sedimentary pyrite formation an update sedimentary pyrite formation during early diagenesis is a major process for controlling the oxygen level of the atmosphere and the sulfate concentration in seawater over geologic time the amount of pyrite that may form in a sediment is limited by the rates of supply of decomposable organic matter dissolved sulfate and reactive detrital iron minerals organic matter appears to be the major control on pyrite formation in normal non euxinic terrigenous marine sediments where dissolved sulfate and iron minerals are abundant by contrast pyrite formation in non marine freshwater sediments is severely limited by low concentrations of sulfate and this characteristic can be used to distinguish ancient organic rich fresh water shales from marine shales under marine euxinic conditions sufficient h2s is produced that the dominant control on pyrite formation is the availability of reactive iron minerals calculations based on a sulfur isotope model indicate that over phanerozoic time the worldwide average organic carbon to pyrite sulfur ratio of sedimentary rocks has varied considerably high cs ratios during permo carboniferous time can be explained by a shift of major organic deposition from the oceans to the land which resulted in the formation of vast coal swamps at that time low cs ratios compared to today during the early paleozoic can be explained in terms of a greater abundance of euxinic basins combined with deposition of a more reactive type of organic matter in the remaining oxygenated portions of the ocean the latter could have been due to lower oceanic oxygen levels and or a lack of transportation of refractory terrestrial organic matter to the marine environment due to the absence of vascular land plants at that time

the anaerobic oxidation of methane and sulfate reduction in sediments from gulf of mexico cold seeps we determined the geochemical characteristics of sediments and measured rates of the anaerobic oxidation of methane aom and sulfate reduction sr in samples collected near thermogenic structure ii gas hydrate mounds and in areas lacking hydrates along the continental slope in the gulf of mexico we used radiotracer c 14 and s 35 techniques to determine rates of aom and sr over depth in sediment cores abundant mats of white and orange beggiatoa spp were common in areas of active seepage and these sediments were enriched in hydrogen sulfide and methane in cores collected from areas without beggiatoa or hydrate concentrations of redox metabolites showed little variation over depth and these sites were inferred to be areas of low seepage integrated aom rates were low in beggiatoa free cores 0 05 mmol m 2 day 1 and averaged 2 8 4 6 mmol m 2 day 1 in seep cores that contained beggiatoa or gas hydrate integrated sr rates were also low in beggiatoa free cores 1 mmol m 2 day 1 and averaged 54 94 mmol m 2 day 1 in cores with beggiatoa or hydrate rates of sr generally exceeded rates of aom and the two processes were loosely coupled suggesting that the majority of sr at gulf of mexico hydrocarbon seep sites is likely fueled by the oxidation of other organic matter possibly other hydrocarbons and oil rather than by aom

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

foredeeps versus subduction zones the geologic characteristics of foredeeps and accretionary wedges suggest that these features are distinguishable on the basis of the direction of the associated subduction east north east dipping subduction related accretionary wedges show high relief and broad outcrops of metamorphic rocks they are associated with shallow foredeeps with low subsidence rates in contrast west dipping subduction related accretionary wedges show low relief and involve mainly sedimentary cover the related foredeeps are deep and have high subsidence rates this differentiation is useful both for oceanic and continental subductions e g eastern vs western pacific subductions or east dipping alpine vs west dipping apenninec subductions in a cross section of the alps the ratio of the area of the orogen to the area of the foredeeps is at least 2 1 whereas this ratio is 0 22 1 for the apennines these ratios explain why foredeeps related to east or northeast dipping subduction are quickly filled and are bypassed by clastic rocks whereas foredeeps related to west dipping subduction maintain a deep water environment longer these differences support the presence of an eastward asthenospheric counterflow relative to the westward drift of the lithosphere detected in the hot spot reference frame even in the mediterranean where no hot spots are present in this interpretation the apennines foredeep was caused by the eastward push of the mantle acting on the subducted slab whereas the foredeeps in the alps were caused by the load of the thrust sheets and the downward component of movement of the upper adriatic plate these forces contrast with the upward component of the eastward mantle flow

ch 4 consuming microorganisms and the formation of carbonate crusts at cold seeps to understand the role played by microorganisms in the formation of cold seep carbonates we conducted an integrated microbial mineralogical and organic geochemical study of methane related authigenic carbonate crusts formed on eastern mediterranean mud volcanoes we show that supersaturation with respect to carbonate minerals is induced by microbial anaerobic oxidation of methane combined lipid biomarker analysis and 16s rrna gene surveys identified a highly diversified methane consuming archaeal community possibly comprising novel species implying that the anaerobic oxidation of methane is phylogenetically widespread and directly implicating these organisms in the process of crust precipitation moreover pore water sulphate gradients produced by co occurring methane based sulphate reduction exert the main control on aragonite versus magnesian calcite precipitation we propose that this may be the dominant mode of carbonate crust formation at cold seeps world wide in agreement with aquatic chemistry predictions and explaining carbonate mineralogy

a new approach to discern the hydrocarbon sources oil vs methane of authigenic carbonates forming at marine seeps abstract numerous marine hydrocarbon seeps have been discovered in the past three decades the majority of which are dominated by methane rich fluids however an increasing number of modern oil seeps and a few ancient oil seep deposits have been recognized in recent years oil seepage exerts significant control on the composition of the seep dwelling fauna and may have impacted the marine carbon cycle through geological time to a greater extent than previously recognized yet distinguishing oil seep from methane seep deposits is difficult in cases where 13ccarb values are higher than approximately 30 due to mixing of different carbon sources here we present a comparative study of authigenic carbonates from oil dominated site gc232 and methane dominated site gc852 seep environments of the northern gulf of mexico aiming to determine the geochemical characteristics of the two types of seep carbonates we analyzed 1 major and trace element compositions of carbonates 2 total organic carbon toc total nitrogen tn and carbon isotope 13ctoc of residue after decalcification 3 sulfur isotope signatures of chromium reducible sulfur crs 34scrs and residue after crs extraction 34stos as well as 4 sulfur contents tos of residue after crs extraction carbonates from the studied oil seep are dominated by aragonite and exhibit lower 34scrs values suggesting carbonate precipitation close to the sediment surface in addition oil seep carbonates are characterized by higher toc and tos contents and higher toc tn ratios as well as less negative 13ctoc values compared to methane seep carbonates probably reflecting a contribution of residual crude oil enclosed in oil seep carbonates very low 13ctoc values as low as 68 7 vpdb and low toc tn ratios of methane seep carbonates indicate that the enclosed organic matter is derived mainly from the biomass of methanotrophic biota this study presents new geochemical data that will allow the discrimination of oil seep from methane seep deposits although some of the geochemical patterns are likely to be affected by late diagenesis if applied with caution such patterns can be used to discern the two end member types of seepage oil seeps and methane seeps in the geological record

methane derived authigenic carbonates formed by subduction induced pore water expulsion along the oregon washington margin authigenic magnesian calcite dolomite and aragonite are precipitated in the uppermost terrigenous sediments of the washington oregon accretionary prism by subduction induced dewatering these distinctive carbonates are methane derived and occur at sites of concentrated pore water expulsion unique biologic communities that subsist at least indirectly on methane suess et al 1985 are also found at some of these sites the methane which is dominantly biogenic is carried to the uppermost sediments of the prism by fluids and is oxidized by sulfate reducers before being incorporated into a carbonate cement carbonate precipitation occurs below the oxic layer probably no deeper than several centimetres to a few metres below the seabed cementation may be induced by three factors 1 increased carbonate alkalinity resulting from microbial sulfate reduction 2 decreased co 2 solubility resulting from a pressure decrease when the pore water escapes the prism and or 3 the addition of ca 2 and mg 2 ions from sea water near the sediment water interface the convergent margin setting engenders precipitation of authigenic carbonates in several ways compressive stresses induce anomalously rapid compaction and dewatering rates and they may cause overpressuring in migrating pore water thereby delaying precipitation of carbonates until pressure is released near the sediment water interface structural deformation of the accretionary prism creates pathways such as fault zones secondary fracture porosity and dipping permeable layers often exposed by mass movement for efficient advection and expulsion of methane enriched pore water these characteristic conditions which lead to the precipitation of methane derived carbonates may be found at other convergent margins

silurian s type granite related w mo mineralization in the nanling range south china a case study of the pingtan w mo deposit abstract the pingtan deposit in southwestern hunan province is a newly discovered large sized w mo deposit this deposit is situated in the northwestern part of the miao ershan granite batholith western nanling range the tungsten mineralization is mainly hosted in biotite monzogranite and the alteration related to mineralization is controlled by a ne trending fault zone in this paper we present new molybdenite re os and zircon u pb ages zircon lu hf isotope and ree geochemical data aiming to constrain the w mo mineralization age and ore hosting granite petrogenesis in the pingtan w mo deposit molybdenite re os dating of eight ore samples yielded a weighted average model age of 427 0 5 4 ma mswd 0 24 the la icp ms zircon u pb analysis of two biotite monzogranite yielded 206pb 238u ages of 430 8 2 4 ma and 431 0 1 8 ma respectively suggesting that the w mo mineralization is spatial temporally associated with the biotite monzogranite the ore related granites have high contents of sio2 and k2o belong to weakly to strongly peraluminous a cnk 1 00 1 30 and geochemically classified as s type affinity molybdenite re contents 2 262 7 297 g g zircon ehf t 10 34 5 87 and 176hf 177hf 0 282241 0 282376 values of the biotite monzogranite suggest that the ore forming materials are predominantly derived from the crust this is the first identification of tungsten mineralization related to silurian s type granites caledonian granites in the miao ershan granite intrusion indicating caledonian is an important mineralization period of w in the western part of nanling range south china

geochemical correlation of pyrobitumen fills with host mid cretaceous black flysch group basque cantabrian basin western pyrenees abstract abundant syndepositional pyrobitumen fills occur within albian hydrothermal vent carbonates of the organic rich black flysch group in the basque cantabrian basin indicating that these carbonates were charged with oil during albian times a carbon isotopic study of pyrobitumens and samples of candidate oil generating rocks jurassic and albian host rock units as well as carboniferous sourced condensate was undertaken to test an albian source hypothesis for the pyrobitumens on the basis of similar isotopic ratio values the pyrobitumens show a strong positive correlation with the host black flysch group this is supported by stahl type curves and a sofer plot which show that the pyrobitumens best match the host albian deposits whereas the jurassic source rock and the carboniferous sourced condensate plot separately this new albian pyrobitumen source correlation demonstrates the existence of an oil generating rock unrecognised till now in the basque cantabrian basin the mid cretaceous black flysch group

