global correlation of the radiolarian faunal change across the triassic jurassic boundary precise comparison of the change in radiolarian faunas 3 5 m above a u pb zircon dated 199 6 0 3 ma tuff and approximately coincident with a negative 13 c anomaly in the queen charlotte islands b c canada with inuyama japan sequences indicates that major global changes occurred across the triassic jurassic t j boundary nearly 20 genera and over 130 rhaetian species disappeared at the end of the triassic the index genera betraccium and risella disappear and the final appearance of globolaxtorum tozeri livarella valida and pseudohagiastrum giganteum sp nov are also diagnostic for the end of the triassic the low diversity hettangian survival fauna immediately above the boundary is composed mainly of small primitive spumellarians with spongy or irregularly latticed meshwork and rod like spines and new genera charlottea udalia and parahsuum s l first appear in the lowest hettangian in both localities irrespective of different sedimentation rates and sedimentary environments such as shelf to upper slope queen charlotte islands and deep sea below carbonate compensation depth ccd inuyama radiolarians show a similar turnover pattern at the t j boundary

correlating the end triassic mass extinction and flood basalt volcanism at the 100 ka level new high precision u pb geochronology from volcanic ashes shows that the triassic juras sic boundary and end triassic biological crisis from two independent marine stratigraphic sections correlate with the onset of terrestrial fl ood volcanism in the central atlantic mag matic province to 150 ka this narrows the correlation between volcanism and mass extinc tion by an order of magnitude for any such catastrophe in earth history we also show that a concomitant drop and rise in sea level and negative 13 c spike in the very latest triassic occurred locally in 290 ka such rapid sea level fl uctuations on a global scale require that global cooling and glaciation were closely associated with the end triassic extinction and potentially driven by central atlantic magmatic province volcanism

offscraping accretion of jurassic chert clastic complexes in the mino tamba belt central japan abstract detailed structural and biostratigraphical analysis of the jurassic inuyama sequence a coherent chert clastic complex in the mino tamba belt central japan clarifies the evolution of accretionary processes at shallow structural levels the inuyama sequence is characterized by a series of stacked thrust sheets each sheet consists of an early triassic to middle jurassic oceanic plate stratigraphy composed of four lithologic units which are in ascending order siliceous claystone ribbon chert siliceous mudstone and clastic rocks the structural features of the inuyama sequence demonstrate a four stage progressive deformation 1 a decollement was initiated within the siliceous mudstone when this sequence was just seaward of the deformation front clastic dikes and sills formed at the horizon just above the decollement at this time 2 the stratigraphic section above the decollement was imbricated by in sequence thrusting in the frontal part of the wedge this initial stage of thrusting and imbrication was followed by 3 the formation of duplex structures with fault related folds within the lower stratigraphic section as the decollement stepped down section to the lowest siliceous claystone interval finally 4 these thrust packages were overprinted by secondary prism thickening in the form of out of sequence thrust faulting

low latitude and southern hemisphere origin of anisian triassic bedded chert in the inuyama area mino terrane central japan paleomagnetic and paleontologic studies of middle triassic to earliest jurassic radiolarian bedded chert in the inuyama area southern mino terrane of central japan have shown that the chert was deposited in an equatorial region with a paleolatitude between 10 n and 10 s and in particular the lower to middle anisian chert depositional basin was situated in the southern hemisphere the chert has four characteristic components of remanent magnetization the highest blocking temperature component carried by hematite shows positive fold and reversal tests and is regarded as the primary remanent magnetization acquired just after deposition the other three components are interpreted as a present field overprint and two postfolding remagnetizations the absolute tilt corrected inclinations of the primary component are less than 20 for all the samples of middle triassic to earliest jurassic age with the mean inclination of the lower to middle anisian chert being 11 0 4 3 paleomagnetic polarity reversals observed for the lower to middle anisian chert are well correlated with those of the european triassic sections under paleontologic age constraints using radiolarians and conodonts provided that the anisian chert in inuyama was deposited in the southern hemisphere this conclusion illuminates the paleogeographic evolution of the chert bearing accretionary complexes not only in japan but along the eastern margin of asia as well

well documented travel history of mesozoic pelagic chert in japan from remote ocean to subduction zone the mino tanba belt in southwest japan a segment of the cordilleran type orogenic chain of jurassic east asia is composed mainly of a middle upper jurassic subduction accretion complex in which triassic and lower jurassic bedded radiolarian cherts occur as large allochthonous units structurally interlayered with middle upper jurassic clastic rocks high resolution microfossil conodont and radiolaria research has identified very low average sedimentation rates of about 0 5 g cm 1000 yr in the chert units similar to those of modern pelagic sediments accumulated in open ocean environments judging from the low average sedimentation rate high purity of biogenic silica long duration of continuous deposition 50 m y and wide along strike extent 1000 km the bedded radiolarian cherts in the mino tanba belt are best understood as ancient pelagic sediments that accumulated in open ocean environments accordingly the alleged origin in smaller marginal basins is untenable upward lithologic change from bedded chert to overlying siliceous mudstone in the uppermost portion of chert sequences suggests the gradual landward approach of the oceanic plate toward a trench the tectonic interlayering of these cherts and coarse grained terrigenous elastics is a secondary feature that was added through duplexing underplating in the subduction zone on the basis of the primary stratigraphy and field occurrence of triassic bedded chert in the mino tanba belt newly proposed are an idealized oceanic plate stratigraphy and a generalized travel history of a cordilleran type bedded chert from its birth at a mid oceanic ridge to its demise at a subduction zone

an attempt to constrain the age duration and eruptive history of the karoo flood basalt naude s nek section south africa we have carried out paleomagnetic sampling of a similar to 750 m sequence of the karoo large igneous province naude s nek pass south africa k ar dating cassignol gillot has been performed on four samples from the 650 m upper unit mean age 179 2 1 8 ma and a sample from the lower unit 184 8 2 6 ma a succession of two phases of volcanism is suggested the lower 25 flows 115 m thick have recorded a reversed polarity the next 23 flows 135 m thick are transitional and contribute a detailed record of the van zijl 1962 jurassic reversal the upper 38 flows 500 m thick have normal polarity directional groups dgs of lava flows with quasi identical remanence directions indicate eruption durations too short to have recorded geomagnetic secular variation and hence are interpreted as single eruptive events altogether 19 dgs and 10 sheet lobes yield a sequence of 29 distinct directions this could correspond to a total eruptive activity shorter than 3000 years less than one per mil of the total duration over which the section was emplaced we obtain a new paleomagnetic pole for south africa at similar to 180 ma lambda 75 2 degrees n phi 276 4 degrees e a 95 5 8 degrees n 19 which is consistent with earlier reports

