effect of ocean oxidation on the chemical structure of marine kerogen abstract the burial of organic matter om in marine sediments is an important control on global climate and petroleum formation on geological timescales while the oxygen exposure time of sediment has been shown to affect the efficiency of organic carbon burial and influence om properties in recent sediments the implications for the chemical composition of kerogen have not been tested this study tests the hypothesis that oceanic redox conditions are an important control on the molecular structure and composition of kerogen samples from a number of outcropping late cretaceous mudstones of the eagle ford formation were chosen spanning a gradient of paleo redox depositional conditions oxic sub oxic to anoxic and the bulk molecular composition of the kerogen was determined using solid state 13 c nuclear magnetic resonance nmr spectroscopy the nmr spectral properties of kerogen covaried with redox sensitive trace metal abundance whereas the thermal maturity and om source biomarkers were relatively invariant anoxic environments favor the preservation of alkyl c moieties while kerogen formed in oxic depositional environments was enriched in aromatic c this study is the first to demonstrate that diagenetic consequences of bottom water redox conditions are retained in the molecular structure of the kerogen macromolecule on geological timescales

a two step model for dynamical dike propagation in two dimensions application to the july 2001 etna eruption we developed an hybrid numerical model of dike propagation in two dimensions solving both for the magma trajectory and velocity as a function of the source overpressure the magma physical properties density and viscosity as well as the crustal density and stress field this model is used to characterize the influence of surface load changes on magma migration towards the surface we confirm that surface loading induced by volcanic edifice construction tends both to attract the magma and to reduce its velocity in contrast surface unloading for instance due to caldera formation tends to divert the magma to the periphery retarding eruption in both cases the deflected magma may remain trapped at depth amplitudes of dike deflection and magma velocity variation depend on the ratio between the magma driving pressure source overpressure as well as buoyancy and the stress field perturbation our model is then applied to the july 2001 eruption of etna where the final dike deflection had been previously interpreted as due to the topographic load we show that the velocity decrease observed during the last stage of the propagation can also be attributed to the local stress field we use the dike propagation duration to estimate the magma overpressure at the dike bottom to be less than 4 mpa this approach can be potentially used to forecast if where and when propagating magma might reach the surface when having knowledge on the local stress field magma physical properties and reservoir overpressure

development of a subvolcanic structure by the interaction of liquid filled cracks abstract the interaction of liquid filled cracks may be an important process for magma accumulation and the development of subvolcanic structures the horizontal interaction was studied through the stress analyses around pressured cracks in various regional stress fields the vertical interaction was studied using gelatin experiments buoyaney driven cracks coalesce more easily than pressure cracks the theory of the three dimensional crack interaction was discussed there are two types of crack interaction the interaction between liquid filled cracks may cause coalescence of cracks the interaction between a liquid filled crack and a solid filled crack never causes coalescence the stress relaxation by ductile or brittle behavior or by the driving out of magma decreases the local stress field generated by the accumulation of magma filled cracks as the regional differential stress increases and the minimum compressive principal stress becomes tensile magma filled cracks become parallel to each other as the supply rate of magma filled cracks becomes relatively large or as the regional differential stress decreases and the minimum compressive stress increases the arrangement of magma filled cracks varies from an offset pattern to a radial one because the local compressive stress field cannot be decreased this process leads to the development of subparallel or radial dikes in two dimensions or a dike sheet complex in three dimensions a large magma chamber such as a sphere or a cylinder is not always necessary for the development of a basaltic volcano in case of the interaction between liquid filled cracks magma filled cracks coalesce easily into one large crack and diminish the local compressive stress field last the theory of the crack interaction is applied to developments of various volcanoes the fissure pattern of hekla volcano iceland is explained in terms of the variation of the stress relaxation the difference in fissure pattern between izu oshima and miyakejima volcanoes japan is interpreted by the variation of the differential stress the local stress balance including the stress relaxation is kept in the developments of etna volcano italy and kilauea volcano hawaii

experimental modelling of ground deformation associated with shallow magma intrusions abstract active volcanoes experience ground deformation as a response to the dynamics of underground magmatic systems the analysis of ground deformation patterns may provide important constraints on the dynamics and shape of the underlying volcanic plumbing systems nevertheless these analyses usually take into account simplistic shapes sphere dykes sills and the results cannot be verified as the modelled systems are buried in this paper i present new results from experimental models of magma intrusion in which both the evolution of ground deformation during intrusion and the shape of the underlying intrusion are monitored the models consisted of a molten vegetable oil simulating low viscosity magma injected into cohesive fine grained silica flour simulating the brittle upper crust oil injection resulted is sheet intrusions dykes sills and cone sheets the initial topography in the models was flat while the oil was intruding the surface of the models slightly lifted up to form a smooth relief which was mapped through time after an initial symmetrical development the uplifted area developed asymmetrically at the end of the experiments the oil always erupted at the steepest edge of the uplifted area after the experiment the oil solidified the intrusion was excavated and the shape of its top surface mapped the comparison between the uplifted zone and the underlying intrusions showed that 1 the complex shapes of the uplifted areas reflected the complex shapes of the underlying intrusions 2 the time evolution of the uplifted zone was correlated with the evolution of the underlying intrusion and 3 the early asymmetrical evolution of the uplifted areas can be used to predict the location of the eruption of the oil the experimental results also suggest that complex intrusion shapes inclined sheet cone sheet complex sill may have to be considered more systematically in the analyses of ground deformation patterns on volcanoes

