tricyclic terpane maturity parameters response to heating by an igneous intrusion the effects of thermal maturation upon the abundance and composition of the tricyclic terpanes have been investigated within a single sedimentary horizon within the dun caan shale member isle of skye scotland intruded by a 0 9 m thick tertiary dolerite dyke heating by the igneous body caused the concentrations of all 13 h 14 h and 13 h 14 h tricyclic terpanes to increase towards or within the effective oil window recording generation from abundant non hydrocarbon precursors such as kerogen and asphaltene bound components progressive changes in tricyclic terpane composition accompany these concentration changes an increase in the c23 maturity parameter towards the dyke resulted from the relatively greater rate of generation of the isomer combined with the earlier decline in concentration by degradation or isomerisation of the component the tricyclics tricyclics hopanes parameter shows a dramatic increase within the latter part of the oil window due to the greater relative thermal stability of the tricyclic terpanes the quantitative data demonstrate the importance of the processes of generation from non hydrocarbon fractions of the sedimentary organic matter and thermal degradation in the operation of tricyclic terpane maturity parameters

significance of europium anomalies in silicate melts and crystal melt equilibria a re evaluation although europium speciation in silicate melts partly reflects prevailing oxygen fugacities melt composition and structure play the major role in determining eu2 eu3 ratios and europium partitioning into mineral phases experimental evidence by different investigators on the magnitude of the compositional effect on eu2 eu3 provides consistent results only if account is taken of the oxygen buffer system employed in the experiments the medium dependent reduction of europium can be understood in terms of the preferential stabilization of eu2 by a strong aluminosilicate complex in the melt phase and to a much lesser degree by metasilicate complexes the stability of these complexes increases as the field strength of the associated cation species decreases hence eu2 aluminosilicate complexes are preferentially stabilized relative to trivalent lanthanides in melts of appropriate composition and their presence minimizes the enthalpy of the melt the influence of these complexes is particularly pronounced in melts with a high feldspathic component and a strongly polymerized structure their petrogenetic influence is best documented through the behaviour of europium relative to the other lanthanides during anhydrous anatexis in high grade metamorphic terrains and in the anomalous europium partition coefficients of phenocryst phases which formed during the crystallization of highly silicic magmas

changes in bulk properties and molecular compositions within new zealand coal band solvent extracts from early diagenetic to catagenetic maturity levels abstract the bulk properties and bitumen molecular compositions of a rank series of 38 humic coals from the new zealand coal band cretaceous cenozoic have been analysed to investigate early maturation processes affecting coaly organic matter through diagenesis to moderate catagenesis rank s r 0 0 11 8 r o 0 23 0 81 the samples comprise a relatively restricted range of vitrinite rich coal types formed largely from higher land plant material under relatively oxic conditions but with a significant contribution from microbial biomass with increasing rank total organic carbon contents show a general increase whereas moisture and asphaltene contents decrease bitumen yields also decrease through the stages of diagenesis and early catagenesis rank s r r o r 5 6 r o 0 40 as indicated by the constant occurrence and gradual increase of isoprenoids e g pristane and phytane and hopanoids in their more mature configuration this early phase of catagenesis not previously recognised in new zealand coals is followed at rank s r 9 r o 0 55 by the main catagenesis phase characterised by a more rapid increase in the generation of hydrocarbons including total n alkanes isoprenoids and hopanes changes in the maturity of new zealand coals can be traced by the carbon preference index and several hopane maturity parameters including 22 s 22 s 22 r and

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

distribution and isomerization of c31 c35 homohopanes and c29 steranes in oligocene saline lacustrine sediments from qaidam basin northwest china abstract the 22s 22s 22r ratios for c 31 c 35 homohopanes and the 20s 20s 20r ratio for c 29 steranes were measured by gas chromatography mass spectrometry gc ms on six oligocene saline lacustrine rock samples from a borehole located in the western qaidam basin northwest china these ratios vary significantly and irregularly with burial depth from 2831 m to 3054 m around the threshold of the oil generation window in addition 22s 22s 22r ratios also vary substantially among different homologs within the same sample generally decreasing from c 31 to c 35 homohopanes the distribution patterns of homohopanes for the six samples are unusual such as c 31 32 c 33 c 34 35 or c 31 c 32 c 33 34 35 or c 31 32 c 33 34 35 all of these observations can be mainly ascribed to the release of bound hopanes and steranes from kerogen and other macromolecules the 22s 22s 22r ratios of c 31 c 32 and c 33 homohopanes decreased while that of c 34 homohopanes increased for two samples yhs1 and yhs6 after pyrolysis at low temperatures 180 270 c a major reversal of 20s 20s 20r ratio for c 29 steranes was observed at 240 c for sample yhs1 but at 270 c for sample yhs6 the distributions of homohopanes for these two samples after pyrolysis changed from their original patterns toward the normal pattern c 31 c 32 c 33 c 34 c 35 these results reflect the influences of thermal degradation and direct isomerization of the free biomarkers and the release of bound biomarkers from kerogen and other macromolecules during pyrolysis

solution properties of rare earth elements in silicate melts inferences from immiscible liquids abstract the partitioning behavior of rare earth elements ree between immiscible silicate liquids was investigated as a function of temperature and total ree oxide concentration ree preferentially partition into the end member liquids that are rich in network modifying cations with two liquid partition coefficients greater than any other cation the two liquid partition coefficients of ree in a given experiment are essentially identical to one another no evidence was seen to suggest that the solution mechanisms of ree in high silica liquids vary with differences in their ionic radii two lattice models of trace element solution behavior fail to remove the compositional dependence of ree two liquid partition coefficients due to the assumption that all network forming and network modifying cations mix ideally with one another as a result it is probably incorrect to derive physical interpretations from the results of the application of two lattice models the results are applied to the origins of the lree enriched phenocryst matrix partition coefficients seen for some ferromagnesian minerals in high silica rhyolites since liquids with extremely high concentrations of t o t linkages do not strongly discriminate between the ree on the basis of their ionic radii the anomalous ree crystal matrix partition coefficient patterns are best explained as the result of contamination of these minerals by lree accessory phases

geochemistry and correlation of crude oils from reservoirs and source rocks in southern biyang sag nanxiang basin china abstract the paleogene hetaoyuan formation a sequence of gray to dark calcareous mudstone and dolomitic mudstones is the main source rock and reservoir in the biyang sag nanxiang basin eastern china organic geochemical analysis study performed on 57 source rock samples from the hetaoyuan formation demonstrates poor to abundant organic matter content ranging from 0 24 5 4 wt toc content characterized by oil prone type ii kerogen eleven crude oil samples from the hetaoyuan formation in southern biyang sag were analyzed using bulk properties and molecular methods to determine their maturity and origin the results suggest that the crude oils exhibit different maturity and source organic matter three groups of oils were identified by integrated analysis of gas chromatography gas chromatography mass spectrometry stable carbon isotope physical properties and gross composition of crude oil group a oils defined as low mature oil are characterized by high density viscosity sulfur content and low saturated hydrocarbon content this group of oils has relatively high values of ph n c 18 c 24 c 26 and gammacerane index indicating that the original organic matter had more contribution from terrigenous plants and was deposited in saline and stratified water columns under anoxic conditions group b oils defined as normal maturity oil are characterized by moderate density viscosity sulfur content and moderate saturated hydrocarbon content this group of oils has relatively low values of ph n c 18 c 24 c 26 and gammacerane index and displays a slight predominance of c 29 steranes indicating that the original organic matter had more contribution from marine algae and was deposited under sub oxic to anoxic conditions with low salinity group c oils defined as light oil are characterized by low density viscosity and abundant saturated hydrocarbons representative source rock samples were selected for further correlation the results of oil source rock correlation suggest that crude oils from the eh 2 member of hetaoyuan formation are mixture derived from source rocks in the eh 2 member and upper layer of the eh 3 member while oils from the upper and lower layer of the eh 3 member correlate with source rocks in the upper and lower layers of the eh 3 member respectively

pyrolysis of kerogens in the absence and presence of montmorillonite i the generation degradation and isomerization of steranes and triterpanes at 200 and 300 c abstract the sterane and triterpane biomarker distribution obtained from extracted bitumens and kerogen pb pyrolysate bitumens of immature cretaceous black shale cbs and rocky mountain coal rmc at 200 and 300 c in the presence and absence of montmorillonite reveal that the generation release of biomarkers was more significant than isomerization at 200 c pyrolysis whereas isomerization and degradation were most important at 300 c pyrolysis montmorillonite has a pronounced catalytic effect on these reactions i e generation isomerization and degradation the ratios of c29 20 s s r steranes and c31 and c32 s s r hopanes display reversals with heating time at 200 c pyrolysis irrespective of the presence or absence of montmorillonite whereas they increased uniformly with thermal stress at 300 c pyrolysis the extent of isomerization occurring at chiral centers in ring systems and in acyclic systems are different it has been confirmed that the isomerization at the c22 and c20 position of the extended hopanes and the steranes respectively are slower than those of the hopanes and the steranes in the 300 c pyrolysis the c27 steranes increased relative to c29 steranes with heating time in the pyrolysate of the rocky mountain coal kerogen this phenomenon is more significant in the presence of montmorillonite the increase may indicate either the formation of secondary c27 steranes or the early loss of c29 steranes relative to c27 steranes in a sedimentary basin isomerization probably occurs in the bitumen and kerogen at different rates these data show that maturation indices may be reversed with depth by using the examples of 20 s s r and 22 s s r where the rate of generation of the compounds from kerogen is faster than the rate of isomerization reactions occurring in the bitumen with time and temperature

