magnetic susceptibility as a high resolution correlation tool and as a climatic proxy in paleozoic rocks merits and pitfalls examples from the devonian in belgium low field magnetic susceptibility in measurements are quick and sensitive enabling the creation of high resolution records making in an attractive correlation tool and a proxy for paleoclimate and paleoenvironments in geologically young material foremost in cenozoic sediments in belongs to the geoscientist s toolkit however in is a convolved signal and may reflect other processes than the often implicitly inferred depositional conditions diagenesis remagnetization and low grade metamorphism can potentially obscure the original depositional in signal this aspect is particularly important when interpreting in records from paleozoic rocks here we review data obtained from a large sample collection of middle to upper devonian sections in belgium comparison of in trends with paleoenvironmental indicators facies and with detrital input proxies zr th ti al allowed to assess the persistence of depositional trends furthermore the in signal was deconvolved into its dominant mineralogical contributions with the help of magnetic property analysis the main results are pointing to a magnetic signal dominated by fine grained magnetite of which paleomagnetic analysis indicated a formation during carboniferous remagnetization this prompts a potentially strong influence of post depositional processes and it complicates the interpretation of in records in terms of depositional environments however in most of the sections there is a relatively good relationship between in trends and facies evolution and between in and geochemical proxies for detrital inputs this indicates that the newly formed magnetite grains would at least partly remain where they are formed and this allows a relative preservation of the original signal despite the strong influence of diagenesis two sections show a stronger impact of diagenesis where for about half of these sections the primary depositional information is lost the eifelian givetian monts de baileux section was selected for time series analysis of the in series the average spectral misfit asm method is applied to explicitly evaluate the null hypothesis of no orbital signal and in this section there is 99 05 chance that the ms signal is reflecting an orbital imprint

pedogenic carbonate formation recrystallization versus migration process rates and periods assessed by 14c labeling 1 under arid to semihumid climatic conditions dissolution of primary carbonate and recrystallization with carbon c from soil co2 leads to accumulation of significant amounts of pedogenic secondary carbonate most soils of arid and semiarid regions contain a carbonate accumulation horizon the depth of which is related to climatic conditions and properties of parent material it remains unclear whether this carbonate migrates from the upper horizons before or after recrystallization with soil co2 the aim of this study was to determine recrystallization rates during initial pedogenesis and to estimate the accumulation depth of secondary carbonate based on c isotopic exchange during secondary carbonate formation in an experiment with alternating moisture conditions maize grown on 1 m high loess filled columns was pulse labeled in14co2 atmosphere every 3 weeks after 6 months portions of secondary recrystallized caco3 were determined in 5 cm segments based on 14c respired in the rhizosphere and subsequently incorporated into newly formed secondary carbonate more than 80 of recrystallized carbonate ca14co3 was leached from the uppermost 15 cm of the loess column and more than 70 of total secondary carbonate were accumulated in a depth between 15 and 50 cm based on the recrystallization rate calculated for the uppermost 15 cm of the loess column 1 77 0 26 10 5 day 1 between 300 and more than 1 700 years are necessary for complete decalcification of the upper 15 cm our modeled data are consistent with formation of calcic horizons under relatively humid conditions

relationships between heavy metals distribution and organic matter cycling in mangrove sediments conception bay new caledonia mangroves of new caledonia act as a buffer between a lagoon of more than 20 000 km2 and the island which suffers intense processes of erosion resulting from urbanization and natural resources exploitation this preliminary study aims at determining how heavy metals are distributed in mangrove sediments and pore waters in relationship with their organic content to reach our goal a series of 50 cm deep cores were collected in the mangrove of conception bay the various coring sites are representative of live forests avicennia marina rhizophora stylosa dead forest and intertidal unvegetated area the ranges of concentrations in sediments were the following mol g 1 cu 0 08 to 0 51 co 0 01 to 0 38 ni 0 03 to 3 55 cr 0 36 to 3 11 zn 0 68 to 2 36 mn 1 13 to 5 0 and fe 22 64 to 721 69 heavy metals distribution within sediments and pore water appear to result from diagenetic processes linked to om decomposition beneath the dead avicennia forest and in the unvegetated sediments the higher the organic content the higher the metal concentration in the solid phase beneath living mangrove stands despite a higher organic content as well as higher sulphur content heavy metals concentrations were not higher than those measured in the other sampling sites beneath these forests redox conditions were mainly controlled by the length of waterlogging and the activity of root system we suggest that because of the specificity of the avicennia root system and its position in the intertidal zone heavy metals are more bioavailable and potentially more mobile than beneath rhizophora stand

cyclicities in triassic platform carbonates synchronizing radio isotopic and orbital clocks sedimentary cycles recorded in young sediments are often attributed to fluctuations of the earth s climate on a 10 4 10 6 year scale which in turn is governed by periodic variations in solar insolation linked to orbital milankovitch parameters a spectacular example of cyclic stratal patterns in ancient deposits is the middle triassic latemar carbonate platform w dolomites n italy based on spectral analyses from previous studies a superimposition of precession 20 ka and eccentricity 100 ka controlled sea level fluctuations has been suggested to account for the stacking hierarchy at latemar with 20 ka being assigned to each highest order depositional cycle zircon u pb isotopic ages from volcanic ash layers within the cyclic succession corroborated by biostratigraphic constraints suggest that the average time interval for every individual cycle is significantly smaller than the shortest milankovitch period and therefore challenge previously published interpretations relating distinct spectral peaks to the above mentioned hierarchy however our new spectral data indicate that cyclicities resembling milankovitch characteristics might exist but on an entirely different scale our findings show that frequency spectra should only be interpreted in combination with robust age control they also encourage the search for complementary mechanisms controlling carbonate deposition

influence of sedimentary setting on the use of magnetic susceptibility examples from the devonian of belgium bulk magnetic susceptibility measurements on sedimentological samples from all geological periods have been used widely in the last two decades for correlations and as a proxy for sea level variations this paper explores the link between magnetic susceptibility depositional setting and environmental parameters these environmental parameters include distal proximal transects microfacies successions and fourth order trends on different carbonate platform types platform ramp carbonate mound or atoll during different devonian stages eifelian givetian and frasnian average magnetic susceptibility values over a distal proximal trending facies succession vary markedly with depositional setting on carbonate platforms average magnetic susceptibility generally increases towards the top of shallowing upward sequences on a distal proximal transect average magnetic susceptibility is intermediate for the deepest facies decreases for the reef belts and increases to a maximum in the back reef zone in ramps and atolls magnetic susceptibility trends clearly differ average magnetic susceptibility generally decreases towards the top of shallowing upward sequences and is highest in the deepest facies the strong relationship between magnetic susceptibility facies and sequences implies a strong environmental influence however the different responses in the different platform types suggest that sea level changes leading to variation in detrital input is not the only parameter controlling average magnetic susceptibility values other primary or secondary processes also probably influenced magnetic mineral distribution primary processes such as carbonate production and water agitation during deposition are probably key factors when carbonate production is high the proportion of magnetic minerals is diluted and the magnetic susceptibility signal decreases high water agitation during deposition will also selectively remove magnetic minerals and will lead to low average magnetic susceptibility values these parameters explain the lowest values observed on the reef platform inner ramp and atoll crown which are all in areas characterized by higher carbonate production and greater water agitation during deposition the lowest values observed in the lagoon inside the atoll crown can be related to detrital isolation by the atoll crown however other parameters such as biogenic magnetite production or diagenesis can also influence the magnetic signal diagenesis can change magnetism by creating or destroying magnetic minerals however the influence of diagenesis probably is linked strongly to the primary facies permeability amount of clay or organic matter and probably enhanced the primary signal the complexity of the signal gives rise to correlation problems between different depositional settings thus while magnetic susceptibility has the potential to be an important correlation tool the results of this investigation indicate that it cannot be used without consideration of sedimentary processes and depositional environments and without strong biostratigraphical control

magnetostratigraphy susceptibility of the přidolian lochkovian silurian devonian gssp klonk czech republic and a coeval sequence in anti atlas morocco abstract the magnetosusceptibility event and cyclostratigraphy msec record for the p idolian lochkovian silurian devonian global boundary stratotype section and point gssp klonk prague basin czech republic is described and used to establish a magnetostratigraphy susceptibility profile for the gssp gssp msec data are summarized into three magnetozones msz the tma msz late p idolian with 13 msszs mssz the klonk msz latest p idolian and earliest lochkovian with 17 msszs and the voskop msz early lochkovian with 7 msszs the base of klonk mssz 2 is coincident with the base of lochkovian and the devonian the proposed magnetostratotype for the p idolian lochkovian boundary is supported by ms data from a nearby core through the gssp sequence and into the upper ludlow three additional mszs are recognized for the portion of the core sequence older than the gssp boundary sequence the extension of the mszs and msszs away from the proposed magnetostratotype is tested by comparison with a lochkovian sequence in the western sahara of southeastern morocco mszs are the result of global sea level fluctuations that alter base level and the pattern of erosion and influx of detrital paramagnetic mineral components into the marine environment large scale transgressive and regressive patterns interpreted from the msec data establish that the silurian devonian boundary in the barrandian region falls between a short lived transgressive pulse in the latest p idolian and an equally short lived regressive pulse in the earliest lochkovian msszs identified in the gssp and core sequences are the result of variation in climate cycles and the resulting periodicity can explained by either the 38 9 ka silurian and devonian equivalent of the modern 54 ka obliquity cycle or the eccentricity cycle of 106 ka periodicity use of the obliquity periodicity gives a duration for the barrandian lochkovian of 4 46 ma which agrees with the most recent geochronometric estimate of 4 5 ma for the lochkovian use of the eccentricity periodicity gives a duration for the barrandian lochkovian of 12 16 ma which agrees with the previous geochronometric estimates of 12 2 and 12 5 ma for the lochkovian in any case the cyclic nature of the msec data established by the msszs can be explained by variations in the rate of supply of weathered terrigenous paramagnetic grains to the marine system these variations in supply occurred due to climate changes resulting from the either the obliquity or eccentricity of the earth s orbit knowledge of the periodicity of lochkovian cycles in the barrandian area allows estimation of the rates of sediment accumulation the duration of fossil ranges and the rates of evolution depending on the choice of obliquity or eccentricity to explain the cyclicity in the barrandian lochkovian the estimated rate of sediment accumulation in the gssp outcrop averaged either 51 or 140 ka m the range of the graptoloid monograptus uniformis angustidens wholly contained within the lochkovian sequence at the gssp is also estimated at either 51 or 140 ka

the role of ocean atmosphere reorganizations in glacial cycles abstract a case is made that glacial to interglacial transitions involve major reorganizations of the ocean atmosphere system such reorganizations constitute jumps between stable modes of operation which cause changes in the greenhouse gas content and albedo of the atmosphere only in this way can the rapidity of glacial terminations the hemispheric synchroneity and symmetry of mountain glaciation and the large polar air temperature and dustiness variations be accounted for if these reorganizations are driven in some fashion by orbitally induced seasonal insolation changes then the connection between insolation and climate is most likely through impacts of fresh water transport on the ocean s salinity distribution

structure and composition of calcified roots and their identification in calcareous soils abstract fine white branching structures isolated from calcareous soils in southern france were shown by microscopy and by chemical and mineralogical analysis to be calcified roots these structures occur mainly in rendzinas calcic xerosols and cambisols that are dense or rich in fines and where drainage is slow visible to the naked eye they can locally represent up to a quarter of the soil mass calcified roots consist of calcite elements whose mean size varies from 60 to 80 m and which retain the structure of the original cells of the root cortex each calcified cell has a central nucleus composed of two crystals on average and is coated with a thin mineral layer that seems to be poorly crystallized some retain organic remnants and the structure of cell walls calcified cells contain tubes less than 1 m in diameter which appear to have formed by weathering although they have generally not been recognized as calcified roots similar microstructures have been indicated in some calcareous soils and calcretes both present day and ancient ones that suggests that calcified roots are widespread and that their occurrence contributes to the genesis of some calcareous soils

