sediment hosted geothermal systems review and first global mapping abstract sediment hosted geothermal systems shgss are hybrid geological systems where volcanic and sedimentary domains interact leading to mixtures of inorganic and organic gases typically characterized by geothermal thermometamorphic or mantle derived co2 and biotic microbial or thermogenic ch4 shgss occur in sedimentary basins crossed by magmatic intrusions or involved in volcanic plumbing systems these systems can be of considerable interest for petroleum exploration and natural greenhouse gas emission studies but systematic studies for their characterization and worldwide distribution are missing here we provide a review of shgss identified so far and propose methodological criteria for their definition and identification based on integrated geological and gas geochemical parameters we find that shgss are typically characterized by a fluids dominated by mantle or decarbonation methamorphic co2 50 vol b considerable amounts of ch4 and heavier hydrocarbons at least 1 5 vol generally up to 30 40 vol produced by microbial or thermogenic degradation of organic matter hosted in sedimentary rocks c tectonically active sedimentary basins back arc rift zones and foredeep generally hosting petroleum fields and within 300 km from recent or ancient volcanic centers this analysis resulted in a global map including a first set of 33 shgss located in north america central and eastern europe far east eastern oceania and northern new zealand and a second set of potential shgs prone areas occurring also in south america north africa middle east and kamchatka the present shgs map can evolve on the basis of more detailed geological analysis and new gas geochemical data

the palaeocene eocene carbon isotope excursion constraints from individual shell planktonic foraminifer records the palaeocene eocene thermal maximum petm is characterized by a global negative carbon isotope excursion cie and widespread dissolution of seafloor carbonate sediments the latter feature supports the hypothesis that the petm and cie were caused by the rapid release of a large mass greater than 2000gt c of 12c enriched carbon the source of this carbon however remains a mystery possible sources include volcanically driven thermal combustion of organic rich sediment dissociation of seafloor methane hydrates and desiccation and oxidation of soil sediment organics a key constraint on the source s is the rate at which the carbon was released fast rates would be consistent with a catastrophic event e g massive methane hydrate dissociation whereas slower rates might implicate other processes the petm carbon flux is currently constrained by high resolution marine and terrestrial records of the cie in pelagic bulk carbonate records the onset of the cie is often expressed as a single or multiple step excursion extending over 10 4 years individual planktonic shell records in contrast always show a single step cie with either pre excursion or excursion isotope values but no transition values benthic foraminifera records which are less complete owing to extinction and diminutive assemblages show a delayed excursion here we compile and evaluate the individual planktonic shell isotope data from several localities we find that the most expanded records consistently show a bimodal isotope distribution pattern regardless of location water depth or depositional facies this suggests one of several possibilities i the isotopic composition of the surface ocean atmosphere declined in a geologic instant 500yr ii that during the onset of the cie most shells of mixed layer planktonic foraminifera were dissolved or iii the abundances or shell production of these species temporarily declined possibly due to initial ph changes

no evidence for thermogenic methane release in coal from the karoo ferrar large igneous province abstract the early jurassic toarcian oceanic anoxic event t oae and concurrent negative carbon isotope 13 c excursion have recently been attributed to either the release of methane ch 4 clathrates or thermogenic ch 4 gas associated with the karoo ferrar large igneous province lip into coals and organic rich shales 12 c enriched thermogenic ch 4 production associated with the karoo ferrar would result in residual material being 12 c depleted nearer the intrusions in this study geochemical analyses carbon isotopes volatile matter vm vitrinite reflectance r o are reported for two coal transects associated with dykes intruding the no 4l coal in the highveld coalfield karoo basin south africa vm decreases from over 35 to around 15 in one transect and the second transect shows a less pronounced decrease from 25 to 16 accompanying the decrease in vm content is an increase in r o from background levels of around 0 7 to over 4 adjacent to the dyke used as a palaeo geothermometer r o values indicate background temperatures of 100 c increasing to 300 c close to the contact despite changes in vm and r o there are no significant changes in 13 c certainly not of the magnitude that would be expected associated with large scale thermogenic ch 4 generation these and other gondwanan coals have low vitrinite and liptinite contents components more prone to ch 4 generation in part explaining the modest decreases in vm adjacent to the dykes this combined with the relatively narrow metamorphic aureole surrounding the intrusions and the likelihood that at least some of the volatiles generated by the intrusion were trapped as coalbed ch 4 or condensed as pyrolytic carbon suggests only limited ch 4 release in addition based on original estimates of moisture contents in these coals and the depth at time of intrusion 1 000 2 000 m the dykes would have lost most of their energy heating and evaporating water thus having very little remaining energy to generate thermogenic ch 4

