anatomy of a mixed marine non marine lowstand wedge in a ramp setting the record of a barremian aptian complex relative sea level fall in the central neuquen basin argentina

the oldest evidence for birds in northern gondwana small tridactyl footprints from the middle jurassic of msemrir morocco we revise a famous set of fossil footprints that were described in the mid 1980s from the middle jurassic bathonian of morocco and that have often been considered to be an early record for mesozoic birds if correct these tracks are the oldest records of birds from gondwana and would have critical biogeographic and palaeobiological implications the oldest skeletal fossils of avians are from the late jurassic of germany laurasia thus these important historical footprints are re described and re examined and new analyses are carried out on the additional tracks that also occur on the surface but that have never been described before all the tracks on the surface show the same morphological characteristics though their size is variable and are compared here to known dinosaur and bird ichnotaxa we used a laser scanner to generate a 3d digital model of the slab this new approach allowed detailed descriptions of the specimens the identification of new footprints on the surface and the conclusion that they were likely left by non avian dinosaurs rather than birds we show the potential of this new approach to the study of fossil footprints and trackways high resolution imaging and laser scanning add new information fundamental for a revision of the criteria for distinguishing between closely related vertebrate groups in this case dinosaurs and birds

the upper jurassic kimmeridgian fluvial aeolian systems of the southern neuquen basin argentina abstract the kimmeridgian quebrada del sapo formation in the southernmost neuquen basin in argentina represents a succession up to 40 m thick of coarse to fine grained fluvial deposits overlain by aeolian deposits these fluvial aeolian deposits reflect a significant palaeogeographic change in the basin and are related to a major tectonically enhanced relative sea level fall the fluvial section is dominated by braided channel fine grained ephemeral and sheetflood deposits aeolian facies are dominated by dune deposits with minor sandsheet and interdune units changes in the nature of both fluvial and aeolian sedimentation within the studied area suggest a regional variability of accommodation sediment supply conditions the regional changes of the aeolian succession likely reflect different relative positions within a major erg in the upwind margin of the erg a shallow water table promoted water lain sedimentation in interdune areas whereas in the central parts of the erg dry sediment accumulation took place above the regional water table level the vertical transition observed in the quebrada del sapo formation from fluvial to aeolian deposits may be the result of a local climatic change to drier conditions due to the development of a climatic barrier imposed by growth of a magmatic arc to the west alternatively the vertical transition could be related to a lowering of the water table associated with the compartmentalization of the basin during a period of low sea level

classification of dolomite rock textures abstract dolomite rock textures can be classified according to crystal size distribution and crystal boundary shape the classification scheme presented here is largely descriptive but carries genetic implications because size distribution is controlled by both nucleation and growth kinetics and crystal boundary shape is controlled by growth kinetics size distributions are classified as unimodal or polymodal crystal boundary shapes are classified as planar or nonplanar if the evidence permits a complete classification includes a description of recognizable allochems matrix and void filling allochems and preexisting cements may be unreplaced partially replaced replaced mimically or replaced nonmimically allochems may be dissolved leaving molds matrix can be unreplace partially replaced or replaced by a unimodal or polymodal size dolomite unimodal size distributions generally indicated a single nucleation event on a unimodal substrate polymodal sizes can be formed by multiple nucleation events on a unimodal or polymodal substrate or differential nucleation on an originally polymodal substrate planar crystal boundaries develop when crystals undergo faceted growth and nonplanar boundaries develop when crystals undergo nonfaceted growth nonplanar boundaries are characteristic of growth at elevated temperature 50 c and or high supersaturation both planar and nonplanar dolomite can form as a cement replacement of caco3 or neomorphism of a precursor dolomite

origin and consequences of cyclic ice rafting in the northeast atlantic ocean during the past 130 000 years deep sea sediment cores recovered from the northeast atlantic ocean were examined in order to elucidate the influence of the earth s orbital parameters on major ice rafting analyses of coarse grained ice rafted debris and planktonic foraminifers revealed a strong reaction to the precession signal since 130 000 yr b p dropstone layers have been deposited each half period of a precessional cycle 11 000 1000 yr ice rafting occurs during times of winter minimum summer maximum insolation and summer minimum winter maximum insolation in the first case high summer insolation forces meltwater discharge from the ice sheets into the polar seas which subsequently enhances formation of sea ice during the winter in the second case growth of continental ice enhances iceberg production which also leads to a salinity reduction of surface seawater both situations result in a southward penetration of polar water thus the marine record of dropstones documents ice rafting not only during weichselian stades but also during cold events within interstades the regularity of ice rafting yields a useful framework to calibrate and elucidate climatic changes not only in the region of the north atlantic ocean but also in remote areas such as the pacific ocean and the antarctic

an application of hierarchical bayesian modeling to better constrain the chronologies of upper paleolithic archaeological cultures in france between ca 32 000 21 000 calibrated years before present abstract investigations of chronology play a key role in the majority of archaeological research endeavors and are particularly pertinent to examinations of culture environment relationships especially during periods characterized by rapid and marked climatic variability and environmental reorganization rigorous evaluations of available data and robust methods are required if one wishes to reconstruct reliable chronologies and this is especially the case when examining periods that are associated with a relatively few radiometric measurements such is the case for the upper paleolithic archaeological record documented in present day france from 32 000 to 21 000 calibrated years bp we take into account critically examined radiocarbon measurements from contextually secure archaeological contexts and employ a recently developed method of hierarchical bayesian modeling to reconstruct the chronology of archaeological cultures from the middle gravettian to the badegoulian the calculated chronological intervals for each typo technologically defined culture phase are compared to the greenland ice core climatic record and a terrestrial paleoenvironmental record from bergsee lake southern germany itself expressed in calendar years calculated with the same calibration curve employed in our age model thereby permitting each archaeological culture to be correlated accurately with documented paleoclimatic variability

gregarious behaviour among non avian theropods inferred from trackways a case study from the cretaceous cenomanian candeleros formation of patagonia argentina abstract gregarious behaviour among dinosaurs has been inferred from several lines of evidence monospecific bonebeds skeletal morphology phylogenetic inferences comparison with modern ecosystems and parallel trackways with particular characteristics but is relatively poorly documented for non avian theropods here we report five parallel theropod trackways of large track size average length of 28 cm in the cretaceous cenomanian candeleros formation from northwestern patagonia argentina the tracks are provisionally assigned to aff asianopodus pulvinicalx and considering the autopod morphology of the theropod taxa documented in the candeleros formation abelisaurid theropods are suggested as trackmakers the trackways possess similar stride speed estimation direction and preservational features and track show uniform depth and do not overlap physical barriers i e large fluvial channels or perennial lake that could influence the direction of the theropod trackmaker gaits were not recognized in the section taking into account these considerations a gregarious behaviour for the abelisaurid theropod trackmakers is proposed the tracks are preserved as shallow undertracks in a medium grained sandstone bed deposited in a floodplain setting the tracking surface is interpreted as the overlaying layer of muddy siltstone the occurrence of swelling clays and microbial mats in the track bearing level could have contributed to the substrate stabilization and their role in the preservation is discussed

