early diagenetic silica deposition in algal cysts and spores a source of sand in black shales abstract devonian black shales deposited on the north american craton contain abundant tasmanites cysts although these are typically flattened because of compaction a small proportion are filled with diagenetic silica the latter are spherical to ellipsoidal 0 1 0 5 mm and filled with chalcedony microquartz and megaquartz and single quartz crystals chalcedonic cyst fillings are preserved best in cheat and phosphate nodules whereas megaquartz and single quartz crystals are most common in shale matrix together with colloform textures this suggests that the various silica types originated from recrystallization of early diagenetic silica deposits thin sandstone beds in the chattanooga shale e g bransford sandstone contain abundant quartz sand that is much coarser than the detrital quartz component of the underlying black shales because of this their quartz component is thought to have been transported over considerable distances from the basin margin however because certain shale horizons contain as much as 10 silicified cysts that upon reworking could have yielded quartz grains of fine to coarse sand size the quartz component of these sandstone beds may actually have formed in situ indeed petrographic examination of the sandstone beds shows them to contain quartz grains with morphological and textural features of cyst quartz e g rounding sphericity chalcedony pyrite inclusions lobate grain margins thus silica deposition in algal cysts may provide a significant component of intrabasinal quartz sand in shale sequences distinction of this type of quartz from extrabasinal detrital quartz is important to the reconstruction of the depositional history of shale sequences

variations of hydraulic properties of granular sandstones during water inrush effect of small particle migration the evaluation of the hydraulic properties evolution of granular sandstones in relation with groundwater inrush within faults is an important issue for mining engineering applications this paper presents the results of an experimental investigation of small particle migration from granular sandstone samples under different original porosities particle size compositions and water flow pressures a new rock testing system has been setup to carry out the tests based on the results it is observed that the overall permeability evolution during the tests can be divided into four different phases including i re arrangement of large rock fragments ii water inrush with substantial particle migration iii continued moderate particles seepage and iv steady state water flow the crushing of edges and corners of large rock fragments and the evolution of the fracture network has mainly been observed in the first two phases of the tests the results indicate that the migration of small particles has an essential effect on permeability and porosity increase during water inrush through fractured sandstone the samples with higher original porosity higher percentage of fine particles in their formation and under higher water flow pressures achieve higher permeability and porosity values when the test is complete furthermore using the measured data the performances of a number of empirical models for permeability evolution in fractured porous media have been studied the prediction results indicate that not all of the fractures in a sample domain contribute in small particle migration there are parts of the fracture network that are not effective in particle flow a sample with less original porosity more fine particles and under lower water pressure shows less ineffective fractures therefore using the concept of the effective porosity fracture is sufficient enough for the flow calculation

numerical calibration of the devonian carboniferous boundary two new u pb isotope dilution thermal ionization mass spectrometry single zircon ages from hasselbachtal sauerland germany the hasselbachtal section sauerland germany is an auxiliary global stratotype of the devonian carboniferous boundary and one of the most important reference sections for the evolution of the latest famennian to earliest tournaisian pelagic fauna biostratigraphically well controlled altered volcanic ash layers metabentonites intercalated in the section afford a perfect opportunity for a numerical fixing of this important paleozoic period boundary we have performed u pb isotope dilution thermal ionization mass spectrometry id tims analyses on sub microgram sized single zircons and zircon fragments extracted from two metabentonites beds 79 and 70 in the lowermost tournaisian part of the section bed 79 metabentonite is positioned directly above the devonian carboniferous boundary within the siphonodella sulcata conodont zone five concordant analyses form a cluster with a 2 0 6 pb 3 3 8 u concordia age of 360 5 0 8 ma zircons of the next younger metabentonite bed 70 in the lower siphonodella duplicata conodont zone yielded a tightly grouped cluster of 10 concordant analyses with a 2 0 6 pb 2 3 8 u concordia age of 360 2 0 7 ma on the basis of these two new single zircon ages and previously published late famennian u pb id tims ages the devonian carboniferous boundary is reinterpolated herein to 360 7 0 7 ma

mechanical behavior of groundwater seepage in karst collapse pillars abstract groundwater inrush has an impartible relationship with geological structures such as karst collapse pillars kcps which are widely distributed in north china in order to study the mechanism of groundwater inrush from coal seam floor the variable mass dynamics and nonlinear dynamics were introduced a mechanical model plug model is established to describe the behavior of water seepage flow in coal seam floor containing kcp the study shows that 1 if the mass of the kcp keeps steady the water seepage velocity in the kcp and the surrounding rocks will reach a constant value soon 2 if the mass of the kcp and the surrounding rocks increases by grouting etc the seepage velocity in the kcp and the surrounding rocks will reach its minimum value gradually and 3 if the mass of the kcp and the surrounding rocks decreases by scouring the flow velocity in the kcp and the surrounding rocks shows a monotone increase the water flow may change into pipe flow especially when a large number of the mass of the kcp and the surrounding rocks enters into goaf road which may lead to instable flow and cause groundwater inrush

magnetostratigraphy susceptibility of the přidolian lochkovian silurian devonian gssp klonk czech republic and a coeval sequence in anti atlas morocco abstract the magnetosusceptibility event and cyclostratigraphy msec record for the p idolian lochkovian silurian devonian global boundary stratotype section and point gssp klonk prague basin czech republic is described and used to establish a magnetostratigraphy susceptibility profile for the gssp gssp msec data are summarized into three magnetozones msz the tma msz late p idolian with 13 msszs mssz the klonk msz latest p idolian and earliest lochkovian with 17 msszs and the voskop msz early lochkovian with 7 msszs the base of klonk mssz 2 is coincident with the base of lochkovian and the devonian the proposed magnetostratotype for the p idolian lochkovian boundary is supported by ms data from a nearby core through the gssp sequence and into the upper ludlow three additional mszs are recognized for the portion of the core sequence older than the gssp boundary sequence the extension of the mszs and msszs away from the proposed magnetostratotype is tested by comparison with a lochkovian sequence in the western sahara of southeastern morocco mszs are the result of global sea level fluctuations that alter base level and the pattern of erosion and influx of detrital paramagnetic mineral components into the marine environment large scale transgressive and regressive patterns interpreted from the msec data establish that the silurian devonian boundary in the barrandian region falls between a short lived transgressive pulse in the latest p idolian and an equally short lived regressive pulse in the earliest lochkovian msszs identified in the gssp and core sequences are the result of variation in climate cycles and the resulting periodicity can explained by either the 38 9 ka silurian and devonian equivalent of the modern 54 ka obliquity cycle or the eccentricity cycle of 106 ka periodicity use of the obliquity periodicity gives a duration for the barrandian lochkovian of 4 46 ma which agrees with the most recent geochronometric estimate of 4 5 ma for the lochkovian use of the eccentricity periodicity gives a duration for the barrandian lochkovian of 12 16 ma which agrees with the previous geochronometric estimates of 12 2 and 12 5 ma for the lochkovian in any case the cyclic nature of the msec data established by the msszs can be explained by variations in the rate of supply of weathered terrigenous paramagnetic grains to the marine system these variations in supply occurred due to climate changes resulting from the either the obliquity or eccentricity of the earth s orbit knowledge of the periodicity of lochkovian cycles in the barrandian area allows estimation of the rates of sediment accumulation the duration of fossil ranges and the rates of evolution depending on the choice of obliquity or eccentricity to explain the cyclicity in the barrandian lochkovian the estimated rate of sediment accumulation in the gssp outcrop averaged either 51 or 140 ka m the range of the graptoloid monograptus uniformis angustidens wholly contained within the lochkovian sequence at the gssp is also estimated at either 51 or 140 ka

investigation on the characteristics of overlying strata caving in the chengchao iron mine china in this study a comprehensive assessment of the overlying strata caving characteristics of mental mines is conducted for the non pillar sublevel caving method especially considering the geological features and rock mass characteristics in general the overlying strata caving process can be divided into four stages the intermittent roof caving stage the crack extension and surface subsidence stage the karst collapse stage and the mining induced collapse stage roof caving is an intermittent process with higher caving occurring in stronger rock masses and occurs more easily in weaker rock masses due to gaps generated in the overlying rock mass the bulking coefficient of the overlying strata is much greater than the laboratory measured value it also varies with the mining advance lines during the crack extension and surface subsidence stage the surface deformation is less extensive when the rock strength is greater and the gradient of surface deformation is lower when the rock mass integrity is lower thus higher mining height and lower rock mass quality result in greater surface deformation furthermore weak planes such as faults and joints can help to generate fissures in weathered rock masses these fissures create passageways for groundwater flow which accelerates crack extension and connection in reverse in addition surface collapses can be divided into karst collapses and mining induced collapses because a large number of fissures and a high karst rate create favorable conditions for karst collapse significant variations in groundwater levels can induce karst collapse at the surface with high negative pressure forming in the karst caves mining induced collapses are mainly related to the mining depth mining height and the properties of the overlying rock mass underground mining is a major factor in surface collapse and heavy rainfall can induce a delayed but sudden collapse

