late pleistocene holocene climatic and vegetational history of the brazilian caatinga the fossil dunes of the middle sao francisco river palynological studies of a peat bog sequence with a basal date of 10 990 80 yr b p provide a history of vegetational and climatic changes in the icatu river valley located inside a large system of stabilized sand dunes at the middle sao francisco river at 10o24 0 s 43o13 0 w in northeastern brazil the present day vegetation of the valley is vereda a mauritia vinifera palm swamp forest bordered by a narrow strip of semi deciduous tropical forest the adjacent dunes are stabilized by arboreal caatinga and cerrado vegetation in some areas the palynological profile of the saquinho locality within this valley was divided into five pollen zones zone sa1 10 990 10 540 yr b p contains pollen of taxa found in present amazonian and atlantic forests as well as from montane taxa thus suggesting very humid climatic conditions synchronous with more reduced temperatures zone sa2 10 540 6790 yr b p has pollen spectra from a vegetation type dominated by mauritia suggesting progressive warming and high humidity levels the period between 8920 and 8910 yr b p has rapid sedimentation rate few thermoluminescence tl dates pronounced increase of mauritia and ilex pollen suggesting a very moist climate from 8910 to 6790 yr b p there is a progressive decline in forest taxa and a gradual increase of caatinga and cerrado taxa on the landscape zone sa3 6790 ca 6230 yr b p does not contain palynomorphs possibly indicating semi arid conditions zone sa4 ca 6230 ca 4535 yr b p marks the return of mosaic vegetation composed of gallery forest cerrado and caatinga taxa indicating moister climatic conditions a marked decline in moisture levels characterizes the period between 4240 yr b p and present as suggested by an increase in caatinga and cerrado species and a decline in gallery forest taxa zone sa5 ca 4535 yr b p present establishes the present vegetational and climatic pattern of the icatu river valley 1999 elsevier science b v all rights reserved

late quaternary landscape evolution in the atlantic plateau brazilian highlands tectonic and climatic implications of fluvial archives abstract this paper identifies and discusses the major phases of relief evolution resulting from fluvial processes during the late quaternary in the quadrilatero ferrifero qf region atlantic plateau and contextualises them as strong indicators of the past tectonic and climatic influences on landscape evolution in the brazilian highlands seven regional phases of fluvial level development terraces and modern floodplains were identified based on geomorphological and stratigraphic aspects and dated between 83 ka and the present although older records occur in some valleys up to 140 ka they are poorly preserved and therefore ambiguous in interpretation river valleys in the qf are generally narrow and deeply dissected favouring intense erosion processes thus inhibiting the preservation of early and middle quaternary fluvial archives most of the seven phases identified were followed by periods of river downcutting into bedrock however river incision rates vary significantly and indicate that the paraopeba river catchment belongs to a more active tectonic block there was an association of the regional phases with climatic oscillations that may have influenced the rhythms of the fluvial incision driest coldest periods were marked by the formation of fluvial depositional successions with duricrusts repeated formation of terraces with conglomeratic duricrusts may be related to lower rates of river incision in some valleys some other factors such as the existence of knickpoints the size of each river catchment and its position in the regional river system trunk river or tributary as well as in the regional tectonic arrangement may have influenced the capacity of the rivers to respond differently to the same climatic and tectonic regional events

bryozoan faunas in the middle miocene of hungary biodiversity and biogeography a study of the badenian middle miocene marine deposits of hungary yielded a rich bryozoan fauna of 238 species comprising 59 cyclostomes 176 cheilostomes and 3 ctenostomes six palaeobiogeographic groups have been identified among this fauna on the basis of the present day and fossil distribution of the species similarities within the central paratethys and between the central paratethys the mediterranean and the atlantic have then been calculated using jaccard s index the results indicate strong affinities between the central paratethyan basins of hungary austria poland and romania the higher number of species and the lower level of endemism observed in hungary is explained by the vicinity of this basin to the entrance of the water seaway connecting the mediterranean to the paratethys a decrease in taxonomic diversity between the early and the late badenian is also observed accompanied by the absence of most tropical taxa from the late badenian this points towards a less optimal climate and a more pronounced isolation of the badenian sea from the oceanic waters the major result of the comparative study between central paratethyan and mediterranean bryozoan faunas is the presence of numerous common species the number of endemic paratethyan species is however relatively high indicating that the bryozoan faunas of both seas evolved in a relative isolation the exchange of faunas between the mediterranean and the paratethys was probably regulated by an anti estuarine circulation permitting an easier incursion of mediterranean species into the paratethys but hindering the paratethyan endemics from entering the mediterranean the stronger affinity between hungarian and mediterranean faunas also shows that this basin was closer to the entrance of the water seaway connecting the two areas and thus the mediterranean species entered more easily the similarity index between central paratethys and atlantic faunas is much lower than with the mediterranean this indicates that the palaeobiogeographic domain formed by the mediterranean and the paratethys was relatively homogeneous during the middle miocene and that the relationships with the atlantic were weaker exchange of benthic organisms between the central paratethys and the indo pacific during the middle miocene is considered here as extremely improbable

the collapse of megafaunal populations in southeastern brazil whether humans or climate change caused the extinction of megafaunal populations is actively debated caves in the lagoa santa provide mixed assemblages of megafauna and human remains however it remains uncertain the extent to which humans and megafauna interacted or overlapped temporally here we present the first paleoecological record from lowland south america that tracks the decline of megafauna and its ecological implications we provide a data set for pollen charcoal and sporormiella from two lakes in southeastern brazil that span the last 23 000 yr the data showed reduced abundances of sporormiella and an inferred megafaunal population decline that began 18 000 yr ago with the functional extinction occurring between 12 000 and 11 500 yr ago population declines coincided with wet events the age of the final megafaunal decline is within the range of the first human occupation of the region our data are consistent with climate causing the population collapse with humans preventing population recovery and inducing extinction we did not observe some of the ecological repercussions documented at other sites and attributed to the megafaunal extinction habitat specific ecological consequences of the extinction add to the heterogeneity of late pleistocene and early holocene landscapes

hydrological modelling of a pleistocene landslide dammed lake in the santa maria basin nw argentina abstract around 30 000 14 c yr bp multiple landslides in the quebrada de cafayate 26 s 66 w dammed the rio de las conchas and caused a lake in the santa maria basin nw argentina since climate could have played a major role in landslide generation we used a lake balance model to compare the present day climate with the conditions during landsliding this model reveals that a hypothetical present day lake would stabilize around 70 m below the reconstructed paleolake level the volume of the water body would be one third of the corresponding paleolake volume however a minimum 10 15 increase in mean annual precipitation accompanied by at least a 3 4 c drop in temperature would result in a stable lake level at the reconstructed elevation this result implies wetter and cooler conditions at 30 000 14 c yr bp as compared to the present wetter climate in turn could help to explain enhanced landsliding in the quebrada de cafayate during this time

amazonia during the last glacial abstract new data on the vegetational history and quaternary geology of amazonia permit an improved reconstruction of past environments in amazonia during the last glacial period although limited data from rondonia carajas and guyana show that in certain areas savanna type vegetation and savanna forest had replaced the rain forest during the late pleniglacial ca 22 000 13 000 yr b p the amazonian forest may have been split up into one major west amazonian and several other medium size forest areas this suggests a decline in rainfall of 500 to 1000 mm a reduction of 25 to 40 temperatures may also have been 2 to 6 c 4 2 c lower than today possibly substancially influencing amazonian vegetation during the humid middle pleniglacial 55 000 26 000 yr b p rivers carried a lot of water and sediment resulting in the deposition of lower terrace sediments with one dry interruption around 40 000 yr b p carajas and katira in carajas there is evidence of dry periods ocurring at about 40 000 yr b p and during the early pleniglacial ca 60 000 yr b p rivers carried little water and incised into the low terrace sediments during the dry late pleniglacial water levels rose during the late glacial 13 000 10 000 yr b p or at the beginning of the holocene 10 000 yr b p sedimentation in and of the present inundation valleys commenced after that

the badenian evaporite basin of the northern carpathian foredeep as a model of a meromictic selenite basin the hydrography and brine flow patterns in the middle miocene badenian evaporite basin of the northern carpathian foredeep in ukraine poland and the czech republic are reconstructed based on studies of the peculiar conformably oriented bottom grown gypsum crystals present in the selenite deposits along the basin margin the crystal apices are turned in a similar horizontal direction that is interpreted as the product of consistent flow of the bottom brines during crystal formation similarly the regular millimetre scale growth zoning in these crystals presumably reflects the annual stratification mixing pattern in the brine column typical of monomictic basins in the central deeper parts of the basin deposition was dominated by nachloride and the selenitic facies are lacking these central areas are interpreted as being meromictic during the oriented selenite deposition the permanent pycnocline separated a mixolimnion at the surface from an anoxic euxinic monimolimnion at the bottom where direct evaporative crystallization of gypsum was not possible the mixolimnion which extended far onto the shallow margin of the basin showed only a seasonal annual pycnocline and monomictic hydrography oriented selenites grew just in this mixolimnetic marginal zone under predominantly counterclockwise

