subsurface seepage dynamics and flow types in a messinian paleoseep system maiella mts central italy abstract the subsurface feeder complexes of mud volcanoes and seepage systems potentially provide valuable information on the evolution of seepage dynamics ancient seepage systems in outcrops allow for the observation of expulsion features which are otherwise commonly beyond seismic resolution in the maiella hydrocarbon seep area the evolution of fluid migration through the sedimentary column during the messinian salinity crisis generated distinctive seep plumbing features geological responses and geochemical signatures in the brecciated limestones unit the fluid migration pathways evolved from funnel shaped feeder channels flow mobilized sediments into hydrofractured microbial carbonate buildups limestone buildups and finally into blow out micropipes in the host sediment patchy limestones as overpressure dissipated through the plumbing system the flow mobilized sediments 13c down to 24 5 pdb 1 correspond to the highest flow rates in the whole area whereas the patchy limestones 13c down to 39 3 pdb 1 correspond to the slowest flow rates within the intrusive zone the limestone buildups show different degrees of hydrofracturing that reflect different flow rates 13c down to 27 5 pdb 1 the fluid transport mechanisms evolved from focused venting through neoformed feeder channels where sediments elutriated from depths were carried out the sediment prone response to fluid migration to high rate seepage triggering high hydrofracturation in the microbial buildups while the hydrocarbon rich fluids contemporaneously triggered authigenic precipitation the mineral prone response to fluid migration progressive upward and lateral flow deceleration resulted in gradually weaker hydrofracturing of the microbial buildups and finally only local cementation in the form of carbonate patches within the host sediments

review of fossil chemosynthetic assemblages in japan abstract seventy five fossil chemosynthetic assemblages of cretaceous to holocene age have been discovered in japan many are interpreted to have been cold seep dependent and one is associated with a whale fall fossil hydrothermal vent assemblages have not been found in japan non seep assemblages of solemyids lucinids and or thyasirids are not included in this study various combinations of five diagnostic features characterize cold seep assemblages 1 the abundant and often exclusive occurrence of large invertebrate taxa suspected of harboring chemosynthetic bacteria 2 associated authigenic carbonates greatly depleted in 13c 3 a three dimensional distribution of the assemblage that is laterally restricted 4 associated pockmark or diapir related sedimentary structures and 5 the presence of conduit related tectonic or sedimentological structures such as faults slumps or debris flows excluding the whale fall assemblage we can divide cenozoic fossil chemosynthetic assemblages in japan into three types regardless of geochronologic age type i is dominated by vesicomyid bivalves and or tube worms characterized by its allochthonous or parautochthonous mode of occurrence in deep water greater than 1000 m settings along with tectonically or sedimentologically induced structures such as faults slumps diapirs or debris flows likely dependent on seepage controlled by subduction related tectonism and or on methane coming from the drastic decomposition of gas hydrate type ii is dominated by vesicomyid bivalves in most cases the species differ from those in type i and is characterized by autochthonous occurrences in muddy sediments from less than 1000 m water depth type iii is dominated by lucinoma and or conchocele and characterised by autochthonous occurrences in muddy sediments from depths of less than 300 m a living community similar to the type ii and iii assemblages has not yet been observed in the seas around japan it is noteworthy that no tectonically or sedimentologically induced structures have been observed in and around the type ii and iii fossil localities although the muddy sediments sometimes show brecciated facies that suggest an explosive effusion of methane

subdued state of tectonism of the great basin interior relative to its eastern margin based on deep resistivity structure abstract lower crustal fluid content and physical state of the central and eastern subprovinces of the great basin are compared on the basis of their deep electrical resistivity structure as derived from two detailed east west profiles of magnetotelluric mt soundings a simple but powerful and effective transformation of each profile s data allows derivation of a single characteristic mt sounding for each subprovince which is essentially free of the effects of middle to upper crustal lateral heterogeneity the characteristic soundings are amenable to layered earth inversion yielding broad scale model resistivity profiles into the uppermost mantle a striking difference in lower crustal electrical resistivity is apparent between the two subprovinces the tectonically more active eastern domain has a lower crustal conductance of 3000 siemens s at a model depth around 15 km while that of the relatively subdued great basin interior is only 750 s with a depth around 22 km thicknesses of the two subprovince conductors are resolvable independent of their resistivity 20 km at 7 m in the east and 15 km at 20 m in the interior this allows estimates of fluid filled porosity in the deep crust assuming highly saline brines and predominantly grain edge interconnection nominal values are 0 4 vol for the eastern subprovince but only 0 15 vol for the central region these porosities are consistent with fluid percolation models for ductile crustal rocks assuming on going fluid replenishment by basaltic underplating in the eastern great basin and with little fluid input occurring in the central great basin in the last 5 10 ma resistivity of the uppermost mantle in both regions is greater than that of the lower crust this implies relatively lesser fluid melt contents or poorer interconnection in the shallow mantle

palaeogene and neogene cold seep communities in barbados trinidad and venezuela an overview palaeogene and neogene fossiliferous carbonates from barbados trinidad and northern venezuela are interpreted to have formed at ancient cold seep sites the hydrocarbon seepage that fuelled these chemosymbiotic ecosystems was related to tectonic activity in the southern caribbean region particularly the subduction of the caribbean plate beneath the north atlantic plate the carbonates and fossils from the scotland district north eastern barbados are eocene miocene in age and are associated with two distinct tectonic units the sub oceanic fault zone and a diapiric melange the sub oceanic fault zone is the tectonic junction between accretionary prism sediments and over lying thrust sheets of fore arc basin sediments the loading of the thrust sheets caused methane rich fluids to be expelled from the accretionary prism sediments and channelled to the sea floor via the sub oceanic fault zone where it supported chemosymbiotic invertebrate communities containing vesicomyid lucinid thyasirid solemyid and nuculanid bivalves a variety of gastropods and possibly vestimentiferan tube worms the diapiric melange is considered to represent sediment that failed under pressure in the accretionary prism and was remobilised as a diapir that extruded onto the sea floor providing a conduit for methane and other hydrocarbons that sustained a chemosynthesis based community of vesicomyid lucinid and nuculanid bivalves and various gastropods the geological setting of fossiliferous carbonates known as freeman s bay limestone in southwest trinidad has been less fully investigated the freeman s bay limestone is a member of the miocene lengua formation which is believed to have formed in a fore deep basin on lapping onto an accretionary prism formed by the subduction of proto caribbean crust beneath the south american plate the carbonates and fossils of the fbl including the bivalves pleurophopsis unioides van winkle 1919 and thyasira adoccasa van winkle 1919 lucinids nuculanids and bathymodiolins and provannid and other gastropods are interpreted to have formed at palaeo seep sites on the accretionary prism little is currently known about the geological setting of the fossils collected from the miocene huso member of the pozon formation from northern venezuela but a seep origin is strongly suspected based on the taxa present like the fossil assemblages from barbados and trinidad the venezuelan material is dominated by vesicomyid bivalves together with lucinid thyasirid bathymodiolin and solemyid bivalves and various gastropods these taxa are characteristics of modern cold seep communities most comparisons between the fossil caribbean and modern seep fauna are necessarily at the generic or family level although in some cases individual species are found at both ancient and modern seep sites for example the gastropod cataegis meroglypta is found in seep carbonate from the sofz of barbados and the fbl of trinidad as well as at modern seeps on the barbados prism at the generic level this study has revealed the first fossil occurrences of abyssochrysos and provanna in the caribbean such temporal and spatial links further the understanding of both local and global patterns of biogeographic distribution of cold seep fauna

crustal assimilation in basalt and jotunite constraints from layered intrusions abstract to constrain the amount and rate of crustal contamination that is possible in basaltic and jotunitic magma and to gain an insight into the physical and thermal processes of assimilation in crustal magma chambers we have modelled published sr and nd isotopic data from three layered intrusions well exposed sequences of cumulates with no evidence of magma recharge provide direct records of concurrent assimilation and fractional crystallization afc the key to the modelling is that f the mass fraction of magma remaining in the chamber can be estimated from the thicknesses of the studied cumulate sequences this allows afc model curves to be fitted to the isotopic data by varying r the ratio of the rate of mass assimilated to the rate of mass crystallized the results of modelling show that r is nearly constant in 800 to 2000 m thick sequences of cumulates displaying up section decreases in anorthite content of plagioclase increases in whole rock sr 0 initial 87 sr 86 sr and decreases in whole rock e nd 0 initial e nd the r values of the layered sequences range from 0 12 in the fongen hyllingen intrusion over 0 20 in the bjerkreim sokndal intrusion to 0 27 in the hasvik intrusion the total amount of assimilation the bulk crust magma ratio reaches values of 0 08 0 19 and 0 28 at the level of the most contaminated samples after 60 to 80 crystallisation whereas the instantaneous crust magma ratio of the most contaminated magmas were respectively 0 14 0 46 and 0 70 for the three intrusions innumerable country rock xenoliths occur in the three layered intrusions and played a crucial role in the assimilation process the xenoliths spalled off the roofs of the magma chambers during magma emplacement and their initial temperature and composition relate to r in the intrusions in the hasvik intrusion r 0 27 the initial temperature of the country rocks was 450 c and the xenoliths were fusible metasediments and therefore produced a high fraction of partial melt that could be assimilated in the bjerkreim sokndal intrusion r 0 20 the country rocks were initially at temperatures of 640 880 c but included both refractory massif type anorthosite and fusible gneisses in the fongen hyllingen intrusion r 0 12 the country rocks were cooler 300 c and the xenoliths include refractory metabasalt dominant and fusible metapelite we argue that the refractory metabasalt and anorthosite xenoliths acted mainly as heat sinks resulting in reduced r values in fongen hyllingen and bjerkreim sokndal intrusions heating of refractory and fusible xenoliths and melting of fusible xenoliths absorbed sensible and latent heat of the magma energy balanced modelling shows that up to 75 of the heat available was absorbed by xenoliths within the magma chambers promoting higher rates of cooling and crystallisation than would have resulted from loss of heat to the envelope of country rocks alone the high r values reflect the amount of heat absorbed by heating and melting country rock within the magma chambers themselves and their constancy reflects the ready availability of fusible xenoliths

fabric and formation of grapestone concretions within an unusual ancient methane seep system eocene bulgaria terra nova 23 56 61 2011 abstract authigenic carbonates at methane seeps provide valuable information on the evolution of seepage dynamics in this study we report on an unusual type of 13c depleted 13c 44 8 to 8 3 v pdb vienna peedee belemnite calcite cemented grapestone concretion composed of small spheroidal nodules 0 1 15 cm across associated with an ancient seep setting in eocene marine sediments pobiti kamani area ne bulgaria field observations suggest that the nodules started to grow close to the ancient sea floor and apparently were agitated by fluid flow promoting their spheroidal shape the precipitation of calcite between sand grains started at multiple closely spaced nucleation sites induced by locally elevated calcite supersaturation in response to anaerobic microbial consumption of ascending methane consecutive nodule growth continued deeper in the sediment with the formation of dark and light concentric bands surrounding one or more nodule cores the occurrence of similar grapestone concretions at seeps might indicate changing redox conditions at the seep site