the toarcian radiolarian event in bedded cherts from southwestern japan abstract a drastic faunal turnover of radiolarians in the early toarcian termed the toarcian radiolarian event tre recognized in bedded chert sequences of southwestern japan is marked by the first co appearance of the genus praeparvicingula and mesosaturnalis hexagonus and by high diversity among multicyrtids the event resulted in the replacement of latest triassic through earliest jurassic taxa by late jurassic to early cretaceous taxa at tre levels in bedded cherts in southwestern japan the size of radiolarians decreased drastically reworked conodont fossils appeared and anoxic sediments black cherts with fes2 nodules were deposited the lithologic and faunal changes suggest that global marine environmental changes including the occurrence of anoxia caused the tre

the heartbeat of the oligocene climate system a 13 million year continuous record of oligocene climate from the equatorial pacific reveals a pronounced heartbeat in the global carbon cycle and periodicity of glaciations this heartbeat consists of 405 000 127 000 and 96 000 year eccentricity cycles and 1 2 million year obliquity cycles in periodically recurring glacial and carbon cycle events that climate system response to intricate orbital variations suggests a fundamental interaction of the carbon cycle solar forcing and glacial events box modeling shows that the interaction of the carbon cycle and solar forcing modulates deep ocean acidity as well as the production and burial of global biomass the pronounced 405 000 year eccentricity cycle is amplified by the long residence time of carbon in the oceans

global radiolarian zonation for the pliensbachian toarcian and aalenian jurassic radiolarians from 220 samples in queen charlotte islands b c williston lake b c east central oregon baja california sur southern spain austria slovenia turkey oman japan and argentina were studied in order to construct global zonation for the pliensbachian toarcian and aalenian stages well preserved faunas from continuous stratigraphic sections in queen charlotte islands provide the most detailed record for this time interval and all collections are tied to north american ammonite zones or assemblages collections from nearly all other areas lack independent dating except for early toarcian carbon isotope dating in slovenia and late aalenian ammonites in spain a database of 197 widely distributed updated taxonomic species was used to construct a unitary association ua zonation for the interval a global sequence of 41 uas was obtained for the top of the sinemurian to the base of the bajocian the first and the last uas represent the late sinemurian and the early bajocian respectively the remaining 39 uas were merged into nine zones four early pliensbachian one late pliensbachian one early toarcian one middle late toarcian and two aalenian according to prominent radiolarian faunal breaks and ammonite data the new zones are the canutus tipperi katroma clara zone latest sinemurian earliest pliensbachian zartus mostleri pseudoristola megaglobosa hsuum mulleri trillus elkhornensis and gigi fustis lantus sixi zones early pliensbachian eucyrtidiellum nagaiae praeparvicingula tlellensis zone late pliensbachian napora relica eucyrtidiellum disparile zone early toarcian elodium pessagnoi hexasaturnalis hexagonus zone middle and late toarcian higumastra transversa napora nipponica zone early aalenian and mirifusus proavus transhsuum hisuikyoense zone late aalenian these zones can be correlated worldwide and link previously established ua zonations for the hettangian sinemurian and the middle to upper jurassic the new zonation allows high resolution dating in the studied interval and provides a solid basis for analyzing faunal turnovers and the paleobiogeography of jurassic radiolarians

regular and irregular climatic cycles and the belemnite marls pliensbachian lower jurassic wessex basin time series of carbonate and organic carbon values are reported for 10 5 m of the belemnite marls the light and dark marl beds form decimetre scale couplets and metre scale bundles light marls are carbon poor and carbonate rich whereas dark marls and laminated shales are carbon rich and carbonate poor sediment composition appears to have been indirectly controlled by climate the regular couplets may record orbital precession cycles 20 ka however the bundles cannot be linked to changes in eccentricity rather they apparently record irregular large amplitude climatic variations with periods of a few hundred thousand years it should not be assumed that 100 400 ka cyclicity in climate related sedimentary sequences can be explained only by orbital forcing

influence of the changing lunar orbit on the astronomical frequencies of pre quaternary insolation patterns the sensitivity of the frequencies of the earth s orbital elements involved in the astronomical theory of paleoclimates obliquity and climatic precession to the earth moon distance and consequently to the length of the day and to the dynamical ellipticity of the earth is investigated for the last billions of years but the new frequencies have been computed for the last 440 million years only a time interval over which data and a model of the earth were available moreover we consider only the impact of the changing precessional parameter assuming that the fundamental frequencies of the planetary motion are steady at the geological time scale under such hypotheses the shortening of the earth moon distance and of the length of the day back in time induces a shortening of the fundamental astronomical periods for obliquity and precession a shortening that is larger for longer periods

volcanism and deep ocean acidification across the end triassic extinction event abstract the end triassic extinction event marks one of the big five mass extinction events of the phanerozoic the ultimate cause of the extinction is considered to be volcanic activity at the central atlantic magmatic province camp yet the underlying nature of global environmental changes that accompanied the biotic turnover remains elusive here we present chemical and mineralogical studies across the end triassic extinction level of the deep sea chert sequence inuyama japan depleted hematite content normalized by terrigenous material predated the end triassic extinction level with significant rock color change from brick red to purple which is consistent with the rock magnetic records of hematite reported this suggests the loss of authigenic hematite possibly due to the acidification of bottom water and the underlying sediment pore water this timing is consistent with the initial eruption of camp volcanism suggesting a catastrophic release of greenhouse gases as a cause of deep ocean acidification across the end triassic extinction interval mgo al2o3 fe2o3 al2o3 and al2o3 sio2 increased with change in color from purple to dusty red this trend became close to those of weathered camp basalts in arid area implying that it became the considerable source of aeolian dust in cherts after the end triassic extinction event these temporal relations support the synchrony among the initial eruption of camp deep ocean acidification and the end triassic extinction similar rock color changes of cherts might have potential information for the volcanisms and deep ocean acidification in other geologic events

revisiting the jurassic geomagnetic reversal recorded in the lesotho basalt southern africa summary we carried out a detailed and continuous palaeomagnetic sampling of the reversed to normal geomagnetic transition recorded by some 60 consecutive flow units near the base of the lesotho basalt 183 1 ma after alternating field or thermal cleaning the directions of remanence are generally well clustered within flow units in contrast the thermal instability of the samples did not allow us to obtain reliable palaeointensity determinations the geomagnetic transition is incompletely recorded due to a gap in volcanic activity attested to both by eolian deposits and a large angular distance between the field directions of the flows underlying or overlying these deposits the transition path is noticeably different from that reported in a pioneering work carried out in 1962 the most transitional virtual geomagnetic poles vgps are observed after the volcanic hiatus once continents are replaced in their relative position 180 myr the post hiatus vgps cluster over russia however two successive rebounds from that cluster are found with vgps reaching repeatedly the eastern asia coast thus the vgp path is not narrowly constrained in palaeolongitude the decrease in intensity of magnetization as the field deviates from the normal or reversed direction suggests that the decrease in field magnitude during the reversal reached 80 90 per cent we conclude that although the reversal is of a dipole of much weaker moment than that which existed on average during cenozoic time the characteristics of the reversing geodynamo seem to be basically similar

