centrifuge modelling of laccolith intrusion abstract laccolith intrusion has been investigated by centrifuge modelling silicone putty representing magma with bingham rheology is intruded by overburden pressure through a circular conduit into a stack of paraffin wax layers which represent sedimentary strata the model intrusions evolve through a sequence of geometric forms similar to those exhibited by natural laccoliths the results are also in accord with published mathematical analyses of laccolith formation the model magma first flows laterally between overburden layers to form a sill as the sill increases in area the cover strata are arched upwards into a sinusoidal bending form subsequently the overburden fails abruptly by kinking above the periphery of the intrusion and the form changes to a cupola separated from surrounding horizontal strata by a sharp inflection in the layering finally strata on the flanks of the cupola undergo a second episode of localized failure the top of the dome becomes flat and the dipping flanks become a monoclinal flexure surrounding this kink form a number of variables influence this evolution increased overburden strength thickness of overburden strata and total thickness of overburden all prolong the bending form to larger intrusion size delay the localized failure which marks the cupola and kink stages and reduce the aspect ratio of the intrusion at all stages effectively bonded overburden interfaces have a similar effect but interfaces with sharply defined yield strengths enhance development of the monoclinal flexure magmatic driving pressure affects the rate of intrusion but not the evolution of its form intrusion rate is also influenced by magma flow properties and probably by the form of the feeder conduit the range of final forms preserved by natural laccoliths probably results from competition between rate of intrusion controlled by driving pressure and conduit geometry and rate of chilling of magma in the laccoliths the model laccoliths form in times that scale to between one and a few tens of years in agreement with available estimates for natural laccoliths

experiments simulating surface deformation induced by pluton emplacement abstract we present centrifuge experiments to study the surface deformation induced by shallow pluton emplacement in a rheologically stratified crust sand simulates the topmost brittle crust plastilina and denser silicone represent more and less competent crustal portions respectively lighter silicone simulates a buoyant intrusion in the models density differences affect the rate of intrusion but not their evolution or shape whereas viscosity and strength stratifications control both the shape and rate of the intrusions with a higher viscosity contrast 10 2 4 between the intrusion and the embedding media the rise of the lighter silicone induces a laccolith like intrusion responsible for doming and thinning of the overburden an apical depression may form inducing silicone extrusion conversely with a lower 10 1 viscosity contrast the overburden and the intrusion exhibit a lens shaped form with a broad central depression bordered by an upward flexure towards the periphery a sag in the floor of the intrusion is commonly observed no silicone extrusion occurred the intrusion is a hybrid between a laccolith and a lopolith the comparison with nature 1 confirms roof uplift as an important means of accommodating space during pluton emplacement and 2 suggests that where roof uplift plays a major role pluton emplacement can induce a well correlated sequence of events at surface doming the development of a depression and extrusion

organic geochemical characteristics and generating potential of source rocks from the lower middle jurassic coal bearing strata in the east junggar basin nw china abstract the junggar basin located in nw china is a large intracontinental superimposed basin samples were collected from the lower middle jurassic coal bearing strata of the eastern junggar basin and include mudstones carbargilites and coal the origin of organic matter thermal maturity paleoenvironment of sediment deposition and hydrocarbon potential of drill core samples was investigated organic geochemical analysis performed on 65 source rock samples indicates a wide range of toc values from 0 81 wt to 81 06 wt this study combined sedimentology biomarker organic petrography and stable carbon isotopic composition of kerogen and extracts analysis demonstrating the organic matter of the source rocks is derived from terrestrial higher plants with a minor contribution of aquatic algae and microbes rock eval data elemental composition of kerogen and odd over even normal alkane distribution reveal immaturity to low maturity with a humic type organic matter the source rocks were deposited in a freshwater oxic to sub oxic environment indicated by high pr ph ratios a predominance of c29 steranes low tricyclic terpanes and a low gammacerane index high dia regular c29 sterane ratios and moderate to high c29 c30 hopane ratios found in most samples are related to the presence of clay minerals based on the following parameters h c vs o c toc s1 s2 hydrogen index saturated hydrocarbons aromatic hydrocarbons and chloroform a we concluded that the samples collected from organic rich coal bearing strata may yield not only gas but also have the capability to generate and release liquid hydrocarbons

australasian asphaltite strandings their origin reviewed in light of the effects of weathering and biodegradation on their biomarker and isotopic profiles abstract asphaltites long known to strand along the coastline of southern australia and as distantly as new zealand and macquarie island are widely regarded as artefacts of submarine oil seepage their remarkably uniform composition suggests a common source marine shale containing sulphur rich type ii kerogen probably deposited during an early cretaceous oceanic anoxic event oae suitable hydrocarbon kitchens may exist in the offshore bight and otway basins the physical character of the asphaltites including laminations and flow structures and their degree of alteration which is not the result of biodegradation or extensive water washing suggest an origin from subsurface tar mats subsequently exposed by the incision of submarine canyons with the possible formation of asphaltic volcanoes api gravities of 4 18 impart quasi neutral buoyancy implying many asphaltites were submerged drifters prior to stranding their degree of weathering reflecting at least in part the residence time in the marine environment for any individual asphaltite specimen this will depend on the proximity of the seafloor seep to the stranding site an important consideration when attempting to locate their point of origin this study investigates the hydrocarbon biomarker signatures and n alkane 13 c profiles of asphaltite specimens from stranding sites on the eyre peninsula n 2 kangaroo island n 4 and the limestone coast n 3 south australia and the south island of new zealand n 2 sub samples of the interior and weathered surface of each specimen were analysed no distinction could be made between strandings based on their source dependent molecular and isotopic signatures confirming their common origin comparison of the interior and exterior sub samples revealed subtle although consistent differences given their degree of degradation and isotopic variance these australasian asphaltites seem to be products of low intensity seeps in the ceduna sub basin of the bight basin and or morum sub basin of the otway basin

petroleum degradation and associated microbial signatures at the chapopote asphalt volcano southern gulf of mexico abstract at the chapopote knoll in the southern gulf of mexico deposits of asphalt provide the substrate for a prolific cold seep ecosystem extensively colonized by chemosynthetic communities this study investigates microbial life and associated biological processes within the asphalts and surrounding oil impregnated sediments by analysis of intact polar membrane lipids ipls petroleum hydrocarbons and stable carbon isotopic compositions 13c of hydrocarbon gases asphalt samples are lightly to heavily biodegraded suggesting that petroleum derived hydrocarbons serve as substrates for the chemosynthetic communities accordingly detection of bacterial diester and diether phospholipids in asphalt samples containing finely dispersed gas hydrate suggests the presence of hydrocarbon degrading bacteria biological methanogenesis contributes a substantial fraction to the methane captured as hydrate in the shallow asphalt deposits evidenced by significant depletion in 13c relative to background thermogenic methane in sediments petroleum migrating from the subsurface stimulates both methanogenesis and methanotrophy at a sulfate methane transition zone 6 7 m below the seafloor in this zone microbial ipls are dominated by archaeal phosphohydroxyarchaeols and archaeal diglycosidic diethers and tetraethers bacterial ipls dominate surface sediments that are impregnated by severely biodegraded oil in the sulfate reduction zone diagnostic ipls indicate that sulfate reducing bacteria srb play an important role in petroleum degradation a diverse mixture of phosphohydroxyarchaeols and mixed phospho and diglycosidic archaeal tetraethers in shallow oil impregnated sediments point to the presence of anaerobic methane oxidizing anme 2 and anme 1 archaea respectively or methanogens archaeal ipls increase in relative abundance with increasing sediment depth and decreasing sulfate concentrations accompanied by a shift of archaeol based to tetraether based archaeal ipls the latter shift is suggested to be indicative of a community shift from anme 2 and or methanogenic archaea in shallower sediments to anme 1 methanogenic archaea and possibly benthic archaea in deeper sediments

biomarker distributions in australian oils predominantly derived from terrigenous source material oils found in many australian sedimentary basins contain a relatively high input of terrigenous organic source material a study of a large number of these oils has permitted a number of biomarker distributions to be determined that appear to be characteristic for oils derived from terrigenous source material these features include the presence of sesquiterpanes absence of tricyclic terpanes relatively high concentrations of a c24 tetracyclic terpane predominance of c29 steranes presence of two unidentified c27 and c30 terpanes and virtual absence of 18 h oleanane the latter observation is significant since it appears that 18 h oleanane appears only in oils of tertiary age derived from terrigenous source material an attempt has also been made to compare the results for the australian oils with published results for oils derived from terrigenous source material in other parts of the world the number of reports in the literature for these oils is fairly limited but it appears that some of the observations for the australian oils can be extended to them this study is an initial attempt to devise a classification scheme that can be used to determine the origin of an oil unambiguously from biomarker parameters in order for this approach to be successful a relatively large number of biomarker parameters need to be assigned as characteristic of a particular type of source material

the evidence of along arc differential uplift of the shimanto accretionary complex fission track thermochronology of the kumano acidic rocks southwest japan abstract the kumano acidic rocks kars are the most extensive of the tertiary granitic bodies in the southwest japanese fore arc they intrude the cretaceous lower miocene shimanto accretionary complex perturbing its initial thermal records related to accretion to assess the timing of igneous activity and subsequent cooling history of the kars fission track ft ages were measured on seventeen zircon and three apatite samples along with four zircon confined track lengths samples were collected mainly from the granite porphyry of the kars along two traverses intersecting expected isotherms zircon and apatite ages show good agreement at approximately 15 ma and in conjunction with the observed track lengths suggest rapid uniform cooling of the kars in the temperature range 100 300 c in addition based on the petrographie features of the kars the inferred thermal history is best explained by rapid cooling subsequent to the eruption of felsic magma the rapid cooling of the kars at approximately 15 ma indicates that the basement shimanto accretionary complex in the area had already cooled at that time ft apatite ages of 10 ma were reported in the muroto peninsula which is about 100 km southwest of the kii peninsula these contrasting results suggest differential uplift of the shimanto accretionary complex along its length presumably caused by some features characterizing the subducting shikoku basin furthermore the cooling age of the kars places constraints on the ages of the orbulina datum and the clockwise rotation of southwest japan

controls on caldera structure results from analogue sandbox modeling we conducted scaled analogue sandbox models of caldera formation in order to understand the effects of chamber depth and orientation on the spatial and temporal development of calderas dry sand contained in a 1 m diameter cylinder served as a crustal rock analogue and a water filled 0 6 m diameter rubber bladder served as an analogue magma chamber scaling parameters included a length ratio l of 2 5 10 5 and a stress ratio of 1 8 2 4 10 5 in contrast to some previous analogue models the viscosity of the fluid in the chamber and its withdrawal rate were properly scaled generally deformation began with broad sagging followed by an arcuate or linear outward dipping fault that formed on one side of the caldera this fault propagated laterally around the caldera in both directions sometimes joining other faults and typically forming an overall polygonal structure as subsidence continued the caldera grew incrementally outward and progressively formed a series of concentric outward dipping faults lastly a peripheral zone of extension and pronounced sagging and commonly an inward dipping outer fault related to extension developed at the surface as the depth of the chamber increased 1 the area of faulting decreased 2 the symmetry of the caldera was affected and 3 the coherence of the subsiding block decreased tilting the chamber caused highly asymmetric subsidence to occur in this case faults formed first where the bladder was shallowest subsidence then shifted rapidly to where the bladder was deepest producing an elongate trapdoor caldera that was deepest where the bladder was deepest our experiments highlight the roles of sagging and faulting during caldera subsidence surface fault patterns both in our experiments and at natural calderas are frequently not circular the aspect ratio of the block above the magma chamber controls the shape of the caldera which is frequently polygonal the faults at natural calderas determine locations and migration of eruptive vents the degree of subsidence the style of postcal dera resurgent magmatism and the extent of hydrothermal circulation our experiments reveal details of how calderas grow outward incrementally and demonstrate that asymmetric subsidence along linear and arcuate faults is common to many calderas

