multiple impacts across the cretaceous tertiary boundary abstract the stratigraphy and age of altered impact glass microtektites microkrystites ejecta layers from the chicxulub crater are documented in late maastrichtian and early danian sediments in mexico guatemala belize and haiti in northeastern mexico two to four ejecta layers are present in zone cf1 which spans the last 300 ky of the maastrichtian the oldest ejecta layer is dated at 65 27 0 03 ma based on sediment accumulation rates and extrapolated magnetostratigraphy all younger ejecta layers from the maastrichtian and early danian parvularugoglobigerina eugubina zone pla l may represent repeated episodes of reworking of the oldest layer at times of sea level changes and tectonic activity the k t boundary impact event 65 0 ma is not well represented in this area due to widespread erosion an early danian pla l ir anomaly is present in five localities bochil actela coxquihui trinitaria and haiti and is tentatively identified as a third impact event at about 64 9 ma a multiimpact scenario is most consistent with the impact ejecta evidence the first impact is associated with major deccan volcanism and likely contributed to the rapid global warming of 3 4 c in intermediate waters between 65 4 and 65 2 ma decrease in primary productivity and onset of terminal decline in planktic foraminiferal populations the k t boundary impact marks a major drop in primary productivity and the extinction of all tropical and subtropical species the early danian impact may have contributed to the delayed recovery in productivity and evolutionary diversity

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

magnetostratigraphy of the cretaceous tertiary boundary at agost spain a detailed magnetostratigraphic investigation of the agost section spain containing the cretaceous tertiary k t boundary is reported thermal demagnetization contrary to alternating field demagnetization succeeds in revealing the polarity of the characteristic remanent magnetization although an overlap in blocking temperature spectrum exists with a normal polarity secondary magnetization component the k t boundary occurs at two thirds from the base of a reversed polarity zone and by comparison with earlier results 1 this polarity zone is correlated to chron c29r linear regression of sedimentation rates in other sections with an established magnetostratigraphy and containing the k t boundary yields an age of 66 45 ma for this boundary on the basis of this age and the magnetic reversal ages of the berggren et al 13 polarity time scale new first appearance fad ages around the k t boundary are suggested for the planktonic speciesmorozovella trinidadensis bolli 66 04 ma morozovella pseudobulloides plummer 66 34 ma eoglobigerina taurica bang 66 41 ma and globigerina eugubina luterbacher premoli silva 66 43 ma

reducing uncertainty in the climatic interpretations of speleothem δ18o 1 we explore two principal areas of uncertainty associated with paleoclimate reconstructions from speleothem 18o 18ospel potential non stationarity in relationships between local climate and larger scale atmospheric circulation and routing of water through the karst aquifer using a 18ospel record from turkey the csiro mk3l climate system model and the karstfor karst hydrology model we confirm the stationarity of relationships between cool season precipitation and regional circulation dynamics associated with the north sea caspian pattern since 1 ka stalagmite 18o is predicted for the last 500 years using precipitation and temperature output from the csiro mk3l model and synthetic 18o of precipitation as inputs for the karstfor model interannual variability in the 18ospel record is captured by karstfor but we cannot reproduce the isotopically lighter conditions of the sixteenth to seventeenth centuries we argue that forward models of paleoclimate proxies such as karstfor embedded within isotope enabled general circulation models are now required

tektites in cretaceous tertiary boundary rocks on haiti and their bearing on the alvarez impact extinction hypothesis relic tektites are associated with a pt group metal abundance anomaly and shocked minerals in a thin marl bed that marks the k t boundary on haiti the presence of these three impact produced materials at the precise k t boundary enormously strengthens the alvarez impact extinction hypothesis the tektites occur in smectite spherules that have external shapes typical of tektites their chemical and physical properties are broadly similar to those of other tektite groups except that the haitian tektites have lower si and higher fe ca and na on average they contain more sc v cu zn ga sr sn and ba and less cr ni co b mn and hf than other tektite groups amounts of rare earth elements ree in the tektites indicate that their progenitor materials were not melted mafic or ultramafic oceanic crust rather they were sedimentary deposits having a bulk composition of andesite rare tektites contain unusually high amounts of cao 20 and s 0 4 and these data suggest that some target materials consisted of caso4 anhydrite beds occur in the subsurface at two candidate impact sites chicxulub and manson sm nd isotopic data for the tektites indicate that the melted precursor sediments were most likely deposited less than 400 m y between the late cretaceous and silurian periods major chemical changes accompanied the diagenetic change of glass to smectite the haitian tektites are the first datable impact products in k t boundary rocks and 40ar 39ar ages of the glass show that the k t boundary and impact event are coeval at 64 5 0 1 ma

