probable benthic macroalgae from the ediacara member south australia abstract the ediacara biota records the rise of morphologically complex macroscopic eukaryotes including animals and other heterotrophs eltonian ecology demands that ediacaran ecosystems must have been supported by primary producers e g cyanobacteria phytoplanktonic eukaryotes benthic macroalgae but the fossil record of ediacaran primary producers has not been fully documented particularly with respect to benthic macroalgae hampering a complete understanding of ediacaran ecosystems here we provide systematic description of probable benthic macroalgal fossils from the ediacara member of the rawnsley quartzite at the national heritage site nilpena in south australia these fossils include flabellophyton stupendum sp nov f typicum liulingitaenia irregularis sp nov and longifuniculum cf dissolutum previously informally referred to as bundles of filaments bof they are characterized by bundled filaments that can be twisted loosened or otherwise deformed although many are fragmented some specimens of flabellophyton stupendum sp nov f typicum and possibly longifuniculum cf dissolutum bear structures that resemble variants of pseudorhizostomites and mop but interpreted here as holdfasts suggesting that in life these were epibenthic organisms attached to the substrate atypical populations of relatively small ediacara type fossils are found on a bedding surface dominated by benthic macroalgae suggesting that together with microbial mats these primary producers were beneficial for juvenile settlement of ediacara type organisms potentially contributing both oxygen and nutrients although debates about animal affinity dominate ediacaran paleontology this study highlights the importance of benthic macroalgae in ediacaran ecosystems

microbial mercury transformations in marine estuarine and freshwater sediment downstream of the idrija mercury mine slovenia abstract the idrija mine the second largest hg mine in the world ceased operation in 1995 but still delivers large quantities of hg downstream including into the northern adriatic sea 100 km away transformation of hg species in sediment in sites over 60 km from the mine including marine sites in the adriatic sea was measured to determine the ability of the system to transform and mobilize hg and to produce methylmercury mehg cores from a freshwater impoundment a brackish estuarine site and three marine sites in the gulf of trieste were sectioned anaerobically and hg methylation and mehg demethylation activities determined using radio techniques 203hg for methylation and 14c mehg for demethylation total and dissolved hg and mehg were determined as were other geochemical parameters in addition rates of so4 reduction were determined in marine sediment using a 35s technique mercury was readily methylated and demethylated at all sites marine sediment was investigated in winter and summer with rates of hg transformation and so4 reduction corresponding only in winter methylation of hg in summer displayed subsurface peaks that may have been influenced by bioturbation total hg and mehg were most abundant in the freshwater estuarine and near shore marine sites but dissolved pore water hg and mehg were highest in the estuarine region where s cycling appeared ideal for the mobilization of hg the impoundment sediment also seemed to be a hotspot of hg transformations mehg demethylation occurred via the oxidative demethylation pathway co2 produced from mehg except in surficial sediment offshore in the gulf during winter where sediment was more oxidizing and significant amounts of ch4 were liberated during mehg degradation via reductive demethylation the ch4 formation was likely due to an increased influence from the expression of mehg degradative enzymes encoded by the mer detoxification bacterial genetic system the freshwater site also liberated ch4 from mehg but it appeared to be due to oxidative demethylation by methanogenic bacteria

environmental interpretation and a sequence stratigraphic framework for the terminal proterozoic ediacara member within the rawnsley quartzite south australia abstract fossils of the ediacara biota are confined to preservational windows in the ediacara member of the rawnsley quartzite pound subgroup from the flinders ranges south australia the base of the ediacara member is a type 1 sequence boundary incised into the partly lithified chace quartzite member of the rawnsley quartzite the ediacara member and the upper half of the rawnsley quartzite comprise the rawnsley depositional sequence bounded above by the early cambrian uratanna depositional sequence the rawnsley sequence developed over an erosional surface cut into the chace quartzite member with some 250 m of relief southeasterly directed palaeovalleys are filled with a sequence of massive sandstone and laminated siltstone passing up into well bedded sandstone at lowstand local channels were filled by massive sand the highstand systems tract consists of several parasequence sets of laminated siltstone and channelized amalgamated massive sandstone overlain by interbedded siltstone and sandstone grading up into well bedded clean sandstone impressions of soft bodied ediacaran organisms are preserved above the valley fill facies on sandstone partings within upward shoaling delta front environments between storm and fairweather wavebase the ediacara member is in places conformably overlain by up to 500 m of sandstone of the same lithofacies as those underlying the member distinctive microbial mat bound sand laminae described as petee structures are characteristic of the rawnsley quartzite above and below the ediacara member during deposition of the ediacara member colonization of the deeper substrates by microbial mat communities enabled preservation of the ediacara biota the erosional surface at the base of the ediacara member is one of at least four incision events recorded in the terminal proterozoic and early cambrian succession of the adelaide geosyncline the similarity of incision filling lithofacies of the rawnsley and uratanna sequences has in condensed sections led to confusion between the depositional sequences characteristic trace and body fossil assemblages provide the only clear distinction between depositional cycles spanning the proterozoic cambrian boundary

a note on induced stress changes in hydrocarbon and geothermal reservoirs abstract earthquakes have been induced by oil and gas production where pore pressures have decreased in some cases by several tens of mpa it has previously been suggested that such earthquakes are caused by poroelastic stressing of crust surrounding the reservoir induced earthquakes are also common in geothermal fields such as the geysers where strong correlations between both steam production and condensate injection and earthquake activity have been observed over the last several decades stress measurements within hydrocarbon reservoirs show that the least horizontal stress decreases with declining reservoir pressure as predicted by poroelasticity for circular disk shaped reservoirs isothermal reduction in pore pressure induces a relative horizontal tension within the reservoir production induced stressing may promote frictional sliding on pre existing faults within the reservoir itself normal faulting is promoted if the regional stress is extensional and the biot coefficient is sufficiently large 0 85 for reasonable coefficients of friction on the other hand dilatant fracturing and normal faulting are always promoted in extensional environments near the edge of the reservoir or in regions of high pore pressure gradient it is suggested that such fracturing could enhance fracture permeability in tight rocks adjacent to portions of the reservoir that experience large reductions in pore pressure due to production in regional compressional environments production modestly favors reverse faulting above and below the reservoir the ratio of thermal to poroelastic stress can be quite large in geothermal reservoirs such as the geysers reservoir wide energy balance considerations suggest that the average temperature has declined at the geysers by 6 c during the past 20 years reservoir average stress changes are thus on the order of 2 mpa and are certainly much larger near injection wells and steam producing fractures

probability of a given magnitude earthquake induced by a fluid injection 1 fluid injections in geothermic and hydrocarbon reservoirs induce small earthquakes 3 m 2 occasionally however earthquakes with larger magnitudes m 4 occur we investigate magnitude distributions and show that for a constant injection pressure the probability to induce an earthquake with a magnitude larger than a given value increases with injection time corresponding to a bi logarithmical law with a proportionality coefficient close to one we find that the process of pressure diffusion in a poroelastic medium with randomly distributed sub critical cracks obeying a gutenberg richter relation well explains our observations the magnitude distribution is mainly inherited from the statistics of pre existing fracture systems the number of earthquakes greater than a given magnitude also increases with the strength of the injection source and the tectonic activity of the injection site our formulation provides a way to estimate expected magnitudes of induced earthquakes it can be used to avoid significant earthquakes by correspondingly planning fluid injections

a microscopic sedimentary succession of graded sand and microbial mats in modern siliciclastic tidal flats microscopic studies of thin sections from modern siliciclastic tidal flat sediments in the southern north sea demonstrate the significant role of microbial mats in the buildup of sedimentary sequences this is documented by a unit only a few millimetres thick it starts at the base with a fine to medium grained quartz sand often containing secondary pores fenestrae type merging gradually into finer sediments the lower siliciclastic part is superposed by an upper organically dominated layer built by microbial mats within the organic material single quartz grains without any contact to each other are oriented with their long axes parallel to the bedding planes each siliciclastic part in the lower section of the unit indicates the initial deposition of coarser grains in a stronger flow regime followed by gradually decreasing flow velocities each microbial mat in the upper part essentially represents a period of low sedimentation rate during its growth grains still settle down onto the mat and become bound in the organic matrix the orientation of these grains with their long axes parallel to the bedding plane points to an energetically suitable position to gravity achieved by the friction reduction of the soft organic matter repeated depositional events followed by low rate deposition cause the buildup of various units there is no visible reworking of the former surfaces since the microbial mats prevent erosion during periods of increased flow the buildup is characteristic of siliciclastic sediments repeatedly occupied stabilized and fixed by microbial films or mats