the toarcian oceanic anoxic event early jurassic in the neuquen basin argentina a reassessment of age and carbon isotope stratigraphy abstractthe toarcian oceanic anoxic event t oae is recorded by the presence of globally distributed marine organic carbon rich black shales and a negative carbon isotope shift with 13corg values as low as 33 interrupting an overarching positive excursion here we present new biostratigraphic data and high resolution 13corg data from two southern hemisphere localities arroyo serrucho in the north and arroyo lapa in the south of the neuquen basin argentina previous studies at these localities aimed to provide an accurate numerical age for the t oae and characterization of its carbon isotope stratigraphy the new carbon isotope data and ammonite biostratigraphy presented here from arroyo serrucho show the t oae to be recorded lower in the section than supposed by previous authors thus calling into question the published age of the t oae in this section a newly investigated exposure at arroyo lapa north shows a complex carbon isotope record with at least three high amplitude fluctuations in the h

rapid magma emplacement in the karoo large igneous province abstract understanding the dynamics of continental large igneous provinces lips relies on precise dating of basaltic rocks lip research has traditionally focused on dating lavas often neglecting the volumetrically important sill intrusions in underlying sedimentary basins here we present u pb zircon and baddeleyite ages for fourteen new samples of karoo lip sills and dykes spaced by as much as 1100 km across the half million square kilometer karoo basin the samples yield remarkably coherent ages ranging from 183 0 0 5 to 182 3 0 6 myr probability modeling indicates that basin scale emplacement took place within an interval of about 0 47 myrs less than 0 90 myrs with 95 confidence and could even have represented a single magma emplacement event combining the new ages with the estimated volume of sills in the karoo basin gives an emplacement rate of 0 78 km3 yr which is higher than previous estimates upper crustal magma storage may account for these high rates the results challenge the view that melt emplacement in a sedimentary basin is a prolonged process support a scenario of pulsating catastrophic events within a narrow time frame and strengthens the hypothesis linking lips and sill emplacement to global environmental crises

57fe mossbauer spectroscopic analysis of deep sea pelagic chert effect of secondary alteration with respect to paleo redox evaluation abstract chemical states of iron in the pre jurassic pelagic deep sea cherts are used as one of redox indicators of lost deep oceans e g the permian triassic boundary case primarily red hematite bearing cherts were often altered secondarily into greenish gray cherts we examined the pattern of secondary change in chemical state of iron associated with color change in the middle triassic chert beds at hisuikyo in central japan by 57fe mossbauer spectroscopy three sets of chert bed with the lateral color change from red to greenish gray were analyzed the analyses confirmed that the red cherts contain hematite paramagnetic fe3 and paramagnetic fe2 whereas the greenish gray cherts contain paramagnetic fe3 and paramagnetic fe2 without hematite the greenish gray parts contain larger amounts of paramagnetic fe2 component of amorphous siderite like mineral in contrast to the red parts have lesser amounts these results confirmed that the primary hematite has changed into paramagnetic fe2 bearing minerals in accordance with the color change by the secondary alteration further comparison with the pyrite bearing primary black to dark gray cherts was discussed with respect to the evaluation for primary redox change in the past oceans

duration of the early toarcian carbon isotope excursion deduced from spectral analysis consequence for its possible causes abstract the marked 3 8 negative carbon isotope excursion associated with the early toarcian oceanic anoxic event oae 183 myr ago in the early jurassic period is thought to represent one of the most important perturbations of the c cycle in the last 200 myr however the origin of this excursion remains strongly debated primarily due to uncertainties in the estimation of its duration which ranges from 200 kyr to 1 myr here we present a new orbital calibration of the early toarcian carbon isotope excursion based on spectral analyses of two independent datasets generated from the sedimentary record of two hemipelagic sections from portugal peniche and sw germany dotternhausen in order to better constrain the timescale and hence the origin of this excursion these analyses reveal that orbital cycles exert a strong influence on both the calcium carbonate content in portugal and on the greyscale of black shales in germany which allow us to propose a duration of 1 9 myr for the early toarcian and of 900 kyr for the entire carbon isotope excursion the shift towards lower carbon isotope values lasted 150 kyr and carbon isotope values remained low for 450 kyr the subsequent increase of carbon isotope values lasted 300 kyr this calibration suggests that the sustained input of isotopically light carbon at the origin of the excursion occurred over 600 kyr and thus dismisses causal mechanisms implying relatively small source reservoirs such as the massive dissociation of methane hydrates in the light of our new cyclostratigraphic timescale the massive input of isotopically light carbon associated with the emplacement of the karoo ferrar basaltic province appears as the most likely cause of the toarcian global carbon isotope excursion we also show that the c isotope perturbation coincided with a transition from precession eccentricity dominated cycles to obliquity eccentricity dominated cycles suggesting that the oae was marked by a fundamental change in the response of the climate system which allowed the obliquity signal normally better recorded at high latitudes to be a dominant forcing factor of short term sedimentary cycles at tropical latitudes

paleomagnetism of triassic and jurassic red bedded chert of the inuyama area central japan a paleomagnetic study was conducted on triassic and jurassic red bedded chert from the inuyama area central japan paleomagnetic specimens were collected from single chert beds at nine sites within mesoscopic 1 5 m folds whose ages were determined by radiolarian fossils progressive thermal demagnetization experiments were conducted and three of the four magnetization components provided tectonic implications component d unblocking temperature of 560 680 c from six sites passes the fold test with the mesoscopic folds paleolatitude was estimated as 12 3 15 6 n or s 19 0 10 5 n or s and 25 7 16 7 n or s for 237 ma 223 5 ma and 210 ma respectively in the case of northern latitude a northward migration of 5 6 9 cm yr is estimated between 237 ma and 210 ma with no significant latitudinal migration from 210 ma to 160 ma component c unblocking temperature of 350 530 c has normal polarity and is thought to have been acquired as a chemical remanent magnetization carried by magnetite which was acquired as synfolding magnetization with the sakahogi synform the magnetization is considered to have been acquired through heating in the accretionary wedge during the cretaceous normal superchron 120 5 83 5 ma component b unblocking temperature of 200 350 c has reversed polarity and is thought to have been acquired as a thermoviscous remanent magnetization after the bending of the sakahogi synform the most probable period of the magnetization acquisition is between c27r and c24r 58 63 ma after the emplacement of late cretaceous granitic batholiths

