the schilfsandstein and its flora arguments for a humid mid carnian episode recently intensified research on the mid carnian episode stimulated discussions about the mid carnian climate and a supposed humid climate shift this basin scale study on the schilfsandstein the type example of the mid carnian episode applied sedimentological palynological and palaeobotanical proxies of the palaeoclimate to a large dataset of cored wells and outcrops the results demonstrate the primary control of circum tethyan eustatic cycles on the central european basin where transgressions contributed to basin scale facies shifts the palaeoclimate proxies point to a uniform arid to semi arid carnian climate with low chemical weathering and high evaporation consequently transgressions into the central european basin led to increased evaporation forcing the hydrological cycle the increased runoff from source areas resulted in high groundwater stages on lowlands characterized by hydromorphic palaeosols and intrazonal vegetation with hygrophytic elements during lowstands reduced evaporation and runoff led to increased drainage and desiccation of lowlands characterized by formation of vertisols calcisols and gypsisols and zonal vegetation with xerophytic elements the proposed model of sea level control on the hydrological cycle integrates coeval and subsequent occurrences of wet and dry lowlands hydromorphic and well drained palaeosols and intrazonal and zonal vegetations thus the schilfsandstein does not provide arguments for a humid mid carnian episode supplementary material datasets of palynomorph eco group peg and macroplant eco group meg analyses are available at https doi org 10 6084 m9 figshare c 4182593

oriented grain growth and modification of frozen anisotropy in the lithospheric mantle abstract seismic anisotropy throughout the oceanic lithosphere is often assumed to be generated by fossilized texture formed during deformation at asthenospheric temperatures close to the ridge here we investigate the effect of high temperature and high pressure static annealing on the texture of previously deformed olivine aggregates to simulate residence of deformed peridotite in the lithosphere our experiments indicate that the orientation and magnitude of crystallographic preferred orientation cpo will evolve due to the preferential growth of grains with low dislocation densities these observations suggest that texture and stored elastic strain energy promote a style of grain growth that modifies the cpo of a deformed aggregate we demonstrate that these microstructural changes alter the orientation distributions and magnitudes of seismic wave velocities and anisotropy therefore static annealing may complicate the inference of past deformation kinematics from seismic anisotropy in the lithosphere

low frequency electrical impedance of partially molten gabbro the effect of melt geometry on electrical properties abstract electrical impedance of partially molten gabbro was measured as a function of the frequency of the applied electric field the impedance of the partially molten gabbro was mainly controlled by the volume and geometry of partial melt which were observed with an optical microscope study of the quenched sample the experimental results are interpreted by a theory that formulates the electrical property of rocks containing partial melt taking ionic diffusion in the melt into account the theory evaluates the contributions from two types of melt geometry distributed in the rock matrix namely 1 a nearly isolated melt pockets and 2 b connected melt along grain boundaries according to the theory connected melt mainly contributes to the increase of net conductivity while melt pockets increase displacement current and cause the frequency dependence of impedance the characteristic ionic diffusivity in melt pockets was determined from the peak frequency of the imaginary part of impedance the magnitude of diffusion coefficient is estimated to be of the order of 10 7 to 10 6 cm 2 sec this suggests that sodium iron magnesium and or calcium ions mainly carry the electric charge in partial melt the observed frequency dependence of impedance is considered to reflect ionic polarization in melt pockets due to the migration of these alkali ions toward solid melt interfaces the present experimental and theoretical work suggests that electrical properties of the earth s upper mantle may involve an intrinsic frequency dependence associated with ionic diffusion in the frequency range of geomagnetic observation if a partial melt zone exists the analysis of the earth s conductivity structure may be inadequate if such intrinsic frequency dependence of mantle media is neglected

transport properties of olivine grain boundaries from electrical conductivity experiments grain boundary processes contribute significantly to electronic and ionic transports in materials within earth s interior we report a novel experimental study of grain boundary conductivity in highly strained olivine aggregates that demonstrates the importance of misorientation angle between adjacent grains on aggregate transport properties we performed electrical conductivity measurements of melt free polycrystalline olivine fo90 samples that had been previously deformed at 1200 c and 0 3 gpa to shear strains up to 7 3 the electrical conductivity and anisotropy were measured at 2 8 gpa over the temperature range 700 1400 c we observed that 1 the electrical conductivity of samples with a small grain size 3 6 m and strong crystallographic preferred orientation produced by dynamic recrystallization during large strain shear deformation is a factor of 10 or more larger than that measured on coarse grained samples 2 the sample deformed to the highest strain is the most conductive even though it does not have the smallest grain size and 3 conductivity is up to a factor of 4 larger in the direction of shear than normal to the shear plane based on these results combined with electrical conductivity data for coarse grained polycrystalline olivine and for single crystals we propose that the electrical conductivity of our fine grained samples is dominated by grain boundary paths in addition the electrical anisotropy results from preferential alignment of higher conductivity grain boundaries associated with the development of a strong crystallographic preferred orientation of the grains

karst aquifer evolution in fractured porous rocks the evolution of flow in a fractured porous karst aquifer is studied by means of the finite element method on a two dimensional mesh of irregularly spaced nodal points flow within the karst aquifer is driven by surface recharge from the entire region simulating a precipitation pattern and is directed toward an entrenched river as a base level during the early phase of karstification both the permeable rock matrix modeled as triangular elements and fractures within the rock matrix modeled as linear elements carry the flow as the fractures are enlarged with time by chemical dissolution within the system calcite carbon dioxide water flow becomes more confined to the fractures this selective enlargement of fractures increases the fracture conductivity by several orders of magnitude during the early phase of karstification thus flow characteristics change from more homogeneous pore controlled flow to strongly heterogeneous fracture controlled flow we study several scenarios for pure limestone aquifers mixed sandstone limestone aquifers and various surface recharge conditions as well as the effect of faulting on the aquifer evolution our results are sensitive to initial fracture width faulting of the region and recharge rate

triassic evaporites of iberia sedimentological and palaeogeographical implications for the western neotethys evolution during the middle triassic earliest jurassic abstract this paper deals with the middle triassic to earliest jurassic evaporite sedimentation in the epicontinental eastern iberian platform this deposition occurred under extensional regime during the westwards migration of the neotethys ocean at the start of the pangea break up although attention is focused on the evaporitic episodes recorded in the epicontinental germanic triassic of the platform the evaporite units in the carbonatic alpine triassic are also considered in the epicontinental triassic up to six evaporitic episodes which alternated with three carbonatic episodes and a siliciclastic one occurred between the anisian and the lower hettangian the evaporitic episodes may be divided into two groups the stratigraphic units of the older group have similar characteristics in salinity and facies and were formed in chloride rich evaporitic mudflats in the younger group the salinity and depositional features display considerable differences and the environments evolved from evaporitic mudflats to extensive salterns the different evolutive trends in the evaporites of the two groups suggest major re structuration of the platform after the sedimentation of the siliciclastic units of the middle keuper carnian humide episode progressive marine influence in the assemblage of the six evaporitic episodes is deduced from the changing nature of the evaporites and their host sediment all the evaporite units accumulated as transgressive and highstand systems tracts the close relationship between evaporite units and thick accumulation suggests that the structural control played a major role in the sedimentation in the alpine triassic the presence of evaporites interbedded in the allochthonous carbonate units is documented lateral correlation of the evaporite units of the epicontinental and the alpine types of triassic allows us to reconstruct the facies continuum across the original iberian platform such a west to east transect illustrates the palaeogeography structural evolution and major depositional controls in the platform during the period under study the deduced evaporitic pattern could be applied to other triassic platforms which acted as epeiric seaways for the westward advance of the neotethys

