does an asymmetric thermohaline ice sheet oscillator drive 100 000 yr glacial cycles a hypothesis is presented that late quaternary 100 000 yr glacial cycles are driven by an asymmetric thermohaline ice sheet oscillator that emerged in the global climate system 650 000 950 000 yr ago perhaps when the main source of northern hemisphere deep water production shifted south from the arctic into the nordic seas it is hypothesised that the asymmetry is due to the increasing difficulty after 950 000 years ago of resetting an interglacial mode of the critical nordic limb of the salinity conveyor once it switches off and an ensuing iceberg flux enters the areas of downwelling a possible reason for both a southward shift and the resulting asymmetry is uplift of the greenland scotland submarine ridge from activity of the iceland mantle plume in this hypothesis an individual 100 000 yr glacial cycle begins when the northernmost limb of the salinity conveyor in the nordic seas is curtailed or even switched off perhaps due to the growing strength of competing antarctic bottom water aabw generated by interglacial recession of the west antarctic ice sheet wais from the west antarctic rift system such recession produces southern marginal seas where dense shelf water can collect and overflow into the abyss when northern ice sheets nucleated by this circulation switch develop marine components that calve icebergs into the nordic seas the salinity conveyor can no longer revert to an interglacial mode from orbital forcing as it did prior to 950 000 yr ago in order to reset an interglacial circulation mode of the conveyor ice sheets must continue to grow for 100 000 years until they capture enough excess volume to produce a gravitational collapse of marine based components so massive that all grounded ice is flushed from north atlantic continental shelves the outburst of icebergs produced by this collapse cripples the glacial mode of overturning in the northern north atlantic once this collapse ends however the nordic seas become nearly free of icebergs for the first time in 100 000 years because of the depletion of adjacent marine based components as a consequence north atlantic salinity increases rapidly switching the conveyor into a vigorous interglacial mode of operation and hence terminating the glacial cycle by lowering sea level the prolonged growth of northern hemisphere ice sheets during each 100 000 yr cycle drives antarctic grounding lines seaward across continental shelves squeezing off the source of densified shelf waters that feed aabw sea level rise and increased basal melting however caused by the subsequent collapse of northern ice sheets and the reintroduction of north atlantic deep water into the southern ocean reverses the process forcing retreat of antarctic grounding lines from their advanced last glacial maximum positions this retreat opens marginal seas for renewed formation of dense shelf water by expanding marginal seas and hence the source of dense shelf water ongoing recession of the wais strengthens aabw during the course of an interglaciation eventually forcing a thermohaline circulation switch in the nordic seas and initiating yet another 100 000 yr glacial cycle the 100 000 yr duration of each cycle is set by two factors inertia is built into the system by the long time required for ice sheets to grow to the excess volume necessary for a marine collapse that resets the salinity conveyor into an interglacial mode eccentricity driven changes in the amplitude of the precession or tropical half precession signal give rise to warming events that trigger such a collapse of excess ice about each 100 000 yr

late mississippian glacio eustasy recorded in the eastern paleo tethys ocean south china abstract long lived and extensive glaciation during the carboniferous and early permian has been the focus of many studies over the past decade revealing systematic changes in sea level and climatic conditions the nature of the inception of carboniferous glaciation however remains poorly resolved with uncertainty regarding the timing and dynamics of buildup of continental ice sheets here we present detailed sedimentary facies and depositional cycles from upper mississippian shallow water platform and contemporaneous carbonate slope successions from the eastern paleo tethys ocean region south china to reveal systematic variations that provide insight into the sedimentary response to the onset of carboniferous glaciation based on detailed sedimentological logging and facies analysis four upper visean cycles and four serpukhovian cycles were identified from the carbonate platform yashui section bounded by either subaerial surfaces or zones or transgressive surfaces the cycle tops roughly correspond to intervals rich in normally graded bioclastic wacke to packstones and with distinct rises 1 in conodont 18opo4 in the carbonate slope naqing section in particular the four serpukhovian cycles correlate well to depositional cycles defined in the lower yangtze platform succession of south china and in the cyclothemic successions in the donets basin ukraine suggesting a glacio eustatic control most likely caused by repeated advance and retreat of gondwana glaciation during the onset but prior to widespread glaciation across the mid carboniferous boundary

fluvial response to paleo equatorial climate fluctuations during the late paleozoic ice age the maritimes basin of atlantic canada preserves a 12 km thick stratigraphic succession deposited within a low latitude predominantly continental setting during the late paleozoic this paper examines the utility of using such successions for paleoclimate analysis with specific reference to changes in fluvial style modern rivers in the subhumid and semiarid tropics preserve a suite of features that are distinct from those in humid and arid environments these features include an abundance of sedimentary structures formed under froude transcritical to supercritical flow conditions and the presence of in situ vegetation growing within the channel environment this fluvial style is indicative of prolonged low flow conditions punctuated by intense precipitation events in a strongly seasonal climatic setting fluvial channel bodies within the maritimes basin preserve a remarkably similar style compared with these modern systems suggesting that a subhumid strongly seasonal paleoclimate was the dominant imprint on parts of the preserved successions strongly seasonal deposits are concentrated within four discrete stratigraphic intervals e1 e4 ranging in duration from 2 to 6 m y these intervals are correlated across the entire basin and between basins characterized by markedly different tectonic regimes which suggests that a coherent regional climate signal is recorded intervals are separated by deposits characteristic of humid and arid river systems and the alternation between these different fluvial styles implies that several pronounced long term changes in precipitation and runoff regimes occurred during the carboniferous within the region furthermore these intervals broadly coincide with major periods of southern hemisphere glaciation which suggests that glaciation had a profound and controlling effect on paleotropical climate

milankovitch cycles and carboniferous climate cyclical permo carboniferous sea level fluctuations have long been linked to glacial interglacial fluctuations on gondwanaland similar to the pleistocene such fluctuations may in turn have been driven by variations in orbital insolation forcing herein we report results from climate model simulations that examine the effect of milankovitch insolation variations on the climate of the gondwanan supercontinent utilizing maximum summer insolation values typical of interglacials we simulate completely snow free conditions with summer temperatures at the south pole 20 c modifying orbital configuration to minimum summer insolation receipt results in a large area of below freezing temperatures comparison of model generated summer snow cover for the latter run with reconstructions of glacial ice extent indicates a good first order agreement these calculations support the cyclothem model and suggest that the entire glacial interglacial couplet for the carboniferous can be simulated with a minimum number of adjustable parameters

late paleozoic glacial episodes in gondwanaland reflected in transgressive regressive depositional sequences in euramerica the late paleozoic glaciation of gondwanaland comprised two short episodes in the famennian i and visean ii confined to brazil and adjacent northwest africa and a long episode that started in the namurian iiia of eastern australia and bolivia argentina expanded to cover much of gondwanaland in the stephanian asselian iiib and collapsed in the early sakmarian iiic dropstones in eastern australia indicate that small ice centers lingered to the kazanian across the belt of low latitudes north of gondwanaland short ranging fossils in widespread shallow marine and paralic deposits indicate synchronous deposition of transgressive regressive sequences in different parts of euramerica these sequences correlate with glacial events in gondwanaland at three levels a four major regressions in euramerica in the famennian 1 visean 2 namurian 3 stephanian 4 and the tastubian transgression that preceded the sterlitamakian regression 5 also recorded in gondwanaland correlate with glacial episodes i ii and iiia iiib and iiic b the time interval of cyclothemic deposition in euramerica brigantian or latest visean to sterlitamakian correlates with that of glacial episode iii and c the dominant period of the euramerican cyclothems as estimated from the middle and late pennsylvanian deposits of the mid continent of north america and of the thickest known gondwanaland glacigenic sediment the earliest permian lyons group of western australia is 0 4 ma equivalent in turn to the long orbital eccentricity period of the quaternary ice age and the dominant period of fluctuation of the late miocene antarctic ice cap the three levels of correlations confirm wanless and shepard9s 1936 hypothesis that the late paleozoic cyclothems are controlled largely by sea level fluctuations related to the gondwanaland glaciation

latest chesterian carboniferous initiation of gondwanan glaciation recorded in facies stacking patterns and brachiopod paleocommunities of the antler foreland basin idaho stacking patterns of facies and brachiopod communities of latest chesterian middle carboniferous units of east central idaho record an increase in the frequency and amplitude of sea level changes water depth as inferred from lithology and paleoecology provides the basis for quantifying sea level fluctuations the surrett canyon formation is dominated by thick sequences of subtidal carbonates the arco hills formation consists of thin parasequences of mixed carbonate and siliciclastic lithologies representing sea level changes up to 50 m in amplitude bounded by flooding surfaces overlying the arco hills the bluebird mountain formation very fine grained quartz arenite dolomite and unfossiliferous limestone records a major lowstand just below the mid carboniferous boundary increased amplitude and frequency of sea level changes in the antler foreland basin initiated at the c naviculus a unicornis conodont zone boundary which occurs at the base of the arco hills formation these are interpreted as 4th order glacio eustatic sea level changes related to the onset of gondwana glaciation comparable to those seen in the illinois basin alaska and elsewhere

the origins of shallow water carbonate lithofacies thickness distributions one dimensional forward modelling of relative sea level and production rate control the observation that shallow marine carbonate strata often have exponential lithofacies thickness distributions is one of the most fundamental results in carbonate stratigraphy in recent years because it is an observation that can be tested for its repeatability in various outcrop and subsurface examples and also because it raises the question of what sedimentary processes and climatic and oceanographic settings might lead to formation of a particular lithofacies thickness distribution this observation in turn links to the significant issue of how carbonate strata record climatic and oceanographic change through geological time this study applies a simple one dimensional numerical stratigraphic forward model of carbonate platform strata dougal to study how relative sea level oscillations could control lithofacies distribution dougal records platform top carbonate accumulation influenced by water depth dependent sediment production in euphotic oligophotic and aphotic production profiles with a lag depth controlling onset of production results from five single model runs highlight the issue of non stationary behaviour where statistical properties of the strata change with elevation up the section and show that exponential lithofacies thickness distributions can be generated from an entirely deterministic model results of multiple model runs 27 200 in total spanning a range of production and accommodation creation rates demonstrate that the three main controls on carbonate lithofacies distribution in this one dimensional model are i complex variations in the rate of creation of accommodation here due to high frequency glacio eustatic oscillations ii rate of sediment production dominated in these model runs by euphotic production rates and iii operation of autocyclic oscillations in deposition driven by a lag depth effect and formed during certain high frequency rising limbs on the glacio eustatic curve in these multiple model runs only ca 13 of the total runs created exponential distributions compared with 28 in the documented outcrop examples suggesting that other processes not included in this model play an important role more work is required to determine what these processes might be obvious candidates would be the various sedimentary processes that occur in three dimensions on platform tops such as sediment transport and variations in rate and type of sediment production related to biological variability and other process that occur in other different depositional settings for example sediment transport on slopes

