organic geochemistry of oils and condensates in the kekeya field southwest depression of the tarim basin china this study shows that the oils and condensates in the kekeya field in the tarim basin nw china belong to a single family most likely derived from marine shale source rocks deposited under oxic suboxic conditions with mixed terrigenous and algal bacterial organic inputs the maturity data clearly indicate that the paraffinic condensates were not formed by thermal cracking of oil during late catagenesis ro 1 2 both the oils and condensates were generated within the normal oil window whereas addition of gaseous hydrocarbons from a separate source resulted in migration fractionation and hence spuriously high heptane indices age specific biomarkers show that the oils and condensates were not generated from the mesozoic cenozoic strata but from the carboniferous permian sections 1d basin modeling results are consistent with this interpretation suggesting that the mesozoic eocene strata are currently immature with respect to hydrocarbon generation and expulsion deep seated faults may have provided routes for upward fluid migration at the time of active deformation during several pulses of the himalayan orogeny the favored targets for further petroleum exploration in front of the kunlun mountains include the deep structures within the carboniferous permian strata for indigenous petroleum accumulations and anticlines and stratigraphic traps within the mesozoic cenozoic sections that are cut by deep seated thrust faults where secondary petroleum accumulations most likely occurred

the use of the common pb isotope composition of detrital k feldspar grains as a provenance tool and its application to upper carboniferous paleodrainage northern england k feldspar is a common detrital mineral in sandstones it contains little u or th and hence the common pb isotope composition of unaltered k feldspar is that of the source rock pb isotope variations in igneous and metamorphic crustal rocks define broad spatial patterns that make the pb signature of detrital k feldspar grains a useful provenance tool however it is unclear how robust this signal is and to what extent it can be modified by weathering transport burial diagenesis and or exposure to hydrothermal fluids this study reports an evaluation of the technique using two granite arkose pairs from helmsdale northern scotland and shap northwest england where the composition of the detrital grains can be compared to feldspars in the granite from which they were derived the results of this test have informed a pilot study using the pb isotope composition of detrital k feldspar in upper carboniferous fluvial sedimentary rocks of northern england to constrain the sediment routing pb isotope compositions have been measured using an in situ high resolution single grain technique that can distinguish original composition heterogeneity and subsequent alteration within individual sand grains the results for the granite arkose pairs show that the common pb isotope signature of the detrital k feldspar grains matches the in situ feldspars in the source granites the signal is independent of grain size medium grained sand to granules but alteration along a paleo regolith at helmsdale has resulted in perturbations in pb composition and an increase in the errors on the analyses the application of the technique to arkosic carboniferous serpukhovian bashkirian millstone grit group sandstones in the pennine basin reveals two discrete populations of k feldspars that cannot be distinguished petrographically matching of the compositions to potential sourcelands to the north and northeast of the basin suggest a far traveled 500 km source of k feldspar from the archean paleoproterozoic lewisian rocks of northwest scotland or their extension to the north but also an equally important proximal source emanating from the southern uplands belt of scotland in what would have been the lower part of the hinterland drainage basin of the millstone grit

estimating volcanic plume heights from depositional clast size 1 tephra deposits retain a considerable amount of information about the nature of volcanic eruptions with plume height commonly inferred from maximum clast size measurements however current methods for inferring plume height from maximum clast size lose some of the accuracy in measurements made in the field and have limited application when trying to constrain the uncertainty in these parameters here a predictive numerical model is used to determine plume height from maximum clast size found in a deposit plume height is an essential parameter for inferring eruption magnitude as it is explicitly related to mass eruption rate we investigate the effects of different atmospheric and wind profiles allowing the input conditions to be location specific for each eruption the use of a predictive model reduces the uncertainty in determining plume height as it retains the detail of measurements made in the field and incorporates the uncertainty in these measurements in the results in the form of a probability distribution we have applied this approach to fall deposits from the 1991 eruption of pinatubo one of the few plinian eruptions in which the true height of the plume is well known the predicted plume heights are in good agreement with those found from satellite measurements this new approach provides a method for determining plume height from poorly preserved fall deposits from which a limited amount of data can be sampled leading to large uncertainties in the field measurements

geochemical characterisation of middle devonian oils in nw alberta canada possible source and maturity effect on pyrrolic nitrogen compounds abstract molecular geochemical compositions of a suite of middle devonian sourced and reservoired oils from the rainbow zama shekilie sub basins in n w alberta canada reveal the presence of at least two oil families in the study area the distribution of each oil family is geographically restricted to a single sub basin consistent with the oils being sourced locally within a series of closed generation migration trapping systems the diversity in the biomarker distributions of the oils indicates the wide range of depositional environments and source materials existing in each sub basin rather than mixing of end member oils across different sub basins clear maturity differences are observed between the oils from the rainbow and zama subbasins pre cretaceous thermal anomalies along the reactivated regional precambrian basement faults are proposed as one of the major causes for the relatively high maturity levels for the middle devonian source rocks in the study area we infer that depositional environment and thermal maturity have had a strong impact on the geochemical characteristics of the saturated and aromatic hydrocarbons in the rainbow shekilie zama oils but may not influence the pyrrolic nitrogen compounds to a significant extent however recognition of possible source and maturity effects on pyrrolic nitrogen compounds in other studies suggests that these factors should be considered before the pyrrolic nitrogen compounds are used to characterize petroleum migration

xanthones novel aromatic oxygen containing compounds in crude oils abstract xanthone and its alkylated homologues were determined to be present in 64 of 69 investigated oils from offshore norway central graben viking graben haltenbanken this is the first description of xanthones in crude oils these compounds were identified by comparison with authentic standards by coinjection based on mass spectra and relative retention times on two different gc columns the elution order of the four methylxanthones was established as 1 4 2 3 by using a bpx 5 column about 2 3 of the oils contain concentrations of xanthone lower than 5 g g oil but some oils are clearly enriched in the parent compound the highest amount of xanthone in the sample set was 38 g g oil the relative abundance of xanthone the sum of the methylxanthones and the sum of the c 2 xanthones is mainly controlled by maturity partitioning processes may effect changes in the distribution of methylxanthones as observed for a biodegradation sequence from the gullfaks field molecular dynamics calculations support the observation of a better preservation of the shielded isomers 1 and to a lesser extent 4 methylxanthone in the oil phase compared to the non shielded isomers 2 and 3 methylxanthone the ratio of these two different isomer groups may be useful as an indicator of secondary migration distances as demonstrated for an oil sequence from the tampen spur and haltenbanken oils however biodegradation could also cause an increase of the shielded isomers relative to the non shielded isomers due to sterical hindrance by the methyl groups restricting access to the oxygen functionalities the origin of xanthones in crude oils and source rocks is not known but they could be generated as diagenetic products formed by oxidation of xanthenes in the reservoir or originate by geosynthesis from aromatic precursors

molecular memory effects recording the accumulation history of petroleum reservoirs a case study of the heidrun field offshore norway abstract the immobile portion of the oil occupying the pore space of reservoir sandstones which is mostly represented by visible impregnations is shown by the present study to contain geochemical signals that record their filling history the clue to unravelling these signals is sequential extraction of such impregnations of residual oil by a high pressure solvent flow through cell in which the solvent percolates through the intact and primary pore system of the rock sample gas chromatography mass spectroscopy gc ms analysis of residual oils extracted from samples of certain reservoir sandstones within the heidrun field offshore norway reveal significant contrasts in the chemical maturity of the first and the last fractions recovered as high as 0 69 versus 0 50 for the mpi 1 ratio corresponding to 0 79 versus 0 67 rc the hypothesis is proposed that by using this extraction technique oil impregnations from different portions of the pore system i e from large versus small pores are obtained separately this interpretation is especially supported by the regular occurrence of reservoir sandstones in which the residual oil exhibits maturity contrasts between those fractions extracted from large and small pores of the same rock within the heidrun field the distribution of reservoir sandstones with such maturity contrasts is strictly controlled by their position in the oil column and the location of their fault compartment these contrasts are interpreted to reflect the maturity levels of end members of the petroleum charges which have filled this trap during an extended period of geological time reservoir sandstone samples containing such end member charges are limited to the uppermost portion of the oil column lower in the oil column the pore system of all reservoirs contains oil impregnations of a uniform maturity level regardless of their pore size origin this distribution is believed to indicate an early stage of the accumulation history of the heidrun field characterised by the formation of a palaeo oil water contact well above the present one moreover the four fault compartments studied each controlled by bordering faults with different sealing capacities were not filled during the same stages of the accumulation history in summary the present study has shown that oil impregnations depending on their location within the pore system of individual reservoir sandstones can retain molecular memory effects which in turn allow the accumulation history of petroleum fields to be reconstructed

petroleum migration and mixing in the northwestern junggar basin nw china constraints from oil bearing fluid inclusion analyses abstract abundant oil bearing fluid inclusions are present in four reservoir sandstone samples from the slope and fault zone areas in the northwestern margin of the junggar basin nw china free oil in intergranular pores adsorbed oil on grain surfaces and petroleum in inclusions hosted by mineral grains of these samples were analyzed by gas chromatography and gas chromatography mass spectrometry analytical results indicate similar biomarker distributions in the three bitumen fractions of the samples collected from the slope area which correlate well with characteristic of the source rocks in the lower permian fengcheng formation this is in contrast to the fault zone where the three bitumen fractions vary significantly in their geochemical signatures suggesting that all of the three permian source sequences rocks including the lower permian jiamuhe and fengcheng formations and the middle permian lower wuerhe formation have been mature and contributed to the oils in the fault zone the presence of an unresolved hydrocarbon hump and a full range of unaltered n alkanes in the gas chromatograms of samples collected from the fault zone indicate an earlier hydrocarbon biodegradation and subsequent injection of fresh oils distinctly different from that in the slope area petrographic and microthermometric investigations of oil bearing fluid inclusions suggest a single oil charge in the slope area to the lower triassic reservoir occurring during the late triassic to early jurassic time in the fault zone oil migration and mixing took place mainly during the late triassic to early jurassic and cretaceous followed by gas migration in the tertiary period the different petroleum migration and mixing histories in the slope and fault zones are attributed to the effect of fault controlled oil and gas migration

