seismic stratigraphy of the southeastern black sea shelf from high resolution seismic records abstract high resolution seismic reflection profiles obtained from the shelves off the samsun and trabzon coasts southeastern black sea have revealed the existence of two distinct reflectors r and t reflector r forms the boundary between the upper depositional sequence a and the lower depositional sequence b seismo stratigraphically upper sequence a is characterized by stratified simple complex and lenticular seismic reflection configurations which imply changing depositional systems and or conditions changes of source and supply of sediments due to the relative change of sea level additionally the observed onlapping pattern within this sequence denotes rising of sea level during the last post glacial transgression the mounded seismic facies beyond the steep gradients on the shelf area of trabzon imply slump masses the lower depositional sequence b on the samsun and trabzon shelves is commonly characterized by chaotic reflection configurations which are interpreted either as strata deposited in a variable relatively high energy setting or as initially continous strata that have been deformed additionally the presence of some parallel subparallel reflections within this sequence denotes its stratified character the upper boundary of sequence b reflector r reflects a pre holocene unconformity probably caused by falling sea level at the time of the last glacial maximum additionally toplap termination at the upper boundary of sequence b indicates a stillstand of sea level at 91 m depth during the last glacial maximum based on borehole data sequence b is composed of consolidated sand and gravel admixtures in the samsun area and basalt agglomerate tuff series in the trabzon area reflector t forms the boundary of a zone of anomalous reflections acoustic turbidity at that are interpreted to represent gas in the sediments of the upper depositional sequence a the gas accumulations tend to occur in blanket and curtain forms depending on their appearances on seismic records

the rigid grain net rgn an alternative method for estimating mean kinematic vorticity number wm the use of porphyroclasts rotating in a flowing matrix to estimate mean kinematic vorticity number wm is important for quantifying the relative contributions of pure and simple shear in penetratively deformed rocks the most common methods broadly grouped into those that use tailed and tailless porphyroclasts have been applied to many different tectonic settings however attempts have not been made to unify the various methods here we propose the rigid grain net rgn as an alternative graphical method for estimating wm the rgn contains hyperbolas that are the mathematical equivalents to the hyperbolic net used for the porphyroclast hyperbolic distribution phd method we use the rgn to unify the most commonly used wm plots by comparing the distribution of theoretical and natural tailless porphyroclasts within a flowing matrix test samples from the south tibetan detachment tibet yield indistinguishable results when the rgn is compared with existing methods because of its ease of use ability for comparing natural data sets to theoretical curves potential to standardize future investigations and ability to limit ambiguity in estimating wm the rgn makes an important new contribution that advances the current methods for quantifying flow in shear zones 2006 elsevier ltd all rights reserved

ig mapper a new arcgis toolbox for the geostatistics based automated geochemical mapping of igneous rocks abstract this work introduces a user friendly fast and effective tool for the automated geochemical mapping of igneous rocks to provide a geospatial representation of petrological parameters through the application of either deterministic or stochastic interpolation techniques the geostatistical approach allows mapping to be extended to areas where igneous rocks are hidden under sedimentary cover also introducing an estimate of the interpolation reliability this new gis based automated procedure which is mostly constructed with the arcgis model builder as a graphical code designer can generate three main types of outputs 1 interpolation maps of major and trace elements isotopic compositions and derived parameters to provide valuable geospatial information regarding the genetic and structural relationships between magmatic bodies 2 lithological maps that are based on the geostatistical interpolation of major element data and mirror the main geochemical classification diagrams of plutonic rocks and 3 interpolation checking maps which provide an estimate of the geostatistical interpolability for one specific parameter at a time this last output is expressed in the form of an empirical index stochastic interpolation index which highlights the randomness level of a specific value distribution this automated lithological mapping function is an entirely new tool based on five original python scripts which makes it possible to interpolate on a georeferenced map the compositions deriving from the most used geochemical classification diagrams this new tool package is presented here by using a portion of the serre batholith in central calabria southern italy to illustrate the potential of this method to open new research perspectives in igneous petrology

distribution and transport of hydrocarbons in surface sediments of the alaskan outer continental shelf abstract surface sediments from the outer continental shelf of alaska were analyzed for hydrocarbons as part of an environmental survey sponsored by noaa blm sediments were collected from the proposed oil lease areas of beaufort sea southeastern bering sea norton sound navarin basin gulf of alaska kodiak shelf and lower cook inlet data on normal and branched alkanes and di and triterpenoids from capillary gas chromatography gc and gas chromatography mass spectrometry gc ms indicate that the area displays little evidence of petroleum hydrocarbons i e seeps except at a few isolated stations beaufort sea sediments have the highest hydrocarbon budget whereas kodiak shelf sediments have the lowest the molecular markers of the hydrocarbons are of a mixed marine autochthonous and terrestrial allochthonous origin norton sound and cook inlet sediments contain the highest levels of terrigenous lipids and kodiak shelf the lowest the abundance of alkenes implies that relatively low oxidizing conditions exist in some of the depositional areas studied suggesting that extraneous petroleum hydrocarbons introduced into these sediments would be expected to have a relatively long residence time the distribution of polynuclear aromatic hydrocarbons pah is complex and shows a pyrolytic origin the data on perylene strongly favor the hypothesis that it is performed from terrigenous precursors and transported into the marine environment with no apparent in situ generation polynuclear aromatic hydrocarbons of diagenetic origin are probably dominant in gulf of alaska and kodiak shelf sediments two stations north of kalgin island in lower cook inlet and one in southeastern bering sea show typical weathered petroleum distribution of n alkanes and triterpenoids probable pathways of transport and fate of petroleum hydrocarbons in case of an oil spill are also briefly discussed

composition and exhalation flux of gases from mud volcanoes in taiwan many mud volcanoes are distributed along the tectonic sutures in southern taiwan and can be divided into five zones based on their relative positions in different tectonic domains most active mud volcanoes are exhaling methane dominated gases nevertheless some gases show unusual carbon dioxide dominated and or nitrogen excess compositions this implies that there are multiple sources for the gas compositions of mud volcanoes in taiwan

strain memory of 2d and 3d rigid inclusion populations in viscous flows what is clast spo telling us abstract we model the development of shape preferred orientation spo of a large population of two and three dimensional 2d and 3d rigid clasts suspended in a linear viscous matrix deformed by superposed steady and continuously non steady plane strain flows to investigate the sensitivity of clasts to changing boundary conditions during a single or superposed deformation events resultant clast spos are compared to one developed by an identical initial population that experienced a steady flow history of constant kinematic vorticity and reached an identical finite strain state allowing examination of spo sensitivity to deformation path rotation paths of individual triaxial inclusions are complex even for steady plane strain flow histories it has been suggested that the 3d nature of the system renders predictions based on 2d models inadequate for applied clast based kinematic vorticity gauges we demonstrate that for a large population of clasts simplification to a 2d model does provide a good approximation to the spo predicted by full 3d analysis for steady and non steady plane strain deformation paths predictions of shape fabric development from 2d models are not only qualitatively similar to the more complex 3d analysis but they display the same limitations of techniques based on clast spo commonly used as a quantitative kinematic vorticity gauge our model results from steady superposed and non steady flow histories with a significant pure shearing component at a wide range of finite strain resemble predictions for an identical initial population that experienced a single steady simple shearing deformation we conclude that individual 2d and 3d clasts respond instantaneously to changes in boundary conditions however in aggregate the spo of a population of rigid inclusions does not reflect the late stage kinematics of deformation nor is it an indicator of the unique mean kinematic vorticity experienced by a deformed rock volume

evaluation of possible gas microseepage mechanisms petroleum microseepage anomalies over petroleum accumulations are commonly explained by rapid vertical migration of colloidal gas bubbles through fracture networks this article is a theoretical anal ysis of this mechanism and of continuous gas phase flow in frac tures the gas bubble ascent mechanism is much slower than re ported microseepage velocities so it cannot account for observed microseepage in contrast continuous gas phase flow through frac tures can equal or exceed reported microseepage velocity while maintaining total flux low enough so that petroleum accumulations can exist for geological lengths of time fracture entry pressure for bubbles is more than twice that of a continuous gas phase so con tinuous gas phase migration also requires a lower pressure threshold before initiating seepage vertical microseepage is therefore best explained by the same mechanism interpreted for macroseepage although this article provides a theoretically justified mecha nism for microseepage it also shows why interpretation of surface microseepage signals is problematic fracture geometry controls seepage velocity and flux so geochemical anomalies may indicate an increase in fracture aperture as well as possible subsurface ac cumulations larger fractures require very low gas capillary entry pressures so in some settings surface seepage could result from fractures over stratal migration pathways as well as over petroleum accumulations

the curinga girifalco line in the framework of the tectonic evolution of the remnant alpine chain in calabria southern italy in the peri mediterranean metamorphic belts the tectonic evolution of the calabria peloritani terrane during the dominant compressive tectonics of the eocene represents one of the most problematic points in palinspastic restorations a matter of particular debate is its shortening which could have occurred during the alpine or the apennine subduction in this regard a crucial joint is provided by the kinematics of one of the most relevant shear zones such as the curinga girifalco line cropping out in central calabria this shear zone juxtaposed a nearly complete hercynian crustal section i e the sila and serre unit onto the remnants of the castagna unit the data in the available literature on ductile kinematics from the south eastern branch of the curinga girifalco line indicate a downward movement of the hanging wall in the present paper we show new ductile kinematic data and petrographic evidence from outcrops in the north western and south eastern branches of the curinga girifalco line our results highlight the coherent kinematics of the eocene shortening during the alpine subduction system followed by late eocene oligocene to early miocene dominantly ductile extensional reworking relating to the apennines subduction system

