dynamic characteristics of a ground fissure site abstract the seismic response of an active ground fissure site was simulated by a shaking table test and a flac3d numerical simulation model coupled dynamic ground motions of earthquake and fissure activity were loaded on the model the characteristics of the fissure site that is the movement of the hidden fissure the uneven subsidence the acceleration and the lateral and vertical soil pressures were monitored and analyzed the following observations were made from this study the subsidence of the hanging wall was greater than that of the footwall the stretch caused by the uneven subsidence led to the appearance of the hidden fissure and the gradual widening of the fissure the peak acceleration in the hanging wall was larger than that of the footwall the pga increased with the height of the site the magnification coefficient of the pga had the largest value in the fissure and the magnification coefficient of the pga decreased with earthquake intensity the increments of lateral and vertical soil pressure also increased with earthquake intensity the vertical soil pressure at the location of the fissure was the largest these dynamic characteristics are vital to the safety design of underground structures in a fissure site

physical simulation of ground fissures triggered by underground fault activity abstract numerical modeling and physical simulation experiment are two important steps to investigate the stress and strain fields of overlying strata but sometimes it is very difficult to do the test of the physical experiment on a large scale soil sample due to the financial consideration and the available test site to investigate the features of the ground fissures prevailing in xi an city we undertook in this study a series of physical simulation tests on the large scale soil sample to analyze the stress and displacement fields caused by the underlying normal fault activity comparing with the fracturing modes of the ground fissures and the failure patterns of construction building it is evident that the experiment results coincide with the failure patterns of the building but not with the fracturing modes of the ground fissures which indicate that the ground fissures in xi an may be an old fracture surface having already spread to superficial layer covered by a very thin layer of loose soils and the groundwater over pumping is just a factor to make them exposed on the ground surface

characteristics and genesis mechanism of ground fissures in taiyuan basin northern china abstract since the 1980s ground fissures in the taiyuan basin have experienced blowouts resulting in a significant but hidden danger to cities in the basin this paper describes the plane and damage characteristics of the ground fissures based on the findings of field investigations and mapping most ground fissures in the basin were determined as linear with pinch out reappearances on the surface they were characterized by both horizontal tension with maximum widths and vertical offsets of up to 40 and 15 cm respectively the ground fissure strikes in the basin were observed to be consistent with those of nearby active faults and the long axis direction of the groundwater depression funnel the roads and houses that lie across the fissures were determined to be the most affected by ground fissure disasters in the basin the primary damage modes for the roads were vertical offset and surface collapse whereas buildings experienced foundation failure and tensile damage profiles obtained through geological drilling and trench exploration further revealed obvious tension and synsedimentary characteristics of the ground fissures correlated with existing faults correlation analysis shows that the formation of ground fissures in taiyuan basin is mainly related to faults and excessive groundwater extraction theoretical analysis revealed that the size and activity of ground fissures in the basin were positively correlated with four factors the dip of faults in an area regional tensile stress difference between the thicknesses of aquifers on either side of a fault and groundwater exploitation the significant increase in ground fissure activity since the 1980s mainly reflects uncontrolled groundwater discharge hence prevention of excessive groundwater exploitation in the basin would mitigate the destructive effects of the ground fissures

the relationship between the geometry of normal faults and that of the sedimentary layers in their hanging walls abstract we derive an analytical expression that relates the shape of a fault in cross section to the shape of the bedding horizons in its hanging wall block the expression assumes that the hanging wall deforms by simple shear and that the footwall remains undeformed throughout although this paper concentrates on normal faults the expression is equally valid and applicable to thrust faults the direction of simple shear in the hanging wall block is arbitrary and has a dramatic effect on the predicted fault or bedding geometry there is no reason to believe that the simple shear occurs on vertical planes as is commonly assumed in graphical approaches to this problem and ignoring the presence of inclined simple shear is likely to lead to considerable underestimates of the amount of extension across normal faults and in the amount of shortening across thrusts similar though more complicated expressions can be obtained when compaction within the hanging wall block is taken into account for a planar normal fault such compaction may result in the development of a hanging wall syncline