the natural weathering of staurolite crystal surface textures relative stability and the rate determining step mineral surface textures on naturally weathered c of staurolite monoclinic pseudo orthorhombic fe4al18sis046 rtals indicate that staurolite weathering is general1 interface limited etch pits on naturally weathered staurolites are disi shaped extensive par allel to oio and thin perpendicular to 010 010 is the plane of weak bonding and weak cleavage and the orientation of common stacking defects in the staurolite lattice any of which could account for preferen tial dissolution in this orientatxon staurolite weathers very slowly relative to most other silicate minerals this may be due to presence of stable kyanite like ribbons in the staurolite structure or to the low site energy of the fe site in the staurolite structure compared to other orthosilicates staurolite weathering is interface limited in most weath erin environments although staurolite contains enough al to coat itsel f completely with a non porous protective surface layer of al hydroxides during weathering protective surface layers apparently form only in some bauxites where a1 is abundant the capacity of staurolite to form protective surface layers around itself in most weath ering environments is a parently limited by its slow weathering which prevents the release o product forming elements especially al at rates sufficient to produce local supersaturation with respect to second ary minerals

regolith residence time and the concept of surface age of the piedmont peneplain the common upland weathering profile on foliated metamorphic rocks on the appalachian piedmont between alabama and maryland includes a 50 cm 1 m thick clay rich soil b horizon over 10 20 m of saprolite the saprolite retains the volume fabric and structure of the underlying parent rock but has lost about one third of the mass of the parent rock where the saprolite is thickest beneath upland drainage divides those divides are of loow slope and relief the flatness of the piedmont drainage divides provides the appearance of a planation surface of accordant summits or peneplain i interpret this flatness to be the result of three active processes volume reduction during compaction of saprolite into soil loss of mass in dissolved solids draining the soil b horizon and loss of mass from the soil surface by erosion of clay size particles the cumulative effects of these upland processes are to convert saprolite into soil to limit soil thickness and residence time and to limit the age of the oldest residual soils on the surface this results in a continual lowering of the piedmont peneplain surface this interpretation is corroborated by evidence of topographic inversion of fluvial gravels since the miocene near the fall line study of baseflow dissolved solids draining piedmont basins indicates a minimum rate of saprolite production of about 4 m ma 1 this minimum rate of production near the fall line is less than the estimated rate of surface lowering and saprolite consumption during the late tertiary and quaternary periods of topographic inversion measurement of cosmogenic 10be inventories in two 15 20 mores of piedmont upland regolith indicate a minimum residence time of residual soil and saprolite of about 1 ma this indicates a possible maximum rate of saprolite production and erosion of about 20 m ma 1 using the best available evidence therefore the typical piedmont upland regolith has a residence time of between 1 and 5 ma residence times may not be the same everywhere and ages may vary systematically across the surface the geomorphic evidence of topographic inversion and similar regolith profiles in other humid temperate and tropical regions strongly suggests that production and removal of piedmont saprolite has been an ongoing quaternary process and that most of the piedmont regolith is significantly younger than 5 ma independent geophysical evidence suggests that the rate of uplift probably involving tilting of parts of the piedmont blue ridge and valley and ridge has averaged between 5 and 20 m ma 1 through the cenozoic

chemical weathering of mafic rocks in boreal subarctic environment northwest russia under influence of glacial moraine deposits abstract chemical weathering of mafic rocks represents substantial sink of atmospheric co2 yet the mechanismes of this process in high latitude regions are poorly understood this work addresses geochemical migration and partitioning of major and trace elements between rock soil and surface waters during chemical weathering of mafic rocks and soil formation under the influence of a glacial moraine in the northwestern russian subarctic we used multidisciplinary approach which included major and trace element chemical analysis sr isotopic measurements and mineralogical structural and microscopic investigations quaternary pleistocene deposits were observed even in the deepest horizons of soil profiles and confirm a strong moraine influence as most soils showed podzolic features chemical and sr isotopic analyses revealed a strong impact of the moraine on soil chemistry and mineralogy mineralogical studies showed the presence of non aeolian quartz and zircon in soils which were not linked to the nature of the parental rocks i e mafic and felsic at the same time we observed the presence of etch pit corrosion on the surface of zircons and feldspars and a newly formed matter adjacent to the surface of primary phases the chemical index of alteration cia showed weak or no weathering of rocks within the soil profile and the weathering intensity scale confirmed the felsic chemical composition of soils developed over mafic and ultramafic rocks analysis of sr radiogenic isotopes demonstrated preferential removal of easily weatherable and less radiogenic minerals over the full depth of soil profile and a more radiogenic signature of the granitic moraine compared to mafic and felsic bedrocks the composition of most surface waters reflected the weathering of silicate rocks but did not allow for distinguishing purely mafic source the chemical weathering rates of ultramafic rocks were calculated to be higher than those for the granitic till but the moraine depositions which dominate this region hide evidence of the real weathering process this could be due to retention of mg and ca in soil due to precipitation of secondary phases such as mg vermiculite or divalent cation adsorption on mineral organic or organo mineral phases as a result weathering rates estimated for the olivinite rock appear to be lower than the weathering rates of mafic rocks reported in other boreal and subarctic regions overall the felsic moraine deposits are capable to sizably decrease the weathering intensity of mafic rocks which should be taken into account for chemical weathering modelling of high latitude regions subjected to glaciation in the past

geochemical comparison of fluid inclusion and present day oil accumulations in the papuan foreland evidence for previously unrecognised petroleum source rocks abstract petroleum production in papua new guinea is limited to the papuan fold belt present day oil accumulations in fields such as iagifu hedinia and gobe are thought to be mainly derived from clay rich jurassic marine source rocks containing terrestrially derived organic matter that were deposited under oxic conditions in this study other generative source rocks in the papuan foreland are indicated using fluid inclusion fi oil data from three wildcat wells koko 1 bujon 1 and kimu 1 which were drilled on the bosavi arch detailed organic geochemistry of these fi oils and associated free oils or oil stains suggests that none of these were generated from the aforementioned jurassic source rocks instead at least three different generative source rocks are indicated firstly a marine probably late cretaceous or younger source rock deposited under reducing conditions is indicated by the bujon 1 fi oil this source rock had a moderate contribution from higher plant organic matter including oleanane and or lupane the bujon 1 fi oil has similarities with fi oils from the iagifu 7x and p nyang 2x wells in the papuan fold belt secondly an algal dominated lacustrine source rock is indicated by the biodegraded koko 1 rft crude oil the unbiodegraded fi oil from koko 1 and the bujon 1 oil stains from the toro and imburu formations these lacustrine oils have high abundances of tricyclic terpanes pregnane homopregnane and gammacerane contain carotane and have high c26 c25 tricyclic terpane ratios the source of the lacustrine oils is inferred to contain moderate amounts of terrestrial organic matter indicated by a dominance of c29 steranes and abundant aromatic higher plant biomarkers and could be gypsiferous shales embedded in oligocene miocene carbonates or triassic age sediments deposited on igneous basement during early rifting associated with the break up of gondwana the kimu 1 fi oil was generated from a mature marine suboxic source rock but has a different geochemical composition to free oil from a similar interval which was derived from a carbonate rich source rock none of the fi oils correlate well with oil families previously described in papua new guinea accordingly the oils recovered from fis in this part of the papuan basin support the presence of laterally varying source rock compositions and qualities and indicate that there are opportunities to develop new charge models for features across the papuan foreland furthermore koko 1 bujon 1 and kimu 1 fi oils have different geochemical compositions compared to the associated free oils or oil stains indicating that each of these localities has a multi phase charge history further work to lower exploration risk in the papuan foreland should be directed to understanding the distribution maturity and expulsion history of these newly recognised potential source rocks

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

residual oil as a tool in migration and filling history analysis of petroleum reservoirs ghazal field saudi arabia abstract stepwise extraction and molecular analysis of non recoverable oil from intact reservoir core plugs is used to provide constraints on the accumulation history of petroleum in the permo carboniferous unayzah reservoirs at the ghazal field saudi arabia when integrated with existing tools such as oil geochemistry gas geochemistry stable carbon isotopes fluid inclusions and thermal modeling the sequential extraction approach helped decode a previously unrecognized component of the hydrocarbon accumulation history in particular it indicates that the region received early petroleum charges that were less mature than currently produced light oil and gas condensates possibly from the prolific early silurian qusaiba shale source rock and other sources this has significant implications for prospecting for additional oil particularly in the north northwest of the ghazal region where paleo oil accumulations may have been displaced or spilled the lower portion of the unayzah reservoir unayzah c remained water wet during early filling of the upper reservoir unit unayzah a and appears to have been filled only by a late oil charge anomalous molecular and carbon isotopic behavior of residual oil extracts from the uppermost segment of the unayzah reservoir where the free oil first of the sequential extracts is less mature 0 95 rc and isotopically lighter 13c 31 15 than the adsorbed oil last sequential extract 1 05 rc 13c 29 65 suggests a late oil contribution or bitumen contamination from the overlying khuff formation

rio tinto sedimentary mineral assemblages a terrestrial perspective that suggests some formation pathways of phyllosilicates on mars abstract the presence of extensive phyllosilicate deposits from the early noachian of mars are often interpreted as having formed from neutral to subalkaline solutions in this paper we examine the rio tinto fluvial basin an early mars analog that hosts clay production and sedimentation along the entire course of the river at rio tinto phyllosilicate minerals including clays and micas are sourced by volcanosedimentary bedrock of rhyolitic and andesitic composition affected by carboniferous hydrothermal alteration pleistocene to modern acidic weathering of those materials chemically altered the volcanic and sedimentary materials to k na clay montmorillonite smectites kaolinite assemblages in paleosoils and fractures while physical weathering degrades phyllosilicates more resistant to acidic attack during the wet season phyllosilicates are eroded transported and deposited from both acidic headwaters and neutral tributaries during the dry season sulfates and nanophase oxyhydroxides co precipitate late summer storms that cause fast flooding events mix illite quartz feldspars iron oxides and other minerals in fluvial deposits where these minerals are stabilized and aggrade until the following wet season as a result chemical precipitates primary phyllosilicates and secondary clays form mineral admixtures that explain the compositional diversity of the fluvial deposits these deposits reveal the persistence of smectites whose occurrence is explained given that the reaction kinetics under acidic conditions of degradation is lowered by seasonal discharges of the river the longevity of phyllosilicate minerals within fluvial deposits depends on climatic and geochemical conditions and processes which are in turn are correlated to temperature persistence of water hydrological cycling hydrogeochemistry and composition of the source materials in the basement these parameters are universal and have to be characterized in order to understand the distribution of mineral composition on any planetary surface including mars

