temporal buffering of climate driven sediment flux cycles by transient catchment response abstract the marine sedimentary record can exhibit a systematic cyclicity that is consistent with climate variability driven by milankovitch scale forcing milankovitch band cyclicity is widely interpreted in the hemipelagic and pelagic sediments of the marine realm and in terrestrial paleoenvironments has been observed in lacustrine sediments soils and river floodplain successions it remains unclear however if and how mountain catchments as a primary sediment source respond to these high frequency 6 yr climatic cycles and whether particulate sediment flux signals can be expected to be recorded in the clastic sedimentary record of adjacent basin fills recent field and theoretical studies suggest that mountain catchments respond transiently to high frequency forcing and so sediment discharge from the catchment is a non linear function of forcing variables using a catchment basin model we demonstrate that climate driven cyclicity in particulate sediment discharge is strongly damped when the period of climate variability is shorter than the response timescale of the eroding landscape given that the response timescale of landscapes is of the order of 10 6 yr and that milankovitch driven climate cyclicity is of the order of 10 4 10 5 yr it is likely that climate driven perturbation of upland catchments at these periods will be strongly damped by transient landscape behaviour our results therefore suggest that stratigraphy built by particulate fluxes from upland catchments and long term trends in the sediment delivery to the ocean may be relatively insensitive to short term climate variability

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

the latemar a flat topped steep fronted platform dominated by microbialites and synsedimentary cements abstract facies analyses on the latemar isolated carbonate platform suggest a higher proportion of microbial carbonates compared to literature this is evident especially in the margin upper slope zone where microbial boundstone associated with tubiphytes calcareous sponges botryoidal aragonite and radiaxial fibrous cements extended down to 250 m water depth the latemar flat topped high relief platform has been subdivided into five different facies belts inner and outermost platform margin upper and lower slope each facies belt represents subtidal environments except for the inner platform which is characterized by a peritidal facies association point counting analysis was carried out on ca 90 thin sections to quantify the different platform components microbialite and cements are most abundant they represent respectively ca 40 and ca 34 of the whole platform volume these results suggest that carbonate production at latemar occurred in a m factory microbial carbonates as well as early marine cements are most abundant on the upper slope margin and outermost platform although microbialites are found in all facies belts the presence of supratidal sedimentary facies restricted only to the inner platform and of a completely subtidal outermost platform suggests a new depositional profile for the latemar the central portion is occupied by the flat platform interior cyclically subaerially exposed facies of the subtidal outermost platform surround the inner platform and display a progressive increase in depth toward the margin the margin is submerged and essentially constituted by microbial and cement boundstone the slope is characterized by steep clinoforms 35 dominated by in situ microbialites in the upper middle portion 0 250 m depth evidently precipitated by non light dependent microbially influenced processes the lower slope is mostly detrital poor in platform top derived sediments and dominated by margin and upper slope derived rudstone and grainstone all these observations are in agreement with the slope shedding model observed in the pennsylvanian microbial margin in asturias n spain and allow the interpretation of the latemar as a flat topped steep fronted platform dominated by microbialites and cement boundstones

comparative high resolution chemostratigraphy of the bonarelli level from the reference bottaccione section umbria marche apennines and from an equivalent section in nw sicily consistent and contrasting responses to the oae2 abstract the bonarelli level bl from the upper cenomanian portion of the reference bottaccione section central italy is characterized by the presence of black shales containing high toc concentrations up to 17 and amounts of caco 3 near to zero in the absence of carbonate and consequently of relative carbon and oxygen isotopic data the elemental geochemistry revealed to be a very useful tool to obtain information about the palaeoclimatic and palaeoceanographic evolution of the tethys ocean during the oae2 based on several geochemical proxies rb v ni cr si ba the bl is interpreted as a high productivity event driven by increasingly warm and humid climatic conditions promoting an accelerated hydrological cycle the enrichment factors of peculiar trace metals zn cd pb sb mo u provide further insight about the h 2 s activity at the seafloor during the organic rich sediment deposition and permitted us to evaluate the use of ba as palaeoproductivity tracer in conditions of high rate of sulphate reduction by comparing geochemical records from the reference bottaccione section central italy with those previously obtained for the coeval calabianca section northwestern sicily different degrees of oceanic anoxia were delineated and ascribed to different abundance and type degradable or refractory of organic matter which are limiting factors in the bacterial sulphate reduction reactions and in subsequent euxinic conditions at seafloor in the tethys realm based on a ciclostratigraphic approach consistent fluctuations at 100 ky scale in the chemostratigraphic signals from the two sections are inferred to be expression of a strong orbital climatic forcing driving changes in the oceanic environment during the bl deposition

on the use of cycle thickness diagrams as records of long term sealevel change during accumulation of carbonate sequences analysis of variation in changing rates of accommodation space creation as represented by stratigraphic thickness has become an integral part of ongoing investigations into the origin of ancient meter scale upward shoaling cyclic marine carbonates groupings of thicker than average and thinner than average cycles within long stratigraphic sections have been thought to represent the influence of long term eustatic sealevel variation on rates of accommodation space creation under conditions of constant basin subsidence statistical analysis demonstrates that a large percentage of early paleozoic cyclic carbonate sequences contain thickness distributions indistinguishable from those anticipated for random associations of cycles and that only a few have characteristics commensurate with long term changes in rate of accommodation space creation moreover in those cases where some extraneous control is suggested computational considerations readily demonstrate that change in subsidence rate and or diffe

dolomitization of the latemar platform fluid flow and dolomite evolution abstract the anisian ladinian latemar platform northern italy presents a spectacularly exposed outcrop analogue for dolomitized carbonate reservoirs in relation to fracture controlled igneous intrusions although the latemar is one of the best studied carbonate platforms worldwide timing and evolution of dolomitization and the link to fractures and dikes have not been explored in detail previous dolomite observations are based on a stratigraphically limited portion of the platform this study extends observations to the complete exposed interval in which dolomite bodies occur including those within the less accessible valsorda valley numerous parallel mafic dikes crosscut the latemar platform and border several of its large dolomite bodies 50 m wide 100 m high within dikes and along dike carbonate contacts there are abundant dolomite veins that are geochemically related to surrounding dolomite bodies dolomitization is the result of limestone interaction with hydrothermal fluids delivered along these dikes at dike boundaries impermeable marble aureoles exist derived from contact metamorphism the marble aureoles have locally shielded surrounding limestone from dolomitizing fluid dolomite occurs only where the protective marble is missing or crosscut by fractures based on geometric relationships we conclude that dikes and their damage zones formed the pathways for the dolomitizing fluids and functioned as boundaries for dolomite bodies from field observations and petrography we established a detailed paragenesis dolomitization started shortly after dike emplacement there is an evolution in the fe content of matrix dolomite and dolomite veins from highly ferroan dolomite to non ferroan saddle dolomite alternating with episodes of silica cementation non ferroan calcite precipitation followed dolomitization possibly indicating concurrent depletion in mg this stage likely resulted in further limestone recrystallization rather than dolomitization stable and radiogenic isotopes suggest that the dolomitizing fluid comprised carnian seawater with elevated fe and mg from interaction with other lithologies possibly the nearby predazzo intrusion

triassic latemar cycle tops subaerial exposure of platform carbonates under tropical arid climate the triassic latemar platform in the dolomites italy is the site of several ongoing controversies perhaps the most interesting debate focuses on apparent cyclic deposition within the latemar platform whose nature and duration are still open to debate further disagreement concerns the lack of meteoric diagenesis related isotope shifts at cycle tops that bear circumstantial petrographic evidence for subaerial emergence here an evaluation of the nature of latemar cycle tops is presented combining evidence from previous work and new field petrographic and geochemical data cycle tops are ranked according to increasing exposure duration and spatial extent type i surfaces lacking unequivocal evidence of prolonged supratidal conditions type ii dolomite caps formed in warm evaporitic intertidal lagoonal waters followed by exposure of perhaps intermediate duration type iii clastic rich red calcareous horizons with some showing platform wide extent representing prolonged supratidal conditions and type iv discontinuities in tepee belts genetically related to type ii and iii surfaces but likely representing shorter lived exposure stages petrographic and geochemical criteria indicate that most diagenesis occurred in the shallow marine and burial domain whilst an extensive meteoric overprint of cycle tops is lacking this is underlined by the scarcity of meteoric diagenetic fabrics such as gravitational cements that where present are here interpreted as marine vadose in origin the scarcity of carbon and oxygen isotope signatures commonly assigned to subaerial exposure stages is best explained in the context of mid triassic climate the low latitude tropical but arid setting of the latemar situated in the western extension of the tethys ocean its isolation from nearby continental areas and overall short term emergence episodes are in agreement with a limited degree of meteoric alteration of most cycle tops high amounts of aeolian clastic material beneath some cycle tops along with high fe and mn elemental abundances argue for intermittent subaerial conditions this study proposes an enhancement of the classical allan and matthews 1982 isotope model for subaerial exposure under strongly arid climates as the subaerial exposure nature of latemar cycle tops and therefore eustasy as the cause for cyclicity have been previously challenged due to the lack of meteoric induced isotopic signatures the outcome of this study is of significance for the ongoing latemar stratigraphic controversy