oolitic sandbody depositional models and geometries mississippian of southwest britain implications for petroleum exploration in carbonate ramp settings abstract a 1000 m thick early mississippian carbonate supersequence the carboniferous limestone of southwest britain consists of three third order depositional sequences these comprise parasequences in various configurations and the whole forms a carbonate ramp stack within this framework five major oolitic carbonate sandbodies developed a castell coch limestone b stowe oolite c brofiscin oolite d gully oolite and e high tor limestone the depositional regime was storm and wave dominated throughout and the major sandbodies represent a range of progradational carbonate beaches barriers and detached subtidal shoals analysis of the three dimensional shapes and distribution of these five examples shows that they evolved to produce three major carbonate sandbody geometries a strings b sheets and c wedges these geometries are characterised using the five field examples and offered as a template which may assist in the exploration and reservoir modelling of petroleum rich high energy ramp systems progradation for up to 40 km of barrier islands stowe oolite and beach ridge plains gully oolite formation generated strings and thick sheets individually up to 10 20 m thick thin shoreface retreat carbonate packstone grainstone sheets up to 5 m thick high tor limestone developed during transgressions as veneers across flooding surfaces these are comparable with sheet sands developed in siliciclastic shelf depositional systems progradation for up to 30 km and vertical aggradation of shoreline detached oolite shoals castell coch limestone brofiscin oolite generated basinwards expanding or thinning wedges up to 30 m thick tectonically controlled stacking of strandplain sheets produced a composite carbonate sandbody up to 80 m thick gully oolite the intrinsic sedimentary and extrinsic eustacy tectonism climate factors which controlled these sandbody geometries are addressed establishing the positions of the sandbodies accurately within depositional sequences allows them to be located within inferred seismic sequence geometries and provides one possible solution to the difficult problem of predicting carbonate facies distribution in subtle stratigraphic plays in this ramp system the most homogeneous sandbodies up to 30 m grainstones with greatest reservoir facies potential are represented by shoal belt wedges potential grainstone reservoir facies in the prograding shorelines are limited to the upper parts of individual shoreface sequences max 10 m grainstones for shoreline carbonate sandbodies the greatest reservoir and stratigraphic trapping potential exists in the earliest ramp parasequences where enveloping offshore sediments are siliciclastic mudstones in later stages potential seals are likely to be less reliable low porosity outer ramp carbonates

the tindouf basin a marine refuge during the serpukhovian carboniferous mass extinction in the northwestern gondwana platform abstract several macrofaunas and microfossils of the carboniferous saharan basins have longer stratigraphic ranges than those of other basins in the western palaeotethys realm particularly in the tindouf basin morocco algeria foraminifers are particularly abundant and diverse in the serpukhovian and basal bashkirian compared to coeval basins and some taxa have longer ranges than in the neighbouring reggan and bechar basins although this effect is more marked compared to the western palaeotethyan assemblages in europe several rugose coral species are recorded from the early bashkirian that previously were considered to have disappeared in the serpukhovian the tindouf basin as one of the most western saharan basins in north africa shows the greatest stratigraphic ranges of taxa which diminish eastwards evidence for a mass extinction event during the serpukhovian in the tindouf basin has not been clearly recognized although a possible influence of glaciation is observed in the faunal diversity eustatic sea level changes were experienced in tindouf with the cyclic pattern of sedimentation but warm water ocean currents from the palaeoequator were able to maintain tropical conditions on the platform tectonics in the area led to emerging land masses and barriers and created a partly isolated basin in this sector of the western part of the sahara platform in northern gondwana the combination of those factors controlled the environmental conditions in the area allowing the persistence of the fauna for longer stratigraphic ranges than its equivalent counterparts in the western palaeotethys

a sedimentological and cyclostratigraphic evaluation of the completeness of the mississippian pennsylvanian mid carboniferous global stratotype section and point arrow canyon nevada usa the mississippian pennsylvanian global stratotype section and point gssp are hosted within a shallow water dominantly carbonate succession in the lower part of the bird spring formation at arrow canyon nevada usa the boundary is marked by the first appearance datum fad of the conodont declinognathodus noduliferus sensu lato it is shown that the boundary interval is punctuated by numerous subaerial hiatuses represented by palaeokarstic surfaces and palaeosols which divide strata at this location into fourth order glacio eustatic cycles a well developed palaeosol horizon occurs d noduliferus it also coincides with a very marked facies change and a second order shift in cycle stacking patterns these characteristics violate international commission on stratigraphy guidelines which state that gssps should be chosen in sections showing continuous sedimentation and lacking vertical facies changes at or near the boundary because the mid carboniferous is an icehouse interval cyclostratigraphy is a powerful tool for high resolution correlation a comparison of the cyclostratigraphy of mid carboniferous strata at arrow canyon and in northern england indicates that a large number of glacio eustatic sea level oscillations are not recorded at arrow canyon and that this section contains over 25 missed beats of milankovitch band duration equating to a hiatus of 1 ma

the early carboniferous courceyan arundian monsoonal climate of the british isles evidence from growth rings in fossil woods the british isles lay at a palaeolatitude of 4 s during the early carboniferous courceyan arundian period this paper examines fossil gymnosperm wood from ten localities in western ireland and southern scotland in order to analyse palaeoclimate fifty two percent of the 77 fossil wood specimens studied exhibit growth rings that possess subtle discontinuous ring boundaries and ring increments of narrow but variable width these growth rings are qualitatively and quantitatively analysed and are shown to bear a close similarity to growth rings in modern araucarian conifer woods these araucarian growth rings are formed in response to tropical rainfall seasonality linked to monsoonal circulation the findings of this study therefore support earlier palaeoclimatic interpretations based on sedimentological evidence which suggest that the british isles experienced a monsoonal climate during the early carboniferous courceyan arundian period

the onset of the permo carboniferous glaciation reconciling global stratigraphic evidence with biogenic apatite δ18o records in the late visean the 18 o values of phosphatic microfossils recovered from nw ireland are used to determine the timing and magnitude of cooling associated with the onset of the carboniferous glaciation microfossil fish 18 o apatite demonstrates a 2 4 v smow shift which once corrected for 18 o seawater changes owing to evolving ice volumes equates to an approximate 4 5 c reduction in equatorial sea surface temperature between the earliest asbian and the mid brigantian late visean both conodont and microfossil fish 18 o apatite indicate stabilization of an icehouse climate during the brigantian and into the serpukhovian substantial late visean cooling identified herein is in good agreement with global glacioeustatic records supplementary material further information on the palaeogeography lithostratigraphy and palaeoenvironments of the sections examined as well as the sample composition and analytical methods of oxygen isotope analyses is available at http www geolsoc org uk sup18511

geomagnetic field for 0 3 ka 2 a new series of time varying global models 1 steadily increasing numbers of archeomagnetic and paleomagnetic data for the holocene have allowed development of temporally continuous global spherical harmonic models of the geomagnetic field extending present and historical global descriptions of magnetic field evolution the current work uses various subsets of improved data compilations details of which are given in a companion paper by donadini et al 2009 and minor modifications of standard modeling strategies using temporally and spatially regularized inversion of the data and cubic spline parameterizations for temporal variations to produce five models with enhanced spatial and temporal resolution for 0 3 ka spurious end effects present in earlier models are eliminated by enforcing large scale agreement with the gufm1 historical model for 1650 1990 a d and by extending the model range to accommodate data older than 3 ka age errors are not considered as a contribution to data uncertainties but are included along with data uncertainties in an investigation of statistical uncertainty estimates for the models using parametric bootstrap resampling techniques we find common features but also significant differences among the various models indicating intrinsic uncertainties in global models based on the currently available holocene data model cals3k 3 based on all available archeomagnetic and sediment data without a priori quality selection currently constitutes the best global representation of the past field the new models have slightly higher dipole moments than our previous models virtual axial dipole moments vadms calculated directly from the data are in good agreement with all corresponding model predictions of vadms these are always higher than the spherical harmonic dipole moment indicating the limitations of using vadms as a measure of geomagnetic dipole moments

microfacies and carbon isotope records of mississippian carbonates from the isolated bama platform of youjiang basin south china possible responses to climate driven upwelling changes in mississippian global paleogeography derived from the reconfiguration of the continents have been suggested to result in a change in oceanic circulation carbon cycling as well as in global cooling here integrated 13ccarb chemostratigraphy and foraminiferal biostratigraphy across the mississippian late tournaisian visean early serpukhovian mfz6 mfz16 foraminiferal biozones of the gongchuan section located in the isolated bama platform in the youjiang basin south china are presented the 13ccarb trend shows an abrupt decline during late visean asbian early brigantian mfz13 14 this decline is also observed in subequatorial western euramerica whereas coeval sections in subequatorial eastern euramerica show consistently elevated 13c values across the entire visean the 13c decline in western euramerica and the south china block eastern paleo tethys coincides with a global regression with a suggested glacioeustatic origin the onset of high frequency climate and sea level oscillations and the closure of the rheic seaway between euramerica and gondwana we propose a model explaining the divergence of 13c records resulting from the closure of the rheic seaway and development of upwelling zones in the western margin of euramerica and the eastern paleo tethys realm quantitative microfacies analysis across the mississippian succession in the gongchuan section shows facies independent disappearance of corals and increased proportion of cortoids and filter feeding organisms at the onset of the asbian 13c decline which may support an increase in nutrient level that can be expected as a result of upwelling

the anatomy of a mississippian visean carbonate platform interior uk depositional cycles glacioeustasy and facies mosaics abstract late visean platform interior carbonate strata of northern england and wales have traditionally been interpreted to comprise shallowing up cyclothems the upper boundaries of which are marked by unconformities that record subaerial exposure events these strata were deposited during what is understood to be a greenhouse to icehouse transition and the cyclothems are assumed to reflect glacioeustatic sea level oscillations associated with this climatic change importantly these interpretations reflect a qualitative model which assumes that facies respond in a simple way to water depth variations and so migrate and stack in a predictable pattern as eustatic sea level fluctuates exposure surfaces and most facies are however laterally discontinuous across the platform tops quantitative statistical analysis and simple 1d stratigraphic forward modelling suggest that the observed vertical facies stacking patterns on the derbyshire and north wales platforms are not cyclical the most ordered arrangement of facies that could be interpreted as ideal cycles in each section are variable within and across the platforms this observational and analytical evidence suggests that instead of a simple dominant external glacioeustatic forcing on sedimentation a model commonly proposed for the late visean carbonate strata of northern england and wales strata were deposited as a facies mosaic under variable hydrodynamic conditions influenced by autogenic processes as well as local environmental fluctuations in salinity and temperature and perhaps in conjunction with glacioeustasy and syn rift tectonic processes which occurred from metre scale to kilometre scale as suggested by the ideal cycles

onset of late palaeozoic glacio eustasy and the evolving climates of low latitude areas a synthesis of current understanding studies of depth sensitive carbonate successions in the uk indicate that regular orbitally forced glacio eustatic sea level oscillations which characterized the late palaeozoic started abruptly around 330 ma early asbian the gondwanan ice sheet was highly sensitive to orbitally forced variations in solar insolation and the resultant sea level oscillations had an approximate 100 ka periodicity studies of fossil soils and palaeokarst from low latitude settings suggest that pre asbian climates were relatively stable with infrequent changes however climatic changes became increasingly frequent in the asbian and brigantian with regular fluctuations of a sub 100 ka periodicity occurring during glacial lowstand intervals

