coulomb failure of earth s brittle crust controls growth emplacement and shapes of igneous sills saucer shaped sills and laccoliths abstract tabular intrusions are common features in the earth s brittle crust they exhibit a broad variety of shapes ranging from thin sheet intrusions sills saucer shaped sills cone sheets to more massive intrusions domed and punched laccoliths stocks such a diversity of intrusion shapes reflects different emplacement mechanisms caused by contrasting host rock and magma rheologies most current models of tabular intrusion emplacement assume that the host rock behaves purely elastically whereas numerous observations show that shear failure plays a major role in this study we investigate the effects of the host rock s coulomb properties on magma emplacement by integrating 1 laboratory models using dry coulomb granular model hosts of variable strength cohesion and 2 limit analysis numerical models our results show that both sheet and massive tabular intrusions initiate as a sill which triggers shear failure of its overburden along an inclined shear damage zone at a critical sill radius which depends on the emplacement depth and the overburden s cohesion two scenarios are then possible 1 if the cohesion of the overburden is significant opening of a planar fracture along the precursory weakened shear damage zones to accommodate magma flow leads to the formation of inclined sheets or 2 if the cohesion of the overburden is negligible the sill inflates and lifts up the overburden which is dissected by several faults that control the growth of a massive intrusion finally we derive a theoretical scaling that predicts the thickness to radius aspect ratios of the laboratory sheet intrusions this theoretical prediction shows how sheet intrusion morphologies are controlled by a mechanical equilibrium between the flowing viscous magma and coulomb shear failure of the overburden our study suggests that the emplacement of sheet and massive tabular intrusions are parts of the same mechanical regime in which the coulomb behavior of the earth s brittle crust plays an essential role

controls of basement faults on the geometry and evolution of compressional basement involved structures foreland basement involved structures commonly occur in front of major fold thrust belts as irregular chains of uplifts the variation in the map and three dimensional 3 d geometries of individual structures and their mutual spatial and angular relationships are strongly suggestive of the influence of preexisting basement discontinuities three dimensional experimental models were constructed to determine the function of preexisting frontal and lateral discontinuities in determining the geometry of the structures the models consisted of two layers with stiff clay representing the basement and soft clay representing the sedimentary cover laser scanning and 3 d surface modeling were used to determine the map geometry to compare the models with examples of natural structures from the rocky mountain foreland in wyoming planar discontinuities result in doubly plunging structures terminating against a frontal fault with a linear trace sheep mountain anticline whereas intersecting fault sets with sharp or curved intersections result in trapdoor geometries grass creek anticline opposite dipping faults result in uplifted blocks with varying relief and orientations of the structures depending on the relative orientations of the two fault trends significant strike slip faulting along the frontal fault only occurs when the angle between the two fault trends exceeds 30 chains of structures show offsets or relay patterns commonly accompanied by changes in the orientations of adjacent structures the sage creek steamboat butte chains the hamilton dome wagonhound anticline chain the maverick springs circle ridge chain and the grass creek walker dome trend in the rocky mountain foreland are examples of these configurations these patterns suggest the influence of preexisting frontal or lateral discontinuities on the trends and locations of structures lateral discontinuities are either preexisting controlling the lateral extent of structures or form during deformation to accommodate the formation of structures formed along offset frontal faults preexisting lateral faults that penetrate the entire basement commonly result in surface lateral faults bounding the surface structures however reverse faults in the basement connected by buried lateral faults result in surface structures with overlaps between them a relay of reverse faults in the basement not connected by lateral faults may develop parallel or oblique structures with transfer zones between them the mapped geometries of the experimental models and the orientations of secondary faults provide predictive analogs that can be used in the interpretation of surface and subsurface structures

impact of host rock heterogeneity on failure around pressurized conduits implications for finger shaped magmatic intrusions abstract rock failure accommodating the emplacement of magmatic intrusions is controlled by the local stress regime within the host rock most of the mechanical models addressing rock failure conditions e g for a given tectonic regime or magma overpressure simplify the stress calculation by assuming the homogeneity of the host rock properties in this study we highlight the importance of local heterogeneities in controlling the localization of the deformation and the failure mechanism around a magmatic intrusion we numerically model the elastoplastic deformation of a heterogeneous host rock intruded by an overpressurized magmatic body of cylindrical or finger shaped geometry the plastic component of the deformation is considered with a mixed mode mechanism allowing dilatant and shear displacements to act simultaneously our simulations are performed for small strain amplitudes that reflect the pre failure conditions of the host we assess the subsequent failure mechanism of the system based on the development of the localized strain patterns the heterogeneity in the model is introduced by a stochastic perturbation of the host rock cohesion with characteristic wavelength and amplitude we show that a relatively small perturbation of 10 of the cohesion field can efficiently localize the plastic deformation and control the subsequent emplacement mechanism we further investigate a more realistic geological scenario in which the intrusion resides within sedimentary layers of contrasting strength resulting in both heterogeneity and anisotropy of mechanical properties in the host rock our model reproduces similar deformation patterns as observed around finger shaped magma intrusions within the vaca muerta shales in the neuquen basin argentina we conclude that heterogeneities within the host rock may locally seed dilatant shear faults around magmatic conduits and finger shaped intrusions and result in the development of a process zone of length scale in order with the intrusion radius length scale

magmatism and petroleum exploration in the brazilian paleozoic basins abstract petroleum exploration in the paleozoic sedimentary basins of brazil has proven very challenging for explorationists except for the solimoes basin in which transcurrent tectonism formed prospective structural highs brazilian paleozoic basins lack intense structural deformation and hence the detection and prospecting of place is often difficult magmatic intrusive and associated rocks in all these basins have traditionally been considered heat sources and hydrocarbon traps the role of tholeiitic basic dikes in the generation migration and accumulation of petroleum in the anhembi oil occurrence sao paulo state is discussed herein it follows that similar geological settings in other paleozoic basins can be regarded as promising sites for oil accumulation that warrant investigation via modern geological and geophysical methods

structure emplacement mechanism and magma flow significance of igneous fingers implications for sill emplacement in sedimentary basins abstract field and seismic observations show that numerous sills exhibit lobate morphologies each lobe corresponds to a distinct igneous segment exhibiting a finger like shape the long axis of which is commonly interpreted as a magma flow indicator robust understanding of the emplacement mechanisms of finger shaped sills and direct observations supporting finger orientation as magma flow indicator are lacking in this paper we present the results of detailed structural mapping on an exceptional easily accessible 1 km long outcrop in the neuquen basin argentina that exhibits a sill its contacts and the structures in the finely layered sedimentary host rock we show that the sill is made of distinct segments that grew inflated or coalesced we also demonstrate that the fingers were emplaced according to the viscoelastic fingering or viscous indenter models with no field evidence of tensile elastic fracture mechanism as commonly assumed in mechanical models of sill emplacement we identified new structural criteria at the intrusion s contacts for inferring magma flow direction during the magma emplacement our small scale structural observations carried out on a seismic scale outcrop have the potential to considerably aid the structural interpretation of seismic data imaging igneous sills i e to fill the standard gap between outcrop scale field observations and seismic scale geophysical data

sill geometry and emplacement controlled by a major disconformity in the tarim basin china abstract igneous sills are widely distributed in sedimentary basins worldwide sill emplacement has significant impacts on structural and thermal evolutions of sedimentary basins and also provides important insights into volcanic and sub volcanic processes dyke deflection and sill formation are largely controlled by mechanical layering of the host rock and a number of mechanisms have been proposed however most models of sill formation are based much on numerical and analogue modeling for many natural sills the key mechanism governing the dyke deflection and sill formation remains to be discussed and in some cases controversial to better understand the control of mechanical layering on sill formation and test the existing models we study detailed geometries of igneous sills from the central part of the tarim basin china based on seismic reflection data and borehole data nineteen igneous sills which are expressed as packages of high amplitude reflections are observed and they were all emplaced in the upper ordovician strata at current burial depths of about 5 8 km the sills can be classified into three geometric types type 1 saucer shaped sills type 2 strata concordant sills and type 3 hybrid sills which have the characteristics of both type 1 and 2 the geometry of the saucer shaped sills is typical and comprises three distinct parts a flat inner sill inclined sheets and in many cases flat outer sills all the bases of the saucer shaped sills coincide with the disconformity between the middle and upper ordovician strata the m disconformity indicating that the disconformity controlled the sill geometry and emplacement depth in the basin the m disconformity is characterized by a lithological change from underlying limestones to overlying mudstones we suggest that among the three main mechanisms for the deflection of dykes into sills namely cook gordon debonding stress barriers and elastic mismatch the cook gordon debonding is the dominant mechanism in the study area this is a mechanism by which a weak contact opens up ahead of a vertically propagating dyke allowing the dyke to be deflected into a sill when the dyke meets the open contact this study indicates that the control of mechanical layering of the host rock on sill formation is largely depends on the host rock lithologies and confirms again that the saucer shape is the fundamental sill geometry under the control of layering

