palaeoenvironmental reconstruction of a middle miocene alluvial fan to cyclic shallow lacustrine depositional system in the calatayud basin ne spain the middle miocene sedimentary fill of the calatayud basin in north eastern spain consists of proximal to distal alluvial fan floodplain and shallow lacustrine deposits four main facies groups characteristic of differentsedimentary environments are recognized 1 proximal and medial alluvial fan facies that comprise clast supported gravel and subordinate sandstone and mudstone the latter exhibiting incipient pedogenic features 2 distal alluvial fan facies formed mainly of massive mudstone carbonate rich palaeosols and local carbonate pond deposits 3 lake margin facies which show two distinct lithofacies associations depending on their distribution relative to the alluvial fan system i e front lithofacies a comprising massive siliciclastic mudstone and tabular carbonates or lateral lithofacies b showing laminated and or massive siliciclastic mudstone alternating with tabular and or laminated carbonate beds and 4 mudflat shallow lake facies showing a remarkable cyclical alternation of green grey and or red siliciclastic mudstone units and white dolomitic carbonate beds the cyclic mudflat shallow lake succession as exposed in the orera composite section ocs is dominantly composed of small scale mudstone carbonate dolomite cycles the mudstone intervals of the sedimentary cycles are interpreted as a result of sedimentation from suspension by distal sheet floods the deposits evolving either under subaerial exposure or water saturated conditions depending on their location on the lacustrine mudflat and on climate the dolomite intervals accumulated during lake level highstands with mg rich waters becoming increasingly concentrated lowstand to highstand lake level changes indicated by the mudstone dolomite units of the small scale cycles reflect a climate control from dry to wet conditions on the sedimentation in the area the spatial distribution of the different lithofacies implies that deposition of the small scale cycles took place in a low gradient shallow lake basin located in an interfan zone the development of the basin was constrained by gradual alluvial fan aggradation additional support for the palaeoenvironmental interpretation is derived from the isotopic compositions of carbonates from the various lithofacies that show a wide range of 1 8 o and 1 3 c values varying from 7 9 to 3 0 pdb and from 9 2 to 1 7 pdb respectively more negative 1 8 d and 1 3 c values are from carbonate rich palaeosols and lake margin carbonates which extended in front of the alluvial fan systems whereas more positive values correspond to dolomite beds deposited in the shallow lacustrine environment the results show a clear trend of 1 8 o enrichment in the carbonates from lake margin to the centre of the shallow lake basin thereby also demonstrating that the lake evolved under hydrologically closed conditions

quaternary palaeohydrological evolution of a playa lake salada mediana central ebro basin spain this research was partly funded by the national science foundation usa under the ear 941 8657 programme and by the eead csic project number z 5 96 this is limnological research center contribution number 527

vegetation changes and hydrological fluctuations in the central ebro basin ne spain since the late glacial period saline lake records abstract although the central ebro basin northeastern iberian peninsula is both the northernmost semi arid area in europe and one of the regions with the largest biodiversity it has been insufficiently studied in terms of past climate variability due to the scarcity of suitable sites for palaeoenvironmental analyses previous studies from ephemeral saline lakes in the area mainly based on palynological data show abrupt and rapid arid humid transitions throughout the last glacial cycle highlighting a complex palaeohydrological evolution new cores from two saline lakes la playa and la salineta in the los monegros area provide multi proxy records including sedimentology geochemistry and pollen indicators this study together with a detailed review of the main saline records from the central ebro basin enables us to reconstruct the main features of the palaeoclimate evolution during the last glacial cycle one of the main results of this study is the alternation of humid and dry phases as a characteristic of the climate evolution during the late glacial additionally the study suggests an important role of the increased flow from the pyrenean rivers during deglaciation in the hydrological balance of the central ebro basin the early holocene is the wettest period of the studied sequences contrasting with the aridity of the middle holocene interval which is frequently absent as a result of intense aeolian erosive processes the lack of archaeological remains associated with the middle holocene neolithic also supports increased aridity that would have impeded human settlements although anthropogenic activity partially masks the climate signal from the palynological data in the uppermost part of the studied sequences there is some sedimentological evidence for a climate change during the last 2000 yr resulting in a recovery of average saline lake levels in the central ebro basin

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

paleoenvironmental and paleohydrochemical conditions of dolomite formation within a saline wetland in arid northwest australia abstract groundwater dolocrete occurring within the fortescue marsh a large inland wetland in the pilbara region of northwest australia has been investigated to provide paleoenvironmental and paleohydrological records and further the understanding of low temperature dolomite formation in terrestrial settings over the quaternary period two major phases of groundwater dolocrete formation are apparent from the presence of two distinct units of dolocrete based on differences in depth 18o values and mineral composition group 1 g1 occurs at depth 20 65 m b g l below ground level and contains stoichiometric dolomite with 18o values of 4 02 0 71 group 2 g2 is shallower 0 23 m b g l occurring close to the current groundwater level and contains ca rich dolomite secondary calcite with a comparatively lower range of 18o values 7 74 and 6 03 modelled 18o values of paleogroundwater from which older g1 dolomite precipitated indicated highly saline source water which had similar stable oxygen isotope compositions to relatively old brine groundwater within the marsh developed under a different hydroclimatic regime the higher 18o values suggest highly evaporitic conditions occurred at the marsh which may have been a playa lake to saline mud flat environment in contrast g2 dolomite precipitated from comparatively fresher water and modelled 18o values suggested formation from mixing between inflowing fresher groundwater with saline brine groundwater within the marsh the 18o values of the calcite indicates formation from brackish to saline groundwater which suggests this process may be associated with coeval gypsum dissolution in contrast to the modern hydrology of the marsh which is surface water dependent and driven by a flood and drought regime past conditions conducive to dolomite precipitation suggest a groundwater dependent system where shallow groundwaters were influenced by intensive evaporation

abiotically formed primary dolomite in the mid eocene lacustrine succession at gebel el goza el hamra ne egypt an approach to the role of smectitic clays abstract this study discusses the role of smectitic clays in the formation of an abiotic physio chemical primary dolomite within an evaporative alkaline saline marginal lake system in the absence of carbonate precursor and microbes the present work has been achieved in terms of textural mineralogical and geochemical characteristics of dolostones in the mid eocene bartonian lacustrine succession cropping out at gebel el goza el hamra shabrawet area ne egypt this lacustrine succession is 15 16 m thick and made up of alternating horizontal beds of dolostone marlstone and mudrock that show some pedogenic and subaerial exposure features the dolostones are composed mainly of dolomite 60 90 smectite 20 30 and quartz grains 5 10 the dolomite comprises fine crystalline rhombs to micro spherical crystals with no obvious relics of microbial activity and or carbonate precursor it is ordered nearly stoichiometric with 46 50 mole of mgco 3 and has 18 o and 13 c values ranging from 0 44 to 2 96 vpdb and 0 93 to 8 95 vpdb respectively the smectite occurs as thin mats that are commonly intergrown and associated with dolomite mineralogical textural and stable isotopic results of the dolomite indicated that the dolomite was formed as an abiotic primary precipitate in alkaline saline lacustrine systems in this respect the gel like highly viscous smectitic medium plus progressive co 2 degassing elevated evaporation low sedimentation rate low sulphates level and alkaline soil solution lowered the kinetic barriers of dolomite precipitation from solution and promoted the incorporation of mg 2 in the structure of dolomite consequently the presence of smectitic clays in evaporative saline lakes is significant for dolomite formation because they can generate a gel like highly viscous medium and provide mg 2 that can facilitate the physcio chemical precipitation of primary dolomite from solution at ambient temperatures however more work is needed to better characterize the role of clays during dolomite formation in alkaline lacustrine environments at ambient temperatures

sedimentology and stable isotopes from a lacustrine to palustrine limestone deposited in an arid setting climatic and tectonic factors miocene pliocene opache formation atacama desert chile abstract field relations petrography gis and geochemistry of a late miocene pliocene limestone the opache formation calama basin atacama desert chile shows that depositional facies diagenetic histories and isotopes differ from eastern to western parts of the basin we recognize two facies lacustrine characterized by ostracod diatom mudstone and wackestone and palustrine characterized by both shallow water and pedogenic features gis analysis of the basin topography reveals an intrabasinal low in the eastern area and steeper hydrological gradients to the west with the calama constriction restricting flow between east and west petrography and geochemical results confirm that the calama constriction influenced depositional parameters ponding groundwater to the east forming a shallow lake and creating palustrine conditions to the west our analyses indicate that lake waters were less enriched in 13c or 18o than palustrine waters even though petrologic studies show that the lacustrine carbonates have a complex diagenetic history derived from groundwater rich in dissolved minerals this seemingly contrary observation can be reconciled if an important source of water for the western carbonates was sourced from the pacific ocean and was less evolved whereas eastern limestones precipitated from water which had become depleted in 18o during transport from the east today moisture from the pacific very rarely if ever reaches inland as far as calama indicating that during the late miocene mid pliocene breakdown in the temperature inversion due to weakened or absent upwelling in the cold coastal pacific current allowed moisture from the pacific to reach inland this changing atmospheric circulation pattern may have also affected upper level airflow that today blocks eastern sourced moisture from crossing the andes allowing it to reach farther westward into the atacama region during the late miocene pliocene together these moisture sources were sufficient to produce carbonate rich palustrine and lacustrine environments in the calama basin

palaeogene lacustrine record in mallorca nw mediterranean spain depositional palaeogeographic and palaeoclimatic implications for the ancient southeastern iberian margin abstract middle bartonian middl1e eocene and chattian upper oligocene lacustrine and alluvial lacustrine successions exist in mallorca northwestern mediterranean they yield a significant palaeobiological record comprising fossil land plants and vertebrates and constitute the best available depositional record for a preliminary palaeogeographic and palaeoclimatic analysis of the northeastern part of the palaeogene southern iberian margin western tethys both lacustrine systems developed under similar warm and humid climatic conditions increasingly affected by seasonal and or pluriannual rhythms marked by changing precipitation patterns these climatic conditions were mainly caused by the low palaeolatitude where the lacustrine systems evolved the still probable although decreasing influence of indo pacific warm surface currents and the occurrence of very extensive marine water masses adjacent to wide emerged continental zones the palaeogene lacustrine systems were shallow and characterised by low gradient depositional conditions they were perennial open freshwater oligosaline carbonate lakes where eutrophy thermal meromixis and anoxic bottom conditions could develop allowing the accumulation and preservation of macrophytic plant remains of the circum lacustrine marginal belt and neighbouring terrestrial mesophytic zones the higher plant algal bacterial organic contribution balance favoured the generation of mineable huminitic coal seams carbominerites and of gas prone kerogene type iii and iib source rocks the hydrogen bicarbonate rich waters led to high biogenic and inorganic bio induced carbonate sediment production biogenic muds cyanobacterial incrustations and travertine and tufa precipitation constituted the major carbonate products moreover the high ph conditions in the lacustrine water bodies and in the lacustrine sediment pore waters favoured bacterial sulphate reduction contributing to organic sulphur enrichment in coals these highly alkaline conditions also resulted in some cases in the exceptionally good preservation of chlorophyllinite a rare liptinite maceral recorded in the eocene coal deposits the middle eocene lacustrine system did not evolve in a very well defined tectonic setting characterised by the generation of low uplifts and gently subsiding basins terrigenous contributions from the source areas and clastic sedimentation were restricted to river mouths high autochthonous carbonate production and accumulation characterised most of the remaining lacustrine zones a significant spring recharge of the lacustrine zones is suggested by the well developed spring related travertine deposits by contrast the oligocene lacustrine zones developed both in fluvial related floodplains and in the distal zones of a major alluvial system which was fed from tectonically active source areas located to the nw of the island a more significant water runoff contribution is suggested for this system although underground recharge could also be substantial

