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

loess and floods high resolution multi proxy data of last glacial maximum lgm slackwater deposition in the flinders ranges semi arid south australia abstract terrace remnants of late pleistocene fine grained valley fill deposits silts deeply entrenched by ephemeral traction load streams in arid areas remain a puzzle they have been attributed to a variety of origins ranging from lacustrine to alluvial floodplains we here report a centimetre scale multi proxy study of a 7 m section of silts in the semi arid flinders ranges of south australia which span the lead up to and peak of the last glacial maximum lgm the results of detailed lithostratigraphic mapping high resolution parametric particle size analysis automated mineralogy induced magnetic susceptibility carbon stable isotope geochemistry and a chronostratigraphy based on 27 ams radiocarbon and 6 luminescence ages are discussed in terms of sediment provenance depositional environment and weathering history with the aim of reconstructing the regional palaeo environment the data are consistent with a fluctuating aeolian fluvial interplay dominating the extended lgm environment with a greater impact on the landscape than all combined geomorphic processes since then accordingly weathered slope mantles and loess accessions were eroded and entrained by numerous small and at least a dozen large scale flood events and trapped in an intra montane floodplain extending into brachina gorge upstream of this narrow constriction recurrent backflooding is discussed resulting in a thick sequence of layered to laminated slackwater couplets aggradation and degradation of valley fills appear to be largely controlled by fine sediment supply from the valley slopes replenished by wind blown dust from upwind playa lakes and source bordering dunefields in conclusion this study demonstrates how dust storms and flooding rains can account for pluvial features previously explained by the opposing effects of reduced precipitation and evaporation in the colder more arid glacial landscape of southern australia

magnetostratigraphical dating of loess deposits in china the age of chinese loess deposits has long been disputed biostratigraphical and earlier magnetostratigraphical investigations placed the entire loess formation within the pleistocene the new palaeomagnetic measurements reported here on a bore hole section near lochuan shaanxi province suggest a clearly defined magnetic polarity zonation which extends below the olduvai subchron a late pliocene age of 2 4 myr is assigned to the oldest loess sediments measured the intensity variations of natural remanent magnetization nrm and low field magnetic susceptibility are indicative of climatic changes during loess deposition

refining the early devonian time scale using milankovitch cyclicity in lochkovian pragian sediments prague synform czech republic abstract the early devonian geological time scale base of the devonian at 418 8 2 9 myr becker et al 2012 suffers from poor age control with associated large uncertainties between 2 5 and 4 2 myr on the stage boundaries identifying orbital cycles from sedimentary successions can serve as a very powerful chronometer to test and where appropriate improve age models here we focus on the lochkovian and pragian the two lowermost devonian stages high resolution magnetic susceptibility in 5 to 10 cm sampling interval and gamma ray spectrometry grs 25 to 50 cm sampling interval records were gathered from two main limestone sections po ar cs 118 m spanning the lochkov and praha formations and pod barrandovem 174 m praha formation both in the czech republic an additional section bran ovy 65 m praha formation was sampled for grs every 50 cm the in and grs records are very similar so in variations are driven by variations in the samples paramagnetic clay mineral content reflecting changes in detrital input therefore climatic variations are very likely captured in our records multiple spectral analysis and statistical techniques such as continuous wavelet transform evolutive harmonic analysis multi taper method and average spectral misfit were used in concert to reach an optimal astronomical interpretation the po ar cs section shows distinctly varying sediment accumulation rates the lochkovian essentially equivalent to the lochkov formation fm is interpreted to include a total of nineteen 405 kyr eccentricity cycles constraining its duration to 7 7 2 8 myr the praha fm includes fourteen 405 kyr eccentricity cycles in the three sampled sections while the pragian stage only includes about four 405 kyr eccentricity cycles thus exhibiting durations of 5 7 0 6 myr and 1 7 0 7 myr respectively because the lochkov fm contains an interval with very low sediment accumulation rate and because the praha fm was cross validated in three different sections the uncertainty in the duration of the lochkov fm and the lochkovian is larger than that of the praha fm and pragian the new floating time scales for the lochkovian and pragian stages have an unprecedented precision with reduction in the uncertainty by a factor of 1 7 for the lochkovian and of 6 for the pragian furthermore longer orbital modulation cycles are also identified with periodicities of 1000 kyr and 2000 2500 kyr

management of ambiguities in magnetostratigraphic correlation abstract magnetostratigraphy is a powerful tool to provide absolute dating of sediments enabling robust and detailed chronostratigraphic correlations it is based on the correlation of a magnetic polarity column observed and measured in a given sediment section to a magnetic polarity reference scale where polarity changes are well dated via other independent methods however magnetostratigraphic correlations are loose as they are only constrained by binary magnetic chrons i e normal or reversal and their thickness which are both defined from depth variations of the magnetic remanent directions the thickness of a given magnetic polarity zone is a function of time and sediment accumulation rate which may not be stationary leading to ambiguities when performing the correlations to address these ambiguities a numerical method based on the dynamic time warping algorithm is proposed magnetostratigraphic correlations are computed in order to minimise the local variation of the accumulation rate the main advantage of the proposed method is to automatically provide a set of reasonably likely correlations this set can then be scrutinised for further analysis and interpretation however the likelihood of a correlation should be handled carefully as it depends on the information content of the magnetostratigraphic section itself and remain ultimately valid by ancillary constraint nevertheless the method gives consistent results on difficult synthetic cases that simulate abrupt variations of the sedimentation rate insights on true sections debated by previous authors are also given

