burial history of palaeozoic strata in belgium as revealed by conodont colour alteration data and thickness distributions thickness distributions of devono carboniferous formations and their relationship to conodont colour alteration indices cais from over 500 sample locations in belgium and northern france have been studied to reconstruct the thermal alteration and burial history of palaeozoic rocks the depositional centre during eifelian through visean times was located in the subsiding southern part of the dinant basin forming a thick sedimentary pile of probably more than 3 5 km in order to explain conodont cais chiefly resulting from upper carboniferous sedimentation two different depositional centres are considered giving rise to approximately 4 5 km of sediment in the central part of the dinant and namur basins as a consequence of the northward shifting variscan fold belt the upper carboniferous succession in the southern part of the dinant basin and in the rocroi area was reduced or absent conodont cais together with other thermal alteration data from the condroz massif indicate that this area was a structural high for most of the devonian the brabant massif was probably covered with approximately 1 5 2 0 km of upper carboniferous sediments in the south and less than 1 0 km in the central and northern parts in the central campine basin visean strata could have been buried by 3 5 4 5 km of upper carboniferous rocks

internal layer tracing and age depth accumulation relationships for the northern greenland ice sheet clues to previous ice sheet structure and long term glaciological processes are preserved in the internal layering configuration of the greenland ice sheet information about these internal layers has been retrieved over many parts of the ice sheet with the university of kansas ice penetrating radar we report on the coherence of these layers over very large distances describe a method of tracing these layers along thousands of kilometers of flight line and do so for one flight during the 1999 program for arctic regional climate assessment parca aircraft campaign we determine the ages of these layers based on information at the grip ice core site and extend these ages along the flight line to camp century where they are compared to modeled derived age estimates these ages agree with each other to between 2 and 15 differences that can be substantially reduced with minor changes to the model parameters accumulation rate and shear layer depth finally we are able to derive estimates of accumulation rates along the flight line by fitting the age depth data from layer tracing to a dansgaard johnsen model with a minimization technique providing estimates that match recent accumulation patterns within a few centimeters per year

carbon isotope excursions and sea level change implications for the frasnian famennian biotic crisis new carbon and oxygen isotope data from carbonates spanning the frasnian famennian f f boundary in the guilin area south china show a broad positive 13 c rise and fall with sharp short lived negative 13 c events this pattern is comparable to that in europe and north america the integration of the isotope stratigraphy with high resolution sequence stratigraphy corroborates the onset of the positive 13 c excursion during a third order sea level fall in the latest frasnian this can best be explained through increased burial of c org during the sea level fall brought about by increased organic productivity caused by increased continent derived nutrient flux to the ocean due to enhanced weathering through the proliferation of land plants in the devonian this scenario would have resulted in anoxic and eutrophic conditions over epicontinental seas and blooms of cyanobacteria creating a highly stressful and fragile ecosystem for oligotrophic normal marine benthic organisms and leading to their massive decline the global third order sea level fall near the end of the frasnian may have led to gas hydrate dissociation giving the negative 13 c events and caused wild climatic fluctuations the subsequent short term events of sea level rise anoxia and eutrophication in the latest part of the f f transition would have placed additional environmental stresses on the already weakened biota leading to their further demise

anisotropy of schists contribution of crustal anisotropy to active source seismic experiments and shear wave splitting observations we have made sets of five independent compressional and shear wave velocity measurements which with density allow us to completely characterize the transverse isotropy of samples from five metamorphic belts the haast schist terrane south island new zealand poultney slate chugach phyllite coldfoot schist and pelona schist united states these velocity measurements include compressional wave velocities for propagation parallel perpendicular and at 45 to the symmetry axis shear wave velocity for propagation and particle motion perpendicular to the symmetry axis and shear wave velocity for propagation parallel to the symmetry axis velocity measurements were made up to pressures of 1 gpa 35 km depth where microcracks are closed and anisotropy is due to preferred mineral orientation our samples exhibit compressional wave anisotropy of 9 20 as well as significant shear wave splitting metamorphic terranes that are anisotropic to ultrasonic waves may also be anisotropic at the scale of active and passive seismic experiments our data suggest that a significant thickness 10 20 km of appropriately oriented steeply dipping foliation schist in the crust could contribute as much as 45 of observed shear wave splitting our data set can also be used to model the effects of crustal anisotropy for active source seismic experiments in order to determine if the anisotropy of the terrane is significant and needs to be taken into account during processing and modeling of the data

glacial interglacial variations in central east antarctic ice accumulation rates past rates of ice accumulation in central east antarctica are defined poorly for the last glacial period ice cores from which current estimates are based are limited in number there is one deep ice core at vostok station one at dome f and two others currently being extracted at dome c and dronning maud land and are restricted spatially they are one dimensional here spatial variations in ice accumulation rates during the last glacial are calculated from isochronous internal ice sheet layering measured by airborne ice penetrating radar data the layers are used to identify the stratigraphy around five east antarctic ice domes isochrons are dated by linking them to the vostok ice core and in one case the epica dome c ice core this chronostratigraphy allows the depth age function to be identified across the ice sheet a simple ice flow model using the depth age measurements as input is then used to determine the spatial and temporal variation in east antarctic ice accumulation over the last glacial cycle the lowest rates of ice accumulation were predicted in the full glacial period to the south of dome a and ridge b there are two possible explanations for this 1 the ice divide topographies may have caused a precipitation shadow in the ice age 2 with the expansion of the ross ice shelf the area to the south of dome a and ridge b would be at the very centre of the ice sheet and hence at a maximum distance from the ocean moisture source r 2002 elsevier science ltd all rights reserved

extending the vostok ice core record of palaeoclimate to the penultimate glacial period the ice core record of local temperature dust accumulation and air composition at vostok station antarctica now extends back to the penultimate glacial period 140 200 kyr ago and the end of the preceding interglacial this yields a new glaciological timescale for the whole record which is consistent with ocean records temperatures at vostok appear to have been more uniformly cold in the penultimate glacial period than in the most recent one concentrations of co2 and ch4 correlate well with temperature throughout the record

an alternative model for positive shifts in shallow marine carbonate 13c and 18o positive shifts in global seawater d 13 cdic are related to changes in the ratio of organic relative to inorganic carbon burial in oceanic basins whereas factors such as climatic cooling and the accumulation of polar ice are known to cause positive shifts in d 18 o here an alternative model is proposed for the formation of local positive isotope shifts in shallow marine settings the model involves geochemically altered platform top water masses and the effects of early meteoric diagenesis on carbonate isotopic composition both mechanisms are active on modern sub tropical carbonate platforms and result in low carbonate d 13 ca ndd 18 o relative to typical oceanic values during high amplitude transgressive events the impact of isotopically light meteoric fluids on the carbonate geochemistry is much reduced and 13 c depleted platform top water mixes with open oceanic water masses having higher isotope values both factors are recorded as a transient increase in carbonate 13 c and 18 o relative to low background values these processes must be taken into consideration when interpreting the geochemical record of ancient epeiric seas

anomalous diffusion of electromagnetic eddy currents in geological formations controlled source electromagnetic em induction in some geological formations isshown here to be compactly described by an anomalous subdiffusion process such aprocess which is not universal is governed by a fractional diffusion equation oralternatively the convolutional form of ohm s law a subdiffusing eddy current vortex or electromagnetic smoke ring propagates in such a way that its position of medianintensity overruns its position of peak intensity this behavior is not allowed in classicaldiffusion but is a simple consequence of diffusion within a stationary fractal medium a similar analysis has been applied to understand heavy tailed traveltime distributions thatappear in certain hydrological time series the tell tale signature of anomalouselectromagnetic diffusion is a slope b of the magnetic zero crossing moveout curve that isconstant with transmitter receiver rx offset and significantly different from unity neither lateral heterogeneity nor unixial anisotropy can generate such a constant slopemoveout curve with an economy of model parameters controlled source em data fromtwo sites in texas and one in new mexico are used in this study to test the eddy currentsubdiffusion hypothesis

controls of extreme isotopic enrichment in modern microbialites and associated abiogenic carbonates abstract microbialites and abiogenic carbonates of the closed basin hypersaline lake laguna negra catamarca province argentina are highly enriched in both 13c and 18o these carbonates precipitate in the zone of recharge where lake water mixes with groundwater we examined the processes controlling the isotopic evolution of input waters in order to better interpret the isotopic compositions of the carbonates large enrichments of 13c in dissolved inorganic carbon and 18o in water occur as input groundwater chemically evolves these enrichments can be explained through the abiotic processes of water equilibration evaporation degassing and carbonate precipitation the 13c and 18o contents of lake carbonates are consistent with equilibrium precipitation from lake water indicating that the currently ongoing processes can explain the isotopic patterns observed in carbonates isotopic compositions of these microbialites are largely unrelated to the biological processes controlling microbialite formation a pattern that may be generalizable to other settings however the isotopic compositions of these microbialites record information about their depositional environment

diagenesis of devonian reefal carbonates in the oscar range canning basin western australia abstract the oscar range part of the extensive devonian reef complex of the northern canning basin is a large atoll 80 10 km in which frasnian and famennian late devonian reefs grew around an emergent island of precambrian metasedimentary rocks many sediments in the oscar range had high depositional porosities but this porosity was largely occluded by diagenetic alteration diagenesis included marine cementation dolomitization pressure solution burial cementation and karstification field mapping petrography cathodoluminescence and carbon and oxygen isotope analyses have been used to document six major diagenetic episodes that affected oscar range sediments earliest cementation occurred in the marine environment where reef margin and associated subfacies developed abundant non luminescing radiaxial fibrous and microcrystalline calcite cements based on convergent covariant isotopic trends marine cements had a characteristic late devonian oxygen signature of 4 5 0 5 pdb and a carbon signature of 2 0 0 5 pdb in well cemented parts of the reef complex synsedimentary neptunian fissures formed and were filled with cement and sediment cements in these fissures have isotopic ratios that are essentially identical to the values determined for marine cements thereby suggesting that the fissures acted as conduits f r seawater flow and cementation early in the history of the reef complexes marine diagenesis was followed by marine burial and possible meteoric phreatic cementation and dolomitization marine cements are overgrown by non luminescing scalenohedral cements that grade into banded bright and non luminescing blocky calcite cements that are common on the platform but are missing in many reef margin and marginal slope deposits banded luminescence may represent fluctuating reducing and oxidizing conditions in pore waters across the intermittently emergent platform the reef complexes however were generally drowned reefs with little chance for prolonged meteoric exposure this sedimentologic evidence suggests that banded luminescing cements may have formed in the marine burial environment the next cement generation consists of non luminescing non ferroan bloc y calcites that occur throughout the reef complex stratigraphic relationships combined with isotopic results 18o 6 0 to 9 0 13c 2 0 suggest that this spar is a burial cement resulting from late devonian through early carboniferous burial the reef complex was exhumed and eroded in the late carboniferous dedolomite dolo moldic porosity pisolitic calcrete crusts iron oxide stained blocky cements and deep 200 m sinkholes formed at the unconformity surface non ferroan irregularly banded moderate to bright luminescing blocky calcite precipitated throughout the reef complex unconformity related cements calcrete crusts and dedolomites have distinctive isotopic signatures that show little variation in oxygen 7 0 to 9 0 but have a broad range of carbon values 1 5 to 8 0 highly negative carbon values are probably related to the interaction of meteoric fluids with isotopically light soil gas at the er sion surface in post carboniferous time most of the remaining porosity was filled with non ferroan bright luminescing blocky calcite that formed by pressure solution reprecipitation during burial isotopic analyses 18o 8 0 to 12 0 13c 1 5 support a burial origin for this generation of cements these cements fill primary porosity tension gashes along stylolites and hairline fractures along which hematite is leached a final generation of ferroan homogeneous dull to non luminescing blocky calcite cement formed in a late burial event that according to isotopic evidence 18o 10 5 to 15 0 13c 2 0 to 9 0 was probably related to movement of basinal brines through the reef complexes