biomarkers challenge early miocene loess and inferred asian desertification 1 fine grained miocene sediments from tianshui basin northeastern tibetan plateau have received intense attention recently because these sediments were identified as loess the presence of early miocene loess pushes the timing of initiation of inland asian desertification from 8 ma back to 22 ma however mudflat distal fan and shallow lake sediments of miocene have also been reported in tianshui basin consequently the origin of these fine grained miocene sediments in this area remains controversial here we investigate then alkane biomarker characteristics of neogene sediments from a north south transect of exposures within tianshui basin and compare these molecular distributions with those published quaternary loess to help resolve the disputed origin we found thatn c23 and n c25 alkanes sourced from either aquatic macrophytes or palustrine plants are ubiquitous in the miocene sediments from tianshui basin but are largely absent in quaternary loess this striking difference between n alkane distributions in the tianshui samples and the quaternary loess casts doubt on an eolian origin for the tianshui samples and challenges the hypothesis of an early miocene onset of asian interior desertification

migrated oil on novaya zemlya russian arctic evidence for a novel petroleum system in the eastern barents sea and the kara sea in this article we present evidence for the migration of cretaceous or younger oil into paleozoic strata on the islands of novaya zemlya russian arctic originating from the surrounding basins of the barents sea and the kara sea we thus suggest a novel petroleum system for the greater barents sea and kara sea regions organic geochemical data reveal that medium mature petroleum is hosted in overmature paleozoic rocks onshore novaya zemlya this petroleum likely migrated from the surrounding offshore sedimentary basins of the kara and barents seas into the onshore strata on a broad front covering 400 km 248 mi along the archipelago thus the findings describe the remnants of petroleum migration on a regional scale high maturities of the examined onshore strata vitrinite reflectance ro of 1 9 4 0 and conodont color alteration index values of 4 6 render the indigenous origin of the medium mature petroleum unlikely organic geochemical characteristics of the migrated hydrocarbons lead us to suggest the existence of a hitherto undescribed marine shale source rock with some contribution of terrigeneous organic matter the 13c isotope values varying within a range of 5 for bulk extracts as well as for individual n alkanes and isoprenoids suggest isotopic heterogeneity of the organic source facies the source rock units are inferred to have released hydrocarbons mostly at oil window maturities higher than 0 6 ro the occurrence of n alkanes and isoprenoids as well as abundant and partially degraded tricyclic terpanes indicates mixed undegraded and heavily biodegraded oil this suggests several petroleum charges with varying degrees of microbial degradation occurrences of oleanane high ratios of c28 to c29 steranes and elevated 24 norcholestane and 24 nordiacholestane ratios suggest cretaceous or tertiary source rocks

recognition of a novel precambrian petroleum system based on isotopic and biomarker evidence in yangtze platform south china abstract the precambrian doushantuo formation is regarded as a possible petroleum source rock horizon with toc values of 0 85 1 85 and type i kerogen in northwestern sichuan basin yangtze platform south china while showing high to post mature thermal maturity a set of outcropping bitumen and oil sands from various reservoirs display overall depleted values of 13 c from 36 to 32 average 35 typical of a precambrian source in addition the sterane distributions in these bitumens and oils are unusual compared to marine phanerozoic oils with a predominance of c 29 members as well as their triaromatic counterparts high amounts of 20 n alkylpregnane with very low diasteranes indicate restricted sulfur rich conditions typical of an anoxic carbonate source rock this interpretation is supported by some other specific biomarkers such as abundant 30 norhopane and c 24 tetracyclicterpane and elevated c 35 hopane furthermore the presence of gammacerane indicates a saline stratified water column hydrocarbons extracted from the solid bitumen and oil sands have many compositional characteristics in common with other oils derived from precambrian carbonate source rocks from elsewhere this implies the existence of a precambrian marine petroleum system in the yangtze platform with the doushantuo carbonate as the likely source it is supposed that the reduction of temperature and pressure following basin uplift resulted in petroleum fractionation deasphalting in lower paleozoic reservoirs with the fractionated oils having migrated along the faults becoming trapped in stratigraphically younger reservoirs where the petroleum underwent heavy biodegradation

analogue models of laccolith formation abstract this paper describes dynamically scaled analogue models of laccolithic intrusions experiments consisted of the injection of a newtonian fluid low viscosity silicone putty into a sandpack with or without an interbedded ductile layer of silicone putty acting as a potential decollement level boundary conditions were chosen to analyze the influence of the thickness of the brittle cover and of the decollement layer on the pattern of intrusion further experiments were made to examine the effects of an extensional regime during intrusion experiments showed that 1 laccolith formation requires the occurrence of a decollement layer between two competent units 2 the critical thickness of the decollement layer necessary for laccolith formation decreases with increasing depth 3 laccoliths change from lenses to bell shaped with decreasing overburden 4 for a constant thickness of the decollement layer the largest diameter of laccoliths is proportional to the thickness of the overburden and 5 a syn injection gravitational sliding regime results in an asymmetric laccolith with amplification of the bell shape

extended 3β methylhopanes up to c45 in source rocks from the upper cretaceous qingshankou formation songliao basin northeast china abstract 3 methylhopanes methylated at the c 3 position of the a ring have been detected ubiquitously in sedimentary rocks with carbon numbers of c28 and c30 c36 these compounds have been attributed to aerobic methanotrophs due to their strongly 13c depleted compositions here we report 3 methylhopanes with carbon numbers up to c45 in source rocks from the first member of the upper cretaceous qingshankou formation songliao basin northeast china the extended homologues up to c45 might be derived from long chain alkyl bacteriohopanetetrols by consecutive enzymatic additions of a c5 sugar extremely 13c depleted compositions combined with a high 3 methylhopane index suggest an intense ch4 cycle induced by blooms of aerobic methanotrophs in the songliao paleo lake

australian offshore natural hydrocarbon seepage studies a review and re evaluation abstract surprisingly few natural hydrocarbon seeps have been identified in australia s offshore basins despite studies spanning thirty years early studies of natural hydrocarbon seepage around the australian margin were generally based on the geochemical analysis of stranded bitumens water column geochemical sniffer sampling synthetic aperture radar or airborne laser fluorosensor later studies involved the integration of these remote sensing and geochemical techniques with multi channel and shallow seismic a review of these earlier studies indicates that many seepage interpretations need to be re evaluated and that previous data sets when placed in a global context often represent normal background hydrocarbon levels low recent burial and subsidence rates are not favourable for high rates of seepage there are also difficulties in proving seepage on high energy shallow carbonate shelves where seabed features may be rapidly re worked and modern marine signatures are overprinted on authigenic seep carbonates thus the relatively few sites of proven natural hydrocarbon seepage in australia s offshore sedimentary basins can be reconciled relative to their geological occurrences and the dominantly passive margin setting active thermogenic methane seepage on the yampi shelf the only proven documented occurrence in australia is driven by deposition of a thick late tertiary carbonate succession and late miocene tectonic reactivation therefore to increase the success of detecting and correctly interpreting natural hydrocarbon seepage data need to be analysed and integrated within the context of the local geological setting and with an understanding of what is observed globally

molecular marker and carbon isotope geochemistry of ordovician oils in the tuofutai bulge northern tarim basin implications for oil maturity source characteristics and ﬁlling directions abstract the tuofutai bulge in the tabei uplift of tarim basin western china has become a hot spot for petroleum exploration in recent years fifteen ordovician oil samples from 15 wells in the tuofutai bulge were analyzed for biomarkers and carbon isotopes using gas chromatography mass spectrometry and stable carbon isotope analysis to constrain its depositional environment thermal maturity source rocks and the possible petroleum charging directions the samples were characterized by abundant terpenoids relatively high contents of c29 regular steranes and dibenzothiophene relatively low ratios for pr ph and c22 c21 tricyclic terpanes and high ratios of c35 c34 homohopanes results suggest that the source rocks for the oils were deposited in a reducing marine carbonate and marl environment cambrian and ordovician source rocks contribute to the oils and the middle to upper ordovician source rocks exert a greater contribution n alkanes and abundant 25 norhopanes in the saturated fractions suggest that the oil is a mixture of early biodegraded oil and late normal crude oil charged at later time data from methyldiamantane parameters suggest that the crude oil is in a high maturity stage the tracing of oil charging suggests that preferential migration directions are primarily from south to north connected with oil migration along the shenbei no 1 fault from the shuntuoguole lower uplift to the south of tabei uplift

paleoclimatic fluctuations inferred from leaf wax n alkane records in central tibet in the late oligocene to early miocene abstract climatic variations and their forcing mechanisms in tibet are highly significant for understanding the environmental effects of the tibetan plateau through its controlling on atmospheric circulation here we present new leaf wax n alkanes from cenozoic lacustrine sediments in the lunpola basin of central tibet to constrain long term paleoclimatic changes our results suggest that the paleoclimate from the late oligocene to early miocene was generally stable but tending slightly towards cold dry from 25 5 to 23 2 ma followed by a trend towards warm humid between 23 2 and 21 7 ma and finally by a more arid and highly oscillating climate after 21 7 ma our results compare favorably with the proxies of marine 18o records which suggests that the general long term trend since the late oligocene has been a response to global temperature variations moreover spectral analysis of 13c31 and 2h31 data reveals that relative humidity exhibits 400 kyr cycles controlled mainly by periodic changes in global ice volumes

effects of stress in the evolution of large silicic magmatic systems an example from the miocene felsic volcanic field at kii peninsula sw honshu japan abstract miocene felsic volcanic field at the kii peninsula mfvk in southwest japan allows us to reveal temporal and spatial change of a large felsic volcanic system in response to changes in the local and regional stress field the mfvk was active episodically ejecting more than a few hundred cubic kilometers of magma in a span of hundred thousand to million years remnant of this large scale volcanism is characterized by a broad area of deeply incised and complex cluster of collapse calderas in the kii peninsula major conduits for ash flow tuff eruptions lie on the margins of the mfvk paleostress orientation of the hmax was inferred from lithologic distribution and structure in rocks in the mfvk the optimal tectonic stress orientation at the time of the mfvk formation was nne ssw to the present azimuth approximately 1500 km 3 of magma were erupted from the mfvk during a duration of 0 1 million to 1 6 myr this suggests an area normalized eruption rate of 10 2 to 10 3 km 3 ka km 2 this long term eruption rate of the mfvk is at the high end of rates for other large felsic volcanic fields lfvfs and ranks as one of the larger rates of lfvf worldwide the large eruption rate of the mfvk and the formation of a large magma chamber is discussed in relation to tectonic stress although a compressional stress field favors the formation of a sill like large magma chamber a larger magma supply rate is more essential we believe that a large rate of magma supply in combination with local and regional stress conditions in the early development of the mfvk promoted magma accumulation over eruption leading to the development of a large silicic magma chamber we suggest that such a large magma chamber can generate excess pressure inside the chamber itself that results in a local tumescence and counteracts the tectonic compressional stress field allowing magma to reach the surface this scenario is the most plausible explanation for the large eruption rates of caldera volcanoes under a compressional stress field the case of the mfvk is similar to the toba caldera indonesia which lies adjacent the geologic suture zone of wrench faults the sumatra faults

