magnetic susceptibility as a high resolution correlation tool and as a climatic proxy in paleozoic rocks merits and pitfalls examples from the devonian in belgium low field magnetic susceptibility in measurements are quick and sensitive enabling the creation of high resolution records making in an attractive correlation tool and a proxy for paleoclimate and paleoenvironments in geologically young material foremost in cenozoic sediments in belongs to the geoscientist s toolkit however in is a convolved signal and may reflect other processes than the often implicitly inferred depositional conditions diagenesis remagnetization and low grade metamorphism can potentially obscure the original depositional in signal this aspect is particularly important when interpreting in records from paleozoic rocks here we review data obtained from a large sample collection of middle to upper devonian sections in belgium comparison of in trends with paleoenvironmental indicators facies and with detrital input proxies zr th ti al allowed to assess the persistence of depositional trends furthermore the in signal was deconvolved into its dominant mineralogical contributions with the help of magnetic property analysis the main results are pointing to a magnetic signal dominated by fine grained magnetite of which paleomagnetic analysis indicated a formation during carboniferous remagnetization this prompts a potentially strong influence of post depositional processes and it complicates the interpretation of in records in terms of depositional environments however in most of the sections there is a relatively good relationship between in trends and facies evolution and between in and geochemical proxies for detrital inputs this indicates that the newly formed magnetite grains would at least partly remain where they are formed and this allows a relative preservation of the original signal despite the strong influence of diagenesis two sections show a stronger impact of diagenesis where for about half of these sections the primary depositional information is lost the eifelian givetian monts de baileux section was selected for time series analysis of the in series the average spectral misfit asm method is applied to explicitly evaluate the null hypothesis of no orbital signal and in this section there is 99 05 chance that the ms signal is reflecting an orbital imprint

milankovitch period uncertainties and their impact on cyclostratigraphy abstract astronomically calibrated cyclostratigraphy relies on correct matching of observed sedimentary cycles to predicted astronomical drivers such as eccentricity obliquity and climate precession however the periods of these astronomical cycles in the past are not perfectly known because i they drift through time ii they overlap and iii they are affected by the poorly constrained recession history of the moon this paper estimates the resulting uncertainties in ancient milankovitch cycle periods and shows that they lead to i problems with using milankovitch cycles for accurate measurement of durations potential errors are around 25 by the start of the phanerozoic ii problems with correctly identifying the milankovitch cycles responsible for observed period ratios e g the ratio for long eccentricity short eccentricity overlaps within error with the ratio for short eccentricity precession and iii problems with verifying that observed cycles are milankovitch driven at all the probability of a random period ratio matching a predicted milankovitch ratio within error is 20 70 in the phanerozoic milankovitch derived ages and durations should therefore be treated with caution unless supported by additional information such as radiometric constraints

geologic evidence for chaotic behavior of the planets and its constraints on the third order eustatic sequences at the end of the late paleozoic ice age abstract high resolution 948 samples measurements of anhysteretic remanent magnetization arm were performed on the 200 m thick early middle permian maokou formation of the shangsi section south china the arm variations are quasi periodic and the wavelengths of significant cycles collectively present a ratio of 20 5 2 1 throughout the formation corresponding to long orbital eccentricity short orbital eccentricity obliquity and precession cycles a strong obliquity 44 and 33 kyr signal suggests that waning and waxing of the ice sheet in eastern australia at the end of the late paleozoic ice age lpia exerted a significant influence on global climate and sea level a floating astronomical time scale ats is developed using the 405 kyr orbital eccentricity cycle as an astronomical calibration target this results in estimation of the roadian and wordian stages duration as 3 7 0 4 myr and 2 9 0 4 myr respectively prominent 2 myr cycles likely originated from earth and mars secular frequencies g4 g3 and 1 myr cycles from s4 s3 these periodicities are shorter than those observed in the cenozoic era which may be due to the chaotic behavior of the planets but still reflecting 2 1 secular resonance between earth and mars third order eustatic sequences are linked to the s4 s3 obliquity term which suggests a glacioeustatic controlling mechanism during this transitional stage from paleozoic icehouse to mesozoic greenhouse

cyclostratigraphic calibration of the frasnian late devonian time scale western alberta canada until now the duration of the frasnian stage has remained very poorly constrained hampering a detailed understanding of sedimentation processes and environmental and evolutionary change in this study timeseries analyses of high resolution 10 20 k y magnetic susceptibility data identify sixteen 405 k y eccentricity cycles in the magnetic susceptibility stratigraphy of the frasnian late devonian derived from carbonate platform and surrounding slope and basin deposits in western alberta canada previous studies demonstrated the generally consistent pattern of magnetic susceptibility change across the alberta basin and thus demonstrated the utility of magnetic susceptibility stratigraphy as a refi ned regional correlation tool compared to biostratigraphy in the present study we show that the magnetic susceptibility stratigraphy of the frasnian interval in western alberta has been signifi cantly infl uenced by astro nomical forcing using the sixteen 405 k y eccentricity cycles as a geochronometer we constructed a frasnian astronomical time scale this time scale indicates a duration of 6 5 0 4 m y for the frasnian calibrating this duration to the best available devonian chronology the absolute age of the givetian frasnian boundary is recalculated to 383 6 3 0 ma and the age of the frasnian famennian boundary is recalculated to 376 7 3 0 ma these new absolute ages take into account the astronomically derived duration of the frasnian but they also yield a narrowing of the error margins of the absolute ages by several hundreds of thousands of years

