precessional climate cyclicity in late cretaceous early tertiary marine sediments a high resolution chronometer of cretaceous tertiary boundary events we report well dated late cretaceous and early tertiary precessional climatic cycles recorded by rhythmic carbonate maxima and minima in south atlantic deep sea sites spectral analyses of digitized sediment color a suitable carbonate proxy show prominent regularities in the spacing marl carbonate beds magnetostratigraphic dating over a number of magnetic chrons constrains the duration of the cycles which can be detected over at least 20 myr of sedimentation at 7 coring locations their mean absolute period of23 5 4 4kyr agrees closely with the predicted late cretaceous precessional period of 20 8 kyr because they can be matched to a physical forcing mechanism with a known repeat time the cycles offer a new high resolution tool to measure rates of climate change before and after the cretaceous tertiary k t boundary from counts of carbonate cycles we derive the position of the k t boundary within c29r at 350 kyr after the base of the reversal the constancy of cycle thickness linearly related to sedimentation rate and amplitude up to the boundary clay does not give evidence for climate instability preceding the boundary orbital chronometry records a step function decrease in sediment accumulation rate at the cretaceous tertiary boundary that is consistent with a geologically instantaneous event

deep channels in the cenomanian danian chalk group of the german north sea sector evidence of strong constructional and erosional bottom currents and effect on reservoir quality distribution reflection seismic lines from the schillgrund high in the german north sea sector show that the sea floor deposition of the upper cretaceous danian chalk group was extremely irregular the cenomanian campanian part of the group is up to 600 m 1968 ft thick and is dominated by pelagic relatively horizontally deposited chalk it was tilted toward the southwest close to the campanian maastrichtian boundary time and was overlain by up to 800 m 2625 ft of onlapping maastrichtian danian chalk that was eroded and reworked by powerful synsedimentary bottom currents a north south to north northwest south southeast trending slope parallel multistorey channel system branching toward the northwest into smaller laterally directed arms was developed in maastrichtian danian times it was more than 200 km 124 mi long up to 15 km wide 9 mi and 200 m 656 ft deep the main channel system was eroded by powerful contour parallel bottom currents interpreted as having flowed toward the southeast based on the depositional geometry of the channel fill successive channel axes were systematically shifted downslope leaving a series of slightly offset nested slope parallel channels the channels were filled laterally obliquely or longitudinally by chalk drifts sediment gravity flows were a factor locally but were not integral parts of the depositional system erosion winnowing sorting and redeposition by the bottom currents are interpreted to have resulted in channel parallel porosity permeability zones the seismic data indicate that the chalk adjacent to the main channels retained high porosity calculated from logs in an exploration well drilled in 2005 the chalk is of excellent reservoir quality with effective porosity averaging 37 reaching 50 and some levels are completely unconsolidated the influence of powerful syndepositional bottom currents on the anisotropy of reservoir properties of chalk is only now beginning to be realized chalk having traditionally been considered a monotonous and uniform rock type

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

deep earth structure major developments in earth structure in the last four years have been concentrated in the description of the earth s lateral heterogeneity the regions that are heterogenous and the per cent variation of velocity and density in each region most studies find that lateral variation is concentrated in the upper 400 and lower 200 km of the mantle a radially symmetric earth model has been defined that represents the best average fit to seismic data in a broad frequency band sampling many regions p and s velocity is found to increase in zones of 50 km or less at 400 and 650 to 700 km depth the model is transversely anisotropic in the upper mantle it possesses a vertical axis of symmetry such that the elastic constants are different for vertical propagation than for horizontal and intermediate angles of propagation the real earth generally exhibits azimuthal anisotropy as well but the azimuthal anisotropy cannot be resolved by a global average of data the nature and magnitude of the anisotropy agrees with that found in ultramafic samples of the upper mantle in attenuation models of intrinsic attenuation have included the dispersive properties of intrinsic anelasticity and constructed relaxation models consistent with an observed frequency dependence of q in the body wave band there has been progress in mapping the scattering properties of the lithosphere attenuation due to scattering in the crust and lithosphere has been shown to have strong effects on the amplitudes of seismic waves at local and teleseismic distances

laminated bioturbated cycles in maastrichtian chalk of the north sea oxygenation fluctuations within the milankovitch frequency band the maastrichtian chalk of the southern central graben danish north sea is a homogeneous pure white coccolithic chalk mudstone deposited in a deep epeiric shelf sea which covered large parts of northern europe the sediment displays a pronounced cyclicity marked by decimetre thick bioturbated beds alternating with slightly thinner non bioturbated mainly laminated beds the laminated half cycles consist of alternating millimetre thick graded high porosity laminae and non graded low porosity laminae the cyclicity has been interpreted previously as caused by periods of slow background sedimentation and bioturbation interrupted by periods of rapid deposition of laminated beds with the latter reflecting random and local resedimentation processes based on textural and structural analysis the millimetre scale non graded laminae are interpreted as having been deposited directly from pelagic rain of pelleted coccoliths representing the primary production the graded laminae were deposited from small volume low density turbidity currents and suspension clouds the sedimentation rates of the cyclical chalk are similar to those known elsewhere and the lamination is interpreted as having been preserved from destruction through bioturbation by anoxic conditions at the seafloor bioturbated laminated cycles are thus formed by slow sedimentation during alternating seafloor redox conditions probably on a milankovitch scale a direct implication of this interpretation is that the cycles are areally widespread probably extending throughout the southern central graben area and may be useful for correlation and high resolution cyclostratigraphy in the chalk fields of the danish north sea if the laminated half cycles represent a few rapid resedimentation events with a high sedimentation rate as suggested by most workers then the sediment would not be truly cyclic but would represent event sedimentation within a pelagic background represented by the bioturbated beds in this case the cycles would have very limited potential for correlation

latest cretaceous earliest paleogene vegetation and climate change at the high southern latitudes palynological evidence from seymour island antarctic peninsula abstract fluctuations in late cretaceous climate were already influencing biotic change prior to the environmental upheaval at the cretaceous paleogene k pg boundary but their general nature magnitude and timing remain controversial a high resolution dataset on terrestrially derived palynomorphs is presented from the high southern palaeolatitudes that unlocks details of small scale climate variability throughout this period of significant global change specifically this is a quantitative spore and pollen analysis of an expanded uppermost cretaceous to lowermost paleogene maastrichtian earliest danian shallow marine sedimentary succession from seymour island off the northeastern tip of the antarctic peninsula then as now located at 65 s using nearest living relatives the first detailed vegetation habitat and climate reconstruction is presented for the emergent volcanic arc at this time on the coastal lowlands a cool to warm temperate rainforest is envisaged growing in a riverine landscape with both wet river margin pond and relatively dry interfluve canopy gap habitats diverse podocarps and southern beech trees grew alongside angiosperm herbs and shrubs in mean annual temperatures of 10 15 c higher altitude araucarian forests gave way to open ericaceous heathland beyond the tree line in subalpine to alpine conditions with mean annual temperatures of a cold 5 8 c there is no exact modern botanical equivalent but the closest modern flora is that of the andes of southern chile and argentina maastrichtian climate is shown to have fluctuated from cool humid conditions through a rapid warming 2 million years prior to the k pg transition followed by cooling during the earliest danian a trend supported by previous work on this interval

spatial and temporal variation in european neogene large mammals diversity abstract large mammals diversity i e ungulates or hoofed mammals is investigated over the whole european geographic area and through a period extending from the late oligocene around 27 ma ago to the early pliocene around 3 ma ago qualitative and quantitative spatial and temporal patterns are discussed thanks to the analysis of a large dataset of localities 695 that yielded large mammals and distributed over this period and area we show that the miocene is a key period in the installation of modern faunas in europe modern ruminants mainly cervids and bovids largely develop during the period considered and replace the oligocene inherited dominant faunas these replacements are triggered by different factors often extrinsic and constitute the roots of the present situation indeed a complex interplay between geographic palaeogeographic reorganisations and climatic factors warming and cooling events can be invoked to understand how faunas change geography seems to play a crucial role in the early miocene when it allows migration routes to open between europe asia and africa and in turn leads to a drastic increase of ungulate diversity that seems to be maintained in the middle miocene under the warm equable climates of the miocene climatic optimum the late miocene sees a global climatic deterioration leading to a decline in large mammals diversity and represents the root of the extant depleted situation regional comparisons indicate that endemism was already strong in the miocene especially in south eastern europe and that strong climatic belts already seem to have an impact on mammal communities since the late miocene the roots of the extant situation endemism and low diversity are therefore more complex and probably older than previously thought they are to be looked for before the quaternary climatic cycles and are the by product of deep time geographic and climatic events

contourite drifts moats and channels in the upper cretaceous chalk of the danish basin during the late cretaceous high global sea level meant that most of the nw european craton was flooded by the deep epeiric chalk sea the classical paradigm for chalk deposition envisages a quiet rain of minute skeletal debris of coccolithophorid algae and other pelagic organisms deposited as horizontal flat lying pelagic oozes with local redeposition by slumps slides and debris flows along faults and other structural features seismic data from the danish basin and elsewhere necessitate a revision of this paradigm these demonstrate that the chalk sea floor had a considerable relief commonly of more than a hundred metres amplitude comprising moats drifts mounds and channels seismic sections from the kattegat sea illustrate the development in the maastrichtian of a deep moat adjacent to a topographic ridge formed over the inverted nw se trending sorgenfrei tornquist zone the moat was up to 120 m deeper than its sw flank which was formed by an internally complex elongate drift up to 20 km wide with an estimated length of ca 200 km smaller mound like features channels and clinoform beds are superimposed on the large scale relief the sea floor relief is interpreted to have formed in response to persistent bottom currents flowing parallel to bathymetric contours the initial build up of the broad gently convex up sheeted drift was controlled by relatively low velocity bottom currents the region of highest current velocity was gradually shifted ne wards towards the inversion zone ridge resulting in the formation of the deep moat flanked by the elongate drift the current is interpreted to have flowed from the se towards nw on the basis of the internal architecture of the elongate drift and the nw ward branching and decrease in moat relief the architecture and morphology of the moat drift and other features of the chalk sea floor are in all aspects similar to contourite systems of modern continental margins it is accordingly proposed that the fundamental physical oceanographic concept contour currents and their resulting contourite drifts is extended to include the deep epeiric seas which covered nw europe during the late cretaceous