measurement of adsorbed and total 232th 230th ratios from marine sediments the predictable in situ production of 230th from the decay of uranium in seawater and its subsequent removal by scavenging onto falling particles provides a valuable tool for normalizing fluxes to the seafloor we describe a new application determination of the 232th that dissolves in the water column and is removed to the seafloor 232th is supplied to the ocean in continental minerals dissolution of which leads to a measurable standing stock in the water column sedimentary adsorbed 232th 230th ratios have the potential to provide a proxy for estimating the amount of dissolved material that enters the ocean both today and in the past ten core top samples were treated with up to eight different leaching techniques in order to determine the best method for the separating adsorbed from lattice bound thorium in addition separate components of the sediments were analyzed to test whether clay dissolution was an important contribution to the final measurement there was no systematic correlation between the strength of acid used in the leach and the measured 232th 230th ratios in all cases clean foraminifera produced the same ratio as leaches on bulk sediment in three out of five samples leaches performed on non carbonate detritus in the 63 mu m size fraction were also identical without additional water column data it is not yet clear whether there is a simple one to one correlation between the expected deep water 232th 230th and that produced by leaching especially in carbonate rich sediments however higher ratios and associated high 232th adsorbed fluxes were observed in areas with high expected detrital inputs the adsorbed fraction was 35 50 of the total 232th in seven out of ten samples our 230th normalized 232th fluxes are reasonable by comparison to global estimates of detrital inputs to the ocean in nine cases out of ten the total 230th normalized 232th flux is greater than predicted from the annual dust fall at each specific location but lower than the average global detrital input from all sources

palaeoclimate analysis using spectral gamma ray data from the aptian cretaceous of southern england and southern france abstract the abundance and half lives of potassium k uranium u and thorium th make these three elements the dominant sources of gamma rays detected in rocks both at outcrop and in the subsurface with the advent of the spectral gamma ray tool sgr the variation shown by these three elements in rocks has been considered to reflect sorting at flooding surfaces and changes in the weathering regime of sediment source lands k and u are considered to be more soluble than th thus elevated th to k or u ratios in soils and eroded clays can reflect hot humid climates and palaeoclimates this study makes an assessment of the usefulness of sgr data to palaeoclimate studies by comparing changing th k and th u ratios from a known period of palaeoclimate change to extensive published and new data from other analytical methods new sgr data from the cretaceous of southern england and southern france compare favourably to outcrop sedimentological facies interpretations and laboratory geochemical data palaeoclimate data from two other sections northern germany northern italy are compared as controls to the study together these analyses suggest that there was a gradual change from semi arid climate in the barremian and early aptian to a semi humid climate in the mid aptian superimposed on this long term rise in humidity were a number of short term ammonite zone length changes in th k and th u ratios and the abundance of climate sensitive materials this study shows that sgr data are more useful than originally thought when problems of overprinting from heavy minerals and diagenesis are overcome outcrop and borehole spectral gamma ray logs from mudstones or the clay rich beds of mixed successions may be used to interpret past patterns of hinterland weathering

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

outcrop gamma ray logging and its applications examples from the german triassic abstract gamma ray logging of outcrops is a quick and simple yet powerful technique to better correlate well data with surface geology it is particularly useful for integrated sequence stratigraphic analysis and for reservoir and aquifer characterisation using outcrop analogues three examples from the triassic of the cratonic german basin are discussed 1 shallowing upward cycles in the upper muschelkalk carbonate ramp with retrogradational and progradational stacking patterns 2 evaporite to red bed cycles of the gipskeuper 3 fluvial architecture across the terminal alluvial plain system of the stubensandstein such outcrop analog studies help 1 to calibrate subsurface well log data 2 to evaluate the heterogeneity of subsurface reservoirs and aquifers and 3 to provide improved data for quantitative reservoir modelling

carbon isotope stratigraphy across the silurian devonian transition in podolia ukraine evidence for a global biogeochemical perturbation the carbon and oxygen isotope composition of marine carbonates 13 c and 18 o respectively are studied in the fossiliferous stratigraphically well constrained and remarkably expanded successions of podolia sw ukraine spanning the silurian devonian transition significant isotopic shifts are directly comparable to previously published global secular trends in well preserved brachiopod calcite isotopic ratios from this region and therefore may be taken as a reliable primary record of seawater 13 c changes the sections reveal a major positive 13 c excursion with an amplitude above 6 beginning in the upper pridoli and reaching peak values as heavy as 4 2 in the lowermost lochkovian this turnover in carbon cycling is followed by a general trend toward more negative 13 c values in the upper lochkovian the podolian isotopic signals provide strong support for the previously inferred global biogeochemical perturbation across the silurian devonian transition reflecting a complex combination of palaeogeographical biogeochemical and evolutionary processes in the late caledonian geodynamic setting with a likely undervalued role of the expanding vegetation in vast near coastal shallows and deltas