late frasnian sedimentation cycles in the appalachian basin possible evidence for high frequency eustatic sea level changes abstract during the late frasnian 11 fourth order progradational retrogradational marine sedimentation cycles were deposited in the appalachian foreland basin mapping based primarily on subsurface data demonstrates the continuity of these cycles over a distance of 700 km cyclicity in distal facies occurs as alternations of organic rich and organic poor shales two of the organic shales can be correlated with the transgressive kellwasser beds of europe in more proximal facies recurring lobes of siltstone and sandstone were deposited based on lithologic indices the temporal pattern shows significant variation in the strength of relative facies change during deposition in particular two times of particularly pronounced progradation correspond to previously recognized eustatic sea level falls the correlation of portions of appalachian basin depositional cyclicity with global sea level events suggests that the entire sequence of 11 cycles with estimated average duration of around 100 150 ka were the result of high frequency eustatic sea level changes this in turn would be consistent with a brief period of late frasnian glaciation as others have previously suggested

application of brillouin optical time domain reflectometry to dynamic monitoring of overburden deformation and failure caused by underground mining abstract brillouin optical time domain reflectometry botdr a fully distributed optical fiber sensing technology was applied to monitoring the deformation behavior of overlying strata during underground mining three types of optical cables metal kieso sensing optical cable mks glass fiber reinforced sensing optical cable gfrs and 10 m interval fixed point sensing optical cable 10 m ifs were embedded vertically into two boreholes that are located 582 m and 1746 m from the open off cut respectively the strain distribution characteristics of the cables and variations of the mechanical and hydraulic properties in the overburden were analyzed with consideration of the lithology and mining positions the results show that mks cable has better performance in strength and accuracy than the gfrs and 10 m ifs cables the strata in front of the panel provided front bearing loads and were compressed in the vertical direction as the panel passed the cables to approximately 90 m the tensile stress increased and the peak value moved up gradually with the occurrence and development of the caved zone the strains of the lower optical drill were negative and in the compression state throughout the monitoring process the upper cable showed a process from compression to tension while the lower cable showed a process from compression through tension to compression in addition the strain distribution of the cables corresponded well with the strata the vertical compression of the strata appears to be inversely proportional to their young s modulus tensile failure dominates in the overlying strata during the mining process with the advancing of the panel the tensile failure zone moved upward episodically and the height of the fractured zone reached the maximum where the distance between the face and cable was approximately 90 or 100 m compared with the traditional monitoring methods botdr monitoring provided more accurate data on the dynamic height of the fractured zone the research results are of practical significance for monitoring overburden deformation under mining and they are helpful to prevent or mitigate water inrush and surface ecological geological disasters

calibrating the devonian time scale a synthesis of u pb id tims ages and conodont stratigraphy the recalibrated devonian time scale represents an important improvement of devonian chronology regarding two aspects firstly a data set of 13 biostratigraphically well bracketed u pb id tims zircon and monazite ages constitutes the framework of the scale secondly approximately time linear biostratigraphic scales have been used for the interpolation between the isotopic ages the new construction thus represents a biochronometric time scale which allows the assignment of numeric ages not only to stage boundaries but also to each biozone boundary the method of interpolation applied also enables the projection of the geochronological error onto the time scale according to the newly calibrated scale the devonian lasted 57 4 5 7 ma from 418 1 3 0 to 360 7 2 7 ma this is compared to previously published time scales the longest time span ever calculated for this period the age interpolations for the eight stage boundaries are famennian tournaisian devonian carboniferous 360 7 2 7 ma frasnian famennian 376 1 3 6 ma givetian frasnian 383 7 3 1 ma eifelian givetian 388 1 2 6 ma emsian eifelian 391 9 3 4 ma pragian emsian 409 1 3 8 ma lochkovian pragian 412 3 3 5 ma pridolian lochkovian silurian devonian 418 1 3 0 ma full size table table options view in workspace download as csv the duration of the middle devonian is calibrated here as quite short with 8 2 ma and the emsian and the famennian are the longest stages with interpolated durations of 17 2 and 15 4 ma respectively together all devonian stages contain 57 conodont zones including subzones according to the standard conodont zonation giving a mean duration of about 1 ma in the highly resolved part of the time scale mid eifelian to the devonian carboniferous boundary zonal resolution averages 0 6 ma in contrast the lowest resolution is shown in the early emsian to mid eifelian interval with zonal durations of up to 5 5 ma serotinus zone

the height of fractured water conducting zone in undermined rock strata the height of fractured water conducting zone is of significant importance for the safety of underground mining because of the conspicuous discrepancy of the height of fractured water conducting zone in bulianta coal mine as predicted by the traditional method with those observed in practice a systematic research has been carried out the study indicates that two aspects should be taken into account firstly the traditionally proposed empirical formula in prediction of the height of fractured zone was based on the conditions of single slice mining where the mining height was less than 3 m and the total slice mining height was limited within 15 m in such a case it would not be suitable to predict the maximum fractured zone height for the conditions where a single mining height is larger than 3 m secondly the stratum structure such as the thick and strong rock layer termed as key stratum plays an important role in controlling of the height of movement in the overburden physical model tests by making use of a similar material illustrate that if the vertical distance from the primary key stratum to the coal seam is shorter than a certain value then the developing fracture zone will extend above the key stratum into the top of bedrock resulting in a larger height of water conducting zone than is calculated by the empirical method the outcome of the work presented will be helpful in practice to prevent the overburden aquifer inrush and to avoid mine water hazard

height of water conducting fractured zone in a coal seam overlain by thin bedrock and thick clay layer a case study from the sanyuan coal mine in north china the accurate determination of the height of the water conducting fractured zone hwcfz in a coal seam covered by thin bedrock and thick clay layer is crucial for aquifer protection mine safety and eco environmental conservation using the sanyuan coal mine in north china as a case study theoretical analysis numerical simulation and field measurements were used to analyze the regularity of the hwcfz in this area per mechanical theory a geometrical model for calculating rock bending and subsidence was established two arcs of equal curvature and lengths and opposite curvature direction were used to fit the curve section of intermediate rock layer after bending the theoretical method for solving the hwcfz was given by calculating the rock layer s tensile ratio in addition rock failure process analysis rfpa software was used to simulate the development of the water conducting fractured zone wcfz during the mining process and the hwcfz was measured by the drilling fluid loss measurement both which verified the feasibility of the theoretical calculation to determine the primary controlling factors affecting the hwcfz the seepage characteristics and plastic properties of the quaternary clay layer were also analyzed using laboratory tests results show that the quaternary clay with a depth greater than 130 m has a permeability coefficient of e 10 m s a liquidity index less than 0 25 and a plasticity index more than 17 indicating the clay layer is impermeable and of great importance to inhibiting the development of wcfz the research can provide significant theoretical insights for effectively preventing water hazards on mine roofs

new u pb zircon ages and the duration and division of devonian time newly determined u pb zircon ages of volcanic ashes closely tied to biostratigraphic zones are used to revise the devonian time scale they are 1 417 6 1 0 ma for an ash within the conodont zone of icriodus woschmidti i w hesperius early lochkovian 2 408 3 1 9 ma for an ash of early emsian age correlated with the conodont zones of po dehiscens lower po inversus 3 391 4 1 8 ma for an ash within the po c costatus zone and probably within the upper half of the zone eifelian and 4 381 1 1 3 ma for an ash within the range of the frasnian conodont palmatolepis punctata pa punctata zone to upper pa hassi zone u pb zircon ages for two rhyolites bracketing a palyniferous bed of the pusillites lepidophyta spore zone are dated at 363 8 2 2 ma and 363 4 1 8 ma respectively suggesting an age of363 ma for a level within the late famennian pa g expansa zone these data together with other published zircon ages suggest that the base and top of the devonian lie close to 418 ma and 362 ma respectively thus lengthening the period by20 over current estimates we suggest that the duration of the middle devonian eifelian and givetian is rather brief perhaps no longer than 11 5 myr 394 ma 382 5 ma and that the emsian and famennian are the longest stages in the period with estimated durations of15 5 myr and 14 5 myr respectively 1998 elsevier science b v all rights reserved

bulking factors and extents of caved zones in weathered overburden of shallow abandoned underground workings abstract a comparison between the bulking factor and height of the caved zone for different weathered subsurface rocks over shallow abandoned mines and for strong rocks at intermediate and large depths of longwall mining is performed in this study vertical boreholes drilled from the ground surface have been used to detect the height of caving in weathered w and very weathered vw rock mass overlying abandoned underground workings at a shallow depth and then to calculate the bulking factor it is found that key parameters that control the bulking factor k and the ratio between the heights of caving and mining h h are different for w and vw rocks in w rocks such parameters are the rock strength of immediate roof and rock porosity whereas those for vw rocks are rock quality designation rqd and standard linear fracture intensity p10 it is argued that h h in vw rocks increases according to linear logarithmic law with an increasing ratio p10 rqd in the immediate roof and p10 in four rock layers over the immediate roof observations show that vw rocks exhibit smaller values of k 1 06 1 165 and larger h h 6 07 15 6 compared to w rocks having 1 09

