the puglia uplift se italy an anomaly in the foreland of the apenninic subduction due to buckling of a thick continental lithosphere the apenninic foreland shows two distinct structural signatures comparing the central adriatic sea and the puglia region during the pliocene pleistocene the central adriatic underwent high subsidence rates due to the eastward rollback of the hinge of the west dipping apenninic subduction the puglia region and the bradanic foredeep are located southward along strike in the same foreland but in contrast with the central adriatic after pliocene early pleistocene subsidence they underwent uplift since the middle pleistocene the geometry and the kinematics of the frontal accretionary wedge and related foreland changed from that moment on between the two areas at the front of the central northern apennines off scraping and subsidence continued whereas the foredeep and foreland of the southern apennines were buckled those differences are interpreted as being due to the larger subduction hinge rollback rate since middle pleistocene of the central adriatic lithosphere 70 km thick with respect to the thicker puglia 110 km the different thicknesses of the continental crust and lithosphere were inherited from the mesozoic rifting that disrupted the adriatic plate the different thicknesses appear to have controlled the variable degree of flexure of the lithosphere and its asthenospheric penetration rate the tremiti e w alignment is the right lateral lithospheric transfer zone of those different tectonic regimes the consequent different dip of the subduction in the two sections steeper west of puglia could also explain the lower elevation of the southern apennines compared to their central northern sector

a high relative sea level stand in the middle holocene of southeastern tunisia abstract study of the marine holocene deposits in southeastern tunisia shows bioclastic beaches at elevations ranging between 0 and 100 cm above high tide level a h t l depending on the elevation of these fossilized shorelines the ages obtained are different the age of the older deposits ranges between 5900 and 4000 14cc yr b p 6400 4300 calendar yr b p there deposits consist of bioclastic beaches attaining an elevation of about 40 to 100 cm a h t l the younger deposit is dated at around 2100 14c years ago 1850 calendar yr b p and is found today at the same elevation as the present sea level this deposit also consists of bioclastic beach material and contains pottery fragments postglacial melting should not be responsible for this observed higher relative sea level stand because deglaciation ended about 7000 6000 14c years ago fairbanks 1989 furthermore the regularity of the paleobeach deposit elevation over a broad area in southeastern tunisia suggests that tectonics cannot explain the emergence the emergence of up to 1 m of marine deposits dating back to between 5900 and 4000 14c yr b p should rather be interpreted as the result in the region of a postglacial hydro isostatic rebound as predicted in the theological models of continental margins by for example clark et al 1978 and lambeck 1993 the present situation was reached 2100 14c years ago

rapid cold water formation and recrystallization of relict bryophyte tufa at the fall creek cold springs alberta canada the fall creek tufa is a relict mid to late holocene freshwater carbonate spring deposit that is formed almost entirely of calcite encased cratoneuron commutatum gametophytes the spring is presently active emitting 13 c meteorically derived waters but it is not precipitating calcite wood embedded in the youngest part of the tufa yielded a radiocarbon 14c date of 310 50 years bp the oldest parts of the deposit could not be dated by radiocarbon methods because of a lack of embedded organics the fall creek tufa however probably began forming 5000 years bp in response to the same wet climatic conditions that initiated calcite precipitation at miette hot springs in jasper national park and the cave and basin hot springs in banff national park the relict deposit is composed largely of calcite cements that were precipitated around the bryophytes with lesser amounts of internal sediments the tufa formed through a repeated four stage developmental process that involved i encrustation ii enc