methanogenic calcite 13c depleted bivalve shells and gas hydrate from a mud volcano offshore southern california methane and hydrogen sulfide vent from a cold seep above a shallowly buried methane hydrate in a mud volcano located 24 km offshore southern california in 800 m of water bivalves authigenic calcite and methane hydrate were recovered in a 2 1 m piston core aragonite shells of two bivalve species are unusually depleted in 13c to 19 13c the most 13c depleted shells of marine macrofauna yet discovered carbon isotopes for both living and dead specimens indicate that they used in part carbon derived from anaerobically oxidized methane to construct their shells the 13c values are highly variable but most are within the range 12 to 19 this variability may be diagnostic for identifying cold seep hydrate systems in the geologic record authigenic calcite is abundant in the cores down to 1 5 m subbottom the top of the methane hydrate the calcite is depleted in 13c 13c 46 to 58 indicating that carbon produced by anaerobically oxidized methane is the main source of the calcite methane sources include a geologic hydrocarbon reservoir from miocene source rocks and biogenic and thermogenic degradation of organic matter in basin sediments oxygen isotopes indicate that most calcite formed out of isotopic equilibrium with ambient bottom water under the influence of gas hydrate dissociation and strong methane flux high metal content in the mud volcano sediment indicates leaching of basement rocks by fluid circulating along an underlying fault which also allows for a high flux of fossil methane

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

multiple dolomitization events along the pozalagua fault pozalagua quarry basque cantabrian basin northern spain the pozalagua quarry in the basque cantabrian basin of northern spain exposes a unique set of fault associated dolomites that can be studied on a decametre scale the dolomites developed along the pozalagua fault system in slope deposited limestones of albian age following marine phreatic diagenesis the limestones were subject to meteoric karst formation the resulting cavities were filled either by angular limestone fragments in a black clay rich matrix or by cave floor pond now dolomitized sediments the subsequent diagenetic history reflects repeated periods of fracturing fluid expulsion dissolution and cementation contrasting fluid pulses resulted in the formation of a network of hydrothermal karst and the subsequent development of coarse crystalline calcite cement zebra dolomite recrystallized coarse crystalline dolomite elongated blue grey coarse crystalline dolomite cement in the open fault and finally coarse crystalline saddle dolomite decimetre size reworked host rock fragments present in the latter two dolomite phases probably reflect roof collapse fragments of a cave system that developed along the pozalagua fault system however there are also metre scale host rock fragments that apparently float in the coarse crystalline saddle dolomites implying that either fragment assimilation was a widespread process or violent expulsion of fluids occurred along the pozalagua fault system the presence of pre dolomite and post dolomite stylolites parallel to bedding supports a linkage between the diagenetic events and the late albian tectonism that affected the region

gold deposits of china a special issue of ore geology reviews this volume of ore geology reviews is dedicated to dr feng jun nie and credits his significant contribution to understanding the ore deposits of china in recent years he has dedicated his life to the study of mineralization in the north china craton and central asian orogen to the north and that is the focus of this volume

large scale porphyry type mineralization in the central asian metallogenic domain a review abstract a series of porphyry type cu mo au deposits including some giant world class deposits such as kounrad aktogai kal makyr oyu tolgoi and chalukou occur in the central asian metallogenic domain camd the outline of the camd almost overlaps with that of the central asian orogenic belt caob which is located between the east europe siberia tarim and north china cratons the camd comprises sparsely exposed tectonic slices of precambrian high grade metamorphic basement rocks that are sandwiched between phanerozoic accretionary complexes and arc rocks according to geological metallogenic geochronological and tectonic setting characteristics the camd comprises three metallogenic provinces 1 the kazakhstan cu au mo 2 the mongolia cu au and 3 the northeast china mo cu metallogenic provinces early paleozoic 490 to 440 ma and late paleozoic 330 to 295 ma large scale porphyry type mineralization in the kazakhstan metallogenic province is intimately associated with the evolution of the central tianshan yili northern tianshan kokchetav chingiz paleozoic arc system which was terminated by the late permian closure of the western segment of the paleo asian ocean in contrast the 370 ma and 240 ma porphyry type mineralization of the mongolia metallogenic province is related to the tuva mongolia arc collage system that was formed during the evolution of the paleo asian ocean in the paleozoic and the mongol okhotsk ocean in the early mesozoic furthermore the northeast china metallogenic province was affected by three distinct geodynamic processes that were associated with the paleo asian mongol okhotsk and paleo pacific oceans during the paleozoic 250 ma the early mesozoic 200 ma and the late mesozoic 200 90 ma respectively except for the early paleozoic cu mineralization at duobaoshan 480 ma and bainaimiao 440 ma the porphyry type mineralization of this metallogenic province is predominantly characterized by widespread mesozoic mo mineralization in general porphyry type deposits of the camd have geological structural metallogenic alteration and fluid characteristics which are consistent either with those related to the oceanic subductional arc settings of the circum pacific metallogenic domain or with those of the continental collisional environment in the tethyan metallogenic domain the involvement of highly oxidized intermediate to felsic magmas is fundamental for the formation of porphyry deposits even though the prevalent mash and slab melting models can be employed to interpret the genesis of some porphyry cu deposits in the camd a here newly suggested model which is based on pre enriched mafic lower crust and the subduction of a relictic mid oceanic ridge is thought to explain the large scale copper mineralization in the balkhash west junggar metallogenic belt of the kazakhstan metallogenic province nevertheless most of the porphyritic suites associated with the mo deposits in the northeast china metallogenic province have relatively depleted mantle like neodymium and hafnium isotopic compositions suggesting that the ore forming granitic magma may have predominantly been derived from juvenile lower crust upwelling of asthenosphere may have triggered the melting of the lower crust during post collisional extension subsequent to the closure of the paleo asian ocean in the triassic the subduction of the paleo pacific ocean in the jurassic and the thinning of the lithosphere caused by rollback of the paleo pacific plate in the cretaceous ancient crustal components were only locally found to have been involved in the magma source of several medium large mo deposits

porosity of sediments in accretionary prisms and some implications for dewatering processes rapid dewatering largely through loss of porosity is one of the most striking changes affecting deformed sediments in accretionary prisms analysis of porosity from sample and seismic data confirms that porosity in accretionary prisms is significantly less than that in basinal strata of similar lithology more specifically the porosity depth gradient increases arcward across the prism until porosities less than 10 occur within a few kilometers of the surface in deeper parts of the prism dewatering and volume reduction occur not only during loss of porosity but also during dehydration and metamorphic reactions calculations involving volume change lead us to define a function which reflects total volume reduction the distribution of the relative intensity of dewatering within the prism can be calculated from the porosity contours and trajectories of sediment elements an initial attempt indicates that in the toe region the rate of dewatering is accelerated at depth relative to the basinal section and may be greatest near the base of the prism toward the rear of the prism the maximum rate of dewatering occurs at progressively shallower depths several lines of evidence suggest that in addition to gradual diffuse dewatering localized zones of strong dewatering are associated with zones of intense shear this model of shear dewatering based on critical state soil mechanics suggests that sediments adjacent to the basal decollement should be strongly dewatered

chemical and boron isotope compositions of tourmaline in the hadamiao porphyry gold deposit inner mongolia china abstract the hadamiao porphyry gold deposit in inner mongolia china is located in the northern margin of the north china craton ncc tourmaline is a common mineral in hydrothermal veins and granitic rocks contemporaneous with the mineralized granite porphyry in this deposit the tourmaline can be divided into six types including magmatic tourmaline tur m1 in granite porphyry dikes magmatic hydrothermal transitional tourmaline tur m2 in nodular granitic rocks and hydrothermal tourmalines in early tourmaline veins tur v1 gold bearing quartz tourmaline chalcopyrite veins tur v2 breccia cements tur v3 and late carbonate quartz veins tur v4 the gold mineralization is closely related to the occurrence of tur v2 almost all the tourmalines from the hadamiao deposit belong to the alkali group and show a schorlitic dravitic composition except for some tur m1 belonging to uvite the concentrations of most elements in different tourmaline types overlap tur m1 has higher ca w th u pb mn and zr contents than other types and the hydrothermal tourmalines v1 v4 show slightly higher ba cu and y contents than tur m1 and tur m2 the concentration of au in tur m1 and tur m2 can reach up to 80 ppb and is higher than that in tur v1 the au content in tur v2 is an order of magnitude higher than that in other stages of tourmaline systematic contrasts in major and trace element compositions between magmatic and hydrothermal tourmalines are attributed to the assimilation of the country rock by the magmatic hydrothermal system the six types of tourmaline exhibit variable 11b values ranging from 8 7 to 21 2 tur m1 shows the highest 11b values of 15 1 to 21 2 and tur v2 yields the lowest values ranging from 8 7 to 5 4 the boron probably came from two sources with different isotopic compositions one with high positive 11b values and the other with negative 11b values magmatic hydrothermal fluids could have provided isotopically light boron for hydrothermal tourmalines whereas the heavy boron in magmatic tourmaline was probably derived from marine carbonates that are widespread in the study area the magma related to the mineralization and the one containing magmatic tourmaline may have experienced different degrees of interaction with wall rocks resulting in the diversity of 11b values in hadamiao tourmaline

a kinetic model for the pattern and amounts of hydrate precipitated from a gas steam application to the bush hill vent site green canyon block 185 gulf of mexico 1 we construct a linear kinetic model of hydrate crystallization from a gas stream we use this model to predict the fraction of gas that crystallizes as hydrate in the subsurface of bush hill and the depth profile of subsurface hydrate accumulation this is possible because the bush hill vent is fed by reservoir gas from the nearby jolliet field whose composition is known on the average 9 of the vent gas is precipitated as hydrate in the subsurface although other explanations are possible the observed vent gas compositions and the greater range of hydrate gas compositions are consistent with a single source gas whose venting rate varies by a factor of at least 3 over periods of a few years or less the predicted depth profile of hydrate accumulation and the hydrate content of the bush hill mound suggest that between 1 1 109 and 2 8 109 m3 stp of gas may have accumulated as hydrate between the seafloor and 614 m depth for the radiometrically and geologically suggested system age of 10 000 years the time average venting rate is 106 m3 yr 0 7 106 kg yr if distributed evenly across the 600 m diameter mound as suggested by echo sounder images the methane flux is 3 2 kg m2 yr this is 103 times that inferred for hydrates associated with bottom simulating seismic reflectors the subsurface hydrate accumulation and the cumulative methane venting are related we show how both may be estimated from measurements of vent gas composition bottom water temperature and geothermal gradient