charging of the penglai 9 1 oil field bohai bay basin china functions of the delta on accumulating petroleum abstract the penglai 9 1 pl9 1 oil field which contains china s third largest offshore oil accumulation in place reserves greater than 2 28 10 8 ton or 1 49 10 9 bbl was found in shallow reservoirs 700 1700 m 2297 5577 ft within the most active fault zone in east china the pl9 1 field contains two oil bearing series the granite intrusions in mesozoic mz and both the sandstone reservoirs in neogene guantao ng and neogene minghuazhen nm formation the origins of the pl9 1 field both in terms of source rock intervals and generative kitchens were determined by analyzing biomarker distributions for 61 source rock samples and 33 oil samples the mesozoic granite intrusions which hold more than 80 of the oil reserves in the field were charged in the west by oil generated from the third member es 3 of the shahejie formation in the bodong depression the neogene reservoirs of the pl9 1 field were charged in the west by oil generated from the third member es 3 of the shahejie formation in the bodong depression and in the south by oil generated from the first member es 1 of the shahejie formation in the miaoxibei depression interactive contact between the large fan delta and the mature source rocks residing in the es 3 formation of the bodong depression resulted in a high expulsion efficiency from the source rocks and rapid oil accumulation in the pl9 1 field which probably explains how can this large oil field accumulate and preserve within the largest and most active fault zone in east china

particle sedimentation and diffusive convection in volcanic ash clouds 1 understanding the longevity of volcanic ash clouds generated by powerful explosive eruptions is a long standing problem for assessing volcanic hazards and the nature and time scale of volcanic forcings on climate change it is well known that the lateral spreading and longevity of these clouds is influenced by stratospheric winds particle settling and turbulent diffusion observations of the recent 2010 eyjafjallajokull and 2011 grimsvotn umbrella clouds as well as the structure of atmospheric aerosol clouds from the 1991 mt pinatubo event suggest that an additional key process governing the cloud dynamics is the production of internal layering here we use analog experiments on turbulent particle laden umbrella clouds to show that this layering occurs where natural convection driven by particle sedimentation and the differential diffusion of primarily heat and fine particles give rise to a large scale instability where umbrella clouds are particularly enriched in fine ash this particle diffusive convection strongly influences the cloud longevity more generally cloud residence time will depend on fluxes due to both individual settling and diffusive convection we develop a new sedimentation model that includes both sedimentation processes and which is found to capture real time measurements of the rate of change of particle concentration in the 1982 el chichon 1991 mt pinatubo and 1992 mt spurr ash clouds a key result is that these combined sedimentation processes enhance the fallout of fine particles relative to expectations from individual settling suggesting that particle aggregation is not the only mechanism required to explain volcanic umbrella longevity

chemical and isotopic evidence for secondary alteration of natural gases in the hetianhe field bachu uplift of the tarim basin h2s and co2 are found in elevated concentrations in the reservoirs near the carboniferous ordovician unconformity in the hetianhe field of the tarim basin nw china chemical and isotopic analyses have been performed on produced gases formation waters and reservoir rocks to determine the origin of co2 and h2s and to explain the heterogeneous distribution of isotopic and geochemical characteristics of petroleum fluids it is unlikely that h2s and co2 had a mantle component since associated helium has an isotope ratio totally uncharacteristic of this source instead h2s and co2 are probably the result of sulphate reduction of the light hydrocarbon gases lhg increasing h2s concentrations and co2 co2 c1 4 values to the west of the hetianhe field occur commensurately with increasingly heavy hydrocarbon gas 13c values however thermochemical sulphate reduction is unlikely because the temperatures of the reservoirs are too low no h2s or rare pyrite was detected in deeper reservoirs where more tsr should have occurred and inferred 34s values of h2s from late stage pyrite in the carboniferous and ordovician reservoirs are as low as 24 9 such low 34s values discount the decomposition of organic matter as a major source of h2s and co2 bacterial sulphate reduction of the light hydrocarbon gases in the reservoir possibly coupled indirectly with the consumption of organic acids and anions is most likely the result is the preferential oxidation of 12c rich alkanes due to the kinetic isotope effect and decreasing concentration of organic acids and anions modern formation water stable isotope data reveal that it is possible that sulphate reducing bacteria were introduced into the reservoir by an influx of meteoric water from the west by way of an inversion related unconformity this may account for the apparently stronger influence of bacterial sulphate reduction to the west of the hetianhe field and the consequent greatest decrease of the 13c co2 values and the greatest increase in 13c values of the alkane gases

chemical weathering in a tropical watershed luquillo mountains puerto rico ii rate and mechanism of biotite weathering abstract samples of soil saprolite bedrock and porewater from a lower montane wet forest the luquillo experimental forest lef in puerto rico were studied to investigate the rates and mechanisms of biotite weathering the soil profile at the top of a ridge in the rio icacos watershed consists of a 50 100 cm thick layer of unstructured soil above a 600 800 cm thick saprolite developed on quartz diorite the only minerals present in significant concentration within the soil and saprolite are biotite quartz kaolinite and iron oxides biotite is the only primary silicate releasing significant k and mg to porewaters although biotite in samples of the quartz diorite bedrock is extensively chloritized chlorite is almost entirely absent in the saprolite phyllosilicates phyllosilicate grains are present as 200 1000 m wide books below about 50 cm depth x ray diffraction xrd and electron microprobe analyses indicate that the phyllosilicate grains contain a core of biotite surrounded by variable amounts of kaolinite lattice fringe images under transmission electron microscope tem show single layers of biotite altering to two layers of kaolinite suggesting dissolution of biotite and precipitation of kaolinite at discrete boundaries some single 14 a layers are also observed in the biotite under tem the degree of kaolinitization of individual phyllosilicate grains as observed by tem decreases with depth in the saprolite this tem work is the first such microstructural evidence of epitaxial growth of kaolinite onto biotite during alteration in low temperature environments the rate of release of mg in the profile calculated as a flux through the soil normalized per watershed land area is approximately 500 mol hectare 1 yr 1 1 6 10 9 molmg msoil 2 s 1 this rate is similar to the flux estimated from mg discharge out the rio icacos 1000 mol hectare 1 yr 1 or 3 5 10 9 molmg msoil 2 s 1 indicating that scaling up from the soil to the watershed is possible for mg release the rate of mg release from biotite normalized to brunauer emmett teller bet surface area is calculated using a mass balance equation which includes the density and volume of phyllosilicate grains porewater chemistry and flux and soil porosity the mean rates of biotite weathering calculated from k and mg release rates are approximately 6 and 11 10 16 molbiotite mbiotite 2 s 1 respectively significantly slower than laboratory rates 10 12 to 10 11 molbiotite mbiotite 2 s 1 the discrepancy in scaling down from the soil to the laboratory is probably explained by 1 differences in weathering mechanism between the two environments 2 higher solute concentrations in soil porewaters 3 loss of reactive surface area of biotite in the saprolite due to kaolinite and iron oxide coatings and or 4 unaccounted for heterogeneities in flow path through the soil

geological conditions and geochemical effects of secondary petroleum migration and accumulation the processes of secondary petroleum migration and reservoir filling remain among the least understood steps with respect to the characterisation and economic assessment of a petroleum system spatial heterogeneities of compositions of unaltered petroleum within individual fields have repeatedly been recognised and interpreted to result from compositional changes of multiple petroleum charges during the accumulation history in combination with limited degree of in reservoir mixing of petroleum fluids england w a mackenzie a s mann d u quigley t m 1987 the movement and entrapment of petroleum fluids in the subsurface j geol soc london 144 327 347 leythaeuser d ruckheim j 1989 heterogeneity of oil composition within a reservoir as a reflection of accumulation history geochim cosmochim acta 53 8 2119 2123 most previous attempts to improve this situation have aimed at an understanding of the conditions and effects of the flow of petroleum fluids by studying case histories on regional or field scales in the study reported here we have in addition attempted to reconstruct the mode of filling of sandstone reservoir rocks on pore scales

temporal resolution of an oil charging history a case study of residual oil benzocarbazoles from the gidgealpa field reservoired oil is usually a mixture of multiple discrete petroleum charges unravelling the contribution and character of each charge is amongst the most daring challenges in petroleum geochemistry this paper describes an approach that involves the evaluation of both free and residual oils to reconstruct the history of petroleum accumulation within the multireservoir gidgealpa field located in the cooper and eromanga basins of central australia porewall coating residual oils form by reservoir wetting processes and grow continuously by adsorption of polar compounds retaining molecular information on the first oil that was present in the pore system such sequentially recovered residual oils proved useful in reconstructing the record of oil charges to the gidgealpa ridge using araucariacaean markers for source discrimination and the benzocarbazole a a c ratio bcr for identification of the source region five discrete charging events were distinguished in contrast to most previous studies benzocarbazole distributions were found to be independent of lithofacies organic facies and maturity however alkylated carbazoles did exhibit a pronounced facies dependency the application of alkylcarbazoles as source markers in the study area provides the first evidence of the expulsion of petroleum from cambrian marine source rocks in the underlying warburton basin 2007 elsevier ltd all rights reserved

carbazole distributions in rocks from non marine depositional environments abstract pyrrolic nitrogen compounds have been studied from extracts of the rocks collected from the tertiary saline lacustrine strata in the qaidam basin and the middle lower jurassic coal bearing strata in the turpan basin nw china biomarker signatures revealed the presence of three sample groups related to saline lacustrine conditions in the qaidam basin and freshwater lake and swamp depositional settings in the turpan basin significant differences in carbazole distributions were observed among the sample groups from different depositional environments generally a strong predominance of 1 4 1 5 dimethylcarbazoles over 1 3 1 6 dimethylcarbazoles was found for the qaidam rocks from the saline lacustrine settings with a ratio of 1 3 1 6 1 4 1 5 dimethylcarbazole ranging from 0 35 to 0 66 while enhanced amounts of 1 3 1 6 dimethylcarbazoles relative to 1 4 1 5 dimethylcarbazoles were detected for the turpan samples from the swamp environments with the 1 3 1 6 1 4 1 5 dimethylcarbazole ratio 0 8 samples from the freshwater lake environments in the turpan basin showed intermediate values for the 1 3 1 6 1 4 1 5 dimethylcarbazole ratio in addition a predominance of 2 4 dimethylcarbazole over 2 6 dimethylcarbazole was observed for the qaidam samples whereas most turpan samples showed elevated amounts of 2 6 dimethylcarbazole relative to 2 4 dimethylcarbazole moreover 3 methylcarbazole occurred as the least abundant c 1 carbazole isomer for most qaidam rocks while the turpan samples from swamp settings often showed an enhanced abundance of 3 methylcarbazole the 1 3 1 6 1 4 1 5 dimethylcarbazole ratio was observed to have a positive correlation with 3 4 methylcarbazole 2 6 2 4 dimethylcarbazole and pr ph respectively these observations may indicate that c 1 and c 2 carbazoles with a methyl group at c 3 c 6 prevailed for swamp settings whereas isomers with a methyl at c 4 c 5 were dominant for the freshwater or saline lacustrine environments although variations in benzocarbazoles were detected in the bitumens an obvious correlation was not observed for the different depositional environments

