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

the cenomanian turonian oceanic anoxic event in the south atlantic new insights from a geochemical study of dsdp site 530a abstract one of the key objectives of deep sea drilling project dsdp leg 75 was to shed light on the underlying causes of cretaceous oceanic anoxia in the south atlantic by addressing two major hypotheses productivity productivity driven anoxia vs enhanced ocean stratification leading to preservation of organic matter and black shale deposition here we present a detailed geochemical dataset from sediments deposited during the cenomanian turonian c t transition and the global oceanic anoxic event 2 oae 2 at dsdp site 530a located off shore namibia southeast angola basin north of walvis ridge to characterise the succession of alternating black and green shales at this site and to reconstruct the evolution of their paleoenvironmental setting we have combined data derived from investigations on bulk organic matter biomarkers and the inorganic fraction the location of the c t boundary itself is biostratigraphically not well constrained due to the carbonate poor but organic matter rich facies of these sediments the bulk 13corg record and compound specific 13c data in combination with published as well as new biostratigraphic data enabled us to locate more precisely the c t boundary at dsdp site 530a the compound specific 13c record is the first of this kind reported from c t black shales in the south atlantic it is employed for paleoenvironmental reconstructions and chemostratigraphic correlation to other c t sections in order to discuss the paleoceanographic aspects and implications of the observations at dsdp site 530a in a broader context e g with regard to the potential trigger mechanisms of oae 2 global changes in black shale deposition and climate on a stratigraphic level an approximation and monitoring of the syndepositional degree of oxygen depletion within the sediments bottom waters in comparison to the upper water column is achieved by comparing normalised concentrations of redox sensitive trace elements with the abundance of highly source specific molecular compounds these biomarkers are derived from photoautotrophic and simultaneously anoxygenic green sulphur bacteria chlorobiacea and are interpreted as paleoindicators for events of photic zone euxinia in contrast to a number of other oae 2 sections that are characterised by continuous black shale sequences dsdp site 530a represents a highly dynamic setting where newly deposited black shales were repeatedly exposed to conditions of subtle bottom water re oxidation presumably leading to their progressive alteration into green shales the frequent alternation between both facies and the related anoxic to slight oxygenated conditions can be best explained by variations in vertical extent of an oxygen minimum zone in response to changes in a highly productive western continental margin setting driven by upwelling

anoxic vs dysoxic events reflected in sediment geochemistry during the cenomanian turonian boundary event cretaceous in the umbria marche basin of central italy abstract one of the most spectacular expressions of global oceanic anoxic events oaes of the cretaceous is the livello bonarelli of central italy deposited during the cenomanian turonian boundary event ctbe or oae2 at around 93 5 ma at furlo in the umbria marche basin in italy the bonarelli consists of approximately 1 m of c org rich shales interbedded with radiolarian rich layers and contrasts sharply with the extensive over and underlying siliceous limestones several minor c org rich intervals herein termed black levels average thickness 4 5 cm are interbedded within the scaglia bianca beneath the bonarelli x ray fluorescence and icp ms analyses show that these sediments consist of different mixing systems with three end members 1 sio 2 caco 3 scaglia bianca 2 average shale caco 3 black levels and 3 average shale sio 2 bonarelli given the sharp lithologic contacts and the little geochemical mixing between the groups these are thought to represent rapid switching events between sedimentary modes major element concentrations are generally low except for si and p owing to dilution by silica up to 96 and carbonates as al normalised ratios for elements such as ti or zr taken as proxies for higher energy environments are close to average shale values excess sio 2 is most likely linked to biogenic processes rather than quartz element al ratios of ti mg k rb and zr are fairly constant pointing to a mostly homogeneous source area the black levels and bonarelli are characterised by lower mg al ratios compared to the scaglia bianca sediments suggesting variability in chlorite input which could be linked with short term sea level drops indicated by ti al ratios the bonarelli sediments are severely depleted in mn which is indicative of oxygen depleted bottom water conditions and an open marine environment while the black levels appear to have been deposited in a much more restricted setting a model involving partial physical isolation of the furlo site by a sill coupled to omz variations by extra basinal forcing mechanisms is proposed to account for these conflicting data based on re mo ratios the bonarelli sediments were deposited under varying oxygen depletion levels from suboxic to anoxic while re mo ratios in the black levels show deposition under less oxygen deficient conditions most minor elements many of them redox sensitive or sulphide residing are strongly enriched in the c org rich sediments further documenting the absence of oxygen and potential availability of hydrogen sulphide in the water column at times while high zn concentrations suggest elevated submarine hydrothermal activity during this time interval ba is also present in very high concentrations up to 1 4 with an average weighed concentration of 0 6 for the entire bonarelli and is probably indicative of high paleoproductivity in this area this is further supported by high p concentrations hinting at nutrient availability at this site

sedimentary mercury enrichments as a marker for submarine large igneous province volcanism evidence from the mid cenomanian event and oceanic anoxic event 2 late cretaceous oceanic anoxic event 2 oae 2 during the cenomanian turonian transition 94 ma was the largest perturbation of the global carbon cycle in the mid cretaceous and can be recognized by a positive carbon isotope excursion in sedimentary strata although oae 2 has been linked to large scale volcanism several large igneous provinces lips were active at this time e g caribbean high arctic madagascan ontong java and little clear evidence links oae 2 to a specific lip the mid cenomanian event mce 96 ma identified by a small 1 positive carbon isotope excursion is often referred to as a prelude to oae 2 however no underlying cause has yet been demonstrated and its relationship to oae 2 is poorly constrained here we report sedimentary mercury hg concentration data from four sites three from the southern margin of the western interior seaway and one from demerara rise in the equatorial proto north atlantic ocean we find that in both areas increases in mercury concentrations and hg toc ratios coincide with the mce and the oae 2 however the increases found in these sites are of a lower magnitude than those found in records of many other mesozoic events possibly characteristic of a marine rather than atmospheric dispersal of mercury for both events combined the new mercury data presented here are consistent with an initial magmatic pulse at the time of the mce with a second greater pulse at the onset of oae 2 possibly related to the emplacement of lips in the pacific ocean and or the high arctic

biogeochemical assessment of sources of organic matter and paleoproductivity during the early aptian oceanic anoxic event at shatsky rise odp leg 198 this study investigates organic rich sedimentary sequences deposited during the early aptian oceanic anoxic event oae1a at sites 1207 and 1213 on shatsky rise odp leg 198 in the west central pacific biomarker analyses provide evidence of the algal and bacterial origin of organic matter om in these sediments where the abundance of steroidal components particularly sterenes and sterones suggests that the om includes major contributions from eukaryotic sources in an environment characterized by high phytoplankton productivity the presence of alkenones at site 1213b is diagnostic of om derived from representatives of haptophyte algae among the calcareous nannoplankton and their 13c values average 31 6 are consistent with those expected during elevated pco2 the occurrence and prominence of 2 methylhopanes and 2 methylhopanones indicates significant contributions to the om from cyanobacteria which are also likely contributors of hopanoids based on their 13c compositions these biomarker data suggest that oceanic conditions perhaps nitrate or iron limited were conducive to cyanobacteria production during oae1a which appears to distinguish this event from other cretaceous oae

