origin of tar mats in petroleum reservoirs part ii formation mechanisms for tar mats abstract tar mats and oil legs from several marine source rock derived oil fields including the ula and oseberg fields in the north sea and an unidentified north american example have been analysed geochemically in all cases the tar mats were derived from the same petroleum system as the oil leg oils and were found in the most porous and permeable portions of the reservoir comparing case history data with published data on the subsurface solubility characteristics of asphaltenes in petroleums it is possible to eliminate some potential tar mat formation mechanisms and suggest the most likely causative mechanisms thus the adsorption of asphaltenes on reservoir clays and light to moderate levels of biodegradation are considered unlikely to contribute to tar mat formation in the ula field thermal degradation of the oil in the carrier and reservoir causing asphaltene precipitation may be a major contributing factor to the tar mats there in the oseberg field increased gas solution in the oil leg may have contributed to deasphaltation tentative mass balance calculations the extreme pressure dependence of asphaltene solubility in subsurface crude oils the occurrence of tar mats in zones of elevated permeability plus a simple transport model suggest that during secondary migration an asphaltene rich petroleum phase may be produced in dipping carrier beds and may be carried into the reservoir contributing in some instances to tar mat formation

hydrocarbon composition of authigenic inclusions application to elucidation of petroleum reservoir filling history abstract geochemical analysis of petroleum inclusions trapped in authigenic feldspar and quartz in the ula formation in the north sea ula oil field revealed a petroleum of markedly different composition than the oil presently in the reservoir using microthermometry and the burial history as a dating tools it is concluded that the petroleum in the k feldspar inclusions was present in the more porous and permeable parts of the ula formation as early as 45 75 my bp when the field was at a depth of about 1 0 1 5 km as compared with the current depth of 3 4 km this early petroleum which was trapped as inclusions in authigenic k feldspar shows a distinctly different distribution of tricyclic terpanes and pentacyclic triterpanes from that of the current petroleum charge in the ula formation which was derived from the mandal formation source rock in late neogene time molecular parameters show that the oil in the k feldspar inclusions is significantly less mature than the crude oil in the present reservoir the approximate 90 c temperature increase occurring after entrapment of the early petroleum in kfeldspar the field is currently at 143 c appears not to have reset the low maturity signature of the oil in the k feldspar inclusions this could suggest that the temperature in the inclusions is too low for isomerization selective thermal degradation to occur lack of catalysts or that there are other controls on the ratio of some of these parameters still parameters like the ratio of c21 to c28 triaromatic steroids and those based on dimethyl and trimethyl naphthalenes are comparatively similar in both the inclusions and in the reservoir crude the oil inclusions in authigenic quartz and albite formed from about 10 my bp burial depth 2 5 km until the present burial depth 3 4 km are interpreted as representing a palaeo petroleum charge having a composition intermediate between the oil found in k feldspar inclusions and the oil charge in the present reservoir our data suggest strongly that the petroleum trapped in the inclusions in quartz and plagioclase represents progressive dilution of the early reservoired oil now found only in k feldspar inclusions with oil from the mandal formation analysis of solution gas in these inclusions suggests that the first petroleum associated gas to arrive at the trap from the progressively maturing mandal formation had a much wetter composition than the current reservoir solution gas to explain the present comparatively drier and isotopically lighter reservoir solution gas composition the inference is made that there has been a recent during formation of k feldspar inclusions 45 75 my bp maturation of the upper jurassic mandal formation the main source rock in this region was limited possibly to the graben axis this suggests that the petroleum found in the k feldspar inclusions was most likely derived from a deeper post caledonian palaeozoic formation

