geochemical and textural evidence for early shallow diagenetic growth of stratigraphically confined carbonate concretions upper devonian rhinestreet black shale western new york laterally persistent carbonate concretionary horizons are conspicuous to the upper devonian frasnian rhinestreet black shale of the western new york state appalachian plateau field observations including randomly tilted concretions and differential compaction of host sediment laminae around concretions are consistent with early diagenetic growth in unconsolidated sediment further estimates of pre cementation host sediment porosity based on the volume percentage of caco3 cement 74 93 and perhaps most importantly the preservation of a cardhouse clay fabric in mudstones collected from concretion pressure shadow regions suggest that concretionary growth occurred rapidly within perhaps a meter of the seafloor petrographic examination sem of matrix carbonate samples collected from six concretions reveals a relatively porous 4 7 framework of calcite micrite and microsparite euhedral pyrite most abundant near concretion rims disseminated pyrite framboids and randomly oriented detrital clay platelets and domains c isotopic compositions of rhinestreet concretion matrix carbonate range from 13 9 to 1 7 pdb suggesting derivation of c from a mixed source that included depleted and isotopically heavy c slightly to moderately depleted o isotopic compositions 3 8 to 6 8 pdb do not corroborate the shallow depth of concretion growth suggested by field and textural observations the vertically confined nature of most rhinestreet concretions their large size oblate ellipsoidal shape variable c isotope compositions and absence of any evidence that concretions were sited at local concentrations of organic matter suggest an origin by anaerobic ch4 oxidation early pre concretion sulfate reduction and associated pyrite framboid formation that occurred throughout the host sediment was renewed in thin shallow zones of uncompacted sediment the concretionary horizons by ch4 and isotopically heavy dissolved carbonate diffusing upward from the zone of biogenic methanogenesis to the base of the sulfate reduction zone probably little more than a meter below the seabed local variations in the mix of isotopically light ch4 and heavier dissolved carbonate may have been responsible for the wide range of 13c isotopic compositions of rhinestreet concretions crucial to this mechanism is a pause in deposition that would have held the zone of carbonate precipitation at a fixed distance below the ocean floor long enough for the large concretions to grow evidence that sedimentation slowed or even stopped during concretion growth includes 1 laminae that can be traced through concretions with no observed systematic changes in thickness and 2 minimal concretion center to edge variations in estimated pre cementation porosity a resumption of sedimentation and related burial brought concretion growth in each horizon to an end the moderately depleted 18o values of rhinestreet concretions probably reflect the resetting of o isotopic compositions by warm fluids migrating through the permeable concretions during burial

organic carbon burial rate and the molybdenum proxy theoretical framework and application to cenomanian turonian oceanic anoxic event 2 1 in this study the controls on organic carbon burial and molybdenum accumulation in ancient strata are investigated through an integration of biogeochemical modeling and data analysis critical aspects of the study are employment of a biogeochemical model for organic matter degradation to explore the controls on pore water sulfide generation and authigenic molybdenum accumulation and use of accumulation rate data for mo oc caco3 fe and ti to reconstruct organic matter remineralization processes the model results form a conceptual framework for the interpretation of primary production estimates and geochemical burial fluxes calculated on the basis of a high resolution orbital timescale for the cenomanian turonian c t oceanic anoxic event 2 interval in the western interior basin the results of this study suggest that the strong correlation between source rock development and intervals of transgression in the geologic record such as the c t could reflect a confluence of biogeochemical processes within sediments that obviates the need for large magnitude changes in primary production levels or oceanographic conditions such as prolonged periods of stable water column stratification

meteoric like fabrics forming in marine waters implications for the use of petrography to identify diagenetic environments petrographic fabrics have long been used to identify meteoric diagenesis of carbonate sediments however on the basis of oxygen isotopic data we document similar fabrics forming in marine pore fluids in the shallow subsurface of great bahama bank therefore petrographic fabrics alone are not reliable indicators of diagenetic environments even for shallow water sediments in our study skeletal grainstones show two distinct diagenetic assemblages either dissolution of aragonitic grains and minimal cementation high permeability intervals or abundant blocky spar cement and neomorphism of aragonitic skeletal grains low permeability intervals these marine burial fabrics are present as shallow as 110 m below sea level well above the aragonite compensation depth a feature that must be considered for models of diagenesis in ancient carbonate sediments marine burial diagenesis may be important in ancient carbonate sediments deposited in moderate water depths or in shallow water during rising sea level where meteoric diagenesis is suppressed

origin of minor limestone shale cycles climatically induced or diagenetic the opinion is widely held that each limestone bed in minor limestone shale cyclic sequences however modified subsequently by diagenesis reflects an environmental event on the assumption that this is true attempts have recently been made to relate limestone shale cycles to climatic variations affected by milankovitch orbital cycles a test is proposed and illustrated mainly with reference to the blue lias formation of dorset england that appears to indicate that many limestones can be produced solely by rhythmic unmixing of caco 3 during diagenesis unless such limestones can be clearly distinguished from those that record genuine environmental signals orbital cycle analysis based on such sequences will give meaningless results

contribution of calcareous nannoplankton to carbonate deposition a new approach applied to the lower jurassic of central italy abstract the upper pliensbachian lower toarcian somma section central italy which displays alternation of limestone marl lithotypes was investigated for its calcareous nannofossil and caco3 contents in order to evaluate the contribution of calcareous phytoplankton to the carbonate fraction of rocks a new method was applied combining a recently developed technique for nannofossil absolute quantification and measurements of nannofossil size our study suggests that nannofossils did not produce the bulk of carbonate mud in the studied section although they contribute to different extents to the pelagic carbonate fraction the contribution of both coccoliths and mainly the incertae sedis schizosphaerella to the carbonate fraction was important only in periods of reduced accumulation rates and or during clay deposition the highest estimated carbonate production by nannofossils in the studied section is around 83 of the total carbonate content but in a sample containing only 12 8 wt caco3 the observed limestone marl alternations therefore result from cyclical export of carbonate mud from the shallow latium abruzzi carbonate platform to the umbria marche basin and only subordinately from changes in nannoplankton productivity

dinoflagellate cyst concentration as an independent reference for monitoring mineral mobilization in stylolites abstract the absolute abundance of dinoflagellate cysts in chalk samples can be used as an independent reference for analysis of mineral mobilization in stylolites the mineralogy of eleven samples from chalks from the dan field danish north sea was studied by electron microscopy bse x ray diffraction and atomic absorbtion spectrometry aas and palynologically using the abundance of dinoflagellate cysts as a reference it can be demonstrated that diagenetic mobilization of pyrite has occurred along stylolites and that primary anomalies in composition have influenced stylolite genesis

albian pelagic rhythms piobbico core abstract the piobbico core of aptian albian pelagic rhythmites in italy has been used to explore ways of extracting quantitative time series of geological chemical physical and biological parameters from stratigraphic sequences recognition of the precession obliquity and eccentricity cycles the option frequencies has permitted time resolution to the 104 year level individually these time series curves furnish a potential basis for precise correlations collectively they track the evolution of the depositional system in detail including its response to orbital forcing orbital cycles primarily influenced oceanic fertility and carbonate productivity by foraminifera and coccoliths as well as the aeration of bottom waters redox cycle three short magnetic reversals occur w thin the ticinella praeticinensis zone frequency spectra of variations in magnetic intensity inclination and declination yield milankovitch frequencies which are only partly explained as responses to mineralogy a computer simulation used berger s astronomically calculate precession index to drive 1 carbonate flux and 2 depth of bioturbation this achieved a stratigraphy remarkably similar to that observed each step in the computer simulation transfers spectral power from precession to eccentricity work on the piobbico core continues while project albicore aims to explore the patterns of rhythmicity in the praeticinensis zone of other areas end page 1164