the timing of marid metasomatism in the kaapvaal mantle an ion probe study of zircons from marid xenoliths abstract the precise timing of metasomatic events in the kaapvaal craton lithospheric mantle is poorly constrained and therefore it has proven difficult to relate mantle metasomatism in the source to igneous activity at the surface a suite of mica amphibole rutile ilmenite diopside bearing xenoliths marid represents the product of such metasomatic fluids or melts in this paper we report results of a shrimp and cathodoluminescence study on zircons from four marid samples from the kimberley cluster of pipes textures combined with experimental evidence suggest that zircons are late crystallizing phases in marids that form close to the solidus where the major precipitating phases are phlogopite and k richterite cathodoluminescence patterns reveal a complex growth history of the zircons involving strong deformation repeated events of crystallization resorption and or modification of the zircon composition possibly over several millions of years many of the u pb ages are significantly older than the intrusion age of the group i kimberlites of the kimberley cluster zircon ages in a marid xenolith from the wesselton kimberlite vary in the range 113 3 ma to 142 3 ma compared with a pipe age of 84 3 ma in two samples from the de beers bultfontein or dutoitspan pipes ages range from 85 5 to 119 2 ma in one and 80 4 to 90 2 ma in the other the ages obtained for the latter are indistinguishable from the pipe age of kimberlites belonging to the younger group i kimberlite event ca 80 95 ma zircons in this sample as well as the younger ages in the other may reflect real ages but most likely have lost radiogenic pb as a result of deformation and fluid or melt interaction the presence of pre group i ages in two of the samples demonstrates unambiguously that the metasomatism that yielded the older crystallization ages cannot be related to the group i kimberlite event instead minimum ages for the marid zircons coincide with the period of group ii kimberlite magmatism in the central to southeastern kaapvaal craton this coincidence in ages would be consistent with the contention based on experimental evidence that marid type rocks can be derived from group ii precursor magmas by olivine fractionation and exsolution of a carbonatitic component an alternative possibility not excluded by the zircon minimum ages is a genetic relation between marid metasomatism and karoo magmatism

a mid cretaceous petroleum source rock in the north atlantic region implications of the nanok 1 fully cored borehole hold with hope northeast greenland abstract the cenomanian turonian transition includes the youngest of the two so called cretaceous oceanic anoxic events sometimes also referred to as the bonarelli event this is an interval of global deposition of organic rich oceanic deposits including some of the most prolific petroleum source rocks of the world however in the greater north atlantic realm little direct evidence of notable volumes of rich cenomanian turonian petroleum source rocks exists as part of a major study of the cretaceous succession in northeast greenland between 2009 and 2012 a fully cored borehole nanok 1 on eastern hold with hope was drilled to penetrate a poorly or non exposed stratigraphic succession including the cenomanian turonian transition the nanok 1 penetrated 160 5 m of cenomanian to campanian clastic deposits and terminated at a td of 168 35 m in an igneous intrusion although none of the deposits penetrated qualify as a petroleum source rock a downwards increasing trend in petroleum source potential starting at c 100m hint at the existence of such rocks at levels deeper than the td of the well the downwards increasing trend in petroleum generation potential is curtailed by maturation from c 140m but assuming the trend would have prevailed were it not for the intrusion the presence of at least a marginal source rock would be expected at the level of the sill and deeper the presumed existence of petroleum source rocks below the td of the borehole is supported by the presence of marked oil staining in sandstones i e migrated petroleum at shallower levels of the drilled succession the hopane and sterane distributions and stable carbon isotopic compositions and age specific nordiacholestane ratios of the oil stains are compatible with an origin from the cretaceous succession while the jurassic can be ruled out the oil stains recorded were probably generated from a marine shale source rock of cretaceous age containing a significant proportion of terrigenous organic matter the possible presence of at least one marginal petroleum source rock in the mid cretaceous succession at the nanok 1 location has implications for the exploration potential of the conjugate margin hence comparison of sediment accumulation histories of the more and voring basins and northeast greenland suggests that the presumed source rock was deposited before the accommodation space at the nanok 1 location was exhausted thus coeval sediment starvation and deposition of more condensed and richer petroleum source rocks may have prevailed in the offshore basins to the east during the mid late cenomanian this potential source rock will thus be slightly older than cenomanian turonian source rocks that are important worldwide

a new method of comparing extended hopane distributions variations in extended hopane distributions are now routinely applied in assessing anoxia in ancient marine sediments and for oil source correlation studies current parameters based on the extended hopanes focus on the predominance of the c35 17 homologues 22s r isomers and thus reveal little information on the overall distribution we present here a new method of characterising extended hopane distributions using a combination of a c31 c33 c35 ternary diagram and a hopane odd even predominance parameter hoep this allows the distinction of virtually all extended hopane distributions the ternary figure is particularly useful in characterising large numbers of distributions and for correlation purposes the application of this figure to a set of north sea data reveals the existence of a continuum of extended hopane distributions

experimental evidence for a relationship between liquid immiscibility and ore formation in felsic magmas abstract geological studies demonstrate that liquid immiscibility in felsic magma closely associates with the ore forming process in order to obtain experimental evidence demonstrating the relationship between the ore forming process and liquid immiscibility in felsic magma we carried out a series of experiments at high temperature and atmospheric pressure the experimental results show that the granite kbf 4 na 2 moo 4 system is a homogeneous melt at high temperature with decrease in temperature however the melt decomposes into two immiscible melts silicate melt and ore forming melt the ore forming melt exists as globules in the silicate phase molybdenm ca na mg p mn f b and oh are concentrated in these globules the ore forming melt is characterized with very low sio 2 and al 2 o 3 concentrations but the concentration of moo 3 and cao is very high in contrast the silicate melts are significantly enriched in sio 2 and al 2 o 3 and depleted in moo 3 and cao in the silicate melt the concentrations of network modifying elements e g mo ca na p mg and volatiles f oh are very low the differences between the two immiscible melts exist not only in chemical composition but also in structure the ore forming melt structurally consists of moo 4 moof 4 b oh 4 and oh while the silicate melt is si0 4 because of the difference in composition and structure the two immiscible melts possess different physical properties compared to silicate melt the ore forming melt has a lower density and viscosity which permits the globules to behave as bubbles in granite magma and to move and concentrate in the upper part of magma chamber this process is probably responsible for the concentration of ore forming elements in the upper part of granite bodies and their immediate aureoles the present experimental results suggest that liquation in felsic magma can be the first step in the ore forming process during granitoid evolution

heterogeneity of free and occluded bitumen in a natural maturity sequence from oligocene lake enspel abstract sedimentation in oligocene lake enspel was rapidly terminated by a basaltic lava flow this introduced a preservational barrier while imparting a natural flash pyrolysis during which the organic matter in underlying stratigraphic units was subjected to rapid thermal maturation resulting in hydrocarbon generation samples from these strata exhibit a steep maturity gradient 0 25 1 07 optical vitrinite reflectance or ro over uniform organofacies this offers the opportunity to investigate bitumen generation during rapid thermal maturation mechanistically in particular the nature of bitumen 2 occluded bitumen which is only recoverable after the digestion of the mineral matrix and was frequently dismissed as an artifact of incomplete extraction elaborate sequential extraction of the contact metamorphic sequence of oil shales at enspel revealed systematic changes in bitumen composition these trend progressively towards those of occluded bitumen which exhibits a systematically elevated thermal maturity a higher degree of catalytic biomarker rearrangement and the conspicuous absence of molecular signatures from vascular plants that are present in the free bitumen one plausible explanation involves a contribution of allochthonous clay adsorbed organic matter to bitumen 2 this could represent a mixture of older reworked bitumen and an early diagenetic snapshot of clay adsorbed organic matter alternatively a close association of early generated bitumen with clay minerals may have led to enhanced isomerization and catalytically influenced uniformization of alkane signatures deviations from the expected relationships between various thermal maturity parameters suggest variable dependence on the time pressure temperature pathway i e metamorphic facies the maturation of organic matter likely behaves differently under a contact metamorphic regime or during rapid subsidence and exhumation as compared to slow maturation during regional subsidence our data also suggest that geologically brief shallow intrusive or extrusive magmatism might not be as destructive to the sedimentary hydrocarbon inventory as hitherto thought this study draws attention to the small scale compositional heterogeneity of bitumen that can be studied using sequential extraction methods more importantly it suggests that occluded bitumen could potentially harbor information on organic matter that pre dates in situ primary productivity and may be derived from allochthonous biomass and detrital input

effects of extreme heating on the elemental and isotopic compositions of an upper cretaceous coal abstract intrusion of igneous sills into coal seams in the maastrichtian vermejo formation of colorado new mexico rapidly and severely altered the organic matter content of the coal organic carbon concentrations drop from 65 in coal samples distant from sills to between 5 and 38 in coal samples close to a sill changes in organic matter c n ratios and 13 c values relative to distance from the sill indicate preferential losses of isotopically light forms of carbon from the coal the relatively high toc concentration elevated c n ratio and more negative 13 c value of coal closest to the sill suggest that rapid pyrolysis immobilized the thermal products as partially graphitized or mineral forms of carbon