the shallow depth emplacement of mafic intrusions on a magma poor rifted margin an example from the bight basin southern australia abstract three dimensional 3d seismic data has provided important insights into how magma is transported and stored in sedimentary basins much of our understanding is based on volcanic rifted margins in contrast the magma plumbing systems of magma poor rifted margins are less well studied this study uses 3d seismic data to describe the magma plumbing system of the bight basin igneous complex a volcanic province located along the magma poor southern australian margin here magma emplacement occurred in the mid eocene some 40 million years after the onset of seafloor spreading our data images a variety of 5 270 m thick 2 23 km diameter mafic intrusions that are confined to within 1200 m of the paleoseabed intrusions emplaced at 200 m depth formed hybrid and compound sills and are typified by elongate lava flow like morphologies intrusions emplaced at depths of 200 1200 m formed saucer shaped and compound sills as well as laccoliths approximately 60 of the intrusions have lava flows and volcanogenic vents above their shallowest tips as shown from previous studies this suggests that the intrusions played a crucial role in transporting magma to the paleoseabed furthermore many of the intrusions are overlain by forced folds highlighting the role of magma emplacement in inducing overburden deformation the sills and laccoliths rarely form interlinked complexes and instead most commonly occur as isolated bodies this suggests that they were fed by dykes we infer that high rates of magma ascent in the dykes prevented their transition into sills within sediments at 1 2 km depth our study highlights that the magma plumbing system of the bight basin igneous complex contains a diversity of magmatic intrusions the morphology of which is linked to their emplacement depth host sediment rheology and the physical properties of the magma this plumbing system contrasts markedly with those found along better studied volcanic rifted margins

zircon dating ties ne atlantic sill emplacement to initial eocene global warming abstract the earth experienced rapid greenhouse gas induced global warming during the palaeocene eocene thermal maximum petm the source of the gas is however debated we have for the first time determined the ages of magmatic sills in the voring basin offshore norway zircon u pb ages of 55 6 0 3 and 56 3 0 4 ma demonstrate that sill emplacement was synchronous with the petm within small errors this discovery strengthens the hypothesis that global warming was triggered by rapid release of greenhouse gases generated by heating of organic rich sediments around intrusions in the ne atlantic rather than from dissociation of gas hydrates supplementary material u pb data are available at http www geolsoc org uk sup18392

seismic characteristics and evolution of post rift igneous complexes and hydrothermal vents in the lingshui sag qiongdongnan basin northwestern south china sea abstract the study of morphology distribution and characteristics of igneous complexes has great significance to the understanding of magma plumbing processes geodynamics and tectonic evolution of continental margins previous studies concentrated partly on the magma rich rifted basins where the lateral magma transport mainly affects the igneous complexes connection and distribution however due to seismic wave shielding effects of the large shallow magmatic bodies the underlying igneous complexes and their corresponding magma plumbing systems in the magma poor rifted margins are still in debate in this study 2d 3d seismic data and well data are utilized to describe the morphology architecture and spatial temporal distribution of igneous complexes in the lingshui sag of the qiongdongnan basin northwestern south china sea margin the identified igneous complexes include 98 intrusive sills and feeder dykes beneath some of the isolated sills twenty six cone shaped mounds that overlie intruded sills through internal disturbed conduits were also described drilled well samples and seismic expressions suggest that these mounds are hydrothermal vents a uniform bottom mounds horizon of these vents suggests that they probably formed at the same time constrained by biostratigraphic data and sedimentation rate of underlying and overlying sedimentary layers the magma emplacement was dated to the middle miocene ca 14 6 ma most of the hydrothermal vents are distributed along the f2 fault zone and have direct linkage with the underlying sills while the large sill complexes that are connected with limited vents are mainly present above the hyperextended continental crust where the crust thins to 6 10 km the sills intruded into different layers from the lower oligocene to the lower miocene and the emplaced depth of sills is 1 2 6 3 km whether or not they feed any vents above unlike most of the large volume and laterally linked sills found in the magma rich rifted margins the scattered distribution of sills at different levels indicates that dykes probably play an important role in magma transport which might coexist with numerous polygonal or small faults and interference reflections this work highlights the critical role of basin structures in controlling the distribution of post rift igneous complexes in magma poor margins including thinned continental crust sedimentary thickness and faults

