determination of the shear strength of unsaturated soils using the multistage direct shear test the determination of the shear strength of unsaturated soils is generally more complicated time consuming and expensive compared to the determination of the shear strength of saturated soils although much research has been done on unsaturated soil testing methods there is still a strong need to translate these studies into practice further studies are needed on practical testing methods that can reduce both the cost of and time associated with shear strength testing of unsaturated soils this paper presents a comprehensive evaluation of the validity of using the multistage direct shear test as a rapid and practical method to determine the shear strength of unsaturated soils the laboratory tests were performed using a newly constructed modified direct shear test apparatus that allows independent control of matric suction referred to as a suction controlled multistage direct shear test unsaturated shear strength was established using multistage loading over a range of net normal stresses and matric suction values shear strength parameters obtained from the multistage tests are compared with those from conventional direct shear tests using multiple soil specimens recommendations are given on how to carry out multistage direct shear tests to ensure reliable unsaturated shear strength measurements the tests were performed on undisturbed soil samples obtained from the riverbank of the lower roanoke river in eastern north carolina usa

potential evidence of fossilised neoproterozoic deep life sem observations on calcite veins from oppaminda creek arkaroola south australia scanning electron microscopy revealed micron sized globular and coccoid objects associated with filaments and mucus like patches in antitaxial fibrous calcite veins from oppaminda creek northern flinders ranges south australia chemically the objects only differ from their calcite caco3 matrix by a higher sulphur content the 585 ma veins formed at about 3 6 km below the surface fluid inclusions indicate a temperature of formation of about 60 80 c and not exceeding 100 c a non biogenic origin of the objects is discussed but considered unlikely instead morphology chemistry and size distribution all indicate that the objects are fossilised microbes that lived in the veins at the time and depth of vein formation

formation and maintenance of shear zones the processes that initiate and maintain prograde ductile shear zones are not well understood we have performed shear experiments 1 to 3 on a fine grained 100 150 m gneiss 59 quartz 28 plagioclase 13 aligned but not interconnected biotite to determine the evolution of deformation mechanisms that produce dramatic strain weakening and localization at conditions 1 5 gpa 800 c dot gamma 2 10 5 s where pure quartz aggregates deform homogeneously by dislocation creep initial yield occurs where stress concentrations at the tips of weak biotite grains produce semibrittle deformation in intervening quartz or plagioclase allowing local biotite interconnection by slip on 001 and initiating strain weakening after yield the interconnected biotites kink and thus strengthen but the highly strained parts of grains react to a fine grained mixed phase assemblage which deforms by grain size sensitive creep allowing further strain weakening and localization at 3 3 the strain and strain rate in the 100 m thick shear zone are 100 times that of the enclosing host rock similar to the localization observed in natural shear zones thus the processes that initiate strain localization are not necessarily the same as those that preserve the weak shear zone and once formed a shear zone may be permanently weakened

freshwater carbonates within a late triassic siliciclastic fluvial system in a gondwana rift basin the maleri formation india abstract spring related carbonates are valuable repositories for information on physical and biotic environments of the past however for mesozoic and earlier records their use is limited due to their low preservation potential and difficulties in accurate identification of the carbonate type this study aims to characterise the source of carbonate clasts preserved as thin beds of cross bedded grainstones in late triassic siliciclastic fluvial deposits the maleri formation pranhita godavari rift basin india the microfabric and stable isotopic compositions of the grainstones and thin and discontinuous beds of impure limestones of this formation are presented here these features help in identifying the freshwater carbonate precipitating environments that existed in an ancient continental rift basin though such deposits are not primarily preserved in this case the microfabric of the carbonate grains provides evidence for carbonate precipitation in aquatic environment related to karstic springs taking together the microfabric stable isotopic compositions as well as the associated geological and palaeontological information it could be shown that the calcium carbonate precipitation took place in palustrine pools related to tufa like spring systems and in alluvial swamps under a pluvial climatic setting this research thus demonstrates that carbonate grains derived from spring related carbonate deposits formed mainly near the margins of rift basins can be incorporated into nearby siliciclastics if interpreted correctly they can be used in reconstructing ancient karstic carbonate environments even when in situ primary record is not preserved therefore making it possible to access the information stored in freshwater carbonates

archaean granulites of the limpopo belt zimbabwe one slow exhumation or two rapid events the peak of high temperature low pressure anticlockwise granulite facies metamorphism in the northernmost part of the northern marginal zone of the limpopo belt has been dated at 2591 4 ma using conventional u pb zircon geochronology on a syntectonic charnockite intrusion the thermal peak of 800 c at 0 5 gpa reflects a strong perturbation of the geotherm and was reached during compressional deformation and coincides with vast granite intrusion into the overlying craton the coincidence of the temperature t maximum and compression is thought to be a response to lithospheric mantle thinning that resulted in granite emplacement and a consequent change in upper crustal rheology after initial exhumation and cooling these high temperature low pressure rocks resided at a comparatively shallow depth 10 km for 620 ma field microstructural and geochronological investigation of a low temperature overprint establishes that reworking and final exhumation occurred at 1 97 ga along discrete greenschist facies thrusts the 40ar 39ar laser ablation of hornblende and biotite and pb pb step leaching of sphene are shown to be useful geochronometers in dating the low grade assemblages our results indicate that early proterozoic deformation lasted 10 to 20 ma however a number of ages intermediate between the events at 2 6 and 2 0 ga have been reported for the northern marginal zone these include pb pb garnet ar ar step heating amphibole and u pb zircon ages such ages suggest that these minerals were partially rejuvenated below their commonly believed closure temperature reinterpreting these intermediate ages as partial overprint or inheritance was possible in the northern marginal zone due both to the large time gap between the two tectonometamorphic events and the use of a multimethod multichronometer approach these observations call for great caution when extrapolating mineral ages into cooling histories especially so when the resulting cooling is slower than thermally and or mechanically possible and suggests that the geochronometry in other regions that underwent multiple tectono metamorphic events may need to be reassessed

mechanisms of weak phase interconnection and the effects of phase strength contrast on fabric development abstract to determine how deformation mechanisms and fabrics evolve during the strain weakening and localization that accompany the transition from a load bearing framework to an interconnected weak phase shear experiments were conducted on a fine grained gneiss 58 quartz interconnected 28 plagioclase dispersed 13 biotite aligned but dispersed at 745 and 800 c 1500 mpa and two strain rates 2 10 5 and 2 10 6 s 1 in experiments with a high phase strength contrast hpsc 25 and 45 between dispersed biotite and framework quartz grains biotite grains become interconnected due to stress concentration at their tips that allow local semi brittle flow of intervening quartz and cataclasis of intervening plagioclase in the higher temperature hpsc samples the biotite partially dehydrated in high strain zones a single narrow shear zone formed because the psc between the quartz and biotite reaction product layers remained high in the lower temperature hpsc samples there was no reaction and a penetrative s c fabric formed the fabric is defined by the many multiply interconnected biotite strands that formed because the psc between the quartz and biotite decreased as the biotites kinked in slower strain rate experiments with a much lower psc 10 biotite interconnection occurs by shearing into quartz quartz boundaries where new weak strain free recrystallized grains form at low strain a weak s c fabric forms but it evolves to an s c fabric as the psc decreases with strain thus the magnitude of the strength contrast between a weak phase and its matrix influences the mechanism of weak phase interconnection the degree of strain localization and the fabric