astronomical tuning of the aptian stage from italian reference sections a high resolution grayscale series of the pelagic fucoid marls piobbico core central italy shows strong pervasive lithological rhythms throughout the aptian interval a hierarchy of centimeter to meter scale cycles characterizes the rhythms when calibrating 1 m cycles to earth s 405 k y orbital eccentricity cycle these rhythms correspond to the periods of the eccentricity obliquity and precession index tuning to orbital eccentricity cycles provides a high resolution time scale for the aptian correlation to the cismon core northern italy extends the tuning to the aptian barremian boundary the tuning indicates a minimum duration of 13 42 m y for the aptian stage where previous estimates range from 6 4 to 13 8 m y the combined aptian albian astronomical tuning of the entire 77 m long piobbico core and part of the cismon core provides a 25 85 m y long astronomically calibrated time scale for earth history

climatic and oceanic changes during the middle late ordovician transition in the tarim basin nw china and implications for the great ordovician biodiversification event abstract the middle late ordovician transition darriwilian to sandbian age witnessed a major pulse of the great ordovician biodiversification event gobe and distinctive oceanic geochemical fluctuations such as coeval negative c and sr isotope excursions in this study investigations into geochemical variations notably the hg abundance or hg toc have been carried upon the organic rich black shale of the middle upper ordovician saergan formation to unravel the causes of this pulse based on these data three phases were identified phase 1 0 to 3 m is characterized by rising hg toc up to 138 ppb wt and ti al values as well as high ciacorr corrected chemical index of alteration values 68 9 72 3 with negligible enrichment of redox sensitive elements rse and nutrient elements e g u 5 2 ppm v 153 ppm mo 1 8 ppm p2o5 0 2 suggesting intensified volcanism which could have emitted significant amounts of greenhouse gases thereby leading to climate warming in contrast phase 2 3 to 11 m is characterized by decreasing hg toc and ti al ratios relatively low though slightly fluctuating ciacorr values generally depleted in rse except moderately enriched u up to 14 6 ppm and increased p al and ba al ratios implying weakening volcanic activity and subsequent climate cooling and the potential for improved seawater ventilation as a result of oceanic upwelling phase 3 sandbian age 11 13 m witnessed continuous decrease in hg toc ratio an increase in ti al and ciacorr values fairly low values of rse enrichment and p al and ba al ratios indicating recurrent climate warming and the potential for slowed oceanic circulation and attenuated upwelling of nutrient rich deep waters onto the shallow shelf these changes could have diminished bioproductivity and organic output onto the seafloor this study offers insights into volcanic climatic oceanic interactions during a major pulse of the gobe around the middle late ordovician transition while black shales were extensively deposited

sea level curve for the middle to early late ordovician in the armorican massif western france icehouse third order glacio eustatic cycles abstract this contribution deals with the middle to early late ordovician of the armorican massif western france the aim is to reconstruct a multi order eustatic curve from the stratigraphic record the studied section crozon peninsula area shows sediments deposited in tidal to storm dominated shelf environments a sequence analysis facies and stacking pattern analyses combined with a gamma ray record and a backstripping procedure was carried out chitinozoan assemblages provide the biostratigraphic framework including time calibration the stratigraphic succession is dominated by the stacking of sequences representing different orders of sea level change i e very high formosa and pissotensis biozones of the darriwilian the reconstructed sea level curve reveals that most of the third order cycles comprise three fourth order cycles of assumed 400 kyr duration this 1 2 myr duration of the ordovician third ordersequences suggests that they may be related to long period obliquity cycles an orbital forcing characteristic of icehousesequences in the late cenozoic and the quaternary these results imply that the major part of the middle and early late ordovician was characterized by icehouse conditions and third orderglacio eustatic cycles a time calibration of the chitinozoan biozones was developed from the sequential analysis it suggests that the early darriwilian biozones from henryi to calix biozones have short durations of several 10 to several 100 kyr whereas the pissotensis biozone has a temporal extent of several myr extending into the early sandbian

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

astronomical cycles in the serpukhovian moscovian carboniferous marine sequence south china and their implications for geochronology and icehouse dynamics abstract the late paleozoic ice age ca 335 260 ma lpia has long been considered as an analogy for the cenozoic ice age since the oligocene the impact of astronomical forcing on the lpia glaciation has been hampered due to the low resolution multi million year scale time framework in the present study high resolution cyclostratigraphy based on magnetic susceptibility ms covering the serpukhovian to late moscovian icehouse climate has been investigated in the luokun section of south china power spectral analysis of the ms series reveals 3 44 4 m 0 8 1 07 m 0 3 0 32 m and 0 17 0 19 m thick sedimentary cycles based on the available biostratigraphic constraints calibrating the 3 44 4 m cycles to the 405 kyr eccentricity cycles indicates short eccentricity 136 and 100 kyr short obliquity 34 kyr and precession 19 and 15 9 kyr orbital bands in addition to long eccentricity 405 kyr band we assigned the basal serpukhovian and moscovian stages in luokun with the numerical ages from geological time scale 2012 to construct two floating time scales ranging from 331 55 0 5 ma to 323 2 0 5 ma and from 315 34 0 35 ma to 310 17 0 35 ma respectively the modulation of main obliquity s4 s3 term has a main periodicity of 1200 kyr the modulation of 100 kyr eccentricity g4 g3 term shows a main periodicity of 2400 kyr with subordinate periodicities of 1620 and 1200 kyr for the serpukhovian and a main periodicity of 1600 kyr for the moscovian they may provide the geological evidence for a chaotic resonance associated with interactions between the orbits of mars and the earth in the carboniferous a duration of 7 68 0 15 myr was estimated for the serpukhovian stage eight higher accumulation rate events due to glacioeustatic drawdown were temporally constrained and show close correspondence to far field and near field reconstructions of the lpia glaciation glacioeustasy was paced with 405 kyr long eccentricity and 1 2 myr obliquity amplitude cycles during the serpukhovian and moscovian stages likely indicating the nature in the warmer icehouse world similar to that of the oligocene to pliocene

