multi scale study of the role of the biofilm in the formation of minerals and fabrics in calcareous tufa abstract three sites of actively forming tufa two barrage systems and one terraced slope system located in northern calabria italy and in north east england have been investigated with the purpose of studying the neo formed carbonate minerals at the interface with the organic components that compose the associated biofilms several depositional facies are distinguished notably peloidal to aphanitic laminar and dendrolitic fabrics composed of micrite and microsparite and isolated botryoids and continuous crusts composed of sparite all fabrics occurring in all depositional facies are organized into layers with a more or less well developed seasonal cyclicity low mg calcite precipitates more or less constantly during all seasons within the active depositional zone this extends for a few hundred microns upon the external surface of the deposits where the biofilm occurs the latter is composed of a heterogeneous community of green algae filamentous cyanobacteria and other types of prokaryotes actinobacteria and fungi with a variable amount of extracellular polymeric substances eps porous micro columns 50 to 150 m in size separated by interstitial spaces characterize the active depositional zone here precipitation always begins with organomineral nanospheres 10 to 20 nm diameter both along the external surfaces and within internal cavities of the micro columns by replacing degraded organic matter and at point sites suspended within living cyanobacterial tufts along the external surface of their sheaths indicating that the biological activities of the biofilm are crucial with its living organisms and non living organic matter organomineral nanospheres successively agglutinate to form irregular to rod shaped crystal aggregates 100 200 nm in size that with their further agglutination create two basic types of larger more ordered crystal structure polyhedrons in the range of 1 2 m and minute triads of calcite fibres varying in length from 0 4 short triads to 1 m long triads basic crystal structures coalesce to form larger crystals mainly tetrahedrons tens of microns in size that constitute the micro columns

lower palaeozoic stratigraphy in the southern and central amanos mountains south central turkey formations of cambrian and ordovician age originally identified by the letters a to e in the southern amanos mountains are reviewed using lithostratigraphic units known from the western taurus mountains and south eastern turkey the youngest cambrian rocks in the southern amanos belong to the sosink formation and their age based on trilobite evidence ranges from the badulesia zone to the solenopleuropsis zone of the middle cambrian they are overlain unconformably by conglomerates dated as triassic by means of plant fossils ordovician rocks seydisehir formation approx arenig and bedinan formation caradoc in part are exposed further north in the central amanos the unusual position of the allochthonous ophiolites which rest in part directly upon lower palaeozoic rocks is discussed

microbial origin for pedogenic micrite associated with a carbonate paleosol champagne france abstract micro rods have been observed in indurated carbonate horizons 30 cm thick that overlie a periglacial chalk formation in contact with the present day soil champagne france they are numerous in the upper part of the hardened layers variations in micro rod morphologies are related to progressive biomineralization of organic matter transforming purely organic rods into calcite mineralized rods undergo diagenesis and their arrangement evolves from a random mesh fabric to recrystallized micritic platelets to microsparite two types of organic micro rods have been observed bacilliform and thread like bacteria mineralogically micro rods are low magnesian calcite crystallographically their length is parallel to the 104 axis and they grow along the 010 plane micro rods can be associated with needle fiber calcite they increase the caco3 content of the primary matrix and infill its microporosity their diagenetic evolution into microsparite contributes to soil layer induration

impact of drainage on soil forming mechanisms in a french albeluvisol input of mineralogical data in mass balance modelling research on soil pedogenesis has mainly focused on the long term soil formation and has most often neglected recent soil evolutions in response to human practices such recent soil evolutions are however of considerable interest to study the timing of soil forming processes in response to changes in environmental conditions in this paper we model the albeluvisol evolution in response to agricultural drainage this was considered as a model case to study the velocity of mineralogical changes in soil as a result of eluviation and redox processes we used a space for time substitution approach in combination with mass balance modelling based on mineralogical data in order to identify and characterise the mineralogical transformations responsible for the recent soil evolution in response to subsurface drainage this approach allowed demonstrating that the main effects of subsurface drainage are i increasing precipitation of mn oxides and mn rich ferrihydrite with decreasing distance to the drain as a result of the change in redox conditions and ii increasing loss of clay sized oxides and smectites due to the enhanced eluviation in the vicinity of the drain both processes induce significant matter fluxes in comparison with those that occurred over the long term soil formation nowadays the precipitation of mn oxides and mn rich ferrihydrite seems to still be active in the studied soil on the opposite the eluviation process appears less active than immediately after the drainage network installation if not totally inactive it thus demonstrates that some soil processes may have significant impact on the soil mineralogical composition even if they are only active over very short periods of time after a change in environmental conditions

expression of andic and spodic properties in tephra influenced soils of northern idaho usa abstract tephra from mount mazama crater lake has strongly influenced genesis and morphology of forest soils in the selkirk mountains of northern idaho characteristics associated with andisols and their intergrades are common in soils throughout the area in addition tephra influenced soils of the higher elevations exhibit properties of spodosols as well this study was initiated to examine development and relative expression of these properties along an elevational transect with its associated bioclimatic gradient this paper presents data from three soils that encompass the range in expression of andic and spodic properties found along this gradient cooler moister soils of the higher elevations have formed under subalpine fir forest and are strongly influenced by volcanic ash as indicated by color naf ph glass content and quantities of oxalate extractable fe al and si additionally podzolization processes have created e bhs horizon sequences in these soils within the last 6800 years the clay fraction of the very strongly acid e horizon is dominated by a well crystallized smectite mineral formation of an e horizon has effectively erased andic characteristics such as accumulation of short range order minerals sroms high naf ph and high p retention soils of the middle elevations have formed under western hemlock forest and also have significant ash influence these soils have properties transitional to those of the higher elevation spodosols and do not exhibit the overprint of podzolization processes eluvial horizons are absent although there has been significant accumulation of metal organic complexes and inorganic sroms in the upper horizons of these andisols soils of the lower elevations have developed under relatively warmer and drier conditions associated with the lower end of the western hemlock forest zone and have comparatively less volcanic ash influence the ash has been extensively mixed with coarse textured glacial drift and as a result these lower elevation soils lack the morphological or chemical properties associated with spodosol development but do exhibit weak andic characteristics

vegetation influence on soil formation rate in a proglacial chronosequence lys glacier nw italian alps abstract climate change has huge impacts on alpine ecosystems one of the most visible effects in the alps is glacier retreat since the end of the little ice age lia which caused the exposure of previously glaciated surfaces these surfaces are open air laboratories verifying theories regarding ecosystem and soil development in order to increase our knowledge on the effects of time and vegetation primary succession on soil development in proglacial areas we sampled soils and surveyed plant communities on stable points in the proglacial area of the lys glacier in the italian north western alps valle d aosta region the sampling points were located on dated sites based on literature and or historical photographs glacial till is attacked by weathering processes immediately after deposition and stabilization with a consequent loss of soluble compounds decrease of ph and primary mineral weathering the speed of these processes was largely increased after the establishment of a continuous vegetation cover thanks to the organic matter accumulation caused by litter input and root decomposition below the soil surface on sialic glacial tills below timberline and under a quasi climax larch rhododendron forest fast and steady decrease in ph values increase in organic matter content and horizon differentiation were observed in particular genetic eluvial horizons formed in approximately 60 years while diagnostic albic horizons were developed after ca 90 years pointing to an early start of the podzolization processes cheluviations of fe and secondarily al were analytically verified however illuviations of fe al and organic matter in incipient b horizons were not sufficient to obtain diagnostic spodic horizons on lia materials under grazed grassland below timberline and alpine prairie above timberline acidification and weathering were slightly slower and no redistribution with the depths of fe and al oxi hydroxides was observed a cambic bw horizon developed on the oldest lia moraines therefore it seemed that this fast onset of the podzolization process in comparison to other proglacial chronosequences in the alps was mainly driven by vegetation properties rather than by specific climatic conditions

production and cycling of natural microbial exopolymers eps within a marine stromatolite extracellular polymeric secretions eps that are produced by cyanobacteria represent potential structuring agents in the formation of marine stromatolites the abundance production and degradation of eps in the upper layers of a microbial mat forming shallow subtidal stromatolites at highborne cay bahamas were determined using 14 c tracer experiments and were integrated with measurements of other microbial community parameters the upper regions of a type 2 reid r p visscher p t decho a w stolz j bebout b macintyre i g dupraz c pinckney j paerl h prufert bebout l steppe t des marais d 2000 the role of microbes in accretion lamination and early lithification of modern marine stromatolites nature london 406 989 992 stromatolite mat exhibited a distinct layering of alternating bgreenq cyanobacteria rich layers layers 1 and 3 and bwhiteq layers layers 2 and 4 and the natural abundance of eps varied significantly depending on the mat layer the highest eps abundance occurred in layer 2 the production of new eps as estimated by the incorporation of 14 c bicarbonate into eps occurred in all layers examined with the highest production in layer 1 and during periods of photosynthesis i e daylight hours a large pool i e up to 49 of the total 14 cbicarbonate uptake was released as low molecular weight mw dissolved organic carbon doc this doc was rapidly mineralized to co2 by heterotrophic bacteria eps degradation as determined by the conversion of 14 c eps to 14 co2 was slowest in layer 2 results of slurry experiments examining o2 uptake following additions of organic substrates including eps supported this degradation trend and further demonstrated selective utilization by heterotrophs of specific monomers such as acetate ethanol and uronic acids results indicated that natural eps may be rapidly transformed post secretion by heterotrophic degradation specifically by sulfate reducing bacteria to a more refractory remnant polymer that is relatively slow to accumulate a mass balance analysis suggested that a layer specific pattern in eps and low mw doc turnover may contribute to major carbonate precipitation events within stromatolites our findings represent the first estimate of eps

strong coherence between solar variability and the monsoon in oman between 9 and 6 kyr ago variations in the amount of solar radiation reaching the earth are thought to influence climate but the extent of this influence on timescales of millennia to decades is unclear a number of climate records show correlations between solar cycles and climate1 but the absolute changes in solar intensity over the range of decades to millennia are small2 and the influence of solar flux on climate is not well established the formation of stalagmites in northern oman has recorded past northward shifts of the intertropical convergence zone3 whose northward migration stops near the southern shoreline of arabia in the present climate4 here we present a high resolution record of oxygen isotope variations for the period from 9 6 to 6 1 kyr before present in a th u dated stalagmite from oman the 18o record from the stalagmite which serves as a proxy for variations in the tropical circulation and monsoon rainfall allows us to make a direct comparison of the 18o record with the 14c record from tree rings5 which largely reflects changes in solar activity6 7 the excellent correlation between the two records suggests that one of the primary controls on centennial to decadal scale changes in tropical rainfall and monsoon intensity during this time are variations in solar radiation