organic geochemical proxies of paleoceanographic paleolimnologic and paleoclimatic processes abstract organic matter constitutes a minor fraction of marine and freshwater sediments yet its important contribution to the sedimentary record can be used to reconstruct marine and continental paleoenvironments the organic matter content of sediments is the residue of past biota the amounts and types of organic matter present in sediments consequently reflect environmental conditions that impacted ecosystems at different past times general sources of the organic matter are inferred from bulk properties such as elemental compositions carbon and nitrogen stable isotope ratios rock eval pyrolysis data and organic petrography details of organic matter origins are refined by analyses of biomarker molecular compositions source changes are proxies for fluctuations in sea level oceanic surface currents and continental climates algal paleoproductivity rates are indicated by organic carbon mass accumulation rates and carbon and nitrogen stable isotopic compositions these parameters record past availability of nutrients and therefore are proxies of surface mixing in the oceans and amount of land runoff to lakes sea surface paleotemperatures are recorded by the number of carbon carbon double bonds in lipid biomarkers produced by marine algae larger proportions of the double bonds are proxies for the cooler surface waters that accompanied periods of global glaciation and intervals of enhanced upwelling the 13c and d values of plant organic matter record past concentrations of carbon dioxide in the atmosphere and changes in delivery of atmospheric moisture respectively diagenesis which causes the concentration and composition of organic matter in sedimentary settings to differ from those of the original biologically synthesized materials can bias organic geochemical paleoenvironmental records the magnitude of this potential source of misinformation must always be considered and evaluated comparison of multiple organic geochemical proxies of past conditions helps to compensate for the effects of diagenetic alterations and thereby to improve interpretations of paleoenvironmental change

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

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

mechanics of fluid driven fracture growth in naturally fractured reservoirs with simple network geometries 1 a numerical model has been developed for fluid driven opening mode fracture growth in a naturally fractured formation the rock formation contains discrete deformable fractures which are initially closed but conductive because of their preexisting apertures fluid flow that develops along fractures depends on fracture geometry defined by preexisting aperture distribution offsets along a fracture path and intersections of two or more fractures the model couples fluid flow elastic deformation and frictional sliding to obtain the solution which depends on the competition between fractures for permeability enhancement the fractures can be opened by fluid pressure that exceeds the normal stress acting on them and by interactions with intersecting closed fractures experiencing coulomb type frictional slip the newtonian fluid is assumed to flow through the conductive fractures according to a lubrication equation that relates the cube of an equivalent hydraulic aperture to fracture conductivity the rock material is assumed to be impermeable and elastic this paper provides the governing equations for the multiple fracture systems and the solution methods used flow distribution and fracture growth in conductive fracture sets are simulated for a range of geometric arrangements and hydraulic properties numerical results show that elastic interaction between fracture branches plays a controlling role in fluid migration although initial apertures can give rise to a preferential fluid flow direction during the early stage in the presence of offsets fracture segments subject to strong compression are difficult to open hydraulically and their resulting smaller permeability can increase overall upstream fracture pressure and opening the patterns of fluid flow become more complicated if fractures intersect each other a portion of injected fluid is lost into closed empty fractures that cut across the main hydraulic fracture and this delays the pressure increases required for fracture growth past the crosscutting fracture the nonlinear fluid loss rate depends on the geometric complexities of the fracture sets and on the fluid viscosity sometimes fracture growth can be accelerated by the fast fluid transport along an intersected relatively conductive natural fracture

the geometry of echelon fractures in rock implications from laboratory and numerical experiments abstract the traces of echelon joints veins and dikes in rock range from curving to straight theoretical analyses using boundary element numerical methods have concluded that straight open fractures imply a significant remote differential stress whereas curving traces imply a more nearly isotropic stress we present a series of laboratory experiments which investigate the two dimensional propagation paths of echelon fractures in pmma plates as a function of the applied biaxial loading and the initial geometry of a simple fracture array the experimental results support the theoretical conclusions and verify the accuracy of the numerical method at the grain scale rock does not rigorously conform to the assumptions of isotropy homogeneity and linear elasticity demanded by the numerical method nevertheless results from crack path stability theory suggest that small scale deviations of a fracture from the ideal path generally do not affect its large scale behavior fracture paths which become kinked or curved by local heterogeneities are found to self correct to a path governed by competition between the fracture tip and remote stress fields provided the remote differential stress is non zero this enhances our confidence that the numerical method can be used to produce and explain realistic fracture geometries in rock an unexpected experimental result is the non perpendicular intersection of fractures grown in the laboratory free surface boundary conditions require that the walls of an open fracture be free of shear stress the principal stresses are therefore aligned with the crack wall and we might consequently expect an approaching opening mode fracture either to intersect the free surface at a right angle or to turn away and follow an asymptotic nonintersecting path experimental and numerical modeling however shows how the near tip stresses generated by an approaching fracture dominate the local stress field and allow it to propagate along an oblique path very close to intersection with the adjacent free surface