a record of astronomically forced climate change in a late ordovician sandbian deep marine sequence ordos basin north china abstract the late ordovician pingliang formation on the southwestern margin of the ordos basin north china consists of rhythmic alternations of shale limestone and siliceous beds to explore the possible astronomical forcing preserved in this lithological record continuous lithological rank and magnetic susceptibility ms stratigraphic series were obtained from a 34 m thick section of the pingliang formation at guanzhuang power spectral analysis of the ms and rank series reveal 85 5 cm to 124 cm 23 cm to 38 cm and 15 cm to 27 cm thick sedimentary cycles that in ratio match that of late ordovician short eccentricity obliquity and precession astronomical cycles the power spectrum of the ms time series calibrated to interpreted short orbital eccentricity cycles aligns with spectral peaks to astronomical parameters including 95 kyr short orbital eccentricity 35 3 kyr and 30 6 kyr obliquity and 19 6 kyr and 16 3 kyr precession cycles the 15 cm to 27 cm thick limestone shale couplets mainly represent precession cycles and siliceous bed deposition may be related to both precession and obliquity forcing we propose that precession forced sea level fluctuations mainly controlled production of lime mud in a shallow marine environment and transport to the basin precession and obliquity controlled biogenic silica productivity and temperature dependent preservation of silica may have been influenced by obliquity forcing

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

cyclostratigraphic calibration of the famennian stage late devonian illinois basin usa abstract the late devonian biosphere was affected by two of the most severe biodiversity crises in earth s history the kellwasser and hangenberg events near the frasnian famennian f f and the devonian carboniferous d c boundaries respectively current hypotheses for the causes of the late devonian extinctions are focused on climate changes and associated ocean anoxia testing these hypotheses has been impeded by a lack of sufficient temporal resolution in paleobiological tectonic and climate proxy records while there have been recent advances in astronomical calibration that have improved the accuracy of the frasnian time scale and part of the famennian the time duration of the entire famennian stage remains poorly constrained during the late devonian a complete late frasnian early carboniferous succession of deep shelf deposits accumulated in the epieric sea in illinois basin of the central north american mid continent a record of this sequence is captured in three overlapping cores h 30 sullivan and h 32 the h 30 core section spans the f f boundary the sullivan section spans almost all of the famennian and the h 32 section sampled spans the interval of the upper famennian and the d c boundary to have the best chance of capturing milankovitch cycles 2000 rock samples were collected at minimum 5 cm interval across the entire sequence magnetic susceptibility ms was measured on each sample and the preservation of climatic information into the ms signal was verified through geochemical analyses and low temperature magnetic susceptibility acquisition to estimate the duration of the famennian stage we applied multiple spectral techniques and tuned the ms signal using the highly stable 405 kyr cycle for sullivan and the obliquity cycle for the h 30 and h 32 cores based on the correlation between the cores we constructed a famennian floating astronomical time scale which indicates a duration of 13 5 0 5 myr an uncertainty of 0 5 myr was estimated for the uncertainties arising from the errors in the stratigraphic position of the f f and d c boundaries and the 405 kyr cycle counting interpolated from the high resolution u pb radiometric ages available for the devonian carboniferous boundary we recalibrated the frasnian famennian boundary numerical age to 372 4 0 9 ma

differential energy radiation from two earthquakes in japan with identical mw the kyushu 1996 and tottori 2000 earthquakes we examine two closely located earthquakes in japan that had identical moment magnitudes m w but significantly different energy magnitudes m e we use teleseismic data from the global seismograph network and strong motion data from the national research institute for earth science and disaster prevention s k net to analyze the 19 october 1996 kyushu earthquake m w 6 7 m e 6 6 and the 6 october 2000 tottori earthquake m w 6 7 m e 7 4 to obtain regional estimates of radiated energy e s we apply a spectral technique to regional 200 km waveforms that are dominated by s and lg waves for the thrust fault kyushu earthquake we estimate an average regional attenuation q f 230 f 0 65 for the strike slip tottori earthquake the average regional attenuation is q f 180 f 0 6 these attenuation functions are similar to those derived from studies of both california and japan earthquakes the regional estimate of e s for the kyushu earthquake 3 8 1014 j is significantly smaller than that for the tottori earthquake e s 1 3 1015 j these estimates correspond well with the teleseismic estimates of 3 9 1014 j and 1 8 1015 j respectively the apparent stress a e s m with equal to rigidity for the kyushu earthquake is 4 times smaller than the apparent stress for the tottori earthquake in terms of the fault maturity model the significantly greater release of energy by the strike slip tottori earthquake can be related to strong deformation in an immature intraplate setting the relatively lower energy release of the thrust fault kyushu earthquake can be related to rupture on mature faults at a subduction environment the consistence between teleseismic and regional estimates of e s is particularly significant as teleseismic data for computing e s are routinely available for all large earthquakes whereas often there are no near field data

