accumulation patterns of tertiary calcareous nannofossils around extinctions quantitative analysis of accumulation of tertiary calcareous nannofossil species allows a precise evaluation of their extinction patterns and thus of their biostratigraphic value accumulation of species commonly shows marked variability indicating that short sample intervals are necessary for estimating the true ranges the stratigraphic resolution which can be achieved is primarily determined by the sediment accumulation rate and the depth of homogeneous sediment mixing caused by bioturbation at about the time of extinction the accumulation usually shows a final sharp decline which often is followed by a tail of strongly reduced accumulation having a duration in the range of 2 3 103 to 4 5 105 years it is shown that this tail represents accumulation caused either by true production or postdepositional sediment mixing because of the difficulties involved in distinguishing these two casual mechanisms from each other biostratigraphic indications defined by the final sharp decline are generally superior in terms of synchroniety and ease of identification to those defined by the absolutely last occurrence

the late maastrichtian nannofossil record of climate change in the south atlantic dsdp hole 525a abstract the phytoplankton response calcareous nannofossils to the late maastrichtian climate evolution is investigated in the south atlantic dsdp hole 525a and compared to published geochemical and micropaleontological data the results point to a succession of dramatic climatic fluctuations cool water indicators ahmuellerella octoradiata kamptnerius magnificus and nephrolithus frequens suggest cool surface water conditions prevailed during chron c30n at the top of c30n their sudden drop in abundance the last occurrence of b constans and the concomitant increase in the tropical species micula murus suggest warming and lower surface water productivity an m murus acme within chron c29r reflects maximum warming during the last 100 kyr of the maastrichtian the decrease in m murus and increase in cool water indicators reflect rapid cooling with the cool climate persisting over the calcareous nannoplankton response to climate change correlate with similar findings in the equatorial atlantic hole 1258a and parallels the stable isotope record of planktic and benthic foraminifera of dsdp hole 525a as well as the decline in 187os 188os comparison of this marine record and the continental climate record in north america suggests a link between deccan volcanism and the late maastrichtian warm event

evolution of upwelling in the atlantic ocean basin understanding the evolution of the surface circulation and the patterns of upwelling in the atlantic is important not only because of the ocean s crucial role in the present day thermohaline circulation in supplying heat to high latitudes but also because of the significant petroleum reservoirs found around the basin in this paper we examine the upper ocean circulation during four time slices the kimmeridgian c 155 ma the cenomanian c 100 ma the maastrichtian c 70 ma and the early eocene c 50 ma using a 1 5 layer reduced gravity ocean model for each time slice the upwelling fields predicted from simulations of wind driven upper layer circulation are compared with the deep sea and continental margin sedimentary records the boundary configurations at each time slice are the subject of sensitivity tests where matching of both deep sea and coastal sedimentary records with the model predicted upwelling fields is used to suggest best fits between model and geological data our model runs are consistent with there being a deep water connection to the pacific at each time period after the kimmeridgian with such a link being most important to the geological ocean model match in the maastrichtian no period after the kimmeridgian produced a stable ocean simulation with a deep water connection to tethys our simulations c 100 ma suggest that a deep water connection between the north and south atlanctic was not established until after the cenomanian all time slices show a clear western boundary current in the north atlantic although generally only a third to half the strength of today s a similar difference is found between tropical palaeo productivity at each run and today s more productive atlantic ocean we conclude that upwelling and anoxia are not necessarily independent means of producing organic rich marine sediments most such sedimentary deposits laid down during the four time slices can be linked to the presence of upwelling zones thus where anoxia is well established we suggest that upwelling may help supply organic material to the de oxygenated bottom waters

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

calcareous nannofossil response to late cretaceous climate change in the eastern tethys zagros basin iran abstract coniacian to maastrichtian changes in calcareous nannofossil assemblages have been investigated in the eastern tethyan shahneshin section central zagros basin iran the nannofossil assemblages are mainly composed of watznaueria spp avg 54 retecapsa spp avg 7 9 cribrosphaerella ehrenbergii avg 7 7 and micula spp avg 5 7 throughout the late campanian there is a trend to lower abundances in watznaueria spp together with increasing abundances of c ehrenbergii and arkhangelskiella cymbiformis which are considered in this basin as the main cool water taxa our results reveal that despite a diagenetic impact on calcareous nannoflora a number of primary paleoecological trends are preserved which depict well features of the progressive late cretaceous cooling the first pronounced cooling episode occurs across the late campanian to early maastrichtian the onset of pronounced cooling in the eastern tethys appears to occur prior to the campanian maastrichtian boundary event cmbe 13c negative excursion in contrast with the boreal realm where pronounced cooling only occurs in the early maastrichtian postdating the onset of the cmbe the coincidence of this earlier cooling in the zagros basin with an interval characterized by a significant increase in benthic foraminifera suggests an amplified response of the assemblage due to a change to shallower environments hence the late campanian calcareous nannofossil assemblage turnover in central zagros is either a response to an early cooling trend in the eastern tethys or to sea level fall or both the mid maastrichtian warming and late maastrichtian cooling episodes are also delineated in the nannofossil assemblage of shahneshin and likely correlate with similar episodes in the boreal realm

latitudinal migration of calcareous nannofossil micula murus in the maastrichtian implications for global climate change micula murus is one of the main calcareous nannofossil biostratigrapic markers of tethyan and intermediate provinces in the upper maastrichtian uppermost cretaceous a review of its first occurrence at 14 deep sea sites and sections shows that it is time transgressive from the tropical realm of the atlantic and pacific oceans to the intermediate latitudes of the north atlantic south atlantic indian ocean and the northern tethys m murus remained confined to the tropical realm for 1 2 m y in the early late maastrichtian thus supporting high latitudinal thermal gradients it subsequently spread out in the late maastrichtian to temperate latitudes and to the tethys in coincidence with the onset of a thermohaline circulation change at 67 5 ma suggesting a major change in surface water circulation and interocean communications

the end cretaceous in the southwestern tethys elles tunisia orbital calibration of paleoenvironmental events before the mass extinction an integrated study of magnetic mass susceptibility ms bulk stable isotopes and calcareous nannofossil paleoecological changes is undertaken on the late maastrichtian of the elles section tunisia spanning the last ca 1 myr of the cretaceous a cyclostratigraphic analysis reveals the presence of milankovitch frequencies and is used for proposal of two distinct orbital age models and to provide ages of important stratigraphic horizons relative to the age of the cretaceous paleogene boundary k pgb principal component analysis pca performed on the nannofossil assemblage reveal two main factors pca1 mostly representing fluctuations of d rotatorius p stoveri lithraphidites spp retecapsa spp staurolithites spp micula spp and pca2 mostly representing fluctuations of a regularis c ehrenbergii micula spp rhagodiscus spp w barnesiae and zeugrhabdotus spp variations in pca1 and pca2 match changes in bulk 13c and 18o respectively and suggest changes in surface water fertility and temperatures and associated stress the variations in abundances of high latitude taxa and the warm water species micula murus and in bulk 18o delineate fast changes in sea surface paleotemperatures as in many other sites an end maastrichtian greenhouse warming is highlighted followed by a short cooling and an additional warm pulse in the last 30 kyr of the maastrichtian which has rarely been documented so far orbital tuning of the delineated climatic events is proposed following the two different age models calcareous nannofossil assemblages highlight a decrease in surface water nutriency but their species richness remains high through the latest maastrichtian indicating in tunisia a weak impact of deccan volcanism on calcareous nannoplankton diversity before the mass extinction

