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

subsurface seepage dynamics and flow types in a messinian paleoseep system maiella mts central italy abstract the subsurface feeder complexes of mud volcanoes and seepage systems potentially provide valuable information on the evolution of seepage dynamics ancient seepage systems in outcrops allow for the observation of expulsion features which are otherwise commonly beyond seismic resolution in the maiella hydrocarbon seep area the evolution of fluid migration through the sedimentary column during the messinian salinity crisis generated distinctive seep plumbing features geological responses and geochemical signatures in the brecciated limestones unit the fluid migration pathways evolved from funnel shaped feeder channels flow mobilized sediments into hydrofractured microbial carbonate buildups limestone buildups and finally into blow out micropipes in the host sediment patchy limestones as overpressure dissipated through the plumbing system the flow mobilized sediments 13c down to 24 5 pdb 1 correspond to the highest flow rates in the whole area whereas the patchy limestones 13c down to 39 3 pdb 1 correspond to the slowest flow rates within the intrusive zone the limestone buildups show different degrees of hydrofracturing that reflect different flow rates 13c down to 27 5 pdb 1 the fluid transport mechanisms evolved from focused venting through neoformed feeder channels where sediments elutriated from depths were carried out the sediment prone response to fluid migration to high rate seepage triggering high hydrofracturation in the microbial buildups while the hydrocarbon rich fluids contemporaneously triggered authigenic precipitation the mineral prone response to fluid migration progressive upward and lateral flow deceleration resulted in gradually weaker hydrofracturing of the microbial buildups and finally only local cementation in the form of carbonate patches within the host sediments

experimental studies of the fluidization of layered sediments and the formation of fluid escape structures experiments demonstrate that fluid escape structures can be produced as a result of unstable fluidization behaviour where a lower base layer of granular material is inhibited from fluidizing by the presence of an overlying non fluidizing top layer before the base layer can fluidize the weight of the overlying material must be balanced and this is accomplished by base layer material pressing against the bottom surface of the confining top layer forming a static layer this static layer allows the top layer to lift away from the base layer which is then free to fluidize a water filled crack forms below the static layer and as this grows instability causes the static layer and top layer to bend and conical voids to form below the antiformal sections rupture occurs at the apex of the water void allowing the underlying water and fluidizing material to burst out through the top layer the fluidized base layer material then flows through the rupture until all of this material except that in the static layer is deposited above the previously overlying layer and a stable fluidization system results the top layer material is bent upwards around the rupture and the resulting pillar type escape structure is preserved if flow then ceases the vigour of the burst out is greatest when the base layer material has a grain size 15 of the top layer material if the base layer grain size is less than 8 of the top layer then base layer material will pass through the top layer pore spaces without forming an escape structure if cohesive material is present escape structures form when a layer of fine grained cohesive material overlies a layer of cohesionless material at low flow rates small pipes with scattered angular bends pierce the top layer and base layer material passes through them the base layer material is ejected on to the top layer and builds up around the mouth of each pipe to form constructional structures sand volcanoes this is in contrast to the cohesionless experiments where the weight of material being deposited on the top layer caused an ejecta filled depression to form around the rupture if flow then ceases both the pipes and the sand volcanoes are preserved at high flow rates where the base layer fluidizes the top cohesive layer becomes fragmented small fragments circulate within the fluidizing base layer and are preserved as floating clasts large fragments sink to the bottom of the fluidizing base layer erosion of the bottom surface of these larger fragments causes this surface to become convex downward the experimentally derived structures are similar to pillar type structures observed in the field and the processes described can be used to investigate the development of these structures fluidization experiments also demonstrate the genesis of dish structures and the cohesive behaviour can be applied to the deformation of these structures after initial formation