effect of bathymetric curvature on gulf stream instability in the vicinity of the charleston bump abstract the effect of the isobathic curvature on the development and evolution of gulf stream frontal waves meanders and eddies in the vicinity of the charleston bump a topographic rise on the upper slope off charleston south carolina referred to as cb hereinafter is studied using the hybrid coordinate ocean model hycom baroclinic and barotropic energy transfers from the gulf stream to its meanders and eddies that appear as cold and warm anomalies are computed for four different cases in case i the curvature of the isobaths is artificially reduced and the cb is removed from the bathymetry in this simulation the simulated gulf stream meanders were barely noticeable in the study region energy transfer from the gulf stream to meanders and eddies was negligible in case ii the curvature of the isobaths was the same as in case i but a bump of the scale of the cb was added to the bathymetry in this simulation gulf stream meanders were amplified while passing over the cb in case iii the cb w

hummocky cross stratification tropical hurricanes and intense winter storms most previous workers have inferred a storm origin for hummocky cross stratification which typically occurs in shallow marine deposits on the modern earth the only storms capable of profoundly affecting shallow marine depositional environments are severe tropical cyclones hurricanes and mid latitude winter wave cyclones intense winter storms this paper examines the palaeogeographic distribution including palaeolatitude and palaeogeographic setting of 107 occurrences of hummocky cross stratification ranging in age from the proterozoic to recent in each of these stratigraphic units both palaeolatitude and palaeogeography are consistent with a direct storm influence associated with the passage of hurricanes or winter storms directly over the site of deposition this palaeogeographic evidence lends support to the inferred storm origin for hummocky cross stratification further the distribution of the structure suggests that most occurrences 73 were generated by tropical hurricanes the remaining 27 being generated by intense mid latitude winter storms the preferential generation of hummocky cross stratification by hurricanes is consistent with 1 the known differences in the nature of the bottom flows generated by the two major storm types and 2 the inferred nature of the flows which form hummocky cross stratification hurricanes couple less effectively with the water column than do intense winter storms due to this ineffective coupling hurricane generated bottom flows tend to be oscillatory or multidirectional dominant with only minor unidirectional components of motion in contrast intense winter storms generally do couple effectively with the water column generating bottom flows which possess a dominant or significant unidirectional component most previous workers have suggested that hummocky cross stratification forms under oscillatory or multidirectional dominant flow thus it is conceptually reasonable that the vast majority of ancient occurrences of hummocky cross stratification were probably hurricane generated as suggested by the aforementioned palaeogeographic distribution the proterozoic palaeozoic neogene and quaternary were times when global climate was similar to that of today the distribution of hummocky cross stratification deposited during these times suggests that both hurricanes and intense winter storms occupied latitudinal belts during these times which were essentially identical to those occupied by their modern counterparts the mesozoic and palaeogene were non glacial times when global climate was much warmer than that of today the distribution of hummocky cross stratification deposited during this interval suggests that hurricanes occurred more frequently at higher latitudes during non glacial times than they do at present the possibility of a broadened hurricane belt during the mesozoic and palaeogene is consistent with climatic considerations a limited number of mesozoic and palaeogene rock units containing hummocky cross stratification were deposited in palaeogeographic settings that preclude a direct hurricane influence these examples were deposited in the middle latitudes suggesting that intense winter storms continued to form hummocky cross stratification in the middle latitudes during these much warmer times some previous workers have suggested that tsunamis may be capable of generating hummocky cross stratification the palaeogeographic distribution of the structure does not support an origin due to tsunamis lacustrine examples of hummocky cross stratification reported herein are the first known non marine occurrences they suggest that storm effects strongly influence the sedimentary record of some lakes

a middle late pleistocene palustrine lacustrine travertine system borj edouane unit nw tunisia sedimentology stable isotopes and palaeohydrological implications the carbonate borj edouane unit represents the northernmost documented middle late pleistocene continental carbonate deposits in tunisia the unit consists of two main facies associations asymmetrically distributed 1 calcrete palustrine laminar crust 2 microbialites the first accumulated carbonate formed in the distal zone of alluvial fans calcretes and in shallow lakes subjected to periodic exposure palustrine facies that occupied the westernmost strip of the basin the second association formed in permanent lakes stromatolites oncoids and planar stromatolites located in the central areas of the basin fed by springs associated with a concentration of vertical faults in the eastern area of the basin travertine facies at time of deposition these facies communicated with the lake via a transitional lacustrine travertine environment transitional travertine stromatolite facies all facies show a restricted range of 18o values around 5 8 0 5 suggesting formation from paleoprecipitation largely of atlantic derivation brought about by westerly winds as for the 13c values these show a wide range 6 4 to 11 7 overall relatively high values for all facies with the lower values corresponding to the calcrete palustrine association and the higher ones linked to the microbialite facies the trend in travertines probably mimics an increasing influence of carbon derived from dissolution of carbonate bedrock of the cretaceous substrate while that of palustrine samples records increasing respired c contribution the sedimentological and isotopic characteristics of the borj edouane unit reflect wetter conditions at the time of deposition and point to a humid period at the middle late pleistocene transition

petrographic and geochemical evidence for the formation of primary bacterially induced lacustrine dolomite la roda white earth pliocene central spain upper pliocene dolomites white earth from la roda spain offer a good opportunity to evaluate the process of dolomite formation in lakes the relatively young nature of the deposits could allow a link between dolomites precipitated in modern lake systems and those present in older lacustrine formations the la roda mg carbonates dolomite unit occur as a 3 5 to 4 m thick package of poorly indurated white massive dolomite beds with interbedded thin deposits of porous carbonate displaying root and desiccation traces as well as local lenticular gypsum moulds the massive dolomite beds consist mainly of loosely packed 1 to 2 m sized aggregates of dolomite crystals exhibiting poorly developed faces which usually results in a subrounded morphology of the crystals minute rhombs of dolomite are sparse within the aggregates both knobbly textures and clumps of spherical bodies covering the crystal surfaces indicate that bacteria were involved in the formation of the dolomites in addition aggregates of euhedral dolomite crystals are usually present in some more clayey sepiolite interbeds the thin porous carbonate mostly dolomite beds exhibit both euhedral and subrounded bacterially induced dolomite crystals the carbonate is mainly ca dolomite 51 54 mol caco3 showing a low degree of ordering degree of ordering ranges from 0 27 to 0 48 calcite is present as a subordinate mineral in some samples sr mn and fe contents show very low correlation coefficients with mg ca ratios whereas sio2 and k contents are highly correlated 18o and 13c values in dolomites range from 3 07 to 5 40 pdb mean 0 06 1 75 and from 6 34 to 0 39 pdb mean 3 55 1 33 respectively samples containing significant amounts of both dolomite and calcite do not in general show significant enrichment or depletion in 18o and 13c between the two minerals the correlation coefficient between 18o and 13c for dolomite is extremely low and negative r 0 05 whereas it is higher and positive r 0 47 for calcite the lacustrine dolomite deposit from la roda is interpreted mainly as a result of primary precipitation of dolomite in a shallow hydrologically closed perennial lake the lake was supplied by highly saturated hco3 co32 groundwater that leached dolomitic mesozoic formations precipitation of dolomite from alkaline lake waters took place under a semi arid to arid climate however according to our isotopic data strong evaporative conditions were not required for the formation of the la roda dolomite a significant contribution by bacteria to the formation of the dolomites is assumed in view of both petrographic and geochemical evidence

influence of an offshore shift in the gulf stream on waters of the south carolina continental shelf abstract a 4 3 month long dataset from moorings on the continental shelf off south carolina during 1986 showed unusual midrecord shifts in bottom pressure temperature stratification and alongshelf currents the gulf stream moved farther offshore during the second half of the time period this offshore position appears to have facilitated gulf stream influence on shelf waters all across the continental shelf

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

lacustrine stromatolites as multi scale recorders of climate change insights from the miocene ebro basin sedimentological 13c and 18o data from stromatolites in a lower and middle miocene sequence from the ebro basin n spain are used to assess the potential of ancient lacustrine stromatolite lamination as an archive of palaeoenvironmental and palaeoclimatic change the isotopic evolution through the studied sequence supports a general trend toward less saline conditions with time stromatolites and muddy grainy laminated limestones developed in lake water that underwent little renewal compared with other carbonate facies the palaeoclimatic value of the stable isotope changes and concurrent textural variations in calcite stromatolite lamination is studied at different orders of cyclicity stromatolite lamination consists of simple laminae dark dense light dense and light porous grouped into alternating composite light and dark laminae 13c and 18o analyses in consecutive composite laminae bulk sampling yielded a cyclic pattern that mimics textural variations light laminae with lower 13c and 18o values reflect higher precipitation evaporation ratio p e and more influence of biogenic 12c dark laminae with higher 13c and 18o values reflect drier conditions more complete atmospheric co2 exchange with water and photosynthetic 12co2 uptake textural features of laminae support these results the dark laminae are related to higher calcite saturation in lake water during drier periods isotopic values from high resolution sampling through a 2 1 cm thick stromatolite reveal palaeoclimate variations at different temporal scales isotopic variation in 3rd order cyclicity of alternating light dark simple laminae is recording seasonal p e variations light and dark composite laminae 2nd order cyclicity correspond to pluriannual dominantly humid or dry conditions respectively a gradual succession from light to dark composite laminae forms the 1st order cycles driven by decreasing p e through longer pluriannual periods resulting in lake level lowering the stromatolites are thus recording lake level changes of centennial to millennial scale