regional and global changes around the triassic jurassic boundary reflected in the late norian hettangian history of the apennine basins abstract palaeogeographic restorations for the late triassic and early jurassic of the west mediterranean area show that significant facies changes occurred in this period the study of three basinal successions in the northern central and southern apennines indicates that changes in ecological conditions occurred at the same time in different palaeogeographic and geodynamic domains the early mesozoic evolution of the apennines is controlled by the opening of two oceans the ionian east mediterranean tethys to the south east and the alpine ocean to the north west the lagonegro basin in the southern apennines was the northern continental margin of the ionian tethys from the triassic while the la spezia basin in the northern apennines became part of the south eastern continental margin of the alpine ocean in the middle late jurassic the third studied basin mt camicia basin in the gran sasso central apennines was an intra platform basin from the early norian up to the late hettangian early sinemurian during the norian hettangian period these basins were not directly connected to each other being separated by wide carbonate platforms and show different evolutionary trends stratigraphic studies in these successions place the triassic jurassic boundary in 6 8 m thick intervals with anoxic facies in the three basins relevant facies changes are also recorded in the late norian in the northern apennines the sedimentation of sulphate evaporites ended being replaced by the rhaetavicula contorta facies whilst in the southern apennines lagonegro basin the deposition of radiolarites began the end of evaporite accumulation can be explained by a climate change from arid to humid conditions and it is also probably linked to an extensional phase preceding the jurassic rifting of the alpine ocean and may therefore have a regional significance nevertheless it corresponds to the spread of the r contorta facies into other parts of southern europe from france to germany and austria the beginning of radiolaritic sedimentation in the lagonegro basin could be related to the rise of atmospheric co2 content linked to volcanic activity in the ionian ridge these facies changes reflect changes of environmental conditions that caused the decline of some fossil associations favoring the development of opportunistic forms e g triasina hantkeni the end triassic extinction coupled with an anoxic episode in all the examined basins immediately preceded a new environmental change documented by the recovery of the carbonate platforms with oolitic facies and different associations the evolution of all these basins suggests that geodynamics were probably responsible for regional events and that at certain moments development reflected global effects as a response to new connections between formerly different domains the central atlantic magmatic province camp volcanism considered as one of the possible causes for the end triassic mass extinction would have had even greater importance if coupled with the volcanism linked to the rifting of the ionian tethys

triassic climates state of the art and perspectives abstract the climate of the triassic period was characterized by a non zonal pattern dictated by a strong global monsoon system with effects that are most evident in the tethys realm this strong monsoonal regime is related to the aggregation of the pangaean supercontinent which by triassic time was already completed climate oscillations existed within this framework the harsh hot house climatic conditions that characterized the late permian and perhaps precipitated the end permian mass extinction were probably maintained during the early triassic and may account for the impoverished but distinctive faunal and floral lower triassic associations although metazoan reef builders were probably the most affected group carbonate production remained high at least in the western tethys realm the middle triassic was characterized locally by humid episodes although their geographical distribution has yet to be clarified the carnian pluvial event marks an episode of increased rainfall documented worldwide was the most distinctive climate change within the triassic different hypotheses have been proposed for its causes changes of atmospheric or ocean circulation driven by plate tectonics a peak of the global monsoon due to maximum continent aggregation or triggering by the eruption of a large igneous province subsequently the late carnian and norian seem to have been climatically stable although minor climatic changes have recently been described even from this time period finally the end triassic extinction event is also associated with climate change specifically warming and increased rainfall but this evidence comes mostly from the northern parts of the central atlantic magmatic province and the global pattern of climate change at the triassic jurassic boundary has still to be resolved many facets of triassic climate are intriguing and deserve further research however palaeoclimate studies on the triassic have so far been carried out only locally with different proxies those proxies will require inter calibration in order to depict correctly the temporal and geographical patterns of triassic climate

palaeoenvironments of the late triassic rhaetian sea implications from oxygen and strontium isotopes of hybodont shark teeth the oxygen and strontium isotopic composition of 125 teeth of the hybodont sharks lissodus and hybodus from various late triassic rhaetian bone bed localities in the central european basin are used as environmental and ecological tracers for the shallow epicontinental rhaetian sea the preservation of tooth enameloid was ascertained by cathodoluminescence microscopy mean 18op values differ regionally across the rhaetian sea with values of 18 6 0 6 near the western gate 16 1 0 8 in the east 15 4 0 6 in the southeast and 17 7 0 9 in the south the 18op values in the eastern rhaetian sea are 4 5 lower relative to tethyan seawater while teeth from the southern and western parts close to the marine gates are less fractionated the strontium isotopic composition of teeth from most localities is more radiogenic in comparison to late triassic seawater the observed spatial 18op trend in the rhaetian sea indicates a shift from marine to brackish conditions in the south and west towards extensively brackish conditions with salinities of less than 16 in the east thus confirming the existence of two marine gates brackish conditions persisted throughout early rhaetian times and were maintained by increased fluvial discharge from the vindelician bohemian and fennoscandian highs as a result of enhanced atmospheric moisture availability in the course of the rhaetian transgression the 18op values of lissodus and hybodus indicate euryhaline behaviour of rhaetian hybodonts by exceeding modern shark intraspecific variability the lack of accordance in 18op values between different isotopically conspicuous localities in the rhaetian sea contradicts a basin wide migration pattern differences between co site taxa might indicate some degree of niche partitioning

environmental control on the end of the dolomia principale hauptdolomit depositional system in the central alps coupling sea level and climate changes abstract the norian in the western tethys is characterised by the deposition of early dolomitised inner platform facies dolomia principale hauptdolomit dp hd bordered on the landward side by terrigenous coastal deposits keuper and on the seaward side by calcareous backreef and reefal facies dachstein limestone passing basinward to open sea sediments hallstatt facies the inner carbonate platform is locally lombardy basin carnic alps central austroalpine dissected by normal faults leading to the development of intraplatform troughs close to the norian rhaetian boundary sedimentation records an abrupt environmental change both on platform top and basins all over the western tethys e g western carpathians transdanubian range alps central apennine the top of the dolomia principale locally emerged reflecting a major eustatic sea level fall emersion is recorded in favourable settings by the development of polycyclic paleosols up to 30 m thick in the norian intraplatform basins the succession is capped by 4 to 8 m of thin bedded fine grained limestones yielding abundant remnants of fishes and terrestrial reptiles fossil concentration as well as sedimentological features is indicative of reduced sedimentation rates due to decreased carbonate production induced by the emersion of the platform top the sea level fall was followed by deposition of mixed fine grained siliciclastic carbonate successions e g riva di solto shale kossen beds rhaetavicula contorta beds fatra formation stratigraphic evidence indicates a dry climate in the western tethys during the norian as indicated by the presence of evaporites burano apennine and arid to semi arid coastal to playa settings upper keuper germany in contrast the basal layers of the basinal shales show evidence of wet climate the end of the norian depositional system records two different phenomena 1 an important sea level fall was responsible for the emersion of the platform top and deposition of a condensed horizon in the basins and 2 transition from dry to humid climate the observed evolution is explained with a global cooling which caused the rapid sea level fall responsible for the abrupt end of the dp hd depositional system and the shift of the boundary between arid and temperate climate belts which modified the distribution and amount of rainfall triggering the deposition of shales along the western tethys margin