off ridge alkaline magmatism and seamount volcanoes in the masirah island ophiolite oman abstract the masirah ophiolite offers an unique opportunity to study well preserved small seamount structures obducted seamounts have not been described up to now and from the present day ocean floor they are almost exclusively known from bathymetric studies the thin oceanic crust of the masirah ophiolite was formed at a ridge transform intersect in upper jurassic time it was overprinted and reworked by a major intra oceanic tectono magmatic event at mid cretaceous time that has been well dated owing to the presence of interstratified sedimentary rocks late hauterivian to early barremian c 130 125 ma this mid cretaceous magmatism produced alkaline volcanic rocks ranging in chemistry from alkalibasalts to rhyolites volcanism occurred in a nw se extensional regime small elongate submarine volcano structures seamounts developed within widespread alkalibasaltic pillow lava and pillow breccia deposits which are interfingered with deep marine pelagic sediments the volcanoes reached a maximum of a few kilometres in diameter and a few hundred metres in height the seamounts are built up of basic to acid subvolcanic stock or sheet like intrusions several generations of dikes vent agglomerates and pyro to epiclastic deposits the latter range from coarse breccias to finely stratified lapilli and record explosive volcanism in a deep marine environment in the magma chambers under the volcanoes local differentiations to trachytic and rhyolitic members took place the alkaline rocks show a pronounced ocean island basalt oib character indicating the considerable contribution of a mantle plume source hotspot as cause of the volcanism we propose a combination of original transform setting followed by drift past the marion hotspot during the major plate tectonic reorganization between greater india madagascar and africa starting in mid cretaceous time

methodology for bounding calculations of nuclear criticality of fissile material accumulations external to a waste container at yucca mountain nevada abstract the possibility of nuclear criticality however remote in the vicinity of the proposed repository at yucca mountain nevada generates justified concerns and may impact the performance of the repository a heuristic approach is presented here for determining the amount spatial distribution and other characteristics of fissile material accumulation in the rock beneath a waste package that could contribute to such an event this study is concerned primarily with waste packages containing special spent fuel from the department of energy and high level nuclear waste glass mixing with less alkaline waters and the subsequent drop in ph is the mechanism that is most efficient for precipitating fissile material from the waste package internal leachate in contrast to natural deposits in which redox changes are the main precipitation driver external accumulation size is determined by 1 computing the chemical composition of the leachate leaving a package as its internal materials degrade with the batch geochemical code eq3 6 2 determining precipitation of fissile material into mineral phases using the 1d geochemical code phreeqc as the effluent mixes with percolation water and 3 heuristically scaling results to a 3d volume and computing the criticality coefficient using the code mcnp loci for accumulation are the multiple lithophysal cavities and the fracture system a bounding conservative approach is used by necessity in step 3 nuclear criticality is sensitive to small variations in the distribution of fissile material and parameters of natural systems vary by orders of magnitude because the most likely combinations of parameters are not conducive to nuclear criticality this study focuses on extreme values of parameter probabilistic distributions such as limited flow into the package associated with a large percolation rate combinations of material degradation rates favoring actinide release and very high host rock porosity values by considering these combinations most favorable to criticality but unlikely it was concluded that external nuclear criticality is not a concern at the proposed repository

seamount abundances and distributions in the southeast pacific abstract sea beam bathymetry was recorded for 17 277 km of ship track in the southeast pacific and has been analyzed for seamount population characteristics all the ship tracks are over the pacific plate and most fall along 7 lines parallel to the east pacific rise between 7 s and 22 s the lines fall into three age categories one line is over 0 5 2 ma crust three are over 5 10 ma crust and three are over 30 40 ma crust seamount locations were recorded diameters were manually estimated and heights were measured if the swath crossed the seamount center over 382 features were counted along the entire ship track with heights ranging from 50 m to over 2500 m with sampling most consistent at heights between 100 m and 1000 m height to radius ratios vary considerably suggesting that seamount shapes do not scale to a single parameter the observed variety of morphological forms demonstrates that there is a wide range of seamount shapes for small features the distribution of sizes for the population was approximated by exponential dependence and by power law dependence using methods developed by smith and jordan 17 the power law distribution overestimates abundances at the smallest size ranges and both distributions fail to predict abundances of large seamounts determined from wide beam data 17 size distributions were also determined for seamounts in each seafloor age category almost all small seamounts appear to be produced on crust younger than 0 5 2 ma while the number of larger seamounts increases to 5 10 ma for all size ranges observed here the number of seamounts at 5 10 ma and at 30 40 ma is roughly identical these observations suggest that most small seamounts are formed on very young thin lithosphere that permits the passage of small volumes of magma small volumes would cool in older thicker lithosphere before reaching the surface although larger magma bodies might not numerous small sources of melt must exist near the ridge crest to supply the small seamounts probably trapped remnants of the large scale upwelling

cretaceous sedimentary rocks on the masirah ophiolite sultanate of oman evidence for an unusual bathymetric history autochthonous sedimentary rocks on the masirah ophiolite preserve a record of vertical movements of their oceanic basement the masirah ophiolite was formed in the uppermost jurassic and subsequently underwent thermal subsidence for about 20 ma as documented by pelagic sediments submarine alkali basaltic volcanism in the lower barremian marks the onset of rapid basement uplift to or above sea level carbonate platforms grew in barremian mid aptian time on highs of oceanic basement the uplift is interpreted as the result of transpressive tectonism along a large oceanic fracture zone the platforms submerged in the mid aptian and reached the ccd in the albian ribbon cherts were deposited during the albian to santonian time the first influx of siliciclastic detritus shed from the arabian craton is recorded in coniacian sandstones ophiolitic conglomerates interfinger in the campanian to mid maastrichtian with continent derived sandstones reflecting regional compressive tectonism crystalline exotics deposited in the late maastrichtian are derived most likely from the precambrian basement of arabia whilst the origin of the sedimentary exotics dated triassic to cretaceous remains unclear the masirah ophiolite was overthrust at the cretaceous tertiary boundary by an upper ophiolite nappe and emplaced onto the margin of southeast oman

1 ma east pacific rise oceanic crust and uppermost mantle exposed by rifting in hess deep equatorial pacific ocean abstract a series of dives with the french submersible nautile has been conducted in the region of the galapagos triple junction at the tip of the cocos nazca propagator most of the dives were devoted to the study of hess deep a rift valley produced by rifting of oceanic crust created at the axis of the very fast spreading east pacific rise the dives have enabled the structures and lithologies to be assessed and confirmed earlier dredging evidence for abundant basal crust and mantle rocks on an intra rift ridge located to the north of the axis of hess deep this shows that this situation is not specific not slow spreading ridges a nearly complete and unique log of young 1 ma crust and uppermost mantle representative of very fast accretion can be reconstructed even though the section is discontinuous and highly dismembered we propose two models that can explain the exposure on the ocean floor of the deep foundation of the oceanic crust one model stresses symmetry and vertical tectonics through isostasy diapirism of serpentinized mantle another model requires a larger amount of extension and emphasizes asymmetry with denudation of the upper crust through low angle detachment faulting in both models which differ mainly in the structure at depth amagmatic extension of east pacific rise crust by the cocos nazca propagator tip results in uplift and denudation of lower crust and upper mantle

three series of rearranged hopanes in toarcian sediments northern italy abstract a suite of 36 shales and marls from the toarcian oceanic anoxic event section at three localities in northern italy was found to contain variable contents of three series of rearranged hopanes 17 diahopanes c 27 and c 29 34 and trace c 35 18 neohopanes c 27 and c 29 30 and an unidentified early eluting series c 27 and c 29 35 principal component analysis pca shows the 17 diahopanes and the early eluting rearranged hopanes to closely covary suggesting a related diagenetic mechanism for the formation of their rearranged skeletons a general covariance with diasteranes is also noted the 18 neohopanes show no covariance with diasteranes or the other two series of rearranged hopanes we also report 2 methyl analogues of the 17 diahopanes and early eluting rearranged hopanes we propose that the neohopanes may be at least partly derived from different biohopanoid precursors than the other two series of rearranged hopanes and that the diagenetic origin of the neohopane structure differs from that of the 17 diahopanes and the unidentified early eluting series

assessment of the eruptive activity and identification of the mud breccia s source in the olimpi mud volcano field eastern mediterranean abstract even though the intensity and frequency of the eruptive episodes of deep sea mud volcanoes mvs substantially regulate the methane fluxes into the hydrosphere and the development of the near seafloor sulfate zone that affects the position of the gas hydrate stability zone these factors are not yet adequately investigated moreover the evaluation of the eruptive sediment s thermal maturity may provide solid documentation of the petroleum generation potential in high depths below seafloor bsf hence the present study through the integration of sedimentary facies analysis with hydrocarbon biomarker analysis based on the concentrations of long chain c25 c35 n alkanes hopanes and steranes supported by swath bathymetry data examined five sediment cores recovered from the gelendzhik moscow milano leipzig and heraklion mvs of the olimpi mud volcano field omvf on the central mediterranean ridge the main objective of this investigation was to assess the modern eruptive activity in the omvf and identify the mud breccia s origin and mobilization depth based on its maturity level and the ages of the source beds among the studied mvs milano leipzig and heraklion appear recently active while moscow perhaps remains in dormancy for at least one century the eruptive activity in the omvf seems to be generally vigorous and persistent while it is linked with several source beds of variable stratigraphy or environmental condition the multiple eruptive episodes occurring as uninterrupted events or via pulses create conditions that perhaps favour high releases of methane into the water column as well as the growth of the gas hydrate phase near the seafloor the identified modern mudflows appear thermally immature for oil generation while they most probably originate from terrestrial source beds located not deeper than 2 km bsf a messinian age could be suggested for the principal sources of the very soft to soft mud breccias of the omvf while stratigraphic horizons of early middle miocene might be proposed as the likely major sources for the firm to very stiff mud breccias of the area

hopane derived triterpenoids in soils the occurrence distribution and degradation pathways of hopanoid triterpenes have been studied in thirteen soil samples with varying degrees of biological activity hopanoids were shown to occur in all samples suggesting that they are not only ubiquitous in subaquatic sediments but also in soils hop 22 29 ene was generally predominant in the hydrocarbons whereas the 17 h 21 h bishomohopanoic acid c32 was the major component in the acids the concentrations of hopanes were usually rather low except in acidic peat the distribution in carbon number of hopanes and hopanoic acids showed great similarities with those of moderately oxic subaquatic sediments intact bacteriohopane tetrol widespread in microorganisms and the main precursor of geohopanoids was identified in substantial amounts in a peat exposed to groundwater oscillations

