geomorphology and palaeoclimatology of some upper cretaceous palaeosols in central india abstract the late cretaceous maastrichtian lameta formation exposed around jabalpur in central india comprises a pedogenically modified fluvial succession accumulation of early diagenetic calcite cement during penecontemporaneous pedogenesis has transformed the fluvial sandstones into calcareous sandstones the microscopic features of the palaeosol material include floating grain fabric root traces laminated micrite microspar micrite envelopes and corona structures illuvial clay envelopes poikilotopic spars and minor amounts of siliceous grain and void cutans the palaeosol profiles of the lameta formation can be classified into eleven different types nine of which are comparable to present day mature aridisols and two to inceptisols nine to thirteen palaeosol profiles are present in the individual sections of the lameta formation within the study area each profile comprises two to four distinct pedohorizons arranged in vertical succession there are six types of pedohorizons present in the area of study namely partly altered hosts light coloured and poorly cemented horizons horizons with root traces and root related alterations horizons of subspherical glaebules horizons of platy fused glaebules and subhorizontal root traces and horizons with solution features they show many characteristics similar to the present day soil horizons for example those termed c bk k a and e by pedologists the palaeosol characteristics show correspondence to the nature of fluvial channel migration and the depth of the groundwater table controlled by the geomorphic setting a shallow groundwater table favoured the development of rootmat bearing and gleyed horizons horizons with vertical root traces and glaebules occur where the groundwater table was low mature and thin palaeosols developed in those parts of the lameta fluvial tract that were characterized by stable channels and wide floodplains in contrast thin and comparatively immature soils occurred in the parts where laterally migrating channels were operative the characteristics of the lameta palaeosols suggest that a hot and semiarid climate prevailed for most of the time represented by the lameta formation but short term wet spells occurred during the initial and the terminal phases of the lameta accumulation the low latitudinal palaeoposition of india and the absence of the palaeo monsoon circulation might have produced the hot and semiarid climatic setting during this time

sedimentology of quaternary perched springline and paludal tufas criteria for recognition with examples from guadalajara province spain outcrop scale geometries and bed relationships of ambient temperature freshwater carbonates are poorly understood because many described tufas have been dismantled by erosion and present only part of a particular depositional model at the field scale four end member models encompass the tufa continuum 1 perched springline 2 paludal 3 fluvial and 4 lacustrine tufas individual bed types can occur with variable dominance within several of these models but one or more beds are characteristically dominant only within a single tufa model so it can be differentiated from relatively isolated outcrop fragments two models perched springline tufas and paludal tufas are known in outline only in the literature despite being present within the quaternary deposits of most karstic regions perched springline tufas generally form lobate fan shaped mound morphologies on hillslopes and develop from single or multiple spring resurgences mature deposits show a subhorizontal top and a steep face on the downflow side the steep outer zones of tufa mounds may be developed into cascades with moss curtains or can be dominated by shallow rimstone pools according to face angle tufa deposits lying downslope of the mounds are usually detrital in nature especially if some dismantling of the mound has occurred the relatively thin subhorizontal lobe top deposits commonly contain organic rich deposits paludal tufas develop predominantly in waterlogged valley bottom situations where line sourced waters emerge from valley side and bottom aquifers lime mud precipitation predominates in these sites mud is deposited as subhorizontal laminites that thin towards the valley axis and downstream of resurgences tufa spring mounds may form where lesser volumes of water are involved individual tussocks phytoherm cushions of grasses and rushes are the most diagnostic feature of the model but sapropels and peats may be intercalated diagenesis in both models is rapid lithification of individual beds is virtually instantaneous and always occurs before the decay of the associated living vegetation the resulting highly porous and permeable fabrics remain fresh in holocene tufas but aggrading neomorphism and partial spar infill of vegetation moulds is common in older deposits dissolution in many perched springline tufas is small scale many large cavities are primary but with later coatings of speleothems early removal of organics from paludal tufas is responsible for autobrecciation and differential compaction

palustrine carbonates and the florida everglades towards an exposure index for the fresh water environment abstract palustrine carbonates are shallow fresh water deposits showing evidence of subaqueous deposition and subaerial exposure these facies are common in the geological record the intensity of modification is highly variable depending on the climate and the length of emergence palustrine limestones have previously been interpreted as marginal lacustrine deposits from fluctuating low salinity carbonate lakes but several problems remain with existing facies models 1 palustrine carbonates possess a lacustrine biota but commonly display fabrics similar to those of calcretes and peritidal carbonates 2 the co occurrence of calcrete horizons and karst like cavities is somewhat unusual and appears to indicate contemporaneous carbonate precipitation and dissolution in the vadose zone 3 the dominance of gray colors indicates water saturation apparently inconsistent with the evidence for strong desiccation overprint 4 profundal lake deposits are generally absent from palustrine sequences and sublittoral facies commonly make up only a small proportion of total thicknesses 5 no good modern analogue has been identified for the palustrine environment analogy with the florida everglades suggests a re interpretation of palustrine limestones not as pedogenically modified lake margin facies but as the deposits of extensive very shallow carbonate marshes the distribution of environments in the everglades is determined by the local hydrology reflecting the control of seasonal water level fluctuations and topography climate and topography were the main controls on deposition of ancient palustrine carbonates as in peritidal sequences aggradational cycles are capped by a range of lithologies evaporites desiccation and microkarst breccias calcretes lignite or coal horizons etc permitting interpretation of the climate careful analysis of lateral facies variations may permit reconstruction of subtle topography consideration of the florida everglades as a modern analogue for the palustrine environment has suggested the development of an exposure index for fresh water carbonates

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

factors of paleosol formation in a late cretaceous eolian sand sheet paleoenvironment marilia formation southeastern brazil abstract the marilia formation which crops out in southeastern brazil is interpreted as a late cretaceous eolian sand sheet area the sedimentary succession ca 110 m thick is characterized by alternating strata of eolian deposits and paleosols the paleosols constitute more than 66 of the thickness and are an important element in the interpretation of the paleoenvironmental controlling factors which affected the soil formation in this eolian sand sheet in this paper six paleosol profiles are described and assigned to two pedotypes itaja and apore the itaja pedotype is constituted of a sequence of five superimposed polygenetic profiles which show different phases of clay illuviation and carbonate precipitation and it has been classified as aridisol the apore pedotype overlies the itaja pedotype this pedotype shows an increase in leaching cia k ratios reddening and illuvial clay features in respect to itaja and has been classified as alfisol the analysis of the factors which controlled the soil formation revealed that both pedotypes formed on a stable landscape probably covered by a community of low stature plants in which the soils had sufficient time to develop very mature profiles the changes in soil forming processes were driven principally by variations in available soil moisture from precipitation using depth to carbonate functions from bk and cia k proxy from bt horizons of the itaja pedotype mean annual precipitation map estimates range from 240 to 1078 mm yr respectively these contrasting climatic conditions resulted in the superimposition of arid or semi arid with more humid climates and determined the considerable change in the pedogenic features with many horizons showing the interlacing of calcite and clay features in the apore pedotype cia k proxy from bt horizons estimates that averaged map was around 900 mm yr and the prevalent humid conditions can be attested by soil properties and abundance and depth of root traces our results show that the diversity in pedotypes is mainly attributed to differences in paleoclimatic conditions during maastrichtian time and that eolian sedimentation was restricted to periods of harsh arid conditions as in semi arid climates with map estimates around 240 mm yr the formation of soils with well developed calcic horizons was possible

control of terrestrial stabilization on late devonian palustrine carbonate deposition catskill magnafacies new york u s a abstract upper devonian frasnian terrestrial strata of south central new york contain palustrine and lacustrine carbonate deposited within the well developed catskill clastic wedge succession these nonmarine limestone beds 8 50 cm thick were repeatedly subaerially exposed and subjected to pedogenic processes palustrine features include subaerial exposure surfaces with soil crusts pseudo microkarst and microkarst brecciation desiccation cracks horizontal planar and circumgranular cracks and rhizoliths lacustrine carbonate sedimentation was derived primarily from biogenically induced precipitation and from degradation of calcified charophyte stems and ostracodes these deposits accumulated in relatively shallow water depths probably 10 m the results of stable isotope analyses 13c 4 0 to 4 7o oo pdb 18o from 6 8 to 8 7o oo pdb reveal covariance between 13c and 18o values the high degree of covariance r 0 75 suggests that these late devonian carbonate lakes were hydrologically closed high rates of surface water productivity resulted in the heavier 13c values late devonian carbonate lakes developed as a result of landscape stabilization by the developing rhizosphere in addition plants of small to moderate stature functioned as clastic filters trapped terrigenous clastic sediment along lake margins and thereby permitted carbonate sedimentation to occur in a system otherwise dominated by terrigenous clastics these upper devonian lacustrine deposits contain the oldest recognized occurrence of palustrine facies the temporal distribution of palustrine carbonate deposits therefore appears limited to post silurian strata

growth patterns and implications of complex dendrites in calcite travertines from lýsuholl snaefellsnes iceland calcite dendrite crystals are important but poorly understood components of calcite travertine that forms around many hot springs the l suholl hot spring deposits located in western iceland are formed primarily of siliceous sinters that were precipitated around numerous springs that are now inactive calcite travertine formed around the vent and on the discharge apron of one of the springs at the northern edge of the area the travertine is formed largely of two types i and ii of complex calcite dendrite crystals up to 1 cm high that grew through the gradual addition of trilete sub crystals the morphology of the dendrite crystals was controlled by flow direction and the competition for growth space with neighbouring crystals densely crowded dendrites with limited branching characterize the rimstone dams whereas widely spaced dendrites with open branching are found in the pools many dendrite bushes in the pools nucleated around plant stems growth of the dendrite crystals was seasonal and incremental calcite precipitation was driven by rapid co2 degassing of co2 rich spring waters during the spring and summer during winter when snow covered the ground and temperatures were low opal a precipitated on the exposed surfaces of the dendrites segmentation of dendrite branches by discontinuities coated with opal a and overgrowth development around sub crystals resulted from this seasonal growth cycle the calcite dendrite crystals in the l suholl travertine differ in morphology from those at other hot springs such as those at lake bogoria kenya and waikite in new zealand comparison with the calcite dendrite crystals found at those sites shows that dendrite morphology is site specific and probably controlled by carbonate saturation levels that in turn are controlled by the rate of co2 degassing and location in the spring outflow system

palaeoenvironmental significance of palustrine carbonates and calcretes in the geological record interest in palustrine carbonates and calcretes has increased over the last 20 years since they contain significant environmental information much of the work performed in this area has focused on either of two types of terrestrial carbonate palustrine carbonates or calcretes pedogenic and groundwater yet their simultaneous study shows there may be a gradual transition from one form to the other revealing the interplay between pedogenic sedimentary and diagenetic processes three main factors control the formation of these carbonates the position of the water table the host rock and the period of sub aerial exposure in pedogenic calcretes precipitation of carbonate takes places mostly in the vadose zone above the water table and within a previous host rock or sediment in groundwater calcretes the precipitation of carbonate also occurs within a previous host rock and around the groundwater table in palustrine carbonates however the precipitation of lime mud occurs in a lacustrine water body palustrine carbonates necessarily form on previous lacustrine mud whereas both types of calcretes may form on any type of sediment or soil the sub aerial exposure time needed to form palustrine carbonates may by relatively short even a season whereas pedogenic calcretes need more time several years to millions of years groundwater calcretes do not form on the topographic surfaces so there is no need of sub aerial exposure however stable surfaces favour the development of thick groundwater calcretes small fluctuations in the water table cause gradual transitions of these three types of terrestrial carbonates and the subsequent mixture of their characteristic features causing difficulties in the interpretation of these carbonates the formation of these carbonates is controlled by palaeoenvironmental factors both commonly form in semi arid climates arid climates are also suitable for calcretes but sub humid conditions are more suitable for palustrine carbonates more indications of climatic conditions may be obtained through the analysis of the d18o content of both calcretes and palustrine carbonates and from the depth of the horizon containing carbonate nodules in pedogenic calcretes vegetation is also important in the formation of these types of carbonates data on the prevailing vegetation can be obtained from the analysis of the micro and macrofabric as well as from the d13c signal of the primary carbonates which in pedogenic carbonates has also been used to estimate atmospheric pco2 during the phanerozoic these terrestrial carbonates are widely distributed on floodplains and distal areas of alluvial basins their presence and characteristics can be used as indicators of aggradation subsidence or accommodation rates and therefore as indicators of different tectonic regimes even though the study of these carbonates has notably increased in recent years much less is known about them than about marine carbonates presently there is much emphasis on obtaining a general model for sequence stratigraphy in terrestrial basins with a need to include the carbonates analysed in this paper