carbon isotope composition of hydrothermal petroleums from guaymas basin gulf of california abstract petroleum hydrocarbons are a major emanation from the active hydrothermal vent fields of guaymas basin the samples we describe here occur in hydrothermal mound crusts which have been collected in situ with a submersible the relative concentrations of the compound classes in the hydrothermal petroleum are highly variable with the following ranges saturate hydrocarbons 1 60 aromatic hydrocarbons 18 38 nso compounds 10 27 and asphaltenes 0 2 25 the sulfur concentrations range between 1 2 and 3 4 the s rich hydrothermal petroleums tend to be low in saturated hydrocarbons and high in nso and asphaltenes components and vice versa stable c isotope concentrations in whole hydrothermal petroleum vary little 13c 21 2to 22 2 0 vs pdb carbon isotope patterns for the compound classes are similar to typical crude oils with the saturated hydrocarbons being depleted in 13c 22 9 to 21 7 0 and asphaltenes being relatively enriched 20 5 to 20 8 0 the variability decreases from saturates to aromatics nso and asphaltenes this indicates that the hydrothermal petroleums oirginate from one source the higher variability in the non asphaltic compound classes is attributed to distillation and or biodegradation effects organic matter in recent unaltered sediments in the immediate vicinity of the hydrothermal vents has an average 13c of approximately 20 5 0 in a range consistent with their being the source for the oils this simlarity supports the contention that the hydrothermal petroleums are pyrolysis products of the immature sediments which are permeated by the hydrothermal fluids

molybdenite re os and u pb zircon dating and genesis of the dayana w mo deposit in eastern ujumchin inner mongolia abstract the dayana w mo deposit in eastern ujumchin of inner mongolia is a quartz vein type deposit in the mid western part of the central asian orogenic belt caob biotite monzogranite quartz porphyry and hornfels host w mo in quartz veins based on spatial relationships molybdenite was deposited first followed by wolframite this contribution presents precise laser ablation inductively coupled plasma mass spectroscopy la icp ms u pb zircon dating and geochemical analysis of the biotite monzogranite the u pb dating shows that the monzogranite is 134 1 ma major and trace element geochemistry shows that the monzogranite is characterized by high sio 2 and k 2 o contents a right inclined shape of the chondrite normalized ree patterns enrichment of large ion lithophile elements liles and depletion of high field strength elements hfses such as nb p ba the monzogranite is high k calc alkaline has a strong negative eu anomaly eu eu 0 04 0 45 low p 2 o 5 content high a cnk of 1 2 enriched in large ion lithophile elements liles such as rb th u nd and hf and notably depleted in ba sr p ti and nb these characteristics define the dayana monzogranite as a highly fractionated peraluminous granite re os isotopic analysis of seven molybdenite samples from the deposit yield an isochron age of 133 3 ma mswd 2 2 which indicates that the monzogranite and ore have the same age within error are probably genetically related and related to a major early cretaceous mineralizing event in china known as the yanshanian

thermogenic hydrocarbons from the offshore calypso hydrothermal field bay of plenty new zealand hydrothermal gases from shallow seafloor vents in the bay of plenty new zealand contain co2 ch4 and the higher gaseous hydrocarbons up to i n c4h10 the gases are similar to those discharged at fumaroles on the nearby white island carbon isotope compositions for co2 fall between 3 4 and 5 5 pdb and reflect a shallow magmatic carbon source the 13c values of ch4 range from 24 6 to 28 9 pdb and the d values vary between 122 and 135 smow the ch4 isotope values and the presence of the higher hydrocarbon compounds such as c2h6 and c3h8 with 13c values near 20 pdb suggest hydrocarbon production by high temperature maturation of sedimentary organic matter and mixing 1 1 of the thermogenic ch4 with abiogenic ch4 long chained hydrocarbons occur in dredged samples close to the active vents their n alkane distribution has a high to moderate odd even predominance and an extensive hopane series indicative of higher land plant waxes and prokaryotic membranes in the source substantial amounts of unsubstituted polynuclear aromatic hydrocarbons pah mark the transition from aliphatic to aromatic dominated bitumens consistent with extensive source maturation resulting from thermal stress the bitumens are interpreted as pyrolysates derived from buried near coastal vegetation and terrestrial detritus under various thermal regimes mixed with immature seafloor organic matter

evidence from fluid seeps atop serpentine seamounts in the mariana forearc clues for emplacement of the seamounts and their relationship to forearc tectonics abstract the mariana forearc is a non accretionary forearc with numerous seamounts dredge hauls from these seamounts are composed primarily of serpentinite indicating a non volcanic origin in addition dredged carbonate samples reveal 1 the presence of aragonite in water depths greater than the aragonite compensation depth 2 unusual porosity and cement types 3 light carbon and heavy oxygen isotopic compositions and 4 an unusual trace element geochemistry of aragonite and calcite these mineralogic petrologic and geochemical characteristics formed the basis of a prediction that methane bearing fluids are venting from these seamounts subsequent to this prediction submersible dives on a mariana forearc seamount found and sampled chimneys seeping cool water that contains dissolved methane the serpentine substrate beneath the chimneys appears to form from cold gravitational flows of serpentine material fluid inclusion contents of chimney samples also show an earlier history of methane as well as longer chain hydrocarbons aromatics and acetate ions drilling into the flank and the summit of this seamount by the ocean drilling program during leg 125 confirmed the presence of methane other light alkanes and organic acids in the present day interstitial pore fluid of the cores the presence of aromatic compounds and organic acids if derived from the maturation of organic compounds indicates a thermogenic origin for these volatiles strontium isotopic ratios of the aragonitic chimney samples and of the present day interstitial waters range from present day seawater values to significantly lower values the strontium isotopic ratios of the pore waters within the seamount trend toward a relatively less radiogenic composition with increasing depth below the seafloor this strontium isotopic signature is probably not the consequence of near surface processes but more likely a contribution from an igneous source deeper in the lithosphere the lack of a large accretionary prism in the mariana forearc removes the complication of fluid contribution from dewatering of the prism by compression during convergence as in the oregon washington or barbados margins the organic compounds in the fluid inclusions and interstitial pore fluids as well as the isotopic and the geochemical composition of the carbonates and the dissolved constituents suggest that fluids are derived from dewatering compression and dehydration of subducted sediments and the subducting plate furthermore the composition of the fluid is influenced by thermal maturation of organics in subducted sediments as well as by a contribution from a deep igneous source

zircon u pb hf o and molybdenite re os isotopic constraints on porphyry gold mineralization in the bilihe deposit ne china abstract the bilihe gold deposit in inner mongolia is situated in the central asian metallogenic domain its major orebody ii is a porphyry type body spatially and temporally associated with granodiorite porphyry and granite aplite in this study the timing of gold mineralization is precisely constrained by using the zircon u pb dating for pre mineralization intrusions and the molybdenite re os dating for later molybdenite veins furthermore zircon hf o isotope analyses have also been carried out to decipher the nature of primary magma zircon u pb dating shows that the granodiorite porphyry and the granite aplite were emplaced at 269 2 ma and 270 2 ma respectively indicating the gold mineralization occurring no earlier than 269 ma meanwhile molybdenite veins are developed within the fractures and commonly cut across the auriferous veins thus combined with a molybdenite re os isochron age of 268 1 ma the gold mineralization in the bilihe deposit can be precisely restricted to ca 269 ma zircon ehf t values are mostly positive 1 6 11 3 along with high 18o values of 6 20 7 63 suggesting a mixed source between mantle materials and ancient continental crust such as the bainaimiao group for the bilihe magma it is also supported by the presence of the captured detrital zircons in these intrusions given a universally metallogenic environment for porphyry gold deposits a thicken crustal setting related to the collisional intermission of the paleo asian ocean is favored to interpret the formation setting of the bilihe deposit

origin of cacl brines in devonian formations western canada sedimentary basin abstract the majority of waters in devonian formations of the western canada sedimentary basin are high salinity ca cl brines this relatively rare type of brine is of economic interest because of its association with both oil and hydrothermal ore deposits these brines are important sources of ca2 mg2 and ore metals in sedimentary basins it is possible to generate the ca cl brines by modification of residual evaporite brines the evaporation of devonian sea water produced large quantities of gypsum and halite such as the prairie formation residual brines were not retained in the evaporating system quantities of dense halite saturated brine sufficient to account for the high salinity formation waters in the basin were lost syndepositionally the cl and br content of waters within devonian formations in the basin can be explained by dilution of the residual evaporite brines brine composition was modified as a result of density driven reflux to depths of several kilometers this placed concentrated brines in contact with precambrian basement rocks at elevated temperatures 100 300 c the most important reactions between the brine and basement rocks appear to involve albitization of feldspars further modification of the brines occured as cements formed in devonian carbonates volumetrically the most important of these is dolomite in addition some devonian carbonates were dolomitized during ascent along faults mg2 was lost from hot brines as dolomite formed