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

dike surface lineations as magma flow indicators within the sheeted dike complex of the troodos ophiolite cyprus mesoscopic flow lineations and anisotropy of magnetic susceptibility ams have been measured for dikes within the cretaceous age troodos ophiolite with the goal of comparing the direction of initial magma flow through dike conduits immediately following crack propagation with that of flow of subsequent magma emplaced during later stages of dike growth dike margin indicators of flow include cusp axes and elongate vesicles found high in the ophiolite pseudostratigraphy and ridge and groove structures termed hot slickenlines found throughout the complex a unique flow direction is determined where elongate vesicles near dike margins display imbrication with respect to the margin significant changes in vesicle elongation directions across dikes likely indicate either changes in magma flow direction after dike propagation or back flow of magma during the waning stages of intrusion surface lineations generally lie subparallel to the direction of flow inferred from ams determinations on cores within 5 cm of dike margins surface lineations also lie subparallel to the long axis e1 of the orientation ellipsoid defined by long axes of groundmass plagioclase phenocrysts measured in sections from ams cores correlation of surface lineations with interior indicators of flow ams plagioclase trachytic texture indicate that the surface features are good proxies for grain scale magma flow directions during dike propagation in troodos dikes orientations of surface flow features in the dikes of the troodos ophiolite indicate an approximately equal mix of subhorizontal to near vertical magma flow contradicting the paradigm of primarily vertical flow of magma beneath continuous axial magma chambers at oceanic spreading centers our data are consistent with a model of magma emplacement both vertically and horizontally away from isolated magma chambers beneath axial volcanoes spaced along a ridge crest

evidence that coupling to magma chambers controls the volume history and velocity of laterally propagating intrusions 1 in this paper i present a simple analytical solution for the unsolved problem of a propagating dike coupled to a magma chamber as recognized by segall et al 2001 the flow of the magma from a chamber to a dike is described by an ordinary differential equation for the unknown pressures of chamber and dike the most intuitive assumption on magma exchange is that the volume gained by the intrusion equals the volume lost by the chamber this constraint however implies a chamber so large that its pressure does not drop during the feeding process and an incompressible magma that does not expand or vesiculate as it intrudes models assuming constant driving pressure fail to explain observations here mass conservation constrains pressure as magma flows from the chamber to the dike and the compressibilities of magma and sources control volume changes these assumptions allow me to decouple the equations and solve the system analytically the model predicts that chamber and dike volume change exponentially with time as v t v 1 exp t the asymptotic volume v and the timescale are found to be functions of rock magma chamber and dike parameters and of the initial pressure conditions assuming that the intrusion is shaped as an elongating cuboid its velocity is found to change as v v0exp t where v0 is the initial dike velocity the model is successfully tested against the best observations available for lateral dike propagation events the volume history of chamber and dike during the 2000 miyakejima intrusion japan and dike velocity during the 1978 krafla event iceland and during some intrusions following the 2005 event in afar ethiopia this paper confirms and extends the results of a previous study by rivalta and segall 2008 who found the final ratio between dike volume and the volume withdrawn from the chamber to be rv 1 4 m 3 1 where is the host rock rigidity and m is the magma compressibility here i demonstrate that the formula for rv holds at any time during the intrusion not just at the end this model confirms that some magma chambers behave as stiff magma tanks able to inflate large dikes as balloons and demonstrates that high volume ratios are unlikely if the chamber has a pure sill shape fitting observations with the model allows us to estimate several dike chamber magma and rock parameters

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

direct evidence for organic carbon preservation as clay organic nanocomposites in a devonian black shale from deposition to diagenesis abstract the burial of marine sourced organic carbon oc in continental margin sediments is most commonly linked to oceanographic regulation of bottom water oxygenation anoxia and or biological productivity here we show an additional influence in the devonian woodford shale in which oc occurs as nanometer intercalations with specific phyllosilicate minerals mixed layer illite smectite that we term organo mineral nanocomposites high resolution transmission electron microscopic hrtem images provide direct evidence of this nano scale relationship while discrete micron scale organic particles such as tasmanites algal cysts are present in some lamina a strong relation between total organic carbon toc and mineral surface area msa over a range of 15 toc indicate that the dominant association of organic carbon is with mineral surfaces and not as discrete pelagic grains consistent with hrtem images of nanocomposites where periods of oxygenation are indicated by bioturbation this relationship is modified by a shift to lower oc loading on mineral surfaces and reduced msa variability likely resulting from biological mixing and homogenization of the sediment oxidative burn down of oc and or stripping of oc from minerals in animal guts the toc msa relationship extends across a range of burial depths and thermal maturities into the oil window and persists through partial illitization where illitization occurs the loss of mineral surface area associated with the collapse of smectite interlayer space results in a systematic increase in toc msa and reorganization of organic carbon and clays into nano scale aggregates while the woodford shale is representative of black shale deposits commonly thought to record heightened marine productivity and or anoxia our results point to the importance of high surface area clay minerals for oc enrichment given that the vast majority of these clay minerals are formed in soils before being transported to continental margin settings their mineralogy and attendant preservative potential is primarily a function of continental climate and provenance making these deposits a sensitive recorder of land as well as oceanographic change

constraints on dike propagation from continuous gps measurements the january 1997 east rift zone eruption on kilauea volcano hawaii occurred within a network of continuous global positioning system gps receivers the gps measurements reveal the temporal history of deformation during dike intrusion beginning 8 hours prior to the onset of the eruption the dike volume as a function of time estimated from the gps data using elastic green s functions for a homogeneous half space shows that only two thirds of the final dike volume accumulated prior to the eruption and the rate of volume change decreased with time these observations are inconsistent with simple models of dike propagation which predict accelerating dike volume up to the time of the eruption and little or no change thereafter deflationary tilt changes at kilauea summit mirror the inferred dike volume history suggesting that the rate of dike propagation is limited by flow of magma into the dike a simple lumped parameter model of a coupled dike magma chamber system shows that the tendency for a dike to end in an eruption rather than intrusion is favored by high initial dike pressures compressional stress states large compressible magma reservoirs and highly conductive conduits linking the dike and source reservoirs comparison of model predictions to the observed dike volume history the ratio of erupted to intruded magma and the deflationary history of the summit magma chamber suggest that most of the magma supplied to the growing dike came from sources near to the eruption through highly conductive conduits interpretation is complicated by the presence of multiple source reservoirs magma vesiculation and cooling as well as spatial variations in dike normal stress reinflation of the summit magma chamber following the eruption was measured by gps and accompanied a rise in the level of the pu u o o lava lake for a spheroidal chamber these data imply a summit magma chamber volume of 20 km3 consistent with recent estimates from seismic tomography continuous deformation measurements can be used to image the spatiotemporal evolution of propagating dikes and to reveal quantitative information about the volcanic plumbing systems