delimitation of ground failure zones due to land subsidence using gravity data and finite element modeling in the queretaro valley mexico abstract sedimentary basins of arid and semiarid zones are often subject to regimes of intense ground water withdrawal as it is normally the only source of water for development of communities an associated phenomenon is land subsidence which can develop to ground failures and consequently damage to infrastructure aquifer deformation can be analyzed using a stress strain or a flux force approach depending on the aquifer material compact or loose and on whether the water withdrawal forms a predominant flow direction toward a cone of depression geometry of the aquifer system also plays an important role as uneven thickness induces differential compaction and hence tensional and shear stresses on the ground mass in this work we present a stress strain approach to analyze subsidence for an unconfined aquifer of varying thickness this is done in two steps namely when the aquifer is in equilibrium and when it is totally depleted using this scheme in a region where ground failure is evident a portion of the aquifer system of the queretaro valley is analyzed the geometry of the hydrologic basement is first modeled using gravity measurements properly correlated with wells and field data then a stress analysis is implemented using the finite element method in order to identify probable zones of ground weakness which are calibrated with known ground failures the results indicate that both tensional and shear stress are present which induce ground failure in the form of surface faults

land subsidence and ground failure associated to groundwater exploitation in the aguascalientes valley mexico ground failure associated with land subsidence due to groundwater withdrawal is the main geotechnical hazard in the aguascalientes valley causing enormous economic loss by damage to public and private properties including urban infrastructures the aguascalientes valley forms a tectonic graben flanked by north to south trending normal faults where the hydrologic hydrogeologic and anthropogenic conditions are favorable for ground deformation the intensive withdrawal of groundwater has produced a critical decline in potentiometric levels particularly beneath the aguascalientes city where most of the ground failures have occurred most of the ground failures observed in this valley are directly linked to irregularities of the bedrock and buried paleo channels currently the damage caused by ground failures is variable and considerable even though local government is aware of this problem and has undertaken actions in order to mitigate the ground failure related damages for instance mapping the location of ground failures in the entire valley carrying out resistivity surveys aimed at detecting incipient ground failures and buried cracks and carrying out gravimetric surveys for detecting zones in the subsoil with the geologic conditions for the potential development of ground failures

acetate and propionate in landfill leachates implications for the recognition of microbiological influences on the composition of waters in sedimentary systems routine monitoring of landfill leachates provides information concerning aqueous systems in which anaerobic microbiological processes influence water chemistry propionate and acetate are substrate and product respectively of metabolism by bacteria that have an obligate syntrophic relationship with sulfate reducing bacteria the stoichiometry of the bacteriological metabolic reactions indicates a 1 1 molar proportionality for acetate and propionate this is observed for landfill leachates consistent with the known biological control on their organic acid anion contents similar data for oil field waters show the same 1 1 molar proportionality for reservoirs where bacterial sulfate reduction is known to take place at temperatures up to about 95 c in contrast to the 3 2 proportionality acetic acid propionic acid observed in higher temperature systems these observations suggest that 1 1 molar proportionality for acetate and propionate may be characteristic of natural systems where anaerobic bacterial activity occurs including bacterial sulfate reduction

development characteristics and mechanisms of damage causing urban ground fissures in datong city china abstract a set of widely developed ground fissures within the datong basin northern china have inflicted serious damage to farm fields roads houses and building foundations in datong city such emergence of large scale ground fissures is rare in urban areas the formation mechanisms of these features were therefore investigated in detail through surveying mapping trenching drilling and geophysical prospecting the 11 fissures in datong city are located on the hanging wall of the kouquan fault part of regional horst and graben terrain and run approximately parallel with a dominant strike of ne34 70 and a maximum length of 5 5 km these structures occur in clear zones with similar directions and lateral distributions on the surface they possess evident synsedimentary fault characteristics including y shaped trapezoidal and traction structures in their profiles the synergistic action of different tectonic factors and groundwater exploitation is responsible for fissure formation under the influences of regional tensile stress upper mantle uplift and fault block movement activity along local faults created hidden fracture systems within the hanging wall the over exploitation of groundwater in the region subsequently accelerated fracture growth and varying vertical compressibility of the strata on both sides of the local fault resulted in uneven subsidence on the surface generating tensile zones and promoting the appearance of fissures at the edges of settlement funnels