investigating links between ecology and bifacial tool types in western europe during the last glacial maximum we apply eco cultural niche modeling ecnm using the genetic algorithm for rule set prediction to reconstruct the ecological niches exploited by middle solutrean and upper solutrean populations during the latter stages of heinrich event 2 and the early part of the last glacial maximum respectively we focus on the upper solutrean technocomplex and its regionally distinct styles of hunting weaponry to investigate whether regional cultural variability reflects a link between material culture and ecology our analytical approach uses archaeological and geographic data in conjunction with high resolution paleoclimatic simulations and vegetation reconstructions for the two climatic phases in question our results indicate that cultural choices behind the production of specific projectile point types have at some level an ecological basis and are linked to particular environments we also find that the identified pattern of upper solutrean territoriality has an ecological foundation but that its stylistic expression in the variation of diagnostic armature types is likely a byproduct of cultural drift we argue that ecnm is an effective means with which to evaluate the paleoecological pertinence of archaeologically defined artifact types and to identify the ecological and cultural mechanisms underlying material culture variability

climatic reconstruction in europe for 18 000 yr b p from pollen data an improved concept of the best analogs method is used to reconstruct the climate of the last glacial maximum from pollen data in europe in order to deal with the lack of perfect analogs of fossil assemblages and therefore to obtain a more accurate climate reconstruction we used a combination of pollen types grouped according to plant phenology and present climate constraints rather than pollen percentages for each individual taxon the distribution of pollen taxa into plant functional types pfts is aimed to reflect the vegetation in terms of biomes which have a wider distribution than a species the climatic variables are then calibrated on these pfts using an artificial neural network technique the use of pfts allowed us to deal with situations where pollen assemblages have only partial modern analogs the method is applied to the glacial steppic vegetation in europe using 15 pollen records north of the pyrenees alps line the reconstructed temperatures were lower than today 30 10 degrees c for the temperature of the coldest month t c and 12 3 degrees c far the annual mean t ann south of that line t c and t ann anomalies were respectively 15 5 degrees c and 10 5 degrees c the available moisture index and annual precipitation were also lower than present 60 20 north of mediterranean sea 800 100 mm for precipitation in italy and greece the available moisture was 20 lower with a precipitation anomaly of ca 600 200 mm southward the moisture index was close to that at present 20 and precipitation was lower 300 300 mm c 1998 university of washington

calibrating fault seal using a hydrocarbon migration model of the oseberg syd area viking graben abstract it is widely acknowledged that fault rock capillary properties are important in controlling the distribution of hydrocarbons in sedimentary basins and methods exist for predicting the capillary seal capacity of prospect bounding faults however fault seal capacity is rarely incorporated into models of hydrocarbon migration this paper presents the results of migration modelling of the oseberg syd area of the viking graben incorporating fault rock capillary properties seal capacity is calculated in the model as a function of shale gouge ratio sgr i e the percentage shale in the sequence moved past a point on a fault over 3000 model realisations were run for different sgr to fault seal capacity relationships and the calculated hydrocarbon distributions were compared with known distributions realisations were ranked according to the closeness of fit between model and actual oil water contacts for 7 traps the best fit to all 7 traps was provided by realisations with significant seal capacity at sgr values greater than ca 0 2 a value which is in agreement with an independently derived fault by fault calibration between sgr and seal capacity the level of fill calculated for an individual trap is extremely sensitive to minor changes in the seal capacity relationship because it is controlled not only by the seal capacities of the faults that bound the trap but also by the pattern of fill spill of upstream traps this sensitivity to minor changes in seal capacity introduces large uncertainties when fault seal capacity relationships are used in a predictive mode and emphasises the requirement for migration modelling in fault seal prospect evaluation

paleoenvironmental framework of dinosaur tracksites and other ichnofossils in early cretaceous mixed siliciclastic carbonate deposits in the neuquen basin northern patagonia argentina abstract the study of the uppermost section of the early cretaceous agrio formation in northern patagonia neuquen basin where dinosaur tracks assigned to cf therangospodus pandemicus are exposed tracksites i and ii evidence mixed marginal marine siliciclastic carbonate deposits the succession was divided in two intervals a lower one containing theropod tracks recorded on top of subtidal oolithic limestones with tiny wave ripples suggesting shoreline fluctuations and subaerial exposure tidal influence is recognised by fining upward and prograding cycles starting with subtidal carbonates and ending with fine grained siliciclastic deposits at the top or rarely laminites dolomitization affects subtidal deposits generated in an alkaline media stressful for tracemakers intertidal facies include abundant heterolithic deposits coquinas composed of gastropods encrusted by multilayered bryozoans and muddy levels with incipient mud cracking invertebrate ichnofossils recognized from tidally dominated deposits include arenicolites kouphichnium and rhizocorallium the upper interval is a transgressive regressive cycle that starts with dark shales deficiently oxygenated and covered by prograding sandstones and finally sand flat deposits this interval contains gyrochorte hillichnus and ophiomorpha documented in wave influenced sandstones dinosaur tracks as well as hillichnus attributed to tellinoid bivalves and kouphichnium assigned to xiphosurans imply the activity of producers rarely recorded previously as body fossils in marginal marine deposits of southern south america previous paleogeographic schemes are questioned by our analysis which shows evidence of extremely shallow and tide controlled sedimentation sometimes with subaerial exposure with high cyclicity related to a marginal marine depositional setting and lack of significant erosion by the overlying unit as traditionally was suggested

textural and geochemical alternations in late cenozoic bahamian dolomites dolomitized intervals of a core from san salvador island bahamas exhibit variations of two texturally and geochemically distinct end members in the pliocene section of the dolomitized interval the two end members alternate in a pattern that may reflect originally and or diagenetically modified depositional facies formerly mud free intervals locally capped by exposure surfaces are massive crystalline mimetic dolomites cm muddier sediments are replaced by friable microsucrosic dolomites ms cm and ms dolomites also differ in porosity 30 permeability 100 md mol mgco3 44 9 vs 47 7 mol oxygen isotopic composition 1 7 vs 2 7 and strontium content 241 vs 106 ppm these data indicate that depositional and diagenetic fabric are the principal controls governing the distribution of dolomite types differences in texture and geochemistry are suggested as arising through differential rates of crystallization produced as a result of variations in permeability and reactivity of the precursor sediments and rocks

the maastrichtian danian maimara tracksite yacoraite formation salta group quebrada de humahuaca argentina environments and ichnofacies implications fil console gonella carlos alfredo consejo nacional de investigaciones cientificas y tecnicas centro cientifico tecnologico conicet tucuman instituto superior de correlacion geologica universidad nacional de tucuman facultad de ciencias naturales e instituto miguel lillo departamento de geologia catedra geologia estructural instituto superior de correlacion geologica argentina