relative efficiency of the selective preservation and degradation recondensation pathways in kerogen formation source and environment influence on their contributions to type i and ii kerogens abstract a new pathway based on the selective preservation of insoluble and non hydrolysable macromolecules occurring as such in living organisms was recently shown to be involved in kerogen formation here we discuss the relative importance of this pathway and of the classical degradation recondensation process in the genesis of microalgae and bacteria derived kerogen fractions to this end a three dimensional diagram was established reflecting the contribution of the selective preservation pathway versus the average composition of the source organisms and depositional conditions this diagram reveals that the selective preservation mechanism probably played a major role in the formation of most of the above kerogens in addition to emphasizing the quantitative importance of this new pathway such a large contribution is consistent with the high oil potential typical of type i and ii kerogens and accounts for the morphological diversity observed in these fossil materials

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

the mechanics and dynamics of sills in layered elastic rocks and their implications for the growth of laccoliths and other igneous complexes abstract the recent experimental work by kavanagh et al kavanagh j l menand t and sparks r s j 2006 an experimental investigation of sill formation and propagation in layered elastic media earth planet sci lett 245 799 813 shows that lithological discontinuities and rigidity contrasts can control the formation and dynamics of sills at interfaces separating upper rigid strata from lower weaker strata the present paper extends this work and focuses on its implications in terms of the length and time scales associated with the development of laccoliths and other igneous complexes sill formation controlled by rigidity contrasts is shown to provide a growth mechanism for laccoliths the formation of a sill provides favourable rigidity anisotropy for the emplacement of subsequent sills so that laccoliths grow by over accretion under accretion or even mid accretion of successive sills in accord with field data this model predicts that laccoliths grow mainly by vertical expansion representing the cumulative thickness of their internal sills while maintaining a comparatively constant lateral extend the model also predicts that the time scale over which laccoliths form is essentially determined by the cumulative time between successive sill intrusions also sill dynamics are controlled by viscous dissipation of the fluid along their length which have consequences for the size and shape of sills viscously controlled dynamics would enable sills to propagate further and thus to grow thicker than dykes of similar magmas these dynamics would also enable sills to propagate faster and thus to induce non elastic deformations in surrounding rocks that could deviate them from the interface they originally follow this would allow them to feed new sills along other interfaces and could assist in the formation of the step structures and saucer shapes that are commonly observed in sill complexes

first indications of the formation of kerogen amorphous fractions by selective preservation role of non hydrolysable macromolecular constituents of eubacterial cell walls abstract two marine kerogens supposed to contain an important bacterial component were analysed and their spectroscopic and pyrolytic features compared with those of the amorphous non hydrolysable macromolecular materials bacterans isolated from extent bacteria examination by transmissio electron microscopy revealed that dontrien lower toarcian shales paris basin is essentially composed of amorphous organic matter and osb3 marl slate formation n e england is exclusively amorphous the formation upon kerogen pyrolysis of series of products 3 methylalkanes dimethylalkanes ethylesters and alcohols characteristic of bacteran pyrolysates is consistent with the contribution of bacterans to the formation of these two kerogens the nature and distribution of the acids of the pyrolysates indicate that bacterial biomass was implicated in osb3 and dontrien kerogen formation via two pathways bacteran selective preservation and incorporation of partly degraded lipids comparison between dontrien and osb3 indicates a weaker contribution of the selective preservation pathway to osb3 kerogen whereas bacteria lipid incorporation may have been more significant in osb3 kerogen the selective preservation pathway was so far considered as restricted to the formation of kerogens having retained some of the morphological features of the source organisms an important point derived from this study is therefore the ability of this pathway to also contribute to the formation of amorphous kerogens