quaternary tephrochronology helps define conditioning factors and triggering mechanisms of rock avalanches in nw argentina abstract ten previously defined quaternary tephra layers from northwestern argentina are described here in terms of electron microprobe analyses of glass shards in addition xrf analyses of three tephras alemania buey muerto and el paso ash were performed the alemania ash and buey muerto ash occur within 1 m of each other stratigraphically in several outcrops and exhibit identical glass chemistry as well xrf analyses show that both tephras have identical composition based on stratigraphic relations and age determinations these tephras can clearly be separated as two individual layers tephra ages were defined relatively by ams 14c dates of organic material by 10be surface exposure ages of landslides in stratigraphic association with these tephra layers or directly by 40ar 39ar ages of mineral separates or fission track dating of zircons ages of these tephra layers constrain the temporal distribution of large landslides rock avalanche type in northwestern argentina temporal distribution shows that these large collapses concentrated in deeply incised valleys during climate periods characterized by enhanced precipitation and run off in addition in the tonco valley tephra characteristics also suggest earthquake triggering of coeval landsliding in this valley four landslides one with a 10be age of 7820 830 yr lie in direct contact atop un redeposited paranilla ash showing the coeval age of these landslides the age of the dated landslide deposit coincides with the age of soft sediment deformation structures in nearby lake deposits with an ams 14c age of 7430 7570 cal yr bp

assessment of the debris flow susceptibility in tropical mountains using clast distribution patterns abstract channel morphometric parameters and clast distribution patterns in selected basins of the ferriferous quadrangle tropical mountains brazil were analyzed in order to assess susceptibility to debris flows median bed surface clast size d 50 in the main stream channel of these basins shows a coarsening downstream trend with drainage areas of up to 6 km 2 which is attributed to debris flow dominated channels by some authors the composition and roundness of the bed load clast sand and the presence of allochthonous large boulders throughout the channels also suggest the occurrence of past debris flow in the region luminescence optically stimulated loe dating points out that debris flow could have occurred as a consequence of climate changes in the late pleistocene and holocene and it can now be triggered by deforestation or extreme rainfall events there has not been any record of past debris flow in the study area or in other mountainous regions of brazil where debris flows have recently occurred thus the adopted approach can be useful to assess debris flow susceptibility in this and other similar areas

two paleoecological histories spanning the period of human settlement in southeastern brazil the absence of human occupation sites in southeastern brazil during the mid holocene has been referred to as the archaic gap 8970 1940 cal a bp and is predicted to have resulted from increased aridity a ca 14 000 cal a pollen history from two well dated lake sediment cores located within the archeological district of lagoa santa in the state of minas gerais southeastern brazil was used to test this hypothesis our analyses indicated that the present cerrado and tropical semi deciduous forest mosaic persisted throughout the mid holocene until ca 5500 cal a bp and the lagoa santa region did not experience especially dry conditions during the holocene period the early holocene pollen spectra contained an assemblage of cold adapted taxa such as podocarpus myrsine and araucaria co occurring with taxa from cerrado e g caryocar a replacement of cold taxa by the modern cerrado semi deciduous forest vegetation took place progressively but appears to have been completed by the mid holocene no evidence of sustained drought was found in sedimentation or forest composition nor any prolonged dry event in the study region holocene dryness as an explanation for the abandonment of lagoa santa region is not supported by the palynological analyses conducted in this study rather it is suggested that unpredictable climate may have underlain that abandonment copyright 2012 john wiley sons ltd

the last 50 000 years in the neotropics southern brazil evolution of vegetation and climate abstract in the lagoa campestre lake of salitre 19 s 46 46 w 970 m elev there are plant taxa belonging to many ecological groups that are encountered nowhere else at this latitude frequent incursions of polar advections causing cooling and humidity a cool and foggy climate in the middle of the depression and warmer temperatures on the surrounding slopes help to maintain all these groups within a fairly restricted area late pleistocene holocene climatic change has had a considerable impact on the flora and vegetation of salitre the pollen record of the 6 m deep core lc3 shows how cold forest trees such as araucaria angustifolia and drimys brasiliensis semi deciduous forest halophytic plants and peat bog started to develop on this site the initial period between c 50 000 and 40 000 yr b p was an arid phase not recorded in any other neotropical lowland site it was followed by a period of high moisture levels 40 000 to 27 000 yr b p with a maximum estimated at c 35 000 yr b p the late glacial maximum is missing because of a gap in sedimentation humidity gradually increased during the late pleistocene between 16 000 and 11 000 yr b p the early holocene 9500 to 5000 yr b p is characterized by a more marked seasonal pattern and higher temperatures reaching a maximum c 5000 yr b p the spread of semi deciduous forest between 4000 and 3000 yr b p attests to a return of humidity comparison with the serra negra section 19 s 46 45 46 w 1170 m elev not far from salitre confirms the high moisture rates recorded at c 35 40 000 yr b p although temperatures were cooler at the altitude of serra negra as is attested by the presence of araucaria forest and also confirms the strong impact of polar advections on the climate of southeastern brazil

the transylvanian basin romania and its relation to the carpathian fold and thrust belt insights in gravitational salt tectonics abstract interpretation of regional seismic profiles stratigraphic and sedimentologic data improved insights in the evolution of the transylvanian basin the basin evolution was coeval with the post mid cretaceous to recent deformation of the carpathian mts four tectonostratigraphic megasequences are differentiated upper cretaceous rift paleogene sag lower miocene flexural basin and middle to upper miocene backarc sequence dominated by gravitational tectonics the mid miocene continental collision in the eastern carpathians is associated with the rising carpathians this uplift enhanced the differential load which together with the high heat flow induced by late miocene to pliocene arc volcanism triggered large scale mio pliocene gravity spreading of the salt overburden this mega slide comprises three structural domains as follows extensional weld upslope contractional folds central and contractional toe thrust downslope the diapirs in the east indicate a pre shortening reactive passive growth stage the central folds are mostly the result of late shortening basement involved thrusting uplifted the toe thrust domain by the late pliocene the late neogene to recent carpathians uplift backarc volcanism and gravity spreading are largely coeval

vegetation and fire variability in the central cerrados brazil during the pleistocene holocene transition was influenced by oscillations in the sasm boundary belt abstract this study investigates historical fire regimes and arboreal cover variability in the brazilian cerrados a large neotropical savanna ecosystem during the pleistocene holocene transition and early holocene and then tests whether the observed variation is linked to south american summer monsoon sasm variability we present high resolution pollen xrf and charcoal records from lagoa feia located in central cerrados and assess how they compare with other pollen records from the surrounding region to investigate regional trends of vegetation and fire regime variability our results show that the pleistocene holocene transition was marked by a wet episode which included moist forest expansion and rising lake levels that correlates well with increased monsoon activity in a large area of central south america during the same period this wet episode chronologically coincides with the younger dryas cold episode in the northern hemisphere our data revealed moisture declines in central cerrados after 11 2 kyr bp along with centennial scale fluctuations from dry to wet conditions throughout the early holocene period until around 6 kyr bp these dry wet oscillations are associated with weakened sasm activity and repeated shifts of its belt position during this time range fire activity increased in central cerrados just after the onset of drier conditions during the early holocene and likely contributed to decreased arboreal cover at that time a trend of increasing moisture in the region was observed after 6 kyr bp our study reveals how centennial and millennial scale changes in monsoon activity influenced arboreal cover diversity and fire regimes in the central cerrados

holocene palaeoenvironmental reconstruction in norteastern brazi inferred from polen charcoal and carboon isotope records soils in the barreirinhas region maranhao state were sampled for 613 c analysis and buried charcoal fragments in the soils were radiocarbon dated three soil profiles collected in forested areas around the lagoa do caqo and one in a woody savanna mixture of non arboreal and arboreal species located approximately 10 km southeast of the lagoa were studied a high resolution pollen record was obtained from lake sediments showing that forest vegetation was predominant in the area in the early holocene from approximately 10 000 14c yr bp the pollen spectrum gradually changed suggesting the dominance of open savanna communities these were transformed to a more forested landscape woody savanna from approximately 7500 yr bp the lake sediments also record evidence of fire indicated by buried charcoal particles at several soil depths during the holocene the 613 c analysis of soil organic matter som indicates that from between approximately io0000 yr bp and 9000 yr bp to 4000 yr bp a woody savanna

strontium isotope composition of middle miocene primary gypsum badenian of the polish carpathian foredeep basin evidence for continual non marine inflow of radiogenic strontium into evaporite basin strontium isotope compositions of ancient sulphate deposits not only provide chemostratigraphic information but also offer insight into the system in which the evaporites precipitated primary gypsum from two middle miocene badenian sections in southern poland shows steadily higher 87sr 86sr ratios than those expected from a marine derived formation the ratios are interpreted as the result of increasing inflow into the basin at the time of gypsum precipitation palaeogeographic reconstructions suggest that riverine runoff sources were situated in the west and east european platforms to the north and east respectively and the carpathians to the south which are mostly composed of mesozoic sedimentary rocks their dissolution cannot be responsible for the higher 87sr 86sr ratios recorded we conclude that archaean and palaeoproterozoic igneous and supracrustal rocks of the ukrainian shield were the source of the higher 87sr 86sr ratios recorded in the badenian primary gypsum a distinctive decreasing trend of 87sr 86sr ratios from western ukraine to southern poland is explained by a consistent direction of brine inflow during gypsum crystallization typical cyclonic circulation controlled by the coriolis effect

