permo carboniferous magmatism of the northeast german basin abstract variscan continent continent collision in central europe was followed by a period of syn to late tectonic magmatism involving the extrusion of large volumes of permosilesian age volcanic rocks particularly in the northeast german basin the volcanic suite up to ca 2000 m thick comprises rhyolites acid and basic andesites and tholeiitic and alkali basalts tectono geochemical analysis in conjunction with volume calculations and petrography reveals changes in volcanic activity over time a total of five eruptive stages are recognised beginning in the stephanian and extending up into the upper rotliegend permian these include the stephanian late carboniferous andesite pre ignimbrite stage i lower rotliegend permian age explosive ignimbrite stage ii post ignimbrite stage iii late rhyolite stage iv and upper rotliegend permian age late basalt stage v in addition several volcanic centres including at least two large caldera like structures are recognised the total calculated volume for the northeast german basin volcanics is ca 48 000 km3 comprising rhyolitic rocks and ignimbrites ca 70 andesitic rocks ca 26 and basalts with cogenetic dolerites ca 4 regional variations in composition and geochemistry are related to diverse crust mantle regimes which correlate with differing positions relative to the heterogeneous basement of the variscan foredeep or within the rhenohercynian orogenic zone the crustal thickening and increasing generation depth of the mafic magmas from north to south may reflect the presence of a pre existing subduction influenced basaltic magma source

geochemical characteristics and comparison of the basic rocks of the lizard complex and the basaltic lavas within the hercynian troughs of sw england the s cornish basaltic rocks constitute a separate chemical province relative to the rest of the sw england hercynian volcanic suites in particular they are characterized by a lower incompatible element abundances b generally lower large ion lithophile high field strength element ratios and c being mildly enriched in the light ree within this province some of the basalts have chemical features akin to incompatible element enriched morb tectonically the s cornish province can be divided into a the s cornish melange zone n lizard roseland area and b the mylor sedimentary trough penwith camborne area both of which contain localized basaltic lavas these basalts are compared with the lizard ophiolite and associated hornblende schists which have compositions ranging from depleted to enriched morb the exotic volcanic megaclasts within the melange zone are not chemically related to the ophiolite and as such do not represent the dismembered volcanic portion of the lizard ophiolite if the lizard ophiolite and the hornblende schists represent different segments of a palaeozoic oceanic area lying to the s the ocean floor type hercynian basalts of s cornwall are interpreted as an abortive attempt to produce oceanic crust in a rifted continental margin during the early devonian

variation of the present day stress field within the north german basin insights from thin shell fe modeling based on residual gps velocities abstract we present a finite element based dynamic modeling study of the recent stress conditions within the north german basin which is part of the central european basin system based on geological geophysical and geomorphological data after compilation and evaluation of existing data thin shell modeling is applied to understand the recent structural evolution of the central european basin system cebs and its transition towards the baltic shield in contrast to previous modeling approaches we include a complex pattern of major faults from the alpine front to the sorgenfrei tornquist zone stz and gps measured residual velocities to define the boundary conditions of the model major deviations of the stresses occur along strong contrasts in the lithospheric structure and influence the stress pattern significantly high intraplate compression is a responsible large scale reactivation of the faults associated with the pre existing basin framework in northern central europe with an important record on vertical motions the modeled slip subsidence rates of the faults in the north german basin are in the order of 0 01 and 0 2 mm year 1 which are in accordance with field observations because no fault exhibits large quaternary displacement rates in the study area

gravitational orogenic collapse vs plate boundary stresses a numerical modelling approach to the permo carboniferous evolution of central europe a two dimensional thermo mechanical finite element model is used to study the permo carboniferous evolution of central europe along a lithosphere scale transect from the variscan internides to the undeformed foreland the study concentrates on a quantitative evaluation of the processes controlling late orogenic extension and destruction of the variscides particularly the gravitational instability of thickened crust modelling results suggest that gravitational forces along cannot reproduce the observed timing and amount of permo carboniferous crustal thinning tensile plate boundary forces are required in addition to gravitation to restore a crustal thickness of approximately 30 km in the variscan internides stresses as little as 10 mpa result in up to 28 extension and a good fit between observed data and model predictions it is concluded that the stephanian to rotliegend evolution in the vicinity of the modelled traverse resulted not from gravitational forces inherited from variscan crustal thickening but was related to a change in orientation of the plate boundary stresses at the end of the westphalian

constraining the cause of the end guadalupian extinction with coupled records of carbon and calcium isotopes abstract a negative c 13 excursion in carbonate sediments near the guadalupian lopingian middle late permian boundary has been interpreted to have resulted from a large carbon cycle disturbance during the end guadalupian extinction event ca 260 ma however the carbon isotope data alone are insufficient to uniquely determine the type and magnitude of perturbation to the global carbon cycle calcium isotopes can be used to further constrain the cause of a carbon isotope excursion because the carbon and calcium cycles are coupled via caco3 burial in this study we present coupled carbon and calcium isotope records from three guadalupian lopingian g l sections in china penglaitan and chaotian and turkey koserelik tepe the c 13 and ca 44 40 records differ among our studied sections and do not co vary in the same manner no section shows c 13 and ca 44 40 changes consistent with massive rapid volcanic co2 emissions or methane clathrate destabilization additionally many sections with large 3 changes in c 13 exhibit o 18 evidence for diagenetic alteration only one section exhibits a large excursion in the ca 44 40 of limestone but the absence of a similar excursion in the ca 44 40 of conodont apatite suggests that the limestone excursion reflects a mineralogical control rather than a perturbation to the global calcium cycle hence we interpret the large isotopic changes observed in some sections to have resulted from local burial conditions or diagenetic effects rather than from a large carbon and calcium cycle disturbance perturbations to the global carbon and calcium cycles across the g l transition were much less intense than the disturbances that occurred across the subsequent permian triassic boundary this finding is consistent with the much smaller magnitude of the end guadalupian extinction relative to the end permian

geodynamic model for the palaeozoic crustal consolidation of western and central europe abstract the crystalline basement of western and central europe consists of a mosaic of crustal elements which were consolidated during pre grenvillian the grenvillian dalslandian morarian cadomian caledonian and hercynian orogenic cycles contemporaneous with the caledonian suturing of the precambrian laurentia greenland and fennosarmatian shields a number of gondwana derived cadomian micro cratons were accreted to the southern margin of laurasia following the late caledonian paroxysm the devonian and early carboniferous evolution of europe was dominated by continued northward subduction of the proto tethys plate at an arc trench system parallelling the southern margin of laurasia the accretion of additional gondwana derived continental fragments back arc rifting and a sinistral translation of major proportions between the laurentia greenland and the fennosarmatian sub plates the acadian and bretonian orogenies were of the pacific type the visean collision of gondwana with laurasia marked the onset of the himalayan type variscan orogeny during which collision related compressive stresses overpowered the devonian early carboniferous back arc rift systems and caused the development reactivation of a subduction zones the central armorican and saxothuringian successor basins became folded and destroyed during the latest visean whilst the variscan foredeep became scooped out in part by nappes involving the basement during the late westphalian major crustal shortening during the variscan diastrophism was accompanied by the anatectic remobilisation of subducted crustal and upper mantle material and a widespread syn and late orogenic magmatism the latest carboniferous early permian reorientation of the convergence direction between gondwana and laurasia induced the development of a complex wrench fault system transecting the variscan fold belt and an extensive post orogenic volcanism the hypotheses summarised here require confirmation by further palaeomagnetic and radiometric data and faunal analyses

the shale gas potential of tournaisian visean and namurian black shales in north germany baseline parameters in a geological context carboniferous black mudrocks with known petroleum potential occur throughout northern germany however despite numerous boreholes exploring for conventional hydrocarbons the potential for shale gas resources remains uncertain therefore an integrated investigation was conducted to elucidate the shale gas potential for three different carboniferous facies incorporating baseline parameters from sedimentological and organic geochemical analyses tournaisian namurian fine grained rocks of the culm facies with type ii iii kerogen were deposited in the basin center toc contents of up to 7 occur in the lower alum shale 3 6 vrr and up to 6 in the upper alum shale 4 4 vrr bands of organic rich black shales reflecting sea level variations controlled by global eustatic cycles occur within the tournaisian visean kohlenkalk facies north of the rhenish slate mountains and in the rugen island area in both areas the organic matter is characterized by a kerogen type ii iii with toc contents of up to 7 and maturities of up to 4 2 and 1 8 vrr respectively black hemipelagites intercalated with coarser grained silt and sandstones occur in the synorogenic flysch formation of the namurian a along the southern basin margin toc contents vary from 0 5 to 2 0 with type iii kerogen dominated organic matter and maturities of up to 2 5 vrr the baseline parameters presented in this paper indicate a shale gas potential for the sediments of the culm facies on the southern basin margin and of the kohlenkalk facies in the rugen area

