compositional variability in oils and formation waters from the ayoluengo and hontomin fields burgos spain implications for assessing biodegradation and reservoir compartmentalization abstract the main scope of this work is the geochemical characterization of 12 crude oils and formation waters of the ayoluengo oilfield basque cantabrian basin nw spain to delineate its reservoir compartmentalization the ayoluengo oil characteristics were also compared with data obtained from crude oil and formation water of the hontomin 2 well located 25 km to the se of ayoluengo the 13 ayoluengo and hontomin oil samples are very similar in composition bulk properties and isotopic signature indicating that these oils are genetically related however the hontomin oil is more mature and it is slightly biodegraded which suggests some differences in the reservoir environments the molecular parameters of both oils confirm a marine origin related to a liassic source rock coincident with the occurrence of lateral facies changes along the sedano sub basin on the other hand the connate waters are analogous and both classified as chloride calcium type given the complex nature of the sedimentology and structures of the reservoir gas chromatographic fingerprints of the analyzed crude oils have been used to detect minor variations in composition that are indicative of reservoir compartmentalization

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

magnetotelluric imaging of upper crustal convection plumes beneath the taupo volcanic zone new zealand 1 broadband mt magnetotelluric data were recorded that form an array of measurements at the south eastern margin of the tvz taupo volcanic zone in the central north island of new zealand these array data are used to investigate mechanisms by which the tvz s extraordinarily high heat flux is transported to the surface taken together with seismological data these mt data show compelling evidence that support a model of hydrothermal convection within the brittle upper 6 7 km part of the crust both 2 d and 3 d inversion models of these mt data show vertical low resistivity zones that connect surface geothermal fields to an inferred magmatic heat source that lies below the brittle ductile transition

biomarker maturity parameters for high maturities calibration of the working range up to the oil condensate threshold abstract in a study of oils and source rocks from the kimmeridge clay united kingdom and the hanifa qatar formations several biomarker maturity parameters with working ranges up to vr e vitrinite reflectance equivalent 1 0 oil condensate threshold have been identified and calibrated this represents a significant improvement compared to commonly used biomarker maturity tools sterane and hopane isomerisation with their maturity maximum of approximately vr e 0 7 early part of oil window these new parameters are 1 the absolute concentrations of steranes and hopanes decreasing gradually with increasing maturity 2 the ratio of tricyclic terpanes tricyclic terpanes hopanes increasing with maturity 3 the ratio of diasteranes 14 h 17 h steranes depending both on maturity and on source rock lithology and 4 the ratio of t s t m 22 29 30 trisnorneohopane 22 29 30 trisnorhopane increasing rapidly at very high maturities during artificial maturation experiments the biomarker maturities described in the natural samples were also known to be time temperature dependent up to rather severe laboratory heating conditions this corresponds with the working range up to high maturity levels as observed in the natural samples

magma chamber and crustal channel flow structures in the tengchong volcano area from 3 d mt inversion at the intracontinental block boundary southeast of the tibetan plateau

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

crustal structure beneath aso caldera southwest japan as derived from receiver function analysis abstract aso volcano experienced a huge pyroclastic eruption 90 thousand years ago and formed a large caldera 18 km 25 km in order to test the hypothesis of a magma body in the mid and lower crust that has been suggested geophysically and geochemically we investigated seismic velocity discontinuities and velocity structure beneath aso caldera using receiver functions and a genetic algorithm inversion we confirm the existence of the moho at depths between 30 km and 35 km and a large velocity anomaly should exist in the deep portion of the crust beneath aso caldera from imaging of receiver functions observed only at stations outside the caldera as a result of a more detailed examination with ga inversion a low velocity layer is detected at depths between 10 km and 24 km beneath the western part of the caldera s wave velocity of the layer is estimated to be 2 0 2 4 km s we estimate that the low velocity layer contains at most 15 melt or 30 aqueous fluid the layer exists near the conrad and at the same depths as the swarm of the low frequency earthquakes and a compressional and dilatational deformation source which are expected to be caused by fluid movement beneath the middle eastern part of the caldera fluid contained in the layer might be related with huge pyroclastic eruptions of aso volcano

magma recharging beneath the weishan volcano of the intraplate wudalianchi volcanic field northeast china implied from 3 d magnetotelluric imaging

organic geochemical characteristics of the mesoproterozoic hongshuizhuang formation from northern china implications for thermal maturity and biological sources abstract the mesoproterozoic hongshuizhuang formation 1 4 ga from northern china consists of organic rich sediments which record important environmental and biological information from that time organic and element geochemistry techniques were used to assess the syngeneity and indigeneity of hydrocarbons and the thermal maturity and biological sources of the organic matter in the hongshuizhuang formation results from a slice extraction experiment indicate that the exterior of the core was subjected to contamination from drilling sampling and storage whereas the organic matter in the interior shale core slices was indigenous the organic matter in the interior argillaceous dolomite core slices might have been affected by the migration of oil it is important to remove the outside of the core prior to solvent extraction as this increases the possibility of analysis of indigenous hydrocarbons the source rocks of the oil are the black shales of the hongshuizhuang formation aliphatic and aromatic hydrocarbon distributions indicate that the hongshuizhuang formation samples have a low thermal maturity in the early to middle oil window 0 6 0 8 ro equivalent based on comparison with middle velkerri formation rocks of about the same age in the mcarthur basin northern australia these data are consistent with results based on the values of tmax and protobitumen reflectance and suggest that the samples contain well preserved organic matter that has not been thermally destroyed the redox conditions indicated by the pristane phytane pr ph ratios are not consistent with other evidence the correlations between n c20 n c21 major elements and pr ph indicate that the pr ph ratios are influenced by biological sources and mineralogy rather than by redox conditions pr and ph may have been derived not only from chlorophyll a but also from archaea the short and long chain n alkanes in the hongshuizhuang formation were derived from anoxic clay rich environments and oxic carbonate rich environments respectively the biomarkers observed in the hongshuizhuang formation indicate that the organic matter was primarily derived from prokaryotes