numerical evaluation of mechanisms driving early jurassic changes in global carbon cycling the early jurassic early toarcian ca 183 ma carbon cycle perturbation is characterized by aabout 5 parts per thousand delta sup 13 c excursion in the exogenic carbon reservoirs a 1000 ppm rise in atmospheric co sub 2 and a 6 7 degrees warming two proposed explanations for this presumed global carbon cycle perturbation are the liberation of massive amounts of isotopically light ch4 from 1 gondwanan coals by heating during the intrusive eruption of the karoo ferrar large igneous province lip or 2 the thermal dissociation of gas hydrates carbon cycle modeling indicates that the release of ch4 from gondwanan coals synchronous with the eruption of the karoo ferrar lip fails to reproduce the magnitude or timing of the co sub 2 and delta sup 13 c excursions however sensitivity analyses constrained by a marine cyclostratigraphically dated delta sup 13 c record indicate that both features of geologic record can be explained with the huge input of about 15 340 24 750 gt c over about 220 k y a result possibly pointing to the involvement of hydrothermal vent complexes in the karoo basin the simulated release of 6000 gt c from gas hydrates also reproduces aspects of the early toarcian rock record but the large mass involved raises fundamental questionsmore about its formation storage and release less

pacing of the toarcian oceanic anoxic event early jurassic from astronomical correlation of marine sections abstract the early toarcian oceanic anoxic event oae in the early jurassic period is associated with a major negative carbon isotope excursion cie mass extinction marine transgression and global warming the toarcian oae is thought to have been caused by flood basalt magmatism and may have been a trigger for mass extinction however these proposed causes of the toarcian oae and associated biotic crisis are not adequately resolved by a precise chronology the duration of the toarcian oae has been estimated to be anywhere from 0 12 to 0 9 myr most recently 0 74 to 3 26 myr from u pb dating the cie associated with the toarcian oae has a similar pattern at numerous localities and there is evidence that the marine carbon isotope variations recorded astronomical forcing signals here we estimate a duration of 620 kyr for the main negative cie 860 kyr for the polymorphum zone and 1 58 myr for the levisoni zone based on 405 kyr astronomical eccentricity tuning of the marine section at peniche portugal this 405 kyr tuned series provides a 2 5 myr continuous high resolution chronology through the early toarcian there are 6 or possibly 7 short eccentricity cycles in the main cie interval at peniche to confirm this astronomically based estimate we analyzed three other sections at yorkshire uk dotternhausen germany and valdorbia italy from marine carbon isotopic series these four stratigraphic sections from early jurassic western tethys record the toarcian oae with 6 prominent carbon isotope cycles in the cie that span a 600 100 kyr duration the peniche 405 kyr tuned series indicates that the pre and post cie intervals experienced strong precession eccentricity forced climate change whereas the cie interval is marked by dominant obliquity forcing these dramatic and abrupt changes in astronomical response in the carbon isotopes point to fundamental shifting in the early toarcian paleoclimate system that was directly linked to the global carbon cycle

synchrony between early jurassic extinction oceanic anoxic event and the karoo ferrar flood basalt volcanism a well known second order mass extinction took place during the pliensbachian and toarcian stages of the early jurassic first recognized as a minor pliensbachian peak in the global extinction rate it has alternatively been interpreted as a regional response to the early toarcian oceanic anoxic event detailed studies established it as a global long term event spanning five successive ammonoid zones here we present a revised time scale based on highprecision u pb ages resolved to the zone level which suggests that elevated extinction rates were sustained for about 4 m y and peak extinction occurred at 183 ma recent isotopic dating of flood basalts from the southern gondwanan karoo and ferrar provinces documents a culmination in volcanic activity ca 183 ma the onset of volcanism is recorded as an inflection and start of a rapid rise of the seawater 87 sr 86 sr curve the synchrony of voluminous flood basalt eruptions and biotic crises as already noted for three of the major mass extinctions permits a causal relationship which in this case may be mediated by widespread oceanic anoxia

evolutionary patterns and palaeobiogeography of pliensbachian and toarcian early jurassic radiolaria recent studies on the global distribution of pliensbachian and toarcian polycystine radiolarians allowed us to examine faunal turnovers and the biogeography through this critical time interval around a major ecologic and biotic crisis the analysis is based on the distribution of 167 species belonging to 69 genera significant variations in the ratio between the number of originating and extinct species have been recognized during the early early pliensbachian fads greatly exceeded lads and the maximum diversity was reached in the late early pliensbachian the trend then reversed with the number of lads exceeding fads throughout the late pliensbachian and early toarcian extinction interval recovery started in the middle and late toarcian when the number of fads again surpassed the number of lads three differing evolutionary patterns are observed amongst radiolarian genera through the studied time interval the largest group diversified rapidly in the early pliensbachian and experienced higher extinction rates in the late pliensbachian and early toarcian a second group exhibited no major changes and a third group of mainly spongy spumellarians was successful during the extinction interval the overall trend of radiolarian diversity is in a fairly good agreement with that of other marine faunas ammonites and also benthos but shows an inverse correlation with diversity trends of phytoplankton correlation with concomitant environmental changes indicates that radiolarian radiation extinction rates were not consistently linked with temperature fluctuations or sea level changes it is also evident that the diversity decrease started well before the early toarcian negative 13c peak and the oceanic anoxic event oae the extinction interval corresponds well to the duration of a short term anomaly in the strontium isotope record including the rapid decrease of 87sr 86sr values in the late pliensbachian as well as the rapid increase in the early toarcian this coincidence supports the hypothesis that the predominance of extinctions over originations was caused by a series of climate and environmental changes related to intensified magmatic activity some distinct biogeographic differences have been observed generic differences are most strongly displayed by the presence or absence of a particular genus or by changes in abundance while species differences range from greater variability to having completely different species in separate palaeolatitudinal realms two groups of genera are distinguished those that are common to abundant in the tethys low latitudes and rare to absent in mid to high latitudes and those common to abundant in mid to high latitudes and rare to absent in the tethys

geochronological constraints on post extinction recovery of the ammonoids and carbon cycle perturbations during the early jurassic abstract this paper presents the first quantitative study of the early jurassic recovery of ammonoids after the end triassic mass extinction based on detailed u pb id tims isotope dilution thermal ionization mass spectrometry geochronology from ash bed zircons placed within a clear phylogenetical and biochronological framework at the subzonal and species level this study was triggered by the discovery of a rich peruvian succession of ammonites deposited concomitantly with an unusually large number of ash beds two major phases of rediversification are observed during the psiloceras spelae and angulaticeras zones that correspond to positive peaks in the 13corg curve providing a possible link between biodiversity and the global carbon cycle in the case of the post extinction recovery the development of the earliest hettangian ammonites occurs within the genus psiloceras which begins with the occurrence of p spelae and then explodes into worldwide development of smooth psiloceratids of the psiloceras planorbis group s l this rapid biodiversification likely occurred less than 100 ka after the end triassic crisis the genus psiloceras occupied all the possible ecological niches worldwide from the pacific deep waters to the nw european shallow deposits and also in some rare tethyan occurrences like at germig in tibet this global dispersion allowed the differentiation of the group in several major phyla the schlotheimiidae discamphiceratinae arietitidae and lytocerataceae which were the roots of all other jurassic and cretaceous ammonites

