cyclicities in triassic platform carbonates synchronizing radio isotopic and orbital clocks sedimentary cycles recorded in young sediments are often attributed to fluctuations of the earth s climate on a 10 4 10 6 year scale which in turn is governed by periodic variations in solar insolation linked to orbital milankovitch parameters a spectacular example of cyclic stratal patterns in ancient deposits is the middle triassic latemar carbonate platform w dolomites n italy based on spectral analyses from previous studies a superimposition of precession 20 ka and eccentricity 100 ka controlled sea level fluctuations has been suggested to account for the stacking hierarchy at latemar with 20 ka being assigned to each highest order depositional cycle zircon u pb isotopic ages from volcanic ash layers within the cyclic succession corroborated by biostratigraphic constraints suggest that the average time interval for every individual cycle is significantly smaller than the shortest milankovitch period and therefore challenge previously published interpretations relating distinct spectral peaks to the above mentioned hierarchy however our new spectral data indicate that cyclicities resembling milankovitch characteristics might exist but on an entirely different scale our findings show that frequency spectra should only be interpreted in combination with robust age control they also encourage the search for complementary mechanisms controlling carbonate deposition

climatically versus eustatically controlled sediment supply driven cycles carbonate siliciclastic high frequency sequences in the valanginian of the neuquen basin argentina carbonate siliciclastic high frequency sequences are formed by reciprocal sedimentation in siliciclastic dominated successions the carbonate rich interval is typically associated with transgressive conditions and relatively low terrigenous influx particularly in distal parts of the marine basin however key questions for each individual case are what sort of depositional system developed during transgressions and what controls sediment supply fluctuations this paper integrates outcrop and subsurface data to present a high resolution sequence stratigraphic study of small scale 2 18 m carbonate siliciclastic cycles deposited during the valanginian in a proximal distal transect of the neuquen basin western argentina and discusses those key issues carbonate hemicycles in this study are composed of cross bedded oolitic skeletal grainstones and packstones to massive skeletal floatstones which accumulated in carbonate ramps with high biogenic production in their distal sector bivalves serpulids echinoids and significant contribution of non biogenic ooids material in inner ramp settings siliciclastic material is present only at the base of the hemicycles but rapidly diminishes upwards these carbonate hemicycles have retrogradational staking patterns in proximal sectors and less obvious trends in distal areas the siliciclastic hemicycles comprise shallowing upward successions that include mudstones bioturbated muddy sandstones sandstones with hcs and scs and bioturbated sandstones these facies were collectively deposited in a storm and wave influenced offshore shoreface depositional system during normal regressions these shoreface systems were likely fed by littoral drift from riverine inputs located tens of kilometers to the south the duration of the investigated small scale transgressive regressive cycles can be estimated in 50 to 150 kyr and they are bounded by marine transgressive surfaces placed at the bases of carbonate hemicycles the bounding discontinuities together with the sequence architecture do not suggest periods of sea level falls between cycles nor high amplitude relative sea level changes during a cycle formation additionally the low proportion of mixed sediments suggests rapid changes in the rate between terrigenous supply and carbonate productivity the resulting sequence architecture cannot be reasonably explained by autocyclic controls or eustatic changes alone it is argued here that high frequency changes in sediment supply driven by orbitally induced climate fluctuations could be a better explanation for these sequences particularly in the context of a long term relative sea level rise in this scenario periods of low siliciclastic influx during extreme arid conditions would develop a negative balance with accommodation and prompt carbonate systems and transgression on the other hand during more humid conditions relatively high sediment flux would temporarily overcome long term accommodation producing the regressive siliciclastic hemicycles as this scenario does not require high frequency sea level falls it would satisfactorily explain the observed sequence architecture the distal mulichinco carbonate hemicycles would be hard to distinguish from transgressive fossiliferous rich deposits that characterize transgressive regressive cycles in clastic systems in the mulichinco case however these carbonate hemicycles are recording the onset of carbonate ramps not the trapping of siliciclastic sediments in transgressive coasts e g filling estuaries this alternative scenario ultimately controlled by reciprocal sedimentation could be common in epicontinental basins developed under arid to semiarid conditions and its identification could provide additional templates for basin scale correlations and hydrocarbon exploration within carbonate siliciclastic small scale cycles

evidence of orbital forcing in lake level fluctuations in the middle eocene oil shale bearing lacustrine successions in the mudurnu goynuk basin nw anatolia turkey abstract mudurnu goynuk basin of the sakarya zone in nw anatolia comprises ca 1500 m thick paleocene eocene terrestrial to shallow marine succession overlying the late cretaceous deeper marine progradational fore arc sediments formed in a foreland setting in relation to southerly situated izmir ankara suture zone this terrestrial succession regionally known as kizilcay group comprises a thin