in situ carbonation of peridotite for co2 storage the rate of natural carbonation of tectonically exposed mantle peridotite during weathering and low temperature alteration can be enhanced to develop a significant sink for atmospheric co2 natural carbonation of peridotite in the samail ophiolite an uplifted slice of oceanic crust and upper mantle in the sultanate of oman is surprisingly rapid carbonate veins in mantle peridotite in oman have an average 14c age of 26 000 years and are not 30 95 million years old as previously believed these data and reconnaissance mapping show that 104 to 105 tons per year of atmospheric co2 are converted to solid carbonate minerals via peridotite weathering in oman peridotite carbonation can be accelerated via drilling hydraulic fracture input of purified co2 at elevated pressure and in particular increased temperature at depth after an initial heating step co2 pumped at 25 or 30 c can be heated by exothermic carbonation reactions that sustain high temperature and rapid reaction rates at depth with little expenditure of energy in situ carbonation of peridotite could consume 1 billion tons of co2 per year in oman alone affording a low cost safe and permanent method to capture and store atmospheric co2

pedogenic gradients for iron and aluminum accumulation and phosphorus depletion in arctic and alpine soils as a function of time and climate pedogenically significant chemical extracts of iron aluminum and phosphorus are related mainly to time in chronosequences from baffin island canadian arctic the alpine sierra nevada and wind river range western united states the alpine khumbu glacier area himalaya nepal and the alpine southern alps new zealand based on the accumulation index for fe and al and the depletion index for p in each region the following ranking of chemical pedogenic development is obtained southern alps khumbu glacier area wind river range sierra nevada coastal baffin island inland baffin island the ranking mainly follows regional climate with the greatest accumulation and depletion to the warmest and wettest environment and the least accumulation and depletion in the coldest and driest environment

palaeoclimate interpretation of stable isotope data from lake sediment archives the isotope composition of authigenic and biogenic carbonates and diatom silica are commonly used as palaeoclimate proxies from lake sediments this article reviews the controls on the isotope composition of lacustrine skeletal and non skeletal deposits and illustrates how stable isotope studies contribute to an understanding of changes in temperature precipitation patterns evaporation and the carbon cycle it highlights the differences in the palaeoclimate potential of a wide range of lakes ranging from open to closed lake basins a large number of the case histories but not all are drawn from studies of temperate lakes from europe large closed lake systems in the tropics and elsewhere lose water predominantly through evaporation and contain sediments with variable and generally high 18o values fluctuations in the isotope composition of authigenic or biogenic minerals are mainly a function of long term changes in the precipitation evaporation ratio in contrast small open lakes which have a degree of through flow typically contain sediments with 18o values that vary by no more than a few these variations are generally ascribed to variations in temperature or the isotope composition of precipitation p from which either an annual or seasonally specific signal can be gained these types of lakes are common in northern europe and at high altitudes the interpretation of isotope data from a lacustrine succession requires a knowledge of the local processes that might control and modify the signal their effects need to be quantified and a robust calibration using the modern lake system is necessary to establish the relationship between the measured signal the isotopic composition of the host waters and climate

the morphology and function of thrombolitic calcite precipitating biofilms a universal model derived from freshwater mesocosm experiments microbialites with laminar stromatolite and thrombolitic thrombolite fabrics are ubiquitous within the cenozoic freshwater sedimentary record however the biology and physiology of the living prokaryote microphyte biofilms which produced them is only now becoming understood the present contribution describes a flowing water experimental mesocosm study spanning over 2 5 years and run under near natural conditions this work focussed on microbial biofilm precipitation mechanisms which produce thrombolitic carbonate micro fabrics capable of preservation in the geological record in particular the roles of microbial guilds and carbonate precipitation processes were examined and recorded at all stages of thrombolite development the mesocosm experiments convincingly demonstrated that the biofilm community actively encouraged calcium ion precipitation derived from flowing waters this precipitation took the form of amorphous calcium carbonate nanosphere clusters these clusters were not randomly distributed within the biofilm extracellular polymeric substances but were focussed in the close vicinity of living filament and coccoid bacterial clusters within individual living biofilm layers significantly the precipitates never replaced microbial cell walls and never buried the living microbes during nanosphere precipitation extracellular polymeric substances were progressively occluded from between the developing nanosphere clusters however extracellular polymeric substances were never totally removed from within the amorphous calcium carbonate clusters until they had neomorphosed into microspar crystals the orientation of precipitating microspar crystals within the biofilm appeared to be controlled by the host extracellular polymeric substance fabric cf typical crystal growth from solid substrates precipitates were organized around the margins of a cancellate microfabric developed by a range of microbial guilds within each biofilm layer this produced a distinct thrombolitic fabric within the biofilm which was quite distinct from laminar stromatolite fabrics it is concluded that the mesocosm grown freshwater biofilms and their associated microbialite calcite micro fabrics present a universally applicable model importantly they provide a mechanism for thrombolite micro fabric developments throughout the geological record

skeletal crystals of calcite and trona from hot spring deposits in kenya and new zealand abstract skeletal crystals are hollow crystals that develop because their outer walls grow before their cores the presence of skeletal crystals of calcite three types trigonal prisms hexagonal prisms and plates and trona in hot 90 c spring deposits in new zealand waikite springs and ohaaki pool and kenya lorusio hot springs shows that they can form in natural sedimentary regimes analysis of samples from these deposits shows that this crystal morphology develops under disequilibrium conditions that are unrelated to a specific environmental or diagenetic setting skeletal crystals transform into solid crystals when subsequent precipitation fills their hollow cores in some cases this may involve precipitation of crystalline material that has a sieve like texture in other xamples the skeletal crystal provides a framework upon which other materials can be precipitated some of the skeletal hexagonal calcite crystals from new zealand for example are thinly coated with amorphous silica walls in the skeletal trigonal calcite prisms from waikite springs are formed of subcrystals that mimic the shape of the parent crystal similarly plate like skeletal crystals from lorusio are formed of densely packed subcrystals that are 0 5 m long conversely the walls of the skeletal hexagonal calcite crystals from ohaaki pool and the skeletal trona crystals from lorusio are not formed of subcrystals recognition of skeletal crystals is important because they represent growth that follows the reverse pattern of normal growth failure to recognize that crystal growth followed the skeletal motif may lead to false interpretations concerning the growth of a crystal for example the standard interpretation of zoned crystals using the a priori assumption that growth proceeded from the crystal core to the crystal face cannot always be used

record of cenozoic sedimentation from the amanos mountains southern turkey implications for the inception and evolution of the arabia eurasia continental collision abstract the sedimentary succession of the southern amanos mountains bordering the eastern margin of the karasu rift in south central turkey provides a record of environmental change from the eocene lutetian to the upper miocene tortonian that charts the final evolution of the northern margin of the arabian plate prior to and during continental collision eocene shallow marine carbonates hacidagi formation are interpreted as the youngest unit of the arabian passive margin succession deposited on a northwards facing carbonate ramp subsequent deformation and uplift took place during the oligocene represented by folding of the eocene and older strata this is interpreted to be the result of initial continental collision between arabia and eurasia unconformably overlying the eocene limestone are lower miocene conglomerates sandstones and palaeosols up to 150 m thick kici formation these were deposited in a range of marginal marine settings consisting of alluvial fan fan delta facies flood plain as well as basinal facies subsequently during the middle miocene local patch reefs developed in restricted areas kepez formation followed by upper miocene sediments gokdere formation composed of relatively deep water hemipelagic marl with clastic interbeds which represent a transgression during this period the upper miocene becomes sandier upwards this records the regression from the relatively deep water facies to coastal sediments water depth gradually became shallower until during pliocene time the area became continental in nature by the quaternary rifting had resulted in the development of the karasu rift with active alluvial fans along the margins and braided rivers depositing coarse conglomerates in the axial zone these conglomerates are interbedded with basaltic lava flows that resulted from the region extension across the area this research shows that initial continental collision occurred in this area after the lutetian 40 4 ma and before the aquitanian 23 03 ma supporting the hypothesis that the southern neotethys ocean closed during the late eocene to oligocene this was a time of climatic change including the onset of southern hemisphere glaciation in which the closure of the southern neotethys may have had played an important role

tufas and travertines of the mediterranean region a testing ground for freshwater carbonate concepts and developments actively forming travertine and tufa sites are widespread in temperate and warm climates such as the mediterranean region but also develop in other climatic regimes from the arctic to equatorial latitudes the terms travertine and tufa are sometimes applied indiscriminately today however each has a specific definition most studied deposits are active or of quaternary especially holocene age there are fewer tertiary and even less late mesozoic examples on record in part this is because of a recognition problem as these deposits commonly preserve as fragmentary erosional remnants physico chemical precipitation of calcium carbonate is commonly considered to be the main mechanism contributing to tufa and travertine deposition rapid cooling of waters further aids the process in thermal travertine sites however biomediation of calcium carbonate associated with prokaryote microphyte biofilms is now recognized to be equally important in slow flowing and near static sites much of this precipitation occurs in close association with cyanobacterial heterotrophic bacterial and diatoms the mediterranean region figures significantly in the development of travertine and tufa research consequently this article employs key literature on mediterranean examples to illustrate developments and concepts in freshwater carbonate research modern work started in the 1950s and defined many previously unknown outcrops many such sites became the targets for early radiocarbon dating studies since the late 1970s a number of laboratory based and field based classification schemes have been proposed some schemes were based on associated macrovegetation types others were based on petrological characteristics or on geometry and sedimentary facies characteristics of late the sedimentological modelling has benefited greatly from the use of shallow geophysical techniques in order to better define the internal geometries of the deposits two distinct research strands were developed during the 1990s both aimed at a better understanding of environmental change the first considered biocomponents the research was multifaceted and ranged from exploring the role of micro organisms in cement and lime mud precipitation to biostratigraphic analysis of contained pollen and invertebrate remains these provided proxy environmental information which has helped to define past climate variability in the region the second research strand focussed on geochemical signatures as a proxy tool for defining environmental change this definition was made possible by new petrological studies which have greatly aided the recognition of primary depositional fabrics this improved knowledge has reduced the sampling dangers of diagenetic contamination inherent in earlier geochemical studies lithofacies modelling has also brought to light important early post depositional neomorphic changes which obscure primary fabrics and complex diagenetic histories have been revealed stable isotope signatures of carbon and oxygen have also been used to define palaeo water temperature fine tuning of depositional time frames has also been achieved from absolute dating techniques employing radiocarbon and uranium thorium