geochemistry and tectonic setting of lewisian clastic metasediments from the early proterozoic loch maree group of gairloch nw scotland abstract the early proterozoic 2 0 ga loch maree group lmg of the lewisian complex consists of a supracrustal sequence of metasedimentary schists and associated tholeiitic metavolcanic amphibolites within the archaean basement the metasediments comprise three main mapped units the flowerdale schists kerrysdale schists and charlestown schists together with numerous narrower bands the dominant clastic metasediments within the schist units semipelites and psammites are chemically distinguished as a series of greywackes and lithic sandstones with variable lil and transition element abundances fractionated ree patterns and overall compositions similar to paas three chemical groups are recognized whose range of composition largely reflects the mixing between two main source components lewisian gneissose basement with an intermediate acid continental crust composition and local rift related amphibolites with a primitive tholeiitic composition which also incorporates components not preserved within the lmg the geochemistry of the clastic metasediments confirms a previous tectonic model for the lmg as an intracontinental extensional rift receiving clastic detritus from the adjacent uplifted basement as well as from internal volcanogenic sources

dolomite abundance and stratigraphic age constraints on rates and mechanisms of phanerozoic dolostone formation increasing dolomite abundance with age relative to limestone has long been accepted as one of the general truisms of sedimentary geology a relationship which suggests that dolomitization is a cumulative process occurring slowly over the full burial history of a carbonate sequence however reevaluation of data in support of this assumption indicates that although relative dolomite abundances do change significantly throughout phanerozoic carbonate sequences no data set demonstrates any direct correlation between dolomite content and age whereas tabulation of available data does suggest greater amounts of dolomite formation during periods of continental flooding global mass balance calculations of potential magnesium sources also indicate that most dolomite has formed from marine or marine derived fluids at the earth9s surface this conclusion is indirectly supported by significant short term period scale changes in phanerozoic dolomite abundance a variation which would be more attenuated if dolomitization were dominantly a burial process dolomitization may be enhanced during times of global transgression higher atmospheric pco 2 and lower calcite saturation state in shallow marine settings

late cretaceous cenozoic evolution of the north german basin results from 3 d geodynamic modelling abstract the late cretaceous cenozoic evolution of the north german basin has been investigated by 3 d thermomechanical finite element modelling the model solves the equations of motion of an elasto visco plastic continuum representing the continental lithosphere it includes the variations of stress in time and space the thermal evolution surface processes and variations in global sea level the north german basin became inverted in the late cretaceous early cenozoic the inversion was most intense in the southern part of the basin i e in the lower saxony basin the flechtingen high and the harz the lower crustal properties vary across the north german basin north of the elbe line the lower crust is dense and has high seismic velocity compared to the lower crust south of the elbe line the lower crust with high density and high velocity is assumed to be strong lateral variations in lithospheric strength also arise from lateral variations in moho depth in areas where the moho is deep the upper mantle is warm and the lithosphere is thereby relatively weak compression of the lithosphere causes shortening thickening and surface uplift of relatively weak areas tectonic inversion occurs as zones of preexisting weakness are shortened and thickened in compression contemporaneously the margins of the weak zone subside cenozoic subsidence of the northern part of the north german basin is explained as a combination of thermal subsidence and a small amount of deformation and surface uplift during compression of the stronger crust in the north the modelled deformation patterns and resulting sediment isopachs correlate with observations from the area this verifies the usefulness and importance of thermomechanical models in the investigation of intraplate sedimentary basin formation

ca and mg isotope constraints on the origin of earth s deepest δ13c excursion abstract understanding the extreme carbon isotope excursions found in carbonate rocks of the ediacaran period 635 541 ma where 13 c of marine carbonates 13 c carb reach their minimum 12 for earth history is one of the most vexing problems in precambrian geology known colloquially as the shuram excursion the event has been interpreted by many as a product of a profoundly different ediacaran carbon cycle more recently diagenetic processes have been invoked with the very negative 13 c values of ediacaran carbonates explained via meteoric alteration late stage burial diagenesis or growth of authigenic carbonates in the sediment column thus challenging models which rely upon a dramatically changing redox state of the ediacaran oceans here we present 257 44 40 ca and 131 26 mg measurements along with mg mn and sr data from carbonates of the ediacaran aged wonoka formation fm of south australia to bring new isotope systems to bear on understanding the shuram excursion data from four measured sections spanning the basin reveal stratigraphically coherent trends with variability of 1 5 in 26 mg and 1 2 in 44 40 ca this ca isotope variability dwarfs the 0 2 0 3 change seen coeval with the permian triassic mass extinction the largest recorded in the rock record and is on par with putative changes in the 44 40 ca value of seawater seen over the phanerozoic eon changes in both isotopic systems are too large to explain with changes in the isotopic composition of ca and mg in global seawater given modern budgets and residence times and thus must be products of alternative processes relationships between 44 40 ca and sr and 26 mg and mg are consistent with mineralogical control e g aragonite vs calcite limestone vs dolostone on calcium and magnesium isotope variability the most pristine samples in the wonoka dataset preserving sr concentrations in the 1000s of ppm range and 44 40 ca values inherited from an originally aragonitic polymorph have 13 c carb of 8 to 7 thereby providing strong geochemical evidence that extremely negative 13 c carb values are primary products of the ediacaran surface environment

the calcium riverine and hydrothermal isotopic fluxes and the oceanic calcium mass balance calcium isotope ratios relative to seawater were studied in natural waters in order to constrain the ca isotopic flux to the oceans and to discuss the oceanic ca budget this study includes the analysis of 1 ca isotopes in continental waters at the regional scale of the upper rhine valley and 2 the determination of the 44ca values of some major rivers and hydrothermal vents the data indicate that the global 44ca variability of the studied waters with a maximal range of 1 is limited and must be linked to mass fractionation processes at the scale of a small watershed aubure vosges france the 44ca river flux changes due to the variation of the proportion of waters resulting from chemical alteration of rocks and biologically fractionated soil solutions ca isotopes could therefore be an important tool to quantify the impact of the plants and the biosphere on the river water chemistry at the regional scale of the rhine valley as well as at the global scale of world rivers the 44ca variability of river samples ranges from 0 5 to 1 without any relationship with the lithology of the watershed or the climate similarly the 44ca value of hydrothermal vents is also uniform and close to the mean value of river waters consequently the 44ca flux to the ocean should remain rather constant through time with a mean of 1 1 0 2 this value confirms that the ca budget of the present day seawater is in steady state this was not necessarily the case in the past non steady state periods should have been due to intensity variations of incoming and outcoming ca fluxes rather than to the variations in their isotopic signatures

the solubility of halite as a function of temperature in the highly saline dead sea brine system the dead sea brine is characterized by high ionic strength 9 10 m and a ca cl composition the lake is currently saturated with respect to aragonite gypsum and halite harned s rule is applied to calculate the saturation index of halite in the dead sea brine system this system includes brines at ionic strengths in the range of 9 l 6 1 derived from evaporating dead sea brine to facilitate the calculation we determined new interaction coefficients experimentally these were found to be a function of the ionic strength of the solution as well as of the temperature 25 c anaa mgc12 0 002611 0 00905 anac1 caci 0 001501 0 00650 3 5 c anac l m cl 0 002831 0 01972 anacl caci 0 002071 0 01851 50 c anaci m l 0 002261 0 01416 anaci cacl 0 001561 0 01315 the new parameters are used to predict the effect of temperature on halite precipitation in the lake from both the evaporating surface layer and the entire upper water body the calculated weight of halite expected to precipitate before the onset of carnallite precipitation is on the order of lo o t at the present rate of evaporation at least 120 yr will pass before that point is reached

3d lithosphere scale density model of the central european basin system and adjacent areas abstract to analyze the first order structural features characterizing the crust and the lithospheric mantle below the central european basin system and adjacent areas a new lithosphere scale 3d structural density model has been derived that integrates published knowledge with 3d gravity modeling with this study we aim to integrate previous results on sub domains of the study area and regional results of limited resolution in conjunction with 3d gravity analysis to derive the configuration of the lower crust and lithospheric mantle that is consistent with the known density distribution of the sediment fill and with observed deep seismic data as well as with observed gravity the derived 3d density model resolves the internal configuration of the crystalline crust below the central european basin system and adjacent areas at the regional scale and shows that the crystalline crust is characterized by a layered structure the upper to middle crystalline crust is characterized by relatively low seismic p wave velocities and densities it shows strong variations in thickness across the study area that partly correlate spatially with the inherited segmentation in response to crustal amalgamation this upper to middle crystalline crust is underlain by a continuous high density high velocity lower crustal layer locally more than 30 km thick beneath the east european craton and generally decreasing in thickness from the older to the younger tectonic domains though the thickness of this high density lower crust is generally small below the permo cenozoic central european basin system it can reach locally more than 18 km below the northeast german and the norwegian danish basins the derived depth to the lithosphere asthenosphere boundary confirms previously proposed geometries and is up to 230 km deep beneath the precambrian domain but less than 100 km deep beneath the phanerozoic domains implying that the average thermal gradient is higher in the phanerozoic lithosphere than in the precambrian part

