stable isotope composition of late pleistocene holocene eobania vermiculata muller 1774 pulmonata stylommatophora shells from the central mediterranean basin data from grotta d oriente favignana sicily abstract this paper presents stable isotopic results oxygen and carbon from both modern and late pleistocene holocene shells of the land snail eobania vermiculata muller 1774 from favignana island sicily it aims to contribute to the understanding of climate and vegetation history of this region during formation of upper palaeolithic mesolithic and meso neolithic deposits of grotta d oriente ort results from both an evaporative model fbm and an empirical regional isotopic model i e linear relation between oxygen isotopic composition of shells 18 os and those of local precipitation 18 op indicate that the 18 os values of modern specimens are mainly controlled by local temperature relative humidity and 18 op at the time of snail activity data also suggest that the modern snails are nocturnally active almost all year round in the study area the carbon isotopic compositions of shells 13 cs of the same specimens indicate a diet prevalently or exclusively composed of c3 vegetation the 18 os values of late pleistocene specimens suggest that climate conditions at 14 2 ka cal bp were similar to the present day in agreement with additional 18 os records from southern italy by contrast early middle holocene shells are notably 18 o depleted and suggest wetter conditions possibly combined with a decrease in isotopic composition of precipitation source compared to the present day when compared with regional palaeoclimatic records a large scale isotopic response to millennial scale changes in atmospheric and hydrological conditions e g enhanced rainfall in the central eastern mediterranean is observed during the early middle holocene the 13 cs of late pleistocene and holocene specimens are consistently higher than those of modern ones for the late pleistocene this could be reasonably explained in terms of water stressed vegetation on the other hand this seems to be less valid for holocene counterparts when the climate was wetter probably 13 cs values result from the combination of distinct competing factors involving atmospheric co 2 concentration seasonal water budget vegetation type cover and other carbon sources results reveal coherent relationships between regional 18 os and 13 cs demonstrating that late pleistocene holocene land snail shell remains from archaeological sites may provide useful snapshots of past seasonal climate conditions

oxygen isotope signatures from land snail helix melanostoma shells and body fluid proxies for reconstructing mediterranean and north african rainfall abstract in this paper we show that oxygen isotope ratios from the shell carbonate of the land snail helix melanostoma reflect local rainfall parameters stable oxygen isotopes were measured in the body fluid 18 o body and shells 18 o shell of live collected h melanostoma along a north south transect across the gebel akhdar in northeast libya 18 o body ranged between 8 1 and 13 0 whilst 18 o shell ranged between 1 0 and 2 8 to investigate the relationship between snail oxygen isotope composition and climate these measurements were correlated with ambient air temperature relative humidity rainfall amount and the 18 o composition of rainwater 18 o rain strong and significant correlations were found between 18 o shell and 18 o rain and between 18 o shell and rainfall amount r 2 0 79 and 0 85 respectively suggesting that h melanostoma shells can be used as a proxy for past rainfall conditions when combined in multiple linear regressions 18 o rain and rainfall amount explained 90 of the variance in 18 o shell r 2 0 90 simple and multiple linear regressions were used to develop predictive models for these climate parameters as h melanostoma shells are commonly found in mediterranean and north african archaeological and geological deposits the predictive equations developed in this study hold great potential for reconstructing pleistocene to holocene rainfall and aridity patterns in the gebel akhdar and for assessing the relationship between environmental changes and human behavioural changes

late pleistocene holocene eolian deposits of the southern buenos aires province argentina a preliminary model abstract the aim is to reconstruct the sedimentological history of the late pleistocene holocene eolian deposits of southern buenos aires province hence a preliminary model is proposed in order to analyze the different stages of the sedimentological cycle the deposits include sandy loess fine sand sheets and dunefields the southern buenos aires province represents the depositional area whereas the source and transport environments are located in the northern patagonian andes and northern extra andean patagonia according to the mineralogical characteristics of the material explosive volcanism is considered the predominant process of particle formation particularly as generator of pyroclastic deposits which were reworked by different erosive processes glacial fluvial eolian during the late glacial maximum and the holocene alluvial deposits which were mainly generated by fluvial erosion of volcaniclastic sedimentary units were deposited along the floodplains of the colorado and negro rivers including those distal segments located in the emerged offshore platform the fluvial regime depended upon the regime of the glaciers hence it reflected the major glacial fluctuations which took place in the andes floodplains were deflated by southwest winds transporting the material towards the southern buenos aires province sandy loess and loessial sands and to la pampa province dunefields

a multi proxy study of holocene environmental change recorded in alluvial deposits along the southern coast of the pampa region argentina analyses of fossil records of molluscs stable isotopes of carbon and oxygen diatoms and palynomorphs from alluvial deposits at arroyo claromeco in the southern pampa region of argentina provide an integrated reconstruction of rapid holocene environmental change related to marine and palaeoclimate influences the major events recorded include i disturbances produced by marine influences in close proximity to the coast before ca 7700 cal a bp ii a short term decrease in salinity associated with freshwater influx between ca 7700 and 7400 cal a bp in response to eustatic adjustment as sea level rose iii an increasing input of marine water related to the holocene sea level highstand and greater evaporative conditions between 7400 and 6450 cal a bp and iv evaporative processes linked to a pronounced climatic variability that triggered changes in water chemistry during the last ca 6000 cal a bp concurrently with the late holocene sea level fall a comparison of coastal and continental stable isotope records from the pampa region reveals that evaporation and a negative precipitation evaporation p e ratio balance strongly influenced water chemistry in the coastal region and was as important an influence as marine water during the period of maximum sea level highstand copyright 2014 john wiley sons ltd

holocene trends in 18o in land snail shells from the negev desert and their implications for changes in rainfall source areas abstract the 18o value of the carbonate of land snail shells is related to the 18o content of precipitation which in turn relates to the source region and trajectory of the rain bearing air masses analyses of 18o of the shell carbonate of 76 radiocarbon dated holocene samples of the land snail trochoidea seetzeni from the northern negev desert in southern israel were carried out and the results were compared to modern snails from the same region early holocene 18o values are similar to modern but during the period centered around 6500 6000 yr b p a depletion of some 2 below modern is observed a change in the atmospheric circulation pattern for this period is thus indicated most likely an increase in the frequency of storm systems reaching the region from north eastern africa by 3500 yr b p 18o values had reached modern levels and indicate a stable pattern of atmospheric circulation since that time

recrystallization of shell carbonate in soil 14c labeling modeling and relevance for dating and paleo reconstructions abstract mollusk shells are commonly present in a broad array of geological and archaeological contexts the shell carbonate can serve for numerical age determination 14 c and as a paleoenvironmental indicator 18 o 13 c shell carbonate recrystallization in soils however may re equilibrate the carbon c isotopic signature with soil co 2 the equilibration dynamics remain poorly understood because of the absence of suitable experimental approaches here we used the artificial 14 c labeling technique to study the process of shell carbonate recrystallization as a function of time organic free and organic containing shell particles of protothaca staminea were mixed with loess or a carbonate free loamy soil the mixtures were placed in air tight bottles where the bottle air containing 14 co 2 p co 2 2 the 14 c activity of shells was measured over time and related to the recrystallization of shell carbonate recrystallization of shell carbonate already began after one day the recrystallization rates were 10 3 day 1 in organic containing shell embedded in soil and 1 6 10 2 day 1 in organic free shells in loess removal of organic compounds increased shell porosity and so increased the contact surface for exchange with soil solution organic free shells recrystallized much faster in loess 0 56 in 56 days than in other treatments recrystallization was 2 to 7 times higher in loess in the presence and absence of organic compounds respectively than in carbonate free soil loess carbonate itself can recrystallize and accumulate on shells leading to overestimation of shell carbonate recrystallization a model for shell carbonate recrystallization as a function of time was developed the model considers the presence or absence of organic compounds in shell structure and geogenic carbonates in the embedding matrix the model enabled all results to be fitted with r 2 0 98 the modelled time necessary for nearly full recrystallization 95 of shell carbonate was 88 years for organic free shells in loess and up to 770 years for organic containing shells in carbonate free soil after this period the original isotopic signature will vanish completely and will be replaced by a new 13 c and 14 c signature in the shell structure thus shell carbonate recrystallization may proceed relatively rapidly in terms of geologic time this is necessary to consider in the interpretation of dating results and paleoenvironmental reconstructions

sand dune geometry of large rivers during floods the geometry of lower regime bed forms in several large sand bed rivers is investigated during average and flood conditions the van rijn method is revised because it generally underpredicts the dune height of most large rivers around the world during floods in large sand bed rivers upper regime plane bed is not necessarily obtained when t 25 both parameters describing dune height and dune steepness do not decrease as the transport stage parameter t increases in the range 10 t 25 the analysis of bed form data during large floods on the meuse river and the rhine river branches indicates that both the dune height and length generally increase with discharge while dune steepness remains relatively constant a reasonable approximation of the wavelength is 6 5 h where h is the flow depth the dune height varies as a function of the depth h and median grain size d50 estimates can be obtained by 2 5 h 0 7d0 350

