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

carbon isotopes and event stratigraphy near the ordovician silurian boundary yichang south china abstract the organic carbon isotope data through the unweathered ordovician silurian boundary strata at the wangjiawan riverside section which is c 180 m southeast of the wangjiawan north section the gssp for the base of the hirnantian stage upper ordovician show that a positive 13 c org excursion begins just below the base of the hirnantian stage and peaks in the lower part of the n extraordinarius biozone this is followed by an interval of slightly reduced 13 c values and a second peak of 2 above pre hirnantian values which occurs in the lower part of the n persculptus biozone upper hirnantian the peaks in 13 c org values can be correlated well with episodes of glacial expansion described from africa and peri gondwanan europe evidence from sedimentological faunal and geochemical data from south china as well as the evidence of glacial sediments in north africa all suggests a short lived glaciation of 1 ma in the ordovician south pole region consisting of at least two major pulses the first phase of gradual glacial expansion began just before the hirnantian epoch and the second phase ended with rapid melting in the late hirnantian early n persculptus biozone

time resolved seismic tomography detects magma intrusions at mount etna the continuous volcanic and seismic activity at mount etna makes this volcano an important laboratory for seismological and geophysical studies we used repeated three dimensional tomography to detect variations in elastic parameters during different volcanic cycles before and during the october 2002 january 2003 flank eruption well defined anomalous low p to s wave velocity ratio volumes were revealed absent during the pre eruptive period the anomalies trace the intrusion of volatile rich 4 weight percent basaltic magma most of which rose up only a few months before the onset of eruption the observed time changes of velocity anomalies suggest that four dimensional tomography provides a basis for more efficient volcano monitoring and short and midterm eruption forecasting of explosive activity

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

development and applications of double difference seismic tomography double difference dd tomography is a generalization of dd location it simultaneously solves for the three dimensional velocity structure and seismic event locations dd tomography uses a combination of absolute and more accurate differential arrival times and hierarchically determines the velocity structure from larger scale to smaller scale this method is able to produce more accurate event locations and velocity structure near the source region than standard tomography which uses only absolute arrival times we conduct a stability and uncertainty analysis of dd tomography based on a synthetic data set currently three versions of the dd tomography algorithms exist tomodd tomofdd and tomoadd tomodd assumes a flat earth model and uses a pseudo bending ray tracing algorithm to find rays between events and stations while tomofdd uses a finite difference travel time algorithm and the curvature of the earth is considered both codes are based on a regularly distributed inversion grid with the former for a local scale and the latter for a regional scale in contrast tomoadd adapts the inversion mesh to match with the data distribution based on tetrahedral and voronoi diagrams we discuss examples of applying dd tomography to characterize fault zone structure image high resolution structure of subduction zones and determine the velocity structure of volcanoes

response of the inter tropical convergence zone to southern hemisphere cooling during upper ordovician glaciation stable isotope ratios of whole rock carbonates and faunas from three low latitude upper ordovician sections demonstrate a coherent pattern of shifting subtropical and tropical water masses and associated climate belts we suggest that tropical water beneath the inter tropical convergence zone 18o 10 to 15 was isotopically light reflecting high sea surface temperatures sst and reduced sea surface salinity sss subtropical water in both the northern and southern hemispheres is characterised by 18o values from 4 to 6 our interpretation is consistent with the published results from physical chemical modeling of ordovician seawater composition and climate models deriving absolute temperature and salinity values from ordovician 18ocarb data is problematic as they could reflect sst sss ice volume and potentially a variable diagenetic overprint and currently no independent constraints exist for any of these variables the itcz was positioned at 10 n of the equator during the early katian consistent with the likely position of the region of peak sea surface temperature sst during the late katian boda event the itcz moved across the equator to 10 s by analogy with the pliocene this resulted in a symmetrical distribution of sea surface currents about the equator this led to a net increase in heat flow towards the poles and lower latitudinal temperature gradients potentially explaining the migration of warm water faunas to higher southern latitudes during the boda event during the hirnantian the itcz shifted north of the equator resulting in a reduced poleward heat transport itcz position has been proposed as a likely forcing mechanism of neogene glaciation and the evidence from the ordovician suggests a discrete palaeo itcz whose position was controlled by solar insolation and latitudinal temperature gradients linked to ice volume changes and hadley cell dynamics we hypothesize that the position of the itcz was sensitive to the growing hirnantian ice sheet during the late ordovician we propose that latitudinal movement of the itcz during the late ordovician resulted in a major atmosphere ocean circulation re organization higher pco2 estimates for the ordovician caused more extreme changes in this circulation that were the likely primary cause of biotic mass extinction if the monsoon is considered an off equator itcz then we provide direct evidence of an ordovician monsoonal climate

evidence for stability in coda q associated with the egion central greece earthquake of 15 june 1995 one hundred seventy two seismograms recorded at one seismological station located close to the source region of the egion ms 6 2 15 june 1995 earthquake were used to measure values of q from the decay of the earthquake coda the collected data were compared between events that occurred before and after the main event the analysis showed no significant temporal variation in the value of coda q for the region

