oceanic anoxic cycles orbital prelude to the bonarelli level oae 2 abstract the prelude to the second global oceanic anoxic event of the cretaceous oae 2 as recorded in the classic sections of the scaglia bianca formation in the umbria marches region of italy is characterized by an oscillation between black to gray organic rich cherts and white pelagic limestones spectral analysis of these lithologic alternations reveals a robust set of cycles whose periods are remarkably similar to the orbital cycles calculated by laskar et al laskar j robutel p joutel f gastineau m correia a c m levrard b 2004 a long term numerical solution for the insolation quantities of the earth astronomy and astrophysics 428 261 285 bandpass filtering shows that the 140 80 kyr signal approximates the envelope of the 26 16 kyr signal just as expected if these components represent responses to orbital eccentricity and precession matching the presumed eccentricity signal to the theoretical eccentricity of laskar et al yields an age for the base of the bonarelli level onset of oae 2 in italy of 94 21 ma 93 72 ma provides an alternative consistent with radiometric constraints from a correlative section in the western united states given the strong orbital control on the cyclic deposition of the organic rich precursors of oae 2 within the scaglia bianca formation we hypothesize that the timing of oae 2 itself is similarly controlled by astronomical variations indeed the occurrence of oae 2 coincides with a protracted period of unusually low insolation variation owing to simultaneous nodes in all orbital parameters we speculate that other oaes similarly coincided with insolation nodes and dampened seasonality from this perspective some but perhaps not all of the oaes may be periodic events reflecting cycles of oceanic anoxia that predictably punctuated a 50 myr period of cretaceous climate

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

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

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

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

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

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

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

astronomical tuning of the aptian stage from italian reference sections a high resolution grayscale series of the pelagic fucoid marls piobbico core central italy shows strong pervasive lithological rhythms throughout the aptian interval a hierarchy of centimeter to meter scale cycles characterizes the rhythms when calibrating 1 m cycles to earth s 405 k y orbital eccentricity cycle these rhythms correspond to the periods of the eccentricity obliquity and precession index tuning to orbital eccentricity cycles provides a high resolution time scale for the aptian correlation to the cismon core northern italy extends the tuning to the aptian barremian boundary the tuning indicates a minimum duration of 13 42 m y for the aptian stage where previous estimates range from 6 4 to 13 8 m y the combined aptian albian astronomical tuning of the entire 77 m long piobbico core and part of the cismon core provides a 25 85 m y long astronomically calibrated time scale for earth history

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

a record of glacial interglacial alternations in pleistocene sediments off new jersey expressed by clay mineral grain size and magnetic susceptibility data abstract clay mineral grain size and magnetic susceptibility measurements have been performed on a high resolution sampling of pleistocene clayey silts and silty clays drilled at odp site 902 hole d located on the upper slope off new jersey nw atlantic the combination of data from different techniques and their comparison with 18 o and gamma ray attenuation porosity evaluator grape data allow us to clearly distinguish between sediments deposited during glacial and interglacial cycles glacial sediments are poorly sorted rich in either clay or sand and characterized by the abundance of chlorite and high magnetic susceptibility values in contrast interglacial sediments are well sorted silt dominated and poor in chlorite the hudson river and its tributaries draining the appalachian highlands appear to constitute the perennial sources of the detrital input including quartz feldspars amphibole and a clay fraction dominantly composed of illite random mixed layers and kaolinite during glacial stages the terrigenous sedimentation was enhanced by additional input of chlorite from glacial erosion in northeastern america the variations in chlorite amounts supplied to the ocean were probably controlled by the ice sheet advances and retreats these variations are quantified by the kaolinite chlorite ratio k c which constitutes a reliable marker of glacial and interglacial influences on the terrigenous sedimentation

astronomical calibration of the maastrichtian late cretaceous abstract recent improvements to astronomical modeling of the solar system have contributed to important refinements of the cenozoic time scale through astronomical calibration of sedimentary series we extend this astronomical calibration into the cretaceous on the base of the 405 ka orbital eccentricity variation thanks to the recovery of well preserved maastrichtian sedimentary series from odp ocean drilling program holes 1258a leg 207 equatorial atlantic 1267b leg 208 south atlantic 762c leg 122 indian ocean and dsdp deep sea drilling program hole 525a leg 74 south atlantic cyclostratigraphic analysis is performed on high resolution measurements of magnetic susceptibility on sediments cored during legs 207 and 208 and gray level variations of sediment color obtained from core photographs from legs 122 and 74 astronomical control on sedimentation is evident at every site with the presence of cycles corresponding to forcing by precession obliquity and orbital eccentricity variations identification of these cycles leads to the definition of a detailed cyclostratigraphic frame covering nearly 8 ma from the upper campanian to the cretaceous paleogene k pg boundary durations of each magnetochron from c32r 2r to c29n are inferred by cycle counting astronomical calibrations of maastrichtian sedimentary series are proposed based on the 405 ka eccentricity variation according to the most recent astronomical solution la2010a two different ages are suggested for the k pg boundary considering the uncertainty of the long term variation of the 405 ka eccentricity cycle the first proposal provides a cretaceous paleogene boundary age of 65 59 0 07 ma and the second an age of 66 0 07 ma which is coherent with the most recent radio isotopic datings magnetochron boundaries and the campanian maastrichtian boundary are dated relative to these numerical ages of the k pg boundary