erosional history of the eastern tibetan plateau since 190 kyr ago clay mineralogical and geochemical investigations from the southwestern south china sea a high resolution study of clay mineralogy and major element geochemistry has been conducted on high sedimentation rate cores md01 2393 and md97 2150 collected off the mekong river mouth in the southwestern south china sea in order to reconstruct the erosional and weathering history of the mekong basin the chronology is based upon planktonic foraminiferal oxygen isotope records combined with carbonate stratigraphy clay minerals and major element results suggest that the mekong river is the major sedimentary source over the past 190 kyr for both cores illite and chlorite were derived mainly from the eastern tibetan plateau kaolinite was derived mainly from active erosion of inherited clays from reworked sediments in the middle part of the mekong basin smectites originated mainly through chemical weathering of parent aluminosilicate and ferromagnesian silicate under warm and humid conditions in the middle to lower parts of the mekong basin smectites illite chlorite and smectites kaolinite ratios coupled to k2o sio2 and al2o3 sio2 ratios allow us to reconstruct a history of chemical weathering versus physical erosion good correlations between those ratios suggest monsoon controlled weathering and erosion over the eastern tibetan plateau and the mekong basin variations with time scales of 0 3 0 6 kyr for the last 70 kyr and 1 2 kyr for 70 190 kyr ago in the chemical weathering erosional history are strongly related to the east asian monsoon evolution which is itself related to the summer solar radiation calculated for the northern hemisphere d 2004 elsevier b v all rights reserved

limestone and the problem of radiocarbon dating of land snail shell carbonate in order to test the role of limestone in producing anomalously old radiocarbon ages in land snail shells 14 c analyses were performed on shell carbonate of modern land snails from limestone and nonlimestone areas of jamaica no anomaly was found in snails from the nonlimestone area implying that such material is suitable for radiocarbon dating snails from limestone areas produced variable anomalies of as much as 3 120 yr due to incorporation of 14 c free limestone into shell carbonate all rock scraping snails and most leaf litter feeding snails from limestone areas showed anomalous 14 c contents because of the variability in 14 c content even within species no standard correction factor for limestone anomaly can be applied however dating error can be minimized by selecting ecologically appropriate species or by comparison of analyses of several fossil species within a stratum to their modern counterparts

the plio pleistocene record of the central eastern pampas buenos aires province argentina the chapadmalal case study abstract the plio pleistocene record of central eastern pampas argentina is preserved in loess like sediments exposed in the sea cliffs south of mar del plata the uplift of the andes during miocene triggered the deposition of wind blown material the source areas are located about 1000 km away in western argentina volcanic ashfalls play a significant role in the formation of eolian sediments which were reworked and redeposited by aqueous transport in a flat low relief landscape under varying climatic conditions vertebrate fossil assemblages document warm and wetter pliocene and early pleistocene climates during montehermosan and uquian land mammal ages more arid and cooler conditions alternating with humid and warmer intervals prevailed during the middle to late pleistocene in ensenadan and lujanian land mammal ages the chapadmalal locality is the best exposed and most complete section almost all the units have been modified by pedogenesis truncated paleosols as well as pedogenic and non pedogenic calcretes are very frequent throughout the stratigraphic succession several paleosurfaces with prominent paleosols and calcretes suggest that sedimentation was an episodic process with numerous depositional gaps recording relatively long lasting intervals of landscape stability the depositional events represent alternations of fluvial and eolian sedimentation low frequency catastrophic episodes played an important role in the sedimentation process

stable isotope δ18o δ13c and δd signatures of recent terrestrial communities from a low latitude oceanic setting endemic land snails plants rain and carbonate sediments from the eastern canary islands abstract stable isotopes of oxygen and carbon extracted from fossil land snail shells have been used increasingly to interpret past environments to evaluate the utility of this approach for low latitude oceanic islands populations of the modern helicid land snail theba geminata a species also abundant in the quaternary fossil record of the region were sampled at ten low altitude d and 2 v smow for 18 o ranging from 11 to 2 v smow and from 2 6 to 0 7 v smow respectively the local vegetation is heterogeneous including c 3 c 4 and cam plants 13 c values vary from 13 0 to 29 0 v pdb across plant species of the 24 species five are c 4 15 are c 3 and four are cam plants the 18 o values for shells represent a narrow range of values from 0 3 to 2 5 v pdb which is consistent with the low climate seasonality typifying low latitude oceanic settings hypothetical model of the expected 18 o value for shell aragonite precipitated in equilibrium suggests that the most negative 18 o shell represent the closest estimate for 18 o rain water the 13 c values of shells range from 9 4 to 1 7 v pdb the most positive 13 c values are attributed to a diet based on c 4 plants the comparison of 13 c values of soft tissues and shells suggests that snails ingested notable amounts from 20 up to 40 of foreign carbonates consequently fossil shells with the most negative 13 c values should be selected for radiocarbon dating in future geochronological studies of the region the 13 c values of body tissues vary from 12 0 to 27 2 v pdb indicating that land snails consumed c 3 and c 4 plants indiscriminately the mean carbon isotopic composition averaged across multiple fossil specimens may thus provide a useful tool for reconstructing paleoclimates and paleoenvironments throughout the quaternary history of the canary islands and other comparable low latitude oceanic settings

palaeoclimates in central and south america since 18 000 bp based on pollen and lake level records abstract the last 18 ka of palaeoclimates are discussed at 3 ka intervals based on palaeoenvironmental changes shown in pollen and lake level records from central and south america a total of 61 pollen records fulfill the requirements of continuity and chronology to be used in this synthesis 8 records from tropical and subtropical lowlands in central and south america 7 records from the central american highlands 26 records from the high andes north and south of the equator 2 records from the southern subtropics and 18 from the southern andes and subantarctic islands palaeoclimatic interpretation of the pollen records is semiquantitative based on bioclimatic parameters such as e g elevational temperature gradients or latitudinal precipitation gradients that can be related to vegetation zonation additional palaeoclimatic information is obtained from lake level records derived either from dated shorelines or from the limnological history of lake sediment sections large scale palaeoclimatic comparison of the proxy data records indicates that full and late glacial climates throughout central and south america were cooler than today by about 4 to 5 c but that moisture patterns showed regional differentiation thus in both the southern subtropics and high latitudes in southern chile conditions were substantially moister than today during full and late glacial times whereas everywhere else conditions were far drier than today in terms of palaeocirculation this scenario can be interpreted as a poleward shift of the subtropical as well as the westerly circulation a scenario that has been suggested by palaeoclimatic simulations from general circulation models gcm another major palaeoclimatic aspect predicted by the gcm simulations is the suppressed early holocene summer monsoon in the southern subtropics although proxy records are few from this zone their palaeoenvironmental history during that time shows a period of aridity that would support the model one of the most controversial aspects of south american palaeoclimates concerns the existence of a younger dryas equivalent a cold period between 11 and 10 ka bp based on the existing data from south america that show a great diversity of palaeoclimatic trends the concept of an interval that is characterized by the same climatic signal as documented for the north atlantic seems too simplistic moreover at this point only very few records have been analysed in sufficient detail to yield unambiguous climatic information for the interval in question the principal outcome of this palaeoenvironmental and palaeoclimatic synthesis is the better understanding of the type and quality of data available at present and the realization of regions and periods where much more and concerted effort is needed to address problems of intra and interhemispheric palaeoclimatic correlations only then can questions concerning the mechanism of climatic change be tackled successfully

the use of land snail shells in paleoenvironmental reconstruction fossil land snail shells constitute a valuable source of paleoenvironmental information for the quaternary they can be dated by a variety of methods including radiocarbon amino acid racemization and epimerization and perhaps also thu and esr the vast majority of paleoenvironmental studies based on land snail shells have examined the faunal composition of fossil assemblages from which a variety of paleoenvironmental characteristics such as biome temperature and moisture conditions have been reconstructed still there are a number of problems involved in using this approach and these are discussed shell morphology has occasionally been used to reconstruct such factors as rainfall and temperature stable isotope studies on quaternary land snails include analysis of 18o values of organic matter in the shells to reconstruct c4 plant distributions from which rainfall amounts can be inferred and analysis of 18o values of shell carbonate from which trends in the oxygen isotope composition of rainfall can be reconstructed stable carbon isotopes of shell carbonate have also been studied but their interpretation is not clear amino acid epimerization analysis dalloisoleucinel isoleucine ratios of land snail shells has been used for estimation of paleotemperatures some potential uses of land snail shells for paleoenvironmental reconstruction include the study of stable isotopes of h and n periodic growth lines and deposits of pedogenic carbonates on the shells

the occurrence of obtuse junction angles and changes in channel width below tributaries along the mekong river south east asia classic descriptions of drainage patterns suggest that confluence angle is determined by the shape of the drainage basin unless constraining factors such as the geological structure affect stream flow downstream changes in channel width below tributary junctions have long been associated with tributary inputs of flow and sediment analysis of tributary junction geometry and channel width changes in large rivers and over large reaches is sparse the lower mekong basin exhibits a generally dendritic drainage network despite flowing through a diverse array of geological settings publicly available spot 5 imagery from google earth was used to identify and catalogue junction geometries and downstream changes in channel width below tributary junctions along a 2200 km reach of the mekong river of the 284 junctions identified the majority 66 2 were acute however 12 4 8 were found to be normal 90 and 75 30 were found to be obtuse this latter number is in contrast to previous studies over similar spatial scales which found little evidence of obtuse junctions meander extension of the incoming tributary and deflection of the tributary across bedrock shoulders were found to be the dominant geomorphological causes of obtuse tributary junctions the relationship between the width of the tributary channels and the width of the mainstem upstream and downstream of the confluences was analysed it was observed that over the whole reach a slight narrowing occurred immediately below tributary junctions although the changes themselves were small the slight net narrowing is shown to be statistically significant the observed relationship is shown to vary considerably with geology the geological control suggests that complex factors play important roles in determining changes to channel width across large systems and that simple cause effect relationships do not hold in such complicated geological settings