local and global effects on the early pliocene mediterranean stable isotope records abstract stable isotope analyses of the planktonic foraminifer globigerinoides obliquus from the monte singa section in south calabria italy yielded detailed early pliocene oxygen and carbon records which are directly calibrated to the numerical time scale two major local mediterranean signals are recognized 1 relatively rapid alternations of wet and dry climatic conditions with an average periodicity of 0 02 ma these are considered to reflect fluctuations in precipitation and run off volume 2 superimposed longer term alternations of relatively wetter and relatively drier intervals believed to reflect latitudinal shifts of precipitation zones or intensification of precipitation in an existing zone after an attempt had been made to reduce these local overprints to a minimum the isotope records for the mediterranean were compared with previously published ones from the pacific and atlantic oceans two approximately contemporaneous isotope events were found but in general there is little similarity between the mediterranean and extra mediterranean records therefore our records probably reflect the mediterranean paleoclimatologic and paleoceanographic development rather than global climatic signals

tertiary carbonate dissolution cycles on the sierra leone rise eastern equatorial atlantic ocean abstract most of the tertiary section on sierra leone rise off northwest africa consists of chalk marl and limestone that show cyclic alterations of clay rich and clay poor beds about 20 60 cm thick on the basis of biostratigraphic accumulation rates the cycles in oligocene and miocene chalk have periods which average about 44 000 years and those in eocene siliceous limestone have periods of 4000 27 000 years several sections were sampled in detail to further define the cycles in terms of content of caco 3 clay minerals and relative abundances of calcareous nannofossils extending information gained by analyses of pleistocene cores from the continental margin of northwest africa to the tertiary cycles on sierra leone rise both dilution by noncarbonate material and dissolution of caco 3 could have contributed to the observed relative variations in clay and caco 3 however dissolution of caco 3 as the main cause of the carbonate clay cycles on the sierra leone rise rather than dilution by clay is suggested by the large amount of change several thousand percent in terrigenous influx required to produce the observed variations in amount of clay and by the marked increase in abundance of dissolution resistant discoasters relative to more easily dissolved coccoliths in low carbonate parts of cycles the main cause of dissolution of caco 3 was shoaling of the carbonate compensation depth ccd during the early neogene and climatically induced fluctuations in the thickness of antarctic bottom water

quantification of deep time orbital forcing by average spectral misfit quantification of milankovitch orbital cyclicity within ancient strata has become a principal tool for refinement of the geologic time scale however accurate characterization of the orbital signal in deep time paleoclimate records is commonly challenged by inadequate radiometric time constraints for calibration of the spatial rhythms to temporal periods this problem can potentially introduce large errors into derivative orbital timescales in this study we develop a new method for the identification and calibration of orbital cyclicity in cyclostratigraphic records the method average spectral misfit or asm yields an objective estimate of the optimal sedimentation rate for a stratigraphic interval that preserves a record of orbital forcing the technique also provides a formal statistical test for rejecting the null hypothesis no orbital signal application of the method to assess orbital cyclicity in the upper bridge creek limestone member turonian of the western interior basin highlights the utility of this new cyclostratigraphic tool and provides a means to independently evaluate conflicting interpretations of the lithologic cycles importantly asm offers a new consistent standard by which orbital timescales may be compared hence the quality of an orbital timescale can be formally qualified by reporting its average spectral misfit and null hypothesis significance level this technique will permit improvement of mesozoic cenozoic orbital timescales and extension of orbital time scale development into the paleozoic as the method is not dependent upon well constrained radiometric age data

quantitative variations in the valanginian ammonite fauna of the vocontian basin southeastern france within limestone marl cycles and within parasequence sets abstract the ammonite assemblages between beds and interbeds are examined this quantitative analysis was carried out on limestone marl alternations in the valanginian vergol section drome located in the vocontian basin southeast france there is a strong faunal contrast between beds and interbeds the calcareous beds are characterized by high relative abundances of neocomitids and olcostephanids whereas the marls are marked by a high relative frequency of phylloceratids significant modifications of the composition of ammonite spectra are also observed from the base to the top of some parasequence sets the variations in bathymetry and trophic drifts linked to the climatic fluctuations may have controlled the ammonite assemblages the increase in bathymetry in marls was thus probably beneficial to phylloceratids which are a deep water group the high planktonic production in limestones could explain the great relative abundance of neocomitids and olcostephanids which lived in the upper part of the water column

stable isotopic and carbonate cyclicity in lower cretaceous deep sea sediments dominance of diagenetic effects abstract oxygen and carbon isotopic variability of the dominant m carbonate fraction within bedded organic carbon rich lower cretaceous sediment intervals from various dsdp sites are closely correlated with preservational changes in the carbonates isotopic fluctuations are absent where carbonate contents vary little and where the carbonate fraction is dominated by biogenic phytoplankton remains within each of the studied intervals oxygen and carbon isotopic ratios become increasingly more negative in samples with carbonate contents higher than about 60 in which the proportion of diagenetic microcarbonate increases rapidly carbon isotopic ratios show a trend towards positive values in samples with carbonate contents of less than 40 and strong signs of dissolution the taxonomic composition of nannofossil assemblages varies little within single intervals despite significant differential diagenesis among individual beds this points towards ecological stability of oceanic surface waters during the deposition of alternating beds bedding is however closely related to changing bioturbation intensity indicating repeated fluctuations of the deep water renewal rates and oxygen supply various microbial decomposition processes of organic matter leading to bed specific differential carbonate diagenesis resulted in an amplification of primary bedding features and are considered responsible for most of the observed fluctuations in the stable isotopic ratios and carbonate contents

fluorine mobility during early diagenesis of carbonate sediment an indicator of mineral transformations abstract the abundant occurrence of calcium carbonate minerals in marine sediment their well documented dissolution or precipitation during diagenesis and their high f content suggest that carbonate mineral diagenesis may be an important influence on f behavior in marine sediment to test this hypothesis we have examined the geochemistry of f in shallow carbonate mud bank sediment of florida bay usa the f content of biogenic calcium carbonate in florida bay varies with mineralogy positively correlates with the mg content of calcite and occurs in similar abundance to sr high mg calcite f sr 2 4 mol mol aragonite 0 53 0 79 mol mol low mg calcite 0 22 mol mol models of porewater distributions direct solute flux measurements and reaction rate estimates over the upper 0 16 cm of sediment from bob allen key bank predict net fluxes out of the sediment of 170 mol f m2 d 230 mol sr m2 d and 5 6 mmol ca m2 d the net solute flux ratio of f sr 0 71 mol mol is consistent with dissolution of aragonite or high mg calcite but f ca and sr ca ratios 28 mmol mol and 40 mmol mol respectively are 3 10 that of biogenic carbonate sources selective dissolution of a high f and sr content phase or more likely based on dissolution experiments concurrent dissolution and reprecipitation of phases with different f and sr contents account for this discrepancy the loss of f sr and ca to fluorapatite precipitation as predicted from a stoichiometric model of phosphate release can be added to the transport reaction model predicted net fluxes a resulting more complete mass balance model incorporating both carbonate mineral reactions and fluorapatite formation yields total release estimates of f sr and ca of 770 mol 332 mol and 53 mmol m2 d respectively calcium carbonate minerals apparently undergo transformation whereby 34 mmol high mg calcite m2 d and 19 mmol aragonite m2 d dissolve and 46 mmol low mg calcite m2 d precipitates ignoring other cations besides ca if no fluorapatite formation occurs the required fluxes are that 23 mmol aragonite m2 d dissolves and 3 4 mmol high mg calcite m2 d and 14 mmol low mg calcite m2 d precipitate net loss of caco3 from the deposit by dissolution is 6 7 mmol m2 d 3 of the accumulation flux the magnitude of these fluxes could cause significant mineralogical and chemical changes on rapid time scales in nearshore carbonate sediment fluorine is probably mobile in other carbonate deposits undergoing diagenetic alteration on short and longer time scales and is a powerful additional constraint on the rates and nature of carbonate mineral diagenesis