groundwater systems in bare and covered karst aquifers evidence from tracer tests hydrochemistry and groundwater ages the east guilin region contains a karst dominated hydrological system along the lijiang river the two main topographic characteristics of the basin are peak cluster depression and peak forest despite the fact that these areas represent adjacent units they have different groundwater movement patterns this study describes the groundwater and solute movement in the different hydrogeological sub regions via several techniques our results indicated that the topographic boundary between the peak cluster depression and the peak forest is clear however a transition zone exists between these topographic zones and it can be determined in terms of groundwater movement we employed several methods that are widely considered to be effective tracer tests were conducted in the transition zone hydrochemistry techniques were used in the peak forest and groundwater age dating based on cfcs was employed throughout the study area the main conduits could be found in the transition zone but the groundwater flow was much slower in the transition zone than in the mountain peak cluster area minor conduits also accounted for a high proportion of the total flow in the transition zone the solute migration within the plain which was determined by analyzing the nitrates was controlled by mixing and distance effects the maximum nitrate concentration was limited at the local scale the nitrate concentration gradient at the regional scale was not related to the groundwater movement indicating that the groundwater recharged in a dispersed manner and discharged at discrete locations along the river the age dating revealed that the groundwater was older in the plain than in the bare mountain zone this was due to the strong mixing of young and old water which was the result of the characteristics of the karst media in the aquifer our investigation of the groundwater system in a bare covered karst aquifer provides data for decision making in effective groundwater management

a small unextractable melt fraction as the cause for the low velocity zone abstract throughout the oceanic asthenosphere there exists a zone of seismic velocities that are lower than would be predicted the cause of this low velocity zone lvz whether partial melt or solid state mechanisms has been debated for decades we investigate the lvz by considering seismic and magnetotelluric data from tectonically stable 70 myr old lithosphere in the central pacific ocean we utilise recent experimental advances on the influence of partial melt and seismic attenuation results show that the lvz is characterised by a small volume of interconnected melt and by low hydrogen contents beneath the lvz the asthenosphere does not contain partial melt but has high hydrogen contents and low attenuation values indicating large grain sizes and or low oxygen fugacities to explain these observations we propose that a small amount of unextractable melt is trapped in the asthenosphere after melting at mid ocean ridges

an olivine fabric database an overview of upper mantle fabrics and seismic anisotropy we present a unique database of 110 olivine petrofabrics and their calculated seismic properties the samples come from a variety of the upper mantle geodynamic environments ophiolites subduction zones and kimberlites with a wide range of micro structures a phenomenological relationship is established between p and s wave seismic anisotropy and the degree of crystal alignment fabric strength seismic anisotropy increases rapidly at low fabric strength before reaching a near saturation level of 15 to 20 for p waves and 10 to 15 for s waves despite a large variation in the symmetry of fabric patterns the average seismic properties of the different fabric micro structural and geodynamic settings have similar anisotropies in both magnitude and symmetry hence it would seem possible to determine some measure of fabric strength from seismic anisotropy if the dimensions of the anisotropic region are known but not geodynamic environment or details of the petrofabric pattern a simple pattern of seismic anisotropy characterises the average sample of the database which has the following features the polarisation plane of the fastest s wave is parallel or sub parallel to the foliation plane the maximum shear wave splitting is parallel to the y structural direction in foliation plane and normal to the lineation the maximum of the p wave velocity is parallel to the high concentration of 100 axes which is sub parallel to the lineation the 100 orientation distribution has the greatest influence on the p wave seismic anisotropy the 100 and 001 orientation distributions have the greatest influence on the symmetry of s wave anisotropy although the magnitude of anisotropy is influenced by the distribution of all three principal axes although the database only contains olivine petrofabrics this statistical study clearly shows that seismic anisotropy can be used to deduce the orientation of the structural frame in the upper mantle 1998 elsevier science b v all rights reserved

electrical properties of fine grained olivine evidence for grain boundary transport 1 to investigate the mechanisms responsible for electrical conduction and deduce the relation between grain size and conductivity the electrical conductivity of synthetic polycrystalline forsterite with grain sizes between 1 1 0 4 and 4 7 2 4 m was measured at temperatures up to 1470 c and at 0 1 mpa pressure the complex impedance plots display one clear arc indicating a single dominant conduction mechanism bulk conductivity is inversely proportional to the grain size of the different samples this relation suggests that the electrical conductivity of the samples is controlled by grain boundary diffusion of the charge carriers the apparent activation energy q for diffusion of the charge carriers between 1180 and 1470 c lies between 315 39 and 323 15 kj mol this resembles previous data on grain boundary diffusion of mg in forsterite a geometrical model of less conducting cubic grains and more conducting grain boundaries agrees well with the experimental data this model is applied to predict the conductivity contrast between fine grained shear zones and less deformed regions in the lithosphere upper mantle shear zones are predicted to have 1 5 2 orders of magnitude higher conductivity than less deformed regions in the lithosphere this means grain boundary transport probably has an important role in the existence of anomalously high conductivity zones in the upper mantle and that fine grained shear zones might be detected using magnetotelluric methods

delineating vulnerability of karst aquifers using hydrochemical tracers in southwestern china karst groundwater is particularly vulnerable to contamination long term hydrochemistry auto monitoring combined with laboratory analyses has shown that the chemograph demonstrates changes in the system in order to determine the primary groundwater vulnerability a relationship between hydrochemical changes and the origin of vulnerability in six karst spring catchments in southwestern china is discussed the reason and physical meaning of the hydrochemical changes in the spring are explained based on tracer tests and physical chemical process in the s31 spring the results prove that the hydrochemical changes show the origin of vulnerability and also can be its expression generally autogenic recharge in bare karst is concentrated in epikarst zone forming bypass flow and shaft flow which causes dilution of ca2 the chemograph reflects the percentage of concentrated and diffuse recharge the higher the ratio of concentrated recharge the higher the grade of groundwater vulnerability due to ca2 hco3 sec ph and temperature in water can change for kinds of reasons during their transport more karst systems with variable natural and human factors are discussed protective layer allogenic water recharge and transform of surface stream and subterranean river can change the origin shape of hydrochemical curve under this circumstance more indicators need to be monitored especially contaminant related ions such as nitrate in order to clearly understand the contribution of concentrated and diffuse recharge to water chemistry after comparing the traditional groundwater vulnerability assessment and the methods based on hydrochemical change rainfall protective layer epikarst transient storage and karst network should be more concerned when the work is done auto monitoring of karst is more and more popular in southwestern china therefore it is suggested that the hydrochemical methods should be used as a primary expression of vulnerability giving a direct reference for karst water management

groundwater table fluctuations recorded in zonation of microbial siderites from end triassic strata in a terrestrial triassic jurassic boundary succession of southern sweden perfectly zoned sphaerosiderites are restricted to a specific sandy interval deposited during the end triassic event underlying and overlying this sand interval there are several other types of siderite micromorphologies i e poorly zoned sphaerosiderite spheroidal ellipsoid siderite spherical siderite and rhombohedral siderite siderite overgrowths occur mainly as rhombohedral crystals on perfectly zoned sphaerosiderite and as radiating fibrous crystals on spheroidal siderite concretionary sparry microspar and or micritic siderite cement postdate all of these micromorphologies the carbon isotope composition of the siderite measured by conventional mass spectrometry shows the characteristic broad span of data probably as a result of multiple stages of microbial activity sims secondary ion mass spectrometry revealed generally higher 13c values for the concretionary cement than the perfectly zoned sphaerosiderite spheroidal siderite and their overgrowths which marks a change in the carbon source during burial all the various siderite morphologies have almost identical oxygen isotope values reflecting the palaeo groundwater composition a pedogenic freshwater origin is supported by the trace element compositions of varying fe mn ratios and low mg contents fluctuating groundwater is the most likely explanation for uniform repeated siderite zones of varying fe mn ratios reflecting alternating physiochemical conditions and hostility to microbial life activity bacterially mediated siderite precipitation likely incorporated mn and other metal ions during conditions that are not favourable for the bacteria and continued with fe rich siderite precipitation as the physico chemical conditions changed into optimal conditions again reflecting the response to groundwater fluctuations

