carbon and oxygen isotope stratigraphy of the lower mississippian kinderhookian lower osagean western united states implications for seawater chemistry and glaciation a positive carbon isotope 1 3 c excursion has been recognized in upper kinderhookian and early osagean carbonates in three sections in southeast idaho and nevada the oldest 1 3 c peak 7 is dated to the isostichaconodont zone and a younger peak occurs in the typicus zone the shifts are recorded in a range of carbonate lithofacies representing various water depths along the shelf lithofacies sampled for 1 3 c and 1 8 o at the samaria mountain section in southeast idaho record the shallowest water conditions indicated by cross bedded skeletal and peloidal grainstones the deepest water conditions are present in the pahranagat range section in eastern nevada which consists mainly of bioturbated lime mudstone and skeletal wackestone the 1 3 c values from these widely separated sedimentary basins show a consistent trend that correlates with early mississippian curves generated from brachiopod calcite in western europe and the midcontinent of north america as well as dolomites in utah and wyoming 1 8 o values become more positive up section generally paralleling the positive trend in 1 3 c during the late kinderhookian no subaerial exposure surfaces are recognized in the sections examined in southeast idaho and nevada and at least the 1 3 c trends are interpreted as primary seawater fluctuations sea level changes occurred near the beginning of the late kinderhookian 1 3 c shift early to middle parts of the isosticha zone and within the peak of the 1 3 c excursion kinderhookian osagean boundary although tectonic changes associated with the antler orogeny have likely modified the eustatic signature

on the coupling between the harang reversal evolution and substorm dynamics a synthesis of superdarn dmsp and image observations 1 the harang reversal is a prominent feature frequently observed in the electric and magnetic field patterns in the high latitude auroral zone and plays an important role in substorm dynamics a comprehensive set of instruments including super dual auroral radar network superdarn defense meteorological satellite program dmsp and imager for magnetopause to aurora global exploration image is used to investigate the relationship between the harang reversal and substorms on the basis of nine events that have been analyzed we find that the harang reversal forms and becomes well defined during the growth phase azimuthal flows equatorward of the harang reversal a majority of which are in the subauroral region enhance during the growth phase the observations indicate that subauroral polarization streams saps and the harang reversal evolve together as part of the growth phase development of the region 2 current system furthermore the substorm auroral onset is seen to occur quite near the center of the harang flow shear which suggests that the substorm upward field aligned current develops there after onset the evolution of convection flows in the vicinity of the harang region depends strongly on their location relative to that of the onset saps flows equatorward of the harang reversal suddenly increase at the substorm onset flow shear east of the auroral onset relaxes after the onset and poleward flows part of a clockwise vortex are observed west of the auroral onset after the onset these observations demonstrate the strong coupling between the harang reversal evolution and substorm dynamics and suggest that the nightside region 2 physics is closely related to substorm dynamics

late devonian glaciation in south america abstract an ice age in famennian late devonian time is documented by the presence of diamictites with striated faceted and polished pebbles rhythmites with dropstones erratic boulders and striated pavements and deformed sandstones the glacigenic beds occur in three huge intracratonic basins solimoes amazonas and parnaiba and in one pericratonic basin acre in northern brazil other possible late devonian diamictites may occur elsewhere in brazil and africa which if confirmed would extend considerably the area affected by this glacial age the onset of the late devonian glaciation caused a global narrowing of the warm climatic belts sharp regression increased clastic sedimentation massive biotic extinction reduced biochemical deposition and unconformities this resulted in important facies changes in the world geological record ice centers moved from northern africa to southwestern south america from late ordovician to early silurian time from mid silurian to early late devonian time no record of glaciation is known in late late devonian time intermittent glaciation began again in central south america and from late late devonian to early late permian time ice centers migrated towards antarctica across south america and south africa the devonian and ordovician silurian glaciations together with the better known permo carboniferous glaciations may all have primarily resulted from the shifting position of the gondwana continent with respect to the south pole

quantitative radiometric and biostratigraphic calibration of the pennsylvanian early permian cisuralian time scale and pan euramerican chronostratigraphic correlation a quantitative biostratigraphic and radiometric calibration is presented for the pennsylvanian through early permian global time scale based upon high precision isotope dilution thermal ionization mass spectrometer id tims u pb zircon ages for interstratified ash beds in the parastratotype sections of the southern urals of russia twenty four ash bed ages in three outer ramp and basinal sections of the pre uralian foredeep bracket the biotic definitions of global stages and regional substages from the base of the upper pennsylvanian kasimovian stage to the base of the lower permian artinskian stage four additional ash bed ages in two sections of the eastern slope of the urals constrain the global bashkirian and serpukhovian stages quantitative stratigraphic methods conop9 are applied to a compilation of over 2000 bioevents in 22 stratigraphic sections supplemented by our dated volcanic horizons to refine the pennsylvanian early permian global time scale significant shifts in the duration of several stages are demonstrated ranging from one to six million years compared with prior estimates the unprecedented density of radiometric calibration points for the pennsylvanian permian transition provides a high resolution 0 1 ma global chronostratigraphic standard for testing and improving biostratigraphic correlations across euramerica we integrate radiometric ages biostratigraphic correlation and cyclostratigraphic tuning of major cyclothems to the long period 404 ka eccentricity cycle to elucidate the tempo magnitude and forcing of eustatic changes and cyclothemic deposition associated with the waxing and waning of gondwanan ice sheets and establish a pan euramerican chronostratigraphic framework for most of pennsylvanian and early permian time

