cyclostratigraphy of lower triassic terrestrial successions in the junggar basin northwestern china abstract the astrochronology for the early triassic has been constructed from well preserved marine successions however astronomical analyses of terrestrial strata have continued to be rare and problematic physical logs natural gamma ray logging data from two wells in the junggar basin northwestern china cover the entire lower triassic terrestrial baikouquan formation and have been shown to be a powerful tool in cycle analysis therefore these logs offer an excellent opportunity to detect astronomically forced sedimentation in a terrestrial setting from mid to high latitudes power spectral analysis revealed that the sedimentary cycles had wavelengths of 31 3 35 9 m 8 4 10 0 m 4 0 4 6 m and 4 0 m these are interpreted to correspond to the orbital eccentricity cycles of 405 kyr and 100 kyr and to the obliquity cycles of 51 kyr and 34 kyr respectively we thus established an astronomical time scale for the studied interval assuming that the 31 3 35 9 m cycles represent the 405 kyr eccentricity cycles this astrochronology indicated that the duration of the baikouquan formation was 2 0 0 1 myr statistical evaluations of optimal sediment accumulation rates using the correlation coefficient approach showed that the rates of the investigated successions were approximately 6 0 12 0 cm kyr orbitally controlled climate change was the major dynamic mechanism for the formation of early triassic fan delta successions in the junggar basin

timing of recovery from the end permian extinction geochronologic and biostratigraphic constraints from south china four volcanic ash beds bracket the early middle triassic boundary as defined by conodont biostratigraphy in a stratigraphic section in south china high precision u pb dates of single zircons allow us to place the early to middle triassic olenekian anisian boundary at 247 2 ma magnetic reversal stratigraphy allows global correlation the new dates constrain the early triassic interval characterized by delayed biotic recovery and carbon cycle instability to 5 m y this time constraint must be considered in any model for the end permian extinction and subsequent recovery

the pangaea megamonsoon records evidence from the triassic mungaroo formation northwest shelf of australia abstract an integrated analysis in this study of paleogeographic paleontologic seismic and sedimentologic data has been used to explain the effect of the pangaean megamonsoon on the whole triassic especially the middle late triassic mungaroo formation in the north carnarvon basin northwest shelf of australia our results show that the three triassic formations from bottom to top locker shale mungaroo formation and brigadier formation comprise a complete depositional cycle and correspond to an undeveloped strong and weak monsoon periods respectively during the strong monsoon period of the mungaroo formation the palynological evidences exhibited mixture spore pollen characteristics of the hygrophytic assemblage spore pollen from the pteridophyte spores seed ferns and cycads pollen in humid environment of lowlands and coastal plain and the xerophytic assemblage pollen from the drought tolerant plants of the interior mountainous areas the sedimentary evidences of the mungaroo formation show low angle shingled progradational seismic reflection configuration the highly seasonal variations in precipitation during deposition of the mungaroo formation exhibited typical sandwiched depositional characteristics of coarse channels sandstone fining upward fluvial aggradational cycles facs with poor to moderately sorting and angular to subangular roundness organic mudstone and coal seam interbedded finally in contrast to today s typical examples of poyang lake delta a shallow water braided delta conceptual depositional model of the mungaroo formation is formed with a large proximal and distal delta plain and small delta front the model results serve mainly to indicate the importance of various climate forming factors climate topography eustatic whereas tectonic activity unlikely played any significant role in this process

the indosinian orogeny a perspective from sedimentary archives of north vietnam the triassic stratigraphic framework for the song da and the sam nua basins north vietnam suffers important discrepancies regarding both the depositional environments and ages of the main formations they contain using sedimentological analyses and dating foraminifer biostratigraphy and u pb dating on detrital zircon we provide an improved stratigraphic framework for both basins a striking feature in the song da basin located on the southern margin of the south china block is the diachronous deposition over a basal unconformity of terrestrial and marine deposits the sedimentary succession of the song da basin points to a foreland setting during the late early to the middle triassic which contrasts with the commonly interpreted rift setting on the northern margin of the indochina block the sam nua basin recorded the activity of a proximal magmatic arc during the late permian up to the anisian this arc resulted from the subduction of a southward dipping oceanic slab that separated the south china block from the indochina block during the middle to the late triassic the song da and sam nua basins underwent erosion that led to the formation of a major unconformity resulting from the erosion of the middle triassic indosinian mountain belt built after an ongoing continental collision between the south china and the indochina blocks later during the late triassic as syn to post orogenic foreland basins in a terrestrial setting the song da and sam nua basins experienced the deposition of very coarse detrital material representing products of the mountain belt erosion

permian and triassic greenhouse crises paleoclimatic time series from permian and triassic paleosols reveal transient episodes of unusually warm and wet conditions interrupting long periods of cool and dry conditions usual for calcareous red paleosols some of these paleoclimatic events are known from stomatal index of fossil lepidopteris leaves to have been episodes of elevated global atmospheric co2 the magnitude of 19 known permian and triassic greenhouse crises varied considerably and they offer new evidence for the relationship between paleoclimate and atmospheric co2 levels these greenhouse crises also had marked effects on global lowland vegetation introducing frost sensitive tropical lycopsids to high latitudes and drought tolerant conifers to low latitude lowlands greenhouse events punctuate phases in plant evolution ottokaria callipteris plumsteadia rufloria lidgettonia tatarina pleuromeia and dicroidium scytophyllum floras greenhouse events also punctuate the evolution of reptilian dynasties successive pelycosaur dinocephalian dicynodont rhynchosaur and dinosaur faunas and respiratory adaptations such as enlarged bony secondary palate greenhouse crises of the late and middle permian were the most severe known and suggest a role for atmospheric pollution with ch4 and co2 in those mass extinction events probably from thermogenic cracking of coals by intrusive feeder dikes of flood basalts because of formalities in boundary definition these mass extinctions are neither end permian nor end guadalupian but upper changhsingian and mid capitanian respectively

new magnetobiostratigraphic results from the ladinian of the dolomites and implications for the triassic geomagnetic polarity timescale abstract we investigated for magnetostratigraphy the rio nigra and rio frommer stratigraphic sections from alpe di siusi seiser alm dolomites northern italy in order to improve the calibration of the triassic time scale both sections are characterized by ammonoid and conodont associations typical of longobardian late ladinian middle triassic age moreover the rio nigra section is constrained by a u pb zircon date of 237 77 0 05 ma building on the recently verified newark hartford astrochronological polarity timescale for the late carnian rhaetian plus the hettangian and through magnetostratigraphic correlations of an updated inventory of tethyan marine stratigraphic sections from the literature some of which are provided with u pb zircon age constraints we propose a revised geomagnetic polarity time scale for the entire triassic

conjunctive use of spectral gamma ray logs and clay mineralogy in defining late jurassic early cretaceous palaeoclimate change dorset u k abstract detrital clay mineralogy is controlled by weathered source rock climate transport and deposition that in turn influence the spectral gamma ray sgr response of resultant sediments whilst a palaeoclimate signal in clay mineralogy has been established in some ancient successions the sgr response remains contentious largely because the data sets have yet to be collected at the same or appropriate vertical scales to allow comparison in addition the influence of organic matter on sgr is not always considered here we present clay mineralogical total organic carbon toc and sgr analyses from the late jurassic and early cretaceous of the wessex basin a period of previously documented palaeoclimate change the aim of this paper is to estimate the sensitivity of sgr as palaeoclimatic tool sgr and clay mineral data having been collected at the same sample points making this one of the most rigorous comparison of clay mineral and sgr to date overall the correlation between high thorium potassium or thorium uranium and kaolinite associated with a well established palaeoclimate change shows that elevated thorium may be used as a proxy for humid palaeoweathering as suggested by few previous studies

long term cycles of triassic climate change a new δ18o record from conodont apatite jat and isw gratefully acknowledge financial support from the australian research council dp1096252 mr is grateful for financial support from progetto d ateneo 2009 cpda090175 09 and 2012 cpda 121100 and prin 2008 2008bef5z7 005

infiltration of fine sediment into a coarse mobile bed a phenomenological study experiments were undertaken to study the nature of granular interaction in running water by examining the influence of fine grain inputs to a coarser sediment bed with a mobile surface video recordings of grain sorting by both kinetic sieving and spontaneous percolation are used to diagnose the critical processes controlling the overall bed response kinetic sieving takes place in the mobile bed surface with the finer sediment moving to the bottom of the bedload transport layer at the interface with the underlying quasi static coarse bed we show that the behavior at this interface dictates how a channel responds to a fine sediment input if by spontaneous percolation the fine sediment is able to infiltrate into the underlying quasi static bed the total transport increases and the channel degrades however if the fine sediment input rate exceeds the transport capacity or is geometrically unable to infiltrate into the underlying bed it forms a quasi static layer underneath the transport layer that inhibits entrainment from the underlying bed resulting in aggradation and an increase in bed slope this article is protected by copyright all rights reserved

early triassic productivity crises delayed recovery from world s worst mass extinction the recovery of life after the latest permian extinction was protracted over early triassic time detailed geochemistry of marine sections along northwest pangea indicates that upwelling ceased at the extinction event nitrogen stable isotope data suggest that this was associated with progressive increase in nutrient stress throughout the early triassic coincident with a significant decrease in organic carbon content despite pervasive anoxic to euxinic conditions we argue that the early triassic hothouse both reduced marine productivity and deepened the nutricline reducing the overall rate of nutrient delivery to the photic zone creating an early triassic nutrient gap when oceans finally cooled by middle triassic time renewed nutrient upwelling and onset of organic rich shale deposition occurred across northwest pangea marking the final return of global marine productivity

