maintenance of continental boundary layer shear through counter gradient vorticity flux in a barotropic model the use of a classical eddy parametrization in the analysis of continental boundary currents leads to the diffusion of momentum and relative vorticity and fails to recognize that the relevant eddies are dominated by the conservation of potential vorticity which in turn may produce an increase in the mean relative vorticity to illustrate this effect we examine a non inflected barotropic shear flow destabilized by the cross steam variation in the bottom topography of a continental slope the finiteamplitude evolution of the waves is analysed in a simple model with a step like bottom topography and with a piecewise uniform potential vorticity distribution the increase in maximum mean vorticity is computed for various values of the rossby number and the topographic elevation and it is suggested that a similar effect taking into account the isopycnal topography as well as the isobaths could maintain the large inshore shear of the gulf stream cross shelf transport of different water types i e potential vorticity and passive tracers are also computed and suggested to be pertinent to the more realistic oceanic problem involving baroclinic effects the numerical calculation employs the well known method of contour dynamics and the green s function appropriate for the step like topography is derived

practical approaches to identifying sealed and open fractures for one essential ingredient of permeable fracture networks degree of fracture pore space preservation in large fractures i show how the characterization challenge presented by sparse fracture sampling can be overcome by measuring a surrogate the abundance of rock mass cement that precipitated after fractures ceased opening sampling limitations are overcome because the surrogate is readily measured in small rock samples including sidewall cores and cuttings permitting site specific diagnosis of the capacity of fractures to transmit fluid over a wider range of sample depths than conventional methods allow a diverse core database shows that this surrogate correctly predicts where large fractures are sealed information on timing of fracture opening relative to cement sequence can be obtained in two ways first evidence of fracture movement history and cement sequences in sparse large fractures can be extrapolated to areas having only cement data alternately evidence of fracture timing can be acquired from sealed micrometer scale fractures distribution of porosity reducing cement is commonly heterogeneous from bed to bed and location to location in siliciclastic and carbonate rocks however because patterns of sealed or open fractures cannot be delineated using fracture observations alone surrogates have practical value for production fairway mapping and other applications in which identifying open fractures is essential this study highlights the vital interplay among structural and diagenetic processes for fracture porosity preservation or destruction

mobilizing salt magma salt interactions salt sequences form an integral part of many sedimentary basins worldwide many of these basins have experienced igneous activity either syn or post deposition of the salt sequences despite this little work has so far been undertaken to understand magma salt interactions within the subsurface and how aspects such as salt halokinesis may be influenced by igneous activity within this paper we detail the first direct description of relationships and textures that are developed during intrusive igneous salt interaction we show that salt composition appears to play a dominant role in controlling where igneous intrusions invade laterally through salt sequences in a sedimentary basin in particular we illustrate that hydrous salts such as carnallite act as preferential horizons for lateral magma intrusion this lithological control appears primarily related to the heating and subsequent dehydration reaction of carnallite which causes the carnallite to behave as viscous fluidal horizons resulting in the non brittle emplacement of magma and spectacular peperitic salt magma mingling textures we suggest that heating and transformation of carnallite and other hydrous salts into viscous fluidal horizons during igneous intrusion within a regional salt sequence may act as a possible trigger for contemporaneous halokinesis by creating fluid like viscous detachment layers over longer time scales however a solidified rigid boxwork of dikes and sills may create zones of increased mechanical strength that will locally inhibit further salt flow

oil generation by igneous intrusions in the northern gunnedah basin australia abstract the origin of extensive oil staining recorded over a 120 m interval of the jurassic pilliga sandstone in the fully cored bellata 1 well northern gunnedah basin has been investigated using conventional organic geochemical techniques the borehole intersects 451 m of permian and triassic strata overlain by 640 m of jurassic and cretaceous sediments igneous intrusions occur mainly within the lower part of the triassic napperby formation where the vitrinite reflectance profile shows the effect of significant local heating r v up to 2 43 within the intruded interval lower reflectance values r v 0 57 0 74 occur in the unaffected parts of the permian sequence with even lower values in places due to either marine influence or liptinite rich lacustrine organic facies hydrocarbon biomarkers in the oil stain in the pilliga sandstone indicate its derivation from a higher plant rich shaley source a methylphenanthrene index of 1 48 calculated vitrinite reflectance r c 1 29 for the oil suggests expulsion from a late mature source rock none of the potential source rock samples analysed appear to have attained such a maturation level except those from the lower part of the napperby formation affected by intrusions source specific biomarkers from this formation show several parallels with those of the oil stain but differ from those in the permian goonbri and maules creek formations and the upper parts of the napperby formation a jurassic source can also be excluded based on the immaturity of that part of the section and the absence of jurassic specific biomarkers in the oil stain

robust 1d inversion and analysis of helicopter electromagnetic hem data ground based electrical and electromagnetic methods are used systematically for quantitative hydrogeologic investigations in denmark in recent years a desire for faster and more cost efficient methods has led to growing interest in the possibility of using airborne systems and in 2001 a number of test flights were performed using a frequency domain helicopter borne electromagnetic hem system we perform a theoretical examination of the resolution capabilities of the applied system quantitative model parameter analyses show that the system only weakly resolves conductive near surface layers but can resolve layer boundary to a depth of more than 100 m modeling experiments also show that the effect of altimeter errors on the inversion results is serious we suggest a new interpretation scheme for hem data founded solely on full nonlinear 1d inversion and providing layered earth models supported by data misfit parameters and a quantitative model parameter analysis the backbone of the scheme is the removal of cultural coupling effects followed by a multilayer inversion that in turn provides reliable starting models for a subsequent few layer inversion a new procedure for correlation in the model space ensures model sections with slow lateral variations in resistivity normally assumed in sedimentary environments a field example from a danish survey demonstrates that the interpretation scheme can produce satisfactory results within the limitations of the system