astronomical calibration of the danian stage early paleocene revisited settling chronologies of sedimentary records across the atlantic and pacific oceans abstract astronomical tuning of sedimentary records to precise orbital solutions has led to unprecedented resolution in the geological time scale however the construction of a consistent astronomical time scale for the paleocene is controversial due to uncertainties in the recognition of the exact number of 405 kyr eccentricity cycles and accurate correlation between key records here we present a new danian integrated stratigraphic framework using the land based zumaia and sopelana hemipelagic sections from the basque basin and deep sea records drilled during ocean drilling program odp legs 198 shatsky rise north pacific and 208 walvis ridge south atlantic that solves previous discrepancies the new coherent stratigraphy utilises composite images from odp cores a new whole rock 13c isotope record at zumaia and new magnetostratigraphic data from sopelana we consistently observe 11 405 kyr eccentricity cycles in all studied danian successions we achieve a robust correlation of bioevents and stable isotope events between all studied sections at the 100 kyr short eccentricity level a prerequisite for paleoclimatic interpretations comparison with and subsequent tuning of the records to the latest orbital solution la2011 provides astronomically calibrated ages of 66 022 0 040 ma and 61 607 0 040 ma for the cretaceous paleogene k pg and danian selandian d s boundaries respectively low sedimentation rates appear common in all records in the mid danian interval including conspicuous condensed intervals in the oceanic records that in the past have hampered the proper identification of cycles the comprehensive interbasinal approach applied here reveals pitfalls in time scale construction filtering techniques in particular and indicates that some caution and scrutiny has to be applied when building orbital chronologies finally the zumaia section already hosting the selandian global boundary stratotype section and point gssp could serve as the global danian unit stratotype in the future

cyclostratigraphy and astronomical tuning of the late maastrichtian at zumaia basque country northern spain the standard geological time scale for the cretaceous is still largely based on seafloor anomaly profiles combined with radio isotopic tie points the astronomical tuned time scale with its much higher resolution and accuracy has recently been extended to the k pg boundary and is being extended into the cretaceous to construct such a time scale for the cretaceous we selected the upper maastrichtian of the zumaia section in the basque country northern spain which contains a cyclic alternation of limestones and marls deposited in a hemipelagic setting the paleogene portion of the zumaia section has previously been studied for a joint cyclostratigraphic radioisotopic intercalibration of the age of the k pg boundary here we present a high resolution cyclostratigraphic framework for the upper maastrichtian latest cretaceous of the zumaia section in the basque country northern spain with new biostratigraphic and magnetostratigraphic data bed to bed correlation with the nearby sopelana section provides additional bio and magnetostratigraphic constraints the stacking pattern of the lithologies shows a hierarchy that reflects the combined influence of the orbital parameters of precession and eccentricity this is confirmed by time series analyses of lithological and geochemical data indicating a strong influence of eccentricity modulated precession on latest cretaceous climate the expression of the 405 kyr eccentricity cycle serves as primary signal for astronomical tuning we provide two tuning options depending on absolute k pg boundary ages of 65 56 and 65 97 ma the logged part of the section encompasses nine and a half 405 kyr cycles in total and spans 3 9 myr the acquired cyclostratigraphic framework provides ages for characteristic planktonic foraminiferal events magnetic reversals and carbon isotope excursions and resolves the late maastrichtian time scale in unprecedented detail with relative age uncertainties o 100 kyr the high resolution and large amplitude of shifts in d 13 c on the 405 kyr and 1 2 myr scales allow for global

astronomical duration of polarity chron c31r lower maastrichtian cyclostratigraphy of odp site 762 indian ocean and the contessa highway section gubbio italy the duration of polarity chron c31r is estimated with a cyclostratigraphic approach two sites are investigated odp site 762 indian ocean and the contessa highway section gubbio italy cyclostratigraphic analysis is performed on greyscale variations site 762 and magnetic susceptibility variations contessa section both sites reveal an astronomical control of the sedimentation highlighted by the identification of all the orbital periodicities cyclostratigraphic signals are tuned on 405 ka eccentricity cycles extracted from the la04 astronomical solution in both sites cycle counting gives an estimate of the duration of polarity chron c31r of about 2 09 0 03 ma

orbital forcing and sedimentary sequences abstract the variation of eccentricity is connected with the most celebrated attempts to determine a limited portion of geologic time in the elaboration of the theory of the ice age that bears his name croll correlated two important epochs of glaciation with epochs of eccentricity computed to have occurred 100 000 and 210 000 years ago as the analysis of the glacial history progresses these correlations will eventually be established or disproved and should they be established it is possible that similar connections may be made between events far more remote gilbert 1900 p 15 16 but the precessional motion pulses steadily on through the ages like the swing of a frictionless pendulum its throb may or may not be caught by the geological process which obtains in a particular province and in a particular era but whenever the conditions are favorable and the connection is made the record should reflect the persistence and the regularity of the inciting rhythm gilbert 1900 p 18

astronomical calibration of the maastrichtian late cretaceous abstract recent improvements to astronomical modeling of the solar system have contributed to important refinements of the cenozoic time scale through astronomical calibration of sedimentary series we extend this astronomical calibration into the cretaceous on the base of the 405 ka orbital eccentricity variation thanks to the recovery of well preserved maastrichtian sedimentary series from odp ocean drilling program holes 1258a leg 207 equatorial atlantic 1267b leg 208 south atlantic 762c leg 122 indian ocean and dsdp deep sea drilling program hole 525a leg 74 south atlantic cyclostratigraphic analysis is performed on high resolution measurements of magnetic susceptibility on sediments cored during legs 207 and 208 and gray level variations of sediment color obtained from core photographs from legs 122 and 74 astronomical control on sedimentation is evident at every site with the presence of cycles corresponding to forcing by precession obliquity and orbital eccentricity variations identification of these cycles leads to the definition of a detailed cyclostratigraphic frame covering nearly 8 ma from the upper campanian to the cretaceous paleogene k pg boundary durations of each magnetochron from c32r 2r to c29n are inferred by cycle counting astronomical calibrations of maastrichtian sedimentary series are proposed based on the 405 ka eccentricity variation according to the most recent astronomical solution la2010a two different ages are suggested for the k pg boundary considering the uncertainty of the long term variation of the 405 ka eccentricity cycle the first proposal provides a cretaceous paleogene boundary age of 65 59 0 07 ma and the second an age of 66 0 07 ma which is coherent with the most recent radio isotopic datings magnetochron boundaries and the campanian maastrichtian boundary are dated relative to these numerical ages of the k pg boundary