stable carbon isotope record of middle to late holocene climate changes from land snail shells at hinds cave texas abstract stable carbon isotope ratios of shell carbonate and shell organic matter from land snails rabdotus alternatus from hinds cave texas are used to reconstruct the climate history of the drier western part of the southern great plains present mean annual rainfall of 400 mm over the last ca 5000 yr ams radiocarbon analyses of four individual shells from each of two strata indicate that there are no problems of reworking or age mixtures within strata however burning is evident in many shells amino acid composition and racemization were used to identify shells that had been significantly heated and these were rejected for isotopic analysis because of possible alteration of the isotopic signal fourteen samples of snails from hinds cave each consisting of 2 6 individual shells from the same provenience were radiocarbon dated by ams and analyzed for stable carbon isotopes in addition a sample collected alive ca ad 1890 from a nearby site was analyzed to represent modern conditions the shells show no decrease in organic content with age indicating good preservation of shell organic matter both the organic and carbonate isotope values show similar temporal trends the oldest samples 4100 4600 cal yr bp are relatively depleted in 13 c maximum 13 c values are reached at ca 3500 cal yr bp thereafter there is a regular depletion in 13 c with the recent sample showing the lowest 13 c value the change in the isotopic values over time is quite large range of 4 5 for organic matter and indicates substantial climatic changes the variations in isotopic values are interpreted as resulting primarily from changes in moisture conditions affecting the abundance of drought adapted cam crassulacean acid metabolism plant species enriched in 13 c thus relatively moist mid holocene conditions are indicated with increasingly dry conditions reaching a maximum at ca 3500 cal yr bp followed by progressively moister conditions through the late holocene

a survey of small scale spatially periodic distortions of auroral forms high resolution television observations by the university of calgary portable auroral imager of the small scale spatially periodic distortions of auroral forms known as curls are presented during winter 1995 and 1997 field trips to rabbit lake saskatchewan canada a large amount of video data containing auroral curls was acquired analysis of this data set has led to much improved insight into the properties of these features observed spatial and temporal characteristics are presented with results compared to those of earlier surveys wherever applicable striking parallels between the characteristics of these 1 km scale size curls and the characteristics of the 100 km scale size auroral spirals observed by the freja uv imager are pointed out and discussed in terms of shear driven instabilities in addition observations of the interesting new phenomena of auroral kinks and spinning auroral patches are briefly described

a rare landform yerkopru travertine bridges in the taurids karst range turkey two examples of travertine bridges are observed at 8 to 15 m above stream level in the lower zamanti basin eastern taurids turkey yerkopru 1 and yerkopru 2 bridges are currently being deposited from cool karstic groundwaters with log pco2 10 2 atm the surface area and the total volume of travertine in yerkopru 1 bridge are 4350 m2 and 40 000 m3 whereas the values for yerkopru 2 are 2250 m2 and 20 000 m3 respectively the interplay of hydrogeological structure local topography calcite saturated hanging springs algal activity and rapid downcutting in the streambed appear to have led to the formation of travertine bridges aeration through cascades and algal uptake causes efficient carbon dioxide evasion that enhances travertine formation algal curtains aid lateral development of travertine rims across the stream model calculations based on a hypothetical deposit in the form of a half pyramid implied that lateral development should have occurred from both banks of the stream in the yerkopru 1 bridge whereas one sided growth has been sufficient for yerkopru 2 the height difference between travertine springs and the main stream appears to be a result of pleistocene glaciation during which karstic base level lowering was either stopped or slowed down while downcutting in the main stream continued copyright 2002 john wiley sons ltd

did changes in late last glacial and early holocene atmospheric co2 concentrations control rates of tufa precipitation gases trapped within arctic antarctic and greenland ice cores document a dramatic increase in atmospheric co2 levels by almost 100 in the period between the last glacial maximum and the late holocene the authors note an apparent correlation between increases in levels of atmospheric co2 during this period and an episode of mass deposition of freshwater carbonate tufas and travertines as changes in atmospheric co2 levels are likely to affect carbonate deposition tucker and wright 1990 we propose the hypothesis that a relationship exists between increasing atmospheric co2 levels and tufa deposition

structure and dynamics of the nightside poleward boundary sounding rocket and ground based observations of auroral electron precipitation in a rayed curtain 1 the cascades2 auroral sounding rocket provides a case study for comparing multipoint in situ ionospheric observations of a nightside auroral poleward boundary intensification with ground based optical observations of the same event cascades2 was launched northward from poker flat alaska on 20 march 2009 at 11 04 ut the 13 min flight reached an apogee of 564 km over the northern coast of alaska the experiment included a five payload array of in situ instrumentation ground cameras at three different points under the trajectory multiple ground magnetometers the poker flat incoherent scatter radar pfisr radar and the time history of events and macroscale interactions during substorms themis spacecraft in the magnetotail the rays of the poleward boundary intensification pbi curtain have along arc motions of 8 5 km s and along arc spacings of 16 km modulated maximum energy envelopes and energy fluxes of the associated electron precipitation correspond to this spatial structure of the visible rays the electron precipitation is additionally modulated at a higher frequency and velocity dispersion analysis of these 8 hz signatures implies alfvenic wave particle acceleration of an ambient ionospheric electron source occurring a few hundred km above the observation point these observations parameterize the curtain of alfvenic activity above the pbi event both in the dispersive ionosphere and in the magnetotail reconnection region the along arc variations in brightness correspond to variations in precipitating electron energy flux interpreted as an along arc modulation of the maximum energy of the alfvenic wave particle acceleration process this is a new interpretation of the formation of rayed structures in auroral curtains we consider the various possible magnetospheric and ionospheric drivers for the control of the observed along arc structuring and motions