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

the fold analysis challenge a virtual globe based educational resource abstract we present an undergraduate structural geology laboratory exercise using the google earth virtual globe with collada models optionally including an interactive stereographic projection and javascript controls the learning resource challenges students to identify bedding traces and estimate bedding orientation at several locations on a fold to fit the fold axis and axial plane to stereographic projection data and to fit a doubly plunging fold model to the large scale structure the chosen fold is the sheep mountain anticline a laramide uplift in the big horn basin of wyoming we take an education research based approach guiding students through three levels of difficulty the exercise aims to counter common student misconceptions and stumbling blocks regarding penetrative structures it can be used in preparation for an in person field trip for post trip reinforcement or as a virtual field experience in an online only course our kml scripts can be easily transferred to other fold structures around the globe

geologic stereo mapping of geologic structures with spot satellite data geologic note 1 the spot imaging system launched in 1986 by the french national space agency cnes provides two significant advances for mapping geological structures from satellite imagery increased spatial resolution of key structural and stratigraphic elements and stereoscopic capabilities for making strike and dip measurements quantitative stereo mapping with spot data may be done using hard copy images and conventional equipment such as stereo plotters or by displaying images on a video monitor in stereo viewing format the latter method is a new remote sensing technique particularly relevant to the exploration community this technique allows development with minor expenditure and training of an effective stereo mapping capability on existing image processing systems or o stand alone personal computers spot stereo data is particularly useful for mapping low amplitude and highly deformed structures surface structure maps generated from stereo imagery data can be applied to exploration at two levels at early stages such maps can be used to establish the style trend size and spatial distribution of structures in a basin and to investigate key tectonic elements at more advanced prospecting stages these maps can be used to constrain subsurface mapping of structures located in areas of poor seismic data quality this latter technique however may require the support of higher resolution stereo aerial photography

an integrated crustal velocity field for the central andes 1 we present an integrated velocity field for the central andes derived from gps observations collected between january 1993 and march 2001 that eliminates the velocity bias between the south america nazca plate project snapp and central andes gps project cap velocity fields published by norabuena et al 1998 and bevis et al 1999 the reference frame is realized by minimizing the motion of eight continuous gps stations and one rover gps station located in the stable core of the south american plate the rms horizontal motion of these stations is just 1 1 mm yr the amplitude of these residual motions is roughly compatible with expected levels of measurement error in our new solution five of the six snapp stations located just outside the orogenic belt are effectively stationary and the velocities for adjacent cap and snapp stations now agree at a level consistent with their formal uncertainties

geological controls on shallow gas distribution and seafloor seepage in an arctic fjord of spitsbergen norway abstract this study integrates high resolution shallow and deep geophysical datasets to study the seabed seepage systems linked to subsurface shallow gas and geological features influencing the fluid flow in nordfjorden central spitsbergen arctic norway this is one of the tributary fjords of the isfjorden fjord system in spitsbergen which has the highest density of pockmarks ranging up to 20 km2 the 535 pockmarks identified manually in the 300 km2 large study area have diameters ranging from 10 m to 212 m and depth varying between 1 m and 8 m sub surface seep related acoustic features such as enhanced reflections acoustic blanking and turbidity zones recorded on 55 km of new high resolution sub bottom acoustic data suggest shallow gas free and or dissolved occurrences in the marine sediments beneath the pockmarks structural features thrust faults and associated folds belonging to the palaeogene west spitsbergen fold and thrust belt and early cretaceous igneous sills have been interpreted on 2d multichannel seismic data in the triassic and permian successions some of these faults and igneous sills form seafloor ridges where pockmark density is high and they are typically aligned acoustic flares attributed to active gas seepage from the seafloor were imaged in the water column in the southern part of nordfjorden above the sub surface shallow gas occurrences and thrust faults the integrated analysis of these geophysical datasets suggests that the near seafloor tectonically deformed stratum plays an important role in the up dip propagation of fluids liquids and or gas distribution of shallow gas in marine sediments and seepage at the seafloor

3 d modeling of geologic maps from surface data recent discoveries in earth sciences are mostly related to technologies allowing graphical representations of volumes we present a way to produce mathematically and geometrically correct three dimensional 3 d geologic maps consisting of the volume and shape of all geologic features of a given area the method is innovative in that it only uses surface information based on the combination of a standard geologic map a satellite image and a digital elevation model it is based on a modeling algorithm that only uses surfaces calculated from scattered data points and that intersects them following a series of geologically sound rules the major advantage of using such technology is that it provides the user with a way to quantify geology to illustrate how a 3 d geologic map can be computed we explain the steps taken to build a dummy model with simple faulting and depositional sequencing the case study chosen to illustrate the method is the beirut watershed lebanon an area with relatively simple geology the 3 d visualization and cross sections help in the understanding of the geometrical relationship between the different geologic features allowing a reexamination of the tectonic history of the area during the late mesozoic

an appraisal of groundwater quality in seymour and blaine aquifers in a major agro ecological region in texas usa aquifer based groundwater quality assessment offers critical insight into the major hydrochemical processes and aids in making groundwater resources management decisions the texas rolling plains trp spanning over 22 counties is a major agro ecological region in texas from where highest groundwater nitrate no3 levels in the state have been reported in this study we present a comparative assessment of major hydrochemical facies pertaining to no3 contamination and a host of species such as sulfate so42 chloride cl and total dissolved solids tds in different water use classes in the seymour and blaine aquifers underlying the trp aquifer stratified groundwater quality information from 1990 to 2010 was obtained from the texas water development board and aggregated over decadal scale high groundwater salinization was found in the municipal water use class in the blaine aquifer with about 100 87 and 50 of observations exceeding the secondary maximum contaminant level for tds so42 and cl respectively in the 2000s 2000 2010 the no3 contamination was more alarming in the seymour aquifer with 82 and 61 of observations respectively exceeding the maximum contaminant level mcl in the irrigation and municipal water use classes in the 2000s salinization was more influenced by so42 and cl in the blaine aquifer and by no3 in the seymour aquifer high no3 mcl observations in the seymour aquifer occurred in the ca hco3 and ca mg hco3 facies the domains of fresh water recharge and anthropogenic influences e g agricultural activities waste disposal high so42 cl and tds observations in the blaine aquifer dominated the ca cl na cl and mixed ca mg so4 cl facies indicating evaporite dissolution mixing and solute exchange and lack of fresh recharge

4d imaging of fracturing in organic rich shales during heating to better understand the mechanisms of fracture pattern development and fluid escape in low permeability rocks we performed time resolved in situ x ray tomography imaging to investigate the processes that occur during the slow heating from 60 to 400 c of organic rich green river shale at about 350 c cracks nucleated in the sample and as the temperature continued to increase these cracks propagated parallel to shale bedding and coalesced thus cutting across the sample thermogravimetry and gas chromatography revealed that the fracturing occurring at approx 350 c was associated with significant mass loss and release of light hydrocarbons generated by the decomposition of immature organic matter kerogen decomposition is thought to cause an internal pressure build up sufficient to form cracks in the shale thus providing pathways for the outgoing hydrocarbons we show that a 2d numerical model based on this idea qualitatively reproduces the experimentally observed dynamics of crack nucleation growth and coalescence as well as the irregular outlines of the cracks our results provide a new description of fracture pattern formation in low permeability shales

thermal impact of igneous sill complexes on organic rich formations and implications for petroleum systems a case study in the northern neuquen basin argentina abstract numerous sedimentary basins in the world host voluminous igneous sill complexes i e stacking of sills that are emplaced in different levels of the sedimentary sequence when sills are emplaced in organic rich sedimentary formations they can considerably affect the thermal and maturation history of the hydrocarbon source rock and can be highly relevant elements of the petroleum system most models of the thermal impacts of igneous sills on source rock consider one or few intrusions however the parameters that govern host rock maturation related to full sill complexes remain unclear in this contribution we integrate borehole data and thermal 2d modelling to quantify the temperature and maturation effects of a sill complex in a 2d section on the sedimentary formations of the neuquen basin argentina in this basin extensive magmatic activity took place during oligocene miocene and upper miocene age there are numerous magmatic intrusions dominantly sills emplaced in organic rich shale formations in the study area our modelling results show that 1 the source rock maturation in the study area was dominantly triggered by the sills so that the area would be immature without the sills 2 multiple sills have more pronounced thermal impact than a single thick sill 3 volumes of host rock between intrusions can have different degree of maturation depending on intrusion spacing and 4 the temperature of the host rock at the time of sill emplacement controls to a great extent the thermal and maturation impact of the sills our work provides valuable insights into how the sills affected hydrocarbon generation during oligocene miocene and upper miocene magmatic activity in the neuquen basin in addition our study suggests that most of the kerogen has been transformed to hydrocarbon in areas where the sills are located

recharge source and hydrogeochemical evolution of shallow groundwater in a complex alluvial fan system southwest of north china plain many cities around the world are developed at alluvial fans with economic and industrial development and increase in population quality and quantity of groundwater are often damaged by over exploitation in these areas in order to realistically assess these groundwater resources and their sustainability it is vital to understand the recharge sources and hydrogeochemical evolution of groundwater in alluvial fans in march 2006 groundwater and surface water were sampled for major element analysis and stable isotope oxygen 18 and deuterium compositions in xinxiang which is located at a complex alluvial fan system composed of a mountainous area taihang mt alluvial fan and yellow river alluvial fan in the taihang mountainous area the groundwater was recharged by precipitation and was characterized by ca hco3 type water with depleted 18o and d mean value of 8 8 18o along the flow path from the mountainous area to taihang mt alluvial fan the groundwater became geochemically complex ca na mg hco3 cl so4 type and heavier 18o and d were observed around 8 18o before the surface water with mean 18o of 8 7 recharged to groundwater it underwent isotopic enrichment in taihang mt alluvial fan chemical mixture and ion exchange are expected to be responsible for the chemical evolution of groundwater in yellow river alluvial fan transferred water from the yellow river is the main source of the groundwater in the yellow river alluvial fan in the south of the study area and stable isotopic compositions of the groundwater mean value of 8 8 18o were similar to those of transferred water 8 9 increasing from the southern boundary of the study area to the distal end of the fan the groundwater underwent chemical evolution from ca hco3 na hco3 to na so4 a conceptual model integrating stiff diagrams is used to describe the spatial variation of recharge sources chemical evolution and groundwater flow paths in the complex alluvial fan aquifer system