search for impact remains at the frasnian famennian boundary in the stratotype area southern france abstract in order to detect whether the end frasnian worldwide biotic crisis is related to an extraterrestrial impact the global stratotype section of the frasnian famennian boundary and auxiliary sections within the stratotype area have been examined for impact indicators iridium ni rich spinel bearing spherules and glassy microtektites this area is particularly well suited to the search for discrete events because it exhibits biostratigraphically continuous sections of sedimentologically homogenous off shore deposits different environmental settings on oxygenated deep water seamounts such as the stratotype section at coumiac and in oxygen depleted depressions la serre section are available the latter is investigated in more detail because it is the least condensed across the boundary which is determined by the first occurrence of the typical morphotype of palmatolepis triangularis the indicator of the first famennian conodont biozone samples from the biostratigraphically defined boundary and adjacent levels failed to provide significantly high ir values and no ni rich spinel or microtektite has been recovered this is in contradiction with the results of earlier investigations carried out by h geldsetzer on the same section in contrast the values of ir concentrations that we measured are always very low or not detectable the small overabundances observed in some samples which are about two orders of magnitude lower than what is currently observed at the cretaceous tertiary boundary are probably due to the accumulation of the normal flux of cosmic dust during periods of relatively low depositional rates or to a terrestrial origin at present we have no evidence that an extraterrestrial impact occurred at the f f transition

spinel from archean impact spherules abstract large meteorite impacts are recorded in distal fall deposits preserved in two early archean greenstone belt sequences 3 2 3 5 ga mapping stratigraphie and geochemistry studies have been used to identify at least four impact layers in the barberton greenstone belt of southern africa and one in the pilbara greenstone belt of western australia spherules that represent impact melt droplets distinguish these impact layers from associated tuffs spinel with unusual compositional traits occurs within spherules in two of these impact layers spinel is the only preserved primary phase and is found within up to 10 of the spherules in the best preserved layers some spherules contain up to 40 spinel which is often the only primary phase that crystallized within the spherules spinel morphologies include dendrites and skeletal octahedra typical of those found in high temperature melts spinel compositions are similar to those of cenozoic impacts including very high ni and ferric iron contents but the archean spinel is distinctive in being composed dominantly of the chalcophile elements fe ni cr and v this spinel is not metamorphic or metasomatic in origin closely associated komatiites in the underlying onverwacht group both fresh and highly altered have unaltered spinel with igneous compositions and morphologies quite distinct from the impact spinel characteristics of spinel preserved in these archean impact spherules suggest a rather complex series of steps following a large bolide impact initial high temperature reduction produced melt droplets some of which were immiscible silicate metal sulfide density differences allowed separation of some of these immiscible melts which subsequently evolved independently and formed spherules with highly variable chalcophile element contents oxidation during atmospheric reentry increased ni fe and fe 3 fe 2 in the chalcophile siderophile melts archean impact spinel has higher ni fe than cenozoic impact spinel though distinctly lower fe 3 fe 2 which probably reflects a substantially less oxidizing atmosphere during the archean the archean atmospheric oxidation may in fact be a transient phenomenon associated with a large impact into the terrestrial ocean resulting in very high atmospheric h 2 o h 2 bolide size is estimated to be 24 km in diameter based on the average diameter of 0 85 mm for the spinel bearing spherules this estimate is consistent with the observed ir fluence in spinel bearing impact layers of approximately 5 3 mg cm2 which would be produced by a 30 km diameter chondritic bolide

magnesioferrite from the cretaceous tertiary boundary caravaca spain abstract magnesioferrite grading toward magnetite has been identified as a very small but meaningful constituent of the basal iron rich portion of the cretaceous tertiary k t boundary clay at the barranco del gredero section caravaca spain this spinel type phase and others of the spinel group found in k t boundary clays at many widely separated sites have been proposed as representing unaltered remnants of ejecta deposited from an earth girdling dust cloud formed from the impact of an asteroid or other large bolide at the end of the cretaceous period the magnesioferrite occurs as euhedral frequently skeletal micron sized octahedral crystals the magnesioferrite contains29 11 ppb ir which accounts for only part of the ir anomaly at this k t boundary layer 52 1 ppb ir major element analyses of the magnesioferrite show variable compositions some minor solid solution exists toward hercynite spinel and chromite magnesiochromite a trevorite nichromite nife 2 o 4 nicr 2 o 4 component is also present the analyses are very similar to those reported for sites at furlo and petriccio umbria italy on the basis of the morphology and general composition of the magnesioferrite grains rapid crystallization at high temperature is indicated most likely directly from a vapor phase and in an environment of moderate oxygen fugacity elemental similarity with metallic alloy injected into rocks beneath two known impact craters suggests that part of the magnesioferrite may be derived from the vaporized chondritic bolide itself or from the mantle there is no supporting evidence for its derivation from crustal target rocks

the chicxulub asteroid impact and mass extinction at the cretaceous paleogene boundary the cretaceous paleogene boundary similar to 65 5 million years ago marks one of the three largest mass extinctions in the past 500 million years the extinction event coincided with a large asteroid impact at chicxulub mexico and occurred within the time of deccan flood basalt volcanism in india here we synthesize records of the global stratigraphy across this boundary to assess the proposed causes of the mass extinction notably a single ejecta rich deposit compositionally linked to the chicxulub impact is globally distributed at the cretaceous paleogene boundary the temporal match between the ejecta layer and the onset of the extinctions and the agreement of ecological patterns in the fossil record with modeled environmental perturbations for example darkness and cooling lead us to conclude that the chicxulub impact triggered the mass extinction

discovery of the oldest european ruminant in the late eocene of bulgaria did tectonics influence the diachronic development of the grande coupure abstract we describe the oldest known european ruminant bachitherium thraciensis sp nov from late eocene latest bartonian or early priabonian strata in bulgaria the new specimen which possesses the most primitive dental morphology known in the bachitheriidae family predates its western european relatives by at least 4 5 myr the discovery suggests that ruminants dispersed into europe in a series of east to west waves preceding and following the eocene oligocene boundary probably originating from asia the oldest ruminant reported here migrated into southeastern europe during a second wave comprising the grand coupure dispersal event ruminants moved into western europe at the eocene oligocene boundary a third wave composed by bachitheriidae and tragulidae arrived in western europe 2 myr later in the earliest oligocene the origin of this east to west diachronism was probably facilitated by orogenesis that episodically allowed dispersal of ruminants from asia through southeastern europe and into western europe in what we herein term the bachitherium dispersal event however none of the abundant perissodactyl fauna from southeastern europe migrated to western europe during this time because like their relatives in central asia they may not survive to terminal eocene cooling and aridity

regional travel time and slowness measurements for p waves in the distance range 40 57 a method for analysing travel times measured at a large array or a network of seismographs from many earthquakes within a specific region has been developed approximate relative station corrections are calculated from the residuals on a least squares line or least squares quadratic form fitted through the times for each earthquake and may be improved by iteration after a preliminary travel time curve has been derived accurate relative baseline corrections for each earthquake are also calculated iteratively and an optimum slowness distance curve is determined from the combined corrected travel times from all earthquakes using a trade off procedure calculations using synthetic travel time data suggest that abrupt changes in slowness of 0 4 s deg 1 due to the presence of triplications are generally resolvable provided that the effects of lateral variations are small even with random epicentre mislocations in the range 0 5 slowness measurements at a network of temporary stations deployed across australia do not show any discontinuities in slowness greater than 0 2 s deg 1 in the distance range 45 54 similar measurements at the warramunga array from the same source regions however suggest the presence of complexity in the slowness curve at distances close to 50 relative arrival times at the temporary network generally have standard deviations less than 0 25 s thus suggesting that details of structure finer than those derived from conventional travel time studies can be resolved

further evidence for radial velocity anomalies in the lower mantle wright andlyons 1981 used a least squares matching technique lmm and an adaptive processing method adp to study the behaviour of slowness and azimuth measurements made on two synthetic interfering wavelets having different arrival vectors and onset times we have applied these results to the analysis of real array seismograms some of the effects generated synthetically are frequently observed on real seismograms of earthquakes recorded at yellowknife at distances close to 50 and 90 we have also processed sufficient data to illustrate how the interference phenomenon can be used to confirm the presence of radial velocity anomalies in the lower mantle numerousp arrivals from south american earthquakes at distances between 78 and 98 suggest the presence of two radial velocity anomalies at depths close to 2400 and 2730 km below the caribbean region these anomalies also appear to vary laterally

end cretaceous brachiopod extinctions in the chalk of denmark the results of a detailed study of the brachiopods of the most complete cretaceous tertiary boundary in denmark nye kl v show an extinction pattern for this marine invertebrate group compatible with that reported for pelagic foraminifera and coccoliths and with the impact scenario the extinction is abrupt coinciding with the maastrichtian danian boundary there is no warning in the form of decreasing density decreasing diversity or early extinction of specialized groups the basal few meters of the danian are almost devoid of brachiopods and a danian brachiopod fauna starts almost as abruptly as the maastrichtian fauna disappeared the new fauna is similar to the maastrichtian as regards density and diversity and at maximum six species are common to both stages the northwest european masstrichtian chalk is composed mainly of the remains of coccoliths and pelagic foraminifera the mass extinction of these groups led to a total cessation of chalk production the chalk is overlain by a thin clay bed deposited partly under anoxic conditions this combination of anoxia and clay deposition coupled with a cessation of productivity led to the extinction of specialized groups such as the chalk brachiopods the surviving species included forms that could survive in well aerated shallow marine waters on substrates other than chalk

