nonexplosive and explosive magma wet sediment interaction during emplacement of eocene intrusions into cretaceous to eocene strata trans pecos igneous province west texas abstract eocene intrusion of alkaline basaltic to trachyandesitic magmas into unlithified upper cretaceous maastrichtian to eocene fluvial strata in part of the trans pecos igneous province in west texas produced an array of features recording both nonexplosive and explosive magma wet sediment interaction intrusive complexes with 40 ar 39 ar dates of 47 46 ma consist of coherent basalt peperite and disrupted sediment two of the complexes cutting cretaceous strata contain masses of conglomerate derived from eocene fluvial deposits that at the onset of intrusive activity would have been 400 500 m above the present level of exposure these intrusive complexes are inferred to be remnants of diatremes that fed maar volcanoes during an early stage of magmatism in this part of the trans pecos province disrupted cretaceous strata along diatreme margins record collapse of conduit walls during and after subsurface phreatomagmatic explosions eocene conglomerate slumped downward from higher levels during vent excavation coherent to pillowed basaltic intrusions emplaced at the close of explosive activity formed peperite within the conglomerate within disrupted cretaceous strata in the conduit walls and within inferred remnants of the phreatomagmatic slurry that filled the vents during explosive volcanism a younger series of intrusions with 40 ar 39 ar dates of 42 ma underwent nonexplosive interaction with upper cretaceous to paleocene mud and sand dikes and sills show fluidal billowed quenched margins against the host strata recording development of surface instabilities between magma and groundwater rich sediment accentuation of billowed margins resulted in propagation of intrusive pillows into the adjacent sediment more intense disruption and mingling of quenched magma with sediment locally produced fluidal and blocky peperite but sufficient volumes of pore fluid were not heated rapidly enough to generate phreatomagmatic explosions this work suggests that trans pecos texas may be an important locale for the study of subvolcanic phreatomagmatic processes and associated phenomena eocene intrusions in the study area underwent complex interactions with wet sediment at shallow levels beneath the surface in strata as old as maastrichtian which must have remained unlithified and rich in pore water for 20 25 ma

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

rhyolitic globular peperites from the aznalcollar mining district iberian pyrite belt spain physical and chemical controls abstract globular peperites are exposed along the aznalcollar mining district iberian pyrite belt ipb spain these rocks originated by mingling of a low viscosity rhyolitic sill with unlithified wet sediments highly amygdaloidal up to 80 vol millimeters to centimeters across rhyolite globules extend from the upper contact of the sill for several centimeters into fine grained volcaniclastic host rocks the sill is very similar to other rhyolites in the ipb in terms of petrography and chemistry it is aphyric to very sparsely quartz phyric with small quartz phenocrysts vesicularity has been measured in the sill as vesicle area fraction determined by point counting over a rectangular grid and number density per unit area determined by counting every vesicle within the grid area amygdale distribution measured within the sill indicates a process by which vesicles migrated vertically from the lower portions of the sill to the roof zone we suggest that this migration process caused local density changes large enough to allow the rhyolitic magma to become buoyant enough to move through the overlying sediments producing globular peperites globular structures are preserved when rhyolite globules entered the wet sediment

magma sediment mingling in an ordovician rift basin the plouezec plourivo half graben armorican massif france the plouezec plourivo basin ppb armorican massif is an ordovician half graben filled with red bed deposits lying on a cadomian metamorphic basement peperites crop out along its northeast coastal sector in connection with diverse magmatic and hydrothermal products combining field structural observations and geochemical analyses of magmatic rocks leads us to propose a model of emplacement of peperites in an extensional setting the ppb peperites result from mingling between magma and initially wet sediment the main corresponding facies consist of rounded magmatic bodies corrugated lava sediment contacts and a remarkable thin sheet of fluidized sediment extending over about 100 m parallel and c 10 cm above the base of a porphyritic lava flow a few ppb peperites formed under a dominant brittle regime are autoclastic breccias at the base of a lava flow and polymict breccias including both fluidal and blocky volcanic clasts sediment fluidization formation of vapor films magma sediment density contrasts and non explosive fragmentation are the main mechanisms invoked to generate the ppb peperites the c 100 m extended sediment derived sheet lying near the base of a lava flow likely formed by diapiric rise of fluidized sediment through molten lava we show that silicic contamination accompanied these peperitic processes

geochemistry of cretaceous oceanic red beds a synthesis abstract this paper summarizes the geochemistry of cretaceous oceanic red beds corbs their depositional conditions and their significance in reconstructing marine environments we report major and minor element compositions of carbonate clayey and siliceous corbs and compare these with average element compositions of carbonates deep sea carbonates deep sea clays and average shale compositions element distributions in carbonate corbs are mostly similar to average carbonate compositions in particular sr concentrations are more comparable to average carbonates than deep sea carbonate sr concentrations clayey corbs are high in al ti k and fe their minor element compositions are more similar to average shale than deep sea clay which generally has higher values in minor elements in comparison siliceous corbs have at least two times lower al but higher si concentrations than clayey corbs we further speculate on possible reactions involved in iron mobilization and corb formation

mid cretaceous oceanic red beds in the umbria marche basin central italy constraints on paleoceanography and paleoclimate abstract detailed studies of the mid cretaceous sedimentary strata in the umbria marche basin in italy revealed that aside from several well known organic rich black shale horizons that record oaes several varicolored mainly reddish horizons indicate oxic conditions at the ocean bottom eight such horizons have been identified in aptian cenomanian sequences in the umbria marche basin the dysoxic oxic beds alternate regularly but not cyclically and seem to be the result of non random processes their occurrence is not a completely random process the duration of deposition of these oceanic red beds orbs varies from 0 13 my orb4 recorded in the ticinella primula zone to 4 54 my for orb1 which spans the globigerinelloides ferreolensis zone to the ticinella bejaouaensis zone in the piobbico core mid cretaceous orbs are not a local phenomenon because they occur in the tethyan deposits in the southern and austrian alps the carpathians the northern caucasus the central north atlantic in northeastern england and in the western himalayas they provide evidence for periodic changes in redox conditions at the ocean bottom such changes could have been caused by changes in bioproductivity basin geometry sedimentation rates paleocirculation and or production of bottom waters with higher content of dissolved oxygen in response to changes in paleoclimate we suggest that the periodic inflow of colder more oxygenated bottom waters was the probable cause of orbs development either as a result of changes in the ocean bottom topography or as a result of brief cool climate periods however reliable proxies for changes in deep ocean circulation are still lacking if orbs were the result of the paleoclimate and therefore indirectly caused by changes in co2 in atmosphere they document the increased sensitivity and instability of the mid cretaceous climate thus changes in ocean dynamics were on a scale of several hundred thousand years to several million years which has not been considered by most theories of co2 cycling mid cretaceous greenhouse paleoclimate and paleocean dynamics

lithofacies microfacies and depositional environments of upper cretaceous oceanic red beds chuangde formation in southern tibet the gyangze basin located in southern tibet is one of the representative areas for cretaceous oceanic red beds corbs we investigated and inter correlated several new corb outcrops in the western and southeastern part of the gyangze area in addition to the previously described chuangde section the corbs in the gyangze basin mainly consist of shales thin bedded marls re sedimented limestones and clasts supported conglomerates breccias planktonic foraminifers in the carbonate rocks within corbs belong to the globotruncana ventricosa and globotruncanita calcarata zones indicative of middle campanian age the facies assemblages in the different sections indicate that the depositional environments of corbs range from outer base of slope apron to basin zones within carbonates we observed microfacies types characteristic of basin open deep shelf margin or toe of slope environments gravity transport resulted from the steepening of the sea floor in the gyangze basin owing to subduction during the campanian relatively oxic bottom water conditions prevailed below the toe of slope environment in the gyangze basin during corb deposition however the presence of gray clasts within a multicoloured matrix suggests less oxic conditions at shallower water depths within the basin c 2010 elsevier b v all rights reserved

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

water magma interaction some theory and experiments on peperite formation experiments using molten thermite as a magma analog produce peperite when the melt interacts with wet sand these experiments also show explosive behavior developing strombolian and surtseyan like bursts the results demonstrate that the application of fuel coolant interaction fci theory is appropriate for interpretation of peperites the theory described includes discussion of the importance of mass interaction ratios of wet sediment and magma rs which determine thermal equilibrium temperature limits and contact interface dynamics the dynamics of the interface between magma and wet sediments involves heat transfer over a wide range of rates from passive quenching to explosive fragmentation a vapor film layer develops at the interface and acts both as an insulating barrier promoting passive quenching as well as a potential energy reservoir that can cause magma fragmentation mingling of the magma with wet sediments and explosive quenching when the vapor film becomes unstable an important parameter in determining the behavior of the vapor film is the value of rs which controls whether heat can be convectively removed from the layer as more is being added from its contact with magma if rs 1 for fully saturated sediments there is enough water in the sediments to make convective heat flow effective in quenching the magma but below that value there is the potential that the vapor film will be unstable producing highly dynamic phenomena including explosive fragmentation at values of rs 0 1 there is insufficient water to allow the escalation of explosive fragmentation

carbon sequestration activated by a volcanic co 2 pulse during ocean anoxic event 2 ninety four million years ago during ocean anoxic event 2 there was a marked increase in the burial of organic carbon in marine sediments measurements of stomata in fossil leaves show that the two main pulses of carbon burial were associated with a decline in atmospheric co2 levels of up to 26 the cretaceous ocean anoxic event 2 about 94 million years ago is thought to be linked to extensive volcanism which triggered a biogeochemical chain of events that eventually led to widespread marine anoxia and a remarkable increase in carbon burial in marine sediments1 2 3 it has been suggested that the event was accompanied by a substantial decrease in atmospheric co2 concentrations4 but the quantification of the drawdown remains controversial5 6 here we reconstruct atmospheric co2 concentrations throughout the ocean anoxic event from counts of the stomata in fossil leaves and use terrestrial carbon isotopes to link the reconstruction to marine records of the event7 8 we find that before the onset of ocean anoxia atmospheric co2 concentrations increased by 20 over background levels of 370 100 70 ppm this was part of a long term rise in atmospheric co2 levels presumably caused by volcanism which reached a peak of 500 400 180 ppm however two pulses of extensive carbon burial during the ocean anoxic event as indicated by positive carbon isotope excursions are associated with decreased atmospheric co2 concentrations we conclude that the sequestration of marine organic carbon led to a decrease in atmospheric co2 concentration of up to 26 during ocean anoxic event 2