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

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

a new proxy for cretaceous paleoceanographic and paleoclimatic reconstructions coiling direction changes in the planktonic foraminifera muricohedbergella delrioensis among some modern and recent fossil species of planktonic foraminifera the proportion of left to right coiled shells in a population appears to be temperature dependent the relative abundance of each morphotype reflecting ecological preferences a similar relationship is identified among muricohedbergella delrioensis carsey 1926 at the cenomanian turonian stage boundary in mid latitude sites of the western interior seaway including the pueblo type section the increase of sinistral m delrioensis in the assemblage is related to higher 18 o carb values and decrease in inner porosity which suggests that changes in the coiling direction in this morphospecies could represent a new proxy for constraining sea surface temperature sst variations as surface dwellers muricohedbergellids were not accepted manuscript 2 affected by oceanic anoxic event oae2 and provide a continuous paleoclimatic signal throughout the cenomanian turonian boundary interval furthermore genetic evidence obtained from extant foraminifera indicates that shifts of coiling ratios in planktonic foraminifera species can express the signature of distinct genetic types which are revealed through their opposite coiling directions coiling direction could be a genetic trait implying that cryptic species may occur in the mesozoic

basalt seawater interaction the plenus cold event enhanced weathering and geochemical change deconstructing oceanic anoxic event 2 cenomanian turonian late cretaceous oceanic anoxic event 2 cenomanian turonian ca 94 ma represents a major palaeoceanographic phenomenon that took place during an interval of extreme global warmth when large amounts of organic matter entered the marine burial record probably triggered by increased availability of nutrients for planktonic biota three sections eastbourne sussex uk raia del pedale campania italy and tarfaya morocco recording this event illustrate the influence on marine geochemistry of mafic volcanic rock seawater interaction anoxia to euxinia and re oxygenation and cooling during the so called plenus cold event the eastbourne section represents the organic lean epicontinental pelagic deposits of the english chalk the raia del pedale section represents a shallow water platform carbonate on the tethyan continental margin also largely devoid of organic matter and the tarfaya core represents an atlantic margin site where cyclically bedded organic rich sediments were well developed correlation between all three sections is readily achieved by biostratigraphy and carbon isotope stratigraphy 13ccarb and 13corg over the oceanic anoxic event 2 interval represented by a characteristic broad positive carbon isotope excursion the stratigraphic range of the plenus cold event defined by the presence in two discrete levels of boreal fauna and an excursion to heavier oxygen isotope values in the english chalk can be identified in raia del pedale and tarfaya by using the carbon isotope curve as a correlative tool similarly a section in southern france allows its co existing osmium isotope excursion to relatively unradiogenic values to be placed in the context of the oceanic anoxic event in all three analysed sections a fall to lower osmium isotope values clearly pre dated the onset of oceanic anoxic event 2 as defined by the initial rise in carbon isotope values allowing the putative magmatic mafic event as a trigger for the oceanic anoxic event an initial drop in sulphur isotope ratios 34scas at eastbourne correlates with the osmium isotope curve suggesting that isotopically light sulphur could have been derived from a mafic igneous source re oxygenation of sediments of all three investigated sections during the plenus cold event is variably illustrated by change in cerium calcium iodine calcium molybedenum calcium and uranium calcium ratios according to the redox behaviour of the elements in question and whether controls on seawater chemistry were local or global in nature changes in molybdenum isotope ratios from tarfaya and portions of the sulphur isotope curve from eastbourne and raia del pedale also indicate the probable presence of more oxygen rich bottom waters during the plenus cold event oxidation by such waters of previously deposited organic rich shales as well as loss of anoxic euxinic sinks is credited with temporarily enriching global seawater in a range of other redox sensitive trace metals for example v cr co ni cu zn and cd during ongoing basalt seawater interaction indicated by persistent relatively non radiogenic osmium isotope seawater values however early diagenetic enrichment of manganese in the english chalk over much of the oceanic anoxic event interval is broadly correlative in time with relatively low osmium isotope values in sections elsewhere a relationship that may be due to the lack of affinity of manganese with carbon rich shales hence allowing relatively elevated concentrations of the element in marine waters to persist during leaching of mafic rocks unlike other redox sensitive species the calcium isotope and lithium isotope ratios from eastbourne and raia del pedale indicate an increase in global weathering during the initial phase of oceanic anoxic event 2 and the shift in strontium isotopes and osmium isotopes to more unradiogenic values during the event suggests that not only construction but also destruction of one or more large igneous provinces was probably a proximal cause of this major palaeoceanographic phenomenon by elevating nutrient levels and planktonic productivity in large tracts of the world ocean globally widespread carbon burial and silicate weathering are both identified as important mechanisms for drawing down atmospheric carbon dioxide that in the absence of overwhelming volcanogenic replenishment of this greenhouse gas during the early phase of oceanic anoxic event 2 caused the plenus cold event

organic matter deposition and paleoenvironmental implications across the cenomanian turonian boundary of the subalpine basin se france local and global controls abstract the cenomanian turonian boundary is marked by global sea level highstands and one of the warmest periods of the mesozoic with high pco2 levels linked to a massive magmatic episode this is associated with the establishment of a worldwide marine anoxia the deposition of organic rich facies and disturbances of the global carbon cycle the so called oceanic anoxic event 2 oae2 the pont d issole section s subalpine basin se france sedimentary succession represents the reference record of oae2 in the tethyan domain although its organic fraction is extremely poorly studied therefore the main objectives of this study are the characterization of the pont d issole section s organic matter om for paleoenvironmental interpretation and the assessment of the om thermal maturity using organic petrology and organic geochemistry techniques the organic record characterizes a shallowing up marine system with varying redox and restriction conditions associated with periods of stratified oxygen regimen it displays the presence of two om enrichment episodes with different paleoenvironmental and geodynamic contexts the first om enrichment episode unit th1 is thought to be associated with the global mechanisms that trigger oae2 and is characterized by a palynofacies association co dominated by amorphous om and marine microplankton reflecting a context of high sea level this is followed by the plenus cold event unit th2 characterized by a decrease in amorphous om and increase in marine microplankton representing a reoxygenation associated with an increase in water level and an apparent decrease in temperature disappearance of classopollis sp the second om enrichment episode unit th3 and base of unit th4 is characterized by an association dominated by amorphous om the occurrence of freshwater microplankton and the development of a restricted environment with low sea level these depositional conditions are thought to be connected to the beginning phases of basin closure promoted by the regional tectonic framework compressive trend between africa and europe the molecular fraction showed the presence of unsaturated compounds monoaromatic steranes monoaromatic anthrasteroids and the biological hopanes indicating a low thermal evolution for the om this is corroborated by biomarkers ratios and organic petrographic data namely vitrinite reflectance 0 29 rr the presence of paleozoic reworked om in the samples was also identified presenting a more complex thermal history than the cretaceous om this om is possibly related to the subaerial erosion of hercynian massifs