the evolution of the serie dei laghi strona ceneri and scisti dei laghi the upper component of the ivrea verbano crustal section southern alps north italy and ticino switzerland abstract the serie dei laghi is the upper intermediate component of the exposed crustal section of massiccio dei laghi in the southern alps the latter including also the ivrea verbano zone its oldest event is a sedimentary cycle at least of early paleozoic age it starts with a pelitic sequence scisti dei laghi that later suffered a tectono metamorphic event of rather high pressure this event is recorded by rare mineral and textural relics detected in the scisti dei laghi of the m gambarogno area later an arenaceous sequence strona ceneri was deposited it is now represented at the base by basaltic metatuffites resulting from the reworking of an ophiolite belt then followed by paragneisses with detrital phenoclasts ceneri gneiss and by fine grained gneisses gneiss minuti during the ordovician conspicuous tonalitic to granitic masses were emplaced the induced thermal disturbance and the circulation of pegmatitic stage magmatic residuals caused contact metamorphism and granitization in the sedimentary country rocks during the hercynian a main prograde event generated the regional foliation with isoclinal geometry and transposed character a syn kinematic stage produced medium grade parageneses of relatively high pressure static recrystallization and sillimanite growth then followed during the uplift due to the combined action of hydration and decompression margarite bearing coronitic textures grew around kyanite a retrograde metamorphism was then recorded by the appearance of greenschist facies parageneses at particular structural sites the formation of the cossato mergozzo brissago cmb and pogallo fault system against the ivrea verbano zone as well as the schlingen folds in the northeast is of late hercynian age along the cmb fault calc alkaline dykes and stocks appinites were intruded probably towards the end of the upheaval but deep enough to induce partial melting in their country rocks between val d ossola and valsesia the hercynian evolution is concluded by the early permian magmatic cycle that gave rise to both extrusive rhyolitic sheets and to granitic epiplutonic bodies accompanied by mafic dykes in mesozoic times the serie dei laghi was dissected by many extensional faults these partly reactivated the hercynian lineaments such as the cmb and pogallo lines during the alpine orogenic cycle the serie dei laghi was affected by s verging cataclastic overthrusts

depositional facies and aqueous solid geochemistry of travertine depositing hot springs angel terrace mammoth hot springs yellowstone national park u s a petrographic and geochemical analyses of travertine de positing hot springs at angel terrace mammoth hot springs yellow stone national park have been used to define five depositional facies along the spring drainage system spring waters are expelled in the vent facies at 71 to 73 8c and precipitate mounded travertine composed of aragonite needle botryoids the apron and channel facies 43 728c is floored by hollow tubes composed of aragonite needle botryoids that encrust sulfide oxidizing aquificales bacteria the travertine of the pond facies 30 62 8c varies in composition from aragonite needle shrubs formed at higher temperatures to ridged networks of calcite and aragonite at lower temperatures calcite ice sheets calcified bubbles and aggregates of aragonite needles fuzzy dumbbells pre cipitate at the air water interface and settle to pond floors the prox imal slope facies 28 54 8c which forms the margins of terracette pools is composed of arcuate aragonite needle shrubs that create small microterracettes on the steep slope face finally the distal slope facies 28 30 8c is composed of calcite spherules and calcite feather crys tals despite the presence of abundant microbial mat communities and their observed role in providing substrates for mineralization the com positions of spring water and travertine predominantly reflect abiotic physical and chemical processes vigorous co 2 degassing causes a 12 unit increase in spring water ph as well as rayleigh type covariations between the concentration of dissolved inorganic carbon and corre sponding d 13 c travertine d 13 c and d 18 o are nearly equivalent to aragonite and calcite equilibrium values calculated from spring water in the higher temperature 50 738c depositional facies conversely

micrometer scale porosity as a biosignature in carbonate crusts we formed calcite crusts in the presence and absence of the heterotrophic bacterium desulfovibrio desulfuricans strain g20 to investigate microbial morphological signatures in fast accreting carbonate precipitates submicrometer to micrometer sized pores micropores were present and ubiquitous in the g20 crusts but absent in abiotically precipitated crusts bacterial micropores resemble inclusions under transmitted light but have distinct size biological shapes and patterns swirling or dendritic and are distributed differently from common fluid inclusions we observed similar porosity in both modern and ancient carbonate crusts of putative biotic origin our experiments support the microbial origin of micropores and help define specific criteria whereby to recognize these features as biosignatures in the rock record

small microbialites from the basal triassic mudstone tieshikou jiangxi south china geobiologic features biogenicity and paleoenvironmental implications abstract we report small microbialites from the calcareous mudstone slightly above the permian triassic boundary ptb in the tieshikou section southern jiangxi province south china the newly found microbialite is a bowl like structure which contrasts with the surrounding calcareous mudstone the small microbialite is composed of columnar forms and fan shaped structures mini columnar structures resemble mini stromatolites in plane view most branches are patchy or strip shaped with clotted structures resembling that of a thrombolite fan shaped cement precipitates are comprised of multiple crystal fans that have a radiating texture and that show distinct growth laminae the radiating fabrics are represented by rod shaped filaments under sem which are interpreted as calcified trichomes filaments prominent micropores occur within the rods and they may be the plane views of multiple sheaths of the false branching zone of trichomes thus both the columnar forms and radiating fans are probably microbial in origin moreover three types of nano sized structures intraparticle micropores fibrous biofilms and filamentous sheaths are also pronounced in both the columnar structures and cement fans of the tieshikou microbialite all suggestive of biogenicity these well preserved fibrous biofilms probably represent calcified extracellular polymeric substances eps and linear sheaths are interpreted as the traces of bacterial activities during the precipitation of dolomite crystals the tieshikou microbialite therefore shares similar biogenetic mechanisms with other ptb microbialites the combination of the absence of pyrite framboids slightly negative carbon isotope values and an association with abundant ammonoids bivalves and gastropods indicates oxic conditions during the growth of the tieshikou microbialite moreover the nodular preservational state resembles widely distributed nodular mudstones or muddy limestones of the lower triassic successions worldwide this implies that nodular mudstone or argillaceous limestones may also have been deposited in microbe rich environments in which terrigenous supply was abundant

syn tectonic magmatism and the development of compositional layering ungava orogen northern quebec canada abstract layer and foliation parallel emplacement of granitic veins was an important process in the regional development of compositional layering in now exhumed middle crustal sections of both archean and paleoproterozoic age in the northern ungava peninsula quebec canada in the archean superior province diorite and tonalite plutons were penetratively deformed and metamorphosed at granulite facies conditions coeval with voluminous granitic magmatism the paleoproterozoic narsajuaq arc contains evidence for contemporaneous magmatism transpressional deformation and granulite facies metamorphism prior to its collision with the superior province basement in both plutonic domains regional compositional layering is defined by 1 metre to kilometre scale alternation of generally well foliated tonalite and quartz diorite bodies and 2 centimetre to kilometre scale variably deformed granitic veins and sheets that lie parallel to layering tectonic foliation in the host rocks syn tectonic intrusion of a substantial portion of the veins along extension fractures sub parallel to layering foliation i e at high angle to the regional shortening direction is interpreted to have occurred due to the combination of a strong anisotropy and high magma pressures compositional layering generated and or enhanced by this process may contribute to the overall seismic reflectivity of the middle and lower crust

bacterial mineralization patterns in basaltic aquifers implications for possible life in martian meteorite alh84001 to explore the formation and preservation of biogenic features in igneous rocks we have examined the organisms in experimental basaltic microcosms using scanning and transmission electron microscopy four types of microorganisms were recognized on the basis of size morphology and chemical composition some of the organisms mineralized rapidly whereas others show no evidence of mineralization many mineralized cells are hollow and do not contain evidence of microstructure filaments either attached or no longer attached to organisms are common unattached filaments are mineralized and are most likely bacterial appendages e g prosthecae features similar in size and morphology to unattached mineralized filaments are recognized in martian meteorite alh84001