multicomponent analysis of ftir spectra quantification of amorphous and crystallized mineral phases in synthetic and natural sediments abstract the study of weathering and erosion processes requires the establishment of a mass balance of minerals from the soils towards the sedimentation area this calls for the development of quantitative tools that can be applied to mixtures of finely divided and sometimes poorly crystallized minerals found in soils and sediments we present here the use of fourier transform infrared ftir absorbance spectroscopy in the mid infrared as a method to calculate mineral modes for such materials samples were prepared using the kbr disc method this ensures that lambert beer s law is valid a quantitative determination of the mineral content from various blends was performed by making a multicomponent analysis of the experimental spectrum using the spectra of each component in the mixture to check the validity of the procedure the multicomponent analysis was performed on spectra from synthetic mixtures of standard minerals quartz kaolinite gibbsite amorphous silica good agreement between actual and computed wt was obtained in the range 1315 315 cm 1 this application of ftir spectroscopy was used to quantify the mineral components of a lacustrine sediment cored at salitre minas gerais brazil the major phases are organic matter kaolinite gibbsite quartz anatase and amorphous silica phytoliths and sponge spicules fifty three samples were analyzed quantitative results from ftir spectroscopy were compared to chemical analyses to assess the validity of the method for the natural sediments phases with no sharp diagnostic spectral features such as anatase or amorphous silica were quantified using the multicomponent analysis the variations of the main mineral phases along the core reflect the mechanisms of transfer from the surrounding soils to the sediment area and the role of the vegetal cover over the drainage area

resedimentation of basin centre sulphate deposits middle miocene badenian of carpathian foredeep southern poland abstract the middle badenian anhydrite sections in the central part of the carpathian foredeep consist mainly of interbedded laminated anhydrite and anhydrite breccia these facies display features characteristic of redeposited sediments such as distortions due to slumping erosional boundaries and graded bedded laminae lamination in laminated anhydrite is rarely regular and often accompanied by disruptions the predominance of clasts of laminated anhydrite combined with the observed brecciation of laminated anhydrite indicates that a short distance for transport and even in situ reworking were common a high degree of convolution indicates that some reworked sediments were unconsolidated when they moved but in many cases they were probably at least partly lithified this is evidenced by the anhydrite breccia consisting of clasts of laminated anhydrite as well as the brecciation in situ the resedimentation processes have not been related to regional bathymetrical differences as indicated by minor differences along seismic profiles a great deal of redeposition within the basin centre of the middle badenian evaporite basin combined with the in situ brecciation suggests that the triggering mechanism for redeposition could be earthquakes they generated mass flows and eventually turbidites so that earlier deposited grains could be redeposited this implies that in other evaporite basins the laminar facies might be at least partly related to redeposition and not necessarily to changes of surface brine concentration as usually supposed

millennial to secular time scale impacts of climate and sea level changes on mangroves from the doce river delta southeastern brazil this work integrates geomorphological sedimentological and palynological data with radiocarbon dating as well as 13c 15n and c n from sedimentary organic matter to provide a model of mangrove dynamics during the evolution of a wave dominated delta in southeastern brazil mangrove dynamics are analyzed within the context of millennial and secular climatic and sea level changes tidal flats positioned at highest limit of the intertidal zone along the edge of a lagoon sheltered by beach ridges were occupied by wetlands represented by mangrove and herbaceous vegetation during the mid holocene high sea level after considering the relative sea level fall and relatively higher fluvial sediment discharge during the last 6350 years progradation took place along this shoreline resulting in extensive beach ridge deposits that overlie transgressive muds this process led to loss of mangrove area similar dynamics were repeated at 3043 cal yr bp although in a relatively more distal i e seaward posi

quaternary of the pantanal west central brazil abstract the pantanal is a tectonic depression located at the left margin of the upper paraguay river the paraguay is the trunk river of an alluvial depositional tract composed by several large marginal alluvial fans the taquari fan being the largest one the present landscape is a complex tropical wetland characterized by month long floods every year with geomorphic features derived from the present conditions and others inherited from successive pleistocene and holocene climates some areas containing ponds are landscape relicts generated by eolian deflation during the last glacial maximum many ponds closed depressions isolated from the superficial waters by vegetated crescent ridges of fine sands were interpreted as salt pans bordered by lunette sand dunes initiation of the modern wetland has occurred during the pleistocene holocene transition with the change to a more humid climate and the individualization of lacustrine systems active tectonics has been playing an important role in the development of the pantanal landscape nowadays the paraguay river meanders in a large flood plain with extensive swamp surfaces being structurally constrained by faults in the west border of the basin sedimentation within the pantanal wetland is also affected by tectonic activity especially along faults associated with the transbrasiliano lineament

sedimentology of badenian middle miocene gypsum in eastern galicia podolia and bukovina west ukraine primary gypsum is the main evaporite mineral in the middle miocene badenian of the west ukraine the lower part of the gypsum sequence is built of autochthonous gypsum while the upper part is composed of allochthonous gypsum that formed following a major tectonically induced change in basin morphology this change resulted in the destruction of the gypsum deposited on the margins of the basin and formation of redeposition features autochthonous gypsum facies were deposited in two main environments 1 giant gypsum intergrowths precipitated from highly concentrated brines 2 very shallow subaqueous gypsum deposited in a vast brine pan the brine pan was characterized by a facies mosaic that reflects an interplay of concentrated brines from the central part of the evaporite basin and diluted brines due to the influx of continental meteoric waters the facies continuum microbial gypsum bedded selenite massive selenite sabre gypsum indicates increasing salinity of the brine with time this type of facies pattern has been established in recent salinas that are analogous to badenian gypsum in their lateral facies changes however the pattern of facies distribution with respect to the open sea in the badenian basin is opposite to that found in recent salinas the pattern of the badenian gypsum facies in the ukraine indicates that facies repetition may have been related to climatically controlled salinity changes and not to depth changes as is commonly used to explain the repetition of sulphate facies in a vertical succession

millennial scale vegetation and climatic changes from an early to mid holocene lacustrine archive in central ganga plains using multiple biotic proxies abstract the indo gangetic floodplains have many abandoned meander cut offs and oxbow lakes that can serve as potential archives for high resolution paleoclimatic reconstruction previously a few of these lakes have been investigated for understanding the regional holocene climatic history but these studies are generally limited by a lack of high chrono stratigraphic resolution to develop an understanding of the role of local and or regional climate forcings an oxbow lake baraila tal in the central ganga plains has been studied using multiple biotic proxies such as pollen phytoliths diatoms and sponge spicules millennial scale climatic fluctuations and vegetation history for the early to mid holocene period have been reconstructed using 17 ams radiocarbon dates from two trenches 3 4 m deep five major biotic zones have been delineated between 13 2 and 4 8 kyr bp zone i 13 12 kyr bp shows small patches of dry tropical woody flora along with tall c4 grass indicating a moderately dry climate the presence of low temperature herbs indicates an active ne monsoon but the paucity of arboreals indicates a weakened indian summer monsoon ism the high percentages of phacotus lenticularis cysts in zone ii 12 9 kyr bp indicate the presence of stagnant lime rich inland waters under relatively colder climatic conditions the appearance of evergreen forest groves around 11 5 kyr bp indicates an increase in humidity and lake deepening was inferred between 10 9 and 10 3 kyr bp sediment accumulation rate shows a sudden drop at 10 3 kyr bp indicating a complete cut off of the oxbow lake from the fluvial channel zone iii 9 8 kyr bp records millennial scale drying with a complete absence of aquatic pollen between 8 9 and 7 7 kyr bp the expansion of short c4 grass in zone iv 8 7 kyr bp further indicates drier conditions zone v 7 5 kyr bp shows very high percentages of sponge spicules that flourish in clear waters and represents a strengthened ism and a subsequent lake expansion

multiepisodic evaporite sedimentation as an indicator of palaeogeographical evolution in foreland basins south eastern pyrenean basin early middle eocene extensive deposition of marine evaporites occurred during the early middle eocene in the south eastern pyrenean basin north east spain this study integrates stratigraphic and geochemical analyses of subsurface data oil wells seismic profiles and gravity data together with field surveys to characterize this sedimentation in the foredeep and adjacent platform four major evaporite units were identified the oldest was the serrat evaporites unit with a platform slope basin configuration thick salina and sabkha sulphates accumulated on the platform whereas resedimented and gravity derived sulphates were deposited on the slope and salt and sulphates were deposited in the deep basin in the subsequent unit vallfogona evaporites thin sulphates formed on the platform whereas very thick siliciclastic turbidites accumulated in the foredeep however some clastic gypsum coming from the platform gypsarenites and gypsum olistoliths was intercalated in these turbidites the following unit the beuda gypsum formation developed in a sulphate platform basin configuration where the topography of the depositional surface had become smooth the youngest unit the besalu gypsum formed in a shallow setting this small unit provides the last evidence of marine influence in a residual basin sulphur and oxygen isotope compositions are consistent with a marine origin for all evaporites however 34s and 18o values also suggest that except for the oldest unit serrat evaporites there was some sulphate recycling from the older into the younger units the south eastern pyrenean basin constitutes a fine example of a foreland basin that underwent multiepisodic evaporitic sedimentation in the basin depositional factors evolved with time under a structural control decreasing complexity is observed in the lithofacies as well as in the depositional models together with a diminishing thickness of the evaporite units