palaeoclimatic cyclicity in central mediterranean pliocene sediments the mineralogical signal abstract a high resolution x ray mineralogical study of four pliocene sediment sections from the central mediterranean punta piccola sicily monte singa and vrica calabria odp hole 964 a ionian sea shows cyclic opposite abundance variations of two groups of clay minerals the first is dominated by palygorskite and kaolinite whose abundance maxima can be interpreted as resulting from periods of aridity on the african continent allowing their transport as wind blown dust the second is dominated by smectite whose abundance maxima can be interpreted as indicative of periods of abundant rainfall on the mediterranean borderlands these variations in abundance show a 22 ky cyclicity implying a control by the precession of the earth s orbit sapropels and sapropelic layers always occur in the smectite rich beds and therefore appear to have been deposited during the wet periods

climatic forcing of cyclic carbonate sedimentation during the last 5 4 million years along the west florida continental margin abstract ocean drilling project odp hole 625b from 890 m water on the west florida carbonate ramp slope provides a continuous 235 m long record of cyclic sedimentation responding to global climatic change and regional tectonics over the past 5 4 ma relatively rapid sedimentation rates 5 cm 1000 yr and a 30 cm sampling interval 6 10 000 yr permit a high resolution investigation of milankovitch influenced carbonate sedimentation on a continental margin total carbonate percent coarse 63 m and oxygen isotope data exhibit good correlation with established mid and late pleistocene composite records indicating that the climate signal recorded on the west florida slope closely parallels the global climate signal obtained from deep sea sediments a high amplitude low frequency 100k yr eccentricity signal of the past 800k yr is unique within the 5 4 ma record of total carbonate and percent coarse prior to this the data are characterized by lower amplitude variations and less regular periodicities the interval from 0 8 to 2 8 ma consists of low amplitude fluctuations with periodicities widely distributed in the obliquity band 30 60k yr from 2 8 to 5 4 ma the data show larger amplitude aperiodic variations sedimentation from the present to 2 8 ma was controlled primarily by sea level fluctuations associated with changing global ice volumes during periods of lowered sea level fine grained terrigenous sediments from the mississippi and other rivers diluted the end page 1070 indigenous pelagic carbonate sediments of the west florida slope the interval from 0 8 to 2 8 ma differs from the late quaternary in that smaller sea level oscillations and less extensive north american ice sheets resulted in smaller amplitude sediment cycles sediments older than 2 8 ma record aperiodic fluctuations caused perhaps by loop current circulation responding to the final closing of the isthmus of panama between 3 5 and 4 0 ma intensified circulation may have transported and redeposited terrigenous sediments from the mississippi delta fan to the west florida carbonate ramp creating high amplitude but aperiodic sediment cycles this study demonstrates that milankovitch orbital variations can create well developed primary pelagic sedimentary cycles on continental margins and that such cycles are not restricted to the very deep sea the data from odp 625b in conjunction with other contemporaneous cores from contrasting settings provide the opportunity to obtain a quantitative understanding of the interactions between external orbital forcing climate and continental margin sedimentation

recognition of cyclic and non cyclic environmental changes in the mediterranean pliocene a palynological approach the interval between 2 8 and 2 3 ma b p from the south italian singa section has been investigated for its dinoflagellate cyst and sporomorph contents in order to facilitate palaeoenvironmental interpretation the following curves are derived from the data the ratios sporomorphs dinoflagellate cysts protoperidinioid gonyaulacoid dinoflagellate cysts warm cold water indicating dinoflagellate cysts inner neritic oceanic dinoflagellate cysts outer neritic oceanic dinoflagellate cysts and the reworked dinoflagellate cysts per gram of sediment furthermore the already available 18o curve has been used calibration of changes in the sporomorph dinoflagellate ratio against the computed astronomical insolation curve leads to an improved age assessment for the section frequency analysis on the curves shows the 23 41 and 100 ka frequency components to be most important phase and amplitude differences between the filtered 23 41 and 100 ka frequency components are used for environmental interpretation the 23 ka frequency band is best explained by changes in runoff induced transport the 41 ka frequency components are classified in a group with short response time to orbital forcing and a group with longer response time those signals having a short response time are attributed to local precipitation induced changes in runoff those signals having a longer response time are mainly attributed to changes in global temperature and to a lesser extent to changes in global ice volume finally longer term cyclic and non cyclic changes are mainly attributed to temperature and sea level variation

divergent behavior of the swash zone in response to different foreshore slopes and nearshore states abstract ultrasonic distance sensors were used to measure changes in bed elevation to a resolution of 0 1 mm following individual swash excursions in the high tide swash zone of an intermediate foreshore changes in bed elevation are related to depth averaged eularian swash velocities estimated by assuming mass balance of the swash discharge also measured using the ultrasonic distance sensors early in the study may 21 25 2008 the alongshore uniform foreshore had a cross shore slope of 0 18 and was fronted by a nearshore bar that forced wave breaking at low tide towards the end of the study june 5 9 2008 the foreshore had a slope of 0 12 and was fronted by a nearshore terrace that developed as the innermost bar migrated landward despite similar inshore wave heights and periods during these times the steeper foreshore eroded by 0 69 m 3 m 1 while the more gently sloped foreshore accreted by 0 21 m 3 m 1 the divergent behavior of the swash zone is attributed to the welding of the innermost bar to the foreshore creating a shallow nearshore terrace that saturated the inshore wave field this in turn led to a faster uprush velocity that promoted the landward advection of sediment picked up over the shallow terrace it is argued that accretion in the upper swash zone was the result of a larger supply of sediment at the base of the foreshore and a transformation of the wave field by the shallower depths of the welded feature in this respect swash hydrodynamics and morphological change can only be made if the swash zone is considered within the context of the broader nearshore state

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

the significance of palynofacies fluctuations in the greenhorn formation cenomanian turonian of the western interior basin usa abstract in the greenhorn limestone formation of the pueblo section colorado the palynofacies in the hartland shale member is remarkably homogeneous this is in marked contrast to that of the overlying bridge creek limestone member in which the alternating limestones and marlstones are characterized by rhythmic variations in the terrestrial phytoclasts such variations appear to be related to milankovitch cycles as well as to both the dilution and productivity models the marine palynofacies includes three dinocyst associations and scytinascia foraminiferal linings changes in the marine palynofacies do not appear to be related to the cyclical limestone marlstone deposits however the alternating dinocyst associations suggest mesotrophic oligotrophic rhythms in the surface waters the discrepancy between the dinocyst cycles and the lithological couplets could reflect the modulation of the sea level rises in the milankovitch frequency band by a barrier during deposition of the hartland shale member within the second order t6 transgression of kauffman the discrepancies between the foraminifer nannofossil and dinocyst fluctuations are interpreted as reflecting specific responses by each planktic group to global oceanographic changes and diagenesis