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

the pennsylvanian permian transition in the low latitude carbonate record and the onset of major gondwanan glaciation abstract recent studies suggest a marked expansion of glacial ice across much of gondwana beginning in the earliest permian because expansion of glacial ice results in a lowering of sea level the imprint of ice expansion should be evident worldwide as significant exposure event hiatuses or other evidence for sea level drop at or near the pennsylvanian permian boundary this literature review investigates the signature of an early permian expansion of gondwanan ice through examination of stratigraphic records from eight carbonate dominated palaeotropical regions across pangaea tropical carbonate environments are used because most form in tectonically quiescent regions and are sensitive indicators of eustatic change correlation between stratigraphic sections is achieved using the most current biostratigraphic and absolute time constraints available all studied sections show a sequence boundary or basinward shift in facies at or near the pennsylvanian permian boundary supporting the hypothesis of a significant expansion of glacial ice and global eustatic lowstand beginning in the early permian by contrast a series of mid sakmarian kungurian transgression events in the palaeotropics are interpreted to reflect the asynchronous deglaciation of gondwana the stratigraphic framework developed herein will allow for better correlations among stratigraphic records from gondwana and northern pangaea which will ultimately improve the understanding of how carbonate systems respond to global icehouse conditions such as during the late palaeozoic

multi carbonate component reconstruction of mid carboniferous chesterian seawater δ13c abstract this study presents the first stratigraphically continuous 13ccarb record for the chesterian interval developed from antler foreland basin platform successions the bulk carbonate derived 13c curve was constructed using 700 biostratigraphically constrained samples providing a 105 yr resolution a multi component study of 13c and 18o variability in petrographically and geochemically screened abiotic and biogenic calcite components delineates the degree of preservation and 13c heterogeneity in these ancient epicontinental carbonates furthermore it constrains the influence of kinetic and vital effects and local to regional scale c cycling on their 13ccarb values the 13c and 18o values of micrites and bulk carbonates overlap regardless of lithofacies and show minimal intrasample variability overall biogenic calcite 13c and 18o values are higher than the average isotope compositions of bulk carbonates and micrites although 13c values in contemporaneous samples are only minimally 0 3 2 std err of 0 3 different relative to much larger differences in 18o values although brachiopod 13c and 18o values are higher than average bulk carbonate and micrite values their 13c values exhibit considerable isotopic variability by taxa and ultrastructure notably the 13c values of brachiopod secondary shell layers overlap with bulk carbonate micrite and marine cement 13c values conversely 13c values of brachiopod tertiary prismatic layers including composita are on average 2 to 5 higher than the 13c values of contemporaneous bulk carbonates micrites and brachiopod secondary shell layers an observed average 2 decrease in the 13c values of secondary cross bladed laminar layers in productids relative to contemporaneous bulk carbonate micrite and marine cement values suggests a previously unrecognized kinetic and or vital effect on carboniferous productid 13c values given that they have the highest 18o values of all analyzed components the observed higher 13c values in these tertiary prismatic layers are comparable to greater than the 13c enrichment 1 previously documented in pennsylvanian composita the overlap in 13c values of bulk carbonates with diagenetically screened microdrilled matrix marine cements and brachiopod secondary shell layers indicates that the chesterian bulk carbonate derived 13c values may reliably record to within 1 the evolution of ambient seawater 13c in the outer carbonate ramp of the antler basin comparison of the chesterian 13c record to the bulk carbonate c isotope curve derived from the arrow canyon nv carbonate succession further suggests that these bulk carbonate derived 13c records are reliable proxies of the composition and trends in seawater 13c regionally along the equatorial eastern panthalassan margin the newly resolved chesterian stratigraphy documents multiple 13c excursions including previously unrecognized significant c isotope shifts a shift to higher frequency and amplitude shorter term 13c fluctuations in the upper third of the chesterian stage occurred simultaneously with a change in stratigraphic cyclicity from dominantly 3rd order to 4th order carbonate cycles suggesting a mechanistic linkage between ambient seawater 13c and sea level fluctuations in the antler basin this change in the character of the shorter term 13c fluctuations coupled with a subsequent significant 4 positive c isotope excursion across the mid carboniferous boundary previously recognized in all carboniferous curves is interpreted to record the onset of late paleozoic glaciation and glacio eustasy

ferrolysis in arundian alluvial palaeosols evidence of a shift in the early carboniferous monsoonal system an unusual clay mineral assemblage from early carboniferous arundian palaeosols in south wales contains a three component kaolinite chlorite like material smectite mixed layer clay this is interpreted as the product of ferrolysis a complex process involving dissolution of clays a d the subsequent production of interlayered varieties from the repetitive reduction and reoxidation of iron compounds in seasonally waterlogged surface water grey soils support for this interpretation comes from the distribution of iron species iron concretions and vertic features in the palaeosol profile which indicate formation under strongly seasonal dry hydromorphic conditions the appearance of the ferrolytic pa iaeosol indicates a shi from a dry to a wet type monsoonal regime in late arundian times

the time dependence of intense archeomagnetic flux patches 1 the long term temporal behavior of intense geomagnetic flux patches at the core mantle boundary and the relation with lower mantle lateral heterogeneity are under debate we apply an algorithm to detect centers of intense flux patches and track their time evolution in a recent archeomagnetic field model in order to study the kinematics of such intense magnetic flux patches on millennial timescale we find that most intense flux patches appear near the edge of the tangent cylinder quasi stationary periods with small oscillations of patches occur more than drifts detailed comparison of the archeomagnetic patches behavior with that seen in numerical dynamos with tomographic heat flux boundary conditions suggests that core mantle thermal coupling could be the cause of a statistical preference for some longitudes on the long term which does not exclude significant time spent away from the preferred longitudes this could explain the roughly coincident locations of high latitude patches in the historical geomagnetic field with that of the time average paleomagnetic field together with the much weaker patches intensity in the latter alternating eastward and westward drifts are also observed the drifts are more westward than eastward especially in the southern hemisphere indicating that the time average zonal core flow may also be driven by core mantle thermal coupling an average patch lifetime of 300 years is found which we hypothesize may indicate the vortex lifetime in the outer core

geomagnetic field evolution during the laschamp excursion abstract since the last geomagnetic reversal 780 000 years ago the earth s magnetic field repeatedly dropped dramatically in intensity this has often been associated with large variations in local field direction but without a persistent global polarity flip the structure and dynamics of geomagnetic excursions and especially the difference between excursions and polarity reversals have remained elusive so far for the best documented excursion the laschamp event at 41 000 years bp we have reconstructed the evolution of the global field morphology by using a bayesian inversion of several high resolution palaeomagnetic records we have obtained an excursion scenario in which inverse magnetic flux patches at the core mantle boundary emerge near the equator and then move poleward contrary to the situation during the last reversal leonhardt r fabian k 2007 paleomagnetic reconstruction of the global geomagnetic field evolution during the matuyama brunhes transition iterative bayesian inversion and independent verification earth planet sci lett 253 172 195 these flux patches do not cross the hydrodynamic boundary of the inner core tangent cylinder while the last geomagnetic reversal began with a substantial increase in the strength of the non dipolar field components prior to the laschamp excursion both dipolar and non dipolar field decay at the same rate this result suggests that the nature of an upcoming geomagnetic field instability can be predicted several hundred years in advance even though during the laschamp excursion the dipolar field at the earth s surface was dominant the reconstructed dynamic non dipolar components lead to considerable deviations among predicted records at different locations the inverse model also explains why at some locations no directional change during the laschamp excursion is observed

polar glaciers and life at the equator the history of dinantian and namurian carboinferous climate biotic migration patterns provide a history of relative climate change that can be used to study dinantian and namurian carboniferous climates high latitude warming between the middle and late visean may have been caused by the collision of laurussia and gondwana high latitude cooling and equatorial warming between the namurian a and b may have been caused by the onset of glaciation in the southern hemisphere patterns of faunal migration and extinction and floral radiation were similar during namurian and miocene glacial onsets and provide criteria for assessing other extinction events tied to changes in paleoclimate

rapid onset of late paleozoic glaciation on gondwana evidence from upper mississippian strata of the midcontinent united states direct evidence of the late paleozoic glaciation of gondwana from glacial deposits suggests that geographically extensive continental glaciation began some time in the namurian late mississippian however the timing and characteristics of the onset of glaciation are poorly understood because of a lack of reliable paleontological control and reworking of initial glacial deposits by subsequent glacial advances indirect evidence of glaciation preserved in unconformity bounded low latitude ramp sequences in the illinois basin united states suggests that geographically extensive continental glaciation of gondwana actually began in the late visean an abrupt change from carbonate dominated sequences bounded by disconformities with little evidence of erosion to mixed carbonate siliciclastic sequences bounded by unconformities with deep incised valleys was likely produced by a three fold increase in the magnitude of eustatic sea level fluctuations the increase in the magnitude of sea level fluctuations was likely driven by an equally abrupt increase in ice volume and marks the onset of the geographically extensive late paleozoic glaciation of gondwana a possible explanation for the rapid onset of glaciation is the closing of the equatorial seaway between laurussia and gondwana closing of this seaway would have led to an abrupt change in oceanic and atmospheric circulation patterns that could have initiated major continental glaciation in the southern hemisphere

equatorial aridity and climatic oscillations during the early carboniferous southern britain evidence from palaeosols palaeokarsts and styles of meteoric diagenesis shows that the early carboniferous climate of southern britain was dominantly seasonally semi arid this semi aridity occurred while the region was in an equatorial palaeolatitudinal position the cause of the seasonal aridity was possibly the deflection of easterly winds into a major low pressure zone set up over gondwana during the southern hemisphere summer

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

response of carboniferous permian mid oceanic seamount capping buildup to global cooling and sea level change akiyoshi japan abstract we discuss the response of a carboniferous permian mid oceanic atoll type carbonate buildup to global cooling and sea level fluctuation during gondwana glaciation our examination focused upon the stratigraphic distribution of emergence indicative diagenetic features as a proxy for sea level falls and we correlated their timing with hiatuses indicated by fusuline biostratigraphic discontinuities and the demise of warm adapted metazoan reef builders we examined the pennsylvanian moscovian to lower permian asselian shallow marine limestone succession ca 500 m thick of the akiyoshi limestone group southwest japan reconstructed as a mid oceanic seamount capping buildup in the panthalassan ocean the examined succession is dominated by atoll lagoon facies with subordinate coral chaetetes patch reefs and calci microbial mounds we have recognized several stratigraphic intervals less than 60 m thick in the examined succession in which emergence indicative diagenetic facies are concentrated these facies include the microcodium structure pendant cements recrystallization and algal casts each of the intervals occurs immediately below a fusuline zone boundary and represents a sea level fall event which lasted presumably 1 ma or less possibly reflecting the sea level fluctuation of third order cycles the emergence event in late kasimovian is the most prominent in the series of moscovian through asselian emergence events and resulted in a dissolution unconformity indicated by a fusuline biostratigraphic discontinuity we infer that many intercalations of less freshwater altered limestone in these stratigraphic intervals resulted from short lived emergence resubmergence episodes possibly due to the high frequency glacio eustyaic sea level fluctuation we also showed that the demise of warm adapted metazoan reef builders of corals and chaetetes happened nearly synchronously with the culmination of gondwana glaciation we hypothesize that the demise of these warm adapted reef builders is a biotic response of the akiyoshi buildup to the severe and prolonged global cooling during the pennsylvanian to early permian icehouse period the akiyoshi metazoan reef builders were replaced by calci microbes phylloid algae and calci sponges that exhibit an increasing significance during the lower to middle permian our results reveal the distinct sedimentary and biotic responses of a panthalassan atoll to global cooling and sea level fluctuation during gondwana glaciation in the southern hemisphere we conclude that carboniferous permian mid oceanic atoll stratigraphy has significant archival potential for recognizing the global palaeoclimatic change

lithostratigraphy and biostratigraphy of the lower carboniferous mississippian carbonates of the southern askrigg block north yorkshire uk a rationalized lithostratigraphy for the great scar limestone group of the southeast askrigg block is established the basal chapel house limestone formation assessed from boreholes comprises shallow marine to supratidal carbonates that thin rapidly northwards across the craven fault system onlapping a palaeotopographical high of lower palaeozoic strata the formation is of late arundian age in the silverdale borehole its northernmost development the overlying kilnsey formation represents a southward thickening and upward shoaling carbonate development on a south facing carbonate ramp foraminiferal algal assemblages suggest a late holkerian and early asbian age respectively for the uppermost parts of the lower scaleber force limestone and upper scaleber quarry limestone members significantly younger than previously interpreted the succeeding malham formation comprises the lower cove limestone and upper gordale limestone members foraminiferal algal assemblages indicate a late asbian age for the formation contrasting with the holkerian age previously attributed to the cove limestone the members reflect a change from a partially shallow water lagoon cove limestone to more open marine shelf gordale limestone coincident with the onset of marked sea level fluctuations and formation of palaeokarstic surfaces with palaeosoils in the latter facies variations along the southern flank of the askrigg block including an absence of fenestral lime mudstone in the upper part of the cove limestone and presence of dark grey cherty grainstone packstone in the upper part the gordale limestone are related to enhanced subsidence during late asbian movement on the craven fault system this accounts for the marked thickening of both members towards the greenhow inlier