shear band foliation as an indicator of sense of shear field observations in central spain the macizo de nevera a paleozoic basement inlier surrounded by essentially flat lying mesozoic cover rocks of central spain exhibits an extremely consistent system of steep dextral strike slip faults different faults have a variable amount of displacement but their en echelon arrangement and similar sense of displacement imply a cogenetic origin a maximum displacement of 1 0 km corresponding to an averaged angular shear strain of 1 5 and peak values of 6 6 occurs along the central part of the 6 km long truchas ductile shear zone an early axial plane cleavage is locally deflected into the truchas shear zone and superposed by coarse shear band foliation the consistent angular relationship between the new foliation and the shear zone boundary confirms the megascopic sense of shear

cyanobacterial tufa calcification in two freshwater streams ambient environment chemical thresholds and biological processes abstract calcareous freshwater streams near bad urach southwest germany were studied to determine the environmental limits to cyanobacterial calcification daily variations in temperature ph calcium concentration and alkalinity were measured at seasonal intervals from september 1993 to january 1995 in two small woodland streams with lengths of 1 0 and 1 5 km the principal cause of supersaturation in these fast flowing streams is inorganic carbon dioxide outgassing from resurging groundwater locally enhanced by turbulence at waterfalls and cascades photosynthetic uptake of carbon dioxide and temperature effects are negligible nonetheless organic substrates particularly cyanobacteria dominated microbial mats and biofilm significantly localize precipitation by providing suitable nucleation sites precipitation rates on artificial substrates up to 2 2 mm yr on limestone correlate with high saturation index values copper substrates inhibited microbial colonization and received negligible encrustation tufa formation and external calcium carbonate encrustation of cyanobacteria are conspicuous where the annual wateq4f saturation index exceeds 0 8 and are slightly below 0 7 calcium carbonate impregnation of cyanobacterial sheaths has not been observed we infer that in these fast flowing streams cyanobacteria utilize co2 in photosynthesis whereas elsewhere in sluggish freshwater cyanobacteria utilize hco3 leading to sheath impregnation by calcium carbonate even where saturation index is only 0 2 0 3 thus photosynthetic influence on cyanobacterial calcification appears to be negligible in fast flowing co2 rich streams and cyanobacterial calcification takes the form of external encrustation in slow flowing co2 poor streams and lakes cyanobacteria preferentially utilize bicarbonate and sheath impregnation can result modern tropical marine carbonate shelves have saturation indices commonly in the range 0 62 0 82 and cyanobacterial calcification is negligible extrapolation suggests that cyanobacterial calcification could occur in present day seas if saturation index exceeded 0 8 this level corresponding with heavy calcification in the freshwater streams studied may have been widespread in marine environments in the geological past at times when calcified cyanobacteria and environmentally influenced non skeletal calcium carbonate precipitates were abundant

travertines in the northern hula valley israel this study describes the field and petrographic relationships of a widespread deposit of pleistocene travertines in the northern hula valley northern israel the travertines interfinger with conglomerate deposits and basaltic lava flows field relationships and radiometric dating indicate that the travertines accumulated intermittently over the past million years and their formation virtually stopped 25 000 years ago the travertines are characteristically highly porous some of the pores as well as some spar filled voids preserve the shapes of stalks and leaves the abundance of plant material suggests that photosynthesis rather than bacterial or abiogenic processes was the main mechanism which induced carbonate precipitation the reasons for travertine accumulation in the past and for the cessation of its formation today are ascribed to differences in the palaeogeographic setting in the past water flow is viewed as having been mostly sluggish and a widespread and shallow sheet of water was formed the lush vegetation combined with the relatively long residence time of the water in the area led to increased efficiency of the calcium carbonate precipitation today by contrast water flows rapidly in gorges precipitating only a small fraction of its load of dissolved calcium carbonate the conjectured change in hydrological conditions is ascribed to rejuvenation of faulting activity in the late quaternary