deposition floral composition and sequence stratigraphy of uppermost triassic rhaetian coastal coals southern sweden abstract two uppermost triassic rhaetian coal beds a and b bed bjuv member southern sweden deposited at the margin of the danish basin were investigated in order to interpret the peat forming environments in a sequence stratigraphic context and to establish the peat forming vegetations of the precursor mires peat formed close to the coastline and was governed by base level watertable rise linked to relative sea level rise which is emphasized by rare occurrences of marine phytoplankton micrhystridium lunnomidinium scaniense and rhaetogonyaulax rhaetica in the b bed a maximum flooding surface mfs7 between the coal beds a and b shows that peat accumulation occurred as a coastal response to the continued transgression of the danish basin that culminated with deposition of the coal bearing bjuv member the lower b bed accumulated in a transgressive systems tract tst and the upper a bed in a highstand systems tract hst the b bed consists of coal and coaly mudstone intervals showing that peat formation repeatedly was outpaced by relative watertable rise the huminite rich coal intervals indicate peat formation under oxygen deficient stagnant water conditions where the peat accumulation rate balanced the watertable rise overall low ts values indicate a freshwater mire the base of coal bed b marks the start of a relative decrease in creation of accommodation space and the surface between the sediments and coal bed b represents a terrestrialisation surface tes the palynofloral composition suggests that the initial mire was characterised by dipterid dicksoniacean tree ferns and marattialean ground ferns and few canopy trees dominated by cupressacean taxodiacean wet loving conifers with subordinate bennettitalean and caytonialean trees the coal intervals in the b bed represent terrestrialisation situations characterised by a reduced ratio of accommodation rate peat accumulation rate the palynology of these intervals indicates establishment of canopy trees primarily cupressacean taxodiacean conifers accompanied by bennettitaleans and caytonialeans with an understory of marattialean ground ferns and rarer tree ferns flooding surfaces fs and accommodation reversal surfaces ars in the b bed reflect changes in the rate of watertable rise the coaly mudstone intervals represent paludification situations with an upward increasing ratio of accommodation rate peat accumulation rate in general the palynology of the b bed suggests a coal floral composition that was dominated by mid and upper canopy plants consisting of cupcressaceaen taxodiaceaen trees probably occupying areas with standing water while ginkgos cycads bennettiales and caytoniales and other seed ferns grew in less wet areas understory plants were less abundant whereas a ground cover of ferns mainly of the families marattiales and osmundales as well as lycophytes may have been pronounced the upper surface of the b bed is a give up transgressive surface guts above which peat accumulation was replaced by siliciclastic deposition the palynofloral composition suggests an open mire dominated by ground ferns and probable tree ferns with minor bennettitalean and caytonialean mid canopy trees and with hardly any upper canopy trees the a bed is considerably richer in inertinite compared to the b bed the palynofloral and petrographic change correlates with an increase in fire activity across the triassic jurassic boundary and deforestation of the early jurassic mires

marine and terrestrial sedimentation across the t j transition in the north german basin abstract the global mesozoic sea level rise contributed to the stepwise flooding of the central european basin ceb across the t j transition and transformed the ceb from a late triassic inland playa to an early jurassic semi enclosed inland sea the calibration of sections from north germany and thuringia using high resolution palynomorph and ammonite biostratigraphy contributes to the improved temporal and spatial resolution of this decisive period the herein proposed deltoidospora concavisporites dc zone placed between the rhaetian ricciisporites polypodiisporites rp zone and the hettangian pinuspollenites trachysporites zone marks the transitional zone of overlapping rhaetian and hettangian palynomorphs in brackish marine brackish and terrestrial environments of the north german basin ngb thus the dc zone enables the identification of the t j transition in the ngb following a short term ingression in the late norian corollina porcellispora subzone the first rhaetian transgression contributed to substantial marine terrestrial facies shifts the diachronous transgressive onlap of brackish marine strata culminated in a first rhaetian maximum flooding in the upper corollina enzonalasporites zone to lower rhaetipollis limbosporites rl zone after a regressive maximum in the middle rl zone the next transgression culminated in a second rhaetian maximum flooding in the upper rl zone following the end triassic regression herein assigned to the upper rp zone the diachronous transgressive onlap of marine shales marks the change to marine jurassic environments the herein proposed deltoidospora concavisporites dc zone placed between the rhaetian ricciisporites polypodiisporites rp zone and the hettangian pinuspollenites trachysporites zone marks the transitional zone of overlapping rhaetian and hettangian palynomorphs in brackish marine brackish and terrestrial environments of the north german basin ngb thus the dc zone enables the identification of the t j transition in the ngb at the western gate of the ceb the onset of marine hettangian strata with ammonites dated as the p erugatum biohorizon at st audrie s bay postdates the base hettangian gssp by 250 kyr from there to thuringia the diachronous onlap of marine hettangian strata with ammonites herein dated as the p plicatulum biohorizon took place over 100 kyr the first jurassic maximum flooding is dated as the interval of the p psilonotum to p plicatulum biohorizons lower planorbis zone rhaetian hettangian 3rd order sequences of the ceb correlate with contemporaneous sequences described from tethyan and peri tethyan basins pointing to circum tethyan eustatic cycles the 4th order sequences are evident in the rhaetian hettangian but only a set of rhaetian 4th order sequences can be correlated in the ngb so far

triassic jurassic weathering and clay mineral dispersal in basement areas and sedimentary basins of southern sweden abstract the basement rocks of southern sweden were deeply weathered in late triassic through cretaceous times and possibly even earlier sub mesozoic saprolites formed presumably due to long term warmth and humidity in conjunction with decomposition of abundant organic matter and subsequent infiltration of acidic water the upper parts of the weathering profiles were subjected to intense leaching and kaolinitisation whereas the less evolved deep weathering front is enriched in smectite thus any erosion prior to full regolith development or extraordinary deep erosion released less developed smectite rich weathering material to the late triassic jurassic receiving basins mesozoic sedimentary successions in southern sweden show high detrital smectite and or kaolinite contents moderate illite contents and low chlorite contents compatible with expected mid latitude warm equable greenhouse conditions norian and older triassic haematite cemented continental arkoses and smectite dominated clays smectite kaolinite were clearly formed in arid settings from the rhaetian and throughout the jurassic humid onshore conditions sustained abundant plant and peat accumulation early diagenetic meteoric flushing and intense chemical weathering kaolinite is therefore a dominating detrital clay mineral in these sedimentary successions kaolinite illite chlorite and smectite i s minor quantitative variations in clay mineralogy within the humid climate rhaetian jurassic sedimentary successions are difficult to interpret in deltaic coal bearing successions the detrital clay mineral composition is conspicuously constant kaolinite illite chlorite possibly due to post depositional clay mineral transformation conversely in shallow marine deposits some quantitative variation is notable kaolinite illite variable smectite chlorite this may reflect that the original detrital composition was better preserved in shallow marine settings smectitic clay minerals associated with gypsum and caliche nodules ambiguously indicate increased aridity towards the end of the jurassic