diffuse emission of carbon dioxide methane and helium 3 from teide volcano tenerife canary islands diffuse emission of co2 ch4 and he was investigated in the summit crater of teide volcano tenerife canary islands the results indicate that teide volcano releases abundant co2 not only from its active crater but also from its flanks as diffuse soil emanations the spatial distribution of these emanations correlates quite closely with that of geothermal anomalies and manifestations our flux measurements indicate a total output of 380 ton day 1 of co2 and 1 6 on day 1 of ch4 by diffuse degassing from the he co2 ratios and the co2 flux we estimate a diffuse he flux of 0 052 mol year 1 isotopic analysis of carbon in soil gas samples from sites of high soil co2 flux indicates a magmatic origin for the co2 also reported by high he 4he ratios of 5 50 and 5 87 ra the origin of methane is more uncertain with low 13c values suggesting a biogenic contribution

a flow law for dislocation creep of quartz aggregates determined with the molten salt cell we have used the molten salt cell to conduct an experimental study on the rheology of a natural quartzite containing 0 15 wt water co axial deformation experiments were conducted at constant piston displacement rates approximating constant strain rates at low strain the strengths of our natural quartzite measured in the molten salt cell are approximately half those measured at the same conditions in solid media because unlike solid confining media molten salt does not contribute to the strength of the sample it reduces the friction on the moving piston and it allows clear identification of the hit point we have limited the experimental conditions to those required for dislocation creep and have used only steady state flow stresses measured during climb accommodated dislocation creep to calculate the flow law parameters two flow laws were determined one for samples containing minor amounts of melt 1 2 and one for melt free samples in both cases the power law stress exponent n is 4 0 0 9 which is greater than that previously reported in flow laws for dislocation creep of quartz aggregates determined in solid media the activation energy q is 137 34 kj mol 1 for samples with melt and 223 56 kj mol 1 for those without within the range of previously determined values for quartz aggregates containing 0 1 wt water the pre exponential term a is 1 1 10 4 2 mpa ns 1 for samples without melt and 1 8 10 8 2 mpa ns 1 for those with melt the lower strengths measured in the molten salt cell indicate that previous piezometer relations for quartz experimentally determined in solid media are not correct extrapolation of the flow law for melt free aggregates to natural strain rates predicts higher strengths than most previous quartz flow laws however accurate extrapolation requires determining the dependence of flow stress on fh2o and or ah

gas geochemistry and methane emission from dushanzi mud volcanoes in the southern junggar basin nw china abstract there are many mud volcanoes in the southern margin of the junggar basin northwest china of which the dushanzi area is the most typical and active one emitting large amount of greenhouse gases associated with water and mud the emitted gas is dominated by methane average 90 1 together with other gases such as ethane 4 84 5 46 propane 0 06 0 90 co 2 0 67 1 0 and n 2 2 8 3 3 the carbon 13 c 1 and hydrogen d isotopic ratios of methane are in the ranges of 40 6 to 45 0 and 221 to 249 respectively whereas carbon isotope ratios of ethane 13 c 2 are 25 2 to 27 6 based on 13 c values the released gas is characterized as a thermogenic coal type and possibly originated from the middle low jurassic coal bearing sequences according to the gas source correlation and regional geology helium isotopes show a crustal source the methane flux of dushanzi mud volcanoes from both macro seepage craters vents and micro seepage ground soil exhalation ranged over the orders of magnitude from 0 4 2 7 kg d 1 and 4950 mg m 2 d 1 on average respectively positive ch 4 fluxes from dry soil were widespread throughout the investigated areas the total ch 4 emission from dushanzi mud volcanoes is estimated to be at least 22 6 tons a 1 of which about 89 is from micro seepage surrounding the mud volcano vents

tectonic evolution of gulf of anadyr and formation of anadyr and navarin basins the gulf of anadyr is underlain by two major sedimentary basins kresta basin and east anadyr trough that trend east to southeast and contain in places more than 9 km 29 500 ft of fill the basins are flanked on the east and north by the okhotsk chukotsk volcanic belt a broad bedrock high composed of plutonic and volcanic rocks that extends from eastern siberia along the inner bering sea shelf at least to st matthew island the east anadyr trough extends onshore and connects with the larger anadyr basin which underlies the lowlands between the koryak range and okhotsk chukotsk volcanic belt of eastern siberia new seismic reflection and refraction data reveal that anadyr basin is separated from navarin basin by anadyr ridge a southeast northwest trending bedrock high that is characterized by high amplitude short wavelength magnetic anomalies anadyr ridge may be an offshore extension of the melange belt underlying the koryak range sonobuoy refraction data indicate that the velocity profile of strata in east anadyr trough is similar to that in navarin basin structurally the basins are different navarin basin is complex and contains both compressional and extensional elements whereas anadyr basin is a simple broad crustal sag semicircular in outline correlation of our reflection data from the offshore part of the anadyr basin including the east anadyr trough and kresta basin with d illing data onshore allows us to differentiate three distinct sequences in the offshore portion of the basin these sequences are separated by two strong reflectors agr and s and are tentatively identified with increasing depth as boundaries separating the neogene and paleogene and paleogene and mesozoic respectively in the northeastern corner of the gulf of anadyr across the anaut uplift shallow beds are folded and broken by faults that commonly offset the sea floor furthermore earthquake epicenters recorded landward of anadyr basin from cape navarin to the southwest and around the chukotsk peninsula to the northeast suggest recent tectonic movement in the gulf of anadyr near cape navarin and near kresta bay we believe that anadyr basin originally formed as a fore arc basin during the cretaceous as a result of underthrusting of the kula plate beneath siberia the collision of the kula plate with siberia resulted in the formation of the okhotsk chukotsk volcanic arc north of anadyr basin and the koryak melange belt south of the basin anadyr basin continued to subside during the cenozoic and ajor uplift in the koryak range occurred in the late miocene to pliocene

gas seepage from tokamachi mud volcanoes onshore niigata basin japan origin post genetic alterations and ch4 co2 fluxes abstract methane and co 2 emissions from the two most active mud volcanoes in central japan murono and kamou tokamachi city niigata basin were measured in from both craters or vents macro seepage and invisible exhalation from the soil mini and microseepage molecular and isotopic compositions of the released gases were also determined gas is thermogenic 13 c ch4 from 32 9 to 36 2 likely associated with oil and enrichments of 13 c in co 2 13 c co2 up to 28 3 and propane 13 c c3h8 up to 8 6 suggest subsurface petroleum biodegradation gas source and post genetic alteration processes did not change from 2004 to 2010 methane flux ranged within the orders of magnitude of 10 1 10 4 g m 2 d 1 in macro seeps and up to 446 g m 2 d 1 from diffuse seepage positive ch 4 fluxes from dry soil were widespread throughout the investigated areas total ch 4 emission from murono and kamou were estimated to be at least 20 and 3 7 ton a 1 respectively of which more than half was from invisible seepage surrounding the mud volcano vents at the macro seeps co 2 fluxes were directly proportional to ch 4 fluxes and the volumetric ratios between ch 4 flux and co 2 flux were similar to the compositional ch 4 co 2 volume ratio macro seep flux data in addition to those of other 13 mud volcanoes supported the hypothesis that molecular fractionation increase of the bernard ratio c 1 c 2 c 3 is inversely proportional to gas migration fluxes the ch 4 emission factor total measured output divided by investigated seepage area was similar to that derived in other mud volcanoes of the same size and activity the updated global emission factor data set now including 27 mud volcanoes from different countries suggests that previous estimates of global ch 4 emission from mud volcanoes may be significantly underestimated

a new estimate of global methane flux from onshore and shallow submarine mud volcanoes to the atmosphere a new estimate of global methane emission into the atmosphere from mud volcanoes mvs on land and shallow seafloor is presented the estimate considered a lower limit is based on 1 new direct measurements of flux including both venting of methane and diffuse microseepage around craters and vents and 2 a classification of mv sizes in terms of area km2 based on a compilation of data from 120 mvs the methane flux to the atmosphere is conservatively estimated between 6 and 9 mt y 1 this emission from mvs is 3 6 of the natural methane sources and is comparable with ocean and hydrate sources officially considered in the atmospheric methane budget the total geologic source including mvs seepage from seafloor microseepage in hydrocarbon prone areas and geothermal sources would amount to 35 45 mt y 1 the authors believe it is time to add this parameter in the intergovernmental panel on climate change official tables of atmospheric methane sources

