geoforschungszentrum anomaly magnetic map gamma a candidate model for the world digital magnetic anomaly map the world digital magnetic anomaly map wdmam is an ongoing effort toward the mapping of worldwide available aeromagnetic data it is led by a task force of the international association for geomagnetism and aeronomy iaga and aims at distributing a global map in printed and digital forms in this paper we describe in detail our candidate model which has to be evaluated by the iaga task force together with five other candidate maps after discussing the quality of the available data we show a simple but effective method applied to successfully process reduce and merge together individual compilations the near surface data are corrected using global field models and further refined with two dimensional polynomial corrections after the upward continuation to 5 km altitude data are resampled to a 3 minute grid and merged together we then calculate a spherical harmonic model up to degree 199 and analyze the magnetic spectrum of the global map this helps us to confirm that wavelengths larger than 400 km are spurious at a global scale in aeromagnetic compilations therefore we substitute them using a satellite based lithospheric field model mf5 to degree 100 finally our proposed candidate map for wdmam is presented

development and flow structures of sand injectites the hind sandstone member injectite complex carboniferous uk abstract the hind sandstone member of the carboniferous craven basin occurs within a thick succession of marine mudstone and is here interpreted as a sandstone injectite complex injectites take the form of i sills ii upwards emplaced dykes iii downwards emplaced dykes iv a sedimentary laccolith and v sandstone bodies remobilised in situ the remobilised and injected sand originated from small turbidite scour fills and potentially a more significant sand body such as a submarine slope gully fill the sedimentary laccolith appears to jack up the units it injects and is filled by sandstone with a chaotic fabric suggestive of brecciation of partly cemented sand the laccolith and sill dominated nature are suggestive of relatively shallow remobilisation sills are commonly laterally gradational with upwards emplaced dykes and in some cases these feed apparently downwards emplaced dykes a series of flow structures are preserved within some of the injectites and these provide clues to the emplacement history crack propagation direction is inferred from the orientation of undulating crests developed on the upper and lower surfaces of injectites peak flow is indicated by scour marks resembling flute and tool marks which are superimposed onto these undulating surfaces internal flow structures highlighted by pyrite mineralistion record the waning stage of injection the observed flow structures suggest that the apparent crack propagation direction was generally oblique to the peak flow and nearly perpendicular to the direction of late stage fluidised sediment flow crack propagation relates to the local stress field whilst injection flow may be related to the local pore pressure distribution recognition of this suite of structures may provide a useful interpretational tool for other injectites in both core and outcrop pore fluid overpressure which drove injection developed through the migration of petroleum and mineralising fluids from the underlying bowland shales and older limestones a complex brecciated fracture network within the mudstones underlying the injectites records fluid migration pathways sliced blocks and thin sections from injectites reveal flow structures defined by iron pyrite mineralisation the trigger is here related to growth of compressional structures and associated syn sedimentary slumps which occur at the same stratigraphic level as the injectites

clastic intrusions in deep sea fan deposits of the rosroe formation lower ordovician western ireland abstract the rosroe formation contains discordant elastic intrusions and essentially stratiform clastic intrusions up to 40 cm thick that display little evidence of injection features of the elastic intrusions such as upper surface irregularities and tapered lateral margins also occur in wedged clastic layers up to 30 cm thick in the rosroe formation and suggest they may be injected sheets a few of the mostly granule grade injected sheets in the rosroe formation contain banding that is remarkably similar to the banding in the formation s stratified pebbly sandstone together with the existence of essentially stratiform injected sheets the banding suggests that some elastic sills in deep sea fan deposits may be indistinguishable from normally deposited beds contactual features sharp upper contacts upper surface irregularities truncation of superjacent strata upper surface inclusions nesting and blunt steep and tapered lateral margins and internal characters lenticular breccia and trains of aligned laminite clasts of the elastic intrusions in the rosroe formation provide tentative criteria for the identification of clastic sills that simulate normally dep sited beds in deep sea fan deposits

petrofacies of eocene sand injectites of the tumey giant injection complex california usa abstract the forearc succession of great valley group in central california provides some of the best examples of giant sand injection complexes in the world and is therefore considered valuable analogues for injectite systems in the subsurface several sand injection complexes are well described in the outcrop and subsurface however the petrographic characteristics of injectites are still poorly documented in this paper we present the results of an integrated study of field observations quantitative and qualitative sandstone petrography provenance and petrofacies analysis of the tumey giant injection complex tgic in order to understand its lithostratigraphy and petrological evolution and its impacts on reservoir petrofacies characteristics and fluid migration the tgic intrudes into a 450 m thick deep water succession of slope mudrocks and sandy channel fills of the kreyenhagen shale eocene forming an interconnected network of sandstone sills dykes and injection breccias the complex generated a horizontal and vertical plumbing system for fluid migration connecting isolated sandy channel fills among low permeability mudrocks the primary detrital composition diagenetic products microtextures and provenance signatures allowed for the definition and discrimination of depositional and intrusive petrofacies and their genetic relations petrofacies associations confirm that the gypsum cemented feldspathic litharenites from the kreyenhagen shale channel fills are the only source for the injection complex eodiagenetic compaction and extensive gypsum cementation reduced the primary porosity of the complex while telodiagenetic dissolution of autigenic constituents formed pervasive secondary porosity the underlying calcite cemented arkosic sandstones of the lodo and domengine formations acted as barriers for fluid flow aiding lateral fluid migration and overpressure buildup within the overlying kreyenhagen channel fills intense grain microfracturing occurred during sand remobilization and injection along with erosion of the host mudrocks this study has significance for the generation of reliable stratigraphic and petrological models for sand injection complex genesis and evolution that consequently can help the understanding and exploration of injectite complexes elsewhere