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

a geochemical evaluation of perennial spring activity and associated mineral precipitates at expedition fjord axel heiberg island canadian high arctic abstract two groups of perennial springs are observed in the canadian high arctic at expedition fjord on axel heiberg island at colour peak and gypsum hill saline discharge 1 3 2 5 molal nacl produces a variety of calcite travertine and gypsum rich precipitates saturation index calculations of the spring waters at colour peak suggest co 2 degassing from the waters causes calcite precipitation gypsum precipitation dominates at gypsum hill where spring waters have lower alkalinity and higher so 4 concentrations mineral accumulations form both channel and rimstone pool morphologies as a result of varying slope conditions at colour peak confined flow in steep slope areas develop massive structures in contrast to more friable porous accumulations in areas where waters fan out on shallower slopes these morphological variations lead to corresponding varying apparent rates of mineral precipitation mineral precipitation at gypsum hill is far less notable as a result of lower discharge rates and annual degradation by icing formation microscopic observations and geochemical analyses of the channel precipitates at colour peak reveal alternating light calcite spar and dark anhedral microcrystalline calcite combined with organic matter and non carbonate minerals laminae rimstone pools forming in lower sections of spring discharge are composed of accumulations of large euhedral calcite crystals interbedded with allochthonous inputs high concentration of dissolved solids is responsible for slow travertine precipitation rates which occurs during winter this precipitation is further retarded during summer months by the introduction of crystal growth inhibitors such as fe 3 and deposition of organic matter and soil sediments

holocene aeolian morphogenetic phases in southern italy problems in 14c age determinations using terrestrial gastropods abstract radiocarbon age determination is one of the most important methods for dating holocene events in particular it has been used to reconstruct the sequence of aeolian morphogenetic phases along the apulia and basilicata coasts southern italy in these areas three main holocene morphogenetic phases have been recognized using radiocarbon data obtained from sub fossil terrestrial gastropods archaeological data and osl analyses those of the middle holocene period of the greek roman time and of the middle ages sub fossil terrestrial gastropods have been considered suitable indicators in the detecting holocene climate environmental changes however it is well known that they could show problems as chronological indicators mainly due to aging effects induced by i micro particles of calcite aragonite in the shell structure derived from the local substratum and ii a variation of co 2 content in the plants eaten in order to verify these hypotheses living terrestrial gastropods were collected from coastal areas and analysed using ams the results indicate that many living gastropods gave ages of 1500 years older than those expected thus confirming the aging effect as 14 c ages of middle and late holocene aeolian morphogenetic phases obtained from terrestrial gastropods seem to be confirmed by archaeological data and osl analyses the aim of this work is to verify if the age anomalies obtained from modern gastropods could be extended to the entire holocene period

rayleigh taylor type instability in auroral patches 1 based on observations by a high resolution narrow field of view ccd camera we found small scale 5 25 km finger like structures at the western boundary of auroral patches in images obtained at gillam geomagnetic latitude 65 5 n canada in january 2008 since shear motion was not observed along the boundary of the patches we suggest that these structures are formed by macroscopic rayleigh taylor type plasma instability arising in the magnetospheric equatorial plane from the force balancing of the eastward magnetic tension force and the westward pressure gradient force

how fast does tufa grow very high resolution measurement of the tufa growth rate on artificial substrates by the development of a contactless image based modelling device