palaeoclimatic interpretation of clay minerals in marine deposits an outlook from the continental origin abstract as distribution of clay minerals in modern oceans seems to be controlled by contemporary climates marine clays in ancient deposits have been widely used to reconstruct palaeoclimates in this review we examine this question mainly from the continental origin of the clay minerals and show the difficulties of retrospective analysis of the influence of climate on common marine deposits we examine successively how soils develop and behave are reworked and palaeoweatherings are preserved focusing the review on kaolinitic soils indicative of tropical wet climates several stages intervene between the time of clay mineral development in soils and their final deposition in the basin 1 the persistence over geological times of huge amounts of kaolinitic palaeoweathering materials in the landscapes may seriously alter the palaeoclimatic signal of kaolinite in the sedimentary record although the kaolinite deposited in recent sediments of the world oceans is consistent with wet climatic zones this is mainly because the major kaolinitic and bauxitic palaeosurfaces coincide with the tropical areas where kaolinite is still developing at present 2 possible development of deep kaolinitic profiles at high latitudes and cold conditions under co 2 enriched palaeoatmospheres or even by unusual acidic weathering linked with dry climates is misleading palaeoenvironments for palaeoclimatic reconstruction 3 erosion and transport processes always cloud the signal to some extent because frequently erosion products from the bedrock and different soil horizons will be mixed and major drainage systems may include soils of different climatic zones 4 the arrival of the soil clay assemblages in the basin inevitably lags against their formation on the continent and may occur several million years after formation of the soils on the continent and climate may have considerably changed at that time it is pointed out that sedimentologists and palaeoclimatologists should consider the complexity of the relations between soil and sedimentary clay minerals soil formation rates are slow and therefore the resolution of the palaeoclimatic record in marine clay may not be closer than 1 or 2 ma at present the palaeoclimatic interpretations of marine clay assemblages are yielding at best nothing more than rather broad palaeoclimatic information this approach cannot achieve the same degree of resolution as other techniques such as isotope or microfossil studies clay mineral assemblages may provide integrated records of overall climatic impacts whereas other techniques are more likely to reveal local or temporary climates

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

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

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

high resolution cyclostratigraphic analysis from magnetic susceptibility in a lower kimmeridgian upper jurassic marl limestone succession la meouge vocontian basin france abstract high resolution magnetic susceptibility ms analysis was carried out on a lower kimmeridgian alternating marl limestone succession of pelagic origin that crops out at la meouge vocontian basin southeastern france the aim of the study was to characterize the strong dm scale sedimentary cyclicity of the succession at a very high resolution and to analyze the cycles for evidence of astronomical forcing from marl to limestone ms varies progressively and closely tracks the highest frequency cyclicity corresponding to the basic marl limestone couplets long term wavelength cycling modulates the high frequency cyclicity couplets and appears to be controlled by clay content spectral analysis of the ms record reveals the presence of the complete suite of orbital frequencies in the precession obliquity and eccentricity 95 128 ka and 405 ka bands with very high amplitude of the precession index cycles originating from dm scale couplets 405 ka eccentricity cycles are very pronounced in the ms maxima of the marl members of the couplets suggesting eccentricity driven detrital input to the basin 405 ka orbital tuning of the ms maxima further sharpens all of the orbital frequencies present in the succession these results are similar to those of previous studies at la meouge that used carbonate content observed in field our results are also in accordance with cyclostratigraphic studies in spain and canada that report dominant precession index forcing by contrast in the kimmeridge clay dorset uk obliquity forcing dominates cyclic sedimentation with weaker influence from the precession index ammonite zone duration estimates are made by counting the interpreted precession cycles and provide an ultra high resolution assessment of geologic time in sum this study demonstrates the power of the ms as a proxy in characterizing the high resolution cyclostratigraphy of mesozoic sections particularly in alternating marl limestone successions and for high resolution correlation and astronomical calibration of the geologic time scale

the late hauterivian faraoni oceanic anoxic event in the western tethys evidence from phosphorus burial rates in the uppermost hauterivian sediments of the western tethys a short lived anoxic event faraoni event is documented both in the form of an interval enriched in organic matter pelagic realm and in a condensed interval enriched in glauconite and phosphate shelf realm this latter interval represents the onset of a drowning episode on the helvetic carbonate platform along the northern tethyan margin that lasted throughout the early barremian this drowning episode marks a turning point in the way the platform carbonate factory functioned during the hauterivian carbonate production was dominated by heterozoans whereas during the late barremian a photozoan assemblage developed that is preserved in the so called urgonian limestone the late hauterivian faraoni oceanic anoxic event is of particular interest because it is not accompanied by a major positive shift in y 13 c unlike other oceanic anoxic events during the cretaceous valanginian early aptian cenomanian turonian boundary we have analyzed four hemi pelagic sections with regards to their phosphorus content to better understand the palaeoceanographic conditions related to this anoxic event and the associated changes in the shallow water carbonate factory the sections are

