ground penetrating radar assisted saturation and permeability estimation in bimodal systems near surface investigations often require characterization of vadose zone hydraulic parameters conventional sampling or borehole techniques for estimating these parameters are costly time consuming and invasive all of which limit collection of hydrogeological data at a spacing needed for detailed site characterization incorporation of two or three dimensional densely sampled geophysical data with conventional hydrological data increases the amount of data available for the characterization and thus has the potential to significantly improve the hydraulic parameter estimates over those obtained from borehole data alone the hydraulic estimation procedure can be greatly improved by incorporating dielectric information potentially available from ground penetrating radar gpr a noninvasive high resolution geophysical method the procedures for collecting and processing gpr data in the format needed for the proposed estimation technique are relatively new and still a topic of research our method requires as a starting point the ability to estimate dielectric constants from gpr data numerical experiments were performed to investigate the general utility of the gpr assisted estimation technique under a range of conditions three bimodal systems were investigated each system being composed of a sand facies together with another facies with a larger clay volume fraction each facies was defined using characteristic values of clay content porosity and permeability using dielectric information and petrophysical relations degree of saturation and intrinsic permeability values at each location within the three systems were identified for bimodal systems a dielectric constant measurement corresponds to two possible values of saturation and intrinsic permeability at each location single values of saturation and intrinsic permeability were estimated from these values using the principle of maximum likelihood results from case studies demonstrate that a combination of gpr data with conventional borehole data significantly improves the estimates of saturation and has the potential to improve the estimates of permeability over those obtained from well bore data alone the proposed method should be especially advantageous for vadose zone characterization in areas favorable for gpr data acquisition where detailed hydraulic parameter information is required but the drilling of numerous boreholes is prohibited

the evolution of the western ligurian flysch units and the role of mud diapirism in ancient accretionary prisms maritime alps northwestern italy the western ligurian flysch units represent an upper cretaceous to paleogene accretionary prism overthrust onto the paleo european continental margin during the collisional stages of the alpine orogeny eocene their precollisional evolution has been reconsidered according to the data collected through extensive field mapping the study of lowgrade metamorphism and by considering more strictly the processes documented in modern convergent zones

seep carbonates in a thrust related anticline at the leading edge of an orogenic wedge the case of the middle late miocene salsomaggiore ridge northern apennines italy abstract seep carbonates are important indicators of submarine fluid expulsion and dewatering of sediments along convergent margins and accretionary prisms in the northern apennine compressional wedge seep carbonates usually occur in pelitic successions from different settings of the middle late miocene foreland basin system in serravallian foredeep deposits of the salsomaggiore area seep carbonates cemented and or encrusted coarse grained sandstones and conglomerates fluid expulsion strictly related to variable intensities in tectonic stresses generated seep carbonate facies and sediment instabilities depending on the position of the fluid pathway feeders within the salsomaggiore ridge a middle late miocene intra basinal high at the leading edge of the apenninic orogenic wedge this site provides a unique opportunity for analyzing depositional characters and the three dimensional distribution and evolution of a seepage system in a thrust related anticline the resulting evolutionary model shares common features with recent ridges in other accretionary wedges in this model a strict relationship between tectonics seepage and sediment instability during a major tectonic phase is outlined

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

miocene chemoherms of the northern apennines italy in the miocene of the northern apennines methane derived limestones from various geologic settings represent important examples of fossil chemoherms and provide a basis for more accurate interpretations of seepage systems the systematic study of fossil chemoherms has allowed the definition of new field and compositional criteria for the recognition of these deposits which were previously based almost exclusively on negative carbon isotope composition and peculiar chemosynthetic communities this has constrained the relations between seepage and sedimentary and tectonic instability processes we suggest that the peculiar brecciated structures associated with fossil chemoherms are related to diapirism of overpressured pelitic sediments due to fluid venting fluidization of sediments increases the instability of mudstones in which chemoherms are contained thus favoring gravity slumping processes and the reworking of many chemoherms

the structure and geomorphology of the dashgil mud volcano azerbaijan the large scale and small scale 10 m structure and geomorphology of the active dashgil mud volcano in central azerbaijan have been studied through historical records it is known that this mud volcano has major eruptions every 6 32 years the activity observed during two field trips in 1995 consisted of low energy venting and debouching of mud water oil and gas from three mud pools salses and about 20 individual cones gryphons located on the summit plateau of the mud volcano besides the bubbling mud pools ranging from 30 to 75 m across and the cones ranging from 0 8 to 3 m height a 200 m long string of about 10 sinter mounds was found on the summit plateau the internal structure of the mud volcano and the processes responsible for the observed dashgil geomorphology are discussed assuming the dashgil mud volcano to be continuously active with an average methane production similar to that observed in 1995 between the rare major eruptions we have conservatively estimated the dashgil mud volcano to produce an annual amount of at least 800 sm3 standard cubic metres of gas mainly methane which is emitted directly into the atmosphere this estimate indicates that the natural contribution of atmospheric greenhouse radiatively active gases from the world s terrestrial and submarine mud volcanoes is highly significant

mud volcanism in the gulf of cadiz results from the ttr 10 cruise a new deep water mud volcano field between 2000 and 3500 m water depth was discovered in the deep south portuguese margin as well as several new mud volcanoes in the south spanish and western moroccan margins of the gulf of cadiz during the ttr 10 training through research unesco ioc cruise in july august 2000 this work followed the discovery of a large mud volcano field in the gulf of cadiz first investigated during the ttr 9 cruise gardner 2001 geophys res lett 28 339 342 kenyon et al 2000 ioc technical series no 56 the discoveries were made based on a seamap side scan sonar mosaic and multibeam bathymetry seabeam collected in the area by the naval research laboratory nrl washington dc usa in 1992 kindly released for this purpose single channel seismics long range side scan sonar okean tv controlled grab hull mounted 3 5 khz profiler and coring were used to investigate several seafloor features observed on the side scan sonar imagery in the south iberia spanish and moroccan margins of the gulf of cadiz which were confirmed to be mud volcanoes the typical structures related to fluid venting in the gulf of cadiz are essentially represented by conical mud volcanoes with diameters ranging from several tens of meters to 4 km and heights that can reach 200 m some of these structures appear to be aligned along major conjugate ne sw and nw se trending faults that can be identified on the side scan sonar imagery the new field discovered in the south portuguese margin is the deepest in the gulf of cadiz area and includes three new mud volcanoes bonjardim olenin and carlos ribeiro which seem to be quite active with near surface gas hydrate occurrence and a high saturation in h2s and hydrocarbon gases mainly methane in the mud breccia and overlying pelagic sediments gas hydrates were recovered from the bonjardim mud volcano an intensely gassified mud breccia with one fragment of semi consolidated claystone with a thin bituminous veneer at the surface was recovered from the carlos ribeiro mud volcano the fauna recovered consists mainly of pogonophoran worms belonging to several species and undetermined species of foraminifera three new mud volcanoes were also discovered in the nw moroccan margin rabat student and jesus baraza these show a richer fauna that includes several species of molluscs polychaetes pogonophoran worms crustaceans echinoderms and some fragments of dead coral madrepora and lophelia carbonate crusts were recovered from the student mud volcano the ginsburg mud volcano discovered during the previous ttr 9 cruise was revisited and gas hydrates recovered once again a new mud volcano was also discovered in the spanish margin tasyo where evidence was found of coral build ups on the hard substratum of the mud volcanic edifice

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

a lost tethyan evaporitic basin evidence from a cretaceous hemipelagic meta selenite red chert association in the eastern mediterranean realm

the pliocene age stirone river hydrocarbon chemoherm complex northern apennines italy abstract the stirone river section in the italian northern apennines hosts a rare example of pliocene age hydrocarbon imprinted carbonates in the mediterranean basin associated with deep water hemipelagic lithologies these include meter sized dolomite cemented chimneys micritic brecciated limestones lucina mudstones and chemosymbiotic bivalve shells some such chimneys show 13 c values as low as 37 5 vpdb suggesting subsurface precipitation of authigenic dolomite induced by anaerobic oxidation of methane triggered by consortia of sulphate reducing bacteria these carbonates are interpreted as part of the plumbing system related to hydrocarbon expulsion onto the seafloor resulting from hydrocarbon enriched defluidization processes dated at an interval at 3 6 3 3 ma and associated with the thrust related salsomaggiore structure

the cenozoic ch4 derived carbonates of monferrato nw italy a solid evidence of fluid circulation in the sedimentary column abstract two types of methane derived carbonates each with different lithological and paleontological signatures have been distinguished in the oligocene miocene sediments of monferrato nw italy 1 irregularly shaped metre sized rock bodies characterized by the widespread occurrence of remains of large bivalves lucina sp these bodies include two subtypes differing in the lithological characteristics of the cemented sediments a lucina rich marly limestones encased in langhian outer shelf marls they document a slow seepage of ch4 rich fluids at the paleo sea floor b lucina bearing cemented mud breccias found either as cemented masses in the original stratigraphic position or as redeposited blocks within upper messinian chaotic block in matrix sediments these carbonate bodies document the activity of submarine mud volcanoes during the late messinian in particular they document intermittent fluid emission ranging from violent eruptive phases responsible for the extrusion of soft mud breccias at the sea floor to quiet degassing phases that promoted colonization by chemosymbiotic communities and localized cementation 2 very irregularly shaped strongly cemented mainly coarse grained clastic sediments reaching the lateral extent of few hundred meters and the thickness of few tens of meters they occur within oligocene to messinian sediments lack remains of chemosymbiotic taxa and are highly fractured with fractures filled with sediments and cements these carbonate cemented masses here referred to as macroconcretions result from the precipitation of carbonate cements within buried sediments flushed by ascending ch4 rich fluids they document a complex fluid circulation pattern in the sedimentary column in which so4 rich waters were drawn from surrounding sediments by the fast and prolonged flow of ch4 rich fluids and promoted anaerobic oxidation of methane and the precipitation of carbonate cements the polyphase network of clastic dykes and veins that characterize macroconcretions is related to an intermittent fluid flow regime dykes formed during fast upward flows of sediment rich fluids whereas carbonate filled veins formed during slower degassing phases the local lithostratigraphic and structural framework allow to correlate genetically and chronologically the macroconcretions to lucina bearing mud breccias consequently macroconcretions are here regarded as the result of cementation along fluid conduits feeding messinian mud volcanoes at the sea floor the massive release of fluids could have played a role in triggering large scale mass wasting events responsible for the emplacement of sedimentary melanges including ch4 derived rocks in the messinian