meteoric burial diagenesis of middle pennsylvanian limestones in the orogrande basin new mexico water rock interactions and basin geothermics abstract stable isotopic compositions of cyclic middle pennsylvanian gobbler formation limestones record two stages of alteration early open system meteoric diagenesis during episodic subaerial exposure stabilized cycle top carbonate in the presence of meteoric fluid at high water rock ratios 400 4000 subsequent closed system burial diagenesis stabilized meteoric and residual marine carbonate in the presence of connate pore fluids at elevated temperatures to 150 c and low water rock ratios 1 0 10 present 18o distributions record normal to high geothermal gradients 27 86 c km during burial stabilization high basin center geothermal gradients probably resulted from elevated heat flow due to rapid crustal extens on and subsidence of the orogrande basin during the late pennsylvanian a dike injection lithospheric extension model with 40 oceanization best accounts for subsidence and geothermal patterns of the orogrande basin

carbon isotope chemostratigraphy and precise dating of middle frasnian lower upper devonian alamo breccia nevada usa abstract at hancock summit west nevada western usa uppermost givetian upper middle devonian and lower and middle frasnian lower upper devonian rocks of the lower guilmette formation include in stratigraphic sequence carbonate platform facies of the conodont falsiovalis transitans and punctata zones the type alamo breccia member of the middle punctata zone and slope facies of the punctata and hassi zones the catastrophically deposited alamo breccia and related phenomena record the 382 ma alamo event produced by a km scale bolide impact into a marine setting seaward of an extensive carbonate platform fringing western north america re evaluation of conodonts from the lower guilmette formation and alamo breccia member together with regional sedimentologic and conodont biofacies comparisons now firmly locates the onset of the johnson et al 1985 transgressive regressive t r cycle iic which occurred after the start of the punctata zone within a parautochthonous megablock low in the alamo breccia whole rock carbon isotope analyses through the lower guilmette formation and alamo breccia member reveal two positive 13ccarb excursions 1 a small 3 excursion which is possibly correlative with the falsiovalis event previously identified from sections in western europe and australia occurs below the breccia in the upper falsiovalis zone to early part of the transitans zone and 2 a large multi part excursion dominated by a 6 positive shift begins above the start of the punctata zone and onset of t r cycle iic and continues above the alamo breccia ending near the punctata hassi zonal boundary this large excursion correlates with the punctata event a major positive 13c excursion previously recognized in eastern laurussia and northern gondwana consistent with previous studies at hancock summit west the punctata event is apparently not associated with any regional extinctions or ecosystem reorganizations in the study area onset of the main punctata event began after the start of both the punctata zone and t r cycle iic and preceded the alamo impact by less than 650 k y as inferred from conodont biochronologic and regional rock accumulation rate estimates although complicated by the heterolithic high energy deposits of the alamo breccia the carbon isotope record of the breccia and post breccia beds does not indicate a major impact correlative perturbation to the carbon cycle this study extends recognition of the punctata event to western laurussia further reinforcing the potential global scale of the event and its potential importance to understanding early to middle frasnian marine geochemistry and palaeoenvironments based on previous models and our observations increased tectonic activity increased nutrient flux to oceans increased marine bioproductivity widespread anoxia and increased organic carbon burial were all likely key factors in driving the punctata event excursion furthermore periodic eustatic and regional relative sea level rises may have played an important role in promoting organic carbon burial and in maintaining a link between the primary open marine geochemical signal and that recorded on the shallow marine lower guilmette carbonate platform

the late devonian frasnian famennian f f biotic crisis insights from δ13ccarb δ13corg and 87sr 86sr isotopic systematics a severe biotic crisis occurred during the late devonian frasnian famennian f f transition f367 myr here we present d 13 ccarb d 13 corg and 87 sr 86 sr isotopic systematics from identical samples of two sections across f f boundary in south china which directly demonstrate large and frequent climatic fluctuations 200 kyr from warming to cooling during the f f transition these climate fluctuations are interpreted to have been induced initially by increased volcanic outgassing and subsequent enhanced chemical weathering linked to the rapid expansion of vascular plants on land which would have increased riverine delivery to oceans and primary bioproductivity and subsequent burial of organic matter thereby resulting in climate cooling such large and frequent climatic fluctuations together with volcanic induced increases in nutrient e g biolimiting fe toxin sulfide and anoxic water supply and subsequent enhanced riverine fluxes and microbial bloom were likely responsible for the stepwise faunal demise of f f biotic crisis d 2005 elsevier b v all rights reserved

subtidal carbonate cycles implications for allocyclic vs autocyclic controls thick successions of repetitive metre scale subtidal carbonate cycles require that short term sedimentation rates approximate long term accumulation rates in order to maintain submergence below peritidal depths intrinsic processes such as storm and wave reworking and redistribution may act to inhibit aggradation into the zone of optimal carbonate production the presence of subtidal vs peritidal carbonate cycles may be a function of energy regime that in turn may relate to platform morphology the ultimate control on stacked subtidal cycles appears to be eustasy acting in concert with intrinsic processes such as storm and wave reworking

deciphering the impact of diagenesis overprint on negative δ13c excursions using rock magnetism case study of ediacaran carbonates yangjiaping section south china rock magnetism is used here to investigate the genesis of one of the puzzling negative carbon isotopic excursions of the neoproterozoic in the yangtze platform south china a detailed characterization of the magnetic mineralogy which includes low temperature and high field magnetometry and classical magnetic measurement arm irm susceptibility was therefore performed along upper doushantuo and lower dengying formations outcropping in the yangjiaping section the derived magnetic parameters show variations that can be interpreted as variations in magnetic grains size and in oxide contents they show that the magnetic content is significantly reduced in samples presenting negative 13ccalcite values we interpret this as a result of magnetite dissolution and secondary carbonate precipitation during early diagenesis bacterial sulfate reduction combined with c and o isotopic data paleomagnetic techniques thus show that the upper doushantuo lower dengying negative excursion of the yangjiaping section is largely due to diagenesis although the preservation of a genuine 13c excursion of lower magnitude from 7 down to 0 instead of down to 9 as usually considered cannot be ruled out a corrected 13ccarbonate chemostratigraphic curve is therefore proposed the unambiguous identification of a strong diagenetic component for this excursion casts doubts on the primary nature of other potentially time equivalent negative excursions of the yangtze platform and thus to its correlation to negative excursions in other cratons i e shuram excursion more generally this study illustrates the potential of magnetic mineralogy characterization a low cost time efficient and non destructive technique as screening tool for diagenetic overprints of 13c and 18o

calibrating the devonian time scale a synthesis of u pb id tims ages and conodont stratigraphy the recalibrated devonian time scale represents an important improvement of devonian chronology regarding two aspects firstly a data set of 13 biostratigraphically well bracketed u pb id tims zircon and monazite ages constitutes the framework of the scale secondly approximately time linear biostratigraphic scales have been used for the interpolation between the isotopic ages the new construction thus represents a biochronometric time scale which allows the assignment of numeric ages not only to stage boundaries but also to each biozone boundary the method of interpolation applied also enables the projection of the geochronological error onto the time scale according to the newly calibrated scale the devonian lasted 57 4 5 7 ma from 418 1 3 0 to 360 7 2 7 ma this is compared to previously published time scales the longest time span ever calculated for this period the age interpolations for the eight stage boundaries are famennian tournaisian devonian carboniferous 360 7 2 7 ma frasnian famennian 376 1 3 6 ma givetian frasnian 383 7 3 1 ma eifelian givetian 388 1 2 6 ma emsian eifelian 391 9 3 4 ma pragian emsian 409 1 3 8 ma lochkovian pragian 412 3 3 5 ma pridolian lochkovian silurian devonian 418 1 3 0 ma full size table table options view in workspace download as csv the duration of the middle devonian is calibrated here as quite short with 8 2 ma and the emsian and the famennian are the longest stages with interpolated durations of 17 2 and 15 4 ma respectively together all devonian stages contain 57 conodont zones including subzones according to the standard conodont zonation giving a mean duration of about 1 ma in the highly resolved part of the time scale mid eifelian to the devonian carboniferous boundary zonal resolution averages 0 6 ma in contrast the lowest resolution is shown in the early emsian to mid eifelian interval with zonal durations of up to 5 5 ma serotinus zone

carbon isotope geochemistry of the frasnian famennian transition abstract carbon isotope records for inorganic and total organic carbon toc as well as for individual organic biomarkers show two positive excursions in the late frasnian with comparable shape and amplitude in 13c the positive shifts in 13c can be correlated with the deposition of the kellwasser horizons the inorganic carbon isotope excursions are explained by an enhanced organic carbon burial that is expected to lower the concentration of oceanic dissolved co2 toc 13c values do not exhibit a larger shift than that recorded by inorganic carbon 13c values this is unexpected since a decrease in the dissolved co2 concentration should result in lower carbon isotope fractionation during photosynthesis ep 13c values of presumed algal biomarkers low molecular weight n alkanes pristane phytane although offset by 2 5 exhibit essentially identical records as toc and confirm this unexpected result it is proposed that high atmospheric and oceanic co2 concentrations during the devonian resulted in maximum photosynthetic fractionation any change in the co2 concentration would thus not affect ep as such 13c of primary organic carbon and 13ccarb will exhibit parallel excursions the data imply that carbon isotopes and the relationship between ep and co2 will not be effective to study changes in pco2 levels during the devonian since co2 concentrations were too high

cyclic ramp to basin carbonate deposits lower mississippian wyoming and montana a combined field and computer modeling study abstract the lower mississippian lodgepole lower madison formations 20 225 m thick developed along a broad 700 km storm dominated pericratonic ramp three types of fifth order upward shallowing cycles are recognized across the ramp to basin transition peritidal cycles consist of very shallow subtidal facies overlain by algal laminated tidal flat deposits which are rarely capped by paleosol breccia layers shallow subtidal cycles consist of stacked ooid grainstone shoal deposits or deeper subtidal facies overlain by ooid skeletal grainstone caps deep subtidal cycles located along the outer ramp consist of basal sub storm wave base limestone argillite overlain by storm deposited limestone which are capped by hummocky stratified to massive skeletal ooid grainstone deep subtidal c cles pass downslope into ramp slope facies composed to rhythmically interbedded limestone and argillite with local deep water mud mounds no upward shallowing cycles occur within the ramp slope facies average cycle durations calculated along the outer ramp are between 30 110 ky the fifth order cycles are stacked to form three third to fourth order depositional sequences which are recognized by regional transgressive regressive facies trends and cycles stacking patterns ramp margin wedges rmw developed during long term sea level fall and lowstand and consist of cyclic crinoidal bank and oolitic shoal facies which pass downdip into deep subtidal cycles transgressive systems tracts tst which onlapped the ramp during long term sea level rise include thick shallow and deep subtidal cycles peritidal cycles are restricted to the inner ramp highstand systems tracts hst developed during long term sea level highstand and fall and along the ramp are composed of early hst shallow subtidal cycles overlain by late hst peritidal cycles shallow through deep subtidal cycles characterize the hst along the ramp slope two dimensional computer modeling of the cyclic sequences suggests that for the assumed water depths of facies fifth order sea level oscillations of at least 20 25 m were required to generate deep subtidal cycles along the ramp slope synthetic sequences run with fifth order sea level amplitudes end page 1194 and tst deposition a feature not observed in the actual sequences other factors in addition to fifth order sea level oscillations likely played a role in generating synchronous peritidal and deep subtidal cycles during hst deposition these factors may include short term climatic changes which influenced the depths to storm wave reworking the moderate amplitude sea level oscillations suggested by the cyclic sequences may reflect the initial effects of carboniferous glaciation that was occurring in gondwana