estimating carboniferous sea level fluctuations from gondwanan ice extent the magnitude of carboniferous sea level fluctuations is not well known but the estimates are important for constraining cyclothem models in this paper we apply area volume relations developed for quaternary ice sheets to estimate the glacio eustatic component of sea level fluctuations in the carboniferous utilizing the best estimate of gondwanan ice area at the time of its greatest extent we arrive at a figure of 60 15 m for the isostasy corrected glacio eustatic component this value is nearer the lower limit of sea level estimates for cyclothem fluctuations from other sources

onset of the late paleozoic glacioeustatic signal a stratigraphic record from the paleotropical oil shale bearing big snowy trough of central montana u s a

palaeohydrological characteristics and palaeogeographic reconstructions of incised valley fill systems insights from the namurian successions of the united kingdom and ireland namurian carboniferous eustatic fluctuations drove the incision and backfill of shelf crossing valley systems located in humid subequatorial regions which are now preserved in successions of the united kingdom and ireland the infills of these valleys archive the record of palaeoriver systems whose environmental hydrological and palaeogeographic characteristics remain unclear a synthesis of sedimentological data from fluvial strata of 18 namurian incised valley fills in the united kingdom and ireland is undertaken to elucidate the nature of their formative river systems and to refine regional palaeogeographic reconstructions quantitative analyses are performed of facies proportions of geometries of incised valley fills and related architectural elements and of the thickness of dune scale sets of cross strata reconstruction of the size of the drainage areas that fed these valleys is attempted based on two integrative approaches flow depth estimations from dune scale cross set thickness statistics and scaling relationships of incised valley fill dimensions derived from late quaternary examples the facies organization of these incised valley fills suggests that their formative palaeorivers were perennial and experienced generally low discharge variability consistent with their climatic context however observations of characteristically low variability in cross set thickness might reflect rapid flood recession perhaps in relation to sub catchments experiencing seasonal rainfall variations in facies characteristics including inferences of flow regime and cross set thickness distributions might reflect the control of catchment size on river hydrology the degree to which is considered in light of data from modern rivers palaeohydrological reconstructions indicate that depth estimations from cross set thickness contrast with observations of barform and channel fill thickness and projected thalweg depths exceed the depth of some valley fills limitations in data and interpretations and high bedform preservation are recognized as possible causes with consideration of uncertainties in the inference of catchment size the palaeogeography of the valley systems has been tentatively reconstructed by integrating existing provenance and sedimentological data the approaches illustrated in this work can be replicated to the study of palaeohydrological characteristics and palaeogeographic reconstructions of incised valley fills globally and through geological time

development of the late paleozoic glaciations of the south american gondwana in western argentina abstract the late paleozoic ice age in the south american segment of gondwana consisted of several glaciations which can be grouped into two main glacial periods the oldest of them occurred in late early to early late carboniferous time and the younger in early permian time paleontological evidence in the western argentine precordillera supports a late visean age for the beginning and a probable early westphalian age for the end of the carboniferous glacial period in this span of time subsidence and deposition of glacial debris took place in the western mobile belt and in patagonia but no sediments of that age were deposited in the eastern portion of the south american gondwana where subsidence started later a carboniferous glacial sequence is remarkably well preserved in the san eduardo group on the western flank of the precordillera where at least three distinct glaciations are recognized this sequence can be taken as a reference section for the carboniferous glacial deposits shorter than the former and probably restricted to the asselian epoch the permian glacial period is better known the evidence for it is well developed in eastern south american gondwana although a relic is also present in the precordillera the recognition of two glacial periods within the late paleozoic ice age is supported by the existence of a long lasting interglacial which seemingly began in the late westphalian and lasted until the end of the carboniferous period this major interglacial period is inferred from the total absence of glacial features in the upper carboniferous sequences in spite of the existence of a mountainous belt parallel to the pacific during the carboniferous period the presence of marine beds and glacial drift well to the east of these ranges suggests that it was not altitude that was the main factor in determining the formation of glaciers but latitude plus a global change in temperature it is argued that the ice sheets extended greatly during the carboniferous glaciations and reached neighboring areas of the paganzo basin in central argentina

high precision u pb zircon ca id tims dates from western european late visean bentonites three new u pb zircon chemical abrasion isotope dilution thermal ionization mass spectrometry dates obtained from late visean belgian bentonites are reported and are used to estimate the periodicity of early warnantian shallowing upwards carbonate parasequences that are interbedded with the dated bentonites early warnantian parasequences exhibit mean cycle periodicity values that are consistent with the c 100 ka milankovitch cycle which is the dominant milankovitch frequency recognized from recent pleistocene glacial records and thus strengthen the arguments for 1 these sedimentary cycles being of glacio eustatic origin and 2 the initiation of the main phase of late palaeozoic glaciation before the start of or during earliest warnantian times the new dates also provide additional high precision age constraints for the improved calibration of the mississippian time scale using the new dates the stratigraphical age of the clyde plateau volcanic formation midland valley of scotland is revised from holkerian to early asbian supplementary material u pb zircon ca id tims data tables and the method of the mean cycle periodicity calculations are available at www geolsoc org uk sup18747

permo carboniferous climate early pennsylvanian to late permian climate development of central europe in a regional and global context a well justified stratigraphical correlation of continental successions and new palaeogeographic reconstruction of pangaea reveal new insights into the northern pangaean climate development influenced by palaeogeography palaeotopography glacio eustatic sealevel changes and ocean currents the overall permo carboniferous aridization trend was interrupted by five wet phases these are linked to the gondwana icecap the aridization and weakening of wet phases over time were not only caused by the drift of northern pangaea to the arid climatic belt but also by the successive closure of the rheic ocean which caused the expansion of arid semi arid environments in the lower middle permian the end of the gondwana glaciation rearranged ocean circulation leading to a cold coast parallel ocean current west of northern pangaea blocking moisture coming with westerly winds the maximum of aridity was reached during the roadian wordian the trans pangaean mountain belt was non existent its single diachronous parts never exceeded an average elevation of 2000 m the maximum elevation shifted during time from east to west the hercynian orogen never acted as an orographic east west barrier and the inter tropical convergence zone was widely displaced causing four seasons dry summer winter wet spring autumn at the equator and a strong monsoon system the climate history of the european realm during the late carboniferous pennsylvanian and permian is stored in many solitary basins fig 1 within the hercynian orogen and the foreland basin the story of westphalian climate is well known because of the numerous investigations of the coal bearing variscan foredeep the younger westphalian is characterized by a slight aridization abbink van kronijnenburgvan cittert 2003 oplustil 2004 which was accompanied by an increase of seasonality nevertheless the environment was strongly influenced by the ocean and epi continental seas with multiple transgression events the last extensive marine ingression was the aegir mansfield band westphalian b c the post westphalian climate development is more differentiated and

nongeocentric axial dipole field behavior during the mono lake excursion a new record of the mono lake excursion mle is reported from the summer lake basin of oregon usa sediment magnetic properties indicate magnetite as the magnetization carrier and imply suitability of the sediments as accurate recorders of the magnetic field including relative paleointensity rpi variations the magnitudes and phases of the declination inclination and rpi components of the new record correlate well with other coeval but lower resolution records from western north america including records from the wilson creek formation exposed around mono lake the virtual geomagnetic pole vgp path of the new record is similar to that from another high resolution record of the mle from ocean drilling program odp site 919 in the irminger basin between iceland and greenland but different from the vgp path for the laschamp excursion le including that found lower in the odp 919 core thus the prominent excursion recorded at mono lake california is not the le but rather one that is several thousands of years younger the mle vgp path contains clusters the locations of which coincide with nonaxial dipole features found in the holocene geomagnetic field the clusters are occupied in the same time progression by vgps from summer lake and the irminger basin but the phase of occupation is offset a behavior that suggests time transgressive decay and return of the principal field components at the beginning and end of the mle respectively leaving the nonaxial dipole features associated with the clusters dominant during the excursion

transgressions and regressions a model for the influence of tectonic subsidence deposition and eustasy with application to quaternary and carboniferous examples the position of a coastline in time and space is determined by 1 the vertical displacement and or tilting of the depositional surface 2 the rate of sediment accumulation or erosion across that surface and 3 variation of sea level all three rates of change may vary through time we present computer simulations of coastline movements that illustrate the interaction of the above variables with 1 and 2 held at various defined levels whilst 3 is varied according to the late quaternary glacio eustatic sea level curve the corinth canal section in central greece exposes uplifted late quaternary coastal transgressive cycles each of which may be related to a radiometrically dated c 100 ka duration cycle of sea level change observed stratigraphic sequence geometries are predicted by forward modelling based on the known glacio eustatic history over the last 430 ka milankovitch orbital parameters are calculated for the carboniferous period the obliquity and precession parameters are found to have been significantly shorter than at present a simulation is presented of the effects of sea level changes across low gradient fluvio deltaic environments such as existed in northern england and other parts of the laurentian continental margin during upper carboniferous time

accommodation and sedimentary architecture of isolated icehouse carbonate platforms insights from forward modeling with carb3d abstract a fundamental control on the evolution of carbonate platforms is accommodation the space available for sediment deposition here we adopt a sensitivity analysis approach using the process based forward model carb3d to quantitatively investigate the sedimentary response of isolated carbonate platforms to individual accommodation drivers of eustasy subsidence and surface dissolution sediment production the mechanism invoked to fill accommodation is also investigated fourth order milankovich driven sea level cycles dominate icehouse carbonate sedimentology with 400 ky cycles modulating the effect of 100 ky cycles of comparable magnitude when both cycles are present both overwhelm higher frequency lower amplitude fifth order cycles which are rarely preserved on the platform top subsidence is a fundamental control on sedimentary stacking patterns sequence boundary frequency sbf and platform geometry with rapid subsidence increasing the preservation of platform top sequences most icehouse platforms are subject to extended periods of platform top exposure missed beats when the platform top remains emergent at a sea level maximum are common and create non milankovich sbfs furthermore during platform emergence surface lowering via surface dissolution also creates accommodation for the subsequent platform flooding event with surface dissolution rates in humid climates comparable to moderate rates of subsidence however accommodation generation by surface dissolution is self limiting in as much as accommodation generated by dissolution is rapidly refilled on flooding sediment production is a key control on unfilled accommodation which our simulations suggest is considerable on icehouse platforms increased shallow water 3 m depth sediment production enhances intra platform bathymetric relief between the margin and interior this is driven in large part by a higher sedimentation rate at the margin than in the interior platforms can be flooded to depths up to 45 m during marine transgressions and accommodation often remains unfilled there are two distinct phases of platform top sedimentation during the transgression and early highstand platform margins accumulate at a greater rate than interior sediments generating differential intra platform bathymetry subsequently accommodation in the interior fills by forced regression and progradation from the margins into the platform interior numerical forward models can augment our understanding of icehouse carbonate platform evolution by identifying the nature of the sedimentary response to individual controls they can thus contribute to improving characterization of carbonate reservoirs in icehouse platforms such as the large hydrocarbon fields in the north caspian and s e asia

