seasonal and interannual variation of coccolithophore fluxes and species composition in sediment traps north of gran canaria 29 n 15 w abstract coccolithophore flux variations in sediment traps of the time series station estoc european station for time series in the ocean canary islands located 60 nm north of gran canaria were recorded from april 1993 to december 1996 the 20 cup particle traps were deployed at 1000 and 3000 m below sea surface and sampling intervals ranged from eight days to three weeks coccolith and coccosphere fluxes at both trap depths were characterized by a strong seasonality at 1000 m maximum coccolith fluxes were reached during spring from march to april 1995 and from february to march 1996 highest coccolith fluxes of 4538 106 coccoliths m 2 d 1 occurred at the beginning of march 1996 whereas lowest values of 19 8 106 coccoliths m 2 d 1 were recorded in june 1994 total coccosphere fluxes were constantly low during most of the investigated time interval and showed only high values during the main sedimentation phases from january to march 1995 up to 6 2 106 spheres m 2 d 1 and in march 1996 36 4 106 spheres m 2 d 1 at 3000 m water depth the sedimentation pattern was rather similar to the pattern observed at 1000 m maximum coccolith and coccosphere fluxes were also reached during spring time in february 1994 8200 106 and 15 6 10 6 m 2 d 1 respectively and in march 1996 8114 106 and 32 3 10 6 m 2 d 1 respectively however total coccolith flux peaks at 3000 m were about 2 4 times higher compared to the upper traps probably due to horizontal advection from phytoplankton material from north of the study site this effect also influenced the coccolith caco3 flux estimates mean calculated coccolith caco3 fluxes ranged between 3 9 mg m 2 d 1 for the upper traps 1995 1996 and 9 9 mg m 2 d 1 for the lower traps 1996 coccoliths contributed for about 8 78 of the measured total caco3 fluxes the coccolithophore assemblages were dominated by emiliania huxleyi florisphaera profunda and gephyrocapsa ericsonii during the entire sampling period whereas all other species together generally contributed less than 40 to the total assemblages variability of species compositions at either trap depth was very low indicating similar seasonal flux patterns of the different species

the posidonia shale lower toarcian of sw germany an oxygen depleted ecosystem controlled by sea level and palaeoclimate abstract the lower toarcian posidonia shale is famous for its excellently preserved fossils and its high amount of organic matter up to 16 both quality of preservation and accumulation of organic matter have been explained by permanent anoxic bottom water conditions high resolution geochemical sedimentological and palaeoecological investigations of various sections of the posidonia shale in sw germany however indicate that oxygen availability was variable and ranged from short oxygenated periods to longer term anoxia the benthic macrofauna consists of nine fossil communities and was used in combination with geochemical data to reconstruct a time averaged oxygen curve anoxic conditions prevailed during the deposition of the toarcian black shales they were however punctuated by various short periods weeks to years with oxygenated bottom water conditions sedimentological e g distinctiveness of microlamination siliciclastic content and geochemical parameters e g organic matter content isotopic signatures 18o and 13c molecular redox parameters pristane phytane ratio arylisoprenoids exhibit a remarkable covariation and seem to be controlled by sea level fluctuations maximum oxygen depletion and an extreme negative shift of 13corg values 34 occurred during the early falciferum zone this is explained by the recycling of 12c enriched carbon derived from remineralization of organic matter on and within the substrate during low sea level stand and a highly elevated redox boundary including photic zone anoxia the subsequent transgression permitted enhanced water exchange with the tethyan ocean and caused improvement of living conditions at the end of the falciferum zone other important factors controlling the depositional environment are the overall palaeogeographic situation and climate the early jurassic is the latest period before break up of pangaea and probably was ruled by a strong meridional atmospheric circulation system with pronounced seasonal changes of prevailing trade and monsoon wind systems an estuarine circulation with a positive water balance and surface water with slightly reduced salinity in the summer alternated with an anti estuarine circulation and a negative water balance in the winter during the summer months a stratified water column with anoxic conditions below the halocline developed 18o data indicate low salinity in the surface water during the monsoon influenced summer high productivity was then located in the photic zone and the corresponding isotopically light 18o signal was fixed in the calcareous nannoplankton during the winter months a saline circulation system brought oxygen to the benthic environment favouring temporary benthic colonization especially during times of relative sea level high stand

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

an oscillating trend in phanerozoic non skeletal carbonate mineralogy textural and compositional data on ancient ooids and cements suggest the existence of an oscillating phanerozoic temporal trend in non skeletal carbonate mineralogy the trend shows good correlation with eustatic climatic oscillations proposed by others the most likely mechanism appears to be plate tectonically influenced oscillations in pco2 the vapour pressure of co2 rather than change in oceanic mg ca ratio

the early toarcian anoxia a synchronous event in the western tethys an approach by quantitative biochronology unitary associations applied on calcareous nannofossils during the early toarcian major paleoenvironnemental and paleoceanographical changes occurred leading to an oceanic anoxic event oae and to a perturbation of the carbon isotope cycle although the standard biochronology of the lower jurassic is essentially based upon ammonites in recent years biostratigraphy based on calcareous nannofossils and dinoflagellate cysts is increasingly used to date jurassic rocks however the precise dating and correlation of the early toarcian oae and of the associated 13c anomaly in different settings of the western tethys are still partly problematic and it is still unclear whether these events are synchronous or not in order to allow more accurate correlations of the organic rich levels recorded in the lower toarcian oae this account proposes a new biozonation based on a quantitative biochronology approach the unitary associations ua applied to calcareous nannofossils this study represents the first attempt to apply theuamethod to jurassic nannofossils the study incorporates eighteen sections distributed across western tethys and ranging from the pliensbachian to aalenian comprising 1220 samples and 72 calcareous nannofossil taxa the biograph savary j guex j 1999 discrete biochronological scales and unitary associations description of the biograph computer program memoires de geologie de lausanne 34 282pp and ua graph copyright hammer o guex and savary 2002 softwares provide a discrete biochronological framework based upon multi taxa concurrent range zones in the different sections the optimized dataset generates nine uas using the co occurrences of 56 taxa these uas are grouped into six unitary association zones ua z which constitute a robust biostratigraphic synthesis of all the observed or deduced biostratigraphic relationships between the analysed taxa the ua zonation proposed here is compared to classic calcareous nannofossil biozonations which are commonly used for the southern and the northern sides of tethys the biostratigraphic resolution of the ua zones varies from one nannofossil subzone or part of it to several subzones and can be related to the pattern of calcareous nannoplankton originations and extinctions during the studied time interval the late pliensbachian early toarcian interval corresponding to the ua z ii represents a major step in the jurassic nannoplankton radiation the recognized ua zones are also compared to the carbon isotopic negative excursion and tocmaximum in five sections of central italy germany and england with the aim of providing a more reliable correlation tool for the early toarcian oae and of the associated isotopic anomaly between the southern and northern part of western tethys the results of this work show that the toc maximum and 13c negative excursion correspond to the upper part of the ua z ii i e ua 3 in the sections analysed this suggests that the early toarcian oae was a synchronous event within the western tethys

geochemical and petrographical characterization of fine grained carbonate particles along proximal to distal transects the origin of carbonate ooze particles is often poorly understood this is due to their polygenic origin and potential post depositional alteration here the outcome of a physical separation study with regard to different component classes of micritic carbonates is shown the focus is on grain size and morphology mineralogy and isotope signatures two contrasting proximal to distal transects were investigated 1 the miocene leeward margin of great bahama bank odp leg 166 and 2 the transition between the maiella platform and the umbria marche basin in central italy near the cenomanian turonian boundary in both case settings carbonate particles of biogenic origin include at least three groups of organisms i planktonic foraminifera ii calcareous nannofossils and iii fragments of unspecified neritic skeletal material two further particle types lack diagnostic structures and based on particle size and mineralogy are here referred to as iv macroparticles 5 20 m mainly xenomorphic and v microparticles 12 m mainly automorphic to sub automorphic macro and microparticles represent 50 to 80 of the carbonate phase in slope and toe of slope domains and share characteristic carbon and oxygen isotope signatures macro and microparticles are considered shallow water precipitation products subsequently exported into the slope and toe of slope domains macroparticles are probably related to the fragmentation of neritic skeletal components while microparticles point to inorganic and or bioinduced precipitation in the water column in some cases macro and microparticles may have an early diagenetic origin the identification of the origin of fine grained particles allows for a quantitative assessment of exported in situ and diagenetic carbonate materials in periplatform environments the data shown here represent an important step towards a more complete characterization of carbonate ooze and micrite

toarcian carbon isotope shifts and nutrient changes from the northern margin of gondwana high atlas morocco jurassic palaeoenvironmental implications the early toarcian is marked by a global perturbation of the carbon cycle and major marine biological changes these coincide with a general decrease in calcium carbonate production and an increase in organic carbon burial and culminate in the so called toarcian oceanic anoxic event it is believed that the environmental crisis was triggered by the activity of the karoo ferrar large igneous province in order to further document the early toarcian palaeoenvironmental perturbations carbon isotope total organic matter calcareous nannofossils and phosphorus content of the amellago section in the high atlas rift basin of morocco were investigated this section is extremely expanded compared to the well studied european sections its position along the northern margin of the gondwana continent is of critical importance because it enables an assessment of changes of river nutrient input into the western tethyan realm the carbon isotope curve shows two negative excursions of equal thickness and amplitude at the pliensbachian toarcian boundary and at the transition from the polymorphum to the levisoni zone this confirms the supra regional nature of these shifts and highlights the possible condensation of the first boundary shift in european sections phosphorus content is used to trace palaeo nutrient changes and shows that the two negative carbon isotope shifts are associated with increased nutrient levels confirming that these episodes are related to enhanced continental weathering probably due to elevated greenhouse gases in the atmosphere in the high atlas basin the increase in nutrient levels at the pliensbachian toarcian boundary is moreover likely to be the main factor responsible for the coeval demise of the saharan carbonate platform a middle toarcian event centered on the boundary between the bifrons and gradata zones characterized by a positive carbon isotope excursion and nutrient level rise is documented in the amellago section