creep and time dependent damage in argillaceous rocks abstract this paper presents the results of laboratory tests on the time dependent behaviour of three rocks characterized by a high proportion of clay particles the viscosity of these sedimentary rocks was studied under different loading conditions in uniaxial compression static or cyclic creep tests and quasistatic tests low loading strain rate were performed across various orientations of fabric planes the quasistatic tests showed similarities in the mechanical response of these three argillaceous rocks a late phase of dilation and a linear development of volumetric deformation before the beginning of unstable crack propagation the development of secondary and tertiary creep phases during the creep tests highlighted the existence of a deviatoric stress threshold below which only primary creep is observed long term creep tests also showed that the volumetric variation is not constant during the development of viscoplastic deformations a microstructural analysis of thin sections extracted from specimens after the tests gave evidence of cataclastic and granular creep damage to the argillaceous matrix occurs and no cracks were observed in the quartz and carbonate grains this evidence was also demonstrated for tests with loading at a high strain rate finally this study highlights the significant viscoplasticity of argillaceous rocks the mechanical properties deteriorate rapidly when crack propagation becomes unstable and the viscoplastic strains seem to be due to clay particle slips known as granular creep

late pleistocene mollusc assemblages and inferred paleoenvironments from the andean piedmont of mendoza argentina abstract this paper is focused on the paleoecological analysis of a mollusc succession cropping out on the right margin of la estacada stream in the andean piedmont of mendoza argentina 33 28 s 69 03 w the stratigraphic section mainly composed of fine sands interbedded with levels of silty clays and organic matter records the interval between 35 2 35 5 14c ka b p and 31 5 31 6 14c ka b p the mollusc succession is represented by freshwater and land snails biomphalaria peregrina planorbidae lymnaea viator lymnaeidae succinea meridionalis succineidae rotadiscus amancaezensis charopidae and radiodiscus sp aff radiodiscus quillajicola charopidae the dominance of semi aquatic and hygrophilous land snails suggests the development of a vegetated shallow water body probably a damp habitat occasionally submerged with four main stages of evolution related to fluctuating water levels the abundance of shells together with the stable isotope composition of carbonate shells of l viator 13c and 18o and the presence of radiodiscus sp aff radiodiscus quillajicola and r amancaezensis suggest relatively warm and wet conditions based on its radiocarbon chronology and the paleoecological reconstruction the studied section is recording a mild interval corresponding to an interstadial marine isotope stage 3 of the last glacial cycle

stable isotope composition of land snail body water and its relation to environmental waters and shell carbonate abstract day to day and within day diel variations in d and 18 o of the body water of the land snail theba pisana were studied at a site in the southern coastal plain of israel three phases of variation which relate to isotopic changes in atmospheric water vapor were distinguished 1 on rain days snail water becomes isotopically depleted approximately in the direction of the rain isotope values but always less depleted in d as is atmospheric water vapor 2 during the 1 3 days following a rain the snail water becomes isotopically enriched along a line with slope 18 o space this relates to an increasing influence of humidity derived from the mediterranean sea 3 a period of relative stability of the isotopic composition persists until the next rain event the isotopic variations can be explained by isotopic equilibration with atmospheric water vapor and or uptake of dew derived therefrom during the winter when the snails are active there is only very minor enrichment in 18 o relative to equilibrium with water vapor or dew apparently as a result of metabolic activity but this enrichment becomes pronounced after long periods of inactivity within day variation in body water isotopic composition is minor on non rain days shell carbonate is enriched in 18 o by ca 1 2 relative to equilibrium with body water in most regions the isotopic composition of atmospheric water vapor or dew is a direct function of that of rain because the isotopic composition of snail body water is related to that of atmospheric water vapor and the isotopic composition of shell carbonate in turn is related to that of body water land snail shell carbonate 18 o should provide a reliable indication of rainfall 18 o however local environmental conditions and the ecological properties of the snail species must be taken into account

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

an assessment of sediment transport processes in the lower mekong river based on deposit grain sizes the cm technique and flow energy data abstract the lower mekong river has been an important research topic for at least 15 years notably in the fields of hydrology fluvial geomorphology and the impact of dams recent papers refer mostly to the impact of the lancang chain of hydroelectric dams constructed on the chinese section of the river among the pending scientific questions are 1 the upstream downstream variations in the concentration and yield of suspended sediment and 2 the relative importance of sand in the total yield the general consensus among the scientific community is that the relative importance of sand in suspended load is not the main scientific concern despite its extensive presence in the mekong river channel as noted by geomorphologists and despite its extreme importance for the stability of the delta shoreline in viet nam this paper contradicts the general consensus its objective is to present new information on the processes of sand transport in the lower mekong channel imagery field observations sampling on the river banks and grain size analysis of sand deposits have been carried out between chiang sean downstream of the chinese border and the delta the c m image technique served to discriminate between the various transport processes bedload and different types of suspension this technique helps in understanding the changing processes responsible for downstream sediment transfer in river channels the results of this study are the following 1 discrepancies in the values of annual suspended sediment load detected by different gauging stations have not yet been satisfactorily explained the cm image technique indicates that grain size and the quantity of sand transiting in suspension vs bedload vary from upstream to downstream 2 these upstream downstream differences may be related to the energy of floods energy helps to explain longitudinal variations in the relative importance of the different modes of transport and serves to distinguish between bedload graded and uniform suspension and wash load 3 the mekong is seen as a river carrying mostly silt and clay however the results suggest that sand plays a major role in downstream sediment transfer during floods this result is in line with the large amounts of sand present in the channel its relative importance in the total yield must be reassessed as suggested by walling 2005 2008 as may be expected the role of sand in the stability of the delta shoreline is of prime importance

a catchment scale assessment of anabranching in the 143 000 km2 fitzroy river catchment north eastern australia this paper presents a catchment scale investigation of anabranching in the moderately large 143 000 km2 fitzroy river catchment in north eastern australia the primary aim is to determine whether mapped and remotely sensed data can provide useful information about the characteristics of anabranching in a catchment of this scale anabranching comprises 6 of the total channel network by length and 24 of higher order channels those with catchment areas over 100 km2 three anabranching planform morphologies are described which occur in geographically distinct regions and add to previous descriptions of anabranching rivers sinuosity and link length are calculated for all channels of the mapped channel network a link is a stretch of river between two stream junctions slope mean floodplain width mean annual rainfall and underlying and catchment geology parameters are calculated for links of a stream network derived from a digital elevation model dem in which each link has either a single channel or anabranching morphology anabranching and single channel links do not occupy different ranges of attribute values and a logistic regression analysis was unable to predict anabranching however slope catchment area mean floodplain width length and sinuosity parameters all have significantly different means when comparing single channel with anabranching links although it is shown that the difference in mean floodplain widths is the result of its correlation with catchment area anabranching channels have a tendency towards shorter link lengths lower sinuosities and lower valley slopes and occur at larger catchment areas than single channels these differences are discussed in the context of published hypotheses regarding the cause of anabranching however the spatial resolution and precision of our data limit our ability to investigate controls on anabranching which will require detailed measurement of variables at a reach scale

textural characterization and stratigraphic aspects of the late pleistocene holocene eolian sediments in the sierra de la ventana area buenos aires province argentina abstract textural characteristics of late pleistocene holocene eolian sediments in the sierra de la ventana area buenos aires province argentina are defined and compared with loessic sediments from other areas of the province and with the typical loess of the northern hemisphere these deposits correlate with the stratigraphic units previously established in the study area the study was carried out on samples collected with pedological criterion in the less altered c horizon of two profiles the textural homogeneity which characterizes the sediments of one of the profiles is due to the fact that they were originated on the same parent material on the other hand the differences found within the other profile were inherited from the parent materials the textural features of the sediments analyzed in the present study show the similarity with the loessic sediments described in buenos aires province and show a greater fine sand content than typical loess of the northern hemisphere based on these analyses without taking into account the calcium carbonate content the late pleistocene holocene eolian sediments from sierra de la ventana area are classified as loess sandy loess and eolian silt clayey sand

a suburban inter dike river reach of a large river modern morphological and sedimentary changes the bratislava reach of the danube river slovakia abstract the paper outlines contemporary geomorphic and sedimentary changes 1949 2007 in the suburban inter dike reach of the danube river in bratislava underpinning requirements of its management the studied river reach represents the right bank inter dike area of a tectonically determined bend of the danube river which is about 5 km long with a radius of 1 5 km the landform and floodplain roughness classification schemes show variations in hydraulic and depositional conditions during flooding investigation of landform and floodplain roughness changes and the bank retreat rate is based on the multitemporal interpretation of aerial photographs sedimentological analysis of 10 borings and 20 pit exposures helped to delimit the morphostratigraphic units the process and the rate of the vertical accretion of the modern floodplain were investigated by sedimentological and dendrochronological methods the behaviour of the study reach is dependent on upstream dams in austria dams produce changes in the suspended load regime and a steady riverbed erosion of 2 to 3 5 cm occurs upstream of the study river reach near the slovak austrian border the cunovo dam downstream expediates upstream channel filling in spite of the ongoing channel gravel mining in the danube channel this has resulted in channel bed aggradation of about 1 m since 1992 the bank retreat of about 100 m during 1949 2007 was caused by the natural bank erosion processes as well as by channel straightening as a flood control measure for bratislava the bank shift resulted in the development of the new levee the current overbank deposits differ from the older gravels consisting of a fine grained alluvium varying in thickness from 0 5 m to 1 m the lithofacies of three flood deposits march 2002 august 2002 and september 2007 were examined overbank sediments differentiate with distance from the bank and vertically suburban settings of the study reach and the flood control measures along with the external forcing dams induced changes in channel morphology as well as in floodplain roughness variability this has resulted in changes in the present floodplain sedimentary conditions channel forms and biodiversity the landscape evolved through three distinct evolutionary phases