preservation of forcing signals in shallow water carbonate sediments abstract no consensus has been reached on whether the metre scale cycles that commonly occur in peritidal carbonates are predominately a product of external relative sea level variations allocycles or an intrinsic property of carbonate production generated via the interaction of non linear processes autocycles for any forcing signal such as eustatic sea level change to be detectable in stratigraphy its effects must be preserved here a deterministic three dimensional geological process model is used to explore how such cycles are preserved in the geological record in the presence of autocyclic processes each simulation produced cycle thickness distributions that are statistically indistinguishable from a theoretical poisson process regardless of whether auto or allo cycles dominated spectral analysis of depositional time series constructed from idealised geological sections showed that all detectable signals occurred within the milankovitch forcing frequency bands even when no milankovitch forcing was present thus it is deduced that from any geological section alone external forcing signals are detectable but are not distinguishable from autocyclically produced signals interestingly there is no correlation between the percentage of sediment preserved and the accuracy with which signals are detectable in the preserved sediment in some model realisations even with preservation as low as 40 the correct forcing signal can be detected accurately while conversely sections with preservation as high as 90 can have poor signal preservation the reverse can also be true in other models it is therefore concluded that distinguishing allocyclic and autocyclic forcing in shallow marine or peritidal carbonate successions is likely to be extremely difficult except in cases of extraordinary sedimentary preservation and dating accuracy

bed thickness distributions on mars an orbital perspective studies on earth show that sedimentary bed thickness and bed thickness distributions record information about the processes controlling sediment deposition high resolution digital terrain models dtms such as those derived from the high resolution imaging science experiment hirise now provide the opportunity to quantify bed thickness properties on mars over several orders of magnitude down to the submeter scale this study uses hirise dtms and visible images to measure bed thickness distributions at 10 deposits on mars with the aim of determining whether statistical techniques can provide useful criteria for distinguishing sedimentary depositional processes basic statistics including mean thickness and range are examined as are histograms cumulative frequency plots and log log plots statistical tests interrogate these deposits for thinning or thickening upward trends and the presence of normal lognormal and exponential distributions although there are challenges associated with these methods the statistical analysis of bed thickness coupled with morphological and mineralogical interpretations has the potential to be a powerful tool for characterizing and classifying sedimentary rocks on mars in particular bed thickness statistics are particularly well suited for examining changes in sediment supply and accommodation within martian sedimentary sequences

cyclostratigraphy and the problem of astrochronologic testing abstract when milankovitch cycles are preserved in the geologic record they provide a direct link between chronometer and climate change and thus a remarkable opportunity to constrain the evolution of the surficial earth system the identification of such cycles has allowed exploration of the geologic record with unprecedented temporal resolution and has spurred the development of a rich theoretical framework for climatic change accompanying these successes however has been a persistent skepticism how does one reliably test for astronomical forcing pacing in stratigraphic and paleoclimate data especially when time is poorly constrained from this perspective it would seem that the merits and promise of astrochronology a phanerozoic time scale measured in 20 000 to 400 000 year increments also serves as its achilles heel if the confirmation of such geologically short temporal rhythms defies rigorous hypothesis testing the implications are substantial since much of our understanding of paleoclimate change throughout the cenozoic and beyond is firmly rooted in astrochronologic interpretation in this study a conceptual framework for assessing earth system response to astronomical insolation changes and the propagation of that signal into the geologic record is used as a guide to understand the nature of the problem of astrochronologic testing this framework emphasizes three challenges contamination stratigraphic distortion and temporal calibration a statistical optimization method timeopt meyers 2015 is formulated as a solution to these three challenges providing an approach for astrochronologic testing that objectively evaluates time scale uncertainty while simultaneously identifying an optimal model for climate and depositional system response to astronomical forcing new extensions to the technique are presented allowing explicit reconstruction of distortions to the primary forcing that are known to be omnipresent in the stratigraphic record to illustrate the utility of this approach it is applied to five well studied stratigraphic series throughout the phanerozoic supporting their astronomical origin and yielding constraints on the evolution of the earth system and the astronomical solutions themselves future directions that build on this foundation are discussed including the utility of process based null models approaches for earth system transfer function reconstruction and mapping out ancient solar system behavior and earth moon history using the geologic archive of milankovitch cycles the timeopt approach recognizes astronomy geochronology paleoclimatology and depositional system reconstruction as a unified geoscientific inverse problem

geostatistical earth modeling of cyclic depositional facies and diagenesis in siliciclastic and carbonate reservoirs depositional facies are often described as being organized in cyclic successions that are overprinted by diagenesis most reservoir modelling workflows are not able to reproduce stochastically such patterns herein a novel geostatistical method is developed to model depositional facies architectures that are rhythmic and cyclic together with superimposed diagenetic facies the method uses truncated pluri gaussian random functions constrained by transiograms cyclicity is defined as an asymmetric ordering between facies and its direction is given by a three dimensional vector called shift this method is illustrated on two case studies outcrop data of the triassic latemar carbonate platform northern italy are used to model shallowing upward facies cycles in the vertical direction a satellite image of the modern bermuda platform interior is used to model facies cycles in the windward to leeward lateral direction as depositional facies architectures are modelled using two gaussian random functions a third gaussian random function is added to model diagenesis thereby depositional and diagenetic facies can exhibit spatial asymmetric relations the method is applied in two regions of the latemar carbonate platform that experience two different types of diagenetic transformation syn depositional dolomite formation and post depositional fracture related diagenesis the method can also incorporate proportion curves to model non stationary facies proportions this is illustrated in cretaceous shallow marine sandstones and mudstones book cliffs utah for which cyclic facies and diagenetic patterns are constrained by embedded transition probabilities

stratal thickness frequencies and the prevalence of orderedness in stratigraphic sequences assuming the existence of discernable hierarchies in the thickness and or temporal recurrence of stratal units within sedimentary sequences has become an increasingly important axiom of sequence and cyclostratigraphic studies and multiple orders of stratigraphic cyclicity are now commonly associated with inferred durations and magnitudes of rhythmic variation in global sea level beyond the desire to establish an informal nomenclature relating stratigraphic thickness to periodicity of eustatic change an assumption of stratigraphic orderedness also supports the inference that groups of sedimentary units with distinct modal dimensions in fact do occur with some generally distinct frequency in stratigraphic sequences in contrast to such perceived patterns of stratigraphic order many groupings of sedimentary units exhibit lognormal frequency distributions wherein most of the population has an exponentially increasing frequency of occurrence with linearly decreasing class size such thickness distributions

sedimentology and sequence stratigraphy of a pronounced early ordovician sea level fall on baltica the bjorkasholmen formation in norway and sweden abstract the bjorkasholmen formation consists of interbedded carbonates shales and glauconitic beds and is characterized by heavy bioturbation and few preserved sedimentary structures the unit shows five facies shale glauconitic packstone and three predominantly mud dominated carbonate facies carbonates and shales are arranged in small scale deepening upward cycles a minimum of fourteen of these small scale cycles are recognized in the bjorkasholmen formation they are arranged in stacks of 3 to 5 forming a total of four medium scale cycles separated by decimeter thick shale units based on the predominance of mud rich facies the succession is interpreted to have been deposited in an overall tranquil setting during one mayor sea level fall and subsequent initial rise of third order time estimates suggest that the 14 small scale cycles fall into the milankovitch band of precessional forcing and the overriding medium scale cycles likely represent short eccentricity the sequence stratigraphic interpretation shows that the bjorkasholmen formation is characterized by falling stage lowstand and initial transgressive systems tracts consequently the contact between the bjorkasholmen and the underlying alum shale formation represents the basal surface of forced regression the maximum regressive surface is defined by a hiatus in the oland sections and by shallow marine packstones within mud rich distal ramp carbonates in norway the top of the bjorkasholmen formation represents a flooding surface at the base of the transgressive systems tract a comparison of time equivalent successions worldwide suggests that the bjorkasholmen formation represents a tectonically enhanced lowstand with two overriding short term milankovitch eustatic signals although deposition of the bjorkasholmen formation coincides with the initiation of a foreland basin in the caledonides of norway it remains unclear how these tectonic movements may have lead to the widespread bjorkasholmen lowstand during the early ordovician it is suggested in this study that a combination of compressional forces from avalonia and the caledonian margin may have acted in concert to produce an uplift of larger parts of the baltica plate for a time span of approximately 0 5 myr