signatures of biologically influenced caco3 and mg fe silicate precipitation in hot springs case study from the ruidian geothermal area western yunnan province china hot springs at gongxiaoshe and zhuyuan maximum temperatures of 73 to 84 c respectively are characterized by deposits formed of calcite aragonite non crystalline si mg fe deposits and minor amounts of barite and gypsum the deposits at gongxiaoshe are formed largely of alternating calcite and aragonite laminae whereas those at zhuyuan are formed largely of calcite the calcite is in the form of i pseudodendrites that grew as sub crystals stacked upon each other and ii unattached euhedral and incompletely formed dodecahedral and rhombohedral crystals amorphous caco3 formed of nanoparticles 1 m long is common in some of the zhuyuan deposits but minor in the gongxiaoshe deposits the morphologically diverse arrays of aragonite crystals that lie parallel to bedding were not nucleated on a growth surface many substrates in these deposits are covered with reticulate coatings that are formed largely of si and mg with minor fe and micro granular coatings that are formed largely of si and fe biofilms with their extracellular polymeric substances and microbes are common at both springs the compositionally and crystallographically diverse precipitates at these two springs are attributed to a biologically influenced model with precipitation taking place in micro domains that developed in the extracellular polymeric substances according to this model precipitation varied at the micron scale influenced by the elemental concentrations that developed in the hydrogel of extracellular polymeric substances critically the very low preservation potential of the extracellular polymeric substance and its formative microbes means that the precipitates will rapidly lose evidence of their biotic origin the compositional diversity of the precipitates the crystallographic diversity of the calcite and aragonite with numerous incompletely formed crystals and local concentrations of si mg and fe may however serve as proxies of that biologically influenced precipitation

stable isotope record of palaeoclimatic change in a british holocene tufa a 9 5 m long continuous core through holocene tufa deposits in derbyshire uk was analysed for oxygen and carbon stable isotope variations with a view to palaeoclimatic and palaeoenvir onmental interpretation the depositional environment of the tufa is well understood and dated using 14c and biostratigraphy it is argued that smooth variations of up to 1 in 18o of the tufa calcites are caused by changes in the isotopic composition of regional rainfall which in turn were caused mainly by changes in air temperature palaeoclimate in general lower 13c values for calcite correspond with higher 18o values suggesting a stronger component of soil derived carbon during warmer climatic phases a stable isotope approach to reading terrestrial palaeoclimatic records is of widespread application to holocene and older tufa deposits which are common in carbonate bedrock regions

microbial biomineralization processes forming modern ca mg carbonate stromatolites abstract modern ca mg carbonate stromatolites form in association with the microbialmat in the hypersaline coastal lagoon lagoa vermelha brazil thestromatolites although showing diversi ed fabrics characterized by thin orcrude lamination and or thrombolitic clotting exhibit a pervasive peloidalmicrofabric the peloidal texture consists of dark micritic aggregates of veryhigh mg calcite and or ca dolomite formed by an iso oriented assemblage ofsub micron trigonal polyhedrons and organic matter limpid acicular crystalsof aragonite arranged in spherulites surround these aggregates unlike thearagonite crystals organic matter is present consistently in the dark micriticcarbonate comprising the peloids this organic matter is observed as sub micron at and lamentous mucus like structures inside the interspaces of thehigh mg calcite and ca dolomite crystals and is interpreted as the remains ofdegraded extracellular polymeric substances moreover many fossilizedbacterial cells are associated strictly with both carbonate phases these cellsconsist mainly of 0ae2to4lm in diameter sub spherical rod like and lamentous forms isolated or in colony like clusters the co existence offossil extracellular polymeric substances and bacterial bodies associated withthe polyhedrons of ca mg carbonate implies that the organic matter andmicrobial metabolism played a fundamental role in the precipitation of theminerals that form the peloids by contrast the lack of extracellular polymericsubstances in the aragonitic phase indicates an additional precipitationmechanism the complex processes that induce mineral precipitation in themodern lagoa vermelha microbial mat appear to be recorded in the studiedlithi ed stromatolites sub micron polyhedral crystal formation of high mgcalcite and or ca dolomite results from the coalescence of carbonatenanoglobules around degraded organic matter nuclei sub micron polyhedralcrystals aggregate to form larger ovoidal crystals that constitute peloids subsequent precipitation of aragonitic spherulites around peloids occurs asmicro environmental water conditions around the peloids change keywords bacterial fossils biomineralization microbialite nanoglobules peloids stromatolites

sedimentology of tufa facies and continental microbialites from the palaeogene of mallorca island spain abstract the middle eocene and oligocene basins in northwestern half of mallorca are filled by detrital rocks conglomerates calcarenites and lutites and carbonates deposited in alluvial fluvial palustrine and lacustrine settings the sediment supplied to these continental basins was transported by alkaline bicarbonate rich waters as a consequence these non marine carbonate deposits display extensive developments of diverse kinds of organosedimentary facies the sedimentary record from three localities peguera alaro and sineu enabled one to characterize well preserved eocene tufa deposits as well as eocene and oligocene stromatolites and oncolites a total of ten carbonate facies are described and interpreted the facies related to tufa deposits are diverse types of boundstones rudstones and packstones of bryophytes in situ stems s l phytoclasts etc and associated oncolite rudstones and bioclastic mudstones to packstones these facies deposited in littoral lacustrine and fluvio lacustrine environments oncolites and stromatolites present a great variety of shapes and sizes oncolites from centimetres to several meters in diameter that somehow were conditioned by environmental conditions within shallow lacustrine and fluvial settings three types of lamination apparently dependent on the type of microorganisms responsible for calcite precipitation are distinguished fan shaped and bush shaped grouped filaments and isolated to loosely grouped filaments the 13c and 18o composition of these deposits agrees with carbonate precipitation in freshwater hydrologically open systems with similar carbon sources throughout the eocene and oligocene however eocene and oligocene samples are set apart by the 18o oligocene facies present lower 18o values which might indicate deposition from isotopically less evolved waters perhaps under slightly greater precipitation evaporation conditions tufa facies have the highest 13c composition and show some positive covariation of 13c and 18o primarily reflecting the effects of physical and biological co2 outgassing and maybe also minor evaporation

speleothem evidence from oman for continental pluvial events during interglacial periods growth periods and stable isotope analyses of speleothems from hoti cave in northern oman provide a record of continental pluvial periods extending back over the past four of earth s glacial interglacial cycles rapid speleothem growth occurred during the early to middle holocene 6 10 5 ka b p 78 82 ka b p 120 135 ka b p 180 200 ka b p and 300 325 ka b p the speleothem calcite deposited during each of these episodes is highly depleted in 18 o compared to modern speleothems the d 18 o values for calcite deposited within pluvial periods generally fall in the range of 24 to 28 relative to the vienna peedee belemnite standard whereas modern speleothems range from 21 to 23 the growth and isotopic records indicate that during peak interglacial periods the limit of the monsoon rainfall was shifted far north of its present location and each pluvial period was coincident with an interglacial stage of the marine oxygen isotope record the association of continental pluvial periods with peak interglacial conditions suggests that glacial boundary conditions and not changes in solar radiation are the primary control on continental wetness on glacial interglacial time scales

needle fiber calcite a critical review and a proposed classification abstract from a review of the recent literature and our own observations the different morphologies of needle fiber calcite are classified they can be characterized as monocrystalline rods with or without serrated edges or as polycrystalline chains the simplest monocrystalline habit of needle fiber calcite is the individual micro rod m larger monocrystalline rods ma exist in multiples of two more complex forms are found as paired monocrystalline rods with serrated plates along their length mb this group includes three habits which can be distinguished by the number of plates and their orientation relative to the rod finally there is a monocrystalline form mab intermediate between the categories ma and mb which shows the transition from the simple coupled rods to rods with errated plates although polycrystalline needles p have rarely been reported in the literature three types of morphologies have been identified each type of crystal has a specific origin the m micro rods are physicochemical nuclei or calcified bacteria they do not seem to evolve towards larger or more complex morphologies the ma rods are related to biomineralization inside the fungal sheaths the mb rods postdate liberation of ma rods from mycelian bundles the serrated plates are secondary syntactic crystallizations of physicochemical origin whose growth can be inhibited for various reasons the origin of p chains is less well understood but they seem to be physicochemical crystallizations related to evaporation and desiccation therefore these three groups m ma mb and p have similar morphologies but do not seem to be related genetically the only known link is between the ma and mb rods there is no evolutionary s quence of needle fiber calcite habits but a convergence of forms between crystals whose origins are different and independent structures described in the literature as convoluted random cutane and nest like are the result of either evolution of the mycelian bundles or movement of material and organisms in the soil in the case of m micro rods the microfabric is related to the random precipitation around nuclei in pores filled with a highly supersaturated solution initially the p chains also precipitate without preferential organization and later on the growth seems to preferentially constitute chains although the mechanisms are still not understood moreover needle fiber calcites do not indicate a particular climatic environment

a stalagmite record of changes in atmospheric circulation and soil processes in the brazilian subtropics during the late pleistocene we present a high resolution 116 000 year carbon stable isotope record from a stalagmite from southern brazil which has been precisely dated using the u series method evaluation of carbon and oxygen isotope ratios together with the speleothem growth history suggest that the carbon isotopic composition of the speleothem is primarily controlled by biogenic co2 supply from the soil which is in turn affected by temperature and secondarily rainfall amount thus the speleothem provides evidence of paleoenvironmental change in southern brazil during the last glacial period predominantly high d 13 c values and low stalagmite growth rates reflect persistent cool conditions during most of the glacial period in subtropical brazil this cooling is probably related to an intensified extratropical circulation with more frequent and intense cold surges reaching a maximum at approximately 19 ky b p this cooling tendency is interrupted during periods of high obliquity values within the full glacial period at 93 85 and 47 40 ky b p and after 19 ky b p when a dramatic decrease in d 13 c marks the deglaciation time in the continent unlike d 18 o the d 13 c record does not exhibit a strong response to precessional forcing instead it shows a strong 40 ky obliquity signal here we propose that local temperature and thus the biological processes in the soil are primarily steered by the gradients of temperature between low and mid high latitudes which influence the meridional heat transport these gradient changes in turn are paced by obliquity r 2006 published by elsevier ltd