assessing offsets between the δ13c of sedimentary components and the global exogenic carbon pool across early paleogene carbon cycle perturbations 1 negative stable carbon isotope excursions cies across the paleocene eocene thermal maximum petm 56 ma range between 2 and 7 even after discounting sections with truncated records individual carbon isotope records differ in shape and magnitude from variations in the global exogenic carbon cycle through changes in 1 the relative abundance of mixed components with different 13c within a measured substrate 2 isotope fractionation through physiological change and 3 the isotope composition of the carbon source all three factors likely influence many early paleogene 13c records especially across the petm and other hyperthermal events we apply these concepts to late paleocene early eocene 58 52 ma records from lomonosov ridge arctic ocean linear regression analyses show correlations between the 13c of total organic carbon toc and two proxies for the relative contribution of terrestrial organic components to sediment toc the branched and isoprenoid tetraether index and palynomorphs we use these correlations to subtract the terrestrial component from 13ctoc and calculate marine organic matter 13c the results show that the magnitude of the cie in 13ctoc across the petm is exaggerated relative to the magnitude of the cie in 13cmom by 3 due to increased contributions of terrestrial organic carbon during the event collectively all carbon isotope records across the petm and other major climate carbon cycle perturbations in earth s history are potentially biased through one or more of the above factors indeed it is highly unlikely that any 13c record shows the true shape and magnitude of the cie for the global exogenic carbon cycle for the petm we conclude that cie in the exogenic carbon cycle is likely 4 but it will take additional analyses and modeling to obtain an accurate value for this cie

fault related biogenic mounds in the ceduna sub basin australia implications for hydrocarbon migration abstract the early cenozoic in the bight basin represents a transitional period from the slow to fast oceanic crust spreading of the southern ocean between australia and antarctica this period is characterised by widespread igneous activity and the occurrence of biogenic mound complexes in the proximal part of the ceduna sub basin these mound complexes thrive on local topographic highs exploiting the shut down in siliciclastic sediment supply during the eocene new interpretation of 2d and 3d seismic data from the central ceduna sub basin shows additional undrilled paleocene eocene biogenic mound complexes they display rugose morphology progradational and aggradational internal organisation and high impedance contrast with the surrounding sediments these mounds typically show a clear relationship with underlying reactivated fault segments these faults intersect potential oil mature cretaceous source rock intervals and therefore one plausible mechanism for the development of fault related mound complexes in the central ceduna sub basin relies on natural hydrocarbon seeps along faults supplying nutrients for a benthic chemosynthetic organisms and localised biogenic mound growth the presence of a sub bottom profile anomaly overlaid by a vertical water column acoustic contact in close vicinity of a mound complex support this model the occurrence of seep related biogenic mounds would validate the presence of mature source rock s and hydrocarbon charge in the central ceduna sub basin if confirmed the biogenic mounds would imply fluid migration occurrence until at least the eocene

methane escape from gas hydrate systems in marine environment and methane driven oceanic eruptions 1 huge quantities of ch4 are stored in marine sediment in the form of methane hydrate bubbles and dissolved ch4 in pore water here i discuss the various pathways for methane to enter the ocean and atmosphere including i methane hydrate dissolution or dissociation as it rises through seawater the dissociation rate can be 2 to 3 orders of magnitude greater than the dissolution rate ii the dissolution and expansion of a bubble with or without a hydrate shell as it rises through seawater there is a critical radius which depends on depth above which a bubble would reach the surface or even become larger as it rises i also propose and model the dynamics of a new type of terrestrial gas driven eruptions methane driven oceanic eruptions such eruptions not only represent a yet unrecognized geohazard but also provide a pathway for ch4 to rapidly enter the atmosphere as a greenhouse gas