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

repetitions and cycles in stratigraphy abstract stratigraphic sections show repetitions of similar or identical conditions on all scales from millimeters to many hundreds of meters representing time intervals from possibly seconds to many millions of years any such repetitions have been called cycles to understand the reason why cycles occur a time scale is essential beds can be with or without time information the latter are known as event stratifications the event which triggers the formation of beds or any succession of sediments could be a random effect or it could be part of a mechanism in which cyclic behaviour is due to an oscillating physical system such systems are dynamic systems which means that they involve the transport of masses over distances and in definite time intervals cycles generated by such systems can be used as time units a special example is the earth solar system which can generate cycles from daily periods to orbital variations of thousands and millions of years orbital variations are known as milankovitch cycles and they are the subject of cyclostratigraphy proper the recognition of milankovitch cycles or of any other cycle associated with oscillating systems rests on the regularity or time periodicity of such patterns the correct ways of analysing such cycles are the methods of time series analysis repetition patterns representing time intervals of millions and possibly many hundreds of millions of years are known from sequence stratigraphy we know as yet very little about the mechanisms which generate such long periods of repetition it has been suggested that the earth s crust has reached a state of self organized criticality bak p 1996 how nature works springer new york 212 pp in which case sequence formation could be part of the complexity which undoubtedly is an attribute of the earth s crust and history

triassic latemar cycle tops subaerial exposure of platform carbonates under tropical arid climate the triassic latemar platform in the dolomites italy is the site of several ongoing controversies perhaps the most interesting debate focuses on apparent cyclic deposition within the latemar platform whose nature and duration are still open to debate further disagreement concerns the lack of meteoric diagenesis related isotope shifts at cycle tops that bear circumstantial petrographic evidence for subaerial emergence here an evaluation of the nature of latemar cycle tops is presented combining evidence from previous work and new field petrographic and geochemical data cycle tops are ranked according to increasing exposure duration and spatial extent type i surfaces lacking unequivocal evidence of prolonged supratidal conditions type ii dolomite caps formed in warm evaporitic intertidal lagoonal waters followed by exposure of perhaps intermediate duration type iii clastic rich red calcareous horizons with some showing platform wide extent representing prolonged supratidal conditions and type iv discontinuities in tepee belts genetically related to type ii and iii surfaces but likely representing shorter lived exposure stages petrographic and geochemical criteria indicate that most diagenesis occurred in the shallow marine and burial domain whilst an extensive meteoric overprint of cycle tops is lacking this is underlined by the scarcity of meteoric diagenetic fabrics such as gravitational cements that where present are here interpreted as marine vadose in origin the scarcity of carbon and oxygen isotope signatures commonly assigned to subaerial exposure stages is best explained in the context of mid triassic climate the low latitude tropical but arid setting of the latemar situated in the western extension of the tethys ocean its isolation from nearby continental areas and overall short term emergence episodes are in agreement with a limited degree of meteoric alteration of most cycle tops high amounts of aeolian clastic material beneath some cycle tops along with high fe and mn elemental abundances argue for intermittent subaerial conditions this study proposes an enhancement of the classical allan and matthews 1982 isotope model for subaerial exposure under strongly arid climates as the subaerial exposure nature of latemar cycle tops and therefore eustasy as the cause for cyclicity have been previously challenged due to the lack of meteoric induced isotopic signatures the outcome of this study is of significance for the ongoing latemar stratigraphic controversy

progradation geometries of carbonate platforms examples from the triassic of the dolomites northern italy various types of progradation of triassic carbonate platforms are described from the dolomites of the southern alps the internal and external geometric relationships are exposed in spectacular natural sections and moreover their scale 500 1000 m of thickness is such that they can be compared with features found in seismic profiles the different types of progradation are controlled by a number of factors which normally interact with each other these factors include rate of basinal sedimentation rate of subsidence width of the platform depth of the surrounding basin and eustatic variations of sea level progradation is not a continuous process but episodic moments of massive debris input during which the platform advances alternate with long periods of negligible progradation during which basinal sediments accrete and onlap the toe of slope upper boundary relationships of the prograding platforms include offlap toplap and erosional truncation lower boundary relationships are horizontal climbing and descending progradations a variety of phenomena and circumstances have caused the cessation of progradation of the triassic platforms they include volcanism collapse of margins drowning rapid relative rise of sea level subaerial exposure relative fall of sea level and probably a natural decay of the system in the triassic of the dolomites two main progradation models can be put forward in the ladinian model progradation took place simultaneously with aggradation relative rise of sea level whereas the characteristic feature of the carnian model is toplap relative stillstand of sea level

magnetic susceptibility evolution and sedimentary environments on carbonate platform sediments and atolls comparison of the frasnian from belgium and alberta canada article i nfo magnetic susceptibility ms measurements on carbonate rocks are considered as a proxy for impurities delivered to the carbonate environments in the absence of strong climatic or tectonic variations bulk ms values have been linked to sea level variations because sea level fall increases clastic supply and therefore increases in magnetic mineral deposition in this paper we explore the relationship between the average magnitude of bulk ms with shallowing up sequences and facies evolution in different devonian carbonate complexes similarities and differences between these parameters have been scrutinized in carbonate attached platform and detached platforms mounds and or atolls from belgium and canada in the carbonate attached platforms from belgium and canada the ms patterns are directly related to depositional environment mean ms values increase from the most distal towards the most proximal facies and towards the top of the majority of fourth order shallowing up sequences these trends are in agreement with theoretical background ms increases with regression

magnetosusceptibility event and cyclostratigraphy method applied to marine rocks detrital input versus carbonate productivity magnetic susceptibility data from marine rocks can be used for global correlation due to synchronous variations in global erosion we show here that the magnetic susceptibility signature found in two forms resides mainly in paramagnetic and other detrital constituents in most marine rocks the first form is a short term low magnitude high frequency cyclic climate signature that is often useful for regional correlation the second form is a longer term higher magnitude low frequency signature resulting from transgressive and regressive events that can be used for global correlation fluctuations in detrital input due to eustatic based erosion are the primary cause of events these fluctuations are driven by large scale processes such as global orogenic cycles however variations in carbonate productivity cannot be ruled out when explaining the low magnitude climate driven cyclicity also observed in magnetic susceptibility data sets

evolution of chernozems in the northern caucasus russia during the second half of the holocene carbonate status of paleosols as a tool for paleoenvironmental reconstruction abstract a chronosequence of chernozems buried under kurgans funeral mounds dated archaeologically to 5000 3800 4000 and 1600 1700 years bp as well as the modern surface chernozems were studied to reconstruct environmental change in the central northern caucasus in the second half of the holocene special emphasis was made on the detailed morphological and analytical characteristics of pedogenic carbonates and microscopic investigation of phytoliths in the paleosols buried 5000 years bp carbonates represented by compact micritic pedofeatures are in the uppermost part of the solum neoformed gypsum is found below this differs from the features of the modern soils and the paleosols buried 1600 1700 years bp in which the upper part of the profile is leached pedogenic carbonates occur mostly in the form of diffuse pseudomycelium impregnations and fine films whereas gypsum is absent the comparison of morphological features of the paleosols and the modern soils confirms the general tendency of paleoenvironment evolution from warm and dry in the atlantic period to cooler and more humid in the late subboreal and subatlantic periods the compaction of soil mass and tonguing of humus horizon together with some dissolution of carbonate pedofeatures and signs of high biological activity in the paleosols buried 3800 4000 years bp are thought to indicate contrasting seasonal and annual variations of precipitation in early subboreal period presence of calcified root cells of perfect habit in the paleosols of this chronointerval is also interpreted as evidence of contrasting seasonal climate hard carbonate nodules were found in all chernozems of the chronosequence the size of nodules their internal porosity and recrystallization phenomena increase with age we assume nodules to be relict pedofeatures in the subatlantic paleosols and modern soils which were transformed but not completely destroyed during the late holocene humidification and enhancement of leaching thus a multiphase model of carbonate pedofeatures formation is dominant in the soils studied phytolith assemblages indicate meadow steppe vegetation in the atlantic period later in the subboreal and subatlantic periods forest vegetation appears meadow with some steppe elements associations also determined in the late holocene profiles probably reflect anthropogenic deforestation these results are in good agreement with the interpretation of paleosol s properties we conclude that complex characteristic of pedogenic carbonates which we define with the term carbonate status is one of the most valuable sources of the paleogeographical information in the chronosequences of steppe and forest steppe soils

small scale secondary caco3 accumulations in selected sections of the european loess belt morphological forms and potential for paleoenvironmental reconstruction eighteen important quaternary loess paleosoil sites have been studied across the european loess belt they included approximately 50 buried soils the over and or underlying loess and the present day surface soils where possible from the numerous types of secondary caco3 accumulations recognized only the small scale accumulations are discussed in this paper including calcified root cells caco3 hypocoatings needle fiber calcite powdery calcite coatings earthworm biospheroliths and calcite pseudomorphs on gypsum most of the features studied are found in the rhizosphere microecosystem each of these features showed a unique relationship with organic matter micro organism and plant distribution moisture and leaching processes for example the exceptional abundance of calcified root cells is an indicator of a long stability of soil surface during favorable climatic conditions needle fiber calcite is related to biomineralization of saprophytes in soils with sufficient moisture and decomposing organic matter the presence of powdery calcite coatings covering clay and mn coatings in non calcareous soils indicates a change from leaching to non leaching soil moisture regimes earthworm biospheroids provide arguments for a relative stability of the soil surface without rapid burial processes or drastic prolonged water stress finally gypsum pseudomorphs are indicators of changes in local climatic parameters in addition to a discussion of the genesis and the dynamics of the various accumulations several examples are given to show how these accumulations can be used as indicators of a changing environment such as renewed loess deposition the extent of drought or varying intensity of leaching during the year to conclude various forms of small scale secondary caco3 accumulations are common in the loess paleosoils and each type has the potential to contribute to a better understanding of the evolution of the paleoenvironment therefore it is proposed that their individual presence or absence throughout the pedostratigraphical levels and throughout the paleo topography should be recorded at all scales of observation

