structure of chlorella fusca algaenan relationships with ultralaminae in lacustrine kerogens species and environment dependent variations in the composition of fossil ultralaminae numerous kerogens from marine and lacustrine source rocks and oils shales previously considered as amorphous were recently shown to comprise very thin 10 30 nm thick lamellar structures termed ultralaminae comparative morphological and chemical studies of a lacustrine ultralaminae rich kerogen and of the non hydrolysable biopolymer algaenan isolated from the thin resistant outer walls of a freshwater microalga scenedesmus quadricauda established a close relationship between these two materials chemical correlation was mainly based on the production upon pyrolysis of a series of n alkylnitriles with a bimodal distribution the non hydrolysable biopolymer isolated from the outer walls of the ubiquitous freshwater microalga chlorella fusca exhibits the same morphologicalfeatures as those observed in s quadricauda and in fossil ultralaminae the investigation of c fusca algaenan by solid state 13c nmr and analysis of pyrolysis products revealed that the correlation previously established between s quadricauda and lacustrine ultralaminae also holds for c fusca since the same series of n alkylnitriles with the same distribution is formed upon pyrolysis probably via cleavage of amide functions this confirms that fossil ultralaminae in lacustrine kerogens derive from the algaenans building up the thin outer walls of freshwater microalgae via the selective preservation pathway in addition the analysis of the 2 n alkanones generated on pyrolysis indicates that their distribution depends on the algal species considered accordingly variations in ketone distributions in the pyrolysates of lacustrine ultralaminae rich kerogens may reflect differences in populations of the source microalgae on the contrary changes in n alkylnitrile distribution would not be species dependent but would reflect the lacustrine or marine origin of the considered material

environmental change during the early cretaceous in the purbeck type durlston bay section dorset southern england a biomarker approach abstract the purbeck type section durlston bay dorset uk exhibits littoral lagoonal to lacustrine facies it shows a gradual climatic environmental change from semi arid conditions associated with evaporites at the jurassic cretaceous transition to a more humid climate at the end of the berriasian though generally organic poor total organic carbon toc the distribution of alkanes hopanes and steranes indicates that the origin of the om is mainly algal bacterial and only changed moderately with the climatic evolution the saline and anoxic bottom water conditions indicated for most of the samples point to the recurrence of salinity stratification within the basin a high contribution of odd numbered c 23 c 31 n alkanes from algaenan containing freshwater algae in particular botryococcus is noted for all the samples despite the low abundance of these organisms in the corresponding palynofacies this prominence probably results from the high resistance to degradation and the selective preservation of botryococcus related lipids the subtle balance of aridity and freshwater inputs favoured both an abundance of botryococcus and the development of anoxia leading to the enhanced preservation of om during the intermediate climatic episode while the conditions were less favourable during the semi arid and more humid episodes

recognition of 18β h oleanane in several crudes and tertiary upper cretaceous sediments definition of a new maturity parameter abstract ekweozor et al chem geol 27 11 28 and 29 37 first discovered an unknown compound with a gc retention time very close to that of the 18 h olenane peak in oils and tertiary sediments of the nigerian delta this compound was called j several authors wang et al advances in organic geochemistry 1981 pp 108 113 wiley chichester 1983 schoelle et al ibid pp 156 163 reported the occurrence of 18 h oleanane without underlying the presence of j because of their coelution in this study the presence of j has been confirmed in more than 150 rock extracts and 19 oils from different countries and is identified as the 18 h oleanane by comparison to retention time and mass spectrum and by its coelution with an authentic standard apart from tertiary sediments the 18 h and 18 h oleananes have also been found in upper cretaceous sediments which extends the occurrence of these compounds back in age a maturity correlation has been found between the relative concentration of 18 h oleanane and 18 h oleanane in fact an increase in the 18 h 18 h oleanane ratio has been observed with increasing depth in several wells the 18 h 18 h oleanane ratio has been correlated with other classical maturity parameters i e ts tm ro and tmax

direct measurements of lift and drag on shallowly submerged cobbles in steep streams implications for flow resistance and sediment transport steep mountain streams have higher resistance to flow and lower sediment transport rates than expected by comparison with low gradient rivers and often these differences are attributed to reduced near bed flow velocities and stresses associated with form drag on channel forms and immobile boulders however few studies have directly measured drag and lift forces acting on bed sediment for shallow flows over coarse sediment which ultimately control sediment transport rates and grain scale flow resistance here we report on particle lift and drag force measurements in flume experiments using a planar fixed cobble bed over a wide range of channel slopes 0 004 s 0 3 and water discharges drag coefficients are similar to previous findings for submerged particles c d 0 7 but increase significantly for partially submerged particles in contrast lift coefficients decrease from near unity to zero as the flow shallows and are strongly negative for partially submerged particles indicating a downward force that pulls particles toward the bed fluctuating forces in lift and drag decrease with increasing relative roughness and they scale with the depth averaged velocity squared rather than the bed shear stress we find that even in the absence of complex bed topography shallow flows over coarse sediment are characterized by high flow resistance because of grain drag within a roughness layer that occupies a significant fraction of the total flow depth and by heightened critical shields numbers and reduced sediment fluxes because of reduced lift forces and reduced turbulent fluctuations

estimating mean velocity in mountain rivers it is often necessary to estimate the mean velocity in ungaged mountain rivers but the flow resistance equations available for this purpose require further testing and development such rivers are characterized by coarse bed materials steep slopes and low depths for these conditions boulders protrude well into or completely through the flow and bed roughness is said to be large scale recently three equations specifically intended for large scale roughness have been developed to address this problem data from a mountain river were used to test the equations all were prone to errors of the order of 30 the errors were systematic all the equations tending to overestimate mean velocity compared to observed values an investigation of the possible sources of error suggested that sampling error in the knowledge of bed material size was a major source of uncertainty in the predicted velocities but that this and discharge errors could not wholly account for the observed discrepancies boulder shape is not represented in the equations but this was discounted as an important parameter on the basis of a flume study it was concluded that further research is required to produce a reliable process based flow resistance equation for mountain rivers

calcite dissolution in sediments of the ceara rise in situ measurements of porewater o2 ph and co2 aq in situ electrode measurements of porewater oxygen and ph from four sites on the ceara rise in the western tropical atlantic unequivocally demonstrate that calcite dissolution driven by metabolic co2 produced within the sediments is a significant part of the diagenesis of sedimentary calcite dissolving at least 20 of the calcite rain to the seafloor the first ever in situ absorbance based measurements of porewater co2 aq support the dissolution estimates based on models of the observed ph distributions and are incompatible with scenarios excluding metabolic co2 driven dissolution our dissolution estimates are consistent with those estimated by an independent study of porewater calcium and alkalinity profiles martin and sayles 1996 at this location the consistency of these disparate porewater measurements and our ability to interpret them with simple models of respiration and dissolution implies that no special mechanism is required to describe this process the calcite dissolution rate constant in the sediments of the deepest station in this study is significantly higher than determined by in situ studies at other locations values approach those determined by early laboratory measurements the dissolution rate constant here must be at least two orders of magnitude higher than for calcite in sediments on the ontong java plateau based on in situ electrode measurements there hales and emerson 1996 the calcite solubility consistent with these data is not compatible with that consistent with the ontong java data the reason for this difference is currently unresolved but may be due to the high order of the empirical dissolution rate law assumed in this study

triterpanes and ring a degraded triterpanes as biomarkers characteristic of tertiary oils derived from predominantly higher plant sources abstract a number of oils previously proposed to be derived from terrigenous source materials have been obtained from the taranaki basin new zealand niger delta beaufort mackenzie region taiwan and indonesia and their c24 tetracyclic and c30 pentacyclic terpenoid distributions examined by gc ms and gc ms ms the c24 tetracyclic terpanes are thought to be derived from their corresponding c30 hopane oleanane ursane and lupane counterparts as previously reported a mixture of at least nine c30 pentacyclic terpanes are found to be present with remarkably uniform distributions in oils from these widely separated provinces whilst definitive structures have not been proposed for these compounds information has been obtained as to whether these pentacyclic terpanes are all six membered rings or contain one or two five membered rings the presence of this mixture of tetracyclic and pentacyclic terpanes provides a good indicator for oils derived from terrigenous source materials and in the case of these basins of tertiary age

carbon isotopic composition of hydrocarbons in ocean transported bitumens from the coastline of australia abstract bitumens stranding along the coastlines of the northern territory western australia south australia victoria and tasmania often have biomarker signatures which closely match those of oils of s e asian origin a suite of these bitumens was studied to determine the isotopic signatures of their alkanes and to compare them to similar oils from the central sumatra basin saturated hydrocarbons were separated into a fraction containing n alkanes and isoalkanes and one containing the multibranched cyclic components using adduction into silicalite gas chromatography isotope ratio mass spectrometry gc irms of the n alkanes revealed 13 c signatures covering a wide range of values from 25 5 to 29 pdb but generally falling between those of the botryococcane containing minas and duri oils from the central sumatra basin n alkanes of the minas oil are 3 4 lighter than their duri counterparts the isotopic compositions of pristane and phytane cover a similar range 13 c 24 to 27 botryococcane is consistently heavy with 13 c values in the range 11 to 14 one bitumen sample with no botryococcane but abundant bicadinanes showed n alkane 13 c values in the range 28 to 29 at the light extreme for waxy bitumens in our sample suite sample to sample differences in carbon isotopic signatures of n alkanes are attributed mainly to variations in primary source with weathering and biodegradation as minor causes instances of low precision for replicate analyses 2 are caused by the relative abundance of co eluting isoalkanes overall the isotopic patterns of waxy bitumens from the australian coastline provide independent confirmation of their similarity to central sumatran lacustrine oils on the other hand asphaltic bitumens from the southern australian coastline are isotopically light with n alkane 13 c values in the range 31 5 to 33 this distinctive feature may assist identification of their source

biomarker distributions in australian oils predominantly derived from terrigenous source material oils found in many australian sedimentary basins contain a relatively high input of terrigenous organic source material a study of a large number of these oils has permitted a number of biomarker distributions to be determined that appear to be characteristic for oils derived from terrigenous source material these features include the presence of sesquiterpanes absence of tricyclic terpanes relatively high concentrations of a c24 tetracyclic terpane predominance of c29 steranes presence of two unidentified c27 and c30 terpanes and virtual absence of 18 h oleanane the latter observation is significant since it appears that 18 h oleanane appears only in oils of tertiary age derived from terrigenous source material an attempt has also been made to compare the results for the australian oils with published results for oils derived from terrigenous source material in other parts of the world the number of reports in the literature for these oils is fairly limited but it appears that some of the observations for the australian oils can be extended to them this study is an initial attempt to devise a classification scheme that can be used to determine the origin of an oil unambiguously from biomarker parameters in order for this approach to be successful a relatively large number of biomarker parameters need to be assigned as characteristic of a particular type of source material

thorium 230 profiling in deep sea sediments high resolution records of flux and dissolution of carbonate in the equatorial atlantic during the last 24 000 years variations in carbonate flux and dissolution which occurred in the equatorial atlantic during the last 24 000 years have been estimated by a new approach that allows the point by point determination of paleofluxes to the seafloor an unprecedented time resolution can thus be obtained which allows sequencing of the relatively rapid events occurring during deglaciation the method is based on observations that the flux of unsupported 230th into deep sea sediments is nearly independent of the total mass flux and is close to the production rate thus excess 230th activity in sediments can be used as a reference against which fluxes of other sedimentary components can be estimated the study was conducted at two sites ceara rise western equatorial atlantic and sierra leone rise eastern equatorial atlantic in cores raised from three different depths at each site from measurements of 230th and caco3 changes in carbonate flux with time and depth were obtained a rapid increase in carbonate production starting at the onset of deglaciation was found in both areas this event may have important implications for the postglacial increase in atmospheric co2 by increasing the global carbonate carbon to organic carbon rain ratio and decreasing the alkalinity of surface waters and possibly the north atlantic deep water increased carbonate dissolution occurred in the two regions during deglaciation followed by a minimum during mid holocene and renewed intensification of dissolution in late holocene during the last 16 000 years carbonate dissolution was consistently more pronounced in the western than in the eastern basin reflecting the influence of antarctic bottom water in the west this trend was reversed during stage 2 possibly due to the accumulation of metabolic co2 below the level of the romanche fracture zone in the eastern basin