rapid changes in magma storage beneath the klyuchevskoy group of volcanoes inferred from time dependent seismic tomography abstract we present the results of time dependent local earthquake tomography for the kluchevskoy group of volcanoes in kamchatka russia we consider the time period from 1999 to 2009 which covers several stages of activity of kluchevskoy and bezymianny volcanoes the results are supported by synthetic tests that recover a common 3d model based on data corresponding to different time windows throughout the period we observe a robust feature below 25 km depth with anomalously high v p v s values up to 2 2 we interpret this feature as a channel bringing deep mantle materials with high fluid and melt content to the bottom of the crust this mantle channel directly or indirectly determines the activity of all volcanoes of the kluchevskoy group in the crust we model complex structure that varies over time during the pre eruptive period we detected two levels of potential magma storage one in the middle crust at 10 12 km depth and one close to the surface just below kluchevskoy volcano in 2005 a year of powerful eruptions of kluchevskoy and besymiyanny volcanoes we observe a general increase in v p v s throughout the crust in the relaxation period following the eruption the v p v s values are generally low and no strong anomalous zones in the crust are observed we propose that very rapid variations in v p v s are most likely due to abrupt changes in the stress and deformation states which cause fracturing and the active transport of fluids these fluids drive more fracturing in a positive feedback system that ultimately leads to eruption we envision the magma reservoirs beneath the kluchevskoy group as sponge structured volumes that may quickly change the content of the molten phases as fluids pulse rapidly through the system

late ordovician global warming the boda event there is substantial evidence for mid ashgillian global warming before the latest ordovician hirnantian glaciation as shown by the movement of previously lower latitude benthic faunas such as trilobites and brachiopods to progressively higher latitudes and by an increase in endemic faunas at low latitudes this is shown by faunal dynamics on several paleocontinents and endorsed by published evidence of warmer water sediments from gondwana and elsewhere we term this global warming the boda event

a far field record of the end ordovician glaciation the ellis bay formation anticosti island eastern canada abstract the end ordovician was a critical period in earth history it was a time of global climatic change with large scale continental glaciations a wealth of recent work has documented the stratigraphical records from the near field areas i e from various gondwanan continental relics where glaciation was more severely felt there is an urgent need to re examine the stratigraphic record from the far field areas at greater levels of resolution than it has been hitherto possible in order to understand the timing duration and character at the glaciation centred around the ordovician silurian o s boundary one of the best exposed and most complete stratigraphic records from paleotropical areas near the boundary is on anticosti island in eastern canada the east west trending 200 km long ellis bay hirnantian outcrop belt with superb coastal exposures at both ends of anticosti island is slightly oblique to the paleoshoreline with near shore siliciclastic dominated facies restricted to the eastern part of the island and more offshore carbonate dominated facies present along the central and western parts these mixed carbonate siliciclastic facies accumulated along a storm dominated beach to offshore profile they are organized into a stacked set of shallowing upward offshore to shoreline facies successions typically coarsening upward separated by deepening upward facies successions typically fining upward formed during intervening transgressions high frequency glacio eustatic fluctuations were the dominant control on the development of tr sequences observed in the ellis bay succession of anticosti island although tectonic subsidence had a substantial secondary effect on thickness five tr sequences are recognized allowing for precise correlation along the ellis bay outcrop belt in the eastern sections relatively thin tr sequences are locally bounded by unconformities a typical sequence begins with thin transgressive limestone overlain by a maximum flooding calcareous shale grading up into regressive storm influenced proximal to transitional zone fine sandstone grainstone and shale which are sharply overlain by shoreface to foreshore sandstone grainstone in the central and western sections the thicker tr sequences have more symmetrical transgressive regressive components reflecting greater subsidence compensated by a higher carbonate sediment supply two discrete glacial periods are recognized during the deposition of the hirnantian ellis bay succession with the younger one recording large sea level changes 50 m in magnitude caused by the development of very large ice sheets over western gondwana abundant ice conditions on the globe during the end ordovician and the resulting high amplitude eustasy appear to have left distinctive stratigraphical imprints on mixed paleotropical siliciclastic carbonate ramps

an 34 m y astronomical time scale for the uppermost mississippian through pennsylvanian of the carboniferous system of the paleo tethyan realm

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

orbital scale climate change and glacioeustasy during the early late ordovician pre hirnantian determined from δ18o values in marine apatite this study focuses on the 10 m y before the latest ordovician hirnantian glaciation we test whether orbital scale climatic fluctuations controlled the growth and melting of continental glaciers resulting in glacioeustatic sea level changes and the development of widespread marine sedimentary cycles 18o values of conodont apatite from 14 late ordovician katian cycles range from 17 to 21 isotopic values decrease and are lowest in the deepest water facies and increase and are highest in shallow water facies supporting the hypothesis that glacioeustasy was the dominant control on water depth changes measured intracycle 18o changes of 0 7 2 5 were controlled by changes in ice volume 60 m sea level changes sea surface temperatures 5 c and potentially local increases in seawater evaporation during drier and or windier glacial stages these interpreted orbital scale climate changes and resultant large glacial ice volume changes support recent interpretations of a dynamic and prolonged ordovician greenhouse to icehouse transition