hypersaline brine diagenesis and evolution in the dead sea lake lisan system israel abstract water soluble salts were extracted from 57 aragonite and detrital laminae sampled from the pleistocene lake lisan sediments the solutions and solids were analysed for ca mg na k sr cl so 4 and bicarbonate average na cl mg ca sr ca mg cl ca cl sr cl k cl k na and k mg ratios calculated for seven stratigraphie elevations in the lisan column indicate that the dead sea rift sediment brine system has remained practically closed for 70000 years the soluble salts reflect both the hydrologie evolution of the lake as well as diagenetic processes mg ca ratios systematically decrease in younger sediments and this decline is accompanied by a 1 5 4 fold sr enrichment in aragonite solubles relative to salts extracted from detrital laminae the major process responsible for these observations is dolomitization of sr rich aragonite by interstitial brine diagenesis was triggered by slow desiccation of the lake s sediments after the lisan waters started to recede due to a change in climate very sharp chemical gradients which developed in the sediments after deposition have been preserved because further diagenesis was quenched by the advancing dry out h 2 o loss by evaporation induced difrusional migration of na and cl from aragonite laminae into adjacent detrital layers this lowered the na cl ratio in the aragonite and raised it in the detritus relative to the initial dead sea na cl ratio of 0 26 the early lisan brine was similar in its chemical composition and total salinity to that of the present dead sea

new constraints on the timing of late carboniferous early permian volcanism in the central north sea the permo carboniferous evolution of the central north sea is characterized by three main geological events 1 the development of the west european carboniferous basin 2 a period of basaltic volcanism during the lower rotliegend latest carboniferous early permian and 3 the development of the northern and southern permian basins in late permian times the timing of the late carboniferous permian basaltic volcanism in the north sea is poorly constrained as is the timing of extensional tectonic activity following main inversion during the westphalian due to the propagation of the variscan deformation front results of high precision ar ar dating on basalt samples taken from a core from exploration well 39 2 4 amerada hess in the uk sector of the central north sea suggests that basaltic volcanism was active in the late carboniferous at c 299 ma the presence of volcanics below the dated horizon suggests that the onset of permo carboniferous volcanism in the central north sea commenced earlier probably at c 310 ma westphalian c this is contemporaneous with other observations of tholeiitic volcanism in other parts of nw europe including the oslo graben the north east german basin southern sweden and scotland interpretations of available seismic data show that main extensional faulting occurred after the volcanic activity but the exact age of the fault activity is difficult to constrain with the data available

herringbone calcite petrography and environmental significance abstract herringbone calcite is a previously undescribed carbonate cement and sea floor precipitate that is common in archean carbonates but rare in proterozoic and phanerozoic rocks it is abundant in the 2520 ma campbellrand malmani platform south africa where field relationships such as erosional truncation of layers of herringbone calcite and interbedding of herringbone calcite with grainstones demonstrate that it precipitated from ambient marine water this interpretation is supported by depositional relationships in the 2 6 ga huntsman limestone of the bulawayo greenstone belt zimbabwe the 2 6 ga carawine dolomite australia the 1 90 ga rocknest formation and the 1 8 1 2 ga dismal lakes group canada the ordovician porterfi ld carbonate buildup virginia and various silurian carbonate buildups in the midcontinent united states each of these occurrences is associated with anaerobic depositional environments or organic rich sediments herringbone calcite consists of alternating light and dark crenulated bands each light dark pair is 0 5 1 0 mm thick microscopically each pair of bands consists of a row of elongate crystals with their long axes aligned perpendicular to banding and along the growth direction of the cement the bases of the crystals are optically unoriented but upwards in each crystal the optical c axis rotates until it is perpendicular to crystal elongation the tops of the elongate crystal are thus optically aligned and length slow the light bands of herringbone calcite correspond to the optically oriented parts of the elongate crystals whereas the dark bands correspond to the optically unoriented lower parts of the elongate crystals microspar crystals are also present in some dark ba ds a mg calcite precursor for herringbone calcite now preserved as low mg calcite or dolomite is supported by the presence of micro dolomite inclusions and textural differences between herringbone calcite and textures interpreted as neomorphosed former aragonite or low mg calcite precipitation of herringbone calcite may be consistent with a diffusionally controlled growth model involving branching growth of fibrous crystals and diffusion of a precipitation inhibitor away from the crystallization surface since herringbone calcite is associated with anaerobic depositional environments the inhibitor promoting precipitation of herringbone calcite may be present only in poorly oxygenated sea water thus the stratigraphic distribution of herringbone calcite may be an important indicator of the abundance of oxygen in carbonate depositional environments through time

stable calcium isotopic composition of meteorites and rocky planets abstract new measurements of mass dependent calcium isotope effects in meteorites lunar and terrestrial samples show that earth moon mars and differentiated asteroids e g 4 vesta and the angrite and aubrite parent bodies are indistinguishable from primitive ordinary chondritic meteorites at our current analytical resolution 0 07 sd for the 44 ca 40 ca ratio in contrast enstatite chondritic meteorites are slightly enriched in heavier calcium isotopes ca 0 5 and primitive carbonaceous chondritic meteorites are depleted in heavier calcium isotopes ca 0 5 the calcium isotope effects cannot be easily ascribed to evaporation or intraplanetary differentiation processes the isotopic variations probably survive from the earliest stages of nebular condensation and indicate that condensation occurred under non equilibrium undercooled nebular gas conditions some of this early high temperature calcium isotope heterogeneity is recorded by refractory inclusions niederer and papanastassiou 1984 and survived in planetesimals but virtually none of it survived through terrestrial planet accretion the new calcium isotope data suggest that ordinary chondrites are representative of the bulk of the refractory materials that formed the terrestrial planets enstatite and carbonaceous chondrites are not the enrichment of light calcium isotopes in bulk carbonaceous chondrites implies that their compositions are not fully representative of the solar nebula condensable fraction

age constraints for the thermal evolution and erosional history of the central european variscan belt new data from the sediments and basement of the carboniferous foreland basin in western poland three carboniferous age detrital muscovites from the variscan foreland basin of sw poland and two muscovites from phyllites underlying the basement have been dated by the 40 ar 39 ar step heating and single crystal laser fusion method 40 ar 39 ar analysis of the detrital micas defines step heating preferred ages of 370 7 1 4 363 0 1 9 and 355 0 1 3 ma single crystal laser fusion data indicate little dispersion for the first of three samples with an integrated age that closely matches the step heating data but the latter two describe inhomogeneous populations the white mica concentrate from one phyllite yields a step heating preferred age of 358 6 1 8 ma the second phyllite sample displays an incremental discordant apparent age spectrum representing a mixture of white mica grains of varying ages our most important finding is that the variscan foreland basin was supplied by source rocks that were exhumed and cooled in the late devonian probably as a result of an early variscan collisional event previously largely undocumented although accessible exposures of the variscan basement in sw poland exhibit only a minor component of rocks exhumed before the carboniferous our work suggests that large tracts of rocks with a devonian cooling signature are preserved at depth beneath the foreland basin

a 3 800 million year isotopic record of life from carbon in sedimentary rocks an increased ratio of 12c to 13c an indicator of the principal carbon fixing reaction of photosynthesis is found in sedimentary organic matter dating back to almost four thousand million years ago a sign of prolific microbial life not long after the earth s formation partial biological control of the terrestrial carbon cycle must have been established very early and was in full operation when the oldest sediments were formed

the sulfur system in anoxic subsurface brines and its implication in brine evolutionary pathways the ca chloride brines in the dead sea area abstract important elements in the evolutionary history of saline groundwater might be overlooked when they involve both sulfate removal through reduction and input of sulfate via dissolution these two simultaneous and apparently contrasting processes can result in a negligible net effect on the sulfate concentration isotopic composition of sulfur in sulfate and sulfide can be applied to identify the bacterial sulfate reduction bsr though the extent of the process is difficult to quantify saturation with respect to gypsum may suggest that gypsum dissolution also occurs however a more definite identification of these processes and their quantification can be achieved through the use of ammonium concentration in the anoxic brines this approach assumes that the ammonium is derived only from the oxidation of organic matter through bsr and it requires that the c n ratio in the oxidized organic matter be known a minimum estimate for the sulfate reduction can be obtained when the redfield c n ratio 106 16 is assumed several calculation methods are presented to identify the extent of sulfate reduction prior to concomitant with or following gypsum dissolution that are based on combining sulfur isotopic compositions rayleigh distillation equation and calculated gypsum saturation indices the required assumptions are presented and their validation is discussed the subsurface hypersaline ca chloride brines in the vicinity of the dead sea are taken as a case study here sulfur isotope compositions of sulfate and sulfide and high ammonium concentrations indicate bsr occurs in the subsurface the sulfur isotopic composition of the sulfate makes it possible to distinguish between two major groups of brine and their recent evolutionary histories 1 the qedem shalem thermal brines 34 s so4 21 24 which emerge as springs along the shores and are slightly undersaturated with respect to gypsum 2 dsif tappuah brines 34 s so4 30 60 which are found in shallow boreholes and are saturated to oversaturated with respect to gypsum calculations based on their ammonium content suggest that both groups of brine require apparent unreasonably high oversaturations with respect to gypsum prior to the onset of the reduction this implies that the groundwater systems were open with respect to sulfate and that the sulfate reservoir was replenished continuously or intermittently during the bsr the dsif tappuah brines continue to dissolve gypsum during their bsr the dissolving sulfate is derived from relatively isotopically enriched gypsums 34 s so4 20 such as found in the lisan formation these brines approach the steady state isotopic composition 34 s ss dictated by the combination of the 34 s of the dissolving gypsum and the fractionation factor accompanying bsr the sulfur isotopic composition of the qedem shalem brines implies that most of their ammonium content is derived from an earlier phase of bsr and that the last phase of bsr takes place during the brines rapid ascent to the surface prior to this stage they evolved through either 1 dissolution of gypsum with 34 s so4 20 which occurred after the main bsr in the subsurface 2 a previous phase in which the brines were part of a lake and later percolated to the subsurface as such their isotopic composition and ammonium content were determined by the combined effect of freshwater sulfate input to the lake and bsr in the stratified lake