reducing the risk of finding a working petroleum system using sar imaging sea surface slick sampling and geophysical seafloor characterization an example from the eastern black sea basin offshore georgia abstract as new plays emerge in deepwater settings sea surface slicks are often overlooked as a source of geochemical information to help define potential petroleum systems to demonstrate how sea surface hydrocarbon slicks can be used a case study is presented from the eastern black sea in the rioni basin offshore republic of georgia there source rocks of oligo miocene age maikop are suspected of charging upper miocene deepwater channel levee sands in fold and thrust system traps to reduce exploration risk direct evidence of hydrocarbon generation and migration was sought using sea surface slicks observed there to provide confirmation of charge a collection of diverse data was used first synthetic aperture radar satellite images were utilized to verify the presence of large recurring sea surface slicks over prospective structures these slicks were then sampled for later analysis during the acquisition of 3 d seismic data to verify that the slicks were related to the subsurface expulsion seafloor bathymetric and amplitude data were extracted from the 3 d seismic volume and used to identify potential seafloor features consistent with hydrocarbon seepage some of these seafloor features were found to be coincident with the apparent sea surface origins of the slicks seismic imaging was also used to demonstrate potential migration pathways which may link suspected deep subsurface traps and the seafloor and finally geochemical analysis showed that the compositional characteristics of the slicks hydrocarbons were similar to known maikop sourced oils in the region this combination of data provided a high level of confidence that the seismically imaged traps in offshore republic of georgia are charged suggesting a working petroleum system was present what it cannot tell us is how much petroleum may be in these structures that question can only be answered by the drill bit

tracing the origin of thermogenic hydrocarbon signals in pockmarks from the southwestern barents sea abstract the glacially influenced southwestern barents sea is a promising area for petroleum exploration the present study area which is located in the loppa high region exhibits extensive pockmark fields covering an area of several square kilometers and containing thousands of pockmarks in high density to investigate whether the pockmark formation was driven by petroleum leakage to the surface acting thus as indicators for an active petroleum system gravity cores from selected pockmark and reference sites were investigated using an organic geochemical approach various biomarkers indicative of thermogenic hydrocarbons such as short chain n alkanes with a low carbon preference index alkylcyclohexanes hopanes steranes and diasteranes mixed with biomarkers representing immature organic matter were detected in the pockmark but also in reference cores outside of the pockmark and even from a non pockmark area the abundance and level of thermal maturity of the thermogenic hydrocarbons are comparable between the pockmark and reference sites additionally their distribution with depth is quite similar to those of the immature biomarkers these observations support the conclusion that the thermogenic hydrocarbon signal in the pockmarks is the result of reworked eroded mature material mixed with immature organic matter distributed across the entire area rather than the result of seepage events of thermogenic hydrocarbons through the pockmark system the data show that in the loppa high region the pure presence of petroleum derived hydrocarbons in pockmark areas cannot be used to indicate the presence or leakage of deeper petroleum systems

recognizing and compensating for interference from the sediment s background organic matter and biodegradation during interpretation of biomarker data from seafloor hydrocarbon seeps an example from the marco polo area seeps gulf of mexico usa abstract a suite of seep samples from the vicinity of the marco polo field in the green canyon area of the gulf of mexico provides an exceptional opportunity to study the impact of interference from sediment background organic matter and alteration by biodegradation on thermogenic hydrocarbons from seafloor seeps these seep samples contain a range in both the concentration of seeped hydrocarbons present and level of biodegradation experienced in addition the subsurface oil that sources the seepage was available for comparison the results of the study show that it is essential to have the biomarker data from the sediment s background organic matter when dealing with low concentration seepage these data provide a means to characterize the contribution of background organic matter to the biomarker distributions this in turn allows the identification of thermogenic hydrocarbons when the concentration of seeped oil in seafloor sediments is low in high concentration seepage the hopanes and regular steranes were found to be more susceptible to near surface microbial alteration while tricylic tetracyclic terpanes diasteranes monoaromatic steroids and triaromatic steroids were more resistant if biodegradation is severe enough all biomarker compounds are vulnerable to alteration and very little information is preserved in an effort to reconstruct the altered distributions low temperature pyrolysis of the seeped oils asphaltenes was done to liberate occluded biomarkers compounds although biomarkers were recovered they did not resemble the parent oil characteristics of some of the recovered biomarker distributions suggest alteration by biodegradation this implies the three dimensional structure of the asphaltenes may not offer complete protection from microbial attack these results demonstrate why interpretation of biomarker data from seafloor seeps can be a difficult task care must be taken to recognize contributions from the sediment s background organic matter as well as identify alteration by biodegradation failure to understand these processes can lead to erroneous interpretations being made about the seep s parent oil and source rock

alteration of crude oils from the troll area by biodegradation analysis of oil and water samples abstract biodegradation of crude oil in reservoirs has been extensively studied and is usually considered to be a quasi stepwise process the process is known to increase the acidity of the oil in this paper results from the analysis of crude oils and co produced waters from the reservoir surrounding the troll c platform in the norwegian north sea are presented based on the concentrations of light hydrocarbons in the troll oils simultaneous biodegradation of n alkanes branched alkanes cycloalkanes alkyl benzenes alkyl naphthalenes and methyl phenanthrenes is suggested pronounced relative enrichment of methylcyclopentane cyclohexane and methylcyclohexane provide evidence for a specific recalcitrance of cycloalkanes to biodegradation in this field biodegradation can also be seen in the carbon isotopic signature of the lighter hydrocarbons e g heavy signatures for n pentane and iso pentane the composition of the aromatic acids in the produced waters suggests biodegradation to be their predominant source in the reservoir the occurrence of reduced naphthoic acids previously shown to be specific indicators of anaerobic biodegradation of naphthalene 2 methylnaphthalene and tetralin indicates that the biodegradation took place under anoxic conditions

investigation of hydrocarbon biodegradation from a downhole profile in bohai bay basin implications for the origin of 25 norhopanes abstract a suite of reservoir cores oil sands from a single well in bohai bay basin east china displayed a progressive increase in petroleum biodegradation extent on the basis of bulk composition and 25 norhopane content this fits with the proposal that subsurface petroleum biodegradation is dominantly an anaerobic process and usually occurs at the oil water contact it is likely that sequential microbial degradation of hydrocarbons under anoxic conditions does not occur in a true stepwise fashion but is controlled by various factors such as concentration and solubility of hydrocarbons and their diffusion rate to the oil water contact in fact 25 norhopanes were formed prior to the complete elimination of the acyclic and mono and bicyclic alkanes an inverse response of the 22 s 22 s 22 r ratio between each extended 17 h hopane and its corresponding 25 norhopane was observed as severe biodegradation occurred supporting the proposal that the 25 norhopanes originate from demethylation of hopanes field observation revealed that biomarkers without extended alkyl side chains such as oleanane gammacerane and carotane have significant resistance to biodegradation and can be used as naturally occurring internal standards to evaluate variations in other biomarkers the results suggest that the quantity of 25 norhopanes showed a minor increase as the hopanes decreased significantly i e only partial hopane conversion to the corresponding 25 norhopanes alternative degradation pathways for hopanes might occur in reservoirs in addition to c 25 demethylation

microbial degradation of sedimentary organic matter associated with shale gas and coalbed methane in eastern illinois basin indiana usa molecular biodegradation indices for extracts from five pennsylvanian coals and six new albany shale devonian mississippian samples from the eastern part of the illinois basin help constrain relationships between the degradation of biomarkers and the generation of coalbed methane and shale gas investigation of these gas source rocks of varying thermal maturity from different depths facilitates evaluation of the association of microbial degradation with biogenic gas formation distinct from thermogenic processes extensive biodegradation of both aliphatic and aromatic hydrocarbons is observed in the coal extracts whereas in shale extracts only short chain c15 c19 n alkanes from the shallowest depth appear to be microbially altered with minimal evidence for losses of acyclic isoprenoid alkanes and aromatic hydrocarbons by contrast biodegradation of aromatic hydrocarbons specifically alkylated naphthalenes and phenanthrenes occurs in coal extracts in concert with losses of n alkanes attributable to microbial activity thus the progress of hydrocarbon biodegradation in coals differs from the sequence recognized in petroleum where the effects of microbial alteration of aromatic constituents only appear after extensive losses of aliphatic compounds the extent of hydrocarbon biodegradation in these coals also decreases with depth as recorded by the nc25 nc30 index i e abundance relative to 17 h 21 h hopane among the aliphatic constituents and several aromatic compounds methyl dimethyl and trimethylnaphthalenes phenanthrene and trimethyl and tetramethylphananthrenes however the depth variations in the distributions of aliphatic and aromatic hydrocarbons in the shale extracts primarily reflect the effects of thermal maturity rather than biodegradation overall variations in the extent and patterns of biomarker biodegradation among coals and shales likely reflect their distinct microbial consortia that can be attributed to differences in i surviving microorganisms and inoculations from meteoric water ii the characteristics of the sedimentary organic matter especially the preponderance of aromatic constituents in coals and iii the accessibility to that substrate through pores and cleats these results help constrain the processes involved in biodegradation and controls on its extent which in turn assist in recognizing sites favorable for methanogenesis and improved estimates of biogenic gas resources in the illinois basin

calderas and caldera structures a review abstract calderas are important features in all volcanic environments and are commonly the sites of geothermal activity and mineralisation yet it is only in the last 25 years that a thorough three dimensional study of calderas has been carried out utilising studies of eroded calderas geophysical analysis of their structures and analogue modelling of caldera formation as more data has become available on calderas their individuality has become apparent a distinction between caldera caldera complex cauldron and ring structure is necessary and new definitions are given in this paper descriptions of calderas based on dominant composition of eruptives basaltic peralkaline andesitic dacitic rhyolitic can be used and characteristics of each broad group are given styles of eruption may be effusive or explosive with the former dominant in basaltic calderas and the latter dominant in andesitic dacitic rhyolitic and peralkaline calderas four end member collapse styles occur plate or piston piecemeal trapdoor and downsag but many calderas have multiple styles features of so called funnel and chaotic calderas proposed in the literature can be explained by other collapse styles and the terms are considered unnecessary ground deformation comprises subsidence or collapse essential characteristics of a caldera and uplifting doming and fracturing due to tumescence and or resurgence frequent but not essential collapse may occur on pre existing structures such as regional faults or on faults created during the caldera formation and the shape of the collapse area will be influenced by depth size and shape of the magma chamber the final morphology of a caldera will depend on how the caldera floor breaks up whether collapse takes place in one event or multiple events whether vertical movement is spasmodic or continuous throughout the eruptive sequence and whether blocks subside uniformly or chaotically at one or more collapse centres a meaningful description of any caldera should therefore include number of collapse events presence or absence of resurgence caldera floor coherency caldera floor collapse geometry and dominant composition of eruptives