mixing and biodegradation of hydrocarbons in the daerqi oilfield baiyinchagan depression northern china abstract crude oils in the daerqi oilfield vary greatly in viscosities including normal viscous and highly viscous oils they are also dramatically different in thermal maturity from immature to mature based on biomarker parameters according to bulk and molecular geochemical characteristics crude oils can be classified into three groups in this oilfield group i oils are mature and derived from the deeply buried and relatively old source rocks within the tengger formation and the second member of the arshan formation of early cretaceous age group ii oils are immature to marginally mature and derived from the relatively young source rocks that experienced shallow burial within the first member of the duhongmu formation of earlier cretaceous age group iii oils are mixtures of group i and group ii oils with dominance of the group i oils 70 the viscosity is low for the non biodegraded group i and group iii oils 7 1 24 mpa s but very high for the non biodegraded group ii oils e g 433 104 mpa s for the representative oil da12o1 the group iii oils are similar to the group i oils in gross properties e g gross composition and viscosity but are similar to group ii oils in terms of their molecular maturity parameters the oil reservoirs are currently at a shallow depth

petroleum migration and accumulation in the bozhong sub basin bohai bay basin china significance of preferential petroleum migration pathways ppmp for the formation of large oilfields in lacustrine fault basins abstract this paper discusses migration styles and primary controls of petroleum migration pathways in heterogeneous carrier beds in bozhong sub basin bohai bay basin modeling of secondary petroleum migration pathways has been conducted using a simple three dimensional model which assumes that the positions of petroleum migration pathways are controlled by the morphology of the sealing surfaces the modeling results have accurately predicted the petroleum occurrences and have been supported by petroleum geochemical studies most commercial petroleum accumulations are on the predicted preferential petroleum migration pathways ppmp formed by focusing of numerous small petroleum streams close to the kitchens and most large fields petroleum reserves greater than 1 10 8 ton have more than one preferential petroleum migration pathway to convey petroleum to the traps the focusing of petroleum originated from a large area of the generative kitchens into restricted channels is essential for the formation of large oilfields the strong porosity and permeability heterogeneities of the carrier beds and the relatively high prediction accuracy by a model that does not take into consideration of the effect of heterogeneity suggest that the positions of petroleum migration pathways in heterogeneous carrier beds in the lacustrine fault basins are determined primarily by the morphology of the sealing surfaces at regional scales

acidic biomarkers from albacora oils campos basin brazil abstract acidic biomarkers of 8 different oil samples from albacora oil field campos basin brazil were analyzed in order to obtain additional information about biodegradation and thermal evolution for this purpose we selected oils lacustrine saline origin showing different biodegradation levels and at different distances from the fault that acted as migration pathway in the area previous analyses using hydrocarbon biomarkers suggested a mix of oil charges characterizing two distinct oil cycles interrupted by meteoric water circulation in these reservoirs analyses of the naphthenic acid biomarkers revealed a parallelism between the hydrocarbon and the acidic biomarkers notwithstanding there is evidence that the carboxylic acid biomarkers more resistent to biodegradation can provide information on past reservoir history when most important neutral biomarkers have been biodegraded the limitations to the use of these biomarkers are their de novo synthesis in the biodegradation process and the complexity of the sample manipulation prior to the analysis

hydrochemical evolution of groundwater in gabbro of the troodos fractured aquifer a comprehensive approach abstract ophiolites often form complex fractured multi lithological and highly compartmentalized aquifers that are difficult to characterize groundwater chemistry reflects water rock interactions and can provide insights to groundwater recharge mechanisms flow paths and relative residence time a comprehensive hydrogeochemical modelling approach with phreeqc has been developed to identify water rock interactions and simulate groundwater evolution and mixing with connate water in fractured aquifers the methodology was applied in the gabbro aquifers of troodos massif cyprus the geochemical processes generating the most frequently observed water types were reproduced through modelling based on the overall results a generic evolution path has been identified camghco3 mgcahco3 camgnahco3 ca mg na hco3 so4 namghco3so4 naso4 cl group camghco3 and mgcahco3 types were modelled to occur predominantly in early stages of recharge deep unsaturated zones and longer flow paths result in gradual removal of ca 2 and mg 2 from groundwater through secondary mineral precipitation and in an increase of na 2 and so4 2 the most frequently occurring water types camgnahco3 and mgcanahco3 were modelled to occur at later stages of hydro chemical evolution after secondary mineral precipitation and in closed conditions in regional flow where closed conditions with secondary mineral precipitation prevail water types progressively shift from the hco3 to the naso4 end member group in 38 of the 536 samples from gabbro aquifers in troodos groundwater mixing with connate water at a ratio of 0 999 0 001 occurs

constitutive mass balance relations between chemical composition volume density porosity and strain in metasomatic hydrochemical systems results on weathering and pedogenesis relations characterizing the chemical physical and mechanical changes resulting from metasomatic hydrochemical processes are developed using mass balance models which formally link chemical composition to bulk density mineral density volumetric properties porosity and amount of deformation strain rigorous analysis of aqueous solute transport effects is then made possible in a variety of porous media flow environments including chemical weathering pedogenesis soil formation diagenesis ore deposition and enrichment and metamorphism application of these linear constitutive relations to chemical weathering profiles shows that immobile and locally mobile chemical elements with masses conserved on the scale of soil profiles can be accurately identified from analysis of appropriate data arrays and then used as natural geochemical tracers to infer the nature and extent of hydrochemical weathering processes and volume changes during pedogenesis assumptions commonly made in the past about the supposed immobility of certain elements e g ti and zr become unnecessary quantitative differentiation between the effects of residual and supergene fractionation is then easily made these methods are applied to ni rich laterites developed by weathering of ultramafic rocks showing that during ordinary residual enrichment ni is concentrated by as much as 4 protolith peridotite concentrations this occurs simply by silicate mineral dissolution and removal of chemical elements other than ni e g mg with a corresponding reduction in saprolite density and increase in bulk porosity without significant deformation in contrast laterites with mineable concentrations of ni which are similarly undeformed such as the nickel mountain mine in riddle oregon have experienced in addition to residual enrichment strong supergene enrichment by fractionation of ore elements between a leached zone from which ni is extracted and a complementary enriched zone positioned farther along the direction of ground water flow soil forming processes in podzol chronosequences developed on sandy beach terraces of the mendocino coast of california involved soil column collapse of 60 percent by dissolution of silicate minerals in the albic horizon of al and fe leaching and 70 percent dilation expansion in the overlying organic rich layer by root growth the amount of erosion based upon paleosurface reconstructions using the excess mass of fe al pb ga and cu in the zone of supergene enrichment spodic horizon below the ground water table indicates that subsurface erosion by dissolutional collapse is three times that of surficial erosion finally using published chemical data for ti zr and cr on major bauxite deposits in australia where erosion rates are thought to be low we infer that there may have been major amounts of dissolutional collapse to explain the upwards increase of detrital zircon and rutile in weathering profiles

the influence of facies and depositional environment on the occurrence and distribution of carbazoles and benzocarbazoles in crude oils a case study from the gulf of suez egypt abstract two major hinge zones separate the gulf of suez gos of egypt into three tectonic sub provinces namely the northern central and southern sectors based on bulk and molecular parameters the crude oils from the gos can be subdivided into three groups according to their geographical origin from the three sectors the geochemical characteristics of the oils are consistent with inferred depositional environments of anoxic marine carbonate facies in the central sector compared to a more oxic environment that has received an increased proportion of clastic input in the southern sector while the northern is intermediate in character most of the oils cover a relatively narrow maturity range 0 86 0 98 r c in the peak oil window the biomarker parameter ts ts tm is controlled by variations of facies and depositional environment but not by maturity concentrations of pyrrolic nitrogen compounds in the gos crude oils are in general relatively low but show a large range of variability in crude oils of the northern sector a strong predominance of c 4 and c 5 carbazoles over the lower homologues is observed towards the south the relative abundance of carbazole and the methylcarbazoles increases successively variations within the methylcarbazoles and c 2 carbazoles are rather small and therefore are not useful for a straightforward classification of oil families however atypical patterns in some of the oils particularly from the northern sector give evidence for contributions from yet unidentified local sources which might not be of general importance in the gos petroleum province benzo b carbazole is near or even below detection limit in the gos crude oils the benzocarbazole a a c ratio shows a consistently positive correlation with api gravity pr ph and ts ts tm and a negative correlation with the sulphur content based on these observations it is inferred that facies and depositional environment of the relevant source rocks are the major factors influencing the benzocarbazole distributions in the central sector of the gos in which oils are predominantly sourced from carbonates deposited under strongly reducing conditions a a c values are mainly below 0 5 in the southern sector where source rocks were deposited under less reducing conditions and received significant clastic input as well as in the northern sector the a a c values are mainly above 0 5

coupling chemical weathering with soil production across soil mantled landscapes soil covered upland landscapes constitute a critical part of the habitable world our understanding of how they evolve as a function of different climatic tectonic and geological regimes is important across a wide range of disciplines and depends in part on understanding the links between chemical and physical weathering processes extensive previous work has shown that soil production rates decrease with increasing soil column thickness but chemical weathering rates were not measured here we examine a granitic soil mantled hillslope at point reyes california where soil production rates were determined using in situ produced cosmogenic nuclides 10be and 26al and we quantify the extent as well as the rates of chemical weathering of the saprolite from beneath soil from across the landscape we collected saprolite samples from the base of soil pits and analysed them for abrasion ph as well as for major and trace elements by x ray fluorescence spectroscopy and for clay mineralogy by x ray diffraction spectroscopy our results show for the first time that chemical weathering rates decrease with increasing soil thickness and account for 13 to 51 per cent of total denudation we also show that spatial variation in chemical weathering appears to be topographically controlled weathering rate decreases with slope across the divergent ridge and increases with upslope contributing area in the convergent swale furthermore to determine the best measure for the extent of saprolite weathering we compared four different chemical weathering indices the vogt ratio the chemical index of alteration cia parker s index and the silicon aluminium ratio with saprolite ph measurements of the cia were the most closely correlated with saprolite ph showing that weathering intensity decreases linearly with an increase in saprolite ph from 4 7 to almost 7 data presented here are among the first to couple directly rates of soil production and chemical weathering with how topography is likely to control weathering at a hillslope scale copyright 2006 john wiley sons ltd