nannofacies analysis as a tool to reconstruct paleoenvironmental changes during the early toarcian anoxic event the black shales of lower toarcian schistes carton in france jet rock in england posidonia shale in germany are sediments formed by fine alternations of millimetric to sub millimetric clear and dark laminae a study of polished core surfaces dotternhausen core sw germany was carried out in sem in order to characterize the micro fabrics of different laminae and their content in nannofossils two main intervals were recognized where fabrics and nannofossil content are significantly different in the clay rich interval characterized by high wt toc and a large negative carbon isotope excursion both in carbonates and organic matter the dominant micro fabrics are well foliated or lumpy giving evidence of the absence or reduction of benthic life nannofossils are scarce and only concentrated in discrete laminae separated by large abiotic intervals assemblages are indicative of a deep nutricline but sporadic nutrient inputs occurred as demonstrated by fluctuation in abundance of specimens of the biscutaceae nutrients were probably delivered to the german basin via riverine influx different sized framboids of pyrite were recognized in this interval the smallest ones 2 m being probably precipitated in an anoxic and sulphidic water column the clay rich interval was likely deposited during low sea level in a restricted basin these conditions were followed by a sea level rise and better water mass circulation within the german basin sedimentation records an increase in carbonate deposition organic matter content decreased and carbon isotopes came back to pre excursion values micro fabrics became less markedly laminated pyrite framboids nearly disappeared and rich and diversified nannofossil assemblages are recorded sea water conditions were probably highly fluctuating as indicated by alternation of intervals dominated in turn by schizosphaerella spp flourishing under generally oligotrophic conditions where nutrients were temporarily available in surface waters due to storms and by crepidolithus spp a deep dweller the results of this work fit well with a silled basin model

evidence for a complex valanginian nannoconid decline in the vocontian basin south east france the early cretaceous is punctuated by widespread biocalcification crises these are characterized by decrease in the carbonate platform growth and in the pelagic realm by a decline in nannoconus relative abundance in the calcareous nannofossil assemblages the valanginian nannoconus decline started before the positive 13c excursion characterizing the weissert event the nannoconid decline is investigated in two sections of the vocontian basin la charce and vergol which are biostratigraphically well constrained and contain wellpreserved calcareous nannofossils absolute and relative abundances of nannoconus show a polyphased decline with a first decrease in the interval from the campylotoxus to the verrucosum ammonite subzones before the positive 13c shift and a second decrease from the end of the peregrinus to the base of the radiatus ammonite zones concomitant with the long term decrease in 13c these two declines are separated by an important increase in the nannoconus abundance from the verrucosum to the peregrinus ammonite subzones concomitant with a slight short term decrease of 13c biometric analysis shows size changes of n steinmannii and n kamptneri along the nannoconid decline the patterns of abundances and size changes seem to be related to paleoenvironmental changes mainly characterized by a temperature decrease and variable nutrient supply the described valanginian nannoconid recovery seems to occur during the most intense phase of the cooling event and is recorded in the vocontian basin as well as in the atlantic and tethys oceans these spatial correlations suggest a supra regional character for the valanginian nannoconid recovery event best recorded in the vocontian basin and at low latitudes

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

ammonoid and nannoplankton abundance in valanginian early cretaceous limestone marl successions from the southeast france basin carbonate dilution or productivity a quantification of calcareous nannofossil and ammonoid absolute abundance was carried out in the valanginian limestone marl alternations of the vergol section drome located in the epicontinental vocontian basin southeast france this section is characterised by four centimetric organic carbon rich layers barrande layers b1 b4 the aim of this work is to reconstruct changes in the distribution of nutrients in the water column on the base of the analysis of fossil organisms at different levels of the food chain calcareous nannofossil abundance correlates negatively with carbonate content thus calcareous nannoplankton probably did not produce the bulk of carbonates in the valanginian of the studied section nannofossil abundance was more likely controlled by carbonate mud produced and exported from shallow platform environments to the basin variations of carbonate export controlled by climate and hydrodynamics are responsible for the limestone marl alternations the levels of highest abundance of nannoplankton are interpreted as mainly linked to a reduced accumulation rate and to a minor extent to variations in primary production a dilution by allochthonous carbonate mud is further evidenced by the relationship between total organic carbon toc and calcium carbonate caco3 toc content decreases with increasing caco3 content except for one of the organic carbon rich layers b4 both taphonomy and dilution factors may have partly controlled the variations in macrofauna abundance these can be more likely interpreted as a response to palaeoenvironmental changes of the various taxa with different palaeoecological affinities the high abundance and dominance of bochianitids orthocone ammonoids in the layer b4 can be explained by their opportunistic behaviour and their deep nektonic possibly nektobenthic mode of life their great capacity for vertical mobility may have permitted brief feeding incursions to the bottom waters when the trophic resources were higher in depth than in the surface waters high trophic levels at the sea bottom may have also benefited the bivalves and gastropods which are very abundant in layer b4 the mode of life of different ammonoid families is also discussed

palaeoenvironmental control on sponge microbialite reefs and contemporaneous deep shelf marl limestone deposition late oxfordian southern germany abstract the late oxfordian bimammatum zone deep shelf deposits of southern germany are characterised by abundant reefs that laterally pass into marl limestone alternations the bioconstructions are made from three main components sponges microbialites and allochthonous sediment a detailed morphological analysis of sponge microbialite reefs in the plettenberg section swabian alb southern germany is combined with investigation of calcareous nannofossil assemblages in laterally correspondent marl limestone alternations in order to trace the evolution of palaeoenvironmental conditions during reef development fluctuations of caco3 content in deep shelf deposits provides evidence of a succession of small scale lithological units generally formed by five to six marl limestone couplets within a small scale lithological unit a close link is observed between growth patterns of sponge microbialite reefs and the changes in the nannofossil assemblage composition phases of expansion of the build ups correspond to carbonate deposits characterised by a relative dominance of large oligotrophic nannoplankton species large watznaueria britannica watznaueria manivitiae and schizosphaerella spp marly intervals reveal a high relative abundance of small sized taxa mainly lotharingius hauffii small w britannica and subordinated biscutum dorsetensis and bioconstructions show a net reduction in size or a total demise this suggests that the same palaeoenvironmental parameters controlled at the same time marl versus limestone deposition reef growth phases and calcareous nannofossil assemblage composition successive reef growth phases recognized within a bioherm are correlated to the limestone hemi couplets each reef growth phase is composed of several stacked elementary sequences comprising the following succession i sponge ii microbialites and iii carbonate mud in turn the microbialitic crust is formed of three successive microbial layers 1 a fine crust of dense to clotted micrite 2 a centimetre scale to multicentimetric columnar layer of clotted to peloidal micrite 3 a centimetre scale stromatolitic crust the passage from an initial dense microbial layer with numerous microencrusters to a final stromatolitic crust is interpreted as resulting from an increase of the microbial growth rate mainly driven by changes in the accumulation rate deep shelf deposits resulted from changes in platform carbonate production and export basinwards controlled both by sea level and climate changes climate controlled the intensity of carbonate production in shallow platform environments and export towards the deep shelf as well as the trophic conditions of the deep shelf marine waters low trophic conditions favoured platform carbonate production and export basinwards and a large development of the sponge microbialite reefs in the deep shelf however a high carbonate accumulation rate in the deep shelf was also commonly responsible for the demise of sponge microbialite reefs during unfavourable and higher trophic conditions during marl deposition reduced development and frequent demise of the sponge microbialite reefs is observed

duration of the early bajocian and the associated δ13c positive excursion based on cyclostratigraphy the early bajocian about 172 ma ago was a period of tectonic changes a global carbon isotope positive excursion and biological diversification of marine invertebrates e g ammonites radiolarians and coccolithophores unfortunately both the duration of the early bajocian and the associated palaeoenvironmental changes are still poorly constrained we propose here an estimate of the duration of this sub stage based on a cyclostratigraphic analysis of the carbonate content from the chaudon norante section french subalpine basin france the chaudon norante succession has been correlated with les dourbes section using greyscale variations to detect possible local hiatuses the duration estimated here for the entire early bajocian is 4 082 ma two intervals were identified in the positive 13 c excursion an increase of carbon isotope values lasting 1 36 ma and climax isotope values lasting for 2 72 ma a cooling at high latitudes and warming at low latitudes may have enhanced the earth s temperature gradient leading to an increase in humidity which in turn triggered ocean eutrophication at the origin of the 13 c positive excursion supplementary material the complete dataset presented in the paper a colour version of the figure 8 and correlation of 13 c excursions between our studied site and contemporaneous sites are available at www geolsoc org uk sup18555

depositional sequences in deep shelf environments a response to sea level changes and shallow platform carbonate productivity oxfordian germany and spain abstract oxfordian deep shelf deposits of southern germany and southern spain are characterized by marl limestone alternations that are stacked into small scale medium scale and large scale depositional sequences the german sections contain autochthonous sponge reefs and associated fragments of microbialites whereas the sections studied in spain display tempestites composed of autochthonous deeper water and allochthonous shallow water particles the facies of the german limestones and marl layers has been analyzed in detail condensed intervals implied by glauconitization of particles abundant cephalopods intense bioturbation and generally more marls are also enriched in sponge reefs and associated particles and in nannofossils limestone rich intervals however contain fewer sponges and fewer nannofossils neither bioerosion of sponge reefs nor nannofossil blooms can thus explain the abundance of carbonate mud that forms the limestones consequently it is suggested that most of the carbonate mud is exported from shallow platform areas where carbonate productivity is high the clay fraction was derived from weathering of massifs in the hinterland the observed depositional sequences can be correlated between the studied sections in germany and spain situated in different paleotectonic and paleoclimatic domains and also between deeper water sections and platform sections this suggests that they formed through allocyclical processes comparision with published time scales implies that the small scale and medium scale sequences formed in tune with the 100 kyr and 400 kyr orbital eccentricity cycles respectively however the number of marl limestone alternations is not always consistent with the expected number of 20 kyr precessional cycles 5 per 100 kyr cycle the large scale sequences reflect long term third order sea level changes the observed marl limestone alternations are interpreted to have formed through cyclically varying export of carbonate mud from the platform towards the deep shelf the variations being controlled by climatically induced high frequency sea level fluctuations enhanced marl deposition on the deep shelf can be related to sea level fall causing exposure of the shallow platform and reducing the area of carbonate production or by rapid sea level rise maximum flooding leading to partial or total drowning of the platform and or to retrogradation of facies belts enhanced carbonate deposition occurs during transgression when large production areas are created on the platform or during late highstands when progradation is forced and carbonate mud export enhanced depending on the long term trend of sea level change on which the high frequency fluctuations are superimposed one high frequency 20 kyr sea level cycle can thus create one or two marl limestone alternations or only marly deposits consequently one 100 kyr eccentricity cycle may be formed of a variable number of marl limestone alternations commonly 2 to 8 the studied deeper water depositional sequences thus are strongly linked to the history of the adjacent shallow carbonate platforms