the diagenetic fate of taraxer 14 ene and oleanene isomers abstract the extractable organic matter in holocene to early miocene deep sea sediments from site 645 odp leg 105 in baffin bay contains almost exclusively biological markers of terrigenous origin pentacyclic triterpenoids of the ursene and amyrin oleanene type often occur as the most abundant compounds in the aliphatic hydrocarbon ketone and alcohol fractions of the sediment extract a specific diagenetic reaction involves the conversion of taraxer 14 ene into olean 12 ene in the upper 700 metres of the sedimentary sequence the taraxerene to oleanene conversion is complete before the onset of isomerisation of diasterenes at c 20 in the sediment as well as in laboratory simulation experiments olean 12 ene further isomerises to olean 13 18 ene and olean 18 ene the latter of which may be the direct precursor of 18 h and 18 h oleanane found in sediments containing more mature organic matter and in crude oils the subsurface interconversion of these triterpenoid skeletons indicate that oleanane does not necessarily start life as an oleanoid

comparison of the paleoclimatic significance of higher land plant biomarker concentrations and pollen data a case study of lake sediments from the holsteinian interglacial abstract a sediment core from the dethlingen paleolake holsteinian interglacial northern germany was subjected to integrated organic geochemical and palynological paleobotanical analyses in order to reconstruct past environmental conditions the fractionated lipid extracts were investigated using gas chromatography mass spectrometry gc ms and gc combustion isotopic ratio ms ring a aromatized pentacyclic triterpenoids most likely glutinane derivatives were the only higher plant derived pentacyclic triterpenoids found the saturated ring a degraded triterpenoid des a lupane was the most abundant aliphatic hydrocarbon throughout the core based on published pollen data which imply the strong presence of betula and alnus around the paleolake the des a lupane would be expected to originate mainly from lupane type precursors synthesized by betulaceae the carbon isotopic composition of des a lupane varied from 28 2 to 30 6 and no significant trend or isotopic shift was observed however the discrepancy between the variation in pollen data and biomarker concentration i e quasi absence of diterpenoids in the core argues for a scenario in which the two proxies represent different components of the vegetation in the catchment area of the paleolake

hydrodynamics of steep streams with planar coarse grained beds turbulence flow resistance and implications for sediment transport the hydraulics of steep mountain streams differ from lower gradient rivers due to shallow and rough flows energetic subsurface flow and macro scale form drag from immobile boulders and channel and bed forms heightened flow resistance and reduced sediment transport rates in steep streams are commonly attributed to macro scale form drag however little work has explored steep river hydrodynamics in the absence of complex bed geometries here we present theory for the vertical structure of flow velocity in steep streams with planar rough beds that couples surface and subsurface flow we test it against flume experiments using a bed of fixed cobbles over a wide range of bed slopes 0 4 30 experimental flows have a nearly logarithmic velocity profile far above the bed flow velocity decreases less than logarithmically towards the bed and is non zero at the bed surface velocity profiles match theory derived using a hybrid eddy viscosity model in which the mixing length is a function of height above the bed and bed roughness subsurface flow velocities are large 1 m s and follow a modified darcy brinkman forchheimer relation that accounts for channel slope and shear from overlying surface flow near bed turbulent fluctuations decrease for shallow rough flows and scale with the depth averaged flow velocity rather than bed shear velocity flow resistance for rough planar beds closely matches observations in natural steep streams despite the lack of bed or channel forms in the experiments suggesting that macro scale form drag is smaller than commonly assumed in stress partitioning models for sediment transport

oblique slip deformation in extensional terrains a case study of the lakes tanganyika and malawi rift zones the east african rift system ear is the archetypal continental rift and a widely proposed analogue for the early stages of evolution of passive continental margins the three dimensional structure of parts of the ear has been recently elucidated by a multifold seismic mfs survey of lakes tanganyika and malawi project probe analysis of fault geometries displayed on the probe mfs data coupled with the more extensive 28 khz echosounder data has improved understanding of the geometry and kinematics of the linked fault systems that underlie the lakes in particular it has been recognized that profiles across i e at high angles to the rift elongation commonly display fault geometries that are not readily retrodeformable there must therefore be significant displacement out of the plane of what would conventionally be regarded as dip lines that is perpendicular to rift elongation and parallel to the tectonic transport or extension direction careful determination of fault plane dip and the dip of synrift reflectors in the hanging wall demonstrates that the dip directions of the shallowest faults and the steepest hanging wall sediment dips are oriented either nw or se this defines the direction of maximum fault block rotation and therefore the direction of extension or tectonic transport as nw se oblique to the trend of the regional rift axis and to the apparent strike of many of the major border faults in the survey area the border faults and many other faults imaged on the probe mfs data must therefore have significant components of strike slip motion and the tanganyika and malawi rift zones have undergone extension oblique to and not perpendicular to their axes near dip slip normal faults steeply dipping oblique slip faults and subvertical strike slip or transfer faults have all been recognized in a complex linked fault system that accomplishes the extension the overall orientation of the rift lakes and their internal segmentation are influenced by major preexisting subvertical fault zones within the basement complex accommodation zones act principally as transfer zones that allow switches in gross polarity of the border fault system the detailed geometries of the accommodation zones result from the specific relations between juxtaposed half graben and the strike and internal geometry of the influencing basement structure the variations in fault geometry subsidence water depth and basin or rift morphology can be better explained by an oblique slip extensional model influenced by basement structures than by a simple orthogonal extensional model

air water flows in the presence of staggered and row boulders under macroroughness conditions 1 free surface flow over a rough bed at steep slopes entrains large amounts of air bubbles due to the high interaction between the free surface and the bed materials the assessment of mixed air water flow features in the presence of a three dimensional bed configuration from macroroughness to intermediate roughness conditions can hardly be accomplished with aeration models developed for smooth or stepped bed configurations two phase flow properties were measured over rough bed materials in a setup assembled at the pitlab center at the university of pisa pisa italy coarser protruding materials were incorporated over the rough bed to intensify the aeration in the mixed air water flow flow discharges ranging between 0 02 and 0 09 m2 s and slopes between 0 18 and 0 44 were tested a detailed study of the air water inner layer and flow features over staggered and row coarser material arrangement over the base material was carried out results were compared with literature data on free surface flow over smooth and stepped beds

organic petrology and geochemistry of the carboniferous coal seams from the central asturian coal basin nw spain abstract this paper presents for the first time a petrological and geochemical study of coals from the central asturian coal basin north spain of carboniferous pennsylvanian mainly of moscovian age a paleoenvironmental approach was used taking into account both petrographic and organic geochemical studies vitrinite reflectance r r ranges from 0 5 to 2 5 which indicates a high volatile bituminous to semianthracite and anthracite coal rank the coal samples selected for paleoenvironmental reconstruction are located inside the oil gas prone phase corresponding to the interval between the onset of oil generation and first gas generation and efficient expulsion of oil this phase is represented by coals that have retained their hydrocarbon potential and also preserved biomarker information paleodepositional reconstruction based on maceral and petrographic indices points to a swamp environment with vitrinite rich coal facies and variable mineral matter content the gelification index gi and groundwater influence index gwi indicate strong gelification and wet conditions the biomarkers exhibit a high pristane phytane ratio suggesting an increase in this ratio from diagenetic processes and a high diterpanes ratio this in turn would seem to indicate a high swamp water table and a humid climate the maximum point of coal accumulation occurred during the regressive part of the late moscovian sequence and in the most humid climate described for this period of time in the well known coal basins of europe and north america

the composition and diagenesis of interstitial solutions ii fluxes and diagenesis at the water sediment interface in the high latitude north and south atlantic studies of the major element composition of in situ sampled pore waters are reported for the north atlantic and southern ocean between africa and antarctica the pattern of diagenetic modification of pore water composition is similar throughout the entire atlantic enrichment of na ca2 and alkalinity and depletion of mg2 and k are nearly universal only siliceous oozes consistently provide very limited evidence of cation diagenesis the changes observed and the calculated fluxes across the seawater sediment interface are much the same as those reported previously for other areas of the atlantic and caribbean fluxes of the major cations across the interface continue to be indicated as a major factor in the geochemical cycling of these elements particularly na mg2 and k diagenetic modelling indicates that aerobic oxidation of organic matter and consequent dissolution of caco3 is a dominant reaction throughout the north atlantic the data indicate that o2 oxidation to at least 30 cm is prevalent at nearly all stations dissolution of caco3 in response to the introduction of metabolic co2 can lead to significant post depositional modification of the sediments the modelling also indicates a 1 1 stoichiometric relationship between na release and mg2 uptake by sedimentary components although dissolved silica concentrations in biogenic siliceous sediments are among the highest yet reported 700 m calculations demonstrate that solubility control cannot be through equilibria with the mineral sepiolite further the influence of cation silicate surface phases generally upon solubility is contraindicated by si oh 4 mg2 h relationships evaluation of the influence of fluid advection on pore water profiles indicates that at the stations studied in the north atlantic it is small a more general consideration of the potential contribution of fluid advection to shaping interstitial water profiles demonstrates that advection can be a dominant factor in such circumstances serious misinterpretation of the nature of diagenetic reactions may result from a lack of knowledge and consideration of fluid advection

relationship between petroleum composition and depositional environment of petroleum source rocks crude oils of nonmarine source can be distinguished from those of marine shale source and from oils originating in marine carbonate sequences by using a battery of geochemical parameters as demonstrated with a sample suite of nearly 40 oils a novel parameter based on the presence of c30 steranes in the oil was found to be a definitive indication of a contribution to the source from marine derived organic matter a second novel parameter based on monoaromatized steroid distributions was effective in helping to distinguish nonmarine from marine crudes and can be used to gauge relative amounts of higher plant input to oils within a given basin sterane distributions were similarly useful for detecting higher plant input but were less effective than monoaromatize steroid distributions for making marine versus nonmarine distinctions concentrations of high molecular weight paraffin can also be effective nonmarine indicators but are influenced by maturation and biodegradation processes certain algal derived nonmarine oils may show little high molecular weight paraffin response oils from carbonate sources with a few exceptions can be distinguished by having low pristane phytane ratios low carbon preference indexes and high sulfur contents gammacerane indexes and carbon isotope ratios of the whole crude are not effective in distinguishing these types of environmental differences on a global basis

origin and mixing of crude oils in triassic reservoirs of mahu slope area in junggar basin nw china implication for control on oil distribution in basin having multiple source rocks abstract the origin of crude oils and their varied geochemical features along the western and northern slope of the mahu depression in the junggar basin has been controversial based on the molecular and isotopic geochemistry of hydrocarbons from 46 drill stem test crude oil samples and 36 core samples three oil groups i ii iii and five subgroups i 1 i 2 ii iii 1 and iii 2 have been recognized and oil source correlations have been established the subgroup i 1 oils originated mainly from lower permian fengcheng p 1 f carbonate source rocks subgroup i 2 from p 1 f mudstone source rock and group ii oils from middle permian wuerhe p 2 w mudstone source rock whose potential was underestimated in the past group iii consists of mixed oils i e subgroup iii 1 received contributions from p 1 f carbonates and p 2 w mudstones and subgroup iii 2 is a mixture of oils from p 1 f mudstones and p 2 w generated oils in order to determine the main source rocks the laboratory oil mixing experiments were carried out tricyclic terpane biomarker parameters tts were used to quantify the source contributions whole oil carbon isotope ratios were also used to verify the proportions of different oils in each mixture the results show that subgroup iii 1 oils have diverse mixing ratios in different reservoir subgroup iii 2 oils are mainly from p 1 f mudstones and p 2 w source rock contributes little finally the accumulation process of oil fields along the northern slope of the mahu depression was analyzed and the contributions from different sources were revealed this study provides an effective quantitative method to identify contributions from different lacustrine source rocks to mixed oils in the mahu depression which could be helpful in predicting location and composition of undiscovered oils