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

comparative fem and dem modeling of basement involved thrust structures with application to sheep mountain greybull area wyoming abstract basement involved fold and thrust systems have been widely studied in several locations through field and seismic investigations however our understanding of the geometries of the faults that drive folding and the mechanical conditions within the resulting folds is still limited simulations run using the finite element and discrete element methods have great potential to help determine the mechanical evolution of structures at all scales both methods have been employed to explore the structural evolution of the laramide age sheep mountain anticline located in the eastern bighorn basin of wyoming both sets of simulations are constrained by experimental and well log data and use the same size model domain and mechanical stratigraphy the underlying basement sediment boundary was deformed by a set of prescribed displacements the results of the two simulations are geometrically similar and match previous field based interpretations of the sheep mountain fold to the first order stresses calculated by the two methods were also very similar thus verifying the mechanical comparison differences in the geometric details however provide important perspectives on the capabilities of the two methods for example the major faults producing the sheep mountain fold develop slightly higher dips in the dem simulation than the fem simulation yielding a better match with published interpretations the crest of the anticline is characterized by distributed thinning of shallow strata in the fem simulation and by local extensional faulting in the dem simulation neither simulation reproduced the north south fold splay observed in the field suggesting that this minor feature results from preexisting structure or 3d effects not modeled here

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

3d geometry of growth strata in a fault propagation fold insights into space time evolution of the crevillente fault abanilla alicante sector betic cordillera spain this work presents a 3d geometric model of growth strata cropping out in a fault propagation fold associated with the crevillente fault abanilla alicante sector from the bajo segura basin eastern betic cordillera southern spain the analysis of this 3d model enables us to unravel the along strike and along section variations of the growth strata providing constraints to assess the fold development and hence the fault kinematic evolution in space and time we postulate that the observed along strike dip variations are related to lateral variation in fault displacement along section variations of the progressive unconformity opening angles indicate greater fault slip in the upper tortonian messinian time span from the messinian on quantitative analysis of the unconformity indicate a constant or lower tectonic activity of the crevillente fault abanilla alicante sector the minor abundance of striated pebbles in the pliocene quaternary units could be interpreted as a decrease in the stress magnitude and consequently in the tectonic activity of the fault at a regional scale comparison of the growth successions cropping out in the northern and southern limits of the bajo segura basin points to a southward migration of deformation in the basin this means that the bajo segura fault became active after the crevillente fault abanilla alicante sector for which activity on the latter was probably decreasing according to our data consequently we propose that the seismic hazard at the northern limit of the bajo segura basin should be lower than at the southern limit

geometric characterization of igneous intrusions 3 d seismic insights from the campos basin se brazil abstract igneous intrusions are important for the exploration and appraisal phases of an oilfield due to their impact on petroleum systems their presence can be associated with the generation migration accumulation and entrapment of hydrocarbons in particular 1 sills with low permeability might form barriers to fluid flow and migration 2 sills may re use fracture networks providing insights on fluid migration and interaction s 3 sills may influence source rock maturation 4 sill induced uplifting of overburden and faulting may generate traps and 5 their geometric complexities enables the understanding of the interconnectedness of sill complexes which is the focus of this study therefore we provide a systematic characterization of sill geometries and their morphometric parameters we used three dimensional seismic data calibrated with well logs to interpret sills in the southern campos basin brazil throughout the late cretaceous until the paleogene sills intruded into the cretaceous to the eocene post salt sedimentary sequence including shallow platform carbonates transgressive marls and shales a morphometric analysis assisted by seismic attributes allowed the geometric characterization of sills namely 1 saucer shaped 2 slightly saucer shaped 3 climbing saucer shaped 4 transgressive and 5 rough layer parallel the documented sills comprise a wide range of sizes 0 43 14 35 km2 that increase with depth up to 3 18 km extend vertically from 0 06 to 0 23 km and vary from low 1 82 3 31 to high dip 6 05 15 74 the sill complex area extends over 67 35 km2 this study suggests that a thorough characterization of sill intrusions may have a substantial influence on the prediction of other igneous occurrences the mapped sills might have implications not just on the acoustically similar shallow platform albian carbonates of the macae group but may also provide insightful geometric constraints on the brazilian pre salt igneous intrusions

cenozoic sill intrusion in the central and southern east china sea shelf basin abstract cenozoic igneous rocks dominated by basalts are exposed sporadically onshore east china and they provide important information about the cenozoic evolution of the region importantly their geometries and distribution are still not well constrained in the 200 600 km wide offshore continental shelf region based on seismic profiles this study presents the geometric characteristics of 133 igneous sills that are widely distributed in the central and southern regions of the east china sea shelf basin ecssb sills in high amplitude continuous seismic reflections mostly occur in a time interval of 1 1 3 3 s in multiple seismic profiles corresponding to a depth range of 1 1 4 8 km they can be classified into five types saucer shaped sills strata concordant sills laccoliths inclined sheets and hybrid sills of these the saucer shaped sills predominate strata deformation associated with these igneous sills indicate that sill intrusion has become intense since the miocene and it potentially affected petroleum systems in the ecssb forced folds induced by the sills are prospective petroleum traps we infer that sill intrusion in the ecssb was due to magma upwelling caused by dehydration and or small scale convection in a large mantle wedge above the stagnant pacific slab the subduction of the philippine sea plate resulted in tectonic inversion in the ecssb and extension in the okinawa trough since the early miocene triggered more magmatism in the tectonically thinned ecssb thick sedimentary strata over a thin crust in the ecssb may have induced more intrusive than extrusive cenozoic magmatism

miocene deformation in the orogenic front of the malargue fold and thrust belt 35 30 36 s controls on the migration of magmatic and hydrocarbon fluids abstract the integration of surface observations and sub surface data wellbore and seismic from the orogenic front of the malargue fold and thrust belt allows us to study its kinematics and to interpret the local stress field and its control over fluid magmatic and hydrocarbon migration reverse faults correspond to inverted nnw striking mesozoic normal faults and n s striking cenozoic low angle thrusts parallel to the orogen oblique structures with strike slip movement are also present the magmatic activity in the study area was strongly controlled by this structural framework and the in situ stress field miocene dykes and sills were emplaced in relation to strike slip and reverse faults respectively we propose an evolution of the study region from a foredeep sector in the early middle miocene to a peak in deformation in the late miocene and finally a waning of deformation from the pliocene to the present our structural model suggests that during the evolution of the thrust front the in situ stress field changed from a compressional to strike slip compressional stress field favouring the synchronous emplacement of sills and dykes this alternation of stress regimes favours hydrocarbon migration through both thrusts and subvertical strike slip faults this exchange between both stress regimes is likely related to the similar values of the minimum 3 and intermediate 2 principal stress with an e w oriented maximum principal stress 1 according to the plate convergence vector

integrating worldview 2 imagery and terrestrial lidar point clouds to extract dyke swarm geometry implications for magma emplacement mechanisms abstract dyke geometries are useful indicators of the palaeostress field during magma emplacement in this paper we present a multi scale extraction method of dyke geometries by integrating worldview 2 wv2 imagery and terrestrial light detection and ranging lidar data color composite and fusion wv2 images with 0 5 m resolution were generated by using the gramm schmidt spectral sharpening approach which facilitates the discrimination of dyke swarms and provides the ability to measure the orientation exposed length and thickness of dykes in sub horizontal topographic exposures a terrestrial laser scanning survey was performed on a sub vertical exposure of dykes to obtain lidar data with point spacing of 0 02 m at 30 m the lidar data were transformed to images for extracting dyke margins based on image segmentation then the dyke attitudes thicknesses and irregularity of dyke margins were measured according to the points on dyke margins this method was applied at sijiao island zhejiang china where late cretaceous mafic dyke swarms are widespread the results show that integrating wv2 imagery and terrestrial lidar improves the accuracy efficiency and objectivity in determining dyke geometries in two and three dimensions the ene striking dykes are dominant and intruded the host rock mainly granite with sub vertical dips based on the aspect ratios of the dykes the magmatic overpressure was estimated to be less than 11 5 mpa corresponding to a magma chamber within 6 6 km in the lithosphere