carbon isotope evidence implying high o2 co2 ratios in the permo carboniferous atmosphere abstract theoretical models predict a marked increase in atmospheric o2 to 35 during the permo carboniferous 300 ma occurring against a low 0 03 co2 level an upper o2 value of 35 however remains disputed because ignition data indicate that excessive global forest fires would have ensued this uncertainty limits interpretation of the role played by atmospheric oxygen in late paleozoic biotic evolution here we describe new results from laboratory experiments with vascular land plants that establish that a rise in o2 to 35 increases isotopic fractionation 13c during growth relative to control plants grown at 21 o2 despite some effect of the background atmospheric co2 level on the magnitude of the increase we hypothesize that a substantial permo carboniferous rise in o2 could have imprinted a detectable geochemical signature in the plant fossil record over 50 carbon isotope measurements on intact carbon from four fossil plant clades with differing physiological ecologies and ranging in age from devonian to cretaceous reveal a substantial 13c anomaly 5 occurring between 300 and 250 ma the timing and direction of the 13c excursion is consistent with the effects of a high o2 atmosphere on plants as predicted from photosynthetic theory and observed in our experiments preliminary calibration of the fossil 13c record against experimental data yields a predicted o2 co2 mixing ratio of the ancient atmosphere consistent with that calculated from long term models of the global carbon and oxygen cycles we conclude that further work on the effects of o2 in the combustion of plant materials and the spread of wildfire is necessary before existing data can be used to reliably set the upper limit for paleo o2 levels

glaciation aridification and carbon sequestration in the permo carboniferous the isotopic record from low latitudes to evaluate the isotopic record of climate change and carbon sequestration in the late paleozoic we have compiled new and published oxygen and carbon isotopic measurements of more than 2000 brachiopod shells from carboniferous through middle permian 359 260 ma strata we focus on the isotopic records from the u s midcontinent and the russian platform because these two regions provide well preserved marine fossils spanning a broad time interval both regions show a 18o increase at the mid carboniferous boundary ca 318 ma that roughly correlates with geologic evidence for an expansion of gondwanan glaciers only the russian platform record shows a 18o maximum during the glacial maximum in the asselian in contrast to a previous study korte c jasper t kozur h w and veizer j 2005 18o and 13c of permian brachiopods a record of seawater evolution and continental glaciation palaeogeogr palaeoclimatol palaeoecol 224 333 351 our data show no oxygen isotope evidence for glacial retreat in the early permian but instead show increasing 18o values related to aridification dissimilarity in the 18o trends for the epicontinental seas of north american and the russian platform suggests that at least one region experienced periodic restriction that altered regional salinities and seawater 18o values these results highlight the need for complementary proxies to identify restricted circulation in epicontinental seas carbon isotopic compositions of carbonates exhibit substantial regional variation with low values in western north america intermediate values in the midcontinent and high values in the sverdrup basin russian platform and northern spain nevertheless both u s midcontinent and russian platform records show a late serpukhovian minimum a sharp increase across the mid carboniferous boundary and a minimum centered on the kasimovian the correlative increase in brachiopod 13c and 18o values at the mid carboniferous boundary is our best isotopic evidence for a link between the carbon burial and glaciation in the permo carboniferous