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

calibrating the late ordovician glaciation and mass extinction by the eccentricity cycles of earth s orbit a process based sedimentological analysis of upper ordovician glacial marine rocks in africa suggests that full glaciation of the continental shelf started in the late extraordinarius zone of the hirnantian two cycles of ice sheet growth are represented during full glaciation initial terrestrial ice sheet growth in the early extraordinarius zone influenced the first event of the late ordovician mass extinction retreat of the ice sheet from the shelf ended by the persculptus zone when the second event of the late ordovician mass extinction began eccentricity controlled ice sheet growth is assumed periodicity 0 1 m y hence two cycles of full glaciation lasted 0 2 m y the duration of the extraordinarius zone is estimated as 0 5 m y therefore the minimum duration of the first extinction event was 0 3 m y

pore pressure migration along a normal fault system resolved by time repeated seismic tomography in this study we outline the space and time variations of body wave velocities during one of the best documented series of normal faulting earthquakes the 1997 umbria marche sequence in central italy we show the first ever observations of rock fracturing and fluid overpressure propagation along a fault system by using space time resolved variations of vp vs anomalies four dimensional variations that accompany earthquake migration and precede large aftershocks the vp vs increase observed before the mid october earthquakes was related to a pore pressure increase on fluid filled cracks in the volume around the fault we also document that such variations are measurable only by using s and p wave arrival times

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

magnetic record of milankovitch rhythms in lithologically noncyclic marine carbonates rock magnetic variations record cyclicity within lithologically homogeneous basinal lime mudstones of the lower cretaceous san angel limestone northeastern mexico variations in ferromagnetic mineral concentrations as measured by anhysteretic remanent magnetization arm occur at frequencies consistent with milankovitch orbital rhythms magnetic mineral compositions grain size distributions and grain shapes from digested samples are congruent with far traveled atmospheric dust prevailing winds and the proximity of the cretaceous basin to an african eolian source support the encoding of orbitally modulated changes in wind intensity or source area aridity arm measurements offer great potential to calibrate the pace of depositional processes in carbonates and to investigate high frequency orbitally driven climate change in basinal strata throughout geologic time

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

the effect of geological anisotropies on the detectability of seismic electric signals abstract the detectability of seismic electric signals was examined in relation to the geological anisotropies both at the large scale of geotectonics and neotectonics and at the smaller scale of electric stations the distribution of the detected seismic events in the cases of the ioannina and assiros stations showed a strong dependence upon the geotectonic zonation and especially upon the ophiolite suture zones of north pindos and almopia axios vardar the major neotectonic transcurrent faults did not show an important effect keratea station and especially point a on a granitic dyke showed an extraordinary detectability independant of the geotectonic zonation attributed to the local anisotropy and to its connecton with batholiths at depth within the aegean paleo volcanic arc of upper miocene age

towards a robust and consistent middle eocene astronomical timescale abstract until now the middle eocene has remained a poorly constrained interval of efforts to produce an astrochronological timescale for the entire cenozoic this has given rise to a so called eocene astronomical timescale gap vandenberghe et al 2012 a high resolution astrochronological calibration for this interval has proven to be difficult to realize mainly because carbonate rich deep marine sequences of this age are scarce in this paper we present records from middle eocene carbonate rich sequences from the north atlantic southeast newfoundland ridge iodp exp 342 sites u1408 and u1410 of which the cyclical sedimentary patterns allow for an orbital calibration of the geologic timescale between 38 and 48 ma these carbonate rich cyclic sediments at sites u1408 and u1410 were deposited as drift deposits and exhibit prominent lithological alternations couplets between greenish nannofossil rich clay and white nannofossil ooze the principal lithological couplet is driven by the obliquity of earth s axial tilt and the intensity of their expression is modulated by a cyclicity of about 173 kyr this cyclicity corresponds to the interference of secular frequencies s3 and s6 related to the precession of nodes of the earth and saturn respectively this 173 kyr obliquity amplitude modulation cycle is exceptionally well recorded in the xrf x ray fluorescence derived ca fe ratio in this work we first demonstrate the stability of the s3 s6 cycles using the latest astronomical solutions results show that this orbital component is stable back to at least 50 ma and can thus serve as a powerful geochronometer in the mid eocene portion of the cenozoic timescale we then exploit this potential by calibrating the geochronology of the recovered middle eocene timescale between magnetic polarity chrons c18n 1n and c21n comparison with previous timescales shows similarities but also notable differences in durations of certain magnetic polarity chrons we present a revision of previous astronomical timescales from the equatorial and south atlantic to overcome the differences between different mid eocene astrochronologies using our new records from the north atlantic combined with existing records from the south atlantic odp site 1263 and hole 702b and equatorial atlantic odp site 1260 we revise the durations of magnetic polarity chrons c18n 1n to c21n thereby arriving at a robust and self consistent closure of the middle eocene astronomical timescale gap