petroleum inclusions in sedimentary basins systematics analytical methods and applications abstract fluid dynamics in sedimentary basins is of tremendous interest both from a scientific and an economic point of view integration between fluid inclusion and present day fluid data provides the time aspect necessary for reconstruction of fluid flow paths and can be used for mapping fluid dynamics both on a regional basin scale or on the more local scale of petroleum reservoirs this paper presents a review of analytical and modelling methods for petroleum in fluid inclusions essentially four types of data for petroleum inclusions can be established through analysis and modelling 1 textures which give indirect information of the time aspect 2 fluid composition 3 fluid properties and 4 pressure temperature of trapping during the last decade development of analytical methods for determination of inclusion fluid compositions has taken place traditional correlation studies for characterisation of maturity and source facies may now therefore include fluid inclusion data the development has also been directed towards an improved understanding of the physical properties of petroleum inclusions although these methods are in their early stages concerning precision and accuracy data necessary for fluid flow modelling such as fluid densities viscosities pressure and temperature can be estimated

silicon cycling by plant and its effects on soil si translocation in a typical subtropical area abstract plants play an important role in silicon si cycling of terrestrial ecosystems however how plant si is related to soil si translocation and transformation in subtropical areas with ample weatherable silicates and agricultural activities is largely unknown three typical watersheds with different cropland and forest configurations in subtropical china were selected to investigate the biomass of different plant species including coniferous forest bamboo and paddy as well as the geochemical composition of soil rock vegetation and water the main soil types are lithic udorthents lithic dystrudepts and typic epiaquepts derived from granite si concentrations in rock soil plant and water as well as si cycling fluxes were measured the results show that although a large amount of si is cycled by plants weathering and runoff contribute similarly to or even more significantly than plant cycling high si bio accumulators assimilate and return more si than low si bio accumulators and also cause more phytolith si to be added to the surface soil which decreases desilification rate of surface soil agricultural activities increase silicate weathering stream water si concentrations are not affected by plant si cycling thus both agricultural activities and plant species affect si translocation in contrast to results from strong tropical weathering environments si cycling by plants in this subtropical area with abundant weatherable silicates does not dominate si loss from soil rather it promotes silicate weathering and controls si redistribution in soil profiles

mineralogical and textural criteria for recognizing remnant cenozoic deposits on the piedmont evidence from sparta and greene county georgia u s a two soilkaprolite profiles from ridge crest sites in central georgia were investigated for mineralogical and textural trends to help elucidate the relationship between cenozoic coastal plain deposits landward of the fall line and the piedmont result from the study of a 10 5 m thick sequence in sparta georgia reveal a deep lateritic profile showing complete loss of plagioclase gradational loss of k feldspar vermiculitization of biotite and precipitation of kaolinite and halloysite within the lower 6 m the middle section of the sequence is characterized by authigenic kaolinite halloysite and goethite the upper 1 35 m is quartz rich but also contains k feldspar hydroxy interlayered vermiculite hiv and gibbsite a comparison of grain shape and size indicates a slight textural difference between the upper and middle sections with the fine sand grains of the upper section being more spherical and less angular preliminary results from the study of a 6 35 m sequence in greene country georgia also reveal a deep lateritic profile a sharp soil fabric contact from slightly mottled to highly mottled occurs 3 1 m below the surface this profile is characterized by a bimodal clay mineral abundance distribution as a function of depth this includes an antithetical relationship between kaolinite and hiv where hiv is abundant at the surface decreases with depth increases again at the fabric interface and then decreases with depth it is suggested that the profiles contain paleosols that are a result of deep lateritic weathering subsequent allochthonous deposition of a sedimentary cap and then further chemical weathering the exact relationship between the depositional ages of the veneers and the age duration and climatic conditions for past weathering events are currently poorly constrained recognition of paleo weathering surfaces has potential importance for our understanding of the record of geologic and paleoclimatic change in the southeastern united states identification of such cenozoic sedimentary veneers and paleosols on the piedmont also has potential importance for land use practices from the standpoint of better understanding regional soil terrain properties

applications of petroleum geochemistry to exploration and reservoir management abstract petroleum geochemistry improves exploration efficiency by accounting for many of the variables that control the volumes of crude oil and natural gas available for entrapment including source rock distribution richness and quality thermal maturity and the timing of generation migration accumulation relative to trap formation it is most powerful when used with other disciplines such as seismic sequence stratigraphy and reservoir characterization four key technology milestones form the basis for most modern applications of geochemistry to exploration these are the concepts and applications of 1 petroleum systems and exploration risk 2 biomarkers stable isotopes and multivariate statistics for genetic oil oil and oil source rock correlation 3 calibrated three dimensional thermal and fluid flow modeling and 4 controls on petroleum composition by secondary processes petroleum geochemistry offers rapid low cost evaluation tools to aid in understanding development and production problems some technology milestones in reservoir geochemistry include 1 assessment of vertical and lateral fluid continuity 2 determination of proportions of commingled production from multiple zones and leaky casing 3 prediction of oil quality in reservoir zones and 4 prediction of gas oil and oil water contact locations as described in the conclusions future research will continue a trend toward predictive geochemistry examples of predictive tools that draw major research support include piston core surveys to assess deepwater petroleum systems prior to drilling and three dimensional basin modeling to predict the regional timing of generation migration and accumulation of petroleum among other research objectives models are needed to better predict the distribution and quality of petroleum in reservoirs

mechanisms of petroleum accumulation in the bozhong sub basin bohai bay basin china part 1 origin and occurrence of crude oils the origin of the fourteen major oil fields in the bozhong sub basin bohai bay basin was studied based on the results of rock eval pyrolysis on more than 700 samples and biomarker analysis on 61 source rock samples and 87 oil samples the three possible source rock intervals have different biomarker assemblages and were deposited in different environments the third member of the oligocene dongying formation e3d3 32 8 30 3 ma in age is characterized mainly by high c19 c23 tricyclic terpane 0 75 high c24 tetracyclic terpane c26 tricyclic terpane 2 5 low gammacerane c30 hopane 0 15 and low 4 methyl steranes c29 steranes 0 15 ratios and was deposited in sub oxic to anoxic environments with significant terrigenous organic matter input the first e2s1 35 8 32 8 ma and third e2s3 43 0 38 0 ma members of the eocene shahejie formation have low c19 c23 tricyclic terpane and low c24 tetracyclic terpane c26 tricyclic terpane ratios and were deposited in anoxic environments with minor terrestrial organic matter input but have different abundances of 4 methyl steranes and gammacerane the hydrocarbon generating potential and biomarker associations of these three source rock intervals were controlled by tectonic evolution of the sub basin and climate changes three oil families derived from e2s3 e2s1 and e3d respectively and three types of mixed oils have been identified all large oil fields in the bozhong sub basin display considerable heterogeneities in biomarker compositions and originated from more than one source rock interval which suggests that mixing of oils derived from multiple source rock intervals or multiple generative kitchens and or focusing of oils originated from a large area of a generative kitchen is essential for the formation of large oil fields in the bozhong sub basin e2s3 and e2s1 derived oils experienced relatively long distance lateral migration and accumulated in traps away from the generative kitchen e3d3 derived oils had migrated short distances and accumulated in traps closer to the generative kitchen such a petroleum distribution pattern has important implications for future exploration there is considerable exploration potential for dongying derived oils in the bozhong sub basin and traps close to or within the generative kitchens have better chance to contain oils generated from the dongying formation

apparent gibbsite growth ages for regolith in the georgia piedmont abstract carbon bound in gibbsite collected from a residual weathering profile developed on a paleozoic granite in the georgia piedmont was examined for its 14 c content and found to be geologically young the study site located at the panola mountain research watershed has developed a granite saprolite soil regolith in which 14 c gibbsite model ages deep within the profile c horizon average about 8000 years near the surface a and b horizon 14 c gibbsite model ages range from 2100 to 4200 years quartz has acquired 26 al and 10 be inventories suggesting a near surface residence time of at least 90 000 years this age disparity supports the notion that secondary minerals undergo significant recrystallization as weathering fronts propagate into the landscape combining the results of 14 c 26 al and 10 be analyses offers the potential to assess differential rates of chemical weathering and continental denudation to understand better the links between rates of silicate rock weathering climate and soil residence times

giant irregular pockmark craters in the palaeogene of the outer moray firth basin uk north sea a cluster of irregular pockmark craters of palaeogene age in block 15 18 in the outer moray firth uk north sea have been mapped on 3d seismic data with well control the craters range from 0 5 to 4 km in diameter between 50 and 200 m in depth and have been buried by tertiary subsidence and sedimentation to present day depths of between 1000 and 1400 m sub sea they are circular to elliptical in plan view and are located in a delta front and upper pro deltaic slope position on the dornoch delta the structures are confined to the top of the lower eocene balder formation and regional mapping across the moray firth basin shows they are restricted to an area of ca 15 15 km2 well data show that the craters are sand filled and have excavated an argillaceous and tuffaceous unit the crater filling sands are sealed by overlying mudstone units planar wing like features emanate from the margins of the craters well control indicates that these seismically identified wings consist of sandstone suggesting that the craters have been modified by an episode of sand remobilisation and injection the proposed mechanism for the formation of these structures is large scale fluid eruption probably shallow gas at the early eocene seafloor these craters are significantly larger in size than those typically observed on contemporary sea floors we argue that the gas is more likely to have been sourced from deeper jurassic or carboniferous sediments within the witch ground graben than from shallow biogenic origins these structures rank in scale alongside the largest known pockmarks and demonstrate that natural fluid and hydrocarbon seeps have a long ancestry in this basin