isotopic records of brachiopod shells from the russian platform evidence for the onset of mid carboniferous glaciation we performed isotopic analyses of carboniferous brachiopod shells from the russian platform to examine global and regional environmental change along the western and eastern margins of laurussia during the formation of pangea and specifically to examine the isotopic evidence for the onset of mid carboniferous glaciation shell preservation was evaluated from shell microstructure cathodoluminescence trace element content and isotopic comparison with matrix material most interior nonluminescent nl prismatic shell appears to be chemically well preserved as indicated by low to undetectable si al fe and mn contents with minor exception nl shell 13c and 18o values are higher than those of corresponding cements and matrix the 13c record for the russian platform clearly shows a 3 increase from 2 4 0 7 to 5 5 0 6 in the serpukhovian or early bashkirian this shift was first reported by popp et al popp b n anderson t f sandberg p a 1986 brachiopods as indicators of original isotopic compositions in some paleozoic limestones geol soc am bull 97 1262 1269 but had not been documented for a single region widespread occurrence of high 13c values in the late carboniferous support the interpretation of popp et al with regard to this shift as a record of increased burial of organic carbon north american sections show a mid carboniferous 13c shift of only 1 5 we hypothesize that the reduced 13c shift reflects enhanced upwelling on the epicontinental seas of north america after the closing of the seaway between laurussia and gondwana the 18o record for the russian platform shows a 1 8 increase in the mid carboniferous correlative with increased occurrence of glacial sediments and a drop in sea level as a first approximation ice volume calculations suggest that 0 7 of the mid carboniferous 18o shift is due to changes in seawater 18o and 1 1 is due to 5 c cooling concurrent positive 13c and 18o shifts provide evidence for a relationship between mid carboniferous glaciation and burial of organic carbon presumably through changes in atmospheric co2 levels

obliquity forcing of organic matter accumulation during oceanic anoxic event 2 1 an analysis of orbitally influenced climate sensitive sedimentation is conducted across a meridional transect of the proto north atlantic to reconstruct the behavior of the carbon cycle and climate during oceanic anoxic event 2 oae 2 94 ma midlatitude to near equatorial sites spanning deep ocean to shelf environments are evaluated using a new inverse method for the identification and calibration of orbital influence in ancient strata the results yield consistent independent astrochronologies at each location compatible with the recently published radioisotopic astrochronologic time scale at the cenomanian turonian gssp and thus provide a unified high resolution temporal context for evaluation of the event the proto north atlantic astrochronologies document an amplification of obliquity power during oae 2 indicating that obliquity was the dominant pacemaker of organic matter accumulation by the latter portion of the event the strong obliquity signal suggests an influence of high latitude climate processes across midlatitude deep ocean to tropical shelf environments changes in oceanic circulation during oae 2 represent a likely mechanism for the propagation of a high latitude signal and proxy data from demerara rise reveal the development of a new intermediate water mass source synchronous with the record of obliquity amplification we hypothesize that a dense high latitude water mass displaced a pre existing nutrient rich anoxic deep water layer in the proto north atlantic augmented by enhanced volcanism driving an episode of high productivity that lasted 700 800 ka the development and intensification of the new intermediate deep water source was potentially driven by eustatic sea level rise which created expansive seaways in mid to high latitudes

constraints on pennsylvanian glacioeustatic sea level changes using oxygen isotopes of conodont apatite conodonts from u s midcontinent cyclothems were studied for oxygen isotopes in order to constrain pennsylvanian glacioeustatic sea level fluctuations pennsylvanian deposits of the midcontinent united states are composed of cyclic alternations of thin transgressive limestones offshore gray to black phosphatic shales and thick regressive limestones a sequence that is underlain and overlain by nearshore to terrestrial shales with paleosols and coal beds glacioeustatic sea level fluctuations are considered the primary cause for the formation of these cyclothems oxygen isotope analyses of conodont apatite from the black 20 1 0 5 vienna standard mean ocean water vsmow and gray shale units 20 5 0 5 vsmow show lowest average 18 o values whereas conodont elements from the regressive 21 0 0 3 vsmow and transgressive limestone units 21 1 0 6 vsmow are enriched in 18 o the maximum change in 18 o of conodonts from the black shale and carbonate units from individual cyclothems is 1 7 the 1 7 c difference in 18 o compares relatively well to pleistocene interglacial glacial changes in 18 o of equatorial surface dwelling foraminifers and suggests that pennsylvanian glacioeustatic sea level changes may have been of comparable amplitude however since the pennsylvanian glacial maxima are represented by terrestrial sediments and are not documented in the conodont oxygen isotope record pennsylvanian glacioeustatic sea level changes were probably larger than the 120 m fluctuations recorded for the pleistocene glaciations

high resolution carbon isotope changes in the permian triassic boundary interval chongqing south china implications for control and growth of earliest triassic microbialites abstract high resolution 13 c carb analysis of the permian triassic boundary ptb interval at the laolongdong section beibei near the city of chongqing south china encompasses the latest permian and earliest triassic major facies changes in the south china block scb microbialites form a distinctive unit in the lowermost 190 cm above the top of the changhsing formation latest permian at laolongdong comparable to a range of earliest triassic sites in low latitudes in the tethyan area the data show that declining values of 13 c carb well known globally began at the base of the microbialite high positive values 3 to 4 ppt of 13 c carb in the late permian are interpreted to indicate storage of 12 c in the deep waters of a stratified ocean that was released during ocean overturn in the earliest triassic contributing to the distinctive fall in isotope values this interpretation has been stated by other authors and is followed here the 13 c carb curve shows fluctuations within the microbialite unit which are not reflected in the microbialite structure comparisons between microbialite branches and adjacent micritic sediment show little difference in 13 c carb demonstrating that the microbialite grew in equilibrium with surrounding seawater the early triassic microbialites are interpreted to be a response to upwelling of bicarbonate rich poorly oxygenated water in low latitudes of tethys ocean consistent with current ocean models for the ptb interval however the decline of 13 c carb may be due to a combination of processes including productivity collapse resulting from mass extinction return of deep water to ocean surface oxidation of methane released from methane hydrate destabilisation and atmospheric deterioration nevertheless build up of bicarbonate rich anoxic deep waters may be expected as a result of the partial isolation of tethys due to continental geography release of bicarbonate rich deep water by ocean upwelling in the earliest triassic may have been an inevitable consequence of this combination of circumstances

