oceanic anoxic cycles orbital prelude to the bonarelli level oae 2 abstract the prelude to the second global oceanic anoxic event of the cretaceous oae 2 as recorded in the classic sections of the scaglia bianca formation in the umbria marches region of italy is characterized by an oscillation between black to gray organic rich cherts and white pelagic limestones spectral analysis of these lithologic alternations reveals a robust set of cycles whose periods are remarkably similar to the orbital cycles calculated by laskar et al laskar j robutel p joutel f gastineau m correia a c m levrard b 2004 a long term numerical solution for the insolation quantities of the earth astronomy and astrophysics 428 261 285 bandpass filtering shows that the 140 80 kyr signal approximates the envelope of the 26 16 kyr signal just as expected if these components represent responses to orbital eccentricity and precession matching the presumed eccentricity signal to the theoretical eccentricity of laskar et al yields an age for the base of the bonarelli level onset of oae 2 in italy of 94 21 ma 93 72 ma provides an alternative consistent with radiometric constraints from a correlative section in the western united states given the strong orbital control on the cyclic deposition of the organic rich precursors of oae 2 within the scaglia bianca formation we hypothesize that the timing of oae 2 itself is similarly controlled by astronomical variations indeed the occurrence of oae 2 coincides with a protracted period of unusually low insolation variation owing to simultaneous nodes in all orbital parameters we speculate that other oaes similarly coincided with insolation nodes and dampened seasonality from this perspective some but perhaps not all of the oaes may be periodic events reflecting cycles of oceanic anoxia that predictably punctuated a 50 myr period of cretaceous climate

precessional climate cyclicity in late cretaceous early tertiary marine sediments a high resolution chronometer of cretaceous tertiary boundary events we report well dated late cretaceous and early tertiary precessional climatic cycles recorded by rhythmic carbonate maxima and minima in south atlantic deep sea sites spectral analyses of digitized sediment color a suitable carbonate proxy show prominent regularities in the spacing marl carbonate beds magnetostratigraphic dating over a number of magnetic chrons constrains the duration of the cycles which can be detected over at least 20 myr of sedimentation at 7 coring locations their mean absolute period of23 5 4 4kyr agrees closely with the predicted late cretaceous precessional period of 20 8 kyr because they can be matched to a physical forcing mechanism with a known repeat time the cycles offer a new high resolution tool to measure rates of climate change before and after the cretaceous tertiary k t boundary from counts of carbonate cycles we derive the position of the k t boundary within c29r at 350 kyr after the base of the reversal the constancy of cycle thickness linearly related to sedimentation rate and amplitude up to the boundary clay does not give evidence for climate instability preceding the boundary orbital chronometry records a step function decrease in sediment accumulation rate at the cretaceous tertiary boundary that is consistent with a geologically instantaneous event

eccentricity paced monsoon like system along the northwestern tethyan margin during the valanginian early cretaceous new insights from detrital and nutrient fluxes into the vocontian basin se france high resolution changes in terrigenous and nutrient fluxes into the vocontian basin northwestern tethyan margin were investigated for the late berriasian late valanginian time interval in order to assess the precipitation patterns in the source areas and to evaluate the effect of orbital forcing on the strength of the hydrological cycle in this study new high resolution mineralogical bulk rock and clay fraction and geochemical phosphorus and oxygen isotope data are used from the astronomically calibrated orpierre section for the first time kaolinite detrital and phosphorus accumulation rates kar dar and par are calculated and compared to a set of 547 geochemical and 260 mineralogical published data from other vocontian sections it appears that three regional increases in the kar document three successive humid episodes during the valanginian this is confirmed by contemporaneous increases in dar and partly also in par which highlight higher terrigenous and nutrient fluxes to the vocontian basin during these episodes concomitant decreases in the 18owhole rock signals may reflect higher sea surface temperatures during the early valanginian and the early late valanginian transition the occurrence of the three humid episodes is interpreted to relate to an orbital paced monsoonal circulation pattern through seasonally reversing movements of air mass heat and precipitation over the northwestern tethyan margin in particular based on the correlation between the 405 kyr eccentricity cycles and the kar signal obtained at orpierre an eccentricity influenced monsoonal circulation is proposed as the possible forcing factor behind these climatic patterns the average duration between the climaxes of the three regional wetter episodes is approximately 2 43 myr the wetter and likely also warmer episode at the early late valanginian transition is in step with the onset of the weissert episode in this regard the intensification of monsoonal driven precipitations appears as a possible external forcing factor leading or at least accelerating the important perturbation in the global carbon cycle associated with the weissert episode

orbitally driven redox fluctuations during cretaceous oceanic anoxic event 2 oae2 revealed by a new magnetic proxy abstract recent studies of the cretaceous sedimentary records have documented that rapid redox changes between euxinic sulfidic and ferruginous conditions occurred during the perturbations to the global carbon cycle associated with oceanic anoxic events this observation has major implications for the dynamics of and feedbacks on marine primary productivity and organic carbon burial during these events the high resolution rock magnetic study of a significantly expanded oae2 interval in southern tibet presented here provides further insight into the redox dynamics during the cenomanian turonian oceanic anoxic event 2 oae2 94 ma the ratio of hard isothermal remanent magnetization to magnetic susceptibility hirm is used as a proxy for bottom water redox conditions and shows repeated fluctuations between relatively oxic and dysoxic anoxic conditions in the eastern tethys of the southern hemisphere during oae2 spectral analysis of a log hirm time series reveals cyclical variations at orbital frequencies and the subtle cyclic redox changes are found to occur within the obliquity frequency band moreover variability in redox conditions at the onset of oae2 correlates well with that recently documented for the oae2 interval at tarfaya morocco implying that the cyclic redox variations spanned both hemispheres notably the presence of obliquity signals which dominantly influence high latitude climate processes in the tropics and subtropics of both the northern and southern hemispheres further confirms previously hypothesized more vigorous meridional overturning circulation moc during oae2 and implies the interhemispheric global nature of this major shift in oceanic circulation

planktonic foraminiferal distribution record productivity cycles evidence from the aptian albian piobbico core central italy the aptian albian scisti a fucoidi varicoloured pelagic sediments in central italy show a couplet alternation of carbonate rich carbonate poor layers which are interpreted as the sedimentary expression of precession frequency 19 23 kyr carbonate content chromatic variation and planktonic foraminiferal abundance were analysed at a 1 cm spacing for a 10 m interval of the piobbico core specifically drilled through this formation spectral analysis of these parameters shows a prominent signal equated to the c 100 kyr cycle of orbital eccentricity at a sedimentation rate of 5 mm kyr 1 the coherency of the spectral response of each parameter suggests that a single mechanism controlled the whole sedimentary record detailed study of planktonic foraminiferal distribution of the same section at 1 mm scale resolves the milankovitch frequencies of 41 kyr and 18 to 23 kyr equated with the obliquity and precessional cycles but foraminiferal abundance is not in phase with carbonate content which was largely controlled by calcareous nannofossils but peaked at intermediate carbonate values the proposed model for explaining the discrepancy at the precessional level is that foraminifera thrived at intermediate values of the precession index when the environment was only moderately fertile but stable while during highs of the precession index mixing of the water column increased fertility and caused calcareous nannofossil blooms and restriction of planktonic foraminifera to few and tolerant species the resulting bimodality of foraminiferal abundance per precessional cycle appears to be recorded in the spectrum by peaks at the 11 and 14 kyr levels cross correlation of foraminiferal abundances with the calcium carbonate curve over 1 2 myr intervals produces discrepant results apparent phase lags which we attribute to differences in the response to the fundamental eccentricity cycles