origin of tar mats in petroleum reservoirs part i introduction and case studies abstract three case studies of petroleum reservoirs containing tar mats oseberg field and ula field both from the north sea and a north american field have been studied using a variety of organic geochemical techniques with special emphasis on the geochemistry of the asphaltenes the results were evaluated in combination with the available geological data and with numerical simulations to evaluate possible mechanisms of tar mat formation part ii wilhelms and larter 1994 in part i the petroleum geochemistry of three sets of tar mats is described the tar mat extracts were characterized by a sharp increase in the asphaltene content 20 60 wt compared with the oil leg extracts 1 5 wt the extract yields kg eom t rock in the tar mats ca 4 46 for the oseberg field 8 18 for the ula field and 8 43 for the north american case study are significantly higher than in the corresponding oil leg extracts which have extract yields of ca 1 14 kg t rock the tar mat extracts are geochemically related to the pooled oil as revealed by geochemical fingerprinting including biomarker analysis the tar mats are situated in high porosity and high horizontal permeability sandstone layers above permeability barriers several zones of low extract yield and immature petroleum geochemical characteristics were observed within the oil legs and between tar mats which might represent minor amounts of petroleum generated locally from indigenous organic matter

focused ion beam fib combined with sem and tem advanced analytical tools for studies of chemical composition microstructure and crystal structure in geomaterials on a nanometre scale abstract in order to make meaningful interpretations of trace element and isotopic information from geomaterials prior characterization of the material of interest with respect to structural and chemical homogeneity radiation damage and microstructure is often required transmission electron microscopy tem is a powerful analytical tool that may be used to fully characterise a wide range of synthetic and natural materials the focused ion beam technique fib is an ideal tool for tem sample preparation that allows for the fabrication of electron transparent foils with typical dimensions of 15 10 0 150 m from any region of interest i e site specific and in virtually any material fib sample preparation consumes only a small volume of material approximately 2300 m 3 for a standard foil with the dimensions 15 10 0 150 m leaving most of the material essentially unaffected by the sampling process modern tem facilitates the measurement of chemical composition with unsurpassed spatial resolution e g nanometer scale high resolution imaging and electron diffraction provide important complimentary structural information it is the combination of crystal structure information and chemical composition that allows for the complete characterization of the volume of interest high resolution elemental mapping or line scans may be used to acquire complete energy dispersive x ray analysis edx spectra of a material pixel by pixel subsequent evaluation of the data allows for the correlation of the edx spectrum with the respective elemental map or line scan with an image thus illustrating spatially resolved chemical composition variations at the 0 5 1 0 wt level frequently minerals enclose sub micrometer or even nanometre sized inclusions of minerals fluids or silicate melt which are of great interest to geoscientists nanoinclusions e g in diamond or olivine are of particular interest because they may have preserved their original crystal structure thus providing a geobarometer recording the pressure conditions at the time of formation of the inclusion fib tem are appropriate techniques to sample and subsequently define the chemical composition and the structural state of mineral inclusion on the nanometre scale the combination of fib with an sem allows for 3d information to be obtained from samples including 3d imaging e g phase distribution and volume of the individual phases in symplectites 3d distribution of elements in a specific volume 3d elemental maps and three dimensional texture analysis using electron backscatter diffraction ebsd

geochemistry of oolitic iron ores an electron microprobe study oolitic iron ores are made up of silicate oxide and carbonate minerals that are part of solid solution series the compositions of the minerals can depart from pure end members and show variation among deposits this variability can be quantified using electron microprobe techniques iron silicates are represented by chamositic clays both berthierine and chamosite glauconite was not seen in any of these samples berthierine predominates in younger deposits whereas the paleozoic ores studied contained only chamosite compositions of the chamositic clays however were independent of age iron oxides are mostly goethite in younger deposits or hematite in older deposits both minerals lack appreciable al in solid solution most analyses show small amounts of al but usually balanced by si in the same proportion as in chamosite indicating a slight admixture of clay iron carbonates are siderite with appreciable substitution of ca and mg but not of mn apatite is common but no iron phosphates were found the compositions of the silicates and carbonates are close to those reported for early diagenetic minerals from other types of sedimentary rocks indicating that ironstone formation does not require unusual chemical conditions other than a large supply of iron the analytical results can be used to argue against several hypotheses of ironstone genesis the lack of al in the goethitic and hematitic ooliths is inconsistent with an origin either by redeposition of soil ooliths or by oxidation and leaching of earlier chamositic ooliths the presence of high al contents in the chamositic ooliths shows that they cannot have formed from earlier aragonitic ooliths and the presence of small amounts of chamositic clay and apatite as discrete laminae in goethitic and hematitic ooliths suggests that this type of oolith could also not have formed by replacement of aragonite times of ironstone deposition show a correlation with climate and sea level stands that suggests a mechanism for generating locally high iron concentrations in seawater a combination of a warm humid climate and low average continental relief would intensify lateritic weathering and the formation of iron enriched detritus coincidence of this increased detrital iron supply with intensification and shallowing of the oxygen minimum layer in the ocean could lead to mobilization of iron from offshore shelf clastics to be redeposited near the shoreline in intertidal to shallow subtidal environments