lower palaeozoic evolution of the northeast german basin baltica borderland the vendian silurian succession from a series of boreholes in northeast germany has been petrographically and geochemically investigated evidence suggests that the more northerly vendian and cambrian succession was deposited on a craton which became increasingly unstable in ordovician times similarly the ordovician age succession deposited in the rugen area indicates a strongly active continental margin tectonic setting for the same period by silurian times the region was once more relatively tectonically quiescent although complete closure of the tornquist sea was not complete until latest silurian times the major changes in tectonic regime in the eastern avalonia baltica area recorded from the ordovician suggest that a significant degree of closure occurred during this time

testing urey s carbonate silicate cycle using the calcium isotopic composition of sedimentary carbonates abstract carbonate minerals constitute a major component of the sedimentary geological record and an archive of a fraction of the carbon and calcium cycled through the earth s surface reservoirs for over three billion years for calcium carbonate minerals constitute the ultimate sink for almost all calcium liberated during continental and submarine weathering of silicate minerals this study presents 500 stable isotope ratios of calcium in precambrian carbonate sediments both limestones and dolomites in an attempt to characterize the isotope mass balance of the sedimentary carbonate reservoir through time the mean of the dataset is indistinguishable from estimates of the calcium isotope ratio of bulk silicate earth consistent with the urey cycle being the dominant mechanism exchanging calcium among surface reservoirs the variability in bulk sediment calcium isotope ratios within each geological unit does not reflect changes in the global calcium cycle but rather highlights the importance of local mineralogical and or diagenetic effects in the carbonate record this dataset demonstrates the potential for calcium isotope ratios to help assess these local effects such as the former presence of aragonite even in rocks with a history of neomorphism and recrystallization additionally 29 calcium isotope measurements are presented from odp ocean drilling program site 801 that contribute to the characterization of altered oceanic crust as an additional sink for calcium and whose distinct isotopic signature places a limit on the importance of this subduction flux over earth history

linking changes in tectonic style with magmatism in northern europe during the late carboniferous to latest permian abstract early carboniferous to permian magmatism associated with rifting within the northern foreland of the variscan orogen was widespread across europe during the long period of magmatic activity the regional tectonic setting changed across the region from early carboniferous extension and basin formation to a rifting wrenching style of deformation in the late carboniferous stephanian to early permian wrenching and faulting were accompanied by widespread voluminous and episodic magmatic extrusion intrusion and underplating this was followed by thermal relaxation and the development of the northern and southern permian basins in later permian times thermal relaxation was punctuated by a permo triassic phase of extension and graben formation 40ar 39ar ar step heating dating for mineral separates and whole rock samples of magmatic rocks from southern scandinavia oslo graben and south sweden and rugen north germany provides further radiometric evidence for three of the proposed periods of magmatic activity in the region latest carboniferous to earliest permian ages c 300 310 ma were obtained for volcanic rocks in the oslo graben and dolerite sills and dykes in south sweden and north germany this phase can be time correlated with magmatic activity that occurred throughout europe during large scale dextral wrenching that followed the variscan orogeny a second phase of alkaline intrusions is confined to the oslo graben and related to caldera collapse around c 275 ma the third permo triassic phase c 250 ma is considered to be related to a new tectonic cycle involving extension that triggered minor melting of enriched fertile mantle

relics of evaporated sea water in deep basins of the eastern mediterranean abstract reexamination of data on hypersaline bottom brines from the deep anoxic tyro and bannock basins in the eastern mediterranean reveals that despite their similar chlorinity 6 0 mole kg h 2 o their chemical composition is significantly different the brine in the tyro basin has a na chloride composition na cl 1 with conspicuously low ratios of conservative elements to chloride br cl 2 4 10 4 li cl 1 4 10 5 b cl 1 6 10 4 indicating dissolution of halite in contrast brines from the bannock basin are characterized by an mg chloride signature na cl 0 78 with relatively high ratios of conservative elements to chloride br cl 1 7 10 3 li cl 5 2 10 5 b cl 8 4 10 4 the contents of na mg k li cl br and b in the deep bannock brines brine ii are identical to those in evaporated sea water of a degree of evaporation of 12 13 whereas ca is enriched and so 4 is depleted in contrast to previous studies it is suggested that brine ii from the bannock basin is a relic of ancient evaporated sea water that was slightly modified by sulphate reduction and gypsum dissolution the interstitial ancient evaporated sea water was liberated and accumulated on the sea floor probably during the formation of the deep basins in the bannock area

gypsum as a monitor of the paleo limnological hydrological conditions in lake lisan and the dead sea the isotopic composition and mass balances of sources and sinks of sulfur are used to constrain the limnological hydrological evolution of the last glacial lake lisan 70 14 ka bp and the holocene dead sea lake lisan deposited large amounts of primary gypsum during discrete episodes of lake level decline this gypsum which appears in massive or laminated forms displays 34s values in the range of 14 28 in addition lake lisan s deposits the lisan formation contain thinly laminated and disseminated gypsum as well as native sulfur which display significantly lower 34s values 26 to 1 and 20 to 10 respectively the calculated bulk isotopic compositions of sulfur in the sources and sinks of lake lisan lacustrine system are similar 34s 10 indicating that freshwater sulfate was the main source of sulfur to the lake the large range in 34s found within the lisan formation 26 to 28 is the result of bacterial sulfate reduction bsr within the anoxic lower water body the monimolimnion and bottom sediments of the lake precipitation of primary gypsum from the ca chloride solution of lake lisan is limited by sulfate concentration which could not exceed 3000 mg l the upper gypsum unit deposited before ca 17 15 ka is the thickest gypsum unit in the section and displays the highest 34s values 25 28 yet our calculations indicate that no more than a third of this unit could have precipitated directly from the water column this implies that during the lake level decline that instigated the precipitation of the upper gypsum unit significant amounts of dissolved sulfate had to reach the lake from external sources we propose a mechanism that operated during cycles of high low stands of the lakes that occupied the dead sea basin during the late pleistocene during high stand intervals i e marine isotopic stages 2 and 4 lake brine underwent bsr and infiltrated the lake s margins and adjacent strata as lake level dropped these brines carrying 34s enriched sulfate were flushed back to the shrinking lake and replenished the water column with sulfate thereby promoting massive gypsum precipitation the holocene dead sea precipitated relatively small amounts of primary gypsum mainly in the form of thin laminae 34s values of these laminae and disseminated gypsum are relatively constant 15 0 7 and are close to present day lake composition this reflects the lower supply of freshwater to the lake and the limited bsr activity during the arid holocene time and possibly during former arid interglacials in the levant

the post glacial landscape evolution of the north german basin morphology neotectonics and crustal deformation the recent evolution of the north german basin ngb which is presently a low seismic area was partly affected by glacial loading and unloading of the ice masses major stresses acting within the ngb are induced by the north atlantic ridge push the ongoing alpine collision and the post glacial rebound of fennoscandia present day horizontal stresses within the ngb are directed generally nw se but fan and bend north of 52 n towards nne major basement faults are directed nw se minor faults ne sw and nne ssw and are clearly detectable in geomorphological and satellite lineaments furthermore the drainage pattern and the distribution of lakes in northern germany follow exactly block boundaries and hence mark zones of present day subsidence the understanding of the post glacial morphology and reactivation of faults requires a view into the very heterogeneous crust and upper mantle below the ngb the re adjustment of the individual fault blocks during post glacial relaxation of the lithosphere leads to differential crust dependent uplift and probably to the formation of urstrom valleys the urstrom valleys and terminal moraines in northern germany appear to parallel the major tectonic lineaments and lithospheric block boundaries the lithospheric memory is expressed in the post glacial landscape evolution of the ngb