the early toarcian oceanic anoxic event in the external subbetic southiberian palaeomargin westernmost tethys geochemistry nannofossils and ichnology abstract the analysis of macroinvertebrates trace fossils calcareous nannofossils and geochemistry from pliensbachian to lower toarcian deposits of the subbetic southern spain allows us to interpret the incidence of the toarcian oceanic anoxic event t oae in the boundary between the tethys and the hispanic corridor trace fossils from the marl limestone rhythmite upper pliensbachian to lower toarcian indicate an oxygenated bottom a dark marly interval occurs above a fossil rich condensed surface with a negative excursion of 18o interpreted as evidence of the early toarcian transgression and a climate warming the carbon cycle perturbation is recorded by decreasing caco3 content and the negative excursion of 13c at the base of the serpentinum zone njt 6 nannofossil zone the barren interval for nektonic and benthic organisms at the beginning of the serpentinum zone confirms the oxygen restricted conditions in the sea floor environmental conditions were unfavourable for the development of calcareous nannoplankton as attested by the drop in absolute abundances the deep photic zone seemed to be particularly hostile to phytoplankton as shown by the decrease in relative abundance of the deep dweller mitrolithus jansae related to shoaling of the oxygen minimum zone in the water column increasing values of redox sensitive elements and total organic carbon as well as the record of pyrite framboids

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

response of calcareous nannofossils to the paleocene eocene thermal maximum observations on composition preservation and calcification in sediments from odp site 1263 walvis ridge sw atlantic abstract in this study we present the results of a detailed analysis on calcareous nannofossil assemblages from sediment cores of odp site 1263 southern east atlantic walvis ridge this section represents one of the few complete deep sea sections that document the paleocene eocene thermal maximum petm in the pelagic realm the petm transient event was characterized by a brief but intense interval of global warming a global negative carbon isotope excursion cie and widespread dissolution of seafloor carbonate sediments paired analysis at polarizing light microscope lm and scanning electron microscope sem documents the different behavior of nannofossils through the different phases of the petm at the onset of cie within the cie and during the recovery interval the presence of anomalous specimens and morphotypes within some nannofossil taxa recorded during previous lm high resolution analyses has been further investigated in selected samples at the sem besides the known representatives of the cie petm excursion nanno flora as rhomboaster calcitrapa group and discoaster anartios the analysis revealed the presence of peculiar morphotypes of fasciculithus and deformed specimens of discoaster nobilis group discoaster mediosus and discoaster multiradiatus that are considered related to the anomalous amount of co2 in the ocean atmosphere system during the early phase of petm comparative analyses were performed in few selected samples from other petm sections located at different latitudes in the atlantic and pacific oceans although the anomalous geochemical conditions during the petm cie interval seem to have had some influence on the nannofossil production calcification and assemblage composition it results that local productivity together with post depositional diagenetic conditions were additional important controlling factors on nannofossil assemblages preliminary data from eocene thermal maximum 2 etm2 or elmo suggest that nannofossil malformations are not exclusive of the petm and are associated to other episodes of perturbation of the c cycle

pattern and timing of the early jurassic calcareous nannofossil crisis abstract article history received 27 april 2014received in revised form 12 june 2014accepted 23 june 2014available online 30 june 2014keywords early toarciancalcareous nannofossilsbiocalci cation crisiscarbonate production thetoarciancalcareousnannofossilcrisisassociatedwiththeearlytoarcianoceanicanoxicevent t oae intheearlyjurassicperiodisthoughttorepresentoneofthemostimportantbiocalci cationcrisesduringthemesozo ic occurringsimultaneouslywithaprofounddisturbanceofthecarboncycle however thecausesarestillunderdebate particularly with regard to the pattern timing of the biocalci cation crisis relative roles of intrinsic andextrinsic processes as drivers of the crisis and also causal mechanisms of the t oae in this study a new quanti cation of toarcian calcareous nannofossil abundance and size is presented for thesancerre borehole paris basin france beyond the recognition of a severe biocalci cation crisis de ned bythe major drop in abundance and the reduction in size of the most important pelagic carbonate producerschizosphaerella punctulata for the rst time this study proposes an insight into the pace and timing of thenannoplanktoncrisis atsancerre thecarbonateproductionofthelowertoarciansedimentspreviouslyattribut ed to obliquity forcing of climate allows to estimate a duration of 210 kyr for the biocalci cation crisis andof 120 kyr for the shift towards lower carbon isotope values the onset of the biocalci cation crisis marked bya fertility event lasted 60kyr andthe calciumcarbonate valuesremainedlow for 150 kyr thesubsequent re covery of carbonate and nannoplankton lasted 60 kyr and n550 kyr respectively additionally a link betweenthe biocalci cation crisis the seawater palaeotemperature and the carbon isotope steps can be demonstrated this covariance provides compelling evidence of fundamental change in the response of the climatic warmingand the carbon cycle systems triggering the biocalci cation crisis these observations indicate that thebiocalci cation crisis can be regarded as a direct or indirect consequence of a global warming moreover a de ciency of the biological pump is proposed here as a complementary casual mechanism for explaining thenegative carbon isotope excursion 2014 elsevier b v all rights reserved contents1 introduction 572 thesancerreborehole geologicalsettingandpalaeogeographyoftheparisbasin 573 materialandmethods 583 1 quanti cationofnannofossilabundanceandvolume 583 2 analyticalanalysis 584 results 594 1 calcareousnannofossilpreservation 594 2 stratigraphicdistributionofthecalcareousnannoplankton 594 3 clusterandprincipalcomponentanalyses 594 4 evolution of schizosphaerella size 605 discussion 605 1 thecalcareousnannoplanktonresponsetothet oaeenvironmentalchanges 605 1 1 patternsinnannofossilassemblageswithinpre eventstableenvironmentalconditions 605 1 2 thet oaeperturbationasrecordedbynannofossilassemblages 605 1 3 theenvironmentalrecoveryasrecordedbynannofossilassemblages 605 2 expressionandevolutionofthebiogeniccarbonateproduction 615 3 atimescaleforthenannoplanktoncrisisacrossthet oae 61

a mesozoic time scale we present an integrated geomagnetic polarity and stratigraphic time scale for the triassic jurassic and cretaceous periods of the mesozoic era with age estimates and uncertainty limits for stage boundaries the time scale uses a suite of 324 radiomenc dates including high resolution 40 ar 39 ar age estimates this framework involves the observed ties between 1 radiometric dates biozones and stage boundaries and 2 between biozones and magnetic reversals on the seafloor and in sediments interpolation techniques include maximum likelihood estimation smoothing cubic spline fitting and magnetochronology

secular environmental precursors to early toarcian jurassic extreme climate changes the early toarcian oceanic anoxic event t oae about 183 myr ago was a global event of environmental and carbon cycle perturbations which deeply affected both marine biota and carbonate production nevertheless the long term environmental conditions prevailing prior to the main phase of marine extinction and carbonate production crisis remain poorly understood here we present a similar to 8 myr long record of early pliensbachian middle toarcian environmental changes from the lusitanian basin portugal in order to address the long term paleoclimatic evolution that ultimately led to carbonate production and biotic crises during the t oae paleotemperature estimates derived from the oxygen isotope compositions of well reserved brachiopod shells from two different sections reveal a pronounced similar to 5 degrees c cooling in the late pliensbachian margaritatus spinatum ammonite zones boundary this cooling event is followed by a marked similar to 7 10 degrees c seawater warming in the early toarcian that after a second cooling event in the mid polymorphum zone culminates during the t oae calcium carbonate caco3 contents the amount of nannofossil calcite and the mean size of the major pelagic carbonate producer schizosphaerella all largely covary with paleotemperatures indicating a coupling between climatic conditions and both pelagic and neritic caco3 production furthermore the cooling and warming episodes coincided with major marine regressions and transgressions respectively suggesting that the growth and decay of ice caps may have exerted a strong control on sea level fluctuations throughout the studied time interval this revised chronology of environmental changes shows important similarities with neogene and paleozoic episodes of deglacial black shale formation and thus prompts the reevaluation of ice sheet dynamics as a possible agent of mesozoic events of extinction and organic rich sedimentation c 2010 elsevier b v all rights reserved

discorhabdus as a key coccolith genus for paleoenvironmental reconstructions middle jurassic lusitanian basin biometry and taxonomic status abstract biometric analyses of discorhabdus coccoliths were performed on a set of 29 samples taken from the marl limestone couplets of the reference section of cabo mondego lusitanian basin west portugal late aalenian to early bajocian in age mixture analysis performed on the whole dataset revealed a bimodal length size distribution for the discorhabus pool composed of d striatus and d ignotus the size limit at 5 m proposed here can be reliably used to distinguish both populations but optical characteristics namely birefringence form an additional criterion essential to discriminate the two species an increase in discorhabdus size occurred from the late aalenian to the early bajocian due to a raise in size of the whole discorhabdus pool and in the abundance of d striatus we propose that an increase in discorhabdus size upward in the section is associated with a positive trend in paleoproductivity as supported by the increase of nannofossil accumulation rates as well as the 13 c values of bulk carbonates sampled in the cabo mondego section however the discorhabdus size pattern may also represent a response to sea surface temperature salinity or an evolutionary trend a relative supra regional warming of sea surface water masses is suggested by 18 o values of biogenic carbonates and apatites that were sampled in several mediterranean tethyan settings rise of sea surface temperature may have triggered an increase in the abundances of d striatus as well as of the size of the discorhabdus pool a hypothetical influence of changing sea surface salinity on discorhabdus size or species specific discorhabdus abundances is not supported by our micropaleontological data or by available geochemical data our results also reveal that the increase in discorhabdus size matches the history of calcareous nannofossil turnover radiation diversity and increasing abundances during the middle jurassic