controls on geochemical expression of subaerial exposure in ordovician limestones from the nashville dome tennessee u s a abstract stable isotope and trace element data from 301 samples in six stratigraphic sections largely support previous inferences of subaerial exposure at third order sequence boundaries in mohawkian and cincinnatian limestones of the nashville dome they also reveal the presence of previously unrecognized surfaces of subaerial exposure for example evidence of subaerial exposure at the tops of parasequences suggests that at least some of the latter are better interpreted as high frequency sequences clusters of surfaces of subaerial exposure near some previously interpreted sequence boundaries suggest that the latter may represent sequence boundary zones some surfaces of subaerial exposure are at neither recognized sequence boundaries nor parasequence boundaries and may represent missed beats in which sea level fluctuations are preserved geochemically but not recognized on stratigraphic criteria recognition of these unexpected surfaces of subaerial exposure may in part depend on the close spacing of samples used in this study different sequence boundaries exhibit different degrees of geochemical alteration and more extensive alteration appears to characterize sequence boundaries of greater temporal significance overprinting of exposure surfaces is controlled by accommodation rate in that meteoric alteration as suggested by low c isotope composition and sr concentration is seemingly pervasive in an interval of slow accommodation but not in an interval of rapid accommodation 18o values show little relationship to exposure surfaces in these strata so that sr 13c plots are more useful than 18o 13c plots in recognizing meteoric diagenesis in aggregated data in this data set 13c excursions interpreted to result from pedogenic processes are at most 2 4 and extend at most only 1 5 meters below exposure surfaces less than the extent of such signatures in younger carbonates such minima are best developed in paleo lowland and paleo coastal settings and they are essentially unrecognizable in paleo inland settings where more section was removed by lowstand and transgressive erosion

early devonian conodont graptolite collation and correlations with brachiopod and coral zones central nevada a range chart of some early devonian conodont and graptolite taxa from central nevada is presented it is based on the graphic correlation method of shaw and shows correlations with the established zones for brachiopods and corals as well as conodonts and graptolites it indicates that the hesperius through pesavis conodont zones established for western north america are approximately equivalent to the lochkovian of the czechoslovakian sequence and the pragian begins approximately with the sulcatus zone the chart also indicates that the zones based on different groups do not coincide are of very unequal duration and that intervals of rapid morphologic change correspond to intervals of higher diversity and greater morphologic variation species have significantly diff rent longevities generally those originating during times of greatest morphologic variation being the shorter lived the approximate duration of the species studied is 2 to 10 m y use of the graphic correlation method permits better correlation of shelf and basin faunas and enhances the possibility for constructing accurate shelf margin histories and for correlating provincial shelf faunas with those in other parts of the world

development and application of a model test system for rockfall disaster study on tunnel heading slope to study the motion law of rockfall which collapses from the tunnel heading slope and the dynamic response of the open cut tunnel to the impact a large scale three dimensional model test system is developed by taking the heading slope above a tunnel exit of the under constructed chengdu lanzhou railway as the study object the system consists of high strength model test bench three dimensional release device of falling blocks a high speed video camera and fiber bragg grating monitoring device etc test bench whose largest exterior dimension is 3 4 m 2 m 2 5 m length width height is made of high strength steel framework and tempered glass as body material to realize the visibility of the test process the block releasing device is mainly composed of a releasing box three groups of slide rails hydraulic cylinder and gas cylinder by which can satisfy the requirements of the initial slip angles of rockfall in various test conditions the high speed video camera is adopted to capture the trajectory of the rockfall and video processing software is used to calculate the motion parameters fiber bragg grating monitoring device is adopted to collect the information about force and deformation of the open cut tunnel under the impact of rockfall and to study the dynamic response of the structure similar materials of slopes falling blocks and open cut tunnel are developed based on the existing geo mechanical materials construction of the models and the arrangement of fiber bragg grating monitoring devices are explained systematically in the paper the results of rockfall impact tests show that the mass release height and impact angle of rock blocks have significant effects on the velocity restitution coefficient of blocks after impacting on the open cut tunnel structure the normal restitution coefficient of the block s velocity is basically between 0 3 and 0 45 the model test system is reliable and can be applied in subsequent model test researches of rockfall disasters

upward slicing longwall roadway cemented backfilling technology for mining an extra thick coal seam located under aquifers a case study many water inrush disasters have occurred in mines that were attempting to recover extra thick coal seams located under aquifers this paper presents a technology known as upward slicing longwall roadway cemented backfilling uslcb which can provide a safe and effective solution to extract these seams the fundamentals of the technology are to divide a coal seam into several slices and extract each slice sequentially from bottom to top using longwall roadway mining technology gobs are filled with cemented backfill which then act as a new floor allowing the overlying slices to be mined similar to the overhand cut and fill method this paper also presents the compressive properties of cemented backfill material with various mixing ratios and curing times moreover a physical simulation was conducted to verify the effects of uslcb the results of the simulation indicate that uslcb can be used to control strata movement as well as the height of the water conducting zone hwcz the uslcb was applied at gonggeyingzi coal mine in inner mongolia china the results indicate that the recovery ratio has increased from 39 2 to 95 the backfill ratio reached 95 water inflow decreased from 245 to 120 m3 h and the maximum hwcz was 39 2 m after extracting the entire 21 m of the coal seam the conclusions of this research show that implementing uslcb can significantly improve productivity and safety when extra thick coal seams are mined which are located under aquifers

numerical analysis of the dynamic evolution of mining induced stresses and fractures in multilayered rock strata using continuum based discrete element methods abstract in this study the continuum based discrete element method cdem was adopted to simulate the evolution of mining induced stress and fracturing during roadway tunnelling and mining in multilayered heterogeneous rock strata the cdem integrates the finite element method fem and the discrete element method dem to characterize the mining induced stress evolution the discontinuous fractures separations and caving that occur in the interfaces between multilayered rock strata the maximum tensile stress criterion and the mohr coulomb strength criterion were used to evaluate the tensile and shear failure of the material elements the cdem model for rock strata was constructed by employing image processing and reconstruction approaches using the geometrical and physical parameters that were measured from a real coal mining site the stress evolution and compression deformation of the roof and floor strata were computed to evaluate the criticality of mining induced disasters the constructed model was employed to simulate and analyse the immediate roof collapse immediate floor bulges and the compaction of the collapse blocks as well as the large deformation separation and collapse between the immediate roof and the main roof during coal seam mining it was shown that the proposed method could predict ranges for the caving zone and fracture zone in the rock roofs that were in good agreement with the observation results from the real coal mining site

three dimensional mineral grade distribution modelling and longwall mining of an underground bauxite seam abstract a multi step interpolation approach was proposed to model the three dimensional grade distribution and to demarcate orebody in a thin and anfractuous bauxite seam a pre mining demonstration procedure was established to virtually perform fully mechanized longwall mining in the modelled bauxite seam meanwhile a comprehensive evaluation function expressed by the sum of dilution and loss rates of bauxite was utilized to determine the optimal cutting heights 1 71 2 69 m and a suitable diameter 1 5 m for the cutting drums mounted on a double drum shearer to achieve no waste and high recovery mining of the demarcated 106 026 m3 bauxite orebody in addition a numerical model of strata containing geological defects a karst cave and fault discontinuities joints and stratifications and a mountain was established to simulate the discontinuous motion and overburden fracturing disturbed by the longwall mining in the modelled bauxite seam the results indicated that the overburden presented reliable stability and impermeability in which no large scale caving in goaf no water influx no cave collapse no fault slip and no mountain slope landslide occurred this was due to arched roofs above the karst cave and the mining induced fractured zone the subcritical condition of the longwall panel in the dip section and support from the protective pillar between two adjacent panels

early silurian sea level changes global sea level fluctuated markedly during the early silurian probably as a result of the waxing and waning of ice sheets in the south american portion of gondwana the highest sea levels of the silurian are recorded by the telychian upper crispus lower griestoniensis and spiralis lower lapworthi biozones other highstands occurred in the early aeronian during the convolutus zone mid aeronian guerichi zone and late turriculatus zone early telychian and early sheinwoodian low sea levels characterized much of the argenteus and sedgwickii zones aeronian the utilis subzone late guerichi early turriculatus zones early telychian the late telychian commencing in the mid lapworthi zone and after a period of apparently only small amplitude sea level fluctuations in the late sheinwoodian and earliest homerian the mid late homerian in particular the early nassa zone facies and faunal changes in the lower silurian do not support the p and s model of jeppsson and others but are consistent with the sea level changes proposed herein mid telychian marine red beds appear to have been deposited during a minor sea level fall immediately after a period of very high sea levels rather than during a transgressive episode as previously suggested comparison of the sea level curve presented herein with those constructed in the past is hampered by the lack of precision currently possible in the correlation of early silurian deep water graptolitic and shallow water shelly sequences improving the precision of this correlation should be a priority for future research

void fraction distribution in overburden disturbed by longwall mining of coal voids in overburden disturbed by coal mining provide channels for transfer of heat methane groundwater oxygen exhaust gas and fire fighting materials in the underground environment based on expressions of strata and ground subsidence a group of void fraction distribution models are proposed including porosity in the caved zone the fracture ratio in the bed separation zone and the fissure ratio in the ground subsidence zone combined with a case study of the antaibao coal mine china theoretical calculation and numerical simulation indicate that porosity distribution in the caved zone is u type and the transverse void fractions in the bed separation zone and ground subsidence zone have m type distributions additionally the longitudinal void fraction distribution changes from type to m type along the strike and dip of the coalbed after the complete subsidence of ground the distribution of fractures in the disturbed overburden of the goaf presents a fractured arch and fracture density gradually decreases from arch foot to crown fire prone zones propagating paths of coalbed fires areas prone to water influx and outlets of boreholes used for fire fighting all usually appear around the perimeter of disturbed overburden the transverse void fractions distribution in the bed separation zone changes from type to m type with an increase in the size of the goaf it is suggested that the inlets of gob vent boreholes should be arranged near the center of the bed separation zone in the early stages of longwall mining and around the perimeter in middle to late stages of mining