magnetostratigraphy of the lower triassic beds from chaohu china and its implications for the induan olenekian stage boundary a magnetostratigraphic study was performed on the lower 44 m of the west pingdingshan section near chaohu city anhui province china in order to provide a magnetic polarity scale for the early triassic data from 295 paleomagnetic samples are integrated with a detailed biostratigraphy and lithostratigraphy the tilt corrected mean direction from the west pingdingshan section passes the reversal and fold tests the overall mean direction after tilt correction is d 299 9 i 18 3 305 2 95 1 9 n 19 the inferred paleolatitude of the sampling sites 31 6 n 117 8 e is about 9 4 consistent with the stable south china block scb though the declinations indicate some 101 counter clockwise rotations with respect to the stable scb since the lower triassic low field anisotropy of magnetic susceptibility indicates evidence of weak strain the lower part of the yinkeng formation is dominated by reversed polarity with four normal polarity magnetozones wp2n to wp5n with evidence of some thinner 0 5 m thick normal magnetozones the continuous magnetostratigraphy from the yinkeng formation provides additional high resolution details of the polarity pattern through the later parts of the induan into the lowest olenekian the magnetostratigraphic and biostratigraphic data show that the conodont marker for the base of the olenekian first presence of neospathodus waageni is shortly prior to the base of normal magnetozone wp5n this provides a secondary marker for mapping the base of the olenekian into successions without conodonts this section provides the only well integrated study from a tethyan section across this boundary but problems remain in definitively relating this boundary into boreal sections with magnetostratigraphy

global coal gap between permian triassic extinction and middle triassic recovery of peat forming plants early triassic coals are unknown and middle triassic coals are rare and thin the early triassic coal gap began with extinction of peat forming plants at the end of the permian ca 250 ma with no coal known anywhere until middle triassic 243 ma permian levels of plant diversity and peat thickness were not recovered until late triassic 230 ma tectonic and climatic explanations for the coal gap fail because deposits of fluctuating sea levels and sedimentary facies and paleosols commonly found in coal bearing sequences are present also in early triassic rocks nor do we favor explanations involving evolutionary advances in the effectiveness of fungal decomposers insects or tetrapod herbivores which became cosmopolitan and much reduced in diversity across the permian triassic boundary instead we favor explanations involving extinction of peat forming plants at the permian triassic boundary followed by a hiatus of some 10 m y until newly evolved peat forming plants developed tolerance to the acidic dysaerobic conditions of wetlands this view is compatible not only with the paleobotanical record of extinction of swamp plants but also with indications of a terminal permian productivity crash from delta sup 13 c sub org and total organic carbon of both nonmarine and shallow marine shales 205 refs 3 figs more 3 tabs less

insolation forcing of sub lacustrine debris flows could monsoon intensification have played a role eocene lacustrine green river formation piceance creek basin colorado abstract mudstone breccias deposited by debris flows in the lacustrine green river formation of the piceance creek basin colorado may not represent random and unpredictable events as previously thought spectral analysis of mudstone breccia beds in the wolfridge minerals john savage 24 1 basin center core reveals a record of short eccentricity 94 58 kyr obliquity 50 78 kyr and 39 26 kyr and precession 21 85 kyr and 18 56 kyr of particular interest to this investigation are the records of eccentricity and precession together which indicate that insolation forcing of monsoons occurred every 18 21 kyr and that every 94 kyr insolation maxima exceeded a threshold of 528 w m2 resulting in more significant monsoon amplification strengthened monsoon activity would have led to an increase in precipitation and runoff delivered to the lake this increase in inflow resulted in lake level rise which in turn decreased basin slope stability and triggered periodic sub lacustrine debris flows that deposited the mudstone breccias

timing of the early triassic carbon cycle perturbations inferred from new u pb ages and ammonoid biochronozones based on analyses of single thermally annealed and chemically abraded zircons a new high precision u pb age of 251 22 0 20 ma is established for a volcanic ash layer within the kashmirites densistriatus beds of early smithian age early triassic from the luolou formation northwestern guangxi south china this new date together with recalculated uncertainties of previous u pb ages from the same section m ovtcharova h bucher u schaltegger t galfetti a brayard j guex new early to middle triassic u pb ages from south china calibration with ammonoid biochronozones and implications for the timing of the triassic biotic recovery earth planet sci lett 243 2006 463 475 allows constraining the time framework of the early triassic and leads to an estimated duration of i ca 0 7 0 6 my for the smithian and ii a maximal duration of ca 1 4 0 4 my for the griesbachian dienerian time interval the new u pb age considerably reduces the absolute age gap comprised between the permian triassic boundary and the spathian late early triassic the new age framework provides the basis for the calibration of a new carbonate carbon isotope and ammonoid records of the early triassic luolou fm which in turn are of high significance for global correlations and for carbon cycle modeling this calibration indicates that the most significant and fastest early triassic carbon isotope perturbations occur between the earliest smithian and the early spathian thus spanning a time interval of about 1 my whatever caused these carbon cycle shifts of high intensity and short duration there is evidence for connections between these fluctuations the pulsate recovery of ammonoids and conodonts as well as climate changes

exceptional vertebrate biotas from the triassic of china and the expansion of marine ecosystems after the permo triassic mass extinction abstract the triassic was a time of turmoil as life recovered from the most devastating of all mass extinctions the permo triassic event 252 million years ago the triassic marine rock succession of southwest china provides unique documentation of the recovery of marine life through a series of well dated exceptionally preserved fossil assemblages in the daye guanling zhuganpo and xiaowa formations new work shows the richness of the faunas of fishes and reptiles and that recovery of vertebrate faunas was delayed by harsh environmental conditions and then occurred rapidly in the anisian the key faunas of fishes and reptiles come from a limited area in eastern yunnan and western guizhou provinces and these may be dated relative to shared stratigraphic units and their palaeoenvironments reconstructed the luoping and panxian biotas both from the guanling formation are dated as anisian pelsonian on the basis of conodonts and radiometric dates the former being slightly older than the latter the xingyi biota is from the zhuganpo formation and is ladinian or early carnian while the guanling biota is from the overlying xiaowa formation dated as carnian the first three biotas include extensive benthos and burrowing in the sediments and they were located in restricted basins close to shore further even though the luoping and panxian biotas are of similar age their faunas differ significantly reflecting perhaps palaeogeographically isolated basins between the time of the xingyi and guanling biotas there was a major transgression and the guanling biota is entirely different in character from the other three being dominated by pelagic forms such as large floating crinoids attached to logs very large ichthyosaurs and thalattosaurs and pseudoplanktonic bivalves with no benthos and no burrowing phylogenetic study of the fishes and marine reptiles shows apparently explosive diversification among 20 actinopterygian lineages very early in the early triassic but a later expansion of marine reptile groups in the late olenekian and early anisian this offset in diversification patterns is matched by comparisons of feeding guild categories and body size data new research tools will shed considerable light on the phylogenetic and ecological implications of recovery of mairne vertebrates in the triassic

early middle triassic boundary interval integrated chemo bio magneto stratigraphy of potential gssps for the base of the anisian stage in south china abstract the wantou and youping sections of guangxi south china provide a detailed high resolution integrated calibration of the early middle triassic boundary succession for lithostratigraphy volcanic episodes conodont first occurrences fos ammonoid biostratigraphy geomagnetic polarity inorganic carbon isotopes sea surface temperatures derived from conodont apatite oxygen isotopes and id tims u pb radiometric dating the upper spathian late early triassic magnetostratigraphy is characterized by normal polarity magnetozone lt9n that encompasses the fos of the typical spathian conodonts triassospathodus homeri and gladigondolella carinata the late spathian neopopanoceras haugi ammonoid zone and the beginning of a progressive positive shift in inorganic carbon isotopes the overlying reversed polarity interval lt9r contains two brief normal polarity subzones mt1n and mt2n that can be recognized in several other marine and terrestrial sections the fo of conodont chiosella timorensis sensu stricto a proposed base anisian global marker is near mt1n and near the end of the positive 13 ccarb excursion sea surface temperatures were reported to have cooled by 4 c during this rise in 13 ccarb suggesting a sequestration of carbon dioxide the lowermost anisian at wantou and youping is dominated by normal polarity mt3n with the presence of one major reversed polarity subzone mt3n 1r contains the fo of typical anisian conodonts gladigondolella tethydis magnigondolella alexanderi and has the onset of a plateau in inorganic carbon isotopes values stabilizing around 4 the combination of the fo of conodont chiosella timorensis s s the brief normal polarity zone mt1n and the last portion of the rising carbon isotope trend are suitable for primary proxies for global correlation of the early middle triassic boundary base of anisian to other marine and non marine settings radiometric dates at the wantou and at the guandao sections coupled with a composite cyclostratigraphy for early triassic through anisian indicate that the fo of the conodont chiosella timorensis s s is at approximately 246 7 ma