the three dimensional geometry and growth of forced folds above saucer shaped igneous sills forced folds formed at the seabed immediately overlying shallow 1 km saucer shaped sills along the ne atlantic margin during the early paleogene examples of this sill fold relationship are exceptionally well imaged by high resolution 3d seismic datasets from the ne rockall basin the forced folds are domal in shape 2 4 km in diameter exhibit a structural relief of up to 350 m and comprise sediment volumes of ca 1 km3 a comparison of the thickness distribution across and volume of a saucer shaped sill with a high intrusion diameter to depth ratio and the structural relief and volume of its associated forced fold shows a remarkable equivalence this has the important implication that the structural relief on intrusion related forced folds can be used as an estimate of the thickness of the underlying sill the analysed forced folds are interpreted to have formed through three continual growth stages that are directly linked to the mechanical emplacement of the underlying saucer shaped sills their growth was associated with an increase in faulting of the overlying strata and influenced coeval or subsequent development of polygonal fault systems within the overburden these structures represent a new type of four way dip closed hydrocarbon trap

syndepositional forced folding and related fluid plumbing above a magmatic laccolith insights from outcrop lower cretaceous basque cantabrian basin western pyrenees emplacement of shallow magmatic laccoliths can result in the development of dome shaped forced folds and fractures in the overburden and at the depositional surface these folds and fractures have been described from both outcrop studies and seismic interpretation however the main controls on fold growth and fracture development remain unclear and in some cases controversial this paper presents a new approach in the analysis of the growth of laccolith intrusions and forced folds in this study deep water growth deposits at an outcrop in the basque cantabrian basin north iberia record the coeval formation and evolution of a late albian forced fold and related clastic dike system above the igneous larragan laccolith the vertical succession allows field mapping and characterization of the growth deposits the underlying forced fold and the forcible larragan laccolith at depth the larragan laccolith is 600 m wide and 40 m thick and intrudes an organic rich unit at an original decompacted depth of 450 m a multidisciplinary study sedimentology structure petrology and geochemistry of the growth deposits reveals that the emplacement of the laccolith created a dome shaped upward widening fold which had a final relief of 18 36 m and a width of 850 m at the paleoseabed simultaneously in the hinge zone of the fold local tensional stress induced the formation of a fracture system which subsequently acted as conduits for overpressured ascending fluids methane and water and fluidized sediments originating from the metamorphic aureole of the laccolith this plumbing system reached the paleoseabed where extruded sediments were deposited and methane derived carbonates precipitated a comprehensive model is proposed in which incremental emplacement of magma sheets induced pulsating contact metamorphism folding and fracturing of the overburden and episodic activity of the fluid plumbing system

co2 storage potential of south african coals and gas entrapment enhancement due to igneous intrusions abstract methane outburst events have occurred in some underground coal mines of south africa such as those in twistdraai mine in the highveld coalfield in the early 1990s occurrences of methane outbursts suggest that high gas content in adsorbed and free phase might be present in some sections of the coal seams coal seams might also be friable in those sections allowing pulverisation during outburst the survey of gas outburst events indicates that the locations of high gas emissions were mainly in the vicinity of the igneous intrusions mainly dolerite intrusions these intrusions are a result of post depositional volcanism into coal seams in some major coalfields of south africa such as the highveld coalfield this study was undertaken firstly to investigate potential locations for the occurrence of coal seam gas in south african coal seams with respect to the igneous intrusions and their enhancement effect on gas release and storage of these coals secondly it was thought that as the metamorphosed coals with high ash content were not economically viable for mining they might be potentially suitable for co 2 disposal measurements on 14 coal samples taken in an underground coal mine at various distances from a dolerite dyke show that the adsorption and porosity properties of metamorphosed coals have been enhanced thus increasing their gas storage capacity diffusivity results show that dolerite intrusions would act as enclosures and gas traps for storage of gas gas diffusivity was greater in coals near the dyke by a factor of two in general it is expected that the co 2 storage and gas flow properties of such coals be enhanced due to the heating effect of intrusions making the coals more appealing for possible future sequestration of co 2 from anthropogenic sources

petroleum systems including unconventional reservoirs in intrusive igneous rocks sills and laccoliths this work characterizes the principal components and geological processes involved in atypical igneous petroleum systems systems that can generate hydrocarbons in commercial quantities faster than traditional petroleum systems

satellite images of upwellings and cold filament dynamics as transient effects of violent air sea interactions downstream from the island of sardinia western mediterranean sea a systematic analysis of thermal satellite images of upwellings and cold filament dynamics downstream from the island of sardinia western mediterranean sea covering the years 1984 1985 1989 1990 1993 and 1994 is discussed for this sea the main transient atmospheric forcing comes from bursts of the mistral a north western wind which downstream from sardinia affects a rather calm basin the tyrrhenian sea in early summer particularly clear effects of atmospheric forcings such as gyres upwellings and cold filaments can be observed our analysis provides not only a systematic insight into these phenomena but also some experimental evidence of a novel mechanism of cold filament formation and evolution indeed in july 1989 a nice set of satellite images shows a cold filament rooted to the shallowest part of the wide shelf off olbia which meanders offshore for a few days under the effect of the mistral and of the general circulation it is of interest to underline how stably the filament is rooted to the shelf so that in only one image it appears as an elongated straight segment also the filament s potential vorticity is discussed in order to gain some insight into shelf water fluxes detachment depths and velocities relative to such phenomena