revising and refining the bryozoan zs mart seasonality proxy abstract the zs mart zooid size derived mean annual range of temperature seasonality proxy is based on temperature related variation in the sizes of zooids found in colonies of cheilostome bryozoans it has been used in a number of studies for inferring palaeoseasonality here we present a revised version of the equation for the zs mart proxy based on an appropriate regression analysis and an estimate of the error associated with predicted values we use this improved version to recalculate data used in studies that have employed the zs mart proxy and evaluate their conclusions in light of the revised estimates for seasonal regimes in order to investigate trans colony zooid size profiles in zooid size length and width 1195 zooids from 40 transects through 19 fossil and recent specimens of the malacostegine cheilostome bryozoan acanthodesia were measured using a stereomicroscope with eyepiece graticule the position of zooids within bifurcating rows of acanthodesia colonies is found to influence zooid size and this exemplifies potential problems for studies based on zooid size transects and random sampling of zooids our demonstration that oscillatory signals in zooid size possibly attributable to seasonal temperature regimes can be detected whilst accounting for other sources of variation confirms that a more sophisticated zs mart proxy may prove useful for constraining parameters in ocean models addressing questions about past climate however such a proxy will require more parameters than originally described along with larger raw datasets

floristic changes indicate a cooling climate in the eocene of southern england a major climatic cooling at the close of the eocene the terminal eocene event is suggested by studies of leaf floras in north america1 2 and by oxygen isotope studies of mollusc shells from the north sea3 and of planktonic and benthic foraminifera from the north and south pacific4 climatic fluctuations in the french palaeogene5 8 inferred from palynological studies are difficult to interpret in terms of this single event the pacific faunal studies4 and preliminary palynological evidence from the isle of wight southern england9 indicates an onset of cooling earlier in the eocene we have therefore examined fossil floras fruits seeds pollen and spores from the palaeogene deposits of the london and hampshire basins of southern england which form a continuous sequence from the early eocene we find no evidence for a sudden climatic change at the end of the eocene taken to be near the base of the bembridge marls in the hampshire basin10 our evidence in the form of two major periods of floristic change suggests a more gradual cooling commencing in the latest early eocene

the cretaceous palaeogene boundary succession at stevns klint denmark foraminifers and stable isotope stratigraphy the cretaceous palaeogene boundary exposed at stevns klint denmark provides an important location for the investigation of the end cretaceous event in this work we have used a number of sections across the boundary including the little described expanded stratigraphic sequence at kulstirenden which is located 7 km north of hojerup where most published work is derived using stratigraphical micropalaeontological and stable isotope 18o and 13c data we have shown that there is clear evidence of shallowing in the latest maastrichtian prior to and across the cretaceous palaeogene boundary there are significant changes in sea water temperature including an important cooling event in the very latest maastrichtian the 13c record in the expanded boundary clay fish clay sequence at kulstirenden indicates a number of significant excursions of decreasing magnitude up section the evidence from the distribution of the foraminifers has been incorporated with previous work to develop a sequence stratigraphical interpretation for the succession that can be compared to other cretaceous palaeogene boundary successions in europe

two large meteorite impacts at the cretaceous paleogene boundary the end cretaceous mass extinction has been attributed by most to a single asteroid impact at chicxulub on the yucatan peninsula mexico the discovery of a second smaller crater with a similar age at boltysh in the ukraine has raised the possibility that a shower of asteroids or comets impacted earth close to the cretaceous paleogene k pg boundary here we present palynological and 13 c evidence from crater fi ll sediments in the boltysh impact crater our analyses demonstrate that a post impact fl ora formed on the ejecta layer was in turn devastated by the k pg event the sequence of flrecovery from the k pg event is directly comparable with that in middle north america we conclude that the boltysh crater predated chicxulub by 2 5 k y a time scale that constrains the likely origin of the bodies that formed the two known k pg craters

barium anomaly preceding k t boundary possible causes and implications on end cretaceous events of k t sections in cauvery basin india israel ne mexico and guatemala maastrichtian danian strata of the cauvery basin as well as selected sections of ne mexico guatemala and israel record ba anomalies away from the cretaceous tertiary boundary ktb in addition to common occurrences of geochemical and stable isotopic anomalies across the ktb ba anomalies were recorded in monotonous shallow marine sandstones of the cauvery basin south india which contain minor amounts of ba orthoclase barium anomalies were observed also in shallow marine carbonates in sections of israel ne mexico and guatemala calculation of excess ba with reference to paas post archaen average australian shale comparison of coeval geochemical anomalies depositional pattern and associated petrographic and mineralogical features of the cauvery basin revealed that while a first ba peak was related to detrital influx the second ba peak was coincident with sea level fall which in turn may have been influenced by emission of volatile hydrocarbons and resultant climatic changes in view of intrinsic involvement of ba in various geochemical processes and occurrence of ba anomalies in k t sites distributed around the world ne mexico guatemala and israel it is suggested that probable causes of such widespread ba anomalies should be taken into consideration while analyzing end cretaceous events these observations support the views espoused by many workers who have stated that the k t boundary was also accompanied by many non catastrophic events that might have contributed to environmental stress on marine fauna as a result of which selective multi stage extinctions occurred

petrology and geochemistry of antarctic micrometeorites abstract the petrology and geochemistry of twentythree chondritic dust particles with masses of 1 47 g sizes 100 400 m were recovered from blue ice near cap prudhomme antarctica and studied by inaa asem empa and optical microscopy sample selection criteria were irregular shape and for a subsample black color with the aim of studying as many unmelted micrometeorites mms as possible of thirteen unmelted mms six were phyllosilicate dominated mms and seven were coarsegrained crystalline mms consisting mainly of olivine and pyroxene the remaining ten particles were largely melted and consisted of a foamy melt with variable amounts of relic phases scoriaceous mms thus of the black particles selected an astonishing portion 40 by number consisted of largely unmelted mms although unmelted most phyllosilicate mms have been thermally metamorphosed to a degree that most of the phyllosilicates were destroyed but not melted the original preterrestrial mineralogy is occasionally preserved and consists of serpentine like phyllosilicates with variable amounts of cronstedtite tochilinite like oxides olivine and pyroxene the crystalline mms consist of olivine low ca pyroxene tochilinite like oxides and occasional ni poor metal relics in scoriaceous mms consist of the same phases mineral compositions and the coexistence of phyllosilicates with anhydrous phases are typical of cm and cr type carbonaceous chondrites however the olivine pyroxene ratio 1 and the lack of carbonates sulfates and of very fe poor refractory element rich olivines and pyroxenes sets the mms apart from cm and cr chondrites the bulk chemistry of the phyllosilicate mms is similar to that of cm chondrites however several elements are either depleted ca ni s less commonly na mg and mn or enriched k fe as br rb sb and au in mms as compared to cm chondrites similar depletions and enrichments are also found in the scoriaceous mms we suggest that the depletions are probably due to terrestrial leaching of sulfates and carbonates from unmelted mms the overabundance of some elements may also be due to processes acting during atmospheric passage such as the recondensation of meteoric vapors in the high atmosphere most mms are coated by magnetite of platy or octahedral habit which is rich in mg al si mn and ni we interpret the magnetites to be products of recondensation processes in the high 90 km atmosphere which are therefore probably the first refractory aerominerals identified

the eocene oligocene ungulates from western europe and their environment abstract a survey of paleogene ungulates from western europe is drawn up from the results of previous work on the ungulate lineages of this period and from new data on two groups particularly representative of the oligocene ungulate fauna the ruminants and the cainotheriidae based on new material collected in localities of the quercy phosphorites the history of ungulates from western europe at the eocene oligocene transition is marked by different phases of extinction and origination related to environmental changes in this perspective the relative diversity of groups and the modifications of their tooth morphology which reflect a diet change resulting from vegetation modifications are analysed from the early eocene to the late oligocene in western europe the late eocene and the early oligocene was a period of transition with an important change in faunal and floral composition the diversity analysis of ungulates suggests that the grande coupure is the result of gradual climatic and geographic events that occurred from the middle eocene mammalian paleogene mp 13 14 reference levels to the early oligocene mp 21 22 reference levels during this period it has been demonstrated that important adaptive changes occurred in the ungulate dental pattern selenodonty in artiodactyls semihypsodonty in perissodactyls and appendicular skeleton fusion of the cuboid and navicular bones of the tarsus in artiodactyls these morphological modifications coincided with environmental changes that were less extreme than in north america

pliocene seasonality across the north atlantic inferred from cheilostome bryozoans abstract previous studies have shown an inverse correlation between zooid size in cheilostome bryozoans and ambient water temperature this relationship underlies the mart technique which uses intracolonial variation in zooid size to predict mean annual range in temperature experienced by bryozoan colonies during their life here we apply the mart technique to study early and mid pliocene bryozoans from central america panama costa rica the usa florida south carolina north carolina virginia and the uk suffolk to reconstruct palaeoseasonality across a range of latitudes for the north atlantic during the pliocene epoch compared to the present day our analyses suggest greater seasonality ca 4 5 c in the southern caribbean at the time of cayo agua formation deposition ca 4 25 ma in keeping with inferred upwelling prior to the closure of the isthmian barrier at 2 7 ma bryozoans also indicate seasonal upwelling on the gulf coast of florida in a similar manner to the present day because upwelling can be highly localised and prone to spatial and temporal variation in the gulf of mexico today it contributes little to a broad understanding of pliocene north atlantic waters however mart estimates for the coastal plain region indicate a general reduction in the annual range in temperature relative to the present suggesting that the colder surface waters that today reach south to cape hatteras had less influence in early to mid pliocene times these results along with evidence from other proxies strongly support reduced seasonality and warmer conditions along the eastern seaboard of the usa in the early to mid pliocene finally the mart estimates amongst coralline crag localities provide evidence for an increased annual range in temperature in the southern north sea than at present our study shows that bryozoan mart estimates provide a powerful independent proxy for palaeoseasonality and is the first to demonstrate that the mart technique can be applied to infer palaeoclimates across a wide range of latitudes focusing on a variety of geological formations and geographical regions