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

on the development of zones of reverse shearing in mylonitic rocks abstract most shear zones contain a minor proportion of domains recognizable from thin section to outcrop scale which show an opposing shear sense relative to the overall kinematic framework in this paper we discuss how these universal features result from the evolving deformation strain partitioning that generally accompanies progressive general shear principally in low metamorphic grade shear zones because the rheologic properties and consequently the contributions of the different deformation mechanisms change continuously with progressive strain an individual domain with a predominant deformation mechanism much faster or slower than the average may depart from the general kinematics enhancing the viscosity contrast between adjacent layers and causing locally reverse shear in the domain boundaries care is needed therefore in interpreting opposing shear senses in the same shear zone as indicating superimposed deformation events

geophysical and geochemical evidence for subsurface hydrocarbon leakage in the bering sea alaska abstract geophysical and geochemical surveys were conducted on the bering sea shelf to investigate whether hydrocarbons found in the surficial sediment particularly in association with certain geophysical events indicate the presence and nature of more deeply reservoired oil and gas deposits surface sediment samples were obtained at 1000 sites where high resolution seismic data indicated the presence of gas seepage and or surface faulting in addition sites for background measurements were occupied away from areas of gas seepage results of the geophysical survey show seismic wipeout zones to be present throughout the bering sea shelf sediment samples obtained within the shallow wipeout zones confirm that these features are caused by gas in addition compositional and isotopic analyses indicate that the gas is of biogenic and thermogenic origins the thermogenic leakage appears to be related to localized faulting and shallow structuring the high resolution seismic data therefore provide an excellent tool for locating leakage points thereby enhancing the opportunity of finding migrated thermogenic hydrocarbons in surficial sediments an examination of vertical variability shows the hydrocarbon concentrations to be strongly related to various processes occurring in the surficial sediments core samples must be taken from below the zone of maximum disturbance to obtain unaltered hydrocarbon samples

seafloor gas seeps and sediment failures triggered by the august 17 1999 earthquake in the eastern part of the gulf of izmit sea of marmara nw turkey abstract on august 17 1999 a major earthquake mw 7 4 occurred affecting a large area in northwestern turkey a 150 km long section of the north anatolian fault ruptured from the entrance of the gulf of izmit to golyaka in the east during the earthquake we utilized high resolution shallow seismic data acquired during a post earthquake cruise to find evidence of gas seeps gas charged sediments and sediment failure in the eastern izmit basin of the gulf of izmit the data showed anomalies that suggest the presence of increased gas in the gulf after the earthquake five major zones of offshore mass movement were found in the study area comparison of data collected before and after the earthquake indicates that the apparent amount of gas increased after the earthquake and the mass movement has a causative relationship to the august 17 1999 earthquake therefore we conclude that the seismic event presence of increased gas and the offshore mass movements in the study area are interrelated

styles and regimes of orogenic thickening in the peloritani mountains sicily italy new constraints on the tectono metamorphic evolution of the apennine belt the peloritani mountains constitute the sicilian portion of the calabria peloritani arc italy a tectono metamorphic edifice recording the history of the subduction exhumation cycle during tertiary convergence between the african and european plates here we describe the kinematic and the petrological characteristics of the major shear zones bounding the lowermost continental derived metamorphic units cropping out in the eastern portion of the peloritani mountains both meso and micro scale shear sense criteria indicate a top to the sse tectonic transport during a general evolution from ductile to brittle deformation conditions quantitative thermobarometry on texturally equilibrated phengite chlorite pairs crystallized along the shear bands indicates pressure of 6 8 kbar at temperatures of 360 440 c for the structurally highest units and 3 4 kbar at 380 440 c for the lowest ones this documents an overall inverse type nappe arrangement within the tectonic edifice and a transition from an alpine 13 18 c km 1 to a barrovian type 28 36 c km 1 geothermal gradient during the progress of the alpine orogenic metamorphism in the peloritani mountains the integration of these results allows the peloritani mountains to be considered as a constituent element of the apennine orogenic domain formed during the progressive space time transition from oceanic to continental subduction at the active convergent margin

methane seeps and mud volcanoes in italy gas origin fractionation and emission to the atmosphere molecular composition ch 4 isotopes and gas flux of all main terrestrial mud volcanoes and other methane seeps in italy are being assessed for the first time whereas 74 of the italian gas reservoirs are biogenic about 80 of the seeps release thermogenic gas dry seep gas generally maintains the reservoir c 1 c 2 c 3 bernard ratio while mud volcanoes show molecular fractionation likely occurring during advective migration accordingly a simple and direct use of the bernard parameter might be misleading when applied to mud volcanoes as it could not always reflect the reservoir composition methane flux into the atmosphere from macro seep areas is in the order of 10 2 10 6 t km 2 y 1 microseepage is widespread throughout large areas and on a regional scale it provides the main methane output a first emission estimate for the total hydrocarbon prone area of italy suggests levels of 105 t y 1 comparable to national sources from fossil fuel industry

surface geochemical studies in the norwegian barents sea comparison with drilling results during the last 4 years a number of surface geochemical studies have been undertaken in the barents sea acreage in all of the areas has subsequently been licensed for exploration sampling for surface geochemistry has been undertaken using a gravity corer where samples were taken 2 m below the seafloor the sampling grids were either regular or irregular based on known geological features in the areas or a combination of the two the samples were analyzed for interstitial gas adsorbed gas grain size distribution organic and inorganic carbon content fluorescence of the hexane extract and heavy hydrocarbons in the hexane extract the results from the different areas ranged from barren i e no indication of petrogenic hydrocarbons at the surface anomalies of petrogenic hydrocarbons i e indicating the generation of gas condensate or oil to extremely strong anomalies of oil interpreted as indicators of direct leakage from source rocks or a defective caprock

hydrocarbon seeps in petroliferous basins in china a first inventory abstract natural hydrocarbon seepage is a widespread phenomenon in sedimentary basins with important implications in petroleum exploration and emission of greenhouse gases to the atmosphere china has vast petroleum oil and gas bearing sedimentary basins but hydrocarbon seepage has rarely been the object of systematic studies and measurements based on the available chinese literature we report a first inventory of 932 hydrocarbon seeps or seepage zones 710 onshore seeps and 222 offshore seeps including 81 mud volcanoes 449 oil seeps 215 gas seeps and 187 solid seeps bitumen outcrops the seeps are located within the main 20 mesozoic cenozoic petroliferous sedimentary basins especially along the marginal regional and local faults the type of manifestations oil gas or mud volcano reflects the type and maturity of the subsurface petroleum system and the sedimentary conditions of the basin oil seeps are particularly abundant in the junggar basin gas seeps mostly developed in the lunpola basin in smaller basins of the eastern guizhou and yunnan provinces onshore taiwan and in the offshore yinggehai basin mud volcanoes developed in basins junggar qaidam qiangtang onshore and offshore taiwan that experienced rapid sedimentation which induced gravitative instability of shales and diapirism in comparison to available global onshore seep data bases china results to be the country with the highest number of seeps in the world the massive gas seepage in china could represent a considerable natural source of methane to the atmosphere and a key process that may drive future hydrocarbon exploration

gas charged sediments in the aegean and ionian seas greece abstract during the last fifteen years marine seismic surveys in the aegean and ionian seas have revealed numerous acoustic anomalies i e acoustic turbid zones gas pockets gas plumes enhanced reflectors columnar disturbances wipe outs and meso to micro morphological features such as pockmarks domes mud volcanoes and elongated depressions these are attributed to the presence of gas in sediment interstices the gas charged sediments are found in pleistocene and present day fjord like environments pleistocene and present day deltaic environments lakes and open sea environments the gas found in the quaternary fjord like and deltaic depositional environments is assumed to be of biogenic origin the gas found in the pre quaternary open sea environments is associated with faulting and salt doming and may therefore be of thermogenic origin although the sediment grain size is favourable for the formation of pockmarks the lack of them is probably due to the high seismicity which characterises these regions

hydrocarbon geochemistry in surface sediments of alaskan outer continental shelf part 1 c15 hydrocarbons the c15 hydrocarbons in 220 surface sediments from the outer continental shelf of alaska were analyzed as part of an environmental survey supervised by national oceanic and atmospheric administration and bureau of land management gas chromatography and gas chromatography mass spectrometry were employed for the identification of organic compounds in the bitumen extracts surface sediments from one station in southeastern bering sea and two stations in lower cook inlet display n alkanes and triterpenoid distribution typical of weathered petroleum major faulting in the vicinity of the southeastern bering sea station may account for the leakage of petroleum from subsurface reservoir rocks oil production in upper cook inlet or a hitherto unrecorded seep in the rea could contribute petroleum hydrocarbons to the sediments from the two stations in lower cook inlet apart from these stations there is little evidence of near surface petroleum seeps in the sites investigated

compositions and flux of soil gas in liu huang ku hydrothermal area northern taiwan abstract soil co 2 flux has been considered a useful proxy to remotely monitor volcanic activity in a hydrothermal area within a safe distance the liu huang ku lhk area which is close to the taipei basin and many existing active fumaroles and hot springs was chosen for the first systematic soil gas study in a hydrothermal area of taiwan in 2004 and 2006 the soil co 2 flux was measured by the closed chamber method with a non dispersive infrared detector soil co 2 emission rate was estimated 19 8 0 2 t day 1 and 582 t km 2 day 1 in 2004 and 22 4 0 2 t day 1 and 659 t km 2 day 1 in 2006 respectively these values are close to those reported for other active high co 2 flux hydrothermal areas of the world it implies that magmatic gases are actively degassing from subsurface in northern taiwan helium and carbon isotopic data reveal that soil gas in lhk is mainly derived from the mantle and is mixed with a small amount of crustal and air components the abundance of soil co 2 shows a positive correlation with the 3 he 4 he ratios and total sulfur contents which are considered as magmatic sensitive indicators for the fumarolic samples therefore soil co 2 could be used as a good proxy for future monitoring of magmatic activity in this area