caco3 dissolution in sediments of the ceara rise western equatorial atlantic we have used porewater sampling by in situ techniques including whole core squeezing as well as by shipboard sectioning and whole core squeezing to estimate the rates of sedimentary organic matter oxidation and caco3 dissolution at seven sites on the ceara rise in the western equatorial atlantic ocean porewater no3 profiles at all sites show a pattern indicative of active organic matter oxidation in the upper 15 20 cm of the sediments and in a buried organic rich layer the organic c oxidation rate generally decreases with increasing water depth from a value of 22 mol cm2 y at the shallowest site 3279 m to 14 mol cm2 y at the deepest site 4675 m over this depth range the bottomwaters vary from moderately supersaturated with respect to calcite to strongly undersaturated high resolution alkalinity profiles measured in porewaters collected by in situ whole core squeezing yield estimated ca2 fluxes of 11 mol cm2 y at a site located at the depth of the calcite saturation horizon and 7 6 zmol cm2 y at a moderately undersaturated site ca2 fluxes calculated from profiles in porewaters collected by relatively coarse resolution in situ sampling methods clearly indicate that there is caco3 dissolution above the calcite saturation horizon the dissolution of aragonite may contribute to the dissolution flux at the shallowest site these ca2 fluxes as well as fluxes estimated from a model of sedimentary organic matter oxidation and calcite dissolution indicate that 36 66 of the caco3 rain to the seafloor dissolves at sites at and above the calcite saturation horizon while 52 75 of the rain dissolves at sites below this depth when these results are incorporated into the oceanic caco3 budget of milliman 1993 they indicate that 35 of caco3 production is preserved in the deep sea they suggest a caco3 accumulation rate that is 27 lower than that estimated by milliman 1993 our corg oxidation caco3 dissolution model indicates that a large fraction of the caco3 dissolution that is occurring on the ceara rise is attributable to the neutralization of metabolic acids produced during organic matter oxidation the efficiency with which organic matter oxidation dissolves caco3 that is the ratio caco3 dissolution attributable to organic matter oxidation organic matter oxidation rate generally increases as degree of undersaturation of bottomwaters increases however there are deviations from the general trend that can be attributed to site to site variations in the kinetics of organic matter oxidation and calcite dissolution this result indicates that the dissolution of caco3 as a result of organic matter oxidation in the deep sea may mask the effects of variations in surface water caco3 productivity and bottomwater chemistry on the accumulation rate of caco3 in deep sea sediments

kerogen chemical structure and source organisms in a cenomanian organic rich black shale central italy indications for an important role of the sorptive protection pathway abstract the bonarelli horizon is an important cenomanian turonian black shale in the umbria marche appenines of central italy it appears as the final term of a cyclic deposition of ca 40 thinner laminated clayey or siliceous organic rich levels the kerogen of the cenomanian clayey black level located 12 m below the bonarelli termed nn 8c was examined via microscopic spectroscopic and pyrolytic methods the chemical structure of this kerogen is based on a network of long aliphatic chains linked via ether bridges however in addition to the classical normal chains nn 8c comprises c40 chains with a lycopane skeleton such chains have only been previously reported in kerogen pyrolysates of two samples derived from the microalga botryococcus braunii however any contribution of b braunii can be ruled out in the case of nn 8c kerogen since it is nanoscopically amorphous based on 13c values of their pyrolysis products a common algal origin is demonstrated for the above two types of chains and hence there is a major algal input to this kerogen however some incorporation of bacterial lipids and a low contribution of higher plant material are indicated by the nature of some pyrolysis products although a large contribution of pyrite is noted in the nn 8c sample thus revealing an intense sulphate reducing activity no significant sulphur incorporation took place in the organic matter accordingly the vulcanization pathway is not implicated in the formation of nn 8c kerogen the selective preservation and the degradation recondensation pathways were possibly involved but they are unlikely to have played a major role in fact the sorptive protection process favoured by the clayey nature of the mineral matrix was probably the main pathway implicated in the formation of nn 8c kerogen and this process may have provided an efficient protection to various diagenetically sensitive constituents especially lipids

the influence of organic matter diagenesis on caco3 dissolution at the deep sea floor abstract in situ benthic flux chamber measurements were performed at seafloor locations in the atlantic and pacific oceans where the bottomwaters were supersaturated approximately saturated and undersaturated with respect to calcite there was no evidence of significant dissolution at or above the saturation horizon below the saturation horizon however significant benthic fluxes of titration alkalinity and calcium out of the sediments were observed indicating appreciable dissolution where observed the rate of dissolution is consistent with a rate expression of reaction order 4 5 and a rate constant in the range of 0 05 to 0 5 per day a numerical simulation was constructed to represent organic matter and caco3 diagenesis at the seafloor at the supersaturated and near saturation sites the model over predicts the influence of metabolically produced co2 on the extent of caco3 dissolution it is possible that these results can be reconciled by a better understanding and parameterization of organic matter mineralization and porewater transport processes in surface sediments the primary factors to be considered include 1 the oxidation state of the carbon being oxidized 2 the vertical distribution of oxidation rates including the role of doc in sediment remineralization 3 the influence of nondiffusive transport of near surface porewaters and 4 the influence of episodic depositional events on organic and inorganic carbon cycling

flow resistance estimation in mountain rivers examination of the flow resistance of high gradient gravel and boulder bed rivers using data collected in british mountain rivers with slopes of 0 4 4 shows that there are differences in resistance variation between mountain and lowland rivers and that between site variations do not necessarily reflect at a site variations comparison of data with the familiar resistance equation relating the dracy weisbach friction factor to the logarithm of relative submergence shows that the equation tends to overestimate the resistance in uniform flow the equation also tends to underestimate the rate of change of resistance at a site as discharge varies with high gradients the influences of nonuniform channel profile sediment size distribution channel slope and sediment transport are reviewed but the data do not allow any quantification of these effects instead an empirical approach based on the available data is presented allowing the friction factor to be calculated from the relative submergence with an error of up to n25 to n35 a summary of the field data is included

velocity prediction in high gradient channels summary in 15 mountain stream reaches containing instream wood we characterized velocity and flow resistance at bankfull through low flows these data were 1 used to assess the accuracy of previously published velocity prediction techniques for high gradient channels and 2 were combined with field data from other studies to develop general methodologies for predicting velocity and flow resistance in alluvial and mixed alluvial bedrock channels both with and without step forming instream wood velocity and flow resistance were poorly predicted by variables characterizing grain size and relative grain submergence conversely methods based on detrended standard deviation of bed elevations rz and relative bedform submergence h rz explained up to 84 of the variance in the measured flow resistance coefficients and 97 of the variance in dimensionless velocity with an average velocity of 0 44 m s for the collected measurements velocity was predicted with rms root mean square error as low as 0 071 m s 16 of average when discharge and bedform geometry is known and 0 10 m s 23 when only bedform geometry is known additionally an empirical relationship indicates v u h r z supporting previouslypublished laboratory findings using a field based dataset in complex high gradient channels interactions between instream wood and clasts result in substantially enhanced step heights and flow resistance this compound effect defies description by grain size and relative grain submergence however rz and h rz quantify variability due to both clasts in combination with wood and clasts alone providing relatively accurate predictions for the tested dataset and indicating substantial predictive capabilities in channels where bedforms are the primary source of flow resistance published by elsevier b v

polymethylsqualanes from botryococcus braunii in lacustrine sediments and crude oils abstract a novel hydrocarbon 3 7 18 22 tetramethylsqualane has been identified in extracts from the maniguin 2 well on maniguin island philippines the duri oil from sumatra indonesia and the maoming oil shale from china a related hydrocarbon tentatively assigned the structure 3 7 11 14 tetramethylsqualane occurs in the maniguin samples like c34 botryococcane the tetramethylsqualanes are unusually enriched in 13c compared to co occuring n alkanes and c16 20 acyclic isoprenoids polymethylsqualanes extend the range of distinctive hydrocarbons produced by botryococcus braunii and its fossil counterparts

dissolution of calcite in deep sea sediments ph and o2 microelectrode results abstract we present microelectrode profiles of oxygen ph and porosity measured at in situ depth across the sediment water interface from stations above and below the calcite saturation horizon in the equatorial atlantic resistivity electrode data indicate that the diffusion coefficient for solutes is attenuated by nearly a factor of two within the top centimeter of the sediment lattice oxygen and porosity data are used to estimate that the organic carbon respiration rate of the sediment is 10 15 mol cm 2 yr 1 in these locations comparison of the ph data with numerical model results reveals that sedimentary calcite dissolves in response to respiration in the top few centimeters of sediment even above the saturation horizon we calculate that the effective in situ dissolution rate constant for calcite required to explain these data is the neighborhood of 10 100 d 1 although more data are needed to confirm this result it appears to be at least an order of magnitude less than the rate observed in laboratory stirred reactor experiments

calcite dissolution in sediments of the ontong java plateau in situ measurements of pore water o2 and ph we present in situ electrode measurements of sediment resistivity pore water oxygen and pore water ph from three stations between 2300 and 3000 m depth on the ontong java plateau in the western equatorial pacific one of these stations is also the site of a concurrent benthic chamber incubation experiment jahnke et al 1994 the pore water oxygen data and a steady state diffusion and reaction model constrain the depth dependent rate of oxic respiration in the sediments and imply a diffusive flux of oxygen to the sediments of 10 21 mol cm 2 yr 1 given these respiration rates the pore water ph data cannot be explained without calcite dissolution driven by metabolically produced co2 the dissolution necessary to explain the observations quantified by a statistical approach is 3 5 6 mol cm 2 yr 1 which corresponds to at least 20 40 of the calcite rain to these sediments over 65 of the total dissolution is driven by metabolic co2 oxygen fluxes and net calcite dissolution constrained by the electrode data are compatible with the benthic chamber measurements of jahnke et al 1994 the dissolution flux while a significant part of the early diagenesis of calcite in these sediments is less than would be predicted by earlier models of dissolution and jahnke et al 1994 probably could not distinguish it from zero with the benthic chamber technique the dissolution rates found in this study are lower than previous estimates because the respiration reaction is concentrated near the sediment water interface and the calcite dissolution rate constants are very small the statistical evaluation of the pore water ph data and model constrain the calcite dissolution rate constant to 0 005 0 16 d 1 following the general trend of lower values determined by in situ techniques rather than by laboratory methods

sedimentary and organic geochemical investigation of tertiary lacustrine oil shale in the central tibetan plateau palaeolimnological and palaeoclimatic significances article i nfo the zhuonai lake and lunpori oil shale located in the central tibetan plateau were deposited in a tertiary lacustrine environment in the hoh xil and lunpola basins respectively a combined investigation of sedimentary organic geochemistry and organic carbon isotope was performed to define source rock potential the palaeoenvironment and source of the organic matter three types of facies sequences are developed in the zhuonai lake section and oil shale mainly occurs in the oil shale marl sequence the oil shale silty claystone and oil shale marl facies sequences are developed in the lunpori section both oil shales are finely stratified especially for the lunpori oil shale with thickness of the laminae about 10 m which contains abundant pyrite crystals and fossilized fish bones both the zhuonai lake and lunpori oil shale contain high values of total organic matter toc s2 and hydrogen index hi indicating the oil shales have good oil source rock potential tmax values show an immature stage of organic matter for the zhuonai lake oil shale and thermally marginally mature for the lunpori oil shale because of difference in their burial history lunpori oil shale shows the characteristics of amorphous organic matter aom dominance odd over even predominance maximum n alkanes peak at nc25 or nc23 higher proportion of c29 sterane light 13 corg values 30 0 to 27 4 high concentrations of phytane pr ph ratio ranging from 0 02 to 0 18 high values of gammacerane index up to 25 26 and presence of carotane which are consistent with a reducing stratified and hypersaline palaeo lake with main contribution of algae and bacteria to the organic matter om oil shale samples from the lower and upper part of the zhuonai lake section are characterized by low h c ratios and high o c ratios amorphous humic om and vitrinite dominance odd over even predominance with long chain n alkanes dominance heavy organic carbon isotope and c29nc27 sterane distribution in agreement with a main contribution of land plant the heavy organic carbon isotope suggests the expanding of c4 land plant during the early miocene while the most samples show characteristics of aom dominance maximum peak at nc29 or nc31 and high c27 sterane concentration consistent with a main contribution from algae to the om the pr ph ratio cannot be applied as a measure for redox conditions in the section because of maturity effects biomarker analysis indicates that the salinity during the deposition of the zhuonai lake oil shale was not enhanced the oligocene lunpori oil shale and the early miocene zhuonai lake oil shale recorded the variation of palaeolimnological water chemistry the development history of the palaeo lakes from the oligocene saline to the early miocene fresh water reflects the variation of palaeoclimate from dry to humid in the central tibetan plateau