geological constraints on the precambrian history of earth s rotation and the moon s orbit over the past decade the analysis of sedimentary cyclic rhythmites of tidal origin i e stacked thin beds or laminae usually of sandstone siltstone and mudstone that display periodic variations in thickness reflecting a strong tidal influence on sedimentation has provided information on earth s paleorotation and the evolving lunar orbit for precambrian time before 540 ma depositional environments of tidal rhythmites range from estuarine to tidal delta with a wave protected distal ebb tidal delta setting being particularly favorable for the deposition and preservation of long detailed rhythmite records the potential sediment load of nearshore tidal currents and the effectiveness of the tide as an agent of sediment entrainment and deposition are related directly to tidal range or maximum tidal height and consequent current speed hence the thickness of successive laminae deposited by tidal currents can be a proxy tidal record with paleotidal and paleorotational values being determined by analysis of measured records of lamina and cycle thickness the validity of the findings can be investigated by testing the primary observed values for internal self consistency through application of the laws of celestial mechanics paleotidal and paleorotational values provided by late neoproterozoic 620 ma tidal rhythmites in south australia are validated by these tests and indicate 13 1 0 1 synodic lunar months yr 400 7 solar days yr a length of day of 21 9 0 4 h and a relative earth moon distance a a0 of 0 965 0 005 the mean rate of lunar recession since that time is 2 17 0 31 cm yr which is little more than half the present rate of lunar recession of 3 82 0 07 cm yr obtained by lunar laser ranging the late neoproterozoic data militate against significant overall change in earth s moment of inertia and radius at least since 620 ma cyclicity displayed by paleoproterozoic 2450 ma banded iron formation in western australia may record tidal influences on the discharge and or dispersal of submarine hydrothermal plumes and suggests 14 5 0 5 synodic months yr and a a0 0 906 0 029 the combined rhythmite data give a mean rate of lunar recession of 1 24 0 71 cm yr during most of the proterozoic 2450 620 ma suggesting that a close approach of the moon did not occur during earlier time concentrated study of precambrian tidal rhythmites promises to illuminate the evolving dynamics of the early earth moon system and may permit the lunar orbit to be traced back to near the time of the moon s origin

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

proterozoic milankovitch cycles and the history of the solar system the geologic record of milankovitch climate cycles provides a rich conceptual and temporal framework for evaluating earth system evolution bestowing a sharp lens through which to view our planet s history however the utility of these cycles for constraining the early earth system is hindered by seemingly insurmountable uncertainties in our knowledge of solar system behavior including earth moon history and poor temporal control for validation of cycle periods e g from radioisotopic dates here we address these problems using a bayesian inversion approach to quantitatively link astronomical theory with geologic observation allowing a reconstruction of proterozoic astronomical cycles fundamental frequencies of the solar system the precession constant and the underlying geologic timescale directly from stratigraphic data application of the approach to 1 4 billion year old rhythmites indicates a precession constant of 85 79 2 72 arcsec year 2 an earth moon distance of 340 900 2 600 km 2 and length of day of 18 68 0 25 hours 2 with dominant climatic precession cycles of 14 ky and eccentricity cycles of 131 ky the results confirm reduced tidal dissipation in the proterozoic a complementary analysis of eocene rhythmites 55 ma illustrates how the approach offers a means to map out ancient solar system behavior and earth moon history using the geologic archive the method also provides robust quantitative uncertainties on the eccentricity and climatic precession periods and derived astronomical timescales as a consequence the temporal resolution of ancient earth system processes is enhanced and our knowledge of early solar system dynamics is greatly improved

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

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

latest aspects of earthquake prediction in greece based on seismic electric signals ii abstract since 1983 continuous monitoring of the electrotelluric field has been carried out using an array of measuring stations located at various sites in greece the basic physical properties of the transient changes seismic electric signals ses in the electrotelluric field that are forerunners of earthquakes were first described six years ago since then a large body of data has been collected resulting in new insight into various aspects of the method the present paper reviews the latest developments in ses based earthquake prediction and describes the current procedures used to predict the epicenter and magnitude of an impending earthquake a detailed list of the predictions officially issued in greece during the past 3 years january 1 1987 november 30 1989 is also given public warnings were issued well before the most destructive seismic activity

seismological evidence for differential rotation of the earth s inner core the travel times of seismic waves that traverse the earth s inner core show a small but systematic variation over the past three decades this variation is best explained by a rotation of the inner core that moves the symmetry axis of its known seismic anisotropy the inferred rotation rate is on the order of 1 per year faster than the daily rotation of the mantle and crust