identification of podzols and podzolised soils in new zealand by relative absorbance of oxalate extracts of a and b horizons abstract a method for separating podzols and podzolised soils from other new zealand soils is proposed the method is based on measurement of the optical density of acid oxalate extracts of soils a number of soil leaching sequences and some individual soils are examined it is assumed that the optical density of the oxalate extracts is due mainly to extracted fulvic acid and that detection of appreciable quantities of this material in the b horizon indicates that podzolisation is an active process in the soil the technique separated the soils of the leaching sequences well following the observable increase of podzolic characteristics with increased leaching when the b horizon a horizon odoe optical density of the oxalate extracts ratios were compared with the criteria for the spodic horizon in soil taxonomy soil survey staff 1975 it was found that all soils with a ratio of less than 1 0 did not satisfy spodic horizon criteria and were not classified as podzol podzolised all the soils examined with ratios 1 0 satisfied spodic horizon criteria or were classified as podzol podzolised usually both

calcite moonmilk crystal morphology and environment of formation in caves in the italian alps abstract calcite moonmilk which is a cave deposit formed of calcite crystals and water is found in many caves in the italian alps these modern and ancient deposits are formed of fiber calcite crystals 50 500 nm wide and 1 to 10 m long and polycrystalline chains that have few crystal defects radiocarbon dating indicates that most moonmilk deposits in these caves are fossil and that for most precipitation ceased 6400 cal years bp at the end of the mid holocene hypsithermal in the caves of the italian alps the optimal conditions for formation of calcite moonmilk are 1 a temperature range of 3 5 5 5 c 2 low discharge volumes of seepage waters that are slightly supersaturated sical 0 0 to 0 2 and 3 relative humidity that is at or close to 100 microbial activity apparently did not play an active role in the formation of the calcite moonmilk conditions for moonmilk formation are typically found in caves that are located beneath land surfaces which are soil covered and support a conifer forest precipitation of the fiber calcite crystals apparently involved very slow flow of slightly supersaturated fluids the fact that moonmilk appears to form under a narrow range of environmental conditions means that this cave deposit has potential as a paleoclimatic indicator in high alpine karst areas

rates of weathering and chemical depletion in soils across a chronosequence of lake michigan sand dunes abstract accumulation of soil organic matter and depletion of base cations and trace metals were measured in surface soils i e o horizon and upper 15 cm of mineral soil across a 4150 year soil chronosequence of dune capped beach ridges bordering northern lake michigan within 400 years of beach ridge formation coniferous forest develops soil c and n accumulate to steady state levels of 40 and 1 3 mg ha 1 respectively and the ph of the upper mineral soil decreases from 8 5 to 4 3 as carbonate minerals dissolve after substantial proportions of ca and mg have been removed an incipient spodic horizon can be observed the upper surface of which progressively deepens with increasing soil age analysis of soil strain of the upper mineral soil showed gradual dilation reaching 121 after several centuries of soil development after accounting for soil dilation quantities of ca mg p zn mn fe and v in the upper 15 cm of mineral soil decreased exponentially to low asymptotic levels representing quantities contained in weathering resistant minerals mass balance modeling indicated weathering and elemental losses in the order of decreasing decay constant as ca mg mn zn p v fe al k na ti this sequence is consistent with weathering of carbonates then ferromagnesian minerals then feldspars p levels are tightly coupled with ca losses in soils older than 200 years suggesting that ca rather than fe or al stabilizes p high concentrations of heavy metals in the organic horizon relative to the upper mineral soil indicate atmospheric inputs of industrial pollutants

varying tectonic control on basin development at an active microplate margin latakia basin eastern mediterranean abstract detailed interpretation of multichannel seismic reflection profiles show that the latakia basin evolved in two distinct tectonic stages southeast directed contraction that culminated in the latest miocene followed in the early middle pliocene by progressive transition to partitioned contraction and extension related to the initiation of strike slip along the eastern anatolian transform fault and its marine extensions the miocene fold thrust belt comprises two arcuate culminations enclosing a miocene piggy back depocentre situated on the backlimb of the amanos larnaka ramp anticline in the early middle miocene this piggy back basin was part of a much wider foredeep that also encompassed the miocene successions of the cilicia adana basin complex to the north the misis kyrenia fold thrust belt evolved in the tortonian effectively dividing the foredeep into two large piggy back basins our data demonstrate that a fundamental change in kinematic regime occurred during the messinian to early pliocene involving the onset of strike slip movements resulting in transtension along the northeast trending portion of the main lineaments bounding the latakia basin and continued contraction across the east trending portion of the lineaments in the northeastern portion of the latakia basin southeast directed thrusting ceased in the early messinian and was followed in the lower pliocene by the development of horst and grabzen structures bounded by faults linking onland with the strands of the east anatolian transform fault

stable isotopic compositions of recent freshwater cyanobacterial carbonates from the british isles local and regional environmental controls recent 50 years old freshwater cyanobacterial carbonates from diverse environments streams lakes waterfalls throughout britain and ireland were analysed for their stable carbon and oxygen isotope compositions the mean 18o value of 5 9 pdb for river and stream data represents calcite precipitation in equilibrium with the mean oxygen isotopic composition of precipitation in central britain 7 5 smow assuming a mean water temperature of 9 c the mean 18o of lake data 4 5 pdb is statistically different reflecting the effects of residence time and or variations in the oxygen isotopic composition of rainfall carbon isotopes have wide variations in both fluviatile and lake data sets 3 to 12 pdb these variations are principally controlled in the fluviatile samples by contribution of isotopically light soil zone carbon relative to isotopically heavier carbon from limestone aquifer rock dissolution lake samples have the heaviest carbon isotope values reflecting a trend toward isotopic equilibrium between atmospheric co2 and aqueous hco 3 we infer that isotopic compositions of ancient cyanobacterial carbonates should also record environmental information although the effects of stabilization and diagenesis on primary 18o values will need careful consideration primary carbon isotope compositions should be well preserved although in marine samples values will be buffered by the isotopic composition of aqueous marine bicarbonate

classification and environmental models of cool freshwater tufas abstract tufa deposits are common in the quaternary record facies developments are dependent upon localised carbonate precipitation generally these take the form of phytoherm build ups together with associated detrital deposits derived from disagragation of the former phytoherm cements differ from speleothems and floe calcite accumulations in being biologically mediated or modified this paper recognises the following five types perched spring line cascade fluviatile paludal and lacustrine facies each type is composed of distinctive constructional and detrital sediment associations these unique sediment combinations are the product of an interplay between angle of slope water discharge rate standing water bodies phytal and microbial colonization and ambient temperature the proposed models will be of value in the interpretation of ancient and partially exposed tufas

microbes produce nanobacteria like structures avoiding cell entombment microsedimentary structures referred to as nanobacteria like particles were described from modern carbonate environments where they form in close spatial association with sulfate reducing bacteria srb however the exact mechanism of their formation as well as their paleontological significance remains controversial here we report on an investigation of microbe mineral interactions in experimentally produced carbonate globules the experiments were carried out under anoxic conditions at 30 c with desulfovibrio brasiliensis a srb known to mediate dolomite formation we observed that extracellular polymeric substances eps secreted by the microbial community play a key role in the mineralization process nanobacteria like particles represent the early stage of carbonate nucleation within the eps which progressively evolve to larger globules displaying a grainy texture we excluded the possibilities that these structures are fossils of nanobacteria dissolution surfaces or artifacts created during sample preparation d brasiliensis cells are predominantly located outside of the eps aggregates where mineral growth takes place as a result they remain mobile and are rarely entombed within the mineral this self preservation behavior may not be limited to d brasiliensis other microbes may produce or may have produced during the geological past biogenic minerals through a similar process mineralization within eps explains why microbial relics are not necessarily present in biogenic carbonates

palaeoenvironmental records in holocene spanish tufas a stable isotope approach in search of reliable climatic archives tufa deposits are potential terrestrial archives of palaeoenvironmental and palaeoclimatic information this study assesses the potential of stable isotopic archives from two closely juxtaposed holocene tufa sites in se spain the ruidera site contains deep water lacustrine micrites and tufas whereas the nearby alcaraz site represents a shallow barrage tufa understanding site characteristics is critical to interpreting the stable isotopic variations these holocene lacustrine micrites have isotopic compositions consistent with modern european lake shore microbial carbonates where the isotopic chemistry is strongly influenced by hydrological and residence time effects all the lacustrine micrite d13c values were influenced by microenvironmental microbial effects to some degree because of these effects stable isotope data from lacustrine microbial micrites and tufas will not normally yield precise information on the isotopic composition of palaeoprecipitation temperature or vegetation composition of an area in contrast holocene tufas that formed in shallow fast flowing riverine settings may contain valuable palaeoclimatic archives the tufa deposits must be largely autochthonous as at alcaraz where in situ reed stem encrustations are present records of relative change in air temperature and changes in the source of airmasses are potentially resolvable in the d18o data these interpretations can be verified by other independent climatic data where chronology is constrained variations in riverine tufa d13c values probably record changes in local vegetation and or soil respiration covariation between d18o and d13c values may be intrinsically linked to climatic factors such as aridity tentative palaeoclimatic interpretations for the middle holocene at alcaraz based on the isotope data suggest warming or increasing influence of mediterranean sourced precipitation between approximately 5000 3000 radiocarbon years bp accompanied by increased aridity these interpretations are consistent with the sparse independent palaeoclimatic data and climate modelling results for the holocene of se spain this study supports the growing evidence that well chosen tufa sites could yield valuable palaeoclimatic information

tufa forming biofilms of german karstwater streams microorganisms exopolymers hydrochemistry and calcification to understand mechanisms of tufa biofilm calcification selected karstwater stream stromatolites in germany have been investigated with regard to their hydrochemistry biofilm community exopolymers physicochemical microgradients calcification pattern and lamination in stream waters co2 degassing drives the increase in calcite saturation to maximum values of approximately 10 fold independent from the initial ca2 alkalinity ratio for the cyanobacteria of tufa biofilms a culture independent molecular approach showed that microscopy of resinembedded biofilm thin sections underestimated the actual diversity of cyanobacteria i e the six cyanobacteria morphotypes were opposed to nine different lineages of the 16s rdna phylogeny the same morphotype may even represent two genetically distant cyanobacteria and the closest relatives of tufa biofilm cyanobacteria may be from quite different habitats diatom diversity was even higher in the biofilm at the studied exemplar site than that of the cyanobacteria i e 13 diatom species opposed to 9 cyanobacterial lineages the non phototrophic prokaryotic biofilm community is clearly different from the soil derived community of the stream waters and largely composed of flavobacteria firmicutes proteobacteria and actinobacteria the exopolymeric biofilm matrix can be divided into three structural domains by fluorescence lectin binding analysis seasonal and spatial variability of these structural eps domains is low in the investigated streams as indicated by microsensor data biofilm photosynthesis is the driving mechanism in tufa stromatolite formation however photosynthesis induced biofilm calcification accounts for only 10 20 of the total ca2 loss in the streams and occurs in parallel to inorganic precipitation driven by co2 degassing within the water column and on biofilm free surfaces annual stromatolite laminae reflect seasonal changes in temperature and light supply the stable carbon isotope composition of the laminae is not affected by photosynthesis induced microgradients but from pedley h m rogerson m eds tufas and speleothems unravelling the microbial and physical controls geological society london special publications 336 83 118 doi 10 1144 sp336 6 0305 8719 10 15 00 the geological society of london 2010 mirrors that of the bulk water body only reflecting climate fluctuations tufa stromatolites with their cyanobacterial photosynthesis related calcification fabrics form an analogue to porostromate cyanobacterial stromatolites in fossil settings high in caco3 mineral supersaturation but comparatively low in dissolved inorganic carbon here the sum effect of heterotrophic exopolymerdegradation and secondary ca2 release rather decreases calcite saturation contrary to settings high in dissolved inorganic carbon such as soda lakes geobiological significance of tufa