the t reflection and the deep crustal structure of the voring margin offshore mid norway seismic reflection data along volcanic passive margins frequently provide imaging of strong and laterally continuous reflections in the middle and lower crust we have completed a detailed 2d seismic interpretation of the deep crustal structure of the voring margin offshore mid norway where high quality seismic data allow the identification of high amplitude reflections locally referred to as the t reflection using a dense seismic grid we have mapped the geometry of the t reflection in order to compare it with filtered bouguer gravity anomalies and seismic refraction data the t reflection is identified between 7 and 10 s sometimes it consists of one single smooth reflection however it is frequently associated with a set of rough multiple reflections displaying discontinuous segments with varying geometries amplitudes and contact relationships the t reflection seems to be connected to deep sill networks and is locally identified at the continuation of basement high structures or terminates over fractures and faults the spatial correlation between the filtered positive bouguer gravity anomalies and the deep dome shaped reflections indicates that the latter represent a high impedance boundary contrast associated with a high density and velocity body in 50 of the outer voring margin the depth of the mapped t reflection is found to correspond to the depth of the top of the lower crustal body lcb which is characterized by high p wave velocities 7 km s we present a tectonic scenario where a large part of the deep crustal structure is composed of preserved upper continental crustal blocks and middle to lower crustal lenses of inherited high grade metamorphic rocks deep intrusions into the faulted crustal blocks are responsible for the rough character of the t reflection whereas intrusions into the ductile lower crust and detachment faults are likely responsible for its smoother character deep magma intrusions can be responsible for regional metamorphic processes leading to an increasing velocity of the lower crust to more than 7 km s the result is a heterogeneous lcb that likely represents a complex mixture of pre to syn breakup mafic and ultramafic rocks cumulates and sills and old metamorphic rocks such as granulites and eclogites an increasing degree of melting towards the breakup axis is responsible for an increasing proportion of cumulates and sill intrusions in the lower crust

contact metamorphism and thermogenic gas generation in the voring and more basins offshore norway during the paleocene eocene thermal maximum voluminous volcanic intrusive activity took place in the voring and more basins at the paleocene eocene boundary at about 56 ma this event caused thermal maturation of cretaceous sedimentary rocks in the basins we have estimated the resulting thermogenic gas generation potential from contact metamorphism using numerical simulations calibrated using borehole data the borehole 6607 5 2 from the utgard sill complex in the voring basin contains two c 100 m thick sills and is used as a case study we present both new and compiled data showing that 1 the bulk organic content is reduced towards the sill intrusions 2 a c 1 km thick stratigraphic interval is thermally affected based on vitrinite reflectance data 3 relative emplacement timing can affect the gas yield by up to 25 and 4 some of the thermogenic methane is still present in the aureoles the numerical model is calibrated using data from 11 wells we estimate that the total gas generation potential for the two utgard sills equals that of the troll field c 10 gt ch 4 the largest producing gas field offshore norway we show that in the voring and more basins the total gas generation potential is up to 1500 gt ch 4 c 1100 gt c even from the relatively organic poor cretaceous source rocks with c 1 wt organic carbon with implications for the carbon cycle at the paleocene eocene boundary

two lips and two earth system crises the impact of the north atlantic igneous province and the siberian traps on the earth surface carbon cycle the links between the siberian traps and the end permian mass extinction and between the north atlantic igneous province naip and the paleocene eocene thermal maximum petm demonstrate a critical role for large igneous provinces lips in the disruption of the earth surface carbon cycle escc high precision ages for both volcanic provinces and the associated environmental crises show that in both cases the crisis was contemporaneous with the volcanism the naip comprises two phases the earlier phase 1 c 61 ma and the much more voluminous phase 2 c 56 ma linked to the opening of the ne atlantic the latter triggered the petm the largest cenozoic hyperthermal the siberian traps are significantly more voluminous than the naip and triggered the end permian mass extinction the masses of volcanic co 2 emitted from these provinces may have been much greater than previously suggested as substantial gas may come from intrusive bodies deep within the crust precursory warming due to the accumulation of volcanic co 2 in the atmosphere likely triggered the release of low 13 c methane hydrate although the masses of methane hydrate alone may have been insufficient to account for the observed temperature rises the organic c was likely strongly supplemented by magmatically derived carbon and thermogenic carbon released during emplacement of sills and dykes into c rich sedimentary units more data are required on the volcanic flux rates in order to refine the cause effect relationships between lips and the escc