a 2 3 million year lacustrine record of orbital forcing from the devonian of northern scotland detailed sedimentological examination of onshore sections through cyclic lacustrine deposits of the middle devonian succession of northern scotland has been augmented with offshore data to allow the construction of a continuous 2 3 myr record of orbital forcing these data provide an important record of climatic variance through the devonian which by comparison with other records from this time can significantly improve our understanding of the devonian global climatic system precessional and eccentricity cycles are shown to be dominant by the direct measurement and extrapolation of depositional rates in well exposed sections as well as the analysis of ratios between primary and modulating cycles spectral analysis has confirmed the presence of regular cycles throughout the offshore data which provide a far longer record of orbitally forced cyclicity than previously available the presence of a half precession cycle is also suggested similar up section variations in cycle thicknesses are recorded from both the onshore and offshore succession these variations and those in cycle symmetry are related to a trend from an underfilled to a balanced fill basin state of further importance in controlling cycle thickness is the period of each cycle during which lacustrine conditions and therefore lake level controlled accommodation existed

orbital cyclicities above and below the cretaceous paleogene boundary at zumaya n spain agost and relleu se spain abstract the rhythmicity of hemipelagic limestone marl successions covering the cretaceous paleogene k pg boundary is investigated and evidence of orbital control is presented three sections were surveyed and sampled in detail two are located near agost and relleu in the province of alicante and one near zumaya in the basque country the distance between agost and relleu is about 30 km between agost and zumaya about 600 km the carbonate content of 2779 samples was determined and used as a proxy to determine cyclicities lithologically all three successions are very similar although in the maastrichtian of the zumaya succession 63 7 m 339 light green siliciclastic turbidite layers varying in thickness between 0 1 and 12 cm intercalate with the calcisiltites conventional paleomagnetic and micropaleontologic datum planes are few and show the usual associated uncertainties power spectra based on the few reliable datum planes available are unstable more datum planes were created in an unconventional way i e by visual correlation of the local maxima and minima of the carbonate curves to those of the relevant part of the theoretical eccentricity curve the validity of the method is based on the assumption that the eccentricity periods are considered practically stable throughout geologic time the results support the hypothesis that the carbonate rhythmicity at agost relleu and zumaya are orbitally controlled most likely orbital forcing and random processes play a role in the frequency of occurrence and the thickness of turbidites in the maastrichtian of zumaya the age of the k pg boundary is estimated at 64 56 0 4 ma

rate and synchronicity of environmental changes on a shallow carbonate platform late oxfordian swiss jura mountains recent global change occurs within decades and leaves a significant imprint on shallow carbonate platforms to what extent can rate and synchronicity of environmental changes in the past be evaluated in order to allow comparisons with the processes and products of today sections of a carbonate dominated platform of late oxfordian age have been logged in detail in the swiss jura mountains the time frame based on ammonite biostratigraphy and the hierarchical stacking of the sedimentary sequences suggests that these formed by low amplitude high frequency sea level changes in tune with the orbital cycles the smallest unit the elementary sequence can thus be attributed to the 20 kyr precession cycle by identifying sequence stratigraphic elements such as maximum flooding surfaces within an elementary sequence an even higher time resolution can be obtained and reconstructions of changes in water depth and sea level are attempted sedimentation rates were highly irregular and discontinuity surfaces are common correlation of such surfaces from one section to the other is tentative because they could also have formed locally and are not necessarily synchronous on the scale of elementary sequences the vertical facies evolution permits interpretation of changes in water depth which were produced by eustatic sea level changes allocyclic and or by autocyclic processes the distribution of clay minerals indicates changes of sea level as well as of rainfall in the hinterland biotic changes were controlled by water depth and water quality and also by nutrient and clay input carbon and oxygen isotopes do not show significant shifts within the elementary sequences the original ecological mineralogical and geochemical signals have partly been homogenized because of time averaging through bioturbation and through reworking by storms and because of diagenetic modifications consequently there is potential to interpret environmental changes on the studied carbonate platform but the time resolution is not better than a few thousand years the rates and the synchronicity of the processes leading to the observed environmental changes can thus be estimated only within this time frame

depositional sequences in deep shelf environments a response to sea level changes and shallow platform carbonate productivity oxfordian germany and spain abstract oxfordian deep shelf deposits of southern germany and southern spain are characterized by marl limestone alternations that are stacked into small scale medium scale and large scale depositional sequences the german sections contain autochthonous sponge reefs and associated fragments of microbialites whereas the sections studied in spain display tempestites composed of autochthonous deeper water and allochthonous shallow water particles the facies of the german limestones and marl layers has been analyzed in detail condensed intervals implied by glauconitization of particles abundant cephalopods intense bioturbation and generally more marls are also enriched in sponge reefs and associated particles and in nannofossils limestone rich intervals however contain fewer sponges and fewer nannofossils neither bioerosion of sponge reefs nor nannofossil blooms can thus explain the abundance of carbonate mud that forms the limestones consequently it is suggested that most of the carbonate mud is exported from shallow platform areas where carbonate productivity is high the clay fraction was derived from weathering of massifs in the hinterland the observed depositional sequences can be correlated between the studied sections in germany and spain situated in different paleotectonic and paleoclimatic domains and also between deeper water sections and platform sections this suggests that they formed through allocyclical processes comparision with published time scales implies that the small scale and medium scale sequences formed in tune with the 100 kyr and 400 kyr orbital eccentricity cycles respectively however the number of marl limestone alternations is not always consistent with the expected number of 20 kyr precessional cycles 5 per 100 kyr cycle the large scale sequences reflect long term third order sea level changes the observed marl limestone alternations are interpreted to have formed through cyclically varying export of carbonate mud from the platform towards the deep shelf the variations being controlled by climatically induced high frequency sea level fluctuations enhanced marl deposition on the deep shelf can be related to sea level fall causing exposure of the shallow platform and reducing the area of carbonate production or by rapid sea level rise maximum flooding leading to partial or total drowning of the platform and or to retrogradation of facies belts enhanced carbonate deposition occurs during transgression when large production areas are created on the platform or during late highstands when progradation is forced and carbonate mud export enhanced depending on the long term trend of sea level change on which the high frequency fluctuations are superimposed one high frequency 20 kyr sea level cycle can thus create one or two marl limestone alternations or only marly deposits consequently one 100 kyr eccentricity cycle may be formed of a variable number of marl limestone alternations commonly 2 to 8 the studied deeper water depositional sequences thus are strongly linked to the history of the adjacent shallow carbonate platforms