palaeoclimatic interpretation of high resolution oxygen isotope profiles derived from annually laminated speleothems from southern oman high resolution stable isotope profiles of three contemporaneously deposited stalagmites from a shallow cave in southern oman provide an annually resolved record of indian ocean monsoon rainfall variability for the past 780 years uranium series age dating and counts of annual growth bands enable an excellent age calibration although modern speleothems do not grow in perfect isotopic equilibrium oxygen isotope ratios 18o are a proxy for the amount of monsoon rainfall this is supported by the statistically significant correlation between 18o and the thickness of annual bands whereas 18o is inversely correlated with annual band thickness additionally overlapping 18o profiles are very similar in pattern and range indicating that sample specific noise did not blur the climatic signal the longest oxygen isotope profile derived from stalagmite s3 clearly shows the transition at 1320 ad from a generally wetter medieval warm period to a drier little ice age that lasted from approximately ad 1320 1660 in southern oman the decrease in monsoon rainfall since the 1960s is also obvious in meteorological records from northern africa and india indicating that our speleothem based rainfall records do not only reflect local monsoon rainfall variability

microbialite formation in seawater of increased alkalinity satonda crater lake indonesia abstract the crater lake of the small volcanic island satonda indonesia is unique for its red algal microbial reefs thriving in marine derived water of increased alkalinity the lake is a potential analogue for ancient oceans sustaining microbialites under open marine conditions current reef surfaces are dominated by living red algae covered by non calcified biofilms with scattered cyanobacteria and diatoms minor caco3 precipitates are restricted to the seasonally flooded reef tops which develop biofilms up to 500 m thick dominated by the cyanobacteria pleurocapsa calothrix phormidium and hyella microcrystalline aragonite patches form within the biofilm mucilage and fibrous aragonite cements grow in exopolymer poor spaces such as the inside of dead lysed green algal cells and reef framework voids cementation of lysed hadromerid sponge resting bodies results in the formation of wetheredella like structures hydrochemistry data and model calculations indicate that co2 degassing after seasonal mixis can shift the carbonate equilibrium to cause caco3 precipitation increased concentrations of dissolved inorganic carbon limit the ability of autotrophic biofilm microorganisms to shift the carbonate equilibrium therefore photosynthesis induced cyanobacterial calcification does not occur instead passive diffusion controlled eps mediated permineralization of biofilm mucus at contact with the considerably supersaturated open lake water takes place in contrast to extreme soda lakes the release of ca2 from aerobic degradation of extracellular polymeric substances does not support caco3 precipitation in satonda because the simultaneously released co2 is insufficiently buffered subfossil reef parts comprise green algal tufts encrusted by microstromatolites with layers of fibrous aragonite and an amorphous unidentified mg si phase the microstromatolites probably formed when lake satonda evolved from seawater to ca2 depleted raised alkalinity conditions because of sulfate reduction in bottom sediments and pronounced seasonality with deep mixing events and strong co2 degassing the latter effect caused rapid growth of fibrous aragonite while mg si layers replaced the initially mg calcite impregnated biofilms this could be explained by dissolution of siliceous diatoms and sponge spicules at high ph followed by mg calcite dissolution and mg silica precipitation at low ph due to heterotrophic activity within the entombed biofilms

pedogenic zonation in the well drained soils of the arctic regions abstract pedogenic zonation in the soils of the polar regions is a result of gradients in environmental factors and attendant chemical processes along a latitudinal transect it is best manifested at well drained sites and by soils developed on predominantly silicate rocks selected sites in arctic alaska in the canadian arctic greenland and svalbard adequately fulfill these prerequisites the processes of podzolization decarbonization carbonization pervection and salinization as models of arctic pedogenesis demonstrate that processes occurring in the temperate region also operate in the far north brunification melanization and oxidation are recognized for the first time as current geochemical and pedogenic mechanisms of the arctic region traditional genetic soil names have been retained because they represent a closer relationship to pedogenic processes than the more modern nomenclature the identification the chemical behavior the strength abundance and mobility of the proton donors and conjugate bases are keys to the genesis of soils and the distinction of contrasting soil processes this new approach to the understanding of arctic pedogenesis can be better fulfilled by collecting analyzing and interpreting soil solution obtained in situ

morphology relationship and origin of fiber and dendrite calcite crystals abstract fiber and dendrite calcite crystals formed by abnormal growth conditions are minor but important components of many limestones that have undergone vadose meteoric diagenesis fiber crystals which have a length width ratio of greater than 6 1 are divided into hexagonal fibers rectangular fibers composite fibers and rhomb chains according to their crystal form dendrite crystals are formed of a main stem primary branches and secondary branches random and tangential fiber crystals refer to masses of fibers that have a random distribution or tangentially coat a substrate respectively such crystals may be tightly or loosely packed the shape of fiber and dendrite crystals can be substantially modified by destructive or constructive diagenetic processes destructive modification includes physical breakdown dissolution or micritization constructive modification which usually involves epitaxial growth around the original fiber or dendrite crystal may proceed to the point where the original crystals are completely disguised in extreme cases fiber crystals can be cemented together to form lattices that look like dendrite crystals fiber and dendrite calcite crystals generally form from fluids that are supersaturated with respect to calcium carbonate although experimental data suggest that both types of crystal can form from the same parent fluid there are only rare examples where both are present together in nature such crystals form through biogenically and abiogenically mediated processes the common association of these crystals with plant roots or microorganisms suggests that the organisms can produce conditions suitable for growth of the crystals

holocene itcz and indian monsoon dynamics recorded in stalagmites from oman and yemen socotra abstract high resolution oxygen isotope 18o profiles of holocene stalagmites from four caves in northern and southern oman and yemen socotra provide detailed information on fluctuations in precipitation along a latitudinal transect from 12 n to 23 n 18o values reflect the amount of precipitation which is primarily controlled by the mean latitudinal position of the itcz and dynamics of the indian summer monsoon ism during the early holocene rapidly decreasing 18o values indicate a rapid northward displacement in the mean latitudinal position of the summer itcz and the associated ism rainfall belt with decadal to centennial scale changes in monsoon precipitation correlating well with high latitude temperature variations recorded in greenland ice cores during the middle to late holocene the summer itcz continuously migrated southward and monsoon precipitation decreased gradually in response to decreasing solar insolation a trend which is also recorded in other monsoon records from the indian and east asian monsoon domains importantly there is no evidence for an abrupt middle holocene weakening in monsoon precipitation although abrupt monsoon events are apparent in all monsoon records they are short lived and clearly superimposed on the long term trend of decreasing monsoon precipitation for the late holocene there is an anti correlation between ism precipitation in oman and inter monsoon spring autumn precipitation on socotra revealing a possible long term change in the duration of the summer monsoon season since at least 4 5 ka bp together with the progressive shortening of the ism season gradual southward retreat of the mean summer itcz and weakening of the ism the total amount of precipitation decreased in those areas located at the northern fringe of the indian and asian monsoon domains but increased in areas closer to the equator

soil development on moraines of mendenhall glacier southeast alaska 1 the moraines and soil morphology abstract soils on a sequence of well drained neoglacial moraines up to 240 years old plus an older soil were sampled to investigate soil development through the initial stages of podzolization pebbles and cobbles in the moraines are about 75 to 80 granitic rock computations based on minerals observed optically and on chemical analyses indicate that plagioclase and quartz are the predominant minerals in the fine earth the climate is perhumid leaching of the moraines may have begun before they were free of glacial ice but little organic matter accumulated under the initial vegetative cover of sparse dwarf fireweed 10 year site as alder thicket developed organic matter accumulated rapidly in oi oe and a horizons 38 year site as spruce trees began to replace alder organic matter was lost from the surface mineral soil to form an e horizon and an incipient bs horizon formed below it an oa horizon formed and the a horizon disappeared 70 and 90 year sites organic acid leaching continued to form a spodic bhs horizon in spruce forest 240 year site and a spodic bh horizon in spruce hemlock forest 240 year site hornblende has been etched slightly within 240 years apatite has been lost from e horizons and free fe presumeably in ferrihydrite has accumulated in b horizons the younger moraine soils both with and without incipient bs horizons are typic cryorthents and the 240 year old and older soils with spodic bhs and bh horizons are typic haplocryods they are expected to accumulate more organic matter and become andic humicryods which is the most common subgroup of soils in the area

soil development on moraines of mendenhall glacier southeast alaska 2 chemical transformations and soil micromorphology abstract soils on holocene age moraines of the mendenhall glacier in southeast alaska range from morphologically undeveloped to soils having field identified spodic horizons that are more strongly expressed with increasing soil age a soil chronosequence was sampled to study development of spodic features and to compare the expression of these features with chemical and micromorphological properties organic c accumulates rapidly in these soils with o horizons forming within 38 yr organic c is highly correlated with cation exchange capacity r2 0 92 variable charge r2 0 94 extractable acidity r2 0 83 and 1500 kpa water retention r2 0 97 the ph of the 10 yr old pedon is acidic with a soil ph h20 ranging from 5 0 to 6 4 the ph decreases with soil age with the lowest ph in horizons at the organic mineral contact increases in dithionite citrate sodium pyrophosphate and acid oxalate extractable fe feo are most evident in the 240 yr old soil depth trends for these measured properties within pedons are most distinctive for fe which increases from surface mineral horizons a or e to underlying horizons in all pedons the feo fed ratio increases with soil age in b horizons and in pedons 70 yr this ratio ranges from 0 3 to 0 5 in the e horizons and from 0 4 to 0 83 in b horizons immediately below these data indicate a greater proportion of poorly crystalline fe in illuvial horizons with increasing soil age allophane content is low 240 yr old pedon this chronosequence study indicates that spodic development is achieved within a relatively short period of time in soils of this region