dynamics of the earth magnetic field in the 10 75 kyr period comprising the laschamp and mono lake excursions new results from the french chaine des puys in a global perspective abstract we report here on a new paleomagnetic directions and intensities and coupled k ar and 40 ar 39 ar analysis of 35 different flows emplaced in the chaine des puys during the 75 to 10 kyr interval which contains the mono lake and laschamp excursions there is a remarkable agreement between the new set of absolute volcanic intensities and published sedimentary glopis 75 and cosmogenic 10 be and 36 cl records the laschamp and mono lake excursions are clearly revealed by a very significant intensity drop at 41 2 1 6 ka and 34 2 1 2 ka respectively the duration of the laschamp excursion is 1500 yr and about 640 yr when the drop of paleointensity or the directional change are considered respectively the intensity drop at the mono lake is twice as short in the 7 ka interval separating the two excursions the field intensity recovers to almost non transitional values the rate of decrease of the field intensity during these excursions attains 18 nt yr for the laschamp and even greater value 33 nt yr for the mono lake this figure is for the laschamp excursion similar to the present field intensity decrease in the last two centuries so that one may wonder whether such a high rate of change may be characteristic of an impending geomagnetic event reversal or excursion we suggest that the name auckland excursion should be used for the present day called mono lake

palaeoenvironmental implication of resedimented limestones shed from mississippian permian mid oceanic atoll type buildup into slope to basin facies akiyoshi japan abstract for better understanding of long term environmental changes in a mid oceanic atoll type buildup akiyoshi limestone group we examined the atoll derived carbonate sediments that were contemporaneously shed into the spicular chert of slope to basin facies ota group in the akiyoshi area southwest japan both of these two units are dated as upper visean to capitanian and interpreted as having laterally passed into each other on and around a mid oceanic seamount the resedimented limestone occurs as slab like bodies and isolated and laterally discrete smaller pods and thin beds and laminae in the spicular chert of the ota group the composite succession ca 105 m thick measured in slab like bodies is divided into the lower and upper units each of which consists of the sharp based calcarenite siliceous lime mud siltstone and spicular chert with blocks beds and laminae of calcarenite and siliceous limestone in ascending order the calcarenite forming slabs and smaller blocks are massive and dominantly comprises densely packed coarse crinoid debris and subordinate bryozoan fragments with no or sparse matrix the siliceous lime mud siltstone consists of siliceous sponges spicules minute calcitic skeletal debris and peloidal particles with the matrix of a mixture of lime mud and microcrystalline quartz the calcarenite and siliceous lime mud siltstone beds and laminae in the spicular chert occasionally contain graded and parallel laminae the massive calcarenite and graded calcarenite and siliceous limestone were formed by redeposition mainly of skeletal sands presumably by grain flows with minor debris flows and by mixing of sponge spicule rich siliceous sediments and redeposited lime mud and skeletal debris by muddy turbidites of distal facies respectively these redeposited carbonate sediments were exported from the akiyoshi limestone group onto the spicular sediments of slope to basin facies conodonts fusulinids and smaller foraminifers from the resedimented limestone indicate that the redeposition of the carbonate sediments took place dominantly in late visean to late bashkirian and subordinately in sakmarian to capitanian time the absence of the moscovian to asselian resedimented limestone implies much reduced carbonate shedding during this period the correlation with the interpreted palaeoenvironmental episodes in the akiyoshi buildup shows that late visean to late bashkirian and sakmarian to capitanian carbonate shedding events correspond to the times of generally warm climate and high sea levels in the akiyoshi buildup moscovian to asselian time which lacks records of carbonate shedding nearly corresponds to the moscovian to gzhelian cooling and sea level lowering in the akiyoshi buildup we consider that the shedding of carbonate sediments from the akiyoshi atoll is its depositional response to the warm climate and elevated sea levels and is compared with a sedimentary system of the highstand shedding of carbonates atoll type carbonates equivalent to the akiyoshi limestone group in the akiyoshi terrane also show comparable responses of carbonate shedding into slope and slope to basin facies

depressed rates of origination and extinction during the late paleozoic ice age a new state for the global marine ecosystem rates of origination and extinction for marine animal genera dropped to low levels in latest mississippian time immediately after massive glaciers formed in the southern hemisphere and a second order mass extinction occurred evolutionary turnover and diversity remained low for 50 m y shifting markedly upward precisely when extensive glaciation ended in early permian time all diverse taxa with good fossil records experienced low rates of origination and extinction during this major ice age such sluggish rates would be predicted for faunas of shallow seas on or adjacent to a heavily glaciated supercontinent such as pangea where cool and highly seasonal thermal regimes should dictate that species have broad ecological niches widespread geographic distributions and large and relatively stable populations

three dimensional sequence analysis of a subsurface carbonate ramp mississippian appalachian foreland basin west virginia usa well cuttings wireline logs and limited core and outcrop data were used to generate a regional three dimensional sequence framework for upper mississippian chesterian greenbrier group carbonates in the appalachian foreland basin west virginia usa the resulting maps were used to document the stratigraphic response of the basin to tectonics and to glacio eustasy during the transition into ice house conditions the ramp facies include inner ramp red beds and aeolianites lagoonal muddy carbonates mid ramp ooid and skeletal grainstone shoal complexes and outer ramp wackestone mudstone that grades downslope into laminated silty lime mudstone the facies make up fourth order sequences a few metres to over 90 m 300 ft thick the sequences are bounded along the ramp margin by lowstand sandstones and calcareous siltstones on the ramp sequence boundaries are overlain by thin transgressive siliciclastics and aeolianites and only a few are calichified maximum flooding surfaces on the outer ramp lie beneath deeper water facies that overlie lowstand to transgressive siliciclastic or carbonate units on the shallow ramp maximum flooding surfaces overlie siliciclastic prone transgressive systems tracts that are overlain by highstand carbonates with significant grainstone units interlayered with lagoonal lime mudstones the fourth order sequences are the major mappable subsurface units they are bundled into weak composite sequences which are bounded by red beds in spite of differential subsidence rates across the foreland basin 1 to 3 cm k y up to 25 cm k y eustatic sea level changes controlled regional sequence development thrust load induced differential subsidence of fault blocks coupled with in plane stress controlled the rapid basinward thickening of the depositional wedge whose thickness and facies were influenced by subtle structures such as arches trending at high angles as well as parallel to the margin

coupled sedimentary and δ13c records of late mississippian platform to slope successions from south china insight into δ13c chemostratigraphy abstract variability in stratigraphic accumulation rates and distribution of stratal hiatuses along with strong endemism of index fossils hinder regional to global stratigraphic correlation of the visean serpukhovian v s boundary interval late mississippian and thus geological inferences regarding the onset of the late paleozoic ice age here we integrate high resolution 13c time series with detailed sedimentary facies analysis of late visean early serpukhovian v s carbonate platform to slope successions from south china to evaluate the influences of local depositional and diagenetic processes on 13ccarb and to address the correlation issue analysis of 11 sedimentary facies from 5 outcrop sections indicates a restricted platform setting yashui section dominated by bioclastic wacke packstone to lime mudstone in which paleokarst developed and contemporaneous carbonate slope settings dominated by thin bedded lime mudstones intercalated with slumps and calciturbidites based on vertical facies assemblages three depositional units are recognized recording a significant sea level drawdown across the v s boundary multiple negative 13c excursions 1 can be correlated across the v s boundary interval in several slope sections naqing luokun and narao sections variability in the v s boundary 13c record in some sections is interpreted to record truncation physically by submarine erosion by slumps or chemically during karstification a long term decrease in 13c values through the serpukhovian of the yashui section likely records local influences on carbon cycling in the restricted platform setting this negative 13c trend and associated depositional facies at the yashui section can be correlated to the arrow canyon section usa which together with other coeval global sedimentary and geochemical records indicate a widespread eustatic drawdown in the late visean with initial buildup of gondwanan ice sheets we conclude that integrated sedimentary facies analysis and 13c chemostratigraphy can be used for stratigraphic correlation when interpreted within a well constrained sedimentary and carbon isotope regional framework

late devonian late triassic sedimentary development of the central taurides s turkey implications for the northern margin of gondwana the sedimentary rocks that constitute the northern margin of gondwana stretching from morocco around north africa to oman help to document regional to global sea level change and the evolution of the tethyan ocean to the north such continental margin sediments provide sensitive indicators of eustatic sea level change local to regionalscale tectonics and climatic change the late palaeozoic to triassic period encompasses rifting and sea floor spreading of one or more tethyan oceans some areas particularly morocco and algeria in the west show evidence of compressional deformation related to closure of a hercynian ocean during early carboniferous time late palaeozoic deformation is also documented in oman further southeast in contrast the levant region and egypt both lack evidence of late carboniferous early mesozoic compressional deformation although vertical tectonic movements are evident in the eastern mediterranean region relatively proximal i e southerly areas of the autochthonous gondwana margin are well exposed in north africa however more distal parts of the margin are beneath the mediterranean sea or are exposed in sutured continental terranes within the tethyan orogen however such outcrops provide a unique window into late palaeozoic early mesozoic palaeoenvironments along the northern margin of gondwana

climatic basis for sluggish macroevolution during the late paleozoic ice age rates of origination and extinction for marine invertebrates fell at the onset of the late paleozoic ice age in late mississippian time and remained low until glaciation ended in middle permian time through the use of a database of stratigraphic and geographic occurrences of brachiopod genera these macroevolutionary changes are traced to the loss of genera with narrow latitudinal ranges which had intrinsically high turnover rates at the onset of glaciation in late visean time when glaciation waned in late sakmarian time narrowly distributed genera rebounded abruptly and restored the global fauna to its pre ice age configuration because narrowly distributed brachiopod genera had dominated tropical diversity the major biotic effects of the late paleozoic ice age were felt at low latitudes the climatic regime of this ice age thus altered the marine ecosystem to one characterized by broadly adapted long lived genera

early carboniferous mississippian paleosols from southwest britain influence of climatic change on soil development abstract the clifton down mudstone a mixed peritidal fluvial sequence of arundian late osagean early meramecian age from southwest britain contains a suite of varied cumulative paleosols temporal changes in soil type within this paleosol suite provide evidence for a shift in the climatic regime during arundian times calcic vertisols in the lower part of the sequence developed on floodplains and are equated to a seasonally semi arid climate in which wetter periods induced vertisol development and promoted leaching in contrast a ferric podzol and thionic gleysols characterize the upper part of the succession and are associated with a thick fluvial sandstone interval the ferric podzol probably developed either in a humid tropical or temperate climate and indicates that there was a shift to a more humid climatic regime during late arundian times thionic gleysols with dolocrete horizons represent brackish hydromorphic marsh soils associated with marine incursions and overprint earlier paleosols

sedimentology architecture and depositional setting of the fluvial spireslack sandstone of the midland valley scotland insights from the spireslack surface coal mine

