slope and deep shelf gully sandstones upper jurassic east greenland the upper jurassic hareelv formation of jameson land east greenland occurs in an area of 60 75 km it consists of 200 500 m of black shale with thick closely spaced sandstone bodies the sandstones fill deep steep walled gullies and elongate scours or form more regular laterally extensive parallel sided but erosive gully mouth or lobe deposits both types of sandstone bodies occur completely juxtaposed and systematic vertical or lateral trends in bed thickness or grain size have not been observed the sands were deposited in a deep water shelf basin by high density turbidity currents traveling from basin margin source areas a northeastern source area was represented by a short lived rapidly prograding delta whereas the main northwestern source area was a shallow sandy barrier occurring along the length of a major north northeast striking fault controlled slope voluminous turbidity currents probably were triggered by earthquakes in the fault zone the resulting slope and basinal sand bodies are up to 50 m thick and hundreds of meters wide and may be more than 5 km long in a downcurrent direction they occur in a thick rich oil prone source rock thus they may form potential stratigraphic reservoirs and help drain the source rock the hareelv formation shows important similarities to the ramp facies model for delta fed sand rich turbidite systems however the formation is mainly tectonically controlled and independent of eustatic sea level changes the hareelv formation may serve as a model for an unusual type of stratigraphic hydr carbon reservoir and at least one north sea oil field seems to have formed in an analogous setting

the shallow magma chamber of stromboli volcano italy in this work we integrate artificial and natural seismic sources data to obtain high resolution images of the shallow inner structure of stromboli volcano overall we used a total of 21 953 p readings from an active seismic experiment and an additional 2731 p and 992 s readings deriving from 269 local events the well defined vp vs and vp vs tomograms have highlighted the following i the region where magma cumulates at shallow depths 2 4 km below sea level bsl forming an elongated ne sw high velocity body vp 6 0 km s and vs 3 5 km s with a very fast velocity core 6 5 vp 7 0 km s of 2 km3 ii the presence of some near vertical pipe like structures characterized by relatively high p velocities values mainly linked to past activity e g strombolicchio and iii a near vertical pipe like volume with high vp vs 1 78 1 85 located beneath to the craters down to 1 0 km bsl overlying a deeper region 1 0 to 3 0 km bsl with low vp vs 1 64 1 69 interpreted as the actual and preferential pathway of magma toward the surface our results demonstrate the importance of combining passive and active seismic data to improve in a tomographic inversion the resolution of the volcanic structures and to discover where magma may be stored

geophysical evidence for the locations shapes and sizes and internal structures of magma chambers beneath regions of quaternary volcanism this paper is a review of seismic gravity magnetic and electromagnetic techniques to detect and delineate magma chambers of a few cubic kilometres to several thousand cubic kilometres volume a dramatic decrease in density and seismic velocity and an increase in seismic attenuation and electrical conductivity occurs at the onset of partial melting in rocks the geophysical techniques are based on detecting these differences in physical properties between solid and partially molten rock although seismic refraction techniques with sophisticated instrumentation and analytical procedures are routinely used for detailed studies of crustal structure in volcanic regions their application for magma detection has been quite limited in one study in yellowstone national park u s a fan shooting and time term techniques have been used to detect an upper crustal magma chamber attenuation and velocity changes in seismic waves from explosions and earthquakes diffracted around magma chambers are observed near some volcanoes in kamchatka strong attenuation of shear waves from regional earthquakes interpreted as a diffraction effect has been used to model magma chambers in alaska kamchatka iceland and new zealand one of the most powerful techniques in modern seismology the seismic reflection technique with vibrators was used to confirm the existence of a strong reflector in the crust near socorro new mexico in the rio grande rift this reflector discovered earlier from data from local earthquakes is interpreted as a sill like magma body in the kilauea volcano hawaii mapping seismicity patterns in the upper crust has enabled the modelling of the complex magma conduits in the crust and upper mantle on the other hand in the usu volcano japan the magma conduits are delineated by zones of seismic quiescence three dimensional modelling of laterally varying structures using teleseismic residuals is proving to be a very promising technique for detecting and delineating magma chambers with minimum horizontal and vertical dimensions of about 6 km this technique has been used successfully to detect low velocity anomalies interpreted as magma bodies in the volume range 10 3 10 6 km 3 in several volcanic centres in the u s a and in mt etna sicily velocity models developed using teleseismic residuals of the cascades volcanoes of oregon and california and kilauea volcano hawaii do not show appreciable storage of magma in the crust however regional models imply that large volumes of parental magma may be present in the upper mantle of these regions in some volcanic centres teleseismic delays are accompanied by p wave attenuation and linear inversion of spectral data have enabled computation of three dimensional q models for these areas the use of gravity data for magma chamber studies is illustrated by a study in the geysers clear lake volcanic field in california where a strong gravity low has been modelled as a low density body in the upper crust this body is approximately in the same location as the low velocity body delineated with teleseismic delays and is interpreted as a magma body in yellowstone national park magnetic field data have been used to map the depth to the curie isotherm and the results show that high temperatures may be present at shallow depths beneath the yellowstone caldera the main application of electrical techniques in magma related studies has been to understand the deep structure of continental rifts electromagnetic studies in several rift zones of the world provide constraints on the thermal structure and magma storage beneath these regions

early generation of 20s 5α h 14α h 17α h and 5α h 14β h 17β h steranes in low salinity lacustrine shales abstract a quantitative sterane biomarker study was conducted on a series of paralic freshwater lacustrine shale samples ranging in maturity from immature to near oil window maturity taken from section 3 of the shahejie formation es3 in the liaohe basin n e china concentrations of 5 h 14 h 17 h 20s and 5 h 14 h 17 h steranes remain nearly constant throughout the sample suite however the decrease in the absolute concentrations of the 20r 5 h 14 h 17 h c 29 steranes with increasing maturity results in an increase in the conventionally defined maturity parameters 20s 20 s 20r and sterane ratios in addition the data suggest that relatively early generation of 5 h 14 h 17 h 20s and 5 h 14 h 17 h steranes has occurred in lacustrine sediments with a vitrinate reflectance 0 3 r o the data provide strong support for the major importance of relative thermal stability of epimers but do not exclude the possibility of isomerization as a viable mechanism for production

deflection of dykes into sills at discontinuities and magma chamber formation abstract many rift zones contain composite volcanoes central volcanoes most of which are supplied with magma from shallow crustal magma chambers volcanotectonic studies of eroded rift zones such as in iceland as well as geophysical studies indicate that many shallow magma chambers evolve from sills here i provide field description of sills and extinct magma chambers in the quaternary and tertiary palaeorift zones of iceland focusing on the felsic pluton of slaufrudalur southeast iceland as a fine example of a magma chamber developed through the injection of sills in this paper i review analyse and develop further two related mechanisms for the deflection of dykes into sills and thus the potential initiation of a magma chamber namely a cook gordon debounding delamination and b stress barriers and propose a third mechanism c favourable material toughness ratios due to elastic mismatch difference in young s moduli or stiffnesses of layers in contact in the cook gordon mechanism a weak contact opens up as a result of dyke induced tensile stress this mechanism is likely to operate primarily at shallow depths as is supported by field observations and numerical models a stress barrier is a layer where the local stress is unfavourable to a particular type of rock fracture here a dyke field observations and numerical models show that on meeting a stress barrier a dyke either changes into a sill or becomes arrested the material toughness mechanism indicates that when the upper layer at a contact has the same or less stiffness than the lower layer hosting the dyke there is little tendency for the dyke to become deflected into the contact however when the upper layer is stiffer such as when a stiff basaltic lava flow is on the top of a soft pyroclastic layer the dyke tends to become deflected into the contact to form a sill field results suggest that all these mechanisms may cause dyke deflection into sills and may operate together particularly where the rock consists of alternating soft and stiff layers since the quaternary lava pile in iceland has many more soft hyaloclastite layers than the tertiary lava pile these mechanisms were probably very efficient in generating sills and by implication shallow magma chambers during the quaternary this may be one reason why in comparison with the tertiary lava pile the quaternary lava pile contains so many sills and extinct plutons and active shallow magma chambers