compound specific carbon isotope study on the hydrocarbon biomarkers in lacustrine source rocks from songliao basin abstract stable carbon isotopic composition of organic matter 13 c org and compound specific 13 c values of biomarkers from 15 lacustrine source rocks were analyzed to identify the original paleoenvironment and source organisms the 13 c values of hopanes 13 c hop ranged from 68 7 to 32 and exhibit strongly 13 c depleted values in the lower part of member 1 of the nenjiang formation k 2 n 1 up to 68 7 suggesting an origin from predominantly methanotrophic bacteria 13 c enriched 13 c ga values and significantly 13 c depleted 13 c hop in k 2 n 1 which coincide with water stratification and an intermittent anoxic photic zone represents a shallow chemocline the presence of an intermittent anoxic photic zone which means that the anoxia expanded into the euphotic zone is beneficial for om preservation and results in high values of toc and hi in this section however the absence of gammacerane and 13 c enrichment of 13 c hop in member 2 of nenjiang formation k 2 n 2 reflect a deeper chemocline corresponding to relatively oxidizing conditions and low values of toc and hi moreover the negative correlation of toc vs 13 c org and hi vs 13 c org reflects the control of om formation by sedimentary environments rather than productivity in the water column thus the depth of the chemocline not only controls the abundance of om but also affects the development of the microbial community such as chemoautotrophic bacteria in the deep chemocline and chemoautotrophic and methanotrophic bacteria in the shallow chemocline moreover 13 c ga and 13 c values for 4 methyl steranes are related to water salinity with a higher salinity accompanied by 13 c enrichment in gammacerane and 4 methyl steranes

stable hydrogen isotopic composition of hydrocarbons in torbanites late carboniferous to late permian deposited under various climatic conditions we measured the stable hydrogen isotopic composition d of selected aliphatic compounds in torbanites from scotland and australia covering the late carboniferous to the late permian the torbanites contain organic matter predominantly from a single algal source botryococcus braunii and are of similar thermal maturity the d values of n alkanes in the extracts appear to reflect the depositional palaeoclimate of each torbanite in response to the typical d values of meteoric waters the d values of n alkanes in torbanites deposited at high latitude under glacial conditions are depleted in deuterium by up to 70 relative to n alkanes in a torbanite deposited at low latitude under a tropical climate regime torbanites deposited in mid latitude regions under cool temperature conditions contain n alkanes with d values between those of n alkanes in tropical and glacial sediments a saw toothed profile of d values obtained for the n alkanes in the australian torbanites is attributed to a dual source system perhaps a predominant b braunii input with a second minor contribution from land plants pristane and phytane from two australian torbanites are significantly depleted in deuterium relative to n alkanes in the same samples and a significant difference between the d values of pristane and phytane is suggested to be caused by different sources for the two isoprenoids or isotope effects associated with their derivation from a common phytol precursor the offset between the d of values of n alkanes and isoprenoids is similar to that found in modern biological samples indicating that their indigenous d signatures may have been preserved for at least 260 280 million years

reconstructing past particle fluxes in the tropical atlantic ocean using a research strategy analogous to modern sediment trap studies sediment accumulation patterns on submarine rises can be interpreted in terms of past ocean chemistry and circulation we have followed this research strategy to reconstruct the history of surface water productivity and deep water chemistry and circulation in the eastern equatorial atlantic sierra leone rise and western equatorial atlantic ceara rise during the last glacial maximum 18 000 b p on shallow sections of these rises at depths with little carbonate particle degradation we assume that the accumulation of skeletal carbonate approximates the carbonate production rate in surface water during the last glacial maximum the rate of carbonate productivity was lower in the eastern atlantic than it is today while the western atlantic exhibited no glacial interglacial difference in carbonate productivity based on the difference in carbonate accumulation rates between shallow and deep cores on the rises we observed greater dissolution in both basins during the last glaciation the eastern atlantic always had a lower rate of dissolution than the western atlantic despite having deep water with a lower 13c during the last glacial maximum organic carbon accumulation in the eastern atlantic increased with depth in the water column during the last glaciation suggesting that there was a bathymetric decrease in dissolved oxygen concentration at that time these observations are consistent with a glacial decrease in the production rate of northern source deep water during the last glaciation at that time the mixing zone between northern source and southern source deep water migrated to the north in the atlantic resulting in a greater proportion of corrosive southern source deep water in the western atlantic and entering the eastern atlantic through low latitude fracture zones today the ratio of northern and southern components entering the eastern atlantic is about 4 1 based on 13c and carbonate accumulation our best estimate of this ratio during the last glaciation is 1 1

stratigraphic distribution of macerals and biomarkers in the donets basin implications for paleoecology paleoclimatology and eustacy abstract more than one hundred and thirty coal seams and coaly layers occur in the donets basin donbas twenty eight 52 samples of them ranging in age from serpukhovian late mississipian to gzhelian late pennsylvanian 33 clastics and three limestones were studied in terms of maceral composition sulphur contents and biomarker distribution diterpanes are used to estimate the contribution of different groups of plants and the height of the water table in the swamp hopanes are a measure of bacterial activity in the peat and steranes indicate the relative input of wood and algae stratigraphic trends in these parameters are discussed in relation to paleoenvironment climatic changes and eustacy a tropical climate prevailed in the donbas from serpukhovian to kasimovian times nevertheless periods with drier and wetter conditions can be distinguished based on maceral and biomarker data relatively dry conditions are observed during serpukhovian and vereian times whereas wetter climates with a maximum of coal deposition occurred during the late bashkirian most of the moscovian and the earliest kasimovian no economic coal seams are hosted in upper kasimovian and gzhelian deposits a result of a change to an arid climate our data also suggest climatic changes during sequences of different order for the second order third order and fourth order sequences relatively dry or wet conditions occurred during coal deposition in the lowstand systems tract an intermediate climate during the transgressive systems tract and the maximum flooding and a wet climate during the highstand systems tract the results for high frequency sequences support the cecil s paleoclimatic model an intermediate paleoclimate during lst sandstone and levee siltstone a wet climate during early tst coal and a dry climate during late tst limestone mfs claystone and hst deltaic siltstone coals deposited during maximum flooding periods are more enriched in c27 steranes derived from algae and contain lower proportions of c29 steranes derived from the wood of higher plants

sources and preservation of organic matter in the cretaceous toolebuc formation eastern australia abstract the organic matter rich toolebuc formation of eastern australia was deposited in a lower cretaceous epicontinental sea parameters from biological marker studies indicate that the organic matter is immature to marginally mature for hydrocarbon generation the occurrence of abundant coccoliths and the distribution of alkane biomarkers suggest that the organic matter type ii is largely of planktonic origin and only in the southeastern part of the depositional area can a terrestrial influence be discerned variations in kerogen composition can be attributed to the extent of the oxidation of the source materials and the degree of incorporation of sulphur the atomic h c ratios c 1 1 are remarkably constant for most of the toolebuc formation atomic o c ratios vary from 0 1 and 0 4 and can be related both to depth and paleogeographic position kerogen sulphur contents range up to 7 and the highest values occur in the most carbonate rich sediments total sulphur inorganic organic to carbon ratios in the sediments vary from 1 to

geochemical and palynological investigation of the shengli river marine oil shale china implications for paleoenvironment and paleoclimate abstract the shengli river oil shale located in the north qiangtang depression northern tibet plateau represents a potential large marine oil shale resource in china a geochemical and palynological investigation of the oil shale was performed to reconstruct paleoenvironment and paleoclimate during deposition the total organic carbon toc contents 15 05 20 34 and s 2 values 103 27 129 12 mg hc mg rock of oil shale samples are high and the organic matter consists mainly of type ii kerogen the thermal maturity assessed from pi 0 033 0 036 and t max 433 436 shows an immature to early mature stage of the organic matter analyzed oil shale samples from the shengli river area are characterized by a dominance of low carbon number molecular compositions with high c 21 c 21 2 10 2 83 low pr ph 0 63 0 75 and high concentrations of c 27 sterane and homohopanes c 31 c 35 indicating reducing environments highly saline conditions and a prevalent contribution of algae to organic matter accumulation the analyzed oil shale samples have an uncommonly heavy c isotopic composition ranging in 13 c values of bulk organic matter from 20 79 to 21 78 the enrichment in 13 c is mainly attributed to the high productivity of algae rather than solely the result of hypersalinity composition of palynofloras from oil shale samples suggests that the climate of the qiangtang basin region during the deposition of oil shales was warm and humid or sub humid

a rapid hydroclimate change and its influence on the songliao basin during the santonian campanian transition as recorded by compound specific isotopes abstract reconstruction of the paleoclimate and paleoenvironment of the songliao basin has important theoretical and practical significance to reveal the regional continental climate characteristics and continental organic matter accumulation under the cretaceous greenhouse climate conditions here we report the composition of biomarkers and the stable carbon and hydrogen isotope compositions of n alkanes from nenjiang formation sediments in the songliao basin which provide information on the source of organisms paleoenvironmental conditions and paleoclimate changes during the late cretaceous our hydrogen isotope records of n alkanes displayed a significantly negative shift indicating that a dramatically wet climate occurred during the santonian campanian transition a wet climate such as that during a prolonged rainfall event had a significant impact on the lake and resulted in the lake level increasing and the salinity decreasing in the surface water during this period however the freshwater input increased the salinity difference between the upper and lower water layers which caused stable water stratification to occur in the lake in addition the high total organic carbon toc content indicates high primary productivity because of increased precipitation carrying more terrigenous nutrients into the lake which resulted in eutrophication during this period notably the increased aryl isoprenoid ratios and the occurrence of isorenieratane indicates that photic zone euxinia pze was enhanced during the santonian campanian transition which was possibly due to the dramatic change in the hydroclimate we speculate that the large freshwater input promoted the formation of pze in the lake then pze restricted the habitat available for aerobic organisms which had fatal effects on the lake ecosystem

carbon isotopic compositions of 28 30 bisnorhopanes and other biological markers in a monterey crude oil abstract an immature tar like oil api 3 13 c 23 6 vs pdb from the miocene monterey formation offshore california was selected for a study of carbon isotopic signatures of individual biomarkers the three principal stereoisomers of 28 30 bisnorhopane c 28 have within analytical precision identical carbon isotopic compositions average 13 c 32 3 0 4 and are considerably depleted in 13 c compared to the whole oil these 28 30 bisnorhopanes bnh differ isotopically from c 29 and c 30 17 h hopanes 25 8 and 26 1 and c 31 c 35 extended hopanes 13 c 27 7 and suggest different precursors for the c 28 hopanes than for c 29 c 35 hopanes the relative depletion of bnh of almost 9 compared to the isotopic composition of the whole oil suggests that these hopanes derive from chemoautotrophic bacteria possibly not yet identified h 2 s oxidizers which utilize 13 c depleted substrates the c 29 and c 30 hopanes are within analytical precision isotopically identical 26 and similar to algal derived compounds e g c 27 steranes 25 9 which is consistent with a cyanobacterial source for these hopanes an archaebacterial biomarker 1 1 biphytane 13 c 25 5 likely derived from methanogens is also isotopically similar to c 27 sterane norpristane pristane and phytane liberated by desulfurization of the aromatic and polar maltene fractions show isotopic compositions similar to the same isoprenoids in the free lipids of the bitumen total range from 24 5 to 27 5 this isotopic similarity supports a common origin for the free and sulfur bound forms of these isoprenoids this origin could be algal and or archaebacterial lipids which both show isotopic compositions within the range of the c 18 c 20 isoprenoids like other marine derived organic matter this monterey oil does not show the strong 13 c depletion typical for methylotroph derived compounds characteristically found in organic matter of lacustrine origin this may indicate fundamental differences of methane recycling processes in marine sulfate dominated as compared to lacustrine environments