the transformation of sediment into rock insights from iodp site u1352 canterbury basin new zealand abstract at integrated ocean drilling program iodp expedition 317 site u1352 east of the south island new zealand we continuously cored a 1927 m thick holocene to eocene section where we can uniquely document downhole changes in induration and lithification in siliciclastic to calcareous fine grained sediment using a wide range of petrological physical property and geochemical data sets porosity decreases from around 50 at the surface to 5 10 at the base of the deepest hole with a corresponding increase in density from 2 to 2 5 g cm 3 there are progressive bulk mineral changes with depth including an increase in carbonate and decrease in quartz and clay content grain compaction is first seen in thin section at 347 m below sea floor and intensifies downhole pressure solution chemical compaction begins at 380 m and is common below 1440 m with stylolite development below 1600 m and sediment injection features below 1680 m porewater geochemistry and petrographic observations document two active zones of cementation one shallow eogenetic down to 50 m as evidenced by micritic nodules and pore water geochemistry driven by methane oxidation by sulfate and another burial related cementation zone mesogenetic starting at 300 m a transitional zone occurs between 50 and 300 m our results quantify downhole diagenetic changes and verify depth estimates for these processes inferred from outcrop studies and provide an actualistic example of cementation and compaction trends in a slope setting

the geometry and emplacement of conical sandstone intrusions conical sandstone intrusions with a geometry comparable with that of many igneous sills have been identified using 3d seismic data from large areas of the north sea and faeroe shetland basins these intrusions are of reservoir scale ranging from 100 to 2000 m or so in diameter 50 300 m in height and 1 80 m in thickness aperture they are concentrated in specific stratigraphic intervals in the cenozoic fills of both basins two geometrical end members are recognised and defined here apical cones and flat based bowls the former consist of inward dipping conical inclined sheets meeting at a prominent apex and the latter of similarly dipping discordant margins climbing from the edges of a concordant sheet both end members are associated with domal folds that are interpreted as resulting from the hydraulic elevation of the overburden during intrusion and which are analogous to similar structures associated with bowl shaped igneous sills measurements of aperture versus distance exhibit systematic relationships with the structural relief of these folds offering a potentially predictive method for estimation of sandstone intrusion aperture and reservoir volume prior to drilling a growth model for these end member geometries is presented drawing on existing theory for igneous sill emplacement aperture versus distance plots x are used to illustrate two contrasting models for aperture inflation during propagation but these require much further data before any specific growth model can be adopted

physical modelling of sand injectites abstract sand injectites are structures that result from intrusion of fluidized sand into fractures we have studied them in the tampen spur area of the north sea and have reproduced them experimentally by driving compressed air through layers of sand glass microspheres and silica powder the silica powder was cohesive and capable of hydraulic fracturing whereas the sand and glass microspheres were almost non cohesive and therefore able to fluidize the models were dynamically similar to their natural counterparts for as long as equilibrium was static when the processes became dynamic so that inertial forces were significant the scaling was approximate and the corresponding reynolds numbers differed the experimental apparatus was a square box 1 m 1 m wide resting on a grid of fluid diffusers during the experiments the fluid pressure increased until it attained and surpassed the weight of overburden flat lying hydraulic fractures containing air formed within cohesive and least permeable layers heterogeneities in material properties and layer thicknesses were responsible for localizing fracture networks when any one network broke through to the surface rapid flow of air through the fractures fluidized the underlying mobile materials and even depleted some of the layers some of the fluidized material extruded at the surface through vents forming volcanoes and sheets the remainder lodged at depth forming sand injectites or laccoliths conical sand injectites formed preferentially where layers had high resistance to bending laccoliths formed nearer the surface where overlying layers had low resistance to bending the experimental sand injectites were broadly similar to those in the tampen spur area of the north sea as well as other areas

the ordovician evolution of the south mayo trough western ireland the south mayo trough a broad synclinorium containing a 10 km sequence of early ordovician turbidites passing up into shallow water sandstones is interpreted as a forearc basin with an ophiolitic basement that formed a backstop to an accretionary prism on the northern edge of a north facing arc the arc collided with the laurentian margin in early llanvirn times to deform the dalradian supergroup rifted margin clastic sequence prior to the late llandovery sinistral transcurrent faulting transposed the connemara dalradian terrane to its present position on the outboard ocean ward side of the south mayo trough the south mayo trough was fed principally by arc and ophiolite derived elastics during the arenig with an increasing metamorphic component during the llanvirn the late ordovician transpressional docking of connemara provided the southerly source for high grade metamorphic clasts in the deny veeny formation