how far can hydraulic fractures go a comparative analysis of water flowback tracer and microseismic data from the horn river basin abstract the potential environmental impact of hydraulic fracturing is a significant public concern a key question is how far can fractures go beyond the well we analyze microseismic pressure interaction frac hit and interference and tracer data recorded during fracturing of and production from 52 wells in the horn river basin the results show that the wells communicate through fracture like pathways which allow water gas and proppant flow the lateral and vertical well communications occur at distances above 1 km and up to 130 m respectively well communication may last for over 1 7 years possibly due to proppant flow which prevents complete fracture closure during flowback and post flowback processes

building robust models to forecast the induced seismicity related to geothermal reservoir enhancement abstract near real time seismicity forecasting is critically important for decision making during the reservoir creation phase of enhanced geothermal systems egs to compute within a probabilistic framework the seismic hazard and risk posed by induced seismicity it is necessary to calibrate robust forecast models quantitatively assess their reliability and capture the uncertainty of the process here we test the performance of three model classes each forecasting the induced seismicity observed during the failed 2006 2007 egs reservoir creation underneath basel switzerland each model class represents a logic tree branch that captures the epistemic uncertainty of the process the aleatory variability is accounted for by bootstrapping of the observed seismicity we calibrate each model using a range of updating strategies and quantitatively test the performances of the models using likelihood tests we then define a combined model based on akaike weights and show that the combined model outperforms in our pseudoprospective testing environment all of the individual models we also show that seismicity recorded during the initial one to three days of seismicity several days before the onset of felt seismicity is sufficient for deciding with confidence that the prescribed injection regime will eventually lead to unacceptably high levels of seismicity

textured organic surfaces associated with the ediacara biota in south australia abstract the ediacaran period takes its name from the fossils of the ediacara biota which represent the first appearance of large and diverse assemblages of organisms in the fossil record although the global record of these distinctive body fossils is now well known a previously unrecognized megascopic organic record of textured organic surfaces tos occurs in the ediacara biota however tos is also a feature over a wider range of paleoenvironmental settings where body fossils are unknown in ediacaran siliciclastic successions that have been studied in australia namibia and western north america paleoecological analysis of successive bedding planes of strata from the late ediacaran rawnsley quartzite in the flinders ranges of south australia reveals that tos represent the most common organic features in bedding surface assemblages of the ediacara biota the tos consist of preserved patterned assemblages of textured organic mats fibers and simple tubular body fossils complex ediacara body fossils while striking for their distinctive body plans and dominating some of the beds are relatively minor components of combined overall surface area many elements of tos have previously been miss diagnosed as trace fossils which are in practice limited to two or at most three morphotypes that indicate the presence of bilateria although tos represent a simpler grade of organismic construction than discrete and more complex ediacara body fossils they were preserved in a similar manner marked variability in all components of the biota between successive surfaces suggests that ediacara ecologies fluctuated at short intervals despite an apparently consistent sedimentary regime

fluid induced seismicity guided by a continental fault injection experiment of 2004 2005 at the german deep drilling site ktb 1 recent hydraulic experiments at the ktb site have shown that seismicity induced by long term fluid injection directly into a continental crustal fault remains guided by this fault the seismicity is triggered by pressure perturbations as low as 0 01 1 bars at the hypocenters a combination of sequential one year fluid extraction 2002 2003 and one year fluid injection 2004 2005 experiments has shown that only positive pore pressure perturbation i e injections was able to induce the seismicity moreover the onset of seismicity roughly coincides with the time of compensation of the extracted fluid volume by the following injection this confirms that the pressure diffusion is a dominant mechanism of seismicity triggering by fluid injections the probed fault shows a significant anisotropy and non linearity of its hydraulic behaviour its hydraulic diffusivity is up to one order of magnitude larger than that of surrounding rocks

a diverse calcified cyanobacteria assemblage in the latest ediacaran abstract a three dimensionally preserved phosphatized cyanobacterial fossil assemblage tentatively identified as a distinct calcified cyanobacterial combination of oscillatorialeans and rivulariacean is recognized in the latest ediacaran in the southern shaanxi province china based on the morphological and preservation modes oscillatorialean cyanobacteria herein contain 3 genera which are girvanella obruchevella and subtifloria with thin walled tubes tangled coiled or aligned a kind of fan shaped fossils composed of filaments with tapered trichomes and pseudo branches cambricodium is clarified as calcified rivulariacean cyanobacteria prosperous calcified cyanobacteria co occurring with the earliest mineralized skeletal tubular fossils cloudina and sinotubulites in addition to contributing new morphological and preservation information the discovery of these cyanobacteria perhaps strengthens the case for prosperity in cyanobacterial calcification in the terminal neoproterozoic

characterization of hydraulic properties of rocks using probability of fluid induced microearthquakes the use of borehole fluid injections is typical for exploration and development of hydrocarbon or geothermal reservoirs such injections often induce small magnitude earthquakes the nature of processes leading to triggering of such microseismicity is still not completely understood here we consider induced microseismicity using as examples two case studies of geothermal reservoirs in crystalline rocks and one case study of a tight gas sandstone reservoir in all three cases we found that the probability of induced earthquakes occurring is very well described by the relaxation law of pressure perturbation in fluids filling the pore space in rocks this strongly supports the hypothesis of seismicity triggered by pore pressure moreover this opens additional possibilities of using passive seismic monitoring to characterize hydraulic properties of rocks on the reservoir scale with high precision

organic walled microfossils from the tonian gouhou formation huaibei region north china craton and their biostratigraphic implications abstract the meso and neoproterozoic huaibei group in the huaibei region north china craton ncc is emerging as a target for geobiological and tectonic studies due to its thick unmetamorphosed sediments with well preserved organic walled fossils however the lack of accurate age constraints for this sedimentary sequence dramatically hampers our ability to take full advantage of the rich geological and paleontological history recorded in the huaibei group particularly the depositional age of the uppermost unit of the huaibei group the gouhou formation is a controversial issue although it is widely accepted that there is an unconformity between the gouhou formation and the overlying early cambrian houjiashan formation the magnitude of this unconformity and hence the scale of the underlying tectonic event are unconstrained due to the uncertainty of the sedimentary age for the gouhou formation which has been variously interpreted as cambrian cryogenian ediacaran 720 ma to 541 ma and tonian 1000 ma to 720 ma to improve our knowledge about this sedimentary gap we carried out a biostratigraphic study of the gouhou formation our investigation using a low manipulation maceration technique revealed a diverse organic walled microfossil assemblage a total of 22 taxa have been revealed including a new species dictyosphaera tacita n sp importantly the co occurrence of trachyhystrichosphaera valeria and dictyosphaera in the gouhou formation suggests a likely tonian age the biostratigraphic data indicate an infra cambrian depositional gap of 200 myr between the tonian gouhou formation and cambrian houjiashan formation perhaps driven by a major tectonostratigraphic event

physics based seismic evaluation method evaluating possible seismic moment based on microseismic information due to fluid stimulation abstractthe forecasting and risk assessment of induced seismicity associated with fluid injection have considerable importance for subsurface energy development we have developed a seismic evaluation method called the possible seismic moment posemo model to assess the potential seismic moment that could be released in the future based on current seismic activity the posemo model assumes the existence of a representative parameter that can describe the seismic characteristics of a given field this parameter is defined as the seismic moment density which quantifies the seismic moment able to be released per rock volume the rock volume presumed to be in critical condition because of stimulation is defined as the stimulated rock volume the current stimulation condition for the posemo model can be estimated from the product of these two parameters the difference between the output of the posemo model and the observed cumulative seismic moment corresponds to the cumulative seismic moment that could be