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

a natural pyrolysis experiment hopanes from hopanoic acids abstract the formation or generation of hopanes are important processes during both the natural heating of organic rich sediments and laboratory pyrolysis experiments molecular maturity parameters as well as the amounts ng g rock of the c31 hopanes and c30 c32 hopanoic acids were quantified in a jurassic silty shale horizon isle of skye scotland as a function of distance from an igneous intrusion the maturity profiles of the homohopanes and the hopanoic acids are comparable there is also a correlation between the decreasing amounts of c30 c32 hopanoic acids and concomitant increases in c29 c31 hopanes suggesting that free hopanoic acids could be one potential source of hopanes in this particular horizon other possible sources could include hopanoic acids that are bound into the macromolecular fraction

temperature effects on kerogen and on molecular and isotopic composition of organic matter in pierre shale near an igneous dike abstract a suite of siltstone samples from the upper cretaceous pierre shale from the contact zone of a 130 cm thick igneous dike near wolcott colorado u s a was taken from the contact to 170 cm from the dike to study the effects of temperature on the organic matter the sampled bedding interval was about 10 cm thick so variation in lithology and type of organic matter is minimal vitrinite reflectance values r 0 increase from 0 4 far from the dike to 3 3 near the dike contact geochemical measurements show systematic thermal effects analogous to those often observed for catagenesis and metagenesis in the depth range of 1 4 km within a sedimentary basin the h c ratio of kerogen and the hydrogen index rock eval decrease most rapidly in the 0 6 1 7 r 0 range in which the transformation ratio rock eval increases from 0 1 to 0 3 based on extraction of c 15 compounds the main increase of hydrocarbons and total extractable organic matter occurs between 0 6 and 1 0 reflectance the saturated aromatic hydrocarbon ratio increases almost twofold in this range of maturity however the pristane phytane ratio is essentially constant through the hydrocarbon generation zone but decreases slightly at high levels of thermal alteration r 0 1 2 the 13 c values for aromatic and saturated hydrocarbons are about 27 and 29 respectively and are constant to about 1 0 r 0 then both become heavier by about 2 at higher r 0 values

a tectonic model for ridge transform ridge plate boundaries implications for the structure of oceanic lithosphere abstract the first order geologic and morphologic relationships at along and proximal to ridge transform ridge plate boundaries are used to construct an empirical and speculative tectonic model the distinctive but variable morphotectonic fabric and crustal structure of the transform domain are the product of a tectonic continuum that ranges from very slow rates of strain associated with very thick edges of lithosphere slowly slipping ridge transfrom ridge plate boundaries to extremely high rates of strain associated with very thin edges of lithosphere fast slipping ridge transform ridge plate boundaries the geometry of a ridge transform intersection necessitates the juxtaposition of a relatively cold thick edge of lithosphere against the truncated end of an accreting plate boundary the cold face of lithosphere cools the adjacent wedge of asthenosphere rising beneath the axis of accretion and restricts the amount of partial melting thus attenuating the volume of basaltic melt segregated from the asthenosphere per unit time the shallow level manifestation of this cold edge effect is a thinner oceanic crust at depth the evolving lithosphere thickens rapidly as the cold edge is approached creating changes in the properties of the young lithosphere and forming a weld of upper mantle material against the cold edge of truncating lithosphere the ridge transform weld of upper mantle material creates a shear couple in the lithosphere underlying the intersection resulting in the progressive reorientation of the maximum tensile stress from normal to the ridge axis at some distance from the ridge transform intersection to an oblique angle near the boundary the brittle carapace of oceanic crust that overlies the mantle weld will deform accordingly with the development of oblique dip slip faults the model predicts that the geologic expressions of this cold boundary effect will become more dramatic with increasing thickness of the truncating edge at very slow rates of accretion 100 km juxtapose thick 30 50 km edges of lithosphere against the accreting plate boundary all but nullifying the processes that lead to the emplacement of normal oceanic lithosphere in this environment a relatively strong mantle weld will form at the ridge transform intersection and the thick edges of opposing lithosphere along the length of the transform will tend to confine the strike slip tectonism to a relatively narrow and temporally stable principal transform displacement zone in contrast at very fast rates of accretion large offset transforms 100 km place relatively thin edges of lithosphere

variations in trace element partition coefficients in sanidine in the cerro toledo rhyolite jemez mountains new mexico effects of composition temperature and volatiles trace element partition coefficients have been measured for one plagioclase and five sanidine mineral separates from the cerro toledo rhyolite new mexico sanidine partition coefficients vary substantially and systematically within the cerro toledo rhyolite partition coefficients for ca sr zn la and eu are lowest in the most evolved rhyolites whereas sm and hree partition coefficients are highest rubidium partition coefficients remain constant while those for ba ce and th are variable variations of the sr zn la and eu partition coefficients are correlated with the ca contents and partition coefficients of the sanidines calcium may have controlled the distribution of these elements in the sanidine by modifying the feldspar structure the low ca partition coefficients in sanidines for the most evolved rhyolites may be the consequence of modification of the melt structure possibly due to increased volatile contents at the top of the magma chamber s during evolution of the cerro toledo rhyolite the zn and la partition coefficients between sanidine and melt also may have been controlled by this change in melt structure modelling using major elements and the constant rb partition coefficient for sanidine indicates 70 crystallization of magma during cerro toledo rhyolite time by removal of 68 sanidine and 32 quartz estimates of the volume 1 of initial parental magma and 2 of the magma that crystallized during this period are 11 670 km3 and 8170 km3 respectively the average intrusion rate of silicic magma during cerro toledo rhyolite activity was 35 10 3 km3 a

biological markers in bitumens and pyrolyzates of upper cretaceous bituminous chalks from the ghareb formation israel abstract the sterane and triterpane distributions of three bituminous chalks from the upper cretaceous ghareb formation israel were investigated both in the original extractable bitumens and in extracts obtained after pyrolysis of whole rock and isolated kerogen samples at 450 c pyrolysis was performed in a closed system under hydrous whole rock and anhydrous conditions isolated kerogens the carbon number distributions of steranes and triterpanes differ significantly between original bitumen and pyrolyzates unlike the bitumens in which diasteranes were not detected the anhydrous pyrolyzates contain small amounts of diasteranes the presence of water during pyrolysis leads to an increase of sterane isomerization the abundant formation of diasteranes and an increase of the 18 h trisnorneohopane 17 h trisnorhopane ratio sterane isomerization maturation parameters show a closer match between original bitumen and pyrolyzates after pyrolysis in a closed system when compared with an open system

nd isotope evidence for crust mantle interaction in the generation of a type granitoid suites in labrador canada early proterozoic a type granite suites in labrador northeastern canada have initial nd isotopic compositions that lie between those of a depleted mantle reservoir and the local basement rocks one of these a type granite suites consists of a linear array of discrete plutons that crosses the boundary between an archean craton and an adjoining early proterozoic crustal block the nd of these granites at formation t 1720 ma changes from 8 to 4 across this boundary reflecting changes in the nature and antiquity of the continental crust however in both domains the granites cannot be derived entirely by anatexis of the local basement rocks and apparently require significant amounts of juvenile mantle derived material a type granites have been widely interpreted as anatectic derivatives of lower crustal rocks that were depleted by previous melt extraction the nd isotopic data suggest that these labrador examples were instead mixtures of mantle derived magmas and overlying lower crustal rocks and that new material may have been the volumetrically dominant component 50 90 in most cases as an alternative to the prevalent residual source model it is proposed that the distinctive geochemical characteristics of these a type granites are a function of the high liquidus temperatures and primitive mg rich character of subcrustal magma fluxes in post orogenic and anorogenic environments where such magmas are emplaced into stabilized continental crust further nd isotope studies of other a type granite suites are required to ascertain if models invoking crust mantle interaction are more widely applicable