modeling relative frost weathering rates at geomorphic scales abstract frost damage is a powerful agent of geomorphic change cracks can grow when the ice pressure in pores reaches a threshold that depends on matrix properties and crack geometry mineral surfaces that are preferentially wetted by liquid water rather than ice are coated by premelted liquid at a pressure that is lower than the ice pressure because this pressure difference increases as the temperature cools when the ice pressure is effectively pinned at the cracking threshold temperature gradients induce gradients in liquid pressure that draw water towards colder temperatures porosity increases and frost damage accumulates in regions where water supplies crack growth to apply this understanding over the large spatial and temporal scales that are relevant to evolving landscapes we develop a simple model that tracks porosity changes our central assumption is that frost damage is correlated with porosity increases under conditions where frost cracking takes place accordingly we account for the permeability reductions with decreased temperature that accompany ice growth along porous pathways and derive general expressions for the porosity change through time at particular depths as well as the total porosity increase through all depths beneath a point at the ground surface over the time during which cracking occurs each year to illustrate the resulting patterns of frost weathering we consider a general case in which the permeability has a power law dependence on temperature and the annual surface temperature variation is sinusoidal we find that the degree of frost damage generally decreases with depth except at localized depths where damage is elevated because the rock spends longer times near the threshold for cracking leading to enhanced water supply in comparison with neighboring regions the magnitude of the net expansion that results from porosity changes at all depths beneath the ground surface is increased for seasonal thermal cycles with larger amplitudes with a broad maximum centered on a mean annual temperature near the threshold required for crack growth warmer mean annual temperatures lead to less damage because of the reduction in time during which it is cold enough for cracking whereas colder mean annual temperatures are accompanied by reduced water supply due to the temperature dependence of permeability all of the controlling parameters in our model are tied explicitly to physical properties that can in principle be measured independently which suggests promise for informing geomorphic interpretations of the role of frost weathering in evolving landforms and determining erosion rates

bedrock fracture by ice segregation in cold regions the volumetric expansion of freezing pore water is widely assumed to be a major cause of rock fracture in cold humid regions data from experiments simulating natural freezing regimes indicate that bedrock fracture results instead from ice segregation fracture depth and timing are also numerically simulated by coupling heat and mass transfer with a fracture model the depth and geometry of fractures match those in arctic permafrost and ice age weathering profiles this agreement supports a conceptual model in which ice segregation in near surface permafrost leads progressively to rock fracture and heave whereas permafrost degradation leads episodically to melt of segregated ice and rock settlement

the formation of carbonate cements in the forth and balmoral fields northern north sea a case for biodegradation carbonate cementation and oil leakage during early burial

the process of sand injection internal structures and relationships with host strata yellowbank creek injectite complex california u s a abstract the yellowbank creek injectite complex ycic has excellent exposure of the external geometries and internal structures in a large scale sandstone injectite the ycic has an irregular geometry that can be defined neither as a sandstone dike nor as a sill substantial erosion occurred along the margins between the ycic sandstone and host mudstones that includes scoured basal margins and a scalloped upper margin that cuts up to 5 m into the overlying host mudstones erosion of host mudstone has incorporated significant volumes of mudstone clasts into sandstones at the margins of the injectite using microtextural data corrasion is identified as a typical process by which mudstone is eroded during sand injection corrasion occurs when particles of mudstone are either cut or broken from a cohesive bed as the result of high velocity turbulent flow of sand grains acting as tools corrasion together with scouring and the general erosion of the host mudstone imply high velocity turbulent flow conditions and confirm that the fluidized sand had a sufficiently low viscosity during sand injection to allow turbulence internal structures include laminae of more tightly packed sand grains than occur in the surrounding sandstones and are interpreted to have formed by flow and deposition of injecting sands during waning of flow thus reflecting an overall reduction of pore fluid pressure deformation of laminae into folds defines bands which are aligned parallel to the margins of the sandstone the force driving deformation is likely to have been shear stresses induced between the injected sandstone and the more rigid host mudstone the principal style of deformation is hydroplastic oversteepened laminae and pipes are interpreted to have formed due to post sand injection consolidation and resulted in only minor mobilization of sand

intrusive and extrusive micro melange couplets as distal effects of tidal pumping by a marine ice sheet microscopic soft sediment deformation structures in a 30 x 25 x 12 mm hand specimen of glaciogenic silty mudstone from the permo carboniferous dwyka formation of northern natal in south africa are illustrated by serial sections the processes these structures imply are interpreted using palinspastically restored sections and isopachytes reconstructed from them the sedimentation of silts muds and microrhythmites is found to have been punctuated by episodes of hydraulic activity which resulted in thirteen bodies with the mixed fabrics of micromelanges these are divisible into five melange types 1 subconcordant intrusive 2 disconcordant intrusive 3 subconcordant extrusive 4 near surface with asymmetric internal structures and 5 conformable near surface with internal structures symmetric about the palaeovertical remarkable similarities between isopachs for pairs of micromelanges at different levels in the specimen suggest that intrusive melanges at depth fed contemporaneous extrusive melanges on the sea floor each couplet of melanges with matched isopachs is linked by faults which are interpreted as having acted as hydraulic vents despite only parts of them being infilled by intrusive melange a significant proportion of the succession could consist of sediment recycled from depth by hydraulic extrusion repeated hydraulic intrusions along and extrusions from the same disturbed interface suggest that this interface acted as the distal leaking end of one of the hydraulic sills recently described by von brunn talbot 1986 pulses of pressurized water were transmitted through a prograding marine slope of quickclay by the tidal pumping of a marine ice sheet periodically grounding upslope the results of this analysis are extrapolated to processes operative in subduction complexes all four fabrics described from large scale hydraulic melanges in modern and ancient accretionary prisms are matched on a much smaller scale in our sample from a proglacial submarine slope dismember ment by faults is the only fabric element described from accretionary complexes which is missing from the micro analogues described here