cretaceous sedimentation in the outer eastern carpathians implications for the facies model reconstruction of the moldavide basin abstract the mid cretaceous is characterized by high eustatic sea levels with widespread oxic conditions that made possible the occurrence of globally correlated oceanic red beds however very often these eustatic signals have been overprinted by local tectonics which in turn resulted in lower cretaceous closed and anoxic basins as in the eastern carpathians there the black shale to red bed transition occurs in the latest albian up to the early cenomanian although earlier studies discussed the large scale basin configuration no detailed petrography and sedimentology study has been performed in the eastern carpathians this paper describes the hauterivian to turonian lithofacies and interprets the depositional settings based on their sedimentological features the studied sections crop out only in tectonic half windows of the eastern carpathians part of the vrancea nappe the lithofacies comprises black shales interbedded with siderites and sandstones calcarenites marls radiolarites and red shales the siliciclastic muddy lithofacies in general reflects accumulation by suspension settling of pelagites and hemipelagites in anoxic black shale to dysoxic dark gray and gray to green shales and oxic red shales conditions the radiolarites alternate with siliceous shales and are considered as evidence of climate changes the sandstones represent mostly low and high density turbidite currents in deep marine lobes as well as channel levee systems the source area is an eastern one e g the eastern carpathians foreland given the abundance of low grade metamorphic clasts the hauterivian lower albian sediments are interpreted as deep marine linear and multiple sourced mud dominated systems deposited in a mainly anoxic to dysoxic basin the anoxic conditions existed in the early to late albian but sedimentation changed to a higher energy mud sand dominated submarine channels and levees this coarsening upwards tendency is interpreted as the effect of the aptian to albian compressional tectonics of the carpathians the deepening of the moldavide basin from the cenomanian is most probably linked to a significant sea level rise

albian pelagic rhythms piobbico core abstract the piobbico core of aptian albian pelagic rhythmites in italy has been used to explore ways of extracting quantitative time series of geological chemical physical and biological parameters from stratigraphic sequences recognition of the precession obliquity and eccentricity cycles the option frequencies has permitted time resolution to the 104 year level individually these time series curves furnish a potential basis for precise correlations collectively they track the evolution of the depositional system in detail including its response to orbital forcing orbital cycles primarily influenced oceanic fertility and carbonate productivity by foraminifera and coccoliths as well as the aeration of bottom waters redox cycle three short magnetic reversals occur w thin the ticinella praeticinensis zone frequency spectra of variations in magnetic intensity inclination and declination yield milankovitch frequencies which are only partly explained as responses to mineralogy a computer simulation used berger s astronomically calculate precession index to drive 1 carbonate flux and 2 depth of bioturbation this achieved a stratigraphy remarkably similar to that observed each step in the computer simulation transfers spectral power from precession to eccentricity work on the piobbico core continues while project albicore aims to explore the patterns of rhythmicity in the praeticinensis zone of other areas end page 1164

magma composition and viscosity as controls on peperite texture an example from passamaquoddy bay southeastern canada silurian mafic lava flows and rhyolite sills in the passamaquoddy bay area southeastern canada interacted with wet sediment to produce peperitic breccia the pahoehoe type mafic flows flowed over and bulldozed into wet unconsolidated silt and sand to produce both blocky and fluidal peperite at their lower contacts soft sediment deformation structures in the siltstone adjacent to the flows irregularly shaped vesicles in the siltstone and siltstone filled vesicles in the mafic lava all indicate the sediment was wet at the time of flow emplacement sills of rhyolite emplaced into the same sedimentary sequence also interacted with the wet sediment and produced peperite at both the upper and lower contacts evidence for the rhyolitic magma interacting with wet sediment includes sediment filled vesicles in rhyolite quartz filled vesicles in siltstone and angular non vesicular shards of rhyolite in clastic dykes peperite formed by this process is exclusively blocky the rhyolitic magma in the passamaquoddy bay sequence and other examples of high viscosity magma producing only blocky peperite suggest that in contrast to low viscosity magmas which produce a combination of blocky and fluidal peperite only blocky peperite will form associated with highly viscous rhyolite magma the sediment that interacted with both the mafic and rhyolitic lavas is of similar texture indicating that in this case sediment texture did not control peperite type the change from fluidal to blocky peperite texture may also be controlled in part by the magma temperature and or confining pressure and the generation and maintenance of a steam film at the magma wet sediment interface

turonian oceanic red beds in the eastern alps concepts for palaeoceanographic changes in the mediterranean tethys abstract several transitions of lower to middle turonian pelagic marl limestone cycles into oceanic red beds were studied at high resolution to gain a better understanding of the tethyan marine system before and during red bed initiation and development samples were analysed for mineralogy geochemistry and stable isotope composition in particular carbonate geochemistry of diagenetically largely unaltered calcite was used to explore palaeoceanographic changes in the western tethys principal component analysis of carbonate chemical data showed that the development of red coloured pelagic sediments is accompanied by a shift towards highly oligotrophic conditions in the surface ocean as well as a decrease in hydrothermal activity the formation of red beds is most likely associated with a shift towards more oxic conditions in basins with black shale deposits that eventually resulted in enrichment of thiophile elements in the entire basin depletion in nutrients most likely phosphate and red bed deposition followed the maximum flooding in the early turonian highly productive marsh areas from the proximal european shelf were reworked and supplied nutrients during transgression a gradual nutrient depletion during sea level highstand might be the cause of significantly diminished nutrient availability carbonate production in this low latitude setting was influenced by orbital variation in insolation 20 ka cycle stable carbon isotope stratigraphy reveals low sedimentation rates between 1 and 7 mm kyr and a duration of episodes of cretaceous oceanic red bed deposition between 30 and 360 kyrs

astronomical tuning of the aptian stage from italian reference sections a high resolution grayscale series of the pelagic fucoid marls piobbico core central italy shows strong pervasive lithological rhythms throughout the aptian interval a hierarchy of centimeter to meter scale cycles characterizes the rhythms when calibrating 1 m cycles to earth s 405 k y orbital eccentricity cycle these rhythms correspond to the periods of the eccentricity obliquity and precession index tuning to orbital eccentricity cycles provides a high resolution time scale for the aptian correlation to the cismon core northern italy extends the tuning to the aptian barremian boundary the tuning indicates a minimum duration of 13 42 m y for the aptian stage where previous estimates range from 6 4 to 13 8 m y the combined aptian albian astronomical tuning of the entire 77 m long piobbico core and part of the cismon core provides a 25 85 m y long astronomically calibrated time scale for earth history

late cretaceous chronology of large rapid sea level changes glacioeustasy during the greenhouse world we provide a record of global sea level eustatic variations of the late cretaceous 99 65 ma greenhouse world ocean drilling program leg 174ax provided a record of 11 14 upper cretaceous sequences in the new jersey coastal plain that were dated by in tegrating sr isotopic stratigraphy and biostratigraphy backstripping yielded a late cre taceous eustatic estimate for these sequences taking into account sediment loading com paction paleowater depth and basin subsidence we show that late cretaceous sea level changes were large 25 m and rapid k1 m y suggesting a glacioeustatic control three large d 18 o increases are linked to sequence boundaries others lack sufficient d 18 o data consistent with a glacioeustatic cause and with the development of small 10 6 km 3 ephemeral ice sheets in antarctica our sequence boundaries correlate with sea level falls recorded by exxon production research and sections from northwest europe and russia indicating a global cause although the exxon record differs from backstripped estimates in amplitude and shape

high sea surface temperatures during the early cretaceous epoch the early cretaceous epoch about 145 100 million years ago is generally thought of as a greenhouse period with high atmospheric co2 concentrations1 and high global mean temperatures2 but evidence for episodes of cooler conditions and even transient glaciations has been proposed3 4 5 6 7 8 9 here we present sea surface temperature records spanning the period from 142 to 128 million years ago berriasian barremian ages from low and mid latitudes reconstructed using the tex86 palaeotemperature proxy during this period we find sea surface temperatures exceeding 32 c at 15 20 n and averaging 26 c at 53 s these temperatures substantially exceed modern temperatures at equivalent latitudes and are incompatible with the notion of consistently cooler conditions in the earliest cretaceous moreover we find little variability in the sea surface temperature records even during the valanginian carbon isotope excursion 138 135 million years ago which was thought to be associated with marked temperature fluctuations5 we conclude that the earliest cretaceous was characterized by a warm stable climate with a lower meridional temperature gradient than today

cretaceous anoxic oxic changes in the moldavids carpathians romania abstract this study focused on the cretaceous black shale successions followed by red shales that crop out at the outer regions of the romanian carpathians in the moldavids the oldest parts of the black shale units deposited in an abyssal plain during late valanginian late barremian time they are mainly characterized by hemipelagic and pelagic muddy siliciclastic rocks and carbonates commonly intercalated with fine grained turbidites during the sedimentation of the middle part of the black shale units in the late barremian early albian interval the depth of the basin increased as the carbonate hemipelagic sedimentation was replaced by a mainly siliceous one only a few thin turbidite intercalations are present the youngest part albian pro parte of the black shale units is characterized by a turbiditic sedimentation with mainly sandy sequences of middle and lower deep water fans we may assume that the depth of the basin continuously decreased the presence of authigenic glauconite in the albian sandstones suggests a palaeoenvironmental change linked to the occurrence of oxygenated turbidity current circulation a significant shift in the sedimentation regime in the eastern carpathian moldavids took place in the late albian when cretaceous oceanic red beds corb occurred this type of sedimentation lasted up to the coniacian the lower part of the corbs that contains radiolarites intercalated with variegated shales pyroclastic tuffs and thin sandstones is interpreted as a hemipelagic and pelagic sedimentation in the abyssal plain environment where rarely turbidites occurred upwards there are mainly burrowed variegated red and green shales the youngest parts of corbs are characterized by increased thickness and frequency of the turbidites while the main part of the corb is carbonate free or has very low carbonate content the upper part of these strata becomes rich in marl and mudstone strata indicating a decrease of the basin depth the accumulation of black shales in the eastern carpathians during the late valanginian late albian interval is linked to the existence of a small silled basin of the moldavian trough in which restricted circulation led to the density stratification of the water column resulting in the deposition of anoxic lower cretaceous sediments i e the black shales because of the tectonic deformation that took place within the lower upper cretaceous boundary interval the restricted circulation had changed to an open circulation regime in the moldavian trough hence the anoxic regime was progressively replaced by an oxic one across the albian cenomanian boundary interval the beginning and the end of the corbs in the moldavid units depend thus on various palaeogeographic and palaeoenvironmental settings and it was controlled by the regional tectonic activity