sea level and environmental changes around the devonian carboniferous boundary in the namur dinant basin s belgium ne france a multi proxy stratigraphic analysis of carbonate ramp archives and its use in regional and interregional correlations abstract the paper focuses on high resolution multidisciplinary research on three devonian carboniferous boundary sections in shallow water carbonate rocks in the namur dinant basin belgium france the aim of the study is to provide palaeo environmental reconstructions and correlations supported by several independent quantitative proxies we describe several correlative horizons and provide their sequence stratigraphic interpretation based on facies analysis spectral gamma ray data element concentrations xrf and 13ccarb with foraminifer biostratigraphy age control the most prominent surface is a basal surface of forced regression which is indicated by a sharp basinwards facies shift and a drop in clay gamma ray values and al concentrations at the base of the hastiere and avesnelles formations in more distal settings in proximal settings this surface merges with a hiatus at the devonian carboniferous boundary inferred from foraminifer biostratigraphy this hiatus can be correlated with the global hangenberg sandstone event which indicates a glacioeustatic sea level fall increasing values of zr al k al sr al and mn al coincide with the proximal facies of the falling stage system tract and lowstand system tract in the hastiere and avesnelles formations as a consequence of the enhanced input of siliciclastics and nutrients during low sea levels the top of the middle hastiere member is interpreted as the maximum regression surface which is overlain by transgressive system tract of the upper hastiere member the patterns of gamma ray 13ccarb th k al and zr al curves are well correlated between the studied sections the 13ccarb excursions are correlated with the unnamed excursion in the upper expansa conodont zone carnic alps and with the global hangenberg event s l excursion in the kockeli conodont zone this sequence stratigraphic framework is used for correlations with deltaic successions from the tafilalt basin morocco the basal surface of the forced regression equivalent to the hangenberg sandstone event which is typical for deeper water settings is easily recognisable and correlatable with gaps in more shallow water settings we suggest that it should be taken into account as a possible candidate for the natural solution of the devonian carboniferous boundary in discussions concerning its redefinition

time specific aspects of facies state of the art examples and possible causes abstract the term time specific facies tsf was introduced to the scientific community by the late otto h walliser to refer to unique facies typical of particular narrow intervals some of which were related to bioevents in some senses however the concept was recognized much earlier and is even engrained in the very names of some geologic periods the concept of time specific facies is expanded slightly herein to include distinctive or unique regional to global characteristics of the sedimentary record that characterize particular intervals of geologic time the recognition of time specific and widespread processes in the sedimentary record is a critical step in unraveling the interplay between processes of differing scale these range from very short term but widespread facies that overlap with event deposits to general facies types that may persist for intervals up to 10s of millions of years in duration this paper briefly summarizes the history of development of the tsf concept provides examples to illustrate a few of the key aspects of time specific facies and offers a few tentative explanations for this phenomenon among the factors that control tsfs abrupt changes in redox conditions and early diagenetic mineralization sedimentary condensation often associated with abrupt sea level change altered climate and paleoceanography and biotic evolution and extinction seem to be most critical and permit a preliminary genetic classification of tsfs inevitably however many tsfs reflect multiple effects and some remain largely unexplained

pleistocene climates in china dated by magnetic susceptibility the magnetic susceptibility of loess and interbedded soils in central china varies with the degree of pedogenesis and serves as a proxy measure of climate the concentration of magnetic minerals in the sediment is inversely proportional to sedimentation rates throughout the brunhes epoch susceptibility measurements combined with the reversal stratigraphy provide a time scale that is independent of astronomic chronology on this scale the susceptibility record closely parallels the oxygen isotope fluctuations in deep sea sediments suggesting a close interdependence of the chinese dust falls the volume of land based ice and global climate

the astronomical calibration of the givetian middle devonian timescale dinant synclinorium belgium recent advances in radiometric dating result in significant improvements in the geo logical timescale and provide better insight into the timing of various processes and evolutions within the earth s system however no radiometric ages are contained within the givetian con sequently the absolute ages of the givetian stage boundaries as well as the stage s duration remain poorly constrained as an alternative the analysis of sedimentary cycles allows for the esti mation of the duration of this stage we examined the high resolution magnetic susceptibility signals of four givetian outcrops in the givet area for a possible astronomical imprint to fully understand the rates of evolutionary and environmental change all four sections are firmly corre lated and wavelet analyses of the magnetic susceptibility signals reveal the imprint of astronomical eccentricity forcing the highly stable 405 kyr cycles constrain the duration of the givetian stage at 4 35 0 45 myr which is in good agreement with the international chronostratigraphic chart 5 0 myr the studied sections also exhibit an imprint of obliquity suggesting a climatic telecon nection between low and high latitudes the corresponding microfacies curves demonstrate similar astronomical imprint and thereby indicate that the observed 10 5 year scale cyclicity is the result of climatic and environmental change

the gold content of volcanogenic massive sulfide deposits volcanogenic massive sulfide deposits contain variable amounts of gold both in terms of average grade and total gold content with some vms deposits hosting world class gold mines with more than 100 t au previous studies have identified gold rich vms as having an average gold grade expressed in g t exceeding the total abundance of base metals expressed in wt however statistically meaningful criteria for the identification of truly anomalous deposits have not been established this paper presents a more extensive analysis of gold grades and tonnages of 513 vms deposits worldwide revealing a number of important features in the distribution of the data a large proportion of deposits are characterized by a relatively low gold grade 2 g t with a gradual decrease in frequency towards maximum gold grades defining a log normal distribution in the analysis presented in this paper the geometric mean and geometric standard deviation appear to be the simplest metric for identifying subclasses of vms deposits based on gold grade especially when comparing deposits within individual belts and districts the geometric mean gold grade of 513 vms deposits worldwide is 0 76 g t the geometric standard deviation is 2 70 g t au in this analysis deposits with more than 3 46 g t au geometric mean plus one geometric standard deviation are considered auriferous the geometric mean gold content is 4 7 t au with a geometric standard deviation of 26 3 t au deposits containing 31 t au or more geometric mean plus one geometric standard deviation are also considered to be anomalous in terms of gold content irrespective of the gold grade deposits with more than 3 46 g t au and 31 t au are considered gold rich vms a large proportion of the total gold hosted in vms worldwide is found in a relatively small number of such deposits the identification of these truly anomalous systems helps shed light on the geological parameters that control unusual enrichment of gold in vms at the district scale the gold rich deposits occupy a stratigraphic position and volcanic setting that commonly differs from other deposits of the district possibly due to a step change in the geodynamic and magmatic evolution of local volcanic complexes the gold rich vms are commonly associated with transitional to calc alkaline intermediate to felsic volcanic rocks which may reflect a particularly fertile geodynamic setting and or timing e g early arc rifting or rifting front at the deposit scale uncommon alteration assemblages e g advanced argillic aluminous strongly siliceous or potassium feldspar alteration and trace element signatures may be recognized e g au ag as sb bi hg te suggesting a direct magmatic input in some systems