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

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

morphology and origin of an erosion surface cut into the bad heart formation during major sea level change santonian of west central alberta canada abstract marine sandstones of the early santonian bad heart formation are up to 50 m thick and are underlain and overlain by marine mudstones of the muskiki and puskwaskau formations respectively our examination of 395 well logs in this stratigraphic interval allowed the recognition of many distinctive well log markers correlations of these markers at and below the base of the bad heart indicates a basinward depositional thinning of about 10 cm km the bad heart itself thins from 50 to 2 m northeastward over a distance of 100 km although part of this thinning is probably depositional the truncation of gamma ray and resistivity log markers within the bad heart indicates that there is at least 38 m of erosional topography a paleotopographic map and three dimensional mesh diagram show 1 a relatively smooth high level terrace ending seaward at 2 a main erosive bevel trending nw se across the area the bevel grades seawards into 3 a topography of bumps and hollows which fades into 4 a relatively smooth basin plain most of the erosion was probably due to erosional shoreface retreat through wave scour processes during a major relative lowering of sea level the upper parts of the erosion surface were probably subaerially exposed during maximum lowstand of sea level in outcrop the erosion surface is marked by a thin pebble lag which is in turn overlain by marine mudstones the contact between the conglomerate and underlying sandstone is sharp and locally irregular but gives no hint of the presence of deep regional erosion which can only be demonstrated by using the subsurface data

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

the analysis and interpretation of stratification cycles beds in carbonate successions often form regular patterns either there is a cyclic repetition of beds with different thicknesses or bundles of beds occur separated from each other by some distinct layer any such group will be called a stratification cycle cycles of this type are from 0 5 m to several meters in thickness and they seem to be present throughout the geological column the analysis of sedimentary cycles involves three stages 1 regional mapping is necessary to understand the facies of the sediment establishing the lateral persistence of bedding eliminates the possibility that bedding is caused by diagenetic processes 2 petrographic examination and in particular analyses of primary structures are used to reconstruct the sedimentation conditions during cycle formation such conditions are extremely important for judging the time content of individual beds 3 the quantitative analysis of vertical sections using power spectral methods can find superimposed cycles and enables one to judge their degree of regularity the latter approach is illustrated using lower carboniferous limestone sections from nw ireland as an example spectral analysis finds a stratification cycle of 1 to 3 m in thickness each cycle consists of between five to seven limestone beds upper jurassic limestone marl successions from southern germany and late cretaceous and early tertiary successions from italy show a very similar cyclic pattern the scale of the cycles and their regularity suggest that they are ultimately caused by variations in the earth s orbit possibly by climatic cycles as was postulated by milankovitch however the exact mechanism which links sedimentation with orbital variations is not known

sequence stratigraphy of the red river formation williston basin usa stratigraphic signature of the ordovician katian greenhouse to icehouse transition abstract the upper katian upper ordovician red river formation is a carbonate evaporite supersequence that formed in the epicratonic williston basin of western north america this study focuses on the upper part of the formation in the southern us part of the basin the studied succession is made up of three transgressive regressive sequences rr1 rr2 and rr3 each 0 5 1 m y in duration and composed of relatively few meter scale high frequency cycles parasequences sequence boundaries are characterized by intraclastic breccia laminated dolomite successions that have been truncated and capped by evaporite deposits subaqueous anhydrites within each sequence represent evaporite lowstand systems tracts lsts that formed during relative sea level lows that lead to the precipitation of gypsum later recrystallized into anhydrite in a quiet salina type environment transgressive tst and early highstand systems tracts hst are composed of subtidal facies of predominantly skeletal mudstone to wackestone packstone with abundant burrow mottling late hsts are predominantly composed of peritidal porous laminated dolomite the study illustrates how the sequence stratigraphic framework of carbonate evaporite deposits from the williston basin relates to the late ordovician glacio eustasy transitional climates and low basin subsidence in an arid setting