middle cretaceous calcareous nannofossil biogeography and preservation in the atlantic and indian oceans implications for paleoceanography abstract the quantitative study of calcareous nannofossil preservation and biogeographic distribution puts constraints on paleoceanographic models for the atlantic and indian oceans during the middle cretaceous we establish a dissolution ranking of middle cretaceous calcareous nannofossils based on susceptibility to dissolution a positive correlation of organic carbon content of the sediments and the relative abundance of watznaueria indicates that much of the carbonate dissolution was caused by the release of carbon dioxide during oxidation of organic matter the depth distribution of the most dissolution resistant species watznaueria barnesae shows relative abundance maxima at the deepest sites and a maximum where intermediate waters impinge on slopes this reflects stagnant oxygen poor bottom waters and possibly a mid water oxygen minimum zone with increased deposition and catabolic breakdown of organic matter factor analyses are performed on various data sets for three different time slices ranging in age from late aptian to early albian middle albian and late albian to cenomanian the resulting factors can be related to paleoceanographic conditions such as colder water at high latitudes high fertility upwelling conditions and neritic conditions for all three time intervals a wide tropical to subtropical zone was flanked by boreal and austral zones upwelling conditions probably existed along the north african margin and over the falkland plateau zonal upwelling is tentatively postulated for the northwestern and northeastern margin of the north atlantic in the middle albian and for the eastern margin of the north atlantic off western europe for the late albian to cenomanian we speculate on surface water current patterns location of upwelling regions and haline driven deep circulation for the middle cretaceous

revision of the early middle pleistocene calcareous nannofossil biochronology 1 75 0 85 ma the extant nannofossil biostratigraphic and biochronologic framework for the early middle pleistocene time interval has been tested through the micropaleontological analysis of globally distributed high quality low to mid latitude deep sea successions the quantitative temporal distribution patterns of relative abundances of selected taxa were reconstructed in critical intervals and the following biohorizons were defined first occurrence of medium sized gephyrocapsa spp last occurrence of calcidiscus macintyrei first occurrence of large gephyrocapsa spp last occurrence of large gephyrocapsa spp first occurrence of reticulofenestra asanoi re entrance of medium sized gephyrocapsa spp and last occurrence of reticulofenestra asanoi the detailed patterns of abundance change at these biohorizons were used to generate a detailed biostratigraphy and the biostratigraphic data were transformed into a precise biochronology by means of correlation to isotope stratigraphies and astronomical timescales the degree of isochrony or diachrony of the biohorizons was evaluated biohorizons and are isochronous occurring close to marine isotope stages mis 55 and mis 22 respectively and and are slightly diachronous on the order of 30 40 kyr whereas biohorizons and are confirmed as diachronous on the order of 100 80 and 60 kyr respectively some of the events are clearly controlled by environmental conditions e g the last occurrence of r asanoi related to significant environmental changes associated with the first large amplitude glaciation of the late quaternary mis 22

calcareous nannofossils from the great australian bight iodp site u1512 as a record of the peak and early decline of the mid cretaceous super greenhouse abstract international ocean discovery program drilling in the great australian bight site u1512 provides a record of turonian to santonian hemipelagic sedimentation deposited in an elongate epicontinental basin that opened westward to the southern ocean during the peak and the early decline of the cretaceous hot greenhouse despite its relatively high paleolatitude at about 60 s the biostratigraphy of calcareous nannofossils from this succession is directly correlative to low latitude zonation schemes throughout the turonian to santonian these calcareous nannofossil assemblages are somewhat restricted in species composition lacking some elements generally found in late cretaceous assemblages e g holococcoliths in addition two biostratigraphically important high latitude taxa thiersteinia ecclesiastica and zeugrhabdotus kerguelenesis have biostratigraphic ranges notably shorter than elsewhere indicating range truncation through local extirpation quantitative paleoecological analysis of the calcareous nannofossil assemblages indicates that the major change in the paleoenvironment was the evolution from conditions that were quite warm and had relatively elevated surface water fertility in the turonian to cooler and possibly more oligotrophic conditions in the coniacian santonian the first cooling began at about 92 ma accelerated at about 91 2 ma and then continued to gradually cool during the coniacian santonian this paleotemperature scenario is consistent with those documented from other localities globally

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

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

chemostratigraphic evidence of deccan volcanism from the marine osmium isotope record continental flood basalt cfb volcanism is hypothesized to have played a causative role in global climate change and mass extinctions uncertainties associated with radiometric dating preclude a clear chronological assessment of the environmental consequences of cfb volcanism our results document a 25 decline in the marine 187 os 188 os record that predates the cretaceous tertiary boundary ktb and coincides with late maastrichtian warming we argue that this decline provides a chemostratigraphic marker of deccan volcanism and thus constitutes compelling evidence that the main environmental consequence of deccan volcanism was a transient global warming event of 3 to 5 c that is fully resolved from the ktb mass extinction

biostratigraphy and paleoecologic inferences during the late campanian maastrichtian interval evidence based on calcareous nannofossils from goban spur abstract this paper presents a biostratigraphic revision and a quantitative study of the calcareous nannofossils from dsdp leg 80 hole 550b a total of 42 samples were analyzed revealing 78 species whose preservation varied from slightly to moderately dissolved with slight to severe overgrowth biostratigraphy indicates deposition during the late campanian to late maastrichtian incorporating zones uc15d to uc20b the quantitative nannofossil data recovered shows that watznaueria barnesiae and micula staurophora dominate the assemblages which can be attributed to a low preservation potential for the depositional environment cold water taxa kamptnerius magnificus ahmuellerella octoradiata and arkhangelskiella cymbiformis are present in very low percentages with their maximum values occurring inside the uc17 biozone

marine biodiversity through the late cenomanian early turonian palaeoceanographic controls and sequence stratigraphic biases changes in the marine macro and microfauna sedimentary geochemistry and surface water palaeoproductivity through the last 500 000 years of the cenomanian and first 300 000 years of the turonian are documented these are based on the succession at eastbourne the thickest and most complete section through the late cenomanian and early turonian in the anglo paris basin two levels of rapid faunal and geochemical change are identified one coincident with a significant increase in siliciclastic input at the base of the plenus marls member and the other with a marked drop in surface water productivity near the top of the same unit faunal change is demonstrated to be largely a pattern of immigration emigration rather than true extinction and our sequence stratigraphical analysis shows that it was coincident with major sea level changes no evidence is found to support the hypothesis that reduced bottom water oxygenation developed and was responsible for extinctions amongst the benthos in mid shelf environments the onset of pure chalk facies is interpreted to mark the breakdown of shelf break fronts and the spread of oligotrophic oceanic waters over much of the continental shelf initiated by rising sea level the cenomanian turonian event far from recording a mass extinction of shelf fauna is most probably an artifact caused by a significant switch in the nature of the surviving sedimentary record as a result of a major but perfectly ordinary oceanographic change

biostratigraphic subdivision and correlation of upper maastrichtian sediments from the atlantic coastal plain and blake nose western atlantic