massive dissociation of gas hydrate during a jurassic oceanic anoxic event in the jurassic period the early toarcian oceanic anoxic event about 183 million years ago is associated with exceptionally high rates of organic carbon burial high palaeotemperatures and significant mass extinction heavy carbon isotope compositions in rocks and fossils of this age have been linked to the global burial of organic carbon which is isotopically light in contrast examples of light carbon isotope values from marine organic matter of early toarcian age have been explained principally in terms of localized upwelling of bottom water enriched in 12c versus 13c refs 1 2 5 6 here however we report carbon isotope analyses of fossil wood which demonstrate that isotopically light carbon dominated all the upper oceanic biospheric and atmospheric carbon reservoirs and that this occurred despite the enhanced burial of organic carbon we propose that as has been suggested for the late palaeocene thermal maximum some 55 million years ago the observed patterns were produced by voluminous and extremely rapid release of methane from gas hydrate contained in marine continental margin sediments

the timing of paleoenvironmental change and cause and effect relationships during the early jurassic mass extinction in europe the early jurassic marine mass extinction is one of several crises thought to coincide with anoxia transgression and warming caused by catastrophic release of gas hydrates however high resolution study of expanded sections in yorkshire england reveal that only the first of these factors is truly coincidental with extinction the well known transgression and large negative carbon isotope perturbation attributed to massive release of methane from gas hydrates occur after these events the anoxic event is developed diachronously in the european area with anoxia developing and fading away earlier in the mediterranean region compared with the nw european record however for a brief interval in the mid semicelatum subzone anoxia was simultaneously developed throughout the european region and it is this time that is marked by extinction of both benthic and pelagic marine fossils the sea level curve is also more complex than hitherto assumed with a minor regression occurring late in the semicelatum subzone shortly after the extinction the toarcian crisis occurred during a phase of global warming but the postulated release of methane from gas hydrates is too late to be implicated in the extinction mechanism as indeed is a recently reported cooling event from within the warming trend

trade wind fetch related variations in equatorial undercurrent depth speed and transport a dynamical model is developed to examine the dependence of equatorial undercurrent depth speed and volume transport on trade wind fetch the model ocean is linear continuously stratified vertically diffusive and formulated on the equatorial beta plane analytical solutions are derived in closed form for realistic choices of model parameters results indicate that the undercurrent would be significantly shallower and weaker in the atlantic than in the pacific because of the shorter atlantic trade wind fetch

hydrothermal venting of greenhouse gases triggering early jurassic global warming abstract the climate change in the toarcian early jurassic was characterized by a major perturbation of the global carbon cycle the event lasted for approximately 200 000 years and was manifested by a global warming of 6 c anoxic conditions in the oceans and extinction of marine species the triggering mechanisms for the perturbation and environmental change are however strongly debated here we present evidence for a rapid formation and transport of greenhouse gases from the deep sedimentary reservoirs in the karoo basin south africa magmatic sills were emplaced during the initial stages of formation of the early jurassic karoo large igneous province and had a profound influence on the fate of light elements in the organic rich sedimentary host rocks total organic carbon contents and vitrinite reflectivity data from contact aureoles around the sills show that organic carbon was lost from the country rocks during heating we present data from a new type of geological structures termed breccia pipes rooted in the aureoles within the shale of the western karoo basin the breccia pipes are cylindrical structures up to 150 meters in diameter and are mainly comprised of brecciated and baked black shale thousands of breccia pipes were formed due to gas pressure build up during metamorphism of the shales resulting in venting of greenhouse gases to the toarcian atmosphere mass balance calculations constrained by new aureole data show that up to 1800 gt of co2 was formed from organic material in the western karoo basin about 15 times this amount of co2 27 400 gt may have formed in the entire basin during the intrusive event u pb dating of zircons from a sill related to many of the pipes demonstrates that the magma was emplaced 182 5 0 4 million years ago this supports a causal relationship between the intrusive volcanism the gas venting and the toarcian global warming

high precision geochronology links the ferrar large igneous province with early jurassic ocean anoxia and biotic crisis abstract apparent synchrony between eruption emplacement of large igneous province lip magmas and mass extinction has led to the implication of magmatism as a primary trigger of global scale environmental change evaluating the efficacy of magmatism as a driver of global change depends on the relative timing of magmatism and environmental change and the magma effusion intrusion rate both of which can be constrained by high precision geochronology early jurassic pliensbachian toarcian global ocean anoxia and acidification carbon isotope perturbations and biotic crisis have been linked to synchronous eruption and emplacement of the karoo and ferrar lips to better constrain the timing and duration of ferrar magmatism we apply the single crystal chemical abrasion u pb id tims method to zircon crystals isolated from twenty ferrar lip sills and lavas and the dufek intrusion dates suggest that both intrusive and extrusive ferrar magmatism occurred over an interval of 349 49 kyr beginning with intrusive magmatism as early as 182 779 0 033 ma lava eruption was synchronous with and in some cases postdates intrusion when coupled with existing geochronology on the karoo province our dates confirm broad synchrony between karoo and ferrar magmatism though karoo magmatism began demonstrably prior to ferrar magmatism starting as early as 183 246 0 045 ma the short lived magmatic history of the ferrar lip makes it a plausible trigger for early jurassic environmental change

astronomical cycle origin of bedded chert a middle triassic bedded chert sequence inuyama japan abstract astronomical forcing is one of the main drivers of climate change and astronomical cyclicity recorded in sediments provides a clue to understand the dynamics of the global climate system bedded cherts consist of rhythmic alternations of chert and shale beds although previous studies have hypothesized that the origin of bedded chert is related to astronomical cycles e g fischer 1976 hori et al 1993 conclusive proof remains elusive to explore this possibility we established a continuous high resolution lithostratigraphy of middle triassic bedded chert in central japan the average duration of each chert shale couplet is 20 kyr similar to that of the precession cycle spectral analysis of a bed number series of thickness variations in chert beds was performed assuming that each chert shale couplet represents a 20 kyr precession cycle the results reveal cycles involving approximately 200 20 5 and 2 3 beds corresponding to periodicities of approximately 4000 400 100 and 40 60 kyr respectively by further assuming that the 20 bed cycle represents a 405 kyr eccentricity cycle of constant and stable periodicity we converted the bed number series to a time series spectral analysis of the time series revealed distinct periodicities of 3600 117 97 and 38 kyr in addition to 405 kyr besides 3600 kyr these periodicities agree well with the 120 95 and 37 kyr periodicities for eccentricity cycles and the obliquity cycle during the triassic moreover we detected amplitude modulation of the approximately 100 kyr cycle of thickness variations in chert beds with a 405 kyr periodicity which may correspond to amplitude modulation of 100 kyr climatic precession cycle with the 405 kyr periodicity the approximately 3600 kyr periodicity described above and 1800 kyr periodicity manifested as the amplitude modulation of the 405 kyr cycle are correlated to present day long term eccentricity cycles of 2400 and 4800 kyr evolved by chaotic behavior of solar planets collectively these similarities in the periodicities of dominant cycles their hierarchy and the nature of amplitude modulation of cycles in chert bed thickness with those of astronomical cycles strongly support the hypothesis that the sedimentary rhythm of bedded chert is paced by astronomical cycles thereby indicating the potential of bedded chert as a template for a mesozoic cyclostratigraphy