untangling the palaeocene climatic rhythm an astronomically calibrated early palaeocene magnetostratigraphy and biostratigraphy at zumaia basque basin northern spain abstract the magnetostratigraphy of a 54 m long section above the cretaceous tertiary boundary at the sea cliff section of zumaia in the basque basin northern spain has been established the section encompasses the entire danian and the lower part of the selandian stages as indicated by calcareous plankton biostratigraphy the studied interval consists of hemi pelagic limestone marl alternations in the form of couplets and bundles which range from centimetre decimetre to metre scale respectively and a few thin bedded calcareous turbidites the magnetostratigraphy based on samples from about 200 stratigraphic levels allows the identification of six reversal boundaries from chron c29r to c26r at a bed level the spatial or temporal evolution of periodicities from a lithologically coded series is studied with the continuous wavelet transform technique a preliminary age model based on the standard ck95 gpts indicates that the basic lithologic carbonate marl couplet corresponds to the 19 23 kyr precession cycle 21 31 cm cycle in the depth domain and that a bundle cycle usually groups of four to six basic couplets with global periodicity centred at 1 22 m corresponds to the 110 kyr eccentricity cycle we have tuned the bundle cycles to the va03 r7 eccentricity orbital solution astrophys j 592 2003 620 630 following an initial match of a node of the 2 4 ma eccentricity modulatory cycle in the target time series to particularly carbonate rich bundles from the upper part of the zumaia section that displays significant power of a 4 4 m period cycle corresponding to the 404 kyr eccentricity cycle consistency between lithologic patterns and characteristics in the eccentricity target is reasonably met although the 404 kyr eccentricity cycle is not persistent throughout the tuning however appears robust as it brings the age of the k t boundary at 65 8 ma it is argued that a sea level signal tectonically driven is superimposed on the climatic forcing at the milankovitch band masking the full expression of the low frequency astronomical periods we provide a cycle tuned duration for all intervening early palaeocene polarity chrons and estimate relative ages for bioevents the cycle tuned chronology indicates that the ck95 gpts overestimates the duration of chrons c28 and c27 by 20 and 26 respectively our data may prove useful to better constrain early palaeocene biostratigraphy of calcareous plankton and in the redefinition of the boundary between the danian and selandian stages

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

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

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

is the transition impact to post impact rock complete some remarks based on xrf scanning electron microprobe and thin section analyses of the yaxcopoil 1 core in the chicxulub crater the transition from impact to post impact rocks in the yaxcopoil 1 core is marked by a 2 cm thick clay layer characterized by dissolution features the clay overlies a 9 cm thick hardground overlying a 66 cm thick crossbedded unit consisting of dolomite sandstone alternating with thin micro conglomerate layers with litho and bioclasts and the altered remains of impact glass now smectite the micro conglomerates mark erosion surfaces microprobe and backscatter sem analysis of the dolomite rhombs show an early diagenetic complex zoned idiomorphic overgrowth with mn rich zones possibly formed by hot fluids related to cooling melt sheet in the crater the pore spaces are filled with several generations of coelestite barite k feldpar and sparry calcite xrf core scanning analysis detected high mn values in the crossbedded sediments but no anomalous enrichment of the siderophile elements cr co fe and ni in the clay layer shocked quartz occurs in the crossbedded unit but is absent in the clay layer the basal paleocene marls are strongly dissolved and do not contain a basal paleocene fauna the presence of a hardground the lack of siderophile elements shocked quartz or ni rich spinels in the clay layer and the absence of basal paleocene biozones p0 and pa all suggest that the top of the ejecta sequence and a significant part of the lower paleocene is missing due to the high energy sedimentation infill a hiatus at the top of the impactite is not unexpected but there is nothing in the biostratigraphy geochemistry and petrology of the yaxcopoil 1 core that can be used to argue against the synchroneity of the end cretaceous mass extinctions and the chicxulub crater