maximum extent of ice sheets in morocco during the late ordovician glaciation new field data demonstrate that during the late ordovician hirnantian glaciation an ice sheet expanding northwestwards over the anti atlas range reached into the southern meseta of northern morocco its growth to a glacial maximum position resulted in extensive subglacial erosion and deformation including the development of soft sediment striated surfaces and streamlined subglacial bedforms preserved between the high atlas of marrakech and rehamna these features imply that this ice mass extended 200 km further than previously thought and increase its size by at least ca 190 000 km2 comparable in area to the uk correlation between a measured section in the high atlas of marrakech and that of the southern meseta identifies sedimentary evolution within an ice contact system common to both these findings imply that the west african craton and northern morocco were in full glaciological communication during the latest ordovician palaeogeographic reconstruction shows that beyond the ice sheet south and southeastward palaeoslopes persisted on the shelf a palaeohigh beyond the main ice sheet was a major source for sand feeding delta systems that grew along the shelf as far as the shelf break this palaeohigh probably formed as a result of rift shoulder uplift and supported a satellite ice mass in the eastern meseta a thick 350 m underflow dominated deep marine fan was fed both from this shelf delta system and from glaciogenic debris derived from the main ice sheet the occurrence of this unexpected deep marine area in northern morocco implies that continued northward advance of the ice sheet was hampered by a dramatic break in bathymetry two depositional units are recognised across the meseta containing four distinct sedimentary cycles each recognised as a glacioeustatic response to the waxing and waning of ice masses elsewhere in west gondwana

the late ordovician mass extinction abstract near the end of the late ordovician in the first of five mass extinctions in the phanerozoic about 85 of marine species died the cause was a brief glacial interval that produced two pulses of extinction the first pulse was at the beginning of the glaciation when sea level decline drained epicontinental seaways produced a harsh climate in low and mid latitudes and initiated active deep oceanic currents that aerated the deep oceans and brought nutrients and possibly toxic material up from oceanic depths following that initial pulse of extinction surviving faunas adapted to the new ecologic setting the glaciation ended suddenly and as sea level rose the climate moderated and oceanic circulation stagnated another pulse of extinction occurred the second extinction marked the end of a long interval of ecologic stasis an ecologic evolutionary unit recovery from the event took several million years but the resulting fauna had ecologic patterns similar to the fauna that had become e

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

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

periodic variations in the earth s electric field as earthquake precursors results from recent experiments in greece abstract the results obtained during an extensive investigation of the variations in the earth s electric field at three tectonically active areas in greece and their relation to the occurrence of earthquakes are described in all three cases a 24 h periodic oscillation of the earth s electric field was observed prior to large imminent earthquakes one of which was the september 13th 1986 measuring ms 6 2 r earthquake which devastated the city of kalamata finally two physical processes which could explain the above phenomenon are proposed

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

visual identification and quantification of milankovitch climate cycles in outcrop an example from the upper ordovician kope formation northern kentucky

high resolution stable isotope stratigraphy of upper ordovician sequences constraints on the timing of bioevents and environmental changes associated with mass extinction and glaciation the two phases of the late ordovician mass extinction are approximately coeval with the periods of rapid climate change associated with the onset and demise of the gondwanan glaciation in this paper we argue that the distinctive late ordovician carbon isotope profile provides a chronostratigraphic ruler against which a sequence of environmental and biotic events may be located the ruler also allows regional and global high resolution correlation of successions representing very different environments cores from the upper ordovician succession of estonia and latvia record a large 1 3 c c a r b o n a t e excursion up to 6 with a similar profile shape the consistent relationship between the chemostratigraphy and biostratigraphy in the baltic region suggests that the isotope profile has a regional chronostratigraphic value the presence of similar profiles in nevada united states suggests that the excursion is a global chronostratigraphic signal this interpretation enables a detailed correlation to be made between upper ordovician shallow marine and basinal sequences that have wholly different faunas successions in the baltic area and in canada that do not display the model profile are interpreted as incomplete reinter pretation of these important successions significantly modifies the global database used to assess the pattern of diversity change during the mass extinction key levels of environmental change have been located against the carbon isotope profile new oxygen isotope data from brachiopod and ostracode calcite set tight limits on the start of the glacial events cooling and sea level fall started at the same stratigraphic level as the start of the carbon isotope excursion the later rise in sea level and fall in oxygen isotope values record the end of the glaciation these restrict the duration of the main glaciation to only 1 5 graptolite zones we propose that models of the carbon cycle should be adapted to be consistent with the temporal relationships between carbon cycling sea level fall and temperature change documented here the chronostratigraphic ruler provided by the carbon isotope profiles is used as a scale to determine the sequence of biotic changes and to allow high resolution correlation of biotic events at different locations this approach identifies regional similarities and differences in the patterns of extinction the main phase of graptolite extinction in the monitor range nevada for example is synchronous with the chitinozoan extinction in the baltic region but chitinozoan taxa survive to higher levels in nevada the benthic faunas in the baltic region demonstrate that the main extinction event corresponded with the beginning of the isotope excursion at the start of the hirnantian the level at which the marine environment started to change rapidly but that there were further extinctions of species within the early hirnantian the cold adapted hirnantia fauna did not appear immediately after the extinction in this area the relationship between the second phase of extinction and the carbon isotope excursion is less clear but the available data suggest that the extinction coincides with a time of rapid environmental change but not at the inception of environmental change as happened in the first phase

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

geoelectric variations related to earthquakes observed during a 3 year independent investigation we present observations of the geoelectric field prior to some earthquakes the data were collected during a three year 1992 1994 independent experimental investigation of van at the university of patras seismological center the recorded signals were a gradual variations of the electric field gvef b periodic variation of the electric field pvef and c seismic electric signals ses