did cooling oceans trigger ordovician biodiversification evidence from conodont thermometry the ordovician period long considered a supergreenhouse state saw one of the greatest radiations of life in earth9s history previous temperature estimates of up to 70 c have spawned controversial speculation that the oxygen isotopic composition of seawater must have evolved over geological time we present a very different global climate record determined by ion microprobe oxygen isotope analyses of early ordovician silurian conodonts this record shows a steady cooling trend through the early ordovician reaching modern equatorial temperatures that were sustained throughout the middle and late ordovician this favorable climate regime implies not only that the oxygen isotopic composition of ordovician seawater was similar to that of today but also that climate played an overarching role in promoting the unprecedented increases in biodiversity that characterized this period

siliceous volcanic associations of the northern balkhash ophiolite zone central kazakhstan biostratigraphy sedimentation and tectonic evolution in the middle late ordovician abstract the northern balkhash zone is the largest and the most complex ophiolite zone of the junggar balkhash region in the west of the central asian orogenic belt the zone encompasses serpentinite melange containing fragments of dunite harzburgite dunite verlite pyroxenite complexes layered and isotropic gabbro sheeted dikes and plagiogranites along with stacks of tectonic slivers composed of siliceous siliceous basaltic and siliceous volcanic tuffaceous units conodont finds suggest the middle late darriwilian age of the siliceous basaltic itmurundy fm while the siliceous basalt tiuretai siliceous kazyk and the siliceous tuffaceous uzuntobek formations are close in age extend from the top of darriwilian to the base of katian the siliceous clastic tuffaceous sediments of the obaly fm are the sandbian and katian in age and the volcanic sedimentary dzhamanshuruk fm is broadly upper ordovician dating of these units has also permitted recognition of the units with intricate thrust and fold structure species of the genera periodon pygodus and scabbardella dominate in the conodont assemblages in cherts an uneven distribution of the conodonts in sections is caused by variable siliceous sedimentation rate that depends on productivity of radiolarians the petrochemistry of the volcanics in the itmurundy fm suggests that they correspond to oib and e morb being formed within seamounts or oceanic plateaus while the tiuretai basalts are close to n morb erupted within a spreading center the felsic volcanics in the dzhamanshuruk fm have demonstrated an island arc affinity the proposed evolution model suggests that during the middle late ordovician tectonic settings changed successively from the spreading center to island arc within the northern balkhash zone of the junggar balkhash region

astronomically forced climate change in the late cambrian abstract we report evidence for milankovitch cycles in two drill cores from the cambro ordovician alum shale formation of scandinavia the signal is preserved in elemental abundances recorded at high stratigraphic resolution by core scanning xrf analysis 0 2 mm resolution the new data enable us to establish a floating timeline calibrated to the stable 405 kyr eccentricity cycle for a 8 7 myr interval across the miaolingian furongian boundary this interval spans the steptoean positive carbon isotope excursion spice which is recorded in the 13 corg in the studied drill cores we calculate the durations of the olenus superzone to 3 4 0 2 myr the parabolina superzone to 1 9 0 3 myr the leptoplastus superzone to 0 33 0 18 myr the protopeltura superzone to 0 51 0 20 myr and the spice event straddling the paibian and lower main part of the jiangshanian stage to 3 0 0 2 myr the sedimentation rate shows similar trends at both drilling locations and is inversely correlated to eustatic sea level changes in certain time intervals opening tantalizing new prospects of using cyclostratigraphic analyses of shales to track eustatic sea level variations the identification of obliquity cycles enables us to calculate the cambrian earth moon distance as well as the day length at 493 ma to 368 9 2 3 106 m and 21 78 0 29 hr respectively

theory of chaotic orbital variations confirmed by cretaceous geological evidence variations in the earth s orbit and spin vector are a primary control on insolation and climate their recognition in the geological record has revolutionized our understanding of palaeoclimate dynamics and has catalysed improvements in the accuracy and precision of the geological timescale yet the secular evolution of the planetary orbits beyond 50 million years ago remains highly uncertain and the chaotic dynamical nature of the solar system predicted by theoretical models has yet to be rigorously confirmed by well constrained radioisotopically calibrated and anchored geological data here we present geological evidence for a chaotic resonance transition associated with interactions between the orbits of mars and the earth using an integrated radioisotopic and astronomical timescale from the cretaceous western interior basin of what is now north america this analysis confirms the predicted chaotic dynamical behaviour of the solar system and provides a constraint for refining numerical solutions for insolation which will enable a more precise and accurate geological timescale to be produced