a genetic model of hydrocarbon derived carbonate chimneys in shelfal fine grained sediments the enza river field northern apennines italy abstract methane derived authigenic carbonate mdac concretions have been recently exposed in the pleistocene argille azzurre fm outcropping along the enza riverbanks northern apennines foothills italy the relations between the sediment deposition the coeval tectonic deformation and the mdac concretions have been investigated to unravel the mechanism of methane migration through the sediments and the processes leading to mdac occurrence the biogenic methane responsible for the formation of mdac chimneys and slabs has been generated in the organic rich pliocene sediments located in the po plain subsurface the gas migrated up dip towards the northern apennines foothills the mdac cements are mainly composed of dolomite whose precipitation requires thousand years and the absence of so 4 in the pore fluids according with the sedimentation rates of the mdac hosting pleistocene succession the sulphate methane transition zone migrated upwards faster than time required for dolomite precipitation therefore the connate water migrating together with the methane could have acted as second dic source allowing the mdac formation also in the methane rich zone

inversion of tracer test data using tomographic constraints 1 we have developed a methodology for inverting tracer test data using zonation information obtained from two dimensional radar tomograms to improve the typically overly smooth hydraulic conductivity fields obtained from conventional inversion of tracer test data the method simultaneously yields two dimensional estimates of hydraulic conductivity as well as petrophysical relationships that relate hydraulic conductivity to radar velocity these relationships can be assumed to be stationary throughout the area of investigation or to vary as a function of zonation using a synthetic three dimensional hydraulic conductivity field we apply the developed inversion methodology and explore the impact of the strength and stationarity of the petrophysical relationship as well as the impact of errors that are often associated with radar data acquisition such as unknown borehole deviation we find that adding radar tomographic data to tracer test data improves hydrogeological site characterization even in the presence of minor radar data errors the results are contingent on the assumption that a relationship between radar velocity and hydraulic conductivity exists therefore the applicability of the proposed method may be limited to field sites where this condition is partially or fully satisfied

bayesian method for hydrogeological site characterization using borehole and geophysical survey data theory and application to the lawrence livermore national laboratory superfund site a stochastic bayesian approach for combining well logs and geophysical surveys for enhancing subsurface characterization is presented the main challenge we face is in creating the bridge to link between ambiguously related geophysical surveys and well data the second challenge is imposed by the disparity between the scale of the geophysical survey and the scale of the well logs our approach is intended to integrate and transform the well log data to a form where it can be updated by the geophysical survey and this tends to be a convoluted process our approach starts with generating images of the lithology conditional to well logs each lithology image is then used as the basis for generating a series of shaliness images conditional to well log data shaliness images are converted to resistivity images using a site specific petrophysical model relating between shaliness resistivity and lithology to create the necessary interface with the cross well resistivity survey the lithology and resistivity images are then updated using cross well electromagnetic resistivity surveys we explored the limits of the approach through synthetic surveys of different resolutions and error levels employing the relationships between the geophysical and hydrological attributes which are weak nonlinear or both the synthetic surveys closely mimic the conditions at the llnl superfund site we show that the proposed stochastic bayesian approach improves hydrogeological site characterization even when using low resolution resistivity surveys

marine pore water sulfate profiles indicate in situ methane flux from underlying gas hydrate marine pore water sulfate profiles measured in piston cores are used to estimate methane flux toward the sea floor and to detect anomalous methane gradients within sediments overlying a major gas hydrate deposit at the carolina rise and blake ridge u s atlantic continental margin here sulfate gradients are linear implying that sulfate depletion is driven by methane flux from below rather than by the flux of sedimentary organic matter from above thus these linear sulfate gradients can be used to quantify and assess in situ methane flux which is a function of the methane inventory below

high resolution shallow seismic experiments in sand part ii velocities in shallow unconsolidated sand we conducted a shallow high resolution seismic reflection and refraction experiment on a sandy beach the depth of investigation was about 2 m we interpret the data using the hertz mindlin contact theory combined with gassmann s equation these were used to obtain the vertical velocity profile then the profile was computed from seismic data using the turning rays approximation the normal moveout nmo velocity at the depth of 2 m matches the velocity profile as a result we developed a method to invert measured velocity from first arrivals i e velocity versus distance into velocity versus depth using only one adjustable parameter this parameter contains all the information about the internal structure and elasticity of the sand the lowest velocity observed was about 40 m s it is noteworthy that the theoretical lower bound for velocity in dry sand with air is as low as 13 m s we find that modeling sand as a quartz sphere pack does not quantitatively agree with the measured data however the the

authigenic carbonates in upper miocene sediments of the tertiary piedmont basin nw italy vestiges of an ancient gas hydrate stability zone a wide array of carbonate rich rocks has been recognized in the tertiary piedmont basin nw italy hosted in lower messinian slope deposits carbonate cements show negative 13 c values and positive 18 o values suggesting that carbonate precipitation was induced by microbial degradation of methane produced from gas hydrate destabilization two groups of rocks have been distinguished 1 lucina bearing mud breccias representing the seafloor product of an ancient seepage site and 2 lucina free concretions originating below the sediment water interface within this group two subtypes have been further distinguished stratiform concretions and cylindrical concretions stratiform concretions result from precipitation of dolomite in the pores of muddy sediments some of them display a brecciated structure others show a network of septarian like cracks that are empty filled with sediments or zoned carbonate cements their internal features are related to the formation of gas hydrates within the sediments and to their destabilization thus these rocks mark a portion of the sedimentary column located within a paleo gas hydrate stability zone cylindrical concretions represent ancient fluid conduits related to the upward migration of ch 4 rich fluids subsequent to gas hydrate destabilization the carbonate rich rocks of the tertiary piedmont basin stand as one of the first examples of methane derived rocks that record successive episodes of dissociation and re formation of gas hydrates and they provide precious elements to model the general evolution of a portion of the sedimentary column located within the hydrate stability zone

carbon oxygen and strontium isotopic constraints on fluid sources temperatures and biogeochemical processes during the formation of seep carbonates secchia river site northern apennines abstract understanding authigenic seep carbonate formation provides clues for hydrocarbon exploration and insights into contributions to gas budgets of marine environments and the atmosphere seep carbonates discovered in the outcropping succession along the secchia riverbanks near modena italy belong to the argille azzurre formation of early pleistocene age deposited in an upper shelf environment overlying the miocene foredeep successions which include hydrocarbon fields the fluid migration from the hydrocarbon fields up to the surface is presently active on land and started in the marine succession during the late miocene authigenic globular carbonate concretions and carbonate chimneys are interspersed along the strata throughout the section a comprehensive geochemical characterisation of the carbonates has been carried out to understand the processes leading to their formation the carbonate concretions are the record of past hydrocarbon vents linked to the miocene petroleum system of the northern apennines the samples are composed of 50 microcrystalline dolomite the 13 c signatures identify two groups in the samples according to different type of formation processes globular concretions have positive values that suggest an influence of co 2 associated to secondary methanogenesis due to microbial degradation of higher hydrocarbons the analysed chimney with negative 13 c values is interpreted as former conduit where carbonate precipitation is promoted by anaerobic oxidation of methane coupled with sulfate reduction the 18 o range coupled with 87 86 sr signatures indicate that the contribution of deep connate water from the miocene reservoirs is up to 23 during the formation of the globular concretions the connate water occurrence is also documented by higher ambient temperatures the different isotope signatures in seep carbonates result from the relative contribution of the recognised gas and water components linked to different plumbing systems and fluid supply from a well defined hydrocarbon field the seep carbonate characteristics have enlightened variations in biogeochemical processes which can be rarely quantified in ancient and present day marine environments

mapping permeability in heterogeneous aquifers using hydrologic and seismic data a new method is presented for identification of the permeability distribution in near surface aquifers in addition to using the usual sparsely sampled pressure and permeability data the method incorporates densely sampled seismic data as obtained from a reflection or tomography survey along with empirical relationships between seismic and hydraulic properties the procedure is to first estimate by hydrologic inversion a pressure field then the velocity permeability pressure relationship is used to map the inverted pressure and measured seismic data to multivalued estimates of the permeability of those the most probable value based on the hydrologic inversion is selected in synthetic case studies the tremendous increase in coverage offered by the seismic data leads to dramatically better results in terms of both accuracy and resolution an appealing feature is the use of relatively easy to acquire pressure data a second is the incorporation of geophysical data which can sample an entire aquifer remotely without the need for an expensive and invasive drilling program

two 30 000 year high resolution greyvalue time series from the santa barbara basin and the guaymas basin this paper is included in the special publication entitled geological evolution of ocean basins results from the ocean drilling program edited by a cramp c j macleod s v lee and e j w jones two 30 000 year records of sedimentary greyvalues from the santa barbara basin and the guaymas basin are presented the records exhibit substantial variability on all timescales from millennial to annual strong shifts towards darker greyvalues parallel the postglacial sea level rise approximately 1500 year cycles occur persistently in both records spectral analyses proved the existence of gleissberg 86 year sunspot 11 year 22 year and el nino 3 9 year cycles in almost all cores from both sites in particular el nino southern oscillation forcing could be traced back until the end of the last glacial cold period both time series show a high degree of similarity both in the time and the frequency domain indicating equivalent system responses to external forcing events

derivation of site specific relationships between hydraulic parameters and p wave velocities based on hydraulic and seismic tomography derivation of site specific relationships between hydraulic parameters and p wave velocities based on hydraulic and seismic tomography brauchler r 1 doetsch j 1 2 dietrich p 3 sauter m 4 eth zurich department of earth sciences sonneggstrasse 5 8092 zurich switzerland now at earth sciences division lawrence berkeley national laboratory one cyclotron road berkeley ca 94720 ufz helmholtz centre for environmental research department monitoring and exploration technologies permoserstrasse 15 04318 leipzig germany geoscientific centre university of gottingen goldschmidtstrase 3 37077 gottingen germany