distribution and mechanism of the ground fissures in wei river basin the origin of the silk road wei river basin wrb is the origin of the ancient and new silk road and it is located in southern fen wei graben system china since 1950s hundreds of ground fissures have formed in this affluent basin and these ground fissures have become the main geohazard in wrb this paper used a series of geological investigations such as site investigation trench excavation geological drilling and geophysical survey to understand the distribution and mechanism of formation of the ground fissures in wrb the results are 1 212 ground fissures in wrb were located in xi an xianyang weinan city and they have clear orientations mainly distributed from nee to sww nw to se and e to w moreover the ground fissures are accompanied by active faults along the same directions 2 ground fissures in wrb can be divided into two types some ground fissures display obvious horizontal and vertical separations on the earth surface whereas others only display obvious horizontal separations on the earth surface 3 ground fissures in wrb are triggered by four factors viz basin structure active fault human activities and loess erosion 4 the mechanism for the formation of ground fissures has also been proposed tectonic faulting is the fundamental cause of ground fissures in the wei river basin and imbalances in the man land caused by human actives accelerated the ground fissures activities 5 many effective measures have also been proposed to mitigate the hazards of ground fissures in wrb such as planning engineering measures controlling the exploitation of groundwater and monitoring this research will be helpful in safeguarding the sustainable development of the silk road economic belt

evolution and origin of the ground fissures in xian china large scale extraction of ground water in xian has resulted in significant drawdown of the phreatic surface and in land subsidence across this ancient capital of china it has also triggered the rejuvenation of the normal faults in the upper portions of the quaternary deposits underlying the city leading to surface rupturing and the development of ground fissure zones across the city these ground fissure zones are structurally controlled in the sense that they are directly linked to the normal faults in the quaternary deposits all trending in an east northeasterly direction in essence they are the surface expressions of the deeper faults under current drawdown conditions the ground fissures have resulted in extensive property damage along their paths of propagation this paper describes their occurrence their possible causative mechanism and the resultant damage of necessity xian will still be dependent on ground water supply to a large extent in the years ahead however ground water extraction will have to be managed in an environmentally sustainable manner in order to minimize the geological hazards associated with the ground fissures

the origin and impact of the shizhuang ground fissure yingxian area datong basin china abstract the datong basin is part of the regionally extensive fenwei graben system a major tectonic zone impacted by active tectonics and the resulting damage to life and infrastructure the basin also contains the shizhuang ground fissure system in this study the likely origin surface extent and fissure subsurface characteristics are explored by traditional methods surveying mapping trenching drilling and seismic exploration the shizhuang ground fissure is located at the intersection of the xiaoshikou fault and the southern liuleng margin fault in yingxian county it has a length of 2 1 km excellent continuity and semi elliptical surface morphology the dislocation of strata induced by the fissure increases significantly as the depth increases the strata bend downward and form typical traction structures near the fissure plane indicating that the fissure has prominent synsedimentary fault characteristics the fissure causes serious damage to houses farmlands roads and public facilities featuring large tensile cracks and vertical dislocations the resulting data and interpretations indicate that 1 the ground fissures connect to two major subsurface active faults which lay the tectonic foundation for the fissure 2 accelerated groundwater extraction has reactivated the underlying faults and exacerbated fissure development and 3 mitigation is best achieved by cessation of excessive groundwater pumping appropriate engineering design and local avoidance for placement of critical structures this paper provides a heretofore generally unknown example promotes research on the mechanisms of fissures and has guiding significance for disaster prevention and reduction in this area

on the role of isostasy in the evolution of normal fault systems the footwalls of west dipping normal faults that separate the west central colorado plateau from the basin and range province record at least 5 7 km and perhaps as much as 15 20 km of west side up neogene uplift with an axis just 10 20 km west of undeformed plateau strata the uplift is expressed as folding and steep faulting in pre tertiary cratonic and disconformably overlying neogene strata forming a basement cored anticline and coincident topographic high on the western margin of the plateau the authors interpret the uplift as a nonelastic response of the crust to buoyancy forces accompanying the tectonic denudation of the plateau margin profound isostatically driven deformation of the footwalls of major normal faults may be common in extensional terrains calling into question several assumptions fundamental to existing models of the evolution of normal fault systems