mud volcanoes the most important pathway for degassing deeply buried sediments abstract this paper discusses the nature of the phenomenon of mud volcanism with respect to degassing of deeply buried sediments mud volcanoes are defined as geological structures and their main elements are described based on the nature of activity mud volcanoes are grouped in to three main types and the relationship between each type and corresponding morphological expression is discussed the presented up to date data of the world geographical distribution of mud volcanoes show that they approximate to 1800 individuals a detail overview of geological environments in which they occur helps to deduce some necessary conditions for mud volcano formation the basic mechanisms of mud volcano formation are discussed specifically the fluid pressure hypothesis and some triggering events are identified the most common investigation approach and some criteria for recognizing of a submarine mud volcano on side scan sonar records and seismic sections are given mud volcanism in the mediterranean ridge an accretionary complex and black sea abyssal plane a back ark basin with tectonic regime of extension are described as case studies to show variety in morphology and common factors in development of mud volcanoes the manifestation of continuous gas migration through mud volcanoes is clarified and the attempt made to quantify the gas release shows that mud volcanoes are one of the significant natural sources of atmospheric methane emitting a total amount of about 10 3 to 12 6 tg annually

terrestrial methane seeps and mud volcanoes a global perspective of gas origin abstract a global database of gas composition and methane stable isotopes of 143 terrestrial mud volcanoes from 12 countries and 60 seeps independent from mud volcanism from eight countries was compiled and examined in order to provide the first worldwide statistics on the origin of methane seeping at the earth s surface sixteen seep data were coupled with their associated subsurface reservoirs the surface seepage data indicate that at least 76 of the mud volcanoes release thermogenic gas with only 4 biogenic and 20 with mixed character the average 201 data of methane concentration and methane carbon isotope ratios 13 c 1 of mud volcanoes are 90 v v and 46 4 respectively the other types of seeps which are independent from mud volcanism have an average 13 c 1 value that is slightly higher 42 9 gases from mud volcanoes are generally lighter more methane less ethane and propane than their associated reservoir gases suggesting a molecular fractionation during advective fluid migration other types of seeps especially dry seeps maintain the reservoir c 1 c 2 c 3 bernard ratio mud volcanoes behave like a natural refinery and the origin of gas more isotopically enriched than 50 and with c 1 c 2 c 3 500 should be attributed to a thermogenic source rather than partial oxidation of biogenic gas some data that appear biogenic in the bernard diagram can be explained by molecular fractionation of mixed gas consequently the bernard parameter may be misleading when applied to mud volcanoes since it does not always reflect the original gas composition the mechanisms of the molecular advective segregation should be studied quantitatively by specific models and experiments

middle miocene out of sequence thrusting and successive exhumation in the peloritani mountains sicily late stage evolution of an orogen unraveled by apatite fission track and u th he thermochronometry 1 apatite fission track aft and u th he ahe thermochronometry are applied to constraint the thermal history of the basement rock forming the peloritani mountains in northeast sicily italy aft ages range between 29 0 5 5 ma and 5 5 0 9 ma while ahe ages vary from 19 4 ma to 3 3 ma most aft ages are younger than the overlying terrigenous sequence that in turn postdates the main orogenic phase through the coupling of the thermal modeling with the stratigraphic record a middle miocene thermal event is revealed this event affected an inner intermediate portion of the peloritani mountains and is confined by the distribution of the aft ages 15 ma the u shaped pattern of aft ages along n s transects across the mountain chain is consistent with burial below a thrust stack that is a few km thick created by an out of sequence thrusting phase that affected the inner portion of the belt the tectonic load was then removed initially by erosion enhanced by the high relief at 10 7 ma the difference between young aft and ahe ages is used to infer a rate of exhumation of 0 3 mm yr for this stage the gap between the youngest ahe ages and the sedimentary record above indicate a final exhumation stage with increasing rates of denudation 1 3 mm yr since the pliocene times due to extensional tectonics

hydrocarbon geochemistry in surface sediments of alaskan outer continental shelf part 2 distribution of hydrocarbon gases the distribution of c1 to c4 hydrocarbon gases in surficial sediments from the alaskan continental shelf was determined as part of a regional environmental survey sponsored by national oceanic and atmospheric administration and bureau of land management noaa blm methane ethane ethene propane propene n butane and iso butane were observed in low concentrations 0 1 10 ppb as weight gas to dry weight sediment in nearly all of the 190 sediment samples examined with methane exceeding c2 to c4 hydrocarbons in abundance by about a factor of 10 no gasoline range c5 to c8 hydrocarbons were detected above blank levels ethene was found generally to be more abundant than ethane while propane was slightl more abundant than propene the correlation between these hydrocarbons suggests a common possibly biogenic origin sediments from norton sound have anomalously high methane concentrations probably as a result of biological methanogenesis in subsurface organic rich peat layers most of the regions sampled showed median values of the c1 c2 c3 ratio of 20 the generally low c1 concentrations probably resulted from the selective loss of c1 by biologic oxidation or ebullition from the surface sediments no major c2 to c4 hydrocarbon anomalies were discovered however at some stations in kachemak bay kodiak shelf and norton sound anomalously high c3 c3 1 ratios indicated the poss ble presence of thermogenic gases at depth

seismic and geochemical evidence for shallow gas in sediment on navarin continental margin bering sea marine seismic studies coupled with geochemical investigations demonstrate that hydrocarbon gases are ubiquitous in the near surface 250 m or 820 ft depth sediment of the navarin continental margin in the northern bering sea three types of acoustic anomalies appear to be related to the presence of gas in the sediment these anomalies are most prevalent in the northern half of the navarin basin acoustic anomalies attributed to gas hydrates and to diagenetic boundaries are present on seismic records of the lower slope between navarinsky and zhemchug canyons hydrocarbon gases methane through butanes are common in the surface 5 m or 17 ft depth sediment of the navarin continental margin methane the most abundant hydrocarbon gas is present in amounts ranging from 84 000 to 1 l l of wet sediment these concentrations are two to three orders of magnitude greater than the other hydrocarbon gases the highest concentrations of methane greater than 1 000 l l were measured in sediment of navarinsky canyon and over the central part of the navarin basin the source of methane is mainly biogenic but the hydrocarbon gas compositions in 17 of 141 cores suggest the presence of thermogenic gas most of these 17 cores are from the continental slope at water depths greater than 150 m 490 ft no direct correlation could be found between acoustic anomalies and gas concentrations in the sediment this lack of correlation is probably due to the limited penetration of the gravity corer and the spotty distribution of hydrocarbon concentrations

theories and applicability of grain size piezometers the role of dynamic recrystallization mechanisms abstract the average grain size d arising from dynamic recrystallization drx is often used as an indicator of flow stress however a theoretical basis for the scaling relation between d and has yet to be well established in this paper theories for the development of recrystallized grain size are reviewed and their applicability is examined special attention is paid to the dependence of the d relation on drx mechanisms steady state drx is classified into discontinuous drx with bulging blg nucleation grain boundary migration gbm and continuous drx with subgrain rotation sgr nucleation gbm the nucleation and growth model derived from derby ashby theory describes the former case whereas that derived from shimizu theory applies to the latter a static energy balance model derived from twiss theory is applicable to subgrain size but not to recrystallized grain size the lower limit of grain size is possibly constrained by a change in deformation mechanism from dislocation creep to diffusion creep because deformation induced grain size reduction ceases in the diffusion creep field scaling relations determined in the laboratory support the shimizu model in the case of sgr gbm the theoretical piezometer calibrated for quartz suggests significant temperature effects under low temperature metamorphic conditions

gas charged sediments on the inner continental shelf off western india abstract high resolution seismic reflection profiles on the inner continental shelf less than 60 m water depth off india from 10 n to 22 n show 5 35 m of weakly stratified acoustically transparent clays at water depths of 15 50 m the subbottom profiles are characterized by anomalous seismic signatures in the form of acoustic maskings these extend from the underlying late pleistocene unconformity often stretching along the bedding planes and occasionally surfacing on the sea bed these acoustic maskings could be due to shallow hydrocarbon gases mainly methane which might have been derived from biogenic sources or geothermal processes or both

direct evidence of middle oligocene extension in the calabria peloritani terrane from co seismic faulting the pseudotachylyte bearing shear zones of palmi southern calabria italy the variscan crystalline basement of the calabria peloritani terrane cpt in southern italy was partly reworked by ductile and brittle shear zones throughout the alpine tectonic evolution from thickening to exhumation although evidence of extensional tectonics in the cpt has already been found and roughly constrained to the oligocene onward no attempt has ever been made to directly date brittle fault movements structural meso and micro scale kinematic and petrographic analyses and 40ar 39ar laser experiments reveal that the pseudotachylyte bearing shear zones of the palmi area in southern calabria formed in response to extensional shearing 33 5 ma ago and overprinted compressional tectonic structures results provide the first direct evidence of middle oligocene co seismic faulting in the area and confirm the role of extensional tectonics in promoting the oligocene exhumation of the calabria basement