a giant oil seep at a salt induced escarpment of the sao paulo plateau espirito santo basin off brazil host rock characteristics and geochemistry abstract an international research cruise named iata piuna took place on the sao paulo plateau on may 2013 in the campos and espirito santo basins off brazil the cruise was carried ou on board the research vessel r v yokosuka that hosts the human operated vehicle hov shinkai 6500 it aimed at finding chemosynthetic communities composed of organisms capable of generating their own vital energy by metabolizing organic and inorganic compounds related to seeps identification of these organisms could provide information for understanding the origin of life since they may resemble primitive organisms that existed in the initial stages of life on earth during leg 2 may 10 24 2013 however dives on the northern part of the sao paulo plateau at the espirito santo basin led to the discovery of a giant oil seep the seep ca 3 nautical miles ca 5 6 km in length is located along an outcrop of eocene rocks on a salt induced escarpment of the plateau and at a water depth of ca 2700 m the 200 m relief of the seafloor suggests that the seep takes place along an active fault system driven by salt diapirism the oil was analyzed and identified as a severely biodegraded marine oil generated by carbonate rocks within a minibasin located to the east of the escarpment this represents valuable exploratory information because it proves that an active petroleum system is present in the context of minibasins associated with salt diapirism in the area

igneous evolution of a complex laccolith caldera the solitario trans pecos texas implications for calderas and subjacent plutons the solitario is a large combination laccolith and caldera herein termed laccocaldera with a 16 km diameter dome over which developed a 6 2 km caldera this laccocaldera underwent a complex sequence of predoming sill laccolith and dike intrusion and concurrent volcanism doming with emplacement of a main laccolith ash flow eruption and caldera collapse intracaldera sedimentation and volcanism and late intrusion detailed geologic mapping and 40ar 39ar dating reveal that the solitario evolved over an interval of approximately 1 m y in three distinct pulses at 36 0 35 4 and 35 0 ma the size duration and episodicity of solitario magmatism are more typical of large ash flow calderas than of most previously described laccoliths small volumes of magma intruded as abundant rhyolitic to trachytic sills and small laccoliths and extruded as lavas and tuffs during the first pulse at 36 0 ma emplacement of the main laccolith doming ash flow eruption and caldera collapse occurred at 35 4 ma during the most voluminous pulse a complex sequence of debris flow and debris avalanche deposits megabreccia trachyte lava and minor ash flow tuff subsequently filled the caldera the final magmatic pulse at 35 0 ma consisted of several small laccoliths or stocks and numerous dikes in caldera fill and along the ring fracture solitario rocks appear to be part of a broadly cogenetic metaluminous suite peralkaline rhyolite lava domes were emplaced north and west of the solitario at approximately 35 4 ma contemporaneous with laccolith emplacement and the main pulse in the solitario the spatial and temporal relation along with sparse geochemical data suggest that the peralkaline rhyolites are crustal melts related to the magmatic thermal flux represented by the main pulse of solitario magmatism current models of laccolith emplacement and evolution suggest a continuum from initial sill emplacement through growth of the main laccolith although the solitario laccocaldera followed this sequence of events our field and 40ar 39ar data demonstrate that it developed through repeated episodic magma injections separated by 0 4 to 0 6 m y intervals of little or no activity this evolution requires a deep long lived magma source well below the main laccolith laccoliths are commonly thought to be small shallow features that are not representative of major silicic magmatic systems such as calderas and batholiths in contrast we suggest that magma chambers beneath many ash flow calderas are tabular floored intrusions including laccoliths evidence for this conclusion includes the following 1 many large plutons are recognized to be laccoliths or at least tabular 2 the solitario and several larger calderas are known to have developed over laccoliths and 3 magma chambers beneath calderas which are as much as 80 km in diameter cannot be as deep as they are wide or some would extend into the upper mantle the solitario formed during a tectonically neutral period following laramide deformation and preceding basin and range extension therefore space for the main laccolith was made by uplift of its roof and possibly subsidence of the floor not by concurrent faulting laccolith type injection is probably a common way that space is made for magma bodies of appreciable areal extent in the upper crust

seafloor facies related to upward methane flux within a giant pockmark of the lower congo basin the origin of the cold fluid venting from a giant pockmark within the lower congo basin has been elucidated based upon results of precise mapping submersible dives gravity coring and isotopic analyses realized under a total ifremer cooperative project zaiango and biozaire projects during four dives of the ifremer rov victor 6000 the bottom was filmed hard and soft samples were lifted from the sediment and water samples were collected with a ctd rosette system the detailed dip map shows that the 800 m wide giant pockmark is a composite feature due to the coalescence of multiple 100 m wide depressions that displays a broad range of biological mineralogical and chemical features on the seafloor leading to a seafloor anomaly recorded on the multibeam imagery methane rich fluids migrating through the sedimentary column from a buried palaeochannel clearly react with the sulphate rich circulating sea water to produce hydrogen sulphide and bicarbonate ions this situation leads to a concentrical arrangement of the sedimentary facies with methane related features in the centre and sulphide related features at the periphery this organization is correlated with high levels of methane up to 20 mol l measured in the centre of the giant pockmark responsible for the crystallization of gas hydrates at the bottom in this model the concentrical organization of mineralogical and biological features reflects a geochemical partitioning related to the peripheral progressive mixing of the methane flux

experimental studies of collapse calderas we present experiments to investigate the formation of calderas using inflatable balloons in a medium of fused alumina powder this system provides a model of a magma chamber in an homogeneous elastic media which scales to volcanic systems in terms of geometry and strength of the media three kinds of experiment were performed i the balloon was inflated and then deflated simulating pre emption tumescence and caldera collapse ii the balloon was deflated without prior inflation simulating caldera formation without pre eruption tumescence iii three balloons were inflated and deflated in a line simulating multiple magma chambers the influence of magma chamber shape was investigated using different shaped balloons balloon inflation formed a dome with a surface pattern of shallow polygonal fractures centrally and radial fractures peripherally uplift occurs along deep inward dipping concentric reverse faults deflation generated depressions with an outer set of concentric ring fractures surrounding a central funnel formed by sagging along numerous minor faults some of which formed during doming during collapse the concentric reverse faults were converted to normal faults and the radial normally faulted fractures were converted to reverse faults without prior tumescence an outer set of near vertical ring faults surround a flat central depression due to collapse of a coherent block an inner set of outward dipping reverse ring faults also develop the experimental caldera area increased with balloon size and increased as the balloon depth decreased for a given balloon volume and depth collapse area is significantly smaller if doming had occurred prior to collapse arcuate fractures can provide the pathways for magma ascent during pre emption tumescence smith bailey 1968 but the shallow radial and polygonal fracture systems may also influence vent location changes in fault geometry and sense of movement extension to compression and vice versa occur when subsidence initiates and can account for changes in vent location that occur in many eruptions multiple overlapping collapse calderas are associated with magma chamber migration whereas nested calderas can result from the activity of a single magma chamber

natural oil slicks in the gulf of mexico visible from space natural oil seepage in the gulf of mexico causes persistent surface slicks that are visible from space in predictable locations a photograph of the sun glint pattern offshore from louisiana taken from the space shuttle atlantis on may 5 1989 shows at least 124 slicks in an area of about 15 000 km2 a thematic mapper tm image collected by the landsat orbiter on july 31 1991 shows at least 66 slicks in a cloud free area of 8200 km2 that overlaps the area of the photograph samples and descriptions made from a surface ship from aircraft and from a submarine confirmed the presence of crude oil in floating slicks the imagery data show surface slicks near eight locations where chemosynthetic communities dependent upon seeping hydrocarbons are known to occur on the seafloor additionally a large surface slick above the location of an active mud volcano was evident in the tm image in one location the combined set of observations confirmed the presence of a flourishing chemosynthetic community active seafloor oil and gas seepage crude oil on the sea surface and slick features that were visible in both images we derived an analytical expression for the formation of floating slicks based on a parameterization of seafloor flow rate downstream movement on the surface half life of floating oil and threshold thickness for detection applying this equation to the lengths of observed slicks suggested that the slicks in the atlantis photograph and in the tm image represent seepage rates of 2 2 30 m3 1000 km 2 d 1 and 1 4 18 m3 1000 km 2 d 1 respectively generalizing to an annual rate suggests that total natural seepage in this region is of the order of at least 20 000 m3 yr 1 120 000 barrels yr 1

the study on the source of the oil seeps and bitumens in the tianjingshan structure of the northern longmen mountain structure of sichuan basin china abstract the tianjingshan structure of the northern longmen mountain is located in the north of the sichuan province china two primary source rocks are present in this region the overmature infracambrian lower cambrian source rocks and the mature upper permian source rocks oil seeps and solid bitumens occur extensively in the mesozoic and paleozoic marine strata indicating good exploration prospects in this area however oil to source correlation in the tianjingshan structure is difficult due to both high maturity of the lower cambrian source rocks and severe biodegradation of oil seeps and bitumens in this work one oil seep from the permian qixia formation and two severely degraded bitumens from the cambrian strata in the tianjingshan structure were correlated with their potential source rocks hydropyrolysis was used to release biomarkers bound to kerogen of the overmature lower cambrian source rock the released biomarkers were used for the oil to source correlation together with those indexes resistant to thermal degradation and biodegradation based on the geochemical data and the petroleum geological settings of the area it can be inferred that the cambrian ordovician and silurian bitumens with light bulk isotopic values commonly 13 c

25 norhopanes formation during biodegradation of petroleum in the subsurface abstract quantitative data from petroleum systems in china liaohe basin and canada athabasca tar sands support the theory that 25 norhopanes are produced during biodegradation of petroleum in the subsurface within a single oil column both case histories showed increasing severity of degradation indicated by destruction of hopanes and production of 25 norhopanes downward to the oil water contact in the athabasca samples between the peters k e moldowan j m 1993 the biomarker guide interpreting molecular fossils in petroleum and ancient sediments prentice hall englewood cliffs new jersey p 363 scale of biodegradation levels 5 9 concentrations of c 28 20s triaromatic steroids and other biodegradation resistant compounds increased by 35 reflecting a concentration effect as a consequence of removal of more degradable compounds over the same interval the concentrations of c 28 17 25 norhopane and c 29 17 25 norhopane increased by an order of magnitude thus requiring that the balance be met by their net production during degradation a detailed molecular investigation of the athabasca bitumen revealed that c 30 17 hopane degrades faster than c 29 17 hopane whilst the rate of formation of both c 29 17 25 norhopane and c 28 17 25 norhopane are similar complicating a straightforward interpretation of demethylation of hopanes to form 25 norhopanes hopane degradation in the athabasca tar sand may also occur without the production of 25 norhopanes the results show that even within a single petroleum accumulation a number of mechanisms control changes in the abundance and composition of hopanes and 25 norhopanes