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

experimental evidence for fluidization processes in breccia pipe formation results of small scale fiuidization spouting and channeling experiments suggest that similar processes may have been involved in the formation of many breccia pipe features various cylindrical parallel plate and boxlike model containers were filled with mixtures of particulate materials ranging from clay sized powdered kaolinitc to 1 cm gravel and each container was attached at its base to a large volume compressed air source features generated during the course of the various experimental runs are analogous to the majority of features observed in breccia pipes complex branching fracture systems developed in models containing abundant cohesive material appear to be similar to incipient crackle breccias steep walled funnel to cone shaped conduits formed readily and in some models inward dipping fractures ring fractures marginal shear folds and or downwarps and or high angle normal faults developed in adjacent material thorough mixing of heterogeneous particulate materials from throughout the stratigraphic column commonly was achieved and blocks of more cohesive materials were readily rounded and comminuted convective particle motion spouting was most effective in the mixing process and was accompanied by downwarping and fragmentation of adjacent strata downward migration of wall rock blocks along conduit margins and generation of annular zonation of conduit filling material in some systems annular size classification resulted in fine layering parallel to conduit walls crude centroclinally nested saucer bedding developed in some experiments where air fall ejecta were generated and these beds commonly were transported essentially intact downward within the pipe during a bubbling fiuidization event a gas streaming or channeling process in which finer material was elutriated or cleared out of coarser material led to the formation of channelways or chimneys which in natural systems would provide excellent avenues for introduction of later magma or hydrothermal solutions in model systems enriched in strongly cohesive clay sized particles accretionary pelletal spherules commonly were generated fluidization and related processes have been defined to describe highly controlled industrial systems problems of scale and strength of materials are significant when comparing experimental with geologic systems but the striking similarity of many features observed in both experimental and natural breccia pipe systems suggests that a similar genetic process is reasonable although many pipes clearly are not formed by fiuidization and related processes these processes may be important in the development of or some developmental stage of some breccia pipes

heavy mineral sorting in downwards injected palaeocene sandstone siri canyon danish north sea abstract post depositional remobilization and injection of sand are often seen in deep water clastic systems and have been recently recognised as a significant modifier of deep water sandstone geometry large scale injectite complexes have been interpreted from borehole data in the palaeocene siri canyon near the danish central graben of the north sea hydrocarbon province the emplacement of large scale injectite complexes has been commonly attributed to seismic activity and consequent sand liquefaction however due to very small differences in textural and compositional properties and the lack of depositional structures in deep water sandstones the distinction between in situ and injected or remobilized sandstones is often ambiguous large scale heavy mineral sorting in 10 m thick units is observed in several reservoir units in the siri canyon and has been interpreted to represent the depositional sorting in this study we describe an example of effective shear zone sorting of heavy minerals in a thin downwards injected sandstone dyke which was encountered in one of the cores in the cecilie field siri canyon differences in sorting pattern of heavy minerals are suggested as a tool for petrographic geochemical distinction between in situ sandstones and their related injectites especially where primary sedimentary structures are removed by fluidization or minor remobilization

basin floor fans in the north sea sequence stratigraphic models vs sedimentary facies discussion original article shanmugan g r b bloch s m mitchell g w j beamish r j hodgkinson j e damuth t straume s e syvertsen and k e shields 1995 aapg bulletin v 79 p 477 512

liquefaction fluidization and erosional structures associated with bituminous sands of the bracklesham formation middle eocene of dorset england at hengistbury head dorset the boscombe sands middle eocene bracklesham formation are of estuarine channel facies a mud filled channel is exposed the banks and eastern flank of which have a black carbonaceous stain the degraded remains of a bitumen at the time of deposition the bitumen rendered the sediment firm and it was extensively burrowed by a thalassinoides forming organism crustacean the bituminous sand on the eastern channel bank suffered brecciation and dilation as a result of liquefaction and flowage of the underlying sediments this is thought to have been due to rapid expulsion of pore water possibly as a result of seismic shock the layers of bituminous sand below the surface were ruptured during water escape resulting in localized zones of rapid flow causing fluidization and the development of dewatering pipes up to 1 2 m long the estuarine sediments were subsequently transgressed during which the bituminous sand was exposed on the seafloor when it was eroded into a hummocky topography and heavily burrowed blocks of bituminous sand were reworked into the marine basal conglomerate composed mainly of flints demonstrating the remarkable strength of the bituminous cement

formation of fluidization pipes during liquefaction examples from the uratanna formation lower cambrian south australia usually well preserved fluidization pillars and sand filled fluidization pipes occur within submarine channel sands of the basal uratanna formation lower cambrian in the adelaide geosyncline of south australia the morphology of these structures reflects complex lateral and vertical movement of fluids during liquefaction and dewatering fluidization pipes acted as conduits for highly concentrated upward directed fluid flow the formation and maintenance of these pipes was dependent upon the development of a pipe wall composed of clay plugged fine sand formed during initial fluidization this lining acted as a permeability barrier confining and concentrating fluidized flow within the pipe each of the pipes is surrounded by a cylindrical fluidization halo in which leakage through the pipe lining produced partial fluidization of the surrounding sediment fine scale structures within these haloes indicate that fluids flowed radially and upward out of the fluidization pipes at an acute angle these fluids merged with and influenced the orientation and size of adjacent fluidization pillars the fluidization pipes of the uratanna formation may represent unusual preservation of the unstable fluid flow conditions that occur during incipient fluidization of sand beds