floodplain deposits channel changes and riverbank stratigraphy of the mekong river area at the 14th century city of chiang saen northern thailand abstract riverbank stratigraphy and paleochannel patterns of the mekong river at chiang saen provide a geoarchaeological framework to explore for evidence of neolithic bronze age ad 5th century yonok and ad 14 16th century lan na cultures typical bank stratigraphy charted on the thailand side is imbricate cobble gravel overlain by 5 10 m of reddish brown sandy silt the silt section is composed chiefly of 1 2 to 2 m thick layers of massive silt without paleosols interpreted as near channel floodplain and gently inclined levee deposits laid down by episodic infrequent large floods the surface soil is dark brown clay loam 20 m since lan na time and has exposed a silt filled moat a radiocarbon age of 1475 cal yr ad was obtained from charcoal at the bottom of the moat beneath 5 6 m of silt lag material from erosion of the silt banks contains neolithic and bronze age artifacts out of stratigraphic context as well as ceramics and bricks of lan na age these artifacts as well neolithic artifacts obtained from a 1972 excavation near the mouth of the kham river indicate long human habitation of this riverbank area in northern thailand the mekong is mostly in a bedrock canyon but shifting topography along the active strike slip mae chan fault has formed the upstream 2 5 km wide floodplain at chiang saen and downstream has diverted the river into a broad s shaped loop in the otherwise straight course of the river a 1 7 ma basalt within the bedrock channel 45 km downstream of chiang saen indicates little vertical incision by the river satellite images show former channels in the chiang saen area meander point bar scrolls radii of curvature 1 2 km and floodplain edges as arcuate cuts of similar curvature into the saprolite mantled bedrock hills these features indicate channel avulsion occurred by meander loop cutoff in the past brick buddhist monuments of the 14th 16th century were built upon the floodplain with meander features on the thai and laos side of the river indicating that these meandering channel features and the broader floodplain are mostly older than 600 years

evaluation of part of the mekong river using satellite imagery abstract large rivers of the world are difficult to investigate this is essentially due to the logistical problems involved when attempting to study rivers that are about a thousand kilometres or more in length and drain basins of appropriate dimensions this creates difficulties in river management and also in determining the possible impact on the river system of specific development projects or basin land use changes we demonstrate the capability of satellite images a huge number of which are currently archived in various centres around the world to provide at least a coarse scale solution to these problems a significant amount of work can be done even without the application of any special remote sensing technique about 14 000 km 2 of the middle mekong basin in lao pdr has been studied the mekong is the 12th longest river in the world and is ranked eighth in terms of mean discharge the mekong is worth investigating for several reasons 1 it has a fascinating and complicated physiography 2 little published information exists for the basin at least for the part selected for the case study 3 various development plans have been drawn up for the mekong with possible environmental impact on the basin and the river the images are used in conjunction with the limited geomorphic and hydrologic data available in order to 1 provide a concise account of the local geomorphology 2 map environmental degradation and sediment transfer in parts of the basin and 3 determine the nature of possible environmental impact associated with certain proposed development projects on the river this is carried out by searching through the spot satellite images archived at the centre for remote imaging sensing and processing national university of singapore selecting and studying clear scenes and comparing the 1996 1998 and 1999 images of the study area to record changes over time primarily the study is a demonstration in combining remote sensing and geomorphology for environmental management of a large river system it is also a plea for transforming the satellite images accumulating in various archives to useful geomorphological databases given the scale of large rivers satellite images are excellent tools for their investigation

morphological evolution and dynamics of a large sand braid bar jamuna river bangladesh the initiation and evolution of a kilometre scale sand braid bar was monitored during a 28 month survey period from 1993 to 1996 in one of the world s largest braided rivers the jamuna river bangladesh repeated bathymetric surveys through two monsoon flood seasons combined with bar top surveys during exposure of the bar at low flow provide the most detailed chronology of braid bar growth yet compiled for a large sand bed river during rising and peak flow of the 1994 monsoon flood a 1 5 km long 0 5 km wide 12 m high symmetrical mid channel bar was deposited in the centre of a major channel downstream of a zone of flow convergence and significant bank erosion initial deposition and growth of the bar core were probably caused by amalgamation of dunes that are present in the jamuna channels at all flow stages bar top aggradation continued through downstream migration of an accretionary dune front a 3 m high angle of repose slipface that was composed of amalgamated 0 5 to 1 m high dunes at waning and low flow the mid channel bar widened by up to 1 km through the lateral accretion of dunes onto the margins of the initial bar core a low velocity zone in the sheltered wake region of the bar tail led to the accumulation of substantial volumes of silts and clays during the rising and peak flows of the next monsoon flood the mid channel bar extended its bar tail by up to 1 5 km as one of the anabranches became dominant and flow was deflected across the bar tail accretion at the bar tail generated a lobate transverse bar front with a 10 m high angle of repose avalanche face emergence of several smaller bars along this depositional front produced an overall reach morphology that more closely resembled an alternate bar rather than several mid channel bars the conversion of a mid channel bar to an alternate bar is contrary to many previous descriptions of the braiding process

environmental conditions framing the first evidence of modern humans at tam pa ling laos a stable isotope record from terrestrial gastropod carbonates abstract mainland southeast asia is a key region to interpret modern human migrations however due to a scarcity of terrestrial proxies environmental conditions are not well understood this study focuses on the tam pa ling cave site in northeast laos which contains the oldest evidence for modern humans in indochina dating back to mis 4 70 8 ka snail remains of camaena massiei found throughout the stratigraphic sequence contain a valuable oxygen and carbon isotope record of past local vegetation and humidity changes our data indicate that before the last glacial maximum lgm northeast laos was characterized by a humid climate and forested environments with the onset of the lgm a major climatic shift occurred inducing a sharp decrease in precipitation and a significant decline in woodland habitats in favor of the expansion to more open landscapes only during the holocene did forests return in northeast laos resembling present conditions the first homo sapiens arriving in indochina therefore encountered landscapes dominated by woodlands with a minor proportion of open habitats

paleoenvironments and paleoclimates in tierra del fuego and southernmost patagonia south america abstract a continuous paleoclimatic history for the past 14 000 years is presented based on palynological records from south of latitude 50 s in south america prior to 12 500 yr b p dry empetrum heathlands not mesic tundra dominated throughout the high southern latitudes indicating high winds annual precipitation of less than 300 mm and freezing temperatures year round after 12 500 yr b p steppe replaced the heathlands suggesting decrease in wind intensity increase in effective moisture and increase in temperatures when forests expanded at 9000 yr b p along the rainward side and at 8000 yr b p in the rainshadow side of the andes precipitation reached holocene levels judging from the greater openness of the early holocene forests including those in the rainward part of the region precipitation levels probably ranged between 500 and 800 mm comparable to those from today s forest steppe transition after a pronounced mid holocene dry event the late holocene forests appeared more closed than the early holocene forests suggesting greater effective moisture probably related to cooler temperatures the high latitude paleoclimatic history differs from that of lower latitudes as far as the actual amplitude of change and the climatic signal is concerned low moisture levels prior to 12 500 yr b p between latitudes 45 and 55 c suggest that the westerly stormtracks responsible for precipitation patterns in southern south america may have been located year round closer to the equator than today the precipitation increase at 12 500 yr b p that extended only as far south as 50 s indicates that the stormtracks had shifted poleward but did not reach tierra del fuego by 9000 yr b p the stormtracks had shifted to the high southern latitudes but the large seasonal latitudinal shift comparable to the modern situation equatorwards in winter and polewards in summer did not develop until after 4500 yr b p

bajada de rahue province of neuquen argentina an interstadial deposit in northern patagonia abstract pollen and diatom analyses of a radiocarbon dated lacustrine section in the temperate andean region of argentina rahue province neuquen suggest interglacial type climatic conditions between 27 000 and 33 000 yr b p with environments that resemble the modern conditions at the locality this finding correlates with a woodland record from central chile interpreted as reflecting conditions substantially warmer and drier prior to 27 000 yr b p than during the following full glacial period it also appears to relate to the global paleoclimatic scheme derived from deep sea records suggesting interhemispheric synchroneity of such broad scale palaeoclimatic phases

paleolimnological record of the pampean plains argentina as a natural archive of south american hydroclimatic variability since the lgm to the current warm period abstract laguna mar chiquita lmc 30 54 s 62 51 w is a highly variable and shallow saline lake located in the pampean plains of argentina the paleolimnological record of lmc contains information on the environmental variability that occurred in a large area of southern south america since the last glacial maximum lgm until the present as inferred from the diatom assemblages sedimentary features and geochemical proxies prolonged intervals of high and lowstands have caused variations in water salinity trophic state and sedimentary processes this is the first paleolimnological reconstruction covering the hydroclimatic variability that occurred over the last 25 000 cal yr bp in the argentinean pampean region results are in accordance with well known global climatic phases the late pleistocene record is characterized by a scenario dominated by lowstands hypersaline and oligotrophic lake conditions radiocarbon ages 25 000 19 000 cal yr bp indicate that the onset of the record is coeval with the lgm later a progressive lake water level increase was registered at 17 000 cal yr bp which can be assigned to the heinrich stadial 1 a shift toward comparatively drier conditions identified in the record between 14 700 and 13 000 cal yr bp can be chronologically related to the antarctic cold reversal the transition from the late pleistocene to the holocene 13 500 10 500 cal yr bp is recorded by highstand phases while the early holocene record is characterized by high to intermediate water levels the hydrological reconstruction corresponding to the mid holocene is characterized by alternating phases of high lowstands the onset of the late holocene record is marked by the development of dry conditions and thus lowstand phases while around 1300 cal yr bp a distinct water lake level increase is recognized this humid phase ascribed to the medieval climatic anomaly is followed by the record of lowstands between 500 and 1000 cal yr bp being coeval with the little ice age the uppermost part of the record of lmc encompasses the current warm period showing a marked shift towards high lake water level conditions the hydrological variability registered in the paleolimnological record highlights the importance of laguna mar chiquita as an outstanding paleoclimate sensor of hydroclimatic variations for a large area of south eastern south america