sterane isomerisation and moretane hopane ratios in crude oils derived from tertiary source rocks the extent of sterane isomerisation reactions and the moretane hopane ratios of 234 crude oils taken world wide from a wide variety of source rocks of differing geological ages have been measured this data indicates that in 78 crude oils derived from tertiary source rocks sterane isomerisation reactions as determined by the 20s 20s 20r ration of the c29 5 h 14 h 17 h normal steranes and the c29 iso iso normal ratio iso 5 h 14 h 17 h are mainly incomplete and sometimes considerably so in addition the same crude oils have 17 h 21 h moretane 17 h 21 h hopane ratios which are significantly greater predominantly in the range 0 10 0 30 than those of crude oils derived from older mature source rocks mainly less than 0 1 this data for crude oils lends support to the hypothesis proposed by mackenzie and mckenzie 1983 for source rock extracts that the time temperature constraints of sterane isomerisation reactions are such that the time available for isomerisation in tertiary sediments is generally insufficient despite generation of crude oil at relatively high temperatures an alternative hypothesis is that the incomplete sterane isomerisation of tertiary crude oils may be due to generation of these crude oils from their deltaic land plant containing source rocks under low heating conditions a third hypothesis proposes that the tertiary crude oils may have picked up the incompletely isomerised steranes from immature sediments during migration although possible in particular instances such a mechanism does not appear to be generally applicable since in that case the phenomenon would then appear to be restricted to the tertiary the higher moretane hopane ratios of the tertiary crude oils could suggest that constraints similar to those applying in sterane isomerisation also operate in the conversion of moretane to 17 h hopane

molecular correlation of crude oils and oil components from reservoir rocks in the tazhong and tabei uplifts of the tarim basin china molecular data from a large set of source rock crude oil and oil containing reservoir rock samples from the tarim basin demonstrate multiple sources for the marine oils in the studied areas of this basin based on gammacerane c31 hopane and c28 c27 c 28 c 29 sterane ratios three of the fifteen crude oils from the tazhong uplift correlate with cambrian lower ordovician source rocks while the other crude oils from the tazhong uplift and all 39 crude oils from the tahe oilfield in the tabei uplift correlate with middle upper ordovician source rocks these two ratios further demonstrate that most of the free oils and nearly all of the adsorbed and inclusion oils in oil containing reservoir rocks from the tazhong uplift correlate with cambrian lower ordovician source rocks while the free and inclusion oils in oil containing carbonates from the tahe oilfield correlate mainly with middle upper ordovician source rocks this result suggests that crude oils in the tazhong uplift are partly derived from the cambrian lower ordovician source rocks while those in the ordovician carbonate reservoirs of tahe oilfield are overwhelmingly derived from the middle upper ordovician source rocks the scatter of c23 tricyclic terpane c23 tricyclic terpane c30 17a 21b h hopane and c21 c21 rc29 sterane ratios for the free and inclusion oils from oil containing carbonates in the tahe oilfield possibly reflects the subtle organofacies variations in the source rocks implying that the ordovician reservoirs in this oilfield are near the major source kitchen in contrast the close and positive relationship between these two ratios for oil components in the oil containing reservoir rocks from the tazhong uplift implies that they are far from the major source kitchen

unusual biomarker maturation ratio changes through the oil window a consequence of varied thermal history abstract saturated and aromatic biomarker ratios continue to change systematically through the oil window and into the gas condensate window to high vitrinite reflectances r o 1 16 in mature marine and lacustrine mesozoic clastic samples from a south african basin two of the ratios reverse above r o 0 9 these unusual maturation effects result from isolated periods of high rates of maturation increase the basin cooled regionally after the break up of gondwana but high heating rates prevailed during the late cretaceous early tertiary as africa moved across a hotspot and again in the late tertiary as a result of a possible hotspot and hydrothermal event

generation and expulsion of oils from permian coals of the sydney basin australia abstract organic geochemical and petrological assessment of coals coaly shales and fine grained sediments coupled with organic geochemical analyses of oil samples all from permo triassic sections of the southern sydney basin australia have enabled identification of the source for the widely distributed oil shows and oil seeps in this region the permian coals have higher hydrogen indices higher liptinite contents and much higher total organic matter extract yields than the fine grained sediments a variety of source specific parameters obtained from n alkanes regular isoprenoids terpanes steranes and diasteranes indicate that the oil shows and seeps were generated and expelled predominantly from higher plant derived organic matter deposited in oxic environments the source and maturity related biomarkers and aromatic hydrocarbon distributions of the oils are similar to those of the coals the oil coal relationship also is demonstrated by similarities in the carbon isotopic composition of the total oils coal extracts and their individual n alkanes extracts from the permo triassic fine grained sediments on the other hand have organic geochemical signatures indicative of mixed terrestrial and prokaryotic organic matter deposited in suboxic environments which are significantly different from both the oils and coal extracts the molecular signatures indicating the presence of prokaryotic organic matter in some of the coal extracts and oils may be due to thin sections of possibly calcareous lithologies interbedded within the coal measures the genetic relationship between the oils and coals provides new evidence for the generation and expulsion of oils from the permian coals and raises the possibility for commercial oil accumulations in the permian and early triassic sandstones potentially in the deeper offshore part of the sydney basin