significant increases in global weathering during oceanic anoxic events 1a and 2 indicated by calcium isotopes abstract calcium isotope ratios 44 42ca were measured in carbonate rich sedimentary sections deposited during oceanic anoxic events 1a early aptian and 2 cenomanian turonian in sections from resolution guyot mid pacific mountains coppitella italy and the english chalk at eastbourne and south ferriby uk a negative excursion in 44 42ca of 0 20 and 0 10 is observed for the two events these 44 42ca excursions occur at the same stratigraphic level as the carbon isotope excursions that define the events but do not correlate with evidence for carbonate dissolution or lithological changes diagenetic and temperature effects on the calcium isotope ratios can be discounted leaving changes in global seawater composition as the most probable explanation for 44 42ca changes in four different carbonate sections an oceanic box model with coupled strontium and calcium isotope systems indicates that a global weathering increase is likely to be the dominant driver of transient excursions in calcium isotope ratios the model suggests that contributions from hydrothermal activity and carbonate dissolution are too small and short lived to affect the oceanic calcium reservoir measurably a modelled increase in weathering flux on the order of three times the modern flux combined with increased hydrothermal activity due to formation of the ontong java plateau oae1a and caribbean plateau oae2 can produce trends in both calcium and strontium isotopes that match the signals recorded in the carbonate sections this study presents the first major element record of a weathering response to oceanic anoxic events

geochemistry and organic petrography of cretaceous sediments of the calabar flank southeastern nigeria abstract detailed bulk geochemistry and organo petrography of outcrop cretaceous sediments with no significant effects of weathering from the calabar flank southeast nigeria were performed to understand the organic carbon source accumulation and degradation and paleo climatic paleoceanographic and paleoenvironmental conditions in west africa during early cretaceous aptian to maastrichtian times this study was based on microscopic elemental analyses organic carbon nitrogen iron and sulphur rock eval pyrolysis and carbon isotope analyses in general the calabar flank shales are characterised by highly variable total organic carbon toc contents which range between 0 1 in aptian albian mfamosing limestone and 9 9 in the awi formation sediments the organic matter om is a mixture of immature to early mature marine and terrigenous om of types iii and iv this is indicated by low hydrogen indices hi value 10 190 mg hc g toc tmax 417 460 c vitrinite reflectance ro 0 39 0 62 ro low to high c n ratios 3 4 1158 0 and high amounts of terrigenous macerals vitrinite inertinite based on carbon isotope c n ratios and sulphate reduction index sri om degradation up to 70 sri 2 5 is most pronounced for shales deposited in a marine environment the geochemical and petrographic data indicate that local factors such as low bioproductivity down slope transport and redeposition of sediments from a fluvial deltaic basin to nearshore facies shallower oxic and mildly oxygen deficient environments humid arid paleogeographic conditions specifically controlled the amount and quality of the om during aptian mastrichtian stages where marine sediments have been assumed to be deposited during the global anoxic events therefore the order of the main factors controlling om content in sediments are input of terrigenous material transported from the land low om productivity by marine photoautotrophs low preservation

the mid cenomanian event prelude to oae 2 a detailed synthesis of litho and biostratigraphic investigations of the cenomanian pelagic limestones of the scaglia bianca formation in the umbria marche basin shows that the bonarelli level which is the regional sedimentary expression of the oae 2 represents the climax of a 2 myr long cycle of black shale deposition that began in the mid cenomanian planktonic foraminiferal rotalipora cushmani zone this long term cycle began with a prominent short term event named mid cenomanian event mce which is associated with several changes in the biotic and abiotic records in particular a comparison of the available litho bio and chemostratigraphic data from the umbria marche basin allows recognition of the mce based on a a significant change in the sedimentary and tectonic regimes b a reorganisation of planktonic foraminiferal assemblages c a major change in benthic foraminifera d a major turnover in the radiolarian assemblages e a 0 7 positive shift in the carbon isotope values and f a positive shift of carbonate sr ca ratio moreover the mce is preceded 400 kyr by a short term 0 5 negative excursion in the oxygen isotope record the above mentioned changes in carbon and oxygen isotope values can be confidently correlated over different basins and oceans and seem to occur in correspondence with a major sea level fall these lines of evidence define the mce as an outstanding event associated with large scale changes in the oceanic structure and palaeoclimate the mce and the subsequent cyclical deposition of organic rich beds serve as a case study to better understand differences and similarities between mesozoic black shales and cenozoic sapropels and related palaeoceanographic changes controlled by orbital climate cycles

high resolution stable isotope records from the upper cretaceous rocks of italy and spain glacial episodes in a greenhouse planet high resolution 13c and 18o records from upper albian to lower santonian pelagic carbonates of the contessa quarry section in italy exhibit large positive oxygen isotopic excursions of 1 in the lower cenomanian and upper turonian coniacian strata within the uncertainties of biostratigraphic correlation these positive excursions appear to correspond to times of large sea level regressions in global sequence stratigraphic sea level curves several lines of evidence suggest that the major 18o excursions in contessa reflect episodes of global cooling and not differential diagenesis numerical models of oxygen isotope exchange during diagenesis show that a high contrast in the degree of alteration would be required to produce these signals as artifacts of diagenesis and lithological data provide no evidence for such large contrasts in the degree of alteration furthermore although precise correlation with a section in the south of spain is hampered by stratigraphic complexities the general sequence of major positive 18o excursions is reproduced it is unlikely that differential diagenesis would produce similar artifacts in multiple sites one explanation for the link between episodes of global cooling and sea level falls is that global cooling events led to polar ice sheet accumulation lowering sea level although ice free conditions have been inferred from evidence for a much warmer climate in late cretaceous time our results suggest that the relationship between continental high latitude ice sheets and overall climatic warmth warrants further examination