abrupt deep sea warming at the end of the cretaceous climatic and oceanographic variations during the last 2 m y of the maastrichtian inferred from high resolution 10 k y stable isotope analysis of the mid latitude south atlantic deep sea drilling project site 525 reveal a major warm pulse followed by rapid cooling prior to the cretaceous tertiary boundary between 66 85 and 65 52 ma cool but fluctuating temperatures average 9 9 and 15 4 c in intermediate and surface waters respectively this interval is followed by an abrupt short term warming between 65 45 and 65 11 ma which increased temperatures by 2 3 c in intermediate waters and decreased the vertical thermal gradient to an average of 2 7 c this warm pulse may be linked to increased atmospheric pco 2 increased poleward heat transport and the switch of an intermediate water source from high to lowmiddle latitudes during the last 100 k y of the maastrichtian intermediate and surface temperatures decreased by an average of 2 1 and 1 4 c respectively compared to the maximum temperature between 65 32 and 65 24 ma

interaction between bottom currents and slope failure in the late cretaceous of the southern danish central graben north sea the nw european chalk group was deposited in a deep epicontinental sea traditionally conceived as a quiet depositional setting that was only affected by redeposition along structural highs the chalk sea was however locally affected by powerful bottom currents during some periods three dimensional seismic reflection data from the southern central graben show abundant intra chalk morphological elements concentrated at two stratigraphic levels within the turonian campanian sequence both levels are topped by extensive unconformities the geometry of the elements produced by alongslope processes is interpreted as caused by se directed bottom currents flowing between the bo jens and adda ridges the highest current intensities led to the formation of the two unconformities judged by the occurrence of the largest current formed channels and drifts at these two stratigraphic levels this sea floor topography was locally modified by large scale downslope mass transport stratigraphical coincidence of the largest slumps and bottom current erosion suggests a coupling between downslope and alongslope processes current erosion impinged upon the slopes during periods of highest current speeds destabilizing the slope sediments and triggering slumping the smoothing of the bathymetry following local relaxation of the tectonic inversion accounted for the coeval deactivation of alongslope and downslope processes during the succeeding maastrichtian deposition

benthic faunal response to late maastrichtian chalk marl cyclicity at rordal denmark abstract chalk marl cyclicity is a common and characteristic feature of the upper cretaceous chalk group of nw europe the mainly small sized benthic fauna from an upper maastrichtian cyclic chalk marl succession at rordal denmark is analysed in order to interpret the composition and structure of the benthic fauna and to test if faunal density diversity composition and mode of life substrate were controlled by changes in lithology the material comprises 21 bulk samples weighing 5 kg each collected from all chalk and marl half cycles the samples were washed and sieved and yielded a total of 25 974 specimens these are referred to at least 75 species and 15 bryozoan morphotypes and form the basis for the establishment of 10 guilds the lithological cyclicity is not reflected by the distribution of individual species or by changes in average adult size but there is generally a higher species diversity and density in chalk compared to marl the chalk thus represents times of more favourable living conditions higher environmental stability and probably higher nutrient influx no changes in guilds between marl and chalk are found the variation in substrate character between the two lithologies was thus too small to have exerted any significant influence on the mode of life of the benthic fauna in spite of a difference in clay content averaging 10 two different fossil associations are recognized each covering one to two chalk marl cycles and characterized by a distinct fauna with similar ecological requirements if the chalk marl couplets represent precession cycles within the milankovitch band then the change from one association to the other and back again may represent the 100 000 years eccentricity cycle based on a calculated sedimentation rate of 6 cm ka 1

impact induced phase transformations at 50 60 gpa in continental crust an epma and atem study strongly shocked gneiss fragments from the allochthonous polymict breccia of the 23 ma old haughton impact crater were studied by optical microscopy electron probe microanalysis epma and analytical transmission electron microscopy atem the study is focused on the substantiation of shock induced phase transformations in rock forming minerals and their implications for post shock thermal regimes and impact age dating in the gneiss fragments the original layering is largerly preserved although all the minerals have experienced dramatic phase transformations chemically the various shock generated decomposition regions still reflect the pre shock mineralogy however significant heterogeneities exist on the 10 100 m scale four different regions of decomposition products can be distinguished epma 1 shocked biotite rich regions with strong variations in si al k fe and mg on the 10 m scale 2 shocked quartz with about 3 al and k and traces of fe and mg 3 a region with al si 1 which does not correspond to any pre shock mineral and 4 shocked k feldspar showing a significant deficit in k and traces of fe and mg on the nanometer scale a uniform bimodal reaction pattern emerges all minerals are transformed to new crystals embedded in a silica rich glass the shock generated crystals are 1 spinel in shocked biotite 2 quartz cristobalite and coesite in shocked quartz 3 an unknown polymorph of corundum al2o3 in feldspar and in the al si 1 region and 4 mullite in association with sio2 glass in shocked sillimanite grains all crystals range in size between 0 05 and 1 0 m taking into account estimated durations and pressure temperature conditions for shock wave passage and post shock temperatures the reactions observed can be ascribed to high temperatures during and after pressure release the different mineral glass parageneses suggest temperatures in excess of 1400 c moreover given the small size of the newly formed minerals very rapid cooling down to 1200 c is required

modeling the formation of the k pg boundary layer abstract in this paper we investigate the formation of the cretaceous paleogene k pg boundary layer through numerical modeling the k pg layer is widely agreed to be composed of meteoritic material and target rock from the chicxulub impact site that has been ejected around the globe and mixed with local material during final deposition the observed composition and thickness of the k pg boundary layer changes with azimuth and distance from the impact site we have run a suite of numerical simulations to investigate whether we can replicate the observational data with a focus on the distal k pg layer and the impact glasses at proximal sites such as beloc haiti previous models of the k pg ejecta have assumed an initial velocity distribution and tracked the ejecta to its final destination here we attempt to model the entire process from impact to the arrival of the ejecta around the globe our models replicate the observed ejecta thickness at proximal sites and the modeled ejecta is composed of sediments and silicate basement rocks in agreement with observational data models that use a 45 impact angle are able to replicate the total ejecta and iridium volume at distal sites and the majority of the ejecta is composed of meteorite and target sediments sub vertical impacts generate too little iridium and oblique impacts of 30 degrees generate too much however in contrast to observations models that involve ballistic transport of ejecta lead to ejecta thickness decreasing with increasing distance and are unable to transport shocked minerals quartz and zircon from the chicxulub basement rocks around the globe we suggest that much of the k pg ejecta is transported non ballistically and that the most plausible mechanism is through re distribution from a hot expanding atmosphere the results are important for future investigations of the environmental effects of the chicxulub impact

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

fossil horses and carbon isotopes new evidence for cenozoic dietary habitat and ecosystem changes in north america abstract the transformation from low crowned to high crowned horse teeth during the miocene has traditionally been interpreted as an adaptive response to the spread of savanna grasslands during the middle miocene by about 15 m y ago carbon isotope data from 50 north american horse teeth spanning eocene to pleistocene age indicate that savanna grasslands presumably dominated by c 4 grasses as they are today first became widespread much later than do horses with high crowned teeth prior to 7 m y horses had a c 3 based diet and after 7 m y horses started eating c 4 grasses this change in diet occurred when the major drop in the diversity of horses occurs during the late miocene the change in vegetation reflected in horses diet may be related to a significant reduction in atmospheric co 2 level toward the end of the miocene which provided the c 4 grasses with an adaptive advantage and led to their expansion at the expense of c 3 plants

pliocene climate and seasonality in north atlantic shelf seas this paper reviews north atlantic shelf seas palaeoclimate during the interval 4 3 ma prior to and incorporating the mid pliocene warm period ca 3 29 2 97 ma fossil assemblages and stable isotope data demonstrate northwards extension of subtropical faunas along the coast of the carolinas virginia yorktown and duplin formations relative to the present day suggesting a more vigorous florida current with reduced seasonality and warm water extending north of cape hatteras reconstructed annual range for virginia 12 30 c this interpretation supports conceptual models of increased meridional heat transport for the pliocene sea temperatures for florida lower pinecrest beds were similar to or slightly cooler than summers 25 27 c today and were probably influenced by seasonal upwelling of cold deep water reduced seasonality is also apparent in the coralline crag formation of the southern north sea with ostracods suggesting winter sea temperatures of 10 c modern 4 c however estimates from pliocene bivalves 3 6 16 6 c are similar to or cooler than the present day this mixed signal is problematic given warmer seas in the carolinas virginia and climate model and oceanographic data that show warmer seas in the mid pliocene eastern north atlantic this may be because the coralline crag formation was deposited prior to peak mid pliocene warmth

regional variations in spinel compositions an important key to the cretaceous tertiary event spinel found in spherules from cretaceous tertiary boundary sediments exhibits a wide range in composition and is distinguished from typical igneous spinel by high mg al and ni relatively low ti and cr and high fe2o3 feo solid solution compositions range from nearly pure magnetite to magnesioferrite to relatively pure mgal2o4 spinel the ni spinel trevorite is also a common component a regional variation in composition is also observed spinel from two north pacific sites has higher mg and al and lower ni and fe than spinel from two european sites and one south atlantic site the most probable source of the spinel is crystallization from molten silicate droplets produced from a major impact event the regional variations may provide a key to locating the impact site s