temperature effects on kerogen and on molecular and isotopic composition of organic matter in pierre shale near an igneous dike abstract a suite of siltstone samples from the upper cretaceous pierre shale from the contact zone of a 130 cm thick igneous dike near wolcott colorado u s a was taken from the contact to 170 cm from the dike to study the effects of temperature on the organic matter the sampled bedding interval was about 10 cm thick so variation in lithology and type of organic matter is minimal vitrinite reflectance values r 0 increase from 0 4 far from the dike to 3 3 near the dike contact geochemical measurements show systematic thermal effects analogous to those often observed for catagenesis and metagenesis in the depth range of 1 4 km within a sedimentary basin the h c ratio of kerogen and the hydrogen index rock eval decrease most rapidly in the 0 6 1 7 r 0 range in which the transformation ratio rock eval increases from 0 1 to 0 3 based on extraction of c 15 compounds the main increase of hydrocarbons and total extractable organic matter occurs between 0 6 and 1 0 reflectance the saturated aromatic hydrocarbon ratio increases almost twofold in this range of maturity however the pristane phytane ratio is essentially constant through the hydrocarbon generation zone but decreases slightly at high levels of thermal alteration r 0 1 2 the 13 c values for aromatic and saturated hydrocarbons are about 27 and 29 respectively and are constant to about 1 0 r 0 then both become heavier by about 2 at higher r 0 values

volcanism in a compressional andean setting a structural and geochronological study of tromen volcano neuquen province argentina we document evidence for growth of an active volcano in a compressional andean setting our data are surface structures and 39ar 40ar ages of volcanic products on tromen volcano tromen is an active back arc volcano in the andean foothills of neuquen province argentina its volcanic products are unconformable upon mesozoic strata of the neuquen basin the volcano straddles a n s trending pop up which formed during e w shortening the main underlying structures are eastward verging thrusts their traces curve around the eastern foot of the volcano minor folds and faults also occur in the volcanic cover of tromen as a result of e w shortening new 39ar 40ar ages for these volcanic rocks are younger than 2 27 0 10 ma and show that tromen has been active almost continuously from the late pliocene to the holocene we conclude that volcanism and thrusting have been coeval and that magma must have reached the surface in a tectonic setting of horizontal compression our results have wider implications for magmatic processes in such settings

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

delineation of temporal variability and governing factors influencing the spatial variability of shallow groundwater chemistry in a tropical sedimentary island summary an attempt has been made to delineate the temporal variability and factors governing the shallow groundwater chemistry using analysis of variance anova and multivariate analysis notably r mode factor fa and hierarchical cluster analysis hca subsequently geostatistical isoplethic maps were applied to convey better understanding on the distribution of selected groundwater parameters the manukan island s shallow aquifer with sedimentary setting that constantly abstracted for freshwater supply has been selected for this study one way anova suggested that neither changes of tide level nor rainfall volume appeared to exert significant influence on the groundwater chemistry of the small island rather the groundwater chemistry was greatly governed by influence from seawater intrusion which characterized by considerable amount of ca na and cl such condition was well explained by a piper diagram where most plots were situated at the middle diamond shaped diagram indicating mixing condition fa likewise revealed that the shallow groundwater receives marked influence from carbonate dissolution and silicate weathering processes especially boreholes located in the inland area this can be clearly noted from the distinct groupings of relationships among different factors hca classified boreholes into three groups according to their locations in the coastal area suggesting significant chemical variations between boreholes with distance from coast such distribution pattern was particularly evident in the isoplethic map overall it appears that the shallow groundwater in the tropical island is not an appropriate source for drinking water in concern to its exceptionally high salinity and several elevated minor elements mn pb and se for this it is suggested that efforts in exploring other alternative sources should be performed outright

quantitative structural analysis using remote sensing data kurdistan northeast iraq the use of remote sensing data increases the efficiency of field mapping especially in areas with difficult access or where geologic fieldwork is expensive or hazardous this study presents a newly developed software tool for interactively mapping and measuring the spatial orientation i e dip angle and dip direction of finite planar geologic structure from digital elevation models dems the orientations of planar data e g sedimentary bedding or fault planes are derived by approximating a virtual plane to the intersection of the planar feature with the dem topography to increase the informative value of the dem satellite images can be draped onto the topographic data set the software tool was tested in the zagros fold and thrust belt northeast of erbil kurdistan northeast iraq where the stratigraphy has been deformed into subcylindrical fold trains computed orientations have been compared with actual dip angles and directions measured in the field under favorable conditions moderately dipping planes strong competence contrast between stratigraphic boundaries intersection with a rugged topography low vegetation statistical comparison of computed data with the field measurements demonstrates that the spatial data set can be reproduced from the dem within an average error of approximately 10 the strength of the method is demonstrated by integrating field data with computed values from inaccessible areas resulting in a reasonably well constrained balanced geologic cross section

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

conical folds an artefact of using simple geometric shapes to describe a complex geologic structure abstract reliance on diagrams and tangent plots to describe fold geometry has created an unwarranted status for conical folds at the expense of periclines analysis of virtual periclines using synthetic stereograms tangent diagrams and geologic curvature analysis demonstrates small portions of periclines are cylindrical the more significant non cylindrical portion of periclines allows for a mathematically permissible but unrealistic geometrical representation as portions of cones we demonstrate cones are an extremely poor geometric representation of both the virtual periclines and examples of natural non cylindrical folds conical folds if they exist terminate at a point the amplitude to width ratio and the plunge of the crestal line must remain constant towards the fold terminus with a gaussian curvature of zero in contrast the amplitude to width ratio plunge along the crestal line and gaussian curvature of periclines vary towards the fold terminus these differences have important implications for the rheological modeling of folds and while realistic dynamic models for periclines exist models for conical fold formation remain conceptual we suggest that in order to advance our understanding of how folds form it may be pointless to continue the misconception of conical folds as an accurate geometric representation of how folds end

the impact of freshwater and wastewater irrigation on the chemistry of shallow groundwater a case study from the israeli coastal aquifer differences in the impact of irrigation with freshwater versus wastewater on the underlying shallow groundwater quality were investigated in the coastal aquifer of israel seven research boreholes were drilled to the top most 3 5 m of the saturated zone the water table region wtr in the agricultural fields the unsaturated zone and the wtr below the irrigated fields consist mainly of clayey sands while the main aquifer comprises mainly of calcareous sandstones and sands we show that the salinity and composition of the groundwater at the wtr are highly variable over a distance of less than 1 km and are controlled by the irrigating water and the processes in the overlying unsaturated zone tritium data in this groundwater 4 6 tritium units tu support that these water are modern recharge the water at the wtr is more saline and has a different chemical composition relative to the overlying irrigation water high sar values sodium adsorption ratio in wastewater irrigation lead to absorption of na c onto the clay and release of ca 2c into the recharging water resulting in low na cl 0 4 compared to 1 2 in the wastewater and high ca cl ratios in contrast in the freshwater irrigated field the irrigation water pumped from the aquifer na clz0 9 sarz0 6 is modified into na rich groundwater na clz2 0 due to reverse base exchange reactions the high no3 concentration 100 mg l in the wtr below both fields is derived from the agricultural activities in the freshwater field the source of no3 is fertilizer leachates whereas in the wastewater field where less fertilizers are applied nitrate is probably derived from nitrification of the nh4 in the wastewater some of the original inorganic nitrogen in the wastewater is consumed by the agricultural plants resulting in a lower inorganic n cl ratio in the wtr as compared to that in the wastewater this study demonstrates the important role of the composition of irrigation water combined with lithology and land use in determining the quality of the water that recharge the aquifer below agricultural fields q 2004 elsevier b v all rights reserved

neotectonics in the foothills of the southernmost central andes 37 38 s evidence of strike slip displacement along the antinir copahue fault zone 1 the antinir copahue fault zone acfz is the eastern orogenic front of the andes between 38 and 37 s it is formed by an east vergent fan of high angle dextral transpressive and transtensive faults which invert a paleogene intra arc rift system in an out of sequence order with respect to the cretaceous to miocene fold and thrust belt 3 1 1 7 ma volcanic rocks are folded and fractured through this belt and recent indicators of fault activity in unconsolidated deposits suggest an ongoing deformation in spite of the absence of substantial shallow seismicity associated with the orogenic front neotectonic studies show the existence of active faults in the present mountain front the low shallow seismicity could be linked to the high volumes of retroarc derived volcanic rocks erupted through this fault system during pliocene and quaternary times this thermally weakened basement accommodates the strain of the antinir copahue fault zone absorbing the present convergence between the south america and nazca plates