the ichnogenus rhizocorallium classification trace makers palaeoenvironments and evolution rhizocorallium is one of the oldest known trace fossils with wide distribution through the phanerozoic and all over the world originally introduced from the epicontinental triassic of central germany its high morphological lability gave reason for the subsequent erection of about twenty ichnospecies the study of newly collected material from the type area and many specimens from various collections permits the conclusion that rhizocorallium jenense and rhizocorallium commune are the only valid ichnospecies of rhizocorallium the type ichnospecies r jenense is a comparatively small inclined and heavily scratched firmground burrow with passive fill while r commune consists of extensive more or less horizontal burrows with occasionally scratched marginal tubes and an actively filled spreite between the tubes the faecal pellets coprulus oblongus are typically associated with r commune morphological variations of r commune are captured in ichnosubspecies and varieties of this ichnospecies and can aid a refined reconstruction of palaeoenvironments a review of more than 180 records from the literature reveals the common confusion of both ichnospecies which has consequences for the application of rhizocorallium in facies interpretations the end members of both ichnospecies may be linked by transitional forms which suggests the same kind of trace maker polychaetes are the most likely producers of marine rhizocorallium based on their long ranging occurrence morphological features appearance of faecal pellets associated soft body remains and modern analogues r commune occurs from early cambrian to holocene while r jenense just appears after the end permian mass extinction probably as a consequence of an adapted firmground burrowing lifestyle of its producer fluvial r jenense are probably produced by mayfly larvae in homology to marine polychaete burrows a consequent application of the newly established classification scheme allows for a more rigorous application of rhizocorallium in the reconstruction of palaeoenvironments thus palaeozoic and mesozoic r commune are restricted to the cruziana ichnofacies of shallow marine environments while in cenozoic time similar forms are also found in deep marine deposits r jenense on the other hand is a constituent of the widespread glossifungites ichnofacies and aside from continental environments occurs in peritidal to deep marine deposits several studies have demonstrated the value of rhizocorallium for interpreting sequence stratigraphical surfaces current directions and fluctuations in salinity and oxygen

orbital and sub orbital scale climate impacts on vegetation of the western mediterranean basin over the last 48 000 yr article i nfo high resolution pollen analysis of alboran sea core md95 2043 provides a 48 ka continuous vegetation record that can be directly correlated with sea surface and deep water changes the reliability of this record is supported by comparison with that of padul sierra nevada spain marine isotope stage mis 3 was characterised by fluctuations in quercus forest cover in response to dansgaard oeschger climate variability mis 2 was characterised by the dominance of semi desert vegetation despite overall dry and cold conditions during mis 2 heinrich events hes 2 and 1 were distinguished from the last glacial maximum by more intensely arid conditions taxon specific vegetation responses to a tripartite climatic structure within the hes are observed in mis 1 the bolling allerod was marked by rapid afforestation while a re expansion of semi desert environments occurred during the younger dryas the maximum development of mixed quercus forest occurred between 11 7 and 5 4 cal ka bp with forest decline since 5 4 cal ka bp on orbital timescales a long term expansion of semi desert vegetation from mis 3 into mis 2 reflects global ice volume trends while holocene arboreal decline reflects summer insolation decrease the influence of precession on the amplitude of forest development and vegetation composition is also detected

vertebrate track bed stratigraphy at new megatrack sites in the upper wellenkalk member and orbicularis member muschelkalk middle triassic in carbonate tidal flat environments of the western germanic basin this article examines the high resolution track horizon and track bed stratigraphy at two new middle triassic megatrack sites in nw germany the first megatrack site consists of the localities hagen and detmold and spans over a distance of about 30 km in the upper wellenkalk member of the uppermost lower muschelkalk pelsonian the second megatrack site was found between niederlistingen and ostheim over a distance of 10 km in the orbicularis member of the lowermost middle muschelkalk illyrian at all track sites the track beds are mud cracked microbial laminates and yellow dolomites products of microbial mats in carbonate tidal flat environments vertebrate tracks rhynchosauroides tirolicus abel procolophonichnium haarmuehlensis holst smit veenstra as well as scratch marks and undichna isp are abundant recently 11 track beds have become known from the upper roet member upper bunter to the marl dolomite member middle muschelkalk in the germanic basin six of these track beds build megatrack sites with an extent of 10 400 km the result is a completely different picture of the bathymetry during bithynian to illyrian in the germanic basin a flatter basin with a surrounding carbonate tidal flat belt changing its position periodically

mixed siliciclastic and carbonate sediments a proposed first order textural and compositional classification sediments that are composed of mixtures of siliciclastic and carbonate material occur in both the modern and the ancient to date there is no commonly used classification of this type of sediment a descriptive first order classification system is proposed here that is applicable to most mixed sediments and their lithified equivalents the sediments are composed of four components 1 siliciclastic sand sand sized quartz feldspar etc 2 mud mixtures of silt and clay 3 allochems carbonate grains such as peloids ooids bioclasts and intraclasts 20 m in size and carbonate mud or micrite 20 m in size these components define a tetrahedra whose subdivision produces eight general classes of mixed sediment the name of a class reflects both the dominant grain type and the most abundant antithetic component for example a rock that contains greater than 50 siliciclastic material of which most is sand sized and subordinate allochems is termed an allochemic sandstone other rock names include micritic sandstone allochemic and micritic mudstone sandy or muddy allochem limestone and sandy or muddy micrite prefixes and adjectives can be added to these terms to include dolomitic sediments conglomeratic textures and biogenic constituents

the sauropod diversity of the la amarga formation barremian neuquen argentina abstract a study of the abundant and undescribed isolated and associated bones and teeth from the la amarga formation barremian of neuquen argentina permitted the recognition of additional clades of sauropod dinosaurs basal titanosauriforms both basal and derived titanosaurs and rebbachisauroid diplodocoids which are now added to the already known dicraeosaurids and a recently published basal diplodocoid these forms substantially increase the knowledge on the early cretaceous sauropod diversity in gondwana

neandertal extinction and the millennial scale climatic variability of ois 3 population models seeking climate as a triggering factor for the extinction of neandertals and the colonisation of europe by anatomically modern humans are contradictory due to uncertainties in the dating methods in the cultural attribution of archaeological layers and to the lack of terrestrial continuous and well dated palaeoclimatic sequences this is particularly the case for the iberian peninsula where neandertal populations seem to have survived later than in other regions of europe a review of the available palaeoclimatic evidence for ois3 of iberia reveals that this mainly consists of low resolution fragmentary ill dated and often ill interpreted records correlation between palaeoenvironmental sequences from two images pollen rich deep sea cores and archaeological data from western europe the electronic archive of the radiocarbon dates is available at qsr website http www elsevier nl locate quascirev indicates that aurignacian moderns colonised france and the north of iberia at the onset of the h4 event during this cold episode a probable contraction of neandertal populations is recorded in southern iberia where no aurignacian settlements are detected such a decline in population density is correlated with the particular desert steppe like environments made up of artemisia chenopodiaceae and ephedra characterising the h4 of this area while reducing the size of neandertal populations this inhospitable environment may have favoured their persistence in this region mainly exploiting herds of herbivores adapted to graminees rich grasslands the aurignacian moderns were probably not interested in colonising these arid mediterranean biotopes and did that only after the h4 event