viscoplastic self consistent and equilibrium based modeling of olivine lattice preferred orientations implications for the upper mantle seismic anisotropy anisotropy of upper mantle physical properties results from lattice preferred orientation lpo of upper mantle minerals in particular olivine we use an anisotropic viscoplastic self consistent vpsc and an equilibrium based model to simulate the development of olivine lpo and hence of seismic anisotropy during deformation comparison of model predictions with olivine lpo of naturally and experimentally deformed peridotites shows that the best fit is obtained for vpsc models with relaxed strain compatibility slight differences between modeled and measured lpo may be ascribed to activation of dynamic recrystallization during experimental and natural deformation in simple shear for instance experimental results suggest that dynamic re crystallization results in further reorientation of the lpo leading to parallelism between the main 010 100 slip system and the macroscopic shear thus modeled simple shear lpos are slightly misoriented relative to lpos measured in natural and experimentally sheared peridotites this misorientation is higher for equilibrium based models yet seismic properties calculated using lpo simulated using either anisotropic vpsc or equilibrium based models are similar to those of naturally deformed peridotites errors in the prediction of the polarization direction of the fast s wave and of the fast propagation direction for p waves are usually 15 moreover overestimation of lpo intensities in equilibrium based and vpsc simulations at high strains does not affect seismic anisotropy estimates because these latter are weakly dependent on the lpo intensity once a distinct lpo pattern has been developed thus both methods yield good predictions of development of upper mantle seismic anisotropy in response to plastic flow two notes of caution have nevertheless to be observed in using these results 1 the dilution effect of other upper mantle mineral phases in particular enstatite has to be taken into account in quantitative predictions of upper mantle seismic anisotropy and 2 lpo patterns from a few naturally deformed peridotites cannot be reproduced in simulations these abnormal lpos represent a small percent of the measured natural lpos but the present sampling may not be representative of their abundance in the earth s upper mantle

giant magmatic water reservoirs at mid crustal depth inferred from electrical conductivity and the growth of the continental crust the formation of the continental crust at subduction zones involves the differentiation of hydrous mantle derived magmas through a combination of crystallization and crustal melting however understanding the mechanisms by which differentiation occurs at depth is hampered by the inaccessibility of the deep crust in active continental arcs here we report new high pressure electrical conductivity and petrological experiments on hydrated andesitic melt from uturuncu volcano on the bolivian altiplano by applying our results to regional magnetotelluric data we show that giant conductive anomalies at mid crustal levels in several arcs are characterized by relatively low amounts of intergranular andesitic partial melts with unusually high dissolved water contents 8 wt h2o below uturuncu the altiplano puna magma body apmb displays an electrical conductivity that requires high water content up to 10 wt dissolved in the melt based on crystal liquid equilibria and melt h2o solubility experiments such a super hydrous andesitic melt must constitute about 10 of the apmb the remaining 90 being a combination of magmatic cumulates and older crustal rocks the crustal ponding level of these andesites at around 6 kbar pressure implies that on ascent through the crust hydrous magmas reach their water saturation pressure in the mid crust resulting in decompression induced crystallization that increases magma viscosity and in turn leads to preferential stalling and differentiation similar high conductivity features are observed beneath the cascades volcanic arc and taupo volcanic zone this suggests that large amounts of water in super hydrous andesitic magmas could be a common feature of active continental arcs and may illustrate a key step in the structure and growth of the continental crust one sentence summary geophysical laboratory conductivity and petrological experiments reveal that deep electrical conductivity anomalies beneath the central andes cascades and taupo volcanic zone image the ponding of super hydrous andesitic melts which contributes to the growth of continental crust

electrical conductivity of wadsleyite at high temperatures and high pressures abstract the electrical conductivity of wadsleyite aggregates has been determined under the broad range of thermodynamic conditions using the impedance spectroscopy for a frequency range of 10 2 to 10 6 hz two branches are observed in the complex impedance one at high frequency range showing a half circle originated at z real part of impedance z imaginary part of impedance 0 in the z z plot and another branch in the low frequency range the results from high frequency semi circles correspond to the electric properties of a sample whereas the results from a low frequency branch correspond to the electrode effects from the analysis of the results from the semi circles we have identified two distinct mechanisms of electrical conduction having different activation enthalpies and different sensitivity to oxygen fugacity and water content one mechanism dominating at water poor condition has a high activation enthalpy 147 kj mol and the conductivity increases with oxygen fugacity we suggest that electrical conduction in this regime is due to charge transfer involving ferric iron polaron conduction under water rich conditions electrical conductivity increases with water content but decreases with oxygen fugacity and the activation enthalpy is smaller 88 kj mol we infer that electrical conduction in this regime is due to protons the activation enthalpy in this regime is insensitive to water content and the conductivity is proportional to water content c w as c w r with r 0 72 the value of r is smaller than one suggests that minority defects such as h m or h are responsible for electrical conduction our results show that a completely dry transition zone is incompatible with most of the geophysical observations on the mantle transition zone and some water 0 1 0 3 wt in the pacific is required to explain the observed electrical conductivity

thin lithosphere beneath the central appalachian mountains a combined seismic and magnetotelluric study abstract a joint analysis of magnetotelluric and sp receiver function data collected along a profile across the central appalachians highlights variations in regional lithospheric structure while the interpretation of each data set by itself is non unique we identify three distinct features that are consistent with both the resistivity model and the receiver function image 1 thin lithosphere beneath the appalachian mountains 2 somewhat thicker lithosphere to the east of the mountains beneath the coastal plain and 3 a lithosphere asthenosphere boundary that deepens to the west of the mountains in some regions the correspondence between seismic velocity discontinuities and resistivity mark the base of the lithosphere while in other locations we see seismic discontinuities that are contained within the lithosphere at the western end of our profile a transition from highly resistive lithosphere to more conductive mantle represents the transition across the grenville front the thickness of lithosphere beneath the grenville terrain is 140 km lithosphere at the eastern end of the profile has a thickness that is not well constrained by our coverage but is at least 110 km thick this lithosphere can be associated with a broader region of high resistivity material seen to extend further south directly beneath the appalachian mountains lithospheric thickness is inferred to be as thin as 80 km based on observations of elevated mantle conductivities and a westward dipping seismic converter electrical conductivities in the uppermost asthenospheric mantle are sufficiently high 0 1 s m to require the presence of a small volume of partial melt the location of these elevated conductivities is close offset 50 km to the west to eocene volcanic outcrops in and around harrisonburg va our observations speak to mechanisms of intraplate volcanism where there is no divergent or convergent plate motion to trigger mantle upwelling or obvious fluid release either of which can facilitate melting instead we suggest that small scale mantle convection related either to pre existing lithospheric thickness variations or to lithospheric loss through delamination coupled with relative plate motion with respect to the underlying asthenosphere can trigger small amounts of melting this melt migrates upslope along the base of the lithosphere potentially thermally eroding the lithosphere resulting in further thinning