characteristics and origin of carbon isotopes of n alkanes in crude oils from the western pearl river mouth basin south china sea abstract the quantitative characterization of carbon isotopes of n alkanes is commonly carried out in organic geochemical studies possible controls on carbon isotopes include source organic matter maturity fractionation during oil expulsion and migration and the mixing of different oils in this study of the origin of crude oils in the western pearl river mouth basin the influences of all of these factors have been considered in reaching a conclusion carbon isotopes of n alkanes in the crude oils and the extracts of the two effective source rocks the wenchang and enping formations in the basin exhibit clear differences the wenchang source rocks have heavy 13 c values that remain almost constant or become slightly heavier with increasing carbon number the enping source rocks have light 13 c values that become lighter with increasing carbon number two groups of oils in this area were identified based on the carbon isotopes of the n alkanes groupioils are similar to extracts of the wenchang source rocks however the groupiioils are different from both the wenchang and enping source rocks and the carbon isotopic profiles of their n alkanes exhibit a v feature with increasing carbon number the results of artificial thermal maturation experiments indicate that from the early stage to the peak stage of oil generation with easyro between 0 64 and 1 02 the 13 c values of n alkanes in the pyrolysis oils become heavier by about 3 with increasing thermal maturity but the shape of the carbon isotopic profiles are not significantly changed calculated 13 c values of n alkanes in mixed artificial pyrolysis oils indicate that the mixture of oils generated from the same source rocks with different maturities could not change the carbon isotopic profile of the n alkanes however a mixing of the wenchang and enping oils could give the v feature in the profiles similar to the groupiioils in this area the groupiioils appear to be mixed wenchang and enping oils the latter being the dominant component in the mixture we conclude that the source organic matter and the degree of mixing are the main factors controlling the carbon isotopic characteristics of n alkanes in crude oils in the western pearl river mouth basin

self aeration and friction over rock chutes in uniform flow conditions interaction between the free surface and the bed material in flow over rock chutes under macroroughness conditions leads to a high air entrainment into the flow the note reports on an experimental study about air diffusion features in the flow over a long rock chute air concentration profiles and water depths over a uniform bed material were measured an empirical equation for the average air concentration in macroroughness condition for steep slopes is proposed a new darcy weisbach equivalent friction factor for long chutes as a function of the slope and the relative equivalent depth has also been found

regional geology depositional environment and maturity of organic matter of early to middle jurassic coals coaly shales shales and claystones from the eastern pontides ne turkey abstract jurassic coals coaly shales shales and claystones from the eastern pontides in ne turkey have been investigated using microscopical petrophysical and detailed organic geochemical methods in order to determine their catagenetic stage to reveal the composition of the organic matter and to discuss the depositional environment the liassic dogger period in the eastern pontides was characterised by the presence of a rift system which resulted in rock units of very variable lithology and facies coal seams ranging from a few centimetres to several decimetres and intercalated with shales claystones and sandstones occur within the basal part the aggi formation as well as in the uppermost part the hamurkesen formation of the rift deposits all coal seams investigated are at a catagenetic maturation stage corresponding to subbituminous b up to low volatile bituminous ranks they represent a depositional environment of short lived swamp areas with intense aerobic reworking of the higher plant detritus by heterotrophic bacteria but with possible anaerobic microenvironments at deeper levels at least some coal seams were influenced temporarily by marine ingressions most samples are impure humic coals with highly variable chemical compositions as indicated by the broad range of their hydrogen contents this variation in hydrogen content is partly attributed to variable contributions of algal material on the other side considering several analytical results the hydrogen variation is primarily due to bacterial reworking that affected the composition of the organic matter to variable extent and resulted especially in an enrichment of bacterial lipids bacterial reworking by an active microbial community within the upper layer of the peat swamp is inferred from elevated concentrations of iso alkanes even exceeding those of the corresponding n alkanes in several samples which to the best of our knowledge have not been observed with coals before

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

petroleum source rock assessment in non marine sequences pyrolysis and petrographic analysis of australian coals and carbonaceous shales a series of australian coals and terrestrial sediments ranging in age from permian through tertiary have been analyzed to assess their petroleum source character and the suitability of various techniques for assessment of source rock potential in non marine sequences the procedures used include organic petrography rock eval pyrolysis elemental analysis and quantitative pyrolysis gas chromatography the latter procedure was used to assess the potential yield of paraffins which is critical to the assessment of most non marine source rocks principal components analysis was used to assist in the analysis of the data although the petroleum potential of the samples follows the broad trends in petrographic composition established for australian coals i e relative proportions of vitrinite inertinite and liptinite there is much variation which cannot be explained petrographically at the maceral group level further pyrolytic hydrocarbon yield is not related to overall elemental composition below an atomic h c ratio of 1 0 the yield of phenols in flash pyrolysis is related to depositional setting as well as degree of maturation the yield and carbon number distribution of normal hydrocarbons in flash pyrolysis varied widely depending on the age nature and amount of liptinite macerals particularly in samples with hydrogen indices below 300 liptinite poor 10 samples may yield significant amounts of hydrocarbons but typically they have a low wax content sporinite rich and liptodetrinite rich samples give lower yields of normal hydrocarbons these are predominantly of lower molecular weight suberinite and to a lesser extent cutinite are associated with high yields of waxy normal hydrocarbons but some samples with high yields did not contain large amounts of these maceral the correlation of tmax to vitrinite reflectance varies with petrographic composition the results have implications for the way source rock analyses are conducted and interpreted in non marine sequences

chemical evidence of kerogen formation in source rocks and oil shales via selective preservation of thin resistant outer walls of microalgae origin of ultralaminae abstract new structures termed ultralaminae were recently observed by transmission electron microscopy usually in high amounts in a number of kerogens from oil shales and source rocks morphological similarities were noted between ultralaminae and the thin ca 15 nm resistant outer walls composed of non hydrolyzable macromolecules algaenans commonly occurring in extant chlorophyceae especially in the cosmopolitan genus scenedesmus identification of the pyrolysis products of s quadricauda algaenan showed i a highly aliphatic structure based on a macromolecular network of long up to c32 polymethylenic chains probably cross linked by ether bridges and ii a close correlation based on the formation of n alkylnitriles between this algaenan and two ultralaminar kerogens the rundle oil shale mainly composed of ultralamina accumulations and the green river shale ultralaminae dispersed within an amorphous matrix these fossil ultralaminae therefore likely originated from the selective preservation of the thin algaenan containing outer walls of scenedesmus and or of other chlorophyceae containing outer walls of a similar morphology and composition relative distributions of n alkylnitriles and of n alkanoic acids in the pyrolysates of s quadricauda algaenan and of the rundle oil shale indicated that nitriles are not derived from secondary reactions of carboxylic acids but originate from preexisting nitrogen functions likely amides previous evidence of kerogen formation via selective preservation of algaenans was restricted to rather uncommon kerogens the present results added to ultralamina common occurrence and abundance point to a wide involvement and to a large contribution of the selective preservation of algaenan containing thin outer walls of chlorophyceae in the formation of kerogens in a number of lacustrine source rocks and oil shales all the available information suggest that the three way correlation selective preservation of algaenans from thin resistant chlorophycean outer walls formation of fossil ultralaminae presence of n alkylnitriles with a typical distribution in the pyrolysates of ultralaminar kerogens observed in this study might be of a general character

round shaped riprap stabilization in overtopping flow a series of 26 tests was performed on a riprap layer in which median round shaped stones ranging from 32 3 to 99 1 mm from 1 27 to 3 90 in were subjected to overtopping flow conditions embankment slopes range from 10 to 45 with median stone sizes ranging from 23 9 to 104 2 mm from 0 94 to 4 1 in the database was analyzed yielding a unique expression in which the median size of a round shaped stone can be predicted as a function of the unit discharge embankment slope and coefficient of uniformity it was determined that the requisite round shaped stones range from 5 to 42 larger than angular stones to stabilize the riprap layer for similar flow conditions with unit flows of 0 2 cm s and slopes of 40 the maximum deviation between rounded and angular shaped stone may approach 70 as flow and bed conditions are extrapolated

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

sesquiterpanes diterpanes and other higher terpanes in oils from the taranaki basin of new zealand abstract the bi tri and tetracyclic terpenoids in crude oils from the taranaki basin of new zealand have been studied the distribution of c14 c15 and c16 bicyclanes was essentially invariant amongst the various fields a suggestion is made that the proportion of rearranged to total drimanes may be related to maturity and the ratio of homodrimane to drimane may be related to depositional environment mass spectra are reported for a number of unidentified sesquiterpanes including possibly norbisabolane and bisabolane the distribution of bi tri and tetracyclic diterpanes was very similar to that of crude oils from the gippsland basin of south east australia the occurrence of rimuane was confirmed 8 h labdane was identified and 4 h 18 norisopimarane was tentatively identified isopimarane dominated the diterpane distribution of oils from the maui field in the south west of the basin and its abundance gradually diminished in a north westerly direction until it became a minor component of oil from the new plymouth field this trend coincided with an increase in the complexity of the triterpane distribution and with the oleanane content of the oils these northwards trends also followed the evolution of coal deposits in the region the diterpanes in these oils had the same structure as those which occur in extant trees of the araucariaceae and podocarpaceae which flourish in new zealand today and did so even more extensively in the past coal measures formed from forests of such trees are probably the source of the diterpanes a situation analogous to that in the gippsland basin of south eastern australia tricyclanes of the cheilanthane series were not detected in any of the taranaki oils lending support to the view that these tricyclanes occur most abundantly in oils derived from marine sources c24 tetracyclanes secotriterpanes occurred abundantly in all the oils as they do in terrigenous oils from other parts of the world

hydrocarbon biomarkers thermal maturity and depositional setting of tasmanite oil shales from tasmania australia this study represents the first geological and organic geochemical investigation of samples of tasmanite oil shale representing different thermal maturities from three separate locations in tasmania australia the most abundant aliphatic hydrocarbon in the immature oil shale from latrobe is a c19 tricyclic alkane whereas in the more mature samples from oonah and douglas river low molecular weight n alkanes dominate the extractable hydrocarbon distribution the aromatic hydrocarbons are predominantly derivatives of tricyclic compounds with 1 2 8 trimethylphenanthrene increasing in relative abundance with increasing maturity geological and geochemical evidence suggests that the sediments were deposited in a marine environment of high latitude with associated cold waters and seasonal seaice it is proposed that the organism contributing the bulk of the kerogen tasmanites occupied an environmental niche similar to that of modern sea ice diatoms and that bloom conditions coupled with physical isolation from atmospheric co2 led to the distinctive isotopically heavy 13c values 13 5 to 11 7 for the kerogen 13c data from modern sea ice diatoms 7 supports this hypothesis isotopic analysis of n alkanes in the bitumen 13 5 to 31 suggest a multiple source from bacteria and algae on the other hand the n alkanes generated from closed system pyrolysis of the kerogen 15 are mainly derived from the preserved tasmanites biopolymer algaenan the tricyclic compounds mean 8 both in the bitumen and pyrolysate have a common precursor they are consistently enriched in 13c compared with the kerogen and probably have a different source from the n alkanes the identification of a location where the maturity of the tasmanite oil shale approaches the oil window raises the possibility that it may be a viable petroleum source rock