transient global cooling at the onset of early aptian oceanic anoxic event oae 1a the onset of the early aptian oceanic anoxic event oae 1a ca 120 ma coincided with a major perturbation of the carbon cycle which is reflected in the sedimentary carbon isotope record triggering mechanisms duration and climatic repercussions of this episode of accelerated organic matter burial remain poorly constrained here we present millennial scale bulk rock carbon and oxygen isotope data from a marly subtropical intrashelf basin la bedoule southeast france with unusually high sedimentation rates which track the onset of oae1a in unprecedented resolution our record reveals that the negative low amplitude delta 13 c excursion preceding oae1a lasted 100 k y implying that enhanced volcanic co 2 emission and or pulsed methane dissociation over a prolonged time span were instrumental in triggering oae1a the main positive carbon isotope shift at the onset of oae1a previously regarded as continuous occurred stepwise over an extended period of 300 k y transient climate cooling during the initial delta 13 c increase probably reflects ephemeral high latitude glaciation triggered by changes in radiative forcing and drawdown of atmospheric co 2

new oxygen isotope evidence for long term cretaceous climatic change in the southern hemisphere a new composite 18 o record generated from calcareous fine fraction and bulk sediments from the exmouth plateau details long term cretaceous climatic change at mid latitudes in the southern hemisphere assessment of new and previously published 18 o data indicates that a mid cretaceous global climatic optimum was achieved sometime between the time of the cenomanian turonian boundary and the middle turonian when surface ocean paleotemperatures were the highest of the past 115 m y periods of cooling and warming that reversed the general patterns were superimposed on long term aptian turonian warming and turonian maastrichtian cooling trends respectively extrapolation of southern hemisphere paleotemperature trends to maastrichtian paleotemperature data from a low latitude pacific guyot implies that maximum mid cretaceous low latitude paleotemperatures could have been in excess of 33 c

aeromagnetic mapping of the structure of pine canyon caldera and chisos mountains intrusion big bend national park texas analysis of aeromagnetic and gravity data reveals new details of the structure igneous geology and temporal evolution of the prominent enigmatic ca 32 ma pine canyon caldera and the chisos mountains big bend national park texas the main caldera fi lling pine canyon rhyolite the oldest member of the south rim formation is reversely magnetized allowing it to be used as a key marker bed for determining caldera fi ll thickness modeling of gravity and magnetic anomalies indicates that the pine canyon rhyolite is probably thicker in the northeastern part of the caldera lineaments in the magnetic data suggest the presence of buried faults beneath the caldera that may have led to increased downdrop in the northeast versus the southwest allowing a thicker section of caldera fi ll to accumulate there the pine canyon caldera has been interpreted as a downsag caldera because it lacks surfi cial faulting so these inferred faults are the fi rst mapped features there that could be responsible for caldera collapse the caldera boundary correlates well with the margins of a gravity low general features of the caldera match well with basic models of downsag calderas meaning that the pine canyon caldera may be a classic example of downsagging of which few well described examples exist in terms of a geophysical signature the source of a long wavelength magnetic high over the chisos mountains is interpreted as a previously unknown broad intrusion the long axis of which trends parallel to a major crustal boundary related to the ouachita orogeny or an even earlier precambrian margin this feature represents the largest intrusion 28 34 km diameter 1 4 km thick 700 3000 km 3 in volume in an area where relatively small laccoliths are ubiquitous the intrusion most likely represents a long lived 1 m y reservoir replenished by small batches of magma of varying composition as refl ected in the variation of eruptive products from the pine canyon and sierra quemada calderas the intrusion may represent the easternmost occurrence of voluminous tertiary magmatism in the southwestern united states

trace metal remobilization in the interstitial waters of red clay and hemipelagic marine sediments interstitial water samples from the guatemala basin and the coast of baja california have been analyzed for manganese iron copper nickel and nitrate the data provide a systematic look at changes in trace metal diagenesis proceeding from red clay to highly reducing nearshore sediments in red clay sediments the nitrate concentrations suggest that only aerobic respiration is occurring manganese and iron are below detection nickel concentrations remain the same as in bottom seawater but copper shows a pronounced maximum just at the sediment water interface proceeding to hemipelagic sediments denitrification becomes increasingly important and manganese and iron remobilization occur in the sediments the linear manganese and nitrate profiles suggest regions of production or consumption separated by zones of diffusion this differs from the conventional picture of a continuous series of reactions within the sediments manganese reduction always occurs before iron reduction the pore water nickel correlates well with manganese in these sediments suggesting that nickel is associated with mno2 in the solid phase the pore water flux ratio of manganese and nickel agrees well with the ratio in solid phase authigenic oxides copper still displays a core top concentration maximum as well as a second maximum associated with the remobilized manganese the calculated ratio of the cu c flux ratios support the argument for copper remobilization during organic carbon oxidation comparison of the upward and downward diffusive fluxes with the rate of copper buried by sedimentation shows that at least half of the copper buried must be of diagenetic origin and less than 25 of the copper reaching the sediments is buried

variation in peperite textures associated with differing host sediment properties peperites formed by mixing of magma and wet sediment are well exposed along punta china baja california mexico where two sills intrude a section of lava flows limestones and volcaniclastic rocks irregular lobes and dikes extend from the sills several meters into host sediments including highly comminuted flow top breccias lithic lapilli tuff breccias and shelly micrites whereas intrusive contacts with lava flows are sharp and planar where one sill intruded both coarse grained volcaniclastic rock and fine grained limestone textural differences between the hosts produced strikingly different styles of peperite blocky masses of the basaltic intrusions up to 1 m in size were dispersed for distances up to 3 m into host lithic lapilli tuff breccias the blocks consequently underwent in situ fragmentation as they were rapidly quenched the high degree of dispersion resulted from steam explosions as the magma enveloped pockets of water in the coarse grained permeable host elutriation of fine grained material from vertical pipes in tuff breccia above the lower sill provides evidence for meter scale fluidization of the host the contact zone between the basaltic magma and the shelly micrite host resembles a mixture of two viscous immiscible fluids fluidal peperite intrusion occurred behind a stable vapor film which entrained lime mud particles and carried them off grain by grain as magma advanced into the host thin section scale elutriation pipes formed microglobular peperite represents a frozen example of a fuel coolant interaction fci between basaltic magma and fluidized micrite host the intimate intermixing of magma and host at the submillimeter level is attributed to fluid instabilities developed along the magma vapor host interface such intimate intermixing of magma and water bearing fragmental debris is commonly a precursory step toward explosive hydrovolcanism

the former presence of organic matter caused its later absence burn down of organic matter in oceanic red beds enhanced by bioturbation eocene variegated shale carpathians eocene oceanic red beds that formed in a well oxygenated setting at low sedimentation rates below the calcite compensation depth are effectively barren of organic carbon in the present state recurrent distal low erosive turbidites preserve the bioturbated zone underneath that documents seasonal and long term fluctuating accumulation of considerable amounts of organic matter on the sea floor as evidenced by scolicia the producers of this trace fossil exploited nutritious organic matter conserved in turbidite buried sea floor deposits over the long term slow average sedimentation of hemi pelagic oxic red mud led to long oxygen exposure times and low burial of organic matter consequently trace fossils representing persistent sediment feeding modes are of small size although the food limited setting appears appropriate for producers of graphoglyptids such stationary burrows have not been encountered because seasonal deposition of organic matter fostered at least temporary surface layer feeding organisms for instance producers of nereites irregularis that intensively reworked the sediment and hence hindered graphoglyptid production these findings confirm palaeoceanographic modelling results that suggest upwelling in the study area during the eocene this article is protected by copyright all rights reserved

causes of oxic anoxic changes in cretaceous marine environments and their implications for earth systems an introduction abstract this special issue originated from a session at the 33th international geological congress oslo norway in august 2008 causes of oxic anoxic changes in cretaceous marine and non marine environments and their implications for earth systems igcp 463 and 555 convened by chengshan wang michael wagreich and bradley sageman the session aimed at bringing together contributions that shed light on the anoxic to oxic changes in the world oceans during the cretaceous including discussion on consequences for today s global change

progressive palaeoenvironmental change during the late barremian early aptian as prelude to oceanic anoxic event 1a evidence from the gorgo a cerbara section umbria marche basin central italy abstract during oceanic anoxic event 1a oae 1a 120 ma li et al 2008 organic carbon rich layers were deposited in marine environments under anoxic conditions on a global scale in this study palaeoenvironmental conditions leading to this event are characterised by studying the upper barremian to the lower aptian succession of the gorgo a cerbara section central italy for this an integrated multi proxy approach 13ccarb 13corg 18o phosphorus total organic carbon toc bulk rock mineralogy as well as redox sensitive trace elements rstes has been applied during the late barremian thin organic rich layers occur episodically and associated corg ptot ratios indicate the presence of intermittent dysoxic to anoxic conditions coarse correlations are observed between toc p and biogenic silica contents indicating links between p availability productivity and toc preservation however the corresponding 13ccarb and 18o records remain quite stable indicating that these brief periods of enhanced toc preservation did not have sufficient impact on the marine carbon reservoir to deviate 13c records around the barremian aptian boundary toc enriched layers become more frequent these layers correlate with negative excursions in the 13ccarb and 13corg records possibly due to a warming period as indicated by the 18o record during the earliest aptian this warming trend is reverted into a cooling trend which is then followed by an important warming step near the onset of oceanic anoxic event 1a oae 1a during this time period organic rich intervals occur which are characterised by the progressive increase in rste the warming step prior the onset of oae 1a is associated with the well known negative spike in 13ccarb and 13corg records an important peak in p accumulation rste enrichments and corg ptot ratios indicating the prevalence of anoxic conditions the selli level itself may document a cooling phase rste enrichments and corg ptot ratios confirm the importance of anoxic conditions during oae 1a at this site the gorgo a cerbara section is interpreted to reflect the progressive impact of palaeoenvironmental change related to the formation of the ontong java plate basalt plateau which started already around the barremian aptian boundary and culminated into oae 1a

the disappearance of the ammonitico rosso abstract results of the research for the reconstruction of the tethys paleoenvironments show that the ammonitico rosso disappeared in the late berriasian no typical analogues have been recorded so far in younger levels the ammonitico rosso basically developed during the rifting of the continental margins pointing up the phases of the tethys opening it is found on tilted block tops and slopes as well as in the related basins the ammonitico rosso developed especially in areas characterized by a complex paleogeography such as apulia or southern iberia few occurrences are reported from the central atlantic margins although the information is scarce and only available by deep sea drilling cores the maps 1 20 000 000 of middle toarcian early kimmeridgian and late tithonian paleoenvironments of the tethys illustrate the gradual disappearance of this characteristic facies this disappearance in the berriasian is correlated with 1 the increase of biogenic e g the bloom of nannoplankton and clastic sediment supply development of flysch facies 2 the establishment of an oceanic circulation which was not suitable for the ar formation from the himalayan branch of the tethys to the caribbean 3 the end of the rifting of the western tethys continental margins around late jurassic early cretaceous times which began to sink because of thermal subsidence 4 the evolution of oceanic chemistry however these factors were controlled by the global paleogeographic evolution the tethys ocean occupied a triangle shaped area bounded by huge continental masses situated in roughly tropical latitudes the gradual fragmentation of pangaea and cretaceous tertiary continental collisions definitely modified the global paleogeography never again producing this kind of ocean