palaeoclimatic cyclicity in central mediterranean pliocene sediments the mineralogical signal abstract a high resolution x ray mineralogical study of four pliocene sediment sections from the central mediterranean punta piccola sicily monte singa and vrica calabria odp hole 964 a ionian sea shows cyclic opposite abundance variations of two groups of clay minerals the first is dominated by palygorskite and kaolinite whose abundance maxima can be interpreted as resulting from periods of aridity on the african continent allowing their transport as wind blown dust the second is dominated by smectite whose abundance maxima can be interpreted as indicative of periods of abundant rainfall on the mediterranean borderlands these variations in abundance show a 22 ky cyclicity implying a control by the precession of the earth s orbit sapropels and sapropelic layers always occur in the smectite rich beds and therefore appear to have been deposited during the wet periods

mesozoic thermal history of the prebetic continental margin southern spain constraints from apatite fission track analysis apatite fission track analysis was applied to triassic and cretaceous sediments from the south iberian continental margin to unravel its thermal history apatite fission track age populations from triassic samples indicate partial annealing and point to a maximum temperature of around 100 110 c during their post depositional evolution in certain apatites from cretaceous samples two different fission track age populations of 93 99 and around 180 ma can be distinguished track lengths associated with these two populations enabled thermal modelling based on experimental annealing and mathematical algorithms these thermal models indicate that the post depositional thermal evolution attained temperatures 70 c which is consistent with available vitrinitereflectance data thermal modelling for the cretaceous samples makes it possible to decipher a succession of cooling and heating periods consisting of a a late carboniferous permian cooling followed by b a progressive heating episode that ended approximately 120 ma at a maximum tof around 110 c the first cooling episode resulted from a combination of factors such as the relaxation of the thermal anomaly related to the termination of the hercynian cycle the progressive exhumation of the hercynian basement and the thermal subsidence related to the rifting of the bay of biscay reactivated during the late permian jurassic thermal evolution deduced from the inherited thermal signal in the cretaceous sediments is characterized by progressive heating that ended around 120 ma this heating episode is related to thermal subsidence during jurassic rifting in agreement with the presence of abundant mantle derived tholeiitic magmas interbedded in the jurassic rocks the end of the jurassic rifting is well marked by a cooling episode apparently starting during neocomiam times and ending at surface conditions by albian times

a review of mesozoic climates there is overwhelming evidence based on the distribution of distinctive sediments and fossils and oxygen isotope data that the climate of the mesozoic world was appreciably more equable than that of today with no polar ice caps but precise quantitative data are not available except for an episode of late cretaceous cooling there is no good documentation of any significant change in global temperature distributions through the era the distribution of coals and evaporites together with other criteria indicates a pattern of humid arid and zones appreciably different in important respects from that of today during the triassic and jurassic western pangaea in low to middle latitudes was largely arid but in the early cretaceous the lands on the margin of the newly opening central atlantic and western tethys experienced a humid climate by late cretaceous times arid zones had become very restricted in extent because of insufficient suitable data attempts at climatic modelling have had only modest success and only to a limited extent can the major long term changes in climate between the permian and the present be explained in terms of changing geography the most probable explanation of mesozoic equability is an increased atmospheric co 2 content a number of enigmas remain such as the existence of flourishing forests in polar palaeolatitudes whereas for the late cenozoic short term climatic changes can be related successfully to variations in the geometry and mechanics of the earth sun system there is a long way to go before comparable success can be claimed for the mesozoic

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

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

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

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

a quantitative study of lower cretaceous cyclic sequences from the atlantic ocean and the vocontian basin se france milankovitch type periodicity was identified within lower cretaceous cyclic sequences from the western central atlantic ocean and the vocontian basin southeast france through application of the walsh spectral method to detailed stratigraphic sections the repetitious bedding in these sequences appears to be the product of cyclic climatic changes controlled by the orbital forcing obliquity seems to be the most important and persistent orbital element responsible for cyclic sedimentation whereas precession is less important upper berriasian and valanginian strata from the atlantic ocean contain indications of eccentricity induced periodicity and of a nonlinear response of the climatic system variations in orbitally tuned pelagic sedimentation rates in the atlantic ocean correlate with the changes in the character of cycles and with the occurrence of calcareous turbidites therefore this suite of sedimentary features are responding to evolving paleoceanographic conditions and possible relative sea level fluctuations the orbitally tuned durations of the valanginian and hauterivian stages in the vocontian basin are a minimum of 5 9 and 5 3 m y respectively

evaluation of the astronomical time scale for the paleocene and earliest eocene abstract the astronomical tuned time scale is rapidly extended into the paleogene but due to the existence of an eocene gap different tuning options had to be presented for the paleocene these options differ both in number and tuning of 405 kyr eccentricity related cycles and are only partially consistent with recalculated 40 ar 39 ar constraints for the cretaceous paleogene k pg and paleocene eocene p e boundaries in this paper we evaluate the cyclostratigraphic interpretation of records from odp leg 198 and 208 sites and the zumaia section to solve the problem of the different tuning options we found that the interval between the k pg boundary and the early late paleocene biotic event elpe comprises 17 instead of 16 405 kyr eccentricity related cycles as previously proposed while the entire paleocene contains 25 405 kyr cycles starting from 40 ar 39 ar age constraints for the k pg boundary a new tuning to 405 kyr eccentricity is presented for the paleocene and earliest eocene which results in ages of 66 0 and 56 0 ma for the k pg and p e boundaries respectively this tuning introduces considerable differences in age for a number of nannofossil events at odp sites 1209 and 1262 in the interval between 61 and 63 ma but eliminates large and abrupt changes in the seafloor spreading rate the tuning seems further consistent with recalculated 40 ar 39 ar ages for ash layer 17 of early eocene age however despite this apparent consistency with existing radio isotopic constraints an alternative 405 kyr younger or less likely older tuning cannot be excluded at this stage