effect of a dolerite intrusion on triterpane stereochemistry and kerogen in rundle oil shale australia abstract stereochemical changes of triterpanes present in extracts from an immature oil shale sequence intruded by a 3 m dolerite sill have been studied by gas chromatography mass spectrometry gc ms the steric configuration of the hopanes was observed to change from one dominated by the thermally less stable 17 h 21 h configuration at some distance from the intrusion to one dominated by the thermally more stable 17 h 21 h and 17 h 21 h configurating in the immediate vicinity of the intrusion in addition severe alteration of the kerogen appeared to have taken place as a result of the contact metamorphism and high concentrations of extractable organic matter were observed below the intrusion characterization of the kerogens by curie point pyrolysis has enabled the effects of the intrusion on the shales to be monitored

flow pattern variability in natural fracture intersections we use numerical simulations to examine the variability of flow patterns in representative fracture intersection geometries in contrast to existing studies of perfectly orthogonal intersections we demonstrate that more realistic geometries lead to a rich spectrum of flow patterns moreover numerical solutions of the navier stokes equations in these fracture intersections indicate that non linear inertial effects become important for reynolds numbers as low as 1 100 such reynolds numbers often exist in naturally fractured formations particularly in karst systems and in the vicinity of wells during pump tests

alkali zirconosilicates in peralkaline rocks based on the crystal chemistry of alkali zirconosilicates azs it is argued that zr in silicate melts is a network modifier rather than a complex former with the aid of silicate melt theory the late crystallization of azs in peralkaline melts can be explained the high ks ns and high q calculated in some norms of peralkaline rocks but not expected from the modes is the result of calculating zrsio4 rather than k na 2zrsio5 xsio2

ahdeb oil field mesopotamian basin iraq reservoir architecture and oil charge history the ahdeb oil field is located in the mesopotamian basin of central iraq within a northwest southeast trending anticline seven oil bearing layers exist in the eastern area in the field but there is only one oil bearing layer in the western area this study reveals that the reservoir filling process resulted from the difference in the elements in the petroleum system the oil generation and migration process and the formation of the structural trap most oils in the field with pristane phytane 1 and a high relative abundance of hopanes exceeding c30 were generated from the upper jurassic lower cretaceous chia gara formation whereas some oils were generated from the lower cretaceous ratawi and zubair formations the mid upper cretaceous reservoirs in the field are composed of lime grainstones packstones and wackestones the main oil accumulation occurred during the maastrichtian coinciding with peak oil generation from the chia gara formation with a 50 transformation ratio from organic matter to oil the reservoirs of the eastern structural trap in the field were filled with large amounts of medium to heavy oils after the formation of two structural traps in the western area in the mid miocene oils pre existing in the second layer of the khasib formation in the east began migrating toward the structural traps in the west during the late miocene as verified by relatively higher 1 4 methylcarbazole and 1 8 2 7 dimethycarbazole ratios of oils in the west than that in the east and residual solid bitumen in the east the strike slip fault might also have restricted oil or gas migration during the miocene limiting oil accumulation in the west

release of kerogen bound hopanoids by hydropyrolysis hydropyrolysis was used to determine the concentrations of kerogen bound hopanoid hydro carbons the samples characterized were a recent sediment priest pot english lake district and three source rock kerogens green river shale draupne shale and jet rock shale the hydropyroly zate of a hopanoid producing bacterium methylobacterium organophilum showed that this procedure does not overly obscure the original isomer compositions of the samples characterized although signifi cant side chain cleavage does occur which is inevitable with any pyrolysis method notable diaerences are observed between the composition of pyrolyzates and bitumen extracts for each of the source rock kerogens the overall level of hopane isomerization within the pyrolyzate is significantly lower than in the corresponding extracts this is particularly the case for the draupne sample the pyrolyzate of which contains 17b 21b hopanes though these are absent in the bitumen diaerences in isomeric com position of the pyrolyzates are in line with the isomer contents of the bitumen extracts the abundance of kerogen derived hopanes is highly variable both in terms of absolute concentration and also relative to the concentration of hopanes in the bitumen this is in part due to maturity diaerences but deposi tional environment and diagenetic conditions may also exert a control on kerogen bound hopane con centration these results show that hydropyrolysis provides valuable data on the concentration of kerogen bound hopanes whilst largely preserving their original isomeric composition 1998 elsevier science ltd all rights reserved

aluminum coordination in metaaluminous and peralkaline silicate melts incremental amounts of na2o and k2o added to immiscible melts in the mgo cao tio2 al2o3 sio2 system cause a decrease in critical temperature phase separation and change in the pattern of al2o3 partitioning al2o3 which is concentrated in the low sio2 immiscible melts in the alkali free system is increasingly partitioned into the high sio2 immiscible melt as the alkali aluminium ratio is increased however k2o is more effective than na2o in stabilizing al2o2 in the sio2 rich melt the coordination changes occurring in the aluminosilicate melts upon the addition of the alkali oxides are described by caal2o4 2siok 2kalo2 siocaosi where k or na displaces ca as the charge balancing cation for the networkforming alo4 tetrahedra the increased stability of the alo4 species in the highly polymerized sio2 rich melt and the consequent shrinkage of the miscibility gap is ascribed to positive configurational entropy and negative enthalpy changes associated with the formation of k na alo4 species element partition systematics indicate that na k alo2 species favor the more polymerized caal2o4 and tio2 species the less polymerized silicate structure in the melt

formation and evolution of the masirah ophiolite constrained by paleomagnetic study of volcanic rocks abstract the extrusive rocks of the lower ophiolitic nappe of masirah island oman were paleomagnetically studied four mean directions of magnetization were isolated one at low temperature the others at high temperature the low temperature component found in most samples corresponds to a recent viscous and or chemical remagnetization the high temperature component found at three sites in the centre area is interpreted as a possible primary magnetization acquired during extrusion or more probably as an early remagnetization related to subsequent hydrothermal alteration and indicates formation of the masirah ophiolite around a paleolatitude of 40 s close to the present position of the west somali basin a second high temperature component found in three other sample sites in the hakl and in the thumi areas is probably a chemical remagnetization related to the emplacement of the upper ophiolite nappe in late maastrichtian to paleocene times finally a last high temperature component found only in the two sites from naft area could be a post tectonic remagnetization acquired in oligocene or miocene times or represents differential tilting of pillows and sedimentary blocks the high temperature components are usually fairly scattered due to the very complex tectonic history of the area nevertheless the relation between the defined paleopoles and the indian polar wander is unambiguous and the evolution of the masirah ophiolite from formation up to the emplacement of the second ophiolitic nappe is clearly related to the northward movement of the indian plate this new paleomagnetic study rules out the possibility of a common or related origin for the masirah and the semail ophiolites

biomarker transformations as constraints for the depositional environment and for maximum temperatures during burial of opalinus clay and posidonia shale in northern switzerland abstract samples from two argillaceous formations opalinus clay and posidonia shale of near identical maturity from northern switzerland were subjected to a geochemical characterisation of organic matter and to confined system pyrolysis experiments throughout the study area the characteristics of organic matter are similar indicating a spatially homogeneous sedimentary facies posidonia shale contains marine organic matter deposited in a reducing environment while a predominantly terrigenous source and a more oxidising environment of deposition was identified for opalinus clay in the western and central parts of the study area organic maturity is close to the onset of oil generation in the easternmost part a higher maturity has been reached due to a deeper burial below thick tertiary molasse deposits isothermal pyrolysis experiments were conducted at temperatures between 250 and 390 c over 24 h bitumen yields increase along similar pathways for both opalinus clay and posidonia shale but the maximum values are displaced by 10 20 c data pertaining to maturity were determined from gc ms analyses of saturated hydrocarbons and specific attention was given to c 29 sterane and c 32 hopane isomerisation ratios the evolution of these parameters with rising temperature is slightly different in the two formations which is attributed to the contrasting organic facies the pyrolysis data together with literature data from natural basins were used to calculate kinetic parameters for c 29 sterane and c 32 hopane assuming a single step isomerisation scheme according to the arrhenius law the resulting values based on pyrolysis data alone are very similar to those based on the combination of pyrolysis and natural data activation energies are similar in both formations while the frequency factors are up to one order of magnitude higher for posidonia shale when compared to opalinus clay for the benken site maximum temperature during cretaceous burial was calculated on the basis of the kinetic data using the tti approach the resulting temperatures of 75 80 c are 5 10 c below those derived in the literature from apatite fission track analysis vitrinite reflectance and basin modelling

source rock characterization and oil to source rock correlation of a cambrian ordovician fold and thrust belt petroleum system western newfoundland abstract in this study we use biomarker and isotope data to address the complexities of petroleum system analysis in fold thrust systems specifically related to hydrocarbon generation and migration such as variable thermal maturities of source rocks complex migration pathways and mixing source rocks extracts and oil samples are taken from paleozoic rocks along the appalachian structural front in western newfoundland oil seeps along this fold and thrust belt have motivated episodic exploration efforts over the last 150 years however economic development has been unsuccessful to date in part because of the complex nature of oil to source relationships pyrolysis analyses identify promising source intervals in lower ordovician floian formations with an excellent source potential containing type i ii organic matter toc up to 9 35 hi up to 840 a second good source interval identified within the late cambrian furongian continental slope and rise sediments contains type ii iii organic matter toc up to 2 34 hi 380 source rock samples from outcrops are marginally mature to mature with tmax values between 436 and 447 geochemical analyses of source rock extract imply a clastic shale dominated source rock with a minor contribution from carbonate source rocks chemometric analyses yield 3 extract groups groups 1 and 2 contain lower ordovician samples with organic matter derived from oxidized micro plankton with varying amounts of gleocapsomorpha prisca extract group 3 originates from cambrian samples and shows evidence of a bacterial derived organic matter similar genetic relationships among 10 oil samples from natural oil seeps and abandoned well sites are indicated by high resolution biomarker analyses seven oil samples originated from ordovician source rocks that produced high api oils with low bisnorhopane hopane tricyclic hopane ratios and high sterane concentrations supporting interpretation of a source containing algal derived organic matter three oils originated from cambrian shales these high api oils show high bisnorhopane hopane and tricyclic hopane ratios low sterane concentrations and low carbon isotope values all indicative of organic matter derived from bacteria generated over a wide range of maturities 0 98 1 26 ro thermal maturity sensitive biomarkers and naphthalene ratios show that source rocks generated oils with a wide range of maturities related to their dipping character in the imbricated thrust stack the cambrian source generated oils that locally experienced secondary cracking during acadian inversion whereas the ordovician source generated oil with low maturities after the acadian inversion oil operaters exploring fold and thrust belt petroleum systems may expect extreme changes of oil properties for example api gravity in spacially restricted areas