completing the neogene geological time scale between 8 5 and 12 5 ma a much improved high resolution magnetostratigraphy is presented for the interval between 8 5 and 12 5 ma in the deep marine astronomically tuned monte dei corvi beach section in northern italy this section contains the formally designated boundary between the middle and upper miocene defined by the tortonian gssp the natural remanent magnetization is carried by an unusual low temperature component of primary origin according to interpretations of isothermal remanent magnetization irm acquisition curves the palaeomagnetic signal is most probably carried by iron sulphides such as greigite or pyrrhotite the resultant magnetostratigraphy is reliable and can be straightforwardly calibrated to the astronomically tuned neogene time scale atnts2004 showing that the section ranges from chron c5an 2n up to c4 2r 1 the inferred correlation of the tortonian gssp to the older part of chron c5r 2n is confirmed thereby guaranteeing global correlation potential in addition the monte dei corvi beach section has been re tuned to the new numerical solution la2004 for the interval between 8 5 and 12 9 ma this exercise shows that the characteristic cycle patterns are not consistent with a single solution with fixed values for dynamical ellipticity and tidal dissipation for the younger part of the section sedimentary cycles show an excellent fit with intricate details of precession obliquity interference in the nominal la2004 1 1 solution however this solution produces serious mismatches between the sedimentary cycles and the precession obliquity interference in the interval older than 10 2 ma for this interval changes in tidal dissipation value while keeping dynamical ellipticity constant at its present day value are necessary to maintain a perfect fit a detailed visual comparison reveals a very good to excellent fit with la2004 1 1 2 and to lesser extent with la2004 1 0 5 however la2004 1 1 2 is the preferred tuning target for the moment in the interval older than 10 2 ma the astronomical re tuning on precessional scale to la2004 1 1 yielded slightly different astronomical ages for each basic cycle and hence also for the calcareous plankton events and magnetic reversal boundaries with uncertainties ranging within a few thousand years the age of the tortonian gssp turns into 11 625 ma instead of the previously published 11 608 ma our ages should replace existing ages in the astronomically tuned neogene time scale atnts2004

lower cretaceous stage durations combining radiometric data and orbital chronology towards a more stable relative time scale abstract we propose an alternative calibration of lower cretaceous stage durations constrained by direct absolute dating of each stage combined with orbital chronology ten glauconitic horizons sampled in the vocontian basin se france from the base of the lower hauterivian to upper albian yielded k ar ages from 123 3 1 7 ma to 96 9 1 4 ma respectively the relative duration of each stage has been derived by cyclostratigraphy previously obtained in the south east france and central and south italy basins using the gl o standard from the albian cenomanian boundary at 95 3 ma as the anchor point a cyclostratigraphic age for each stage boundaries has been extrapolated and thus compared with the k ar ages this shows a very well defined linear correlation which demonstrates the robustness of the proposed durations of the lower cretaceous stages the estimated durations are 5 3 0 4 my 5 1 0 3 my 6 8 0 4 my and 11 6 0 2 my for the hauterivian barremian aptian and albian stages respectively it also shows that glauconite minerals are powerful radiochronometric tools when precisely stratigraphically defined and carefully selected moreover the large discrepancy of the estimated aptian duration of more than 6 my between the most recent published time scale and this study highlights the problem of the radiometric calibration of the m 0 magnetic chron finally the stage durations and boundary ages proposed here bring strong constraints towards the calibration of the lower cretaceous time scale such accurate temporal calibration is required before any relationship between major biological crises and magmatic emplacement for instance could be further investigated

late quaternary variability of ocean circulation in the southeastern south atlantic inferred from the terrigenous sediment record of a drift deposit in the southern cape basin odp site 1089 during leg 177 of the ocean drilling program an expanded sequence of pliocene to holocene calcareous muds was recovered at site 1089 on a drift deposit in the southern cape basin se south atlantic the reconstruction of detrital sources and modes of sediment transport gives insight into the operational modes of regional current systems in response to climate variability over the last 590 kyr as inferred from sedimentological and mineralogical parameters of the terrigenous sediment fraction terrigenous sediments mainly originate from african sources with minor contributions from distant southern sources south america and antarctica and are supplied by circumpolar water masses north atlantic deep water nadw and surface currents of the agulhas current changes in clay mineralogy as tracers of deep and shallow ocean circulation best displayed by variations in quartz feldspar ratios and kaolinite chlorite ratios of clay reflect both the northward displacement of nadw injection into the antarctic circumpolar current and a weakening of agulhas current leakage from the indian ocean around south africa to the south atlantic during glacial stages sub stages and stadials modifications of these regional current patterns are consistent with perturbations in global conveyor circulation and climate variability on milankovitch and sub milankovitch time scales elevated mass accumulation rates of terrigenous matter generally document high particle fluxes and focusing effects by bottom current action throughout the late quaternary current sorting and coarsening of terrigenous mud independently of its source signals prevails during interglacial periods and is linked to a stronger flow of antarctic bottom water and the invigoration of deep contour currents in response to long term changes 100 kyr cyclicity in antarctic ice sheet dynamics high amplitude fluctuations in global sea level and increased bottom water formation

an assessment of the suitability of individual rhythmic carbonate successions for astrochronological application abstract a manual is presented to assist in assessing the suitability of individual calcareous rhythmites for high resolution stratigraphic applications and orbital dating while the astrochronological approach offers an unprecedented high temporal resolution for stratigraphy caution is required to carefully choose suitable rhythmites for the analysis diagenesis is known to distort or mimic primary signals in particular in carbonate rhythmites to keep orbital dating a reliable method the choice of sedimentary successions has to be undertaken with utmost scrutiny here we review and evaluate the methods that have been used for assessing the record of primary signals in calcareous rhythmites the goal is to provide the orbital stratigrapher with tools for a straightforward and systematic assessment of such successions

differential diagenesis of sedimentary components and the implication for strontium isotope analysis of carbonate rocks geochemical analyses of various components foraminifera coccoliths and siliciclastic fractions of limestone and marl samples from the marine trubi formation early pliocene of southern italy revealed subtle diagenetic contamination the coccolith fraction is altered from its original value both in its trace element sr rca mgrca ferca mnrca narca all

unit stratotypes for global stages the neogene perspective abstract recent developments in integrated high resolution stratigraphy and astronomical tuning of continuous deep marine successions invalidate arguments against the designation of unit stratotypes for global stages the basic building blocks of the standard global chronostratigraphic scale gcs for the late neogene global stratotype section and point gssp sections may also serve as unit stratotypes covering the interval from the base of a stage up to the level that time stratigraphically correlates with the base of the next younger stage in a continuous and well tuned deep marine succession the added value of such sections as unit stratotype lies in the integrated high resolution stratigraphy and astronomical tuning which combined provides an excellent age control with an unprecedented resolution precision and accuracy within the entire stage as such they form the backbone of the new integrated late neogene time scale and provide the basis for reconstructing earth s history in this way a stage is also defined by its content and not only by its boundaries our unit stratotype concept strengthens the importance of time rock units by allowing the introduction of astronomically defined chronozones as formal chronostratigraphic units thereby arguing against the elimination of the dual classification of chronostratigraphy and geochronology extending this concept to older time intervals requires that well tuned continuous deep marine sections are employed thus necessitating the employment of multiple hole i odp sites for defining remaining stages and stage boundaries in at least the cenozoic and cretaceous and possibly the entire mesozoic evidently the construction of the geological time scale including the gcs should be based on the most appropriate sections available while where possible taking the historical concept of global stages into account