foraminiferal and nannofossil paleoecology and paleoceanography of the cenomanian turonian eagle ford shale of southern texas article i nfo the uppercretaceous of central texas isdominated by a broad shallow carbonate platformcalled thecomanche platform that occupies an important gateway between the epeiric western interior seaway wis of north america to the open marine gulf of mexico tethys we investigated the cenomanian turonian eagle ford shale on and adjacent to the comanche platform to determine whether the eagle ford shale has an affinity with the western interior and if so determine where the transition from western interior to open ocean is located we were also interested in the relationship if any between the organic rich facies of the eagle ford and oceanic anoxic event 2 oae2 our work is based on quantitative foraminiferal population counts and associated sedimentary particles including inoceramid prisms sand glauconite and pyrite grains calcareous nannofossil assemblages carbon isotopes and total organic carbon toc from three sites across a range of paleowater depths an outcrop in lozier canyon in terrell county west of langtry tx an outcrop at bouldin creek outside of austin tx and swift energy s fasken a 1h core in webb county tx the highest toc intheeagle ford occurs beforethe onset of oae2 6 at loziercanyon 7 atboth bouldincreek and the fasken core and then declines steadily through the rest of the section except for a small increase at the end of oae2 at lozier and a fairly large post oae2 increase at bouldin creek nannofossil paleoproductivity indicators zeugrhabdotusand biscutum track tocatbouldincreekandinthefaskencoreanddisplaysimilar trends to those observed inthe western interior seawayto the north benthic foraminiferalabundances increase astoc decreasesand the lithology shifts from laminatedblack shale to bioturbatedlight gray shale low oxygen tolerant infaunal neobulimina spp appear first and gradually increase in abundance epifaunal benthics appear soon after this oxygenation trend continues through the oae2 interval and the upper eagle ford contains a diverse epi and infaunal benthic foraminiferal assemblage and macrofossil assemblage this trend of decreasing toc and nannofossil paleoproductivity indicators coupled with increasing benthic foraminiferal abundance and diversity and seafloor oxygenation corresponds to rising sea level based on foraminiferal and nannofossil events toc trends and changes in lithology both platform sites have a strong affinity with the western interior with lozier canyon being the most similar the fasken core bears all the characteristics of an open ocean site except for the fact that peak toc occurs before oae2 this suggests that the oceanographic boundary between wis and tethys can be placed on the edge of the comanche platform productivity was likely driven by bathymetry induced upwelling caused by restriction between the wisand tethys during times of low sea level as sea level rose upwelling diminished and productivity decreased this explains why the fasken core adjacent to the platform margin and in the center of this upwelling zone displays the same toc trends as the platform sites organic carbon content in the seaway was controlled by stratification and enhanced preservation but this was also reduced by rising sea level which is why the two areas show parallel trends

deflection and propagation of fluid driven fractures at frictional bedding interfaces a numerical investigation propagation of fluid driven or hydraulic fractures deflected at bedding interfaces in layered sedimentary rocks and subsequent fluid invasion is investigated numerically using a two dimensional boundary element model the fracture is driven by an incompressible newtonian fluid injected at a constant rate the frictional stress on the interface is assumed to obey coulomb s frictional law without cohesion the bedding interface can be given a non zero minimum fluid conductivity a numerical scheme that deals with both rock deformation and fluid flow is presented and its accuracy is verified in terms of comparisons with existing results to explore the mechanisms involved in fluid and fracture invasion into the interface parametric studies are carried out for different elastic modulus contrasts in situ stresses interfacial frictional coefficients distances from the injection point to the interface and fluid viscosities the results are provided as time dependent variations of displacements fluid pressures contact stresses and fluid fronts fracture deflection and fluid invasion into the interface are found to rely essentially on local stress and deformation states at the intersection point fluid invasion and fracture growth may be delayed or inhibited when the interface is subjected to large confining stress or when fluid viscosity is relatively low for cases where the fluid driven fracture originates in the softer layer in this case a greater layer parallel tensile stress is produced and can lead to fracture propagation through the bedding contact low to medium frictional strength is found to promote fluid penetration and t shaped fracture formation by interfacial opening if the hydraulic fracture originates in a stiffer layer fluid invasion into bedding contacts can occur smoothly without the occurrence of interface closure and the fracture is thus terminated by forming a t shaped fracture at the bedding interface for fracture deflection into and growth along the interface in the absence of interface closure the long time responses resemble the solution for a fluid driven fracture growing along a frictionless interface with vanishing toughness

modeling the growth of laccoliths and large mafic sills role of magma body forces 1 the use of elastic plate theory to model the emplacement of laccoliths and large mafic sills has been debated for nearly 40 years these intrusions typically attain a horizontal width that is large relative to the emplacement depth provided that large scale plasticity and or heterogeneity is not observed in the overlying host rock it should then be valid to approximate its deformation based on analysis of a thin elastic plate with effective properties that are the consequence of interaction among heterogeneities that are small relative to the size of the intrusion but the predictions that are usually cited from elastic plate theory are characterized by bell shaped geometry in contrast to the flat topped steep sided geometry typical of many laccoliths or the nearly uniform thickness typical of large mafic sills this fact has motivated several alternate explanations of laccolith and large mafic sill emplacement nonetheless elastic plate theory should be revisited in light of the fact that previous elastic plate based predictions have in general not taken into account an appropriate fracture propagation condition fluid flow in the growing intrusion and importantly the influence of the weight of the magma on intrusion growth we present a model for the growth of circular intrusions that accounts for all of these factors the model predicts the appropriate geometry for both laccoliths and large mafic sills the predicted thickness to length relationships are also consistent with field data hence while it may sometimes be appropriate there is in general no fundamental need to appeal to large scale rock plasticity in order to explain observed intrusion geometries and it may in fact be appropriate to understand the growth of laccoliths and large sills in light of a single underlying mechanical model

comparative 14c and osl dating of loess paleosol sequences to evaluate post depositional contamination of n alkane biomarkers there is an ongoing controversial discussion as to whether n alkane lipid biomarkers and organic matter of loess in general reflect a synsedimentary paleoenvironmental climate signal or whether they are significantly affected by postdepositional contamination for example related to root and rhizomicrobial activity in order to address this issue at our study site the middle to late weichselian loess paleosol sequence gleina in saxony germany we determined and compared radiocarbon ages of bulk n alkanes and sedimentation ages as assessed by optically stimulated luminescence osl dating the bulk n alkanes of the four dated samples yielded calibrated 14c ages ranging from 24 1 to 49 7 cal ka bp 95 4 probability ranges while the three uppermost n alkane samples are well within the range or even slightly older than the osl inferred sedimentation ages the lowermost n alkane sample is slightly younger than the osl ages there is hence little or no evidence at our study site for n alkanes in loess paleosol sequences being significantly contaminated by deep subsoil rooting or microbial processes we propose a 14c isotope mass balance calculation for estimating such contaminations quantitatively radiocarbon dating of bulk n alkanes might have great potential for quaternary research and we encourage further comparative 14c and osl studies

