late cenomanian to middle turonian high resolution carbon isotope stratigraphy new data from the munsterland cretaceous basin germany abstract new high resolution carbon isotope stratigraphies from two basinal pelagic carbonate successions in northern germany halle and oerlinghausen munsterland cretaceous basin resolve late cenomanian to early mid turonian carbon cycle variations at timescales of less than 100 kyr beside the major carbon isotope excursion of the late cenomanian oceanic anoxic event oae 2 11 small scale distinct features are precisely resolved in the 13c carbonate curve and related to boreal macrofossil zonations the small scale carbon isotope events correspond to secular 13c carbonate variations identified previously in the english chalk the boreal high resolution 13c carbonate curve shows a detailed coincidence with two tethyan 13c curves from italy what demonstrates the interregional significance of the 13c dates and allows their correlation within error limits of 40 kyr furthermore the new 13c curve enables the calibration of boreal and tethyan macro and microfossil zonations accordingly the tethyan calcareous nannoplankton boundary nc13 nc14 corresponds to the boreal fo of c woollgari the index taxon for the lower middle turonian boundary the cyclic appearance and the temporal spacing of the small scale carbon isotope events suggest that orbital forcing exerted control on surface water productivity and organic matter preservation at the sea floor

cenomanian turonian carbon isotope events recorded in terrestrial organic matter from northern japan carbon isotopic fluctuations recorded in terrestrial organic matter from the upper cretaceous cenomanian turonian succession of hokkaido japan show a remarkably similar pattern to isotopic fluctuation in carbonate carbon reported from southern england and the italian apennines chronological correlation for the cenomanian turonian section of japan is based on planktonic foraminiferal biostratigraphy with some additional data from macrofossils allowing a detailed comparison of isotope stratigraphies for japan and europe three distinct features of the isotope profile namely a positive spike near the cenomanian turonian boundary a shoulder in the lower middle turonian and a level segment in the middle upper turonian are observed in japan these features are biostratigraphically comparable and correlative with isotope profiles reported from europe the single factor influencing isotopic composition of both terrestrial organic carbon and marine carbonate carbon is isotopic change in the global co2 reservoir of the ocean atmosphere system if these three carbon isotope features are synchronous they may be inferred as having been caused by global phenomena and as providing global high resolution chemo stratigraphic markers carbon isotope stratigraphy could be an important bridge between terrestrial inland sequences and marine sequences

ocean circulation and calcareous nannoplankton evolution during the jurassic and cretaceous abstract spatial and temporal distribution of calcareous nannoplankton aid in the reconstruction of ocean circulation during the cretaceous biogeographic patterns of calcareous nannoplankton during the late cretaceous are mostly zonal reflecting mostly latitudinal gradients of surface water temperature during the middle cretaceous calcareous nannofossil assemblages are more strongly affected by surface water fertility concentration of limiting nutrients especially in a wide tropical belt between 50 and 45 n latitudes major upwelling regions off northwest africa in the south atlantic and the equatorial pacific divergence are apparent temporal changes in the composition of middle cretaceous nannofloras are indicative of changes in surface water fertility and vertical mixing at frequencies of tens to hundreds of kiloyears ka changes in the intensity of atmospheric circulation with frequencies close to the milankovitch cycles appear to be the ultimate cause of these minor changes in the circulation of the upper ocean calcareous nannofossil preservation patterns show that during the middle cretaceous deep waters were quite homogeneous with respect to carbonate saturation in the atlantic ocean but not in the indo pacific ocean where a more distinctive calcite compensation depth ccd is apparent water mass structure of the major oceans during the mesozoic was thus quite different taxonomic evolution of calcareous nannofossils was also strongly affected by ocean circulation and fertility major peaks in the rates of diversification coincide with anoxic events that is periods of increased preservation of organic carbon in the oceans which coincide with high sea level stands during anoxic events ocean circulation was sluggish vertical mixing was slow deep ocean ventilation poor and the concentration of limiting nutrients in surface waters was low increased competition for limiting nutrients and possibly preferential cropping of the dominant forms by zooplankton resulted in increased rates oof speciation during anoxic events periods of major production of nannofossil carbonate coincided with low sea level stands when oceans were more vigorously stirred and surface waters were more fertile the first such period was the latest jurassic when calcareous nannoplankton invaded the open oceans and became the major carbonate producers in the pelagic realm during the mesozoic the frequency of peaks and troughs in evolutionary rates is on the order of 10 30 ma and appears to be irregular the coincidence of periods of anoxia with high sea level stands which in turn appear to be caused by more rapid sea floor spreading indicates that the ultimate diving forces of nannoplankton evolution are processes in the earth s mantle these major tectonically driven fluctuations in ocean atmosphere circulation with frequencies of a few million to a few tens of millions of years are hereby named fischer cycles superimposed astronomically driven milankovitch cycles affected relative abundance patterns but not taxonomic evolution of calcareous nannoplankton rates of nannoplankton extinction are about five times higher than background rates at the end of the jurassic and orders of magnitude higher in the latest cretaceous possibly indicating a terrestrial or extraterrestrial catastrophe

forcing mechanisms for mid cretaceous black shale formation evidence from the upper aptian and lower albian of the vocontian basin se france calcareous nannoplankton palynomorph benthic foraminifera and oxygen isotope records from the supraregionally distributed niveau paquier early albian age oceanic anoxic event 1b and regionally distributed niveau kilian late aptian age black shales in the vocontian basin se france exhibit variations that reflect paleoclimatic and paleoceanographic changes in the mid cretaceous low latitudes to quantify surface water productivity and temperature changes nutrient and temperature indices based on calcareous nannofossils were developed the nutrient index strongly varies in the precessional band whereas variations of the temperature index reflect eccentricity since polar ice caps were not present during the mid cretaceous these variations probably result from feedback mechanisms within a monsoonal climate system of the mid cretaceous low latitudes involving warm humid and cool dry cycles a model is proposed that explains the formation of mid cretaceous black shales through monsoonally driven changes in temperature and evaporation precipitation patterns the lower albian niveau paquier which has a supraregional distribution formed under extremely warm and humid conditions when monsoonal intensity was strongest bottom water ventilation in the vocontian basin was diminished probably due to increased precipitation and reduced evaporation in regions of deep water formation at low latitudes surface water productivity in the vocontian basin was controlled by the strength of monsoonal winds the upper aptian niveau kilian which has a regional distribution only formed under a less warm and humid climate than the niveau paquier low latitude deep water formation was reduced to a lesser extent and or on regional scale only the threshold for the formation of a supraregional black shale was not reached the intensity of increases in temperature and humidity controlled whether black shales developed on a regional or supraregional scale at least in the vocontian basin the increased preservation of organic matter at the sea floor was more significant in black shale formation than the role of enhanced productivity

nannofloral extinction and survivorship across the k t boundary at caravaca southeastern spain detailed qualitative and quantitative studies of the calcareous nannofloral assemblages were carried out on 65 cm across the k t boundary interval of the caravaca section preservation of nannofloral assemblages is moderate to good reworking was identified in the lowermost danian but did not essentially influence the rest of the section studied the nannofloral study shows that most of the cretaceous taxa disappeared in the bfalloutq lamina a bio event which is synchronous with the mass extinction of the planktonic foraminifera and with significant geochemical anomalies beside these events a rapid decline of the calcareous nannofossils is recorded in the uppermost 12 cm of the maastrichtian about 4 ky prior to the k t boundary such decline becomes more pronounced in the transitional layer just below the k t boundary therefore predating the main extinction event this pattern is in agreement with other evidences of an unstable ecosystem and inputs of cold water taxa in this area with typical tethyan upper maastrichtian nannofossil assemblages two successive blooms of thoracosphaera spp followed by that of braarudosphaera bigelowii were identified at the base of the danian in the upper part of the studied sequence nannoflora records are already dominated by survivor as well as by incoming taxa showing an early pioneer calcareous nannofloral ecosystem about 25 ky after the k t boundary mass extinction event d 2005 elsevier b v all rights reserved

the cenomanian turonian boundary event and dinocyst record at ganuza northern spain abstract an excellent record of the cenomanian turonian transition zone occurs in an expanded section near the village of ganuza northern spain the sequence at ganuza shows no evidence of stratigraphic discontinuities and consists of an alternation of marl marly limestone and limestone which were deposited in a middle to outer shelf environment our results from palynological residues of 34 samples from the section indicate that number of cysts per gram of dry bulk sediment varies between a total of 7 and 236 and includes more than 130 taxa species diversity varies between 25 and 49 species and subspecies per sample the spiniferites ramosus group together with two other important taxa trichodinium castanea and exochosphaeridium phragmites dominate cyst assemblages other common taxa include palaeohystrichophora infusorioides canningia reticulata pterodinium cingulatum coronifera oceanica florentinia mantellii cleistosphaeridium aciculare dapsilidinium laminaspinosum and xenascus ceratioides successive last occurrences of florentinia cooksoniae litosphaeridium siphoniphorum and epelidosphaeridia spinosa uppermost cenomanian and the first occurrence of senoniasphaera rotundata lower turonian are used to characterize the transition from cenomanian to the turonian our results show that dinocysts occur continuously throughout the ganuza section across the c t boundary event marked by only a slight decrease in species diversity the most significant variation in the ganuzan section in relation to the c t boundary event is a decrease in cyst abundance from late cenomanian to earliest turonian the decline occurred just above a level marked by a benthic foraminiferal turnover as well as the extinction of rotalipora cushmani dinocyst minimum abundances occurred slightly later than minimum abundances of nannofossils our dinocyst results are thus consistent with a decrease in productivity during the latest cenomanian a new cycle is marked by a strong recovery of dinocysts immediately above the boundary event although a subsequent decrease recurred higher in the section dinoflagellates have a more general opportunistic behaviour than foraminifera and calcareous nannoflora and such behaviour may offer a viable explanation to account for the different patterns of response observed between the dinocysts and the other microfossil groups