geometry and controls on the development of igneous sill related forced folds a 2 d seismic reflection case study from offshore southern australia emplacement of magma in the shallow subsurface can result in the development of dome shaped folds at the earth s sur face these so called forced folds have been described in the fi eld and in subsur face data sets although the exact geometry of the folds and the nature of their relation ship to under lying sills remain unclear and in some cases controversial in this study we use high quality two dimensional 2 d seismic refl ection and borehole data from the ceduna sub basin offshore southern australia to describe the structure and infer the evolution of igneous sill related forced folds in the bight basin igneous complex thirty three igneous sills which were em placed 200 1500 m below the paleo seabed in upper cretaceous rocks are mapped in the ceduna sub basin the intrusions are expressed as packages of high amplitude refl ections which are 32 250 m thick and 7 19 km in diameter we observe fi ve main types of intrusion type 1 strata concordant sills type 2 weakly strata discordant trans gressive sills type 3 saucer shaped sills type 4 laccoliths and type 5 hybrid intru sions which have geometric characteristics of intrusion types 1 3 these intrusions are overlain by dome shaped folds which are up to 17 km wide and display up to 210 m of re lief the edges of these folds coincide with the margins of the underlying sills and the folds display the greatest relief where the underly ing sills are thickest the folds are therefore interpreted as forced folds that formed in response to emplacement of magma in the shallow subsurface the folds are onlapped by lutetian middle eocene strata indicat ing they formed and the intrusions were em placed during the latest ypresian ca 48 ma we demonstrate that fold amplitude is typi cally less than sill thickness even for sills with very large diameter to depth ratios suggest ing that pure elastic bending forced folding of the overburden is not the only process ac commodating magma emplacement and that supra sill compaction may be important even at relatively shallow depths based on the ob servation that the sills intruded a shallowly buried succession the discrepancy between fold amplitude and sill thickness may refl ect loss of host rock volume by fland pore fl uid expulsion from poorly lithifi ed water rich beds this study indicates that host rock composition emplacement depth and deformation mechanisms are important controls on the style of deformation that oc curs during intrusive igneous activity and that forced fold amplitude may not in all cases refl ect the thickness of an underlying igneous intrusion in addition the results of this study suggest that physical and numeri cal models need to model more complex host rock stratigraphies and rheologies if they are to capture the full range of deformation mechanisms that occur during magma em placement in the earth s shallow subsurface

landform characterization using geophysics recent advances applications and emerging tools abstract this paper presents an overview of the strengths and limitations of existing and emerging geophysical tools for landform studies the objectives are to discuss recent technical developments and to provide a review of relevant recent literature with a focus on propagating field methods with terrestrial applications for various methods in this category including ground penetrating radar gpr electrical resistivity er seismics and electromagnetic em induction the technical backgrounds are introduced followed by section on novel developments relevant to landform characterization for several decades gpr has been popular for characterization of the shallow subsurface and in particular sedimentary systems novel developments in gpr include the use of multi offset systems to improve signal to noise ratios and data collection efficiency amongst others and the increased use of 3d data multi electrode er systems have become popular in recent years as they allow for relatively fast and detailed mapping novel developments include time lapse monitoring of dynamic processes as well as the use of capacitively coupled systems for fast non invasive surveys em induction methods are especially popular for fast mapping of spatial variation but can also be used to obtain information on the vertical variation in subsurface electrical conductivity in recent years several examples of the use of plane wave em for characterization of landforms have been published seismic methods for landform characterization include seismic reflection and refraction techniques and the use of surface waves a recent development is the use of passive sensing approaches the use of multiple geophysical methods which can benefit from the sensitivity to different subsurface parameters is becoming more common strategies for coupled and joint inversion of complementary datasets will once more widely available benefit the geophysical study of landforms three cases studies are presented on the use of electrical and gpr methods for characterization of landforms in the range of meters to 100 s of meters in dimension in a study of polygonal patterned ground in the saginaw lowlands michigan usa electrical resistivity tomography was used to characterize differences in subsurface texture and water content associated with polygon swale topography also a sand filled thermokarst feature was identified using electrical resistivity data the second example is on the use of constant spread traversing cst for characterization of large scale glaciotectonic deformation in the ludington ridge michigan multiple cst surveys parallel to an 60 m high cliff where broad 100 m synclines and narrow clay rich anticlines are visible illustrated that at least one of the narrow structures extended inland a third case study discusses internal structures of an eolian dune on a coastal spit in new zealand both 35 and 200 mhz gpr data which clearly identified a paleosol and internal sedimentary structures of the dune were used to improve understanding of the development of the dune which may shed light on paleo wind directions

evolution of a potential vorticity front over a topographic slope abstract using the methodology of contour dynamics the evolution of an interface separating two regions of constant potential vorticity is considered the model equations are those for barotropic nondivergent flow over a topographic slope adjoined by a coastal barrier the main focus is on the processes which lead to wave breaking for small amplitude waves and in general agreement with previous related work it is found that wave steepening leads to the formation of thin filaments the key parameter is found to be the ratio of the background potential vorticity to the discontinuity of potential vorticity across the front with other parameters such as the topographic slope and the distance to the coast playing a relatively less significant role