ice growth in a spherical cavity of a porous medium we consider an idealized problem of a sphere of ice growing symmetrically in a spherical cavity within a porous rock in order to identify and quantify different physical mechanisms that can result in fracturing the rock we show that if the permeability of the rock is very small then high pressures can develop in the cavity as the water inside it expands on freezing however given typical permeabilities of most rocks the pressure is relieved by flow out of the cavity through the rock pores when ice fills the cavity there remains a microscopic film of water separating the ice from the rock owing to disjoining forces and these forces can stress the rock and have the potential to fracture it the elastic pressure in the rock depresses the freezing temperature which can limit the potential for fracturing this simple example reveals the important interactions between disjoining forces elasticity and fluid flow in determining the pressure exerted during freezing of water saturated cavities in rocks

clastic dykes of the devono carboniferous horton bluff formation nova scotia storm related structures in shallow lakes abstract clastic dykes are common in the late devonian to early carboniferous horton bluff formation of nova scotia where they occur in wave dominated shoreline deposits of lacustrine shoaling upward cycles the dykes typically less than 25 cm wide and 40 cm in vertical extent project downward into clayshale from broad loads at the base of elongate isolated lenses of hummocky cross stratified siltstone ptygmatic folding of the dykes reflects a shale siltstone compaction ratio of 2 3 times and maximum depth of dyke penetration prior to compaction was 1 m dyke orientation parallels the orientation of wave ripple crests and the elongation direction of the siltstone lenses dyke formation was penecontemporaneous with sedimentation dyke and load formation was probably initiated in shallow water during storms which promoted sediment failure through cyclic wave loading microseisms and rapid deposition of hcs bearing siltstone lenses reversed density gradient and uneven sediment loading from silt lenses probably promoted downward emplacement loads reflect ductile failure of surficial water rich mud whereas dykes reflect downward injection of silt following brittle failure of underlying more compacted mud the depositional slope provided a tensional stress that controlled the fracture direction orthogonal to the slope of the failed sediment

mechanisms and controls on the formation of sand intrusions sandstone intrusions are found in all sedimentary environments but have been reported most commonly from deep water settings they also appear to be more frequently developed in tectonically active settings where applied tectonic stresses facilitate development of high fluid pressures within the sediments a variety of mechanisms have been cited as triggers for clastic intrusions these include seismicity induced liquefaction application of tectonic stresses excess pore fluid pressures generated by deposition related processes and the influx of an overpressured fluid from deeper within the basin into a shallow sand body the formation of sandstone dykes and sills is investigated here by considering them as natural hydraulic fractures when the seal on an unconsolidated overpressured sand body fails the resulting steep hydraulic gradient may cause the sand to fluidize the fluidized slurry can then inject along pre existing or new fractures to form clastic intrusions the scale and the geometry of an intrusive complex is governed by the stress state depth and pre existing joints or faults within the sedimentary succession as well as the nature of the host sediments for the simplest tectonic setting where the maximum stress in a basin is vertical gravitational loading small irregular intrusions commonly result in the formation of sills at shallow depths within a few metres of the surface whereas at greater depth dykes and sills forming clastic intrusion networks are more typical a simple relationship is derived to calculate the maximum burial depth at which a dyke sill complex forms as a function of the source bed to sill height the bulk density of the surrounding sediments and the ratio of the vertical to horizontal effective stresses k 0 when applied to three examples of large scale dyke sill complexes developed within paleocene and eocene deep water reservoir sand bodies of the north sea maximum burial depths in a range of 375 to c 500 m 450 700 m and 550 850 m are estimated for intrusion of each of the three complexes

high resolution local magnetic field models for the martian south pole from mars global surveyor data we present two high resolution local models for the crustal magnetic field of the martian south polar region models sp130 and sp130m were derived from three component measurements made by mars global surveyor at nighttime and at low altitude 200 km the availability area for these data covers the annulus between latitudes 76 and 87 and contains a strongly magnetized region southern parts of terra sirenum adjacent to weakly magnetized terrains such as prometheus planum our localized field inversions take into account the region of data availability a finite spectral bandlimit spherical harmonic degree l 130 and the varying satellite altitude at each observation point we downward continue the local field solutions to a sphere of martian polar radius 3376 km while weakly magnetized areas in model sp130 contain inversion artifacts caused by strongly magnetized crust nearby these artifacts are largely avoided in model sp130m a mosaic of inversion results obtained by independently solving for the fields over individual subregions robust features of both models are magnetic stripes of alternating polarity in southern terra sirenum that end abruptly at the rim of prometheus planum an impact crater with a weak or undetectable magnetic field from a prominent and isolated dipole like magnetic feature close to australe montes we estimate a paleopole with a best fit location at longitude 207 and latitude 48 from the abruptly ending magnetic field stripes we estimate average magnetization values of up to 15 a m

sediment flow and deformation sfd layers evidence for intrastratal flow in laminated muddy sediments of the triassic osawa formation northeast japan abstract thin chaotic layers containing abundant intraformational mud clasts are found in the offshore laminated mudstone of the triassic osawa formation in northeast japan the geometry and internal structures of the layers are somewhat similar to those of slump slide or debris flow deposits however the layers have both upper and lower erosional contacts projections of host sediments and mud clasts with planed surfaces are identified beneath the upper contact of the layers closely packed sheet form or ellipsoidal mud clasts are embedded in a poorly sorted fine to coarse grained sandy matrix some mud clasts are tightly folded or show imbricated stacking internal layering structures are also well developed in the layers the above features strongly suggest soft sediment deformation as horizontal displacement of sand and mud under buried conditions here we term these layers sediment flow and deformation sfd layers deformation layers with similar attributes have been identified by some prior authors as in the case of flow of liquefied and or fluidized host sand and clastic sill intrusion however the sfd layers described herein have more complex structure indicating advanced deformation occurrence of the sfd layers is stratigraphically limited to the uppermost part of the osawa formation which is overlain by sand rich submarine fan deposits the fukkoshi formation it suggests that the stress field caused by differential loading of overlying deposits facilitated intrastratal flow and sill intrusions of sand the vertical confinement was also controlled by the anisotropy in physical properties such as tensile strength of laminated mud and or conditions of gentle slope