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

microbial carbonates the geological record of the calcified bacterial algal mats and biofilms summary deposits produced by microbial growth and metabolism have been important components of carbonate sediments since the archaean geologically best known in seas and lakes microbial carbonates are also important at the present day in fluviatile spring cave and soil environments the principal organisms involved are bacteria particularly cyanobacteria small algae and fungi that participate in the growth of microbial biofilms and mats grain trapping is locally important but the key process is precipitation producing reefal accumulations of calcified microbes and enhancing mat accretion and preservation various metabolic processes such as photosynthetic uptake of co2 and or hco3 by cyanobacteria and ammonification denitrification and sulphate reduction by other bacteria can increase alkalinity and stimulate carbonate precipitation extracellular polymeric substances widely produced by microbes for attachment and protection are important in providing nucleation sites and facilitating sediment trapping microbial carbonate microfabrics are heterogeneous they commonly incorporate trapped particles and in situ algae and invertebrates and crystals form around bacterial cells but the main component is dense clotted or peloidal micrite resulting from calcification of bacterial cells sheaths and biofilm and from phytoplankton stimulated whiting nucleation interpretation of these texturally convergent and often inscrutable fabrics is a challenge conspicuous accumulations are large domes and columns with laminated stromatolite clotted thrombolite and other macrofabrics which may be either agglutinated or mainly composed of calcified or spar encrusted microbes stromatolite lamination appears to be primary but clotted thrombolite fabrics can be primary or secondary microbial precipitation also contributes to hot spring travertine cold spring mound calcrete cave crust and coated grain deposits as well as influencing carbonate cementation recrystallization and replacement microbial carbonate is biologically stimulated but also requires favourable saturation state in ambient water and thus relies uniquely on a combination of biotic and abiotic factors this overriding environmental control is seen at the present day by the localization of microbial carbonates in calcareous streams and springs and in shallow tropical seas and in the past by temporal variation in abundance of marine microbial carbonates patterns of cyanobacterial calcification and microbial dome formation through time appear to reflect fluctuations in seawater chemistry stromatolites appeared at 3450 ma and were generally diverse and abundant from 2800 to 1000 ma inception of a proterozoic decline variously identified at 2000 1000 and 675 ma has been attributed to eukaryote competition and or reduced lithification thrombolites and dendrolites mainly formed by calcified cyanobacteria became important early in the palaeozoic and reappeared in the late devonian microbial carbonates retained importance through much of the mesozoic became scarcer in marine environments in the cenozoic but locally re emerged as large agglutinated domes possibly reflecting increased algal involvement and thick micritic reef crusts in the late neogene famous modern examples at shark bay and lee stocking island are composite coarse agglutinated domes and columns with complex bacterial algal mats occurring in environments that are both stressed and current swept products of mat evolution ecological refugia sites of enhanced early lithification or all three

climatic and tectonic controls on carbonate deposition in syn rift siliciclastic fluvial systems a case of microbialites and associated facies in the late jurassic this work provides new insights to assess the factors controlling carbonate deposition in the siliciclastic fluvial systems of rift basins sedimentological and stable isotope data of microbialites and associated carbonate facies along with regional geological information are shown to reveal the influence of climate and tectonics on the occurrence and attributes of carbonate deposits in these settings the vega formation a 150 m thick lower kimmeridgian siliciclastic fluvial sequence in asturias province northern spain constitutes a candidate for this approach this unit includes varied facies stromatolites rudstones packstones and wackestones containing oncoids intraclasts charophytes and shell bioclasts marlstones and polygenic calcareous conglomerates that formed in a low gradient fluvial lacustrine system consisting of shallow low sinuosity oncoid bearing channels and pools within marshy areas with sporadic coarse alluvial deposition the sedimentological attributes indicate common erosion by channel overflow and rapid lateral changes of subenvironments caused by water discharge variations the carbonate fluvial lacustrine system developed near uplifted marine jurassic rocks the occurrence of the system was conditioned by normal faults active during the deposition of the unit that favoured i springs of hco3 ca rich water from a rhaetian sinemurian carbonate rock aquifer and ii carbonate deposition in areas partially isolated from the adjacent siliciclastic fluvial system the microbialite 13c and 18o values support deposition in a hydrologically open system fed by ambient temperature meteoric water with riparian vegetation three types of lamination in the stromatolites and oncoids reflect distinct morphological types of cyanobacterial communities the textural pattern of lamination parallels 13c and 18o changes suggesting short term cycles of precipitation and temperature a moderately to strongly contrasted seasonal and or pluriannual precipitation regime is inferred from the cyclic 13c pattern of the lamination and from the discontinuous and asymmetrical growth of oncoids thus the isotopic and sedimentological attributes of the carbonate deposits were linked to short term climate changes associated with semi arid conditions consistent with the studied climatic zone

stable isotope geochemical study of pamukkale travertines new evidences of low temperature non equilibrium calcite water fractionation abstract in this paper we present the first detailed geochemical study of the world famous actively forming pamukkale and karahayit travertines denizli basin sw turkey and associated thermal waters sampling was performed along downstream sections through different depositional environments vent artificial channel and lake terrace pools and cascades of proximal slope marshy environment of distal slope 13 c travertine values show significant increase from 6 1 to 11 7 pdb with increasing distance from the spring orifice whereas the 18 o travertine values show only slight increase downstream from 10 7 to 9 1 pdb mainly the co 2 outgassing caused the positive downstream shift 6 in the 13 c travertine values the high 13 c values of pamukkale travertines located closest to the spring orifice not affected by secondary processes suggest the contribution of co 2 liberated by thermometamorphic decarbonation besides magmatic sources based on the gradual downstream increase of the concentration of the conservative na k cl evaporation was estimated to be 2 5 which coincides with the moderate effect of evaporation on the water isotope composition stable isotopic compositions of the pamukkale thermal water springs show of meteoric origin and indicate a local meteoric water line of denizli basin to be between the global meteoric water line craig 1961 and western anatolian meteoric water line imsek 2003 detailed evaluation of several major and trace element contents measured in the water and in the precipitated travertine along the pamukkale mm section revealed which elements are precipitated in the carbonate or concentrated in the detrital minerals former studies on the hungarian egerszalok travertine kele et al 2008a b 2009 had shown that the isotopic equilibrium is rarely maintained under natural conditions during calcite precipitation in the temperature range between 41 and 67 c in this paper besides the detailed geochemical analyses along downstream sections we present new evidences of non equilibrium calcite water fractionation in lower temperature range 13 3 to 51 3 c our measurements and calculations on natural hot water travertine precipitations at pamukkale and egerszalok revealed that the 18 o travertine is equal with the 18 o hco3 at the orifice of the thermal springs which means that practically there is no oxygen isotope fractionation between these two phases high rate of co 2 degassing with rapid precipitation of carbonate could be responsible for this as it was theoretically supposed by o neil et al 1969 thus for the determination of the deposition temperature of a fossil travertine deposit we propose to use the water bicarbonate oxygen isotope equilibrium fractionation instead of the water travertine fractionation which can result 8 9 c difference in the calculated values our study is the first detailed empirical proof of o neil s hypothesis on a natural carbonate depositing system the presented observations can be used to identify more precisely the deposition temperature of fossil travertines during paleoclimate studies

temporal and environmental significance of microbial lamination insights from recent fluvial stromatolites in the river piedra spain despite extensive research the environmental and temporal significance of microbial lamination is still ambiguous because of the complexity of the parameters that control its development a 13 year monitored record of modern fast accreting calcite stromatolites mean 14 mm year 1 from artificial substrates installed in rapid flow in the river piedra north east spain allows comparison of the sedimentological attributes of successive six month depositional packages with the known climatic hydrophysical and hydrochemical parameters of the depositional system the stromatolites are formed of dense porous and macrocrystalline composite laminae the dense and porous composite laminae which are composed of two to eight laminae consisting largely of calcified cyanobacteria are characterized by i dense composite laminae up to 15 mm thick mostly with successive dense laminae and minor alternating dense and porous laminae and ii porous composite laminae up to 12 mm thick consisting mainly of porous laminae alternating with thinner dense laminae most of the dense composite laminae formed during the warm periods april to september whereas most of the porous composite laminae developed in the cool periods october to march each dense and porous composite lamina represents up to or slightly longer than six months the alternation of these two types of composite laminae parallels seasonal changes in temperature the dense and porous laminae result from shorter for example intraseasonal variations in temperature insolation and hydrological conditions the macrocrystalline laminae with crystals 100 m long occur isolated and grouped into composite laminae up to 1 7 mm thick their occurrence suggests the absence or poor development of microbial mats over periods of weeks to several months thus stromatolite lamination can record different order periodic and non periodic changes in the magnitude of environmental parameters over a single year these results hold important implications for the temporal and environmental interpretation of lamination in microbial structures

regional tectonic framework of the pranhita godavari basin india abstract the pranhita godavari gondwana rift pgr has a co genetic relationship with permo triassic reactivation of the narmada son geofracture nsg the satpura gondwana basin represents the terminal depocentre against the nsg which restricted the northwestward propagation of the pgr the ne sw tensional stress responsible for the nw se trending pgr could not propagate beyond the ramp formed by uplift along the nsg and transformed kinetically into an ene directed horizontal shear along the nsg inducing large scale strike slip movements the latter dynamics were responsible for ene extension of the satpura rift as a pull apart basin the pgr extends up to the present east coast of india where it is apparently terminated by the ne sw trending bapatla ridge along the eastern ghat rift egr the subsurface data however shows that the pgr extends across the bapatla ridge and continues beneath the cretaceous tertiary sediments of the krishna godavari basin kg in the egr thus the permo triassic pgr appears to have continued in the indo antarctic plate before the cretaceous break up the egr during break up of the continents cuts across the pgr and the kg basin was superimposed on it the pgr site is located on a paleo suture between the dharwar and bastar proto cratons the master faults developed bordering the rift and the intra rift higher order faults followed the pre existing fabric the transverse transfer zones manifested as basement ridges divide the rift into segments of tectono sedimentary domains the major domains are the chintalapudi godavari and chandrapur sub basins each of which subsided differentially the central godavari sub basin subsided most and shows maximum structural complexity and sediment accommodation the rifting started with initial half graben faulting along the northeastern master fault and expanded by successive half graben faulting this gave rise to intra basinal horsts and grabens which exercised control on the syn rift sedimentation the southeastern boundary fault developed as a strike slip fault in response to plate rotation and the rift expansion was constrained by it the basin fill sediments were deposited during two rifting events early permian to early jurassic lower gondwana rifting and early cretaceous upper gondwana rifting the lower gondwana sedimentation started with a pre rift crustal sagging over the rift site and was filled by glaciogenic talchir sediments this was followed by syn rift fluvial sedimentation in repeating cycles during the early to late rift stages early cretaceous chikiala and gangapur sediments were deposited during the upper gondwana rifting the fluvial cycles were tectonically controlled during each rift stage the absence of igneous intrusions indicates that the pgr is a passive rift in contrast to the rifts developed in the nsg zone