radiolarian palaeoecology and radiolarites is the present the key to the past abstract radiolarian productivity pulses and related radiolarite deposition are phenomena difficult to understand from an exclusively actualistic viewpoint evolutionary selection pressure among silica secreting marine plankton both radiolarians and diatoms has led toward more economic usage of rapidly shrinking nutrient resources including dissolved silica of the photic zone in the late cenozoic oceans and in particular a substantial modification of oceanic cycle by the diatom explosive radiation even if there is a proved link between biomineralization and dissolved silica loading among the phytoplankton only the relative independence of modern siliceous planktic biotas from the available silica pool reflects mainly their progressive physiological specialisation during evolutionary history oceanic chemistry and productivity as well as patterns of circulation upwelling have changed radically during the phanerozoic radiolarites apparently represent an anachronistic facies as exemplified by their long lived and ocean wide distribution in palaeo pacific and hitherto highlighted actualistic models of localized intra oceanic wind driven upwelling loci are of largely questionable applicability in addition to plate drift hypersiliceous domains and intervals are explainable mostly by a large scale volcano hydrothermal activity during major plate boundary reconfigurations which in many ways favoured siliceous biotas acme and their skeletal remains accumulation and preservation factors tied to rapid voluminous submarine eruptions such as thermal buoyant megaplumes and basin overturns offer a viable alternative for traditional climatic circulation scenarios in case of hypersiliceous high productivity events irrelevant to greenhouse to icehouse climatic change the evolving carbon and silica cycles were coupled through the greenhouse effect and enhanced chemical weathering volcano hydrothermal and tectonic uplift events related mostly to extensive rifting and or accelerated oceanic spreading were the endogenous driving force that created this perturbation of the exogenous system the present biogeochemical cycle is representative only for the overall silica depleted post eocene oceanic ecosystems which broadly correlates with a major expansion of diatoms groups extremely efficient in silica removal and closely linking the silica budget with phosphorus and nitrogen cycles thus an orthodox uniformitarian approach to biosiliceous sedimentation based on a silica starved vigorous ocean is of limited significance when applied to the pre neogene settings especially in the peculiar planktic habitats of epeiric seas as well as during biotic crises marked by strong geotectonic overprint the major turnovers in marine siliceous biota composition in particular after the end permian radiolarite gap may have been coupled with discernible changes in an increasing biological control on the long term oceanic silica cycling punctuated equilibrium the evolutionary turnovers have induced a stepdown decrease of dissolved silica levels through the phanerozoic contemporaneously with the general secular trend of upward scaling of nutrient related ecological processes and increased effectiveness of resource utilization

mushy magma beneath yellowstone a recent prospective on the yellowstone caldera discounts its explosive potential based on inferences from tomographic studies which suggests a high degree of crystallization of the underlying magma body in this study we show that many of the first teleseismic p wave arrivals observed at seismic stations on the edge of the caldera did not travel through the magma body but have taken longer but faster paths around the edge after applying a number of waveform modeling tools we obtain much lower seismic velocities than previous studies 2 3 km sec v p and 1 1 km sec v s we estimate the physical state of the magma body by assuming a fluid saturated porous material consisting of granite and a mixture of rhyolite melt and water and co 2 at a temperature of 800 c and pressure at 5 km 0 1 gpa we found that this relatively shallow magma body has a volume of over 4 300 km 3 and is about 32 melt saturated with about 8 water plus co 2 by volume

paleoreconstruction by biological markers abstract during diagenesis and conversion of the original lipid fraction of biological systems to petroleum hydrocarbons the following four basic events needed for paleoreconstruction can be monitored by biological markets 1 sourcing 2 maturation 3 migration and 4 biodegradation actual cases of applying biological markers to petroleum exploration problems in different parts of the world are demonstrated cretaceous and phosphoria sourced oils in the wyoming thrust belt can clearly be distinguished from one another by high quality source fingerprinting of biomarker terpanes using gas chromatography mass spectrometry identification of recently discovered biological markers head to head isoprenoids allows subtle source differentiation between oils from sumatra the degree of crude oil maturation in basins from california alaska russia wyoming and louisiana can be assessed by specific novel biomarker ratios 20s 20r sterane epimers field evidence from such interpretation is confirmed by laboratory pyrolysis of the rock an example of immature sumatra rock is given extensive migration is documented by biomarkers in several oils the effect of biodegradation on biomarker steranes and terpanes is exemlified in a california basin all biological marker results are consistent with the geological setting and add a new dimension in assisting the petroleum explorationist toward paleo reconstruction

the influence of elastic thickness non uniformity on viscoelastic crustal response to magma emplacement application to the kutcharo caldera eastern hokkaido japan

pore pressure embrittlement in a volcanic edifice the failure mode of porous rock in compression dilatant or compactant is largely governed by the overlying lithostatic pressure and the pressure of pore fluids within the rock wong solid earth 102 3009 3025 1997 both of which are subject to change in space and time within a volcanic edifice while lithostatic pressure will tend to increase monotonously with depth due to the progressive accumulation of erupted products pore pressures are prone to fluctuations during periods of volcanic unrest for example an increase in pore fluid pressure can result in rock fracture even at depths where the lithostatic pressure would otherwise preclude such dilatant behaviour a process termed pore fluid induced embrittlement we explore this phenomenon through a series of targeted triaxial experiments on typical edifice forming andesites from volcan de colima mexico we first show that increasing pore pressure over a range of timescales on the order of 1 min to 1 day can culminate in brittle failure of otherwise intact rock irrespective of the pore pressure increase rate we record comparable accelerations in acoustic emission and strain prior to macroscopic failure we further show that oscillating pore fluid pressures can cause iterative and cumulative damage ultimately resulting in brittle failure under relatively low effective mean stress conditions we find that macroscopic failure occurs once a critical threshold of damage is surpassed suggesting that only small increases in pore pressure may be necessary to trigger failure in previously damaged rocks finally we observe that inelastic compaction of volcanic rock as we may expect in much of the deep edifice can be overprinted by shear fractures due to this mechanism of embrittlement pore fluid induced embrittlement of edifice rock during volcanic unrest is anticipated to be highest closer to the conduit and as a result may assist in the development of a fractured halo zone surrounding the conduit potentially explaining commonly observed near conduit outgassing at many active volcanoes further rock embrittlement at depth may create transient outgassing pathways by linking fracture networks near the edifice to larger scale regional fault systems our experimental results affirm that pore pressure fluctuations associated with volcanic unrest may play a crucial role in dictating the evolution of a volcanic system

the 2016 kumamoto mw 7 0 earthquake a significant event in a fault volcano system the 2016 kumamoto earthquake sequence occurred on the futagawa hinagu fault zone near the aso volcano on kyushu island the sequence was initiated with two major m w 6 0 foreshocks and the mainshock m w 7 0 occurred 25 h after the second major foreshock we combine gps strong motion synthetic aperture radar images and surface offset data in a joint inversion to resolve the kinematic rupture process of the mainshock and coseismic displacement of the foreshocks the joint inversion results reveal a unilateral rupture process for the mainshock involving sequential rupture of four major asperities the slip area of the foreshocks and mainshock and the aftershock loci form a detailed complementary pattern the mainshock rupture terminates near the rim of the caldera leaving a 10 km long gap of aftershocks this area is characterized by high temperature and low shear wave velocity density and resistivity which may be related to the partially melted geothermal condition ductile material property near the volcano may act as a material barrier to the dynamic rupture topographic weight of the caldera increases compressional normal stress on the fault plane which may behave as a stress barrier long term seismic hazard and deformation behaviors related to these two types of barriers are discussed in terms of the associated frictional mechanism significant postseismic creeps observed near the volcano area indicates a velocity strengthening frictional behavior near the rupture termination which confirms that the material barrier mechanism is likely the dominant rupture termination mechanism