prediction of subsidence due to coal mining in raniganj coalfield west bengal india abstract raniganj coalfield is in a major coal producing area and suffers subsidence problems due to underground mining the occurrence of a thick coal seam at shallow depth is the main reason for the subsidence and as a result collapses have occurred in many coal mines in recent years we attempt to predict the subsidence occurring in indian coalfields in general and in particular in the raniganj coalfield using a visco elastic model in this model we have considered the coal seam as a beam resting between visco elastic media which deform due to transverse shear after mining the governing equations have been solved for two cases coal mines with a rigid hard and b flexible soft overburdens the ground subsidence has been computed for two coal mines the computed subsidence profiles of the ratibati and shivadanga coal mines of the raniganj coalfield are compared and the results show a reasonable match between the predicted and observed subsidence in the case of ratibati coal mine in the case of shivadanga coal mine the predicted subsidence profile is found to be larger than the observed profile however the bottom of the observed troughs is found to match the predicted troughs detailed analyses have been carried out to investigate the effect of mine parameters on the subsidence

the numerical age of the devonian carboniferous boundary the shrimp ion microprobe has been used to date zircons in a 1 cm thick bentonite located in the hasselbachtal auxiliary global stratotype section through the devonian carboniferous boundary in germany and a tuff located at a similar biostratigraphic level in australia multiple replicate analyses have yielded indistinguishable ages and indicate 353 2 4 0 ma 2 as the age of the boundary obtaining an age for the boundary in the german reference section depended on the ability of shrimp to date a small sample and to target small areas of structurally complex zircons future refinements of the age of this boundary may depend on re analysis of this uniquely placed bentonite and this highlights the value of defining biostratigraphic stratotypes in the vicinity of known dateable horizons

insights on why graphic correlation shaw s method works in 1964 a b shaw presented a method of correlating fossiliferous sedimentary rocks based on interpretation of graphic plots of first and last occurrences of taxa because there is no way to determine the true total ranges of fossil taxa it is instructive to test the accuracy of the method using hypothetical datasets the dataset used here consists of 16 taxa in six sections with differing known rates of rock accumulation in all graphs a single straight line correlation was a reasonable interpretation the resulting ranges after the first and third rounds of compositing reproduce the true ranges but with small errors slight errors in the positioning of individual correlation lines are more likely to lengthen ranges artificially than to shorten them shaw s method works well because whereas actually sampled ranges will be shorter than true ranges errors in correlation will be likely to extend some ranges this or any exercise using simulated data is useful only if the hypothetical situation resem

radiation from seismic sources in cased and cemented boreholes far field stationary phase approximations are often used to study the radiation of p and s waves from seismic sources located in boreholes usually with an assumption of low frequency and in application to uncased boreholes these two assumptions allow explicit analytical results for the radiation patterns to be derived as boundary condition equations can be solved analytically in fairly simple forms applying the same methodology to cased and cemented boreholes however is much more difficult because of the increased number of simultaneous boundary condition equations i circumvent this difficulty by solving the boundary condition equations numerically using propagator matrices as is generally done in the calculation of synthetic full waveform acoustic logs in this way the assumption of low frequency is also avoided and a generalized stationary phase solution for sources in general concentrically layered borehole models is easily obtained computation of the radiation patterns for cased and uncased boreholes in various formations shows that the amplitude reduction because of the introduction of casing is a function of both source type and of formation velocities axial stress sources are less affected by the casing than either radial stress or volume injection sources and as formation velocity decreases the effect of the casing becomes more significant as the impedance contrast between steel and the formation becomes larger the new generalized stationary phase solution also shows that as frequency approaches 1000 hz the results obtained by low frequency approximations for stress sources can be inaccurate and that the energy radiated from the source becomes more highly directed in the horizontal directions the radiation pattern begins to change relatively rapidly as a function of frequency so that the resulting observations from broad band sources will show changes in waveforms that mimic the effects of attenuation these changes occur because the length of the source becomes important as wavelength decreases demonstrating the need to consider the influence of frequency as well as casing and cement on source radiation

evolutionary dynamics of pragian dacryoconarida lower devonian tentaculitoidea evidence from palaeontological data and 13c of marine carbonates from czech republic abstract a detailed palaeontological study was performed on 38 successive assemblages of dacryoconarids tentaculitoidea sampled along the cerna rokle section praha basin czech republic this section represents the whole pragian stage lower devonian and roughly corresponds to a 6 ma time span dacryoconarid assemblages change in abundance and diversity oxygen and carbon isotope compositions of the dacryoconarid bearing carbonates were measured to evaluate the possible influence and control of the environmental conditions on the evolutionary dynamics of the dacryoconarid faunas large and rapid 13c excursions occur in the marine carbonate sequence of the cerna rokle section some of which apparently correspond with faunal variations however no clear and simple relationship appears between carbon isotope ratio fluctuations and dacryoconarid evolutionary dynamics occurrence and extinction of the dacryoconarid species appear to be mainly related to biotic factors environmental variations cannot be regarded as having preponderantly influenced the dacryoconarid evolution which more probably resulted from intrinsic biotic factors

prediction of water inrush risk areas in process of mining under the unconsolidated and confined aquifer a case study from the qidong coal mine in china the unconsolidated cenozoic formation is well developed in the qidong coal mine water inrushes from the bottom unconsolidated cenozoic aquifer which is the confined aquifer have happened several times during mining in the north mining area of the qidong coal mine to predict the water inrush risk areas in the south mining area of the qidong coal mine where some working faces have just begun to mine the engineering analogy method is used on basis of the fisher s discriminant model from the actual mining situation in the north mining area six main influence factors including the effective thickness the specific yield and the load transfer coefficient of the aquifer the effective thickness of the protective bedrock layer the fractal dimensional value of bedrock faults and the distance between the key hard stratum and the primary mineable coal seam are selected as discriminant indexes and their corresponding data in the north mining area of the qidong coal mine are served as training samples on this basis the fisher s discriminant model for water inrush is established and water inrush risk areas including the safety the medium risk and the risk areas of no 61 82 and 9 primary mineable coal seams in the south mining area of the qidong coal mine are predicted by the model the model s accuracy is 90 4 the scatter diagram of training samples shows obviously classified effect and the field verification indicates that the predicted type is consistent with the actual type results show that the discriminant model is well applied in the engineering analogy method and the water inrush risk areas predicted by the discriminant model contribute to the subsequent mining in the south mining area in the qidong coal mine

effect of sand grain size on simulated mining induced overburden failure in physical model tests abstract to investigate the influence of sand grain size sgs on mining induced overburden failure in physical model tests uniaxial compressive experiments on rock like material with various sgss were performed and two sgss 0 0 5 and 0 5 1 mm were selected the young s modulus uniaxial compressive strength and tangent modulus were larger in rock like material samples with finer sgs and the failure mode changed from mostly shear failure to tensile failure with rising sgs as the mechanical characteristics of coarser sand samples are weaker the overburden breakage distance was shorter in the coarser sand model and the ratio of the average breakage distance between the two models was 1 688 the extent of the overburden fracture was heavier in the coarser sand model and closer pattern to that of the actual coal mine a large database of the heights of the overburden caved zone hcz and fractured zone hfz values with various mining height hm based on previous studies was compiled to obtain best fit parabolic empirical formulas the hcz hm and hfz hm ratios measured in the field were similar to those estimated by the proposed empirical formulas the discrepancy between the physical model test and field measurement may be explained by the fracture pattern in the overburden of the caved zone in the form of layered rectangles unlike the polygonal forms in the coal mine we propose four recommendations to optimize the physical model for such tests from the perspective of sgs the results and recommendations presented here can provide a useful guide for coal mining scientists and engineers designing models for testing of coal mining conditions

a zoning model for coal mining induced strata movement based on microseismic monitoring a microseismic monitoring technique is adopted to investigate the distribution regularity of microseismic events released by the coal mining induced roof rock mass along the vertical and horizontal directions in combination with mine geological data on the basis of the quantity and energy distributions of the microseismic events recorded using the microseismic monitoring technique a zoning method is first established for the roof strata movement in the vertical and horizontal directions the vertically zoning method is then applied to analyze the microseismic monitoring results obtained in the dongjiahe coal mine which divides rock mass into six zones along the vertical direction i e the caved zone the block zone the vertical fracture through going zone the vertical fracture zone the separation zone and the continuous zone the horizontally zoning model divides the roof strata movement into three zones i e the calm zone the generation zone impacted by working face and the historical generation zone after that based on the horizontally zoning model a method is developed to determine the displacement angle using the microseismic monitoring data which has been verified in the dongjiahe coal mine