inferring rock fracture evolution during reservoir stimulation from seismic anisotropy we have analyzed seismic anisotropy using shear wavesplitting measurements made on microseismic events recorded during a hydraulic fracture experiment in a tight gas reservoir in carthage east texas microseismic events were recorded on two downhole arrays of three component sensors the geometry of which provided good ray coverage for anisotropy analysis a total of 16 633 seismograms from 888 located events yielded 1545 well constrained shear wave splitting measurements manual analysis of splitting from a subset of this data set reveals temporal changes in splitting during fracturing inversion using the full data set allows the identification of fracture strike and density which is observed to vary during fracturing the recovered fracture strike in the rock mass is parallel to directions of regional borehole breakout but oblique to the hydraulic fracture corridor as mapped by the microseismic event we relate this to en echelon fracturing of preexisting cracks the magnitude of shear wave splitting shows a clear temporal increase during each pumping stage indicating the generation of cracks and fissures in a halo around the fracture corridor which thus increase the overall permeability of the rock mass our results show that shear wave splitting analysis can provide a useful tool for monitoring spatial and temporal variations in fracture networks generated by hydraulic stimulation

mercury contamination of coastal sediments as the result of long term cinnabar mining activity gulf of trieste northern adriatic sea abstract the isonzo river mouth has been the source of hg in the gulf of trieste northern adriatic sea since the sixteenth century making this shallow basin one of the most contaminated marine areas in the length of time and amount of metal accumulated the occurrence and behaviour of total hg range 0 064 30 38 g g 1 average 5 04 g g 1 median 3 10 g g 1 n 80 and related size fractions in sediments of this coastal area were investigated in detail the relationship between total hg and the fine silt clay 210 pb dated core collected in the central part of the gulf was also compared to other heavy metals fe cr cu mn ni and zn a preliminary estimate of hg enrichment shows that the first 50 cm of sediment in the central sector of the gulf of trieste are noticeably contaminated reaching a maximum of up to 25 fold above the proposed natural regional background of 0 17 g g 1 the vertical trend is well correlated to historical data of hg extraction activity at the idrija mine

scaling of seismicity induced by nonlinear fluid rock interaction 1 fluid injections into geothermal systems sometimes can produce significant seismic events with magnitudes of up to 4 however in the case of hydraulic fracturing of hydrocarbon reservoirs such events occur extremely seldom in the last case in contrast to the former one the structure of rocks is being actively destroyed e g opening of tensile fractures and the fluid rock interaction is strongly nonlinear e g a strong increase of permeability what is the role of this nonlinearity we consider nonlinear pore pressure diffusion to explain features of seismicity we formulate seismicity triggering front its propagation is sensitive to a grade of nonlinearity to spatial dimension of diffusion and to the injection rate we show that a probability of an event with a magnitude larger than a given one increases proportionally to the injected mass an increase of this probability with time is insensitive to the nonlinearity we compare different borehole experiments in some cases the injection produces clearly nonlinear impact on rocks in others this impact is approximately linear we find a well agreement with our theory we observe an insensitivity of temporal increments of magnitude probability to the grade of nonlinearity these increments are controlled by injection rate increments in contrast nonlinear fluid rock interactions are characterized by a strong dominance of small earthquakes defects activated by a nonlinear diffusion possibly obey gutenberg richter statistics with anomalous high b values in the case of a linear diffusion magnitude distributions of events are probably inherited from pre existing fracture systems

effective stress history and the potential for seismicity associated with hydraulic fracturing of shale reservoirs the influence of effective stress history on reservoir stability and the response to hydraulic fracturing are simulated for two hypothetical shale reservoirs it is numerically demonstrated that the effective stress history influences the present day stability of faults and natural fractures any assumption of a homogeneous stress state is shown to be unrealistic in the majority of fractured shale reservoirs the simulations demonstrate that depending upon the effective stress history shear displacements can be induced by stress changes associated with stimulation without a change of fluid pressure in the destabilized fractures elastoplastic shale and other fractured reservoirs are shown to have a memory of past geomechanical states these numerical findings demonstrate the value of interpreting reservoir effective stress history when planning fluid injection a previous case history is summarized to illustrate the overwhelming dependence of stress history analyses on a wide spectrum of earth science disciplines it also illustrates the application of stress history analyses to activities other than hydraulic fracturing the current inexperience of effective stress history description means that new approaches must be identified to optimize the necessary multidisciplinary investigations supplementary material details of the simulations are available at www geolsoc org uk sup18743

injection induced fracturing process in a tight sandstone under different saturation conditions to investigate the influence of local hydraulic condition on the water injection induced fracture behavior in tight sandstone injection tests under triaxial compression were conducted on samples collected from the sichuan basin china by means of acoustic emission ae monitoring the fracturing behaviors of two samples of different water saturation patterns partly saturated the middle part was dry and fully saturated are investigated experiment results indicate that the local hydraulic condition plays a governing role in the mechanical properties ae productivity fracture nucleation and the geometry of the shear fracture zone during axial loading stage the partly saturated sample demonstrated 35 higher elastic modulus than the fully saturated sample during the injection induced fracturing stage progressively increasing ae activity and dilatancy with increasing injected water volume were observed preceding the dynamic fracture in the partly saturated sample demonstrating a positive feedback between damage growing and fluid flow more aes were located in the dry or partially saturated regions at water front and thus produced dilatancy however the fully saturated sample shows very low ae activity 5 of that in partly saturated sample which was initiated immediately before the dynamic fracture phase due to the very low permeability 0 001 md volume of water injected into the fully saturated sample during the loading and creep stages is very limited indicating the observed large dilatancy is governed by pore pressure increasing due to stress compaction ae hypocenters demonstrated that an irregular shear fracture zone was created in the partly saturated sample while a relatively flat shear plane was formed in the fully saturated sample

affirming life aquatic for the ediacara biota in china and australia the ediacara biota has been long championed as a snapshot of the marine ecosystem on the eve of the cambrian explosion providing important insights into the early evolution of animals fossiliferous beds in the eponymous ediacara member of south australia have been recently reinterpreted as paleosols and ediacara fossils as lichens or microbial colonies that lived on terrestrial soils this reinterpretation here dubbed the terrestrial ediacara hypothesis would fundamentally change our views of biological evolution just prior to the cambrian explosion we take a comparative paleobiology approach to test this hypothesis the ediacara member shares a number of forms with assemblages in ediacaran marine black shales in south china shales that show no evidence of pedogenesis thus the shared ediacara fossils and by extension other co occurring fossils are unlikely to have been terrestrial organisms a terrestrial interpretation is also inconsistent with functional morphological evidence some of the shared forms are not morphologically adapted to address the most critical challenges for terrestrial life e g mechanical support and desiccation thus the terrestrial ediacara hypothesis can be falsified on comparative paleobiological and functional morphological grounds and we urge paleopedologists to critically reevaluate evidence for pedogenesis in the ediacara member and other ediacaran successions

juan de fuca subduction zone from a mixture of tomography and waveform modeling seismic tomography images of the upper mantle structures beneath the pacific northwestern united states display a maze of high velocity anomalies many of which produce distorted waveforms evident in the usarray observations indicative of the juan de fuca jdf slab the inferred location of the slab agrees quite well with existing contour lines defining the slab s upper interface synthetic waveforms generated from a recent tomography image fit teleseismic travel times quite well and also some of the waveform distortions regional earthquake data however require substantial changes to the tomographic velocities by modeling regional waveforms of the 2008 nevada earthquake we find that the uppermost mantle of the 1d reference model ak135 the reference velocity model used for most tomographic studies is too fast for the western united states here we replace ak135 with mt7 a modification of an older basin and range model t7 we present two hybrid velocity structures satisfying the waveform data based on modified tomographic images and conventional slab wisdom we derive p and sh velocity structures down to 660 km along two cross sections through the jdf slab our results indicate that the jdf slab is subducted to a depth of 250 km beneath the seattle region and terminates at a shallower depth beneath portland region of oregon to the south the slab is about 60 km thick and has a p velocity increase of 5 with respect to mt7 in order to fit waveform complexities of teleseismic gulf of mexico and south american events a slab like high velocity anomaly with velocity increases of 3 for p and 7 for sh is inferred just above the 660 discontinuity beneath nevada