buoyancy driven fracture ascent experiments in layered gelatine laboratory experiments on air filled fracture propagation in solidified homogeneous and layered gelatine have been carried out providing an analogue model for magma filled dikes ascending in the crust the effects of layering on fracture velocity and shape have been analyzed in detail the free surface is found to accelerate approaching fractures layering accelerates or decelerates fractures approaching discontinuities of the elastic parameters depending on the value of the rigidity contrast the shape of fractures are strongly influenced as they pass from one layer to another the observed cross sectional shape when crossing a layer interface and the acceleration with decreasing rigidity can be explained with theoretical models our experiments also reproduce the arrest of fractures in proximity of joints and the formation of sills in the layer below the interface these findings could help in the interpretation of accelerated seismicity and deformation rates observed in volcanic areas

sill morphology and comparison of brittle and non brittle emplacement mechanisms magmatic sheet intrusions contribute significantly to the upper crustal magma transport network the emplacement mechanism of the magmatic sheets controls the final geometry of the intrusions and the characteristics of host rock deformation previous observations have highlighted the preponderance of brittle structures associated with shallow level sheet intrusions however recent studies have suggested that non brittle host rock behaviour also occurs particularly related to the formation of magma fingers during shallow level sill intrusion here we examine both brittle and non brittle intrusion mechanisms and expand upon them with field observations from a series of widespread and variable magmatic systems non brittle emplacement appears primarily associated with viscous flow of the host rock during intrusion and is therefore intimately linked to the contemporaneous host rock rheology as well as magma dynamics purely brittle and non brittle emplacement processes are found to be end members with many intrusions containing evidence of both behaviours deriving the host rock characteristics is therefore important for discerning potential diagnostic intrusion indicators and intrusion geometries both within the field and in modelling incorporation of variable host material behaviours in numerical and analogue modelling tuned using direct field observations may consequently further our understanding of the controls on shallow level intrusion

recognition and source correlation of migrated hydrocarbons in upper jurassic hareelv formation jameson land east greenland organic geochemical analysis of an interbedded shale sandstone sequence from the upper jurassic hareelv formation jameson land east greenland has revealed oil shows in the sandstones consistent with petroleum generation and migration a comparison of the molecular characteristics of extractable material from the sandstones with those of kerogen and bitumen from the shales indicates that the most likely origin of these shows is generation within the shales with expulsion and short range migration into the sandstones this conclusion is based on comparisons of biological marker distributions stable carbon isotopic compositions of extractable material and kerogen and pyrolysate compositions of kerogen and asphaltenes oil from a seep in the savoia halvo region south of jameson land can be correlated to the jurassic sandstone oil shows based on similar isotopic compositions and asphaltene pyrolysate distributions impregnation of both sandstones and shales throughout the sequence by products generated at higher maturities is considered unlikely but cannot be ruled out by the existing data the molecular characteristics of the sandstone hydrocarbons exhibit a striking similarity to those of oils from the mid norway region the similar geologic ages of the hareelv formation and the kimmeridge clay of northwestern europe which is the acknowledged source of the mid norway oils and the geographic proximity of the two regions at the time of early north atlantic rifting indicate that hydrocarbons from these present day distant regions have been generated from very similar organic facies deposited under similar environmental conditions these results are significant in that in addition to stratigraphic correlation of depositional sequences on both margins of the early rifted north atlantic the hydrocarbons generated from source rocks contained in these sequences now can als be geochemically correlated the results also suggest that jurassic hydrocarbon source facies deposited throughout the early north atlantic are geochemically similar a trait imparted to their generation products

evolution and facies architecture of paleogene surtseyan volcanoes on chatham islands new zealand southwest pacific ocean abstract this paper reports for the first time phreatomagmatic deposits and preserved surtseyan tuff cones in the chatham islands new zealand fieldwork has located the relicts of at least six closely spaced paleogene surtseyan cones and associated volcaniclastic sediments within the red bluff tuff formation the complete stratigraphic section of the cones consists of two parts 1 the lower part represents volcanic aggradational processes that constructed tuff cones in a short period of time and is composed of a bedded interval of explosively fragmented vesicular glassy basaltic pyroclasts ash and lapilli sizes as well as feeder dykes pillow lavas and pillow sills and 2 the upper part represents the rapid denudation of these cones by shallow marine currents or gravity flows reflecting the instability of the tephra pile forming the cones and a much later marine faunal colonization stage e g corals brachiopods molluscs etc erosion could have occurred almost immediately after or even during the emplacement of the volcanic pile similar to what occurred at surtla vent a satellite submerged cone of the basaltic island volcano surtsey iceland the waiareka deborah volcanics bridge point aorere point and lookout bluff surtseyan cones otago new zealand and marion and prince edward islands southwest indian ocean amongst others by contrast the complete faunal colonization and stabilization of a diverse marine community could have taken hundreds or perhaps even thousands of years to reach their acme following the volcanic pulses the structural textural and compositional characteristics of the red bluff tuff formation support a phreatomagmatic mode of fragmentation similar to that at surtsey volcano iceland the red bluff tuff sequence represents one of the most complete marine tuff cones described in the geologic record

role of sills in the development of volcanic fields insights from lidar mapping surveys of the san rafael swell utah analysis of airborne and terrestrial lidar data demonstrates that 0 4 km 3 of magma cooled in sills at shallow 1 km depth in the now eroded pliocene san rafael swell distributed volcanic field utah usa the volumes of each of seven sills are estimated from three dimensional 3 d models of the lidar data and range from 10 4 to 10 1 km 3 directions of magma flow during emplacement are interpreted from precise sill thickness measurements and measurements of linear vertical offsets within the sills helping to identify feeder conduits and dikes 3 d map relationships derived from lidar data demonstrate that magma flowed into and out of sills from these active dikes and eruptive conduits mapped sill volumes account for 92 of intrusive material within the 50 km 2 study area we conclude that sills played a significant role in modifying eruption dynamics during activity in san rafael and suggest that monitoring of sill inflation and deflation in active distributed volcanic fields may provide key information about unrest and potential eruption dynamics

paradox in bulk and molecular geochemical data and implications for hydrocarbon migration in the inter salt lacustrine shale oil reservoir qianjiang formation jianghan basin central china abstract this study analyzes the bulk and molecular geochemical data of 56 core samples of the eocene qianjiang formation a confined source rock unit embedded with salt intervals formed in a hypersaline lacustrine setting in central china these source rocks within a single evaporative cycle collected from a recent shale oil exploration well are highly laminated consisting of both intra and inter salt shales both organic pores and matrix pores serve as storage for hydrocarbon generated from kerogen within the source rock because the contrast in density between kerogen and oil conversion of kerogen to oil inevitably leads to the increase in pore pressure and oil expulsion from kerogen within the same source rock unit impregnation of source rocks by expelled oils from nearby mature source rocks or from the organic rich laminae within the same source rock units leads to anomalous rock eval pyrolysis data characterized by an abnormally high s1 peak a high production index pi a suppressed tmax and other anomalies it is contradictory that both rock eval pyrolysis data and sterane isomerization ratios of the studied inter salt shale samples indicate strong impact of allochthonous hydrocarbons in the source rocks whereas most aliphatic biomarker parameters obtained from the solvent extracts of these shales still provide useful information on the vertical variation in organic source input and depositional environment of the host rocks this study provides insights into the bulk and molecular geochemical data interpretation particularly in the inter salt shale oil system evaluation in inferring the prevailing directions and pathways of diagenetic fluid movement and hydrocarbon migration

environmental cycles in the late jurassic northwest european epeiric basin interaction with atmospheric and hydrospheric circulations abstract despite the large size and the heterogeneity of the northwest european late jurassic kimmeridgian lower tithonian epeiric basin the sedimentary environment was rather uniform in general deposition of mudstones and the microlaminated organic rich sediments took place under low oxic to anoxic conditions detailed environmental analysis clearly points to a seasonal alternation of aerobic with anaerobic conditions in substrate and bottom water resulting in one year life cycles in the benthic environment the widespread uniformity of facies and the seasonal alternation in the oxygen budget of the benthic environments are best explained by a summer to winter change in the atmospheric circulation of the northern hemisphere this change strongly influenced the oceanographic situation in the northwestern european epeiric basin superposed on this one year cyclicity three more hierarchical levels of cycles are stratigraphically recorded they reflect a complex history of orbital forced and non orbital forced climatic changes and or eustatic sea level fluctuations in the late jurassic