an assessment of the suitability of individual rhythmic carbonate successions for astrochronological application abstract a manual is presented to assist in assessing the suitability of individual calcareous rhythmites for high resolution stratigraphic applications and orbital dating while the astrochronological approach offers an unprecedented high temporal resolution for stratigraphy caution is required to carefully choose suitable rhythmites for the analysis diagenesis is known to distort or mimic primary signals in particular in carbonate rhythmites to keep orbital dating a reliable method the choice of sedimentary successions has to be undertaken with utmost scrutiny here we review and evaluate the methods that have been used for assessing the record of primary signals in calcareous rhythmites the goal is to provide the orbital stratigrapher with tools for a straightforward and systematic assessment of such successions

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

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

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

the evidence and implications of polar ice during the mesozoic abstract the mesozoic perhaps representing the longest period of warmth during phanerozoic earth history contains in general sparse and frequently equivocal evidence for polar ice although this time is undoubtedly punctuated by oscillations in climate whether sufficient to lead to polar cooling and the formation of polar ice an inviting mechanism to account for faunal and floral distribution patterns and large scale sea level change has been widely debated mesozoic evidence for glacial conditions includes abraded rock surfaces generally unsorted stone rich beds and the presence of dropstones rafted by ice within a finer grained host sediment faunal and floral evidence has also been utilised to determine the presence or absence of cold or sub freezing polar conditions together with more indirect evidence for glacial conditions derived from general circulation model gcm simulations of climate the analysis of clay mineral distributions glendonite abundance and palaeontological and sedimentological evidence for globally synchronous sea level change the extent of possible glacial environments during the mesozoic has been established by plotting published reports of glacial sediments on palaeogeographic reconstructions the general clustering of evidence at high palaeolatitudes suggests that the extent of polar ice during the mesozoic is likely to have been approximately one third the size of the present day based on such evidence a number of episodes of cold or sub freezing polar climates during the bajocian bathonian tithonian volgian valanginian and aptian are recognised evidence exists possibly also for a cold episode during the early jurassic pliensbachian although poorly constrained owing to limited biostratigraphical control the longevity of these events may be represented by a cold snap within a stage although undoubtedly the possible smearing of ages may have had the effect of lengthening and hence promoting the importance of these proposed events the climate regime of the earth during these times may be hypothesised to be characterised by a relatively steep pole to equator temperature gradient where low latitude regions are as warm or warmer than today the evidence to support such reasoning includes sharp increases in the areal distribution of both glendonites and deposits with affinities to glacial tillites and dropstones for these times coincidental falls of sea level arid events and an increased bipolarity of faunas at these times imparts further confidence that these events were of a magnitude to effect the earth as a whole

comparative evolution of material flux through two dsdp successions from central atlantic and gulf of mexico preliminary results of a new approach to sedimentary dynamics in pelagic environments abstract a method for gaining knowledge of sedimentary fluxes is applied to early cretaceous sequences containing high frequency sedimentary cycles the cycles are used to determine the relative fluctuations of 1 the sedimentation rate and 2 carbonate and silicate terrigenous fluxes expressed as linear values proportional to the real fluxes visual and automatic image analysis of black and white core photographs have been used to calculate the masses of different materials deposited in equal time intervals and to determine the distribution of the material within lithological units of cores according to a scale of grey intensities characters of these distributions allow definition of a flux variability index assumed to be negatively correlated to ocean continent distance related itself to sea level at dsdp sites 534 western atlantic off florida and 535 gulf of mexico the valanginian hauterivian interval has been chosen for determining the relative variations of carbonate and silicate terrigenous linear fluxes their variability and their distribution within lithological cycles these data provide information about the relative importance of carbonate sources lands platforms and plankton and their evolution and of other forcings upon planktonic productivity such as supply of nutrients from the continents and upwelling by comparing the data in the two sites it is possible to detect common climate and eustasy and local factors tectonics and upwelling which have controlled the material fluxes compared with site 534 site 535 was supplied by more numerous active and close carbonate sources and less active but closer terrigenous sources at the two sites carbonate flux was controlled by common factors sea level being the most prominent one terrigenous flux was submitted to more local controls this new method for investigating pelagic deposits should be tested on other deep sea sedimentary sequences

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

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

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

hafnium isotope stratigraphy of ferromanganese crusts a cenozoic record of hafnium isotopic compositions of central pacific deep water has been obtained from two ferromanganese crusts the crusts are separated by more than 3000 kilometers but display similar secular variations significant fluctuations in hafnium isotopic composition occurred in the eocene and oligocene possibly related to direct advection from the indian and atlantic oceans hafnium isotopic compositions have remained approximately uniform for the past 20 million years probably reflecting increased isolation of the central pacific the mechanisms responsible for the increase in87sr 86sr in seawater through the cenozoic apparently had no effect on central pacific deep water hafnium