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

permian triassic boundary interval in the abadeh section of iran with implications for mass extinction part 1 sedimentology the uppermost permian strata of the abadeh section in iran consist of 56 m of skeletal limestone abadehian that grades upward into 18 m of grey bioturbated lime mudstone djulfian which in turn grades upward to 18 m of red nodular wackestone dorashamian containing an abundant pelagic fauna the overlying lowermost triassic includes two enigmatic layers at its base immediately above the boundary is a 1 m thick layer of inorganically precipitated synsedimentary carbonate cement the cement is composed of 10 20 cm long crystals oriented either perpendicular to the bedding or as dome shaped features resembling botryoids about 0 5 m of wackestone overlies the cement layer the second layer is a 1 5 m thick grainstone overlying the cement horizon and consists of recrystallised spherical grains ooids or peloids the remainder of unit a is composed of 100 m of grey bioturbated to nodular lime mudstone the lithofacies succession of the uppermost permian is interpreted to represent deposition under increasing water depth related to rising of relative sea level which led to drowning of the carbonate platform to below storm wave base sedimentologic characteristics lithology wide distribution and slow sedimentation rates indicate that strata immediately below the permian triassic p t boundary dorashamian interval were deposited in deep oxygenated waters the enigmatic lowermost triassic synsedimentary carbonate cement and grainstone layers are interpreted to have been deposited in shallow waters indicating a rapid and major drop in relative sea level at the end of permian time in this area followed by a relative sea level rise during the earliest triassic precipitation of synsedimentary cement immediately above the p t boundary in iran and elsewhere south china suggests a global change in ocean chemistry one possible explanation is that dissolved calcium and bicarbonate concentrations in seawater increased sufficiently to promote spontaneous carbonate precipitation a rare event in the phanerozoic but common during precambrian time alternatively a massive heating event could have resulted in co2 degassing and decreases in oceanic carbonate solubility both leading to inorganic synsedimentary carbonate precipitation inorganic precipitation of synsedimentary carbonate cement may indicate that biochemical production of carbonate was halted due to the p t boundary events our study indicates that shallow and moderately deep waters during the latest permian were well oxygenated in the open ocean setting of the central tethys sea in iran therefore p t mass extinction scenarios that invoke upon widespread marine anoxia should be viewed with caution

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

mid cretaceous albian santonian sea surface temperature record of the tropical atlantic ocean paleoclimate records of geologic time periods characterized by extreme global warmth such as the mid cretaceous are important for a better understanding of the earth9s climate system operating in an exceptionally warm mode here we applied an organic geochemical proxy tex 86 on organic matter rich albian santonian sediments recovered from ocean drilling program leg 207 sites 1258 and 1259 on demerara rise to reconstruct sea surface temperatures ssts in the western equatorial atlantic preceded by a stepwise cenomanian warming trend 31 35 c the onset of the cretaceous thermal maximum coincided here with the cenomanian turonian boundary event once established this extreme warm climate regime characterized by averaged tropical ssts close to 35 c lasted up to the turonian coniacian transition two pronounced cooler intervals 2 3 c interrupt this otherwise remarkably stable record providing the first 18 o independent evidence for middle turonian cooling that previously has been attributed to glacioeustatic sea level lowering coniacian ssts decline stepwise reaching a minimum in the santonian 32 33 c where cooling is most pronounced presumably concomitant with the first progressive opening of a deep water passage through the equatorial atlantic gateway

isotopic evidence for glaciation during the cretaceous supergreenhouse the turonian 93 5 to 89 3 million years ago was one of the warmest periods of the phanerozoic eon with tropical sea surface temperatures over 35 c high amplitude sea level changes and positive 18 o excursions in marine limestones suggest that glaciation events may have punctuated this episode of extreme warmth new 18 o data from the tropical atlantic show synchronous shifts 91 2 million years ago for both the surface and deep ocean that are consistent with an approximately 200 000 year period of glaciation with ice sheets of about half the size of the modern antarctic ice cap even the prevailing supergreenhouse climate was not a barrier to the formation of large ice sheets calling into question the common assumption that the poles were always ice free during past periods of intense global warming

iron rich carbonate tidal deposits angepena formation south australia a redox stratified cryogenian basin abstract the cryogenian angepena formation ca 650 ma of south australia records deposition in a peritidal environment equivalent to and landward of the balcanoona reef complex and offers valuable insights into shallow marine chemistry during the nonglacial interlude between two global ice ages the sedimentary facies comprise an iron rich marine red bed succession and include red mudcracked dolomitic shales tepee dolostone crossbedded intraclastic ooid grainstone and tepee related sheet cavities with marine cements these facies are interpreted to have been deposited in a cryogenian tidal flat to subtidal setting that is laterally equivalent to the reefal and back reef environments of the balcanoona formation marine cements from this environment are characterized by well preserved non and bright cathodoluminescent zoning and strong negative to slightly positive cerium ce anomalies ce ce we suggest that the angepena formation is indicative of intermittent synsedimentary iron oxide precipitation in an oxidized peritidal environment in an otherwise strongly ferruginous and anoxic oceanic setting large negative ce anomalies develop over a narrower depth range when compared to modern oxic marine settings highlighting the importance of dissolved mn and fe concentrations in controlling the magnitude of the negative ce anomalies overall coupled sedimentological and geochemical evidence suggest a neoproterozoic shallow marine system at the interface of an oxidizing atmosphere and an anoxic ferruginous marine system

a co2 decrease driven cooling and increased latitudinal temperature gradient during the mid cretaceous oceanic anoxic event 2 article i nfo the mid cretaceous is thought to be a greenhouse world with significantly higher atmospheric pco2 and sea surface temperatures as well as a much flatter latitudinal thermal gradient compared to the present this time interval was punctuated by the cenomanian turonian oceanic anoxic event oae 2 93 5 myr ago an episode of global massive organic carbon burial that likely resulted in a large and abrupt pco2 decline however the climatic consequences of this pco2 drop are yet poorly constrained we determined the first high resolution sea surface temperature sst record across oae 2 from a deep marine sedimentary sequence at ocean drilling program odp site 1276 in the mid latitudinal newfoundland basin nw atlantic by employing the organic palaeothermometer tex86 we found that ssts across the oae 2 interval were extremely high but were punctuated by a remarkably large cooling 5 11 c which is synchronous with the 2 5 5 5 c cooling in sst records from equatorial atlantic sites and the plenus cold event because this global cooling event is concurrent with increased organic carbon burial it likely acted in response to the associated pco2 drop our findings imply a substantial increase in the latitudinal sst gradient in the proto north atlantic during this period of global cooling and reduced atmospheric pco2 suggesting a strong coupling between pco2 and latitudinal thermal gradients under greenhouse climate conditions

cretaceous oceanic red beds corbs different time scales and models of origin abstract the cretaceous oceanic red bed corb is a newly opened window on global oceanic and climate changes during the cretaceous greenhouse world as a result of the international geoscience programmes 463 494 and 555 2002 2010 corbs have been documented in many places by numerous publications the principle goal of this paper is to summarize scientific advances on corbs including chronostratigraphy sedimentology mineralogy elemental and isotopic geochemistry and their relationship to oceanic anoxic events oaes palaeoclimate and palaeoceanography we propose a new geochemical classification of the corbs using cao al 2 o 3 and sio 2 values which lithologically refer to marly clayey and cherty corbs respectively detailed mineralogical studies indicate that hematite goethite and mn 2 bearing calcite are the minerals imparting the red color of corbs hematite clusters of several to tens of nanometers in the calcite structure are the main cause of the red coloring of limestones and the mn 2 bearing calcite gives additional red color goethite was thought to form originally with hematite and was subsequently transformed to hematite during late diagenesis chronostratigraphic data allow the distinction of two groups of corbs by their durations short term corbs are generally less than 1 myr in duration and seem to be on the scale of milankovitch cycles during the deposition of cretaceous reddish intervals from odp cores 1049 and 1050 low primary productivity and relatively high surface temperature resulted in low organic carbon flux into the sediments which reduced oxygen demand and produced oxidizing early diagenetic conditions in such an oxic environment iron oxides formed imparting the reddish color the long term corbs depositional events lasted longer than 4 myr and may be a possible consequence of the oaes enhanced amounts of organic carbon and pyrite burial during and after the oaes would have resulted in a large and abrupt fall in atmospheric co 2 concentration which probably induced significant global climatic cooling during and after the oaes global cooling would have enhanced formation of cold deep water increasing its oxidizing capacity due to the greater content of dissolved oxygen and would promote formation of oceanic red beds sedimentological mineralogical and geochemical data indicate that corbs were deposited under highly oxic oligotrophic conditions probably at a low sedimentation rate the cretaceous red and white limestones from italy have similar compositions of terrestrial input sensitive elements al ti k mg rb zr higher contents of fe 2 o 3 and depleted redox sensitive elements v cr ni and u and micronutrient elements cu zn indicating similar provenance sources but red limestones were deposited under more oxic conditions at the sediment water interface than white limestones the cretaceous red shales such as those from the north atlantic and tibet have similar mineralogy and geochemistry as the late cenozoic red clays in the pacific ocean and the environment where both are formed was well oxidizing at a very low sedimentation rate we compiled seventeen published stratigraphic examples of phanerozoic oceanic red beds including the late cenozoic red clays in the pacific different hypotheses explain the origin of red pigmentation of limestones and shales including 1 detrital origin of iron derived from continental weathering 2 iron bacterial mediation at the time of sedimentation and 3 iron oxidation in oligotrophic highly oxic environment additional research on phanerozoic oceanic red beds is needed in order to better document their origin and palaeoceanographic and palaeoclimatic significance

interoceanic variation in the rare earth major and trace element depositional chemistry of chert perspectives gained from the dsdp and odp record rare earth element ree major and trace element abundances and relative fractionations in forty nodular cherts sampled by the deep sea drilling project dsdp and ocean drilling program odp indicate that the ree composition of chert records the interplay between terrigenous sources and scavenging from the local seawater major and non ree trace element ratios indicate that the aluminosilicate fraction within the chert is similar to nasc north american shale composite with average pacific chert including 7 nasc like particles indian chert 11 nasc atlantic chert 17 nasc and southern high latitude shl chert 53 nasc using la as a proxy for ree approximations of laex the amount of la in excess of that supplied by the detrital aluminosilicate fraction indicate that pacific chert contains the greatest laex 85 of latotal and shl chert the least 38 of latotal as shown by interelement associations this laex is most likely an adsorbed component onto aluminosilicate and phosphatic phases accordingly chert from the large pacific ocean where deposition occurs relatively removed from significant terrigenous input records a depositional ree signal dominated by adsorption of dissolved rees from seawater pacific chert cece 1 and lanybn 0 8 1 resulting from adsorption of local ce depleted seawater and preferential adsorption of lrees from seawater e g lanybn 0 4 which increases the lanybn ratio recorded in chert chert from the atlantic basin a moderately sized ocean basin lined by passive margins and with more terrigenous input than the pacific records a mix of adsorptive and terrigenous ree signals with moderately negative ce anomalies and lanybn ratios intermediate to those of the pacific and those of terrigenous input chert from the shl region is dominated by the large terrigenous input on the antarctic passive margin with inherited cece 1 and inherited lanybn values of 1 2 1 4 cece does not vary with age either throughout the entire data base or within a particular basin overall cece does not correlate with p2o5 concentrations even though phosphatic phases may be an important ree carrier this and previous studies of the large scale controlling parameters of sedimentary rees across ocean basins collectively indicate that ree indices of depositional regime e g cece lanybn laex are reproducible in a variety of sediment and rock lithologies ages and ocean basins and present a coherent tool for paleoceanographic and tectonic basin reconstructions