monsoon climate of the early holocene climate experiment with the earth s orbital parameters for 9000 years ago values for the precession and obliquity of the earth 9000 years ago indicate that the global average solar radiation for july 9000 years ago was 7 percent greater than at present when the estimated solar radiation values are used in a low resulation climate model the model simulates an intensified continent scale monsoon circulation this result agrees with paleoclimatic evidence from africa arabia and india that monsoon rains were stronger between 10 000 and 5000 years ago than they are today

astronomical calibration of the toarcian stage implications for sequence stratigraphy and duration of the early toarcian oae the toarcian oceanic anoxic event t oae of the early jurassic period involves one of the largest perturbations of the carbon cycle in the past 250 ma recorded by a pronounced negative carbon isotope excursion cie numerous studies have focused on potential causes of the t oae and cie but are hampered by an uncertain timescale here we present high resolution 2 kyr magnetic susceptibility ms measurements from the marine marls of the sancerre couy drill core southern paris basin spanning the entire toarcian stage the ms variations document a rich series of sub milankovitch to milankovitch frequencies precession obliquity and eccentricity with the periodic g2 g5 405 kyr and quasi periodic g g 2 4 myr cenozoic mean periodicity eccentricity terms being the most prominent the ms related g g variation reflects third order eustatic sequences and constrains the sequence stratigraphic framework of the toarcian stage in addition ms variations reveal a modulation of g g by g g eccentricity related cycles suggesting that sea level change was the main control on the deposition of the toarcian sancerre marls in tune with the astro climatic frequencies the stable 405 kyr cyclicity constrains a minimum duration of the toarcian stage to 8 3 myr and the well documented cie associated with the t oae to 300 to 500 kyr the 405 kyr ms timescale calibrates the periodicity of the prominent high frequency c cycles that occur in the decreasing part of the cie to 30 to 34 kyr consistent with the toarcian obliquity period predicted for an earth experiencing sustained tidal dissipation

paleomagnetism of red cherts a case study in the inuyama area central japan this study is an attempt to isolate and identify the primary magnetization in red cherts red chert samples from a middle triassic sequence in the inuyama area 35 4 n 137 0 e central japan have a multicomponent magnetization which is delineated by thermal demagnetization two of the components have high coercivity and high blocking temperatures one is carried by hematite and the other by magnetite the former was concluded to be the primary magnetization for two reasons 1 it predates intraformational folding and 2 it records geomagnetic reversals the other component which accounts for the dominant part of natural remanent magnetization was probably acquired at a time long after the deposition two paleomagnetic results were drawn from the middle triassic red chert sequence 1 the mean inclination of the samples in the sequence was 1 4 6 8 therefore the paleolatitude amounts to 0 7 3 4 in contrast to the paleolatitude expected from the paleopole of eurasian continent which is about 70 and 2 the magnetostratigraphy of this sequence indicates that two geomagnetic epochs in the middle triassic are considerably longer more than several million years than the average of those in the cenozoic

redox change in sedimentary environments of triassic bedded cherts central japan possible reflection of sea level change middle triassic radiolarian bedded cherts in the mino belt central japan include a sequence showing an abrupt facies change from the lower to the upper where grey black bedded cherts enriched in carbonaceous matter and framboidal pyrite are overlain by brick red hematitic bed ded cherts brownish yellow chert enriched in goethite and purple red chert occur at the boundary between the grey black bedded cherts and the brick red bedded cherts this facies change is in accor dance with stratigraphic variations of geochemical characteristics the lower section grey black bedded cherts compared with the upper section brick red bedded cherts are enriched in ctot and stot and are characterized by lower mno tio 2 higher feo fe 2 o 3 total iron as fe 2 o 3 and more variable fe2o3 tio2 values some of the lower section samples in addition are characterized by an enrich ment in some transition metals ni cu and zn the covariation of mineralogical and geochemical characteristics indicates that sedimentary environments and diagenetic processes were different between the lower and the upper section bedded cherts during the deposition of the lower section bedded cherts the sedimentary environment was anoxic and bacterial sulphate reduction occurred during the early diagenetic stage in contrast the upper section bedded cherts were subjected to less reducing diagenetic processes active sulphate reduction did not occur the change of sedimentary environment and diagenetic process at the site of deposition is likely to be attributed to the fluctuated concentration of dissolved oxygen in the water mass of a semi closed marginal ocean basin which was potentially caused by sea level change that occurred during middle triassic time

evolution of the cenozoic carbon cycle the roles of tectonics and co2 fertilization cenozoic carbon fluxes associated with rock weathering sediment burial and volcanic degassing are calculated from the mass balance equations coupling marine isotopic records of carbon both organic and inorganic strontium and osmium the result is confirmed by the good match between modeled carbonate sedimentation rates and carbonate sedimentation rates previously integrated from ocean basins worldwide the coevolution between weathering and burial of carbonate suggests that marine carbonate accumulation was regulated mainly by the recycling of carbonate rocks which mediated the bicarbonate ion concentration of the oceans a reduction in co2 effusion to the atmosphere caused by reduced volcanic degassing from 52 to 15 ma and tectonically enhanced organic rock exhumation since 15 ma is also observed these changes in co2 effusion are balanced by concomitant changes in co2 sequestration by silicate weathering and organic carbon burial importantly we demonstrate a clear decoupling of modeled silicate weathering rates from global climate over the last 15 ma this observation is inconsistent with temperature mediated mineral dissolution acting as the key mechanism facilitating the co2 silicate weathering feedback process however we instead observe a clear coupling positive correlation between modeled silicate weathering organic carbon burial and atmospheric co2 concentration we suggest that co2 fertilization effects on terrestrial biomass productivity and plant weathering could have represented a major negative feedback process helping to balance atmospheric co2 at least during the cenozoic ice house periods