fluid control of localized mineral domains in limestone pressure solution structures grain to grain and stylolitic solution structures in two central appalachian siluro devonian limestone macroscale folds contain one of four distinct mineral assemblages that are characterized by the dominant iron phase mineral present 1 chloritegillitegpyritegcalciteg quartzgtio2ggoethite 2 chloritegillitegpyrite altered to iron oxide hydroxidegcalcite gquartzgtio2 3 chloritegilliteg magnetitegcalcitegquartz and 4 chloritegilliteggoethitegcalcitegquartzgtio2 optical reflectance microscopy and sem eds was used to characterize the mineralogy and mineral morphology of these structures geochemical modeling was used to constrain the conditions of formation and preservation the primary control on solution structure mineral assemblage was the redox conditions present in the solution structures during burial and deformation the redox conditions on the microscale may have been controlled by the local fluid chemistry and the presence absence of hydrocarbons and organic acids within the formation fluids and the influx of externally derived fluids by fracture formation during the folding process the wide variation in mineralogy of the solution structures shows that they were chemical factories where a variety of chemical reactions took place during rock dissolution in particular the formation of authigenic magnetite in solution structures has significant implications for paleomagnetic applications and use of anisotropy of anhysteretic remanent magnetization and anisotropy of magnetic susceptibility fabrics q 2005 elsevier ltd all rights reserved

the middle and upper lochkovian lower devonian conodont successions in key peri gondwana localities spanish central pyrenees and prague synform and their relevance for global correlations detailed correlation based on conodont sequences between middle and upper lochkovian carbonate successions from two key peri gondwanan regions the spanish central pyrenees and the prague synform is attained for the first time this correlation facilitates the definition of tie points for further multidisciplinary studies that seek to establish high resolution temporal subdivision and global correlation some intervals have a precision of less than 0 5 ma which is significantly greater than in previous studies the estimated elapsed time considered herein is about 3 2 ma and is subdivided into five major zones of global scope transitanstrigonicus trigonicus kutscheri kutscheri pandora b pandora b gilberti and gilberti steinachensis b by providing tie points and globally applicable criteria this research contributes to the international cooperative effort to subdivide the devonian standard stages into globally recognised substages

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

the role of strain localization in magma injection into a transtensional shear zone variscan belt sw iberia this study deals with the interaction between deformation and magmatism in mid to deep crustal domains the relation is analysed between migmatites and shear zones and the spatial distribution of leucogranitoid veins and dykes running through a footwall migmatite system and reaching a transtensional shear zone operated under amphibolite to greenschist facies metamorphic conditions boa fe shear zone variscan belt sw iberia statistical results show that the frequency of width and spacing of the leucogranitoid dykes conform to power law distributions comparable with observations in volcanic systems the fractal geometry of the distribution of leucogranitoid dykes highlights the development of a dense framework of thinner weakly or non mineralized veins and dykes formed at higher nucleation growth ratios in the footwall migmatite system that contrasts with the emplacement of thicker dykes associated with strongly mineralized thinner veins within the shear zone the volume of injected leucogranitoid dykes in the shear zone is lower as compared with the footwall and is comparable with an expanding footwall shear zone with non coaxial flow and volume increase the boa fe shear zone seems to form a physical barrier to the transport of magma to the hanging wall

redistribution of rare earth elements during diagenesis of turbidite hemipelagite mudrock sequences of llandovery age from central wales