piecing together the puzzle of the ediacara biota excavation and reconstruction at the ediacara national heritage site nilpena south australia abstract patterns of origination and evolution of early complex life on this planet are interpreted largely from the fossils of the precambrian soft bodied ediacara biota excavation and reconstruction of beds of the ediacara member of the rawnsley quartzite at the national heritage ediacara fossil site nilpena in the flinders ranges of south australia has exposed nearly 300 square meters of fossiliferous bedding planes as a result the taphonomy and sedimentology of the succession are well constrained rendering it possible to disentangle ecological from environmental and taphonomic signals the fossil record that is preserved on these beds is a function of a number of factors including 1 sedimentary environment 2 initial colonization 3 nature of textured organic surfaces 4 duration of time between episodes of disturbance and 5 biostratinomic processes the excavation and reconstruction of beds at nilpena yield an exceptional and unique opportunity to examine not only the taxonomic composition of ediacara communities but also their ecological character at various stages of development preserved ecological snapshots of fossil assemblages range from immature communities of small bodied individuals associated with poorly developed organic mats to communities characterized by a high diversity of macrofaunal taxa wide range of body sizes and the presence of dense textured organic surfaces

seismic hydraulic fracture migration originated by successive deep magma pulses the 2011 2013 seismic series associated to the volcanic activity of el hierro island in this manuscript we present a new interpretation of the seismic series that accompanied eruptive activity off the coast of el hierro canary islands during 2011 2013 we estimated temporal variations of the gutenberg richter b value throughout the period of analysis and performed high precision relocations of the preeruptive and syneruptive seismicity using a realistic 3 d velocity model our results suggest that eruptive activity and the accompanying seismicity were caused by repeated injections of magma from the mantle into the lower crust these magma pulses occurred within a small and well defined volume resulting in the emplacement of fresh magma along the crust mantle boundary underneath el hierro we analyzed the distribution of earthquake hypocenters in time and space in order to assess seismic diffusivity in the lower crust our results suggest that very high earthquake rates underneath el hierro represent the response of a stable lower crust to stress perturbations with pulsatory character linked to the injection of magma from the mantle magma input from depth caused large stress perturbations to propagate into the lower crust generating energetic seismic swarms the absence of any preferential alignment in the spatial pattern of seismicity reinforces our hypothesis that stress perturbation and related seismicity had diffusive character we conclude that the temporal and spatial evolution of seismicity was neither tracking the path of magma migration nor it defines the boundaries of magma storage volumes such as a midcrustal sill our conceptual model considers pulsatory magma injection from the upper mantle and its propagation along the moho we suggest within this framework that the spatial and temporal distributions of earthquake hypocenters reflect hydraulic fracturing processes associated with stress propagation due to magma movement

revised neoproterozoic and terreneuvian stratigraphy of the lena anabar basin and north western slope of the olenek uplift siberian platform abstract the early to mid neoproterozoic pre glacial sedimentary succession of the lena anabar basin northeast siberian platform records protracted faulting and subsidence possibly as part of the widespread continental rifting and the break up of rodinia there is a significant stratigraphic unconformity separating the pre glacial neoproterozoic strata and the overlying upper ediacaran succession in the lena anabar basin with the terreneuvian strata most likely to be deposited in a foreland of the central taimyr accretionary belt the cryogenian sensu strictum i e younger than 720 ma and lower ediacaran deposits are missing in the area in this study we assess the palaeontological content of the precambrian and terreneuvian strata of the lena anabar basin and the adjacent north western slope of the olenek uplift and revise the chronostratigraphy of the region with special emphasis to biostratigraphic index taxa for the pre glacial neoproterozoic section we establish the new tukulan kulady taimylyr formations and redefine the khastakh formation we also refine the ediacaran and terreneuvian stratigraphy by formalising the maastakh khatyspyt and turkut formations of the khorbusuonka group whereas the kessyusa formation is raised to group rank and subdivided into the syhargalakh oppokun mattaia and chuskuna formations the proposed stratigraphic correlation scheme is based upon depositional unity and is consistent both lithologically and biostratigraphically providing a robust framework for future stratigraphic sedimentological and palaeobiological studies

magnitudes of induced earthquakes and geometric scales of fluid stimulated rock volumes sometimes rock stimulations by fluid injections into geothermal boreholes are able to trigger perceptible or even potentially damaging earthquakes this does not seem to be the case for hydraulic fracturing of hydrocarbon reservoirs reasons for such a difference and factors defining magnitudes of induced earthquakes triggered tectonicly as well as induced artificially remain unclear we analyzed microseismic data obtained by fluid stimulations at different geothermal and hydrocarbon sites this analysis indicates that a rupture corresponding to a fluid induced earthquake seems to be only probable along a surface located mainly inside a stimulated rock volume we approximated the stimulated volume by an ellipsoid and compared the statistics of induced events with the statistics of randomly distributed thin flat disks modeling rupture surfaces we found that one of the main factors limiting the probability to induce a large magnitude event is the minimum principal axis of a fluid stimulated rock volume

carbonate hosted avalon type fossils in arctic siberia avalon type fossils are crucial to understanding the origin of phanerozoic ecosystems but their usual occurrence in volcaniclastic and siliciclastic facies greatly limits their paleobiological resolution the unique carbonate hosted assemblage of the khatyspyt formation on the olenek uplift of north central siberia promises a much enhanced anatomical and paleo ecological view of these enigmatic organisms avalon type fossils are preserved by authigenic carbonate cementation in intervals of finely laminated nodular limestones khatyspyt type taphonomic window interbedded silicified calcareous mudstones yield diverse carbonaceous compressions occasionally with taphonomic phantoms of avalon type taxa miaohe type taphonomic window styles of moldic preservation do not appear to be taxon selective and therefore cannot alone be responsible for the morphological distinctiveness of ediacaran macrofossils and the profound disparity in the taxonomic composition between fossil assemblages on the other hand the exclusion of avalon type fossils from carbonaceous compressions miaohe type preservational window is a real taphonomic signal that provides an important constraint on the properties of certain ediacaran tissues

seaweeds through time morphological and ecological analysis of proterozoic and early paleozoic benthic macroalgae abstract benthic marine macroalgae or seaweeds are key ecological players in oceans today and have been since the proterozoic to date however morphological and evolutionary patterns for precambrian macroalgae have been documented only in rather broad terms to refine our understanding in this critical interval we updated a dataset of proterozoic to early paleozoic noncalcified macroalgal fossils preserved as macroscopic carbonaceous compressions the data were analyzed using non parametric multidimensional scaling nmds and functional form group ffg approaches in order to characterize morphological and ecological evolutionary patterns of these macroalgae at the broadest scale the results show progressive increases in thallus size morphospace range and aspects of ecological complexity such as canopy heights surface area volume ratios and functional form groups through time these trends however are not always monotonous in particular significant increases in proterozoic macroalgal morphological diversity and maximum size appear to have occurred in the neoproterozoic tonian and ediacaran periods respectively analysis of ediacaran macroalgal assemblages shows that macroalgae broadly follow the ediacara like fossil assemblages with a significant drop in most studied metrics in the terminal ediacaran stage 550 539 ma the latter event occurs during the kotlinian crisis experienced by ediacara type macro organisms highlighting the possibility that this extinction event during the ediacaran cambrian transition affected both macroalgae and ediacara type macro organisms our analysis also confirms an ordovician increase in the morphological and ecological diversity of macroalgae

trace fossil evidence for ediacaran bilaterian animals with complex behaviors abstract distinguishing ediacaran trace fossils from tubular body fossils can be a challenge and several ediacaran fossils previously interpreted as animal traces have been shown to be tubular body fossils nonetheless true ediacaran trace fossils are present but they are relatively few and morphologically simple dominated by horizontal trails and shallow burrows such simple morphologies have been taken as evidence for a modest behavioral complexity and limited geobiological impact of animal bioturbators before the cambrian explosion here we report three types of trace fossils horizontal tunnels surface tracks trails and vertical traces from the latest ediacaran dengying formation 551 541 ma in the yangtze gorges area of south china cross cutting tunnels and the presence of scratch marks indicate that these traces are unlikely tubular body fossils instead these three types of traces likely represent animal activities related to under mat feeding epibenthic locomotion and temporary dwelling respectively we show that these three types of traces were constructed by the same bilaterian animals that had moderately complex interactions with microbial mats to exploit nutrients and o 2 resources these animals heralded a new age in ecosystem engineering animal sediment interaction and biogeochemical cycling