geochemical and sedimentologic variations in inter annually laminated sediments from santa monica basin abstract laminated sediments were recently discovered in the center of santa monica basin california continental borderland and extend from the present day to at least the little ice age ca 1600 a d unlike the annual varves observed in santa barbara basin the light dark lamination couplets observed in 210 pb dated cores from the center of santa monica basin occur at 3 to 6 year intervals very similar in length to the el nino southern oscillation enso phenomena the mechanisms that control the temporal patterns of laminations in this basin are unknown potential causal mechanisms of lamination formation in santa monica basin include 1 changes in the flux of terrigenous vs marine organic carbon and detritus 2 surface water processes which affect marine productivity and organic carbon flux to the sediments and 3 deep water processes which affect oxygen renewal and preservation of organic matter within the basin a box core from the central portion of santa monica basin was analyzed using a suite of geochemical sedimentary and micropaleontologic techniques in order to a investigate which if any of these mechanisms has contributed to the occurrence of laminations and b reconstruct proxy records of climate change samples were extracted from this core at 1 mm increments and provide a temporal resolution of 1 3 years per sample a resolution which is comparable in length to the thickness of individual laminae within the core geochemical and micropaleontologic analyses of core samples provide paleoclimatic and paleoceanographic records which are comparable to and extend beyond historical regional and global climate records in addition to direct comparisons between these records spectral analysis was used to investigate whether there were similar patterns of variability that would implicate dominant forcing functions in the historic and proxy records herein we present preliminary results of records from ca 1860 to the present our results suggest that organic carbon fluxes are the dominant factors that affect lamination variability input of organic carbon is primarily a function of primary productivity and to a lesser extent a function of percentage of terrestrial input thus 1 and 2 are both mechanisms of lamination formation stability of 3 only allows preservation of the record of these variations variations in southern california rainfall appear to be linked to decadal scale variations in downcore density profiles and thus cause variations in the thickness and character of the laminations in the deepest portions of this basin thus filtered density records can be used to reconstruct general paleo rainfall trends which compare well with historic rainfall records variations in the isotopic composition of total organic carbon toc are compared to historic enso and climate records and primarily reflect changes in the relative contribution of marine organic carbon to the basin variations in the carbon isotopic composition of n pachyderma mirror changes in the sedimentary 13 c toc record from santa monica basin and suggest that primary productivity is the primary control on the flux of organic carbon to the sediments and exerts a strong influence on the interannual variability in lamination composition variations in paleo sea surface temperatures generated from the oxygen isotopic composition of n pachyderma correlate well with historical sst records and suggest potential usage as a proxy for general paleosst patterns oxygen sensitive assemblages of benthic foraminifera bolivina argentea and b spissa have been used to identify potential large scale flushing events and construct a historical record of variations in deep water oxygen levels spectral analysis of regional historic records indicate dominance of short term enso length and long term decadal patterns of climate variability the short term enso signal is not dominant in the santa monica proxy records however strong decadal length signals are identified in all of the proxy records and suggest that the dominant forcing mechanisms in santa monica basin may be decadal in length

anoxic events productivity rhythms and the orbital signature in a mid cretaceous deep sea sequence from central italy albian pelagic sediments from the umbrian apennines exhibit rhythmic bedding in outcrop high temporal resolution 4 kyr spacing sampling of carbonate si and al along a 1 6 m y interval of core demonstrates that changes in accumulation rate of calcareous and siliceous microorganisms were controlled by insolation cycles optical densitometry logging correlates variations of geochemical parameters to episodes of deep sea anoxia indicated by numerous black laminated zones black shales harmonic analysis of data shows oscillations at three frequencies which correspond closely in estimated duration and ratio to the modern eccentricity and precessional orbital cycles as in pleistocene marine sequences the eccentricity approximately 100 kyr term dominates the sedimentary variance in the umbrian cycles anoxic episodes occur in phase with a limestone marl repetition and reflect minima of the precessional 21 kyr cycle the covariance of carbonate and silica with estimates of foraminiferal abundances suggest that carbonate cycles are the result of changes in surface productivity of calcareous organisms rather than an effect of dissolution or diagenesis recognition of orbital cyclicity provides a tool for making quantitative estimates of these changes productivity during anoxic events was uniformly low 0 4 0 5 g cm2 kyr carbonate 0 05 g cm2 kyr silica but it rose to high levels during oxygenated periods 1 2 5 g cm2 kyr carbonate 0 1 0 3 g cm2 kyr silica vertical overturning and organic carbon flux decreased during anoxic episodes but decreased oxygenation of the deep water led to enhanced preservation of the organic matter delivered the degree of paleoceanographic variability indicated by this study requires that accepted notions of climate stability and oceanic quiescence during nonglacial times be reassessed

testing periodicity of depositional cyclicity cisco group virgilian and wolfcampian texas abstract periodicities of 15 cyclic sections of the cisco group are tested through gamma and spectral analyses the sections are composed of marine and nonmarine carbonate and siliciclastic rocks deposited on the eastern shelf north central texas in late pennsylvanian and early permian time gamma analysis generates facies dependent thickness time conversion factors s to construct corrected time series which are more realistic than the uncorrected series obtained by proportional conversion positive and stable s and improved resolution of the corrected spectra indicate successful tuning on the cisco spectra a short eccentricity peak 95 131 ky is the most prominent and persistent long eccentricity 413 ky and obliquity 34 and 43 ky peaks are persistent and precessional index peaks 17 and 21 ky are less persistent a persistent peak of period 50 80 ky may be a combination tone between obliquity and precessional index cycles non milankovitch peaks are sporadic the validity of gamma and spectral results is indicated by consistent estimated ages among the cisco sections and reasonable effective sedimentation rates calculated on the basis of milankovitch spectral calibrations the results combined with geologic evidence suggest that the cisco cyclicity was controlled dominantly by milankovitch climatic 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

hunting for paleoclimatic periodicities in a geologic time series with an uncertain time scale an 8 m section of a mid cretaceous albian deep sea sediment core from piobbico italy contains 2 cycles m compositional oscillations as postdepositional chemical migration in the core is weak the relative amount of carbonate is a primary indicator of cretaceous paleoclimate variability we report results of spectral analysis of two series caco3 wt measurements taken at roughly 2 cm intervals and a more densely sampled photodensitometer record of light dark variation the uncertainty in the age depth relation i e unknown fluctuations in sedimentation rate hampers a detailed assessment of the suggested eccentricity correlation we fit for long term time scale greater than 75 kyr fluctuations in sedimentation rate by tracking the local frequency modulation of the dominant harmonic in the data series assuming the true input signal to be monochromatic we estimate uncertainty in the observed local frequency by means of a statistical jackknife we fit a smoothed cubic spline to the set of discrete frequency modulation estimates specifying a 2 n misfit criterion where n is the number of frequency estimates from this analysis we infer fluctuations of a factor of two in the sedimentation rate which occur predominately on a time scale of 400 kyr we generate tuned series using several candidate age depth relations from the carbonate and densitometer series the tuned carbonate series returns greater correlation with the modern milankovitch periodicities the 2 cycles m energy resolves principally into two harmonic components whose frequency ratio corresponds to an observational accuracy of 1 2 to that of the 97 0 and 127 6 kyr eccentricity oscillations at frequencies lower than 2 cycles m we find harmonic oscillations whose phase correlates with the beating envelope of the 2 cycles m energy in a manner consistent with the modern milankovitch insolation we also observe a sinusoidal oscillation of lower amplitude with period scaled by those of the presumed eccentricity oscillations of 39 2 1 1 kyr which agrees with the period of the modern obliquity cycle after correction for the effects of tidal friction oscillations corresponding to milankovitch precessional frequencies are not established owing possibly to low signal level and unknown short term deposition fluctuations the tuned densitometer series recovers few new periodic features although its inferred age depth relation correlates well with that of the carbonate series we calibrate the depth variable downcore to the orbital cycles to estimate r 5 0 0 15 m m y as the effective sedimentation rate

astronomical frequencies for pre quaternary palaeoclimate studies the sensitivity of the earth s orbital frequencies involved in the astronomical theory of palaeoclimates to the earth moon distance and consequently to the length of the day and to the dynamical ellipticity of the earth has been investigated for the last billion years the shortening of the earth moon distance and of the length of the day back in time induces a shortening of the fundamental astronomical periods for the obliquity and the precession a shortening which is larger for the longer periods these periods of precession and obliquity influenced by the changing earth moon distance length of the day and dynamical ellipticity of the earth have been recomputed for the last 440 million years