ore deposit types and tectonic evolution of the iberian pyrite belt from transtensional basins and magmatism to transpression and inversion tectonics abstract a new interpretation of the structural evolution of the iberian pyrite belt ipb and volcanogenic massive sulfide mineralization vms is presented in this work based on a review of the ore deposit types the analysis of the hosting volcanic sequences and the tectonic evolution the vms deposits of the ipb are hosted by volcanic and siliciclastic rocks four main volcano sedimentary sequences vsc from vsc0 to vsc3 have been assumed the main deposits being located in the vsc0 and at the top of the vsc2 we have defined three main sectors oriented approximately e w and hosting the vms deposits in the northern sector which is mostly located in spain graben basins and local pull aparts are the main structures in this sector two belts can be distinguished the deposits being located at the top of the vsc2 felsic volcanism rio tinto type ipb deposits in the central sector both in spain and portugal half graben basins are the most common structures and the deposits are mostly located in the vsc0 andesitic volcanic sedimentary sequence tharsis type ipb deposits in the southern sector which is only located in portugal a graben basin with a pull apart is again the main structure and the deposits are located in black slates and at the top of a felsic volcanism strunian in age vsc0 the deposits located in graben basin with a pull apart are essentially felsic volcanic hosted with some siliciclastic material mostly black shales by contrast those located in half graben basins are mainly hosted by black shales with minor amounts of andesitic rocks the tectonic evolution shows that as a result of a counterclockwise rotation of the stress axes the formation of the ipb and the associated ore deposits took place during several episodes from transtension with the development of both graben with pull aparts and half graben basins through left lateral e w shearing to transpression at the beginning of the transtensional process several extensional roughly e w trending faults that developed graben and half graben basins were generated and the first volcanic andesite rhyolite rocks vsc0 formed the tharsis type deposits mainly hosted by black slates with some volcanic rocks were formed in the central sector while the neves corvo type deposit hosted by black slates and felsic volcanism formed in the southern one after a period characterized by barren mafic volcanism vsc1 a sinistral shear affected the previous fractures due to the stress axis rotation and felsic crustal volcanism started vsc2 rhyolites and dacites were particularly abundant in two graben basins which developed rollovers in pull apart zones forming the rio tinto type deposits in the northern sector the thermal increase associated with vsc0 and vsc2 gave rise to the development of crustal scale hydrothermal convective cells which generated both types of deposits after a barren vsc3 felsic volcanism subsequently during the variscan transpressional phase the e w extensional faults were reactivated as reverse faults affecting the volcanic sequence vsc0 to vsc3 as well as the interbedded sedimentary rocks mostly black shales as has been recognized at the rio tinto deposit buttressing must have played a significant role in the geometry of inverted structures and the vms ores were intensely recrystallized it should be emphasized that this new regional geological model for the ipb is an approach to provide a better insight into vms deposits and could be a key point for further studies providing a new tool to improve knowledge of the vms mineralizations and exploration guidelines elsewhere in the ipb

carbon and oxygen isotope record across pridoli to givetian stage boundaries in the barrandian basin czech republic abstract carbon and oxygen isotope composition and the chemistry of limestones clayey limestones and shales were studied across stage boundaries from pridoli to givetian in the barrandian basin no substantial isotopic shifts were found at the pragian emsian and emsian eifelian boundaries a gradual shift in 13c values from 2 6 to 3 6 was observed in pridoli and lochkovian limestones this shift is inferred to have been related to a combination of higher productivity increased deposition of organic matter and shallowing of the basin the global kacak otomari event just below the eifelian givetian boundary is marked by an abrupt change in carbon isotopic values from about 1 to 3 in pelagic carbonates no 13c shift was found in shallow water carbonates at the eifelian givetian boundary high 18o values up to 1 3 in pragian emsian and early eifelian limestones indicate that the barrandian basin was relatively isolated from the world ocean during those intervals lower 18o values up to 7 5 in late eifelian limestones may indicate the end of isolation

quantitative allochem compositional analysis of lochkovian pragian boundary sections in the prague basin czech republic abstract quantitative allochem compositional trends across the lochkovian pragian boundary event were examined at three sections recording the proximal to more distal carbonate ramp environment of the prague basin multivariate statistical methods principal component analysis correspondence analysis cluster analysis of point counted thin section data were used to reconstruct facies stacking patterns and sea level history both the closed nature allochem percentages and their centred log ratio clr coordinates were used both these approaches allow for distinguishing of lowstand transgressive and highstand system tracts within the praha formation which show gradual transition from crinoid dominated facies deposited above the storm wave base to dacryoconarid dominated facies of deep water environment below the storm wave base quantitative compositional data also indicate progradative retrogradative trends in the macrolithologically monotonous shallow water succession and enable its stratigraphic correlation with successions from deeper water environments generally the stratigraphic trends of the clr data are more sensitive to subtle changes in allochem composition in comparison to the results based on raw data a heterozoan dominated allochem association in shallow water environments of the praha formation supports the carbonate ramp environment assumed by previous authors

warming or cooling in the pragian sedimentary record and petrophysical logs across the lochkovian pragian boundary in the spanish central pyrenees abstract high resolution petrophysical correlation methods were applied for the first time to mid paleozoic rocks of the pyrenees the methods included magnetic susceptibility measurements ms gamma ray spectrometry grs and alignment of ms logs using the dynamic time warping dtw algorithm conodont biostratigraphy provided the basic framework necessary for work with the grs and ms logs despite differences in the sediment patterns and accumulation erosion rates the logs from two selected sections in the spanish central pyrenees show a striking symmetry that correlates well with the previously published logs from the barrandian area in the czech republic the high similarity between the petrophysical records from paleogeographically related but distant areas has the potential to contribute to the current discussions about the eustatic and climatic changes that took place in the overall greenhouse settings where evidence for any polar ice sheets is still absent in addition to the extant evidence of a major lochkovian pragian offlap combined with sea level lowering known from the north america evidence about a major sea level fall and drastic reconstruction of the climatic system in the pragian is now expanding over significant parts of the peri gondwanan belt the data from spain provide many new details about this change including the phenomenon of a stratigraphically condensed upper lochkovian a dramatically different type of sedimentation in the pragian and a grs th and ms anomalous stratigraphic interval in the middle pragian the multifaceted evidence allows us to determine the essential parts of the pragian as a still hot and humid period even with the strong differences from the possibly extremely hot lochkovian

