the late devensian 22 000 bp irish sea basin the sedimentary record of a collapsed ice sheet margin the late devensian 20 ka bp glacial geology of the irish sea basin 4000 km2 is an event stratigraphy recording the entry of marine waters into a glacio isostatically depressed basin and the rapid retreat of the irish sea glacier as a tidewater ice margin marine limits occur up to 140 m o d across much of the central basin the ice margin was uncoupled from its bed exposing a subglacially scoured topography to glaciomarine processes the irish sea glacier was a major drainage conduit of the last british ice sheet calving of the marine ice margin resulted in fast flow surging of ice streams recorded by drumlin fields around the northern basin margin and tunnel valleys rapid evacuation of the basin may have stranded large areas of dead ice in peripheral zones e g cheshire shropshire lowlands and initiated the collapse of the ice sheet thick wedges of ice contact glaciomarine sediments were deposited during ice retreat as morainal bank complexes by successive tidewater ice margins stabilized at pinning points around the irish sea coast where morainal banks occur on the seaward side of drumlin swarms there is a clear sequential relationship between rapid ice loss from calving ice margins the development of fast flowing ice streams drumlinization and the pumping of subglacial sediment to tidewater raised delta complexes are locally associated with marine limits along the high relief coastal margins of wales east central ireland and the lake district associated valley infill complexes record downslope resedimentation of heterogenous sediments into the marine environment during ice retreat co eval offshore deposits are represented by well stratified glaciomarine complexes that infill a subglacially scoured topography that shows networks of tunnel valleys glaciomarine mud drapes occur well to the south of the maximum limit of grounded ice in the basin e g north devon scilly islands southern ireland the age of these distal sediments previously mapped as pre devensian tills is constrained by amino acid ratios basin rebound following deglaciation was rapid with over 100 m recovery in 3 ka and was followed by a low marine still stand peat accumulating in offshore areas now as much as 55 m below sea level has been drowned by the postglacial eustatic rise in sea level the glacio sedimentary model identified in this paper involving rapid ice retreat and related sedimentation triggered by rising relative sea level suggests that isotatic downwarping is an important mechanism for deglaciating continental shelves

hydrocarbon potential and depositional environment of the lower cretaceous black mudstones and shales in the coastal guangdong province china abstract the mesozoic especially the cretaceous sequences in the northern south china sea scs are important potential targets of oil and gas exploration however they are currently poorly understood we use organic petrology and geochemistry to evaluate the hydrocarbon potential and study depositional environment of the cretaceous black mudstones and shales from the dayawan section in the guangdong province china these mudstones and shales yield total organic carbon toc contents of 0 63 2 76 and most samples meet the requirement for higher toc source rocks organic matters in the mudstones and shales were sourced mainly from higher plants as well as subordinate benthic macroalgae organic petrology and geochemical data suggested that the organic matters were dominated by type iii and minor type ii and generally have low thermal maturity thus we evaluated the black mudstones and shales have a potential for hydrocarbon generation especially gas prone pr ph trace elements and mixture source of organic matter suggested that these black mudstones and shales formed in a coastal lacustrine environment characterized by weakly oxidizing weakly reducing conditions and low salinity a marine transgression developing in the middle part of the section was recognized generally the northern scs which exhibits the more marine influence likely contains source rocks with higher toc contents and better organic matter types the cretaceous source rocks with higher liquid hydrocarbon generation potential may occur locally in the pearl river mouth basin

hydrocarbon source rock potential and elemental composition of lower silurian subsurface shales of the eastern murzuq basin southern libya abstract a shallow borehole was drilled in lower silurian rhuddanian lower aeronian tanezzuft formation siliciclastic sediments at the eastern margin of the murzuq basin shale samples were retrieved from the borehole to study their source rock potential and trace element geochemical composition thirty shale samples analysed from borehole cdeg 2a reveal three geochemically distinct intervals shales from the top 23 38 m interval are weathered and have negligible organic content shales from the middle 38 42 m interval have moderate to good organic richness 0 6 1 7 wt toc with hydrogen index hi values up to 443 mg s2 g toc shales from the bottom 42 51 m interval have poor to moderate organic richness 0 07 0 8 wt toc with hi values up to 277 mg s2 g toc all samples have limited source rock potential and are immature to early mature for hydrocarbon generation it is unlikely that they have ever been buried deeper than 2 km low toc values inorganic geochemical redox proxies ce anomaly authigenic u th u v cr ni co and v sc indicate that the lower silurian tanezzuft formation shales from borehole cdeg 2a were deposited under oxic bottom waters explaining their relatively low toc values deposition took place in a shallow marine environment in a proximal position with regard to an early silurian palaeo shoreline this combined rock eval pyrolysis and whole rock geochemical study provides new insights into the silurian source rock distribution and hydrocarbon prospectivity in central north africa

geochemical compositions and depositional conditions of upper jurassic and lower cretaceous yorkshire clays england fifty three samples from the oxford kimmeridge and speeton clays of the yorkshire area have been analysed petrographically and geochemically by x ray diffraction x ray fluorescence atomic absorption and combustion toc major elements and the following trace elements have been determined rb sr ba cr v co ni cu zn and mo p 2 o 5 rb ba cr and v show positive correlation to the clastic fraction quartz feldspar and clay minerals cao mno and sr and to a lesser extent ni cu and zn seem to be positively correlated to calcite while fe 2 o 5 mno mgo and co are linked to siderite stratigraphical variations of element element ratios have been used to obtain sedimentological information from the petrographical and geochemical data the oxford clay with its coarse and immature clays was deposited in a regressive development an upwards shallowing with ventilated deposition of more mature and altered clastic material took place throughout the unit during deposition of the kimmeridge clay more reducing conditions existed and finer grained smectite rich sediments were formed the fine grained speeton clay was deposited during changing depositional conditions varying ventilation in a generally regressive development several sedimentological breaks characterize the unit

oxygen and carbon isotope trends and sedimentological evolution of a meromictic and saline lacustrine system the holocene medicine lake basin north american great plains usa abstract the succession of sedimentary subfacies in the medicine lake basin south dakota usa documents numerous changes in total dissolved solids tds lake level and the nature and stability of meromixis during the holocene the lake formed about 10 6 ka b p when coarse clastics and massive fine grained muds were deposited in a well mixed freshwater system subsequently the lake became saline and meromictic depositing a finely laminated unit composed of variegated and gray muds organic facies gypsum and aragonite laminae phototrophic bacterial plate communities bpc at the chemocline were significant producers of pelagic organic matter relatively high lake levels at least 10 m higher than today but saline and meromictic conditions predominated through the early to mid holocene at the end of this phase lake level dropped and stable meromixis was disrupted sands and massive or banded muds were deposited in sublittoral areas and benthic microbial communities bmc spread over the lake replacing bpcs as the predominant microbial producers when lake level rose again massive and laminated units were deposited under less saline conditions another pronounced episode of low lake level and high salinity followed the most recent sediments are sapropels massive or banded muds and littoral sands the 18o record from authigenic aragonite shows more positive values during the arid mid holocene interval with an abrupt increase at the end of this period followed by generally more negative values during the cooler and wetter late holocene the small range of 18o values 3 suggests that the lake was well buffered against high frequency climatic cycles probably as a result of groundwater modulation we postulate that meromixis and the type of photosynthetic microbial communities dominating the basinal region of the lake system either bpcs or bmcs exerted major controls on the carbon cycle and consequently on the development of isotopic trends linking 13c and 18o values more negative 13c values during the early and mid holocene are interpreted as a consequence of the predominance of 12c enriched microbial carbon from bpcs examples of both covariant and inverse covariant isotope trends between 13c and 18o values occur in the medicine lake record inverse covariant trends characterize long periods of stable meromixis when bpcs predominate over bmcs we hypothesize that well developed water stratification caused by greater influx of relatively 18o depleted freshwater induces higher productivity at the chemocline and consequently more positive 13c values in the precipitated carbonates unstable phases of meromixis or holomictic conditions are characterized by a predominance of bmcs or other biogenic producers over bpcs and a number of other factors combine to promote covariant trends the medicine lake record is consistent with the paleoclimatic interpretation for the northern great plains of a more arid early and middle holocene followed by an abrupt transition to a relatively cooler and wetter late holocene the sedimentary succesion in medicine lake documents a much more fluctuating and abrupt climate behavior than suggested by the vegetation paleorecord and suggest a late holocene climate punctuated by arid episodes

formal quaternary stratigraphy what do we expect and need at the start of my inqua career a reasonable target for the long term development of quaternary stratigraphy was the construction of a table that listed a number perhaps fewer than a dozen perhaps more of stages for each of the chief regions of the earth and which reliably indicated how these stages should be correlated from region to region a second target was to estimate ages for the stage boundaries finally some workers may have looked towards a series of global stages with the hope that these would be defined in their own region rather than in the alps for some researchers the target has not changed nor does its attainment appear much closer however there are now many whose requirement is that we create time series of environmental and climatic change with ever increasing temporal resolution along with correlation lines that are precise enough to permit global synoptic reconstruction funding for this research is justified partly on the grounds that it will give us increased confidence in our ability to forecast climatic change during the next century hence far from only being of academic interest long term planning of energy based economies indirectly depends upon it there is a danger that some excellent research by members of the inqua community becomes marginalized because the stratigraphic framework through which the research is communicated does not meet modern requirements oxygen isotope stratigraphy as it was quasi formalized by shackleton and opdyke 1973 and 1976 only applies to marine sediments containing foraminifera suitable for oxygen isotope analysis on the other hand there can be no doubt that as an informal standard means of communication oxygen isotope stratigraphy has been incredibly valuable even in settings where it is very hard to justify its use formal stratigraphy is intended to enable precise communication in research publications and in maps and i believe that in this regard there is more to be gained by improving correlation to the ocean oxygen isotope record than by working to define stage boundary stratotypes with continent scale utility

palaeoenvironmental significance of palustrine carbonates and calcretes in the geological record interest in palustrine carbonates and calcretes has increased over the last 20 years since they contain significant environmental information much of the work performed in this area has focused on either of two types of terrestrial carbonate palustrine carbonates or calcretes pedogenic and groundwater yet their simultaneous study shows there may be a gradual transition from one form to the other revealing the interplay between pedogenic sedimentary and diagenetic processes three main factors control the formation of these carbonates the position of the water table the host rock and the period of sub aerial exposure in pedogenic calcretes precipitation of carbonate takes places mostly in the vadose zone above the water table and within a previous host rock or sediment in groundwater calcretes the precipitation of carbonate also occurs within a previous host rock and around the groundwater table in palustrine carbonates however the precipitation of lime mud occurs in a lacustrine water body palustrine carbonates necessarily form on previous lacustrine mud whereas both types of calcretes may form on any type of sediment or soil the sub aerial exposure time needed to form palustrine carbonates may by relatively short even a season whereas pedogenic calcretes need more time several years to millions of years groundwater calcretes do not form on the topographic surfaces so there is no need of sub aerial exposure however stable surfaces favour the development of thick groundwater calcretes small fluctuations in the water table cause gradual transitions of these three types of terrestrial carbonates and the subsequent mixture of their characteristic features causing difficulties in the interpretation of these carbonates the formation of these carbonates is controlled by palaeoenvironmental factors both commonly form in semi arid climates arid climates are also suitable for calcretes but sub humid conditions are more suitable for palustrine carbonates more indications of climatic conditions may be obtained through the analysis of the d18o content of both calcretes and palustrine carbonates and from the depth of the horizon containing carbonate nodules in pedogenic calcretes vegetation is also important in the formation of these types of carbonates data on the prevailing vegetation can be obtained from the analysis of the micro and macrofabric as well as from the d13c signal of the primary carbonates which in pedogenic carbonates has also been used to estimate atmospheric pco2 during the phanerozoic these terrestrial carbonates are widely distributed on floodplains and distal areas of alluvial basins their presence and characteristics can be used as indicators of aggradation subsidence or accommodation rates and therefore as indicators of different tectonic regimes even though the study of these carbonates has notably increased in recent years much less is known about them than about marine carbonates presently there is much emphasis on obtaining a general model for sequence stratigraphy in terrestrial basins with a need to include the carbonates analysed in this paper