late jurassic early cretaceous hydrocarbon seep boulders from novaya zemlya and their faunas the paper describes late jurassic early cretaceous seep carbonate boulders from the russian arctic island of novaya zemlya collected in 1875 by a e nordenskiold during his expedition to siberia the carbonates are significantly depleted in heavy carbon isotopes 13c values as low as ca 40 and show textures typical for carbonates formed under the influence of hydrocarbons such as fibrous carbonate cements and corrosion cavities the rocks contain index fossils of late oxfordian early kimmeridgian late tithonian jurassic and latest berriasian early valanginian cretaceous age the fossil fauna is species rich and dominated by molluscs with subordinate brachiopods echinoderms foraminifera serpulids and ostracods most of the species including two chemosymbiotic bivalve species likely belong to the background fauna only a species of a hokkaidoconchid gastropod and a possible abyssochrysoid gastropod can be interpreted as restricted to the seep environment other seep faunas with similar taxonomic structure are suggestive of rather shallow water settings but in case of novaya zemlya seep faunas such structure might result also from high northern latitude

an upper jurassic methane seep limestone from the fossil bluff group forearc basin of alexander island antarctica an anomalous upper jurassic limestone bed 3 m thick is present within the volcaniclastic infill of a forearc basin exposed on alexander island antarctica the limestone formally designated the gateway pass limestone bed contains laminated crusts and blocks including hardgrounds showing radial fibrous and botryoidal calcite cements carbon isotope values are very negative delta 13 c of 33 5 per thousand to 44 6 per thousand pdb indicating a methane oxidation origin for the carbonate the limestone bed formed around a submarine cold seep in the antarctic peninsula forearc basin adjacent to the accretionary prism in contrast to adjacent nearly barren sea floor the limestone also yields a benthic island assemblage containing abundant gastropods and bivalves the seep is directly comparable to certain jurassic seeps at the convergent margin of the northeast pacific and both are related to subduction at the eastern proto pacific margin

shallow water methane seep faunas in the cenomanian western interior seaway no evidence for onshore offshore adaptations to deep sea vents sulfi de rich environments in shallow water were considered as sites where animals acquired preadaptations enabling them to colonize deep sea hydrothermal vents and seeps or where they survived extinction events in their deep sea habitats here we document late cenomanian shallow water seep communities from the tropic shale in the western interior seaway united states as a possible refutation of these hypotheses the late cenomanian was a time of extremely warm deep water temperatures which supposedly facilitated adaptations to the deep sea and of widespread oceanic anoxia oceanic anoxic event 2 that supposedly extinguished deep water vent and seep faunas contrary to the expectations the taxa of the tropic shale seeps were not found at coeval or younger deep water seep or vent deposits furthermore a cluster analysis of faunal similarity among cretaceous vent and seep faunas revealed no distinction between pre and post cenomanian seep faunas but instead strong similarities among aptian to late cretaceous seep faunas this suggests that a low temperature gradient from shallow to deep water did not facilitate invasions of deep sea vents and seeps from shallow water and that preadaptation for living at deep sea vents and seeps did not evolve at shallow water methane seeps the vast majority of adaptations to successfully colonize deepsea vents and seeps were most likely acquired below the photic zone

mapping magnetic sources at the millimeter to micrometer scale in dunite and serpentinite by high resolution magnetic microscopy abstract rock samples can have wide range of magnetic properties depending on composition amount of ferromagnetic minerals grain sizes and microstructures here we used scanning magnetic microscopy a highly sensitive and high resolution magnetometric technique to map remanent magnetic fields over a planar surface of a rock sample the technique allows for the investigation of discrete magnetic mineral grains or magnetic textures and structures with submillimeter scale resolution here we present a case study of magnetic scans of pristine and serpentinized dunite thin sections from the reinfjord ultramafic complex in northern norway the magnetic mineralogy is characterized by electron microprobe scanning electron and optical microscopy and with rock magnetic methods in serpentinized samples the magnetic carrier is end member magnetite occurring as large discrete grains and small grains in micron scale veins by contrast the pristine dunite sample contains large cr spinel grains with very fine equant exsolutions ranging in composition from ferrichromite to end member magnetite forward and inverse modeling of the magnetic anomalies is used to determine the remanent magnetization directions and intensities of discrete magnetic sources observed in the scanning magnetic microscopy the fine scale magnetization of the rock sample is used to investigate the magnetic carriers and the effect of serpentinization on the magnetic properties of the dunite modeling shows that the dipolar magnetic anomalies that are mapped by scanning magnetic microscopy are caused by grains with heterogeneous magnetic sources the intensity of the magnetization and the amount of magnetic minerals are higher in the serpentinized sample than the pristine dunite sample consistent with the measured bulk magnetic properties furthermore the serpentinized samples show a larger variability in the direction of the magnetization and a stronger heterogeneity with respect to the pristine sample the ability to rigorously associate components of the bulk magnetic properties to individual mineral phases creates new possibilities for rock magnetic paleomagnetic and exploration applications

changing redox conditions at cold seeps as revealed by authigenic carbonates from alaminos canyon northern gulf of mexico anaerobic oxidation of methane in anoxic sediments at cold seeps often leads to formation of authigenic carbonates close to the seafloor along continental margins recent work however indicated that the redox conditions in sediments may vary to some degree during seepage activity in order to shed new light on the extent of this variability authigenic carbonates from alaminos canyon lease block 645 of the northern gulf of mexico have been characterized by means of inorganic and organic geochemistry the carbonates were collected from seep deposits representing various seafloor morphologies including extensive pavements mounds fractured carbonate slabs surrounded by dense bivalve shells and vestimentiferan tubeworm colonies the deposits almost entirely consist of aragonite the 18o values of aragonite vary from 2 6 to 5 8 v pdb suggesting precipitation in slight disequilibrium with the surrounding pore fluids the 13c values of aragonite between 33 9 and 20 4 v pdb agree with variable amounts of carbonate derived from oxidation of thermogenic methane and crude oil methane was primarily oxidized in an anaerobic process as revealed by the presence of 13c depleted molecular fossils of methane oxidizing archaea 13c values as negative as 118 and sulfate reducing bacteria 13c values as negative as 97 the syntrophic partners in the anaerobic oxidation of methane the observed inventories of molecular fossils in the authigenic carbonates mirror those of known consortia of anaerobic methane oxidizing archaea anme and sulfate reducing bacteria namely the anme 2 desulfosarcina desulfococcus dss and anme 3 desulfobulbus dbb consortia in contrast the same carbonates exhibit shale normalized rare earth elements patterns that all display real negative ce anomalies ce ce 0 78 suggesting that at least temporarily oxic conditions prevailed the episodic occurrence of oxic conditions is confirmed by the presence of molecular fossils of aerobic methanotrophic bacteria including 4 methylcholesta 8 14 24 dien 3 ol and two bacteriohopanepolyols aminotetrol and aminotriol the 13c values of the biomarkers of aerobic methanotrophs are as negative as 58 and are consequently less 13c depleted than the molecular fossils of the prokaryotes performing anaerobic oxidation of methane a pattern in accord with culture experiments overall our results suggest that redox conditions at cold seeps are variable this variability probably reflects changes in seepage flux the combination of an inorganic and an organic geochemical approach used here is promising to better assess the variability and diversity of past fluid and gas expulsion at seeps

high temperature hydrothermal origin for fractured carbonate reservoirs in the blackburn oil field nevada geologic note 1 preliminary petrographic and fluid inclusion studies of drill cuttings and core from the blackburn oil field reveal that many of the oil saturated fractures veinlets and breccias in the dolomite reservoir rock may be of high temperature hydrothermal origin textures of the earliest formed fracture veinlet networks and breccias suggest development by explosive hydrothermal fracturing the veinlets themselves preserve evidence that high temperature fluids favorable for such natural hydrothermal rock rupture once circulated in these rocks primary fluid inclusion homogenization temperatures indicate that early vein dolomite precipitated from hydrothermal brines at temperatures exceeding 350 degrees c 662 degrees f younger quartz sphalerite galena veinlets developed from dilute aqueous solutions at temperature of more than 225 degrees c 437 degrees f the high paleotemperatures recorded by early vein dolomite in the now much cooler about 120 degrees c or 248 degrees f blackburn reservoir rock imply an ancient magmatic heat source in this case almost certainly a small granodiorite stock tertiary adjoining and possibly underlying the field other carbonate hosted petroleum reservoirs in eastern nevada are also intimately associated with felsic intrusives we propose that igneous related high temperature hydrothermal fracturing could have created reservoir porosity and permeability at some or all of these fields and that future petroleum exploration in the basin and range might profitably incorporate the search for concealed plutons

geometry and kinematics of the grant range brittle detachment system eastern nevada u s a an end member style of upper crustal extension documenting the range of styles of normal faulting is fundamental to understanding crustal extension here geologic mapping field relationships and deformed and restored cross sections illustrate the geometry and kinematic development of a system of west vergent detachment faults in the grant range in eastern nevada faults exhibit brecciation and stratigraphic cutoff angles of 5 15 at all structural levels and deform a 10 km thick section of paleozoic and paleogene rocks the fault system is folded across an anticlinal culmination which grew during extension as indicated by progressively increasing interlimb angles and incision in the axial zone the eastern limb consists of an imbricate stack of faults that were emplaced from bottom to top in the western limb several faults exhibit apparent thrust relationships the oldest faults are cut by a 29 ma dike and the highest preserved fault cuts 32 ma volcanic rocks that restore to paleodepths of 1 km retrodeformation of folding and minimal structural relief and angularity across a paleogene unconformity indicate the faults were active at 5 15 angles retrodeformation of offset indicates 49 km 98 extension we propose a model of stationary sustained isostatic uplift and incision at the culmination axis a fixed hinge with updip excision producing bottom to top growth of the imbricate stack and downdip excision producing apparent thrust relationships the fault system exhibits similarities to core complex detachment systems though it is confined to upper crustal levels and there are no preserved high angle or listric normal faults indicating a unique extension style dominated by low angle excision

geothermometry from brine analyses lessons from the gulf coast u s a abstract geothermometers based on mineral water equilibria are of limited use at temperatures characteristic of hydrocarbon production from sedimentary basins metastable detrital phases such as alkali feldspars and plagioclase persist to temperatures characteristic of the deepest wells sasmpled approaching 200 c and equilibria involving stable phases such as albite illite and quartz are not commonly achieved empirical relations such as that between mg and li are more successful in predicting subsurface formation water temperatures than are equilibrium relations involving quartz carbonates or feldspars the concentrations of most components in saline formation waters seem to be governed by kinetic rather than by equilibrium considerations