strontium isotopic chemical and sedimentological evidence for the evolution of lake lisan and the dead sea precise strontium isotope ratios combined with chemical analyses and sedimentological information are used to monitor the water sources and the evolution of the dead sea and its late pleistocene precursor lake lisan 70 18 kyr b p the materials analyzed include bulk aragonite water leached soluble salts and residual aragonite and gypsum from the lisan formation in the perazim valley near the sw shore of the dead sea the residual aragonite and the associated soluble salts display systematic fluctuations in 17sr86sr ratios between 0 70803 and 0 70806 and from 0 70805 to 0 70807 respectively in individual soluble salt residual aragonite pairs the soluble salt displays a higher 87sr86sr ratio gypsum samples yield 17sr86sr ratios similar to the soluble salts from adjacent layers in the section this shows that in individual samples the source of sr in aragonite was distinct from that in soluble salts and the gypsum the sterility of the lisan sediments their strictly nonbioturbated fine lamination and their high content of chloride salts indicate that lake lisan was a saline or even hypersaline water body in the absence of alternative sources of hco3 and s042 the abundance of primary aragonite and gypsum in the lisan column reflects an import of very large volumes of freshwater into the otherwise saline lake resulting in a density stratification of this water body the history of the upper water layer and that of the lower brine is reflected in the chemical and strontium isotope composition of the aragonite and in that of the associated soluble salts and in the gypsum samples respectively whereas the bicarbonate and much of the ca2 required for aragonite crystallization were supplied by the freshwater the complementary ca2 and sr 2 were added by the lower brine the upper water layer of lake lisan acted as a so42 capacitor during the lake s rise periods it was removed therefrom as prominent gypsum beds upon climatic induced drier period mixing or even complete overturn of the lake the evolution of lake lisan took place between two distinct modes the first was characterized by an extensive supply of freshwater and resulted in a rise of the lake s level a density layered structure and precipitation of aragonite the second mode was marked by a diminishing freshwater input resulting in mixing or complete overturn of its water and precipitation of gypsum these two modes reflect the climatic evolution of the region in the late pleistocene which fluctuated between drier and wetter periods the transition to the holocene is accompanied by the dry up of lake lisan and its contraction to the present dead sea

the sources and evolution of sulfur in the hypersaline lake lisan paleo dead sea d 34 s values in gypsum are used to evaluate the fate of sulfur in the hypersaline lake lisan the late pleistocene precursor of the dead sea 70 14 ka bp and applied as a paleo limnological tracer the ca chloride lake lisan evolved through meromictic periods characterized by precipitation of authigenic aragonite and holomictic episodes characterized by enhanced gypsum precipitation the lake deposited two major gypsum units the blower gypsum unitq deposited at 56 ka showing d 34 s values of 18 20x and the bupper gypsum unitq deposited at 17 ka displaying significantly higher d 34 s values of 26 28x laminated and disseminated gypsum residing within the aragonite exhibit d 34 s values in the range of 26x to 1x the isotopic composition of the gypsum was dictated by freshwater sulfate input that replenished the upper layer of the lake the mixolimnion bacterial sulfate reduction bsr that occurred under the anoxic conditions of the lower brine the monimolimnion and mixing between these two layers during meromictic periods the sulfate reservoir in the lower brine was replenished by precipitation of gypsum from the upper layer and its subsequent dissolution due to sulfate deficiency induced by bsr activity this process describes a bsulfur pumpq mechanism and its effect on d 34 s in the water can be modeled by a modified rayleigh distillation equation steady state d 34 s values 40x were reached in the lower brine after long meromictic periods following overturn episodes induced by diminishing freshwater input and lake level decline large quantities of d 34 s enriched gypsum precipitated the negative d 34 s values in laminated and disseminated gypsum provide evidence for bsr activity in the lower brine that removed isotopically depleted sulfides from the water column causing significant isotopic enrichment of remaining sulfate following the lake desiccation the sediments were exposed and the latter sulfides oxidized and re crystallized as gypsum d 2005 elsevier b v all rights reserved

seismic interpretation of dinantian carbonate platforms in the netherlands implications for the palaeogeographical and structural development of the northwest european carboniferous basin the northwest european carboniferous basin is characterized by a series of carbonate platforms and intervening shale dominated troughs during the dinantian sub period these structures have been mainly found along the margins of the basin here we present the results of an investigation of high quality 3d seismic surveys which has allowed the construction of a palaeogeographical and structural framework of the dinantian sub period in the centre of the northwest european carboniferous basin analysis of these data has revealed a series of structures characterized by flat tops well developed slopes and onlap by overlying strata these geometrical features suggest that the structures represent dinantian carbonate platforms an interpretation that is supported by recently published well data these findings suggest the following sequential depositional and structural model for the area 1 during the tournaisian stage carbonate sedimentation took place in basinal areas 2 continued subsidence probably induced by rifting resulted in the gradual onlap of carbonate deposition onto topographically higher areas 3 during the late visean stage rimmed shelf deposition took place by analogy with observations from the uk and belgium the seismically mapped structures represent these rimmed shelf carbonate platforms 2010 geological society of london

40k 40ca isotopic constraints on the oceanic calcium cycle the contributions of crustal silicates to the oceanic calcium cycle are investigated using high precision 40 k 40 ca measurements in archean and proterozoic carbonates river waters and a series of terrestrial and extraterrestrial mafic ultramafic samples using a multidynamic data collection scheme with strict controls on instrumental mass fractionation we show that a reproducibility of 0 35 e units 2 is obtained for the 40 ca 44 ca ratio using the thermofinnigan triton this represents an improvement by a factor of 3 compared with previous generations of data well defined excesses of 40 ca from 40 k decay were found in river waters draining the himalayas but not in the mississippi and columbia rivers all marine carbonate samples ranging in age from archean to recent show no discernable effects of 40 k decay to within the limit of 0 35 e units 2 in 40 ca 44 ca our results therefore indicate that the ca isotopic composition of seawater has remained constant and indistinguishable from that of the mantle for the past 3 5 ga despite the influx of radiogenic calcium delivered by weathering of the high k ca components of the continental crust thus over most of geologic time the contributions of the high k ca sources from the continents are far below the contributions of hydrothermal sources mass balance constraints indicate that unless the present day contribution of continental silicates is much less than 8 of the river ca flux the total hydrothermal flux of calcium must exceed the input from high temperature vents at ridge axes by at least one order of magnitude the present day oceanic mass balance requires a high input of calcium 4 15 10 12 mol ca yr at low temperature hydrothermal sites

kinetics of gypsum nucleation and crystal growth from dead sea brine abstract the dead sea brine is supersaturated with respect to gypsum 1 42 laboratory experiments and evaluation of historical data show that gypsum nucleation and crystal growth kinetics from dead sea brine are both slower in comparison with solutions at a similar degree of supersaturation the slow kinetics of gypsum precipitation in the dead sea brine is mainly attributed to the low solubility of gypsum which is due to the high ca 2 so 4 2 molar ratio 115 high salinity 280 g kg and to na inhibition experiments with various clay minerals montmorillonite kaolinite indicate that these minerals do not serve as crystallization seeds in contrast calcite and aragonite which contain traces of gypsum impurities do prompt precipitation of gypsum but at a considerable slower rate than with pure gypsum this implies that transportation inflow of clay minerals calcite and local crystallization of minerals in the dead sea does not prompt significant heterogeneous precipitation of gypsum based on historical analyses of the dead sea it is shown that over the last decades as inflows to the lake decreased and its salinity increased gypsum continuously precipitated from the brine the increasing salinity and ca 2 so 4 2 ratio which results from the precipitation of gypsum lead to even slower kinetics of nucleation and crystal growth which resulted in an increasing degree of supersaturation with respect to gypsum therefore we predict that as the salinity of the dead sea brine continues to increase accompanied by dead sea water level decline although gypsum will continuously precipitate the degree of supersaturation will increase furthermore due to progressively slower kinetics

calcium isotopic evidence for rapid recrystallization of bulk marine carbonates and implications for geochemical proxies abstract strontium and calcium isotopic data for bulk carbonate solids and pore fluids from odp sites 1170 and 1171 are presented the data suggest that bulk carbonate sediments actively exchange with coexisting pore fluids over tens of millions of year time scales recrystallization rates constrained by sr isotopes and sr elemental data are 3 per ma at 1170a and 7 per ma at 1171a the pore fluid chemistries at both sites are affected by advection which occurs in the downwards direction at 1170 25 m ma and upwards at 1171a 250 m ma both the direction and the rate of advection are reflected by the width of the diffusive boundary layer for sr at both 1170a 300 m and 1171a 50 m compared to odp site 807a 150 m where no chemically detectable advection is occurring recrystallization is supported not only by interpretations of pore fluid data but also by the alteration of the bulk solid this is especially true at 1171a where advection drives significant alteration of sr ca mg ca and 87sr 86sr numerical simulations of pore fluid geochemical and isotopic evolution over tens of millions of years conducted with a depositional time dependent reactive transport model suggest that recrystallization rates in the upper tens of meters of the sedimentary section at both sites are more rapid than suggested by the sr geochemical data when the sr constrained rates are applied to the pore fluid ca isotope data the model does not predict pore fluid 44ca within analytical uncertainty the simulations indicate rates that are initially 20 to 40 per ma in young