a strategy for frequency spectra of quaternary climate records the paleoclimatic variability at frequencies ranging from 10 4 cycle per year cpy to 10 5 cpy is investigated using a set of four deep sea cores from the atlantic pacific and indian oceans dominant features are the presence of orbital frequencies corresponding to mean periods of 117 7 43 6 24 9 and 19 3 kyr these are statistically significant according to such advanced spectral tools as blackman tukey maximum entropy and the highly efficient thomson technique however the main purpose of this paper is methodological describing the statistical analyses of time series with modern methods in order to stress their relative power advantages and disadvantages the more advanced statistical methods confirm the coincidence of the dominant periods in the deep sea cores and those in the astronomical elements including combination tones three frequency bands of high paleoclimatic variability centred at 15 4 13 and 10 8 kyr are indeed also detected these two last periods are very close to those predicted by the climatic non linear model of ghil and le treut and found by pestiaux et al and yiou et al

a long geoclimatic record from the permian a 260 000 year continuous annual geoclimatic time series has been compiled from the varved permian castile and bell canyon formations of the delaware basin southeastern new mexico and southwestern texas the last 200 000 years of the record was obtained from calcite laminated anhydrite and anhydrite laminated halite which formed as a result of seasonal and annual deposition in the evaporite basin the time series is based on measured thickness of individual varves analyses of calcium sulfate calcium carbonate and organic matter were made on 50 year intervals in the evaporite part of the sequence time series of the major components were examined by using smoothed graphic plots variance spectra and moving correlation coefficients the longest oscillation recorded in the series that may be of climatic origin has a period of about 100 000 years the calcium sulfate record contains 9 11 distinct oscillations with an average period of about 20 000 years the strongest oscillation has a preferred spectral period of 2700 years and is recorded throughout the series as thickness changes in calcium sulfate as events controlling halite deposition and as episodes of basin freshening a broad spectral response near a period of about 200 years reflects changes in sulfate carbonate and halite thickness shorter periods do not have consistent spectra the time series contains no preferred periods that have not already been identified in previously described records the climatic changes appear to be the result of a deterministic response to orbital effects at the longer periods and stochastic processes at the shorter periods an unusually strong response near 2700 years is associated with episodic freshening of the basin this period has been well established in the holocene paleoclimatic record and its presence in the permian suggests a deterministic origin

effect of precessional insolation changes on cretaceous climate and cyclic sedimentation the often striking presence of cyclical beddings has frequently been noted in cretaceous marine sediment deposits in many instances these beddings appear to have periodicities similar to those of the earth s orbit i e its precession obliquity and eccentricity variations in the primary deposition of ocean sediments are strongly linked to atmosphere land ocean interactions we report a set of numerical experiments using an atmospheric general circulation model that are designed to examine the sensitivity of mid cretaceous climate to insolation changes due to the precessional cycle we restrict attention to a single orbital parameter because most limestone black shale bedded sequences were deposited at low latitudes where precessional insolation variations predominate we varied systematically the precessional index between the maximum positive and negative values calculated over the last 2 m y and used mid cretaceous paleogeographic and paleotopographic reconstructions and zonally symmetric sea surface temperatures based on earlier work by barron and washington surface wetness and albedo values appropriate for grassland were prescribed uniformly over all land regions to capture the seasonality of precession we employed both perpetual january and perpetual july simulations changes in surface heating due to the imposed insolation anomalies resulted in a strong basically linear response of monsoonal circulations dominated by changes over the northern hemisphere the hydrologic cycle shows a significant response over many regions the low latitude proto south atlantic region varies from a strong net sink for water vapor excess precipitation to a strong source excess evaporation over the precession cycle this variation is consistent with an alternation between a stagnant stratified ocean basin with anoxic bottom water and an evaporative basin that produces bottom water that is warm saline and oxygenated the portion of the tethys ocean that overlays the limestone black shale sequences now found in present day italy does not exhibit comparable behavior but the reconstruction of orography and basin boundaries in this region is less known the simulations show however that as the monsoonal flow over south proto asia intensifies water vapor evaporated in this part of tethys is prevented from crossing the proto alps into the interior of the continent thereby remaining in the tethian drainage basin as a result central proto asia shifts between arid and moist conditions with precessional variations the water vapor budget over northeast africa varies systematically from zero seasonality to a marked wet dry seasonal cycle the deposition of eolian material can be inferred from a combination of continental aridity favorable mean wind directions and significant wind variances in our experiments the mean surface and upper winds often show a systematic response to precession but surface wind variances show a systematic response only in isolated regions our simulations do not provide a simple mechanism to explain the cyclicity in eolian deposition that has been reported for north central tethys

orbital tuning as an inverse problem chronology of the early aptian oceanic anoxic event 1a selli level in the cismon apticore 1 orbital tuning the process of fitting sedimentary cycles to orbital periodicities can estimate with high resolution the timing and duration of key events in the geological record we formulate here orbital tuning as the inverse problem of finding the variation in sedimentation rate that matches sediment cycles with orbital periodicities instead of obtaining a single best estimate we apply a bayesian formulation and define a probability distribution of sedimentation rate variations that result in powerful orbital periodicities by sampling this distribution with a monte carlo method we quantify the uncertainty in the inferred sedimentation rates due to uncertainties in the tuning periods and to components of the sedimentary signal that are unrelated to orbital cycles the method is applied to the chronology of a 30 m interval in the cismon apticore borehole southern alps italy that includes the early aptian oceanic anoxic event 1a selli level estimated to last 1 11 0 11 ma 95 interval the 13c record shows a sudden negative shift of about 1 at the base of the selli level 22 47 ka followed by a recovery to preshift values in 240 ka consistent with a scenario where light carbon is quickly added and then flushed out of the ocean atmosphere system

spectral effects of time depth nonlinearities in deep sea sediment records a demodulation technique for realigning time and depth scales carbon 14 dating and percent caco3 in late pleistocene sediments suggest that deepsea sedimentation rates vary cyclically and that this cyclicity is related to climate sedimentation rate variability leads to nonlinearity in the time depth mapping function this nonlinearity can have profound affects on signal spectra leading to the development of harmonics and intermodulation tones these distortion effects in the spectra give a direct indication of the degree of nonlinearity thereby providing a tool for realigning time and depth scales a tuning technique is developed which assumes a direct link between climate as measured in 18o from planktonic foraminifer tests and sedimentation rates a criterion of spectral simplicity as quantified in the varimax norm is used to demodulate the input spectrum application of this technique to an equatorial pacific piston core erdc 84 found peak glacial sedimentation rates to be 30 higher than peak interglacial rates a figure in good agreement with 14c based estimates from the same area this technique is compatible with other time scale tuning techniques such as those using orbital parameters and in combination with these other techniques provides a method for fine tuning any late pleistocene record

cyclic sedimentation in the shallow marine upper permian kennedy group carnarvon basin western australia abstract the upper permian kennedy group of the carnarvon basin western australia was deposited while the merlinleigh sub basin was undergoing thermal subsidence and the global climate was warming from the carboniferous permian glaciation to the mesozoic greenhouse conditions the kennedy group comprises siliciclastic sedimentary rocks dominated by sandstones in the lower part with coarsening up cycles from mudstones to very coarse sandstones and granule conglomerates in the upper part cycles were observed and logged in the field and although many types of cycles were found three main motifs describe most of the cycles cycle motifs are defined based on the dominance of the various facies mooka motif cycles are dominated by fine grained and bioturbated facies interpreted as deposition during relative sea level highstand with only thin laminated or cross bedded sandstones interpreted as deposited during relative sea level fall binthalya motif cycles are dominated by laminated and cross bedded sandstones and coolkilya motif cycles consist of alternating laminated and bioturbated beds a hierarchy of cycles was observed in the field and this correlated well with spectral analysis of logged parameters spectral analysis of section log data and data sets corrected for the effects of compaction and sedimentation rates detected regular cyclicity geochronology of the kennedy group is not well enough constrained to allow the cycle periods in time to be calculated but ratios of the different scale cycle thicknesses correlate well with ratios of the milankovitch orbital cycles that have been calculated for the permian the presence of regular cyclicity and even bed thicknesses across large distances are not consistent with tectonic or autocyclic models of cycle formation the cycles are more likely to have been caused by fluctuating eustatic sea levels perhaps enhanced by changing amounts or seasonality of precipitation both sea levels and climatic fluctuations would ultimately be controlled by the milankovitch orbital cycles