effect of regional topography and hydrology on the lacustrine isotopic record of miocene paleoclimate in the rocky mountains drummond c n wilkinson b h lohmann k c and smith g r 1993 effect of regional topography and hydrology on the lacustrine isotopic record of miocene paleoclimate in the rocky mountains palaeogeogr palaeoclimatol palaeoecol 101 67 79 oxygen isotopic compositions of upper miocene 9 2 m y lacustrine limestone from northwestern wyoming range from 21 5 to 35 2 0 pdb and are the lightest yet reported for a non marine carbonate sequence these values require that lake water was greatly depleted in 180 relative to modern meteoric precipitation and indicate that most inflow was sourced as meltwater from glaciers in the adjacent gros ventre range assessment of climatic factors influencing the isotopic composition of global meteoric water indicates either that nearly all of miocene precipitation in the southern rocky mountains was derived from large lake systems in the snake river plain and northern great basin to the west or that gros ventre catchment elevations were up to 2300 m higher than at present because erosion rates in modern alpine regions suggest that subaerial denudation could only account for up to 1200 m of post miocene elevation reduction any additional lowering must reflect the influence of post laramide epeirogeny during basin and range extensional tectonism lacustrine isotopic data therefore provide boundary conditions on the timing and magnitude of changes in late cenozoic paleoclimate topography hydrology and tectonism in the western wyoming portion of the rocky mountains

the influence of source depositional conditions on the hydrocarbon and nitrogen compounds in petroleum from central montana usa abstract the hydrocarbon and pyrrolic nitrogen compound compositions of 21 crude oils from reservoirs in the heath tyler amsden and swift morrison formations of central montana have been investigated by combined gas chromatography mass spectrometry the biomarker and aromatic hydrocarbon data enabled recognition of three composition types within the heath tyler amsden oils the swift morrison oils displayed different hydrocarbon characteristics and are classified as a separate oil group a number of geochemical parameters e g dibenzothiophene phenanthrene c 20 triaromatic steroid hydrocarbon c 20 c 28 triaromatic steroid hydrocarbons indicate strong variations in petroleum composition from north to south across the region oils from the central montana uplift with high relative c 27 diasteranes c 29 steranes and ts ts tm suggests increasing clay contribution to the source while abundant gammacerane indicates the development of hypersaline conditions with restricted circulation oils from the bull mountain basin represented by the amsden oils show relatively low c 27 diasteranes c 29 steranes and ts ts tm ratios indicating increasing carbonate contribution to the source while the decrease of a gammacerane contribution suggests decreasing salinity levels which may explain the dominance of tricyclic terpane and hence their precursors to the source organic matter while the changes recorded by the biomarker and aromatic hydrocarbon compositions show strong regional variations the nitrogen compounds do not respond so strongly however weak trends coinciding with source carbonate content were apparent in the following ratios 1 8 dimethylcarbazole 1 8 dimethylcarbazole 1 ethylcarbazole and carbazole sum of c 2 carbazoles the second parameter may be responding to variations in salinity since it co varies with the behaviour exhibited by the tricyclic terpanes the source information that can be extracted from biomarkers and aromatic hydrocarbons suggests that primary migration and compositional fractionation during expulsion has exerted little influence on this fraction of petroleum meanwhile primary migration and compositional fractionation during expulsion appear to effect the carbazole and benzocarbazole distributions thereby limiting their application as indicators for source rock facies composition

the shedding of an anticyclonic eddy from the alaskan stream as observed by the geosat altimeter the evolution of a meander into an anticyclonic eddy which separates from the alaskan stream in the vicinity of the central aleutian islands is observed in two years of sea surface height anomalies computed from geosat exact repeat mission altimeter data the trajectory of the center of mass is estimated using a modified perpendicular bisector method eddy separation is inferred to occur where the trajectory makes a distinct turn to the southwest the observed region of meander growth and eddy separation agrees with that predicted by theory the evolution of meander eddy height and radius is estimated from least squares fits of the data to an axially symmetric gaussian profile the heights and radii are used to calculate the strength vorticity and energetics of the meander eddy ekman dynamics are assumed to govern the eddy decay spin down times based on vorticity are much longer than those based on energetics this is consistent with an eddy s ability to maintain its integrity as it decays representative height diameter and velocity scales of the eddy are characteristic of rings spawned by other current systems assuming a ring structure for this eddy the estimated ring volume represents a 21 transport anomaly referenced to the mean annual transport into the bering sea

organic petrology and geochemistry of eocene suzak bituminous marl north central afghanistan depositional environment and source rock potential abstract organic geochemistry and petrology of eocene suzak bituminous marl outcrop samples from madr village in north central afghanistan were characterized via an integrated analytical approach to evaluate depositional environment and source rock potential multiple proxies suggest the organic rich toc 6 wt bituminous marls are immature for oil generation e g vitrinite ro 1 indicating organic input from marine algae and or bacterial biomass and sterane hopane ratios are low 0 12 0 14 monoaromatic steroids are dominated by c28 clearly indicating a marine setting high gammacerane index values 0 9 are consistent with anoxia stratification and may indicate intermittent saline hypersaline conditions stable c isotope ratios also suggest a marine depositional scenario for the suzak samples consistent with the presence of marine foraminifera including abundant planktic globigerinida and rare benthic discocyclina and nummulites biomarker 2 methylhopane for photosynthetic cyanobacteria implies shallow photic zone deposition of madr marls and 3 methylhopane indicates presence of methanotrophic archaea in the microbial consortium the data presented herein are consistent with deposition of suzak bituminous marls in shallow stratified waters of a restricted marine basin associated with the southeastern incipient or proto paratethys geochemical proxies from suzak rock extracts s content high polar content c isotopes normal r c27 29 steranes and c29 c30 and c26 c25 hopane ratios are similar to extant data from paleogene oils produced to the north in the afghan tajik basin this observation may indicate laterally equivalent strata are effective source rocks as suggested by previous workers however further work is needed to strengthen oil source correlations

how to find high quality petroleum source rocks in saline lacustrine basins a case study from the cenozoic qaidam basin nw china abstract despite having made significant contributions to global hydrocarbon occurrences source rocks in saline lacustrine basins show great mineralogical and organic geochemical heterogeneity and the controlling mechanism is weakly studied here we use the cenozoic qaidam basin as an example to compare the organic and inorganic parameters of fine grained sediments in different lacustrine facies and to figure out the characterization and distribution of effective petroleum source rocks in saline lacustrine systems organic inorganic database of six selected boreholes show that in the bench margin high gradient lacustrine system fine grained sediments in sublittoral brackish mesosaline zones containing low chlorides

multi year meanders and eddies in the alaskan stream as observed by topex poseidon altimeter the birth life and decay of long lived anticyclonic eddies or meanders in the alaskan stream are observed from topex poseidon t p satellite their surface height anomalies approach 72 cm average diameter is about 160km and they live for 1 to 3 years propagating along the stream with mean speed of 2 5 km d 1 of the six observed the last three were formed after the first t p observations in september 1992 of these two evolved from eddies near alaskan panhandle in winter drifting across the northern gulf of alaska before entering the alaskan stream while another formed in the stream west of shelikof strait

trace element characterisation of cretaceous orange basin hydrocarbon source rocks trace elements in the kerogen fraction of hydrocarbon source rock samples from two wells obtained from the cretaceous units of the orange basin south africa were determined using x ray fluorescence spectrometry in order to determine their distribution and geochemical significances the concentrations of the elements as ce co cu fe mo ni pb and v determined ranged from 0 64 to 47 300 ppm for the samples analysed the total organic carbon toc values indicate that the samples are organic rich but did not show any trend with the distribution of the trace metals except ce mo and pb dendrogram cluster analysis discriminated the samples into three groups on the basis of their level of thermal maturity thermal maturity has a significant effect on the distribution of the trace metals cobalt ni and v ni ratios and cross plots of the absolute values of v and ni indicate that the samples had significant marine organic matter input the v and ni contents and v v ni ratio indicate that the organic matter of the source rocks had been deposited in reducing conditions despite the similarities in the organic matter source input and depositional environment of the organic matter of the samples from the two well cross plots of co ni versus v ni and mo ni versus co ni were able to reveal subtle differences cluster analysis of the samples was also able to reveal the subtle thermal maturity differences of the samples

lower middle jurassic nonmarine source rocks and petroleum systems of the northern qaidam basin northwest china the qaidam basin is a nonmarine petroliferous basin on the northeastern margin of the tibet plateau potential source rocks are reported from tertiary saline lacustrine deposits and jurassic freshwater lacustrine or terrestrial strata the jurassic source rock is similar in terms of depositional system lithology age and organic geochemistry to nonmarine jurassic rocks that are thought to be potentially significant hydrocarbon sources in many basins of central asia including the tarim junggar and other important petroleum producing basins these jurassic source rocks were deposited in freshwater lacustrine systems in intracontinental foreland style basins during the early and middle jurassic these lacustrine strata are associated with coals and coaly mudstones with possible secondary importance as hydrocarbon source rocks oils from the northern qaidam basin can be divided into two groups based on molecular indicators of depositional environment and age diagnostic biomarkers those derived from this jurassic freshwater lacustrine source rock and those derived from a tertiary hypersaline lacustrine source rock the correlation of some qaidam oils to a jurassic source establishes a petroleum system involving these nonmarine jurassic source rocks oils of this petroleum system have been produced from tertiary and mesozoic reservoirs in anticlinal and thrust related traps in northeastern qaidam maturation modeling of the jurassic source rock indicates that these oils were generated and expelled during the miocene pliocene in much of northern qaidam the geological context of the basin suggests that drainage within the basin primarily was vertical probably mainly along faults until evaporite or overpressured shale seals were encountered in the overlying cenozoic section documentation of this petroleum system suggests other exploration targets remain underevaluated in northern and southwestern qaidam furthermore the northern qaidam petroleum system is a useful analog to interpret the role of similar jurassic source rocks in other sparsely documented basins of central asia

effects of mesoscale eddies on the flow of the alaskan stream 1 using a high resolution pan arctic ice ocean model forced with realistic atmospheric data we examine the mean transport and temporal and spatial variability within the alaskan stream model results are analyzed and compared with observations including satellite altimetry and ctd measurements the mean net transport of the alaskan stream is found to be between 34 and 44 sv intensifying downstream mesoscale eddies are found to periodically move along the path of the alaskan stream and alter the mean position of the typically westward flowing current however the strength of the current is not reduced as an anticyclonic eddy passes a point along the path instead there appears to be an offshore or southward shift in the current velocity core stationary measurement instruments may not be able to detect this shift in position over the slope if their southernmost location does not coincide with the current shift due to an eddy this may result in recording of a weakened or sometimes reversed flow finally we examine and demonstrate that modeled eddies within the alaskan stream have dominant effect on northward transport and variability through the eastern and central aleutian island passes