modelling flanking structures using deformable high axial ratio ellipses insights into finite geometries flanking structures develop locally around material inhomogeneities the evolution of these structures is investigated here by modelling peturbations around a deformable ellipse using a 2d analytical solution non unique instantaneous and finite geometries are predicted and it is shown that in terms of slip and curvature complex histories are possible under simple shear whereas under pure shear instantaneous geometries map directly into finite state geometries single flanking structures are of limited use in kinematic analysis but can help constrain the kinematics when interpreted in conjunction with other structural features flanking structures exhibiting a range of ce cross cutting element orientations have more potential as kinematic indicators flanking structures serve as an excellent example of the role that material homogeneity can play in locally producing complex structures in a relatively simple bulk flow field

large scale folding in the upper part of the ivrea verbano zone nw italy new geological mapping has led to a new interpretation of the large scale superimposed folding in the upper part of the ivrea verbano zone italian alps the region is widely held to represent an upended section through lower continental crust of northern italy the dominant fold structure extending some 40 km along strike is the massone tight to isoclinal antiform with a hinge line strongly curved through 115 this folds pre existing large scale folds that formed during regional migmatization probably during the hercynian orogeny to form a type 2 interference geometry the region then suffered post orogenic mafic magmatic underplating and other magmatism accompanied by crustal stretching with contact metamorphism and migmatization causing the imposition of the final pattern of metamorphic isograds the ivrea verbano zone was brought into contact with the overlying metamorphic rocks of the serie dei laghi on a major shear zone sub solidus stretching continued though displacements on low angle high temperature shear zones most of the ivrea verbano zone was finally tilted to the vertical and emplaced into its present position after the mesozoic era and probably during alpine orogenesis forming the vertical limb of a crustal scale double kink

on the valency state of radiogenic lead in zircon and its consequences in zircon u pb systematics extreme robustness up to the temperatures of granulite facies and anatexis contrasts with apparently easy loss of radiogenic pb at low temperatures often without any metamorphic event being in evidence here we propose that this paradoxical behaviour can be understood with the hypothesis that radiogenic pb in zircon is tetravalent we review data and arguments in favour of this hypothesis diffusion profiles calculated for pb sup 2 in a 25 micro m radius zircon xenocryst in a melt at 1000 c combined with the incompatibility of pb sup 2 or for a zircon core inside a younger zircon rim at this temperature show age effects that should have been observed in sims dating further in zircon evaporation as well as in leaching experiments common pb is generally released preferentially to radiogenic pb after removal of less radiogenic pb the evaporation record generally shows pure radiogenic pb during the final evaporation steps the distribution of residual pb in a leached titanite revealed by pixe is similar to that of ti lastly xanes spectra of a 1 ga old titanite predominantly radiogenic pb and an alpine one predominantly common pb are significantly different although the former does not resemble that ofmore pbo sub 2 the arguments why radiogenic pb should be tetravalent are based on analogies with studies relating to the tetravalent state of sup 234 th and the hexavalent state of sup 234 u which show that alpha recoil in silicates generates a strongly oxidizing environment at the site where the recoiling nucleus comes to rest further a zircon grain being small should remain highly oxidizing in its interior by the constant loss of beta particles maintaining the 4 state of radiogenic pb from its effective ion radius similar to that of zr sup 4 and its charge pb sup 4 has to be compatible in the zircon lattice also by analogy with u sup 4 th sup 4 and hf sup 4 its diffusivity should be several orders of magnitude lower than that measured for pb sup 2 in zircon these factors can account for the extreme retentivity of u pb clocks even at high temperatures on the other hand radiogenic pb situated in alpha recoil damaged sites could be leached out by any electrolyte solution that reduces it to the divalent state making it both incompatible and soluble thus discordia can be generated in weathering the curious observation that discordant archaean zircon suites generally define trends to lower intercepts at up to 800 ma instead of zero appears to reflect a c 14 to 28 better average accessibility to leaching of radiogenic sup 207 pb compared to sup 206 pb in accord with the somewhat higher recoil energy of the last branched alpha decays in the sup 235 u chain less

microbial kinetic controls on calcite morphology in supersaturated solutions recognizing microbial imprints in the morphology of calcium carbonate minerals that form in very supersaturated solutions containing a high level of dissolved inorganic carbon dic is challenging to better define criteria for this purpose we have analyzed the influence of sulfate reducing bacterium desulfovibrio desulfuricans strain g20 on the morphology of calcite in such solutions g20 does not induce large shifts of ph or alkalinity under these conditions but its uptake of millimolar sulfate and lactate decreases the number of anhedral crystals and stimulates growth of subhedral spar crystals relative to the abiotic controls in addition organic compounds associated with the basal growth medium purified exopolymeric substances produced by g20 and lypopolysaccharide stimulate the growth of anhedral crystals and crystals with rounded edges at low supersaturation index si of calcite the effect of organic compounds is reduced at higher si where rhombohedral habits dominate our results suggest that the local production and uptake of kinetic inhibitors within microbial biofilms may be an important control on calcite morphology in supersaturated solutions

origin and diagenesis of quaternary travertine shrub fabrics rapolano terme central italy millimetre to centimetre sized arborescent shrub like calcite precipitates are common constituents of hot water travertine shallow pool deposits of quaternary age at rapolano terme tuscany italy in the presently forming travertines the shrubs consist of apparently random associations of i micrite aggregates and ii subhedral to euhedral rhombic spar crystal aggregates in thin section the micrite aggregates appear dark and the spar rhomb aggregates light giving the shrubs a mottled appearance travertines are basically produced by caco3 precipitation due to degassing and evaporation of the spring waters although biological influence may also stimulate precipitation the formation of masses of erect shrubs rather than dense crystal crusts that form on slopes is probably due to limited water flow in the pool environments microbes including bacteria and diatoms are important influences on shrub microfabric and external shape the micrite aggregates are associated with bacteriform bodies seen as tiny rods and spheres the micrite precipitates around these bodies and in adjacent biofilm spar rhomb precipitation appears to be external to the biofilm and may be related to the presence of diatoms which are locally closely associated with the spar rhombs although an essentially inorganic origin particularly for the more euhedral rhombs cannot be ruled out in the older quaternary travertines the original microfabric of the shrubs has been diagenetically altered the original mottled appearance of the shrubs has become uniformly dark and micritic and the evidence for the dual micritic and spar rhomb origin of the shrubs is obscured or destroyed spar micritization of the shrubs is probably due to abiotic and locally biotic dissolution previous studies did not recognize the diagenetic micritization and attributed shrub formation entirely to bacterial activity

the theoretical effect of metasomatism on sm nd isotopic systems abstract if sm and nd are mobilized during fluid rock interaction fractionation of the ratio between sm and nd in geological units may take place the fractionation can be characterized by a fractionation factor f which can attain any value between d sm d nd and 1 d sm d nd depending on the fluid rock ratio during ree transfer if such fractionations are not recognized this will induce errors in sm nd isotopic interpretations of age and provenance of the affected geological units the apparent ages and nd values are functions of the true values f and the time lapse between petrogenesis and secondary disturbance the functional relationships can be closely approximated by direct proportionalities