regional sand injectite architecture as a record of pore pressure evolution and sand redistribution in the shallow crust insights from the panoche giant injection complex california abstract observations on outcrop of a regionally developed sand injectite are used to infer and estimate the pore pressure conditions in the shallow crust that caused the fluidization and injection of tens of cubic kilometres of sand the estimated pore fluid pressures at the base of the injection complex at 1500 m burial depth below a regionally developed shale dominated seal are from 22 26 to 25 08 mpa which respectively correspond to 0 81 and 0 95 lithostatic pressure a theoretical basis for prediction of sand injection is defined and applied to the prediction of pore pressure at the time of sand injection the depth at which seal failure occurred and the density and granular content of the fluidized flow lateral variations in the style and abundance of sandstone intrusions are described and these all fit into a remarkably uniform tripartite division of parent units an intrusive complex and an extrusive complex a sill zone intrusions are dominated by sills occurs in a restricted stratigraphic interval 200 270 m thick location of the base of the sill zone is directly related to the thickness of the overburden and an isobaric surface at the time of sand injection the lithostatic equilibrium surface is defined at the base of the sill zone when the sills formed an extended period of supra lithostatic pressure occurred within the sill zone

sequence development during uplift palaeogene stratigraphy and relative sea level history of the outer moray firth uk north sea abstract published models of sequence stratigraphy have been derived from studies of the depositional history of subsiding basins during the palaeogene sediment accumulation in the outer moray firth basin of the north sea coincided with episodes of basin uplift palaeogene trends in coastal onlap and relative sea level in this basin have been estimated directly from seismic data and reveal two long duration cycles of relative sea level fall and rise the first cycle comprising over 800 m fall followed by 500 m rise was initiated in the earliest palaeocene and lasted approximately 9 my the second cycle began in the early eocene and resulted in approximately 70 m fall and 150 m rise in relative sea level over 13 my the duration of both of these cycles can be defined as second order superimposed on both of these long term second order cycles are higher frequency variations in relative sea level with periodicities of around 1 5 my and amplitudes of up to 150 m these shorter cycles are associated with the deposition of sequences identified on the seismic data one of the effects of this superimposition was to either subdue or enhance the development of systems tracts within the sequences enhancement took place where the sea level trends were similar on both the long and the short duration curves e g both rising systems tracts were subdued where sea level trends were opposed in general lowstands and transgressive systems tracts showed significant enhancement within a sequence when the sequence coincided with the steeply falling and steeply rising portions respectively of the long duration relative sea level cycle groups of these skewed sequences are stacked in certain distinct patterns termed sequence sets the pattern type is again dependent on the coincidence of the group of sequences with the second order cycle in general downstepping sequence sets are associated with the steeply falling part of the second order cycle progradational sequence sets with the gently falling to gently rising portion and retrogradational sequence sets with the steeply rising portion these stacking patterns reflect large scale changes in accommodation volume the multi sequence depositional record of a tectonically driven long duration cycle of relative sea level can be considered as a composite sequence where its systems tracts are composed of sequence sets