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

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

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

multiproxy approach to understanding the origin of cretaceous pelagic limestone marl alternations dsdp site 391 blake bahama basin limestone marl alternations are usually directly interpreted to reflect cyclic palaeoenvironmental signals however uncertainty in such interpretations stems from the differential diagenesis that most limestone marl alternations have undergone differential diagenesis results in markedly different alterations between limestones and marls and in the loss of comparability of many measurable parameters for an unequivocal interpretation of the origin of rhythmic alternations diagenetically robust parameters or parameters that clearly indicate the degree of diagenetic bias are required the present study uses a multiproxy approach independent biotic sedimentary and geochemical parameters in order to unravel the palaeoenvironmental signal recorded in valanginian early cretaceous limestone marl alternations from the blake bahama basin dsdp site 391 using this approach terrestrial and marine influences can be distinguished changes in nutrient levels estimated and prediagenetic differences in the non carbonate fraction constrained surprisingly no systematic variations in any of these parameters were observed between limestone and marl layers implying that none of these was directly responsible for the formation of the rhythmic alternation hence none of the current models of sedimentary formation of limestone marl rhythmites is applicable here calcareous nannofossils are equally well preserved in limestone and marl layers ruling out their dissolution in marl layers as a source of the calcite cement in the limestone beds sr values of 700 900 p p m indicate that aragonite may have been present in the original pelagic sediment the assumption of fine grained sedimentary aragonite imported from nearby carbonate platforms as the source of the cement would explain a number of otherwise enigmatic features in these rhythmites including the source of the calcite cement observed in the limestones the equally good preservation of calcareous nannofossils in limestones and marls and the higher concentration of calcareous nannofossils in marl layers the study demonstrates that examination of diagenetically inert parameters or parameters in which diagenetic effects can be filtered can yield unexpected results clearly careful analysis of such parameters needs to be undertaken in order to make reliable palaeoenvironmental interpretations from rhythmite successions

discussion of placed rock as protection against erosion by flow down steep slopes by w l peirson j figlus s e pells and r j cox

shallow water aragonite recorded in bundles of limestone marl alternations the upper jurassic of sw germany abstract characteristically limestone marl alternations are conspicuous in outcrop because of differential weathering the marls being predisposed to stronger deterioration superimposed on the bedding rhythms are in many cases lower frequency meter scale rhythms so called bundles these bundles are eye catching from a distance and are typified by variations in thickness of limestone beds and marl interbeds the palaeoenvironmental significance of the bundles received markedly less attention in the literature than the origin of the small scale couplets here we focus on the palaeoenvironmental significance of the bundles by reconstructing the initial mineralogical composition as an example we present a classical limestone marl alternation from the upper jurassic oxfordian kimmeridgian of sw germany that is typified by two orders of bundles superimposed on the limestone marl couplets our method of reconstruction of the original mineralogical composition of the precursor sediment of limestone marl alternations is based on a diagenesis model that assumes dissolution of aragonite and reprecipitation as calcite cement as the major mechanism of early diagenesis calculated initial clay aragonite and calcite contents show rhythmic variations on a scale of several meters that correspond to the bundles as seen in the outcrop limestone dominated parts of the bundles correspond to intervals of elevated aragonite content in the precursor sediment but not necessarily to elevated calcite contents additionally an overlain fluctuation in initial mineralogy on the order of tens of meters mega bundles reflecting the former local subdivision of the sw german upper jurassic into weisjura alpha beta and gamma is observed the limestone dominated weisjura beta lower kimmeridgian is the interval with highest initial aragonite content our new method allows for quantification of initial mineralogical composition as aragonite and calcite usually have different sources shallow water benthic versus planktic this approach potentially adds significant new possibilities for palaeoceanographic interpretation of calcareous rhythmites in the jurassic example the observed variations in reconstructed aragonite content are interpreted as variations in flooding events and related export of aragonitic material from marginal shallow water platforms

round shaped riprap stabilization in overtopping flow a series of 26 tests was performed on a riprap layer in which median round shaped stones ranging from 32 3 to 99 1 mm from 1 27 to 3 90 in were subjected to overtopping flow conditions embankment slopes range from 10 to 45 with median stone sizes ranging from 23 9 to 104 2 mm from 0 94 to 4 1 in the database was analyzed yielding a unique expression in which the median size of a round shaped stone can be predicted as a function of the unit discharge embankment slope and coefficient of uniformity it was determined that the requisite round shaped stones range from 5 to 42 larger than angular stones to stabilize the riprap layer for similar flow conditions with unit flows of 0 2 cm s and slopes of 40 the maximum deviation between rounded and angular shaped stone may approach 70 as flow and bed conditions are extrapolated

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 origin of rhythmic bedding in the pliocene trubi formation of sicily southern italy abstract foraminiferal palynological stable isotope geochemical clay mineralogical and granulometric data have been gathered for the successive layers of four rhythmic alterations of relatively carbonate poor and carbonate rich beds in the early pliocene trubi formation of sicily southern italy the marly rhythmites consist of a grey layer and a white more indurated layer in which an additional beige less indurated layer is intercalated they are therefore more complex than the well known marl limestone couples elsewhere these rhythmites probably originate from the alternate predominance of increased dilution of river supplied terrigenous material grey and decreased carbonate production in the surface waters beige the grey layers are considered to correspond to periods of increased local run off and higher surface water temperatures and productivity the beige layers signal more arid and cooler climatic conditions lower surface water productivity and stronger or more frequent dust loaded southern winds the white layers apparently reflect intermediate climatic and environmental conditions these periodical changes probably brought about by astronomical precession appear to have occurred not only during the pliocene but also during the late miocene

microspar development during early marine burial diagenesis a comparison of pliocene carbonates from the bahamas with silurian limestones from gotland sweden comparison of ultrastructures in pliocene periplatform carbonates from the bahamas with silurian limestones from gotland sweden reveals that despite the differences in primary sediment composition and age they reflect a similar mechanism of lithification in both sequences calcite microspar was formed as a primary cement at an early stage of marine burial diagenesis neither significant compression nor meteoric influence are necessary for the formation of calcite microspar a model is proposed for the process of microsparitic cementation of fine grained aragonite needle muds comprising four stages 1 unconsolidated aragonite dominated carbonate mud 2 precipitation of microspar that engulfs aragonite needles 3 dissolution of aragonite resulting in pitted surfaces of the microspar crystals and 4 slight recrystallization our results contradict the widespread opinion that microspar necessarily is a product of secondary recrystallization of a previously lithified micrite

rare earth elements in limestone marlstone couplets from the albian cenomanian cismon section venetian region northern italy assessing ree sensitivity to environmental changes abstract we have studied the ree distribution through the albian cenomanian interval of a stratigraphic succession cismon section scaglia variegata formation venetian prealps consisting of rhythmically alternating carbonate rich and carbonate poor strata which are the sedimentary expression of systematic variations of surface fertility and bottom water redox conditions in the depositional basin limestone semicouplets show seawater like shale normalized patterns hree enriched with negative ce anomalies and high er nd ratios indicating a clear dependence on the ree chemistry of surface seawaters marlstones and shales exhibit flatter patterns more moderate ce anomalies and low er nd good correlations between er nd ce ce and mn suggest that superimposed on ree signatures imparted by detrital and biogenic phases the ree composition shows evidence of their sensitivity to palaeoredox conditions resulting in ree fractionation and ce cycling ree data are consistent with results from previous stratigraphic and geochemical major and trace elements investigations in reflecting palaeoenvironmental conditions rhythmically varying from efficiently mixed seawater during the limestone deposition to oxygen depleted bottom waters at the time of marlstone deposition

riprap design for overtopping flow near prototype flume studies were conducted in which riprap protected embankments were subjected to overtopping flows embankment slopes of 1 2 8 10 and 20 were covered with riprap layers with median stone sizes of 1 2 4 5 and or 6 in each riprap layer was tested by slowly increasing the discharge to failure riprap design criteria for overtopping flows were developed for estimating incipient stone movement and riprap layer failure as a function of the unit discharge stone shape median stone size and embankment slope incipient stone movement occurred at approximately 74 of the riprap layer failure unit discharge it was determined that rounded shape stone should be oversized approximately 40 to provide comparable protection of an angular shape stone flow channelization was observed to occur at approximately 88 of the unit discharge at failure a flow concentration factor of approximately 1 to 3 was introduced for sizing stone