molybdnite re os isotope age of bilihe large size porphyry gold deposit in sunid right banner of inner mongolia and its geological significance situated in sonid right banner of inner mongolia the bilihe gold deposit lies within the caledonian hyperplasia orogenic belt sandwiched between north china north margin kangbao chifeng fault and wenduermiao xilamulun fault in the middle eastern section of the central asian orogenic belt the host rock in the bilihe gold deposit is a set of neutral acidic volcanic rocks sedimentary rocks which can be divided into andesites in the lower part and rhyolites with related clastic rocks in the upper part the concealed gold bearing sub volcanic intrusive complex composed mainly of granodiorite porphyry monzogranite porphyry is closely related to the minera lization four types of mineralization have been identified namely quartz vein type tectonic fracture zone altered rock type explosion breccia type and porphyry altered rock type the first three mineralization types are controlled by faults breccia pipes veins and volcanic bodies as well as their supporting structures the gold deposit belongs to the sub volcanic hydrothermal type which has been subjected to intense erosion and hence only partially preserved the most important mineralization type is the porphyry alteration type and the proven resources of this type of mineralization account for more than 90 of the total resources of the mining area the porphyry type mineralization occurs in the inner and exo contact zone between hypo volcanic complex body and overlying volcanic rocks as well as volcanic clastic rocks especially in the inner contact zone it is the first time that a large sized porphyry gold deposit was found in the northern margin of north china plate i e the bilihe large size porphyry gold deposit in sunid right banner of inner mongolia in order to identify the porphyry gold copper metallogenic age the authors used re os isotope to test 6 molybdnite samples collected from the porphyry which yielded the isochron age of 272 7 1 6 ma mswd 0 57 redefinition of the late paleozoic ore forming geological event of the bilihe gold deposit has provided new evidence for the convergent plate structural system in the northern part of north china in late paleozoic recognized some basic geological problems of the northern part of north china and given enlightenments in search for low temperature shallow seated porphyry gold polymetallic deposits in the magmatic arc environment of the middle east segments of the central asian orogenic belt in late paleozoic

integrated petrographic and geochemical record of hydrocarbon seepage on the voring plateau authigenic carbonate crusts nodules and chemoherms were sampled from pockmarks and mud diapirs on the southern part of the voring plateau during the ttr 8 and ttr 10 marine expeditions a petrographic and geochemical study was carried out to investigate their possible relationship with the seepage of hydrocarbon fluids all authigenic carbonates are depleted in 13 c 31 6 13 c 18 o 18 o 4 6 18 o 18 o rich fluid the occurrence of different carbonate mineral phases aragonite calcite dolomite is possibly related to varying dissolved sulphate concentrations in the diagenetic environment fluid inclusion microthermometry and raman spectroscopy indicate the presence of an aqueous hydrocarbon mixture inside the inclusions this seepage mixture was almost certainly immiscible resulting in heterogeneous trapping

permian magmatic sequences of the bilihe gold deposit in central inner mongolia china petrogenesis and tectonic significance abstract the bilihe gold deposit is located in the eastern section of the ondor sum yanji suture at the southern margin of the xing an mongolian orogenic belt xmob and the northern margin of the north china craton ncc central inner mongolia the magmatic rocks in the ore district are generally high k calc alkaline enriched in lree zr and hf and depleted in hree nb ta and p the magmatic evolution sequences are norite gabbro granodiorite porphyry granite or norite gabbro andesite dacite porphyry granodiorite which show a trend of decreasing tio2 feo mgo cao and p2o5 with increasing sio2 in the bilihe ore district hydrothermal processes were coeval with granitic magmatism for a period of 17 myr 272 255 ma the ages of the granite granodiorite porphyry granodiorite and dacite porphyry are 271 5 264 1 ma 269 8 255 8 ma 268 3 ma and 268 6 259 4 ma respectively the magmatic rocks contain magmatic hydrothermal and magmatic hydrothermal zircons the magmatic zircons have ce 4 la 2 5 the hydrothermal zircons have ce 3 ppm and smn lan

hydrothermal petroleum in mineralized mounds at the seabed of guaymas basin petroleum has been dredged from an active hydrothermal mound area in the southern rift of guaymas basin gulf of california this organic matter is composed of gasoline range aliphatic and aromatic hydrocarbons and predominantly residual polar asphaltic material the aliphatic hydrocarbons of two bitumen samples have very different boiling range and composition both samples contain polynuclear aromatic hydrocarbons and olefins which indicate formation at pyrolytic temperatures the overall compositional data indicate an origin from biological detritus by thermal alteration and rapid quenching by hydrothermal removal followed by condensation at the seabed

mid cretaceous hydrothermal vents and authigenic carbonates in a transform margin basque cantabrian basin western pyrenees a multidisciplinary study a comprehensive study of authigenic carbonates and associated fauna in late albian organic rich deep water deposits the black flysch group reveals that carbonate precipitation was a by product of the anaerobic oxidation of hydrocarbon rich hydrothermal fluids the authigenic carbonates are exposed along the kardala and alkolea sea cliffs in the western pyrenees the two vent carbonates occur 1 km apart adjacent to the synsedimentary right reverse mutriku fault but in contrasting structural domains the kardala carbonates occur on a structural ridge hangingwall and the alkolea carbonates are positioned at the base of an erosional scarp folded downward footwall the similarity in pattern of the carbonate phases and complex paragenetic events for both vent precipitates implies that hydrothermal fluid generation processes and pore water evolution during early and late diagenesis were similar nevertheless a comparison of the geochemistry fossil fauna and morphology of carbonate structures of both precipitates suggests that the vented hydrocarbon type flow intensity and temperature of hydrothermal fluids were different at the kardala vent intense focused flow of hot up to 109 c oil rich fluids were generated allowing the development of a relatively abundant chemosynthesis based fauna in contrast at the alkolea vent diffuse flows of warm thermogenic methane rich fluids were expelled to the sea floor and no chemosynthetic fauna developed these differences are related to the contrasting structural setting of each locality similar d 13 corg values for both pyrobitumen fills and host unit organic matter suggest that the hydrocarbon source was the black flysch group contact alteration of these organic rich sediments by syndepositional hydrothermal fluids generated hydrothermal petroleum oil and gas hydrocarbons which probably migrated updip to the sea floor by contemporary compression tectonics

warm tropical ocean surface and global anoxia during the mid cretaceous period the middle of the cretaceous period about 120 to 80 myr ago was a time of unusually warm polar temperatures1 repeated reef drowning in the tropics2 and a series of oceanic anoxic events oaes that promoted both the widespread deposition of organic carbon rich marine sediments and high biological turnover3 4 5 6 7 8 the cause of the warm temperatures is unproven but widely attributed to high levels of atmospheric greenhouse gases such as carbon dioxide7 8 9 10 11 12 in contrast there is no consensus on the climatic causes and effects of the oaes with both high biological productivity and ocean stagnation being invoked as the cause of ocean anoxia3 4 5 6 7 8 here we show using stable isotope records from multiple species of well preserved foraminifera that the thermal structure of surface waters in the western tropical atlantic ocean underwent pronounced variability about 100 myr ago with maximum sea surface temperatures 3 5 c warmer than today this variability culminated in a collapse of upper ocean stratification during oae 1d the breistroffer event a globally significant period of organic carbon burial that we show to have fundamental stratigraphically valuable geochemical similarities to the main oaes of the mesozoic era our records are consistent with greenhouse forcing being responsible for the warm temperatures but are inconsistent both with explanations for oaes based on ocean stagnation and with the traditional view reviewed in ref 12 that past warm periods were more stable than today s climate

stromatolite reef crusts early cretaceous spain bacterial origin of in situ precipitated peloid microspar peloidal crusts are significant components of early cretaceous aptian reef carbonates in eastern spain the crusts form steep sided laminated deposits on coral and other skeletal surfaces their microfabric consists almost entirely of silt sized peloids in fenestral microspar matrix this microfabric contrasts with more poorly sorted and generally finer grained detrital wackestone packstone fabrics of the adjacent reef matrix scarcity of incorporated grains indicates that the crusts did not trap many particles it is proposed that the crusts are stromatolites and that peloids and inter peloid space were created concurrently by bacterial degradation of organic matter as they developed inter peloid voids were protected from infiltration of extraneous sediment by the organic rich exterior surface of the stromatolite even spacing of the peloids within microspar may reflect self organization of bacterial colonies in the decaying organic matrix compressed and partly amalgamated peloids marginal to burrows in the stromatolites suggest that the peloid fabrics were initially only partially lithified the grainstone like peloid fabric is therefore interpreted as having formed in situ by very early diagenetic processes driven by heterotrophic bacteria

pyrite re os and zircon u pb dating of the tugurige gold deposit in the western part of the xing an mongolia orogenic belt china and its geological significance abstract the tugurige gold deposit in the northeastern margin of the north china craton ncc and western part of the xing an mongolia orogenic belt xmob is a large tonnage quartz vein type deposit with a resource of 24 t at about 4 g t au gold mineralization is hosted by porphyritic syenogranite and controlled by nw trending faults our study provides the first precise age for the tugurige gold mineralization and host porphyritic syenogranite the u pb age of zircons from the syenogranite is 276 2 ma and re os dating of six pyrite separates from the deposit yields an isochron age of 268 15 ma the results show that the ages of syenogranite and gold mineralization are the same within error furthermore geological and geochronological evidence indicate that the syenogranite and gold mineralization have very close genetic relationships and that they are products of permian magmatism related to post collisional extension of the central asian orogenic belt caob the initial os isotopic compositions 187 os 188 os 1 26 0 69 of pyrite indicate that the source of os and by inference other ore related materials are derived from the crust the late paleozoic is an important period in which economic gold mineralization was deposited in the caob

saddle dolomite as a by product of chemical compaction and thermochemical sulfate reduction petrographic stable and radiogenic isotope trace element and fluid inclusion data from the devonian nisku reef trend in the subsurface of alberta canada suggest that saddle dolomite was a by product of chemical compaction and thermochemical sulfate reduction in subsiding dolomitized rocks furthermore thermochemical sulfate reduction may be representative of other processes that increase the amount of saddle dolomite via an increase in carbonate alkalinity the data also confirm that saddle dolomite is most likely to form at elevated temperatures from hypersaline brines