use of charophyte carbonates as proxy indicators of subtle hydrological and chemical changes in marl lakes example from the miocene bicorb basin eastern spain abstract the lower alluvial unit in the miocene bicorb basin contains several metric scale limestone intervals which record episodic shallow lacustrine environments in an alluvial setting developed during the early stage of the basin s evolution five main carbonate facies have been differentiated in the lacustrine limestones although calcite charophyte incrustations predominate and constitute the most striking features of these deposits the thinnest limestone intervals correspond to deposits from charophyte meadows in ponded shallow depressions in floodplains the thickest limestone intervals are mainly formed by banded limestones and usually correspond to diverse types of regressive sequences that have been interpreted as resulting from the infill of shallow lakes the sedimentological features and sequences show noticeable differences in the gradient of the littoral zones and the amount of palustrine deposits with models proposed for marl lakes charophytic carbonates from the best preserved facies show similar microtextures to those from recent charophyte incrustations the variations in stable isotopes 13 c 18 o for these primary carbonates occur in parallel with luminescence variations and correspond to hydrological changes and variations in solute composition and eh ph status in the lake waters the carbonates that display moderate to strong diagenetic modifications show a diverse degree of compaction aggrading neomorphism strong cementation and nodulization the isotopic values for these are arranged in diverse clusters there is a correlation between the degree of luminescence and the 13 c this suggests that hydrological and hydrochemical variations both in the lacustrine and diagenetic environments are being recorded in parallel we emphasize the need for further comparative studies between recent and ancient charophytic carbonates as these carbonates have been used in palaeoenvironmental reconstructions special attention must be paid to the diagenetic changes in ancient charophytic marls

freshwater limestone in an arid rift basin a goldilocks effect abstract the olduvai basin 3 s situated just west of the east african rift system in northern tanzania contains a two million year record of paleoclimate and paleoenvironmental change as well as a rich archive of vertebrate paleontology including hominins milankovitch precession cycles 20 kyr regulate the mean annual precipitation 250 700 mm yr and the 2500 mm yr evapotranspiration results in a negative hydrologic balance despite persistent aridity extensive deposits of freshwater limestone punctuate the stratigraphic record between 2 and 1 ma lake olduvai occupied the basin and its sediments are a proxy for climate driven cycles three limestones 1 84 1 80 and 1 36 ma in age which formed within lake margin floodplains adjacent to the lake were studied to determine their depositional environment using field relations sedimentary structures fossils petrography and stable isotope and major element geochemistry the three limestones are similar in that they contain peloidal micrite siliciclastic detrital grains and rhizoconcretions abundant faunal remains gastropods ostracods charaphytes and fish indicate that ponded water was relatively fresh and alkaline geochemical and stable isotope data indicate two types of groundwater sourced carbonate producing waters a deeper sourced fluid that was enriched in iron and manganese due to extended water rock interactions and a shallower groundwater that traveled through alluvial fan deposits regional faults tapped the deeper groundwater producing carbonate at spring sites while seeps associated with basinward changes in alluvial fan slopes drew on shallower groundwater sources isotope compositions indicate that fault related waters experienced some evaporation as water moved away from the spring sites while compositions of the seep related carbonate remained relatively constant pedogenic alteration and meteoric calcite cementation affected the carbonate when the spring and seep sites dried out secondary strontium rich dolomite precipitated within the limestones during burial under paleo lake olduvai sediments and fluids during periods of lake expansion integrating these data within the geological context of regional paleoclimatic and local environmental change indicates that the freshwater carbonates formed periodically when the conditions were just right i e a goldilocks effect carbonates near the basin center formed from groundwater flowing under a hydraulic head from faults or fractures during the falling limbs of milankovitch cycles when the lake was in recession carbonates near the basin margin formed from an increased rate of groundwater seepage that occurred only on the rising limbs of cycles in both contexts the continuous flow of groundwater with surface evaporation and co2 degassing optimizes the conditions for limestone formation in this arid environment these results help explain the formation of freshwater limestones in the rift basin link the carbonates to specific portions of milankovitch cycles and document that localized sources of potable water were present for use by hominins in olduvai gorge during an important period of human evolution

use of a multilayer snow model to assess grazing conditions for reindeer high density snow layers deteriorate grazing conditions for reindeer during winter we compare two different methods for identifying past winters with difficult grazing conditions for reindeer in kautokeino northern norway a long term climate analysis based on monthly values of precipitation and temperature 1900 2011 demonstrated that the reported winters were difficult to identify systematically the processes leading to hard layers or ground ice layers occur on daily not monthly timescales and whether or not specific conditions are problematic depends on the development throughout the winter not just on single values to better analyse the weather conditions and development over time that favour the formation of high density snow layers we apply the multilayer model snowpack over the period 1956 2010 we simulate the evolution of the snowpack by forcing the model with 6 hour interval meteorological data the model output was analysed by summing up the vertical extent of the simulated high density snow layers 350 kg m 3 for each winter these results were compared with historical records of difficult winter grazing conditions reported in the period 1956 2010 in particular the heavy losses of reindeer during the catastrophic 1967 68 winter were caused by the occurrence of ground ice together with long snow cover duration this unfavourable coincidence is well reproduced by our model results together with eight of the ten reported difficult winters

latest oligocene late miocene lacustrine systems of the north central part of the ebro basin spain sedimentary facies model and palaeogeographic synthesis abstract in the central part of the ebro basin spain north of the ebro river three allostratigraphic or tectosedimentary units differentiated within the latest oligocene late miocene upper agenian vallesian interval are sedimentologically characterized these deposits represent carbonate and sulphate lacustrine environments fed by pyrenean alluvial systems luna system and huesca system in each unit several facies associations or lithofacies were mapped these interfinger through time gypsum lithofacies occupy the southernmost part of the study area and are surrounded by carbonate and or detrital lithofacies to the north each lithofacies consists of different carbonate sulphate and or detrital facies arranged in simple sequences decimetres to metres thick the four types of sequences characterized reflect a complex shallowing evolution involving carbonate or sulphate contexts thus each lithofacies represents the sedimentation in a particular lacustrine or alluvial subenvironment a single lacustrine system is proposed for the central part of the basin its evolution followed cycles of water level variations which caused kilometre scale migrations of the lake shoreline in this model two distinct situations or lakes alternated through time a one represents high levels associated with a single body of dilute carbonate water where massive carbonate facies formed influenced by organism proliferation these lakes had wide palustrine vegetated margins in which bioturbated facies developed b the other represents low levels that correspond to a playa lake model laminated sulphate deposits formed in the lake waters while nodular gypsum originated in the surrounding saline mud flats and within the exposed previously deposited carbonate sediments transitions from one situation to the other including minor water level fluctuations within carbonate sedimentation conditions were marked by the development of laminated and stromatolitic facies lake level variations were caused by climatic cycles and gave rise to the simple sequences and to the lithofacies lateral relationships recognized in this study correlation among tectosedimentary units in the studied pyrenean domain and in the iberian domain of the ebro basin shows that for units n1 and n2 the facies that resulted from dilute carbonate waters are rare in the lacustrine areas of the iberian margin this indicates that a strong hydrological contrast existed between both regions on this basis a theoretical asymmetrical facies model is proposed for the single lacustrine basin that extended over these regions

lacustrine carbonates and pedogenesis sedimentology and origin of palustrine deposits from the early cretaceous rupelo formation w cameros basin n spain the berriasian rupelo formation of the w cameros basin consists of a 2 200 m thickness of marginal and open lacustrine carbonate and associated deposits open lacustrine facies contain a non marine biota with abundant charophytes both stems and gyrogonites ostracods gastropods and rare vertebrates carbonate production was mainly biogenic the associated marginal lacustrine palustrine facies show strong indications of subaerial exposure and exhibit a wide variety of pedogenic fabrics silicified evaporites found near to the top of the sequence reflect a short hypersaline phase in the lake history the succession was laid down in a low gradient shallow lake complex characterized by wide fluctuations of the shoreline carbon and oxygen stable isotope analyses from the carbonates show non marine values with ranges of 13 from 7 to 11 and 18 from 3 to 7 5 differences in the isotopic composition of open lacustrine carbonates are consistent with sedimentary evidence of variation in organic productivity within the lake analyses from the entire sample suite plot on a linear trend isotopic compositions become lighter with increasing evidence of pedogenic modification this suggests progressive vadose zone diagenesis and influence of meteoric waters rich in soil derived co2 the stable isotope data thus support evidence from petrography and facies relations that palustrine limestones form through pedogenic modification of lake carbonates

lateral and vertical variations in sedimentology and geochemistry of sub horizontal laminated travertines cakmak quarry denizli basin turkey abstract the laterally extensive sub horizontal laminated travertine deposits outcropping in the cakmak quarry denizli basin turkey allows reconstructing their three dimensional geobody architecture based on field observations detailed petrographic and geochemical analyses stable carbon and oxygen isotopes major and trace elements the most important controlling porosity permeability parameters in this lacustrine dominated facies in relation to microfacies and diagenetic modifications were constrained sedimentological analyses and the observed architectural geometries allowed to subdivide the sub horizontal carbonate succession into three main depositional units these units in turn based on macro and microscopic observations were subdivided into nine dominant lithotypes reflecting an overall shrub flat and a marsh pool depositional setting the shrub flat facies mainly comprises dendritic shrub crusts boundstone pustular grainstone and clotted micrite mudstone to boundstone in contrast the marsh pool environment is dominated by coated reed rudstone to boundstone cryptalgal silty bioclast rich bioturbated mudstone and peloidal packstones the diagenetic study revealed that the sediments were affected by dissolution cementation sparmicritization recrystallization and local formation of fe oxi hydroxides and chalcedony among the diagenetic products in particular the calcite cements were investigated applying micro analysis of stable carbon and oxygen isotopes accordingly the co variation between the obtained isotopic values and the elemental concentrations sr mg na and s point to a thermogene fluid system that likely circulated through the subsurface limestones dolomites and evaporites of the lycian nappes these findings ensure an in depth understanding of continental carbonate deposition i e sub aqueous travertines in the context of a lacustrine depositional system