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

relict pleistocene calcareous tufa of the chlupacova sluj cave the bohemian karst czech republic a petrographic and geochemical record of hydrologically driven cave evolution abstract the tufas of the presently shallow chlupacova sluj cave document an unusual history of deeper to shallower hydrologic processes in cave evolution the wider geological context of the cave along with fluid inclusion and stable isotope c and o analyses of calcite from tectonic veins cutting through its wallrock are evidence of the origin of the cave in the deeper subsurface under the influence of ascending 25 70 c warm saline 2 0 22 3 wt eq nacl waters driven by regional hypogene processes the formation of calcite veins which occurred at 700 400 ka was probably coeval with the early stages of cave development however two generations of tufa formed in the later pleistocene during the mature shallow subsurface stage of cave development when daylight and cold meteoric waters penetrated the cave through ceiling windows and tectonic fractures the first generation tufa which consists of cauliflower like aggregates of hollow outward radiating carbonate tubules covered with isopachous banded calcite cements is interpreted as ancient bryophyte tufa that was deposited about 620 140 530 110 ka the presence of microscopic biomorphic fabrics resembling micro stromatolites calcareous algal chambers calcite crystals with cloudy cores and clear sparitic rims and specific biomarkers identified in tufa extracts suggest that in addition to mosses algae and bacteria may have also been instrumental in promoting the deposition of tufa tufa stable isotope c and o characteristics and fluid inclusion contents point to deposition of this first generation tufa from fresh water with a minor admixture of higher hydrocarbons at the surface temperature post dating the first generation tufa minute grains of exotic minerals e g stibnite gothic arch calcite gypsum mn minerals opaline silica and sparry calcite were precipitated in the tufa moulds and between carbonate tubules as cements these minerals suggest at least one event in which hydrothermal waters entered the cave from below after deposition of the first tufa from cool meteoric waters in this hydrothermal phase the cave may have been a hot spring the second generation tufa originated during the riss wurm interglacial at 121 2 1 107 2 6 ka following a period of intense water erosion that partly erased older spelean deposits from cave walls this tufa consists of highly porous friable crudely laminated carbonate sediments with floral and molluscan remains characteristic of common cold water karstic tufa this and the earlier tufa were in turn covered by later fine grained cave sediments contributing to the preservation of pleistocene tufa that records an alternation of deep and shallow waters in the cave over at least the last 500 000 years

rapid sea level rise in the gulf of maine usa since ad 1800 two sea level records from salt marshes in coastal maine are derived from foraminiferal analyses and ams 14 c 210 pb 137 cs and pollen chronology both records cover the period from ad 800 until the present and show corresponding patterns of sea level change when corrected for trends which could accommodate millennial scale isostatic adjustments the records provide a detailed sea level chronology for the last few centuries and thus link the instrumental tide gauge record with the long term geological record of sea level change results show that sea level was relatively stable between ad 800 and 1300 and reached a lowstand around ad 1800 which was preceded by an oscillation in the eighteenth century since ad 1800 sea levels in the gulf of maine have risen by 0 3 0 4 m the onset of this rise corresponds with regional climatic warming and could be interpreted as thermal expansion of the gulf of maine and north atlantic sea surface sea level rise possibly slowed temporarily during the mid nineteenth century but twentieth century rates are unprecedented in the last millennium and correspond with hemispheric warming

factors controlling present day tufa dynamics in the monasterio de piedra natural park iberian range spain depositional environmental settings sedimentation rates and hydrochemistry the tufa record and hydrochemical characteristics of the river piedra in the monasterio de piedra natural park ne spain were studied for 6 years the mean discharge of this river was 1 22 m3 s the water was supersaturated with calcium carbonate the hco3 ca2 and tdic concentrations decreased along the 0 5 km long studied stretch whereas the calcite si showed no systematic downstream or seasonal variation over the same stretch several sedimentary subenvironments exist in which four broad types of tufa facies form 1 dense laminated tufa stromatolites 2 dense to porous massive tufa 3 porous coarsely laminated tufa with bryophytes and algae and 4 dense hard laminated deposits in caves the half yearly period thickness and weight of sediment accumulated on 14 tablets installed in several subenvironments showed that the deposition rate was greater in fast flowing river areas and in stepped waterfalls and lower in slow flowing or standing river areas and in spray and splash areas mechanical co2 outgassing is the main factor controlling calcite precipitation on the river bed and in waterfalls but this process does not explain the seasonal changes in depositional rates the deposition rates showed a half yearly period pattern recorded in all fluvial subenvironments persistent over time 5 26 mm 0 86 g cm2 in warm periods 2 26 mm 0 13 g cm2 in cool periods mass balance calculations showed higher calcite mass values in warm 21 58 mg l than in cool 13 68 mg l periods this biannual variation is mainly attributed to the seasonal differences in temperature that caused changes in inorganic calcite precipitation rate and in biomass and the correlative photosynthetic activity tufa sedimentation was therefore controlled by both physicochemical and biological processes the results of this study may help test depositional rates and their environmental controls and thus assess the climatic and hydrological significance of ancient tufas in semi arid conditions in particular in the quaternary