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

plio pleistocene time evolution of the 100 kyr cycle in marine paleoclimate records to constrain theories for the dynamic evolution of global ice mass through the late neogene it is important to determine whether major changes in the record were gradual or rapid of particular interest is the evolution of the near 100 kyr ice age cycle in the middle pleistocene we describe and apply a new technique based on multiple taper spectral analysis which allows us to model the time evolution of quasi periodic signals this technique uses both phase and amplitude information and enables us to address the question of abrupt versus gradual onset of the 100 kyr periodicity in the middle pleistocene we analyzed three long 2 6 m y time series from deep sea drilling project dsdp site 607 midlatitude atlantic and ocean drilling program odp site 677 equatorial pacific the published time scales for these sites differ significantly influencing the interpretation of the mid pleistocene climate transition when the data series are expressed on the same time scale there is evidence for a coherent 18o signal at both sites in the eccentricity and obliquity frequency bands consistent with variations in global ice volume as the causative factor if the shaddeton et al 1990 time scale for odp 677 is accepted the amplitude match between the 18o obliquity cycle and the 65 n insolation derived from the recent astronomical solution of laskar 1988 1990 is excellent for times t 2 3 ma if the ruddiman raymo time scale for dsdp 607 is accepted the 41 kyr 18o cycle has enhanced amplitude between 1 0 and 1 5 ma relative to the late pleistocene t 1 0 ma implying a nonlinear earth system response to obliquity insolation cycles we do not find compelling evidence for an abrupt change in the 100 kyr 18o signal although we cannot rule it out at this time if the shackleton et al 1990 time scale for odp 677 is accepted our three 18o records are consistent with a low amplitude 100 kyr cycle between 1 2 and 2 6 ma whose local period of oscillation alternates between the 95 and 124 kyr eccentricity periods and a gradual increase in the 100 kyr 18o signal between 0 5 amd 1 0 ma the dsdp 607 time scale is more favorable to an abrupt jump in amplitude for the 95 kyr 18o envelope but not in the 124 kyr envelope rather long period 18o fluctuations appear phase locked with the 124 kyr eccentricity cycle some 300 400 kyr prior to its growth in amplitude and phase lock with the 95 kyr eccentricity cycle in the late pleistocene

toward an orbital chronology for the early aptian oceanic anoxic event oae1a 120 ma abstract the early aptian oceanic anoxic event oae1a 120 ma represents a geologically brief time interval in the mid cretaceous greenhouse world that is characterized by increased organic carbon accumulation in marine sediments sudden biotic changes and abrupt carbon isotope excursions indicative of significant perturbations to global carbon cycling the brevity of these drastic environmental changes

milankovitch climatic origin of mid cretaceous black shale rhythms in central italy the earth s orbital variations reflected in pleistocene ice volume were also recorded in non glacial times carbonate production in pelagic mid cretaceous sediments quantified by calcium carbonate and optical densitometry time series reflects the orbital eccentricity and precessional cycles minimal eccentricity brought deep sea anoxia most of the sedimentary variability of this 100 myr old sequence lies within the milankovitch orbital frequency band

calcareous nannofossils and milankovitch cycles the example of the albian gault clay formation southern england a quantitative study of calcareous nannofossil assemblages was carried out on the albian gault clay formation england this unit consists of grey marly claystones and marlstones with phosphatic nodules and glauconitic layers as minor lithologies two cores were analyzed in detail to focus on changes in nannofloral assemblages and consider their significance preservation of calcareous nannofossils is excellent and therefore diagenesis cannot be invoked to explain not even partially the changes registered in assemblages fast fourier spectral analysis was performed on percentages of selected nannofossil species fluctuations in abundance of both biscutum constans and watznaueria barnesae regarded as fertility and non fertility indices respectively appear to be orbitally driven because spectral analysis showed periodicities of approximately 41 kyr obliquity cycle and 100 kyr short eccentricity cycle in all the spectra the axial obliquityc cycle is a strong signal as expected at these high latitude sites from the boreal realm the same pattern was observed in another fertility controlled taxon zygodiscus cf erectus but cross correlation shows that its abundance plot is displaced with respect to that of b constans orbital perturbations induce variations in climate and ocean circulation because they influence the earth s insolation and seasonality during times of high seasonality strong gradients cause vigorous oceanic circulation a better cycling of nutrients and higher fertility whereas during times of low seasonality low gradients induce more sluggish circulation and lower fertility the carbonate content of the gault clay cores is not correlatable to the higher fertility indices as the abundance curves of b constans w barnesae and z cf erectus are displaced with respect to caco3 content variations this also means that cyclicity in nannofossil assemblages is not a result of diagenesis but an original signal abundance fluctuations of repagulum parvidentatum and combined parhabdolithus asper p splendens colder and warmer water indicators respectively provide evidence for orbital periodicities suggesting that also cyclic variations of surface water temperature might have influenced the nannofossil assemblage patterns within the gault clay

turonian to santonian paleoenvironmental changes in the cretaceous western interior sea the carlile and niobrara formations in southern alberta and southwestern saskatchewan canada abstract the upper cretaceous upper colorado group including the carlile and niobrara formations reveals a complex and dynamic marine basin system in southern alberta and southwestern saskatchewan an integrated study of the lower offshore to shelf environment including sedimentology geochemistry petrophysics and micropaleontology demonstrates how sea level fluctuations played a major role in the facies distribution and paleogeography of the interior seaway paleogeographic maps depicting seven time slices covering the late turonian to santonian illustrate general lithologies and their distribution in the north central part of the interior seaway of north america these maps are based on data from southern alberta and southwestern saskatchewan integrated with studies of time equivalent strata in neighboring regions in western canada and northwestern u s the interior seaway reached its maximum extent during the peak transgression of the greenhorn cycle early turonian and the basin was gradually infilled starting in the late turonian with the carlile formation the boundary between the carlile and niobrara formations is an angular unconformity where up to 20 m of the upper carlile formation was eroded at this time late late turonian the interior seaway was a narrow strait of a few hundred kilometers with its basin axis in eastern alberta marginal marine sandstones were deposited in western alberta cardium formation and central saskatchewan north central montana bowdoin sandstone the overlying transgressive part of the niobrara cycle shows multiple dramatic basin changes with two examples of relative lowstand and complete basin drainage implied by the verger member coniacian these rapid lowstand events occurred within periods of marine mudstone deposition which indicate shelfal to offshore conditions during deposition of the medicine hat member early to middle santonian changes from a shaly to a sandy shelf took place with deposition of thirteen sandstones in the vicinity of the bow island arch of southern alberta during lowstand periods with low accommodation the bow island arch affected sedimentation whereas during high accommodation the arch had no influence a subtle syncline in the northwest part of the study area is the primary reason for deposition of the main gas producing sandstone of the medicine hat member the maximum extension of the interior seaway during the niobrara cycle occurred in the late santonian with the deposition of the first white specks member

m sequence geomagnetic polarity time scale mhtc12 that steadies global spreading rates and incorporates astrochronology constraints 1 geomagnetic polarity time scales gptss have been constructed by interpolating between dated marine magnetic anomalies assuming uniformly varying spreading rates a strategy to obtain an optimal gpts is to minimize spreading rate fluctuations in many ridge systems however this has been possible only for a few spreading centers we describe here a monte carlo sampling method that overcomes this limitation and improves gpts accuracy by incorporating information on polarity chron durations estimated from astrochronology the sampling generates a large ensemble of gptss that simultaneously agree with radiometric age constraints minimize the global variation in spreading rates and fit polarity chron durations estimated by astrochronology a key feature is the inclusion and propagation of data uncertainties which weigh how each piece of information affects the resulting time scale the average of the sampled ensemble gives a reference gpts and the variance of the ensemble measures the time scale uncertainty we apply the method to construct mhtc12 an improved version of the m sequence gpts late jurassic early cretaceous 160 120 ma this gpts minimizes the variation in spreading rates in a global data set of magnetic lineations from the western pacific north atlantic and indian ocean nw of australia and it also accounts for the duration of five polarity chrons established from astrochronology cm0r through cm3r this gpts can be updated by repeating the monte carlo sampling with additional data that may become available in the future