gold mineralization in the northern margin of the north china craton influence of alkaline magmatism and regional tectonic during middle paleozoic mesozoic abstract the northern margin of north china craton nncc has undergone multiple tectonic and magmatic episodes associated with numerous gold mineralization during devonian to cretaceous the origin of gold mineralization is a subject of debate in the nncc but there is a consensus on a metamorphic hydrothermal origin and a magmatic hydrothermal origin for this study we focused on four gold districts including the daqingshan zhangjiakou west liaoning and changbaishan from west to east we specifically constrain the link between the hadamengou dongping jinchanggouliang erdaogou and haigou gold deposits and their magmatic episodes the dahuabei and haigou granites and dongping syenite rocks have an alkaline affinity in contrast the xitaizi jinchanggouliang and xiaoxigou granites as well as the duimiangou quartz monzonites are calc alkaline with high alkaline rocks they are predominantly metaluminous and high fractionated i type granites except the xiaoxigou granite which is a type granites with peraluminous nature this indicates a variable mixing between depleted mantle derived mafic magma and ancient crust derived magma the magmatic events overlap the gold mineralization episodes in the nncc we have identified four magmatic episodes during middle paleozoic to mesozoic at 400 320 ma 245 221 ma 199 161 ma and 143 125 ma on the other hand gold mineralization was emplaced from carboniferous to cretaceous 390 110 ma with a peak in the middle jurassic 170 160 ma the available sulfur oxygen and carbon isotopic data from the studied nncc gold deposits suggest that the ore forming fluids were derived from a mixture of magmatic fluids and meteoric waters that flow in the wall rocks except for the hadamengou and jinchanggouliang gold deposits both late deposits present a multi source involving organic matter and other regional crustal rocks as shown by their positive 34s values 0 6 18 5 the intrusive rocks and sulfides in the nncc display similar lead isotope data suggesting that the lead isotopes might have similar origin the gold forming materials resulting from the mixing of these fluids are the product of several alkaline magmatism activities in this region hence this study has proved that gold mineralization is spatially and temporally related to the alkaline magmatism in the nncc the dominant tectonic events in the nncc are marked by post collisional or anorogenic geodynamical setting which is characterized by high alkaline features and andean type arc related to subduction geodynamical setting and characterized by calc alkaline features of the studied rocks both tectonic events are controlled by 1 the collision between the ncc and the bainaimiao arc 2 the subduction of the paleo asian ocean plate beneath the ncc 3 the collision between the siberian craton and the ncc and 4 the subduction of the western paleo pacific beneath the ncc these tectonic regimes are expressed by a transitional regime changing from compression to extension at western and an extensional regime at western and eastern parts of the nncc respectively

dolomite occurrence evolution and economically important associations abstract dolomite is not a simple mineral it can form as a primary precipitate a diagenetic replacement or as a hydrothermal metamorphic phase all that it requires is permeability a mechanism that facilitates fluid flow and a sufficient supply of magnesium dolomite can form in lakes on or beneath the shallow seafloor in zones of brine reflux and in early to late burial settings it may form from seawater from continental waters from the mixing of basinal brines the mixing of hypersaline brine with seawater or the mixing of seawater with meteoric water or via the cooling of basinal brines bacterial metabolism may aid the process of precipitation in settings where sulfate reducing species flourish and microbial action may control primary precipitation in some hypersaline anoxic lake settings dolomite is a metastable mineral early formed crystals can be replaced by later more stable phases with such replacements repeated a number of times during burial and metamorphism each new phase is formed by the partial or complete dissolution of an earlier dolomite this continual re equilibration during burial detracts from the ability of trace elements to indicate depositional conditions and resets the oxygen isotope signature of the dolomite at progressively higher temperatures because subsurface dolomite evolves via dissolution and reprecipitation a bed of dolomite can retain or create porosity and permeability to much greater burial depths and into higher temperature realms than a limestone counterpart dolomitization also creates new crystals with new rhomb growth following the dissolution of less stable precursors repetition of this process without complete pore cementation can generate intercrystalline porosity a number of times in the rock s burial history intercrystalline porosity is a highly interconnected style of porosity that gives dolomite reservoirs their good fluid storage capacity and efficient drainage the fact that many dolomite reservoirs formed via brine reflux means that they sit beneath an evaporite seal in both platform and basinwide evaporite settings the same association of evaporites sulfate source and entrained hydrocarbons means that burial conditions are also suitable for thermochemical sulfate reduction and the precipitation of base metals this tends to occur at higher temperatures 60 c 80 c and so the resulting dolomites tend to be ferroan and consist of saddle shaped crystals

characteristics genesis and parameters controlling the development of a large stratabound htd body at matienzo ramales platform basque cantabrian basin northern spain abstract at matienzo basque cantabrian basin northern spain a large stratabound htd body 4 by 2 km 2 and 80 400 m thick delimited by two parallel sinistral strike slip faults is exposed in aptian carbonates the margins of the htd body are characterised by dolomite tongues indicating that some limestone beds were more prone to dolomitisation however no clear relationship between htd occurrence and precursor limestone facies can be established massive limestone beds as found at the top of the htd body act as barriers to hydrothermal processes since no dolomite is present in or above these beds three types of dolomites have been differentiated i e 1 matrix 2 coarse crystalline and 3 zebra dolomite the distribution of the dolomite types is attributed to ascending fluid flow and changing degree of dolomite oversaturation the dolomite body was formed by two dolomitisation phases under burial conditions no indications for a synsedimentary early diagenetic dolomitisation have been observed the first dolomitisation phase is characterized by ferroan dolomite and the second by non ferroan dolomite the two htd phases are characterised by depleted 18 o values ranging between 10 and 16 v pdb 13 c values similar to the aptian albian marine signature and homogenisation temperatures of primary fluid inclusions between 120 c and 150 c the dolomitising fluid was enriched in 87 sr compared to aptian seawater excluding the latter as an unmodified fluid source for dolomitisation microthermometry of primary fluid inclusions indicates that the dolomitising fluid evolved from a moderate saline 9 7 14 0 wt nacl to a more saline 10 9 21 0 wt nacl h 2 o nacl brine the dolomitising fluid likely originated from evaporated seawater fluid circulation through the dolomitised strata is inferred to have taken place during the tectonically active period of the late albian throughout which important sinistral strike slip movements along basement faults occurred

a comprehensive approach to the study of methane seep deposits from the lincoln creek formation western washington state usa a comprehensive approach using palaeontology petrography stable isotope geochemistry and biomarker analyses was applied to the study of seven small methane seep carbonate deposits these deposits are in the oligocene part of the lincoln creek formation exposed along the canyon and satsop rivers in western washington each deposit preserves invertebrate fossils many representing typical seep biota authigenic carbonates with 1 3 c values as low as 51 pdb reveal that the carbon is predominately methane derived carbonates contain the irregular isoprenoid hydrocarbons 2 6 11 15 tetramethylhexadecane crocetane and 2 6 10 15 19 pentamethylicosane pmi lipid biomarkers diagnostic for archaea these lipids are strongly depleted in 1 3 c 1 3 c values as low as 120 pdb indicating that archaea were involved in the anaerobic oxidation of methane small filaments preserved in the carbonate may represent methanotrophic archaea archaeal methanogenesis induced the formation of a late diagenetic phase brownish calcite consisting of dumbbell shaped crystal aggregates that exhibit 1 3 c values as high as 7 pdb clotted microfabrics of primary origin point to microbial mediation of carbonate precipitation downward directed carbonate aggregation in the seeps produced inverted stromatactoid cavities large filaments interpreted as green algae based on their size shape arrangement and biomarkers imply that deposition occurred in places in water no deeper than 210 m

an early jurassic deep water stromatolitic bioherm related to possible methane seepage los molles formation neuquen argentina an assemblage of microbial stromatolites and worm tubes makes up a limestone bioherm 15 m thick and 60 m in diameter enclosed in marls and dark shales of the early jurassic los molles formation neuquen basin argentina the los molles formation is a basinal unit consisting primarily of shales silts and sandstone turbidites deposited after the first general marine transgression in the basin below storm wave base in relatively deep water poorly oxygenated conditions the bioherm is composed of stacked stromatolites 1 4 m in diameter and 1 2 m thick they initially grew horizontally tabular stromatolites or vertically columnar stromatolites and later became domal equidimensional to asymmetric structures they often display vertical and overturned flanks each stromatolite consists of micritic laminae alternating with early botryoidal cements which make up the bulk of the structure calcareous worm tubes are embedded in peloidal micrite associated with the stromatolites the growth of the assemblage was uninterrupted by terrigenous input the diagenetic sequence indicates evolution from marine phreatic to burial environments isotopic values for micrite worm tubes early botryoidal cements and spar cements yield very negative 13c values down to 33 and negative 16o values down to 11 these depleted values indicate precipitation in very anomalous conditions in the jurassic ocean under the influence of methane rich fluids these characteristics suggest that the stromatolitic bioherm formed in relation to methane seeps in the seafloor of the neuquen basin it is suggested that the structure grew within the photic zone although a chemosynthetic component cannot be excluded minimum depositional depth has been estimated at 50 m and could be up to 100 m the vent fluids would have migrated through shallowly buried early rift faults which bound underlying depocenters infilled with continental clastic and volcanic rocks the origin of these fluids could be related to magmatic activity which resulted in accumulation of the syn rift volcanics alternatively the structure could indicate seepage related to the presence of hydrocarbon accumulations in the syn rift succession during the jurassic the importance of which is being gradually acknowledged in the petroleum system of the neuquen basin

widespread venting of methane rich fluids in late cretaceous campanian submarine springs tepee buttes western interior seaway u s a from new mexico to montana campanian shales contain abundant submarine spring and seep deposits aligned along early laramide basement faults from spring conduit to sea floor characteristic lithofacies are a a vuggy pelletoid micrite core to 30 m height 5 m width b lucinoid bivalve coquina in pelletoid micrite or grainstone c carbonate slump breccias in shale d concretion bearing shale and e organic rich shale stable isotope analyses of early zoned marine core rock cements suggest a an oxidized methane source for the carbonate carbon b venting of methane charged fluids along active fracture zones and c methanogenesis in older and coeval organic carbon rich muds six consistently zoned foraminifer and macrofaunal communities suggest a strong environmental stress gradient over a few metres from spring vents to the adjacent sea floor these methane springs and their biotas were dynamic and episodically active over a 1 25 m y time span