biological marker analysis and stable carbon isotopic composition of oil seeps from tonga abstract petroleum samples collected from shallow holes at two locations on tongatapu tonga have been analysed by computerized gas chromatographic mass spectrometric and stable carbon isotopic techniques the gross composition absence of n alkanes and isoprenoids in the aliphatic hydrocarbon fractions presence of ring a b demethylated hopanes and narrow carbon isotopic composition of the hydrocarbon fractions indicate the samples are moderately to severely biodegraded crude oils the nearly identical terpane distribution and carbon isotopic composition of samples from both locations indicate a common origin the aliphatic hydrocarbon fractions contain a thermodynamically stable assemblage of steranes and triterpanes indicating an advanced stage of thermal maturity for the oil samples these results imply that if the oils have been generated within sediments on the tonga platform the source beds are probably in the more deeply buried and thermally mature western section of the platform

post spreading deformation and associated magmatism along the iberia morocco atlantic margins insight from submarine volcanoes of the tore madeira rise abstract a new high resolution bathymetric map combined with a regional digital elevation model dem analysis reveal the modalities of occurrence and emplacement of post spreading magmatism along the nne ssw oriented 1000 km long tore madeira rise tmr as well as its relationship with the activity of major fault systems including the estremadura fault system esf and the azores gibraltar fracture zone agfz morphological and structural analysis of the bathymetric map were performed to map volcanic features such as eruptive cones vents and fissures together with faults along the tmr the new bathymetric map shows that the main nnw sse seamount alignment is formed by three structurally distinct volcanic massifs the tore the josephine and the southern volcanic groups the majority of the volcanoes of each group emplaced within or along specific portion of pre existing faults esf and agfz including splay fault releasing bend fault tips and interaction zones between different segments magmas were channelled into sub vertical pre existing lithospheric faults that acted as preferential pathways for the vertical magma ascent migration and final eruption of magma are controlled by the local stress variation induced by complex fault geometries change in plate kinematics as well as strong shear zone anisotropy as suggested by the emplacement within localised areas of transtension we conclude that post spreading magma emplacement in the southern part of the iberia margin was related to the development of a transtensional plate boundary between the iberian and african plate during the late cretaceous more generally our findings emphasize that the distribution of volcanism as the expression of the interaction between shallow plate tectonic and mantle processes should be included in plate kinematic reconstruction this study also demonstrates that the accurate mapping of oceanic seafloor is pivotal to better understand tectono magmatic evolution of volcanic seamount chains and geological processes in oceanic domains

how hydrofractures become arrested fluids in the earth s crust are commonly transported by hydrofractures such as dykes and mineral veins many of which become arrested at various crustal depths hydrofractures are commonly arrested some showing blunt tips at contacts between soft low young s modulus and stiff high young s modulus layers for example many dyke tips are arrested at contacts between soft pyroclastic rocks and stiff basaltic lava flows and vein tips at contacts between soft marl and stiff limestone theoretical models indicate that overpressured buoyant hydrofractures in homogeneous isotropic host rocks should normally reach the surface in layered host rocks however abrupt changes in young s moduli horizontal discontinuities and layers with unusually high fracture perpendicular stresses encourage hydrofracture arrest it is proposed that for layer parallel loading stiff layers favour hydrofracture arrest during active compression but soft layers during extension it is concluded that for hydrofracture propagation to occur the stress field along its potential pathway must be essentially homogenous

bitumen accumulation in grosmont platform complex upper devonian alberta canada the upper devonian grosmont formation a broad carbonate platform complex in alberta canada contains an estimated 300 billion bbl of bitumen it has been suggested that these vast reserves are related to lower cretaceous athabasca oil sands detailed gas chromatographic mass spectrometric studies of a wide range of biologic marker compounds confirm this suggestion the grosmont formation contains bitumen of similar maturity and source to the athabasca deposit but it has been subjected to a greater degree of biodegradation and water washing possibly as a result of its reservoir rock characteristics the difference in the degree of biodegradation is manifested by the absence of bicyclic terpanes and by the reduced concentrations of the c30 and the 22r epimers of the extended hopanes in the grosmont bitumen also the greater degree of water washing of the grosmont bitumen is inferred from the observed distribution of the bicyclic tricyclic and tetracyclic terpenoid sulfides which shows a characteristic loss of the lower molecular weight members in the carbonate bitumen the correlation established here between the two deposits suggests that if the precursor oil has indeed undergone long distance migration the paleozoic carbonates could have acted as a path for migration finally the observed distribution of steranes in the grosmont bitumen corresponds to the suggestion that the mannville group shales were not the major source rocks of the oil sand and carbonate bitumen accumulations of northern alberta

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

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

effect of solidification on a propagating dike 1 magma migration through the brittle crust from depth occurs by the propagation of hydraulic fractures or dikes volcanic eruptions occur at the last stage if and when a propagating dike reaches the surface dike propagation involves complex physics because of several processes that are simultaneously occurring such as viscous flow of magma rock fracture elastic deformation of the host rock and potentially large changes of the physical properties of the magma crystallization degassing solidification etc currently the most practical way in the field or in terms of field measurements to follow the migration of magma before it reaches the surface is the analysis of the seismicity generated nevertheless a physical model that quantitatively relates the flux of magma in the dike to the seismicity is lacking we present here laboratory experiments involving propagation of a fluid filled crack such that the fluid solidifies upon contact with the cold elastic host we show that this can lead to a way of estimating the flux of the injection as a function of the surface creation rate the latter is shown to be a more reliable gauge of magma flux than the upward propagating velocity in the geologic application of a propagating dike the rate of creation of surface area may be related to the rate of release of seismic energy although this latter relation needs further work to be quantitatively reliable our new model nevertheless indicates how a new general framework can be constructed

spatial analysis of an intra plate basaltic volcanic field in a compressional tectonic setting south eastern australia abstract the newer volcanics province nvp is a pliocene to recent intra plate basaltic volcanic field bvf that has formed in a compressive tectonic setting v

three dimensional seismic imaging of ancient submarine lava flows an example from the southern australian margin this work comprises a part of the great australian bight deepwater marine program gabdmp for funding this project the gabdmp is a csiro research program sponsored by chevron australia the results of which will be made publicly available 3d seismic data was gratefully provided by tgs ihs are thanked for access to seismic interpretation software spectral decomposition was carried out using foster findlay associates geoteric software sverre planke and tracy gregg are thanked for constructive reviews

the petroleum geochemistry of canadian beaufort tertiary non marine oils abstract molecular isotopic and elemental data for a set of 28 paleogene and 3 cretaceous oils from the mackenzie delta and offshore canadian beaufort sea have been evaluated the depositional environment and organic matter characteristics of the source units for these oils have been predicted the paleogene oils of the canadian beaufort are molecularly distinctive and clearly contain a major land plant component oleanane and the 17 h and 17 h 24 28 bisnorlupanes are present as well as the following compound types 24 norlupanes and possibly higher homologues de a lupane noroleanenes norursene dehydroabietane 28 30 bisnorhopanes several molecular and isotopic characteristics are useful in assessing and ordering the extent of biodegradation and thermal maturation of these oils the cretaceous oils are separately sourced from the paleogene oils the latter oils comprise two distinct land plant derived genetic families distinguished by the presence absence of 24 28 bisnorlupanes 24 norursene 24 norlupane and 24 noroleanenes the kugmallit richards family contains each of these compound types and is considered to originate from the eocene richards formation in contrast lupanoids and noroleanenes are absent in oils of the reindeer moose channel family the occurrence of 28 30 bisnorhopane and or oleanane in these oils suggests a paleocene origin although these source rock predictions are supported by the available data they must be considered speculative until detailed molecular isotopic and elemental compositional data are available regionally for potential source rocks of the eocene and paleocene source units in the canadian beaufort

source rock evaluation by pyrolysis gas chromatography a pyrolysis gas chromatography system has been developed for the rapid evaluation of potential source rocks for the determination of organic richness and maturation this system uses the pyrolysis methods previously described however the determination of hydrocarbon production type and the identification of contamination by migrated hydrocarbons or drilling additives are accomplished by gas chromatographic gc analysis of the thermal extracts and pyrolysis products of rock samples or isolated kerogens the production type is recognized either qualitatively by gc fingerprint traces or quantitatively by hydrocarbon composition c1 to c6 c6 to c11 c11 from the kerogen peak ii pyrolysate oil prone erogens are recognized by gc traces with a full spectrum of c1 to c28 hydrocarbons or by high concentrations of c11 compounds in contrast gas prone kerogens are characterized by the predominance of light hydrocarbons from c1 to c4 and higher contributions of aromatic compounds mixed type production is intermediate in character between the two contaminants are identified from the gc analysis of the thermally extractable material in peak i possible mineral organic matter reactions during sample heating make interpreting data from whole rock samples more difficult