methane emission from the mud volcanoes of sicily italy 1 mud volcanoes represent the largest expression of natural methane release into the atmosphere however the gas flux has never been investigated in detail methane output from vents and diffuse soil degassing is herewith reported for the first time measurements were carried out at 5 mud volcano fields around sicily italy each mud volcano is characterized by tens of vents and bubbling pools in the quiescent phase methane emission from single vents ranges between 0 01 and 6 8 kg day diffuse soil leakage around the vents is in the order of 102 104 mg m 2 d 1 an exceptional flux of 106 mg m 2 d 1 was recorded close to an everlasting fire soil ch4 flux is positive even at large distances from the mud volcano fields suggesting a diffuse microseepage over wider areas a total of at least 400 tons ch4 per year can be estimated over the area investigated alone 1 5 km2

methane exchange between coal bearing basins and the atmosphere the ruhr basin and the lower rhine embayment germany a precise knowledge of methane exchange processes is required to fully understand the recent rise of atmospheric methane concentration three of these processes take place at the lithosphere atmosphere boundary bacterial consumption of methane and emission of bacterial or thermogenic methane this study was initiated to quantify these processes on a regional scale in the ruhr basin and the lower rhine embayment since these areas are subject to bituminous coal and lignite mining natural and anthropogenically induced methane exchange processes could be studied the methane emission and consumption rates and their carbon isotope signal were measured at the lithosphere atmosphere boundary using flux chambers on most of the soils studied methane consumption by bacteria was identified thermogenic methane was released only at some of the natural faults examined in active and abandoned bituminous coal mining areas methane emissions were restricted to small areas where high emission rates were measured the carbon isotope composition of methane at natural faults and in mining subsidence troughs was typical of thermogenic methane 45 to 32 d 13 c methane exchange balancing revealed that natural methane emissions from these two basins represent no source of atmospheric importance however methane release by upcast mining shafts dominates the methane exchange processes and is by about two orders of magnitude greater than methane consumption by bacterial oxidation in the soils 2000 elsevier science ltd all rights reserved

neogene quaternary evolution of the forearc and backarc regions between the serre and aspromonte massifs calabria southern italy abstract the role of tectonics in the neogene quaternary evolution of the forearc basin between the serre and aspromonte massifs located in the southern calabria is widely documented in the exposed sedimentary successions the structuration of these different basins is due to the southeastward migration of the calabrian terranes which led to the subduction of the ionian lithosphere and the spreading of the tyrrhenian back arc basin the area is dominantly displaced by two nw se and ne sw oriented regional fault systems these fault systems were active during the infilling of the neogene quaternary basins and represent complex tear fault systems that accommodated stress generated in the accretionary prism during the subduction of the ionian lithosphere furthermore these structures play a relevant role as part of recent seismotectonic processes which controlled the late quaternary geodynamic evolution of the area

accurate differential stress measurement using the molten salt cell and solid salt assemblies in the griggs apparatus with applications to strength piezometers and rheology abstract calibrations have been developed for the molten salt cell and solid salt assemblies used in tri axial griggs type piston cylinder deformation apparatus griggs apparatus that enable accurate differential stress determinations in both assemblies at high pressures and high resolution differential stress measurements in the molten salt cell elastic response of the apparatus was characterized by loading alumina and wc rods and flow strengths were measured for high purity nickel and molybdenum and a ti zr mo alloy in replicate experiments in a griggs apparatus and a heard tri axial gas apparatus gas apparatus at identical pressures temperatures and strain rates the elastic response of the griggs apparatus is nonlinear at low total loads 1 760 mpa on a 5 mm diameter sample but becomes linear at loads greater than 15 kn plastic deformation experiments on water insensitive metals indicate that differential stresses measured in the molten salt cell msc and solid salt ssa assemblies in the griggs apparatus are greater than those measured in the gas apparatus at all conditions but vary systematically and reproducibly a simple linear calibration gas apparatus 0 73 griggsmsc 10 mpa where differential stress 1 3 can be applied to the differential stresses obtained using the msc in the griggs apparatus to obtain sample flow strength a similar linear calibration gas apparatus 0 73 griggsssa 48 mpa 30 mpa can be applied to the differential stresses obtained using the griggs apparatus with a solid salt assembly to obtain accurate sample flow strength these calibrations have been tested by applying them to mechanical data for carbonates deformed in the griggs apparatus and gas apparatus the calibrations are also applied to data from previous studies performed in the griggs apparatus on clinopyroxenites and quartzites and compared to results from similar experiments using the gas apparatus when the experimental starting materials and conditions are the same the recalculated flow strengths measured in the griggs apparatus experiments agree with those measured in the gas apparatus however discrepancies in differential stress are still observed in cases where starting materials differ or water available to silicate samples varies presumably through hydrogen diffusion through sample jackets and hydrogen fugacities of the surrounding confining media

mud volcanism an updated review abstract mud volcanism or sedimentary volcanism represents one of the most intriguing phenomena of the earth s crust with important implications in energy resource exploration seismicity geo hazard and atmospheric budget of greenhouse gases since the first review papers were issued at the beginning of 2000s a large amount of new geological geophysical and geochemical data has been acquired which clarified ambiguous concepts and significantly improved our knowledge of mud volcanism here we offer an updated review of the knowledge and implications of mud volcanoes with emphasis on the terminology used to describe different processes and structures the physical chemical and morphological characteristics of the several fluid emission structures the chemical properties of the released fluids in particular the molecular and isotopic composition of the gas the mud volcano formation dynamics and the several implications for petroleum exploration geo hazards and global atmospheric methane budget this review integrates new fluids data collected in azerbaijan and is complemented with field observations from various mud volcano provinces worldwide although the total number of mud volcanoes on earth is still uncertain 600 main onshore structures with a large variety in shapes and sizes are documented in recent global data sets and several thousand are assumed to exist in the oceans it is clear that a mud volcanoes are broadly distributed throughout the globe in active margins compressional zones of accretionary complexes thrust and overthrust belts passive margins deep sedimentary basins related to active plate boundaries as well as delta regions b they are specifically located in hydrocarbon bearing basins along anticline axes strike slips and normal faults and fault related folds in petroleum systems c they represent a specific category of natural gas oil seepage manifestation often related to deep and pressurised reservoirs d the main engine driving mud volcanism is given by a combination of gravitative instability of shales and fluid overpressure build up followed by hydrofracturing e hydrocarbons are generally of thermogenic origin while microbial gas is released in only a few cases mud volcanism on other planets e g mars and titan and microbial activity associated with gas seepage represent emerging issues and opportunities for future research

the effects of a meso alpine collision event on the tectono metamorphic evolution of the peloritani mountain belt eastern sicily southern italy

stable positions of rigid objects in non coaxial flow a study in vorticity analysis abstract distortions of a homogeneous fabric which occur around rigid objects in rocks deformed by non coaxial ductile flow are useful to determine the sense of shear but also contain information on other aspects of the flow rigid objects in a non coaxial flow fall into two categories those which are permanently rotating and those which can reach stable positions at high finite strain the orientation of such immobilized objects with respect to eigenvectors of instantaneous flow is a function of the vorticity number of the flow the ratio of instantaneous stretches and the axial ratio of the object in naturally deformed rocks immobilized rigid objects may be recognized from the geometry of the surrounding fabric tails of recrystallized material around porphyroclasts in a mylonite rotate towards parallellism with the extensional eigenvector of the flow and the shape of tails reflects the rotational behaviour of the porphyroclast the axial ratio of immobilized porphyroclasts and their orientation with respect to the tails can theoretically be used to determine the vorticity number of the flow and deviations from isochoric plane strain in practice such an analysis is as yet difficult but a tentative example is given of the way in which the vorticity number can be calculated from a population of feldspar porphyroclasts in a quartzite mylonite from the french pyrenees

microstructural investigation of naturally deformed leucogneiss from an alpine shear zone southern calabria italy in order to reveal any correlation between the preferred orientation of quartz and progressive intensity of strain a suite of deformed leucogneiss collected within a ductile shear zone outcropping in calabria southern italy was investigated based on the microstructural approach and matrix clast relationships the method applied here may be useful for appraising the connection between deformation mechanisms of constituent minerals and bulk textural properties of naturally sheared rocks accordingly quartz c axis orientation patterns were determined by image assisted analysis results revealed a correlation between finite strain and textural features as strain increases the matrix develops at the expense of the clast counterpart which is instead progressively reduced in both size and amount

production consumption and migration of methane in accretionary prism of southwestern taiwan to systematically quantify the production consumption and migration of methane along a continental margin 210 sediment cores were collected from offshore southwestern taiwan and analyzed for their gas and aqueous geochemistry these data combined with published results were used to calculate the diffusive methane fluxes across different geochemical transitions and to develop scenarios of mass balance to constrain deep microbial and thermogenic methane production rates within the accretionary prism the results showed that methane diffusive fluxes ranged from 2 71 10 3 to 2 78 10 1 and from 1 88 10 1 to 3 97 mmol m 2 d 1 at the sulfate methane transition zone smtz and sediment seawater interfaces respectively high methane fluxes tend to be associated with structural features suggesting a strong structural control on the methane transport a significant portion of ascending methane 50 is consumed by anaerobic oxidation of methane at the smtz at most sites indicating effective biological filtration gas compositions and isotopes revealed a transition from the predominance of microbial methane in the passive margin to thermogenic methane at the upper slope of the active margin and onshore mud volcanoes methane production and consumption at shallow depths were nearly offset with a small fraction of residual methane discharged into seawater the flux imbalance arose primarily due to the larger production of methane through deep microbial and thermogenic processes at a magnitude of 1 512 43 096 tg myr 1 methane and could be likely accounted for by the sequestration of methane into hydrate forms and clay absorption