mechanics of two interacting magma driven fractures a numerical study to understand magma focusing from broad melting zones in the crust propagation in brittle rocks of two interacting dikes ascending from a single deep source has been modeled using a time dependent plane strain hydraulic fracturing model the source is assumed to generate a constant influx rate to feed the dike growth which is also aided by buoyancy effects in contrast to uncoupled model results the simultaneous parallel growth of two dikes to a certain distance is found to occur provided that the two dikes are initially of different heights which might be produced either by previous magma intrusion or during nucleation the shorter dike will chase the longer one and they can either progressively merge or continue subparallel growth at a reduced spacing depending on the deviator stress between the vertical and horizontal stresses and the initial lateral separation with parameters given in dimensionless forms numerical results reveal the mechanics for simultaneous ascents of two subparallel dikes in that dike interaction can produce a low stress field which is just above the tip of the shorter dike favorable to growth of the shorter dike the energy analysis indicates that the energy required for two subparallel dikes is less than that for a single dike during the late time buoyancy viscosity propagation stage where considerable ascent occurs this growth behavior might provide the mechanism for simultaneous instead of sequential growth of various dikes in a single set

fracture mode analysis and related surface deformation during dyke intrusion results from 2d experimental modelling surface deformation analysis in volcanic edifices in response to shallow magma intrusion is crucial for assessing volcanic hazards in this paper we discuss the effect of dyke propagation mode on surface deformation through 2d laboratory models our experimental setup consists of a hele shaw cell in which a model magma is injected into a cohesive model crust using an optical image correlation technique particle imaging velocimetry we measured the surface deformation the displacements and the strain field induced by magma emplacement within the country rock we identify two types of intrusion morphologies types a and b which exhibit two evolutional stages during the first stage both types resulted in a vertical dyke at depth its propagation was controlled by both shear deformation and tensile opening the model surface lifted up to form a smooth symmetrical dome resulting in tensile cracks during the second stage types a and b experiments differ when the dyke reaches a critical depth in type a the intrusion gradually rotates forming an inclined sheet dipping between 451 and 651 this rotation results in asymmetrical surface uplift and shear failure upon the tip of the dyke in type b the dyke tip interacts with tensile cracks formed during the first stage this fracture controls the subsequent propagation of the dyke toward the surface in both types of experiments intrusions result in surface uplift which can be accommodated by reverse faults our study suggests that dykes propagate as viscous indenters rather than linear elastic fracturing

dykes cups saucers and sills analogue experiments on magma intrusion into brittle rocks magma is transported in the crust by blade like intrusions such as dykes sills saucers and also collects in thicker laccoliths lopoliths and plutons recently the importance and great number o

the cenomanian turonian eagle ford group of south texas insights on timing and paleoceanographic conditions from geochemistry and micropaleontologic analyses abstract the interbedded organic rich marls and limestones of the eagle ford group of south texas were deposited on the shelf of the central texas platform during the upper cenomanian through the turonian micropaleontological analyses of thin sections and residue samples from subsurface cores taken in atascosa and karnes counties yielded 13 biostratigraphic datums which were integrated with calcareous nannofossil datums stable carbon isotopic and bulk inorganic geochemical analysis to gain an understanding of the paleoceanographic conditions of the study area and their relationship to regional and global events the paired thin section residue sampling was necessitated by poor recovery of planktonic foraminifera in washed samples which were however abundant in most thin sections lower eagle ford marls were deposited under euxinic conditions produced by a stratified water column periodic enhanced water column mixing increased oxygen levels and surface water primary productivity which promoted calcite diagenesis and generation of limestones containing calcispheres and radiolaria an oxygenated bottom water mass entered the basin in the uppermost cenomanian prior to the onset of oceanic anoxic event oae 2 causing a spike in benthic foraminiferal diversity and decreasing preservation of organic matter although the lower portion of the upper eagle ford is age equivalent to oae2 as indicated by positive shift in 13corg it contains less organic matter and evidence of more oxygen than the lower eagle ford so deposition of the eagle ford black shales is not contemporaneous to oae2

a constant influx model for dike propagation implications for magma reservoir dynamics 1 most observations of seismicity rate during dike propagation on basaltic volcanoes show 1 rate stationarity despite possible variations of the dike tip velocity 2 frequent lack of clear and monotonic hypocenter migration following dike propagation and 3 event occurrences located backward with respect to the dike tip position on these bases the origin of the seismicity contemporary to dike intrusion within basaltic volcanoes cannot be solely related to the crack tip propagation seismicity rather appears to be the response of the edifice itself to the volumetric deformation induced by the magma intruding the solid matrix the volume change induced into the volcano edifice over time by the intruding magma is equal to the magma flux injected into the dike from the reservoir the consequence of this is that the stationary seismicity rate observed during the intrusion is a proxy for the magma flux withdrawn from the reservoir we consider a two phase dike propagation model including a first vertical propagation followed by a lateral migration along a lithological discontinuity we explore 1 under which geophysical conditions the vertical dike is fed at constant flow rate of magma and 2 dike propagation patterns implications entailed by constant volumetric flux on the piton de la fournaise volcano case study suggest a minimum size for the magma reservoir of about 1 km3 and a maximum value for the initial magma reservoir overpressure of about 2 2 mpa considering similar magma inflow rates during vertical and lateral dike propagation phases we reproduce independent estimates of propagation velocities rise times and injected volumes when applying the model to the august 2003 piton de la fournaise eruption