an overview of biomineralization processes and the problem of the vital effect biomineralization links soft organic tissues which are compositionally akin to the atmosphere and oceans with the hard materials of the solid earth it provides organisms with skeletons and shells while they are alive and when they die these are deposited as sediment in environments from river plains to the deep ocean floor it is also these hard resistant products of life which are mainly responsible for the earth s fossil record consequently biomineralization involves biologists chemists and geologists in interdisciplinary studies at one of the interfaces between earth and life leadbeater and riding 1986 biomineralization refers to the processes by which organisms form minerals the control exerted by many organisms over mineral formation distinguishes these processes from abiotic mineralization the latter was the primary focus of earth scientists over the last century but the emergence of biogeochemistry and the urgency of understanding the past and future evolution of the earth are moving biological mineralization to the forefront of various fields of science including the earth sciences the growth in biogeochemistry has led to a number of new exciting research areas where the distinctions between the biological chemical and earth sciences disciplines melt away of the wonderful topics that are receiving renewed attention the study of biomineral formation is perhaps the most fascinating truly at the interface of earth and life biomineralization is a discipline that is certain to see major advancements as a new generation of scientists brings cross disciplinary training and new experimental and computational methods to the most daunting problems it is however by no means a new field the first book on biomineralization was published in 1924 in german by w j schmidt schmidt 1924 and the subject has continued to intrigue a dedicated community of scientists for many years until the early 1980s the field was known as

provenance and depositional environment of rhenohercynian synorogenic greywackes from the giessen nappe germany the giessen nappe of the south eastern rhenish massif can be subdivided into a northern group and southern group of frasnian lower carboniferous greywackes that differ slightly in their sedimentology clast petrography heavy mineral assemblages and bulk geochemistry

thrust loads and foreland basin evolution cretaceous western united states two dimensional modeling of loading during the formation of the idaho wyoming thrust belt shows that regional isostatic compensation by flexure of an elastic lithosphere is sufficient to control the formation of a foreland basin the flexural rigidity of the lithosphere is inferred to have been approximately 1023 nm 1030 dyne cm on the basis of palinspastic comparison of predicted downwarping due to the thrust plate loads to the shape of the sedimentary wedge on the west side of the cretaceous western interior seaway erosion of part of the uplifted thrust plates redistributed the load depositing it farther to the east thereby causing subsidence over a much wider area than could have been accomplished only by the loading by thrust plates paleotopography after major cretaceous thrust events was calculated the resulting mountainous terrain gentle alluvial plain and flat sea floor correspond well with the topography of the modern foreland thrust belt and basin system in the andes of south america and to paleogeographic reconstructions in the western united states thrust belt topography is controlled by the subsurface geometry of the thrust faults particularly the positions of ramp zones and by isostatic subsidence

post variscan evolution of the lithosphere in the rhine graben area constraints from subsidence modelling in the area of the cenozoic rhine rift system crustal and lithospheric thicknesses range between 24 and 35 km and 60 and 120 km respectively this rift system transects the deeply truncated variscan orogen and superimposed permo carboniferous wrench induced troughs and late permian and mesozoic thermal sag basins at the time of its westphlian consolidation the variscan orogen was probably characterized by 45 60 km deep crustal roots that were associated with its rheno hercynian saxo thuringian saxo thuringian bohemian and bohemian moldanubian sutures all of which are transected by the cenozoic rhine rift system during the stephanian early permian wrench induced disruption of the variscan orogen subducted lithospheric slabs were detached causing upwelling of hot mantle material during the resulting thermal surge partial delamination and or thermal thinning of the continental mantle lithosphere induced regional uplift at the same time the variscan orogenic roots were destroyed and crustal thicknesses reduced to 28 35 km in response to the combined effects of mantle derived melts interacting with the lower crust regional erosional unroofing of the crust and on a more local scale by its mechanical stretching towards the end of the early permian the potential temperature of the asthenosphere returned to ambient levels with this regional long term thermal subsidence of the lithosphere commenced controlling the development of a new system of late permian and mesozoic thermal sag basins however the evolution of these basins was repeatedly overprinted by minor short term subsidence accelerations that reflect the build up of far field stresses related to rifting in the tethyan and atlantic domains comparison of observed and modelled subsidence curves suggests that in the area of the rhine rift system the lithosphere had equilibrated with the asthenosphere at the end of the cretaceous at depths of 100 120 km before it became thermally destabilized again by cenozoic rifting and plume related magmatism modelled subsidence curves indicate that by the end of early permian times the thermal thickness of the remnant mantle lithosphere ranged between 10 and 50 km in areas that were later incorporated into mesozoic thermal sag basins this corresponds to mid permian thermal lithosphere thicknesses of 40 80 km the geological society of london 2004

transformation of a magmatic arc and an orogenic root during oblique collision and it s consequences for the evolution of the european variscides mid german crystalline rise the architecture of the european variscides has been subdivided by kossmat 1927 into paleogeographically coherent units which are presently interpreted as former plate fragments the mid german crystalline rise mgcr separates two fragments rhenohercynian and saxothuringian belts at the site of an inferred plate boundary and reequilibrated orogenic root the commonly favoured model interprets the mgcr as the magmatic arc on saxothuringian crust above a south dipping subduction zone in upper devonian and carboniferous times data from the mgcr the kinematic evolution of the mid european variscides and first order volume balancing suggest a reinterpretation of this unit which challenges classical views on the mgcr as well as on the subdivision of variscan architecture the mgcr is composed of two rock groups with different tectonic identity a lower carboniferous low pressure high temperature magmatic arc association on lower paleozoic basement rests tectonically on a stack of medium pressuremedium temperature rocks of inferred rhenohercynian origin the latter were tectonically accreted to the base of the overriding plate by tectonic underplating the entire process was controlled by oblique convergence this led to regional partitioning of the plate kinematic vector into contractional domains lower rhenohercynian plate and back arc area of the upper saxothuringian plate bulk heterogeneous plate margin parallel extensional domains mgcr and plate margin parallel wrench domains mgcr boundaries during this process material was continually transferred from the lower plate to the upper plate uplifted and exhumed by net crustal extension the concomitant removal of parts of the former arc and the entire orogenic root necessitates a reappraisal of variscan architecture and evolution

calcium isotope record of phanerozoic oceans implications for chemical evolution of seawater and its causative mechanisms a total of 280 brachiopods of ordovician to cretaceous age complemented by published data from belemnites and planktonic foraminifera are used to reconstruct the evolution of calcium isotope composition of seawater 44 40casw over the phanerozoic the compiled 44 40casw record shows a general increase from 1 3 nist srm 915a at the beginning of the ordovician to 2 at present superimposed on this trend is a major long term positive excursion from the early carboniferous to early permian as well as several short term mostly negative oscillations a numerical model of the global cycles of calcium carbon magnesium and strontium was used to estimate whether the recorded 44 40casw variations can be explained by varying magnitudes of input and output fluxes of calcium to the oceans the model uses the record of marine 87sr 86sr ratios as proxy for seafloor spreading rates a record of oceanic mg ca ratios to estimate rates of dolomite formation and reconstructed atmospheric co2 discharge and erosion rates to estimate continental weathering fluxes the model results indicate that varying magnitudes of the calcium input and output fluxes cannot explain the observed 44 40casw trends suggesting that the isotope signatures of these fluxes must also have changed as a possible mechanism we suggest variable isotope fractionation in the sedimentary output flux controlled by the dominant mineralogy in marine carbonate deposits i e the oscillating calcite aragonite seas the ultimate control of the calcium isotope budget of the phanerozoic oceans appears to have been tectonic processes specifically variable rates of oceanic crust production that modulated the hydrothermal calcium flux and the oceanic mg ca ratio which in turn controlled the dominant mineralogy of marine carbonates hence the 44 40casw as to the causes of the short term oscillations recorded in the secular 44 40casw trend we tentatively propose that these are related to variable rates of dolomite formation and or to changing chemical composition of the riverine flux in particular and ratios induced by variable proportions of silicate vs carbonate weathering rates on the continents

sedimentological and diagenetic controls of gas in lower and early upper carboniferous sediments ne germany abstract fine grained organic rich paleozoic sediments are proven source rocks for conventional gas systems in nw europe and large unconventional gas reservoirs are assumed in lower to early upper carboniferous black shales however despite numerous boreholes exploring for hydrocarbons the shale gas potential remains uncertain this paper comprises detailed information on the sedimentary structure and lithofacies associations along with spatial distribution thickness thermal maturity organic and inorganic petrology as well as geochemistry and mineralogy of lower to early upper carboniferous black shales in ne germany to unravel the evolution of shale gas relevant properties sediments of the kohlenkalk formation carboniferous limestone in the rugen island area were deposited on an extensive deep water carbonate shelf transgressive regressive cycles led to the formation of an up to 2000 m thick intercalation of mud and limestones high total organic carbon contents 2 4 7 0 wt of a mainly type ii iii kerogen have been deposited under dysoxic to anoxic conditions and attained favorable present day thermal maturities 0 8 1 8 vrr indicating a shale oil potential in the upper part of the succession and a shale gas potential in the deeper parts sediments of the altmark north brandenburg culm synorogenic flysch formation were deposited as a turbidity current derived intercalation of a sand silt mud interbedded and black mudrock lithofacies in a deep marine siliciclastic slope to basinal setting the 1900 m thick succession has toc contents of 0 5 2 wt and present day thermal maturities of 2 3 3 2 vrr indicating a possible hybrid gas accumulation in areas where the succession is buried