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

distribution and genesis of calcitic pedofeatures within a rapidly aggrading loess paleosol sequence in china abstract the distribution of calcitic pedofeatures within part of a buried paleosol complex on gaolanshan mountain near lanzhou in the western semi arid part of the loess plateau of china is interpreted in terms of a pedosedimentary model controlled by changes in dominance of regional climatic monsoonal forces during periods of moderate loess accumulation rates and moisture availability accretionary pedogenesis was characterised by localised dissolution and redistribution of calcite and development of compound calcitic depletion concentration pedofeatures these took one of two forms i equigranular hypidiotopic calcitic coatings or infillings 100 350 m and calcitic depletion hypocoatings the reconstruction provides the basis for explaining the ubiquitous occurrence of high concentrations of sand size grains and nodules of calcite within weakly leached horizons of other paleosols in the western part of the loess plateau of china their presence reflects not only the influence of semi arid conditions prevailing during the main stable soil forming intervals but also preceding drier periods of accretionary pedogenesis associated with transitional changes in relative dominance of dry northwesterly winter monsoons responsible for the transport of the dust to that of moist southwesterly and southeasterly monsoons the study emphasises the general need for a pedosedimentary approach when attempting to interpret loess paleosol sequences

use of a limited area model nested in a general circulation model for regional climate simulation over europe a limited area model lam nested in a general circulation model gcm is applied to the simulation of wintertime january climate over europe the output of a coarse scale gcm is used to drive a high resolution lam over an area including central and western europe the british isles with adjacent oceans and the western mediterranean the models used are the community climate model ccm1 of the national center for atmospheric research ncar and the pennsylvania state university ncar mesoscale model mm4 the january climatology of a 10 year simulation with the standard ccm1 at a 7 5 4 5 r15 longitude latitude resolution is first analyzed the model simulates realistic average large scale circulations major storm tracks and large scale precipitation patterns over the region although cyclogenesis over the mediterranean is not captured due to the coarseness of the model topography using the output of the r15 simulation to provide driving lateral boundary conditions 10 januaries are simulated with the nested mm4 at 70 km grid point spacing a spacing sufficient to resolve the main topographical features and coastlines of western europe two storm cases simulated with the nested mm4 are discussed in detail which show how the model captures cyclogenetic processes over the mediterranean and in the lee of the alps and simulates realistic development of synoptic systems owing to its better representation of topography and coastlines the nested mm4 produces a regional distribution of climatic variables such as precipitation surface air temperature cloudiness and snow cover which is much more realistic than that of the driving ccm1 alone and compares well with high resolution observations

magnetostratigraphic investigations of the middle triassic badong formation in south china magnetostratigraphic sampling of the middle triassic badong formation in south china was conducted at three sections a dual polarity characteristic remanent magnetization chrm resolved from most samples by thermal demagnetization is shown to have been acquired prior to folding the primary nature of the chrm is corroborated by the discovery of the same magnetic polarity at equivalent stratigraphic levels in more than one section the relative sample vgp virtual geomagnetic pole latitudes define nine magnetozones for the three major constituent members of the formation comparison with the mid triassic magnetic polarity sequence observed from the western tethyan region appears to indicate that the bulk of the badong formation is anisian in age and that ladinian sediments are largely missing this agrees with palaeontological and stratigraphic evidence in the region and supports the view that ladinian regression is a major event in the geological evolution of south china which may signal the onset of amalgamation of the yangtze block yb with the north china block ncb

investigation of vegetation history of buried chernozem soils using near infrared spectroscopy nirs abstract the environmental conditions of the evolution of chernozems in central europe have not been satisfactory explained in this paper seven buried chernozems were investigated using near infrared spectroscopy nirs in order to get information about the former vegetation cover near infrared nir data were collected from organic matter of recent natural grasslands and forests the spectra from these two groups of soils were perfectly discriminated by a multivariate statistical analysis the statistical model was applied on the buried soils there are four types of vegetation development within the chernozems before the burial comparison to other paleoenvironmental proxies shows no major contradiction and confirms the potential of the nirs as a paleopedological proxy the identified changes of vegetation are from grassland vegetation to forest vegetation and vice versa these changes bring new data to the discussion about the pedogenesis of chernozems according to the radiocarbon dating buried soils developed and were preserved not only in the preboreal and the boreal but also in later phases of the holocene

an investigation of boundary forcing sensitivities in a regional climate model the sensitivity of a regional climate model to lateral upper and lower dynamical forcing is evaluated for a pan arctic domain the experiments focus on a month long case study of may 1990 but the results are shown to be extendable to january and july 1990 although the control simulation is found to adequately represent major tropospheric circulation features a large negative geopotential height bias of up to 700m is found at the upper levels of the model experiments find these biases are remedied through the replacement of a reflective rigid lid upper boundary condition with a local wave absorbing layer geopotential height biases are reduced to a maximum underestimation of only 50m at the upper boundary substantial improvement is also found in the simulated temperature and zonal wind profiles transient heat and momentum fluxes and stationary eddies as seen through the eliassen palm flux divergence with this wave absorbing upper boundary condition in place additional improvement is found using a gravity wave drag parameterization appropriate for this domain s 100km horizontal resolution additional sensitivity to lateral forcing is examined and the relative role of the upper boundary condition to skillful simulations within the arctic basin domain is discussed

paleoenvironmental reconstruction based on the morphology and distribution of secondary carbonates of the loess paleosol sequence at suttő hungary abstract micro and macroscale secondary carbonates were investigated from the loess paleosol sequence of sutt hungary as secondary carbonates are formed in pedosedimentary environments they designate how the microecosystem adapts to dust accretion besides pedogenic aspects the hints of diagenesis can be tracked especially concerning leaching effects the main goal of this study was to make an attempt whether the distribution related signals of secondary carbonates combined with their genetic properties can be used for paleoenvironmental reconstruction the elaborated method is wet sieving of bulk loess paleosol samples in order to 1 separate secondary carbonates to describe morphological properties partly with the help of scanning electron microscopy and 2 provide a depth related semiquantitative distribution the semiquantitative distribution is ordered to the marine isotope stage units of the sutt sequence mis 6 to 2 the mis 6 section is characterized by presumably slower dust accumulation and raises the possibility of a multiphase leaching history throughout the profile lower dust accumulation rates with increasing aridity are assumed upwards in mis 5 mis 4 is typified by arid conditions and the alternation of lower and higher dust accumulations certain properties of paleosol development and frost deformation related to secondary carbonates can be distinguished in mis 3 dust accumulation rates are presumed to be consistent upwards in this section during mis 2 different sedimentation stages are distinguished but generally they show a decreasing trend upwards to the modern soil this work serves as a complementary method which may help to refine the paleoenviromental signals of the sutt loess paleosol sequence to determine relative sedimentary phases the limitations of the method have to be taken into consideration as the results are semiquantitative

magnetostratigraphy and palaeoclimatic significance of late tertiary aeolian sequences in the chinese loess plateau summary the aeolian red clay sequence in the central part of the chinese loess plateau was investigated in an attempt to obtain magnetostratigraphic and palaeoclimatic records from the results we deduce that aeolian dust accumulation and the related east asia palaeomonsoon system began at least 7 6 myr ago and that the tibetan plateau had reached a significant elevation by that time the late tertiary palaeoclimatic history of the red clay as reflected by magnetic susceptibility is reconstructed for the time period 7 6 2 5 ma increases in aeolian dust accumulation for the last 7 6 myr appear to have a close relation with the uplift processes of the tibetan plateau the remarkable increase of aeolian dust accumulation beginning at 3 2 ma appears to reflect the influence of an increasing global ice volume on the east asian monsoon and aeolian dust accumulation

diagenetic versus detrital origin of the magnetic susceptibility variations in some carbonate frasnian famennian boundary sections from northern africa and western europe implications for paleoenvironmental reconstructions to provide a new insight into the diagenetic versus detrital origin of the magnetic susceptibility variations in ancient carbonate sequences a study was conducted within four frasnian famennian platform carbonate sections from germany france and morocco the study includes along section magnetic susceptibility and carbonate content measurements complemented by analyses of magnetic hysteresis parameters inorganic geochemistry and clay mineralogy our results show that the magnetic susceptibility evolution is dominantly controlled by the variations in the concentration of low coercivity ferromagnetic magnetite grains and to a lesser extent of paramagnetic clays in more detail hysteresis ratios suggest the coexistence of two magnetite populations with significantly different grain size 1 a dominantly coarse grained detrital fraction including a mixture of multi domain and single domain particles 2 an authigenic fine grained fraction composed of a mixture of single domain and superparamagnetic particles despite a diagenetic imprint on the clay assemblages no relationship is established between magnetic susceptibility and illite crystallinity therefore discarding a noticeable distortion of primary within section magnetic susceptibility evolution the overall inherited character of the magnetic susceptibility fluctuations is corroborated by a significant correlation of magnetic susceptibility with terrigenous proxies zr th the poorer correlation of magnetic susceptibility with the fe content is consistent with the existence of a very fine grained authigenic magnetite component that possibly induces a global magnetic susceptibility increase at the section scale but no distortion of the within section evolution the magnetic susceptibility curves presented here provide a general record of climate driven detrital influx and carbonate productivity through frasnian lower famennian times