development of the mozambique and ruvuma sedimentary basins offshore mozambique two major sedimentary basins have been identified on the continental margin of mozambique mozambique basin and ruvuma basin the formation of the basins is related to the break up of gondwana and opening of the western part of the indian ocean the basins are relatively young having developed discordantly to the structural plan of gondwana sedimentary basins the history of the formation of the east african continental margin sedimentary basins within mozambique has been studied on the basis of the present day concept of gondwana break up and madagascar s drift with respect to africa two stages in the history of the east african basins can be recognized late gondwana and post gondwana the late gondwana stage 303 157 ma is typified by sedimentary and volcanogenic rocks of the karoo group the post gondwana stage 157 0 ma corresponds to the period of active gondwana break up and the formation of indian ocean marginal basins the mozambique basin occupies both central and southern parts of the coastal plain of mozambique extending onto the continental shelf and slope the sedimentary fill is composed of upper jurassic cretaceous and cenozoic rocks which discordantly overly the karoo basalts the upper jurassic occurs as continental red beds mostly distributed within buried grabens cretaceous rocks occur as terrigenous sediments of continental and marine genesis cenozoic deposits are of predominantly marine and deltaic origin the ruvuma basin situated in the north of mozambique is part of an extended east african marginal basin which includes parts of the coastal plains and continental margins of tanzania and kenya the basement of the basin is composed of crystalline and metamorphic rocks of pre cambrian age the sedimentary fill is represented by continental terrigenous karoo sediments marine and lagoonal jurassic deposits and marine and deltaic rocks of cretaceous and cenozoic age the main difference between the sedimentary fill of the mozambique and ruvuma basins is related to the changing sedimentary environment in the period of gondwana break up jurassic and early cretaceous when the drift of madagascar and sea floor spreading took place and the marine basin gradually extended southwards between the east african margin and madagascar from the late cretaceous on the sedimentary environment within both basins was similar the mozambique and ruvuma basins forming a single system on the east african continental margin the main stages of the basins development are illustrated by a series of palaeogeographic reconstruction maps

biomarker characterisation and hydrous pyrolysis of bitumens from tertiary volcanics queen charlotte islands british columbia canada abstract a number of bitumen samples have been recovered from vugs and fractures in outcropping tertiary basalts of the queen charlotte islands off the west coast of british columbia canada n alkanes and acyclic isoprenoids are not present and the polycyclic biomarker distribution of the four samples analyzed by gc and gc ms has been altered one sample contains no remaining recognizable biomarkers two bitumens were also obtained from lower jurassic potential source rocks including one from the sandilands formation which was considered previously to be the most likely source of the tertiary bitumens although these two bitumens were also taken from outcrops they are considerably less biodegraded the sandilands formation bitumen contains 28 30 bisnorhopanes and since these compounds were not detected in the tertiary bitumens there is no evidence from the initial results for a sandilands formation contribution to the hydrocarbons in the tertiary basalts the presence of 18 h oleanane in the saturate fraction of two of the tertiary bitumens from widely separated locations indicates that they are at least partially sourced from tertiary organic matter because the distribution of biomarkers in some samples has been severely affected by biodegradation the asphaltenes of the bitumens were hydrously pyrolysed and the saturate fractions of the resulting pyrolysates analysed for possible additional information on the origin of the bitumens the pyrolysates from the more degraded samples contain compounds not detected in the saturate fractions of the original bitumen and show some of the expected characteristics of the original non degraded bitumen however the compounds most useful for correlation are not present in the pyrolysates apparently due to their non incorporation into the kerogen macromolecule our results suggest that hydrous pyrolysis of asphaltenes is of limited use in the correlation of biodegraded samples and in determining their origins

zircon saturation in silicate melts a new and improved model for aluminous and alkaline melts the importance of zircon in geochemical and geochronological studies and its presence not only in aluminous but also in alkaline rocks prompted us to think about a new zircon saturation model that can be applied in a wide range of compositions therefore we performed zircon crystallization experiments in a range of compositions and at high temperatures extending the original zircon saturation model proposed by watson and harrison earth planet sci lett 64 295 304 1983 and boehnke et al chem geol 351 324 334 2013 we used our new data and the data from previous studies in peraluminous melts to describe the solubility of zircon in alkaline and aluminous melts to this effect we devised a new compositional parameter called g left left 3 cdot text al 2 text o 3 text sio 2 text na 2 text o text k 2 text o text cao text mgo text feo right right molar proportions which enables to describe the zircon saturation behaviour in a wide range of rock compositions furthermore we propose a new zircon saturation model which depends basically on temperature and melt composition given by with 1 errors ln left text zr right left 4 29 pm 0 34 right left 1 35 pm 0 10 right cdot ln g left 0 0056 pm 0 0002 right cdot t left circ c right where zr is the zr concentration of the melt in g g g is the new parameter representing melt composition and t is the temperature in degrees celsius the advantages of the new model are its straightforward use with the g parameter being calculated directly from the molar proportions converted from electron microprobe measurements the temperature calculated given in degrees celsius and its applicability in a wider range of rocks compositions our results confirm the high zircon solubility in peralkaline rocks and its dependence on composition and temperature our new model may be applied in all intermediate to felsic melts from peraluminous to peralkaline compositions

petrologie du granite peralcalin du lac brisson labrador central nouveau quebec ii mineralogie et modalites de cristallisation mineral zonation in the quebec labrador brisson lake peralkaline granite displays quartzose and feldspathic lithofacies arranged concentrically the latter occupying the centre of the intrusion the zonation is the result of successive magmatic pulses in the feldspathic facies agpaitic crystallization began under hypersolvus conditions around 720 c with pf 0 1 gpa subsolvus crystallization involving enrichment of the residual liquid in f continued to below 500 c the quartzose facies is more differentiated and its composition was controlled by feldspar fractionation early quartz crystallization is partly explained by the high content of f in the magma the mafic mineral succession is in both facies li and zn rich arfvedsonite with an important ferrorichterite component which crystallized along with alkali feldspar under low aenigmatite contemporary of amphibole or anterior destabilized to form neptunite astrophyllite aegirine or arfvedsonite primary titaniferous aegyrine contemporary w

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

fluoride silicate melt immiscibility and its role in ree ore formation evidence from the strange lake rare metal deposit quebec labrador canada pegmatites and adjacent subsolvus granites two alkali feldspars of the mid proterozoic strange lake pluton quebec labrador canada host potentially economic concentrations of high field strength elements hfse including the rare earth elements ree zirconium and niobium previous studies have proposed that these concentrations were the result of a com bination of extreme fractionation of a peralkaline granitic magma and later hydrothermal remobilization however the recent discovery of melt inclusions which after heating to 900 or 950 c quench to immiscible fluoride and silicate glasses suggests an additional mechanism of hfse concentration crystallized melt inclusions are common in quartz phenocrysts of the early hypersolvus and transsolvus granite after heating four types of inclusions were discerned type 1 inclusions quench to a single silicate glass containing a high concen tration of zr nb and ti quenching of type 2 inclusions produces a zr nb ti rich silicate glass containing a globule of calcium rich fluoride glass with a high concentration of the ree the third inclusion type is similar to type 2 except that the calcium rich fluoride glass contains a globule of ree fluoride glass up to 50 wt total ree type 4 inclusions contain calcium fluoride glass with multiple silicate globules we propose that during or soon after emplacement the early granitic magma exsolved a calcium fluoride melt into which rare earth elements ree partitioned preferentially the conjugate silicate melt was consequently depleted in ca and the ree and enriched in zr nb and ti crystallization of the fluoride melt occurred late in the crystallization history of the silicate magma allowing it to accumulate in the volatile rich residual magma that formed the pegmatites this played a major role in the extreme enrichment of the pegmatites in ca f and ree crystallization of the pegmatites proceeded inwards from an outer zone in which feldspars quartz arfvedsonite and zirconosilicate minerals dominate to a core where the immiscible fluoride liquid collected and crystallized fluorite and ree minerals fluid exsolved from the silicate melt reacted with the products of both the silicate and fluoride melts remobilizing most of the hfse including the ree this study reports a rare example of silicate fluoride melt immiscibility and the first in which such immiscibility played a role in concentrating the ree to potentially economic levels 2014 elsevier ltd all rights reserved