the carbonate signal and calcareous nannofossil distribution in an upper jurassic section balingen tieringen late oxfordian southern germany total abundance assemblage composition and the stratigraphic distribution of the six most abundant species of calcareous nannofossil were analysed in the upper oxfordian succession of balingen tieringen western swabian alb south germany this locality represents a deep shelf less than 200 m environment that is strongly influenced by its proximity to the jura shallow platform nannofossil abundance negatively correlates with carbonate content as well as with accumulation rate calcareous nannofossils thus did not produce the bulk of carbonates and their abundance was essentially controlled by the import of allochthonous carbonate mud gradual increase in carbonate content in the balingen tieringen succession can be related to an intensified carbonate mud export from the jura shallow platform to the swabian alb deep shelf during the late oxfordian changes in the nannofossil assemblage composition along the profile are interpreted as primary although a partial control by diagenesis on the assemblage can not be completely excluded the coccoliths lotharingius hauffii watznaueria britannica cyclagelosphaera margereli watznaueria barnesae watznaueria manivitae and the incertae sedis schizosphaerella spp display their highest relative abundance one after the other in a stratigraphic order this nannofossil succession parallels the gradual increase in allochthonous carbonate mud accumulation on the deep shelf as well as the gradual decrease in the intensity of siliciclastic input recorded on the jura shallow platform this suggests a climatic control by humidity on shallow platform carbonate production and export basinwards and on nutrient availability in deep shelf surface waters that itself controlled the nannofossil assemblage composition therefore the succession of highest relative abundance of l hauffii w britannica c margereli w barnesae w manivitae and schizosphaerella spp can represent a trophic preference continuum from more eutrophic to oligotrophic conditions

calcareous nannofossil assemblages of oceanic anoxic event 2 in the equatorial atlantic evidence of an eutrophication event the calcareous nannofossils of the cenomanian turonian boundary interval of sites 1258 and 1260 ocean drilling program leg 207 have been studied in order to understand the depositional environment during oceanic anoxic event 2 oae2 in the equatorial atlantic nannofossil assemblages show a significant change in relative abundances during the positive 13 corg excursion interval the strong increase of the high productivity indicator zeugrhabdotus erectus and the simultaneous decrease of the oligotrophic taxa watznaueria barnesiae and watznaueria fossacincta are indicative of enhanced fertility the decrease of eprolithus floralis may be attributed to the surface water temperature increase during oae2 which is however not very significant 2 3 c as suggested by published tex86 data it seems more likely that the decrease of e floralis during oae2 was evoked by the breakdown of water column stratification indicating it as a deep dwelling species which prefers stratified waters with a deep nutricline prediscosphaera spp and retecapsa ficula which show a significant increase in relative abundances during oae2 seem to prefer eutrophic environments while amphizygus brooksii and zeugrhabdotus noeliae lower surface water fertility gartnerago segmentatum broinsonia spp watznaueria biporta and seribiscutum gaultensis decrease in abundances during oae2 it is not clear if they preferred an oligotrophic environment cooler surface waters or if they were inhabitants of the lower photic zone published geochemical data suggest that enhanced fertility and higher temperatures during oae2 may have been caused by submarine volcanic activity through the release of biolimiting micronutrients into the ocean and carbon dioxide into the atmosphere the breakdown of water column stratification may have increased further nutrient availability 2007 elsevier b v all rights reserved

the early toarcian and cenomanian turonian anoxic events in europe comparisons and contrasts two intervals of mesozoic time are demonstrably of sufficient geological brevity to qualify readily for the term anoxic event the earlyfalciferum zone orexaratum subzone of the toarcian and thewhiteinella archaeocretacea interval zone that straddles the cenomanian turonian boundary both periods of time saw regional deposition of anomalously organic rich strata black shales accompanied by a positive 2 pdb carbon isotope excursion in coeval biogenic carbonates and significant faunal change the duration of both events was probably less than half a million years and both were preceded by regional erosion and possible upwelling coincident sea level rise and transgression is likely a european view of these events however spotlights some significant differences whereas thefalciferum zone organic matter is generally more concentrated and more hydrogen rich on the palaeo european shelf than on the tethyan continental margins the reverse holds true for the black shales formed during thewhiteinella archaeocretacea interval zone furthermore the carbon isotope composition offalciferum zone organic matter from both north european and tethyan sites is anomalously negative compared to that developed in thewhiteinella archaeocretacea interval zone differing planktonic organisms may have been involved and their possible diverse ecological requirements may go some way to explaining the nature and distribution of facies deposited during these two events

u pb and re os geochronology of the aptian albian and cenomanian turonian stage boundaries implications for timescale calibration osmium isotope seawater composition and re os systematics in organic rich sediments abstract presented is the first absolute age for the basal albian from the schwicheldt ton member gault formation vohrum germany a 206 pb 238 u age of 113 1 0 3 ma is determined for chemically abraded zircon from a tuff horizon 65 cm above the aptian albian boundary the new u pb age although within uncertainty of the gts 2008 determination 112 1 ma is nominally older the younger gts 2008 basal albian age is obtained from cyclostratigraphy using an 40 ar 39 ar age from the base cenomanian the nominal difference between the gts 2008 age and new basal albian age is consistent with the documented ca 0 65 bias between u pb and 40 ar 39 ar geochronology the new 206 pb 238 u age calls into question a recently published age for the basal albian 106 9 0 4 ma determined from k ar glauconite analysis as well as the k ar age for the gl o international standard rhenium osmium isotope analysis of the basal albian grey clay of the schwicheldt ton member gault formation and basal turonian grey shale of the schwarz weisse wechselfolge hesseltal formation recording oceanic anoxic event 2 yields low and similar 187 re 188 os values 49 167 that are positively correlated with 187 os 188 os values for both sections imprecise re os ages 6 9 2 that overlap the stratigraphic boundary ages are determined aptian albian 108 9 6 2 ma cenomanian turonian 91 5 8 6 ma although the re os data suggest that organic rich sediments other than black shales are potentially amenable for re os geochronology the large uncertainties contrast with that from previous re os organic rich sediment studies the latter show sample sets with a significant spread in 187 re 188 os ratios several hundred units the imprecise re os geochronology presented here relates to the limited spread in the 187 re 188 os values the redox conditions of deposition are suggested to control the 187 re 188 os ratio of an organic rich sediment however trace element and re os data for samples from nw germany and previous re os geochronology studies show no direct relationship between 187 re 188 os values and the redox condition of the water column these results suggest that the fractionation of re and os in organic rich sediments is not controlled by water column redox conditions instead re os fractionation in organic rich sediments may be controlled by sedimentation rate recharge of re and os to the water column and or post deposition mobility of re and os within the sediment the initial os isotope composition of an organic rich sediment is inferred to reflect the seawater composition at the time of deposition for the cenomanian turonian boundary grey shale a seawater os composition of 0 33 0 02 is determined this os isotope composition contrasts with that of the stratotype section at pueblo colorado 0 15 and for those obtained from furlo italy and odp site 1260b 0 5 this data may suggest that the cenomanian turonian ocean was not homogeneous with respect to os suggesting either alternate oceanic circulation or basin dynamics

calcareous nannofossils of the cenomanian turonian boundary interval from the boreal realm wunstorf northwest germany abstract the cenomanian turonian boundary interval ctbi is marked by an intense climatic warming presumably caused by large magmatic eruptions this warming was characterised by one of the most prominent mesozoic perturbations of the carbon cycle the oceanic anoxic event 2 oae2 which is marked by a well pronounced positive carbon isotope excursion cie sediments of the oae2 interval often consist of organic rich black shales suggesting widespread bottom water anoxia during the ctbi this study focuses on calcareous nannofossils from the ctbi of a european section wunstorf core northwest germany a total of 105 samples were examined for calcareous nannofossils using the settling technique eight bioevents last occurrences corollithion kennedyi lithraphidites acutus first occurrences rotelapillus biarcus corollithion exiguum eprolithus octopetalus eprolithus eptapetalus quadrum gartneri eiffellithus eximius have been recognised throughout the middle cenomanian to middle turonian interval with the exception of eleven samples preservation is moderate to good calcareous nannofossils are abundant mean 2 0 billion specimens g sediment and highly diverse mean 58 species sample assemblages are dominated by watznaueria spp 32 3 prediscosphaera spp 13 4 zeugrhabdotus spp 11 2 and biscutum spp 10 5 pre oae2 and also post oae2 nannofossil assemblages show high abundances of biscutum spp 20 indicative for stable mesotrophic conditions the assemblages of the oae2 itself are marked by high values for watznaueria spp and low frequencies of biscutum spp making oligotrophic conditions during the oae2 likely high absolute abundances of organic walled dinoflagellates and the occurrence of frequent stress tolerant nannofossil genera like retecapsa spp in the organic rich intervals suggest however a deposition of black shales enhanced by high primary productivity thus dinoflagellates and calcareous nannofossils are interpreted to reflect different seasonal signals during the time of black shale deposition short term high fertile seasons allowed the blooming of the organic walled dinoflagellates whereas calcareous nannofossils dominated the longer oligotrophic seasons the black shale deposition was supported by the formation of large amounts of organic matter during fertile seasons as well as by surface water stagnation during oligotrophic seasons

late cretaceous cenomanian maastrichtian calcareous nannofossils from goban spur dsdp sites 549 551 implications for the palaeoceanography of the proto north atlantic abstract the early late cretaceous cenomanian early turonian is thought to have been one of the warmest periods of the phanerozoic this period was characterised by tropical sea surface temperatures of up to 36 c and a pole to equator gradient of less than 10 c the subsequent turonian maastrichtian was characterised by a continuous climatic cooling peaking in the maastrichtian this climatic cooling and the resulting palaeoceanographic changes had an impact on planktic primary producer communities including calcareous nannofossils in order to gain a better understanding of these cenomanian maastrichtian palaeoceanographic changes calcareous nannofossils have been studied from the proto north atlantic goban spur dsdp sites 549 551 in order to see potential differences between open oceanic and shelf dwelling nannofossils the data from goban spur have been compared to findings from the european shelf northern germany a total of 77 samples from goban spur were studied for calcareous nannofossils revealing abundant mean 6 2 billion specimens g sediment and highly diverse mean 63 species sample nannofossil assemblages the dominant taxa are watznaueria spp mean 30 7 prediscosphaera spp mean 18 3 zeugrhabdotus spp mean 8 3 retecapsa spp mean 7 2 and biscutum spp mean 6 6 the cenomanian assemblages of both goban spur open ocean and wunstorf shelf are characterised by elevated abundances of high fertility taxa like biscutum spp zeugrhabdotus spp and tranolithus orionatus early turonian to maastrichtian calcareous nannofossil assemblages of goban spur are however quite different to those described from european sections oceanic taxa like watznaueria spp retecapsa spp and cribrosphearella ehrenbergii dominate in goban spur whereas the fertility indicators biscutum spp and t orionatus are more abundant in the european shelf assemblages this shift from a homogeneous distribution of calcareous nannofossils in the cenomanian towards a heterogeneous one in the turonian maastrichtian implies a change of the ocean circulation the eddy ocean system of the cenomanian was replaced by an oceanic circulation similar to the modern one in the turonian maastrichtian caused by the cooling the increased pole to equator gradients resulted in an oceanic circulation similar to the modern one