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

transvaal supergroup carbonates implications for paleoproterozoic δ18o and δ13c records abstract the paleoproterozoic interval is characterized by the first evidence for incontrovertibly free oxygen in the ocean atmosphere system in this study carbonates from the transvaal group the silverton lucknow rooinekke and particularly the duitschland formations were analyzed for isotopes of carbon oxygen and strontium in order to constrain models dealing with the patterns of seawater evolution although the trace element data showed variable alteration of the carbonate samples selected samples with a lesser degree of alteration yielded interpretable results the best measured 87sr 86sr isotope value of 0 7031 at 2 35 ga ago fits well with the published curve for precambrian seawater confirming that paleoproterozoic budget of sr was dominated by input from continental sources during the paleoproterozoic times carbonates with 13c values of about 10 are known to have been present worldwide and they have been studied also during this research the observation that in the duitschland formation such high isotope values and normal marine values were both present within a single formation indeed within its single beds suggested that the large spread of 13c values reflects local or regional rather than global phenomena the oxygen isotope data show a large spread of values from 3 to 16 while their corresponding 13c signals are almost unchanged over this entire range with the lucknow and silverton formations clustering around 10 and the rooinekke formation around 2 the duitschland formation has a bimodal distribution with both 13c populations present the last formation also contains samples with 18o as low as 20 particularly in the vicinity of the bushveld intrusive body these highly 18o depleted samples show homogenization of 13c values towards 5 modelling suggests that the trends could have resulted from post depositional alteration by basinal fluids at near surface to about 50 c temperatures in a rock buffered system the duitschland formation samples particularly at duitschland farm the locality closest to the bushveld complex were then further altered at temperatures up to about 80 c in response to this intrusion

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

water column anoxia enhanced productivity and concomitant changes in δ13c and δ34s across the frasnian famennian boundary kowala holy cross mountains poland the investigation of the trace element and organic geochemistry of the frasnian famennian boundary section at kowala holy cross mountains poland shows that the lower water column was oxygen deficient during late frasnian and early famennian times the abundance and carbon isotopic composition of diaryl isoprenoids biomarkers indicative for green sulfur bacteria prove that euxinic waters reached into the photic zone at least episodically total organic carbon toc contents show two maxima that are time equivalent to the kellwasser horizons deposited in shallower water settings enhanced toc concentrations are explained by a higher primary productivity presumably as a consequence of an enhanced nutrient supply from the continent the increase in the abundance of hopanes and bituminite suggests that the bacterial contribution to toc increased at the frasnian famennian transition the sulfur isotopic composition of pyritic and organically bound sulfur shows a 27 excursion across the boundary the observation that the 34s values of organic bound sulfur closely resemble that of pyrite sulfur indicates a common sulfur source likely early diagenetic sulfide a change in the 13c of total dissolved inorganic carbon as a consequence of an enhanced burial of 12c enriched organic carbon is indicated by a 3 excursion measured for toc as well as for individual n alkanes and isoprenoids the burial of large amounts of organic carbon is expected to result in a decrease in pco2 and should affect the photosynthetic carbon isotope fractionation ep the fact that we observe no change in ep can be explained by the circumstance that ep was most probably at maximum values as a consequence of high atmospheric and oceanic dissolved co2 concentrations during the devonian

evidence for perturbation of the carbon cycle in the middle frasnian punctata zone late devonian new carbon isotopic data from the devonian of ardennes belgium and partly from the holy cross mountains poland highlight an abrupt and high amplitude negative excursion in the punctata conodont zone published information from moravia and china suggests that this middle frasnian negative excursion jointly with the preceding large scale positive shift should be used as a global chemostratigraphic marker causation scenarios for this negative punctata event are correlated neither with major biota turnover nor major sea level changes but may be related to 1 the alamo impact event that led to 2 the massive dissociation of methane hydrates and 3 the rapid onset of global warming

the detection of lateral anisotropy of the ocean floor by electromagnetic methods summary in a typical marine controlled source electromagnetic csem experiment one or more self contained receivers capable of measuring small variations in the electromagnetic field are located in an array on the sea floor a remote horizontal electric dipole is towed close to the sea floor by a surface vessel variations in the current through the dipole cause correlated variations in the electric and magnetic fields at the receivers the variations contain information about the distribution of electrical conductivity of the subsurface rocks the electrical conductivity is related to such critical physical parameters as porosity temperature and fluid content published studies of the response of the sea floor to electromagnetic excitation have not included any systematic variation in the sea floor conductivity with horizontal direction a horizontally isotropic oceanic lithosphere is not an appropriate assumption particularly in the vicinity of the ridge here for example in the near surface layers basalts are extruded onto the sea floor within the very narrow fissured neo volcanic zone the fissures may be filled with sea water and sediment which are better conductors than typical basalt alternatively as time progresses they may become sealed with hydrothermal mineral deposits which can be less conductive than the host rocks in both instances the electrical conductivity of the composite material in the direction oriented along the fisures parallel to the ridge will be greater than that in the transverse direction measures of anisotropy on sea floor of varying age are an indication of the history of the tectonic activity at the ridge the electromagnetic effects of lateral anisotropy are examined through the study of the response of a simple double half space model an upper half space representing sea water is connected to a lower half space representing anisotropic crustal material a general theory describing the excitation of this model by any transient electromagnetic source is developed and the step on responses for systems composed of a horizontal electric dipole transmitter and horizontal magnetic and electric field receivers are computed the results of previous work indicate that following a change in current in the transmitter two distinct changes in horizontal electric field strength separated in time are observed at the receiver the first is caused by the diffusion of the electromagnetic field through the relatively resistive sea floor the second is caused by diffusion through the relatively conductive sea water the times at which the two events occur are robust measures of the isotropic conductivity of the sea floor and the sea water respectively the results of this study show that shape and time of the initial change in the electric field varies systematically with both the average conductivity and the anisotropy of the sea floor for some orientations of the transmitter and the receiver the effect of increasing the anisotropy is similar to the effect of increasing the average conductivity the initial event is delayed however there are orientations for which increasing the anisotropy actually results in an earlier arrival natural science and engineering research council in canada

pre and synorogenic burial metamorphism in the ardenne and neighbouring areas rhenohercynian zone central european variscides abstract the rhenohercynian zone of the central european variscides contains in the central ardenne eifel brabant campine region of belgium france germany and luxemburg an omnipresent thermal overprint which reaches in places uppermost epizonal conditions because of its distribution and structural relationships this metamorphism cannot be explained by a singular tectonometamorphic event field and microstructural observations new illite crystallinity and other data relating to this metamorphism are presented together with a review of existing petrological illite crystallinity vitrinite reflectance conodont alteration index and fluid inclusion data and their relationship to small and regional scale geological structures three distinct geotectonic situations can be described which overlap and alternate in space and time 1 the oldest metamorphism which reached epizonal conditions can be localized in the pre devonian basement rocks of the brabant massif and with minor evidence of the stavelot massif further south it is clearly related to a pre variscan caledonian deformation event and could be of burial origin 2 the main regional metamorphism affected all devonian and carboniferous rocks and the lower palaeozoic basement highs of the ardenne eifel area it does not exceed diagenetic conditions in some areas but reaches maximal values of 500 c and 400 mpa in the serpont and rocroi massif areas theye and fransolet 1993 robion et al 1995 it is pre to synkinematic to the main variscan contractional penetrative deformation and correlates well with the age and thickness of the sedimentary cover rocks the metamorphism is associated with the pre carboniferous preorogenic rifting stage of the rhenohercynian basin and documents the peak of subsidence and sediment accumulation we interpret it as diastathermal metamorphism it reaches its maximum in the low grade metamorphic zones of the ardenne area which are inverted synsedimentary structures 3 the diastathermal metamorphism is overprinted in the central part of the ardenne eifel area middle devonian to carboniferous rocks of the dinant synclinorium by an anchizonal beginning epizonal metamorphism in the foreland basins north of the midi fault zone it reaches diagenetic to lowermost anchizonal conditions it is the expression of the burial by thick synorogenic mid to upper carboniferous cover rocks which were deposited in piggyback and foreland basins this clastic wedge relates to the carboniferous contraction of the rhenohercynian basin whose metamorphosed rocks were themselves affected by the deformation of the advancing orogenic front

shallowing upward sequences in purbeckian peritidal carbonates lowermost cretaceous swiss and french jura mountains purbeckian carbonates in the swiss and french jura goldberg formation lower berriasian comprise shallow subtidal intertidal supratidal low energy high energy marine brackish freshwater and hypersaline facies these facies are arranged in small 0 2 1 5 m thick sequences which display a dominant shallowing upward component and which form the fundamental units of the highly structured purbeckian sedimentary record six types of small scale sequences can be recognized a intertidal to supratidal overprinting of shallow lagoonal facies b algal marsh sequence with frequent dolomitization c sabkha sequence often associated with collapse breccia d tidal flat sequence with desiccation features e lacustrine sequence f terrestrial overprinting of subtidal or intertidal facies episodic event deposits such as tempestites are superimposed thin transgressive beds which rework elements of the underlying facies are frequently found at the base of the sequences green marls and black pebbles are common at the top and indicate long subaerial exposure the sequences are often incomplete as subtidal facies may be absent or their upper part can be eroded lateral facies changes are common which is due to the very shallow and partly emergent purbeckian platform where various depositional environments were juxtaposed however many sequence boundaries are well developed and can be correlated over large parts of the study area the purbeckian shallowing upward sequences were generated by climatically controlled sea level changes autocyclic processes occurred locally but were overprinted by drops of sea level affecting the entire platform the small scale sequences are most probably related to the 20 000 year cycle of the precession of the equinoxes larger sequences with usually well developed emersion surfaces are attributed to the 100 000 and 400 000 year eccentricity cycles of the earth s orbit identification and correlation of sequence boundaries makes it possible to set up a framework of isochronous surfaces which often cut across facies boundaries and thus to interpret in detail the palaeogeographic sedimentological and diagenetic evolution of the purbeckian peritidal carbonate environments

isotopic evidence for geochemical decoupling between ancient epeiric seas and bordering oceans implications for secular curves isotopic analysis of conodonts and their host limestones sampled between two regionally extensive altered volcanic ash layers in eastern laurentia shows that a 454 ma epeiric sea maintained large lateral differences in nd and c isotope compositions this is consistent with inferred temperature salinity defined epicontinental water masses and restricted circulation between epicontinental and oceanic environments because the majority of old marine fossils and sedimentary rocks are known from epeiric seas some isotope excursions in ancient marine strata may originate from expansion and contraction of geochemically distinct epicontinental water masses rather than global scale changes in the state of the earth ocean system

allocyclic control on late devonian buildup development southern canadian rocky mountains abstract parasequence stacking patterns in upper devonian fairholme group reef complexes of the southern canadian rocky mountains suggest that deposition and buildup stratigraphy were controlled by superimposed short term and long term fluctuations in relative sea level correlation of these stacking patterns from one reef complex to another reveals a hierarchy of fifth order and third order sea level changes the flume platform and overlying upper cairn biostrome consist of meter scale shallowing upward parasequences these are interpreted to have been deposited during short term high frequency fifth order oscillations of relative sea level superimposed on this high frequency cyclicity are larger broadly shallowing upward trends in which dominantly subtidal meter scale parasequences or subtidal noncyclic intervals gradually sometimes abruptly pass upward into peritidal parasequences of comparable thickness these sequences are regionally correlative and are the product of third order driving mechanisms of extrabasinal origin collectively the flume upper cairn and overlying peechee members represent a single depositional sequence sensu vail et al 1977 the various order of cyclicity are best developed in the eastern main ranges where greater syndepositional subsidence allowed for increased sediment accumulation the development of entirely subtidal parasequences and the regional correlation of larger scale groups of vertically stacked subtidal and peritidal parasequences suggest a syndepositional allocyclic control on buildup development rather than an autocyclic one however large uncertainties in the calculated durations of both the high frequency parasequences and the larger scale sequences and assumptions inherent in these calculations obscure the evidence for possible milankovitch control on the development of the cairn formation instead late devonian differential subsidence related to the formation of the antler flysch basin is invoked to explain the regionally correlative large scale groupings of parasequences

accumulation at south pole comparison of two 900 year records two 900 year records of annual accumulation at south pole are compared to evalu ate the origin and significance of observed variations despite difficulties establishing absolute timescales due to problems identifying annual layer markers the two records can be correlated with confidence after moderate smoothing this correlation shows that over the time period considered 1050 1956 a d no climatically significant changes in accumulation occurred in stead fluctuations preserved in the two cores reflect spatial variations in snow accumulation as sociated with nonuniform deposition induced by surface relief on the scale of several kilometers