micromorphology of calcitic features in highly calcareous soils of fars province southern iran abstract the micromorphology of calcitic pedofeatures in highly calcareous arid and semiarid soils of the fars province southern iran has been studied in order to determine their genesis and distribution in different climatic regions available soil moisture soil temperature soil texture vegetation and availability of calcium carbonate are amongst the main factors determining the type and morphology of calcitic features size and frequency of microcrystalline calcite nodules and coatings increase from aridic to xeric but decrease again towards the areas with a ustic moisture regime cytomorphic and acicular calcite are observed mainly in areas with an ustic moisture regime and a denser vegetative growth but rarely in xeric areas layered pendents of calcite are common beneath coarser fragments but are considered as relicts of a more humid paleoclimate calcite depletion pedofeatures are observed in xeric mesic areas with higher available soil moisture ultraviolet uv violet vl and blue light bl fluorescence and cathodoluminescence cl studies proved to be useful in differentiating in this region pedogenic from geogenic calcite all types of pedogenic calcite were uv and bl fluorescent but didn t show cl whereas limestone fragments showed cl but no uv bl fluorescence the absence of cl in the studied pedogenic calcite samples is suggested to be related to the oxidative environment hindering mobilisation of mn

weathering of carbonate materials in ancient maya constructions rio bec and dzibanche limestone and stucco deterioration patterns carbonate materials limestone and lime stuccos were widely used in ancient maya construction deterioration of these materials presents a major problem for the conservation of maya architectural heritage however the mechanisms of deterioration and their interaction with the diverse inner structures of these materials are still insufficiently understood we performed micromorphological and mineralogical research of the limestone alteration in the buildings of rio bec and stuccos in dzibanche two late classic maya sites in the southern yucatan peninsula dissolution and recrystallization of calcite were found to be universal and the most important weathering process in both materials dissolution is selective affecting mostly micrite larger crystals especially rhombohedral calcitic pseudomorphs developed after dolomite are more stable selective dissolution of micritic cement of limestones and stuccoes enhances physical breakdown by producing numerous pores and loosening bounds between coarser inclusions this process clearly controls the deterioration grade of different limestones those with more intensive fragmentation and powdering have higher contents of micrite secondary carbonates are represented mostly by acicular calcite filling fissures and forming coatings on the outer surface clear spatial relation to fungi and roots and their similarity to well known soil neoformations indicate biogenic origin of these neoformations in most cases they contribute to macroscopic powdering being loose however in the cracks of some limestones they form dense infillings which could plug the fractures and prevent further advance of weathering to the core of the stone neoformed sulfates and iron oxides are fewer but also participate in the deterioration

needle fiber calcite a critical review and a proposed classification abstract from a review of the recent literature and our own observations the different morphologies of needle fiber calcite are classified they can be characterized as monocrystalline rods with or without serrated edges or as polycrystalline chains the simplest monocrystalline habit of needle fiber calcite is the individual micro rod m larger monocrystalline rods ma exist in multiples of two more complex forms are found as paired monocrystalline rods with serrated plates along their length mb this group includes three habits which can be distinguished by the number of plates and their orientation relative to the rod finally there is a monocrystalline form mab intermediate between the categories ma and mb which shows the transition from the simple coupled rods to rods with errated plates although polycrystalline needles p have rarely been reported in the literature three types of morphologies have been identified each type of crystal has a specific origin the m micro rods are physicochemical nuclei or calcified bacteria they do not seem to evolve towards larger or more complex morphologies the ma rods are related to biomineralization inside the fungal sheaths the mb rods postdate liberation of ma rods from mycelian bundles the serrated plates are secondary syntactic crystallizations of physicochemical origin whose growth can be inhibited for various reasons the origin of p chains is less well understood but they seem to be physicochemical crystallizations related to evaporation and desiccation therefore these three groups m ma mb and p have similar morphologies but do not seem to be related genetically the only known link is between the ma and mb rods there is no evolutionary s quence of needle fiber calcite habits but a convergence of forms between crystals whose origins are different and independent structures described in the literature as convoluted random cutane and nest like are the result of either evolution of the mycelian bundles or movement of material and organisms in the soil in the case of m micro rods the microfabric is related to the random precipitation around nuclei in pores filled with a highly supersaturated solution initially the p chains also precipitate without preferential organization and later on the growth seems to preferentially constitute chains although the mechanisms are still not understood moreover needle fiber calcites do not indicate a particular climatic environment

a new gravity wave drag scheme incorporating anisotropic orography and low level wave breaking impact upon the climate of the uk meteorological office unified model a new anisotropic gravity wave drag parametrization scheme which represents high drag states modelled on hydraulic jump flow blocking and internal wave reflection theory including trapped lee waves is presented the scheme is shown to represent the breaking of waves over mountains better than previous schemes by comparison with mesoscale simulations of pyrex case studies extended simulations of the meteorological office unified model at climate resolution are presented showing the impact of the new scheme and a combination of the scheme with a new orographic roughness parametrization results show a changed distribution of surface gravity wave surface stress mostly due to mountain anisotropy and a greater tendency for lower troposphere wavc drag inclusion of the orographic roughness parametrization halves the gravity wave stress the combined effect of these schemes for climate integrations being a slight improvement to the tropospheric flow

facies and petrophysical signature of the tournaisian visean lower carboniferous sea level cycle in carbonate ramp to basinal settings of the wales brabant massif british isles we studied the relationships between stratigraphic distribution of outcrop spectral gamma ray magnetic susceptibility and carbonate facies stacking patterns across the regionally significant transgressive regressive cycle at the tournaisian visean boundary tn v early carboniferous in southern great britain and ireland south wales north staffordshire and dublin basin the tn v boundary coincides with a prominent climatic pulse connected with the late paleozoic glaciation of gondwana the aim was to correlate the gamma ray and magnetic susceptibility log patterns in carbonate ramp and basin settings and discuss the global regional nature and magnitude of this transgressive regressive cycle a robust ramp to basin correlation was produced based on the log patterns facies stacking patterns and foraminifer biostratigraphy the concentrations of k and th the clay gamma ray values and partly magnetic susceptibility are dependent on facies and show systematic changes along the inferred bathymetric profile from inner ramp to outer ramp and basin a model of carbonate productivity driven dilution of fine grained siliciclastics in caco3 as the major control on the petrophysical patterns is discussed the cleaning up and cleaning down petrophysical trends are related to down dip and up dip shifts of the carbonate factory with changing relative sea level in middle to outer ramp and basin settings this generates petrophysical trends just opposite to paleozoic carbonate shelves where peaks in magnetic susceptibility are known to be associated with peak regressions a distinct late tournaisian to early visean regressive to transgressive cycle with a prominent sequence boundary located close to the tn v stage boundary can be seen in the sections glacioeustatic origin of the sequence boundary is inferred from its correlation with tn v boundary sections from europe carbon isotope data from south china and the glacial deposits in the southern hemisphere mentioned by previous authors

mechanisms in the development of anomalous sea ice extent in the western arctic a case study interannual cycles and trends in arctic ice cover are dominated by strong regional variability arctic sea ice extent exhibited a record minimum within the arctic basin during september 1990 dominated by a rapid retreat in the chukchi east siberian and laptev seas simulations using a coupled regional model reproduced the enhanced cyclonic activity and enhanced ice melt which led to this large retreat in sea ice cover sensitivity experiments showed that accurate initial ice conditions are crucial for a realistic simulation of the ice anomaly pointing to the need for adequate spin up in coupled model experiments it was also found that thermodynamic melt can account for the bulk of the total loss in ice mass over the summer season in 1990 but without dynamics the spatial patterns characteristic of the ice reductions are not reproduced well also transport of ice was crucial to initiate the formation of the anomaly even if the formation was delayed until later in the season the ice albedo feedback is important in allowing the continued formation of the ice anomaly throughout the summer interannual variations in atmospheric circulation that yield regional differences in ice thickness provide a preconditioning that significantly affected development of the ice anomaly this suggests that circulation modes play an important role in determining ice severity along the siberian coast

the latemar a middle triassic polygonal fault block platform controlled by synsedimentary tectonics abstract detailed field mapping of a middle triassic carbonate buildup the latemar in the western dolomites northern italy has been carried out the latemar is an isolated carbonate buildup that nucleates on a fault bounded structural high horst cut into the underlying late anisian carbonate bank of the contrin fm this study demonstrates that extensional synsedimentary tectonics is the main factor controlling its geometry and provides an age for this tectonic phase in an early phase slopes were mostly composed of well bedded clinostratified grainstones and rudstones in a later stage the deposition of grainstones was accompanied by the emplacement of clinostratified megabreccias the upper portion of slopes is a microbial boundstone with abundant tubiphytes and patches or lenses of grainstone boundstones may occasionally expand into the platform interior and downward to the base of the slope the depositional profile was that of a mounded platform the buildup is dissected by a dense framework of high angle fractures and faults and by magmatic and sedimentary dikes exhibiting two principal directions trending nnw sse and ene wsw faults trending wnw ese were also observed magmatic dikes are related to the emplacement of the nearby predazzo intrusion and are thus upper ladinian kinematic indicators of strike slip activity were observed on fault planes trending nne ssw and nnw sse that can be attributed to cenozoic alpine tectonics faults magmatic dikes and sedimentary dikes show systematic cross cutting relationships with strike slip faults cutting magmatic dikes and magmatic dikes cutting sedimentary neptunian dikes ene wsw and wnw ese faults are cut by all other structures and record the oldest tectonic activity in the region structural analysis attributes this tectonic phase to an extensional stress field with a direction of maximum extension oriented ca n s several lines of evidence including sealed faults and growth wedge geometries allow us to recognize this old tectonic phase as syndepositional and to date it to the latest anisian avisianum and crassus ammonoid biochronozones the horse shoe shape of the platform and its margins rectilinear for long tracts are explained by the existence of a network of extensional faults whose activity lasted for part of the growth of the platform the latemar is thus a polygonal fault block platform controlled by synsedimentary tectonics the resulting sedimentary architecture is that of a growth wedge deposited probably on the uplifted side of a submerged half graben continuous reactivation of faults at platform margins locally determined anomalous facies transitions with well layered platform interior directly in contact with the clinostratified slopes

grain size geochemistry magnetic susceptibility proxies in identifying sources and factors controlling distribution of metals in a tropical estuary india the aim of this study is to understand the various sources and factors controlling the abundance and distribution of the metals through the analyses of selected metals iron manganese chromium copper zinc and cobalt sand silt clay organic carbon and magnetic susceptibility of the surface sediments of zuari estuary in three different seasons total suspended matter tsm concentration and salinity of near surface and bottom waters were also measured the study undertaken for three seasons based on 18 selected stations all along the estuary indicated that the concentration of most of the metals were comparatively higher during pre monsoon than in monsoon and post monsoon seasons further along the length of the estuary high concentrations were observed at lower middle and lower estuary and also at few stations at the upstream end salinity distribution of tsm size of the sediment organic matter geomorphological setup fresh water input from land and release of industrial waste within the estuary played a role in distribution and concentration of metals magnetic measurements indicated the dominance of haematite like minerals and helped in understanding the source and depositional processes