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

environmental impact of volcanic margin formation late rift stage uplift and subsequent massive transient volcanism during breakup of rifted volcanic continental margins constrain paleoenvironments by modifying basin geometry and the composition of the atmosphere hydrosphere and thus biosphere on regional and global scales the early tertiary north atlantic breakup history shows that lava emplacement was accompanied by regional ashfalls and that extrusive complexes influenced paleogene oceanic and continental margin circulation and sedimentation temporal correspondence with the terminal paleocene deep sea extinction event and the earliest eocene greenhouse suggests a global impact possibly by enhanced atmospheric co 2 levels leading to polar warming and thereby changing patterns of deep water formation in this context transient subaerial volcanism at continental margins should be considered with the much discussed continental flood basalt provinces and oceanic plateaus

evidence of a modern deep water magmatic hydrothermal system in the canary basin eastern central atlantic ocean new seismic profiles bathymetric data and sediment rock sampling document for the first time the discovery of hydrothermal vent complexes and volcanic cones at 4800 5200 m depth related to recent volcanic and intrusive activity in an unexplored area of the canary basin eastern atlantic ocean 500 km west of the canary islands a complex of sill intrusions is imaged on seismic profiles showing saucer shaped parallel or inclined geometries three main types of structures are related to these intrusions type i consists of cone shaped depressions developed above inclined sills interpreted as hydrothermal vents type ii is the most abundant and is represented by isolated or clustered hydrothermal domes bounded by faults rooted at the tips of saucer shaped sills domes are interpreted as seabed expressions of reservoirs of ch4 and co2 rich fluids formed by degassing and contact metamorphism of organic rich sediments around sill intrusions type iii are hydrothermal volcanic complexes originated above stratified or branched inclined sills connected by a chimney to the seabed volcanic edifice parallel sills sourced from the magmatic chimney formed also domes surrounding the volcanic cones core and dredges revealed that these volcanoes which must be among the deepest in the world are constituted by oib type basanites with an outer ring of blue green hydrothermal al rich smectite muds magmatic activity is dated based on lava samples at 0 78 0 05 and 1 61 0 09 ma k ar methods and on tephra layers within cores at 25 237 ky the subvent hydrothermal volcanic complex constitutes the first modern system reported in deep water oceanic basins related to intraplate hotspot activity

latest on the absolute age of the paleocene eocene thermal maximum petm new insights from exact stratigraphic position of key ash layers 19 and 17 abstract we constructed a precise early eocene orbital cyclostratigraphy for dsdp site 550 leg 80 goban spur north atlantic utilizing precession related cycles as represented in a high resolution x ray fluorescence based barium core log based on counting of those cycles we constrain the exact timing of two volcanic ash layers in site 550 which correlate to ashes 19 and 17 of the fur formation in denmark the ashes relative to the onset of the paleocene eocene thermal maximum petm are offset by 862 kyr and 672 kyr respectively when combined with published absolute ages for ash 17 the absolute age for the onset of the petm is consistent with astronomically calibrated ages using the current absolute age of 28 02 ma for the fish canyon tuff fct standard for calibrating the absolute age of ash 17 is consistent with tuning option 2 in the astronomically calibrated paleocene time scale of westerhold et al 2008 westerhold t rohl u raffi i fornaciari e monechi s reale v bowles j and evans h f 2008 astronomical calibration of the paleocene time palaeogeography palaeoclimatology palaeoecology v 257 p 377 403 using the recently recalibrated absolute age of 28 201 ma for the fct standard is consistent with tuning option 3 in the astronomically calibrated paleocene time scale the new results do not support the existence of any additional 405 kyr cycle in the early paleocene astronomically tuned time scale

high velocity breakup related sills in the voring basin off norway multichannel seismic reflection profiles in the hel graben v0ring basin reveal a sill complex at approximately 5 km depth it is associated with exceptionally high 7 4 km s 1 seismic wide angle velocities the existence of observable wide angle arrivals shows that the sills act as efficient waveguides seismic reflection data and amplitude modeling constrain the thickness of individual sills to approximately 100 m sonic logs from sills of similar thickness on the nearby utgard high show an average velocity of 7 0 km s 1 such high velocities require an olivine gabbroic sill composition and emplacement under conditions which allowed growth of relatively large crystal sizes a possible reason for such an emplacement environment is the hei graben s role as an intrusion center during breakup volcanism this would provide the necessary duration of the magmatic activity as well as locally increased melt volumes and cooling times sill complexes of this kind decrease the accuracy of determined velocity fields and crustal geometries below the top of the sill complex affecting depth conversion and gravity modeling furthermore the results question the concept of lower crustal bodies as large scale homogeneous accumulations of mafic melt