biostratigraphy and magnetostratigraphy of the cretaceous tertiary sopelana section basque country remarkably thick sequences of upper cretaceous and lower tertiary sediments outcrop on the northern coast of the basque country we have sampled the well exposed section along the sopelana beach over 150 m spanning roughly from middle maastrichtian 71 ma to lower paleocene 66 ma for both biostratigraphic and magnetostratigraphic studies thermal demagnetization of 400 specimens revealed both normal and reversed recent overprints unblocked below 200 c and both normal and reversed characteristic directions at higher temperatures 200 450 c in the grey limestones 350 550 c in the redder marls and limestones thermal and af demagnetization and monitoring of weak field susceptibility are consistent with some form of titano magnetite as the main carrier of magnetization 259 demagnetization diagrams yielded two nearly antipodal clusters of directions which are still polluted by some 20 remaining recent overprint the overall mean direction in stratigraphic coordinates is d 356 i 51 3 consistent with what is expected for eurasia at ktb time magnetic stratigraphy outlines a succession of eight polarity intervals and is rather straightforward except for two highly complex zones 52 to 40 m and 28 to 26 m below the ktb where the magnetic polarity appears to flip at an unreasonable rate biostratigraphic check allows unambiguous assignment of several chrons with the recognition of the gansserina gansseri abathomphalus mayaroensis globigerina eugubina eoglobigerina edita e pseudobulloides and e trinidadensis zones the magnetostratigraphic section therefore begins in chron 31r and ends in 29n further detailed study of the complex zones reveals that specimens there have a distinct magnetic behaviour susceptibility increases beyond 400 c indicating instability and mineralogical change intensities are higher than elsewhere and more scattered and a higher unblocking temperature higher coercivity magnetic component is uncovered this component which is absent from the rest of the section could be an early chemical remagnetization indeed the complex zones contain larger amounts of chlorite a sign of more intense diagenesis we have therefore discarded samples showing this anomalous behaviour and have retained only the 223 samples where demagnetization was achieved by 450 c the thicker lower complex zone reduces to a reversed chron which we propose to correlate with 30r we have identified an extra short reversed event within chron 30n for which independent support is found in dsdp sites 524 and 577a and possibly in gubbio finally the high sedimentation rate section at sopelana 25 m ma in the maastrichtian 7 m ma in the danian displays one of the best resolved on land magnetostratigraphies around ktb time the two complex zones of early remagnetization form an echo which may have been generated some 100 kyr after deposition of the sediments the ktb itself occurs approximately halfway to 3 5 up 29r in terms of time

astronomical calibration of the paleocene time the first complete cyclic sedimentary successions for the early paleogene from drilling multiple holes have been retrieved during two odp expeditions leg 198 shatsky rise nw pacific ocean and leg 208 walvis ridge se atlantic ocean these new records allow us to construct a comprehensive astronomically calibrated stratigraphic framework with an unprecedented accuracy for both the atlantic and the pacific oceans covering the entire paleocene epoch based on the identification of the stable long eccentricity cycle 405 kyr high resolution x ray fluorescence xrf core scanner and non destructive core logging data from sites 1209 through 1211 leg 198 and sites 1262 1267 leg 208 are the basis for such a robust chronostratigraphy former investigated marine odp sites 1001 and 1051 and land based e g zumaia sections have been integrated as well the high fidelity chronology is the prerequisite for deciphering mechanisms in relation to prominent transient climatic events as well as completely new insights into greenhouse climate variability in the early paleogene we demonstrate that the paleocene epoch covers 24 long eccentricity cycles we also show that no definite absolute age datums for the k pg boundary or the paleocene eocene thermal maximum petm can be provided by now because of still existing uncertainties in orbital solutions and radiometric dating however we provide two options for tuning of the paleocene which are only offset by 405 kyr our orbitally calibrated integrated leg 208 magnetostratigraphy is used to revise the geomagnetic polarity time scale gpts for chron c29 to c25 we established a high resolution calcareous nannofossil biostratigraphy for the south atlantic which allows a much more detailed relative scaling of stages with biozones the re evaluation of the south atlantic spreading rate model features higher frequent oscillations in spreading rates for magnetochron c28r c27n and c26n

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

signal analysis of cyclicity in maastrichtian pelagic chalks from the danish north sea abstract low field bulk magnetic susceptibility has been determined on maastrichtian chalk samples from a drill core from the dan field in the danish north sea fast fourier transformations fft have been used to detect possible cycles in the magnetic susceptibility data power spectra from the complete section and from sub sections of the magnetic susceptibility reveal two cyclicities of ca 0 4 cycles m and ca 1 7 cycles m which are present on a 90 confidence level signal analysis of natural gamma ray wire line log data supports these findings sedimentation rate estimates place the cycles in the milankovitch frequency band artificial time series are used to study the applicability of the fft to identifying cyclicity in chalks expected geological distortions e g hiati and sedimentation rate variations are introduced into the time series to investigate the response of the frequency spectra different methods of handling missing data intervals are also examined

magnetic characterization of cretaceous tertiary boundary sediments rock magnetic properties across several k t boundary sections have been investigated to reveal any possible magnetic signature associated with the remains of the impact event at the end of the cretaceous studied sections locations vary in distance to the chicxulub structure from distal agost and caravaca spain through closer odp hole 1049a blake nose north atlantic to proximal el mimbral and la lajilla mexico a clear magnetic signature is associated with the fireball layer in the most distal sections consisting of a sharp increase in susceptibility and saturation isothermal remanent magnetization sirm and a decrease in remanence coercivity magnetic properties in these sections point to a distinctive ferrimagnetic phase probably corresponding to the reported mg and ni rich highly oxidized spinels of meteoritic origin at closer and proximal sections magnetic properties are different although there is an increase in susceptibility and sirm associated with a rusty layer placed on top of the siliciclastic deposit in proximal sections and with a similar limonitic layer on top of the spherule bed that defines the boundary at blake nose the magnetic properties indicate a mixture of iron oxyhydroxides dominated by fine grained goethite based on previous geochemical studies at blake nose and new geochemical and pge abundance measurements performed in this work at el mimbral this goethite rich layer can be interpreted as an effect of diagenetic remobilization and precipitation of fe there is not enough evidence to assert that this fe concentration layer at proximal sections is directly related to deposition of fine meteoritic material magnetic geochemical and iridium data reject it as a primary meteoritic phase