the distribution of total and methylmercury concentrations in soils near the idrija mercury mine slovenia and the dependence of the mercury concentrations on the chemical composition and organic carbon levels of the soil although the mining activity of the idrija mine in slovenia ceased in 1995 a large amount of mining dregs containing high concentrations of mercury remains in the area the mining dregs were transported with river flow and deposition along the idrija river to estimate the dispersion and change in the chemical form of mercury a total of 28 soil core samples were taken around the river the individual core samples were separated into layers for the analysis of their chemical composition carbon contents total mercury t hg and methylmercury mehg concentrations the chemical composition measured by x ray fluorescence spectrometry was useful to estimate the dispersion of tailings the fluvial terrace soil had a chemical composition similar to that of the tailings and could be distinguished clearly from the forest soil the highest t hg concentration 1 100 mg kg 1 was observed in the fluvial terrace soil near the mine although the concentration decreased gradually along with distance from the mine concentrations higher than 200 mg kg 1 of t hg were still observed in the fluvial terrace soil approximately 20 km downstream from the mine in the vertical distribution of t hg in the hillslope soil a higher value was observed in the upper layers which suggests the recent atmospheric deposition of mercury the concentration of mehg was the lowest at the riverside and higher in the hillslope soil which was the opposite of the t hg distribution the total organic carbon content tracked similarly with the distribution of mehg and a linear relation with a significantly high correlation coefficient was obtained the distinction may be related to the different dispersion process of mercury and the organic carbon contents may be an important factor for mehg formation

role of seepage forces on seismicity triggering 1 borehole fluid injection is commonly used for geological sequestration of carbon dioxide underground storage of natural gas waste injections and during stimulations and development of geothermal and hydrocarbon reservoirs typically the injection process induces significant seismicity with some earthquakes as large as magnitude four induced seismicity has also been observed around producing hydrocarbon boreholes recently it has been argued that some induced seismicity data can be explained by a highly nonlinear fluid diffusion mechanism or by the propagation of fluid pressure pulses the nature of the nonlinearity and the mechanisms by which a pressure pulse can trigger seismicity are still uncertain in this paper i show that the same spatiotemporal variation of seismicity can be explained and predicted by linear diffusion coupled to deformation of a linear poroelastic medium by calculating the propagation of coulomb yielding stress cys perturbation with time it is demonstrated that seismicity can be triggered by this perturbation the change of cys along the diffusion front is caused by seepage forces which are body forces generated by fluid pressure gradients and can explain induced seismicity during borehole fluid injection and extraction using published experimental data i demonstrate how the spatiotemporal distribution of fluid induced seismic events can be used for reservoir modeling and characterization

organic walled microfossils from the tonian tongjiazhuang formation of the tumen group in western shandong north china craton and their biostratigraphic significance abstract neoproterozoic successions in western shandong of north china craton contain fine grained siliciclastic rocks which offer a unique opportunity to explore the neoproterozoic biosphere in this study we have revealed a well preserved and diversified microfossil assemblage from the tongjiazhuang formation tumen group in western shandong north china craton which is characterized by abundant smooth walled sphaeromorphic acritarchs and cyanobacterium like filamentous forms and relatively low abundance of more complex acritarchs a total of 40 microfossil taxa belonging to 20 morphological genera have been identified most of which are described for the first time from the tongjiazhuang formation of the tumen group in western shandong including simia sp trachyhystrichosphaera aimika t botula germinosphaera bispinosa unnamed sp a jacutianema solubila and pololeptus rugosus the tongjiazhuang assemblage revealed in this study is much more diverse than previously reported and well comparable to the tonian liulaobei and gouhou assemblages in the xuhuai region particularly the occurrence of t aimika t botula g bispinosa j solubila and p rugosus indicates a late mesoproterozoic to tonian age for the tongjiazhuang formation in addition the occurrences of macroscopic carbonaceous compressions including chuaria tawuia assemblage from the tongjiazhuang formation and tawuia and sinosabellidites from the shiwangzhuang formation are consistent with geochronological data suggesting a tonian age for the tongjiazhuang fulaishan and shiwangzhuang formations of the middle and upper tumen group while the heishanguan and erqingshan formations of the lower tumen group are likely late mesoproterozoic to tonian in age thus available biostratigraphic data lithostratigraphic correlation and geochronological data suggest that the whole tumen group is late mesoproterozoic to tonian in age rather than cryogenian or ediacaran this study significantly improves our knowledge about the diversity of the tonian biosphere and implies a 200 300 million years unconformity the great unconformity between the late mesoprotoerozoic to tonian tumen group and the early cambrian liguan formation in western shandong

remarkable preservation of microbial mats in neoproterozoic siliciclastic settings implications for ediacaran taphonomic models abstract it is beyond doubt that the appearance of infaunal bioturbation and metazoan biomineralization across the ediacaran cambrian transition irreversibly affected the nature of marine sediment architecture and biogeochemistry here we review those changes in relation to their likely effect upon the processes of fossil preservation especially within siliciclastic sediments processes of soft tissue preservation in siliciclastic settings from the ediacaran period including microbes and microbial mats as well as ediacaran macrofossils are here reviewed within this context highlighted examples include the exceptional preservation of microbes found in association with wrinkle structures and ediacaran macrofossils in england and newfoundland replicated by silicate minerals and in the white sea region of russia replicated by iron sulphide these occurrences show that soft tissue preservation in siliciclastic settings went well beyond that typical for ediacaran macrofossils alone and also extended to similar modes of preservation in associated microbes using these new observations it can be argued that several existing explanations for ediacaran fossil preservation can be united within a biogeochemical model that involves evolution of the sediment mixed layer across this transition

fluid induced microseismicity in pre stressed rock masses summary we model microseismicity triggered by fluid injection on the basis of the theory of poroelasticity accounting for the external stress field consideration of the fully coupled poroelastic field equations enables us to apply a coulomb failure criterion using pore fluid pressure and stress tensor as well as the coefficient of friction the poroelastic fields are calculated with the finite element method simulating fluid injection with constant injection rate into a 2 d domain the influence of diffusivity injection rate and stress field on the occurrence of microseismicity is analysed and compared to simulations based on pore fluid pressure diffusion only we show that an anisotropic initial stress field causes elongated microseismic clouds these clouds are indistinguishable from those generated in poroelastic solids under isotropic stress but exhibiting anisotropic hydraulic diffusivity this similarity shows that microseismicity distributions dependent on both the hydraulic properties and the coupling of pore fluid pressure to the stress field in particular neglecting the influence of the external stress field may lead to overestimation of the anisotropy of diffusivity tensor components furthermore the results of our numerical simulations are strongly sensitive to changes of fluid injection rate

interactions between ediacaran animals and microbial mats insights from lamonte trevallis a new trace fossil from the dengying formation of south china abstract a new ichnogenus and ichnospecies lamonte trevallis is formally described from the shibantan member limestone of the upper ediacaran dengying formation yangtze gorges area south china it is characterized by horizontal tunnels connected with short vertical burrows and surface trails the horizontal burrows are elliptical or bilobed in transverse cross section preserved in full relief and filled with carbonate intraclasts micrites as well as calcite and silica cements they occur exclusively in silty crinkled and microlaminated layers that are interpreted as amalgamated cyanobacterial microbial mats no burrows have been found in intraclastic layers adjacent to the microlaminated layers the vertical traces are filled with the same material as the burrows but they typically project through the crinkled microlaminae and are exposed on the bedding surface the surface tracks are always preserved in negative epirelief or positive hyporelief and consist of two parallel series of either sharp scratch marks or small knobs the burrow infill has 18ocarb and 13ccarb values distinct from but intermediate between microlaminated and intraclastic layers consistent with petrographic observation that burrow infill consists of a mixture of early carbonate cements intraclasts and micrites bedding plane bioturbation intensity 20 40 measured as percentage of bedding plane area covered by l trevallis traces is comparable to similar measurements in pre trilobite cambrian carbonates the exclusive occurrence of l trevallis within microbial mats may have both taphonomic and ecological significance these mats may have provided firm substrates and localized geochemical conditions that contributed to the structural integrity of the burrows and they may have also facilitated early diagenetic cementation of burrow infill thus facilitating burrow preservation the close association of these burrows with microbial mats implies that the trace producers actively mined cyanobacterial mats to exploit oxygen or nutrient resources the trace makers of l trevallis were better able to utilize the resources around them than many other ediacaran trace makers and provide an ichnological record of a flourishing benthic ecology in late ediacaran oceans at the dawn of the agronomic revolution