colour origin of upper cretaceous pelagic red sediments within the eastern pontides northeast turkey characteristic samples of upper cretaceous pelagic red sediments from different parts of the eastern pontides ne turkey have been investigated by x ray diffraction xrd x ray fluorescence xrf and scanning electron microscopy coupled with energy dispersive analyses sem edax the red sediments are composed of limestone and muddy limestone and characterized by abundant planktonic foraminifers hematite content ranges from 0 5 to 3 0 wt electron microscope observations suggest that the hematite pigment has a diagenetic origin the red colour is due to presence of hematite pigment and indicates oxidizing conditions during early diagenesis in a relatively deep marine environment

planktonic and benthic foraminiferal extinction events during the last 100 m y abstract five major planktonic and benthic foraminiferal extinction events occurred during the past 100 m y at the cenomanian turonian c t boundary at the cretaceous tertiary k t boundary in the latest paleocene in the late eocene and in the early middle miocene to clarify the character of the five events i estimated 1 paleo waterdepths and paleoenvironments where foraminifera were affected 2 the duration of each extinction event and 3 evaluated possible causes for each extinction event on the basis of recent literature these extinction events can be classified into three fundamentally different types 1 the mass extinction event at the k t boundary was abrupt and concentrated among surface dwelling species 2 extinctions at the c t boundary and during the latest paleocene were abrupt and mainly affected intermediate and deep water taxa over short periods 3 the late eocene and early middle miocene events affected surface and deep water species and involved stepwise or gradual extinctions over a long period 4 m y i attributed the extinction events to 1 a bolide impact for the k t event 2 a decrease in dissolved oxygen in intermediate and deep waters due to climatic warming for the c t and latest paleocene events and 3 long term global cooling for the late eocene and early middle miocene events the following relationships exist between the causes and types of extinction events 1 large extraterrestrial impacts strongly affected surface dwelling organisms in short term extinction events 2 intermediate and deep water low oxygen conditions induced by climatic warming have severely affected intermediate and deep water organisms over medium and short terms

the whole rock cerium anomaly a potential indicator of eustatic sea level changes in shales of the anoxic facies abstract the whole rock cerium anomaly tested for outer shelf upper slope stratigraphic sections from the middle ordovician through the lower silurian of scotland is proposed as an empirical technique to develop a eustatic 3rd order or finer scale sea level curve this interval was chosen as it straddles the well documented late ordovician glaciation and can be defined by graptolite zones the anomaly is calculated from neutron activation analysis of low carbonate phosphate free fossil free field identified shales of the graptolite facies by comparison of the normalized cerium content with the linearized trend of the normalized composition of other rare earth elements in order of atomic number for sections originally deposited in the main pycnocline below the surface mixed layer values of the anomaly for a given sample would indicate its position on the redox curves developed for the early paleozoic by wilde 1987 changes in the anomaly that are positive with time would indicate a lowering of sea level as the apparent depth on the redox curve would reflect more oxic conditions relative changes negative with time would indicate a rise in sea level as the apparent depth reflects more anoxic conditions depending on the vertical sample spacing and the time interval sampled resolution of the order of 1 m y might be achieved thus the vail et al 1977 curves of the 3rd order 1 to 10 m y or of finer scale could be obtained by this technique with the proper choice of section accordingly for the early through middle paleozoic when the main pycnocline was anoxic this geochemical technique could be used to develop eustatic sea level curves and additionally offer an independent calibration for seismic stratigraphy as well as an indicator of glacial interglacial climatic sequences or eustatic changes due to fluctuations in global ridge crest volumes

a model for the origin and petrogenesis of the red stromatactis limestone of paleozoic carbonate mounds abstract from study of the devonian recifs rouges of belgium and the silurian mounds of the quebec appalachians we propose that deposition of the red stromatactis limestone facies of cambrian devonian carbonate mounds was controlled by sponges and that the red color and stromatactis result from early diagenesis within a few meters below the substrate water interface in the deep marine environment the common presence of sponge body fossils as well as various stages of sponge preservation ranging from easily delineated to indiscernible bodies in the belgian recifs rouges support the conclusion that a large part of the red finely crystalline limestone originated from early cementation of sponge communities or spicule rich organic mats derived from degradation of sponge communities the role of bacteria and other microbes although widely advocated as the main primary builders of carbonate mounds is difficult to assess microbial communities may have contributed to mound accretion as primary builders and or mud producers but their presence cannot be documented we suggest that they may have acted as agents for concurrent sponge putrefaction and early cementation biodiagene is during the sulfate reduction phase under alkaline ph and anoxic conditions we interpret stromatactis as a spar body that resulted from early marine cementation of a cavity network created by excavation of uncemented material in partly indurated decaying sponges and spicule rich organic mats derived from degradation of sponge communities through circulation of interstitial water in the uppermost few meters of the sediment this cavity network was connected to sea floor and flushed by oxic waters that changed the diagenetic environment from anoxic to oxic converting amorphous iron sulfide to hematite and giving the facies its red color recognition of the dominant role of sponge communities in the construction of red stromatactis limestone mounds of the cambrian devonian time interval has important implications for the geological record this community was the main deep water mound building community during this time but is difficult to recognize because of its variable but often poor preservation

the phosphorus cycle phosphogenesis and marine phosphate rich deposits abstract phosphorus in the form of phosphate is an essential nutrient and energy carrier on many different levels of life and a key element in mediating between living and lifeless parts of the biosphere one of the most important aspects of the phosphorus cycle is its vital role in governing productivity thereby interacting with the exogenic part of the carbon cycle which in turn is important in regulating earth s climate phosphorus is a prime element to be traced in earth s history because it allows for the reconstruction of long term feedback mechanisms between climate environment and ecology and of global change as such marine sedimentary phosphate deposits are particularly suited to study aspects of the phosphorus cycle because in the case of ubiquity their origin may result from a general acceleration of the global phosphorus cycle sources of sedimentary phosphate are microbial breakdown of buried organic matter and redox driven phosphate desorption from iron and manganese oxyhydroxides dissolved sea water phosphate represents an additional source which may become important in the formation of phosphatic hardgrounds the main locus of phosphogenesis is near the sediment water interface but phosphogenesis also occurs at greater sediment depths current induced winnowing and transport processes along the sea floor concentrate phosphate precipitates into deposits which exhibit internal stratification patterns typical for the prevailing hydraulic energy regime in a sequence stratigraphic context phosphate deposits preferentially occur along marine or maximum flooding surfaces consequent sedimentary reworking may result in the transfer of phosphates to highstand or lowstand deposits bio chemical weathering on continents represents the most significant source of bioavailable phosphorus this implies that long term changes in marine phosphorus levels and with these changes in marine ecology productivity rates and ratios of exported carbonate carbon and organic carbon are a response to changes in continental weathering rates a compilation of marine sedimentary phosphorus burial rates for the last 160 myr suggests that natural variations have occurred that span one order of magnitude for the late jurassic cretaceous and most of the paleogene the phosphorus cycle appears to have been accelerated in times of climate warming which was most likely due to the spreading of zones of humid climate and more intense continental weathering in the neogene the phosphorus cycle appears to have responded to changes in glacially induced weathering this suggests that uniform interpretations with respect to the emplacement of major phosphorite deposits should be treated with caution integrated analyses of the sedimentary and biogeochemical context of phosphorite occurrences may help to identify paleoenvironmental conditions as well as to improve our understanding of periods of enhanced phosphate accumulation periods which were usually characterized by steep gradients in the development of climate and environment with regard to the complexity of feedback mechanisms between the phosphorus cycle and the biosphere the present day input rates of phosphate into the world s oceans should be of great concern they are more than doubled by anthropogenic means and affect ecological systems on a rapidly increasing scale

peperite a review of magma sediment mingling the study of peperite is important for understanding magma water interaction and explosive hydrovolcanic hazards this paper reviews the processes and products of peperite genesis peperite is common in arc related and other volcano sedimentary sequences where it can be voluminous and dispersed widely from the parent intrusions it also occurs in phreatomagmatic vent filling deposits and along contacts between sediment and intrusions lavas and hot volcaniclastic deposits in many environments peperite can often be described on the basis of juvenile clast morphology as blocky or fluidal but other shapes occur and mixtures of different clast shapes are also found magma is dominantly fragmented by quenching hydromagmatic explosions magma sediment density contrasts and mechanical stress as a consequence of inflation or movement of magma or lava magma fragmentation by fluid fluid shearing and surface tension effects is probably also important in fluidal peperite fluidisation of host sediment hydromagmatic explosions forceful intrusion of magma and sediment liquefaction and shear liquification are probably the most important mechanisms by which juvenile clasts and host sediment are mingled and dispersed factors which could influence fragmentation and mingling processes include magma host sediment and peperite rheologies magma injection velocity volatile content of magma total volumes of magma and sediment involved total volume of pore water heated presence or absence of shock waves confining pressure and the nature of local and regional stress fields sediment rheology may be affected by dewatering compaction cementation vesiculation fracturing fragmentation fluidisation liquefaction shear liquification and melting during magma intrusion and peperite formation the presence of peperite intraclasts within peperite and single juvenile clasts with both sub planar and fluidal margins imply that peperite formation can be a multi stage process that varies both spatially and temporally mingling of juvenile clast populations formed under different thermal and mechanical conditions complicates the interpretation of magma fragmentation and mingling mechanisms