documenting the reliability and utility of the γ method as applied to cyclic sections using forward modeling abstract the problem of determining if cyclic sections which are older than 5 m y in age were deposited in response to orbital control is discussed gamma analysis a method which uses the assumption that effective accumulation rates are facies dependent to minimize differences in cycle duration is presented as a possible solution to this problem while the assumptions of analysis are generally not met by geologic data the effective accumulation rates estimated may be instrumental in recovering a spectrum which reveals orbital control we address the problem of assessing the reliability of results by performing analyses on three cyclic time series generated by a forward model our results show that exact accumulation rates are not likely to be obtained by the method however the accumulation rates obtained markedly improve the time scale resulting in a spectrum from which one could distinguish orbital forcing if present only when spectra of cyclic data show predicted orbital peaks can analysis be considered to yield effective accumulation rates which are more nearly like the true effective accumulation rates than the assumption of a single effective accumulation rate for all facies

middle triassic orbital signature recorded in the shallow marine latemar carbonate buildup dolomites italy a new time frequency analysis of sea level controlled carbonate platform cycles in the middle triassic latemar massif dolomites italy reveals a strong depositional signature with characteristics of dominant forcing by climatic precession modes corresponding to long and short precession components at 1 21 7 k y and 1 17 6 k y underwent amplitude modulations matching earth9s orbital eccentricity with major frequency components at 1 400 k y 1 125 k y and 1 98 k y obliquity appears as a minor component at 1 35 4 k y the latemar signature thus constitutes the oldest pristine milankovitch signature yet observed in the geologic record its fidelity rivals that of the pliocene pleistocene record originally used to confirm the theory of orbitally forced climates this evidence deepens a widely noted disagreement between radiometric and cyclostratigraphic time scales for the latemar buildup the latemar cycles indicate that orbitally forced sea level oscillations were operative in the ice free middle triassic hothouse world

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

major element analysis of cyclic black shales paleoceanographic implications for the early cretaceous deep western tethys lower cretaceous sediments are frequently characterized by a well expressed cyclicity while the processes influencing environments above the carbonate compensation depth ccd are reasonably well understood almost nothing is known about the deep ocean cretaceous sub ccd sediments from the tethys and atlantic oceans typically show rhythmic black green shale successions to gain insight into the nature of these black green shale cycles we performed detailed geochemical analyses x ray fluorescence rock eval and reactive iron analysis on a 3 m long section of latest aptian age the major element distribution of the analyzed shale sequence indicates a periodic change from a high productivity and well oxygenated green shale mode to a low productivity oxygen deficient black shale mode it is proposed here that the preservation of organic matter was dependent on the strength of salinity driven deepwater generation furthermore the data show that the corg content covaries with changes in the detrital composition therefore we hypothesize that tethyan deepwater circulation was sensitive to changes in the monsoonal system time series analysis suggests that these changes are periodic in nature although we are currently unable to prove that the dominant periodicity is related to the precession component of the milankovitch frequencies

seeing red in cyclic stratigraphy spectral noise estimation for astrochronology 1 fundamental to the development of astronomical time scales is the recognition of oscillatory variability within stratigraphic data and its evaluation relative to a null noise hypothesis in this study monte carlo simulations are used to investigate the suitability of two commonly used noise hypotheses the conventional and robust ar1 approaches and the results highlight important limitations in both for cyclostratigraphic application perhaps most problematic the robust ar1 method can result in inflated confidence level estimates and excessive clumping of false positives within the low frequency portion of the spectrum especially when the underlying noise process has a high lag 1 autocorrelation given typical cyclostratigraphic records this technique will often impose significant eccentricity band variability even in the case of pure ar1 noise an alternative spectral noise estimation method is proposed to overcome these problems which simultaneously allows for departures from the ar1 assumption and obtains high statistical power that is the ability to accurately identify astronomical signals when they are present in the data we apply the method to un tuned 18o data from miocene sediments of the ceara rise indicating statistically significant spectral power at frequencies that are consistent with the published orbital interpretation of weedon et al 1997 furthermore evaluation of the frequency arrangement of the significant spatial bedding periods using the average spectral misfit method for astrochronologic testing reveals that the null hypothesis of no orbital influence can be rejected with a high degree of confidence the 99 8 confidence level

a long marine history of carbon cycle modulation by orbital climatic changes pacing of the marine carbon cycle by orbital forcing during the pliocene and pleistocene ice ages past 2 5 million years myr is well known as older deep sea sediment records are being studied at greater temporal resolution it is becoming clear that similar fluctuations in the marine carbon system have occurred throughout the late mesozoic and tertiary despite the absence of large continental ice sheets over much of this time variations in both the organic and the calcium carbonate components of the marine carbon system seem to have varied cyclically in response to climate forcing and carbon and carbonate time series appear to accurately characterize the frequency spectrum of ancient climatic change for the past 35 myr much of the variance in carbonate content carries the polar signal of obliquity 41 000 years 41 kyr forcing over the past 125 myr there is evidence from marine sediments of the continued role of precessional 21 kyr climatic cycles repeat patterns of sedimentation at about 100 400 and 2 400 kyr the modulation periods of precession persistently enter into marine carbon cycle records as well these patterns suggest a nonlinear response of climate and or the sedimentation of organic carbon and carbonates to precessional orbital perturbations nonlinear responses of the carbon system may help to amplify relatively weak orbital insolation anomalies into more significant climatic perturbations through positive feedback effects nonlinearities in the carbon cycle may have transformed orbital climatic cycles into long wavelength features on time scales comparable to the residence times of carbon and nutrient elements in the ocean

normalized remanence in sediments of the western equatorial pacific relative paleointensity of the geomagnetic field piston cores from the ontong java plateau collected during the eurydice expedition have been used to estimate regional geomagnetic paleointensity rock magnetic measurements of the sediments show that 1 the remanence is carried by stable pseudo single domain magnetite 2 the grain sizes and concentrations are relatively uniform with respect to the normalization technique and 3 susceptibility is an adequate parameter for normalizing remanent intensity in order to determine relative variations in the intensity of the paleomagnetic field we therefore have measured the remanent intensity both natural and demagnetized to 15 mt and susceptibility of archive quarters of three cores at centimeter intervals using an automated through bore magnetometer a further test of the normalized intensity records is provided by the coherence function between the normalized remanence and the susceptibility of the cores one of our cores displays high coherence over a broad range of frequencies while for two others coherence is insignificantly different from zero at the 95 level of confidence oxygen isotopic records paleontological datum levels and the brunhes matuyama boundary provide an independent temporal framework for inter core comparison when the two cores which pass our acceptance criteria are placed on a common time scale the coherence between the normalized intensity records is significantly different from zero at well above the 95 level of confidence suggesting some common input signal over the same band of frequencies furthermore there is a great deal of similarity between the records from the ontong java plateau and a record from core rc10 167 taken some 3000 km to the north the distribution of intensities obtained from these sedimentary records has the same shape as the absolute virtual dipole moment data obtained from lava flows 0 5 ma with a slightly smaller standard deviation the inter core agreement within a single region the similarity of records from 3000 km apart and the general correspondence of statistical character of these sediments with lava flow data all argue that the normalized intensity records presented here reflect variations in the intensity of the ancient geomagnetic field spectral analysis of the paleointensity time series shows that there a is significant enhancement of variance concentrated in frequencies around 33 thousand years over the period 0 350 ka this feature is however lacking for the period 350 700 ka

re evaluation of the large deep earthquake of january 21 1906 abstract the large deep earthquake of january 21 1906 is re evaluated using old seismogram data and updated analysis techniques from the p and pp p time data the hypocentre parameters are determined as follows origin time 13h 49min 35s latitude 33 8 n longitude 137 5 e depth 340 km the body wave magnitude m b is re evaluated from the amplitude and periods of p pp and s waves the average value of 7 4 is obtained this value is the smallest among any values assigned previously to this shock and it is denied that the earthquake is the world s largest deep shock in this century the focal mechanism is estimated from the p wave first motions and amplitude distribution of p and s waves synthetic body waves are used to constrain the mechanism and to determine the seismic moment the mechanism solution suggests the down dip compression typical of this region a seismic moment of 1 5 10 27 dyn cm is obtained this value and the re evaluated value of m b are consistent with the moment b relation obtained for other deep earthquakes