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

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

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

orbitally forced climate and sea level changes in the paleoceanic tethyan domain marl limestone alternations lower kimmeridgian se france abstract high resolution analysis of multiple climatic proxies was carried out on a 8 5 m lower kimmeridgian interval of a pelagic marl limestone succession at ch teauneuf d oze vocontian basin southeastern france the aim of the study was to characterize the orbitally controlled sedimentary cyclicity and to decipher paleoclimatic and paleoceanographic changes all analysed proxies magnetic susceptibility carbonate content manganese content and bulk carbon and oxygen stable isotopes 13c and 18o respond in synchrony to orbitally forced climate change precession index cycles modulated by short 100 kyr eccentricity cycles are strongly expressed in magnetic susceptibility carbonate and mn contents but less so in 18o obliquity cycles are expressed in manganese and particularly in 13c the orbital forcing was conferred to these rhythmic pelagic sediments via paleoclimatic and paleoceanographic changes as follows detrital input and marine carbonate production are recorded by the magnetic susceptibility and carbonate signals with strong precession cyclicity calcareous nannofossil analysis shows the omnipresence of coccoliths and debris of coccoliths in the marls and limestones suggesting that the carbonate production was in largest part in situ precession index may exert oscillations in the antagonist marine surface productivity and detrital flux processes via solar radiation change oxygenation of the seafloor leading to redox cycles is detected in the manganese signal and supported by the 13c record with a strong expression of the obliquity finally paleotemperature variations were deduced from the 18o record although this latter has been in part perturbed by diagenesis in sum the variations in the studied proxies suggest a depositional model of combined climate and sea level cycles forced in concert by earth s orbital parameters in particular the limestones represent warmer climates and higher sea levels and the marls colder climates and lower sea levels this depositional model concurs with a previous depositional model of deep water carbonates of the german kimmeridgian while is in opposition to a previous one of the same section in the vocontian basin

milankovitch scale palaeoclimate changes in pale dark bedding rhythms from the early cretaceous hauterivian and barremian of eastern england and northern germany abstract early cretaceous valanginian albian successions in northwestern europe occupy an ideal palaeoceanographic location in which to study the interplay between the arctic boreal and tethyan seaways or realms marine early cretaceous sediments of the north sea borderlands north germany eastern england are dominated by fine grained siliciclastic deposition with carbonates occasionally this succession is characterised by visually striking bedding rhythms comprising calcareous and less calcareous clays or pale dark alternations on a scale of 0 5 1 m such rhythmic sedimentation becomes most dominant in the early to late hauterivian parts of the early barremian and in the aptian this study concentrates on late hauterivian sections in england and germany which have remained relatively unaffected by deep burial tectonism or diagenesis changes in geochemistry are related to floral and faunal alternations and thus directly to palaeoenvironment the wide range of palaeontological and geochemical analyses show conclusively how bedding rhythms developed in the milankovitch band are the result of palaeoclimate change pale layers were tethyan influenced in their microflora and fauna indicating warm surface waters that were poor in nutrients and developed during warm seasonally arid hinterland climates dark layers were boreal influenced displaying features consistent with cooler waters rich in nutrients such dark layers reflect cooler more humid hinterland conditions the coincidence of tethyan taxa with bundles of pale layers displaying high gamma ray emission and elevated radioactive element contents suggests transgressive or condensed beds the bundling of pale dark rhythms coincides with the long term milankovitch eccentricity cycle this paper documents direct links between the reaction of hinterland weathering marine floras and floras to milankovitch scale changes in bed lithology and thickness

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

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

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

orbital tuning of a lower cretaceous composite record maiolica formation central italy 1 a high resolution pelagic bulk carbonate stable isotope record from a central tethyan lower cretaceous composite section is presented three well exposed sedimentary sequences chiaserna monte acuto bosso and gorgo a cerbara sections central italy cropping out throughout the maiolica formation were correlated by a detailed magnetostratigraphy lithostratigraphy and calcareous plankton biostratigraphy in order to reconstruct a continuous composite record from the middle berriasian to the lower aptian the integrated stratigraphy of the three sequences provided an accurate time framework for the new high resolution c isotope curve which is presented in this study the composite 13c signal recorded in the depth domain was analyzed by combined lomb scargle periodogram and weighted wavelet z transform wwz weighted wavelet amplitudes wwa foster wavelet spectral methodologies both appropriate for unevenly sampled curves these tools allowed us to unravel the main frequencies modulating the record and their hypothetical shift in depth respectively the long term 400 000 and 2 400 000 years eccentricity cycles were consistently recorded throughout all the composite record once band pass filtered in these two periodicity bands and compared to the lithologic pattern cycles identified throughout the composite sequence the 13c signal was used as a valuable proxy record for a reliable construction of an orbital tuning of the early cretaceous an estimated age for all the different stratigraphic events recognized throughout the composite record was reported in particular the reestimated ages of the paleomagnetic chrons documented in the upper part of the record show differences with those reported by gradstein et al 2004 up to 2 m y the valanginian carbon shift present in the middle part of the composite sequence was estimated to be 2 3 m y long the good agreement between the estimated age of the base of this positive carbon isotope excursion 136 34 m y and the predominant volcanic phase associated to the parana etendeka large igneous province intrusion confirmed a possible cause effect link between the two events