lower cambrian shelf and shelf margin buildups flinders ranges south australia1 carbonate buildups in the flinders ranges of mid early cambrian age grew during a period of high archaeocyath diversity and are of two types 1 low energy archaeocyath sponge spicule mud mounds and 2 high energy archaeocyath calcimicrobe calcified microbial microfossil bioherms mud mounds are composed of red carbonate mudstone and sparse to abundant archaeocyath floatstone have a fenestral fabric display distinct stromatactis contain abundant sponge spicules and form structures up to 150m wide and 80 m thick bioherms are either red or dark grey limestone and occur as isolated small structures 2 20 m in size surrounded by cross bedded calcarenites and calcirudites or as complexes of mounds and carbonate sands several hundreds of metres across red bioherms comprise masses of white epiphyton with scattered archaeocyaths and intervening areas of archaeocyath rich lime mudstone grey bioherms are complex intergrowths of archaeocyaths encrusting dark grey renalcis and thick rinds of fibrous calcite cement the bioherms were prone to synsedimentary fracturing and exhibit large irregular cavities up to 1 5 m across lined with fibrous calcite the buildups are isolated or in contiguous vertical succession mud mounds occur alone in low energy frequently nodular limestone facies individual bioherms and bioherm complexes occur in high energy on shelf and shelf margin facies the two types also form large scale shallowing upward sequences composed of basal deep water mud mounds grading upward into archaeocyath calcimicrobe bioherm complexes and bioherms in cross bedded carbonate sands the uppermost sequence is capped by ooid grainstone and or fenestral to stromatolitic mudstone the calcimicrobe and metazoan associations form the two major biotic elements which were to dominate reefs throughout much of subsequent phanerozoic time

morphology of a crater filling lava lake margin the peninsula tuff cone tule lake national wildlife refuge california implications for formation of peperite textures abstract a crater filling lava lake basalt at the peninsula tuff cone in northeastern california has features on its base formed by interaction of the basalt with wet hydrovolcanic tuff a spectrum of features including elongated streamlined flute shaped lobes and irregular corrugations are exposed on the base of the lava lake flute shaped lobes range in amplitude from several centimeters to 0 5 m plunge downdip with respect to the subjacent layered tuff toward the center of the crater and are better defined at depths more than 3 m below the lava lake surface these may have been formed by growth of rayleigh taylor instability waves caused by the density contrast between the wet tuff and basalt combined with directed stress from flow of the lava lake radially outward from the crater formation of an insulating vapor film at the wet tuff basalt interface and downward pressure exerted by the lava lake allowed the edge of the lava lake to quench gradually and prevented formation of peperite at greater depths in the lake corrugations exposed on the upper 1 5 m of the lava lake margin increase in size from several millimeters to 10 cm in amplitude toward the top of the lava lake and approximately parallel the surface corrugations may be the remnant of fluidal peperite preserved on the edge of the lava lake where the peperite was eroded or may be deformation features formed within an insulating vapor film due to oscillation of the vapor film these were formed higher in the lava lake where the lava lake basalt was thinner wet tuff deposits confining the lava lake were thinner and temperature differences between the wet tuff and lava were greater if corrugations represent deformation of the lava edge within the vapor film rather than peperite formation they preserve an intermediate process that is involved in the formation of peperite this study offers a unique opportunity to evaluate some of the initial mechanisms involved in the formation of peperite based on features preserved in the lava where the host rock in this case hydrovolcanic tuff has been eroded but the properties of the host rock are known from adjacent exposures

provenance and distribution of tethyan pelagic and hemipelagic siliceous sediments pindos mountains greece abstract the broad range of time over which ribbon bedded cherts were deposited does not extend into the present marine environment and no ribbon cherts have been recovered from the sea floor by the deep sea drilling project the depositional environment of bedded cherts is difficult to determine but extra silicic impurities in the rock may offer clues about the provenance of the non biogenic component to test the usefulness of relative abundances of the extra silicic components in extracting information on the depositional environment of the chert i analyzed the major element chemistry of chert samples from a broad range of environments including ophiolite associated chert from the franciscan formation of california deep sea chert and porcellanite from the northwest pacific dsdp leg 32 shallow pelagic shelf chert nodules from the chalk of britain continental marginal basin chert from the monterey formation of california and continental marginal basin chert from the pindos zone of greece the ratios feo a12o3 tio2 a12o3 and a1 a1 fe mn were considered in detail the interpretative logic is simple but empirically supported by observations of these ratio values at different depositional environments in the pacific a1 is concentrated most highly in continental material while fe and mn are more concentrated in pelagic sediments feo a12o3 can be used to differentiate between ophiolite associated chert and chert associated only with other sediments tio2 a12o3 is not a useful indicator possibly because of the equalizing effect of widespread eolian transport the a1 a1 fe mn ratio was measured in detail in one stratigraphic section in central continental greece this ratio varied with the type of sediment admixture decreasing in value after the influx of ophiolite debris bearing sediments even when their presence was undetectable in hand sample or under petrographic microscope to help clarify the paleogeography of the main study area the pindos zone and to identify sources and dispersal patterns of extra basinal materials isopach maps of sedimentary facies of the pindos were constructed superimposed directly upon the series of imbricated thrust slices that comprise the pindos zone the maps are at best compressed pictures of the pindos sea floor persistent regional variation of facies thicknesses over time suggests the existence of several smaller depressions surrounded by submarine highs in the pindos basin

cretaceous oceanic red beds as possible consequence of oceanic anoxic events article i nfo oceanic anoxic events oaes represent brief periods of burial of large amounts of organic carbon in the oceans during cretaceous time burial of organic carbon which preferentially sequestered isotopically lighter carbon during oaes resulted in positive 13 c excursions of 2 3 recognizable in global ocean these deposits are typically dark grey to black shales considered to be the result of interaction between extreme warm climate ocean circulation high bioproductivity and organic carbon preservation less interest has been given to periods between oaes when oxic deep sea deposits such as red marls and red shales were deposited during mid and late cretaceous the latter deposits are associated with very low content of organic carbon and oxic depositional environments which dominated western tethys in post turonian time up to the early eocene feedbacks among geochemical cycles in response to decreasing global temperatures increasing deep ocean circulation forced by high latitude deep water formation along the antarctic margin and widening and deepening of the interconnections between the oceanic basins may have been responsible for the major paleoceanographic change from deposition of organic carbon rich black shales during mid cretaceous to world wide deposition of cretaceous oceanic red beds corbs in the late cretaceous the presence of corbs sandwiched between mid cretaceous oaes may reflect major climate and paleoceanographic changes in a contrast to extremely warm climates during the oaes the corbs suggest cold periods and therefore oscillating climate shifts that have seldom been considered during modeling of cretaceous

iron bacterial mediation in phanerozoic red limestones state of the art different pathways can be proposed to explain the origin of the red pigmentation present in many phanerozoic limestones we investigate three possible models 1 telogenetic alteration 2 detrital input and 3 role of iron bacteria the third hypothesis is supported by our data for a number of phanerozoic series by this hypothesis not only can we highlight the importance of the microenvironments at the dysoxic anoxic water sediment interfaces for the bacterial fe oxidation but also can conclude that the dred limestonest have no particular paleogeographic meaning the seven studied red successions are rather poor in iron 350 ppm in the ammonitico rosso without large fluctuations the pigmentation is due to the dispersion of submicrometric hydro oxides now hematite formed by bacterial mediation during early diagenesis in various microaerophilitic environments different ferruginous morphs e g filaments coccoids microstromatolites suggest the presence of iron bacteria the limiting factor is the oxygen content which was low in these very quiet and relatively deep environments the presence of iron bacteria is also confirmed by iron isotope analysis on the ammonitico rosso fe isotopic compositions have been analyzed on residues as well as on leachates of red and grey facies of the same interval d 56 fe values are systematically lower in the red residues varying from 1 19x to 0 34x compared to the grey ones 0 27x to 0 09x this indicates a significant accumulation of lighter isotopes in the red parts suggesting that hematite have been formed via a biological pathway d 2005 elsevier b v all rights reserved

quantitative analysis of iron oxide concentrations within aptian albian cyclic oceanic red beds in odp hole 1049c north atlantic abstract aptian albian sediments in core 12x of hole 1049c odp leg 171b are characterized by high frequency cycles that consist of alternating layers of red and green white clayey chalk and claystone the first derivative curves of diffuse reflectance spectra drs for samples of different colors reveal that red brown and orange samples show clear peaks corresponding to hematite and goethite following treatment using the cbd citrate bicarbonate dithionite procedure the red samples lost their red color and corresponding peaks in the first derivative curve and became greenish or whitish therefore hematite and goethite are the minerals responsible for the reddish change in sample color however these minerals behave differently from each other in terms of determining the color of sediment hematite imparts a red color whereas goethite imparts a yellow color therefore a change in the proportions of hematite and goethite can cause a change in sediment color from orange to brown to obtain the absolute contents of iron oxides in these sediments we performed a quantitative analysis using drs with multiple linear regression the results reveal that the albian brown beds contain 0 13 0 82 hematite average value 0 51 and 0 22 0 81 goethite average value 0 58 the aptian orange beds contain 0 19 0 46 hematite average value 0 35 and 0 29 0 67 goethite average value 0 50 x ray diffraction analysis of the aptian and albian cycles reveals no clear variations in mineral content with sediment color it is suggested that hematite and goethite were derived from oxic environments during the period of deposition and early diagenesis the oxic conditions were probably determined by the low accumulation rate of organic matter and the high content of dissolved oxygen in bottom water

fluidization of wet sediments during the emplacement and cooling of various igneous bodies during the emplacement and cooling of igneous bodies fluidization of wet sediment by water vapour may occur by heating or by pressure relief during the opening of fractures momentary fluidization causes sediment reconstitution and local transport continuous fluidization can result in substantial sediment displacement theoretical considerations show that fluidization due to heating is not likely to occur at depths where pressure is much greater than 312 bars studies of the emplacement of sills of andesite ayrshire fluid rhyolite ramsey island and viscous rhyolite moelwyn hills recognize a wide range of phenomena attributable to wet sediment fluidization and in places modify existing interpretations the transgressive bases of the subaqueously welded ash flow tuffs of the capel curig volcanic formation are consistent with emplacement attended by fluidization of the subjacent sediment evidently fluidization is a means by which large volumes of wet sediment can be replaced by igneous material with minimal disturbance of the remaining host also fluidization can result in exceptionally complex contact relationships between sedimentary host and intrusive rocks and can cause fractures formed during cooling to be thoroughly pervaded by sediment fluidization is commonly associated with the formation of peperites

incremental dilation of magma filled fractures evidence from dykes on the isle of skye scotland abstract localised swarms of narrow 10 120 mm basaltic dykes occur at offsets and terminations of some larger basaltic dykes in skye scotland these narrow dykes cut and chill against each other and the larger dyke and its country rock the narrow dykes can only be traced a short distance into the larger dyke before terminating some of these terminations show the central parts of both dykes merging as the chilled margins vanish at other terminations the later dyke outcrop narrows progressively to a point these all show that after initial dilation and some crystallisation of material in the dyke fissure there were additional up to 11 increments of dilation increments were sufficiently spaced in time for preceding injections to have become solid time spans separating initial and later dilation may be sufficient for local crystallisation of dykes up to 3 2 m thick away from these terminations the dyke fissure remained an open void occupied by flowing magma during the successive increments of dilation this paper demonstrates that fluid filled dyke fissures can vary in width with time an observation consistent with the modern theoretical models of dyke emplacement that relate dyke width to magma input pressures and other magmatic parameters dyke offsets and terminations with late dilational increments are shown to provide a variety of other information on flow crystallisation and sealing of dyke fissures