methane emission from mud volcanoes in eastern azerbaijan methane ch4 flux to the atmosphere was measured from gas vents and for the first time from soil microseepage at four quiescent mud volcanoes and one everlasting fire in eastern azerbaijan mud volcanoes show different activity of venting craters gryphons and bubbling pools with ch4 fluxes ranging from less than one to hundreds of tons per year microseepage ch4 flux is generally on the order of hundreds of milligrams per square meter per day even far away from the active centers the ch4 flux near the everlasting fires on the order of 105 mg m 2 d 1 represents the highest natural ch4 emission from soil ever measured the specific ch4 flux to the atmosphere between 102 and 103 t km 2 yr 1 was similar to specific flux from other mud volcanoes in europe at least 1400 tons of ch4 per year are released from the investigated areas it is conservatively estimated that all onshore mud volcanoes of azerbaijan during quiescent activity may still emit 0 3 0 9 106 t of ch4 per year into the atmosphere the new data fill a significant gap in the worldwide data set and confirm the importance of geologic sources of greenhouse ch4 although they are not yet considered in the climate study budgets of atmospheric ch4 sources and sinks

preparation and deformation of synthetic aggregates of quartz synthetic quartz aggregates of low porosity have been fabricated from natural quartz powder impure silica gel and high purity silicic acid by hydrothermal isostatic pressing at 300 mpa the resulting specimens have water contents comparable to those of natural quartzites and have been used for deformation tests the flow stress at 1200 1300 k was found to vary in an inverse relationship to the water pressure estimated under the assumption that the measured water content homogeneously filled the measured porosity it is questionable that the natural quartz origin specimens were fully equilibrated in respect to the activity of the water but equilibration has probably been achieved in the amorphous silica origin specimens which crystallized under the experimental conditions in the deformation of the latter materials the experimental activation energy at water pressures approaching the confining pressure was found to be about 150 kj mol 1 for both however the impure gel origin material gave a stress exponent of about 2 3 whereas the high purity silicic acid origin material gave a stress exponent of about 4 in spite of the grain sizes being about 90 m and 20 m respectively it is concluded that while the impure specimens have higher intragranular strengths there is also a significant contribution of grain boundary processes to the strain in them which is absent in the high purity specimens

fluid expulsion in terrestrial sedimentary basins a process providing potential analogs for giant polygons and mounds in the martian lowlands abstract on earth burial of fine grained sediments in offshore passive margins e g underwater fans and deltas commonly results in fluid expulsion features including large scale polygonal fractures mud volcanoes and pockmarks comparison of resulting offshore polygons and mud volcanoes with giant polygons and high albedo mounds in the chryse acidalia region of mars shows the terrestrial and martian features to be similar in size morphology geologic context and general co occurrence within the same basin these similarities suggest that the process of terrestrial fluid expulsion may provide an analog that could link the giant polygons and mounds in chryse and acidalia to a single process moreover while the terrestrial offshore polygons and mud volcanoes commonly develop in the same basins these features do not necessarily occur in exactly the same locations within those basins as they are independent responses to compaction and dewatering thus the fluid expulsion analog does not require that the martian giant polygons and mounds have identical distributions this is the situation in chryse and acidalia where the giant polygons and mounds are extensively developed and generally have overlapping distributions but where each set of features may occur in places without the other this fluid expulsion analog is enhanced by the fact that giant polygons and mounds in chryse and acidalia co occur in a regional sense and in a geologic setting that is consistent with a fluid expulsion model of formation implications of this analog may impact our view of the role of water in the depositional history of the martian lowlands

ch4 and co2 emissions from mud volcanoes on the southern margin of the junggar basin nw china origin output and relation to regional tectonics

thermogenic hydrocarbons in unconsolidated sediment of eel river basin offshore northern california thermally produced hydrocarbons were recovered from unconsolidated sediment ponded within a bathymetric depression on the surface of a shale diapir in the offshore eel river basin of northern california evidence that the hydrocarbons are thermogenic consists of the following 1 very high concentrations of hydrocarbon gases particularly ethane through butanes c2 c4 2 methane having a carbon isotopic composition relative to the pdb standard of 43 and 44 per mil 3 presence of gasoline range c5 hydrocarbons and 4 presence of a complex mixture of heavy hydrocarbons c15 with n alkanes having a petroleumlike distribution this mixture of gaseous and liquid hydrocarbons likely originated deep within the basin an migrated to the surface through fractures and faults developed during the emplacement of the diapir the presence of thermogenic hydrocarbons in unconsolidated surface sediment indicates that conditions for petroleum generation have existed within this offshore basin

gas flux to the atmosphere from mud volcanoes in eastern romania gas flux measurements have for the first time been taken from vents and soil of eastern romania mud volcanoes the largest geological structures in europe releasing methane into the atmosphere in the quiescent phase the methane emission from single vents is up to 28 t yr 1 diffuse soil microseepage is of the order of 10 2 10 5 mg m 2 day 1 a total output of at least 1200 tonnes of ch4 per year can be conservatively estimated over the area investigated alone 2 3 km 2 helium fluxes are up to five orders of magnitude higher than the average flux in a stable continental area pointing to a close link between mud volcanoes and crustal degassing through faults crossing the deep hydrocarbon reservoirs these data represent a key contribution towards refining global ch4 emission estimates which indicate mud volcanoes as a significant and unavoidable source of greenhouse gases for the atmosphere

in situ raman detection of gas hydrates exposed on the seafloor of the south china sea gas hydrates are usually buried in sediments here we report the first discovery of gas hydrates exposed on the seafloor of the south china sea the in situ chemical compositions and cage structures of these hydrates were measured at the depth of 1 130 m below sea level using a raman insertion probe rip gh that was carried and controlled by a remotely operated vehicle rov faxian this in situ analytical technique can avoid the physical and chemical changes associated with the transport of samples from the deep sea to the surface natural gas hydrate samples were analyzed at two sites the in situ spectra suggest that the newly formed hydrate was structure i but contains a small amount of c3h8 and h2s pure gas spectra of ch4 c3h8 and h2s were also observed at the scs sgh02 site these data represent the first in situ proof that free gas can be trapped within the hydrate fabric during rapid hydrate formation we provide the first in situ confirmation of the hydrate growth model for the early stages of formation of crystalline hydrates in a methane rich seafloor environment our work demonstrates that natural hydrate deposits particularly those in the early stages of formation are not monolithic single structures but instead exhibit significant small scale heterogeneities due to inclusions of free gas and the surrounding seawater there inclusions also serve as indicators of the likely hydrate formation mechanism these data also reinforce the importance of correlating visual and in situ measurements when characterizing a sampling site

the origin of muddy sand sediments associated with mud volcanism in the horonobe area of northern hokkaido japan 1 the origin of muddy sand and gas in muddy sand sediments in the horonobe area of northern hokkaido japan was investigated by analyzing the mineralogical and chemical compositions of the sediments and the chemical isotopic compositions of the gas x ray fluorescence and x ray diffraction analyses indicate that chemically the muddy sand is derived from a mixing of components from the hakobuchi and overlying formations and that the characteristic mineral of the muddy sand is heulandite which in the study area has been detected only in the hakobuchi formation these results suggest that the sediments ascended from depths of at least 2200 2400 m the 13cch4 values and the methane ethane propane ratios of the gas indicate that the primary origin of the methane is by thermogenic decomposition of coal bearing beds in the haboro or hakobuchi formations or further deep sources this study provides new data on processes of onshore mud volcanism in japan and contributes to an understanding of processes of subsurface mass transport in regions of mud volcanic activity

activation of gas bubble emissions indicated by the upward decreasing lead 210 activity at a submarine mud volcano ty1 offshore southwestern taiwan abstract a submarine mud volcano mv known as ty1 is one of the largest conical structures found offshore southwestern taiwan active gas bubble emissions at the flat crest of the mud volcano disperse sediment particles into the water column changes in the mud volcanism of ty1 were revealed by radiograph and grain size analysis of the sediment cores 210 pb geochronology was applied to the near seafloor sediments to reveal the detailed mud volcanism from the deposition rate in a 58 cm long sediment core taken from the northern margin of the crest known as ty1 n 170 the size and frequency of the mud clasts decrease upward the clasts are smaller than 8 mm above a sediment depth of 34 cm below the sea floor cmbsf sediments between 0 and 19 cmbsf are massive and particles larger than 2 mm are absent an enrichment of coarse silt sized particles in the massive sediment unit and the restricted distribution of the unit suggest that the massive unit was generated by re deposition of sediment particles that were dispersed into the water column by gas bubble emission these characteristics suggest that during the last mud volcanism of ty1 there was a decrease in mud eruption energy and gas bubble emission became the main activity in core ty1 s 440 taken from the southern slope a massive sediment unit enriched with coarse silt sized particles is intercalated between mud breccia structures this suggests repeated mud breccia flows caused by ty1 the excess 210 pb activity present in the massive sediment unit of ty1 n 170 suggests activation of gas bubble emission in the massive unit a decrease in excess 210 pb activity appears upward toward the seafloor the highest value is 3 1 dpm g at 19 8 cmbsf 26 4 g cm 2 in cumulative mass values lower than 1 0 dpm g are distributed 2 8 6 8 cmbsf 3 6 8 8 g cm 2 the upwardly decreasing trend is opposite that of the reference core from which a reasonable areal sedimentation rate was obtained using a constant flux constant sedimentation model the anomalous depth profile at the massive unit indicates an increasing rate of sediment deposition which originated from the activation of gas bubble emission