evaluation of the astronomical time scale for the paleocene and earliest eocene abstract the astronomical tuned time scale is rapidly extended into the paleogene but due to the existence of an eocene gap different tuning options had to be presented for the paleocene these options differ both in number and tuning of 405 kyr eccentricity related cycles and are only partially consistent with recalculated 40 ar 39 ar constraints for the cretaceous paleogene k pg and paleocene eocene p e boundaries in this paper we evaluate the cyclostratigraphic interpretation of records from odp leg 198 and 208 sites and the zumaia section to solve the problem of the different tuning options we found that the interval between the k pg boundary and the early late paleocene biotic event elpe comprises 17 instead of 16 405 kyr eccentricity related cycles as previously proposed while the entire paleocene contains 25 405 kyr cycles starting from 40 ar 39 ar age constraints for the k pg boundary a new tuning to 405 kyr eccentricity is presented for the paleocene and earliest eocene which results in ages of 66 0 and 56 0 ma for the k pg and p e boundaries respectively this tuning introduces considerable differences in age for a number of nannofossil events at odp sites 1209 and 1262 in the interval between 61 and 63 ma but eliminates large and abrupt changes in the seafloor spreading rate the tuning seems further consistent with recalculated 40 ar 39 ar ages for ash layer 17 of early eocene age however despite this apparent consistency with existing radio isotopic constraints an alternative 405 kyr younger or less likely older tuning cannot be excluded at this stage

climatic fluctuations and sea surface water circulation patterns at the end of the cretaceous era calcareous nannofossil evidence abstract new paleoecological data are presented for late maastrichtian calcareous nannofossil assemblages of the indian ocean and the boreal epicontinental chalk sea these data are compiled with recent results in the tropical atlantic pacific and tethys oceans in order to characterize environmental changes by the end of the cretaceous era the paleobiogeographic distribution of the warm water species micula murus is updated and indicates the existence of major sea surface currents in the late maastrichtian atlantic ocean similar to the present day the end maastrichtian greenhouse warming is characterized at tropical and subtropical latitudes by an increase in abundance of m murus and the temporary disappearance of the high fertility marker biscutum constans in the boreal realm the greenhouse episode is marked by a contemporaneous acme of watznaueria barnesiae coincident with very rare occurrences of m murus and other tropical nannofossil species which have never been reported before at boreal latitudes a review of cyclostratigraphic and calcareous nannofossil data in the atlantic pacific indian and tethys oceans points to the following evolution of sea surface paleotemperatures for the last ca 350 380 kyr of the cretaceous the end maastrichtian greenhouse warming lasted on average a little more than 200 kyr and was followed by a ca 100 120 kyr cooling in the tethys a 30 40 kyr additional pulse of warming is highlighted immediately below the cretaceous paleogene boundary these findings indicate an important instability of the climate system at the end of the maastrichtian most likely caused by deccan volcanism the calcareous nannofossil species richness dropped during the end maastrichtian greenhouse warming which may indicate environmental stress and or ocean acidification however nannoplankton diversity returned rapidly to higher values after this climatic episode and remained high up to the cretaceous paleogene boundary no significant extinction is recorded in this biotic group prior to the boundary clay

comments on the paper magnetostratigraphy of the cretaceous tertiary boundary at agost spain by j j groot r b g de jonge c g langereis w g h z ten kate and j smit commentaire de l article de j j groot r b g de jonge c g langereis w g h z ten kate et j smit paru dans earth planet sci lett vol 94 1989 pp 385 397

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

orbital forcing in turbidite accumulation during the eocene greenhouse interval the influence of astronomically driven short term climate change milankovitch cycles on deep marine turbidite systems is not well known particularly in the case of long term greenhouse intervals with no significant glacio eustatic sea level fluctuations this study carried out at the gorrondatxe section global stratotype section and point for the base of the lutetian stage in the western pyrenees demonstrates that the characteristics of lower middle eocene fan fringe basin plain turbiditic and pelagic deposits varied in line with orbitally forced fluctuations in seasonal rainfall runoff and terrigenous input to the sea reduced turbiditic activity during the formation of pelagic limy precessional hemicouplets indicates subdued seasonality and low terrigenous input conversely turbidity currents were more frequent had greater energy and were more voluminous during the formation of pelagic marly hemicouplets suggesting precessional hemicycles with strong seasonality and heavy summer rainfall these differences at precessional time scales were enhanced at maximum eccentricity because turbiditic activity was most intense when boreal summer occurred at perihelion i e maximum seasonality but declined when it occurred at aphelion at minimum eccentricity with relatively weak seasonality throughout one or more than one precessional cycle 21 kyr turbiditic activity remained relatively low the pattern observed at the gorrondatxe fan fringe basin plain succession implies that the orbitally forced environmental changes must also have affected the inner and middle parts of the submarine fan the astronomical influence on terrigenous sediment input also determined the changing characteristics of the pelagic sedimentation thus terrigenous sediment contribution to pelagic sedimentation fluctuated by a factor of five during opposite precessional situations at maximum eccentricity whereas there was almost no fluctuation at minimum eccentricity