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

organically bound iodine as a bottom water redox proxy preliminary validation and application abstract carbonate associated iodine i ca has been used as a proxy of local upper ocean redox conditions and has successfully demonstrated highly dynamic spatial and temporal patterns across different time scales of earth history to further explore the utility of iodine as a paleo environmental proxy we present here a new method of extracting organically bound iodine iorg from shale using volumes of samples on the order of tens of milligrams thus offering the potential for high resolution work across thin shale beds the ratio of iorg to total organic carbon i toc in modern surface and subsurface sediments decreases with decreasing bottom water oxygen which may be used to reconstruct paleo redox changes as a proof of concept we evaluate the i toc proxy in holocene sediments from the baltic sea landsort deep iodp 347 and discuss those data within a framework of additional independent redox proxies e g iron speciation and mo the results imply that i toc may be sensitive to hypoxic suboxic conditions complementary to proxies sensitive to more reducing anoxic euxinic conditions then we test the usage of i toc in sediments deposited during late cretaceous cenomanian turonian oceanic anoxic event oae 2 from 94 million years ago ma we generated i toc and iorg records from six oae 2 sections tarfaya morocco furlo central italy demerara rise western equatorial atlantic cape verde basin eastern equatorial atlantic south ferriby uk and kerguelen plateau southern indian ocean which provide a broad spatial coverage generally i toc decreases over the interval recorded by the positive carbon isotope excursion the global signature of oae 2 suggesting an expansion of more reducing bottom water conditions and consistent with independent constraints from iron speciation and redox sensitive trace metals e g mo relatively higher i toc values thus more oxic conditions are recorded at two high latitude sites for oae 2 supporting previous model simulations cgenie that indicated higher bottom water oxygen concentrations in these regions our results also indicate that organic rich and oxygenated seafloors are likely a major sink of iodine and correspondingly influence its global seawater inventory

upper kellwasser carbon isotope excursion pre dates the f f boundary in the upper devonian lennard shelf carbonate system canning basin western australia abstract here we report four high resolution carbon isotope records in addition to trace element data for the frasnian famennian f f boundary interval in the lennard shelf carbonate system of the canning basin western australia this region lacks the characteristic black shale horizons associated with the global late devonian kellwasser extinction events yet still exhibits a trend in carbon isotope character similar to what has been reported from elsewhere in the world two positive 13c excursions with 3 4 amplitudes enrichments in select trace element ratios suggest that both excursions are related to periods of oxygen deprivation and perhaps increased biological productivity given the continuous and stratigraphically expanded nature of lennard shelf sections together with high density sampling constrained by both conodont biostratigraphy and magnetostratigraphy we observe that the upper kellwasser isotope excursion maximum 13c values and associated trace element enrichments occur distinctly lower than the f f boundary level these results have implications for the paleoenvironmental conditions leading up to the late devonian mass extinction in terms of ocean chemistry and circulation patterns this data set allows for a rare detailed look at the temporal relationship between the kellwasser events and the f f boundary and constrains the pattern of carbon isotope perturbations at the intra zonal scale

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

oil and gas habitats of the south atlantic introduction the south atlantic hydrocarbon province defined for the purposes of this volume the south atlantic comprises the atlantic ocean south of a direct line from tangier morocco to the guyana venezuela border and north of a direct line from cape town south africa and cape horn argentina at the end of 1997 this region contained 4 3 of the world s total discovered oil reserves and 2 4 of the world s total discovered gas reserves petroconsultants 1998 on the basis of the 1997 figure six countries brazil argentina nigeria gabon congo brazzaville and angola host 96 3 of the region s oil reserves and 92 1 of the region s gas reserves figure 1 illustrates the geographical distribution of the reserve splits table 1 gives the details one hundred years of discoveries voluminous basin margin asphalts in west africa cote d ivoire to angola argentina brazil and surinam attracted the serious attention of entrepreneurs from the late 1800s as discussed in more detail by dolan shallow wells were drilled soon afterwards on seep locations though with little commercial success more systematic explorations began on both margins in the 1930s and in 1941 the first large discovery the candeias field in the reconcavo basin of brazil was made the reserves of this field are now placed at 120 mmbo success did not materialize in west africa until 1955 when the small benfica field was discovered in the kwanza basin of angola thereafter following the first giant field discovery in the niger delta in 1958 west african reserves rose

does large igneous province volcanism always perturb the mercury cycle comparing the records of oceanic anoxic event 2 and the end cretaceous to other mesozoic events mercury hg is increasingly being used as a sedimentary tracer of large igneous province lip volcanism and supports hypotheses of a coincidence between the formation of several lips and episodes of mass extinction and major environmental perturbation however numerous important questions remain to be answered before hg can be claimed as an unequivocal fingerprint of lip volcanism as well as an understanding of why some sedimentary records document clear hg enrichment signals whilst others do not of particular importance is evaluating the impact of different volcanic styles on the global mercury cycle as well as the role played by depositional processes in recording global hg cycle perturbations here new mercury records of cretaceous oceanic anoxic event 2 oae 2 94 ma and the latest cretaceous 67 66 0 ma are presented oae 2 is associated with the emplacement of multiple predominantly submarine lips the latest cretaceous with subaerial volcanism of the deccan traps both of these connections are strongly supported by previously published trends towards unradiogenic osmium os isotope values in globally distributed sedimentary records hg data from both events show considerable variation between different locations attributed to the effectiveness of different sediment types in registering the hg signal with lithologically homogeneous records documenting more clear hg enrichments than sections with major changes in lithology such as limestones to claystones or organic rich shales crucially there is no geographically consistent signal of sedimentary hg enrichment in stratigraphic records of either oae 2 or the latest cretaceous that matches os isotope evidence for lip emplacement indicating that volcanism did not cause a global hg perturbation throughout the entire eruptive history of the lips formed at those times it is suggested that the discrepancy between os isotope and hg trends in records of oae 2 is caused by the limited dispersal range of hg emitted from submarine volcanoes compared to the global scale distribution of os a similar lack of correlation between these two proxies in uppermost cretaceous strata indicates that although subaerial volcanism can perturb the global hg cycle not all subaerial eruptions will do so these results highlight the variable impact of different volcanogenic processes on the efficiency of hg dispersal across the globe factors that could influence the impact of lip eruptions on the global mercury cycle include submarine versus subaerial volcanism volcanic intensity or explosivity and the potential contribution of thermogenic mercury from reactions between ascending magma and surrounding organic rich sediments

quaternary sediments in central edmonton alberta canada stratigraphy distribution and geotechnical implications abstract borehole logs were used to determine the stratigraphy and distribution of sedimentary units in central edmonton the quaternary sediments overlying upper cretaceous sedimentary bedrock consist of preglacial fluvial sand and some gravel glaciofluvial sand and gravel a glacial diamicton complex composed of melt out and flow diamictons glaciofluvial sand and silt glaciolacustrine silt and clay and minor deposits of postglacial fluvial sand the glacial sediments represent deposition during one major glaciation in the late wisconsinan the diamicton complex has an intermediate stratigraphic position in the quaternary sequence is generally thick and laterally continuous and serves as a satisfactory substrate for many deep foundations and tunnels including part of the light rail transit system seepage and block failures during tunnelling in the diamicton complex are mainly due to abundant saturated sand lenses in the upper part of the complex the lateral continuity of the diamicton complex is interrupted by sand infilling a meltwater channel incised into bedrock tunnelling is difficult and costly within the sand due to seepage and collapse mapping of the meltwater channel and associated outwash deposits allowed adjustment of the tunnel alignment to avoid intersection with the channel over the meltwater channel deposits of outwash sediments and flow diamictons form a broad surface ridge