a paleoceanographic model for the late campanian early maastrichtian sedimentation in the polish carpathian flysch basin based on nannofossils abstract the study is a qualitative and semi quantitative analysis of calcareous nannofossils in marlstone and calcareous mudstone beds in a 4 6 m thick section of the kropivnik fucoid marls late campanian early maastrichtian in the skole nappe of the polish outer carpathians this turbiditic succession is conspicuous by its short term alternation of marlstone rich and siliciclastic rich packages ca 1 m thick a model for paleoceanographic control on sedimentation is proposed on the basis of nannofossil assemblages in the studied section the nannofossils form assemblages of mixed synsedimentary taxa derived from diverse marine environments differing in trophy water temperature and distance from land the mixing occurred due to submarine resedimentation processes the nannofossils indicate that the siliciclastic rich packages were deposited during periods of lowered water temperature decreased calcareous nannoplankton production and oligotrophic to mesotrophic water conditions which corresponded to the sea level fall and lowstand anti estuarine circulation and downwelling due to arising shelf break front are inferred as the factors responsible for oligotrophy in contrast in the marlstone rich packages the calcareous nannofossils indicate sedimentation during periods of significantly increased calcareous nannoplankton production which corresponded to the sea level rise and highstand the increased nannoplankton production is attributed to estuarine circulation and upwelling the changes in sea level and water circulation conform to the climate changes postulated independently for the late campanian early maastrichtian

multiproxy approach for determination of nature and origin of carbonate micro particles so called micarb in pelagic sediments abstract carbonate fractions of pelagic and hemipelagic sediments may contain significant proportions of microcrystalline 6 m calcitic particles with no specific structure so called micarb depending on the authors this term is related to different descriptions and yet there is no clear consensus on their origin although micarb can dominate the sediment compositions in the pelagic realm their isolation from the other carbonate particles is not easy due to their small size the use of a granulometric separation method of the main carbonate particles allows the characterization and quantification of the compositions of the carbonate phases of the sediments and gives access to the geochemical signatures oxygen and carbon stable isotopes and mineralogical characteristics of each type of carbonate particles in the sediments this approach was applied to three sections the mid pliocene punta piccola section south sicily the upper campanian bidart section sw france and the aptian sediments from la marcouline quarry se france the quantifications showed quite important proportions up to 70 of the carbonated phases of micarb in the sections studied excepted in the mid pliocene punta piccola samples however depending on the sedimentary context it appears that those fine calcitic particles may result from fine biogenic fragmentation aptian la marcouline quarry authigenic precipitation in the water column mid pliocene punta piccola section or they may have an allochthonous origin upper campanian bidart section based on these interpretations it is then possible to estimate precisely the composition of the carbonate fractions in each studied section this work shows that except for the bidart sediments which are dominated by fine exported carbonate mud the other sections mainly consist in biogenic carbonates

whiting related sediment export along the middle miocene carbonate ramp of great bahama bank modern aragonite needles are present all along the modern leeward margin of great bahama bank odp leg 166 while middle miocene sediments contain needles only in more distal areas sites 1006 and 1007 in contrast to the rimmed flat topped platform topography during the plio pleistocene the miocene great bahama bank morphology is a carbonate ramp profile this might imply a different location and precipitation type for miocene aragonite needles in this study aragonite needles in miocene sediments were isolated using a granulometric separation method furthermore the isolation of the various carbonate components enables the identification of primary versus diagenetic components the miocene aragonite needles are concentrated in the finest granulometric sediment fractions 12 m the fraction specific geochemical analyses 13c 18o and sr elemental abundance represent useful tools to assess the possible sources of the aragonite mud the geochemical variation of the fractions rich in pristine aragonite needles and the characteristics of the needle morphology point to whiting phenomena as the main sediment source and algal fragmentation as a minor component both components indicate shallow water environments as the main sediment source area ramp top related fine grained particles now present at distal sites were likely exported as suspended material similar to present day transport mechanisms the scarcity of needles at proximal sites is probably linked to hydrodynamic processes but dissolution and recrystallization processes cannot be excluded the granulometric separation approach applied here enables a better characterization of the finest carbonate particles representing an important step towards the discrimination between primary and diagenetic fine grained components

coccolith δ18o and alkenone records in middle pliocene orbitally controlled deposits high frequency temperature and salinity variations of sea surface water 1 the calcareous nannoplankton flora is strongly controlled by water masses and is sensitive to ambient nutrient levels in consequence fossil remains of calcareous nannoplankton are useful tools for paleoceanography although they are the major producers of carbonates in the pelagic realm their use as a seawater 18o recorder is not easy due to their small size and the difficulty in isolating them from the bulk carbonate using a granulometric separation technique minoletti et al 2001 it is now possible to concentrate coccoliths in monospecific fractions we applied this method on three precession cycles insolation cycles i 288 to i 282 from the mid pliocene punta piccola section south sicily which led to an almost pure pseudoemiliana lacunosa fraction it was then possible to measure the isotopic signatures 18o and 13c and alkenone unsaturation ratio on the same recorder p lacunosa this permits a precise reconstruction of environmental conditions temperature and salinity that prevailed in the upper photic zone during the cyclic deposition of these sediments our data provide a clear confirmation that sapropelic marl formation occurred during a wetter climate compared to the deposition of the marly limestones moreover these results point out that salinity variations are not as previously thought always the primary factor that controlled the deposition of these cyclic events this study is a step forward in the utilization of calcareous nannoplankton isotopic records in paleoenvironmental reconstructions

book reviewdiagenesis in sediments and sedimentary rocks 2 developments in sedimentology 25b g larsen and g v chilingar editors elsevier amsterdam 1983 vii 572 pp us 117 00 dfl 275

size variations of the calcareous nannofossil taxon discoaster multiradiatus incertae sedis across the paleocene eocene thermal maximum in ocean drilling program holes 690b and 1209b abstract size measurements of the calcareous nannofossil taxon discoaster multiradiatus were carried out across the paleocene eocene thermal maximum petm in ocean drilling program holes 690b maud rise weddell sea and 1209b shatsky rise pacific ocean morphometric investigations show that d multiradiatus specimens are generally larger at odp site 1209 than at odp site 690 a limited increase in size of d multiradiatus is recorded at odp site 1209 whereas significant enlargements characterize odp site 690 preservation is comparable at both sites nannofossils are moderately preserved with some evidence of etching overgrowth in the petm interval yet d multiradiatus variations do not correlate with preservation state and morphometric data most likely represent primary signals rather than diagenetic artifacts there is a direct relationship between d multiradiatus size and paleotemperatures largest specimens are coeval with global warming associated with the petm inferred to result from excess atmospheric co2 due to partial oxidation of massive quantities of methane size increases and largest specimens of d multiradiatus occur at different stratigraphic levels within petm at odp sites 690 and 1209 a marked shift in diameter size was observed at the onset and peak of the carbon isotopic excursion cie at odp site 690 but only at the end of cie and initial recovery interval at odp site 1209 this diachroneity is puzzling but indeed correlates well with reconstructed changes in surface and thermocline water masses temperature and salinity in the petm interval at low and high latitudes the presumed high concentrations of carbon dioxide seem to have not influenced the morphometry of d multiradiatus the major size increase of d multiradiatus in the cie of odp site 690 could represent the migration of larger sized allochtonus specimens that moved from peri equatorial subtropical areas to higher latitudes during the warmest interval of the petm although no direct evidence of distinct populations subpopulations has been obtained from the frequency diagrams as a result we infer that d multiradiatus is a proxy of water masses stratification and might be used for deriving temperature salinity nutrient conditions in the mixed layer and thermocline and their dynamics

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

evidence for major environmental perturbation prior to and during the toarcian early jurassic oceanic anoxic event from the lusitanian basin portugal the timing and causal relationships between the pronounced negative c isotope excursion and paleoenvironmental perturbations associated with the toarcian oceanic anoxic event early jurassic remain unclear particularly because biotic crises and carbonate production decrease appear to have been initiated earlier than the main c isotope anomaly here we present a new quantification of late pliensbachian early toarcian calcareous nannofossils abundance and size from the peniche reference section portugal together with o and c isotope records of well preserved brachiopod shells from the same section the brachiopod shell 13c curve parallels that of bulk carbonate and records two pronounced negative isotopic excursions close to the pliensbachian toarcian boundary 2 and during the toarcian oceanic anoxic event 3 5 our results indicate that both c isotope negative excursions were characteristic of benthic and shallow water environments suggesting that these two carbon cycle perturbations affected all epioceanic reservoirs coeval shifts toward lower values of brachiopod oxygen isotope compositions and closely correlated northward migrations of mediterranean ammonite fauna suggest that both events coincided with major rises in seawater temperatures probably as a result of increased co2 levels and enhanced greenhouse conditions co2 induced changes in seawater chemistry likely affected the calcification potential of both neritic and pelagic systems as evidenced by synchronous drops of platform derived carbonate accumulation and drastic reductions in size 3 m of the main pelagic carbonate producer schizosphaerella we suggest that the early toarcian paleoenvironmental crisis occurred in two distinct episodes that were most likely related to two successive phases of intense volcanic degassing in the karoo ferrar province