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

effect of a dolerite intrusion on triterpane stereochemistry and kerogen in rundle oil shale australia abstract stereochemical changes of triterpanes present in extracts from an immature oil shale sequence intruded by a 3 m dolerite sill have been studied by gas chromatography mass spectrometry gc ms the steric configuration of the hopanes was observed to change from one dominated by the thermally less stable 17 h 21 h configuration at some distance from the intrusion to one dominated by the thermally more stable 17 h 21 h and 17 h 21 h configurating in the immediate vicinity of the intrusion in addition severe alteration of the kerogen appeared to have taken place as a result of the contact metamorphism and high concentrations of extractable organic matter were observed below the intrusion characterization of the kerogens by curie point pyrolysis has enabled the effects of the intrusion on the shales to be monitored

aptian to recent compressional deformation foothills of the neuquen basin argentina abstract the neuquen basin lies in north western patagonia on the eastern foreland of the andes it formed as a rift basin in the early mesozoic and contains some 5000 m of triassic to aptian sediment mainly marine as a result of andean orogeny the western edge of the basin now forms part of the foothills we describe some of the main compressional structures drawing on surface and sub surface data we argue that regional eastward dips are due to west verging thrust displacements on the andacollo loncopue fault system during a late cretaceous peruvian phase aptian to campanian continental sediment accumulated in a retro arc foreland basin which was mainly of flexural origin nevertheless more than 1500 m of late cretaceous sediment accumulated in the footwall of the east verging agua amarga thrust the peruvian phase was responsible also for transpressional reactivation of a rift transfer zone the huincul arch the incaic phase eocene was responsible for north westerly trending folds and thrusts reactivation of cretaceous thrusts abundant andesitic lavas and high level intrusions and a swarm of north easterly trending bitumen dykes the quechua phase miocene to recent produced northerly trending folds and thrusts and a miocene foreland basin containing some 1000 m of basalt lava flows structures that formed during the incaic and quechua phases are broadly compatible with the history of convergence at the pacific margin of south america as deduced from plate reconstructions

remote surface mapping using orthophotos and geologic maps draped over digital elevation models application to the sheep mountain anticline wyoming remote mapping of surface structures can be conducted by draping digital orthophotos and geologic maps over digital elevation models in geographic information systems formational contacts can be mapped by viewing the intersections of these contacts with the topography on a true to scale three dimensional image bedding orientations can be determined from 1 the trends and slopes of dip slopes or 2 best fit planes to multiple points of intersection of a bedding surface with the topography the methods are tested against mapped formation contacts and bedding attitudes for the sheep mountain anticline in the bighorn basin wyoming detailed mapping of formation contacts is improved by careful observations of the contacts on three dimensional images interpreted bedding attitudes from slope and multiple point solutions show strong positive correlations with field measurements this mapping method provides an efficient and accurate alternative to stereoscopic mapping using aerial photographs and satellite images particularly for remote and inaccessible areas

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

fold thrust styles in the absaroka thrust sheet caribou national forest area idaho wyoming thrust belt abstract the bear creek big elk and black mountain anticlines are macroscopic structures located in the hanging wall of the absaroka thrust within the idaho wyoming fold thrust belt structural mapping of the area was conducted by draping existing geologic maps and digital orthophotos over digital elevation models dem to obtain a three dimensional perspective of the area the map was further refined by reconnaissance field mapping of selected outcrops construction of balanced cross sections suggests that these structures detach at three stratigraphic levels within the cambrian gros ventre formation devonian darby formation and triassic dinwoody formation the folds in the upper stratigraphic package consist of symmetric to asymmetric detachment folds which show variable vergence along trend the structures in the lower stratigraphic packages primarily evolved as low amplitude detachment folds which were subsequently displaced over fault ramps to form fault bend folds or duplexes the duplex geometries in the cambro ordovician units under the bear creek and poker peak anticlines vary from independent anticlines in the south to completely overlapping stacks in the north the macroscopic structural patterns of folds proposed in this study will be useful in interpreting subsurface structures in other parts of the idaho wyoming fold thrust belt

quantification of the water balance and hydrogeological processes of groundwater lake interactions in the pampa plain argentina this paper gives an account of the assessment and quantification of the water balance and the hydrogeological processes related to lake groundwater interaction in the pampa plain by using hydrogeochemical isotopic and flow numerical modeling techniques la salada is a permanent shallow lake with an area of 5 8 km2 located on the se of buenos aires province a total of 29 lake water samples and 15 groundwater samples were collected for both hydrochemical analysis and environmental stable isotope determination water table depths were measured in wells closed to the lake groundwater samples appear grouped on the local meteoric water line suggesting a well mixed system and that rainfall is the main recharge source to the aquifer water evaporation process within la salada is also corroborated by its isotopic composition the model that best adjusts to la salada lake hydrochemical processes includes evaporation from groundwater calcite precipitation with co2 release and cationic exchange the annual water balance terms for the lake basin indicates for each hydrological component the following values 1 16 e08 m3 rainfall 8 15 e07 m3 evapotranspiration 1 90 e06 m3 runoff 1 55 e07 m3 groundwater recharge 6 01 e06 m3 groundwater discharge to the lake 9 54 e06 m3 groundwater discharge to the river 5 00 e05 m3 urban extraction and 4 90 e06 m3 lake evaporation integrated analysis of hydrochemical and isotopic information helped to calibrate the groundwater flow model to validate the conceptual model and to quantitatively assess the basin water balance

hydrologic and geologic factors controlling surface and groundwater chemistry in indian wells owens valley area southeastern california usa the indian wells owens valley area is located in the semi arid basin and range province which is characterized by alternating mountains and alluvial basins surface water resources are limited in this arid region and water demand is mainly met by groundwater pumpage in a classic basin and range groundwater system water flows from recharge areas in the mountains to discharge areas in adjacent valleys discharge areas are generally occupied by playas where large amounts of salt deposition occur due to evaporating groundwater hydrochemical data from a total of 1368 spring surface and well water samples collected over an 80 year period were used to evaluate water quality and to determine processes that control water chemistry q mode hierarchical cluster analysis hca was employed for partitioning the water samples into hydrochemical facies also known as water groups or water types five major water groups resulted from the hca analysis the samples from the area were classified as recharge area waters ca na hco3 water and na ca hco3 water transition zone waters na hco3 cl water and discharge area waters na cl water and more concentrated na cl water spatial plots of the major statistical groups show that the samples that belong to the same group are located in close proximity to one another suggesting the same processes and or flowpaths inverse geochemical models of the statistical groups were developed using phreeqc to elucidate the chemical reactions controlling water chemistry the inverse geochemical modeling demonstrated that relatively few phases are required to derive water chemistry in the area in a broad sense the reactions responsible for the hydrochemical evolution in the area fall into four categories 1 silicate weathering reactions 2 dissolution of salts 3 precipitation of calcite amorphous silica and clay minerals and 4 ion exchange

geologic stereo mapping of geologic structures with spot satellite data reply the spot imaging system launched in 1986 by the french national space agency cnes provides two significant advances for mapping geological structures from satellite imagery increased spatial resolution of key structural and stratigraphic elements and stereoscopic capabilities for making strike and dip measurements quantitative stereo mapping with spot data may be done using hard copy images and conventional equipment such as stereo plotters or by displaying images on a video monitor in stereo viewing format the latter method is a new remote sensing technique particularly relevant to the exploration community this technique allows development with minor expenditure and training of an effective stereo mapping capability on existing image processing systems or on stand alone personal computers spot stereo data is particularly useful for mapping low amplitude and highly deformed structures surface structure maps generated from stereo imagery data can be applied to exploration at two levels at early stages such maps can be used to establish the style trend size and spatial distribution of structures in a basin and to investigate key tectonic elements at more advanced prospecting stages these maps can be used to constrain subsurface mapping of structures located in areas of poor seismic data quality this latter technique however may require the support of highermore resolution stereo aerial photography less