density and size distribution of seamounts in the eastern pacific inferred from wide beam sounding data theoretical expressions relating the distribution of apparent seamount heights per unit length of ship track to the distribution of actual seamount heights per unit area of seafloor are derived for both narrow beam and wide beam echo sounders the shapes of seamounts are approximated as truncated right circular cones of constant slope e height to radius ratio and flatness f i e a seamount of basal radius r has a height h r a flat top of radius fr and a slope angle of arctan e the set of all seamounts in a given physiographic province is assumed to be a poissonian ensemble specified by a function v r the average number of seamounts per unit area for which r r a simple choice for the size distribution of seamounts and one shown to be consistent with data in the eastern pacific is to specify that it decays exponentially with r v r vo exp r in the case of a profile of length l taken in water of depth d with a wide beam echo sounder half beam width the shallow slope deep water approximation e 1 e d yields that the expected number of seamounts with apparent heights h h is n h l 2 1 ed 2 fh lv0e h we apply this sampling theory to apparent height data measured from 44 020 km of wide beam profiles on pacific crust of post mesozoic age although the spatial distribution of seamounts in the eastern pacific is certainly not poissonian the abundance statistics do not involve spatial correlations and we show they are robust with respect to deviations from the poisson model provided the statistics are interpreted as averages over the area actually sampled by the track lines the observed falloff of apparent heights in the eastern pacific is very nearly exponential justifying our use of an exponential model of seamount size distribution the shape parameters are estimated from multibeam surveys of pacific seamounts an analysis of 30 features in the height range 200 4000 m yields 0 21 0 011 and f 0 21 0 028 using these parameters we obtain vo 4 0 1 1 10 9 m 2 and 6 3 0 8 10 4 m 1 these values imply that per 106 km2 in the eastern pacific there are 1600 400 seamounts with summit heights greater than 300 m and 200 60 greater than 1000 m integrated over the entire size distribution seamounts occupy about 6 of the seafloor area and constitute about 0 4 of the oceanic crustal volume our estimates of seamount abundance are appreciably greater than those of most other authors a discrepancy we attribute primarily to the sampling bias of previous studies which generally used uncorrected map counts this hypothesis is corroborated by a comparison of our statistics with map count data for seamounts of heights exceeding 2000 m compiled for the eastern central pacific from the scripps charts above 3000 m the map counts are consistent with the predictions of the exponential model but below this height they are biased to low values

methane sorption capacities and geochemical characterization of paleozoic shale formations from western peninsula malaysia implication of shale gas potential abstract thick sequences of overmatured paleozoic black shales formation were deposited in the western peninsula wp malaysia which can be considered as the potential shale gas reservoir therefore to study the shale gas potential of the paleozoic silurian permian shale formations 146 samples from seven formations were collected from wp malaysia a combination of methane sorption capacities geochemical and trace element studies have been performed on the shale samples the results indicate that the high pressure up to 15 mpa methane sorption capacity of the silurian devonian devonian carboniferous and permian shales are between 0 079 and 0 154 0 056 and 0 113 0 052 and 0 094 and 0 085 and 0 169 mmol g rock respectively at 30 c methane sorption capacities of the wp malaysia shale were found to be greatly similar to sorption values of hot shales from posidonia germany barnett usa and longmaxi china shales the measured total organic carbon toc generally exceeded 2 wt average of 4 wt except for carboniferous shales 1 wt the biomarker analysis and tmax values revealed that the kerogen has evolved into the metagenesis stage the organic matter is likely comprises hydrogen rich kerogen deposited under marine conditions in dysoxic to anoxic environment after a comprehensive analysis the silurian devonian devonian and permian shales in western peninsula malaysia can be classified as potential gas shales based on their high toc contents presence of type iii kerogen high thermal maturity and significant methane sorption capacities

a time slice approach to the history of cenozoic sedimentation in the indian ocean abstract results from drilling at over 100 sites have been combined with a new plate tectonic model to produce a series of palinspastic maps which represent snap shots of the changing patterns of sediment accumulation in the indian ocean through the cenozoic the maps clearly delineate the main sedimentary depocenters and show how the sedimentary record has responded on an oceanwide scale to major changes in paleogeography tectonics paleocirculation and or climate paleogene sediment accumulation rates were generally low with significant accumulation in only limited areas suggesting weak ocean circulation and stable well stratified conditions by contrast the vigorous thermohaline circulation of the neogene resulted in substantial widespread sedimentation accumulation rates were generally high and displayed a wide range of values following rapid growth of the east antarctic ice sheet in the mid miocene carbonate sedimentation has been progressively restricted to the shallow ridges and plateaus of the western indian ocean but accumulates there with locally high rates the link between tectonics and terrigenous sedimentation is exemplified by the major deep sea fans off east africa zambezi fan and india indus and bengal fans which developed in response to uplift and erosion beginning in late oligocene time in the east african rift system and the himalayas respectively although maps from only five widely spaced times are shown the methodology is such that a continuous series of maps at intervals as close as 1 m y can readily be generated ultimately the combination of such time slice maps with the results of detailed time series studies will provide a powerful tool for understanding past oceanic environments

observation of sections of oceanic crust and mantle cropping out on the southern wall of kane fz n atlantic the objective of the 20 nautile dives of the recent kanaut cruise was to study the southern wall of the kane fracture zone from its eastern intersection with the mid atlantic ridge mar to 5 myr in age the geological mapping shows four successive massifs wrench faulted and slightly tilted the transform facing walls of these massifs exhibit outcrops of fresh and serpentinized peridotites gabbros and basalts the entire crustal exposure is cataclased and metamorphosed to greenschist facies

vitrinite reflectance and molecular geochemistry of jurassic sediments the influence of heating by tertiary dykes northwest scotland vitrinite reflectance measurements from sedimentary rocks adjacent to six dykes from sites across the inner hebrides indicate that the lateral extent of thermal alteration is reasonably similar and proportional to dyke thickness d t with alteration starting to take effect at 70 d t detailed sampling of a jurassic siltstone adjacent to a 0 9 m dyke reveals that the zone of maximum extractable organic matter eom wt g rock equivalent to the oil window is relatively narrow ca 25 of the d t the position of this oil window relative o the vitrinite reflectance profile is comparable with that from burial maturation gas chromatograms of the aliphatic hydrocarbon fractions reveal i a shift from branched and cyclic dominated hydrocarbons to an increasing predominance of straight chain components and ii the carbon number distribution of the n alkanes shifts towards the shorter chain homologues with decreasing distance from the dyke contact apart from the methylphenanthrene index mpi1 changes in each of the molecular maturity parameters are initiated by the the thermal effects of the dyke between 80 and 70 d t from the contact the mpi1 parameter was the most sensitive maturity indicator in that it responded to the dyke emplacement even in the distal samples i e distance from dyke contact 140 d t a significant reduction in toc at the dyke contact suggests that the synthesis gas reaction may have occurred i e the reaction of organic matter with steam resulting in the formation of carbon monoxide this reaction may be associated with the vitrinite reflectance reversal this study suggests that these particular dykes have had only a local effect on the maturity of the intruded sediments

confined pyrolysis of tertiary lacustrine source rocks in the western qaidam basin northwest china implications for generative potential and oil maturity evaluation abstract the parameter s 1 s 2 genetic potential of rock eval analysis is widely used as an evaluation of the genetic potential for the source rocks oligocene miocene saline lacustrine source rocks in the western qaidam basin have low total organic c contents toc most around 0 5 with a few exceptions 1 0 mineral matrix effects are substantial for source rocks with low toc resulting in relatively low s 1 and s 2 peaks based on the results of confined pyrolyses sealed au capsules on 6 oligocene miocene source rocks from the western qaidam basin with toc ranging between 0 48 and 2 22 the relationship between the s 1 s 2 parameter and the maximum amount of extracted bitumen or saturated and aromatic hydrocarbons sa after the confined pyrolysis has been established as follows bitumen mg g rock 1 4924 s 1 s 2 0 3201 r 0 987 or sa saturates aromatics mg g rock 0 7083 s 1 s 2 0 4045 r 0 992 based on these formulas the amounts of hydrocarbons generated from source rocks can be reasonably estimated the typical crude oils with low biomarker maturities in this region appear substantially different to the pyrolysates of these six rocks at 180 300 c but comparable to the pyrolysates at 320 c and higher temperatures based on molecular parameters this result in combination with the physical and gross compositions of the crude oils suggests that the majority of these crude oils were generated from the source rocks during the main oil generative stage possibly at a maturity higher than r o 0 74

petrologie du granite peralcalin du lac brisson labrador central nouveau quebec 1 mode de mise en place et evolution chimique the lake brisson peralkaline granite in labrador which by way of its age of 1189 ma is the most recent phase of the gardar magmatic stage was intruded in the middle proterozoic at the margin of a granulitic complex retrograded to an amphibolite facies during aphebian and of an elsonian adamellite pluton it shows a petrographie zonation feldspathic facies at the center quartzose facies including early quartz at the edge suggestive of a permissive multiphase intrusion and is characterized by deuteritic alteration via metalliferous fluids zr y nb be rare earths all facies are na peralkaline well evolved and represent end members of a differentiated magmatic suite of the designated a type the relative behavior of the major elements indicates that the facies differentiation was controlled by fractional crystallization and was also greatly influenced by alkaline feldspath and by increase of f o2 in the final stage of evolution the trace elements contents significantly higher than those