early jurassic schizosphaerellid crisis in cantabria spain implications for calcification rates and phytoplankton evolution across the toarcian oceanic anoxic event 1 the toarcian oceanic anoxic event 183 myr ago represents a global perturbation marked by increasing organic carbon burial and a general decrease in calcium carbonate production likely triggered by elevated carbon dioxide levels in the atmosphere here we present quantitative analyses of calcareous nannofossil diversity and abundance from the castillo de pedroso section in cantabria northern spain we compare these data with geochemical data c and o isotopes obtained from biogenic and bulk carbonate records in order to highlight the response of calcareous phytoplankton to major climatic and paleoceanographic changes the pliensbachian toarcian boundary is characterized by an abrupt decrease in abundance of schizosphaerella punctulata the most important lithogenic contributor to hemi pelagic carbonates in the early jurassic the early toarcian nannofloral assemblages show an increase in abundance of mitrolithus jansae and small sized r selected taxa and a progressive decrease in s punctulata percentages the deep dwellers m jansae and s punctulata experienced a major crisis slightly prior to the deposition of the toarcian black shales that are characterized by high abundances of eutrophic taxa such as lotharingius spp and biscutum spp the return of s punctulata associated with lower percentages of eutrophic taxa was observed just above the toarcian black shales the toarcian episode reveals that high co2 levels and increasing primary productivity probably triggered a shift in abundance from highly calcified nannoliths such as s punctulata and m jansae to small sized r selected coccoliths that overall record a biocalcification crisis at the onset and during the toarcian episode

calcareous nannofossil changes during the late callovian early oxfordian cooling phase calcareous nannofossil quantitative and biostratigraphic analyses integrated with carbon and oxygen stable isotopes were carried out on the core andra agence nationale pour la gestion des dechets radio actifs france htm 102 across the callovian oxfordian boundary drilled at cirfontaines en ornois department de haute marne eastern france calcareous nannofossil assemblages at the callovian oxfordian transition are dominated by the genus watznaueria an increase in abundance of biscutum spp and a group which consists of axopodorhabdus spp a atavus a rahla and a cylindratus podorhabdus grassei octopodorhabdus decussatus hexapodorhabdus cuvillieri family axopodorhabdaceae and triscutum spp correlates with a significantpositiveexcursionin 18 osuggestingthatthesegroupswereprobablyadaptedtocoolersurfacewaters apositiveincrease in 13 c values is coupled with high abundances of eutrophic taxa such as zeughrabdotus erectus biscutum spp and small sized watznaueria britannica and a decrease in abundance of the big and oligotrophic taxa schizosphaerella punctulata and watznaueria manivitae climate cooling across the callovian oxfordian boundary probably triggered a breakdown in stratification of surface waters leading to more intense nutrient recycling and higher primary productivity that favoured the shift in abundance of small sized eutrophic taxa in the east paris basin

middle jurassic coccolith fluxes a novel approach by automated quantification coccolithophores major pelagic carbonate producers underwent important changes during the latest aalenian early bajocian ca 170 ma middle jurassic specifically a new genus called watznaueria diversified and started dominating the coccolith assemblages while this change in the coccolith assemblages is already known the impact on coccolith absolute abundances and fluxes is still misunderstood here we tested for the first time on mesozoic deposits an automated counting method using the syraco system and then compared these results with a classic counting method two neural networks were created based on the shape birefringence and size of coccoliths the first of which contained only one class and the second of which was composed of six classes based on the morphological criteria used for the neural networks coccoliths were not identified at the species level we quantified coccolith absolute abundances and estimated fluxes for the latest aalenian early bajocian in two well dated and correlated sections cabo mondego in portugal and chaudon norante in france there is a strong linear correlation between classic and automatic counting r 0 8 supporting the latter as a reliable method for coccolith absolute abundance and flux quantification in spite of under or over estimation by automatic counting with respect to classic counting the absolute abundance stratigraphic trends are remarkably similar under or over estimation may be reduced by further technical improvements such as automatic focus at cabo mondego coccolith fluxes increased from 0 2 109 coccoliths m2 yr in the latest aalenian to 700 109 coccoliths m2 yr in the middle of the laeviuscula ammonite zone early bajocian remaining high for the rest of the early bajocian at chaudon norante a similar trend was observed this coccolith flux increase is therefore considered to be a supra regional event matching an important 13cbulk carbonate positive excursion the carbon isotopic positive excursion along with the onset of radiolarian sedimentation and coccolith fluxes is related to a gradual increase in the fertility of the oceans during the early bajocian and is likely associated with warmer and more humid climates and associated enhanced continental weathering

the southern oscillation part iii associations with the trades and with the trough in the westerlies of the south pacific ocean abstract differences of sea level pressure between pairs of stations in the south pacific ocean are used to examine the trades and the trough in the westerlies during the development of the phase of the southern oscillation when pressures fall over the tropical pacific equatorial waters warm and rainfall increases in many otherwise dry places it is demonstrated that this phase is characterized by an appreciable enhancement of the annual cycle of the trades and the trough compared to the year before the warm event of 1982 followed this pattern closely

reply to the comment on orbitally forced climate and sea level changes in the paleoceanic tethyan domain marl limestone alternations lower kimmeridgian se france by s boulila m de rafelis l a hinnov s gardin b galbrun p y collin palaeogeography palaeoclimatology palaeoecology 292 2010 57 70 abstract a recent paper by boulila et al 2010 reports on orbitally forced cycles recorded as marl limestone alternations in one lower kimmeridgian section chateauneuf d oze se france tethyan domain in an attempt to illustrate the in situ i e pelagic origin of carbonates in marls and limestones the authors challenged the results of previous work concerning sections from other tethyan areas of similar age which demonstrate that nannofossil abundance is originally higher in marls than in limestones boulila et al 2010 present data acquired with optical and scanning electron microscopes estimating nannofossil contribution to the rocks however their selected illustrations do not support a high contribution of the nannofossils to the carbonate fraction of their samples or their interpretation of the finest fraction of the rocks micarbs furthermore according to their data on carbonate content of the rocks they did not analyse true marl limestone alternations but slightly argillaceous limestones and limestones boulila et al 2010 also criticize earlier work providing a sequence stratigraphy interpretation of the chateauneuf d oze section however contrarily to these earlier works they did not consider platform to basin correlations that are essential in order to understand the sedimentary dynamics at the basin wide scale this comment challenges the work by boulila et al 2010 that largely underestimates the role of carbonate production on shallow platforms and its subsequent export basinwards as a major mechanism controlling the sedimentation in epicontinental basins

abundance and size changes in the calcareous nannofossil schizosphaerella relation to sea level the carbonate factory and palaeoenvironmental change from the sinemurian to earliest toarcian of the paris basin abstract abundance and size changes in the calcareous nannofossil schizosphaerella are investigated throughout the upper sinemurian to lowermost toarcian of the sancerre couy core paris basin measurements from 116 samples are compared to 487 and 411 measurements of caco3 content and total organic carbon toc content respectively our results confirm that schizosphaerella was better adapted to proximal areas than coccoliths as expressed by the stepwise rise in abundance of schizosphaerella followed later on by the rise in abundance of coccoliths during the major transgression of the sinemurian the new results show that changes in the size of schizosphaerella were mostly a response to early jurassic temperature variations coldhouse greenhouse changes large average sizes of schizosphaerella correspond mostly to proximal cool environmental conditions of the late sinemurian medium average sizes correspond to more distal conditions and cool surface waters whereas small average sizes are associated with warm episodes these results suggest that the size response of schizosphaerella to the early toarcian oceanic anoxic event and to preceding environmental perturbations of the early jurassic was probably not a physiological response to lower calcification but rather represent changes in abundances of different ecophenotypes or sub species related to climate change the contribution of schizosphaerella carbonate caco3schizo to the total carbonate bulk caco3 in the paris basin was minor

proterozoic magnetic overprinting of archaean rocks in the canadian superior province we have measured the various components of natural remanent magnetization nrm exhibited by mafic extrusive and intrusive rocks from the abitibi subprovince of the canadian precambrian shield in addition to providing what seems to be a primary archaean pole for the region the results testify to three episodes of magnetic overprinting at approximately 2 600 2 100 and 1 800 myr respectively the two earlier episodes coincide with the intrusion of matachewan and abitibi diabase dyke swarms here and elsewhere in the superior province magnetic overprinting in these cases extends far beyond areas of surficial dyke exposure the third episode postdates magmatic activity in the abitibi region but coincides in age with the 1 900 1 700 myr hudsonian orogeny in the churchill and bear provinces and the penokean orogeny in the southern province although magnetic overprints presumed to be of this age were known previously from abitibi dykes1 and nipissing sills2 4 our data are the first evidence of a 1 800 myr magnetic overprinting on a regional scale in the superior province

a calcareous nannofossil and organic geochemical study of marine palaeoenvironmental changes across the sinemurian pliensbachian early jurassic 191 ma in portugal the sinemurian pliensbachian boundary 191 ma is acknowledged as one of the most important steps in the radiation of planktonic organisms especially primary producers such as dinoflagellates and coccolithophores to date there is no detailed study documenting changes in planktonic assemblages related to palaeoceanographic changes across this boundary the aim of this study is to characterize the palaeoenvironmental changes occurring across the sinemurian pliensbachian boundary at the sao pedro de moel section lusitanian basin portugal using micropalaeontology and organic geochemistry approaches combined calcareous nannofossil assemblage and lipid biomarker data document for a decrease in primary productivity in relation to a major sea level rise occurring above the boundary the lusitanian basin was particularly restricted during the late sinemurian with a relatively low sea level a configuration that led to the recurrent development of black shales after a sharp sea level fall the basin became progressively deeper and more open during the earliest pliensbachian subsequently to a major transgression this sea level increase seems to have been a global feature and could have been related to the opening of the hispanic corridor that connected the tethys and palaeo pacific oceans the palaeoceanographic and palaeoclimatic changes induced by this opening may have played a role in the diversification of coccolithophores with the first occurrence or colonization of tethyan waters by placolith type coccoliths