coeval biochemical and biophysical weathering processes on quaternary sandstone terraces south of rabat temara northwest morocco despite numerous investigations on substrate inhabiting microflora especially lichens very little is known about the colonization of coastal escarpments by lithobiontic micro organisms inland of a retreating coastline in africa reported herein are the results of a combined field observation and microscopy study focusing on the connection between microrelief of the substrate colonies of lithobiontic micro organisms in particular the lichen xanthoria parietina and microstructures of putative bacterial origin the occurrence of weathering pits in which the early stages of the biotic development occurs and the subsequent disintegration of the rock indicate that lichens mosses and fungi act synergistically by alternating chemical and mechanical weathering penetration of grains by expansion and contraction of the hyphae depletes the rock matrix and contributes to the mechanical breakdown of the rock calcite rhombs on the weathered surfaces of the calcite cemented sandstones are severely etched with well developed rhomb shaped etch pits spiky calcite holes or has one or more of the faces removed and their cores exposed and leached nanofilaments c 100 700 nm and nanomicrobial fruiting bodies c 250 nm emanating from micropores appear to be common on affected crystalline structures weddellite present immediately below the thallus is a strong indicator of biomineralization quartz responds differently to chemical weathering by producing peeling structures and microbrecciation features the dissolution of these crystals appears to be a surface reaction controlled process mediated by microbial microfilaments and nanofilaments a model is proposed firstly indicating early stage biochemical weathering followed by biophysical weathering disintegration of the rock outcrops in due to a complex interplay of several events probably beginning at the nanoscale with penetration of sites on crystal faces copyright 2006 john wiley sons ltd

multistage accretion and exhumation of the continental crust ivrea crustal section italy and switzerland the ivrea crustal section exposes in map view all levels of the southern alpine continental crust from ultramafic mafic and felsic granulite facies rocks of the deep crust ivrea verbano zone through medium grade basement rocks strona ceneri zone and val colla zone to unmetamorphosed permo mesozoic sediments the oldest part of the crustal section is preserved in the medium grade basement units which are interpreted to be the overprinted remains of an ordovician 440 480 ma magmatic arc or forearc complex during variscan subduction this arc was technically underplated by a carboniferous accretion subduction complex 320 355 ma containing metasediments and slivers of rheic oceanic crust presently found in the ivrea verbano zone during the late stages of variscan convergence 290 320 ma lithospheric delamination triggered magmatic underplating and lead to polyphase deformation under amphibolite to granulite facies conditions this was broadly coeval with extensional exhumation and erosion of the variscan overprinted ordovician crust presently exposed in the strona ceneri and val colla zones post variscan transtensional tectonics 270 290 ma were associated with renewed magmatic underplating mylonitic shearing and incipient exhumation of the lower crust in the ivrea verbano zone this coincided with the formation of elongate basins filled with volcanoclastic sediments in the upper crust early mesozoic tethyan rifting of the southern alpine crust 180 230 ma reduced crustal thickness to 10 km or less in the lower crust most of this thinning was accommodated by granulite to retrograde greenschist facies mylonitic shearing the lower crust was exhumed along a large noncoaxial mylonitic shear zone that was linked to asymmetrical rift basins in the upper crust the composite structure resulting from this complex evolution is probably typical of thinned late variscan continental crust on the passive margins of western europe alpine faulting and folding 20 50 ma fragmented the crustal section the originally deepest levels of the crustal section in the ivrea verbano zone as well as some segments of the basement cover contact were steepened whereas other parts of the crustal section particularly the strona ceneri zone underwent only minor to moderate alpine rotation

tectonic sequence diagrams and the structural evolution of schists and gneisses in multiply deformed terranes the current practice of numbering deformation phases d 1 d n in a multiple deformed terrane obscures the link between data and inference and can lead to erroneous interpretations routine production of tectonic sequence diagrams tsds allows a method whereby all deformation and metamorphic mineral growth events their overprinting and duration based on relative timing are systematically recorded different hypotheses as to correlation of tsds across a region can then be assessed objectively including correlation of characteristic sequences that can often be recognized in tsds from single outcrops tsds ensure that absolute dating is applied to specific events within a sequence eliminating the practice where a date is imprecisely correlated tsds also place a focus on the independent character of events here confirmed by absolute dating here we demonstrate how tsds show that many fold nappes are recumbent folds transected by later unrelated ductile shear zones tsds also show that p t t paths and exhumation rates must include starting and stopping of events periods of quiescence and changes in tectonic mode from shortening to extension tsds allow objective analysis of the complexity present in many metamorphic tectonites but which is obscured by conventional methodology

microbial nucleation of calcium carbonate in the precambrian microbial sulfate reduction is thought to stimulate carbonate precipitation in modern stromatolites yet whether this metabolism was important in shaping precambrian stromatolites is unknown here we use geochemical modeling to suggest that the influence of sulfate reduction on the saturation index of calcite si is negligible when seawater is in equilibrium with high pco 2 as is thought for the precambrian our laboratory experiments with heterotrophic bacteria in a medium mimicking precambrian seawater chemistry show that even if sulfate reduction does not significantly change the si the presence of bacteria stimulates calcite precipitation over sterile controls by effectively increasing the si over a ph range from 7 3 to 7 8 under our experimental conditions dead cells stimulate in situ carbonate precipitation equally if not more than active sulfate reducing bacteria heterogeneous nucleation of calcite by microbial cell material appears to be the driving mechanism that explains this phenomenon

microstructure variability in freshwater microbialites pavilion lake canada abstract calcite microbialites in pavilion lake british columbia exhibit a diverse range in macro morphology biomass abundance porosity and mineral content to evaluate the role of microorganisms in their formation samples collected from a range of depths were examined by scanning electron microscopy sem and synchrotron radiation based micro x ray fluorescence xrf spectroscopy to characterize both their outer surfaces as well as internal structures observed trends in both surface colonization as well as microbialite framework with increasing lake depth include decreasing microbial abundance on outer surfaces as well as increasing ratios of carbonate biomass in the microbialites microscopic investigations of the interiors show bacteria and algae entrapped within calcite with this calcite exhibiting micropores and casts similar in size and shape to microorganisms based on these observations it is hypothesized that microbialite development in pavilion lake initiates calcite precipitation in phototrophic microbial mats i e combined phototrophy and heterotrophy followed by heterotrophic oxidation of organic matter leading to eventual carbonate infilling of the microbial mineral matrix in addition an observed shift from cyanobacteria to algae with increasing lake depth suggests variability in contemporary conditions controlling microbialite growth and diagenesis high photosynthetic growth rates at shallower depths result in significant porosity and friability due to biomass accumulation outpacing carbonate precipitation at intermediate depths lower light levels and slower growth rates of phototrophs lead to a greater proportion of the microbialite matrix being in filled by carbonate carbonates precipitate initially within the bacteria eps matrix with abundant uncalcified algae maintaining microbialite porosity in the deepest waters the presence of only sparse algal colonization as well as fine grained laminated metal rich sediments covering microbialites suggests that present day insolation levels are too low to support the development of photosynthetic microbial mats as a consequence heterotrophic carbonate precipitation has progressively in filled these microbialite interiors to create lithified calcite fabrics that exhibit minimal porosity but preserve the casts of microorganisms as biosignatures while the origin of microbialites in pavilion lake remains unknown current observations provide valuable information in evaluating how environmental conditions influence microbialite growth in a freshwater lacustrine environment