calculating bed load transport in steep boulder bed channels 1 steep rough channels occupy a large fraction of the total channel length in mountainous regions most sediment mobilized on hillslopes must pass through these streams before reaching lower gradient channels steep channels have wide grain size distributions that are composed of finer more mobile sediment and large rarely mobile grains the large grains can bear a significant portion of the total shear stress and thereby reduce the stress available to move the finer sediment conventional bed load transport equations often overpredict the sediment flux in steep channels by several orders of magnitude we hypothesize that sediment transport equations overpredict the sediment flux because they do not 1 account for the stress borne by rarely mobile grains 2 differentiate between highly and rarely mobile sediment and 3 account for the limited availability of mobile sediment here we modify a conventional bed load transport equation to include these three effects we use measurements of the flow bed properties and sediment flux in a small steep flume to test this equation we supply gravel at a constant rate through fields of regularly spaced immobile spheres and measure the bed coverage by gravel and sphere protrusion the percent of the sphere that protrudes above the gravel deposit for a given sphere spacing the proportion of the bed covered by gravel increases and the sphere protrusion decreases with greater sediment supply thus bed coverage and immobile grain protrusion may serve as proxies for sediment availability in steep rough streams unlike most transport equations that we tested our modified bed load equation predicts sediment fluxes to within an order of magnitude of the measured values our results demonstrate that accurately predicting bed load transport in steep rough streams may require accounting for the effects of local sediment availability coverage by mobile sediment and drag due to rarely mobile particles

estimation of flow through and over armored slopes models developed for the transient routing of intense rainfall on small armored slopes depend on expressions for flow resistance below and above the surface of the armored layer a series of 52 experiments are conducted in two flumes to collect data on the basic relationships of flow resistance crushed rock of 26 155 mm median diameter is placed on embankments with slopes ranging from 0 01 to 0 2 and subjected to steady flow in the flumes flow through the rock layer is found to be approximately proportional to the rock layer porosity the square root of the slope and the mean diameter of the rock and weakly proportional to the stage the portion of flow through the filter layer generally cannot be neglected flow resistance decreases and conveyance greatly increases when the stage exceeds the depth of the rock layer a model for flow both beneath and above the rock surface on an armored slope is synthesized from formulas developed for flow in rubble dams and darcy weisbach formulas developed for flow

variation in pyrolysate composition of sediments from the jurassic walloon coal measures eastern australia as a function of thermal maturation examination of a natural maturity sequence from the jurassic walloon coal measures by quantitative flash pyrolysis gas chromatography py gc and low temperature sealed tube pyrolysis reveals systematic changes in pyrolysate composition in particular gas to oil ratios composition of gas and liquid normal hydrocarbons aromatic and heteroatom content are examined for this immature oil prone rock as it is taken artificially and naturally through the oil window liquid hydrocarbon generation giving a product with a high wax content is shown to occur over a relatively narrow range of maturation significant quantities of gas are generated and the gas to oil ratio remains relatively constant during the main phase of oil generation this reflects a uniform distribution of oil and gas precursors in the original labile kerogen at higher rank where increasing generation from the residual refractory kerogen occurs there is a progressive decrease in the yield of liquid hydrocarbons concomitant with an increase in the gas to oil ratio

biogeochemistry of the miocene lacustrine deposit at clarkia northern idaho u s a abstract the lipid preservation observed in the sediments from clarkia reflects an extremely immature thermal history many biomarkers have still retained functionality even after 17 20 million years the soluble components are predominantly higher plant and algal derived lipids and the original sources for these compounds are still preserved in the sediment thus biogeochemical data are in agreement with the associated palaeontological evidence chemical changes noted in the lipids preserved in these sediments are similar to those observed in modern fresh water mesotropic or eutrophic lacustrine sediments therefore it can be inferred that the processes that operate in modern lacustrine sediments are similar to those that took place within the sediments at clarkia 17 20 million years ago

petrology of two tertiary oil shale deposits from queensland australia sediments from two queensland tertiary lacustrine oil shale deposits the lowmead and duaringa basins have been petrologically characterized from standard x ray powder diffraction analyses backscattered electron microscopy and electron microprobe data the results presented illustrate the potential of backscattered electron imagery for the study of diagenesis in fine grained organic rich sediments the lowmead formation consists of lamosites claystones and brown coals deposited in freshwater lacustrine and fringing peat swamp environements their dominant constituents are kaolinite and quartz with opaline silica and siderite important as eogenetic phases despite its similar geological setting the duaringa formation contains a more varied lithological assemblage with less organic matter being preserved freshwater lacustrine claystones and lamosites are interbedded with carbonate sediments deposited during periods of saline alkaline conditions in the lake within these carbonate sediments major growth of eogenetic mineral phases occurred principally dolomite and analcite as in the lowmead basin siderite is an important eogenetic phase in the duaringa formation two types of sideritic ironstone band occur throughout both basins sphaerosiderites within claystone coal sediments and fine grained bands of siderite within lamosites the bulk mineralogy of the siliciclastic detritus shows no significant trends with depth within either basin

the relationship between sedimentary organic carbon isotopic composition and organic biomarker compound concentration abstract a study of organic biomarker compounds which could serve as tracers of terrigenous and marine sedimentary organic matter sources was performed on samples from a 208 7 m hydraulic piston core hole dsdp hole 619 from the hemipelagic pigmy basin in the northern gulf of mexico organic carbon normalized concentrations of total long chain c37 c39 alkenones and some individual c27 c29 desmethyl sterols were determined to be useful proportional indicators tracers of preserved marine and terrigenous organic carbon respectively the alkenones whose only known source is marine phytoplankton of the class prymnesiophyceae generally occurred in higher concentrations in interglacial isotope stages 1 and 5a b than in the intervening glacial stages sterols c27 c29 apparently of a dominantly terrigenous origin occurred in lower concentrations during interglacial stages than in glacial stages tracers of both terrigenous and marine organic matter appear to be affected by the differential diagenetic alteration of the biomarker corg ratios as indicated by a simple first order kinetic model the lack of any desmethylor 4a methylsterol which is linearly related to the proportion of marine sedimentary organic matter as scaled by 13corg indicates that either 1 1 sedimentary diagenesis has obscured the biomarker corg vs 13corg record 2 2 phytoplanktonic assemblage changes caused variations in the biomarker corg ratio of the primary input preferential preservation of terrigenous sterols may result in a biased sedimentary record of sterol input which could be misinterpreted as indicating solely terrigenous sterol sources a simple model which characterizes the effects of sedimentary diagenesis on the relationship between corg normalized biomarker ratios and 13corg demonstrates the potential problems of long term differential diagenetic skewing on those tracer records

application of an eutrophic lake model to the origin of ancient organic carbon rich sediments in this paper we approach the problem of the origin of organic carbon rich sediments by using an integrated isotopic and organic geochemical study of the annual productivity eutrophication cycle in the water column of lake greifen switzerland and the historical expression of such cycles as found in the sediments the lake greifen water column and sediment studies reveal that 13c carbonate organic matter is correlated with the hydrogen indices hi of kerogens explicable in terms of changing productivity and preservation of the organic matter and the co2 budget of the water body the lake model implies that if high productivity in co2 limited surface waters high nutrient co2 ratio was controlling the preservation of organic matter a correlation between decreasing 13c carbonate organic matter and increasing hi values may be observed in contrast if low to moderate productivity in co2 unlimited surface waters low nutrient co2 ratio where bottom water anoxia promotes the preservation of organic matter a correlation between increasing 13c carbonate organic matter and increasing hi values may be observed application of this model to two well known jurassic sequences gave a correlation of increasing hi values with decreasing 13c carbonate organic matter for the kimmeridge clay formation united kingdom and increasing hi values with increasing 13c carbonate organic matter for the early toarcian shales france this suggests that the controlling factor of the former deposit was high primary bioproductivity and of the latter deposit anoxic bottom water conditions

flow resistance of rock chutes with protruding boulders steep and short rough channels such as rock chutes are used in river restoration as grade stabilization structures the stability of these channels can be increased using boulders placed over the base material the boulders can be placed with different configurations such as randomly or in rows in each case their presence affects the geometry of the channel and modifies the hydraulic resistance this paper shows the results of tests conducted on rough channels with or without the insertion of protruding boulders the parameters that influence the flow resistance such as slope relative submergence and blocks disposition were systematically investigated to describe the hydraulic behavior of the structure the aim is to define a relationship useful for practical design which relates the flow resistance in terms of both darcy weisbach friction factor and manning coefficient the results were combined with available data for loose rock riprap to determine new experimental relationships

variations in organic matter composition in sediments from lake huguang maar huguangyan south china during the last 68 ka implications for environmental and climatic change abstract this study presents a continuous and long term palaeoenvironmental and palaeoclimatic record from a lacustrine sediment core lake huguang maar at the northern coast of the south china sea extending back to about 68 cal ka bp we provide a comprehensive ecosystem analysis from the opportunity to combine organic geochemical and palynological data several climatically induced changes to the flora and fauna have been recognised from 68 to 58 and 48 to 40 5 cal ka bp relatively depleted 13 c toc 31 3 to 25 0 and 13 c values of mid and long chain n alkanes 34 3 to 30 2 as well as high percentages of tropical pollen indicate a vegetation dominated by subtropical tropical forest c 3 plants an expansion of a mixed c 3 c 4 open grassland between 58 and 48 and particularly after 40 5 cal ka bp mirrors drier climatic conditions in conjunction with a lowering of atmospheric co 2 concentrations 13 c toc 24 1 to 16 8 and 13 c values of n alkyl lipids 28 9 to 24 1 are heavier higher percentages of non arboreal pollen were observed and the wood grass lignin index wgli from open pyrolysis py gc indicates a higher input of grass lignin abundant oxidised terrigenous particles that resulted from increased fire activity and or greater erosion rates are a further hint of enhanced dryness the clear drop in moisture availability suggests that this site is sensitive in fluctuations of the summer and winter monsoon activity in accordance with other proxy records in south east asia the response of the aquatic ecosystem is documented by an extremely large 13 c shift of algal derived botryococcenes from 35 4 to 6 2 which records a change towards a bicarbonate carbon source at low dissolved co 2 concentrations

roughness of loose rock riprap on steep slopes a study was conducted to determine the roughness of rock riprap laid on steep slopes tests were conducted in a 1 07 m wide flume and two 2 74 m wide field scale structures using angular riprap with median diameters d50 ranging from 52 to 278 mm and bed slopes s0 ranging from 0 028 to 0 333 m m empirical relationships were developed to predict the manning roughness coefficient as a function of d50 and s0 the darcy weisbach friction factor was predicted as a function of d d84 the relative submergence newly developed equations are applicable for riprap placed on slopes from 2 8 33 roughness coefficients calculated using the developed equations were compared with roughness coefficients calculated using equations developed from observations on natural mountain streams

compound specific stable carbon isotope analysis as a tool for correlating coal sourced oils and interbedded shale sourced oils in coal measures an example from turpan basin north western china molecular geochemical methods have shown that it is often diacult to diaerentiate between coal and interbedded shale sourced oils even though coals and interbedded shales may exhibit considerable organic influx variation e g land plant vs algal organic matter due to the changes of depositional setting however compound specific stable carbon isotopic compositions are sensitive to the source input variations typically specific molecules are more depleted in 13 c with increasing content of aqueous biota this hypothesis is examined and exemplified by comparing the stable carbon isotopic ratios of n alkanes from source rock extracts and related oils of the turpan basin northwestern china stable carbon isotopic values of n alkanes extracted from coals and interbedded shales show that d 13 c values of n alkanes with less than 20 carbon atoms vary only slightly however there are dramatic changes in the isotopic compositions of higher molecular weight n alkanes furthermore n alkanes from coal extracts are enriched in 13 c relative to that of interbedded shales with excursions up to 2 3 this comparison enables the diaerentiation of coal and interbedded shale sourced oils and provides information useful in assessing the hydrocarbon system of a basin 2000 elsevier science ltd all rights reserved

the triggering of debris flow due to channel bed failure in some alpine headwater basins of the dolomites analyses of critical runoff the debris deposits at the bottom of very steep natural channels and streams in high mountain areas can be mobilized by runoff triggering a water sediment mixture flow known as debris flow the routing of debris flow through human settlements can cause damage to civil structures and loss of human lives the prediction of such an event or the runoff discharge that triggers it assumes an interest in risk analyses and the planning of defence measures the object of this study is to find a method to determine the critical runoff value that triggers debris flow as a result of channel bed failure historical and rainfall data on 30 debris flows that occurred in six watersheds of the dolomites north eastern italian alps were collected from different sources field investigations at the six sites together with the hydrologic response to the rainfalls that triggered the events were performed to obtain a realistic scenario of the formation of the debris flow there occurred field observations include a survey along the channel of the triggering reach of debris flow with measurements of the channel slope and cross section and sampling of debris deposits for grain size distribution simulated runoff discharge values based on the rainfall recorded by pluviometers were then compared with values obtained through experimental criteria on the initiation and formation of debris flow by bed failure the results are discussed to provide a plausible physical based method for the prediction of the triggering of debris flow by channel bed failure copyright 2007 john wiley sons ltd