carbon isotope lateral variability in a middle frasnian carbonate platform belgium significance of facies diagenesis and sea level history abstract carbon isotopic variations of frasnian shallow water carbonates from belgium are related to facies and major sea level trends the influence of the diagenetic overprint was assessed in order to determine the primary signal of the frasnian carbonates shallow water microfacies are characterized by biostromes with stromatoporoids and lagoonal deposits dominated by carbonate mud and calcareous algae with subaerial exposure surfaces the diagenetic history was controlled by three main events early meteoric diagenesis short term subaerial exposure during deposition late meteoric diagenesis major famennian regression and burial diagenesis the oxygen isotopic values are almost constant with respect to facies original material carbonate mud and cement and sedimentological units no differences before or after the main regression this homogeneity is related to resetting during late meteoric diagenesis the carbon isotopic values are related to facies with the more negative values for the shallowest facies and to major sea level variations most negative values after the main regression this pattern is interpreted as being related to primary signals this trend was enhanced by early meteoric diagenesis and the influence of more negative values from paleosols the carbon isotope patterns reflect the influence of sea level and water circulation on shallow water deposits and this influence implies that shallow water carbonates are not necessarily good material for assessing the primary isotopic values of the ocean because of the influence of long residence time aging of the platform top water and because of early diagenesis

a chronology for the dome c deep ice core site through radio echo layer correlation with the vostok ice core antarctica ice at the new dome c drill site is correlated directly with the vostok ice core record using internal radio echo layering in the antarctic ice sheet layering observed on 60 mhz radar records at ice depths greater than 1000 m is a result of electro magnetic wave reflections from acidic ice layers formed it is assumed by volcanic eruption derived aerosols these acidic layers represent isochronous surfaces within the ice sheet we are able to trace five prominent layers for over 500 km across the antarctic ice sheet between vostok and the new ice core site at dome c this correlates the stratigraphy and depth age relationship between the two sites the thickness of ice deposited over the last glacial cycle 120 000 years at dome c is 300 m greater than at vostok and at comparable depths the ice at dome c is between about 10 000 and 25 000 years younger than at vostok

depletion of 13c in seawater σc02 on modern carbonate platforms significance for the carbon isotopic record of carbonates seawater co2 from modern carbonate platforms bahama banks and florida is depleted in 13c by as much as 4 relative to open ocean water depletion in 13c is caused by isotopically light co2 input from respiration of marine and terrestrial organic matter during water mass residence on the bank as such depletion in 13c is related to changes in water chemistry driven by evaporation freshwater discharge and caco3 withdrawal deviation of modern platform seawater 13c values away from those of surface seawater suggests that 13c values of ancient cratonic carbonate must be cautiously interpreted initial depositional environment as well as alteration during diagenesis must be considered in extracting valid secular trends for oceanic 13c variation

late devonian carbon isotope stratigraphy and sea level fluctuations canning basin western australia the upper devonian reef complexes of the canning basin contain some of the world s best exposed continuous stratigraphic sections through the frasnian famennian boundary the facies distribution and composition of these reef complexes record interactions among sea level changes sediment supply ocean chemistry and paleoecology changes in relative sea level produced spatial shifts in reef platform development and regional changes in sediment supply that can be correlated across facies boundaries using a combination of sequence stratigraphy biostratigraphy and carbon isotope stratigraphy during the lowstand interval below the frasnian famennian boundary the reef margin advanced down the reef slope in shallow water environments and siliciclastics locally dominated in the marginal slope environment compilation of a broad late frasnian to early famennian sequence stratigraphic framework for the canning basin demonstrates that transgressive intervals correlate to positive carbon isotopic excursions within the basin these isotopic shifts also can be correlated to time equivalent positive carbon isotopic excursions reported from transgressive intervals in europe thus the late frasnian transgressions in the canning basin were primarily eustatic rather than tectonic in origin and positive carbon isotopic signatures of the kellwasser horizons are globally correlative c 2002 elsevier science b v all rights reserved

cyclostratigraphy and high frequency carbon isotope fluctuations in upper cretaceous shallow water carbonates southern italy a detailed carbon isotope study has been carried out on a santonian upper cretaceous carbonate platform succession that crops out at monte sant erasmo southern italy previous centimetre scale studies on this succession have shown that high frequency eustatic changes resulting from the earth s orbital fluctuations controlled the hierarchical organization of the depositional and early diagenetic features in elementary cycles bundles groups of three to five elementary cycles and superbundles groups of three or four bundles the elementary cycles which correspond to single beds suggest a control caused by earth s precession the bundles and superbundles record the short 100 kyr and long 400 kyr eccentricity periodicity respectively the 1 3 c signal of the monte sant erasmo succession is cyclic in nature and may be considered to be a reliable proxy for the sedimentary evolution and related sea level history of the analysed sequence the carbon isotope cyclicity is recorded at bundle and superbundle level but it is not evident at the scale of the elementary cycles at least with the sampling interval used in this study spectral analysis of the 1 3 c record shows two main peaks corresponding to the short and long eccentricity periodicity whereas the precession signal is not evident in the power spectrum in addition lithofacies analysis shows that in each bundle and superbundle higher c isotope values occur in sediments characterized by marine cements whereas lower values are normally found in more restricted deposits overprinted by early meteoric diagenesis early diagenesis driven by periodic sea level fluctuations developed in either shallow subtidal marine diagenesis or subaerial exposed meteoric overprint sedimentary environments and directly influenced the carbon isotope signature as a consequence the 1 3 c record at monte sant erasmo reflects high frequency climatic oscillations controlling both environmental and early diagenetic changes the long term isotopic record is similar to that of contemporaneous pelagic sections in england and elsewhere in italy it is concluded that the 1 3 c signature of shallow water carbonates such as those of monte sant erasmo offers great potential for correlation with coeval sections including those of the pelagic realm

paleoreef maps evaluation of a comprehensive database on phanerozoic reefs to get a better understanding of controls on reef development through time we created a comprehensive database on phanerozoic reefs the database currently comprises 2470 reefs and contains information about geographic position paleoposition age reef type dimensions environmental setting paleontological and petrographical features and reservoir quality of each buildup reef data were analyzed in two qualitatively different ways the first type of analysis was by visualization of paleogeographic reef distribution maps five examples late devonian early permian late triassic late jurassic middle miocene are presented to show the potential of paleoreef maps for paleogeographic and paleoclimatological reconstructions the second type of analysis was a numerical processing of coded reef characteristics to realize major trends in reef evolution and properties of reef carbonates the analysis of paleolatitudinal reef distributions through time shows pronounced asymmetries in some time slices probably related to climatic asymmetries rather than controlled by plate tectonic evolution alone the dominance of particular reef builders through time suggests that there are seven cycles of phanerozoic reef development first curves for the phanerozoic distribution of bioerosion in reefs bathymetric setting and debris potential of reefs are presented the observed pattern in the temporal and spatial distribution of reefs with reservoir quality may assist in hydrocarbon exploration statistical tests on the dependencies of reefal reservoir quality suggest that large size high debris potential low paleolatitude high amount of marine aragonite cement and a platform shelf edge setting favor reservoir quality reefal reservoirs are significantly enhanced in times of high evaporite sedimentation elevated burial of organic carbon low oceanic crust production low atmospheric co2 content and cool paleoclimate as well as when they are present in aragonite oceans

local controls on carbon cycling in the ordovician midcontinent region of north america with implications for carbon isotope secular curves abstract the carbon isotope record from ancient epicontinental seas may contain much more of a local scale carbon cycling signal than is generally appreciated a unique opportunity exists to examine this issue in the case of the late ordovician mohawkian sea of eastern laurentia where the millbrig k bentonite stratigraphic framework has been used to delineate a time slice at 454 ma extending over 1 500 000 km2 of the eastern united states across the time slice carbonate and organic carbon 13c vary by 4 5 and 7 5 respectively a spatial variation that is as large as temporal secular changes in epeiric sea 13c that have been reported in the past these new data are considered in the context of geographic variations in lithological biological and other geochemical sediment characteristics collectively these sediment properties distinguish regions of the mohawkian sea which likely differed in terms of the nature and relative importance of carbon cycling processes water column depth and structure and barriers to free exchange of water across the mohawkian sea may have been overarching factors in the development of these regions raising the possibility that changes in circulation patterns such as those caused by sea level change played a role in driving secular carbon isotope excursions by changing the rate of exchange of dissolved inorganic carbon between water masses if the observed effects of local carbon cycling on the distribution of mohawkian sea 13c were commonplace in ancient epicontinental marine environments it would imply that local scale carbon cycling may have left a nontrivial imprint on epeiric sea records of secular variations in 13c in addition to the imprint left by changes in the global carbon cycle this may have contributed to the broad scatter in 13c values observed in the paleozoic portion of the global carbon isotope secular curve

differentiating anisotropy and lateral effects using azimuthal resistivity offset wenner soundings azimuthal resistivity surveys increasingly are being used by hydrogeologists in the identification and characterization of fractured rocks in these investigations electrical resistivity is measured as a function of azimuth about a fixed central point in most recent published examples any observed change in apparent resistivity with azimuth is interpreted as being indicative of fracture anisotropy however interpretation of rotational sounding data is actually more complicated as azimuthal variations in apparent resistivity are also produced by the presence of dipping stratigraphy and other lateral changes in formation resistivity such effects are generally overlooked because the field techniques normally employed are incapable of detecting them consequently it is quite probable that the results of many published surveys have been wrongly interpreted an alternative field procedure and interpretation methodology has been developed to differentiate anisotropy dipping layers and lateral effects this approach makes use of the offset wenner technique and examines the different responses of the individual wenner resistances above different geological structures analysis of data obtained using the azimuthal offset wenner technique from sites in britain and ireland have successfully identified subsurface structures and determined the anisotropy where it is present

internal ice sheet radar layer profiles and their relation to reflection mechanisms between dome c and the transantarctic mountains causes of ice sheet layering at ice depths greater than about 900 m in a transect between dome c and the transantarctic mountains are examined using 60 mhz radar data collected in the 1970s by the u k u s danish collaboration normally a dual frequency technique is required for accurate determination of internal reflection mechanisms however by extracting the depth related features of 60 mhz radar profiles and comparing them with the dual frequency data collected by the japanese antarctic research expedition we have identified a simple method to estimate internal reflection mechanisms two zones can be distinguished 1 the c a zone where change in electrical conductivity due to variation in acidity is the major cause of internal reflection and 2 the p cof zone where change in dielectric permittivity due to crystal orientation fabrics is the major cause of internal reflections our analysis shows that the radar data reveal the development of p cof zones in regions where large amounts of ice shearing are expected this analysis shows how a similar interpretation of the full radar data archive may reveal information on internal reflection mechanisms across a large part of the east antarctic ice sheet

stable isotope signatures associated with palaeosols pennsylvanian holder formation new mexico the holder formation pennsylvanian virgilian of southern new mexico usa consists of limestones interbedded with siliciclastics it was deposited during times of glacio eustatic sea level change and was exposed subaerially during multiple sea level lowstands microcomponents and whole rock samples of limestones were analysed for 13c and 18o values to examine the method of whole rock isotopic analysis for detecting subaerial exposure events and to determine the diagenetic processes acting during subaerial exposure whole rock isotopic shifts are not consistently present across petrographically identified subaerial exposure surfaces apparently whole rock isotopic shifts do not result from wholesale replacement of the host sediment during soil formation however the isotopic shifts are present in calcareous soil precipitated microcomponents such as rhizoliths laminated crusts and soil precipitated cements the components are heterogeneous in isotopic composition but converge on a meteoric calcite line at about 18o 5 5 these microcomponents are heterogeneous in distribution and may either dominate or be a minor constituent of the whole rock at a single stratigraphic horizon without petrographic selection of palaeosol components the detection of whole rock isotopic shifts may depend on the selection or chance sampling of a rock containing abundant microcomponents precipitated in a soil environment only minor whole rock isotopic shifts come from those rocks bearing no evidence of exposure and bearing lithological characteristics suggesting subaerial exposure was unlikely