thermal regime interreservoir compositional heterogeneities and reservoir filling history of the dongfang gas field yinggehai basin south china sea evidence for episodic fluid injections in overpressured basins the dongfang gas field located in a diapir structure zone is the largest gas field found in the yinggehai basin a strong thermal anomaly caused by hydrothermal fluid flows occurs in the gas field as evidenced from drill stem test and fluid inclusion homogenization temperatures rock eval tmax vitrinite reflectance and clay mineral transformation profiles such a thermal anomaly suggests focused rapid flow of deeply sourced hydrothermal fluids which has shifted the threshold depth to the onset of hydrocarbon generation upward by about 500 m the dongfang gas field shows considerable variation in nitrogen and carbon dioxide content with nitrogen content ranging from less than 5 to 31 2 and carbon dioxide content ranging from less than 1 to 88 9 hydrocarbon gases and associated condensates show high maturities and have been generated most probably from the meishan and sanya formations of miocene age carbon dioxide in gases with co2 content less than 10 is organic in origin whereas carbon dioxide in gases with co2 content higher than 10 is inorganic in origin and has been generated from high temperature decomposition of carbonates most gases display negative d15n values gases with nitrogen content higher than 15 always contain organic co2 co2d13c values lighter than 10o oo and the nitrogen contents decrease as the d13c values for methane and ethane become heavier suggesting an organic origin of the nitrogen gas generated in the catagenetic stage source rock ro 2 0 before the significant thermal decomposition of carbonate took place systematic interreservoir compositional heterogeneities occur in the gas field which along with the thermal regime and fluid inclusion homogenization temperature measurements give a clear suggestion of the reservoir filling history methane dominated gases with relatively high nitrogen content and a small amount of organic co2 accumulated first and carbon dioxide rich gases with hydrocarbon components of higher maturity injected into the reservoir later interreservoir compositional heterogeneities which have the advantage of being unaffected by in reservoir mixing processes can be effective indicators of the field filling history especially when they are studied in combination with fluid inclusion and reservoir diagenesis analyses the short lived transient nature of the thermal effect of fluid flow and the wide variation of the toluene n heptane values seem to suggest episodic fluid injections from the overpressured systems into the reservoirs

a new straight chain hydrocarbon biomarker associated with anaerobic methane cycling abstract 13c depleted e and z n tricos 10 enes are prominent biomarkers in an anaerobic microbial mat at black sea methane seeps these n alkenes co occur with archaeal irregular c25 isoprenoid hydrocarbons namely 2 6 10 15 19 pentamethylicosane pmi and enes pmi low 13c values 73 and 77 for n tricosenes and pmi imply the anabolism of methane carbon by their source biota the n tricosenes apparently originate from microorganisms closely associated with if not identical to isoprenoid producing methane metabolizing archaea methane seep deposits of tertiary to jurassic ages showed the absence of n tricosenes but 13c depleted n tricosane 13c as low as 87 a plausible diagenetic product was observed in enhanced concentrations in 7 out of 9 samples studied it is proposed that a preference of n tricosane over the enveloping n alkanes may provide a specific hydrocarbon fingerprint for the anaerobic cycling of methane in ancient settings

translithospheric mantle diapirism geological evidence and numerical modelling of the kondyor zoned ultramafic complex russian far east we report new structural microstructural petrological and major and trace element data on ultramafic rocks from the kondyor zoned ultramafic complex in far east russia the ultramafic rocks are subdivided into three subconcentric lithologies from core to rim 1 a metasomatic domain where generally phlogopite rich dykes pervasively intrude dunite 2 a main dunite core 3 a pyroxenite rim the ultramafic rocks have nearly vertical contacts with the surrounding archaean basement gneisses quartzites and marbles and hornfelsed riphean sediments the hornfelsed sediments show a relatively steep 60 outward dipping layering which rapidly flattens to horizontal away from the inner contact although the riphean sediments define a dome like structure the inward shallow dipping foliation of the dunites indicates a synformal structure detailed petro structural investigations indicate that the kondyor dunites were deformed by solid state flow under asthenospheric mantle conditions the outward textural change from coarse to fine grained equigranular dunite and the outward increasing abundance of subgrains and recrystallized olivine grains suggest dynamic recrystallization while fluid circulation was channelized within the core metasomatic zone with a decreasing melt fraction from core to rim and also suggest that solid state deformation induced grain size reduction towards the cooling border of the kondyor massif based on their geochemistry the dunites are interpreted as mantle rocks strongly affected by reaction with melts similar to the jurassiccretaceous aldan shield lamproites rim pyroxenites were formed by a melt consuming peritectic reaction implying the existence of at least a small conductive thermal gradient around the dunite body while the latter was still at near solidus temperature conditions this suggests that the zoned structure of kondyor was initiated at mantle depths most probably within the subcontinental lithosphere upon cooling the lamproitic melts were progressively focused in the central part of the massif and drained into vein conduits where they reacted with the wall rock dunite two dimensional numerical modelling based on finite differences with a marker in cell technique incorporates temperature dependent rheologies for both molten and non molten host rocks the modelling consolidates the structural petrological and geochemical interpretations which show that the dunites represent the synformal flat lying apex of an asthenospheric mantle diapir triggered by fluid pressure channelized in the core which nearly reached the earths surface we conclude that translithospheric mantle diapirism is an important mode of mass transfer in the earth

initial characterization of cold seep faunal communities on the new zealand hikurangi margin abstract cold seep communities have been known from the north atlantic and north pacific for more than 20 years but are only now being explored in the southern hemisphere while fisheries bycatch had suggested the presence of cold seeps on the new zealand margin the biodiversity and distribution of these communities remained unknown explorations using towed cameras and direct sampling gear revealed that cold seep sites are abundant along the new zealand hikurangi margin initial characterization of the faunal communities at 8 of these sites indicates a fauna that is associated with particular sub habitats but which varies in abundance between sites community composition is typical at higher taxonomic levels of cold seep communities in other regions the dominant symbiont bearing taxa include siboglinid tube worms vesicomyid clams and bathymodiolin mussels at the species level much of the seep associated fauna identified so far appears either to be new to science or endemic to new zealand seeps suggesting the region may represent a new biogeographic province for cold seep fauna some overlap at the species and genus level is also indicated between the sampled seep communities and the fauna of hydrothermal vents on the kermadec arc in the region further taxonomic and genetic identifications of fauna from this study will allow us to fully test the levels of species overlap with other new zealand chemosynthetic ecosystems as well as with other cold seep sites worldwide these apparently novel communities exhibit evidence of disturbance from a deep bottom trawl fishery and appear to be threatened along the entire new zealand margin as bottom fisheries mining and fossil fuel exploitation move into deeper waters seep communities may be endangered worldwide necessitating the initiation of conservation efforts even as new seep ecosystems are discovered and explored our findings highlight the unique nature of anthropogenic impacts in the deep sea in which reservoirs of biodiversity can be impacted long before they are even known

finger structures in the lille kufjord layered intrusion finnmark northern norway highly irregular contacts are developed between peridotite and troctolite in layers forming the uppermost part of a transition zone between two of the cyclic units of the lille kufjord intrusion the upwardly directed peridotite fingers crosscut both the feldspar lamination and the feldspathic xenoliths in the troctolite and are interpreted as the result of the replacement of troctolite by peridotite similar structures are developed in the rhum ultrabasic pluton replacement may have been caused by the migration of a more hydrous and magnesian magma trapped initially in olivine or olivine clinopyroxene cumulates into plagioclase olivine cumulates precipitated from a basaltic liquid

assimilation of crustal xenoliths in a basaltic magma chamber sr and nd isotopic constraints from the hasvik layered intrusion norway contaminated layered intrusions known thousands of recrystallized strontium and neodymium isotopic data for mafic cumulates chilled tabular xenoliths of metasedimentary origin enclosed in the cumulates margins and adjacent crustal rocks of the hasvik layered intrusion are thought to represent the remnants of the assimilated material north norwegian caledonides are reported together with new the xenoliths spalled off the roof during magma emplacement and mineralogical and whole rock analytical data to constrain the extent together with the elevated temperatures 400 600 c of the midand effect of the assimilation of crustal xenoliths in a basaltic crustal country rocks led to a high degree of assimilation in the magma chamber initial sr sr 700 ma of 0 7045 and end hasvik magma chamber 700 ma of 3 03 for the chilled margin which has a tholeiitic composition akin to the chilled rocks of the skaergaard intrusion demonstrate that the parental magma was derived from a depleted mantle source the basal cumulates 0 335 m show an up section decrease in sr sr from 0 7045 to 0 7038 and a correlative

characteristics and origin of the gas and condensate in the yinggehai basin offshore south china sea evidence for effects of overpressure on petroleum generation and migration three superimposed pressure systems have developed in the yinggehai basin the strongly overpressured rocks have abnormally low vitrinite reflectance ro and rock eval tmax values and display abnormal c15 hydrocarbon distributions such organic maturity anomalies were confirmed to be the result of overpressure retardation commercial gas fields with carbon dioxide content up to 93 and gas shows with nitrogen content more than 50 have been found in the basin methane and carbon dioxide dominated gases have low c2 hydrocarbon contents less than 4 and heavy methane 13c and d values and the associated condensates have high diamondoid indices and very low c25 saturated hydrocarbon concentration at the same time the methane and carbon dioxide dominated gases have high branched and cyclic light hydrocarbon contents and associated condensates have abnormally low heptane and isoheptane values low sterane isomerization values and abnormally high concentrations of isoprenoid hydrocarbons relative to adjacent n paraffins these distinct characteristics seem to result from the effects of overpressure on both hydrocarbon generation and migration

relation between extensional geometry of the northern grant range and oil occurrences in railroad valley east central nevada in the northern grant range heterogeneous neogene extension was dominated by synchronous arching and attenuation attenuation was accomplished along a stacked set of attenuation faults that formed at low angles to bedding as the paleozoic carbonate and paleogene rocks arched about a north northwest axis the style and amount of attenuation was controlled by lithologic character and structural depth of rock units and by geometry of the arch on the steeper west side of the grant range arch the curviplanar low angle attenuation faults converge into a single shallowly west dipping fault zone along which the stratigraphic juxtaposition of mississippian units over middle cambrian units and late cretaceous granite marks the zone of maximum attenuation the distinct geometry o the arched westward converging low angle fault array is seen in windows into the deeper structure low on the west side of the range we conclude that arching and heterogeneous extension resulted from uplift of the grant range relative to the structural basin of railroad valley to the west this structural differentiation is expressed as a complex zone of subparallel to bedding shallow dipping attenuation faults rather than as a simple high angle range front fault seismic and drill hole data indicate that low angle attenuation faults in the range extend into railroad valley and control the structure buried in the valley mississippian and paleocene to eocene petroleum source rocks and devonian to oligocene reservoir rocks in railroad valley oil fields are in extensively fractured rocks of the upper plate to the major extensional fault system thus relatively cold upper plate rocks immature with respect to hydrocarbon generation were brought relatively down into contact with hotter lower plate rocks by neogene attenuation faulting oil in railroad valley which is sourced from rocks as young as eocene was probably generated by this juxtaposition during neogene crustal attenuation and subsequently migrated into upper plate fractured reservoi s

hierarchies of overpressure retardation of organic matter maturation case studies from petroleum basins in china the effects of overpressure on different aspects of organic matter maturation have been examined in three basins using multiple parameters overpressure in the yinggehai basin has retarded kerogen maturation hydrocarbon generation and thermal cracking of long chain normal hydrocarbons as well as evolution of isoprenoid hydrocarbons overpressure in the dongpu depression bohai bay basin seems to have retarded the maturation of bulk kerogens reflected by rock eval tmax the thermal cracking of long chain normal hydrocarbons and the evolution of isoprenoid hydrocarbons but seems to have had no detectable effects on vitrinite reflectance overpressure in the qiongdongnan basin has had no detectable retardation effects on all aspects of organic matter maturation the observed phenomena suggest differential retardation of organic matter maturation that is different organic matter maturation reactions and different maturity parameters have been retarded by overpressure to different degrees in the same overpressured system and four hierarchies of overpressure retardation hierarchy i retardation is defined as the state where the overpressure has retarded all aspects of organic matter maturation and is proposed to have been caused by the combination of high formation pressure and excess pressure a high water organic matter ratio and strong retention of reaction products in an early developed strong persistent overpressured system hierarchy ii retardation refers to the case in which all aspects of organic matter maturation except the maturation of hydrogen poor kerogens especially vitrinite have been retarded and seem to have been caused by early developed moderate to strong persistent overpressure hierarchy iii retardation refers to the situation where overpressure has retarded only the thermal cracking of liquid hydrocarbons but has had no detectable effect on the maturation of both hydrogen rich and hydrogen poor kerogens and is proposed to have been caused by moderate to strong persistent overpressures that began to develop around peak oil generation hierarchy iv retardation is defined as the situation where overpressure has had no detectable retardation on all aspects of organic matter maturation and may have been caused by cases wherein the overpressure developed too late the intensity of the overpressure was too low the duration of the overpressure was too short or overpressured fluids had been expelled frequently resulting from both the diversities of organic matter maturation reactions and the complexities of overpressure generation and development the hierarchies of overpressure retardation in different basins may be quite different and it is necessary to use multiple parameters to understand the evolution of the petroleum systems in overpressured basins