weathering of ilmenite from granite and chlorite schist in the georgia piedmont ilmenite grains from weathering profiles developed on granite and ultramafic chlorite schist in the georgia piedmont were studied for evidence of morphological and chemical alteration ilmenite rich concentrates from the fine sand 90 150 m component were studied to test the assumption that there is no difference between ilmenite in the parent rock and that in colluvium delivered to primary drainage systems ilmenite grains in the granite profile are rounded to subhedral and commonly contain hematite exsolution blebs dissolution pits are observed along the boundaries of the exsolution blebs with goethite occurring as an alteration product ilmenite grains in the schist profile occur as fractured anhedral grains with uncommon lamellae of rutile grain fractures are filled with goethite and hematite particularly in the b horizon ilmenite from the granite profile is mn rich 7 15 mol mntio3 whereas ilmenite from the schist profile contains only 1 2 mol mntio3 and up to 8 mol mgtio3 two populations of grains develop in both profiles grains with abundant exsolution blebs and fractures alter through a proposed two step reaction mechanism it is proposed that ilmenite first undergoes a solid state transformation to pseudorutile via an anodic oxidation mechanism oxidized fe and mn diffuse from the structure and precipitate as goethite and mno2 pseudorutile is ephemeral and undergoes incongruent dissolution to form anatase hematite and goethite the second population of grains experienced only slight oxidation and dissolution on grain surfaces and they persist through the weathering profile the fe2 content of competent ilmenite grains is somewhat lower in the c horizon compared with grains in the host rock in horizons above the c horizon the fe2 contents of the ilmenite are similar to those in the host rock this study shows that using ilmenite minor element chemistry as a tracer for sediment provenance is a valid technique however textural features of ilmenite in colluvium may be distinct from those in the parent rock also the production of secondary phases such as anatase goethite and hematite in soil profiles results in part from the alteration of ilmenite

petroleum migration and mixing in the pearl river mouth basin south china sea abstract two oil groups have been investigated in the pearl river mouth basin using their geochemical characteristics in combination with source data the two oil groups may be extrapolated into two end member oils petroleum populations a and b the oil population a with abundant 4 methylsteranes derived from the deeper wenchang source rocks migrated and accumulated earlier the oil population b with absent 4 methylsteranes was expelled from the enping source rocks and is associated with a relatively later phase of migration and accumulation the two distinctive oil populations migrated updip through the marine blanket like sandstone carriers within the zhuhai formation to accumulate in a series of traps along the main migration pathways at different times most of the accumulations are mixtures of the two end member oils the variations of 4 methylsterane concentrations in the accumulations can be related to the contributions from the two sources the oils which migrated furthest contain greater contributions from the wenchang source rocks whereas those with shorter migration paths have greater contributions from the enping sources the later migrated oils closer to the depression areas are highly mature and the former oils in the liuhua oil fields are of relatively low maturity which may indicate the main migration direction along the hui liu structure ridge hlsr oils with abnormally high maturity in the middle of the hlsr may suggest oil filling points from which branch conduits connected the source kitchens to the main migration pathway oils with abnormally low maturities may reveal minor contributions from some small sags in the dongsha massif in a latest phase

clay transformation and pedogenic calcite formation on a lithosequence of igneous rocks in northwestern iran abstract knowledge about the pathways of pedogenic calcite formations and clay transformations on igneous rocks in semiarid regions plays a vital role in the commentary of soil development on these rocks the present study was conducted to explore the weathering stages and pathways for the formation of pedogenic calcite in soils developed on selected plutonic and volcanic rocks in a semiarid climate in north western iran the soils developed on plutonic rocks were found to be in the primary stage of weathering with very few pedogenic calcites except for soil developed on alkali granite which contained few calcitic pedofeatures calcitic crystallitic b fabrics and calcitic pedofeatures were found in all soils developed on volcanic rocks in situ weathering of ca bearing minerals such as plagioclases amphiboles and pyroxenes could be the possible explanation for the accumulation of pedogenic calcite in the absence of calcareous parent rocks in the studied area micritic calcite was observed to be the dominant form in most of the soils developed on volcanic rocks indicating a rapid precipitation of calcium carbonate smectite kaolinite and mica illite were present in the soils developed on plutonic rocks and the clay content in these soils was less than that of the volcanic rocks feldspars plus mica were supposed to be the most likely source minerals for the formation of pedogenic illite which could be consequently transformed into smectite in these semi arid environments smectite mica illite and kaolinite were the most abundant clay minerals in the soils developed on dacite and andesite rocks while a minor quantity of vermiculite occurred only in andesite derived soils smectite as the dominant mineral and some kaolinite with fairly constant variation in content with depth were observed in the soils formed on hornblende andesite and pyroxene andesite this could indicate that the smectite had the authigenic origin and was formed most likely from the weathering of plagioclase hornblende and pyroxene in general in situ crystallization of pedogenic carbonates and high quantities of smectite in the clay fraction confirmed that the soils formed on volcanic rocks were more developed than those on plutonic rocks in the studied semiarid region moreover our results showed that releasing calcium from ca bearing minerals in igneous rocks in conjunction with biological activities resulted in pedogenic calcite formation

maturity effect on carbazole distributions in source rocks from the saline lacustrine settings the western qaidam basin nw china abstract carbazole distributions and biomarker compositions have been investigated in a series of source rocks from the tertiary strata in the western qaidam basin nw china typical biomarker signatures high gammacerane high c 35 hopane and low pr ph indicate a saline lacustrine environment maturity parameter c 29 sterane s s r ranges from 0 06 to 0 58 indicating immature ca 0 35 stages significant variations were observed for carbazole distributions with maturation as for c 1 carbazoles the relative amounts of 1 mc methylcarbazole show a decrease trend in the immature stage and an increase trend in the mature stage while the other three isomers 2 3 and 4 mcs show a generally opposite change indicating a two stage variation as for c 2 carbazole isomers complex variations were observed for their relative amounts an overall increase for 1 7 dmc dimethylcarbazole a slight two stage change for 1 8 and 1 3 dmcs and a marked two stage variation for 2 4 2 5 and 2 6 dmcs comparison of the distributions of carbazole and benzocarbazoles revealed a preferential generation for benzocarbazoles at high maturity levels benzocarbazole ratio a a c varies only in a narrow range 0 52 0 61 in the entire maturity range suggesting limited maturity dependence the results here support the idea that carbazole distributions have strong maturity effect in a wide maturity range and the two stage variations for some pyrrolic nitrogen isomers may indicate their different geochemical controls between the immature and mature stages

meta gabbro weathering in the georgia piedmont usa implications for global silicate weathering rates abstract the mineral assemblages in a vertical weathering profile developed over a meta gabbro terrain were studied for their stoichiometry and relative abundances the site is located in the piedmont province in the southeast portion of the appalachians orogenic belt in a forested residual landscape and a temperate climate the soil is classified as a fine mixed thermic ultic hapludalf and defined by distinct a b and c horizons with thicknesses of 17 62 and 250 cm respectively the primary mineral assemblage consists of 44 wt andesine 40 hornblende 6 quartz 4 biotite 3 ilmenite titanomagntite rutile sphene grains and 3 epidote quantitative xrd detailed xrd clay mineralogy and thin section petrography revealed the incipient breakdown of the primary minerals to vermiculite after biotite oxidation randomly ordered mixed layer mica vermiculite smectite as grain coatings kaolin group minerals after mafic silicate dissolution goethite and hematite vermiculite after biotite expandable clay coatings and all the primary minerals with exception to quartz are dissolved away from the a horizon hydroxy interlayered vermiculite and minor amounts of gibbsite occur as tertiary phases in the a horizon using mineral stoichiometries and average abundances for the parent rock and c b and a horizon estimates of primary mineral mass loss were determined the bicarbonate to silica ratio expected from the mineral loss reactions is 6 times higher than the ratio observed in average groundwater of the georgia piedmont this suggests that although weathering of mafic terrains is important to the long term process of transferring co 2 to the oceans the present day contribution of silicate weathering in temperate climates may be more largely influenced by the weathering of felsic terrain

chemical speciation of redox sensitive elements during hydrocarbon leaching in the junggar basin northwest china abstract bleaching related to seepage of petroleum fluids and subsurface migration of crude oil and natural gas can alter the chemical and mineralogical properties of rocks while concurrently depleting hydrocarbon reservoirs mud volcanoes constitute one type of petroleum seepage present in several areas on the southern margin of the junggar basin in the xinjiang uygur autonomous region nw china the results of xrd xrf xanes and mossbauer spectroscopy on rock samples collected from areas affected by these mud volcanoes revealed an enrichment of certain minerals and elements as well changes in mineralogical molecular or ionic carrier species after bleaching reddish sedimentary rocks showed depletion in silica and enrichment of calcium magnesium manganese and iron other elements including aluminum potassium sodium and titanium were largely unchanged reduced iron and sulfur compounds predominated in the bleached rocks producing changes in color from the original reddish into green deep gray and black iron and calcium were associated with carbonates indicating carbonation of these elements during the bleaching processes manganese also appeared to be associated with carbonate though not with sulfate even though sulfate was present in the bleached rocks alkaline conditions were apparently the dominant because reduced manganese would have been absent under acidic condition the alteration of certain minerals clay minerals in particular was also observed in bleached rocks the alteration of smectite group minerals to chlorite and muscovite for example mineralogical and geochemical changes in rocks bleached by hydrocarbon fluids could provide a better overall understanding of bleaching processes and may have applications in surface geochemical exploitation and remote imaging

reactant product textures volume relations and implications for major element mobility during natural weathering of hornblende tallulah falls formation georgia blue ridge u s a natural weathering of hornblende from the tallulah falls formation georgia u s a takes place under thoroughly leached oxidizing conditions at the earliest stage of weathering corrosion of hornblende forms denticulated terminations with only minimal porosity apparent within the partially pseudomorphic kaolin group weathering product or between it and the reactant mineral isovolumetric replacement of hornblende by kaolin group clay or precursor products implies inheritance of parent mineral silica tetrahedra by the weathering products and largely immobile behavior of si during early weathering aluminum normally considered immobile or minimally mobile during weathering must be imported into early stage weathering products more advanced weathering of hornblende forms denticulated terminations separated from the earlier formed products by a large continuous peripheral void porosity is much more conspicuous at this stage late stage ferruginous products precipitate from fe mobilized in solution dissolved fe to form the late stage goethite can be entirely derived from the parent hornblende requiring only short transport distances for aqueous fe between the source parent mineral and the location of product precipitation textural and volumetric relationships between naturally weathered hornblende and its partially pseudomorphic weathering products suggest structurally controlled immobility of much parent mineral si and considerable mobilization of al at early stages of weathering but at more advanced stages of weathering the textural and volumetric relationships are consistent with immobility of al and fe and leaching of substantial si and all base cations