rate and synchronicity of environmental changes on a shallow carbonate platform late oxfordian swiss jura mountains recent global change occurs within decades and leaves a significant imprint on shallow carbonate platforms to what extent can rate and synchronicity of environmental changes in the past be evaluated in order to allow comparisons with the processes and products of today sections of a carbonate dominated platform of late oxfordian age have been logged in detail in the swiss jura mountains the time frame based on ammonite biostratigraphy and the hierarchical stacking of the sedimentary sequences suggests that these formed by low amplitude high frequency sea level changes in tune with the orbital cycles the smallest unit the elementary sequence can thus be attributed to the 20 kyr precession cycle by identifying sequence stratigraphic elements such as maximum flooding surfaces within an elementary sequence an even higher time resolution can be obtained and reconstructions of changes in water depth and sea level are attempted sedimentation rates were highly irregular and discontinuity surfaces are common correlation of such surfaces from one section to the other is tentative because they could also have formed locally and are not necessarily synchronous on the scale of elementary sequences the vertical facies evolution permits interpretation of changes in water depth which were produced by eustatic sea level changes allocyclic and or by autocyclic processes the distribution of clay minerals indicates changes of sea level as well as of rainfall in the hinterland biotic changes were controlled by water depth and water quality and also by nutrient and clay input carbon and oxygen isotopes do not show significant shifts within the elementary sequences the original ecological mineralogical and geochemical signals have partly been homogenized because of time averaging through bioturbation and through reworking by storms and because of diagenetic modifications consequently there is potential to interpret environmental changes on the studied carbonate platform but the time resolution is not better than a few thousand years the rates and the synchronicity of the processes leading to the observed environmental changes can thus be estimated only within this time frame

quantification of deep time orbital forcing by average spectral misfit quantification of milankovitch orbital cyclicity within ancient strata has become a principal tool for refinement of the geologic time scale however accurate characterization of the orbital signal in deep time paleoclimate records is commonly challenged by inadequate radiometric time constraints for calibration of the spatial rhythms to temporal periods this problem can potentially introduce large errors into derivative orbital timescales in this study we develop a new method for the identification and calibration of orbital cyclicity in cyclostratigraphic records the method average spectral misfit or asm yields an objective estimate of the optimal sedimentation rate for a stratigraphic interval that preserves a record of orbital forcing the technique also provides a formal statistical test for rejecting the null hypothesis no orbital signal application of the method to assess orbital cyclicity in the upper bridge creek limestone member turonian of the western interior basin highlights the utility of this new cyclostratigraphic tool and provides a means to independently evaluate conflicting interpretations of the lithologic cycles importantly asm offers a new consistent standard by which orbital timescales may be compared hence the quality of an orbital timescale can be formally qualified by reporting its average spectral misfit and null hypothesis significance level this technique will permit improvement of mesozoic cenozoic orbital timescales and extension of orbital time scale development into the paleozoic as the method is not dependent upon well constrained radiometric age data

tracking variable sedimentation rates and astronomical forcing in phanerozoic paleoclimate proxy series with evolutionary correlation coefficients and hypothesis testing abstract this paper addresses two fundamental issues in cyclostratigraphy and paleoclimatology identification of astronomical forcing in sequences of stratigraphic cycles and accurate evaluation of variable sedimentation rates the technique presented here considers these issues part of an inverse problem and estimates the product moment correlation coefficient between the power spectra of astronomical solutions and paleoclimate proxy series across a range of test sedimentation rates the number of contributing astronomical parameters in the estimate is also considered our estimation procedure tests the hypothesis that astronomical forcing had a significant impact on proxy records the null hypothesis of no astronomical forcing is evaluated using a monte carlo simulation approach the test is applied using a sliding stratigraphic window to track variable sedimentation rates along the paleoclimate proxy series in a procedure termed ecoco evolutionary correlation coefficient analysis representative models with constant and variable sedimentation rates and pure noise and mixed signal and noise series are evaluated to demonstrate the robustness of the approach the method is then applied to cenozoic mesozoic and paleozoic paleoclimate series the cenozoic case study focuses on a high resolution paleocene eocene iron concentration series from odp site 1262 leg 208 covering the paleocene eocene thermal maximum and eocene thermal maximum 2 events the ecoco time calibrated iron series confirms previous findings of a role for long term astronomical forcing of these eocene events the mesozoic case study applies ecoco to the classic late triassic newark depth rank series of eastern north america the estimated high resolution sedimentation rate map in this case demonstrates a causal link between variations in depositional environment and sedimentation rate finally the paleozoic case study supports the cyclostratigraphic interpretation of a devonian magnetic susceptibility series at la thure belgium and provides new insights into changes of the depositional setting at this location taken together ecoco is a powerful tool for simultaneously evaluating sedimentation rates and astronomical forcing for paleoclimate series throughout the phanerozoic

timing of recovery from the end permian extinction geochronologic and biostratigraphic constraints from south china comment and reply bucher et al s comment 2007 1 on our recently reported age for the olenekian anisian boundary in south china lehrmann et al 2006 2 concerns a discrepancy between our results and a preliminary age from a nearby section reported in a field excursion guide lehrmann et al 2005 3

resolving milankovitchian controversies the triassic latemar limestone and the eocene green river formation although orbital forcing is commonly proposed as the driver of ancient sedimentary rhythms the lack of adequate independent time control radio isotopic data to calibrate these cycles has stood as a major challenge to evaluation of the hypothesis here i apply a new statistical approach to evaluate cyclicity in two historically important rhythmic units for which orbital forcing has been proposed the triassic latemar limestone dolomites italy and the eocene green river formation wyoming usa a major advance of the new method is its explicit evaluation of the null hypothesis of no orbital signal the null hypothesis can be rejected with a high degree of confi dence in the latemar limestone probability 0 30 and green river formation probability 0 07 the analyses also resolve controversies about the specifi c orbital calibrations at each site both data series reveal the expected precession obliquity and eccentricity orbital components and yield astrochronologies that are consistent with proposed radio isotopic based time scales

high resolution stratigraphy and zircon u pb geochronology of the middle triassic buchenstein formation dolomites northern italy precession forcing of hemipelagic carbonate sedimentation and calibration of the anisian ladinian boundary interval orbitally forced cyclic variations in sedimentary sequences provide evidence for short term fluctuations of earth climate and a tool for high resolution timescale calibration we here present stratigraphic and geochronological evidence for precession forcing in middle triassic hemipelagic limestones of the buchenstein formation dolomites northern italy high resolution stratigraphy of several correlative sections of the buchenstein formation documents a coherent cycle pattern isotope dilution thermal ionization mass spectrometry zircon u pb geochronology of tuffs bracketing the cyclic interval reveals an average cycle duration of 18 5 2 1 kyr consistent with a shorter climatic precession cycle in the middle triassic compared with today this suggests a predominantly precession controlled climate in this low latitude setting of the western tethys and allows high precision calibration of the anisian ladinian boundary interval from integrating cyclostratigraphic and u pb geochronological constraints our best estimate for the age of the anisian ladinian boundary is 241 464 0 064 0 097 0 28 ma we also provide precise estimates for lithostratigraphic boundaries biostratigraphic markers and magnetic reversals within the boundary interval stratigraphic intervals with elevated sedimentation rate record a sub milankovitch signal that may be equivalent to patterns in adjacent carbonate platforms such as the latemar platform the origin of this sub milankovitch signal remains unknown but highlights the potential to investigate shorter term climatic variations in mesozoic sedimentary sequences supplementary material isotope dilution thermal ionization mass spectrometry u pb and laser ablation inductively coupled plasma mass spectrometry trace element data tables as well as the results of the bayesian age modelling are available at https doi org 10 6084 m9 figshare c 3861817

astronomical forcing of terrestrial climate recorded in the pleistocene of the western tarim basin nw china abstract astronomically forced variations of climate are well documented in lacustrine and marine settings however few studies have examined astronomical forced cycles within quaternary fluvial fan successions to explore whether milankovitch cyclicity might also be present in fluvial fan successions we carried out high resolution gamma ray gr from downhole logging magnetic susceptibility ms rb sr and total organic carbon toc analysis of a core from an 800 m borehole kt11 from the kashgar region in the western tarim basin china spectral analyses of the gr ms and rb sr data reveal cycles with 70 m 30 m and 14 m wavelengths these pertain to relative variations in grain size electron spin resonance esr dating and magnetostratigraphy imply that the cored interval spans the past 1 1 myr this age span constraint coupled with the comparison of the ratios of these cycle wavelengths to expected ratios of milankovitch frequencies suggests that these cycles represent 100 kyr short eccentricity 40 kyr obliquity and 20 kyr precession frequencies respectively we constructed an astronomical time scale ats spanning the past 1 13 myr using the 100 kyr short eccentricity period the average accumulation rate is about 70 cm kyr for this 800 m core succession and the evolutive spectrum emphasizes that long term sedimentation rates were stable we also applied correlation coefficient coco analysis to identify the astronomical forcing thus we conclude that orbitally forced climate change was the main driver of stratigraphic alternations between sand and clay rich intervals in the kashgar region during maxima of the 100 kyr short eccentricity cycles which correspond to interglacial intervals more chemical weathering and increased seasonal runoff delivered a larger amount of relatively coarser grained sediments to the fluvial fan in the kashgar region and vice versa the mid pleistocene transition mpt at ca 0 9 to 0 65 ma is also well recorded in our gr and rb sr data and is characterized by a shift in dominant cycle period from 41 kyr obliquity to 100 kyr eccentricity after 0 65 ma the average toc content decreases whilst rb sr values increase which suggests that there was an increase in regional aridity of the kashgar region in the western tarim basin following the mpt this regional change is synchronous with the trend toward aridification observed throughout central asia