sequence development influenced by intermittent cooling events in the cretaceous aptian greenhouse adriatic platform croatia depositional sequences capped by peritidal carbonates and breccias on the aptian adriatic carbonate platform croatia were studied to evaluate evidence for glacioeustasy within an age framework constrained by carbon isotope chemostratigraphy sequence ad1 17 60 m 56 197 ft thick uppermost barremian lower aptian is dominated by shallow subtidal parasequences sequence ad2 7 13 m 23 43 ft thick lower aptian lowermost upper aptian contains oceanic anoxic event oae 1a associated with lagoonal laminated carbonates sequence ad3 3 8 m 10 26 ft thick probably is lower upper aptian and likely is separated by a major hiatus from sequence ad4 8 20 m 26 66 ft thick uppermost aptian which spans oae1b both ad2 and ad3 are dominated by peritidal parasequences updip in the lower transgressive systems tract and upper highstand systems tract and by subtidal parasequences elsewhere whereas sequence ad4 is dominated by shallow subtidal parasequences low accommodation rates 4 0 6 0 cm 1 6 2 4 in in the earliest aptian decreasing to approximately 1 0 cm k y 0 3 in k y later promoted widespread breccia development during relative sea level falls aided by tectonic warping the sequence capping breccias eccentricity dominated cyclicity restriction of peritidal facies to late highstands and coeval off shelf oxygen isotope records all suggest that sea level falls occurred during times of cooling and had a significant glacioeustatic component these intermittent cooler periods and continental ice buildup punctuated the aptian greenhouse climate

orbital cyclicity in the eocene of angola visual and image time series analysis compared abstract photographic coverage of hemipelagic eocene marls of angola africa supplemented by limited sampling shows rhythmic stratification patterns of two types a hierarchically cyclic variation in calcium carbonate clay ratios forming couplets grouped into bundles at ratios of ca 5 1 these are coupled with b a redox cycle of bottom waters expressed in darkness of sediment organic carbon and variations of the ichnofauna these patterns resemble those previously observed in the pelagic albian scisti a fucoidi of italy visual study and time series analysis based on image processing provide ratios compatible with those of milankovitch theory whereas the chronostratigraphic control in angola does not afford a basis for an independent chronology the similarity to the italian albian supports attribution of these rhythmicities to orbital forcing

fault propagation ductile strain and displacement distance relationships abstract displacement distance analysis of fault related fold structures can reveal important information about the distribution of fault displacement and in some cases the history of fault propagation this method is commonly used to 1 determine the ratio of displacement rate to propagation rate s p ratio 2 predict the location of unconstrained fault tips 3 determine the location of fault nucleation points and 4 evaluate structural interpretations although the displacement distance approach represents a potentially useful method for gaining information about displacement parallel fault propagation histories of natural fault related fold structures the theoretical relationship between s p and relative stretch er that forms the basis of this method remains essentially untested because displacement rates and propagation rates are generally unknown for natural structures these relationships can only be objectively tested by analysing model structures with known geometries strain distributions and fault propagation histories displacement distance analysis of different fault related fold models reveals that 1 displacement distance relationships are highly dependent on the nature of the hanging wall strain 2 relative stretch is not related to s p in any general way 3 fault tip locations cannot always be predicted by linear extrapolation of displacement distance trajectories 4 displacement maxima are not necessarily indicative of fault nucleation points in all cases and 5 although calculation of s p ratios from observed relative stretch magnitudes may not be appropriate the use of displacement distance relationships can nonetheless be useful in comparing structures and improving structural interpretations

lunar nodal tide and distance to the moon during the precambrian the pace of tidal evolution for the past 450 myr implies an earth moon collision some 1 500 2 000 myr bp see ref 1 an event for which there is no corroborating evidence here we present the first direct determination of the lunar distance in the precambrian we interpret a 23 3 0 3 yr periodicity preserved in a 2 500 myr bp australian banded iron formation bif 2 as reflecting the climatic influence of the lunar nodal tide which has been detected with its modern 18 6 yr periodicity in some modern climate records3 10 the lunar distance at 2 500 myr bp would then have been about 52 earth radii the implied history of precambrian tidal friction is in accord with both the more recent palaeontological evidence and the long term stability of the lunar orbit the length of the milankovitch cycles that modulate the ice ages today11 13 also evolve with the earth moon system their detection in the precambrian sedimentary record would then permit an independent determination of the lunar distance

time scale evaluation and the quantification of obliquity forcing abstract the geologic time scale serves as an essential instrument for reconstructing earth history astrochronology linking regular sedimentary alternations to theoretical quasi periodic astronomical rhythms often provides the highest resolution age models for strata that underlie the time scale although various methods for testing astronomically tuned time scales exist they often present challenges such as the problem of circularity here we introduce an approach to extract a reliable obliquity envelope from astronomically tuned data avoiding the effects of frequency modulations that can artificially introduce astronomical beats this approach includes 1 the application of a broad obliquity filter followed by 2 a hilbert transform and 3 a low pass filter of the amplitude envelope to 4 test the significance of correlation between amplitude envelope and astronomical solution these data amplitudes provide a robust means to evaluate the climate response to obliquity forcing and more specifically to test the significance of correlation with the theoretical astronomical solution in a manner similar to the phase randomized surrogate approach previously introduced for the evaluation of precession tuning synthetic astronomical ice sheet models and several quaternary climate proxy records where obliquity can be a dominant component of astronomically driven climate variability are used to demonstrate the feasibility of the proposed method and yield new insight into climate system evolution