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

concretion morphology classification and genesis abstract a discussion of the most relevant morphological features of concretionary bodies and the different classifications and the criteria involved in these classifications is presented together with suggestions for improvements to the various classification schemes the meaning of syngenetic diagenetic and epigenetic related to the relative timing and environment of growth of concretionary bodies is also reviewed and discussed the replacement of mixed morphogenetic classifications which lead to conflicting results by classification categories based on textural features is proposed because the identification of the genetic environment of a concretionary body tells little about its history i recommend defining growth patterns in which the successive steps associated with changes in composition and or texture and the development of new structures are recorded a new path is presented that accounts for the contradiction between textural and isotope features which suggests respectively syngenetic and diagenetic or even epigenetic signatures this new path is characterized by the preservation of large porosities over very long time spans and down to depths that are somewhat greater than expected due to the inhibition of normal compaction caused by early overpressuring this overpressuring is the result of the development of hydraulic seals since approximately the syngenetic phase times the concepts of force of crystallization and displacive growth are also reviewed it is being suggested to discard some controversial interpretations of their actual importance for true concretionary displacive growth under epigenetic conditions in accordance with other authors the conclusion is reached that displacive growth is only possible if the shear strength of the host is very low and the stress field within the host is almost hydrostatic a new model the symcompactional concretionary growth model is proposed which explains how a concretionary body generally a nodule can grow while its host thins down by compaction this overpressured undercompacted model will be useful for the interpretation of an assemblage of features such as injection dikes hydraulic breccias cone in cone structures among others that are thought to be representative of the former presence of overpressured horizons these overpressured horizons could serve as detachment planes in paleotectonically active basins seals that could have controlled the movement of brines and hydrocarbons during the diagenetic evolution of the basin can also be assessed this is relevant for the identification of maturation conditions the potential development of secondary fracture permeability due to hydraulic fracturing in buried areas of the basin can also be evaluated based on the identification of formerly overpressured horizons in outcrops the origin of concretions is generally a geological puzzle clifton 1957

thickness and spatial distributions of clastic dykes northwest sacramento valley california abstract the geometry and distribution of the clastic dykes of the ono district north sacramento valley are examined within stream sections five traverses along dry stream beds provide good exposure allowing the spacing thickness and geometry of the dykes to be recorded the spatial and thickness distribution of the dykes are considered using cumulative frequency plots allowing a visual estimation of a best fit distribution dyke thickness conforms best to a log normal distribution there is also a characteristic minimum dyke thickness in a traverse and this is attributed to the minimum aperture that a fluid with sand clasts is able to exploit dyke spacing however shows a good correlation with a power law distribution for four traverses suggesting that there is a mechanistic control on the spatial distribution plotting dyke thickness against minimum dyke spacing reveals that thin dykes do not generally intrude in isolation unlike veins and igneous dykes clastic dykes continue to provide preferential pathways for fluid flow subsequent to their intrusion thus inhibiting intrusion in the area surrounding a pre existing dyke a combination of this process and dyke branching provides the best model for the observed spatial and thickness distribution of clastic dykes seen in the ono district california

reinterpretation of depositional processes in a classic flysch sequence pennsylvanian jackfork group ouachita mountains arkansas and oklahoma discussion the pennsylvanian jackfork group in the ouachita mountains of arkansas and oklahoma has conventionally been interpreted by many workers including us as a classic flysch sequence dominated by turbidites in a submarine fan setting however normal size grading and bouma sequences indicative of turbidite deposition are essentially absent in these sandstone beds they appear massive i e structureless in outcrop but when slabbed reveal diagnostic internal features these beds exhibit sharp and irregular upper bedding contacts inverse size grading floating mudstone clasts a planar clast fabric lateral pinch out geometries moderate to high detrital matrix up to 25 sigmoidal deformation duplex structures and contorted layers all these features indicate sand mplacement by debris flows mass flows and slumps mud matrix in these sandstones was sufficient to provide cohesive strength to the flow discrete units of current ripples and horizontal laminae have been interpreted to represent traction processes associated with bottom current reworking the dominance of sandy debris flow and slump deposits nearly 70 at degray spillway section and bottom current reworked deposits 40 at kiamichi mountain section and the lack of turbidites in the jackfork group have led us to propose a slope setting our rejection of a submarine fan setting has important implications for predicting sand body geometry and continuity because deposits of fluidal turbidity currents in fans are laterally more continuous than those of plastic debris flows and slumps on slopes a turbidite dominated fan model would predict an outer fan environment with laterally continuous sheetlike sandstones for the jackfork group in southern oklahoma and western arkansas whereas a debris flow slump model would predict predominantly a slope environment with disconne ted sandstone bodies for the same area