deep sea paleotemperature record of extreme warmth during the cretaceous oxygen isotope analyses of well preserved foraminifera from blake nose 30 n paleolatitude north atlantic and globally distributed deep sea sites provide a long term paleotemperature record for the late albian maastrichtian interval that is difficult to reconcile with the existence of significant cretaceous ice sheets given reasonable assumptions about the isotopic composition of cretaceous seawater our results suggest that middle bathyal water temperatures at blake nose increased from 12 c in the late albian through middle cenomanian to a maximum of 20 c during the latest cenomanian and earliest turonian bottom waters were again 12 c during the middle campanian and cooled to a minimum of 9 c during the maastrichtian correlative middle bathyal foraminifera from other ocean basins yield paleotemperature estimates that are very similar to those from blake nose comparison of global bottom water temperatures and latitudinal thermal gradients suggests that global climate changed from a warm greenhouse state during the late albian through late cenomanian to a hot greenhouse phase during the latest cenomanian through early campanian then to cool greenhouse conditions during the mid campanian through maastrichtian

ichthyolith strontium isotope stratigraphy of a neogene red clay sequence calibrating eolian dust accumulation rates in the central north pacific abstract cenozoic pelagic red clays of predominantly eolian and hydrogenous origin blanket much of the central north pacific ocean basin the eolian component is a key indicator of past paleoclimatic conditions thus cenozoic atmospheric circulation can potentially be reconstructed through provenance studies of pacific red clays provided there are precise age controls methods commonly employed in the past to date red clay cores have included cobalt accumulation rates ichthyolith biostratigraphy magnetostratigraphy and ichthyolith strontium isotope stratigraphy the first two dating methods yield ages with large uncertainties while magnetostratigraphy is only relevant to cores with accumulation rates in excess of 1 mm kyr ichthyolith strontium isotope stratigraphy has shown promise as a chronological tool in marine studies but has been only sparingly employed in the dating of marine red clay sequences in this study we present a complete age depth profile for a large diameter piston core from the central north pacific ocean ew9709 pc 01 32 5 n 141 2 w consisting of 11 m of primarily wind deposited dust to generate this age depth profile strontium isotopic compositions were determined on fish teeth ichthyoliths previously cleaned of contaminants using a newly modified reductive cleaning procedure ages were determined by reference to the recently refined sr isotope curve for neogene seawater comparison with nearby giant piston core ll44 gpc3 reinforces the accuracy of our methods the data for ew9709 pc 01 indicate a fairly constant sediment accumulation rate of 0 45 mm kyr over most of the 24 myr time period represented by this core

marine red staining of a pennsylvanian carbonate slope environmental and oceanographic significance abstract red stained platform facies are a common feature of many carbonate settings throughout the geological record although the mechanisms involved in red staining of subaerially exposed or argillaceous peri platform limestones are reasonably well understood the environmental and oceanographic significance of red carbonates often remains uncertain here sedimentological sequence stratigraphic geochemical paleontological and quantitative bathymetric data from pennsylvanian red intervals across a well exposed carbonate platform top and slope are documented and interpreted in a process oriented context on the upper slope 80 350 meters below the shelf break red intervals alternate with gray mainly microbial algal boundstones on the lower slope 350 600 meters below the shelf break redeposited red stained mud builds matrix supported breccia tongues interbedded with predominantly redeposited clast supported carbonate debris the presence of large volumes of fibrous calcite biocementstones as well as firmgrounds point to low sedimentation rates or omission in terms of sequence stratigraphy red intervals occur within maximum flooding intervals and reflect near platform drowning elevated 18o values 2 3 and an essentially cool water heterotrophic biotic association in red intervals on platform top and slope suggest deposition during sea level highs associated with colder water masses and high nutrient levels the most likely drivers are an elevated thermocline and upwelling the red staining is the result of iron oxidation which occurred during early diagenesis likely by iron bacteria these red intervals provide an important bathymetric benchmark against which other mainly paleozoic red facies can be tested and calibrated

glendonites as a paleoenvironmental tool implications for early cretaceous high latitude climates in australia glendonites calcite pseudomorphs after the metastable mineral ikaite caco3 6h2o occur in the late aptian interval of the bulldog shale in the eromanga basin australia and in other early cretaceous basins at high paleolatitudes ikaite precipitation in the marine environment requires near freezing temperatures not higher than 4 c high alkalinity increased levels of orthophosphate and high pco2 the rapid and complete transformation of ikaite to calcite at temperatures between 5 and 8 c provides an upper limit on the oxygen isotopic composition of the pore waters 2 6 w 3 4 smow if it is assumed that these pore waters are representative of the shallow eromanga basin the calculated w can be used to reassess belemnite fossil oxygen isotopic paleotemperatures temperature recorded by fauna living in the basin at the time of ikaite precipitation data previously reported as 11 to 16 c assuming w 0 0 smow yield paleotemperatures ranging from 1 to 5 c squarely in the range of ikaite stability the low w indicates hyposaline conditions most likely caused by mixing high latitude meteoric waters with seawater the 18o depleted low temperature waters suggest that the region was at least seasonally colder than previously accepted

timing of diagenetic haematite growth in red pelagic limestones from gubbio italy abstract magnetite haematite and to a minor extent maghaemite are recognised in the cretaceous and paleocene red pelagic limestones at gubbio the magnetite is detrital or biological whereas the haematite grew during diagenesis from a goethitic precursor thermal and af demagnetization of samples collected from close to reversal boundaries indicate that the various magnetization components do not record the polarity reversal at exactly the same stratigraphic level in the few tens of centimetersbelow a recorded geomagnetic reversal defined by the magnetite magnetization some of the haematite grains are magnetized in the post reversal field the blocking temperature spectra of this haematite fraction with post reversal magnetization are found to shift toward higher temperatures as the reversal boundary is approached the blocking temperature spectra reflect the grain size spectra of the haematite which we interpret as arising by the continual nucleation of grains down to a certain burial depth where the conditions are no longer conducive to further haematite growth the depth below reversal boundaries to which haematite with post reversal magnetization can occur is estimated to be about 60 cm after compaction and is equivalent to a time of about 105 years for these particular sediments a detailed study of the magnetization components at reversal boundaries indicates that the first diagenetic growth of haematite through the single domain critical volume occurs prior to the mechanical fixation of the detrital or biological magnetite subsequently the diagenetic haematite grains do not rotate in response to the ambient geomagnetic field polarity as easily as the magnetite because of their occurrence as pigmentary coatings on larger non magnetic grains

deep water facies succession around the cenomanian turonian boundary in the outer carpathian basin sedimentary biotic and chemical records in the silesian nappe poland abstract facies succession organic carbon stable isotopes and chemical data together with benthic foraminiferal records from the barnasiowka trzeme nia composite section silesian nappe poland reflect changing oceanographic conditions across the cenomanian turonian transition in one of the largest basins of the outer carpathians whose floor was situated beneath the calcium compensation depth the sediments consist of non calcareous radiolarian shales turbidite intercalations rich in foraminifers and sponge spicules as well as siliciclastics and black shales with marine type of organic matter toc up to 6 5 wt corresponding to global oceanic anoxic event 2 the base of oae 2 has been identified on the basis of organic carbon isotope data as a positive excursion from 26 0 to the peak of 23 2 in the latest cenomanian the top of the oae 2 lies within a succession of oxidized siliceous manganiferous sediments including a fe mn layer with macronodules the organic rich sedimentation continued for about 400 kyr at a rate of ca 5 5 mm kyr and finished before the start of the turonian deep water agglutinated foraminiferal diversification and extinction of several taxa occurred during the early part of the oae 2 due to expanding bottom water anoxia chemical indices and benthic foraminiferal assemblages reveal periodic intervals of intensification and expansion of oxygen minimum zone at the basin floor before and after the oae 2 two early diagenetic ferromanganese layers with macronodules and siliceous manganiferous red and green shales directly overlying the organic rich facies reflect changes in oxygenation of the bottom water related to changes in their dynamics which took place near the c t boundary and in the earliest turonian this condensed fe mn succession records the maximum flooding of the late cenomanian early turonian transgression

evidence for late cretaceous late turonian climate cooling from oxygen isotope variations and palaeobiogeographic changes in western and central europe trends of stable oxygen isotope data through four european sections of middle upper turonian sediments show three phases of synchronous variations each phase having a duration of about 250 ka the isotopic variations are independent of local facies sedimentary thickness and diagenetic history two positive 18 o shifts are associated with a southward spread of northern macrofaunas this coincidence of geochemical and palaeontological data implies that the 18 o trends reflect a southward shift of cooler water masses this southward extension of cooler waters was caused by changes in ocean circulation and was associated with a major regression in the early late turonian

contrasting interactions of two magmas with the same water saturated hosts big bend national park texas abstract rhyolitic and mafic dikes cut lower tertiary sediments tuffs and mafic lavas of the eocene oligocene chisos formation in big bend national park texas two contrasting magmas injected into the same hosts under the same conditions provide a controlled experiment on magma host interaction peralkaline rhyolite dikes are extensive and stand in bold topographic relief on contact surfaces against mudstones close packed spheroids of chilled rhyolite indicate vigorous movement of magma within envelopes of fluid against sandstones the rhyolite dike contacts are more irregular and locally protrude as blunt fingers into the wall rock against mafic lava flows dike contacts are planar and the rhyolite is less altered mafic dikes cut the rhyolite dikes some contacts of these mafic dikes are peperitic indicating intrusion into soft wet sediment and tuff the same hosts of the older rhyolitic dikes must also have been water saturated and unconsolidated higher viscosity and lower temperature prevented rhyolite magma from forming detached bodies or engulfing its host to form peperites estimated pressures and contact temperatures approximate or exceed the critical point of water indicating that the fluid envelopes at rhyolite dike contacts were very unstable because even small temperature fluctuations would have produced wide variations in fluid density around the critical point the resulting volume instability triggered rapid pulsations in the fluid envelope deforming the contacts where permeability of the host was low hot fluid accumulated at contacts but where permeability was high fluid could escape before reaching high temperature