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

rare earth elements in pore waters of marine sediments abstract the rare earth elements rees were measured in pore waters of the upper 25 cm of sediment from one site off peru and three sites on the california margin the pore water ree concentrations are higher than sea water and show systematic down core variations in both concentration and normalized pattern from these analyses and from comparison to other chemical species measured dissolved fe mn ba oxygen nitrate phosphate it is suggested that pore water rees can be grouped into three categories those that are from an fe source those that are from a poc source and cerium oxide rees from the fe source appear where anoxia is reached they have a distinctive middle ree mree enriched pattern the concentrations in this source are so elevated that they dominate ree trends in the fe oxide reduction zone the net result of flux from the poc source is relative enrichment of heavy rees hrees over light rees lrees reflecting remineralizing poc and complexation with doc a common linear ree pattern seen in both oxic and anoxic sediments is associated with this poc source as well as a hree enriched pattern that is seen in surficial sediments at the peru site overall the pore water results indicate that mn oxides are not an important carrier of rees in the oceans a ree biogeochemical model is presented which attempts to reconcile ree behavior in the water and sediment columns of the oceans the model proposes that poc fe oxide and ce oxide sources can explain the ree concentration profiles and relative abundance patterns in environments ranging from oxic sea water to anoxic pore water the model is also consistent with our observation that the ce anomaly of pore water does not exceed unity under any redox condition

roughness of loose rock riprap on steep slopes a study was conducted to determine the roughness of rock riprap laid on steep slopes tests were conducted in a 1 07 m wide flume and two 2 74 m wide field scale structures using angular riprap with median diameters d50 ranging from 52 to 278 mm and bed slopes s0 ranging from 0 028 to 0 333 m m empirical relationships were developed to predict the manning roughness coefficient as a function of d50 and s0 the darcy weisbach friction factor was predicted as a function of d d84 the relative submergence newly developed equations are applicable for riprap placed on slopes from 2 8 33 roughness coefficients calculated using the developed equations were compared with roughness coefficients calculated using equations developed from observations on natural mountain streams

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

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

discussion of round shaped riprap stabilization in overtopping flow by steven r abt christopher i thornton humberto a gallegos and craig m ullmann

differential diagenesis of rhythmic limestone alternations supported by palynological evidence alternating cemented and uncemented fine grained layers from pliocene periplatform carbonates of the great bahama bank have fundamentally different diagenetic features the cemented layers consist predominantly of microspar interpreted as an early marine shallow burial cement the intercalated uncemented softer layers are devoid of microspar cement and exhibit signs of mechanical compac tion precursor sediments of both cemented and uncemented layers apparently consisted largely of aragonite needles the needles in the compacted layers show signs of dissolution suggesting that the calcium carbonate required for cementation of the uncompacted layers was provided by aragonite dissolution within the compacted layers the lack of compaction in the cemented layers shows that cementation and hence aragonite dissolution in the adjacent compacted layers took place in the shallow burial realm the dissolved carbonate was trans ported by diffusion to adjacent layers and reprecipitated as calcite cement thereby preventing significant compaction of these layers these processes are not yet complete in the material examined and some aragonite remains in the compacted layers the sedimentary composition of the two rock types compacted and uncompacted is similar indicating a similar precursor sediment for both between 1 5 and 7 times the concentration of palynomorphs oc curs in the compacted layers apparently the result of passive diage netic enrichment although the trigger for diagenetic differentiation has not been determined the pure limestone succession studied here appears to serve as a clay free analog to limestone marl alternations

cyclostratigraphic analysis of pelagic carbonates at monte dei corvi ancona italy and astronomical correlation of the serravallian tortonian boundary cyclostratigraphic analysis of pelagic carbonates at monte dei corvi ancona italy and astronomical correlation of the serravallian tortonian boundary spectral analysis of high resolution calcium carbonate data from a 2 m y long section from the upper miocene pelagic limestone marl sequence at monte dei corvi italy indicates orbital forcing of depositional cycles at frequencies corresponding to eccentricity obliquity and precessional cycles identification of these milankovitch cycles dated by 4 0 ar 3 9 ar ages from two biotite rich volcanic ash layers within the section allows us to correlate this section with the astronomical time scale by matching low frequency variations in calcium carbonate content with the orbital eccentricity this correlation yields precise numerical ages for any stratigraphic level within the analyzed section including the two volcanic ash layers and the serravallian tortonian boundary dated here as 11 32 ma the eccentricity based correlation also allows us to tune the data resulting in enhanced power in the obliquity and precessional frequencies supporting the initial hypothesis of orbital control of these lithologic cycles

limestone marl alternations as environmental archives and the role of early diagenesis a critical review limestone marl alternations and other micritic calcareous rhythmites have long appealed to sedimentologists as they appeared to directly reflect high frequency environmental change in particular when orbital forcing gained popularity amongst sedimentologists and paleoclimatologists in 1980s such rhythmites seemed to offer an ideal tool for high resolution chronostratigraphy and environmental reconstruction however in spite of the fact that orbital forcing has become a routine interpretation of calcareous rhythmites and that the processes of formation of calcareous rhythmites are considered well understood research in the past 10 years again has questioned their primary origin and their direct interpretability detailed petrographic paleontological and geochemical data from numerous successions through geological time provided the basis for testing whether or not the regular alternation of limestone beds and marl or shale interlayers represents bimodally fluctuating environmental conditions in a direct way in particular these data supplemented by box model simulations imply that post depositional alteration diagenesis has the potential to not only seriously distort primary environmental signals but also to mimic primary signals this questions the use of micritic calcareous rhythmites for high resolution chronostratigraphy and for environmental interpretations where independent data of diagenetically inert parameters are not available diagenetic changes appear to have a yet widely underestimated influence on the appearance of limestone marl alternations and other calcareous rhythmites the aim of the present review is to summarize new approaches and give an overview of our research results in this field of the past decade this review also aims at pointing to still enigmatic aspects that need to be addressed before the interpretation of micritic calcareous rhythmites can be considered a reliable tool for high resolution chronostratigraphy and paleoenvironmental interpretation

the mineralogical composition of precursor sediments of calcareous rhythmites a new approach previous studies in silurian carbonates from gotland sweden have led to a model for the development of limestone marl alternations this model postulates that early diagenesis of precursor sediments without strong primary differences can result in a differentiation by selective dissolution of aragonite in marl beds and reprecipitation of calcite cement in limestone beds this model is described as a set of mathematical equations that quantify the diagenetic processes aragonite dissolution and calcite reprecipitation that occur during the formation of limestone marl interbeds from a hypothetical homogeneous precursor sediment the calculations demonstrate that resulting hypothetical limestone marl alternations show characteristic mathematical relationships between the ratios of the bed thicknesses of limestones and marls on one side and the carbonate contents on the other by reversing this model the original mineralogical composition of the precursor sediment of real world rhythmic successions can be determined in this study alternations from the silurian of gotland the cambrian devonian and mississippian of north america the jurassic of france and germany and the cretaceous of france are shown to exhibit mathematical relationships similar to those calculated for hypothetical precursor sediments without primary differences therefore the mineralogical composition of their precursor sediments can be estimated in contrast the clear mismatch shown by the lower jurassic belemnite marls from dorset indicates that these rhythms did not suffer an early diagenetic overprint our model helps to differentiate between rhythmites with strong depositional variations and those without however it cannot indicate whether a given alternation is the product of rhythmic diagenesis of a homogeneous precursor sediment or the result of diagenetic enhancement of subtle underlying sedimentary rhythms for horizontally correlated patterns such as laterally extensive beds and layers of nodules an a priori unknown external signal has to be assumed