palaeosalinity variations in the early cretaceous of the neuquen basin argentina evidence from oxygen isotopes and palaeoecological analysis abstract the neuquen basin is a stratigraphically and economically important early cretaceous depocentre located in west central argentina the early valanginian to early barremian succession upper vaca muerta mulichinco and agrio formations contains a rich fossil record with abundant bivalves and ammonoids palaeosalinities are determined systematically throughout the succession based on an oxygen isotope analysis of unaltered oyster shells from two localities in neuquen province a total of 188 oyster samples from 52 stratigraphic levels were processed a total of 52 mean values of 18o isotope are used to calculate palaeosalinities assuming an estimated water temperature of 25 c the observed range of palaeosalinities between the maximum and the minimum is 19 which is in conflict with published accounts of this being a fully marine succession the isotopic data are combined with independent faunal evidence to evaluate palaeosalinity variation both laterally and temporally significant fluctuations in water salinity are indicated with a clear tendency to increase from brachyhaline to euhaline and near hyperhaline conditions through time the fluctuations were probably due to dilution from normal marine water caused primarily by variations in rainfall and continental runoff in addition the presence of a volcanic island arc along the western margin of the basin may have at least partially isolated the basin from the marine waters of the pacific ocean also a gulf shaped basin may have inhibited hydrodynamic exchange with the ocean while enhancing retention of continental waters

cross scale adaptive behaviors during the upper paleolithic in iberia the example of vale boi southwestern portugal abstract it is now rather evident that concomitant with the advent growth and disappearance of the traditionally defined western european upper paleolithic techno complexes a series of discrete eco cultural niches would have existed within iberia vale boi and its surroundings may represent one of these niches since its lengthy and fairly complete archaeological record clearly attests that the region was an attractive location for hunter gatherer communities for over 10 000 years from the first modern human occupations c 32 ka cal bp ago a set of very specific cultural adaptive markers seem to have been developed in response to the particularities of the regional ecological background some of these strategies such as intensive subsistence practices raw material specialized use among others were resilient through time and apparently impermeable to the major shifts in the techno typological novelties brought about with the advent of each upper paleolithic phase even with the appearance of quite unique and broad scale technologies e g solutrean regional markers and identity have been kept clearly showing that each level of the adaptive system seem to have operate at its own pace this paper focus on long term adaptive choices and on how and why hunter gatherers inhabiting vale boi manage to absorb change and re organize their system under new techno complex cultural patterns while still retaining efficiently the same regional adaptive idiosyncrasies within the theoretical framework of panarchy and the cross scale resilience model we argue that cross scale interactions between creative and conserving niche specific behavioral adaptations were the keystone for the sustainability of hunter gatherer cultural systems across the late pleistocene

millions of reptile tracks early to middle triassic carbonate tidal flat migration bridges of central europe reptile immigration into the germanic basin abstract discoveries of vertebrate track sites in central europe have occurred in 75 localities in carbonate tidal flats of the middle triassic in the germanic basin carbonate tidal flats were wide span mapped resulting in the finding of millions of small to medium sized reptile tracks in the west of the basin the sediment of the lower muschelkalk to basal upper muschelkalk contains at least 21 track horizons whereas in the eastern part more typically marine conditions were present here tidal flats with additional track beds started earlier during the upper bunter and demonstrated marine ingression from the eastern silesian gate during low stands these tidal flats comprised inter peninsula bridges which allowed migration of reptiles only two medium to small prolacertilian reptiles which were fully adapted to these environments left any kind of track a large thecodont reptile such as euparkeria was the potential predator that may rarely have hunted the main small trackmakers macrocnemus and hescherleria

malargue group maastrichtian danian deposits in the neuquen andes argentina implications for the onset of the first atlantic transgression related to western gondwana break up abstract the discovery of marine to brackish and fresh water carbonates in the inner agrio fold and thrust belt at pichaihue neuquen argentina located to the west of the andean orogenic front imposes important constraints on the paleogeography of the first atlantic transgression in the neuquen basin related to the break up of western gondwana the constraints on the timing and areal extent of these deposits shed light on the early uplift history of the southern andes these limestones are part of the maastrichtian danian malargue group which was previously only known from its exposures in the extra andean area representing foreland basin deposits the presence of stromatolites oncoids serpulids bivalves and gastropods as well as silicified stems of macrophytes indicates a shallow marine partially brackish environment associated with non marine deposits these strata are interfingered with and overlie distal tuffs and proximal pyroclastic flows whose geochemical characteristics point to a magmatic arc source shrimp u pb dating of volcanic zircons of these tuffs yielded an age of 64 3 0 9 ma that confirms the correlation to the maastrichtian paleocene marine transgression from the atlantic ocean the change in the paleoslope of the basin from pacific ocean transgressions to this atlantic transgression is related to the uplift and deformation of the agrio fold and thrust belt the pichaihue limestone is unconformably deposited on volcanic agglomerates which in turn unconformably overlie early cretaceous deposits based on these data it is confirmed that the cretaceous uplift of the andes was episodic at these latitudes with a first pulse in the cenomanian and a second one in pre maastrichtian times the episodic uplift is also related to an eastward migration of the thrust front and the volcanic arc related to a previously proposed shallowing of the subduction zone these episodes were controlled by the western gondwana break up and the beginning of absolute motion of south america toward the west

overview of glacial atlantic ocean mapping glamap 2000 glamap 2000 presents new reconstructions of the atlantic s sea surface temperatures sst at the last glacial maximum lgm defined at both 21 500 18 000 years b p last isotope maximum and 23 000 19 000 years b p maximum glacial sea level low stand and orbital minimum of solar insolation epilog working group see mix et al 2001 these reconstructions use 275 sediment cores between the north pole and 60 s with carefully defined chronostratigraphies four categories of core quality are distinguished more than 100 core sections provide a glacial record with subcentennial to multicentennial scale resolution sst estimates are based on a new set of almost 1000 reference samples of modern planktic foraminifera and on improved transfer function techniques to deduce sst from census counts of microfossils including radiolarians and diatoms new proxies also serve to deduce sea ice boundaries the glamap 2000 sst patterns differ significantly in crucial regions from the climap 1981 reconstruction and thus are important in providing updated boundary conditions to initiate and validate computational models for climate prediction

h4 abrupt event and late neanderthal presence in iberia heinrich event 4 h4 is well documented in the north atlantic ocean and the adjacent continents as a cooling event 39 000 yr before present bp to quantify the impact of this event with respect to climate and vegetation over the iberian peninsula we perform numerical experiments using a high resolution general circulation model forced by sea surface temperatures before and during h4 our model simulates an expansion of aridity over the peninsula during h4 a desertification of the south and a replacement of arboreal by herbaceous plants in the north all of which are in agreement with contemporaneous pollen sequences from marine cores located off the iberian peninsula our simulations demonstrate that the h4 marine event imprinted drastic changes over southern iberia which would not have favoured its occupation by anatomically modern humans therefore providing a plausible explanation for the delayed extinction of neanderthals in this region inferred from the archaeological record