on the origin of cenozoic and mesozoic third order eustatic sequences abstract the origin of third order eustatic sequences is reviewed by comparing recent sequence stratigraphic data to the latest best constrained astronomical model middle eocene to holocene icehouse sequences correspond to 1 2 myr obliquity cycles constraints from oxygen isotope records highlight the link between icehouse sea level lowerings sequence boundaries and 1 2 myr obliquity nodes mesozoic greenhouse sequences show some relation with the 2 4 myr eccentricity cycles suggesting that orbital forcing contribute to sea level change we suggest that during the icehouse large ice sheets associated with significant glacioeustatic changes 25 m up to 120 m changes were mainly governed by obliquity forcing during icehouse worlds obliquity forcing was the stongest control on global sea level and depositional sequences additionally during the middle eocene third order sequences were glacioeustatically driven in tune with 1 2 myr obliquity cycle suggesting that the presence of significant ice sheets is earlier than previously supposed i e early eocene in contrast during greenhouse worlds e g ephemeral small to medium sized or no ice sheets 0 25 m glacioeustatic changes the expression of obliquity in the sedimentary record is weak and intermittent instead the eccentricity signature which is the modulator of climatic precession is documented moreover we presume that greenhouse sequences on the myr scale are global and hence cannot be caused by regional tectonism e g intraplate stress or mantle hot blobs instead the eccentricity link implies a weaker glacioeustatic control because thermoeustasy is too small to explain the sea level changes stratigraphically well documented fourth order sequences may be linked to the astronomically stable strongest amplitude 405 kyr eccentricity cycle and possibly to 160 200 kyr obliquity modulation cycles fifth order sequences to the short 100 kyr eccentricity cycles and finally sixth order sequences to the fundamental obliquity 40 kyr and climatic precession 20 kyr cycles these astronomical cycles could be preserved in the sedimentary record and have been demonstrated to control sea level changes accordingly by placing depositional sequence orders into a high resolution temporal framework i e orbital periodicities standardization of eustatic sequence hierarchy may be possible

conodont biostratigraphy and astronomical tuning of the lower middle ordovician liangjiashan north china and huanghuachang south china marine sections abstract in this study systematic conodont biostratigraphy and cyclostratigraphy are carried out on ordovician sections from the north china and south china blocks the liangjiashan section situated on the north china block margin accumulated shallow marine carbonate during the early ordovician the huanghuachang section gssp for the dapingian stage situated on the south china block margin accumulated thinly bedded carbonates and minor clastics in a deep shelf environment conodont biostratigraphy and 405 kyr long eccentricity cycles interpreted from the liangjiashan and huanghuachang sections are used to establish an astronomical time scale ats for the early middle ordovician period the ats indicates that the duration of the floian stage is 7 08 0 405 myr the temporal ranges of lower middle ordovician conodont biozones are also estimated the durations of the serratognathus bilobatus serratognathus extensus oepikodus communis oepikodus evae and baltoniodus triangularis zones are 1 0 myr 5 1 myr 0 2 myr 0 8 myr and 0 2 myr respectively the evolution of the ratio of obliquity to total power and short eccentricity power to total power depicts periodicities of 1 myr for the s4 s3 term and 1 9 myr shifting to 1 myr for the g4 g3 term the shift in the g4 g3 term may indicate a chaotic transition in the mars and earth orbital motions from a s4 s3 2 g4 g3 to s4 s3 g4 g3 resonance state during the early ordovician

astronomical cycles of middle permian maokou formation in south china and their implications for sequence stratigraphy and paleoclimate abstract high resolution 930 samples magnetic susceptibility ms and anhysteretic remanent magnetization arm analyses were conducted on the 49 m thick middle permian maokou formation at dukou south china spectral analysis of covariant ms and arm series reveal milankovitch cycles with eccentricity obliquity and precession a 5 7 myr floating 405 kyr eccentricity cycle calibrated astronomical time scale was constructed and used as a geochronometer for estimating the durations of the conodont zones the results indicate that the durations of the jinogondolella postserrata j altudaensis j prexuanhanensis and j xuanhanensis conodont zones were 490 kyr 560 kyr 820 kyr and 750 kyr respectively the 405 kyr calibrated ms and arm series also show prominent 1 myr cyclicity which may correspond to the secular frequencies of earth and mars s 4 s 3 in the middle permian the early capitanian time interval was synchronous with the kamura cooling event and the accentuated obliquity cycling may signal ice sheet expansion the modulations of the obliquity have a close relationship with third order eustatic sequences of the wordian and capitanian stages suggesting a glacioeustatic origin during the middle permian

stability of the astronomical frequencies over the earth s history for paleoclimate studies the expected changes over the past 500 million years in the principal astronomical frequencies influencing the earth s climate may be strong enough to be detectable in the geological records and such effects have been inferred in several cases calculations suggest that the shortening of the earth moon distance and of the length of the day back in time induced a shortening of the fundamental periods for the obliquity and climatic precession from 54 to 35 41 to 29 23 to 19 and 19 to 16 thousand years over the last half billion years at the same time the precessional constant increased from 50 to 61 arc seconds per year the changes in the frequencies of the planetary system due to its chaotic motion are much smaller their influence on the changes of the periods of climatic precession obliquity and eccentricity of the earth s orbit around the sun can be neglected eccentricity periods used for quaternary climate studies may therefore be considered to have been more or less constant for pre quaternary times