biostratigraphic and radiometric age data question the milankovitch characteristics of the latemar cycles southern alps italy the combination of age diagnostic fossils in platform carbonates geometrical relationships with coeval basinal successions and single zircon u pb ages from volcaniclastic layers in basinal deposits constrain the age of a cyclic succession in the interior of the latemar platform to a narrow time span in the middle triassic with a duration shorter than 5 m y precession induced milankovitch band sea level oscillations are therefore excluded as controls for most of the 600 platform cycles reported from latemar statistical evaluation and graphic space time analyses of cycle stacking patterns alone may therefore not allow an unambiguous recognition of milankovitch frequencies in ancient platform carbonates

stable isotope compositions of pedogenic carbonates and soil organic matter in a temperate climate vertisol with gilgai southern russia abstract a vertisol gilgai complex from the north caucasus russia was studied to evaluate the climatic and environmental conditions governing pedogenesis the stable isotope compositions of soil organic matter som and carbonate pedofeatures in the vertisol record a complex but interpretable pedogenic history variability in the isotopic composition of pedogenic carbonate as a function of morphology position in gilgai microrelief and soil depth emphasizes the importance of these parameters to interpreting pedogenic conditions the isotopic compositions and age of som record evidence of pedogenesis in an earlier 5000 yr bp environment that was warmer and drier than modern conditions with a significant component of c4 flora up to 30 this portion of the soil history is preserved only in the deepest portions of the microlow 140 cm or in the central portion of the microhigh chimney a change to cooler and wetter conditions was accompanied by a shift to an ecosystem dominated by c3 vegetation 95 and resulted in a wetter soil environment particularly in gilgai microlow positions most pedogenic carbonate preserves isotopic compositions reflecting only the more recent climate history the wetter environment contributed to recrystallization of pedogenic carbonate nodules and formation of soft carbonate masses there are systematic differences in the isotopic composition of hard nodules and soft masses that indicate the influence of greater soil water evaporation a greater proportion of xerophytic plants and or lower rates of soil respiration in the gilgai microhighs self consistent interpretation of the pedogenic and paleoclimate history of these vertisols requires consideration of a full suite of information including carbonate pedofeature micromorphology the stable isotope composition and age absolute and relative of these features and other soil characteristics

magnetic hysteresis of limestones facies control abstract the hysteresis properties of 116 non red marine limestones from 92 localities indicate that remanence is carried by magnetite of pseudo single domain psd and small multidomain md size pelagic limestones have paramagnetic matrices and hysteresis properties compatible with larger psd or md grain sizes of magnetite probably associated with detrital clay minerals introduced by pelagic rain out thus they may be less suitable recorders of stable remanence other limestone facies excepting dolomitized examples have diamagnetic matrices they include shallow subtidal limestones which tend to have smaller psd sizes of magnetite as do backreef lagoonal undifferentiated shelf and reef facies it is believed that the wide geographical and temporal range of samples minimizes effects related to post compaction groundwater flow late diagenesis and that the associations recognized should be tested in future studies

the influence of paleogeomorphology on the stable isotope signals of paleosols abstract the stable carbon and oxygen isotope composition of three different local variations of the same mis5e paleosol horizon were studied in the ver ce loess paleosol sequence hungary these variations developed in local top paleoslope and paleovalley topographic positions with characteristic secondary carbonate features such as hypocoatings hcs based on the 13c 18o enrichment or depletion of the secondary carbonate samples the so called stable isotope matrix sim was established and this was used to characterize stable isotope signals as potential paleoenvironmental indicators to complete the sim box and whiskers plot analysis of 13c and 18o values were elaborated on the pedogenic horizons of the paleosol variations the joint application of the sim and the box and whiskers plot analysis revealed the way in which the climatic stable isotope signal of hcs can be overwritten by the various topographic positions of the hosting paleosols the local top paleosol variation will necessarily have developed under climatic influence the expected transition from cold to warm phases as loess deposition characterized by upbuilding pedogenesis was followed by more effective soil development due to the takeover of topdown pedogenesis was characterized by increasingly negative stable isotope values in the upward succession of genetic horizons in the sequence the same transition was identified by different stable isotope patterns in the case of the other two paleosol variations the paleovalley position implies hydromorphic effects and significant evapotranspiration under denser vegetation cover the paleoslope position was affected by abrupt environmental changes such as run off processes triggered by higher precipitation leading to continuous disturbance in the course of the development of the sequence

facies architecture of an isolated carbonate platform tracing the cycles of the latemar middle triassic northern italy the 720 m thick succession of the middle triassic latemar massif dolomites italy was used to reconstruct the lagoonal facies architecture of a small atoll like carbonate platform facies analysis of the lagoonal sediments yields a bathymetric interpretation of the lateral facies variations which reflect a syndepositional palaeorelief based on tracing of lagoonal flooding surfaces the metre scale shallowing upward cycles are interpreted to be of allocyclic origin short term sea level changes led to subaerial exposure of wide parts of the marginal zone resulting in the development of a tepee belt of varying width occasional emergence of the entire lagoon produced lagoon wide decimetre thick red exposure horizons the supratidal tepee belt in the backreef area represented the zone of maximum elevation which circumscribed the sub to peritidal lagoonal interior during most of the platform s development this tepee rim the subtidal reef and a sub to peritidal transition zone in between stabilized the platform margin the asymmetric width of facies belts within individual metre scale cycles was caused by redistribution processes that reflect palaeowinds and storm paths from the present day south and west the overall succession shows stratigraphic changes on a scale of tens of metres from a basal subtidal unit overlain by three tepee rich intervals separated by tepee poor units composed of subtidal to peritidal facies this stacking pattern reflects two third order sequences during the late anisian to early middle ladinian

palaeoclimatic indicators in soils buried under archaeological monuments in the eurasian steppe a review the russian experience of the local reconstruction of the eurasian steppe climate during the last 5000 years based on geoarchaeological approaches is reviewed examples of traditional palaeoclimatic reconstructions in russia based on organic matter highly soluble salts and gypsum content and location of salts and gypsum horizons in the profile of buried soils are given pedogenic carbonate as a palaeoclimatic indicator is considered the possibilities of the quantitative reconstruction of the palaeoprecipitation based on magnetic properties of buried soils are observed the innovative approach of palaeoclimatic reconstruction based on soil microbiology methods is reviewed the problem of temporary transformation of palaeoclimatic indicators in buried soils is shown a methodology for the interpretation of palaeoclimatic indicators of buried soils for a local palaeoclimatic reconstruction is given

revisiting the quaternary development history of the western new caledonian shelf system from ramp to barrier reef abstract the present paper is based on the study of a new core tenia 3 151 20 m long and revisitation of previous core data from the western new caledonian barrier reef based on variations in lithology and stable isotope signatures and the occurrence of unconformity surfaces the tenia 3 sequence is subdivided into ten units regarded as deposited during interglacial high sea levels five detrital and two framework facies are delineated using their biological and textural attributes including coral growth forms and assemblages these facies are interpreted as representative of outer to inner carbonate shelf ramp to barrier reef environments variations in the facies within each stratigraphic unit occur mainly as vertical transitions from lower energy and probably deeper to higher energy probably shallower settings the succession of depositional events is reconstructed using all available age criteria including lithostratigraphy magnetostratigraphy uranium series dating and nannofossil biostratigraphy shallow water coral communities appear to have been developed as soon as carbonate deposition started at around 1 2 million years ma but the initiation of typical coral reef tracts is likely to have occurred not prior to 0 40 million years during marine isotope stage mis 11 carbonate deposition previous to mis 11 is considered to have operated along an open shelf margin i e a ramp or non rimmed platform based on the re examination of the core dataset previously acquired from the new caledonian reefs the coral communities dominated by massive forms mainly poritids are assumed to have remained stable in composition over the past 1 4 ma similarly as indicated by a preliminary study of pollen assemblages in the core the composition of terrestrial flora dominated by podocarpaceae and araucariaceae has not apparently suffered significant change over the past 1 ma and reflects climate conditions cooler and drier than today mean subsidence rates are derived tentatively over the past 1 ma from the stratigraphic position at present reached by the top of depositional units mean rates of 0 08 mm yr 1 for the western new caledonian margin are consistent with past sea level estimates the quaternary depositional history of the new caledonian shelf margin appears to have been controlled by both the amplitude of sea level changes and by differing vertical tectonic movements comparison between the depositional shelf histories from western new caledonia north eastern australia southern belize and the ryukyu islands supports the assumption that coral populations over the early and mid pleistocene developed as non reefal communities along ramp systems not forming continuous outer shelf reef rims at a global scale quaternary reef rimmed platforms are likely to have initiated after the mid pleistocene climate transition from marine isotope stage 11 at about 0 4 ma

high resolution estimate for the depositional duration of the triassic latemar platform a new magnetostratigraphy and magnetic susceptibility cyclostratigraphy from basinal sediments at rio sacuz italy 1 a new magnetostratigraphy and magnetic susceptibility cyclostratigraphy from middle triassic basinal sediments at rio sacuz northern italy suggests a depositional duration of 1 myr for most of the 670 m carbonate latemar platform giving a high resolution estimate for the duration for the latemar s deposition the new magnetostratigraphy from rio sacuz clarifies the ambiguities in a previous magnetostratigraphic study of the latemar caused by lightning strike remagnetizations our rio sacuz study was unaffected by lightning using thermal demagnetization we show a normal reversed normal reversed sequence at the latemar correlated locality of rio sacuz with a polarity interval duration of 0 25 0 5 myr for the middle triassic this gives a depositional duration of 1 2 myr rock magnetic experiments show that the magnetic carrier is magnetite suggesting a primary depositional age remanence measurement of magnetic susceptibility at 1 m intervals from rio sacuz reveals eight short eccentricity cycles 95 125 kyr bundled into slightly more than two 405 kyr long eccentricity cycles indicating a more precise duration for the rio sacuz section of 0 8 to 1 myr the shorter depositional duration required by this study forces a sub milankovitch time scale of 1 2 kyr for the latemar platform s meter scale rhythmic bedding and provides strong evidence for nonorbitally driven climate change in the middle triassic