giant irregular pockmark craters in the palaeogene of the outer moray firth basin uk north sea a cluster of irregular pockmark craters of palaeogene age in block 15 18 in the outer moray firth uk north sea have been mapped on 3d seismic data with well control the craters range from 0 5 to 4 km in diameter between 50 and 200 m in depth and have been buried by tertiary subsidence and sedimentation to present day depths of between 1000 and 1400 m sub sea they are circular to elliptical in plan view and are located in a delta front and upper pro deltaic slope position on the dornoch delta the structures are confined to the top of the lower eocene balder formation and regional mapping across the moray firth basin shows they are restricted to an area of ca 15 15 km2 well data show that the craters are sand filled and have excavated an argillaceous and tuffaceous unit the crater filling sands are sealed by overlying mudstone units planar wing like features emanate from the margins of the craters well control indicates that these seismically identified wings consist of sandstone suggesting that the craters have been modified by an episode of sand remobilisation and injection the proposed mechanism for the formation of these structures is large scale fluid eruption probably shallow gas at the early eocene seafloor these craters are significantly larger in size than those typically observed on contemporary sea floors we argue that the gas is more likely to have been sourced from deeper jurassic or carboniferous sediments within the witch ground graben than from shallow biogenic origins these structures rank in scale alongside the largest known pockmarks and demonstrate that natural fluid and hydrocarbon seeps have a long ancestry in this basin

a theoretical model of the fracture of rock during freezing we present a mathematical model for the breakdown of porous rock by the growth of ice within cracks the model is founded upon well established principles of fracture mechanics and recent advances in soil physics ijong with the assumption that progressive crack growth results from water migrating to ice bodies in cracks much as water migrates to ice lenses in freezing soil our model predicts crack growth rates compatible with empirical data calculations for a granite and a marble indicate that sustained freezing is most effective in producing crack growth when temperatures range from 4 c to 15 c at higher temperatures thermodynamic limitations prevent ice pressure from building up sufficiently to produce significant crack growth at lower temperatures the migration of water necessary for sustaining crack growth is strongly inhibited in hydraulically open systems in which pore water pressure remains near atmospheric pressure during the freezing process crackgrowth rates during continuous cooling will generally be greatest at low rates of cooling less than 0 1 0 5 c h at higher rates of cooling the influx of water to growing cracks is significantly inhibited the model delineates clearly the role of material parameters elastic moduli fracture mechanical properties grain size and shape and crack size environmental conditions temperature temperature gradient water pressure and time in frost damage to rocks our calculations along with recent experimental work on water migration in freezing rocks fukuda 1983 lead us to question the widely accepted importance of two phenomena freezing of water in sealed cracks and freeze thaw cycling in the fracture of rock exposed to natural freezing conditions

fluidization and injection in the deep water sandstones of the eocene alba formation uk north sea the nauchlan member of the late eocene alba formation uk north sea consists of a deep water channel fill that was extensively modified by post depositional sand remobilization and injection sandstone textures facies associations and the geometry of the channel fill were affected a suite of sand rich facies was produced by large scale fluidization and injection within the channel fill and above it these facies termed here unstratified facies are characterized by the absence of stratification surfaces and by discordant relationships with bedding in the adjacent succession they reflect variable degrees of disruption of the primary sedimentary structures caused by escaping pore fluid the velocity of which is estimated at least in the order of 0 1 ms 1 adjacent mudstones were severely disrupted by hydraulic fracturing and fragments of fractured mudstone were incorporated into the fluidized sand average porosity was decreased in the sandstones affected by fluidization two main phases of sand injection are inferred to occur at different burial depths a shallow burial phase below 100 m produced thin dykes with ptygmatic folds the second phase occurred at the boundary between eocene and oligocene 300 m burial depth and resulted in large scale tabular wing like dykes that project from the edges of the channel fill the significant pore fluid overpressure which was required to hydraulically fracture the thick mudstone seal and to fluidize the large volume of sand was likely to be built up by static liquefaction of the source sand and was possibly enhanced by hydrocarbon gas influx

evidence of frost cracking inferred from acoustic emissions in a high alpine rock wall ice formation within rock is known to be an important driver of near surface frost weathering as well as of rock damage at the depth of several meters which may play a crucial role for the slow preconditioning of rock fall in steep permafrost areas this letter reports results from an experiment where acoustic emission monitoring was used to investigate rock damage in a high alpine rock wall induced by natural thermal cycling and freezing thawing the analysis of the large catalog of events obtained shows i robust power law distributions in the time and energy domains a footprint of rock micro fracturing activity induced by stresses arising from thermal variations and associated freezing thawing of rock ii an increase in ae activity under sub zero rock temperatures suggesting the importance of freezing induced stresses ae activity further increases in locations of the rock wall that are prone to receiving melt water these results suggest that the framework of further modeling studies theoretical and numerical should include damage elastic interaction and poro mechanics in order to describe freezing related stresses