western davis strait a volcanic transform margin with petroliferous features abstract we present a compilation of the western davis strait region offshore southeastern baffin island nunavut canada with new subsurface geological structural details and observations regarding past hydrocarbon occurrences from scientific and commercial exploration this consists of seismic mapping with archival data correlated with a filtered marine bouguer anomaly gravity compilation and magnetic data sets covering northern saglek basin the western part of the lady franklin basin and the ungava fault zone from south of baffin bay a regional seismic horizon for mapping basin architecture comes from the top of the paleogene volcanic syn magmatic zone where pervasive volcanic flows and intrusions are intermingled with the sedimentary section the seismic depth map to the top of the regional volcanic seismic horizon shows pre rift sedimentary basins having maximum depths of approximately 4 5 km flanking the shallower ungava fault zone correlation of bouguer anomaly gravity and magnetic data interpretations with the seismic mapping indicate that over some areas true crystalline basement is deeper than can be determined by reflection seismic as the base of the syn magmatic section is not resolvable for seismic mapping extensive paleogene mafic intrusives and extrusive basalts dominate the architecture of this volcanic rifted margin as seen by the dominant high amplitude magnetic anomalies associated with many deeper structures the over 250 km long davis strait fault is recognised as the key structural element of the ungava fault zone ufz and valley complex the adjoining davis strait high maps on seismic as a continuous structure running the length of davis strait plunging southwards to a bouguer gravity high feature that terminates the western end of the extinct eocene spreading zone south of davis strait this horn shaped structural feature establishes the presence of an accommodation zone with multiple faults and localised thrust faulting as required to fit the complex mechanics for strike slip motion that occurs along the south end of this transform fault system the revised marine bouguer anomaly gravity data set also defines two new near shore grabens east of cumberland sound the southern tariut basin and the northern imaqpik basin each extending over 100 km in length with sediment thicknesses of at least 4 km these pre rift basins most likely originate from the paleozoic based on seafloor dredge and nearby shallow drill cores from previous studies the hydrocarbon charge of a previously unexplained petroliferous shallow marine drill core that is adjacent the eastern edge of the tariut basin is attributed to paleozoic source rocks that have undergone enhanced thermal maturation from sill intrusion associated with rifting the imaqpik basin shows strong evidence of a hydrocarbon system from the proximity of clustered interpreted sea surface oil slicks mapped from satellite radar images and a local zone of anomalously high dissolved methane measured within the water column that originates from the seafloor immediately east of cape dyer at the northern limit of that basin the overlying cape dyer flood basalt field extends from limited onshore exposures into the offshore and maps with magnetic data over an area of approximately 13 000 km2 this extrusive feature and it s implicit underlying intrusive components are likely the unconventional heat source for the anomalous enhanced thermal maturation of paleozoic to paleogene source rocks in these pre rift basins that host this previously unrecognised petroleum system

generating a high resolution global gravity model for oil exploration part 2 marine satellite altimeter derived gravity in the continental gravity compilations 1986 1995 available marine gravity surveys were patchy and resulted in an ever growing reliance on satellite altimeter derived gravity data the early satellite work by haxby lamont doherty geological observatory encouraged getech to get involved in its own processing of these data using repeat mission data in the second half of the 1990s after the main continental compilations had been completed geosat and european remote sensing ers 1 geodetic mission data became available with combined track spacing of 3 to 4 km at the equator

the deep crustal structure of the mafic ultramafic seiland igneous province of norway from 3 d gravity modelling and geological implications

rayleigh wave phase velocity maps of tibet and the surrounding regions from ambient seismic noise tomography ambient noise tomography is applied to the significant data resources now available across tibet and surrounding regions to produce rayleigh wave phase speed maps at periods between 6 and 50 s data resources include the permanent federation of digital seismographic networks five temporary u s program for array seismic studies of the continental lithosphere passcal experiments in and around tibet and chinese provincial networks surrounding tibet from 2003 to 2009 totaling 600 stations and 150 000 interstation paths with such a heterogeneous data set data quality control is of utmost importance we apply conservative data quality control criteria to accept between 5000 and 45 000 measurements as a function of period which produce a lateral resolution between 100 and 200 km across most of the tibetan plateau and adjacent regions to the east misfits to the accepted measurements among passcal stations and among chinese stations are similar with a standard deviation of 1 7 s which indicates that the final dispersion measurements from chinese and passcal stations are of similar quality phase velocities across the tibetan plateau are lower on average than those in the surrounding nonbasin regions phase velocities in northern tibet are lower than those in southern tibet perhaps implying different spatial and temporal variations in the way the high elevations of the plateau are created and maintained at short periods 20 s very high velocities are imaged in the tarim basin the ordos block and the sichuan basin these phase velocity dispersion maps provide information needed to construct a 3 d shear velocity model of the crust across the tibetan plateau and surrounding regions

hydrocarbon seep carbonates of a miocene forearc east coast basin north island new zealand an ancient hydrocarbon seep province of 14 isolated authigenic carbonate deposits has been identified in fine grained deep marine siliciclastic strata of the miocene east coast basin north island new zealand these forearc sediments have been uplifted and complexly deformed into accretionary ridges adjacent to the still active hikurangi convergent margin older active and passive margin strata mid cretaceous to oligocene in age underlie the neogene sequence and contain oil and gas prone source rocks older mesozoic meta sedimentary rocks constitute the backstop against which the current phase of subduction related sedimentation has accumulated 24 ma present the seep carbonates up to 10 m thick 200 m across archive methane signatures in their depleted carbon isotopes to 13c 51 7 pdb and contain chemosynthesis based paleocommunities e g worm tubes bathymodioline mussels and vesicomyid lucinid and thyasirid bivalves typical of other cenozoic and modern seeps northern and southern sites are geographically separated and exhibit distinct lithological and faunal differences structural settings are variable seep associated lithologies also are varied and suggest carbonate development in sub seafloor seafloor and physically reworked diapiric expansion gas explosion gravity slide or debris flow settings similar to italian apennine seep deposits of overlapping ages peculiar attributes of the new zealand miocene seep deposits are several including digitate thrombolites of clotted microbial micrite encased in thick isopachous horizons and botryoids of aragonite seep plumbing features are also well exposed at some sites displaying probable gas explosion breccias filled with aragonite tubular concretions fluid conduits and carbonate cemented thin sandstone beds and burrows within otherwise impermeable mudstones a few seeps were large enough to develop talus debris piles on their flanks which were populated by lucinid bivalves and terebratulid brachiopods firmgrounds and hardgrounds were common as evidenced by trace fossil associations or caryophyllid coral thickets atop some seep carbonate deposits thus the new zealand examples show strong evidence of formation in sediments at or just beneath the seafloor but some were clearly exhumed by erosion to sustain later non seep epifaunal and boring paleocommunities

late cretaceous maastrichtian shallow water hydrocarbon seeps from snow hill and seymour islands james ross basin antarctica fossil hydrocarbon seeps are present in latest cretaceous maastrichtian volcaniclastic shallow shelf sediments exposed on snow hill and seymour islands james ross basin antarctica the seeps occur in the snow hill island formation on snow hill island and are manifest as large sized cement rich carbonate bodies containing abundant thyasirid bivalves and rarer ammonites and solemyid bivalves these bodies have typical seep cement phases with 13c values between 20 4 and 10 7 and contain molecular fossils indicative of terrigenous organic material and the micro organisms involved in the anaerobic oxidation of methane including methanotrophic archaea and sulphate reducing bacteria on seymour island the seeps occur as micrite cemented burrow systems in the lopez de bertodano formation and are associated with thyasirid solemyid and lucinid bivalves and background molluscan taxa the cemented burrows also have typical seep cement phases with 13c values between 58 0 and 24 6 there is evidence from other data that hydrocarbon seepage was a common feature in the james ross basin throughout the maastrichtian and into the eocene the snow hill and seymour island examples comprise the third known area of maastrichtian hydrocarbon seepage but compared to most other ancient and modern seep communities the james ross basin seep fauna is of very low diversity being dominated by infaunal bivalves all of which probably had thiotrophic chemosymbionts but which were unlikely to have been seep obligates absent from the james ross basin seep fauna are typical obligate seep taxa from the cretaceous and the cenozoic reasons for this may have been temporal palaeolatitudinal palaeobathymetric or palaeoecological

13c depleted biphytanic diacids as tracers of past anaerobic oxidation of methane abstract 13 c depleted biphytanic diacids containing 0 2 pentacyclic rings are abundant biomarkers in cenozoic methane seep limestones the strong 13 c depletion 132 to 96 suggests that they derive from euryarchaea metabolizing methane they occur with other biomarkers typically associated with anaerobic oxidation of methane such as crocetane pentamethylicosane pmi archaeol hydroxyarchaeol and glycerol dibiphytanyl glycerol tetraethers gdgts in contrast to gdgt derived biphytane hydrocarbons the biphytanic diacids appear to be almost exclusively derived from methanotrophic euryarchaea

exploration drilling and reservoir model of the platanares geothermal system honduras central america abstract results of drilling logging and testing of three exploration core holes combined with results of geologic and hydrogeochemical investigations have been used to present a reservoir model of the platanares geothermal system honduras geothermal fluids circulate at depths 1 5 km in a region of active tectonism devoid of quaternary volcanism large artesian water entries of 160 to 165 c geothermal fluid in two core holes at 625 to 644 m and 460 to 635 m depth have maximum flow rates of roughly 355 and 560 l min respectively which are equivalent to power outputs of about 3 1 and 5 1 mw thermal dilute alkali chloride reservoir fluids tds 1200 mg kg are produced from fractured miocene andesite and cretaceous to eocene redbeds that are hydrothermally altered fracture permeabillity in producing horizons is locally greater than 1500 and bulk porosity is 6 a simple fracture dominated volume impedance model assuming turbulent flow indicates that the calculated reservoir storage capacity of each flowing hole is approximately 9 7 106 l kg cm 2 tritium data indicate a mean residence time of 450 yr for water in the reservoir multiplying the natural fluid discharge rate by the mean residence time gives an estimated water volume of the platanares system of 0 78 km3 downward continuation of a 139 c km conductive gradient at a depth of 400 m in a third core hole implies that the depth to a 225 c source reservoir predicted from chemical geothermometers is at least 1 5 km uranium thorium disequilibrium ages on calcite veins at the surface and in the core holes indicate that the present platanares hydrothermal system has been active for the last 0 25 m y