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

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

the impact of milankovitch scale climatic forcing on sediment supply abstract stratigraphy is the main technique to predict the occurrence of potential reservoirs and seals in the oil industry stratigraphic tools used are stratigraphic observations from drilled wells rock samples and wireline logs and seismic interpretation nowadays computer modelling allows scenario forecasting of the sequence to be expected application of these tools indicates that the key input parameters are initial basin topography subsidence eustasy and sediment supply the first three parameters are usually well constrained or can readily be deduced from well and seismic data however the fourth sediment supply is loosely defined and because of that it is used to calibrate the model in the present article the controls on sediment supply are reviewed and the impact of in particular milankovitch scale climatic forcing on sediment supply is tested on the neogene of the niger drainage and delta system sediment supply is controlled by a complex interplay of geographic and climatic factors such as 1 relief or mountain height 2 the size and temporal storage capacity of the drainage area 3 overall climate 4 amount and seasonality of precipitation and 5 vegetation cover studies in geomorphology have indicated that although complex computer models can be made to predict erosional product for the present a large scale sediment supply prediction should be based on the combination of palaeogeographical palaeoclimatological and erosion potential maps more detailed sediment supply predictions should include milankovitch scale variations the climatic impact of these variations is mainly felt when we are in a transition between two climates then the area will experience regular climatic changes from e g wet rainforest to dry monsoonal climate or low to high sediment supply respectively this concept was tested in the forward modelling package stratagem on the neogene of the niger delta four scenarios were evaluated using various combinations of large and milankovitch scale sediment supply curves combined with global or milankovitch scale eustatic sea level curves the results confirm the impact of both large scale and milankovitch scale climatic forcing on sediment supply however in an icehouse world the various scenarios also suggest that the effect of eustatic sea level fluctuations overshadows the impact of milankovitch scale sediment supply by contrast in a greenhouse world the impact of milankovitch scale sediment supply is expected to be more significant in the absence of significant sea level fluctuations

interpreting structural geometry in fold thrust belts why style matters abstract structural interpretation in fold thrust belts has become reliant on a few idealized geometric models i e fault bend fault propagation and detachment folding and their quantitative methods for section construction and validation we couple historical review with selected outcrops to show that there is a substantially greater range of solutions available for interpreting the geometry and evolution of thrust belt structures than implied by these idealized models examples are documented and lessons drawn from comparing structural interpretations developed in the foothills of the canadian rockies with those in the western alps both show a range of structural geometries with regional variations that reflect variations in the pre kinematic stratigraphic template locally fold thrust development can localize on pre existing structures thus consideration of the precursor geology is essential for structural interpretation using a case study from the papuan fold belt we show that even with seismic data assessing the role of basement in structural development can be uncertain the idealized models offer only a narrow range of possible geometries for constructing cross sections and developing structural understanding in fold thrust systems failure to consider alternatives and the inherent interpretation uncertainty has biased understanding of thrust systems leading in turn to over optimistic risk assessment and repeated drilling surprises

a dominant tectonic signal in high frequency peritidal carbonate cycles a regional analysis of liassic platforms from western tethys abstract meter scale peritidal carbonate cycles are a common feature of the geological record but debate continues about what processes lead to their formation three conceptual models or a combination thereof are commonly invoked to explain cycle formation eustasy tectonics or autocyclicity these three models are tested with a large new dataset from different early jurassic plate margins from western tethys study of seven logged sections from spain italy greece tunisia morocco and gibraltar enables an analysis of the possible roles of local versus regional patterns and controls on cyclicity within a sinemurian time slice cycle types are diverse and include shallowing upward cycles parasequences but also deepening upward and diagenetic cycles high frequency sequences and subtidal cycles numbers of cycles per section and cycle stacking patterns within this time slice vary from section to section statistical tests runs tests time series and bundling all indicate random stacking of cycles within sections and an absence of any bundling of thicknesses or of facies trends assessment of cycle types by their occurrence and stacking patterns indicates little support for either eustasy or autocyclicity being the dominant cycle forming mechanism however the variability in numbers of cycles per section thickness variations of the sections cycle type variability and randomness of stacking patterns all favor a pulsed tectonic control for the creation and filling of accommodation space this conclusion is further supported by evidence that has largely arisen during the course of this study of syndepositional extensional tectonics in the sinemurian on these rifted tethyan margins although tectonics appears to be the dominant control superimposed eustasy and or autocyclic processes cannot be discounted