models for circulation patterns in epicontinental seas applied to paleozoic facies of north america craton circulation in epicontinental seas develops in response to thermohaline wind driven and tidal motions in various climatic geographic and bathymetric settings mass balance relations in a seaway are established by the relative rates of outflow inflow freshwater and ocean water and evaporation which constrain two contrasting styles of epicontinental circulation quasietuarine circulation qec is established where rates of freshwater influx exceeds evaporation surface outflow from a seaway with qec typically is balanced by inflow of oceanic water at depth a density stratification can be established below the limits of vertical mixing a bottom layer of oxygen poor or anoxic water may develop in a seaway with or without an entrance sill if the bottom waters are derived from the oxygen minimum zone of the open ocean or if organic productivity exceeds the limits of aerobic respiration upwelling may be promoted in specific epicontinental settings with qec antiestuarine circulation aec is developed in arid climates where evaporation exceeds freshwater influx evaporative concentration in the surface layer causes oxygenated water to sink bottom outflow of denser more saline water is balanced by surface inflow from the open ocean a sill or barrier may inhibit bottom circulation in seas with aec permitting development of a basal brine layer stagnation in the brine layer may lead to oxygen depletion seas with aec commonly are characterized by extensive carbonate evaporite facies geographic and stratigraphic syntheses of lithofacies and biofacies provide the empirical basis for interpretations of seaway dynamics in ancient epicontinental settings examples from the upper ordovician maquoketa formation and upper devonian lime creek sweetland creek formations of cratonic north america are interpreted in the context of stratified qec patterns in each case oxygen poor to anoxic waters appear to have impinged along the basin slope below the margin of an oxygenated carbonate shelf upwelling along the shelf margin in the maquoketa example helps explain the distribution of phosphatic sediments a stratified aec pattern is interpreted for the gower formation silurian of eastern iowa a barrier to bottom circulation at the mouth of an embayment in the epicontinental sea resulted in a basal layer of hypersaline water devoid of shelly benthos surface water salinities increased progresively shoreward within the embayment but benthic organisms flourished where carbonate mounds built upward into the oxygenated layer

δ18o and δ13c of permian brachiopods a record of seawater evolution and continental glaciation abstract two hundred sixty four 18 o and 13 c values of permian articulate brachiopod shells were analyzed and 81 of these values were characterized as well preserved and biostratigraphically well defined these were then utilized for construction of baseline oxygen and carbon isotope curves for the permian interval in addition 21 13 c whole rock values are reported for the wordian and capitanian the early permian asselian to artinskian times are characterized by 2 5 decrease in oxygen isotope values from 0 7 to 3 3 v pdb this is attributed to a 4 7 c increase in temperature in the southern urals concomitant with the retreat of the permo carboniferous ice sheets and return of the 18 o depleted melt water into the oceans the late permian samples from iran jolfa at kuh e ali bashi and china meishan yield 18 o values and presumably temperatures similar to those that followed the termination of the large scale glaciation in the lower permian in between the upper kungurian to capitanian samples from the delaware basin guadalupe mountains are enriched in 18 o at 1 5 to 3 we have no definitive explanation for these data but tentatively suggest that the anomaly can potentially be a result of evaporative enrichment of seawater in 18 o due to intracratonic arid setting of the basin the 18 o enriched nature of the zechstein samples 1 2 to 2 5 on the other hand is in all probability a reflection of the high evaporation rates in the zechstein sea the permian interval is characterized by a relatively constant 13 c at about 4 the exceptions are again the brachiopods from the delaware basin guadalupe mountains which show 1 6 increase in the guadalupian to values of up to 5 9 in the wordian a tentative explanation as in the case of oxygen is based on the proposition that the semi enclosed delaware basin was likely stratified with sequestration of the 13 c depleted carbon to the deeper water layers and a complementary 13 c enrichment in the upper oxygenated layer the coeval open ocean water dic may have been similar to that of the remainder of the permian interval at 4 as indicated by whole rock carbonate samples from oman sicily and iran in the latest permian the trend mimics the well known 13 c drop at the permian triassic boundary