holocene climatic variations in northern patagonia argentina abstract seventeen playa lakes in patagonia between 39 and 47 s were cored with the aim of reconstructing the vegetational climatic and geomorphological history by means of sedimentological and palynological analysis the paper discusses the initial results from two salt lakes salina anzoategui 39 00 23 s 63 46 30 w and salina piedra 40 34 59 s 62 40 26 w lying in closed depressions at the northeastern margin of the arid diagonal of patagonia both the sedimentological and the palynological results of the analyzed sediment cores from these playa lakes suggest prevailing arid climatic conditions with mainly aeolian morphodynamic processes during the mid holocene in late holocene times the climate changed to more semi arid conditions with a higher rainfall frequency and more frequent fluvial input into the lake possibly reflecting greater influence from the atlantic high pressure cell leading to more distinct seasonality

climatic events during the late pleistocene and holocene in the upper parana river correlation with ne argentina and south central brazil most quaternary studies in brazil are restricted to the atlantic coast and are mainly based on coastal morphology and sea level changes whereas research on inland areas is largely unexplored the study area lies along the parana river state of parana brazil at 22 43 s latitude and 53 10 w longitude where the river is as yet undammed paleoclimatological data were obtained from 10 vibro cores and 15 motor auger holes sedimentological and pollen analyses plus tl and 14c dating were used to establish the following evolutionary history of late pleistocene and holocene climates first drier episode 40 000 8000 bp first wetter episode 8000 3500 bp second drier episode 3500 1500 bp second present wet episode 1500 bp present full size table table options view in workspace download as csv climatic intervals are in agreement with prior studies made in southern brazil and in northeastern argentina

late quaternary of the middle caqueta river area colombian amazonia the late quaternary history of the middle caqueta river area in colombia northwestern amazonia is described based on observations of river bank sections radiocarbon dates and palynological analyses of organic layers in floodplain and low terrace sediments of the caqueta river it is shown that the late pleistocene and holocene climatic changes that took place in the andean cordilleras were related to the depositional and erosional history of the caqueta river in the colombian amazonian lowlands the low terrace sediments consist of sandy and gravelly deposits covered by clays that sometimes contain lenses of peaty material from these organic low terrace sediments seven finite radiocarbon dates were obtained of middle pleniglacial age between 56 000 and 30 000 yr bp the coarse textured basal deposits of the low terrace apparently stem from the early part of the middle pleniglaciai period during which the effective rainfall in the andes was relatively high and the andean glaciers had a considerable extension palynological data from silty sediments with organic remains at one site show an interval when drier and more open types of vegetation on poor soils must have covered a larger area than today but amazonian forest was still the dominating type of vegetation this interval might correspond to one of the middle pleniglacial savanna intervals from eastern amazonia carajas no organic sediments from the upper pleniglacial period were found and hence radiocarbon dates were not obtained in the andes this period had a very cold climate with low effective rainfall and in the east amazonian carajas area it is characterised by the relative extension of open savanna vegetation the river run off and sediment transport must have been much lower than in the middle pleniglacial and the caqueta river cut itself down in its own sediments two late glacial radiocarbon datings obtained at one site ca 12 500 yr bp indicate the existence of a late glacial sedimentation phase separated from the holocene sequence by a minor erosional phase organic layers in the holocene floodplain sediments yielded 28 radiocarbon dates between 10 000 and 355 yr bp holocene sedimentation started with the rapid deposition of sandy clay possibly in a partly permanently inundated caqueta valley during the major part of the holocene silty clays were deposited with a dominant seasonal inundation cycle

late pleistocene climate change and erosion in the santa maria basin nw argentina present erosion and sediment flux in the semiarid intra montane santa maria basin nw argentina are compared with con ditions during a period of wetter and more variable climate at about 30 000 14 c yr ago the results suggest that the influence of climate change on the overall erosional sediment budget is significant mainly because of a change in the erosion regime coupled with an increase in mass movements the most effective mechanism to increase landslide activity in this environment is a highly variable climate on interannual timescales in contrast quaternary changes in erosional budgets due to variations in moisture regimes is small in the santa maria basin because the magnitude of a potential increase in background erosion as well as enhanced landsliding is smaller than typical levels of uncer tainty of erosional budgets for such large basins it is not likely that climate driven erosional unloading can influence tectonic style and rates in this semiarid environment on time scales of several thousands to a few tens of thousands of years

southern oscillation signal in south american palaeoclimatic data of the last 7000 years abstract during strong el nino events rainfall anomalies and changes in wind patterns are observed in different regions of south america along the central brazilian coast during the 1983 el nino year the frontal systems were blocked to the south provoking a reversal of the longshore sand transport long duration reversals of longshore transport were also recorded in holocene beach ridge terraces from the rio doce coastal plain this led to the formulation of a model relating these reversals of longshore transport to el nino like conditions el nino like conditions are past average climate situations that generate the same perturbations as the strong el nino events observed during the last decade they are likely to correspond to the long duration low phase of the southern oscillation to confirm this hypothesis we compared the holocene beach ridge record with other palaeoenvironmental records from regions where strong el nino events would have a substancial signal as well 1 water level fluctuations of lake titicaca 2 a pollen and sediment record in an eastern amazonian lake 3 changes of the rio xingu discharge in eastern amazonia and 4 variations of sand supply at the rio piura and rio chira outlets in the sechura desert the occurrences of el nino like conditions were numerous before 3900 3600 yr b p absent between 39003600 and 2800 2500 yr b p and infrequent after 2800 2500 yr b p

vegetation dynamics during the late pleistocene in the barreirinhas region maranhao state northeastern brazil based on carbon isotopes in soil organic matter abstract the study place is in the barreirinhas region maranhao state northeastern brazil a vegetation transect of 78 km was studied among four vegetation types restinga coastal vegetation cerrado woody savanna cerradao dense woody savanna and forest as well as three forested sites around lagoa do caco located approximately 10 km of the transect soil profiles in this transect were sampled for 13c analysis as well as buried charcoal fragments were used for 14c dating the data interpretation indicated that approximately between 15 000 and 9000 14c yr b p arboreal vegetation prevailed in the whole transect probably due to the presence of a humid climate approximately between 9000 and 4000 3000 14c yr b p there was the expansion of the savanna probably related to the presence of drier climate from 4000 3000 14c yr b p to the present the results indicated an increase in the arboreal density in the area due to the return to a more humid and probably similar climate to the present the presence of buried charcoal fragments in several soil depths suggested the occurrence of palaeofires during the holocene the vegetation dynamic inferred in this study for northeastern brazil is in agreement with the results obtained in areas of amazon region based on pollen analysis of lake sediments and carbon isotope analysis of soil organic matter som implying than similar climatic conditions have affected these areas during the late pleistocene until the present

the hydrological setting occurrence and significance of gypsum in late quaternary salt lakes in south australia well exposed often laminated gypsum sequences occur in many quarternary salt lakes in southern south australia the gypsum in the salt lakes is classified by increasing grain size into gypsite gypsarenite and selenite the salt lakes are classified by age and hydrological setting into coastal salinas which are holocene sea water fed groundwater lakes and continental playas which are late pleistocene endorheic basins a study of the relationships between coastal salina hydrology and the associated gypsum deposition has shown the different types of gypsum form under distinct hydrological regimes as the hydrology above a coastal salina depositional surface changes through time so does the type of gypsum deposited application of a gypsum depositional model derived from a study of the coastal salina gypsum to those portions of a continental playa gypsum unit where deposition is no longer occurring confirms the applicability of the model to non salina gypsum deposits

temperature and precipitation record in southern chile extended to 43 000 yr ago southern chile 41 56 s in the belt of westerly winds receives mostly heavy precipitation reaching 8 500 mm yr 1 near 50 s and decreasing northwards and southwards from this latitude to 1 500 mm mean january summer temperatures near sea level along the latitudinal gradient are 8 16 c refs 1 2 dense rain forest covers much of the region to 48 s south to cape horn magellanic moorland prevails and rain forest becomes limited modern pollen measured in surface samples reflects the distribution of plant species in the vegetation we have now applied regression equations relating present day pollen to temperature and precipitation to fossil pollen data at taiquemo to assess climatic conditions during the quaternary the results extend our previous record of the past 16 000 yr at alerce3 beyond the lateglacial to 43 000 yr bp for the 27 000 yr interval they show mean january temperatures of 10 12 c and mean annual precipitation centred around 1 000 mm except during the time span of 31 000 43 000 yr bp when amounts increased to 4 000 mm in general fluctuations correspond to the isotopic climatic reconstruction in antarctica4 and to changes inferred from pollen data at comparable latitudes in tasmania5 8 and new zealand9 10