geochemical anomalies at the cenomanian turonian boundary northwest new mexico a high resolution section of 64 carbonates and calcareous shales from northwest new mexico spanning the cenomanian turonian c t boundary is examined for selected elemental concentrations as well as carbon isotopic and molecular distributions spatial and temporal sampling resolutions for the entire sample set are 1 spl 19 cm and 1 spl 33 ka respectively in proximity to the c t boundary respective spatial and temporal resolutions increase to 1 spl 10 cm and 1 spl 17 ka results show the occurrence of several geochemical anomalies all with coincident maxima at about 0 5 m below the c t boundary stable carbon isotope ratios of the kerogen and the aliphatic and aromatic hydrocarbon fractions increase by approximately 4 within 20 m of the boundary this entire c t boundary event isotope anomaly occured over approximately 2 5 ma a 5 fold increase in the concentrations of u and th occurs synchronous with the isotope excursion although this u th spike occurs over a period of only 0 2 0 3 ma elevated u and th concentrations at this spike co occur with a the highest 20s 20s 20r sterane epimer ratios b c27 c27 30 sterane homolog ratios and c the lowest n alkane yields in kerogen pyrolyzates these observations suggest an effect of radiogenic heat production on the organic matter in the section the origin of the carbon isotope excursion is attributed as in previous studies to atmospheric co2 drawdown in latest cenomanian time caused by rapid burial of organic matter due to a global marine transgression the u and th spike is probably secondary perhaps resulting from adsorption of these elements onto clays concentrated at the c t boundary although the occurrence of coeval maxima for these isotopic and elemental anomalies suggests a common cause extrapolation of the co2 drawdown model to explain the u th anomaly is unwarranted at this time ongoing mineralogical analysis of clays and carbonates close to the c t boundary in the red wash section may ultimately explain the occurrence of this u and th spike

crustal magma pathway beneath aso caldera inferred from three dimensional electrical resistivity structure at naka dake cone aso caldera japan volcanic activity is raised cyclically an example of which was a phreatomagmatic eruption in september 2015 using a three dimensional model of electrical resistivity we identify a magma pathway from a series of northward dipping conductive anomalies in the upper crust beneath the caldera our resistivity model was created from magnetotelluric measurements conducted in november december 2015 thus it provides the latest information about magma reservoir geometry beneath the caldera the center of the conductive anomalies shifts from the north of naka dake at depths 10 km toward naka dake along with a decrease in anomaly depths the melt fraction is estimated at 13 15 at 2 km depth moreover these anomalies are spatially correlated with the locations of earthquake clusters which are distributed within resistive blocks on the conductive anomalies in the northwest of naka dake but distributed at the resistive sides of resistivity boundaries in the northeast

reservoir characterization and hydrocarbon accumulation in late cenozoic lacustrine mixed carbonate siliciclastic fine grained deposits of the northwestern qaidam basin nw china abstract late cenozoic lacustrine mixed carbonate siliciclastic sequences in the northwestern qaidam basin nw china are mainly composed of high porosity and low permeability fine grained rocks but have big potentials of oil gas commercial production however how these fine grained rocks generate high quality reservoirs and accumulate hydrocarbons remains poorly known this study focuses on shallow buried shang youshashan formation middle late miocene n22 and shizigou formation late miocene pliocene n23 reservoirs and hydrocarbons in xiaoliangshan area of the northwestern qaidam basin we conduct mineralogy petrography and porosity and permeability analysis for reservoir rocks and biomarker analysis for hydrocarbons and potential source rocks the results indicate that the n22 high quality reservoirs are dominated by fractured marlstones and lime mudstones and constitute structural traps whereas the n23 hydrocarbon reservoirs are mainly composed of siliciclastic dominantly rocks and form stratigraphic lithologic traps similar biomarker ratios between crude oil samples and paleogene organic matter rich rocks reveal that hydrocarbons in the shallow system were likely derived from deep buried source rocks rather than late cenozoic lacustrine fine grained rocks themselves in this case large scale vertical fractures created by kink band structures in the northwestern qaidam basin are supposed to facilitate hydrocarbon migration and accumulation preliminary production data and exploration well oil gas test results demonstrate highest yields and thus large hydrocarbon potentials in the n22 marlstone and lime mudstone reservoirs collectively we suggest that relatively high permeability fractured and carbonate rich reservoirs on structural highs are favorable targets for future oil gas exploration in the northwestern qaidam basin this petroleum system provides a typical and significant example for hydrocarbon exploration and development in mixed carbonate siliciclastic fine grained rocks of nonmarine petroliferous basins

three dimensional electrical resistivity structure of the kuju volcanic group central kyushu japan revealed by magnetotelluric survey data abstract the kuju volcano group in the southwestern part of the oita prefecture japan consists of more than 20 volcanoes distributed over an area of approximately 400 sq km on october 11 1995 a phreatic eruption occurred on the eastern flank of mt hossho in the central part of the kuju volcano a second eruption occurred in mid december 1995 producing an ash volume of approximately 5000 m3 therefore clarifying the thermal and hydrologic processes occurring beneath the entire kuju volcano area is important because the geothermal areas beneath active volcanoes may be important to the development of geothermal energy the largest geothermal power plant in japan otake hatchobaru power plant 120 mw is located 5 km west of mt hossho and mt iwoyama to identify the structures associated with the hydrothermal systems beneath the kuju volcano area we performed a wide band magnetotelluric survey the survey data were collected at 63 observation points around the kuju volcano from september october 2015 the resulting primary three dimensional resistivity structure model clarified that a resistivity structure 50 m predominates the kuju volcano area a highly conductive structure 10 m exists around the iwoyama kuju area extending in depth towards the northeastern part of iwoyama based on the results of previous studies the former can be interpreted as a lava and pyroclastic deposit whereas the latter corresponds to a magmatic fluid pathway and hydrothermal altered layers