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

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

quantitative structural analysis with stereoscopic remote sensing imagery we employ powerful stereoscopic methods with satellite imagery to obtain surface bedding attitude measurements these data are used to constrain geologic structures in three dimensions using quantitative structural models we document a numerical method for measuring the strike and dip of bedding using stereoscopic pairs of air photos as well as landsat thematic mapper and spot images in examples from the north american and andean cordilleras these remote measurements prove consistent with direct surface control and subsurface structures imaged in seismic reflection profiles remotely derived measurements are combined with subsurface data to generate balanced structural interpretations that define complex structural traps using fault related folding theory these remote sensing methods can provide a low cost and rapid means of delineating prospects and leads

tectonic control on hydrocarbon generation in the northwestern neuquen basin argentina the petroleum systems of the malargue fold thrust belt in the northwestern neuquen basin argentina comprise multiple reservoir and seal rocks and three major source rocks of the lower jurassic los molles formation fm the lower tithonian to lower valanginian vaca muerta fm and the lower hauterivian to lower barremian agrio fm the thermal history of the mesozoic source rocks has been reconstructed using one dimensional and two dimensional modeling the most important factors that affected the source rock maturation are the timing of maximum late cretaceous to paleogene burial and the heat flow during back arc extension we postulate that synclines have been buried over longer periods and source rock maturation ceased earlier in anticlines accordingly hydrocarbon generation from the vaca muerta fm and agrio fm has started during the campanian despite late stage magmatic activity causing local thermal perturbations the models suggest that the thermal field has been dominated by conductive heat transport and that heat flow has been a response to the evolution from back arc extension to orogenic shortening high heat flows of 85 mw m2 during back arc extension between the latest cretaceous and paleogene have been modeled two main source pods supply hydrocarbons until the present they are related to structurally deep footwall positions of thrust faults active since the late cretaceous and to deep frontal synclines having formed through late stage thick skinned tectonics since the neogene modeling of hydrocarbon fluid type is consistent with existing oil fields exhibiting light and medium oils with api between 22 api and 39 api charged from early to peak mature source rocks

structural and microstructural evolution of the rattlesnake mountain anticline wyoming usa new insights into the sevier and laramide orogenic stress build up in the bighorn basin the rocky mountains in western us provide among the best examples of thick skinned tectonics following a period of thin skinned tectonics related to the sevier orogeny the compressional reactivation of basement faults gave birth to the so called laramide uplifts arches the bighorn basin located in wyoming is therefore a key place to study the transition from thin to thick skinned tectonics in orogenic forelands especially in terms of microstructural and stress strain evolution our study focuses on a classic laramide structure the rattlesnake mountain anticline rma wyoming usa a basement cored anticline located in the western part of the bighorn basin stress and strain evolution analysis in folded sedimentary layers and underlying faulted basement rocks were performed on the basis of combined analyses of fractures fault slip data and calcite twinning paleopiezometry most of the fractures are related to three main tectonic events the sevier thin skinned contraction the laramide thick skinned contraction and the basin and range extension serial balanced cross sections of rma and displacement profiles suggest that all thrust faults were coeval evidencing strain distribution in the basement during faulting the comparison of rma with another structure located in the eastern edge of the bighorn basin i e the sheep mountain anticline sma allows to propose a conceptual model for the geometric and kinematic evolution of laramide related basement cored anticlines finally the stress evolution is reconstructed at both the fold scale and the basin scale we show that the evolution of stress trends and magnitudes was quite similar in both structures rma and sma during laramide times thick skinned tectonics in spite of different stress regimes during sevier thin skinned tectonics and post laramide times stress trends and fracture patterns were different in these two structures these results suggest that the distance to the orogenic front influenced the fracture patterns but not the foreland stress magnitudes which were likely controlled by the structural style

thermal alteration of cretaceous black shale by diabase intrusions in the eastern atlantic ii effects on bitumen and kerogen abstract the thermal effects of three one major and two minor miocene diabase intrusions on cretaceous black shales from dsdp site 41 368 have been analyzed a concentration gradient was observed especially for the hydrocarbons decreasing towards the major intrusion and between the three sills the thermally altered samples in the proximity of and between the sills contained elemental sulfur and an excess of thermally derived pristane over phytane whereas the unaltered sediments contained no elemental sulfur and more phytane than pristane a maximum yield of the extractable hydrocarbons was observed at a depth of 7 m below the major sill two classes of molecular markers were present in this bitumen suite the first was sesqui di and triterpenoids and steranes which could be correlated with both terrigenous and autochthonous sources they were geologically mature and showed no significant changes due to the thermal stress the second class was found in the altered samples which contained only polynuclear aromatic hydrocarbons with low alkyl substitution and sulfur and oxygen heterocyclic aromatic compounds these compounds were derived from pyrolytic reactions during the thermal event kerogen was isolated from all of these samples but only traces of humic substances were present the h c n c 13 c 34 s and d all exhibit the expected effects of thermal stress the kerogen becomes more aromatized and richer in 13c 34s and d in the proximity of and between the sills maturation trends were also measured by the vitrinite reflectance and electron spin resonance where the thermal stress could be correlated with an elevated country rock temperature and an increased degree of aromaticity the effects of in situ thermal stress on the organic rich shales resulted in the generation and expulsion of petroliferous material from the vicinity of the sills

thickness matters influence of dolerite sills on the thermal maturity of surrounding rocks in a coal bed methane play in botswana abstract global studies suggest that igneous intrusions usually have thermal aureole thicknesses between 30 and 250 of the intrusion thickness here we discuss data and 1d thermal maturity models from nine coreholes wells drilled in botswana to explore for coal bed gas the coreholes penetrated multiple dolerite sills with thicknesses ranging from 1 2 m to 73 4 m the sills intruded the sedimentary rocks in the jurassic period and significantly affected the rank properties and thermal maturity of permian coals the thermal influence of the sills extends for 5 53 m away from their contacts with surrounding rocks the relatively thick 13 m sills have thermal aureole thicknesses of 31 137 of the sill thickness in line with global observations however the relatively thin 1000 of the sill thickness significantly larger than previously reported from most other locations affected by igneous intrusions thin sill intrusions in coals and organic rich shales may lead to the generation of larger volumes of ch4 other hydrocarbon gases and co2 than previously thought affecting the safety in coal mines and gas resources

synrift magmatism in a cenozoic rift basin from 3d seismic data wichianburi sub basin phetchabun basin thailand part 1 distribution and timing of intrusions and forced folds the late oligocene pliocene wichianburi sub basin phetchabun rift thailand has undergone three phases of development late oligocene early miocene c 16 ma east west extension on predominantly nnw sse to north south striking faults 16 ma c 3 ma ne extension on nnw sse north south and ne sw trending faults and 3 ma to present post rift subsidence the basin was also affected by intrusive and extrusive igneous activity from 24 to 2 ma the relationships among the structure rift basin stratigraphy and sheet intrusions are unusually well documented as a result of extensive hydrocarbon exploration drilling and 3d seismic data together with the production of hydrocarbons from igneous sills the oldest igneous activity c 24 13 ma lies sw of the wichianburi sub basin where extrusive rocks exposed at the surface have been dated by k ar and 40ar 39ar methods the overall igneous activity youngs from the south of the basin to the north 11 9 ma numerous domal folds occur across the basin the sill and laccolith dimensions the rate of fold development the variable timing of fold formation and the fold geometry all indicate that the folds are related to magma emplacement not tectonic inversion fold formation occurred at c 16 15 and 12 11 ma in single or multiple stages the timing of folding coupled with the radiometric dating of some sills k ar 39ar 40ar indicates that the greatest amount of intrusive activity occurred between 16 and 11 ma the 16 ma date coincides with the switch from east west to nw se extension which promoted dilatancy within the upper crust along a range of synrift fault orientations and some pre rift trends the burial history of the main depocentre shows that miocene sill emplacement occurred at depths

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

the neuquen super basin with more than 6000 m of sedimentary thickness and several superimposed petroleum systems the neuquen basin of argentina has all the elements to be considered a super basin the basin developed during the triassic early jurassic in a rift environment that generated a localized petroleum system continued subsidence during the early jurassic resulted in the first marine ingression los molles formation total organic carbon toc 1 7 this unit matured 120 to 55 m y a before the formation of major structures with the exception of the huincul high a fast marine flooding in a retroarc setting occurred during the latest jurassic early cretaceous at its base lies the vaca muerta formation a 50 to 1000 m thick world class source rock composed by calcareous shales and marls toc 2 9 this unit reached maturity at 95 ma when the only traps available were structures along the huincul high or stratigraphic a new marine ingression occurred during the early cretaceous depositing bituminous shales and marls agrio formation toc 2 5 that matured during the paleogene these superimposed petroleum systems combined with different structural settings gave rise to numerous plays and trapping configurations that resulted in the discovery of 14 billion boe in addition the unconventional potential of the vaca muerta is now being developed with estimated resources of 91 5 tcf and 14 3 billion bbl of oil the neuquen basin has gone through three main phases of development conventional tight and unconventional after a century of production the basin still shows a wide variety of opportunities for both conventional and world class unconventional plays

modelling of gas generation following emplacement of an igneous sill below lusi east java indonesia highlights we have tested a hypothesis where a sill intrusion is present at depth near lusi we have calculated the co2 generation following the emplacing a 150 m sill in an organic rich sequence at 4 5 km this scenario may provide the co2 currently emitted from lusi and are consistent with geological information abstract the lusi mud eruption started in 2006 and is located near the arjuno welirang volcanic complex in northeastern java lusi is characterized by the eruption of aqueous vapor co2 and ch4 in addition to mud breccia and boiling water however the ultimate driving force for the eruption remains unclear here we investigate if lusi could have been driven by the heat released from a deep seated igneous sill originating from the neighboring volcanic arc we have used a 1d thermal model to calculate the production of co2 from thermally matured organic matter in the contact aureole of a hypothetical 150 m thick sill the sill is tentatively emplaced at 1100 c at 4 5 km depth within the organic rich eocene ngimbang formation the carbon gas produced from the thermal perturbation reaches a peak of 1357 kg m2 y co2 equivalents shortly after sill emplacement stressing the efficiency of organic matter transformation in contact aureoles our simulations show that during the first 1000 years after emplacement 53 5 ton co2 m2 is produced in the contact aureole when scaled to a sill size of 150 m 25 km2 i e a sill volume of 3 75 km3 the aureole has the potential to generate a total of 1350 mt co2 during the first 1000 years with a peak generation of about 34 mt co2 y we conclude that contact metamorphism in our hypothetical geological scenario generates co2 in the gigaton range and represents a plausible source for the lusi gas