earth s lithospheric magnetic field determined to spherical harmonic degree 90 from champ satellite measurements summary the champ magnetic field mission is providing highly reliable measurements from which the global lithospheric magnetic field can be determined in unprecedented resolution and accuracy using almost 5 yr of data we derive our fourth generation lithospheric field model termed mf4 which is expanded to spherical harmonic degree and order 90 after subtracting from the full magnetic field observations predicted fields from an internal field model up to degree 15 an external field model up to degree two and the predicted magnetic field signatures for the eight dominant ocean tidal constituents we fit and remove remaining external fields and polar electrojet signatures in a track by track scheme from a subset of least disturbed tracks we estimate the mf4 model by least squares damping ill determined coefficients by regularization the resulting mf4 model provides a good representation of the lithospheric field down to an altitude of about 50 km at lower latitudes with reduced accuracy in the polar regions crustal features come out significantly sharper than in previous models in particular bands of magnetic anomalies along subduction zones become visible by satellite for the first time

large scale liquefaction and fluidization in the cap chat melange quebec appalachians the cap chat melange crops out discontinuously for 200 km along the south shore of the st lawrence river in the gaspe peninsula it is located just south of logan s line the northern limit of the humber zone with the taconian foreland basin this melange is composed of dismembered rocks of the adjacent formations in particular the lower ordovician riviere ouelle and middle ordovician tourelle formations with lesser contributions by the middle ordovician des landes and the cambrian orignal formations blocks in the melange vary in size from a few centimetres to several kilometres with well preserved internal stratigraphy in the larger blocks the distribution of blocks is not uniform and the composition of the surrounding matrix changes with corresponding changes in block composition tectonic processes mostly extensional and compressional faulting are responsible for some of the chaotic aspects of the melange however the main mechanism was as follows i large scale liquefaction of the mudstone rich riviere ouelle formation ii sinking with consequent dismembering of the tourelle formation into this underlying weakened riviere ouelle formation and iii fluidization of the lowermost sand beds of the tourelle formation resulting in abundant sandstone sills and dikes in the riviere ouelle formation

the nature and significance of sand intrusions in a hydrocarbon rich fold and thrust belt eastern carpathians bend zone romania sand intrusions are commonly associated with hydrocarbon bearing clastic reservoirs and they can host a significant part of the reserves they modify the depositional sandbody architecture and can have an impact on the petroleum system elements their significance and complex architecture is difficult to assess in the subsurface due to limited resolution of seismic or core data outcrop analogues are key to better understand these complex reservoirs in the eastern carpathians bend zone the oligocene and lower miocene succession offer spectacular exposures of deep water siliciclastic rocks modified by remobilization and sand intrusion processes these rocks are also present in producing fields in this area sills can be as thick as the depositional sandstones c 4 m and sill dominated outcrops can provide a net gross net sandstone to shale ratio of about 35 50 we quantified their architecture in a study of the timing and mechanism of emplacement their relationship to regional tectonics and their impact on reservoir connectivity the intrusions are interpreted to be syn tectonic related to the major mid miocene compression in this part of the carpathian mountain belt the intrusions lead to a large increase in vertical and horizontal connectivity our results will help to improve reservoir characterization and production in these reservoirs

rapid tectonic exhumation detachment faulting and orogenic collapse in the caledonides of western ireland collision of the oceanic lough nafooey island arc with the passive margin of laurentia after 480 ma in western ireland resulted in the deformation magmatism and metamorphism of the grampian orogeny analogous to the modern taiwan and miocene new guinea orogens after f470 ma the metamorphosed laurentian margin sediments dalradian supergroup now exposed in connemara and north mayo were cooled rapidly 35 jc m y and exhumed to the surface we propose that this exhumation occurred mainly as a result of an oceanward collapse of the colliding arc southwards probably aided by subduction rollback into the new trench formed after subduction polarity reversal following collision the achill beg fault in particular along the southern edge of the north mayo dalradian terrane separates very low grade sedimentary rocks of the south mayo trough lough nafooey forearc and accreted sedimentary rocks of the clew bay complex from high grade dalradian meta sedimentary rocks suggesting that this was a major detachment structure in northern connemara the unconformity between the dalradian and the silurian cover probably represents an eroded major detachment surface with the renvyle bofin slide as a related but subordinate structure blocks of sheared mafic and ultramafic rocks in the dalradian immediately below this unconformity surface probably represent arc lower crustal and mantle rocks or fragments of a high level ophiolite sheet entrained along the detachment during exhumation orogenic collapse was accompanied in the south mayo trough by coarse clastic sedimentation derived mostly from the exhuming dalradian to the north and to a lesser extent from the lough nafooey arc to the south sediment flow in the south mayo trough was dominantly axial deepening toward the west volcanism associated with orogenic collapse rosroe and

fluid flow features in hydrocarbon plumbing systems what do they tell us about the basin evolution abstract fluid flow features such as sandstone intrusions mud volcano systems and pockmarks represent well known geological structures generated due to flow of fluids in the subsurface however the integration of fluid flow features in quantitative and qualitative basin analysis is still in its infancy this study presents a review and a qualitative integration of fluid flow features in basin analysis of the danish north sea area and of salt mini basins offshore angola based on results from six case studies focusing on the detection mapping and evaluation of features related to focused fluid flow in these areas in the study the diversity of seismically imaged fluid flow features in hydrocarbon plumbing systems is reviewed and their utility is demonstrated this is done by focusing on the aspects of fluid flow related features that can be integrated into basin analysis studies and how these may help us increase the understanding of basin evolution and to achieve the major goals of basin analysis such as understanding the depositional and tectonic context of the basin and the presence and extent of hydrocarbons particularly concerning the determination of fluid flow timing triggers sources and routes fluid flow features represent a major but underused tool in basin analysis