a new approach to an absolute timescale from measurements of orbital cycles and sedimentary microrhythms when the sedimentary microrhythms of two groups of jurassic zones forming part of the chronostratigraphical scale are analysed against recent radiometric age scales there is good agreement with present day cycles resulting from the obliquity of the ecliptic sedimentary microrhythms resulting from orbital forcing can be used to establish either the relative or the true length of chronostratigraphical zones and thus provide a new approach towards an absolute timescale such a scale will be powerful in the analysis of other cycles and perturbations in the geological record

diachronous pattern of milankovitch cyclicity in late albian pelagic marlstones of the north german basin abstract the occurrence correlation and preservation of high frequency cyclicity has been studied in pelagic marlstones across an epicontinental basin wavelet analysis has been used for detection and extraction of stationary periodicity and gradual random and abrupt sedimentary changes from gamma ray and carbonate content data in three upper albian successions in the north german basin the sections represent the basin center a salt diapir edge and a submarine swell the mean sedimentation rate varies from 11 cm ka in the basin center to 0 8 cm ka on the submarine pompeckj swell respectively the major periodicity of 0 7 13 m most likely represents milankovitch cycles of 100 ka eccentricity the length of major periodicity of each section depends on sedimentation rate and ranges from 0 7 to 13 m up to 15 periodic sedimentary cycles are embedded in a transgressive regressive cycle from 101 5 to 99 ma regional correlation indicates that preservation of periodic sedimentation shifts diachronously throughout the north german basin periodic cyclicity does not occur during the early transgressive phase and across regional sequence boundaries in early late albian the preservation of periodic cyclicity shifts diachronously according due to the preservation of undisturbed pelagic sedimentation the degree of disturbances in sedimentation limits the preservation of periodicity more than the mean sedimentation rate undisturbed sedimentation started in the basin center at higher subsidence in an early stage transgression on the other side increased terrigeneous supply during regression favored the preservation of periodic sedimentation for longer time along the more off shore submarine pompeckj swell other high frequency milankovitch cycles i e obliquity precession are more sensitive to disturbances and less preserved than eccentricity cycles

detection quantification and significance of hiatuses in pelagic and hemipelagic strata temporal gaps in the stratigraphic record have important implications for the interpretation of stratigraphically rapid geochemical and paleobiologic changes for the development of high resolution time scales e g orbital time scales and for deciphering the response of depositional systems to climatic change and basin evolution e g accommodation space vs sediment supply in ancient pelagic and hemipelagic strata the identification of relatively short hiatus 10 3 10 6 years is commonly challenged by the resolution limits of geochronologic techniques in this study a quantitative method is developed to identify and quantify hiatuses in strata where milankovitch orbital cycles are documented the new method is based on the interpretation of evolutive harmonic analysis eha results and permits estimation of minimum durations for the temporal gaps application of this technique to an optical densitometry data series derived from the cenomanian turonian c t bridge creek limestone member permits quantification of hiatus within the unit and addresses important questions about abrupt changes in biogeochemical proxy records across the boundary interval integration of the new method with stratigraphic data and geochemical burial flux estimates permits a detailed reconstruction of the controls on sediment delivery and hiatus generation including a refined analysis of the orbital scale linkages between climate and sedimentation d 2004 elsevier b v all rights reserved

whither cyclostratigraphy testing the gamma method on upper pleistocene deep sea sediments north atlantic deep sea drilling project site 609 1 abstract gamma analysis a procedure for tuning cyclic sediments in which gamma is defined as 1 sedimentation rate was applied to the upper pleistocene gray scale record of deep sea drilling project site 609 from the north atlantic the spectrum of the gamma tuned time series produces eccentricity obliquity and precession index signals when the primary periodicity is tuned to the precessional beat frequency however the timescales are significantly too long suggesting that some of the primary cycles used in the gamma tuning procedure have higher frequency than the precessional beat by filtering the specmap calibrated time series at i 0 12 kyr the spurious cy cles are removed from the tuning procedure in this case the resulting gamma corrected spectra look much more like that of the specmap tuned time series however the time series remains slightly too long forward modeling is consistent with the results from modeling the core that is the gamma method is quite robust at revealing orbital periodicity in an orbitally controlled re cord for which sedimentation rates are facies dependent however the method does not produce an accurate time series criteria for complete rejection of gamma results are clarified as either 1 least squares results include negative gamma values or 2 the resulting spectrum does not show an or bital signature variation on sedimentation rates greater than 5 result in incorrect time series however variations on sedimentation rates as high as 15 generally reproduce strong orbital spectra and occasionally the method can also generate an orbital spectrum with up to 25 noise the method is not as robust in predicting gamma values or sedimentation rates although it generally distinguishes facies with relatively high sedimentation rates from facies with relatively low sedimentation rates the values predicted may be incorrect by a factor of2 thus while gamma tuning of the time series is an improvement over observed thicknesses the resulting timescale is not correct the implications of these results for cyclostratigraphy are significant the generation of an orbital spectrum from a time series that is demonstrably incorrect casts doubt on cyclicity as a dating tool

origin of the cretaceous bridge creek cycles in the western interior united states abstract alternating beds of burrowed limestone and laminated organic carbon rich marlstone in the bridge creek member of the greenhorn formation were deposited during maximum transgression of the cenomanian turonian sea in the western interior of the united states one view of the origin of the bridge creek limestone marlstone rhythms holds that they represent dilution cycles produced by alternating climates within the western interior the marlstones recording wet episodes when high runoff produced a sediment laden brackish lid on the seaway and the limestones recording dry episodes when runoff was low and the water column well mixed a second view holds that the rhythms represent productivity cycles the limestones representing times of high productivity of calcareous planktonic skeletons and the marlstones representing times of low productivity in this view the rhythms were produced by alternations in vertical circulation that characterized much of the world ocean at the time the productivity origin of the rhythms is supported by the presence of abundant calcispheres in the limestone beds the concentration of clay size quartz in many of the limestone beds the comparatively high 18 o and low 13 c in limestone beds the similarity in proportion of clay minerals in marlstone and limestone beds the pelagic depositional rate of the bridge creek member and by the discovery that bridge creek deposition began with a marlstone and not a limestone bed the dilution model is not consistent with these features and it has not been supported by modeling of paleoclimates and lithofacies that were predicted from it nor by macrofaunal distributions within the seaway the dilution model is not consistent with the occurrence of diverse and abundant planktonic foraminifera in both marlstone and limestone beds which indicate that near normal marine salinities prevailed during deposition of both bed by bed analysis of the bridge creek member may provide an analog for events in the tethys that are poorly recorded in deposits from the deep sea itself

integrated quantitative stratigraphy of the cenomanian turonian bridge creek limestone member using evolutive harmonic analysis and stratigraphic modeling abstract secular changes in bulk sedimentation have a significant impact on the preservation of climatic signals in rhythmically bedded strata in this study a quantitative cyclostratigraphic methodology is developed to use these signal distortions as a means to reconstruct sedimentation the method exploits a moving window fourier technique that we designate evolutive harmonic analysis eha we calibrate this methodology to a specific set of geologic conditions i e changes in bulk sedimentation using a series of stratigraphic models and then apply the technique to the cenomanian turonian greenhorn formation of the western interior basin application of eha to strata that preserve a record of orbital forcing allows the reconstruction of a high resolution sedimentation history in which bulk sedimentation rates and hiatuses are quantified using the data on bulk sedimentation rate rates of accumulation for geochemical proxies representing detrital biogenic and authigenic contributions to the sediment can be calculated by integrating these quantitative assessments of siliciclastic dilution primary production and depositional redox conditions within a high resolution chronostratigraphic framework we are able to deconvolve secular trends in hemipelagic sedimentation during the late cenomanian early turonian in the western interior basin this integrated quantitative stratigraphic approach allows a reevaluation of hypotheses for the accumulation of excess organic matter in the western interior basin during the interval representing oceanic anoxic event ii