high resolution seismic analysis of the coastal mecklenburg bay north german basin the pre alpine evolution the pre alpine structural and geological evolution in the northern part of the north german basin have been revealed on the basis of a very dense reflection seismic profile grid the study area is situated in the coastal mecklenburg bay germany part of the southwestern baltic sea from the central part of the north german basin to the northern basin margin in the grimmen high area a series of high resolution maps show the evolution from the base zechstein to the lower jurassic we present a map of basement faults affecting the pre zechstein the pre alpine structural evolution of the region has been determined from digital mapping of post permian key horizons traced on the processed seismic time sections the geological evolution of the north german basin can be separated into four distinct periods in the rerik study area during late permian and early triassic evaporites and clastics were deposited salt movement was initiated after the deposition of the middle triassic muschelkalk salt pillows which were previously unmapped in the study area are responsible for the creation of smaller subsidence centers and angular unconformities in the late triassic keuper especially in the vicinity of the fault bounded grimmen high in this area partly lower jurassic sediments overlie the keuper unconformably the change from extension to compression in the regional stress field remobilized the salt leading to a major unconformity marked at the base of the late cretaceous

crustal scale thrusting and extension in the hercynian schwarzwald and vosges central europe the hercynian outcrop areas in the schwarzwald of sw germany and vosges of easternmost france consist from north to south of three major lithotectonic complexes very low to medium grade metamorphics of the saxothuringian belt the polymetamorphic central gneiss complex and the tectonic melange of the southern complex juxtaposition of these three complexes occurred by oblique convergent motions in early carboniferous time the saxothuringian belt is part of a major se dipping accretionary wedge that consists of lower paleozoic meta sedimentary and metaigneous rocks and superimposed upper devonian to lower carboniferous synorogenic volcanics and elastics the central gneiss complex consists of polymetamorphic paragneisses orthogneisses metabasites and meta ultramafics dipping to the nw the southern complex consists of an imbricated melange of north to nw dipping synorogenic elastics volcanics and blocks of ultramafics and gneissic basement the central gneiss complex cgc experienced pervasive hercynian low pressure high temperature metamorphisrn before it was emplaced against and thrust over the sedimentary and volcanic fill of the adjacent synorogenic basins this convergence 340 330 ma produced mylonitic cataclastic shear zones in the cgc the most significant shear zones are the se verging todtnau fault zone between the cgc and the southern complex and the nw verging lubine fault zone between the central gneiss complex and the rocks of the saxothuringian belt these two fault zones enclose a bivergent pop up of the polymetamorphic basement the todtnau fault zone probably extends for more than 100 km along strike and can be traced to a depth of 10 km by deep seismic reflection studies detachment probably occurred along a mid crustal zone of anatexis expressed by a domain of low seismic reflectivity between about 10 and 15 km crustal thickening during early carboniferous convergence led to an extensional phase of crustal reordering between about 330 and 280 ma that was accompanied by the massive rise of posttectonic granitic plutons from middle to high crustal levels simultaneous creation of a structural lamination in the refractory lower crust neglected the main convergent tectonic boundaries it produced a basin and range type lower crust and mantle crust transition in early permian time and involved a major advective input of heat

solubilities of gypsum and halite in the dead sea and in its mixtures with seawater1 the solubilities of gypsum cas04 2h 0 and halite nacl in aqueous solutions with ionic strengths between 3 and 13 were studied under ambient conditions mixtures of mediterranean seawater and dead sea brines evaporated to various degrees served as experimental solutions the practical solubility constant of gypsum k mca x vlso eq was found to be related to the ionic strength i of the solution by the empirical expression lox 5 498 0 3769z this relationship was then applied to calculate the degree of saturation with respect to gypsum dsg of the present dead sea water column calculations indicate that the entire dead sea water column ionic strength 9 10 is saturated or even slightly oversaturated with respect to both minerals studied

mid devonian to mid permian floral and faunal regions and provinces summary the middle to late palaeozoic biota in seas adjacent to the caledonide appalachian orogen included an abundant generally cosmopolitan benthos in both carbonate and clastic environments where low clastic sediment input permitted organic reefs and build ups were characteristic of this tropical area early devonian biogeographic provinces did not persist into later times the pelagic fauna dominated by ammonoidea bivalvia conodonts and vertebrates was rich rapidly evolving and again cosmopolitan vertebrates and conodonts in particular were wide ranging among the land plants heterospory and arborescence evolved during the middle and late devonian in a number of classes particularly the lycopsida and progymnospermopsida genera were largely cosmopolitan during this time and only one floristic region can be recognized worldwide although there is some evidence for slight provincial floral variation outside laurussia during the early carboniferous arborescent lycopsida were abundant three floristic regions can be identified worldwide of which one is the circum tethyan region including laurussia kazakhstania and china two floral provinces are recognized within the laurussian part of this region in late carboniferous and early permian times when gymnosperms replaced the pteridophytes as the dominant forms there is a more clear cut separation of floral regions and by early permian two floral regions are recognized within laurussia which are clearly different from those away from this land mass non marine bivalvia and vertebrates were highly cosmopolitan from mid devonian time onwards with amphibia appearing in greenland in the late devonian and reptiles appearing in eastern canada and western europe in westphalian a time

upper carboniferous and lower permian tectonostratigraphy on the southern margin of the central north sea hydrocarbon exploration in uk licence blocks 31 26 and 39 2 on the southern margin of the central north sea in 1996 and 1997 proved the presence of a palaeozoic sedimentary succession previously undescribed in the area biostratigraphic data from the sediments and radiometric dating of interbedded basaltic lavas indicate that the succession spans the upper carboniferous westphalian b to lower permian asselian interval this has been informally split into three sedimentary units the lower flora sandstone is of westphalian b c age this clastic interval is overlain by the first of two main lavas which is in turn overlain by the westphalian c d to stephanian upper flora sandstone the flora sandstones are interpreted to be lithostratigraphic equivalents to the schooner formation of the southern north sea the flora sandstones are separated from the grensen formation by an angular unconformity possibly related to variscan asturic inversion the grensen formation is in turn overlain by a second basaltic lava flow both basaltic units are assigned to the inge volcanics formation rotliegend group petrographic data indicate that the grensen formation also forms part of the rotliegend group a major extensional event of permian age post dates all of these strata extensional faults are planed by a regional unconformity saalian unconformity that is overstepped by permian to cretaceous strata

continental weathering following a cryogenian glaciation evidence from calcium and magnesium isotopes a marked ocean acidification event and elevated atmospheric carbon dioxide concentrations following the extreme environmental conditions of the younger cryogenian glaciation have been inferred from boron isotope measurements calcium and magnesium isotope analyses offer additional insights into the processes occurring during this time data from neoproterozoic sections in namibia indicate that following the end of glaciation the continental weathering flux transitioned from being of mixed carbonate and silicate character to a silicate dominated one combined with the effects of primary dolomite formation in the cap dolostones this caused the ocean to depart from a state of acidification and return to higher ph after climatic amelioration differences in the magnitude of stratigraphic isotopic changes across the continental margin of the southern congo craton shelf point to local influences modifying and amplifying the global signal which need to be considered in order to avoid overestimation of the worldwide chemical weathering flux

hydrothermal alteration of basalt by seawater under seawater dominated conditions fresh mid ocean ridge basalt glass and diabase have been reacted with seawater at 150 300 c 500 bar and water rock mass ratios of 50 62 and 125 using experimental apparatus which allowed on line sampling of solution to monitor reaction progress these experiments characterize reaction under what we have called seawater dominated conditions of hydrothermal alteration in an experiment at 300 c basalt glass undergoing alteration removed nearly all mg2 from an amount of seawater 50 times its own mass in the process the glass was converted entirely to mixed layer smectite chlorite anhydrite and minor hematite removal of mg from seawater occurred as a mg oh 2 component incorporated into the secondary clay this produced a precipitous drop in solution ph early in the experiment accompanied by a dramatic increase in the concentrations of fe mn and zn in solution as mg removal neared completion and the glass was hydrolyzed ph rose again and heavy metal concentrations dropped at water rock ratios of 62 and 125 and 150 300 c the mineral assemblage produced was similar to that at a water rock ratio of 50 solution chemistry however contrasted with the earlier experiment in that mg concentrations in solution were greater and ph lower this caused significant leaching of heavy metals at 300 c nearly all of the na ca cu zn and co2 and most of the k ba sr and mn were leached from the silicates h2s al si and possibly co were also significantly mobilized whereas v cr and ni were not little or no seawater sulfate was reduced although submarine hot spring solutions sampled to date along mid ocean ridges clearly come from rock dominated hydrothermal systems evidence from ocean floor metabasalts and from heat flow studies indicates that seawater dominated conditions of alteration prevail at least locally both in axial hightemperature systems and in ridge flank systems at lower temperatures