outcrop analogues of pockmarks and associated methane seep carbonates a case study from the lower cretaceous albian of the basque cantabrian basin western pyrenees abstract late albian deep water sediments of the black flysch group in the basque cantabrian basin western pyrenees preserve a fossil pockmark field including methane seep carbonates and associated macrofauna the geometry of the pockmarks is reconstructed from repeated lens shaped turbidite deposits with centrally located carbonate bodies early diagenetic carbonate phases such as clotted micrite and yellow calcite with 13c values as low as 41 6 and hydrocarbon biomarkers e g 2 6 10 15 19 pentamethylicosane with strong depletions in 13c indicate that the carbonates precipitated due to anaerobic oxidation of methane the pockmarks probably formed due to subsidence induced by dewatering and degassing of the gas charged seabed perhaps enhanced by the weight of the carbonate bodies the macrofauna resembles that of other late mesozoic deep water methane seeps world wide and is dominated by large lucinid and caspiconcha bivalves and hokkaidoconchid gastropods during late diagenesis the carbonate 18o values were reset to a narrow range of 12 to 10 the remaining pore spaces and fissures were filled with pyrobitumen and additional carbonate phases precipitated potentially due to thermochemical sulfate reduction processes

on the potential generality of depth related ecologic structure in cold seep communities evidence from cenozoic and mesozoic examples faunal communities inhabiting hydrocarbon seeps in the deep sea today show a depth related change in their ecologic structure the proportion of obligate endemic taxa increases with depth while the abundance of predators and other background taxa decreases here the fossil record of seep communities is investigated for similar gradients the middle eocene to middle miocene deep water cold seep deposits in western washington state usa are from different depths those of the middle to late eocene humptulips bear river and whiskey creek sites lived in depths of 500 to 2000 m those of the late oligocene to middle miocene seep communities of the lincoln creek and astoria formations in depths of 16 to 900 m these seeps were inhabited by the same taxa that inhabit cold seeps today and like their modern analogs they show an increasing proportion of obligate taxa and a decreasing abundance of predators and other background taxa with depth also among late mesozoic seep sites a depth related change in the proportion of obligate taxa is apparent seep communities in shallow shelf settings harbor virtually no obligates while seep communities in outer shelf to slope settings show a high proportion of obligates although the constituting species have different taxonomic affinities than their cenozoic and extant counterparts unlike in modern examples differences between seep communities from outer shelf and slope depths were not seen it is hypothesized that due to the higher mesozoic sea levels many seep communities on the continental shelves were located below the photic zone where an obligate seep fauna could develop because an increase in the proportion of obligate taxa with depth can be seen both in the cenozoic and in the late mesozoic despite the different taxonomic affinities of the obligate taxa it is suggested here that this depth related structure is a general feature of seep faunas independent of the taxa that express this pattern

stable isotope evidence for chemosynthesis in an abyssal seep community communities of abundant organisms similar to those which surround the hydrothermal vents of the east pacific rise epr occur in 3 266 m of water in the gulf of mexico they were discovered with the alvin at 26 02 n 84 55 w in an area where pore waters seep from the cretaceous limestones of the adjacent platform at the contact between the florida escarpment and the holocene hemipelagic sediments of the abyssal gulf because of the unusual abundance of organisms in this deep sea environment and the taxonomic similarities to the chemosynthetically based communities which surround the hydrothermal vents on the epr the seep communities are suspected to exist on a local non photosynthetic food source1 we have now measured isotope ratios in tissues of organisms which surround these saline seeps to determine the origin of the local food chain the tissues have extremely negative 13c 42 to 77 pdb and 15n 2 72 to 9 34 air values such highly fractionated carbon and nitrogen isotopes are unknown in food chains based on photosynthesis suggesting that these communities are chemosynthetic the cause of this extreme fractionation is attributed either to assimilation from local supplies of isotopically depleted methane and ammonium or to biochemical fractionation the tissues of these animals contain significant amounts of 14c 60 modern so the source of this fractionated carbon is not predominantly fossil methane

cenozoic attenuation detachment faulting a possible control on oil and gas accumulation in east central nevada 1 current explanations for low angle younger over older faults in eastern nevada are 1 a master detachment extending through the crust 2 mid crustal ductile extension and 3 local gravity sliding none of these explanations are fully supported by field evidence our field evidence indicates that thermally induced ductile extension beneath the white pine and schell creek ranges produced low angle normal faults in competent units above and detachment faults along ductile shales thin brittle units between shale detachments fragmented by low angle normal faulting were pulled apart into isolated lenticular detachment structures duck creek valley a neogene graben similar to railroad valley may have formed in a zone of weakness caused by oligocene attenuation suggesting that potential oil producing basins in nevada may contain subsurface detachment structures oligocene attenuation may have contributed to fracturing of reservoirs brittle units local thinning of source rocks ductile units and formation of structural traps on detachment topography lateral variation in fracture density by creating barriers to updip migration also may contribute to oil accumulation other favorable structures could be large early miocene gravity slide blocks sealed by neogene basin fill in basins similar to railroad valley these structures should be prime exploration targets because oil generation occurred after the structures formed

lipid biomarker patterns of methane seep microbialites from the mesozoic convergent margin of california abstract in order to reconstruct biogeochemical pathways at mesozoic methane seeps a set of late jurassic tithonian to early cretaceous aptian albian 13 c depleted seep limestones from forearc strata in western california were subjected to detailed molecular isotopic biomarker analyses two of the microbial carbonate deposits are turbidite hosted fault related whereas one is hosted in serpentinite in a diapir related setting the limestones contain 13 c depleted archaeal lipid biomarkers such as crocetane 13 c 80 and pmi 100 indicative of an involvement of anaerobic oxidation of methane aom in carbonate precipitation isotopically depleted crocetane in the tithonian sample represents the oldest reported occurrence of this compound at methane seeps in the set of samples a series of strongly 13 c depleted regular c 21 to c 24 isoprenoids possibly results from diagenetic alteration of archaeal sesterterpanylglycerol diethers as suggested by the presence of the putative intermediate 3 7 11 15 19 pentamethylicosanoic acid 13 c depleted 17 h 21 h and 17 h 21 h hopanes c 30 c 34 with 22 s and 22 r isomer couplets c 31 are present in all samples in distributions indicative of a moderate thermal maturity low 13 c values 78 to 60 suggest that these are derived from anaerobic bacteria involved in aom notably 22 s isomers are consistently enriched in 13 c relative to their 22 r counterparts our samples represent 70 myr of seepage activity and aom along the mesozoic margin of western california filling the gap between the currently oldest methane seep biomarker record from the oxfordian late jurassic and the more widely recognised cenozoic examples

large rock avalanche deposits eastern basin and range utah emplacement diagenesis and economic potential large rock avalanche deposits are a common component of the basin fill within the extensional tectonic terrain of the basin and range these deposits recently have been interpreted to host oil and gas within the railroad valley area of eastern nevada large blocks of brecciated bed rock are a primary component of these avalanche deposits and are potentially excellent oil and gas reservoirs our work provides further insight into the emplacement and economic potential of these deposits exposed large rock avalanche deposits of the miocene oak city formation on the western margin of the canyon range utah contain coherent breccia blocks up to 3 5 km long 1 km wide and 200 m thick these deposits were derived from the near vertical dipping bed rock of the adjacent canyon range and now are exposed as much as 5 5 km from the range front within the sevier desert basin emplacement was relatively rapid as indicated by three well developed breccia facies within the carbonate breccia blocks stratigraphically from the base the facies include 1 matrix rich breccia 2 jigsaw breccia and 3 crackle breccia the deposits were cut and segmented by a series of syndepositional normal faults that developed during late miocene and post miocene extension primary porosity w s reduced by cement soon after burial cathodoluminescence cement patterns indicate that initially the basinward breccia blocks were more deeply buried relative to the water table than the breccia blocks proximal to the canyon range after initial cementation the basinward blocks were uplifted relative to the water table secondary porosity approaches 8 in the carbonate blocks and is greater than 14 within the jigsaw breccia the size and porosity of these breccia blocks indicate their potential as reservoir targets

polyorogenic 40ar 39ar mineral age record within the kalak nappe complex northern scandinavian caledonides the kalak nappe complex is composed of variably retrogressed middle proterozoic basement and imbricated polydeformed metasedimentary cover successions which at least in part appear to have originated within the late proterozoic early palaeozoic baltoscandian miogeocline mafic alkaline plutons seiland igneous suite occur within uppermost structural units of the nappe complex 40 ar 39 ar incremental release mineral ages suggest local differences in tectonothermal evolution within the kalak nappe complex post metamorphic cooling dates of c 490 ma are locally recorded by hornblende within the structurally highest tectonic unit suggesting significant orogenic activity occurred during and or immediately prior to the arenig a distinctly later metamorphic overprint occurred in the silurian and was of sufficient magnitude to everywhere rejuvenate ar systems in muscovite and nepheline and locally in hornblende this was followed by relatively rapid post metamorphic cooling through hornblende and muscovite ar closure temperatures between c 425 and 415 ma the complex tectonic history suggested for the kalak nappe complex is generally similar to that previously outlined for the central swedish caledonides together 40 ar 39 ar mineral ages from these widely separated areas indicate that significant tectonothermal activity occurred along the baltoscandian margin prior to the silurian this activity appears at least in part to have been associated with formation of a late cambrian early ordovician accretionary wedge over a westward dipping subduction zone during initial closure of the iapetus ocean

geology compositional heterogeneities and geochemical origin of the yacheng gas field qiongdongnan basin south china sea the yacheng gas field is located in the footwall of the no 1 fault the boundary fault between the yinggehai and qiongdongnan basins the main reservoir is the fan delta sandstones in the lingshui formation the seals are meishan for m ation shales near the no 1 fault and lingshui formation shales away from the no 1 fault all strata are normally pressured in the gas field except for the meishan formation the meishan formation is overpressured near the no 1 fault in the gas field and in the adjacent yinggehai basin away from this fault into the qiongdongnan basin the overpressure diminishes an obvious thermal anomaly occurs below 3600 m in the gas field this anomaly characterized by an abrupt increase in drill stem test and fluid inclusion homogenization temperatures vitrinite reflectance ro and rock eval tmax and by an abnormally low temperature ro tmax gradient diminishes away from the yinggehai basin the gases and condensates have abnormally high aromatic hydrocarbon contents and show obvious heterogeneities away from the no 1 fault the c2 hydrocarbon content and c2 scn increase carbon dioxide content decreases d13c values for methane ethane and carbon dioxide become lighter the heptane and isoheptane values decrease and the relative contents of aromatic hydrocarbons both in c6 c7 light hydrocarbons and in the condensates decrease such heterogeneities reflect the reservoir filling process and origin of the gas field the gas field was charged from both the qiongdongnan and the yinggehai basins hydrocarbons sourced from the qiongdongnan basin have relatively low maturities whereas hydrocarbons from the yinggehai basin have relatively higher maturities and seem to have been in association with hydrothermal fluids the hydro thermal fluids from the yinggehai basin in which methane ethane carbon dioxide and especially aromatic hydrocarbons dissolved under the high temperature and high pressure subsurface conditions migrated along the no 1 fault and caused the abnormally high concentration of aromatic hydrocarbons as well as the thermal anomalies in the gas field especially near the no 1 fault