earth fissures in jiangsu province china and geological investigation of hetang earth fissure earth fissures are a geohazard in jiangsu province china they can be caused by earthquakes and active faults underground mining groundwater extraction and landslides in order to establish a provincial rehabilitation plan in jiangsu a range of monitoring programs surveys geological investigations and modeling have been implemented or planned one of the focuses of the project is the land subsidence and earth fissures caused by excessive groundwater withdrawal in suzhou wuxi and changzhou su xi chang area southern jiangsu province hetang earth fissure within the su xi chang area was first reported in 1995 and a series of investigation has been conducted since then the site investigations and geophysical survey in 1997 have recognized the causative factor as the excessive groundwater drawdown coupled by the underlying bedrock ridge an open trench excavation in 2007 and a plane strain analysis suggest that hetang earth fissures may have cracked from the bedrock ridge to ground surface geological drilling in 2007 has further confirmed the existence and configuration of the ridge and extracted soil samples for laboratory tests to obtain soil parameters for numerical analyses and modeling of land subsidence and earth fissures in the su xi chang area jiangsu china the laboratory tests are currently in progress and the result of numerical analyses and modeling is expected to be presented in the near future

carbonate cementation in a sequence stratigraphic framework upper cretaceous sandstones book cliffs utah colorado abstract three macroscopic diagenetic features can be recognized in the sandstones of the upper cretaceous desert member of the blackhawk formation and castlegate sandstone of the mesaverde group exposed in the book cliffs utah each of which have distinctive form geometry and stratigraphic distribution diagenetic alterations are 1 leached zones whitecaps up to 10 m thick beneath coal beds 2 large up to 8 m concretionary carbonate cemented bodies in amalgamated shoreface and thin fluvial sandstones and 3 thin up to 2 m laterally extensive carbonate cemented horizons beneath major marine flooding surfaces each feature has distinct petrographic and geochemical signatures and formed through discrete diagenetic processes large isolated carbonate cemented bodies are composed of ferroan dolomite most of which precipitated during early diagenesis field and petrographic data coupled with stable isotope data early cements 13c 2 5 to 3 4o oo vpdb 18o 7 8 to 12 0o oo vpdb 87sr 86sr 0 7078 later cements 13c 3 1 to 5 7o oo vpdb 18o 12 0 to 15 1o oo vpdb 87sr 86sr 0 7093 suggest precipitation from meteoric fluids input into sediments during times of relative sea level fall the source of carbonate for the dolomite cement was dissolution of detrital dolomite from beneath coals by organic acids and subsequent mobilization by meteoric fluids carbonate precipitation in laterally extensive cement horizons appears to have started as a result of hiatus in sediment accumulation during marine flooding events relative sea level rise cement precipitation in these horizons continued through sediment burial as a result of organic matter oxidation reactions in overlying organic rich mudstones the results of this study show a link between sedimentation related to changes in relative sea level and diagenesis leading to the potential for the development of process based predictive models of early diagenesis in depositional successions

modern ground failure in the garlock fault zone fremont valley california modern ground failures ranging from renewed displacement on 2 5 km long fault scarps to 1 km long tension cracks occur in fremont valley california most of the failures formed along pre existing holocene fault scarps that are part of the tectonically active garlock fault system the failures began to form in the 1960s and currently affect an area of 17 km 2 that is coincident with ground water level decline induced by pumping for crop irrigation several observations indicate that these failures were caused by water level decline rather than natural tectonism first modern ground failure began after water level started to decline and was restricted to the area affected by decline land subsidence was associated with this decline and appears to be caused by aquifer compaction second geodetic monitoring from 1977 to 1982 of faults near the center of the cone of depression demonstrated that fault creep occurred during periods of seasonal water level decline and stopped during periods of seasonal water level recovery by contrast faults near the margin of the cone of depression where water levels declined at a constant rate moved at a steady rate third surface strain fields near failures suggest that subsurface fault associated deformation was restricted to aquifer level depths and fourth seasonal rebound of the land surface across one fault was caused by elastic expansion of the aquifer system that was induced by large seasonal water level recovery