model experimental research on deformation and subsidence characteristics of ground and wall rock due to mining under thick overlying terrane abstract based on the prototype of a mine a physical simulation test is conducted the characteristics of the deformation and failure of the ground surface and the wall rock around a goaf as well as the creep behavior of the wall rock deformation and the failure mechanism are analyzed the simulation test has greatly improved our understanding on the wall rock s deformation and failure characteristics for the first time digital close range photogrammetry was used to measure the displacements in a sectional model test the measurements by this technique agreed very well with those obtained by other methods such as using dial gauges

physical modelling of subsidence from sequential extraction of partially overlapping longwall panels and study of substrata movement characteristics field examples of subsidence from sequential extraction of overlapping coal longwall panels have shown that complex and unexpected subsidence effects can occur physical models comprising sand and plaster obeying relevant similarity rules were used to investigate the subsidence mechanisms displacements within the models were measured using a combination of optical transducers photogrammetry and laser scanning the observed results were compared with finite element models the models demonstrate that the incremental subsidence and substrata movement profiles after lower seam extraction can be separated into three different zones these zones undergo different horizontal and vertical movement characteristics the zone of overlap of the two longwall panels undergoes greater total subsidence compared to a single seam of equivalent thickness the limit angle of the subsidence also differs at the two ends of the lower extraction as a result of the effects of the previously mined out area above

two new emsian early devonian u pb zircon ages from volcanic rocks of the rhenish massif germany implications for the devonian time scale so far only few biostratigraphically well constrained isotopic ages constitute the geochronological framework of the devonian period to expand this sparse dataset two new u pb isotope dilution thermal ionization mass spectrometry id tims zircon ages were obtained from volcanic rocks of the rhenish massif germany these rocks are interbedded in emsian lower devonian marine sedimentary successions that are well documented by index fossils given that the u pb zircon data represent primary crystallization and eruption ages they provide an important contribution to the devonian time scale the older sample a stratiform volcaniclastic layer hans platte is collected from bundenbach hunsruck the type locality of the lower emsian hunsruck slate a cluster of five coherent single zircon analyses obtained from this layer yielded a weighted mean 206 pb 238 u age of 407 7 0 7 ma which is regarded as the time of eruption of the pyroclastic rock biostratigraphically the layer can be assigned to the upper part of the polygnathus excavatus conodont zone the younger u pb age was obtained from the global stratotype section and stratigraphic point section at wetteldorf eifel where the k bentonite hercules i is intercalated 13 m below the lower middle devonian boundary in the uppermost part of the polygnathus costatus patulus conodont zone some of the 19 single zircon analyses obtained from this bentonite appear to document significant influences of inheritance the 13 youngest points are however concordant and form an elongated cluster along concordia with 206 pb 238 u ages between 392 2 and 407 7 ma given the risky assumption that this age scattering is exclusively caused by varying amounts of inheritance the youngest point of this cluster represents the analysis with the least or no inheritance in this case its 206 pb 238 u age of 392 2 1 5 ma should approach the eruptional age of the bentonite the ages presented here in combination with u pb id tims zircon and monazite ages from other workers allow a recalibration of the early emsian to early eifelian interval of the devonian time scale the result is a duration of the emsian stage excluding the basal emsian p kitabicus conodont zone of more than 17 2 ma and an emsian eifelian early middle devonian boundary age of 391 8 0 4 ma

the durations of silurian graptolite zones recently published radiometric data show the duration of the silurian period to be approximately 32 ma significantly longer than previous estimates radiometric and graphic correlation studies demonstrate considerable variation in the durations of the four silurian epochs approximately 13 ma for the llandovery 4 ma for the wenlock 5 ma for the ludlow and 10 ma for the p idoli using this new geochronological data figures for average graptolite zone duration are presented for each epoch ranging from as little as 0 44 ma in the wenlock to 1 43 ma in the p idoli the figures provide a refined subdivision of the silurian timescale of value to studies which use silurian graptolite zones to calibrate geological processes

characterising the multi seam subsidence due to varying mining configuration insights from physical modelling abstract multi seam mining induced subsidence profile is observed to be different from that of single seam mining understanding the characteristics of multi seam subsidence is the first step in achieving reliable subsidence predictions characteristics of multi seam subsidence are investigated by means of several sand plaster physical models geological and site specific parameters are kept constant in all the models in order to compare the multi seam subsidence parameters for different mining configurations based on observations from the physical models it is concluded that the panel configurations of the two seams have significant impact on the multi seam subsidence development based on the relative location of the panels the multi seam mine area can be divided into different zones to which suitable subsidence characteristics can be assigned dividing the mine area into different zones enables characterisation of the strata movement and multi seam subsidence for various multi seam configurations the proposed characterisation of the multi seam subsidence can also be utilised in subsidence prediction methods in order to achieve reliable prediction results

millennial scale paleoclimate cycles recorded in widespread palaeozoic deeper water rhythmites of north america rhythmically interbedded limestone and shale or limestone and chert rhythmites are a common feature of many deep water phanerozoic carbonate marine deposits seventeen different palaeozoic rhythmite successions from across north america 8 studied in detail 9 studied in reconnaissance are described and summarized individual rhythmite couplets 4 20 cm thick are composed of fine grained laminated to massive detrital limestone alternating with shale or marl or laminated spiculitic chert stratigraphic and primary depositional features within rhythmites and associated facies indicates that the carbonate rich and carbonate poor interbedding is the result of repetitive changes in sediment input primary rather than due to diagenetic redistribution of calcareous material secondary the average duration of individual rhythmite couplets is calculated using spectral analysis to determine couplet thickness combined with biostratigraphically calibrated undecompacted average sediment accumulation rates the duration of rhythmite couplets from the eight well studied successions ranges between 150 and 4900 yrs with the majority lying between 1000 and 3000 yrs i e millennial scale the paucity and low diversity of skeletal and trace fossils preserved suspension laminae lack of sediment reworking and facies associations indicate rhythmite accumulation was favored by 1 deposition below storm wave base which limited reworking by currents 2 dysaerobic bottom waters which restricted bioturbation and intermixing of interbedded lithologies and 3 proximity to nearshore carbonates supplying abundant fine grained detrital carbonate these combined conditions were best met along flooded subtropical continental shelves or epeiric seas during my scale 3rd order sealevel rises the rhythmic alternation between carbonate rich and carbonate poor layers is interpreted to represent millennial scale paleoclimatic changes related to 1 wet dry climate cycles which influenced the amount of continent derived eolian and or fluvial sediment input 2 variations in offshore transport via storm generated or density currents of nearshore derived terrigenous or carbonate sediments and or 3 changes in wind driven upwelling and availability of recycled biogenic silica the various rhythmite successions accumulated under dramatically different paleoenvironment and paleogeographic conditions including active to passive tectonic settings equatorial to subtropical latitudes long term icehouse through greenhouse climatic conditions calcite versus aragonitic seas variable atmospheric co2 concentrations before and after land plant and animal evolution and across widely varying ocean basin configurations if our short term paleoclimatic interpretations for the rhythmites are correct then it is apparent that millennial scale climate changes occurred over a very wide spectrum of paleoceanographic paleogeographic paleoclimatic tectonic and biologic conditions and over time periods from the cambrian to the quaternary given this it is difficult to invoke models of internally driven thermohaline oceanic oscillations or continental ice sheet instabilities to explain their origin instead we suggest that

investigation of movement and damage of integral overburden during shallow coal seam mining abstract most prediction methods used to calculate mining induced subsidence are empirical which cannot explain the mechanism of fundamental rock strata movement in this paper based on key stratum theory and the mechanical analysis of overburden a new analytical solution the analogous hyperbola subsidence model ahsm was proposed to describe the movement and damage of inner burden mining induced rock strata movement was verified using the distinct element method udec to assess the performance of the theoretical model three subsidence parameters smax t sgoaf smax d h generally used to describe surface subsidence trough agree with statistical field measurements of the south coalfield in australia the surface subsidence and the movement boundary in the overburden are very close to the theoretical predictions additionally the primary key stratum damages the least in the overlying strata its broken length is the smallest the width of subsidence trough and maximum surface subsidence increase as the primary key stratum drops

a conodont based silurian chronostratigraphy ranges of 79 conodont species are used to effect a graphic correlation of upper llandoverian pridolian silurian rocks in 30 stratigraphic sections in europe and north america a silurian composite standard section css developed by this method provides the total stratigraphic ranges for all species for which there is information in the system these ranges are stated in terms of the sequence of silurian rocks at cellon austria which is the standard reference section srs the llandoverian wenlockian and ludlovian pridolian boundaries are recognized based on the position of the golden spike in the boundary stratotypes the leasows hughley brook and pozary sections which form parts of the css range data for graptolite species in ten of the stratigraphic sections are used to approximate positions of all other boundaries between silurian series and stages that have been designated in boundary stratotypes that are not parts of the composite standard section the pridolian is shown to have had a longer duration than either the ludlovian or wenlockian and the llandoverian possibly approximated the pridolian in duration the css is divisible into 48 standard time units stu9s of conceptually equal length hence the chrono stratigraphy based on it resolves at a level two to four times higher than any previously proposed for the silurian the css is also divided into a succession of conodont chronozones that are based on zones proposed by walliser 1964 aldridge 1972 and barrick and klapper 1976 conodont chronozones can be recognized with confidence only in sections that are parts of the css framework