dynamics of abundance of the mid to late pridoli conodonts from the eastern part of the silurian baltic basin multifractals state shifts and oscillations

cyclostratigraphic record of the triassic a critical examination high frequency fourth and fifth order cyclicity is a common feature of sedimentary sequencesinalldepositionalsettings whiletectonismandautocyclicprocessesare clearlyrespon sible for this cyclicity in some instances many cases are interpreted as resulting from orbitally forced variations in solar insolation at the milankovitch frequencies that is the precession and short and long eccentricity cycles at scales of tens of thousands to hundreds of thousands of years this forcing is presumed to have controlled sedimentation through periodic changes in climate or sea level examples of interpreted milankovitch frequency cyclicity occur throughout the triassic record and include much of the german triassic the alpine triassic and the newark supergroup of north america the cyclostratigraphy of these sections has been used as a tool for intrabasinal and interbasinal correlation and for chronostratigraphy these interpretations are not always without controversy however as conceptual arguments and radio isotopic age data have called some of these conclusions into question the stratigraphic record is inherently cyclical but the scale of this cyclicity varies in scale from the outcrop to the continental the largest scale or first order cycles are those that are truly continental in scope as they are thought to record changes in sea level caused by the operation of the wilson cycle at a scale of hundreds of millions of years prothero 1990 jacquin graciansky 1998 second order cycles corresponding to the sedimentary sequences of sloss 1963 last from tens of millions up to one hundred million years and are generally considered the result of long term trends in eustasy potentially in direct proportion to the activity of the mid ocean ridges the cause of the third order sea level cycles of millions of years duration is not well understood these cycles are often apparent at the basin scale and may be related to short term tectonic activity higher frequency fourth and fifth order cycles frequently are evident at the outcrop scale fourth order cycles include the classic cyclothems of the carboniferous e g heckel 1986 and have periods in the range of hundreds of thousands of years whilefifth order cyclesoperate at frequencies of tens of thousands of years these high frequency fourth and fifth order cycles are often referred to as milankovitch cycles due to the match of their interpretedperiodswiththecalculatedmilankovitch orbital frequences it is these high frequency cycles thatarethefocusofmuchmoderncyclostratigraphy and the record and application of these cycles in the triassic system is the focus of this chapter

quantification of input and compositional variations of calciturbidites in a middle triassic basinal succession seceda dolomites southern alps triassic calciturbidites were studied in a 100 m long core and nearby outcrops of the basinal buchenstein formation to determine composition and thickness variations the quantity of recognized turbidite sediment relative to background sediment changes from 15 by volume in the lower part to 60 in the upper part reflecting the steady progradation of nearby platforms the composition of the sand fraction of 214 turbidites was point counted in thin sections micrite peloids average 23 and lithoclasts 16 are by far the most dominant constituents they are interpreted as two different varieties of in situ precipitated micrite automicrite which probably formed under the influence of microbes and constitute the principal building material of the adjacent platforms platform derived skeletal grains amount to only 0 5 variations in turbidite composition were quantified using spearman s rank correlation and cluster analysis the most significant compositional variations seem to be related to hydrodynamic sorting in the turbidity currents and to the gradual shift from distal to more proximal turbidites in the core as the platforms prograded basinward cluster analysis of the 214 samples shows a major subdivision into micrite and sparite dominated turbidites clusters associated with micrite dominated turbidites are enriched in radiolaria and thin shelled bivalves whereas the clusters related to sparite dominated turbidites show an abundance of lithoclasts this subdivision seems strongly related to sorting effects in a turbidity current point counting of turbidites in nearby outcrops revealed a lateral variation in composition proximal turbidites are sparite dominated and enriched in lithoclasts distal portions are chiefly micrite with an open ocean biota thin shelled bivalves radiolaria this differentiation resembles the vertical change in composition of thick turbidite beds and is attributed to different settling rates of the various grains in the turbidity current there is no indication that turbidite composition fluctuated significantly under the influence of sea level fluctuations this is not surprising because the dominant automicrite facies of the platforms only migrates laterally but does not change much during sea level cycles

mid triassic integrated u pb geochronology and ammonoid biochronology from the balaton highland hungary ladinian middle triassic strata of the balaton highland west central hungary comprise interbedded marine carbonate and volcaniclastic rocks the sediments are noted for their rich ammonoid faunas which allow detailed biostratigraphic subdivision and correlation for the first time isotopic dating of the tuff layers was carried out to calibrate the age of ammonoid zones and subzones four successive horizons were dated from the felsouu ors section a candidate stratotype for the base of the ladinian stage within the reitzi zone which is interpreted here as the basal ladinian unit the following biostratigraphically tightly constrained u pb zircon ages were obtained felsoeoersensis subzone 241 1 0 5 ma liepoldti subzone 241 2 0 4 ma reitzi subzone 240 5 0 5 and 240 4 0 4 ma a redeposited tuff from the gredleri zone at liter yielded an additional u pb age of 238 7 0 6 ma the new isotopic ages are in agreement with published u pb dates from the southern alps together they allow estimation of the start of the ladinian at 241 5 ma and of the end of the stage at 237 ma a duration of

mechanisms of multidecadal atlantic meridional overturning circulation variability diagnosed in depth versus density space abstractmultidecadal variability of the atlantic meridional overturning circulation amoc is examined based on a comparison of the amoc streamfunctions in depth and in density space in a 700 yr present day control integration of the fully coupled community climate system model version 3 the commonly used depth coordinate amoc primarily exhibits the variability associated with the deep equatorward transport that follows the changes in the labrador sea deep water formation on the other hand the density based amoc emphasizes the variability associated with the subpolar gyre circulation in the upper ocean leading to the changes in the labrador sea convection combining the two representations indicates that the 20 yr periodicity of the amoc variability in the first half of the simulation is primarily due to an ocean only mode resulting from the coupling of the deep equatorward flow and the upper ocean gyre circulation near the gulf stream and north atlantic current in addition the density based amoc

high resolution stratigraphy and zircon u pb geochronology of the middle triassic buchenstein formation dolomites northern italy precession forcing of hemipelagic carbonate sedimentation and calibration of the anisian ladinian boundary interval orbitally forced cyclic variations in sedimentary sequences provide evidence for short term fluctuations of earth climate and a tool for high resolution timescale calibration we here present stratigraphic and geochronological evidence for precession forcing in middle triassic hemipelagic limestones of the buchenstein formation dolomites northern italy high resolution stratigraphy of several correlative sections of the buchenstein formation documents a coherent cycle pattern isotope dilution thermal ionization mass spectrometry zircon u pb geochronology of tuffs bracketing the cyclic interval reveals an average cycle duration of 18 5 2 1 kyr consistent with a shorter climatic precession cycle in the middle triassic compared with today this suggests a predominantly precession controlled climate in this low latitude setting of the western tethys and allows high precision calibration of the anisian ladinian boundary interval from integrating cyclostratigraphic and u pb geochronological constraints our best estimate for the age of the anisian ladinian boundary is 241 464 0 064 0 097 0 28 ma we also provide precise estimates for lithostratigraphic boundaries biostratigraphic markers and magnetic reversals within the boundary interval stratigraphic intervals with elevated sedimentation rate record a sub milankovitch signal that may be equivalent to patterns in adjacent carbonate platforms such as the latemar platform the origin of this sub milankovitch signal remains unknown but highlights the potential to investigate shorter term climatic variations in mesozoic sedimentary sequences supplementary material isotope dilution thermal ionization mass spectrometry u pb and laser ablation inductively coupled plasma mass spectrometry trace element data tables as well as the results of the bayesian age modelling are available at https doi org 10 6084 m9 figshare c 3861817

resolving milankovitchian controversies the triassic latemar limestone and the eocene green river formation although orbital forcing is commonly proposed as the driver of ancient sedimentary rhythms the lack of adequate independent time control radio isotopic data to calibrate these cycles has stood as a major challenge to evaluation of the hypothesis here i apply a new statistical approach to evaluate cyclicity in two historically important rhythmic units for which orbital forcing has been proposed the triassic latemar limestone dolomites italy and the eocene green river formation wyoming usa a major advance of the new method is its explicit evaluation of the null hypothesis of no orbital signal the null hypothesis can be rejected with a high degree of confi dence in the latemar limestone probability 0 30 and green river formation probability 0 07 the analyses also resolve controversies about the specifi c orbital calibrations at each site both data series reveal the expected precession obliquity and eccentricity orbital components and yield astrochronologies that are consistent with proposed radio isotopic based time scales