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

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

tempestite frequency curves a key to late ordovician and early silurian subsidence sea level change and orbital forcing in the anticosti foreland basin quebec canada following partial closure of the northern iapetus ocean along the newfoundland segment of the st lawrence promontory subsidence along the anticosti platform was influenced by residual thermal subsidence renewed tectonic loading by thrust sheets to the south and sediment loading basement subsidence calculated by removing the effects of sediment loading was between 2 and 5 cm ka in the caradocian increasing to 8 6 cm ka in the pusgillian and cautleyan and reaching a maximum of 17 7 cm ka in the rawtheyan during deposition of the princeton lake and vaureal formations a marked decline in subsidence beginning in the hirnantian and continuing into the early silurian may reflect decoupling of thrust loads to the south although a further stage of thrust loading may have occurred in the aeronian during deposition of the lower part of the jupiter formation storm frequency curves produced using tempestite abundance thickness and grain size through more than a kilometre of carbonate strata on antico

late ordovician mass extinction a new perspective from stratigraphic sections in central nevada integrated sequence stratigraphic biostratigraphic and chemostratigraphic analyses of three stratigraphic sections in central nevada indicate that late ordovician glaciation induced sea level fall produced diachronous stepwise faunal turnover in graptolites conodonts chitinozoans and radiolarians and also triggered a strong but transient positive 13c excursion this pattern is very different from that described for most mass extinction events

high frequency eustatic sea level changes during the middle to early late ordovician of southern jordan indirect evidence for a darriwilian ice age in gondwana abstract the middle to early late ordovician hiswah and dubaydib formations in southern jordan provide a well constrained sedimentary record of 4th and 3rd order relative sea level change along the northern tectonically quiescent subpolar gondwana continental margin cyclic deposition occurred on a wave and storm dominated microtidal shelf dominated by shoreface and offshore transition zone facies cycles are commonly bounded by amalgamated bounding surfaces sb ts or sb mfs and are characterised by stacked transgressive systems tracts tsts the small facies dislocation across key sequence bounding surfaces indicates a 15 50 m change in relative sea level fourth order sequences are hypothesized to be paced by the long eccentricity 405 kyr cycle and consequently 3rd order sequences are calculated to be 1 2 m y and 2 4 m y long these correlate with the global eustatic sea level curve in comparison with mesozoic and cenozoic sequence stratigraphical data we conclude that the 1 2 m y cycles correspond with long obliquity cycles predominant in icehouse conditions and the 2 4 m y cycles with the long eccentricity cycle predominant during greenhouse conditions we propose a darriwilian ice age during which orbitally induced cold snaps caused the expansion and amalgamation of small medium scale ice sheets the reduced size of the correlative positive carbon isotope excursion compared to that in the hirnantian may indicate that the darriwilian ice sheets only reached the sea in a few places the absence of glacio terrestrial deposits of middle ordovician age is most likely due to subsequent glacial erosion during repeated ice advances up to and including those in the hirnantian the existence of darriwilian ice sheets is consistent with zooplankton province distributions that indicate a polar front at 40 s during the ice age it is likely that polar ice existed throughout the ordovician

climate response to orbital forcing across the oligocene miocene boundary spectral analyses of an uninterrupted 5 5 million year my long chronology of late oligocene early miocene climate and ocean carbon chemistry from two deep sea cores recovered in the western equatorial atlantic reveal variance concentrated at all milankovitch frequencies exceptional spectral power in climate is recorded at the 406 thousand year ky period eccentricity band over a 3 4 million year period 20 to 23 4 my ago ma as well as in the 125 and 95 ky bands over a 1 3 million year period 21 7 to 23 0 ma of suspected low greenhouse gas levels moreover a major transient glaciation at the epoch boundary approximately 23 ma mi 1 corresponds with a rare orbital congruence involving obliquity and eccentricity the anomaly which consists of low amplitude variance in obliquity a node and a minimum in eccentricity results in an extended period approximately 200 ky of low seasonality orbits favorable to ice sheet expansion on antarctica

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

long periodic variations in the earth s obliquity and their relation to third order eustatic cycles and late neogene glaciations abstract evolutive spectra of four high resolution climatic proxy records reveal that the spectral power in the obliquity frequency band increases during five well defined intervals in the last 5 3 million years these intervals correspond to periods of high amplitude variations in the tilt obliquity of the earth s axis connected with a 1 2 myr cycle and to sea level lowstands of third order eustatic cycles in the haq et al 1987 curve this implies that the development of major plio pleistocene glaciations proceeded episodically and that third order cycles are glacio eustatically controlled in at least two of these intervals sinistrally coiled neogloboquadrinids entered the mediterranean at times of glacial periods one interval starts around 2 8 ma and is characterized by the first occurrence of n atlantica s another interval begins at the plio pleistocene boundary around 1 8 ma and is characterized by the common occurrence of sinistrally coiled n pachyderma also during the late miocene third order cycles correlate well with the 1 2 myr cycle of obliquity a significant drop in the third order eustatic curve starting at the tortonian messinian boundary for instance coincides with a period of high amplitude variations in the obliquity time series connected with the 1 2 myr cycle