eustatic and tectonic control on the distribution of marine seismites examples from the upper ordovician of kentucky usa abstract widespread zones of soft sediment deformation are not ubiquitous throughout the rock record rather they are associated with orogenic sediments and are concentrated in specific portions of depositional sequences characterized by deformation prone facies upper ordovician soft sediment deformation features exposed in kentucky are here interpreted as the result of seismically induced thixotropic fluidization of muds resulting in foundering of denser silts and carbonate sands and corresponding diapiric injection of muds severity of soft sediment deformation is associated with sediment density gradients bed thicknesses and varying magnitudes of triggering events the widespread nature 5000 km 2 of multiple deformation horizons argues for a seismic trigger resulting from reactivation of multiple basement faults eight large scale 3rd order depositional sequences were examined for the presence of specific deformation features and stratigraphic position of those intervals the regular distribution of deformation prone facies throughout the upper ordovician seems to have been regulated by eustatic fluctuations seismicity generated by far field tectonics provided the triggering mechanism to disrupt deformation prone strata the record of seismites and their co occurrence with k bentonites provides a meter of intensity and timing of tectophases of the taconic orogeny

a field study of seismic attenuation in layered sedimentary rocks ii crosshole data summary a series of crosshole seismic experiments have been performed at the imperial college borehole test site in northumberland england using a detonator source and hydrophone receivers the holes have been drilled through a horizontally layered sequence of carboniferous limestones shales and sandstones estimates of intrinsic q were obtained for frequencies between approximately 500 hz and 1 5 khz a comparison with the results of part i suggests evidence of frequency dependent intrinsic q with attenuation at 1 khz being significantly greater than at 100 hz no change of intrinsic attenuation with ray direction from horizontal oo to 60 was observed however since no high frequency crosshole data for ray angles between 60 and vertical is available we cannot entirely discount the possibility that the difference in intrinsic q estimates from the vertical vsp data part i and the crosshole data is due at least in part to anisotropic intrinsic attenuation

low frequency radiation from point sources in a fluid filled borehole far field displacement fields have been derived for an impulsive point force acting on a fluid filled borehole wall under the assumption that the borehole diameter is small compared to the wavelength involved the displacements due to an arbitrary source can be computed easily by combining the solutions for the impulsive sources in general the borehole source generates not only longitudinal and vertically polarized shear waves but also horizontally polarized shear waves this study also indicates that only the axisymmetric motion around the borehole due to normal stress is affected by the fluid in the borehole in the long wavelength limit the presence of the fluid does not affect the radiation from tangential sources into the surrounding medium

on prevention and mechanism of bed separation water inrush for thick coal seams a case study in china bed separation can occur in overlying strata especially in hard and soft interbedded roof strata if these strata prone to form bed separation are rich aquifers water can accumulate into bed separation and maybe cause a serious water hazard under the condition of water inflow passages existence therefore studying these types of roof water inrush mechanisms forecasting roof water inrush and formulating preventive and control measures in advance are extremely important to a mine in this paper we takes the typical case of water inrush in the workface number 1121 at hongliu coal mine as an example and study the mechanism of water inrush in detail primarily field drilling with water leakage and color tv observations showed that the maximum height of the water conducting fractured zone was 12 50 times the thickness of the coal seams which spread to the overlying coarse grained sandstone aquifer secondly the numerical simulation indicated that bed separation storage space was prone to form under the combination of coarse grained sandstone and mudstone geological structure the detection using uwtem revealed that the groundwater accumulated in this bed separation and formed a water bag bed separation water when the water bag reached a certain degree water bursting happened with the main roof collapsing finally prevention effective drainage methods and successful experiences with bed separation water have been summarized and it will have a major significance to coal mines suffering from bed separation water inrush

separation and fracturing in overlying strata disturbed by longwall mining in a mineral deposit seam abstract mining induced fractures influence the stability of overburden and may provide pathways for transferring heat and mass in underground environment a novel approach was proposed to quantify the separation and fracture evolution in the undermined overburden consisting of 1 theoretical distribution models of the void ratios of fractures vrfs based on analytical evaluation of key strata subsidence and 2 numerical modeling using the universal distinct element code and a sequence of image post processing procedures for a longwall mining panel both theoretical calculations and numerical simulations indicated that vrf first increased rapidly then gradually decreased and finally stabilized to a minimum from the surrounding edges of disturbed strata to their centers and gradually decreased from deep to shallow strata the fractures exhibited a fracture rich arch distribution type along a vertical section numerous fractures occurred around the arch feet near the perimeters of mined out area and or arch crown near the center of disturbed strata the distributions of vrfs show the heights shapes and damage intensities of fractured zones and can also be used as porosity parameters to determine the permeabilities of mining disturbed overburdens therefore the vrf models can be used as a quantitative parameter to assess the extent of possible risk zones e g for water inflow into the mine or escape of hazardous fluids to the surface

quantifying uncertainties in attenuation estimation at methane hydrate bearing zones using sonic waveform logs abstractapplication of seismic attenuation estimation using sonic waveform data is limited because the estimation methods have not yet been fully developed although the median frequency shift method is considered to be effective and robust compared to the conventional spectral ratio method we demonstrated that the median frequency shift methods strongly depend on reference data under lower signal to noise ratios we modified an existing median frequency shift method not to depend on arbitrarily choosing a reference value and to quantify the uncertainties in attenuation estimation furthermore we implied the optimum selection of receiver pairs used for more stable attenuation analysis our numerical experiments supported the advantage of the proposed method although our main findings by applying the proposed methods in methane hydrate bearing sediments are almost consistent with past field sonic logging measurements we find some differences in the magnitude of attenuation values compared to existing s

on the origin and significance of pyrite spheres in devonian black shales of north america abstract devonian black shales deposited on the north american craton contain abundant tasmanites cysts that are typically preserved as flattened circular discs on bedding planes work by the present authors shows that cysts can be preserved as pyrite infill casts that are expressed as sand size whole and geopetal half spheres of pyrite at the bases of thin black shale layers these occur in situ at many stratigraphic levels in the distal prodelta facies of the catskill delta complex of new york as well as in laterally equivalent black shales in tennessee and kentucky reworked pyrite casts usually dominated by whole spheres form lenticular lag accumulations and hydraulic placers together with plant debris and phosphatic particles bone debris conodonts an earlier model for the formation of pyrite spheres in gas bubbles is rejected in favor of formation within uncompressed tasmanites cysts direct observation of cyst cuticle in association with pyrite spheres suggests that localized bacterial sulfate reduction in tasmanites interior voids led to formation of localized pyrite deposition in a manner similar to that described from certain ammonoid chamber settings cyst fill commenced with formation of framboidal pyrite followed by later diagenetic pyrite cementation between framboids these fills show geopetal features and appear to have formed within the redox zone below the sediment water interface although described here from the upper devonian comparable pyrite textures are also known from proterozoic cambrian ordovician and silurian sediments they probably occur throughout the sedimentary record and in mudstone successions they may prove to be an important source of sand size grains in areas far removed from the basin margins as such they may be important for detection of erosive events and strong bottom currents and provide valuable information about the depositional history of mudstone successions

height of the mining induced fractured zone above a coal face abstract the development height of a gas conducting fracture zone gfz in the gob overlying strata is crucial to the gas drainage and safe production of a coal mine in order to address the issues of excessive gas concentration and uncertain gfz height in no 7435 face overlying strata of kongzhuang coal mine china the caving characteristics of overlying strata were explored using both physical experiments on similar materials and numerical simulations of particle flow code pfc software and verified each other the relationship of cracks development to porosity changing characteristics was introduced to quantitatively determine the height of the local gfz the quantified gfz heights were compared with those measured using the in situ drilling flow method the results showed that 1 pfc software could accurately simulate the overlying strata caving behaviors thus saving manpower materials and financial resources needed for related physical experiments and 2 the temporospatial distribution characteristics of porosity could be used to forecast gfz height and are of significant importance for determination of gfz overall the conclusions are of engineering significance for accurate arrangement of boreholes for gas drainage and reduction of mine gas disasters

chronometric calibration of mid ordovician to tournaisian conodont zones a compilation from recent graphic correlation and isotope studies three available graphic correlation analyses are used to calibrate mid palaeozoic conodont zonations sweet s scheme for the mid to upper ordovician kleffner s for the mid to upper silurian and murphy berry s for the lower and middle lower devonian the scheme of sweet is scaled by applying the high precision u pb zircon date of tucker and others for the rocklandian and linked with that of kleffner by scaling the graptolite sequence of the ordovician silurian global stratotype section to fit two similarly derived dates from this sequence the top of kleffner s scheme all of murphy berry s as well as standard zones to the frasnian are calibrated by using tie points of the latest cambridge bp time scale gts 89 however the recent microbeam zircon date by claoue long and others for the hasselbachtal devonian carboniferous auxiliary stratotype is used to calibrate the standard famennian zones also the similarly derived but preliminary determination reported by roberts and others from the isismurra formation of new south wales is tentatively taken as the top of the tournaisian and so used to calibrate tournaisian zones despite the considerable extrapolation required to compile these schemes and their inherent errors the resultant time scale closely agrees with other dates of tucker and others from the llanvirn as well as the gts 89 homerian gorstian tie point this suggests that stratigraphic methods can be usefully applied to geochronometry the llandovery appears to have lasted longer 16 m y than usually envisaged and the ordovician silurian boundary may need to be lowered to approximately 443 5 ma certainly chrons varied widely in duration and further stratigraphic studies to estimate their relative durations as well as high resolution dating for their calibration will be crucial to more accurate biochronometries