carbon dioxide emissions from deccan volcanism and a k t boundary greenhouse effect a greenhouse warming caused by increased emissions of carbon dioxide from the deccan traps volcanism has been suggested as the cause of the terminal cretaceous extinctions on land and in the sea we estimate total eruptive and noneruptive co2 output by the deccan eruptions from 6 to 20 1016 moles over a period of several hundred thousand years based on best estimates of the co2 weight fraction of the original basalts and basaltic melts the fraction of co2 degassed and the volume of the deccan traps eruptions results of a model designed to estimate the effects of increased co2 on climate and ocean chemistry suggest that increases in atmospheric pco2 due to deccan traps co2 emissions would have been less than 75 ppm leading to a predicted global warming of less than 1 c over several hundred thousand years we conclude that the direct climate effects of co2 emissions from the deccan eruptions would have been too weak to be an important factor in the end cretaceous mass extinctions

early to late maastrichtian environmental changes in the indian ocean compared with tethys and south atlantic abstract planktic foraminiferal analysis including species populations diversity trends high stress indices and stable isotopes of the latest campanian through maastrichtian in the south atlantic tethys and indian oceans reveal four major climate and faunal events that ended with the cretaceous paleogene k pg formerly cretaceous tertiary k t mass extinction the prelude to these events is the late campanian cooling that reached minimum temperatures in the earliest maastrichtian base c31r correlative with low primary productivity and species diversity event 1 begins during the persistent cool climate of the early maastrichtian lower c31r when primary productivity rapidly increased accompanied by rapid species originations attributed to increased nutrient influx from increased upwelling erosion during the sea level fall 70 6 ma and ninety east ridge volcanism during event 2 upper c31r to lower c30n climate rapidly warmed by 2 3 c in deep waters and peaked at 22 c on land primary productivity remained high and diversification reached maximum for the entire cretaceous we attribute this climate warming to intense ninety east ridge volcanic activity beginning 69 5 ma accompanied by rapid reorganization of intermediate oceanic circulation enhanced greenhouse conditions due to the eruption of deccan phase 1 in india resulted in detrimental conditions for planktic foraminifera marking the end of diversification global cooling resumed in event 3 c30n species diversity declined gradually accompanied by dwarfing decreased large specialized species increased small ecologically tolerant taxa and ocean acidification event 3 is mainly the result of enhanced weathering and volcanogenic co2 adsorption by the oceans during the preceding warm event 2 that led to cooling and lower ph in the surface ocean event 4 marks the last 250 kyr of the maastrichtian c29r which began with the largest deccan eruptions phase 2 that caused rapid climate warming of 4 c in deep waters and 8 c on land acid rain and ocean acidification leading to a major carbonate crisis preceding the k t mass extinction

the k pg boundary at brazos river texas usa an approach by marine palynology two cores and one outcrop section from the cretaceous palaeogen k pg boundary interval at the brazos river area texas usa have been high resolution sampled and analysed fully quantitatively by marine palynology the results have been compared and integrated with data from micropalaeontology sedimentology and isotope geochemistry from the same sections within all three sections the k pg boundary defined as the base of the p0 foraminifera zone and the onset of a negative carbon isotope anomaly closely corresponds to the appearance of lowermost danian organic walled dinocysts based on various palynological proxies as well as on sedimentologic features a sequence stratigraphic subdivision of the sections is proposed from a synopsis of all three sections a long term punctuated drop of relative sea level is indicated starting at about the top of the upper cretaceous cf2 foraminifera zone and reaching a minimum within the upper p1a zone of the lower palaeogene this is followed by a prominent transgression starting within the p1a p1b boundary interval the event deposit ed a siliciclastic unit located well below the base of the p0 foraminifera zone in the present sections most probably represents a combination of both episodic relative sea level fall and lag deposit due to initial transgression it is preceded by significant fluctuations of climatic boundary conditions with cool climates correlating to heavier 13c values and increased p g ratio of dinocysts suggestive of higher marine primary productivity across the k pg boundary a prominent increase and spike of the warm temperate waters dinocysts fraction is documented represented mainly by trithyrodinium evittii which is accompanied by climatic warming and an episodic relative sea level rise thus prominent paleo environmental changes and sea level fluctuations precede and coincide with the k pg boundary proper these data are inconsistent with a single catastrophic impact as the cause for the k pg boundary event but suggest relative longer term environmental stress as finally leading to end cretaceous crisis of the biosphere between the ed and the k pg boundary proper the gradual increase to peak abundance in trilete spores demonstrates a significant time lag between these two horizons according to the distinct distribution of this peak abundance it cannot be excluded that an impact tsunami event is related to the lower portion of the ed in contrast no significant changes within most palynologic proxies are documented across the yellow clay layer below the ed documented within one of the sections and recently suggested as the original chicxulub impact ejecta horizon this questions the impact origin of this horizon or at least suggests only little consequences of this event on the ecosystem

calcareous nannoplankton assemblage changes linked to paleoenvironmental deterioration and recovery across the cretaceous paleogene boundary in the betic cordillera agost spain abstract investigations of calcareous nannoplankton assemblages including species richness and abundance data were performed across the k pg boundary interval at agost se spain between 100 cm and 100 cm below and respectively above the boundary at a considerable high resolution averaging 2 cm from a total of 98 species of the upper maastrichtian only 13 survived mass extinction while the rest of the 86 vanished in the k pg fallout layer a slight progressive decline in species richness and abundance was observed toward the top of the maastrichtian where mixed assemblages consisting of both cold water taxa and typical tethyan ones are present four successive acme events were observed i e markalius inversus and the calcareous dinoflagellate genus thoracosphaera starting from the base of the paleocene followed by those of braarudosphaera bigelowii and neobiscutum parvulum the most prominent acme intervals belong to thoracosphaera spp and b bigelowii opportunistic taxa for which the survival strategy may be linked to their capability to encyst and survive severe environmental deterioration at the upper part of the studied succession calcareous nannoplankton assemblages are already dominated by survivor species as well as incoming ones showing an early pioneer calcareous nannoplankton ecosystems about 35 40 kyr after the k pg boundary correlation between the calcareous nannoplankton assemblage fluctuation including species richness and abundance and the paleoenvironmental changes such as the eustatic and climatic modifications are also discussed

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

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

turbulent structure in compound open channel flows an investigation of three dimensional 3 d turbulent structure including turbulence driven secondary currents in compound open channel flows is a very important topic in hydraulic and river engineering as well as in fluid mechanics in this study accurate measurements in fully developed compound open channel flows are conducted by means of a fiber optic laser doppler anemometer flda secondary velocities can be measured very accurately with the present 3 d measurement system the characteristics of compound open channel flows are recognized in the junction region between the main channel and flood plain whereas the characteristics of rectangular open channel flows are observed in a region near the sidewall of the main channel strong inclined secondary currents which are associated with a pair of longitudinal vortices are generated in the junction region between the main channel and the flood plain the primary mean velocity field is directly influenced by these secondary currents turbulence i