controls on facies architecture of a large triassic carbonate platform the great bank of guizhou nanpanjiang basin south china abstract the great bank of guizhou gbg is an exceptionally well exposed isolated triassic platform in the nanpanjiang basin of south china the platform is exhumed with its depositional profile preserved and is dissected by a faulted syncline that exposes a complete and uncomplicated cross section providing a unique opportunity to evaluate mechanisms involved in its birth evolution and demise the gbg formed near the southern margin of the yangtze platform during a deepening event that expanded the nanpanjiang basin and drowned the region surrounding the gbg in the latest permian initial accumulation of the gbg began in the latest permian with small reef mounds and open marine skeletal packstones following the end permian extinction cyanobacterial boundstones grew over the bank top during the early triassic the gbg developed a low relief bank profile with mobile oolite shoals at the margin shallow subtidal and peritidal deposits in the interior and gentle slopes dominated by pelagics debris flow deposits and turbidites at the basin margin in the middle triassic anisian the gbg developed a progressively steepening profile rimmed with massive tubiphytes reefs the platform was flat topped with tidal flat deposits across the interior basin margin deposition was dominated by turbidites and debris flow deposits but eventually shifted to avalanche and rock fall deposits as the slopes steepened to the angle of repose in the middle triassic ladinian an erosional escarpment up to 1700 m high developed at the margin platform margin strata are bedded packstones similar to interior strata whereas breccias at the basin margin contain coral boundstone clasts suggesting erosion of reefs from the escarpment a restricted subtidal lagoon formed in the interior producing an atoll like morphology later a flat topped profile was restored as tidal flats spread across the interior in the beginning of the late triassic deepening contributed to termination of the gbg before siliciclastic turbidites and shales were deposited over the platform in contrast with the well known platforms of the dolomites of northern italy the gbg contains abundant muddy carbonates and a progressively steepening bank to reef rimmed and escarpment architecture the italian platforms contain little mud and have angle of repose pinnacle geometries the gbg s larger size increased mud production and protected it from extensive winnowing of mud which in turn resulted in off bank shedding of muddy sediments that were stable on relatively gentle basin margin slopes which progressively steepened and ultimately led to avalanche deposits and a high relief erosional escarpment in contrast the lesser mud content of the dolomites platforms forced avalanche and talus deposition to dominate throughout deposition of basin margins which in turn produced their angle of repose geometries

recovery tempo and pattern of marine ecosystems after the end permian mass extinction high resolution sampling of more than 10 000 microfossils from seven late permian middle triassic paleoequatorial sections in south china refutes claims for a 5 m y recovery delay after the end permian mass extinction we show that level bottom seafloor diversity began to recover in the early smithian little more than 1 m y after the mass extinction while recovery of reef building metazoans began 4 m y later in the anisian a further mass extinction in the late smithian identified in the pelagic fossil record is weakly manifest as a temporary pause in diversification among benthic communities in the early triassic of south china the offshore diversity increase began before then in shallower settings the recovery from the end permian mass extinction in south china was therefore significantly more rapid and environmentally more complex than hitherto known

microfacies and multi isotope records of anisian sequences from the upper yangtze block possible responses to tectonics and climate driven relative sea level change the middle triassic epoch is the key to understanding the environment changes after the permian triassic mass extinction the anisian badong formation is a carbonate and siliciclastic succession deposited on the yangtze platform upper yangtze block in this paper we use facies analysis combined with sequence stratigraphy of the badong formation in the nashuixi section yangtze block to discuss the anisian relative sea level changes microfacies analyses were used to define ten microfacies in four depositional facies zones tidal flat restricted platform restricted to open platform and open platform indicating an epeiric platform depositional environment the lowstand transgressive and highstand systems tracts and two sequences were identified sequence stratigraphy interpretations indicate that relative sea level at nashuixi experienced two rises in the middle anisian which is correlated with those in the yangtze block confirming that sea level changes during the anisian were of eustatic origin however a distinct regression at nashuixi occurred in the late bithynian to iiiyrian while the global sea level rose which is likely to be caused by interference from regional tectonics during iiiyrian the carbon and oxygen isotopic shifts in the nashuixi section exhibit two negative values stage in the time near end of aegean and early pelsonian which is well correlated with the global typical sections indicating two middle anisian warming events our study indicated that the relative sea level at nashuixi was controlled by global sea level change and regional tectonics indosinian orogeny and the c and o isotopes records respond to global climate change

high precision time space correlation through coupled apatite and zircon tephrochronology an example from the permian triassic boundary in south china accurate and precise dating of individual volcanogenic beds that spread across multiple sedimentary successions is a powerful tool to untangle stratigraphic age contradictions since these horizons are deposited synchronously in this study we show that combining apatite chemistry with zircon age th u ratio and hf isotope composition leads to reliable lateral correlation of volcanic horizons across sections representing disparate biological chemical and physical paleoenvironments we correlate two volcanogenic horizons across six sedimentary sections straddling the permian triassic boundary ptb in the nanpanjiang basin south china including the last permian bed below the unconformity in shallow water sections of the luolou platform we place the ptb in our sections at the marked lithological change in order to avoid the difficulties that arise from the diachronism of the index conodont hindeodus parvus the first occurrence of which defines the ptb at the global stratotype section and point at meishan our new data demonstrate that these volcanogenic beds are contemporaneous and cogenetic allowing us to pool high precision u pb zircon ages from the same horizon across several sections and dating the last permian volcanic event in this basin at 252 048 0 033 ma we show that the mineral chemistry of apatite and zircon of intra and interbasin wide volcanogenic beds provides tie points against which biozones carbon isotopes astronomic cycles and geomagnetic polarity time series can be stringently tested

an assessment of the suitability of individual rhythmic carbonate successions for astrochronological application abstract a manual is presented to assist in assessing the suitability of individual calcareous rhythmites for high resolution stratigraphic applications and orbital dating while the astrochronological approach offers an unprecedented high temporal resolution for stratigraphy caution is required to carefully choose suitable rhythmites for the analysis diagenesis is known to distort or mimic primary signals in particular in carbonate rhythmites to keep orbital dating a reliable method the choice of sedimentary successions has to be undertaken with utmost scrutiny here we review and evaluate the methods that have been used for assessing the record of primary signals in calcareous rhythmites the goal is to provide the orbital stratigrapher with tools for a straightforward and systematic assessment of such successions

are light dark coupled laminae in lacustrine shale seasonally controlled a case study using astronomical tuning from 42 2 to 45 4 ma in the dongying depression bohai bay basin eastern china abstract as a typical sedimentary structure in fine grained rocks laminae are widely distributed in shales and mudstones in sedimentary basins the shahejie formation 42 2 45 4 ma formed during the eocene of the paleogene in the dongying depression of china is recognized as a typical area to study lacustrine shale according to the composition of different lamina four types of couplets are identified including carbonate clay couplets carbonate organic couplets clay organic couplets and carbonate clay organic triplets all couplets are composed of light and dark layers a combination of core images microscopic observations mineral compositions geochemical data carbon and oxygen isotopes and strontium isotopes verifies that the laminae are primarily developed in a saline and anoxic or even euxinic environment with a high organic matter om flux through astronomical cycle analysis of the natural gamma ray gr curve from sample site well ny1 the data suggest that the lacustrine shale laminae are formed annually with an average duration of 1 34 yr the formation of laminae is affected by the season which is closely related to the seasonal growth and death of algae during the period of algae growth a large number of light colored carbonate laminae are deposited whereas when the algae dies organic matter accumulates at the bottom of lakes and forms dark organic rich laminae the interbedded and lenticular laminae which are subdivided by layering characteristics are primarily affected by diagenesis in postdepositional processes study of the laminae is helpful in understanding the formation process of lacustrine shale and it provides invaluable sources of information for paleoclimate reconstruction

large perturbations of the carbon cycle during recovery from the end permian extinction high resolution carbon isotope measurements of multiple stratigraphic sections in south china demonstrate that the pronounced carbon isotopic excursion at the permian triassic boundary was not an isolated event but the first in a series of large fluctuations that continued throughout the early triassic before ending abruptly early in the middle triassic the unusual behavior of the carbon cycle coincides with the delayed recovery from end permian extinction recorded by fossils suggesting a direct relationship between earth system function and biological rediversification in the aftermath of earth s most devastating mass extinction

cyclostratigraphy of the global stratotype section and point gssp of the basal guzhangian stage of the cambrian period abstract the cambrian is the first period of the phanerozoic during which numerous major geological and biological events occurred understanding these events requires a high resolution time scale the luoyixi section in guzhang hunan province china is the global stratotype section and point gssp for the guzhangian stage here magnetic susceptibility and 13c data were used to conduct cyclostratigraphic analyses covering the upper drumian through lower guzhangian stages the results of the power spectral analyses and average spectral misfit analyses indicate that the 25 25 53 m 6 25 6 91 m 1 90 2 03 m and 1 08 1 19 m sedimentary cycles may represent long eccentricity short eccentricity obliquity and precession cycles respectively a 1400 kyr floating astronomical time scale was constructed using the stable 405 kyr eccentricity cycles to calibrate the agnostoid trilobite zones the obtained fundamental obliquity period 30 7 0 7 kyr implies 370 180 1220 km vs 384 000 km for present day for the earth moon distance and 21 58 0 18 h vs 23 93 h for present day for the length of day during the middle cambrian 500 ma