how fast are soil forming processes in quaternary sediments of a tropical floodplain a case study in southeast brazil abstract floodplains are depositional features of a channel valley associated with a specific climatic and hydrologic regime of a drainage basin in tropical conditions sediments can be quickly weathered by soil forming processes and tend to obliterate pre existing sedimentary structures therefore the objective of many studies on floodplains is to identify and discuss such sedimentary features mostly those related to the morphology of channel deposits additionally a qualitative approach to identify aspects of pedological evolution in these environments has been attempted in few studies the purpose of this study was to interpret the intensity and the time of alluvial sediment weathering by pedogenetic processes in tropical humid conditions soil profiles were analyzed in different environments of deposition in the pardo river floodplain southeast brazil by accounting for sedimentary facies and pedological features supported by multi proxy data provided from geochemistry macro and micromorphology grain size total carbon total nitrogen 13 c isotopic analysis and 14 c osl optically stimulated luminescence dating based on the results we identified that pedogenetic features and soil horizon distributions were closely related to sediment architecture grain size and position in the floodplain in the pardo floodplain fluvic gleysols loamic and clayic with moderately to strongly developed structures were identified in overbank fine sediments fluvic cambisols clayic were found in abandoned paleomeanders fluvic cambisols loamic in sandy scrollbars gleyic acrisols clayic cutanic differentic in channel deposits which presented a 130 cm thick bt horizon with illuvial clay coatings and histosols fluvic with high contents of total carbon 11 9 and 26 8 in histic horizons in small scale avulsive systems deposits were dated to between 35 000 and 700 years bp 13 c isotopic data revealed a trend toward enriched values in older samples 14 21 in which c 4 plants dominated and a relative impoverishment of the values in more recent samples 26 9 to 27 9 this result was consistent with the tendency of the distribution of c 3 plants to increase over that of c 4 plants favored by the warmer and wetter climate since the upper holocene in this study a fluvic gleysol profile of

forest changes in the amazon basin during the last glacial maximum we report here the discovery of forest beds in the amazon basin radiocarbon dated to the wisconsin wurm glaciation these are the first dates from the last glaciation determined on amazonian samples the locality is in ecuador at 1 100 m elevation near the upper limit of the present amazonian rainforest both pollen spectra and podocarpus wood in the deposits suggest that vegetation comparable to the present andean forest grew at least 700 m lower than it does now suggesting a temperature depression of at least 4 5 c for the amazon lowlands

post evaporitic restricted deposition in the middle miocene chokrakian karaganian of east crimea ukraine abstract in the middle miocene of east crimea gypsum evaporites formed in a shallow basin from mixed seawater nonmarine waters are overlain by marl siltstone and claystone which contain a few horizons of stromatolitic limestone the thickness and abundance of the stromatolitic horizons increase up the section in the siliciclastic portion of the section a very poor and taxonomically impoverished assemblage of benthic foraminifers jadammina nonion haynesina astrononion and eponides is recorded it is typical for a shallow water marsh or lagoon environment with a lowered salinity accordingly the brackish conditions prevailing during gypsum precipitation in east crimea continued afterwards although at the end of evaporite deposition the basin became desiccated and then it was rapidly reflooded by brackish water the impoverished biota and the occurrence of microbialites in the ptashkino section indicate extremely unfavourable conditions for most living organisms during the deposition of both the terrigenous and carbonate beds the water salinity thus was probably not only lowered but also anomalous in composition if compared to normal marine water the occurrence of carbonate stromatolitic horizons is probably related to the periodic shallowing of the basin caused by a drop of the lake water table driven by climatic factors the resulted changes allowed for a growth of the bizarre microbial serpulid communities that gave birth to most of the stromatolites in karaganian time the eastern paratethys was a huge lake isolated from the tethys this lake responded to any climatic fluctuation that in turn might lead to water level oscillations in humid climate periods the lake could be open with a surface outflow and when it was drier it could be a closed system without surface outflow gypsum evaporites and stromatolitic carbonates are clear evidence of strong evaporation in a dry climate that probably induced water level fall in the whole basin however all the time the environmental conditions were predominantly brackish even during gypsum precipitation as suggested by the chemical composition of fluid inclusions in gypsum similar conditions may be expected in other evaporite hosted predominantly brackish basins such as some messinian basins of the eastern mediterranean where some evaporites were deposited in the oligohaline to mesohaline conditions typical of the lago mare deposits

chronology causes and progression of the messinian salinity crisis the messinian salinity crisis is widely regarded as one of the most dramatic episodes of oceanic change of the past 20 or so million years 1 3 earliest explanations were that extremely thick evaporites were deposited in a deep and desiccated mediterranean basin that had been repeatedly isolated from the atlantic ocean1 2 but elucidation of the causes of the isolation whether driven largely by glacio eustatic or tectonic processes have been hampered by the absence of an accurate time frame here we present an astronomically calibrated chronology for the mediterranean messinian age based on an integrated high resolution stratigraphy and tuning of sedimentary cycle patterns to variations in the earth s orbital parameters we show that the onset of the messinian salinity crisis is synchronous over the entire mediterranean basin dated at 5 96 0 02 million years ago isolation from the atlantic ocean was established between 5 59 and 5 33 million years ago causing a large fall in mediterranean water level followed by erosion 5 59 5 50 million years ago and deposition 5 50 5 33 million years ago of non marine sediments in a large lago mare lake sea basin cyclic evaporite deposition is almost entirely related to circum mediterranean climate changes driven by changes in the earth s precession and not to obliquity induced glacio eustatic sea level changes we argue in favour of a dominantly tectonic origin for the messinian salinity crisis although its exact timing may well have been controlled by the 400 kyr component of the earth s eccentricity cycle

holocene dryness and human occupation in brazil during the archaic gap an overview of the archaeological data produced over the last decades for brazil coupled with a background of recent paleoenvironmental studies suggests that during the mid holocene vast areas of central brazil ceased to be occupied by human groups independent data from dated human skeletons rock shelter stratigraphy and chronology of open air sites converge to support the inference that these areas were depopulated or altogether abandoned paleoenvironmental data suggest that dryness events constitute the major cause behind the observed trends this phenomenon expands the already perceived notion that climatic stresses had a major role in the shaping of human settlement patterns in marginal environments such as deserts and high altitude settings

a multi proxy evidence for the transition from estuarine mangroves to deltaic freshwater marshes southeastern brazil due to climatic and sea level changes during the late holocene abstract the present study investigates a paleo estuary at the doce river delta southeastern brazil through a multi proxy approach that links palynology diatoms sedimentology and geochemistry analyses i e total c total n 13 c and 15 n these analyses temporally synchronized with five radiocarbon ages revealed environmental changes from marine to continental over the last 7550 years the studied sedimentary succession recorded the upward transition from estuarine channel until 7550 cal yr bp to estuarine central basin 7550 to 5250 cal yr bp deposits the latter containing increased mangrove vegetation marine and marine brackish water diatoms the range of geochemical values 13 c 30 10 15 n 2 8 and c n 4 40 also indicate marine estuarine organic matter and c 3 terrestrial plants to that time interval a following period recorded two phases lake ria 5250 to 400 cal yr bp and fluvial channel 400 cal yr bp until modern age during this stage mangroves were replaced by trees shrubs and herbs grasses due to the disconnection with the marine realm as a result the corresponding sediments contain only organic matter sourced from freshwater and c 3 terrestrial plants 13 c 29 26 15 n 0 8 and c n 10 45 the equilibrium between fluvial sediment supply and relative sea level changes during the holocene controlled the morphologic and vegetation changes in the studied littoral the estuary became established during the early holocene as a resulted of a eustatic sea level rise when the fluvial sediment supply to the coast was relatively lower due to a dry period however during the late holocene the climatic force was more significant to the development of coastal morphology due to a wet period that caused an increase in sandy sediment supply to coastal system then the increase of fluvial discharge associated to a relative sea level fall caused a marine regression and shrinkage of mangroves during the late holocene the evaluation of mangrove dynamics according to climatic and sea level changes mainly during the late holocene is essential for the understanding of their survival ability under future scenarios with a probable accelerated sea level rise and intensification of extreme climatic events in southeastern brazil for the next century