zinc and cadmium isotope evidence for redox driven perturbations to global micronutrient cycles during oceanic anoxic event 2 late cretaceous abstract this study uses organic rich sediments from the tarfaya basin morocco to assess the cd and zn isotope response to dramatic global palaeoenvironmental change during the cenomanian turonian interval late cretaceous these organic rich continental margin deposits include an expression of oceanic anoxic event 2 oae 2 94 ma an interval associated with the spread of low oxygen marine environments and widespread burial of organic rich sediments due to placement of the tarfaya basin in a region of upwelling and relatively constant local environmental conditions the stratigraphic variations in 114 cd and 66 zn values largely reflect changes in the seawater isotopic composition of the sub surface proto north atlantic ocean positive shifts of 0 2 0 3 away from background values in 114 cd and 66 zn are observed during the main phase of the positive carbon isotope excursion associated with oae 2 these isotopic shifts are coeval with decreases in cd toc and zn toc ratios and thus imply that drawdown of isotopically light cd and zn from seawater inventories was a result of extensive burial of these metals in organic rich marine sediments globally low 66 zn values during the plenus cold event a cooler episode during oae 2 are similar in timing and magnitude to variations found in the english chalk eastbourne uk and support the inference of a global control on these isotopic excursions the 66 zn values during the plenus cold event are taken to record global oxygenation possibly including the remobilization of isotopically light zn from continental margin sediments a considerably smaller change in 114 cd values for this interval implies that the cd and zn isotope systems can provide information about slightly different environmental processes with global seawater composition with respect to zn also being influenced by the magnitude of oxic removal sinks and isotopically light zn input fluxes from sediments and hydrothermal fluids

recognition of paleobiochemicals by a combined molecular sulfur and isotope geochemical approach study of organic matter in immature sediments from a messinian evaporitic basin shows that consideration of structures modes of occurrence and carbon isotopic compositions of free and sulfur bound carbon skeletons allow identification of biochemical precursors detailed information concerning biotic communities present during deposition of sediments can be retrieved in this way moreover unprecedented biochemicals were recognized these extend the horizon of biomarker geochemistry

pleistocene hydrology of north america the role of ice sheets in reorganizing groundwater flow systems 1 while the geomorphic consequences of pleistocene megafloods have been known for some time it has been only in the past 2 decades that hydrogeologists and glaciologists alike have begun to appreciate the important impact that ice sheet aquifer interactions have had in controlling subsurface flow patterns recharge rates and the distribution of fresh water in confined aquifer systems across north america in this paper we document the numerous lines of geochemical isotopic and geomechanical evidence of ice sheet hydrogeology across north america we also review the mechanical thermal and hydrologic processes that control subsurface fluid migration beneath ice sheets finite element models of subsurface fluid flow permafrost formation and ice sheet loading are presented to investigate the coupled nature of transport processes during glaciation deglaciation these indicate that recharge rates as high as 10 times modern values occurred as the laurentide ice sheet overran the margins of sedimentary basins the effects of ice sheet loading and permafrost formation result in complex transient flow patterns within aquifers and confining units alike using geochemical and environmental isotopic data we estimate that the volume of glacial meltwater emplaced at the margins of sedimentary basins overrun by the laurentide ice sheet totals about 3 7 104 km3 which is about 0 2 of the volume of the laurentide ice sheet subglacial infiltration estimates based on continental scale hydrologic models are even higher 5 10 of meltwater generated these studies in sum call into question the widely held notion that groundwater flow patterns within confined aquifer systems are controlled primarily by the water table configuration during the pleistocene rather groundwater flow patterns were likely much more complex and transient in nature than has previously been thought because pleistocene recharge rates are believed to be highly variable these studies have profound implications for water resource managers charged with determining sustainable pumping rates from confined aquifers that host ice sheet meltwater

pacific 187 os 188 os isotope chemistry and u pb geochronology synchroneity of global os isotope change across oae 2 studies of oae 2 sections beyond the atlantic ocean western interior seaway wis and european pelagic shelf are limited here we present initial osmium isotope stratigraphy 187os 188os osiosi from two proto pacific sites that span the cenomanian turonian boundary interval ctbi the yezo group yg section hokkaido japan and the great valley sequence gvs california usa to evaluate the 187os 188os seawater chemistry of the proto pacific additionally we combine new 206pb 238u zircon ca id tims geochronology from five volcanic tuff horizons of the yezo group section to test and facilitate inter basinal integration with the wis using radio isotopically constrained age depth models for both sections and quantitatively constrain the absolute timing and duration of events across the ctbi the yg shows an almost identical osiosi profile to that of the wis and very similar to that of other sites of the proto atlantic and european pelagic oceans turgeon and creaser 2008 and du vivier et al 2014 the characteristics of the osiosi profile are radiogenic and heterogeneous 0 55 0 85 prior to the oae 2 and synchronous with the inferred oae 2 onset the osiosi abruptly become unradiogenic and remain relatively homogeneous 0 20 0 30 before showing a gradual return to more radiogenic view the mathml sourceosi 0 70 throughout the middle to late oae 2 a206a206pb 238u zircon age of an interbedded tuff hk017 in the adjacent horizon to the first unradiogenic osiosi value constrains the age of the osiosi inflection at 94 44 0 14 ma94 44 0 14 ma this age including uncertainty agrees with the interpolated age of the same point in the osiosi profile 94 28 0 25 ma94 28 0 25 ma in the only other dated oae 2 section the wis indicating a coeval shift in seawater chemistry associated with volcanism at the oae 2 onset at the levels of temporal resolution ca 0 1 myr further prior to the onset of oae 2 an enhanced radiogenic inflection in the osiosi profile of the yg is correlative within uncertainty with a similar trend in the wis based on the u pb age depth model the interpolated ages 94 78 0 12 ma94 78 0 12 ma and 94 66 0 25 ma94 66 0 25 ma for this osiosi inflection in the yg and wis respectively indicate that palaeocirculation was sufficient to simultaneously influence transbasinal seawater chemistry in contrast the pre oae 2 osiosi profile for the gvs is disparate to that of the yg and those of the proto atlantic and european pelagic shelf locations we interpret the pre oae 2 heterogeneous osiosi values 0 30 0 95 to record a palaeobasin that was regionally influenced interchangeably by both unradiogenic hydrothermal flux and radiogenic continental flux os we conclude that the osiosi profiles from the proto pacific sections record both trends that are consistent globally oae 2 onset syn and post oae 2 but also show regional differences pre oae 2 between oae 2 sections worldwide as such the osiosi profiles coupled with u pb geochronology facilitate the correlation of oae 2 stratigraphy and demonstrate both regional and global ocean dynamics