the occurrence and origin of late paleozoic remagnetization in the sedimentary rocks of north america although it has been known for 25 years that some paleozoic sedimentary rock units in europe and north america were remagnetized during pennsylvanian or permian time it is only very recently that the complex and widespread nature of the late paleozoic remagnetization phenomenon has been generally acknowledged it is now recognized that many paleozoic paleomagnetic poles for north america that were once considered reliable are in fact the result of remagnetization and as a consequence the paleomagnetic data base for the paleozoic is undergoing rapid and drastic revision the causes of late paleozoic remagnetization in north america are currently the focus of much interest and active research the remagnetization can reside in either hematite or magnetite and different remagnetization mechanisms have been important in different settings chemical remagnetization processes some related to specific diagenetic events are dominant in hematite bearing sandstones and carbonates in magnetite bearing carbonates both chemical and thermoviscous remagnetization processes appear to have been important but it is difficult to determine which process is the dominant one in some settings some of the observed remagnetizations can be linked to the migration of chemically active and perhaps hot fluids during the mountain building events that affected much of the continent during the late paleozoic paleomagnetic studies promise to be important in assessing the role of orogeny in driving fluid migrations within sedimentary basins and in constraining the age of the migrations and the nature of the fluids

micromorphological fabrics and developmental stages of carbonate nodular forms related to soil characteristics abstract carbonate nodules often constitute the first stage of calcrete formation micromorphological analysis of carbonate nodules and nodular fabrics in different soil materials shows that their development is a function of several factors nature of the host matrix texture porosity carbonate and non carbonate clay distribution bulk density and the interactions among them different micromorphological stages therefore exist in different soil materials in calcareous medium textured soil materials the stages of nodule formation are related to the increase of the density of the nodule caused by the accumulation of microcalcites in such a soil material the following stages occur 1 microcalcites within the low to moderate density matrix 2 microcalcites of moderate to high density and moderately dense diffuse nodules parallel calcans may occur 3 microcalcites of high density with dense microcalcitic nodules during these stages the amount of non carbonate clay decreases but is homogeneously dispersed and disseminated with the microcalcites in general the size of microcalcites 1 8 m is inversely related to the clay content in non calcareous medium to fine textured soil materials secondary carbonate precipitates in intrapedal and or interpedal voids as large sparry crystals due to pedoturbation processes the nodules thus formed are subjected to recrystallization resulting in a microsparry pattern the development stages are 1 few calcans and crystal chambers 2 crystic nodules mainly of sparry crystals and an increase of calcans and crystic chambers 3 recrystallized nodules composed mainly of microspars in coarse grained materials secondary carbonates precipitate directly in voids as sparry crystals and the resulting nodules are of the crystic type the large crystals are often subjected to recrystallization in partly calcareous coarse grained materials with additions of calcareous dust particular micromorphological carbonate forms occur in the c horizon cutanic calciasepic fabric forms besides zones of crystic fabric which gradually become calciasepic in the b horizon and include the typical nodular forms of the calcareous medium textured soil material together with appreciable amounts of glaebular halos the processes leading to the formation of these stages occur essentially without a significant biogenic influence where carbonate segregation occurs as rhizomorphs surrounding active roots the fabric is always micritic even in coarse textural soil material

modeling the thermodynamics of a sea ice thickness distribution 1 sensitivity to ice thickness resolution a one dimensional ice thickness distribution model is presented to determine the minimum number of ice thicknesses necessary to resolve the area averaged annual cycles of ice thickness and turbulent fluxes the baseline case includes 40 ice thickness categories ice thickness and area meltwater ponds ice salinity and age snow cover and surface albedo evolve independently for each ice category a ridging and ice export parameterization and a coupled one dimensional ocean mixed layer model are also included sensitivity studies indicate that 16 ice thickness categories can accurately resolve the baseline annual cycles of area averaged ice thickness and the summertime turbulent fluxes in this model provided that one third of the thickness categories represent ice thinner than 0 8 m resolving the distribution of ice in this thickness range is important in simulating the area averaged ice characteristics wintertime values of the turbulent fluxes differ from the baseline by up to 1 w m 2 for fewer than 40 ice thickness categories the large difference in turbulent fluxes between open water and ice thicker than 1 6 m makes the area averaged value sensitive to the number of ice thickness categories since this number can affect the categories that are merged the categories that melt completely ice that is ridged and the resolution of the ice thickness distribution this makes an accurate simulation of the baseline wintertime turbulent fluxes difficult model simulations with fewer than 40 categories provide a reasonable estimate of the baseline response to a surface longwave heat flux perturbation of greater than 5 w m 2 the annually area averaged ice thickness is within 10 cm the model response to a heat flux perturbation of less than 5 w m 2 is similar for a wide range of ice thickness categories since the thickness distribution of ice thinner than 1 m is not affected

the alaskan arctic frontal zone forcing by orography coastal contrast and the boreal forest abstract experiments have been conducted with a regional climate model to indicate the conditions required to generate preferred regions of frontal activity in the alaskan region several objective methods of frontal identification were first investigated it was found that the vertical component of relative vorticity a thermal front parameter t850 n where t850 is the 850 hpa temperature and n is a unit vector in the direction of the 850 hpa temperature gradient and a parameter derived from the q vector as a measure of vertical motionwere useful in combination to determine the occurrence of fronts the preferred locations for frontal activity were located to the southern side of the eastern brooks range and over the alaska range these diagnostics were then used to characterize frontal frequency in a series of experiments removing topographic and vegetation contrasts it was found that the removal of the treeline contrast and its associated heating gradient had a small effect on frontal frequ

topographically generated gravity waves in the brooks range alaska amplified wind events are identified over the brooks range in alaska with observed wind speed increasing from calm to 5 ms 1 over 24 to 36 hours in simulations using an limited area climate system model the wind events are captured consistently although generally display greater strength than observed cooling associated with the wind events lead to an identification of the ne region of the north slope of alaska below the inversion as the source region for the air flow analysis of the wind event of 7th january 1992 supports the nonlinear hydraulic model of gravity waves

the middle triassic magnetostratigraphy from the peri tethys basin in poland abstract the paper presents the first complete magnetic polarity scale obtained for the middle triassic of the northern peri tethys area the roetian and muschelkalk deposits of southern poland upper silesia the holy cross mountains were studied paleomagnetically the obtained paleopole a 52 n 143 e fits well to the middle triassic ca 240 ma segment of the stable european apwp a set of various quality characteristic directions isolated in 106 samples was used for construction of the composite polarity scale this peritethyan scale has been tied with conodont zonation and referred to the scale erected earlier in the tethyan realm comparison of both scales indicates that the whole roetian succession in the southern polish basin should be correlated with the latest olenekian the normal marine sedimentation ceased in the polish basin as early as in the late fassanian time the obtained magnetostratigraphic scale combined with the sequence stratigraphic framework enables a reliable chronological correlation of the late olenekian ladinian succession over the entire peri tethys basin

microcodium revisited root calcification products of terrestrial plants on carbonate rich substrates abstract microcodium is a problematic calcitic microfeature of many calcretes and calcareous paleosols in the cretaceous and tertiary continental and marine successions of the peri tethyan realm the main controversy about the microcodium structures is their origin and possible relation with calcified plant roots microcodium and rhizogenic root formed microfabrics were studied in calcrete profiles within the paleocene shallow marine carbonate succession in southwestern slovenia the prominent laminar calcrete horizons contain abundant calcite aggregates 150 m to 1 cm in size with perfectly preserved structural details of plant root tissues morphology and structure of these aggregates indicate that they formed through biologically controlled precipitation of calcium carbonate within the root cortical cells the morphologies intermediate between the typical microcodium aggregates composed of a single layer of individual elongate pyramidal or prismatic crystals of calcite measuring 100 500 m in length and 20 70 m in width and calcified roots with multilayer arrangement of isodiametric cells were observed and this supports previous rhizogenic interpretations of microcodium structures intermediate forms show that the typical microcodium aggregates formed through morphological transformation of the root tissue by growth of the calcite within the cortical cells which distorted the cell shape calcification of roots and the creation of microcodium structures can be explained as an effective nutrient acquiring mechanism used by certain types of terrestrial plants inhabiting nutrient poor calcareous substrates the widespread occurrence of microcodium in almost unaltered shallow marine limestones indicates that its formation took place during early stages of paleosol development probably reflecting specific types of vascular plants of a pioneer community that were able to colonize carbonate substrates during the early phases of subaerial exposure

climatic implications of alternating clay and carbonate formation in semiarid soils of south central montana abstract evidence for climatic change is found in petrographic thin sections from soils formed on glaciofluvial deposits of rock creek and the lower clarks fork montana these soils presently in a semiarid climate range from late pliocene to holocene in age and have undergone periodic fluctuations in soil moisture caused by climatic changes in the lower parts of soil b horizons accretion of illuvial layers of clay argillans occurs mainly during wet glacial climatic periods whereas carbonate precipitates mainly during dry interglacial climatic periods thin section studies of the argillan and carbonate layers show that 1 post pinedale soils that have formed only in the present interglacial climate contain areas of secondary carbonate unrelated to argillans 2 soils formed on outwash of successively older glaciations contain proportionately more alternating layers of argillans and carbonate and 3 the maximum number and sequence of layers in a soil correspond to the number of local cycles of glacial outwash deposition and subsequent stream incision that followed the beginning of soil formation these cycles are inferred to correspond to local glacial interglacial fluctuations the correspondence between the microscopic record and the glacial outwash record for rock creek suggests that some of the climatic changes seen in the marine oxygen isotope record did not strongly affect the study area

high resolution rock magnetic cyclostratigraphy in an eocene flysch spanish pyrenees 1 a rock magnetic cyclostratigraphy based on anhysteretic remanent magnetization arm intensity variations was developed for the eocene arguis formation in the spanish pyrenees the arguis formation was sampled for arm cyclostratigraphy rock magnetic and paleomagnetic analyses rock magnetic measurements indicate that the dominant magnetic mineral controlling the arm cyclostratigraphy is depositional magnetite using thermal demagnetization a detailed magnetostratigraphy was developed for the arguis to provide an absolute time framework for the arm cyclostratigraphy the magnetostratigraphy is carried by a combination of depositional magnetite and secondary iron sulfides spectral analysis of the magnetostratigraphically scaled arm time series reveals the presence of significant milankovitch frequencies including eccentricity obliquity and precession the arm time series was tuned to the orbital eccentricity model for the eocene coherency analysis indicates that the eccentricity tuned arm is in phase with october november insolation for this site s paleolatitude varying amounts of terrigenous input delivered by a fluvial source at orbital time scales during the rainy season and diluted by a relatively constant input of marine carbonate is the most likely explanation for the cyclicity of the arm record the absolute age resolution of the arm chronostratigraphy is 1 or less based on an age offset with the reference chronology that was used for the eocene the offset in age between the two chronologies may be due in part to the uncertainty in the chron ages for this part of the eocene the relative age resolution within the arm chronostratigraphy is much better