variation in alkylphenol distributions in a homogenous oil suite from the dhahaban petroleum system of oman as part of a study to determine the effect of migration processes on the abundance and distribution of alkylphenols in crude oils we have analysed a homogeneous suite of 15 oils from the dhahaban petroleum system in oman that lies along a secondary migration pathway in a foreland basin setting geochemical parameters based on aliphatic hydrocarbon biomarkers and aromatic hydrocarbon concentrations and ratios suggest a similar maturity and source facies for the oils despite the wide variation in relative petroleum migration distance up to c 260 km given the similarity in source facies and maturity characteristics of the oils we conclude that the observed variations in alkylphenol concentrations in this sample suite are controlled mainly by secondary migration processes the majority of the oils are not degraded and in these samples we observe a significant decrease in total alkylphenol concentration within the first c 50 km relative migration distance supporting similar studies on north sea petroleum systems and suggesting that alkylphenols may be useful as geotracers over shorter migration distances there is little evidence of systematic migration distance related variation in the relative abundance of individual alkylphenol isomers or homologue groups the alkylphenol distributions in two biodegraded oils in the sample suite both from relatively shallow reservoirs were dominated almost completely by phenol and this is discussed in the context of the microbial production and alteration of phenols and the influence of water washing on the content and distribution of phenols in crude oils

oil filling history of the ordovician oil reservoir in the major part of the tahe oilfield tarim basin nw china abstract the ordovician oil reservoir in the tahe oilfield northern tarim basin is so far the largest marine oil reservoir in china ordovician oil was sampled from 73 exploration production wells in the oilfield according to oil oil correlation all the ordovician oil samples belong to the same oil population of mature to high mature phase based on the coexisting intact n alkane series evident ucm and 25 norhopanes in the oil as well as the bimodal distribution pattern of homogenization temperatures t h ranging from 80 to 100 c and from 115 to 135 c respectively in fluid inclusions within the reservoir rocks it is concluded that the oil reservoir has been twice charged during its oil filling history by means of 1d basin modeling the measured t h values can be related to relevant geological ages of 429 415 ma and of 8 2 ma respectively i e the middle to late silurian and the miocene to pliocene representing two phases of oil filling and entrapment using independent molecular parameters e g the 4 1 mdbt ratio and total concentrations of pyrrolic n compounds as indicators to reconstruct the oil filling process in the reservoir oil filling pathways can be traced and mapped the general orientation of oil filling is from south to north in the oil reservoir therefore it can be predicted that its source kitchen should be on the south side of the oilfield most probably at the shuntuoguole uplift between the awati and manjiaer depressions

the controls on the composition of biodegraded oils in the deep subsurface part 1 biodegradation rates in petroleum reservoirs abstract biodegradation rates in oilfields have been assessed conservatively using whole oil column minimum rate estimates diffusion controlled oil column compositional gradient modelling and mixed oil kinetic models biodegradation rate constants first order are around 10 6 10 7 yr 1 for hydrocarbons in the degradation zones these corresponding well with zero order field wide minimum rate estimates of about 10 8 kg hydrocarbons kg oil year for the whole oil column with biodegradation induction times of around 1 2 ma to perturb an entire oil column for light oil reservoirs and 10 20 ma for heavy oil reservoir degradation the results indicate that where we see continuous gradients in the oil columns degradation must have been occurring episodically for many millions of years to remove the n alkanes from an oil i e about 10 of an oil around ca 15 ma is needed for a heavy oil ca 5 ma for a light n sea oil the timescales of oilfield degradation and filling are thus very similar and consequently the degree of biodegradation will be substantially controlled by oilfield charge history assessment of mixed degraded non degraded oil occurrence provides an independent confirmation that these rates are realistic and that timescales of degradation and field charging are similar the maximum effective rate constant of degradation ultimately controlled by the limiting effect of diffusion of alkanes to the oil water contact owc ca 10 4 yr 1 for a 130 m thick oil column first order rate constant is well above the estimated rate constants indicating oil biodegradation rate is not limited by electron donor supply i e hydrocarbons but by supply of nutrients or oxidants this suggests that diffusive transport of nutrients and electron acceptors in the aquifer to the site of biodegradation may be adequate to maintain the low rate biosphere

an example of enhanced tephra deposition driven by topographically induced atmospheric turbulence spatial variations in the thickness and grain size characteristics of tephra fall deposits imply that tephra depositional processes cannot be fully captured by models of single particle sedimentation from the base of the eruption plume here we document a secondary thickness maximum in a 9 75 ka tephra fall deposit from chaiten volcano chile cha1 eruption this secondary thickness maximum is notably coarser grained than documented historical examples being dominated by medium grained ash and an origin via particle aggregation is therefore unlikely in the region of secondary thickening we propose that high levels of atmospheric turbulence accelerated particles held within the mid to lower troposphere 0 to 6 km towards the ground surface we suggest that this enhancement in vertical atmospheric mixing was driven by the breaking of lee waves generated by winds passing over elevated topography beneath the eruption plume lower atmospheric circulation patterns may exert a significant control on the dispersal and deposition of tephra from eruption plumes across all spatial scales particularly in areas of complex topography

fractionation of benzocarbazoles between source rocks and petroleums the concentrations of the a and c isomers of benzocarbazoles in a number of crude oils and source rock bitumens were obtained by in house methods and from reported published data the changes in benzocarbazole concentrations and the benzocarbazole a a c ratio relating to source maturity facies and migration are described with increasing source maturity in north sea oils and source rocks up to 0 85 vitrinite reflectance equivalent benzocarbazole concentrations increase due to generation followed by a decrease above 0 85 vitrinite reflectance equivalent due to expulsion dilution by newly generated hydrocarbons comparison of benzocarbazole concentrations between reservoired petroleum and related source petroleum revealed a concentration bias in favour of source petroleum where concentrations of benzocarbazoles reached up to 10 times that found in equivalent reservoired petroleum the differences in benzocarbazole concentrations between related oils and source rocks indicate that the major fractionation is introduced during primary migration and expulsion because when secondary migration is limited as in the miller field we see extensive benzocarbazole fractionation between reservoired petroleum and associated source petroleum the relationships between source rock toc content and petroleum benzocarbazole concentrations and a a c ratios indicate that source organic matter exerts a strong influence on benzocarbazole distributions the introduction of a reservoir source fractionation parameter rsfp defined as the ratio between the concentrations of benzo a benzo c carbazole in reservoired petroleum versus the concentration of benzo a benzo c carbazole in source petroleum enables description of the relationship between reservoired petroleum and source petroleum from different petroleum systems petroleum deriving from clastic source rocks demonstrated high levels of benzocarbazole fractionation between reservoired petroleum and source petroleum during primary and secondary migration compared to petroleum deriving from carbonate systems the rsfp parameter may also be used to examine fractionation effects during migration between different compound types the more polar benzocarbazoles are fractionated more strongly than dibenzothiophene and phenanthrene between reservoired petroleum and source petroleum whereas sometimes source maturity signals do dominate the benzocarbazole signals in migrated oils in other circumstances often associated with clastic source rocks no clear maturity signal is transferred to migrated oils

a dynamic biodegradation model suggested by petroleum compositional gradients within reservoir columns from the liaohe basin ne china abstract a suite of petroleum reservoir extracts from the liaohe basin ne china was analyzed to investigate the effects and controls of biodegradation on petroleum composition systematic changes seen as marked gradients in petroleum bulk composition component concentrations and molecular indicators have been observed in two biodegraded oil columns in the es3 column 1700 1850 m biodegradation has removed substantial amounts of normal and isoprenoid alkanes more severe biodegradation occurs in the shallower es1 column 1500 1650 m with both steranes and hopanes being partially removed temperature has an overall control on biodegradation in the two columns a lower reservoir temperature leading to a higher degree of biodegradation however observed variation in the degree of biodegradation in the es3 column at different sites is controlled by water leg size with a higher level of degradation being associated with a thicker water leg the supply of nutrients from the water leg is thought to have a significant impact upon the degree of biodegradation in addition to water leg size nutrient supply the compositional gradients also are controlled by the relative rate of mixing of fresh oil charge gradients can only be conserved in biodegraded petroleum columns if the rate of diffusive mixing is similar to or lower than the rate at which the hydrocarbons are removed a biodegradation model is proposed that couples geochemical and geological factors to provide a coherent approach for assessing the impact of degradation on petroleum our geochemical study indicates that biodegradation occurs mainly within a narrow region at or near the base of the oil column the stable compositional gradients are produced after an initial induction period involving diffusive transport of alkanes to the oil water contact owc and diffusion of biodegradation products such as 25 norhopanes and other metabolites away from the reaction site the mixing of continuously charged oil with residential biodegraded oil by diffusion may be considered as one of the most important factors controlling the biodegradation process the conceptual model illustrates all of these processes and opens the possibility of model driven prediction of oil properties and sweetspot location in reservoirs

hydrogen isotopic compositions of individual alkanes as a new approach to petroleum correlation case studies from the western canada sedimentary basin isotopic compositions of carbon bound hydrogen in individual n alkanes and acyclic isoprenoid alkanes from a number of crude oil samples were measured using gas chromatography thermal conversion isotope ratio mass spectrometry the precision of this technique is better than 3 for most alkanes compared to the large range of d variation among the samples up to 160 the oils were selected from major genetic oil families in the western canada sedimentary basin with source rocks ranging in age from ordovician and possibly cambrian to cretaceous the hydrogen isotopic composition of alkanes in crude oils is controlled by three factors isotopic compositions of biosynthetic precursors source water d values and postdepositional processes the inherited difference in the lipid s biosynthetic origins and or pathways is reflected by a small hydrogen isotopic variability within n alkanes but much larger differences in the d values between n alkanes and pristane phytane the shift toward lighter hydrogen isotopic compositions from paleozoic to upper cretaceous oils in the wcsb reflects a special depositional setting and or a minor contribution of terrestrial organic matter the strong influence of source water d values is demonstrated by the distinctively lower d values of lacustrine oils than marine oils and also by the high values for oils with source rocks deposited in evaporative environments thermal maturation may alter the d values of the alkanes in the oil to some extent but secondary oil migration does not appear to have had any significant impact the fact that oils derived from source rocks that could be of cambrian age still retain a strong signature of the hydrogen isotopic compositions of source organic matter and source water indicates that d values are very useful for oil source correlation and for paleoenvironmental reconstructions