fault and bed rotation during continental extension block rotation or vertical shear abstract for almost a century the view has existed that the tilting of blocks between closely spaced planar normal faults is rigid body rotation this interpretation requires only simple geometry and has consequently found widespread application however it is not consistent with the deformation expected around normal faults given the present knowledge of stress fields and rheology in basement in the brittle upper crust which is better regarded instead as distributed vertical simple shear rigid body rotation and vertical shear involve different relations between fault and bed tilting and thus predict different initial fault dips for particular present day dips of faults and beds these two schemes also predict different amounts of extension and it is consequently important to establish which is correct with this aim in mind we examine normal faults associated with neogene extension in western turkey and the western united states and with mesozoic extension in the north sea except where extension and the associated tilting are minimal rigid body rotation predicts unrealistically steep initial fault dips some extensional basins also exhibit reversals of normal fault polarity and tilt polarity of beds which are incompatible with rigid body rotation we therefore conclude that the general cause of the tilting is vertical shear not rigid body rotation this has three main observational consequences first the heave on any normal fault equals the amount of extension across it second no feature near a normal fault can rotate through the vertical a normal fault thus cannot rotate through the vertical and appear as a reverse fault third any initially vertical feature near a normal fault will remain vertical a vertical dyke in the tilted surroundings of a normal fault is thus not necessarily younger than the extension that caused the tilting

characteristics and mechanism of sanyuan ground fissures in the weihe basin china abstract shuanghuaishu ground fissures in sanyuan county ones of over 200 ground fissures developed in the weihe basin are well known for their sudden occurrence which often cause severe damage to the infrastructures after heavy rainfall in order to reveal the origin of their formation the geological background developmental characteristics and genetic mode of the shuanghuaishu ground fissures were investigated in details by surveying mapping trenching geological drilling geophysical prospecting and field water immersion the fissures are almost parallel with a ne50 ne65 strike and the obvious linear length is 800 m these characteristics are well consistent with the secondary faults of the liquan pucheng heyang fault the fissures cause damage to buildings and farmlands in the form of a horizontal tensile crack and subsidence the deeper the stratum is the bigger fault displacement of the stratum it will be so these fissures possess the characteristics of synsedimentary faults regarding their genesis the fissures were generated under the coupling action of multiple factors the regional extension caused secondary faults of the liquan pucheng heyang fault to slip resulting in a fracture system in the surface strata during the period of heavy rainfall large volumes of water seeped into these hidden fissures causing a strong erosion and washout effect on the soil filled in the fissures this process promoted the formation of the current ground fissures

differential compaction mechanism for earth fissures near casa grande arizona precise gravity measurements indicate that earth fissures or tension cracks caused by ground water withdrawal within a 10 km 2 area southeast of casa grande arizona are associated with relief on the buried interface between the alluvial aquifer and underlying bedrock all of the fissure zones which have a cumulative length of 8 7 km occur above either ridges or steps in the bedrock surface intersecting fissure zones overlie intersecting bedrock features and the angle of intersection of the zones accurately reflects the angle between the bedrock features these relations suggest that the fissures are forming in response to localized differential compaction caused by localized variations of aquifer system thickness topographic profiles across fissures on undisturbed desert floor confirm differential compaction proportional to the variations in aquifer thickness the occurrence of the fissures at points of maximum convex upward curvature in profiles of both the topographic and buried bedrock surfaces indicates that the fissures result from tensile strains caused by bending of the strata above the buried bedrock features in response to the differential compaction tensile strains at failure are estimated to range from 0 02 to 0 2 on the basis of modeling of the bending process

ground cracks in ethiopian rift valley facts and uncertainties abstract no accurate relationship has been obtained in this study between ground cracks in ethiopian rift valley and the most common causes of earth fissures such as aquifer system compaction and increased horizontal seepage stresses this is due to the fact that the level of groundwater withdrawal responsible for these processes is still negligible in ethiopia if aquifer system compaction and increased horizontal seepage stresses have a certain role then it should be through the long term effect of groundwater flow from basins to neighboring lakes the ground cracks appeared also not to have a direct link with active faulting or distant earthquakes structurally the ethiopian rift valley is dominated by ne sw trending tensional faults but no evidence is obtained in this study to associate the process of surface cracking with major tectonics however an aseismic elastic strain which originates at depth and propagates upward through sediments without the formation of bedrock faults could result in conditions conducive to the development of cracks then fissures might ultimately be created after heavy rainfalls by near surface processes such as piping and hydrocompaction along water line sources