stratigraphy and geochronological constraints of the serra sul formation carajas basin amazonian craton brazil abstract the carajas basin amazonian craton hosts extensive neoarchean to paleoproterozoic sedimentary archives which are still poorly constrained regarding their depositional settings ages and type of basin in which they have been deposited in this study we performed detailed sedimentological investigations and u pb dating of detrital zircon in four drill cores intercepting the recently defined serra sul formation our data show that this formation corresponds to various shallow to deep subaqueous environments shallow water environments are characterized by local occurrences of microbially mediated structures while deep water environments are characterized by polymictic conglomerates resulting from the mixing of materials of different origins during downslope debris flow both sedimentary facies and common occurrence of syn sedimentary deformations attest for recurrent slope instabilities geochronological investigations allow to define a maximum depositional age of 2684 10 ma that is several tens million years younger than other neoarchean sedimentary units of the carajas basin major peaks in age distribution indicate that the serra sul formation derives from local sources that constitute the basement of the carajas basin the infilling of the carajas basin by local sources together with sedimentary facies and depositional environments attesting for slope instabilities suggest that the serra sul formation was deposited during an active extensional tectonic phase such neoarchean to early paleoproterozoic tectonic setting compares with those documented in many other cratons worldwide and suggests that it could correspond to the break up of one of the first documented supercontinent

the 2 1 ga old injectite network of the franceville basin gabon architecture origin and implications on manganese mineralization abstract detailed sedimentological investigations on numerous outcrops and drill core sections in the 2 1 ga old franceville basin gabon provide evidence for a large scale injectite network the injectites were formed by the injection of sands through a thickness of about 150 m of the fb1 member and now cover a minimum area of 70 km 2 corresponding to the bangombe plateau but are also recognized close to franceville 35 km farther south east the injectite lithology corresponds to a mud or carbonate supported sandstone characterized by a loose and uncompacted fabric contrasting with the host rock because the injectites are often parallel to subparallel to the stratification they were misinterpreted as depositional beds by previous authors at outcrop the injectite bodies exhibit sill dyke wing and protrusive geometries emplaced during early burial within poorly compacted material with partial wall erosion and dissociation the source of the sand material is attributed to a channel levee turbidite depositional system located in the lower part of the fb1 member these deposits were buried by a thick biochemical muddy cap deposited during a starvation phase which increased the seal capacity of the system this type of architecture has a high potential to develop compaction disequilibrium during burial moreover in the case of the francevillian injectites the abundance of microbial organic matter favoured early methane degassing and lateral charging of the sand reservoir the overpressure in the channels was periodically released during early burial through the effect of rapid sedimentary and tectonic loading and possible seismic activity the fluidized sand was injected according to a symmetrical wing pattern thus the injected masses caused a local decrease in the grade of the lateritic manganese ore deposit of the bangombe plateau

fifth generation lithospheric magnetic field model from champ satellite measurements 1 six years of low orbit champ satellite magnetic measurements have provided an exceptionally high quality data resource for lithospheric magnetic field modeling and interpretation here we describe the fifth generation satellite only magnetic field model mf5 the model extends to spherical harmonic degree 100 as a result of careful data selection extensive corrections filtering and line leveling the model has low noise levels even if evaluated at the earth s surface the model is particularly suited for inferring large scale structure and composition of the lithosphere it is also meant to serve as the long wavelength part of continental and global scale marine and aeromagnetic anomaly maps

on the geographical distribution of induced time varying crustal magnetic fields 1 a long standing question in geomagnetism is whether the time variation of the induced crustal field is a detectable quantity and if so at which spatial wavelengths we tackle this problem with the help of a forward modeling approach using a vertically integrated susceptibility vis grid of the earth s crust for spherical harmonic degrees 15 90 we estimate the root mean square of the crustal magnetic field secular variation to amount 0 06 0 12 nt yr at the terrestrial surface between epochs 1960 2002 5 the geographical distribution of the signal shows absolute values reaching 0 65 1 30 nt yr over south america unfortunately most of the world magnetic observatories currently lie on quasi stationary features where the crustal field signal variations are expected to be very low however this long sought signal could be detected over well chosen regions provided that satellite observatory and repeat station measurements are available over several decades

magnetic anomaly map of the world merging satellite airborne marine and ground based magnetic data sets abstract we report here a simple but practical method to combine systematically the magnetic surveys of disparate specifications from marine ground aeromagnetic and satellite platforms that aims to be helpful in the framework of the world digital magnetic anomaly map project because the satellite coverage and data quality is more uniform than near surface surveys it is adopted as the base map for wavelengths larger than 400 km and up to spherical harmonic degree inclusive of 16 2500 km after checking that satellite models and large aeromagnetic wavelengths are not consistent we filter out wavelengths longer than 400 km in aeromagnetic compilations existing regional grids and when available individual surveys are merged to give a more uniform spatial variation of the magnetic anomalies the effects of merging the grids are examined by plotting profiles and difference maps of the overlapping regions a preliminary global map is obtained after combining the magnetic anomaly map with the downward continued champ satellite derived magnetic anomaly map forthcoming availability of new datasets as well as improvements in the procedure will help to produce increasingly reliable maps