sedimentology and depositional architecture of tufas deposited in stepped fluvial systems of changing slope lessons from the quaternary anamaza valley iberian range spain the pleistocene and holocene tufas of the anamaza valley stepped build ups up to 70 m thick along the valley consist of several depositional stages separated by erosional surfaces eight associations of tufa and related carbonate facies plus minor polygenic detrital facies represent the processes that occurred in different fluvial and related environments the bedrock lithology and structure controlled the location of the knickpoints along the valley and allowed separation of two stepped stretches with distinct conceptual facies models the moderate slope model includes extensive standing water areas dammed by barrage cascades in the lakes bioclastic silts sands and limestones along with phytoclastic and marly at places peaty sediments formed abundant stem phytoherms account for extensive palustrine areas the high slope model consists of smaller dammed areas between close up cascades and barrage cascades which were composed primarily of moss phytoherms and phytoclastic tufas an outstanding feature is the extensive steep reach with phytoclastic and polygenic detrital sediments and stepped cascades consisting of stromatolitic and moss phytoherms there the steep slope limited the preservation of stem phytoherms and favoured erosion the geometry and thickness of the sedimentary fill wedge shaped units composed of cascade and barrage cascade deposits downstream and dammed and gentle sloped channel deposits upstream are therefore different for each model multi storey wedges are a distinctive feature of the high slope model the initial knickpoint geometry and the tufa aggradation progradation ratio on such steep surfaces for example related to changes in discharge controlled the growth style of the cascades or barrage cascades and hence the extent thickness and vertical evolution of the upstream deposits the sedimentological attributes and stable isotope composition of the carbonate facies suggest a higher and more variable precipitation evaporation ratio during the pleistocene than during the holocene consistent with an overall decrease in the river discharge this evolution was coupled with warm conditions which prevailed during the stages of tufa formation these results may help to assess architectural patterns in interpreting other basins and underscore the significance of tufas as records of past hydrology and climate

multispectral observations of auroral rays and curls two cases of discrete aurora are presented in which auroral curls and auroral rays respectively were seen the aurora was imaged by two spatially separated imagers with a long pass filter main

the quaternary travertine deposits of europe and asia minor abstract a summary is provided of the published information relating to all aspects of quaternary travertine formation in europe west of the ural mountains the deposits have been divided into two broad groups the meteogene travertines which result primarily from the degassing of soil borne aqueous co 2 and thermogene deposits resulting from the degassing of thermally generated co 2 meteogene deposits are rare above latitude 58 n and in regions where the mean annual air temperature is below 5 c a significant positive correlation exists between mean air temperature and travertine deposit thickness the combined effects of temperature and rainfall are used to provide a zoned map showing the travertine forming potential of limestones within the region information from 14 c dating indicates that deposition reached a maximum in the period 5 10 ka bp and is currently limited by land and water management practices in the populated areas thermogene deposits occur in regions of high co 2 discharge resulting from tectonic activity such as italy and turkey where there is much vulcanism these travertines are frequently more massive and less readily weathered than meteogene deposits fully referenced information is provided for 320 important mostly well studied sites 227 meteogene 93 thermogene of which 156 are currently active

statistical study of auroral spirals we present results of a statistical study of 189 auroral spiral forms the data set was collected by a systematic examination of the images recorded at five all sky camera asc stations in northern fennoscandia and svalbard during the winters 1996 1997 and 1997 1998 for every spiral we defined the time of occurrence diameter direction of motion arid distance between the adjacent spirals wavelength in cases of spiral streets the magnetic activity level was determined by using the magnetic north component bx recorded at the asc station and the local auroral electrojet index il index computed by using the data from the image magnetometer network the typical values of the diameter wavelength and ratio between diameter and wavelength were 25 75 km 125 175 km and 2 6 respectively according to our asc data set spirals are more common in the magnetic postmidnight sector than previous satellite observations suggest spirals drift predominantly in the same direction as the large scale ionospheric convection our observations of the average drift speed of spirals of 4 km s are comparable to the corresponding values of other auroral small scale structures statistical analysis revealed that spirals occur most frequently under magnetically quiet il 200 nt conditions and thus they cannot always be considered as precursors of substorm activity