paired carbonate organic carbon and nitrogen isotope variations in lower mississippian strata of the southern great basin western united states abstract the early mississippian k o kinderhookian osagean carbon isotope 13c excursion or tice mid tournaisian carbon isotope excursion is one of the most prominent positive 13c excursions of the phanerozoic recent studies raise uncertainties about the representative shape single vs double spikes and magnitude of this 13c excursion 3 to 6 in south china 5 5 in europe and 7 in north america and the 3 unidirectional increase in nitrogen isotopes across the 13c excursion which is unanticipated considering the amount of organic carbon burial required to form the 13c excursion and the resultant oxygen increase and global cooling to test if stratigraphic completeness and spatial isotope variations caused such uncertainties we have conducted paired carbonate carbon 13ccarb organic carbon 13corg and nitrogen 15n isotope analyses across the k o interval in two well exposed sections of the southern great basin western united states the two sections represent proximal shallow water and distal deep water depositional settings of a west dipping carbonate ramp in the distal ramp section where no exposure surface is present both 13ccarb and 13corg show double spikes with peak 13ccarb values up to 7 and a negative shift down to 4 between the peaks in the proximal shallower water section where two karstic disconformities are observed 13corg shows similar double spikes but 13ccarb displays only a single peak with the highest value of 5 5 the missing 13ccarb spike is likely caused by diagenetic alteration below a karstic disconformity that lowered 13ccarb but not 13corg values resulting in smaller magnitude of the 13ccarb excursion these features suggest that the 7 magnitude and double spikes are more representative of the k o 13c excursion in the southern great basin the smaller magnitude of the k o 13ccarb excursion in some sections of the great basin and the tice in other sections globally may have overprinted with local environmental diagenetic signal or resulted from stratigraphic hiatus truncation which needs to be clarified in future research the 15n across the k o 13c excursion in the distal ramp section is decoupled from 13c with the majority of 15n values around 4 1 that do not show any obvious temporal trend in contrast 15n values in the shallow water section is coupled with the k o 13c excursion with a 3 positive shift from 4 to 7 at the rising limb of the 13c excursion and a negative shift from 7 to 1 2 at the falling limb of the 13c excursion the 15n trend from the distal ramp section is in some extent comparable with that documented from a section in south china while the coupled 13c 15n pattern in the proximal section seems better explain the potential redox change across a prominent 13c excursion considering the sensitivity of 15n to redox conditions of depositional environments a more comprehensive 15n study in a broader paleogeographic context is required to better understand the interactions between carbon and nitrogen cycles across the k o interval a critical transition from the mid paleozoic greenhouse clime to late paleozoic ice age lpia

nature of radio echo layering in the antarctic ice sheet detected by a two frequency experiment a two frequency radio echo sounding experiment was carried out at dome fuji the second highest dome in east antarctica and along a 1150 km long traverse line from the dome to the coast the goal was to determine the dominant causes of the radio echo internal reflections and to investigate their possible changes with depth ranges and regions from the two frequency 60 mhz and 179 mhz radio echo responses at various sites we distinguished four zones each of the zones is characterized by a dominant cause of radio echo internal reflection as follows in the pd zone changes in dielectric permittivity are mainly due to density fluctuations in the pcof zone changes in dielectric permittivity are mainly due to changes in crystal orientation fabrics and in the ca zone changes in electrical conductivity are mainly due to changes in acidity induced by past volcanic eruptions in each of these three zones the changes occur commonly along isochrones in addition a basal echo free zone the fourth zone was found to appear always below the pcof zone these four zones and their distribution suggested variations of the physical conditions within the ice sheet

sequence stratigraphy of a late devonian ramp situated reef system in the western canada sedimentary basin dynamic responses to sea level change and regressive reef development the alexandra formation located in the northwest territories of canada is formed of a late devonian frasnian reef system that developed on a gently sloping epicontinental ramp in the western canada sedimentary basin high resolution sequence stratigraphic analysis of its deposits delineates two reef complexes that are separated by a type i sequence boundary the second reef complex developed on the outer ramp basinward of the first after sea level fell 17 m stratigraphic complexity of the second reef complex was a result of its initiation during forced regression and its development through an entire cycle of sea level rise followed by sea level fall its highstand systems tract was not characterized by high rates of carbonate production or sediment shedding rather these features took place as sea level fell after its highstand systems tract the sequence stratigraphic framework of this regressive reef system highlights a number of depositional parameters that differ from high relief shelf situated reef systems with steep narrow margins these have implications for understanding the controls on the development of ramp situated reef systems and the nature of reef systems with gently sloping profiles this study demonstrates that the development of stromatoporoid reef systems may be far more complex than generally realized and that high resolution sequence stratigraphy may provide the tools for better understanding of complex often enigmatic aspects of these systems

a tentative chronology for the epica dome concordia ice core a tentative age scale edc1 for the last 45 kyr is established for the new 788 m epica dome c ice core using a simple ice flow model the age of volcanic eruptions the end of the younger dryas event and the estimated depth and age of elevated 10be about 41 kyr ago were used to calibrate the model parameters the uncertainty of edc1 is estimated to 10 yr for 0 to 700 yr bp up to 200 yr back to 10 kyr bp and up to 2 kyr back to 41 kyr bp the age of the air in the bubbles is calculated with a firn densification model in the holocene the air is about 2000 yr younger than the ice and about 5500 yr during the last glacial maximum

age vs depth of glacial ice at south pole knowledge of age as a function of depth in glacial ice is important for both glaciology and paleoclimatology for sites near a ridge or dome an ice flow model together with information on accumulation rate provides a first approximation if the accumulation rate is high enough annual layering of isotopes and dust measured in a solid core can provide a precise age vs depth relationship for south pole the flow geometry is not simple and no deep core exists nevertheless by remotely sensing peaks in scattering and absorption of light from pulsed sources buried at depths down to 2200 m we have been able to determine age vs depth for ages up to 65 000 years analysis of radar isochrons by siegert and hodgkins provides a rough extension of the age vs depth model to 165 000 years near bedrock

ice sheet radar layering and the development of preferred crystal orientation fabrics between lake vostok and ridge b central east antarctica abstract airborne radar data at 60 mhz are analysed to examine the flow of ice between the ridge b ice divide and the vostok station subglacial lake in central east antarctica interferometric sar ice surface velocities show how three radar transects are aligned along the general direction of ice flow internal layering within the ice sheet is used to determine changes in the vertical component of ice flow along the transects these data indicate ice sheet flow is related strongly to subglacial topography in one transect ice flows in a conventional base parallel manner down a relatively uniform subglacial slope in the direction of ice flow in the other two transects internal layers show the flow of ice over a large subglacial hill upstream of lake vostok across the stoss face of this subglacial hill analysis of the radar reflections from internal layers show that layers of ice with a preferred crystal orientation are likely to develop this process results in layers of ice with a preferred crystal fabric across lake vostok at ice depths greater than 2 8 km evidence to support our analysis comes from the vostok ice core where layers of ice with noticeable crystal alignment are abundant at ice depths greater than 2 7 km

high resolution correlation of the homerian carbon isotope excursion silurian across the interior of the midland platform avalonia uk new 13 c carb and microfacies data from hereford worcestershire and the west midlands allow for a detailed examination of variations in the homerian carbon isotope excursion silurian and depositional environment within the much wenlock limestone formation of the midland platform avalonia uk these comparisons have been aided by a detailed sequence stratigraphic and bentonite correlation framework microfacies analysis has identified regional differences in relative sea level change and indicates an overall shallowing of the carbonate platform interior from hereford worcestershire to the west midlands based upon the maximum 13 c carb values for the lower and upper peaks of the homerian carbon isotope excursion cie the shallower depositional setting of the west midlands is associated with values that are 0 7 and 0 8 higher than in hereford worcestershire at the scale of parasequences the effect of depositional environment upon 13 c carb values can also be observed with a conspicuous offset in the position of the trough in 13 c carb values between the peaks of the homerian cie this offset can be accounted for by differences in relative sea level change and carbonate production rates while such differences complicate the use of cies as a means of high resolution correlation and caution against correlations based purely upon the isotopic signature it is clear that a careful analysis of the depositional environment can account for such differences and thereby improve the use of carbon isotopic curves as a means of correlation

geochemistry of brachiopods oxygen and carbon isotopic records of paleozoic oceans abstract combined trace element and isotope studies of 319 brachiopods covering the ordovician to permian time span show that 13c and 18o in well preserved specimens varied during the paleozoic the overall 13c secular trend is in accord with the previously published observations but its details are obscured by vital isotopic fractionation effects at generic level nonetheless the results suggest that the negative correlation between marine 13ccarbonate and 34ssulphate deteriorates at time scales of 106 years due to the long residence time and thus slow response of so42 in the ocean for oxygen isotopes all devonian and older specimens have 18o of 4 while the well preserved permian samples have near present day 18o of about 1 pdb this isotopic dichotomy is probably not due to post depositional phenomena salinity or biogenic fractionation effects this leaves open the perennial arguments for a change in 18 o 16 o of sea water versus warmer ancient oceans the present data are difficult to explain solely by the temperature alternative the coincidence of the proposed shift in 18o with the large late paleozoic changes in marine 87 sr 86 sr 13 c 12 c 34 s 32 s and sea level stands argues for a tectonic cause and for a change in 18 o 16 o of sea water although such explanation is difficult to reconcile with global balance considerations and with isotopic patterns observed in alteration products of ancient basalts and ophiolites whatever the precise cause or combination of causes the implications for tectonism and or paleoclimatology are of first order significance

dating the vostok ice core by an inverse method using the chronological information available in the vostok records we apply an inverse method to assess the quality of the vostok glaciological timescale the inversion procedure provides not only an optimized glaciological timescale and its confidence interval but also a reliable estimate of the duration of successive events our results highlight a disagreement between orbitally tuned and glaciological timescales below 2700 m i e 250 kyr b p thousands of years before present this disagreement could be caused by some discontinuity in the spatial variation of accumulation upstream of vostok moreover the stratigraphic datings of central greenland ice cores grip and gisp2 appear older than our optimized timescale for the late glacial this underlines an unconsistency between the physical assumptions used to construct the vostok glaciological timescale and the stratigraphic datings the inverse method allows the first assessment of the evolution of the phase between vostok climatic records and insolation this phase significantly varies with time which gives a measure of the nonlinear character of the climatic system and suggests that the climatic response to orbital forcing is of different nature for glacial and interglacial periods we confirm that the last interglacial as recorded in the vostok deuterium record was long 16 2 2 kyr thousands of years however midtransition of termination ii occurred at 133 4 2 5 kyr bp which does not support the recent claim for an earlier deglaciation finally our study suggests that temperature changes are correctly estimated when using the spatial present day deuterium temperature relationship to interpret the vostok deuterium record

chemostratigraphy and magnetic susceptibility of the late devonian frasnian famennian transition in western canada and southern china implications for carbon and nutrient cycling and mass extinction we investigate the late devonian frasnian famennian extinction interval in western alberta and south china to shed light on the palaeoecological and palaeoceanographic conditions that characterize this biotic crisis both the lower and upper kellwasser events are documented in western canada only the upper kellwasser event has been evaluated in south china our multi proxy geochemical approach reveals that these events are characterized by positive d 13 c and d 15 n excursions and increasing magnetic susceptibility canada china and increases in detrital al si ti zr productivity cu ni zn and redox mo u v elemental proxies canada we interpret these trends as part of a systemic palaeoecological shift associated with the development of wide spread terrestrial forests and their alteration of chemical mechanical weathering patterns increase in detrital proxies is thus interpreted as resulting from pedogenically driven weathering on the con tinents that nutrified epeiric and continental margin seas high biological productivity led to eutro phication and development of suboxic to anoxic conditions during both events and probably euxinic conditions during the upper kellwasser event in western canada positived 13 c excursions are the telltale signature of excessive carbon burial while redox proxies and d 15 n records indicate