thermodynamics of organic transformations in hydrothermal fluids hydrothermal fluids obtain organic compounds through diverse pathways in submarine systems organic compounds are already dissolved in seawater that is heated and transformed into hydrothermal fluids through water rock reactions microbes inhabiting hydrothermal systems produce metabolites that enter the fluids and cells can be carried into the reaction zones by circulating fluids and pyrolyzed analogous sources of organic compounds can be anticipated in continental systems with the possible addition of novel plant and soil derived organic compounds from the surface in addition hydrothermal systems possess large potentials for abiotic organic synthesis that may add a novel suite of compounds when sedimentary rocks are present ancient biogenic organic matter can be mobilized or transformed by hot fluids these transformations accompany the generation of petroleum coal and other fossil fuels suggesting that expectations for hydrothermal transformations can be built on those that occur in sedimentary basins likewise some types of ore deposition are accompanied by transformations of organic compounds and metal organic complexes may be involved in enhancing the transport of metals in ore forming and other crustal fluids with these thoughts in mind this review starts with an inventory of the types of organic compounds found in hydrothermal systems and some ways that hydrothermal organic compounds are transformed methane can be generated biotically and abiotically from organic or inorganic reactants and since it lacks a carbon carbon bond some researchers would not consider it to be an organic compound nevertheless more data exist for methane in hydrothermal fluids than for any organic compound that fits the definition methane has been quantified in continental and submarine hydrothermal fluids fumarolic gases associated with hydrothermal systems oil field brines deep fluids in sedimentary basins and igneous basement rocks fluids associated with active serpentinization and fluid inclusions in minerals from ore deposits sedimentary basins and deep crustal settings recent examples include

the neotectonics of the aegean an alternative view minor reverse faults in widely dispersed neogene outcrops in the central aegean have led several people to suggest that the regional extension which started in the lower pliocene or earlier was interrupted by short periods of compression the durations of these postulated compressional episodes are short compared to the time scale on which convective forces acting on the base of the lithosphere can change thus possible mechanisms for driving such motions are limited in this paper we offer alternative explanations for these observations and in particular show that these apparently compressional episodes are probably not regional in extent and may not be truly compressional in origin in some places they are more likely to be a consequence of the considerable rotation that is found in extensional terranes the plio quaternary paleogeography of the central aegean is satisfactorily explained by uplift in the footwall blocks of normal faults and does not require regional compression studies of the faulting associated with recent large earthquakes suggest that the sort of microtectonic analysis which is typically carried out on small faults in surficial sediments is more likely to reflect the internal deformation of blocks bounded by major fault structures than be a reliable indicator of regional stress patterns

characteristics and mechanism of the longyao ground fissure on north china plain china abstract among more than 1000 ground fissures developed over the past 30 years having induced severe geohazards in the north china plain the longyao ground fissure in hebei province is famous for its longest length and causing the worst damage and widest influence in this region in order to reveal the origin of its formation the geological background developmental characteristics and genetic mode of the longyao ground fissure were investigated in detail by geological surveys measurements trenching drilling and seismic exploration this fissure has a total length of 39 km and is characterized by normal fault extension left lateral slip and dominant along polyline distribution these characteristics are well consistent with its underlying fault the nei jv fault the fissure causes the damage to buildings structures along a polyline and in the form of a horizontal tensile crack subsidence and shear failure according to the trenching drilling and shallow seismic profiling this fissure possesses the characteristics of synsedimentary faults reflecting the historical stages of fissure activities regarding its genesis this fissure was generated under the coupling action of multiple factors which took shape after the earthquake and was enlarged under the action of groundwater pumping the regional extension first caused a fracture system in the surface strata and then the action of seismic activities started to control the fracture and finally the pumping action of excessive groundwater and other influential factors promoted the formation of the current ground fissure