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

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

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

extinction dissolution and possible ocean acidification prior to the cretaceous paleogene k pg boundary in the tropical pacific abstract biotic perturbations and changes in ocean circulation during the maastrichtian stage of the latest cretaceous raise questions about whether the biosphere was preconditioned for the end cretaceous mass extinction of calcareous plankton a brief acme of inoceramid clams at 71 ma on shatsky rise in the tropical north pacific was followed by their extinction during the mid maastrichtian event at 70 1 ma associated with an abrupt warming of deep waters this was later followed by an interval of intense dissolution beginning 67 8 ma at odp site 1209 2387 m the late maastrichtian dissolution interval was initially gradual and is characterized by a low planktic benthic p b ratio highly fragmented planktic foraminifera mostly an absence of larger taxa low abundances of smaller taxa extremely low planktic foraminiferal numbers and low planktic foraminiferal and nannofossil species richness a partial recovery in carbonate preservation and calcareous plankton simple diversity began 250 kyr prior to the k pg boundary associated with the incursion of a younger more enriched 13c deep water mass although total abundances of planktic foraminifera in the sediment remained a tiny fraction of their earlier maastrichtian values a second brief dissolution event occurred 200 kyr before the boundary evidenced by renewed increase in planktic fragmentation but without a decrease in p b ratio our data show that changing deep water masses coupled with reduced productivity and associated decrease in pelagic carbonate flux was responsible for the first 1 6 myr dissolution interval while deccan traps volcanism may have caused surface ocean acidification 200 kyr prior to the k pg mass extinction event

nannoplankton productivity fluctuations and rhythmically bedded pelagic carbonates of the greenhorn limestone upper cretaceous abstract comparison of calcareous nannofossil assemblages from rhythmically interbedded calcareous shales and adjacent bioturbated chalks of the greenhorn limestone cenomanian turonian of the western interior basin indicate significant changes in phytoplankton paleocommunity structure between lithotypes significantly higher shannon diversity and evenness values in the chalk assemblages indicate more stable surface water conditions with lower fertility three taxa indicative of high surface water fertility are significantly more abundant in marlstone assemblages which suggests that calcareous shale marlstone deposition corresponded with fluctuating surface water conditions with relatively high fertility the higher surface fertility and concomitant production of organic matter resulted in sediment anoxia during marlstone deposition leading to high rates of organic carbon storage reduced phytoplankton production during chalk deposition allowed oxygenation of the sea floor and establishment of diverse benthic invertebrate communities

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

maastrichtian climate productivity and faunal turnovers in planktic foraminifera in south atlantic dsdp sites 525a and 21 abstract stratigraphic faunal and isotopic analyses of the maastrichtian at dsdp sites 525a and 21 in the south atlantic reveal a planktic foraminiferal fauna characterized by two major events an early late maastrichtian diversification and end maastrichtian mass extinction both events are accompanied by major changes in climate and productivity the diversification event which occurred in two steps between 70 5 and 69 1 ma increased species richness by a total of 43 and coincided with the onset of major cooling in surface and bottom waters and increased surface productivity the onset of the terminal decline in maastrichtian species richness began at 67 5 ma and the first significant decline in surface productivity occurred at 66 2 ma coincident maximum cooling to 13 c in surface waters and the reduction of the surface to deep temperature gradient to less than 5 c major climatic and moderate productivity changes mark the mass extinction and the last 500 kyr of the maastrichtian between 200 and 400 kyr before the k t boundary surface and deep waters warmed rapidly by 3 4 c and cooled again during the last 100 kyr of the maastrichtian surface productivity decreased only moderately across the k t boundary species richness began to decline during the late maastrichtian cooling and by k t boundary time the mass extinction had claimed 66 of the species viewed within the context of maastrichtian climate and productivity changes the k t mass extinction could have resulted from extreme environmental stress even without the addition of an extraterrestrial impact

stable isotopes and geochemistry of a campanian maastrichtian pelagic succession mudurnu goynuk basin nw turkey implications for palaeoceanography palaeoclimate and sea level fluctuations this study focuses on the palaeoclimatic evolution and relative sea level fluctuations of the northern branch of neotethys during the late campanian early danian the studied succession ismailler section is located in the mudurnu goynuk basin nw turkey and dominated by apparently continuous pelagic muddy deposits stable isotopic and elemental compositions of the mudrocks are investigated in order to evaluate the palaeoceanographic conditions as well as broad tectonic reconstruction of the basin the mudrock geochemistry suggests a tectonic reorganization during late campanian as reflected by a distinct shift from felsic to mafic sediment provenance in the ismailler section five 13c events are identified four or which are well correlatable with major events in other records around the world such as the late campanian event lce campanian maastrictian boundary cmb and the late maastrichtian event lme the relative sea level variations in the basin typically match both short and long term global sea level fluctuations the remaining globally uncorrelatable 13c event does coincide with tectonic uplift and the abrupt negative 13c shift and is inferred to be the result of regional factors the dominance of worldwide events in the records of the relatively restricted ocean branch reflects the strength of global factors

variability in late cretaceous climate and deep waters evidence from stable isotopes abstract strong climatic and temperature fluctuations mark the late campanian and maastrichtian as indicated by stable isotope records from the equatorial pacific site 463 and middle and high latitude south atlantic sites 525 689 and 690 the first major global cooling decreased intermediate water temperatures iwt by 5 6 c between 73 70 ma at the same time sea surface temperature sst decreased by 4 5 c in middle and high latitudes intermediate waters iw temporarily warmed by 2 c in low and middle latitudes between 70 68 5 ma global cooling resumed between 68 5 65 5 ma when iwt decreased by 3 4 c and sst by 5 c in middle latitudes about 450 ka before the cretaceous tertiary boundary rapid global warming increased iwt and sst by 3 4 c though sst in the tropics changed little during the last 200 ka of the maastrichtian climate cooled rapidly with iwt and sst decreasing by 2 3 c during the global cooling at 71 70 ma and possibly at 67 65 5 ma the sources of cold intermediate waters in the equatorial pacific indo pacific and south atlantic were derived from the high latitude north pacific in contrast during the global climate warming between 65 2 65 4 ma the middle latitude south atlantic was closest to the source of iw production and implies that the low latitude tethys played a major role in global climate change climate changes sea level fluctuations and associated restricted seaways appear to be the most likely mechanisms for the alternating sources of iw production

nannofossil diversity and equitability and fine fraction δ13c across the cretaceous tertiary boundary at walvis ridge leg 74 south atlantic abstract the isotopic composition and diversity of nannofossils were studied in cores from the deep sea drilling project dsdp sites 525a 527 528 and 529 from the walvis ridge south atlantic to better understand the changes which occurred across the cretaceous tertiary boundary k t boundary the stratigraphic range of the samples is from thearkhangelskiella cymbiformis zone in the maastrichtian to theheliolithus kleinpelli zone in the danian nannofossil diversity was high shannon weaver diversity index h 2 5 3 in the late cretaceous but decreased sharply h 1 across the k t boundary the 13c values also decrease across the k t boundary at the four sites suggesting a reduction in surface productivity in the south atlantic concomitant with the reduction in diversity during the danian nannofossil diversity and 13c show some recovery approximately 500 700 k y after the boundary event however not until 2 5 ma after the boundary event did diversity become constant diversity values similar to those for the late cretaceous were not attained again in the early paleocene interval studied carbon isotopic compositions similar to those from the cretaceous were not attained until 4 5 ma after the k t event