complex reservoir geometries in a deep water clastic sequence gryphon field ukcs injection structures geological modelling and reservoir simulation abstract the balder formation sandstone reservoir of the gryphon field was deposited during the late paleocene early eocene while the background sedimentation comprised pelagic shales and tuffs sediment gravity flows transported sands from the shelf area in the west the crawford ridge acted as a barrier to sediment transport in the east causing the sands to be deposited predominantly as massive sand bodies as flow velocities decreased during burial sand remobilisation and injection occurred possibly localised around faults cored intervals show a range of injection structures from thin cm scale dykes to more massive metre scale chaotic intrusive features the cross cutting nature of the injection structures as observed in core and in seismic sections accounts for the high degree of reservoir connectivity observed in the field a study was undertaken with the objective of constructing a 3d geological model for dynamic reservoir simulation in order to evaluate future development activities in the field as previous purely deterministic models had proven unsuitable the complex depositional and post depositional history of the gryphon field reservoir has resulted in a system for which there is no published analogue to aid in 3d reservoir modelling preliminary stochastic models based on analogues chosen to reflect the reservoir sand body geometries did not match the field production history the fact that both the deterministic and fully stochastic models were unsuitable suggested that a novel approach was required to model this field subsequent models constructed using a combination of stochastic and deterministic models have proven successful in matching the production history of the field and evaluating infill opportunities

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

seismic imaging of complex geometry forward modeling of sandstone intrusions abstract sandstone intrusions form large bedding discordant sandstones that intruded into finer grained less permeable host strata they form naturally sand propped hydraulic fractures that constitute a connected network of permeable conduits through which fluids escape to the earth s surface saucer shaped sandstone intrusions are among the largest volume intrusions and are commonly resolved on seismic data outcrop analogues of seismically resolved saucers shaped intrusions reveal that many attendant intrusions in particular dikes are undetected in seismic data seismic forward modeling of a detailed outcrop description of a saucer shaped intrusion demonstrates that intrusions steeper than 45 are undetected and that up to 40 of the entire volume of sandstone intrusions is not seismically imaged wedge geometry associated with discordant contacts between different lithologies causes constructive and destructive amplitude interference creating imaging artefacts of sandstone thickness and geometry comparison of the outcrop seismic models with 3d seismic data from volund oilfield demonstrate both the similarity of the saucer shaped intrusions and the distribution and quantity of dikes that may be undetected ca 78 using subsurface data lack of detection of dikes has direct implications on the valuation of upward migration of fluids and an overestimation of seal capacity this therefore has major implications when using seismic data to evaluate waste sequestration or to execute hydrocarbon or groundwater exploration and production

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

what do the cajon pass stress measurements say about stress on the san andreas fault comment on in situ stress measurements to 3 5 km depth in the cajon pass scientific research borehole implications for the mechanics of crustal faulting by mark d zoback and john h healy

clastic dike swarms and the structural evolution of the foreland fold and thrust belt of the southern andes clastic dike swarms are intruded into a cenozoic foreland fold and thrust belt in southern chile the dike material consists of sandstone and conglomerate with clasts as much as 25 cm in diameter brecciated wall rocks are also found in the clastic matrix the dikes often exceed 50 cm in width and hundred of metres in length in outcrop and are oriented overwhelmingly transverse to fold axes and parallel to cross joints the dike swarms are concentrated near the toe of major thrusts where they are found injected into the hanging wall a regional axial planar spaced cleavage is developed in the clastic dikes and sills clearly postdating injection of clastic material dike injection postdates at least the initiation of extension fractures the cross joint set within the swarms the dike intrusions represent as much as 20 extension parallel to fold axes in addition to several percent extension represented regionally by the cross joints the structural features of the dike swarms and their geometric relationship to other structures suggest rapid single phase injection the arrival of the front edge of a thrust on an already highly overpressured sedimentary sequence would cause an instantaneous increase in the overburden pressure and therefore could result in injection of a dense slurry of wet coarse sediments along preexisting planes of weakness field relationships of mesoscopic structures suggest the following evolution cross joint development incipient cleavage development initiation of thrusting and buckling clastic dike injection regional spaced cleavage development and associated late stage tightening of folds

experimental soft sediment deformation structures formed by the liquefaction of unconsolidated sands and some ancient examples the effects of liquefaction in saturated sand bodies under a variety of driving forces are described from shaking table experiments and structures from the geological record are presented which are analogous to the experimental structures the collapse of sloping heaps of cross bedded sand under a gravitational body force generates low angle essentially uncontorted stratification a basal zone of shearing may be present with steepened and folded foresets stretching of foresets may be accommodated on normal faults and bottomsets may be contorted into inclined folds in natural systems the substrate may also liquefy causing deformation driven by an unevenly distributed confining load stratification in the surface bedform is flattened and stratification in the substratum contorted experiments failed to produce relative displacement at the interface between stacked sand bodies liquefaction of gravitationally unstable systems in sands generates load structures comparable to those from sand mud systems recumbent folded deformed cross bedding is formed by current shear over a liquefied bed as has been inferred from field and theoretical analyses shear of nonliquefied sand forms angular folds other deformation mechanisms such as fluidization or seepage may generate structures similar to all of these local water escape structures driven by fluidization occur in the upper parts of some liquefied sand bodies they include cusps sand volcanoes and clastic dykes transient cavities formed in some experiments and seemed to be preserved as breached cusps although the experiments tried to isolate individual driving forces driving forces may operate together and there may be a continuum between deformation driven by water escape and deformation driven by loading different structures from those described here may form where liquefaction develops in a buried layer as opposed to at the sediment surface