acoustic emissions monitoring during inelastic deformation of porous sandstone comparison of three modes of deformation in some reservoirs large deformations can occur during oil or gas production because of the effective stress change for very porous rocks these production operations can be sufficient to cause inelastic deformation and irreversible damage rock formations can undergo deformation by different mechanisms including dilatancy or pore collapse in the laboratory it has been shown that the inelastic deformation and failure mode of porous rocks are pressure sensitive indeed when subjected to an overall compressive loading a porous rock may fail by shear localization compaction localization or by cataclastic compaction acoustic emission ae records provide important information to understand the failure mode of rocks the spatial evolution of damage as well as the source mechanisms can be followed using this technique in this paper we present three different laboratory axisymmetric compression experiments performed on bleurswiller sandstone which enable us to compare the acoustic emission signature of these three modes of deformation our data show that compaction localization and cataclastic compaction are characterized by similar acoustic signatures in terms of ae sources characteristics and evolution of ae number in comparison to the acoustic signature from shear localization this implies similar micromechanisms involved during compaction bands formation and cataclastic compaction

spatiotemporal variations in the b value of earthquake magnitude frequency distributions classification and causes abstract interpretation of the b value of earthquake frequency magnitude distributions has received considerable attention in recent decades this paper provides a comprehensive review of previous investigations of spatial and temporal variations in b value including their classification and possible causes based on least squares regression of seismicity data compiled from the neic iris and isc catalogs we find an average value of 1 02 0 03 for the whole earth and its two hemispheres consistent with the general view that in seismically active regions the long term average value is close to unity nevertheless wide ranging b variations 0 3 b 2 5 have been reported in the literature this variability has been interpreted to arise from one or more of the following factors prevailing stress state crustal heterogeneity focal depth pore pressure geothermal gradient tectonic setting petrological environmental geophysical characteristics clustering of events incomplete catalog data and or method of calculation excluding the latter all of these factors appear to be linked directly or indirectly with the effective state of stress although time dependent changes in b value are well documented conflicting observations reveal either a precursory increase or decrease in b value before major earthquakes our compilation of published analyses suggests that statistically significant b variations occur globally on various timescales including annual monthly and perhaps diurnal taken together our review suggests that b variations are most plausibly linked with changes in effective stress

hydraulic fracturing controlled dynamics of microseismic clouds 1 several dynamic processes related to propagation of hydraulic fracture modify the stress state in rocks and therefore they are relevant for triggering of microseismicity for instance these are the creation of a new fracture volume fracturing fluid loss and its infiltration into reservoir rocks as well as diffusion of the injection pressure into the pore space of surrounding rocks and inside the fracture using real data we show that some of these processes can be seen from features of spatio temporal distributions of the induced microseismicity especially the initial stage of fracture volume opening as well as the back front of the induced seismicity starting to propagate after termination of the fluid injection can be well identified and used for reservoir engineering

correlation of tremor activity with tidal stress in the northern cascadia subduction zone 1 we analyze hourly data from five tremor episodes in the northern cascadia subduction zone over the period 2003 2005 provided by the tremor activity monitoring system tams all five tremor episodes correspond to slow slip events observed by gps fourier decomposition is used to separate the hourly tremor counts for each episode into long period 0 2 2 cpd components the tidal component of the observations is compared with theoretical stress variations at depths of 20 30 and 40 km with 40 km being the depth of the interpreted subduction thrust interface the stress variations are predicted by a 2 d ocean tide loading model combined with estimates of stress variations from earth tides we find that the shear stress in the thrust direction and the compressive normal stress on shallow dipping surfaces correlates with the data significantly better than the confining stress over the range of depths investigated the relative amplitudes of tidal shear stress and compressive normal stress result in positive coulomb stress favoring slip peak tremor activity occurs at times of maximum tidal shear stress in the thrust direction which would assist slow slip and would suggest that tidal tremor and slip are colocated the response of the tremor to tidal shear stress is roughly proportional to the mean activity level controlled by tectonic conditions of stress and pore pressure a significant nontidal daily variation in tremor activity of unknown origin is identified

earthquakes triggered by silent slip events on kīlauea volcano hawaii silent earthquakes or slow slip events happen so slowly that they cannot be detected by conventional seismographs but now the availability of gps data means that they can be followed in detail segall et al report on a series of small earthquakes on k lauea volcano hawaii the earthquakes at depths of 7 to 8 km appear to be triggered by otherwise silent slow slips though small triggered earthquakes of this type can be used to help quantify the increased hazard due to slow slip events slow slip events or silent earthquakes have recently been discovered in a number of subduction zones including the nankai trough1 2 3 in japan cascadia4 5 and guerrero6 in mexico but the depths of these events have been difficult to determine from surface deformation measurements although it is assumed that these silent earthquakes are located along the plate megathrust this has not been proved slow slip in some subduction zones is associated with non volcanic tremor7 8 but tremor is difficult to locate and may be distributed over a broad depth range9 except for some events on the san andreas fault10 slow slip events have not yet been associated with high frequency earthquakes which are easily located here we report on swarms of high frequency earthquakes that accompany otherwise silent slips on k lauea volcano hawaii for the most energetic event in january 2005 the slow slip began before the increase in seismicity the temporal evolution of earthquakes is well explained by increased stressing caused by slow slip implying that the earthquakes are triggered the earthquakes located at depths of 7 8 km constrain the slow slip to be at comparable depths because they must fall in zones of positive coulomb stress change triggered earthquakes accompanying slow slip events elsewhere might go undetected if background seismicity rates are low detection of such events would help constrain the depth of slow slip and could lead to a method for quantifying the increased hazard during slow slip events because triggered events have the potential to grow into destructive earthquakes

the effects of thermal stress and fluid pressure on induced seismicity during stimulation to production within fractured reservoirs we use a continuum model of reservoir evolution to explore the interaction of coupled thermal hydraulic and chemical processes that influence the evolution of seismicity within a fractured reservoir from stimulation to production events occur from energy release on seeded fractures enabling moment magnitude frequency and spatial distribution to be determined with time event magnitudes vary in the range 2 to 2 with the largest event size 2 corresponding to the largest fracture size 500 m and a prescribed stress drop of 9 mpa modelled b values 0 6 0 7 also correspond to observations 0 7 0 8 for response in the cooper basin australia we track the hydrodynamic and thermal fronts to define causality in the triggering of seismicity the hydrodynamic front moves twice as fast as the thermal front and envelops the triggered seismicity at early time days to month with higher flow rates correlating with larger magnitude events for later time month to years thermal drawdown and potentially chemical influences principally trigger the seismicity but result in a reduction in both the number of events and their magnitudes

on the physics based processes behind production induced seismicity in natural gas fields author s zbinden d rinaldi ap urpi l wiemer s abstract 2017 american geophysical union all rights reserved induced seismicity due to natural gas production is observed at different sites worldwide common understanding states that the pressure drop caused by gas production leads to compaction which affects the stress field in the reservoir and the surrounding rock formations and hence reactivates preexisting faults and induces earthquakes in this study we show that the multiphase fluid flow involved in natural gas extraction activities should be included we use a fully coupled fluid flow and geomechanics simulator which accounts for stress dependent permeability and linear poroelasticity to better determine the conditions leading to fault reactivation in our model setup gas is produced from a porous reservoir divided into two compartments that are offset by a normal fault results show that fluid flow plays a major role in pore pressure and stress evolution within the fault fault strength is significantly reduced due to fluid flow into the fault zone from the neighboring reservoir compartment and other formations we also analyze scenarios for minimizing seismicity after a period of production such as i well shut in and ii gas reinjection in the case of well shut in a highly stressed fault zone can still be reactivated several decades after production has ceased although on average the shut in results in a reduction in seismicity in the case of gas reinjection fault reactivation can be avoided if gas is injected directly into the compartment under depletion however gas reinjection into a neighboring compartment does not stop the fault from being reactivated

ediacaran body and trace fossils in miette group windermere supergroup near salient mountain british columbia canadarevision of the paper was carried out by dr guy narbonne following the passing away of both hans hofmann deceased may 19 2010 and eric mountjoy deceased june 18 2010 after manuscript submission siliciclastic beds in the upper part of the miette group in southeastern british columbia have yielded an assemblage of late ediacaran soft bodied macrofossils and trace fossils the macrofossils comprise aspidella bradgatia and miettia salientensis gen et sp nov the ichnofossils include archaeonassa cochlichnus didymaulichnus gordia halopoa helminthoidichnites helminthopsis planolites and a large unnamed crawling trace in addition two types of unidentified problematica are recorded representing either tubular vendotaenia like body fossils or trace fossils the bradgatia constitutes the youngest occurrence of this type of fossil and is the first to be recorded from laurentia having previously been noted only in avalonia with cloudina and namacalathus in associated shallow water platform carbonates the miette biota in the study area contains a combination of namibian type and avalonian type elements