calcareous nannofossil biostratigraphy and assemblages of the cenomanian turonian boundary interval implications for the origin and timing of oceanic anoxia a detailed nannofossil zonation has been derived for the cenomanian turonian boundary interval consisting of three zones two subzones and nine additional biohorizons this biostratigraphy based on the investigation of numerous sections from europe north america and africa allows accurate correlation of sections from shelf and deep sea environments the increased resolution helps solve several pertinent paleoceanographic and sedimentologic problems in this time period facies patterns are variable in this interval for numerous reasons a widespread hiatus occurred in the latest cenomanian and earliest turonian in much of northwest europe and may have been an indirect result of peak marine transgression in parts of the deep tethys dissolution of carbonate took place in undersaturated bottom waters or during early diagenesis only a few boundary sections mostly within the western interior united states are characterized by continuous carbonate deposition in many sections a 13c excursion which has been associated with the burial of large amounts of marine organic matter coincides with a facies change lower ratios of coccolith carbonate to micrite and poorer nannofossil preservation this excursion therefore may be strongly overprinted by diagenesis numerous nannofossil events indicate that the carbon excursion is slightly diachronous between sequences of the western interior and that the shift occurred distinctly later in this region than in northwest germany the data obtained do not invalidate the concept of a cenomanian turonian ocean wide anoxic event but show how local tectonic climatic and oceanographic perturbations have masked the global scenario in particular they indicate that carbon shifts may be basinal and not always oceanic phenomena a conclusion which can be rationalized with overall sluggish middle cretaceous circulation nannofossil assemblages in almost all sequences observed contain exceptionally high abundances of two dissolution resistant taxa in particular samples eprolithus floralis and broinsonia sp however the overall composition of assemblages does not change dramatically in the boundary interval in contrast to the macrofossils and foraminifera which suffered widespread extinctions

cenomanian turonian and δ13c and δ18o sea level and salinity variations at pueblo colorado stable isotopes of the surface dwelling planktic foraminifera hedbergella planispira its abundance variations and mineralogical analysis of the cenomanian turonian at pueblo co reveal cyclic variations in surface salinity due to changes in precipitation freshwater influx marine incursions and long term sea level fluctuations hedbergella planispira is a proxy for salinity variations as indicated by 2 4 more negative 18o values in intervals of peak abundances as compared to intervals with reduced populations negative 18o values reflect periods of brackish surface waters caused by freshwater influx during wet humid periods accompanied by increased clastic transport more positive 18o values reflect more normal marine salinities as a result of arid periods and or marine incursions and correlate with intervals of increased biogenic carbonate deposition the magnitude of salinity variations during the low sea level of the hartland shale is twice that during the sea level transgression of the bridge creek limestone the rapid positive 13c shift that marks the onset of oceanic anoxic event 2 oae 2 at pueblo occurred over a period of about 100 ky 93 90 94 00 ma and coincided with the major sea level transgression that culminated in the deposition of the basal bridge creek limestone a positive 13c shift also occurred in the rotalipora cushmani zone prior to oae 2 and coincided with a sea level rise and enhanced preservation of terrestrial organic matter the likely cause for oae 2 is depletion of 12c in the water column as a result of high primary productivity whereas an earlier r cushmani zone event was primarily caused by increased input of terrigenous organic matter both 13c events are associated with enhanced organic matter preservation and anoxic or dysoxic bottom waters

enhanced productivity led to increased organic carbon burial in the euxinic north atlantic basin during the late cenomanian oceanic anoxic event 1 three cenomanian turonian c t 93 5 ma black shale sections along a northeast southwest transect in the southern part of the proto north atlantic ocean were correlated by stable carbon isotope stratigraphy using the characteristic excursion in 13c values of both bulk organic matter om and molecular fossils of algal chlorophyll and steroids all three sites show an increase in marine organic carbon oc accumulation rates during the c t oceanic anoxic event oae the occurrence of molecular fossils of anoxygenic photosynthetic green sulfur bacteria lack of bioturbation and high abundance of redox sensitive trace metals indicate sulfidic conditions periodically reaching up into the photic zone before as well as during the c t oae during the c t oae there was a significant rise of the chemocline as indicated by the increase in concentrations of molecular fossils of green sulfur bacteria and mo al ratios the presence of molecular fossils of the green strain of green sulfur bacteria indicates that euxinic conditions periodically even occurred at very shallow water depths of 15 m or less during the c t oae however bottom water conditions did not dramatically change as indicated by more or less constant v al and zn al ratios at site 367 this suggests that the increase in oc burial rates resulted from enhanced primary productivity rather than increased anoxia which is supported by stable carbon isotopic evidence and a large increase in ba al ratios during the c t oae the occurrence of the productivity event during a period of globally enhanced organic carbon burial rates i e the c t oae points to a common cause possibly related to the formation of a deep water connection between north and south atlantic basins

tomographic inversion for the three dimensional seismic velocity structure of the aswan region egypt the thurber iterative simultaneous inversion program is used to determine the three dimensional p wave velocity structure in the aswan seismic region of egypt the tomographic inversion presented in this study is based on 1131 p phase observations at 13 stations from 89 local earthquakes all of which occurred within the kalabsha fault zone the assumed initial velocity model is that deduced from local explosion experiments the results indicate that the aswan region is characterized by a heterogeneous crust consisting of a shallow low velocity zone and a deeper high velocity anomaly seismic velocity structure within the shallow part demonstrates that the inferred change in velocity exists primarily across the east west trending kalabsha fault scarp whereas the high velocity zone is located south of this fault two well resolved low velocity zones appear within the upper 6 km of the crust the first coincides with a graben structure located between the kalabsha and seiyal faults and the second exists between the n s kurkur fault and the main axis of lake aswan both low velocity zones occupy an area of approximately 30 40 km located along the western bank of the lake the most significant result of this study is that the location of the deeper high velocity anomaly coincides with the concentration of seismic activity in the lower crustal layer

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

response of calcareous nannoplankton to the late cretaceous oceanic anoxic event 2 at oued bahloul central tunisia abstract oued bahloul is a reference section for the cenomanian turonian that was located on the north african palaeomargin where oceanic anoxic event 2 oae2 is represented by black limestones and grey marls biostratigraphic study allowed the identification of calcareous nannofossil uc3 to uc6 zones quantitative analyses of calcareous nannofossil assemblages indicate that high fertility surface water conditions predominated throughout most of the oae2 interval the most eutrophic conditions probably developed during deposition of the lowermost part of the whiteinella archaeocretacea zone uc3 to uc4 zones where nannofossil derived fertility indices reach high values and the small zeugrhabdotus gr predominates over biscutum spp the temperature index based on calcareous nannofossil assemblages indicates a warming at the beginning of the oae2 followed by progressive cooling the same trend indicated by 18 o bulk values the significant proportion of holococcoliths suggests high stress conditions in surface waters during most of the oae2 interval the enrichment in redox sensitive elements together with the abundance of low oxygen tolerant benthic foraminifera indicates dysoxic conditions both in the deep water column and sea bottom at the beginning of the oae2 w archaeocretacea zone geochemical detrital proxies indicate an enhanced rate of terrigenous supply during the oae2 interval resulting from increased riverine influx related to a more humid climate enhanced fluvial run off increased nutrient input to marine surface waters contributing to eutrophication recorded by calcareous nannoplankton and planktic foraminifera plankton consumption of surface water nutrients increased organic matter production whose decay contributed to the decrease in dissolved oxygen generating increasingly dysoxic anoxic conditions and favoring preservation of organic matter although low latitude nannofossil assemblages such as those of oued bahloul reflect an increase in nutrient availability during the oae2 interval assemblages from mid latitude areas record a decreased nutrient content

late maastrichtian warming in the boreal realm calcareous nannofossil evidence from denmark abstract the climate of the mid to late cretaceous was probably one of the warmest of the phanerozoic but by the late maastrichtian distinctly cool high latitude regions had developed studies from low latitude sites have demonstrated that the late maastrichtian cooling was punctuated by two pulses of warming but the response of nannoplankton to climatic fluctuation in the mid to high northern latitudes is not well documented a high resolution nannofossil study was undertaken on subsurface chalk sections of denmark which provide a stratigraphically complete record of late maastrichtian sedimentation of nannofossil ooze in an extensive mid to high latitude carbonate province the quantitative nannofossil data from cored sections through the upper maastrichtian chalk reveal subtle but significant shifts in taxa interpreted as having been sensitive to temperature fluctuations arkhangelskiella cymbiformis kamptnerius magnificus lucianorhabdus cayeuxii nephrolithus frequens and watznaueria barnesiae and indicate two late maastrichtian warming events correlatable with those of low latitude records and a decrease in surface water temperatures in the latest maastrichtian

volcano topography structure and intrinsic attenuation their relative influences on a simulated 3d visco elastic wavefield the seismic wavefield recorded on volcanoes can be significantly influenced by path effects scattering from the topography and internal volcanic structure can play a dominant role in the recorded seismograms intrinsic attenuation is also thought to play an important role in the characteristics of volcano seismic signals we use 3d numerical modelling of wave propagation in elastic and visco elastic media including complex velocity models and topography to investigate the scattering and attenuation characteristics of synthetic seismograms we generate 5 distinct volcano models and simulate wave propagation through these models using shallow and deep double couple broadband sources we then analyse 129 synthetic seismograms calculated on the free surface the synthetic seismograms resemble vt a and vt b events the scattering effect of the topography alone is capable of producing complex seismograms the introduction of an internal velocity structure increases the duration of these seismograms while the introduction of intrinsic attenuation decreases the duration but not the complexity we fitted our synthetic seismograms to the diffusion in a half space model to quantify the scattering and attenuation coefficients the scattering quality factor measured on all 129 stations for all 5 volcano models was similar therefore we deduce that the topography appears to be the dominant scatterer the intrinsic attenuation quality factor for each of the specific models cannot be accurately recovered using the diffusion in a half space model the measured quality factor is not only sensitive to the attenuation properties but also to the structural properties in all cases the scattering is more dominant than the intrinsic attenuation