phytoplankton evidence for the timing and correlation of palaeoceanographical changes during the early toarcian oceanic anoxic event early jurassic the causes and duration of the early toarcian anoxic event are controversial integration of data from calcareous and organic phytoplankton provides a biochronological framework that allows precise correlations across the western tethys in particular the carinolithus superbus nannofossil zone can be used to correlate the levels enriched in organic matter and the related 13 c negative excursion although a variable duration is given in the literature for this negative excursion it is likely that it lasted between 520 and 650 ka increased atmospheric p co 2 related to excess volcanic emissions magmatic activity in the karoo and ferrar provinces had an impact on climate and ocean chemistry and marked the inception of a biotic crisis affecting many organisms the beginning of the crisis within shallow carbonate platforms documented at southern latitudes predates the levels enriched in organic matter dinoflagellate cysts experienced a decrease in abundance in the c superbus zone until they temporarily disappeared the nannoplankton crisis was twofold a decrease in size and low calcified specimens are observed in addition to a drastic decrease in absolute abundance the increased atmospheric p co 2 as a result of the magmatic activity and temporarily amplified by transient methane release could have been the trigger for the biocalcification crisis which first affected the probably more reactive neritic system and eventually the nannoplankton community

calcium isotope evidence for dramatic increase of continental weathering during the toarcian oceanic anoxic event early jurassic abstract the early toarcian was punctuated by pulses of massive carbon injection that are thought to have triggered through increased greenhouse conditions elevated continental discharge and nutrient input marine anoxia seawater acidification and species extinctions nevertheless the mode and tempo of changes in continental weathering across this interval remains highly debated leading to considerable uncertainty about the main causes of these perturbations in this study we present calcium isotope measurements 44 40ca of well preserved brachiopods and bulk rock samples from the hemipelagic strata of pliensbachian toarcian age of peniche in portugal in order to constrain changes in the calcium cycle and hence changes in continental weathering during the early toarcian the data reveal a similar trend as carbon isotope data from the same section and show negative excursions of about 0 5 at the pliensbachian toarcian transition pl to and at the base of the toarcian oceanic anoxic event t oae interval the comparison of 44 40ca ratios recorded in brachiopods and bulk rock corrected for variable dolomite contribution indicates that these excursions reflect changes in the global isotopic composition of seawater rather than changes in the dominant mineralogy of calcifying organisms or in hydrological budget of the considered basin box modeling results suggest that the pl to and t oae 44 40ca excursions can be explained by a transient 90 decrease of carbonate accumulation due to seawater acidification followed by a 500 increase in continental weathering rates the sharp increases in continental weathering inferred from the 44 40ca ratios seem overall consistent with lower toarcian sedimentological and biotic records that document rapid crises in carbonate production followed by episodes of increased calcium carbonate burial nevertheless the maximum of carbonate burial recorded by most nw european basinal successions occurs several hundreds of kyrs after that predicted by box modeling results this mismatch either implies that the european records of carbonate accumulation do not reflect global trends or that the fundamental processes related to the removal of excess alkalinity caused by increased continental weathering are more complex than previously appreciated based on the amount of ca input simulated by box modeling the injection of tens of thousands of gigatons of carbon with an isotopic composition 13c comprised between 6 and 14 appears as the most likely causes of the 13c excursions characterizing these two events these results indicate that environmental and biotic changes of the pl to and t oae were mainly caused a cascade of environmental changes triggered by the massive carbon emissions from the karoo ferrar volcanism

the impact of calcareous nannofossils on the pelagic carbonate accumulation across the jurassic cretaceous boundary abstract calcareous nannofossils were important producers of pelagic carbonates in mesozoic oceans in order to better understand the origin of mesozoic pelagic carbonates we studied upper jurassic to lower cretaceous sediments in the central atlantic ocean dsdp sites 105 367 534a with respect to their content of calcareous nannofossils the interval under investigation is characterized by a significant increase in the deposition of carbonate rich sediments a trend that goes along with the rapid radiation of calcareous nannofossils the assemblage composition and the size variation of common taxa were analyzed and subsequently the contribution of this phytoplankton group to the pelagic carbonate accumulation was calculated results reveal two long term changes of the nannofossil assemblage composition 1 the early tithonian coccolith assemblages are of low diversity watznaueria spp cyclagelosphaera spp zeugrhabdotus spp whilst the mid to late tithonian assemblage is dominated by nannoliths conusphaera mexicana polycostella beckmannii nannoconus spp and large sized watznaueria 2 the early berriasian is characterized by a shift from the late tithonian nannolith rich assemblage to a highly diverse coccolith assemblage morphometric studies of the placolith genus watznaueria show for all three dsdp sites large sized forms of this genus in the mid and late tithonian followed by a decrease of up to 2 m for the mean size in the earliest berriasian at dsdp site 105 the studied nannolith taxa show an increase in size during the mid tithonian to berriasian interval the records of both nannofossil carbonate estimates and the measured bulk rock carbonate reveal two periods of increase in the nannofossil carbonate record of dsdp site 105 a first significant increase of the carbonate accumulation is observed in the mid and late tithonian probably caused by mass occurrences of strongly calcified taxa c mexicana p beckmannii nannoconus spp watznaueria cf manivitae this interval is here named nannofossil calcification event nce the second carbonate maximum in the late berriasian is related to a rise in absolute abundances of nannofossils this peak is amplified by an overall increase of the sedimentation rate the calculated accumulation rates of nannofossils nannofossil carbonate and bulk rock carbonate for the late berriasian are on the same scale as values from recent ocean surface sediments a comparison of nannofossil carbonate values with the bulk rock carbonate content shows that on average only 27 of the total carbonate can be explained by our nannofossil carbonate estimates this discrepancy is most likely caused by the high amount of unidentifiable micrite and fragments of calcareous nannofossils other factors contributing to the error are possible inaccuracies in the determination of absolute abundances and nannofossil volume calculations the nce occurs during a long term sea level fall dry climate and presumed low pco 2 levels a decline in abundance of strongly calcified nannofossils coincides with the opening of the pacific atlantic seaway via central america which may have had a substantial impact on the palaeoceanographic situation in the central atlantic ocean these changes are here considered to have at least partly caused the shifts in abundance size and assemblage composition of calcareous nannofossils observed across the jurassic cretaceous boundary interval

new insights in the pattern and timing of the early jurassic calcareous nannofossil crisis abstract the toarcian calcareous nannofossils crisis associated with the early toarcian oceanic anoxic event t oae in the early jurassic period is thought to represent one of the most important biocalcification crises during the mesozoic occurring simultaneously with profound disturbance of the carbon cycle however the causes are still under debate particularly with regard to the pattern timing of the biocalcification crisis relative roles of intrinsic and extrinsic processes as drivers of the crisis and also causal mechanisms of the t oae in this study a new quantification of toarcian calcareous nannofossil abundance and size is presented for the sancerre borehole paris basin france beyond the recognition of a severe biocalcification crisis defined by the major drop in abundance and the reduction in size of the most important pelagic carbonate producer schizosphaerella punctulata for the first time this study proposes an insight into the pace and timing of the nannoplankton crisis at sancerre the carbonate production of the lower toarcian sediments previously attributed to obliquity forcing of climate allows estimating a duration of 210 kyr for the biocalcification crisis and of 120 kyr for the shift towards lower carbon isotope values the onset of the biocalcification crisis marked by a fertility event lasted 60 kyr and the calcium carbonate values remained low for 150 kyr the subsequent recovery of carbonate and nannoplankton lasted 60 kyr and 550 kyr respectively additionally a link between the biocalcification crisis the seawater palaeotemperature and the carbon isotope steps can be demonstrated this covariance provides compelling evidence of fundamental change in the response of the climatic warming and the carbon cycle systems triggering the biocalcification crisis these observations indicate that the biocalcification crisis can be regarded as a direct or indirect consequence of a global warming moreover a deficiency of the biological pump is proposed here as a complementary causal mechanism for explaining the negative carbon isotope excursion

spatial and temporal distribution of calcareous nannofossils along a proximal distal transect in the lower jurassic of the umbria marche basin central italy abstract three upper pliensbachian lower toarcian successions of the umbria marche basin were analysed for sedimentology and calcareous nannofossil content across a 120 km long transect from proximal to distal areas with respect to the shallow latium abruzzi platform the uppermost part of the corniola unit uppermost pliensbachian and the marne di monte serrone formation p p lower toarcian polymorphum to levisoni ammonite zones that contains organic matter rich levels were studied in the three localities the analysis of the sedimentary structures in the studied successions indicates that the basin was a shallow water system above storm wave base during the late pliensbachian early toarcian the stratigraphic evolution of the sedimentary structures recorded in the studied localities shows that the upper pliensbachian corresponded to a regressive sedimentary interval whereas a complete transgressive regressive relative sea level cycle occurred during the lower toarcian polymorphum zone a further transgression occurred in the lowermost levisoni zone lower toarcian changes from carbonate dominated to marl dominated sediments form decimetre to metre scale lithological units that can be correlated from succession to succession and may have resulted from short term sea level and or palaeoenvironmental variations the mean duration of these lithological units suggests that they formed in tune with the first orbital eccentricity cycle 100 ka the analysis of calcareous nannofossil quantities abundance per mm2 of the smear slide percentage mean abundance shows both spatial and temporal changes in the community structure schizosphaerella spp and crepidolithus crassus were more abundant in proximity to the shallow latium abruzzi platform these two taxa were likely affiliated to oligotrophic conditions in marine surface waters explaining why they were generally more abundant in carbonate rich intervals than in marls mitrolithus jansae is interpreted as being a deep dwelling species which was more abundant during rising sea level in the earliest toarcian species of the genera lotharingius biscutum and calyculus were more abundant when higher trophic conditions occurred and were thus more common during periods of marl deposition the stratigraphic distribution of calcareous nannoplankton and its interpretation in terms of palaeoecological affinities allow three main phases in the environmental evolution during the early toarcian anoxic event to be recognised the first phase corresponds to a long term transgression and high nannoplankton abundance in distal areas mainly lotharingius biscutum and calyculus species suggests high productivity that may have resulted from upwelling the beginning of accumulation and preservation of organic matter in the sediments occurred during this phase the scarcity of nannoplankton during the second phase may indicate oligotrophic conditions in surface waters possibly due to water stratification during the highest sea level stand a high abundance of schizosphaerella spp and c crassus is recorded in proximal areas probably resulting from sporadic nutrient input from continental or shallow platform areas the maximum of organic matter preservation is recorded during this phase during the third phase relative sea level fall and efficient water mixing by frequent storm events led to enhanced nannoplankton productivity in proximal and distal areas and to a decrease in organic matter accumulation in the umbria marche basin