benthic foraminiferal response to the middle eocene climatic optimum meco in the south eastern atlantic odp site 1263 the response of marine biota to the middle eocene climatic optimum meco is still poorly constrained specifically changes in deep sea benthic foraminiferal faunas have been documented at few locations only we carried out a quantitative study of benthic foraminiferal assemblages at lower bathyal odp site 1263 walvis ridge se atlantic providing documentation of the response of benthic foraminiferal assemblage to the meco in an open ocean setting there was no major temporary or persistent assemblage turnover in benthic foraminiferal faunas in the se atlantic ocean the benthic foraminiferal accumulation rates bfar and assemblage composition indicate that the delivery of food to the seafloor increased during the early stages of surface and deep sea warming during this period the absolute and relative abundance of phytodetritus exploiters increased pronouncedly indicating that the increase in the flux of organic matter to the sea floor was largely seasonal or otherwise pulsed during later stages and peak warming of meco in contrast the flux of organic matter to the seafloor declined markedly as shown by a decrease in both infaunal and epifaunal benthic foraminiferal accumulation rates the low flux of organic matter during the more extreme parts of the meco thus did not favor one of these broad groups but affected all common taxa paleoceanographic reconstructions combined with data on benthic foraminifera suggest that the meco warming was the main cause of the reduction in the flux of organic matter to the sea floor by increasing the metabolic rates of pelagic consumers which thus used more food preventing it from reaching the sea floor as well as increasing remineralization of organic matter in the water column

fibrous calcite veins overpressures and primary oil migration the fibrous calcite veins found parallel to the bedding of certain shales may have been formed during burial as a consequence of overpressuring their presence could even be indicative of former overpressures this suggestion if it can be upheld carries implications for theories of primary oil migration

clastic pipes and mud volcanism across mars terrestrial analog evidence of past martian groundwater and subsurface fluid mobilization abstract clastic pipes are cylindrical injection features that vertically crosscut bedding with sharp contacts terrestrial pipes have cylindrical morphologies massive or radially graded interiors and raised outer rims increased grain size and subsequent cementation along the more porous edges makes the rims more resistant to weathering pipes have crosscutting relationships with other pipes due to multiple formation events or migrating eruption centers and are associated with other soft sediment deformation features terrestrial clastic pipes form via liquefaction and fluidization which require a near surface groundwater system to initiate i e sand sized sediments must be saturated for pipes to form clastic pipes cm to 1000 m diameters occur on mars across multiple time periods and terrains and are recognized in both rover and orbital imagery a conical or cylindrical geometry and massive interior core characterize these features the pipes on mars show various geomorphic expressions and are classified into five types by the presence or absence of a raised outer rim or a central pit these types are interpreted to represent the erosional evolution of pipes at different stages from their initial surface eruptive structures to their weathered remnants eroded conical hills martian pipes formed via fluidization as evidenced by 1 raised outer rims possibly indicating textural differences along the pipe edges from traction interactions of fluid suspended sediment 2 crosscutting relationships with other pipes suggesting reactivated fluidization pathways or migrating eruptive vents and 3 close spatial association between pipes and other features thought to form by soft sediment deformation e g contorted bedding integration of terrestrial analog data with the mars observations provides evidence for past martian groundwater and subsurface fluid mobilization