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

dolomite chimneys as possible evidence of coastal fluid expulsion uppermost otago continental slope southern new zealand abstract a suite of carbonate chimneys slabs and ridges occur on a 1 km 2 220 m deep terrace on the uppermost continental slope east of the otago peninsula new zealand carbonate content and petrographic observations suggest cementation took place just below the sediment water interface encrustation borings and the abundance of chimneys and carbonate debris observed today on the uppermost slope suggest that the chimneys have been exhumed and are relict features with a maximum radiocarbon age of 33 000 550 yr b p negative 13 c values of 4 9 to 12 8 pdb indicate that the carbon contained within the cement was derived from the biogenic degradation of organic matter a 18 o composition of 4 9 to 5 4 pdb suggests a marine origin palaeotempertures of precipitation are consistent with modern bottom water temperatures cement in the chimneys is considered to be derived from aquifer forced ground water marine in character and sourced from the exposed inner middle shelf during glacially lowered sea level this contrasts with the tectonically induced fluid flow proposed for vent sites on convergent margins

submersible study of mud volcanoes seaward of the barbados accretionary wedge sedimentology structure and rheology abstract in 1992 the nautile went to a mud volcano field located east of the barbados accretionary wedge near 13 50n using nannofossil analysis on cores we determined the sedimentation rate and provided a new estimation of the age of the mud volcanoes 750 000 years for the oldest one six structures have been explored with the submersible nautile and manifestations of fluid venting chimneys carbonate cementation and chemosynthetic communities were observed on all sedimentological analysis identifies two sources of diapiric mud most mud volcanoes expel mud containing late miocene to quaternary faunae that have the same composition as sediments drilled above the barbados wedge decollement one volcano also contains older oligocene taxa with a mud composition corresponding to the sedimentary sequence below the decollement we use diving observations to map the fine scale morphology the distribution of chemosynthetic fauna and define two end member types of structures mud pies flat topped mud volcanoes and conical mounds mud pies atalante and cyclops are characterised by the presence of a lake of highporosity mud 70 to 75 in their central parts chemosynthetic benthic communities calyptogena colonies and sponge bushes are concentrated in the outer parts contrasting morphologies of the two mud pies indicate different stages of activity cyclops is growing whereas atalante is collapsing expulsion of water and methane occurs mostly through the mud lake and may be stronger during the collapse phase on conical mounds there are no mud lakes fluid venting concentrates near the summit and occurs through carbonate cemented chimneys which form within the sediment viscosity measurements have been carried out on mud samples from the two mud pies and one conical mound all mud samples have a plastic fluid behaviour the plastic threshold decreases with porosity and thixotropy is observed for a porosity of more than 70 an analogue experiment shows that for this thixotropic mud shearing in the feeding conduit liquefies the mud which then spreads to form a mud pie conical mounds form when the mud remains plastic we show that the dissociation of methane hydrate is the cause of the high porosity in mud pies and confirm that these structures are a consequence of large scale dissociation of methane hydrate at the base of its stability field dissociation of hydrates before and during ascent is only slightly contributing to the pore fluid in conical mounds but solid hydrates still present in the mud may contribute to its buoyancy

a miocene mud volcano and its plumbing system a chaotic complex revisited monferrato nw italy abstract chaotic deposits are frequently reported in the geological literature and are commonly interpreted as olistostromes or tectonic melanges a chaotic complex in the cenozoic succession of monferrato nw italy consists of interbedded mud breccia and burrowed silty clays that are pierced by sheared mud breccias and embed carbonate cemented blocks these may be represented by microcrystalline limestones or strongly cemented matrix supported breccias locally containing remains of chemosymbiotic organisms lucinid bivalves moreover cylindrical concretions up to 15 cm in diameter and 1 m long occur in the chaotic complex and crosscut bedding planes at high angles the cement of all these lithified portions is mainly dolomite characterized by low 13c values from 10 3 to 23 pdb and 18o values up to 7 pdb the 13c values testify to precipitation of carbonates induced by microbial oxidation of methane whereas the markedly positive 18o signature ubiquitous in the cylindrical concretions is the evidence for the presence and destabilization of gas hydrates the studied section provides a well exposed example of the geological record of the birth life and death of a mud volcano unsheared soft mud breccias represent mud flows along the flanks of the volcano whereas sheared mud breccias are the result of the injection of unconsolidated overpressured fine grained sediments both taking place during eruptive phases they were followed by more quiet stages of hemipelagic sedimentation burrowing and ch4 seeping the cylindrical concretions represent the first described ancient example of the chimneys observed in present day mud volcano settings they are the remnants of a cold seep plumbing network that crosscut the mud volcano edifice the chimneys were the pathway for the expulsion toward the sea floor of gas and sediment charged fluids likely originated from destabilization of methane gas hydrates the association of mud breccias and methane derived carbonates may not be due to mass gravity flows but can be primary and therefore is a diagnostic criterion for recognizing chaotic deposits due to mud volcano activity in the geological record

stable isotopic ratios and origins of the carbonates associated with cold seepage at the eastern nankai trough two types of cold seeps were located at the eastern nankai trough 1 seeps on sediment covered seafloor of 3800 3600 m in depth at the toe of the accretionary prism and 2 those between 1900 and 2100 m situated on the backthrust of the accretionary prism covered with rough outcrops of calcareous sandstones fragments of sandstone pipes or chimneys cemented with calcite were recovered from type 1 seeps whereas in type 2 seeps massive carbonate cemented sandstones and silty sandstones were obtained many of which contain cemented fragments of different lithologies and textures including dense aggregates of fossilcalyptogena type clam shells the carbon isotopic ratios of the carbonates in these sediments range from 36 to 56 pdb the carbonates formed by mixing between isotopically light carbonate ions derived from biogenic methane carried from depth in advecting fluids and heavy marine sedimentary carbonates sharp isotopic gradients in carbon and sometimes also in oxygen from the mixing processes are still retained across the walls of the sandstone pipes from type 1 seeps whereas the isotopic ratios of the samples from type 2 seeps exhibit variation patterns related to lithologies and textures and confirm the presence of several generations of carbonate cement within a single specimen these facts and the oxygen isotopic ratios of live and fossil clam shells recovered from the survey areas suggest that the cold seeps started at least during the last glaciation and have experienced repeated destruction and reformation due to episodic supply of methane rich fluid of different isotopic ratios and or temperature

the chimney forest of the deep montenegrin margin south eastern adriatic sea a spectacular field of columnar carbonates has been discovered on the montenegrin margin in the southern adriatic sea at a depth of about 450 m the site exposes many columnar carbonates protruding from the substrate or abated on the bottom such carbonates attain maximum visible lengths of ca 60 cm with diameters up to 20 cm display an annular growth and are either hollow or plugged by indurated sediment petrographic and geochemical analyses document the pervasive presence of dolomite and 13c values as low as 30 vpdb these chimneys are therefore interpreted as former conduits related to hydrocarbon expulsion in this sector of the adriatic basin however available data suggest that hydrocarbon flows at this site have ceased our results show that chimneys formed inside the local depositional units glacial pleistocene shelf shelly rich muddy sediment and were successively exhumed from the host sediment today the chimneys offer substrate to benthic life including cold water corals and sponges the u series dating of these carbonate concretions is complicated by the presence of a significant fraction of detrital sediment which represents a major source of initial 230th ams 14c and 87sr 86sr dating of shells embedded in one of the chimney provided ages beyond the range of radiocarbon dating and 600 kyrs indicating a pleistocene age of the host sediment uncorrected u series dating of the carbonate chimneys yielded and age of ca 250 270 kyrs providing a temporal upper limit for conduit formation driven by lithification caused by the degradation of seeping hydrocarbons in addition u th dating of cold water coral bases settled on chimneys indicates a holocene age for their first exposure after exhumation and subsequent function as hard substrate for benthic organisms the montenegrin chimney forest is a rare case where many such carbonate columnar concretions are still in their original vertical position

late miocene seep carbonates and fluid migration on top of the montepetra intrabasinal high northern apennines italy relations with synsedimentary folding abstract during the miocene hydrocarbon seep carbonates located atop intrabasinal highs and associated with sediment instability formed commonly at the deformation front of the northern apennine collisional orogen the parallelism between the structural trend and the distribution of seep carbonates suggests a close relationship between tectonics and gas fluid emission the montepetra intrabasinal high was formed during the closure stage of the foredeep being related to the synsedimentary growth of an anticline field geometry suggests that detachment folding was the leading mechanism of anticline growth and synsedimentary instability along the anticline flanks ten different bodies of seep carbonates occur in the tortonian early messinian sediments nine in the hinge zone and one in the southern backlimb of the anticline foraminiferal study geochemistry facies investigation and the three dimensional geometry of carbonate bodies with respect to the encasing terrigenous sediments indicate a protracted late tortonian early messinian activity of fluid migration with re mobilization and ascent of sediments from the core of the anticline stabilization of chemosynthesis related communities and in situ brecciation seepage atop the intrabasinal high was fed by different circuits one related to the compaction dewatering of shallow tortonian early messinian sediments and a deeper one related to the deformation of the anticline core and to the activity of detachment surfaces and of faults propagating through the sedimentary cover

miocene tubular concretions in east coast basin new zealand analogue for the subsurface plumbing of cold seeps the uplifted accretionary prism of east coast basin in hikurangi margin north island new zealand exposes late miocene slope mudrocks whangaehu mudstone 10 carbonate in coastal cliffs north of cape turnagain that contain conspicuous tubular carbonate concretions 50 85 carbonate supporting near central conduits pipe and bulbous morphologies dominate ranging in exposed length up to 5 m and up to 1 m in diameter the concretions were formed by the precipitation of micritic dolomite and calcite cement within the host mudstone at shallow burial depths 100 m 13c values of the cement range from 22 to 13 pdb and are interpreted to reflect carbonate precipitation from either the extensive anaerobic oxidation of methane aom and or mixing of microbial methane and methanogenic co2 aom is confirmed by lipid biomarker evidence indicating that methane oxidation occurred in the sediments at the time of carbonate precipitation the mixed dolomite calcite mineralogies and the trend of 13c in the tubular concretions from strongly negative to strongly positive values are interpreted to reflect methane oxidation from the onset of ascent through to the end of a migration event depleted and enriched 18o values suggest an evolved fluid source influenced by the dissociation of gas hydrates collectively our results indicate that the tubular concretions within the upper slope mudstones delineate parts of the subsurface plumbing network of a cold seep system on the late miocene paleo hikurangi margin in which the fluids were sourced from ascending methane the intermediate location of the whangaehu concretions between older early miocene seep carbonates to the west and modern ones offshore to the east indicates a progressive eastwards shift with time of a long lived if only periodically active seep system the concretionary plumbing features at whangaehu provide a conceptual model for subsurface fluid pathways and seep related processes beneath the modern hikurangi margin seabed and possibly also for other modern and ancient cold seep carbonate systems

significance of mud volcanism 1 mud volcanism and diapirism have puzzled geoscientists for 2 centuries they have been described onshore and offshore in many places on earth and although they occur in various tectonic settings the majority of the features known to date are located in compressional tectonic scenarios this paper summarizes the main thrusts in mud volcano research as well as the various regions in which mud volcanism has been described mud volcanoes show variable geometry up to tens of kilometers in diameter and several hundred meters in height and a great diversity regarding the origin of the fluid and solid phases gas predominantly methane water and mud may be mobilized at subbottom depth of only a few meters but in places can originate from several kilometers depth with minor crustal or mantle input the possible contribution of mud extrusion to global budgets both from quiescent fluid emission and from the extrusive processes themselves is important in regions where mud volcanoes are abundant such as the collision zones between africa and eurasia fluid flux through mud extrusion exceeds the compaction driven pore fluid expulsion of the accretionary wedge also quiescent degassing of mud volcanoes may contribute significantly to volatile budgets and hence to greenhouse climate