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

petroleum generation timing and source in the northern longmen shan thrust belt southwest china implications for multiple oil generation episodes and sources the temporal evolution of hydrocarbons 500 million bbl and its relationship to the orogenic events of the longmen shan thrust belt have been extensively debated the hydrocarbons occur as solid bitumen as dykes and or coatings within along faults fractures and as present day oil seeps here utilizing organic geochemistry we demonstrate that all of the bitumen exhibit similar organo geochemical characteristics and were sourced from the upper neoproterozoic lower cambrian doushantuo and qiongzhusi formations in contrast the organic geochemistry of the present day oil seeps are distinct from that of the bitumen and suggest that the source is the permian dalong formation bitumen re os data indicate that the upper neoproterozoic lower cambrian doushantuo and qiongzhusi formations underwent two temporally distinct oil generation events initial oil generation occurred during the late cambrian early ordovician prior to the caledonian orogeny and secondly during the jurassic 165 ma coinciding with the indosinian yanshan orogenies in contrast the re os data of the present day oil seeps are too similar to yield a meaningful age although the source is considered to have undergone hydrocarbon maturation between the triassic and jurassic the temporal hydrocarbon evolution in the longmen shan thrust belt also provides an understanding of the hydrocarbon evolution and future exploration of the adjacent petroliferous sichuan basin

post 19 ka b p eruptive history of ulleung island korea inferred from an intra caldera pyroclastic sequence ulleung island is a quaternary volcanic island located in the mid western part of the east sea sea of japan back arc basin which has erupted from the pliocene until the late holocene this study focuses on reconstructing the latest eruptive history of the island by describing the sedimentological and stratigraphic characteristics of the most recent trachytic phonolitic pyroclastic sequence named the nari tephra formation this formation is preserved as a succession of unwelded pyroclastic and epiclastic deposits within an embayed margin of the nari caldera the embayment acted as a topographic trap for proximal pyroclastic deposits and contains a complete record of the past 19 000 years of eruption history the formation includes evidence for five separate eruptive episodes member n 1 to n 5 with intervening weathered and or soil horizons indicating hundreds to thousands of years of repose between each eruption eruption styles and depositional mechanisms varied between and during individual episodes reflecting changing dynamics of the magma plumbing system magmatic gas coupling and a variable role of external water extra caldera sequences show that only a few of these eruptions generated sustained eruption columns or pyroclastic density currents pdcs large enough to overtop the caldera wall thus tephra sequences outside the caldera provide an underestimate of eruption frequency and care needs to be taken in the interpretation and correlation to distal tephra sequences recognized in marine and terrestrial records in addition topographic effects of caldera structures should be considered for the assessment of pdc related hazards in such moderately sized pyroclastic eruptions

distribution controlling factors and oil source correlation of biodegraded oils in the bohai offshore area bohai bay basin china the vast majority of discovered oils in the bohai offshore area have undergone biodegradation varying from 1 to 9 on the pm scale a scale to rank the level of biodegradation proposed by peters and moldowan 1993 the distribution and biodegradation extent of all discovered oils in the bohai offshore area were investigated systematically using geologic and geochemical data to reveal controlling factors of varying levels of biodegraded oils based on the analysis on environment and maternal significances and the resistance to degradation of biomarkers the biomarker parameter assemblage that is suitable for the oil source correlation of severely biodegraded oils higher than pm 6 in the bohai offshore area was determined spatial distribution and biodegradation extent are mainly controlled by current burial depth the duration of biodegradation the area of the oil water contact owc and a late strike slip movement of the tanlu fault almost all biodegraded oils are found in shallow reservoirs above 2000 m the longer the oils are present in these reservoirs or the larger the area of owc the reservoirs show the greater the extent of biodegradation will be the late strong strike slip movement of the tanlu fault may have significantly enhanced the biodegradation extent of several oils in fields located in the tanlu fault zone by introducing oxygenated freshwater from the surface or near surface and creating a more suitable environment for biodegradation c19 tricyclic terpane c23 tricyclic terpane c19 c23 tt c24 tetracyclic c26 tricyclic terpane c24 tet c26 tt and gammacerane c24 tetracyclic gam c24 tet do not seem to be influenced by biodegradation and show obvious differences between the three different source rock intervals such a biomarker parameter assemblage can be used successfully to determined the origin of severely biodegraded oils higher than pm 6 by correlating with extracts of possible source rocks in the bohai offshore area

structural eruptive and intrusive evolution of the grizzly peak caldera sawatch range colorado volcanic and shallow intrusive features of the deeply dissected 34 ma grizzly peak caldera in west central colorado record evolution of the magmatic center from pre caldera through post resurgent stages pre caldera dikes zones of hydrothermally altered rocks and lava flows formed along a circular swarm of cone sheet fractures around the site of the future caldera early largely rhyolitic uppercrustal magmatism culminated in the caldera forming eruption of the grizzly peak tuff intracaldera tuff is zoned from high silica rhyolite at the base to low silica rhyolite at the eroded top and further contains dacite to mafic latite pumice lumps in two heterogeneous tuff layers in the upper third of the preserved section half of the erupted tuff ponded in the 17 by 23 km 600 km 3 caldera filling the asymmetric depression to a compacted thickness locally 2 7 km including intercalated rock avalanche megabreccias shed from ring fault scarps the asymmetric caldera has an inner ring fracture zone that separates two structural segments that collapsed to different depths caldera fill buried collapse structures as they formed the inner ring fracture zone is a growth or syn depositional fault in the single cooling unit tuff welded tuff ring dikes are locally exposed at erosion levels below the caldera fill these dikes are remnants of fissure vents in the outer ring fracture zone following collapse the grizzly peak caldera was uplifted forming a complexly faulted resurgent dome resurgence resulted partly from emplacement of a composite granodiorite laccolith now exposed in the eroded core of the dome a belt of mafic latite to rhyolite porphyry dikes and small stocks formed across the center of the domed caldera during the waning of the magmatic center latite intrusions in this suite represent the penetration of relatively mafic magma to the surface following solidification of the felsic subcaldera batholith

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

petroleum evolution within the tarim basin northwestern china insights from organic geochemistry fluid inclusions and rhenium osmium geochronology of the halahatang oil field the newly discovered halahatang oil field in the northern tarim basin has a potential resource of more than 70 billion bbl of oil oil organic geochemical data from the halahatang oil field indicate that the oils are of moderate maturity biodegraded and represent one oil family derived from the same paleozoic marine source modeling of coeval aqueous and hydrocarbon bearing inclusion data provide fluid trapping temperatures and pressures of 100 c to 110 c and approximately 39 to 59 mpa 5656 8557 psi respectively the fluid inclusion data coupled with the previous basin model studies suggest a single prolonged oil migration event during the permian the re os isotope data of the oil yields an early permian re os age of 285 48 ma the age agrees with the timing of maturation of the paleozoic source via burial history modeling but is slightly older 5 55 m y than the oil migration and accumulation timing implied by the basin modeling coupled with fluid inclusion analysis and the published reservoir illite k ar dates thus the oil re os date suggests that oil generation in the halahatang depression of the tarim basin occurred during the early permian rather than the silurian as previously proposed with subsequent oil migration and accumulation occurring during the middle late permian as recorded by basin modeling coupled with fluid inclusion analysis and illite k ar dating in addition to promoting petroleum exploration in the tarim basin this study which combines crude oil re os isotope dating and traditional analytical methods organic geochemistry and fluid inclusion analysis to constrain petroleum evolution is applicable to hydrocarbon systems worldwide

preliminary video spatial analysis of cold seep bivalve beds at the base of the continental slope of israel palmahim disturbance abstract seafloor video surveys were carried out with the rov max rover in the palmahim disturbance pd area offshore israel in september 2016 during the eurofleets2 semseep cruise on board the r v aegaeo preliminary observations of distribution and frequencies of bivalve accumulations show that they are mostly composed by lucinoma kazani shells valves are distributed mainly along the base of authigenic carbonate crusts in association with bacterial mats and inside inactive chimney like structures sometimes associated with crabs and living tubeworms however no living molluscs were observed the relation between distribution of bivalve beds and seepage activity is not straightforward in the pd area however the presence of these accumulations and the size of l kazani suggest that seepages may have lasted for at least one decade before its reduction cessation that induced l kazani mortality the presence of few articulated valves of this species indicates that they were alive up to one year before the rov observations and their different preservation state may imply different seepage phases this research shows that chemosymbiotic benthic communities may be used as a proxy for better understanding the past dynamics of fluid emissions at the seafloor however further quantitative studies are needed to confirm these observations

marine seepage variability and its impact on evaluating the surface migrated hydrocarbon seep signal abstract detection of chemically identifiable hydrocarbon oil and gas seepage is an important tool in offshore exploration generated and or trapped oil and gas can leak to near surface sediments and ocean in detectable concentrations the seepage surface expression is controlled by hydrocarbon generation regional pressure regimes and migration pathways the migrated hydrocarbon concentration and composition varies due to seepage rates and near surface physical and biological processes that can alter the signal a seepage continuum exists from large volume oil and gas seeps known as macro seepage to lower volume seeps known as micro seepage only detectible with special sampling and analysis understanding the impact of migrated hydrocarbon concentration relative to in situ organic material and locally derived microbial hydrocarbons is critical this paper describes factors that control the near surface geochemical signal as well as the challenges in deciphering the migrated hydrocarbon signature to evaluate subsurface hydrocarbon generation and entrapment

data processing and recognition of seepage and microseepage anomalies of acid extractable hydrocarbons in the south slope of the dongying depression eastern china abstract the successful use of near surface anomalous signals exhibited in all petroliferous basins must lead to great development in petroleum exploration the elementary equations and methods for objective and accurate separation of anomalous signals from background signals are the most critical requirements in these surface geochemical surveys therefore we have worked up a series of fundamental equations and methods for eliminating surface interference and influences of geological conditions on anomaly intensities and recognizing multi type anomalies of uni and multi variates by using statistics fractal geometry wavelet analysis and artificial neural networks these equations illustrate that the threshold i e the boundary between background and micro seepage anomalies is determined by means standard deviations and prior probabilities of background and micro seepage anomalies when multi normality is met and that the traditional equation for the threshold background mean plus one or two standard deviations is not correct in the face of many new equations and methods it is important how to comprehensively use them to resolve the problems in geochemical surveys a geochemical survey in the south slope of the dongying depression eastern china provides a good opportunity to address this issue the anomalies obtained with the traditional equation do not reflect oil gas fields this study reveals three problems in the previous data processing and anomaly recognition 1 the surface interference caused by the variation of soil composition was not identified and removed 2 the influence of caprock thickness on anomaly intensities was not revealed and eliminated and 3 the micro seepage related to oil gas pools and seepage related to faults anomalies were not separated and correctly recognized furthermore the interaction of these problems makes the data processing and anomaly recognition more difficult to ensure effective elimination of the surface interference and caprock thickness influence and correct recognition of uni variate anomalies we iteratively applied the wavelet analysis based methods to eliminate the surface interference and caprock thickness influence and statistical methods with new fundamental equations to recognize uni variate anomalies of seepage and microseepage and then multi variate anomalies of seepage and microseepage were recognized with our fundamental equations and the corresponding methods in the results the seepage anomalies display a string bead shaped pattern and are distributed along faults and the micro seepage anomalies are ring shaped and coincide with oil gas pools sandbodies or traps therefore reprocessing of geochemical data with our fundamental equations and methods combined in an iterative manner can resolve the complicated problems in data processing and anomaly recognition and thus greatly improve the predictive capability of surface geochemical survey