lead isotope systematics of the giant massive sulphide deposits in the iberian pyrite belt lead isotope analyses were performed on 26 polymetallic massive sulphide deposits of the iberian pyrite belt as well as on overlying gossans and associated volcanic rocks all the massive sulphide deposits except for neves corvo and nearly all the volcanic rocks show very similar isotopic compositions grouped around 18 183 206pb 204pb 15 622 207pb 204pb and 38 191 208pb 204pb indicating that most of the ore deposit lead was derived from the same continental crust environment as the associated volcanic rocks the isotopic compositions are representative of the average south iberian crust during the devonian to early carboniferous dinantian and their constancy implies a homogenization of the mineralizing fluids before the deposition of the massive sulphides from hydrothermal fluids circulating through interconnected regional fracture systems this isotopic constancy is incompatible with multiple small independent hydrothermal cells of the east pacific rise type and fits much better with a model of hydrothermal convections driven by magmatic floor heating neves corvo is the only south iberian massive sulphide deposit to have a heterogeneous isotopic composition with in particular a highly radiogenic stanniferous ore 206pb 204pb of the cassiterite is 18 40 a model of lead mixing with three components is proposed to explain these variations 1 one derived from the devonian to early carboniferous dinantian continental crust that generated all the other massive ores 2 an eohercynian stanniferous mineralization partly remobilized during the formation of the massive sulphides but independent of them and 3 a precambrian continental crust component the juxtaposition of three different sources places neves corvo in a specific paleogeographic situation that could also explain its mineralogical specificity the geodynamic context that best explains all the obtained isotopic results is one of an accretionary prism the fact that lead isotope signatures of the gossans are almost identical to those of the underlying massive sulphides means that this technique could be a useful exploration tool for the iberian pyrite belt

petrophysical record of the late silurian shallow water carbonate facies across the lau event prague synform czech republic and dynamic time warping alignment of the magnetic susceptibility logs

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

magnetization carriers of grey to red deep water limestones in the gssp of the givetian frasnian boundary puech de la suque france signals influenced by moderate diagenetic overprinting limestones at the puech de la suque global boundary stratotype section and point gssp of the givetian frasnian boundary show a drastic change towards much higher magnetic susceptibility values in the givetian rocks different rock magnetic parameters indicate that ferromagnetic minerals are the main controlling factor the ferromagnetic fraction is composed of low magnetite type and high coercivity hematite and goethite phases confirmed by the spectral reflectance high coercivity minerals are fluctuating along the section with a higher abundance in the basal frasnian these phases may be of secondary origin and produced during burial stage the magnetite type phase contains two different grain size populations the identified that stable single domain superparamagnetic ssd sp particles are of diagenetic origin and their amount decreases slightly upwards a second group of magnetite grains correspond to coarse grained particles identified using the squareness v coercive force plot it is tentatively suggested here that these particles present throughout the section are of primary origin on the contrary the paramagnetic minerals underwent a clear diagenetic overprinting and may represent secondary minerals the presence of a primary ferromagnetic carrier allowed the use of spectral analyses leading to the detection of spectral peaks at 1 25 and 4 cycles m which can be interpreted as the result of 405 kyr and 100 kyr eccentricity forcing respectively

cretaceous oceanic red beds as possible consequence of oceanic anoxic events article i nfo oceanic anoxic events oaes represent brief periods of burial of large amounts of organic carbon in the oceans during cretaceous time burial of organic carbon which preferentially sequestered isotopically lighter carbon during oaes resulted in positive 13 c excursions of 2 3 recognizable in global ocean these deposits are typically dark grey to black shales considered to be the result of interaction between extreme warm climate ocean circulation high bioproductivity and organic carbon preservation less interest has been given to periods between oaes when oxic deep sea deposits such as red marls and red shales were deposited during mid and late cretaceous the latter deposits are associated with very low content of organic carbon and oxic depositional environments which dominated western tethys in post turonian time up to the early eocene feedbacks among geochemical cycles in response to decreasing global temperatures increasing deep ocean circulation forced by high latitude deep water formation along the antarctic margin and widening and deepening of the interconnections between the oceanic basins may have been responsible for the major paleoceanographic change from deposition of organic carbon rich black shales during mid cretaceous to world wide deposition of cretaceous oceanic red beds corbs in the late cretaceous the presence of corbs sandwiched between mid cretaceous oaes may reflect major climate and paleoceanographic changes in a contrast to extremely warm climates during the oaes the corbs suggest cold periods and therefore oscillating climate shifts that have seldom been considered during modeling of cretaceous

dating diagenetic monazite in mudrocks constraining the oil window authigenic monazite nodules increasingly recognized in pre mesozoic mudrock successions provide a means for dating diagenesis by exploiting trace uranium within the monazite structure but dating is difficult in practice because of zonation and abundant host rock inclusions we report here a refined technique that has yielded a date of 419 14 ma 2 mswd 1 2 for a 17 point pb pb regression age from a telychian silurian late llandovery mudrock from central wales shrimp analyses of monazite nodules from the same horizon are consistent with this and additionally demonstrate concordance of the u pb and th pb systems these results open the door to providing robust dates for a phase of burial related diagenesis which in wales seems approximately coincident with and perhaps was related to hydrocarbon expulsion