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

deposition of a saline giant in the mississippian windsor group nova scotia and the nascent late paleozoic ice age abstract saline giants are vast marine evaporite deposits that currently have no modern analogues and remain one of the most enigmatic of chemical sedimentary rocks the mississippian windsor group ca 345 ma maritimes basin atlantic canada is a saline giant that consists of two evaporite rich sedimentary sequences that are subdivided into five subzones sequence 1 is composed almost entirely of thick halite belonging to subzone a osagean sequence 2 is in unconformable contact and comprised of stacked carbonate evaporite peritidal cycles of subzones b through e meramecian subzone b the focus of research herein documents the transition from wholly evaporitic to open marine conditions and thus preserves an exceptional window into the processes forming saline giants lithofacies stacking patterns in subzone b reveal that higher order fluctuations in relative sea level produced nine stacked parasequences interpreted to reflect high frequency glacioeustatic oscillations during the onset of the late paleozoic ice age each parasequence reflects progradation of intertidal and sabkha sediments over subtidal carbonate and evaporite deposits dissimilarities in cycle composition between sub basins imply the development of contrasting brine chemistries from differing recharge rates with the open ocean what the windsor group shows is that evaporite type is ostensibly linked to the amplitude and frequency of sea level rise and fall during deposition true saline giants like the basinwide evaporites of sequence 1 apparently require low amplitude long frequency changes in sea level to promote the development of stable brine pools that are only periodically recharged with seawater by contrast the high amplitude short frequency glacioeustatic variability in sea level that controlled the accumulation of peritidal evaporites in subzone b produce smaller subeconomic deposits with more complex facies relationships

rugose coral biostromes in the late visean mississippian of nw ireland bioevents on an extensive carbonate platform abstract the extensive upper visean asbian platform carbonates in nw ireland bricklieve limestone fm glencar limestone fm and dartry limestone fm contain distinctive rugose coral biostromes which are dominated by different species of the genus siphonodendron these are in stratigraphic sequence pauciradiale biostrome oldest martini biostrome and several junceum biostromes youngest they represent bioevents caused by special short lasting ecological conditions and can be used as approximately synchronous horizons to correlate within the region the pauciradiale biostrome is the thickest laterally most persistent and most variable in facies and biotic composition of all biostromes it formed on a tectonically influenced platform with a landward seaward zonation from northwest to southeast mainly above storm wave base and below fair weather wave base the northwestern streedagh facies is characterized by the presence of clusters of large sheet like colonies of s pauciradiale the intermediate o donnell s rock facies is unique for the predominance of the fasciculate genus solenodendron the southeastern bricklieve facies represents the amalgamation of autochthonous and allochthonous coral debris and bioclastic debris with localized small patches of coral boundstone mass occurrences of fasciculate rugose corals re appear in the martini biostrome this biostrome developed in a shallower water setting just above fair weather wave base on a levelled carbonate platform the junceum biostromes are thinner decimetre to some metres thick and less persistent they formed in deeper water mostly below storm wave base except for the composite 2nd junceum biostrome of the bricklieve mountains which records a period of shallowing according to facies and coral morphologies which were compared with modern scleractinian growth forms sea level variation exerted one of the strong controls on the rise and decline of the biostromes the pauciradiale biostrome formed during an extended shallowing upward cycle in a depth interval leading to the climax of siphonodendron pauciradiale the cycle ended with the development of the martini biostrome in shallow water its demise is probably caused by drowning during the late asbian sea level rise during that time slice the junceum biostromes flourished in deeper water on the platform coral growth ceased almost completely after formation of the junceum biostromes during the falling sea level of the latest asbian siliciclastic input and resulting turbidity as well as turbulence formed a complex cascade of ecological constraints in addition to the local tectonic influences they combined to result in the depth factor which controlled the distribution of predominating coral populations and the succession of the different biostromes in the asbian of nw ireland

origin and age of the manila high and associated big lake sunklands in the new madrid seismic zone northeastern arkansas uplift of the manila high and subsidence of the south flowing little river during the great new madrid earthquakes of 1811 1812 formed the present lake in big lake basin of northern arkansas this is the most recent deformation of the 19 km long manila high that began between 11 000 and 5400 yr ago and is time transgressive toward the south at least 4 m of holocene uplift occurred on the northern portion of the manila high prior to initiation of the little river distributary in mid holocene time the distributary is deflected around the high and overbank sediment derived from it thins and is locally absent across the northern highest portion of the high deformation along the southern end of the high began between 3500 and 2000 yr ago since 3500 yr b p 2 m of uplift appears to have caused a reduction in gradient anastomosing upstream of the uplift and incision of the little river across the uplift north of the manila high in the big lake basin the little river has an increased aggradation rate 10 times that of the preuplift rate cores collected in and adjacent to big lake indicate that the little river was ponded twice apparently in response to deformation in 1811 1812 and between 90 b c and a d 1640

the upper mississippian bluefield formation in the central appalachian basin a hierarchical sequence stratigraphic record of a greenhouse to icehouse transition abstract the upper mississippian chesterian bluefield formation is the basal unit of the predominantly siliciclastic mauch chunk group in the appalachian basin this formation developed in a northeast southwest oriented foreland trough fronting the alleghanian highlands to the southeast regional cross sections and isopach maps of the bluefield formation in southeastern west virginia southwestern virginia and southeastern kentucky define a depocenter in the southeastern part of the study area and a paleovalley system along the basin margin to the northwest at most localities facies that make up the bluefield formation are stacked into 1 15 m thick upward shallowing parasequences each of which is capped by a flooding surface these parasequences are stacked into four regionally correlatable depositional sequences on the margins of the depocenter incised valleys and fewer meter scale parasequences characterize the depositional sequences stacking of parasequences into sequences reflects a hierarchy of greenhouse type fifth order and icehouse type fourth order sea level cycles superimposed on a differential subsidence history related to early alleghanian thrust loading the bluefield depocenter experienced greater total accommodation which prevented incision during lowstands instead lowstands are typified by preservation of fifth order coal bearing parasequences in the depocenter basin margin areas experienced less total accommodation which resulted in development of fourth order lowstand valleys and erosion of parasequences this study demonstrates that both tectonic and eustatic forcing mechanisms controlled stratigraphic evolution of the bluefield formation

conodont biostratigraphy of the mid carboniferous boundary in western ireland two stratigraphic sections spanning the mid carboniferous boundary were examined in the clare shale formation of the shannon basin in western ireland calcareous nodules intermittently occur within these generally non calcareous organic rich shales and these have yielded serpukhovian and bashkirian conodont elements the biostratigraphic range of the irish material is illustrated here for the first time results show that the mid carboniferous and arnsbergian chokierian boundaries are coincident at ballybunion gnathodus girtyi is restricted to the lower part of the serpukhovian stage late mississippian while g bilineatus bollandensis persists into much younger strata close to the first occurrence of declinognathodus noduliferus s l one element belonging to g postbilineatus is also present these findings support the argument that d noduliferus s l developed from g b bollandensis rather than from g girtyi the biostratigraphical tool for the identification of the mid carboniferous boundary globally and the suitability of the section at arrow canyon usa as a gssp may therefore need to be reassessed

deep sea sediment records of the laschamp geomagnetic field excursion 41 000 calendar years before present 1 we have recovered two new high resolution paleomagnetic records of the laschamp excursion 41 000 calendar years b p from deep sea sediments of the western north atlantic ocean the records document that the laschamp excursion was characterized locally by 1 declination changes of 120 2 inclination changes of more than 140 3 1200 year oscillations in both inclination and declination 4 near 90 out of phase relationships between inclinations and declinations that produced two clockwise loops in directions and virtual geomagnetic poles vgps followed by a counterclockwise loop 5 excursional vgps during both intervals of clockwise looping 6 magnetic field intensities less than 10 of normal that persisted for almost 2000 years 7 marked similarity in excursional directions over 5000 km spatial scale length and 8 secular variation rates comparable to historic field behavior but persisting in sign for hundreds of years all of these features with the exception of anomalously large directional amplitude are consistent with normal magnetic field secular variation comparison of our laschamp excursion paleomagnetic records with other late quaternary excursion records suggests that there is a group of excursions which we term class i which have strikingly similar patterns of field behavior and likely share a common cause as part of the overall core dynamo process three general models of secular variation are described that can qualitatively produce class i excursions on the basis of these observations we conclude that class i excursions epitomized by the laschamp excursion are more closely related to normal secular variation and are not necessarily a prelude to magnetic field reversal

imprint of the late palaeozoic ice age on stratigraphic and carbon isotopic patterns in marine carbonates of the orogrande basin new mexico usa the permian records one of the most extreme climate transitions of the phanerozoic yet the climatic and environmental dynamics of this interval and their effects on neritic carbonate systems remain poorly constrained new stratigraphic and carbon isotope records from uppermost pennsylvanian to lower permian strata of the orogrande basin in south central new mexico usa provide fresh insights into the response of palaeotropical carbonate systems to the growth and demise of ice sheets on gondwana the earliest permian acme of glaciation is recorded in the orogrande basin as a series of subaerial exposure surfaces marked by highly variable 13c values that tend toward values as low as 6 these stratigraphic and isotopic patterns are interpreted to reflect the retreat of the sea from the basin during glacial expansion younger lower sakmarian to kungurian strata deposited during the long decline of the late paleozoic ice age are characterized overall by higher and more uniform 13c values 2 to 5 and show no evidence of long term subaerial exposure however these strata record two short lived excursions toward more negative 13c values these excursions occur through intervals that record shifts toward shallower and more restricted conditions in the orogrande basin the timing of these shifts corresponds to two periods of glacial expansion across eastern australia during late sakmarian to early artinskian and kungurian time these relationships suggest that pulses of glacial expansion in eastern gondwana were of sufficient magnitude to have caused relative sea level fall and possibly environmental change in the orogrande basin the results from this study suggest that marine chemistry depositional environments and sea level in the orogrande basin were profoundly influenced by epochs of gondwanan glaciation these inferences help improve the understanding of how palaeotropical carbonate systems responded to the effects of cryospheric changes during the acme and waning stages of the late palaeozoic ice age

odp site 1063 bermuda rise revisited oxygen isotopes excursions and paleointensity in the brunhes chron an age model for the brunhes chron of ocean drilling program odp site 1063 bermuda rise is constructed by tandem correlation of oxygen isotope and relative paleointensity data to calibrated reference templates four intervals in the brunhes chron where paleomagnetic inclinations are negative for both u channel samples and discrete samples are correlated to the following magnetic excursions with site 1063 ages in brackets laschamp 41 ka blake 116 ka iceland basin 190 ka pringle falls 239 ka these ages are consistent with current age estimates for three of these excursions but not for pringle falls which has an apparent age older than a recently published estimate by 28 kyr for each of these excursions termed category 1 excursions virtual geomagnetic poles vgps reach high southerly latitudes implying paired polarity reversals of the earth s main dipole field that apparently occurred in a brief time span 2 kyr in each case several times shorter than the apparent duration of regular polarity transitions in addition several intervals of low paleomagnetic inclination low and negative in one case are observed both in u channel and discrete samples at 318 ka mis 9 412 ka mis 11 and in the 500 600 ka interval mis 14 15 these category 2 excursions may constitute inadequately recorded category 1 excursions or high amplitude secular variation

late mississippian limestone sedimentary environment in southern pembrokeshire bullslaughter bay wales evidence of meteoric diagenesis and hypersaline features bullslaughter bay in southern pembrokeshire uk exposes sections of upper mississippian limestone strata in many places the rock suffered an isovolumetric alteration during a period of sea level oscillations we used multiple approaches to study the weathered rocks combining sedimentological petrographic and isotopic compositions 18o and 13c values two main microfacies are recognized i packstones grainstones characteristic of an open marine shallow subtidal intertidal environment with a high degree of agitation slightly elevated salinity and temporary subaerial exposure and ii mudstones wackestones in a lagoonal setting and intertidal or supratidal environments with a pedogenetic influence in both cases a complex diagenetic story which started early in a meteoric environment induced a strong alteration producing loose sediments in place of the parent rock calcretization at or near the sediment surface in the vadose zone was one of the most widespread diagenetic modes it could be associated with beachrocks carbon and oxygen stable isotope analyses from more or less weathered limestones support the petrographic data they show non marine values with 13c ranges of from 2 13 to 1 75 and 18o from 6 05 to 4 66 these values are systematically lower than those of the middle carboniferous seawater some periods of low sea level and subaerial exposure allowed gypsum to form neoformation of euhedral quartz by probable replacement after sulfate and halite pseudomorphs after gypsum in a hypersaline environment are documented for the first time in southern pembrokeshire the studied weathered limestones present a complex diagenetic evolution related to sea level oscillations in a range of hot and contrasting seasonal climates