magmatic events and sour crude oils in the malargue area of the neuquen basin argentina abstract heavy medium oils 14 5 27 9 api in a studied field of malargue area in the neuquen basin argentina have associated gas that produces between 0 and 4000 ppm h 2 s and 0 6 103 kg h 2 s day being able to discriminate between biological and inorganic h 2 s sources is essential to the oil field s economy h 2 s associated with anaerobic bacteria sulfate reduction bsr might be mitigated using biocompetitive technologies or bactericides whereas abiotic h 2 s from geological sources can be controlled only by sequestration in surface facilities and oil field management if the h 2 s distribution in different oil pay zones field compartments and origin are well known the isotopic signatures of the h 2 s 34 s range between 2 3 and 7 8 which suggests magmatic sources laccoliths in the malargue area associated with tertiary magmatic events were mapped out many decades ago petrographic descriptions of igneous samples are consistent with andesitic magmas that bore sulfur bearing fluids which are considered the principal source of h 2 s associated hydrothermal fluids as recorded by secondary minerals induced rapid tsr thermochemical sulfate reduction reactions as documented by mineral phases seen in sem most of the h 2 s neuquen basin has been linked to bsr bacterial sulfate reduction however we document a geological origin for the h 2 s which is tied to magmatic events organic geochemistry and fluid inclusion data allow for an early local generation of hydrocarbons linked to burial followed by a second pulse of light hydrocarbons gas and h 2 s associated with the magmatic event water geochemistry and the lithology of oil pay zones are used to predict the distribution of h 2 s in each well wells with less than 20 ppm of h 2 s are linked to meteoric waters and siliciclastic pay zones

how contact metamorphism can trigger global climate changes modeling gas generation around igneous sills in sedimentary basins abstract large volumes of greenhouse gases such as ch4 and co2 form by contact metamorphism of organic rich sediments in aureoles around sill intrusions in sedimentary basins thermogenic gas generation and dehydration reactions in shale are treated numerically in order to quantify basin scale devolatilization we show that aureole thicknesses defined as the zone of elevated metamorphism relative to the background level vary within 30 250 of the sill thickness depending on the temperature of the host rock and intrusion besides the sill thickness in shales with total organic carbon content of 5 wt ch4 is the dominant volatile 85 135 kg m3 generated through organic cracking relative to h2o generation from dehydration reactions 30 110 kg m3 even using conservative estimates of melt volumes extrapolation of our results to the scale of sill complexes in a sedimentary basin indicates that devolatilization can have generated 2700 16200 gt ch4 in the karoo basin south africa and 600 3500 gt ch4 in the voring and more basins offshore norway the generation of volatiles is occurring on a time scale of 10 1000 years within an aureole of a single sill which makes the rate of sill emplacement the time constraining factor on a basin scale this study demonstrates that thousands of gigatons of potent greenhouse gases like methane can be generated during emplacement of large igneous provinces in sedimentary basins

diagenesis in porosity evolution of opening mode fractures middle triassic to lower jurassic la boca formation ne mexico abstract opening mode fractures joints in middle triassic to lower jurassic la boca formation sandstones northeastern mexico have patterns of fracture porosity mineral fill structures and size distributions not previously described from outcrop patterns match those found in cores from many basins we used aperture measurements along lines of observation scanlines fracture trace maps petrography high resolution scanning electron microscope sem based cathodoluminescence and fluid inclusions to characterize fracture populations open fractures are lined by quartz that precipitated while fractures were opening whereas sealed fractures additionally contain calcite deposited after fractures ceased opening large fractures and arrays of contemporaneous microfractures have consistent power law aperture size scaling over approximately three orders of magnitude our results imply that open fractures and fracture sizes depend on diagenetic state the interplay of fracture mechanics and diagenetic history is a determinant on effective porosity within fractures and thus open fracture persistence connectivity and fluid flow

joint inversion of geophysical data summary by jointly inverting several different kinds of geophysical measurements at a site we avoid some of the ambiguity inherent in the individual methods we show how this can be done for the combination of dc resistivity and magnetotelluric measurements on a layered medium by considering a simple 3 layer model the combination resolves the resistivity of the thin resistive second layer even though neither of the two methods can do so alone the method is then applied to field data from a shallow sedimentary basin a blind zone occurs beneath a thick near surface conductive shale by a study of the eigenvalue structure of the model it can be seen that resolution in this zone would be slightly enhanced by higher frequency magnetotelluric data but additional dc data at larger spacing would yield no improvement

coal metamorphism by igneous intrusion in the raton basin co and nm implications for generation of volatiles abstract the raton basin contains a series of tertiary mafic dikes and sills that have altered millions of tons of coal to natural coke and may have played a minor role in generating some of the large coalbed methane resources currently being exploited in this region four outcrops within the raton basin were selected to investigate local coal rank elevation and volatile generation due to intrusive activity coal and organic shale samples were collected on traverses across meter scale dikes and sills and were analyzed for vitrinite reflectance total organic carbon bulk carbon isotopic ratios and coke petrography reflectance patterns in the contact aureoles of the dikes display very consistent concave up patterns with reflectance values returning to background within one intrusion width from the contact bulk coal samples collected across dikes display an increase in 13c of approximately 1 approaching all contacts reflectance patterns within the contact aureoles of sills do not decrease significantly until one half of an intrusion width away from the contact but then drop steeply to background values by one intrusion width away bulk coal samples display complex isotopic patterns approaching sills with an initial increase in 13c followed by a steep decrease of approximately 1 5 approaching the top contacts the distinct isotopic and reflectance patterns for dikes and sills may indicate that the coal in the contact aureoles of the sills experienced a longer heating duration than the coal near the dike contacts this longer heating duration was due to the low thermal conductivity of coal which acts as a thermal insulator to the sills that intrude coal beds this style of intrusion is commonly observed throughout the central portions of the raton basin by contrast dikes intrude a variety of country rock types and are not insulated by coal heat may escape the contact zone through nearby sandstones or shales based on reflectance patterns hydrothermal convection played a role in heat transfer away from dikes data from both the dike and sill contacts suggest that time plays a role in controlling peak vitrinite reflectance values at least over the short heating durations tens of years expected for meter scale intrusions decreasing total organic carbon values approaching all contacts suggests the generation and escape of volatile species such as methane isotopic values within the contacts of dikes are consistent with the loss of 12c enriched methane the isotopic pattern observed at the contacts of sills may be due to accumulation of 12c rich pyrolytic carbon close to the contacts which is supported by petrographic observations even though multiple thin sheet intrusions are insignificant for conductive heating on a basin scale methane generation by sheet intrusions was volumetrically important in the raton basin because sills preferentially intrude coal beds in this region