quaternary paludal tufas from the ben younes spring system gafsa southwestern tunisia interactions between tectonics and climate abstract tufa deposits that can be fit into a single depositional model are restricted to relatively few publications in the geological literature this paper presents a detailed sedimentological study of quaternary early holocene paludal tufas partly exposed in the ben younes piedmont field data reveal five main paludal lithofacies phytoherm framestones sapropelitic tufa microdetrital tufa microbial laminites and lime muds radiocarbon dating of residual organic matter in tufa shows that the tufa ranges in age from 8790 50 to 3230 60 bp most tufa deposits appear to remain preserved during the different stages of their development lithification and diagenetic modifications of tufa show two major trends an increase in the average carbonate grain size and non selective dissolution of the fabric where deposits are exposed to meteoric diagenesis the studied tufas are water limited and the importance of climate in their formation is as major as implied in other mediterranean equivalents the predominance of paludal conditions in this area is controlled by the flat substrate the spring locations and the water supply the gafsa strike slip fault aside its tectonic role acts as a major regional sill that controlled paleoflow directions discharge locations content volume rate and fluctuations of the water supply

does climate control the morphological fabric of freshwater carbonates a comparative study of holocene barrage tufas from spain and britain abstract calcium carbonate production in most freshwater tufa systems is controlled by a combination of physico chemical precipitation and biomediation associated with procaryote microphyte biofilms inorganic precipitation is dominant under turbulent flow regimes whereas biomediation necessitates sluggish flow or static water we show here that temperature is also likely to affect tufa formation rates and architecture leading to the development of a clearly definable range of fabrics two contrasting models are proposed warm semi arid tufas well seen in the ruidera pools national park albacete province central spain where tufa barrages consist of vertical narrow rimmed arcuate structures frequently these are bounded both upstream and downstream by deep lakes laterally accreting mammilate stromatolites dominate the upper two thirds of lake margin subaqueous overhangs whereas conical growth forms dominate shady basal parts of subaqueous overhangs dense reed stands grow in thin peats on top of the vertical lake margin walls resistivity survey and percussion augering show up to 20 m of earlier lake fill which is banded into dark and pale beds the upper 10 m accumulated in 4600 years there is little or no preservation of organic material within these deposits cool temperate tufas typified by slowly accumulating barrage tufas at caerwys n wales and alport n derbyshire uk transverse barriers across valleys are dominated by arcuate buttress developments built up of downstream facing tabular carbonate sheets pools upstream of the barriers are shallow dominated by clotted lime mud and organic sapropels in their depocentres and stromatolite dominated laminar to low domes or oncoidal facies in broad marginal zones marginal stands of semi aquatic vegetation are rooted in thick peats but frequently are also encrusted around their exposed stems by oncoidal carbonate fabric preservation is good for the carbonate material however marginal peats rapidly oxidise and stem encrustations collapse to produce cylindrical oncoid beds depocentre sapropels are always preserved and contain important pollen records otherwise rare in carbonate regions carbonates in both models accumulate relatively rapidly they have a moderate preservation potential within late cenozoic terrestrial successions the distinctly different characteristics of their preserved fabrics should allow recognition of two contrasting climatic models for fluvial barrage tufas in ancient deposits

facies evidence of hydroclimatic regime shifts in tufa depositional sequences from the arid naukluft mountains namibia the naukluft mountains on the eastern edge of the central namib desert contain numerous largely inactive fluvial tufas within headwater streams of the ephemeral tsondab river which currently terminates in a vlei in the namib sand sea extensive tufa barrage deposits have been mapped and described along the brandfontein river a small 6 5 km long tributary of the tsondab river here a series of large barrages have developed along the river system which culminate in a large tufa cascade feature at the mountain front tufa facies at brandfontein include cemented colluvial and fluvial gravels and boulders moss tufas as well as reed and root facies the sequences provide evidence of several cut and fill phases which are interpreted as indicating alternating periods of tufa deposition and fluvial downcutting the brandfontein tufas are used to propose a three phase arid fluvial tufa deposition model in which erosive high magnitude low frequency floods punctuate periods of quiescence and tufa deposition extensive downstream prograding ramped barrages and tufa cemented fluvial gravels are key components of this tufa deposition model which illustrates the role of climate and topography in shaping tufa deposit morphologies

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

the effect of drainage reorganization and climate on the sedimentologic evolution of intermontane lake systems the final fill stage of the tertiary ebro basin spain abstract stratigraphic and sedimentologic analyses and geochemical data from the middle and late miocene record in the southwestern central sector of the ebro basin have allowed the evolution of its neogene final fill stage to be characterized and its controlling factors to be discerned the focus of these analyses was the distinct depositional environments that occurred over time tecto sedimentary units t6 t7 and t8 twelve main associations of lacustrine palustrine fluvial and alluvial facies revealed that the sedimentary processes leading to the formation of the units occurred in different environments in units t6 and t7 middle and late aragonian i e langhian serravallian and in unit t8 vallesian turolian i e tortonian the depositional environments of units t6 and t7 encompassed a closed shallow carbonate lake system with wide palustrine fringes the lake was fed by small sandy and gravelly channels flowing from the southwest iberian range and a sandy fluvial system from the north pyrenees inputs were also received from a southeastward flowing axial fluvial system as the mouths of these systems commonly formed small deltaic sandy lobes on the northern lake margins the evolution of unit t6 and in particular that of unit t7 was greatly influenced by pyrenean tectonics the depositional environments of unit t8 included the occurrence of the as but this system was soon replaced by an open shallow carbonate lake surrounded by wide and shallow oncoid bearing channels and palustrine tufaceous areas on its west southwest margin distinct depositional events from the south and west which involved intra t8 erosion resulted in minor coarse alluvial deposits the carbonate system of unit t8 occurred in an open depression created after local erosion of the pre t8 deposits and subsequent northward shifting of the as since early deposition of unit t8 the origin of which was related to late contractile deformation in the northwestern iberian range bicarbonate and calcium rich water from the mesozoic carbonate rocks in the iberian range fed the t8 system sedimentologic 13c 18o and trace element data support the change from closed to open drainage and strongly suggest a general climate trend toward wetter and cooler conditions which is consistent with the middle late miocene climate evolution of other european regions despite the general timing coincidence between unit t8 deposition and the opening process of the ebro basin the attributes of the t8 deposits are inconclusive to support the previous hypothesis that the fluvial lacustrine palustrine system could be directly connected to the emptying drainage of the basin into the mediterranean sea instead the results of this study demonstrate the combined influence of tectonics and climate on the evolution of the final fill stage of this part of the ebro basin these results may be useful for assessing the influence of such allocyclic factors on the sedimentologic hydrologic and geochemical evolution of other intermontane lake basins

composition structure and evolution of a lacustrine carbonate margin dominated by microbialites case study from the green river formation eocene wyoming usa abstract during mid eocene times the northwestern margin of the gosiute lake wyoming has been characterised by the extensive development of a microbialite dominated carbonate sequence corresponding to the laney member of the green river formation thus providing a potential analogue for petroleum carbonate reservoirs developed in similar marginal lacustrine settings a detailed sedimentological study carried out on the little mesa plateau near labarge sw wyoming allows the reconstruction of 1 lateral and vertical facies variations of the carbonate sequence across the margin 2 development patterns of complex microbial bioconstructions and 3 the evolution of the margin through time the carbonate sequence up to 18 m thick starts with the deposition of sandy limestones which fill channels in the underlying siliciclastic unit of the cathedral bluff formation the increasing microbial contribution in the upper part of the sequence results in the development of large insect microbial build ups which represent up to 80 of the total volume of the carbonate deposits and which aggregated to form reef like geometries up to several tens of metres in diameter including bioherms spur and groove alignments and reef flat structures the initiation and development of the lacustrine carbonate platform was controlled both by the general lake expansion associated to the eocene climatic optimum and by local drainage diversions responsible for a new water inflow in the basin from the northern volcanic provinces short term lake level changes driven by high frequency climate fluctuations which are superimposed to this general transgressive trend may explain the discontinuous and polygenic growth of the individual insect microbial build ups the basin infilling by prograding alluvial volcaniclastic deposits originated from the northwestern volcanic province caused the rapid turn off of the marginal lacustrine carbonate factory during mid eocene time

facies model of a semiarid freshwater wetland olduvai gorge tanzania the sedimentology and stratigraphy of a freshwater wet land in early pleistocene 1 75 ma volcaniclastic deposits olduvai gorge tanzania are characterized using texture mineralogy micro fossils and stratigraphic description to create a depositional facies model the freshwater wetland was located on the margin of a semi arid closed basin containing a playa lake the lake margin deposits are dominated by two distinct lithologies waxy claystones and earthy sediments waxy sediments are olive green dense claystones that con tain authigenic minerals such as trona and represent a fluctuating saline alkaline lake hay 1976 earthy sediments are beige friable siltstones that contain siliceous microfossils bone fragments and minor pebbles they represent the freshwater wetland microfossils from the earthy sediments and diatomites indicate freshwater marsh biota with some rare salt tolerant species associated lithofacies are diatomite carbonate and sandstone interpretation of vertical and lateral lithofacies variations in the 2 km 2 wetland based on 50 excavations identified seven distinct sub environments spring deposits perennial marsh pool ephemeral wet land fringing wetland wetland channel and ephemeral stream the stratigraphic sequence estimated to represent an 40 50 kyr long interval indicates that persistent 10 3 yr wet periods prevailed dur ing the deposition of thick waxy clays when the lake expanded and flooded the wetlands and equally long intervening dry periods caused the lake to contract allowing the flourishing of wetlands and accretion of earthy sediment the lithofacies associations in the olduvai paleo wetland provides an important first step in the development of a de positional environmental model for freshwater wetlands that can be tested elsewhere particularly in arid and semiarid settings

basin scale changes in floodplain paleosols implications for interpreting alluvial architecture abstract floodplain paleosols in time equivalent strata of the willwood for mation differ in terms of paleodrainage and degree of pedogenic development ancient soils were more poorly drained and more strongly developed in one area compared to a second area about 45 km away this difference in drainage is attributed to parent material the more poorly drained paleosols formed in an area with less permeable clay rich floodplain deposits in the stratigraphic interval that accumulated more slowly paleosols are more strongly developed less numerous and thicker than in the more rapidly accumulating stratigraphic interval these differences are attributed not only to different sediment accumulation rates which are commonly considered to control the degree of ped ogenic development but also to differences in avulsion frequency a simple model is offered to show how paleosols change with varying basin subsidence rates and the relationship between avulsion frequency and accumulation rate when avulsion frequency increases more rapidly than sediment accumulation rate an increase in subsidence rate causes strongly developed paleosols to be overlain by a stratigraphic interval with paleosols that are less well developed thinner and more densely spaced when avulsion frequency is not related to accumulation rate as early models of alluvial architecture assumed an increase in subsidence rate produces a stratigraphic section in which strongly developed paleosols are overlain by paleosols that are less well developed thicker and more widely spaced study of the thickness and degree of development of floodplain paleosols can be used together with more traditional studies of alluvial architecture to provide a clearer understanding of the factors that influenced the stratigraphic architecture in a particular alluvial basin