evolution of major environmental geological problems in karst areas of southwestern china karst terrains are generally regarded as a fragile and vulnerable environment china s karst is mainly developed in pre triassic old phase hard compact carbonate rock the lack of soil cover in bare karst land can enhance desertification its underground drainage system can aggravate both drought and flooding problems the interconnected surface and subsurface conditions allow for easy contamination by pollutants moreover karst terrains quite often suffer from a series of engineering problems such as water infiltrating into mines or transportation tunnels leakage from reservoirs and failure of building foundations as resources and energy exploitation intensified in recent years karst areas in southwest china faced some severe geo environmental problems in order to find out how the problems action and evolution in recent years field and laboratory investigations were conducted in guangxi autonomous region guizhou yunnan guangdong hunan hubei provinces and chongqing municipality about 100 experts from the provincial geological survey and graduate students took part in this project several symposiums were held during those 3 years besides the in situ survey data were collected from hydrogeological survey results since 2000 when the new round of land resources investigation began after analyzing these data rock desertification drought and flooding and contamination and engineering geological environmental problems were considered the most prevalent problems in karst areas in southwestern china the status of each problem is elaborated upon in this paper and should be considered for future sustainable development

onshore climate change during the late triassic marine inundation of the central european basin sedimentological pedological and palynological evidence reveal radically increasing onshore humidity during the rhaetian marine invasion of central europe along the north eastern margin of the central european basin southern sweden pre rhaetian aridity favoured the formation of carnian redbeds with calcrete which were succeeded by norian hematite cemented conglomerates arkoses arkosic wackestones and smectititic mudstones deposited on braidplains and in lakes superimposed autochthonous coals and gleysols indicate the rhaetian onset of year round humidity chemically mature sandstones kaolinitic mudstones and luvisols also formed at this time influenced by a permanent vegetation cover which lowered soil ph and strongly intensified chemical weathering the rhaetian deposits accumulated in floodplain lakes repeatedly subjected to sediment infill plant colonization and palaeosol development the humidity shift resembles that contemporaneously recorded in the north sea region

causal or casual link between the rise of nannoplankton calcification and a tectonically driven massive decrease in late triassic atmospheric co2 on the basis of a global carbon climate numerical model we reconstructed atmospheric carbon dioxide concentrations over the first 60 million years of the mesozoic our analysis indicates that pco2 declined from more than 3000 ppmv to less than 1000 ppmv with a drastic drop during the late triassic the fast northward drift of pangea exposed a large continental surface to warm and humid equatorial climate thus promoting co2 consumption through weathering this massive drawdown of atmospheric co2 is consistent with sedimentological and geochemical data of the rock record and correlates with the primary radiation of calcareous nannoplankton a biological revolution shifting the global carbonate sink from shallow water environments to the open oceans our numerical model shows that at time tectonics via weathering increased the ph of the oceanic surface waters by 0 3 units corresponding to a 50 decrease in h concentration this may have provided the ultimate environmental trigger which unlocked the newly oxidized mesozoic open oceans to pelagic nannobiocalcification

pressure effect on electrical conductivity of mantle olivine abstract we report new measurements of electrical conductivity of olivine that were made in a multi anvil press using solid buffers mo moo2 to stabilize oxygen partial pressure the temperature range was 1000 c 1400 c and the pressure range was 4 10 gpa when pressure effects are interpreted as activation volumes in the arrhenius equation they yield values of order 0 6 0 6 cm3 mole values of the pre exponential factor 0 are of the order of hundreds of s m and the zero pressure activation energy is about 1 5 ev in agreement with laboratory measurements at lower pressure conditions in addition we analyzed older literature data which produced a similar result but with larger variation the common practice of assuming that the pressure effect on electrical conductivity of olivine in the earth s upper mantle depends weakly on pressure has rested on uncertain grounds these new observations suggest that for upper mantle conditions depths of 80 200 km neglecting pressure effects on olivine conductivity is justified a weak pressure effect also supports the small polaron fe3 model as the dominant conduction mechanism although the mainly positive activation volumes argue for a component of lattice deformation when applied to the depth range 200 400 km in the earth the laboratory data yield conductivities of order 10 2 s m slightly lower than the range of geophysical conductivity profiles but well within this range after allowing for probable effects of oxygen activity and temperature uncertainty

re evaluation of electrical conductivity of anhydrous and hydrous wadsleyite abstract recent laboratory electrical conductivity measurements of the main mantle constituent minerals have represented considerable efforts to determine the effects of water content on electrical conductivity however there are large discrepancies between the results of yoshino et al 2008a and those of dai and karato 2009a on hopping conduction and the effects of water on the electrical conductivity of wadsleyite to investigate the cause of these discrepancies the electrical conductivity of anhydrous and hydrous wadsleyite were newly measured under low and high temperature conditions by impedance spectroscopy the conductivity values of dry wadsleyite aggregates with less than 2 ppm h2o by weight were similar to those for hopping conduction reported by yoshino et al 2008a and distinctly higher than those of dai and karato 2009a for hydrous wadsleyite at temperatures below 1000 k the electrical conductivity in an arrhenius plot was repeatable along the heating cooling paths and was similar to the results of yoshino et al 2008a the impedance spectrum in the complex impedance plane of hydrous wadsleyite showed a semicircular shape and the infrared spectrum did not show any shape change after the conductivity measurements in contrast when the temperature exceeds 1000 k the electrical conductivity in an arrhenius plot showed higher activation enthalpy the impedance spectra were greatly distorted and the impedance arc contained at least two relaxation processes this shape is similar to those reported by dai and karato 2009a who measured the conductivity above 1000 k the infrared spectra showed a large contribution from molecular water after conductivity measurements suggesting significant dehydration during the conductivity measurements in summary the results obtained from conductivity measurements at higher temperatures 1000 k do not represent the proton conduction in the grain interior

the late rhaetian transgression in southern sweden regional and global recognition and relation to the triassic jurassic boundary palynological investigations of rhaetian outcrops and drillcores in combination with subsurface data from wells in scania southern sweden have revealed the presence of marine dinoflagellate cysts in sedimentary strata that were previously considered to have been deposited in a mainly terrestrial environment two distinct dinocyst events are identified one older event where persistent rare to common occurrences of rhaetogonyaulax rhaetica and lunnomidinium scaniense indicates deposition in shallow marine and marginal marine environments this lunnomidinium interval is preceded and succeeded by assemblages with rare to common r rhaetica and can be correlated with the mid to late rhaetian r rhaetica zone it is associated with spore pollen assemblages of the mid rhaetian rhaetipollis limbosporites zone the younger event the r rhaetica maximum interval is characterised by mass occurrence of r rhaetica with less common or absent dapcodinium priscum in association with a dark grey to black mudstone shale the introduction of d priscum in association with the over whelming abundance of r rhaetica allows correlation with the transition between the r rhaetica zone and the succeeding d priscum zone and signals fully marine conditions the r rhaetica maximum interval is associated with spore pollen assemblages of the late rhaetian ricciisporites polypodiisporites zone and is in sweden succeeded both lithostratigraphically and palynostratigraphically by the t j transition the r rhaetica maximum interval corresponds to a late rhaetian maximum flooding event that took place in a shallow gently sloping embayment that covered the danish basin area during the late triassic early jurassic this maximum flooding event can be recognised in late rhaetian strata from different parts of the northern hemisphere it is an important temporal constraint on the t j boundary as it is associated with the disappearance of triassic marine faunas appears to coincide with the onset of the main pulse of camp volcanism immediately precedes the initial carbon isotope excursion and the global sea level drop that characterises the t j transition