source rock deposition controlled by tectonic subsidence and climate in the western pearl river mouth basin china evidence from organic and inorganic geochemistry abstract interest in factors controlling lacustrine source rock deposition has increased over the last few decades because this type of deposits contain significant petroleum resources generally tectonic subsidence and climate are the two root causes as they control the accommodation potential water column properties and sources of organic matter in this study coupling organic geochemical and elemental geochemical data two potential source rocks i e the eocene wenchang formation e 2 w and oligocene enping formation e 3 e were investigated two models were finally raised to explain deposition of the two set of source rocks according to their paleoclimatic and tectonic properties the source rock potential shows a strong heterogeneity the second member of the eocene wenchang formation e 2 w 2 is characterized by high organic matter content and oil prone kerogen type in contrast the first member of the eocene wenchang formation e 2 w 1 and the oligocene enping formation e 3 e are characterized by low organic matter content and gas prone kerogen type the primary productivity and depositional environment exhibit notable differences between the two potential source rocks horizons and show an obvious variation from the depocenter to the slope and can be best explained by the coevolution of tectonic subsidence and climate during the e 2 w depositional stage low sediment supply led to mudstone deposited in deep lacustrine environment and resulted in underfilled lake basin the low water inflow provided little terrigenous organic matter low bicadinane perylene and floranthene contents and oxygen besides the low area depth ratio impeded the water circulation thus resulted in shallow thermocline and anoxic suboxic bottom environment abundant dibenzothiophene and high c 35 c 31 22s hopane ratios therefore abundant algae which contributed to the high amorphous organic matter aom content can be preserved the warm and wet climate high mn mg ratios gave birth to autochthonous organism such as dinoflagellates and pavlova gyrans abundant 4 methyl sterane during the e 3 e depositional stage the sufficient sedimentary supply resulted in expanding shallow lacustrine and swamp environment the higher area depth ratio and high sediment supply made environment unstable and can be strongly influenced by external environment broader range of mn mg ratios enough terrigenous organic matter tom was transported to the slope but little to the depocenter the slightly hot and dry climate low mn mg ratios led to decreasing autochthonous organism and evaporation environment the shallow water depth and relative dry climate resulted in saline suboxic dysoxic acid bottom environment the co variation of organic and inorganic indexes indicates the combination is a valid method in reconstructing source rock depositional models

environmental response to volcanic activity and its effect on organic matter enrichment in the permian lucaogou formation of the malang sag santanghu basin northwest china abstract lacustrine organic rich fine grained rocks are widespread in the second member of the permian lucaogou formation p2l2 in the malang sag santanghu basin with complex lithology and significant changes of lithofacies due to frequent volcanic activity in this study the mineralogical and petrological characteristics types of organic matter om and effect of volcanism on the sedimentary environment and om accumulation were analyzed using organic carbon and oxygen isotopes as well as major and trace element data the results revealed that the p2l2 was characterized by mixed deposition of volcanic ash and carbonate minerals with four main rock types tuff dolomitic tuff tuffaceous dolomite and dolomite the fine grained rocks dominantly contain type i and ii1 kerogens which were in a low mature stage and exhibited excellent original hydrocarbon generative potential when volcanic activity was strong large amounts of nutrients were released by the volcanic ash which then entered the lake in turn promoting the blooming of phytoplankton and causing the 13c values in the tuff to decrease in addition the paleotemperature decreased for a short time and the suboxic euxinic environment was conducive to the preservation of om resulting in high total organic carbon toc content in the tuff in contrast during intermittent or weak periods of volcanic activity the climate was hotter and drier and evaporation resulted in a sustained increase of salinity consequently the growth of algae was restricted which brought about an increase in the 13c values and relatively low toc content in the dolomite the relationships among primary productivity redox conditions clastic influx proxies and toc content illustrate that primary productivity was the most vital control on the accumulation of om high primary productivity was mainly driven by volcanic ash falls meanwhile high salinity and suboxic euxinic conditions were beneficial to the preservation of om giving rise to a high degree of om enrichment

petroleum systems of the zhu iii subbasin pearl river mouth basin south china sea the zhu iii subbasin is one of three subbasins in the pearl river mouth basin in the northern shelf of the south china sea the zhu iii belongs to a rift basin initiated in the paleogene being a part of the rifting lake group of paleogene age in the pearl river mouth basin the evolution of the zhu iii subbasin can be divided into three stages lacustrine facies of the early stage paleocene middle oligocene bay facies of the middle stage late oligocene and open shallow marine of the late stage neogene forming respectively source reservoir and seal rocks the lacustrine sediments include the wenchang formation oil source rock and the enping formation gas source rock which are the source rocks of two petroleum systems in the study area the zhu iii subbasin experienced three obvious tectonic movements of which the tenso shear movement in the late oligocene and extensional movement at the end of the middle miocene formed the main oil bearing structures in the study area oil and gas exploration results synthetic study of geochemical and thermal modeling of the two source rocks diagenesis and organic inclusions and basin modeling show that there are two petroleum systems in the zhu iii subbasin the wenchang zhujiang petroleum system in wenchang b sag and the enping zhuhai petroleum system in the wenchang a sag in the two petroleum systems hydrocarbon generation migration and accumulation peaks are late miocene holocene

uniform geothermal gradient and heat flow in the qiongdongnan and pearl river mouth basins of the south china sea abstract the pearl river mouth basin prmb and qiongdongnan basin qdnb are oil and gas bearing basins in the northern margin of the south china sea scs geothermal survey is an important tool in petroleum exploration a large data set comprised of 199 thermal conductivities 40 radioactive heat productions 543 measured geothermal gradient values and 224 heat flow values has been obtained from the two basins however the measured geothermal gradient data originated from diverse depth range make spatial comparison a challenging task taking into account the variation of conductivity and heat production of rocks we use a uniform geothermal gradient to characterize the geothermal gradient distribution of the prmb and qdnb results show that in the depth interval of 0 5 km the uniform geothermal gradient in the prmb varies from 17 8 c km to 50 2 c km with an average of 32 1 6 0 c km in comparison the qdnb has an average uniform geothermal gradient of 31 9 5 6 c km and a range between 19 7 c km and 39 5 c km heat flows in the prmb and qdnb are 71 3 13 5 mw m 2 and 72 9 14 2 mw m 2 respectively the heat flow and geothermal gradient of the prmb and qdnb tend to increase from the continental shelf to continental slope owing to the lithosphereic crustal thinning in the cenozoic

origin and occurrence of crude oils in the zhu1 sub basin pearl river mouth basin china the origin of the seventeen major oil fields in the zhu1 sub basin pearl river mouth basin prmb was studied based on the results of rock eval pyrolysis on more than 370 samples and biomarker analysis on 31 source rock samples and 63 oil samples the two possible source rock intervals have different biomarker assemblages and were deposited in different environments the wenchang formation e2w 56 5 32 ma is characterized mainly by low c19 c23 tricyclic terpane 0 4 ratios and were deposited in anoxic to suboxic environments with important contribution from pediastrum and dinoflagellates the enping formation e3e 32 30 ma has high c19 c23 tricyclic terpane high c24 tetracyclic terpane c30 hopane widely variable yet overally high bicadinane t c30 hopane and low 4 methyl steranes c29 steranes ratios and were deposited in freshwater lacustrine to swamp conditions with significant terrigenous organic matter input according to oil source correlation three oil classes can be identified in the zhu1 sub basin class 1 oil is e2w derived and occurs widely class 2 oil is e3e derived and refers to oils from f field in the north of the huizhou depression class 3 oil is a mixture of oils generated from e2w and e3e only distributed in the huizhou depression and on its southern margin the petroleum distribution pattern is mainly controlled by the distribution of source rocks and the migration pathways of oils this research has important implications for future exploration

origin of nama basin bitumen seeps petroleum derived from a permian lacustrine source rock traversing southwestern gondwana abstract biodegraded bitumens associated with quartz and calcite veins in the cambrian fish river subgroup sediments of the nama group of southern namibia have a geochemical signature diagnostic for organic matter that was deposited in a saline lacustrine palaeoenvironment in particular they contain abundant gammacerane carotane and 3 methylhopanes while 24 isopropyl cholestanes and dinosteroids are not detectable sealed tube hydrous pyrolysis of asphaltene and polar fractions yielded saturated hydrocarbons amenable to c isotopic analysis and these analyses show unusually low 13 c values these combined characteristics are also present in immature bitumens from the permian irati formation of brazil and a saline lacustrine facies of the whitehill formation in the karoo basin south africa we conclude that the bitumens originated from whitehill equivalent strata of the kalahari basin deposited in what was an extensive saline lacustrine basin in southwestern gondwana during the early permian in southern africa source rocks of the whitehill formation are generally immature for petroleum generation and it is therefore likely that the nama bitumens were expelled by contact metamorphism during emplacement of karoo dolerite sills and dykes in the jurassic

guidelines for evaluating petroleum source rock using programmed pyrolysis rock eval pyrolysis is used to rapidly evaluate the petroleum generative potential and thermal maturity of rocks accurate conclusions require programs every 30 60 ft 9 18 m understanding of interpretive pitfalls and supporting data such as visual kerogen vitrinite reflectance and elemental analyses the generative potential of coals is commonly overestimated by pyrolysis and is best determined by elemental analysis and organic petrography most coals show high s2 s3 5 and low hi values 300 mg hc g toc migrated oil and mud additives which alter rock eval data can sometimes be removed by special processing for immature rocks bimodal s2 peaks and pi values over 0 2 indicate contamination pyrolysis downgrades organic poor clay rich rocks which show lower hi and higher tmax values than isolated kerogen because of adsorption of pyrolyzate on the clays tmax values for small s2 peaks 0 2 mg hc g toc are unreliable tmax is affected by maturation organic matter type contamination and the mineral matrix s3 is sensitive to inorganic and adsorbed carbon dioxide and to instrumentation problems acidification of carbonate rich samples and proper maintenance improves s3 measurement constant sample weights 100 mg are recommended below a threshold weight tmax increases by up to 10 c and other parameters decrease organic rich samples which overload the detector can be diluted with carbonate detector linearity is determined by pyrolyzing various weights of an organic rich rock

a north atlantic tephrostratigraphical framework for 130 60 ka b2k new tephra discoveries marine based correlations and future challenges abstract building chronological frameworks for proxy sequences spanning 130 60 ka b2k is plagued by difficulties and uncertainties recent developments in the north atlantic region however affirm the potential offered by tephrochronology and specifically the search for cryptotephra here we review the potential offered by tephrostratigraphy for sequences spanning 130 60 ka b2k we combine newly identified cryptotephra deposits from the ngrip ice core and a marine core from the iceland basin with previously published data from the ice and marine realms to construct the first tephrostratigraphical framework for this time interval forty three tephra or cryptotephra deposits are incorporated into this framework twenty three tephra deposits are found in the greenland ice cores including nine new ngrip tephras and twenty separate deposits are preserved in various north atlantic marine sequences major minor and trace element results are presented for the new ngrip horizons together with age estimates based on their position within the ice core record basaltic tephras of icelandic origin dominate the framework with only eight tephras of rhyolitic composition found new results from marine core md99 2253 also illustrate some of the complexities and challenges of assessing the depositional integrity of marine cryptotephra deposits tephra based correlations in the marine environment provide independent tie points for this time interval and highlight the potential of widening the application of tephrochronology further investigations however are required that combine robust geochemical fingerprinting and a rigorous assessment of tephra depositional processes in order to trace coeval events between the two depositional realms