oil source correlation in the slope of the qikou depression in the bohai bay basin with discriminant analysis abstract the commonly used tools for oil source correlation such as mass chromatograms of biomarkers and bivariate cross plots of geochemical parameters cannot deal with multiple geochemical parameters and plenty of samples simultaneously leading to uncertainties in the results and even failures sometimes in this paper the discriminant analysis da is selected from supervised machine learning algorithms as it is superior to the commonly used tools as well as other multivariate statistical methods with the accumulation of geochemical data of source rocks and oils in the slope of the qikou depression the main source rocks in the third es3 and first members es1 of the paleogene shahejie formation were deposited in similar depositional environments the source rocks cannot be distinguished with the commonly used tools we firstly extended geochemical parameters and then used stepwise da to select informative parameters and to develop a discriminant model for oil source correlation the 22 selected parameters are supported by geochemical characteristics of the source rocks in the study area the da of these parameters for oil source correlation achieved a high correct rate of original validation 96 8 and leave one out cross validation 89 4 indicating a sufficient discriminatory power the oil source correlation results with high posterior probabilities showing strong similarity between the sources and oils coincide with geological conditions and illustrate that there is still much exploration potential in the study area especially for the es3 petroleum system all these illustrate that da is one of the most useful tools for oil source correlation with the accumulation of geochemical data of source rocks and oils

origin of giant vein type bitumen deposits in the northwestern junggar basin nw china implications for fault controlled hydrocarbon accumulation abstract giant vein type bitumen deposits in the wuerhe region within the northwestern junggar basin of nw china are representative examples of similar bitumen deposits that are found in a number of other locations in both china and elsewhere these deposits can provide information on regional tectonics as well as insights into hydrocarbon and bitumen exploration but the origin of the deposits remains unclear this study focuses on determining the origin of the wuerhe bitumen deposit using field petrological and geochemical data results show that the bitumen veins are generally hosted by shallow high angle fault systems located within the nose of the wuerhe fault fold the bitumen is of low maturity and has an organic origin having formed by secondary alteration most likely biodegradation of crude oil sourced from the lower permian fengcheng formation p1f the bitumen contains high concentrations of carotane and gammacerane low concentrations of ts and diasteranes and comprises in ascending order of concentration c20 c21 c23 tricyclic terpanes and c27 c28 c29 regular steranes the bitumen was most likely formed during the early cretaceous under the control of faults a fault controlled model is presented for hydrocarbon migration and accumulation and the subsequent formation of this bitumen within the northwestern junggar basin this model suggests that future hydrocarbon exploration should focus on the cores of fault fold noses and areas of minor fold nose near deep seated fault zones especially where these areas correspond to potential moderate to shallow depth jurassic cretaceous reservoirs the new model should be able to guide exploration in other basins with similar tectonic settings of this study i e superimposed thrusting compression and transtension

geological controls on focused fluid flow associated with seafloor seeps in the lower congo basin a synthesis of backscatter imagery coupled with a large 3d seismic dataset in the lower congo basin lcb reveals a patchy distribution of features interpreted to be associated with fluid seepage from 300 m to 2500 m water depth with the exception of one region of anomalous backscatter positive relief mounds all inferred seep sites occur in negative relief pockmarks the extensive 3d seismic dataset in the lcb offers a unique opportunity to study the plumbing system that is feeding surface cold seep systems and in general to reconstruct the relationship between tectonics and fluid flow in continental margins the fluid seeps in the lcb are associated with morphologically stratigraphically or tectonically controlled focused fluid flow the integration of the geophysical datasets backscatter imagery coupled to 3d seismic clearly indicates that fluid seeps are not randomly distributed but their seabed organization reflects 1 the location of the underlying structure reservoir or trap where the fluids are coming from 2 the geometry and morphology of the reservoir trap and 3 the discontinuities in the sedimentary column along which fluids have migrated in the lcb seafloor pockmarks are always associated with underlying tectonic structures fault zones salt diapirs polygonal faults or buried sedimentary bodies turbiditic channels erosional surfaces whereas they never occur above sub horizontal parallel stratified fine grained sediments even if triggering processes can not be clearly defined here we propose a model of seafloor fluid seep organization which represents a new tool for identifying the geometry of flow pathways and the underlying buried bodies where the fluids are originating from this qualitative 3d model provides insight into the geohydrologic processes of continental margins

magnetotelluric imaging of the sw japan forearc a lost paleoland revealed abstract we investigated the crustal structure of the kii peninsula in the southwestern japan forearc using the magnetotelluric mt method we found two upper crustal anomalies 1 a sub horizontal conductive layer dipping northwest at depths of 5 10 km beneath the cretaceous accreted terrane 2 a resistive block at depths of 2 15 km beneath the tertiary accreted terrane the former is interpreted as a flysh unit the latter is consistent with the high velocity structure detected by refraction experiments and may be a lost continental fragment of the kuroshio paleoland such a continental fragment has been predicted by sedimentological studies but there had been no geophysical supporting evidence the mid crustal seismicity clusters near the bottom of the resistive body this suggests that the lost paleoland is beneath the current forearc we also found a conductive layer in the deep crust consistent with seismic reflectors at 15 25 km depth this implies trapped free water reflecting a geotherm of 400 c

protection of organic matter by mineral matrix in a cenomanian black shale abstract three types of pathways degradation recondensation natural sulphurization and selective preservation are commonly considered for the formation of kerogen dispersed in sedimentary rocks a fourth pathway has been recently put forward however from studies on recent marine sediments the so called sorptive protection mechanism this pathway is based on the adsorption of otherwise labile organic compounds onto minerals thus preventing their diagenetic degradation and promoting their subsequent condensation into kerogen the main results of the present study are derived from a combination of microscopic and pyrolytic methods applied on a cenomanian kerogen they provide i evidence on an ancient material for a crucial role of the mineral matrix both in organic matter om preservation during kerogen formation and in kerogen stability once formed ii indications that the dominant protective process likely involves physical protection by minerals resulting from alternation of organic and clay nanolayers of approximately 100 nm in thickness rather than om adsorption as molecular monolayers and iii observations of the relatively poor stability of an isolated kerogen contrary to the inertness commonly assumed for fossil macromolecular organic matter

experimental study of caldera formation scaled experiments have been carried out on caldera collapse mechanisms using silicone as analogue magma and dry sand as analogue rock experiments were carried out in two and three dimensions using a range of roof aspect ratios thickness width 0 2 to 4 5 appropriate for caldera collapse they reveal a general mechanism of collapse only weakly dependent on the shape of the reservoir for low roof aspect ratios 1 subsidence starts by flexure of the roof and the formation of outward dipping reverse ring faults which in turn trigger formation of peripheral inward dipping normal ring faults the subsidence always occurs asymmetrically in cross section the reverse faults delimit a coherent piston bounded on each side by an annular zone of inwardly tilted strata located between the reverse and normal ring fault sets the surface depression consists of a nondeformed area piston surrounded by an annular extensional zone tilted strata for high aspect ratios 1 multiple reverse faults break up the roof into large pieces and subsidence occurred as a series of nested wedges 2 d or cones 3 d the extensional zone dominates the surface depression in the case where preexisting regional faults do not play a major role the collapse mechanics of calderas probably depends strongly on the roof aspect ratio calderas with low roof aspect ratios are predicted to collapse as coherent pistons along reverse faults the annular extensional zone might be the source of the large landslides that generate intracaldera megabreccias collapse into magma reservoirs with high roof aspect ratios may be the origin of some funnel calderas where explosive reaming is not dominant

formation of caldera periphery faults an experimental study changing stresses in multi stage caldera volcanoes were simulated in scaled analogue experiments aiming to reconstruct the mechanism s associated with caldera formation and the corresponding zones of structural weakness we evaluate characteristic structures resulting from doming chamber inflation evacuation collapse chamber deflation and cyclic resurgence inflation and deflation and we analyse the consequential fault patterns and their statistical relationship to morphology and geometry doming results in radial fractures and subordinate concentric reverse faults which propagate divergently from the chamber upwards with increasing dilation the structural dome so produced is characterised bysteepening in the periphery whereas the broadening apex subsides pure evacuation causes the chamber roof to collapse along adjacent bell shaped reverse faults the distribution of concentric faults is influenced by the initial edifice morphology steep and irregular initial flanks result in a tilted or chaotic caldera floor the third set of experiments focused on the structural interaction of cyclic inflation and subsequent moderate deflation following doming caldera subsidence produces concentric faults that characteristically crosscut radial cracks of the dome the flanks of the edifice relax resulting in discontinuous circumferential faults that outline a structural network of radial and concentric faults the latter form locally uplifted and tiltedwedges half grabens that grade into horst and graben structures this superimposed fault pattern also extends inside the caldera we suggest that major pressure deviations in magma chamber s are reflected in the fault arrangement dissecting the volcanoflanks and may be used as a first order indication of the processes and mechanisms involved in caldera formation

geochemistry of organic rich cretaceous and jurassic mudstones in the west lewis and west flannan basins offshore north west scotland implications for source rock presence in the north east rockall trough the west lewis and west flannan basins serve as important calibration sites for understanding the source rock distribution and quality in the north eastern part of the rockall trough in the west lewis basin two shallow boreholes penetrated organic rich oil prone bathonian mudstones which were deposited in a fresh to brackish water environment these mudstones will generate oils rich in paraffins upon maturation organic rich oil prone ryazanian mudstones were discovered in both the west lewis and west flannan basins they are offshore marine mudstones with a predominance of algal organic matter akin to the kimmeridge clay in the north sea and basins west of shetland the bathonian mudstones will generate their hydrocarbon products at higher temperatures than the ryazanian mudstones the presence of lower cretaceous and middle jurassic oil prone mudstones in basins on the hebrides shelf is intriguing and suggests that similar source rocks may be present along the north eastern margin of the rockall trough

a structural outline of the yenkahe volcanic resurgent dome tanna island vanuatu arc south pacific abstract a structural study has been conducted on the resurgent yenkahe dome 5 km long by 3 km wide located in the heart of the siwi caldera of tanna island vanuatu arc south pacific this spectacular resurgent dome hosts a small caldera and a very active strombolian cinder cone the yasur volcano in the west and exhibits an intriguing graben in its central part detailed mapping and structural observations make it possible to unravel the volcano tectonic history of the dome it is shown that following the early formation of a resurgent dome in the west a complex collapse caldera plus graben occurred and this was associated with the recent uplift of the eastern part of the present dome eastward migration of the underlying magma related to regional tectonics is proposed to explain this evolution

the laccolith stock controversy new results from the southern henry mountains utah domes of sedimentary strata at mount holmes mount ellsworth and mount hillers in the southern henry mountains record successive stages in the growth of shallow 3 to 4 km deep magma chambers whether the intrusions under these domes are laccoliths or stocks has been the subject of controversy according to g k gilbert the central intrusions are direct analogues of much smaller floored intrusions exposed on the flanks of the domes that grew from sills by lifting and bending of a largely concordant overburden according to c b hunt the central intrusions are cylindrical stocks sheathed with a zone of shattered sedimentary rocks and the small flanking sills and laccoliths grew laterally as tongue shaped masses from the discordant sides of these stocks new geologic mapping demonstrates that the sedimentary overburden now partially eroded from the domes was uplifted about 1 2 km at mount holmes 1 8 km at mount ellsworth and at least 2 5 km at mount hillers the radii of the domes are similar between 5 and 7 km the strata over the domes have a doubly hinged shape consisting of a concave upward lower hinge and a concave downward upper hinge a limb of approximately constant dip joins these two hinges and dips 20 at mount holmes 50 to 55 at mount ellsworth and 75 to 85 at mount hillers the distal portion of each dome is composed of a gently dipping peripheral limb 3 to 4 km long presumably underlain by sills and minor laccoliths although geologic cross sections and regional aeromagnetic data for the three domes are consistent with floored laccolithic central intrusions these data alone do not rule out the possibility of a stock at depth at mount hillers paleomagnetic vectors indicate that tongue shaped sills and thin laccoliths overlying the central intrusion were emplaced horizontally and were rotated during doming through about 80 of dip this sequence of events is not consistent with the emplacement of a stock and subsequent or contemporaneous lateral growth of sills and minor laccoliths growth in diameter of a stock from about 300 m at mount holmes to nearly 3 km at mount hillers as hunt suggested should have been accompanied by considerable radial shortening of the sedimentary strata and a style of folding which is not observed geologic and geophysical data and mechanical models support a laccolithic origin for the central magma chambers underlying the domes