real time and in situ assessment of conduit permeability through diverse long period tremors beneath aso volcano japan abstract long period signal lps 0 2 2 s and very long period signal vlp 2 100 s observed in the shallow volcanic plumbing system are typically repetitive and time invariant in their location and source mechanism offering in situ probes of hot fluid transport over the eruption cycles while the amplitude and activity of volcanic tectonic earthquakes and lp events have been commonly used to infer overpressure within their source region one missing link is an observable that may permit inference on the change in the permeability of the conduit plug wall which can regulate the degree of pressurization affect the mechanical strength of the surrounding rock and consequently the likelihood of an upcoming eruption here we show that during the 2011 2016 eruption cycle at aso volcano in japan long period tremor events a vlp of 15 s period with opposite waveform polarity can be systematically detected and categorized as pressurization and depressurization events in the same crack like conduit we suggest that depending on the strength of the surrounding rock and the permeability of the crack like conduit wall plug pressurization due to magmatic heat and vaporization is more likely to occur when a less permeable conduit plug wall can effectively keep the gas inside the crack like conduit on the other hand depressurization is prone to occur if the conduit wall plug permeability is sufficiently high to allow gas to escape from the conduit considering the amplitude of lpt proportional to the conduit overpressure contrasting energetics of these diverse lpt events allows us to define whether the conduit is prone to pressurization or depressurization providing a framework to infer how the permeability of the conduit wall plug may evolve over an eruption cycle

three dimensional electromagnetic imaging of upwelling fluids in the kyushu subduction zone japan a three dimensional 3 d lithospheric scale electrical resistivity model developed using network magnetotelluric network mt data contains structures associated with arc magmatism beneath kyushu island in the southwest japan arc kyushu island where the philippine sea plate psp subducts beneath the eurasian plate can be divided into northern and southern volcanic regions separated by a nonvolcanic region many active quaternary volcanoes occur along the volcanic front vf associated with the psp in the two volcanic regions our 3 d electrical resistivity model shows three different shapes of upwelling fluid like conductive anomalies indicative of either slab derived aqueous fluid and or partial melt beneath the volcanic and nonvolcanic regions a conductive anomaly in the northern volcanic region located at some distance from the subducting psp extends from the surface to depths of 70 km depth extends from the surface to depths of 100 km in the nonvolcanic region the upper region of a relatively conductive anomaly extends upward to a depth of 50 km along the subducting plate the degrees of magmatism and the relative contribution of slab derived fluids to the magmatism vary spatially in the one nonvolcanic and two volcanic regions

three dimensional seismic velocity structure beneath aso volcano kyushu japan tomographic results for p and s wave velocity structure beneath the active aso volcano kyushu japan using 800 well recorded earthquakes and ten shots recorded by an eight station seismic network are presented a 68 variance reduction was achieved upon simultaneous inversion for hypocenter and velocity structure well resolved velocity anomalies associated with the active crater reveal heterogeneity up to 26 slower and 18 faster in p velocity and up to 31 slower and 22 faster in s velocity than the one dimensional model the largest anomaly is seen over the upper 11 km in the central and northern parts beneath the central cones two low velocity regions are imaged the first region a 10 15 km region encompassing the upper 3 km centered near the caldera wall at tateno valley is characterized by p velocities up to 19 slower 20 for s the second low velocity region is associated with the central cones and active magma conduit system at 6 km depth velocities as low as 4 3 km s up to 26 in p and 2 km s 31 slower in s characterize the 7 km wide volume the magma chamber is roughly spherical in shape centered at 6 km depth flattens at 10 km depth and is located between mt kishima mt eboshi and mt naka the present focus of magmatism a sharp velocity contrast at the depth of 3 km with high velocities to the southwest and lower velocities to the northeast characterizes different abutting structures associated with the oita kumamoto tectonic line

organic geochemistry of carboniferous source rocks and their generated oils from the eastern junggar basin nw china abstract carboniferous source rocks have been gaining increasing attention after the discovery of the kelameili gasfield in the eastern junggar basin in 2005 two sets of source rocks within the lower carboniferous dishuiquan formation c 1d and upper carboniferous batamayineishan formation c 2b respectively have been identified in this area in this paper clear differences between these two source rocks are demonstrated in molecular and carbon isotopic compositions the c 1d source rocks in comparison with the c 2b source rocks have remarkably lower pr n c 17 ratio higher ts ts tm and c 30 diahopane c 30 diahopane c 30 hopane ratios lower concentration of c 24 tetracyclic terpane relative to c 23 and c 26 tricyclic terpanes and higher gammacerane c 31 hopane ratio 13 c values of individual n alkanes decrease with carbon number for c 1d source rocks while the opposite is true for c 2b source rocks among the 10 oils collected from the studied area four were generated exclusively from c 1d source rocks while the others were mainly derived from c 1d source rocks but contaminated by a small or trace amount of oil components which were derived from the c 2b middle permian pingdiquan formation p 2p and lower jurassic source rocks the free adsorbed and inclusion oils from three oil containing volcanic reservoir rocks within the c 2b formation generally correlate with c 1d source rocks based on molecular and carbon isotopic data however the three types of oil from the same reservoir rock vary significantly in molecular and carbon isotopic compositions reflecting facies and maturity changes of charging oil during the reservoir filling

depositional environment and hydrocarbon source potential of the permian gondwana coals from the barapukuria basin northwest bangladesh article barapukuria coal basin is situated in dinajpur district of the northwestern part of bangladesh a total of eight coal samples have been collected from two different locations of the basin and analyzed using organic geo chemical and organic petrological methods the extracted organic matter of the studied samples is a mixture of type iii and type ii kerogen as evaluated by the source rock analyzer sra and pygc pyrograms the measured total organic carbon toc ranges from 61 to 74 wt and the recovered extractable organic matter eom varies from 27 561 to 41 389 ppm these results suggest that the coals are ranked as good quality source rock the hydrocarbon yield has been calculated which is also high and it ranges from 12 192 to 20 799 ppm the organic matter is thermally mature for hydrocarbon generation considering their tmax and measured mean vitrinite reflec tance values of 431 to 435 c and 0 72 to 0 81 ro respectively the hopane 22s 22s 22r moretane hopane ratio and sterane parameters are also in support of these thermal maturity assessment