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

a multidisciplinary approach to understanding carbonate deposition under tectonically controlled hydrothermal circulation a case study from a recent travertine mound in the euganean hydrothermal system northern italy a multidisciplinary study was carried out on an upper pleistocene travertine mound montirone hill abano terme south of padova veneto italy with the aim of developing a comprehensive understanding of the processes interacting in structurally controlled thermal springs and the consequent deposition of thermal limestones the sedimentology geochemistry structural characteristics and hydrogeology of the mound which is associated with the euganean geothermal field and the related complex structural framework of the schio vicenza fault system were investigated a palaeo environmental model of the deposit has been reconstructed clarifying the connection between the travertine deposition and the regional structural setting calcium rich thermal waters rose from spring orifices estimated temperature from 54 c to 61 c based on geochemical calculations and produced a mound made of coalescent shield like bodies the dominant lime mudstone facies resulted from the accumulation of lime mud at the bottom of shallow crater like basins located on top of stacked cones soft sediment deformations affecting the lime mud sediment were most probably produced by the recurrent uprising of gas bubbles the overlying crystalline crusts were deposited on the flanks of the mound by waters overflowing from the vents with laminar flux a deep hydrothermal circuit with a long period of water rock interaction is supported by geochemical analyses furthermore a local extensional regime enhancing the migration of thermal fluids to the surface is inferred based on the results of the structural analysis carried out on the fault fracture mesh that affects the mound these results corroborate the well established relation among travertine deposits hydrothermal systems and fault systems and substantiate the structurally controlled conceptual model of the euganean hydrothermal system suggesting that both the thermal and the fault systems were active at least since 34 ka

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

diagenesis or dire genesis the origin of columnar spar in tufa stromatolites of central greece and the role of chironomid larvae two greek pleistocene tufa stromatolites were examined petrographically and with stable isotope geochemistry to determine whether calcite spar is of primary or diagenetic origin the younger ca 100 ka tufa from zemeno primarily is micritic with primary columnar calcite spar restricted to areas immediately above chironomid larval tubes this relationship suggests that chironomid larval feeding behaviour is responsible for the development of zemeno tufa columnar calcite probably involving biological substances smeared onto the tufa surface most micritic crystals are not suitably oriented to allow later post depositional growth resulting in columnar fabrics the older ca 1 ma predominantly sparry tufa from nemea contains some chironomid tubes and organic cyanobacterial filaments preserved in crystal fans but also contains many fabrics found in primary speleothem spar columnar spar here is unlikely to be the result of post depositional crystal growth a comparison of stable isotopic trends between the two tufa deposits suggests that both contain interpretable seasonal trends and implies little or minor post depositional alteration of either tufa consequently there is no basis for the common assumption that sparry tufa fabrics must be of diagenetic origin

constraints on pleistocene pluvial climates through stable isotope analysis of fossil spring tufas and associated gastropods kharga oasis egypt abstract stable isotope analyses of fossil spring carbonates tufas and freshwater gastropods melanoides tuberculata from the currently hyperarid western desert of egypt indicate that this region received enough precipitation to support a small perennial lake during the height of the oxygen isotope stage 6 5e pluvial event and a substantial volume of spring discharge during prior pluvial phases tufa and gastropod oxygen isotope ratios are generally low relative to modern precipitation in the region confirming that the majority of pleistocene pluvial precipitation came from an atlantic source as determined by previous workers mean tufa 13c 2 pdb suggests a significant proportion of c4 vegetation in the recharge area of the tufa depositing springs while the paucity of tufas with 13c greater than 0 suggests that equilibrium between spring water and atmospheric co2 represented an endpoint for the evolution of spring water carbon though spring carbonate deposition requires a substantial increase in humidity in central egypt relative to modern conditions high variation in tufa 18o up to 4 within individual stratigraphic units as well as positive covariance between tufa carbon and oxygen isotope ratios reflect significant effects of evaporation on spring water during tufa formation similarity in 18o and 13c values of tufas from different stratigraphic units indicates that climatic conditions did not vary significantly among pluvial phases recorded by spring carbonate deposition the lack of substantial carbonate formation at tufa localities during the holocene pluvial phase however suggests that tufa deposition represents substantially wetter conditions than have existed during holocene time

depositional properties and geochemistry of holocene perched springline tufa deposits and associated spring waters a case study from the denizli province western turkey the guney waterfall area is a perched springline tufa site developed on the southeast slope of the buyuk menders river near guney town in the denizli province western turkey the site is away 12 km from the town and 72 km from the city center of denizli the spring waters emerge from the boundary between palaeozoic marble and micaschist and precipitated tufa deposits downslope at the altitudes ranging from 220 to 400 metres the tufa deposits cover an area of about 20 hectars flat upper surfaces of the deposits are indicative of mature stage the waters are of the ca hco3 type and supersaturated with respect to caco3 the stable isotope values of the spring waters are 49 94 for 2h and 7 15 for 18o the 13c and 18o values of active and passive tufa samples are in the range from 9 13 to 6 0 and from 8 44 to 7 40 respectively these isotopic values are typical for fresh water tufa the passive tufas give the 14c age in the range from 2000 to 5800 yr bp according to the 14c age data passive tufas are not older than holocene the stable isotope composition is similar south european examples

anatomy and controlling factors of a late cretaceous aeolian sand sheet the marilia and the adamantina formations nw bauru basin brazil abstract few previous studies have given significant consideration to the palaeosols in aeolian sand sheet sedimentary successions and mainly to their palaeoenvironmental and stratigraphic meaning in interaction with the deposits these themes are considered in this study that deals with the depositional architecture and the factors controlling the construction accumulation and preservation of an ancient aeolian sand sheet that forms part of the adamantina and marilia formations in the bauru basin late cretaceous brazil in the nw portion of the bauru basin these two units ca 220 m thick consist of sandstone and secondarily of sandy conglomerate and mudstone and are characterised by vertically alternated palaeosols and deposits facies analyses of the deposits and macroscopic characterisation of the palaeosols in 45 outcrops were integrated with laboratory analyses that consisted in descriptions of slabs of rock samples petrographic analyses clay mineralogy determination geochemical analyses of the major oxides and micromorphological characterisation of the palaeosols three architectural elements were recognised palaeosols wind ripple dominated aeolian sand sheet deposits and ephemeral river deposits the palaeosols constitute 66 of the entire sedimentary succession and consist principally of aridisols and subordinately of alfisols vertisols and entisols the wind ripple dominated aeolian sand sheet deposits 25 are composed of sandstone organised in translatent climbing wind ripple strata and secondarily of sandstone and mudstone deposited by infrequent floods the ephemeral river deposits 9 consist of sandy conglomerates 4 m thick and ca 2 km wide wind ripple dominated aeolian sand sheet deposits formed during relatively dry climate period on an unstable topographic surface of an aeolian sand sheet where aeolian deposition or erosion prevailed palaeosols and ephemeral river deposits formed in a more humid climate period on a stable topographic surface of the aeolian sand sheet six bounding surfaces permitted the subdivision of the study formations into genetic geological bodies revealing different spatial and temporal orders two first order surfaces separate mature palaeosol profiles aridisols alfisols and vertisols from overlying aeolian deposits or other mature palaeosol profiles a second order surface separates immature palaeosols entisols from overlying aeolian deposits a third order surface constitutes the channel bottom a fourth order surface is located at the bottom of flood deposits a fifth order surface divides translatent wind ripple the constructional phase of the aeolian sand sheet occurred during the relatively dry climate period when the available sediment was supplied from the material originally deposited by rivers and stored during a more humid period primary supply and by soil erosion during a drier climate secondary supply the accumulation surface was controlled during the drier climate by cemented bk horizons over aridisols and by the force of the wind blowing over the other soils or deposits otherwise during the more humid climate the accumulation surface was a stabilised surface represented by the soil preservation was dominated by tectonically induced subsidence and burial

stable isotopes of holocene calcareous tufa in southern poland as paleoclimatic indicators abstract the isotopic composition of oxygen in freshwater calcareous tufa seems to be a sensitive indicator of past climatic changes results of measurements of c 18 o and c 13 c in tufa samples dated with the 14 c method are used to reconstruct holocene climatic changes in southern poland values of c 18 o obtained on tufa samples from four sites raclawka rzerzu nia trzebienice sieradowice representing different hydrodynamic conditions of tufa sedimentation seem to form a selfconsistent series these values with some simplifying assumptions concerning the course of tufa sedimentation were therefore used to estimate mean annual temperatures in the interval ca 9500 2000 yr b p when the resulting curve of thermal changes in southern poland is compared with changes of deposition and erosion of tuffaceous sediments and with results of other methods of reconstruction of paleoclimate in central europe a reasonable agreement among the different specific methods is seen

late permian vertebrate community of the pranhita godavari valley india abstract the kundaram formation of the pranhita godavari valley yields the only late permian multispecies terrestrial vertebrate assemblage from india this includes various medium and small dicynodonts such as endothiodon oudenodon kingoria emydops cistecephalus and pristerodon at present two species of endothiodon e mahalanobisi and e uniseries are known apart from these dicynodonts the kundaram vertebrate fauna also contains a medium sized gorgonopsian and a small captorhinid the material from the red mudstone dominated kundaram formation includes numerous isolated disarticulated skulls and lower jaws postcranial elements are relatively rare except for a few broken limb ends and vertebrae the bones are encrusted by iron rich matrix and most of them had suffered deformation this skull dominant accumulation is attributed to prolonged aerial exposure prior to burial resulting in disarticulation of the skeletons and subsequent inundation by floodwater the limb bones and other postcranial elements of the already disarticulated skeletons were winnowed out by shallow competent flow while the relatively heavier skulls and lower jaws resisting transportation were buried near the site of death the late permian scenario of the pranhita godavari valley was characterised by the dominance of herbivores this abundance of herbivores at the base and the presence of relatively few carnivores and omnivores at the top of the kundaram food pyramid indicate a trophic structure similar to that of the modern day terrestrial ecosystem