bryozoan growth mirrors contrasting seasonal regimes across the isthmus of panama abstract two highly environmentally contrasting localities on either side of the isthmus of panama were chosen to investigate the response of zooid size to differing seasonal regimes within colonies of cupuladriid bryozoans the bocas del toro region in the southern caribbean experiences a very low mean annual range of temperature mart while as a result of seasonal upwelling the gulf of panama in the eastern pacific experiences a high mart profiles of zooid size from ancestrula to colony margins were made on colonies from both localities results reveal that in colonies from the gulf of panama zooid size varies cyclically while in colonies from the bocas del toro region no strong trends are observed hence paralleling the respective seasonal temperature regimes these data support previous evidence that zooid size varies inversely with temperature we propose that given good taxonomic understanding profiling zooid size in this way could provide important information on aspects of life histories in both fossil and recent cupuladriids we were also able to show that the amount of variation in zooid size within cupuladriid colonies correlates well with the mart which the colony experiences this approach may be used to provide data on absolute marts over geological time by analysing zooid sizes in fossil cupuladriids the abundance of cupuladriids in the neogene of central america suggests that this technique could provide important corroborative data on regional environmental changes associated with the closure of the central american isthmus

crystalline micrometeorites from greenland blue lakes their chemical composition mineralogy and possible origin among the different populations of cosmic particles found in the greenland cryoconites the irregular shaped population is probably the most interesting one because it provides direct information about the nature of small meteoroids that impact the earth petrographic and trace element analyses of this material reveal two main families labelled as coarse grained cg and fine grained fg which have respectively compact and porous structures we have restricted our study to the coarse grained particles which contain large relic minerals and thus are well adapted to the sem and microprobe analysis techniques we compare the mineralogical associations of 49 coarse grained particles to that of meteorites and find that a majority of them belong to the same population of mineral grains previously found in cm chondrites and a minority of ordinary chondrites

abrupt climate change and transient climates during the paleogene a marine perspective detailed investigations of high latitude sequences recently collected by the ocean drilling program odp indicate that periods of rapid climate change often culminated in brief transient climates with more extreme conditions than subsequent long term climates two examples of such events have been identified in the paleogene the first in latest paleocene time in the middle of a warming trend that began several million years earlier the second in earliest oligocene time near the end of a middle eocene to late oligocene global cooling trend superimposed on the earlier event was a sudden and extreme warming of both high latitude sea surface and deep ocean waters imbedded in the latter transition was an abrupt decline in high latitude temperatures and the brief appearance of a full size continental ice sheet on antarctica in both cases the climate extremes were not stable lasting for less than a few hundred thousand years indicating a temporary or transient climate state geochemical and sedimentolog

stable isotope and foraminiferal changes across the cretaceous tertiary boundary at stevns klint denmark arguments for long term oceanic instability before and after bolide impact event abstract stable isotope and planktic and benthic foraminiferal analyses of the k t boundary transition at stevens klint denmark indicate a 100 500 kyr long period of instability in oceanic bottom water temperature and sea level during the latest maastrichtian from 2 7 m below and up to the k t boundary bottom water temperatures gradually cooled about 1 5 c as surface water temperatures remained constant at the k t boundary bottom water temperatures decreased additionally 3 c and then returned to pre boundary values just above the boundary interval coincident with the onset of the first temperature decrease there was a prominent sea level fall estimated between 50 100 m as observed in benthic and planktic foraminiferal assemblages as well as in a decreasing surface to bottom 13 c gradient about 40 cm below the iridium rich k t boundary clay sea level began to rise poor preservation of foraminifera above the k t boundary allows only tentative interpretation of danian events at stevns klint however sea level generally continued to rise interrupted by short sea level falls associated with the observed sea level changes are three important hiatuses at the contact between the white chalk and overlying grey white bryozoan chalk about 2 7 m below the k t boundary at or near the top of the fish clay zone pla parvularugoglobigerina eugubina missing and at the contact of the cerithium limestone and overlying bryozoan limestone about 60 cm above the k t boundary part of zone plc missing these unconformities are coeval with hiatuses observed in many continental shelf sections and indicate a global eustatic rather than regional isostatic response notable is that at stevns klint the episode of oceanic instability is registered over approximately the same stratigraphic interval in which supposed extraterrestrial amino acids occur a circumstance that may indicate a connection a gradual positive shift in 13 c is registered in both benthic and planktic foraminiferal assemblages in the upper maastrichtian at stevns klint the positive shift is followed by a prominent negative 13 c shift 1 3 at the k t boundary an upper maastrichtian positive 13 c excursion followed by a negative 13 c anomaly at or near the k t boundary has previously been observed in deep sea cores from the pacific ocean and the weddell sea antarctica implying a global event previous suggestions of a relation between the uppermost maastrichtian positive 13 c excursion and sea level variation are not supported by the data for stevns klint

les rongeurs de l eocene terminal et de l oligocene d europe comme indicateurs de leur environnement abstract palaeoecological interpretation of the occurrence of certain rodents in late eocene and oligocene strata from western europe is based on the establishment of five dental categories roughly linked with diet and environment time changes in species diversity and relative abundance in these categories are analyzed for the late eocene and oligocene periods the sequence is geographically limited quercy auvergne to avoid the mixing of environments that results from too general compiling cooling at the beginning of the late eocene created open areas testified by the occurrence of hypsodont rodents the great decrease in rodent diversity and species turnover at the grande coupure is probably related to the important decrease in temperature at the eocene oligocene boundary the less important diversity decrease at the mas de pauffie level mp 26 is perhaps an indication of a recurrent cooling at the beginning of the late oligocene maximum aridity also occurred at this level the calibration and correlation of these events with global events like the 29 ma decrease in temperature or the 30 ma great marine regression are discussed the decrease in abundance of issiodoromys with the great increase in species iversity of categories i and ii no to weakly hypsodont teeth during the late oligocene mark the development of forests related to increased moisture and temperature the analysis of time specific changes in the theridomyidae from their first occurrence to their extinction is related to the principal environmental events

stable seafloor conditions sea level and food supply during the latest maastrichtian at brazos river texas abstract the cretaceous paleogene k pg boundary extinction event is inextricably linked to the chicxulub impact environmental changes like sea level changes and changes in food supply prior to or after the impact could however have contributed to the biotic turnover in this study benthic foraminifera from two cores from the brazos river area in texas are quantitatively analyzed in order to reconstruct environmental changes across the k pg boundary cluster analysis as well as non metric multidimensional scaling reveals three distinct benthic foraminiferal assemblages an upper maastrichtian assemblage a post impact assemblage and a lower danian assemblage the rather uniform upper maastrichtian assemblage at brazos river composed of e g clavulinoides midwayensis gavelinella dumblei cibicidoides harperi gyroidinoides aequilateralis and bulimina kickapooensis indicates a stable paleodepth of about 75 100 m up to the k pg boundary food supply indicators such as percentage buliminaceae and foraminiferal numbers suggest a relatively low and stable food supply during this interval environmental disruption caused by the chicxulub impact led to the settlement of a typical pioneer assemblage characterized by endobenthic morphotypes such as ammobaculites spp and pseudouvigerina naheolensis during the early danian the typical midway type benthic foraminiferal shelf fauna e g alabamina midwayensis anomalinoides acutus gyroidinoides subangulatus praebulimina carseyae and cibicidoides alleni developed indicating a paleodepth of 75 100 m no clear water depth changes can be derived from the benthic foraminiferal record during this interval although the sedimentary record suggests a shallowing followed by a transgressive pulse in zone p1a food supply indicators suggest a lower food supply in the early danian than during the upper maastrichtian because of the stability of the late maastrichtian environment we conclude that environmental disruption caused by the impact was most likely the principal cause of the benthic foraminiferal turnover across the k pg boundary observed at brazos river

environmental change prior to the k t boundary inferred from temporal variation in the morphology of cheilostome bryozoans abstract fluctuations in the marine environment just prior to the k t extinction event have been inferred from several geological sections around the world most previous studies have employed isotope or trace element proxies this study uses morphological changes in erect and free living cheilostome bryozoans as a proxy to investigate environmental change through the final stages of the maastrichtian at the nye klov section in denmark the metrics used are 1 mean zooid size as a proxy for temperature 2 intracolony variation in zooid size as a proxy for degree of seasonality 3 density of defensive avicularia as a proxy for palaeoproductivity and 4 colony size and asymmetry as proxies for unfavourable environmental conditions three semi distinct phases in the benthic environment are evident the lowest 3 5 m of the roughly 4 5 m section experienced apparently normal marine conditions next low estimates of benthic seasonality and highly symmetrical and large colonies with many avicularia indicate a time of increased environmental stability subsequent to this quiescence the uppermost 20 cm of the section witnessed environmental volatility and deterioration with mean zooid sizes in all species falling dramatically suggesting a rapid warming or dysoxic event sharply increasing seasonality estimates implying unusual oceanographical states and the growth of small asymmetrical colonies with few avicularia all suggesting unfavourable conditions these data therefore indicate that strong environmental perturbations occurred just prior to the k t boundary in the danish basin such events may have contributed to biotic turnover at the k t boundary because cause and effect in macroevolution can be delayed however potential mechanisms of turnover need to be robustly tested within a detailed palaeoenvironmental framework construct from a suite of independent proxies