latest permian to middle triassic cyclo magnetostratigraphy from the central european basin germany implications for the geomagnetic polarity timescale in central germany the about 1 km thick mainly clastic germanic lower triassic buntsandstein consists of about 60 sedimentary cycles which are considered to reflect variability in precipitation within the epicontinental central european basin most probably due to solar induced short eccentricity cycles they provide a high resolution cyclostratigraphic framework that constitutes the base for creating a composite geomagnetic polarity record in which this paper presents a middle buntsandstein to lowermost muschelkalk magnetostratigraphy obtained from 6 outcrops and 2 wells where a total of 471 samples was collected combined with recently established records a well documented magnetostratigraphy for the upper zechstein to lowermost muschelkalk latest permian to middle triassic of central germany has been constructed encompassing an overall stratigraphic thickness of about 1 3 km and 22 magnetozones derived from about 2050 paleomagnetic samples along with available biostratigraphy this multi disciplinary study facilitates detailed links to the marine realm in order to directly refer biostratigraphically calibrated triassic stage boundaries as well as radioisotopic ages to the buntsandstein cyclostratigraphy and conversely to contribute to calibrating the geologic timescale 2007 elsevier b v all rights reserved

astronomical forcing and sedimentary noise modeling of lake level changes in the paleogene dongpu depression of north china abstract challenges in interpreting continental sequence stratigraphy and typically uncertain geochronology hinder the understanding of paleolake evolution and hydrocarbon exploration in terrestrial basins the dongpu depression in north china is a lacustrine basin with abundant hydrocarbon resources an accurate chronology for the paleogene stratigraphy in the dongpu depression is lacking and the mechanism of lake level variation remains unclear in this study we utilize high resolution gamma ray logs to conduct a cyclostratigraphic analysis of the shahejie formation which is a paleogene succession in the dongpu depression characterized by sandstones and dark mudstones interbedded with thin salt rocks time series analysis reveals evidence for 405 kyr eccentricity cycles in the gamma ray series which is supported by statistical modeling of optimal sedimentation rates tuning of the gamma ray data to this 405 kyr eccentricity cyclicity enables a 14 7 myr long astronomical time scale to be constructed this astrochronology is anchored to the astronomical age of the dongying formation shahejie formation boundary 28 86 ma in the bohai bay basin thus providing an absolute timescale for the studied interval that extends from 28 86 ma to 43 59 ma using this anchored astrochronology we show that a recently established sedimentary noise model for inferring sea level change in marginal marine settings can be used to similarly infer lake level fluctuations in terrestrial basins in particular sedimentary noise modeling of the tuned gamma ray series reveals high resolution changes in sedimentary noise that are indicative of lake level variations linked to million year scale i e 4 8 myr 2 4 myr and 1 2 myr astronomical forcing these inferred changes in lake level are supported by previously published sequence stratigraphic interpretations moreover an evolutionary correlation coefficient ecoco analysis of the gamma ray series also indicates recurrent distortions in sedimentation that may be linked to lake level changes this study provides new methods for the assessment of paleolake level variations as well as insights into the connection between astronomical forcing and lake evolution across long timescales in terrestrial basins

effects of sand addition on turbulent flow over an immobile gravel bed 1 the factors controlling the complex interaction of a coarse streambed with flow and sediment are difficult to measure however planning for reservoir flushing or dam removal requires knowledge of these interactions in both cases impounded sediments are introduced to channel beds that have had fine sediment particles removed without replacement the channel bed pore space interacts with the flow and provides storage for particles in order to address the need for information on such systems an adjustable slope recirculating laboratory flume was used to study the changes in flow and turbulence caused by sand added to an immobile gravel bed detailed measurements were made using an acoustic doppler velocimeter that collected three velocity components at a rate of 200 hz because of the rough nature of the bed individual velocity profiles varied significantly therefore in order to determine general trends the data were spatially averaged over six 10 20 cm planes parallel to the bed with the lowest plane about 2 cm below the maximum gravel elevation the increasing elevation of sand relative to the gravel layer resulted in decreased bed shear stress decreased reynolds stress increased relative turbulence intensity and a near bed shift toward sweep dominated turbulence

obliquity forced climate during the early triassic hothouse in china the start of the mesozoic era is marked by roughly 5 m y of earth system upheavals including unstable biotic recovery repeated global warming ocean anoxia and perturbations in the global carbon cycle intervals between crises were comparably hospitable to life the causes of these upheavals are unknown but are thought to be linked to recurrent siberian volcanism here two marine sedimentary successions at chaohu and daxiakou south china are evaluated for paleoclimate change from astronomical forcing in these sections gamma ray variations indicative of terrestrial weathering reveal enhanced obliquity cycling over prolonged intervals characterized by a 32 8 k y periodicity with strong 1 2 m y modulations these suggest a 22 h length of day and 1 2 m y interaction between the orbital inclinations of earth and mars comparing the 1 2 m y obliquity modulation cycles in these sections with early triassic records of global sea level temperature redox and biotic evolution suggests that long term astronomical forcing was involved in the repeated climatic and biotic upheavals that took place throughout the early triassic

cyclostratigraphy and astrochronology case studies from china abstract a high precision geologic time scale is the essential key for understanding the earth s evolutionary history and geologic processes astronomical tuning of orbitally forced stratigraphic records to construct high resolution astronomical time scales ats has led to a progressive refinement of the geologic time scale over the past two decades in turn these studies provide new insights regarding the durations and rates of major earth events evolutionary processes and climate changes all of which provide a scientific basis for contextualizing and predicting future global change trends south china hosts some of the best exposed and well dated neoproterozoic through mesozoic stratigraphic sections in the world many of which are suitable for cyclostratigraphy and calibrating the geologic time scale in north china several cenozoic oil bearing basins have deep boreholes with continuous sampling and or well logging that enable derivation of astronomically tuned time scales for an improved understanding of basin evolution and hydrocarbon generation this special issue focuses on case studies of astrochronology and applied cyclostratigraphy research using reference sections within china in this introductory overview we 1 summarize all existing astrochronology studies of the neoproterozoic through cenozoic sections within china that have been used to enhance the international geologic time scale 2 examine briefly the astronomically forced paleoclimate information recorded in various depositional systems and the modern techniques employed to analyze the periodicity of these signals encoded within the sedimentary record and 3 summarize the 20 contributions to this special issue of palaeogeography palaeoclimatology palaeoecology on cyclostratigraphy and astrochronology case studies from china

particle velocity and concentration profiles in bedload experiments on a steep slope depth profiles of particle streamwise velocity concentration and bedload sediment transport rate were measured in a turbulent and supercritical water flow one size 6 mm diameter spherical glass beads were transported at equilibrium in a two dimensional 10 steep channel with a mobile bed flows were filmed from the side by a high speed camera particle tracking algorithms made it possible to determine the position velocity and trajectory of a very large number of particles approximately half of the sediment transport rate was composed by rolling grains and the other half by saltation this revealed a complex structure with several concentration and flux peaks due to rolling and one peak due to saltation with an increase of the sediment transport rate the depth structure remained the same at the water granular interface with peak value increases but with no shift in elevations the saltation region expanded towards higher elevations with an increase of the particle velocity commensurate to the water velocity the proportion of the sediment transport rate in saltation did not vary significantly the particle streamwise velocity profiles exhibited three segments an exponential decay in the bed a linear increase where rolling and saltation co existed and above this a logarithmic like shape due to saltating particles these results are comparable to profiles measured and modelled in dry granular free surface flows and in more intense bedload such as sheet flows copyright 2014 john wiley sons ltd

astronomically forced variations in gamma ray intensity late miocene hemipelagic successions in the eastern mediterranean basin as a test case amplitude variations of the gamma ray record of late miocene hemipelagic successions on crete correlate remarkably well with the amplitude variations of a published theoretical insolation curve chemical analyses of the sediments show a linear relation between radiation total counts above 400 kev and u enrichment due to authigenic formation of u containing minerals under anaerobic conditions the studied sections which are paleomagnetically and biostratigraphically and cyclostratigraphically well constrained and more than 100 km apart can be correlated on basis of gamma ray count rates

cycle calibrated magnetostratigraphy of middle carnian from south china implications for late triassic time scale and termination of the yangtze platform abstract thick successions from the margins of the triassic yangtze platform of the south china block record a transition from carbonate rich facies zhuganpo formation and equivalents to clastic rich facies xiaowa formation and equivalents during the carnian early late triassic that mark the final phase of termination of this long lived platform cyclostratigraphy derived from spectral gamma ray sgr intensity curves was combined with magnetostratigraphy of two sections in guizhou province wayao transect and its upward extension into the geopark wayao in guanling county and the laishike section in zhenfeng county and one location in sichuan province hanwang section the cyclostratigraphy from all the guizhou sections indicates a persistent suite of ca 34 m 9 m and 1 8 m cycles which are consistent with the ratios of orbital climate oscillations caused by long eccentricity 405 kyr short eccentricity 100 kyr and precession 20 kyr the magnetostratigraphy of all sections is consistent with the cyclicity and characteristic sgr features thereby enabling a cycle tuned magnetic polarity scale spanning 2 4 myr the main feature is a 1 3 myr interval of reversed polarity containing brief normal polarity subchrons and this reversed polarity chron appears to correspond to the significant reversed polarity dominated interval spanning the upper half of the trachyceras aonoides through the lower half of the austrotrachyceras austriacum ammonoid zones of the upper julian the lower substage of carnian this magnetostratigraphic correlation implies that the termination of the yangtze platform is coeval with the beginning of the mid carnian episode of climatic disruption in europe which is locally called the carnian pluvial event or wet intermezzo and with the temporary cessation of the platform carbonates in the dolomites the cycle scaled magnetic polarity time scale supports the short tuvalian long norian age model of the late triassic in which the base of the cycle tuned polarity pattern from the newark group of eastern north america is younger than the end of the julian substage