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

petrology of caliche derived peloidal calcirudite calcarenite in the late triassic maleri formation of the pranhita godavari valley south india abstract the maleri formation late triassic of the pranhita godavari valley south india is a continental red bed sequence represented mainly by red clays with a few sheet like bodies of channel fill sandstone crudely bedded and cross bedded peloidal calcirudite calcarenite occurs at the base of fining upward sequences in multistorey sand bodies and also as discrete solitary lenses within red clay the calcirudite calcarenite consists mainly of calcite cemented spherical peloids which are made up of micrite and microspary calcite with microfabrics characteristic of caliche pure calcitic peloids are often reddened and those having a quartzose component are generally not red the paucity of broken and abraded peloids close association with intraformational materials and other evidence indicate a local source of the peloids the microfabric of the peloids suggest their derivation from caliches available evidence favours a pedogenic origin for the peloids which mostly developed by displacive precipitation in a set up of alternate wetting and drying the lack of in situ caliche profiles in the maleri sequence and the rarity of compound grains imply that the peloids were derived from incipient caliche profiles which were localized at or near the surface and were completely stripped off by subsequent erosion the ghost caliche profiles suggest the presence of periodically stable levels in the maleri alluvial plain and low to moderate rates of alluviation the residence intervals of channels were long enough to allow incipient pedogenesis in the temporarily stable inactive areas in the present context the predominance of smectite in fines the poor floral content the maleri faunal assemblage and the paucity of evaporites point to a low seasonal rainfall in a semi arid climatic environment

the lower permian freshwater carbonates of the slawkow graben southern poland sedimentary facies context and stable isotope study abstract during early permian times the post hercynian rift valley known as the slawkow graben was filled with typical continental molasse deposits including fanglomerates and olistolites playa flat sediments with evaporites volcaniclastics and carbonates deposited in small spring fed basins oasis environment lithofacies variability lithofacies relationships sedimentary structures and paleokarst data indicate a highly changeable sedimentary environment controlled by climate syndepositional faulting and accompanying volcanism differential uplift resulted in a high relief topography the basin margin mountains probably having a relative altitude of up to 1000 m the stable isotopic composition 13 c 18 o of the spring related carbonates indicate seasonal temperature differences of up to 15 c a value that is close to the average annual temperature amplitude in the present day subtropical zone other environmental indicators e g red beds evaporites braided stream sediments corroborate the isotopic interpretation a longer term 6 7 year cycle reflected in 18 o composition of the carbonate is attributed to rainfall fluctuations

the criteria for the biogeneicity of microbially induced sedimentary structures miss in archean and younger sandy deposits abstract the identification of fossils or biogenic sedimentary structures in rocks of archean age is difficult because similar lithological features could rise from purely physical or chemical processes alone therefore it is important to define criteria that serve the secure definition of a fossil or structure in question as of biological origin such criteria have been established for stromatolites and microfossils this contribution discusses the 6 criteria of biogeneicity of microbially induced sedimentary structures miss those structures are found in sandy deposits of early archean age to the present and rise from the interaction of benthic microbiota with physical sediment dynamics the six criteria for their biogeneicity are i miss occur in rocks of not more than lower greenschist facies ii in stratigraphic sections miss correlate with turning points of regression trangressions iii miss correlate with a characteristic depositional facies that enhances the development and the preservation of microbial mats iv the distribution of miss correlates with the ancient average hydraulic pattern v the geometries and dimensions of fossil miss correspond to that of the modern ones vi the miss include at least one of 9 specific microtextures

recognition and implications of eocene tufas and travertines in the chadron formation white river group badlands of south dakota there are few descriptions of pre quaternary tufa or travertine yet these deposits have important climatic hydrological and tectonic implications in the badlands of south dakota the late eocene chadron formation contains a variety of tufa fluvial lacustrine paludal and perched springline types travertine and calcrete pedogenic and non pedogenic types in fluvial channels tufas and tufa barrages oncolites tufa lithoclast conglomerates and phytoherms are transitional to travertines pseudostromatolitic boundstone gravels and small pinnacle resurgences with rimstone edges and pools lacustrine tufas formed in small ponds adjacent to other types of tufas and are similar to the low energy bench margin facies types observed in modern groundwater fed temperate zone hardwater lakes paludal tufas are laterally discontinuous sheets of pisoid intraclast wackestone that fill palaeotopography distal perched springline tufas are mounds of numerous sloping tufa sheets concretions and rhizoliths associated with palaeosols are recognized as pedogenic calcretes whereas non pedogenic calcretes are variably cemented vertically oriented conduits for palaeogroundwater discharge that are located in fault zones these deposits resulted from palaeogroundwater discharge along faults during the late eocene coeval unroofing of the black hills uplift created a regional groundwater flow system through karsted palaeozoic limestones exposed in the black hills the chadron formation is an avulsion dominated siliciclastic unit yet important bodies of carbonate accumulated in it as a result of groundwater processes

stable isotope characterization of the miocene lacustrine systems of los monegros ebro basin spain palaeogeographic and palaeoclimatic implications the lacustrine carbonate facies from three allostratigraphic units n1 n2 and n3 of miocene age in the los monegros region ebro basin are characterized isotopically the dominant facies are marls laminated limestones stromatolitic limestones massive limestones and bioturbated limestones these are associated with lacustrine sulphate deposits and distal alluvial facies palaeohydrological reconstructions of the study area are supported by the isotopic and the mineralogical composition of the carbonates massive and bioturbated limestones occupy a very similar compositional domain and have the lowest isotopic compositions of all the facies 9 18opdb 4 5 and 6 4 13cpdb 0 4 reflecting a short residence time of the water and variable commonly high influence of biogenic co2 laminated limestones and stromatolites define a comparatively enriched domain with 18o values ranging from 6 to 0 and 13c values ranging from 3 5 to 0 these values indicate stronger evaporation and enhanced 12c assimilation due to intense biological activity during periods of longer water residence time marls have isotopic values intermediate between these two domains and correspond to periods of lacustrine dilution dolomite bearing samples mainly laminated and stromatolitic facies show a 18odol cal 7 5 with respect to calcite from the same facies while 13c values show very little enrichment up to 1 the positive correlation r 0 85 between 18o and dolomite contents suggests that dolomite resulted from the progressive evaporative concentration of a single water mass and not from the mixing of waters of different compositions the dolomite is thought to be primary or at most the product of very early diagenetic processes the isotopic composition of the facies and their spatial and temporal variations depend on the depositional environment and were constrained by changing regional paleogeography isotopic trends from units n1 to n3 upper agenian vallesian period display a regular depletion in heavy isotopes that indicates a climatic change towards wetter conditions

preservation of elemental and isotopic source identification of sedimentary organic matter the amount and type of organic matter in the sediments of lakes and oceans contribute to their paleoenvironmental and paleoclimatological records only a small fraction of the initial aquatic organic matter survives destruction and alteration during sinking and sedimentation selective degradation modifies the character of the surviving small fraction of organic matter which becomes incorporated in bottom sediments organic matter alterations can continue to sub bottom depths of hundreds of meters corresponding to millions of years source and paleoenvironmental information nonetheless remains preserved in the molecular elemental and isotopic compositions of organic matter c n and 13c values of total organic matter in particular appear to retain paleoenvironmental information for multi myr time periods

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

the distribution and discrimination of shallow authigenic carbonate in the pliocene pleistocene palomas basin southern rio grande rift nine types of authigenic carbonate are present in the pliocene pleistocene alluvial fan and axial fluvial sediment of the palomas half graben in the southern rio grande rift pedogenic and other vadose carbonate includes 1 pedogenic carbonate of stage ii and stage iii morphology underlying bw and bt horizons 2 mudstones in which the carbonate nodules may be pedogenic or the result of shallow groundwater invasion of the vadose zone 3 pedogenic calcic nodules and tubules in eolian sand and 4 gully bed cement of proximal fan conglomerates formed by infiltration and evaporation of surface runoff shallow groundwater carbonate exists as 5 thin 30 50 cm massive beds with an upper fringe of nodules and tubules precipitated at the water table and in the capillary fringe 6 thick 1 5 3 m massive beds deposited by lateral flow of groundwater or at springs and 7 thin 30 cm calcified root mats associated with near surface water saturated sediment or springs phreatic spar cements 8 occupy the interstices of conglomerates and sandstones and locally exist as 9 oriented concretions groundwater carbonates are best developed near the toes of the large hanging wall derived alluvial fans whereas phreatic cement preferentially exists in footwall derived alluvial fan conglomerates pedogenic carbonate is distinguished from groundwater carbonate by the association with other diagnostic paleosol horizons a predominantly vertical arrangement of root traces peds desiccation cracks and calcic tubules and by gradational contacts the 13 c and 18 o values are similar among pedogenic and shallow groundwater carbonate although locally nodules in eolian sand and gully bed cement have higher 18 o values perhaps due to the effects of evaporation some phreatic cements may be distinguished from pedogenic and shallow groundwater carbonate by lower values of 13 c and 18 o authigenic carbonate in footwall derived alluvial fan sediment has consistently higher values of 13 c than that in hanging wall derived sediment which may reflect differences in vegetative type and or density on either side of the basin

palaeosols as indicators of geomorphic stability in two old red sandstone alluvial suites south wales palaeosols fossil soils are abundant in the alluvial late silurian early devonian moor cliffs formation and rat island mudstone freshwater west formation of south dyfed south wales the palaeosols occur in thick mudstones deposited on floodplains under a seasonal semi arid climate and represent vertisol type soils simple single profiles are rare and most of the mudstone intervals exhibit complex overprinted profiles however a major difference exists between the palaeo vertisols in each of the two units studied the moor cliffs formation contains thick floodplain intervals with evidence of frequent erosion and reactivation of earlier soil horizons the associated coarser channel deposits mainly represent ephemeral streams the alluvial system was unstable flashy and prone to extensive stripping of stored floodplain sediment arroyos unstable ephemeral stream channels probably developed during this interval evidence for any marine influence on soil development is missing and previous speculations that the formation may represent deposition in an upper intertidal or supratidal system are not supported the rat island mudstone represents a complete contrast in that there was little or no stripping of floodplain sediments the channel deposits are typically of the fining upwards type representing more stable low sinuosity channels and with ephemeral stream floods by integrating the palaeosols a more detailed picture of the geomorphic history of these units can be formulated comparison with contemporary drainage basins indicates that a change in climate was a possible cause for the differences between the two units less frequent and more severe storms occurring during the deposition of the rat island mudstone

climatic control on palaeohydrology and cyclical sediment distribution in the plio quaternary deposits of the guadix basin betic cordillera spain abstract a cyclical pattern can be observed in the central sector of the guadix basin southern spain in the late pliocene quaternary alluvial fan deposits prograding into its axial valley a climatic significance has been attributed to this cyclicity on the basis of sedimentological and preliminary isotopic studies the progradation phases of the alluvial fans are here attributed to more arid time intervals in which the vegetation cover would be less developed erosion and sediment supply would be higher and base level would be lower in contrast the time intervals during which the fluvial system sediments dominated the area are inferred to be wetter and base level higher with vegetation cover retaining the soils and preventing erosion permanent water supply to the river would therefore facilitate the aggradation of the floodplain and prevent progradation of the fans starting from a litho bio and magnetostratigraphical frame provided for the area an age is assigned to the alternation of the reddish sediments of the transverse alluvial fans and the greyish to white fluvio lacustrine sediments of the axial drainage system a cyclicity of ca 100 ky has been identified in most of the alluvial fan progradation phases falling within milankovitch high frequency eccentricity periodicities correlation of the phases with insolation curves is accordingly discussed as a possible origin for the cyclicity finally the results offer new insights into early hominin occupation patterns in the region through the identification of predictable resources of permanent fresh water that would have remained available throughout the recorded time span that includes the early middle pleistocene transition even during times of aridification

influence of equatorial waves on the genesis of super typhoon haiyan 2013 abstractthe influence of equatorial wave disturbances on the genesis of super typhoon haiyan 2013 is investigated through spectral composite and ensemble sensitivity analysis of various observational datasets in combination with predictions from an operational ensemble under the favorable large scale environmental conditions of the asian monsoon combined with the madden julian oscillation mjo the incipient haiyan develops from a cyclonic disturbance that originates from a train of westward propagating mixed rossby gravity mrg waves haiyan eventually develops in the monsoon trough region at the leading edge of the moist mjo phase that has strong low level convergence high moisture content and weak shear along with high sea surface temperature these favorable environmental conditions promote the intensification of deep moist convection that facilitates the development of the cyclonic disturbance from an mrg wave into a tropical depression which later intensifies rapidly into super typhoon ha