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

evolution of the marine stable carbon isotope record during the early cretaceous a focus on the late hauterivian and barremian in the tethyan realm abstract in order to improve our understanding of the relationships between the late hauterivian oceanic anoxic faraoni event contemporaneous platform drowning along the northern tethyan margin and global environmental change in general we established high resolution 13 c and 18 o curves for the late hauterivian and the entire barremian stage these data were obtained from whole rock carbonate samples from the veveyse de ch tel saint denis section switzerland the fiume bosso section and the nearby gorgo a cerbara section central italy and the angles section barremian stratotype france we observe an increase of 0 3 in mean 13 c values within sediments from the middle hauterivian subsaynella sayni ammonite zone to the hauterivian barremian boundary 13 c values remain essentially stable during the early barremian during the latest early barremian and most of the late barremian 13 c values increase slowly until the imerites giraudi zone and the latest barremian is characterized by a negative trend in 13 c values with minimal values at the barremian aptian boundary during the earliest aptian 13 c mean values start to rise again and attain 2 25 we interpret the evolution of the 13 c record as resulting from the interaction between changes in the carbon cycle in the tethyan basin and the adjacent platforms and continents in particular changes towards warmer and more humid conditions on the continent and coeval phases of platform drowning along the northern tethyan margin may have contributed to enhance the oceanic dissolved inorganic carbon dic reservoir which may have pushed the 13 c record towards more negative values and exerted a general attenuation on the 13 c record from this may have come the general change from a heterozoan to a photozoan carbonate platform community which influenced the evolution in 13 c values by increasing the export of aragonite and diminishing export of dissolved organic carbon into the basins

cyclostratigraphy of the reference section for the cretaceous white chalk of northern germany lagerdorf kronsmoor a late campanian early maastrichtian orbital time scale new carbonate records of the upper campanian lower maastrichtian white chalk of northern germany at lagerdorf kronsmoor represent a continuous succession suitable for time series analysis the boreal chalk succession is characterized by several intervals of reduced carbonate content in the basiplana spiniger polyplocum upper langei and upper grimmensis granulosus to pseudoobtusa boreal macrofossil zones which are mainly related to periods of increased detrital supply results of spectral analysis on the carbonate time series allow the detection of the periodicities of long and short eccentricity the long eccentricity signal can be extended to the entire upper campanian comprising a total of 15 25 long eccentricity cycles a minimum time span of 6 2 ma and an age of 77 5 0 4 ma for the lower upper campanian boundary the long eccentricity cycles detected from chalk carbonate contents correlate with long eccentricity cycles detected in self potential logs of boreholes proving their significance within different depositional settings and rates of subsidence in the north german basin the biostratigraphic consistent occurrence of long eccentricity cycles provides evidence for the completeness of the sedimentary record the long term intervals of increased detrital supply are the expression of increased progradation of clay minerals related to a long term sea level fall with superimposed short sea level falls within a 2 5 million year interval spanning the campanian maastrichtian boundary it cannot be decided from the present state of knowledge if this signal is controlled by increased erosion due to uplift of inverted structures by eustatic sea level fall or a combination of both the detection of the long eccentricity suggests an orbital forcing superimposed on a long term regressive trend

detection quantification and significance of hiatuses in pelagic and hemipelagic strata temporal gaps in the stratigraphic record have important implications for the interpretation of stratigraphically rapid geochemical and paleobiologic changes for the development of high resolution time scales e g orbital time scales and for deciphering the response of depositional systems to climatic change and basin evolution e g accommodation space vs sediment supply in ancient pelagic and hemipelagic strata the identification of relatively short hiatus 10 3 10 6 years is commonly challenged by the resolution limits of geochronologic techniques in this study a quantitative method is developed to identify and quantify hiatuses in strata where milankovitch orbital cycles are documented the new method is based on the interpretation of evolutive harmonic analysis eha results and permits estimation of minimum durations for the temporal gaps application of this technique to an optical densitometry data series derived from the cenomanian turonian c t bridge creek limestone member permits quantification of hiatus within the unit and addresses important questions about abrupt changes in biogeochemical proxy records across the boundary interval integration of the new method with stratigraphic data and geochemical burial flux estimates permits a detailed reconstruction of the controls on sediment delivery and hiatus generation including a refined analysis of the orbital scale linkages between climate and sedimentation d 2004 elsevier b v all rights reserved

orbital forcing of calcilutite marl cycles in southeast spain and an estimate for the duration of the berriasian stage cyclicities observed in a hemi pelagic rhythmic calcilutite marl succession of late berriasian age near caravaca southeast spain match well with the quasi periodicities of the milankovitch model the shortening of the precession and obliquity in pre quaternary times is taken into account the interval of the miravetes formation studied has a thickness of 77 5 m extends from the base of the calpionellopsis simplex subzone d1 to the top of the calpionellopsis oblonga subzone d2 and has an estimated duration between 1 1 and 2 9 ma the evolution of the cyclicities in this succession was analyzed by comparing the spectra of ten successive overlapping segments from this comparison we conclude that 11 m at the top and base of the succession show variations in accumulation rate disregarding these parts the spectrum of the remaining interval 56 m reveals well defined spectral peaks the cyclicity is ascribed to orbital forcing because all cycles longer than the bedding cyclicity can be matched with the known orbital quasi periodicities reported in berger and others 1989a 1989b this match with milankovitch cyclicities produces a considerably more precise estimate for berriasian zone durations the range of the duration of the combined calpionellid subzones d1 and d2 reduces to an interval between 1 1 and 1 2 ma and the length of the entire berriasian stage is estimated to fall between 2 9 and 3 1 ma