accumulation and mixing of hydrocarbons in oil fields along the murteree ridge eromanga basin south australia abstract the murteree ridge is a focus for up dip migration from two major hydrocarbon kitchens within the intracratonic cooper carboniferous triassic and eromanga jurassic cretaceous basins of south australia the accumulation histories of nine oil fields along and adjacent to the ridge have been reconstructed by sequential solvent extraction and analysis of residual oils in sandstone core plugs from their stacked reservoirs four cretaceous reservoir units received multiple oil charges that varied widely in source affinity from mostly jurassic and or cretaceous to overwhelmingly permian in origin the distributions of residual oil saturations in live and palaeo columns are consistent with the existence of two compartments with the uppermost pools cadna owie murta showing the highest permian inputs these accumulations represent the earliest escape of low maturity cooper sourced oil into overlying eromanga strata this initial charge was displaced upwards into the shallower traps by subsequent hydrocarbon pulses three separate permian charge episodes can be recognised the corresponding dst oils 0 6 0 7 rc represent either the compositional average of all charges to their respective reservoirs or a continuation of the alternating filling pattern observed for successive charges oils in the hutton jurassic reservoir of the outlying kerrina and mudlalee fields to the northeast appear to be mixtures of two distinct early permian oil families variably co mingled with locally derived jurassic and possibly cambrian hydrocarbons

quantitative fluorescence techniques for detecting residual oils and reconstructing hydrocarbon charge history abstract two new fluorescence techniques quantitative grain fluorescence qgf and quantitative grain fluorescence on extract qgf e can detect palaeo oil zones and current residual oil zones in petroleum wells respectively qgf and qgf e measure the fluorescence emission spectra of trace fluorescence from reservoir grains and their extracts qgf is measured on dry disaggregated reservoir grains after a cleaning procedure involving solvent hydrogen peroxide and acid whereas qgf e is measured on the solvent extract from the qgf cleaned grains palaeo oil zones have distinct qgf spectra with spectral peaks between 375 and 475 nm and elevated fluorescence intensities compared with spectra for rocks that have always been water saturated current and residual oil zones have distinct qgf e spectra with spectral peaks at around 370 nm and elevated qgf e intensities compared with that for current water zones both qgf and qgf e responses increase upwards from the palaeo oil water and residual oil water contacts respectively an oil producing well from timor sea nw australia was investigated in detail using the qgf and qgf e techniques to illustrate how they can be used to reconstruct hydrocarbon migration history

geochemical characteristics and implications of hydrocarbons in reservoir rocks of junggar basin china abstract a practical sequential extraction approach has been applied to two core samples collected from oil zones of triassic sandstones in junggar basin northwest china five bitumen fractions were obtained from each sample using this approach these fractions are free oil components in inter granular pores bitumen 1 adsorbed oil components on grain surfaces and liberated by hcl treatment bitumen 2 oil bearing fluid inclusions hosted by grains bitumen 3 and adsorbed oil components on clay mineral surfaces and liberated by hcl and hcl hf treatments bitumens 4 and 5 striking differences have been observed both in bulk compositions and in aliphatic biomarker distributions e g terpanes and steranes among the five bitumen fractions this phenomenon is ascribed to the indigenous compositional variations and differential maturation behaviors between adsorbed oil components in a network of polar compounds resins and asphaltenes and free oil components in even a same oil charge in addition to fractional adsorption effects and compositional changes of the oil charges in reservoir rocks during filling process the molecular compositions and homogenization temperatures of oil bearing fluid inclusions in these two samples indicate that trapping of these types of inclusions apparently ceased in sample a while continued in sample b after the initial oil charge suggesting that the relative content of polar components in the initial oil charge compared to the later oil charges plays a dominant role controlling the trapping of oil bearing fluid inclusions in an oil saturated zone sequential extraction studies are important and useful for reservoir geochemistry especially in the cases where only limited samples of oil and reservoir rocks are available and or where compositional heterogeneity of free oils has disappeared in a reservoir karlsen d a nedkvitne t larter s r bjorlykke k 1993 hydrocarbon composition of authigenic inclusions application to elucidation of petroleum reservoir filling history geochim cosmochim acta 57 3641 3659

fluid geochemistry of the acqui terme visone geothermal area piemonte italy the main geothermal reservoir of acqui terme visone hosts na cl waters which are in chemical equilibrium at 120 130 c with typical hydrothermal minerals including quartz albite k feldspar illite chlorite or smectite anhydrite calcite and an unspecified ca al silicate in the acqui terme visone area these geothermal waters ascend along zones of high vertical permeability and discharge at the surface almost undiluted or mixed with cold shallow waters to the sw of acqui terme other ascending geothermal waters either undiluted or mixed with low salinity waters enter relatively shallow secondary reservoirs where they reequilibrate at 65 70 c both chemical and isotopic data indicate that bacterial so4 reduction affects all these waters especially those discharged by the secondary reservoirs therefore geothermal waters must get in contact with oil acquiring the relatively oxidized organic substances needed by so4 reducing bacteria this oil water interaction process deserves further investigations for potential economic implications

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

geochemical study of crude oils from the xifeng oilfield of the ordos basin china abstract the xifeng oilfield is the largest newly discovered oilfield in the ordos basin in order to determine the possible source crude oils collected systematically from the oilfield and an adjacent oilfield have been examined isotopically and molecularly the predominance of long chain n alkanes high abundance of c29 sterane lower ratios of c25 c26 tricyclic terpane and c25 tricyclic terpane c24 tetracyclic terpane and high c24 tetracyclic terpane c24 tetracyclic terpane c26 tricyclic terpanes ratio in the studied oils suggest generation from a source with mixed terrigenous and algal bacterial organic matter the presence of diterpenoid hydrocarbon with abietane skeletons is characteristic of the main contribution of higher land plants to the oils the biomarker distributions in the oils show that they were formed under a weakly reducing freshwater environment molecular maturity parameters indicate that the crude oils are mature the oil source rock correlation and oil migration investigation suggest that the oils in the xifeng oilfield originated from the source rocks of the yanchang formation deposited in a shallow to deep freshwater lacustrine environment especially chang 7 source rocks the data from the distribution of pyrrolic nitrogen compounds indicate that the charging direction of the chang 8 crude oils is mainly from the zhuang 12 well northeast of the oilfield toward the southwest this direction of oil migration is consistent with that indicated by regional geological data

sedimentation from strong volcanic plumes 1 we develop descriptions of the key processes influencing tephra dispersal from strong volcanic plumes these are characterized by the development of a subvertical eruption column in the atmosphere that forms a spreading current at a level of neutral buoyancy we describe the propagation of the spreading current due to both gravity and wind advection using scaling arguments and a simplified geometry to model particle sedimentation in a windy as well as a wind free environment new parameterizations are used to describe the wind field below the spreading current particle aggregation and particle density variations we conducted a broad study to investigate the effects of these processes and made comparisons with field observations the greatest variations resulted from wind advection below the spreading current which shifts the plume corner mass accumulation and the position of transitions in fallout regimes downwind particle aggregation strongly depends on the initial grain size distribution and significantly affects deposit thinning depending on the aggregate size and density and on the relative amount of aggregating particles small aggregates can reproduce secondary maxima of mass accumulation when sedimenting in a wind field variation of particle density also affects the resulting thinning trend the model provides acceptable reproduction of observations of the propagation of the spreading current tested with the plinian phase of the 18 may 1980 eruption of mount st helens and of observed thinning of tephra fallout deposits tested with deposits from mount st helens 1980 askja d 1875 quizapu 1932 minoan eruption 3 6 ka b p novarupta a 1912 and hudson 1991

aromatic biomarkers as indicators of source depositional environment maturity and secondary migration in the oils of cambay basin india abstract aromatic biomarkers have been analysed for source depositional environment maturity and secondary migration in crude oils from different formations of paleocene to eocene age in the ahmedabad mehsana block of north cambay basin and the broach block of south cambay basin north cambay basin oils are characterized by a high abundance of 1 2 5 and 1 2 7 trimethylnaphthalenes tmn and low to medium ratio of dibenzothiophene phenanthrene and low ratio of pristane phytane indicates that these oils have been derived from a source containing predominantly higher plants and that the organic matter was deposited in restricted marine or lacustrine environments in anoxic to suboxic conditions the relative abundance of 1 2 7 tmn suggests that it was derived from the structural degradation of oleanane type triterpenoids present in angiosperms south cambay basin oils are less abundant in 1 2 5 and 1 2 7 tmns and low ratio of dibenzothiophene phenanthrene and high ratio of pristane phytane indicating that the oils were derived from higher plant source organic matter deposited under marine or fluvial deltaic environment in oxic conditions maturity sensitive ratios based on phenanthrene naphthalene dibenzothiophene and their alkyl substituted isomers have been used to calculate the equivalent vitrinite reflectance these parameters indicate a wide range of thermal maturity of the oils ranging from 0 60 to 0 93 vrc methylphenanthrene index and methyldibenzothiophene ratios indicate that the maturity of north and south cambay basin oils are different the north cambay basin oils are less mature than south cambay basin oils pyrrolic nitrogen distribution indicates that the alkylated carbazoles and benzocarbazoles are more abundant in south cambay basin oils as compared to north cambay basin oils these data indicate that north cambay basin oils are less migrated compared to south cambay basin oils this systematic investigation of the aromatic biomarkers in oils of cambay basin has resulted in a new generation migration and entrapment model that has led to the development of new exploration leads

variation of geochemical risk associated with the use of ophiolitic washing mud as refilling material in a basalt quarry of the northern apennine italy ophiolitic sequences in northern apennines are usually exploited as source of raw material for civil engineering works grinding procedures of basalts imply the production of dusts with relatively high concentration of phes this paper studied the increase of geochemical risk when washing mud produced at sasso di castro quarry site tuscany is reused as rock keeper in a near dismissed quarry and highlighted geochemical fractionation produced on the base of different mineral hardness co cr ni and v concentration measured in washing mud were higher than the limits fixed by the italian law but compatible with background values the mobility of these four elements during future weathering processes were estimated by considering the element transfer coefficients and assuming weathered rocks and soils as two different natural analogues of the future state of washing mud the future concentration was estimated by considering the average lifetime of mineral grains calculated through their dissolution rate molar volume and grain diameter the variations of geochemical concentrations were used to estimate the percentage increase of the geochemical risk at the displacement place after 50 years the associated geochemical risk is still considerably lower than the probability to be damaged by a single landslide event