a multi proxy approach to decode the end cretaceous mass extinction mass extinctions generally involve a complex array of interrelated causes and are best evaluated by a multi proxy approach as applied here for the end cretaceous mass extinction this study documents and compares the planktic foraminiferal records carbonate dissolution effects stable isotopes and magnetic susceptibility in france bidart austria gamsbach and tunisia elles in order to explore the environmental conditions during the uppermost maastrichtian plummerita hantkeninoides zone cf1 leading up to the mass extinction planktic foraminiferal assemblages at bidart and gamsbach appear to be more diverse than those at elles with unusually high abundance 20 30 and diversity 15 species of globotruncanids in the two deep water sections but lower abundance 10 and diversity 10 species at the middle shelf elles section oxygen isotopes in zone cf1 of elles record rapid climate warming followed by cooling and a possible return to rapid warming prior to the mass extinction the onset of high stress conditions for planktic foraminifera is observed 50 60 cm below the ktb at bidart and gamsbach and 4 5 m below the ktb at elles due to much higher sediment accumulation rates these intervals at bidart and gamsbach record low magnetic susceptibility and high planktic foraminiferal fragmentation index fi at elles bidart and gamsbach an increased abundance of species with dissolution resistant morphologies is also observed at gamsbach the correlative interval in india records significantly stronger carbonate dissolution effects in intertrappean sediments between the longest lava flows ending with the mass extinction based on current evidence this widespread dissolution event stratigraphically coincides with the climate cooling that follows the late maatrichtian global warming and may be linked to ocean acidification due to deccan volcanism the estimated 12 000 28 000 gigatons gt of co2 and 5200 13 600 gt of so2 introduced into the atmosphere likely triggered the carbonate crisis in the oceans resulting in severe stress for marine calcifiers leading to mass extinction

calcareous nannofossil biostratigraphy and paleoecology of the cretaceous tertiary transition in the central eastern desert of egypt abstract the gebel qreiya and nearby wadi hamama sections of the central eastern desert are among the most complete k t boundary sequences known from egypt the two sections were analyzed spanning an interval from l 83 myr below to about 3 myr above the k t boundary a 1 cm thick red clay layer at the k t boundary at gebel qreiya contains an ir anomaly of 5 4 ppb the high resolution study and well preserved nannoflora provide good age control and the first quantitative records of calcareous nannofossil assemblages for paleoecological interpretations across the k t transition in egypt four zones micula murus micula prinsii np1 and np2 were distinguished and correlated with other nannofossil and planktonic foraminiferal zonations that are broadly applicable for the eastern tethys region latest maastrichtian assemblages are abundant and diverse though cretaceous species richness progressively decreased across the k t boundary dominant species include arkhangelskiella cymbiformis micula decussata and watznaueria barnesae with high abundance of dissolution resistant m decussata reflecting periods of high environmental stress thoracosphaera blooms mark the k t boundary and are followed by an acme of the opportunistic survivor braarudosphaera bigelowii the first appearance of the new tertiary species cruciplacolithus primus and an acme of coccolithus cavus pelagicus these successive abundance peaks provide the basis for subdivision of the early danian zones np1 and np2 into five subzones correlation of selected nannofossil taxa from the egyptian sections with those from various onshore marine and deep sea sections provides insights into their paleoenvironmental and paleoecological affinities

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

volatile fluxes during flood basalt eruptions and potential effects on the global environment a deccan perspective abstract we examine the role that flood basalt eruptions may have played during times of mass extinction through the release of volcanic gases continental flood basalt provinces have formed by numerous eruptions over a short period of geologic time characteristically a few million years within this period a short lived climactic phase that lasts about 1 ma typically emplaces a large proportion of the lava volume this phase consists of a series of huge eruptions each yielding 10 3 10 4 km 3 of magma each eruption lasted on the order of a decade or more and built an immense p hoehoe dominated lava flow field by eruptive activity along fissures tens to hundreds of km long high fire fountains emanating from vents along the fissures at times sustained eruption columns that lofted gas and ash into the upper troposphere and lower stratosphere while the lava flows covered huge areas the combination of large eruption magnitudes maintained high effusion rates during eruptions and the repeated nature of the characteristic large scale eruptive activity occurs in earth history only during periods of flood basalt volcanism based on recent analogs and determination of volatile contents of ancient flood basalt lavas we estimate that individual eruptions were capable of releasing 10 000 tg of so 2 resulting in atmospheric loadings of 1000 tg a 1 during a sustained decade long eruptive event we apply this model of flood basalt volcanism to estimate the potential mass of co 2 and so 2 released during formation of the 65 ma deccan province the deccan lava pile contains the record of hundreds of enormous p hoehoe flow fields erupted within a period of about 1 ma consequently atmospheric perturbations associated with so 2 emissions from just one of these long lasting eruptions were likely to have been severe and constantly augmented over a decade or longer by contrast the amounts of co 2 released would have been small compared with the mass already present in the atmosphere and thus much more limited in effect individual eruptions were followed by hiatuses of hundreds to thousands of years during which the gas contributions to the atmosphere would be recycled it is clear that the nature and potential atmospheric impact of a series of huge volume repeated long term degassing events requires further investigation in conjunction with appropriate climate models

calcareous nannofossil evidence for the existence of the gulf stream during the late maastrichtian 1 upper maastrichtian calcareous nannofossil assemblages from eight cores on the south carolina coastal plain onshore set and three deep sea drilling sites from the continental slope and abyssal hills offshore set were analyzed by correlation and principal component analysis to examine the ancient surface water thermal structure in addition a temperature index derived from independently published paleobiogeographic information was applied to the sample data all three methods indicate a strong separation of the samples into onshore and offshore sets with the offshore data set exhibiting significantly warmer paleotemperatures the great disparity between these two sample sets indicates that there was a strong thermal contrast between the onshore and offshore surface water masses that persisted throughout the late maastrichtian despite evident short term changes in fertility productivity and community structure this suggests the gulf stream was present as a major oceanographic feature during the late maastrichtian

the calcareous nannofossil biostratigraphic framework of the late maastrichtian danian north sea chalk abstract the calcareous nannofossil biostratigraphy of cored maastrichtian tor formation and danian ekofisk fm chalk sections from 10 selected wells of the greater ekofisk area central north sea was studied wells come from the edda tor se tor ekofisk and eldfisk fields among others more than 1000 m of cores were examined and about 500 samples were selected and analysed most of them quantitatively the main emphasis was placed on the danian sequence and on the k t boundary biostratigraphy provided detailed subdivision for the danian sediments intra danian hiatuses were detected and consistently recorded at the regional scale extensive mass movement was observed highlighting the complex depositional history during this time interval intervals of cretaceous chalk were found embedded in the danian sequence well 2 5 7 redeposited by slides as discrete chalk packages similarly lower danian intervals were recognised as transported into younger danian sediments well 2 4 b19a an attempt to reconstruct a regional stratigraphic picture for the area north of edda field including ekofisk se tor and tor fields has been made this suggests the following salient features the k t boundary of three wells of the northern sector of the studied area tor field is preceded by a prediscosphaera stoveri acme suggesting the presence of a rather complete maastrichtian sequence below the boundary above the k t boundary a few tens of centimetres of generally clay enriched pelagic chalk of the basal danian d1 biantholithus sparsus zone are present in most of the studied wells above this a condensed section often marked by hard ground levels or clay rich intervals was detected in almost all the wells the sedimentary expression of upper d1 above cruciplacolithus primus fad d2 and d3 time interval is lacking or extremely reduced in some cases sediments whose age is near the early late paleocene boundary were found unconformably overlying pelagic chalk referred to d5 d6 biozones