topographic mapping from interferometric synthetic aperture radar observations interferometric synthetic aperture radar observations provide a means for obtaining high resolution topographic terrain maps from data acquired simultaneously at two slightly displaced antennas calculation of the three dimensional coordinates of all the points in a radar image can be made from the combination of along track slant range and interferometer fringe measurements thus the result compensates for the layover exhibited by conventional radar maps and removes the false targets generated by multiple signal paths to a given object in the scene we have derived a topographic map of a portion of the san francisco bay area utilizing data that were recorded by a radar system mounted on a nasa cv990 aircraft and processed by a general purpose digital computer this map displays the height above sea level of a region approximately 11 km by 10 km in size sampled on an 11 m pixel grid uncertainties in the estimated height result from imprecise knowledge of the observational geometry radar bandwidth limitations and finite signal to noise ratios for our system each factor contributed approximately 3 4 m to a relative rms error of about 6 m additional global errors of the order of 10 m can result from inaccurate monitoring of aircraft attitude the statistical variation of the height measurements from the ocean portion of the map which we can presume to be quite flat is 2 10 m rms which is consistent with the theoretical estimate comparison of our results with u s geological survey contour maps indicates a high degree of correlation between the two sets of altitude data

regional controls on the geochemical evolution of saline groundwaters in the edwards aquifer central texas geochemical and isotopic parameters are used to evaluate models for the evolution of saline groundwaters in the edwards aquifer which lies on the northwestern margin of the gulf of mexico sedimentary basin saline groundwaters termed badwaters range in salinity from 1000 to 12 500 mg l 1 total dissolved solids models for badwater evolution must account for complexities owing to 1 the range in compositions of saline basinal fluids that may migrate into the edwards aquifer from its down dip section and from underlying hydrostratigraphic units 2 the range of depositional diagenetic and mineralogic variations in the hist aquifer rocks 3 volcanic and intrusive igneous rocks that locally crosscut the aquifer 4 extensive faulting which in places juxtaposes edwards aquifer units with adjacent hydrostratigraphic units calcium mg na so4 cl and hco3 variations define six badwater hydrochemical facies strontium isotope values of freshwaters 87sr86sr 0 7077 0 7086 badwaters 0 7076 0 7094 and brines from aquifer rocks down dip 0 7078 0 7097 are nearly all higher than the range of most edwards aquifer rocks 0 7074 0 7077 and volcanic and intrusive igneous rocks that crosscut the aquifer 0 7032 0 7055 argillaceous carbonate rocks that underlie the edwards aquifer are likely sources of sr with high 87sr86sr values transitions between the hydrochemical facies in some locations correspond to changes in depositional environments in aquifer rocks and to changes in the intensity of faulting through the aquifer major element mineral saturation state and srca 87sr86sr variations in badwaters of the westernmost aquifer region indicate that incongruent dissolution of gypsum and recrystallization of calcite control the geochemical evolution of these badwaters srca na cl 87sr86sr variations in badwaters of extensively faulted areas to the east of the westernmost aquifer region are consistent with fluid mixing processes involving at least five endmember fluids including 1 saline groundwaters from two underlying hydrostratigraphic units 2 two endmember brines from down dip edwadrs aquifer equivalent units and 3 freashwaters that have interacted extensively with aquifer rocks the compositions of badwaters from the northeasternmost region reflect fluid mixing between freshwaters and saline groundwaters from underlying hydrostratigraphic units

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

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

capo granitola sciacca fault zone sicilian channel central mediterranean structure vs magmatism abstract the tectonic framework of the northern sector of the capo granitola sciacca fault zone cgsfz a nne oriented lithospheric strike slip fault zone located in the sicilian channel southern italy has been reconstructed with the aim to clarify the relationships between geometry and kinematics of the structures and the occurrence and distribution of the magmatic manifestations observed in the area this has been achieved by the interpretation of a large dataset composed of 2 d multichannel seismic profiles chirp profiles magnetic data and borehole information in addition to the volcanic edifices known in the graham and terribile banks this study has allowed to recognize several other magmatic manifestations the magmatic occurrences consist of small volcanic cones buried magma ascents and potential igneous sills the cgsfz is bounded by two strike slip fault systems the capo granitola fault system cgfs to the west and the sciacca fault system sfs to the east dominated by positive flower structures generated by tectonic inversion of nne oriented late miocene extensional faults only the southern part of the cgfs shows the presence of a sub vertical n s oriented strike slip master fault the sector between the two fault systems does not show a significant pliocene quaternary tectonic deformation except for its southern part hosting the terribile bank which is dissected by wnw to nw trending normal faults developed during late miocene and later reactivated this set of faults is currently active at the terribile bank whereas is buried by pliocene quaternary deposits in the central and northern sectors of the cgsfz the observed magmatism is driven by a mechanism of non plume origin magmas have used as open paths the faults of the cgfs and sfs which cut the whole lithosphere reaching the asthenosphere and producing partial melting by simple pressure release most of the magmatism develops along the strike slip master fault associated with the cgfs and the normal faults affecting the terribile bank the magmatic feeding of the terribile bank would be related to lateral magma migration coming from the structures of the sfs which would use the open pathways represented by active normal faults in the central northern part of the cgsfz magmas migrate upward along lithospheric faults then move laterally and rise toward the surface through nne and nw trending buried normal faults these late miocene faults do not reach the surface and this may have favoured the emplacement of igneous sills which in turn may explain the observed volcanic centres

using orthographic projection with geographic information system gis data to constrain the kinematics the central range fault zone trinidad abstract fold geometry versus axis orientation can be used to constrain the kinematics of transpressional plate boundaries this approach is typically based on bedding orientation data collected in the field however in some regions outcrop quality is insufficient to provide enough measurements we extract orientation data from a georeferenced geologic map and a digital elevation model and to constrain the kinematics of a poorly exposed active transpressional boundary the central range fault zone in trinidad strike and dip orientations are calculated based on contact positions extracted from the digital geologic and topographic datasets the uncertainties in the both horizontal position and elevation of the contact are propagated into the final kinematic analysis analysis of folds adjacent to the central range fault suggests the angle of oblique convergence in transpression varies from 20 to 85 the majority of folds however are consistent with a large component of contraction i e 50 the analysis also suggests folding in the central range records a minimum of 3 9 km of contraction 3 km of strike slip motion and 4 9 km of total plate motion the range of values reflects uncertainties in the position of the folded contacts we interpret the overall kinematics of deformation amount of shortening and homogeneity of the finite strain field to indicate that active deformation on the central range fault zone has not yet accumulated enough strain to overprint the effects of earlier pre strike slip pre middle miocene fold and thrust style tectonics

spatial and temporal variability of the chemistry of the shallow groundwater in the alluvial fan area of the luanhe river north china groundwater in the alluvial fan area of the luanhe river north china was monitored every 2 months for a year subsequently the temporal and spatial variability in the hydrochemical characteristics of the water was investigated using hierarchical cluster analysis hca and a trilinear piper diagram it is found that the spatial variability in the groundwater composition from different monitoring wells has obvious differences even if the distance between many of the wells is small also the difference in the ion concentration was found to be up to fivefold for the same monitored well research has indicated that the groundwater s chemical characteristics are mainly controlled by soil type the amount of precipitation the luanhe river the groundwater and human factors the thickness and continuous distribution of clay influences the velocity and ion exchange rate of the groundwater flow this results in the amount of total dissolved solids in the groundwater increasing from upstream to downstream in the flood season june july and august ion concentration gradually decreases as a result of the increased recharging of the groundwater due to precipitation classification using hca indicates that the samples can be clustered into different groups according to correlation coefficients also the chemical composition of the water from monitoring wells near the luanhe river is approximately consistent with that from the luanhe river this implies that the samples have some compositions resulted from the mixing of groundwater and river water the piper diagram indicates that ca2 mg2 and hco3 ions are the predominant ones present i e the type of groundwater is of the ca mg hco3 type