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

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

new gps constraints on the africa eurasia plate boundary zone in southern italy 1 southern italy is a key area for understanding the tectonic processes in the africa eurasia collision zone we analyze new gps measurements carried out between 1994 and 2001 the results are presented in terms of time series trajectories and velocities of crustal motion as well as a geodetic strain rate field while central italy corsica sardinia and the tyrrhenian sea move like the eurasian plate the overall motion of the sicily rift zone region matches african plate motion unexpected are the north northwest directed motions of northeastern sicily and the eolian islands most striking on the deformation field are a north south oriented compression along the northern sicilian coast compression between apulia and northwestern greece as well as extension in the sicily rift zone and the interior of sicily

astronomically forced cyclicity in the upper ordovician and u pb ages of interlayered tephra oslo region norway abstract the late ordovician world experienced a series of huge volcanic eruptions recorded as the big deicke millbrig and kinnekulle bentonites together with numerous thinner beds the kinnekulle event can be traced across northwestern europe u pb zircon ages are here presented of both the kinnekulle k bentonite and the uppermost recorded tephra layer in the upper ordovician of the oslo region norway the tephras are located in the upper part of the arnestad formation sandbian south of oslo and gave ages of 454 52 0 50 ma the kinnekulle k bentonite and 453 91 0 37 ma the upper grimstorp k bentonite the dated tephras are separated by a 7 m thick shale succession with subordinate nodular limestone beds although the two u pb ages overlap within errors statistical considerations indicate a most likely time interval of about 600 kyr between the tephras high resolution magnetic susceptibility logging in the same section shows cycles that likely represent changes in sediment supply in response to astronomical forcing spectral analysis shows the presence of long 400 kyr and short 100 kyr eccentricity bands and obliquity components in the 30 kyr band precessional cycles are not detected based on this method it is possible to estimate a time interval of 766 kyr between the two tephra events and the radiometric dating therefore does not exclude a milankovitch interpretation of the cycles this opens new possibilities for understanding the evolution of one of the world s best preserved ordovician marine systems

cyclostratigraphy and its revolutionizing applications in the earth and planetary sciences over the past 25 yr the science of stratigraphy has evolved to include time correlative data from vastly disparate components of the earth system not least of these is the global signal afforded by cyclostratigraphy which has recorded the evolution of earth s astronomical milankovitch forcing of insolation and the paleoclimate system fossil astronomical signals are collected from cyclic sedimentary sequences by detailed sampling and study of facies geochemistry mineralogy rock magnetism color etc in step with the documentation of astronomically forced paleoclimate from ever older older geologic times innovations in computational science have provided ever longer high accuracy astronomical model targets that can be used for time scale calibration the earth s orbit is affected by motions of other planets notably the orbital perihelia of venus and jupiter which impose a dominant 405 k y eccentricity cycle on earth s orbital evolution the large mass of jupiter stabilizes this cycle over hundreds of millions of years the cyclostratigraphic record of 405 k y cycles is therefore often used to correct chronologies affected by variable sedimentation earth s shape and rotation rate are influenced by tidal dissipation and climate friction these effects affect earth s precession rate through time thus a record of earth moon evolution is also embedded in cyclostratigraphy the geochronologic value of cyclostratigraphy has been affirmed through intercalibration with high precision radioisotope dating which today has the potential to define the ages of stratigraphic horizons with 2 uncertainties at the scale of a precession cycle precession index phasing relative to that of the obliquity elucidates the seasonal nature of astronomical forcing of the paleoclimate system cyclostratigraphy contributes to our knowledge of planetary dynamics for times prior to the current ca 50 ma limit of accurate astronomical solutions and it will guide our future understanding of solar system evolution and the evidence for chaotic diffusion astronomical modeling is undergoing its own revolution with development of new numerical integrators to extend accuracy further back in time finally space exploration has revealed prominent sedimentary bedding and ice stratigraphy on the surface of mars with patterns suggestive of astronomical forcing analogous to earth

seismic energy release in mexican subduction zone earthquakes we estimated radiated seismic energy es from 18 shallow thrust mexican subduction zone earthquakes 4 1022 m 1 1 1028 dyne cm 11 h 37 km using digital accelerograms from the guerrero accelerograph array and neglecting stations with large site effects es is computed by integrating squared velocity spectra after applying geometrical spreading and q corrections we discarded epicentral recordings for the largest michoacan event we find that log es m 4 152 0 275 which gives a median value of es m and apparent stress a of 7 1 10 5 and 24 bars respectively the median es m value is in accordance with gutenberg and richter s g r 1956 formula for es in which es m 5 10 5 is implicit worldwide es m data where es is computed from local records mostly fall between 5 10 5 and 5 10 4 for events with m 1022 dyne cm on the other hand es m values generally lie between 5 10 6 and 5 10 5 if es is estimated from teleseismic records especially anomalous are the es m data from kikuchi and fukao 1988 for large and great earthquakes which fall near 5 10 6 thus while es from local data suggests that the g r relation seldom overestimates seismic energy release the teleseismic data point to the contrary the cause of this discrepancy may lie in the difficulty of resolving incoherent radiation from the fault and inappropriate choice of t in the analysis of teleseismic data