a global lithospheric magnetic field model with reduced noise level in the polar regions 1 due to persistent ionospheric current systems at high latitudes satellite magnetic measurements have high noise levels in the polar regions consequently small scale lithospheric features are much more difficult to resolve there than at lower latitudes using linear combinations of spherical harmonics sh we define localized functions which are band limited to a given maximum degree thus a model s sh resolution can be varied over the globe we produce a lithospheric field model from champ satellite data which resolves features to sh degree 90 at low latitudes but only to sh degree 60 in the polar regions the new model can be downward continued from satellite altitude to the earth s surface without generating spurious high latitude anomalies citation lesur v and s maus 2006 a global lithospheric magnetic field model with reduced noise level in the polar regions geophys res lett 33 l13304

environmental controls of frost cracking revealed through in situ acoustic emission measurements in steep bedrock 1 frost cracking the breakdown of rock by freezing is one of the most important mechanical weathering processes acting on earth s surface insights on the mechanisms driving frost cracking stem mainly from laboratory and theoretical studies transferring insights from such studies to natural conditions involving jointed bedrock and heterogeneous thermal and hydrological properties is a major challenge we address this problem with simultaneous in situ measurements of acoustic emissions used as proxy of rock damage and rock temperature moisture content the 1 year data set acquired in an alpine rock wall shows that 1 liquid water content has an important impact on freezing induced rock damage 2 sustained freezing can yield much stronger damage than repeated freeze thaw cycling and 3 that frost cracking occurs over the full range of temperatures measured extending from 0 down to 15 c these new measurements yield a slightly different picture than previous field studies where ice segregation appears to play an important role

extending comprehensive models of the earth s magnetic field with orsted and champ data summary a new model of the quiet time near earth magnetic field has been derived using a comprehensive approach which includes not only pogo and magsat satellite data but also data from the orsted and champ satellites the resulting model shows great improvement over its predecessors in terms of completeness of sources time span and noise reduction in parameters with its well separated fields and extended time domain of 1960 to mid 2002 the model is able to detect the known sequence of geomagnetic jerks within this frame and gives evidence for an event of interest around 1997 because all sources are coestimated in a comprehensive approach intriguing north south features typically filtered out with other methods are being discovered in the lithospheric representation of the model such as the s atlantic spreading ridge and andean subduction zone lineations in addition this lithospheric field exhibits significantly less noise than previous models as a result of improved data selection the f region currents through which the satellites pass are now treated as lying within meridional planes as opposed to being purely radial results are consistent with those found previously for magsat but an analysis at orsted altitude shows exciting evidence that the meridional currents associated with the equatorial electrojet likely close beneath the satellite besides the model a new analysis technique has been developed to infer the portion of a model parameter state resolved by a particular data subset this has proven very useful in diagnosing the cause of peculiar artefacts in the magsat vector data which seem to suggest the presence of a small misalignment bias in the vector magnetometer

the satellite along track analysis in planetary magnetism summary many physical characteristics of planets such as their topography magnetic and gravitational fields are routinely detected and measured by spacecrafts at satellite altitudes even if little is known about the measured signal it is possible to separate the large scale components from other contributions by a spectral analysis carried out along the spacecraft orbit this procedure which dates back to the early age of the satellite era is routinely applied with spherical harmonics analysis for the study of large scale planetary magnetic fields particularly those that vary rapidly in time in this paper we review the approximations of this procedure for investigating internal and external magnetic fields of planets we show that the magnetic field analyses along the orbits are limited by a finite frequency resolution that is known to introduce a spectral leakage this leakage may lead to artificial spatio temporal variations of the magnetic field such as an apparent internal field secular variation an asymmetry of the magnetospheric field and a regional distortion of the lithospheric field structures we quantify the errors for the earth s lithospheric field and display its distribution in the spatial and the spectral domains we also discuss these limits for the moon and mars lithospheric magnetic fields our analytical results illustrate the pros and cons of the orbit by orbit analyses and should allow us to avoid the pitfall of geophysical overinterpretation of some artificial magnetic field variations

evolution of the mechanical behaviour of limestone subjected to freeze thaw cycles the frost weathering of three french limestones lens ls migne mi and savonnieres sa with different physico mechanical properties during the freeze thaw cycles was studied the weathering evolution in stone samples undergoing the freeze thaw cycles was monitored by measurement of following properties total porosity p wave velocity static elastic moduli uniaxial compressive strength and toughness the thermo mechanical behaviour of stones was also studied by measurement of the strain and temperature in surface and centre of sample during one freeze thaw cycle these results mainly the weathering observed for sa 73 with a degree of saturation of 73 and a lack of weathering for ls with a degree of saturation of 90 show that it is impossible to define a unique critical degree of saturation for different stones and this varies from stone to stone the shrinkage and or the expansion of samples during the crystallization phase were determined the shrinkage is related to the migration of water away from tiny pores towards larger cavities where ice has already formed the expansion is attributed on the one hand to the rise in pressure that comes from the water which flows towards the ice front and on the other hand to the relatively important quantity of ice formed when thermal contraction and the contraction due to migration dominate the elastic moduli static moduli and dynamic moduli was found to be affected the most by frost weathering and is a real sensor of first micro crack initiation whereas the uniaxial compressive strength and the porosity were found to be affected the least