combined textural and stable isotopic data as proxies for the mid cretaceous paleoclimate a case study of lacustrine stromatolites in the gyeongsang basin se korea abstract microbial interference of the prevailing sedimentary dynamics during stromatolite growth records vital biogeochemical information which reflects the prevailing paleoclimatic conditions this study documents the simultaneous geochemical and textural changes in mid cretaceous lacustrine stromatolites gyeongsang basin se korea deposited in a semi arid setting fibrous calcite micrite couplets in the stromatolites occurring in the sinyangdong hwasan and banyawol formations constitute the basic growth cycles and can be divided into first second and third order cycles second order cycles show couplets with gradual textural changes from fibrous calcite to micrite laminae and three different types of micrite are present sometimes one type of micrite evolves into another within the second order cycle in the sinyangdong stromatolites consistent enrichments in 18o and depletion in 13c towards micrites within the sinyangdong and hwasan stromatolite couplets and a concomitant depletion of both isotopes from fibrous calcite to micrite in the banyawol sample can be observed these shifts reflect paleohydrological changes in the lake water related to paleoproductivity and paleosalinity fluctuations relatively higher paleosalinity values within the sinyangdong lake water system is registered by higher 18o values of fibrous calcite and micrite in the sy 3 than in the sy 1 and sy 2 stromatolites the consistent shifts in 18o and 13c isotopes in different textural growth fabrics indicate that paleohydrological factors could play a significant role in the formation of these primary lacustrine carbonates textural changes shown by the frequency of the growth cycles also corresponds with oxygen and carbon isotopic values these results appear to have been influenced by climate related paleohydrological changes

isotopic hydrology and paleohydrology of the madagi kenya natron tanzania basin during the late quaternary abstract three generations of stromatolites mark the recent extension of paleolakes in the magadi natron basin on the border between tanzania and kenya the last two generations are observed some 50 m above the modern lakes level they are respectively attributed to the beginning of the last interglacial and to the pleistocene holocene transition analysis of the morphology and texture of the stromatolites reveals an ecological zonation between 0 and 10 14 m below the shoreline their relatively high 18o and 13c values reflect a long residence time for the paleolake water which would have been favorable to the establishment of an isotopic equilibrium between atmospheric co2 and the dissolved inorganic carbon despite deep carbon inputs in relation to carbonititic volcanism a study of the 18o 2h and 13c contents in the hydrothermal springs perennial rivers and lacustrine brines indicates that during the last period of significant renewal of the deep saline groundwater precipitation was depleted in heavy isotopes when compared to modern precipitation this difference corresponds to a drop of about 600 1000 m in altitudinal hydroclimatic zones finally a comparison between the modern and paleohydrological data leads us to believe that the stabilization of the paleolake shorelines at the same altitude can be attributed to control by the water table level in the aquifer of the basaltic plateaus east of the basin

dedolomitization and other early diagenetic processes in miocene lacustrine deposits ebro basin spain abstract a variety of meteoric diagenetic features reveal the development of a syngenetic karst on lacustrine deposits of the ebro basin diagenetic processes that operated on lacustrine laminated and stromatolitic carbonates include the following 1 a first syndepositional stage with processes such as dolomitization desiccation and related breccia formation and sulphate precipitation either as lenticular gypsum crystals or nodules this stage took place under progressive evaporation due to lake level fall when the previous carbonate deposits became exposed as a supra littoral fringe surrounding saline mud flats of adjacent sulphate depositional environments 2 a second early diagenetic stage in which processes such as sulphate dissolution and collapse brecciation dedolomitization calcite spar cementation and silicification occurred as a result of meteoric water input that caused a progressive rise in lake level light isotopic compositions 13 c and 18 o of diagenetic calcites versus heavier compositions in primary laminated and stromatolitic limestones confirm a meteoric influence the syngenetic karst is best developed at the boundary between two allostratigraphic units and coincided with one of the extensive stages of sulphate deposition at the end of the early miocene the karst facies occurred in an area that was a low relief barrier that separated two sites of sulphate deposition during low lake levels this indicates that the karst development was controlled by topographic changes within the basin and record a shift from arid to wetter climatic conditions as suggested by the overlying freshwater carbonate deposits the presence of diagenetic features such as those described in the central ebro basin affecting saline lacustrine carbonates is relevant because they can be used as indicators of subaerial exposure periods in terrestrial environments and they also reveal important palaeogeographic and palaeoclimatic events of basinal extent

isotope hydrology of early paleogene lake flagstaff central utah implications for cordilleran evolution lacustrine sediments from paleogene foreland basins of the north american cordillera serve as powerful integrators of information on climatic and tectonic conditions but episodes of hydrologic connection between basins may confound straightforward interpretations we use stable isotope ratios of carbon and oxygen in authigenic carbonates of the flagstaff formation in central utah to investigate the history of the lake system which produced these sediments flagstaff limestone and dolostone exhibit isotopic compositions consistent with having formed from the same fluid at surface conditions indicating high evaporative concentration was unnecessary to drive dolomite precipitation isotopic data are consistent with the flagstaff formation having been produced by a large lake which occupied its basin from the late paleocene into the early eocene lake flagstaff was hydrologically distinct from lake uinta to the north but may have been connected to lake claron in the south paleoaltimetry estimates suggest that the mean elevation of lake flagstaff9s catchment in the sevier highlands did not exceed 1 5 km the growing evidence from stable isotope data that cordilleran elevations were relatively low in the early paleogene is in stark contrast to structural and sedimentological evidence for a high nevadaplano and a topographically rugged sevier thrust belt

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

snow crystal growth with varying surface temperatures and radiation penetration the temperature field is derived for a sinusoidally varying surface temperature with varying solar radiation penetration the growth rates of snow crystals are calculated to explain the rapidly growing layers of faceted crystals i e depth hoar that form just below the surface at high altitudes and in polar snow the solutions also show that a layer of wet snow can exist just below the surface even on days when the surface temperature remains sub freezing

the bude formation lower westphalian sw england siliciclastic shelf sedimentation in a large equatorial lake the 1300 m thick turbiditic bude formation was deposited in a lake lake bude but disagreement persists over whether the environment was a deltaic or deep water fan the tectonic setting of the lake was the northern flank of a northerly advancing variscan foreland basin close to the westphalian palaeo equator palaeocurrents indicate sediment sourcing from all quadrants except the south there is a dm m scale cyclicity whereby sandstone bodies comprising amalgamated event beds alternate with mudstone intervals containing non amalgamated event beds the ideal cycle is a symmetrical coarsening up fining up cycle consisting of three facies i 2 and 3 arranged in 12321 order facies 3 in the middle of the cycle is an amalgamated sandstone body up to 10 m thick which interfingers laterally with thin cm mudstone layers the sandstone body comprises amalgamated beds of very fine sandstone which are largely massive and up to 0 4 m thick channels are absent except for scours up to 0 2 m deep which truncate the interfingering mudstone layers sandstone bodies are inferred to be tongue shaped in three dimensions facies 1 and 2 completing the 12321 cycle are respectively dark grey fine and light grey coarse varved mudstone containing thin 0 4 m sandstone event beds fossils and burrows indicate that facies 1 and 2 were deposited respectively in brackish rarely marine and fresh water hence the ideal cycle 12321 reflects an upward decrease then increase in salinity brackish fresh brackish this is attributed to the lake sill being periodically overtopped by the sea due to glacio euitatic sea level oscillations the resulting oscillations in lake depth produced the coarsening up fining up regressivetransgressive cyclicity the central sandstone body representing the regressive maximum event beds are interpreted as river fed turbidites deposited during catastrophic storm floods combinedflow ripples and other wave influenced structures occur in event beds throughout the ideal cycle suggesting deposition of the entire bude formation above storm wave base the proposed environment is a shelf of continental shelf dimensions but lacustrine instead of marine sandstone bodies are interpreted to be river connected tongues or lobes the absence of cycles containing nearshore or emergent facies is attributed to i the lake sill preventing the water level from falling below sill level thereby insulating the lake floor from eustatically forced emergence and ii relatively distal deposition beyond the reach of shoreline progradations the lack of palaeoflow from the south is attributed to a now eroded deep water trough lying to the south in front of the northerly advancing orogen some facies 2 laminated mudstone beds grade laterally into massive and or contorted beds interpreted as in situ seismites facies 4 consistent with an active foreland basin setting development of seismites was possibly facilitated by gas bubbles and or weak cohesion in the fresh water bottom mud the late quaternary black sea with its broad northwestern shelf is probably a good physiographical analogue of lake bude and was likewise fresh at times

palaeogeographic palaeoclimatic palaeohydrological and chemical biochemical controls on accumulation of late eocene coastal lacustrine palustrine limestones southern england abstract the shallow lacustrine to palustrine hatherwood limestone member of the late eocene headon hill formation southern england is in a succession of fluvio estuarine and laguno lacustrine siliciclastic sediments it is up to 8 0 m thick and is subdivided by metric scale palaeotopographic erosion surfaces one of which underlies lenticular humic siliciclastic mudstones the limestone lithologies are 1 biocalcilutites biocalcisiltites 2 biocalcarenites 3 calcirudites and 4 laterally discontinuous laminar and fenestral crusts lithology 1 accumulated in a low energy shallow lacustrine depositional environment indicated by the predominance of pulmonate pond snails in the mollusc assemblage in contrast lithologies 2 and 3 are the coarse grained fills of shallow palaeotopographic lows and also form basal lags and palaeokarst fills lithology 3 comprises remnant autochthonous lags that resulted from selective erosion during lacustrine transgressions brecciation and proto intraclast to nodular differentiation in lithology 2 suggests derivation of the intraclasts from subaerially and pedogenically modified shallow lacustrine muds laminar crusts 4 0 5 6 0 cm in thickness display irregularly undulose and anastamosing laminations 150 400 m thick that display differential staining by iron oxide the abundance of rootlet traces and calcitised parenchymatic root tissues in the fenestral crusts suggests a palustrine depositional environment for these lithologies the siliciclastic mudstone lithologies are 1 black humic muds and 2 blue green silty muds and marls the high c n molar ratio of the black muds suggests derivation of the humic content mainly from vascular plants in local wetlands the mollusc assemblage of the blue green siliciclastic muds resembles floodplain lake assemblages from the regional palaeogene succession mean stable isotopic values for limestone samples of 4 75 1 53 for 13 c and 2 77 1 47 for 18 o indicate a relatively heavy tendency within published spectra for tertiary lacustrine carbonates the 18 o isotope results agree with published subtropical surface water palaeotemperatures for this succession the total characteristics of the member therefore suggest a shallow lacustrine to palustrine depositional environment pedogenic overprinting and mechanical reworking displayed by the limestones are attributable to seasonal fluctuations of water level during lake highstands but in this marine influenced setting major long term lake lowstands resulting in deep erosion and palaeokarsting of the limestones may be attributable to falls in relative sea level the biocalcilutites and humic muds accumulated during the ensuing lake transgressions