light hydrocarbon gasoline range parameter refinement of biomarker based oil oil correlation studies an example from williston basin abstract we evaluated geochemical compositions of 189 crude oils produced from paleozoic reservoirs across the williston basin emphasis is placed on compositional variations in the gasoline range i c 5 h 12 n c 8 h 18 to verify the biomarker based classification of oil families the oils belong to four distinct compositional oil families a b c and d broadly confined to specific stratigraphic intervals the unique character of each oil family evident from their n alkane and biomarker signatures is supported by distinctive gasoline range characteristics in general and c 7 mango parameters in particular an invariance in the k1 parameter among oils from a single compositional group is observed for most of the oils the k1 ratio although relatively constant within each suite of oils is different for each oil family clearly indicating their compositional distinction other mango parameters n2 p2 p3 show a similar reflection of the oil families however while c 7 parameters provide excellent evidence for distinct familial association of oils from families a b and d family c often overlaps with the latter two families perhaps indicating greater genetic and source heterogeneity in the family c oils nevertheless differences in the gasoline range composition suggest that the existing biomarker based classification of oil families can be more universally applied throughout the entire williston basin moreover because the light hydrocarbon parameters prove very useful in refining oil oil correlations routine gasoline range analysis shows good potential as a supplementary component in geochemical correlation of crude oils especially when high levels of thermal maturity decrease the usefulness of biomarker compounds

the ratios of dibenzothiophene to phenanthrene and pristane to phytane as indicators of depositional environment and lithology of petroleum source rocks abstract the ratio of dibenzothiophene to phenanthrene and the ratio of pristane to phytane when coupled together provide a novel and convenient way to infer crude oil source rock depositional environments and lithologies such knowledge can significantly assist in identifying the source formation s in a basin thereby providing valuable guidance for further exploration the ability to infer this information from analysis of a crude oil is especially valuable as frequently the earliest samples in a new area may be shows and or drill stem test samples from exploratory wells which are characteristically drilled on structural highs stratigraphically remote from the source formation s a cross plot of dibenzothiophene phenanthrene versus the pristane phytane ratios measured on seventy five crude oils from forty one known source rocks ranging in age from ordovician to miocene consistently classified the oils into the following environment lithology groups marine carbonate marine carbonate mixed and lacustrine sulfate rich lacustrine sulfate poor marine and lacustrine shale and fluvial deltaic carbonaceous shale and coal the dibenzothiophene phenanthrene ratio alone is an excellent indicator of source rock lithology with carbonates having ratios 1 and shales having ratios the dibenzothiophene to phenanthrene and the pristane to phytane ratios can also be used to classify source rock paleodepositional environments the classification scheme is based on the premise that these ratios reflect the different eh ph regimes resulting from the significant microbiological and chemical processes occurring during deposition and early diagenesis of sediments the dibenzothiophene phenanthrene ratio assesses the availability of reduced sulfur for incorporation into organic matter and the pristane phytane ratio assesses the redox conditions within the depositional environment interpretation of these ratios has been aided by quantitative biomarker analysis and by carbon isotope data for pristane and phytane obtained by gas chromatography isotope ratio mass spectrometry

the transfer of organic signatures from bedrock to sediment abstract a case study in the canadian arctic demonstrates how an organic geochemical signature in the regional bedrock can be transferred by erosion and redeposition to younger geological formations and surface sediments the hydrocarbon composition recorded in laurentian lower palaeozoic carbonate bedrock was incorporated into overlying miocene and quaternary formations and modern mass waste alluvium snow ice and proglacial deposits and further distant in ice rafted detritus the retention of the original geological organic signature is reflected in consistent thermal maturities hopane ratios and environmental indicators sterane distributions in the modern sediments the geological signature is variably mixed with a modern microbial organic signature reflected in high values of carbon preference index and diploptene these data show that hydrocarbon occurrences in bedrock may be detected by the analysis of surface detritus especially in carbonate terrains however they also indicate that environmental signatures may be misleading if they are inherited from older geological units

organic geochemistry of impactites from the haughton impact structure devon island nunavut canada organic matter in impactites from the 24 km wide and 39 ma old haughton impact structure canadian high arctic is a mixture of fossil and modern biological components the fossil component represents a conventional oil that was generated from lower palaeozoic marine source material before impact and permeates bedrock dolomites biomarker maturity parameters record the thermal effect of the mid tertiary impact maturity influenced sterane rearranged hopanoid and triaromatic steroid ratios all increase towards the centre of the impact structure where thermal alteration was greatest the heating was probably dominated by an impact related hydrothermal system as such systems last long enough for kinetically based thermal alteration to occur kinetically related biomarker data suggest that the hydrothermal heating lasted for c 5000 years biomarkers are also preserved in dolomite clasts within impact melt breccia and indicate strong thermal alteration modern biological contamination of the rocks is responsible for the superposition of two geochemical signatures which could be cyanobacteria non marine algae or higher plant matter onto the fossil component but they can be recognized and distinguished the data show that the impact structure system holds a record of both the pre impact organic signature and the thermal signature of the impact and thereby indicates that organic geochemistry is a valuable tool in documenting the response of rocks to impacts

imaging a low viscosity zone beneath the kutcharo caldera eastern hokkaido japan using geodetic data abstract geodetically observed volcano deformation has been analysed in terms of either elastic or viscoelastic crustal rheology for which the presence of magma has usually been considered as a deformation source from a rheological viewpoint however a magma and the peripheral rocks it influences are presumably low viscosity materials which allows detection of the presence of magma as a zone that has rheologically less strength in this study using a 3 dimensional finite element model that introduces a rectangular low viscosity zone lvz into relatively high viscosity crust the response of the linear maxwell viscoelastic crust to the emplacement of a spheroidal sill is adopted for interferometric synthetic aperture radar insar data of the kutcharo caldera eastern hokkaido japan to image a spatial crustal viscosity variation the observed temporal displacement at the surface point where the line of sight los displacement is largest in the deformation field requires the lvz to have a spatially uniform viscosity of 4 5 10 17 pa s the lvz is also required to be present immediately below a 5 km elastic layer down to mid crustal depths or deeper with a horizontal extent of at least 10 km models with acceptable minimum sizes of lvz are found to satisfy the overall temporal displacement field with root mean square misfits of less than 2 cm the geodetic data reasonably accept the presence of an lvz beneath the kutcharo caldera that is consistent with the magnetotelluric image of the accumulated magma providing the mechanical aspect of the low resistivity domain the lvz model behaviour suggests an important implication that the accumulation of magma in the middle to lower crust is detectable using geodetic data after magma emplacement into the upper crust where the deformation rate represents the degree of magmatic influence on the crustal viscosity