sub milankovitch and milankovitch forcing on a model mesozoic carbonate platform the latemar middle triassic italy basic shallowing upward cycles shu cycles and five bundled megacycles in the latemar platform have been widely regarded as a model example for precessional and eccentricity forcing in the mesozoic based on bio chronostratigraphic data recent studies questioned this particular type of milankovitch forcing on the latemar cyclic series we present an integrated model that incorporates i new cyclostratigraphic data ii new and existing bio chronostratigraphic data and iii new spectral analyses the basic shu cycles in the latemar reflect sub milankovitch control cycle bundles of 1 4 5 megacycles shu cycles indicate precessional forcing they do not reflect eccentricity superimposed on precessional forcing spectral analyses reveal highly significant ratios in the large scale cycle bundlings stacking patterns of 1 9 9 and 1 24 0 shu cycles represent obliquity and short eccentricity forcing both sub milankovitch and milankovitch forcing potentially controlled shallow subtidal carbonate deposition in mesozoic greenhouse times cyclostratigraphic models require an integrated approach including bio and chronostratigraphic data

required but disguised environmental signals in limestone marl alternations the nature of rhythmic carbonate rich successions such as limestone marl alternations has been and still is subject to controversy the possibility of an entirely diagenetic origin for the rhythmic calcareous alternations is discarded by most authors one problem with an entirely diagenetic self organized development of limestone marl alternations is the fact that limestone and marl beds in many examples are laterally continuous over hundreds of meters or even kilometers in an entirely self organized system lateral coupling would be very limited thus one would expect that rather than laterally continuous beds randomly distributed elongate nodules would form we address the origin of limestone marl alternations using a computer model that simulates differential diagenesis of rhythmic calcareous successions the setup uses a cellular automaton model to test whether laterally extensive rhythmic calcareous alternations could develop from homogeneous sediments in a process of self organization our model is a strong simplification of early diagenesis in fine grained partly calcareous sediments it includes the relevant key mechanisms to the question whether an external trigger is required in order to obtain laterally extensive limestone marl alternations our model shows that diagenetic self organization alone is not sufficient to produce laterally extensive correlatable beds although an external control on bedding formation could be considered to have solved the problem as commonly assumed we here suggest an interesting third possibility the rhythmic alternations were formed through the interaction of both an external trigger and diagenetic self organization in particular we observe that a very limited external trigger either in time or amplitude readily forms correlatable beds in our otherwise diagenetic model remarkably the resulting rhythmites often do not mirror the external trigger in a one to one fashion and may differ in phase frequency and number of couplets therefore the interpretation of calcareous rhythmites as a one to one archive of climate fluctuations may be misleading parameters independent of diagenetic alteration should be considered for unequivocal interpretation

inorganic geochemistry of albian sediments from the lower saxony basin nw germany palaeoenvironmental constraints and orbital cycles abstract within the international albicore project upper albian sediments from a 245 m core kirchrode i drilled in hannover were studied by inorganic geochemical methods more than 650 samples minimum sample spacing 0 5 m were analysed for major and minor element concentrations this chemical database was used to reconstruct the depositional environment and to investigate the influence of high frequency milankovitch cycles on the chemical composition of the sediments the chemical composition of the sedimentary sequence is primarily controlled by variations in carbonate content corresponding to ca al ratios variations in both ti al and si al ratios are interpreted as fluctuations in detrital composition resulting from increases in smectite and quartz content in the upper section of the core high amounts of reactive iron but low pyrite concentrations the lack of enrichment of redox sensitive trace elements v cr and high mn concentrations indicate oxic bottom water conditions and the absence of an oxygen minimum zone for the upper albian at the kirchrode site the nutrient related trace elements ba p zn suggest a generally oligotrophic setting with slightly elevated productivity only in the uppermost upper albian only one layer was identified as containing volcanogenic material at 87 20 m this layer is characterised by elevated montmorillonite zr and nb mass balance calculations for the entire core suggest that the high mn values cannot be explained by riverine input alone therefore a coastal oxygen minimum zone south of the kirchrode site is postulated as an additional mn source cyclic variations in both carbonate content and al normalised concentrations of predominantly detrital elements like si and ti are seen in a 60 m interval 40 100 m where sedimentological palaeontological and geochemical data suggest stable depositional conditions although carbonate cyclicity cyclicity in detrital input and nutrient related element abundances do not correlate with each other three strong peaks in the results of spectral analysis of these chemical data for this interval appear to correspond to milankovitch frequencies in the eccentricity obliquity and precession bands

sedimentary vs diagenetic control on rhythmic calcareous successions pliensbachian of asturias spain the diagenetic overprint in rhythmic hemipelagic successions can either enhance or change the original distribution of caco3 but it is difficult to evaluate its effect because in most field examples it is not possible to distinguish between sedimentary and diagenetic features the rhythmic succession of the pliensbachian of asturias spain shows alternation of bioclastic and laminated burrowed intervals the original content of carbonate brought by storms from shallow areas was larger in the bioclastic horizons however there is a widespread mismatch between facies alternations and the observed lithological rhythms the diagenetic redistribution of caco3 resulted in successive limestone marl clay couplets that do not match either in number or in the location of the boundaries the sedimentary cycles defined by facies alternations we conclude that interpreting the limestone marl rhythms as a direct response to primary changes is highly questionable unless there is unequivocal proof of a sedimentary origin of the alternation of the two lithologies

sedimentation cycles and their diagenesis on the slope of a miocene carbonate ramp bahamas odp leg 166 numerous small scale depositional cycles are present in the miocene sediments of seismic sequence m along the margin of great bahama bank odp leg 166 these cycles consist of decimetre to metre scale alternations between light grey and dark grey black wackestones packstones the light grey layers are well cemented and nearly uncompacted they contain planktonic and benthic foraminifera and bioclasts bioturbation in these layers is moderate the dark grey wackestones packstones are uncemented strongly compacted and normally strongly bioturbated the main components are planktonic foraminifera and fine grained bioclasts the dark layers are rich in aragonite and organic carbon and contain around 80 carbonate the light layers show low aragonite and organic carbon contents combined with carbonate values of up to 97 5 light 13c and slightly negative 18o values were observed in the dark uncemented layers while the cemented intervals show heavy 13c values and slightly more positive 18o values the carbon isotope signal between the dark and the light layers shows variations of up to 1 45 both 13c and 18o co vary with carbonate content the formation microscanner images reflect the changes in carbonate mineralogy the natural gamma ray tool shows that variations in siliciclastic content of the examined succession displays a different frequency than the cyclic alternations in carbonate mineralogy the internal stacking pattern of the cycles is closely tied to sea level the dark layers are deposited during rising sea level while the light layers reflect sediment production and export during highstand and falling sea level these cycles thus represent a rather continuous sediment shedding pattern that is clearly related to the ramp morphology and differs from the highstand shedding pattern typical for rimmed flat topped platforms most measured parameters suggest that primary sediment composition played an important role in the cementation process the primary differences in composition were enhanced during shallow burial diagenesis the initially high content of metastable carbonate phases in the periplatform sediments triggered rapid cementation of the primary aragonite rich layers leading to the formation of the light beds dissolution of metastable high mg calcite and aragonite was followed by in situ precipitation of more stable dolomite and calcite diagenesis was enhanced by the coarse grain size of the primary aragonite rich layers in contrast the more pelagic dark calcite rich layers were only slightly affected by diagenesis and could preserve their aragonite content the uncemented layers subsequently were subject to strong mechanical compaction whereas the cemented beds stayed nearly uncompacted