soft zones in the glacial till in downtown edmonton high rise buildings in downtown edmonton have generally been founded on spread footings in glacial till early geotechnical work proposed a geological model comprising uniform very dense basal lodgement till however recent work shows that the till is more complex being variable in both material type and consistency a case history is described that exemplifies this variability it is concluded that early experience with the dense tills has led to an overconfident approach to soil investigation in this area and that a thorough site investigation is required

iron limitation in the western interior seaway during the late cretaceous oae 3 and its role in phosphorus recycling and enhanced organic matter preservation the sedimentary record of the coniacian santonian oceanic anoxic event 3 oae 3 in the north american western interior seaway is characterized by a prolonged period of enhanced organic carbon oc burial this study investigates the role of fe in enhancing organic matter preservation and maintaining elevated primary productivity to sustain black shale deposition within the coniacian santonian aged niobrara formation in the usgs 1 portland core iron speciation results indicate the development of a reactive fe limitation coeval with reduced bioturbation and increased organic matter preservation suggesting that decreased sulfide buffering by reactive fe may have promoted enhanced organic matter preservation at the onset of oae 3 an fe limitation would also provide a feedback mechanism to sustain elevated primary productivity through enhanced phosphorus recycling additionally our results demonstrate inconsistencies between fe based and trace metal redox reconstructions iron indices from the portland core indicate a single stepwise change whereas the trace metal redox proxies indicate fluctuating redox conditions during and after oae 3 using fe speciation to reconstruct past redox conditions may be complicated by a number of factors including fe sequestration in diagenetic carbonate phases and efficient sedimentary pyrite formation in a system with limited fe supply and high levels of export production

paleoceanographic significance of high resolution carbon isotope records across the cenomanian turonian boundary in the western interior and new jersey coastal plain usa carbon isotope measurements have been made on bulk carbonate and organic matter in three sections across the cenomanian turonian boundary the stratigraphy records the positive carbon isotopic excursion that is associated with the major oceanic anoxic event oae2 comparison of toc and isotopic data in sections from a range of different environments suggests that the positive excursion is a response to increased burial of organic matter in the deep ocean the lack of coupled negative shifts in 13corg and 13ccarb records at the onset of oae2 does not support a causal role for volcanism or methane hydrate dissociation

the northern gulf of mexico during oae2 and the relationship between water depth and black shale development despite their name oceanic anoxic events oaes are not periods of uniform anoxia and black shale deposition in ancient oceans shelf environments account for the majority of productivity and organic carbon burial in the modern ocean and this was likely true in the cretaceous as well however it is unlikely that the mechanisms for such an increase were uniform across all shelf environments some like the northwest margin of africa were characterized by strong upwelling but what might drive enhanced productivity on shelves not geographically suited for upwelling to address this we use micropaleontology carbon isotopes and sedimentology to present the first record of oceanic anoxic event 2 oae2 from the northern gulf of mexico shelf here oae2 occurred during the deposition of the well oxygenated inner neritic lower estuarine lower tuscaloosa sandstone the overlying organic rich oxygen poor marine tuscaloosa shale is entirely turonian in age we trace organic matter enrichment from the spinks core into the deepwater gulf of mexico where wireline log calculations and public geochemical data indicate organic enrichment and anoxia throughout the cenomanian turonian boundary interval redox change and organic matter preservation across the gulf of mexico shelf were driven by sea level rise prior to the early turonian highstand which caused the advection of nutrient rich oxygen poor waters onto the shelf this results in organic matter mass accumulation rates 1 2 orders of magnitude lower than upwelling sites like the nw african margin but it likely occurred over a much larger geographic area suggesting that sea level rise was an important component of the overall increase in carbon burial during oae2

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

biochemostratigraphy of an upper albian turonian succession from the southeastern neo tethys margin sw iran abstract a neo tethyan upper albian turonian hemi pelagic carbonate succession sarvak formation accessible in outcrop in the zagros sw iran was investigated using sedimentology microfacies analysis planktonic foraminifera biostratigraphy and carbon isotope stratigraphy the succession contains six biozones including thalmanninella th appenninica th globotruncanoides rotalipora cushmani whiteinella archaeocretacea helvetoglobotruncana helvetica and marginotruncana schneegansi some of these biozones show variable stratigraphic positions throughout the tethyan and boreal realms that hinder correlation of the studied iranian section with european reference sections therefore the correlation of the existing biostratigraphic framework was complemented by carbonate carbon isotope stratigraphy based on bulk carbonate material despite the low resolution of the presented carbon isotope record pronounced global events including the late turonian events cenomanian turonian boundary ctb event oae 2 and albian cenomanian boundary acb event can be distinguished the 13c excursions provide global synchronous time lines for correlation the distinguished biozones were compared among the sections regarding their stratigraphic positions relative to these time lines the correlation tentatively suggests that the biostratigraphic datum marking the acb is diachronous with an se nw trend first appearance datum fad of th appenninica varies from the upper albian to the lower cenomanian the fad of th globotruncanoides is also variable from the upper albian to the lower cenomanian however the middle cenomanian turonian biozones including rotalipora cushmani and whiteinella archaeocretacea zones are synchronous elevated pco2 contributed to the gradual increase of the sst sea surface temperature during the cenomanian and the dramatic climax at the earliest turonian this trend closely correlates with the change from the diachronous acb biozones to synchronous ctb biozones possibly increasing ssts provided temperature tolerance range for the species throughout different latitudes and assisted their rapid distribution moreover the warming raised the sea level from the latest albian to turonian that inundated landbridges resulting in an enhanced marine circulation and faster distribution of planktonic species throughout the neo tethys ocean

sedimentation in the tethyan pelagic realm during the cenomanian monotonous settling or active redistribution sea bottom processes of the pelagic realm are still not completely understood and represent an intriguing subject this paper focuses on the relationships between normal settling processes redistribution of sediments and oceanographic parameters in a pelagic setting during the cenomanian five key tethyian localities in the cenomanian umbria marche and belluno basins have been studied in order to understand the interplay among sea bottom processes that acted on the sea floor the dataset consists of the mm scale sedimentological description of the sections complemented by microfacies analysis on selected samples different sedimentological indications such as presence of intraclasts lined forams pervasive plane parallel lamination suggest a continuous reworking under action of bottom currents with varying intensity and direction all the identified facies are here illustrated in detail and organized in a comprehensive schematic facies framework the facies matrix that leads to recognize two depositional facies suites the settling dominated and the traction current dominated under different oxygenation conditions our results suggest that settling of biogenic and inorganic particles represents the main source of pelagic sediments but not the unique depositional process under the action of sea bottom currents of different intensity sediments are continuously redistributed on the sea floor all the collected evidences contribute to the proposal of a comprehensive depositional model for these reworked and redistributed fine grained sediments that represent true calcareous pelagic contourites the model suggests that the identified traction related facies can be used as a proxy for bottom current intensity and indirectly as an indicator of changing ventilation regimes at the sea floor through time