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

organic molecular evidence of seafloor hydrocarbon seepage in sedimentary intervals down a core in the northern south china sea abstract the hydrocarbons in sedimentary organic matter om at site 4b in the pearl river mouth basin prmb northern south china sea scs were analyzed the odd even predominance oep of long chain n alkanes n c24 with cpi carbon preference index values from 1 62 to 3 80 and n c29 n c31 being the two most abundant in most of the samples are strongly indicative of a terrestrial higher plant source and the even odd predominance eop distribution of mid chain n alkanes n c16 22 suggests a marine bacterial input probably chemical autotrophic bacteria however the biomarker distributions at the 65 70 cm 80 85 cm and 85 90 cm intervals show a similar to those of crude oils which were characterized by a dominance of an unresolved complex mixture ucm in the n c20 region low cpi values 9 of total tricyclic terpanes c30 hopane these features are typical characteristics of mature om that has experienced catagenesis and metagenesis suggesting that outside hydrocarbons migrated into these three intervals in terms of petroleum systems developed in the prmb hydrocarbon seepage from deep source rocks via a diaper structure and fault system is proposed to be responsible for the occurrence of this mature om

identification of the static backstop and its influence on the evolution of the accretionary prism in the nankai trough abstract to reveal the origin of a backstop and its influence on the evolution of the accretionary prism we analyzed reflection seismic data acquired in the nankai trough off the kii peninsula the deformation features of the forearc basin sequence show that the landward accretionary prism close to the coast was not deformed after the development of the forearc basin about 2 4 ma the surface of the landward prism can be identified as strong amplitude reflector indicating that the landward prism has higher seismic velocity therefore the landward accretionary prism inferred to be of higher strength constitutes a static backstop based on seismic and geologic observations we interpret that the backstop was generated due to the large age differences of accreted material resulting from an inferred hiatus in subduction between 13 and 6 ma the time dependent processes such as the igneous activity in middle miocene further contribute to the development of the backstop a ridge structure beneath the forearc basin located trenchward of this backstop and running roughly parallel to it appears to reflect activity on an ancient splay fault the strike of the ancient splay fault runs parallel to the backstop identified in this study and oblique to the current trench this geometry suggests that location and mechanical behavior of this splay fault system is influenced by the backstop and its distribution could be related to the coseismic rupture area

oil source correlation for the paleo reservoir in the majiang area and remnant reservoir in the kaili area south china abstract there are different viewpoints on the oil source correlation of the majiang paleo reservoir and the neighbouring kaili remnant reservoir in the southern guizhou depression of china three potential source rocks in this depression could be inferred the lower cambrian marine mudstone lower silurian shale and lower permian mudstone most of the potential source rocks are of high maturity the solid bitumens and oil seepages in the southern guizhou depression suffered severe secondary alterations such as thermal degradation and biodegradation the solid bitumens of the majiang paleo reservoir are also of high maturity the oil seepages and soft bitumen of the kaili remnant reservoir were severely biodegraded all these secondary alterations may obscure oil source correlations by routine biomarkers thus it is very important to select appropriate biomarker parameters for the oil source correlation in this work biomarkers resistant to thermal degradation and biodegradation and the data of organic carbon isotopic compositions were used for the correlation the 13c values of n alkanes in asphaltene pyrolysates were also used to make oil oil and oil source correlations between severely biodegraded oils the results indicate that the lower cambrian marine mudstones are the main source for the ordovician silurian o s solid bitumens of the majiang area and the ordovician silurian oil seepages and soft bitumens of the kaili area remnant reservoir in the eastern kaili area might have been charged at least twice by the oil generated from the lower cambrian marine source rocks

rhyolite intrusions in the intracaldera bishop tuff long valley caldera california abstract drilling of the long valley exploratory well on the resurgent dome in the long valley caldera revealed 300 m cumulative thickness of granophyric intrusions within the 1180 m thick 760 ka intracaldera bishop tuff the intrusions are aphyric to sparsely plagioclase phyric high silica high barium and low strontium rhyolites they resemble the lavas of the early rhyolite the first phase of post caldera volcanism a mean 40 ar 39 ar age of 590 17 ka from a part of a shallow intrusion is coeval with early rhyolite volcanism a second mean age of 454 17 ka from the same intrusion may reflect either younger early rhyolite activity with no external equivalent or hydrothermal resetting of the argon system hydrothermal alteration of the intrusions is characterized by introduction of quartz calcite and pyrite and formation of illite smectite high co 2 content of fluids apparently inhibited zeolite formation alteration varies locally within intrusions and intrusive groups and does not vary systematically with depth oxygen shows consistent depletion of the 18 o isotope from an initial magmatic composition of 6 0 to 8 5 to values ranging from 1 4 to 0 4 the constant oxygen isotope depletion most likely reflects alteration of intrusions due to local emplacement induced hydrothermal circulation rather than a caldera scale hydrothermal system in contrast 18 o depletion of the host bishop tuff increases regularly with depth except at an intrusive contact a pre early rhyolite geothermal gradient of approximately 70 c km was inferred this is substantially higher than the current gradient but substantially lower than expected for the case of a conductive regime over a shallow residual magma chamber either the intrusions were fed from a deep chamber or a cool hydrologic recharge regime was established early in caldera history the age thickness and suspected lateral extent of these shallow intrusions are such that emplacement of the intrusions rather than inflation of a shallow chamber is responsible for resurgence of the central long valley caldera similar intrusions occur in another well on the resurgent dome lv13 21 but not in wells located off the dome

arcuate pyroclastic conduits ring faults and coherent floor at kumano caldera southwest honshu japan abstract at the 41 23 km miocene kumano caldera in southwestern japan a large arcuate pyroclastic breccia unit is interpreted as the dissected conduit for voluminous explosive eruptions the pyroclastic breccia and associated granite porphyry occur along the southern margin of the caldera these rocks collectively as much as 22 km long and 800 m wide intrude the arcuate fault bounding the southern caldera margin the breccia is interpreted as the vent facies of ash flow tuff adjacent to the caldera based on similar lithologies phenocryst modes of juvenile clasts and matrix character cataclasites along the major faults include both country rocks and pyroclastic breccia yet some cataclasite blocks are contained within the pyroclastic breccia these geometric and textural relations suggest that the faulting took place during caldera forming eruption prevolcanic sedimentary rocks enclosed by the arcuate faults are interpreted as the dissected coherent floor of the caldera which were subsided several hundreds to a thousand meters no large scale piecemeal disruption of the caldera floor is evident orientations of striations with the cataclasites and altitudes of the base of the tuff suggest the asymmetric trap door subsidence of this caldera the overall caldera geometry is the nested trap door piston cylinder subsidence each 21 15 and 25 23 km in diameter in contrast to previous interpretation of a funnel shape

caldera resurgence during magma replenishment and rejuvenation at valles and lake city calderas a key question in volcanology is the driving mechanisms of resurgence at active recently active and ancient calderas valles caldera in new mexico and lake city caldera in colorado are well studied resurgent structures which provide three crucial clues for understanding the resurgence process 1 within the limits of 40ar 39ar dating techniques resurgence and hydrothermal alteration at both calderas occurred very quickly after the caldera forming eruptions tens of thousands of years or less 2 immediately before and during resurgence dacite magma was intruded and or erupted into each system this magma is chemically distinct from rhyolite magma which was resident in each system 3 at least 1 km of structural uplift occurred along regional and subsidence faults which were closely associated with shallow intrusions or lava domes of dacite magma these observations demonstrate that resurgence at these two volcanoes is temporally linked to caldera subsidence with the upward migration of dacite magma as the driver of resurgence recharge of dacite magma occurs as a response to loss of lithostatic load during the caldera forming eruption flow of dacite into the shallow magmatic system is facilitated by regional fault systems which provide pathways for magma ascent once the dacite enters the system it is able to heat remobilize and mingle with residual crystal rich rhyolite remaining in the shallow magma chamber dacite and remobilized rhyolite rise buoyantly to form laccoliths by lifting the chamber roof and producing surface resurgent uplift the resurgent deformation caused by magma ascent fractures the chamber roof increasing its structural permeability and allowing both rhyolite and dacite magmas to intrude and or erupt together this sequence of events also promotes the development of magmatic hydrothermal systems and ore deposits injection of dacite magma into the shallow rhyolite magma chamber provides a source of heat and magmatic volatiles while resurgent deformation and fracturing increase the permeability of the system these changes allow magmatic volatiles to rise and meteoric fluids to percolate downward favouring the development of hydrothermal convection cells which are driven by hot magma the end result is a vigorous hydrothermal system which is driven by magma recharge

molecular and isotopic evaluation of the maturation history of the organic matter in an ordovician aquiclude michigan basin evidence for late diagenetic biodegradation abstract previous characterization of a low permeability 10 16 kh 10 12 m s 1 and high salinity 5 m of cl 10 seawater salinity aquiclude in upper ordovician aged sediments situated on the eastern flank of the michigan basin where a deep geological repository for low and intermediate level nuclear waste is proposed suggested a microbial origin for ch4 and co2 based on their stable isotope values ch4 is believed to have been produced and trapped during the paleozoic in a relatively discrete and high organic matter om horizon at the shale carbonate transition to further investigate the efficiency of confinement of this aquiclude here we present detailed isotopic and geochemical stratigraphic profiles of om and biomarkers with the objective of understanding the origin of ch4 and its relative timing of confinement classical diagnostic ratios of polycyclic aromatic hydrocarbons relative abundances of hopanes and degraded hopanes coupled to dual compound specific isotopic analysis of n alkanes as well as 13c analysis on different fractions of om were measured a partitioning of the ordovician sedimentary succession into two systems is observed with an upper system that is self sourced and confined hosting the microbially derived ch4 with evidence of late diagenetic om biodegradation and a lower system that reveals later secondary oil migration which has overprinted the organic geochemical record we propose a conceptual model that would explain the generation and preservation of this paleo bioreactor over time using the maturation history reconstruction derived from this dataset this work not only provides essential field empirical evidence of a relationship between methanogenesis and late diagenetic biodegradation but also shows the power of dual compound specific isotope analyses in deciphering between different maturation processes affecting om in natural subsurface settings