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

stacking pattern of cyclic carbonate platform strata lower cretaceous of southern apennines italy detailed sedimentological analysis of aptian albian shallow water carbonate platform strata from monte faito southern italy reveal composite sea level change the organization of the lithofacies and their related diagenetic overprint have allowed the identification of 50 elementary cycles they often show exposure related diagenetic features superimposed on subtidal deposits suggesting drops of relative sea level elementary cycles are grouped into 16 bundles forming six superbundles the hierarchical organization of the cycles are interpreted to be related to composite eustatic sea level fluctuations driven by the earth s orbital perturbation in the milankovitch frequency band moreover the systematic variation of superbundle thickness and the general evolution of the lithofacies reflects variations of accommodation potential defining longer term environmental changes different lithofacies forming elementary cycles are frequently separated by bedding planes that when viewed in a sequence stratigraphic context are interpreted as transgressive surfaces maximum flooding surfaces or sequence boundaries this allows the recognition of lowstand transgressive and highstand deposits in the cyclic units considering both the bundle superbundle ratio and the sequence stratigraphic interpretation of the superbundles a chronostratigraphic diagram illustrating both gaps at bundle level and their expected location along the section was created it establishes that the section developed over about 2 4 ma

cat scan in marine stratigraphy a quantitative approach abstract computed axial tomography cat scan gives a pseudo 3d representation of sedimentary cores sediments may be described and numerically processed from digitized high resolution images a 150 m long borehole was drilled and sampled at ile aux coudres middle estuary of the st lawrence quebec and analysed by a tomodensitometer cat scanner this borehole represents mainly the illinoian sangamonian transition series isotopic stage 5e 130 80 kyr b p of a post glacial glacioisostatic marine invasion and the subsequent regressive prodelta four representative samples 900 mm long were chosen for analysis from a transition zone between glacial and prodeltaic sediments they have been described from tomographic longitudinal and transversal sections from ct number series and also from classical analysis such as grain size organic matter and carbonates ct numbers reflect sedimentary characteristics and are closely linked to grain size and to organic matter carbonates are only weakly correlated probably because of its low concentration bed thickness and numerical processing of ct number series are used to characterize lamina and allow for depicting sub annual annual and longer periodicities clay facies fine and thick rhythmites and isolated diamicton beds were identified from bottom to top the first sample contains homogeneous clay rhythmites typical of a distal environment the second is composed of diamictons and thin alternating light dark annual lamina sets in the third sample annual light dark rhythmites are slightly thicker and display subtle semi annual cyclicities in the fourth sample annual rhythmites are several centimetres in thickness and contain preserved sub annual events of possible seasonal cyclicity this succession of facies and associated stratal periodicities may be typical of transgressive sedimentation in a basin such as the st lawrence estuary during the transition from glacial to non glacial conditions

new age constraints on counter clockwise rotation of ne japan summary the miocene basaltic andesitic lavas and cretaceous granites were sampled in the abukuma terrane of northeast honshu for geochronological and palaeomagnetic investigations to determine precise timing of counter clockwise rotation of ne japan characteristic component with unblocking temperature of 560 590 c is isolated from 26 sites of the takadate and ryozen formations and 12 sites of the cretaceous granites concordant northwesterly palaeomagnetic directions d 265 331 are observed in the cretaceous granites of the abukuma terrane the cretaceous mean palaeomagnetic direction from this terrane d 313 5 i 54 6 95 6 3 and n 20 is almost identical to oligo miocene 33 20 ma palaeomagnetic direction reported from the japan sea side of ne japan as well as to the cretaceous palaeomagnetic direction reported from the kitakami terrane this type of behaviour clearly suggests that the abukuma terrane underwent a coherent counter clockwise rotation as a part of ne japan after 20 ma conventional potassium k argon ar dating method performed on the plagioclase grains revealed distinctive ages of 14 44 0 88 and 16 52 0 82 ma for the takadate formation 11 sites and the ryozen formation eight sites respectively this type of behaviour indicates that two independent episodes of volcanic activities were probably responsible for the production of igneous rocks in the takadate and ryozen areas northerly declination is obtained from the takadate formation d 355 3 i 39 4 95 11 6 while slightly westerly deflected declination appears in the ryozen formation d 333 5 i 58 0 and 95 9 6 the here presented results therefore suggest that the province of ne japan was still experiencing a counter clockwise rotation at 16 5 ma however by 14 4 ma the rotational motion has completely ceased compared with the available palaeomagnetic and geochronological data from sw japan rotational motion in both provinces of ne and se japan has already been ceased by 14 ma thus any additional evidence regarding the complete cessation of rotational motions in ne japan will provide a key to understand the timing of opening in the japan sea

dolomite formation in the shallow seas of the alpine triassic the alpine triassic units of switzerland northern italy and western austria offer an extensive geological archive in which the enigmatic process of dolomite formation can be studied in a palaeoenvironmental context recent studies clearly demonstrate that large amounts of the alpine triassic dolomites are late diagenetic or hydrothermal nevertheless as part of multiple generations of diagenetic overprint some generations of fine crystalline ca rich dolomite appear strictly confined to their depositional facies and show signs of very early formation at surface temperatures in specific ancient depositional environments in this review three cases of alpine triassic dolomites are discussed where dolomite rocks may have formed during or soon after sedimentation the sedimentary facies indicate contrasting palaeoenvironmental conditions and hence document three different possible processes of dolomite formation i in the dolomite mountains northern italy dolomite beds of the partly isolated middle triassic anisian ladinian latemar platform are confined to the very top of shallowing upward lagoonal facies cycles ii dolomite beds of the san giorgio basin southern switzerland an intra platform basin that opened during the anisian ladinian transition are associated with organic carbon rich shales which were deposited in a deeper water environment under anoxic conditions iii in the entirely dolomitized platform facies of the dolomia principale hauptdolomit formation a very early generation of fine crystalline dolomite occurs in the shallowest part of evaporative peritidal cycles this platform extended over thousands of square kilometres along the tethys margin during the late triassic carnian and norian and large amounts of carbonate were deposited under hypersaline sabkha like conditions representing three distinct depositional environments these three different triassic systems show features in common with several dolomitization models developed from the study of modern dolomite forming environments for example the sabkha model the evaporative lagoon lake model the organogenic model and the microbial model although these actualistic models may be applicable to reconstruct the palaeoenvironmental conditions during dolomite formation dolomite forming processes during the triassic were apparently quite different from the modern world in terms of distribution and scale recent developments in stable isotope geochemistry and high resolution geochemical probing offer the possibility to make better reconstructions of triassic palaeoceanographic conditions and suggest a non actualistic approach to better understand dolomite formation during the triassic

improving the upper triassic numerical time scale from cross correlation between tethyan marine sections and the continental newark basin sequence abstract magnetostratigraphic cross correlations between biochronologically well dated tethyan marine sections and the astronomically tuned sedimentary sequence from the continental newark basin eastern north america help to improve the upper triassic time scale we show here that the most recent radiometric results constraining the age of the base and top of the upper triassic 237 and 200 ma respectively strengthen the chronostratigraphic calibration of the newark sedimentary sequence proposed by krystyn et al earth planet sci lett 203 2002 343 351 these results allow one to reconcile the milankovitch based cyclostratigraphy from the newark sequence the magnetostratigraphic data from both marine and continental environments and upper triassic biostratigraphy including data on tethyan marine faunas and on terrestrial vertebrates according to this calibration the successive upper triassic stages would have very different durations 10 myr for the carnian 237 227 ma 25 myr for the norian 227 202 ma and 2 myr for the rhaetian 202 200 ma but only if the entire rhaetian is recorded in the newark sequence we further show that the biozone durations in the upper triassic would have been highly variable and as a whole would have lasted much longer than in the lower and middle triassic