meganodular limestone of the pagoda formation a time specific carbonate facies in the upper ordovician of south china abstract the decimeter scale 3 d network structure of the upper ordovician pagoda formation in south china has been an enigmatic sedimentary feature and a case of non uniformitarian carbonate depositional system without modern analog the network bands are developed pervasively throughout the entire pagoda formation superficially resembling desiccation or syneresis cracks especially in bedding plane view with decimeter scale sub polygonal to irregularly sinuous patterns detailed petrographic analysis however shows that the crack like network bands have the same carbonate matrix skeletal grains and overall fabrics as the rock they surround in this study we demonstrate that the network structure is not generated by shrinkage cracks but is rather a time specific lithofacies it originated from prolonged growth of nodular carbonate controlled by the convergence of several geological and paleoclimatic factors including a a protracted sea level highstand lasting for about 5 myr b an interval of tectonic quiescence favoring the dominance of carbonate production with minimal siliciclastic input and c location of the south china paleoplate in the hurricane free paleoequatorial zone devoid of severe storm disturbances between the fairweather and maximum storm wave bases normally 15 120 m depths favoring long term uninterrupted growth of caco3 meganodules on a mid shelf substrate this study corroborates recent paleogeographic reconstructions that position the south china paleoplate on the equator during the late ordovician

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

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

anomalous electrotelluric residuals prior to a large imminent earthquake in greece abstract periodic anomalies period 24 h have been observed in the electrotelluric field prior to a large imminent earthquake in greece the periodic anomaly is modulated by an exponential term which implies that successive peaks increase toward the time of the impending earthquake it is shown that the amplitudes of the periodic variations are much bigger than those accompanying changes of the geomagnetic field

enhancement of seismic electric signals using magnetotellurics abstract during two field studies carried out in greece in 1986 and 1987 1988 electric precursors superimposed on the telluric field and the time dependence of the magnetotelluric apparent resistivity were studied using the magnetotelluric method applied in the frequency band of 0 00028 0 5 hz the recognition of any transient electric signal in the telluric field was improved by reducing the main part of the magnetotelluric induction by making use of a residual electric field the residual field is defined as the difference between the measured electric field and the field which is calculated by multiplying the measured magnetic field with the magnetotelluric impedance tensor in concordance with a previous study this method is shown to be rather effective one conclusion from our study is that it is practical to employ the residual field method in a continuous daily analysis within an earthquake prediction research experiment we have demonstrated that suspected electric transients are revealed as anomalies of non magnetic origin after a careful analysis in three cases significant transient electric signals were classified as suspected seismic electric signals they were clearly resolved on the residual field and all correlated well in time with three earthquakes occurring close to the stations during the time of recording

obliquity and precessional forcing of continental snow fall and melt implications for orbital forcing of pleistocene ice ages abstract milankovitch theory posits that earth s orbital cycles were the primary forcing of pleistocene ice age cycles through their strong influence on summer insolation at high latitudes accordingly milankovitch theory predicts ice volume should vary at both obliquity and precessional periods however early pleistocene global ice volume varied mainly at the obliquity period with weak variability at the precessional period suggesting that milankovitch theory is not sufficient to explain the ice age cycles here we describe the results from a series of coupled ocean atmosphere general circulation model experiments using the fast ocean atmosphere model that systematically investigate the influence of precession and obliquity on continental snowfall and potential ablation our model results identify three factors that magnify the influence of obliquity forcing on the global ice volume first high latitude snowfall variability is dominated by changes in earth s axial tilt second hemispheric changes in net snowfall due to earth s precession are out of phase and largely cancel to produce a very small global snowfall change third snowmelt variability over antarctica responds greatly to changes in obliquity that intensify accumulation over obliquity cycle we discuss the implications of these factors for existing hypotheses that account for the variability in the ice volume record

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

time dependent seismic tomography summary of methods for measuring temporal changes in seismic wave speeds in the earth seismic tomography is among those that offer the highest spatial resolution 3 d tomographic methods are commonly applied in this context by inverting seismic wave arrival time data sets from different epochs independently and assuming that differences in the derived structures represent real temporal variations this assumption is dangerous because the results of independent inversions would differ even if the structure in the earth did not change due to observational errors and differences in the seismic ray distributions the latter effect may be especially severe when data sets include earthquake swarms or aftershock sequences and may produce the appearance of correlation between structural changes and seismicity when the wave speeds are actually temporally invariant a better approach which makes it possible to assess what changes are truly required by the data is to invert multiple data sets simultaneously minimizing the difference between models for different epochs as well as the rms arrival time residuals this problem leads in the case of two epochs to a system of normal equations whose order is twice as great as for a single epoch the direct solution of this system would require twice as much memory and four times as much computational effort as would independent inversions we present an algorithm tomo4d that takes advantage of the structure and sparseness of the system to obtain the solution with essentially no more effort than independent inversions require