stable isotope analyses on the last 30 ka molluscan fauna from pampa grassland bonaerense region argentina abstract fossil and living shells of terrestrial and freshwater molluscs collected from various sites in the bonaerense and patagonia regions of argentina were analysed for their stable isotope content as a possible tool for palaeoclimatic and palaeoenvironmental reconstruction the oxygen isotope composition of calcareous shell from freshwater samples was interpreted in terms of a change in moisture condition and the related evaporative effect on surficial bodies of water linked to a climatic shift the carbon isotope composition mainly records changes in biological productivity interpretation of the isotopic composition of the land snail carbonate is more complex and worldwide data from living shells have been used to decipher to some extent the palaeoenvironmental record contained in their isotopic composition overall the interpretations deduced from isotopic data of land snails as well as from nearby freshwater molluscs are quite comparable the isotopic data suggest that arid conditions occurred between 35 and 15 ka b p and warmer conditions around 35 25 ka b p a shift toward a new phase comparable with the present meteorological and climatic situation probably began around 9 ka b p and it was linked to some short but severe climatic fluctuations thus suggesting that high climatic stress characterised this period moreover a trend toward slightly arid conditions is suggested by isotopic data possibly sometimes after 5 ka the differences arising from the geographical location and the short duration of each single series studied still hamper an extensive interpretation of the isotopic data

paleoenvironment of the folsom archaeological site new mexico usa approximately 10 500 14c yr b p as inferred from the stable isotope composition of fossil land snail shells abstract well preserved aragonitic land snail shells vallonia from late pleistocene eolian sediment in the folsom archaeological site in new mexico exhibit an overall decrease of 18opdb from maximum values of 2 7 more positive than modern to younger samples with lower average values of about 3 6 within the modern range the age of the samples approximately 10 500 14c yr b p suggests that the decrease in 18o may manifest climatic changes associated with the younger dryas some combination of increased relative humidity and cooler temperatures with decreased 18o of precipitation during the times of snail activity can explain the decrease in shell 18o a well known paleoindian bison kill occurred at the folsom site during this inferred environmental transition average 13c values of the aragonite shells of the fossil vallonia range from 7 3 to 6 0 among different archaeological levels and are not as negative as modern values this suggests that the proportion of c4 vegetation at the folsom site approximately 10 500 14c yr b p was greater than at present a result which is consistent with other evidence for higher proportions of c4 plants in the region at that time

small scaled environmental changes indications from stable isotopes of gastropods early miocene korneuburg basin austria the korneuburg basin with mainly upper lower miocene karpatian sediment filling is divided by the mollmannsdorf oberganserndorf swell into two sub basins characterised by different environmental settings paleoecological data indicate a marine northern part and a mainly estuarine southern part nevertheless short termed marine ingressions from the north allowed marine faunas ostracods molluscs and echinoids to temporarily settle the southern part of the basin the carbon and oxygen isotopic composition of gastropod shells from these different environmental settings were investigated highest 18o and 13c values are found in turritella shells from the northern part of the basin and in turritella shells from layers interpreted as a marine ingression in the south generally components of the mudflat fauna tympanotonos cinctus granulolabium bicinctum terebralia bidendata and ocenebra crassilabiata have slightly lower isotope values considerable freshwater influx in the southern part is documented by abundant freshwater genera such as melanopsis which show low carbon and oxygen isotope values data of identical taxa especially turritella and granulolabium reflect a trend from higher isotope values at the marine northern part to slightly lower values in the mainly estuarine southern part of the basin differences in 18o between the marine and the estuarine assemblages are interpreted to be caused by changes in salinity and isotopic composition of ambient water rather than by temperature paleotemperature estimates derived from oxygen isotope data are in good agreement with existing paleoclimatic proxies for the korneuburg basin hence an annual range of the sea surface temperature from 13 to 26 c can be predicted within that protected basin

the stable isotope archive of lake pannon as a mirror of late miocene climate change abstract lake pannon was a long lived miocene and pliocene lake system in central europe with a famous endemic mollusc fauna the radiation of melanopsid gastropods and dreissenid bivalves has been explained simply by the opportunity to settle empty ecological niches after the extinction of marine life at the end of the middle miocene this model however fails to explain the offset in the timings of evolutionary pulses in different mollusc families stable isotope data oxygen carbon indicate a strong climatic forcing on these radiations moreover the investigated time span covers the well known vallesian optimum and subsequent crises in european terrestrial ecosystems during the late miocene the new palaeoclimatic data on the strongly changing isotope patterns of mollusc aragonite of lake pannon might shed light on the mechanisms acting during this crucial period according to the new interpretation the early lake 11 6 ma was still influenced by the latest middle miocene dry spell this phase coincided with a pronounced radiation of melanopsid gastropods during the warm early late miocene 10 ma humidity increased and culminated in a phase with high summer precipitation this caused a reorganisation of the coastal deltaic faunas suppressing the radiation of melanopsids on the other hand high nutrient loads favoured the dispersion of filter feeding dreissenids despite steadily declining salinity lake pannon remained an alkaline lake with pronounced stratification that was apparently periodically disrupted only during the humid early late miocene a separation of the isotope data into genera and ecological guilds is the prerequisite for discussing overall trends of long lived lake systems

geodynamic impact on the stable isotope signatures in a shallow epicontinental sea analyses were made of a mollusc based meta dataset of 859 d 13 c and d 18 o data of miocene nearshore settings in the european paratethys sea and its descendant lake pannon the observed trends document a strong tie to geodynamics which are largely decoupled from miocene open ocean isotope curves semi to fully enclosed initially marine water bodies such as the paratethys sea are prone to switching seawater isotope signatures because they respond rapidly to changes in the evaporation precipitation ratio two phases of positive deviations of oxygen isotope values of water relative to the modern ocean value smow occurred during the middle miocene both were initiated by tectonic constrictions of the seaways and became amplified by global warming and regionally decreasing precipitation with the final disintegration of the paratethys the marine isotope signatures vanish instead the observed isotope trends suggest a comparably simple system of an alkaline lake with steadily declining salinity the oceanderived paratethys sea may thus act as a key for understanding isotope trends in epicontinental seas

sedimentation in the manwan reservoir in the upper mekong and its downstream impacts abstract dam construction on upper streams retains sediment and causes a series of effects downstream china planned eight dams on the main stream of the upper mekong lancang river of which the manwan and the dachaoshan dams were completed and put into use in 1993 and 2003 from 1993 when the manwan dam started to store water to 2003 the annual mean sediment trapped by the reservoir is estimated as 26 9 28 5 10 6 t a or 295 9 313 5 10 6 t over the 11 years the reservoir capacity loss caused by the annual sediment trapped is around 20 7 21 9 10 6 m 3 a or 227 6 241 2 10 6 m 3 over the 11 years equivalent to 21 5 22 8 of the total storage capacity of the manwan reservoir sediment trapped by the manwan reservoir produced different effects on the sediment variations downstream suspended sediment concentration ssc and sediment discharge at gajiu station 2 km downstream of the reservoir was affected most significantly but yunjinghong station 401 km further downstream saw lesser effects further downstream at chiang saen 746 km distant ssc responded to the reservoir sedimentation in a different way from the yunjinghong station with an obvious decline at the beginning of the reservoir impoundment but started to recover since 1997 this was corroborated by the result of a granger causality test on the monthly ssc time series at yunjinghong and chiang saen indicating that there was no evident causality between the sediment series of the two stations

exchanges of sediment between the flood plain and channel of the amazon river in brazil sediment transport through the brazilian sector of the amazon river valley a distance of 2010 km involves exchanges between the channel and the flood plain that in each direction exceed the annual flux of sediment out of the river at obidos 1200 mt yr 1 the exchanges occur through bank erosion bar deposition settling from diffuse overbank flow and sedimentation in flood plain channels we estimated the magnitude of these exchanges for each of 10 reaches of the valley and combined them with calculations of sediment transport into and out of the reaches based on sediment sampling and flow records to define a sediment budget for each reach residuals in the sediment budget of a reach include errors of estimation and erosion or deposition within the channel the annual supply of sediment entering the channel from bank erosion was estimated to average 1570 mt yr 1 1 3 the obidos flux and the amount transferred from channel transport to the bars 380 mt yr 1 and the flood plain 460 mt yr 1 in channelized flow 1230 mt yr 1 in diffuse overbank flow totaled 2070 mt yr 1 1 7 the obidos flux thus deposition on the bars and flood plain exceeded bank erosion by 500 mt yr 1 over a 10 16 yr period sampling and calculation of sediment loads in the channel indicate a net accumulation in the valley floor of approximately 200 mt yr 1 over 16 yr crudely validating the process based calculations of the sediment budget which in turn illuminate the physical controls on each exchange process another 300 400 mt yr 1 are deposited in a delta plain downstream of obidos the components of the sediment budget reflect hydrologic characteristics of the valley floor and geomorphic characteristics of the channel and flood plain which in turn are influenced by tectonic features of the amazon structural trough