contact metamorphic devolatilization of shales in the karoo basin south africa and the effects of multiple sill intrusions abstract quantification of fluid generation during contact metamorphism of shale is important for the understanding of metamorphic processes fluid flow in sedimentary basins and perturbations of the global carbon cycle in this study we provide geochemical and numerical analyses from the organic rich ecca group in the karoo basin south africa which was affected by contact metamorphism from multiple sill intrusions in the early jurassic organic matter was efficiently converted to hydrocarbons during contact metamorphism and complete loss of organic carbon in the innermost aureole is common mineral dehydration reactions are evident from the occurrence of metamorphic minerals like biotite and loss of the clay fraction towards the intrusive contact we have developed a numerical model in order to quantify fluid production from both inorganic and organic reactions during contact metamorphism the modelling results are constrained by data from two case studies in the karoo basin in order to obtain reliable estimates of the carbon loss from metamorphism of shale we show that single thin 15 m thick sills have a gas production potential of several gigatons of methane ch4 if emplaced over a 1000 km2 area furthermore the vertical spacing between simultaneously emplaced sills has an important influence on the gas generation potential when two sills are emplaced with a vertical spacing of 7 times the intrusion thickness the total ch4 generation is up to 35 more than for two separate sills data and modelling from five sills emplaced within the ecca group show hydrocarbon generation throughout the organic rich section with total carbon loss next to the sills this has implications for the fluid production and metamorphism in volcanic basins where multiple sills are common

methane release from igneous intrusion of coal during late permian extinction events abstract unusually large and locally variable carbon isotope excursions coincident with mass extinctions at the end of the permian period 253 ma and guadalupian epoch 260 ma can be attributed to methane outbursts to the atmosphere methane has isotopic values 13c low enough to reduce to feasible amounts the carbon required for isotopic mass balance the duration of the carbon isotopic excursions and inferred methane releases are here constrained to 10 000 yr by counting annual varves in lake deposits and by estimating peat accumulation rates on paleogeographic maps the most marked carbon isotope excursions form linear arrays back to plausible methane sources end permian siberian traps and longwood bluff intrusions of new zealand and end guadalupian emeishan traps of china intrusion of coal seams by feeder dikes to flood basalts could create successive thermogenic methane outbursts of the observed timing and magnitude but these are unreasonably short times for replenishment of marine or permaf

hydrothermal venting of greenhouse gases triggering early jurassic global warming abstract the climate change in the toarcian early jurassic was characterized by a major perturbation of the global carbon cycle the event lasted for approximately 200 000 years and was manifested by a global warming of 6 c anoxic conditions in the oceans and extinction of marine species the triggering mechanisms for the perturbation and environmental change are however strongly debated here we present evidence for a rapid formation and transport of greenhouse gases from the deep sedimentary reservoirs in the karoo basin south africa magmatic sills were emplaced during the initial stages of formation of the early jurassic karoo large igneous province and had a profound influence on the fate of light elements in the organic rich sedimentary host rocks total organic carbon contents and vitrinite reflectivity data from contact aureoles around the sills show that organic carbon was lost from the country rocks during heating we present data from a new type of geological structures termed breccia pipes rooted in the aureoles within the shale of the western karoo basin the breccia pipes are cylindrical structures up to 150 meters in diameter and are mainly comprised of brecciated and baked black shale thousands of breccia pipes were formed due to gas pressure build up during metamorphism of the shales resulting in venting of greenhouse gases to the toarcian atmosphere mass balance calculations constrained by new aureole data show that up to 1800 gt of co2 was formed from organic material in the western karoo basin about 15 times this amount of co2 27 400 gt may have formed in the entire basin during the intrusive event u pb dating of zircons from a sill related to many of the pipes demonstrates that the magma was emplaced 182 5 0 4 million years ago this supports a causal relationship between the intrusive volcanism the gas venting and the toarcian global warming

challenges in geophysical mapping of glaciotectonic structures abstractglaciotectonic complexes have been recognized worldwide traditionally described on the basis of outcrops or geomorphological observations in the past few decades geophysics has become an integral part of geologic mapping which enables the mapping of buried glaciotectonic complexes the geophysical methods provide different types of information and degrees of resolution and thus a different ability to resolve the glaciotectonic structures we evaluated these abilities on the basis of an integrated application of four commonly used geophysical methods airborne transient electromagnetics high resolution reflection seismic geoelectrical and ground penetrating radar gpr we covered an area of 100 km2 in a formerly glaciated region in the western part of denmark the geologic setting was highly heterogeneous with glaciotectonic deformation observed in the form of large scale structures in the seismic and airborne transient electromagnetic data to small scale structures seen in the gpr and g