seasonal fluctuations in sea level on the south carolina shelf and their relationship to the gulf stream near bottom pressure measurements obtained over a 9 month period in 1978 on the outer continental shelf off south carolina document that sea level rose 35 to 50 cm between july and october records of coastal sea level showed a similar rise when the pressure and coastal sea level records were corrected for the effects of wind stress and temperature the largest portion of the rise in the two variables remained the amplitude of the change in residual sea level was largest at the shelf break 28 cm and decayed to 22 cm at the coast the relatively small magnitude of the decay suggests that alongshelf pressure gradients imposed at the shelf break have minimum alongshelf wavelengths of 2000 km the changes in residual sea level were seasonal and associated with seasonal changes in the transport of the gulf stream the 3 years of residual sea level records examined here indicate that the amplitude of a typical decrease in transport of the gulf stream off south carolina between july and october has a strong interannual variability the change in transport can be 50 lower to over 100 higher than the historical average the residual sea level records also suggest that a change in transport of the gulf stream is not strongly related to the onshore offshore position of the gulf stream

multi proxy paleoenvironmental reconstruction of saline lake carbonates paleoclimatic and paleogeographic implications priabonian rupelian issirac basin se france abstract a 200 m thick carbonate succession has been deposited in shallow water saline lake environments during the priabonian rupelian in the issirac basin south east france the palaeoenvironmental and palaeogeographic significance of such saline lake carbonates has been characterized on the basis of a multi proxy analysis including 1 depositional and diagenetic features 2 biological components molluscs ostracods benthic foraminifers characean and 3 carbon oxygen and strontium stable isotopes biological associations are indicative of dominantly shallow

holocene dolomitization of calcium carbonate sediments from the coastal sabkhas of abu dhabi u a e a stable isotope study secondary dolomitization of holocene calcium carbonate sediments occurs beneath the coastal sabkhas of abu dhabi u a e a stable isotope study of the sabhka sediments and brines indicates that the

palaeoenvironmental and tectonic significance of miocene lacustrine and palustrine carbonates ait kandoula formation in the ouarzazate foreland basin morocco abstract the ouarzazate basin is the southern foreland basin to the high atlas mountains in morocco the sedimentary fill records a sequence dating from the eocene to pleistocene that records the interplay between tectonics and climate this study presents the first stable isotope and facies analyses of the middle to late miocene ait ibrirn lacustrine member ait kandoula formation these data test whether the basin was internally draining and enable the development of palaeoenvironmental models for the middle to late miocene five sedimentary facies of lacustrine and palustrine limestones are interbeddded with extensive sequences of palaeosols and fluvial sandstones and conglomerates often associated with evaporite gypsum development these facies can be divided into two facies associations related to water depth and sub aerial exposure within the basin in the serravalian and early tortonian shallow water successions dominate the stratigraphy typical of underfilled foreland basin settings furthermore carbonate 18o and 13c isotopes from the sections show covariance confirming that these carbonates were deposited within a hydrologically closed basin however late tortonian to messinian carbonates do not demonstrate the covariance typical of endorheic basins additionally the facies association indicates the presence of deeper water lake systems demonstrating that the basin was externally draining at this time these results question the established view of tectonic stagnation in the late miocene and suggest that the cenozoic sediments of the ouarzazate basin contain a rich and untapped record of climate change and tectonic evolution on the edge of the sahara desert

periodicity in stromatolitic lamination a potential record of enso nao and sunspot in the miocene lacustrine record of the ebro basin spain abstract the spectral decomposition of time series obtained from ancient rock records can be used to study the similarity between the dynamics of present day and past climate systems a high resolution periodicity analysis of luminance and lamina thickness of lacustrine stromatolites in the ebro basin northeast of iberian peninsula reveals a significant signal of interannual and decadal climatic variability in the miocene this is one out of very few works that presents the use of spectral analysis to estimate the potential of stromatolite lamination as multiple scale recorders of climate parameters the effects of precipitation and evaporation variations on stromatolite lamination have been detected at three orders of cyclicity based on textural and high resolution stable isotope analyses c and o obtained in prior studies these analyses also revealed that the light and dark simple lamina couplets are identified with annual cycles third order isotopic cycles in the present study the spectral analysis results obtained through different paths in five stromatolite specimens reveal significant periods in the power spectrum at around 2 5 3 7 5 7 10 and 22 years these cycles can be correlated with the typical oscillation bands of different climate related agents the 2 5 year period corresponds to the quasi biennial oscillation qbo or to the biennial component of the el nino southern oscillation enso or to the north atlantic oscillation nao the 3 to 5 and 5 to 7 year bands can be linked to enso or nao variability second order isotopic cycles the 8 to 11 year bands fit the 11 year schwabe first order isotopic cycles and 22 to 23 year fit the 22 year hale sunspot cycles thus the stromatolite growth was controlled by enso nao and solar activity cycles the close relationship between these climate related agents makes it difficult to specify the dominant agent controlling the stromatolite growth nevertheless the significant periods obtained from this study within interannual 2 5 3 7 5 7 years decadal 10 22 years and even multidecadal bands 37 42 years support the existence and concurrence of enso and nao precursors during the early and middle miocene

model for dry snow metamorphism by interparticle vapor flux kinetic growth metamorphism lowers the mean number of bonds between the ice particles in snow during the beginning state of snow metamorphism at a large mean temperature gradient significant particle growth occurs only at preferred growth sites three dimensional approximations of the sink source geometry are introduced to model particle growth and shrink rates the calculations show that enhanced growth occurs at very small and at large sink source distances the consideration of growth rate enhancement by differences in radii of curvature between sink source particles accounts for metamorphism at very low mean temperature gradients final particle size distributions and the reduction of the particle number density by metamorphism are calculated and may be compared with measured distributions

climatic and environmental indications of carbon and oxygen isotopes from the lower cretaceous calcrete and lacustrine carbonates in southeast and northwest china abstract carbon and oxygen isotopic ratios were determined from 100 lower cretaceous samples from four carbonate bearing facies in southeast se and northwest nw china for palaeoclimatic and palaeoenvironmental analyses the samples were interpreted as sediments within sublithofacies of distal alluvial ponds sf1 open shallow lakes sf2 littoral lakes sf3 and marshes sf4 results of analyses show in se china 13c values range between 5 0 and 3 0 with a negative trend through time and 18o values are all negative 19 3 7 4 in nw china 13c values range from 4 0 to 4 0 with periodic change and 18o values range between 18 0 and 1 5 both relatively heavy values and pronounced covariances of most 13c and 18o indicate semiarid climate and domination of closed brackish lakes marshes and ponds in nw and se china during the early cretaceous of them positive 13c 0 0 to 4 0 and relatively heavy 18o 5 0 to 1 5 values suggest interruptions of arid evaporation in intermittences of the early hauterivian in sw fujian of the middle aptian in west jiuquan basin of the late aptian in sw ordos basin and of the late aptian early albian in liupanshan basin in a short interval of the early aptian the hot and humid climate occurred in local sw zhejiang by high kaolinite content and in west jiuquan basin by warm flora could be an exception particularly extremely negative 18o values mainly 19 0 9 0 indicate relatively low temperature in se fujian in the berriasian barremian in liupanshan basin in the late aptian in sw ordos basin in the late albian and in west jiuquan basin in the mid late aptian which is supposed to attribute to the presence of 2500 m 4500 m in elevation more positive values and more covariance ratios of 13c and 18o in nw china than in se china and in mainland china than in america indicate a arider climate in former than in later probably attributing to the palaeogeography in distance to sea a tentative correlation of the early cretaceous 13c value excursion of calcretes shows a good compatibility between marine oaes and terrestrial carbonate sediments and between nw china and america continents implying a global response to carbon cycle in both marine and terrestrial environments the feature suggests the potential of global correlation and application of terrestrial calcrete 13c excursions in pre cenozoic

the last glacial maximum on spitsbergen svalbard most scientists have concluded previously that the west coast of spitsbergen svalbard remained ice free during the late weichselian between 25 000 and 10 000 yr b p we conclude that the glaciation was more extensive terraces that were postulated to have been ice free are covered by a thin late weichselian till sudden drop in the marine limit and basal radiocarbon dates of raised glaciomarine sediments demonstrates that the glaciers in the main fjords isfjorden and van mijenfjorden terminated west outside of the fjord mouths basal radiocarbon dates from glaciomarine clay above till in cores from the continental shelf west of spitsbergen yielded ages of about 12 500 yr b p from which we conclude that the ice extended to the shelf edge based on the extent of amino acid diagenesis in radiocarbon dated molluscs the duration of the maximum extension of the late weichselian glaciation was short certainly less than 10 000 years during the ice free period preceding that glaciation at least back to 40 000 yr b p the glaciers on svalbard were not significantly larger than at present as shown by marine deposits close to the glacier snouts many radiocarbon dates place deglaciation of the outer coast at about 12 500 yr b p at about 10 000 yr b p the rest of the archipelago rapidly became ice free

origin of groundwater helium and temperature anomalies in the cambay region of gujarat india abstract a survey of natural helium in soil gas and groundwater was undertaken in the cambay region of gujarat india the cambay basin known for high heat flow is a graben characterised by nnw sse trending major fault system and successive down faulting along sympathetic faults parallel to major trendline and orthogonal faults cutting across several wells indicated higher than atmospheric equilibration concentration of helium referred to as anomalous helium concentration these wells generally had high groundwater temperature and appear to be located along basement faults in the study area particularly on both eastern and western flanks of the cambay basin groundwater helium anomalies are explained through a conceptual model as originating largely from within the crystalline basement through radioactive decay in the form of plumes localised by the major faults and fractures groundwater temperature anomalies originate due to setting up of a shallow 1 2 km depth convective circulation again along major faults and fractures which facilitate both upward and downward migration of groundwater the sedimentary cover acts as a dispersive medium therefore no significant helium anomalies are seen within the cambay graben that has more than 3 km thick sedimentary cover it is thus seen that even though helium and groundwater have different origins the faults and fractures in the crust can associate anomalous concentrations of helium and groundwater temperatures along themselves in a longitudinally distributed manner by providing preferred pathways for migration of helium and by facilitating establishment of convective hydrothermal circulation of groundwater