low oxygen levels in earliest triassic soils an earliest triassic methane postapocalyptic greenhouse following the permian triassic p t extinction event was proposed on the basis of evidence of deeply weathered paleosols at high latitudes with features of low latitude soils and low stomatal index values of seed fern leaves reexamination of distinctive phyllosilicates unique to a single stratigraphic level in paleosols located just above the isotopically defined permian triassic boundary in australia and antarctica furnishes additional tests of this hypothesis illite is the dominant clay mineral in earliest triassic paleosols from antarctica but the paleosols also contain conspicuous green nodules of coarsely crystalline berthierine examples from the geologic record and from experimental studies indicate that the formation of berthierine is restricted to reducing conditions the occurrence of this unusual mineral in soils may indicate soil oxygen consumption by the influx of atmospheric methane to form carbon dioxide which in turn warmed the earliest triassic giving rise to a postapocalyptic greenhouse

depositional setting and origin of berthierine oolitic ironstones in the lower miocene terengganu shale tenggol arch offshore peninsular malaysia abstract berthierine oolitic ironstones have been found in the subsurface lower miocene strata of the tenggol arch area offshore peninsular malaysia the ironstones occur within a 30 to 50 m thick laterally extensive unit of very finely laminated to massive dark green mudstone known as the terengganu shale this shale unit was deposited during a regional marine transgression over the tenggol arch which is a fault bounded pre tertiary basement high that separates the cenozoic intracratonic malay and penyu basins at the southwestern margin of the ancestral south china sea the oolitic ironstone beds up to 45 cm thick have sharp erosional bases and are composed of mainly berthierine ooids and pisoids some terrigenous quartz feldspar clasts and locally phosphatic ooids thicker ironstone beds occurring in the lower part of the shale unit show gradation from granule sandstone to oolitic ironstone sedimentological evidence suggests that the oolitic ironstones were deposited as offshore shelf storm layers the close association of terrigenous clastic grains with the berthierine ooids suggests that these ooids were derived from lateritic soils on land transformation of the lateritic soil ooids into berthierine ooids possibly via an intermediate odinite phase took place under reducing early diagenetic conditions like many other ironstone deposits described in the literature the terengganu ironstones were deposited during a period of sea level highstand coincident with a marked reduction in terrigenous coarse grained sediment influx palynological evidence further suggests that deposition of the terengganu shale took place during a dry climatic phase which may have caused the reduction of terrigenous influx into the basin and promoted ironstone accumulation phosphatic ooids are found in the ironstones deposited near the inferred early miocene shelf edge and they are texturally similar to phosphatic ooids described from modern continental margins they were probably formed during early diagenesis near the sediment water interface under anoxic bottom conditions and then were subsequently reworked and mixed with the berthierine ooids the occurrence of phosphatic ooids near the paleo shelf edge suggests that the anoxic bottom conditions favorable for phosphate deposition may have been related to upwelling at the paleo shelf margin

organic geochemistry of crude oils from the vienna basin and an assessment of their origin abstract a representative collection of oil samples and neogene rock samples from the vienna basin has been analyzed by organic geochemical methods the relatively high maturity of the crude oils and the characteristics of their hydrocarbon composition makes it unlikely that they are derived from the neogene sediments of the vienna basin furthermore investigation of the rock samples also showed that these sedimentary strata do not have the potential for generation of liquid hydrocarbons however there is some potential for gas generation even the deepest neogene sediments 4000 m depth just have reached the onset of the hydrocarbon generation zone from these results it has to be concluded that the bulk of the oil found so far in the vienna basin originated from pre tertiary sediments below the neogene basin