mesozoic source rocks and petroleum systems of the northeastern qaidam basin northwest china the qaidam basin is a continental petroliferous basin located in northwest china its northern sector is an important hydrocarbon province where one of the earliest oil discoveries in china was made although mesozoic source rocks are understood to be important parts of qaidam petroleum systems the identification and distribution of mesozoic source rocks in the subsurface are poorly understood middle jurassic coal measures and associated shales have long been considered to be the primary mesozoic source rocks for the northeastern qaidam basin without any support from subsurface geochemical and geological data however new data have been gathered from earlier mesozoic sediments that were penetrated by the lengke 1 well a deep scientific well with a total depth of 5200 m 17 060 ft the well was drilled on the lenghu structural belt in 1997 and documented other effective source rocks geochemical analyses indicate that lower jurassic mudstones are good to excellent source rocks for the commercial oil wells in the lenghu area the upper middle jurassic shales are very good source rocks for the commercial oil wells in the yuka area two source rock intervals in the northeastern qaidam basin allow for two petroleum systems to be distinguished the lower jurassic lower jurassic tertiary and middle jurassic upper jurassic the lower jurassic lower jurassic tertiary petroleum system with a geographical extent of 15 000 km2 5800 mi2 and a cumulative amount of source rocks between 200 and 700 m 650 and 2300 ft represents a favorable target for future exploration the middle jurassic upper jurassic petroleum system however may have a lower exploration potential because of a smaller area 1500 km2 580 mi2 and a thinner cumulative amount of source rocks 100 200 m 330 650 ft

pennsylvanian continental cyclothem development no evidence of direct climatic control in the upper freeport formation allegheny group of pennsylvania northern appalachian basin abstract the occurrence of lacustrine carbonates in the allegheny group upper middle pennsylvanian continental cyclothems of the northern appalachian basin has been attributed to climatic alternation of wet coal deposition and dry carbonate deposition periods however we present evidence from facies associations coal and carbonate petrography and carbonate stable isotope geochemistry for a uniformly wet climate throughout deposition of one of the earliest continental cyclothems the upper freeport formation uff we propose a depositional model comprising a large wetland complex drained by an anastomosed fluvial system containing a mosaic of channels freshwater siliciclastic and carbonate lakes and peat bogs swamps on a siliciclastic floodplain carbonate phases represent bio induced precipitates modified by lake dynamics and not evaporative deposits absence of covariant isotopic trends between 18o and 13c and a relatively small range of 18o values 1 9 to 6 4 pdb that are close to or lighter than predicted paleoprecipitation for the pennsylvanian equatorial regions indicate hydrologically open short residence time lake systems in support of our sedimentary model combined sedimentologic and isotopic data do not indicate reduced effective moisture precipitation evaporation during intervals of limestone deposition the uff lakes developed in a relatively wet climate zone without significant episodic closure due to climatically induced water deficit lithologic patterns within the uff cyclothem are primarily attributed to the evolution of anastomosed fluvial systems controlled by subsidence in an active foreland basin rather than to short term climatic change or eustacy

geochemical characteristics and origins of natural gas in the zhu iii sub basin pearl river mouth basin china abstract the zhu iii sub basin is an important petroliferous region in the south china sea where hydrocarbon distribution shows strong heterogeneity with oil primary produced from the wenchang b depression and gases from the wenchang a depression however a mixture of oil and gases are produced from the surrounding qionghai and shenhu uplifts the origin generation history and migration pathway of oil have been intensively studied but no study have been done directly on the gas which restricts future petroleum exploration in this study natural gas molecular compositions were measured on 46 samples stable carbon isotopic composition were measured on 39 samples and light hydrocarbon composition were measured on 30 samples results indicate that natural gases in the zhu iii sub basin are mainly composed of hydrocarbon gases with abundant co2 and n2 the hydrocarbon gases are all thermogenic gases which are mainly derived from the oligocene enping formation e3e 35 30 ma the contribution of the eocene wenchang formation e2w 56 35 ma to natural gases increases from the wenchang a depression to the south boundary fault sbf and surrounding uplifts this is caused by the early generated natural gases with more contribution from the e2w and dissolved in oils that migrated to the surrounding qionghai and shenhu uplifts natural gases and oil in the surrounding uplifts and near the sbf therefore avoided secondary cracking due to the high gas migration rate through the sbf and lateral sandstone carrier beds whereas natural gases in the wenchang a depression mainly originated from the secondary cracking of oil the equivalent vitrinite reflectance values of source rocks when the natural gases were generated varied from 0 6 to 1 5 based on carbon isotope differences between hydrocarbons indicating mature to high mature stage co2 with abundance less than 10 mainly originated from organic matter decomposition co2 with abundance more than 15 was sourced from the deep mantle and crust and mainly concentrated in the deep layers near the sbf which cuts into the basement n2 is probably the product of in situ reservoir alteration such as biodegradation in shallower layers our study on the geochemical characteristics and origins of the natural gas will enable a better understanding of petroleum system in the zhu iii sub basin and provide theoretical basis for optimizing future petroleum exploration strategy detailed study on shallow layers in the qionghai and shenhu uplifts and deep layers near the sbf are needed because exploration risks are relatively high in these plays

major and trace element geochemistry of bay of bengal sediments implications to provenances and their controlling factors major and trace elements of sediments from a 13 m long piston core sk187 pc33 from the western bay of bengal have been investigated in this study to infer about the changes in provenances and related controlling factors during the last glacial interglacial period factor analysis of these geochemical dataset ascertains dominant role of riverine supply of sediments in regulating the geochemistry of sk187 pc33 sediments the al normalized major k and ti and trace elemental cu and cr ratios of these marine sediments fall within the ranges observed for their major provenances viz ganga brahmaputra and the godavari krishna gk rivers and depth profiles of these ratios showed significant variations with synchronous excursion at around the last glacial maxima lgm implying a change in their provenances with relatively reduced himalayan contribution during this climatic event relatively higher cia and ti ca ratios with lower k al ratios of these sediments during the holocene hint intense chemical weathering in the river basins in response to strengthened monsoon during this period inverse model calculation of al normalized elemental ratios of the sediments estimated an average sediment contribution of 66 13 and 34 13 from the himalayan and the peninsular indian rivers to the core site respectively consistent with the depth profiles of elemental ratios the estimated sediment contributions from the himalayan rivers are observed to decrease by 20 from the himalayan rivers particularly that of the ganga to the studied location during the lgm lowering of sediment supply from the himalaya ganga during the lgm is due to weakening of south west monsoon and reduction in available exposure area for weathering due to extent of glacier cover outcomes of this study underscore the strong linkage between erosion and climate

cenozoic tectonic subsidence in deepwater sags in the pearl river mouth basin northern south china sea the cenozoic tectonic subsidence of the deepwater area in the pearl river mouth basin northern south china sea is studied by subsidence analysis via backstripping calculations based on data of newly interpreted sequence boundaries in the subsidence analysis local porosity depth parameters were estimated based on well data the paleo water depth parameters and lithology were estimated for all grid nodes based on well data and sedimentary system maps and ages of sequence boundaries were adjusted according to the international chronostratigraphic chart v2013 01 sensitivity analysis shows that these are essential to ensure the quality of the subsidence analysis in the slope areas maps of tectonic subsidence rates of 18 cenozoic sequences were constructed and spatial temporal variations of the tectonic subsidence were discussed the subsidence was restricted in the baiyun and liwan sags before 30 ma and extended to uplifts after 30 ma this indicates that the 30 ma unconformity is the breakup unconformity that separated the syn rift and post rift sequences four substages of post rift subsidence were identified by cyclic changes in the rate and pattern of tectonic subsidence at boundaries of 23 3 ma 17 2 ma and 11 9 ma respectively anomalous post rifting tectonic subsidence was significant and totaled to similar to 1200 m at the center of the baiyun sag and punctuated by rapid subsidence and uplift events the baiyun event was manifested in the study area by a short lived uplift event in 23 9 23 3 ma followed by a short lived rapid subsidence in 23 3 19 8 ma in the central study area this localized rapid subsidence caused northward jump and anti clockwise rotation of the shelf break two order teeterboard seesaw like subsidence was observed in the study area in the post rifting stage suggesting elastic deformations of the crust and lithosphere c 2014 elsevier b v all rights reserved

lacustrine environmental evolution and implications on source rock deposition in the upper cretaceous paleocene of the south yellow sea basin offshore eastern china abstract lacustrine source rocks are well developed within the upper cretaceous paleocene in the south yellow sea basin sysb in offshore eastern china understanding the deposition of these source rocks could provide critical information for hydrocarbon exploration in the sysb as well as reveal the paleoenvironment across the cretaceous paleogene boundary in eastern china this study investigates the lacustrine environmental evolution during the upper cretaceous taizhou formation k2t to paleocene funing formation e1f within the sysb and its implications on source rock deposition based on core observation combined with organic geochemical indicators multiple maturity parameters vitrinite reflectance tmax and biomarker isomerization ratios reveal that the organic matter om has reached early oil window maturity the om of source rocks is dominated by kerogen type ii iii liptinite and vitrinite anoxic saline brackish deep to semi deep lacustrine environments prevailed during the deposition of k2t2 second member of the k2t e1f2 second member of the e1f and e1f4l lower unit of fourth member of the e1f the deposition of three intervals was influenced by marine incursion as evidenced by geochemical and paleontological results low to moderate toc contents avg 0 78 wt to 1 91 wt which corresponds to low to moderate terrestrial om input are observed through three intervals abundant freshwater together with high terrestrial om flowed into the lacustrine environments during the deposition of e1f4u upper unit of fourth member of the e1f leading to dysoxic oxic and freshwater conditions high terrestrial om input is probably the major controlling factor for relatively high toc contents avg 2 49 in the e1f4u an evolution from balanced fill to overfilled lake type is observed in the upper cretaceous paleocene of sysb consistent with an evolution from semi arid to humid paleoclimate conditions the e1f4u and e1f2 source rocks exhibit fair to good potential whereas poor to fair potential is present in the e1f4l and k2t2 source rocks compared with the paleogene source rocks in onshore eastern china the upper cretaceous paleocene source rocks in the sysb probably hold good potential for generating commercial quantity of oil although further study on hydrocarbon generation kinetics of source rocks and overall basin history are needed

application of tetracyclic polyprenoids as indicators of input from fresh brackish water environments abstract c30 tetracyclic polyprenoids tpp are most prominently observed in samples derived from low salinity i e fresh to brackish lacustrine environments and are generally present in low levels in samples derived from saline i e marine and saline lacustrine environments a near shore facies of the chonta formation peru that has no marine palynomorphs but abundant chlorococcalean green algal nonmarine palynomorphs has high levels of tpp suggesting green algae or chlorophyta are a possible source for the tpp compounds the ratio between a c30 tpp compound and 27 norcholestanes is useful for assessing this nonmarine algal input moderate elevations of tpp above what is common in marine derived samples were found in ostensibly marine source rocks and oils from certain basins of western and northern south america middle magdalena colombia maracaibo venezuela and trinidad basins this is likely due to transport from the nonmarine to the marine environment because of an influx of fresh water into the near shore marine environment alternatively oils from these basins may have inputs from near shore shallow marine algae with chemistry similar to that found in lacustrine settings the tpp ratio in conjunction with other environmental indicators such as 4 methyl steranes or hopane sterane ratio is useful for differentiating marine and nonmarine influences in pre salt oils and source rocks of west africa the tpp ratio used with other environmental indicators gammacerane c29 steranes c30 steranes and age diagnostic biomarkers dinosteranes 4 methylsteranes can be useful in differentiating among nonmarine source facies for example in the turpan hami basin china permian saline lacustrine and jurassic lacustrine deltaic facies can be discriminated