palaeoenvironmental implication of resedimented limestones shed from mississippian permian mid oceanic atoll type buildup into slope to basin facies akiyoshi japan abstract for better understanding of long term environmental changes in a mid oceanic atoll type buildup akiyoshi limestone group we examined the atoll derived carbonate sediments that were contemporaneously shed into the spicular chert of slope to basin facies ota group in the akiyoshi area southwest japan both of these two units are dated as upper visean to capitanian and interpreted as having laterally passed into each other on and around a mid oceanic seamount the resedimented limestone occurs as slab like bodies and isolated and laterally discrete smaller pods and thin beds and laminae in the spicular chert of the ota group the composite succession ca 105 m thick measured in slab like bodies is divided into the lower and upper units each of which consists of the sharp based calcarenite siliceous lime mud siltstone and spicular chert with blocks beds and laminae of calcarenite and siliceous limestone in ascending order the calcarenite forming slabs and smaller blocks are massive and dominantly comprises densely packed coarse crinoid debris and subordinate bryozoan fragments with no or sparse matrix the siliceous lime mud siltstone consists of siliceous sponges spicules minute calcitic skeletal debris and peloidal particles with the matrix of a mixture of lime mud and microcrystalline quartz the calcarenite and siliceous lime mud siltstone beds and laminae in the spicular chert occasionally contain graded and parallel laminae the massive calcarenite and graded calcarenite and siliceous limestone were formed by redeposition mainly of skeletal sands presumably by grain flows with minor debris flows and by mixing of sponge spicule rich siliceous sediments and redeposited lime mud and skeletal debris by muddy turbidites of distal facies respectively these redeposited carbonate sediments were exported from the akiyoshi limestone group onto the spicular sediments of slope to basin facies conodonts fusulinids and smaller foraminifers from the resedimented limestone indicate that the redeposition of the carbonate sediments took place dominantly in late visean to late bashkirian and subordinately in sakmarian to capitanian time the absence of the moscovian to asselian resedimented limestone implies much reduced carbonate shedding during this period the correlation with the interpreted palaeoenvironmental episodes in the akiyoshi buildup shows that late visean to late bashkirian and sakmarian to capitanian carbonate shedding events correspond to the times of generally warm climate and high sea levels in the akiyoshi buildup moscovian to asselian time which lacks records of carbonate shedding nearly corresponds to the moscovian to gzhelian cooling and sea level lowering in the akiyoshi buildup we consider that the shedding of carbonate sediments from the akiyoshi atoll is its depositional response to the warm climate and elevated sea levels and is compared with a sedimentary system of the highstand shedding of carbonates atoll type carbonates equivalent to the akiyoshi limestone group in the akiyoshi terrane also show comparable responses of carbonate shedding into slope and slope to basin facies

shocked quartz in the cretaceous tertiary boundary clays evidence for a global distribution shocked quartz grains displaying planar features were isolated from cretaceous tertiary boundary clays at five sites in europe a core from the north central pacific ocean and a site in new zealand at all of these sites the planar features in the shocked quartz can be indexed to rational crystallographic planes of the quartz lattice the grains display streaking indicative of shock in x ray diffraction photographs and also show reduced refractive indices these characteristic features of shocked quartz at several sites worldwide confirm that an impact event at the cretaceous tertiary boundary distributed ejecta products in an earth girdling dust cloud as postulated by the alvarez impact hypothesis

the cretaceous tertiary boundary at beloc haiti no evidence for an impact in the caribbean area abstract the k t boundary at beloc in haiti is characterized by a bed containing more or less spheroidal globules composed of either smectite or calcite a small fraction of these objects still contains well preserved glass particles which have been interpreted as the remains of tektites resulting from a bolide impact in the caribbean area however beloc glasses are markedly different from tektites and microtektites their structure and composition suggest that they are not impact generated products but are likely of volcanic origin on the other hand in sections which have probably preserved their original stratigraphy the globule bed showing well developed grading appears first in the sedimentary column followed by the ubiquitous cretaceous tertiary boundary ktb clay layer containing ir and ni rich spinels granulometric considerations indicate that the globule bed and the ir and spinel rich clay layer correspond to two distinct events we conclude that the globules at the ktb depositional sequence of beloc represent a local volcanic event slightly preceding the great ktb cosmic catastrophe our observations do not provide any unequivocal evidence that a cratering event occurred nearby

spheroids at the cretaceous tertiary boundary are altered impact droplets of basaltic composition sand size spheroids of k feldspar in the cretaceous tertiary c t boundary clay at caravaca southern spain were interpreted by smit and klaver as having solidified from a melt resulting from the impact of a large extraterrestrial body sand size spheroids of k feldspar glauconite and magnetite quartz have been found in the c t boundary clay in northern italy and spheroids of k feldspar and pyrite were found in the boundary clay at deep sea drilling project site 465a in the central pacific these spheroids have textures similar to those of rapidly crystallized feldspar and mafic silicates they are interpreted as diagenetically altered microcrystalline spherules of basaltic composition produced by the impact of a large asteroid in an ocean basin at the end of the cretaceous they are analogous to the glassy microtektites produced by impacts on more siliceous target rocks 21 references 4 figures

siderophile rich magnetic spheroids from the cretaceous tertiary boundary in umbria italy the magnetic fraction of some cretaceous tertiary k t boundary sediments sampled at two locations in italy contains a spheroidal component which has retained some relict mineral textures and possibly mineral chemistry from the k t event the spheroids contain small crystals 1 50 m of magnetite in a highly altered groundmass these crystals are commonly skeletal indicating formation by rapid growth from a high temperature liquid variable concentrations of ni mg and al differing by at least a factor of 5 in the magnetite may also reflect a relict chemistry these spheroids contain higher concentrations of ir and probably other siderophiles than the bulk sediment and may have been an important carrier for these elements at 65 myr this discovery supports evidence for a major accretionary event at the end of the cretaceous

faunal stability during the early oligocene climatic crash abstract traditional neo darwinism views species as highly flexible entities which adapt to climatic change by gradually evolving new morphologies of the 177 species of mammals from the upper eocene lower oligocene 37 30 ma white river group in the high plains most species are static for 2 4 million years on average and some persist much longer only three examples of gradualism can be documented in the entire fauna and these are mostly size changes contrary to expectations most mammalian species show no change during the earliest oligocene climatic crash 33 2 ma in spite of the fact that the vegetation changed from dense forests to open forested grassland mean annual temperatures dropped 13 c and conditions got much drier and more seasonal only a few mammalian lineages speciated a few more went extinct and the vast majority 62 out of 70 persisted through this climatic event with no observable response whatsoever this evidence shows that organisms are much less responsive to the environment than short term neontological studies suggest

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

late miocene atmospheric co2 concentrations and the expansion of c4 grasses the global expansion of c4 grasslands in the late miocene has been attributed to a large scale decrease in atmospheric carbon dioxide co2 concentrations this triggering mechanism is controversial in part because of a lack of direct evidence for change in the partial pressure of co2 pco2 and because other factors are also important determinants in controlling plant type distributions alkenone based pco2 estimates for the late miocene indicate that pco2 increased from 14 to 9 million years ago and stabilized at preindustrial values by 9 million years ago the estimates presented here provide no evidence for major changes in pco2 during the late miocene thus c4 plant expansion was likely driven by additional factors possibly a tectonically related episode of enhanced low latitude aridity or changes in seasonal precipitation patterns on a global scale or both

dinoflagellate based sea surface temperature reconstructions across the cretaceous tertiary boundary abstract quantitative analysis of organic walled dinoflagellate cyst dinocyst assemblages from closely spaced samples across the cretaceous tertiary boundary ktb at el kef nw tunisia caravaca se spain and stevns klint e denmark allows for reconstructions of sea surface temperature sst trends the combined dinocyst based sst curves indicate relatively stable warm conditions during the latest maastrichtian in contrast to strongly fluctuating and on average cooler conditions during the earliest danian in detail the results indicate cooling across the ktb immediately followed by an interval of pronounced warming the latter recorded in all studied sections two more cooling pulses may be recognized in the overlying interval followed by a gradual return to stable relatively warm conditions our data furthermore show that these ktb related climatic changes invoked distinct migration among organic walled cyst producing dinoflagellates a group not pushed to extinction at the ktb recordable in both hemispheres recent models predict periods varying between several months to 8 13 yr of global cooling impact winter and reduced solar transmission as a direct result of the chicxulub ktb impact followed by relatively long term excess co 2 related global warming our results are in line with such models but suggest that the impact related cooling phase may have lasted longer and that marked climatic instability continued to some 100 000 yrs following the ktb event s

benthic extinction and recovery patterns at the k t boundary in shallow water carbonates denmark abstract benthic extinction at the k t boundary in the danish basin is abrupt and indistinguishable from the termination of maastrichtian white chalk deposition the danian benthic fauna already fully established in the earliest danian nannoplankton zone np1 is essentially an impoverished maastrichtian fauna established through direct survival or limited evolution within well established clades already present in the maastrichtian of the danish basin however recovery of the early danian community is initially retarded the transition is illustrated in some detail for the locality nye klov here the lower 2 3 m of danian strata corresponding largely to the lower np1 subzone contains an extremely impoverished highly unusual dead zone community dominated by bourgueticrinid crinoids associated with other presumed soft ground specialists and devoid of such important faunal elements as cyclostome bryozoans brachiopods calcitic bivalves etc over the next metres the dead zone fauna is gradually replaced by more ordinary faunas and about 6 m above the boundary the characteristic early danian bryozoan limestone community is fully established

lilliput effect in late maastrichtian planktic foraminifera response to environmental stress the lilliput effect marks morphologic and intraspecies size reductions in response to environmental stresses commonly associated with the aftermath of mass extinctions this study shows that the lilliput effect is a universal biotic response associated with greenhouse warming mesotrophic or restricted basins shallow marginal settings and volcanically active regions during the late maastrichtian sedimentary sequences analyzed from tunisia egypt texas argentina the south atlantic and indian ocean reveal that the biotic stress response appears uniform regardless of the cause varying only with the degree of biotic stress overall late maastrichtian environments span a continuum from optimum conditions to the catastrophic mass extinctions with a predictable set of biotic responses relative to the degree of stress induced by oxygen salinity temperature and nutrient variations as a result of climate and sea level changes and volcanism early stages of biotic stress result in diversity reduction and the elimination of large specialized species k strategists leading to morphologic size reduction via selective extinction disappearances and intraspecies dwarfing of survivors later stages of biotic stress result in the complete disappearance of k strategists intraspecies dwarfing of r strategists and dominance by low oxygen tolerant small heterohelicids at the extreme end of the biotic response are volcanically influenced environments which cause the same detrimental biotic effects as observed in the aftermath of the k t mass extinction including the disappearance of most species and blooms of the disaster opportunist guembelitria