hydrothermal system beneath aso volcano as inferred from self potential mapping and resistivity structure abstract we conducted self potential sp surveys sequentially from part to part over the central cones of aso volcano since august 1998 by december 2001 the compiled sp map revealed large sp anomalies on the central cones the main feature of the sp map is a w shaped profile along the ns transect over the central cones it is probable that this characteristic sp profile is produced by the combination of hydrothermal upwelling in the middle and topographic effect a positive anomaly showing a large concentric pattern has appeared after correcting the topographic effect to evaluate this sp anomaly we implemented a numerical code that calculates electric potential produced by arbitrarily positioned current sources and sinks in any three dimensional resistivity structure a layered structure obtained from a time domain electromagnetic tdem field experiment was used for the resistivity model the estimated current source is 300 a being located in a conductive layer around the sea level meanwhile sinks were estimated to sit on a circular area corresponding to the marginal part of the conductive layer water and heat budget study gives a lower limit of water mass transfer from depth to the bottom of the crater lake of nakadake this value was used to estimate the equivalent current in either case of electro kinetic ek mizutani h ishido t 1976 a new interpretation of magnetic field variation associated with the matsushiro earthquakes j geomag geoelectr 28 179 188 or rapid fluid disruption rfd process johnston m j s byerlee j d lockner d 2001 rapid fluid disruption a source for self potential anomalies on volcanoes j geophys res 106 b3 4327 4335 this comparison suggests that the former process is preferable to explain the observed sp anomaly from these results we infer a large scale hydrothermal system beneath the central cones of aso volcano in which the fluid flow initiates from the surrounding area converging to the central vent to transport the heat and materials up to the crater lake of nakadake through a vapor filled conduit

tomography from 26 years of seismicity revealing that the spatial extent of the yellowstone crustal magma reservoir extends well beyond the yellowstone caldera the yellowstone volcanic field has experienced three of earth s most explosive volcanic eruptions in the last 2 1 ma the most recent eruption occurred 0 64 ma forming the 60 km long yellowstone caldera we have compiled earthquake data from the yellowstone seismic network from 1984 to 2011 and tomographically imaged the three dimensional p wave velocity vp structure of the yellowstone volcanic system the resulting model reveals a large low vp body interpreted to be the crustal magma reservoir that has fueled yellowstone s youthful volcanism our imaged magma body is 90 km long 5 17 km deep and 2 5 times larger than previously imaged the magma body extends 15 km ne of the caldera and correlates with the location of the largest negative gravity anomaly a 80 mgal gravity low this new seismic image provides important constraints on the dynamics of the yellowstone magma system and its potential for future volcanic eruptions and earthquakes

the preservation of fossil biomarkers during meteorite impact events experimental evidence from biomarker rich projectiles and target rocks a devonian siltstone from orkney scotland shows survival of biomarkers in high velocity impact experiments the biomarkers were detected in ejecta fragments from experiments involving normal incidence of steel projectiles at 5 6 km s 1 and in projectile fragments from impact experiments into sand and water at 2 5 km s 1 the associated peak shock pressures were calculated to be in the range of 110 147 gpa for impacts of the steel projectiles into the siltstone target and hydrocode simulations are used to show the variation of peak pressure with depth in the target and throughout the finite volume projectiles thermally sensitive biomarker ratios including ratios of hopanoids and steranes and the methylphenanthrene ratio showed an increase in thermal maturity in the ejecta and especially the projectile fragments measurement of absolute concentrations of selected biomarkers indicates that changes in biomarker ratios reflect synthesis of new material rather than selective destruction their presence in ejecta and projectile fragments suggests that fossil biomarkers may survive hypervelocity impacts and that experiments using biomarker rich rock have high potential for testing survival of organic matter in a range of impact scenarios

assessing the syngeneity and indigeneity of hydrocarbons in the 1 4 ga velkerri formation mcarthur basin using slice experiments abstract many applications involving analysis of the hydrocarbons in petroleum systems rely upon the assumption that there has been no contamination of the sample precambrian basins are particularly susceptible to hydrocarbon overprinting from contamination due to both age and commonly a low total organic carbon toc content in this study three cores mcmanus 1 walton 2 and shea 1 from the deep marine 1 46 ga old velkerri formation mcarthur basin were subjected to slice experiments and analysis using gas chromatography mass spectrometry gc ms internal slices had consistent hydrocarbon signals providing strong evidence that the organic matter om in the inner slices was indigenous in all three cores both the aliphatic and aromatic hydrocarbon signatures indicated that the exterior of the core was exposed to contamination from both the drilling and sawing processes this contamination overprinted and had the potential to completely obscure the indigenous hydrocarbon signal highlighting the importance of the removal of the exterior portion of the core prior to analysis even for organic rich rocks aromatic ratios indicated all cores were within the oil window and that mcmanus 1 had the highest maturity and walton 2 the lowest walton 2 was the only core to contain biomarkers above the limit of detection lod evidence of high bacterial input to the om included the presence of hopanes bicyclic sesquiterpanes and monomethyl alkanes steranes were absent or below the lod in all cores suggesting a very low or zero contribution from eukaryotes to this deep water low o 2 depositional environment

evidence for the contemporary magmatic system beneath long valley caldera from local earthquake tomography and receiver function analysis 1 we present a new p wave and s wave velocity model for the upper crust beneath long valley caldera obtained using local earthquake tomography and receiver function analysis we computed the tomographic model using both a graded inversion scheme and a traditional approach we complement the tomographic vp model with a teleseismic receiver function model based on data from broadband seismic stations mlac and mkv located on the se and sw margins of the resurgent dome inside the caldera the inversions resolve 1 a shallow high velocity p wave anomaly associated with the structural uplift of a resurgent dome 2 an elongated wnw striking low velocity anomaly 8 10 reduction in vp at a depth of 6 km 4 km below mean sea level beneath the southern section of the resurgent dome and 3 a broad low velocity volume 5 reduction in vp and as much as 40 reduction in vs in the depth interval 8 14 km 6 12 km below mean sea level beneath the central section of the caldera the two low velocity volumes partially overlap the geodetically inferred inflation sources that drove uplift of the resurgent dome associated with caldera unrest between 1980 and 2000 and they likely reflect the ascent path for magma or magmatic fluids into the upper crust beneath the caldera