composition of modern stream sand in a humid climate derived from a low grade metamorphic and sedimentary foreland fore thrust belt of north georgia abstract conditions of tectonics and drainage in north central georgia provide an excellent natural laboratory to study the composition of stream sand derived from a low grade metamorphic and sedimentary foreland fold thurst belt under humid climatic conditions the streams head in a high relief phyllite schist and metasandstone terrain and flow westward across a bounding fault into lower relief paleozoic shales cherty carbonates and quartz arenites the relative abundance of the source rock types in the drainage basin of each sample site was determined and a source rock ratio was calculated as the ratio of the area underlain by metamorphic rock to the total area of the drainage basin low grade metamorphic source rocks supply subequal amounts of monocrystalline quartz polycrystalline quartz and foliated quartz mica rock fragments to stream sediment whereas sand from the sedimentary source terrain consists primarily of monocrystalline quartz a surprisingly large number of pelitic rock fragments and chert mixing of sediment from both source rock types is recognizable on the quartz provenance diagram of young 1976 by a high instability index unstable polycrystalline quartz total polycrystalline quartz and a low polycrystallinity index polycrystalline total quartz this diagram is especially sensitive to the presence of sandstones as source rocks which further decreases the polycrystallinity index the ratio of metamorphic rock fragments to total rock frag ents also is directly related to the source rock ratio modern sand derived from the foreland fold thurst belt of north georgia can be distinguished from neogene subduction complex derived sand and collision orogen derived sand on qfl lmlslv and qplsmlvm provenance diagrams by containing less total feldspar more total quartz and no volcanic rock fragments the concepts developed from the recent sand are applied to the mississippian parkwood formation alabama and the cretaceous muddy formation montana the results suggest that both sandstone units were derived from foreland fold thrust belts but that the parkwood source area contained a greater proportion of low grade metamorphic source rocks than the source area of the muddy

calcium isotope δ 44 40 ca fractionation along hydrothermal pathways logatchev field mid atlantic ridge 14 45 n we investigate the logatchev hydrothermal field at the mid atlantic ridge 14 degrees 45 n to constrain the calcium isotope hydrothermal flux into the ocean during the transformation of seawater to a hydrothermal solution the ca concentration of pristine seawater ca sw increases from about 10 mm to about 32 mm in the hydrothermal fluid endmember ca hydend and thereby adopts a delta ca 44 40 hydend of 0 95 0 07 parts per thousand relative to seawater sw and a sr 87 sr 86 isotope ratio of 0 7034 4 we demonstrate that delta ca 44 40 hydend is higher than that of the bedrock at the logatchev field from mass balance calculations we deduce a delta ca 44 40 of 1 17 0 04 parts per thousand sw for the host rocks in the reaction zone and 1 45 0 057 parts per thousand sw for the isotopic composition of the entire hydrothermal cell of the logatchev field the values are isotopically lighter than the currently assumed delta ca 44 40 for bulk earth of 0 92 0 187 parts per thousand sw skulan j depaolo d j and owens t l 1997 biological control of calcium isotopic abundances in the global calcium cycle geochim cosmochim acta 61 12 2505 2510 and challenge previous assumptions of no ca isotope fractionation between hydrothermal fluid and the oceanic crust zhu p and macdougall j d 1998 calcium isotopes in the marine environment and the oceanic calcium cycle geochim cosmochim acta 62 10 1691 1698 schmitt a d chabeaux f and stille p 2003 the calcium riverine and hydrothermal isotopic fluxes and the oceanic calcium mass balance earth planet sci lett 6731 1 16 here we propose that ca isotope fractionation along the fluid flow pathway of the logatchev field occurs during the precipitation of anhydrite two anhydrite samples from the logatchev hydrothermal field show an average fractionation of about delta 44 4c ca 0 57 parts per thousand relative to their assumed parental solutions ca isotope ratios in aragonites from carbonate veins from odp drill cores indicate aragonite precipitation directly from seawater at low temperatures with an average delta ca 44 40 of 1 54 0 08 parts per thousand sw the relatively large fractionation between the aragonite precipitates and seawater in combination with their frequent abundance in weathered mafic and ultramafic rocks suggest a reconsideration of the marine ca isotope budget in particular with regard to ocean crust alteration c 2008 elsevier ltd all rights reserved

the tectonosedimentary evolution of the northern margin of the carboniferous foreland basin of ne germany abstract the geometry and evolution of the northern margin of the carboniferous foreland basin in ne germany was examined in terms of depositional environments petrographic and geochemical data lower carboniferous units are carbonate rich and predominantly marine by namurian times continental environments are established along the northern basin margin with turbiditic sedimentation persisting in the south the upper carboniferous succession is continental and clastic the sandstones were derived from a quartz rich source located to the north with subordinate sedimentary input basin evolution and the development of a characteristic marine to continental sedimentary succession while being predominantly controlled by flexure induced by the variscan orogen to the south was also influenced by eustatic sea level variations and more localised tectonic movements

contraints on the evolution of the mid german crystalline rise a study of outcrops west of the river rhine several small outcrops along the western rhinegraben escarpment expose rocks which represent the western prolongation of the so called mid german crystalline rise this basement ridge separates the rhenohercynian and saxothuringian zones of the variscan belt of europe and thus marks the boundary between the external and the internal zones the variable rock association includes an orthogneissamphibolite complex weakly deformed low grade sediments devonian and visean and a number of different syn to post orogenic granodioritic to granitic intrusives all crosscut by late lower carboniferous undeformed lamprophyric dikes and unconformable overlain by permian sediments and volcanics

biological control of calcium isotopic abundances in the global calcium cycle measurements of 44ca 40ca expressed as 44ca were made on igneous rocks and on shell and bone material from modern organisms to investigate the magnitude and origins of calcium isotopic fractionation in nature the results document a span of 4 in 44ca measured with the double spike technique to a precision of 0 15 volcanic rocks including basalt and rhyolite show little variability and cluster near 44ca 0 0 2 systematic analysis of biological samples indicates that biological processing of calcium discriminates against heavy isotopes and that biological fractionation is the primary generator of calcium isotopic fractionation in nature preliminary data suggest that calcium becomes isotopically lighter as it moves through food chains calcium carbonate shells of marine microorganisms and deep sea carbonate ooze have 44ca about 1 0 lower than seawater this fractionation causes seawater to be enriched in heavy calcium 44ca 0 9 relative to igneous rocks marine organisms consequently are isotopically heavier than their terrestrial counterparts at similar trophic level the calcium isotopic composition of living and fossil organisms may record information on diet and environment

constraints on evaporation and dilution of terminal hypersaline lakes under negative water balance the dead sea israel abstract the response of hypersaline terminal lakes to negative water balance was investigated by studying brines evaporating to extreme salinities in sinkholes along the western coast of the dead sea and during on site evaporation experiments of the dead sea brine density and temperature were determined in the field and all samples were analyzed for their major and a few minor solutes the activity of h 2 o a h2o in the brines was calculated and the degree of evaporation de was established using sr 2 as a conservative solute the relations between density and water activity were obtained by polynomial regression and the relation between the lake s volume and level was established using hall s 1996 hypsographic model for the dead sea basin relating the results to the modern long term relative humidity rh over the basin shows that a the lowermost attainable level of a terminal lake undergoing evaporation with no inflow is dictated by the median rh this level represents equilibrium between the brine s a h2o and rh b small saline water bodies with high surface to volume ratios a v such as the hypersaline brines in the sinkholes are very sensitive to short term changes in rh in these the brines a h2o closely follows the seasonal changes c the level decline of the dead sea due to evaporation under present climatic conditions and assuming no inflow to the lake may continue down to 516 537 m below mean sea level bmsl corresponding to a water activity range of 0 46 0 39 in its brine in equilibrium with the overlying relative air humidity this suggests that the lake level cannot drop more than 100 m from its present level and d the maximum rh values that existed over the precursor lake of the dead sea lake lisan during geologically reconstructed minima levels can be similarly calculated

soft sediment deformation of late pleistocene sediments along the southwestern coast of the baltic sea ne germany a 1 460 m long profile of a late glacial subglacial glacio fluvial glacio limnic and glacio deltaic sequence exposed at a cliff section on usedom island sw baltic sea coast is described the sequence is up to 31 m thick and shows sedimentary structures typical of a glacial setting soft sediment deformation is encountered and is associated with changes in lithology these deformations include liquefaction slumping and faulting as the most plausible cause earthquake induced shaking is discussed the associated neotectonic activity is seen as a consequence of the postglacial isostatic crustal rebound as the deglaciation earthquake ratio diminishes with time and as the rebound is phasing out no large earthquakes are anticipated for northern germany although in conclusion the lithosphere of the north german basin has to be regarded as weakened by repeated ice loading and deloading