late oligocene early miocene landscape evolution of the lake mead region during the transition from sevier contraction to basin and range extension late oligocene to miocene sedimentary strata of the lake mead nevada region hold evidence that can test models of central basin and range extension and tectonic evolution and illuminate paleodrainage systems related to the carving of the grand canyon in this region sevier contraction and a period of relative tectonic quiescence predate miocene extension and magmatism the herein revised rainbow gardens formation formerly the oldest member of the horse spring formation is found throughout the lake mead area and spans the transition from quiescence to the start of extension new detailed stratigraphic work within the rainbow gardens formation including paleocurrent analyses stable isotope geochemical data new 40 ar 39 ar dates tephrochronologic data and ongoing structural studies was used to build a detailed chronostratigraphic framework and reconstruct the rainbow gardens basin through time our results show that the basin formed by a combination of inherited topography and tectonic events outside the lake mead region prior to ca 25 ma sedimentation rates sedimentary facies patterns and the lack of evidence for syndepositional faulting indicate that the basin did not form during extensional faulting although recent work suggests that this basin was modified by uplift to the south between 18 and 20 ma initially the basin recorded fluvial sedimentation within the center of an e ne trending inherited valley with two facing gravel dominated bajadas on either side as the valley filled rivers from the caliente volcanic field to the north delivered an influx of volcaniclastic material into a broad area of marshes and ephemeral lakes in the final stages of sedimentation just prior to the onset of extension at ca 17 ma the basin filled with limestone in a series of shallow lakes understanding the development and evolution of this basin is crucial for testing models of extension as recorded by the younger horse spring formation in addition the detailed sedimentology and stratigraphy place constraints on models of the formation of the grand canyon and suggest that a paleo colorado river did not deposit sediment in the lake mead area between 25 and 17 ma this work highlights the importance of detailed basin analyses which are crucial companions to structural tectonic and geomorphologic studies aimed at understanding the complex evolution of lithospheric and landscape changes across a large region

composition of inland waters with marine like fauna and inferences for a miocene lake in spain abstract knowledge of the ionic composition of athalassic non marine waters where marine like organisms currently live allows to evaluate their ionic and total dissolved solid tds tolerance ranges together with other ecological data these chemical parameters can be used to interpret hydrological and hydrochemical conditions in ancient lake basins where analogous faunas have been recorded an example of such a utilization of the biological record is presented for miocene clastic dominated lacustrine deposits of the tertiary ebro basin of ne spain which contain marine like fossils comparison of the deduced chemical parameters for the miocene lake waters with the chemical composition of recent groundwaters and saline springs in the same area allows us to infer a similar mode of solute acquisition this implies that there were important cl so 4 saline inflows to the miocene lakes

modern dolomite deposition in continental saline lakes western victoria australia microcrystalline dolomite forms a major constituent of holocene sediments of numerous continental saline playa lakes in southeastern australia the lake waters are highly supersaturated with respect to dolomite as well as other mg carbonates but undersaturated or near saturation with respect to calcite and aragonite the dolomite shows no replacement textures and most likely formed by direct precipitation conditions in these lakes that appear conducive to the precipitation of dolomite are 1 high salinity 2 high mg ca ratios and 3 high alkalinity the moderate sulfate levels of the brines do not seem to be inhibiting carbonate precipitation

late oligocene early miocene paleosols of distal fluvial systems ebro basin spain abstract the study of paleosols can be a vital tool in the paleoenvironmental interpretation of continental deposits because their physical and chemical characteristics are a reflection of variations in aspects of soil formation changes in paleosol characteristics can be used to determine the architecture and nature of parent material paleosol maturity topography climate and soil forming organisms including vegetation cover on the ancient floodplain and can be utilized to recreate a palaeocatena furthermore paleosols can provide quantitative data on paleoclimate where other sources such as organic matter and pedogenic carbonate are absent late oligocene early miocene strata exposed in the ebro basin spain have been identified as proximal alluvial fan fluvial and lacustrine continental facies in parts of the distal fluvial system pedogenically altered channel and overbank deposits interfinger with ephemeral lacustrine facies three main paleosol types developed in these sediments and have been described and compared to modern soils entisol like early successional soils inceptisol like young soils and alfisol like open woodland soils paleoenvironmental reconstructions suggest a mosaic of ecotypes with areas of open woodland composed of shrubs herbs and small trees and other plants of low stature and with each ecotype being controlled primarily by fluctuating paleohydrological conditions from field observations and geochemical analysis the climate was found to be humid continental mean annual temperature mat 10 14 c 4 c mean annual precipitation map 450 830 mm yr 1 200 mm yr 1 these results indicate that climatic conditions were wetter than the present day ebro basin mat 14 c map 320 mm yr 1 and differ from previous interpretations of an arid to semi arid environment based on sedimentological criteria alone

a theoretical determination of the characteristic equation of snow in the pendular regime a partir de donnees experimentales de drainage sur des colonnes de neige l equation caracteristique de la neige est determinee pour des teneurs en eau assez elevees mais lorsque celle ci est sous forme d inclusions fluides isolees une methode theorique est utilisee pour determiner cette equation

nonmarine evaporitic sedimentation and associated diagenetic processes of the southwestern margin of the ebro basin lower miocene spain abstract in the southwestern margin of the tertiary ebro basin northeastern spain several evaporitic units are found among distal alluvial fan deposits they are made up of bioturbated microlenticular primary gypsum secondary nodular and meganodular gypsum after anhydrite chert nodules and charophyte limestones these evaporites formed in shallow saline lakes along the basin margin during the early early miocene autol gypsum unit and the late early miocene ablitas gravalos and ribafrecha gypsum units the lakes were fed principally by deeply circulated groundwaters loaded with dissolved salts from the old evaporite formations mainly triassic rocks that make up the surrounding mountain chains shallow meteoric waters of low concentration also reached the lakes episodically concentration of these waters led to deposition of microlenticular gypsum and charophytic carbonates which were then intensely bioturbated early diagenetic chert nodules and nodular anhydrite also formed in the early stages of burial large anhydrite nodules meganodules overprinted these sedimentary and early di genetic deposits with more advanced burial the primary gypsum was profoundly anhydritized in some areas with subsequent exhumation the anhydritized zones were transformed to secondary gypsum marginal lakes acted as preconcentrators of drainage waters coming from the surrounding mountain chains causing early precipitation of low solubility salts as ca carbonates gypsum and silica the remaining dissolved salts then drained toward the basin center where gypsum anhydrite glauberite polyhalite and halite precipitated in contemporaneous high salinity lakes

theory of metamorphism of dry snow the growth of ice particles in dry seasonal snow is caused by vapor diffusion among particles due to temperature gradients imposed on the snow cover the diffusion is calculated by using the potential field solutions for electrostatically charged particles the stereography of snow is represented by using a log normal distribution function for a geometrical enhancement factor defined here reasonable crystal growth rates and supersaturations are found the transition between the growth of highly faceted crystals and the growth of highly rounded crystals is determined by the critical supersaturation for the onset of dislocation aided growth thermal convection and the continuous movement of vapor around the particles due to the imposed temperature gradient are accommodated in the theory although both have little effect relative to the interparticle diffusion the growth of a layer of faceted crystals just below semi permeable crusts is explained by showing that crusts can cause the local supersaturation to exceed the critical value faceted crystals are shown to grow most rapidly in the lower warmer portions of the snow cover because of temperature effects on growth rate

global aridity during the early miocene a terrestrial paleoclimate record from the ebro basin spain abstract paleosols are an important tool in the paleoclimatic and paleoenvironmental interpretation of continental deposits and can provide a high resolution proxy for paleoclimate results from geochemical climofunctions applied to early miocene strata exposed in the ebro basin spain demonstrate that mean annual precipitation was the dominant control on paleosol type and indicate that the paleoclimate was considerably wetter during the early miocene by up to 1150 mm yr 1 in comparison to modern values placing it in a subhumid climatic regime rather than an arid semiarid regime as previously suggested by sedimentological and paleontological approaches by making comparisons with published data on paleoclimate during the early miocene this article stresses the importance of regional climatic changes in global paleoclimatic interpretation

environmental controls on perennial and ephemeral carbonate lakes the central palaeo andean basin of bolivia during late cretaceous to early tertiary times abstract in the central palaeo andean basin potosi basin of bolivia the up to 450 m thick el molino formation campanian maastrichtian to early tertiary includes two main carbonate lacustrine episodes each of different extent and duration these episodes are separated by an extensive development of alluvial facies floodplain deposits and limestones deposited in playa lakes or isolated ponds the el molino formation has been investigated in six different areas of the potosi basin and affords the opportunity to document climatic and tectonic controls on the development of perennial and ephemeral carbonate lacustrine systems the first lacustrine episode originated predominantly in perennial lakes with wave dominated low gradient ramp type margins outer marginal lacustrine facies include winnowed oolitic grainstones ostracod packstones and microbialite bioherms more agitated areas were characterized by nearshore oolitic bars with associated thrombolite mounds the fossil content and the lack of significant precipitation of evaporites indicate that the lake waters were of low salinity probably oligohaline during most of this period after the first lacustrine episode the widespread development of terrigenous alluvial facies floodplain deposits with interspersed playa lakes or isolated ponds in depressions on the floodplain may indicate a change in the net water budget the second lacustrine episode is dominated by dark micritic limestones and to a lesser extent microbialite bioherms which developed under semiarid climatic conditions this episode includes the deposits of ephemeral saline locally alkaline shallow lakes which were characterized by low energy low gradient ramp type margins the stable isotopic analysis of 163 carbonate samples covering the different facies and depositional settings displays a wide range of values 14 2 18 o and 12 9 13 c that is typical of nonmarine environments the distribution of the values indicates that during the deposition of the el molino formation the basin was hydrologically closed and experienced no strong hydrogeographical changes except for variations in the palaeolake level related to fluctuations in the regional p e ratio these are recorded by two main isotopic trends related to changes between perennial and ephemeral lacustrine conditions lacustrine sedimentation was controlled predominantly by climatically driven hydrological changes with repeated oscillations of the water level expansion and contraction and subsequent fluctuations in the width of lacustrine facies belts

a numerical model to simulate snow cover stratigraphy for operational avalanche forecasting laws of snow metamorphism have been introduced in a numerical model which simulates the evolution of temperature density and liquid water profiles of snow cover as a function of weather conditions to establish these laws the authors have summarized previous studies on temperature gradient and on wet snow metamorphism and they have also conducted metamorphism experiments on dry or wet fresh snow samples an original formalism was developed to allow a description of snow with parameters evolving continuously throughout time the introduction of laws of metamorphism has improved significantly the derivation of the settlement of internal layers and of snow covered albedo which depend on the simulated stratigraphy i e the type and size of snow grains of different layers of the snow cover the model was tested during a whole winter season without any re initialization comparison between the simulated characteristics of the snow cover and the observations made in the field are described in detail the model proved itself to be very efficient in simulating accurately the evolution of the snow cover stratigraphy throughout the whole winter season