terminal cretaceous warming event in the mid latitude south atlantic ocean evidence from poleward migration of contusotruncana contusa planktonic foraminifera morphotypes abstract spatial and temporal patterns in test size and shape test conicity and spiral roundness and absolute abundance accumulation rate of the planktonic foraminifer contusotruncana contusa were studied in the south atlantic ocean dsdp sites 356 516 525 and 527 during an interval corresponding to the last 800 kyr of the cretaceous the variation in absolute abundance of c contusa was characterised by alternating periods of high and low abundance some of these periods were traceable across the entire mid latitude south atlantic ocean while the mean spiral roundness did not show any interpretable patterns a sudden increase of the mean test size and mean test conicity occurred between 65 3 and 65 2 ma based on linear interpolation within the cretaceous part of subchron c29r at all sites studied indicating a poleward migration followed by rapid withdrawal of the low latitude c contusa morphotypes from the mid latitude south atlantic ocean we suggest that this event was caused by a short period of surface water warming in the southern mid latitudes corresponding to the brief high latitude warming event and associated faunal migrations in the boreal and austral realms

comment on extinction dissolution and possible ocean acidification prior to the cretaceous paleogene k pg boundary in the tropical pacific abstract criticism of the age model used by dameron et al in press is commented hereby this criticism essentially concerns the age of the first occurrence of calcareous nannofossil micula prinsii at shatsky rise central pacific which should not be considered older than 66 6 ma rather than 67 3 ma as considered by the authors although this criticism does not fundamentally change the environmental and paleoceanographic interpretations of dameron et al in press the age of this bioevent influences quite a lot the time scale used for the latest maastrichtian and thus the actual age of the termination of their main dissolution interval and the duration of the partial recovery in carbonate preservation we recommend the authors to modify their age model and to provide alternative durations and ages for the sequence of events in the end maastrichtian interval as such revised ages constitute an important base for comparison with the timescale of deccan volcanism and other end cretaceous perturbations

nannofossil assemblages fine fraction stable isotopes and the paleoceanography of the valanginian barremian early cretaceous north sea basin calcareous nannofossil assemblages have been investigated in three sections from around the margins of the early cretaceous north sea basin both absolute number of nannofossils per gram and relative percent of the assemblage of different taxa abundance data have been collected absolute abundances up to 10 billion nannofossils per gram are somewhat higher than those reported previously from other stratigraphic intervals stratigraphic correlation of trends in assemblage data in different sections points toward the existence of large uniform water masses stable over long 0 5 to 1 m y time periods these water masses contained a characteristic nannoplankton which appears to have been driven largely by variations in fertility possibly tied to changes in sources of surface waters which in turn may have been controlled by relative sea level fine fraction isotopic data show fluctuations on shorter time periods 0 1 to 0 5 m y we postulate that some of these isotopic fluctuations were controlled by relative changes in sea level which affected the balance of surface waters derived from runoff and those imported from the boreal sea these oceanographic changes appear to have affected nannofossil assemblages only in discrete intervals data are available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington dc 20009 document p95 001 2 50 payment must accompany order

modelling massive sulphate aerosol pollution following the large 1783 laki basaltic eruption abstract the climatic impact of volcanic eruptions depends mainly on the amount of sulphur rich gases released into the stratosphere these are rapidly converted to sulphate aerosols which result in cooling of the lower troposphere and warming of the lower stratosphere these gases are retained in the stratosphere and then concentrated by atmospheric processes forming acid fog near the earth s surface with potentially dramatic environmental consequences on plants animals and humans we have modelled such emissions in the case of the unusually large 1783 1784 basaltic fissure eruption of laki iceland using an atmospheric general circulation model results show good agreement with historical observations such as typical time taken by individual pulses to reach continental europe or geographical extent of the deadly haze that covered much of the northern hemisphere the model could be adjusted to predict the climatic consequences of very large eruptions up to the scale of massive flood basalts and test the proposal that these are the main agent in most mass extinctions of life on earth

foraminiferal dissolution at shallow depths of the walvis ridge and rio grande rise during the latest cretaceous inferences for deep water circulation in the south atlantic abstract a high resolution 10 20 kyr record of variations in caco3 content and dissolution was established for latest cretaceous last 0 7 myr deep sea sediments from the south atlantic ocean dsdp site 516 from the rio grande rise and sites 525 and 527 from the walvis ridge the degree of fragmentation of planktonic foraminifera dfp was used as a measure of calcite dissolution high negative correlations between dfp and other independent measures of carbonate dissolution percentage of sand fraction absolute abundance of planktonic foraminifera and planktonic benthic foraminiferal ratio validate its use as a sensitive index of calcite dissolution in upper maastrichtian deep sea sediments very high dfp and a significant negative correlation between dfp and caco3 content suggest that site 516 was located below the foraminiferal lysocline during the entire interval studied such a shallow position of the lysocline paleodepth of site 516 was 1 2 km may be explained by upwelling of corrosive deep waters along the southern margin of the rio grande rise sites 525 and 527 were located above the foraminiferal lysocline however three short periods of enhanced dissolution were recognised at site 525 paleodepth 1 km and one interval of strong dissolution was identified at site 527 paleodepth 2 7 km the lack of correspondence between the dissolution regimes at sites from the walvis ridge suggests limited deep water communication across this physiographic barrier two of the dissolution maxima recognised at site 525 correspond to carbonate maxima at site 527 variations in upwelling intensity along the walvis ridge resulting in fluctuations in primary productivity in this area may be the proximal cause of both carbonate cycles at site 527 and dissolution cycles at site 525 we suggest that development of the bottom ekman layer between a hypothetical westward geostrophic current and the topographical height of the rio grande rise walvis ridge system may be a plausible hydrodynamical explanation for the proposed upwelling along the southern margin of this topographical structure

short term environmental changes in the cretaceous tethyan ocean micropalaeontological evidence from the early albian oceanic anoxic event 1b to better understand the linkage between climate and ocean circulation under greenhouse conditions we have studied calcareous nannofossils palynomorphs and benthic foraminifera from the early albian oceanic anoxic event 1b black shale oae 1b in the vocontian basin se france we propose that monsoonal activity resulting from precessional forcing and modulated by eccentricity driven temperature changes represents the driving factor of oae 1b formation in low latitudes with the onset of oae 1b increasingly warm and humid conditions stronger winds and enhanced terrestrial input led to higher surface water productivity therefore increased productivity is an important factor for oae 1b formation in the vocontian basin however monsoonally forced productivity changes are a regional climate signal only the supraregional occurrence of the oae 1b is probably due to a reduction of deep water formation in the low latitudes under extremely warm and humid conditions leading to enhanced preservation of organic matter