contrasting atmospheric and climate dynamics of the last glacial and holocene periods our present climate is relatively stable compared to that of the last glacial maximum about 20 000 years ago palaeoclimate records obtained from ice cores1 2 and deep sea sediment cores3 for the last glacial period show abrupt temperature changes on timescales of a few hundred years which have been attributed to cycles of ice build up and release associated with large ice sheets dansgaard oeschger cycles and heinrich events 3 and their coupling to ocean circulation4 5 but little is known about the dynamics of the atmosphere during the last glaciation ice sheets influence atmospheric circulation and studies using general circulation models have suggested stormier more variable atmospheric dynamics during the last glacial maximum than today6 9 here we report the results of an analysis of temporal trends over the past 91 000 years in the oxygen isotope signatures of a high resolution ice core record from greenland1 2 this analysis provides direct evidence that atmospheric circulation during the last glaciation was more turbulent than it is today

xiphosurid trackways in a lower cretaceous tidal flat in patagonia palaeoecological implications and the involvement of microbial mats in trace fossil preservation abstract lower cretaceous trackways assignable to xiphosurids were recently found in tidally influenced marginal marine deposits of the agrio formation patagonia argentina the aim of this paper is to describe these trace fossils in detail discuss their conditions of preservation make palaeoecological and taphonomic inferences from them and analyse the importance of their palaeogeographic location these trace fossils are assigned to kouphichnium and five track morphotypes are established microbially induced sedimentary structures miss are associated with the trackways scanning electron microscope sem studies document the involvement of microbial mats in the preservation of the trackways by the presence of cyanobacteria like filament sheaths the microbial mats enabled preservation of the tracks by binding and biostabilisation of the sediment surface the mostly likely producers of the trackways are from the subfamily limulinae the studied surface could represent a high tide mating ground associated with a very shallow water deposit on a warm cretaceous tidal flat these records are the first convincingly documented trackways produced by xiphosurids in the early cretaceous worldwide and the second fossil record of this group from the cretaceous in the southern hemisphere

estimates of upper palaeolithic meta population size in europe from archaeological data abstract three databases 2961 georeferenced archeological sites simulated climatic variables simulating a typical warm phase of the isotopic stage 3 ios3 project and ethnographic of hunter gatherers hg were used to estimate the size growth rate and kinetics of the metapopulation of hg during four periods of the upper paleolithic in europe the size of the metapopulation was obtained by multiplying a demographic density per 100 km 2 by the size of the population territory of hg demographic density for each period was calculated by successively backprojecting a reference density obtained for the late glacial with inter period growth rate of the archeological sites from the aurignacian to the glacial maximum the metapopulation remained in a positive quasi stationary state with about 4400 5900 inhabitants 95 confidence interval ci95 1700 37 700 inhabitants during the glacial maximum the metapopulation responded to the cold i by moving the northern limits of its maximum expansion zone towards the low latitudes by 150 500 km from west to east ii by concentrating in few refuge zones mainly perigord cantabria and the iberian coasts iii by becoming perhaps distributed in smaller groups than during the pre and post glacial maximum the metapopulation reached 28 800 inhabitants ci95 11 300 72 600 during the mid late glacial recolonisation

dolomite occurrence evolution and economically important associations abstract dolomite is not a simple mineral it can form as a primary precipitate a diagenetic replacement or as a hydrothermal metamorphic phase all that it requires is permeability a mechanism that facilitates fluid flow and a sufficient supply of magnesium dolomite can form in lakes on or beneath the shallow seafloor in zones of brine reflux and in early to late burial settings it may form from seawater from continental waters from the mixing of basinal brines the mixing of hypersaline brine with seawater or the mixing of seawater with meteoric water or via the cooling of basinal brines bacterial metabolism may aid the process of precipitation in settings where sulfate reducing species flourish and microbial action may control primary precipitation in some hypersaline anoxic lake settings dolomite is a metastable mineral early formed crystals can be replaced by later more stable phases with such replacements repeated a number of times during burial and metamorphism each new phase is formed by the partial or complete dissolution of an earlier dolomite this continual re equilibration during burial detracts from the ability of trace elements to indicate depositional conditions and resets the oxygen isotope signature of the dolomite at progressively higher temperatures because subsurface dolomite evolves via dissolution and reprecipitation a bed of dolomite can retain or create porosity and permeability to much greater burial depths and into higher temperature realms than a limestone counterpart dolomitization also creates new crystals with new rhomb growth following the dissolution of less stable precursors repetition of this process without complete pore cementation can generate intercrystalline porosity a number of times in the rock s burial history intercrystalline porosity is a highly interconnected style of porosity that gives dolomite reservoirs their good fluid storage capacity and efficient drainage the fact that many dolomite reservoirs formed via brine reflux means that they sit beneath an evaporite seal in both platform and basinwide evaporite settings the same association of evaporites sulfate source and entrained hydrocarbons means that burial conditions are also suitable for thermochemical sulfate reduction and the precipitation of base metals this tends to occur at higher temperatures 60 c 80 c and so the resulting dolomites tend to be ferroan and consist of saddle shaped crystals

modeling the water masses of the atlantic ocean at the last glacial maximum 1 we produced gridded monthly sea surface boundary conditions for the atlantic ocean at the last glacial maximum lgm based on the sea surface temperature reconstruction of the glamap project we used an ocean general circulation model ogcm subject to these sea surface boundary conditions and a corresponding wind stress field from an atmospheric general circulation model to study the differences in the distribution of the main water masses between the lgm and the present our global ogcm is characterized by high vertical resolution low vertical diffusion and isopycnal mixing and hence allows for a realistic representation of the hydrology and circulation of the modern atlantic ocean according to a series of lgm experiments with an increasing sea surface salinity anomaly in the weddell sea the ventilated thermocline was colder than today by 2 3 c in the north atlantic ocean and in the experiment with the largest anomaly 1 0 beyond the global anomaly by 4 5 c in the south atlantic ocean its depth was reduced by 50 m on average most notably in the tropics in the north atlantic ocean the outcrop locations of the thermocline isopycnal surfaces migrated southward by 5 10 and the ventilation increased in the south atlantic ocean the mixed layer and thermocline water masses were dominated by cold water originating from drake passage and the import of warm water from the indian ocean was reduced to about 4 sv or 40 of its modern value antarctic intermediate water was colder by 3 4 c and could be traced as far as 10 n the meridional overturning rates of north atlantic deep water nadw and antarctic bottom water aabw in the atlantic ocean were similar to those of the present day experiment 9 10 sv and 4 sv respectively however nadw cooled by 2 5 c and aabw by 1 c aabw was near the freezing point of seawater at the surface and the saltiest water mass in the atlantic ocean even saltier than nadw we show that the differences between the lgm and the present day experiments can be traced back to the changes in the subpolar and interhemispheric sea surface density gradients