hydrothermal vent complexes offshore northeast greenland a potential role in driving the petm tgs are thanked for access to data and dwarika maharjan is thanked for help with kingdom software andy saunders and mads huuse are thanked for insightful constructive reviews and tamsin mather is thanked for editorial handling

seismic stratigraphy of the post breakup succession offshore northeast greenland links to margin uplift abstract the timing of the continental breakup between norway and greenland and the subsequent plate tectonic motions are well understood however due to the remote location of the northeast greenland shelf relatively few details about the tectonosedimentary response to the tectonism following the breakup have previously been published this article gives new insights into the structural and sedimentary history of the northeast greenland shelf with an emphasis on the post breakup tectonics using state of the art 2d seismic data the results of this study clearly shows a highly dynamic post breakup tectonic setting with pronounced kilometre scale fault offsets tilting of the danmarkshavn basin and pronounced progradational events the tectonosedimentary events are linked with the passage of the icelandic mantle plume south of the northeast greenland shelf based on tectonostratigraphic interpretations and integration of data from odp 913 this study constructs a temporally robust model for the post breakup succession significant post breakup uplift and tectonism related to thermal uplift is present on the margin it is observed that the icelandic hot spot passes relatively close by the northeast greenland shelf

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

the morphology of intrusion related vent structures and their implications for constraining the timing of intrusive events along the ne atlantic margin intrusion related vent structures found within palaeocene sediments and near the palaeocene eocene transition in basins along the ne atlantic margin have been studied in detail using 3d seismic data the vents formed at the palaeo seabed as a result of sill intrusion and the vent fill ranges in composition from entirely remobilized sedimentary to dominantly magmatic the vents are commonly developed above sill edges and crests in sills to which they are linked by pipe and diatreme like structures the vents also develop above the upper tips of deep seated faults and at fault intersections the vents can be used to constrain the approximate timing of igneous sill intrusion and duration of hydrothermal activity it is estimated that using the seismically constrained stratigraphic context of these vents to establish the timing of sill emplacement is associated with an uncertainty of 100 ka and up to as much as 800 ka interpretation of the vents indicates that sill intrusion took place during a number of discrete phases within the palaeocene and earliest eocene these structures and their timing of formation have important implications for climate change studies basin scale processes including fluid flow and diagenesis as well as hydrocarbon exploration

the importance of subsurface lithology in controlling magma storage v eruption an example from offshore southern australia the volumetric relationship between the intrusive and extrusive components of volcanic fields is difficult to constrain this is because either the erupted products are commonly eroded or the intrusions are concealed by overburden three dimensional seismic data therefore offer a unique opportunity to study ancient volcanic provinces as these datasets can image both components without the need for erosional dissection this study is based on 3d seismic data from the bight basin igneous complex bbic a volcanic province constructed within a sedimentary basin offshore southern australia we demonstrate that the bbic contains abundant sills and laccoliths emplaced within deltaic sediments the intrusions have a total volume of 92 111 km 3 and the lava flows and volcanoes have a combined volume of 66 76 km 3 dense rock equivalent this indicates that the ratio of intrusive extrusive products for the bbic is between 1 1 and 2 1 the architecture of the bbic contrasts markedly with the neighbouring newer volcanics province nvp which lacks abundant sills and laccoliths because lava flows and volcanoes in the nvp were dominantly fed by dykes hosted in basement rock we suggest that subsurface lithology plays an important role in causing sill formation and determining the total volume of magma stored in the subsurface