facies architecture and diagenesis of belgian late frasnian carbonate mounds abstract late frasnian petit mont member carbonate mounds occur in the southern part of the dinant synclinorium and in the philippeville anticline sw belgium these mounds are 30 to 80 m thick and 100 to 250 m in diameter they are embedded in shale nodular shale and argillaceous limestone based on facies mapping of 14 buildups and related off mound sediments these mounds typically started from below the photic and storm wave base zones and builtup into shallow water environments above an argillaceous limestone substrate the first carbonate mound facies consists of spiculitic wackestone with stromatactis pm1 which becomes progressively enriched in crinoids and corals pm2 then in peloids stromatoporoids and cyanobacteria pm3 pm4 consists of algal coral peloid wackestone and packstone with green algae and thick algal coatings a core of algal and microbial bindstone pm5 sporadically occurs within large mounds the uppermost part of these mounds may show a recurrence of facies pm2 and pm1 pm1 to pm3 are coloured red by hematite derived from microaerophilic iron bacteria pm4 and pm5 are grey the transition from the aphotic to the cyanobacterial photic zone is recorded in the succession pm2 pm3 the transition from the cyanobacterial to the green algal photic zone is recorded by pm3 pm5 storm wave base was reached within pm3 and fair weather wave base within pm5 this paleobathymetric interpretation suggests a depth of 100 150 m during initial establishment of pm1 three types of mounds can be distinguished on the basis of geometry and facies architecture 1 les bulants type mounds display a continuous vertical facies succession pm2 3 4 5 and low relief 2 although exhibiting the same facies succession as les bulants les wayons type mounds show a distinct relief with steep flanks and bioclastic talus 3 st remy mounds consist exclusively of pm1 and pm2 bioclastic flank deposits are not observed from 1 to 3 these mound types represent successive deepening down a ramp biostratigraphic correlation on a regional scale provides good evidence that relative sea level changes largely controlled lateral and vertical transitions of facies beyond that hypoxic conditions are indicated by the sponge and iron bacteria consortium in lower parts of the mounds this is in agreement with the general assumption of stratified water masses during late frasnian preceding the prominent lower kellwasser crisis cementation began with a radiaxial synsedimentary cement a fringe of meteoric phreatic cement initially nonluminescent then with a bright orange luminescence occurs in all mounds it is contemporaneous with a nonluminescent pervasive cement of grainstones deposited in littoral areas differentiation between the reducing mounds and the oxidizing littoral area resulted from better aquifer circulation in sedimentary bodies close to the recharge area late burial cements occlude all the remaining porosity and are contemporaneous with the opening of the variscan fracture system

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

sequence stratigraphy and platform evolution of lower middle devonian carbonates eastern great basin lower middle devonian carbonates 270 400 m thick of the eastern great basin were deposited along a low energy westward thickening carbonate platform six regional facies representing peritidal shallow subtidal stromatoporoid biostrome deep subtidal slope and basin environments are recognized four third order 1 5 2 5 m y durations transgressive regressive sequences are identified across the platform to basin transition based on deepening and shallowing patterns in regional facies intensity and stratigraphic distribution of subaerial exposure features and stacking patterns of fourth to fifth order upward shallowing peritidal and subtidal cycles transgressive systems tracts along the basin slope are characterized by upward deepening successions of proximal through distal turbidites overlain by fine grained hemipelagic deposits shallow platform transgressive systems tracts are composed of stacks of thicker than average peritidal cycles overlain by subtidal cycles or noncyclic deep subtidal facies maximum flooding zones along the shallow platform are composed of stacked peritidal cycles dominated by subtidal facies noncyclic deep subtidal facies or distinct deeper subtidal units within successions of restricted shallow subtidal or peritidal facies highstand systems tracts along the basin slope are composed of hemipelagic deposits overlain by distal through proximal turbidites highstand systems tracts along the shallow platform are characterized by upward shallowing succession of cyclic peritidal through shallow subtidal facies sequence boundary zones 2 16 m thick along the shallow platform are composed of exposure capped peritidal and subtidal cycles that exhibit upsection increases in the proportion of tidal flat subfacies and increases in the intensity of cycle capping subaerial exposure features sequence boundary zones along the basin slope 6 20 m thick are composed of upward shallowing successions of proximal turbidites or by platform margin peloid shoal deposits the absence of exposure features and meter scale cycles within basin slope sequence boundary zones indicates that the combined rates of third through fifth order sea level fall rates were less than tectonic subsidence rates sequence stratigraphic correlations between contrasting facies belts of the basin slope section na and the edge of the shallow platform section tm were independently verified with high resolution conodont and brachiopod biostratigraphy correlation of sequences 1 4 with transgressive regressive sequences of similar age in the western midwestern and eastern united states western canada and europe indicates they are eustatic in origin systems tract scale correlations across the study area indicate that the platform evolved from a homoclinal ramp to a distally steepened ramp then into a flat topped platform sequences 1 2 an incipiently drowned intraplatform basin developed during sequence 3 as the result of third order sea level rise and differential sediment accumulation rates between the platform margin and intraplatform basin during deposition of highstand systems tract 3 progradation infilled the intraplatform basin resulting in a flat topped platform a distally steepened ramp developed during transgressive systems tract maximum flooding zone 4 and evolved into a flat topped platform during highstand systems tract 4 deposition the four sequences stack in an aggradational to slightly progradational pattern keep up style sedimentation and are bound by sequence boundary zones rather than unconformities suggesting that greenhouse climate modes and second order accommodation gains related to the lower portion of the second order kaskaskia sequence controlled sequence scale stacking patterns

subaerial exposure and deposition of shallowing upward sequences evidence from stable isotopes of purbeckian peritidal carbonates basal cretaceous swiss and french jura mountains purbeckian lowermost cretaceous peritidal carbonates are characterized by open marine lagoonal intertidal and lacustrine facies arranged in milankovitch type shallowing upward sequences shallowing upward sequences typically consist of 2 6 individual beds the sequences may be i complete ii incomplete or ii pedogenetically overprinted reflecting the duration of subaerial exposure and or the extent of erosion and pedogenetic modification at the cycle tops the stable isotopic composition of the peritidal micrites reveals homogenous 6 o values attributed to diagenetic stabilization in a meteoric water buffered system carbon isotopes show three distinctly different carbon isotope patterns dependent on the completeness of the shallowing upward sequences complete shallowing upward sequences consist of l6 individual carbonate beds the carbon isotope values show a facies dependent pattern open marine carbonate muds record enriched 6i3c values of 0 28 while lagoonal 0 82 intertidal 2 46 10 and lacustrine micrites 2 96 are increasingly depleted this distinct pattern is explained by carbonate mud deposition in environments of differing salinity and marine influence incomplete sequences 2 5 carbonate beds are characterized by depleted 6 c values below subaerial exposure surfaces that become progressively enriched in c with increasing depth pedogenetically overprinted sequences 1 3 carbonate beds show strong i3c depletion throughout the sequence with little variation in the carbon isotopic composition the depleted values 4 51 10 of the pedogenetically altered micrites suggest that modification during subaerial exposure was associated with equilibration with meteoric solutions enriched in isotopically light soil gas coz the duration of subaerial exposure is the most crucial factor determining the extent of pedogenetic alterations the completeness of the shallowing upward sequences and the carbon isotope pattern the recorded patterns clearly illustrate that micrites have a good potential for the preservation of their primary carbon isotopic composition if the duration of subaerial exposure is rather brief otherwise the recorded carbon isotope patterns may support sequence stratigraphic analysis by providing a refinement of the time stratigraphic interpretation

stable isotope δ13ccarb and org δ15norg and trace element anomalies during the late devonian punctata event in the western canada sedimentary basin late devonian marine deposits in the western canada sedimentary basin were analyzed for 1 accumulations of bioproductivity and paleoredox trace element proxies and for 2 variations of 13c carb and org and 15norg in order to understand and interpret the regional history of the global yet short term punctata event geochemical perturbation statistical correlations suggest that changes in detrital input and associated micronutrient delivery were the main driver of a eutrophication event noted early and possibly also late in the punctata zone around the isolated miette platform manifested by increased toc positive 13c excursions and concurrent enrichments of all elemental proxies evaluation of data within a regional sequence stratigraphic perspective revealed a eustatic sea level influence with proxy accumulations associated mostly with early transgression iic1 deposition and preservation of organic matter rich facies occurred during conditions of enhanced primary production and facilitated bottom water suboxia anoxia following eutrophication lower 15norg and 13corg values predominated and persisted throughout much of the punctata zone before rebounding toward its close suggesting a time interval of environmental stagnation and lower overall productivity during which n2 fixing autotrophs may have had an ecological advantage under nitrate limited conditions the punctata event approximately coincided with the advent of archaeopterid forest expansion beginning around mid frasnian time which fundamentally altered the nature of continental weathering through extensive soil formation and increased nutrient delivery to the oceans this evolutionary event may have amplified the detrital influx already elevated by sea level lowstand and early transgression and increased denudation of rising mountain ranges in near equatorial regions

isotope signatures associated with early meteoric diagenesis the environments in which carbonate diagenesis proceeds have been documented in previous studies of holocene and late pleistocene sediments and limestones on barbados west indies variations in the carbon and oxygen isotopic composition of limestones produced during early freshwater diagenesis have been observed in this study to occur in specific patterns six potentially useful patterns emerge when one views stable isotope data within a stratigraphic framework 1 the subaerial exposure surface is characterized by strongly 12c enriched limestones 13c compositions of underlying limestones grow progressively heavier with increasing depth 2 the subaerial exposure surface may also be marked by slight 18o enrichment 3 an abrupt shift in 18o values may differentiate sediments above the exposure surface from those below 4 sediments altered in the marine meteoric mixing zone may be characterized by positive covariance between their 18o and 13c compositions 5 the vadose phreatic boundary may be marked by a sharp increase in 13c values in the seaward portions of a fresh groundwater system and 6 samples contemporaneously altered in a single fresh groundwater system within an areally restricted region should display a narrow range of 18o and a wide range of 13c compositions analysis of samples from five palaeozoic and mesozoic formations which contained petrographic evidence of early freshwater diagenesis showed that isotope patterns similar to those observed in barbados limestones have been preserved in rocks as old as mississippian these isotope patterns could prove to be useful for identifying diagenetically induced porosity trends in carbonate rocks they might be used to identify limestones diagenetically altered in meteoric environments to identify mixing zone cements and dolomites and to trace the regional and vertical distributions of early meteoric groundwater systems in ancient carbonate formations

widespread complex flow in the interior of the antarctic ice sheet it has been suggested that as much as 90 of the discharge from the antarctic ice sheet is drained through a small number of fast moving ice streams and outlet glaciers fed by relatively stable and inactive catchment areas here evidence obtained from balance velocity estimates suggests that each major drainage basin is fed by complex systems of tributaries that penetrate up to 1000 kilometers from the grounding line into the interior of the ice sheet this finding has important consequences for the modeled or estimated dynamic response time of past and present ice sheets to climate forcing

detection of near surface horizontal anisotropy in a weathered metamorphic schist at llano uplift texas by transient electromagnetic induction abstract the use of transient controlled source electromagnetic prospecting to detect buried steeply dipping foliation in metamorphic rocks is illustrated with data acquired over the precambrian packsaddle schist in the llano uplift of central texas the azimuthal variation of the transient voltage at a given transmitter receiver separation about a fixed central point is consistent with the forward model response of a homogeneous halfspace exhibiting horizontal electrical anisotropy the loop loop exploration configuration is ideally suited to probe horizontal anisotropy a quantitative match of the forward response to the observed data produces reasonable electrical conductivity values and coefficient of anisotropy for resistive crystalline geological materials the most conductive direction consistently lies within a few degrees of the geologically mapped foliation strike direction the electrical anisotropy is strongest below the near surface weathered layer within the more competent bedrock the agent responsible for generating the anistropy cannot be definitively determined because it is likely to be a combination of geological factors such as weathering compositional banding and microcracking all of which enhance electrical conductivity parallel to the plane of foliation the transient electromagnetics is supplemented by dc resistivity and seismic surveys the elastic anisotropy is evident in the near surface weathered layer but it may not persist very deep into the underlying competent schist the exposure of foliated schist at the surface is not sufficient to rule out a possible role for systematically aligned macrofracture sets as a secondary cause of the observed anisotropy

tectonic fabric of the subcontinental lithosphere evidence from seismic magnetotelluric and mechanical anisotropy abstract knowledge of anisotropy is key to our understanding of tectonic fabrics in the lithosphere and sublithospheric mantle anisotropy provides a unique constraint on the character of past and present deformation and thus is critical to our understanding of dynamics of the plate tectonic system in particular how continents with their thick lithospheric mantle roots form stabilize and interact with underlying mantle regions improved observational methods and rapid developments of geophysical inversion techniques are contributing to more realistic earth models that include various types of anisotropy and heterogeneity a more robust characterization of anisotropic parameters can be achieved by integrating complementary datasets incorporating constraints from seismology magnetotellurics geodynamics and mineral physics valid comparisons between different measures of anisotropy however require a solid understanding of the principles and limitations of the various techniques to this end we briefly summarize a new compilation of original articles with a common focus on anisotropy of continental lithosphere including theory laboratory experiments and observations that span a range of different geophysical techniques