the role of attenuation in the formation of the railroad valley structural basin east central nevada detachment control of petroleum reservoirs the eastern boundary of railroad valley has long been considered a large displacement steep normal fault by mapping a low angle fault called the white pine detachment wpd from the ranges into the valley we show that steep normal faulting was not a significant process in the formation of railroad valley the wpd or its equivalent extends throughout the white pine and grant ranges as shown by mapping of previous authors well data show that it is also present in railroad valley our structure contour map of the wpd based on surface and subsurface data shows that the wpd dips uniformly from the ranges into railroad valley and is not displaced significantly by high angle faulting even if high angle faulting were assumed the maximum displacement consistent with the data would be 2000 ft 610 m much smaller than the total structural relief of at least 16 000 ft 4880 m between the grant range and the adjacent valley structural elevations in the valley are low because the paleozoic section has been greatly attenuated a related contribution to structural relief is uplifting of the ranges caused by diapiric emplacement of plutons in response to tectonic unloading the wpd is only one of many detachments in railroad valley we propose that most or all of the oil reservoirs are in attenuated brittle blocks between detachments seals are provided by detachments or by the discontinuous nature of associated fracturing attenuation by juxtaposing hot infrastructure rocks with rocks that normally occur thousands of feet above the granitic and metamorphic basement may have contributed to maturation of source rocks begin page 1154

brachiopods and chemosymbiotic bivalves in phanerozoic hydrothermal vent and cold seep environments a compilation of 37 fossiliferous phanerozoic marine deposits interpreted to represent ancient hydrothermal vent or cold seep habitats reveals that articulate brachiopods particularly rhynchonellides and terebratulides were relatively common constituents of these chemosynthetic settings from the devonian through the early cretaceous but were rare in such paleoenvironments from the late cretaceous to the present late devonian vent and seep settings were dominated by rhynchonellides dzieduszyckia eoperegrinella morphologically similar to cretaceous seep restricted peregrinella all of which are purported to be closely related phylogenetically bivalve genera with extant chemosymbiotic descendants first appeared in vent seep deposits during the late jurassic and were prevalent therein after the early cretaceous these bivalves include members of five families vesicomyidae mytilidae solemyidae thyasiridae lucinidae lucinids and thyasirids are the dominant groups represented ancient hydrothermal vent and cold seep settings may provide clues to delineate better which factors e g biotic interactions differential recovery following the permian triassic mass extinction have influenced overall evolutionary patterns of dominance among brachiopods and bivalves through the phanerozoic

modification of fracture porosity by multiphase vein mineralization in an oligocene nontropical carbonate reservoir taranaki basin new zealand the nontropical oligocene carbonate rich tikorangi formation is an important oil producer in the taranaki basin new zealand hydrocarbons are hosted and produced from mineralized natural fracture systems petrographic trace element stable isotope 18o and 13c and fluid inclusion data have enabled a complex sequence of eight paragenetic events to be determined the tikorangi formation host rock was cemented by low mg calcite event 1 during burial diagenesis from temperatures of 27c corresponding to 0 5 km burial and continued until 37c 1 km burial depth producing tight pressure dissolved fabrics with essentially no porosity and permeability the host rock was partially dolomitized 5 50 event 2 by ca and fe rich dolomite rhombohedra at burial depths and temperatures of 1 0 1 5 km and 35 50c without secondary porosity development subsequent brittle fracturing formed by neogene compression event 3 is constrained to a period following lithification and dolomitization but before precipitation of first generation vein calcite event 4 this initial ferroan low mg vein calcite formed after a period of burial from fe rich meteorically modified fluids at temperatures of about 50 60c and 1 4 1 9 km burial depth baroque dolomite formed event 5 following a period of mg enriched basinal fluid input precursory to hydrocarbon emplacement per se the dolomite formed mainly as a primary cement but also as a calcite replacement at temperatures following further burial to 2 2 5 km and temperatures of 65 80c formation of celestite and quartzine phases event 6 coincided with or marginally postdated dolomite at similar depths and temperatures to event 6 and formed as both replacements and cements second generation ferroan vein calcite formed event 7 at cooler temperatures 53 65c perhaps resulting from the introduction of cooler meteoric fluids from upsection the presence of petroleum fluid inclusions in the second generation calcite suggests precursory hydrocarbon bearing fluids have migrated along with aqueous fluids from about 10 ma with hydrocarbon emplacement event 8 occurring in the last 6 m y following a period of rapid late miocene burial an improved understanding of the paragenesis of the tikorangi formation may assist in hydrocarbon production from its reservoirs

cretaceous methane seep deposits from new zealand and their fauna abstract six cretaceous methane seep deposits are reported from the raukumara peninsula eastern north island new zealand dinoflagellate dating indicates a late albian to mid cenomanian age for three deposits from port awanui and a mid campanian age for two deposits from waipiro bay and for one from owhena stream the dominant petrographic fabric of the carbonates is detrital micrite and the numerous fenestrae and vugs are filled with various cements including two types of non detrital micrite and botryoidal and banded fibrous calcites these petrographic features in combination with negative 13c values of early diagenetic micrites as low as 29 2 vs v pdb and 13c depleted molecular fossils such as the archaeal biomarkers pentamethylicosane 97 vs v pdb and biphytane 99 and the bacterial biomarker anteiso c15 fatty acid 47 reveal that sulfate dependent anaerobic oxidation of methane aom induced the formation of these deposits the carbonates preserve a typical mollusk dominated late mesozoic deep water seep fauna including the large modiomorphid bivalve caspiconcha the lucinid bivalve ezolucina and limpets hokkaidoconchids and a large abyssochrysoid among the gastropods with close biogeographic relationships to north pacific seep faunas of cretaceous age in contrast to the general marine mollusk fauna of new zealand which shows a high degree of endemism in both the cenozoic and recent new zealand s cretaceous to present day seep faunas consist largely of taxa known from coeval seeps around the world thus while deep water seeps in new zealand were repeatedly or continuously colonized by members of the global seep fauna the general mollusk fauna of the new zealand region developed a considerable degree of endemism during this time

magnetotelluric transect of long valley caldera resistivity cross section structural implications and the limits of a 2 d analysis twenty four magnetotelluric mt soundings have been collected in an east west profile across the center of long valley caldera the average station spacing is approximately 1 km and appears adequate to sample the important features of the upper crustal and deeper resistivity structures additional control on the shallowest resistivity is provided by a continuous profile of time domain electromagnetic soundings coincident with the western portion of the mt line our mt data set reveals numerous resistivity structures which illuminate the evolution and present state of the long valley system many of these have been quantified through two dimensional 2 d finite element modeling emphasizing the transverse magnetic tm mode important structural components include low resistivity layers 0 5 1 5 km deep under the eastern half of the caldera beneath the axial graben of the resurgent dome and under the west caldera moat most of this layering appears to lie in post caldera early rhyolite tuffs and the upp

a new constraint on the antiquity of anaerobic oxidation of methane late pennsylvanian seep limestones from southern namibia late pennsylvanian seep limestones ca 300 ma enclosed in the ganigobis shales in southern namibia formed by microbial activity the process that induced carbonate precipitation was the anaerobic oxidation of methane the presence of 13 c depleted pentamethylicosane pmi 113 and a mixture of crocetane and phytane 112 in concert with similarly 13 c depleted pseudohomologous series of regular isoprenoids reveals that methanotrophic archaea oxidized methane anaerobically at the ancient seep site biphytane and a c 39 pseudohomologue are other archaeal molecular fossils with 13 c values of 99 and 97 respectively the former presence of sulfate reducing bacteria as the syntrophic partners of methanotrophic archaea in the anaerobic oxidation of methane is indicated by isotopically depleted iso and anteiso alkanes these compounds most probably derive from non isoprenoidal monoethers and diethers synthates of sulfate reducing bacteria these findings show that anaerobic oxidation of methane is at least 300 m y old extending the record of this process for 140 m y as the molecular fossils of archaea and bacteria are preserved in a product of their own metabolic activity i e methane derived carbonates with 13 c values as low as 51 the syngenicity of molecular fossils and enclosing deposits is unambiguous this reveals that microbially formed rocks can represent excellent archives for studying past biogeochemical processes

geology and geothermal origin of grant canyon and bacon flat oil fields railroad valley nevada eastern nevada s grant canyon and bacon flat oil fields show strong evidence of formation in a still active moderate temperature geothermal system modern manifestations of this system include unusually elevated oil reservoir temperature at shallow depth 116 122 c at 1 1 1 6 km and dilute na hco3 cl thermal waters directly associated with hot oil hydrogen and oxygen isotopic compositions indicate that these thermal waters are meteoric in origin but were probably recharged prior to the holocene before 10 ka the waters apparently ascended to oil reservoir elevations after deep heating in response to the normal regional thermal gradient there is no evidence for a modern magmatic heat source the beginning of oil reservoir evolution at both fields is recorded by late stage fracture filling quartz in the vuggy brecciated paleozoic dolostone reservoir rocks oil and aqueous solutions were trapped as fluid inclusions in the quartz at temperatures comparable to those now prevailing in the reservoirs apparent salinities of the aqueous inclusions closely match the actual concentrations of current oil field waters and the quartz has the oxygen isotopic composition predicted for its crystallization from these waters at contemporary temperatures present day and fluid inclusion temperatures define essentially coincident isothermal profiles through and beneath the oil reservoir interval a phenomenon consistent with near constant convective heat transfer since inception of the eothermal system textural and mineralogic clues indicate that hot waters circulating in this system also increased porosity by dissolving carbonate minerals and helped seal reservoir margins by precipitating silica and kaolin more importantly the rising thermal waters may have aided oil transport and accelerated source rock maturation through an increase in the shallow 3 km local thermal budget along with the aforementioned fluid inclusion and isotopic evidence radiometrically dated life spans for numerous extinct geothermal systems epithermal ore deposits in the basin and range make it likely that the grant canyon bacon flat system and associated oil reservoirs are no older than 2 5 ma

portrait of a giant deep seated magmatic conduit system the seiland igneous province abstract the seiland igneous province sip northern norway contains 5000 km2 of mafic and ultramafic intrusions with minor alkaline carbonatite and felsic rocks that were intruded into the lower continental crust at a depth of 25 to as much as 35 km the sip can be geochemically and temporally correlated to numerous dyke swarms throughout scandinavia at 560 610 ma and is linked to magmatic provinces in w greenland and ne america that are collectively known as the central iapetus magmatic province cimp revised mapping show that the sip exposes 85 90 layered tholeiitic alkaline and syeno gabbros 8 10 peridotitic complexes 2 5 carbonatite syenite and diorite that formed within a narrow gravimetric data implies an average thickness of igneous rocks of 4 5 km and also features six deep lithospheric roots of ultramafic rocks extending min 9 km into the crust together the root structures represent the main volcanic conduits conveying thousands of km3 of mafic ultramafic melts from the asthenosphere to the lithosphere the ultramafic complexes were predominantly emplaced into the layered gabbros at four major igneous centres respectively nordre brumandsfjord melkvann kvalfjord and reinfjord all complexes are situated in a right way up position and are steep sided forming large plugs a marginal hybrid zone forms at the contact with country rock and transitions gradually from olivine mela gabbro over pyroxenites that grades in to an olivine clinopyroxenite zone which is followed by a wehrlite zone and finally the centre of the complexes comprises pure dunite from pyroxenite to dunite olivine changes from fo72 to fo85 and clinopyroxene from di80 to di92 i e the complexes observe a reverse fractional crystallisation sequence with time parental melt compositions modelled from early dykes indicate komatiitic to picritic melts with 16 22 wt mgo cr of 1594 ppm and ni of 611 ppm which were emplaced at 1450 1500 c melt compositions calculated from clinopyroxene compositions from reinfjord are oib like with lree enriched over hree the high abundance of carbonatites and lamproites demonstrates the volatile rich nature of the mantle source region and is further corroborated by the unusually high abundance of magmatic sulphides 0 5 1 and carbonated and hydrous assemblages c 1 throughout the region in reinfjord they are also closely associated with pge cu ni reef deposits essentially the ultramafic complexes in the sip comprises deep seated transient magma chambers that facilitated mixing and homogenisation of a rich diversity of fertile asthenospheric melts en route to the upper parts of the continental crust