amorphous calcium carbonate associated with biofilms in hot spring deposits abstract calcium carbonate nanoparticles are intimately associated with crystalline calcite and aragonite in the eryuan gongxiaoshe and zhuyuan hot springs water temperature 75 c which are located in yunnan province china the nanoparticles

mesoproterozoic biogenic thrombolites from the north china platform thrombolites are abundant in the subtidal dolostones of the mesoproterozoic wumishan formation ca 1 50 1 45 ga in the north china platform three major components are identified within the thrombolites irregular mesoclots micritic matrix and spar filled voids the mesoclot generally comprises a relatively organic rich micritic core and a microsparitic outer layer that consists of fibrous aragonite pseudocrystals with less organic matter in the core of mesoclots abundant fossilized organic remnants such as putative coccoidal and filamentous bacteria and mucus to film like extracellular polymeric substance eps are closely associated with organomi nerals including nanoglobules and submicron scale poly hedrons in exceptionally well preserved mesoclots their outer layers commonly contain micropores displaying as bacterial molds and filamentous bacteria fossils the matrix of mesoclots consists mainly of micropeloids 20 30 l mi n diameter and minor terrigenous detritus some mesoclots have denticulate edges and their matrix shows growth laminations that envelope the outlines of mesoclots these features indicate that the mesoclots are primary and they were mineralized earlier than the surrounding matrix the mineralization of mesoclots may have proceeded in two stages 1 organomineralization of the cores through replacement of organic matter by minute organominerals resulting from anaerobic degradation of bacteria and eps and 2 inorganic precipitation of the outer layers fostered by an increase in carbonate alkalinity in micro environ ment due to organic matter decomposition the thrombo lites from the mesoproterozoic wumishan formation may have formed through complex interactions between microbes and environments and represent the earliest known precambrian biogenic thrombolites

paleoclimatic reconstruction in northern oman based on carbonates from hyperalkaline groundwaters abstract a paleoclimatic reconstruction for the past 35 000 years for northern oman is based on an unusual approach using travertines and fracture calcites associated with hyperalkaline springs high ph groundwaters ph up to 11 9 discharge from the mantle sequence of the oman ophiolite as the product of modern low temperature serpentinization under arid climatic conditions hyperalkaline discharge occurs at the surface uptake of atmospheric co 2 precipitates characteristic laminated travertines accompanied by strong kinetic depletion of 13 c and 18 o pluvial climates supporting a shallow bicarbonate groundwater flow system and vegetation are recorded by fracture calcites with equilibrium stable isotope contents and calcite replaced roots and stems all such carbonates have modern initial 14 c contents allowing radiocarbon dating and paleoclimatic reconstruction for the late pleistocene and holocene our reconstruction shows a dominantly wet late pleistocene up to 19 000 yr b p when a phase of climatic deterioration began leading to a period of hyperaridity which dominated from ca 16 300 to 13 000 yr b p the early holocene pluvial occurred from 12 500 to ca 6500 yr b p and was followed by renewed climatic deterioration and the current phase of hyperaridity comparison of this paleoclimatic reconstruction with that for lacustrine deposits from the a rub al khali of central saudi arabia and the summer insolation driven monsoon record of east africa and the arabian sea is remarkably good

ferrihydrite and allophane in four andepts from hawaii and implications for their classification abstract the mineralogy and composition of the waimea kukaiau akaka and hilo soils on the island of hawaii were studied using methods which included moessbauer spectroscopy and chemical dissolution the hilo soil which experiences 3000 mm year rainfall and the akaka soil 3800 mm year rainfall both contain large amounts about 25 of iron oxides of short range order together with other iron oxides gibbsite and allophane the iron oxides of short range order have characteristics similar to those of the reactive mineral ferrihydrite which is known to occur in a wide range of soils these characteristics however in two respects x ray diffraction and acid oxalate solubility do not rule out the presence or admixture of the much less known feroxyhite another closely related iron oxide of short range order most samples from these two soils dry irreversibly to give hard aggregates a property probably related to the presence of the iron oxides of shortrange order both the hilo and the akaka soils are classified as hydrandepts in the current usda soil taxonomy in the new proposed order of andisols these two soils would become hydrudands it is desirable to recognise the presence of short range order iron oxides in these soils the kukaiau soil currently classified as a dystrandept which occurs in a lower rainfall zone 1500 mm year contains about 25 allophane and lesser amounts of ferrihydrite other iron oxides and gibbsite the waimea soil occurs in the lowest rainfall zone 1000 mm year and the dominant mineral is halloysite but some allophane ferrihydrite and hematite are also present this soil is currently classified as a eutrandept under the andisol proposal the kukaiau and waimea soils would be a hapludand and a haplustand respectively quartz mica and other layer silicates were present in all four of the soils suggesting that there have been additions of eolian material

variation in soil surface area in a chronosequence of soils from glen feshie scotland and its implications for mineral weathering rate calculations abstract the inorganic component of soil horizons from a chronosequence of six soils developed in glen feshie scotland shows an increase in surface area with soil age and a decrease in surface area with increasing depth in the soil profiles surface area increases due to the development of discontinuous porous coatings on mineral grains the preferential dissolution of specific areas of individual minerals resulting in complex highly irregular grain shapes and a general reduction in grain size due to dissolution the discontinuous coatings consist predominantly of oxalate extractable al si oxyhydroxides and account for between 61 and 94 of the total inorganic surface area failure to take into account the increase of mineral surface area with time can lead to predictions of decreasing mineral dissolution rate with soil age in contrast to laboratory studies which assume that mineral dissolution can reach a steady state the difference between total and reactive mineral surface area may help to explain the frequently reported result that laboratory measured mineral dissolution rates are up to several orders of magnitude greater than those measured in the field

minerals formed and mineral formation from volcanic ash by weathering abstract weathering of volcanic ash and pumice is unique regarding minerals formed and mineral formation these minerals include allophane imogolite opaline silica and some halloysites and have distinctive structures and properties studies on the surface and subsurface weathering of various volcanic ashes in different settings are reviewed this review illustrates that relatively rapid weathering of finely comminuted volcanic ash well reflects the effects of climate vegetation and time and produces various combinations of weathering products the moisture regime the nature and amount of organic matter incorporated the deposition of volcanic ash as overburden and the chemical and mineralogical composition of parent ash are important in controlling the mineral formation in weathered volcanic ash

podzolization over ophiolitic materials in the western alps natural park of mont avic aosta valley italy abstract soil surveys carried out on ophiolitic rocks and till under subalpine forest in the natural park of mont avic aosta valley west italian alps revealed the unexpected occurrence of soils showing a horizon set typical of the podzols podzolization is uncommon on mafic and ultramafic substrata the translocation of organo metallic compounds in soils developed from such parent materials slows down considerably due to the high fe and mg contents the high base saturation and the close to neutral ph in order to determine the real origin and evolution of such soils 6 pedons selected among 83 profiles with a similar podzol morphology were sampled and analyzed chemical mineralogical and petrographic analyses of the sampled soils and parent materials were performed and correlation analysis of the obtained data was carried out results show that in favourable environmental conditions mainly climate and vegetation even mafic and ultramafic parent materials can undergo different degrees of podzolization due to the adopted diagnostic criteria the most common classification systems particularly the wrb do not allow satisfactory taxonomic arrangement of such soils

mineralogy of some italian andosols with special reference to the origin of the clay fraction abstract the mineralogy of four italian andosols derived from volcanic material either oversaturated or undersaturated with respect to silica has been investigated by xrd em and ir the crystalline clay minerals in all four profiles are essentially similar consisting of abundant halloysite with moderate illite and 14a intergrade material minor kaolinite and occasional gibbsite the soils also contain large amounts of imogolite and proto imogolite allophane with the exception of illite all these clay minerals are believed to be of pedogenic origin halloysite occurs in the dehydrated form in the surface horizons but becomes progressively more hydrated with depth at depths of 1 4 m the clay fraction consists almost entirely of fully hydrated halloysite supporting the suggestion that halloysite forms best in a stagnant moisture regime where there is a depositional overburden acting as a silica source em observations show that the halloysite may have spherical morphology and may be intimately associated with gas vesicles in pumice grains where it probably forms by the transformation of allophanic material it seems likely that dehydrated halloysite slowly converts to poorly crystallized kaolinite in the upper horizons of these profiles the origin of the 2 1 minerals is more problematical illite is probably inherited from mica in the parent material but the 14a intergrade material is so poorly ordered that a pedogenic origin seems more likely than formation by inheritance or by transformation of pre existing 2 1 silicates

new insights into biological influence on the geochemistry of freshwater carbonate deposits abstract ambient temperature freshwater carbonates tufas have outstanding potential as palaeoclimate archives however it has proven difficult to constrain the behaviour of the geochemical parameters on which important proxy systems rely current thinking on the development of trace element ratios in tufa rests upon an assumption of precipitation driven by degassing of co2 with the final precipitate being in equilibrium with ambient river water this study provides evidence that although supersaturation is largely regulated by degassing precipitation in sterile flowing systems does not occur throughout the air water interface but only at lines of intersection between this interface and a solid surface precipitation at the bottom as is normal in river sites is not found to occur however when benthic microbial communities biofilms are present extensive precipitation does occur within them in preference and or addition to that at the air water interface precipitation is therefore not purely a consequence of degassing and some microbiological influence is necessary to generate precipitates analogous to nature we further investigate whether these biofilms alter the behaviour of trace elements within tufa systems in addition to modulating the sites and mechanisms of precipitation via a series of experiments biofilms are shown to accumulate large inventories of calcium and other dissolved ions ba sr and mg and we demonstrate that this process is chemoselective in favour of ions with low charge densities these observations have consequences for interpretation of trace element records from tufas based on an assumption of equilibrium with river water and also for other carbonate deposits associated with biofilm activity travertines marine stromatolites lacustrine and soil carbonates speleothems conversely our study provides new insight into the reasons for discrepancy of tufa mg ca ratios from expectation and thus provides encouragement for the potential of mg ca palaeothermometry in freshwater carbonate systems