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

paleosols in shallow marine carbonate sequences abstract shallow water carbonate sequences in the geological record commonly exhibit numerous exposure surfaces reflecting emersion of sediment due to progradation processes and sealevel oscillations some ancient platform sequences contain hundreds of such surfaces associated with paleosols fossil soils typically calcretes a wide range of macro and microstructures are associated with these calcretes which are reviewed profile types and stages in profile development can be defined the nature of the exposure surface and associated paleosols can be used to identify the nature of the prevailing climate although hydromorphic effects related to marine flooding of the platforms can modify the paleosols a potentially important use of paleosols is to define the nature of sequence boundaries several studies have identified sets of paleosols with varying maturities reflecting changes in rates of accommodation space creation during sealevel rises and falls

global change in the late devonian modelling the frasnian famennian short term carbon isotope excursions a model of the global biogeochemical cycles coupled to a energy balance climate model the combine model is used to identify the causes of two large n 13 c value excursions across the frasnian famennian f f boundary we test a scenario that links the sea level rise to stratification of the proto tethys ocean through the formation of warm saline deep waters in extended epicontinental seas even though this scenario can produce dysoxia below 100 m depth it fails to increase the global burial flux of organic carbon and thus seawater n 13 c values since stratification of the ocean leads to decreased productivity in surface waters several scenarios postulating a continental origin of the perturbations in the late devonian biogeochemical cycles are then tested we found that weathering of platform carbonates exposed during the early famennian sea level fall can account for a maximum positive shift in n 13 c value of 0 7x at the end of the sea level fall episode another 1 0x increase in n 13 c might originate from rapid spreading of vascular land plants near the f f boundary postulating that higher plants globally increased the weatherability of continental surface and that colonized continental area increased by 30 across the f f boundary finally the n 13 c excursion observed at the base of upper rhenana zone and the rapid increase of the carbon isotope ratios at the f f boundary require an increase of phosphorus delivery to the ocean by 40 coeval with the sea level rises once the calculated n 13 c values are in agreement with the measured data the combine model calculates a decrease in atmospheric pco2 from pre perturbation 2925 ppmv in the lower rhenana conodont zone to 1560 ppmv in the upper triangularis zone this decrease in pco2 is due to the increase in burial of organic matter during the kellwasser events and increased continental weatherability triggered by the spreading of continental vascular plants these changes occur within 4 million years the corresponding global climatic cooling reaches 4 4 c at the pole and 2 1 c at the equator f 2003 elsevier b v all rights reserved

cyclostratigraphy of middle devonian carbonates of the eastern great basin abstract middle devonian carbonates 250 430 m thick of the eastern great basin were deposited along a low energy westward thickening distally steepened ramp four third order sequences can be correlated across the ramp to basin transition and are composed of meter scale upward shallowing carbonate cycles or parasequences peritidal cycles shallow subtidal facies capped by tidal flat laminites constitute 90 of all measured cycles and are present across the entire ramp the peritidal cycles are regressive and transgressive prone upward deepening followed by upward shallowing facies trends approximately 80 of the peritidal cycle caps show evidence of prolonged subaerial exposure including sediment filled dissolution cavities horizontal to vertical desiccation cracks rubble and ka st breccias and pedogenic alteration locally these features are present down to 2 m below the cycle caps subtidal cycles capped by shallow subtidal facies are present along the middle outer ramp and ramp margin and indicate incomplete shallowing submerged subtidal cycles 64 of all subtidal cycles are composed of deeper subtidal facies overlain by shallow subtidal facies exposed subtidal cycles are composed of deeper subtidal facies overlain by shallow subtidal facies that are capped by features indicative of prolonged subaerial exposure dissolution cavities and brecciation average peritidal and subtidal cycle durations are between approximately 50 and 130 k y fourth to fifth order the combined evidence of abundant exposure capped peritidal and subtidal cycles transgressive prone cycles and subtidal cycles correlative with updip peritidal cycles indicates that the cycles formed in response to fourth to fifth order glacio eustatic sea level oscillations sea level oscillations of relatively low magnitude 10 m are suggested by the abundance of peritidal cycles the lack of widely varying water depth dependent facies within individual cycles and the presence of noncyclic stratigraphic intervals within intrashelf basin slope and basin facies noncyclic intervals represent missed subtidal beats when the seafloor lay too deep to record the effects of the short term sea level oscillations exposure surfaces at the tops of peritidal and subtidal cycles represent one or more likely several missed sea level oscillations when the platform lay above fluctuating sea level but the amplitude of fourth to fifth order sea level oscillation s were not high enough to flood the ramp the large number of missed beats exposure capped cycles specifically in sequences 2 and 4 results in fischer plots that show poorly developed rising and falling limbs subdued wave like patterns consequently the fischer plots are of limited use as a correlation tool for these particular depositional sequences the abundance of missed beats also explains why milankovitch type cycle ratios 5 1 or 4 1 are not observed and why such ratios would not be expected along many peritidal cycle dominated carbonate platforms

past and present accumulation rate reconstruction along the dome fuji kohnen radio echo sounding profile dronning maud land east antarctica we used internal ice layers from a radio echo sounding profile between the kohnen and dome fuji deep drilling sites to infer the spatio temporal pattern of accumulation rate in this sector of dronning maud land east antarctica continuous internal reflection horizons can be traced to about half of the ice thickness and have a maximum age of approximately 72 7 ka bp to infer palaeo accumulation rates from the dated layers we derived the thinning functions from a flow calculation with a high resolution higher order model of dronning maud land embedded into a three dimensional thermomechanical model of the antarctic ice sheet the method takes into account complex ice flow dynamics and advection effects that cannot be dealt with using traditional local approaches we selected seven time intervals over which we determine the average accumulation rate and average surface temperature at the place and time of origin of the layer particles our results show lower accumulation rates along eastern parts of the profile for the late holocene 0 5 ka bp than are shown by existing maps which had no surface control points during the last glacial period we find a substantially lower accumulation rate than predicted by the usual approach linking palaeo accumulation rates to the condensation temperature above the surface inversion layer these findings were used to fine tune the relation between accumulation rate and temperature

a multilayered water column in the ediacaran yangtze platform insights from carbonate and organic matter paired δ13c abstract large carbon isotope fluctuations have been systematically reported for ediacaran carbonate rocks the meaning of which remains controversial in order to better understand the mechanisms behind such variations we present new paired 13c data on carbonates 13ccarb and their associated organic matter 13corg from a shelf margin section yangjiaping of the doushantuo formation in this section the doushantuo formation starts with cap dolostones presenting 13ccarb values around 5 and 13corg values between 30 3 and 27 6 up section phased variations in 13ccarb and 13corg describe positive and negative excursions while their difference 13cdol org 13ccarb 13corg remains around 29 2 these new data allow the first reconstruction of lateral variations of 13ccarb 13corg and 13ccarb org for a shelf to basin cross section of the yangtze platform south china after integration with results reported previously for two other sections across the yangtze platform the isotope signals reveal strong lateral heterogeneities with complex variations of 13ccarb and 13cdol org in the inner shelf section phased variations in the shelf margin section with positive 13ccarb and 13cdol org close to 29 and dominantly negative 13ccarb with 13corg as low as 35 in the basin these variations are incompatible with the idea that the 13ccarb can systematically be used as a proxy of ocean surface waters assuming that 13ccarb are acquired in bottom waters and or upper sediments we show that the heterogeneous 13ccarb and 13cdol org are compatible with a stratified water column composed of up to three layers i an oxic surface layer where dissolved inorganic carbon dic is probably in isotope equilibrium with the atmosphere ii an intermediate euxinic layer with a lower 13cdic due to organic matter oxidation by ongoing sulphate reduction iii a bottom euxinic layer that seems to be restricted to the inner shelf lagoonal facies lacking sulphate containing methane and with a higher 13cdic due to dic production by methanogenesis if our model holds true it suggests that not only negative but also positive ediacaran carbon isotope excursions may reflect ocean stratification the positive excursion possibly recording a sulphate free methanogenic layer at the bottom of restricted basins

does burial diagenesis reset pristine isotopic compositions in paleosol carbonates abstract sedimentological study of early oligocene continental carbonates from the fluvial dagshai formation of the himalayan foreland basin india resulted in the recognition of four different types namely soil palustrine pedogenically modified palustrine and groundwater carbonates stable oxygen and carbon isotopic 18 o and 13 c analyses of fabric selective carbonate microsamples show that although the pristine isotopic compositions are largely altered during deep burial diagenesis complete isotopic homogenization does not occur 18 o and 13 c analyses of 200 calcrete and palustrine carbonates from different stratigraphic horizons and comparison with 18 o of more robust bioapatite fossil vertebrate tooth phase show that dense micrites 70 carbonate invariably preserve the pristine 18 o value mean of 9 8 while altered carbonates show much lower 18 o value 13 8 such inhomogeneity causes large intra sample and intra soil profile variability as high as 5 suggesting that soils behave like a closed system where diagenetic overprinting occurs in local domains a simple fluid rock interaction model suggests active participation of clay minerals to enhance the effect of fluid rock ratio in local domains during diagenesis this places an upper limit of 70 micrite concentration above which the effect of diagenetic alteration is minimal careful sampling of dense micritic part of the soil carbonate nodules therefore does provide pristine isotopic composition and it is inappropriate as proposed recently to reject the paleoclimatic potential of all paleosol carbonates affected by burial diagenesis based on pristine 13 c value of 8 8 0 2 in soil carbonates an atmospheric co 2 concentration between 764 and 306 ppmv is estimated for the early oligocene 31 ma dagshai time these data show excellent agreement between two independent proxy records viz soil carbonate and marine alkenone and support early oligocene survival of the antarctic ice sheet

lakes beneath the ice sheet the occurrence analysis and future exploration of lake vostok and other antarctic subglacial lakes abstract airborne geophysics has been used to identify more than 100 lakes beneath the ice sheets of antarctica the largest lake vostok is more than 250 km in length and 1 km deep subglacial lakes occur because the ice base is kept warm by geothermal heating and generated meltwater collects in topographic hollows for lake water to be in equilibrium with the ice sheet its roof must slope ten times more than the ice sheet surface this slope causes differential temperatures and melting freezing rates across the lake ceiling which excites water circulation the exploration of subglacial lakes has two goals to find and understand the life that may inhabit these unique environments and to measure the climate records that occur in sediments on lake floors the technological developments required for in situ measurements mean however that direct studies of subglacial lakes may take several years to happen

comparison of organic and inorganic carbon isotope patterns across the frasnian famennian boundary abstract the carbon isotopic composition of organic matter is reported for two frasnian famennian boundary sections from the rheinische schiefergebirge germany during the late frasnian 13 c org values commonly range from 27 5 to 26 highest 13 c org values around 24 are encountered immediately above and below the kellwasser horizons all samples from the kellwasser horizons are depleted in 13 c org by 2 5 to 4 7 this depletion is explained by a higher proportion of biomass derived from isotopically depleted chemoautotrophic bacteria a comparison of the positive 13 c excursions shows that the 13 c org shifts precede the 13 c carb shifts by some 10 5 years consequently 13 c values document a shift towards lower values below the upper kellwasser horizon a contribution of terrestrial organic matter as well as a thermal alteration of the 13 c org signals do not provide compelling explanations for the earlier 13 c org shift increases in primary productivity or carbon burial rate will change the co 2 aq content of surface waters affect the carbon isotope fractionation during photosynthetic carbon uptake and thus enrich organic carbon in 13 c however both processes cannot account for the earlier onset of the 13 c org shift because the 13 c carb record should document the resulting 13 c enrichment in surface waters as well a reduction in the calcium carbonate precipitation rate due to the global extinction of the reef ecosystem may have played an important role in reducing the co 2 aq content of surface waters without changing the isotopic composition of surface waters whether this process or other factors such as a rise in sea surface temperature or a change in the phytoplankton association account for the earlier onset of the positive shift in the 13 c org curve must be determined by further studies that may be able to confirm the global significance of the reported 13 c org pattern in frasnian famennian boundary sections from other parts of the globe