mass wasting and hiatuses during the cretaceous tertiary transition in the north atlantic relationship to the chicxulub impact deep sea sections in the north atlantic are claimed to contain the most complete sedimentary records and ultimate proof that the chicxulub impact is cretaceous tertiary boundary ktb in age and caused the mass extinction a multi disciplinary study of north atlantic dsdp sites 384 386 and 398 based on high resolution planktonic foraminiferal biostratigraphy carbon and oxygen stable isotopes clay and whole rock mineralogy and granulometry reveals the age stratigraphic completeness and nature of sedimentary disturbances results show a major hiatus across the ktb at site 384 with zones cf1 p0 and p1a missing spanning at least 540 ky similar to other north atlantic and caribbean localities associated with tectonic activity and gulf stream erosion at sites 386 and 398 discrete intervals of disturbed sediments with mm to cm thick spherule layers have previously been interpreted as the result of impact generated earthquakes at the ktb destabilizing continental margins prior to settling of impact spherules however improved age control based on planktonic foraminifera indicates spherule deposition in the early danian zone p1a 2 upper parvularugoglobigerina eugubina zone more than 100 ky after the ktb at site 386 two intervals of white chalk contain very small 63 m early danian zone p1a 2 assemblages 65 and common reworked cretaceous 35 species in contrast the in situ red brown and green abyssal clays of this core are devoid of carbonate in addition high calcite mica and kaolinite and upward fining are observed in the chalks indicating downslope transport from shallow waters and sediment winnowing via distal turbidites at site 398 convoluted red to tan sediments with early danian and reworked cretaceous species represent slumping of shallow water sediments as suggested by dominance of mica and low smectite compared to in situ deposition we conclude that mass wasting was likely the result of earthquakes associated with increased tectonic activity in the caribbean and the iberian peninsula during the early danian well after the chicxulub impact

global climate change and planktic foraminiferal response in the maastrichtian 1 the lengthy warm stable climate of the cretaceous terminated in the campanian with a cooling trend interrupted in the early and latest maastrichtian by two events of global warming at 70 68 ma and at 65 78 65 57 ma these climatic oscillations had a profound effect on pelagic ecosystems especially on planktic foraminiferal populations here we compare biotic responses in the tropical subtropical tethyan open ocean and mesotrophic zin valley israel and oligotrophic tunisia slopes which correlate directly with global warming and cooling the two warming events coincide with blooms of guembelitria an extreme opportunist genus best known as the main survivor of the cretaceous paleogene k pg catastrophe in the maastrichtian guembelitria bloomed in the uppermost surface water above shelf and slope environments but failed to reach the open ocean as it did at k pg the coldest interval of the late maastrichtian 68 65 78 ma is marked by an acme of the otherwise rare species gansserina gansseri a deep dwelling keeled globotruncanid the g gansseri acme event can be traced from the deep ocean even onto the tethyan slope marking copious production and circulation of cold intermediate water this acme is abruptly terminated by extinction of the species a dramatic reversal attributed to a short term global warming episode this extinction corresponds precisely with the second bloom of guembelitria that began 300 kyr prior to the k pg event the antithetical relationship between blooming of guembelitria and the g gansseri acme reflects planktic foraminiferal sensitivity to warm cool warm cool climatic oscillations marking the end of the cretaceous

a high resolution marine 187os 188os record for the late maastrichtian distinguishing the chemical fingerprints of deccan volcanism and the kp impact event abstract a composite late maastrichtian 65 5 to 68 5 ma marine osmium os isotope record based on samples from the southern ocean odp site 690 the tropical pacific ocean dsdp site 577 the south atlantic dsdp site 525 and the paleo tethys ocean demonstrates that subaerially exposed pelagic carbonates can record seawater os isotope variations with a fidelity comparable to sediments recovered from the seafloor new results provide robust evidence of a 20 decline in seawater 187os 188os over a period of about 200 kyr early in magnetochron c29r well below the cretaceous paleogene boundary kpb confirming previously reported low resolution data from the south atlantic ocean new results also confirm a second more rapid decline in 187os 188os associated with the kpb that is accompanied by a significant increase in os concentrations complementary platinum pt and iridium ir concentration data indicate that the length scale of diagenetic remobilization of platinum group elements from the kpb is less than 1 m and does not obscure the pre kpb decline in 187os 188os increases in bulk sediment ir concentrations and decreases in bulk carbonate content that coincide with the os isotope shift suggest that carbonate burial flux may have been lower during the initial decline in 187os 188os we speculate that diminished carbonate burial rate may have been the result of ocean acidification caused by deccan volcanism

new geochemical evidence for the onset of volcanism in the central atlantic magmatic province and environmental change at the triassic jurassic boundary the late triassic early jurassic was a time of major global change however the fundamental processes driving these changes are less than clear we have determined the re and os abundances and os isotope compositions of marine mudrock samples that span the triassic jurassic boundary in the uk and have established that major isotopic and geochemical shifts in the composition of seawater took place in the latest triassic we argue that these shifts were caused by the sudden initiation of widespread igneous activity within the central atlantic magmatic province associated with rifting of the supercontinent pangea the os isotope composition of seawater responded rapidly to these events demonstrating that the seawater os isotope system has great potential in identifying the nature and precise timing of major environmental change

north atlantic warming during global cooling at the end of the cretaceous differences in regional responses to climate fluctuations are well documented on short time scales e g el nino southern oscillation but with the exception of latitudinal temperature gradients regional patterns are seldom considered in discussions of ancient greenhouse climates contrary to the expectation of global warming or global cooling implicit in most treatments of climate evolution over millions of years this paper shows that the north atlantic warmed by as much as 6 c 1 5 decrease in 18o values of planktic foraminifera during the maastrichtian global cooling interval we suggest that warming was the result of the importation of heat from the south atlantic decreasing north atlantic 18o values are also associated with increasing gradients in planktic 13c values suggesting increasing surface water stratification and a correlated strengthening of the north atlantic polar front if correct this conclusion predicts arctic cooling during the late maastrichtian beyond implications for the maastrichtian these data demonstrate that climate does not behave as if there is a simple global thermostat even on geologic time scales

new latitude based nannofossil zonations for the campanian maastrichtian of the south atlantic ocean and their paleoceanographic implications the global evolution of calcareous nannofossils during the campanian maastrichtian interval is not fully understood and nannofossil zonations for the central and south atlantic ocean are yet to be constructed here we test the applicability of previous calcareous nannofossil zonations developed for other ocean basins for biostratigraphy in the south atlantic ocean and refine campanian maastrichtian biostratigraphy in the region we document calcareous nannofossil distributions at deep sea drilling project dsdp and ocean drilling program odp sites from the high mid and low latitudes in the south atlantic ocean dsdp sites 354 356 511 525a and 530a and odp sites 690c 700b 661a and 1258a combining nannofossil occurrences with magnetostratigraphic schemes previously constructed for some of the sites we propose three new zonations tied to the global magnetostratigraphic chrons with distinct bio horizons selected at different latitudinal regions in this study we present detailed definitions of new south atlantic ocean low latitude sal south atlantic mid latitude sam and south atlantic high latitude sah zonations we identified significant diachronism of some species between latitudes throughout the campanian and maastrichtian these species diachronism mainly between zonal markers from low and mid latitudes during the late maastrichtian was probably related to migration patterns due to fundamental paleoceanographic changes

calcareous nannofossil and dinoflagellate stratigraphy across the cretaceous tertiary boundary at hor hahar israel in israel the cretaceous tertiary k t boundary at hor hahar occurs within the interval from the top of the ghareb formation maastrichtian to just below the horizon of dark marl and clay within the overlying taqiye formation paleocene the studied interval contains all the calcareous nannofossil zones micula prinsii latest maastrichtian markalius inversus np1 earliest paleocene andcruciplacolithus tenuis np2 early paleocene they correlate in sequence with theabathomphalus mayaroensis p0 p1a p1b and p1c planktic foraminiferal zones the palynological assemblages consist mainly of dinocysts with only few pollen grains and spores these assemblages are used to interpret five stratigraphic phases of environmental change across the k t boundary in the hor hahar section in the latest maastrichtian there is an overwhelming dominance of the nannofossilmicula decussata which probably reflects environmental stress preceding the terminal cretaceous mass extinction a nearshore marine environment at the boundary is suggested by the increase in number of specimens of the dinocystcyclonephelium and by the predominance of terrigenous organic matter sediment there followed two episodes of transgression and regression the calcareous cyst producing dinoflagellatethoracosphaera futterer 1976 becomes dominant in two episodes at the boundary and approximately one meter above it it alternates in abundance with the organic walled dinoflagellates which suggests that different environmental parameters were operating for each group maastrichtian dinocysts decline in abundance toward the k t boundary they reach greatest abundance and species diversity at the same strata where foraminiferids recover after their mass extinction at the boundary calcareous nannofossils recover only later in the early paleocene changes in 13c and total organic carbon as as well as dinocyst and nannofossil composition indicate an episode of strong ecological stress about one meter above the boundary