origin and timing of sand injection petroleum migration and diagenesis in tertiary reservoirs south viking graben north sea petrographic fluid inclusion and carbon and oxygen stable isotope studies of tertiary injectite reservoirs in the south viking graben of the north sea allow an understanding of the origin and timing of sand injection petroleum migration and diagenesis injection from shallowly 400 m 1300 ft buried paleocene and eocene unconsolidated sandstones occurred at the end of the eocene probably in response to earthquake activity liquid oil was already present in the parent sands prior to injection and leaked from the injectites to the seabed upward migrating oil and basinal brines mixed with downward invading mixed meteoric marine pore fluids in the injectites causing extensive biodegradation of the oil biodegradation of oil provided the driver for early carbonate cementation in injectites causing diminished reservoir quality however early carbonate cementation also sealed off the injectites as potential escape routes for petroleum from the underlying parent sands oil and gas continued to migrate into the reservoir parent sands upon increased burial causing a mixing of high api oil with the early charged extensively biodegraded low api oil the study of early diagenetic imprints reveals the evolution of injectite reservoirs which forms the basis for understanding how to explore and develop them

the alba field ocean bottom cable seismic survey impact on development alba field in the central north sea uk block 16 26 consists of eocene age high porosity unconsolidated turbidite channel sands sealed by low permeability shales at an average subsea depth of 1900 m the main channel is approximately 9 km long and 1 5 km wide and can be up to 100 m thick figure 1 the channel contains discrete bodies of intrareservoir shales that can cause significant drilling completion and production problems immediately overlying the main alba sand channel several wells have encountered thin discontinuous oil saturated brioc sands

making a homogenite an outcrop perspective into the evolution of deformation within mass transport deposits abstract mass transport deposits mtds may show a variety of deformation aspects from poorly deformed layers to highly deformed and homogenized deposits as a result of the different kinds of mass transport processes involved in their evolution previous studies indicate that the downslope flow transformation of mtds is characterized by increasing disaggregation mixing and homogenization of a non to poorly lithified protolith which may ultimately generate a homogenite we here explore the role of deformation processes in the disaggregation and mixing of sediments that tend to lead to sediment homogenization and so may also control the evolution of mtds using the itarare group of the parana basin southern brazil as our case study we examine several types of structures in mtds with varying degrees of mass disaggregation and discuss the role of deformation process in the continuum homogenization of the sediment three deformational facies df 1 df 2 and df 3 were identified and interpreted as recording varying stages of homogenization of sediments disaggregation and mixing within the incipient mature and evolved flows respectively these different stages show transitional aspects that indicate a continuum homogenization the comparison between structural assemblages and the amount of matrix in the three different deformational facies indicates a close relationship between styles of deformation and the homogenization expected for mass flows the processes that promoted disaggregation include boudinage faulting layer parallel shearing and marginal deformation of intrabasinal clasts while mixing processes that generate matrix include shearing and liquefaction fluidization of sediments

regional fractures i a mechanism for the formation of regional fractures at depth in flat lying reservoirs 1 regional fractures may form slowly at depth in extension and parallel to regional horizontal tectonic compression such fracture sets can be common in reservoirs despite the absence of flexure of the strata and are commonly important contributors to reservoir permeability such fractures make good targets for deviated wells high formation pore pressure is crucial to creating low effective confining stresses and brittle rock properties in the reservoirs conditions conducive to fracturing despite deep burial but pore pressure does not exceed the least principal stress and does not cause tensile fracturing the mechanism of natural hydraulic fracturing is incompatible with the characteristics of most regional fracture sets rather many regional fractures form duri g far field compression initiate at locally induced tensile stresses caused by flaws in the rock and propagate in the plane of the maximum and intermediate compressive stresses the differential stress required for initiation and propagation of regional fractures is well below that necessary for shear failure in the presence of high pore pressure fractures can be held open at depth by a tectonic basinwide dilatancy of the strata and the open void space commonly becomes mineralized

the origin of consolidation laminae and dish structures in some deep water sandstones abstract consolidation laminae and dish structures form high density zones that are interpreted to have formed by disruption of primary structures during gravitational collapse of the grain framework during water escape and consolidation they are not associated with higher contents of clay size material than adjacent units but the chloritic clay minerals associated with consolidation laminae and dish structures have a different microtexture than observed elsewhere clay mineral texture has a direct effect on petrophysical characteristics in particular water saturation and conductivity in hydrocarbon saturated intervals ct scans identify consolidation laminae and dish structures as zones of high density that correspond to tighter packing of sand grains and are unrelated to clay distribution dish structures may form independently of consolidation laminae or by further modification of fragmented consolidation laminae