astronomical forcing of middle permian terrestrial climate recorded in a large paleolake in northwestern china abstract geological records of milankovitch cycles provide a temporal framework for reconstructing earth climate evolution and mapping out the history of the ancient solar system understanding the fundamental celestial mechanics driving astronomical rhythms during the permian period from stratigraphic record is challenging because of the inherent limitations of astronomical solutions the chaotic nature of solar system motion and the paucity of cyclostratigraphic studies of geological records the junggar and adjacent basins of northwestern china constituted a large tectonic lake in the middle permian which deposited one of the thickest and richest petroleum source rock intervals in the world constructing an accurate timescale for the permian junggar basin is critical to understand the processes that controlled organic carbon burial as well as paleoclimatic and paleoenvironmental background conditions in this study detailed spectral analyses of natural gamma ray ngr data were performed on the lacustrine muddy dominated lucaogou formation from five exploitation wells the results reveal significant meter scale sedimentary cycles of 37 8 m 10 7 10 m 3 85 3 2 m and 2 0 1 58 m reflecting oscillations in lithologies variations in changing clay content within the mudstone sandstone and dolomite these cycle wavelength ratios match well with those of the milankovitch cycles predicted for middle permian period the depositional duration of the lucaogou formation was estimated at 3 myr correlation of the 1 2 myr obliquity modulation cycles among the ngr logs sedimentation rates and lake levels of the junggar basin as well as with the middle permian global sea level suggests that long term astronomical grand cycles tightly forced climatic and sedimentary processes throughout the lucaogou formation according to two independent approaches we reconstruct middle permian astronomical parameters earth precession constant k and fundamental frequencies terms gi i 1 2 3 4 5 and calculate astronomical periods eccentricity obliquity and precession these results document astronomical forcing of paleozoic lake systems constrain earth moon orbital evolution and refine the fundamental astronomical frequencies of the solar system during the middle permian

milankovitch band cyclicity in bedded halite deposits contemporaneous with late ordovician early silurian glaciation canning basin western australia abstract the mallowa salt of the early palaeozoic carribuddy group canning basin western australia is a halite mudstone anhydrite dolomite evaporite sequence of late ordovician to early silurian age deposited in barred marginal marine to ephemeral saltpan and saline mudflat environments bhp utah minerals potash exploration well gingerah hill no 1 obtained drill core of a 477 m stratigraphic interval of the mallowa salt which permitted the study of geochemical variations in a thick halite sequence contemporaneous with late ordovician early silurian glaciation on other continents a strip of uniform width was continuously ground from the core and the powdered rock bagged at 1 m intervals for geochemical assay the resulting geochemical stratigraphic series display conspicuous cyclicity several orders of cycles ranging from 3 m to100 m stratigraphic thickness are discernible in the plots of minor constituents br mgo and k2o in extracted soluble salts and also in the plots of na2o and total salts content fast fourier transform fft of the br mgo and k2o series gives principal spectral peaks in the 0 00 0 10 cycles m frequency band at 250 113 35 4 22 1 and 19 7 m as well as peaks at 65 m and between 2 8 and 13 5 m fft of the na2o and total salts series shows dominant spectral peaks at 220 259 and 109 114 m if the strongest spectral peak at 113 m is taken to represent the relatively stable eccentricity period of 100 ka and a constant net rate of accretion assumed for long sections the other main periods in the mallowa salt as exemplified by the br spectrum would be31 3 3 0 19 6 1 1 and17 4 1 1 ka these figures are consistent with predicted late ordovician early silurian 440 ma periods for obliquity 30 5 ka and precession 19 3 and 16 4 ka based on evolutionary change in the earth moon system additional spectral peaks identified with implied periods of approximately 206 233 57 5 8 12 and 2 5 3 5 ka also may be of palaeoclimatic relevance the relative amplitudes and structure of spectral peaks in the 0 00 0 10 cycles m frequency band support the identification of climatic oscillations forced by orbital cycles the data indicate a precession eccentricity dominated pattern which accords with the know low palaeolatitude

end ordovician extinctions a coincidence of causes the end ordovician hirnantian extinction was the first of the five big phanerozoic extinction events and the first that involved metazoan based communities it comprised two discrete pulses both linked in different ways to an intense but short lived glaciation at the south pole the first occurring at or just below the normalograptus extraordinarius graptolite biozone mainly affected nektonic and planktonic species together with those living on the shallow shelf and in deeper water whereas the second within the n persculptus graptolite biozone was less focused eradicating faunas across a range of water depths in all about 85 of marine species were removed proposed kill mechanisms for the first phase have included glacially induced cooling falling sea level and chemical recycling in the oceans but a general consensus is lacking the second phase is more clearly linked to near global anoxia associated with a marked transgression during the late hirnantian most recently however new drivers for the extinctions have been proposed including widespread euxinia together with habitat destruction caused by plate tectonic movements suggesting that the end ordovician mass extinctions were a product of the coincidence of a number of contributing factors moreover when the deteriorating climate intensified causing widespread glaciation a tipping point was reached resulting in catastrophe

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