the evolution of the core surface flow over the last seven thousands years 1 we analyze the core surface flow over the last seven thousands years derived from cals7k 2 a continuous model of the geomagnetic field and its secular variation for the period 5000 bc to 1950 ad this model relies on indirect observations of the geomagnetic field through the sampling of natural archives lake sediments lavas and archaeological artifacts an extensive comparison between gufm1 a historical field model spanning the interval 1590 to 1990 and cals7k 2 is carried out while both are similar in their descriptions of the large scale core field their agreement compares poorly in terms of secular variation the differences are primarily caused by the different data quality used to build these models such a comparison is essential for assessing the reliability of the results of flow inversion we seek instantaneous core flow solutions that are purely toroidal and tangentially geostrophic for which we can reasonably neglect the effect of magnetic diffusion our flow solutions suggest that the core surface flow undergoes different regimes of zonal flow direction with epochs of mainly westward flow alternating with epochs of mainly eastward flow the episodes of eastward and westward flow are robust as they are obtained for purely toroidal and tangentially geostrophic flow the changes in the large scale zonal flow direction seem to recur with a typical period of between 540 and 1050 years variations in thermal and magnetic winds occurring on timescales comparable with the convective overturn of the liquid outer core could account for the observed zonal flow variations

carbon oxygen isotope signal of mississippian slope carbonates appalachians usa a complex response to climate driven fourth order glacio eustasy abstract mississippian chesterian ramp slope muds in virginia deposited on the margin of a rapidly subsiding foreland basin were not significantly reset isotopically by regional meteoric aquifer systems that affected units on the adjacent platform carbon and oxygen isotopic ratios of these muds tend to covary at the scale of the twelve 4th order sequences that dominate the platform succession the 13 c values of the slope muds range from 0 5 to 4 pdb and lie in the range of least altered contemporaneous brachiopods from north america indicating little resetting of carbon isotopes by diagenesis there is an approximately 1 to 2 decrease in 13 c in the maximum flooding zone relative to the lowstand followed by a positive shift upward in the highstand before becoming more negative toward 4th order correlative conformities meteoric diagenesis might have reset some sediments just beneath a sequence boundary to lighter values it cannot account for the observed shifts evident throughout the sequences the 13 c enriched values in 13 c profiles could be due to increased productivity during glacial stages the increased productivity during glacial stages was probably due to increased ocean circulation coupled with shallowing which brought the ramp top into waters with more 13 c enriched dissolved inorganic carbon with the opposite effects occurring during deglaciation the 18 o values of muds range from about 2 2 to about 4 6 pdb falling within and beyond the lighter part of the range of contemporaneous north american brachiopods mii h s grossman e l yancey t e 1999 carboniferous isotope stratigraphies of north america implications for carboniferous paleoceanography and mississippian glaciation geol soc am bull 111 960 973 these values likely have been reset by burial diagenesis and perhaps by some meteoric diagenesis just beneath correlative conformities the sequences show negative excursions of 1 to 2 in 18 o in the maximum flooding zone relative to the lowstand and then become more positive upward in the highstand then decrease toward the correlative conformities some of the preserved signal could reflect ice volume changes although this would account for only 0 5 to 1 change the ice volume effect during lowstands plus cooling of ramp top waters and small increases in salinity due to increased aridity in the appalachian basin could account for the remaining 0 5 to 1 5 of oxygen isotope excursions with the opposite effect occurring during high sea levels the 18 o and 13 c of the appalachian ramp slope facies lack the strong 3rd order trends of the mid continental united states and europe the remnant 4th order carbon and oxygen isotope signal is similar in structure to cenozoic deep sea isotope profiles that are due in large part to 4th order glacio eustasy this would be compatible with onset of late paleozoic glaciation of gondwana

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

revised stratigraphic framework of pre westphalian carboniferous petroleum system elements from the outer moray firth to the silverpit basin north sea uk

integration of static and dynamic data and high resolution sequence stratigraphy to define reservoir architecture and flow units within a super giant gas condensate and oil field kazakhstan abstract the upper serpukhovian mississippian interval of the karachaganak reservoir comprises stratified platform interior carbonates which are characterised by relatively high porosity and matrix permeability maximum 23 8 and 2198 md respectively and comprise high frequency fourth order glacio eustatic cycles based on static geological and dynamic well test and production data this cyclicity exerts a strong control on gas migration pathways and reservoir quality is predictable within a third and fourth order sequence stratigraphic framework that defines two discrete flow units the contribution to flow made by fourth order cycles within flow units is dependent on their position within third order transgressive or highstand systems tracts an upper flow unit comprises thick up to 40 m fourth order cycles within a third order transgressive systems tract these fourth order cycles contain large scale clinoformal bedforms can be correlated for up to 6 km and are the main pathways of injected gas through the upper serpukhovian reservoir a lower flow unit comprises fourth order cycles within a third order highstand systems tract that are thinner and less laterally continuous than those in the upper flow unit and contribute far less to horizontal gas flow pressure data indicate that vertical permeability baffles are developed at the third order sequence boundary that separates the two flow units linked to diagenetic alteration during prolonged subaerial exposure and also within the low porosity mud rich transgressive bases of thick fourth order cycles of the upper flow unit that formed during periods of increased accommodation space across the platform top during third order transgression the scale at which this data set is observed is critical to understanding the dynamic behaviour of the reservoir relatively small differences in the composition of microfacies of cycles within both flow units do not explain the variations in dynamic data this variation is better explained within the broader context of the sequence stratigraphic framework as defined from analysis of cycle stacking patterns thicker high frequency cycles deposited in increased accommodation space on the platform top during third order transgressive intervals are key to developing thick intervals of net pay

palaeoecological and possible evolutionary effects of early namurian serpukhovian carboniferous glacioeustatic cyclicity early namurian serpukhovian carboniferous sedimentary cycles in the throckley and rowlands gill boreholes near newcastle upon tyne uk consist of fossiliferous limestones overlain by usually unfossiliferous black mudstone followed by sandstones and often by thin coal seams sedimentological and regional geological evidence suggests that the largest are high amplitude cycles probably of glacioeustatic origin 13 c bulk organic matter delineates marine and non marine conditions because of the large difference between terrestrial and marine 13 c and indicates that full marine salinity was only intermittent and resulted from glacioeustatic marine transgression superimposed on a background of inundation by freshwater from large rivers which killed off the marine biota palynology suggests that plant groups including ferns and putative pteridosperms were affected by changing sea level and that there is a theoretical possibility of connection between cyclicity and the first appearance of walchiacean conifer like monosaccate pollen such as potonieisporites long term terrestrial and marine increasing 13 c organic may reflect the onset of major glaciation in gondwana as there is evidence to suggest that the two are coeval but no specific mechanism can be suggested to link the trends

50 million year long record of glacial to postglacial marine environments preserved in a carboniferous lower permian graben northern perth basin western australia abstract the perth basin is an intracratonic rift in western australia and contains a carboniferous to cretaceous infill in excess of 12 km thick some 2 km of mid carboniferous to lower permian glacially influenced marine strata spanning the serpukhovian to kungurian about 50 my form one of the longest late paleozoic cold climate successions preserved anywhere in gondwana and record the transition from full glacial to postglacial conditions at high 70 paleolatitudes the great thickness of the succession reflects an abundant supply of glaciclastic sediment from the adjacent ice covered yilgarn craton and continued subsidence along the darling urella fault system the oldest part of the basin fill comprises a 1 5 km thick succession of massive and laminated marine mudstones with striated dropstones nangetty formation deposited in a fiord like environment from plumes of suspended sediment dilute turbidity currents and icebergs meltwater inputs are recorded by erosionally based multistory channels filled with coarse grained gravity flow facies wicherina member deposited on a fan delta along the steep faulted basin margin the nangetty formation passes upward into a regressive succession of postglacial mudstones holmwood shale with bioclastic calcarenites and marine macrofossils capped by sandstone and mudstone facies high cliff sandstone deposited in a storm influenced inner shelf setting on the outer margins of coalesced fan deltas along the basin margin the overlying irwin river coal measures contain a flora that indicates colonization of fan deltas and the yilgarn craton by ferns and lycopods an overlying thick transgressive shale with ice rafted debris carynginia formation records renewed subsidence but continuing seasonally cool climates where coarse debris was rafted by ice into a marine embayment the sedimentology of the perth basin highlights the key role of glacial meltwaters in transporting coarse and fine grained clastic sediment to marine basins rather than direct glacial processes per se the equivalent terrestrial record of glaciation and climate change across the yilgarn craton at this time is very limited

high precision u pb calibration of carboniferous glaciation and climate history paganzo group nw argentina the duration and geographic extent of carboniferous glacial events in southern gondwana remain poorly constrained despite recent evidence for a more dynamic glacial history than previously considered we report 10 high precision 2 0 1 u pb ages for the permian carboniferous paganzo group nw argentina that redefi ne the chronostratigraphy of the late paleozoic paganzo and rio blanco basins and signifi cantly refi ne the timing of glacial events and climate shifts in the western region of southern gondwana radiometric calibration of the paganzo group indicates three pulses of carboniferous glaciation in the mid visean the late serpukhovian to earliest bashkirian and between the latest bashkirian to early moscovian an abrupt shift in depositional style from high sinuosity single storied fl uvial deposits and clay rich paleosols to low sinuosity multi storied feldspathic fluvial deposits inter calated with eolianites and calcic paleosols is constrained to the latest moscovian and earliest kasimovian these constraints indicate a relatively abrupt climate shift from humid subhumid to nonseasonal semiarid regional climate conditions that occurred signifi cantly earlier than previously inferred early permian this period of high latitude aridity was contemporaneous with a shift to dryland depositional environments and a major vegetation regime shift documented throughout the pangean paleotropics in the pennsylvanian

radiogenic isotope composition of carboniferous seawater from north american epicontinental seas abstract abundant marine sedimentary deposits accumulated in the epeiric seas of north america during the carboniferous period 359 299 ma when the earth s climate shifted from a global greenhouse to icehouse geochemical records extracted from these deposits are often assumed to reflect global ocean processes and are increasingly being used to infer relationships between tectonism carbon cycling and climate change we analyzed radiogenic isotopes sr nd in biogenic apatite along a north american transect to constrain the degree of coupling between the epicontinental seas and the open ocean in many samples the primary sr signal is altered however the original nd isotopic composition of the biogenic apatite seems to be preserved the end t values range from 8 6 to 4 5 in the us midcontinent basins and from 11 4 to 5 7 at arrow canyon nevada usa indicating the development of an east west geochemical gradient throughout the pennsylvanian this apparent decoupling of the epicontinental seas from the open ocean was established by the latest mississippian thus circulation of waters between epicontinental seaways of western us and the basins to the east and south was periodically restricted shifts toward unradiogenic nd at arrow canyon seem to correspond with glacio eustatic changes across the mid carboniferous boundary these end t variations may have been caused by changes in weathering rates sources marine circulation or a combination of both