calcareous nannofossils as paleoproductivity indicators in upper cretaceous organic rich sequences in israel abundant and diverse calcareous nannofossil assemblages were found in organic rich carbonate sequences which accumulated in a campanian maastrichtian upwelling belt along the southeastern tethys the sequences studied represent the inner shallower and the outer deeper parts of the upwelling belt the paleoenvironmental significance of selected nannofossil taxa and their utility in productivity reconstruction was established by comparing their distribution to foraminifera and dinocyst based productivity profiles based on the calcareous nannofossil assemblages a high productivity group and a low productivity group of species were determined the distribution of these groups agrees well with the dinocyst and foraminifera based productivity curves and hence can be used to record paleoproductivity changes the ratio between the high productivity and low productivity nannofossil groups the nannofossil index of productivity nip is proposed here as a productivity proxy that can be utilized in reconstructing basinal productivity development a quantitative analysis of the nannofossil assemblages indicates that their abundance and diversity increase towards the open sea in the outer and less productive part of the upwelling belt in the inner and more productive part of the upwelling belt the nannofossils assemblages become less abundant and less diverse relative to those of the open marine environment micula decussata and watznaueria barnesae are common to abundant in most samples m decussata becomes more abundant in poorly preserved samples on the other hand the distribution of w barnesae matches better with intermediate productivity levels

geochemical and climatic effects of increased marine organic carbon burial at the cenomanian turonian boundary perhaps the most significant event in the cretaceous record of the carbon isotope composition of carbonate1 2 other than the 1 2 5 negative shift in the carbon isotope composition of calcareous plankton at the cretaceous tertiary boundary3 is the rapid global positive excursion of 2 13c enrichment which took place between 91 5 myr and 90 3 myr late cenomanian to earliest turonian c t boundary event 1 4 5 this excursion has been attributed to a change in the isotope composition of the marine total dissolved carbon tdc reservoir resulting from an increase in rate of burial of 13c depleted organic carbon which coincided with a major global rise in sea level5 during the so called c t oceanic anoxic event oae 6 here we present new data from nine localities which demonstrate that a positive excursion in the carbon isotope composition of organic carbon at or near the c t boundary7 8 is nearly synchronous with that for carbonate and is widespread throughout the tethys and atlantic basins fig 1 as well as in more high latitude epicontinental seas the postulated increase in the rate of burial of organic carbon may have had a significant effect on co2 and o2 concentrations in the oceans and atmosphere and consequent effects on global climate and sedimentary facies

the cenomanian turonian boundary event oae2 and palaeoenvironmental change in epicontinental seas new insights from the dinocyst and geochemical records abstract organic walled dinoflagellate cyst dinocyst and geochemical records across the cenomanian turonian boundary ctb are presented for the nw european reference section at eastbourne england dinocyst and nannofossil fertility indexes indicate that an upwelling driven productivity pulse accompanied a eustatic sea level fall that preceded by at least 40 kyr the global rise in 13 c values that marks the onset of oceanic anoxic event 2 oae2 and the deposition of black shales in the deep ocean a marine productivity collapse in the latest cenomanian is evidenced by the falling absolute and relative abundance of peridinioid dinocysts believed to be the product of heterotrophic dinoflagellates this biotic change accompanied transgression and sharply rising sea surface temperatures following an atlantic wide episode of short lived cooling geochemical tracers provide evidence of caribbean colombian plateau volcanism the increase in water depth caused by the latest cenomanian transgression resulted in less eutrophic waters in epicontinental seas where ctb biotic turnover was driven largely by water mass changes rather than oxygen depletion the species richness absolute abundance ratio of dinocysts is proposed as a water mass stability proxy

changes in calcareous nannofossil assemblages across the paleocene eocene transition from the paleo equatorial pacific ocean quantitative analyses of selected calcareous nannofossils in deep sea sections recovered from the paleo equatorial pacific odp leg 199 provide new information about biostratigraphy biochronology and the evolutionary history of calcareous nannofossils across the paleocene eocene transition interval the sediment cores from odp leg 199 represent the first continuous paleocene eocene boundary sections ever to be sampled in the central equatorial pacific ocean calcareous nannofossil assemblages are studied to document the distribution of biostratigraphically useful taxa such as ericsonia discoaster fasciculithus rhomboaster and tribrachiatus focus is given to the evolution of the rhomboaster tribrachiatus lineage in the lower eocene interval at site 1215 and on the stratigraphic relationship of these taxa relative to species in the genus fasciculithus critical intervals of north atlantic dsdp site 550 have also been re examined the tribrachiatus digitalis morphotype was described at site 550 from an interval affected by down hole contamination partly originating from within the tribrachiatus orthostylus range the t digitalis morphotype represents an evolutionary transitional form between t contortus and t orthostylus entering the stratigraphic record within the range of the former species and disappearing within the lower part of the range of the latter species the subzonal subdivision of zone np10 hence collapses lithological and colour variability reflecting orbital cyclicity occur in the lower eocene of site 1215 permitting a relative astronomical age calibration of the tribrachiatus taxa the distinct rhomboaster spp discoaster araneus association also occurs in the paleo equatorial pacific ocean together with a marked decrease in diversity of fasciculithus spp site 1220 reveals a short peak abundance of thoracosphaera spp just above the p e boundary interval which probably reflects a stressed surface water environment

lithology and biostratigraphy of upper cretaceous marine deposits from the haţeg region romania palaeoenvironmental implications abstract this paper presents the lithological and biostratigraphical mainly based on calcareous nannofossils record of the marine sediments which crop out in the nw and se ha eg regions upper cretaceous marine deposition starts in these two regions in the early cenomanian both in the cc9 calcareous nannofossil zone and within uc1 uc2 biozones respectively in nw ha eg a hemipelagic sequence composed of red shales and marlstones followed by white marlstones probably associated with a deep water paleoenvironment marked the beginning of upper cretaceous marine sedimentation in the se marine deposition started with sandstones and calcarenites interlayered with actaeonella and ytruvia coquina indicating an infralittoral paleoenvironment from the cenomanian up to the coniacian the marine setting becomes progressively shallower in the two upper cretaceous marine depositional ha eg areas this change is marked by the occurrence of outer shelf deposits in the nw and inner shelf sediments up to infralittoral ones in the se these deposits are followed by lower santonian upper campanian turbidites in the nw and by lower santonian campanian pro parte red marlstones and upper campanian turbidites in the se the marine sedimentation ends in nw ha eg with distal turbidites late campanian in age placed in the cc22 calcareous nannofossil zone in the uc15d subzone respectively slightly above the first occurrence of the nannofossil uniplanarius trifidus towards the end of the campanian conglomerates and sandstones with actaeonella and ytruvia coquina yielding reworked nannofloras including late campanian taxa occur in se ha eg associated with the paroxysmal laramian tectonic phase continental deposition started probably within the campanian maastrichtian boundary interval both in the nw and se parts of the ha eg region during the late cretaceous interval different paleoenvironmental settings may be distinguished in the nw ha eg where a deep marine basin developed for most of the early cenomanian up to the late campanian interval and in the se ha eg characterised by an outer oscillating basin with an episodic shallow water deposition in the same interval despite the various backgrounds of the two regions some common regional events such as the early middle cenomanian and the early santonian early late campanian sea level highstand as well as the late cenomanian coniacian sea level lowstand were recognised in both investigated areas

the cenomanian turonian boundary at eastbourne sussex uk a proposed european reference section the cenomanian turonian boundary ctb section at eastbourne sussex england is the thickest at outcrop in the anglo paris basin is rhythmic throughout rich in macro micro and nanno fossils and shows less diagenetic alteration than other sections in nw europe geochemical and biostratigraphic data are all related to detailed rhythmic lithostratigraphy allowing correlation with the global boundary stratotype section to within 20 000 years and accurate estimates of rates of changes very detailed stable isotope curves for oxygen and carbon are presented and show that the build up phase of the ctb carbon excursion had two portions separated by a trough patterns of occurrence of coarse fraction benthic foraminifera 250 mm show two peaks of extinction corresponding to the two build up phases of the carbon excursion benthic and planktic foraminifera ostracods and calcareous nannofossils all show declines in diversity and abundance across the ctb foraminifera also decline significantly in size key biomarker events for the ctb include first occurrences of the ammonites fagesia catinus and mammites nodosoides the bivalve mytiloides the planktic foraminifera helvetoglobotruncana praehelveticaand marginotruncana renzi and the calcareous nannofossils quadrum intermedium q gartneri and eprolithus octopetalus and last occurrences of the ammonite sciponoceras the planktic foraminifera rotalipora greenhornensis and r cushmani the calcareous nannofossils corolithion kennedyi axopodorhabdus albianus lithraphidites acutus rhagodiscus asperand microstaurus chiastius cyclostratigraphy allows very precise correlation of isotopic and bioevents with other sections in europe and north america eastbourne is recommended as a nw european standard section 1999 elsevier science b v all rights reserved

short term euxinia coinciding with rotaliporid extinctions during the cenomanian turonian transition in the middle neritic eastern north atlantic inferred from organic compounds oceanic anoxic event 2 oae2 which occurred during the cenomanian turonian c t transition and lasted 1 m y is characterized by a positive global carbon isotopic excursion and stepwise extinctions in marine biota to examine temporal variations in the dissolved oxygen content of the water column shallow marine c t sediments from northern spain were analyzed for concentrations of dibenzothiophenes which are indicators of euxinic depositional environments and 2 3 6 trimethylarylisoprenoids which probably indicate photic zone euxinia the positive excursion in 13 c values of carbonates is accompanied by short term 10 3 10 4 yr and long term 10 5 yr increases in dibenzothiophene and 2 3 6 trimethylarylisoprenoid concentrations suggesting that the bottom water and photic zone of the eastern marginal sea of the north atlantic ocean were euxinic two of the short term increases in organic compound concentrations took place just after the last occurrence of the planktonic foraminifers rotalipora greenhornensis and r cushmani these transient maxima indicate that the extinction of both planktonic foraminifers was due to short term oaes lasting 10 3 10 4 yr

cenomanian turonian composite δ13c curve for western and central europe the role of organic and inorganic carbon fluxes abstract detailed 13 c stratigraphies have been published recently for several cenomanian turonian pelagic sections of southern england and the lower saxony basin of germany the observed changes in the 13 c record provide a useful tool for high resolution stratigraphic correlation and are used here to create a composite cenomanian turonian 13 c curve in a time related framework a best fit curve to 673 carbon isotope data is provided using the lowess regression scatterplot smoother the long term trend of the smoothed composite 13 c profile varies on time scales of 10 6 years and shows stable 13 c values through the lower cenomanian an increase in the middle and upper cenomanian with a major positive excursion around the cenomanian turonian boundary and a decrease through the lower and middle turonian short term fluctuations vary on time scales of 10 5 years and dominated the 13 c signal in the higher middle and upper turonian changes of the cenomanian turonian 13 c record have commonly been explained by variations in the organic carbon flux to the sedimentary reservoir in response to eustatic sea level change however mass balance consideration suggests also an influence of carbonate production and burial rate on the 13 c signal enhanced inorganic carbon burial increased the ratio of the inorganic to organic carbon fluxes and shifted the 13 c 12 c ratio to more negative values this pattern may be observed in the early and middle turonian 13 c long term record and correlates with the spatial expansion of pelagic carbonate deposits in epicontinental seas short term 13 c variations could be either a directly response to short term sea level changes reflecting local conditions in the european epicontinental sea or could represent changes in oceanic 12 c storage in response to the varying intensity of thermohaline circulation