paleoenvironments source rock potential and thermal maturity of the upper benue rift basins nigeria implications for hydrocarbon exploration abstract the upper benue rift comprising the gongola and yola basins in nigeria consist of the aptian albian bima formation the yolde formation cenomanian turonian gongila pindiga dukul formation turonian coniacian and gombe formation campanian maastrichtian to evaluate the maturity and source rocks potential vitrinite reflectance rock eval pyrolysis and infrared spectroscopy were carried out on 52 shale samples collected from boreholes mine quarries and outcrop sections in the gongola basin mean random vitrinite reflectance rom values range from 0 45 in the gombe formation to 0 69 in the pindiga formation and to 0 82 in the bima formation reflectance values in the yola basin also increase with stratigraphic age ranging from 0 73 in the dukul formation to 0 94 in the yolde formation and up to 1 37 in the bima formation total organic carbon toc values in the pindiga and gongila shales are between 0 4 to 2 4 averaging 0 75 toc contents from 0 10 to 12 9 averaging 1 2 are contained in the yolde formation of the yola basin tmax values from the pyrolysis of shales in the gongola basin range from 419 to 435 c whereas for shales in the yola basin they range from 431 to 442 c plots of hi vs tmax for kerogen classification indicate the prevalence of type iii kerogens in the gongila and pindiga shales although there are some indications of type ii iii kerogens in the yolde shales of the yola basin our preliminary data suggest that cretaceous successions in the gongola basin are thermally immature to marginally mature whereas source rocks in the yola basin are thermally mature with respect to hydrocarbon generation the predominance of type iii kerogens in the gongola basin suggest their potential to generate gas in the deeply buried sections the dukul and yolde formations with type ii iii kerogens may have generated some quantities of oil and gas in the deeper non emergent sections

fracture evolution in oil producing sills of the rio grande valley northern neuquen basin argentina oil producing sills are commonly considered atypical reservoirs although they can hold significant exploration potential the need for a better understanding of fracture properties and petroleum system characteristics for this and similar igneous rock plays is the main motivation of our study we explore the evolution of this play type by an analysis of the los cavaos oil field located in the malargue fold belt of the neuquen basin argentina integrating multiscale fracture data from outcrops and subsurface the field was created by a combination of intrusions and mild miocene pliocene inversion production stems from thick cavity zones in naturally fractured andesitic sills emplaced in upper jurassic shale source rocks orientation patterns fracture spacing and length of fracture sets in the sill are consistent over several orders of magnitude large multiply connected and weakly cemented fractures are responsible for excellent interconnectedness in the reservoir fracture density is correlated with fault proximity indicating a cogenetic evolution during active deformation abundant fractures in core with strike slip to oblique striations support transpressional overprint during and after fracture formation although it is challenging to separate cooling from tectonic fractures we propose two phases of fracturing marked by a coexistence of subvertical and oblique fractures together with transpressional striae petrographic evidence suggests initial local oil expulsion and migration through microfractures with opening displacements of 0 01 to 1 mm followed by subsequent charging of the evolving intrasill cavity system as well as the bulk fracture system during cooling and mild deformation we suggest that the observed patterns may be extrapolated to sills in similar geotectonic settings

effects of igneous intrusions on coalbed methane potential gunnedah basin australia abstract the gunnedah basin nsw australia contains more than 500 gt of coal and has been the subject of recent coalbed methane exploration large areas of the basin contain igneous intrusions and large areas of coal have been heat affected as a consequence a detailed study has been undertaken of coal seams intersected in a cored coalbed methane exploration drillhole in which two sill form igneous intrusions are present comparisons are made between coals that are unaltered and coals that have been heat affected using petrographic and chemical data coal seam gas desorption data and gas chemical analysis data results demonstrate that the two igneous intrusions have had a very positive effect on coalbed methane development the gas content in a number of heat affected coal seams within thermal aureoles above and below the sills is substantially higher than in adjacent unaffected coal seams in addition the intrusions have had little effect on gas quality the coals in the heat affected zone were found to contain gas with approximately 95 methane the coals in the thermal aureoles were found under the microscope to contain characteristic micropores and slits which collectively may serve to enhance gas adsorption capacity permeability and gas desorption gas contents below each of the sills is substantially higher than above the sill confirming earlier results that the sills appear to have acted as a reservoir seal during and for some time after intrusion the background coal rank in acm yannergee ddh 1 is in the high volatile bituminous range the igneous intrusions have resulted in an increase in rank such that large areas of coal have moved into the optimal thermogenic gas generation window this rank increase has affected a major part of the coal bearing sequence

examples of resolution improvement in geoelectrical soundings applied to groundwater investigations1 one simulation and two field examples from new jersey illustrate resolution improvement in geoelectrical soundings applied to groundwater exploration layered earth parameter resolution is derived from data obtained with the commonly used methods of resistivity induced polarization ip and transient electromagnetic tem soundings resolution improvement is achieved by simultaneous inversion of two or more data sets and by constraining parameters of the inverse problem a quantitative analysis showing the contribution of ip data to the resolution of geo electric sections is presented simultaneous inversion of simple ip data with conventional resistivity and resistivity tem data sets resulted in improved parameter resolution ip data improved resolution in three ways 1 by decoupling correlated layered earth parameters 2 by adding information to a geological interpretation about a second physical property namely chargeability and 3 by increasing the electrical information available

rise and emplacement of magma during horizontal shortening of the brittle crust insights from experimental modeling 1 magmatic activity tends to concentrate at plate margins at divergent margins extensional tectonics provide steep conduits for magma to reach the surface at rapidly convergent margins such as the andes one might imagine that horizontal compression prevents the rise of magma nevertheless volcanoes are also common in order to study the mechanisms by which magma rises in a compressional context we resorted to laboratory experiments in which a brittle crust was shortened while magma was intruding our model materials were 1 cohesive fine grained silica powder representing brittle crust and 2 molten low viscosity vegetable oil representing magma in general horizontal shortening and injection were coeval but independent processes thrust faults accommodated the shortening while overpressured oil formed hydraulic fractures in those experiments where there was no shortening injection resulted in a saucer shaped intrusive body in the other experiments where there was shortening oil formed a basal sill before rising along thrust faults once in place the sill lubricated the base of the model so that arcuate thrusts formed at the leading edge of a plateau uplift of the plateau promoted further intrusion of oil at depth in general the pattern of deformation and intrusion depended on the kinematic ratio r between rates of shortening and injection the lengths of the basal sill and plateau increased with decreasing r on the basis of these results we have reexamined two natural examples of magmatic complexes which were emplaced in compressional tectonic settings tromen volcano in argentina and the boulder batholith of montana