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

growth rate observation from the moss built checa travertine terrace central spain in situ observations of fossil and living specimens of the calcicolous mosses bryum pseudotriquetrum cratoneuron commutatum and catoscopium nigritum revealed very fast calcite depositional rates rhythmic layering in the fossil mosses corresponding with the seasonal climatic cycle suggests that the moss curtain occupied by these three mosses maintains the deposition of spongeous travertine layers at a mean rate of 4 cm a 1 a mean depositional rate of 4 2 cm a 1 may be calculated from measurements of the loss of bicarbonate from the springwater after it percolated through the moss curtain these rates suggest that the 8 m high travertine terrace of checa with a surface area of 800 m 2 did not exist two millennia ago mosses could be put to man s use for creating natural overgrowths on artificial surfaces an idea based on an allusion by wallner he observed that the thread forming blue green algae vaucheria builds travertine deposits at an annual rate of 0 7 1 4 cm we observed that the mosses cratoneuron commutatum and bryum pseudotriquetrum may form spongeous travertine layers at respective maximum rates of 11 and 14 cm a 1 this would reduce the time required to build natural overgrowths on artificial objects to a practical period of months

modern lacustrine stromatolites walker lake nevada abstract the walker river drainage basin occupies about 10 000 km2 in western nevada and parts of california and is essentially a closed hydrologic system which drains from the crest of the sierra nevada in california and terminates in walker lake nevada walker lake trends north and is about 27 4 km long and 8 km wide with water depths exceeding 30 5 m the lake is situated in an asymmetric basin with steep alluvial fans flanking the western shoreline wassuk range and more gentle but areally more extensive alluvial fans flanking the eastern shoreline gillis range exposed lake terraces and the present shoreline of walker lake record a sequence of pleistocene and holocene stromatolitic and tufaceous carbonate deposits small generalized and columnar stromatolites frequently encrusted on exposed coarse grained clasts or bedrock are present along parts of the nearshore margin of walker lake and at elevated lake stands columnar stromatolites as much as 4 cm high are subcylindrical to club shaped discrete and laterally linked at the base with local branching these digitate stromatolites start as wavy generalized stromatolites which are vertically transitional to small laterally linked cabbage heads with laminae which thicken over the crests although algal structures are not well preserved in the older stromatolites recent precipitation of low magnesium calcite occurs as smooth encrustations and as tiny mounds which are consistently associated with a diverse seasonally variable green and blue green algal community including cladophora glomerata ulothrix cf aequalis gongrosira schizothrix amphithrix janthina calothrix homeothrix spirulina anabaena lyngbya and entophysalis cladophora glomerata and a species of ulothrix which are the two most abundant algae within the walker lake stromatolite community are known to condition semi alkaline lake water by the removal of co2 from bicarbonate during photosynthesis such conditioning results in the precipitation of calcium carbonate which is trapped and bound by an understory of green and blue green algae the occurrence of stromatolites in highly siliciclastic lakes seems to be restricted to shoreline and nearshore environments and can be used to locate ancient lake margins

width and structure of mesoscale optical auroral arcs arc widths were calculated for 3126 stable auroral arcs observed by an all sky camera located in gillam manitoba the camera is filtered to accept 5577 a emissions and has a single pixel spatial resolution of 1 7 km at zenith the measured mean width of stable mesoscale arcs located within 5 of magnetic zenith is 18 km with a standard deviation of 9 km the width distribution exhibits a steep cutoff below 8 km when combined with studies of small scale auroral structure this cutoff suggests a gap in the occurrence of arcs with widths of order 1 km this feature of the arc width spectrum argues against the notion of a turbulent cascade of energy from larger to small scales residuals from the gaussian fits are only about 3 of the arc amplitude on average indicating little sub structure within arcs at scales down to the measurement resolution

climatic and tectonic significance of late pleistocene and holocene tufa deposits in the mijares river canyon eastern iberian range northeast spain