chlorite chemical composition change in response to the eocene oligocene climate transition on the northeastern tibetan plateau abstract the eocene oligocene climate transition eoct at 34 ma is a pronounced environmental reorganization that occurred in the cenozoic era and has been extensively studied via marine archives however to date there is still a less well dated continental record across the eoct which can mostly be attributed to a lack of suitable proxies used in the varied continental settings in terms of sedimentary facies provenance and climate thus resulting in a poor understanding of the continental response to this transition located on the northeastern tibetan plateau the qaidam basin is filled with continuous and well exposed cenozoic fluvio lacustrine sediments cenozoic lacustrine sediment has been proven to be an ideal archive to study the continental climatic response to the eoct here we present the detailed mineralogical and elemental composition of chlorite a widespread clay mineral in continental sediments formed by rock weathering collected from a lacustrine sequence in the northern qaidam basin to constrain the onset of the eoct and the related climatic response the results show that chlorite abundance crystallinity indices intensity ratios of chlorite diagnostic peaks and chemical composition collectively exhibit remarkable changes at 34 3 ma to be more specific the well crystallized fe mg rich chlorites were characterized by a high fe content before the eoct and turned into high mg content mg chlorites with poor crystallinity the chlorite chemical composition change is assumed to have been related to regional drying after the eoct thus providing new insights into the continental paleoenvironmental change based on this novel proxy

magnetostratigraphy and biostratigraphy of cretaceous tertiary continental deposits ager basin province of lerida spain abstract at fontllonga northeast spain province of lerida a nearly continuous outcrop covers the stratigraphic interval from the maastrichtian to the thanetian in continental deposits magnetostratigraphy of the section was determined from 72 samples the magnetic polarity sequence was satisfactorily correlated with chrons 32r to 26r top of lower maastrichtian to lower thanetian chron 29r in which the k t boundary occurs is unambiguously recognizable considering the biostratigraphic data charophyte ostracod palynomorph the k t boundary occurs in the uppermost part of the microchara cristata subzone which includes late cretaceous and early palaeocene species this subzone is interpreted as an interval of crisis following the late maastrichtian extinctions and preceeding the palaeocene radiation no ir rich horizon has been yet found in this section the stratigraphic position of the last dinosaur remains found in the chron 31n interval leaves open the question of a causal link between the extinction of cretaceous reptiles and the k t event

extinction survivorship and evolution of planktic foraminifera across the cretaceous tertiary boundary at el kef tunisia an expanded sediment record at el kef shows that the k t boundary extinctions of planktic foraminifera extend over an interval from 25 cm below the geochemical boundary ir anomaly to 7 cm above species extinctions appear sequential with complex large ornate forms disappearing first and smaller less ornate forms surviving longer the 14 species extinctions below the boundary appear unrelated to an impact event cretaceous species survivorship is greater than previously assumed about 10 species survive 22 into subzone p1a globigerina eugubina all cretaceous survivors are small primitive forms which are generally smaller than their ancestors in cretaceous sediments species evolution after the k t event occurs in two pulses the first new paleocene species evolve in the basal black clay zone po immediately after the major cretaceous extinctions evolving species are small and primitive similar to cretaceous survivors the second pulse in species evolution occurs in the lower part of subzone p1b with the appearance of larger more diverse species the first major increase in carbonate sedimentation and productivity occurs at this time and signals the recoveyr of the ecosystem nearly 300 000 years after the k t event the species extinctions prior to the generally assumed impact event implied by the ir anomaly and the long recovery period of the ecosystem thereafter cannot be explained by a single impact but suggest that multiple causes may be responsible such as climatic changes volcanism a sea level drop production of warm saline bottom water and the chemical consequences associated with increased salinity

formation of spinels in cosmic objects during atmospheric entry a clue to the cretaceous tertiary boundary event abstract magnetic spinels produced by oxidation of extraterrestrial objects in the atmosphere have a composition distinct from terrestrial spinels they are characterized by a high iron oxidation state arising from crystallization under high oxygen fugacities and a high nickel concentration due to the relatively high abundance of this element in extraterrestrial material the iron oxidation state increases from micrometeorites to meteoroid ablation material and to impact generated products this reflects a progressive increase of the oxygen fugacity corresponding to decreasing altitudes of crystallization spinels found at the cretaceous tertiary boundary are similar to those that crystallized from meteoroid ablation material and impact generated products supporting the view that a collisional event did occur at the end of the cretaceous

placers of cosmic dust in the blue ice lakes of greenland a concentration process occurring in the melt zone of the greenland ice cap has produced the richest known deposit of cosmic dust on the surface of the earth extraterrestrial particles collected from this region are well preserved and are collectable in large quantities the collected particles are generally identical to cosmic spheres found on the ocean floor but a pure glass type was discovered that has not been seen in deep sea samples iron rich spheres are conspicuously rare in the collected material

early archaean spherule beds in the barberton mountain land south africa no evidence for impact origin abstract detailed petrographical and geochemical studies are reported for several well documented occurrences of spherule rich layers in the barberton mountain land south africa which were previously inferred by lowe and co workers to be the result of early archaean meteorite impacts in contrast we made the following observations the textures of most spherules are not necessarily the result of impact but could instead be the product of radial or intersertal growth of crystals during secondary mineral formation there is no difference in the content of siderophile elements between spherule layers and layers devoid of spherules the siderophile element abundances are high where sulphide minerals e g pyrite gersdorffite and chalcopyrite and or chromite are present independent of the presence or absence of spherules high contents of e g ir up to 2700 ppb ni 0 96 wt and cr 1 6 wt were found in various samples abundances of these elements in chondritic meteorites are approximately 600 ppb 1 4 wt and 0 35 wt respectively resulting in respective meteoritic components in these samples of 450 70 and 460 we do not accept these high concentrations as primary meteoritic signatures impact melt rocks have typically 1 of a meteoritic component furthermore spherules of any kind are very rare in known impact deposits including the k t boundary if present at all they are not usually associated with any significant ir or pge anomaly the high abundances of the siderophile elements in some barberton samples and their enrichment in secondary minerals indicate that these elements have been remobilized and reconcentrated the pge interelement ratios have changed during remobilization as well thus the pge abundance patterns and ratios are not primary and cannot be used as an argument in favour of an impact origin either nickel rich cr spinels which are found in some of the barberton spherule samples have low fe 3 fe total ratios these ratios are incompatible with an extraterrestrial or impact origin because such impact derived spinels including those found at the k t boundary are highly oxidized and also have different chemical compositions there is also no indication of any evidence of shock metamorphism associated with the barberton spherule layers which is the commonly accepted definitive criterion for recognition of an impact origin this is unusual because such evidence is preserved even in heavily altered samples from deeply eroded archaean impact structures we conclude that while these spherule layers are clearly unusual and deserve further attention there is no convincing evidence for an origin by impact we suggest that they were formed by volcanic processes followed by extensive hydrothermal alteration

evolution of early cenozoic marine temperatures the equator to high southern latitude sea surface and vertical temperature gradients are reconstructed from oxygen isotope values of planktonic and benthic foraminifers for the following five time intervals late paleocene early eocene early middle eocene late eocene and early oligocene paleotemperatures are calculated using standard oxygen isotope temperature equations with adjustments to account for 1 variations in sea water 18o related to changes in global ice volume over time and 2 latitudinal gradients in surface water 18o these reconstructions indicate that sea surface temperatures sst of the southern oceans in the early eocene were as high as 15 c whereas temperatures during the late paleocene and early middle eocene reached maximum levels of 10 12 c by the late eocene and early oligocene high latitude sst had declined to 6 and 4 c respectively for most of the early paleogene low latitude sub tropical temperatures remained constant and well within the range of holocene temperatures 24 ndash 25 c but by the late eocene and early oligocene declined to values in the range of 18 to 22 c the late paleogene apparent decline in tropical temperatures however might be artificial because of dissolution of near surface foraminifera tests which biased sediment assemblages toward deeper dwelling foraminifera moreover according to recent plate reconstructions it appears that the majority of sites upon which the late eocene and early oligocene tropical temperatures were previously established were located either in or near regions likely to have been influenced by upwelling global deepwater temperature on average paralleled southern ocean sst for most of the paleogene we speculate based on the overall timing and character of marine sea surface temperature variation during the paleogene that some combination of both higher levels of greenhouse gases and increased heat transport was responsible for the exceptional high latitude warmth of the early eocene

platinum group elements in a 3 5 ga nickel iron occurrence possible evidence of a deep mantle origin the bon accord ba ni fe deposit occurs in chemically depleted ultramafic rocks of the circa 3 5 ga jamestown ophiolite complex in the barberton greenstone belt of the kaapvaal craton south africa the host rocks of the ba body are high temperature ultramafic tectonites which probably represent the upper mantle residue from which the overlying magmatic rocks were separated during partial melting ba is unusual both mineralogically and chemically it consists of a rare ni rich assemblage ni oxide bunsenite spinels trevorite nichromite and silicates e g liebenbergite the ni end member olivine and their altered equivalents nio average 38 and feo fe2o3 average 34 are the major chemical constituents the cu and s contents are very low both 2000 c lower mantle high ni fe and ni co ratios relative to c 1 chondrite suggest that ba might have been derived from siderophile rich material that remained in the lower mantle after inefficient core formation a model is presented wherein such a metal silicate heterogeneity is fractionated and oxidized during ascent through the mantle in a thermal plume which originates in the lowermost mantle the d layer some of its residue is finally incorporated as pods into the lithospheric mantle during formation of the archean oceanic crust inclusion of such fractionated pods in the old subcontinental keel of the kaapvaal craton might constitute a potential pge source which could have been tapped by subsequent magmatic activity