magmatic underplating extension and crustal reequilibration insights from a cross section through the ivrea zone and strona ceneri zone northern italy the thermal impact of magmatic underplating at various crustal levels is studied along a traverse through the ivrea verbano zone and strona ceneri zone in northern italy geochronological and petrologic data are compared to a two dimensional thermal kinematic model field data and numerical simulation show the strong disturbance of the temperature field in the lower and intermediate crust in relation to magmatic underplating leading to granulite to amphibolite facies metamorphism as well as reequilibration of mineral chemical and isotopic systems magmatic underplating leaves a crust with an apparently heterogeneous tectonometamorphic evolution as information on the earlier history is preserved only at upper crustal levels

paleoclimatic significance of lacustrine microbialites a stable isotope case study of two lakes at torres del paine southern chile article two patagonian lakes studied here lago sarmiento and laguna amarga are located within the orographic rain shadow formed to the east of the southern patagonian ice field in the andes range major thrombolite colonies are present in lago sarmiento whereas widespread stromatolites occur in laguna amarga based on the characterization of the hydrologic system of these two lakes together with an estimation of the isotopic balance and an analysis of the equilibrium conditions between the water and biologically induced carbonates it is concluded that the microbialites of lago sarmiento are better suited as paleotemperature indicators than those of laguna amarga lago sarmiento thrombolites contain unique carbonate mineral species in which carbonate precipitation occurs close to isotopic equilibrium and where the variation in water temperature controls fractionation of the stable oxygen isotope the results indicate that at 1215 cal yr bp the level of the lake was at 85 m a s l with a temperature close to 9 3 c was at 82 m a s l at 600 cal yr bp with a temperature close to 8 5 c this coincides with the timing of the northern hemisphere medieval warming period at 183 cal yr bp the level of the lake was at 80 m a s l with a cooler temperature close to 7 7 c representing a colder period coinciding with the timing of the little ice age lia an interesting outcome of this study is that it reinforces the idea that the 13 c signal in carbonate deposits can be an effective tool in distinguishing between inorganic and biologically induced precipitation

porosity in bacterially induced carbonates focus on micropores bacteria are responsible for the precipitation and accumulation of some significant carbonate deposits prime examples are hot spring travertine accumulations bacteria induce precipitation of carbonate minerals immediately surrounding their cell walls and in doing so entomb themselves within the crystals subsequently a generation of abiotically precipitated clear spar commonly cements cell colonies as well as the initial bacterially induced carbonate the relatively rapid decay of the bacterial fossils consequently results in localized abundances of unconnected microporosity this submicron to micron size porosity is not normally detected by standardized porosity evaluations these pore systems which are especially abundant in hot spring travertine deposits can influence density measurements and therefore any calculations in which density is a factor the pores have been found to be abundant within different bacterially induced features such as shrubs peloids and oncoids other forms of porosity common in hot spring travertines include shelter porosity foam rock and some highly irregular early dissolution of the carbonate caused by the abundance of nonmarine waters coursing through these rocks

cryptic intertidal microbialites in beachrock heron island great barrier reef implications for the origin of microcrystalline beachrock cement microbialites with microcolumnar growth morphology occur on the surfaces of solution enlarged crypts in modern beachrock an heron island great barrier reef australia the microbialites consist predominantly of felted aragonite but blocky mg calcite and fringes of acicular aragonite also occur a variety of microbial bodies and filaments occur within and on the surface of the microbialites although most heron beachrock is cemented by isopachous fringes of acicular aragonite irregular micritic cement is common adjacent to the microbialites the micritic cement consists predominantly of felted aragonite and contains microbial filaments and organic matter similar to those in the microbialites both the microbialite and the micritic cement are interpreted to be biologically induced although physico chemical models including co2 degassing and evaporation are commonly held to be sufficient to promote the formation of beachrock the similarity of heron cryptic beachrock microbialite with micritic beachrock cements supports the contention that some beachrock cements are biologically induced additionally the primary difference between fringes of acicular aragonite and the felts of aragonite in microbialites appears to be that the former nucleated on a well defined surface of organic matter whereas the latter nucleated within a framework of organic matter that contained irregularly disposed nucleation sites hence aragonite fringe cements may also be localized and or induced by films of organic matter c 1999 elsevier science b v all rights reserved

single mineral pbpb dating a new stepwise leaching procedure applied to ca bearing silicates enables the selective recovery of radiogenic and common pb from a mineral and thus makes single phase pbpb dating possible this permits independent dating of rock forming minerals within a paragenetic sequence and the direct combination of age data with petrological results furthermore the stepwise leaching technique has the advantage over multi phase pbpb dating in that it does not require initial pb isotope equilibrium among the phases but may be used to test it the presence of microscopic solid inclusions which complicate dating of single phases if they are not in equilibrium with the host can be traced via the behaviour of the 208pb 204pb ratio through the various leaching steps this constitutes a major advantage over conventional bulk phase pbpb dating in addition the precision of an isochron age can be improved relative to that of the bulk mineral approach since the 207pb 204pb and 206pb 204pb data spread is significantly enhanced therefore the technique may both be used to date younger phases and or minerals with less favourable u pb ratios and to extend the applicability of self consistent p t t modelling

westward continuation of the craton limpopo belt tectonic break in zimbabwe and new age constraints on the timing of the thrusting the umlali thrust zone has been mapped between the granite greenstone rocks of the zimbabwe craton and the granulite facies rocks of the limpopo belt a tectonic break had not been previously recognized in the southwest because of the intrusion of syn to post kinematic porphyritic granites these intrusions locally obliterate evidence for the tectonic break although in some localities the associated mylonites are preserved as xenoliths within the intrusive porphyritic granite bodies the porphyritic granite bodies were emplaced during and after the main regional fabric forming event a u pb zircon age of 2627 7 ma obtained from a late kinematic microgranite is interpreted to be the minimum time of thrusting a whole rock rb sr age of 2583 52 ma obtained from plutonic rocks and retrogressed zones within the north marginal zone falls within error of the zircon age suggesting widespread magmatic and hydrothermal activity coeval with the thrusting

proterozoic transpressive deformation in the northern marginal zone limpopo belt zimbabwe a major tectono metamorphic event affected the southern half of the northern marginal zone of the limpopo belt at 2 0 ga structural analysis along a 43 km long profile perpendicular to strike shows extension inclined toward the northeast extension parallel to axes of folds that uplift the southeast of the section i e the central zone of the limpopo belt and dextral shear these deformation patterns developed coevally the lineations form distinct tightly clustered groups that occur together in the profile there is no evidence for superimposed deformation or deformed lineations nor are lineations observed cross cutting each other this single episode of deformation can therefore be called transpression petrographic and thermobarometric evidence support this kinematic picture in that decreases of both pressure 2 5 kb and temperature 150 c are documented from southeast to northwest across strike 39 ar 40 ar step heating of metamorphic hornblende from amphibolites has yielded ages of

sm nd evidence for the age and origin of a mississippi valley type ore deposit mississippi valley type mvt ore deposits represent the relatively common product of large scale fluid transport in the continental lithosphere yet the models for their genesis have been more controversial and unconstrained than those of any other class of giant ore deposit1 2 here we show that sm nd isotope data can be used to determine the age and origin of an mvt deposit sm nd data for fluorites from the north pennine orefield are difficult to explain unless some of the mineralization is of mesozoic rather than the traditionally accepted palaeozoic age furthermore the nd and sr isotopie compositions of the fluorites do not support a variety of recent models that include derivation of the components from the mantle the lower palaeozoic basement or the underlying buried granite which served to focus the flow of hydrothermal fluids