biodegradation of oil in uplifted basins prevented by deep burial sterilization biodegradation of crude oil by bacterial activity which has occurred in the majority of the earth s oil reserves is known to reduce greatly the quality of petroleum in reservoirs for economically successful prospecting for oil it is therefore important to understand the processes and conditions in geological formations that lead to oil biodegradation although recent studies speculate that bacterial activity can potentially occur up to temperatures as high as 150 degrees c refs 3 4 it is generally accepted that effective petroleum biodegradation over geological timescales generally occurs in reservoirs with temperatures below 80 degrees c ref 2 this appears however to be at odds with the observation that non degraded oils can still be found in reservoirs below this temperature here we compile data regarding the extent of oil biodegradation in several oil reservoirs and find that the extensive occurrence of non biodegraded oil in shallow cool basins is restricted to those that have been uplifted from deeper hotter regions of the earth we suggest that these petroleum reservoirs were sterilized by heating to a temperature around 80 90 degrees c during deep burial inactivating hydrocarbon degrading organisms that occur in the deep biosphere even when such reservoirs are subsequently uplifted to much cooler regions and filled with oil degradation does not occur implying that the sterilized sediments are not recolonized by hydrocarbon degrading bacteria

stability and facies association of early diagenetic mineral assemblages an example from a jurassic ironstone mudstone succession u k abstract sedimentological and petrographic data from two lower liassic ooidal ironstones the frodingham and pecten ironstones and associated mudstones from eastern england have been collected within these ironstones early diagenetic berthierine siderite and minor glauconite have a limited lateral extent associated with an intrabasinal high the market weighton swell this mineral assemblage passes laterally and vertically into mudstones and silty mudstones within which pyrite is the dominant early diagenetic iron mineral the ironstones are stratigraphically condensed having experienced low net sediment accumulation rates and shallow high energy conditions thermodynamic considerations indicate that berthierine and siderite should be stable in anoxic environments where sulfide activity is negligible pyrite is rare within the ironstones suggesting that sulfate reduction was a negligible process during ironstone formation where pyrite is present it postdates berthierine and siderite indicating that sulfate reduction may have been a later process in some beds we propose that berthierine and siderite were precipitated during suboxic diagenesis where sulfate reduction was inhibited and iron reduction was the dominant process of organic matter oxidation suboxic diagenesis resulted from the extended periods of physical and biological sediment reworking during ironstone deposition which favored the oxidation of iron minerals and aerobic egradation and loss of organic matter berthierine formed during early suboxic diagenesis at the expense of detrital clays and iron oxides during later suboxic diagenesis pore water bicarbonate activities increased leading to siderite precipitation early glauconite also formed in places and it seems likely that it formed close to the oxic suboxic interface the predominance of pyrite in the mudstones indicates that sulfate reduction was the major process of organic matter oxidation during early diagenesis

stratigraphic correlation of late palaeocene sand deposits in the sogne basin area of the danish and norwegian central north sea a stratigraphic analysis of late palaeocene sands of the sogne basin and the western part of the norwegian danish basin shows that the sand bodies are of differenct ages the geographic distribution of the sand deposits shows that they are related to underlying mesozoic structures suggesting a controlling effect of tertiary tectonics on the deposition of sand during the late palaeocene however the structural setting of various sand bodies varies from reactivation of older faults and reactivation of salt structures the local character of the structures active during the late palaeocene introduces minor depressions with no lateral connection the sand bodies which are interpreted as having been deposited in these depressions are thus in general separate bodies with no lateral connection the fennoscandian shield and eroded mesozoic sediments along the fennoscandian border zone are suggested as source area for the late palaeocene sand deposits