glacial sedimentary processes and environmental reconstruction based on lithofacies glacigenic sediments exposed in pits around villeneuve near edmonton alberta are subdivided into facies based on grain size sedimentary structure glacially induced deformation and faulting and groove marks two diamicton facies are recognised one of which is interpreted as a primary till deposited directly from glacier ice and the other as a product of mass movement the diamicton facies are closely associated with current bedded facies interpreted as fluvioglacial deposits the stratigraphic sedimentological and tectonic aspects of these fluvial deposits suggest subglacial deposition in channels and cavities at any one place the glacier appears to have alternated between being attached to the bed causing thrusting and sole marking and being separated from the bed by a cavity in which fluvial and mass movement sediments accumulated the net result is a highly complex and laterally variable stratigraphy produced by a single glacial advance the correct interpretation of such sequences is essential if lithostratigraphy is to be used to establish glacial history in addition the interpretations presented here have implications regarding the formation of soft zones in till they indicate that the soft zones are beds of sorted sediment redeposited by mass movement

terrestrial and marginal marine record of the mid cretaceous oceanic anoxic event 2 oae 2 high resolution framework carbon isotopes co 2 and sea level change abstract oceanic anoxic event 2 oae2 c 94 5 93 9 ma offers insight into the mechanisms of past climate change linked to organic productivity and carbon sequestration it has been studied extensively but the vast majority of data come from marine records thus providing an incomplete view of past climate dynamics here we integrate new high resolution data and published records on depositional environments the carbon isotope composition of bulk organic carbon 13corg and plant cuticles 13ccut and stomatal index values a proxy for pco2 in well preserved terrestrial through marginal marine archives of the initial phase of oae2 the study area is located on the western margin of the western interior seaway southwestern utah age constraints are based on a new u pb bentonite age and correlation to an orbitally calibrated interval of the bridge creek limestone n alkane abundance suggests predominance of terrestrial contributions to bulk organic carbon for most samples despite similarities between carbon isotope variations and transgressive regressive shoreline movements it is argued that 13corg and 13ccut are not strongly affected by local variables a series of negative 2 carbon isotope excursions is identified and attributed to changes in the size and isotopic value of the atmospheric co2 reservoir the temporal spacing of these anomalies 80 120 kyr is consistent with changes in insolation modulated by orbital eccentricity a systematic phase shifted relationship between the negative carbon isotope excursions and transgressive increments further suggests a link between carbon cycle perturbations and meter scale sea level change on the 100 kyr time scale a conceptual model involving insolation controlled aquifer charge discharge and biomass burial degradation in the monsoonal belt is proposed the framework presented here is available to facilitate further research on the interplay of terrestrial and oceanic carbon reservoirs during oae2

the early toarcian jurassic anoxic event stratigraphic sedimentary and geochemical evidence detailed paleogeographic studies in the southern alps suggest that an oxygen minimum model is appropriate for interpreting conditions on tethyan continental margins advection of manganese in this low oxygen layer may explain the local occurrence of carbonate ores of this element carbon sulfur and iron sulfur ratios although showing considerable scatter suggest that bottom waters at this time were locally euxinic containing free hydrogen sulfide this oceanic anoxic event was preceded by significant faunal turnover of ammonites in tethys and accompanied by widespread extinction of benthos in northern europe in response to the lateral spread of anoxic bottom waters during transgression similar changes may be recognized in other parts of the world other anoxic events may have taken place during the jurassic but documentation is as yet meagre furthermore models for such phenomena remain largely speculative although upwelling and increased planktonic productivity commencing in pre toarcian time are favored for the falciferum zone event documented here from author

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

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

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

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

early turonian pelagic sedimentation at moria umbria marche italy primary and diagenetic controls on lithological oscillations abstract the upper cretaceous of the umbria marche basin italy consists of an alternation of calcareous and siliceous fine grained sedimentary rocks in which the calcareous lithologies are predominant the cenomanian succession is dominated by white micritic limestones and contains a black shale horizon bonarelli level in its uppermost part which is the regional expression of oceanic anoxic event 2 in the turonian the rocks gradually become red upwards and are referred to as cretaceous oceanic red beds the lithological variability in the succession reflects the local response of sedimentary systems to varying local and global environmental conditions in this study local processes behind the transition from black shale to red bed deposition and in particular behind lithological oscillations within the lowermost turonian are studied and placed in their global context sediment colour composition geochemistry and nannofossil content were studied using samples of the scaglia formation at moria umbria marche basin the results show that following the cenomanian turonian boundary terrigenous input decreased and its composition was different in calcareous and siliceous oozes organic productivity was high during the deposition of siliceous ooze due to upwelling and varied on orbital timescales the alternation between the siliceous and calcareous ooze was further controlled by carbonate dissolution small fluctuations in the calcite compensation depth ccd had a significant impact on sediment composition because depositional depth was between the lysocline and the ccd diagenesis resulted in the segregation of carbonate and silica in the concentration of terrigenous material in smarl interbeds and in the enhancement of bedding after the earliest turonian ocean circulation patterns changed seawater temperatures declined slowly and seawater became better oxygenated productivity and terrigenous input also declined and the resulting combination of oxygen demand in the sediments and sedimentation rates favoured the formation of authigenic haematite in the sediments which led to their reddening

chemostratigraphy versus biostratigraphy data from around the cenomanian turonian boundary a detailed isotopic profile is presented for a stratigraphically expanded cenomanian turonian boundary section in chalk facies exposed at eastbourne sussex and compared with data from pueblo colorado in both sections macro and micropalaeontological markers first appearances and disappearances are well constrained and their relative positions and relationship to the structure of the carbon isotope curve are identical this consistent relationship between two independent phenomena one geochemical the other biostratigraphical is taken as evidence for the likely synchroneity of both the biostratigraphical markers and the carbon isotope excursion in these two areas this interpretation contrasts with suggestions made recently by other authors whose data have been taken to imply a lack of correlation between the carbon isotope excursion in europe and north america