multiple landslide clusters record quaternary climate changes in the northwestern argentine andes the chronology of multiple landslide deposits and related lake sediments in the semi arid eastern argentine cordillera suggests that major mass movements cluster in two time periods during the quaternary i e between 40 and 25 and after 5 14 c kyr bp these clusters may correspond to the minchin maximum at around 28 27 14 c kyr bp and titicaca wet periods after 3 9 14 c kyr bp the more humid conditions apparently caused enhanced landsliding in this environment in contrast no landslide related damming and associated lake sediments occurred during the coipasa 11 5 10 14 c yr bp and tauca wet periods 14 5 11 14 c yr bp the two clusters at 40 25 and after 5 14 c kyr bp may correspond to periods where the el nin o southern oscillation enso and tropical atlantic sea surface temperature variability tav were active this however was not the case during the coipasa and tauca wet periods lake balance modelling of a landslide dammed lake suggests a 10 15 increase in precipitation and a 3 4 c decrease in temperature at v30 14 c kyr bp as compared to the present in addition time series analysis reveals a strong enso and tav during that time the landslide clusters in northwestern argentina are therefore best explained by periods of more humid and more variable climates 2003 elsevier science b v all rights reserved

lithofacies diagenetic spectra and sedimentary cycles of messinian late miocene evaporites in se spain abstract messinian evaporites have been deposited within a number of connected basins that formed the so called betic strait in se spain during the late miocene pre syn and postevaporitic sedimentary successions may well be compared with other strata of the same age surrounding the mediterranean sea there is no evidence for a cataract like connection of these basins with a strong unidirectional flow regime before and during the formation of messinian evaporites as previously suggested the most frequently occurring gypsum lithofacies presumably related to shallow water depositional environments are crystalline selenitic gypsum grass like gypsum laminated gypsum and cross bedded gypsarenite only few real sabkha type chicken wire alabastrine gypsum have been identified evenly laminated gypsum together with graded gypsarenites turbidites gypsrudites debrites and slumps is restricted to basins or parts of basins with considerable paleoslopes evidence for diagenetic overprinting is abundant in all outcrop areas studied this includes the formation of giant gypsum twin crystals super cones and alabastrine nodular gypsum the formation of messinian evaporites in se spain is thought to be controlled by a superimposed third order sea level lowstand smaller sedimentary units fall well into the range of fourth to sixth order cyclic and rhythmic successions they are clearly related to basin dynamics or to autogenetic processes of the local facies zone facies dynamics none of the smaller scale cycles fourth and higher order as observed in outcrops are related to high frequency eustasy

from the semiarid landscapes of southwestern usa to the wet tropical zone of southeastern brazil reflections on the development of cuestas pediments and talus abstract classical geomorphological models consider that escarpment retreat of cuesta landforms is fastest in arid and semiarid regions which would be expected to lead to increased talus production however this is in disagreement with the piedmont zone of the colorado plateau cliffs arid semiarid region of southwestern usa where talus is as inconspicuous as the deposits of the cuesta escarpment footslopes of the parana basin wet tropical region of southeastern brazil thus this paper discusses the evolutionary processes of cuesta escarpments pediments and piedmont deposits in both wet tropical regions and arid zones considering the key areas of the serra geral ridge in the parana basin and the eastern central colorado plateau as examples this manuscript constitutes a comprehensive and critical review of the principal literature on the landform development of such regions research has revealed that despite the production of sediment fine coarse from the escarpments in the arid southwestern usa geochemical weathering and freeze thaw cycles quickly destroy talus deposits furthermore chemical weathering dissolves minerals and forms caverns within the rock walls of mesas and in amphitheaters and canyons influencing escarpment retreat directly despite mechanical processes being the most important factors controlling landform development on the other hand in regions characterized by the wet tropical climate of brazil geochemical processes are more intense and they destroy the talus very quickly enhancing deep weathering however mechanical morphogenesis is also frequent in such regions forming in deforested areas features very similar to those found in the badlands of dry zones chemical and physical mechanical processes have very different intensities in dry arid and wet tropical areas but these processes are very relevant to landform development in both environments the rates of escarpment retreat are higher in the dry areas of the colorado plateau than estimated for the brazilian tropical zones which is in accordance with classical models these variations are probably related not only to climate but also to lithological differences the tops of the mesas on the colorado plateau are supported by thin strongly cemented conglomeratic fluvial sandstones whereas the caprocks of the brazilian cuesta landforms comprise thick basalt flows capped by ferruginous cuirasses in some cases lithological characteristics are more important than climate regarding escarpment retreat

tertiary basin evolution along the northeastern margin of the tibetan plateau evidence for basin formation during oligocene transtension the development of high topography associated with the indo asian collision plays a central role in ongoing debates over the linkages between development of the tibetan plateau and climate in northeastern tibet the widespread appearance of coarse terrestrial sediment during the oligocene is commonly interpreted to herald the development of a foreland basin in response to crustal thickening along the present day margin of the plateau however a lack of direct observations relating sediment accumulation to fault activity leaves this interpretation uncertain here we present new stratigraphic observations along the northern margin of the longzhong basin that provide insight into the tectonic setting of basin development a combination of field and subsurface observations including the geometry of basin bounding faults sedimentary provenance paleoflow direction isopach and sedimentary facies distribution patterns constrains basin evolution from the middle tertiary through quaternary time our results suggest that ne sw extension across normal faults controlled development of accommodation space in the northern longzhong basin during the oligocene to early miocene continued sediment accumulation from the mid miocene through pliocene occurred in a broad shallow basin consistent with thermal subsidence following extension basin inversion initiated between 10 ma and 6 ma associated with the development of the modern haiyuan fault system our results imply that the onset of tertiary sedimentation in the longzhong basin does not represent a developing foredeep associated with a nascent tibetan plateau but rather reflects transtensional deformation inboard of extensional basins along the east asian margin

marine to non marine sedimentation in the upper miocene evaporites of the eastern betics se spain sedimentological and geochemical evidence abstract several neogene basins in the eastern betics contain a record of thick upper miocene evaporites the inner basins those located distal to the mediterranean coast include evaporite units ranging from the late tortonian to the early messinian whereas the marginal basins those located in the vicinity of the mediterranean coast include evaporite units corresponding to the late messinian that are linked to the salinity crisis the sedimentological and geochemical comparison of the evaporites in the inner and marginal basins enable us to show their differences in the modes of deposition under local structural controls and differentiated palaeogeography in the inner basins of the murcia alicante region a number of evaporite units have been differentiated whose gypsum lithofacies have 1 variable strontium contents with mean values primary gypsum between 1121 and 2380 ppm 2 isotopic compositions of sulphur 34 s ranging from those characteristic of the tertiary marine water 20 3 to 25 5 to those characteristic of the triassic sulphates 8 0 to 16 0 the latter suggesting recycling of the sulphate anion in meteoric waters intermediate values 17 4 to 19 6 are attributed to mixed mother brines and 3 strontium ratios 87 sr 86 sr comprised between 0 70804 and 0 70888 these values range from those of the tertiary marine water to those exceeding the triassic sulphates suggesting additional continental contributions from country rocks and hydrothermal solutions the comparison between the sulphur and strontium isotopic compositions of the sulphates together with the study of the biota present in the marls associated with the gypsum allows us to distinguish between marine continental and mixed units in the marginal basins of the eastern betics where single evaporite units characterized by selenitic gypsum prevail 1 the strontium contents are more homogeneous with mean values primary gypsum between 493 and 625 ppm 2 the isotopic compositions of oxygen 18 o and sulphur 34 s are comprised between 12 2 and 14 8 and between 22 0 and 23 5 respectively and 3 the strontium ratios 87 sr 86 sr vary from 0 70890 to 0 70895 all these isotopic values reveal a marine origin and the lack of contribution of significant continental water during the late messinian evaporite deposition in the betic strait these characteristics are similar to those of the lower evaporite

simple model for downstream variation of median sediment size in chilean rivers a simple theory is developed to account for the observed downstream variation of the median sediment size in chilean rivers based on a reach wise equilibrium sediment transport concept the theory makes use of a bedload transport equation linked with a resistance equation to estimate the median sediment diameter as a function of channel slope with the flow reynolds number and bedload concentration as parameters both meyer peter and muller s and ackers and white s formulas are used alternatively as bedload equations a manning strickler type of formulation is used as a resistance relationship the resulting model is validated against field data corresponding to 150 rivers in central chile covering slopes in the range of 0 04 8 61 with median sediment size in the range of 0 3 250 mm despite the simplicity of the present theory and the somewhat bold assumptions made in its derivation the estimated variation of the median sediment size with channel slope follows the same trend as the field data most of the scatter of these data falls within the theoretical limits given by the estimated range of values of the parameters of the model

middle to late miocene sequence stratigraphy of the transylvanian basin romania abstract the history of middle to late miocene evolution of the transylvanian basin was determined by the bordering carpathian orogen evolution the tectonic events being well recorded by the sedimentary history the basin evolved in a back arc setting under a regional compressional stress field the major tectonic events produced during the late sarmatian and post pannonian were related to the reactivation of the pre badenian fault systems the transylvanian basin got uplifted after the late pannonian during the pliocene and at least 500 m of sedimentary cover was eroded based on seismic and well log interpretation core and outcrop sedimentology and microfauna eight sequences were defined the early middle miocene sequences are roughly synchronous to five 3rd order global sea level cycles most of the recognized sequence boundaries are enhanced by regional tectonic events the sedimentary evolution was also strongly influenced by salt tectonics active starting with the late sarmatian two sequences were identified in the lower badenian deposits the third sequence late early badenian to early mid badenian preserves information about deeper shelf settings the lowstand of the following sequence was responsible for the deposition of the salt formation late mid badenian an important lithostratigraphic marker in the sedimentary record of the basin in general the upper badenian deposits parts of the 4th and 5th sequences belong to deep marine submarine fan systems the sarmatian partially 5th 6th and partially 7th sequences was characterized by diverse salinity conditions stretching from brackish to hypersaline and by high tectonic instability which induced several significant relative sea level falls during that time deltaic north and fandeltaic east systems fed submarine fans stacked between salt related submarine heights channeled deep marine depocenters most of the pannonian deposits partially 7th and 8th sequences belong to submarine fan systems but shallower facies were also found in the western and eastern part of the basin