applications of algebraic reconstruction techniques to crosshole seismic data tomographic imaging techniques were applied to two crosshole data sets to determine the velocity structures and the reliability and resolution of the algorithms on real data the experiments were carried out at the retsoff salt mine in new york and at the underground radioactive waste study site at the stripa mine facility in sweden the traveltimes at restoff were high quality and were obtained over raypaths of up to 500 m in length the structure was quite complicated with velocity contrasts up to 50 percent the stripa site was in granitic rock with velocity contrasts of only a few percent the dimensions of the experiment were small with maximum ray lengths of just over 10 m the data at this site were collected with very high accuracy source and receiver locations were measured to better than 1 0 mm and traveltimes were read to 0 001 ms a number of algorithms similar to the algebraic reconstruction techniques art used in medical imaging have been applied to the data some modifications of the algorithms such as the application of weighting schemes damping parameters and curved raypaths were performed the resulting velocity fields were compared to the known fields and with each other to determine an optimal method the algorithms were found to be a rapid reliable means of reconstructing the slowness field of real data low velocity zones were recovered with accuracy in location and value it was also found that great care was necessary in application of the techniques to ensure that proper damping parameters are used and the proper number of iterations taken otherwise poor reconstructions will result

late oligocene miocene sedimentary evolution of the critical alps apennines junction the monferrato area northwestern italy the monferrato is a key area of the alps apennine junction it consists of a tertiary succession resting on apennine related units in turn overridden by the alpine basement the superficial expression of this crustal discontinuity is the rio freddo deformation zone separating the alpine related torino hill domain from the monferrato stratigraphic analyses allow the recognition of different fault bounded oligo miocene successions interpreted as tectonostratigraphic units some of these corresponded to high standing blocks others to subsiding basins the facies distribution reflects a transpressional tectonic regime in this general framework of wrench tectonics sedimentation was influenced by palaeoceanographic factors during the early and latest burdigalian while tectonics played the dominant role during the aquitanian and the late burdigalian the uniform extent and the unconformable basal boundary of the langhian deposits suggest that the different tectonostratigraphic units presently composing the monferrato area were in place by langhian times

a simultaneous inversion of seismic traveltimes and amplitudes for velocity and attenuation it is possible to efficiently use traveltime and amplitude information to infer variations in velocity and q with little additional computation terms accounting for source radiation pattern and receiver coupling may be included in the inversion the methodology is based upon a perturbation approach to paraxial ray theory the perturbation approach linearizes the relationship between velocity deviations and traveltime and amplitude anomalies using the technique we infer the velocity and attenuation structure at a fractured granitic site near raymond california a set of four well pairs are examined and each is found to contain two zones of strong attenuation the velocity variations contain an upper low velocity region corresponding to the uppermost attenuating zone the location of these zones agrees with independent well log and geophysical data the velocity and attenuation anomalies appear to coincide with extensively fractured sections of the borehole and may indicate fracture zones rather than individual fractures

exhumed hydrocarbon seep authigenic carbonates from zakynthos island greece concretions not archaeological remains in zakynthos island greece authigenic cementation of marine sediment has formed pipe like disc and doughnut shaped concretions the concretions are mostly composed of authigenic ferroan dolomite accompanied by pyrite samples with 80 dolomite have stable isotope compositions in two groups the more indurated concretions have 18o around 4 and 13c values between 8 and 29 indicating dolomite forming from anaerobic oxidation of thermogenic methane hydrocarbon seep in the sulphate methane transition zone the outer surfaces of some concretions and the less cemented concretions typically have slightly heavier isotopic compositions and may indicate that concretion growth progressed from the outer margin in the ambient microbially modified marine pore fluids inward toward the central conduit where the isotopic compositions were more heavily influenced by the seep fluid sr isotope data suggest the concretions are fossil features possibly of pliocene age and represent an exhumed hydrocarbon seep plumbing system exposure on the modern seabed in the shallow subtidal zone has caused confusion as concretion morphology resembles archaeological stonework of the hellenic period

anatomy and origin of carbonate structures in a miocene cold seep field miocene calcite concretions resembling modern carbonate structures that form at cold seeps are present in fractured opal ct porcelanites that are interbedded with mudstones in coastal cliffs at santa cruz california the morphologies of the carbonate structures differ markedly from conventional concretions and are spatially aligned with orthogonal joints in the porcelanites the structures contain tubular holes that are identical to fluid and gas conduits in modern carbonate seep structures the orientations of these tubes suggest that fluid and gas flow was both vertical and horizontal the latter along extensional joints that formed preferentially in the brittle silica rich layers that had enhanced bedding parallel permeability petrographic and isotopic characteristics of the carbonate structures indicate that calcite precipitation occurred in a shallow subseafloor environment in either the zone of microbial sulfate reduction or of methanogenesis prior to or possibly simultaneously with the silica phase transformation of opal a in diatom shells to opal ct

structure and emplacement of mud volcano systems in the south caspian basin the term mud volcano system is coined to describe the set of structures associated with a constructional edifice mud volcano and feeder complex that connects the volcano to its source stratigraphic unit three dimensional 3 d seismic data from the south caspian basin are used to investigate the structural elements and evolution of these systems mud volcano systems initiate via early kilometer scale biconic edifices termed pioneer cones these are fed by fluidization pipes tens of meters in width subsequent kilometer scale mud volcanoes grew via persistent extrusion fed by numerous additional fluidization pipes injected in the country rock this subvolcanic intrusion complex creates a densely intruded cylindrical zone similar in cross section to gryphon swarms observed at an outcrop onshore wall rock erosion and compaction of the intruded zone leads to the collapse of a downward tapering cone enveloping the cylindrical zone capped by ring faults that define a kilometer scale caldera that downthrows the overlying mud volcano mud volcanoes get buried during basin subsidence and can look like intrusive laccoliths at first glance on seismic data reactivation of mud flow through a conduit system generates a stack of superimposed mud volcanoes through time large volcanoes continue to dewater during burial and may locally remobilize this model of mud volcano evolution has similarities with igneous and salt tectonic systems to reduce drilling and geologic uncertainty mud volcano system extent and impacts on a reservoir can be assessed on 3 d seismic data simon stewart received his ph d from the imperial college london in 1992 in 1992 2000 he was seismic interpreter at amerada hess in support of exploration and appraisal drilling in the north sea in 2000 he moved to bp and has since worked on structural geology and well planning in the americas middle east and the former soviet union his special interest is in the integration of structural geology and seismic interpretation richard davies received his ph d from the university of edinburgh in 1995 in 1995 2003 he was with mobil and exxonmobil working on field development and exploration the north sea the west of shetlands and the west niger delta deep water slope in 2003 2005 he was a senior lecturer in earth sciences at cardiff university united kingdom currently he is professor and director of cerees center for research into earth energy systems durham university united kingdom his special interest is in seismic scale expression of fluid migration and diagenesis

relicts of mud diapirism of the emerged wedge top as an indicator of gas hydrates destabilization in the manila accretionary prism in southern taiwan hengchun peninsula abstract due to oblique collision of the luzon volcanic arc and eurasian passive margin in taiwan we observe southward progression of mountain building processes consequently the southernmost tip of taiwan represents the most recently emerged part of the orogen the hengchun peninsula the area shows evidence of a trench slope basin that emerged in the holocene with landforms that bear submarine characteristics in the late pleistocene lagoonal sediments blanket the basin however the deeper deposits maanshan formation can be found on the surface in several areas we document that the maanshan formation was brought to the surface through upwelling structures mud diapirs as a consequence of fast and overpressured sedimentation from the emerging orogen although fast erosional processes continuously reorganize the new landscape we are able to capture relicts of fast eroding inactive mud volcanoes these unique features are preserved on the surface due to shielding by coral terraces during the shallowing and the lagoonal period of the basin stable carbon 13c and oxygen 18o isotope analysis performed on samples of carbonate blocks of cold vents collected on the outcrops of the maanshan formation confirm classic seep carbonates origins we also identify a mud core anticline below the study area acting as the main source for the mud volcanoes and a possible cause of the uplift of the trench slope basin two multichannel seismic profiles from marine surveys along with a synthesis of several previous surveys helped construct a model of the characteristics of mud diapirism in southeastern offshore taiwan

gas hydrate dissociation in the lorca basin se spain during the mediterranean messinian salinity crisis abstract the tortonian marls which were deposited in the lorca basin se spain prior to the messinian tripoli formation contain discontinuous levels of indurated nodules and massive layers up to a few meters thick of diagenetic dolomite the oxygen and carbon isotopic compositions of these dolomites indicate that the carbonate diagenesis occurred mostly in 13c rich and 18o rich to 18o poor solutions the vertical distribution of the values of these dolomites is interpreted as the result of the past occurrence of gas hydrate reservoirs where the methane source probably originated from the organic rich marls we postulate that the gas hydrates contained in the tortonian marls were destabilized during the water level drops related to the messinian salinity crisis associated sedimentary structures include numerous syn sedimentary deformations and brecciation which are the expression of important sedimentary instabilities which could have been generated during the gas hydrates decomposition

fluid venting in the eastern aleutian subduction zone fluid venting has been observed along 800 km of the alaska convergent margin the fluid venting sites are located near the deformation front are controlled by subsurface structures and exhibit the characteristics of cold seeps seen in other convergent margins the more important characteristics include 1 methane plumes in the lower water column with maxima above the seafloor which are traceable to the initial deformation ridges 2 prolific colonies of vent biota aligned and distributed in patches controlled by fault scarps over steepened folds or outcrops of bedding planes 3 calcium carbonate and barite precipitates at the surface and subsurface of vents and 4 carbon isotope evidence from tissue and skeletal hard parts of biota as well as from carbonate precipitates that vents expel either methane or sulfide dominated fluids a biogeochemical approach toward estimating fluid flow rates from individual vents based on oxygen flux measurements and vent fluid analysis indicates a mean value of 5 5 0 7 l m 2 d 1 for tectonics induced water flow wallmann et al 1997b a geophysical estimate of dewatering from the same area von huene et al 1997 based on sediment porosity reduction shows a fluid loss of 0 02 l m 2 d 1 for a 5 5 km wide converged segment near the deformation front our video guided surveys have documented vent biota across a minimum of 0 1 of the area of the convergent segment off kodiak island hence an average rate of 0 006 l m 2 d 1 is estimated from the biogeochemical approach the two estimates for tectonics induced water flow from the accretionary prism are in surprisingly good agreement

modeling the impact of solute recycling on groundwater salinization under irrigated lands a study of the alto piura aquifer peru summary studies of groundwater quality in arid and semi arid lands show that irrigation return flow is one of major factors contributing to aquifer salinization existing mathematical models do not account explicitly for solute recycling during irrigation on a daily scale which is considered as an important salinization input the main objective of this research was to develop a mathematical numerical model that can simulate impact of irrigation return flow by coupling water and solute fluxes at the soil surface with quality of water pumped from the aquifer this was obtained with a quasi 3d model representing flow in the vadose zone aquifer system by series of 1d richards equations in a variably saturated zone and by a 3d flow equation in groundwater the 3d advection dispersion equation is solved in the entire domain concentration of irrigation water is calculated at each time step as a function of concentration of both surface water and groundwater extracted at specific locations the model was applied to simulate the impact of irrigation on groundwater salinization of alto piura aquifer northern peru over thirty years three scenarios were considered i use of flood irrigation and groundwater extraction the present situation ii increase of groundwater pumping by 50 compared to the first scenario and iii transition from flood irrigation to drip irrigation thus decreasing irrigation volume by around 60 compared to the first scenario results indicate that in different irrigation areas the simulated increase rates of total dissolved solids in groundwater vary from 3 5 to 15 17 mg l year depending on hydrogeological and hydrochemical conditions volumes of water extracted and proportion between surface water and groundwater applied the transition from flood irrigation to drip irrigation decreases the negative impact of return flow on groundwater quality however drip irrigation causes faster soil salinization compared to flood irrigation irrigation return coefficients were calculated in the order of 21 23 and 22 24 for the first and second scenarios respectively