episodic rifting and subsidence in the south china sea the south china sea experienced at least three stages of rifting and two intervening stages of sea floor spreading since the early cretaceous its evolution can be described by an episodic model of tectonism one of thermal cooling and subsidence pulsed by temporally and spatially confined heating events analysis of regional geologic and geophysical data suggests episodes of rifting and associated thermal activities initiated during the late cretaceous the late eocene and the late early miocene the rift system corresponding to the first episode trends northeast southwest whereas those of the second and third trend east west these two trends coincide with the orientations of the major tectonic lineations within the basin age estimates from heat flow and bathymetric data suggest the oceanic crust in the southwest subbasin is considerably older 55 ma than that in the northwest 35 36 ma or east 32 ma subbasins the episodic tectonic model is supported by basin subsidence analysis subsidence especially subsidence rate curves derived from the regional well data demonstrates that unlike a classic atlantic passive margin thermal subsidence in the south china sea was punctuated by rapid subsidence events which are chronologically consistent with the rifting episodes in terms of hydrocarbon potential the episodes of rifting and drifting would be conducive to the development of overprinted structures and the deposition of several discrete transgressive packages of source rocks and reservoirs separated by widespread unconformities the thermal maturity of sedimentary organic matter affected by episodic rifting and subsidence may be greater than expected on a purely passive margin of equivalent age that had not experienced repeated heating

lacustrine source rock deposition in response to co evolution of environments and organisms controlled by tectonic subsidence and climate bohai bay basin china three paleogene syn rift intervals from the bohai bay basin the most petroliferous basin in china were analyzed with sedimentological and geochemical techniques to characterize the lateral source rock heterogeneities to reveal the environmental and ecological changes through geologic time and to construct depositional models for lacustrine source rocks under different tectonic and climatic conditions the third es3 and first es1 members of the eocene shahejie formation and the oligocene dongying formation ed display widely variable total organic carbon contents hydrogen indices and visual kerogen compositions suggesting changes in organic facies from deep to marginal sediments carefully selected deep lake facies samples from any interval however display fairly uniform biomarker composition these three intervals have distinctly different biomarker assemblages which indicate weakly alkaline freshwater lakes with a moderately deep thermocline during es3 deposition alkaline saline lakes with shallow chemocline during es1 deposition and acidic freshwater lakes with deep unstable thermocline during the deposition of the dongying formation such environmental changes corresponded to changes in subsidence rate and paleoclimate from rapid subsidence and wet climate during es3 deposition through slow subsidence and arid climate during es1 deposition to rapid subsidence and wet climate during ed deposition and resulted in synchronous changes in terrigenous organic matter input phytoplankton community and primary productivity the co evolution of environments and organisms controlled by tectonic subsidence and climate accounted for the deposition and distribution of high quality lacustrine source rocks with distinctly different geochemical characteristics most rift basins experienced changes in subsidence rates and possibly changes in climates during their syn rift evolutions the models constructed in this paper may have important implications for source rock prediction in other lacustrine rift basins

using element geochemistry and detrital zircon geochronology to constrain provenance of the eocene sediments in the deep water area of the pearl river mouth basin south china sea abstract as the largest sag in the zhu ii depression within the pearl river mouth basin the baiyun sag bys lies in an area of interaction among the eurasian plate pacific plate and indian plate the bys mainly experienced the paleogene rift stage and neogene quaternary post rift stage thick syn rift sediments in the bys have recorded the nature of provenance and provide an excellent record of regional tectonic evolution prior to the opening of the south china sea in this study elemental geochemical analysis combined with published zircon detrital u pb dating results are applied to better understand the provenance change and tectonic setting of the bys during the eocene in this respect the chondrite normalized ree patterns of eocene samples from six wells are highly similar to upper continental crust ucc and post archean australian shale paas particularly with respect to lree enrichment significantly negative eu anomalies and slight ce anomalies geochemical results confirm that the bys eocene sediments were derived from a continental island arc to an active continental margin in addition the rock types of sources and the relatively narrow detrital zircon ages show that mesozoic intermediate felsic igneous and metamorphic rocks derived from local topographic highs contributed to infilling most of the bys furthermore the results show that the panyu low uplift began to accept large sediments transported by the paleo pearl river from the south china coast during the active syn rift stage prior to the opening of the south china sea

influence of volcanic and hydrothermal activity on organic matter enrichment in the upper triassic yanchang formation southern ordos basin central china abstract based on the field investigation of oil shales in the southern ordos basin detailed observations and systematic sample analyses of core samples from a well that penetrated an oil shale the influence of volcanic and hydrothermal activity on the chang 8 chang 7 members of the yanchang formation on organic matter om enrichment was geochemically and petrologically analyzed according to maceral analyses and rock pyrolysis the kerogen types of the samples in the study area are widely distributed those of the oil shale with the highest om abundance are mostly type ii i and are immature or in a stage of low maturity six layers of tuff and tuffaceous mudstone were identified by core observation and element characteristics they are characterized by higher total rare earth element ree and ce values and th contents and lower la yb n and eu values mineral assemblages of anhydrite pyrite marcasite and relevant diagrams of the elemental geochemistry confirmed the existence of hydrothermal deposits the high yn hon and u th ratios and total sulfur ts contents indicate that the chang 7 member experienced four episodes of intense hydrothermal activity early in the chang 73 member volcanic ash and hydrothermal fluids brought in a large amount of nutrients which not only increased primary productivity but also increased the salinity of the water column enhanced anoxia in the sedimentary environment of the lake bottom promoted the preservation of om and finally formed the oil shale layer with the richest om however the strong volcanic eruption in the late chang 73 member led to changes in the regional climate causing it to dry and become colder and resulting in a decrease of primary productivity earthquakes triggered by volcanism resulted in turbidite deposits which destroyed the preservation and diluted the enrichment of om this study reveals in detail the influence of volcanic and hydrothermal activity on om enrichment during the evolution of the basin and thereby deepens our theoretical understanding of om enrichment

biomarker and n alkane isotope profiles for tertiary oils relationship to source rock depositional setting abstract biomarker and n alkane isotope profiles have been measured for 29 late cretaceous tertiary oils from se asia china papua new guinea new zealand and the u s a the results are interpreted with respect to six kinds of source rock depositional setting fluvio deltaic fd freshwater transitional tr lacustrine lac saline lacustrine sal marine deltaic md and marine carbonate mc a comparison of biomarker and n alkane isotope results suggests that parameters such as the oleanane hopane ratio may overestimate the higher plant contribution to marine oils the abundance of bicadinanes is much more variable than that of oleanane probably because of a specific association with the highly resinous dipterocarp hardwoods of se asia however traces do occur in an oil from outside the paleogeographic range of the dipterocarp family confirming that there is also a more general angiosperm source the bicadinane isomeric distribution is shown to depend on maturity leading to new maturity parameters which are resistant to even very heavy biodegradation retention indices based on the regular hopane series are provided for the main bicadinane and methyl bicadinane isomers and for a group of oleanane related triterpanes of unknown structure the presence of the latter compounds may indicate locally deposited as opposed to transported higher plant matter in the source source rock depositional setting is the primary control on the shape of the n alkane isotope profile with negatively sloping curves being characteristic of fd and tr oils and flat or positively sloping curves typical of marine oils the difference is probably related to the bacterial reworking of higher plant matter in the fd environment a slight isotopic anomaly at n c 17 correlates with the abundance of algal derived steranes and may indicate a minor marine contribution to the source of an fd oil

evolution of ocean temperature and ice volume through the mid pleistocene climate transition earth s climate underwent a fundamental change between 1250 and 700 thousand years ago the mid pleistocene transition mpt when the dominant periodicity of climate cycles changed from 41 thousand to 100 thousand years in the absence of substantial change in orbital forcing over this time an increase occurred in the amplitude of change of deep ocean foraminiferal oxygen isotopic ratios traditionally interpreted as defining the main rhythm of ice ages although containing large effects of changes in deep ocean temperature we have separated the effects of decreasing temperature and increasing global ice volume on oxygen isotope ratios our results suggest that the mpt was initiated by an abrupt increase in antarctic ice volume 900 thousand years ago we see no evidence of a pattern of gradual cooling but near freezing temperatures occur at every glacial maximum

the bytham river reconsidered abstract the english midlands is one of the most important regions for british pleistocene geology the middle pleistocene glacial sediments of the region termed the wolston formation overlie deposits of a pre existing river system the baginton formation the latter are characteristically composed of quartz rich sediment derived from underlying triassic bedrock this sw ne aligned proto soar system was overridden by the wolstonian ice its lack of terraces or discrete sedimentary units implies that the river can only have existed for a limited period the deposits accumulated during a period of climate change from boreal interstadial to subarctic conditions a reinterpretation of these sediments as the headwaters of a pre anglian bytham river aligned towards east anglia across the fenland where they were linked to the ingham formation deposits found favour for two decades this was especially so when the wolston formation sediments were reassigned to the earlier anglian stage however recent work has shown that the bytham river could not have existed in the form suggested by some authors since pre anglian age fluvial sediments are absent from the eastern fenland margin except possibly certain deposits at high lodge suffolk therefore a re examination of the evidence is required it is concluded that the wolstonian glaciation late saalian marine isotope stage mis 6 indeed post dates that during the anglian stage elsterian mis 12 in addition it appears that the baginton proto soar stream as originally conceived almost certainly did not exist before the early wolstonian early saalian stage following a significant period of fluvial incision rather than being aligned towards east anglia the substantial proto soar flowed into south lincolnshire and thence potentially to the north sea via the wash and the silver pit depression by contrast the pre anglian ingham formation deposits of central east anglia were almost certainly deposited by a separate proto trent river that drained the east midlands over an extended period as a left bank thames tributary together these conclusions reinforce the view that the main drainage alignment in southern england during the pre anglian period was nw to se parallel to the regional tilt of the landmass

comprehensive source rock evaluation of the kazhdumi formation in the iranian zagros foldbelt and adjacent offshore abstract the kazhdumi formation is regarded as one of the most prolific hydrocarbon sources in the zagros foldbelt and adjacent offshore rock eval pyrolysis data were collected from 2300 rock samples of the kazhdumi formation in 64 wells core and cutting including 37 oil and gas fields and five outcrops 200 vitrinite reflectance measurements were carried out to calibrate and map thermal maturity over the study area palynofacies analyses and thermal history modeling were applied on the wells located in the study area based on the total organic carbon toc map the kazhdumi formation toc values range from 0 to 11 in the central part of dezful embayment its average value is about 5 while average toc value of the kazhdumi formation is lower than 0 5 in qatar gawbandi paleo high hydrogen index hi values represented types ii and iii kerogen for central part of the dezful embayment and qatar gawbandi paleo high respectively t max ranges from 370 to 455 c in the study area the maximum and minimum values for this parameter are recorded in the central dezful embayment and central persian gulf anticlines respectively vitrinite reflectance vr r map also confirms the concluded results of t max data reconstructed burial history and thermal modeling of three wells are also in full agreement with the results of other maturity evidence t max and vr r palynofacies analyses revealed that this formation in the central persian gulf south pars field clearly represents the dominance of terrigenous elements which were resulted from a close proximity to a fluvio deltaic source however towards the northwest amorphous organic matter aom dominates in central dezful embayment indicating a distal dysoxic anoxic environmental condition