late quaternary vegetational and climatic changes in the pampa grassland of argentina abstract the vegetation and climate of the pampa grassland argentina during the late quaternary are reconstructed from pollen recovered from dated stratigraphic sections from arroyo walls and from archaelogical excavations prior to 10 500 yr b p herbaceous psammophytic steppe existed in the central part of the pampa grassland while xerophytic woodland associated with psammophytic and halophytic steppe occurred in the southwestern part of the pampa these types of vegetation and the continental conditions that prevailed in the area of the present day coast 38 s indicate subhumid dry climate and annual precipitation 100 mm lower than present a subsequent change toward a vegetation characteristic of ponds swamps and foodplains or toward environments with locally more effective moisture occurred ca 10 500 yr b p suggesting annual precipitation close to modern levels or a higher availability of water in the central part of the pampa grassland this type of vegetation existed until 8000 yr b p when it was replaced by grassland communities that lasted until 7000 yr b p in the southwestern part of the pampa grassland this vegetation developed before 7000 yr b p and persisted until ca 5000 yr b p sea level higher than the present ca 6200 yr b p is consistent with sharp modification of the vegetation and development of local halophytic communities dominant at 38 s a return to subhumid dry conditions occurred after 5000 yr b p the late holocene vegetation is characterized by pollen assemblages similar to the psammophytic and halophytic communities of the southern pampa grassland associated with communities with more edaphic conditions at the same time at 38 s a sea level regression is suggested by the dominance of fresh water pollen assemblages and micropaleontological remains the trend toward humid temperate conditions ca 1000 yr b p suggested by vertebrate remains characteristic of temperate and humid conditions as well as a very short but dry episode during the 18th century suggested by the geology are not clearly evidenced in the pollen sequences vegetational and climatic changes are explained by the latitudinal shifts and changes in intensity of the southern atmospheric circulation and changes in sea level

quaternary mollusc assemblages from the lower basin of salado river buenos aires province their use as paleoenvironmental indicators abstract quaternary mollusc assemblages preserved in the salado basin are described and analyzed in order to reconstruct past environments and evaluate spatial and temporal variations five localities were analyzed in which 48 998 individuals of eight continental gastropod species were recovered heleobia parchappii antillorbis nordestensis biomphalaria peregrina drepanotrema heloicum uncancylus concentricus pomacea canaliculata succinea meridionalis and miradiscops brasiliensis as well other species typical of marine estuarine environments have been found among which heleobia australis is highlighted based on changes in the composition and abundance of the assemblages different environments could be recognized quaternary mollusc assemblages have low taxonomic heterogeneity and spatial and temporal variations assemblages recovered from late pleistocene early holocene sediments are characterized by low species richness and abundance with a single species in numerous examples in the middle holocene the shells became more constant and more diverse late holocene assemblages have high species richness freshwater terrestrial and amphibious habits and show some differences among different localities several episodes of flooding have been identified through the record of fossiliferous horizons with high density of shells mainly heleobia parchappii these events that affected the area of influence of the salado river occurred at least during the late holocene

the campo laborde site new evidence for the holocene survival of pleistocene megafauna in the argentine pampas abstract investigations have been carried out at the campo laborde archaeological site in the argentine pampas some issues related to pleistocene extinctions and the survivals of some species of megafauna into the early holocene are discussed at the site of campo laborde abundant bones of giant ground sloth megatherium americanum some from other pleistocene fauna doedicurus sp and neosclerocaliyptus sp and very few from extant fauna e g vizcacha lagostomus maximus patagonian hare dolichotis patagonum and peccary tayassu sp were found in association with two quartzite tools 128 microlithic debris from different raw material and two informal bone tools each of the species is represented by only one individual and only one bone of m americanum and one of d patagonum show cut marks different lines of evidence suggest that campo laborde is a giant ground sloth procurement site on the border of an ancient swamp where the prey was also initially butchered one of the recovered tools is the stem of a broken bifacial projectile point which would have been used as a hunting weapon based on the stratigraphic position this site could date to the early holocene six ams 14 c ages from m americanum bone collagen support this age although there is a wide chronological span between ca 9700 and 6700 bp the evidence obtained from campo laborde as well as from the la moderna site indicates that some pleistocene species such as giant ground sloth and some glyptodon d clavicaudatus and neosclerocaliyptus sp survived in the pampas until the early holocene therefore these megafauna coexisted with early hunter gatherers for several millennia and were exploited

megafauna extinction in south america a new chronology for the argentine pampas abstract the megafauna extinction in south america was one of the most profound events with the loss of 50 genera 83 three orders disappeared notoungulata proboscidea litopterna as did all large xenarthrans but how this fits into global extinction is uncertain mainly due to the lack of chronological resolution in recent years there has been an increase in the number of radiocarbon dating at archeological and paleontological sites but this information varies greatly from area to area in south america and few data can be considered to constitute a taxon date the timing of the late pleistocene extinction in the pampas is poorly established most taxa only appear in the biostratigraphic context and many reported 14 c dates do not meet rigorous criteria for accepting dates including reports suggesting survival of megafauna into the holocene in the present paper we evaluate the published radiocarbon dates in the pampas and present 20 new radiocarbon dates for paleontological sites in order to establish a more accurate extinction window for the key taxa these new dates are sufficiently robust to assess correspondences among last appearance records of megafauna first appearance records of humans and the younger dryas to holocene climatic transition in the argentine pampas these results highlight the need for greater effort in taxa selection for dating

paleoenvironmental reconstruction by pollen analysis from loess sequences of the southeast of buenos aires argentina abstract a model of the dynamics of pollen dispersion and deposition in relation to loess deposition is proposed it is based on pollen analysis of three discontinuous loess sequences of late pleistocene holocene age that are located at the archaeological locality of cerro la china buenos aires province argentina 37 57 s 58 37 w deposition and accumulation of loess and pollen were interpreted in terms of their provenance and transport using the tauber 1967 and pye 1987 models for pollen and dust dispersal respectively three pollen zones can be distinguished based on changes in pollen assemblages the final late pleistocene early holocene interval is represented by pollen zone 3 loess deposits have been accumulated in an environment with a locally high effective moisture loess deposition would have occurred synsedimentarily with extra regional local and regional pollen taxa the relationship between pollen dispersal and possible extra regional pollen sources indicate predominantly w sw winds this zone is truncated by an erosive episode hence the successional process of the community could not be reconstructed for the early holocene the middle holocene is represented by pollen zone 4 deposition of loess began in an environment with predominantly herbaceous communities pollen concentration increases towards the top of the zone and may represent a buried soil this would imply a change towards more stable and humid conditions than those at the beginning of the deposition extra regional pollen concentration suggests a comparatively high local and regional pollen productivity rather than a change in wind direction a slight erosive episode constitutes the upper boundary of zone 4 and is related to new drier conditions zone 5 occurs during historical times and is represented by graminous steppe communities and over representation of local taxa

paleoclimatology of the casas del rincon villafranchian series spain from stable isotope data abstract stable isotope analyses were performed on 49 samples of lacustrine carbonate and 69 samples of carbonatic shells of both aquatic and terrestrial gastropods from the pliocene series of casas del rincon jucar river area spain in agreement with the paleontological data the isotope results indicate that the series was deposited under variable climatic and environmental conditions when compared with the paleoclimatic evolution idicated by marine series in western mediterranean area the series of casas del rincon appears to record the marked climatic deterioration which took place about 3 1 3 2 m y ago a chronological succession is proposed for the faunistic events of the studied series the rincon 1 vertebrate fauna is probably 2 5 2 6 m y old

climatic variations in the argentine plains during the last 18 000 years the last deglacial hemicycle was characterized by a general increase in temperature and precipitation in the region with a few significant departures from this general trend the present ne sw climatic gradient was maintained throughout the entire period except in the upper holocene the following sequence of events is apparent if the present climate is taken as a reference base 1 a 18 000 8500 yr b p arid and cool with aeolian sand ad loess deposition patagonian fauna climatic isolines temperature precipitation etc were located some 750 km northeast of their present positions 2 b 8500 3500 yr b p humid subtropical with brazilian fauna pedogenesis and fluvial dynamics climatic limits migrated about 800 900 km southwest of their former positions 3 c 3500 1000 yr b p dry subtropical aeolian dynamics the normal latitudinal climatic gradient was interrupted by the occurrence of an anticyclonic centre which stabilized the climate over an area of some 1 600 000 km2 4 d 1000 yr b p little ice age climate was similar to the present one over much of the plains but the northeastern extremity was warmer 5 e little ice age climatic deterioration in the southern belt was characterized by generalized aeolian activity and migration of isolines more than 150 km to the northeast in that area 6 f present climate 19th and 20th centuries subtropical humid in the east and dry in the west