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

waxy bitumen stranding in southern australia a geochemical study of multiple oil families and their likely origins abstract reports of bitumen stranding on the ocean beaches of southern australia date back to the early days of european settlement previous investigations have shown that this coastal bitumen comprises three categories of stranded petroleum waxy bitumen asphaltite and oil slicks all three varieties are physically and chemically distinct from each other and bear no geochemical resemblance to any indigenous australian crude oil this study focuses on the most common variety waxy bitumen which accounted for 90 of the strandings on six south australian beaches repeatedly surveyed during 1991 1992 geochemical analysis of 96 individual specimens collected from these survey sites and other beaches in south australia and western victoria has shown them to be variously weathered high wax crude oils of paraffinic to aromatic intermediate bulk composition elemental isotopic and biomarker differences allow their assignment to at least five oil families with inferred source facies that range from deep freshwater lacustrine through paludal and deltaic to euxinic marine possibly deposited within different sedimentary basins family 1 2 and 3 waxy bitumens all contain biomarkers derived from the freshwater alga botryococcus sp and tropical angiosperms notably dipterocarps similar biomarker assemblages are unknown in australian sedimentary basins but are common in cenozoic crude oils and source rocks throughout western indonesia family 4 waxy bitumens lack these biomarkers but do contain dinosterane and 24 n propylcholestane indicative of a marine source affinity while the carbon isotopic signatures and high pristane phytane pr ph ratios of family 5 waxy bitumens are consistent with their origin from coal rich source rocks deposited in fluvial to deltaic sedimentary successions the majority of these waxy bitumens represent an oceanic influx of non indigenous southeast asian crude oils carried into the waters of southern australia by the leeuwin current although they are likely to originate from natural seepage within the indonesian archipelago it is unknown whether the parent oils emanate from submarine seeps or from inland seepages which are then carried to the sea by rivers the common practice of tanker cleaning operations in the java and banda seas may augment the supply of natural bitumen to the beaches of australia

origin of variations in organic matter abundance and composition in a lithologically homogeneous maar type oil shale deposit gerce pliocene hungary despite having an homogeneous lithology the largest hungarian maar type deposit gerce oil shale pliocene has previously been shown to exhibit substantial variations in organic matter quantity and quality with depth this het erogeneity is also reflected in the present study by large variations in bitumen abundance and composition for 23 samples from gerce well 6 core based on the above bitumen data four samples were selected that were representative of the whole set which exhibit contrasting features scanning and transmission electron microscopy showed the occurrence of extensively altered botryococcus colonies in this deposit gc ms and gc c ir ms of the saturated hydrocarbon fractions of the bitumen of these samples reveal a predominant algal contribution along with a variable bacterial input the relative abundance of these two contributions in the four selected samples is also reflected by dif ferences in ftir and solid state 13 c nmr spectra of the isolated kerogens curie point pyrolysis gc ms of these kerogens revealed a relatively high terrestrial contribution in one sample and confirmed the variable input of algae and bacteria the above diaerences in relative contributions account for the variations in organic matter quantity and quality observed along the core 2000 elsevier science ltd all rights reserved

carbon isotopic composition of an isoprenoid rich oil and its potential source rock despite the multiple controls on the carbon isotopic composition of organic matter 13c values for saturated and aromatic hydrocarbon fractions for over 300 norwegian north sea central graben oils range from 26 to 31 and from 24 to 30 respectively however for one oil well 2 2 5 13c values for the saturate and aromatic fractions are 21 5 and 22 significantly enriched in 13c relative to the isotopic compositions of all oil fractions investigated the saturate hydrocarbon fraction of the 2 2 5 oil is comprised predominantly of low molecular weight c20 primarily regular acyclic isoprenoids also present are c36 c40 irregular acyclic isoprenoids these compounds are composed of various combinations of tail to tail condensed c15 c20 regular isoprenoid subunits resulting in pseudo homologous series with six to nine methyl groups the isotopic compositions of both high and low molecular weight isoprenoids are around 19 this is in marked contrast to n alkane 13c values ca 31 and it is clear that isoprenoid 13c values dictate the 13c value of the saturate fraction the same 13c enriched isoprenoids are present in a thin 1 m immature oil shale facies hudlestoni biozone of the kimmeridge clay formation kcf dorset uk moreover the relatively immature kcf sediment contains unique high molecular weight isoprenoid thiophenes and thianes whose structures indicate that sulfur has reacted with functional groups in the isoprenoid precursor s interiors this suggests that these novel high molecular weight isoprenoids were probably biosynthesized as such reasons for their profound 13c enrichment and predominance are discussed although the kcf facies located in the southern uk cannot be a direct source of the north sea 2 2 5 oil a related north sea facies seems plausible since an isotopically enriched toc zone has been reported in a well also from the central graben

microelectrode studies of organic carbon degradation and calcite dissolution at a california continental rise site fine scale porewater profiles of resistivity o2 ph and pco2 were measured in situ with microelectrodes at a site on the california continental rise they are reported here with more traditional measurements of shipboard porewater no3 alkalinity and tco2 and sediment organic c and caco3 profiles a numerical model encompassing diffusion advection and multiple reaction terms is applied to these data to characterize organic carbon degradation and caco3 dissolution processes near the sediment water interface a benthic o2 flux of 58 mol cm 2 yr 1 over the top 1 mm sediment is estimated based on one measured sub mm depth scale o2 profile the numerical model indicates that this high o2 consumption rate is related to a very labile fraction of organic c which has a degradation rate constant of approximately 4 5 10 8 s 1 1 4 yr 1 and which is not mixed downward by biological mixing seasonality in the benthic o2 consumption rate of this site may be attributed to variations in the input rate of this highly labile organic c degradation rate constants of the bulk organic c by oxygen reduction and by nitrate reduction are estimated to be about the same 1 10 9 s 1 the organic c rain rate responsible for the bulk organic c is estimated to be 53 mol cm 2 yr 1 this estimate exceeds the average rain rate determined by sediment trap collections at this site saturation state profiles calculated from the in situ ph and pco2 data and from modelling the in situ o2 and ph data both indicate that the porewater is undersaturated with respect to calcite to a depth of at least 8 cm the dissolution rate constant of calcite in this caco3 poor station is determined to be 5 10 day 1 assuming the reaction order is 4 5 which is close to the minimum estimates for environments richer in calcite a uniform calcite dissolution rate constant therefore may be adequate for representing carbonate dissolution in global scale models of ocean chemistry

biomarker evidence for botryococcus and a methane cycle in the eocene huadian oil shale ne china the saturated and unsaturated hydrocarbons of two samples hd 19 and hd 21 from the same section of the middle eocene lacustrine huadian oil shale in ne china were identified and shown to be mainly from algal and bacterial sources comparison of the two samples provided an opportunity to explore the contribution from telalginite to the hydrocarbon profiles cells identified from microscopy as botryococcus in the telalginite of hd 21 were confirmed as belonging to the l race of b braunii from the presence of monoaromatic lycopane derivatives and small amounts of several lycopadienes lycopane was abundant and was probably derived from biohydrogenation of lycopadienes and related lipids on the basis of d 13 c values hopane distributions showed a dominance of those with the biological 17b 21b stereochemistry as expected for an immature shale with low amounts of 17b 21a hopanes moretanes and 17a 21bhopanes two hopenes were also abundant and assigned as c29 and c30 neohop 13 18 enes which occurred together with the c29 and c30 hop 17 21 enes these had depleted carbon isotope values 43 7 to 50 8 indicative of production by methane oxidizing bacteria methanotrophs the high proportion of hopanoids with carbon numbers c32 indicates extensive post depositional diagenetic alteration of bacteriohopanepolyols as well as a direct input of c30 hopanoids the data clearly indicate that there was active utilization of methane in this lacustrine depositional setting but isoprenoid hydrocarbon biomarkers for methanogens such as pentamethylicosane pmi and squalane were in surprisingly low abundance it is possible that these bacterial contributions were present as polar lipids the origins of an unusual c38 isoprenoid alkane assigned as bipristane are uncertain but may be from methanogens steranes and sterenes were relatively minor components but abundant diasterenes and 4 methyldiasterenes were present reflecting significant conversion of the original lipid composition by way of clay catalysed diagenesis the biomarker data suggest that the bottom waters in the original depositional environment had low o2 content but the sediments were probably neither sulfidic nor strongly reducing the high content of organic matter in the shale likely reflects both high but fluctuating productivity due to eutrophic conditions in the overlying water and good preservation in the sediments

scale amplification of natural debris flows caused by cascading landslide dam failures debris flows are typically caused by natural terrain landslides triggered by intense rainfalls if an incoming mountain torrent collapses a series of landslide dams large debris flows can form in a very short period moreover the torrent can amplify the scale of the debris flow in the flow direction the catastrophic debris flows that occurred in zhouqu china on 8 august 2010 were caused by intense rainfall and the upstream cascading failure of landslide dams along the gullies in the wake of the incident a field study was conducted to better understand the process of cascading landslide dam failures and the formation of debris flows this paper looks at the geomorphic properties of the debris flow gullies estimates the peak flow discharges at different locations using three different methods and analyzes the key modes i e different landslide dam types and their combinations of cascading landslide dam failures and their effect on the scale amplification of debris flows the results show that five key modes in luojiayu gully and two modes in sanyanyu gully accounted for the scale amplification of downstream debris flows in the zhouqu event this study illustrates how the hazardous process of natural debris flows can begin several kilometers upstream as a complex cascade of geomorphic events failure of landslide dams and erosion of the sloping bed can scale to become catastrophic discharges neglecting recognition of these hazardous geomorphic and hydrodynamic processes may result in a high cost

design of rock protection to prevent erosion by water flows down steep slopes conventional stability analysis methods for determining rock armor size to protect steep tan 0 1 embankments from erosion due to downslope flow do not predict the correct dependency of armor size on the slope consequently such methods become very conservative discharge factor of safety 8 at high slopes we review published large scale measurements recorded in the literature and show that adequate representation of flow aeration is important as proposed by hartung and scheuerlein in 1970 however the assembled measurements show that the hartung and scheuerlein design method is not conservative the aerated flow equations of hartung and scheuerlein when combined with a correctly formulated stability equation yield good collapse of the available large scale data and a conservative design method

the occurrence of bisnorhopane trisnorhopane and 25 norhopanes as free hydrocarbons in some australian shales abstract the triterpenoid hydrocarbons of some west australian shales have been examined by gc ms in addition to the common 17 h 21 h hopanes 17 h 21 h hopanes and 17 h 21 h moretanes 28 30 bisnorhopane 25 28 30 trisnorhopane and 25 norhopanes were identified in the organic extracts in contrast pyrolysates of the solvent extracted sediments contained only the common hopane and moretane series indicating that 28 30 bisnorhopane 25 28 30 trisnorhopane and 25 norhopanes are not bonded to kerogen but rather are present in the sediments as free hydrocarbons