duration and structure of the past four interglaciations reanalysis and additional dating of the devils hole 18o paleotemperature record confirm that the last interglaciation in the great basin the continental analog of marine isotopic substage 5e lasted 22 000 yr consistent with the vostok paleotemperature record which suggests a duration of 19 000 yr for this event in antarctica the three preceding interglaciations in the devils hole record analogs of marine isotopic substages 7e 9c and 11c range from 20 000 to 26 000 yr in duration a 20 000 yr duration for the last interglaciation is consistent with tims uranium series dated sea level high stands thus the widely held view that interglaciations were of 11 000 to 13 000 yr duration and constituted only about 10 of mid to late pleistocene climatic cycles needs reexamination the warmest portion of each interglaciation in the devils hole time series is marked by a 18o plateau signifying apparent climatic stability for periods of 10 000 to 15 000 yr duration

geochemical characterization and depositional environment of source rocks of small fault basin in erlian basin northern china abstract a combined investigation of molecular geochemistry elements and carbon isotopic composition of carbonate distribution was carried out on the early cretaceous mudstones of the tengger formation in the erlian basin northern china to define source rock geochemical characteristics depositional environment and tectonic setting of small faulted basin the biomarkers of mudstone extracts are characterized by short to middle chain n alkanes high cpi values 1 12 a wide range of pr ph 0 4 1 94 relatively high concentrations of c 29 sterane and the presence of relatively low tricyclic terpanes and low gammacerane index values 0 01 0 25 which is consistent with a relatively oxic to anoxic depositional environment of fresh to brackish water conditions with a major contribution of terrigenous organic matter input and a low contribution of aquatic algal bacterial organic matter the oxic to anoxic depositional environment of small fault basins and a fresh and brackish water conditions are also confirmed by reduced sulphur organic carbon ratio and element distribution in these small fault basins the cross plots of 13 c carb and toc show that productivity has an obvious control on source rock development the differences in tectonic settings cause variations in productivity redox conditions and terrigenous organic matter input which account for the distinctly different geochemical characteristics and depositional environment of source rocks in small fault basins

warm humid paleoclimate control of salinized lacustrine organic rich shale deposition in the oligocene hetaoyuan formation of the biyang depression east china abstract lacustrine organic rich shales are widely developed within the oligocene biyang depression in the nanxiang basin in east china and across southeast asia these shales have been proven as hydrocarbon source rocks of crude oil as well as sources and reservoirs of shale oil understanding the deposition of these shales is essential to reconstruct the paleoenvironment and paleoclimate during the oligocene in east china as well as target the potential shale oil resources based on x ray diffraction organic and inorganic petrologic organic and inorganic geochemical and stable isotopic analyses paleoenvironment paleoclimate and hydrocarbon potential of the lacustrine organic rich shales in the oligocene hetaoyuan formation were investigated the mineral composition of hetaoyuan formation organic rich shales is dominated by clay minerals followed by quartz plagioclase calcite dolomite pyrite and gypsum six lithotypes are identified including siltstone silty shale clay shale calcareous shale dolomite shale and massive mudstone the organic matter om of the organic rich shales is dominated by type i kerogen lamalginite maturity parameters tmax biomarker ratios and calculated vitrinite reflectance suggest that the om enters the oil window maturity high toc and generative potential together with high contents of brittle minerals including quartz plagioclase and carbonates reveal the oligocene hetaoyuan formation hold good to very good potential of shale oil exploitation six organic rich shale layers have been identified in the hetaoyuan formation shale layer 1 to 6 from top to bottom among them shale layers 5 and 3 hold the best shale oil potential and therefore be investigated in the present paper shale layer 5 was deposited in a semi deep lacustrine environment under the moderately warm humid paleoclimate further dividing into lower middle and upper units relatively low toc contents av 2 6 wt in the lower unit are probably caused by high sedimentation rate high bioproductivity under favorable preservation conditions led to relatively high toc contents av 3 6 wt in the middle unit less reducing conditions together with moderate low bioproductivity resulted in relatively low toc contents av 2 6 wt in the upper unit warm humid paleoclimate prevailed during deposition of shale layer 3 deepened water depth and formed a deep lacustrine environment the stratified water column led to stable anoxic condition and photic zone euxinia in the saline deep lacustrine environment which enabled the accumulation of high amounts of om av 4 9 wt toc under excellent preservation av hi 710 mg hc g toc the results of core scanning analysis indicate that formation of the laminated shales probably controlled by seasonal fluctuations of paleoclimate

application of biological markers in the assessment of paleoenvironments of chinese non marine sediments abstract in this study we employ molecular organic geochemical data for 22 representative sediment samples from chinese non marine sedimentary basins in an attempt to characterize and assess the non marine depositonal paleoenvironments the samples investigated include oilshale shale mudstone and sodium sulphate rich sediments ranging in age from cretaceous to tertiary it is evidenced by geological and geochemical data that those sediments studied originate from lacustrine environments ranging from freshwater brackish fresh water to hypersaline the aliphatic fractions of the sediment extracts were analyzed by gc and gc ms and relative abundance of compounds and compound classes of normal acyclic and cyclic alkanes were measured from mass chromatograms the results reveal significant differences in the chemical features of the various sample groups which enable them to be characterized and identified in terms of source and or environment related parameters the diagnostic parameters that allow this assessment are the relative abundances of n alkanes acyclic isoprenoid alkanes and 4 methyl steranes hopane sterane ratio gammacerane and homohopane indexes etc in this study data interpretation was also assisted by pattern recognition through principal component analysis the results show that the sample groups of different environmental origin could be unambiguously distinguished on scores plot

the shedding of mesoscale anticyclonic eddies from the alaskan stream and westward transport of warm water abstract the south flowing waters of the kamchatka and oyashio currents and west flowing waters of the alaskan stream are key components of the western sub arctic pacific circulation we use ctd data argo buoys woce surface drifters and satellite derived sea level observations to investigate the structure and interannual changes in this system that arise from interactions among anticyclonic eddies and the mean flow variability in the temperature of the upstream oyashio and kamchatka currents is evident by warming in mesothermal layer in 1994 2005 compared to 1990 1991 a major fraction of the water in these currents is derived directly from the alaskan stream the stream also sheds large anticyclonic aleutian eddies averaging approximately 300 km in diameter with a volume transport significant in comparison with that of the kamchatka current itself these eddies enclose pools of relatively warm and saline water whose temperature is typically 4 c warmer and salinity is 0 4 greater than that of cold core kamchatka eddies in the same density range aleutian eddies drift at approximately 1 2 km d 1 and retain their distinctive warm and salty characteristics for at least 2 years selected westward pathways during 1990 2004 are identified if the shorter northern route is followed aleutian eddies remain close to the stream and persist sufficiently long to carry warm and saline water directly to the kamchatka current this was observed during 1994 1997 with substantial warming of the waters in the kamchatka current and upstream oyashio if the eddies take a more southern route they detach from the stream but can still contribute significant quantities of warm and saline water to the upstream oyashio as in 2004 2005 however the eddies following this southern route may dissipate before reaching the western boundary current region

sensitivity of biomarker properties to depositional environment and or source input in the lower toarcian of sw germany abstract a sequence of lower toarcian sediments which are highly contrasting in their depositional environment over a 5 m depth interval has been investigated in detail for the variability of geochemical properties which are used for source characterization and oil to source correlation lower liassic marls are representative of a well aerated shallow water environment in contrast to the immediately overlying bituminous shales which are deposited under extremely reducing conditions various properties have been found to vary considerably within these two units amongst the most important are carbon isotopic composition of the kerogen the pristane phytane ratios nickel as opposed to vanadyl porphyrins and the c27 dia regular steranes although maturation within the profile does not change some of the maturation dependent biomarker properties such as the monoaromatic steroid side chain cracking and the tm ts ratio exhibit large changes which can be assigned to diagenetic processes another maturation dependent property the 20s 20r epimerization of c29 steranes exhibits smaller changes which could also be due to early diagenetic processes the study suggests that reducing and oxidizing conditions i e eh and ph in the sediment exert an influence on several biomarker precursor product pathways in maturation studies initial variations due to depositional conditions have therefore to be taken into account

source controls on geochemical characteristics of crude oils from the qionghai uplift in the western pearl river mouth basin offshore south china sea abstract the qionghai uplift is a sub uplift tectonic unit in the western pearl river mouth basin though lacking source rocks itself it adjoins the wenchang a sag the wenchang b sag and the qionghai sag which contain significant source rocks for the special geological background the qionghai uplift has become an important accumulation area for oil and gas and the oils in the uplift show significant variation in important geochemical parameters in this study the geochemistry of oils in the qionghai uplift oil pools has been analyzed systematically revealing geographic differences three groups of oils were identified in the northern part of the qionghai uplift group i oils represented by the wc8 3e oil pool located in the northeast group ii oils in the middle represented by the wc13 1 oil pool and group iii oils in the southwest represented by the qh18 1 oil pool according to oil source correlations the oils of the three groups have mixed geochemical characteristics between typical oils sourced from the enping formation in the wenchang a sag and those sourced from the wenchang formation in the wenchang b sag we show that based on knowledge of hydrocarbon generation and evolution of source rocks around the qionghai uplift as well as the formative features of traps within the uplift the geochemical characteristics of the oils are mainly controlled by the distribution of mature hydrocarbon kitchens surrounding the uplift oils in the northeast of the northern qionghai uplift were mainly sourced from the enping formation in the wenchang a sag with a secondary contribution from the wenchang formation in the qionghai sag oils in the middle section are of mixed origin from the enping formation in the wenchang a sag and the wenchang formation in the wenchang b sag oils in the southwest part of the northern qionghai uplift were mainly generated from the wenchang formation in the wenchang b sag this research provides guidance for future exploration of the qionghai uplift

organic and isotope geochemistry of the early cretaceous rift sequence in the camamu basin brazil paleolimnological inferences and source rock models abstract the camamu basin located at the eastern brazilian continental margin is characterized by a thick early cretaceous organic rich rift sequence the integration of bulk geochemical isotopic and biomarker data with paleontological and geological information provided the basis for a better assessment of rift lake evolution hydrological regime redox potential salinity etc and its impact on source rock development pyrolysis and visual kerogen analyses reveal the dominance of lipid rich algal bacterial type i kerogen through the entire rift sequence paleolimnological reconstruction suggests that the lower rift sequence morro do barro formation neocomian was deposited in a fault bounded deep lake with fresh to brackish water stable water column stratification and water bottom anoxia high hydrogen indices 700 900 mg hc gtoc and 13c depleted carbon isotopic composition of the organic matter 13c values around 30 might reflect enhanced organic preservation the recycling of light ch4 generated by methanogenesis and the incorporation of isotopically light lipid rich bacterial biomass on the other hand the upper rift sequence rio de contas formation barremian was probably deposited within a broader shallower lake with a higher frequency of water column overturn and a deeper thermocline high organic carbon contents and strong 13c enrichment of the organic matter 13c excursions of up to 23 are interpreted to have resulted from enhanced primary productivity triggered by an increased input recycling of nutrients favored by lake morphology and humid climate

