposited under euxinic conditions with sulfate and sulfide rich water bodies which doesn t support previously published conclusions of a middle upper ordovician source that marks the slope facies at the margins of structural uplifts

molecular correlation of free oil adsorbed oil and inclusion oil of reservoir rocks in the tazhong uplift of the tarim basin china the free adsorbed and inclusion oils were recovered by sequential extraction from eleven oil and tar containing reservoir rocks in the tazhong uplift of tarim basin the results of gas chromatography gc and gc mass spectrometry analyses of these oil components and seven crude oils collected from this region reveal multiple oil charges derived from different source rocks for these oil reservoirs the initially charged oils show strong predominance of even over odd n alkanes in the range n c12 to n c20 and have ordinary maturities while the later charged oils do not exhibit any predominance of n alkanes and have high maturities the adsorbed and inclusion oils of the reservoir rocks generally have high relative concentrations of gammacerane and c28 steranes similar to the cambrian lower ordovician source rocks in contrast the free oils of these reservoir rocks generally have low relative concentrations of gammacerane and c28 steranes similar to the middle upper ordovician source rocks there are two interpretations of this result 1 the initially charged oils are derived from the cambrian lower ordovician source rocks while the later charged oils are derived from the middle upper ordovician source rocks and 2 both the initially and later charged oils are mainly derived from the cambrian lower ordovician source rocks but the later charged oils are contaminated by the oil components from the silurian tar sandstones and the middle upper ordovician source rocks

superpositional tectonic patterns along the continental margin of the southeastern mediterranean a review abstract resurgent tectonic phases superimposed their structural imprints on the continental margin of the southeastern mediterranean this margin underwent a complete cycle from a margin of a marine basin in the paleozoic to the margin of the incipient neo tethys ocean in the early jurassic through the margin of the mature ocean in the late jurassic cretaceous and paleogene it became the margin of a desiccated marine basin in the late miocene and finally became the margin of a rejuvenated marine basin after the pliocene the margin was affected by folding faulting and intermittent volcanism during the early liassic early neocomian late cretaceous oligocene and early miocene the younger tectonic phases were superimposed on the older ones reactivating them in some places and masking them in others the geological characteristics and this complex tectonic history are masked effectively by the thick messinian evaporitic sequence this smoothing effect was further enhanced by the huge pile of sediments that has been deposited by the river nile since the early pliocene

global glacial isostasy and the surface of the ice age earth the ice 5g vm2 model and grace abstract the 100 kyr quasiperiodic variation of continental ice cover which has been a persistent feature of climate system evolution throughout the most recent 900 kyr of earth history has occurred as a consequence of changes in the seasonal insolation regime forced by the influence of gravitational n body effects in the solar system on the geometry of earth s orbit around the sun the impacts of the changing surface ice load upon both earth s shape and gravitational field as well as upon sea level history have come to be measurable using a variety of geological and geophysical techniques these observations are invertible to obtain useful information on both the internal viscoelastic structure of the solid earth and on the detailed spatiotemporal characteristics of glaciation history this review focuses upon the most recent advances that have been achieved in each of these areas advances that have proven to be central to the construction of the refined model of the global process of glacial isos