a proposed integrated multi signature model for peritidal cycles in carbonates abstract a new integrated multi signature model for meter scale peritidal carbonate cycles presented here is relevant to the interpretation of these cycles in the stratigraphic record meter scale shallowing upward micro facies cycles are the most common type of peritidal parasequence peritidal parasequences are a fundamental component of carbonate sequence stratigraphic models however the existence of meter scale cycles in the geological record has been questioned owing to the failure to prove statistically the existence of these cycles using data on micro facies and stacking pattern taken from previous studies nevertheless the shallowing upwards micro facies interpretive template remains widely used to identify these cycles and parasequences we propose that the sedimentary signatures of meter scale peritidal cycles vary systematically during the various phases of an underlying 3rd order relative sea level cycle although during specific phases of a 3rd order relative sea level cycle meter scale peritidal cycles may be characterized by shallowing upward units e g early transgressive systems tract during other periods the stratigraphic signal of cyclicity may be more cryptic and complex causing them to be overlooked e g late transgressive systems tract and highstand systems tract we also propose that there is a half cycle phase shift in periods of deposition and the formation of drowning surfaces relative to 4th to 5th order relative sea level cycles over the course of a 3rd order relative sea level cycle these points have ramifications for defining parasequences and using stacking patterns to determine peritidal cycle periodicity specifically parasequences defined using flooding surfaces identify sedimentary units that inconsistently partition 4th to 5th order relative sea level cycles at different stages of a 3rd order relative sea level cycle we propose testable new physical stratigraphic signatures for identifying meter scale cycles that have consistent genetic significance each cycle recording a relative sea level cycle characterized by a 4th to 5th order relative sea level rise and fall meter scale peritidal cycles are recorded by an ordered pattern of systematically varying micro facies signatures related to their position within a 3rd order relative sea level cycle the integrated multi signature model of meter scale peritidal carbonate cycles we propose here may assist in explaining the apparently contradictory evidence both for and against their existence in the geological record as a result of the detailed consideration in this paper of the nature of parasequences and their variations with 3rd order relative sea level changes a redefinition of parasequence is required and one is presented here

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

the interpretation of cyclic successions of the middle and upper triassic of the northern and southern alps abstract theories regarding the formation of sedimentary cycles in the 3rd 4th and 5th order bands are reviewed with reference to the middle and upper triassic of the northern calcareous alps nca and southern alps milankovitch autocyclic and tectonic theories are discussed together with an evaluation of concepts of chaotic sedimentation and a case example from the nca concerning eustasy 3rd 4th and 5th order sea level fluctuations were probably a low amplitude low rate phenomenon caused by fluctuations in the volume of mountain glaciers and ocean water during the triassic the mid and late triassic was a non glacial interval in which polar regions may have been ice free so glacio eustasy can not be expected eustatic sea level variations in the 3rd 4th and 5th order bands seem to have left no useful imprint on cyclic successions in the region whatever record there may be is inextricably mixed with two other signals tectonic activity and autocycles the review shows how sedimentation in the triassic of the area was strongly influenced by tectonic activity this is as true for the middle and late triassic of the nca as it is for the southern alps tectonic activity may be responsible for large scale cyclicity 4th to 3rd order scale although seismogenic structures have yet to be identified and described in carbonate successions of the alps candidates do exist slumped and microfaulted layers in laminated sediments of the seefeld basin upper triassic nca have been described as the products of fault movements the sedimentary record from the nca and southern alps also leaves little doubt that autocyclic processes were important in all environments except perhaps the deep sediment starved basins most small scale platform cycles 5th order scale in the region can be related to autocyclic processes and in shallow basinal successions to events such as storms previous workers have not been consistent in their interpretation of cyclic successions in the area applying diverse theories to similar successions so far the steinplatte hochkonig platform with attached kossen basin is the only example interpreted with reference to tectonics and autocyclicity eustasy was probably not the most important factor in cycle generation in the triassic of the nca and southern alps such an approach could prove useful in future studies

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

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

facies architecture of an isolated carbonate platform tracing the cycles of the latemar middle triassic northern italy the 720 m thick succession of the middle triassic latemar massif dolomites italy was used to reconstruct the lagoonal facies architecture of a small atoll like carbonate platform facies analysis of the lagoonal sediments yields a bathymetric interpretation of the lateral facies variations which reflect a syndepositional palaeorelief based on tracing of lagoonal flooding surfaces the metre scale shallowing upward cycles are interpreted to be of allocyclic origin short term sea level changes led to subaerial exposure of wide parts of the marginal zone resulting in the development of a tepee belt of varying width occasional emergence of the entire lagoon produced lagoon wide decimetre thick red exposure horizons the supratidal tepee belt in the backreef area represented the zone of maximum elevation which circumscribed the sub to peritidal lagoonal interior during most of the platform s development this tepee rim the subtidal reef and a sub to peritidal transition zone in between stabilized the platform margin the asymmetric width of facies belts within individual metre scale cycles was caused by redistribution processes that reflect palaeowinds and storm paths from the present day south and west the overall succession shows stratigraphic changes on a scale of tens of metres from a basal subtidal unit overlain by three tepee rich intervals separated by tepee poor units composed of subtidal to peritidal facies this stacking pattern reflects two third order sequences during the late anisian to early middle ladinian

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

magnetostratigraphic confirmation of a much faster tempo for sea level change for the middle triassic latemar platform carbonates new magnetostratigraphic data for the 470 m thick latemar carbonate platform which includes 600 shallowing upward bedding cycles are consistent with litho and biostratigraphic correlations of the section to a 10 m thick interval in the basinal buchenstein beds that most likely represents only 1 m y of deposition according to published u pb single crystal zircon dates a reappraisal of reported cycle stratigraphic analyses of the latemar suggests that the visibly obvious meter scale bedding is not due to milankovitch precessional forcing but rather reflects tempos an order of magnitude faster that may involve millennial scale tidal amplitude variations d 2004 elsevier b v all rights reserved

high resolution estimate for the depositional duration of the triassic latemar platform a new magnetostratigraphy and magnetic susceptibility cyclostratigraphy from basinal sediments at rio sacuz italy 1 a new magnetostratigraphy and magnetic susceptibility cyclostratigraphy from middle triassic basinal sediments at rio sacuz northern italy suggests a depositional duration of 1 myr for most of the 670 m carbonate latemar platform giving a high resolution estimate for the duration for the latemar s deposition the new magnetostratigraphy from rio sacuz clarifies the ambiguities in a previous magnetostratigraphic study of the latemar caused by lightning strike remagnetizations our rio sacuz study was unaffected by lightning using thermal demagnetization we show a normal reversed normal reversed sequence at the latemar correlated locality of rio sacuz with a polarity interval duration of 0 25 0 5 myr for the middle triassic this gives a depositional duration of 1 2 myr rock magnetic experiments show that the magnetic carrier is magnetite suggesting a primary depositional age remanence measurement of magnetic susceptibility at 1 m intervals from rio sacuz reveals eight short eccentricity cycles 95 125 kyr bundled into slightly more than two 405 kyr long eccentricity cycles indicating a more precise duration for the rio sacuz section of 0 8 to 1 myr the shorter depositional duration required by this study forces a sub milankovitch time scale of 1 2 kyr for the latemar platform s meter scale rhythmic bedding and provides strong evidence for nonorbitally driven climate change in the middle triassic

unravelling the influence of water depth and wave energy on the facies diversity of shelf carbonates carbonate sequence stratigraphy is founded on the principle that changes in relative sea level are recorded in the rock record by the accumulation of sediment with relative water depth dependent attributes while at the scale of a shelf to basin transect facies clearly arrange by water depth the relation blurs for depths 40 m the most vigorous zone of carbonate production the reason for this change in behaviour is two fold firstly in shallow water the intrinsic processes of storm and wave reworking influence the seabed through submarine erosion and sediment redistribution secondly facies diversity tends to be greater in shallow water than deep water because of a greater diversity in grain producers remote sensing imagery field observations and hydrodynamic models for two reef rimmed shore attached carbonate platforms in the red sea show neither water depth nor energy regime to be reliable indicators of facies type when considered in isolation considered together however the predictive power of the two variables rises significantly the results demonstrate it to be an oversimplification to assume a direct link between palaeo water depth and depositional diversity of subtidal lithofacies while highlighting the importance of hydrodynamics in directing the accumulation of carbonate sediments in the shallow photic zone while the size distributions of facies extents in the two focus areas follow power laws no direct relation between the lateral continuity of the facies belts and water depth or wave height is reported the work is relevant for the interpretation of metre scale subtidal carbonate cycles throughout the geological record by demonstrating how caution must be applied when inferring palaeowater depths from depositional facies