evolution of permian conodont provincialism and its significance in global correlation and paleoclimate implication the main components of asselian through artinskian conodont faunas found around the world are basically the same and the provincialism is indicated only by less common endemic elements such as gondolelloides and new genus a henderson in north pangea sweetognathus bucaramangus around the equator and vjalovognathus in eastern gondwana provincialism is marked by differences at the species level of mesogondolella neostreptognathodus and sweetognathus during the kungurian and becomes very distinct with differences at the genus level during the guadalupian and lopingian three provinces of permian conodonts referred to as the north cool water province ncwp the equatorial warm water province ewwp and the peri gondwana cool water province gcwp are recognized the ncwp is marked by gondolelloides in the early cisuralian dominance of neostreptognathodus and no or rare sweetognathus in the late cisuralian dominance of merrillina and mesogondolella and absence of sweetognathus in the guadalupian and dominance of merrillina and mesogondolella and absence of iranognathus in the lopingian the ewwp is characterized by the absence of gondolelloides and vjalovognathus in the cisuralian abundance of sweetognathus and pseudosweetognathus in the kungurian late cisuralian jinogondolella and sweetognathus in the guadalupian and clarkina and iranognathus in the lopingian the gcwp is marked by vjalovognathus merrillina in the cisuralian vjalovognathus merrillina and mesogondolella in the guadalupian and vjalovognathus and merrillina in the lopingian mixed faunas are recognized in regions bordering between the ewwp and gcwp including western timor during the artinskian pamirs during the kungurian and the salt range during the guadalupian and lopingian three different conodont zonations are proposed one for each of the three conodont provinces four potential horizons for inter provincial correlation of permian conodonts are recognized they are in ascending order 1 the first appearance of sweetognathus whitei which is closely related to the last occurrence of carboniferous type conodonts such as streptognathodus and adetognathus 2 the first appearance of neostreptognathodus pequopensis 3 the base of the jinogondolella nankingensis zone and 4 the base of the clarkina postbitteri iranognathus erwini zone the spatial and temporal distribution pattern of permian conodonts suggests that temperature is the primary controlling factor evolution of permian conodont provincialism reveals a glaciation during the asselian and sakmarian a global warming during the artinskian a climate cooling in north pangea during the kungurian a continuation of kungurian climate trends in the guadalupian a relatively minor warming during the wuchiapingian a returned cooling in the changhsingian and lower and middle griesbachian and a global warming in the late griesbachian which ended the permian conodont lineage

co2 forced climate and vegetation instability during late paleozoic deglaciation the late paleozoic deglaciation is the vegetated earth9s only recorded icehouse to greenhouse transition yet the climate dynamics remain enigmatic by using the stable isotopic compositions of soil formed minerals fossil plant matter and shallow water brachiopods we estimated atmospheric partial pressure of carbon dioxide pco2 and tropical marine surface temperatures during this climate transition comparison to southern gondwanan glacial records documents covariance between inferred shifts in pco2 temperature and ice volume consistent with greenhouse gas forcing of climate major restructuring of paleotropical flora in western euramerica occurred in step with climate and pco2 shifts illustrating the biotic impact associated with past co2 forced turnover to a permanent ice free world

the stable carbon isotopic composition of organic material in platform derived sediments implications for reconstructing the global carbon cycle in pelagic carbonate sediments the degree to which the 13c values of inorganic and organic fractions co vary has been used to interpret rates of production burial and decomposition of organic carbon this relationship is relatively consistent through time permitting estimates of organic carbon production and preservation however as the majority of pelagic sediments older than 200 myr have been subducted carbonate sediments deposited in epeiric seas and platforms are often substituted for pelagic carbonates in analyses of ancient global carbon cycling there are well known pitfalls to using shallow marine carbonate materials including diagenesis semi isolation of depositional environments and input of different types of sediments with varying inorganic 13c 13cinorganic values which can obscure any global signatures one method used to assess whether global changes in 13c are accurately represented by 13cinorganic records is to examine variations in the 13c of co occurring organic material 13corganic if a 13corganic record co varies with a co occurring 13cinorganic record it is argued that the signals must be related to variations in the global carbon cycle this assumption has been investigated by analysing the isotopic composition of the organic carbon preserved in the uppermost 150 m of periplatform sediments recovered during odp leg 166 from the western margin of great bahama bank the 13corganic values measured in this study were compared to previously published 13cinorganic records measured on identical samples thus allowing a study of the correlation between the two records through time these analyses showed that the correlation coefficient between 13cinorganic and 13corganic increased from the proximal location site 1005 r2 0 1 to the distal site site 1006 r2 0 63 the importance of platform derived carbonate and organic material at the proximal location site 1005 is reflected in the absence of a co variation between inorganic and organic 13c records which exhibit no correlation on the platform itself in contrast the co variance in 13c values at the basinal location site 1006 is explained by a two point mixing model which demonstrates the importance of both pelagic and platform derived carbonate and organic carbon in generating the positive correlation between the organic and inorganic 13c values this results in a correlation between 13cinorganic and 13corganic records at site 1006 that is unrelated to global carbon cycling such data question the applicability of using 13corganic values to support the ability of 13cinorganic values to record global carbon cycling in carbonates recovered from environments where multiple sources of carbonate and organic carbon contribute to the bulk 13c signal