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

degree of supersaturation and precipitation of organogenic dolomite this paper integrates the degree of carbonate saturation into a general model for the origin of dolomite in organic rich marine sediments degradation of organic matter by sulfate reducing bacteria promotes early dolomite precipitation by simultaneously increasing the carbonate alkalinity and lowering the sulfate ion concentration to near zero the interstitial water in organic rich sediments of several deep sea drilling project sites where dolomite is believed to be precipitating is up to 10 sup 3 times supersaturated with respect to near ideal dolomite and up to 10 times supersaturated with respect to calcite the highly supersaturated interstitial waters appear to overcome low temperature kinetic barriers to precipitate a nonideal fine grained calcian dolomite the degree of supersaturation with respect to dolomite decreases and the interstitial water approaches carbonate equilibrium with increasing burial depth at several of these sites removal of sulfate ion is important because sulfate ion may inhibit dolomite precipitation a calcareous sediment is not required but the presence of calcite or aragonite appears to greatly enhance dolomitization by providing an additional source of ca and carbonate ions

a stochastic approach to the characterization of lithofacies from surface seismic and well data heterogeneity of natural geologic formations strongly influences groundwater flow and contaminant migration this study presents a formal stochastic approach for the integration of surface seismic data and well data into the identification of the spatial arrangement location geometry and interconnectedness of lithofacies and incorporating this information in the estimation of the log permeability probability density function pdf to achieve this goal normal move out nmo corrections are applied to the seismic reflection data to estimate interval seismic velocities calibration curves constructed from the well logs transform these velocity estimates into a lithology indicator prior probability field from the well data and the indicator prior probability field the indicator covariance function and its associated confidence limits are computed neighboring lithology logs and the indicator covariance function are then combined to update the indicator probability field the conditional log permeability pdf is finally computed by weighting the log permeability distribution of each lithology with respect to its indicator probability field the effectiveness of the proposed procedure is shown to depend on the quality of the seismic data and the degree of correlation between seismic and hydrogeologic soil properties a synthetic case study is performed which shows that the surface seismic and well data complement each other with optimal results achieved when both types of data are incorporated into a joint identification procedure

acoustic crosswell imaging using asymptotic waveforms seismic waveforms are inverted using an asymptotic method the asymptotic method models amplitudes correctly at the caustics and takes nonstationary raypaths into account when computing the waveforms and thus is an extension of geometrical ray theory using numerical differencing partial derivatives of the data with respect to the model are computed as expected these partial derivatives or sensitivity functions are concentrated along but not confined to raypaths the sensitivity functions enable the formulation of a waveform inversion algorithm which is applied to a synthetic crosswell experiment and a laboratory crosswell experiment the synthetic experiment shows the advantages of the waveform inversion method over conventional traveltime inversion methods boundaries of anomalies are better defined and smearing is reduced the waveform inversion produces a much lower misfit than the traveltime inversion the goal of the laboratory experiment was the detection of a nonaqueous phase liquid napl in water saturated sand the sand was imaged before and after injection of the napl using the waveform inversion method low velocity anomalies were imaged that correlate well with post experiment determination of napl concentrations the low velocity anomaly defocuses the seismic energy however the amplitude reduction due to the low velocity anomaly is not enough to explain the observed low amplitudes we suggest that other mechanisms such as multiple scattering 3 d effects or intrinsic attenuation not included in the asymptotic waveform modeling play an important role in decreasing the amplitude

sluggish and steady focussed flows through fine grained sediments the methane derived cylindrical concretions of the tertiary piedmont basin nw italy abstract in the cenozoic succession of the tertiary piedmont basin nw italy a wide array of methane derived carbonate rocks including both seafloor and sub seafloor products have been reported in the last decades the most intriguing features are cylindrical concretions more than 1 m long and around 10 cm across that were found within fine grained sediments of messinian age in their original stratigraphic position crossing the bedding planes at high angles these concretions result from cementation of the host muddy sediments by intergranular dolomite microcrystals and lack any evidence of exposure at the sea floor their c and o stable isotope signature suggests that dolomite precipitation was induced by anaerobic oxidation of methane possibly sourced by gas hydrate destabilization such cylindrical morphologies are interpreted as the result of carbonate precipitation and cementation of the sediments around fluid conduits and record a relatively long period of steady sluggish flux of methane rich fluids that opened their way rising up through fine grained unconsolidated sediments they formed immediately below the sea floor in a narrow horizon bracketed between the sulphate methane interface and the oxic anoxic interface cylindrical concretions represent only the highest part of pipes through which methane rich fluids flowed up the deeper part of the conduits conversely left no trace in the stratigraphic record because of the lack of chemical microbiological conditions favourable for carbonate precipitation

polyphasic carbonate precipitation in the shallow subsurface insights from microbially formed authigenic carbonate beds in upper miocene sediments of the tertiary piedmont basin nw italy article i nfo authigenic methane derived carbonates hosted in upper miocene slope sediments of the tertiary piedmont basin nw italy are studied by a multidisciplinary approach including petrography stable oxygen and car bon isotopes of carbonates as well as lipid biomarkers in order to explore the relationship between microbial activity and carbonate precipitation in the shallow subsurface the studied rocks show a bed parallel geom etry and are characterized by dolomitic intergranular cement which is typified by positive 13 c values as high as 6 2 vpdb a striking feature of some dolomite beds is an intricate network of septarian like cracks filled with both injected sediments and polyphasic carbonate cements prokaryotic molecular fossils in the dolomite beds comprise archaeol 13 c 40 vpdb and various bacterial dialkyl glycerol diethers dages 13 c 30 vpdb strongly suggesting that dolomite precipitation took place at the interface of the zones of archaeal methanogenesis and bacterial sulphate reduction in contrast extremely negative 13 c values of carbonate cements as low as 56 3 vpdb and various archaeal and bacterial molecular fossils e g pentamethylicosane pmi 106 vpdb are recorded in the crack filling carbonate cements these cements precipitated due to anaerobic oxidation of methane coupled to sulphate reduction we pro pose a scenario for the formation of the diagenetic beds suggesting that carbonate precipitation was the re sult of three microbially driven processes sulphate reduction methanogenesis and finally anaerobic oxidation of methane this unusual sequence was a consequence of a dynamic change of environmental geo chemical conditions and fluid circulation patterns that prevailed in the ancient subseafloor during early dia genesis of the unconsolidated sediments anaerobic oxidation of methane which usually predates methanogenesis during increasing burial postdates methanogenesis in case of the septarian like beds after the beds were affected by crack formation induced by overcritical pore pressure allowing the ingress of sulphate rich water from above and methane rich water from below

predicting aquifer characteristics to enhance hydrogeophysical model in fractured karstified rocks of dammam formation at bahr al najaf basin iraq groundwater represents a major water source in bahr al najaf basin so the knowledge of the aquifer parameters is an essential goal to assess and manage groundwater resources a comprehensive view of the fractured and karstified aquifers within dammam formation at bahr al najaf basin is very important because the karstified environments are very complex this study is an attempt to extract mathematically empirical relationships between the hydraulic parameters and the geoelectrical properties to improve the construction of a hydrogeophysical model instead of using the conventional procedures of pumping tests or drill new well which need great effort and high cost the enhanced hydrogeophysical model shows that the main aquifer has a uniform lithology of carbonate rocks good water saturation and belongs to m dammam member the correlation between hydraulic conductivity k m day and aquifer resistivity rho 0 m gave a logical relationship in such kind of aquifer which has correlation coefficient r2 equals to 0 737 in addition the correlation between transmissivity t m2 day and both of transverse resistance tr m2 and longitudinal conductance sl 1 revealed the similarity in lithological characteristics of middle dammam aquifer due to the approximately equal values of strong r2 0 862 and 0 868 respectively this may be due to the nature of the studied area as a discharge zone which has a good porosity varphi of 22 and a high water saturation sw equals to 1 approximately the extracted relationship of direct proportionality between t m2 day and sl 1 is an important one therefore this relationship can be used directly to calculate t m2 day mathematically in the present study the relations between the hydraulic parameters and the geoelectrical properties are expressed as linear equations instead of nonlinear because we believe that it is mathematically more acceptable and reliable for hard rock aquifers that the m dammam aquifer is confined with a fully saturated thickness in addition the comparison between r2 of the linear and nonlinear relation of t m2 day with tr m2 and t m2 day with sl 1 appeared to have little divergence of r2 equal to 0 028 and 0 001 respectively

melange production and the importance of shale diapirism in accretionary terrains although melanges are widely believed to form in subduction zones there is little agreement as to the mechanism by which the characteristic chaotic aspect of a melange develops1 2 debate centres on the relative effects of gravity sliding down the inner trench slope and shearing along thrust faults during offscraping or underplating2 3 the results of deep sea drilling and mapping of modern accretionary terrains4 combined with geophysical investigation of outer arc regions favour the thrust or fold packet model1 4 8 of accretion although some melange deposits exposed on land appear to fit an olistostrome model better1 9 shale diapirs and mud volcanoes are abundant in many modern accretionary terrains10 12 and probably form as a result of rapid overloading caused by tectonic thickening4 13 an investigation of extensive melange zones in northern irian jaya has now shown that they are the product of shale diapirism which suggests that shale diapirism is an important process in the tectonic mixing of accretionary terrains