use of insolation as a proxy for high frequency eustasy in forward modeling of platform carbonate cyclostratigraphy a promising approach abstract eustatic oscillations driven by milankovitchian astronomical forcing have been interpreted as sea level drivers for high frequency carbonate depositional cycles in studies dating from the mid 1960s forward modeling of these oscillations with respect to their recorded effects on cyclical stacking patterns has only been attempted using generalized parameters for milankovitchian forcing the development of increasingly advanced forward modeling software coupled with the availability of formulas quantifying insolation incoming solar radiation as a function of composite orbital variations allows for the testing of milankovitchian insolation against measured stratigraphy in this case a series of milankovitchian insolation curves were calculated and used to generate proxy sea level curves for use in the carb3d forward modeling package in order to synthesize a series of stacked carbonate strata these synthetic successions are compared against that of the latemar platform middletriassic northern italy which has been interpreted to contain a record of orbital forcing within its stratigraphy while the timing and nature of periodic drivers that affected latemar stratigraphy have stirred a vigorous debate results from this study indicate that use of milankovitchian insolation as a proxy for high frequency sea level oscillations was successful in modeling latemar like stratigraphy with both pure milankovitchian and mixed milankovitchian sub milankovitchian temporal frameworks

geophysical records of dispersed weathering products on the frasnian carbonate platform and early famennian ramps in moravia czech republic proxies for eustasy and palaeoclimate abstract an exceptionally high sea level in frasnian times early late devonian changed many peneplained cratonised and tectonically undisturbed continental margins of tropical belts into carbonate platforms which became covered by thick banks of limestone the stages marked by very pure carbonates developed during partial sea level highstands since when the flooding reached its maximum the shoreline was distant and conditions for reef growth were good an increased extension of emerged flat coastal areas was coupled with an opposite situation when oscillating sea level fell to its momentary minimum and the accommodation space available for accumulation of carbonate material was low subaerially exposed surfaces were subject to weathering and the products were dispersed by aeolian or aquatic means to form layers when these weathering materials were trapped in carbonates this overall scenario relating to the trapping of weathering products in pure carbonates was tested at geographically isolated platform with a stable and only slowly subsiding basement eastern moravia czech republic the amounts of weathering products dispersed in limestone were documented using the combined methods of ray logging ray spectrometry and magnetic susceptibility measuring i e according to their radioactivity k th and u and magnetism fe six third order frasnian eustatic cycles have been inferred from the data with an estimated period of 1 ma the late frasnian and especially the frasnian famennian f f transition brought the total destruction or at least a strong overlay on this hypothetical background setting the record of strong sea level fluctuations in the f f interval is shown in strong oscillations and offsets related to pronounced hiatuses and flooding surfaces such rapid sea level fluctuation is typical for glacioeustatic control although the present estimates of the maximum amplitudes are larger than realisable by glaciation events and may be explained in combination with tectonoeustatic models comparison of sections between the centre and periphery of the platform substantiates the concept that oscillating late frasnian shorelines were rapidly prograding very low sea level stages of early famennian times changed the depositionary systems from extensive platforms to narrow carbonate ramps which were positioned out and down on the extinct reef bank slopes the central parts of the eastern moravian and also other frasnian platforms in the world were not normally covered by f f sediments the transgressive onlaps above any crystalline highs were not observed and therefore the drowned frasnian reefs on their periphery although emphasised by many geologists may reflect sliding or tectonic subsidence on the margins of platform blocks rather than eustatic rise of sea level

records of magnetic properties in quaternary loess and its paleoclimatic significance a brief review due to the successive deposition quaternary loess paleosol sequences potentially provide one of the best terrestrial records of paleoclimatic changes magnetostratigraphy and paleoclimate are two major aspects of magnetic investigation in northern china and other regions of the world the classic loess sections across the chinese loess plateau indicate that wind blown loess deposition began close to the base of matuyama 2 6 ma however progress has also been made in extending the record below the loess into the red clay and the aeolian record can now be carried back beyond 7 ma the surprising similarity between the initial susceptibility is curve obtained from numerous loess paleosol sequences and the oxygen isotope fluctuation from the deep sea sediments provides impressive evidence of the global significance of the magnetic record as a useful proxy in paleoclimatic studies magnetic susceptibility ms has been extensively used to reconstruct the paleoclimate however the actual mechanism of ms enhancement of paleosols remains controversial the important questions why does is fluctuate in loess sections and what are the causes of the is enhancement in paleosols have been matters of debate in the last 10 years currently the viewpoint that pedogenesis plays an important role in the ms enhancement of paleosols has been generally accepted pedogenic magnetite is an important contributor to the ms enhancement is is not only simply controlled by the abundance of strong magnetic minerals but also by their grain size distributions the increment of superparamagnetic sp grains o0 1mm which is induced by pedogenesis could enhance the is of paleosols the formation of sp minerals has been debated as either biotic or abiotic it is now possible to propose a quantitative model for the reconstruction of paleoclimate according to the paleoprecipitation deduced from proxy indicators such as is fluctuation grain size stable isotope composition caco3 content rb sr and ratio of citrate bicarbonatedithionite extractable fe2o3 to total fe2o3 fed fet r 2002 elsevier science ltd and inqua all rights reserved

spectral analysis of the middle triassic latemar limestone abstract the middle triassic latemar limestone in the dolomites region northern italy consists of hundreds of vertically stacked meter scale platform carbonate cycles each cycle is composed of a shallow marine subtidal carbonate unit with a thin centimeter scale vadose diagenetic dolomite cap these latemar couplets are the products of repeated episodes of submergence emergence with durations estimated at 20 000 yr the couplets are arranged in upward thinning bundles of five indicating the presence of a 100 000 year modulating component we examined this high frequency cycling in the platform buildup using a variety of classical and advanced spectral analysis techniques we found si nificant evidence for the presence of a milankovitch forcing signal in this cycling we also present evidence that the adjacent coeval basinal facies the livinallongo formation exhibits a similar bundling pattern in its cm scale hemipelagic carbonate shale alternations we conclude that milankovitch forced small amplitude sea level oscillations were the most likely cause of these middle triassic carbonate rhythms

magnetostratigraphic dating of shallow water carbonates from san salvador bahamas magnetostratigraphic results are reported here from a sequence of late neogene quaternary shallow water carbonate sediments from a continuous core drilled on the island of san salvador bahamas on the basis of the remanent magnetism of 136 samples from a 91 m measured section of core the polarity sequence can be correlated with the magnetic polarity time scale from the gilbert chron early pliocene through the late brunhes chron late pleistocene holocene magnetic polarities were determined on the basis of relative up down direction in the unoriented core extraction studies of the magnetic particles reveal the presence of single domain crystals of magnetite resembling those produced by the magnetotactic bacteria and algae the sequence of reversals provides a minimum of six new major chronostratigraphic markers for the pliocene pleistocene of the bahamas it confirms and refines the local timing of both the lithologic change from skeletal to nonskeletal sediments and the disappearance of coral and molluscan species from the bahamas as upper late pliocene between 2 6 and 2 7 ma that the primary magnetic remanence is preserved in shallow water carbonates including replacement dolomites suggests that this technique could be used to date similar tertiary and possibly even older carbonate sequences the establishment of a reliable magnetostratigraphy provides refined dating of shallow water carbonates and regional faunal appearances or disappearances sediment accumulation rates subsidence and depositional events

upper devonian carbonate platform correlations and sea level variations recorded in magnetic susceptibility abstract this paper concerns the analysis of four outcrops in the frasnian upper devonian of belgium we compare the results of a precise sedimentological analysis with magnetic susceptibility ms data this comparison allows us to improve stratigraphic correlations and to test the relationship between magnetic susceptibility and sea level changes considering the sedimentological study different microfacies have been identified from the external belt dominated by relatively argillaceous open marine facies with crinoids to the biostromal and the lagoonal belt dominated by algae rich muddy facies fourth and third order sequences have also been identified and are probably related to sea level variations magnetic susceptibility data provides us very good fourth order correlations and the link between magnetic susceptibility and different sedimentological parameters is obvious more precisely ms appears to be related to fourth and third order sequences and to microfacies

formation processes and stratigraphic integrity of the middle to upper palaeolithic sequence at cova gran de santa linya southeastern prepyrenees of lleida iberian peninsula sediments from cova gran de santa linya southeastern prepyrenees of lleida iberia are investigated by geoarchaeological means micromorphological textural quartz grain morphoscopy and geochemical analyses are coupled with stratigraphic and sedimentary macroscopic data to provide new insights into the formation processes and the integrity of the occupation layers and embedded sterile deposit documented at the middle to upper palaeolithic boundary direct indicators of the anthropogenic and natural dynamics involved in the deposition and alteration of the sediments investigated are provided results reveal the presence of in situ combustion structures as a major sedimentary indicator of human activity and occupation surfaces at the site the overall good preservation of the combustion residues indicates that occupation layers have been preserved in their original context of deposition traits of surface exposure in parallel to progressive lessening of evidence related to human activity at the top of the middle palaeolithic sequence suggest discontinuity in the occupation of the site and a possible abandonment of the rock shelter at the end of this period formation processes of the sterile deposit documented between the mousterian and the early upper palaeolithic levels involved the accumulation of debris from local sediments and soils as well as from the structure of the rock shelter soil forming dynamics related to palaeoenvironmental moisture fluctuations have also been recorded throughout the sequence investigated and indicate periods of surface stability during the formation of the sterile deposit environmental dynamics active during the formation of the sterile partially disturbed the top of the mousterian layer however our data indicate that such dynamics did not substantially affect the overall integrity of the archaeological record our results highlight the crucial contribution of geoarchaeology and microstratigraphy to the characterisation and assessment of the anthropogenic and natural dynamics involved in the accumulation and taphonomy of middle to upper palaeolithic sequences