astronomical forcing and chronology of the early toarcian early jurassic oceanic anoxic event in yorkshire uk 1 during the early toarcian 183 ma ago a high rate of organic carbon burial globally over a brief interval of time has led to the recognition of a major oceanic anoxic event oae a pronounced negative excursion in the carbon isotope composition of marine organic matter marine carbonate and terrestrial plant material is a key feature of this event but the precise timescale and cause s of this isotopic anomaly are debated associated with the negative carbon isotope excursion is evidence for a coeval rise in seawater palaeotemperature an increase in continental weathering rates and the mass extinction of marine invertebrate species the early toarcian oae provides evidence for the earth s response during rapid climate change and critical to our understanding of the event is a high resolution timescale that allows us to quantify the rates duration and lead lag times of environmental processes in this study we present 2743 new high resolution organic carbon sulphur and carbonate concentration data from samples of well preserved organic rich mudrocks spanning the early toarcian oae in yorkshire uk we have used these data to document the geochemical changes and significantly extend and refine the astronomical timescale across this event our detailed analysis of the relationship between astronomical forcing and carbon isotope changes in both yorkshire and a section from peniche portugal indicates that astronomical forcing paced the timing of major shifts in 13c and hence climate in both sections our analyses also demonstrate that there was a marked increase in the relative strength of astronomical forcing recorded at the onset of the oae and that the recorded nature of astronomical forcing changed during the event both the yorkshire and peniche cyclostratigraphies suggest that one astronomical forcing parameter paced environmental change through the 13c event and that this parameter was obliquity or precession

effects of karoo ferrar volcanism and astronomical cycles on the toarcian oceanic anoxic events early jurassic abstract one of the most profound environmental changes in the mesozoic took place during pliensbachian toarcian early jurassic including oceanic anoxia toarcian oceanic anoxic event t oae the t oae is thought to have been caused by increased atmospheric co 2 triggered by karoo ferrar volcanism this idea however remains debated primarily due to uncertainties in their age constraints of the relevant sedimentary sequences to examine their temporal relationships herein we provide the astronomical time scale of the lower jurassic deep sea bedded chert sequences from the pelagic panthalassa superocean which are exposed in the inuyama area central japan a 405 kyr tuned astrochronology anchored to the end triassic extinction as 201 4 0 2 ma ikeda and tada 2013 allows us to constrain the ages of two black bedded cherts t oae1 and t oae2 the ages of these t oaes overlap u pb ages of karoo volcanic rocks t oae in the european region is also synchronous with the karoo ferrar volcanism based on radiolarian and ammonite biostratigraphic correlation these temporal relationships support the potential impact of karoo ferrar volcanism on t oaes on a global scale on the other hand the onset of t oaes occur at the maxima of 40 kyr 100 kyr and 405 kyr cycles of chert thickness variation the termination of t oaes and the recovery to oxic conditions in pelagic ocean coincide with the minima of 40 kyr 100 kyr and 405 kyr cycles of chert thickness moreover the termination of final black chert and grey chert deposition coincide with the minima of 1800 kyr cycles of chert thickness these temporal relationships imply that orbital scale productivity cycles were important in controlling the onset and termination of t oaes through the carbon cycle dynamics which have been already amplified by karoo ferrar volcanism

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

the early toarcian jurassic anoxic event stratigraphic sedimentary and geochemical evidence detailed paleogeographic studies in the southern alps suggest that an oxygen minimum model is appropriate for interpreting conditions on tethyan continental margins advection of manganese in this low oxygen layer may explain the local occurrence of carbonate ores of this element carbon sulfur and iron sulfur ratios although showing considerable scatter suggest that bottom waters at this time were locally euxinic containing free hydrogen sulfide this oceanic anoxic event was preceded by significant faunal turnover of ammonites in tethys and accompanied by widespread extinction of benthos in northern europe in response to the lateral spread of anoxic bottom waters during transgression similar changes may be recognized in other parts of the world other anoxic events may have taken place during the jurassic but documentation is as yet meagre furthermore models for such phenomena remain largely speculative although upwelling and increased planktonic productivity commencing in pre toarcian time are favored for the falciferum zone event documented here from author

astronomical forcing of a middle permian chert sequence in chaohu south china abstract astronomical forcing has been shown to be a fundamental driver of climate change through geological time pelagic bedded cherts deposited in mesozoic ocean basins with chert mudstone cycles have been shown to contain the imprint of milankovitch astronomical climate forcing in the chaohu region south china we studied a middle permian radiolarian chert sequence gufeng formation with chert mudstone couplets reminiscent of the mesozoic cherts but deposited on a continental shelf spectral analysis of lithologic bed thickness data from two sections of this chert sequence reveals that 13 cm to 20 cm chert mudstone cycles in the stratigraphic domain match theoretical 32 kyr middle permian obliquity cycling together with a hierarchy of other cycles with 12 cm 9 cm 7 cm 6 6 cm and 5 4 cm wavelengths tuning the 13 cm to 20 cm stratigraphic cycles to earth s obliquity cycle periodicity indicates that the cm scale cycles are precession scale variations with a strong 400 kyr amplitude modulation tuning to theoretical precession terms provides further support for the astronomical forcing of the chert sequence we propose that monsoon controlled upwelling contributed to the development of the chert mudstone cycles a seasonal monsoon controlled by astronomical forcing i e insolation influenced the intensity of upwelling stronger upwelling increased radiolarian productivity in the surface ocean increasing silica deposition glacio eustatic oscillations from ice sheet dynamics in southern gondwana modulated terrigenous mud flux to the basin the two processes jointly contributed to the astronomical rhythms of these tropical chert mudstone sequences which are characterized by comparably strong obliquity and precession responses subsequent diagenesis distorted the chert and mudstone layering but not enough to destroy the original stratigraphic patterns the resulting astronomical time scale ats assumes a roadian wordian boundary age of 268 8 ma for the onset of the first chert layer at the base of the sequence and ends at 264 1 ma for a total duration of 4 7 myr

ocean acidification during the early toarcian extinction event evidence from boron isotopes in brachiopods this project was funded by the european union s horizon 2020 research and innovation program under the marie sklodowska curie grant agreement and project base line earth 643084 and by the slovak research and development agency apvv17 0555 and the slovak scientific grant agency vega 0169 19

benthic phosphorus regeneration net primary production and ocean anoxia a model of the coupled marine biogeochemical cycles of carbon and phosphorus we examine the relationships between ocean ventilation primary production water column anoxia and benthic regeneration of phosphorus using a mass balance model of the coupled marine biogeochemical cycles of carbon c and phosphorus p the elemental cycles are coupled via the redfield c p ratio of marine phytoplankton and the c p ratio of organic matter preserved in marine sediments the model assumes that on geologic timescales net primary production in the oceans is limited by the upwelling of dissolved phosphorus to the photic zone the model incorporates the dependence on bottom water oxygenation of the regeneration of nutrient phosphorus from particulate matter deposited at the water sediment interface evidence from marine and lacustrine settings modern and ancient demonstrates that sedimentary burial of phosphorus associated with organic matter and ferric oxyhydroxides decreases when bottom water anoxia dysoxia expands steady state simulations show that a reduction in the rate of thermohaline circulation or a decrease of the oxygen content of downwelling water masses intensifies water column anoxia dysoxia and at the same time increases surface water productivity the first effect reflects the declining supply of oxygen to the deeper parts of the ocean the second effect is caused by the enhanced benthic regeneration of phosphorus from organic matter and ferric oxyhydroxides sedimentary burial of organic carbon and authigenic calcium phosphate mineral francolite on the other hand is promoted by reduced ocean ventilation according to the model global scale anoxia dysoxia leads to a more efficient recycling of reactive phosphorus within the ocean system consequently higher rates of primary production and organic carbon burial can be achieved even when the continental supply of reactive phosphorus to the oceans remains unchanged