control of hydrocarbon seepage intensity on level of biodegradation in sea bottom sediments offshore surface geochemical surveys which target the surface expression of potential migration pathways for sampling such as fault scarps or diapiric features have become a commonly applied approach in the petroleum industry results of such surveys help to reduce risk on key exploration play elements and are used to evaluate prospects and to predict hydrocarbon phase and expected properties based on geochemical surveys conducted by exxonmobil in many basins worldwide there is an interrelation of the seep intensity concentration and level of biodegradation results from offshore west africa where many active macroseeps show moderate to severe biodegradation and a frontier basin offshore united kingdom rockall trough where active microseeps show no evidence of biodegradation are compared the specific biochemical controls on the difference in biodegradation proneness are not known although it appears that a certain threshold of oil concentration is needed to sustain an active bacterial community or to exceed clay adsorption capacities that may protect microseeps from biodegradation it is notable that the 25 norhopane series often considered an indication of severe biodegradation in reservoir oils has not been recognized in even ultra severely biodegraded seeps this suggests that different biodegradation pathways may be followed in marine surface seeps versus those in subsurface hydrocarbon accumulations a likely scenario in light of the fact that physiologically diverse bacterial communities are prevalent under different physiochemical conditions

syntectonic hydrothermal calcite in a faulted carbonate platform margin albian of jorrios northern spain a calcite mass more than 1 5 km long and 20 m wide crops outs along the faulted margin of the albian carbonate platform of jorrios in northern spain the mass contains abundant dissolution cavities up to 7 m long and 1 m high filled with cross stratified quartz sandstone and alternating sandstone calcite laminae similar cavities are also present in a 50 m wide zone of platform limestones adjacent to the calcite mass that are filled with limestone breccias and sandstone the calcite mass has mean 1 8 o values of 19 6 smow whereas platform limestones have mean 1 8 o values of 24 4 smow synsedimentary faulting of the carbonate margin and circulation of heated fault related waters resulted in replacement of a band of limestone by calcite soon after this replacement dissolution by undersaturated fluids affected both the calcite mass and the adjacent limestones percolating marine quartz sand filled all dissolution cavities sometimes alternating with precipitating calcite the resulting cavities and fills which recall products of meteoric diagenesis are attributed to a hydrothermal origin based on their geometry occurrence along the profile and synsedimentary tectonic relationships the early faulting and diagenesis are related to local extensional tectonism in a large scale strike slip setting movements occurred during the early dispar appenninica zone of the late albian

carbon sulfur iron relationships and δ13c of organic matter for late albian sedimentary rocks from the north atlantic ocean paleoceanographic implications abstract cores from six deep sea drilling project sites 367 369 137 386 387 and 603 of the late albian north atlantic ocean were investigated for organic carbon content 13c values of the kerogens maceral composition of the organic matter c s ratios fe toc s relationships and framboidal pyrite size distribution in order to evaluate processes that led to the accumulation of organic matter rich black shale deposits the results show a clear separation of the albian north atlantic into an anoxic eastern part and a mostly oxic western part the eastern north atlantic is dominated by organic matter rich deposits sulfate reduction occurred in an oxygen free water column and resulted in characteristic c s ratios fe toc s relationships and framboidal pyrite size distribution patterns elevated productivity anoxia and high sedimentation rates supported the formation of black shale deposits for most of the western and central parts organic matter sedimentation took place through an oxygenated water column the accumulated organic matter is dominantly of terrigenous origin the deposition of marine derived organic matter was most likely controlled by productivity paleobathymetry and low sedimentation rates

seep carbonates and preserved methane oxidizing archaea and sulfate reducing bacteria fossils suggest recent gas venting on the seafloor in the northeastern south china sea seep carbonates formed by the synergistic metabolism of methane oxidizing archaea moa and sulfate reducing bacteria srb have been found in many places worldwide but have not been found to date in the south china sea mud volcanoes and shale diapirs have been reported in the south china sea however and microscope and geochernical analysis of carbonates dredged where bottom simulating reflectors bsr suggest the presence of gas hydrate on the northeastern continental slope of the south china sea suggest that the carbonates are hydrocarbon seep related carbonates the carbonates we dredged are chimney like and preserve moa srb fossils their very light carbon isotopic compositions 51 25 to 51 76 parts per thousand suggest that their carbon was derived from microbial methane oxidization these seep carbonates and their preserved moa srb fossils imply gas venting has occurred recently on the seafloor in the northeastern continental slopes in the south china sea c 2005 elsevier ltd all rights reserved

cold seep deposits of beauvoisin oxfordian southeastern france and marmorito miocene northern italy microbially induced authigenic carbonates the relation of two well known ancient carbonate deposits to hydrocarbon seepage was confirmed by this study archaea are found to be associated with the formation of oxfordian seep carbonates from beauvoisin and with a miocene limestone from marmorito tube worm limestone carbonates formed due to a mediation by archaea exhibit extremely positive or extremely negative 13ccarbonate values respectively highly positive values 15 reflect the use of 13c enriched co2 produced by methanogenesis low 13c values of the marmorito carbonates 30 indicate the oxidation of seepage derived hydrocarbons likewise the 13c content of specific tail to tail linked isoprenoids biomarkers for archaea was found to be strikingly depleted in these samples as low as 115 the isotopic signatures corroborate that archaea were involved in the cycling of seepage derived organic carbon at the ancient localities another miocene limestone marmorito limestone shows a strong imprint of methanotrophic bacteria as indicated by 13c values of carbonate as low as 40 and biomarker evidence epifluorescence microscopy and field emission scanning electron microscopy revealed that bacterial biofilms were involved in carbonate aggregation in addition to lucinid bivalves previously reported from both localities we infer that sponges from beauvoisin and tube worms from marmorito depended on chemosynthesis as well low 13c values of nodules related to sponge taphonomy 27 indicate that sponges might have been linked to an enhanced hydrocarbon oxidation tube worm fossils from marmorito closely resemble chemosynthetic pogonophoran tube worms from recent cold seeps and are embedded in isotopically light carbonate 13c 30

syntectonic deposits and punctuated limb rotation in an albian submarine transpressional fold mutriku village basque cantabrian basin northern spain deep water syntectonic deposits and angular unconformities record the denudation and deformation history of the middle cretaceous aitzeta structure interpreted here as a monoclinal syncline associated with the high angle reverse mutriku fault basque cantabrian basin northern spain sedimentological and structural analyses combined with a precise chronostratigraphy based on ammonites permit us to document in detail the history of this syncline during 0 53 m y late albian callihoplites auritus subzone tectonism occurred during two major and two minor short lived pulses the sedimentary signatures of these pulses include unconformities and resedimented deposits derived from the uplifted rocks showing inverted clast stratigraphy in contrast intervening phases of tectonic calm were characterized by gentle hemipelagic sedimentation the major tectonic pulses were characterized by strong rotation and uplift of the syncline limb the two major pulses coincided with the lower and upper limits of the auritus subzone respectively and resulted in the following limb rotation and uplift values 42 and 250 m in the first pulse and 66 and 100 140 m in the second pulse a maximum duration of 0 12 m y for each major pulse has been calculated from which limb rotation and uplift rates of 0 35 k y and 2 08 m k y first pulse and 0 55 k y and 0 83 1 16 m k y second pulse are estimated growth strata and angular unconformity geometries temporal variation of deformation rates and bedding parallel faulting indicate folding by progressive limb rotation and associated flexural slip local northwest southeast compression is deduced in formation of the aitzeta syncline the presence of bedding parallel oblique faulting and minor drag folds suggests a component of right oblique movement along the mutriku fault

stromatolitic fabric of authigenic carbonate crusts result of anaerobic methane oxidation at cold seeps in 4 850 m water depth methane seepage leads to mg calcite and aragonite precipitation at a depth of 4 850 m on the aleutian accretionary margin stromatolitic and oncoid growth structures imply encrustation of microorganisms microbial mats in the host sediment with a unique growth direction downward into the sediment forming crust shaped lithologies biomarker investigations of the residue after carbonate dissolution show strong enrichments in crocetane and archaeol which contain extremely low 13c values this indicates the presence of methane consuming archaea and 13c values of 42 to 51 pdb indicate that methane is the carbon source for the carbonate crusts thus it appears that stromatolitic encrustations of methanotrophic anaerobic archaea probably occurs in a consortium with sulphate reducing bacteria and that carbonate precipitation proceeds downward into the sediment where ascending cold fluids provide a methane source strontium and oxygen isotope analyses as well as 14c ages of the carbonates suggest that the fluids come from deep within the sediment and that carbonate precipitation began about 3 000 years ago

archaea mediating anaerobic methane oxidation in deep sea sediments at cold seeps of the eastern aleutian subduction zone cold seeps in the aleutian deep sea trench support prolific benthic communities and generate carbonate precipitates which are dependent on carbon dioxide delivered from anaerobic methane oxidation this process is active in the anaerobic sediments at the sulfate reduction methane production boundary and is probably performed by archaea working in syntrophic co operation with sulfate reducing bacteria diagnostic lipid biomarkers of archaeal origin include irregular isoprenoids such as 2 6 11 15 tetramethylhexadecane crocetane and 2 6 10 15 19 pentamethylicosane pmi as well as the glycerol ether lipid archaeol 2 3 di o phytanyl sn glycerol these biomarkers are prominent lipid constituents in the anaerobic sediments as well as in the carbonate precipitates carbon isotopic compositions of the biomarkers are strongly depleted in 13c with values of 13c as low as 130 3 pdb the process of anaerobic methane oxidation is also reflected in the carbon isotope composition of organic matter with 13c values of 39 2 and 41 8 and of the carbonate precipitates with values of 45 4 and 48 7 this suggests that methane oxidizing archaea have accumulated within the microbial community which is active at the cold seep sites the dominance of crocetane in sediments at one station indicates that probably due to decreased methane venting archaea might no longer be growing whereas high amounts of crocetenes found at other more active stations may indicate recent fluid venting and active archaea comparison with other biomarker studies suggests that various archaeal assemblages might be involved in the anaerobic consumption of methane the assemblages are apparently dependent on specific conditions found at each cold seep environment selective conditions probably include water depth temperature degree of anoxia and supply of free methane