climatic and biotic upheavals following the end permian mass extinction the recovery from the end permian mass extinction was slow and prolonged a temperature reconstruction shows that further biotic crises during the recovery were associated with extreme warmth

astrochronology of the anisian stage middle triassic at the guandao reference section south china abstract a high precision global timescale for the early and middle triassic is the key to understanding the nature pattern and rates of biotic recovery following the end permian mass extinction the guandao section of guizhou province of south china is an important reference section for the magnetic polarity pattern conodont datums geochemical anomalies and interpreted temperature history through the anisian middle triassic we analyzed the high resolution gamma ray and magnetic susceptibility series from the complete anisian stage intensity variations are indicative of fluctuating terrestrial clay influxes showing strong signals that match predicted astronomical solutions for eccentricity and precession astronomical tuning of these series to interpreted 405 kyr long eccentricity cycles yields a 5 3 myr duration for the anisian at guandao when combined with the astrochronology of the early triassic then the projected age of the anisian ladinian boundary relative to the base triassic date of 251 9 ma is 241 5 0 1 ma this provides a 10 myr reference timescale for other key geological events including conodont zones geomagnetic polarity chrons rates of marine carbon and oxygen isotope excursions and global sea level changes that were associated with the repeated biotic crises and recovery episodes after the end permian mass extinction the middle anisian humid phase in ca 244 244 5 ma was probably a global event which may have been linked to the middle anisian warming event and sea level change sea level fluctuations at guandao generally correlate with those in western tethyan and boreal regions in time confirming sea level changes during the anisian were of eustatic origin

smithian spathian boundary event evidence for global climatic change in the wake of the end permian biotic crisis one of the most important carbon cycle perturbations following the end permian mass extinction event straddles the smithian spathian boundary ssb olenekian early triassic this anomaly is characterized by a prominent positive carbon isotope excursion known from tethyan marine rocks its global signifi cance is established here by a new high paleolatitude record spitsbergen paleontological evidence such as boreal palynological data barents sea norway and global patterns of ammonoid distribution indicates a synchronous major change in terrestrial and marine ecosystems near the ssb the reestablishment of highly diverse plant ecosystems including the rise of woody gymnosperms and decline of the formerly dominating lycopods is interpreted as an effect of a major climate change this hypothesis is supported by modeling of ammonoid paleobiogeography the distribution patterns of which are interpreted as a proxy for sea surface temperatures sst the latest smithian thus appears to have been a time of a warm and equable climate as expressed by an almost fl at pole to equator sst gradient in contrast the steep spathian sst gradient suggests latitudinally differentiated climatic conditions we propose that this drastic climate change and the global carbon cycle perturbation were triggered by a massive end smithian co2 injection the ssb event could therefore represent one of the causes for stepwise and delayed recovery of marine and terrestrial biotas in the wake of the end permian biotic crisis

astronomical tuning of the end permian extinction and the early triassic epoch of south china and germany abstract the timing of the end permian mass extinction and subsequent prolonged recovery during the early triassic epoch can be established from astronomically controlled climate cycles recorded in continuous marine sedimentary sections astronomical cycle tuning of spectral gamma ray logs from biostratigraphically constrained cyclic stratigraphy through marine sections at meishan chaohu daxiakou and guandao in south china yields an integrated time scale for the early triassic which is consistent with scaling of magnetostratigraphy from climatic cycles in continental deposits of the germanic basin the main marine mass extinction interval at meishan is constrained to less than 40 of a 100 kyr kilo year cycle i e c 13 is estimated to have lasted c 13 from 2 to 4 across the smithian spathian boundary at chaohu was completed in 50 kyr the earliest marine reptiles in the mesozoic at chaohu that are considered to represent a significant recovery of marine ecosystems did not appear until 4 7 myr million years after the end permian extinction the durations of the griesbachian dienerian smithian and spathian substages including the uncertainty in placement of widely used conodont biostratigraphic datums for their boundaries are 1 4 0 1 0 6 0 1 1 7 0 1 and 1 4 0 1 myr implying a total span for the early triassic of 5 1 0 1 myr therefore relative to an assigned 251 902 0 024 ma for the permian triassic boundary from the meishan gssp the ages for these substage boundaries are 250 5 0 1 ma for base dienerian 249 9 0 1 ma for base smithian base of olenekian stage 248 2 0 1 ma for base spathian and 246 8 0 1 ma for the base of the anisian stage this astronomical calibrated timescale provides rates for the recurrent carbon isotope excursions and for trends in sedimentation accumulation through the early triassic of studied sections in south china

magnetostratigraphic confirmation of a much faster tempo for sea level change for the middle triassic latemar platform carbonates new magnetostratigraphic data for the 470 m thick latemar carbonate platform which includes 600 shallowing upward bedding cycles are consistent with litho and biostratigraphic correlations of the section to a 10 m thick interval in the basinal buchenstein beds that most likely represents only 1 m y of deposition according to published u pb single crystal zircon dates a reappraisal of reported cycle stratigraphic analyses of the latemar suggests that the visibly obvious meter scale bedding is not due to milankovitch precessional forcing but rather reflects tempos an order of magnitude faster that may involve millennial scale tidal amplitude variations d 2004 elsevier b v all rights reserved

late ordovician obliquity forced glacio eustasy recorded in the yangtze block south china abstract a high precision time framework is critical for improving our understanding of three major events the late ordovician mass extinction the hirnantian glaciation and the hirnantian isotopic carbon excursion hice in the present study we conducted detailed cyclostratigraphic analysis of a high resolution 1 2 cm intervals anhysteretic remanent magnetization series obtained from the wanhe section in south china covering the lower katian through hirnantian power spectra and derived average spectral misfit results show that the section records the ensemble of milankovitch cycles with 405 kyr long eccentricity 93 125 kyr short eccentricity 33 8 kyr main obliquity and 17 22 kyr precession periods the obliquity period of 33 8 0 46 kyr indicates a precession constant k of 57 19 0 53 arcsec yr a length of day of 22 37 0 12 h and an earth moon distance of 375 330 722 km vs 384 000 km today during the late ordovician 445 ma the ratios of obliquity band power to total power reveal periodicities of 1 32 myr for the s4 s3 term and 173 4 kyr for the s3 s6 term aided by the highly fluctuating magnetic susceptibility ms we recognized a series of 1 32 myr obliquity forced glacio eustatic cycles with three intervals of sea level rise and climate warming trend characterized by high ms values and two episodes of sea level fall and climate cooling trend before the hirnantian the 405 kyr and subsequent 33 8 kyr calibrations produce an 7 36 myr floating astronomical time scale fats for the studied succession indicating that the estimated durations for the hirnantian stage the worldwide hirnantian glaciation and the first and second phases of the late ordovician mass extinction were 1225 kyr 830 kyr 440 kyr and 540 kyr respectively this work provides a reliable high resolution time framework for further investigation of the major geological events occurred in the late ordovician and improves our knowledge of solar system behaviour and earth moon history during that period

the changing climate framework and depositional dynamics of triassic carbonate platforms from the dolomites abstract the triassic of the dolomites offers a valuable opportunity to investigate the relationships between climate fluctuations and the changing depositional dynamics of carbonate platforms the reconstruction of the large palaeoclimatic modification is based on the synthesis of multiple sedimentological palaeobotanical pedological and geochemical proxies the triassic climate fluctuations were generally fast in nature and were probably associated with a latitudinal shift of the monsoon belts during the triassic the dolomites were placed at an intertropical northern latitude of about 16 18 and were generally dominated by dry climate and elevated temperature at least five pulses toward moister climate are however documented dated to early olenekian middle anisian late ladinian middle carnian and late norian times within this variable climatic scenario the carbonate systems record a global evolutionary trend from late permian early triassic regional shelves rich in loose micrites and bio calcarenites to anisian ladinian synsedimentary cemented steep sided 35 40 high relief platforms and back to carnian low angle ramps moist transgressive episodes were surprisingly prone to the spreading of corals and other colonial reef organisms probably because of the reduced space competition by syndepositional cementation structures the permo triassic boundary extinction dramatically impacted on the calcified organism communities but the carbonate depositional architecture nevertheless stayed almost unaffected through the boundary the early triassic and earliest anisian were commonly associated with hyperhaline sometimes evaporitic conditions intervals of moister climate and efficient river discharge are however documented by earliest induan and early olenekian sediments the latter terrigenous deposits matched a crisis in the carbonate production after a return to arid conditions during the anisian a fluctuation toward moister climate developed associated to a massive continental vegetation cover the anisian tectonic activation of the region fragmented the previous carbonate shelf triggering the development of three generations of fast prograding but globally backstepping isolated platforms recording an increasing role of the synsedimentary cementation a dry climate dominated the late anisian and early ladinian interval at the time a fast subsidence pulse was associated with platform drowning and basinal anoxia only a few aggrading pinnacles were able to survive providing the nuclei for larger prograding platforms during a dry climate interval massive syndepositional cementation generated a major source of carbonate carbonate production stayed active through the ladinian magmatic phase but the onset of volcanism was associated with a large modification in the platform carbonate facies which became dominated by automicrites moist climate phases are well documented again during the late ladinian followed by a return to dry conditions the late ladinian early carnian platforms prograded toward the eastern dolomites depocentre eventually infilling almost the whole of the accommodation space the middle portion of the carnian recorded renewed sharply moist phases associated with the demise of the rimmed platforms and with the return to loose sediment ramps at least four separated humid fluctuations can be identified in this carnian interval alone climate then returned to persistent aridity until the late norian moist phase