chemical cyclicity and correlation of lower lias mudstones using gamma ray logs yorkshire uk natural gamma ray spectrometry on coastal sections from redcar and robin hood9s bay permits the radioactive characterization of five different mudstone units and the construction of an outcrop gamma ray log for the lower lias correlation of these five units with their equivalents in the gamma ray log of the felixkirk borehole located 40 km to the west has been established statistical comparison of tie points in the composite coastal section shows there to be a stratigraphic gap of 10 m between the two localities relative to the continuous section in the felixkirk borehole the distribution of th ppm k and u ppm are generally highly correlated with the total radioactivity however anomalies do occur a peak in the th k ratio can be related to an iron oolitic horizon marking a condensed sequence in the early mid sinemurian a sharp fall in the th k ratio followed by high u values coincides with the early pliensbachian transgression comparison with mineralogical clays and chemical si al and al k ratio v total organic carbon profiles of the same section allows for an evaluation of the significance of radioactive element distribution in terms of grainsize run off and oxygenation indicators a spline curve fitted through the total radioactivity data emphasizes low frequency cyclicity wavelengths of between 10 and 30 m in the outcrop section these cycles appear to be correlatable with cycles of comparable wavelengths in the low pass filtered gamma ray log of the felixkirk borehole sedimentological evidence confirmed high radioactivity peaks correspond to transgressive phases the gamma ray signal of the felixkirk borehole has also been analysed for high frequency cyclicity with an overall rate of accumulation of about 13m ma variation in the milankovitch band is marked by units 5 m or less in thickness evidence for eccentricity obliquity and precession cycles has been found both in borehole and in outcrop a typical shift from lower to higher frequencies occurs consistently in transgressive phases and is related to increased sedimentation rates

evidence of precessional and eccentricity orbital cycles in a tithonian source rock the mid outer carbonate ramp of the vaca muerta formation northern neuquen basin argentina basin to mid ramp cyclic facies of the tithonian vaca muerta formation are exposed in the loncoche creek section of the neuquen basin mendoza province argentina this unit is characterized by a decimeter scale rhythmic alternation of marls shales and limestones and extends from the lower tithonian to the upper berriasian cyclostratigraphic studies based on a detailed facies analysis allowed the identification of cyclic patterns with frequencies within the milankovitch band according to biostratigraphic data the dominant cycle in the studied section has a period of 20 k y which correlates with the earth s axis precession element spectral analysis based on a series of compacted and decompacted cycle thickness identified a subordinate frequency of about 90 to 120 k y which we interpret as the modulation of the precessional cycle caused by the earth s orbital eccentricity the strength of the precession signal together with the absence of a well defined cyclicity attributable to the obliquity orbital cycle i e 40 k y is in agreement with previous data from the northern hemisphere

depositional sequences in shallow carbonate dominated sedimentary systems concepts for a high resolution analysis abstract oxfordian and berriasian sections representing shallow water carbonate dominated sedimentary systems have been studied in the swiss and french jura in spain and in normandy they all display a hierarchical stacking of depositional sequences facies evolution and stacking pattern allow to define elementary small scale medium scale and large scale sequences some depositional sequences display well marked sequence boundaries others are limited by transgressive or maximum flooding surfaces the hierarchical organisation of such sequence stratigraphic elements implies that sea level fluctuations were an important factor in their formation and that these fluctuations had different frequencies the superposition of high frequency sea level changes on a long term sea level trend leads to repetition of diagnostic surfaces defining sequence boundary and maximum flooding zones wherein the corresponding high frequency surfaces are well developed chronostratigraphic tie points permit us to estimate the duration of large scale sequences this time control and the observed hierarchical stacking suggest that the high frequency sea level changes were controlled by climatic cycles in the milankovitch frequency band the variability of stacking pattern and facies evolution between sections illustrates the complexity of the studied environments furthermore because of the minimal accommodation space available in these shallow water settings much of the geologic time is not recorded nevertheless detailed analysis of the depositional sequences allows the interpretation of the evolution of the sedimentary system with a high time resolution thus there is a potential to monitor sedimentological ecological and diagenetic processes on a time scale of 20 to 100 ka

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

cretaceous rhythmic bedding sequences a plausible link between orbital variations and climate abstract simple oscillation cycles have been recognized in cretaceous pelagic sequences as a marked periodicity in carbonate and or organic carbon content the estimated periodicities of these cycles resemble milankovitch type variations in orbital elements however during warm geologic periods the nature of the link between orbital variations and the sedimentary record has been problematic climate model studies show that the intensity of continental margin precipitation in specific low latitude regions is a function of land sea thermal contrast which is sensitive to orbital variations cretaceous climate model simulations are characterized by regions of intense precipitation the locations of which are controlled by geographic configuration in particular in the model simulation the northern margin of the tethys ocean has all the climatic characteristics necessary to exhibit a sensitivity to orbital variations detailed studies of the biota sedimentology and geochemistry of the bedding rhythms in greenhorn cyclothem in the western interior seaway of north america are best interpreted in terms of variations in precipitation runoff and stable stratification of the seaway combined the geologic and model studies support a link between orbital periodicities variations of intense precipitation associated with specific paleogeographic situations and cretaceous bedding patterns this hypothesis has important implications for the sensitivity of the atmosphere hydrosphere lithosphere system to external forcing