sedimentological and geochemical characteristics of a fluvial travertine a case from the eastern mediterranean region a sedimentological and geochemical study was performed on the travertines in the southern part of the usak geothermal field western turkey to assess the applicability of a fluvial tufa facies model in interpreting late quaternary travertine deposits developed along the stream valleys that follow fault and fracture systems modern thermal 31 to 38 c springs are found on the floor of the valley between 480 m and 520 m above sea level the distribution and nature of travertine facies were determined from natural outcrops samples of the travertines and spring water were characterized using a range of geochemical and petrographic methods waterfall slope and pool facies associations consist of various combinations of travertine facies and subordinate detrital facies waterfall and slope facies associations of the older deposits occur where the springs emerged onto a hillslope or topographic break in contrast the pool facies association developed in depressions or flat areas that were fed by thermal springs the youngest generation 1 85 ka precipitated at lower elevations than the older ones 147 to 153 ka stable carbon and oxygen isotope values of the aksaz travertines range between 4 3 and 6 3 vienna pee dee belemnite and 12 6 and 7 2 vienna pee dee belemnite respectively the high d 13 c values suggest that the thermal waters were charged with isotopically heavy co2 of deep origin based on palaeotemperature calculations the temperatures of the palaeosprings are slightly higher up to 44 c than the present equivalents but sometimes the temperature is lower probably due to mixing with the stream water although the thermal waters occasionally are impeded by fluvial activity travertine precipitation occurs in the protected parts of the aksaz stream valley this contribution highlights the applicability of the fluvial facies model for tufa for the interpretation of travertine deposits worldwide

recent freshwater ooids and oncoids from western lake geneva switzerland indications of a common organically mediated origin abstract the shallow water sediments of western lake geneva are composed mainly of sand size coated grains ranging from oncoids to ooids in surficial sediments the coatings consist of anhedral microcrystals of low mg calcite and often show a well developed intercrystalline porous network containing bacteria and residues of degraded mucus nucleation occurs in close association with organic films formed by mucus produced by filamentous cyanobacteria and diatoms similarities between oncoid and ooid cortex crystal size shape and arrangement indicate that the processes controlling the building of these types of particle are identical in subsurface sediments the microstructure of the coatings changes considerably the intercrystalline porosity is reduced by aggrading neomorphism and the micritic porous and organic rich coatings are transformed into a dense xenotopic mosaic with scattered molds of filamentous cyanobacteria this occurrence of ooidal oncoidal sands in lake geneva may help in interpreting ancient lacustrine formations and brings additional information on the processes of genesis and diagenesis of coated grains

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

carbonate deposition in an ephemeral siliciclastic alluvial system jurassic shuttle meadow formation newark supergroup hartford basin usa abstract nonmarine carbonate accumulation from a sedimentologic perspective has multiple possible origins clastic load springs groundwater discharge soil development biochemical seasonal changes cave speleothems and eolian influx many of these carbonates contain diagnostic textures from which origin is easy to ascertain however differentiating between clastic and spring groundwater carbonates especially in depositional systems dominated by siliciclastics is not always simple here criteria for recognition are developed subsurface hydrology and tectonic origin of the depositional basin source rocks surrounding the basin sedimentologic packaging and extent of the carbonates in question as well as their sedimentary structures and fossil content and stable isotopic analyses of the carbonates can all aid in determining carbonate origin and correctly assessing sedimentary and basin evolution the present study focuses on a nonmarine carbonate deposit found within the jurassic shuttle meadow formation of the hartford basin one of many rift basins which formed as a result of the opening of the north atlantic ocean during the late triassic to early jurassic the upper 50 m of the formation at plainville connecticut is interpreted as continental in origin and is composed of five facies red ripple cross laminated muddy siltstones to sandstones fr sr massive red siliciclastic mudstones fm buff fine to medium grained horizontally laminated sandstones sh red to white disrupted calcareous shales fl3 and rare micritic carbonates pm facies fr sr sh and fm are interpreted as an alluvial plain system in an ephemeral setting with bedload sheetflooding as the dominant depositional mechanism similar to the channel country drainage system of central australia in addition preservation of lateral accretion sandstone sheets accretionary benches indicate that the shuttle meadow alluvial system was rapidly accreting the anomalous existence of carbonate beds in facies fl3 and pm in the smf bedload dominated siliciclastic sequence is attributed mainly to the unique nature of the clastic sediment load in the basin no direct evidence for a spring groundwater input is apparent the shallow carbonate lake margin or a pond with vegetation and periodic exposure is envisioned as the depositional environment the intraclastic texture of the micrites with rare primary relict lamination indicates early diagenetic alteration from root penetration desiccation cracks and burrowing

a sedimentological and stable isotopic study of travertines and associated sediments within upper triassic lacustrine limestones south wales uk the upper triassic in south wales is composed of up to 100 m of red dolomitic mudstones of the mercia mudstone group which overlie and are laterally equivalent to basin margin coarse clastic deposits in the sully island and dinas powys areas a series of carbonate deposits was laid down within small basins adjacent to the main bristol channel basin the rocks consist of dolomites containing replaced evaporites overlain by perilittoral freshwater limestones the limestones are fenestral intrasparites and contain abundant pedogenic and stromatolitic horizons as well as locally developed travertines evidence for vadose diagenesis within the limestones is common the travertines consist of sheets of fibrous calcite flowstone associated with pisoids and floe calcite most of the travertines consist of single sheets several millimetres in thickness although mounds up to 1 m in height and 5 m in diameter are also present the topmost metre of the limestones which has been dolomitized is deformed into tepee and megapolygonal structures the carbon and oxygen stable isotopic composition of the limestones suggests that they were precipitated in low salinity waters successive samples from individual bands of flowstone show a covariance of 18c and 13c which is consistent with the mixing of resurgent groundwaters with pools of more evolved waters at the surface the sedimentological and geochemical evidence suggests that the limestones were deposited in a small enclosed basin fed by upwelling meteoric groundwaters in an environment distinct from that in which the laterally equivalent gypsiferous red mudstones were formed

sedimentology and isotopic composition of upper palaeocene to eocene non marine stromatolites eastern ebro basin ne spain stromatolites are abundant in upper palaeocene to eocene fluvial deposits from the eastern ebro basin whereas they are scarce in the lacustrine facies the fluvial stromatolites display a variety of growth forms oncoids domes laminated crusts and locally irregular bioherms these morphologies are related to the hydrological behaviour of the fluvial systems elongate domes dome heads and ovoid to subspherical oncoids accreted in flowing water laminated crusts and small sized cylindrical to lenticular oncoids formed during low discharge and ponding phases in the lacustrine environments only small sized ovoid oncoids occur the main characteristics of the ebro basin non marine stromatolites are 1 laminations and concentric banding exhibited by all morphologies 2 the occurrence of well preserved cyanobacterial filaments in several laminae suggesting that these microbiotas are the major contributors in growth 3 the asymmetrical growth of cortices in domes and oncoids with polar thickening on the upper side suggesting in situ growth under low energy conditions 13c values of carbonate stromatolites range from 11 3 o late palaeocene to 4 4 o middle late eocene during the late palaeocene under tectonically quiescent conditions the 13c values mainly reflect the influence of soil derived co2 during the eocene the progressive uplift of the surrounding catchment areas led to an increase of exposures of mesozoic rocks consequently the 13c values of the eocene stromatolites reflect the influence of the co2 derived from the dissolution of mesozoic marine carbonates there is a 2 5 o shift in 18o values of stromatolites from the late palaeocene to middle late eocene which is consistent with the variation in 18o of precipitation due to changes in altitude of the catchment area during this time the isotopic values of all middle upper eocene laminated crust samples show distinct covariant trends suggesting that these stromatolites were formed either in ponding zones of fluvial channels or in disconnected pools developed during low discharge episodes

carbonate deposition in a fluvial tufa system processes and products corvino valley southern italy in a multi scale approach to the study of the organic and mineral components in an active barrage type tufa system of southern italy neo formed deposits in both natural depositional sites and on inorganic substrates placed in the stream for this study were observed and compared through one year of monitoring dams and lobes representing the basic morpho facies of the deposits are composed of two depositional facies vacuolar tufa a mixture of phytoclastic and framestone tufa and stromatolitic tufa phytoherm boundstone tufa three petrographic components comprise both facies micrite and microsparite often forming peloidal to aphanitc laminar and dendrolitic fabrics and sparite which occurs as isolated to coalescent fan shaped crystals forming botryoids or continuous crusts all fabrics occurring in all depositional facies are organized into layers with a more or less well developed cyclicity which has its best expression in stromatolitic lamination the precipitation of all types of calcite with mg 1 0 to 3 2 mole and sr 0 5 to 0 8 mole takes place more or less constantly during all seasons in spite of the low saturation state of the water the saturation index range is 0 75 to 0 89 within the active depositional zone the latter extends for a few hundred microns through the external surface of the deposit the active depositional zone has a particular micro morphology composed of porous micro columns 50 to 150 m in size separated by interstitial channels mineral precipitation occurs upon both external surfaces and within internal cavities of the micro columns while further point sites of precipitation occur suspended within the masses of cyanobacterial tufts sub spherical mineral units nano spheres 10 to 20 nm in diameter are the basic biotic neo precipitate they commonly form by replacing non living degrading organic matter and at point sites along the external surface of living cyanobacterial sheaths nano spheres agglutinate to form first rod shaped aggregates 100 to 200 nm which then evolve into triads of fibres or polyhedral structures successively both triads and polyhedral solids coalesce to form larger calcite crystals mainly tetrahedrons tens of microns in size that represent the fundamental bricks for the construction of the micro columns in the active depositional zone precipitation is attributed to the presence of a widespread biofilm that occurs in the active depositional zone this is composed of a heterogeneous community comprising epilithic and endolithic filamentous cyanobacteria green algae unicellular prokaryotes actinobacteria and fungi with a variable amount of extracellular polymeric substances no precipitation takes place where the biofilm is absent indicating that the biological activities of the biofilm are crucial with its living organisms and non living organic matter basic aggregates of neo precipitates do not form in association with any one particular type of organic matter substrate but appear to be related to the seasonal temperature variation polyhedral micro crystals mainly precipitate in the colder season short triads in the intermediate seasons and long triads in the warmest conditions these three basic crystal aggregates have a petrographic counterpart respectively in the spar microspar and micrite

a highstand oolitic sequence and associated facies from a late triassic lake basin south west england high energy lake shoreline carbonate sequences are rarely documented in the geological record however one example occurs in the upper triassic mercia mudstone group mmg of southern britain the mmg is one of a number of thick non fossiliferous mudstone deposits associated with north atlantic mesozoic rift basins the origin of the mmg mudstones is the subject of current debate with marine playa lacustrine and alluvial aeolian models having been proposed shoreline features have been documented from the northern margin of the basin but the rarity of such features elsewhere in the mmg has led many workers to doubt a lacustrine origin for the mudstones wave dominated lake shoreline deposits have been recognized in several sections from the southern basin margin in the clevedon area of the bristol channel in south west england these deposits provide evidence for the development of a sizeable perennial to semi perennial hypersaline lake in which the mmg mudstones accumulated shoreline sediments overlie alluvial stream and sheet flood deposits and pass from transgressive gravel conglomerate beach units with bioclasts influenced by shore normal waves deposited under semi humid conditions to lower gradient highstand oolitic sands affected by more varied wave approach deposited under progressively more arid conditions which culminated in lowstand oolitic strand plain deposits overlain by a playa mudflat unit shoreline deposits record a simple shallowing upward transgressive highstand lowstand sequence however a change from a reflective transgressive to dissipative highstand shoreline is believed to represent a climatically induced change in prevailing wind direction shoreline features recognized in the mmg are similar to those of recent playa lacustrine basins of the western united states ooids display a variety of size fracture and dissolution features in addition to beachrock fabrics suggesting that they were originally composed of radial aragonite similar to modern ooids from the great salt lake utah