lithifying microbial mats in lagoa vermelha brazil modern precambrian relics abstract bacterial populations microbial and mineral forming processes and their products were analyzed in lagoa vermelha brazil the microbial mat and underlying sediment were studied as a unique system to define the boundary conditions responsible for high mg calcite and dolomite formation in the uppermost layers of the microbial mat oxygenic photosynthesis and aerobic respiration resulted in calcite precipitation whereas in the underlying anoxic layers of the mat sulfide oxidation and sulfate reduction induced formation of a range of carbonate minerals with increasing mg concentrations the chemical mineralogical and biological conditions presently found in lagoa vermelha may have been more common in the precambrian the microorganisms performing the metabolic processes related to carbonate mineral formation within lagoa vermelha s hypersaline microbial mat may have already been present in the precambrian thus microbial carbonate as a biomineral could be a record of metabolism throughout geological time

the landes de gascogne southwest france periglacial desert and cultural frontier during the palaeolithic abstract during the last glacial period a large part of the aquitaine basin southwest france was a periglacial desert comprising coversands with low relief dune fields surrounded by loess accumulations osl and radiocarbon dates show that the phase of maximum sand deposition coincides with marine isotope stage mis 2 peats and gleyic palaeosoils intercalated within the sands at some sites indicate that vegetation cover was able to develop locally during short events possibly d o interstadials due to raised groundwater levels in interdunal depressions few palaeolithic sites have been discovered in the coversand area in contrast to the peripheral loess region systematic survey along a future highway corridor demonstrates that this paucity of sites is not the result of insufficient survey nor deep site burial but rather reflects an archaeological reality this strongly suggests that the sand area was not attractive for hunter gatherer populations due to its reduced levels of water resources and available vegetation and animal biomass the distribution of cultural markers such as art items and projectile points also shows that the coversand area probably acted as a barrier separating two different cultural sub areas one in the pyrenees and cantabria the other in the perigord as a consequence the commonly accepted view that southwest france as a whole served as a refugia during the cold and arid phases of the pleistocene should be replaced by a more complex one that reflects the fact that a large part of the territory was almost unoccupied and that human populations were concentrated along alluvial valleys

high resolution simulations of the last glacial maximum climate over europe a solution to discrepancies with continental palaeoclimatic reconstructions the analyses of low resolution models simulations of the last glacial maximum lgm 21 kyr bp climate have revealed a large discrepancy between all the models and pollen based palaeoclimatic reconstructions in general the models are too warm relative to the observations especially in winter where the difference is of the order of 10 c over western europe one of the causes of this discrepancy may be related to the low spatial resolution of these models to assess the impact of using high resolution models on simulated climate sensitivity we use three approaches to obtain high resolution climate simulations over europe first an atmospheric general circulation model agcm with a stretched grid over europe second a homogeneous t106 agcm high resolution everywhere on the globe and last a limited area model lam nested in a low resolution agcm with all three methods we have performed simulations of the european climate for present and lgm conditions according to the experimental design recommended by the palaeoclimate modeling intercomparison project pmip model results have been compared with updated pollen based palaeoclimatic indicators for temperature and precipitation that were initially developed in pmip for each model a low resolution global run was also performed as expected the low resolution simulations underestimate the large cooling indicated by pollen data especially in winter despite revised slightly warmer reconstructions of the temperatures of the coldest month and show results in the range of those obtained in pmip with similar models the two high resolution agcms do not improve the temperature field and cannot account for the discrepancy between model results and data especially in winter however they are able to reproduce trends in precipitation more closely than their low resolution counterparts do but the simulated climates are still not as arid as depicted by the data conversely the lam temperature results compare well with climate reconstructions in winter but the simulated hydrological cycle is not consistent with the data finally these results are discussed in regard of other possible causes for discrepancies between models and palaeoclimatic reconstructions for the lgm european climate

lithofacies palaeoecology and palaeoenvironments of the agrio formation lower cretaceous of the neuquen basin argentina abstract the lithofacies and macrofossil guilds of the agrio formation upper valanginian lower barremian have been analysed using evidence from sedimentological taphonomic and palaeoecological studies the study area is agua de la mula and adjacent regions in central neuquen seven lithofacies have been recognized in the field which indicate that the agrio formation was deposited in an open marine ramp depositional system under storm influence lithofacies indicate conditions that range from low energy basin to high energy inner ramp outer and mid ramp deposits are the most abundant macrofossils have been grouped into 16 guilds based on tiering life habit and feeding category the guilds indicate normal benthic oxygen level normal salinity and soft firm muddy and sandy bottoms suspension feeders are more common than deposit feeders suggesting the predominance of suspended food particles over deposited food resources a low input of siliciclastics and possibly other palaeoceanographic conditions allowed the development of oolitic facies in the inner ramp and coral patch reefs in the upper mid ramp for a limited period of time

irregular glacial interstadials recorded in a new greenland ice core the greenland ice sheet offers the most favourable conditions in the northern hemisphere for obtaining high resolution continuous time series of climate related parameters profiles of 18o 16o ratio along three previous deep greenland ice cores1 3 seemed to reveal irregular but well defined episodes of relatively mild climate conditions interstadials during the mid and late parts of the last glaciation but there has been some doubt as to whether the shifts in oxygen isotope ratio were genuine representations of changes in climate rather than artefacts due to disturbed stratification here we present results from a new deep ice core drilled at the summit of the greenland ice sheet where the depositional environ ment and the flow pattern of the ice are close to ideal for core recovery and analysis the results reproduce the previous findings to such a degree that the existence of the interstadial episodes can no longer be in doubt according to a preliminary timescale based on stratigraphic studies the interstadials lasted from 500 to 2 000 years and their irregular occurrence suggests complexity in the behaviour of the north atlantic ocean circulation

the human settlement of central iberia during mis 2 new technological chronological and environmental data from the solutrean workshop of las delicias manzanares river valley spain abstract the recent excavations 2008 2009 conducted at the open air site of las delicias located in the manzanares river valley madrid have revealed new important data for the understanding of the human settlement of central iberia during solutrean times in this paper we present a geomorphological and taphonomic study of the pleistocene deposits of las delicias a technological analysis focused on the bifacial lithic reduction processes documented at the site new optically stimulated luminescence dates and new palynological data together with the existence of numerous solutrean lithic assemblages from the early 20th century excavations of the manzanares terraces these new data highlight the importance of the manzanares valley as a focus of solutrean settlement not only related to flint procurement but also to foraging activities moreover they require reconsideration of central iberia as a virtually unpopulated region during the late pleniglacial mis 2 and of the associated idea of its cultural dependence on the coastal areas of the iberian peninsula we propose new avenues of research aimed at approaching the central region of iberia in its own cultural and ecological terms