intercalibration of radioisotopic and astrochronologic time scales for the cenomanian turonian boundary interval western interior basin usa we develop an intercalibrated astrochronologic and radioisotopic time scale for the cenomanian turonian boundary ctb interval near the global stratotype section and point in colorado usa where orbitally influenced rhythmic strata host bentonites that contain sanidine and zircon suitable for 40ar 39ar and u pb dating paired 40ar 39ar and u pb ages are determined from four bentonites that span the vascoceras diartianum to pseudaspidoceras flexuosum ammonite biozones utilizing both newly collected material and legacy sanidine samples of j obradovich comparison of the 40ar 39ar and u pb results underscores the strengths and limitations of each system and supports an astronomically calibrated fish canyon sanidine standard age of 28 201 ma the radioisotopic data and published astrochronology are employed to develop a new ctb time scale using two statistical approaches 1 a simple integration that yields a ctb age of 93 89 0 14 ma 2 total radioisotopic uncertainty and 2 a bayesian intercalibration that explicitly accounts for orbital time scale uncertainty and yields a ctb age of 93 90 0 15 ma 95 credible interval total radioisotopic and orbital time scale uncertainty both approaches firmly anchor the floating orbital time scale and the bayesian technique yields astronomically recalibrated radioisotopic ages for individual bentonites with analytical uncertainties at the permil level of resolution and total uncertainties below 2 using our new results the duration between the cenomanian turonian and the cretaceous paleogene boundaries is 27 94 0 16 ma with an uncertainty of less than one half of a long eccentricity cycle

high resolution carbon isotope δ13ccarb chemostratigraphy of the lower permian from the u s midcontinent checking the pulse of the late paleozoic ice age high resolution stable isotope chemostratigraphy 13 c carb and 18 o from the asselian and sakmarian stages cisuralian series permian system was carried out on the newby 2 28r core from stevens county sw kansas the cyclothemic strata of the council grove and chase groups sampled in this study record the rapid rise and fall of sea level due to the expansion and contraction of glacial mass during the early permian in the waning phases of the late paleozoic ice age lithologies interpreted to be deposited during higher sea level stand consistently show elevated 13 c carb values when compared with shallower water parts of each cycle and show as much as a 6 0 shift in 13 c carb within single cycles the 13 c carb values recorded here mirror changes in sea level throughout the sampled interval indicating a close correspondence between at least the local carbon cycle of the u s midcontinent and anadarko basin with global ice sheet dynamics and eustatic sea level as has been seen in previous studies however this basin contains generally lower absolute values of 13 c carb compared to other basins such as those in russia moscow basin china yangtze platform and nevada great basin the data presented here represent the first high resolution analysis of carbon cycle dynamics during the early permian and it remains to be seen if the heartbeat of the late paleozoic ice age preserved in this region is recognizable globally

sedimentological record of the late paleozoic glaciation in queensland australia although much is known of the timing geographical extent and character of the late paleozoic gondwanan glaciation its rec ord in eastern australia is poorly resolved some previous investigations have asserted that large parts of australia were covered by a cold based continental ice sheet during the pennsylvanian late carboniferous new data from queensland in northeast australia reported herein however suggest that the glaciation there was restricted to discrete short lived periods in the namurian 315 ma westphalian 311 ma and sakmarian 289 293 ma thick successions in three widely separated areas indicate that the glaciation was confined in each case to local valley or mountain glaciers and that the mainly proglacial sediments were enclosed in every case by substantial intervals of fluvial lacustrine and shallow marine strata deposited under nonglacial conditions accordingly we submit that the cessation of glacial sediment deposition elsewhere in gondwana during the pennsylvanian to earliest permian was due to the decay of glaciers rather than to a transition to a cold based ice sheet or sheets as has been previously suggested the interpretations presented herein make a significant contribution toward constraining the size and extent of glaciation in gondwana which has major implications for late paleozoic world climate and sea level fluctuations