the beast burrowed the fluid followed crustacean burrows as methane conduits abstract an extensive pockmark field with associated methane seep carbonates has recently been reported from the late albian lower cretaceous ubidepea mudstone of the black flysch group in the basque country northern spain but the exact pathways of the migrating methane rich fluids remained elusive here we provide petrographic stable carbon and oxygen isotope evidence that abundant crustacean burrows in the surrounding mudstone preserved as the trace fossil thalassinoides and the seep carbonates themselves have acted as long lasting fluid conduits in this system the thalassinoides infill generations show a diagenetic parasequence often starting with a distinctive lining followed by one to several phases of cementing of the burrow walls and burrow infills and finally late diagenetic sparry calcite that filled the remaining open cavities and conduits the micrite cementing the burrow walls shows negative 13 c values similar to those reported from the seep carbonates indicating that methane oxidation was involved in their precipitation rather than or in addition to the oxidation of other organic matter even the late diagenetic sparry calcite shows 13 c values as low as 30 4 versus pdb providing evidence that these burrows served as fluid conduits for an extended period of time our study supports the growing body of evidence that crustacean burrows play an important role in channeling seeping fluids in such systems we anticipate that this phenomenon is much more widespread than currently appreciated especially in examples where other types of fluid conduits are absent

seafloor manifestations of fluid seepage at the top of a 2000 metre deep ridge in the eastern nankai accretionary wedge long lived venting and tectonic implications abstract the results of the 1989 kaiko nankai diving cruise to the eastern nankai accretionary wedge show that a narrow corridor on the top of a 2000 m deep ridge is characterized by concentrated surface manifestations of fluid seepage and chaotic outcrop orientations suggesting active faulting along a right lateral shear zone modern biological indicators of fluid venting include bivalve vesicomyid species and vestimentiferan tube worms ancient manifestations of fluid venting consist of similar vesicomyid species found in 20 and 150 ka concretions this suggests relatively constant biotypes carbonate deposits including fossil cemented shells were observed near active sites either as paving stones diffuse seepage and cementation cut by channels or as pinnacles local seepage and cementation despite its proximity less than 15 km a nearby 3800 m deep site where substantial fluid discharge occurs seems to be completely separate from the 2000 m deep ridge site the 3800 m deep site differs from its shallower counterpart in terms of its seafloor manifestations and the composition of its fluids the sediment at the top of the ridge ranges in age around 500 300 ka which attests that the transition from a depositional to an erosional stage was younger than 800 ka but older than 200 ka this transition can be due to either the incorporation of this unit from the trench fill into the accretionary wedge front or the uplift of a slope basin the first hypothesis leads to a 2 5 cm yr minimum progradation rate associated with a 2 5 mm yr minimum uplift rate from the paleotrench to the present ridge the second hypothesis implies a recent uplift of a piggy back basin at a minimum rate of 1 mm yr

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

hydrocarbon seepage during the messinian salinity crisis in the tertiary piedmont basin nw italy abstract seep carbonate deposits of messinian age have been recently found in the tertiary piedmont basin nw italy these carbonates are preserved as blocks within a chaotic unit emplaced during the messinian salinity crisis msc they show negative 13 c values from 27 to 15 vpdb that indicate the involvement of hydrocarbon rich fluids in their genesis three types of carbonates are recognised i vuggy carbonates ii lucina carbonates and iii tubeworm carbonates vuggy carbonates are characterised by carbonate pseudomorphs after gypsum and probably formed during the first stage of the msc they are the product of a complex diagenesis influenced by both hypersalinity and seepage of hydrocarbon rich fluids these rocks lack chemosymbiotic assemblages reflecting their formation under extreme environmental conditions inhospitable for most metazoans in contrast lucina and tubeworm carbonates are characterised by chemosymbiotic macrofauna represented respectively by lucina bivalves and putative vestimentiferan tubeworms the latter have not commonly been documented in ancient seep carbonates and have never been reported from the messinian sediments of the piedmont basin both lucina and tubeworm carbonates are interpreted as the product of hydrocarbon seepage during the second msc stage these two types of carbonates formed under less severe conditions than the vuggy carbonates allowing the survival of seep dwelling metazoans during the second msc stage the seafloor was probably characterised by an irregular topography and a thin bottom layer of dense anoxic brines produced by the dissolution of gypsum it is suggested that vestimentiferan worms were able to thrive on morphologic highs with the posterior part of tubes just below the oxic anoxic interface but the anterior part projecting into oxic water the infaunal lucina bivalves were only able to live at seeps with an overlying oxic water column the studied carbonate deposits show features reflecting the uncommon interaction of hydrocarbon rich seep fluids and sulphate enriched waters the latter resulting from both evaporation and dissolution of gypsum and allow to reconstruct the evolution of a seepage system during the msc

hydrodynamic parameters of a sandy soil determined by ground penetrating radar inside a single ring infiltrometer this study shows how mualem van genuchten m vg parameters can be obtained from gpr data acquired during water infiltration from a single ring infiltrometer in the case of a sandy soil water content profiles were generated at various time steps using hydrus 1d based on particular values of the m vg parameters and were converted to dielectric permittivity profiles using the complex refractive index method the gprmax suite of programs was used to generate radargrams and to follow the wetting front progression in depth using the arrival time of the electromagnetic waves recorded by a ground penetrating radar gpr theoretically the 1 d time convolution between reflectivity and gpr signal at any infiltration time step is related to the peak of the reflected signal recorded in the corresponding trace in the radargram we used this relationship to invert the m vg parameters for constant and falling head infiltrations using the shuffled complex evolution sce ua algorithm the method is presented on synthetic examples and on experiments carried out for a sandy soil the parameters inverted are compared with values obtained in laboratory on soil samples and with disk infiltrometer measurements

the place of tubular concretions in hydrocarbon cold seep systems late miocene urenui formation taranaki basin new zealand the late miocene urenui formation cropping out on the eastern margin of taranaki basin currently new zealand s only commercially exploited hydrocarbon basin is dominated by siliciclastic slope mudstone 5 carbonate that locally includes a variety of tubular concretions 50 85 carbonate dominated by commonly large pipe and bulbous varieties as much as 0 5 to more than 10 m 1 6 to 33 ft long and 5 to 70 cm 2 to 28 in across these concretions formed from the precipitation of fine grained calcite or dolomite cement within siliciclastic mud in the shallow subsurface likely 100 m burial most support a central conduit that may be empty or filled with sediment or multiple generations of post shallow burial carbonate cements depleted 13c values of the concretionary calcite cements 40 to 25 pdb indicate that their carbon was sourced from oxidized methane in contrast enriched 13c values of the concretionary dolomite cements 10 to 11 pdb indicate that their carbon was derived from methanogenic co2 and or extensive methane oxidation the range of 18o values for the concretionary cement types 2 to 5 pdb supports precipitation from fluids both depleted and enriched with respect to new zealand miocene marine waters which are suggested to reflect episodes of gas hydrate formation and dissociation respectively the tubular carbonate concretions are interpreted to mark the subsea floor pathways of focused methane infused upward fluid escape and as such they represent a part of the shallow subsurface plumbing system of a cold seep system developed on the continental margin bounding the taranaki basin in the late miocene this margin has been strongly influenced by periodic movements along the major taranaki fault thrust system which coincidentally directly underlies the urenui concretion occurrences and was probably the most likely avenue for active fluid migration within the hydrocarbon seep system the tubular concretions experienced periodic intervals of exhumation and burial caused by margin failure because of greater slope instability from injected fluids and resulted in conglomeratic channel fill deposits within the urenui formation that include mass transported tubular concretions

lower eocene carbonate cemented chimneys varna ne bulgaria formation mechanisms and the a biological mediation of chimney growth abstract in the area of pobiti kamani varna northeast bulgaria massive carbonate cemented columns chimneys up to 1 5 m diameter and 8 m high and horizontal interbeds 1 5 m thickness occur in dispersed outcrops over an area of 70 km2 within loose lower eocene sands field observations and petrographical and stable isotope geochemical characterisation of four studied locations reveal a relationship between these structures and processes of ancient hydrocarbon seepage column and interbed structures both consist of similar well sorted silt to sand sized nummulitic host sediments predominantly cemented by early diagenetic low magnesium calcite filamentous textures about 10 m in diameter and 80 650 m long are only locally detected within interparticle calcite cement of columns column samples from two sites reveal a similar linear and inverse covariant trend of 13c 18o values which was interpreted as a mixing trend between two end member fluid precipitation conditions i e 1 a methane and or higher hydrocarbon derived carbon member characterised by 13c values as low as 43 and marine controlled precipitation conditions with 18o of 1 0 5 v pdb and 2 a member with less contribution of methane which was mixed most likely with less depleted carbon sources explaining 13c values ranging up to 8 v pdb the corresponding depleted 18o values with many samples clustering around 8 v pdb are interpreted in terms of precipitation at elevated temperatures this suggests the venting system was not a true cold seep sensu stricto furthermore column cross transects often document an internal pattern consisting of concentric zones with distinct isotopic signatures which vary between the two end members the mixing and internal pattern of column isotopic data together with petrographical observations are qualitatively interpreted as evidence of alternating precipitation conditions controlled by varying seepage rates of a single fluid source at depth during build up of individual chimney pipes near the sediment surface based on several field observations migration of the hydrocarbon charged fluids in lower eocene times was possibly channelled along ne oriented faults isotopic signatures of calcite cemented horizontal interbeds with depleted 18o ratios as low as 8 88 v pdb and variable 13c 1 to 16 mainly around 5 to 7 suggest that ascending fluids contributed to their cementation or resetted the calcite cement isotopic signature predominantly during periods of active seepage of warmer fluids only few petrographical and preliminary lipid biomarker evidence has been found pointing to the presence or possibly former activity of microbiota involved in carbon cycling and calcite precipitation typical of cold seep settings this may result from diagenetic alteration of organic components however considering the processes of chimney formation a cementation process governed by the inorganic oxidation of hydrocarbons in which interstitial oxygen is rapidly consumed without bacterial mediation is considered

seismic characteristics of fluid escape pipes in sedimentary basins implications for pipe genesis abstract fluid escape pipes were first documented from 3d seismic data over a decade ago and have subsequently been identified in many petroliferous basins worldwide they are characterized on seismic data by vertical to sub vertical zones of reduced reflection continuity that have a columnar geometry in three dimensions the upper terminations of these pipes commonly coincide with pockmarks or palaeo pockmarks signifying a close connection of pipe formation with a high flux fluid expulsion process dimensions range from tens to hundreds of metres in diameter and hundreds to over a thousand metres in height and the slenderness ratio defined as height diameter ranges from 0 8 to over 20 pipes are frequently associated with sub vertical clustering of amplitude anomalies on seismic data related either to the presence of free gas or to cementation linked to the passage of hydrocarbons three mechanisms have been suggested to explain pipe genesis 1 hydraulic fracturing 2 erosional fluidisation and 3 capillary invasion we suggest a further two possible mechanisms in the form of localised collapse by volume loss and synsedimentary flow localisation we review all five mechanisms and conclude that it is unlikely that a single mechanism applies but that combinations of these processes may all occur in particular contexts fluid escape pipes may be far more widespread that currently appreciated and they may play a critical role in secondary hydrocarbon migration and in providing leakage pathways for trapped hydrocarbons through overlying seals