carbonate and silicate biomineralization in a hypersaline microbial mat mesaieed sabkha qatar roles of bacteria extracellular polymeric substances and viruses in a modern peritidal microbial mat from qatar both biomediated carbonates and mg rich clay minerals palygorskite were identified the mat ca 5 cm thick shows a clear lamination reflecting different microbial communities the initial precipitates within the top millimetres of the mat are composed of ca mg si al s amorphous nanoparticles few tens of nanometres that replace the ultrastructure of extracellular polymeric substances the extracellular polymeric substances are enriched in the same cations and act as a substrate for mineral nucleation successively crystallites of palygorskite fibres associated with carbonate nanocrystals develop commonly surrounding bacterial bodies micron sized crystals of low mg calcite are the most common precipitates together with subordinate aragonite very high mg calcite dolomite and ankerite pyrite nanocrystals and framboids are present in the deeper layers of the mat calcite crystallites form conical structures circular to triangular hexagonal in cross section evolving to crystals with rhombohedral terminations some crystallite bundles develop into dumb bell and stellate forms spheroidal organo mineral structures are also common within the mat nanospheres a few tens of nanometres in diameter occur attached to coccoid bacteria and within their cells these are interpreted as permineralized viruses and could be significant as nuclei for crystallite crystal precipitation microspheres 1 to 10 m in diameter result from intracellular permineralization within bacteria or the mineralization of the bacteria themselves carbonates and clay minerals are commonly aggregated to form peloids tens of microns in size surrounded by residual organic matter magnesium silicate and carbonate precipitation are likely to have been driven by ph saturation index redox changes within the mat related to microenvironmental chemical changes induced by the microbes extracellular polymeric substances viruses and their degradation

zircon and monazite petrochronologic record of prolonged amphibolite to granulite facies metamorphism in the ivrea verbano and strona ceneri zones nw italy abstract in order to improve the understanding of thermal tectonic evolution of high grade terranes we conducted a systematic study of textures ree content and u pb ages of zircon and monazite grains extracted from migmatitic metapelites across the amphibolite to granulite facies metamorphic gradient exposed in the ivrea verbano and strona ceneri zones italy this study documents the behaviour of these accessory minerals in the presence of melt the absence of relict monazite grains in the metasediments and the gradual decrease in the size of inherited zircon grains from amphibolite to granulite facies cores indicate partial to total dissolution of accessory minerals during the prograde path and partial melting the retrograde path is marked by i growth of new zircon rims r1 and r2 around inherited cores in the mesosome ii crystallisation of stubby zircon grains in the leucosome especially at granulite facies and iii crystallisation of new monazite in the mesosome stubby zircon grains have a distinctive fir tree zoning and a constant th u ratio of 0 20 together these features reflect growth in the melt conversely the new zircon grains with r1 rims have dark prismatic habits and th u ratios in the ivrea verbano zone the interquartile range iqr of u pb ages on zircon and monazite are interpreted to represent the length of zircon and monazite crystallisation in the presence of melt accordingly they provide an indication on the minimum duration for high temperature metamorphism and partial melting of the lower crust 20 ma and 30 ma in amphibolite and granulite facies respectively in amphibolite facies zircon crystallisation between 310 and 294 ma iqr is interpreted to reflect metamorphic peak condition and earlier retrograde history conversely monazite crystallisation between 297 and 271 ma iqr reflects cooling under 750 c to a temperature close to the solidus in granulite facies zircon crystallisation between 295 and 265 ma iqr is interpreted to reflect high temperature conditions which were attained after peak of metamorphism during isothermal decompression and subsequent cooling under 850 950 c the observed decrease of u pb ages in metamorphic zircon and monazite from amphibolite to granulite facies i e from the middle to the lower crust is interpreted to record slow cooling and crystallisation of the variscan orogenic root at the transition from orogenic collapse to opening of the tethys ocean

ree fractionation and nd isotope disequilibrium during crustal anatexis constraints from himalayan leucogranites abstract the processes controlling rare earth element ree behaviour during crustal anatexis have profound implications not only for ree abundances of crustally derived granites but also for their model nd ages for typical protoliths of anatectic granites such as are exposed in metapelites from the high himalayan crystalline series hhcs a high proportion 90 of bulk rock lree and mree are sited in the accessory phases apatite and monazite and of hree in garnet and apatite mass balance constraints indicate that observed ree abundances of himalayan leucogranites cannot be generated from ree deficient reactant phases in their metasedimentary protoliths muscovite biotite plagioclase and quartz but must result from the dissolution of accessory phases ree and th abundances in anatectic melts are modelled by combining empirical expressions for monazite apatite and zircon solubilities as a function of temperature melt composition and melt water content with analysed accessory phase ree abundances this approach which allows the contribution to the melt from each accessory phase to be identified successfully predicts himalayan leucogranite trace element abundances the lree and th concentrations of a metapelite derived melt are buffered by monazite stability although apatite dissolution contributes up to 10 of lree to the melt together with 50 of the mree and 90 of the hree zircon contributes a negligible proportion of ree to the melt during anatexis dissolution of monazite and apatite in the melt results in 1 increasing ree abundances and lree hree ratios with increasing temperature of melting 2 a negative eu anomaly in the melt 3 high sm nd ratios in the melt relative to its metasedimentary protolith and 4 nd isotope disequilibrium between the melt and its protolith all of these features are observed in the ree geochemistry of himalayan leucogranites the combined effects of sm nd fractionation and nd isotope disequilibrium during anatexis imply that model nd ages calculated for anatectic granites derived from apatite and monazite bearing protoliths should be treated with considerable caution

stromatolites in precambrian carbonates evolutionary mileposts or environmental dipsticks stromatolites are attached lithified sedimentary growth structures accretionary away from a point or limited surface of initiation though the accretion process is commonly regarded to result from the sediment trapping or precipitation inducing activities of microbial mats little evidence of this process is preserved in most precambrian stromatolites the successful study and interpretation of stromatolites requires a process based approach oriented toward deconvolving the replacement textures of ancient stromatolites the effects of diagenetic recrystallization first must be accounted for followed by analysis of lamination textures and deduction of possible accretion mechanisms accretion hypotheses can be tested using numerical simulations based on modern stromatolite growth processes application of this approach has shown that stromatolites were originally formed largely through in situ precipitation of laminae during archean and older proterozoic times but that younger proterozoic stromatolites grew largely through the accretion of carbonate sediments most likely through the physical process of microbial trapping and binding this trend most likely reflects long term evolution of the earth s environment rather than microbial communities

mass occurrence of oncoids at the cambrian series 2 series 3 transition implications for microbial resurgence following an early cambrian extinction abstract the traditional lower middle cambrian transition cambrian series 2 series 3 transition is marked by the first major biotic extinction of the phanerozoic eon this biotic crisis has been arguably linked to changes in ocean chemistry and or marine environments but their casual relationships remain controversial to better understand the microbial responses to paleoceanographic changes across this critical transition we have studied the environmental conditions for mass occurrence of oncoids in the western north china platform oncoids at the lower middle cambrian transition form 1 to 3 m thick massive beds show spherical subspherical morphology and contain 8 14 light dark cortical laminar couplets the light laminae are thicker and contain densely intertwined filamentous cyanobacteria that have calcified sheaths and a prostrate growth pattern the dark laminae are thinner and rich in organic matter relics pyrite framboids and heterotrophic bacteria in most oncoids cortical laminae show the same growth orientation for more than five light dark laminar couplets suggesting much less frequent grain overturning than generally thought both light and dark laminae contain well preserved organomineralization fabrics textures including extracellular polymeric substances epss nanoglobules polyhedrons and micropeloids suggesting oncoid formation in shallow marine environments with high alkalinity and active sulfate reduction the presence of pyrite framboids and heterotrophic bacterial relics implies anoxic dysoxic bottom water conditions stratigraphic correlation indicates that time equivalent oncolites and other microbialites are widespread not only in north china but also in other early cambrian successions globally the mass occurrence of oncoids coincides with the kalkarindji large igneous province of australia a prominent negative 13 c excursion roece or redlichiid olenellid extinction carbon isotope excursion a significant increase in 87 sr 86 sr and a large positive shift in 34 s the coincidence of these events suggests that the early cambrian biotic crisis may have been caused by an ocean anoxic event resulting from enhanced volcanic release of co 2 global warming and increased continental weathering preservation of massive oncolites is likely related to decreased metazoan grazing following an early cambrian biotic crisis during which archaeocyathids and many early cambrian trilobite taxa went to extinction the oncoid mass occurrence provides evidence for the resurgence of microbial life in anoxic dysoxic marine shelf environments concomitant with the early cambrian extinction event