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

channel pattern change downstream from a reservoir an example of wandering braided rivers reservoir induced channel pattern change is an issue of significance both in theory and engineering practice based on data from three major wandering braided rivers in china namely the yongdinghe the hanjiang and the yellow rivers as well as a laboratory experimental study this paper deals with channel pattern change downstream from reservoirs complex response in channel adjustment has been observed in the field and as a result a three stage descriptive model has been established to describe the course of channel pattern change also the three stages have been simulated successfully by a laboratory physical model although the observed tendency of channel pattern change of the three rivers is quite different which has been a matter of controversy for many years among chinese researchers it can be satisfactorily explained by the present complex response model because of different boundary conditions the duration of the three stages for the three rivers is different so the channel pattern change of the three rivers shows a different tendency at each specific stage the present study suggests that schumm s qualitative model for river channel metamorphosis should be modified when used for predicting reservoir induced channel pattern change on a wandering braided river because the model has not taken into consideration the changing erosional resistance of channel boundary material and therefore the resultant feedback effect it cannot predict the whole course of channel pattern change over a long period

evidence for thermohaline circulation reversals controlled by sea level change in the latest cretaceous fluctuations in oxygen 18 o and carbon 13 c isotope values of benthic foraminiferal calcite from the tropical pacific and southern oceans indicate rapid reversals in the dominant mode and direction of the thermohaline circulation during a 1 m y interval 71 70 ma in the maastrichtian at the onset of this change benthic foraminiferal 18 o values increased and were highest in low latitude pacific ocean waters whereas benthic and planktic foraminiferal 13 c values decreased and benthic values were lowest in the southern ocean subsequently benthic foraminiferal 18 o values in the indo pacific decreased and benthic and planktic 13 c values increased globally these isotopic patterns suggest that cool intermediate depth waters derived from high latitude regions penetrated temporarily to the tropics the low benthic 13 c values at the southern ocean sites however suggest that these cool waters may have been derived from high northern rather than high southern latitudes correlation with eustatic sea level curves suggests that sea level change was the most likely mechanism to change the circulation and or source s of intermediate depth waters we thus propose that oceanic circulation during the latest cretaceous was vigorous and that competing sources of intermediate and deep water formation linked to changes in climate and sea level may have alternated in importance

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

disaster opportunists guembelitrinidae index for environmental catastrophes blooms of the disaster opportunist guembelitria species are proxies for environmental catastrophes whether impact or volcanism leading to severe biotic stress crises that may range from temporary exclusion of ecological specialists and generalists to mass extinctions during the late maastrichtian and early danian zones p0 and pla guembelitria blooms show global distributions but with the largest blooms 40 80 guembelitria in low and middle latitudes and only minor blooms 10 20 in high latitudes late maastrichtian guembelitria blooms are so far known from the indian ocean and eastern tethys the most intense guembelitria blooms 60 guembelitria occurred in shallow continental shelf areas slope shelf margins and volcanic provinces of the indian ocean what these environments have in common is high nutrient influx eutrophication either from continental runoff upwelling along continental margins or volcanic input at times of biotic crises guembelitria blooms may have spread rapidly to the exclusion of most or all other species much like today s red tides but with near global distributions a simple model can explain the ecological succession and recovery phases that follow major biotic perturbations caused by impacts or volcanism that lead to exclusion of specialist and most generalist species within such highly stressed environments guembelitria is the only genus to thrive and without competition rapidly reproduce and exponentially increase their populations when nutrients are depleted populations rapidly decrease leading to ecologic niches for other generalists and ecosystem recovery small low o2 tolerant heterohelicid populations mark this second stage followed by small trochospiral and planispiral species with further environmental recovery increasing competition niche development and restoration of a well stratified water mass oligotrophic conditions are restored opening habitats for the highly specialized and diverse species and a return to normal diverse assemblages this ecological succession is observed in association with mantle plume volcanism in the indian ocean and eastern tethys during the late maastrichtian and in association with the k t impact and volcanism during the early tertiary d 2004 elsevier b v all rights reserved

biotic effects of impacts and volcanism the biotic effects of late maastrichtian mantle plume volcanism on ninetyeast ridge and deccan volcanism mirror those of the cretaceous tertiary kt mass extinction and impact event planktonic foraminifera responded to high stress conditions with the same impoverished and small sized species assemblages dominated by the disaster opportunists guembelitria cretacea which characterize the kt mass extinction worldwide similar high stress late maastrichtian assemblages have recently been documented from madagascar israel and egypt biotic effects of volcanism cannot be differentiated from those of impacts though every period of intense volcanism is associated with high stress assemblages this is not the case with every impact the most catastrophic biotic effects occurred at the kt boundary 65 0 ma when intense deccan volcanism coincided with a major impact and caused the mass extinction of all tropical and subtropical species the chicxulub impact which now appears to have predated the kt boundary by about 300 kyr coincided with intense deccan volcanism that resulted in high biotic stress and greenhouse warming but no major extinctions the unequivocal connection between intense volcanism and high stress assemblages during the late maastrichtian to early danian and the evidence of multiple impacts necessitates revision of current impact and mass extinction theories

an astronomical time scale for the maastrichtian based on the zumaia and sopelana sections basque country northern spain the rhythmically bedded limestone marl alternations in the coastal cliffs of sopelana and zumaia in the basque country northern spain permit testing and refining of existing maastrichtian chronologies latest cretaceous the recently established astronomical time scale for the late maastrichtian at zumaia is extended into c31n with the integrated stratigraphy of the sopelana section the cyclic alternations of hemipelagic limestones and marls at sopelana show a strong influence of eccentricity modulated precession together the zumaia and sopelana sections span almost the entire maastrichtian and encompass thirteen 405 kyr cycles spanning a total duration of 5 3 myr from the cretaceous paleogene k pg boundary downwards 405 kyr minima in the lithological magnetic susceptibility and reflectance data records are tuned to successive 405 kyr minima in the new la2011 eccentricity solution assuming a k pg boundary age of 65 97 ma we present orbitally tuned ages of biostratigraphic and magnetostratigraphic events whereas the bases of chrons c29r and c30n were reliably established at zumaia and are in good agreement with previous studies new data from sopelana provide a refinement of the basal age of chron c31r additional planktonic foraminifera and calcareous nannoplankton data from zumaia and new calcareous nannoplankton data from sopelana allow for worldwide correlation of the cyclostratigraphy of the basque country supplementary materials a geological map and additional data are available at www geolsoc org uk sup18696

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