effects of tephra addition on soil processes in spodosols in the cascade range washington u s a abstract a study was conducted in the cascade range of washington state u s a to examine the effects of tephra additions on soil processes occurring in spodosols unleached tephra from the 18 may 1980 mt st helens eruption was applied in 5 or 15 cm depths to soils that had escaped airfall tephra deposition in 1980 but had received periodic additions of tephra during the holocene soil solutions were collected from the major genetic horizons of tephra treated and non treated profiles interpretation of soil solution composition provided an instantaneous record of the response of soil processes to the added tephra soluble salts composed of basic cations ca2 na mg2 k and so42 were initially leached from the tephra basic cations in the leachate displaced h and al3 from the exchange sites in the original upper horizons the soluble salts and al3 migrated through the soil profile where their concentrations were greatly attenuated by interaction with the solid phase calcium k al3 and so42 were strongly retained in the b horizons whereas na mg2 and cl showed little affinity for the solid phase biological uptake anion adsorption exchange reactions and neoformation of minerals may all be responsible for the differential movement of solutes through the soil profile no enhancement of elemental leaching was measured from the c horizon during the first four months of monitoring podzolization the prevailing process in these mountains was relatively unaffected by the addition of tephra

microscopic calcite dendrites in cold water tufa implications for nucleation of micrite and cement dendritic calcite forms in an active cold water tufa system in association with extracellular polymeric substances eps that discontinuously coat bryophytes and cyanobacteria dendrites consist of 100 200 nm thick calcite fibres that form 3d lattice like domains in each dendrite domain fibres have three structurally equal orientations which correspond in disposition to radii from the centre of a calcite unit cell to the convex triple face junctions on its surface fibres do not form in the orientation of the c axis the external form of each dendrite has the shape of half of a shortened octahedron with an upper triangular surface parallel to the substrate dendrite nucleation takes place on or in microbial eps whether microbial cells are present or not and is probably effected by attraction of ca 2 cations to negatively charged eps together with co2 degassing and concomitant ph increase of supersaturated spring water in stream splash zones ensuing dendrite growth is abiogenic and controlled by diffusion dendrite c axes are perpendicular to the substrate probably because the negative charge of eps forces the orientation of ca 2 and co 2 planes within the developing dendrite crystal to be parallel to the eps film surface dendrites are eventually filled and overgrown by solid syntaxial calcite which gradually and completely obliterates the dendrites as more familiar calcite crystal forms develop no trace of the dendritic nucleus remains in the rock record calcite crystal nucleation may take place by this mechanism in many marine and meteoric settings given that microbial eps is now assumed to be virtually ubiquitous in these environments this phenomenon could contribute to the development of familiar fabrics such as marine micrite cement and fibrous calcite cement radial ooids peloids abiogenic stromatolites sea floor precipitates microbialites tufa travertine speleothems and some meteoric cements it may also contribute to the substrate normal orientation of c axes of common cement fabrics

initial soil development and carbon accumulation on moraines of the rapidly retreating werenskiold glacier sw spitsbergen svalbard archipelago article i nfo the rapid retreat of the werenskiold glacier the svalbard archipelago high arctic is leading to an extensive broadening of the proglacial zone covered with recent moraine till on older glacigenic deposits or directly on bedrock schists to study the type and intensity of initial soil development under a harsh periglacial climate a chronosequence of six soils was established between the glacier front and its terminal moraine on 1 to about 80 year old moraines although the surface layer over the entire area of study is frost active the patterned features are not well developed the succession of vegetation mainly saxifraga sp and lichens starts 5 6 years after deglaciation successively covering up to 30 of the soil surface then stagnating present day soil forming processes within the uppermost soil layer comprise initial weathering of primary minerals chlorites and amphiboles carbonate dissolution and base cation leaching associated with ph lowering accumulation of organic matter and nitrogen and an increase in pedogenically derived fe soil development measures are time related and in general fit a logarithmic model the intensity of transformation including organic carbon and nitrogen accumulation started at high rates comparable to those reported in low arctic and alpine environments however in the fourth fifth decade after deglaciation it reached a quasi steady state low annual precipitation is probably a crucial factor that controls plant succession and leaching of carbonates thus limiting mineral weathering organic matter accumulation and soil development on the werenskiold moraines

chemical weathering in the foreland of a retreating glacier chemical denudation rates and strontium isotope ratios in streams vary substantially and systematically in the foreland of the retreating bench glacier in south central alaska to study weathering of young glacier sediments we sampled 12 streams draining a chronosequence of till and moraine soils derived from cretaceous metagraywacke metapelite bedrock both sediment age and vegetation cover increase with distance from the glacier cation denudation rates decline with increasing distance from the glacier whereas silica denudation rates increase carbonate dissolution and sulfide oxidation account for roughly 90 of the solute flux from the youngest sediments biotite alteration accounts for 5 11 of the solute flux its peak contribution is found in the glacier outlet stream silicate weathering is the dominant reaction only in the oldest sediments in a laboratory dissolution experiment using fresh glacial sediment carbonate dissolution dominated the solute flux during the first 700 hours paralleling the behavior of young sediments in the field in contrast to trends in the field the silica flux did not increase after the carbonate was exhausted from the reactor a possible reason for this difference is that establishment of vegetation causes an increase in silicate weathering the 87sr 86sr ratio in the glacier outlet stream is greater than that in proglacial streams and in bulk rock due to a greater contribution of biotite weathering in the outlet than in proglacial streams strontium isotope ratios decline with sediment exposure age in the proglacial streams and are consistent with a carbonate source because the dominant weathering reactions in the young sediments are of carbonate and sulfide rather than silicate minerals weathering at the glacier margin is not an important long term sink for atmospheric co2

the structure and diagenesis of rhizoliths from cayman brac british west indies abstract rhizoliths from the pleistocene ironshore formation are formed of a brown micrite core surrounded by sediment that is well cemented with 1 calcite rhomb chains 2 isolated calcite rhombs 3 calcified spherical bodies 4 types i and ii calcified epilithic and chasmolithic filaments and 5 grain coating calcite needle mats the friable host sediment has significantly less cement and lacks the grain coating calcite needle mats and type ii calcified filaments of the rhizoliths the sediment however contains calcite needles and a cryptocrystalline cement which do not occur in the rhizolith the contrast in the amount and type of cement between the rhizoliths and the encasing sediment points to the significant role that plants can play in carbonate diagenesis not only do the plant roots act as conduits for water of varying composition they also provide sites at which algae fungi and bacteria thrive these microorganisms serve to promote diagenesis in the rhizoliths the occurrence of the sediments in a coastal setting means that they are subjected to many different types of water ranging from freshwater to saltwater such variability along with the associated changes in the water chemistry may be responsible for the considerable variation in the cement associated with the rhizoliths

micromorphology and genesis of quaternary stromatolitic tufa crust within the exposed cretaceous rayda formation in al jabal al akhdar oman abstract this study aimed to improve the understanding of the causes of lamination in terrestrial tufa using samples of terrestrial quaternary stromatolitic tufa deposits occurring within narrow karst grooves carved along the bedding planes of the exposed cretaceous rayda formation in al jabal al akhdar oman these stromatolitic tufa deposits consist wholly of low mg calcite and are formed of vertically stacked laminated planar and digitate like columnar structures lamination is exhibited as vertically stacked couplets of dark micritic and light sparitic laminae significant variations in the abundance and thickness of the micritic laminae as well as progressive changes in the size and fabric of calcite in the sparitic laminae were recognised thorough microscopic and nanoscopic examinations revealed that these laminations initially developed as stacked indistinct micritic laminae formed of calcitic microbialite that had initially precipitated within a biologically active microbial biofilm which thrived on the wet bedrock surface this was followed by the growth of microglobules at certain horizons within the microbialitic laminae forming incipient discontinuous thin sparitic laminae consisting of laterally stacked biogenic skeletal disphenoidal calcite microcrystals the latter were further growing via abiogenic syntaxial precipitation of calcite forming coarsely crystalline dagger shape bladed calcite crystals these processes resulted in the formation of well developed lamination it is therefore suggested that the stromatolitic lamination has been generated through five consecutive stages of biogenic and abiogenic precipitation of calcite within initially developed microbial biofilms stable isotope values 13c and 18o suggest that these tufa deposits had precipitated from continuously renewed freshwater enriched with bicarbonate dissolved from the marine limestone bedrock during a cold pluvial period

freshwater calcite precipitates from in vitro mesocosm flume experiments a case for biomediation of tufas freshwater carbonates tufas develop today from the arctic to the tropics many being localized about springs and upper water courses some quaternary tufas especially in the mediterranean region extend over tens of square kilometres and exceed 30 m in thickness radiometric dating of holocene deposits shows that many have accumulated at an average rate of 1 mm year 1 however local precipitation may be much faster and some holocene deposits may even have outpaced their tropical marine carbonate counterparts recently the study of active sites has attempted to quantify the precipitation mechanisms which lead to tufa deposition however field observation and sampling procedures suffer from the inherent disadvantages of uncontrolled fluctuations in environmental conditions during the study programme these disadvantages compromise any interpretations particularly where controls on spar versus micrite precipitation are concerned many of these problems have been overcome in the current study by the construction and operation of laboratory mesocosm flumes which simulate the natural conditions e g ph flow rate ambient temperature and daylight in which freshwater carbonate tufa is deposited three mesocosms were supplied with natural river water from tufa precipitating streams and two mesocosms were supplied with uv treated sterile river water from the same source one of the untreated flume mesocosms was linked with a calcium reactor which replaced calcium ions removed during the precipitation process in order to maintain tufa growth over extended experimental runs low magnesium calcite precipitates both rhombic sparite grown from long crystallite dendrites and short crystallite dendrite triad precursors and micrite peloids grown from spherulitic precursors were precipitated in intimate association with biofilm extracellular polymeric substances within the four mesocosms supplied with natural river water virtually no tufa like precipitate was obtained from the flumes supplied with uv treated river water a second extended run flume experiment was also carried out for comparison purposes using a calcium hydroxide solution in deionized water collectively these experiments provide convincing evidence confirming that the presence of a microbial biofilm strongly influences the precipitation of carbonates in riverine freshwater settings in particular experimental results show that micropeloidal micrite and short crystallite calcite dendrites are only produced in the presence of microbial extracellular polymeric substances

interglacial growth of tufa in croatia tufa samples from the krka river area in croatia were dated by 14c and 230th 234u methods the study area is situated in the karst region of the southern dinarides 14c ages of 40 tufa samples collected at the waterfalls coincide with the early holocene interglaciation up to 6000 14c yr b p comparison of conventional 14c dates of holocene tufa and those of speleothems in the dinaric karst shows that speleothem formation started several thousand years earlier than tufa growth samples of old tufa deposits from the krka river 17 and plitvice lakes 12 area and speleothem samples from caves in dinaric karst 5 yield 34 230th 234u dates most of which cluster around interglacial marine 18o stage 5 21 eight of 13 older dates belong to interglacial stages 7 and 9 only 5 dates fall within stage 6 and 8 glaciations 230th 234u dates of speleothems and tufa samples from central europe have indicated that these were formed preferentially during warm and humid interglacial and interstadial periods and it appears that this is true of southern croatia as well stable isotope 13c 18o analyses of 40 tufa samples from the krka river area were compared with stable isotope analyses of tufa from the plitvice lakes area the 13c values for both locations are similar and range from 10 to 6 indicating similar conditions of tufa formation a systematic difference between the 18o values of tufa in these two areas reflects the regional distribution of the oxygen composition of precipitation