the cyclostratigraphy intercomparison project cip consistency merits and pitfalls abstract cyclostratigraphy is an important tool for understanding astronomical climate forcing and reading geological time in sedimentary sequences provided that an imprint of insolation variations caused by earth s orbital eccentricity obliquity and or precession is preserved milankovitch forcing numerous stratigraphic and paleoclimate studies have applied cyclostratigraphy but the robustness of the methodology and its dependence on the investigator have not been systematically evaluated we developed the cyclostratigraphy intercomparison project cip to assess the robustness of cyclostratigraphic methods using an experimental design of three artificial cyclostratigraphic case studies with known input parameters each case study is designed to address specific challenges that are relevant to cyclostratigraphy case 1 represents an offshore research vessel environment as only a drill core photo and the approximate position of a late miocene stage boundary are available for analysis in case 2 the pleistocene proxy record displays clear nonlinear cyclical patterns and the interpretation is complicated by the presence of a hiatus case 3 represents a late devonian proxy record with a low signal to noise ratio with no specific theoretical astronomical solution available for this age each case was analyzed by a test group of 17 20 participants with varying experience levels methodological preferences and dedicated analysis time during the cip 2018 meeting in brussels belgium the ensuing analyses and discussion demonstrated that most participants did not arrive at a perfect solution which may be partly explained by the limited amount of time spent on the exercises 4 5 hours per case however in all three cases the median solution of all submitted analyses accurately approached the correct result and several participants obtained the exact correct answers interestingly systematically better performances were obtained for cases that represented the data type and stratigraphic age that were closest to the individual participants experience this experiment demonstrates that cyclostratigraphy is a powerful tool for deciphering time in sedimentary successions and importantly that it is a trainable skill finally we emphasize the importance of an integrated stratigraphic approach and provide flexible guidelines on what good practices in cyclostratigraphy should include our case studies provide valuable insight into current common practices in cyclostratigraphy their potential merits and pitfalls our work does not provide a quantitative measure of reliability and uncertainty of cyclostratigraphy but rather constitutes a starting point for further discussions on how to move the maturing field of cyclostratigraphy forward

minor element zoning and trace element geochemistry of pallasites i report here on an ion probe study of minor element spatial distributions and trace element concentrations in six pallasites pallasite olivines exhibit ubiquitous minor element zoning that is independent of grain size morphology and adjacent phases ca cr ti v and ni concentrations decrease from center to rim by factors of up to 10 while mn is generally unzoned or increases slightly at the very edge of some olivine grains the maximum concentrations of these elements at the center of olivine vary from grain to grain within the same meteorite and among the pallasites studied these zoning profiles are consistent with thermal diffusion during rapid cooling the inferred cooling rates at high temperature regimes are orders of magnitude faster than the low temperature metallographic cooling rates similar to0 5 to 2degreesc ma this suggests that pallasites like mesosiderites have experienced rather complicated thermal histories i e cooling rapidly at high temperatures and slowly at low temperatures

northern hemisphere glaciation and the evolution of plio pleistocene climate noise 1 deterministic orbital controls on climate variability are commonly inferred to dominate across timescales of 104 106 years although some studies have suggested that stochastic processes may be of equal or greater importance here we explicitly quantify changes in deterministic orbital processes forcing and or pacing versus stochastic climate processes during the plio pleistocene via time frequency analysis of two prominent foraminifera oxygen isotopic stacks our results indicate that development of the northern hemisphere ice sheet is paralleled by an overall amplification of both deterministic and stochastic climate energy but their relative dominance is variable the progression from a more stochastic early pliocene to a strongly deterministic late pleistocene is primarily accommodated during two transitory phases of northern hemisphere ice sheet growth this long term trend is punctuated by stochastic events which we interpret as evidence for abrupt reorganization of the climate system at the initiation and termination of the mid pleistocene transition and at the onset of northern hemisphere glaciation in addition to highlighting a complex interplay between deterministic and stochastic climate change during the plio pleistocene our results support an early onset for northern hemisphere glaciation between 3 5 and 3 7 ma and reveal some new characteristics of the orbital signal response such as the puzzling emergence of 100 ka and 400 ka cyclic climate variability during theoretical eccentricity nodes

cyclostratigraphy of the upper cretaceous niobrara formation western interior u s a a coniacian santonian orbital timescale abstract the turonian campanian niobrara formation of the western interior basin u s a is characterized by decimeter scale rhythmic alternations of chalk and marl beds and decameter scale oscillations of chalky and marly facies this study applies recent advances in quantitative cyclostratigraphic analysis to high resolution geophysical records in order to test for an orbital signal we studied records of the entire formation 85 m from two wells in colorado 40 17 n 104 38 w 40 14 n 104 41 w the study utilized high resolution time series of borehole resistivity measured from formation microimager tools fmi advanced spectral techniques indicate the presence of eccentricity obliquity and precession periodicities throughout the study interval deviations of bundling ratios in the lower fort hays member from those predicted by simple eccentricity modulation of precession previously reported in the literature are likely due to the influence of obliquity deconvolution and frequency tracking of orbital components were used to reconstruct sedimentation rates for the niobrara formation and thus develop a high resolution orbital timescale which permits calculations of accumulation rates for sedimentary components and the duration of inclusive stages substages and in some cases biozones the niobrara formation in the studied cores appears to be hiatus free and therefore provides a continuous record of rhythmic deposition for astronomical timescale development the relationship between carbonate content and sedimentation rate throughout the niobrara formation indicates that the decameter scale oscillations of chalk and marl are dominantly driven by variations in siliciclastic flux dilution the duration derived from the orbital timescale between the turonian coniacian and coniacian santonian boundaries is 3 40 0 13 myr which is generally consistent with radiometric estimates for the coniacian the orbitally derived duration of the santonian stage is 2 39 0 15 myr which is very similar to estimates based on curve fitting between radiometric dates development of high resolution orbital chronometers provides excellent time resolution in intervals that lack radiometric time control or where control points are widely spaced

tides and the evolution of the earth moon system summary a model of the tides in a hemispherical ocean is used to investigate the effect of changes in the earth s rotation rate on the power dissipated by the ocean tides the results obtained are then used in an idealized astronomical model to investigate how they affect the history of the earth moon system using the tidal model it is found that at rotation rates higher than that of the present earth the power dissipated by the semi diurnal tides in the ocean drops off rapidly as a result of the increased tidal frequency thus if the earth s rotation rate is doubled from its present value then the rate of energy dissipation in the ocean is reduced to approximately one third of its present value and the tidal torque is reduced by a factor of about 6 the present value for secular acceleration of the moon calculated from the results of the tidal model is 30 5 arcsec century 2 using this value in the astronomical model which has the moon and sun in circular orbits above the equator and assuming that the tidal torque is independent of the tidal frequency the gerstenkorn event is predicted to have occurred 1 3 109 yr ago when the astronomical model is run with a torque determined at all times from the tidal model the reduction in the energy dissipated early in the history of the system leads to a gerstenkorn date of 5 3 109 yr ago however dissipation within the solid earth is found to be important early in the history of the system and when this effect is included it gives a date for the gerstenkorn event of 3 9 109 yr ago

the origin of the 100 000 year cycle in a simple ice age model a one dimensional nonlinear ice age model developed by j imbrie and j z imbrie was used to investigate the 100 000 year cycle in climate records it was already known that the model could mimic the 100 000 year cycle in the climate response but it was not clear how this strong response was created it is shown in this paper that the interference between the spectral components in the solar heating of 19 000 years and 23 000 years gives rise to an amplitude modulation and how this modulation is converted by the nonlinearity to a 100 000 year cycle in the climate response

terrestrial laser scanner imaging reveals astronomical forcing in the early cretaceous of the tethys realm abstract we present the first application of the terrestrial laser scanner tls to cyclostratigraphy and demonstrate the capability of this remote sensing technology in rapid retrieval of high resolution cyclostratigraphic data from typical hemipelagic successions exposed in outcrops with limited accessibility tls infrared imaging is capable of recording up to a distance of 50 m a laser intensity value which is inversely proportional to the abundance of clay minerals in limestones and marls the following characteristics make tls a very useful tool 1 fast data collection 2 high resolution and high accuracy and 3 tls is an active sensor based acquisition process that is independent from environmental conditions as illumination we demonstrate this new methodology with a study of a section in the early cretaceous albian marne a fucoidi formation exposed in the vispi quarry near gubbio central italy the same stratigraphic interval has been studied in detail in a core drilled at a few kilometers away the piobbico core we compare tls results with those obtained previously from the piobbico core and propose a correlation between the two sections results indicate clear cyclicity in the tls data that correlates to the piobbico data this is the first report of correlation at the eccentricity scale in pre cenozoic stratigraphy statistical time series analysis confirms the presence of astronomical parameters with a predominance of eccentricity cycles in agreement with the piobbico core the future application of tls in cyclostratigraphy will rapidly enrich the collection of series with milankovitch cycles needed to build a mesozoic astrochronological time scale