impact of long term climate change and sea level fluctuation on mississippian to permian mid oceanic atoll sedimentation akiyoshi limestone group japan abstract to understand the impacts of long term climatic episodes and sea level changes on mid oceanic atoll sedimentation the stratigraphic changes of litho and bio facies and stratigraphic levels of freshwater diagenetic alteration and biostratigraphic discontinuity of the akiyoshi limestone group upper visean to upper capitanian were reviewed this group records approximately 70 million years of atoll sedimentation in a mid oceanic realm of the panthalassa ocean which developed nearly synchronously with the late paleozoic gondwana glaciation the entire succession of the akiyoshi limestone group was divided into four facies associations skeletal oolitic grainstone muddy limestone muddy limestone skeletal grainstone and reefal limestone associations skeletal oolitic grainstone and reefal limestone associations upper visean to bashkirian are characterized by an abundance of oolite and crinoidal grainstone and reef facies of warm adapted metazoan reef builders corals chaetetes and bryozoans respectively characteristics of skeletal oolitic grainstone and reefal limestone associations indicate their deposition in a warm climate with elevated sea level muddy limestone association moscovian to kasimovian records the demise of the warm adapted metazoan reef builders and frequent emergence events of the buildup many geochemical data support the significant drop in temperature during moscovian through kasimovian time these depositional and biotic events of muddy limestone association indicate that its sedimentation was strongly affected by cool climate and generally low sea level muddy limestone skeletal grainstone association is characterized by an upward increasing significance of calcimicrobes calcareous algae and calcisponges the succession records less frequent emergence events than that of muddy limestone association ii these characters reflect a warming climate and sea level rise in gzhelian to capitanian time the climate episodes and sea level changes interpreted from the akiyoshi limestone group generally correspond to the global trend of mississippian to permian long term climatic change and sea level fluctuation related to the major glacial events of gondwana glaciation the late visean to bashkirian warm climate and elevated sea levels moscovian to kasimovian cooling and sea level lowering and gzhelian to capitanian warming and sea level rise recorded in the akiyoshi buildup are comparable to the global climate model and sea level fluctuation which contain early to middle mississippian pre glacial warm climate and highstands middle to late pennsylvanian cooling and related glacio eustatic sea level fluctuation at the culmination of gondwana glaciation and early to middle permian global warming and sea level rise due to the retreat of gondwana ice sheets akiyoshi atoll sedimentation was most significantly affected pennsylvanian global cooling and related sea level lowering but their impact was short lived the onset of the cooling and frequent emergence events in the akiyoshi buildup occurred delayed approximately 10 millions years later than that of comparable episodes on the pangean shelves the post glacial warming in the akiyoshi buildup started at least several millions of years earlier than in epicontinental seas of the pangea this phenomenon may be due to the palaeoposition of the akiyoshi buildup in a mid oceanic realm of the panthalassa ocean

stratigraphic imprint of the late palaeozoic ice age in eastern australia a record of alternating glacial and nonglacial climate regime stratigraphic and sedimentological data from new south wales and queensland eastern australia indicate that the late palaeozoic ice age comprised at least eight discrete glacial intervals each 1 8 ma in duration here termed glaciations separated by nonglacial intervals of comparable duration these events spanned an interval from mid carboniferous c 327 ma to the early late permian c 260 ma and illustrate a pattern of increasing climatic austerity and increasingly widespread glacial ice from initial onset until an acme in the late early permian followed by an opposite trend towards the final demise of glaciation in the late permian the alternating glacial nonglacial motif suggests that the late palaeozoic ice age was considerably more dynamic than previously thought these patterns are remarkably consistent with recent interpretations of palaeofloral change eustatic sea level fluctuations and co 2 climate glaciation relationships for this interval of time the detailed record of alternating glacial and nonglacial climate mode disclosed herein may facilitate more closely resolved evaluations of stratigraphic records elsewhere notably in far field ice distal northern hemisphere successions

the magnitude of late paleozoic glacioeustatic fluctuations a synthesis a comprehensive literature review shows that the magnitude of eustatic fluctuations varied throughout the carboniferous and permian and that at least eight distinct phases can be recognized facies juxtapositions in carbonate successions and erosional relief in clastic successions indicate that glacioeustatic fluctuations of 20 25 m and occasionally as much as 60 m took place throughout the early mississippian tournaisian a widely recognized glacial period middle mississippian mid chadian through holkerian shallow marine carbonate and clastic successions indicate that eustatic fluctuations were 10 25 m a decrease that matches well with the paucity of coeval glacial deposits late visean asbian through mid brigantian glacioeustatic fluctuations of 10 50 m record the initial phases of ice accumulation in advance of the widespread mid carboniferous glacial event the latest mississippian earliest pennsylvanian mid brigantian through langsettian was a time of widespread glaciation and strata of this age commonly exhibit evidence of glacioeustatic fluctuations of as much as 40 100 m although middle pennsylvanian duckmantian through asturian glacial deposits are present in eastern australia paleovalley depths suggest that coeval glacioeustatic fluctuations were less than 40 m glacioeustatic fluctuations of as much as 100 120 m have been widely reported from late pennsylvanian earliest permian stephanian through mid sakmarian successions in north america an increase that corresponds to the growth of large ice sheets across much of gondwana and the accumulation of ice in the northern hemisphere incision and facies juxtaposition in early middle permian mid sakmarian through kungurian successions in eastern australia indicate that glacioeustatic fluctuations of 30 70 m occurred during the waning stages of major glaciation erosional relief in paleoequatorial carbonates and the presence of coeval glacial deposits in australia suggests that eustatic fluctuations of 10 60 m occurred during the final stages of glaciation in the middle to late permian roadian through capitanian but the modest size of most of these fluctuations makes it difficult to isolate the glacioeustatic signature this review demonstrates that far field cyclic successions record changing glacial conditions in gondwana that the magnitude of glacioeustatic fluctuations was directly related to the volume of glacial ice that carboniferous permian glacioeustasy was more variable than previously recognized and that generalizations from short temporal intervals are probably not representative of the late paleozoic ice age as a whole although any attempt to quantify the magnitude of ancient eustatic changes is based on caveats and assumptions this review incorporates the results of over 100 published papers on the topic in an attempt to minimize the errors inherent in any one study

are beds in shelf carbonates millennial scale cycles an example from the mid carboniferous of northern england abstract the mid carboniferous strata of northern england are characterised by mixed clastic carbonate cycles yoredale cyclothems attributed here to the short eccentricity milankovitch rhythm in a typical cycle transgressive normal marine shelf carbonates are succeeded by marine shales then highstand prodelta mudstones and delta front delta top sandstones with local coals a detailed study of one cycle the great limestone cyclothem of the northern pennines alston block reveals that within the transgressive carbonates the beds averaging 75 cm in thickness and defined by mm shale partings or cm mudrock layers form two thinning upward to thickening upward bed sets individual beds and the bed sets can be correlated across the region oxygen isotope and strontium trace element data also reveal patterns of increasing and decreasing values through the limestone which broadly correspond to the bed thickness cycles the beds are interpreted as millennial scale cycles the result of high frequency arid humid climatic fluctuations the bed sets are interpreted as the response to a longer term arid humid climate and sea level cycle driven by the precession rhythm it is postulated that millennial scale climatic changes which are a well known feature of the quaternary and are here inferred for the carboniferous were responsible for the deposition of the beds that are a characteristic feature of many marine sedimentary successions in the geological record the most likely over riding control is fluctuations in solar output

climatic change during the lower carboniferous in euramerica based on multivariate statistical analysis of palynological data abstract lower carboniferous palynological assemblages show marked differences between north and south euramerica in order to assess these regional differences multivariate statistical analysis has been applied to percentage frequency data from palynological assemblages from twenty different localities of euramerica the principal components resulting have been related to climate sensitive rocks such as coal and evaporites this relationship has been interpreted in terms of humidity curves and climatic zones four climatic zones have been recognized a dry a moderately humid and a humid zone the latter zone may be subdivided into a humid and a very humid zone during the lower carboniferous the humid climatic zone and the related palaeoclimatic equator shifts southwards however the very humid conditions present in the uppermost tournaisian to middle visean of spitsbergen have not yet been reached in the lower namurian of western europe and the u s a the southward shift of the palaeoclimatic equator has been interpreted in terms of a northward drift of the euramerican continent the palaeomagnetic evidence available for this northward drift is briefly discussed

controls on early diagenetic overprinting in icehouse carbonates insights from modeling hydrological zone residence times using carb3d abstract icehouse carbonate diagenesis is complex with carbonate sequences being exposed to multiple meteoric hydrozones vadose zone freshwater lens mixing zone on multiple occasions a forward modeling approach using carb3d has enabled quantitative exploration of the nature of this diagenetic overprinting by explicit simulation of meteoric hydrozone residence times during evolution of an isolated carbonate platform a sensitivity analysis was performed encompassing the fundamental controls on hydrozone residence time frequency and magnitude of sea level variation subsidence rate and climate the latter via its effect on freshwater lens thickness and rate of dissolutional lowering of the land surface residence time within all meteoric hydrozones is characterized by a high degree of lateral continuity vertical continuity is much more limited with significant variations on a fourth order sequence scale across the platform below sequence boundaries prolonged exposure to the vadose zone results from multiple missed beats when the platform remains exposed at relative sea level maxima overprinting gives total meteoric residence times significantly in excess of the duration of exposure of the overlying sequence boundary there is a hierarchy of eustatically driven overprint cycles with higher frequency cyclicity modifying the primary signal generated by lower frequency cycles fifth order cycles thus have only a minor impact on hydrozone residence times whilst third order seismic scale cycles are a critical control and could be used as a first order approximation of the amount of diagenetic overprinting subsidence has a strong control on residence time with greater overprinting at lower subsidence rates but in high subsidence regimes sediment packages move below the zone of meteoric water influence sufficiently rapidly that residence time can be minimal high land surface dissolution rates which result from a wetter climate remove a large proportion of the subaerially exposed sediment and reduce vadose zone residence time higher effective recharge can increase the thickness of freshwater lens and mixing zones which increases residence times significantly residence times in the vadose zone can be directly linked to a sequence stratigraphic framework but for the freshwater lens and the mixing zone this is possible only with a well constrained relative sea level history

carboniferous permian palynostratigraphy of west australian marine rift basins resolving tectonic and eustatic controls during gondwanan glaciations abstract the longest interval of cold climate in earth s phanerozoic history spanned some 55 million years from the namurian late carboniferous to the kungurian early permian when glaciation affected much of high latitude gondwana uncertainty surrounds the timing of glaciation s and the frequency of interglacial episodes ice volumes and the location of ice centres this is because the glacial record is preserved predominantly within marine strata deposited in intracontinental rift basins marginal to onshore ice centres on uplifted basement highs the direct stratigraphic record of glaciation is meagre on adjoining basement highs and extremely difficult to date many basins contain broadly similar threefold lithostratigraphic successions of lowermost glaciomarine diamictite facies middle shales and uppermost carbonate and sandstone rich commonly coal bearing deltaic strata in the absence of absolute age control and infrequent presence of macrofossils such deglaciation sequences are widely assumed to be correlative from basin to basin recording gondwanan deglaciation s and a world wide glacioeustatic sea level rise a newly compiled biostratigraphic database for west australia using first appearance datums of spore pollen types allows correlation of late palaeozoic siliciclastic successions between seven basins bonaparte canning carnarvon collie gunbarrel northern and southern perth basins these extend some 3800 km along australia s western continental margin adjacent to the west australian shield all but the gunbarrel basin contain tripartite glacially influenced successions diamictite shale sandstone biostratigraphic data reveal sharp differences in ages and stratigraphic distributions and marked variations in the thickness of coeval units diamictite shale sandstone successions accumulated diachronously from basin to basin recording a dominant tectonic control on subsidence and relative sea level middle shale units are not exact correlatives between basins and thus are unlikely to simply represent widespread climatically controlled glacioeustatic events instead they are argued to record high relative sea levels during times of maximum synrift subsidence this tectonostratigraphic model can be applied to other intracontinental rift basin successions across gondwana