molecular correlation of free oil and inclusion oil of reservoir rocks in the junggar basin china free oils and inclusion oils oil bearing fluid inclusions of 12 samples collected from the sandstone reservoir formations in the central eastern and northern areas of the junggar basin northwest china were analyzed by gc and gc ms analytical results indicate very similar biomarker distributions within each of the free oils and their associated inclusion oils in the two samples collected respectively from the northwestern and eastern border of the junggar basin the free oil and inclusion oil of sample md1 1 collected from the northwestern border correlate well with the permian source rock of the fencheng formation while those of sample dn1 1 from the eastern border correlate with the permian source rock of the pingdiquan formation in contrast in the central area the free and inclusion oils vary significantly in most cases which suggests variations of sources for oil charges during the filling process these data and the correlation between the free and inclusion oils are consistent with the field and seismic data which show that in areas where samples md1 1 and dn1 1 are located only one available source rock exists while in the central area multiple source rocks are present

mud volcanism and fluid geochemistry in the cheleken peninsula western turkmenistan abstract a geological and geochemical study has been carried out to investigate the relationships between major mud volcano structures and deep fluid migration in the cheleken peninsula in the south caspian basin the fluid geochemistry allowed the origin and migration of the saline waters and the hydrocarbons to be deduced along with the regional source and reservoir rocks the emitted waters formed by the mixing of deep highly saline water from the main source rocks of the maykop fm with the caspian like pore water contained in the pliocene reservoirs the water composition is very similar to that emitted by the mud volcanoes in azerbaijan allowing comparisons to be done between the reservoirs in the western and eastern sides of the south caspian basin the associated oil is derived from a mixed type ii iii kerogen deposited in a sub oxic marine environment and generated during the early oil window the oil biomarkers indicate that the source rock is the maykop fm as previously determined for the other areas of the south caspian basin the spontaneous emissions showing different morphologies are mainly aligned along normal and transtensive fault systems which provide effective pathways for rapid fluid ascent from deep reservoirs to the surface

the occurence of unusual c27 and c29 sterane predominances in two types of oman crude oil abstract two types of oman crude oils reveal unusual sterane distributions type a which is the more common 74 examples is characterised by a predominance of c 29 iso and normal steranes and generally none or only very low relative concentrations of rearranged steranes the triterpanes are characterised by the predominance of the c 29 17 h 21 h norhopane over the c 30 17 h 21 h hopane and non predominant c 20 c 30 tricyclic terpanes the c 29 steranes of this type of crude were not derived from the c 29 sterols of land plant origin frequently proposed as the source of c 29 steranes since there is good geological evidence that these crudes were generated from a pre cambrian source rock a geological period when land plants did not exist the type b crude oil 11 known examples is characterised by a strong predominance of c 27 iso normal and rearranged steranes relatively lower concentrations of 17 h 21 h hopanes and relatively high concentrations of c 20 c 30 tricyclic terpanes the remarkably different biomarker characteristics of these crude oils imply that the organisms active in the depositional environment of the respective source rocks were significantly different

release of bound aliphatic biomarkers via hydropyrolysis from type ii kerogen at high maturity abstract at relatively low maturity kerogen bound aliphatic biomarkers invariably display retarded maturity compared to their free counterparts as a result of the protection afforded by the macromolecular structure this study investigates the release of hopanes and steranes at elevated post oil window maturity from type ii kerogen results for a suite of north sea petroleum source rocks kimmeridge clay formation indicate that below a hydrogen index hi value of ca 300 differences between the free and bound phases for hopane and sterane side chain isomerisation are small however ring isomerisation within the kerogen bound phase is still more retarded for a corresponding series of kerogen samples artificially matured via hydrous pyrolysis both free and bound phase side chain isomerisation reactions are significantly retarded relative to the naturally occurring samples this is consistent with earlier studies but the extent of retardation for ring isomerisation in the bound phase is even more pronounced than for the free phase

a preparation zone for volcanic explosions beneath naka dake crater aso volcano as inferred from magnetotelluric surveys abstract the 1st crater of naka dake aso volcano is one of the most active craters in japan and known to have a characteristic cycle of activity that consists of the formation of a crater lake drying up of the lake water and finally a strombolian type eruption recent observations indicate an increase in eruptive activity including a decrease in the level of the lake water mud eruptions and red hot glows on the crater wall temporal variations in the geomagnetic field observed around the craters of naka dake also indicate that thermal demagnetization of the subsurface rocks has been occurring in shallow subsurface areas around the 1st crater volcanic explosions act to release the energy transferred from magma or volcanic fluids measurement of the subsurface electrical resistivity is a promising method in investigating the shallow structure of the volcanic edifices where energy from various sources accumulates and in investigating the behaviors of magma and volcanic fluids we carried out audio frequency magnetotelluric surveys around the craters of naka dake in 2004 and 2005 to determine the detailed electrical structure down to a depth of around 1 km the main objective of this study is to identify the specific subsurface structure that acts to store energy as a preparation zone for volcanic eruption two dimensional inversions were applied to four profiles across the craters revealing a strongly conductive zone at several hundred meters depth beneath the 1st crater and surrounding area in contrast we found no such remarkable conductor at shallow depths beneath the 4th crater which has been inactive for 70 years finding instead a relatively resistive body the distribution of the rotational invariant of the magnetotelluric impedance tensor is consistent with the inversion results this unusual shallow structure probably reflects the existence of a supply path of high temperature volcanic gases to the crater bottom we propose that the upper part of the conductor identified beneath the 1st crater is mainly composed of hydrothermally altered zone that acts both as a cap to upwelling fluids supplied from deep level magma and as a floor to infiltrating fluid from the crater lake the relatively resistive body found beneath the 4th crater represents consolidated magma these results suggest that the shallow conductor beneath the active crater is closely related to a component of the mechanism that controls volcanic activity within naka dake