biostratigraphy carbon isotopes and cyclostratigraphy of the albian cenomanian transition and oceanic anoxic event 1d in southern tibet abstract during the albian and cenomanian the earth underwent profound climatic and oceanographic changes that were recorded in sedimentary successions on a global scale carbon isotope records spanning this time interval have been established in the western tethys eastern pacific and north atlantic oceans but not yet in the eastern tethys ocean in this paper we present biostratigraphic chemostratigraphic and cyclostratigraphic characteristics of the uppermost albian lowermost cenomanian in an eastern tethyan section youxia southern tibet based on calcareous nannofossil biozones and the bulk rock 13c curve the albian cenomanian boundary interval acbi was identified and correlated to the western tethys and atlantic oceans in the youxia section 13c values range from approximately 0 to 1 3 0 03 to 1 31 four subevents a b c and d were distinguished in the acbi carbon isotope curve via correlation with other sections based on a spectral analysis of the carbonate content we recognized milankovitch short eccentricity 100 kyr and precession 22 2 kyr cycles suggesting that orbital variations modulated depositional processes the duration of the acbi was estimated at 311 kyr while oae 1d lasted for 233 kyr in the eastern tethys ocean consistent with the duration calculated from atlantic ocean records

the calcareous nannofossil response to the end cretaceous warm event in the tropical pacific abstract the response of calcareous nannofossils to the end cretaceous warming is investigated in the tropical pacific dsdp site 577a shatsky rise through the record of species richness shannon diversity distribution patterns and statistical treatments this event is marked by a strong acme of the tropical species micula murus and is accompanied by a decrease of placozygus spiralis the disappearance of biscutum constans and a decrease in bulk 13c indicative of a decrease in primary productivity an increase in abundance of other micula species at site 577a and a drop in species richness recorded in all sites of shatsky rise suggest stressed environmental conditions coincident with the end cretaceous warming the acme of m murus at shatsky rise and in the atlantic ocean is recorded within magnetochron c29r and correlates 1 with the intense warming as expressed in intermediate waters through the 18o of benthic foraminifera and in surface waters through poleward migration reduced diversity and dwarfism in planktonic foraminifer assemblages 2 with a sharp decline in marine 187os 188os chemical marker of deccan volcanic activity and 3 with a rise in the atmospheric pco2 record of terrestrial plants in texas usa probably triggered by deccan volcanic degassing however a drop of calcareous nannofossil cool water taxa in the equatorial and south atlantic as well as a first rise in abundance of m murus in the south atlantic and tropical pacific occur in the topmost part of chron c30n and correlates with the rise in palaeotemperature record of terrestrial plants in north dakota usa this suggests that initiation of the warming in the atmosphere and surface waters may predate the striking warming of intermediate water masses by 150 200 kyr the coincidence and the links between climate change volcanism geochemical and biotic events at the end of the maastrichtian thus remain to be fully elucidated

paleoceanographic changes at the northern tethyan margin during the cenomanian turonian oceanic anoxic event oae 2 abstract the late cenomanian early turonian oceanic anoxic event oae 2 represents major paleoceanographic and faunal perturbations samples from the northern tethyan margin rehkogelgraben eastern alps were investigated in order to trace the paleoceanographic processes paleoecologic conditions were reconstructed by combining the results of assemblage counts of indicative microfossil groups foraminifera and radiolaria assemblages size distributions and abundances show a tripartite subdivision for surface and bottom waters 1 oligotrophic surface conditions and oxic bottom waters with a reasonably high food supply for the late cenomanian interval 2 an oae period with black shales characterized by very low numbers but high diversities and a lack of high productivity indicators among planktic foraminifera low abundances of small sized benthic foraminifera indicate low oxic dysoxic conditions at the seafloor 3 post oae assemblages are characterized by mesotrophic planktic species and benthic foraminifera suggest oxic bottom waters it took about 300 ky to re establish a pelagic carbonate producing regime the semi enclosed basin situation of the penninic ocean is thought to be responsible for differences between the high productivity in the world ocean during the oae 2 and the overall absence of high productivity indicators and high foraminiferal diversities at rehkogelgraben the penninic ocean may have even served as a refuge during the environmental crisis

the ratios of dibenzothiophene to phenanthrene and pristane to phytane as indicators of depositional environment and lithology of petroleum source rocks abstract the ratio of dibenzothiophene to phenanthrene and the ratio of pristane to phytane when coupled together provide a novel and convenient way to infer crude oil source rock depositional environments and lithologies such knowledge can significantly assist in identifying the source formation s in a basin thereby providing valuable guidance for further exploration the ability to infer this information from analysis of a crude oil is especially valuable as frequently the earliest samples in a new area may be shows and or drill stem test samples from exploratory wells which are characteristically drilled on structural highs stratigraphically remote from the source formation s a cross plot of dibenzothiophene phenanthrene versus the pristane phytane ratios measured on seventy five crude oils from forty one known source rocks ranging in age from ordovician to miocene consistently classified the oils into the following environment lithology groups marine carbonate marine carbonate mixed and lacustrine sulfate rich lacustrine sulfate poor marine and lacustrine shale and fluvial deltaic carbonaceous shale and coal the dibenzothiophene phenanthrene ratio alone is an excellent indicator of source rock lithology with carbonates having ratios 1 and shales having ratios the dibenzothiophene to phenanthrene and the pristane to phytane ratios can also be used to classify source rock paleodepositional environments the classification scheme is based on the premise that these ratios reflect the different eh ph regimes resulting from the significant microbiological and chemical processes occurring during deposition and early diagenesis of sediments the dibenzothiophene phenanthrene ratio assesses the availability of reduced sulfur for incorporation into organic matter and the pristane phytane ratio assesses the redox conditions within the depositional environment interpretation of these ratios has been aided by quantitative biomarker analysis and by carbon isotope data for pristane and phytane obtained by gas chromatography isotope ratio mass spectrometry

potential use of stable oxygen isotope composition of thoracosphaera heimii dinophyceae for upper watercolumn thermocline temperature reconstruction abstract to investigate the potential use of the stable isotope composition of the vegetative cysts of the photosynthetic dinoflagellate thoracosphaera heimii for quantitative palaeotemperature reconstructions a method has been developed to purify t heimii cysts from sediment samples stable oxygen and carbon isotopes have been measured on t heimii cysts from 21 surface sediment samples from the equatorial atlantic and south atlantic oceans calculated temperatures based on the palaeotemperature equation for inorganic calcite precipitation generally reflect mean annual temperatures of the upper water column notably of thermocline depths although the present results suggest that the isotopic composition of t heimii shells might be formed in equilibrium with the seawater in which the shells are being formed future investigations are required to determine possible effects of metabolic and kinetic processes on the fractionation process this pilot study therefore forms the basis for future investigations on the development of this tool and the determination of a species specific palaeotemperature equation the wide geographic and stratigraphic distribution of t heimii cysts in sediments the stable position of t heimii within the water column and the high resistance of its cysts against calcite dissolution underline its potential for a wide usability in palaeotemperature reconstructions

onset of the mid cretaceous greenhouse in the barremian aptian igneous events and the biological sedimentary and geochemical responses basalts and biostratigraphy dated at 125 120 ma from the ontong java and manihiki plateaus in the western pacific evidence the largest volcanic event in earth history in at least the past 160 m y the intervening nova canton trough rifted at about 121 118 ma and a number of guyots and seamounts formed concurrently or slightly later geological events that probably were responses to these volcanic tectonic events occurred in the following chronostratigraphic order biotic fluctuations began at about 122 5 ma at about 122 0 ma 87sr 86sr began to decline slowly metal concentrations of co mn pb yb and cu in sediments peaked at about 121 5 121 2 ma changes in planktonic communities and sedimentation culminated in a nannoconid crisis just prior to 120 5 ma and in the selli black shale oae la at about 120 5 119 5 ma a sharp drop in 13c occurred at the beginning of the selli event and rebounded into a longer positive excursion that reached a peak after the selli event at about 119 5 118 5 ma at 120 5 ma 87sr 86sr declined rapidly and reached a minimum at about 116 113 ma we speculate that the intensity of these latter responses suggests a corresponding peak in volcanic tectonic activity at about 121 119 ma

modeling evidence for enhanced el nino southern oscillation amplitude during the last glacial maximum we present a numerical eigenmode analysis of an intermediate el nin o southern oscillation enso model which is driven by present day observed background conditions as well as by simulated background conditions for the last glacial maximum lgm about 21 000 years ago the background conditions are obtained from two lgm simulations which were performed with the national center for atmospheric research climate system model csm1 4 and an earth system model of intermediate complexity ecbilt clio our analysis clearly shows that the leading present day unstable recharge discharge mode changes its stability as well as its frequency during lgm conditions simulated lgm background conditions were favorable to support large amplitude self sustained interannual enso variations in the tropical pacific our analysis indicates that off equatorial climate conditions as well as a shoaling of the thermocline play a crucial role in amplifying the lgm enso mode

carbon and oxygen isotope stratigraphy of the english chalk and italian scaglia and its palaeoclimatic significance a detailed carbon and oxygen isotope stratigraphy has been generated from upper cretaceous coastal chalk sections in southern england east kent culver cliff isle of wight eastbourne and seaford head sussex norfolk coast and the british geological survey bgs trunch borehole norfolk data are also presented from a section through the scaglia facies exposed near gubbio italian apennines wherever possible the sampling interval has been one metre or less both the chalk and scaglia carbon isotopic curves show minor positive excursions in the mid cenomanian mid and high turonian basal coniacian and highest santonian lowest campanian there is a negative excursion high in the campanian in chalk sections that span that interval the well documented cenomanian turonian boundary spike is also well displayed as is a broad positive excursion centred on the upper coniacian a number of these positive excursions correlate with records of organic carbon rich deposition in the atlantic ocean and elsewhere the remarkable similarity in the carbon isotope curves from england and italy enables cross referencing of macrofossil and microfossil zones and pinpoints considerable discrepancy in the relative positions of the turonian coniacian and santonian stages the oxygen isotope values of the various chalk sections although showing different absolute values that are presumably diagenesis dependent show nonetheless a consistent trend the east kent section which is very poorly lithified indicates a warming up to the cenomanian turonian boundary interval then cooling thereafter regional organic carbon burial documented for this period is credited with causing drawdown of co 2 and initiating climatic deterioration inverse greenhouse effect data from other parts of the world are consistent with the hypothesis that the cenomanian turonian temperature optimum was a global phenomenon and that this interval represents a major turning point in the climatic history of the earth