seismic stratigraphy of detroit seamount hawaiian emperor seamount chain post hot spot shield building volcanism and deposition of the meiji drift 1 detroit seamount one of the northernmost seamounts of the hawaiian emperor seamount chain was formed at ca 76 ma new seismic data suggest renewed volcanism as late as 25 m y after initial seamount formation we use high resolution single channel seismic scs data acquired over the summit of detroit seamount in 2001 on ocean drilling program odp leg 197 supplemented by older scs data acquired as part of the gloria mapping program of the u s geological survey to characterize the seismic stratigraphy of detroit seamount volcanic edifices occur on the summit of the seamount and are older than the oldest beds of the meiji drift early oligocene ca 34 ma on the basis of ash layers in odp drill holes we suggest the edifices were active throughout much of the eocene ca 52 34 ma with activity possibly extending into the early oligocene 34 ma hence the age difference between the shield building lavas and the postshield cones on detroit is far greater than the shield postshield age differences observed on the hawaiian islands suggesting that renewed volcanic activity and tectonic collapse may be possible on any of the hawaiian islands we confirm earlier assertions that the thick sediment cap oligocene and younger in age was deposited by an ocean bottom current with a southeastward flow direction along the northeast facing flank of the emperor seamount chain this sediment cap the meiji drift was deposited by a lower velocity current than many other sediment drifts a low angle normal fault dipping 19 suggests topographic collapse of detroit seamount sometime during the eocene or late cretaceous

seismic volcanostratigraphy of large volume basaltic extrusive complexes on rifted margins large volume extrusive basaltic constructions have distinct morphologies and seismic properties depending on the eruption and emplacement environments the presence and amount of water is of main importance while local rift basin configuration erosion and resedimentation determine the overall geometry of the volcanic constructions we have developed the concept of seismic volcanostratigraphy a subset of seismic stratigraphy to analyze volcanic deposits imaged on seismic reflection data the method places special focus on identification and mapping of seismic facies units and the volcanological interpretation of these units interpretation of seismic reflection data along the atlantic and western australia rifted margins reveals six characteristic volcanic seismic facies units named 1 landward flows 2 lava delta 3 inner flows 4 inner seaward dipping reflectors inner sdr 5 outer high and 6 outer sdr these units are interpreted in terms of a five stage tectonomagmatic volcanic margin evolution model comprising 1 explosive volcanism in a wet sediment broad basin setting 2 subaerial effusive volcanism forming gilbert type lava deltas along paleoshorelines 3 subaerial effusive volcanism infilling a fairly narrow rift basin 4 shallow marine explosive volcanism as the injection axis is submerged below sea level and finally 5 deep marine sheet flow or pillow basalt volcanism further erosion and resedimentation processes are particularly important during the shallow marine stages seismic volcanostratigraphy provides important constraints on rifted margin development in particular on the prevolcanic basin configuration relative timing of tectonomagmatic events total amount of volcanic rocks location of paleoshorelines and margin subsidence history these parameters give key boundary conditions for understanding the processes forming volcanic margins and other large volume basaltic provinces

importance of the assimilation of argo float measurements on the meridional overturning circulation in the south atlantic 1 the meridional overturning circulation moc and meridional heat transport mht obtained from two gfdl coupled models with and without data assimilation are examined and compared with observations collected at nominally 34 s in the south atlantic the results demonstrate that the performance of the geophysical fluid dynamic laboratory gfdl coupled data assimilation cda model is quite different between the two periods 1979 2002 and 2003 2007 due to the assimilation of argo data in later period the moc components from the gfdl cda during 1979 2002 are similar to those from gfdl cm2 1 ipcc simulation both give weak boundary currents and strong interior overturning transport compared to observations however after assimilating temperature and salinity profiles from the argo floats the performance of the gfdl cda is greatly improved in terms of representing the observed moc and mht structure the transports of boundary currents are twice as strong as those during pre argo period and the overturning flow in the interior region is reduced possible causes for the changes in model performance are discussed