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

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

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

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

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

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

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

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

late quaternary 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

the mineralogical composition of precursor sediments of calcareous rhythmites a new approach previous studies in silurian carbonates from gotland sweden have led to a model for the development of limestone marl alternations this model postulates that early diagenesis of precursor sediments without strong primary differences can result in a differentiation by selective dissolution of aragonite in marl beds and reprecipitation of calcite cement in limestone beds this model is described as a set of mathematical equations that quantify the diagenetic processes aragonite dissolution and calcite reprecipitation that occur during the formation of limestone marl interbeds from a hypothetical homogeneous precursor sediment the calculations demonstrate that resulting hypothetical limestone marl alternations show characteristic mathematical relationships between the ratios of the bed thicknesses of limestones and marls on one side and the carbonate contents on the other by reversing this model the original mineralogical composition of the precursor sediment of real world rhythmic successions can be determined in this study alternations from the silurian of gotland the cambrian devonian and mississippian of north america the jurassic of france and germany and the cretaceous of france are shown to exhibit mathematical relationships similar to those calculated for hypothetical precursor sediments without primary differences therefore the mineralogical composition of their precursor sediments can be estimated in contrast the clear mismatch shown by the lower jurassic belemnite marls from dorset indicates that these rhythms did not suffer an early diagenetic overprint our model helps to differentiate between rhythmites with strong depositional variations and those without however it cannot indicate whether a given alternation is the product of rhythmic diagenesis of a homogeneous precursor sediment or the result of diagenetic enhancement of subtle underlying sedimentary rhythms for horizontally correlated patterns such as laterally extensive beds and layers of nodules an a priori unknown external signal has to be assumed

a warm equable cretaceous the nature of the problem abstract the nature of the problem of warm equable paleoclimates is defined by investigating the mid cretaceous period the problem consists of three components 1 defining precisely the climatic state during any specified interval of geologic time 2 specifying the external climatic forcing factors which may have been important and 3 understanding the climatic response to any specific modifying influence these components are characterized by limitations of critical importance in understanding paleoclimates the nature of the problem of a warm cretaceous is defined both qualitatively and quantitatively within these limits

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

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

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

high resolution clay mineralogy as a proxy for orbital tuning example of the hauterivian barremian transition in the betic cordillera se spain the response of clay mineral assemblages to potential orbital forcing is tested in mesozoic hemipelagic marl limestone rhythmites of the rio argos section betic cordillera southeastern spain along the section marls are pervasively enriched in kaolinite and illite whereas limestones are enriched in smectite rich illite smectite mixed layers suggesting that marl limestone alternations are produced by cyclic high frequency fluctuations of continental runoff spectral analyses show that clay mineral assemblages evolve accordingly to precession obliquity and eccentricity cycles durations of ammonite zones are assessed at 535 kyr for the late hauterivian pseudothurmannia ohmi zone and at 645 kyr and for the early barremian taveraidiscus hugii zone these durations are in agreement with other cyclostratigraphic estimates but significantly differ from the geologic time scale 2004 and 2008 clay minerals display enhanced amplitude of the eccentricity cycles during the faraoni oceanic anoxic event due to enhanced continental weathering conditions prevailing at that time sedimentary expression of the 405 kyr eccentricity is disturbed by palaeoclimate changes during the faraoni oae challenging the hypothesis of cretaceous oae triggered by eccentricity cycles although palaeoceanographic events e g faraoni oae may induce disturbances in the clay mineral record this study demonstrates the potential of these minerals to be used as a proxy for orbital calibration in mesozoic times

paleoceanographic changes during the early cretaceous valanginian hauterivian evidence from oxygen and carbon stable isotopes we investigated valanginian hauterivian bulk rock and belemnite samples from vocontian basin sections in southeastern france for their stable carbon and oxygen isotope signature firstly because these sections permit calibration with high resolution biostratigraphy based on ammonites and secondly because detailed isotope studies for the hauterivian are lacking the results show that 13c values for bulk rock decrease during the late valanginian early hauterivian with 1 and increase again during the late hauterivian with 1 the 18o signal for bulk rock samples is mostly disturbed by diagenesis the belemnites show carbon and oxygen isotope values that are lower and higher than bulk rock samples respectively we explain this as the result of the belemnites recording a deeper water signal with lighter 13c values and heavier 18o values implicating colder water at greater depth the overall preservation of the belemnites is very good and permits the construction of a paleo temperature trend this trend shows warm deeper water temperatures during the late early valanginian 15 c and progressively cooler temperatures during the late valanginian and early hauterivian 11 c during the late hauterivian temperatures increase again 13 c we relate this cooling trend for deeper water to a second order sea level rise which allowed for the exchange of cold boreal and warm tethyan water masses the influx of cold nutrient rich water had a profound effect on carbonate producing biota along the northern margin of the tethys during the hauterivian leading to prolonged phases of condensation and platform destruction during the early hauterivian the carbonate system along the northern tethyan margin shifted into a green water mode of carbonate production high rates of carbonate production under mesotrophic conditions also observed in other parts of the world meant that the global carbon cycle became buffered shown by the stable trends in carbon isotopes