engineering geology ground surface movement and fissures induced by underground mining in the jinchuan nickel mine the jinchuan nickel mine is the largest underground mine with cut and fill mining in china in 1999 there appeared evident ground surface movement and many ground fissures in jinchuan no 2 mine following an introduction to the engineering geology and mechanical properties of the rock mass in the jinchuan mine areas this paper reveals the features of the measured in situ stresses and puts emphasis on an analysis of the mechanism of surface movement and ground fissures induced by the underground mining with backfill it is indicated that both the fault structures and the alteration contact zones are well developed as the dominant engineering geological characteristics in the jinchuan mine areas the stress redistribution in surrounding rocks resulting from the mining the low stiffness of the filling body the existence of the void space and the influence of on going mining activities is the main reason for the occurrence of surface movement and ground fissures

carbonates and oxalates in sediments and landfill monitors of death and decay in natural and artificial systems subaqueous sediments and landfill waste disposal sites are both natural locations for anaerobic microbiological metabolism where sulphates are reduced to sulphide and organic matter particularly acetate is oxidized and degraded to produce ultimately co 2 and ch 4 the microbiologically mediated geochemical processes in each case are similar however natural sedimentary porewaters can be difficult to sample and monitor whereas landfill sites are relatively easily accessible yielding leachate samples that are routinely monitored over periods of time in both environments carbonate precipitation is predicted to be a normal consequence of anaerobic microbiological activity consistent with changes in leachate composition and the predictions of geochemical modelling initial investigation of scale from a landfill drainage system confirms the presence of calcite together with gypsum and iron minerals calcium oxalate minerals whewellite and weddelite are widespread in their occurrence within septarian concretions from a number of geological formations whewellite is reportedly stable up to 160 c the solubility of calcium oxalate is very low and precipitation readily takes place when oxalate oxalic acid is present derived from fungal processes in sediments and soils calcium oxalate minerals should be expected wherever vegetable matter is decomposing this link can be demonstrated for natural sediments but has yet to be proven for landfill

the role of grain dissolution and diagenetic mineral precipitation in the cycling of metals and phosphorus a study of a contaminated urban freshwater sediment this paper describes the detrital mineralogy early diagenetic reactions and authigenic mineral precipitates for freshwater contaminated sediments deposited in an urban water body the salford quays of the manchester ship canal greater manchester uk these sediments contain a mix of natural and anthropogenic detrital grains detrital grains are dominated by quartz and clay grains whilst anthropogenic grains are dominated by metal rich glass grains concentrated at a depth of 12 17 cm in the sediment as a result of historical inputs sediment porewaters contain significant concentrations of fe mn zn and phosphate bacterial fe iii and mn iv reduction are hypothesised to supply fe2 and mn2 to porewaters with phosphate released from fe oxide reduction or organic matter oxidation petrographic observations indicate that the metal rich glass grains are undergoing chemical dissolution during early diagenesis supplying fe and zn to porewaters the most abundant authigenic mineral in the sediments is vivianite fe3 po4 2 8h2o containing a significant level of redlingite with minor framboidal pyrite fes2 electron microprobe analysis shows the vivianite to contain zn cu and pb suggesting that vivianite acts as a long term sink for these metals in this sediment this implies that authigenic vivianite in freshwater sediments may act as a long term sink for metals in a similar manner to sulphides in marine sediments this study highlights that the nature of detrital and diagenetic mineralogy in addition to porewater and sediment chemistry needs to be considered in assessing contaminated sediments

origin of ground fissures in the shanxi graben system northern china abstract since the 1950s hundreds of ground fissures have occurred in the shanxi graben system in northern china the fissures and related subsidence and differential settlement have caused and are causing substantial damage to homes agricultural land roads canals and other infrastructure although generally similar in appearance the fissures have different origins 1 some fissures coincide with northeast trending faults trenching shows that the fissures extend into the near surface faults increasing vertical offset clay beds and other stratigraphic markers at depth and therefore are probably the surface expression of fault movements 2 some fissures are demonstrably related to accelerated groundwater withdrawal this is particularly apparent in xi an city where groundwater levels have declined by about 15 m within 4 years 3 other fissures owe their origin to the well known process of soil collapse this is particularly common in the silty loessial sediments that occur within most of the valleys that comprise the shanxi graben system