reply to comment by s a shapiro on role of seepage forces on seismicity triggering ismore appropriate because a linear diffusion is a dominanttriggering front mechanism shapiro 2012 in this reply idemonstrate that as long as coulomb stress transfer is thevalid triggering mechanism king et al 1994 stein 1999 freed 2005 steacy et al 2005 and diffusion is linearin heterogeneous rock shapiro 2012 then the seismicitytriggering front should be scaled as t

injection induced seismicity poroelastic and earthquake nucleation effects the standard model of injection induced seismicity considers changes in coulomb strength due solely to changes in pore pressure we consider two additional effects full poroelastic coupling of stress and pore pressure and time dependent earthquake nucleation we model stress and pore pressure due to specified injection rate in a homogeneous poroelastic medium stress and pore pressure are used to compute seismicity rate through the dieterich 1994 model for constant injection rate the time to reach a critical seismicity rate scales with t r2 cfc where r is distance from the injector c is hydraulic diffusivity and fc is a factor that depends on mechanical properties and weakly on r the seismicity rate decays following a peak consistent with some observations during injection poroelastic coupling may increase or decrease the seismicity rate depending on the orientation of the faults relative to the injector if injection induced stresses inhibit slip abrupt shut in can lead to locally sharp increases in seismicity rate tapering the flux mitigates this effect the maximum magnitude event has been observed to occur postinjection we suggest the seismicity rate at a given magnitude depends on the nucleation rate the size distribution of fault segments and if the background shear stress is low the time varying volume of perturbed crust this leads to a rollover in frequency magnitude distribution for larger events with a corner that increases with time larger events are absent at short times but approach the background frequency with time larger events occurring post shut in are thus not unexpected

an investigation of seismicity clustered near the cordel field west central alberta and its relation to a nearby disposal well historically seismicity documented in the western canada sedimentary basin has been relatively quiescent and earthquakes are usually restricted to the foreland belt of the rocky mountains however exceptional clusters of events which have remained active for decades are recognized in alberta in this study we investigate the seismicity in this region using data obtained from recently established regional arrays emphasizing the relationship between a disposal well in the cordel field and a nearby cluster of previously reported earthquakes we explore temporal correlations of wastewater pumping rates and local seismic activity dating back to 1960 we find that the first statistically significant increase in seismicity lags the onset of wastewater injection october 1991 by 3 33 years in particular the waveform similarity of 32 events are analyzed from continuous data recorded at nor a nearby 30 km station operated by the university of alberta starting in september of 2006 results from this analysis suggest that many events are well correlated in the characteristics of the waveforms and thus are likely to share a similar origin and source mechanism the most prolific of these multiplets repeats more than 10 times sporadically throughout the entire duration of recorded data from october 2006 to march 2012 despite the limited availability of nearby stations which adversely affects the resolution of our analysis hypocenter depths could be relatively accurately determined from waveform synthesis and double difference methods the results of our analysis provide first order evidence that the seismicity is consistent with fluid injection induced events

evolution of seismicity in relation to fluid injection in the north western part of the geysers geothermal field the geysers geothermal field located in california usa is the largest geothermal site in the world operating since the 1960s we here investigate and quantify the correlation between temporal seismicity evolution and variation of the injection data by examination of time series through specified statistical tools binomial test to investigate significant rate changes cross correlation between seismic and injection data b value variation analysis to do so we utilize seismicity and operational data associated with two injection wells prati 9 and prati 29 which cover a time period of approximately 7 yr from november 2007 to august 2014 the seismicity is found to be significantly positively correlated with the injection rate the maximum correlation occurs with a seismic response delay of 2 weeks following injection operations those results are very stable even after considering hypocentral uncertainties by applying a vertical shift of the events foci up to 300 m our analysis indicates also time variations of b value which exhibits significant positive correlation with injection rates

mercury concentration in some calcareous soils of western iran with a focus on pedological evolution and weathering process the aim of this study was to evaluate total mercury concentration and its lithogenic and exogenic fractions in some calcareous soils of western iran where water contamination and bioaccumulation of mercury have been reported in the bottomland s reservoir in particular we investigated soil physico chemical properties and weathering conditions related to lithogenic and exogenic fractions of mercury for two groups of calcareous soils with a known comparative pedological evolution and weathering condition that was evident in the presence or absence of underlying layers of accumulated clay our results showed that the total mercury content of the studied soils ranged from 45 40 to 830 36 with a mean of 486 81 g kg 1 furthermore calculation of mercury fractions revealed that lithogenic and exogenic fractions vary slightly according to the three reference elements fe u and nb used in the calculations for the two groups of studied soils the results also illustrated that most of the mercury content is of exogenic origin therefore total mercury variations are closely related to the content of exogenic mercury while the lithogenic fraction exhibited no relationship with total mercury concentration moreover application of the weathering indexes of parker and the cao zro2 molar ratio supported the dependence of lithogenic mercury accumulation on weathering intensity in the studied calcareous soils however the significance of this relationship is stronger for more weathered calcareous soils in such cases fine particle fractions are more developed which encourages carrier phases such as organic materials and iron oxyhydroxides to become involved in more efficient fixation of mercury nevertheless the formation of underlying layers of accumulated clay i e argillic horizons may restrain fixation of exogenic mercury by limiting its atmospheric input

hydraulic stimulation of natural fractures as revealed by induced microearthquakes carthage cotton valley gas field east texas we produced a high resolution microseismic image of a hydraulic fracture stimulation in the carthage cotton valley gas field of east texas we improved the precision of microseismic event locations four fold over initial locations by manually repicking the traveltimes in a spatial sequence allowing us to visually correlate waveforms of adjacent sources the new locations show vertical containment within individual targeted sands suggesting little or no hydraulic communication between the discrete perforation intervals simultaneously treated within an 80 m section treatment i e fracture zone lengths inferred from event locations are about 200 m greater at the shallow perforation intervals than at the deeper intervals the highest quality locations indicate fracture zone widths as narrow as 6 m similarity of adjacent source waveforms along with systematic changes of phase amplitude ratios and polarities indicate fairly uniform source mechanisms fracture plane orientation and sense of slip over

a tale of three taphonomic modes the ediacaran fossil flabellophyton preserved in limestone black shale and sandstone abstract ediacaran macrofossils are typically preserved in three taphonomic modes casts molds in siliciclastic rocks casts molds in carbonate rocks and carbonaceous compressions in black shales only a few taxa are known to be preserved in more than one of these taphonomic modes flabellophyton is a genus that has been previously reported from lower ediacaran black shale of the lantian formation 635 551 ma in south china and upper ediacaran sandstone of the ediacara member 560 550 ma in south australia here we report flabellophyton from upper ediacaran limestone of the shibantan member of the dengying formation 551 539 ma in south china making flabellophyton the only genus that occurs in all three taphonomic modes we also provide a systematic description of flabellophyton based on material from the lantian and dengying formations in south china recognizing three morphospecies f lantianense f typicum sp nov and f obesum sp nov flabellophyton is reconstructed as an erect epibenthic marine organism attached to sandy carbonate and muddy substrates its phylogenetic affinity remains ambiguous though it was historically interpreted as an algal fossil the wide environmental and stratigraphic distribution of flabellophyton allow comparative taphonomic and paleoecological analysis taphonomic analysis of flabellophyton indicates that multiple taphonomic pathways can facilitate the preservation of ediacaran macrofossils as a window into ediacaran paleoecology flabellophyton and other ediacaran fossils played a crucial role in the construction of epibenthic communities in ediacaran oceans and helps to understand the ecological migration and evolutionary expansion from deeper to shallower oceans during the ediacaran period