ground penetrating radar for high resolution mapping of soil and rock stratigraphy ground penetrating radar is a technique which offers a new way of viewing shallow soil and rock conditions the need to better understanding overburden conditions for activities such as geochemical sampling geotechnical investigations and placer exploration as well as the factors controlling groundwater flow has generated an increasing demand for techniques which can image the subsurface with higher resolution than previously possible the areas of application for ground penetrating radar are diverse the method has been used successfully to map ice thickness water depth in lakes bedrock depth soil stratigraphy and water table depth it is also used to delineate rock fabric detect voids and identify karst features the effective application of the radar for the high resolution definition of soil stratigraphy and fractures in bedrock is highlighted the basic principles and practices involved in acquiring high quality radar data in the field are illustrated by selected case histories one example demonstrates how radar has been used to map the bedrock and delineate soil horizons to a depth of more than 20 m two case histories show how radar has been used to map fractures and changes of rock type to 40 m range from inside a mine another case history demonstrates how radar has also been used to detect and map the extent of groundwater contamination the corroboration of the radar results by borehole investigations demonstrates the power and utility of the high resolution radar method as an aid for interpolation and extrapolation of the information obtained with conventional coring programmes with the advent of new instrumentation and field procedures the routine application of the radar method is becoming economically viable and the method will see expanded use in the future

mineralogy geochemistry and petrography of methane derived authigenic carbonates from enza river northern apennines italy abstract a remarkable exposure of carbonate pipe like and slab concretions occurs along the enza riverbanks on the northern apennines foothills italy based upon geochemical and field evidences their genesis has been attributed to microbial governed carbonate precipitation from hydrocarbon enriched fluids the pipe like concretions are thus interpreted as former conduits chimneys marking sites of methane ascent onto the seafloor the resulting enza river chimney field is arranged in a palisade fashion a rare example of such mineralogical and petrographic analyses of some chimneys and slabs document that the dominant cement is dolomite although the chimneys show a rather homogeneous texture a clear zonation is observed in the relative distribution of major and minor elements in their internal and external parts the occurrence of sulphide minerals in the stratigraphically upper samples indicates possible renewal of fluids leakage after a major erosive event

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

a comparative review of upscaling methods for solute transport in heterogeneous porous media the classical fickian model for solute transport in porous media cannot correctly predict the spreading the dispersion of contaminant plumes in a heterogeneous subsurface unless its structure is completely characterized although the required precision is outside the reach of current field characterization methods the advection dispersion model remains the most widely used model among practitioners two approaches can be adopted to solve the effect of physical heterogeneity on transport first based on a given characterization of the spatial structure of the subsurface upscaling methods allow the computation of apparent scale dependent parameters especially longitudinal dispersivity to be used in the classical fickian model in the second approach upscaled non fickian transport equations with scale independent parameters are used in this paper efforts are made to classify and review upscaling methods for fickian transport parameters and non fickian upscaled transport equations for solute transport with an emphasis on their mathematical properties and their one dimensional analytical formulations in particular their capacity to mode scale effects in apparent longitudinal dispersion is investigated upscaling methods and upscaled models are illustrated in the case of two three dimensional synthetic aquifers with lognormal hydraulic conductivity distributions characterized by variance values of 2 and 8 c 2008 etsevier b v all rights reserved

geophysical hydrological identification of field permeabilities through bayesian updating a new bayesian method is developed to identify the spatial distribution of permeabilities in addition to sparsely sampled permeability and pressure data this approach incorporates densely sampled seismic velocity data along with semiempirical relationships between seismic and hydraulic soil properties the procedure consists first of performing a hydrological inversion based solely on the permeability and pressure data in light of the available seismic data the velocity permeability pressure relationships are then used to update in a bayesian sense the image of the permeability field to investigate the usefulness of this approach synthetic case studies are performed these studies demonstrate that even when the seismic data are corrupted by a significant level of error a joint geophysical hydrological inversion can produce improved images of permeability moreover this paper derives rigorously the bounds on the error that can be tolerated in seismic velocities such that they are still useful for hydrological purposes

estimating the hydraulic conductivity at the south oyster site from geophysical tomographic data using bayesian techniques based on the normal linear regression model this study explores the use of ground penetrating radar gpr tomographic velocity gpr tomographic attenuation and seismic tomographic velocity for hydraulic conductivity estimation at the south oyster site using a bayesian framework since site specific relations between hydraulic conductivity and geophysical properties are often nonlinear and subject to a large degree of uncertainty such as at this site we developed a normal linear regression model that allows exploring these relationships systematically although the log conductivity displays a small variation s 2 5 0 30 and the geophysical data vary over only a small range results indicate that the geophysical data improve the estimates of the hydraulic conductivity the improvement is the most significant where prior information is limited among the geophysical data gpr and seismic velocity are more useful than gpr attenuation

methane derived authigenic carbonates of mid cretaceous age in southern tibet types of carbonate concretions carbon sources and formation processes abstract methane derived authigenic carbonates with distinctive structures and morphologies have been documented worldwide but they are rarely found from ancient strata in the eastern tethys ocean the methane derived authigenic carbonates found in southern tibet are developed in calcareous or silty shales of mid cretaceous age in the xigaze forearc basin and in the tethyan himalaya tectonic zone the morphology mineralogy elemental geochemistry and composition of carbon and oxygen isotopes of these carbonates are studied in detail the carbonates have nodular tubular and tabular morphologies they are primarily composed of carbonate cement that binds and partly replaces host sediment grains host siliciclastic sediments are composed mainly of quartz and plagioclase feldspar a few foraminifers and framboidal or subhedral to euhedral pyrite carbonate cements dominantly are micritic calcite with minor contribution of dolomite nodular concretions are characterized by depleted 13c values commonly ranging from 30 to 5 the 13c values show a gradual decrease from the periphery to the center and the cao sio2 fe2o3 al2o3 k2o and tio2 contents generally show a gradual change these features indicate that the nodular concretions grew from an early formed center toward the periphery and that the carbon source of the nodular concretions was derived from a mixture of methane methanogenic co2 and seawater dissolved inorganic carbon the tubular concretions are characterized by 13c values of 8 85 to 3 47 in the shangba section and 27 37 to 23 85 in the upper gamba section unlike the nodular concretions the tubular concretions show central conduits which are possible pathways of methane rich fluids suggesting that the cementation of tubular concretions begins at the periphery and proceeds inward moreover the tubular concretions show morphological similarity with the methane derived carbonate chimneys pipes and slabs reported in present day cold seep settings we suggest that the carbon source of the tubular concretions was derived from a mixture of seawater dissolved inorganic carbon and oxidized methane formed by released hydrate the tabular concretions are characterized by 13c values of 21 87 to 6 67 in the xiege sections these depleted 13c values suggest that the carbon of the tabular concretions was derived at least in part from aom the tabular concretions are characterized by 13c values of 28 81 to 12 99 in the gamba section according to the 13c values and field observation we infer that their carbon source was more likely to be a mixture of the oxidized methane formed by released hydrate and seawater dissolved inorganic carbon

mid eocene giant slope failure sedimentary melanges in the ligurian accretionary wedge nw italy and relationships with tectonics global climate change and the dissociation of gas hydrates upper lutetian bartonian sedimentary melanges corresponding to ancient mud rich submarine mass transport deposits are widely distributed over an area c 300 km long and tens of kilometres wide along the exhumed outer part of the external ligurian accretionary wedge in the northern apennines the occurrence of methane derived carbonate concretions septarians in a specific tectonostratigraphic position below these sedimentary melanges allows us to document the relationships among a significant period of regional scale slope failure climate change the early and mid eocene optimum stages the dissociation of gas hydrates and accretionary tectonics during the ligurian tectonic phase early mid lutetian the distribution of septarians at the core of thrust related anticlines suggests that the dissociation of gas hydrates was triggered by accretionary tectonics rather than climate change the different ages of slope failure emplacement and the formation of the septarians support the view that the dissociation of gas hydrates was not the most important trigger for slope failure the latter occurred during a tectonic quiescence stage associated with a regressive depositional trend and probably minor residual tectonic pulses which followed the ligurian tectonic phase favouring the dynamic re equilibrium of the external ligurian accretionary wedge our findings provide useful information for a better understanding of the factors controlling giant slope failure events in modern accretionary settings where they may cause tsunamis

tertiary structural relationships between alps and apennines the critical torino hill and monferrato area northwestern italy the relationship between the alpine and apenninic orogenic systems is concealed at the surface by tertiary sediments of two main tectono stratigraphic units the alpine related torino hill domain and the apennines related monferrato domain mapping and structural analyses carried out in the area behind the mio pliocene apenninic padane thrust front allow comparison of the kinematic history of the torino hill and monferrato domains these are separate by the transpressive tlio freddo deformation zone rfdz interpreted here as the superficial expression of a crustal discontinuity along which the alpine metamorphic basement overrode the apenninic ligurian nappes during the palaeogene the western monferrato structural setting is the result of i late oligocene burdigalian transpressive tectonics due to lateral displacement between the alps related and the apennines related domains and ii compressive post messinian tectonics related to northward transport along the main padane thrust front post messinian tectonic events affected also the nw vergent asymmetrical torino hill anticline

seismic velocities and poisson s ratio of shallow unconsolidated sands we determined p and s wave velocity depth profiles in shallow unconsolidated beach sand by analyzing three component surface seismic data p and s wave velocity profiles were calculated from traveltime measurements of vertical and tangential component seismograms respectively the results reveal two discrepancies between theory and data whereas both velocities were found to be proportional to the pressure raised to the power of 1 6 as predicted by the hertz mindlin contact theory the actual values of the velocities are less than half of those calculated from this theory we attribute this discrepancy to the angularity of the sand grains assuming that the average radii of curvature at the grain contacts are smaller than the average radii of the grains we modify the hertz mindlin theory accordingly we found that the ratio of the contact radius to the grain radius is about 0 086 the second disparity is between the observed poisson s ratio of 0 15 and the theoretical value 0 008 for random pack of quartz spheres this discrepancy can be reconciled by assuming slip at the grain contacts because slip decreases the shearing between grains poisson s ratio increases

