detection of astronomical cycles in the stratigraphic record by frequency modulation fm analysis abstract frequency modulation fm analysis of a sequence of basinal limestone shale cycles from the upper pliensbachian domaro limestone lombardy pre alps northern italy reveals modulations with multiple low frequencies that closely resemble those of the theoretical equatorial orbitally forced precession dominated insolation there is evidence for a systematic shift in these modulation frequencies that is consistent with a shorter jurassic length of day these results were used to estimate the incremental time scale along the domaro succession revealing a dual frequency signal comparable to the precession separate analysis of the limestones and shales suggests that the limestones were deposited during times of decreasing or low northern spring equatorial insolation nsei and the shales during times of increasing or high nsei we discuss two end member models that could link precession forced insolation to the cyclic basinal sedimentation the ambiguity of the source of carbonate influx into this early jurassic basinal depocenter led us to consider 1 an allodapic mud model in which precession forced sea level oscillations instituted a cyclic production of lime mud in shallow marine environments and subsequent transport into the adjacent basinal environments and alternatively 2 a pelagic ooze model in which precession forced insolation directly forced pelagic productivity and influx into the basin

isotopic modeling of climatic oscillations implications for a comparative study of marine and ice core records a simple climate model of quaternary glaciations is combined with a simple isotopic model in order to study phase relationships between 18o records in deep sea cores and in ice cores power spectra of the model s climatic and isotopic variables show a dominant peak near 100 kyr 1 kyr 1000 years the continuous background of all paleoclimatic spectra smaller peaks at the orbital periodicities of 41 23 and 19 kyr and additional peaks at 14 7 13 11 5 10 4 and 9 5 kyr time lags between the model s isotopic profiles are highly variable ice core events identified as sharp maxima or minima can lead apparently homologous events in the marine record or lag them by a few thousand years this time domain instability of lags is due to the complexity of the power spectrum with its continuous component and large number of lines since the complex spectrum is present in both model and paleoclimatic data we expect lag relations in the data to be quite variable as well independent dating of ice cores is preferable therefore to dating by comparison with marine records absolute dating can be based on a combination of ice flow models and of accelerator mass spectroscopy time averaged cross spectra of independently dated isotopic profiles should be stable and should help us to understand the mechanisms which lead to internal climatic variability

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

incidence of obliquity and precession forced milankovitch cycles in the western mediterranean early messinian sedimentation in the sorbas basin almeria southern spain spectral analysis of the messinian abad marls in the cariatiz section sorbas basin south eastern spain reveals three relevant orders of cyclicity the most significant cycle is in the lowest frequency average thickness of 365 cm 4 5 cycles in the section it is recorded in the composition of planktic foraminiferal assemblages indicative of surface water temperature planktic and benthic stable isotope signals and carbonate proportions the planktic assemblages isotope values and carbonate proportions also record a middle frequency cycle with an average of 177 cm 9 10 cycles in the section the highest frequency cycle average of 132 cm 12 13 cycles in the section is mainly reflected in siliciclastic and calcite proportions age constraints and cycle patterns suggest that the lowest frequency cycle was forced by orbital obliquity whereas the two higher frequency ones are related to precession obliquity seems to have controlled major changes in surface water temperature in the sorbas basin during the early messinian surface water temperature was also affected by precession with changes in weathering and run off spectral analysis has also been applied to vertical shifts of reef facies throughout the progradation of the cariatiz reef this reef is coeval with the cariatiz section vertical shifts of reef talus breccias point to the existence of 4 5 major cycles of sea level change whereas 7 9 higher frequency cycles are reflected in the repeated occurrence of lowstand non reefal deposits correlation with the cycles observed at the cariatiz section suggests that obliquity forced glacio eustatic sea level oscillations in the western mediterranean during the late miocene

forcing of atlantic equatorial and subpolar millennial cycles by precession abundance cycles of the marine alga florisphaera profunda centered on a period of 7600 carbon 14 years 8400 calendar years are present in high resolution records from the equatorial atlantic spanning 0 to 45 000 years ago these cycles correlate with heinrich events 1 through 5 which document rapid changes in continental ice melting around the subpolar north atlantic these variations in f profunda are a direct response to modulation in zonal wind driven divergence produced by a precessional component of orbital variation during a time of reduced eccentricity modulation