aptian dinosaur footprints from the apulian platform bisceglie southern italy in the framework of periadriatic ichnosites abstract new dinosaur tracks have been found near bisceglie bari apulia on loose blocks ascribed to the corato member late bedoulian to early gargasian of the calcare di bari fm the material consists of isolated footprints as well as of short trackways of quadrupedal and bipedal dinosaurs the new tracksite has yielded a quite differentiated dinosaur ichnocoenosis including theropod sauropod thyreophoran and ornithopod footprints the discovery of early aptian dinosaur footprints in the limestone of the carbonate platform of southern italy gives new insights on dinosaur distribution and new palaeontological constraints for the palaeogeographic reconstruction of the mediterranean tethys during the cretaceous the analysis of this and others ichnosites of the periadriatic carbonate platforms gives evidence of repeated emersions and of widespread land vertebrates dwelling the characteristics of the associations suggest that the trackmakers did not constitute a real coevolved association but the occasional co occurrence of taxa after migration the results emphasize the need of both structural and environmental continuity and walking ways between a southern continent and the periadriatic carbonate platforms during the early cretaceous

contrasting impacts of dansgaard oeschger events over a western european latitudinal transect modulated by orbital parameters abstract terrestrial and marine proxies pollen planktic and benthic foraminiferal oxygen isotopes alkenone and foraminifer derived sea surface temperatures ssts ice rafted debris from images deep sea cores md95 2042 and su81 18 37 n 10 w md99 2331 and md03 2697 42 n 9 w and md04 2845 45 n 5 w show that western european and offshore environments were strongly affected by dansgaard oeschger d o and heinrich h events we concentrate here on latitudinal variability in the forest cover extent and composition of western europe during the succession of d o events showing new pollen records for core md04 2845 and for marine isotopic stages mis 3 and 4 of core md99 2331 in general cold ssts characteristic of greenland stadials were contemporaneous with the expansion of semi desert or steppic vegetation while greenland interstadials were synchronous with the expansion of forest our data reveal that the amplitude of atlantic and mediterranean forest expansions differs for any given d o warming during the glacial period 74 18 ka in the western mediterranean d o 16 17 and d o 8 and 7 corresponding to minima in precession were associated with strong expansion of forest cover contrasting with weak expansion of forest cover during d o 14 and 12 the opposite pattern is revealed at the atlantic sites further north the strongest greenland warmings are recorded for d o 19 11 and 8 this contrasting latitudinal climatic scenario is compared with other northern hemisphere records revealing similarities between the mediterranean climate and the asian monsoon regime which may relate to a summer atmospheric teleconnection between the two regions comparable to the present day situation parallels between mediterranean climate enhancement and peaks in global methane ch 4 during the last glacial period suggest a significant role of monsoon activity in determining ch 4 emission from wetlands

climatic changes in eurasia and africa at the last glacial maximum and mid holocene reconstruction from pollen data using inverse vegetation modelling in order to improve the reliability of climate reconstruction especially the climatologies outside the modern observed climate space an improved inverse vegetation model using a recent version of biome4 has been designed to quantitatively reconstruct past climates based on pollen biome scores from the biome6000 project the method has been validated with surface pollen spectra from eurasia and africa and applied to palaeoclimate reconstruction at 6 cal ka bp calendar years the climate was generally wetter than today in southern europe and northern africa especially in the summer winter temperatures were higher 1 5 c than present in southern scandinavia northeastern europe and southern africa but cooler in southern eurasia and in tropical africa especially in mediterranean regions summer temperatures were generally higher than today in most of eurasia and africa with a significant warming from 3 to 5 c over northwestern and southern europe southern africa and eastern africa in contrast summers were 1 3 c cooler than present in the mediterranean lowlands and in a band from the eastern black sea to siberia at 21 cal ka bp a marked hydrological change can be seen in the tropical zone where annual precipitation was 200 1 000 mm year lower than today in equatorial east africa compared to the present a robust inverse relationship is shown between precipitation change and elevation in africa this relationship indicates that precipitation likely had an important role in controlling equilibrium line altitudes ela changes in the tropics during the lgm period in eurasia hydrological decreases follow a longitudinal gradient from europe to siberia winter temperatures were 10 17 c lower than today in eurasia with a more significant decrease in northern regions in africa winter temperature was 10 15 c lower than present in the south while it was only reduced by 0 3 c in the tropical zone comparison of palaeoclimate reconstructions using lgm and modern co2 concentrations reveals that the effect of co2 on pollen based lgm reconstructions differs by vegetation type reconstructions for pollen sites in steppic vegetation in europe show warmer winter temperatures under lgm co2 concentrations than under modern concentrations and reconstructions for sites in xerophytic woods scrub in tropical high altitude regions of africa are wetter for lgm co2 concentrations than for modern concentrations because our reconstructions account for decreased plant water use efficiency

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

dolomite formation within microbial mats in the coastal sabkha of abu dhabi united arab emirates microbial mediation is the only demonstrated mechanism to precipitate dolomite under earth surface conditions a link between microbial activity and dolomite formation in the sabkha of abu dhabi has until now not been evaluated even though this environment is cited frequently as the type analogue for many ancient evaporitic sequences such an evaluation is the purpose of this study which is based on a geochemical and petrographic investigation of three sites located on the coastal sabkha of abu dhabi along a transect from the intertidal to the supratidal zone this investigation revealed a close association between microbial mats and dolomite suggesting that microbes are involved in the mineralization process observations using scanning electron microscopy equipped with a cryotransfer system indicate that authigenic dolomite precipitates within the exopolymeric substances constituting the microbial mats in current models microbial dolomite precipitation is linked to an active microbial activity that sustains high ph and alkalinity and decreased sulphate concentrations in pore waters such models can be applied to the sabkha environment to explain dolomite formation within microbial mats present at the surface of the intertidal zone by contrast these models cannot be applied to the supratidal zone where abundant dolomite is present within buried mats that no longer show signs of intensive microbial activity as no abiotic mechanism is known to form dolomite at earth surface conditions two different hypotheses can reconcile this result in a first scenario all of the dolomite present in the supratidal zone formed in the past when the mats were active at the surface in a second scenario dolomite formation continues within the buried and inactive mats in order to explain dolomite formation in the absence of active microbial metabolisms a revised microbial model is proposed in which the mineral template properties of exopolymeric substances play a crucial role