shallow geothermal anomalies overlying deeper oil and gas deposits in rocky mountain region eight of nine rocky mountain area oil and gas fields surveyed by shallow geothermic methods show hot spots or positive shallow temperature anomalies at depths ranging from 500 ft 150 m to as shallow as 10 ft 3 m the magnitudes of these anomalies generally range from 1 to 3f 0 5 to 1 5c but in one case reached 16f 8 9c at 500 ft 150 m similar shallow thermal anomalies associated with oil or gas fields are reported in russian and other literature the methodology of drilling shallow holes and recording accurate temperatures therein is fairly simple inexpensive and rapid the primary cause of the observed temperature anomalies at and above oil and gas fields is unknown but the writers believe that lateral and upward fluid movements through subsurface rocks are an important contributing factor because four of the fields that show both shallow and deep positive temperature anomalies are stratigraphically controlled and are not on or near crests of structural features the commonly held belief that positive temperature anomalies over oil and gas fields simply reflect structural highs is not supported by our data the addition of shallow geothermal surveys to the suite of conventional exploratory methods should improve exploratory efforts to find new oil and gas fields

the age of the sept iles layered mafic intrusion canada implications for the late neoproterozoic cambrian history of southeastern canada the large sept iles layered mafic intrusion of eastern canada has been precisely dated by u pb zircon methods at 565 4 ma consideration of other magmatic events at that time in southeastern canada reveals three different phases of magmatism the first phase was composed of two tholeiitic dike swarms at 615 ma and 590 ma the second including the sept iles intrusion comprised a widespread series of mostly alkaline intrusions emplaced around 575 565 ma along the rift faults of the st lawrence graben the last phase was composed predominantly of alkali and transitional basalts now exposed in the appalachians erupted during the latest neoproterozoic and early cambrian the second and third phases are best accounted for by the arrival of a major mantle plume near the town of sept iles 565 million years ago the widespread but volumetrically minor alkali magmatism that peaked 10 m y earlier is typical of other plumes elsewhere the plume model is reinforced by sedimentological evidence for a crusta

la q icp ms apatite u pb geochronology using common pb in plagioclase examples from layered mafic intrusions apatite geochronology is a versatile method for providing medium temperature history constraints of magmatic and metamorphic rocks the la icp ms technique is widely applied to u pb geochronology using various minerals apatite u pb geochronology in contrast to e g zircon is compromised by variable amounts of common pb incorporated into the crystal during growth magmatic apatite often shows a sufficient spread in data to obtain a precise and accurate lower intercept age if this is not the case the initial pb isotopic composition needs to be estimated to obtain accurate and precise age information from apatite two approaches are common one being the estimation of common pb from a pb evolution model and the other being the measurement of a coexisting mineral phase that tends to incorporate pb but not u e g feldspar most recent studies applying la icp ms to the analysis of pb isotopes in feldspar utilize either multicollector or magnetic sector mass spectrometers in this study we first evaluate the application of quadrupole mass spectrometry for apatite u pb geochronology combined with pb isotopic measurements in feldspar and compare the results with modeled initial pb isotopic compositions the resulting age information is accurate and precise despite using plagioclase rather than k feldspar as is normally used to define initial pb isotope compositions we apply this method to apatite bearing gabbroic rocks from layered intrusions bushveld bjerkreim sokndal hasvik and skaergaard ranging in age from ca 2 ga to ca 55 ma and generate metamorphic cooling ages generally consistent with the known geologic history of these intrusions

sr nd o isotopic evidence of variable sources of mantle metasomatism in the subcratonic lithospheric mantle beneath the grib kimberlite northwestern russia abstract to provide new insights into the type and extent of mantle metasomatism in the subcratonic lithospheric mantle we examined the sr nd o isotopic compositions of orthopyroxene clinopyroxene garnet ilmenite and phlogopite from sheared garnet lherzolite granular garnet harzburgites and lherzolites and clinopyroxene phlogopite rocks from the grib kimberlite in the arkhangelsk diamond province in northwestern russia clinopyroxene and orthopyroxene from sheared garnet lherzolite initially have a close value of 87sr 86sr t 0 7034 and close weak positive end orthopyroxene and clinopyroxene are in oxygen isotope equilibrium with coexisting olivine clinopyroxene from a garnet harzburgite has a low 87sr 86sr t isotope ratio of 0 70266 clinopyroxene from granular garnet lherzolites has a relatively narrow variation in 87sr 86sr t 0 70456 0 70582 and considerably larger variations in end 4 3 1 0 isotope ratios garnet displays elevated initial 87sr 86sr t values 0 70540 0 70633 ilmenite shows a narrow range in 87sr 86sr t 0 70497 0 70522 coupled with end values of 0 4 and 3 5 these isotopic data suggest granular garnet lherzolite of mantle metasomatism took place during the interaction of kimberlite melts with sclm that contained mica amphibole rutile ilmenite diopside marid type metasomes clinopyroxenes from clinopyroxene phlogopite phlogopite wehrlite xenoliths display a broader range in 87sr 86sr t 0 70486 0 70813 that is significantly higher than the kimberlite values and a circa chondritic end 0 1 1 3 with a restricted 18o range 5 11 5 33 more radiogenic sr isotopic composition decoupled from nd isotopes could have been induced by metasomatic melt fluid related to a subducted material the isotopic compositions of mantle minerals preserve sr nd isotopic evidence of pre kimberlite metasomatic events that were probably due to incomplete reequilibration with ultramafic carbonated melt based on mineral pairs rb sr isochrons and a clinopyroxene based sm nd errochron these mantle metasomatic events correspond to 550 600 ma and 1200 ma episodes of magmatic thermal activity

hydrothermally derived petroleum examples from guaymas basin gulf of california and escanaba trough northeast pacific ocean petroleum is associated with sulfide rich sediment at two active oceanic spreading axes in the northeast pacific ocean in the guaymas basin a spreading axis in the gulf of california petroleum having a wide range of compositions forms by hydrothermal alteration of organic matter in quaternary sediment composed mainly of marine diatomaceous ooze and muddy turbidites in escanaba trough at the southern end of the gorda ridge spreading axis offshore northern california petroleum is formed by hydrothermal processes acting on mainly terrigenous organic material in quaternary turbiditic river derived sediment comparisons of the distributions of hydrocarbons n alkanes isoprenoids terpanes steranes and aromatics show that chemical differences among four petroleum samp es are such that two samples from guaymas basin can be distinguished from two samples from escanaba trough distinguishing characteristics resulting from differences in sources include n alkane distributions and certain sterane ratios distinguishing characteristics resulting from differences in thermal histories of the organic matter include hopane and sterane epimer ratios and various distributions of polycyclic aromatic hydrocarbons these oils differ from conventionally derived petroleum in that they are admixtures of products generated over a wide range of thermal regimes and their generation expulsion and migration occurred simultaneously over an instantaneous geological time period the potential economic significance of hydrothermally derived petroleum is uncertain but the act that petroleum can form at active oceanic spreading axes adds a new facet to understanding the processes of petroleum generation expulsion and migration

remobilized geochemical anomalies related to deep gold zones carlin trend nevada a near vertical fracture set in miocene carlin formation tuffaceous sediments occurs approximately 800 m above a deep carlin type gold ore zone of eocene age at the ren property on the northern carlin trend nevada the fractures 0 2 to 2 cm wide are filled with brown montmorillonite clays and contain a distinctive carlin type geochemical assemblage including au as sb hg tl and s these young in situ geochemical anomalies are thought to originate from a paleogeothermal event that may have been seismically triggered by yellowstone plume bulge relaxation dynamics the passage of the plume immediately north of the carlin trend would have provided increased heat flow which coupled with crustal extension may have allowed metal charged geothermal vapor to be released from depth the hydrothermal remobilization filled dilational fractures in surficial units with vapor phase alteration clays containing the geochemical signature of the deep gold ore zone such fractures if found in other areas of northern nevada s great mineral trends may provide important exploration guidance for deep ore systems

the gardnos impact structure norway petrology and geochemistry of target rocks and impactites abstract the gardnos structure norway is an approximately circular area of anomalously fractured and brecciated rock about 4 5 km in diameter emplaced in a metamorphic terrane composed chiefly of granitic gneisses with minor amphibolite and quartzite the original recognition of gardnos as a deeply eroded impact structure between 900 and 400 ma old has been followed up by detailed petrographic and chemical studies of approximately thirty samples of target rocks and various types of shocked rocks impactites deep erosion of the structure has erased the original rim removed much of the crater fill deposits and exposed large areas at or near the original crater floor however a wide variety of distinctive impactites fractured and blackened quartzites in the sub crater basement rocks lithic breccias and melt bearing breccias are still preserved these impactites show petrographic and chemical characteristics that confirm an impact origin distinctive planar deformation features pdfs in quartz and feldspar incipient melting of feldspar clasts in the melt bearing breccias close matches between the chemical composition of the breccias and mixtures of the target lithologies and the detection of an extraterrestrial component a minor extraterrestrial component 0 15 was detected in the melt bearing breccias based on significantly elevated ir and os contents and lower 187os 188os ratios compared to those in the target rocks the gardnos impactites are significantly enriched in c 5 10x over the exposed target rocks this may reflect the presence of a c rich shale overlying the metamorphic basement at the time of impact this idea is supported by 13c values of 28 1 to 31 5 measured in the impactites mixing calculations show that the chemical compositions of the impactites can be reproduced by mixtures of target rocks ranging from approximately 60 90 wt granite gneiss 0 30 wt amphibolite 0 12 wt quartzite and 3 19 wt of a c rich shale component the deeply eroded state of the structure and the preliminary state of detailed geologic mapping make crater reconstruction difficult one possible scenario involves the impact of a 300 m diameter stony meteorite that released 1019 j of energy and formed a transient cavity 3 km in diameter that evolved to a complex crater 5 km in diameter with a central uplift of about 350 m the original crater was filled with at least 0 3 km3 of allochthonous melt matrix breccias containing about 0 06 km3 of impact melt the structure underwent low grade greenschist metamorphism in caledonian time about 400 ma ago and was subsequently eroded to its present appearance the value of the gardnos structure for further cratering studies lies in its easy access to large areas of the original crater floor zone in the preservation of a possibly complete sequence of crater fill breccias beneath a cap of elastic sediments and in the unusual carbon enrichment of its impactites