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

recent rift related volcanism in afar ethiopia abstract rift zones are the most common magmatic environment on earth however opportunities to observe active rifting are rare and consequently the volcanological characteristics of rift systems are not well understood an ongoing phase of magmatic rifting along a section of the red sea system in afar ethiopia presents an exceptional opportunity to constrain relationships between volcanism and crustal growth here by integrating analyses of satellite images i e modis omi aster and ali with field observations we characterise two recent august 2007 and june 2009 basaltic fissure eruptions in afar and evaluate the role and significance of volcanism in the rifting process both events were brief 36 72 h and erupted 4 4 18 106 m3 of lava from a fissure system 4 6 5 km in length data from the spaceborne ozone monitoring instrument omi suggests total so2 emissions for each eruption of 26 5 kt 2007 and 34 7 kt 2009 consistent with complete degassing of the erupted magma volumes using geodetic models for the intrusive activity in afar we estimate the partitioning of magma between intrusive and extrusive components up to july 2009 to be 180 1 comparing the first order volcanic characteristics and the intrusive extrusive volume balance for the afar volcanism with data from the 1975 1984 krafla rifting cycle iceland suggests that the volcanic flux in afar will rise significantly over the next few years as the stresses are increasingly relieved by dyking and subsequent dykes are able to propagate more easily to the surface as a consequence basaltic fissure eruptions in this section of the afar rift will become of increasing large magnitude as the rifting event matures over the next 5 10 yr using available models of magmatic rifting we forecast the likely size and location of future eruptions in afar

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

growth of an emergent tuff cone fragmentation and depositional processes recorded in the capelas tuff cone sao miguel azores abstract the capelas tuff cone is an emergent surtseyan type tuff cone that erupted in shallow seawater off the coast of sao miguel azores in this paper we present a detailed stratigraphic study which is used to infer depositional processes and modes of fragmentation for the capelas tuff cone deposits the growth of the tuff cone can be divided into three stages based on variations in depositional processes that are probably related to differences in water magma w m ratios the first stage corresponds well to wet surtseyan type activity where wet fallout is the dominant depositional process with only minor representation of pyroclastic surge deposits the second stage of the eruption is suggested to be the result of alternating wet and slightly drier periods of surtseyan activity with an overall lower w m ratio compared to the first stage the drier surtseyan periods are characterized by the presence of minor grain flow deposits and undulating pyroclastic surge deposits that occasionally display relatively dry structures such as strongly grain segregated layers and brittle behavior when impacted by ballistic ejecta the first deposits of the second stage show an intense activity of pyroclastic surges but fallout commonly modified by surges is still the dominant depositional process during the second stage the third stage represents a final effusive period with the build up of a scoria cone and ponded lava flows inside the tuff cone crater phreatomagmatic fragmentation as seen by studies of the fine ash fraction

guidelines for evaluating petroleum source rock using programmed pyrolysis rock eval pyrolysis is used to rapidly evaluate the petroleum generative potential and thermal maturity of rocks accurate conclusions require programs every 30 60 ft 9 18 m understanding of interpretive pitfalls and supporting data such as visual kerogen vitrinite reflectance and elemental analyses the generative potential of coals is commonly overestimated by pyrolysis and is best determined by elemental analysis and organic petrography most coals show high s2 s3 5 and low hi values 300 mg hc g toc migrated oil and mud additives which alter rock eval data can sometimes be removed by special processing for immature rocks bimodal s2 peaks and pi values over 0 2 indicate contamination pyrolysis downgrades organic poor clay rich rocks which show lower hi and higher tmax values than isolated kerogen because of adsorption of pyrolyzate on the clays tmax values for small s2 peaks 0 2 mg hc g toc are unreliable tmax is affected by maturation organic matter type contamination and the mineral matrix s3 is sensitive to inorganic and adsorbed carbon dioxide and to instrumentation problems acidification of carbonate rich samples and proper maintenance improves s3 measurement constant sample weights 100 mg are recommended below a threshold weight tmax increases by up to 10 c and other parameters decrease organic rich samples which overload the detector can be diluted with carbonate detector linearity is determined by pyrolyzing various weights of an organic rich rock

depositional environment and organic geochemistry of the upper permian ravnefjeld formation source rock in east greenland the upper permian ravnefjeld formation in east greenland is composed of shales that laterally pass into carbonate buildups and platforms of the wegener halvo formation the ravnefjeld formation is subdivided into five units that can be traced throughout the upper permian depositional basin two of the units are laminated and organic rich and were deposited under anoxic conditions they are considered good to excellent source rocks for liquid hydrocarbons with initial average toc total organic carbon values between 4 and 5 and hi hydrogen index between 300 and 400 the cumulative source rock thickness is between 15 and 20 m the source rocks are separated and enclosed by three units of bioturbated siltstone with a toc of less than 0 5 and an hi of less than 100 the e siltstones were deposited under relatively oxic conditions the organic geochemistry of the source rocks is typical for marine source rocks with some features normally associated with carbonate evaporite environments low pr ph pristane phytane low cpi carbon preference index distribution of tricyclic and pentacyclic terpanes the establishment of anoxic conditions and subsequent source rock deposition was controlled by eustatic sea level changes the subenvironment paleogeographic setting influx of carbonate material water depth salinity has some influence on a number of bulk parameters toc hi relations toc ts total sulfur relations and in particular biomarker parameters such as pr ph and terpane ratios all the basal shales or shales in the vicinity of carbonate buildups or platforms are characterized by low pr ph high c23 tricyclic terpanes and high c35 and c33 hopanes

organic geochemistry of sediments in new zealand part i a biomarker study of the petroleum seepage at the geothermal region of waiotapu abstract the saturated hydrocarbons from the oil seepage at waiotapu in new zealand were examined by gc and gcms techniques of molecular fingerprinting the petroleum was characterised by a high ratio of phytane nc18 2 37 and low ratios of pr ph 0 64 and saturates aromatics 0 60 this study revealed that the oil was derived from terrigenous organic matter and it had neither migrated from its source nor suffered biodegradation the source rocks were deposited under anoxic conditions and these rocks lay within pleistocene sediments which were immature with respect to oil generation the location of the source rocks within a geothermal field had accelerated the generation of petroleum since the source rocks would have been too young and shallow to generate petroleum in the absence of geothermal energy

deep seated abiogenic origin of petroleum from geological assessment to physical theory the theory of the abyssal abiogenic origin of petroleum is a significant part of the modern scientific theories dealing with the formation of hydrocarbons these theories include the identification of natural hydrocarbon systems the physical processes leading to their terrestrial concentration and the dynamic processes controlling the migration of that material into geological reservoirs of petroleum the theory of the abyssal abiogenic origin of petroleum recognizes that natural gas and petroleum are primordial materials of deep origin which have migrated into the earth s crust experimental results and geological investigations presented in this article convincingly confirm the main postulates of the theory and allow us to reexamine the structure size and locality distributions of the world s hydrocarbon reserves

origin of beatrice oil by co sourcing from devonian and middle jurassic source rocks inner moray firth united kingdom commercial hydrocarbons in the moray firth area of the north sea occur in reservoirs ranging in age from devonian to tertiary with the bulk of the reserves located in upper jurassic and lower cretaceous clastic rocks most hydrocarbon discoveries in this area have been made in the outer moray firth primarily in the witch ground graben a single oil field beatrice has been developed in the inner moray firth area the unusual location and chemical composition of beatrice compared to piper and other north sea oils generated from the kimmeridge clay have contributed to the longstanding controversy on its origin oil source potential in the inner moray firth has been recognized in lacustrine devonian dolomitic siltstones middle jurassic paralic coals upper jurassic marine shales and other rocks however prior to this study only the upper jurassic kimmeridge clay was recognized as a significant effective source rock in the main graben area of the north sea biomarker and stable carbon isotope analyses conclusively show that beatrice oil could not have been generated from the classic kimmeridge clay source rock but is a mixture of products derived from effective devonian and middle jurassic source rocks this work demonstrates the power of a multiparameter geochemical approach in solving this difficult oil to source rock correlation problem use of this approach can lead to the recognition of new exploration plays in previously well explored basins