modelling hydrothermal venting in volcanic sedimentary basins impact on hydrocarbon maturation and paleoclimate highlights numerical model of sill intrusions in sedimentary basins fracture and vent formation due to overpressure generation methane fluxes through a single vent with upscaling to basin scales additional regions in the naip required to correlate methane venting and the petm abstract vent structures are intimately associated with sill intrusions in sedimentary basins globally and are thought to have been formed contemporaneously due to overpressure generated by gas generation during thermogenic breakdown of kerogen or boiling of water methane and other gases generated during this process may have driven catastrophic climate change in the geological past in this study we present a 2d fem fvm model that accounts for explosive vent formation by fracturing of the host rock based on a case study in the harstad basin offshore norway overpressure generated by gas release during kerogen breakdown in the sill thermal aureole causes fracture formation fluid focusing and overpressure migration towards the sill tips results in vent formation after only few tens of years the size of the vent depends on the region of overpressure accessed by the sill tip overpressure migration occurs in self propagating waves before dissipating at the surface the amount of methane generated in the system depends on toc content and also on the type of kerogen present in the host rock generated methane moves with the fluids and vents at the surface through a single large vent structure at the main sill tip matching first order observations violent degassing takes place within the first couple of hundred years and occurs in bursts corresponding to the timing of overpressure waves the amount of methane vented through a single vent is only a fraction between 5 and 16 of the methane generated at depth upscaling to the voring and more basins which are a part of the north atlantic igneous province and using realistic host rock carbon content and kerogen values results in a smaller amount of methane vented than previously estimated for the petm our study therefore suggests that the negative carbon isotope excursion cie observed in the fossil record could not have been caused by intrusions within the voring and more basins alone and that a contribution from other regions in the naip is also required to drive catastrophic climate change

diagenesis and reservoir properties of middle jurassic sandstones traill o east greenland the influence of magmatism and faulting the c 500 m thick middle jurassic sandstones of the fluvial bristol elv and marine pelion formations of the east greenland basin are evaluated here in order to improve the understanding of the processes that influenced the diagenetic evolution the study may help to predict the reservoir properties of sandstones affected by magmatism and faulting both in general and specifically in undrilled areas on and offshore east greenland and in the voring basin on the mid norwegian shelf the study shows a variety of authigenic mineral phases dominated by quartz cement carbonate cement illite and iron oxide one of the clear differences between the two formations is the presence of early carbonate cemented horizons in the marine sandstones these horizons are inferred to reflect a primary concentration of biogenic clasts and fossil shells intense quartz cementation occurs primarily in the fluvial sandstones but the marine sandstones are also highly quartz cemented two episodes of burial and uplift are recorded in the diagenetic sequence and widespread grain crushing in coarse grained intervals is believed to result from overpressure and subsequent compaction due to sudden pressure release along major faults maximum burial depths may only have been around 2000 2500 m cathodoluminescence analyses show that grain crushing was followed by intense quartz cementation the quartz cement is to a great deal believed to have formed due to increased surface area from crushing of detrital quartz grains creating fresh nucleation sites for the quartz cathodoluminescence investigations also show that only minor pressure dissolution has taken place between detrital quartz grains and that the ubiquitous quartz cementation displays several growth zones and was thus in part the result of the introduction of silica rich extra formational fluids related to the flow of hot fluids along reactivated faults and increased heat flow and temperature due to magmatism this interpretation is supported by fluid inclusion homogenization temperatures between 117 and 158 c in quartz cements in one of the two study areas the development of macroscopic stylolites has significantly enhanced quartz cementation probably in connection with thermal convection flow as a result of the magmatic and fault related quartz cementation and illitization the reservoir quality of the sandstone formations deteriorated and changed drastically

eocene to miocene igneous activity in ne greenland northward younging of magmatism along the east greenland margin radiometric dating by the 40 ar 39 ar incremental heating method was carried out on lavas sills dykes and a central intrusion from ne greenland eighteen samples gave acceptable crystallization ages lavas of both lower and upper plateau lava series gave ages in the range 55 5 53 5 ma and cannot be constrained to better than 56 53 ma sills and dykes from traill o to shannon with compositions fairly similar to those of the lavas gave ages of 55 1 51 3 ma contemporaneous with and slightly younger than the lavas alkaline lavas on inland nunataks have ages of 53 50 ma and the kap broer ruys intrusive centre has an age of 48 7 0 5 ma an alkaline sill on hvalroso is much younger at 20 3 0 1 ma there are no pre breakup lavas onshore ne greenland we surmise that the hot mantle of the iceland plume arrived and melted extensively beneath the northern basins only at the time of breakup around 55 ma post breakup intrusive events in ne greenland coincided with plate tectonic events such as reorganization uplift and opening in the north the hvalroso sill represents a local small melting event that may be related to coeval opening of the lena trough supplementary materials details of the source data results and the compositions and locations of the dated samples are available at www geolsoc org uk sup18738

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