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

thermal evolution of cretaceous tethyan marine waters inferred from oxygen isotope composition of fish tooth enamels 1 the evolution of subtropical 30 35 n upper ocean temperatures through the cretaceous is inferred from the oxygen isotope compositions of 64 fish teeth enamel coming from the western tethyan platform mean 18o values of 22 at the berriasian valanginian boundary decrease with oscillations to 18 5 around the cenomanian turonian boundary and progressively increase to 21 5 by the end of the cretaceous the similarity of this oxygen isotope curve for bioapatites from platform environments with those for foraminifera and bulk carbonates that were deposited in deeper waters and at other paleolatitudes indicates that they record global climatic signals major cooling events at the million year scale can be distinguished 1 at the berriasian valanginian boundary and 2 during the earliest late valanginian a third cooling event is detected during the earliest aptian these events already proposed as icehouse interludes during the lower cretaceous are also recorded at subtropical latitudes a progressive warming is identified from the aptian to the cenomanian turonian interval that corresponds to a thermal optimum and then upper ocean temperatures decreased to the maastrichtian minimum isotopic temperatures range from 15 c to 28 c assuming a 18oseawater of 1 for an ice free world taking more realistic 18oseawater values of 0 for tropical waters during glacial periods within the berriasian valanginian interval and earliest aptian or with above average salinities possibly the maastrichtian temperatures are increased by 4 5 c temperature differences between climatic extremes of the valanginian and cenomanian turonian are estimated to have been 10 c latitudinal thermal gradients for the albian cenomanian turonian and maastrichtian were 0 2 0 3 c latitude and thus weaker than modern oceanic values at about 0 4 c latitude

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

paleomagnetic calibration of milankovitch cyclicity in lower cretaceous sediments abstract bedded pelagic limestones of early to mid cretaceous age may record cyclic climate variability driven by changes in the earth s orbit milankovitch cycles if properly calibrated the lithologic cycles could provide sedimentary chronometry at far shorter time scales than biostratigraphy and magnetic stratigraphy the lower cretaceous maiolica formation of northern and central italy displays rythmic bedding in sections whose magnetic reversal sequence is clearly correlated to the upper m series marine anomalies the magnetic reversals divide measured sections into 0 5 2 myr increments in which sedimentation rate assuming continous deposition can be measured to 15 25 accuracy paleomagnetically estimated sedimentation rates over a number of polarity zones establish with one exception a narrow range in periods of the carbonate cycles carbonate couplets have an estimated mean period of 23 5 kyr and prominent modulations in bedding thickness bundling have a mean period of 117 kyr kent and gradstein 1985 time scale the close match of sedimentary periodicities to orbital repeat times implies that the carbonate cycles reflect a combination of professional and eccentricity climatic forcing comparison of measured sections from different locations shows that bed to bed correlations are possible regionally cosistent with the milankovitch hypothesis episodes of barremian black shale deposition occur in the troughs of the short eccentricity cycle as roughly one half of the carbonate marl couplet or about 10 kyr duration it is possible to estimate both the timing relative to the top of reversed chron m 0 and duration of a period of unusual organic carbon rich deposition selli horizon in the early part of the cretaceous long normal magnetic polarity interval by tracing the sedimentary cycles up from the barremian strata

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

depositional changes during the danian selandian transition in loubieng france zumaia spain and sidi nasseur tunisia insights from and limits of rock magnetism depositional changes are studied in three sections encompassing the danian selandian transition loubieng france zumaia spain and sidi nasseur tunisia using magnetic susceptibility as a proxy additional rock magnetic analyses are used to avoid ambiguous interpretation of magnetic susceptibility the magnetic susceptibility measured on 90 to 270 samples per section is mainly controlled by paramagnetic minerals and linked to detrital input major increases in the detrital input are correlated to the end of the latest danian event a hyperthermal and to the danian selandian boundary in loubieng two gradual increases in magnetic susceptibility within limestones beds precede the major detrital input increases and start synchronously with the beginning of the latest danian event and the onset of haematite deposition around the danian selandian boundary respectively this haematite is suspected to be of primary origin based among other things on low magnetic viscosity values which is used here as an indicator of diagenetic origin in haematite and goethite the red levels where haematite is interpreted to be of primary origin could be linked to the hyperthermal event previously hypothesized for the basal selandian the comparison of the magnetic susceptibility chemo and biostratigraphic data between the three sections highlights the condensed nature of the sedimentation around the danian selandian boundary in the sections of the atlantic realm the lower part of the selandian shows a particularly low sedimentation rate at zumaia compared to loubieng and sidi nasseur the latter displays the most complete record of the three

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