vitrinite reflectance and molecular geochemistry of jurassic sediments the influence of heating by tertiary dykes northwest scotland vitrinite reflectance measurements from sedimentary rocks adjacent to six dykes from sites across the inner hebrides indicate that the lateral extent of thermal alteration is reasonably similar and proportional to dyke thickness d t with alteration starting to take effect at 70 d t detailed sampling of a jurassic siltstone adjacent to a 0 9 m dyke reveals that the zone of maximum extractable organic matter eom wt g rock equivalent to the oil window is relatively narrow ca 25 of the d t the position of this oil window relative o the vitrinite reflectance profile is comparable with that from burial maturation gas chromatograms of the aliphatic hydrocarbon fractions reveal i a shift from branched and cyclic dominated hydrocarbons to an increasing predominance of straight chain components and ii the carbon number distribution of the n alkanes shifts towards the shorter chain homologues with decreasing distance from the dyke contact apart from the methylphenanthrene index mpi1 changes in each of the molecular maturity parameters are initiated by the the thermal effects of the dyke between 80 and 70 d t from the contact the mpi1 parameter was the most sensitive maturity indicator in that it responded to the dyke emplacement even in the distal samples i e distance from dyke contact 140 d t a significant reduction in toc at the dyke contact suggests that the synthesis gas reaction may have occurred i e the reaction of organic matter with steam resulting in the formation of carbon monoxide this reaction may be associated with the vitrinite reflectance reversal this study suggests that these particular dykes have had only a local effect on the maturity of the intruded sediments

the role of excess co2 in the formation of trona deposits abstract the prevailing theory for the formation of trona na3 co3 hco3 2 h2o relies on evaporative concentration of na hco 3 water produced by silicate hydrolysis of volcanic rock or volcaniclastic sediments given the abundance of closed drainage basins dominated by volcanics it is puzzling that there are so few trona deposits and present day lakes that would yield dominantly na co3 minerals upon evaporation groundwater in the san bernardino basin southeastern arizona usa and northeastern sonora mexico would yield mainly na co3 minerals upon evaporation but waters in the surrounding basins would not analysis of the chemical evolution of this groundwater shows that the critical difference from the surrounding basins is not lithology but the injection of magmatic co2 many major deposits of trona and na co3 type lakes appear to have had excess co2 input either from magmatic sources or from the decay of organic matter it is proposed that along with the presence of volcanics addition of excess co2 is an important pre condition for the formation of trona deposits

implications of incremental emplacement of magma bodies for magma differentiation thermal aureole dimensions and plutonism volcanism relationships abstract field observations and geophysical data indicate that many igneous bodies grow by amalgamation of successive magma pulses that commonly take the shape of horizontal sheets sills emplacement styles and emplacement rates of magma bodies have fundamental implications on magma differentiation country rock metamorphism and assimilation and for the formation of large magma chambers in the upper crust when a magma body begins to grow by slow accretion of sills each successive intrusion solidifies before the injection of the next one when the system is thermally mature sill temperatures equilibrate above the solidus melts accumulate and older sills can re melt the time needed for each magma injection to cool down and equilibrate with its surrounding is short relatively to the total emplacement time of the body the transition from a mafic crystal poor magma to a partially molten rock that retains a highly differentiated melt is fast whereas the resulting evolved residual melt can reside in the crust for protracted periods as long as temperatures in the system are relatively low highly differentiated melts are generated which may explain the bi modal character and the absence of intermediate compositions in some magmatic provinces the level of emplacement of successive magma pulses controls the shape of the thermal anomaly associated with the magma body growth metamorphism partial melting and assimilation of the country rock are favoured if successive magma sheets are emplaced at or close to the country rock magma body boundary if the magma emplacement rate is low the size of the thermal aureole is controlled by the size of one pulse and not by the size of the entire igneous body understanding emplacement of magma bodies is fundamental for our understanding of the plutonism volcanism relationship magma emplacement rates of several centimetres per year are needed for a magma body to evolve into a large magma chamber able to feed large silicic explosive eruptions the time averaged emplacement rates of plutons are lower than this critical emplacement rate eruptions of 100s to 1000s cubic kilometres of silicic products show that such high volumes of magmas can accumulate in the upper crust this suggests that the emplacement of magma bodies is a multi timescale process with the development of large magma chambers corresponding to the highest magma fluxes because they control magmatic processes and the impact of magma intrusion on the country rock future studies should focus on magma emplacement rates and on magma emplacement geometries these studies should integrate field observation on plutons and geophysical data on active magmatic systems coupled with laboratory experiments and numerical simulations

discrete lithofacies discrimination of jurassic strata using advanced spaceborne thermal emission and reflection radiometer data bighorn basin wyoming usa an investigation of the carbonate sedimentology of the middle jurassic strata bighorn basin north central wyoming proved to be an ideal test of new spaceborne remote sensing platforms with high spatial and spectral resolution to evaluate these new tools it was necessary to i map the occurrence of different lithofacies in at least a part of the area to establish ground truth ii establish the reflectance characteristics of the different lithofacies using portable on the ground systems iii produce maps based on spaceborne remote sensing data that discriminate between the lithological types found in the field and lastly iv evaluate the discrimination by visiting previously unvisited areas in which these rock types are predicted to occur based upon their remote signatures field checking of previously unvisited outcrops demonstrated whether these remote sensing techniques allowed distinction of different lithological outcrops this investigation determined that the new spaceborne tools could distinguish between outcrops of sparse silty oomicrites from sorted biosparites as small as 10 m by 10 m in a study area as large as the bighorn basin the ability to identify very small outcrops with a predicted lithology a priori proved to be a major advantage in maximizing field effort

the relationship between organic maturation the widths of thermal aureoles and the thicknesses of sills in the midland valley of scotland and northern england the contrasting nature of thermal aureoles that surround mid carboniferous alkaline dolerite sills and early permian quartz dolerite silk of the midland valley of scotland and northern england is described the development of the aureoles is influenced by the degree of consolidation of the sediments their volume of pore water when invaded by the magma the time period between deposition of the invaded sediments and emplacement of the intrusion and the degree of organic maturation at the time of intrusion a correlation exists between the logarithms of the thicknesses of sills and thermal aureoles of the quartz dolerites equivalent data for the alkaline dolerites lie more than two standard errors from the regression line for the quartz dolerite plots

thermal effects of igneous intrusions on maturity of organic matter a possible mechanism of intrusion abstract this paper assesses thermal maturation of organic matter near a well dated intrusion in the dsdp 41 368 hole near cape verde rise eastern atlantic and near some other intrusions from the u k u s a and east greenland the traditional numerical model with instantaneous intrusion satisfactorily describes the thermal evolution and thermal maturity aureoles of igneous bodies only if the initial temperature of intrusion is close to or even lower than the solidus temperature calculations in this model with more real values of the intrusion temperature and with consideration of latent heat effects lead to considerable over estimation of thermal influence of the intrusion models which consider formation of the intrusive body over time as distinct from instantaneous intrusion and especially models of emplacement of an intrusive body in the shell of relatively cool magmatic rocks show better agreement between the computed and observed vitrinite reflectance profiles consideration of convective heat flow due to hydrothermal activity arising in the vicinity of the intrusion during its formation and cooling helps to explain the difference between maturation profiles above and below some sills

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

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

digital characterization of thrombolite stromatolite reef distribution in a carbonate ramp system terminal proterozoic nama group namibia the stratigraphic architecture of a terminal proterozoic carbonate ramp system ca 550 ma nama group namibia was mapped quantitatively with digital surveying technologies the carbonate ramp consists of a shoaling upward ramp sequence in which thrombolite stromatolite reefs developed at several stratigraphic levels the reefs are associated with grainstone and heterolithic facies and exhibit diverse geometries and dimensions related to the position in the sequence stratigraphic framework laterally extensive reefs with a tabular geometry developed when accommodation was relatively low whereas discontinuous oblate dome shaped reefs developed during times when accommodation space was relatively high collecting sedimentological and stratigraphic data digitally in an extensive canyon system allowed a comprehensive documentation of the three dimensional 3 d architecture and dimensions of the reefal buildups both deterministic and stochastic methods were used to extend outcrop observations to construct 3 d models that honor the observed stratigraphy in particular the accuracy with which dimensions of reefal buildups can be measured is critically important in the statistical modeling of the dome shaped buildups calculations and corrections can be applied directly to the digital data set and serve as input during model building the final 3 d model faithfully reproduces the outcrop distribution of facies and geological objects and has a high spatial resolution compared with petroleum industry reservoir models the organization of the reefal buildups in the stratigraphic framework has direct implications for reservoir continuity and connectivity in analogous settings the digital characterization and 3 d outcrop models presented in this article can be subsequently used to condition dynamic reservoir simulation modeling of geologically similar areas

magma emplacement in a thrust ramp anticline the gavorrano granite northern apennines italy 1 magma emplacement in the upper crust is often associated with crustal extension whereby space for intrusions is made by dilation along transtensive and strike slip faults the lenticular shape of several intrusions indicates that a further mechanism for magma intrusion is laccolith emplacement with roof uplift of the overburden additionally melts exploit rheological discontinuities e g sedimentary layering during their ascent we present an emplacement model for intrusion of the shallow level gavorrano granite northern apennine italy which is located at the core of an open anticline the shape of the intrusion and structural features of the host rocks are indicative of a synkinematic emplacement in a growing thrust anticline space was provided by the opening of dilatation zones at the core of anticline as a consequence of different amounts of translation between hanging wall and footwall units which were separated by evaporitic rocks these evaporitic units acted as major decollement layers analog models provide results in good agreement with the structural setting of the anticline and emphasize the possibility that melts filled the dilatation zone with the decollement layers further facilitating intrusion