predictive permeability variations in a hermod sand reservoir stine segments siri field danish north sea abstract the hermod sand of the stine segments siri field danish north sea displays large permeability variations 1 600 md these permeability variations represent horizontal layering in the reservoir largely formed by diagenetic processes they have a significant impact on reservoir performance because horizontal producers in fairly thin reservoirs 30 m are protected against bottom water influx and can produce water free for long periods of time this paper presents the results of a detailed multidisciplinary study where the observed variation in permeability can be explained by two main diagenetic phases silica as opal cement and microquartz and berthierine a serpentine mineral that is closely related to chlorite opal microquartz and berthierine cements dominate in separate parts of the reservoir bodies opal microquartz cemented sands have high permeability typically 500 600 md berthierine cement has a different growth pattern in the oil and water zones resulting in intermediate permeability in the oil zone typically 50 100 md and very low permeability in the water zone typically 1 10 md

berthierine formation in reservoir rocks from the siri oilfield danish north sea as result of fluid rock interactions part iii determining mineral stability and co2 sequestering capacity of glauconitic sandstones abstract berthierine was proven as one of the most important products of glauconite alteration in the siri oilfield danish north sea however there is an ongoing debate regarding the main product of glauconite dissolution siderite berthierine or berthierine as a precursor of siderite and or magnesium bearing carbonate in order to investigate the consequences of glauconite dissolution in view of thermodynamic admissibility and the resulting co2 sequestering capacity a hydrogeochemical model which is based on thermodynamics of chemical equilibrium was developed calculating various modeling scenarios helps to conclude on the ph eh conditions of glauconite dissolution as well as of berthierine formation and dissolution in generic aqueous systems under elevated temperature pressure conditions our modeling results highlight that carbonate formation cannot be triggered exclusively by co2 addition into glauconitic sandstones the injection of pure co2 into glauconitic sandstones leads to acidic and anoxic oxidizing conditions under which glauconite remains stable to intensify glauconite alteration by co2 injection glauconitic sandstones have to be in contact with degradable organic matter or alternatively reducing agents have to be co injected with co2 sufficient electron transfer to ferric iron bound in glauconite is the ultimate control for intense glauconite alteration and for subsequent berthierine precipitation once formed berthierine remains stable over a broad ph range and is not transformed to any carbonate under reducing conditions thus co2 injection into glauconitic sandstones under reducing conditions mainly leads to formation of berthierine instead of iron and magnesium carbonates however hydrogeochemical conditions in the subsurface can affect co2 sequestration via glauconite dissolution and the resulting carbonate formation including the ph eh conditions the chemical composition of glauconite and the overall mineralogical composition of glauconitic sandstones

sub b layering in the southern caribbean the aruba gap and venezuela basin abstract multichannel seismic data in the aruba gap region near joides dsdp site 153 verify the presence of a deep sub b reflection one multichannel seismic line trends ne sw on and along the edge of beata ridge and passes within 1 km of site 153 and another line runs n s across the entire aruba gap with the drill site 4 km east from its northern end closely spaced velocity analyses indicate the presence of deep primary reflection events and enable calculation of interval velocities between the a b marker horizons deconvolved true amplitude normal incidence profiles sharply delineate the a b marker horizons and indicate the presence of the sub b reflection event on the ne sw line this deep reflector is best described as a diffuse discontinuous zone relatively horizontal lying about 0 8 seconds of two way travel time below the b reflector with an interval velocity of approximately 5 0 km s between horizon b and this reflection the n s line is more complex since the sub b reflection event is masked by a strong internal multiple from the a b interval in the central and western venezuela basin deep primary reflections beneath horizon b are also observed on the northern and western sides of what appears to be a major fault zone this fault zone separates the smooth b and sub b reflectors on the northern and western sides of this fault zone from what appears to be typical oceanic basement the widespread presence of sub b reflections yielding high interval velocities for the section between these events and horizon b suggest that this material is probably igneous in origin