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

multiple factors in the origin of the cretaceous tertiary boundary the role of environmental stress and deccan trap volcanism a review of the scenarios for the cretaceous tertiary k t boundary event is presented and a coherent hypothesis for the origin of the event is formulated many scientists now accept that the event was caused by a meteorite impact at chicxulub in the yucatan peninsula mexico our investigations show that the oceans were already stressed by the end of the late cretaceous as a result of the long term drop in atmospheric co2 the long term drop in sea level and the frequent development of oceanic anoxia extinction of some marine species was already occurring several million years prior to the k t boundary the biota were therefore susceptible to change the eruption of the deccan traps which began at 66 2 ma coincides with the k t boundary events it erupted huge quantities of h2so4 hcl co2 dust and soot into the atmosphere and led to a significant drop in sea level and marked changes in ocean temperature the result was a major reduction in oceanic productivity and the creation of an almost dead ocean the volcanism lasted almost 0 7 m y extinction of biological species was graded and appeared to correlate with the main eruptive events elements such as ir were incorporated into the volcanic ash possibly on soot particles this horizon accumulated under anoxic conditions in local depressions and became the marker horizon for the k t boundary an oxidation front penetrated this horizon leading to the redistribution of elements the eruption of the deccan traps is the largest volcanic event since the permian triassic event at 245 ma it followed a period of 36 m y in which the earth s magnetic field failed to reverse instabilities in the mantle are thought to be responsible for this eruption and therefore for the k t event we therefore believe that the k t event can be explained in terms of the effects of the deccan volcanism on an already stressed biosphere the meteorite impact at chicxulub took place after the onset of deccan volcanism it probably played a regional rather than a global role in the k t extinctions

lower maastrichtian cyclostratigraphy of the bidart section basque country sw france a remarkable record of precessional forcing abstract cyclostratigraphic analysis of the maastrichtian limestone marl alternations of bidart sw france allows the hypothesis of orbital control on lithological cycles to be evaluated magnetic susceptibility ms oxygen and carbon isotope measurements sampled at a high resolution are analyzed using various cyclostratigraphic tools a statistically significant orbital signal is detected with a remarkable record of the precession corresponding to the limestone marl couplets this well expressed orbital forcing allows the building of a relative cyclostratigraphic time scale for the ms and 13 c records based on the 100 kyr eccentricity cycle the total duration of the section is estimated at 1 44 0 22 myr correlation based on calcareous nannofossil biostratigraphy and comparison of the scaled bidart 13 c record to the astronomically calibrated 13 c signal of odp hole 762c shows that the studied section extends from 71 5 to 70 ma covering the upper part of chron c32n 1n and 2 3 of chron c31r oxygen isotope data suggest a 2 c cooling of sea surface temperatures during the studied interval when placed on the long term 18 o trend of the bidart section this interval is here recognized as the onset of the early maastrichtian cooling event with its excellent record of the precessional forcing the bidart section along with other sections of the basque country is a useful tool for the refinement of the maastrichtian timescale

orbital forcing of calcilutite marl cycles in southeast spain and an estimate for the duration of the berriasian stage cyclicities observed in a hemi pelagic rhythmic calcilutite marl succession of late berriasian age near caravaca southeast spain match well with the quasi periodicities of the milankovitch model the shortening of the precession and obliquity in pre quaternary times is taken into account the interval of the miravetes formation studied has a thickness of 77 5 m extends from the base of the calpionellopsis simplex subzone d1 to the top of the calpionellopsis oblonga subzone d2 and has an estimated duration between 1 1 and 2 9 ma the evolution of the cyclicities in this succession was analyzed by comparing the spectra of ten successive overlapping segments from this comparison we conclude that 11 m at the top and base of the succession show variations in accumulation rate disregarding these parts the spectrum of the remaining interval 56 m reveals well defined spectral peaks the cyclicity is ascribed to orbital forcing because all cycles longer than the bedding cyclicity can be matched with the known orbital quasi periodicities reported in berger and others 1989a 1989b this match with milankovitch cyclicities produces a considerably more precise estimate for berriasian zone durations the range of the duration of the combined calpionellid subzones d1 and d2 reduces to an interval between 1 1 and 1 2 ma and the length of the entire berriasian stage is estimated to fall between 2 9 and 3 1 ma

recognition of cyclicity in the petrophysical properties of a maastrichtian pelagic chalk oil field reservoir from the danish north sea subdivision of the maastrichtian chalk from the danish north sea has proven difficult because of its homogenous composition which is caused by a fairly stable depositional environment nevertheless the chalk petrophysical properties show cyclic behavior that potentially can be used for subdivision petrophysical properties of a 23 m long succession of maastrichtian chalk from the dan field were examined for cyclicity by spectral analysis magnetic susceptibility values measured on plug samples together with the neutron porosity and natural gamma radiation well log data were analyzed both as complete data sets and in subsets to survey the general existence of cycles in the chalk all three properties contain consistent cycles at approximately 2 m wavelength as well as additional frequencies where the relative dominance of the different frequencies differs cross spectral analyses of subsets of the petrophysical parameters provide substantial evidence for the coexistence of the approximately 2 m cycles in the maastrichtian chalk furthermore the magnetic susceptibility carries spectral evidence for a higher frequency because most power spectra of the subsets from the magnetic susceptibility have a spectral peak in the 1 8 2 0 cycles m interval i e approximately 0 5 m cycle the cycles can be interpreted as resulting from the eccentricity 94 5 k y and the precession 22 5 k y of the milankovitch cycles assuming a sedimentation rate of 2 6 cm k y the existence and the understanding of cycles at a submeter scale yield possibilities for an advantageously precise subdivision of chalk reservoirs and correlation between wells begin page 2004