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

a chronology of paleozoic sea level changes sea levels have been determined for most of the paleozoic era 542 to 251 million years ago but an integrated history of sea levels has remained unrealized we reconstructed a history of sea level fluctuations for the entire paleozoic by using stratigraphic sections from pericratonic and cratonic basins evaluation of the timing and amplitude of individual sea level events reveals that the magnitude of change is the most problematic to estimate accurately the long term sea level shows a gradual rise through the cambrian reaching a zenith in the late ordovician then a short lived but prominent withdrawal in response to hirnantian glaciation subsequent but decreasingly substantial eustatic highs occurred in the mid silurian near the middle late devonian boundary and in the latest carboniferous eustatic lows are recorded in the early devonian near the mississippian pennsylvanian boundary and in the late permian one hundred and seventy two eustatic events are documented for the paleozoic varying in magnitude from a few tens of meters to 125 meters

cyclic late katian through hirnantian glacioeustasy and its control of the development of the organic rich wufeng and longmaxi shales south china abstract deposition of the organic rich shales of the wufeng and lowermost longmaxi formations late katian through hirnantian occurred in a relatively stable tectonic setting and commenced at approximately 4 5 myr prior to the end ordovician glacial maximum these organic rich shales are important because they provide a continuous sedimentary record of high frequency eustatic changes associated with ice sheet expansion and shrinkage here we carried out a high resolution cyclostratigraphic study of fe3 series and associated geochemical analysis of the wufeng and lowermost longmaxi shales in order to better understand sea level cyclicity in the late katian through hirnantian ocean the organic rich shales deposited during this interval in the ehd1 drill core yichang china record four major myr scale eustatic cycles which were associated with third order sea level fluctuations within each of these major cycles 3 4 minor eustatic cycles corresponding to 405 kyr long eccentricity astronomical cycles were recognized and representing fourth order eustatic changes the cyclostratigraphic age of this study is generally in agreement with the radiometric dates in gts2012 although the duration of the hirnantian stage is 0 5 myr longer than previously thought this study also infers glacial controls on the depositional environment of the organic rich shales as enhanced cooling triggered ice sheet expansion and concurrent sea level fall leading to higher thermohaline circulation intensity and enhanced paleoproductivity through upwelling and terrestrial influx in contrast warming intervals led to ice sheet shrinkage and concurrent deepening characterized by water column stratification and reduced nutrient supply the results provide evidence in support of continuous continental glaciation in the late katian through hirnantian

astronomical calibration of the middle ordovician of the yangtze block south china abstract establishing a high precision numerical geological time scale for the paleozoic era remains a considerable challenge in this study we conducted detailed cyclostratigraphic analysis on the middle ordovician of the huangnitang section and the core changjin 3 cj 3 zhejiang province south china magnetic susceptibility ms series were obtained from a total of 3909 discrete samples and are used as a paleoclimate proxy indicative of variations in detrital input of magnetic minerals power spectral analyses show that both the section and core have recorded an excellent hierarchy of milankovitch cycles of 405 kyr 101 135 kyr 31 34 kyr and 15 8 21 3 kyr an integrated floating astronomical time scale ats for the section and core was established according to the extracted stable 405 kyr eccentricity cycles this new floating ats suggests that the durations of the darriwilian and dapingian stages were 8 38 0 4 myr and 1 97 0 7 myr and the durations of complete graptolite zones of the middle ordovician were precisely estimated the ratios of band obliquity or short eccentricity power to total power reveal periodicities of 1 2 myr for the s4 s3 term and 1 9 myr for the g4 g3 term and 1 2 myr obliquity cycles may have controlled global third order eustatic sequences during the late darriwilian

stratigraphy of the middle devonian boundary formal definition of the susceptibility magnetostratotype in germany with comparisons to sections in the czech republic morocco and spain abstract one major difficulty in geology is high resolution correlation among widely separated sections especially in the paleozoic where magnetostratigraphy polarity is not well established because rocks are often remagnetized where critical biostratigraphic zonation may be poor or lacking or where structural complexities make correlations very difficult to address this problem we have been using magnetostratigraphy susceptibility measurements here we report our work from the middle devonian in europe and north africa the middle devonian emsian eifelian global boundary stratotype section and point gssp located in the eifel hills western germany was ratified by the international subcommission on stratigraphy in 1985 after careful evaluation of the biostratigraphy for this and many other sections the boundary interval has been characterized using biostratigraphy and the beginning of the eifelian stage has been specifically defined by the first occurrence of the conodont polygnathus costatus partitus we have collected the eifel hills section for magnetic susceptibility ms measurement and here we establish it as the magnetostratotype for the emsian eifelian stage boundary by formally defining the magnetostratigraphy susceptibility for the section we then collected measured and compared the magnetostratotype to four other sections for which conodont biostratigraphy has been studied and where p costatus partitus is present two emsian eifelian sections in morocco and two sections in the czech republic including the emsian eifelian parastratotype finally we have measured the ms for the el puerto creek section in the cantabrian mountains of spain and identified the location of the emsian eifelian boundary within the section based on ms comparison to the gssp in conjunction with excellent biostratigraphic indicators primarily brachiopods while the conodont zonation in the el puerto creek section is poorly defined we believe that the correspondence between the ms and biostratigraphy in the section allows the identification of the emsian eifelian boundary these results indicate that this method can be successfully applied to marine sequences where ambiguities in correlation exist