igneous petroleum systems in the malargue fold and thrust belt rio grande valley area neuquen basin argentina abstract the rio grande valley neuquen basin argentina is a large oil field where voluminous igneous sill complexes are emplaced in different levels of the sedimentary sequence in a fold and thrust belt setting these sills are predominantly emplaced in organic rich units such as vaca muerta and agrio formations and are critical elements of the defined petroleum system as they affect the thermal maturity of the surrounding source rocks and also act as naturally fractured reservoirs in this contribution we integrated structural sections borehole data core descriptions petrophysical laboratory tests and organic geochemistry measurements to characterize the impact of the magmatism in the petroleum system of the rio grande valley oil field especially we focused in evaluating the impact of the sill complexes in hydrocarbon generation migration and accumulation our data shows that 1 intrusions are preferably emplaced in organic rich units 2 a large number of intrusions is observed in areas intensely deformed by imbricated thrusts 3 an increase in the number of intrusions drives stronger and more extensive maturation processes in the vaca muerta formation enhancing notably the cracking of kerogen to hydrocarbon within this unit 4 where the number of intrusions increases the concentration of total gas and methane also increases given that all sills are suitable reservoirs 5 igneous rocks provide a low resistance path for fluids flow and act as the main reservoirs in the study area 6 the reservoir quality of igneous intrusions is dominated by the combination of matrix and fracture framework properties 7 zeolites are the most common type of cement in these reservoirs 8 deep sills located in the vaca muerta formation produce larger volumes of hydrocarbons relative to shallower intrusive reservoirs the rio grande valley oil field offers a world class example of the implications of igneous complexes in hydrocarbon generation migration and accumulation in a compressive tectonic setting of fold and thrust belt

petrographic and geochemical effects of sill intrusions on coal and their implications for gas outbursts in the wolonghu mine huaibei coalfield china abstract since the early 1980s fifteen outbursts have occurred in the huaibei coalfield of china these outbursts were reported to be associated with sills to study the effect of sill intrusions on coal seam and their relationship to methane outbursts eleven samples from the no 10 coal seam were taken from the wolonghu mine at various distances from a diorite sill comparisons were made between unaltered and heat affected coals using petrographic and chemical data micropore characteristics adsorption properties of coal and gas outburst indexes from field approaching the intrusion vitrinite reflectance levels increased from 2 74 to 5 03 and the thermal aureole of the sill 60 m from the sill boundary to sample 9 three zones along this gradient were identified as corresponding to 1 thermal evolution zone no 1 0 5 m from sill 2 thermal evolution zone no 2 5 60 m from sill and 3 unaltered zone the methane adsorption capacity of coal samples in the thermal evolution zone no 2 was generally higher than in the two other zones and the unaltered zone higher than the thermal evolution zone no 1 it is concluded that the contact metamorphism decreased the adsorption capacity of coal and the thermal evolution of sill increased it the trap effect of sill combined with the mudstone and siltstone roof and floor of the no 10 coal seam provided a seal for the formation of a gas pocket abnormally high formation pressures at the no 10 coal seam led to two outbursts

high sampling rate measurement and data treatment for mobile investigations kinematic electrical resistivity tomography kert abstract this paper presents an innovative system which adapts electrical resistivity tomography ert for fast investigation on long transects the device consists in a set of on the go sensors allowing high sampling rate measurement for mobile prospections the weak contact between the mobile sensors and the soil to allow fast investigations induces very noisy raw datasets kinematic electrical resistivity tomography named kert is then associated with a data treatment process a two step process reveals the information contained in the datasets the first focuses on the procedure to remove noise through the use of a low pass filter the assessment of cutoff frequency for smoothing is deduced from a fast fourier transform fft analysis thus the value is adapted to the site and the prospection the second phase consists in calibration of the kert on a conventional static ert at this point a classical static ert was used as a reference and directed on a reduced part of the kert transect the estimation of a factor of calibration xc to correct bias revealed the resistivity variations along the entire transect and in depth in the last part of the paper the validation of the investigation method and data treatment methodology is performed on a real case study a 450 m transect is investigated in 5 min mean speed about 6 km h integrating 10 depths of investigation the steps of data processing are detailed to show the final results consisting in a zonation along the transect

pulled array continuous electrical sounding with an additional inductive source an experimental design study electrical and electromagnetic profiling methods are used extensively in environmental geophysical investigations for many different purposes the pulled array continuous electrical sounding paces method where a tail of electrodes is towed behind a small vehicle while continuously and simultaneously measuring several electrode configurations has been used extensively for mapping the vulnerability of aquifers in denmark measurements are taken every 1 m and 10 15 km of profile can be achieved in one day this paper presents a theoretical study of the resolution capabilities of paces measurements as they are now performed and an experimental design study for including an inductive source in the measuring equipment the joint interpretation of the galvanic data set of ordinary paces measurements with inductive data from a horizontal magnetic dipole source will enhance the resolution capabilities of the data set significantly the study is carried out as an analysis of the uncertainty of the model parameters of one dimensional three layer models using the estimation error variances of the inversion problem the results indicate that the addition of only two frequency data from a magnetic dipole source will substantially improve the resolution of the subsurface resistivity structure the improvement is model dependent but reduction in the relative error of model parameters by an order of magnitude is observed