late quaternary paleosol sediment sequences and landscape evolution along the andean piedmont bolivian chaco abstract as part of the bolivian chaco the andean piedmont is situated in the transitional zone between the tropical humid climate regime to the north amazonia and the subtropical semiarid regime to the south gran chaco in this zone which is sensitive to climatic changes late quaternary landscape and climate history was reconstructed based on detailed sedimentological pedological and geochemical analyses of paleosol sediment sequences along the andean piedmont the determination of characteristic lithofacies allowed correlation between the investigated profiles and their interpretation in terms of paleoenvironmental conditions i e geomorphic stability soil formation or geomorphic activity fluvial or fluvio aeolian sedimentation erosion etc coarse fluvial deposits gravels sands form the base of the investigated profiles and have likely been deposited in a braided river environment with low vegetation cover and intensive discharge events before and during the last glacial maximum well developed paleosols formed in the upper part of these sediments during the lateglacial documenting geomorphic stability high vegetation cover and wet conditions overlying palustrine sediments dated to the early holocene indicate a dramatic change in seasonality i e increased winter precipitation and decreased summer precipitation subsequent erosion followed by accumulation of fluvial and fluvio aeolian sands points to much drier conditions during the mid holocene since 2 9 cal ka bp soil formation indicates a return to geomorphic stability and wetter conditions characteristic of the present day climate interrupted by short arid intervals

the beginning development and termination of the middle miocene badenian salinity crisis in central paratethys abstract middle miocene badenian evaporites of the carpathian region are underlain and overlain by deep water deposits the onset of evaporite deposition was sudden but not synchronous in all facies zones and the deposition of evaporites was controlled by the evolution of carpathian orogen in the carpathian foredeep and most probably in other basins the badenian evaporites represent the lower part of the nn6 zone halite and associated deposits in the central part of the badenian evaporite basin show the same facies successions and marker beds can be traced across and between individual basins characteristic marker beds made it possible to correlate various facies zones of the marginal ca sulfate platform these marker beds seem to reflect events that may be related to sudden and widespread changes in water chemistry which in turn imply major changes in basin hydrology the onset of the evaporitic deposition in the carpathian foredeep was clearly diachronous and the evaporites deposited in the basin centre preceded the beginning of evaporite sedimentation in the marginal basin however depositional history in the marginal basin and the basin centre was the same a general transgressive sequence of evaporites found in the carpathian foredeep resulted from the migration of facies zones induced by the nappe movement isotopic studies of badenian foraminifers occurring below evaporites suggest that the interrupted communication of the paratethys with the ocean was a consequence of eustatic sea level fall possibly related to climatic cooling and it was coupled with a tectonic closure of connection with the tethys thus both tectonics and eustacy have contributed to the origin of salinity crisis sedimentological and geochemical data indicate recycling of evaporites throughout most of the evaporite deposition the recycling at the end of gypsum deposition in the marginal sulfate platform was accompanied by a change in the hydrology of the central paratethys that was tectonically driven and possibly related to the block tectonic phase manifested in the marginal part of the carpathian foredeep basin the change in hydrology implied the dilution of brines by inflowing marine water and this terminated the middle miocene badenian salinity crisis the onset of the badenian salinity crisis shows great similarities to the onset of the messinian salinity crisis and the terminations of both crises were different

rockmagnetic and palaeomagnetic studies of unconsolidated sediments of bukovynka cave chernivtsi region ukraine rockmagnetic palaeomagnetic and paleontological studies of loamy non consolidated sediments of the bukovynka cave chernivtsi region ukraine have been carried out the sections include three main types of deposits 1 fluvial deposits containing travertine grus derived from the karst massif 2 fluvial deposits derived from temporary waterflows from outside the cave 3 aeolian deposits deposits of type 2 and 3 were examined in sections 1 and 2 in the trapeznyi chamber their low field magnetic susceptibility r eflects climatic conditions in the late pleistocene the layer with cave hyena bones has higher magnetic susceptibility and appeared to indicate warmer climate deposits of type 1 and 2 were investigated in the section 3 in the dry chamber of the cave low field magnetic susceptibility of fluvial deposits derived from inside of the karst massif is much higher than for deposits derived from outside the cave deposits in section 3 sharply differ in nrm intensity and keonigsberger ratio the fluvial strata of type 1 in section 3 dated using paleontological remains as holocene contains the record of palaeosecular variations of the geomagnetic field the etrussia excursion dated 2 8 ka bp was found at 1 m depth in section 3 the lowest layer has anomalous polarity

late pleistocene temperature depression and vegetation change in ecuadorian amazonia abstract paleoecological pollen phytolith and wood analyses of sediments radiocarbon dated 33 000 to 26 000 yr b p from two sites in ecuadorian amazonia provide data that suggest a cooling of ca 7 5 c below present in equatorial lowlands from 33 000 to 30 000 yr b p a period of warning followed in which novel species assemblages a blend of montane and lowland floral components persisted for at least 4000 years these data of forest community change from sites lying within the postulated glacial rain forest napo refugium provide the strongest paleoecological refutation of the refugial hypothesis yet obtained the large temperature depression at ca 30 000 yr b p allows the possibility that if maximum cooling at the equator was synchronous with the last glacial maximum lgm of the northern hemisphere freezing temperatures would have been experienced in parts of lowland amazonia between 25 000 and 18 000 b p

comparing modern and pleistocene enso like influences in nw argentina using nonlinear time series analysis methods higher variability in rainfall and river discharge could be of major importance in landslide generation in the northwestern argentine andes annual layered varved deposits of a landslide dammed lake in the santa maria basin 26 s 66 w with an age of 30 000 14c years provide an archive of precipitation variability during this time the comparison of these data with present day rainfall observations tests the hypothesis that increased rainfall variability played a major role in landslide generation a potential cause of such variability is the el nino southern oscillation enso the causal link between enso and local rainfall is quantified by using a new method of nonlinear data analysis the quantitative analysis of cross recurrence plots crp this method seeks similarities in the dynamics of two different processes such as an ocean atmosphere oscillation and local rainfall our analysis reveals significant similarities in the statistics of both modern and palaeo precipitation data the similarities in the data suggest that an enso like influence on local rainfall was present at around 30 000 14c years ago increased rainfall which was inferred from a lake balance modeling in a previous study together with enso like cyclicities could help to explain the clustering of landslides at around 30 000 14c years ago

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

cyclonic brine flow pattern recorded by oriented gypsum crystals in the badenian evaporite basin of the northern carpathian foredeep abstract in the middle miocene badenian within sulfate evaporites formed in the northern carpathian foredeep basin of poland ukraine and the czech republic the apices of the primary bottom grown gypsum crystals selenites are similarly aligned over broad areas and have a common azimuth this crystal orientation is interpreted as the product of a consistent direction of a brine inflow during gypsum crystallization and such a unique commonality is used as a tool for paleocurrent analysis in order to recognize both the local and the regional brine paleocurrents in the basin earlier sedimentologic and stratigraphic studies proved that these beds of oriented selenites were deposited at the same or nearly the same time in a brine not more than a few meters deep it is interpreted that the oriented selenites recorded only the mean flow within the basin mainly from the periods of mixing in the dry season lowstands when the whole brine column down to the bottom was ca sulfate oversaturated the measured paleocurrent vectors showed that the brines flowed along the marginal zone of the carpathian foredeep basin predominantly in a counterclockwise direction this longshore flow is interpreted as a typical cyclonic circulation analogous to those present in recent lakes and semi closed basins in the northern hemisphere where counterclockwise mean water drift is directly or indirectly forced by earth rotation the coriolis effect the detected brine flow directions do not reflect downslope gravity flow of dense brines into the central basinal depths or subbasins that were filling with the halite facies