evaluation of pipe jacking forces based on direct shear testing of reconstituted tunneling rock spoils abstractthe installation of underground trunk sewer lines in the tuang formation of kuching city malaysia used trenchless technology in the form of the pipe jacking method the evaluation of pipe jacking forces mainly involves empirical models developed for soils with rather limited considerations for drives through weathered rock therefore a novel approach is proposed to evaluate strength parameters by reconstituting and subsequently shearing scalped tunneling rock spoils in the direct shear apparatus the direct shear results are then applied to a well established pipe jacking force model which considers arching theory the outcomes indicate that the backanalyzed frictional coefficients avg are not only reliable but also related to their surrounding geologies because of soil structure interaction this study also highlights the significance of lubrication and effect of rock arching in assessing jacking forces the successful characterization of reconstituted tunneling rock spoils in this paper ha

effects of mudstone particle content on compaction behavior and particle crushing of a crushed sandstone mudstone particle mixture abstract the present study focuses on the compaction behavior and particle crushing during the compaction of a crushed sandstone mudstone particle mixture compaction tests and sieve analysis tests in laboratory were performed the effects of the mudstone particle content by weight on the maximum dry density the optimum moisture content and the average relative breakage were analyzed testing results indicate that the values of the maximum dry density and the optimum moisture content of the mixture are increasing then decreases with the increase of the mudstone particle content while the mudstone particle content is about 60 the maximum dry density is near its maximum the average relative breakage during the compaction is decreasing quickly then increases slowly with the increase of the mudstone particle content while the mudstone particle content is about 40 the average relative breakage is near its minimum compared to those of a crushed sandstone particle mixture the maximum dry density of the crushed sandstone mudstone particle mixture is greater and the average relative breakage during the compaction is smaller

the age and origin of the barite fluorite pbzn veins of the sierra del guadarrama spanish central system spain a radiogenic nd sr and stable isotope study fluorite and barite rich veins sulphides of the sierra del guadarrama spanish central system are usually hosted by hercynian granitoids zoned fluorites from one of these veins have a sm nd age of 145 18 ma this age is similar to the k ar ages obtained in other hydrothermal rocks of the spanish central system 156 152 ma and confirms the existence of an important hydrothermal event during the late jurassic probably related to extensional fracturing accompanying the opening of the north atlantic ocean the 87sr 86sr ratio found in fluorite and barite 0 7154 0 7207 is in most cases lower than that found in the host granitoids 0 7194 and 0 7209 suggesting more than one source of strontium this in turn supports previous models that involve mixing of two fluids during mineralization an ascending hot 300 c and low salinity fluid and a shallow cooler 100 c and more saline brine the ascending fluid probably reacted to a variable extent with the host granitoids and the most likely source for the shallow fluid derived from a marine evaporitic environment with a low 87sr 86sr ratio 0 7069 in the late jurassic the calculated end composition of the fluorites 8 8 to 7 6 as well as the 147sm 144nd variation found in this mineral 0 153 0 405 do not conflict with the mixing model although they can be largely explained by interaction of the ascending fluid with the host granitoids sulphur isotopic compositions of sulphides range between 3 4 and 0 8 and those of barites from 15 5 to 15 8 the near 34s value of the sulphides suggests that their sulphur was derived from the hydrothermal leaching of the granitoids by the ascending fluid the 34s value of barite is consistent with upper jurassic marine sulphate as the source of sulphate in the shallow fluid the absence of equilibrium between reduced and oxidized sulphur species can be easily interpreted as a consequence of the short residence time of the mixed fluid in the open fractures at temperatures between 250 and loo c although no pre cretaceous sediments are found on this part of the iberian hercynian basement the data presented here support the existence of a shallow platform joining central spain with the iberian or the subbetic realm in late jurassic times

travertines depositional morphology and the bacterially constructed constituents abstract investigation of travertine accumulations throughout central italy and the west central u s has shown that the carbonate is precipitated in response to both inorganic and organic processes individual deposits range up to 85 m thick and hundreds of square kilometers in areal extent all of the carbonate is low magnesian calcite water chemistry temperature and morphology of the accumulation greatly influence the constituents comprising these deposits harsh environmental situations favor inorganic deposits while increasingly more moderate conditions result in the formation of a greater abundance of organically precipitated material morphological variations of travertine deposits recognized include 1 waterfall or cascade 2 lake fill 3 sloping mound fan or cone 4 terraced ound and 5 fissure ridge gross morphology internal stratification and constituents comprising these deposits vary systematically depending upon the type of accumulation and chemistry of the waters bacterially precipitated calcite forms a large percentage of the carbonate in many travertine accumulations exceeding 90 of the framework grains comprising some of the lake fill deposits bacteria are among the first taxa to inhabit and reproduce in harsh spring environments and produce a variety of fascinating constituents the bacteria are primarily rods generally 0 2 m in diameter and less than 1 0 m in length the rods readily decay resulting in calcite crystals loaded with micropores the basic building block of bacterially constructed travertine is a clump of bacteria averaging 20 m in diameter enclosed in a single crystal of calcite aggregates of these crystals produce a variety of deposits including 1 crudely laminated carbonate mud 2 finely laminat d layers of mud 3 intraclasts 4 foam rock and 5 shrubs the shrubs are most striking commonly forming layers 1 3 cm thick but also producing bacterial pisoids at some locales bacterial stromatolites composed of layers of shrubs alternating with finely laminated layers of bacterial mud comprise essentially the entire deposit the shrub layers are the result of flourishing summer growth of bacteria and furthermore show remarkable daily laminae 0 1 0 5 mm thick the importance of bacteria in the formation of travertine and their universally recognized abundance in modern sediments provides an impetus for a reexamination of the role of bacteria in the origin of other types of ancient deposits

bacterial shrubs crystal shrubs and ray crystal shrubs bacterial vs abiotic precipitation hot water travertine deposits commonly contain shrub like morphologies on the centimeter to meter scale that range from highly irregular forms bacterial shrubs to features that display regular geometric patterns crystal shrubs and ray crystal crusts the bacterial shrubs have been previously recognized as the product of bacterially induced precipitation whereas the ray crystal crusts have been described as due to dominantly abiotic precipitation the bacterial shrubs have a highly irregular morphology similar to woody plants in contrast end member crystal shrubs display distinct crystal habits and regular repeating morphologies i e they commonly have attributes of noncrystallographic as well as crystallographic dendrites there is a complete gradational relationship between the bacterial shrubs and crystal shrubs ray crystal crusts are large fan shaped features composed of subparallel extremely coarse bladed crystals of calcite all three types bacterial shrubs crystal shrubs and ray crystal crusts contain either a dense tangle of bacterial body fossils and or micron sized pores the micropores are bacterial molds the immediately enveloping spar crystals around all three morphologic types are devoid of bacterial body fossils and micropores the bacterial shrubs crystal shrubs and ray crystal crusts are to differing degrees the product of bacterially induced precipitation as well as abiotic mineral precipitation the differences in morphology are due to the relative contribution of bacterially induced precipitation as compared with that of abiotic mineral precipitation bacterially induced precipitates can form in environments too chemically harsh or otherwise inhospitable for other taxa to thrive epiphyton and renalcis commonly formed in occult environments under conditions inhospitable to other taxa consideration of the published descriptions and interpretations concerning epiphyton and renalcis and by analogy the origin of bacterial shrubs have led to the conclusion that epiphyton and renalcis also are bacterially induced precipitates