orbitally induced limestone marlstone rhythms in the albian cenomanian cismon section venetian region northern italy sedimentology calcareous and siliceous plankton distribution elemental and isotope geochemistry abstract a multidisciplinary study of the upper albian cenomanian portion of the cismon section venetian region northern italy was undertaken in order to characterize the cyclic alternations of carbonate rich and carbonate poor layers and to investigate their possible origin and cyclic patterns limestone semicouplets are characterized by abundant radiolarians and micarbs micron sized calcitic fragments common planktonic foraminifera strong bioturbation good oxygenation as expressed by the mn and v v ni parameters high si al ratio low k al in the absence of pyrite and organic matter the marlstone semicouplets are on the contrary frequently laminated rich in pyrite and organic matter with common fish remains in the absence of radiolarians the mn and v v ni parameters indicate that the marlstone deposition occurred in dysoxic to anoxic conditions which allowed the preservation of organic matter the low si al ratio and high k al ratio the latter related to abundant feldspars indicate that marlstones received a substantial contribution from a terrigenous source the abundance of biogenic silica suggests that during limestone deposition surface waters were rather fertile due to an efficient recycling of nutrients from deeper waters the enhanced fertility was coupled with an efficient current system at the welloxygenated sea floor which prevented the organic matter from accumulating during marlstone deposition surface waters were less fertile than in the limestone semicouplets but still within the mesotrophic spectrum as indicated by the presence of fertility index species among calcareous nannofossils whereas the bottom waters were oxygen depleted to accommodate fertility at the surface with stagnation at the bottom the scenario implies an enhanced stratification caused by an increase in freshwater runoff monitored by 18o depleted values in the meantime the water discharge supplied the nutrients to the surface waters necessary for the calcareous nannofossils to proliferate the cyclic organization of limestone marlstone couplets as revealed by power spectral analysis seems to represent climatic cycles the alternating conditions are 1 efficient mixing highly fertile surface and near surface waters and a well oxygenated seafloor to 2 enhanced water runoff or decreased evaporation or both and oxygen depleted bottom waters we suggest that this deterministic sedimentary cyclicity could be explained by periodic orbital climatic cycles in tune with the milankovitch cycles within this scenario the latest cenomanian bonarelli level is an exceptional event marked by a large positive 13c spike it is characterized by high to very high fertility conditions in surface waters caused by increased upwelling that engendered high nutrient levels in near surface waters the enhanced production of organic matter was in excess for the oxygen available at the bottom floor thus allowing the organic matter to accumulate in the sediments

reply to discussion of magnetostratigraphic confirmation of a much faster tempo for sea level change for the middle triassic latemar platform carbonates by d v kent g muttoni and p brack earth planet sci lett 228 2004 369 377 by l hinnov

use of insolation as a proxy for high frequency eustasy in forward modeling of platform carbonate cyclostratigraphy a promising approach abstract eustatic oscillations driven by milankovitchian astronomical forcing have been interpreted as sea level drivers for high frequency carbonate depositional cycles in studies dating from the mid 1960s forward modeling of these oscillations with respect to their recorded effects on cyclical stacking patterns has only been attempted using generalized parameters for milankovitchian forcing the development of increasingly advanced forward modeling software coupled with the availability of formulas quantifying insolation incoming solar radiation as a function of composite orbital variations allows for the testing of milankovitchian insolation against measured stratigraphy in this case a series of milankovitchian insolation curves were calculated and used to generate proxy sea level curves for use in the carb3d forward modeling package in order to synthesize a series of stacked carbonate strata these synthetic successions are compared against that of the latemar platform middletriassic northern italy which has been interpreted to contain a record of orbital forcing within its stratigraphy while the timing and nature of periodic drivers that affected latemar stratigraphy have stirred a vigorous debate results from this study indicate that use of milankovitchian insolation as a proxy for high frequency sea level oscillations was successful in modeling latemar like stratigraphy with both pure milankovitchian and mixed milankovitchian sub milankovitchian temporal frameworks

carbonate platforms in the dolomites area of the southern alps historic perspectives on progress in sedimentology the area of the dolomites in the southern alps exhibits some of the best outcrops of carbonate platforms and platform to basin transitions in the world the region has attracted geologists since the early 19th century and has been a centre of stratigraphic and sedimentological research ever since the interpretation of the platforms in the dolomites as coral reefs dates back to the 1850s and was inspired by the work on modern reefs in the pacific and indian oceans at that time very soon however studies in the dolomites triggered developments of their own fieldwork on these triassic atolls led to a first understanding of the dramatic facies changes at the periphery of reefs and atolls including the recognition of slope facies and basinward transport of platform material by gravity in addition the platforms were used to prove long term syndepositional subsidence on the scale of kilometres as early as 1860 after world war ii the study of modern reefs and platforms led to process based facies models and this in turn guided the sedimentological analysis of the alpine mediterranean belt repeatedly however the roles became reversed and the alpine mediterranean platforms contributed to the fundamental underpinnings of sedimentology in the 1980s mountain size outcrops in the alps and the apennines were recognized as models for the interpretation of shoal water carbonates in seismic data seismic models of outcrops in the dolomites for instance gave rise to the concept of pseudo unconformities i e rapid lateral facies changes that appear as unconformities in seismic images in the 1990s the alpine mediterranean mesozoic along with the north american and european palaeozoic revealed the significance of microbially induced carbonate precipitation in constructing large limestone bodies studies of ancient rocks led this development because this particular carbonate factory is far less prominent now than it was at certain times in the past 2009 the authors journal compilation 2009 international association of sedimentologists

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

meso cenozoic basin and carbonate platform development in the sw dolomites unraveled by basin modelling and apatite ft analysis rosengarten and latemar northern italy abstract the rosengarten and latemar middle triassic carbonate platforms indicate similar subsidence patterns during equivalent times of platform evolution as calculated by numerical basin reverse modelling in the case of rosengarten and latemar thermo tectonic subsidence is the most significant among all three subsidence components thermo tectonic s flexural s compaction induced s hence the influence of differential tectonics as recorded in the formation of structural highs and lows in the dolomites during the lower to middle anisian almost ceases in late anisian times basin modelling of rosengarten and latemar requires the correlation and integration of two sets of chronostratigraphic data from buchenstein fm basin and schlern dolomite fm 1 platform subsidence modelling argues for a microcycle i e a single shallowing upward cycle duration of less than 1 97 ka in the cyclic succession at latemar however previous time series analyses identify milankovitch cyclicities in larger order cycle stacking patterns and thus indicate a microcycle duration of 4 2 ka according to each model total subsidence reaches values of 650 700 m ma 4 2 ka model or 780 850 m ma 1 97 ka model during the first stage of platform evolution as both platforms successfully keep up with this subsidence peak it is evident that the carbonate factory despite its low diversity must have recovered from the p t faunal crisis after this regionally observed peak subsidence drops and triggers fast progradation at rosengarten subsidence in the study area is controlled by active strike slip tectonics and the subsequent formation of a magmatic chamber predazzo monzoni above the deep reaching truden stava line the area close to this tectonic line and to the volcanic centre of predazzo monzoni undergoes a higher heat flow pulse during the late ladinian and is possibly buried at shallower levels than the rosengarten area as shown by fission tracks in apatites the heat flow pulse almost disappears laterally underlining the localised thermal influence of the late ladinian volcano thermal event of predazzo monzoni

spectral analysis of the middle triassic latemar limestone abstract the middle triassic latemar limestone in the dolomites region northern italy consists of hundreds of vertically stacked meter scale platform carbonate cycles each cycle is composed of a shallow marine subtidal carbonate unit with a thin centimeter scale vadose diagenetic dolomite cap these latemar couplets are the products of repeated episodes of submergence emergence with durations estimated at 20 000 yr the couplets are arranged in upward thinning bundles of five indicating the presence of a 100 000 year modulating component we examined this high frequency cycling in the platform buildup using a variety of classical and advanced spectral analysis techniques we found si nificant evidence for the presence of a milankovitch forcing signal in this cycling we also present evidence that the adjacent coeval basinal facies the livinallongo formation exhibits a similar bundling pattern in its cm scale hemipelagic carbonate shale alternations we conclude that milankovitch forced small amplitude sea level oscillations were the most likely cause of these middle triassic carbonate rhythms