earth s precession cycle and quaternary climatic change in tropical africa high abundances of the freshwater diatom melosira spp reflecting eolian input from dry lake beds in tropical africa occur in deep sea sediments of the equatorial atlantic at discrete times during the late quaternary1 2 we report here an approximately 260 kyr record of melosira accumulation in an equatorial atlantic sediment core and demonstrate significant influence of the earth s precessional cycle on the climate of tropical africa

milankovitch band forcing of sub milankovitch climate variability during the pleistocene climate variability at periods from 10 kyr to 12 kyr that originates from milankovitch band forcing is quantified at three locations for the late pleistocene eastern equatorial pacific ocean drilling program site 846 eastern equatorial atlantic odp site 663 and northeastern atlantic deep sea drilling project site 609 variability at these periods is not present in the primary milankovitch forcing so no linear linkage to milankovitch band variations is possible however these periods are equal to harmonics of precession band oscillations the magnitude of interactions between processes that occur at different timescales can only be resolved in time series data through application of higher order statistics through such an application we demonstrate that up to 75 of the variance in the 10 to 12 kyr band in the sediment records is nonlinearly transferred from precession band 19 23 kyr variations within the millennial to sub milankovitch band defined as the band of variance ranging from 15 to 2 kyr approximately 1 3 of the variability in the records studied is consistent with a low frequency milankovitch band origin this variability may derive from high sensitivity of the tropics to summertime insolation in both hemispheres relative to wintertime insolation a mechanism having equatorial origin and related to low latitude precession variations appears consistent with the observations because the phase coupling between 10 to 12 kyr oscillations and precession is resolved this result has implications for development of models which seek to explain global climate variations on this timescale

tectonic control of high frequency depositional sequences with durations shorter than milankovitch cyclicity an example from the pleistocene paleo tokyo bay japan forcing mechanisms of high frequency depositional sequences in late cenozoic successions have commonly been interpreted in terms of glacio eustasy in contrast we demonstrate here the effects of local tectonics in the development of high frequency depositional sequences in a middle and upper pleistocene succession examples are from shallow marine and coastal deposits developed in the paleo tokyo bay japan and are based on a detailed chronostratigraphic framework constructed from dated volcanic ash beds within highstand successions of the glacio eustatic sequences we have mapped locally developed high frequency depositional sequences within areas that have undergone anticlinal uplift these high frequency depositional sequences pass laterally into parasequences overlying marine flooding surfaces in adjacent synclinal areas spatial variation in such stratigraphic features indicates local tectonic movements in the paleo tokyo bay area during rises and highstands of glacio eustatic sea level cycles the duration of such high frequency depositional sequences is estimated as 10 k y shorter than milankovitch cyclicity the present example indicates that local basin tectonics can be an important forcing mechanism of high frequency depositional sequences in pleistocene successions in an active margin basin

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

zoophycos cyclicity during the last 425 ka in the northeastern south china sea evidence for monsoon fluctuation at the milankovitch scale in a deep sea piston core covering the last 425 ka from the northeastern south china sea power spectrum analysis of several core data from sediment parameters has been conducted and compared with