fluid driven multiple fracture growth from a permeable bedding plane intersected by an ascending hydraulic fracture 1 in bedded sedimentary rocks the energy for spontaneous growth of multiple vertical fractures from a bedding plane may be provided by an overpressurized sublayer fracture that connects a fluid source to the bedding plane in this paper using our coupled deformation and flow model we study the processes and mechanisms involved in the formation and interaction of closely space fractures from preexisting flaws or starter fractures located along the bedding plane fracture growth from multiple flaws can be convergent parallel or divergent depending on the factors like contrasts in moduli and far field stresses flaw sizes and locations and initial bed conductivity fluid viscosity and injection rate as well as time the results presented here have been obtained for conditions where fluid viscous dissipation is dominant in contrast to other results available in literature based on uniform pressure assumption equivalent to use of an inviscid fluid it is demonstrated that the earlier a hydraulic fracture starts to extend the more likely it is to become the primary fracture in a system of closely spaced fractures the fracture closest to the fluid source typically grows faster as a result of a higher pressure level because viscous dissipation results in a decrease in pressure with distance from the fluid source but its development does not completely inhibit the growth of other hydraulic fractures simultaneous growth of closely spaced fractures is supported by the local stress and energetic analyses and the fracture distance can be very small their length to spacing ratio is accordingly much larger than that predicted previously under certain circumstances a longer and more permeable fracture may grow to a greater extent than a shorter fracture closer to the fluid source which may grow toward and merge with the longer fracture to create fracture clusters adjacent to a bedding plane

analytical predictions for a natural spacing within dyke swarms dykes often grow next to other dykes evidenced by the widespread occurrence of dyke swarms that comprise many closely spaced dykes in giant dyke swarms dykes are observed to maintain a finite spacing from their neighbors that is tens to hundreds of times smaller than their length to date mechanical models have not been able to clarify whether there exists an optimum or natural spacing between the dykes and yet the existence of a natural spacing is at the heart of why dykes grow in swarms in the first place here we present and examine a mechanical model for the horizontal propagation of multiple closely spaced blade like dykes in order to find energetically optimal dyke spacings associated with both constant pressure and constant influx magma sources we show that the constant pressure source leads to an optimal spacing that is equal to the height of the blade like dykes we also show that the constant influx source leads to two candidates for an optimal spacing one which is expected to be around 0 3 times the dyke height and the other which is expected to be around 2 5 times the dyke height comparison with measurements from dyke swarms in iceland and canada lends initial support to our predictions and we conclude that dyke swarms are indeed expected to have a natural spacing between first generation dykes and that this spacing scales with and is on the order of the height of the blade like dykes that comprise the swarm

numerical modelling of dyke interaction and its influence on oceanic crust formation abstract dykes are an essential element in building oceanic crust most prominent in sheeted dyke complexes in the upper crust since dykes alter the magnitude and orientation of the local stress field they cannot be treated as passive infillings of extensional fractures we use a quasi static iterative 2 d boundary element method allowing for a wholesale movement of fluid filled fractures effects of stress and pressure gradients buoyancy and enclosed fluid mass are considered the implications of the dyke induced stress field are analysed combining the simulation of fracture propagation with computation of dyke interaction dyke interaction occurs by the adaptation of ascending dykes to the stress field caused by previous fractures arrested in the crust and leads to focussing and crossing of dykes examples for applications are introduced concerning e g the generation of a magma chamber and the formation of the sheeted dyke complex our main results are that the interaction between dykes can be considerable and that the most important controlling factor is stress the interaction is small when the horizontal tensional stress is large compared to the pressure in the dyke head otherwise dykes tend to attract each other and to form centres of high dyke density or sill layers

evidence from magnetic fabric for the flow pattern of magma in the mackenzie giant radiating dyke swarm continental flood basalts and their associated swarms of mafic dykes are thought to result from melting in mantle plumes1 3 but the processes by which the resulting magma makes its way from mantle to crust remain obscure here we use magnetic anisotropy measurements to reconstruct the pattern of magma flow in the proterozoic mackenzie dyke swarm our results indicate that magma was injected vertically within 500 km of the focal point of the dyke swarm and then travelled horizontally at all further distances out to at least 2 100 km the sharp transition from vertical to horizontal flow at between 500 and 600 km may correspond to the outer boundary of melt generation in the mantle plume believed to be responsible for the mackenzie igneous events