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

late triassic to late jurassic evolution of the adriatic carbonate platform and budva basin southern montenegro abstract southeastern montenegro is the only part of the adriatic carbonate platform adcp that bears record of its evolution from a ramp through a distally steepened ramp to a platform in this paper we present the sequence stratigraphy of the late triassic to late jurassic rocks from this part of tethys for the first time in the literature we discovered and described three new facies hardground and cerebroid oolites of the livari supersequence and black pebble conglomerate of the tejani supersequence the mid ramp and lower ramp cherty oolite wackestone and mudstone facies of the livari supersequence as well as oolite conglomerate facies of the stari bar supersequence were partially or completely reinterpreted the middle and late triassic rifting separated the adcp from the other south tethyan carbonate platforms and created the intraplatform budva basin the adcp evolved through three morphologic stages a detached ramp livari supersequence rhaetian early toarcian a distally steepened ramp tejani supersequence early toarcian middle callovian and an accretionary rimmed platform stari bar supersequence oxfordian to neogene the rhaetian regression is marked by a regional unconformity surface that represents a type s sequence boundary at the base of the livari supersequence lowstand wedge of the halobia limestone was the oldest sediment in the budva basin tst and hst of the livari supersequence include supratidal and intertidal inner ramp sediments ooid shoals and cyclic shallowing up parasequences of the mid ramp sedimentation rates were high in the inner ramp while budva basin received relatively thin accumulation of siliceous plankton a brief exposure of supratidal flats and ooid bars represents a type p sequence boundary between the livari and the tejani supersequences which was flooded by the early toarcian transgression tst and hst of the tejani supersequence consist of supratidal lagoon and shoal sediments in the inner ramp and deeper water carbonates of the mid and outer ramp highstand shedding of the sediment from the steepened ramp left thick deposits in the budva basin the bathonian regression is marked by a regional unconformity that represents a type s sequence boundary between the tejani and stari bar supersequences stari bar oolite conglomerate is a lowstand wedge of the stari bar supersequence the middle callovian transgression induced aggradation of ooid shoals deep into the platform interior oxfordian coral reefs created a rimmed platform and restricted export of the shallow carbonates into the budva basin

unraveling the origin of carbonate platform cyclothems in the upper triassic durrenstein formation dolomites italy abstract facies analysis of the durrenstein formation central eastern dolomites northern italy indicates that this unit was deposited on a carbonate ramp as evidenced by the lack of a shelf break slope facies or a reef margin together with the occurrence of a molechfor biological association its deposition following the accumulation of rimmed carbonate platforms during the ladinian and early carnian marks a major shift in growth mode of the triassic shallow marine carbonates in the dolomites the durrenstein formation is characterized by a hierarchical cyclicity with elements strongly suggestive of an allocyclic origin including a subaerial exposure features directly above subtidal facies within meter scale cyclothems b purely subtidal carbonate cyclothems c symmetric peritidal carbonate cyclothems and d continuity of cyclothems of different orders through facies boundaries the durrenstein cyclothems are usually defined by transgressive and regressive successions and so most of them probably originated from sea level oscillations their allocyclic origin allows their use for high resolution correlations over distances up to 30 km a stratigraphic section in the tre cime di lavaredo area encompassing the upper part of the durrenstein formation and the lower part of the overlying raibl formation upper carnian was studied using time frequency analysis a strong milankovitch signal appeared when interference arising from a variable sedimentation rate was estimated and removed by tuning the short precession line in a spectrogram all of the principal periodicities related to the precession index and eccentricity calculated for 220 ma are present p1 21 9 ky p2 17 8 ky e1 400 ky e2 95 ky and e3 125 ky along with a peak at a frequency double that of the precession which is a predicted feature of orbitally forced insolation at the equator components possibly related to earth s obliquity at ca 35 ky and ca 46 ky are present as well the recovery of milankovitch periodicities allows reconstruction of a high resolution timescale that is in good agreement with published durations of the carnian based on radiometric ages the recognition of a milankovitch signal in the durrenstein and lower raibl formations as well as in other mesozoic carbonate platforms strongly supports a deterministic and predictable rather than stochastic control on the formation of carbonate platforms carbonate platforms might thus be used in the future for the construction of an astronomical time scale for the mesozoic

lateral variations in sediment composition and bedding in middle triassic interplatform basins buchenstein formation southern alps italy hemipelagic deposits are widespread in triassic sequences of the alpine belt and provide important data for stratigraphy and the study of bedding rhythms the area of the western and central dolomites of northern italy escaped strong alpidic deformation and preserves such deposits in their original palaeogeographic setting the buchenstein formation the object of this study was deposited in up to 1000 m deep middle triassic interplatform basins which extend over an area of 500 km 2 within the dolomites excellent outcrops and volcaniclastic markers allow a detailed correlation of the formation in both laminated anoxic and bioturbated facies down to a bed scale and show its relationship to coeval carbonate platforms correlation of lithostratigraphically well constrained intervals in the bioturbated facies reveal that lateral thickening and thinning of the deposits depends on the amount of shallow water debris in the succession and is a function of the distance to coeval carbonate platform sources in the laminated background deposit thickness variations in limestones and marls parallel the thickness variations in ash layers and were caused by local redeposition of sediment on the basin floor lateral persistence of laminae indicates that bottom currents were weak in the buchenstein basin but were able to redeposit mud in a significant way in the area around seceda and geisler western dolomites a lateral transition from dark grey laminated to grey bioturbated to red bioturbated facies is observed which is probably linked to local relief with different oxygenation conditions on the sea floor a comparison shows that decimetre scale bedding is preserved in all facies types and that the bedding rhythm is partly the result of different cementation of the sediment during early diagenesis correlation of individual layers in the bioturbated facies reveals that beds are thicker and enriched in lime mud in the western part of the basin and decrease in thickness and contain less micrite towards the east further away from the main shallow water areas nearslope calciturbidites change gradually from distinct layers into lateral arrays of micrite nodules and bands further out in the basin these observations point to a platform source of lime mud in the buchenstein basin

millennial scale climate origins for stratification in cambrian and devonian deep water rhythmites western usa abstract basinal facies of the middle cambrian marjum formation western utah and middle devonian denay limestone central nevada are characterized by thin rhythmically interbedded limestone and marl layers deep water rhythmites limestone layers average thickness range of 4 3 5 5 cm are composed of laminated to massive pelleted lime mudstone marl layers average thickness range of 0 7 1 7 cm are characterized by laminated argillaceous dolomitic mudstone the absence of current or wave reworked features paucity of bioturbation and skeletal fossils stratigraphic relationships with adjacent facies and the dark color indicate that limestone and marl layers in both rhythmite successions were deposited in quiet dysaerobic waters below storm wave base both limestone and marl layers are composed of submillimeter thick graded laminae which represent discrete depositional events from dilute density currents generated by high frequency storms or distal turbidity currents fluctuations in primary pelagic productivity cannot account for variations in carbonate influx because calcareous microfossils did not evolve until the mesozoic instead the rhythmic interbedding is interpreted to reflect climatically controlled variations in fluvial and or eolian influx or changes in marine currents storm or distal turbidity currents which transported shallow platform derived carbonate material into the deep water region spectral analysis of carbonate time series were compared to lithologic rank series and particularly for the middle cambrian rhythmites were found to be statistically indistinguishable the durations of significant spectral peaks were estimated from calculating the average sedimentation rates from the two biostratigraphically controlled stratigraphic sections these rates range between 4 3 4 1 cm k y and 21 2 29 2 cm k y for the cambrian and 3 6 1 8 cm k y to 5 1 7 4 cm k y for the middle devonian application of these sedimentation rates to the marjum couplets suggests that individual couplets represent between 190 2100 years of time the denay couplets represent 800 1900 years the good agreement between empirical holocene hemipelagic sedimentation rates and the sedimentologic evidence of relatively high depositional rates for the paleozoic rhythmites supports this millennial scale interpretation these results combined with that from previous work in paleozoic evaporite and carbonate successions suggest that millennial scale paleoclimatic variations affected marine and marginal marine sedimentation as far back in time as the cambrian millennial scale climatic change appears to be a permanent feature affecting the oceans and atmosphere and is apparently largely unaffected by major changes in phanerozoic paleogeography tectonics and atmospheric composition