paleocene cyclic sedimentation in the western north atlantic odp site 1051 blake nose upper paleocene zone cp8b cyclic sediment from ocean drilling program odp site 1051 on blake nose western north atlantic alternates from white carbonate rich to green carbonate poor in response to precessional forcing compositional differences between the two bed types are minor mineral and nannofossil composition of the beds vary subtly but grain size of the terrigenous component and biogenic silica content remain constant iron content determined by sediment magnetic susceptibility and iron intensity determined by a core scanning xrf correlates negatively with carbonate content and are higher in green beds kaolinite content of green beds is slightly higher as well green beds exhibit lower evenness values than white beds for nannofossil assemblages and are more dominated by the species coccolithus dominance by coccolithus indicates more mesotrophic conditions over blake nose during deposition of the green beds which correlates with slightly higher iron and kaolinite contents the absence of change in terrigenous grain size and the absence of any indication of planktonic blooms indicate that there was a minor most likely eolian input of iron and kaolinite during deposition of the green beds the source area was most likely northwest africa which supplied iron and kaolinite when source areas deflated under drier conditions with this scenario kaolinite is an indi cator of drier climate and source area erosion rather than the warmer and or wetter conditions under which it forms in soils during precessional minima or perihelion summer the opposite of our current configuration there was an increased range of seasonal temperatures and an increase in the intensity of summer and winter monsoon circulation as a consequence there was more rainfall in northern africa and drier conditions in the continental interiors at mid latitudes green bed deposition occurred during precessional maxima when the north atlantic was cooler northwest africa drier and the eolian flux to the western north atlantic slightly increased

reconstructing nutricline dynamics of mid cretaceous oceans evidence from calcareous nannofossils from the niveau paquier black shale se france abstract a high resolution calcareous nannofossil record is presented from the lower albian niveau paquier black shale from the vocontian basin se france the niveau paquier black shale represents the regional equivalent of the supraregionally distributed oceanic anoxic event 1b oae 1b to reconstruct surface water fertility a nutrient index based on zeugrhabdotus erectus discorhabdus rotatorius high fertility indicators and watznaueria barnesae low fertility indicator was established using principal component analysis in addition the distribution of nannoconus spp and absolute abundances of coccoliths coccoliths per gram were used for reconstructing nutricline dynamics of the surface waters high surface water fertility coincides with low percentages of nannoconids and vice versa moreover high percentages of nannoconids correlate with low absolute abundances of all other coccoliths based on the observed nannoplankton distribution pattern and a suggested similarity in ecological requirements between nannoconids and the modern taxon florisphaera profunda a model is proposed that couples nannoconid abundances with dynamics of the nutricline time series analyses of the nutrient index show fluctuations within the precessional band the precession controlled fluctuations of the surface water fertility may represent a monsoonal signal with the nutrient supply in the surface waters depending on the strength of monsoonal activity during periods of enhanced monsoonal activity which were characterized by humid conditions and stronger winds mixing of the upper water column was enhanced during that time the abundance of nannoconids decreased as a consequence of enhanced wind stress that improved vertical mixing and led to an entrainment of nutrients into the surface waters this resulted in an increase of primary production during periods of reduced monsoonal activity marked by drier conditions and reduced wind stress the surface waters were depleted in nutrients as a result of a deep nutricline and a reduced nutrient supply to the upper photic zone in a stratified water column percentages of nannoconids increased according to the mechanisms outlined above fluctuations of the nutrient index and nannoconid percentages have been used as a proxy for reconstructing the physical structure of mid cretaceous oceans steered by precession forced monsoonal activity the results of the study show that the formation of the lower albian oae 1b from the vocontian basin occurred under strongly fluctuating surface waters fertility

cyclostratigraphy and the early jurassic timescale data from the belemnite marls dorset southern england time series based on determinations wt of calcium carbonate and total organic carbon have been generated for the entire lower jurassic hemipelagic belemnite marls dorset southern britain this formation was deposited during early pliensbachian time at a paleolatitude of about 35 n in an epicontinental sea that was largely enclosed by the supercontinent of pangea the sequence contains compositionally diverse light and dark marl bedding couplets the thicknesses of which are notably reduced in the upper third of the section the regularity of the couplets in segments of the sequence combined with a regular amplitude modulation indicates an origin that is related to the orbital precession cycle i e one of the milankovitch parameters a timescale is developed by assigning a duration of 20 k y per couplet and this suggests that the entire formation represents at least 1 78 m y using the new timescale bundles of bedding couplets are shown to have periods consistent with the 123 k y component of the orbital eccentricity variations the amplitude of the couplets varies at the same frequencies as the bundle cycles in accordance with the interpretation that the couplets record precession and the bundles record eccentricity however despite having the same frequency of variation there is no consistent relationship coherence between the variations in amplitude of the couplet cycle and the bundle cycles as would be predicted by the eccentricity precession relationship this mismatch can be explained in terms of nonlinear behavior of a climatic system characterized by a varying response time or nonlinear response of the sedimentary system itself the data contain no evidence for orbital obliquity cycles because the obliquity cycle affects insolation principally at high latitudes the climatic factors that indirectly controlled the sedimentary cyclicity must have arisen at relatively low latitudes the belemnite marls timescale indicates highly variable minimum durations for ammonite zones and subzones true durations cannot be determined because it is possible that the succession is incomplete as a result of undetected erosion and or nondeposition a combination of the new results with cyclostratigraphic data from yorkshire northeast england and the southern alps switzerland indicates based on cycle counts that the pliensbachian stage lasted at least 4 82 m y marine sr isotope ratios appear to have decreased linearly from the start of jurassic time until the end of pliensbachian time the rate of decrease in 87 sr 86 sr established using the belemnite marls timescale was 0 000042 m y or less if the main part of the formation is incomplete using this rate with the observed changes in sr isotope ratios gives minimum durations of 2 86 m y for hettangian time 7 62 m y for sinemurian time and 6 67 m y for pliensbachian time

rapid burial diagenesis of deep water carbonates exuma sound bahamas well lithified deep water periplatform limestones of late miocene age occur at subsurface depths from 113 m to total depth of 283 m at ocean drilling program odp site 632 in exuma sound bahamas this occurrence marked by a dramatic increase in compressional wave velocities up to 5 0 km s represents the most rapid transformation of ooze to limestone yet discovered in either periplatform or open ocean settings the burial diagenetic pathway is similar to those for meteoric and deep burial diagenetic environments aragonite dissolves magnesian calcites exsolve or dissolve low mg calcite precipitates as cement and secondary moldic vuggy porosity develops stable isotope ratios suggest precipitation of low mg calcite from cold marine derived pore waters accelerated diagenesis is a response to the influx of large quantities up to 80 of bank derived metastable carbonates and rapid burial via high accumulation rates up to 210 m m y our findings 1 document carbonate mineral stabilization and lithification in a seawater mediated shallow burial diagenetic environment 2 highlight the very high diagenetic potential of periplatform carbonates and 3 call into question the use of seismic velocities as support for the bahama megabank hypothesis

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