orbitally driven fertility cycles in the palaeocene pelagic sequences of the southern alps northern italy abstract palaeocene pelagic sequences cropping out in the southern alps are often characterized by a cyclic alternation of marly and calcareous lithologies in particular two sets of limestone marlstone couplets are well exposed in the ponte nelle alpi and tabiago sections both danian to thanetian in age located in the belluno region venetian prealps and in the brianza region central prealps respectively a multidisciplinary approach was adopted to determine the nature of these alternations by analyzing for each semicouplet the abundance and composition of planktonic foraminiferal faunas the degree of bioturbation and the carbonate content both sections show similar general features the marly semicouplets of ponte nelle alpi and tabiago sections are poor in planktonic foraminifera but enriched in more tolerant for nutrients and temperature foraminiferal forms and they record more oxygenated conditions a possible interpretation of the lithological rhythms suggests that the marly semicouplets were deposited in periods of high seasonality a marked seasonality leading to an increased circulation of water masses induced a nutrient enrichment in surface waters and oxygenated conditions at the seafloor the data prove that the marly semicouplets represents fertile surface waters whereas the calcareous ones record the opposite conditions low seasonality sluggish circulation and fewer nutrients at the sea surface spectral analysis was applied to evaluate the possible periodicities that could have driven the observed cyclicity the periodicities recorded agree with those predicted by the palaeoclimatic milankovitch theory for the precession obliquity and eccentricity cycles the stronger signal associated to obliquity has also been recorded during the mid cretaceous confined to some intervals this inconstancy is probably attributable to the response of the earth to a signal that may only be detected in the low latitudes when climatic or oceanic conditions are particularly favorable to its transmission

kinematic evolution of the tethys belt from the atlantic ocean to the pamirs since the triassic abstract we present an updated series of kinematic reconstructions of the major plates around the tethys from the atlantic ocean to the pamirs between the early jurassic and the present this set is used elsewhere as a basis for paleogeographic maps of the entire region the problems related to the positions of the continents in the lower triassic are also discussed no direct analyses of magnetic anomalies and fracture zones in the atlantic have been made rather all available poles and rotations have been tested in order to eliminate or minimize possible kinematic errors the reconstructions are shown for nine key geological periods which correspond to well recognized magnetic anomalies except for the jurassic cretaceous boundary and the cretaceous tertiary boundary which correspond to interpolated positions paleolatitudes have been drawn using the study of westphal et al 1986 an attempt has been made to take into account the displacements caused by formation of the continental margins and basins by stretching the resulting relative vector of motions along the northern boundary of the tethys shows a significant change 80 m y ago left lateral motion with compression dominates before whereas right lateral motion with compression dominates after to the east rates of motion vary by a factor of three with time and four maxima can be clearly related to tectonic events in the late jurassic late cretaceous eocene and post middle miocene to the west north of apulia on the contrary the motion rate has not changed significantly since the early cretaceous and is close to 1 cm yr as an average these rather complex adjustments in rates and directions of relative motion are produced in great part through a complex migration of the africa eurasia pole of rotation and seem to be mostly governed by the tectonics of the tethys plate boundary

magnetic modeling near selected areas of hydrothermal activity on the mid atlantic and gorda ridges sea surface magnetic and bathymetric data from two areas of observed high temperature hydrothermal activity in the atlantic trans atlantic geotraverse or tag hydrothermal field and pacific sea cliff hydrothermal field and two areas of inferred hydrothermal activity in the atlantic mid atlantic ridge mar at 15 n and 17 n were studied to determine the effect of vent activity on magnetization of the oceanic crust all of the sites examined show a low in the magnetic anomaly in varying degrees magnetization lows within the axial marine magnetic anomaly have been associated with some areas of active and relict high temperature hydrothermal venting a three dimensional magnetic inversion was performed on magnetic and bathymetric data from the tag hydrothermal area on the mid atlantic ridge 26 n and two dimensional magnetic inversions were done on individual profiles from the other study sites the map from the tag area shows a negative in the crustal magnetization solution just to the east of the median valley axis which encompasses the active hydrothermal area a low in magnetization continues up the eastern wall which suggests alteration of the crust a distinct low in magnetization is present within the axial anomaly at the sea cliff hydrothermal field located on the eastern wall of the gorda ridge the magnetization low becomes less pronounced farther south of the known vent field profiles from 15 n and 17 n on the mid atlantic ridge show magnetization lows over areas of inferred hydrothermal activity these lows are present over the the eastern and western walls of the median valley respectively the lows observed in the axial marine magnetic anomaly in these four study sites all occur slightly off axis on crust that is at least 200 000 years old on the mid atlantic ridge and at least 100 000 years old on the gorda ridge on the basis of magnetic modeling and measurements of rock magnetic properties the most probable cause of the low in the magnetization is alteration of the oceanic crust with other subsidiary contributing factors which vary from site to site the magnetization low over tag is most probably due to high temperature hydrothermal alteration of the crust and a thinner layer 2 with possible contributions from reversal events and magma chamber curie isotherm effects the low near the sea cliff hydrothermal field on the gorda ridge is probably the product of tectonically controlled low temperature nonhydrothermal alteration high temperature hydrothermal alteration and magnetic reversal events at 15 n and 17 n on the mar the lows may be produced by alteration of the crust due to possible hydrothermal activity