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

berthierine formation in reservoir rocks from the siri oilfield danish north sea as result of fluid rock interactions part ii deciphering organic inorganic processes by hydrogeochemical modeling abstract berthierine formation reduces the permeability of the glauconitic reservoir sandstones in the siri oilfield danish north sea and is therefore a considerable production factor a new hydrogeochemical batch model that is based on thermodynamics of chemical equilibrium was developed to identify the processes which activated and controlled berthierine formation a good match has been achieved between the mineralogical alteration features observed in the siri field and the results of the batch modeling this match points to the validity of the modeling mechanisms for berthierine formation based on the identified mechanisms the modeling enables to quantify the mass conversion of hydrogeochemical processes in glauconite bearing and berthierine forming water rock gas systems the modeling results reveal that intense berthierine formation in the siri field resulted from in situ glauconite alteration within a more or less closed system due to hydrocarbon degradation driven water rock gas interactions this process is accompanied by formation of secondary sio2 s and potassium mica precipitation of iron bearing carbonates is prevented by berthierine formation although the glauconitic sandstones are rich in iron and carbonate species moreover such systems are brought to disequilibrium by the release of reducing and acidic agents originating from oil degradation and undergo long term diffusion dominated mass fluxes instead of advective mass fluxes

open or closed geochemical systems during diagenesis in sedimentary basins constraints on mass transfer during diagenesis and the prediction of porosity in sandstone and carbonate reservoirs descriptions of mineralogy and textural relationships in sandstones and limestones have been used to establish a sequence of diagenetic events epigenesis involving mineral dissolution and precipitation which have been interpreted to have occurred during the burial history published epigenetic sequences commonly imply a geochemically open system with very significant changes in the bulk chemical composition of the sediments during burial near surface diagenetic reactions may be open involving significant changes in the sediment composition and formation of secondary porosity caused by high pore water flow rates of meteoric water or reactions with sea water near the sea floor calculations show that the bulk chemical composition of the sediments below the reach of high pore water flow rates of meteoric water or hydrothermal convection should remain nearly constant during progressive burial because of limited pore water flow mass transport between shales and sandstones is also limited because the pore water is in most cases buffered by the same minerals so that the concentration gradients are low recent studies show that silica released from clay mineral reactions in mudstones has been precipitated locally as small quartz crystals and not exported to adjacent sandstones if the geochemical constraints for mass transfer during burial diagenetic reactions are accepted the chemical reactions involved in diagenesis can be written as balanced equations this offers the possibility to make predictions about reservoir quality based on assumptions about primary sediment composition related to facies and provenance large scale changes in the bulk composition of sandstones and mudstones during burial diagenesis have been suggested but because such changes cannot be explained chemically and physically no predictions can be made burial diagenetic processes are in most cases not episodic but occur as slow adjustments to increased stress and temperature driving the sediments toward increased mechanical and thermodynamic stability as a result the porosity of a single lithology must decrease during progressive burial but each lithology has a different porosity curve this article discusses quantitative calculations and estimates that show clearly that burial diagenesis must represent geochemically nearly closed systems where mineral dissolution and precipitation must be balanced this provides a theoretical basis for the modeling and prediction of reservoir quality

berthierine formation in reservoir rocks from the siri oilfield danish north sea as result of fluid rock interactions part i characterization abstract berthierine as the only authigenic fe rich clay mineral occurs in an oil bearing glauconite rich sandstone paleocene heimdal member of the lista formation danish north sea based on the results of thin section transmission and scanning electron microscopy five different morphological types of berthierine were identified 1 mainly as grain coatings partly together with authigenic quartz covering detrital grains 2 as pore filling clay in open pores 3 small crystals in transformed glauconite grains 4 small crystals associated with siderite in layers of mica micaceous glauconite and 5 as elongated crystals in siderite concretions although different in occurrence all berthierine types investigated by microprobe analysis are of similar chemical composition suggesting similar precipitation conditions investigations by transmission electron microscopy reveal that fine berthierine crystals display straight parallel layers with a typical lattice fringe spacing of 0 7 nm and that their occurrence is intimately connected to oil phases in pore space partly berthierine textures resemble mineralized oil water emulsions berthierine is more abundant in the oil leg than in the water leg but occurs especially abundant at the oil water contact the coexistence of berthierine together with quartz overgrowth but also its appearance in glauconite indicates that berthierine formed in situ and that it is a product of glauconite dissolution berthierine formation is coupled to the reduction of aqueous fe 3 into fe 2 derived from glauconite dissolution and is related to fluid rock interactions triggered by oil degradation which occurred in the oil filled zone and at the oil water contact the biomarker parameters pristane n c 17 and phytane n c 18 indicate an increased extent of oil degradation at the oil water contact on the one hand soluble oil degradation products methane carbon dioxide and hydrogen changed the hydrogeochemical conditions such as ph pe alkalinity etc and controlled dissolution of glauconite and feldspar on the other hand the changed hydrogeochemical conditions led to berthierine and quartz precipitation in water wet reservoir intervals