investigating biological nitrogen cycling in lacustrine systems by ft icr ms analysis of nitrogen containing compounds in petroleum abstract biological nitrogen cycling plays an important role in bio environmental and petroleum geochemistry until now most research has focused on marine environments using nitrogen isotopes and in contrast nitrogen cycling in lacustrine environments remains poorly understood to fill this knowledge gap we present a case study of crude oils from permian brackish and saline alkaline lacustrine rocks in the junggar basin northwestern china to complement the large variation in nitrogen isotope values in lacustrine sediments we analyzed the pyrrolic n containing compounds of crude oil using negative ion electrospray ionization fourier transform ion cyclotron resonance mass spectrometry esi ft icr ms our results show that pyrrolic compounds derived from biological sources are more abundant in oils from brackish lacustrine settings i e the jimusar sag oils of the junggar basin than in oils from alkaline lacustrine settings i e the mahu sag oils of the junggar basin which is mainly due to greater higher plant contributions to the latter higher plants provide abundant alkaloids and chlorophyll that are the biological precursors of pyrrolic n containing compounds in addition anoxic sulfate type brackish lacustrine settings provide abundant ferrous iron and sulfide that promote n fixation this study provides the first insights into biological n cycling in brackish and alkaline lacustrine systems which has significance for fossil fuel resources and their environmental impacts our data suggest that the n cycling in lacustrine systems might have an important role in entire earth system n budget

analogue models of collapse calderas and resurgent domes collapse calderas and resurgent domes are a common association related to inflation deflation processes in volcanic systems the structure of calderas and domes depends upon the permitted relative movements of crustal volumes at depth the so called space problem in order to study the structures of collapse calderas and resurgent domes and to take the space problem into account several analogue models were made dry quartz sand was used to simulate the rheology of the brittle crust while newtonian silicone putty located at the base of the sand pack simulated the ductile behaviour of the magma a piston moved the silicone putty downward or upward inducing collapse and doming within the sand three separate sets of experiments simulated 1 caldera collapse 2 resurgence and 3 superimposition of resurgence on collapse and vice versa collapse experiments are characterized by the development of two concentric depressions the first formed depression is bordered by outward dipping reverse ring faults the subsequent outer concentric depression is bordered by inward dipping normal ring faults the deformation pattern during resurgence is a function of the overburden thickness t and the dome diameter d for higher t d ratios a dome forms bordered by inward dipping high angle reverse ring faults outward dipping normal ring faults develop at late stages for lower t d ratios the dome shows at late stages a crestal depression accompanied by radial fractures subsequently an apical extrusion of silicone occurs the superimposition of resurgence over collapse and vice versa is characterized by the complete reactivation with opposite kinematics of all the pre existing ring faults during inversion both in caldera and resurgence reverse ring faults form in the early stages due to differential uplift extensional structures subsequently form to accommodate gravitational collapse during the activity of the reverse faults the experiments and the overall similarities with nature suggest that the activity of both reverse and normal faults constitutes a possible solution to the space problem during major collapses or resurgences

modes and times of caldera resurgence the 10 ka evolution of ischia caldera italy from high precision archaeomagnetic dating abstract ischia is a well exposed and densely populated late quaternary caldera in the campanian magmatic province of italy ischia caldera experienced an average uplift rate of 3 3 cm year in the last ca 30 ka and is still actively resurging during the last 10 ka coeval with the resurgence a volcanic field of alkali trachytic to trachyandesitic lava domes lava flows tuff and scoria rings and pumice cones developed mainly on the eastern sector of the caldera along both resurgence related faults and regional nnw and ne striking faults in order to improve both our understanding of the recent volcanic history and the evaluation of future risks on ischia island a high precision archaeomagnetic dating method was applied to the products of 12 volcanic centres with probable age 14 c ages archaeomagnetic and other geochronological data as well as stratigraphic constraints show that during the studied time interval ischia volcanism occurred in five periods separated by phases of quiescence and coeval with earthquake and landslide events this fact suggests a pulsating mode of uplifting and deformations of the ischia resurgence during the two oldest periods of activity 7200 6800 bc and 4100 2300 bc resurgence probably produced a dome shaped structure location and geometry of vents suggest the occurrence of magma uprise along the fractures produced by bending of the overburden crustal block most of magma was emplaced as intrusions at the interior of the resurgent block whereas volcanism was represented by very viscous differentiated and crystallized lavas that emplaced as domes and high aspect ratio flows the resurgent dome caused recurrent lateral collapses that removed about 2 5 km 3 of rocks during the three youngest periods of activity 1800 1000 bc 650 bc 355 ad and 1302 ad resurgence affected a fault bounded asymmetric block this resulted from both a hydrostatic rebound of the crustal block after removal of material involved into huge slope instability triggering an increase in uplift rate and b new influxes of less evolved magma batches into the shallow reservoir that in turn favoured the intense volcanism of the last 4000 years

middle miocene swift migration of the ttt triple junction and rapid crustal growth in southwest japan a review we review recent progress in geological and geophysical investigation in sw japan nankai trough and philippine sea plate psp and propose a hypothesis for the miocene tectonics in sw japan driven by middle miocene swift migration of the ttt trench trench trench triple junction the new hypothesis is based on the new interpretations as follows near trench magmatism in the outer zone of sw japan is ascribed to a collision of proto izu arc in addition to the previous model of an oceanic ridge of the shikoku basin and hot psp subduction the indentation structures at capes ashizuri muroto in shikoku and shiono on the kii peninsula were previously explained by kink folding due to recent e w compression we alternatively suppose the collision of the active arc or topographic peaks such as seamounts inferred from geological and experimental observations the main crustal component in sw japan is suggested to be of igneous plutonic rocks rather than the previous interpretation of cretaceous to tertiary accretionary complexes this is typically illustrated in the outer zone to the north of capes ashizuri muroto and shiono from geophysical observation of gravity anomalies velocity and resistivity together with geological estimations of caldera age and the size of its root pluton episodic crustal growth due to intrusion of igneous rock and subduction of the psp may have stopped after approximately 12 ma and restarted at approximately 6 ma our emphasis for this gap is a cessation and resurgence of subduction rather than the previous interpretation i e decreasing of subduction rate

biodegradation of 25 norhopanes in a liaohe basin ne china oil reservoir a suite of reservoir cores in an oil column from the shuguang oil field liaohe basin ne china was characterized geochemically to investigate the behaviour of 25 norhopanes nhs during biodegradation the extracted bitumens show similar organofacies type and maturity levels with biodegradation as the primary control on compositional variation all bitumens suffered severe biodegradation influence which removed all regular steranes and most of the pentacyclic terpanes leaving nhs as dominant components in total ion chromatograms of the saturated hydrocarbon fraction however the nhs are not the endpoint of hopane destruction they are biodegraded as well biodegradation of nhs can be illustrated by significant depletion in their concentrations and systematic variation in ratios of resistant to vulnerable components throughout the oil column the biodegradation sequence is somewhat similar to normal pentacyclic terpanes among the nh series 18 25 30 bisnorneohopane is the most recalcitrant to biodegradation the 18 22 25 29 30 tetranorneohopane is more resistant to biodegradation than 17 22 25 29 30 tetranorhopane and 34nhs are more resistant than other nhs degradation of nhs provides a new angle to understanding the complicated inter relationships in subsurface biodegraded reservoirs

relationships between mineral surfaces and organic carbon concentrations in soils and sediments abstract relationships between mineral specific surface area and organic carbon oc concentration are examined for sediments and soil a horizons from throughout the world i found published elsewhere that continental shelf sediments from many different regions exhibit downcore loss of oc to a refractory background level which shows a consistent relationship with mineral surface area slope 0 86 mg m 2 oc this trend is equivalent to a monolayer of organic matter over all surfaces and is termed the monolayer equivalent me level sediments and soils from other environments are compared to this empirically derived relationship several continental slope areas show extension of this relationship to considerable depth marked excesses of oc above this trend which persist downcore were found in sediments with high carbonate mineral content or slope sediments with low dissolved oxygen concentrations in the overlying water column about half of the soils examined also adhered to this relationship while soils with high carbonate content low ph or poor drainage showed oc concentrations higher than the me level oc concentrations below the me level are found in deltaic regions and areas with low organic matter delivery such as the deep sea or arid soils the nature of mineral surfaces was examined using n2 adsorption desorption isotherms and most surface area was found to be present as pores with

mechanism of caldera collapse and resurgence observations from the northern part of the kumano acidic rocks kii peninsula southwest japan abstract the northern part of the kumano acidic rocks on the kii peninsula southwest japan formed during miocene felsic igneous activity that involved caldera forming eruptions and subsequent intrusion of a massive sheetlike body of granite porphyry into intracaldera deposits detailed mapping has revealed that the northern part of the kumano acidic rocks has two separate collapse structures that show the structural margin of a caldera one is an arcuate fault zone characterized by several normal faults with gentle dips pyroclastic deposits characterized by the dominance of crystal rich welded ash vary in thickness across the fault zone the ash beds contain numerous boulders on the inner side of the collapse structure representing caldera collapse breccias sourced from the fault scarp during the caldera forming eruption the other is a 1 3 km wide ring dike of granite porphyry that encloses the prevolcanic sedimentary rocks and the pyroclastic deposits and is interpreted as a magma conduit along a subsurface circular fracture the caldera collapse area enclosed by these two structures is elliptical and about 20 30 km in size our observations suggest a coherent piston type collapse for the northern part of the caldera while asymmetric subsidence along the fault zone resulted in trapdoor or piecemeal subsidence in the southern part the ring dike is connected to the sheetlike body of granite porphyry we suggest that this sheetlike intrusion is a laccolith and may have caused resurgent doming of the caldera floor

changes in co2 during ocean anoxic event 1d indicate similarities to other carbon cycle perturbations past greenhouse intervals of the mesozoic were repeatedly punctuated by ocean anoxic events oaes major perturbations to the global carbon cycle and abrupt climate changes that may serve as relevant analogs for earth s greenhouse gas forced climate future the key to better understanding these transient climate disruptions and possible co2 forced tipping points resides in high resolution precise and accurate estimates of atmospheric co2 for individual oaes here we present a high temporal resolution multi proxy pco2 reconstruction for the onset of mid cretaceous albian cenomanian boundary oae1d coupling of pco2 estimates with carbon isotopic compositions 13c of charcoal vitrain and cuticle from the rose creek pit rcp nebraska reveals complex phasing including a lag between the well documented negative 13c excursion defining the onset of oae1d and the co2 increase this lag indicates that increased co2 or other c based greenhouse gases may not have been the primary cause of the negative excursion our study reveals a pco2 increase within the interval of the negative 13c excursion reaching a maximum of up to 840 ppm 95 confidence interval 307 ppm 167 ppm toward its end the reconstructed magnitude of co2 increase 357 ppm is similar to that of late cretaceous oae2 but of smaller magnitude than that of other major carbon cycle perturbations of the mesozoic assessed via stomatal methods e g the toarcian oae toae triassic jurassic boundary event cretaceous paleogene boundary event furthermore our results indicate a possible shared causal or developmental mechanism with oae1a and the toae