carbon and oxygen isotope composition of shell carbonate of desert land snails abstract variation in 13 c 12 c and 18 o 16 o ratios in the shell carbonate of several species of land snails was studied along a climatic gradient in semi arid to arid areas in the southern levant 13 c was found to be enriched in snails from communities having plants with a c 4 photosynthetic pathway depleted 13 c values were found in areas with high mean annual rainfall apparently due to higher input of metabolic co 2 as a result of greater snail activity shell carbonate 18 o values show a weak relation to the 18 o values of rainwater the shell 18 o values are enriched by 2 8 relative to isotopic equilibrium with environmental waters enrichment is suggested to result from metabolic effects on body water with lower activity producing greater enrichment but evaporation could also be a factor consistent differences in both 13 c and 18 o were found among species and may relate to the time when shell deposition occurs as with most paleoenvironmental indicators the application of shell isotopes is complicated by the multiplicity of controls of isotopic composition

late quaternary environmental and climatic changes in central brazil paleoenvironmental changes dating back to 30 000 yr b p documented in a pollen record from central brazil lat 19 s permit the reconstruction of climatic changes related to shifts of the antarctic polar fronts the paleoclimatic inferences were obtained by a study of modern vegetation and pollen distribution taking into account present day climatic parameters at 30 000 yr b p the climate must have been warmer and moister than today judging from the high amount of tree pollen taxa characteristic of floodplain forest from 17 000 to 14 000 yr b p the climate was drier although tree pollen percentages were relatively high after 12 000 yr b p araucaria forest elements increased suggesting a moister and cooler climate the araucaria forest disappeared during a short interval between 11 000 and 10 000 yr b p this could be related to the younger dryas event at the beginning of the holocene the climate became cool and moist again as indicated by the reexpansion of the araucaria forest the latter was progressively replaced by a mesophytic semideciduous forest indicating warmer and drier climate after 8500 yr b p at 5000 yr b p an arid interval was followed by the expansion of mesophytic semideciduous forest elements

stable isotope record in mollusca and pedogenic carbonate from late pliocene soils of central italy abstract the late pliocene younger than 2 5 ma alluvial fan succession of toppetti quarry near todi umbria central italy includes many palaeosols pedogenic carbonate concretions and mollusc remains were separated from 73 palaeosols collected along 150 m of exposure and analysed for their oxygen and carbon stable isotope content 13c and 18o of the pedogenic carbonate and land snail shells suggest that no dramatic change in local climate took place values of the pedogenic carbonates are similar to other data reported for the mediterranean region 18o data suggest a mean annual temperature and or 18o similar to modern climatic conditions carbon isotope data from both land snails and pedogenic carbonate are consistent with a prevailing type c3 vegetation a mixture of forest and c3 grassland sustained by a mean annual precipitation between 300 and 1000 mm mainly in the cool periods of the year seems to be the most likely scenario the limited variation shown by the isotope composition of the biogenic and inorganically precipitated carbonate indicates that the environmental variations are referable mainly to change of humidity rather than temperature

historical climatic extremes as indicators for typical scenarios of holocene climatic periods in the pampean plain abstract the holocene has been marked by two different climatic periods in the pampas one 8 5 3 5 kyr b p characterized by temperatures and precipitation higher than today and the other 3 5 1 4 kyr b p semiarid generating parabolic dunes the humid period produced intense pedogenesis down to 40 lat s and a mobilization of iron oxides to 30 lat s which means tropical climate with temperatures above 20 c and precipitation higher than 2000 mm yr sand deflation and development of parabolic dunes occur under climates with 300 400 mm yr this contribution is based on geological and physical proxies typical weather scenarios of those climates are sporadically reproduced today during extremely humid or dry periods on that basis meteorological parameters of years beyond the thresholds of 2000 and 400 mm yr were processed dry periods were characterized by a large thermal amplitude frosts and stronger winds reproducing the continental anticyclonic circulation of the late holocene humid extremes were warmer than normal lower thermal amplitude with rains produced by local convection processes typical scenarios with precipitation above 2000 mm yr are 21 c mean temperature ca 1 c higher than the present record 27 c maximal annual temperatures 16 c minimal annual temperatures more than 1 c higher than the present as a consequence thermal amplitude was smaller than today virtually without frosts characteristic parameters of the late holocene were mean annual precipitation ca 350 mm yr 15 c mean temperature 22 c maximal annual temperatures 8 c minimal annual temperatures showing significative shifts in the dry season lower than normal monthly maximal and mean temperatures higher than today the result is a thermal amplitude larger than today probably higher quantity of frosts per year stronger winds and lower relative air humidity in comparison with the humid climate extreme complete the scenario

a late pleistocene refugium in mediterranean north africa palaeoenvironmental reconstruction from stable isotope analyses of land snail shells haua fteah libya abstract the late pleistocene to holocene archaeological record of north africa is key to understanding the emergence of anatomically modern humans into west asia and europe and the broadening of subsistence strategies in the shift from hunter gatherer to pastoral agricultural lifeways some contend that these developments were modulated by major shifts in climate and environment evaluation of this hypothesis requires the pairing of local and regional climate records with well dated archaeological sequences the haua fteah archaeological site in the gebel akhdar region of libya provides a key site to test this hypothesis as the cave contains one of the longest and most complete sequences of human occupation in north africa as well as abundant material for palaeoenvironmental reconstruction this study uses stable isotope analyses 18o and 13c of the terrestrial mollusc helix melanostoma to construct a palaeoenvironmental framework for interpreting north african human environment interactions from the upper palaeolithic to the neolithic 30 000 to 5000 years ago the land snail stable isotope records from haua fteah suggests that cool arid conditions in the cave peaked during marine isotope stage mis 2 this stage was however only marginally drier than previous and subsequent stages and coincided with an increase in occupation density in the cave this suggests that the gebel akhdar may have served as an environmental refugium from the more extreme aridity in the surrounding sahara and arid coastal plains for late stone age lsa populations in north africa conditions became progressively wetter towards the holocene however generally wetter conditions were interrupted by two arid episodes at c 8 0 ka and 7 3 ka that appear to coincide with regional changes reflected elsewhere in the mediterranean basin

palaeoenvironmental reconstructions by stable isotopes of middle miocene gastropods of the central paratethys abstract the stable isotopes of carbon and oxygen were used to provide information of mixing of marine and freshwater and subsequently used to determine palaeosalinities in the middle to late miocene st margarethen zollhaus section upper sarmatian mactra zone pannonian a succession of three gastropod assemblages indicates changing environmental conditions from a limnic fluviatile to littoral mudflat and a sublittoral marine environment several shells of the main representatives of the three assemblages potamides hartbergensis hilber granulolabium bicinctum brocchi potamides disjunctus sowerby and additionally shells of lymnaea sp a typical freshwater gastropod and pomatias conicus a terrestrial gastropod were taken for stable isotope analyses oxygen and carbon isotope data of the freshwater endmember are distinctively lower 18 o 4 5 13 c 9 than of the marine endmembers 18 o 2 2 13 c 2 3 in contrast to the expected intermediate isotopic composition between the freshwater and marine environment the shells of supposed brackish environments have higher 18 o values than the shells of the marine environment these higher 18 o values are explained by evaporation which affected the protected areas of riverine to lacustrine environments and small pools on mudflats formerly considered to be the habitats of the brackish assemblages thus the oxygen and carbon isotope data extend the already existing palaeoenvironmental information

late quaternary climatic control on erosion and weathering in the eastern tibetan plateau and the mekong basin abstract high resolution siliciclastic grain size and bulk mineralogy combined with clay mineralogy rubidium strontium and neodymium isotopes of core md01 2393 collected off the mekong river estuary in the southwestern south china sea reveals a monsoon controlled chemical weathering and physical erosion history during the last 190 000 yr in the eastern tibetan plateau and the mekong basin the ranges of isotopic composition are limited throughout sedimentary records 87 sr 86 sr 0 7206 0 7240 and e nd 0 11 1 to 12 1 these values match well to those of mekong river sediments and they are considered to reflect this source region smectites illite chlorite and smectites kaolinite ratios are used as indices of chemical weathering rates whereas the bulk kaolinite quartz ratio is used as an index of physical erosion rates in the eastern tibetan plateau and the mekong basin furthermore the 2 5 6 5 m 15 55 m siliciclastic grain size population ratio represents the intensity of sediment discharge of the mekong river and in turn the east asian summer monsoon intensity strengthened chemical weathering corresponds to increased sediment discharge and weakened physical erosion during interglacial periods in contrast weakened chemical weathering associated with reduced sediment discharge and intensified physical erosion during glacial periods such strong glacial interglacial correlations between chemical weathering erosion and sediment discharge imply the monsoon controlled weathering and erosion

environmental history since 11 000 14c yr b p of the northeastern pampas argentina from alluvial sequences of the lujan river abstract sedimentological malacological and pollen analyses from 14c dated alluvial sections from the lujan river provide a detailed record of environmental changes during the holocene in the northeastern pampas of argentina from 11 200 to 9000 14c yr b p both sedimentary and biological components suggest that the depositional environment was eutrophic alkaline and freshwater to brackish shallow water bodies without significant water circulation during this time bioclastic sedimentation was dominant and the shallow water bodies reached maximum development as the climate became more humid suggesting an increase in precipitation short term fluctuations in climate during the last stage of this interval may have been sufficient to initiate changes in the water bodies as reduction of the volume alternated with periods of flooding the beginning of the evolution of shallow swamps in the wide floodplain or huge wetlands was contemporaneous with a sea level lower than the present one from 9000 and 7000 14c yr b p mesotrophic alkaline brackish probably anoxic swamps existed between 7000 and 3000 14c yr b p anoxic calcareous swamps were formed with subaerial exposure and development of the puesto berrondo soil 3500 2900 14c yr b p a trend to a reduction of water bodies is recorded from 9000 to ca 3000 14c yr b p with a significant reduction after ca 7000 14c yr b p a shift to subhumid dry climate after 7000 14c yr b p appears to be the main cause during this time an additional external forcing toward higher groundwater levels was caused by holocene marine transgression causing changes in the water bodies levels the climate became drier during the late holocene ca 3000 yr b p when clastic sedimentation increased under subhumid dry conditions flood events increased in frequency during this time from ca a d 1790 to present the pollen record reflects widespread disturbance of the vegetation during the european settlement