initial isotopic heterogeneity and secondary disturbance of the smnd system in fluorites and fluid inclusions a study on mesothermal veins from the central and western swiss alps abstract this paper presents sm nd data on hydrothermal fluorites fluid inclusions and leach experiments on samples from the mont blanc and gotthard units swiss alps both areas have experienced alpine greenschist facies overprint 350 and 450 c respectively mont blanc samples represent late variscan fluorites from three individual veins whereas gotthard samples were taken from one hand specimen of probable late variscan age nd concentrations of fluorites range from 3 6 to 23 ppm 147 sm 144 nd ratios from 0 12 to 0 35 none of the samples sets yielded an isochron relationship imperfect correlations indicate apparent ages between late variscan and alpine reflecting neither the formation nor the age of metamorphic overprint reasons are wall rock influence during formation and post formation disturbance secondary fluorite gotthard shows the highest nd concentration and a low sm nd ratio close to that of fluid inclusion fractions a leach experiment showed the same trend even more pronounced 7 of nd and 2 of sm were removed from fluorite by 0 18 n hcl at 100 c hence secondary fluids are likely to leach and fractionate sm and nd and may easily cause dissolution and reprecipitation of fluorite consequently the system is highly suspicious if secondary fluid flow cannot totally be ruled out this is in sharp contrast to previously published conclusions however evidence for rejuvenation of the sm nd system in fluorites is also found in published data sets

dating synmagmatic folds a case study of schlingen structures in the strona ceneri zone southern alps northern italy the strona ceneri zone southern alps contains folds with moderately to steeply inclined axial planes and fold axes and amplitudes of up to several kilometres so called schlingen these amphibolite facies folds deform the main schistosity of late ordovician metagranitoids and are discordantly overlain by unmetamorphic permian sedimentary rocks mutually cross cutting relationships between these folds and garnet bearing leucotonalitic dykes indicate that these dykes were emplaced during folding sm nd systematics and the strongly peraluminous composition of these dykes point to an anatectic origin pb step leaching of magmatic garnet from a leucotonalitic dyke yielded a 321 3 2 3 ma intrusive age rb sr ages on muscovites from leucotonalitic dykes range from 307 to 298 ma interpreted as cooling ages during retrograde amphibolite facies metamorphism conventional u pb data of zircons from an older granodioritic dyke that pre dates the schlingen folds yielded discordant u pb ages ranging from 371 to 294 ma these ages reflect a more complicated multi episodic growth history which is consistent with the observed polyphase structural overprint of this dyke schlingen folding was accompanied by prograde amphibolite facies metamorphism during the thermal peak of which the leucotonalitic dyke material was generated by partial melting in a deeper source region from where these s type magmas intruded the presently exposed level because partial melting may occur in a relatively late stage of a clockwise p t t path or even during decompression on the retrograde path we do not exclude the possibility that schlingen folding had already started in early carboniferous time schlingen folds also occur in penninic and austroalpine basement units with a very similar pre alpine history indicating that variscan folding affected large segments of the future alpine realm

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

effects of particle size distribution on shear strength of accumulation soil abstractthis paper focuses on the effects of particle size distribution on shear strength of accumulation soil a series of direct shear box tests and triaxial tests were performed to characterize the shear strength of the accumulation soil results from the direct shear tests indicate that the range of the angle of shearing resistance of the accumulation soil is 33 5 54 6 and those from the triaxial tests indicate that the angle is 37 2 50 7 the basic properties of the soil such as median particle diameter coefficient of uniformity and gravel content were used to analyze the effects the angle of shearing resistance is generally increasing with increasing median particle diameter and gravel content and decreasing with increasing coefficient of uniformity

multiscale approach to micro porosity quantification in continental spring carbonate facies case study from the cakmak quarry denizli turkey carbonate spring deposits gained renewed interest as potential contributors to subsurface reservoirs and as continental archives of environmental changes in contrast to their fabrics petrophysical characteristics and especially the importance of microporosity 1 mu m are less understood this study presents the combination of advanced petrophysical and imaging techniques to investigate the pore network characteristics of three common and widespread spring carbonate facies as exposed in the pleistocene cakmak quarry denizli turkey the extended pond the dipping crystalline proximal slope facies and the draping apron and channel facies deposits formed by encrustation of biological substrate integrating mercury injection capillary pressure bulk and diffusion nuclear magnetic resonance nmr nmr profiling and brunauer emmett teller bet measurements with microscopy and micro computer tomography mu ct shows that nmr t 2 distributions systematically display a single group of micro sized pore bodies making up between 6 and 33 of the pore space average nmr t 2 cut off value 62 ms micropore bodies are systematically located within cloudy crystal cores of granular and dendritic crystal textures in all facies the investigated properties therefore do not reveal differences in micropore size or shape with respect to more or less biology associated facies the pore network of the travertine facies is distinctive in terms of i the percentage of microporosity ii the connectivity of micropores with meso to macropores and ii the degree of heterogeneity at micro and macroscale results show that an approach involving different nmr experiments provided the most complete view on the 3 d pore network especially when microporosity and connectivity are of interest

what do we really know about early diagenesis of non marine carbonates abstract non marine carbonate rocks including cave spring stream calcrete and lacustrine palustrine sediments are susceptible to early diagenetic processes these can profoundly alter the carbonate fabric and affect paleoclimatic proxies this review integrates recent insights into diagenesis of non marine carbonates and in particular the variety of early diagenetic processes and presents a conceptual framework to address them with ability to study at smaller and smaller scales down to nanometers one can now observe diagenesis taking place the moment initial precipitates have formed and continuing thereafter diagenesis may affect whole rocks but it typically starts in nano and micro environments the potential for diagenetic alteration depends on the reactivity of the initial precipitate commonly being metastable phases like vaterite ca oxalates hydrous mg carbonates and aragonite with regard to the ambient fluid furthermore organic compounds commonly play a crucial role in hosting these early transformations processes like neomorphism inversion and recrystallization cementation and replacement generally result in an overall coarsening of the fabric and homogenization of the wide range of complex primary microtextures if early diagenetic modifications are completed in a short time span compared to the annual to millennial time scale of interest then recorded paleoenvironmental signals and trends could still acceptably reflect original depositional conditions however even compact non marine carbonate deposits may behave locally and temporarily as open systems to crystal fluid exchange and overprinting of one or more geochemical proxies is not unexpected looking to the future relatively few studies have examined the behaviour of promising geochemical records such as clumped isotope thermometry and non conventional stable isotopes in well constrained diagenetic settings ongoing and future in vitro and in situ experimental approaches will help to investigate and detangle sequences of intermediate diagenetic products processes and controls and to quantify rates of early diagenesis bridging a gap between nanoscale molecular lab studies and the fossil field rock record of non marine carbonates