drowning of a carbonate platform as a precursor stage of the early toarcian global anoxic event southern provence sub basin south east france the toarcian oceanic anoxic event is well known as coinciding with a carbonate crisis coupled with organic matter accumulation and perturbation of the carbon cycle expressed by carbon isotope excursions in this palaeoenvironmental setting the present research attempts to better constrain the palaeoenvironmental conditions leading to the drowning of a carbonate platform during late pliensbachian to early toarcian times this study is based on the integrated sedimentological diagenetic and geochemical stable isotopes and rock eval pyrolysis analysis of several stratigraphic successions located in the southern provence sub basin south east france eodiagenetic ferroan calcite cements below two hardground surfaces at the pliensbachian toarcian transition record episodic eutrophication events such events were precursor stages of a global palaeoenvironmental perturbation i e a global carbon cycle perturbation that led to the demise of the carbonate platform and occurred prior to the toarcian oceanic anoxic event subsequently the acme of the palaeoenvironmental deterioration that coincided with the toarcian oceanic anoxic event is recorded by a pronounced negative carbon isotope excursion 3 followed by a positive one 2 87 organic matter preservation and inferred high temperature of surface sea water ca 25 c as given by oxygen isotope values from chondrichthyan tooth enamel sedimentological comparisons as well as chemostratigraphic and biostratigraphical correlations between the early toarcian sedimentary series of the southern provence and eastern dauphinois sub basins indicate that tectonic tilting occurred earlier in the southern provence sub basin this resulted in the preservation of organic rich deposits in the first sub basin and depositional hiatus in the second sub basin thus local conditions such as contrasting structural setting could markedly modify the sedimentary signature of a global climatic event

secular oscillations in the carbonate mineralogy of reef building and sediment producing organisms driven by tectonically forced shifts in seawater chemistry the primary mineralogy of oolites and early marine carbonate cements led sandberg nature 305 1983 19 22 to divide the phanerozoic eon into three intervals of aragonite seas and two intervals of calcite seas hardie geology 24 1996 279 283 has shown that these oscillations together with synchronous oscillations in the mineralogy of marine potash evaporites can be explained by secular shifts in the mg ca ratio of seawater driven by changes in spreading rates along mid ocean ridges the hardie model also predicts that high mg calcite should precipitate along with aragonite as it does in today s aragonite sea we have uncovered oscillations in the carbonate mineralogy of hypercalcifying organisms ones that have produced massive skeletons large reefs or voluminous bodies of sediment that correspond to sandberg s aragonite seas and calcite seas and that are predicted by the hardie model particular groups of corals sponges and algae appear to have been dominant reef builders only when favored by an appropriate mg ca ratio in seawater in early and middle paleozoic calcite seas calcite i reefs were dominated by calcitic tabulate heliolitid and rugose corals and calcitic stromatoporoids in contrast during the period of late paleozoic early mesozoic aragonite seas aragonite ii aragonitic groups of sponges scleractinian corals and phylloid algae as well as high mg calcitic red algae were principal reef builders during late cretaceous time at the acme of calcite ii massive rudists displaced aragonitic hermatypic corals in today s aragonite sea aragonite iii scleractinian corals are again dominant reef builders along with high mg calcitic coralline algae major sediment producing algae exhibit temporal patterns similar to those of reef builders calcitic receptaculitids flourished during calcite i whereas aragonitic dasycladaceans did not become dominant rock formers until aragonite ii during calcite ii calcitic nannoplankton formed massive coccolith chalks in warm shallow seas of the late cretaceous after the mg ca ratio of seawater had reached a very low value and calcium concentration a very high value as the mg ca ratio of seawater rose and calcium concentration fell during the cenozoic era individual coccoliths on average became less massive and encrusted cells less thickly by pliocene time during aragonite iii the prominent genus discoaster secreted only narrow rayed coccoliths that covered less than 25 of the cell surface also during aragonite iii the aragonitic green alga halimeda emerged as the dominant skeletal sediment producer in reef tracts the influence of seawater chemistry on skeletal secretion appears to have been especially strong for morphologically simple taxa that exert relatively weak control over their own calcification such groups include algae sponges corals and bryozoans morphological simplicity also permits these groups to adopt vegetative or colonial modes of growth that confer success in competition for space on reefs this linkage in addition to the basic chemical demands of hypercalcification has given the mg ca ratio of seawater strong control over the success of individual reef building taxa more generally this ratio appears to have strongly influenced evolutionary changes in the skeletal mineralogy of sponges and cheilostome bryozoans throughout their history we conclude that throughout phanerozoic time a chain of causation has extended from mid ocean ridge processes via seawater chemistry to the mineralogical and biological composition of reef communities and bioclastic carbonate deposits

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

the calcareous nannofossil crisis in northern spain asturias province linked to the early toarcian warming driven mass extinction abstract quantitative analysis of late pliensbachian early toarcian calcareous nannofossil assemblages from the west rodiles section asturias northern spain has been performed in order to interpret the paleoenvironmental changes that occurred during this time interval characterized by a major extinction event and especially around the lower toarcian tenuicostatum serpentinum zonal and extinction boundary nannofossil data were statistically treated the shannon diversity index was calculated and results were compared to the stable isotope data and the total organic carbon content to determine the changes recorded in the entire nannofossil communities a principal component analysis was applied during the latest pliensbachian the nannofossil assemblages were dominated by schizosphaerella sp and tubirhabdus patulus followed by the dominance of calcivascularis jansae taxa that probably thrived in rather cold waters the progressive decrease in the relative abundances of both schizosphaerella sp and c jansae coincides with a progressive increase in paleotemperatures during the extinction interval as indicated by the 18o values measured on diagenetically screened belemnite calcite biscutum spp dominated the nannofossil assemblages during the early toarcian tenuicostatum ammonite zone when seawaters were warm in the west rodiles section the extinction boundary coincides with the deposition of the laminated shales where especially high relative abundances of calyculus spp were recorded after the extinction boundary c jansae becomes extinct the relative abundance of biscutum spp sharply decreases and the nannofossil assemblages become dominated by the crepidolithus and lotharingius species which have been interpreted as opportunistic taxa the shannon index fluctuates throughout the studied section although it is especially high after the extinction boundary the covariance between the nannofossil crisis and the evolution of 18obel based seawater paleotemperatures as well as the fact that none of the explanations proposed by other authors seems to explain our observations suggest a clear relationship between the increase in paleotemperature and the changes recorded in our nannofossil assemblages nevertheless we do not discard possible changes in other paleoenvironmental parameters related or not to warming

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

changes in the pelagic fine fraction carbonate sedimentation during the cretaceous paleocene transition contribution of the separation technique to the study of bidart section abstract the bidart section southwestern france displays an almost complete late maastrichtian early danian transition as the cretaceous paleocene k p crisis mainly affects carbonate producers the aim of this study is to precisely evaluate the evolution of pelagic sediments composition across the boundary a new protocol for separation of fine carbonates into discrete size fractions was used 1 to precisely evaluate in weight of carbonate and not only number of particles per gram of rock the contribution of each carbonate component type foraminifera calcareous nannofossils and nonbiogenic carbonates calcite microparticles and calcareous macrocrystals and 2 to measure their isotopic signature and thus constrain the origin of these carbonate particles the maastrichtian pelagic carbonates are mostly biogenic 70 of the bulk carbonate but also contain nonbiogenic carbonates calcite microparticles 4 m due to their isotopic signature calcite microparticles cannot result from fragmentation and partial dissolution of biogenic remains and the most likely origin appears to be early diagenetic processes and or export from shallow water platforms the calcareous macrocrystals derive from an early diagenetic process the lowermost danian sediments are dominated by nonbiogenic carbonates between 50 and 80 of the bulk carbonate nevertheless two kinds of biogenic components are present thoracosphaera operculata and maastrichtian like calcareous nannofossils thoracosphaera operculata is an opportunistic calcareous dinoflagellate which frequently occurs at high abundances in basal danian sediments and is certainly in situ this is confirmed by it showing a danian isotopic signature the maastrichtian like calcareous nannofossils are nannofossils of taxa that indisputably occur in the maastrichtian but which do not occur consistently in later danian strata they show a maastrichtian type isotopic signature which strongly supports the inference that they are mainly reworked from the maastrichtian this study shows that nonbiogenic carbonates are important components of the pelagic carbonate even during periods of normal sedimentation in the crisis interval the biogenic carbonate production drops sharply while calcite microparticles and carbonate macrocrystals remain almost unaffected and represent the major part of the carbonate in the earliest danian sediments finally the sediments return to a composition similar to that of the maastrichtian in m pseudobulloides foraminifera zone

pliensbachian early jurassic calcareous nannofossils from the peniche section lusitanian basin portugal a clue for palaeoenvironmental reconstructions abstract quantitative analysis of early jurassic calcareous nannofossil assemblages from the peniche section in portugal have been performed in order to interpret palaeoenvironmental changes occurring in the lusitanian basin during the late pliensbachian davoei margaritatus and spinatum ammonite zones nannofossil data are compared to already published carbon and oxygen stable isotope data organic matter content wt total organic carbon toc and biomarker analysis a significant change in calcareous nannofossil assemblages and species diversity at the transition between the margaritatus and spinatum ammonite zones matches with the pattern shown by geochemical data this suggests that a profound change in environmental conditions occurred at that time in the davoei and margaritatus ammonite zones in a context of general sea level rise the lusitanian basin was characterized by water column stratification that favoured the sedimentation and preservation of organic matter biomarkers and oxygen isotope trends suggest that stratification of water masses occurred because of low salinity in surface waters the shallowest part of the water column characterized by oligotrophic conditions was inhabited by the probable calcareous dinocyst schizosphaerella spp while the deep dweller crepidolithus crassus flourished in the lower photic zone layers in the spinatum ammonite zone a regressive trend occurred and a salinity increase is inferred on the basis of oxygen isotope values water masses were probably less stratified at that time the upper photic zone nannofossil assemblages were still dominated by schizosphaerella spp whilst in the deep photic zone mitrolithus jansae a mediterranean taxon replaced c crassus a taxon with nw european affinity this pattern may indicate a change in palaeoceanographic conditions related to surface current circulation the sea level fall occurring during the spinatum ammonite zone may have resulted in the partial isolation of the lusitanian basin from the nw europe basins because of the creation of a threshold alternatively tectonic drowning of north african carbonate platforms in the late pliensbachian may have promoted better exchanges of nannoplankton between the lusitanian basin and the mediterranean tethys via the creation of new seaway connections