the recrystallized grain size piezometer for quartz d 1 0 3 56 0 27 s 1 26 0 13 with no change in slope at the regime 2 3 transition and no effect of temperature or a b stability field another experimental piezometer relation for regime 1 of hirth and tullis 1992 differs in slope suggesting that different recrystallization mechanisms require different piezometer calibrations index terms 3902 mineral physics creep and deformation 5120 physical properties of rocks plasticity diffusion and creep 8030 structural geology microstructures 8159 tectonophysics rheology crust and lithosphere 8164 tectonophysics stresses crust and lithosphere citation stipp m and j tullis the recrystallized grain size piezometer for quartz geophys res lett 30 21 2088 doi 10 1029 2003gl018444 2003

timescales and mechanisms of batholith construction constraints from zircon oxygen isotopes and geochronology of the late variscan serre batholith calabria southern italy abstract the late variscan serre batholith in central calabria represents the middle portion c 13 km thick of a tilted crustal section continuously exposed from lower crustal granulites to upper crustal phyllites the batholith is zoned consisting of several granitoid types that were emplaced at depths ranging from c 23 to c 6 km deep strongly foliated quartz diorites and tonalites were emplaced into migmatitic metapelites the intermediate level granitoids are weakly foliated to unfoliated porphyritic granodiorites and monzogranites and the shallowest bodies are two mica granodiorites and granites grading upward to biotite amphibole granodiorites emplaced into paragneisses and phyllites five samples representative of the main granitoid types in terms of both composition and emplacement depth have been dated by shrimp zircon from a lower crustal quartz diorite gave an emplacement age of 297 3 3 1 ma two middle crustal strongly peraluminous k feldspar megacrystic granites were emplaced at 296 1 1 9 ma and 294 9 2 7 ma a middle to upper crustal two mica monzogranite was emplaced at 294 2 2 6 ma and finally an upper crustal weakly peraluminous granodiorite from the batholith roof was emplaced at 292 2 2 6 ma these results are consistent with the development of the batholith by incremental multipulse overaccretion each granitoid body being in a dominantly rigid state before intrusion of the next with little or no possibility of magma mixing the difference in age between the oldest and youngest granitoids from the batholith floor and roof respectively is 5 1 4 0 ma providing an upper limit of about 9 ma on the time taken for batholith construction the presence in the c 296 294 ma granitoids of c 305 302 ma anatectic zircon with varied th u and oxygen isotope compositions indicates a time interval of 8 9 ma between incipient partial melting in the lower crust and magma emplacement in the middle crust the emplacement of the first granitoid bodies into the top of the lower crust was controlled tectonically by the activation of a deep seated shear zone the shallowest granodiorites were emplaced during the waning stages of the shear zone activity producing late to post tectonic contact metamorphism in the upper crustal phyllites and mylonitic paragneisses

a seismogenic zone in the deep crust indicated by pseudotachylytes and ultramylonites in granulite facies rocks of calabria southern italy pseudotachylyte veins frequently associated with mylonites and ultramylonites occur within migmatitic paragneisses metamonzodiorites as well as felsic and mafic granulites at the base of the section of the hercynian lower crust exposed in calabria southern italy the crustal section is tectonically superposed on lower grade units ultramylonites and pseudotachylytes are particularly well developed in migmatitic paragneisses whereas sparse fault related pseudotachylytes and thin mylonite ultramylonite bands occur in granulite facies rocks the presence of sillimanite and clinopyroxene in ultramylonites and mylonites indicates that relatively high temperature conditions preceded the formation of pseudotachylytes we have analysed pseudotachylytes from different rock types to ascertain their deep crustal origin and to better understand the relationships between brittle and ductile processes during deformation of the deeper crust different protoliths were selected to test how lithology controls pseudotachylyte composition and textures in migmatites and felsic granulites euhedral or cauliflower shaped garnets directly crystallized from pseudotachylyte melts of near andesitic composition this indicates that pseudotachylytes originated at deep crustal conditions 0 75 gpa in mafic protoliths quenched needle to feather shaped high alumina orthopyroxene occurs in contact with newly crystallized plagioclase the pyroxene crystallizes in garnet free and garnet bearing veins the simultaneous growth of orthopyroxene and plagioclase as well as almandine suggests lower crustal origin with pressures in excess of 0 85 gpa the existence of melts of different composition in the same vein indicates the stepwise non equilibrium conditions of frictional melting melt formed and intruded into pre existing anisotropies in mafic granulites brittle faulting is localized in a previously formed thin high temperature mylonite bands migmatitic gneisses are deformed into ultramylonite domains characterized by s c fabric small grain size and fluids lowered the effective stress on the c planes favouring a seismic event and the consequent melt generation microstructures and ductile deformation of pseudotachylytes suggest continuous ductile flow punctuated by episodes of high strain rate leading to seismic events and melting

seafloor gas seeps triggered by a northern california earthquake abstract a series of marine surveys using high resolution seismic reflection and side scan sonar profiling was conducted on the klamath river delta from 1977 to 1985 in november 1980 near the middle of this 8 year time period a major earthquake magnitude 7 occurred in the area the earthquake caused liquefaction of shelf deposits off the klamath river and while mapping the sediment failures we observed an inordinate number of gas vents and acoustic anomalies in the sediment gas charging and water column gas clouds our analyses indicate that a change in gas seepage occurred after the earthquake there was a marked increase in gas abundance immediately after the earthquake a gradual decrease over the next year and stabilization at pre earthquake gas levels within five years or less the acoustic anomalies were observed in pre quaternary rocks as well as in surficial holocene deposits and gas seeps overlay truncated anticlines faults and syncline exposures thus the gas released may have been in part thermogenic in origin a large area 20 km 2 on the delta failed during the earthquake and the abundance of gas seeps and craters in the area suggests that sediment degassing may have been an important process contributing to failure

porphyroblast rotation eppur si muove in a number of recent papers the theory has been postulated that porphyroblasts as a rule do not rotate with respect to geographical coordinates and can be used to determine the original orientation of older foliations complex inclusion patterns in spiral garnets have even been used to advocate a new model of orogenesis involving several alternating phases of horizontal shortening and extension critical assessment of the assumptions and data used to support the theory of irrotational porphyroblasts reveals numerous flaws millipede structures used as proof for flow partitioning can also form by other flow geometries evidence quoted to support irrotational behaviour of porphyroblasts is unsound porphyrobl asts do occur in sets with a preferred orientation of the internal foliation trace but these cannot be shown to represent original orientations microstructures which resemble truncation planes in spiral garnets are used as evidence that these structures developed by several phases of deformation and as proof for periodic extension and horizontal shortening in orogenesis they can however also be explained by intermittent growth of a rotating porphyroblast during a single phase of deformation finally porphyroblast sets in which orientation is a function of aspect ratio indicate that porphyroblast rotation with respect to kinematic axes does occur in at least some situations

strain deformation temperatures and vorticity of flow at the top of the greater himalayan slab everest massif tibet this paper presents quantitative data on strain deformation temperatures and vorticity of flow at the top of the greater himalayan slab the data were collected from the tibetan side of the everest massif where two low angle normal faults bound the upper surface of the greater himalayan slab the earlier and structurally lower lhotse detachment and the later and structurally higher qomolangma detachment greenschist to sillimanite grade quartz rich metasedimentary rocks exposed in the rongbuk to north col region of the everest massif are characterized by cross girdle quartz c axis fabrics indicating approximate plane strain conditions fabric opening angles progressively increase with depth beneath the overlying lhotse detachment and indicate progressively rising deformation temperatures of 525 625 50 c at depths of 300 600 m beneath the detachment deformation temperatures of c 450 c are indicated by fabric opening angles in epidote amphibolite facies mylonites located closer to the overlying detachment a top down to the north normal shear sense is indicated by the asymmetry of microstructures and c axis fabrics but the degree of asymmetry is low at distances greater than 400 m beneath the detachment and sillimanite grains are drawn into adjacent conjugate shear bands but still appear pristine indicating that deformation occurred at close to peak metamorphic temperatures these quenched fabrics and microstructures indicate rapid exhumation in agreement with previous isotopic dating studies mean kinematic vorticity numbers w m were independently calculated by three analytical methods calculated w m values range between 0 67 and 0 98 and indicate that although a simple shear component is generally dominant particularly in greenschist facies mylonites located between the lhotse and overlying qomolangma detachments there is also a major component of pure shear in samples located at 400 600 m beneath the lhotse detachment pure and simple shear make equal contributions at w k 0 71 our integrated strain and vorticity data indicate a shortening of 10 30 perpendicular to the upper surface of the greater himalayan slab and confirm that the upper surface of the slab is a stretching fault with estimated down dip stretches of 10 40 assuming plane strain deformation measured parallel to the flow plane transport direction