amphibian burrows and ephemeral ponds of the lower permian speiser shale kansas evidence for seasonality in the midcontinent abstract burrows attributed to the lysorophid brachydectes elongatus occur within a green mudstone lens in the lower permian wolfcampian speiser shale council grove group of eastern kansas the burrow bearing unit consists of a 100 m long lens of massive calcareous silty mudstone with a maximum thickness of 35 cm the lens also contains the fossils of fish amphibians reptiles charophytes stomachara and ostracodes carbonita the mudstone lens pinches out laterally into red pedogenically modified mudstone the burrows occur in three layers at the top of each layer is a subaerial exposure surface indicated by rhizoliths mudcracks and coarse grained lags the mudstone lens is interpreted as the deposit of a shallow ephemeral pond the burrows occur in three vertically and temporally separated clusters with concentrations up to 20 m2 the burrows show two types of architecture type i burrows are elongate elliptical tubes 4 32 cm long and 2 7 cm in width type ii burrows are short elliptical tubes 1 5 3 5 cm in length and 2 5 5 cm in width the burrow fill consists of a mudstone capped by sandy siltstone each burrow layer contains a varying number of articulated and disarticulated lysorophid skeletons within the burrows and surrounding matrix while similar to permian lungfish burrows the architecture and surficial morphology of the lysorophid burrows permits their distinction even in the absence of body fossils the occurrence of burrow layers capped by subaerial exposure surfaces and separated by layers of non burrowed massive mudstone indicates that burrowing occurred in response to episodic perhaps seasonal droughts on the permian coastal plain the lysorophid burrowing behavior is analogous to that of the extant amphibians amphiuma sp and siren intermedia which inhabit rivers and ponds in the southeastern usa

paleoenvironmental changes in the silurian indicated by stable isotopes in brachiopod shells from gotland sweden ratios of stable carbon and oxygen isotopes in brachiopod shells more than 370 specimens esp atrypa reticularis from the silurian of gotland sweden have been analysed preservation of biological skeletal ultrastructures observed in sem micrographs and cathodoluminescence analyses indicate that usually no diagenetical alteration occurs the silurian of gotland consists of 440 m carbonate deposits spanning the late llandovery to late ludlow epochs 431 411 m y repeatedly uniform sequences of micritic limestones and marks are interrupted by complex structured reefs and adjacent platform sediments previously the alteration of facies is interpreted as the result of sea level fluctuations caused by a gradual regression with superimposed minor transgressive pulses the silurian sequence of gotland exhibits principally parallel carbon and oxygen isotope records corresponding closely to the topostratigraphic units lower values occur in periods dominated by deposition of marly sequences higher values are observed in periods dominated by reefs and extended carbonate platforms the isotope ratios are influenced by local as well as global factors the oxygen isotope ratios are interpreted to reflect paleosalinity changes due to varying freshwater input rather than changes in paleotemperature consequently the facies distribution of gotland is interpreted as resulting from changes in terrigenous input caused by different rates of continental weathering and freshwater runoff rather than by sea level fluctuations periods of arid climate and therefore anti estuarine downwelling of oxygenated surface water appear as short episodes of reef growing 1 5 m y in an epoche characterized by a tropic humid climate which causes an estuarine circulation and the upwelling of co2 rich deep water carbon isotope ratios are obviously connected to these changes in circulation by the advection of 13c rich surface water arid episodes or upwelling of 13c depleted deep water humid episodes of a silurian ocean which itself reveals generally euxinic deep water conditions due to the burial of organic carbon in black shales

oxygen isotope values from high latitudes clues for permian sea surface temperature gradients and late palaeozoic deglaciation abstract the permian was a period of waning large scale continental glaciations in the southern hemisphere the waning of these ice sheets during the early permian led to discharge of 18o depleted ice melt water into the oceans this coupled with rising seawater temperatures resulted in a concomitant decline of about 2 5 in the 18o of seawater as recorded by brachiopod shells from low latitude

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

carboniferous permian carbon isotope stratigraphy of successions from china yangtze platform usa kansas and russia moscow basin and urals abstract the pennsylvanian and early permian were times of extreme sea level changes of 100 to perhaps up to 200 m for example glacio eustatic sea level changes are well documented from the us midcontinent moscow basin and yangtze platform where more than 100 stacked subtidal to supratidal sequences have been described in contrast carbonates developed in the ural mountains and south guizhou of the yangtze platform were deposited in ramp and slope settings 13c values of whole rock samples from the us midcontinent and moscow basin were intensively affected by diagenesis only well preserved brachiopod shells maintained their original carbon isotope ratios in contrast limestones deposited in the deeper water slope environments were not affected by meteoric diagenesis and are interpreted to have mainly retained their carbon isotope ratios mean 13c values of slope carbonates of the yangtze platform increase from about 3 during the visean and serpukhovian to 5 at the carboniferous permian boundary and decrease to values around 2 in the early kungurian this positive 13c excursion coincides with low 13c values in the yangtze platform successions which were reset by meteoric diagenesis the highest 13c values recorded in the slope succession coincide with the inferred maximum glaciation that caused pronounced sea level lowstands short lived but significant negative 13c excursions in the chinese slope succession are interpreted to reflect changes in ocean circulation due to sea level rises which caused enhanced production and or preservation of organic matter which influenced the subsequent early diagenetic cementation