strong evidence of high frequency sub milankovitch orbital forcing by amplitude modulation of milankovitch signals abstract high frequency sub milankovitch signals have occasionally been recognised in the sedimentary record but their interpretation is yet controversial the transmission of most information involves modulating the original signal transmission in the geological sense is the process of changing the astronomical signal into insolation climate and finally the observed sediment modulated signals may contain different frequencies from the original and the former can sometimes be recognised more easily than the original ones thus sedimentary cycles belonging to the high frequency band could be interpreted as a possible modulation of the astronomical milankovitch signals to check this possibility a detailed spectral analysis was carried out on a selected marl limestone and limestone jurassic succession in which high frequency signals in the sub milankovitch range with a persistent peak at 13 14 kyr were recognised relationships between frequencies of the registered peaks suggest that the sedimentation pattern is caused by the amplitude modulation am of the milankovitch forcing in am the amplitude of a carrier frequency is modulated according to the value of a signal the spectrum of the resulting am signal is composed of three frequencies the frequency of the carrier and two side tones but the carrier and one side tone may be suppressed without destroying the information the information remains in the other side tone usually the one with the highest frequency this version of am is called single sideband carrier suppressed ssbcs for milankovitch forcing the implication is that the signals are not transmitted as added up sinusoidal signals but both the short eccentricity and the obliquity signals affect the sedimentation pattern by am of the precession signal which is the carrier frequency the sub milankovitch peaks registered in the succession studied reveal the ssbcs am of the original milankovitch signals with the ssbcs frequencies being highly significant in the estimated power spectra after applying conservative tests assuming underlying red noise

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

co seismic geoelectric potential changes observed in japan co seismic signals of geoelectric potential have been observed for several earthquakes eqs in japan it has been argued that if there are precursory changes stronger signals should be at the time of eq our results prove that co seismic signals do exist but they start with the arrival of seismic waves and not at the origin time of eqs their amplitude does not scale with the dipole length both facts indicate that the changes are local effects of passing seismic waves and not due to electric signals emitted from the seismic source observed changes contain two components oscillatory and offset decay ones the former is synchronized with seismic waves whereas the latter with a rise time of a few seconds and a decay time of 0 1 1 hour is suspected to be related to eq induced subsurface hydrological change in both cases the origin of electric potential variations may be electrokinetic

intermittent intense turbulent mixing under ice in the laptev sea continental shelf vertical mixing in the bottom boundary layer and pycnocline of the laptev sea is evaluated from a rapidly sampled 12 h time series of microstructure temperature conductivity and shear observations collected under 100 sea ice during october 2008 the bottom boundary turbulent kinetic energy dissipation was observed to be enhanced 10 4 w m 3 beyond background levels 10 6 w m 3 extending up to 10 m above the seabed when simulated tidal currents were directed on slope upward heat fluxes into the halocline class waters along the laptev sea seabed peaked at 4 8 w m 2 averaging out to 2 w m 2 over the 12 h sampling period in the laptev sea pycnocline an isolated 2 h episode of intense dissipation 10 3 w m 3 and vertical diffusivities was observed that was not due to a localized wind event observations from an acoustic doppler current meter moored in the central laptev sea near the m2 critical latitude are consistent with a previous model in which mixing episodes are driven by an enhancement of the pycnocline shear resulting from the alignment of the rotating pycnocline shear vector with the under ice stress vector upward cross pycnocline heat fluxes from the arctic halocline peaked at 54 w m 2 resulting in a 12 h average of 12 w m 2 these results highlight the intermittent nature of arctic shelf sea mixing processes and how these processes can impact the transformation of arctic ocean water masses the observations also clearly demonstrate that absence or presence of sea ice profoundly affects the availability of near inertial kinetic energy to drive vertical mixing on the arctic shelves

multifactorial control on deposition of epicontinental hemi pelagic carbonates during the earliest kimmeridgian prebetic zone southern spain abstract two successions of marly limestone limestone couplets occasionally with significant intercalations of marls have been investigated in the lower kimmeridgian platynota zone in the central sector of the prebetic zone southern spain the aim of this paper is to identify and evaluate possible interactions between global signals orbital fluctuations climate and eustasy and local regional tectonics forcing deposition and ecospace on an epicontinental shelf high resolution ammonite biostratigraphy together with sedimentological stratigraphical mineralogical data and ecostratigraphic interpretations were re examined to provide evidence for the combined action of tectonics eustasy and insolation fluctuations on sedimentation in two sections which clearly differ in stratal pattern both in the average thickness of limestone beds and in the frequency and character of marl intercalations the detailed analysis of stratal patterns was used to identify and calibrate the influence of the different factors investigated the identification of significant bedding planes in the sections studied enabled the recognition of eight bundles of beds major cycles the analysis and comparison of their internal structure together with the information about tectonic and eustatic influences enabled us to interpret the lower part of the sections bundles 1 and 2 as being forced by interactions between orbital signals and tectonics the upper part bundles 6 7 and 8 as being caused by interactions between orbital signals and eustasy and the middle part bundles 3 4 and 5 as being related mainly to orbital forcing