upward increase of kerogen δ13c in the peru margin upper oligocene possible implications for the cenozoic evolution of atmospheric co2 abstract carbon isotopic composition of predominantly marine kerogen in latest oligocene mudstones of the peru margin odp 682a hole shows an about 3 5 increase with decreasing age py gc and elemental c n ratio analysis of the kerogen plus sulphur isotopic study together with earlier knowledge on geological setting and organic geochemistry results in a better understanding of depositionary environment and allows to separation of the influence of concentration of water dissolved carbon dioxide ce on kerogen 13c from that of other factors bacterial degradation sea surface temperature dic 13c productivity and admixture of land plant om based on this analysis the major part of the kerogen shift is considered as a result of the latest oligocene decrease of marine photosynthetic carbon isotopic fractionation in the peru margin photic zone which in turn possibly reflects a simultaneous drop in atmospheric co2 level uncertainties in the evaluation of the factors affecting the marine photosynthetic carbon isotopic fractionation and the extent of ocean atmosphere disequilibrium do not permit calculation of the decrease of the atmospheric co2

dinosterane and other steroidal hydrocarbons of dinoflagellate origin in sediments and petroleum abstract the steroidal alkanes of a selection of sediments and oils have been examined by gc ms with multiple metastable reaction monitoring specific 4 methyl sterane isomers have been identified by comparison with isomers synthesized from sterols isolated from dinoflagellates an immature marine oil shale and two mature marine oils of triassic to early cretaceous age contained high concentrations of c30 steranes comprising desmethyl 24 ethyl 4 methylcholestane and 4 23 24 trimethylcholestane dinosterane isomers an immature non marine oil shale and two non marine oils of cretaceous to eocene age contained stereoisomers of 24 ethyl 4 methylcholestane as the dominant c30 steranes reaction monitoring analyses in gc ms are particularly suited to unravelling complex distributions of homologous and stereoisomeric steroids encountered in oils and their source rocks

prediction of sediment transport in step pool channels 1 in mountainous drainage networks sediment mobilized on hillslopes must first pass through steep streams before reaching lower gradient channels the bed of steep channels is typically composed of large relatively immobile boulders and finer more mobile gravel most sediment transport equations overpredict sediment flux in steep streams by several orders of magnitude because they do not account for the stress borne by immobile grains and the limited availability of the more mobile sediment we previously developed and tested in flume experiments a sediment transport equation that accounts for these two effects here we modify the parker 1990 bed load equation to include the resistance borne by steps and selective transport of the relatively mobile sediment using a range of hiding functions we test a number of resistance equations and hiding functions combined with our modified and the original parker equations against measured flow and sediment transport in three steep channels our modified sediment transport equation generally predicts the transported sediment volumes to within an order of magnitude of the measured values whereas the unmodified equations do not the most accurate sediment flux predictions were obtained from using our modified equation combined with a hiding function that calculates highly selective transport of the relatively mobile sediment furthermore this hiding function has a critical shields stress that is similar to those reported for lower gradient channels the effects of the immobile steps on flow and sediment transport are not adequately captured by simply increasing the critical shields stress to values reported in steep streams

steranes and triterpanes generated from kerogen pyrolysis in the absence and presence of minerals abstract steranes and triterpanes generated from pyrolysis of immature monterey formation kerogen in the presence and absence of calcite illite and montmorillonite reveal results that are both consistent and divergent with published data that reflect the use of these biological markers as maturation indicators the extent of isomerization of biomarkers generated from pyrolysis of kerogen at 300 c for 2 hours at c 20 in 14 h 17 h steranes at c 22 in 17 h 21 h hopanes and of 17 h 21 h hopanes correspond to early diagenetic stages in rock extracts from sedimentary basins isomerization increases with heating time and after 1000 hours attains values which correspond to the catagenetic stage in sedimentary basins or equivalent to that of mature oil stepwise pyrolysis of the kerogen indicates faster isomerization rates for steranes and triterpanes in the bitumen than for those retained in the kerogen structure confirming earlier studies presence of a mineral matrix can influence the isomerization of steranes and triterpanes considerably comparisons with results from kerogen heated alone for a given maturation stage show that calcite inhibits illite catalyzes slightly and montmorillonite has a pronounced catalytic effect on these reactions this effect results in early isomerization of steranes and hopanes corresponding to the catagenetic stage in the presence of montmorillonite while kerogen or kerogen with calcite held at the same temperature 300 c and time 10 hours only yield isomerized products which correspond to a diagenetic stage further illite and montmorillonite affect various isomerization reactions differently the fastest reaction is the isomerization at c 20 in 14 h 17 h steranes followed by that at c 22 in 17 h 21 h hopanes and the slowest is the formation of 14 h 17 h steranes these results show that maturation measurements of rock or oil samples from sedimentary basins which use biological markers have to take into account the mineral matrix effects which have been largely ignored until present

contrasting variations in the structure and stable carbon isotopic composition of botryococcenes through the last glacial interglacial transition in lake masoko southern tanzania abstract the production and composition of acyclic monocyclic and bicyclic c 34 c 37 botryococcenes in lake masoko sediments covering the last 32 ka show sharp and contrasting variations physicochemical conditions in the water column at ca 32 ka and during the younger dryas ca 12 ka appear to have been favourable for the development of botryococcus braunii race b and apparently promoted methylation and cyclisation reactions during botryococcene biosynthesis although both periods represent contrasting climatic conditions the stable carbon isotopic composition of botryococcenes shows erratic variation both for the same group of compounds exhibiting close structural features from one period to another and between compounds within the same period overall the results suggest complex physiological and or physicochemical controls on the glacial interglacial occurrence of botryococcenes in lake masoko where local environmental parameters may have been more influential than global climatic changes

chemical molecular and isotopic differentiation of organic facies in the tertiary lacustrine duaringa oil shale deposit queensland australia abstract total organic matter extractable organic matter bitumen and pyrolysates released on low temperature sealed tube pyrolysis of kerogen were analysed chemically and isotopically based on bulk bitumen and biomarker parameters the sediments are immature to a depth of approx 1300 m within the terrestrial and lacustrine depositional environments of the tertiary duaringa basin various organic facies have been classified according to inorganic input and maceral abundances of organic matter derived from land plant and algal sources the latter derived mainly from pediastrum and with a varying botryococcus content the lacustrine upper lamosite is chemically and isotopically distinct from the lower lamosite due to a changing algal community relative contributions from allochthonous land plants and for the lower lamosite a slightly more saline and restricted lake environment the lower lamosite is associated with the highest concentrations of c 28 c 30 4 methylsteranes and 13 c depletion in toc in the upper lamosite there is a strong positive correlation between botryococcus content and 13 c enrichment the organically lean claystones have sources nearly identical to the lamosites but the organic matter is diluted due to rapid influx of siliciclastics the terrestrial facies the cannel coal and carbonaceous shales are mainly distinguished from the lacustrine facies by higher relative proportions of c 29 steranes c 30 4 methylsteranes and 13 c values for the pyrolysed hydrocarbons intermediate between the two lamosite facies the carbonaceous oil shale has a composite geochemical signature intermediate between the two end members lamosite and cannel coal oleanane and ring a degraded triterpanes derived from lupane arborane and oleanane skeletons are distributed throughout all organic facies representing both autochthonous and allochthonous higher plant inputs higher concentrations of oleanane and des a lupane are associated with the terrestrial facies hopanes dominate over steranes in all organic facies and their concentration ranges are independent of facies for the lamosites the aliphatic biopolymer algaenan is implicated as the dominant source for n alkanes from analysis of their yields homologue abundances and individual 13 c values in the terrestrial facies resinites are paraffinic and are a major source for the n alkanes released on pyrolysis compound specific analysis of extractable and pyrolysate hydrocarbons allowed deconvolution of different source inputs to free lipids and kerogen for the lamosites low molecular weight n alkanes in the bitumen are derived mainly from a pediastrum source while botryococcus is associated with waxy n alkanes however the situation is reversed in the kerogen pediastrum algeanan has a longer average alkyl chain length than botryococcus algaenan the magnitude of the isotopic differences between single n alkanes released at different temperatures is useful in determining multiplicity of sources

distributions and stable carbon isotopic compositions of biomarkers in torbanites from different palaeogeographical locations abstract the relative distributions and stable carbon isotopic compositions of certain aliphatic and aromatic biomarkers from 11 botryococcus braunii rich torbanites from scotland south africa and australia covering the late carboniferous to late permian were investigated the data was scrutinised for any evidence of molecular features which may be characteristic of palaeogeography the torbanites studied were selected to cover a range of age and palaeoclimatic conditions e g permian and late carboniferous when gondwana was covered by an extensive ice sheet the late permian when the climate warmed from glacial to cool to temperate and the carboniferous when laurasia was located within the equatorial zone all torbanites are composed of abundant n alkanes and novel macrocyclic alkanes which based on similar 13c values are ascribed a common origin all samples are also characterised by a high cyanobacterial input as indicated by abundant hopanoids other biomarker distributions and stable carbon isotopic compositional differences separated the torbanites into three groups which also correlate to three different palaeogeographical palaeoclimatic precincts i group a southern africa and eastern australia temi torbanites which are characterised by a high relative abundance of cyanobacterial and methylotrophic hopanoids abundant branched hydrocarbons and 13c enriched homologous series of monomethylakanes ii group b eastern australia newnes and glen davis torbanites contain relatively high amounts of drimanes and abundant 13c enriched homologous series of monomethylakanes and iii group c scottish torbanites torbane hill and westfield contain high relative amounts of cyanobacterial hopanoids methylotrophic hopanoids and abundant branched aliphatics but no 13c enriched homologous series of monomethylakanes

des a lupane in an east african lake sedimentary record as a new proxy for the stable carbon isotopic composition of c3 plants we studied the high resolution and well dated 25 000 year sedimentary record of lake challa a deep tropical crater lake in equatorial east africa to explore new proxies for paleoenvironmental and paleohydrological change sedimentary biomarker analysis revealed the presence of des a triterpenoids with oleanane ursane and lupane carbon skeletons microbial degradation products of angiosperm plant triterpenoids their increased influx from 16 000 years ago corresponds with previously documented changes in the terrestrial vegetation of the lake challa basin during postglacial warming in particular the relative increase in c3 c4 plant ratio inferred from the stable carbon isotopic signature 13c of sedimentary n alkanes derived from plant leaf waxes in contrast to this n alkane 13c signature the 13c of des a lupane maintains a constant value of 27 4 1 1 across the glacial interglacial transition since des a lupane is derived from c3 plants its 13c signature is here proposed to represent a novel and independent proxy for the time variable carbon isotopic composition of local terrestrial c3 plants which can improve estimates of the c3 c4 plant ratio based on two end member mixing models of n alkane 13c values

distribution of aliphatic des a triterpenoids in the dajiuhu peat deposit southern china abstract aliphatic des a triterpenoids have been tentatively assigned in samples taken from a 260 cm thick peat sequence from the dajiuhu basin of southern china using gas chromatography mass spectrometry gc ms the compounds possessing the carbon skeletons of oleanane ursane or lupane are generally considered as the microbial degradation products of plant triterpenoids under anoxic conditions abundant aliphatic des a triterpenoids were observed only in peat samples during the transitional period from the last glaciation to the early holocene 9 5 11 6 cal 14 c ka bp among these des a lupane is the only saturated ring a degraded compound whilst mono and di unsaturated des a triterpenes are dominated by oleanane and ursane derivatives the mono and di unsaturated des a triterpenes show a strong correlation r 2 0 94 in abundance indicating that they may be derived from the same source or process des a lupane shows no correlation in abundance with the mono or di unsaturated des a triterpenes r 2 des a triterpenoids corresponds to the interval with relatively high sedimentation rate 0 3 mm per year these data indicate that the abundance of aliphatic des a triterpenoids in the dajiuhu peat deposit in the early holocene may result from the prevailing reducing conditions in the water table or surficial sediment and or rapid preservation of the early diagenetic products our study highlights the potential application of des a triterpenes in the reconstruction of palaeoenvironments based on peat sequences