the effects of kinetic sorting on sediment mobility on steep slopes in poorly mobile static armour sorting is usually considered the result of hiding exposure effects we called this effect static sorting in opposition to very efficient grain to grain mechanisms produced by a mobile mixture called kinetic sorting we hypothesized that kinetic sorting can be an important contributor to the morphodynamics of mountain streams and attempted to demonstrate this with new flume experiments two long runs were produced with natural poorly sorted sediments and with transport stages of the coarse fraction defined by the ratio between the shear stress and the critical shear stress for transport smaller and higher than 1 respectively both runs produced an efficient transfer downstream of the injected material but with a major difference the first run no kinetic sorting produced permanent armour figuring clusters akin to what has already been observed in similar experiments the second run with kinetic sorting also produced bed armouring but this armour was periodically totally destroyed leading to substantial bed erosion this phenomenon was explained by kinetic sorting the effects of which are to produce an efficient downward migration of fine materials and bed surface armouring the consequence is that fine materials are hidden to the flow during aggradation allowing the slope to attain values much steeper than would have been expected at equilibrium for the mixture however whereas the surface armouring tends to stabilize the bed construction of a layer of fine sediments at the subsurface also contributes to making it very unstable these two contradictory effects explain the complex bed behaviours and the existence of very large bedload and slope fluctuations copyright 2014 john wiley sons ltd

developing a strategy for accurate definition of a geological boundary through radio isotopic and biochronological dating the early middle triassic boundary south china abstract the ages of critical periods in the geological record of the earth have to be determined and attached uncertainties quantified as precisely and accurately as possible this study tries to find an optimal strategy for sampling for both biochronology and high precision u pb analysis of zircon from ash beds and for the selection and statistical treatment of geochronological data this strategy is applied to the case of the early middle triassic boundary emtb in the southern nanpanjiang basin in south china aiming to obtain the most accurate age information for this boundary with an associated uncertainty the emtb has been located in a sedimentary section near monggan guangxi south china which permitted tight correlation between conodont biozones the carbon isotopic record and high precision zircon u pb data from volcanic ashes two residual maximal horizons were defined using characteristic associations of conodont species accurately bracketing the emtb the lower and upper age limits of these horizons as well as the first occurrence fo of the base middle triassic index fossil chiosella timorensis were numerically calibrated by high precision chemical abrasion isotope dilution thermal ionization mass spectrometry ca id tims u pb dates volcanic zircon in the analyzed ash beds reveals complex system behavior in particular i unresolved lead loss after chemical abrasion and ii pre eruptive growth and or recycling of zircon crystals leading to excess scatter in 206 pb 238 u dates and to violations of the stratigraphic sequence a sufficiently high number of closely spaced ash samples n and of u pb analyses per sample n promotes recognition of such complications two different age models were constructed from weighted mean 206 pb 238 u dates comparing smoothing cubic spline and bayesian interpolation approaches the statistical treatment of the combined datasets allows quantification of the lower and upper limits and associated uncertainties of the two conodont biozones as well as of the fo of c timorensis the age for the emtb is calculated from combined interpolated data at 247 05 0 16 ma the age model derived from bayesian interpolation is considered to be more adapted to the present case where discontinuous changes in sedimentation rates are expected to be important the smoothing spline represents a more parsimonious model producing a simpler solution in terms of smoothness but the model assumptions are too strong for many geological problems the additional freedom in constructing the bayesian interpolating curve presumably leads to more realistic albeit larger confidence intervals

reconstruction of the chaotic behavior of the solar system from geologic records abstract astronomical solutions for planetary orbits beyond several tens of million years myr ago have large uncertainties due to the chaotic nature of the solar system mainly myr scale cycles related with the earth mars secular resonance our only accessible archive for unraveling the earth s orbital variations in the geologic past are sedimentological records yet their reliability and uncertainties are still debated here we describe myr scale orbital signals of early mesozoic monsoon records from two different sedimentary settings lake level records of the equatorial pangea and biogenic silica burial flux of deep sea panthalassa along with a marine carbon isotope compilation although most of the dominant multi myr cycles are not exactly of the same frequency 1 8 myr cycles during 216 210 ma are detected from the two mutually independent sedimentary settings and differ from available astronomical solutions this finding provides not only convincing evidence for the chaotic nature of the solar system in the geological past but also additional constraints on astronomical models on the other hand besides the orbital cycles tectonic forcing and consequent climatic perturbations could also have affected the proxies on multi myr timescales during episodes of large igneous province emplacement such as siberian trap volcanism 252 245 ma wrangellia 233 225 ma central atlantic magmatic province 202 200 ma and karoo ferrar volcanism 184 180 ma if we can distinguish orbital signals from other effects such as tectonic and volcanic processes the multi myr cycles in geologic records have the potential to reconstruct the chaotic evolution of the solar system

astrochronology of the early turonian early campanian terrestrial succession in the songliao basin northeastern china and its implication for long period behavior of the solar system abstract the first complete early turonian early campanian lacustrine succession has been recovered from the sk i south sk is borehole in the songliao basin slb northeastern china we conducted a detailed cyclostratigraphic study of natural gamma ray gr log thorium th log and magnetic susceptibility ms data from this core spectral analysis of the upper quantou formation k 2 q 3 4 qingshankou formation k 2 qn yaojia formation k 2 y and lower nenjiang formation k 2 n 1 2 reveals a hierarchy of meter to decameter scale cycling in the data the wavelength ratios of the cycles in these stratigraphic units are 20 5 2 1 corresponding with those of milankovitch cycle periods of 405 kyr long eccentricity 100 kyr short eccentricity 37 kyr obliquity 20 kyr precession indicating astronomical control on sedimentation an astronomical time scale ats was established by tuning interpreted 405 kyr cycles to a 405 kyr orbital eccentricity target curve and to four sims u pb zircon radioisotope ages this absolute ats provides precise numerical ages for stratigraphic boundaries biozones geological and geophysical events and serves as a basis for correlation of strata and events between marine and terrestrial systems the ages of the c33r c34n geomagnetic polarity boundary in k 2 n 2 and three short reversal events in k 2 y are estimated as 83 633 ma 84 819 84 862 ma 84 982 85 092 ma and 85 240 85 629 ma respectively long period amplitude modulations in the obliquity and eccentricity bands of the 405 kyr tuned gr th series provide strong evidence that long period orbital forcing influenced climate change and depositional processes in the slb the extracted amplitude modulations provide evidence that the orbits of earth and mars were not in secular resonance and were undergoing chaotic interactions during this time although the modulations do not match those of recent astronomical models

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

paleoclimate proxies for cyclostratigraphy comparative analysis using a lower triassic marine section in south china abstract multiple proxies for paleoclimatic and paleoenvironmental change within sedimentary sequences have been developed but understanding their relationships and their relative strengths or weaknesses are required to access a wealth of untapped paleoclimate information we propose two main criteria for multiple proxy datasets to estimate their individual signal to noise levels and to decipher the relationship between multiple proxies first for proxies affected by similar processes then their time dependent changes should be similar second a paleoclimate proxy that is more sensitive to an external forcing such as astronomical forcing is more useful than those that do not have such a response we introduce two methods to evaluate these criteria 1 hierarchical cluster analysis hca probes the relationships among multiple proxies based on similarities of their oscillation patterns and 2 power decomposition analysis pda tests proxy sensitivity to external climate forcing we evaluate 16 high resolution paleoclimate proxies in detail for their applications in paleoclimatology from the marine lower triassic daye formation at the daxiakou section in the three gorges region of south china which has carbonate claystone cycles deposited on an outer ramp the proxies are spectral gamma ray gamma ray intensity potassium uranium thorium thorium uranium and thorium potassium rock color lightness l redness a and yellowness b magnetic susceptibility measured in both laboratory and outcrop anhysteretic remanent magnetization arm lithologic rank simplified lithologic rank and non carbonate fraction carbonate thickness and couplet thickness hierarchical cluster analysis hca gathers these proxies into groups likely affected by the same process the arm and thorium uranium proxies seem to reflect the hinterland weathering process during the early triassic gamma ray potassium uranium thorium magnetic susceptibility and non carbonate fraction proxies refer to terrestrial input the l a and lithologic rank proxies indicate the productivity the redox state and the relative sea level respectively at this section this case study contributes to the understanding of the sensitivity of these types of proxies within marine strata for deep time paleoclimate and astronomical tuned time scales

dual doppler radar analysis of a midlatitude squall line with a trailing region of stratiform rain abstract the mesoscale structure of a squall line system that passed over oklahoma on 22 may 1976 is investigated by dual doppler radar analysis the mature storm consisted of a leading line of deep convection which exhibited organized multicellular structure trailed by an extensive region of stratiform precipitation marked by a radar bright band at the melting level these contrasting radar echo regimes were separated by a narrow band of weak reflectivity at lower levels which has been termed the transition zone while conventional and single doppler radar analyses documented the persistence of this precipitation structure and revealed the corresponding kinematic structure in one part of the mature storm the dual doppler analysis demonstrates the pervasiveness of these features over much of the squall line s length the structure of a midtropospheric maximum of rearward system relative flow crossing the system is particularly well described by the dual doppler data this mesoscale current originat