epigenetic dolomitization and the origin of xenotopic dolomite texture abstract xenotopic texture which is commonly observed in pre cenozoic rocks is defined here as a mosaic of anhedral crystals with irregular or curved intercrystalline boundaries and usually undulatory extinction xenotopic dolomite texture is similar in appearance to neomorphic limestone textures idiotopic dolomite texture euhedral to subhedral crystals with straight intercrystalline boundaries contrasts with xenotopic texture and is commonly observed in both cenozoic and more ancient dolomites texture may be controlled by the temperature at which crystals grow crystal growth theory predicts that at low temperature a smooth crystal surface is energetically favored and atoms are added to crystal faces layer by layer with dislocations acting as nucleation sites this results in faceted crystals and euhedral to subhedral crystal mosaics above a critical roughening temperature crt a rough surface is energetically favored surface nucleation does not require dislocations and atoms are randomly added to the crystal surface resulting in nonfaceted growth and an anhedral crystal mosaic it is hypothesized that a critical roughening temperature exists for dolomite above 50 c xenotopic dolomites are produced by dolomitization of limestone and or neomorphic recrystallization of dolomite at elevated temperature above the crt after burial idiotopic dolomites are produced below the crt by near surface processes and are occasionally produced above crt if growth inhibiting effects of the solution or impurities stabilize crystal faces calcite has a crt below 25 c and therefore develops anhedral crystal mosaics characteristic of neomorphic texture both at near surface and at elevated temperatures synthetic xenotopic dolomite was produced in the laboratory at 250 c and 300 c by dolomitization of aragonite and calcite skeletal fragments and by recrystallization neomorphism of nonstoichiometric cenozoic dolomites xenotopic dolomite resulted from the metamorphic recrystallization of the idiotopic hueco dolomite permian texas near the marble canyon intrusion at temperatures between 350 c and 600 c hydrothermal dolomitization of periclase calcite marble near the intrusion also resulted in a xenotopic texture xenotopic dolomite in the galena group ordovician wisconsin was produced by neomorphism of a preexisting dolomite during the emplacement of lead zinc sulfides at temperatures between 80 c and 227 c in the trenton limestone ordovician michig n xenotopic dolomite replaced limestone during the migration of hot 50 c fluids along fracture systems xenotopic dolomite was not observed in cenozoic dolomites that were subjected to temperatures near surface values only

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

aeolian fluvial interactions and high resolution sequence stratigraphy of a non marine lowstand wedge the avile member of the agrio formation lower cretaceous central neuquen basin argentina abstract accumulation within the unconformity based hauterivian avile sandstone oftheneuque nbasin argentina wascharacterizedbyacloseinteractionbetween uvialandaeolianprocessesdevelopedafteramajorrelativesea leveldropthatalmostcompletely desiccated the entire basin and juxtaposed these non marinedeposits on shallow and deep marine facies aeolian deposits within the avile memberincludedune a1 andsandsheet a2 unitsthatcharacterizethelowerpart of the unit fluvial deposits comprise distal ood units f1 interbeddedwith aeolian dune deposits in the middle part of the succession and low f2 and high sinuosity f3 channels associated with oodplain deposits f4 towards the top the internal characteristics of the aeolian system indicate thatits accumulation was strongly controlled by water table dynamics with thedevelopment of multiple horizontal de ation super surfaces that truncate dunedeposits and form the basal boundary of ood deposits and sand sheet units along term wetting upward trend is recorded throughout the entire unit with anincrease in uvial activity towards the top and the development of a morepermanent uvial system overlying a major erosion surface interpreted as asequence boundary the upward increase in water table in uence might berelated to relative sea level rise which controlled the position of the water tableand allowed the accumulation of tabular aeolian units bounded by horizontalde ation surfaces this high frequency eustatically driven process actedtogether with a long term climatic change towards wetter conditions keywords aeolian uvial interactions argentina avile sandstone creta ceous neuque n basin water table introductionseveral authors have described intertonguingbetween aeolian and uvial deposits in differentbasins suggesting that the interaction betweenthese two processes is common in both modernenvironments langford 1989 and the rockrecord langford chan 1989 herries 1993 thelowercretaceous hauterivian avile sand stone member of the agrio formation is excep tionally well exposed in the central part of theneuque n basin it consists of aeolian and uvialdeposits intercalated between ammonite bearingshales of the lower and upper members of theagrioformation fig 1 ithasbeeninterpretedasa lowstand wedge produced by a major relativesea level drop legarreta gulisano 1989 although the avile sandstone has been dis cussed in terms of its depositional environments veiga vergani 1993 and aeolian processes

global glacial isostasy and the surface of the ice age earth the ice 5g vm2 model and grace abstract the 100 kyr quasiperiodic variation of continental ice cover which has been a persistent feature of climate system evolution throughout the most recent 900 kyr of earth history has occurred as a consequence of changes in the seasonal insolation regime forced by the influence of gravitational n body effects in the solar system on the geometry of earth s orbit around the sun the impacts of the changing surface ice load upon both earth s shape and gravitational field as well as upon sea level history have come to be measurable using a variety of geological and geophysical techniques these observations are invertible to obtain useful information on both the internal viscoelastic structure of the solid earth and on the detailed spatiotemporal characteristics of glaciation history this review focuses upon the most recent advances that have been achieved in each of these areas advances that have proven to be central to the construction of the refined model of the global process of glacial isos

heinrich events massive late pleistocene detritus layers of the north atlantic and their global climate imprint 1 millennial climate oscillations of the glacial interval are interrupted by extreme events the so called heinrich events of the north atlantic their near global footprint is a testament to coherent interactions among earth s atmosphere oceans and cryosphere on millennial timescales heinrich detritus appears to have been derived from the region around hudson strait it was deposited over approximately 500 250 years several mechanisms have been proposed for the origin of the layers binge purge cycle of the laurentide ice sheet jokulhlaup activity from a hudson bay lake and an ice shelf buildup collapse fed by hudson strait to determine the origin of the heinrich events i recommend 1 further studies of the timing and duration of the events 2 further sedimentology study near the hudson strait and 3 greater spatial and temporal resolution studies of the layers as well as their precursory intervals studies of previous glacial intervals may also provide important constraints

changes in sea surface hydrology associated with heinrich event 4 in the north atlantic ocean between 40 and 60 n abstract the changes in distribution of sea surface temperature and salinity in the north atlantic between 40 and 60 n were reconstructed for the time interval between 40 and 30 kyr bp which includes the large iceberg discharge event associated with the deposition of heinrich layer 4 we found that the meltwater input during deposition of heinrich layer 4 resulted in a 1 2 kyr temperature decrease of about 2 c and a salinity decrease in the range of 1 5 3 5 between 40 and 50 n sites above 50 n did not experience significant salinity variations a much larger area was affected by the reduction in sea surface temperature the amplitude of the sea surface temperature shift was however much smaller than the atmospheric temperature changes over greenland at gisp and grip sites

a possible bridge between adria and africa new palaeobiogeographic and stratigraphic constraints on the mesozoic palaeogeography of the central mediterranean area abstract dinosaur records in central and southern italy testify to the occurrence of a diverse dinosaur fauna on the apennine and apulian carbonate platforms at least from the tithonian to the santonian most of the palaeogeographic reconstructions show these domains as topographically isolated areas separated by deep pelagic basins and far from emerged continental areas thus they hardly justify the long lasting occurrence of these terrestrial vertebrates recent studies on the mesozoic panormide carbonate platform western sicily yielded important stratigraphical and palaeontological data which provide evidence for a convincing explanation of this unresolved problem the recent discovery of a theropod bone in mid cretaceous peritidal levels of the panormide platform as well as the anomalous subsidence of this palaeogeographic domain strongly support the existence of a crustal sector filtering bridge which connected africa to adria