shape and intrusion style of the coastal batholith peru abstract the coastal batholith of peru extends over 1600 km parallel to the coast along the andean trend gravity profiles on three traverses across the batholith indicate the geometry is essentially that of a flat slab with average thickness from 2 0 3 2 km and a thick root 4 10 km wide to the west granitic material does not extend to depths greater than 3 km below sea level datum this study supports recent gravity work which indicates plutons are commonly thin 5 km or less in thickness detailed mapping in the lima segment of the coastal batholith reveals thin plutons where space was made dominantly by downward displacement via floor depression however early roof uplift also created some space stoping occurs but is not a major space maker floor depression may be modelled by cantilever or piston mechanisms and although the strong marginal deformation with mylonites tuffisites microbreccia faults and shear zones suggests the piston model best describes the mechanism of emplacement of much of the coastal batholith some space was probably made by a cantilever mechanism in brief space making processes involved early roof uplift and regional doming then floor depression mainly by piston and probably subsidiary cantilever mechanisms and finally local stoping producing the cut out rectilinear nature of the batholith the coastal batholith formed on shallow partial melting of hydrous basaltic marginal basin rocks between 5 and 10 km floor depression occurred as the crustal column foundered into an actively deflating layer of partial melt this is an efficient space making process and is limited here to shallow levels of the upper crust only the melts ascended to within 2 or 3 km of the surface up dyke like conduits then spread horizontally to form tabular plutons

dike propagation through layered rocks 1 dike penetration through a succession of upper crustal layers with different densities is studied with a new numerical code for an individual layer to significantly affect dike ascent its thickness must be of order 1 when scaled to the characteristic length scale for the inflated nose region that develops below the dike tip this characteristic length is l q 1 6 g 1 1 2 g 2 3 where and are the viscosity and buoyancy of magma g and are elastic moduli for the encasing rocks q is the magma flow rate and g gravity for basaltic dikes l is 1 km which is of the same order of magnitude as the typical thickness of sedimentary strata and volcanic deposits in such conditions dike ascent proceeds irregularly with large changes of velocity and width at an interface scaling laws for the ascent rate and dike width are derived penetration through low density layers is determined by a local buoyancy balance in the inflated nose region of the dike independently of the total buoyancy of the magma column between source and tip in such conditions a dike develops an internal overpressure that may be large enough to generate a horizontally propagating sill for this to occur the thickness of the low density layers must exceed a threshold value which depends only on the rock strength and on the average negative buoyancy of magma for basaltic melt we estimate that this threshold thickness cannot be less than about 700 m and is 2 km on average

geochemistry of asphaltenes abstract asphaltenes derived from both oil and source rocks have been studied by pyrolysis gas chromatography the pyrograms obtained at 450 and 550 c show that asphaltene structure is very close to the structure of the kerogen of the same sample they can be interpreted as kerogen moieties resulting from its early evolution therefore they can be used as substitutes of kerogen in genetic studies consequently asphaltenes pyrolysis appear to be a tool in correlation studies for oil oil correlation it can supplement and even replace in the case of degraded oils the information given by hydrocarbon distributions for oil source rock correlations the match between pyrograms of asphaltenes from both oil and source rocks offers more direct possibilities than usual techniques

determination of low level mercury in coralline aragonite by calcination isotope dilution inductively coupled plasma mass spectrometry and its application to diploria specimens from castle harbour bermuda abstract we have developed a technique that combines a high temperature quartz furnace with inductively coupled plasma mass spectrometry for the determination of hg stored in the annual caco 3 bands found in coral skeletons substantial matrix effects presumably due to the discontinuous introduction of co 2 to the gas stream were corrected for by simultaneously supplying a stream of argon containing highly enriched elemental 202 hg o and observing peaks in the 200 hg 202 hg signal as the sample was decomposed primary signal calibration for hg was achieved using gas injections from a saturated vapor standard the absolute instrument detection limit was low about 0 2 fmol with a practical limit of detection 3 of blanks of 2 fmol reproducibility of samples was rsd 15 27 we applied this method to the determination of hg concentrations in two colonies of diploria labyrinthiformis collected from castle harbour bermuda at a site about to be buried under the municipal waste landfill the temporal reconstructions of castle harbour seawater hg concentrations implied by the coral record show a decline throughout the period of record 1949 2008 the coral archived no apparent signal associated with waste disposal practices in the harbour bulk waste land filling or since 1994 disposal of waste incinerator ash and mercury concentrations in the coral did not correlate to growth rate as assessed by linear extension there was however a large and nearly exponential decrease in apparent hg concentration in the harbour which circumstantially implicates the dredging and or landfilling operations associated with the construction of the airport on st david s island

ground surface deformation patterns magma supply and magma storage at okmok volcano alaska from insar analysis 1 intereruption deformation 1997 2008 eruption magma storage had increased by 3 7 5 2 1 0 7 m 3 or 85 100 of the 1997 eruption volume we propose that the supply rate decreased in response to the diminishing pressure gradient between the shallow storage zone and a deeper magma source region eventuallytheeffectsofcontinuingmagmasupplyandvesiculationofstoredmagmacaused acriticalpressurethresholdtobeexceeded triggeringthe2008eruption asimilarpatternof initially rapid inflation followed by oscillatory but generally slowing inflation was observed prior to the 1997 eruption in both cases withdrawal of magma during the eruptions depressurized the shallow storage zone causing significant volcano wide subsidence and initiating a new intereruption deformation cycle

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

effect of anigneous intrusion on oil shale at rundle australia abstract elemental analyses x ray diffraction thermal and isotopic analyses gas chromatography mass spectrometry electron spin resonance nuclear magnetic resonance spectroscopy and demineralizing techniques have been used to evaluate the effect of a small igneous intrusion on rundle oil shale each set of results contributes to an overall appreciation of how in situ pyrolysis of a highly aliphatic kerogen occurs as in previous studies application of a range of methods gives a better understanding than any of the techniques on its own significant conclusions are as follows 1 the shale samples closest to the intrusion contain the least organic matter 2 a micro reservoir for expelled volatiles was identified 1 m below the intrusion 3 the hydrogen deficient carbonaceous residue remaining close to the intrusion produces no oil on further heating and 4 the major effect of the intrusive event was the in situ pyrolysis of the oil shale the severity of alteration decreasing with distance from the contact

a novel approach for recognition and quantification of hydrocarbon migration effects in shale sandstone sequences a detailed organic geochemical study of over 150 samples from two cores with a total combined length of 320 m 1 050 ft through sequences of interbedded source rock type shales 0 84 rm maturity and reservoir sandstones allowed recognition and quantitation of a number of migration effects detailed gas chromatography mass spectrometry of steranes and triterpanes was used to insure that samples being compared to investigate migration effects contain organic matter of a similar type thin shales interbedded in sands and the edges of thick shale units are depleted in petroleum range hydrocarbons to a much higher degree than the centers of thick shale units for the alkanes expulsion occurs with pronounced compositional fractionation effects shorter chain length n alkanes are expelled preferentially and isoprenoid alkanes are expelled to a lesser degree than their straight chain isomers based on material balance calculations expulsion efficiencies were determined and found to be very high in certain instances for thin interbedded shales they decrease from about 80 around c15 to near zero in the c25 region there is no evidence for significant redistribution of steranes and triterpanes in the two sequences compared to c15 to c25 n alkanes they appear relatively immobile the composition of the hydrocarbons impregnating parts of the reservoir sandstones is in agreement with expulsion occurring with pronounced fractionation based on molecular chain length hence consideration of bulk expulsion efficiencies gives an unrealistic picture furthermore the impregnation of a siltstone cap rock from an underlying hydrocarbon accumulation seems to have occurred by bulk oil migration and without significant fractionation the degree of hydrocarbon depletion of some of the shales of both sequences appears to be controlled by compaction and the primary migration process appears to have occurred with chromatographic separation the migration phenomena observed in both sequences lead us to propose that the main phase of expulsion can be preceded by an earlier sta e during which the edges of thick shales and thin interbedded shales appear to be slowly and continuously depleted by the chromatographic processes the composition of the hydrocarbon product accumulating in the reservoirs at this stage appears to be controlled primarily by physical processes rather than by the type and maturity of the organic matter in the generating source rock by this mechanism the origin of accumulations of light oils and gas condensates in low mature sequences bearing predominantly terrestrial derived organic matter can be explained finally the migration effects documented in this study have some consequences for interpretation of geochemical data e g the pristane n c17 ratio a commonly accepted maturity parameter has been shown to be also controlled by the degree of hydrocarbon expulsion