lacustrine microbialite pinnacles in the palaeogene of patagonia argentina facies and controls abstract large carbonate microbialite build ups are relatively uncommon in ancient fresh water lacustrine basins as compared with those marine and saline environments this paper discusses the formation of a large continental lacustrine deposit the oligocene miocene carinao formation in argentina which contains large bioherms the lacustrine formation occurs in n s corridor and is mostly composed by meter scale pinnacles and sheet like carbonate beds that grade to detrital deposits towards the more subsident southern areas the main facies are autochthonous and allochthonous limestones and detrital deposits the autochthonous limestones include the carbonate pinnacles which are about 4 m high and 0 5 m in diameter and coalesce laterally to form very continuous beds several kms the pinnacles are formed by plate like dome vertically elongated and irregular horizontal bioherms most of them with radial structure the bioherms are boundstones of fibrous fans and spherulites and feather calcite crystals micrite and inequigranular calcite mosaics both biogenic and abiogenic processes interfered in carbonate precipitation allochthonous limestones include peloidal ostracod and intraclastic limestones some containing coated grains polymictic conglomerates and cross bedded hybrid arenites deposited in a fluvial deltaic system located at the southwest of the basin 13c values vary between 0 4 and 3 2 vpdb and 18o are comprised between 5 7 and 8 6 vpdb the 87sr 86sr ratios range between 0 7061 and 0 7056 the carinao formation deposited in a fresh water lake sourced by meteoric and deep groundwater tectonics was a main control determining the configuration of the lake system the water supply and the alignment of some bioherms the vertical succession or the different bioherms morphologies reflects well the lake level changes controlled by both tectonic and climate

are current models of tufa sedimentary environments applicable to tropical systems a case study from the gregory river abstract tufa formation in the gregory river tropical northern australia is strongly influenced by high evaporation rates perennially warm water temperatures construction behaviour of aquatic insect larvae and regular high magnitude floods these conditions contrast with those of the cool temperate tufa depositing streams for which sedimentary models have already been developed gregory river tufas occur as multiple series of dams separated by waterholes indicating that under all climatic conditions there is a persistence of hydraulic factors in controlling the dam pool sequence in fluvial tufa systems however at the scale of individual tufa deposits and facies the gregory river system displays a deviation away from current models tufa domes upstream dipping ramps calcite rafts and larval facies are all common and important features in both modern and fossil tufas of the gregory river but they are not included in current tufa models thus specific sedimentary models need to be developed for seasonally humid tropical tufa systems to understand their formation and interpret them correctly in the rock record

distribution of palaeosols and deposits in the temporal evolution of a semiarid fluvial distributary system bauru group upper cretaceous se brazil abstract the stratigraphic and sedimentological knowledge of the bauru group upper cretaceous se brazil is still generally insufficient and controversial a sedimentological and palaeopedological study allowed to interpret the south eastern portion of the bauru group according to the model of a fluvial distributary system this work has two objectives 1 to include palaeosols in the interpretation of a fluvial distributary system and 2 to give detailed information on the sedimentological and stratigraphic features of the se portion of the bauru group in order to support biostratigraphical taphonomic and palaeoecological studies in the south eastern portion of the bauru group three genetic stratigraphic units were described and interpreted here informally called lower intermediate and upper units the lower unit is constituted of muddy sandstone salt flat deposits and sandstone sheet deltas deposits and is interpreted as a basinal part of a fluvial distributary system the intermediate unit is formed of very fine to fine grained sandstone filled ribbon channel and sandy sheet shaped beds suggesting a distal or medial portion of a fluvial distributary system the upper unit does not match with the present models of the fluvial distributary system because mostly constituted of moderately developed well drained medium to fine grained sandstone palaeosols which testify pauses of sedimentation to the order of 104 years preserved features of sedimentary structures suggest that the parent material was formed by occasional catastrophic unconfined flows this unit may represent the most distal portion of a fluvial distributary system generated by retrogradation of the alluvial system due to aridification of the climate the upper unit may be interpreted also as proximal portion of fluvial distributary system if considering the coarser grained and the well drained palaeosols however the absence of channel deposits makes this interpretation unconvincing

discerning the interactions between environmental parameters reflected in d13c and d18o of recent fluvial tufas lessons from a mediterranean climate region abstract 13 c and 18 o of recent continuous tufa records obtained during a monitoring period spanning 3 to 13 years are compared with the corresponding known environmental conditions three rivers in ne iberia located along a 200 km n s transect are used for this comparison the isotopic variations through space and time are discussed in terms of the environmental and geological parameters that operate on different scales focusing on discerning the interactions between these parameters and providing examples of possible misinterpretation of climatic conditions which is important to past climate studies based on isotopic data the calculation of the actual isotopic fractionation coefficients and the comparison with the literature derived coefficients demonstrates that the studied tufa formation was close to isotopic equilibrium to reflect the water temperature the difference between mean measured water temperature tw and mean calculated tw based on 18 o calcite and measured 18 o water is less than 2 7 c tendencies of these calculated tw are similar to the regional air temperature tair tendencies through time in particular in the case of the 13 year record although certain deviations exist over shorter time spans the best agreement between measured and calculated tw and between 18 o calcite based tw tendencies and tair tendencies corresponds to the tufa stromatolite facies differences between the 18 o calcite records of the three rivers cannot be attributed to temperature changes but to the varying influences of groundwater inputs and isotopic rainfall composition in each river without considering these parameters 18 o calcite based tw calculations yield inaccurate results when comparing the study sites 13 c calcite values do not exhibit distinct patterns over time and 13 c calcite variations are likely caused by local processes that do not reflect general environmental changes these findings underscore the significance of accounting for both groundwater behaviour and rainfall stable isotope composition when interpreting climate parameters in carbonate systems particularly when differences between the isotopic signatures of deposits exist in the same region

jurassic hot spring deposits of the deseado massif patagonia argentina characteristics and controls on regional distribution abstract the deseado massif santa cruz province argentinean patagonia hosts numerous middle to late jurassic age geothermal and epithermal features represented by siliceous and calcareous chemical precipitates from hot springs sinters and travertines respectively hydrothermal breccias quartz veins and widespread hydrothermal silicification they indicate pauses in explosive volcanic activity marking the final stages in the evolution of an extensive jurassic ca 178 151 ma volcanic complex set in a diffuse extensional back arc setting heralding the opening of the atlantic ocean published paleo hot spring sites for the deseado massif plus additional sites identified during our recent field studies reveal a total of 23 locations five of which were studied in detail to determine their geologic and facies associations they show structural lithologic textural and biotic similarities with miocene to recent hot spring systems from the taupo and coromandel volcanic zones new zealand as well as with modern examples from yellowstone national park u s a these comparisons aid in the definition of facies assemblages for deseado massif deposits proximal middle apron and distal siliceous sinter and travertine terraces and mounds with preservation of many types of stromatolitic fabrics that likely were controlled by formation temperature ph hydrodynamics and fluid compositions locally the mapped hot spring deposits largely occur in association with reworked volcaniclastic lacustrine and or fluvial sediments silicic to intermediate lava domes and hydrothermal mineralization all of which are related to local and regional structural lineaments moreover the numerous geothermal and significant epithermal those with published minable resources deposits of the deseado massif geological province mostly occur in four regional nnw and wnw hydrothermal structural belts northwestern northern central and southern defined here by alignment of five or more hot spring deposits and confirmed as structurally controlled by aeromagnetic data the northern and northwestern belts in particular concentrate most of the geothermal and epithermal occurrences hence jurassic hydrothermal fluid flow was strongly influenced by the most dominant and long active geological boundaries in the region the outer limits of the deseado massif horst itself

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

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

reworked calcretes their significance in the reconstruction of alluvial sequences permian and triassic minorca balearic islands spain the permian and triassic of minorca balearic islands consists of a 670 m thick red alluvial succession that includes in situ calcrete profiles and reworked calcrete material in the permian succession the calcretes vary from laminar forms developed on the carboniferous basement to weakly developed nodular calcretes in fluvial sediments the palaeosols in the triassic are mostly dolomitic and the profiles reach up to stage iii of soil development spec pap geol surv am 203 1995 1 the clasts formed through reworking of the palaeosol profiles are about 0 5 10 cm across and include mosaics of calcite dolomite crystals brecciated clasts rhizolith fragments and aggregates of clay and or silt these clasts appear in three different types of deposits type 1 corresponds to lenticular bodies that fill small scour surfaces and consists only of intraformational conglomerates these deposits are interpreted as ephemeral channels and sheet floods that represent the interfluvial drainage systems that captured only the precipitation falling on the alluvial plain type 2 includes sand dune 3 d bodies with flat bottoms and convex tops these bodies are about 20 cm high and 2 m wide and were formed by floodwaters that flowed down the levees of the major streams type 3 channel deposits contain reworked calcretes and extrabasinal clasts which overlie erosive surfaces and are found in layers within cross bedded sandstones and conglomerates these are interpreted as channel floor lag deposits of major channels that entered from distant uplands and drained the alluvial plain variations in the aggradation rates of the floodplain resulted in five different infill stages in the lowstand to early transgressive interval as in stages i p1 and iv b1 the fluvial deposits filled palaeovalleys calcretes and reworked calcrete deposits were of difficult formation apart from terraces and preservation accommodation space was at its greatest in the transgressive stages ii p2 and v b2 this caused the greatest aggradation of the floodplains which are formed of thick sequences of fine grained sediments isolated meandering channels weakly developed calcretes compound and reworked calcrete deposits mostly of types 1 and 2 the density of channels notably increased in stage iii p3 highstand interval because of the reduction of accommodation space this could favour the formation of composite or even cumulative palaeosols but of difficult preservation reworked calcrete deposits are mostly of type 3 but types 1 and 2 are also recognised the reworked calcrete deposits are an important part of the permian and triassic fluvial sediments and their occurrence and characteristics are important in order to interpret the infill of terrestrial basins and the construction of floodplains