methane flux from miniseepage in mud volcanoes of sw taiwan comparison with the data from italy romania and azerbaijan abstract mud volcanoes mvs are considered important methane ch4 sources for the atmosphere gas is not only released from macro seepage i e from craters and visible gas bubbling manifestations but also from invisible and pervasive exhalation from the ground named miniseepage ch4 flux related to miniseepage was measured only in a few mvs in azerbaijan italy japan romania and taiwan this study examines in detail the flux data acquired in 5 mvs and 1 dry seep in sw taiwan and further compares with other 23 mvs in italy romania and azerbaijan miniseepage from the six manifestations in sw taiwan mvs and seeps annually contribute at least 110 tons of methane directly to the atmosphere and represents about 80 of total degassing during a quiescent period combining miniseepage flux and geo electrical data from the wu shan ding mv revealed a possible link between gas flux and electrical resistivity of the vadose zone this suggests that unsaturated subsoil is a preferential zone for shallow gas accumulation and seepage to the atmosphere besides miniseepage flux in chu huo everlasting fire decreases by increasing the distance from the main gas channeling zone and molecular fractionation methane ethane ratio is higher for lower flux seepage consistently with what observed in other mvs worldwide measurements from azerbaijan italy romania and taiwan converge to indicate that miniseepage is directly proportional to the vent output and it is a significant component of the total methane budget of a mv a miniseepage vs macro seepage flux equation has been statistically assessed and it can be used to estimate theoretically at least the order of magnitude of the flux of miniseepage for mvs of which only the flux from vents was evaluated or will be evaluated in future this will allow a more complete and objective quantification of gas emission in mvs thus also refining the estimate of the global methane emission from geological sources

gases in taiwan mud volcanoes chemical composition methane carbon isotopes and gas fluxes abstract mud volcanoes are important pathways for ch 4 emission from deep buried sediments however the importance of gas fluxes have hitherto been neglected in atmospheric source budget considerations in this study gas fluxes have been monitored to examine the stability of their chemical compositions and fluxes spatially and stable c isotopic ratios of ch 4 were determined for several mud volcanoes on land in taiwan the major gas components are ch 4 90 air i e n 2 o 2 ar 1 5 and co 2 1 5 and these associated gas fluxes varied slightly at different mud volcanoes in southwestern taiwan the hsiao kun shui hks mud volcano emits the highest ch 4 concentration ch 4 97 on the other hand the chung lun mud volcano cl shows co 2 up to 85 and much lower ch 4 content 4 content 90 with low co 2 1 methane c 2 ethane c 3 propane and 13 c ch4 results with the exception of mud volcanoes situated along the gu ting keng gtk anticline axis showing unique biogenic characteristics only small ch 4 concentration variations 4 emission fluxes for mud volcanoes on land in taiwan fall in a range between 980 and 2010 tons annually if soil diffusion were taken into account the total amount of mud volcano ch 4 could contribute up to 10 of total natural ch 4 emissions in taiwan

microstructural compositional and petrophysical properties of mylonitic granodiorites from an extensional shear zone rhodope core complex greece at the southern boundary of the rhodope massif ne greece the kavala shear zone ksz represents an example of the eastern mediterranean deep seated extensional tectonic setting during miocene time extensional deformation favoured syntectonic emplacement and subsequent exhumation of plutonic bodies this paper deals with the strain related changes in macroscopic geochemical and microstructural properties of the lithotypes collected along the ksz comprising granitoids from the pluton aplitic dykes and host rock gneisses moreover we investigated the evolution of seismic anisotropy on a suite of granitoid mylonites as a result of progressive strain isotropic compressional and shear wave velocities v p v s and densities calculated from modal proportions and single crystal elastic properties at given pressure temperature p t conditions are compared to respective experimental data including the directional dependence anisotropy of wave velocities compared to the calculated isotropic velocities which are similar for all of the investigated mylonites average values v p 5 87 km s 1 v s 3 4 km s 1 v p v s 1 73 and density 2 65 g cm 3 the seismic measurements give evidence for marked p wave velocity anisotropy up to 6 92 at 400 mpa in the most deformed rock due to marked microstructural changes with progressive strain as highlighted by the alignment of mica chlorite minerals and quartz ribbons the highest p and s wave velocities are parallel to the foliation plane and lowest normal to the foliation plane importantly v p remains constant within the foliation with progressive strain but decreases normal to foliation the potential of the observed seismic anisotropy of the ksz mylonites with respect to detectable seismic reflections is briefly discussed

deformation history of the southwestern taiwan foreland thrust belt insights from tectono sedimentary analyses and balanced cross sections abstract analysis of the basin scale and local deformation history and estimates of shortening rates are performed in the southwestern foreland thrust belt of the plio pleistocene taiwan orogen timing of deformational events is constrained using both syntectonic unconformities and other markers of syndepositional tectonic activity three cross sections are investigated and balanced intermediate shortening rates are estimated based on balanced and restored cross sections the total amount of shortening along studied balanced sections results from superimposed thin skinned and thick skinned styles a shallow aseismic thick decollement is located to depth of 6 8 km at the base of thick late miocene shales that behaves as ductile layer the occurrence of a deep seismic decollement to depth of 12 15 km is confirmed by seismicity fault plane solutions of focal mechanisms and a seismic reflection profile providing evidence of reactivated and inverted inherited extensional features beneath the coastal plain three major tectonic stages are recognized within the southwestern foothills which are correlated with local thrusting events the first stage begins at 5 ma with the onset of the taiwan collision and ends at 2 1 6 ma it reflects an initial submarine accretionary stage associated with moderate tectonic activity the second major stage occurs during late pliocene early pleistocene this intermediate collision stage sealed the evolution of the southern foreland thrust wedge from submarine to continental environment in relation with exhumation and denudation of the central range the last stage of deformation begins in the middle pleistocene and continues until present it is associated with high rates of sedimentation and most of the thrusts are activated or reactivated at that time and out of sequence thrusting occurs the collision started synchronously near 5 ma throughout the southwestern taiwan total and intermediate shortening rates are more or less constant through time in studied sections that may suggest that long term deformation in the taiwan foreland thrust belt occurred more or less at steady state since 5 ma the southward decrease of rates of shortening from 3 6 to 4 8 mm year in northern sections to 2 2 mm year in southern section might be related to both influence of indentation by the peikang high to the north and southward transition at the scale of the southwestern foothills from collision to subduction setting the effect of the obliquity of the convergence resulting in regional southward migration of the collision cannot be definitely inferred from this analysis our results place new kinematic and time constraints which must be taken into account in forthcoming geodynamic models of the taiwan collision

structural setting of a transpressive shear zone insights from geological mapping quartz petrofabric and kinematic vorticity analysis in ne sardinia italy

on the post 25 ma geodynamic evolution of the western mediterranean during the neogene and quaternary western mediterranean geodynamics were dominated by the eastward migration of the apenninic arc and associated back arc basins the migration was controlled by retreat of the apenninic slab and was associated with boudinage of the lithosphere in the back arc area palaeo reconstruction of the kinematics of the arc suggests about 775 km of migration from the late oligocene to present along a transect from the gulf of lions to calabria a maximum of 135 km of n s converge occurred between africa and europe during the same time span the western mediterranean was thus mainly shaped by the migration of the slab related to west directed subduction it is hypothesized that minor n s convergence deformed the arc but was not the cause of its formation 1998 elsevier science b v all rights reserved

quantitative microstructural analysis of mylonites formed during alpine tectonics in the western mediterranean realm abstract quantitative microstructural investigations involving new gis based tools are applied to three different types of mylonitic rocks these techniques enable mineral shape distribution maps to be produced thereby allowing the nature and relative percentage of the weakening vs hardening layers as well as their kinematics to be obtained within a statistically meaningful dataset selected rock types are derived from shearing associated with the meso alpine strike slip tectonics of the western mediterranean realm which since the paleocene has involved skarn migmatitic paragneiss and tonalites these rocks belong to a deep seated portion of the original southern european variscan chain known as the calabrian pelortani orogen microstructural maps reveal porphyroclastic domains represented alternatively by feldspar amphibole pyroxene or scapolite that can be distinguished from weakening phase areas characterised by quartz biotite plus quartz or alternatively by calcite when the weakening layer is controlled predominantly by skarns image elaboration of porphyroclastic domains was employed to estimate the dominant shear type with rigid grain analysis indicating a pure shear component of 66 68 for the mylonitic tonalites 62 66 for the mylonitic paragneisses and 58 62 for the mylonitic skarn grain boundary mapping of the quartz rich domains also permits an estimate of shear strain rate which ranges from 1 14 10 12 1 s for mylonitic paragneiss to 5 91 10 12 1 s for mylonitic tonalite and is in accord with high strain zones in natural settings finally our results opened up new perspectives in the interpretation of the kinematics and rheology of this exhumed sector of the southern european variscan chain reflecting the deep seated meso alpine strike slip tectonics of the western mediterranean realm