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 reflection imaging and controls on the preservation of ancient sill fed magmatic vents two dimensional seismic reflection data from offshore southern australia image a series of 2 13 km wide by 50 800 m high sub circular middle eocene age mounds the majority of the mounds occur above tips of igneous bodies intruded into the underlying upper cretaceous succession the mounds are interpreted as the seismic expression of submarine volcanic vents which are amongst the largest and oldest examples ever documented these vents are pristine and have been preserved because of their submarine environment of emplacement and burial in a post eruption sediment drape supplementary material uninterpreted version of the seismic sections presented in figure 3 is available at www geolsoc org uk sup18545

sensitivity of biomarker properties to depositional environment and or source input in the lower toarcian of sw germany abstract a sequence of lower toarcian sediments which are highly contrasting in their depositional environment over a 5 m depth interval has been investigated in detail for the variability of geochemical properties which are used for source characterization and oil to source correlation lower liassic marls are representative of a well aerated shallow water environment in contrast to the immediately overlying bituminous shales which are deposited under extremely reducing conditions various properties have been found to vary considerably within these two units amongst the most important are carbon isotopic composition of the kerogen the pristane phytane ratios nickel as opposed to vanadyl porphyrins and the c27 dia regular steranes although maturation within the profile does not change some of the maturation dependent biomarker properties such as the monoaromatic steroid side chain cracking and the tm ts ratio exhibit large changes which can be assigned to diagenetic processes another maturation dependent property the 20s 20r epimerization of c29 steranes exhibits smaller changes which could also be due to early diagenetic processes the study suggests that reducing and oxidizing conditions i e eh and ph in the sediment exert an influence on several biomarker precursor product pathways in maturation studies initial variations due to depositional conditions have therefore to be taken into account

a combined sedimentological and organic geochemical study of the jurassic cretaceous janusfjellet formation svalbard norway abstract sedimentological facies and organic geochemical analyses of surface samples from black shales of the janusfjellet formation jurassic cretaceous svalbard have been undertaken in order to obtain a better insight into the problems concerning depositional processes and burial history pyrolysis nmr and microscopic data suggest a type iii kerogen in the janusfjellet formation however there are significant variations of the kerogen composition throughout this formation saturated aliphatic fractions of the rock extracts have been analyzed by gc and gc ms differentiation of the gc traces was achieved by using a q mode factor analysis by this analysis two factors were revealed to explain the depositional development of the formation the gc and gc ms analysis of the saturated aliphatic fraction suggest a more marine character of the organic source material than the kerogen analyses the sedimentological and organic geochemical data indicate generally oxic conditions during deposition of the janusfjellet formation under these conditions the labile lipid rich marine parts of the source material have been more degraded than the relatively stable terrestrially derived organic matter resulting in a type iii kerogen composition

the north atlantic igneous province stratigraphy tectonic volcanic and magmatic processes the north atlantic igneous province has been the subject of extensive scientific investigation over the past thirty years with a wide field of knowledge being accumulated recently recognition of the potential role of large igneous provinces in affecting ocean and atmosphere systems and biotic evolutionary pathways has lead to increased interest in this province this has been further stimulated by the expansion in the search for oil and gas in mesozoic and tertiary sediments along the ne atlantic margin an improved understanding of the interaction between igneous and sedimentary processes is vital for the identification of potential hydrocarbon resources the regions covered include continental margin norway east and west greenland the faroe shetland basin and the faroe islands themselves the papers in this book contain new data and interpretations of north atlantic igneous province magmatic processes rift evolution tectonics stratigraphy chemostratigraphy biostratigraphy seismic and isotope stratigraphy and sediment dispersal many of the papers adopt a multidisciplinary approach to tha analysis and interpretation of complex volcanic and sedimentary sequences these new data and the reviews and compilations of existing data provide the reader with access to current research directions in north atlantic igneous province geology

patterns of intraplate volcanism controlled by asthenospheric shear volcanism observed far from plate boundaries in the interior of oceanic and continental plates may result from flow in the underlying mantle comparison between a numerical model of mantle flow and the spatial distribution of intraplate volcanism indicates that rapid shear motion in the mantle may drive melting that causes intraplate eruptions most of earth s volcanism occurs at plate boundaries in association with subduction or rifting a few high volume volcanic fields are observed both at plate boundaries and within plates fed by plumes upwelling from the deep mantle1 the remaining volcanism is observed away from plate boundaries it is typically basaltic effusive and low volume occurring within continental interiors2 3 4 5 6 7 or creating seamounts on the ocean floor8 9 10 11 this intraplate volcanism has been attributed to various localized processes12 such as cracking of the lithosphere8 13 14 small scale convection in the mantle beneath the lithosphere15 16 17 or shear induced melting of low viscosity pockets of asthenospheric mantle that have become embedded along the base of the lithosphere18 here we compare the locations of observed intraplate volcanism with global patterns of mantle flow from a numerical model we find a correlation between recent continental and oceanic intraplate volcanism and areas of the asthenosphere that are experiencing rapid shear due to mantle convection we detect particularly high correlations in the interior of the continents of western north america eastern australia southern europe and antarctica as well as west of the east pacific rise in the pacific ocean we conclude that intraplate volcanism associated with mantle convection is best explained by melting caused by shear flow within the asthenosphere whereas other localized processes are less important

migration of petroleum into vermilion 14 field gulf coast u s a molecular evidence abstract oils and condensates from vermilion 14 field offshore louisiana u s a are compared using sulfur and nitrogen concentrations whole oil carbon isotope ratios and hydrocarbon distributions all parameters suggest large differences in the organic facies of the source rock s and in thermal maturity of the source at the time of expulsion certain bulk geochemical data including n alkane distributions and whole oil carbon isotope ratios suggest that migration fractionation resulted in oils condensates whose molecular distributions are shifted significantly toward lower molecular weight components migration contamination is supported by the occurrence in the oils of unsaturated and thermally unstable hydrocarbons including oleanenes dammarenes and diasterenes and molecular maturity ratios indicative of immature organic matter molecular maturity ratios of the oils increase with increasing reservoir depth regardless of reservoir lithology or formation for example the 20s 20s 20r 5 h 14 h 17 h 24 ethylcholestane ratio increases from 0 05 to 0 58 over a depth range of 6316 ft to 15 563 ft the same ratio for cuttings extracts from two wells in the vermilion 14 field shows lower values although they also increase with increasing depth it is proposed that the vermilion hydrocarbons were generated from deep source rocks approximately 15 000 ft or more and possibly subjected to migration fractionation during movement to shallower reservoirs during migration and after trapping migration contamination added unsaturated hydrocarbons to the oils condensates resulting in anomalously low molecular maturity ratios we suggest further that the combined effects of migration fractionation and migration contamination resulted in oil in the vermilion 14 field that is compositionally different from that which initially left the deep source rock

experimental modelling of shallow magma emplacement application to saucer shaped intrusions abstract saucer shaped dolerite and sandstone intrusions are common in sedimentary basins world wide we have conducted a series of scaled experiments simulating the process of magma emplacement in sedimentary basins with particular attention on the formation of saucer shaped sills the model materials were 1 cohesive fine grained silica flour representing brittle crust and 2 molten low viscosity oil representing magma the experiments were performed in both homogeneous and layered models in all the experiments oil injection resulted in doming of the surface in the homogeneous models the injected oil formed cone sheets and sub vertical dykes cone sheets formed for shallow injection 1 3 cm and vertical dykes formed for deeper injection 4 5 cm in layered models the injected oil always formed saucer shaped intrusions our experimental results show that 1 sill intrusion results in the formation of a dome with melt erupting at the rim 2 layering controls the formation of sills and saucer shaped sills 3 saucer shaped sills are fed from the bottom and the fluid flows upward and outward and 4 the diameter of saucer shaped sills increase with increasing emplacement depth the systematic relation between domes and sills and the depth dependence of sill diameters show that saucer shaped intrusions result from the interaction between a growing flat lying shallow sill and doming of the free surface we conclude that saucer shaped intrusions represent fundamental geometries formed by shallow magma intrusion in stratified basins