long term equilibrium tides extreme equilibrium tides or hypertides are computed in a new equilibrium tidal model combining algorithms of a version of the chapront elp 2000 82 lunar theory with the ber78 milankovitch astronomical expansions for the rerent past a high correspondence exists between computed semidiurnal tide levels and a record of coastal flooding demonstrating that astronomical alignment is a potential influence on such flooding for the holocene and near future maximum tides demonstrate cyclic variations with peaks at near 5000 b p and 4000 a p on the late quaternary timescale variations in maximum equilibrium tide level display oscillations with periods of approximately 10 000 100 000 and 400 000 years because of precessional shifts in tidal maxima between vernal and autumnal equinoxes while flooding occurs under the combined effects of tides and storms via storm surges the most extensive flooding will occur with the coincidence of storms and the rarer hypertides and is thus primarily influenced by hypertides therefore we suggest that astronomical alignment s relationship to coastal flooding is probabilistic rather than deterministic data derived from this model are applicable to 1 archaeological and paleoclimatic coastal reconstructions 2 long term planning for example radioactive waste site selection 3 sealevel change and paleoestuarine studies or 4 ocean meteorological interactions

filtering of milankovitch cycles by earth s geography abstract earth s land sea distribution modifies the temperature response to orbitally induced perturbations of the seasonal insolation we examine this modification in the frequency domain by generating 800 000 yr time series of maximum summer temperature in selected regions with a linear two dimensional seasonal energy balance climate model previous studies have demonstrated that this model has a sensitivity comparable to general circulation models for the seasonal temperature response to orbital forcing on land although the observed response in the geologic record is sometimes significantly different than modeled here differences attributable to model limitations and feedbacks involving the ocean atmosphere cryosphere system there are several results of significance 1 in mid latitude land areas the orbital signal is translated linearly into a large 10 c seasonal temperature response 2 although the modeled seasonal response to orbital forcing on antarctica is 6 c the annual mean temperature effect

the marl limestone rhythmites from the lower kimmeridgian platynota zone of the central prebetic and their relationship with variations in orbital parameters abstract the origin of the rhythmic marl limestone bedding recognized in lower kimmeridgian platynota zone succesions of the central prebetic southern spain is interpreted a detailed analysis was carried out on the basis of field observations and mathematical procedures of two sections characterized by the variable alternation of marly and limestone horizons the study primarily reveals signs of a possible secondary imprint in the stratification however we conclude that this imprint cannot have been sufficiently important to cause the recorded stratification or significantly alter the existing primary bedding the mathematical procedure applied to the thicknesses of the beds reveals the existence of different orders of cyclicity that are not recognizable in the field we were able to date these cycles by detailed biostratigraphy and the application of fourier spectral analysis the close relationship between the timing calculated for the marl limestone rhythms recognized in the lower kimmeridgian platynota zone successions and the periodicity assumed for milankovitch cycles has been shown for the first time in the prebetic zone and leads us to accept the influence of orbital variations on sedimentation in the sector that was studied we have also been able to recognize the influence of local factors which determined differences in the depositional organization in the sections studied