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

kalkowsky s stromatolites revisited lower triassic buntsandstein harz mountains germany abstract the term stromatolite was proposed by kalkowsky 1908 z dt geol ges 60 68 125 for structures he discovered in the carbonates of the lower triassic buntsandstein of the harz mountains in central germany we have re examined these localities to clarify kalkowsky s descriptions and to deduce the environmental conditions of stromatolitic growth the lower buntsandstein was deposited in a closed lacustrine basin the central european permo triassic basin the depositional environment was a playa lake with variable salinity in the centre of the basin oolite beds are intercalated in the mainly siliciclastic succession which is composed of 20 fining upward cycles thought to have been produced by climatic variations stromatolites occur almost exclusively on the surface of oolite beds stromatolitic structures consist of millimetre thick laminated crusts and centimetre high branching columnar forms smaller and bigger 2 m high domes are composed of secondary order columns and intercalated crusts occasionally upper surfaces of the domes are pitted due to syndepositional dissolution despite of the overall intense sparitization two groups of stromatolitic microstructures can be distinguished spongy fenestrate and fan like fabrics the spongy fenestrate fabric is similar to that one caused by the recent cyanobacteria phormidium calothrix and dichothrix and the fan like fabric to rivularia laminated crusts called stromatoid by kalkowsky are interpreted as being of cement origin and formed by quick precipitation the change from columnar to domical forms may reflect changes of hydrodynamic conditions clear photoautotrophism suggests that cyanobacteria or eukaryotes were the dominant organisms involved in the formation of kalkowsky s stromatolites influx of ooids or siliciclastic mud interrupted or terminated the stromatolitic growth the morphology growth pattern and fabrics of stromatolites were most likely controlled by ecological factors which all seem to be related to the general hydro climatic evolution of the lower buntsandstein

the calcareous tufa in the tadrart acacus mt sw fezzan libya an early holocene palaeoclimate archive in the central sahara article i nfo the palaeoclimatic signi cance of calcareous tufa deposits found in the presently hyperarid tadrart acacus massif central sahara sw libya is discussed on the basis of u th datings stable isotope analyses and the regional hydrogeological context these deposits formed mostly between c 9600 and 8100 yr bp the isotopic signature 18 o and 13 c of this tufa indicates that the water forming these carbonates originated as isotopically depleted rainwater as a result of the northward expansion of the sw african monsoon system during the early holocene carbonate sedimentation in the tadrart acacus decreased shortly before c 8000 yr bp attributed to a drop in precipitation in the course of the well known 8 2 kyr event a correlation between tufa development and climate change in n and e africa and in the mediterranean basin during the early holocene is discussed the effect of early holocene climate change on both the landscape and the dwellers living in the tadrart acacus region is also evaluated

retrogressive shear band propagation and spreading failure criteria for submarine landslides the paper proposes a mechanism of submarine spreading failures which combines retrogressive shear band propagation sbp with a series of active block failures in the stable zone of the slope where the gravitational shear stress is smaller than the residual shear strength gradual downhill removal of the failed material causes a decrease in the supporting earth pressure leading to the progressive uphill propagation of the shear band termed here retrogressive sbp and uniquely determining its length which can be linked to the dimensions of the spreading failure block mechanisms two conjugate energy balance based criteria have been formulated for the spreading failure in terms of either the critical depth of the sliding surface or the critical drop of the failed seabed level both criteria have been validated against the observed phenomena presence and absence of the evidence of spreading failure for different landslide depths and a step in the sliding surface in palaeo landslide examples from

ooids in purbeck limestones lowermost cretaceous of the swiss and french jura ooids occurring in the shallow water purbeckian carbonate sediments of the jura mountains can be grouped into six types gradations from one type to another and coexistence of the various types are common type 1 ooids are small and well rounded they display fine concentric micritic laminae in many cases their cortices are dissolved and replaced by void filling spar microsparitic neomorphic replacement occurs locally type 2 ooids are large and have irregular shapes they show fine micritic laminae and occasional layers of fine radial crystals they commonly evolve into oncoids ooids of type 3 display many fine radial cortical laminae and are patchily micritized they are medium in size and mostly well rounded this type of ooid may pass into large irregularly shaped coated grains type 4 ooids have 1 to 4 cortical laminae with a fine radial structure and patchy micritization they are medium in size and well rounded type 5 ooids have only one lamina with a coarse radial structure they are small and well rounded associated are spherical grains containing bundles of elongate crystals ooids of type 6 show superpositions of two or more different radial and or fine micritic laminae the cortical structure may also change laterally in the same lamina the preferential dissolution of type 1 ooid cortices to form oomoulds indicates a primary composition of unstable carbonate sedimentological features and comparison with modern ooid occurrences point to formation on high energy sandbars in normal marine waters type 2 ooids grew in marine lagoonal environments with quiet water and abundant cyanobacteria the radially structured ooid cortices of types 3 4 and 5 show no dissolution features this implies that they were originally composed of stable carbonates or that an unstable carbonate phase was transformed into a stable one at an early stage of diagenesis type 3 ooids occur together with marine faunas and indicate high water energy ooids of type 4 and type 5 originated probably from relatively quiet water of variable salinity coexistence of different ooid types and mixed forms of type 6 implies gradual or rapid changes in hydrodynamic geochemical and microbiological conditions which were a feature of the purbeckian depositional environments

kinematics of the gondwana basins of peninsular india abstract the gondwana successions 1 4 km thick of peninsular india accumulated in a number of discrete basins during permo triassic period the basins are typically bounded by faults that developed along precambrian lineaments during deposition as well as affected by intrabasinal faults indicating fault controlled synsedimentary subsidence the patterns of the intrabasinal faults and their relationships with the respective basin bounding faults represent both extensional and strike slip regimes field evidence suggests that preferential subsidence in locales of differently oriented discontinuities in the precambrian basement led to development of gondwana basins with varying but mutually compatible kinematics during a bulk motion grossly along the present day e w direction the kinematic disparity of the individual basins resulted due to different relative orientations of the basement discontinuities and is illustrated with the help of a simple sandbox model the regional e w motion was accommodated by strike slip motion on the transcontinental fault in the north

paleosols in clastic sedimentary rocks their geologic applications interest in pre quaternary paleosols has increased over the past decade in large part because they have proved to be beneficial in solving diverse geological problems the majority of paleosols are described from continental deposits most commonly from alluvial strata criteria for recognizing these paleosols have been extensively described however classifying them has proved more complicated pre quaternary paleosols are generally classified according to one or more modern soil classification systems although one new classification has been proposed exclusively for paleosols to avoid problems using the modern soil classifications in addition to taxonomic classification paleosols can be categorized according to the interplay among deposition erosion and the rate of pedogenesis when they formed paleosols can be solitary if they formed during a period of landscape stability following the development of an unconformity such paleosols are commonly thick and extremely well developed more commonly paleosols are vertically stacked or multistory because they formed in sedimentary systems undergoing net aggradation if erosion was insignificant and sedimentation was rapid and unsteady compound paleosols generally formed if the rate of pedogenesis exceeded the rate of deposition composite paleosols developed thick cumulative paleosols indicate that erosion was insignificant and that sedimentation was relatively steady both autogenic and allogenic processes can influence depositional and erosion patterns and thus affect the kinds of soils that form consequently paleosols can help to interpret the history of sediment deposition and the autogenic and allogenic processes that influenced a sedimentary basin paleosols are also helpful in stratigraphic studies including sequence stratigraphic analyses they are used for stratigraphic correlations at the local and basinal scale and some workers have calculated sediment accumulation rates based on the degree of paleosol development in addition to their stratigraphic applications paleosols can be used to interpret landscapes of the past by analyzing paleosol landscape associations at different spatial scales ranging from local to basin wide in scope at the local scale lateral changes in paleosol properties are largely the result of variations in grain size and topography at the scale of the sedimentary basin paleosols in different locations differ because of basinal variations in topography grain size climate and subsidence rate paleosols are used to reconstruct ancient climates even to estimate ancient mean annual precipitation map and mean annual temperature mat ancient climatic conditions can be interpreted from modern soil analogs or by identifying particular pedogenic properties that modern studies show to have climatic significance stable carbon and oxygen isotopes are also used to interpret ancient climate and some effort has been made to estimate mat from isotopic composition on the basis of

abiotic versus biotic controls on the development of the fairmont hot springs carbonate deposit british columbia canada the relict fairmont hot springs deposit formed largely of carbonates covers an area of 0ae 5k m 2 and is up to 16 m thick the triangle shaped discharge apron which broadens down valley is divided into a proximal part with beds dipping at 10 and a distal part with beds dipping at 10 to 15 the deposit is formed of the 1 basal macrophyte 2 lower carbonate 3 middle clastic 4 upper carbonate and 5 upper clastic sequences two charcoal samples embedded in the lower carbonate sequence yielded dates of 8690 90 and 8270 70 cal yr bp indicating that much of the deposit formed post glacially during the early to mid holocene deposit aggradation ceased in the mid to late holocene when the fairmont creek valley was incised the lower and upper carbonate sequences which are the thickest sequences are composed of nearly equal parts of travertine abiotic and tufa biotic with feather dendrite travertine radiating dendrite travertine and stromatolite tufa dominating competition between calcite precipitation rates and biotic growth rates controlled the distribution of tufa and travertine across the discharge apron calcite and biotic growth rates were controlled largely by flow velocity across the apron which in turn was controlled by topography and regular fluctuations in spring water discharge volume during times of high spring discharge slow sheet flow over the proximal part of the apron promoted stromatolite growth whereas fast turbulent flow on the distal part of the apron induced rapid feather dendrite formation during times of low spring discharge quiescent shallow evaporative pools conducive to radiating dendrite formation formed on the proximal part of the apron whereas slow flow on the distal part promoted stromatolite growth facies with high calcite supersaturation experienced rapid abiotic dendrite growth that precluded most biotic growth

travertine distinctive depositional fabrics of carbonates from thermal spring systems the terrestrial limestones forming at the emergence of thermal springs show a variety of unusual depositional facies the specific lithological and petrological features of these deposits have few counterparts in the marine and continental karst related carbonates but they are typical of the epigean limestone that has been quarried since antiquity in the surroundings of tivoli rome under the name of travertine where it is still forming in hydro geothermal fields linked to extensional tectonics the physicochemical hydrodynamic and geological conditions specific to the tivoli thermal spring system imply hypersaturated alkaline sulphate warm to hot waters upwelling from springs fed through open fractures faults in extensional and or volcanic regimes these features together with the hydrodynamic behaviour of the water flows running from the vents control the petrogenetic features of the travertine a well bedded mostly finely laminated porous but quite compact limestone the results of a detailed comparative petrological analysis carried out on the lithofacies of travertine limestones and of those observed during formation within numerous active thermal spring fields provide the elements required for an exhaustive textural classification of the travertine lithofacies which has not yet been described systematically according to the genetic processes and fabrics the thermal deposits that originate from such hypersaturated alkaline sulphate warm to hot waters can be subdivided into abiotic crystalline crusts microbially mediated crusts microbialites and granular deposits mostly represented by small accumulations of lime mudstone some of the granular deposits and the microbialites are only partially comparable with analogous sediments forming on tidal flats sabkhas or other continental sites however the facies association of crystalline crusts and laminar curled microbialites has no counterpart in the marine realm the widespread presence of thermophile bacteria and sulphobacteria and the general absence of autochthonous eukaryote organisms unable to live in poisonous sulphate waters are also undeniable evidence of their thermal origin

carbonate deposits in the lower jurassic navajo sandstone southern utah and northern arizona u s a abstract carbonate strata constitute a minor proportion of the widespread eolian lower jurassic navajo sandstone but are vital for understanding the hydrological and paleoecological dynamics of the erg system the carbonate lithologies are in the form of tufa carbonate spring mounds and lacustrine beds predominantly limestone and or dolomite with minor constituents of chert and clastics the tufa mounds and lacustrine carbonate beds occur separately or together where together the springs are interpreted to have sourced water to the lakes where they are not associated with tufa mounds the lacustrine carbonate beds may have formed where the water table intersected the topographic surface through seepage many of the deposits exhibit three common characteristics 1 clastic facies in the carbonate beds that indicate proximity to the lake margin 2 deformation of the lower beds of the carbonate units by catastrophic dewatering events and 3 a variety of weathering features and evaporite crystal molds that indicate periodic subaerial exposure these deposits were also the habitats of a rich terrestrial biota including vertebrates aquatic and terrestrial invertebrates and plants including large trees in addition to the tufa mounds several other mound like structures occur in the carbonate beds as stromatolite mounds carbonate beds draped over primary topography tepee structures and accumulations around tree trunks