mesoscale eddies dominate surface phytoplankton in northern gulf of alaska abstract the hnlc waters of the gulf of alaska normally receive too little iron for primary productivity to draw down silicate and nitrate in surface waters even in spring and summer our observations of chlorophyll sensed by seawifs north of 54 n in pelagic waters 500 m depth of the gulf found that on average more than half of all surface chlorophyll was inside the 4 cm contours of anticyclonic mesoscale eddies the ratio approaches 80 in spring months yet these contours enclosed only 10 of the total surface area of pelagic waters in the gulf therefore eddies dominate the chlorophyll and phytoplankton distribution in surface pelagic waters we outline several eddy processes that enhance primary productivity eddies near the continental margin entrain nutrient and fe rich and chlorophyll rich coastal waters into their outer rings advecting these waters into the basin interior to directly increase phytoplankton populations there in addition eddies carry excess nutrients and iron in their core waters into pelagic regions as they propagate away from the continental margin as these anticyclonic eddies decay their depressed isopycnals relax upward injecting nutrients up toward the surface layer we propose that this transport brings iron and macro nutrients toward the surface mixed layer where they are available for wind forced mixing to bring them to surface these mesoscale eddies decay slowly but steadily perhaps providing a relatively regular upward supply of macro nutrients and iron toward euphotic layers they might behave as isolated oases of enhanced marine productivity in an otherwise iron poor basin we note that much of this productivity might be near or just below the base of the surface mixed layer and therefore poorly sampled by colour sensing satellites it is possible then that eddies enrich phytoplankton populations to a greater extent than noted from satellite surface observations only

a new borehole temperature adjustment in the jeffara basin southeast tunisia inferred source rock maturation and hydrocarbon generation via one dimensional modeling in tunisia most borehole temperatures used to constrain the thermal histories of sedimentary basins were previously corrected using various methods set to best fit domains other than the tunisian basins this study aimed to propose a new method of borehole temperature correction suitable for the jeffara basin southeastern tunisia a total of 92 temperature values including bottomhole temperatures bhts and drill stem test dst temperatures were collected from 11 boreholes in the area the correction method consists of plotting bht versus dst the derived equation generates corrected temperatures close to formation temperatures an error temperature curve following the equation was calculated x depth in meters and y temperature error in c the error varies from to to at depths below 274 m 898 ft a temperature error is proposed according to depth and to the time elapsed since mud circulation ceased intervals to test the method consistency the silurian tannezuft hot shales formation thermal history is simulated using the basinmod 1 d software program two runs were tested based on the new method 1 noncorrected bht and 2 corrected bht the first run indicates that the silurian source rock is at an early stage of the oil window the second run shows that the source rock is mature and even at a late mature stage toward the north oil expulsion has occurred even at an oil saturation expulsion threshold of 5 the results explain gas condensate production in the study area

regional paleohydrologic and paleoclimatic settings of wetland lacustrine depositional systems in the morrison formation upper jurassic western interior usa abstract during deposition of the upper jurassic morrison formation water that originated as precipitation in uplands to the west of the western interior depositional basin infiltrated regional aquifers that underlay the basin this regional groundwater system delivered water into the otherwise dry continental interior basin where it discharged to form two major wetland lacustrine successions a freshwater carbonate wetland lacustrine succession formed in the distal reaches of the basin where regional groundwater discharged into the denver julesburg basin which was a smaller structural basin within the more extensive western interior depositional basin an alkaline saline wetland lacustrine complex lake t oo dichi formed farther upstream where shallower aquifers discharged into the san juan paradox basin which was another small structural basin in the western interior depositional basin these were both wetlands in the sense that groundwater was the major source of water input from surface and meteoric water was limited in both basins lacustrine conditions developed during episodes of increased input of surface water inclusion of wetlands in our interpretation of what had previously been considered largely lacustrine systems has important implications for paleohydrology and paleoclimatology the distal carbonate wetland lacustrine deposits are well developed in the morrison formation of east central colorado occupying a stratigraphic interval that is equivalent to the lower morrison but extends into the upper morrison formation sedimentologic paleontologic and isotopic evidence indicate that regional groundwater discharge maintained shallow hydrologically open well oxygenated perennial carbonate wetlands and lakes despite the semi arid climate wetland deposits include charophyte rich wackestone and green mudstone lacustrine episodes in which surface water input was significant were times of carbonate and siliciclastic deposition in scarce deltaic and shoreline deposits marginal lacustrine deposits include ooid and skeletal packstone grainstone siltstone and sandstone distal lacustrine units are skeletal mudstone wackestone microbialites and laminated siliciclastic mudstone differentiation between wetlands and distal lacustrine units is not always possible palustrine features magadi type chert mtc and evaporites record episodes of increased aridity and exposure farther upstream during deposition of the upper part of the brushy basin member the ancestral uncompahgre uplift imposed a barrier to shallow eastward flowing groundwater that discharged into the san juan paradox basin on the upstream side of the uplift this created the closed hydrologic setting necessary for development of an alkaline saline wetland lacustrine complex lake t oo dichi silicic volcanic ash delivered by prevailing winds from calderas west and southwest of the basin contributed to the pore water evolution in the sediments a distinctive lateral hydrogeochemical gradient reflecting increasing salinity and alkalinity in the pore waters altered the ash to a variety of authigenic minerals that define concentric zones within the basin the basinward progression of diagenetic mineral zones is smectite clinoptilolite analcime potassium feldspar albite the groundwater fed wetlands were shallow and frequently evaporated to dryness scarce laminated gray mudstone beds record distinct episodes of freshwater lacustrine deposition that resulted from intermittent streams that carried detritus well out into the basin

geochemistry grouping and origins of crude oils in the western pearl river mouth basin offshore south china sea abstract thirty seven crude oils and 20 source rocks were selected for detailed molecular geochemical and isotopic analyses in order to establish the genetic relationships between the discovered oils and various petroleum source facies in the western pearl river basin offshore south china sea four groups of oils were identified the group i oils distributed in the southwestern wc19 1 field of wenchang b sag are characterized by high abundance of 4 methyl steranes relative to regular steranes low abundance of bicadinanes and high 13 c values showing good correlation with the medium deep lacustrine source facies in the wenchang formation the group ii oils represent the majority of the discovered oil reserves in the study area including those from the qionghai uplift and the northeast block of the wc19 1 oil field these oils have moderate concentrations of c 30 4 methylsteranes abundant bicadinanes and low 13 c values and correlate well with the shallow lake source facies of the wenchang formation in the wenchang b and a sags the group iii oils found in the wenchang a sag and surrounding areas are devoid of c 30 4 methylsteranes with abundant bicadinanes and similar 13 c values to those of the group ii oils these characteristics show close affinity with the coal bearing sequence in the enping formation thus suggesting a coaly source for these oils the group iv oils found only in the wc8 3 field display intermediate chemical compositions between the group ii and group iii oils most likely from mixed sources in the wenchang a sag these oil source genetic relationships suggest dominantly short distance oil migration and thus strong source facies controls on the geographic distribution of oil and gas fields within the western pearl river mouth basin

tectonic characteristics and evolution history of the pearl river mouth basin abstract on the basis of the new understandings from tens of thousand of kilometres of geophysical material and over 60 exploration and evaluation wells providing data on the pearl river mouth basin prmb this paper analyses the special tectonic position of the prmb where three major plates i e the eurasian the pacific and the indo australian plates meet and interact the characteristics of the basin geological structure and its tectonic evolution are also discussed situated on continental and transitional crust the prmb is a mesozoic cenozoic oil and gas bearing basin developed on caledonian folding basement which was reformed during the mesozoic in the process of its formation and evolution the prmb underwent extension slight compression and re extension with the eruption of intermediate acid and basic magma meanwhile it formed double structural layers with faulting below and depression above and sediments were laid down with marine facies following continental facies hydrocarbons accumulated from continental source rocks in the marine reservoir rocks by using a fracture structure model of the uplift and depression the mechanism of the prmb and its evolution history have been interpreted

molecular isotopic evidence of environmental and ecological changes across the cenomanian turonian boundary in the levant platform of central jordan abstract we evaluated the structure of planktonic communities and paleoenvironmental conditions throughout the cenomanian turonian oceanic anoxic event oae2 by studying bulk geochemical properties and the molecular isotopic composition of source specific hydrocarbons from organic rich sediments deposited in an intrashelf basin at the levant platform central jordan high concentrations of desmethyl and 4 methylsteranes as well as dinosteranes indicate that marine algae including dinoflagellates were the main primary producing organisms the presence of 2 methylhopanes and 13 c enriched hopanes in addition to isotopically enriched aryl isoprenoids evidenced the contribution of cyanobacteria and green sulfur bacteria respectively additionally variable but fairly low 15 n values during oae2 suggest the occurrence of diazotrophy as a likely important process fueling primary production during oae2 in this stratified anoxic continental platform variations in the relative contribution of biomarkers revealed changes in planktonic communities associated with sea level change and water column stratification oae2 was characterized by strong stratification anoxic bottom waters and a deep chemocline as evidenced by high gammacerane and homohopane indices and the absence of photic zone euxinia pze markers respectively however the presence of isorenieratane and its derivatives in post oae black shales points to a shoaling of the chemocline and to pze this interval was also characterized by an exceptionally high abundance of chlorophyll derived pristane and phytane up to 2 mg g 1 toc likely as a result of highly enhanced primary production and organic matter preservation remarkably this high productivity event co occurs with an exceptionally high abundance of calcispheres reported elsewhere to be part of a global bio event

organic matter and trace element rich sapropels and black shales a geochemical comparison a distinct pliocene eastern mediterranean sapropel i 282 recovered from three ocean drilling program odp leg 160 sites has been investigated for its organic and inorganic composition this sapropel is characterized by high organic carbon corg and trace element contents and the presence of isorenieratene derivatives the latter suggests that the base of the photic zone was sulphidic during formation of the sapropel combined with evidence of bottom water anoxia preservation of laminae high redox sensitive trace element contents and the abundance and isotopic composition of pyrite this leads to the tentative conclusion that almost the entire water column may have been anoxic this anoxia resulted from high productivity and not from stagnation because an approximation of the trace element budget during sapropel formation shows that water exchange with the western mediterranean is needed entire water column anoxia has been suggested earlier for several black shales with regard to the depositional environment and the corg content however only the cenomanian turonian boundary event ctbe black shales appear to be comparable to this sapropel the proposed trace element removal mechanism of scavenging and co precipitation in an anoxic water column is thought to be similar for both types of deposits the ultimate trace element source for the sapropel however is seawater whereas it is hydrothermal and fluvial input for ctbe black shales because they have a larger temporal and spatial distribution nonetheless the corg rich eastern mediterranean pliocene sapropel discussed here may be considered to be a younger analogue of ctbe black shales

lake type controls on petroleum source rock potential in nonmarine basins based on numerous empirical observations of lacustrine basin strata we propose a three fold classification of lacustrine facies associations that accounts for the most important features of lacustrine petroleum source rocks and provides a predictive framework for exploration in nonmarine basins where lacustrine facies are incompletely delineated 1 the fluvial lacustrine facies association is characterized by freshwater lacustrine mudstones interbedded with fluvial deltaic deposits commonly including coal shoreline progradation dominates basin fill resulting in the stacking of indistinctly expressed cycles up to 10 m thick in map view the deposits may be regionally widespread but laterally discontinuous and contain strong facies contrasts transported terrestrial organic matter contributes to mixed type i iii kerogens that generate waxy oil type i kerogen is hydrogen rich and oil prone type iii kerogen is hydrogen poor and mainly gas prone the luman tongue of the green river formation wyoming and the honyanchi formation junggar basin china provide examples of this facies association which is also present in the songliao basin of northeastern china the central sumatra basin and the cretaceous doba doseo basins in west central africa 2 the fluctuating profundal facies association represents a combination of progradational and aggradational basin fill and includes some of the world s richest source rocks deposits are regionally extensive in map view having relatively homogenous source facies containing oil prone type i kerogen examples include the laney member of the green river formation wyoming the lucaogou formation junggar basin china the bucomazi formation offshore west africa and the lagoa feia formation campos basin brazil 3 the evaporative facies association represents dominantly aggradational fill related to desiccation cycles in saline to hypersaline lakes and may include evaporite and eolianite deposits sublittoral organic rich mudstone facies are relatively thin but may be begin page 1034 quite rich and widespread the highest organic enrichment coincides with the deepest lake stages low input of land plant organic matter results in minimal lateral contrasts in organic content in some cases a distinctive type i s sulfur rich kerogen may generate oil at thermal maturities as low as 0 45 vitrinite reflectance equivalent examples include the wilkins peak member of the green river formation wyoming the jingjingzigou formation junggar basin china the jianghan and qaidam basins china and the blanca lila formation argentina