the influence of partial melting on the electrical behavior of crustal rocks laboratory examinations model calculations and geological interpretations abstract the complex electrical impedance of a granulite has been determined over the frequency range 10 1 to 105 hz at temperatures between 600 and 1200 c at normal pressure and different oxygen fugacities in the stability field of magnetite the impedance spectroscopic is measurements are compared with the results of melting experiments performed under the same experimental conditions and with the same rock sample as the is measurements a strong increase in the electrical conductivity of about one and a half orders of magnitude is observed during partial melting this increase is explained by the formation of an interconnected network of melt the wetting of the grain surfaces starts slightly above the solidus however complete interconnection of the network is detected at higher temperatures 1070 c and hence higher melt fractions 10 vol this is explained by deviations from the equilibrium fabric of the partially molten sample with a modified brick layer model mblm the electrical conductivity is calculated as a function of the observed melt portion this model is valid if the melt forms a complete interconnected network at the grain boundaries the electrical conductivity at different temperatures was modeled using the results of the melting experiments and the mblm melt 10 s m with ea melt 1 ev solid 0 01 s m with ea solid 1 4 ev the results of the laboratory examinations were applied to different crustal regions where partially molten rocks are assumed to exist the same mblm is used to estimate the melt fraction that is necessary to explain the high conducting zones hczs observed in the crust beneath the andean orogen the pyrenees and the tibetan plateau at least 14 4 and 4 vol of interconnected melt are necessary to produce the observed conductivity respectively the actual amount of melt should be higher due to perturbation problems and melt trapped in pockets

sea level fall carbonate production rainy days how do they relate insight from triassic carbonate platforms western tethys southern alps italy the interplay of sea level fall climate and sedimentological changes is recorded across two sequence boundaries at the top of two triassic carbonate platform systems in the western tethys earliest carnian and norian rhaetian boundary in age paleolatitude 18 25 n the sea level falls caused subaerial exposure of the platform top and decreased carbonate production leading to starvation in the intraplatform basins followed by deposition of shale evidence of freshwater input indicates that the change in sedimentation was driven by increased rainfall on the previously arid european hinterland and tethys coast a uniformitarian approach holocene sea level changes and global warming are coupled with changes in the distribution of precipitation implicates global cooling as the probable cause of the observed sea level climate and sedimentological changes global cooling likely triggered the sea level fall by increased storage of fresh water in continental settings and change in seawater density probably coupled with ephemeral ice sheet development possible even during greenhouse intervals such as the triassic furthermore global cooling caused a shift toward the equator of the poleward boundary of the arid belt this model is supported by the traceability of the sequence boundaries and climate sensitive facies from the tethys shelf up to the european continent the observed association of global climate changes sea level fall sedimentological changes and shift toward humid climate documents how climate sensitive facies record the control exerted by global changes on local sedimentation

protracted fabric evolution in olivine implications for the relationship among strain crystallographic fabric and seismic anisotropy abstract crystallographic fabrics in olivine rich rocks provide critical information on conditions and mechanisms of deformation as well as seismic properties of earth s upper mantle previous interpretations of fabrics produced in laboratory experiments were complicated by uncertainty as to whether the steady state fabric was attained to examine the systematics of the evolution of olivine crystallographic fabrics at high strain we conducted torsion experiments on olivine aggregates to shear strains of up to 20 our results demonstrate that a steady state fabric is not reached until a shear strain 10 a much higher value than previously thought necessary fabrics characterized by girdles of 010 and 001 axes or by clusters of 010 and 001 axes are both observed until now these fabrics were associated with either two different deformation mechanisms or two different sets of deformation conditions here we establish that both fabrics are in fact part of the same evolutionary process an eigenvalue analysis allows the fabric shape to be quantitatively correlated with the magnitude of shear strain misorientation analysis suggests that the observed fabric evolution results from the competition of the two easiest slip systems in olivine 010 100 and 001 100 our results open up the possibility of using olivine crystallographic fabrics or seismic anisotropy to quantitatively evaluate strain histories in both field studies and geophysical investigations of upper mantle rocks

the electrical conductivity of lherzolite between 700oc and 1200oc and time over a period of 1700 hours are reported for a lherzolite nodule from mount porndon australia analysis of complex impedance collected at 100 hz 1 khz and 10 khz indicates that there is significant frequency dispersion in this rock at temperatures below 900oc 1000oc by choosing the resistance of an equivalent parallel rc network at the frequency having minimum phase the effect of dispersion is largely avoided conductivity as a function of time collected following changes in fo2 at 1010 and 1200oc has been analyzed to determine the diffusivity of defects relating fo2 to the electrical conduction mechanism in olivine the diffusivities so obtained are in remarkably good agreement with those determined from strain measurements during creep tests which implies that magnesium vacancies are the rate limiting step for conductivity reequilibration after fo2 changes a longer term process is observed in this rock in which the conductivity drifts upward or downward with a time constant of hundreds of hours after initial reequilibration to gas mix fo2 changes we speculate that this long term drift could be related to equilibration of the iron distribution between coexisting olivine and pyroxene as a function of fo2 the sense is an increase in conductivity olivine gains iron at low fo2 and vice versa the lherzolite conductivity data are not significantly different from measurements made on olivine single crystals and polycrystals even though the rock contains about 34 modal pyroxene this consistency of laboratory measurements of electrical conductivity of olivines from many localities and geological settings supports the use of recent models relating mantle temperature with electrical conductivity in the interpretation of mantle geo electromagnetic soundings

transport and degradation of chlorofluorocarbons cfcs in the pyritic rabis creek aquifer denmark 1 vertical profiles of the chlorofluorocarbons cfc 11 cfc 12 and cfc 113 penetrating aerobic and anaerobic parts of a shallow sandy aquifer show that the cfc gases are degraded in the 1 m thick transition zone from aerobic to anaerobic groundwater in a pyritic sand aquifer at rabis creek denmark two dimensional solute transport simulations with either zero order or first order degradation in the anaerobic zone corroborate this interpretation the transport model was previously calibrated against detailed tritium profiles in the same wells first order degradation is found to best match the observed cfc profiles yielding an approximate half life of a few months for cfc 11 degradation is not as clearly recognized for cfc 12 and cfc 113 but it may occur with rates corresponding to a half life of a few years or more data indicate a geochemical control of the cfc concentration gradient at the redox front and that denitrification and denitrifiers are not of major importance for the observed cfc degradation the responsible mechanism behind the observed degradation is not known but we suggest that reductive dehalogenation by surface bound fe ii on pyrite possibly enhanced by the presence of fe iii bearing weathering products green rust may be a plausible mechanism the observed data and the performed simulations confirm the potential application of the cfc gases as age dating tools in the aerobic part of the investigated aquifer but also that cfc data must be analyzed carefully before it is used as a dating tool in reducing aquifers because degradation may have occurred the use of multiple or alternative tracers should be considered in anaerobic environments

hydrology of the karst aquifer at the experimental site of guilin in southern china abstract the experimental site of guilin is located near the village of yaji at the border of the lijiang plain province of guangxi southern china within upper devonian limestones and dolomitic limestones a karst has developed in accordance with intense fracturing resulting from mesozoic and tertiary tectonic episodes its morphology is characterized by two major types of karst a cone karst peak cluster area bounded by the lijiang plain which comprises a tower or mogote karst peak forest area groundwater discharges from a perennial spring discharge up to 7 m3 s 1 and three intermittent springs discharge less than 5 m3 s 1 some observation boreholes have been drilled on the peak cluster area dolines and on the lijiang plain in front of the spring tracing experiments in the dolines showed that the dolines are connected with the springs the apparent flow velocity ranges between 4 and 180 m h 1 analyses of storm responses of the perennial spring and the variability in time of 18o concentration pointed out the important role played by the flows occurring in the subcutaneous zone of the peak cluster area