overthickening of sedimentary sequences by igneous intrusions the identification of extensive intrusive igneous complexes both in subsurface data and in field studies has resulted in quantification of the volumes of igneous material despite this research there is still little connection established between the amount of igneous material intruded into a basin and its effect on subsequent basin evolution in terms of burial and loading to understand how additional igneous material may influence basin evolution we present work from the faroe shetland basin fsb utilising subsurface data this study highlights that the total estimated thickness of sediment during cretaceous is likely an overestimate as the sedimentary fill consists of significant quantities of igneous material which was emplaced 10 55 ma years after deposition previously this additional igneous material has not been accounted for in estimates of sedimentation rates and the burial history of the fsb importantly petroleum system modelling to understand generation and expulsion of hydrocarbons benefits from correct estimates of basin fill the overthickening of basins by igneous material will affect the timing of hydrocarbon generation and subsequently the proper evaluation of exploration targets in order to fully understand basin evolution the volumes of igneous material and when this material was emplaced must be acknowledged and considered

principles of geochemical prospect appraisal our current understanding of the geochemical processes responsible for the creation of commercial accumulations of oil and gas can be reduced to simple rules and equations to allow the petroleum geologist to use geochemistry to estimate before drilling the likely volumes and compositions of oil and gas delivered to the trap in most sedimentary basins oil is expelled from source rocks between 120 and 150 c whereas most gas and gas condensate are released between 150 and 230 c when the initial potential of source rocks exceeds 10kg mt oil expulsion efficiencies are between 60 and 90 expelled oil and gas migrate as petroleum rich phases driven by fluid potential gradients most flow is laterally updip in beds with effective horizontal permeabilities greater than 1 md in lower permeability rocks the petroleum fluids move vertically up or down along the path of least resistance i e the most permeable or thinnest beds separating them from a high permeability lateral carrier bed the residual saturations of petroleum left behind along the migration pathway are of the order of a few percent of the porosity geochemical analysis of source rocks helps determine the yields and compositions of petroleum fluids expelled in the catchment area of a prospect these fluid masses are converted to volumes from knowledge of the phase relations and densities of petroleum fluids evaluation of the total volume of rock through which the petroleum potentially can migrate and the mean porosity of the rocks that constitute the migration pathway allow migration losses to be assessed these losses constrain both the range of migration of petroleum fluids away from the mature source rock and the volumes of petroleum remaining for entrapment in the prospect

volcanic features of the north rockall trough application of visualisation techniques on 3d seismic reflection data understanding the volcanic processes operating during continental break up is hampered by the subsequent burial of the majority of the volcanic pile beneath thick sedimentary sequences currently located in bathymetrically deep offshore regions although portions of these volcanic systems are currently exposed on land a full understanding of the volcanic structure the eruptive styles and their evolution is not possible as these localities have been partially eroded furthermore as the onshore exposure represents a volumetrically minor part of the entire system the documented eruptive styles may not be representative the increasing availability of 3d seismic reflection data has the potential to significantly enhance our understanding of break up related volcanism as it allows direct access to detailed information from the buried volcanic succession however conventional seismic interpretation methodologies cannot determine lava flow morphologies and as a result eruptive styles and their evolution are still largely based on extrapolation from the accessible onshore outcrop data new 3d seismic volume visualisation techniques allow the buried basalt morphologies to be examined for the first time in a manner similar to outcrop aerial photographic or satellite based observations applying this new approach for 3d seismic data to the north rockall trough u k atlantic margin demonstrates that a range of volcanic features indicative of eruptive style can be determined the data reveal a complex terrain containing lava flows originating from discrete volcanic centres contemporaneous normal faults linear fissures a few kilometres long radial fissures and inflation ridges lava flow morphologies that are indicative of tube fed inflated sheetflows intracanyon flows and elongate subaerial flows that enter water downslope to produce a large hyaloclastite delta are observed

dike emplacement at bardarbunga iceland induces unusual stress changes caldera deformation and earthquakes a 45 km long regional dike was emplaced over a period of 2 weeks in august 2014 at the boundary between the east and north volcanic zones in iceland this is the first regional dike emplacement in iceland monitored with modern geophysical networks the importance of which relates to regional dikes feeding most of the large fissure e g eldgja 934 and laki 1783 and lava shield e g early holocene skjaldbreidur and trolladyngja eruptions during this time the dike generated some 17 000 earthquakes more than produced in iceland as a whole over a normal year the dike initiated close to the bardarbunga volcano but gradually extended to the northeast until it crossed the boundary between the east volcanic zone evz and the north volcanic zone nvz we infer that the strike of the dike changes abruptly at a point from about n45 e coinciding with the trend of the evz to n15 e coinciding with the trend of the nvz this change in strike occurs at latitude 64 7 exactly the same latitude at which about 10 ma dikes in east iceland change strike in a similar way this suggests that the change in the regional stress field from the southern to the northern part of iceland has been maintained at this latitude for 10 million years analytical and numerical models indicate that the dike induced stress field results in stress concentration around faults and particularly shallow magma chambers and calderas in its vicinity such as tungnafellsjokull kverkfjoll and askja in particular the dike has induced high compressive shear and tensile stresses at the location of the bardarbunga shallow chamber and caldera ring fault where numerous earthquakes occurred during the dike emplacement many of which have exceeded m5 the largest m5 7 the first segment of the dike induced high tensile stresses in the nearby part of the bardarbunga magma chamber ring fault resulting in radially outward injection of a dike from the chamber at a high angle to the strike of the regional dike the location of maximum stress at bardarbunga fluctuates along the chamber ring fault boundary in harmony with dike size and or pressure changes and encourages ring dike formation and associated magma flow within the chamber caldera collapse and or eruption in some of these volcanoes is possible most likely in bardarbunga but depends largely on the future development of the regional dike

an experimental investigation of sill formation and propagation in layered elastic media a series of experiments are described where dyed water a magma analogue was intruded into solid gelatine a crustal analogue to investigate the formation of sills we considered a layered gelatine system with contrasting adjacent layers by varying the density and rigidity of the gelatine we found that experimental sills form when the upper layer is more rigid than the lower layer with intrusion occurring in a plane directly below the interface experimental dykes were observed to propagate to the surface when the young s modulus ratio of upper to lower gelatine layers was less than one experimental dyke arrest occurred when the upper layer was more rigid and the interface was strong two varieties of experimental sill formed when the upper layer was more rigid than the lower layer and the interface was sufficiently weak the form of the intrusion depends on the balance of driving pressures and the young s modulus ratio of contrasting adjacent layers when the rigidity ratio is high and there is a large driving pressure the experimental feeder dyke completely converts to propagate as a sill however when the rigidity ratio and driving pressure are both close to one a dyke sill hybrid forms under these conditions the experimental sill formation is accompanied by contemporaneous dyke intrusion into the overlying more rigid layer during sill propagation deformation structures such as faults and en echelon fractures are formed into the lower layer experimental sill propagation dynamics are controlled by viscous dissipation along the length of the sill causing acceleration with increasing length our study suggests that rigidity contrasts may play a major role in the location of sills and development of igneous complexes in ancient cratonic areas the moho is a suitable site for the preferential formation of sills with higher rigidity continental crust overlying weaker mantle mantle plumes impacting ancient continents provide a situation in which large sills can form to fractionate prior to eruption of flood basalts the boundary between the upper and lower crust conrad discontinuity may provide a preferential focus for the emplacement of sheets of silicic magma at continental arcs where the lower crust is weakened by prolonged heating and possible hydration

effect of water washing on c15 hydrocarbon fraction of crude oils from northwest palawan philippines recognition and subsequent correlation of biodegraded and or water washed oils with their unaltered counterparts has been a long recognized problem in petroleum geochemistry because water washing and biodegradation can occur concurrently it is difficult to delineate the individual effects of these two oil altering processes especially on the c15 hydrocarbon fraction both processes can cause an oil to become enriched in sulfur and to have a lower api gravity owing to loss of the more volatile components thus the altered oil may appear to be a high sulfur crude of low maturity altered and unaltered oil fractions extracted from cores of a water washed carbonate reservoir offshore northwest palawan were studied to observe the effect of alteration on correla ion parameters water washing resulted in the following changes 1 depletion of 13c in the c15 branched cyclic alkane fraction whereas virtually no change occurred in isotope composition of the aromatic fraction 2 selective loss of dibenzothiophenes followed by loss of aromatic hydrocarbons and 3 virtually no change in steranes or tricyclic and pentacyclic terpanes with the exception of enhancement of 17 agr h norhopane and decrease of 18 agr h trisnorhopane in situations of severe water washing mild biodegradation also occurred as indicated by the loss of n alkanes and possible selective loss of n alkanes having less than 25 carbon atoms relative to branched alkanes cycloalkanes and aromatic components because cycloalkanes and aromatic hydrocarbons are not generally preferentially utilized by bacteria as long as n alkanes are present the changes observed in these two fractions most likely result from water washing because of the potential for extreme compositional changes in the n alkane and aromatic fractions the most useful correlation parameters between the altered and unaltered oils are sterane and terpane distributions stable carbon isotope ratios are also useful however more studies of oils in which water washing is known to have occurred need to be made to explain the general response or various responses of the isotopic composition of oils to water washing