nitrogen cycle dynamics in the late cretaceous greenhouse abstract great attention has been paid to the origin of anomalously low nitrogen isotope values during the late cretaceous nitrogen isotope values are often as low as 3 and are typically less than 2 even in relatively organic matter lean sediments here we evaluate nitrogen isotope variability during a relatively quiescent phase of the late cretaceous greenhouse between oceanic anoxic events 2 and 3 using the black shales of demerara rise dr selection of this site allows us to isolate some of the factors that control nitrogen cycle dynamics and contribute to low nitrogen isotope values new n isotope measurements from odp site 1259 reveal 15 n values that range from 0 2 to 3 5 and oscillate by 1 5 to 3 over 1 6 million years ma temporal calibration of our data using a new astronomical time scale reveals a strong 100 thousand year ka eccentricity cyclicity in 15 n we attribute this cyclicity to oscillations in the position of the intertropical convergence zone itcz over dr that modulate upwelling intensity chemocline depth and the degree of 15n depletion we also recognize a statistically significant correlation p 0 0022 between the tex86 indices and 15 n with the lowest 15 n corresponding to the highest tex86 indices this relationship suggests that the activity and ecology of ammonia oxidizing thaumarchaeota and the 15 n of dissolved inorganic nitrogen utilized by primary producers are linked we therefore interpret the observed variability in the 15 n data and tex86 indices as primarily reflecting fluctuation of upwelling intensity and chemocline depth and the significant inverse relationship between these data sets suggests that caution should be exercised when interpreting the tex86 in terms of temperature in similar paleoenvironmental settings

the detection and illustration of regular sedimentary cycles using walsh power spectra and filtering with examples from the lias of switzerland power spectral analysis provides an objective method for the detection of regular cyclicity in data recording some oscillating parameter or time series digitization of measured stratigraphic sections is a convenient method for generating long time series during the examination of pelagic sequences for cyclicity related to orbital variations or milankovitch cycles the application of walsh power spectral analysis to stratigraphic sections is outlined and band pass filtering using the walsh transform introduced it is shown that variations in sedimentation rate hiatuses bioturbation and variations in compaction have the effect of damping or destroying spectral peaks the wavelength ratios of spectral peaks are often used during studies of milankovitch cycles to decide which orbital cycles are involved however in some circumstances hiatuses are able to alter wavelength ratios averaged walsh power spectra were generated for three liassic limestone shale sequences from breggia gorge switzerland the 21 000 year 21 ka precession cycle was detected in all three cases the 100 ka eccentricity cycle in two cases and the 41 ka obliquity cycle in one filtering revealed that the supposed 21 ka sedimentary cycles are grouped into packets of four or five small and large amplitude cycles the packets reflect the 100 ka modulation of the 21 ka precession cycle local disruption of the packaging can be used to locate hiatuses in pelagic strata

frequency spectra and paleoclimatic variability of the high resolution 30 1450 ka funza i pollen record eastern cordillera colombia the evolution of orbital periodicities during the quaternary has been studied in the 30 1450 ka funza i pollen record from cores through the sedimentary basin of bogota eastern cordillera colombia the 1178 pollen samples analysed between 2 90 and 340 00 m generate 5 time series with an average time resolution of ca 1200 years our geochronological framework is based on fission track ages on zircon in combination with correlation of the pollen record with the oxygen isotope record of odp site 677 from the eastern pacific the 5 data sets were analysed in the frequency domain with maximum entropy spectrum analysis mesa and thomson multi taper spectrum analysis tmt using a moving 400 ka window with steps of 20 ka frequencies closely related to the milankovitch theory were detected in all 5 data sets the 100 ka period in the arboreal pollen record is restricted to the last ca 800 ka of the quaternary at a confidence level largely higher than 90 periodicities close to 23 ka occur throughout the record at a high significance level above 90 and are strongest in the subparamo data a statistically significant period centred at ca 40 ka also occurs in the funza i record four frequency bands centred at ca 30 ca 15 ca 13 and ca 10 ka were also detected the 5 principle data sets from the funza i pollen record reveal an evolution of orbital frequencies in the middle and late quaternary which are in general agreement with other marine e g imbrie et al 1984 and continental e g kukla et al 1990 records

milankovitch climatic signals in lower triassic olenekian peritidal carbonate successions nanpanjiang basin south china abstract meter scale peritidal carbonate strata from an isolated platform in the nanpanjiang basin of south china were tested for the presence of periodic or quasi periodic climatic signals these signals provide information on factors controlling cyclic sedimentation in the equatorial eastern tethys during the early triassic greenhouse period parasequences are composed of shallowing upward successions of subtidal facies including skeletal packstone and grainstone calcimicrobial boundstone and oolitic packstone and grainstone intertidal laminated lutite and ribbon rock and rare supratidal microbial laminite parasequence stacking patterns display three orders of cyclicity suggesting hierarchical stratigraphic relationships gamma analysis of kominz and bond earth planet sci lett 48 1990 233 244 was used to estimate facies dependent thickness time conversion factors i e s and to construct tuned and untuned time series for two stratigraphic sections spectra of these time series indicate the presence of quasi periodic signals with prominent short eccentricity 94 9 131 2 kyr short obliquity 35 8 kyr and long precessional index 21 2 kyr peaks and minor long eccentricity 412 9 kyr long obliquity 45 3 kyr short precessional index 17 7 kyr and constructional tone 9 7 kyr peaks when calibrated on the tuned spectra thus milankovitch climatic forcing probably greatly influenced sedimentation the calibration indicates that the subtidal facies has a sedimentation rate of 24 6 30 7 cm kyr and the intertidal supratidal facies has a rate of 2 7 6 0 cm kyr the estimated duration of deposition of the two sections is 1139 1423 kyr and corresponds to a stratigraphic completeness of 32 92 the completeness is much greater than that of icehouse stratigraphic records we speculate that variations in carbonate productivity and environmental conditions driven by milankovitch climatic forcing combined with low amplitude sea level fluctuations were likely major controls on cyclic sedimentation furthermore evolutional spectra of the two sections show that dominant milankovitch climatic forcings varied from short eccentricity obliquity to long precessional index during the course of sedimentation some spectral differences between the two sections suggest variations in depositional recording mechanisms of milankovitch climatic signals between platform interior and windward platform margin

causes of anoxia in the world ocean we examine the hypothesis that global scale episodes of anoxia such as occurred in the cretaceous are due to

resolving milankovitch consideration of signal and noise milankovitch climate theory provides a fundamental framework for the study of ancient climates although the identification and quantification of orbital rhythms are commonplace in paleoclimate research criticisms have been advanced that dispute the importance of an astronomical climate driver if these criticisms are valid major revisions in our understanding of the climate system and past climates are required resolution of this issue is hindered by numerous factors that challenge accurate quantification of orbital cyclicity in paleoclimate archives in this study we delineate sources of noise that distort the primary orbital signal in proxy climate records and utilize this template in tandem with advanced spectral methods to quantify milankovitch forced paced climate variability in a temperature proxy record from the vostok ice core vimeux and others 2002 our analysis indicates that vostok temperature variance is almost equally apportioned between three components the precession and obliquity periods 28 a periodic 100 000 year cycle 41 and the background continuum 31 a range of analyses accounting for various frequency bands of interest and potential bias introduced by the saw tooth shape of the glacial interglacial cycle establish that precession and obliquity periods account for between 25 percent to 41 percent of the variance in the 1 10 kyr 1 100 kyr band and between 39 percent to 66 percent of the variance in the 1 10 kyr 1 64 kyr band these results are approximately two to four times greater than those published by wunsch 2004 for the same vostok time series in all cases most of the remaining variance is accounted for by the 100 000 year cycle which is distinct from a background continuum that resembles autoregressive red noise our analysis high lights the importance of a comprehensive assessment of the climate signals in geologic records and underscores the significance of orbital forcing pacing as a primary agent of pleistocene climate change

controls on sedimentation and cyclicity of the boquillas and equivalent eagle ford formation from detailed outcrop studies of western and central texas u s a

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