changes in hydrocarbon maturity indices with coal rank and type buller coalfield new zealand abstract the buller coalfield south island new zealand is an inverted late paleogene basin that contains middle eocene bituminous coals which exhibit considerable variation in both coal rank across basin and coal type in seam twenty two fractionated bitumen extracts of brunner coal measures coal samples from 12 drillholes were analyzed by gc and gc ms to characterize the effect of coal rank and type on conventional hydrocarbon maturity indices at the beginning and end of the oil window 0 56 1 26 ro max the carbon preference index pristane phytane and isoprenoid n alkane ratios evolve throughout the high volatile bituminous b rank stage while other biomarker ratios 18 h 22 29 30 trisnorneohopane 17 h 22 29 30 trisnorhopane ts tm 18 h 21 h 30 norneohopane c 29 ts 17 h 21 h 30 norhopane and c 30 diahopane hopane do not show appreciable change in value until medium volatile bituminous rank various aromatic based ratios appear to be more effective in delineating rank throughout the entire oil window in particular the methylphenanthrene index and vitrinite reflectance are positively correlated over the entire bituminous rank range however subtle changes in depositional conditions variable coal type complicate these rank estimates within a given coal seam variation in cpi isoprenoid n alkane and hopane sterane ratios appear to be related to the hydrogen content of the coal while the homohopane index and the oleanane hopane ratio covary with sulfur content as with depressed vitrinite reflectance values mpi is similarly lowered in the perhydrous samples the mechanisms that control these hydrocarbon parameters during deposition and diagenesis are complex and convoluted however changes in bacterial activity and community with marine incursion appear to play an important role due to these anomalies none of the hydrocarbon maturity indices calculated can be singularly used to constrain coal rank

magmatic evolution and controls on rare metal enrichment of the strange lake a type peralkaline granitic pluton quebec labrador abstract although it is well known that a type granites are enriched in the rare earth elements ree and other high field strength elements hfse the magmatic processes that concentrate these elements are still poorly understood the 1 24 ga strange lake pluton in northern quebec labrador provides an extraordinary example of hyper enrichment in the ree zr and nb in a peralkaline a type granite the pluton consists of two hypersolvus granite units southern and northern and a transsolvus granite all of which contain perthitic alkali feldspar as the earliest major mineral the transsolvus granite also contains separate albite and microcline crystals arfvedsonite a sodic amphibole occurs exclusively as phenocrysts in the transsolvus granite whereas in the hypersolvus granite it is present as a late interstitial phase the primary hfse minerals are zircon monazite ce gagarinite ce and the pyrochlore group minerals magma evolution was monitored by the alumina content in the bulk rock which decreases from the southern to the northern hypersolvus granite and is lowest in the transsolvus granite alkalinity indices and bulk si fe rb ree zr nb concentrations show the opposite trend alkali feldspar compositions mirror the trend shown by the bulk rock i e decreasing al contents are accompanied by increasing si fe3 ree zr and nb contents the major driving forces for the evolution of the hypersolvus magma prior to emplacement were the early separation of a fluoride melt from the silicate melt and the crystallization of alkali feldspar and hfse rich phases zircon monazite ce pyrochlore group an alkali feldspar rich crystal mush containing lree fluoride melt droplets was emplaced as the least evolved southern hypersolvus granite massive fractionation of alkali feldspar led to a sharp increase in h2o and f activity in the magma chamber that triggered the crystallization of arfvedsonite and was followed by emplacement of the northern hypersolvus granite which contained a higher proportion of lree fluoride melt droplets further evolution in the magma chamber led to a transition from a miaskitic to an agpaitic composition the transsolvus granite was intruded in the form of a low viscosity crystal mush of alkali feldspar quartz arfvedsonite after appreciable crystallization of arfvedsonite and lree fluoride melt droplets upon emplacement arfvedsonite and gagarinite ce crystals segregated as cumulates in response to a combination of flow differentiation and gravity settling the immiscible fluoride melt accumulated in a volatile rich residual silicate magma which migrated to the top of the pluton where it formed the f ree rich cores of highly mineralized pegmatites

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

biomarker maturity parameters the role of generation and thermal degradation abstract the effects of burial maturation upon seven molecular maturity parameters and the concentrations of individual biomarkers employed in these parameters have been studied in a well in the barents sea the depth interval between 1400 and 3000 m comprises homogenous eocene claystones with effectively uniform organic carbon content 0 4 0 6 and kerogen type hi of 100 200 mg hc g toc the quantitative biomarker data thus contain minimal interference from organic facies hydrocarbon expulsion effects and the presence of migrated hydrocarbons bulk geochemical data define the hydrocarbon generation threshold or oil window at around 2300 m molecular maturity parameters proceed to equilibrium and in some cases demonstrate inversion at high maturity these molecular changes are associated with major changes in biomarker concentrations the hopane 22 s c 31 hopane and 20 s c 29 sterane parameters proceed as a result of the balance between the relative rates of generation and thermal degradation of the different isomers increased concentrations of the individual isomers are interpreted to be the result of biomarker generation from the kerogen mainly and other macromolecular polar fractions the c 29 sterane parameter and the three parameters involving rearranged hopanes ts 29ts and diahopane operate at higher maturity levels and proceed as a result of the relative rates of thermal degradation of the compound pairs isomerisation in the bitumen may also influence the operation of the parameters involving stereoisomers but must be a relatively minor contribution

transport behavior in three dimensional fracture intersections 1 flow and transport patterns in three dimensional fracture intersections are investigated with emphasis on the occurrence and effects of local flows around each intersection flow and transport simulations indicate that local flow circulations referred to as local flow cells arise because of an interplay between intersection geometry and corresponding boundary conditions for flow along the fracture boundaries local flow cells are thus unique features in three dimensional fracture networks the analysis here suggests that local flow cells have little effect on the overall fluid flow in a fracture network but may constitute an effective mechanism which contributes to the long breakthrough tailing and retardation often observed in transport through discrete fracture networks

experimental mixing variability in intersecting natural fractures laboratory experiments of flow through epoxy replicas of intersecting natural fractures show that solute transport deviates significantly from predictions of two dimensional streamline routing through parallel plate intersections surface roughness in intersecting fractures causes two major discrepancies between mixing experiments and the parallel plate predictions first the fluids exiting the intersection are not uniformly mixed but consist of ribbons with varied solute concentrations which tend to follow streamlines in the flow some of these streams maintain a nearly pure inlet fluid composition as they exit the intersection and traverse the outlet fracture second when the outlet fluids are collected and homogenized we find that this complex redirection of streamlines within natural rough walled fracture intersections results in more total mixing than is predicted by the parallel plate model

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

geochemistry and correlation of oils and source rocks in banqiao sag huanghua depression northern china abstract located in the western part of huanghua depression s central segment in the bohai bay basin the banqiao sag is a significant sedimentary basin the crude oil produced has low density low viscosity low sulfur and high wax content crude oil types include conventional crude as well as condensate oil gas light oil and low maturity oil four possible source rocks are present within the banqiao sag however at present the oil source is not very clear rock eval pyrolysis stable carbon isotope composition and biomarker analysis were conducted on 26 source rock core samples in the banqiao sag to evaluate their characteristics results indicate that the shahejie formation 43 32 8 ma has source rocks that can be graded between poor to excellent quality they were deposited in a marine based reducing environment and rich in organic matter sha 1 member es1 and sha 3 member es3 are considered thermally immature to mature based on various maturity indicators 17 crude oil samples from the banqiao sag were compared with these rocks biomarkers and stable carbon isotope parameters the analyzed crude oils were divided into 4 groups based on carbon isotope composition and q type cluster analysis qca there are two sets of effective hydrocarbon source rocks in the study area s shahejie group i e es1x and es3 contributing to the oil found in the structural belts oil and source rock correlation results indicate that group b1 oil is probably derived from highly mature es3 group b2 oil is most likely derived from a mixed mature es3 and early mature es1 group b3 oil is derived from es3 in tanggu xingang buried hill structural belts and from es1 in immature or low mature stage in banqiao sag group b4 oil is derived from mature es3 in banqiao sag with little early mature es1 this study can highly benefit future oil and gas exploration work in the banqiao sag

hopanoid hydrocarbon maturation by an igneous intrusion abstract the thermal effects of an igneous intrusion 0 9 m thick dyke upon the abundance and composition of hopanes and hopenes are reported for a suite of samples within a single sedimentary horizon a carbonate concretion 1 6 m in diameter from the jurassic dun caan shale member bearreraig bay isle of skye scotland the conventional hopane maturity parameters show normal trends towards the dyke and through the oil window approximately 22 45 cm from the dyke i e 25 50 dyke thickness with the exception of the ts ts tm parameter which shows a progressive fall with increasing maturity until the middle of the oil window when it increases markedly molecular abundances demonstrate that the observed changes in the hopane maturity parameters result from the combined effects of generation presumed to be from kerogen and degradation of individual compounds with isomerization in the free phase being minimal or unimportant the unexpected behaviour of ts ts tm results from the minimal generation of ts compared with tm our data indicate that the ts skeleton is not present in the kerogen and at least under the elevated heating associated with an igneous intrusion may be derived from 18 h 22 29 30 trisnorneohop 13 18 ene in the bitumen thermally induced modifications to hopane carbon number distributions are also reported and show that oil source rock correlations between samples of different maturity must consider the effects of generation degradation of kerogen bound hopanes