controls on volcanism at intraplate basaltic volcanic fields a broad range of controlling mechanisms is described for intraplate basaltic volcanic fields ibvfs in the literature these correspond with those relating to shallow tectonic processes and to deep mantle plumes accurate measurement of the physical parameters of intraplate volcanism is fundamental to gain an understanding of the controlling factors that influence the scale and location of a specific ibvf detailed volume and geochronology data are required for this however these are not available for many ibvfs in this study the primary controls on magma genesis and transportation are established for the pliocene recent newer volcanics province nvp of south eastern australia as a case study for one of such ibvf the nvp is a large and spatio temporally complex ibvf that has been described as either being related to a deep mantle plume or upper mantle and crustal processes we use innovative high resolution aeromagnetic and 3d modelling analysis constrained by well log data to calculate its dimensions volume and long term eruptive flux our estimates suggest volcanic deposits cover an area of 23 100 530 km2 and have a preserved dense rock equivalent of erupted volcanics of least 680 km3 and may have been as large as 900 km3 the long term mean eruptive flux of the nvp is estimated between 0 15 and 0 20 km3 ka which is relatively high compared with other ibvfs our comparison with other ibvfs shows eruptive fluxes vary up to two orders of magnitude within individual fields most examples where a range of eruptive flux is available for an ibvf show a correlation between eruptive flux and the rate of local tectonic processes suggesting tectonic control limited age dating of the nvp has been used to suggest there were pulses in its eruptive flux which are not resolvable using current data these changes in eruptive flux are not directly relatable to the rate of any interpreted tectonic driver such as edge driven convection however the nvp and other ibvfs used for comparison have long term eruptive fluxes that are considerably less than definitive plume related volcanic systems along with their spatio temporal patterns and other analysis it is suggested that the nvp and the vast majority of low and high flux ibvfs appear to be the result of tectonic processes without requiring additional thermal input from a deep mantle source considering a control on volcanism by tectonic processes the range of eruptive flux of ibvfs is related to variations in the rate of the effecting tectonic process mantle composition and the size of the mantle source zone where melt generation and accumulation is taking place

shallow plumbing systems for small volume basaltic volcanoes eruptive dynamics in basaltic volcanoes are controlled in part by the conduit geometry however uncertainties in conduit shape and dike to conduit transition geometry have limited our predictive capability for hazards assessments we characterize the subvolcanic geometry of small volume basaltic volcanoes magmatic volatile driven eruptions 0 1 to 0 5 km3 based on a synthesis of field studies of five basaltic volcanoes exposed to varying degrees by erosion and exhibiting feeder dikes conduits and vent areas 250 m depth study areas include east grants ridge new mexico usa basalt ridge east basalt ridge paiute ridge and southeast crater flat nevada usa basaltic feeder dikes 250 to 100 m deep have typical widths of 4 12 m with smooth host rock contacts rhyolite tuff at depths less than 100 m heterogeneities in the host rock form preferential pathways for small dike splays and sills resulting in a 30 m effective width at 50 m depth the development of a complex conduit at depths less than 70 m is reflected in bifurcating dikes and brecciation and incorporation of the country rock the overall zone of effect at depths less than 50 m is 110 m wide 220 m elongated along the feeder dike based on comparisons with theoretical conduit flow models the width of the feeder dike at depths from 250 to 500 m is expected to range from 1 to 10 m and is expected to decrease to about 1 2 m at depths greater than 500 m the flaring shape of the observed feeder systems is similar to results of theoretical modeling using lithostatic pressure balanced flow conditions sizes of observed conduits differ from modeled dimensions by up to a factor of 10 in the shallow subsurface 50 m depth but at depths greater than 100 m the difference is a factor of 2 to 4 this difference is primarily due to the fact that observed eroded conduits record the superimposed effects of multiple eruptive events while theoretical model results define dimensions necessary for a single steady eruption phase the complex details of magma host rock interactions observed at the study areas contact welding brecciation bifurcating dikes and sills and stoping represent the mechanisms by which the lithostatic pressure balanced geometry is attained the similarity in the normalized shapes of theoretical and observed conduits demonstrates the appropriateness of the pressure balanced modeling approach consistent with the conclusions of wilson and head j geophys res 86 2971 3001 1981 for this type of volcano

volcano growth mechanisms and the role of sub volcanic intrusions insights from 2d seismic reflection data abstract temporal and spatial changes in volcano morphology and internal architecture can determine eruption style and location however the relationship between the external and internal characteristics of volcanoes and sub volcanic intrusions is often difficult to observe at outcrop or interpret uniquely from geophysical and geodetic data we use high quality 2d seismic reflection data from the ceduna sub basin offshore southern australia to quantitatively analyse 56 pristinely preserved eocene age volcanogenic mounds and a genetically related network of sub volcanic sills and laccoliths detailed seismic mapping has allowed the 3d geometry of each mound to be reconstructed and distinct seismic facies within them to be recognised forty six continental basaltic shield volcanoes have been identified that have average flank dips of 3 parallel seismic reflections within the shield volcanoes are interpreted to represent interbedded volcanic and clastic material suggesting that a series of temporally separate eruptions emanated from a central vent the shield volcanoes typically overlie the lateral tips of sills and we suggest that the intermittent eruption phases correspond to the incremental emplacement of discrete magma pulses within the laterally extensive sill complex eight volcanogenic hydrothermal vents which are also associated with the lateral tips of sills were also recognised and these appear to have formed from the seepage of intrusion related hydrothermal fluids onto the seafloor via emplacement induced fractures this work highlights that deformation patterns preceding volcanic eruptions may i be offset from the eruption site ii attributed to intrusions with complex morphologies and or iii reflect magma movement along pre existing fracture systems these complexities should therefore be considered in eruption forecasting models that link pre eruption ground deformation to subterranean magma emplacement depth and volume more generally our study highlights the key role that seismic reflection data can play in understanding the geometry distribution and evolution of ancient and modern volcanic systems

isomerization and aromatization of hydrocarbons and the paleothermometry and burial history of alberta foreland basin the hydrocarbon fractions extracted from 34 cretaceous shales from a cross section of the alberta basin have been analyzed using gas chromatography mass spectrometry particular attention has been paid to the extents to which three temperature dependent geochemical reactions have occurred isomerization of steranes at c 20 isomerization of hopanes at c 22 and aromatization of c ring monoaromatic steroid hydrocarbons estimates of the kinetic constants of these reactions have been published previously therefore constraints may be put on the maximum temperature experienced by the sediments and the time for which this temperature existed the subsidence history of the alberta basin is simulated using a lithospheric flexural model in which the lithosphere is downwarped by the loading of overthrusts in the adjacent cordilleran orogene when overthrusting ceases erosion of the overthrusted region lightens the load and the lithosphere rebounds causing uplift and erosion of the foreland basin major overthrusting and therefore deep burial occurred during the laramide orogeny of late cretaceous to mid tertiary time the extent of chemical reactions suggests that the present maturity of the cretaceous shales is almost entirely a reflection of burial and heating during the laramide orogeny in a manner that is consistent with the lithospheric flexural model for the basin the chemical reactions suggest that the paleogeothermal gradient increased systematically away from the foothills of the rocky mountains along the profile studied that a similar trend exists today suggests this situation has persisted at least since the early stages of the laramide orogeny this variation is best explained by advective heat transfer water entering the basin in the faulted and topographically higher foothills is heated at depth thereby depressing the geothermal gradient this hot water then migrates updip and away from the foothills to enhance the geothermal gradients in the edmonton area and beyond the route of the migrating hot water is similar to that taken by hydrocarbons from devonian and cretaceous source rocks in the deep basin updip to the oil and tar sand accumulations of alberta