a potential vorticity theory for the formation of elongate channels in river deltas and lakes 1 rivers empty into oceans and lakes as turbulent sediment laden jets which can be characterized by a gaussian horizontal velocity profile that spreads and decays downstream because of shearing and lateral mixing at the jet margins recent experiments demonstrate that this velocity field controls river mouth sedimentation patterns in nature diffuse jets are associated with mouth bar deposition forming bifurcating distributary networks while focused jets are associated with levee deposition and the growth of elongate channels that do not bifurcate river outflows from elongate channels are similar in structure to cold filaments observed in ocean currents where high potential vorticity helps to preserve coherent structure over large distances motivated by these observations we propose a hydrodynamic theory that seeks to predict the conditions under which elongate channels form our approach models jet velocity patterns using the flow vorticity both shearing and lateral spreading are directly related to the vertical component of vorticity we introduce a new kind of potential vorticity that incorporates sediment concentration and thus allows study of jet sedimentation patterns the potential vorticity equation reduces the number of fluid momentum equations to one without losing generality this results in a compact analytical solution capable of describing the streamwise evolution of the potential vorticity of a sediment laden jet from initial conditions at the river mouth our theory predicts that high potential vorticity is a necessary condition for focused levee deposition and the creation of elongate channels comparison to numerical laboratory and field studies indicates that potential vorticity is a primary control on channel morphology our results may be useful for designing river delta restoration schemes such as the proposed mississippi delta diversion

surface morphology of columnar joints and its significance to mechanics and direction of joint growth columnar joints in basaltic lava flows display conspicuous bands oriented normal to column axes new observations show that each band contains a single plumose structure and thus represents an individual crack or joint segment formed during a discrete growth event analysis of plumose structure and intersections of cracks leads to a new kinematic model of columnar jointing and provides the first direct proof that columnar joints grow incrementally from exterior to interior regions of solidifying magma bodies columnar joints form by nucleation and growth of new cracks on the edges of older cracks each new crack begins at a point and propagates mostly normal to column axes and along the leading edge of a developing column face where thermal stress is concentrated inward propagation of cracks toward hotter regions is limited by a decrease of thermal stress and by the brittle ductile transition of lava outward and lateral propagation is limited by mechanical interaction with previous cracks and by low thermal stress in already fractured lava cracks often diverge slightly from the planes of previous cracks probably because of spatial and temporal changes in directions of local principal stresses mechanical interaction causes a diverging crack to overlap curve toward and usually intersect the previous crack behind its edge leaving a blind tip that points in the overall growth direction of the columnar joints this and other directional criteria are applied to determine joint growth patterns in several lava flows of the western united states in two tiered and multi tiered flows downward growing columnar joints usually meet upward growing joints well below the middle of the flows which indicates very rapid cooling of upper portions relative to lower portions this supports the idea that convection of water in columnar joints connected to the surface may be an important mechanism for cooling the upper portions of these flows whereas conduction is probably the dominant cooling mechanism at the bases

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

siberian gas venting and the end permian environmental crisis abstract the end of the permian period is marked by global warming and the biggest known mass extinction on earth the crisis is commonly attributed to the formation of the siberian traps large igneous province although the causal mechanisms remain disputed we show that heating of tunguska basin sediments by the ascending magma played a key role in triggering the crisis our conclusions are based on extensive field work in siberia in 2004 and 2006 heating of organic rich shale and petroleum bearing evaporites around sill intrusions led to greenhouse gas and halocarbon generation in sufficient volumes to cause global warming and atmospheric ozone depletion basin scale gas production potential estimates show that metamorphism of organic matter and petroleum could have generated 100 000 gt co2 the gases were released to the end permian atmosphere partly through spectacular pipe structures with kilometre sized craters dating of a sill intrusion by the u pb method shows that the gas release occurred at 252 0 0 4 million years ago overlapping in time with the end permian global warming and mass extinction heating experiments to 275 c on petroleum bearing rock salt from siberia suggests that methyl chloride and methyl bromide were significant components of the erupted gases the results indicate that global warming and ozone depletion were the two main drivers for the end permian environmental crisis we demonstrate that the composition of the heated sedimentary rocks below the flood basalts is the most important factor in controlling whether a large igneous provinces causes an environmental crisis or not we propose that a similar mechanism could have been responsible for the triassic jurassic 200 ma global warming and mass extinction based on the presence of thick sill intrusions in the evaporite deposits of the amazon basin in brazil

release of methane from a volcanic basin as a mechanism for initial eocene global warming a 200 000 yr interval of extreme global warming marked the start of the eocene epoch about 55 million years ago negative carbon and oxygen isotope excursions in marine and terrestrial sediments show that this event was linked to a massive and rapid approximately 10 000 yr input of isotopically depleted carbon it has been suggested previously that extensive melting of gas hydrates buried in marine sediments may represent the carbon source and has caused the global climate change large scale hydrate melting however requires a hitherto unknown triggering mechanism here we present evidence for the presence of thousands of hydrothermal vent complexes identified on seismic reflection profiles from the voring and more basins in the norwegian sea we propose that intrusion of voluminous mantle derived melts in carbon rich sedimentary strata in the northeast atlantic may have caused an explosive release of methane transported to the ocean or atmosphere through the vent complexes close to the palaeocene eocene boundary similar volcanic and metamorphic processes may explain climate events associated with other large igneous provinces such as the siberian traps approximately 250 million years ago and the karoo igneous province approximately 183 million years ago