towards a high resolution global deep sea chronology for the last 750 000 years abstract variations in the ratio of 18 o 16 o as measured in shells of marine calcareous microfossils are primarily dominated by changes in global ice volume hence these variations provide a set of global time lines in deep sea sediments it is likely that the timing of major changes in oxygen isotope values is strongly influenced if not controlled by variations in the geometry of the earth s orbit since the variation of orbital parameters can be accurately calculated the opportunity exists for transforming this orbital chronology into a geological chronology through careful correlation of oxygen isotope records in a set of deep sea cores from the sub antarctic south atlantic and equatorial pacific we have assembled a composite isotopic section spanning the last 750 000 years with an average sedimentation rate of 2 3 cm 1000 years a new chronology for this time period was developed by adjusting the ages of the oxygen isotope stage boundaries in this composite section so as to extend the consistent phase relationships that exist between variations in oxygen isotope ratios and changes in obliquity and precession during the last 300 000 years to the entire 750 000 year record previously identified difficulties in phase locking precession with the filtered isotopic signal between 365 000 and 465 000 years b p have been resolved with the recognition that precessional variations have an average period of 19 000 years and not 23 000 years during this interval since this new age model yields the best match between variations in obliquity and precession and their corresponding frequency components in the oxygen isotope record we believe that it presents the most accurate chronology yet developed for deep sea sediments with this new age model providing the time control power spectral analyses of south atlantic and sub antarctic chemical and biotic indices show that there is a strong tendency for variance to be concentrated at frequencies corresponding to periods of 100 000 41 000 and 23 000 years

the role of sub milankovitch climatic forcing in the initiation of the northern hemisphere glaciation mechanisms responsible for the initiation of major glaciation in the northern hemisphere at about 2 75 million years ago are poorly understood a laminated terrestrial sequence from pula maar hungary containing about 320 000 years in annual layers between 3 05 and 2 60 million years ago provides a detailed record of rates of climatic change across this dramatic transition an analysis of the record implies that climatic variations at sub milankovitch frequencies less than or equal to 15 000 years were an important driving force during this transitional interval and that as the threshold was approached these increased in frequency and amplitude possibly providing the final trigger for the amplification of northern hemisphere ice sheets

paleoclimate of the kimmeridgian tithonian late jurassic world i results using a general circulation model abstract the kimmeridgian tithonian 154 7 145 6 ma middle and late late jurassic was a time of expanded continental rifting increased sea floor spreading and a relatively high eustatic sea level stand these processes collectively caused the fragmentation and flooding of the megacontinent pangea as well as the alteration of the global paleoclimate using a version of the community climate model ccm from the national center for atmospheric research we report two kimmeridgian tithonian paleoclimate seasonal simulations with geologically inferred paleotopography one using a co 2 concentration of 280 ppm pre industrial level and the other 1120 ppm increasing the co 2 four fold warms virtually the entire planet the greatest warming occurs over the higher latitude oceans and the least over the equatorial and subtropical regions simulation of a warmer planet with an elevated greenhouse effect fits the distribution of paleoclimatically sensitive faunas floras and sedimentary rocks model results indicate that sea ice was restricted to the high latitudes of the boreal and austral seas making landfall only in restricted areas the trade winds bring heavy rainfall in december january february to eastern gondwana and in june july august to the tethys sea margins a strong june july august monsoon occurs over southeast asia the distribution of coals correlates to precipitation sufficient to maintain gymnosperm forests and coastal areas where water saturated sediments are a result of eustatic high stands of sea level evaporites are localized to areas of negative precipitation evaporation runoff is restricted to regions of intense precipitation overall the 1120 ppm co 2 simulation provides a reasonable paleoclimate for the kimmeridgian tithonian and provides a standard until a ccm with oceanic heat transport a coupled atmospheric oceanic model or one with a finer grid cell configuration is available the results need further scrutiny in areas with more detailed geologic information

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

repeated subaerial exposure of subtidal carbonate platforms triassic northern italy evidence for high frequency sea level oscillations on a 104 year scale triassic carbonate platforms in northern italy ladinian latemar carnian durrenstein norian dolomia principale consist of hundreds of stacked meter scale cycles each made of a subtidal unit with a cap rock that carries vadose cements pisoids and tepee structures these diagenetic caps are interpreted to be due to subaerial exposure of the subtidal sediments the absence of peritidal deposits rules out progradation as the cause of the exposure i e these are not ginsburg autocycles thus the repeated exposure must be the result of relative sea level oscillations which based on the number of cycles and time intervals involved occurred with an average frequency in the 104 year range we postulate a combination of small scale high frequency eustasy and local tectonic movements e g differential subsidence in the norian and infrequent pulses of uplift in the ladinian to explain the cyclicity and its internal variations