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

permian gondwanaland paleoenvironment inferred from carbon and oxygen isotope records of brachiopod fossils from sydney basin southeast australia abstract the 13 c and 18 o records of permian fossil brachiopods with biostratigraphical age control from southeastern australia have been constructed to investigate the high latitude paleoenvironment of gondwanaland all samples were thin sectioned and examined using petrographic and cathodoluminescence microscopy for evaluating shell preservation elemental compositions of select brachiopod shells were measured using electron probe microanalysis to further evaluate shell preservation within these intervals the average 13 c values of the best preserved non luminescent nl portion of the brachiopod shells are all greater than 5 1 with the highest value 7 0 at lower wandrawandian siltstone late kungurian these carbon isotope values are similar to those of contemporaneous tropical eastern pangea russian platform but heavier than those of western pangea north america the oxygen isotope difference between brachiopods of high southern latitudes and low latitudes fluctuated during early to middle permian the mean 18 o values of the high latitude nl brachiopod shells were more positive than those of the low latitudes in early sakmarian 0 3 early late artinskian 1 1 late kungurian 1 0 roadian 0 2 and wordian 0 7 comparable to those of tropical western pangea in early artinskian 2 1 and early kungurian 2 5 and more negative than those of tropical western pangea in late late artinskian 3 9 assuming the oxygen isotope value for permian seawater in southeast australia was 1 the calculated oxygen isotope temperatures were mostly between 12 c and 16 c reflecting southeast australia s cool high latitude temperature conditions higher apparent oxygen isotope temperatures for the upper pebbly beach formation 29 c late late artinskian berriedale limestone 21 c early artinskian and snapper point formation 22 c early kungurian may be attributed to a combination of warmer climate and lower seawater 18 o in this region

climatic significance of natric horizons in permian asselian palaeosols of north central kansas usa columnar structured horizons have been recognized in ancient coastal palaeosols of several lower permian asselian stratigraphic units of north central kansas these strongly developed columnar polygonal shaped peds are characteristic of sodium influenced natric argillic horizons and are commonly indicative of semi arid to arid environments evaporite features above and below these palaeosols support the conclusion for a dry palaeoclimate the columnar peds are typically 3 15 cm in diameter and exhibit domed tops fine clay fills the cracks between the columnar peds and is generally of a darker colour than the peds each natric horizon has a low value and chroma colour apparently the result of carbonate accumulation the natric horizons in these permian palaeosols appear to have been partially influenced by sodium rich groundwaters root traces and root moulds are found between peds in all natric horizons indicating plant succession after columnar ped formation these sodium influenced palaeosol profiles occur as part of a spectrum of palaeosol types that indicate cyclical climate change associated with glacioeustatic sea level fluctuations

actinium 227 as a deep sea tracer sources distribution and applications abstractactinium is one of the rarest naturally occurring elements on earth we measured its longest lived isotope 227ac half life 21 77 years for the first time in the water column of the southeast pacific the central arctic the antarctic circumpolar current acc and the weddell gyre besides the profile in the southeast pacific which confirms earlier findings about the role of diapycnal mixing for 227ac distribution we found three other different types of vertical profiles these profiles point to a prominent role of advection for 227ac distribution especially in the southern ocean depending on the type of profile found 227ac is proposed as a tracer for different oceanographic questions in the southern ocean up to 4 93 0 32 dpm m 3 227acex 227ac in excess of its progenitor 231pa are found close to the sea floor which are the highest concentrations ever observed in the ocean close to the sea surface in the weddell gyre wg 0 46 0 05 dpm m 3 227acex are detected we use 227acex there to determine the upwelling velocity in the eastern weddell gyre to be about 55 m y 1 in the acc upper and lower circumpolar deep water ucdw and lcdw are found to differ clearly in their 227acex activity high 227acex activities are therefore a promising tracer for recent inputs of lcdw to the sea surface which may help to understand the role of deep upwelling for iron inputs into antarctic surface waters the expected release of 227ac is compared with 228ra to make sure that the large near surface excess in the water column of the southern ocean is not due to lateral inputs by isopycnal mixing results of a model indicate that the 227ac 228ra flux ratio is about 50 times lower on shelves than in the deep sea data from the central arctic and from a transect across the acc confirm that 228ra and 227acex differ strongly in their sources the first measurements of 227ac on suspended matter less than 1 7 of total 227ac close to the sea floor indicate that the particle reactivity of 227ac is negligible in the open ocean in agreement with earlier findings nozaki 1984 despite the extremely low concentrations of 227ac new measurement techniques moore and arnold 1996 point to a comfortable and comparably simple determination of 227ac in the future finally 227acex may become a widely used deep sea specific tracer