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

evidence of two temperate episodes in late pleistocene deposits at marsworth uk in the british quaternary two post cromerian interglacials the hoxnian and the ipswichian are recognized1 evidence of additional interglacials in this interval is widely accepted in the oceanic record of quaternary events2 and the possibility that at least one additional interglacial of this age is represented in britain has been discussed3 5 however in the absence of datable interglacial deposits which are seen to overlie one another the issue has remained controversial we describe here deposits at marsworth uk fig 1 where there is evidence of two temperate episodes and of intervening periglacial conditions stratigraphical superposition is established beyond any reasonable doubt the later deposit relates to the temperate woodland stage of the ipswichian interglacial dating of the earlier temperate material by the 230th 234u disequilibrium method indicates an interglacial episode not previously established in the british quaternary

stratigraphic classification of ancient lakes balancing tectonic and climatic controls lakes and lake deposits present two fundamental paradoxes 1 modern lakes are vastly complicated but the rock records of lakes are relatively simple extensive observations reveal three distinct facies associations of common and widespread occurrence these are referred to here as fluvial lacustrine fluctuating profundal and evaporative facies associations 2 most explanations of modern and ancient lakes attribute their nature to climate but neither modern lake parameters lake size depth and salinity nor the character of ancient lake strata thickness extent lithology correlate with measured or inferred climatic humidity we propose that it is the relative balance of rates of potential accommodation mostly tectonic with sediment water fill mostly a function of climate that controls lake occurrence distribution and character lake basins may be termed overfilled balanced fill or underfilled depending on the balance between these rates we conclude that climate and tectonics exert coequal influence on lake deposits at both mesoscales 1 m to hundreds of meters and macroscales hundreds to thousands of meters

anticyclonic eddies in the alaskan stream abstract anticyclonic eddies propagating southwestward in the alaskan stream as were investigated through analysis of altimetry data from satellite observations during 1992 2006 and hydrographic data from profiling float observations during 2001 06 fifteen long lived eddies were identified and categorized based on their area of first appearance three eddies were present at the beginning of the satellite observations another three formed in the eastern gulf of alaska off sitka alaska and four were first detected at the head of the gulf of alaska near yakutat alaska the other five eddies formed along the as between 157 and 169 w and were named as eddies while the eddies that formed in the gulf of alaska mainly decayed before exiting the gulf of alaska the as eddies mostly crossed the 180 meridian and reached the western subarctic gyre four of five as eddies formed under negative or weakly positive wind stress curls which possibly caused as separation from the coast comparison of eddy propag

palustrine sedimentation in an episodically subsiding basin the miocene of the northern teruel graben spain lacustrine deposits form most of the sedimentary record accumulated throughout the miocene in the northern part of the teruel graben a landlocked basin situated in ne spain three main stratigraphic units units i iii spanning late vallesian to late turolian in age are distinguished in the area the two former units comprise mainly carbonate lacustrine deposits that were deposited in a palustrine or a more permanent but shallow lacustrine setting the latter being related mainly to periods of lake expansion under more humid and cooler climatic conditions in contrast deposition of unit iii characterised by gypsiferous lacustrine sediments in central parts of the basin reflects the influence of source rocks of evaporitic nature upper triassic formations that were emplaced by diapiric uplift in the eastern margin during the middle turolian carbonate lake sediments belonging to units i and ii consist of four main lithofacies associations a distal alluvial lake margin deposits b lacustrine carbonates and pedogenically modified lacustrine carbonates c carbonate fill channels and d organic rich marlstone and carbonate marshes lithofacies association a shows typically a sequential arrangement formed from bottom to top of red mudstone carbonate palaeosols and biomicrite beds sequence type 1a these sequences are interpreted as a result of slow but continuous aggradation of the floodplain areas and subsequent rise of the water table probably reflecting equilibrium between subsidence and sedimentation lithofacies association b consisting of biomicrite beds passing upward into palaeosols sequence type 1b is thought to be caused by marked pulses of tectonic subsidence that created the accommodation space required for fast development of a carbonate lake carbonate fill channels showing erosive lower surfaces dig out on previous channels marsh deposits and or lacustrine carbonates exhibit well developed prismatic structure at their bed tops the sequential arrangement suggests similar tectonic constrains than the envisaged for lithofacies 1b the comparison of depositional styles of the lake systems with the palaeoclimatic evolutionary pattern of the basin throughout the miocene indicates that the combined effect of tectonism climate and source rock played a major role in the stratigraphic framework of the basin during this period

oil source correlation in the fulin basin shengli petroleum province east china the fulin basin is located within the giant shengli petroleum province in east china the source rock in the basin is mainly the lower part of the third member es3 of the eocene portion of the shahejie formation it is composed of organic rich dark mudstone and oil shale of lacustrine origin and contains good quality type i ii kerogen these strata reach the oil generative stage at ro 0 4 0 8 the first member es1 of the oligocene portion of the shahejie formation has excellent oil potential in the nearby gunan basin but is immature in the fulin basin and is not an effective source rock the oil and rock samples from both basins can be grouped into three major families based on biomarkers the first family shows low prph 0 3 and notable carotane typical of carbonate evaporite environments this family exists in es1 rocks and the related oils and is early mature 0 2 0 3 and s r s 0 10 0 20 the second family shows high prph 1 a low gammacerane index 0 2 and abundant 4 methyl steranes indicative of freshwater lacustrine conditions like those in es3 this family shows higher maturation 0 30 0 50 and s r s 0 35 0 55 and notable diasteranes the third family is transitional has source and maturity ratios between the above families and occurs in the es3 unit samples from the basin interior based on biomarker similarities between oils and rock extracts all oils in the fulin basin originated from es3 source rocks slight maturation differences indicate that these oils have been derived from different source areas no oil from es1 is found in the fulin basin suggesting es1 source rocks are too immature to generate commercial oil although the nearby gunan basin has much oil generated from es1 source rocks no migrated oil from es1 in this basin reached the kenli faulted zone because of intervening faults which disrupt migration

land sea correlations in the pleistocene based on isoleucine epimerization in non marine molluscs the correlation between the oxygen isotope stratigraphy of the oceans and continental stratigraphic records is one of the main challenges for quaternary research most continental classifications however are based on techniques and hypotheses that predate recent advances nevertheless the deep sea oxygen isotope global stratigraphic framework has been extended to the continents by means of some long sequences1 but these are exceptional and regional geology is unsatisfactorily classified for correlation with the oxygen isotope signal because successive geological events produced similar evidence homotaxis geochronometric dating is essential for correlation but available methods are highly site regional or sample specific fortunately non marine molluscs are ubiquitous in time and space and here we use the time dependent epimerization of l isoleucine in these fossils to subdivide the pleistocene of the british isles and to identify more events than recognized by the existing classification2 by calibrating the relative aminostratigraphic scale with independent dating methods we have set up a geochronology which is the basis for land sea correlations back to oxygen isotope stage 15

the influence of an alaskan stream eddy on flow through amchitka pass flow into the bering sea through amchitka pass in the central aleutian islands is shown to respond to the presence of a large meander eddy in the alaskan stream south of the pass maximum flow into the aleutian basin of the bering sea occurs when the eddy center lies nearest to the axis of amchitka pass a conceptual model of low frequency circulation variability within the bering sea based upon results of empirical orthogonal function analyses of sea surface height anomalies measured by the geosat radar altimeter is presented

effects of source thermal maturity and biodegradation on the distribution and isomerization of homohopanes in petroleum abstract the distributions of c31 c35 17 21 h homohopanes in marine petroleums can be used to describe redox conditions in the source rock depositional environment for example high c35 homohopane indices c35 c31 c35 are typical of petroleums generated from source rocks deposited under anoxic marine conditions where the c35 backbone of the precursor bacteriohopanetetrol is preferentially preserved homohopane distributions have been used to distinguish petroleums from different organic facies of the same source rock homohopane distributions are altered by secondary processes for example the c35 homohopane index decreases with increasing api gravity and thermal maturity of related oils from the monterey formation offshore california similar decreases in the homohopane index are observed for expelled oils from monterey source rock during hydrous pyrolysis biodegradation can result in selective loss of high or low molecular weight homologs apparently depending on the bacterial population in the reservoir bacterial demethylation of homohopanes appears necessary to explain 25 norhopanes in at least one biodegraded oil hydrous pyrolysis studies of the phosphatic and siliceous members in the monterey formation show that identical heating conditions result in different homohopane c 22 epimer ratios furthermore a reversal in the trend of the epimer ratio at high experimental temperatures is observed for the phosphatic but not for the siliceous lithology this could be caused by the combined effects of isomerization and differential thermal destruction of epimers at high temperatures possibly mediated by rock mineralogy

the origin and distribution of crude oil in zhu iii sub basin pearl river mouth basin china abstract the origin of thirteen major oil fields in zhu iii sub basin pearl river mouth basin was studied by using the results of rock eval pyrolysis on 340 samples and biomarker analysis on 18 source rock samples and 33 oil samples the two possible source rock intervals have different biomarker assemblages and were deposited in different environments the eocene wenchang formation e2w 49 5 35 ma is characterized by high hopane sterane ratio 37 84 high 4 methyl sterane index 0 28 1 06 low gammacerane index 0 10 high bicadinane c30 hopane up to 73 62 but low hopane sterane ratio

the origin and fate of 4 methyl steroid hydrocarbons i diagenesis of 4 methyl sterenes abstract treatment of 4 methylcholest 4 ene under mild acid conditions at low temperatures gives chemical evidence for certain features seen in the distributions of sedimentary 4 methyl steroid hydrocarbons and further indicates that many low temperature diagenetic reactions of steroids are explicable in terms of acid catalysed rearrangements specifically the results provide i indirect evidence that the 4 ene skeleton is a key intermediate in the dehydration of 4 methyl stanols in sediments ii an explanation for the distribution of 4 methyl sterenes and a nor sterenes in the lacustrine messel shale eocene iii an explanation for the presence of 4 methyl steranes in relatively immature sedimentary rocks despite the precursor stanols having the 4 methyl configuration with increasing maturity in the paris basin shales lower toarcian the less stable 4 methyl steranes decrease gradually in abundance relative to their 4 methyl counterparts at a rate fairly similar to the change in pristane stereochemistry