regular terrestrially derived palynofacies cycles in irregular marine sedimentary cycles lower lias dorset uk the lower lias of dorset england comprises prominent limestone marl shale alternations considered to be obliquity orbitally controlled probably enhanced by diagenesis palynofacies analysis the study of microscopic particulate organic matter in a sediment identifies six superimposed palaeo environmental variations through 12 m of this sequence 1 90 cm cycles in abundance of terrestrially derived organic particles 2 45 cm cycles in abrasion of wood particles 3 1 2 1 8 m cycles in shape of wood particles 4 irregular cycles 20 cm to 5 2 m in limestone deposition 5 irregular alternations 50 cm to 2 5 m in shale marl deposition and 6 irregular variation in marine phytoplankton abundance these are interpreted as a obliquity forcing of marine currents bottom water oxygenation and organic preservation b precessional forcing of rainfall position of storm wave base and limestone deposition c eccentricity driven shallow marine energy changes preventing limestone deposition d irregular marine processes affecting shale marl deposition and marine plankton productivity thus three orbital cycles acted simultaneously with different effects on different environments palynofacies analysis is a sensitive tool for extracting palaeoenvironmental information particularly terrestrial variations recorded in marine sedimentary rocks in addition it is demonstrated that regular proxy climatic orbital cycles are preserved within irregular sedimentary sequences

pleistocene climatic variability at astronomical frequencies abstract spectral analysis of geological records show periodicities corresponding to those calculated for the eccentricity 400 and 100 ka the obliquity 41 ka and the climatic precession 23 and 19 ka it is precisely the geological observations of this bi partition of the precessional peak confirmed to be real in astronomical computations which was one of the most impressive of all tests for the milankovitch theory concerning the question of whether or not the observed cycles account for most of the climatic variability having periods in the range predicted by the astronomical theory substantial evidence from cross spectral analysis coherency analysis and modelling is provided that at least near frequencies of variation in obliquity and precession a considerable fraction of the climate variance is driven in some way by insolation changes accompanying changes in the earth s orbit the variance components centered near a 100 ka cycle dominate most ice volume records and seem in phase with the eccentricity cycle although the exceptional strength of this cycle needs a non linear amplification by the glacial ice sheets themselves and associated feedbacks as the insolation spectra change with latitudes and with the type of parameters considered the diversity of the spectra of different climatic proxy data recorded in different places of the world over different periods is used to better understand how the climate system responds to the insolation forcing this study of the physical mechanisms involved is also achieved through the analysis of the log log shape of the geological records and through the comparison in frequency domain between simulated climatic time series and proxy data the evidence both in the frequency and in the time domain that orbital influences are felt by the climate system implies that the astronomical theory may provide a clock with which to date quaternary sediments with a precision several times greater than is now possible

sequence stratigraphy of the upper yeadonian of northern england abstract a detailed study of an upper namurian cyclothem is presented the upper yeadonian basin fill of the pennine basin consists of three deltaic sandstones interbedded with mudstones of a variety of facies the cyclothem is a fourth order cycle representing deposition over a period of a few hundred thousand years the results of the study in terms of sediment accumulation patterns are investigated using the exxon sequence stratigraphic model in addition a simple computer model is presented to illustrate idealized pennine sedimentary fill in a one dimensional succession multiple condensed sequences at the base of cyclothems form part of a transgressive systems tract the succeeding fluvio deltaic facies are interpreted as part of a highstand systems tract the latest yeadonian rough rock sandstone is interpreted as a possible lowstand wedge a high resolution relative sea level curve is also presented for the late yeadonian

cyclostratigraphy of an orbitally driven tithonian valanginian carbonate ramp succession southern mendoza argentina implications for the jurassic cretaceous boundary in the neuquen basin we conducted detailed sedimentological sequence stratigraphic and cyclostratigraphic analyses on four sections of the vaca muerta formation this unit is characterized by a decimetre scale rhythmic alternation of marls and limestones it consists of five facies associations which represent basin to middle carbonate ramp deposits the rhythmic vertical organization shows a well ordered hierarchy of cycles where elementary cycles bundles of cycles and superbundles within the milankovitch frequency band are recognized cyclostratigraphic data allowed us to build a floating orbital scale for the lower tithonian lower valanginian interval in the neuquen basin orbital calibration of these sections is consistent with riccardi s biostratigraphic scheme which places the jurassic cretaceous boundary within the substeueroceras koeneni ammonite zone equivalent to durangites spp jacobi grandis and initial occitanica standard zones