global time scale and regional stratigraphic reference scales of central and west europe east europe tethys south china and north america as used in the devonian carboniferous permian correlation chart 2003 dcp 2003 the boundaries of the devonian carboniferous and permian stages of the global stratigraphic reference scale abbreviated to global stratigraphic scale gss are described in relation to the biostratigraphic and or lithostratigraphic units of the regional stratigraphic reference scales abbreviated to regional stratigraphic scales rss of central and west europe east europe tethys south china eastern tethys and north america in their type regions the boundaries of gss units rarely coincide with those of homonymous rss units moreover the definitions of some rss units have changed several times over the last decades and subsequent misunderstanding of the stratigraphical significance of these changes has often introduced errors into proposed global correlation charts the stratigraphic framework proposed in our global devonian carboniferous permian correlation chart 2003 dcp 2003 devonian carboniferous permian correlation chart 2003 menning m schneider j w alekseev a s amon e o becker g von bitter p h boardman d r bogoslovskaya m braun a brocke r chernykh v chuvashov b i clayton g dusar m davydov v i dybova jachowicz s forke h c gibling m gilmour e h goretzki j grunt t a hance l heckel p h izokh n g jansen u jin y g jones p kading k ch kerp h kiersnowski h klets a klug ch korn d kossovaya o kotlyar g v kozur h w laveine j p martens th nemyrovska t l nigmadganov a l paech h j peryt t m rohn r roscher m rubidge b schiappa t a schindler e skompski s ueno k utting j vdovenko m v villa e voigt s wahlman g p wardlaw b r warrington g weddige k werneburg r weyer d wilde v winkler prins c f work d m 2004 abschlusskolloquium dfg schwerpunktprogramm 1054 evolution des systems erde wahrend des jungeren palaozoikums im spiegel der sedimentgeochemie abstracts univ erlangen germany 2004 p 43 herein abbreviated to dcp 2003 and cited as dcp 2003 in references is an attempt to reduce these errors the dcp 2003 is the stratigraphic base for project 1054 of the deutsche forschungsgemeinschaft dfg the evolution of the late palaeozoic in the light of sedimentary geochemistry this composite time scale has been carefully balanced as far as data allows to remove unnecessary artificial compression and expansion of time intervals biozonations and depositional events the ages selected in dcp 2003 are markedly different to those in the geologic time scale 1989 gts 1989 harland w b armstrong r l cox a v craig l e smith a g smith d g 1990 a geologic time scale 1989 cambridge univ press cambridge harland w b armstrong r l cox a v craig l e smith a g smith d g 1990 a geologic time scale 1989 cambridge univ press cambridge pp 1 263 and in gradstein and ogg gradstein f m ogg j 1996 a phanerozoic time scale episodes 19 1 2 3 4 insert whereas they are closer to those of the geologic time scale 2004 gts 2004 gradstein f m ogg j g smith a g 2004 a geologic time scale 2004 cambridge univ press cambridge pp 1 589 mostly the ages are rounded to the nearest 0 5 ma in order to avoid estimates of questionable accuracy whereas ages of 0 1 ma in the gts 2004 and their error bars of 0 4 ma to 2 8 ma for the devonian to permian stage boundaries suggest an improved accuracy in contrast in the dcp 2003 questionable ages and positions of stratigraphic boundaries are marked by arrows c 2006 elsevier b v all rights reserved

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

color facies changes and global events a hoax a case study from the lochkovian lower devonian in the spanish central pyrenees abstract five pyrenean lochkovian sections are studied aiming at the recognition of the influence of facies changes in biotic global events the wealthy conodont record permits precise age control of strata in the different sections and high precision correlations both regional and intercontinental it also permits identification of major global biotic events for this group of fossils the comparison of the bio and chronostratigraphic framework with the different facies identified in the pyrenean rocks shows that contrasting color and facies changes are not synchronous in the studied sections and that the major biotic events are not directly related to relevant facies shifts these results question the opinion of direct tie relations between strong color changes and global events in the lower devonian and reinforce the value of palaeontological tools for global studies and correlations

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

early devonian lochkovian early emsian bioevents and conodont response in the prague synform czech republic abstract the devonian succession of the prague synform is characterized by two major lithofacies shallow water biodetrital mostly crinoidal limestones that also include a reefal skeletal accumulation of pragian age and a more pelagic facies that is represented mostly by calcisiltites among the several devonian prominent sea level fluctuations some can be traced globally e g the basal pragian and kacak events in recent years conodont biostratigraphy of the early devonian lochkovian pragian and early emsian of the prague synform has been refined the regional subdivision of the lower devonian in its type area has been greatly improved by the integration of new biostratigraphic chemostratigraphic sedimentological and petrophysical data that has in turn strengthened global correlations for this interval in earth s history the complete conodont biozonation of the early devonian interval basal lochkovian earliest emsian in the prague synform includes 17 biozones which can be applied to sections representing various depositional environments and have more global applicability than previously proposed global conodont biozonations the zonal scale enables a precise biostratigraphic delimitation of the major early devonian biotic events silurian devonian boundary event lochkovian pragian event and basal zlichovian event there were major changes in the conodont fauna in response to the silurian devonian boundary and lochkovian pragian events however the basal zlichovian event was only characterized by a very gradual transition in the conodont fauna in parallel to the traditional events defined for the prague synform seven other significant conodont events have been documented these events represent major turnovers in the conodont fauna that have a direct impact on conodont biostratigraphy specifically at a global scale the icriodus and irregularis events are congruent with the lower boundaries of the lochkovian and pragian stages respectively the conodont events established in the prague synform largely reflect variations in the seawater depth but are generally independent of lithological changes within sections of the prague synform

carbon isotope stratigraphy of lochkovian to eifelian limestones from the devonian of central and southern europe lower to middle devonian carbonates of the prague syncline the carnic alps the montagne noire and the cantabrian mountains were investigated for 13ccarb and 13corg these values were measured on bulk rocks selected components and cements many carbonates exhibit primary marine values but some are altered by diagenesis a 13c curve can be presented for the latest pridolian to emsian time interval several sharp or broad positive excursions are obvious in the woschmidti postwoschmidti sulcatus kitabicus late serotinus and kockelianus conodont zones the excursion at the silurian devonian boundary is known worldwide and therefore considered global in nature some of the others are described for the first time from central and southern europe and their global nature has to be verified by further investigations in other regions most excursions relate to and or started during major regressions whereas sea level highstands correspond to minimal 13c values similar relationships between sea level changes and 13c have been observed from other early palaeozoic intervals the transgressive chotec and kacak events are marked by positive isotope excursions this type of combination is usually observed in late palaeozoic to cenozoic black shale events