the influence of pore water chemistry and physiology on the distribution of vesicomyid clams at cold seeps in monterey bay implications for patterns of chemosynthetic community organization analyses of sulfide methane oxygen and co in pore water sampdes from three cold seep sites in monterey bay indicate that fluid chemistry is a strong determinant of the distribution of chemolithoautotrophic vesicomyid clams the distribution of culyptogena pacijca and culyptogenu kilmeri were aligned closely with sulfide concentrations at all cold seeps and reflected species specific capabilities for sulfide binding live clams occurred only in sediment where sulfide was detectable sulfide was not detected in the absence of vesicomyid clams the relative abundances of five vesicomyid species varied greatly among seeps c kilmeri accounted for 85 99 of all vesicomyids at seeps with high sulfide content and c pucijicu dominated 73 seeps with low sulfide levels these species were also partially segregated along sulfide gradients from the center to the margin of seeps analogous to zonation of rocky intertidal communities we hypothesize that the absence of thiotrophic or methanotrophic mytilid mussels from monterey bay cold seeps is related to the lack of physiological specializations for concentrating reduced sulfur compounds or methane and the absence of hypersaline brines that could extend the persistence of methane or sulfide rich fluids very near the sea floor chemosynthetically based communities associated with sulfide and methane seeps are known from various geologic settings along continental margins but remain poorly understood in terms of their geochemistry biology and ecology seeps in the pacific ocean are associated with tectonically induced over pressure of hemipelagic sediments along subducting e g oregon peru japan and transpressional plate margins california barry et al 1997 artesian flow at marine exposures of freshwater aquifers hovland and judd 1988 and buried debris flows in axial valleys of submarine canyons embley et al 1990 most chemosynthetic metazoan symbioses at sea floor seeps depend on sulfur oxidizing bacterial endosymbionts especially in the pacific ocean where vesicomyid clams and vestimentiferan worms are the dominant metazoan groups although seeps in the atlantic ocean have a similar fauna including both vesicomyid clams and vestimentiferan worms these sites differ from pa

marine peloids a product of bacterially induced precipitation of calcite high magnesian calcite peloids are a common constituent of cemented marine carbonate accumulations they are abundant and well developed within both isolated microcavities and surface crusts the nuclei of marine peloids are composed of fossil bacterial clumps encased within anhedral submicron to micron sized high magnesian calcite crystals the marine peloids are similar to silt sized particles found in travertine deposits that also are composed of fossil bacterial clumps and their surrounding calcite coronas these similarities include size 20 60 mu m a cloudy brown nucleus and rims of clear euhedral crystals in addition previous studies have established the presence of fatty acids of bacterial origin within peloidal deposits and enriched stable isotopic signatures have been interpreted as recording organic fractionation concomitant with calcite precipitation these characteristics all indicate that the nuclei of many peloids originate as calcite precipitates within and around clumps of bacteria and that this precipitation was induced by the vital activity of bacterial colonies

fossil seep structures of the monterey bay region and tectonic structural controls on fluid flow in an active transform margin abstract the subsurface plumbing system of ancient seeps of hydrocarbon rich gases and fluids is partially preserved by seep deposits in miocene rocks of the coast ranges and on the seafloor of the monterey bay region in central california the fossil seep related deposits are of two types authigenic carbonates and intrusions of oil saturated sandstones both types occur in fractured and faulted siliceous mudstone and porcelanite layers of the organic rich miocene santa cruz mudstone they are associated with tectonic structures indicating deformation and are located in the proximity of faults the morphology of the seep carbonates is characterized by strong asymmetries and by holes pipes and other types of fluid conduits with orientations parallel to the directions of the local fracture and fault sets thus suggesting structural control over pathways of fluid migration the dominant direction of the conduits in the seep carbonates and of the intrusive dikes northeast southwest differs from the dominant orientation of the tectonic structures of the san andreas fault system northwest southeast previous interpretations of these ancient seep related deposits suggested that lateral changes of the thickness of the cenozoic marine host sediments favored fluid migration from basin depocenters located offshore toward basin margins different driving forces for fluids have been hypothesized including hydrocarbon generation differential compaction and tectonic compression most of the fossil seeps are located on structural highs of the basement and adjacent to offshore basins that form elongated depressions oriented northwest southeast previously unidentified structures that offset the basement along northeast southwest trends cross setting faults paralleling the orientations of the conduits of the seep carbonates and the dikes of oil saturated sandstones were also recognized tectonic deformation block rotations documented by local clockwise rotations of paleomagnetic directions in the coastal ranges and cross faults were probably produced during the late miocene and pliocene to accommodate the shear stress between conjugate faults during eastward shifting of the activity of the san andreas fault system comparison with previous studies on ancient seep deposits regional geology and offshore tectonic data suggest that the fluids that sourced the seeps were driven by episodes of inverse tectonics during which previously extensional depositional basins were involved in episodes of tectonic compression tectonic deformation created cross faults in rotated blocks which could have acted as important conduits for the flow of hydrocarbon rich fluids and gases and fostered the injection of liquefied sands

vast fields of hydrocarbon derived carbonate chimneys related to the accretionary wedge olistostrome of the gulf of cadiz we report the first discovery and sampling of vast fields of hydrocarbon derived carbonate chimneys along the gulf of cadiz continental slope at depths between 500 and 1200 m a large variety of carbonate chimneys more than 200 samples were recovered from four different areas named the diasom tasyo gbf guadalquivir basin and esf east moroccan fields observations from an underwater camera revealed a spectacular high density of pipe like chimneys some of them longer than 2 m lying over the sea floor and some protruding from muddy sediment local fissures and alignment of isolated chimneys were also observed suggesting that their distribution is controlled by fault planes chimneys collected show a wide range of morphological types spiral cylindrical conical mushroom like and mounded with numerous nodule protuberances and ramified fluid channelways the chimneys are mainly composed of authigenic carbonates ankerite fe bearing dolomite and calcite with abundance of iron oxides forming agglomerates of pseudo pyrite framboids n 18 o isotopic values vary from 0 7 to 5 5x whereas n 13 c values indicate that chimney carbonates are moderately depleted in 13 c ranging from 346x to 320x pdb interpreted as formed from a mixture of deep thermogenic hydrocarbons and shallow biogenic methane these vast fields of carbonate chimneys imply new considerations on the importance of hydrocarbon fluid venting in the gulf of cadiz and moreover on the active role of the olistostrome accretionary wedge of the gibraltar arc b 2003 elsevier science b v all rights reserved

diagenetic evolution of the upper cretaceous limestone and sandstone exhumed reservoirs in the western basque cantabrian basin north spain abstract the basque cantabrian basin ne spain has been considered one of the most interesting areas for hydrocarbon exploration in the iberian peninsula since the 60th to 70th of last century this basin is characterized by the presence of numerous outcrops of tar sands closely associated with fractures and triassic diapirs the aims of this work is to establish the diagenetic evolution of the upper cretaceous reservoir rocks with special emphasis in the emplacement of oil and their impact on reservoir quality the studied rocks are constituted of carbonates and sandstones that contain massive quantities of bitumen filling vugs and fractures petrographic results indicate that the carbonate rocks from maestu outcrops are bioclastic grainstones and wackestones whereas the tar sandstones from atauri and loza outcrops are dominated by quartzarenites and subordinated subarkoses the paragenetic sequence of the main diagenetic phases and processes include pyrite bladed and drusy calcite cement calcite overgrowths silicification of bioclasts and microcrystalline rhombic dolomite cement and first stage of oil emplacement blocky calcite cement coarse crystalline calcite cement calcitized dolomite calcite veins saddle dolomite and stylolites filled by the second phase of oil entrance together with the above mentioned diagenetic alterations the arenites are affected by early kaolinitization of feldspars and the scarce formation of clay rim and epimatrix of illite all sandstones and dolomitized carbonate rocks show high intercrystalline and intergranular porosity which is full by biodegraded hydrocarbons solid bitumen the biodegradation affects alkanes isoprenoids and partially hopanes and steranes saturated hydrocarbons aromatics hydrocarbons like naphthalenes phenanthrenes dibenzothiophenes and triaromatics are also affected by biodegradation results indicate that the first hc emplacement corresponds to early stage of calcite and dolomite cementation and the second and more important emplacement is related to fracturation processes resulting in the formation of excellent reservoirs

the jiaodong type gold deposits characteristics origin and prospecting abstract the jiaodong type comprises a unique class of gold mineralisation which includes the linglong type quartz vein hosted and the jiaojia type fracture disseminated style deposits although the type area is in the jiaodong peninsula in ne china where some of the world s richest gold reserves occur we identify similar occurrences in other parts of china and elsewhere in the world under this category the ore fluids migrated upwards forming quartz vein type of gold ore linglong type wherever the ore controlling fractures are at high angles fluid infiltration into the surrounding wall rocks and generation of the jiaojia type disseminated style deposits resulted where the ore bearing fluids encountered low angle fractures on a regional scale the jiaodong type gold mineralisation occurs along the margins of reactivated cratons within the interior of cratons along paleosuture zones or along the junctions of micro blocks and is distinctly different from the classic orogenic gold in terms of their tectonic setting ore characteristics and genetic history unlike skarn and porphyry type of deposits the jiaodong type gold deposits do not always show close spatial relationship with magmatic intrusives and some of the deposits occur distal to plutons 10 km in this paper we evaluate the salient geological geochronological geochemical and isotopic features of the jiaodong type gold deposits and propose some general guidelines for gold prospecting based on case studies we predict that the gold lodes in the jiaodong type mineralised zones might extent vertically up to 3000 m with only minor mineralogical and geochemical variations

hydrothermal alteration of organic matter in sediments of the northeastern pacific ocean part 1 middle valley juan de fuca ridge samples from the ocean drilling program leg 169 in middle valley ne pacific ocean were analyzed to study maturation by accelerated diagenesis and catagenesis of the sedimentary organic matter to hydrothermal petroleum some data from site 858 in middle valley leg 139 are also discussed for completeness sediments at sites 858 and 1036 in middle valley were altered either by the full variety of high temperature fluids which generated hydrothermal petroleum or by accelerated thermal diagenesis of the immature organic matter in situ without specific migration of those petroleum bitumen products the hydrothermal petroleums from the deeper sediments have migrated and accumulated in discrete intervals at shallower depths within a contemporary temperature window of 60 135 c at both of these sites maturation for the n alkanes proceeded from high cpi values immature to 1 0 mature i e strong even c number preference due to their low toc contents these sediments did not generate high amounts of hydrocarbons from the kerogen and thus revealed this unique even c number preference furthermore the significant content of terrestrial organic matter yielded petroleums low in gas and volatiles biomarkers were converted from the biological natural product precursors to the geological derivatives with maturities reflecting the thermal stress high temperature alteration also yielded polynuclear aromatic hydrocarbons