temporal aspects of genetic stratigraphic units in continental sedimentary basins examples from the ebro basin spain abstract the utility of genetic stratigraphy lies with the fundamental relationship between genetic stratigraphic units and correlative intervals of geologic time while high resolution studies may reveal varying degrees of diachroneity that are associated with their bounding surfaces genetic stratigraphic units are generally viewed as chronostratigraphic in nature representing specific periods of basin fill despite the vast literature on basin analysis an evaluation of the temporal character of the boundaries between genetic stratigraphic units particularly in cases where they are conformable has not yet been undertaken the cenozoic ebro basin is a foreland basin on the north eastern iberian peninsula that provides a case for assessing the temporal character of the boundaries between genetic stratigraphic units these units are termed tecto sedimentary units following the method of tecto sedimentary analysis that is used in some continental basins in the ebro basin tecto sedimentary analysis is based on direct field observations in this work magnetostratigraphic data from four tecto sedimentary units units t4 to t7 that span rocks of lower and middle miocene age ca 1000 m thick in the central and western areas of the basin are analysed the study area contains alluvial fluvial and lacustrine deposits that were sourced from pyrenean and iberian areas whose catchments were structured during the collision of iberia and eurasia new magnetostratigraphic data from this study and previously published magnetostratigraphic data enable us to determine the ages of these tecto sedimentary unit boundaries throughout a 200 km long east west transect that extends from the basin centre to the southwestern margin the results indicate that the diachrony of the three boundaries between the miocene tecto sedimentary units through the central ebro basin is less than 0 3 ma where they are conformable this low degree of diachroneity may be attributed to the effects of allogenic largely tectonic processes that operate in the catchment areas and methodological inaccuracies these results provide empirical support to the idea that genetic stratigraphic units are bounded by surfaces that exhibit low amounts of diachroneity where they are conformities

geobody architecture of continental carbonates gazda travertine quarry suttő gerecse hills hungary abstract the gazda quarry is one of the largest outcrops of the present day sutt travertine complex that is situated close to the town of sutt hungary in the pannonian basin sedimentological and petrographical analyses show that the gazda travertine body is built out of phytohermal wavy laminated massive and flat laminated travertine lithofacies representing reed mound slope lacustrine and palustrine depositional environments respectively based on petrographic analyses the following three main textural features were recognized that allow to describe the most common microscopic features 1 micrite textures 2 micritic coatings and crusts and 3 different types of clasts each major lithofacies is characterized by a particular association of these textural types the geometry of the travertine beds follows the antecedent land surface a ne sw striking pre pleistocene valley it is proposed that in this valley travertine precipitation took place along a gently sloping terrain the gazda travertine system was fed by at least two groundwater springs one of them was located ne of the quarry from which waters were flowing along the axis of the valley the other source was located to the east of the gazda quarry and waters joined the main water course along the valley closest to the confluence a phytohermal mound developed with lateral slope and eventual pond depositional systems onlapping and interfingering with the flat laminated lithofacies indicate alternating activity of the two springs fractures observed in the quarry are mainly related to postdepositional gravitational sliding however neotectonic forces resulting in nw se tension also played a role in the formation of the fractures stable oxygen and carbon isotope analyses show that water temperature was approximately 25 c petrographic studies indicate that only syn diagenetic processes affected the precipitates therefore the original stable oxygen isotope signatures characteristic of the depositional environment were preserved detailed sedimentological and geochemical study of the gazda travertine complex allowed small scale facies characterization providing information about the ancient depositional environment and the heterogeneous nature of these carbonates

dolomitization gypsum calcitization and silicification in carbonate evaporite shallow lacustrine deposits this paper describes and interprets the mineral and facies assemblages that occur in carbonate evaporite shallow lacustrine deposits considering the importance of the processes pathway i e dolomitizacion gypsum calcitization and silicification the palaeogene deposits of the deza formation almazan basin central northern spain are selected as a case study to determine the variety of physico chemical processes taking place in carbonate evaporite shallow lakes and their resulting diagenetic features dolostones are the predominant lithology and are composed mainly of dolomite with variable amounts of secondary calcite 5 to 50 which mainly mimic lenticular gypsum pseudomorphs five morphological types of dolomite crystal were identified dolomite tubes dolomite cylinders rhombohedral dolomite spheroidal and quasi rhombohedral dolomite and cocoon shaped dolomite the dolomite cylinders and tubes are interpreted as the dolomitized cells of a widespread microbial community the sequence of diagenetic processes started with growth of microlenticular interstitial gypsum in a calcareous mud deposited on the playa margin mudflats and that sometimes included microbial sediments immediately following growth of gypsum dolomite replaced the original calcite aragonite muds the microbial community and the gypsum partial or total replacement of gypsum by dolomite was related mainly to the biomineralization of endolithic microbial communities on gypsum crystals later calcitization took place under vadose subaerial exposure conditions the development of calcrete in distal alluvial settings favoured the release of silica and subsequent silicification on the playa margin mudflats stable isotope compositions of calcite range range from 9 02 to 5 83 13cpdb and 7 10 to 1 22 18opdb for the dolomite these values vary from 8 93 to 3 96 13cpdb and 5 53 to 2 4 18opdb quartz from the cherts has 18osmow values ranging from 27 1 to 31 1 wide variation and relatively high 18osmow values for dolomite indicate evaporitic and closed hydrological conditions increased influx of meteoric waters reigned during the formation of secondary calcite spar this article is protected by copyright all rights reserved

an energy and mass model of snow cover suitable for operational avalanche forecasting a numerical model has been developed to simulate energy and mass evolution of snow cover at a given location as a function of meteorological conditions precipitation air temperature humidity wind velocity and incoming short wave and long wave radiation this model named crocus was first tested on a well instrumented field during a whole winter showing its ability to simulate the important phenomena affecting the evolution of the snow layers high temperature gradients wetting compaction and melting freezing cycles a second test was conducted at two locations in the french network used for operational avalanche forecasting though the weather observations are made there only twice daily the snow profiles calculated by the model were very close to those obtained once a week by a pit observation crocus proved itself sufficient to be considered now as a useful objective tool for operational avalanche forecasting

depth hoar growth rates near a rocky outcrop observ atio ns of slab a ala nche releases in alpine terrai n ha e led to the hypoth esis that rocky outcrops can inf luence thc spati al distribut ion s of tempe rat ure and heat flow in dry alpine snow covers and thus c011lr ol the local dist ributio n of depth hoar vc investigate the effects of ter rain on crystal growth by using a two di mensional finite elem ent model of heat flow coup led with a model of crystal growth from vapor we used the model to exa mine the inf luence of snow prop ert ies terrain geome try and snow depth on this phenomenon the effect is stron ger in the early winter than in the late win ter because the rock has then had ti me to cool in all cas es wc found that depth hoar grow th occurs pref erentially o er th e rock this sugg est s that snow pit im cstigat ions made over soi l can be m isle ading if rocky out crops are prese nt

the principle of minimum entropy production and snow structure an essential problem in snow science is to predict the changing form of ice grains within a snow layer present theories are based on the idea that form changes are driven by mass diffusion induced by temperature gradients within the snow cover this leads to the well established theory of isothermal and temperature gradient metamorphism although diffusion theory treats mass transfer it does not treat the influence of this mass transfer on the form the curvature radius of the grains and bonds directly empirical relations based on observations are additionally required to predict flat or rounded surfaces in the following we postulate that metamorphism the change of ice surface curvature and size is a process of thermodynamic optimization in which entropy production is minimized that is there exists an optimal surface curvature of the ice grains for a given thermodynamic state at which entropy production is stationary this state is defined by differences in ice and air temperature and vapor pressure across the interfacial boundary layer the optimal form corresponds to the state of least wasted work the state of minimum entropy production we show that temperature gradients produce a thermal non equilibrium between the ice and air such that depending on the temperature flat surfaces are required to mimimize entropy production when the temperatures of the ice and air are equal larger curvature radii are found at low temperatures than at high temperatures thus what is known as isothermal metamorphism corresponds to minimum entropy production at equilibrium temperatures and so called temperature gradient metamorphism corresponds to minimum entropy production at non equilibrium temperatures the theory is in good agreement with genera observations of crystal form development in dry seasonal alpine snow

discriminating between tectonism and climate signatures in palustrine deposits lessons from the miocene of the teruel graben ne spain the upper miocene vallesian turolian unit ii of the teruel graben comprises at its top a 25 m thick sequence of palustrine deposits deposition of the entire unit commenced some 9 to 7 ma ago in a halfgraben basin here via a recent quarry we examine in detail the lateral and vertical distribution of unit ii s palustrine facies and their features to determine the palaeogeography and main controls on deposit formation our findings suggest the deposits formed at a low gradient lake margin with different energy levels these energy levels controlled the type of primary deposit within the lake wackestone to packstone sediments formed in low energy conditions whereas cross bedded rudstones to floatstones formed under higher energy conditions by erosion and redeposition of prior lacustrine deposits pedogenic and diagenetic modifications of the primary sediments took place during sedimentary discontinuities sd when the lacustrine sediments were subaerially exposed these processes serve to explain the formation of eight different palustrine limestones limestones with root traces mottled limestones brecciated limestones flat pebble breccias granular limestones micro karstified limestones with laminar calcretes carbonate mounds and clayey limestones with laminar calcretes based on the features and thicknesses of the modified sediments five different morphological stages i to v of palustrine carbonates are defined stage i is characterized by incipient mottling and brecciation stage ii shows mottling and strong brecciation that lead to the formation of intraclast breccias in which the fragments are mostly in situ in stage iii the primary fabric is totally changed intraclasts have moved and may have lost their initial morphology this stage iii may also be characterized by the formation of micro karst stage iv is typified by the presence of coated grains and thin root mats the chronological data available suggest that the formation of stage iii lacustrine deposition palustrine modification would require about 40 000 yr facies and the sd record changes across short horizontal distances and thus reflect the topography of prior sedimentation modification events small 50 cm highs with micro karst have their sd counterparts in lower areas of the lake in which the sd is indicated by desiccation and mottling the topographic differences of the micro karst were filled by intraclastic rudstones sourced by the adjacent carbonate flats the example examined not only clearly sketches the morphology of ancient palustrine systems or wetlands it also provides evidence that recycling of previous carbonate deposits played an important role as a sediment source apart from biogenic or physical chemical production processes our geochemical data indicate lmc low magnesian calcite as the main component and fe contents lower than 1 except for the mottled areas that are richer in feo stable isotope compositions provide 18o values close to 6 5 vpdb and more varied 13c 3 39 to 6 97 pdb oxygen and carbon values reveal no covariation and clear trends are lacking the homogeneity of 18o values reflects the intense effects of meteoric waters the deposition of these palustrine limestones took place under suitable semi arid to sub humid climates climate could also have a role in determining subaerial exposure periods however its imprint is not easy to detect neither in the geochemical signals nor in the vertical arrangement of the facies this could be attributed to climate changes probably occurring over shorter periods than those that can be recorded in this type of sediment such as the astronomical precession cycles and suggests the unsuitability of palustrine carbonates for detailed palaeoclimate analyses tectonism controlled the location of the main lacustrine depocentre close to the basin s main fault the activity of this normal fault during the sedimentation of unit ii determined long and short term sedimentary sequences such sequences are the response to small scale subsidence pulses followed by the infill of the created accommodation space by shallow lacustrine deposits which underwent early pedogenic and diagenetic processes after subaerial exposure