reconstructing past sea surface temperatures correcting for diagenesis of bulk marine carbonate abstract a numerical model which describes oxygen isotope exchange during burial and recrystallization of deep sea carbonate is used to obtain information on how sea surface temperatures have varied in the past by correcting measured 18o values of bulk carbonate for diagenetic overprinting comparison of bulk carbonate and planktonic foraminiferal 18o records from odp site 677a indicates that the oxygen isotopic composition of bulk carbonate does reflect changes in sea surface temperature and 18o at odp site 690 we calculate that diagenetic effects are small and that both bulk carbonate and planktonic foraminiferal 18o records accurately reflect paleogene warming of high latitude surface oceans biased from diagenesis by no more than 1 c the same is likely to be true for other high latitude sites where sedimentation rates are low at dsdp sites 516 and 525 the effects of diagenesis are more significant measured 18o values of eocene bulk carbonates are more than 2 lower at deeply buried site 516 than at site 525 consistent with the model prediction that the effects of diagenesis should be proportional to sedimentation rate model corrections reconcile the differences in the data between the two sites the resulting paleotemperature reconstruction indicates a 4 c cooling of mid latitude surface oceans since the eocene at low latitudes the contrast in temperature between the ocean surface and bottom makes the carbonate 180 values particularly sensitive to diagenetic effects most of the observed variations in measured 18o values are accounted for by diagenetic effects rather than by sea surface temperature variations we show that the data are consistent with constant equatorial sea surface temperatures through most of the cenozoic with the possible exception of the early eocene when slightly higher temperatures are indicated we suggest that the lower equatorial sea surface temperatures for the eocene and oligocene reported in other oxygen isotope studies are artifacts of diagenetic recrystallization and that it is impossible to reconstruct accurately equatorial sea surface temperatures without explicitly accounting for diagenetic overprinting

mid cretaceous strontium isotope stratigraphy of deep sea sections large variations exist between published mid cretaceous late barremian to early turonian stages seawater sr isotope stratigraphies this has resulted in disparate interpretations of crustal production rates we report on a detailed investigation of seawater sr isotope stratigraphy based on foraminifers and where available on inoceramid bivalves from 12 mid cretaceous deep sea drilling project and ocean drilling program sections the effects of diagenesis are assessed using scanning electron microscope observations and traceelemental analyses but are best distinguished by comparing the 87 sr 86 sr values of similarage samples from different sites strontiumisotope analyses compiled from 9 of 12 sites that have detailed age control define one band of common values this band is used as a composite curve which presumably represents seawater 87 sr 86 sr values the composite curve shows a trough of markedly lower 87 sr 86 sr values in the aptian and early albian stages higher but constant values for the middle albian cenomanian stages followed by a decrease in 87 sr 86 sr values in the early turonian

cenomanian turonian transition in a shallow water sequence of the sinai egypt environmental and depositional changes across the late cenomanian oceanic anoxic event oae2 in the sinai egypt are examined based on biostratigraphy mineralogy 13c values and phosphorus analyses comparison with the pueblo colorado stratotype section reveals the whadi el ghaib section as stratigraphically complete across the late cenomanian early turonian foraminifera are dominated by high stress planktic and benthic assemblages characterized by low diversity low oxygen and low salinity tolerant species which mark shallow water oceanic dysoxic conditions during oae2 oyster biostromes suggest deposition occurred in less than 50 m depths in low oxygen brackish and nutrient rich waters their demise prior to the peak 13c excursion is likely due to a rising sea level characteristic oae2 anoxic conditions reached this coastal region only at the end of the 13c plateau in deeper waters near the end of the cenomanian increased phosphorus accumulations before and after the 13c excursion suggest higher oxic conditions and increased detrital input bulk rock and clay mineralogy indicate humid climate conditions increased continental runoff and a rising sea up to the first 13c peak above this interval a dryer and seasonally well contrasted climate with intermittently dry conditions prevailed these results reveal the globally synchronous 13c shift but delayed effects of oae2 dependent on water depth

isotopic studies in cretaceous research an introduction a scienti c session on isotopic studies in cretace ous research was held within the framework ofthe european geoscience union egu isotopegroup in vienna in 2010 the idea summarizingthe topics in a book materialized during egu 2010 and we are grateful to pier de groot for a very well organized session the participants to this book present a broadrangeof studies groupedin marine sections includ ing oae events and the cretaceous paleoceneboundary mixed marine freshwater as well ascontinental records the investigated pro les arefound worldwide from europe austria romania spain asia china south america brazil colombia andnorthamerica usa andarespan ning from the early cretaceous to the cretaceous paleocene boundary this special publication is addressed to thescienti c investigator interested in isotopic studiescombined with geochemical palaeontological andmineralogical proxies and based on eldwork inorder to elucidate various aspects of cretaceouspalaeoceanography and continental environmentalconditions the isotopic analytical investigations used inthe different studies included in this volume com prise carbon and oxygen isotopic composition ofcarbonates calcite and siderite carbon isotopiccomposition of bulk organic matter or individualbiomarkers in sediments oxygen isotopic compo sition of phosphates oxygen isotopic compositionofsilicatemineralsandwholerock hydrogenisoto pic composition of silicates and whole rock and

further evidence for the development of photic zone euxinic conditions during mesozoic oceanic anoxic events periods in earth history characterized by extensive organic carbon deposition so called oceanic anoxic events oaes are the subject of considerable scrutiny insight into the extent of anoxic conditions in the water column has been provided by the reported occurrence of derivatives of isorenieratene a carotenoid found only in green sulphur bacteria and thus indicative of photic zone euxinia i e a water column containing free h 2 s in north atlantic deep sea sediments deposited during the cenomanian turonian boundary oae2 bonarelli event in this study we have used the distributions of chlorophyll and bacteriochlorophyll degradation products maleimides 1 h pyrrole 2 5 diones and high molecular weight porphyrins to examine further the cenomanian turonian boundary oae2 as well as other oaes of the early toarcian posidonienschiefer event and early aptian selli event in particular methyl isobutyl me i bu maleimide on structural grounds appears to be diagnostic of green sulphur bacteria this compound occurs in five of seven examined marls that record the early toarcian oae marche umbria italy further expanding the geographical range of toarcian sediments where evidence for photic zone euxinic conditions has been found me i bu maleimide occurs in three of six black shales spanning the livello selli marche umbria italy the type locality for the aptian oae1a providing the first evidence for photic zone euxinic conditions during this event with respect to the cenomanian turonian oae maleimide evidence for photic zone euxinic conditions was found in all the north atlantic sites investigated including those characterized by relatively organic lean sediments several tethyan sites and one site off western australia these data indicate that euxinic conditions were common in the water column during mesozoic oceanic anoxic events

c isotope stratigraphy and paleoenvironmental changes across oae2 mid cretaceous from shallow water platform carbonates of southern mexico the stratigraphic and geochemical record of the mid cretaceous cenomanian turonian oceanic anoxic event 2 oae2 has been studied in numerous tethyan and proto atlantic hemi pelagic pelagic successions but little data comes from nearshore carbonate successions from the proto pacific region here we present the results of a combined stratigraphic and 13c study of c t platform carbonates from southern mexico which were deposited within the proto pacific two scales of sedimentary cyclicity are recognized high frequency peritidal and subtidal cycles 0 4 8 m display little evidence of cycle capping subaerial exposure and are not correlative between sections these relationships suggest that the amplitudes of high frequency sea level changes were minimal during the peak mid cretaceous greenhouse longer term transgressive regressive sequences 18 40 m are correlated between sections and using 13c trends can be correlated with sequences developed in northern europe and india the mexican successions were sampled at a high resolution 10 ky for stable isotopes inorganic organic carbon and oxygen total organic carbon insoluble residues and trace metals the 13ccarb curve matches global trends including 6 distinct isotopic stages permitting identification of oae2 despite the lack of characteristic anoxic facies using the 13ccarb trends we tie the previously identified ammonite planktonic foram and nannofossil biostratigraphy from england and the western interior seaway of colorado into the mexican sections the initiation of oae2 defined by an abrupt positive 3 4 13c shift coincides with a long term sea level rise though the sedimentary expression of the deepening is no greater than that observed for any of the other sea level events across the studied interval oae2 termination transition from gradually decreasing to background 13c values is not associated with a particular sea level trend stratigraphic changes in insoluble residues proxy for continental sediment discharge across oae2 are not correlative between sections and do not show consistent systematic relationships with 13c or sea level variations therefore do not support the hypothesis that oae2 was associated with increased continental derived nutrient influx two peaks in trace metal concentrations coincide with the abrupt increase in 13c ratios onset of oae2 and during the transition from elevated to decreasing 13c values near the c t stage boundary these trends are similar to those recorded in coeval deposits of the western interior seaway and are consistent with the hypothesis that oae2 development was related to the release of reduced metals during the short lived 1 my caribbean oceanic plateau basalt eruption in this scenario oxidation of the metals depleted the existing low dissolved o2 concentrations and thermally buoyant plumes of seawater enriched in biolimiting elements mixed with surface waters stimulated primary productivity and further reduced o2 concentrations leading to widespread anoxia and a large positive 13c shift

testing the precision of bioevents deciding which of two bioevents is the less diachronous is a common problem in biostratigraphy the most accurate correlation uses the finest timescale available chemostratigraphy or cyclostratigraphy offer a potential precision of about 10 ka graphic correlation can then be used to test the precision of bioevents and to quantify any mismatch it can also be used to determine in which section any event occurs earlier application of these ideas to correlation of the cenomanian turonian and coniacian santonian boundaries demonstrates that some bioevents are as precise as chemo and cyclostratigraphy but that most are not two problems occur with bioevents first they may not be recognizable in all sections second where they are recognizable they may be diachronous in the former case calculating confidence intervals on known ranges in sections where the relevant fossil has been recorded is an alternative test large confidence intervals suggest that both first and last occurrences of a fossil may be diachronous bioevents at the cenomanian turonian boundary the following bioevents in stratigraphic order appear to be reliable time planes for international correlation the last occurrences of 1 corolithion kennedyi 2 rotalipora greenhornensis 3 axopodorhabdus albianus 4 rotalipora cushmani 5 lithraphidites acutus 6 microstaurus chiastius and 7 the first occurrence of quadrum gartneri at the coniacian santonian boundary only the first and last occurrences of platyceramus undulatoplicatus and the first occurrences of platyceramus cycloides and lucianorhabdus cayeuxii have been identified as potentially reliable bioevents