carbon stable isotopic composition of benthic foraminifera from pliocene cold methane seeps cascadia accretionary margin abstract cold methane seep carbonates preserve the distinctive carbon stable isotope signatures of their ambient porewaters thus facilitating the identification of methane sources and fluid migration pathways this study employs an isotopic indicator from microfossils in a diffuse fossil seep for the recognition and characterization of methane seepage in the rock record benthic foraminifera from the pliocene quinault formation western washington state are plentiful and provide a temporal link between modern and more ancient seeps stable carbon isotope analyses of individual foraminiferal tests revealed a clear distinction between seep and non seep foraminifera infaunal species globobulimina pacifica and nonion basispinatum collected from seep samples exhibited 13 c values that were highly variable and often strongly depleted values ranged from 33 1 to 55 3 pdb in g pacifica and from 2 1 to 42 9 pdb in n basispinatum the epifaunal species cibicidoides mckannai though less depleted also showed considerable variability with 13 c values ranging from 1 7 to 3 1 pdb in contrast non seep specimens were much more enriched and less variable non seep specimens of n basispinatum displayed 13 c values clustering between 0 5 and 1 5 pdb while non seep specimens of c mckannai yielded a range of 1 1 to 1 8 pdb sem analyses and oxygen isotope values of foraminiferal tests indicated minimal diagenetic alteration 13 c values from authigenic blebs small nodules with wispy indistinct boundaries ranged from 8 7 to 38 4 pdb by combining these inorganic carbonate data with the foraminiferal values the association of seep specific bivalves and the present day leakage of thermogenic methane from the nearby garfield gas mound we conclude that these foraminifera precipitated their tests in the presence of methane derived carbon thus they record pore water 13 c depletion and syn depositional fluid flow pathways near the sediment water interface in a seep system active 3 4 mya and continuing onshore and offshore today the range and degree of 13 c depletion in the pliocene microfossils is due to the heterogeneity of seepage caused by different methane sources i e thermogenic and biogenic the tortuosity of fluid migration pathways reaching the seafloor sediments and mixing of seep fluids with dissolved inorganic carbon dic and marine organic carbon

hydrothermal alteration of organic matter in sediments of the northeastern pacific ocean part 2 escanaba trough gorda ridge samples from the ocean drilling program leg 169 in escanaba trough gorda ridge ne pacific ocean were analyzed to study maturation by accelerated diagenesis and or by catagenesis of the sedimentary organic matter to hydrothermal petroleum at site 1038 the hydrothermal petroleums have migrated after generation to shallower horizons the n alkane maturation was indicated by the strong even c number preference i e cpi 1 0 as in the case of middle valley all samples contained admixed organic matter of terrigenous and marine components as indicated by the distributions of the biomarkers the biological precursors were catagenetically altered to their equivalent mature compounds the presence of high molecular weight pahs in some sediment sections at site 1038 reflected the high temperature alteration and reworking of organic matter into mature hydrothermal petroleum at site 1037 the reference hole in the escanaba trough the n alkanes with a strong predominance of odd c number homologs reflected immature non marine lipid components essentially throughout the hole maturation of organic matter was only observed below 450 mbsf with n alkanes showing a cpi 1 0 the strong even c number predominance in those intervals was attributed to initial maturation by high heat flow during the early rifting process

molybdenite re os zircon u pb dating and hf isotopic analysis of the shuangqing fe pb zn cu skarn deposit east kunlun mountains qinghai province china the shuangqing fe pb zn cu deposit is located in the xiangride county of qinghai province china and is a typical example of skarn deposits in the east kunlun mountains skarnization and mineralization took place along the contact zone between carboniferous carbonates and the concealed triassic plagiogranite la icp ms u pb dating of zircons from the plagiogranite has yielded ages of 227 2 1 0 and 226 54 0 97 ma which are interpreted as the emplacement age of the plagiogranite molybdenites separated from ore bearing quartz veins yielded a re os isochron age of 226 5 5 1 ma these age data confirm that both intrusion and related skarn mineralization initiated at 227 ma re contents of molybdenite zircon ehf t and 176 hf 177 hf values fall into the ranges 3 31 to 6 58 g g 8 6 to 0 0 and 0 282403 to 0 28263850 respectively the timing of the shuangqing fe pb zn cu mineralization coincided with a major change in the stress field in east kunlun from transpression to extension related to the partial melting of thickening crustal materials in a post collisional tectonic setting

contact metamorphism of organic rich mudstones and carbon release around a magmatic sill in the basque cantabrian basin western pyrenees abstract recent studies have documented the expulsion of methane and oil to the albian paleoseabed in the basque cantabrian basin they interpret that hydrocarbon generation and expulsion were triggered by seismically recorded magmatic intrusions which metamorphosed organic rich host sediments an outcrop within the basin was selected to investigate organic matter evolution and sediment degassing due to an igneous body this intrusion is a 5 m thick late albian basaltic sill that intruded mudstones of the black flysch group near gorliz north iberia vitrinite and bitumen reflectance profiles and metamorphic mineral distribution in the overburden indicate that the sill produced a thermal effect that increases toward the intrusion defining a 2 m thick minimum contact aureole geochemical profiles of toc s1 s2 hi and pc show a gradual decrease toward the sill indicating organic carbon loss and increase in the thermal maturity of the organic matter in the same direction concordantly gas chromatograms show a loss of n alkanes and a predominance of the shorter chain length homologues adjacent to the sill tmax and pi s1 s1 s2 values increase toward the sill which suggests an increase in the thermal stress and in the extent of kerogen pyrolysis respectively organic carbon loss in the aureole was the result of carbon devolatilization and formation of co2 and ch4 gases the newly formed co2 reacted with pore waters to precipitate 13c depleted carbonate minerals in the aureole and in sill fractures ch4 escaped from the aureole via hydrofractures to the paleoseabed where methane derived authigenic carbonates were formed

the submarine volcanic system of the errigoiti formation albian santonian of the basque cantabrian basin northern spain stratigraphic framework facies and sequences abstract the errigoiti formation located in the central domain of the basque cantabrian basin is an albian to santonian bathyal submarine volcanic system of alkali basaltic character these volcanics occurred in an extensional geodynamic context generated by the drifting of the iberian plate with respect to the european plate stratigraphic analyses reveal the facies distribution and depositional architecture of a longitudinal cross section of the errigoiti volcanic system four facies groups were distinguished sheet lavas sl derived from low viscosity lava flows at high magma discharge rate pillow lavas pl derived from intermediate viscosity lava flows at moderate discharge rate pillow breccias pb derived either from in situ fragmentation of lavas pb1 or rock falling from pillow lava slopes pb2 and stratified volcaniclastites vc derived from volcaniclast resedimentation through gravity flows either by early remobilization vc1 or post volcanic reworking vc2 the facies groups occur in a predictable repetitive succession essentially from base to top an sl pl pb vc stacking pattern this is interpreted to reflect an upward waning in the magma discharge rate five major volcanic sequences make up the errigoiti formation each comprises packages tens to hundreds of meters thick deposited during short time spans of volcanic activity separated by long time intervals of volcanic inactivity consequently boundaries between sequences are associated with marked hiatuses reworked volcaniclasts and or turbidite pelagic sedimentation analysis of lateral and vertical facies evolution enabled us to propose a depositional model consisting of three depositional environments from proximal to distal settings these are amalgamated pillow volcanoes scattered pillow volcanoes and volcanic fringe basically responding to a proximal to distal pl pb pl vc and sl vc evolution of facies associations contemporaneous fossiliferous turbidite pelagic sequences that surround the volcanic succession allow paleobathymetry to be estimated on the basis of biofacies sites with the highest rate of volcanic emission correspond to an average depth of 900 m sites with thinner volcanic pile accumulated at a minimum depth of 1100 m the facies sequence established in this work and the processes involved in its formation are comparable with the sequences and processes described in other submarine basic volcanic systems consequently the depositional model for the errigoiti formation can perhaps serve as a reference model for this type of volcanic system

structurally controlled hydrothermal dolomite reservoir facies an overview structurally controlled hydrothermal dolomite htd reservoir facies and associated productive leached limestones are major hydrocarbon producers in north america and are receiving increased exploration attention globally they include multiple trends in the ordovician locally silurian and devonian of the michigan appalachian and other basins of eastern canada and the united states and in the devonian and mississippian of the western canada sedimentary basin they also occur in jurassic hosts along rifted atlantic margins in the jurassic cretaceous of the arabian gulf region and elsewhere hydrothermal dolomitization is defined as dolomitization occurring under burial conditions commonly at shallow depths by fluids typically very saline with temperature and pressure t and p higher than the ambient t and p of the host formation the latter commonly is limestone proof of a hydrothermal origin for htd reservoir facies requires integration of burial thermal history plots fluid inclusion temperature data and constraints on timing of emplacement hydrothermal dolomite reservoir facies are part of a spectrum of hydrothermal mineral deposits that include sedimentary exhalative lead zinc ore bodies and htd hosted mississippi valley type sulfide deposits all three hydrothermal deposits show a strong structural control by extensional and or strike slip wrench faults with fluid flow typically focused at transtensional and dilational structural sites and in the hanging wall transtensional sags above negative flower structures on wrench faults are favored drilling sites for htd reservoir facies saddle dolomite in both replacive and void filling modes is characteristic of htd facies for many reservoirs matrix replacive dolomite and saddle dolomite appear to have formed near contemporaneously and from the same fluid and temperature conditions the original host facies exerts a major influence on the lateral extent of dolomitization resultant textures pore type and pore volume breccias zebra fabrics shear microfractures and other rock characteristics record short term shear stress and pore fluid pressure transients particularly proximal to active faults high temperature hydrothermal pulses may alter kerogen in host limestones a process designated forced maturation basement highs underlying sandstone and or carbonate aquifers probably overpressured and overlying and internal shale seals and aquitards also may constrain or influence htd emplacement although many questions and uncertainties remain particularly in terms of mg and brine source and mass balance recognition and active exploration of the htd play continues to expand increasing use of three dimensional seismic imagery and seismic anomaly mapping combined with horizontal drilling oblique to linear trends defined by structural sags helps to reduce risk