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

silica diagenesis origin of inorganic and replacement cherts abstract silicification of originally non siliceous sediments affects a wide variety of rock types and materials and ranges from minor to pervasive partial and minor chertification occur mostly in phanerozoic carbonates carbonate bearing sandstones evaporites and fossil wood the source of the silica is predominantly biogenic in petrified wood the silicification mechanism is a permeation or void filling process not a replacement in this example the sequence of silica phase transformation is the same as that in deep sea siliceous sediments in many silicified rocks particularly in certain carbonates the transformation sequence is different from that in radiolarites or diatomites the chemical environment and conditions of early diagenetic chert formation in shallow water carbonates are delineated by the general mixing model of knauth 1979 but remain unknown for most other types an exception are the flint nodules and bands of the english chalk a detailed geochemical study of the paramoudra flint structures by clayton 1986 provided remarkable insight into the replacement process seven different recurring silica fabrics have been recognized in chert replaced carbonates including equigranular microcrystalline quartz or microquartz and megaquartz and fibrous types chalcedony quartzine or length slow chalcedony lutecite zebraic chalcedony and microflamboyant quartz among the latter quartzine and microflamboyant quartz are common in but by no means restricted to chert replaced evaporites for which milliken 1979 recognized a sequence of seven quartz fabrics as a single criterion only anhydrite inclusions in megaquartz quartzine or microflamboyant quartz provide unequivocal evidence for an evaporite precursor the relative timing between silicification and well established diagenetic carbonate reactions shows that virtually all theoretically possible sequences occur chertification of carbonate host sediment thus may take place during early intermediate or late diagenesis and even during anchimetamorphism pervasive to complete silicification has been described in lacustrine pedogenic and hydrothermal volcanogenic rocks and occurs on the scale of individual beds members or entire formations it may affect some of the aforementioned rock types too for example carbonates the source of the silica is predominantly inorganic chert formation in these environments includes direct chemical silica precipitation from solution through a gel stage magadi type cherts result from the conversion of the hydrous sodium silicate magadiite into microcrystalline quartz which has occurred in east african rift valley lakes such as lake magadi in late pleistocene time they are closely related to directly precipitated inorganic cherts which have been observed in alkaline environments of playa lakes silcretes originate from weathering and soil forming processes under climatic and environmental conditions conducive to the formation of duricrusts and laterites in more humid climates however non weathering profile silcretes occur which have been distinguished from weathering profile silcretes four to five different silcrete fabric types have been established including the 1 grain supported or quartzitic 2 floating terrazzo 3 matrix albertinia and opaline and 4 conglomeratic types in volcanic edifices silicification related to hydrothermal activity occurs 1 along the ascent routes of the fluids vents within the volcanic complexes 2 in isolated ponds and depressions on the sea floor where the fluids discharge mostly in the median rift valley of mid ocean ridges and 3 in geothermal areas on land associated with spreading lineaments volcanic islands arcs transform faults or continental hot spots attention has focussed on the associated base metal concentrations and less on the silicification and accompanying iron enrichment processes the precambrian banded iron formations may be indirectly or directly related to hydrothermal volcanic processes the origin of these cherty iron formations certainly requires more than one genetic model and at present remains a major unresolved problem despite massive efforts to tackle it

holocene forcing of the indian monsoon recorded in a stalagmite from southern oman a high resolution oxygen isotope record from a thorium uranium dated stalagmite from southern oman reflects variations in the amount of monsoon precipitation for the periods from 10 3 to 2 7 and 1 4 to 0 4 thousand years before the present ky b p between 10 3 and 8 ky b p decadal to centennial variations in monsoon precipitation are in phase with temperature fluctuations recorded in greenland ice cores indicating that early holocene monsoon intensity is largely controlled by glacial boundary conditions after approximately 8 ky b p monsoon precipitation decreases gradually in response to changing northern hemisphere summer solar insolation with decadal to multidecadal variations in monsoon precipitation being linked to solar activity

speleothems travertines and paleoclimates abstract age data for about 660 speleothems and about 140 spring deposited travertines were collected including many unpublished results these data were plotted as histograms and also as error weighted frequency curves on a 350 000 yr scale these plots clearly show periods of increased speleothem travertine growth as well as times of cessation the periods of most frequent speleothem growth were between approximately 130 000 and 90 000 yr ago and since about 15 000 yr ago such periods before 150 000 yr ago however cannot be yet recognized because of a lack of sufficient data and the associated uncertainties of dates in this age range a comparison with the oxygen isotope record of deep sea core v28 238 shows a clear relationship indicating that terrestrial calcite formation is controlled by paleoclimatic fluctuations the evident climatic stimulation of quaternary calcite formation is readily explained geochemically and is substantiated by the obvious difference in speleothem travertine growth as a function of geographic position

modern pollen rain and vegetational history of the malaspina glacier district alaska abstract seventy surface pollen samples from coastal forest coastal meadow muskeg tree line and alpine tundra communities form a basis for interpreting fossil pollen assemblages in the malaspina glacier district alaska poflen and macrofossil analyses of three radiocarbon dated fossil sections from icy cape indicate that vegetational changes resulting from plant succession can be distinguished from those of migrational and climatic origin vegetation of the early holocene xerothermic interval 10 000 7600 yr b p was dominated by alnus communities wetter conditions ensued enabling generative muskeg surfaces to develop and first picea sitchensis then tsuga heterophylla to expand from areas southeastward climatic cooling in more recent millennia 3500 yr b p to the present is indicated by the appearance and persistent growth of tsuga mertensiana and selaginella selaginoides along this portion of the gulf of alaska coastline

weathering sequence of soils from volcanic ash involving allophane and halloysite new zealand abstract the clay minerals in a series of soils from rhyolitic ash having the same stratigraphy but different leaching environments were estimated quantitatively by oxalate dissolution infrared spectroscopy differential thermal analysis electron microscopy and x ray diffraction three soils were studied in detail these were the kereone soil mean annual rainfall 1200 mm the ohaupo soil 1400 mm and the mairoa soil 2600 mm the kereone soil contained halloysite as the predominant clay mineral whereas the mairoa soil was mainly allophanic the ohaupo soil contained considerable amounts of both allophane and halloysite thus the allophane content of the soils increased as rainfall increased reflecting a sequence of increased l leaching the si concentration in soil solution decreased as rainfall increased also reflecting increasing leaching of the soils at mairoa si is rapidly removed and allophane al si 2 1 with monomeric silicate is formed whereas at kereone less leaching occurs si levels are higher and halloysite al si 1 1 with polymeric silicate is formed at intermediate sites either allophane or halloysite may form the often reported situation of younger allophanic beds overlying older 10 000 year halloysitic beds may not be due to allophane weathering to halloysite but may result from lower temperature and drier climate during the last glacial maximum between 10 000 and 26 000 years before present bp a new weathering scheme for volcanic ash in new zealand is presented

the biogenic origin of needle fibre calcite needle fibre calcite is one of the most ubiquitous habits of calcite in vadose environments caves deposits soil pores etc its origin either through inorganic indirect or direct biological processes has long been debated in this study investigations at 11 sites in europe africa and central america support arguments for its biogenic origin the wide range of needle morphologies is the result of a gradual evolution of the simplest type a rod this rod is the elementary brick which by aggregation and welding builds more complex needles the absence of cross welded needles implies that they are welded in a mould or under a longitudinal and unidirectional constraint before being released inside the soil pores the difference between the lengthening of the needles and the c axis can be explained by the existence of needles observed under a scanning electron microscope in organic sleeves which can act as a mould during rod growth complex morphologies with epitaxial outgrowths on straight rods cannot have grown entirely inside organic microtubes they must result from soil diagenesis after the release of straight rods in a soil free medium whisker crystals are interpreted as the result of growth and coalescence of euhedral crystals on a rod rhomb chains are considered to be the consequence of successive epitaxial growth steps on a needle during variations in growth conditions isotopic signatures for needle fibre calcite vary from 16 63 to 1 10 and from 8 63 to 2 25 for 13c and 18o respectively the absence of high 18o values for needle fibre calcite precludes a purely physicochemical origin evaporative for this particular habit of calcite as epitaxial growth cannot precipitate in the same conditions as initial needles needle fibre calcite stable isotopic signatures should be used with caution as a proxy for palaeoenvironmental reconstructions in addition it is suggested that the term needle fibre calcite should be kept for the original biogenic form the other habit should be referred to as epitaxial forms of needle fibre calcite

revised stratigraphy and relationships of lower palaeozoic rocks eastern taurus mountains south central turkey lithostratigraphic terminology is revised for rocks of ordovician age in the eastern taurus the seydisehir formation of late middle cambrian to early ordovician age is shown to be applicable in the eastern and western taurus as well as in south eastern turkey near deg irmentas northeast of adana the seydisehir formation is overlain with inferred unconformity by clastic strata of ashgill age referred to the ort tepe formation first defined south of hakk ri in the border folds of southeastern turkey palaeontological evidence is cited for the early silurian llandovery age of the unconformably overlying halityayla formation farther south on the coast near ovacik where the ort tepe formation is as yet unrecorded a general model is proposed showing relationships of cambrian and ordovician rocks and faunas in southern and southeastern turkey

mineralogy and weathering processes in recent and holocene tephra deposits of the pacific northwest usa abstract weathering and evolution of minerals in tephra deposits in the cascade range of washington state usa are influenced by climate vegetation time microtopography and in the vicinity of mt st helens naturally acidic precipitation we have observed the interaction of these factors in spodosols developed on holocene tephra in the central cascades and in entisols formed on the 1980 pyroclastic flow of mt st helens weathering regimens in these tephritic soils can be qualitatively characterized by the soil solution composition weathering reactions in the spodosol are driven by organic acids in the upper soil horizons and by carbonic acid in the lower b and c horizons the mineral assemblage in the spodosol reflects in part the chemical regimen dictated by each proton donor the presence of smectite in the highly acidic e horizon ph