proximate environmental forcing in fine scale geochemical records of calcareous couplets upper cretaceous and palaeocene of the basque cantabrian basin eastern north atlantic abstract calcareous couplets are key elements in reconstructing the evolution of a sedimentary basin due to the influence of forcing mechanisms such as climate sea level and tectonism on their depositional patterns proposed forcing mechanisms however are often not mutually exclusive and even constraining the relative importance of different processes is problematic added to the question of discriminating forcing mechanisms a major challenge is to produce high sampling density so that observations lie within temporal resolutions equal to or finer than the timescales on which different forcing operates here we show fine scale 1 sample 2 cm caco3 18o and 13c records and sedimentological observations from three different sites isla de castro sopelana ma and sopelana da with calcareous couplets in the basque cantabrian basin eastern north atlantic to illustrate the potential of fine sampling strategies to help distinguish proximate environmental forcing partial redistribution of carbonate during burial diagenesis has been proposed for these sediments our caco3 18o and 13c data could thus be dismissed as diagenetic signals if only one sample was collected from each bed detailed observations of the fine scale geochemical records however challenge purely diagenetic explanations combined with sedimentology the caco3 18o and 13c values partially altered by diagenesis are interpreted to have resulted from alternating climates the proximate forcing through which alternating climates caused the geochemical patterns though was different in each section due to their specific palaeogeographic positions in the basin and the properties of the seawater masses the proximity of continental areas of high relief to the isla de castro section supported a high continental influence during its deposition the sopelana ma sediments are assigned to a transgressive system tract a condition that is interpreted to have promoted a high influence of oceanic processes in its depositional setting finally a relatively cool oxygen rich water mass with high oxidation potential influenced the geochemical and depositional patterns of sopelana da beyond the climatic and oceanographic dynamics inferred for a basin that linked the western tethys with boreal domains during major marine transgressions of the late cretaceous to palaeocene an implication of our work is that if similar fine scale geochemical records were applied to calcareous couplets spanning major events in earth s history e g ocean anoxic events alternative forcing scenarios leading to and out of these events could be discriminated

mediterranean contributions to cyclostratigraphy and astrochronology in 1895 g k gilbert suggested that rhythmical repetition of patterns in the sequences of strata correspond to orbital variations and could provide a chronology for earth history this suggestion remained a heuristic hypothesis in need of testing in this the mediterranean region latterly played a crucial role its extended sequences of pelagic and lacustrine paludal strata provide long time series of hierarchical rhythmic variations tied directly to biostratigraphy and to magnetic reversals the latter provide historical control and links to astronomically calculated curves that have been extended progressively into the past these comparisons verify the orbital origins of the major sedimentary rhythms and are serving to reduce the age uncertainties of the significant time stratigraphic levels biostratigraphic and magnetostratigraphic zones from an order of ca 500 kyr toward the precessional 20 kyr level this refinement has essentially been reached for the last 14 myr of earth history in the mediterranean and beyond in the pacific ocean the cyclic structure of shallow water platform carbonates is also hierarchical but here the identification with specific orbital cycles has been equivocal and complicated by conflicts with radiometric data in the gap riddled shallow water successions showing hierarchical sequences the identification of some third order fourth order and fifth order sequences or parasequences with orbital forcing is being explored but remains inferential beyond chronology the orbital variations constitute an endless series of experiments similar variations in insolation which resulted in sedimentary patterns formed by a chain of responses extending through atmospheric and hydrospheric dynamics to geological processes and the dynamics of the biotic systems the emerging patterns offer glimpses into the past to reveal previously unexpected phenomena such as systematic oscillations in deep water aeration and unexpected oscillations in composition of upper water plankton patterns that pose new challenges to the understanding of earth history

evidence of an abrupt environmental disruption during the mid paleocene biotic event zumaia section western pyrenees an abrupt environmental disruption occurred in the photic zone and at the seafloor during the mid paleocene biotic event mpbe calcareous nannoplankton planktic foraminifer and benthic foraminifer assemblages at zumaia section western pyrenees underwent a rapid and remarkable transformation the major calcareous plankton assemblage changes suggest a shift from relatively cooler mesotrophic to warmer more oligotrophic conditions indicating a disturbed environment due to the warming of the ocean benthic foraminifer assemblages were also significantly affected by the mpbe diversity of the assemblages and buliminids show net decline and the low food and opportunistic taxa increase in abundance the reorganization of the planktic ecosystem possibly involved changes in the food flux type and quantity to the seafloor thus triggering changes in the benthic communities a 1 negative 13 c shift and a 30 carbonate content decrease are recorded in connection with the biotic event this suggests that during the mpbe as in the paleocene eocene thermal maximum petm an input of a large mass of isotopically depleted carbon into the ocean and atmosphere could have lowered the deep sea ph triggering a rapid shoaling of the lysocline and contributing to greenhouse warming the mpbe was short lived according to the counting of limestonemarl couplets the stratigraphic expression of precession cycles throughout the zumaia section the mpbe lasted for 52 53 k y with the core of the event representing 10 11 k y the zumaia section is the first land based locality in which the mpbe is recognized and described in detail due to its expanded character and excellent paleontological record this section may prove to be a global reference section for the study of this short lived event