chronology of the early toarcian environmental crisis in the lorraine sub basin ne paris basin abstract early toarcian jurassic 183 ma sediments recorded profound environmental changes including mass extinction global warming marine transgression as well as widespread bottom water anoxia and organic matter accumulation on the western tethyan shelf enhanced organic matter accumulation was accompanied by a positive carbon isotope excursion cie in pelagic carbonate which marks the toarcian oceanic anoxic event these environmental changes were accompanied by a major perturbation of the global carbon cycle expressed by negative cie interrupting the positive trend the duration of the carbon cycle perturbation is still debated with estimates for the negative cie range from 200 to 600 kyr here we present ultra high resolution 555 kyr for the tenuicostatum zone and 1310 kyr for the serpentinum zone the durations of the elegantulum and falciferum subzones can be estimated to 790 kyr and 520 kyr respectively a change in the orbital response from eccentricity to obliquity forcing evident from other locations is well expressed in the lorraine sub basin and occurred within the cie interval the strong impact of the obliquity component in post event deposits hints to processes most effective at high latitudes such as the waxing and waning of polar ice paleogeographic features of the western tethyan shelf supported the tele connection of higher to lower latitude processes via water exchange through the viking corridor

present day coccolith fluxes recorded in central eastern mediterranean sediment traps and surface sediments two sediment traps were deployed in time series collection from november 1991 to august 1994 at 3000 and 3500 m respectively above and below the oxygenated sea water anoxic brine interface in the bannock basin central eastern mediterranean here the coccolithophore flux and its contribution to the carbonate particulate flux are presented for the 3000 m trap and compared with the record in eastern mediterranean surface sediments a marked seasonal variation is observed in the fluxes of total mass total coccoliths and whole coccospheres with flux maxima in late winter and spring the annual coccolith flux of 1 1010 coccoliths m 2 year 1 measured in the deep waters of bannock basin is much lower than published data from most other oceanographic settings even when corrected for the trap efficiency of 23 calculated from the 230th flux the biogenic and lithogenic fluxes are primarily controlled by coccolithophore production and saharan dust input respectively the calculated coccolith and coccosphere settling rates estimated from the comparison of maximum pigment concentration in the surface ocean and arrival of maximum flux at 3000 m water depth ranged from 17 to 25 m day 1 for coccoliths and 100 m day 1 for coccospheres at the study site carbonate dissolution is a minor process at both the trap depth and at the sea floor in both oxic and anoxic conditions and there is a high preservation of coccolith caco3 coccolithophores are the main contributor to the biogenic carbonate flux followed by thoracosphaerids emiliania huxleyi and florisphaera profunda followed by syracosphaera helicosphaera carteri and calcidiscus leptoporus are the dominant species in the sediment trap and surface sediments

palaeoenvironmental vs evolutionary control on size variation of coccoliths across the lower middle jurassic size is an easily quantifiable trait probing the respective influence of evolution and palaeoenvironment on organisms through time after the stressed period that spanned across western tethys epicontinental seas during the early toarcian the following rebuilding of a restored water column ecosystem is coeval with the size increase of the lotharingius genus coccoliths one of the main pelagic producers at that time in order to quantitatively assess the coccolith size evolution during a time span of 10 myr measurements of seven morphospecies of lotharingius across the toarcian and early aalenian were performed this study was carried out on a total of 5500 specimens from samples retrieved from two distinctive palaeoenvironmental settings in the western mediterranean tethys three sections from the lusitanian basin in portugal and one section from the causses basin in southern france for each specimen coccolith length width and central area length and width were measured using specific measurement software statistical and data analysis tools were used in order to evaluate significant resemblances and or differences between different size groups and samples two main clusters are acknowledged from this study small sized lotharingius is 4 m in addition to common evolutionary processes changes in palaeoenvironmental conditions were taken into account to explain such a size distribution although background evolution pushed the lotharingius genus toward larger sizes palaeoenvironmental conditions seemed to play an important role in the toarcian early aalenian morphological evolution of this taxon the production of larger coccoliths profited from stable environmental conditions whereas smaller morphotypes dominated during periods marked by stress the transition from small to large lotharingius was synchronous in the two investigated western tethys basins at the bifrons gradata or variabilis ammonite zone boundary middle toarcian thus representing an important event for the lower jurassic calcareous nannofossil biostratigraphy

a comparative study of representative 2d microstructures in shaly and sandy facies of opalinus clay mont terri switzerland inferred form bib sem and mip methods abstract a combination of broad ion beam bib polishing and scanning electron microscopy sem has been used to study qualitatively and quantitatively the microstructure of opalinus clay in 2d high quality 2d cross sections ca 1 mm 2 belonging to the shaly and sandy facies of opalinus clay were investigated down to the nanometre scale in addition mercury intrusion porosimetry mip and x ray powder diffraction experiments have been used to extend characterization of the microstructure to the mm cm scale on bulk volume sample material interestingly both end member samples of the opalinus clay show qualitatively similar mineralogy and pore characteristics as well as a comparable pore size distribution and pore morphology within the different mineral phases and mineral aggregates differences between the facies are mainly due to variations in mineral size and mineral amount present in the alternating layers of the different facies six different porous mineral phases have been identified and the pores have been subdivided into ten different pore types pores visible in the sem images are most abundant in the clay matrix and these seem to follow a power law distribution with a power law exponent of ca 2 25 independent of the sample location furthermore all common mineral grains show characteristic porosity pore shape and pore size distribution in 2d and are proposed to be considered as elementary building blocks for opalinus clay combined these homogeneous elementary building blocks make up the heterogeneous fabric of the different facies of opalinus clay based on extrapolation of the power law size distribution in the clay matrix below sem resolution results in a porosity of 10 25 for clay rich layers 60 90 of clay matrix whereas sand and carbonate layers show an extrapolated porosity of 6 14 these extrapolated porosities are in agreement with water loss and physical porosity measurements performed on bulk material of comparable samples

nannoplankton productivity and diagenesis in the rhythmically bedded toarcian aalenian fiuminata section umbria marche apennine central italy abstract pelagic rhythmic lithotypes crop out in the fiuminata section central italy middle toarcian aalenian in age and provide a good example of cyclic sedimentation within the calcari e marne a posidonia unit the whole succession is made up of a nutty yellowish rhythmic sequence of marlstone and marly limestone beds with similar thicknesses calcareous nannofossil quantitative analyses give a good biostratigraphic resolution of the studied interval and also reveal a different assemblage composition of the carbonate rich lithotypes with respect to the carbonate poor ones schizosphaerella spp which is the dominant taxon in the assemblage shows higher abundances in the limestones conversely coccoliths are more abundant and diverse in the marls such data emphasize a relationship between palaeoenvironmental conditions in the water column nannoplankton productivity and the depositional pattern of the sedimentary basin diagenetic overprint can also account for the different assemblage composition in marlstones and limestones the effects of diagenesis on the original thanatocoenosis have been detected through a detailed analysis of nannofossil preservation this study points out that diagenesis has enhanced without obliterating a primary palaeoenvironmental signal nannoplankton productivity varied in response to differing conditions in the water column schizosphaerella spp seems to be more productive concomitant with the deposition of carbonate rich sediments with bioturbation and abundant radiolarians probably while these sediments were deposited a more vigorous vertical mixing of the water column occurred and trophic resources were good a stable and diversified community of coccolithophorids was established in times of clay deposition when the surface waters were stratified due to their density and nutrients were available both at the sea bottom and in the water column due to the runoff the differing nannoplankton assemblage is tentatively interpreted in terms of a response to milankovitch orbital climatic cycles

phytoplankton response and geochemical evidence of the lower toarcian relative sea level rise in the umbria marche basin central italy abstract quantitative and qualitative analyses have been carried out on the lower toarcian organic rich lithologies of the umbria marche domain marne di monte serrone formation with the aim to emphasize the potential of organic and geochemical parameters as palaeoenvironmental indices the organic matter and phytoplankton data suggest that the palaeoenvironmental evolution of this area was controlled by a third order cyclicity induced by climatic eustatic fluctuations during the early toarcian sea level rise two different phases have been recognized the phase of facies retrogradation referable to the transgressive system tract lying in the early and middle part of the d tenuicostatum zone this phase was characterized by a relative increase of basinal caco 3 a better fertility within the photic zone and a decrease of sea bottom oxygenation and of the micronutrients in surface waters the maximum flooding event at the top of the retrogradation phase corresponds with the maximum of palaeoenvironmental distality sedimentary starvation and total organic carbon toc values the phase of facies progradation corresponding to the high stand system tract occurred in the uppermost portion of the d tenuicostatum zone this phase induced a more efficient water circulation producing a re oxygenation at the sea bottom a better nutrient recycling and a reflourishing of nannoplakton the caco 3 in the basin was mainly extrabasinal because the carbonate platforms started producing and exporting the carbonate mud basinwards again this approach confirms that eustatic fluctuations strongly influenced the variations of phytoplankton total abundance and species diversity and the distribution of organic matter in the sediments it also regards a significant tool for the investigation of lithologies where the lack of significant sedimentary structures does not give detailed palaeoenvironmental information

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