influence of water column anoxia on the burial and preservation of carbon and phosphorus in marine shales abstract organic p and organic c concentrations were measured in several well characterized phanerozoic marine shale sequences with the primary focus being the camp run member of the devonian mississippian new albany shale sequences were selected with close spatial association of bioturbated and laminated sediments which reflect deposition from oxic and anoxic waters respectively average organic c p mole ratios calculated from the data are 150 for bioturbated shales and 3900 for the laminated shales of the new albany differences in the extent and mechanisms of early diagenesis related to the oxygenation of waters at the sediment water interface can account for the c p ratios of buried organic matter low c p ratios of bioturbated sediments are attributed to 1 1 the increased ability of bacteria to store p in well oxygenated environments which leads to the production of low c p ratio bacterial biomass and 2 2 the extensive oxidation of sedimentary organic matter resulting in the formation of residual organic phases with low c p ratios high organic c p ratios of laminated sediments are explained by a combination of 1 1 the limited ability of bacteria to store p under anoxic conditions 2 2 extensive p regeneration from sedimentary organic matter 3 3 enhanced c preservation relative to the bioturbated shales it is also shown that relative to organic c laminated shales are not as effective a p sink as are bioturbated shales this provides a mechanism in anoxic environments for burying large quantities of organic matter without simultaneously sequestering the p needed to sustain further productivity

permo triassic boundary superanoxia and stratified superocean records from lost deep sea pelagic cherts of japan and british columbia canada recorded a long term and worldwide deep sea anoxic oxygen depleted event across the permo triassic or paleozoic and mesozoic boundary 251 2 million years ago the symmetry in lithostratigraphy and redox condition of the boundary sections suggest that the superocean panthalassa became totally stratified for nearly 20 million years across the boundary the timing of onset climax and termination of the oceanic stratification correspond to global biotic events including the end guadalupian decline the end permian extinction and mid triassic recovery

cyclostratigraphy and the early jurassic timescale data from the belemnite marls dorset southern england time series based on determinations wt of calcium carbonate and total organic carbon have been generated for the entire lower jurassic hemipelagic belemnite marls dorset southern britain this formation was deposited during early pliensbachian time at a paleolatitude of about 35 n in an epicontinental sea that was largely enclosed by the supercontinent of pangea the sequence contains compositionally diverse light and dark marl bedding couplets the thicknesses of which are notably reduced in the upper third of the section the regularity of the couplets in segments of the sequence combined with a regular amplitude modulation indicates an origin that is related to the orbital precession cycle i e one of the milankovitch parameters a timescale is developed by assigning a duration of 20 k y per couplet and this suggests that the entire formation represents at least 1 78 m y using the new timescale bundles of bedding couplets are shown to have periods consistent with the 123 k y component of the orbital eccentricity variations the amplitude of the couplets varies at the same frequencies as the bundle cycles in accordance with the interpretation that the couplets record precession and the bundles record eccentricity however despite having the same frequency of variation there is no consistent relationship coherence between the variations in amplitude of the couplet cycle and the bundle cycles as would be predicted by the eccentricity precession relationship this mismatch can be explained in terms of nonlinear behavior of a climatic system characterized by a varying response time or nonlinear response of the sedimentary system itself the data contain no evidence for orbital obliquity cycles because the obliquity cycle affects insolation principally at high latitudes the climatic factors that indirectly controlled the sedimentary cyclicity must have arisen at relatively low latitudes the belemnite marls timescale indicates highly variable minimum durations for ammonite zones and subzones true durations cannot be determined because it is possible that the succession is incomplete as a result of undetected erosion and or nondeposition a combination of the new results with cyclostratigraphic data from yorkshire northeast england and the southern alps switzerland indicates based on cycle counts that the pliensbachian stage lasted at least 4 82 m y marine sr isotope ratios appear to have decreased linearly from the start of jurassic time until the end of pliensbachian time the rate of decrease in 87 sr 86 sr established using the belemnite marls timescale was 0 000042 m y or less if the main part of the formation is incomplete using this rate with the observed changes in sr isotope ratios gives minimum durations of 2 86 m y for hettangian time 7 62 m y for sinemurian time and 6 67 m y for pliensbachian time

new perspectives on orbitally forced stratigraphy this survey of the current status of research into earth s orbitally forced paleoclimatic record summarizes recent developments in the theory of earth s orbital parameters and reviews how various techniques of data collection and analysis have fared in the search and recovery of orbital signals in ancient stratigraphy the emerging significance of the quasi periodicity of earth s orbital variations as a prin cipal tool in the analysis of orbitally forced stratigraphy is discussed in detail five case studies are presented that illustrate new directions in research a time series analysis of discontinuous strata b measurement of ultra high resolution stratigraphic signals c new perspectives on the 100 kyr pleistocene glaciation problem d strati graphic evidence for solar system resonance modes and e evaluating phanerozoic length of day from orbitally forced stratigraphy the study of how earth s orbital parameters came to be recorded in ancient stra tigraphy has recently moved into a new phase of scientific inquiry and discovery notable advances in celestial mechanics and in the analysis of stratigraphic data have given rise to new ways of solving old problems and have uncovered new problems for the first time new tools have facilitated the recovery of extended high resolution orbital signals from stratigraphy advanced analytical techniques have now been fully incorporated into the field an updated theory of earth s orbital parameters provides an accurate ephemeris for the past 16 million years for precision correlation between earth s orbital parameters and orbitally forced stratigraphy some orbital eccentricity modes can be used for orbital stratal cal ibrations to several hundred million years ago these breakthroughs have transformed the study of orbitally forced stratigra phy into an applied field that addresses long standing problems in disciplines as far ranging as geochronology geodynamics and astrodynamics orbital signals provide the framework for a high resolution orbital chronostratigraphy as far back

evidence for enhanced phosphorus regeneration from marine sediments overlain by oxygen depleted waters phosphorus regeneration and burial fluxes determined from in situ benthic flux chamber and solid phase measurements at sites on the californian continental margin peruvian continental slope north carolina continental slope and from the santa monica basin california are reported comparison of these sites indicates that o2 depleted bottomwaters enhance p regeneration from sediments diminishing overall phosphorus burial efficiency based on these observations a positive feedback linking ocean anoxia enhanced benthic phosphorus regeneration and marine productivity is proposed on shorter timescales these results also suggest that o2 depletion in coastal regions caused by eutrophication may enhance p regeneration from sediments thereby providing additional p necessary for increased biological productivity