black shale deposition on the northwest african shelf during the cenomanian turonian oceanic anoxic event climate coupling and global organic carbon burial high resolution geochemical records from a depth transect through the cenomanian turonian c t tarfaya basin northwest african shelf reveal high amplitude fluctuations in accumulation rates of organic carbon oc redox sensitive and sulphide forming trace metals and biomarkers indicative of photic zone euxinia these fluctuations are in general coeval and thus imply a strong relationship of oc burial and water column redox conditions the pacing and regularity of the records and the absence of a prominent continental signature suggest a dynamic depositional setting linked to orbital and higher frequency forcing determining the dominant frequency depends on the definition of the most pronounced oceanic anoxic event oae2 and its duration we propose that eccentricity is the main forcing factor at tarfaya and controlled fluctuations in wind driven upwelling of nutrient rich oxygen depleted intermediate waters from the adjacent atlantic and the periodic development of photic zone and bottom water euxinia on the mid cretaceous northwest african shelf accumulation records clearly identify the basin center as the primary site of sediment deposition with highest temporal variability and an up to six fold increase in oc burial from similar to2 g m 2 yr prior to the oae2 to similar to12 g m 2 yr during the oae2 photic zone and bottom water euxinia alternated with periods of greater oxygenation of the water column in response to climate forcing mass balance calculations imply that similar to2 of the overall global excess oc burial associated with the oae2 was deposited in the tarfaya basin an area that represented only similar to0 05 of the total global c t ocean floor in fact the lateral extent of similar black shales along the african continental margin indicates that this part of the ocean contributed significantly to the global increase in organic carbon burial during the oae2

the middle cenomanian event in the equatorial atlantic the calcareous nannofossil and benthic foraminiferal response abstract in addition to oceanic anoxic event 2 oae2 other perturbations of the carbon cycle occurred during the cenomanian and turonian of which the middle cenomanian event mce is the most prominent one in palaeoecological publications however this event is strongly underrepresented in contrast to the well studied oae2 in order to fill this gap we have studied early cenomanian to late turonian calcareous nannofossil and benthic foraminiferal assemblages of ocean drilling program site 1260 at demerara rise western equatorial north atlantic in order to decipher biotic changes throughout this interval and especially across the mce our data show distinctive changes in the relative abundance of certain calcareous nannofossil taxa and a drastic decrease in benthic foraminiferal diversities and abundances associated with the mce in the lower part of the studied section and prior to the mce a mixed water column with high nutrient availability in the upper photic zone is suggested based on very high relative abundances of the mesotrophic eutrophic nannofossil species biscutum constans around the mce interval certain nannofossil taxa e g rhagodiscus asper show a distinctive decrease in relative abundance while others become more dominant taxa which increase in relative abundance after the mce e g eprolithus floralis are interpreted as either having favoured less eutrophic surface waters or having inhabited deeper parts of the photic zone in a well stratified water column this interpretation is supported by published oxygen isotope and tex86 data which suggest increased water column stratification starting with the mce and lasting to the end of the cenomanian stage as a result of the implementation of a saline intermediate to deep water mass during this interval our study shows that the mce was a significant biotic event in the cenomanian turonian equatorial atlantic characterised by a lasting change of surface and bottom water ecosystems

major and trace element characterization of oceanic anoxic event 1d oae 1d insight from the umbria marche basin central italy abstract the pialli level in the umbria marche basin central italy correlates with the lowermost part of the positive carbon isotopic excursion characterizing the late albian early cenomanian oceanic anoxic event 1d oae 1d high resolution litho bio and chemostratigraphic data from the monte petrano and le brecce sections allow for a bed by bed comparison of the two successions and discriminate local from basin scale signals we present new x ray fluorescence icp ms and toc data for both the limestones and the pialli level shales integrated with available carbonate carbon isotopes and nannofossil temperature and nutrient indices data indicate a homogenous background sedimentation dominated by pelagic carbonates biogenic silica with little contribution by clays the limited variation in lithogenic elements points to an essentially homogeneous detrital source area with limited fluvial terrigenous input higher mn concentrations coupled with low enrichments in redox sensitive elements such as u fe s re mo ag suggest that the pialli level shales represent temporary suboxia without reaching anoxia furthermore p authigenic ba cd and ni enrichments together with nannofossil nutrient index indicate generally low primary productivity conditions along the entire succession with only minor increases for some of the black to dark grey shales of the pialli level the nannofossil temperature index highlights a warm climate during the oae 1d with the warmest conditions experienced during the deposition of the pialli level shales during the late albian the warm and humid climate was interrupted by brief episodes of relatively warmer and less saline surface waters ensuring slower rates of bottom water renewal and producing temporary suboxic conditions such paleoceanographic dynamics would be the continuation of episodic warmer and humid pulses characterizing the late albian interval in the umbria marche basin as such the pialli level can be considered the result of a last episode closing a cycle before the establishment of a steadier climate during the early cenomanian

the cenomanian turonian boundary event on the moroccan atlantic margin agadir basin stable isotope and sequence stratigraphy abstract correlations of four sections constrained by stable isotope stratigraphy and micropalaeontology along a 80 km long e w oriented transect from the western high atlas to the present day coast taghazoute show that the cenomanian turonian boundary event ctbe occurred within shallow water oyster bearing limestones and marls and not in the overlying black shale the age of the laminated shale is early turonian as the planktonic marker helvetoglobotruncana helvetica is found from its first centimetres upward the underlying deposits hosting the ctbe event are bounded by two unconformities interpreted as emersion surfaces and represent the strongest seawardshifts of facies in the local cenomanian sedimentary wedge the 13 c anomaly is only recorded in the coastal taghazoute section not in other sections landward meaning that the ctbe occurred here during a short transgressive phase within an overall regressive trend the lower turonian black shale of the taghazoute section is transgressive onto the second unconformity and pass landward to white evenly laminated chert bearing mudstones then to bioturbated mudstones in the easternmost sections of the transect western high atlas

palaeoenvironmental evolution of the late cretaceous sequence in the tarfaya basin southwest of morocco abstract the late cretaceous sedimentary evolution of the tarfaya basin is reviewed based on late albian campanian outcrops and two cored exploration wells s13 and s75 with a stratigraphic range from the early cenomanian to the late turonian standard sedimentological and micropalaeontological methods were used together with clay mineralogy and organic geochemistry two distinct depositional environments were found the first is late albian early middle cenomanian in age and dominated by terrigenous silici and bioclastic sediments containing primarily terrestrial organic matter with a low organic content abundant illite and chlorite eroded from crystalline rocks outcropping in the anti atlas mountain and mauritanides is present as is abundant kaolinite reworked from soils surrounding the tarfaya basin the second environment comprises late cenomanian campanian sediments characterized by pelagic marls and limestones with a high organic content and a abundant pelagic macro and microfauna these sediments which were probably deposited in an upwelling system are characterized by higher contents of smectite

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