three orders of regional sea level changes control facies and stacking patterns of shallow platform carbonates in the maestrat basin tithonian berriasian ne spain middle tithonian berriasian shallow platform carbonates of the maestrat basin salzedella and montanejos sections ne spain are stacked in sequence stratigraphic units of different orders higher order sequences parasequences and subunits have a shallowing or deepening shallowing evolution they have been related to the short term eccentricity and precession cycles major facies changes and stacking pattern of parasequences reveal the presence of two 2nd order sequences the lower sequence is middle tithonian mid early berriasian in age the upper sequence extends up to the mid late berriasian it is suggested that local subsidence changes along with regional sea level changes controlled the long term evolution of accommodation in the maestrat basin facies evolution stacking pattern and sharp lithological changes have allowed the definition of five 3rd order sequences in the lower sequence in montanejos the transgressive deposits are characterised by the progressive absence of the restricted lagoon facies and the presence of deepening upward intervals in the parasequences the highstand deposits display an increase in siliciclastics and a progressive predominance of restricted lagoon facies some of the 3rd order sequence boundaries match the sequence boundaries identified in other european basins and may be related to sea level falls induced by the long term eccentricity cycle enhanced during periods of long term loss of accommodation

use of organic carbon content as a chronostratigraphic tool abstract in the mulhouse potash basin france the lithology and the organic carbon content reveal an extended succession of recurrent sequences variation in lithology shales anhydrite halite reflects variations in depositional environment organic matter exclusively present in the shaly horizons shows variations in content and origin these changes highlight small variations of their depositional environment which are not detected in the lithology of the shales on the other hand when these variations increase and are large enough they are recorded by the lithology in homogeneous facies i e shaly facies analysis of the distribution of the organic content in sediments thus appears to be an interesting method for determining small variations of the depositional environment the organic carbon signal showsvariations of sedimentation rates over time and can be interesting for small scale geochronology quite a similar duration for each cycle lasting an average of 13 000 3400 yr has been calculated this time span based on biostratigraphy is in agreement with results obtained by lamination counts this duration can be criticized due to the lack of precision of the dating methods but is significantly different from the well known periodicities of milankovitch

neural net aided detection of astronomical periodicities in geologic records abstract astronomically controlled variations in the earth s climate induce cyclic trends in the sedimentary process and record milankovitch periodicity one of the main difficulties to be solved in order to choose among the registered periodicities is the conversion from the spatial i e recurrent variations along the stratal sequences to the temporal domains of the astronomically induced frequencies present in the rock record we discuss here how this problem can be circumvented by teaching a neural net how to recognize periodicities in the signal the application to two sequences of shallow water carbonate deposits from the cretaceous of southern italy has shown this approach to be particularly effective confirming the existence of milankovitch type periodicities in the records examined where climate sediments and biota concomitantly react to the variation in the solar constant induced by secular perturbations of the earth s orbital elements

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

from platform to basin to swell orbital control on sedimentary sequences in the oxfordian spain climatic oceanographic and ecological changes that control the formation and deposition of sediment in shallow and deep depositional environments commonly occur with periodicities of a few 10 000 years consequently in order to interpret sedimentary sequences in the geological past high time resolution is required this is best obtained by cyclostratigraphy three sections have been studied in the oxfordian of north eastern spain one represents a shallow siliciclastic carbonate platform with repetitive subaerial exposures one an intraplatform basin with sponge bioherms and one a swell where iron ooids and glauconite formed the platform section displays a well defined stacking pattern of depositional sequences the deeper water sections are well dated by ammonites the correlation between the three sections is a best fit solution integrating biostratigraphy sequence stratigraphy and cyclostratigraphy it is concluded that the small scale depositional sequences formed in tune with the 100 ka orbital eccentricity cycle an additional factor was differential subsidence that ruled basin morphology

hierarchy of high frequency orbital cycles in cretaceous carbonate platform strata abstract lower cretaceous valanginian hauterivian carbonate platform strata which are well exposed in the matese mountains of the southern apennines italy have been analyzed on a microstratigraphic cm scale to exemplify the high frequency cyclic nature of the mesozoic shallow water sedimentation in southern italy based on the vertical organization of lithofacies and their early diagenetic signature 46 metre scale cycles are recognized these elementary cycles are hierarchically organized into groups bundles and superbundles the elementary cycles are prevalently formed by subtidal deposits and show emersion related features at the top suggesting repeated sea level fluctuations the number of elementary cycles compared to time as constrained by biostratigraphy and their grouping into sets implying higher order complexity in the environmental oscillation suggest an orbital control on sedimentation spectral analysis of recurrent thickness in stratal features defines and quantifies the cyclicity which is characterized by lithofacies thickness periodicities of 1271 391 159 124 and 69 cm linear correlation of the relative ratio set rrs of these periodicities with the corresponding rrs of the orbital perturbation periodicities shows that 1271 and 391 cm fit the 404 220 and 94 890 year cycles of early cretaceous orbital eccentricity 159 and 124 cm fit the 49 010 and 38 030 year cycles of the earth s axial obliquity whereas 69 cm corresponds to the precession periodicity thus the san lorenzello section required not less than 1 6 ma to form at an average rate of 26 mm ka each 400 ka cycle can be viewed as a depositional sequence in which sequence boundaries maximum flooding surfaces and system tract equivalents have been recognized the microstratigraphic approach is very promising for understanding the fine structure of climate related environmental fluctuation recorded by the 3000 m thick carbonate platform successions of the southern apennines over a time span of about 150 ma upper triassic upper cretaceous and for deriving a more precise chronostratigraphy for global correlation