the formation of giant tubular concretions triggered by anaerobic oxidation of methane as revealed by archaeal molecular fossils lower eocene varna bulgaria abstract impressive several meters high tubular concretions in shallow marine calcareous sands and sandstones represent part of the well exposed subsurface plumbing network of an early eocene methane seep system in the balkanides foreland pobiti kamani area varna ne bulgaria an integrated approach including petrography inorganic geochemistry and lipid biomarker analyses was used to reconstruct the evolution of pore fluids and cementation conditions during tube formation and particularly the role of methane related carbonate diagenesis host sediment lithification from marine pore waters was perturbed soon after deposition by oxidation of predominantly microbial methane causing pervasive cementation by a 13 c poor homogeneous calcite cement 13 c values as low as 44 5 v pdb the importance of microbially mediated anaerobic oxidation of methane aom is confirmed by extremely 13 c depleted archaeal biomarkers 13 c values as low as 123 v pdb a suite of macrocyclic dialkyl glycerol diethers mdgd 0 to 2 and sn 3 hydroxyarchaeol comprises a characteristic trait of the eocene tubular concretions and might represent molecular fossils of so far unknown methane oxidizing archaea anme subsurface calcite cementation surrounding the ascending methane plume resulted from the changing pore water chemistry in response to aom and could have on a local scale been encouraged by the concurrent alteration of detrital feldspar fluctuating 13 c up to 8 v pdb and 18 o 0 5 to 9 v pdb signatures within a single tubular sandstone concretion are at least partly the consequence of isotopic resetting during late meteoric water circulation

electrical resistivity hydraulic conductivity relationships in glacial outwash aquifers empirical field relationships between the apparent formation factors from surface resistivity soundings and hydraulic conductivity from pumping tests in fresh water granular aquifers usually show positive correlations these relationships can be adequately explained by theory if consideration is taken of in situ field conditions a sound theoretical basis for relating apparent formation factor to pertinent hydrogeophysical parameters in homogeneous isotropic sand is a three phase parallel resistor model which explicity includes parameters of porewater resistivity grain size and shape porosity tortuosity and intergranular surface conductance the veracity of the theoretical model is supported by data from laboratory tests the model demonstrates that intergranular surface conductance is an important factor at small grain sizes and high porewater resistivities operating to lower the apparent formation factor the model further shows that direct relationships between hydraulic conductivity and formation factor are weak in the normal range of porewater resistivity being strongly dependent on porosity when systematic variation of in situ porosity and aquifer layering effects are considered a simulated field curve relating the apparent formation factor to hydraulic conductivity is shown to compare favorably with the comparable curve from field data for thirteen pumping test sites in southern rhode island both theoretical and empirical results demonstrate a useful positive correlation between aquifer apparent formation factor and hydraulic conductivity quantitative interpretation however is imprecise because of nonuniqueness of interpretation and inherent variation in important aquifer parameters especially porosity

mineralized conduits are part of the uppermost plumbing system of oligocene methane seep deposits washington state usa abstract plumbing systems of marine seeps are complex pathways along which hydrocarbon rich fluids move upward through the sedimentary column in the shallow subsurface seep plumbing systems may become successively filled by methane derived authigenic carbonates resulting in mineralized conduits this work investigates mineralized conduits in the uppermost plumbing network of oligocene seep deposits from the lincoln creek formation in washington state that consist of a paragenetic sequence of authigenic mineral phases at two study sites the pipes grade into the base of seep deposits the studied samples of concentrically mineralized conduits are cylindrical in shape measure 2 3 cm in diameter and are up to 15 cm in length the mineralized conduits are referred to as pipes hereafter the earliest mineral phase in the paragenetic sequence is matrix micrite making up the outer part of the pipes toward their centers the pipes are filled by two intercalated cement phases 1 clear banded and botryoidal aragonite and 2 micro to cryptocrystalline yellow aragonite the innermost portions of the pipes are filled by brownish calcite microspar or pipe filling micrite the observed paragenetic sequences archive successions of biogeochemical processes the 13 c values of clear and yellow aragonite cements range from 50 6 to 41 2 suggesting that their main carbonate source was provided by anaerobic oxidation of methane in contrast the later phases brownish calcite microspar pipe filling micrite are relatively enriched in 13 c 13 c values 2 3 to 3 9 pointing to carbonate precipitation from fluids affected by methanogenesis the size and morphology of the pipes suggest that initial excavation was caused by burrowing organisms the burrows subsequently acted as preferred fluid pathways suggesting that the transport of fluids within near surface sediments at the oligocene seeps was strongly influenced by the activity of the local fauna possible producers of the burrows were sediment dwelling crustaceans specifically callianassid decapods as well as bivalves

tectonically driven mud volcanism since the late pliocene on the calabrian accretionary prism central mediterranean sea abstract mud volcanoes recently discovered on the offshore calabrian arc are investigated at two sites 60 km apart in water depths of 1650 2300 m using swath bathymetry 2d 3d multichannel seismic and cores the seabed and subsurface data provide information on their formation and functioning in relation to tectonic activity during the rapid plio quaternary advance of the accretionary prism fore arc extension and thrust belt compression are seen to have involved two main phases of activity separated by a regional unconformity recording a mid pliocene 3 5 3 0 ma tectonic reorganization the two sites of mud volcanism lie in contrasting tectonic settings inner fore arc basin vs central fold and thrust belt and record differing forms of seabed extrusive activity twin mud cones and a caldera vs a broad mud pie at both sites subsurface data show that mud volcanism took place throughout the second tectonic phase since the late pliocene differing forms of mud extrusion were accompanied by subsidence to form depressions beneath and within extrusive edifices up to 1 5 km thick the basal subsidence depressions point to sources within the succession of thrusts underlying the inner to central arc consistent with microfossils within cored mud breccias from both sites that are derived from strata as old as late cretaceous these results are argued to support a model of mud volcanism in which deeply rooted fluid conduits drive a process of near surface sediment mobilization the onset of extrusive activity is inferred to have been triggered by the mid pliocene tectonic reorganization the change in stress fields which post dates the migration of frontal compression across the area by 4 ma opening pathways for the release of overpressured fluids from deep within the accretionary prism the rising fluids interacted with shallow

spatial correlation structure estimation using geophysical and hydrogeological data the large spatial variability of hydraulic properties in natural geologic systems over a wide range of scales and the difficulty of collecting representative and sufficient hydraulic property measurements using conventional sampling techniques render estimation of spatial correlation parameters difficult further compounding the estimation problem is the observation that the integral scale estimate is a function of the measurement support scale to mitigate these problems we investigate the use of tomographic geophysical data in combination with hydrogeological data in the spatial correlation estimation procedure two synthetic case studies were investigated where the scale of the geophysical measurements were varied relative to the scale of the hydrogeological properties the spatial correlation structure parameter estimation procedure was performed in the spectral domain where analysis of data having different support scales and spatial sampling windows was facilitated comparison of the spatial correlation structure parameters estimated from measured data with those of the synthetic aquifers revealed which type of data tomographic hydrogeological or a combination of both was most effective for recovering spatial correlation statistics under different sampling heterogeneity conditions these synthetic case studies suggest that collection of a few tomographic profiles and interpretation of these profiles together with limited well bore data can yield correlation structure information that is otherwise obtainable only from extensive hydrological sampling

quantifying fluid flow solute mixing and biogeochemical turnover at cold vents of the eastern aleutian subduction zone in situ oxygen fluxes were measured at vent sites in the aleutian trench at a water depth of almost 5000 m using a tv guided benthic flux chamber the flux was 2 orders of magnitude greater than benthic oxygen fluxes in areas unaffected by venting on the continental margin off alaska porewater profiles taken from the surface sediment below a vent site showed high concentrations of sulfide methane and ammonia the reduced carbon and nitrogen compounds are transported to the vent site by fluids expelled from deeper anoxic sediment layers by the forces of plate convergence the tectonically driven fluid flow was determined from the biochemical turnover in vent communities and was found to be 3 4 0 5 m yr 1 a model was used to quantify the transport of silica ca2 and sulfate via diffusion advection and bioirrigation through the surface sediments of a vent site a nonlocal mixing coefficient of 20 30 yr 1 was determined by fitting the model curves to the measured porewater profiles showing that the transport of solutes within the near surface sediments and across the sediment water interface is dominated by the activity of the vent fauna sulfate containing oceanic bottom water and methane rich vent fluids were mixed below the clam colony to produce sulfide and a caco3 precipitate the vent biota shape their immediate environment and control the sediment water exchange and the benthic fluxes at vent sites the oxygen consumption at vent sites is a major sink for oxygen at the study area

the parona chaotic complex a puzzling record of the messinian late miocene events in monferrato nw italy the parona chaotic complex pcc from monferrato nw italy is a melange composed of carbonate cemented blocks floating in a matrix of weakly consolidated mud breccias it forms a minor 1 km2 chaotic sedimentary body enclosed in a larger messinian melange that rests unconformably on older deposits and is followed again unconformably by pliocene sediments three main facies have been recognized in the blocks a bioclastic rudstones and coquinoid grainstones of early messinian age composed of oligotypic assemblages of gastropods and the brackish water bivalve cerastoderma mixed with shallow water marine biota mollusks corallinae algae benthic foraminifers echinoid fragments rare ahermatypic corals these sediments record shallow water carbonate sedimentation with episodic brackish incursions and show a peculiar diagenetic overprint selective dissolution of aragonitic grains and early dolomitic cements b monogenic breccias composed of clasts of coquinoid grainstones floating in a dolomitic microcrystalline matrix c polygenic conglomerates composed of rounded clasts of pre messinian pelagic sediments of lower messinian bioclastic carbonates and of messinian evaporitic carbonates finally a few blocks of strongly cemented micritic limestones interpreted as methane derived carbonates for the geochemical signature of the carbonate phases strongly depleted in 13c are present the matrix enclosing the blocks is a mud breccia containing centimeter sized clasts of marly sediments micropaleontological analyses have shown that lower messinian and upper tortonian planktic foraminifers are mixed with lower miocene oligocene and eocene forms the pcc results from complex processes involving 1 deposition of the peculiar sediments preserved in the blocks and 2 their dismemberment and mixing as for the depositional history composition of the blocks has allowed to sketch the following evolution a deposition of bioclastic rudstones and coquinoid grainstones that are interpreted as lower messinian carbonate platform deposits for their strong compositional and diagenetical similarity with the lower messinian carbonates cropping out in the mediterranean region the monferrato bioclastic sediments are the northernmost example of messinian shallow water carbonates yet known b deposition of monogenic breccias they formed during the evaporitic phase of the messinian that was accompanied by a relative sea level drop and by erosion of the previously deposited coquinas depositional and diagenetical processes during the evaporitic phase are also recorded by clasts of evaporitic carbonates in the polygenic conglomerates c deposition of polygenic conglomerates that are interpreted as upper messinian post evaporitic fan delta facies resulting from an important erosional phase after deposition this succession was dismembered in the blocks forming the present day melange geometry stratigraphic relationships and internal characteristics of the pcc point to an origin related to gravity driven phenomena triggered by tectonics however the faunal mixing in the mud breccias and the occurrence of blocks of methane derived carbonates suggest that mud diapirism also played a role for the genesis of the pcc this latter mechanism which has been poorly considered until now could also have been effective in the genesis of messinian chaotic deposits that extensively crop out in nw italy