gypsum facies transitions in basin marginal evaporites middle miocene badenian of west ukraine in the middle miocene badenian gypsum basin of the carpathian foredeep west ukraine three main zones of gypsum development occur in the peripheral parts of the basin zone i consists entirely of stromatolitic gypsum formed in a nearshore zone zone ii is located more basinward and is characterized by stromatolitic gypsum in the lower part of the section overlain by a sabre gypsum unit zone iii occurs in still more basinward areas and is characterized by giant gypsum intergrowths or secondary nodular gypsum pseudomorphs of these in the lowermost part overlain by stromatolitic gypsum sabre gypsum and then by clastic gypsum units correlation between these facies and zones has been achieved using lithological marker beds and surfaces of particular importance for correlation is a characteristic marker bed usually 20 40 cm thick of cryptocrystalline massive gypsum occurring in zones ii and iii the marker was not distinguished in zone i possibly because this bed is older than the entire gypsum section of that zone these new results strongly suggest that the deposition of giant gypsum intergrowth facies and stromatolitic gypsum facies was coeval in some sections of zones i and ii limestone intercalations have been recorded within the upper part of the gypsum sections considerable scatter of the 18o and 13c values of these limestones indicates variable diagenetic overprints of marine carbonates but a marine provenance of the limestones is confirmed by microfacies analysis some of the limestones are coeval with an intercalation of gypsarenitic mostly laminated gypsum occurring in the sabre gypsum unit of zones ii and iii badenian gypsum formed in extremely shallow water to subaerial environments on broad very low relief areas of negligible brine depth which could be affected by rapid transgressions stable isotope 34s 18o studies of the gypsum demonstrate that the sulphate was of sea water origin or was derived from dissolution of miocene marine evaporites investigations of individual inclusions in the gypsum indicate decreased water salinity when compared with modern marine derived calcium sulphate saturated water groundwater influences are indicated by high calcium sulphate contents of the brines in the evaporite basin the chemical composition of badenian waters was thus a mixture of relic sea water depleted in nacl groundwater enriched in calcium sulphate and surface run off

late quaternary vegetation and climate change in the panama basin palynological evidence from marine cores odp 677b and tr 163 38 abstract the late quaternary paleoenvironmental history from pacific slopes of the western andes is reconstructed by pollen analysis of 32 samples from two marine sediment cores from the panama basin eastern equatorial pacific core odp 677b 83 44 2200 w 1 12 1440 n 3473 m water depth is 185 cm long and spans the last 39 410 years core tr 163 38 81 583 w 1 337 n 2200 m water depth is 103 cm long and covers the last 17 380 years six ecological groups were established mangrove brackish and fresh water swamps terra firma lowland forests broad range taxa andean forests and open vegetation a good correspondence was found between the changes of these ecological groups in the two cores the records evidence the continuous presence of all vegetation types during the last 39 410 years and specially the uninterrupted occurrence of tropical rain forest they record a development from 1 a cold and humid phase 39 410 28 120 yr cal bp with moderately high sea levels 2 the coldest and driest phase in the record 28 120 14 500 yr cal bp accompanied by the lowest sea levels 3 a transitional phase when sea level rose and humid conditions dominated 4 a stage 11 300 5600 yr cal bp of the highest sea levels and moisture conditions including a drier period 7000 yr bp to 5 a final period 5600 yr cal bp present when sea level reached its present height humidity persisted and indicators of disturbance expanded peaks in pollen and spore concentration associated with high river discharge periods indicate periods of higher precipitation around 33 500 28 000 and 12 000 9000 yr cal bp although main vegetation responses seem to reflect rainfall and moisture variations a good correspondence was found between 18o values and percentages of andean and lowland pollen suggesting that vegetation also responded to tempearture changes

the complex transgression and regression history of the northern margin of the palaeogene tarim sea nw china and implications for potential hydrocarbon occurrences abstract the tarim basin is an epicontinental marine basin that developed during the palaeogene in the eastern margin of the paratethys ocean palaeoclimate models suggest that sea level fluctuations were the main driving force causing the palaeogene aridification of asia s interior and the increase in monsoon intensity the palaeogene succession in the northern margin of the south western tarim basin is composed of five lithofacies associations in which two third order sequences and three third order sequence boundaries are present that correspond a complex history of trans and regressions sequence 1 formed in an epicontinental sea during the palaeocene and early eocene whereas sequence 2 represents a transitional stage from marine to terrestrial conditions during the late eocene and oligocene part of this development was synchronous with the development along the southern margin of the south western tarim basin but the transition from marine to continental along the northern margin of the south western tarim basin did not take place until the late eocene when the sea retreated westwards the present contribution can help reconstruct the palaeogene palaeogeography of the paratethys regions and may also facilitate paleoclimate modelling for central asia it also suggests that there is a good hydrocarbon potential in the western and southern parts of the south western tarim basin

depositional environments and facies of the late triassic abu ruweis formation jordan abstract the abu ruweis formation is composed of carbonates evaporites and mudstones with some locally developed pelletic oolitic and stromatolitic limestones the lateral persistence of bedding the purity of the evaporite rocks the alternating arrangement of marine carbonates and evaporites indicates periodic deposition in subaqueous conditions salina petrographic investigations x ray diffraction analysis as well as chemical analysis have shown that the outcropping evaporite beds are mainly composed of secondary gypsum with rare anhydrite relics five microfacies of gypsum were recognized according to their fabrics porphyroblastic and granoblastic gypsum showing polarization texture gypsum pseudomorph after anhydrite laths and satin spar gypsum the textures they display indicate a hydration origin of precursor anhydrite which is in turn rehydrated from primary gypsum some of these anhydrites were formed as a result of replacement processes of the carbonate sediments associated with the evaporites as evidenced from the textural relationships of the carbonate and sulfate minerals the o18 content ranges from 1 45 to 8 38 pdb and the c13 content ranges from 1 52 to 4 73 pdb trace elements analysis has shown that the abu ruweis dolomites are rich in strontium up to 600 ppm and sodium up to 835 ppm the isotope composition and trace elements content as well as the petrographic characteristics point to a penecontemporaneous hypersaline dolomitization origin for the abu ruweis dolomites the evaporites were deposited during a regressive lowstand systems tract whereas the carbonates were deposited under shallow water marine conditions during a highstand systems tract the abu ruweis succession represents a relatively stable arid climate within a rapidly subsiding basin restricted conditions were provided by the development of beach barriers

late quaternary vegetation and coastal environmental changes at ilha do cardoso mangrove southeastern brazil abstract a 190 cm mangrove sediment core from the ilha do cardoso state park state of sao paulo southeastern brazil was analyzed for pollen diatoms as well as carbon and nitrogen isotopes the goal was to determine the dynamics of the coastal terrestrial aquatic ecosystems vegetation history and climate change in this region of the brazilian atlantic rainforest during the late pleistocene and holocene the values for total organic carbon toc from 3 up to 40 c n ratios from 10 up to 130 and 15n 0 to 8 are associated with well preserved aquatic and terrestrial organic matter and possibly influenced by nitrogen cycling e g denitrification that caused 15n enrichment between 40 000 cal yr b p and 23 000 cal yr b p depleted 13c values 28 0 are also observed and indicate the predominance of c3 plants during this time interval the pollen analysis reveals the presence of the genera ilex alchornea weinmannia myrsine symplocos drimys and podocarpus on a site currently occupied by mangrove vegetation these data suggest that in the past prevailed a colder and more humid climate than today with a low relative sea level from 23 000 cal yr b p to 2200 cal yr b p a sedimentary hiatus likely occurred related to an erosive event associated to the post glacial sea level rise since at least 2200 cal yr b p sediments are marked by relatively low c n ratios from 2 to 27 exhibit more enriched 13c from 26 0 to 24 0 and 15n up to 7 values and are characterized by the presence of marine diatoms this indicates the return of the marine coastal line to its current position and consequently the development of mangrove

simulation of the holocene climate over south america and impacts on the vegetation we provide a comprehensive analysis of the holocene climate and vegetation changes over south america through numerical simulations holocene climate for several periods 8 ka 6 ka 4 ka 2 ka an

late glacial and holocene sedimentation and fluctuations of river water level in the caqueta river area colombian amazonia the sequence of late glacial and holocene alluvial sedimentation in the middle caqueta river basin of colombian amazonia is described based on the study of the sediments and palynology of several river bank sections and on 30 radiocarbon dates an early late glacial sedimentation cycle is recognised followed by a minor late late glacial erosion phase the holocene valley fill consists of grey clays often present in the lower part of the sections deposited in open water and silty clays often with faint yellow mottling deposited under a regime of seasonal flooding the base of the holocene sections is formed by sands where exposed in two places the transition of sand to open water grey clay was dated around 10 000 yr bp and there is a suggestion that open water may have been more common at the beginning of the holocene than later when sedimentation by seasonal flooding became important in many places much of the earlier holocene sediments may have been removed by erosion and replaced by younger sediments by a process of lateral aggradation a considerable part of the present valley fill is younger than ca 3500 yr however in several places older holocene sediments are found apparently only little affected by later erosion lying below younger varzea silty clays during the holocene more organic sediments were formed in periods with reduced river discharge related to drier climates in the andes and possibly in amazonia these dry periods deduced from data in the caqueta river area correspond well with dry phases in other parts of northwestern south america e g between approximately 2700 1900 yr bp and approximately 3200 3800 yr bp rates of average net sedimentation calculated from dated sections that apparently lack major hiatuses caused by erosion were high in the lower holocene low during the middle holocene and increase again in the upper holocene levee deposits became coarser and the high river level of the caqueta increased during the late holocene these phenomena may be explained by the increasing influence of man on the vegetation cover in the andean headwater areas and possibly also in the amazonian catchment area of the caqueta river