diagenesis of late proterozoic carbonates the beck spring dolomite of eastern california abstract petrographic and compositional attributes of limestone and dolostone in the beck spring dolomite of eastern california indicate that late proterozoic mineralogies isotopic compositions and diagenetic processes were similar to those inferred for younger phanerozoic marine carbonate sequences allochems in limestones include strontium rich ooids with well preserved concentric banding and cortices of equant neomorphic calcite that commonly exhibit dissolution and compaction features cements include microdolomite rich columnar marine calcite and equant spar calcites are depleted relative to dolomites and become enriched with stratigraphic depth acicular and columnar marine cement and allochems in dolostones display fabrics identical to those in limestones but are isotopically distinct dolomite ooids columnar and acicular cement crystal silt and early luminescent spar cement from four stratigraphic sections define overlapping positive oxygen carbon covariant fields that trend toward depleted calcite compositions early luminescent dolomite spar cement is unconformably overlain by depleted ferroan dolospar fabric data suggest that marine cement and ooids were precipitated as magnesian calcite and aragonite isotopic data suggest that metastable components locally stabilized to calcite during subaerial exposure while laterally dolomitization took place in mixed marine meteoric waters early dolospar precipitation began during replacive dolomitization and late ferroan dolospar precipitated during burial lack of evidence for hypersaline conditions suggests that late proterozoic normal marine carbonate isotopic composition was 0 5 2 018o and 5 3 0 5913c

late jurassic biogeochemical microenvironments associated with microbialite coated unionids bivalvia asturias n spain abstract the vega formation upper jurassic asturias spain contains two kimmeridgian outcrops the abeu and huerres sections with bivalves coated with carbonate microbialites oncoids the bivalve shells in the abeu section were replaced early by calcite while those of the huerres section were dissolved and the moulds filled by late diagenetic cements for the abeu shells there was a loss of sr and a gain of mg fe and mn during the replacement process but much of the original organic matter was retained part of the s present can be linked to this organic matter and part to the sulphate that replaced the carbonate groups in the calcite the thin microbialites inside the shells of some of the huerres bivalves have allowed us to estimate the influence of the growth rate on the incorporation of trace elements in calcite with an approximately six times lower growth rate the internal microbialite incorporates less mg and s and more fe and mn than the external one while maintaining the sr content the trace element content mg s sr fe and mn of the huerres and abeu microbialites are similar these coatings may therefore have been formed in the same type of freshwater but in different microenvironments given the substantial sulphate content of the microbialites from both sections this freshwater probably came from hot springs however the high fe mn ratio of the abeu microbialites suggests a reducing environment during their formation indeed 18o and 13c data confirm that the abeu and huerres microbialites were formed in different microenvironments the positive covariance for 18o and 13c of the abeu microbialites and replaced shells r2 0 83 and the wide range of variation for 18o 2 80 together suggest that the microbialite crusts grew in isolated ponds where evaporation was dominant in the huerres microbialites the positive covariance for 18o and 13c r2 0 59 and the narrow range of variation for 18o 0 74 indicate that the huerres section was formed in a more open environmental system where degassing predominated over evaporation

interplay between tectonics climate and fluvial transport during the cenozoic evolution of the ebro basin ne iberia 1 three dimensional modeling that integrates fluvial sediment transport crustal scale tectonic deformation and lithospheric flexural subsidence is carried out to simulate the landscape and drainage evolution of the ebro sedimentary basin ne iberia the ebro basin underwent a long period of closed intramountain drainage as a result of tectonic topography generation at the pyrenees the iberian range and the catalan coastal range in the late oligocene the catalan coastal range underwent extension leading to the formation of the valencia trough nw mediterranean but the ebro basin remained closed for nearly 15 myr more before the ebro river cut through the remnants of the topographic barrier this drainage opening caused widespread basin incision that shaped spectacular outcrops of the syntectonic and posttectonic infill here we investigate the processes controlling these major drainage changes the modeling results constrained by a large data set on the tectonic and transport evolution of the area predict a closed phase characterized by a large lake in the central eastern ebro basin dry climatic conditions probably lowered the lake level and contributed together with rift flank uplift to prolong this endorheic basin stage the age and amount of reworked sediment after the opening are consistent with an onset of basin incision between 13 and 8 5 ma as a result of lake capture by escarpment erosion and lake level rise associated with sediment accumulation and wetter climatic conditions sea level changes in the mediterranean had no major impact in the large scale drainage evolution of the ebro basin index terms 1625 global change geomorphology and weathering 1824 1886 1815 hydrology erosion and sedimentation 3210 mathematical geophysics modeling 3344 meteorology and atmospheric dynamics paleoclimatology 8102 tectonophysics continental contractional orogenic belts keywords pyrenees drainage evolution lake sediment budget erosion flexure

sedimentological and palaeohydrological responses to tectonics and climate in a small closed lacustrine system oligocene as pontes basin spain a small closed lacustrine system developed during the restraining overstep stages of the oligocene as pontes strike slip basin spain the increase in basin accommodation and the headward spread of the drainage which increased the water input triggered a change from shallow holomictic to deeper meromictic conditions the lower shallow lacustrine assemblage consists of mudstone carbonate cycles recording lacustrine palustrine ramp deposition in a saline lake high sr content in some early diagenetic calcites suggests that aragonite and calcite made up the primary carbonate muds early dolomitization took place together with widespread pedogenic activity the upper deep freshwater lacustrine assemblage includes bundles of carbonate clay rhythmites and fine grained turbidite beds primary calcite and diagenetic siderite make up the carbonate laminae the mg content of the primary carbonates records variations in mg ca ratios in lacustrine waters d 18 o and d 13 c covariance trends in calcite reinforce closed drainage conditions d 18 o data indicate that the lake system changed rapidly from short lived isotopically light periods i e from seasonal to pluriannual to longer steadystate periods of heavier d 18 o i e from pluriannual to millennial the small d 13 c changes in the covariant trends were caused by dilute inflow changing the contributions of dissolved organic carbon in the system and or internal variations in lacustrine organic productivity and recycling in both shallow and deep carbonate facies sulphate reduction and methanogenesis may account respectively for the larger negative and positive d 13 c shifts recorded in the early diagenetic carbonates calcite dolomite and siderite the lacustrine system was very susceptible to high frequency climatically forced water balance variations these climatic oscillations interfered with the lowfrequency tectonic and morphological changes in the basin catchment this resulted in the superposition of high order depositional mineralogical and geochemical cycles and rhythms on the lower order lacustrine infill sequence

palustrine sedimentation and associated features grainification and pseudo microkarst in the middle miocene intermediate unit of the madrid basin spain abstract a rather thick sequence 50 75 m of lacustrine limestones forms the uppermost part of the intermediate unit middle miocene in the ne part of the madrid basin central spain a gradual change from distal alluvial to open lake facies is recorded in this area red mudstones passing vertically to strongly mottled limestones are typical of the transition from distal alluvial to marginal lake deposits a wide variety of facies occur in the marginal lacustrine facies association all of them showing pedogenic features e g root traces alveolar septal structures pseudo microkarst micrites and biomicrites are interpreted as open lacustrine deposits although not as strongly pedogenically modified as the marginal lacustrine facies they still show evidence of subaerial exposure the carbonate sequence was deposited in a low gradient shallow lake system in which slight fluctuations in the water level caused extensive emergence pedogenic processes affected most of the lake deposits but modification was more intense in the marginal facies biogenic activity and mechanical reworking at lake margins led to the formation of pedogenic diagenetic pseudo microkarst and peloidal and or intraclastic limestones

recognition of lake level changes in miocene lacustrine units madrid basin spain evidence from facies analysis isotope geochemistry and clay mineralogy abstract the miocene lacustrine sequence exposed near esquivias in the central area of the continental tertiary madrid basin is formed of two main lithostratigraphic units that represent two different stages of a palaeolake system unit i consists of five lithofacies a nodular carbonates and marls b massive dolostones c bioclastic limestones d mudstones and e chert which are characteristic of sedimentation and early diagenesis in a shallow lacustrine environment two main stages of the same general lowstand situation are reflected in mineralogy and isotope geochemistry results an initial stage is suggested by the presence of non stoichiometric dolomite and trioctahedral smectites high 18o and 13c values of the dolomites 5 5 and 2 9 respectively indicate strongly evaporative conditions a second stage is characterized by the presence of calcite fibrous clay minerals and by generally lower 18o from 1 5 to 6 5 and 13c from 1 to 9 8 values for carbonates which suggest more diluted waters during this lowstand phase of the lake unit ii comprises seven lithofacies a conglomerates b intraclastic mudstones c laminated marls d massive mudstones e diatomaceous marls f laminated bioclastic limestones and g root bioturbated limestones both conglomerates and intraclast mudstones fill sharply eroded contacts in the underlying deposits of unit i we demonstrate how the arrangement of facies supported by isotopic results from the carbonates 18o from 0 7 to 7 2 13c from 4 2 to 8 6 is clearly indicative of deeper lake conditions the basal reworked facies mark the initial phase of a lake transgression in contrast with unit i the clay mineral assemblage from unit ii is mainly detrital clay minerals thus also support the interpretation of a dilute water body consistent with a highstand of the palaeolake

evolution from a freshwater to saline lake a climatic or hydrogeological change the case of gallocanta lake northeast spain sedimentological and hydrogeological studies are combined in order to investigate the environmental conditions of the lacustrine sedimentation during the holocene in gallocanta lake in spain six units have been identified in the sedimentary succession based on sedimentological facies and mineralogy and three depositional stages have been defined 1 alluvial 2 carbonate lake system 3 ephemeral carbonate saline lake system the transition between stages 2 and 3 implies a reduction in water inflows to the lake the 13c isotopical analysis of dolomites points to decaying organic matter as a source of carbon for the dissolved inorganic carbon and evinces that the 13c variations in the lake were probably controlled by organic processes on the other hand 18o values could be controlled by modifications in the hydrological system and not necessarily by climatic changes in this sense from the hydrological study three aquifers can be defined triassic jurassic cretaceous and cenozoic aquifers the lack of coincidence between the surface and subterranean watershed suggests that the transition between the second and third stages is controlled by a shift of the subterranean watershed copyright 2006 john wiley sons ltd