nannofossil carbonate fluxes during the early cretaceous phytoplankton response to nutrification episodes atmospheric co2 and anoxia 1 greenhouse episodes during the valanginian and aptian correlate with major perturbations in the c cycle and in marine ecosystems carbonate crises and widespread deposition of corg rich black shales quantitative analyses of nannofossil micrite were conducted on continuous pelagic sections from the southern alps northern italy where high resolution integrated stratigraphy allows precise dating of early cretaceous geological events rock forming calcareous nannofloras were quantified in smear slides and thin sections to obtain relative and absolute abundances and paleofluxes that are interpreted as the response of calcareous phytoplankton to global changes in the ocean atmosphere system increased rates of volcanism during the formation of ontong java and manihiki plateaus and the parana etendeka large igneous province lip are proposed to have caused the geological responses associated with early aptian oceanic anoxic event oae 1a and the valanginian event respectively calcareous nannofloras reacted to the new conditions of higher pco2 and fertility by drastically reducing calcification the valanginian event is marked by a 65 reduction in nannofossil paleofluxes that would correspond to a 2 3 times increase in pco2 during formation of the parana endenteka lip a 90 reduction in nannofossil paleofluxes which occurred in a 1 5 myr long interval leading into oae1a is interpreted as the result of a 3 6 times increase in pco2 produced by emplacement of the giant ontong java and manihiki plateaus high pco2 was balanced back by an accelerated biological pump during the valanginian episode but not during oae1a suggesting persisting high levels of pco2 in the late aptian and or the inability of calcareous phytoplankton to absorb excess pco2 above threshold values

carbon isotope stratigraphy of cenomanian turonian platform carbonates from the southern apennines italy a chemostratigraphic approach to the problem of correlation between shallow water and deep water successions the carbon isotope record of three sections of shallow water carbonates from the upper cretaceous sequences of the southern apennines italy shows a pronounced positive excursion of about 4 5 using the upper cenomanian cisalveolina fraasi level as a biostratigraphic tie point we correlate this excursion to the oae 2 isotopic event comparison with the standard reference 13 c curve of eastbourne england shows that the overall character of the excursion is clearly reproduced in the shallow water curves chemostratigraphic correlation allows definition of the age of some important shallow water biostratigraphic events to the precision of an ammonite zone using the well established bio chronostratigraphic framework defined in the eastbourne section the onset of the cenomanian turonian isotopic excursion coincides with a transgressive trend recorded by the occurrence of more open marine facies and culminating with an incipient drowning in one of the sections studied our data suggest that the open ocean isotopic signal is most faithfully recorded and preserved in shallow water platform carbonates during transgressive periods when the effects of meteoric diagenesis and seawater ageing are less severe

the cenomanian turonian oceanic anoxic event i stratigraphy and distribution of organic carbon rich beds and the marine δ13c excursion marine strata deposited during late cenomanian and early turonian time display lithological faunal and geochemical characteristics which indicate that significant parts of the world ocean were periodically oxygen deficient at or very close to the cenomanian turonian boundary between 90 5 and 91 5ma ago oxygen deficiencies were particularly marked over a period of 1ma this short lived episode of oceanic oxygen deficiency has been termed the cenomanian turonian oceanic anoxic event oae the widespread distribution of anoxic sediments deposited synchronously during such a short lived event indicates that such sediments are not simply the product of coincidental local climatic or basinal water mass characteristics but are the result of a global expansion and intensification of the cenomanian turonian oxygen minimum zone related to feedback between sea level rise and regional palaeoceanography the palaeoceanography of the cenomanian turonian oae is discussed in detail in a companion paper by arthur et al 1987 from authors

middle and late cenomanian oceanic anoxic events in shallow and deeper shelf environments of western morocco the response of shallow water sequences to oceanic anoxic event 2 and mid cenomanian events 1a and 1b was investigated along the west african margin of morocco north of agadir azazoul and correlated with the deep water sequence of the tarfaya basin mohammed beach based on biostratigraphy mineralogy phosphorus and stable isotopes in the deeper mohammed beach section results show double peaks in 13corg for mid cenomanian events 1a and 1b rotalipora reicheli biozone lower cc10a biozone the characteristic oceanic anoxic event 2 13c excursion rotalipora cushmani extinction top of cc10a biozone and laminated anoxic black shale in the shallow environment north of agadir a fluctuating sea level associated with dysoxic brackish and mesotrophic conditions prevailed during the middle to late cenomanian as indicated by oyster biostromes nannofossils planktonic and benthonic foraminiferal assemblages anoxic conditions characteristic of oceanic anoxic event 2 for example laminated black shales did not reach into shallow water environments until the maximum transgression of the early turonian climate conditions decoupled along the western margin of morocco between mid cenomanian event 1b and the cenomanian turonian boundary as also observed in eastern tethys north of agadir alternating humid and dry seasonal conditions prevailed whereas in the tarfaya basin the climate was dry and seasonal this climatic decoupling can be attributed to variations in the intertropical convergence zone and in the intensity of the north east trade winds in tropical areas

age and paleoenvironment of the cenomanian turonian global stratotype section and point at pueblo colorado biostratigraphy and stable isotopes indicate that the global stratotype section and point gssp at pueblo contains an essentially complete sedimentary record across the global ocean anoxic event oae 2 and the cenomanian turonian boundary the oae 2 d 13 c shift occurred over a period of about 90 ky and was accompanied by a major sea level transgression which at its peak was marked by an incursion of oxygen rich waters creating a benthic oxic zone that lasted about 100 ky a mid cenomanian d 13 c shift sea level transgression and faunal turnover occurred about 2 my before oae 2 d 18 o values of the planktic foraminifer hedbergella planispira and its relative abundance changes reveal cyclic variations in surface salinity due to alternating freshwater influx and marine incursions whereas dominance by the low oxygen tolerant heterohelix species indicates a well developed oxygen minimum zone omz for most of the middle to late cenomanian and early turonian profound faunal changes accompanied these oceanographic events including the extinction of 30 of the species assemblage and an equal gain in evolutionary diversification though the overall combined relative abundances of outgoing and incoming species were less than 2 and 4 respectively of the total assemblages the faunal turnover began with the sea level transgression and rapid increase in d 13 c values and accelerated with the influx of oxygen rich deep water increased water mass stratification and competition during the benthic oxic zone the incursion of oxygen rich deep waters at this time was also observed in morocco and may represent a global event of a still unknown source d 2003 elsevier b v all rights reserved

carbon isotope stratigraphy recorded by the cenomanian turonian oceanic anoxic event correlation and implications based on three key localities we present new detailed carbon isotope records for bulk carbonate total organic carbon toc and phytane from three key sections spanning the cenomanian turonian boundary interval eastbourne england gubbio italy tarfaya morocco with the purpose of establishing a common chemostratigraphic framework for oceanic anoxic event oae 2 isotope curves from all localities are characterized by a positive carbon isotope excursion of c 4 for toc and phytane and c 2 5 for carbonate although diagenetic overprinting appears to have obliterated the primary carbonate carbon isotope signal in at least part of the tarfaya section stratigraphically peak 13 c values for all components are followed by intervals of high near constant 13 c in the form of an isotopic plateau recognition of an unambiguous return to background 13 c values above the plateau is however contentious in all sections hence no firm chemostratigraphic marker for the end point of the positive isotopic excursion can be established the stratigraphically consistent first appearance of the calcareous nannofossil quadrum gartneri at or near the cenomanian turonian boundary as established by ammonite stratigraphy in conjunction with the end of the 13 c maximum characteristic of the isotopic plateau provides a potentially powerful tool for delimiting the stratigraphic extent and duration of oae 2 this oceanic anoxic event is demonstrated to be largely if not wholly confined to the latest part of the cenomanian stage

astronomical calibration of upper campanian maastrichtian carbon isotope events and calcareous plankton biostratigraphy in the indian ocean odp hole 762c implication for the age of the campanian maastrichtian boundary abstract an integrated framework of magnetostratigraphy calcareous microfossil bio events cyclostratigraphy and 13c stratigraphy is established for the upper campanian maastrichtian of odp hole 762c exmouth plateau northwestern australian margin bulk carbonate 13c events and nannofossil bio events have been recorded and plotted against magnetostratigraphy and provided absolute ages using the results of the cyclostratigraphic study and the recent astronomical calibration of the maastrichtian thirteen carbon isotope events and 40 nannofossil bio events are recognized and calibrated with cyclostratigraphy as well as 14 previously published foraminifer events thus constituting a solid basis for large scale correlations results show that this site is characterized by a nearly continuous sedimentation from the upper campanian to the k pg boundary except for a 500 kyr gap in magnetochron c31n correlation of the age calibrated 13c profile of odp hole 762c to the 13c profile of the tercis les bains section global stratotype section and point of the campanian maastrichtian boundary cmb allowed a precise recognition and dating of this stage boundary at 72 15 0 05 ma this accounts for a total duration of 6 15 0 05 ma for the maastrichtian stage correlation of the boundary level with northwest germany shows that the cmb as defined at the gssp is 800 kyr younger than the cmb as defined by belemnite zonation in the boreal realm odp hole 762c is the first section to bear at the same time an excellent recovery of sediments throughout the upper campanian maastrichtian a precise and well defined magnetostratigraphy a high resolution record of carbon isotope events and calcareous plankton biostratigraphy and a cyclostratigraphic study tied to the la2010a astronomical solution this section is thus proposed as an excellent reference for the upper campanian maastrichtian in the indian ocean