integrated monitoring and modelling of ground subsidence in potash mines abstract ground subsidence is a subject of investigation in two potash mines in new brunswick canada geometry of salt and potash deposits and mining methods in the two mines are different the goal of the investigation is to obtain a better understanding of the mechanism of the salt rock deformation and to develop prediction models of gorund subsidence through a comparison of numerical models with observed ground subsidence two monitoring networks have been observed annually over the past several years using terrestrial geodetic measurements of high precision and the satellite global positioning system gps a method for numerical modelling of the behaviour of the salt rock and overlain brittle rocks has been developed the method uses sequential finite element linear elastic solutions in which the salt rock is treated as a non newtonian liquid and the overburden brittle rocks are considered as a non tension material preliminary results are summarized

strontium isotope stratigraphy of the middle devonian brachiopods and conodonts a set of 145 strontium isotope ratios based on skeletal components of emsian to frasnian age reveals a detailed structure of the seawater 87sr 86sr curve that can ultimately serve as a tool for high resolution isotope stratigraphy in the devonian brachiopod and conodont samples were collected in the eifel region of germany the area around the global stratotype for the middle devonian with an apparent average temporal resolution in the 105 y range preservation of the brachiopod shell material has been assessed by optical microscopy sem and cathodoluminescence and only the better preserved internal secondary layer of the shell has been utilized for strontium isotope measurements the 87sr 86sr curve shows a short decline from 0 7081 to 0 7078 through the late emsian followed by short term fluctuations with an amplitude of up to 10 4 around a mean of 0 7078 during the eifelian and givetian and a rise from late givetian into the late devonian the above high frequency oscillations and spikes are likely a reflection of condensed sedimentary records due to erosional and nondepositional events but a direct confirmation for such a scenario can be claimed only for the latest eifelian otomari event insufficient stratigraphic resolution precludes testing for the other events and isotopic spikes conodont skeletal elements even if well preserved at cai 2 5 yielded results that are mostly enriched in radiogenic 87sr if compared to coeval brachiopods although this enrichment is usually within the 10 5 range conodonts despite their superior stratigraphic resolution should be utilized only as a material of second choice in cases where brachiopods are rare or absent

a revised 87sr 86sr curve for the silurian implications for global ocean chemistry and the silurian timescale abstractrecent recalibration of the silurian timescale and improved global chronostratigraphic correlation of silurian strata significantly altered the silurian 87sr 86sr curve and the temporal extent of available data whereas previous silurian 87sr 86sr composites showed a generally monotonic increase throughout the silurian revisions to the silurian timescale now require a major increase in the rate of change in 87sr 86sr at or near the onset of the gorstian age of the ludlow epoch similarly improved chronostratigraphic correlations between silurian outcrops on anticosti island canada and gotland sweden indicate that the middle part of the telychian age which is roughly 10 15 of the total duration of the silurian period is undersampled and underrepresented in silurian 87sr 86sr composites a revised silurian 87sr 86sr curve based on 241 new and published analyses confirms the significant increase in the rate of change of 87sr 86sr toward more radiogenic values near the base of the ludlow ser

evolution mechanism of water flowing zones and control technology for longwall mining in shallow coal seams beneath gully topography the height and evolution mechanism of fractured water flowing zones are of great importance for prevention of water inrush disasters and protection of immediate environments particularly in ecological vulnerable areas in this paper comparative approaches including empirical formula calculation physical simulation numerical simulation and protem transient electromagnetic analysis are employed to identify the development of the fracture zones caused by water flowing so as to ensure mining safety and protection of groundwater in shallow coal seams beneath gully topography an empirical formula was used to calculate the height of the water flowing fracture zone and an experimental study utilizing a model based on a similar material was adopted to analyze the movement and fracture development of the overlying strata results provide a reasonable basis from which a rational mining height may be determined the protem transient electromagnetic apparatus was employed to detect the water flowing structure conductivity of the overlying strata induced by mining beneath gully topography in the field the water flowing fracture of the overlying strata can be estimated according to comprehensive analysis of the apparent resistivity changes of the field gully surface crack development and aquifer water level accordingly the control technologies in the field were implemented and discussed regarding preventing gully water from rushing into underground mining spaces through water flowing fracture zones results indicate that safe and efficient mining of shallow seams beneath gully topography can be achieved by prevention of gully accidents and protecting the surface water resources of the ecological environment

u pb chronology of the ennerdale and eskdale intrusions supports sub volcanic relationships with the borrowdale volcanic group ordovician english lake district u pb analyses of zircons from the ennerdale granitic intrusion and eskdale granite english lake district give ages of 452 4 ma and 450 3 ma respectively these data confirm the sub volcanic association of these intrusions and show that previously published rb sr whole rock and k ar mineral ages do not correspond to the emplacement and cooling of these igneous bodies the new ages show that only two phases of acid magmatism can now be linked to the exposed parts of the lake district batholith the caradoc late ordovician phase was caused by the subductionrelated processes which gave rise to volcanism and was followed by a separate early devonian phase of granite emplacement

high resolution sequence stratigraphy of a mixed carbonate siliciclastic cratonic ramp upper ordovician kentucky ohio usa insights into the relative influence of eustasy and tectonics through analysis of facies gradients abstract detailed facies analysis and event stratigraphy of an upper ordovician rocklandian edenian cratonic ramp succession in eastern north america yields insights into eustatically driven sequence architecture and localized tectonic instability seven predominantly subtidal mixed carbonate siliciclastic depositional sequences 3rd order are identified and correlated across the length of a 275 km ramp to basin profile within the larger depositional sequences 3rd order at least two smaller orders 4th and 5th of cyclicity are recognizable three systems tracts occur within each sequence transgressive tst highstand hst regressive rst and are considered in terms of their component parasequences 5th order generally tsts are composed of skeletal grainstone rudstone facies hsts are dominated by shaly nodular wacke packstone facies and rsts are mostly calcarenite facies systems tracts sequence boundaries and their correlative conformities maximum flooding surfaces and forced regression surfaces were traced from shallow shelf to basinal settings this high resolution framework also provides insight into the timing of tectonic fluctuations on this cratonic ramp during the taconic orogeny and documents the relative influence of tectonism on lateral facies distributions and eustatically derived cyclicity

field investigation of fractures evolution in overlying strata caused by extraction of the jurassic and carboniferous coal seams and its application case study abstract in multiple seam coal mining the fractures induced by the mining of the lower coal seam may propagate to the goaf of the upper coal seam that is mined earlier the fracture connection leads to the leakage of hazardous gas to fully understand the gas leakage due to fracture evolution the electromagnetic based measurement system and the borehole televiewer were adopted in the panel no 8100 in tongxin coal mine datong coalfield china the coal seam thickness is 15 m and it was mined by top coal caving method the resistivity and fracture pattern in distinct zones of rock stratum were detected and the correlation between them was explained clearly we found that the fracture evolves in two stages as the panel working face advances i e fracture propagation and fracture re closure the maximum height of fracture propagation is 150 m in which the height of the caved and the fractured zones are 80 m and 70 m respectively these fractures start to be compacted and are re closed at the distance of 80 m behind the working face the extraction of the panel no 8100 results in the formation of a gas bearing zone gbz with separations and shear fractures rather than connecting the goafs of the carboniferous coal seam ccs and the jurassic coal seam jcs the gbz is located in a region from 80 m to 150 m above the goaf and 80 m behind the working face based on the above findings effective gas drainage approach is proposed to reduce the concentrations of the hazardous gases consisted of ch4 and co after gas drainage the maximum concentrations of ch4 and co drop to 0 5 and 16 63 ppm with reductions of 53 7 and 33 9 respectively

strontium isotope systematics of conodonts middle devonian eifel mountains germany abstract the eifel mountains lithological profile the stratotype for the middle devonian was densely sampled for conodonts to delineate the sr isotopic evolution of coeval sea water the 87sr 86sr curve obtained shows oscillations around a mean of about 0 7078 that have a frequency in the 105 106 yr range and an amplitude in the 10 5 10 4 range these oscillations mimic those obtained on coeval brachiopods diener et al 1996 but are shifted into more radiogenic domains by up to 10 4 model calculations suggest that the shift is due to partial 30 40 early diagenetic equilibration of conodonts with their enclosing bulk rock matrix the reality of partial recrystallisation is supported by visible neoformed blocky apatite crystals on the surface of the conodonts despite their otherwise apparently excellent preservation with cai values of 1 5 2 5 we therefore suggest that studies anticipating use of conodonts as a recorder of paleoceanographic events should be confined to specimens embedded in a relatively clean matrix such as pure limestone even these results should be cross checked by comparison with data on coeval low mg shells such as brachiopods or belemnites