a miocene chemosynthetic community from the ogaya formation in joetsu evidence for depth related ecologic control among fossil seep communities in the japan sea back arc basin abstract two large carbonate bodies within deep water sediments of the uppermost middle miocene ogaya formation at kita kuroiwa niigata prefecture central japan are identified as an ancient hydrocarbon seep site based on petrographic features such as acicular and sparry calcite cements and clotted micrite with 13c values as low as 38 0 vs vpbd and a low diversity fauna of vesicomyid and mytilid bivalves and provannid gastropods compared to well studied coeval seep communities from the japan sea back arc basin species diversity is particularly low at the kita kuroiwa site while the percentage of seep obligate taxa taxa that are restricted to this type of environment is very high largely due to the absence of predatory gastropods such as naticids and buccinids modern seep communities show a decrease in species diversity and an increase in seep obligate taxa with depth due to the lower abundance and diversity of background colonists entering cold seep habitats likewise depth is here considered as the most likely cause for the observed differences in community structure because the kita kuroiwa seep site was located in considerably deeper water 1000 2000 m than the comparable coeval seep sites in the japan sea back arc basin

the application of fluid inclusions to migration of oil and diagenesis in petroleum reservoirs abstract fluid inclusions can be used to interpret thermal history and petroleum maturation and migration relative to burial history temperature pressure and composition data collected from fluid inclusions are used to determine the environment of diagenesis and the timing of cementation and migration cements in petroleum reservoirs contain both oil and aqueous fluid inclusions fluorescence spectroscopy is used to identify oil inclusions and to determine the maturity of entrapped oil the lifetime of fluorescence induced by a pulsed laser is related to the api gravity of entrapped oil interpretation of fluid inclusion data depends on knowing the origin of fluid inclusions and the probability that they survive in the burial environment those aspects of fluid inclusion study are investigated by synthesizing oil and aqueous inclusions in calcite crystals in laboratory experiments examples of how fluid inclusions are used to determine the physico chemical environments of diagenesis in petroleum reservoirs and the timing of cementation and migration are given for the wealden basin england the mishrif formation dubai the smackover formation gulf coast u s a and jurassic sandstones offshore norway in the wealden basin temperature data from fluid inclusions are used to determine that oil migration occurred in the cretaceous and that the reservoir rocks have been uplifted to varying degrees at a time after migration distribution of oil inclusions indicates that generation and migration of oil was principally in the western part of the basin the geochemistry of oil inclusions in calcite cements from the mishrif formation dubai are used to determine the type and maturity of entrapped oil temperature data from oil and water inclusions are used to relate reservoir diagenesis to burial history and the migration of oil in deep smackover reservoirs oil contains h 2 s the origin of the h 2 s is examined by study of fluid inclusions containing h 2 s in jurassic sandstones offshore norway fluid inclusion studies show that silica cementation is related to burial depth whereas a later calcite cementation originated from invasion of a hot fluid

ore related breccias in volcanoplutonic arcs an overview of breccias related to a variety of base metal precious metal and lithophile element deposits in volcanoplutonic arcs permits definition of six possible mechanisms for subsurface brecciation 1 release of magmatic hydrothermal fluids from high level hydrous magma chambers during second boiling and subsequent decompression generates a spectrum of breccia types in which fragments may suffer collapse and or ascent single or multiple intrusion related breccia pipes and pre and intermineral breccias in porphyry copper deposits provide widespread examples 2 magmatic heating and expansion of meteoric pore fluids may lead to brecciation commonly of late or postmineral age and including pebble dikes in porphyry type and related deposits magmatic heating of rocks saturated with seawater may cause submarine hydrothermal eruptions late in the emplacement histories of kuroko type massive sulfide deposits many of the resultant breccias underwent limited sedimentary transport overpressuring of heated fluids beneath semipermeable partly self sealed cap rocks may lead to brecciation and subaerial hydrothermal eruptions in shallow epithermal precious metal settings magmatic heating or tectonic disturbance may have triggered brecciation 3 interaction of cool ground waters with subsurface magma can generate phreatomagmatic explosions postmineral phreatomagmatic diatremes associated with porphyry systems and premineral diatremes with epithermal precious or base metal deposits were generated in this manner these attained the palcosurface to produce pyroclastic base surge and fall deposits that accumulated as tuff rings around maar craters 4 magmatic hydrothermal brecciation may lead to disruption of rocks through to the paleosurface decompression and fragmentation and eruption of the top part of an underlying magma chamber pre and postmineral magmatic diatremes of this sort are inferred to accompany a few porphyry type and other base and precious metal systems they were manifested at the palcosurface by accumulations of pyroclastic fall and flow deposits 5 breccias may result from mechanical disruption of wall rocks during subsurface movement of magma any intrusion related deposit may include such intrusion breccias 6 tectonic breccias resulting from fault displacement may accompany any type of ore deposit a continuum exists between many of these breccia types and it is difficult to identify unique criteria for their unambiguous distinction

pressure conditions for the solidification of the skaergaard intrusion eruption of east greenland flood basalts in less than 300 000 years abstract primary granophyres are differentiated from olivine tholeiitic magma and occur interstitially throughout the cumulus stratigraphy of the skaergaard intrusion east greenland samples from the lower zones a c lza c the middle zone mz and the sandwich horizon sh are included in the present study together with granophyric accumulations in gabbroic pegmatite from lza c fluid inclusions in quartz and the mineral assemblage in the granophyres record the pressure under which the skaergaard intrusion crystallised pegmatitic granophyre from lza c consists mainly of quartz plagioclase an 4 7 and alkali feldspar or 40 80 enclosing an earlier formed assemblage of ferrohastingsitic and ferroedenitic hornblende fayalite fo 4 5 titanite biotite and fluor apatite granophyric quartz albite and alkali feldspar crystallised from water saturated granitic melts near eutectic minimum conditions between 680 and 660 c the pressure of granophyre crystallisation was modelled by the intercept between fluid inclusion isochores and the minimum melt solidus for granitic compositions pressures recalculated to the roof pendant of the intrusion are 0 7 0 5 for lza 2 0 0 2 for lzb c 2 3 0 8 for mz the triple group level and 3 3 1 3 kb for sh amphibole geobarometry independently confirm the pressure estimates for pegmatitic granophyres in lza c the granophyres formed as the intrusion cooled through the minimum melt solidus in lza lzb lzc mz and sh respectively the pressure increase from lza to sh granophyres is explained by progressive burial during cooling of the intrusion and contemporaneous outpouring of 5 3 6 3 2 7 km of flood basalts during the initial opening of the northeast atlantic ocean accordingly the skaergaard intrusion evolved from a subvolcanic magma chamber at emplacement to a more deep seated igneous system during terminal crystallization when the majority of the intercumulus phases formed the present cooling history suggests the intrusion cooled through the temperature of granophyre formation in less than 300 000 years the increase in the pressure of granophyre formation therefore implies that 5 3 6 3 2 7 km of flood basalts were emplaced within this time window

mesogenetic dissolution its role in porosity development in carbonate reservoirs models of porosity formation in carbonate rocks have stressed subaerial exposure and attendant shallow meteoric diagenesis porosity formation also occurs in deep burial or mesogenetic settings as a result of dissolution enlargement of preexisting pores porosity enhancement and creation of new pore systems brines charged with organic acids carbon dioxide and or hydrogen sulfide derived from organic matter diagenesis and thermochemical sulfate reduction are the likely fluids causing significant mesogenetic dissolution enhanced and newly created mesogenetic pore types can mimic pore types formed in shallow meteoric environments and therefore the mesogenetic origin of some porosity may go unrecognized

detection of late cretaceous eustatic signatures using quantitative biostratigraphy this study tested the potential for high resolution quantitative biostratigraphic methods to distinguish tectonic from supposedly eustatic sequences the study employed automated multidimensional graphic correlation using constrained optimization program conop our analysis was based on 15 onshore sections in eastern new zealand spanning the coniacian to maastrichtian stages upper cretaceous and 398 well constrained lowest or highest occurrence records derived from 245 dinoflagellate species the age of the resulting composite section was calibrated using six dated bioevents two of these events were tied to geochemical or paleomagnetic datums following calibration the composite section had an average relative temporal resolution of less than 130 k y through the study interval although the succession of events was not dated to this level of precision in an absolute sense although the conop composite will not resolve unconformities or condensed intervals that occur across all studied sections such global unconformities can be identified using clusters of events that are placed at a single composite level fifteen major event clusters were identified 10 of which coincided closely with sequence boundaries identified in the northern hemisphere the probability of this coincidence arising by chance alone is 8 although these results must be regarded as provisional they suggest that high resolution quantitative stratigraphy can provide a potent tool for the identification and correlation of stratigraphic sequences furthermore our findings add significant support for recent studies that have argued for the presence of late cretaceous eustasy

basin modelling how well have we done model developers have been highly successful in building usable useful and reliable one dimensional models and in convincing explorationists to use them development of convenient universal software played an instrumental role in the acceptance of 1 d modelling the remaining weaknesses in technology and training while serious can be resolved through a few years of intensive work in certain specific areas 2 d and 3 d fluid flow modelling in contrast finds itself today largely in the position occupied by 1 d modelling more than a decade ago the concept of fluid flow modelling has not yet been adequately sold to explorationists mainly because existing software is often inadequate to meet the real needs of exploration personnel development of appropriate software will probably have to precede widespread popularization of fluid flow modelling to improve existing software two major areas must be addressed 1 making models more comprehensive by including all relevant geologic phenomena and 2 making software easier to use

chemoherms on hydrate ridge unique microbially mediated carbonate build ups growing into the water column two active chemoherm build ups growing freely up into the oceanic water column the pinnacle and the south east knoll chemoherms have been discovered at hydrate ridge on the cascadia continental margin these microbially mediated carbonate formations rise above the seafloor by several tens of meters and display a pinnacle shaped morphology with steep flanks the recovered rocks are pure carbonates dominated by aragonite based on fabric and mineralogic composition different varieties of authigenic aragonite can be distinguished detailed visual and petrographic investigations unambiguously reveal the involvement of microbes during the formation of the carbonates the fabric of the cryptocrystalline and fibrous aragonite can be described as thrombolitic fossilized microbial filaments in the microcrystalline aragonite indicate the intimate relationship between microbes and carbonates the strongly 13c depleted carbon isotope values of the samples as low as 48 1 pdb are characteristic of methane as the major carbon source for the carbonate formation the methane rich fluids from which the carbonates are precipitated originate most probably from a gas reservoir below the bottom simulating reflector bsr and rise through fault systems the 18o values of the aragonitic chemoherm carbonates are substantially higher as high as 5 0 pdb than the expected equilibrium value for an aragonite forming from ambient seawater 3 5 pdb as a first approximation this indicates formation from glacial ocean water but other factors are considered as well a conceptual model is presented for the precipitation of these chemoherm carbonates based on in situ observations and the detailed petrographic investigation of the carbonates this model explains the function of the consortium of archaea and sulfate reducing bacteria that grows on the carbonates performing anaerobic oxidation of methane aom and enabling the precipitation of the chemoherms above the seafloor surrounded by oxic seawater beggiatoa mats growing on the surface of the chemoherms oxidize the sulfide provided by sulfate dependent anaerobic oxidation of methane within an oxic environment the contact between beggiatoa and the underlying microbial consortium represents the interface between the overlying oxic water column and an anoxic micro environment where carbonate formation takes place