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

midlatitude shelf seas in the cenomanian turonian greenhouse world temperature evolution and north atlantic circulation 1 an 8 million year record of subtropical and midlatitude shelf sea temperatures derived from oxygen isotopes of well preserved brachiopods from a variety of european sections demonstrates a long term cenomanian temperature rise 16 20 c midlatitudes that reached its maximum early in the late turonian 23 c midlatitudes superimposed on the long term trend shelf sea temperatures vary at shorter timescales in relation to global carbon cycle perturbations in the mid cenomanian and the late turonian two minor shelf sea cooling events 2 3 c coincide with carbon cycle perturbations and times of high amplitude sea level falls although this evidence supports the hypothesis of potential glacioeustatic effects on cretaceous sea level the occurrence of minimum shelf sea temperatures within transgressive beds argues for regional changes in shelf sea circulation as the most plausible mechanism the major carbon cycle event in the latest cenomanian oceanic anoxic event 2 is accompanied by a substantial increase in shelf sea temperatures 4 5 c that occurred 150 kyr after the commencement of the 13c excursion and is related to the spread of oceanic conditions in western european shelf sea basins our oxygen isotope record and published 18o data of pristinely preserved foraminifera allow the consideration of north atlantic surface water properties in the cenomanian along a transect from the tropics to the midlatitudes on the basis of fossil derived 18o estimated w ranges and modeled salinities temperature salinity density ranges were estimated for tropical subtropical and midlatitude surface waters accordingly the cenomanian temperate shelf seas waters have potentially the highest surface water density and could have contributed to north atlantic intermediate to deep waters in the preopening stage of the equatorial atlantic gateway

dynamic mingling of magma and liquefied sediments abstract hydrodynamic mingling of magma and liquefied sediments is generally accepted to represent the key process in the formation of some peperites experimental studies on simulant liquids and calculations based on recent empirical findings in the field of polymer research were undertaken to investigate the effectiveness of this process these studies show that for a wide range of shear rates a laminar flow behaviour of the system magma liquefied sediment can be expected i e turbulent mingling is not a realistic scenario formation of peperitic fabrics with grain sizes on a cm scale can hydrodynamically be explained under realistic intrusion velocities in addition to the hydrodynamics cooling processes must also be considered during peperite formation calculations of the cooling history of the juvenile magmatic component under realistic cooling conditions demonstrate a significant limitation of the hydrodynamic mingling time the consequence for peperite formation under normal intrusion conditions is that domains of magmatic melt and domains of liquefied sediment smaller than 10 cm are not probable however as smaller domain sizes peperitic grain sizes exist in nature we conclude that either those peperites represent the products of explosive events or that hydrodynamic mingling was accompanied by additional fragmentation processes

early triassic oceanic red beds coupled with deep sea oxidation in south tethys abstract carbonate oceanic red beds orbs are unusual in phanerozoic shelf settings but can be widespread during discrete intervals several scenarios have been invoked to explain the origin of these orbs but there remains uncertainty about the process by which the red pigmentation of orbs forms here we propose that the occurrence of orbs at intermediate water depths in shelf regions is controlled by fluctuations in the redox state of deeper waters we have examined early triassic peri gondwana shelf sections in south tibet which show the development of spathian late early triassic orbs at intermediate water depths the red color of these orbs is imparted by randomly dispersed hematite crystals that are microns in size showing weak alteration by late burial diagenesis widespread anoxia in both shelf seas and the oceanic realm was well developed in the early triassic synchronous occurrence of spathian orbs in deep shelf regions is closely related to the improved oxidation in deeper settings from anoxia to dysoxia based on changes in the redox proxy of pyrite framboid sizes it is therefore inferred that prolonged deep water anoxia might serve as source of fe ii for the formation of orbs when intensified upwelling develops the global occurrence of early triassic orbs is coincident with the significant rebound of biodiversity after the permian triassic mass extinction indicating the occurrence of orbs marks the terminal stage of an oceanic anoxic event and orbs can serve as an indicator of the ameliorated marine ecosystem

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

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

resolving eolian volcanogenic and authigenic components in pelagic sediment from the pacific ocean abstract we measured major and trace element concentrations in the operationally defined chemically extracted residual aluminosilicate component of sediment from ocean drilling program sites 1215 and 1256 in the central and eastern equatorial pacific ocean and found that this residual component contains volcanogenic and authigenic aluminosilicates in addition to inferred eolian material while the residual component younger than 20 ma from the central pacific odp site 1215 is similar compositionally to upper continental crust and suggests an increase in the delivery of asian dust material since 20 ma the residual in sediment older than 20 ma indicates significant amounts of volcanogenic and authigenic materials volcanogenic debris comprises as much as 40 of the residual between 23 40 ma which coincides with the mid tertiary ignimbrite flare up that occurred in much of western north america the residual component extracted from the 50 ma biogenic sediment reflects authigenic signatures seawater like negative cerium anomalies and elevated fe si ratios the previously interpreted increase in an andesitic detrital source in north pacific locations may instead be authigenic material presenting significant challenges for many paleoclimate proxies additionally in the eastern pacific odp site 1256 the residual component contains 70 of volcanogenic material most likely originating from central america and also includes refractory barite the ability to separately identify eolian volcanogenic and authigenic materials in the aluminosilicate component of pelagic sediment allows resolution respectively of the climatic geologic and chemical processes contributing to the paleoceanographic archive in this critical oceanic region

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

isotopic evidence for temperature variation during the early cretaceous late ryazanian mid hauterivian oxygen and carbon isotopic compositions have been determined from the belemnite genera acroteuthis and hibolites sampled from the early cretaceous ryazanian hauterivian interval of the speeton clay formation filey bay england the speeton clay formation consists of a series of claystones and calcareous mudrocks deposited in an epicontinental sea 18 o values from belemnites which met petrographic and chemical criteria for well preserved skeletal carbonate indicate warm marine palaeotemperatures c 12 15 c for much of the early valanginian whilst cool temperatures

mesozoic lower jurassic red stromatactis limestones from the southern alps arzo switzerland calcite mineral authigenesis and syneresis type deformation the broccatello lithological unit lower jurassic hettangian to lower parts of upper sinemurian near the village of arzo southern alps southern switzerland is a mound shaped carbonate deposit that contains patches of red stromatactis limestone within the largely bioclastic broccatello unit the stromatactis limestone is distinguished by its early diagenetic cavity system a relatively fine grained texture and an in situ assemblage of calcified siliceous sponges various demosponges and hexactinellids a complex shallow subsurface diagenetic pathway can be reconstructed from sediment petrography in combination with comparative geochemical analysis carbon and oxygen isotopes trace and rare earth elements ree y this pathway includes organic matter transformation aragonite and skeletal opal dissolution patchy calcification and lithification sediment shrinkage sagging and collapse partial ree remobilization and multiple sediment infiltration these processes occurred under normal marine essentially oxic conditions and were independent from local recurring syn sedimentary faulting it is concluded that the stromatactis results from a combination of calcite mineral authigenesis and syneresis type deformation the natural stromatactis phenomenon may thus be best explained by maturation processes of particulate polymer gels expected to form in fine grained carbonate sediments in the shallow subsurface conditions favorable for the evolution of stromatactis appear to be particularly frequent during drowning of tropical or subtropical carbonate platforms

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

traveltime based descriptions of transport and mixing in heterogeneous domains 1 modeling mixing controlled reactive transport using traditional spatial discretization of the domain requires identifying the spatial distributions of hydraulic and reactive parameters including mixing related quantities such as dispersivities and kinetic mass transfer coefficients in most applications breakthrough curves btcs of conservative and reactive compounds are measured at only a few locations and spatially explicit models are calibrated by matching these btcs a common difficulty in such applications is that the individual btcs differ too strongly to justify the assumption of spatial homogeneity whereas the number of observation points is too small to identify the spatial distribution of the decisive parameters the key objective of the current study is to characterize physical transport by the analysis of conservative tracer btcs and predict the macroscopic btcs of compounds that react upon mixing from the interpretation of conservative tracer btcs and reactive parameters determined in the laboratory we do this in the framework of traveltime based transport models which do not require spatially explicit costly aquifer characterization by considering btcs of a conservative tracer measured on different scales one can distinguish between mixing which is a prerequisite for reactions and spreading which per se does not foster reactions in the traveltime based framework the btc of a solute crossing an observation plane or ending in a well is interpreted as the weighted average of concentrations in an ensemble of non interacting streamtubes each of which is characterized by a distinct traveltime value mixing is described by longitudinal dispersion and or kinetic mass transfer along individual streamtubes whereas spreading is characterized by the distribution of traveltimes which also determines the weights associated with each stream tube key issues in using the traveltime based framework include the description of mixing mechanisms and the estimation of the traveltime distribution in this work we account for both apparent longitudinal dispersion and kinetic mass transfer as mixing mechanisms thus generalizing the stochastic convective model with or without inter phase mass transfer and the advective dispersive streamtube model we present a nonparametric approach of determining the traveltime distribution given a btc integrated over an observation plane and estimated mixing parameters the latter approach is superior to fitting parametric models in cases wherein the true traveltime distribution exhibits multiple peaks or long tails it is demonstrated that there is freedom for the combinations of mixing parameters and traveltime distributions to fit conservative btcs and describe the tailing a reactive transport case of a dual michaelis menten problem demonstrates that the reactive mixing introduced by local dispersion and mass transfer may be described by apparent mean mass transfer with coefficients evaluated by local btcs

experimental interaction of magma and dirty coolants the presence of water at volcanic vents can have dramatic effects on fragmentation and eruption dynamics but little is known about how the presence of particulate matter in external water will further alter eruptions volcanic edifices are inherently dirty places where particulate matter of multiple origins and grainsizes typically abounds we present the results of experiments designed to simulate non explosive interactions between molten basalt and various coolants ranging from homogeneous suspensions of 0 to 30 mass bentonite clay in pure water to heterogeneous and or stratified suspensions including bentonite sand synthetic glass beads and or naturally sorted pumice four types of data are used to characterise the interactions 1 visual video observations 2 grainsize and morphology of resulting particles 3 heat transfer data from a network of eight thermocouples and 4 acoustic data from three force sensors in homogeneous coolants with 20 sediment heat transfer is by forced convection and conduction and thermal granulation is less efficient resulting in fewer blocky particles larger grainsizes and weaker acoustic signals many particles are droplet shaped or and vesicular containing bubbles filled with coolant both of these particle types indicate significant hydrodynamic magma coolant mingling and many of them are rewelded into compound particles the addition of coarse material to heterogeneous suspensions further slows heat transfer thus reducing thermal granulation and variable interlocking of large particles prevents efficient hydrodynamic mingling this results primarily in rewelded melt piles and inefficient distribution of melt and heat throughout the coolant volume our results indicate that even modest concentrations of sediment in water will significantly limit heat transfer during non explosive magma water interactions at high concentrations the dramatic reduction in cooling efficiency and increase in mingling help to explain globular peperite and provide information relevant to analyses of premixing associated with highly explosive molten fuel coolant interactions in debris filled volcanic vents