seismic sources in open and cased boreholes theoretical modeling based on the equations of linear elasticity is used to analyze the performance of downhole seismic sources specifically symmetrical radial sources which exert outward pressure on a length of the borehole wall and vertically driven sources clamped to the borehole wall torsional sources radiate pure s waves whose form is independent of the existence of the borehole and therefore requires no special discussion the radial sources discussed are airguns waterguns and implosive sources such sources are in widespread use and development at present from the calculations we find that radial sources emit almost all 99 percent their energy as tube waves which travel along the borehole and not out into the formation vertical sources radiate almost all their energy into the formation as p and s waves however if the casing bond slips the vertical sources lose efficiency and radiate energy as extensional waves along the casing the radial sources are little affected by the quality

vila maria formation silurian parana basin brazil integrated radiometric and palynological age determinations fresh shale samples taken from a well known outcrop section of the silurian vila maria formation located on the northeastern margin of the parana basin tres barras farm goias state central western brazil have been analysed for both palynological and radiometric age determi nations the rocks yielded a fairly diverse age definitive cryptospore assemblage and the same samples proved suitable for rb sr analysis despite silurian sedimentary rocks being rarely suited to radiometric dating techniques this study thus introduces an alternative independent method for estimating the minimum depositional age of the vila maria formation the rb sr age value has been calculated via an isochron diagram that yields 435 9 7 8 ma accordingly the latter value is inter preted as the minimum depositional age of the analysed vila maria strata implying their deposition during llandovery times this concurs with the palynological results which indicate an age no older than early silurian and more particularly favour an early to middle llandovery rhuddanian early aeronian attribution

impact of particle transfer on flow properties of crushed mudstones karst collapse pillar kcp is widespread in north china coalfields where coal extraction above the ordovician limestone aquifer is threatened by the abundant supply of water and a very high hydraulic pressure kcp is composed of rock skeleton and fine fillings which can be transferred under the effect of water flow thus kcp usually functions as a channel for groundwater inrush in order to investigate the mechanism of mining induced groundwater inrush of kcp which was caused by fine fillings transfer a self designed particle transfer permeability testing system was used to test the crushed mudstones flow properties which included fine filling particle transfer rate porosity increase rate and permeability under the conditions of varying pore pressure particle size mixture and compaction level initial porosity the tests indicate fine fillings transfer is the essential reason for mining induced groundwater inrush flow instability of kcp the flow properties changeability during fine particle transfer could be divided into four stages i e initial flow stage flow inrush stage continued particle flow stage and stable flow stage and flow inrush stage which is the key point to cause water inrush due to the crushing of edges and corners and the adjustment of the structure the fluctuation of permeability time relationship mainly distributed in the first two stages which make a change to flow channel moreover with the increasing of pore pressure particle size mixture and initial porosity the water inrush time and stable seepage time decreased more rapidly the fine fillings porosity and permeability increased gradually the efficiency criteria analysis between measurement and calculation permeability shows an empirical equation can fit the relationship between porosity and permeability well and not all of the pore structures were in flow this means there was a part of pores that were invalid but the effective porosity in flow can be treated as calculation value approximately

application of 3d laser scanner optical transducers and digital image processing techniques in physical modelling of mining related strata movement a physical testing protocol for modelling mining related problems has been presented a new method for monitoring fracture propagation pattern has been introduced laser based and optical devices have been used for physical modelling of subsidence multiple seam subsidence has been measured by photogrammetry dic analysis optoncdt and 3d tls

tracking changes in the specific storage of overburden rock during longwall coal mining the hydraulic properties of geologic formations such as specific storage and hydraulic conductivity are known to vary spatially due to formation heterogeneity however they may also change temporally if the formation undergoes mechanical disturbance such as occurs during mining characterising changes in hydraulic properties is important for groundwater systems that are disturbed by mining conventional hydrogeological investigations rely on literature derived values or limited programs of field testing e g pumping test to define specific storage but these approaches do not consider the change in compressibility that may occur due to mechanical disturbance this paper presents for the first time direct in situ measurements of the changes in compressibility and consequently specific storage as a result of mechanical disturbance within geologic formations overlying underground mining operations the in situ measurements of compressibility are derived in this study from the pore pressure response to barometric loading or strains induced by earth tides even prior to disturbance the compressibility obtained from in situ measurements was found to be an order of magnitude lower than that measured on core samples by unconfined strength test in the laboratory the differences in compressibility for the intact formation are likely due to sample disturbance and the differences in strain level imposed by the field and laboratory methods the increase in compressibility of the overburden rock varied with the location of the monitoring site relative to longwall extraction and the level of strain the formation sustained the study found that quantifying the changes in compressibility and consequently specific storage as a result of mine induced disturbance is critical to our understanding of subsidence the extent of depressurization and the impact that mining may have on regional groundwater flow systems

conodont based quantitative biostratigraphy for the eifelian of the eastern anti atlas morocco the measured ranges of 52 conodont taxa present in 7 eifelian sections of the eastern anti atlas in southern morocco have been as sembled by graphic correlation method into a chronostratigraphic framework the anti atlas regional composite developed in this study provides much higher stratigraphic res olution than the traditionally used conodont zonation it allows a subdivision of the eifelian into 65 7 composite standard units derived from the jebel ou driss section which was se lected as the standard reference section the framework appears to have a linear fit to time giving the first image of the relative duration of the conodont zones in the upper emsian to lower givetian interval the costatus kockeli anus and lower varcus chrons appear to have lasted more than two times longer than the partitus australis and or hemiansatus chrons an alternative upper eifelian lower givetian conodont zonation with zones of more equal duration is proposed several conodont index taxa in the anti atlas area display an almost synchronous appearance independent of fa cies conditions and shelf paleobathymetry the analysis by graphic correlation reveals significant differences in rate of sediment accu mulation between the tafilalt platform which had condensed sedimentation 2 5 m m y and the mader basin characterized by rates up to 40 m m y area the devonian rocks offer excellent condi tions for detailed biostratigraphical studies their depositional history reflects the process of disin tegration of the northern margin of the sahara cra ton wendt 1985 1988 in contrast to the rather uniformly developed upper silurian and lower devonian sedimentary rocks differential subsi dence affected the area during eifelian time and thus a platform to basin topography of the shelf began to originate this phase is biostratigraphi cally relatively well constrained conodonts were found in many sections providing a base for cor relation of eifelian rocks in the anti atlas bul tynck and hollard 1980 bultynck and jacobs 1981 bultynck 1985 1987 1989 1991 the fauna dominated by polygnathus elements is lo cally very abundant but some stratigraphically important eifelian index taxa are rare or absent so that the position of some zonal boundaries e g the base of the eifelian cannot be precisely rec ognized this is why bultynck 1987 proposed two alternative conodont zonations for the upper eifelian lower givetian interval in order to provide a more accurate basis for correlation of eifelian rocks and events in north ern africa we used the graphic correlation method to develop a composite standard section based on conodont data from the eastern anti at las our regional chronostratigraphic framework anti atlas regional composite provides a much more linear biostratigraphic subdivision than any previously used conodont zonation it offers moreover the best possible stratigraphic resolu tion useful for detailed analysis of the sedimen tary evolution of the study area during the middle devonian this contribution constitutes a first ap proach in the construction of the eifelian com posite standard with worldwide applicability in conventional biostratigraphy fossil zones are used to achieve correlation the graphic cor relation technique however produces a frame work that is founded on biostratigraphy but inte grates all the biostratigraphic events onto a composite standard this method was developed by shaw 1964 and was subsequently extended e g miller 1977 sweet 1979 edwards 1984 1989 to be applicable to nonpaleontologic and nonunique but chronostratigraphically signifi cant events including magnetic polarity data key lithological marker beds various geophysical log type data and stable isotope logs it constitutes a powerful tool for the analysis of synchroneity or nonsynchroneity of geologic events integrated with sequence stratigraphy and sedimentological data shaw s method of graphic correlation is one of the standard techniques applied in modern basin analysis e g neal et al 1994 geologic setting

mechanisms of the development of water conducting fracture zone in overlying strata during shortwall block backfill mining a case study in northwestern china in this work a shortwall block backfill mining sbbm technique is proposed for the recovery of residual corner coal pillars and irregular blocks left behind during the exploitation of coal mines and a solution is provided for the risks associated with gangue piling and the loss of water resources owing to coal mining based on the theory of beams on elastic foundations a mechanical analysis model was established for calculating the height of a water conducting fracture zone wcfz in the overlying strata of coal mines exploited using the sbbm technique it was found that the key factors influencing the development of the wcfz are the mining height width of the protective coal pillars backfill percentage block length and number of mining blocks the relationships between these factors and the height of the wcfz were obtained by incorporating the relevant parameters in the above mentioned model in the field experiment site it was discovered that the minimum coal pillar width and goaf backfill percentage required to prevent the development of water conducting fractures that could reach an aquifer are 5 m and 65 respectively based on this result the protective pillars of the site were designed to be 5 m wide while the goaf backfill percentage was set as 80 the borehole fluid method was used to measure the height of the wcfz which was found to be 26 8 m this is consistent with the theoretical calculations 27 0 m of this study and thus validates the reliability of the proposed mechanical model the findings of this work will improve the recovery rate of residual coal resources in coal mining areas and they are significant for the refinement of water conservation mining theories