grain boundary sliding in san carlos olivine flow law parameters and crystallographic preferred orientation 1 we performed triaxial compressive creep experiments on aggregates of san carlos olivine to develop a flow law and to examine microstructural development in the dislocation accommodated grain boundary sliding regime gbs each experiment included load and temperature steps to determine both the stress exponent and the activation energy grain boundary maps created with electron backscatter diffraction data were used to quantify grain size distributions for each sample inversion of the resulting data produced the following flow law for gbs gbs 104 8 0 8 2 9 0 3 d0 7 0 1 exp 445 20 kj mol 1 rt with d and gbs in units of mpa m and s 1 respectively although relatively weak crystallographic preferred orientations cpos have 010 maxima parallel to the compression direction along with 100 and 001 girdles perpendicular to the compression direction cpos and subgrain boundary misorientation axes suggest that the 010 100 slip system contributes significantly to deformation we propose that these experimental results are best modeled by a deformation mechanism in which strain is accomplished primarily through grain boundary sliding accommodated by the motion of dislocations extrapolation of our flow laws to mantle conditions suggests that gbs is likely to be the dominant deformation mechanism in both lithospheric shear zones and asthenospheric flow and therefore strong upper mantle seismic anisotropy can not be attributed solely to the dominance of dislocation creep

diffusion in polycrystalline materials grain boundaries mathematical models and experimental data geological relevance of grain boundary diffusion as a rule of thumb diffusion along grain boundaries is several orders of magnitude faster than within minerals and hence it could enable mass transport on much larger spatial scales within geological time scales therefore earth scientists are interested in the transport properties of grain and interphase boundaries and other short circuit diffusion paths such as dislocations or a fluid network since they may provide very efficient transport paths controlling a variety of processes operating on very different spatial scales for example on a micron scale corona formation around minerals is a common phenomenon that is typically controlled by grain boundary diffusion similarly element and isotopic exchange between a physically separated mineral pair used for example as a geothermometer requires transport along grain boundaries metasomatic reaction zones on the centimeter to meter scale are not always simply related to fluid flow but are also induced by fluid assisted diffusive fluxes between two different rock types imposed on each other due to tectonic processes e g miller et al 2009 it has been also argued that the observed strong gradual fractionation of li isotopes on the meter scale was a result of diffusion where a strong contribution comes from grain boundary diffusion within these rocks teng et al 2006 further new data on grain boundary diffusion of siderophile elements and carbon in polycrystalline mgo suggest that grain boundary diffusion provides an efficient mechanism to exchange these elements between the mantle and the core even on the kilometer scale within reasonable time scales hayden and watson 2007 2008 in addition to the significant role of grain boundary diffusion for element transfer in rocks grain boundary diffusion can also dominate the bulk physical properties of rocks e g their viscosity coble creep or electrical conductivity which is for example relevant for the interpretation of

organic facies development within middle jurassic coal seams danish central graben and evidence for relative sea level control on peat accumulation in a coastal plain environment abstract during middle jurassic times peat accumulated in coastal plain environments in an overall transgressive setting in the sogne basin danish central graben in the north sea the coal seams occur in nonmarine to marginal marine deposits coal petrographic analyses of the seams in the west lulu 2 well supplemented with a sequence stratigraphic analysis suggest that peat accumulation was controlled by relative sea level changes in west lulu 2 the coal bearing upper part of the middle jurassic is divided into sequences a and b the sediments of sequence a are part of a transgressive systems tract whereas the overlying sequence b contains lowstand and transgressive systems tract deposits the coals are situated in the transgressive systems tracts the coal seams formed during a rapid relative sea level rise are generally characterized by petrographic features related to a permanently high groundwater table coals formed during a slow rise typically are drier in their petrographic composition the highest pyrite contents are observed in the wet coals the coal seams represent terrestrial equivalents to marine flooding surfaces or to transgressive surfaces if they are situated at the base of a transgressive systems tract a thick coal seam zone is associated with the stratigraphic level of the maximum flooding surface which correlates with the time of formation of the highest accommodation space

lateral relations of deltaic palaeosols from the lower jurassic ronne formation on the island of bornholm denmark abstract the ronne formation which crops out on the southern coast of the danish island of bornholm consists of coal bearing siliciclastic strata a major feature in these sediments is successions of different types of stacked palaeosol profiles beneath coal seams of varying thickness the most obvious and diagnostic properties of these palaeosols are the occurrence of fossil roots and the colour of the horizons penetrated by roots three types of palaeosol profiles represent an association of soils that developed on the ancient tidally influenced lower deltaic plains low relief areas were characterized by hydromorphic conditions due to poor drainage this resulted in the development of waterlogged gleysols in backswamp areas and less acid histosols in closed bays of coastal swamps in the latter case peat bogs were formed in topographically higher areas as levee banks and crevasse splays freely drained podzols developed this soil type was dominated by kaolinite in the clay fraction promoted by acid leaching the morphology and geochemistry of all palaeosols were controlled by the position of the ground water table topography climate and rate of subsidence in the podzol profiles occasional flooding resulted in the formation of spodic b horizons accumulated close to the contemporaneous water table of that time the organic rich top horizons of the podzol and histosols profiles acted as a geochemical barrier and trapped various elements litter decomposition by microorganisms in these soils resulted in a concentration of potassium at the surface thus giving an opportunity to form illite the presence of siderite in the peat bogs suggests that reducing conditions prevailed here at the time of their formation the soils were formed in a humid tropical climate this is indicated by the overall leaching pattern on cations in the podzols and histosols the accumulation of peat in the histosols and the fossil flora

structure of the lithosphere beneath the barotse basin western zambia from magnetotelluric data author posting american geophysical union 2019 this article is posted here by permission of american geophysical union for personal use not for redistribution the definitive version was published in tectonics 38 2 2019 666 686 doi 10 1029 2018tc005246

electrical conductivity anisotropy of dry and hydrous olivine at 8 gpa the effects of dissolved h2o on the electrical conductivity and its anisotropy in olivine fo90 at 8 gpa were investigated by complex impedance spectroscopy at nominally anhydrous conditions conduction along 1 0 0 and 0 0 1 is slightly higher than along 0 1 0 in contrast to observations made at lower pressures in earlier studies increasing h2o content increases conductivities but activation energies are lower and h2o concentration dependent the use of polarized ftir spectroscopy to determine h2o concentrations reveals a weaker than expected effect that water has on olivine conductivity and distinguishes our results from earlier studies based on analyses using non polarized infrared spectroscopy we show that at h2o concentrations of a few hundred wt ppm or less that the dominant conduction mechanism at mantle temperatures continues via small polarons such as that observed for anhydrous olivine our results also suggest that at depths greater than 200 km the presence of h2o may not be necessary to explain regions in the upper mantle where both electrical and seismic anisotropy are observed this can be explained by differences in the pressure dependence of the activation energy for conduction along each of the three crystallographic axes however while electrical anisotropy of anhydrous olivine remains weak at 8 gpa it is nevertheless enhanced by elevated concentrations several hundred wt ppm of dissolved h2o at these conditions dominated by proton hopping conductivity along 0 1 0 is highest approximately an order of magnitude greater than along 1 0 0 additionally at 1000 wt ppm and 1500 c an isotropic conductivity derived from the data is about 1 order of magnitude higher than that for nominally anhydrous olivine thus in regions of the mantle characterized by anomalously high conductivities and both electrical and seismic anisotropy significant amounts of dissolved hydrogen can be expected