oxygen isotope evolution of biogenic calcite and apatite during the middle and late devonian oxygen isotope ratios of well preserved brachiopod calcite and conodont apatite were used to reconstruct the palaeotemperature history of the middle and late devonian by assuming an oxygen isotopic composition of 1 v smow for devonian seawater the oxygen isotope values of eifelian and early givetian brachiopods and conodonts give average palaeotemperatures ranging from 22 to 25 c late givetian and frasnian palaeotemperatures calculated from 18o values of conodont apatite are close to 25 c in the early frasnian and increase to 32 c in the latest frasnian and early famennian oxygen isotope ratios of late givetian and frasnian brachiopods are significantly lower than equilibrium values calculated from conodont apatite 18o values and give unrealistically warm temperatures ranging from 30 to 40 c diagenetic recrystallization of shell calcite different habitats of conodonts and brachiopods as well as non equilibrium fractionation processes during the precipitation of brachiopod calcite cannot explain the 18o depletion of brachiopod calcite moreover the 18o depletion of brachiopod calcite with respect to equilibrium 18o values calculated from conodont apatite is too large to be explained by a change in seawater ph that might have influenced the oxygen isotopic composition of brachiopod calcite the realistic palaeotemperatures derived from 18o apatite may suggest that biogenic apatite records the oxygen isotopic composition and palaeotemperature of palaeozoic oceans more faithfully than brachiopod calcite and do not support the hypothesis that the 18o 16o ratio of devonian seawater was significantly different from that of the modern ocean

radio echo layering in polar ice sheets and past volcanic activity a recent study1 has shown how acidity profiles along dated greenland ice cores can reveal large volcanic eruptions in the northern hemisphere during the past 10 000 yr it has been suggested that these layers of acidic ice in the polar ice sheets may also be detected by airborne radio echo sounding res techniques as stratification echoes2 4 explosive volcanic eruptions eject large amounts of so2 into the stratosphere5 where it forms an h2so4 aerosol6 studies of antarctic snow7 and greenland ice cores2 show that this material can be deposited in layers of large areal extent on polar ice sheets calculations based on observations of these slightly acidic layers show that they should give rise to radar reflections of similar magnitude to those observed for stratification echoes new res data from the antarctic enables the present comparison to be made between observed layer power reflection coefficients prcs and calculated values for reflections from acidic ice layers and from layers of ice of changed density a gap in layering has been identified which seems to coincide with a similar gap reported in greenland at crete8 profiles of layer prc against age show a common pattern for many sites on the antarctic ice sheet this prc age profile may provide a record of explosive volcanic activity for the southern hemisphere over the past 150 000 yr

origin and significance of isotope shifts in pennsylvanian carbonates asturias nw spain abstract the primary variability of the composition and properties of seawater is much greater in the shallow coastal zones than in the main body of ocean water an inadequate understanding of this variability as well as different diagenetic environments severely limit the interpretation of the stable isotope record of shoalwater carbonates in order to investigate this primary and diagenetic variability along a bashkirian moscovian platform to basin transect 13c and 18o analyses have been performed on more than 1000 matrix micrite carbonate cement and brachiopod shell samples in isotope analysis these different carbonate materials tend to complement each other inasmuch as they have different advantages and shortcomings the resulting data reveal spatial trends in 13c and 18o signatures from platform top lower values to basin higher values in the case of 13c from pristine brachiopods this trend can be explained by the long residence time aging of platform top water masses in the case of brachiopod 18o this variance is interpreted to reflect temperature differences between warm surface and colder bottom water separated by a permanent thermocline at about 150 to 200 m beneath the shelf break micrite and marine cement isotopic values from the platform interior were reset lowered during pervasive early meteoric diagenesis in contrast micrite and marine cement isotopic values from the outer platform slope and basin show higher values close to the assumed pennsylvanian seawater isotopic composition this implies that isotopic data from shoalwater carbonates including pristine brachiopod shells might not necessarily reflect paleoceanographic trends of the open ocean water masses because of changes in coastal water mass isotope signature and interaction with early meteoric fluids

biochemostratigraphy of the upper frasnian in the namur dinant basin belgium implications for a global frasnian famennian pre event the upper frasnian sequence of the namur dinant basin in southern belgium consists of mixed siliclastic carbonate succession of a ramp setting where the sequence spans the rhenana linguiformis conodont zones earlier studies investigated the chemostratigraphic variations during the frasnian famennian event but little has been yet known about the nature of the counterpart variations that immediately preceded that time interval despite the scarcity of well preserved brachiopods sixty one calcitic shells were collected mainly from beds of the neuville and les valisettes formations lower and upper rhenana zones to investigate biochemostratigraphic profiles of oxygen carbon isotope and rare earth element ree variations of the time interval immediately before the frasnian famennian boundary the 18o and 13c values of the well preserved shells range from 9 5 to 5 6 vpdb 7 7 1 1 n 33 and from 1 8 to 3 8 vpdb 1 1 1 7 n 33 respectively which are within the documented global values the c and o isotope profiles exhibit parallel shifts particularly at the top of the neuville formation top of the lower rhenana zone which are associated with a sea level rise and shrinkage in the brachiopod community also the th u 0 9 0 6 n 16 and ce ce 2 2 0 5 n 16 ratios suggest deposition under reducing conditions consistent with sea transgression

new insights into geochemical behaviour in ancient marine carbonates upper jurassic ammonitico rosso novel proxies for interpreting sea level dynamics and palaeoceanography elemental concentrations in phanerozoic sea water are known to fluctuate both in time and space with regard to carbonates precipitated from marine fluids elemental concentrations in the carbonate crystal lattice are affected by a complex array of equilibrium and non equilibrium as well as post depositional alteration processes to assess the potential of carbonate elemental chemostratigraphy seven upper jurassic sections were investigated along a proximal to distal transect across the south east iberian palaeomargin the aim was to explore stratigraphic and spatial variations in calcium strontium magnesium iron and manganese elemental abundances the epicontinental geochemical record is influenced by the combination of continental runoff and a significant diagenetic overprint in contrast the epioceanic geochemical record agrees with reconstructed open marine sea water values reflecting a moderate degree of syn depositional to early marine pore water diagenesis establishing a fair degree of preservation of matrix micrite a thorough statistical approach was applied and elemental associations tested for their environmental significance principal component and hierarchical cluster analyses revealed a persistent relation between carbonate magnesium iron and strontium abundances processes related to early diagenetic nodulation in ammonitico rosso facies most probably account for the incorporation of these elements in the calcium carbonate lattice the clear decoupling of carbonate manganese abundance with respect to the remaining elements is documented and related to high sea floor spreading rates and hydrothermal activity during the late jurassic the investigation of potential time fluctuation of geochemical patterns was approached through variogram computation the observed temporal behaviour is most likely to be forced by relative sea level dynamics reflecting late jurassic palaeoceanographic conditions and potential planetary interactions the data obtained in this study highlight the utility of elemental data from carbonate matrix micrites as geochemical proxies for studying the influence of remote trigger factors

a stratigraphic link across 1100 km of the antarctic ice sheet between the vostok ice core site and titan dome near south pole isochronous internal ice sheet layering measured from airborne 60 mhz radar was traced between lake vostok and the titan ice dome 100 km from south pole station antarctica three layers were selected between ridge b and titan dome and between ridge b and lake vostok this layering can be used to correlate the existing vostok ice core across 1100 km of the ice sheet interior our correlation is also matched to the new epica ice core site by using an existing radar link between vostok and dome c stations thus three east antarctic ice domes are linked stratigraphically for the first time through internal ice sheet radar layering our results indicate that the basal layers of ice at titan dome are around 165 000 years old suggesting that this location and by inference the south pole station are prime sites for a high resolution ice core from the last glacial interglacial cycle

sensitivity of the epeiric sea carbon isotope record to local scale carbon cycle processes tales from the mohawkian sea ancient marine carbon isotope records derived from epeiric sea carbonates can bear a strong influence of local scale carbon cycling processes across the late ordovician mohawkian sea of eastern laurentia the carbon isotope compositions d 13 c of contemporaneous sediments range from 2x in the interior of the sea to 2 5x along the margin here we use a box model to explore the relative importance of carbon fluxes within the mohawkian sea from a mass balance perspective in the model the mohawkian sea carbon reservoir is coupled to but distinct from the ocean and atmosphere carbon reservoirs at initial steady state conditions the residence time of carbon in the mohawkian sea is less than 10 years we find that to produce model d 13 c values representative of the range in d 13 c across the mohawkian sea we must divide the sea into an inner region and an outer region and limit dissolved inorganic carbon dic exchange between the two to 15 of the initial steady state unrestricted exchange rate it is also necessary to supply low d 13 c carbon 29x to the inner region of the sea at a rate of 17 4 10 12 mol c yr 1 the required flux of low d 13 c carbon could not have been sustained over the long term by remineralization of organic carbon stored in sediments of the inner region of the mohawkian sea and the geographic d 13 c pattern is unlikely to have been generated by upwelling along the sebree trough rather the low d 13 c flux might have been derived from bryophytedominated terrestrial ecosystems suggesting an important role for terrestrial carbon cycling prior to the advent of vascular plants aninterestingfeatureofthemodelisthattheisotopiccompositionsofboththeepeiric seaandthelargerocean atmospheresystem are sensitive to changes in exchange rates within the epeiric sea this has important implications for interpreting global d 13 c

interplay of autogenic and allogenic processes on the formation of shallow carbonate cycles in a synrift setting lower pliensbachian traras mountains nw algeria

facies and geochemistry across the early middle frasnian transition late devonian on south china carbonate shelf comparison with the polish reference succession abstract dongcun and longmen are two important reference sections for the study of the frasnian carbonate platform of guangxi southern south china at the dongcun section conodonts recovered in the present study provide a robust biostratigraphic framework for the lower middle frasnian interval the studied interval uppermost givetian to middle frasnian basal palmatolepis hassi zone is characterized by repeated shallower and deeper water deposits but the cyclic depositional trend was mainly deepening upward carbon isotopic investigation of bulk samples recognizes a major four step perturbation across the lower middle frasnian boundary which is also evident in the holy cross mountains poland the pattern is reinforced by correlative organic carbon isotopic secular trends from the reference polish sections a prominent long lasting increase in 13ccarb up to 4 5 event iii is evident in the palmatolepis punctata zone but is preceded and followed by rapid negative shifts events ii and iv respectively to ca 0 a weak incipient positive excursion event i is recognized in carbonate carbon only in the upper part of the palmatolepis transitans zone in chinese sections different background isotopic values indicate decoupled isotopically dissimilar hydrothermally affected and mostly oxygenated water masses over the carbonate shelf as shown by trace and rare earth elements the shallower water upslope diagenetically unaltered dongcun succession reveals lighter carbon isotopic ratios on the order of 2 while the less densely sampled and less certainly dated mostly muddy siliceous longmen downslope succession shows 13ccarb levels similar to those recorded worldwide the onset of the bipartite event iii is marked by 13c enrichment of 4 3 at dongcun event iv a light carbon excursion is especially well recorded in the shallow water facies by a 2 5 negative shift the event i excursion in the transitans zone is obscured as in some polish successions but is probably recorded in organic carbon trends slight differences in timing and magnitude of the 13ccarb oscillations may originate from geochemical decoupling between the open ocean and the tectonically active morphologically differentiated epeiric basins nevertheless a global extent for this major punctata event is clear from the similar biogeochemical signals recorded on the distantly separated south laurussian and south china shelves