millennial scale climate changes manifest milankovitch combination tones and hallstatt solar cycles in the devonian greenhouse world sub milankovitch rhythmic features in sedimentary records have been reported from throughout geological time however their origin remains enigmatic in particular during so called greenhouse periods in earth s history to better understand such short term climatic changes we sampled two 3 m thick intervals of early devonian hemipelagic carbonate at 1 cm resolution in the pod barrandovem section czech republic greenhouse conditions prevailed during early devonian times and the chosen resolution enables the detection of millennial scale climate change as recorded by elemental abundances we used a previously published astrochronology for the section to transform the studied series from the stratigraphic into the time domain spectral analysis of the time calibrated log transformed ti records reveal obliquity and precession cycles confirming the applied astrochronology additional spectral peaks with periods of 2 3 2 7 6 8 and 10 12 k y appear in both records furthermore a 1 5 k y periodicity close to the pleistocene dansgaard oeschger oscillation is also identified but only in the record with higher accumulation rate 3 5 cm k y bi coherence spectra reveal that the 6 8 and 10 12 k y periodic components are combination tones of milankovitch cycles we infer the shorter 2 5 k y periodicity to be the result of solar forcing related to the hallstatt cycle these new observations strengthen the case for an external origin of millennial scale features

use of spectral gamma ray signature to interpret stratigraphic surfaces in carbonate strata an example from the finnmark carbonate platform carboniferous permian barents sea spectral gamma ray gr profiles were examined in well 7128 6 1 the stratigraphic reference section of the entirely subsurface finnmark carbonate platform detailed bulk chemical profiling of selected gr peaks shows that potassium k and thorium th are mutually correlated and are a direct index of siliciclastic aluminosilicate content whereas uranium u is uncorrelated with k th and all other chemical components measured uranium tends to be enriched in thin shale and argillaceous carbonate layers within otherwise carbonate dominated intervals uranium is thus associated with aluminosilicate minerals and is not particularly concentrated in dolomite two types of gr peaks are observed potassium thorium dominated peaks are suggested to indicate relatively major transgressions during which aluminosilicate detritus was derived from sources interior to the fennoscandian shield uranium dominated peaks correspond with relatively minor transgressions within intervals of cyclic shallow water carbonate deposits uranium enriched aluminosilicate detritus is suggested to be the product of extended subaerial exposure of the platform during which u was concentrated by groundwater movement these results can be useful as a basis for applying spectral gr signature as a tool for stratigraphic interpretation in uncored or incipiently understood carbonate sections

spectral gamma ray logging of the gres d annot se france an outcrop analogue to geophysical facies mapping and well log correlation of sand rich turbidite reservoirs abstract spectral gamma ray grs logging is a powerful tool in cyclo and sequence stratigraphy of carbonate depositional systems in siliciclastic systems with low chemical maturity the multi component character of sediment complicates the interpretation of such logs this work focuses on understand better the relationships between grs logs and siliciclastic facies stacking patterns using grs measurements combined with lithology modal composition and geochemistry this study is focused on outcrops in the st antonin annot grand coyer chalufy areas of the oligocene gres d annot formation se france the studied siliciclastics reveal moderately high total radioactivity and mean concentrations of k 3 8 u 4 5 ppm and th 13 ppm u and th are predominantly contained within heavy minerals and so tend to be concentrated in mudstones and heterolithic sand mud facies whereas sandstone and conglomerate facies have slightly higher levels of k due to higher contents of k feldspars and micas the abundance of minerals containing radioactive elements and the relatively low compositional contrast between different facies are considered the main reasons why the standard gamma ray measurements provide only a limited proxy for lithology in this case two complete regressive to transgressive cycles were identified based on combined th and th k logs and facies stacking patterns the cycle boundaries are marked by shifts towards coarse grained facies abrupt increase of u and th concentrations and th k ratio within the proximal deposits at the st antonin section in the distal chalufy section the response of the gamma ray proxies to facies shifts is reversed these boundaries interpreted as basal surfaces of forced regression can be correlated with prominent erosional surfaces at the annot section grs logging is a sensitive method capable of indicating changes of genetic depositional units in sand rich turbidite systems however detailed facies analysis mineralogy and geochemistry producing the radioactive signal are necessary to correctly interpret such logs

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

oxygen and carbon stable isotope records of the lochkovian pragian boundary interval from the prague basin lower devonian czech republic abstract climate changes close to the lochkovian pragian event are still widely discussed carbonate 18o and 13c and conodont apatite 18o from medial to distal carbonate ramp sediments were analysed to provide further stable isotope data from the stratotype area in the prague basin the uppermost silurian to lower emsian 18o trends are put into an updated conodont biostratigraphy framework carbonate 18o and 13c are discussed in the context of facies dependent diagenesis the 13c pattern measured from different sections enables the correlation of intervals with development of different facies inside the prague basin positive 13c shifts are often coupled with trends of decreasing computed gamma ray cgr values interpreted as regressions whereas negative 13c shifts commonly coincide with opposite trends in cgr the lochkovian pragian boundary interval coincided with an increase in carbonate 13c and an increase in the 18o of conodont apatite and carbonate which we interpret as consequence of climate cooling generally the lochkovian was warmer than the pragian and earliest emsian