sub milankovitch and milankovitch forcing on a model mesozoic carbonate platform the latemar middle triassic italy basic shallowing upward cycles shu cycles and five bundled megacycles in the latemar platform have been widely regarded as a model example for precessional and eccentricity forcing in the mesozoic based on bio chronostratigraphic data recent studies questioned this particular type of milankovitch forcing on the latemar cyclic series we present an integrated model that incorporates i new cyclostratigraphic data ii new and existing bio chronostratigraphic data and iii new spectral analyses the basic shu cycles in the latemar reflect sub milankovitch control cycle bundles of 1 4 5 megacycles shu cycles indicate precessional forcing they do not reflect eccentricity superimposed on precessional forcing spectral analyses reveal highly significant ratios in the large scale cycle bundlings stacking patterns of 1 9 9 and 1 24 0 shu cycles represent obliquity and short eccentricity forcing both sub milankovitch and milankovitch forcing potentially controlled shallow subtidal carbonate deposition in mesozoic greenhouse times cyclostratigraphic models require an integrated approach including bio and chronostratigraphic data

aragonite dissolution sedimentation rates and carbon isotopes in deep water hemipelagites livinallongo formation middle triassic northern italy hemipelagic nodular limestones are a widespread facies in the triassic of the tethys often considered as being deposited at rather constant sedimentation rates the aim of this paper is to investigate the sedimentation rate variability in a case study from the middle triassic of the dolomites northern italy and to suggest possible causes the nodular cherty limestones of the livinallongo fm and correlated units were studied in four stratigraphic sections and compared to classical successions from the literature correlations between sections are based on ammonoid biostratigraphy and tephra stratigraphy correlation highlighted conspicuous changes in sedimentation rates through time and between sections associated with sedimentological evidence of deep water aragonite dissolution deep water dissolution is believed to have resulted in small hiatuses and in a bias of ammonoid assemblages towards taxa with more resistant shells carbonate petrography and geochemistry provide evidence of differential diagenesis of the livinallongo fm carbonate nodules were lithified at the water sediment interface and their c isotope composition is regarded as a proxy of the d 13 c of middle triassic bottom seawater the onset of nodular cherty limestones occurring contemporaneously at the basin scale and the coeval carbonate platform drowning events are tentatively explained by the inflow and local upwelling of cool deep water from panthalassa into the western tethys d 2005 elsevier b v all rights reserved

evidence for massive discharges of icebergs into the north atlantic ocean during the last glacial period sediments in the north atlantic ocean contain a series of layers that are rich in ice rafted debris and unusually poor in foraminifera1 here we present evidence that the most recent six of these heinrich layers deposited between 14 000 and 70 000 years ago record marked decreases in sea surface temperature and salinity decreases in the flux of planktonic foraminifera to the sediments and short lived massive discharges of icebergs originating in eastern canada the path of the icebergs clearly marked by the presence of ice rafted detrital carbonate can be traced for more than 3 000 km a remarkable distance attesting to extreme cooling of surface waters and enormous amounts of drifting ice the cause of these extreme events is puzzling they may reflect repeated rapid advances of the laurentide ice sheet perhaps associated with reductions in air temperatures yet temperature records from greenland ice cores appear to exhibit only a weak corresponding signal moreover the 5 10 000 yr intervals between the events are inconsistent with milankovitch orbital periodicities raising the question of what the ultimate cause of the postulated cooling may have been

high resolution magnetostratigraphic and lithostratigraphic correlations in middle triassic pelagic carbonates from the dolomites northern italy new magnetostratigraphic and lithostratigraphic data are reported from the pedraces and belvedere limestone sections from the dolomites region of northern italy these sections are comprised of the buchenstein beds of late anisian to ladinian middle triassic age the results from pedraces and belvedere are compared with data from the biostratigraphically and isotopically constrained frotschbach and seceda sections from the literature a satisfactory magnetostratigraphic correlation is obtained on laterally traceable limestone and volcaniclastic intervals these marker beds are then used to extend lithostratigraphic correlations to additional key sections from a palaeogeographically coherent area of around 500 km2 the aim of this study is to unravel the spatial and temporal evolution of the buchenstein basin and the surrounding carbonate platforms platforms in the northwestern dolomites show an early stage of aggradation followed by progradation whereas in the central dolomites the cernera platform after fast initial aggradation drowned and became a pelagic seamount in the intervening buchenstein basin the diverential subsidence between the northwestern and central dolomites is manifested by the lateral increase of thickness of lower pietra verde volcaniclastic sediments accumulation of volcaniclastic material reworked from adjacent carbonate platform slopes characterised the more subsiding and unstable central dolomites in the pelagic carbonate intervals the persistence over tens of kilometres of bedding patterns suggests that carbonate material presumably washed out from the surrounding still active carbonate platforms was volumetrically small and homogeneously distributed throughout the uniformly subsiding buchenstein basin a milankovitch precessional origin for the platform interior cycles at latemar as suggested elsewhere implies a net accumulation rate of 2 m ma or less for the correlative interval of pelagic buchenstein beds this value divers significantly from the average value of around 10 m ma as calculated using high resolution isotopic age data for the buchenstein beds 2000 elsevier science b v all rights reserved

metamorphic control of the magnetic mineralogy of black shales in the swiss alps toward the use of magnetic isogrades abstract the magnetic susceptibility of the helvetic jurassic black shales sampled around the aar and gothard massifs in the swiss alps is due to iron bearing silicates magnetite or pyrrhotite it exhibits a clear correlation with the alpine metamorphism from zeolite to amphibolite facies it firstly decreases due to the breakdown of original magnetite then sharply increases when pyrite is transformed into magnetic pyrrhotite using numerous field measurements of the susceptibility it was possible to carry out a fast and precise mapping of the pyrrhotite in isograde which appears to correspond closely to the stilpnomelane out isograde the matrix susceptibility obtained by means of high field measurements with a cryogenic magnetometer is due to iron bearing silicates and shows only smooth variations with metamorphism both monoclinic and hexagonal pyrrhotites are observed in the high grade area

upper boundary effects in a general circulation model abstract the effects of an artificial upper boundary on the climate of a general circulation model are examined using two versions of the model the complete model has 26 levels extending from the surface to 0 1 mb 65 km and the second version approximates the usual tropospheric general circulation model having 15 levels extending to 10 mb 30 km the two model versions are identical over the common part of the domain vertically propagating kelvin waves are found in the tropics of both versions of the model in the version extending only to 10 mb the kelvin waves are reflected by the top boundary and resemble standing oscillations in the vertical while retaining approximately their original zonal phase speed some of these reflected waves develop much larger lower stratospheric amplitudes than when they are able to propagate freely into the mesosphere placing the topmost model level at 10 mb is found to radically alter the winter stratospheric circulation and to produce significant changes in

stratigraphic significance and resolution of spectral reflectance logs in lower devonian carbonates of the barrandian area czech republic a correlation with magnetic susceptibility and gamma ray logs abstract spectral reflectance sr is a relatively novel technique which is used as a proxy for organic carbon and siliciclastic input in carbonate sediments in particular in core research this study summarizes results from high resolution outcrop sr logging of a lower devonian distal ramp carbonate section of the barrandian area czech republic the sr data were correlated with parallel petrophysical and geochemical data with an aim to improving their cyclostratigraphic and event stratigraphic interpretation potential and the gaps sr data can fill transgressive regressive trends indicated by facies stacking patterns caco 3 data and spectral gamma ray grs logs are well correlated in the regional context and point to third order eustatic sea level fluctuations peak regressions of the tr cycles are sensitively marked by cie l a b parameters and percent reflectance in colour bands the sr and magnetic susceptibility ms data are markedly cyclic on a more detailed scale their inferred periods vary between 49 2 and 205 kyr indicating that they may have been forced by orbital cycles in the milankovitch band the sr and ms cycles are either in phase or out of phase the latter cycles point to a strong diagenetic forcing of the colour cyclicity hematite concentration cycles inferred from sr signal in the pragian red hemipelagic carbonates are interpreted as reflecting changing bottom oxygenation and subsurface redox gradients during early diagenesis the cie l parameter was found to be related to the presence of diagenetic hematite which indicates that cyclostratigraphic analysis of simple greyscale data can be affected by considerable error due to chromacity although the cie l parameter is partly correlated with caco 3 concentrations the ms data are not which suggests that the ms signal can be significantly influenced by diagenetic minerals and its cyclostratigraphic interpretation can be potentially misleading the sr data backed up by grs ms and caco 3 data indicate that the red colour in the pragian hemipelagic limestones originated from early diagenetic hematite precipitation under the conditions of an oxygenated ocean floor this suggests that deep sea bottom oxygentation may have been in operation during the early devonian which is traditionally perceived as a typical greenhouse period the sr data can be obscured in several m thick zones of elevated cie l and other colour changes leaching zones related to postdepositional alteration along subvertical faults however this fault related telogenic alteration has little influence on the ms signal the combined use of sr and ms has a synergic effect and can significantly improve the interpretation of their respective cyclic signals particularly in relation to the diagenetic overprint and possible carriers of the ms

high resolution upb dating of middle triassic volcaniclastics time scale calibration and verification of tuning parameters for carbonate sedimentation abstract we report high resolution single zircon u pb age data for middle triassic volcaniclastic intercalations in biostratigraphically calibrated pelagic successions of the southern alps the results require a redefinition of the chronometric scale for the middle triassic moreover they do not support current models relating cyclic sedimentation in platform carbonates of the dolomites to orbital tuning tight concordant age clusters were obtained for five volcaniclastic layers in three ammonoid biozones of late anisian to early ladinian age two layers in the nevadites secedensis zone yielded identical mean 206 pb 238 u ages of 241 2 0 8 0 8 ma and 241 2 0 8 0 6 ma errors given at the 95 confidence level a layer in the gredleri zone is dated at 238 8 0 5 0 2 ma and two horizons in the archelaus zone yield similar ages of 237 9 1 0 0 7 ma and 238 0 0 4 0 7 ma these results are significantly older than the age values of 233 235 ma assigned to the anisian ladinian boundary by several current time scales 1 4 moreover our estimate of 240 7 241 3 ma depending on biostratigraphic collocation for the anisian ladinian boundary casts doubts on the reliability of age values of 245 250 ma proposed by most time scales for the permian triassic boundary the occurrence of pelagic fossils in basinal sediments as well as in age equivalent shallow marine middle triassic platform carbonates in the dolomites allows the sedimentary sequences of both environments to be correlated the 800 m thick latemar platform western dolomites is characterized by cyclic stacking patterns which have been interpreted as results of milankovitch type high frequency low amplitude sea level fluctuations the 12 m y interval of platform growth postulated from the assignment of orbital periodicities to the platform carbonate cycles 5 6 is in conflict with a maximum time span of 4 7 m y allowed by the present zircon data