sterane distribution of solid bitumen pyrolyzates changes with biodegradation of crude oil in the ouachita mountains oklahoma abstract solid bitumens grahamite and impsonite of southeastern oklahoma have been shown to originate from near surface alteration of crude oil curiale 1981 curiale and harrison 1981 pyrolysis of these solids has been employed to compare the sterane distribution of geographically proximate oils to that of the bitumens the ratio of rearranged to regular steranes is higher in the pyrolyzates than in the oils a finding consistent with a bitumen origin due to biodegradation of oil the remaining presence of steranes particularly regular steranes in the bitumens suggests that sterane occlusion may have occurred prior to or during the alteration process thus removing tetracyclic compounds from the influence of microbial attack these data suggest that pyrolysis gc ms offers a viable approach to correlation problems involving solid bitumens

changes in the ablation zones of glaciers in the western himalaya and the karakoram between 1972 and 2015 abstract observed estimates of changes in the himalayan and karakoram glaciers remain ambiguous because of limited knowledge regarding complex glacier behaviour low quality of remote sensing data and sparse ground based monitoring remote sensing has indicated anomalous behaviour of glaciers in the karakoram during the past two decades attracting scientists attention to the region in this context this study has made detailed estimates of changes in thickness and area of two glaciers the sachen in the western himalaya and the burche in the karakoram to facilitate understanding of recent glacier changes and their potential impacts on water resources this study used several datasets including landsat the shuttle radar topographic mission srtm the ice cloud and land elevation satellite icesat and differential global positioning system dgps in situ measurements from the period 1972 through 2015 the extent of debris cover increased significantly between 1972 and 2014 while the total glacierized area decreased slightly further our study estimated thickness changes after removing recognizable biases and seasonal variations computed through comparisons of icesat data with dgps a thinning trend occurred between 2000 and 2015 suggesting that the glaciers in the western part of the karakoram and himalaya regions have not recently gained mass this study also found non uniform variations within different zones of the glaciers avalanches have fed most of the karakoram glaciers providing spatially heterogeneous thickness changes the frequency of observations data quality acquisition time and local weather affect our observations of temporal changes careful assessment of regularly acquired remote sensing and ground based observations should reduce uncertainty regarding estimates of glacier changes for management of water resources and associated hazards

origin of hematite carrying a late paleozoic remagnetization in a quartz sandstone bed from the silurian rose hill formation virginia usa abstract paleomagnetic and petrographic studies of a quartz sandstone bed from the silurian rose hill formation of the central appalachians show that hematite carrying a late paleozoic remagnetization is authigenic comparison of paleopole positions from the rose hill formation with late paleozoic poles for north america suggests a synfolding remagnetization the sandstone cement is characterized by pore lining hematite pore filling berthierine and intergrowths of hematite berthierine and quartz these cements postdate pressure solution of detrital quartz grains late paleozoic cementation is a consequence of diagenesis associated with alleghanian deformation detrital fe mg silicate grains are believed to have been a local source of fe for some authigenic hematite and berthierine although mass balance calculations suggest that an external source is also required some berthierine aggregates are pseudomorphic after detrital fe bearing silicate grains trace amounts of detrital tourmaline are the only remnants of the detrital fe mg silicates