secular variation in late cretaceous carbon isotopes a new δ13c carbonate reference curve for the cenomanian campanian 99 6 70 6 ma carbon stable isotope variation through the cenomanian santonian stages is characterized using data for 1769 bulk pelagic carbonate samples collected from seven chalk successions in england the sections show consistent stratigraphic trends and 13c values that provide a basis for highresolution correlation positive and negative 13cexcursions and inflection points on the isotope profiles are used to define 72 isotope events key markers are provided by positive 13c excursions of up to 2 the albian cenomanianboundary event mid cenomanian event i thecenomanian turonian boundary event the bridgewick hitch wood and navigation events of late turonian age and the santonian campanian boundary event isotope events are isochronous within a framework provided by macrofossil datum levels and bentonite horizons an age calibrated composite 13c reference curve and an isotope event stratigraphy are constructed using data from the english chalk the isotope stratigraphy is applied to successions in germany france spain and italy correlation with pelagic sections at gubbio central italy demonstrates general agreement between biostratigraphic and chemostratigraphic criteria in the cenomanian turonian stages confirming established relationships between tethyan planktonic foraminiferal and boreal macrofossil biozonations correlation of the coniacian santonian stages is less clear cut magnetostratigraphic evidence for placing the base of chron 33r near the base of the upper santonian is in good agreement with the carbon isotope correlation but generates significant anomalies regarding the placement of the santonian and campanian stage boundaries with respect to tethyan planktonic foraminiferal and nannofossil zones isotope stratigraphy offers a more reliable criterion for detailed correlation of cenomanian santonian strata than biostratigraphy with the addition of campanian 13c data from one of the english sections a composite cenomanian campanian age calibrated reference curve is presented that can be utilized in future chemostratigraphic studies the cenomanian campanian carbon isotope curve is remarkably similar in shape to supposedly eustatic sea level curves increasing 13c values accompanying sea level rise associated with transgression and falling 13c values characterizing sea level fall and regression the correlation between carbon isotopes and sea level is explained by variations in epicontinental sea area affecting organic matter burial fluxes increasing shallow sea floor area and increased accommodation space accompanying sea level rise allowedmore efficient burial ofmarine organic matter with the preferential removal of 12c from the marine carbon reservoir during sea level fall reduced seafloor area marine erosion of previously deposited sediments and exposure of basin margins led to reduced organiccarbon burial fluxes and oxidation of previously deposited organic matter causing falling 13c values additionally drowning of carbonate platforms during periods of rapid sea level rise may have reduced the global inorganic relative to the organic carbon flux further enhancing 13c values while renewed platform growth during late transgressions and highstands prompted increased carbonate deposition variations in nutrient supply changing rates of oceanic turnover and the sequestration or liberation of methane from gas hydrates may also have played a role in controlling carbon isotope ratios

a valanginian early cretaceous boreal nannoplankton excursion in sections from romania abstract in order to resolve both sea level and palaeoclimatic signals for the earliest cretaceous 161 calcareous nannofossil samples of berriasian to valanginian age have been studied from romania these samples are derived from three biostratigraphically well dated sections of tethyan litho and biofacies the nannofossil assemblages recorded are of high diversity reflecting stable warm water conditions typical for the earliest cretaceous of the tethys the floras are characterised by abundant watznaueria spp and nannoconus spp whereas other taxa are less common long term trends on the scale of 1 4 my are reflected by shifts from watznaueria spp dominated assemblages in the lower berriasian to nannoconus spp assemblages in the middle upper berriasian back to watznaueria spp in the upper berriasian lower valanginian and again to nannoconus spp in the upper valanginian these changes are thought to be caused by palaeoclimatic shifts periods with a dominance of cosmopolitan eurytopic watznaueria are thought to reflect cooler humid conditions and well mixed surface waters those with a dominance of nannoconus warmer conditions and a rather stabile surface water stratification crucibiscutum salebrosum very common at high latitudes is extremely rare in the romanian samples it occurs only at one specific interval of early late valanginian age saynoceras verrucosum ammonite zone associated with other rare boreal taxa also restricted to this particular level this boreal nannoplankton excursion is believed to be controlled by sea level rather than by climate since simultaneously tethyan ammonites found their way into the boreal realm

orbital time scale and new c isotope record for cenomanian turonian boundary stratotype previous time scales for the cenomanian turonian boundary ctb interval containing oceanic anoxic event ii oae ii vary by a factor of three in this paper we present a new orbital time scale for the ctb stratotype established independently of radiometric biostratigraphic or geochemical data sets update revisions of ctb biostratigraphic zonation and provide a new detailed carbon isotopic record for the ctb study interval the orbital time scale allows an independent assessment of basal biozone ages relative to the new ctb date of 93 55 ma gts04 the d 13 corg data document the abrupt onset of oae ii significant variability in d 13 corg values and values enriched to almost 222 these new data underscore the difficulty in defining oae ii termination using the new isotope curve and time scale estimates of oae ii duration can be determined and exported to other sites based on integration of well established chemostratigraphic and biostratigraphic datums the new data will allow more accurate calculations of biogeochemical and paleobiologic rates across the ctb

palaeobiogeography of early cretaceous berriasian barremian calcareous nannoplankton in order to assess early cretaceous nannoplankton biogeography we studied a series of sites which provide a north south transect across the atlantic ocean supplemented by sections from the north sea basin barents sea falkland plateau weddell sea antarctica argo abyssal plain nw of australia and neuquen basin argentina quantitative assemblage data were gathered from each site for seven time slices within the berriasian to barremian interval each horizon being determined by a nannofossil datum trends in species relative abundance and measures of diversity evenness and richness provide revealing biogeographic information a broad low to mid palaeolatitude zone 50 degrees n 50 degrees s is flanked in both northern and southern hemispheres by distinct high palaeolatitude zones major changes in assemblage abundance and composition occur across a sharp biogeographic front at around 50 degrees n and s palaeolatitude high palaeolatitude assemblages are lower in species richness and diversity and characterised by the presence of abundant typically bipolar taxa e g crucibiscutum salebrosum a less distinct biogeographic boundary at similar to 40 degrees n is distinguished by the presence absence of rarer but biogeographically significant taxa many of which have previously been assigned to boreal or tethyan provinces continental shelf sites are characterised by lower diversity assemblages with common to dominant diagnostic taxa which vary with palaeolatitude nannoconus and micrantholithus at low palaeolatitudes and biscutum constans and zeugrhabdotus spp at higher palaeolatitudes the latter two taxa are considered to be indicative of elevated surface water fertility and the former two may have been similarly adapted the genus watznoueria is ubiquitously dominant giving the populations an unevenness which appears to be a common feature throughout coccolithophore history c 2000 published by elsevier science b v all rights reserved

calcareous nannofossils and mesozoic oceanic anoxic events abstract twenty five years ago mesozoic oceanic anoxic events oaes were documented and formalised as intervals of widespread to global deposition of organic matter the toarcian early aptian oae1a and latest cenomanian oae2 oaes are truly global in nature commonly carbonate poor and typically represented by organic carbon rich black shales in some areas these oaes are also characterised by abundant radiolarian sands and silts they are associated with negative and positive excursions in the 87sr 86sr record in addition to large global carbon isotope anomalies in carbonate and or organic matter caused by a major perturbation of the global carbon budget increased rates of volcanism during the formation of the ontong java and manihiki and caribbean plates and the karoo ferrar traps are believed to have caused the geological responses associated with oae1a oae2 and the toarcian oae respectively excess volcanogenic co2 in the atmosphere most probably turned the climate into a greenhouse mode accelerating continental weathering and increasing nutrient content in oceanic surface waters via river run off higher fertility in the global ocean was also probably triggered directly by submarine igneous events that introduced enormous quantities of biolimiting metals within hydrothermal plumes because mesozoic oaes are often represented by carbonate poor sediments quantitative studies of calcareous nannofossils have been applied to explore a the causes and effects of igneous tectonic events and climate changes relative to nannofloral increases and crises as well as b dissolution events and c diagenetic modifications characterization of calcareous nannofloras in oae intervals can improve our understanding of the marine ecosystem and biological processes such as photosynthesis biological pump and biomineralisation carbonate pump that affect the organic and inorganic carbon cycle as well as adsorption of atmospheric co2 in the oceans types and rates of nannoplankton production and evolution are interpreted to trace the impact of major palaeoceanographic and palaeoclimatic events in selected sections it has been documented that calcareous nannofloras rapidly reacted to new conditions of fertility and higher pco2 by drastically reducing calcification as in the modern oceans during oaes the increase of nutrients and atmospheric co2 induced higher abundances of nannoplankton producing small placoliths and inhibited the deep photic zone nannoconids and schizosphaerellids similarly to the nannoconid crisis preceding deposition of the early aptian oae1a black shales a schizosphaerellid crisis is detected prior to the toarcian oae both oaes are further characterised by a rapid nannofloral speciation beginning approximately 1 5 myr before the oae but without extinctions global changes during the latest cenomanian oae 2 exerted different influences on calcareous nannoplankton that experienced a turnover due to most extreme environmental conditions this event in fact was a time of extinctions followed by originations within calcareous nannofossils precise timing of the events before during and after oae1a oae2 and the toarcian oae indicates that they were intervals of enhanced oceanic productivity and that anoxia dysoxia post dated biotic changes

early cretaceous calcareous nannofossils from high latitudes implications for palaeobiogeography and palaeoclimate abstract in order to better understand the palaeoceanography and palaeoclimate of the early cretaceous nannofossil data have been obtained from high latitudinal sites from offshore mid norway and from the barents sea no consistent nannofossil data are yet available for early cretaceous high latitudes which should more clearly reflect possible palaeoclimatic changes as recorded in fluctuations of diversity and abundance existing data from france italy romania poland and nw europe germany north sea england have been complemented by material from higher latitudes in order to record the arctic boreal nannofossil assemblages 400 samples from the norwegian shelf and the barents sea have been analysed sixty samples covering the berriasian barremian interval yielded calcareous nannofossils these are derived from cores between 63 and 73 n of present day latitudes the nannofossil assemblages recorded are generally of a low diversity and characterized by abundant watznaueria barnesae and crucibiscutum salebrosum whereas biscutum constans is less common c salebrosum rare or absent at low latitudes is extremely common in the norwegian samples it shows a bipolar distribution especially during valanginian hauterivian times in the early valanginian a distinctive latitudinal gradient in the abundance of c salebrosum impoverished in low latitudes and abundant in high latitudes possibly reflects latitudinal differences in temperature restricted palaeoceanographic settings caused by a sea level lowstand may have amplified these thermal gradients palaeoclimatically this implies the existence of climatic belts throughout parts of the early cretaceous early valanginian hauterivian resulting from considerable temperature gradients from north to south the palaeobiogeographic patterns discussed resulted in the formation of distinctive latitudinally bound nannofossil zones which to a certain extent are similar to those of modern oceans the palaeobiogeographic patterns described support the idea of an ice house phase for the early valanginian and disagree with the suggestion of a globally warm equable climate during that time