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

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

effects of the crustal stress on the growth of dikes conditions of intrusion and extrusion of magma dike growth is analyzed on the basis of the fluid dynamical behavior of incompressible newtonian magma in a spatially uniform fissure of temporally variable width the length and width of the dike vary with the magma pressure at the dike entrance connected to the magma chamber and with the mean stress working normal to the dike walls the mean stress consists of the regional crustal stress and the mean elastic stress which is approximately evaluated using an analytic solution of the crack with a constant aperture the length and width of the dike are determined as a function of time by simple ordinary differential equations the dike can grow when the initial pressure of the entering magma is above the lithostatic pressure and high enough to suppress compression of the crustal stress the assumed size of the initial crack affects the growth only in the duration needed for an initial adjustment stage after this stage the width and length first grow exponentially and then the growth slows as magma is released from the chamber the growth in the later stage is classified into two types when the initial magma pressure is high enough the dike elongates unlimitedly while the width finally decreases this extrusive growth is likely to lead to eruptions the other intrusive growth in which the dike finally stops its growth with a finite length and width occurs when the crustal stress component normal to the fissure is of sufficiently strong extension buoyancy of magma is not very effective in the earlier growth stage but it shifts the marginal condition separating the extrusive and intrusive growths the extrusive and intrusive events that recently happened in izu oshima volcano and izu tobu volcano group japan are interpreted as the examples of these two growth types

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

dyke nucleation and early growth from pressurized magma chambers insights from analogue models abstract nucleation and dyke growth from magma chambers are important yet poorly understood aspects of magma transport in the lithosphere to tackle this issue we conducted qualitative experiments using gelatin and silicone to simulate respectively country rock and magma in our experiments the pressurization of the magma filled reservoir was the main cause of dyke formation rather than the density difference between magma and country rock our results show that an overpressurized magma chamber leads to almost simultaneous nucleation of dykes in different parts of the reservoir especially at places with large angular irregularities where local perturbation of elastic stress occurs early propagation of the leading edge of a dyke results in arc shape tabular intrusions that are controlled by the stresses surrounding the overpressurized magma chamber the overall process of early dyke formation reveals three stages 1 very rapid increase of the fracture length at constant width 2 slow down and probably arrest of the intrusion front and 3 thickening of the intrusion with an almost stationary intrusion front these stages suggest that dyke propagation to the surface occurs through several steps separated by the time needed for the renewal of magma pressure in the reservoir in consequence our experiments suggest that overpressurization of a magma chamber is a necessary condition that must be met to explain why some magmas can reach the surface even when the reservoir is located in a region close to the neutral buoyancy level but that the distribution of such overpressure is a dynamic variable that requires further examination

rupture history of the january 1 1996 ms 6 6 volcanic earthquake preceding the simultaneous eruption of karymsky and akademia nauk volcanoes in kamchatka russia the intensive foreshock mainshock aftershock sequence of earthquakes preceded and accompanied the january 2 1996 simultaneous eruption of the active karymsky and the dormant akademia nauk volcanoes in kamchatka russia the finite fault broad band teleseismic p waveform inversion was applied to the ms 6 6 mainshock of this sequence which occurred on january 1 1996 about 14 hours before the beginning of eruption it was one of the strongest volcano tectonic earthquakes in this century after the 1912 1914 great ms 7 0 volcanic earthquakes related to the katmai alaska and sakurajima japan volcanic eruptions the main feature of the rupture process inferred from the inversion was the breaking of a sequence of four asperities with displacement greater than 200 cm which were situated at depths from 0 to 35 km just beneath the akademia nauk volcano there were no broken asperities beneath the karymsky volcano the majority of small earthquake foci were located out of maximum asperities and filled a space between two zones of asperities at depths from 12 to 20 km the position of broken asperities allows us to suggest that during the large earthquake rupturing an ancient magmatic column beneath the volcano was destroyed small earthquakes which were recorded mainly from 5 to 20 km depth were able only to destroy the intermediate depth part of this column between 12 and 20 km the main work for opening a way to move magma to the surface was made by a large shock which had broken the upper and deep parts of the ancient magma column

surface area control of organic carbon accumulation in continental shelf sediments the relationship between organic carbon oc and grain size found in most continental shelf sediments is here reinterpreted in terms of the surface area of the sediments cores from many north american shelf environments show downcore decreases in oc to similar refractory background concentrations if expressed relative to the surface area of the sediments this consistent concentration is 0 86 mg oc m 2 which is equivalent in concentration to a monolayer of organic matter coating all mineral surfaces a more global collection of sediment water interface samples show that this relationship is even more extensive with exceptions occurring in areas of very high riverine sediment input organic pollution or low oxygen water columns density separations indicate that organic matter is largely adsorbed to mineral grains the microtopography of surfaces was examined with n2 sorption and most surface area was found to be inside pores of 10 nm width these data lead to a hypothesis that organic matter is protected by its location inside pores too small to allow functioning of the hydrolytic enzymes necessary for organic matter decay such protection would likely work in concert with other protection mechanisms such as humification this consistent surface area correlation with oc concentration may explain control of spatial and temporal variations in oc burial rates by sedimentation rates the pore protection hypothesis provides a causal mechanism for this observed control

buoyancy driven crack propagation from an over pressured source the propagation of a liquid filled crack from an over pressured source into a semi infinite uniform elastic solid is studied the fluid is lighter than the solid and propagates due to its buoyancy and to the source over pressure the role of this over pressure at early and late times is considered and it is found that the combination of buoyancy and over pressure leads to significantly different behaviour from buoyancy or over pressure alone lubrication theory is used to describe the flow where the pressure in the fluid is determined by the elastic deformation of the solid due to the presence of the crack numerical results for the evolution of the crack shape and speed are obtained the crack grows exponentially at early times but at later times when buoyancy becomes important the crack growth accelerates towards a finite time blow up these results are explained by asymptotic similarity solutions for early and late times the predictions of these solutions are in close agreement with the full numerical results a different case of crack geometry is also considered in order to highlight connections with previous work the geological application to magma filled cracks in the earth s crust or dykes is discussed