a 70 million year astronomical time scale for the deep sea bedded chert sequence inuyama japan implications for triassic jurassic geochronology abstract the astronomical time scale ats has provided high resolution geochronology however the early mesozoic ats is still under construction partly due to the lack of continuous pelagic sequences of the early mesozoic here we present ca 70 myr long ats constructed from the early mesozoic deep sea bedded chert sequence exposed in the inuyama area central japan the sedimentary rhythms of bedded chert display a full range of climatic precession related cycles 20 kyr cycle as a chert shale couplet and 100 405 2000 to 4000 and 10 000 kyr cycles as chert bed thickness variation the newly established ats inuyama ats is tuned by 405 kyr eccentricity cycle and is anchored at the end triassic radiolarian extinction level as 201 4 0 2 ma this inuyama ats gives ages consistent with the radiometric ages projected to the inuyama deep sea sequence using biostratigraphy and carbon isotope stratigraphy the inuyama ats provides the age constraints for the triassic and jurassic stage boundaries which support the long norian option of muttoni et al 2004 because the deep sea bedded chert sequence covers a long time interval before the cretaceous the ats for the bedded chert will serve as a template for the astrochronology of mesozoic and older ages

orbital forcing of triassic megamonsoon activity documented in lacustrine sediments from ordos basin china abstract the hothouse triassic climate provides a key window to study megamonsoon systems however high quality paleoclimate proxy records are rarely reported from the tethys realm where the seasonal meridional migration of the intertropical convergence zone itcz should be the most remarkable here continuous and well dated proxy records are used to study monsoon activity in the northeastern tethys from the middle triassic lacustrine sediments ch7 black shale yanchang formation in the ordos basin china the proxies including natural gamma ray intensity magnetic susceptibility and element concentrations and ratios u k zr al zr rb and sr rb document a strong precession signal in the sediments we propose that the periodic deposition of the ch7 black shale occurred in response to intensifications in a monsoon driven climate enhanced by the early ladinian warming event climate variability in the ordos basin 25 n reflects the harmonics of 100 kyr 20 kyr and 10 kyr cycles and is highly coherent with solar insolation at 9 latitude suggesting that this monsoon system might have been modulated by tropical solar insolation the dominance of tropical climate processes in this mid latitude monsoon region can be attributed to the dramatic dynamics of the itcz and intense monsoon circulation in the tethys realm

the timing and pattern of biotic recovery following the end permian mass extinction the aftermath of the great end permian period mass extinction 252 myr ago shows how life can recover from the loss of 90 species globally the crisis was triggered by a number of physical environmental shocks global warming acid rain ocean acidification and ocean anoxia and some of these were repeated over the next 5 6 myr ammonoids and some other groups diversified rapidly within 1 3 myr but extinctions continued through the early triassic period triassic ecosystems were rebuilt stepwise from low to high trophic levels through the early to middle triassic and a stable complex ecosystem did not re emerge until the beginning of the middle triassic 8 9 myr after the crisis a positive aspect of the recovery was the emergence of entirely new groups such as marine reptiles and decapod crustaceans as well as new tetrapods on land including eventually dinosaurs the stepwise recovery of life in the triassic could have been delayed either by biotic drivers complex multispecies interactions or physical perturbations or a combination of both this is an example of the wider debate about the relative roles of intrinsic and extrinsic drivers of large scale evolution from a much more devastated planet and biota than the others with only some 10 of species surviving the epme was much harsher than the other mass extinctions during which global species diversity reduced to only about 50 of the pre extinction total 1 2 24 26 this means that the triassic recovery has two profound implications first it may show qualitative as well as quantitative differences from the other post extinction recoveries and second it can act as an exemplar of what to expect at its most extreme when global biodiversity is pushed to the brink there are obvious implications for current concerns about biodiversity loss and recovery resulting from human impacts 27 28 in the past ten years attention has focused on the sedimentary successions in south china these are enormously laterally extensive with some formations extending more than 2 000 km from the zhejiang to yunnan provinces the huge exposures length of the sections and improving dating open up the opportunity to explore physical environmental and biotic changes through the extinction and recovery times in varied marine habitats and compare these with patterns elsewhere in the world fig 1 a fine scale forensic analysis of this extraordinary time in earth s history now becomes possible the end permian mass extinction the epme killed 80 96 of marine animal species and 70 of terrestrial vertebrate species

the triassic timescale new constraints and a review of geochronological data a review of geochronological data underlying the geological time scale for the triassic yields a significantly different time scale calibration than that published in the most recent compi lation geologic time scale 2004 this is partly due to the availability of new radio isotopic data but mostly because strict selection criteria are applied and complications arising from biases both systematic and random are accounted for in this contribution the ages for the base and the top of the triassic are constrained by u pb ages to 252 3 and 201 5 ma respectively these dates also constrain the ages of major extinction events at the permian triassic and triassic jurassic bound aries and are statistically indistinguishable from ages obtained for the siberian traps and volcanic products from the central atlantic magmatic province respectively suggesting a causal link ages for these continental volcanics however are mostly from the k ar 40 ar 39 ar system which requires accounting and correcting for a systematic bias of c 1 between u pb and 40 ar 39 ar isotopic ages the 40 ar 39 ar ages being younger robust age constraints also exist for the induan olenekian boundary 251 2 ma and the early middle triassic olenekian anisian boundary 247 2 ma resulting in a surprisingly short dur ation of the early triassic which has implications for the timing of biotic recovery and major changes in ocean chemistry during this time furthermore the anisian ladinian boundary is con strained to 242 0 ma by new u pb and 40 ar 39 ar ages radio isotopic ages for the late triassic are scarce and the only reliable and biostratigraphically controlled age is from an upper carnian tuff dated to 230 9 ma yielding a duration of more than 35 ma for the late triassic all of these ages are from u pb analyses applied to zircons with uncertainties at the permil level or better the resulting compilation can only serve as a guideline and must be considered a snapshot resolving some of the issues mainly associated with inaccurate and misinterpreted data in previous publi cations however further advances will require revision of some of the data presented here

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

an integrated biostratigraphy conodonts and foraminifers and chronostratigraphy paleomagnetic reversals magnetic susceptibility elemental chemistry carbon isotopes and geochronology for the permian upper triassic strata of guandao section nanpanjiang basin south china abstract the chronostratigraphy of guandao section has served as the foundation for numerous studies of the end permian extinction and biotic recovery in south china guandao section is continuous from the permian triassic boundary to the upper triassic conodonts enable broad delineation of stage and substage boundaries and calibration of foraminifer biostratigraphy as follows changhsingian griesbachian first hindeodus parvus and first appearance of foraminifers postcladella kalhori and earlandia sp griesbachian dienerian first neospathodus dieneri and last appearance of foraminifer p grandis dienerian smithian first novispathodus waageni and late dienerian first appearance of foraminifer hoyenella ex gr sinensis smithian spathian first nv crassatus and last appearance of foraminifers arenovidalina n sp and glomospirella cf vulgaris spathian aegean first chiosella timorensis and first appearance of foraminifer meandrospira dinarica aegean bithynian first nicoraella germanica and first appearance of foraminifer pilammina densa bithynian pelsonian after last neogondolella regalis prior to first paragondolella bulgarica and first appearance of foraminifer aulotortus eotriasicus pelsonian illyrian first pg excelsa and last appearance of foraminifers meandrospira deformata and pilamminella grandis illyrian fassanian first budurovignathus truempyi and first appearance of foraminifers abriolina mediterranea and paleolituonella meridionalis fassanian longobardian first bv mungoensis and last appearance of foraminifer a mediterranea longobardian cordevolian first quadralella polygnathiformis and last appearance of foraminifers turriglomina mesotriasica and endotriadella wirzi the section contains primary magnetic signature with frequent reversals occurring around the permian triassic olenekian anisian and anisian ladinian boundaries predominantly normal polarity occurs in the lower smithian bithynian and longobardian cordevolian predominantly reversed polarity occurs in the upper griesbachian induan olenekian pelsonian and lower illyrian reversals match well with the gpts large amplitude carbon isotope excursions attaining values as low as 2 9 13c and high as 5 7 13c characterize the lower triassic and basal anisian values stabilize around 2 13c through the anisian to carnian similar signatures have been reported globally magnetic susceptibility and synthetic gamma ray logs show large fluctuations in the lower triassic and an overall decline in magnitude of fluctuation through the middle and upper triassic the largest spikes in magnetic susceptibility and gamma ray indicating greater terrestrial lithogenic flux correspond to positive 13c excursions high precision u pb analysis of zircons from volcanic ash beds provide a robust age of 247 28 0 12 ma for the olenekian anisian boundary at guandao and an age of 251 985 0 097 ma for the permian triassic boundary at taiping together the new u pb geochronology from the guandao and taiping sections suggest an estimated duration of 4 71 0 15 ma for the early triassic epoch

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

timing of recovery from the end permian extinction geochronologic and biostratigraphic constraints from south china comment and reply reply bucher et al s comment 2007 1 questioned the validity of our 247 2 ma age estimate for the early middle triassic olenekian anisian o a boundary based on a comparison of recent data from lower guandao section presented by us lehrmann et al 2006 2 with preliminary data reported from