high frequency depositional cycles in the muschelkalk middle triassic of southern poland origin and implications for germanic basin astrochronological scales abstract high frequency depositional cycles are often used for long distance correlations within sedimentary basins and constructing high resolution chronostratigraphic scales calibrated to the orbital clock such an approach has been used for the tropical epicontinental muschelkalk sea covering most of europe in the middle triassic this paper aims at establishing the spatial extent and internal architecture of shallow marine muschelkalk cycles within a small 120 by 50 km area of the germanic basin to identify their local vs regional distribution and cycle forming mechanisms three groups of cycles are distinguished 1 peritidal cycles representing a tidal flat lagoon system which experienced longer periods of emersion 2 shallow subtidal cycles formed around the fair weather wave base and 3 deep subtidal cycles developed around the storm wave base the three cycle types differ markedly in the composition facies homogeneity sedimentary trends hierarchical organization continuity and degree of lateral changeability and complexity which collectively translates into the ease of cycle recognition despite the differences the defined cycles do not extend laterally beyond the studied area and have laterally variable facies heterogeneities sedimentary trends and thicknesses this variability resulted from more or less mosaic infilling of accommodation space reflecting local bathymetry physicochemical conditions and carbonate production and accumulation rates on the platform accommodation space evolved by the interplay of eustatic sea level fluctuations regional subsidence and synsedimentary tectonic block movements but the contribution of these factors changed over time and was to varying degrees masked for each of the three cycle types by intrinsic sedimentary processes the study shows that middle triassic cycles of the germanic basin have a local to sub regional distribution and thereby are inappropriate for basin wide correlations and chronostratigraphic inferences it also strengthens the opinion of several workers that correlation of idealized cycles is unrealistic without checking the horizontal continuity of facies and key surfaces directly in the field

high resolution magnetostratigraphic and lithostratigraphic correlations in middle triassic pelagic carbonates from the dolomites northern italy new magnetostratigraphic and lithostratigraphic data are reported from the pedraces and belvedere limestone sections from the dolomites region of northern italy these sections are comprised of the buchenstein beds of late anisian to ladinian middle triassic age the results from pedraces and belvedere are compared with data from the biostratigraphically and isotopically constrained frotschbach and seceda sections from the literature a satisfactory magnetostratigraphic correlation is obtained on laterally traceable limestone and volcaniclastic intervals these marker beds are then used to extend lithostratigraphic correlations to additional key sections from a palaeogeographically coherent area of around 500 km2 the aim of this study is to unravel the spatial and temporal evolution of the buchenstein basin and the surrounding carbonate platforms platforms in the northwestern dolomites show an early stage of aggradation followed by progradation whereas in the central dolomites the cernera platform after fast initial aggradation drowned and became a pelagic seamount in the intervening buchenstein basin the diverential subsidence between the northwestern and central dolomites is manifested by the lateral increase of thickness of lower pietra verde volcaniclastic sediments accumulation of volcaniclastic material reworked from adjacent carbonate platform slopes characterised the more subsiding and unstable central dolomites in the pelagic carbonate intervals the persistence over tens of kilometres of bedding patterns suggests that carbonate material presumably washed out from the surrounding still active carbonate platforms was volumetrically small and homogeneously distributed throughout the uniformly subsiding buchenstein basin a milankovitch precessional origin for the platform interior cycles at latemar as suggested elsewhere implies a net accumulation rate of 2 m ma or less for the correlative interval of pelagic buchenstein beds this value divers significantly from the average value of around 10 m ma as calculated using high resolution isotopic age data for the buchenstein beds 2000 elsevier science b v all rights reserved

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

discussion of magnetostratigraphic confirmation of a much faster tempo for sea level change for the middle triassic latemar platform carbonates by d v kent g muttoni and p brack earth planet sci lett 228 2004 369 377 abstract kent et al report on new magnetostratigraphic data obtained from the middle triassic latemar carbonate platform dolomites italy the result is important because it addresses the so called latemar controversy and appears to corroborate radioisotope dated ash beds in the latemar platform indicating that the buildup must have taken place in 2 4 million years but not the 9 12 million years of milankovitch forcing inferred from cyclostratigraphic analyses unfortunately kent et al omit basic information that runs contrary to the conclusion that the latemar carbonates have yielded a primary paleomagnetic signal here the missing details are supplied by zooming in on the chronostratigraphic interval that was investigated in sum kent et al s results do not confirm a faster tempo for sea level change for the latemar as much as raise questions about the magnetization of these carbonate rocks there are also shortcomings in kent et al s reappraisal of the cyclic content of the cimon del latemar cdl series that need clarification finally the latemar controversy is examined in the context of the distribution of time in middle triassic stratigraphy of the dolomites

the triassic timescale new constraints and a review of geochronological data a review of geochronological data underlying the geological time scale for the triassic yields a significantly different time scale calibration than that published in the most recent compi lation geologic time scale 2004 this is partly due to the availability of new radio isotopic data but mostly because strict selection criteria are applied and complications arising from biases both systematic and random are accounted for in this contribution the ages for the base and the top of the triassic are constrained by u pb ages to 252 3 and 201 5 ma respectively these dates also constrain the ages of major extinction events at the permian triassic and triassic jurassic bound aries and are statistically indistinguishable from ages obtained for the siberian traps and volcanic products from the central atlantic magmatic province respectively suggesting a causal link ages for these continental volcanics however are mostly from the k ar 40 ar 39 ar system which requires accounting and correcting for a systematic bias of c 1 between u pb and 40 ar 39 ar isotopic ages the 40 ar 39 ar ages being younger robust age constraints also exist for the induan olenekian boundary 251 2 ma and the early middle triassic olenekian anisian boundary 247 2 ma resulting in a surprisingly short dur ation of the early triassic which has implications for the timing of biotic recovery and major changes in ocean chemistry during this time furthermore the anisian ladinian boundary is con strained to 242 0 ma by new u pb and 40 ar 39 ar ages radio isotopic ages for the late triassic are scarce and the only reliable and biostratigraphically controlled age is from an upper carnian tuff dated to 230 9 ma yielding a duration of more than 35 ma for the late triassic all of these ages are from u pb analyses applied to zircons with uncertainties at the permil level or better the resulting compilation can only serve as a guideline and must be considered a snapshot resolving some of the issues mainly associated with inaccurate and misinterpreted data in previous publi cations however further advances will require revision of some of the data presented here

high resolution upb dating of middle triassic volcaniclastics time scale calibration and verification of tuning parameters for carbonate sedimentation abstract we report high resolution single zircon u pb age data for middle triassic volcaniclastic intercalations in biostratigraphically calibrated pelagic successions of the southern alps the results require a redefinition of the chronometric scale for the middle triassic moreover they do not support current models relating cyclic sedimentation in platform carbonates of the dolomites to orbital tuning tight concordant age clusters were obtained for five volcaniclastic layers in three ammonoid biozones of late anisian to early ladinian age two layers in the nevadites secedensis zone yielded identical mean 206 pb 238 u ages of 241 2 0 8 0 8 ma and 241 2 0 8 0 6 ma errors given at the 95 confidence level a layer in the gredleri zone is dated at 238 8 0 5 0 2 ma and two horizons in the archelaus zone yield similar ages of 237 9 1 0 0 7 ma and 238 0 0 4 0 7 ma these results are significantly older than the age values of 233 235 ma assigned to the anisian ladinian boundary by several current time scales 1 4 moreover our estimate of 240 7 241 3 ma depending on biostratigraphic collocation for the anisian ladinian boundary casts doubts on the reliability of age values of 245 250 ma proposed by most time scales for the permian triassic boundary the occurrence of pelagic fossils in basinal sediments as well as in age equivalent shallow marine middle triassic platform carbonates in the dolomites allows the sedimentary sequences of both environments to be correlated the 800 m thick latemar platform western dolomites is characterized by cyclic stacking patterns which have been interpreted as results of milankovitch type high frequency low amplitude sea level fluctuations the 12 m y interval of platform growth postulated from the assignment of orbital periodicities to the platform carbonate cycles 5 6 is in conflict with a maximum time span of 4 7 m y allowed by the present zircon data

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