characteristics and origin of the glass spherules from the paleocene flood basalt province of western greenland abstract glass spherules have been found in several paleocene sandstone beds in central nuussuaq western greenland these beds are a mixture of glass smectite and calcite with rare occurrence of graphite and metal the glass varies from a basaltic to a basic andesitic composition and displays on a micrometer scale mg al ca fe ni and cu enrichments relative to the bulk composition these enrichments are associated with resorbed silicate crystals plagioclase pyroxene and olivine and partly oxidized metal sulphide inclusions the spherules have high co ni cu and ir concentrations positively correlated with fe the high cu content of the glass and the nonmeteoritic ir cu and ir ni or ir co ratios of the spherules exclude a meteoritic origin for these elements these compositional characteristics indicate a purely terrestrial origin and likely result from the contamination of a basaltic andesitic melt by sulphide liquid formed through reduction of a magma by c rich sediments this mechanism has already been proposed to account for the occurrence of fe bearing basalts and andesites in the nuussuaq and disko area this origin is further supported by the high cr content of the glasses consistent with a highly magnesian tholeiitic picrite basalt for the parent magma and the presence of metal sulphide and graphite in the spherule layers the occurrence in the glass of rounded magnetite resulting from the oxidation of sulphide and of dendritic spinel crystals characteristic of a rapid growth from a high temperature melt show that the spherules were quenched in an oxidizing environment we conclude that nuussuaq glass spherules result from rapid and incomplete oxidation of liquid droplets generated by one or several episods of lava fountains

characteristics and mass distribution of extraterrestrial dust from the greenland ice cap extraterrestrial grains with sizes 50 m can now be extracted in large numbers from terrestrial sediments but their origins are still uncertain at least 99 of these grains have been thought to be spherules1 2 resulting from the melting of their parent bodies in the atmosphere which destroyed their mineralogical composition here we present analyses of extraterrestrial grains extracted from six samples of cryoconite3 black dust collected from the melt zone of the greenland ice cap in addition to families of grains never reported before we have found a surprisingly high abundance of unmelted chondritic fragments in which the nonvolatile component of the parent bodies has been well preserved the mass distribution of the grains is very similar to that of the micrometeorite flux at 1 au ref 4 indicating that most of the grains are micrometeorites and not ablation products of larger meteorites these results yield new constraints on the ablation of such greenland micrometeorites as well as guidelines for using them as glaciological and geological markers

oceanic anoxia at the cretaceous tertiary boundary supported by the sulfur isotopic record abstract a temporary and drastic increase in 34s 32s ratio of whole rock sulfide has been recognized just at the cretaceous tertiary boundary within the continuous marine sedimentary sequence of the kawaruppu section in eastern hokkaido japan the apparent extent of fractionation with respect to inferred contemporaneous seawater sulfate in the anomaly zone which includes the boundary claystone at the bottom lies in the range of 25 10 whereas that in the lower and upper siltstone strata is roughly twice as much giving the values in the range of 49 10 the former is quantitatively equivalent in magnitude with the range of kinetic isotope effect in bacterial dissimilatory sulfate reduction and the latter with the typical variation range as observed in sedimentary diagenetic sulfides in ordinary oxic marine basins the present data would strongly support the temporary occurrence of an aerobe free anoxic oceanic sedimentary environment beginning just at the cretaceous tertiary boundary and continuing for approximately 70 000 years probably as a consequence of a certain catastrophic event responsible for the terminal cretaceous mass extinction

gradual mass extinction species survivorship and long term environmental changes across the cretaceous tertiary boundary in high latitudes stable isotope and planktic foraminiferal analyses across the cretaceous tertiary k t boundary transition at nye klov indicate longterm oceanic instability associated with global sea level fluctuations a gradual mass extinction and decreased magnitude of the 13 c shift in high latitudes oceanic instability which began at least 100 kyr before the k t boundary and continued for about 300 kyr into the tertiary was accompanied by a gradual faunal turnover the maximum sea level lowstand during latest maastrichtian is recorded about 75 cm below the k t boundary a sea level rise first in evidence at 20 cm to 40 cm below the boundary continued into zone p0 boundary clay this sea level rise was accompanied by 2 c of cooling in surface and bottom waters prior to the k t boundary 13 c values remained relatively stable up to 10 cm below the k t boundary a negative shift of 0 5 to 1 0 per mil occurred in the boundary clay in both planktic and benthic foraminifera the surface to deep 13 c gradient remained nearly unchanged in contrast to low latitudes where this gradient is virtually eliminated no sudden mass extinction occurred in this cosmopolitan high latitude fauna and nearly all cretaceous taxa thrived well into the tertiary when they gradually disappeared shallow seas dominated by cretaceous survivor taxa and a well developed oxygen minimum zone prevailed during the earliest tertiary short term sea level lowstands are marked by hiatuses at the top of zones p0 and p1a about 50 kyr and 230 kyr after the k t boundary respectively rising sea level reestablished normal marine conditions about 300 kyr to 350 kyr after the k t boundary coincident with the first post k t boundary recovery of the tertiary fauna and extinction of cretaceous survivors during this time high latitude regions temporarily acted as centers of origin and dispersal for planktic foraminifera long term oceanic instability gradual faunal turnover absence of a sudden mass extinction and greatly diminished 13 c shift in high latitudes suggest that a k t boundary bolide impact was not the primary cause for the k t boundary faunal transition moreover these data strongly imply that the destructive effects of the bolide impact would have been greatest in low latitudes and negligible in high latitudes

late maastrichtian chalk mounds stevns klint denmark combined physical and biogenic structures abstract upper maastrichtian chalk exposed at the sigerslev quarry stevns klint denmark is characterized by wavy and mound like bedding geometries outlined by bands of black flint nodules four morphological elements are recognized although bedding geometries are highly variable southward migrating mounds eastward migrating mounds chalk waves and evenly bedded chalk the mounds are interpreted as having been formed by currents carrying fine grained suspended sediment which was primarily deposited on the up current mound flanks bryozoans were prolific on the up current flanks and mound summits which stabilized the mounds increased bed roughness and the overall accumulation rate however accumulation thicknesses do not correlate consistently with bryozoan density the bryozoans were therefore important for the formation of the mounds but the distribution of bryozoans did not solely determine depositional thickness across a mound and thus mound growth pattern relatively long wavelength wavy bedded chalk show gentle convex up geometries and would probably be described as sediment waves if recognized in seismic sections the chalk waves were deposited under weaker current velocities than those active during mound formation the exposed succession is topped by more evenly bedded chalk which was deposited by quiet pelagic fall out of fine grained material the whole succession was deposited on the upper part of the northern flank of a large wnw ese trending 3 km wide depositional ridge with an amplitude of 35 40 m formed by contour parallel wnw ward flowing bottom currents the mounds may have been deposited by regional bottom currents or by spill over currents from the valley south of the large ridge the succession was deposited during varying bottom current intensities and the depositional architecture indicates a complex and dynamic environment the depositional style seems to be controlled by the interplay and relative importance of two end member processes those that were purely physical and related to the interaction between available grain sizes and hydrodynamics and those that were largely biological and associated with benthic growth and sediment trapping of mainly bryozoans examples of end member conditions are known from haute normandy france and the lower danian of stevns klint the structures described here adds to the considerable complexity of depositional styles in chalk

maastrichtian foraminiferal and paleoceanographic changes on milankovitch timescales milankovitch scale alternations in maastrichtian hemipelagic strata from ocean drilling program hole 1050c blake nose provide a natural experiment of paleoceanography and foraminiferal paleoecology in a tropical subtropical greenhouse ocean cycles are 30 50 cm thick and thought to reflect the 21 kyr precessional cycle high planktic 18o values are correlated with high planktic but low benthic 13c values indicating that cooler and or more saline surface waters were associated with higher productivity high productivity intervals are also characterized by high ca concentrations enrichment in feldspar and kaolinite and high relative abundance of heterohelix spp globigerinelloides spp and laeviheterohelix glabrans conversely low productivity intervals have low planktic 18o values high fe and ti concentrations enrichment in quartz illite and chlorite and relative increases in globotruncana spp and pseudoguembelina spp potential forcing mechanisms for observed covariation include cyclic variation in water column stratification variation in continental nutrient fluxes and changes in the intensity of upwelling

extraterrestrial spherules in glacial sediment from the transantarctic mountains antarctica structure mineralogy and chemical composition silicate and glassy spherules of probably extraterrestrial origin have been discovered in glacial till from localities in the beardmore glacier region transantarctic mountains antarctica these spherules are similar in structure appearance and composition to spherules found in deep sea sediments and in greenland most spherules have a shiny and smooth dark surface while some show a characteristic brickwork pattern composed of intergrown olivine crystals and magnetite dendrites several spherules have been sectioned after trace element analysis by inaa the interiors of the spherules contain olivine crystals of varying size predominantly of forsteritic composition set in a glassy fe rich and mg poor matrix the matrix contains very fine grained dendritic magnetite crystals and rare accessory wustite sem and microprobe studies show that most of the spherules have not experienced significant weathering trace element analyses for individual particles confirm the extraterrestrial nature of the spherules they have undifferentiated chondritic rare earth element ree patterns and are enriched in ir and other siderophile elements with ir contents between 10 and 1 000 ppb some spherules have experienced loss of volatile elements and some differentiation of siderophile elements e g ni the antarctic spherules which might be micrometeorites that melted during passage through the atmosphere or ablation spherules are amore significant addition to the collection of extraterrestrial microparticles of key importance is their high abundance in the sediment and the fact that they have been concentrated by glacial action less