stable carbon isotope stratigraphy in the ordovician of south china abstract about 500 samples from 11 ordovician sections in south china have been analysed for their 13 c carb composition four sections are located in the yangtze platform region the remaining seven sections in the jiangnan slope region the sections span more or less the entire ordovician but the sample resolution in its lower part tremadocian to dapingian is lower than in its upper part darriwilian to hirnantian overall the data show a good correlation with the published global isotope curve at the cambrian ordovician boundary positive values are observed in the succeeding tremadocian the values decrease and remain negative into the early floian in the late floian the values increase to slightly positive the correlation of dapingian rocks between the yangtze and the jiangnan regions is somewhat problematic which might be due to high siliciclastic input in the yangtze section in the darriwilian a small positive excursion is observed in the yangtze platform area however it is missing in the jiangnan slope area this excursion probably correlates with the mid darriwilian excursion mdice reported from baltoscandia both chemostratigraphy and conodont biostratigraphy indicate a possible gap between the shihtzupu formation and the pagoda formation i e most of the sandbian is probably not represented in the upper yangtze region the earliest katian is characterised by a pronounced positive excursion correlating with the well known global guttenberg excursion gice in the late katian at least one additional positive excursion was determined the precise biostratigraphy however is not clear and therefore it is not known which of the known four to five remaining katian 13 c excursions identified in baltica correlate s with the one s observed in the present study and further biostratigraphic study is required the lower part of the hirnantian excursion hice is probably not preserved with only small remnants of the hice observed near the base of the kuanyinchiao bed

oligocene climate dynamics a planktonic and benthic foraminiferal stable isotope stratigraphy of the oligocene equatorial pacific ocean drilling program site 1218 was generated at 6 kyr resolution between magnetochrons c9n and c11n 2n 26 4 30 ma on a newly developed astronomically calibrated timescale our data allow a detailed examination of oligocene paleoceanography the evolution of the early cryosphere and the influence of orbital forcing on glacioeustatic sea level variations spectral analysis reveals power and coherency for obliquity 40 kyr period and eccentricity 110 405 kyr orbital bands with an additional strong imprint of the eccentricity and 1 2 myr obliquity amplitude cycle driving ice sheet oscillations in the southern hemisphere planktonic and benthic foraminifera 18o are used to constrain the magnitude and timing of major fluctuations in ice volume and global sea level change glacial episodes related to obliquity and eccentricity variations occurred at 29 16 27 91 and 26 76 ma corresponding to glacioeustatic sea level fluctuations of 50 65 m alteration of high latitude temperatures and antarctic ice volume had a significant impact on the global carbon burial and equatorial productivity as cyclic variations are also recorded in the carbon isotope signal of planktonic and benthic foraminifera the water column carbon isotope gradient and estimated percent carbonate of bulk sediment we also investigate the implications of a close correspondence between oxygen and carbon isotope events and long term amplitude envelope extrema in astronomical calculations during the oligocene and develop a new naming scheme for stable isotope events on the basis of the 405 kyr eccentricity cycle count

oxygenation as a driver of the great ordovician biodiversification event the largest radiation of phanerozoic marine animal life quadrupled genus level diversity towards the end of the ordovician period about 450 million years ago a leading hypothesis for this great ordovician biodiversification event is that cooling of the ordovician climate lowered sea surface temperatures into the thermal tolerance window of many animal groups such as corals a complementary role for oxygenation of subsurface environments has been inferred based on the increasing abundance of skeletal carbonate but direct constraints on atmospheric o2 levels remain elusive here we use high resolution paired bulk carbonate and organic carbon isotope records to determine the changes in isotopic fractionation between these phases throughout the ordovician radiation these results can be used to reconstruct atmospheric o2 levels based on the o2 dependent fractionation of carbon isotopes by photosynthesis we find a strong temporal link between the great ordovician biodiversification event and rising o2 concentrations a pattern that is corroborated by o2 models that use traditional carbon sulfur mass balance we conclude that that oxygen levels probably played an important role in regulating early palaeozoic biodiversity levels even after the cambrian explosion an increase in biodiversity 450 million years ago coincided with a rise in atmospheric oxygen concentrations suggests a geochemical analysis oxygen availability may have thus helped spur the radiation alongside climatic cooling

milankovitch and sub milankovitch cycles of the early triassic daye formation south china and their geochronological and paleoclimatic implications article the mass extinction at the end of permian was followed by a prolonged recovery process with multiple phases of devastation restoration of marine ecosystems in early triassic the time framework for the early triassic geological biological and geochemical events is traditionally established by conodont biostratigra phy but the absolute duration of conodont biozones are not well constrained in this study a rock magnetic cyclostratigraphy based on high resolution analysis 2440 samples of magnetic susceptibility ms and anhysteretic remanent magnetization arm intensity variations was developed for the 55 1 m thick early triassic lower daye formation at the daxiakou section hubei province in south china the lower daye formation shows exceptionally well preserved lithological cycles with alternating thinly bedded mud stone marls and limestone which are closely tracked by the ms and arm variations power spectral wavelet and amplitude modulation am analyses of the arm and ms series reveal strong evidence for the presence of milankovitch to sub milankovitch frequencies dominated by precession index signal and 4 5 ka cycles cy cles expressed by variations in ms and arm were likely controlled by changes in the input of fine grained detrital magnetite which in turn may have been driven by astronomically induced changes in monsoon in tensity in the equatorial eastern paleotethys during the early triassic greenhouse period on the basis of the 100 ka tuning results the astronomically constrained duration of the induan stage is 1 16 ma with the griesbachian and dienerian substages of 490 ka and 670 ka respectively the new astro nomical time scale also provides time constraints for the conodont and bivalve biozones and the carbonate carbon isotope 13 c records of the lower triassic daye formation time constraints for the conodont bio zones include 34 ka for hindeodus parvus 2 4 ka forisarcicella staschei i isarcica 366 ka for neogondolella planata ng carinata 66 ka for neogondolella discreta 255 ka for neospathodus kummeli and 415 ka for neospathodus dieneri the duration for the negative 13 c shift from high 13