use of liquefaction induced features for paleoseismic analysis an overview of how seismic liquefaction features can be distinguished from other features and how their regional distribution and properties of source sediment can be used to infer the location and strength of holocene paleo earthquakes abstract liquefaction features can be used in many field settings to estimate the recurrence interval and magnitude of strong earthquakes through much of the holocene these features include dikes craters vented sand sills and laterally spreading landslides the relatively high seismic shaking level required for their formation makes them particularly valuable as records of strong paleo earthquakes this state of the art summary for using liquefaction induced features for paleoseismic interpretation and analysis takes into account both geological and geotechnical engineering perspectives the driving mechanism for formation of the features is primarily the increased pore water pressure associated with liquefaction of sand rich sediment the role of this mechanism is often supplemented greatly by the direct action of seismic shaking at the ground surface which strains and breaks the clay rich cap that lies immediately above the sediment that liquefied discussed in the text are the processes involved in formation of the features as well as their morphology and characteristics in field settings whether liquefaction occurs is controlled mainly by sediment grain size sediment packing depth to the water table and strength and duration of seismic shaking formation of recognizable features in the field generally requires a low permeability cap above the sediment that liquefied field manifestations are controlled largely by the severity of liquefaction and the thickness and properties of the low permeability cap criteria are presented for determining whether observed sediment deformation in the field originated by seismically induced liquefaction these criteria have been developed mainly by observing historic effects of liquefaction in varied field settings the most important criterion is that a seismic liquefaction origin requires widespread regional development of features around a core area where the effects are most severe in addition the features must have a morphology that is consistent with a very sudden application of a large hydraulic force this article discusses case studies in widely separated and different geological settings coastal south carolina the new madrid seismic zone the wabash valley seismic zone and coastal washington state these studies encompass most of the range of settings and the types of liquefaction induced features likely to be encountered anywhere the case studies describe the observed features and the logic for assigning a seismic liquefaction origin to them also discussed are some types of sediment deformations that can be misinterpreted as having a seismic origin two independent methods for estimating prehistoric magnitude are discussed briefly one method is based on determination of the maximum distance from the epicenter over which liquefaction induced effects have formed the other method is based on use of geotechnical engineering techniques at sites of marginal liquefaction in order to bracket the peak accelerations as a function of epicentral distance these accelerations can then be compared with predictions from seismological models

seismically induced soft sediment deformation structures revealed by x ray computed tomography of boring cores abstract x ray computed tomography ct allows us to visualize three dimensional structures hidden in boring cores nondestructively we applied medical x ray ct to cores containing seismically induced soft sediment deformation structures ssdss obtained from the kanto region of japan where the 2011 off the pacific coast of tohoku earthquake occurred the ct images obtained clearly revealed various types of the seismically induced ssdss embedded in the cores a propagating sand dyke bent complexly by the preexisting geological structure deformed laminations of fluidized sandy layers and two types of downward mass movement ductile downward folding and brittle normal faulting as compensation for upward sand transport through sand dykes two advanced image analysis techniques were applied to the sand dyke ct images for the first time the growcut algorithm a specific digital image segmentation technique that uses cellular automata was used successfully to extract the three dimensional complex sand dyke structures embedded in the sandy sediments which would have been difficult to achieve using a conventional image processing technique local autocorrelation image analysis was performed to detect the flow pattern aligned along the sand dykes objectively the results demonstrate that x ray ct coupled with advanced digital image analysis techniques is a promising approach to studying the seismically induced ssdss in boring cores

evolution of permeability in sand injectite systems abstract sand injectite complexes comprise kilometer scale clastic intrusion networks that act as effective conduits for the migration accumulation and then recovery of hydrocarbons and other fluids an equivalent continuum model is constructed to represent a sand injectite reservoir coupling stress and fluid flow in fractured rock using the continuum simulator toughreact coupled with flac3d to follow deformation and fluid flow a permeability model which uses staged percolation models is proposed to improve permeability estimation of fracture networks by accommodating four different levels of fracture connectivity this permeability model is confirmed against field and laboratory data corresponding to the different connectivities of fracture networks the new constitutive permeability model is incorporated into the coupled hydro mechanical simulator framework and applied to sand injectites with the analysis of permeability evolution mechanisms and mechanical sensitivity the results indicate that when the magnitudes of principal stresses increase in a constant ratio normal closure is the dominant mechanism in reducing fracture aperture and thereby permeability conversely the evolution of stress difference can accentuate aperture and permeability due to an increase in shear dilation for critically or near critically oriented fractures also the evolution of aperture and related permeability of fractured rock are more sensitive at lower stress states than at higher stress states due to the hyperbolic relationship between normal stress and normal closure of the fractures