statistics of fracture strength and fluid induced microseismicity 1 in this paper we develop an approach for estimating the strength of rocks by analyzing fluid induced microseismicity the strength corresponds to the value of critical pressure in the pore space that must be exceeded in order to activate preexisting fractures i e to trigger earthquakes we assume that during hydraulic injection experiments in boreholes microseismicity is mainly triggered by a diffusive process of pore pressure perturbation an analytical solution can be applied to find time dependent pore pressure perturbations in rocks caused by fluid injections characteristics of the spatiotemporal evolution of microseismic clouds can be then used to estimate minimum and maximum pressures necessary to trigger earthquakes moreover we present a method for reconstruction of the full spectrum of rock strength that is we show how to estimate the probability density function of the critical pressure we verify the approach using numerical data and apply it to real data of injection induced microseismicity from two hot dry rock tests in crystalline rocks and one hydraulic fracturing experiment in a sedimentary rock the results show that such an analysis of microseismicity is able to provide us with a completely new feature of natural fractured rocks in situ namely the statistics of their strength we find that very low critical pressures in the range 0 001 1 mpa characterize the strength of preexisting cracks for all data sets analyzed the range of critical pressures is broadly distributed within 3 to 4 orders of magnitude however the probability density functions of critical pressure change very quickly from the zero level to significant values and from significant values to the zero level at the lower and upper limits of their nonvanishing value ranges respectively the lower bound of critical pressure is possibly defined by the magnitude of tidal induced stresses permanently occurring and relaxing in the earth

reservoir characterization using oil production induced microseismicity clinton county kentucky abstract microseismic monitoring tests were conducted from 1993 to 1995 in the seventy six oil field clinton county kentucky oil is produced from low porosity fractured carbonate rocks at 3 no injection operations were conducted gross changes in production rate correlate with event rate event rate lags changes in production rate by 2 to 3 weeks hypocenters and first motion data have revealed previously undetected low angle thrust faults above and below the currently drained depth intervals production history well logs and drill tests indicate that the seismically active faults or fractures are previously drained intervals that have subsequently recovered to hydrostatic pressure via brine invasion storage capacity computed for one of these drained fractures implies that total oil production represents about 20 of total pore volume correlation of older production intervals and well log porosity anomalies with the seismically active faults indicate that the oil reservoir in the study area is primarily a set of compartmentalized low angle thrust faults although low angle fracture sets have not previously been considered in the exploration and development of the area the mapped thrust faults are consistent with other investigators interpretations of oil associated with secondary fracture sets occurring along deeper seated wrench fault structures stress determined from composite focal mechanisms indicates a near surface

dickinsonia liftoff evidence of current derived morphologies abstract dickinsonia an iconic member of the ediacara biota is abundant in the ediacaran deposits found at the nilpena field site south australia despite exquisite fossil preservation at this site many specimens of dickinsonia appear to be incomplete with an apparently missing piece on the periphery orientation measurements from specimens on three fossil beds suggest that these so called missing pieces are aligned irrespective of the axial orientation of dickinsonia the nonrandom orientation of incomplete specimens matches that of other aligned structures found on two of these beds the preferred directionality of this feature suggests the molding of incomplete specimens under the influence of current activity prior to or during burial we propose that this feature originates where part of a dickinsonia was lifted off of the substrate during a storm event and that sand was deposited beneath this lifted portion this model suggests that dickinsonia was easily separated from the sea floor and was not attached to the substrate on which it lived this is consistent with the data from dickinsonia footprints suggesting that dickinsonia was mobile

a constitutive law for rate of earthquake production and its application to earthquake clustering seismicity is modeled as a sequence of earthquake nucleation events in which the distribution of initial conditions over the population of nucleation sources and stress ing history control the timing of earthquakes the model is implemented using solutions for nucleation of unstable fault slip on faults with experimentally derived rate and state dependent fault properties this yields a general state variable constitutive formulation for rate of earthquake production resulting from an applied stressing history to illustrate and test the model some characteristics of seismicity following a stress step have been explored it is proposed that various features of earthquake clustering arise from sensi tivity of nucleation times to the stress changes induced by prior earthquakes the model gives the characteristic omori aftershock decay law and interprets aftershock parameters in terms of stress change and stressing rate earthquake data appear to support a model prediction that aftershock duration defined as the time for rates to return to the back ground seismicity rate is proportional to mainshock recurrence time observed spatial and temporal clustering of earthquake pairs arises as a consequence of the spatial depen dence of stress changes of the first event of the pair and stress sensitive time dependent nucleation applications of the constitutive formulation are not restricted to the simple stress step models investigated here it may be applied to stressing histories of arbitrary complexity the apparent success at modeling clustering phenomena suggests the possibil ity of using the formulation to estimate short to intermediate term earthquake probabil ities following occurrence of other earthquakes and for inversion of temporal variations of earthquake rates for changes in driving stress

microseismic imaging of a geothermal reservoir stimulation exploitation of geothermal heat energy from rocks at depths of several km has been the goal of vari ous projects since the mid 1970s to exploit the energy in these deep rocks poses technical challenges in drilling well completion creation of the heat exchange reservoir at depth and control of seismicity in spite of the difficulties what are now known as enhanced engineered geothermal systems egs offer almost limitless clean energy so it is not surprising that this technology continues to attract investors however commercial energy production from the greatest potential resource hot rock at depths 5 km or temperatures 200 c remains elusive

locating microearthquakes induced by hydraulic fracturing in crystalline rock microearthquakes induced by hydraulic fracturing in crystalline rock at a depth of 3 5 km were located with a precision of better than 30 m to obtain information about the geometry and dimensions of the fracture system produced the induced microseismicity was monitored by a network of five vorehole seismic stations a total of about 800 induced events were reliably located from arrival times event locations show a tabular distribution that strikes 350 sup 0 and dips 65 sup 0 east subparallel to the injection well the injection was intended to produce a fracture system that would hydraulically connect two subparallel wells a lack of fluid communication between them is consistent with a lack of induced microearthquakes near the target wellbore the 150 m thickness of the zone of seismicity far exceeds the relative locational uncertainties the injected fluid appears to have stimulated a zone of rock rather than simply a single fracture the distribution of microseismic events presumably envelopes the zone of fluid paths created by the fracture experiment

aftershock triggering by complete coulomb stress changes 1 we examine the correlation between seismicity rate change following the 1992 m7 3 landers california earthquake and characteristics of the complete coulomb failure stress cfs changes cfs t that this earthquake generated at close distances the time varying dynamic portion of the stress change depends on how the rupture develops temporally and spatially and arises from radiated seismic waves and from permanent coseismic fault displacement the permanent static portion cfs depends only on the final coseismic displacement cfs diminishes much more rapidly with distance than the transient dynamic stress changes a common interpretation of the strong correlation between cfs and aftershocks is that load changes can advance or delay failure stress changes may also promote failure by physically altering properties of the fault or its environs because it is transient cfs t can alter the failure rate only by the latter means we calculate both cfs and the maximum positive value of cfs t peak cfs t using a reflectivity program input parameters are constrained by modeling landers displacement seismograms we quantify the correlation between maps of seismicity rate changes and maps of modeled cfs and peak cfs t and find agreement for both models however rupture directivity which does not affect cfs creates larger peak cfs t values northwest of the main shock this asymmetry is also observed in seismicity rate changes but not in cfs this result implies that dynamic stress changes are as effective as static stress changes in triggering aftershocks and may trigger earthquakes long after the waves have passed

how well do fossil assemblages of the ediacara biota tell time patterns of origination evolution and extinction of early animal life on this planet are largely interpreted from the fossils of the precambrian soft bodied ediacara biota spanning nearly 40 m y of the terminal ediacaran period localities containing these fossils are loosely considered as part of either the avalon white sea or nama associations these associations have been interpreted to have temporal paleobiogeographic preservational and or paleoenvironmental significance surprisingly elements of all three associations occur within the ediacara member of the rawnsley quartzite of south australia an analysis of over 5000 specimens demonstrates that fossil distribution is strongly controlled by facies and taphonomy rather than time or biogeography and that individual taxa vary considerably in their environmental tolerance and taphonomic integrity the recognition that these taxa represent organisms living in various distinct environments both juxtaposed and shared holds strong implications for our interpretation of the record of early animal life on this planet and questions the biostratigraphic utility of the three associations furthermore although in situ soft bodied preservation provides a unique perspective on composition of benthic fossil assemblages the record should not be interpreted as a simple snapshot fossil beds represent a range of preservational modifications varying from current winnowed census samples of benthic communities at different depths and ecological maturity to entirely transported assemblages unless the appropriate environments and taphonomic conditions are present for certain taxa the absence of a particular taxon may or may not indicate its extinction in space or time