climatic and tectonic controls on weathering in south china and indochina peninsula clay mineralogical and geochemical investigations from the pearl red and mekong drainage basins 1 results of clay mineralogy major element geochemistry and sr and nd isotopes in 93 argillaceous samples collected from drainage basins of the pearl red and mekong rivers reveal different degrees of chemical weathering in southeast asia despite similar climate conditions across these regions the kaolinite illite ratio illite chemistry index and illite crystallinity can be used as indicators of chemical weathering intensity these mineralogical proxies combined with the k2o na2o cao molar ratio chemical index of alteration cia and weathering trends observed from major element results indicate intensive silicate weathering in the pearl river basin moderate to intensive in the mekong river basin and moderate in the red river basin although a significant modification of epsilon nd 0 values in our riverine sediments during chemical weathering and transport is unlikely sr 87 sr 86 ratios are controlled by various states of chemical weathering of high sr minerals such as plagioclase rich in na and ca with a linear decrease trend from the pearl mekong to red river basins our results suggest that it is not the warm climate with heavy monsoon precipitation but tectonics playing the most significant role in controlling weathering and erosion processes in south china and indochina peninsula strong physical erosion caused by tectonic activities and river incision along the eastern margin of the tibetan plateau and along the red river fault system is responsible for high contents of primary minerals in the lowlands of red and mekong river basins

holocene 4 5 1 7 cal kyr bp paleoenvironmental conditions in central argentina inferred from entire shell and intra shell stable isotope composition of terrestrial gastropods the isotopic fingerprint of terrestrial gastropods has been increasingly used as a credible natural paleoenvironmental archive most published work has used this proxy at tropical and temperate latitudes of the northern hemisphere and focused on entire shell analysis the present study provides entire shell and intra shell isotopic profiles to infer average and seasonal late holocene environmental conditions in central argentina 30 s shells of plagiodontes daedaleus gastropoda odontostomidae were retrieved from the alero deodoro roca sector b site one of the few archaeological sites in central argentina rich in shells collected by pre hispanic hunter gatherer groups ancient entire shells exhibited values that were 2 5 higher in 13c and 1 8 higher in 18o than modern individuals pointing to higher abundance of c4 plants and overall drier conditions lower relative humidity and or higher rain 18o during 4 5 1 7 cal kyr bp than today in agreement with published regional proxies intra shel

stable carbon and oxygen isotopic variations in modern rabdotus land snail shells in the southern great plains usa and their relation to environment abstract variations of stable isotopic ratios of carbon 13c 12c and oxygen 18o 16o were investigated in modern shells of two species of rabdotus land snails r dealbatus and r alternatus in the southern great plains geographic variation in relation to climate and vegetation microgeographic variation variability among individuals and detailed records of seasonal variations within individual shells were studied stable carbon isotopic ratios in shell carbonate are primarily a function of the isotopic composition of the diet of the snails as represented by the isotopic composition of shell organic matter this in turn reflects the presence or absence of cam crassulacean acid metabolism or c4 plants vegetation density may have a small effect on the carbon isotope ratios microgeographic variation samples within 25 to 300 m is greater than that seen across different climatic regions and points to very local control of isotopic variations predominantly related to vegetation seasonal variations as assessed through serial analysis of individual shells up to 35 samples per shell may provide a means for distinguishing between isotopic influences of perennial cam vs annual c4 plants carbon isotopic variations in time series of shells from a site provide a means of reconstructing temporal changes in environment and climate oxygen isotopic values of shell carbonate are uniform across the region and also show no significant microgeographic variation the oxygen isotopic composition appears to be mainly a function of the rainwater isotopic composition with no direct influence of rainfall amount or evaporative effects the 18o values are only 2 enriched relative to estimated equilibrium with rainwater variability is low sd of 0 8 among sites so the isotopic composition of fossil rabdotus shells can provide a precise record of changes in the isotopic composition of rain over time

dams on the mekong cumulative sediment starvation the mekong river largely undeveloped prior to 1990 is undergoing rapid dam construction seven dams are under construction on the mainstem in china and 133 proposed for the lower mekong river and tributaries we delineated nine distinct geomorphic regions for which we estimated sediment yields based on geomorphic characteristics tectonic history and the limited sediment transport data available we then applied the 3w model to calculate cumulative sediment trapping by these dams accounting for changing trap efficiency over time and multiple dams on a single river system under a definite future scenario of 38 dams built or under construction cumulative sediment reduction to the delta would be 51 under full build out of all planned dams cumulative sediment trapping will be 96 that is once in channel stored sediment is exhausted only 4 of the predam sediment load would be expected to reach the delta this scenario would have profound consequences on productivity of the river and persistence of the delta landform itself and suggests that strategies to pass sediment through around dams should be explored to prevent the consequences of downstream sediment starvation

paleosols in loess deposits of the argentine pampas abstract paleosol studies are in their first stages in argentina as far as we know the soil and paleosols correspond to buried alfisols and mollisols with hydromorphic and carbonatic features the paleosol sequences on loess are made up of a succession of b or c horizons which furthermore are polygenetic as a result of encroachment of each pedogenesis on the underlying loess mantle differences in mineral composition are scarce with the exception of increases in glass shards and phytoliths in some loess mantles the b fabric is mostly stipple speckled or mosaic speckled and microlaminated clay coatings are very common there are also amorphous features related to voids or to the soil matrix evidences of biological activity are present as an excremental fabric on which a fissure microstructure is superimposed the paleosol sequences consist of several loessoid mantles each corresponding to a depositional pulse followed by a quiescent pulse during which pedogenesis took place truncation is considered to be due to eolian fluviatile erosion also there probably are a horizons masked by alteration and pedogenesis a pedogenetic origin of the calcretes with redeposition in the buried paleosols is assumed

stable carbon and oxygen isotopic composition of modern land snails along a precipitation gradient in the mid latitude east asian monsoon region of china abstract the stable oxygen and carbon isotope composition 18oshell and 13cshell of land snail shells preserved in chinese eolian loess deposits have the potential to reconstruct past changes in the east asian summer monsoon easm since the late oligocene to assess the potential of 18oshell and 13cshell for the semi quantitative reconstruction of past variations of the easm we studied modern snails and the corresponding vegetation composition of three distinct ecosystems woodland grassland and mountains spanning a large rainfall gradient 178 1403 mm in the mid latitude east asian monsoon region the results show that different snail species in the three ecosystems have significantly different values of 18oshell and 13cshell the snails in woodland from the eastern plain area have significantly lower 18oshell and 13cshell values than those of snails in grassland from the chinese loess plateau and the snails from the qinba mountains region have values intermediate between the two systematic variations of the 13c of snail shells body tissues and local plants are evident along the rainfall gradient indicating that 13cshell is mainly influenced by the 13c of ingested plants which is controlled by the easm we confirm that 13cshell is a reliable precipitation proxy and we obtained a new empirical equation 13cshell 0 0030 0 0003 map 8 80 0 32 r 0 76 n 74 p

new late pleistocene megafaunal assemblage with well supported chronology from the pampas of southern south america abstract late pleistocene outcrops exposed in buenos aires province argentina represent one of the most informative sources about the paleoecology of south american megafauna however there are no records of an accurately dated carnivore herbivore taphocenosis this paper presents preliminary results of a recent excavation at the margins of the salado river on sediments attributed to the lujan formation late pleistocene early holocene the fossiliferous strata consist of greenish brown sandy clays deposited in a small paleopond environment that was filled by fluvial sediments exhibiting abundant organic matter gypsum and carbonate concretions fieldwork yielded an association of extinct large sized mammals that include the horse hippidion principale the saber tooth cat smilodon populator at least one adult and one juvenile associated specimen a giant ground sloth megatherium americanum and the glyptodont doedicurus clavicaudatus four 14 c dates were performed on organic matter 12 100 100 14 c bp a femur of s populator 13 400 200 14 c bp and a cervical vertebra of hippidion principale 12 860 120 14 c bp and a pelvis of d clavicaudatus 12 380 190 14 c bp situating the site within 12 500 and 13 500 years approximately remarkably some of the recovered specimens exhibit conspicuous bone modifications furrows pits punctures striations and crenulated margins attributed to the activity of a medium large carnivore the association between bones of herbivore mammals with conspicuous modifications produced by a large carnivore and the presence of cub and adult remains of smilodon link this felid with at least part of the excavated association

palaeoclimatological reconstruction using stable isotope data on continental molluscs from valle di castiglione roma italy thirty molluscan shells from twenty levels from the first 4 5 m of a long core drilled in the crater lake of valle di castiglione near rome have been analysed for their oxygen and carbon stable isotope compositions the investigated portion of the core covers the last 14 2 ka bp the large range in 18o 11 suggests that hydrological conditions exercise the main control on the isotopic composition of the biogenic carbonate in the valle di castiglione palaeolake samples younger than about 5 ka show a marked 18o depletion which we attribute to the onset of a temperate wet climate corresponding to the maximum of humidity isotopic results are in good agreement with pollen analyses and prove to be a sensitive tool for reconstructing quaternary climatic evolution from the continental lacustrine sediments of central italy